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Vapor-Phase Halogenation of Hydrogen-Terminated Silicon(100) Using N-Halogen-succinimides
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Surfaces, Interfaces, and Applications

Vapor-Phase Halogenation of Hydrogen-Terminated Silicon(100) Using N-Halogen-succinimides
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Cite this: ACS Appl. Mater. Interfaces 2023, 15, 47, 55139–55149
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https://doi.org/10.1021/acsami.3c13269
Published November 15, 2023

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Abstract

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The focus of this study was to demonstrate the vapor-phase halogenation of Si(100) and subsequently evaluate the inhibiting ability of the halogenated surfaces toward atomic layer deposition (ALD) of aluminum oxide (Al2O3). Hydrogen-terminated silicon ⟨100⟩ (H–Si(100)) was halogenated using N-chlorosuccinimide (NCS), N-bromosuccinimide (NBS), and N-iodosuccinimide (NIS) in a vacuum-based chemical process. The composition and physical properties of the prepared monolayers were analyzed by using X-ray photoelectron spectroscopy (XPS) and contact angle (CA) goniometry. These measurements confirmed that all three reagents were more effective in halogenating H–Si(100) over OH–Si(100) in the vapor phase. The stability of the modified surfaces in air was also tested, with the chlorinated surface showing the greatest resistance to monolayer degradation and silicon oxide (SiO2) generation within the first 24 h of exposure to air. XPS and atomic force microscopy (AFM) measurements showed that the succinimide-derived Hal-Si(100) surfaces exhibited blocking ability superior to that of H–Si(100), a commonly used ALD resist. This halogenation method provides a dry chemistry alternative for creating halogen-based ALD resists on Si(100) in near-ambient environments.

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Introduction

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Area-selective atomic layer deposition (AS-ALD) is a key technology for enabling atomically precise, self-aligned bottom-up manufacturing of thin-film electronic, (1,2) photonic, (3) and quantum devices. (4) This method is often suggested as a higher-resolution replacement for current top-down micromachining techniques that can further advance the development of three-dimensional (3D) integrated circuits. (5) AS-ALD relies on patterned interfaces of growth and nongrowth surfaces (GS and NGS), which sequentially promote and block ALD reactions on the corresponding domains. (6−9) Growth selectivity is typically achieved by patterning ALD resists that block deposition on homogeneous growth-promoting interfaces.
Typical AS-ALD resists include polymeric (10−14) and inorganic (15−19) thin films. They are often deposited via traditional stencil lithography or photolithography, negating the potential high-resolution advantages of AS-ALD. Alternative resist materials include self-assembled monolayers (SAMs) which possess advantages over more traditional resists. (20−24) However, these SAM resists still consist of relatively large molecules (up to 2 nm in length). SAM resists are also predominantly deposited via solution chemistry incompatible with in situ ALD, and their properties are altered near surface defects making their use on nonideal interfaces problematic.
Considering the limitations of SAM resists, recent efforts in AS-ALD have been directed toward the development of atomic resists that can promote or block ALD reactions by changing the surface termination of the deposition substrate. These studies are focused on developing chemoselective atomic resists that can withstand multiple ALD cycles without losing their growth selectivity (i.e., the number of cycles before a resist loses its blocking ability). (25−28)
Past studies have examined the effectiveness of ALD resists which focus on functionalizing Si(100) interfaces. (29,30) In the (100) orientation, the Si/SiO2 interface state density is generally lower than those in the (110) and (111) planes, resulting in a lower density of dangling bonds, higher carrier mobility, and better drive current for Si-based electronics. Currently, hydrogen-terminated silicon (H–Si(100)) is employed as an effective NGS when paired with hydroxylated silicon (OH–Si(100)) which acts as the GS. This basic complementary resist system is valued for its uniform composition and good growth/etch selectivity. (8,31) However, H–Si(100) is reactive and unstable in air, limiting its use in ultrahigh vacuum (UHV) environments and hindering its application in commercial systems for bottom-up processing. Therefore, alternatives to H–Si(100) that maintain its attractive physical and chemical properties, inhibit partial oxidation, and improve the ALD growth selectivity with OH–Si(100) are needed.
Halogenated Si(100) (Hal-Si(100)) is a promising candidate for fabricating semiconductor interfaces used in electronics, (32) nanotechnology, (33,34) and biosensing. (35,36) It is a more stable alternative to H–Si(100) in air and can better maintain the required difference in chemical reactivity on a surface for AS-ALD due to the bulkier structure of the attached halogen species, which effectively shield the underlying NGS from ALD chemistry. (37) Different halogen precursors can be used to passivate Si(100), potentially enabling versatility in inhibiting different types of ALD chemistries. For example, the reaction of 1-octadecanethiol is more favorable on a Cl-terminated Si(100) surface (Cl–Si(100)) than on a Br-terminated surface (Br–Si(100)). (38) Cl–Si(100) also lowers the processing temperature for depositing stable NH2 groups on silicon surfaces using gas-phase ammonia. Furthermore, halogen atoms have demonstrated great potential as possible passivation species for pattern preservation on H-passivated materials under UHV. (39)
Most research on halogenation of crystalline silicon has focused on the Si(111) interface, (32,34−36) but the structural differences between Si(111) and Si(100) result in different reactivities. (40,41) Thus, there is a need to investigate halogen formation on Si(100) more extensively, as it is a more relevant material in semiconductor manufacturing. (42) The current standard for producing Hal-Si(100) involves generating a halogen flux from a solid-state, electrochemical cell in UHV, (43−46) which is slow and not directly compatible with common commercial deposition systems. Others have employed chlorine gas (Cl2) under low-pressure conditions to chlorinate Si(111); (47,48) however, due to the toxicity of Cl2 gas and its problematic incorporation into most vacuum deposition systems, there is a need to find other halogenation molecules that are safer to handle. Some have developed Si(100) halogenation methods using wet chemistry in near-ambient conditions, (34,47,49−51) but these often require prolonged refluxing and generate byproducts that accumulate on the Si(100) surface. Vapor-phase halogenation in mild vacuum is more compatible with other low-vacuum processes such as AS-ALD, but few studies outside of UHV have focused on vapor-phase halogenation of H–Si(100). Nonetheless, H-terminated silicon quantum dots (H-SiQDs) were halogenated using chlorine gas (Cl2) and N-halogen-succinimides (38,52−56) but both methods have resulted in SiQD oxidation and only partial halogenation. Thus, a more efficient vapor-phase halogenation method for Si(100) is needed.
This study reports the use of N-halogen-succinimide molecules as vapor-phase halogenation reagents for crystalline H–Si(100) under near-ambient conditions. N-Halogen-succinimide molecules are often used as a precursor of molecular halogens in radical-type reactions. (34,52,57,58) The reaction likely follows a surface-mediated radical initiator mechanism where the terminal H atoms on a H–Si(100) surface are replaced by Cl, Br, or I atoms. This reaction is likely to proceed through the formation of silicon radicals and molecular halogens, analogous to the allylic or benzylic halogenation of alkanes or alkylbenzenes in the solution phase. (59)
The halogen precursors used in this study were N-chlorosuccinimide (NCS), N-bromosuccinimide (NBS), and N-iodosuccinimide (NIS), which are all commonly used as halogenating and oxidizing agents in organic synthesis and can be handled in air. (35,52,60,61) The resulting monolayers were characterized by using X-ray photoelectron spectroscopy (XPS) and contact angle goniometry. Calculations of surface coverage suggest that the succinimide halogenation achieves a high level of coverage, albeit not complete. The reported halogenation reaction has been shown to have high chemoselectivity and can be used to selectively halogenate H–Si(100) in the presence of hydroxyl-terminated surface sites. The stability of the Hal-Si(100) interfaces in air was investigated using XPS to monitor the concentration of oxide and halogen species on Si(100) over a 72 h period. The results showed that the halogenated substrates degraded at a slower rate than that of H–Si(100). When compared to other vapor-phase halogenation techniques (i.e., halogen flux from an electrochemical cell in UHV, surface exposure to Cl2 gas), N-Hal-succinimides do not require high vacuum environments, are safer to handle, and less corrosive to the deposition instrumentation. The described vapor-phase halogenation conditions are also comparable to the conditions of existing ALD chemistries and can potentially be undertaken inside standard ALD systems. They could be used as an alternative to H resists on Si(100) in self-aligned AS-ALD. Here, we studied the selectivity of the ALD of alumina (Al2O3) on Hal-Si(100) and on H–Si(100). XPS and angle-resolved XPS (ARXPS) data showed that the halogenated monolayers were better at inhibiting the ALD chemistry than H–Si(100). We believe that the development of highly selective and stable ALD resists that can be deposited under mild vapor-phase conditions would have numerous applications in bottom-up semiconductor manufacturing. However, more research is needed to understand the mechanism of defect formation during and after the reaction to further improve the coverage and stability of the halogen resists.

Materials and Methods

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All reagents and solvents were used as received without further purification. Solvents were purchased from Sigma-Aldrich and filtered through a 0.2 μm filter before use. Light-sensitive molecules NCS, NBS, and NIS all with 99% purity were purchased from Sigma-Aldrich and stored in dark environments. Their application was carried out under yellow light. P-doped ⟨100⟩ silicon wafers were purchased from University Wafer, Boston, Massachusetts. XPS spectra were recorded on a Kratos Axis Ultra XPS spectrometer equipped with a mono-Al X-ray source at 200 W power and a pressure of 3.0 × 10–8 mbar. Survey scans were obtained between 0 and 1200 eV with a step size of 1 eV, a dwell time of 200 ms, and a pass energy of 140 eV averaged over 2 scans. Core-level region scans were obtained at the corresponding binding energy ranges with a step size of 0.1 eV, an average dwell time of 260 ms, and a passing energy of 20 eV averaged over 10 scans. Data was processed using CasaXPS software and instrument-specific atomic sensitivity factors. All C 1s peaks were calibrated to 284 eV, and this same binding energy shift was applied to all other spectra besides Si 2p to account for adventitious carbon contamination. Separately, the bulk Si signal in the Si 2p spectra was calibrated to 99 eV for better quantitative assignment of shifts in the spectra. AFM images were recorded on an NT-MDT AFM microscope using a silicon nitride probe (manufacturer: NanoWorld) with a tip radius of <15 nm, a resonance frequency of 67 kHz, and a force constant of 0.32 N/m. The same probe was used for each sample in tapping mode. Goniometry measurements were conducted using ultrapure water. SE scans were recorded using a J.A. Woollam M-2000 ellipsometer.

Preparation of H-Terminated Silicon Surface (H–Si(100))

All glassware was washed with 1× Nano-Strip solution (a stabilized formulation of sulfuric acid and hydrogen peroxide), followed by rinsing with water and isopropyl alcohol (IPA) before being dried in an oven overnight at 130 °C. 4 cm2 Si(100) substrates were soaked in Nano-Strip at 75 °C for 15 min to produce hydroxy-terminated silicon chips (OH–Si(100)). Following the oxidation, the substrates were immersed in a 5% aqueous hydrofluoric acid (HF) solution for 6 min to chemically etch away the native oxide layer and form hydrogen-terminated silicon. The substrates were then quickly rinsed with water and 2-propanol and dried under filtered nitrogen gas.

Halogenation of H-Terminated Silicon with N-Halogen-succinimides (Hal(H)–Si(100))

Freshly prepared H-terminated Si(100) substrates were placed in a vacuum jar along with 0.5 g of N-Hal-succinimide. The jar was evacuated to ∼10–1 mbar and heated to a temperature that was 25 °C below the melting point of each N-Hal-succinimide molecule (e.g., 150 °C for N-bromo-succinimide). These temperatures were selected through experimentation to ensure adequate volatility of the N-Hal-succinimide molecules at the vacuum jar pressure (∼10–1 mbar). The sample was left in the jar for 2 h to fully vaporize 0.5 g of N-Hal-succinimide molecule from the source. Samples were then rinsed with IPA and dried under nitrogen.

Halogenation of OH-Terminated Silicon with N-Halogen-succinimides (Hal(OH)–Si(100))

Freshly prepared H-terminated Si(100) substrates were soaked in Nano-Strip at 75 °C for 15 min, thus undergoing hydroxylation and rendering the surface OH terminated, and placed in a vacuum jar along with 0.5 g of N-Hal-succinimide. The jar was evacuated to ∼10–1 mbar and heated to a temperature that was 25 °C below the melting point of each N-Hal-succinimide molecule for 2 h. Samples were then rinsed with IPA and dried under nitrogen.

Atomic Layer Deposition of Al2O3 Thin Films

Deposition of Al2O3 thin films was carried out using a Cambridge Savannah 200 ALD reactor. Hal-Si(100), H–Si(100), and OH–Si(100) samples were placed in the reactor and heated to 130 °C. Trimethylaluminum (Al(CH3)3) (Hi-k grade, Air Products) and H2O were pulsed for 0.03 and 0.05 s, respectively, by using a nitrogen carrier gas flowing at 20 sccm from sources held at room temperature. The reagent exposures were 6 × 10–4 and 1 × 10–3 Torr-sec during the Al(CH3)3 and H2O pulses, respectively. The base pressure in the reactor between pulses was 0.3 mbar. A 20 s nitrogen purge followed each precursor pulse. This process was repeated for 20 cycles of deposition.

Results and Discussion

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Halogenation of H–Si(100) and OH–Si(100) Using N-Halogen-succinimides

A mild, vapor-based functionalization method that selectively halogenates H–Si(100) over OH–Si(100) can be applied in AS-ALD processes to (1) create an initial NGS for area-selective thin-film deposition and (2) regenerate a NGS during thin-film deposition to extend the selectivity window. Such selective H–Si(100) halogenation can be achieved by exploring the higher reactivity of the H–Si(100) interfaces. In this study, N-Cl/Br/I-succinimides were used to halogenate H–Si(100) under mild vapor-phase conditions. The reactivity of the N-Cl/Br/I-succinimides with OH–Si(100) interfaces was also examined to determine the halogenation selectivity between H–Si(100) and OH–Si(100).
The steps and experimental conditions of these reactions are listed in Figure 1. Si(100) substrates with native oxide were immersed in Nano-Strip solution for 15 min at 65 °C and then rinsed in ultrapure water and isopropanol to remove organic impurities. The native oxide layer was then etched away during a 5 min dip in a 5% HF solution to form a H–Si(100) surface. AFM imaging shown in Figure 1SI confirmed that the HF etch did not affect the surface roughness of the silicon interface. The freshly prepared H–Si(100) surfaces were exposed to an N-Cl/Br/I-succinimide molecule for 2 h in a flask evacuated to 10–1 mbar and heated to the temperature ∼25 °C below the atmospheric melting point of the succinimide molecules (130–170 °C). Similarly, freshly oxidized OH–Si(100) substrates were also reacted with the N-Cl/Br/I-succinimide molecules to assess halogenation selectivity toward H–Si(100) and OH–Si(100). Following the reaction, the substrates were rinsed with isopropanol, dried with filtered nitrogen gas, and analyzed using XPS and contact angle measurements to assess the atomic composition and the halogen coverage before and after the reactions.

Figure 1

Figure 1. Schematic procedure of reaction steps and process conditions for the vapor-phase halogenation of H–Si(100) and OH–Si(100) with N-Hal-succinimides. (1) Si(100) is cleaned and oxidized in Nano-Strip solution before (1 ⇒ 3) direct exposure to an N-Cl/Br/I-succinimide molecule in the vapor phase, alternatively (1 ⇒ 2) the new oxide is re-etched in HF and then (2 ⇒ 3) exposed to the N-Cl/Br/I-succinimide molecules.

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The XPS Cl 2p, Br 3d, and I 3d spectra in Figure 2 all confirm the formation of Si-Hal bonding on the halogenated H–Si(100) (Hal(H)–Si(100)) substrates. In contrast, the XPS signal intensity on halogenated OH–Si(100) (Hal(OH)–Si(100)) was significantly lower. Table 1 shows the relative XPS peak intensities of Cl 2p, Br 3d, and I 3d electrons adjusted by atomic sensitivity factors (ASFs) and normalized by the total Si 2p peak intensity in each sample. Overall, Table 1 shows that halogenation with N-Hal-succinimides resulted in XPS signal intensities 2.8–4 times higher on H–Si(100) than on OH–Si (100). This result was expected due to the more reactive nature of Si–H bonds in interfacial radical-type reactions. (62)

Figure 2

Figure 2. Comparison of XPS spectra from Hal(H)–Si(100) and Hal(OH)–Si(100) surfaces postreaction and an OH–Si(100) standard. Region scans for each respective halogen (Cl 2p, Br 3d, and I 3d) are depicted from left to right.

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Table 1. XPS Ratios of the Hal 2p (or 3d) over Si 2p Electron Signals Were Corrected by the Atomic Sensitivity Factors on Hal(H)–Si(100) and Hal(OH)–Si(100) Substrates after the Halogenation Reaction with N-Hal-succinimidesa
halogenating agentsNCS (Cl)NBS (Br)NIS (I)
 XPS signal ratios of Hal 2p (or 3d)/Si 2p electrons
H–Si(100)0.0280.0170.012
OH–Si(100)0.0100.0050.003
 OH–Si/H–Si halogenation selectivity
 1:2.81:3.51:4
a

Halogenation selectivity of N-Hal-succinimides.

The binding energies of the halogen electrons are consistent with literature data that report halogenation of H–Si(100). Their values suggest the formation of a silicon-halogen species. Specifically, signals at 199.5, 69.5, and 619/631 eV are indicative of Si–Cl, Si–Br, and Si–I formation, respectively. (37,63,64)
Previous studies have relied on XPS to identify the type of halogenated species bonded directly to Si(100). For instance, Silva-Quinones et al. paired XPS measurements with scanning tunneling microscopy (STM) imaging to demonstrate that their method for the chlorination of H–Si(100) resulted in the formation of silicon dichloride (SiCl2) surface species, while bromination yielded complete monobromide (SiBr) monolayer formation. (63) The positions of their Cl 2p and Br 3d peaks are consistent with those in this study and suggest that our method primarily results in the formation of SiCl2 and SiBr bonds.
In order to assess the degree of halogen coverage on each surface, we compared theoretical values, derived from the established overlayer model (65) (eq 1SI), with the values Silva-Quinones et al. (63) calculated in their study on H–Si(100) halogenation. Their scanning tunneling microscopy (STM) results demonstrated that an overlayer model coverage of 0.4 corresponds to a complete monobrominated Br–Si(100) interface. The overlayer model coverage of the Br(H)–Si(100) substrate in our study was calculated to be 0.35, indicating that the bromination of H–Si(100) with N–Br-succinimide resulted in approximately 88% monobromide termination of the surface-exposed silicon atoms. The surface coverages of the chlorinated and iodinated H–Si(100) substrates were subsequently calculated by comparing the ASF-corrected ratio of Br 3d/Si 2p XPS signals with the ASF-corrected ratios of the Cl 2p/Si 2p and I 3d/Si 2p XPS electron signals (Tables 1 and 2). Our findings suggest that NCS chlorination achieved either an incomplete dichloride termination or a complete mixed mono/dichloride termination of the surface-exposed silicon atoms, while NBS bromination achieved 88% coverage of the monobromide silicon species. However, NIS iodination resulted in only 62% monoiodine coverage of the surface silicon atoms. This decrease in the halogenation efficiency from chlorine to bromine to iodine could potentially be attributed to the increase in the atomic size of the halogen species or to the decrease in the Si-Hal bond energy.
Table 2 shows that the Hal-terminated surfaces display higher hydrophobicity than unreacted OH–Si(100) and similar or lower hydrophobicity than untreated H–Si(100), based on water contact angle measurements of halogenated and nonhalogenated substrates (Figure 2SI). This decrease in hydrophobicity from Cl to I can be attributed to the increasing polarizability of halogen atoms in that order and to partial oxidation of the Si–I interface. The observed water contact angle hysteresis of the halogenated surfaces is likely attributed to the incomplete coverage of the halogen species on the surface and the presence of surface oxide species. As expected, the water contact angles of the halogenated OH–Si(100) substrates are comparable with those of the native OH–Si(100) surface due to the low yield of the halogenation reaction on the oxidized surface.
Table 2. Halogen Surface Coverage on Hal(H)-Si(100) Substrates Treated with N-Hal-succinimidesa
halogenating agentsNCS (Cl)NBS (Br)NIS (I)
 monohalogen surface coverage (%)
H–Si(100)1458862
 contact angle (deg) and contact angle hysteresis (deg)
Hal(H)–Si(100)72.5 ± 1.646.9 ± 0.626.2 ± 0.9
27.1 ± 0.124.0 ± 0.120.4 ± 0.1
Hal(OH)–Si(100)21.9 ± 0.424.4 ± 0.525.2 ± 0.7
17.9 ± 0.119.2 ± 0.117.1 ± 0.1
bare OH–Si(100) before halogenation20.7 ± 0.4  
bare H–Si(100) before halogenation67.0 ± 0.4  
a

Water contact angle measurements of Hal(H)–Si(100) and Hal(OH)–Si(100) substrates and a bare OH–Si(100) substrate before the reaction.

XPS region scans of C 1s, O 1s, and SiO2 signal (from the Si 2p spectra) were collected to discern compositional differences in the prepared halogenated monolayers (Figure 3). With a negligible SiO2 peak observed, and only a slight O 1s and C 1s signal detected, the spectra for the H–Si(100) sample demonstrate that the initial oxidative cleaning and HF etching steps effectively removed a majority of organics from the sample surface before halogenation. The region scans for each of the surfaces posthalogenation show little variability in composition. The primary contribution to each of the C 1s spectra is from C–C/C═C bonds at 284 eV. The highest degree of carbon contamination was seen on I(H)–Si(100), a likely result of the higher polarizability of the iodine atom and therefore the higher surface energy of the entire surface. There is good agreement in the size and shape of the SiO2 peaks between both the Cl(H)–Si(100) and Br(H)–Si(100) surfaces and H–Si(100). However, in relation to the OH–Si(100) surface, the SiO2 signal for each of the halogenated surfaces is slightly shifted to a lower binding energy. This is most evident when comparing the SiO2 peaks for OH–Si(100) and I(H)–Si(100) where there is about a 0.3 eV difference in the peak center. This shift is most likely indicative of the newly formed Si-Hal species found on the halogenated samples and absent on the OH–Si(100) and H–Si(100) references. Overall, the dry halogenation process effectively prevents silicon oxidation for chlorination and bromination. The low O content that is observed on these two surfaces can be attributed to the physisorption of water. The O and SiO2 peak areas measured on the I(H)–Si(100) sample were larger likely due to the lower halogen coverage observed on that surface, which allowed surrounding O species to more effectively access the underlying Si–H bonds. This likely explains the higher degree of hydrophilicity that was also observed on I(H)–Si(100). Nevertheless, the degree of Si oxidation that I(H)–Si(100) experiences is still only about a third of what was observed on the reference OH–Si(100) sample.

Figure 3

Figure 3. Comparison of XPS region scans of C 1s, O 1s, and SiO2 (from Si 2p) spectra depicted from left to right for OH–Si(100), H–Si(100), Cl(H)–Si(100), Br(H)–Si(100), and I(H)–Si(100) surfaces. In the bottom row is histograms showing the quantitative XPS characterization of region scans (C 1s, O 1s, SiO2 from Si 2p) for each Hal(H)–Si(100) surface and reference unreacted OH–Si(100) and H–Si(100) surfaces, all normalized by the Si 2p peak intensity which includes contributions from both the bulk Si (SiB) and surface oxide (SiOx) interfaces (the values in the SiOx histogram were normalized by only SiB).

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Stability of Hal(H)–Si(100) Surfaces in Air

The stability of Cl(H)–Si(100), Br(H)–Si(100), and I(H)–Si(100) in an ambient environment was examined by monitoring the surface composition of each surface via ex situ XPS characterization over a 72 h timespan. After the reaction, each halogenated surface was directly transferred into the XPS for measurements. After collecting the data, the samples were unloaded and kept at ambient laboratory conditions for 4 h. Following this, each sample was reloaded into the XPS for additional testing. This same process was repeated at both 24 and 72 h postreaction.
XPS characterization in Figure 4 demonstrated that although each halogenated sample attained roughly the same degree of surface oxidation after 72 h of air exposure, the rate of halogen degradation on Cl(H)–Si(100) was slower than on the other two surfaces. Br(H)–Si(100) and I(H)–Si(100) both experienced more than a 50% drop in halogen signal during the first 4 h, while Cl(H)–Si(100) only exhibited a 32% drop. Deterioration then proceeded slowly during the next 20 h with each surface experiencing less than a 20% additional drop in halogen signal, and by 72 h, there was near-complete desorption of halogen atoms, except on Cl(H)–Si(100) which was retained 29% of its original halogen content. It should be noted that all Cl 2p signals are partially obscured by a Si plasmon, as seen in Figure 3SI, which renders peak identification and characterization slightly more difficult than the other halogen signals. The plasmon was subtracted from all Cl 2p spectra by using a reference Cl 2p spectrum from a bare OH–Si(100) sample.

Figure 4

Figure 4. Stability study consisting of histograms showing the quantitative XPS characterization of halogen, C 1s, O 1s, and SiO2 (from Si 2p) region scans shown from top to bottom, respectively, for I–Si(100), Br–Si(100), and Cl–Si(100) surfaces shown from left to right, respectively, over a 72 h period of air exposure.

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All three surfaces experienced similar rates of O accumulation in the 24 h postreaction, with I(H)–Si(100) having a head start due to its lower initial halogen coverage, as previously discussed. A reference for a theoretical maximum in Si oxidation is the native oxide layer on the freshly oxidized OH–Si(100) surface in Figure 3, where the SiOx2p/SiB2p XPS ratio is 0.16. The SiO2 plot in Figure 4 illustrates that I(H)–Si(100) reached the threshold for full oxide growth after 24 h and then leveled off, while Cl(H)–Si(100) reached full growth after 72 h. Only Br(H)–Si(100) exhibited a SiO2 signal below the max threshold at the end of 72 h. This surface also demonstrated the lowest O 1s signal after 72 h. Frederick et al. also determined that Br(H)–Si(100) demonstrated the highest resistivity to oxidation in their study where they evaluated the stability of UHV-prepared Cl(H)–Si(100), Br(H)–Si(100), and I(H)–Si(100) in a nitrogen gas environment. (37) Consequently, after 72 h, the three halogenated surfaces more or less resembled each other with respect to organic and oxide concentration. Within the first 24 h, the results clearly demonstrate that Cl(H)–Si(100) resisted both surface oxidation and halogen deterioration most effectively.

Hal(H)–Si(100) Surfaces Ability to Inhibit ALD Precursors

Several publications have shown that typical organosilane or phosphonic acid SAMs on Si(100) act as viable ALD resists, but they lose their selectivity due to the hydrolytic desorption promoted by the ALD conditions. (66,67) Nevertheless, due to the long symmetrical aliphatic chains associated with SAMs, they can provide effective shielding of the underlying surface from the ALD chemistry in the defect-free areas. (21) Around defects, due to the disruption of the self-assembly, SAMs are less efficient in protecting the substrates from the ALD reactions. (66,68−70) Such dependence of stability on surface morphology complicates the use of SAM resists on nonideal substrates. Additionally, SAM resists are primarily deposited from solutions (conditions incompatible with in situ resist regeneration). (71,72) Atomic-scale resists, on the other hand, do not rely on self-assembly and can achieve both higher surface coverage and stronger substrate attachment than SAMs. Potentially, they can also achieve higher resolution due to their smaller size. Certain atomic resists can be deposited in the vapor phase, potentially enabling their in situ deposition within the ALD instrumentation. As halogen monatomic resists can be applied in the vapor phase on a variety of surface geometries, they may represent a more effective alternative to SAMs as ALD inhibitors. Hence, the halogenated monolayers investigated in this study were next examined on whether they (1) formed stable enough bonds with Si(100) to adequately block ALD chemistry and (2) could withstand multiple deposition cycles.
This study is specifically interested in the deposition of aluminum oxide (Al2O3), the most common metal oxide film deposited via ALD, and is often used in the production of electroluminescent displays and memory capacitors. (31)
The XPS analysis in Figure 5 demonstrates that after 20 cycles of Al2O3 ALD, the Al-to-Si ratios on H–Si(100) and OH–Si(100) were 5.32 and 7.73, respectively. This illustrates that the ALD chemistry was more selective toward OH–Si(100) which agrees with many studies in the literature. (8,25,31,66,73,74) For example, Longo et al. used density functional theory (DFT) calculations to denote that the adsorption of the metal oxide precursor (Al(CH3)3) experiences a higher kinetic barrier on H-terminated surfaces (∼1.5 eV) than on OH-terminated surfaces (∼0.8 eV). (74) Thus, as OH–Si(100) serves as an ideal GS, it is important to evaluate the ability of each Hal(H)–Si(100) surface to block ALD precursor chemisorption so as to determine their efficacy as potential complementary NGS materials. To test this, Cl(H)–Si(100), Br(H)–Si(100), and I(H)–Si(100) surfaces underwent 20 cycles of Al2O3 deposition. Figure 5 shows that all three halogenated surfaces exhibited lower Al 2p signals and Al-to-Si composition ratios than those found on a corresponding H–Si(100) surface, thus demonstrating the superior blocking ability of the halogenated surfaces. The Al 2p XPS spectra for each surface are presented in Figure 4SI. Cl(H)–Si(100) was the most effective inhibitor, followed by Br(H)–Si(100) and then I(H)–Si(100). This trend is likely due to the higher halogen coverage on Cl(H)–Si(100) than those on Br(H)–Si(100) and I(H)–Si(100). Interestingly, despite there being a more than 2.5 time difference in water contact angle between the Cl–Si(100) and I–Si(100) surfaces, there was only a 12% difference in their respective Al-to-Si ratios, indicating that atomic polarizability and/or partial surface oxidation do not significantly contribute to the reduction of the ALD selectivity. The ALD growth selectivities reported in Table 3 represent the proportion between the surface concentration of Al atoms on the “inhibiting” NGS relative to that of the OH–Si(100) GS. The selectivities of Cl(H)–Si(100), Br(H)–Si(100), and I(H)–Si(100) were 30.0, 27.6, and 24.2%, respectively. H–Si(100) demonstrated a slightly lower selectivity of 18.5%. Thus, in addition to their potential capability of being intermittently redosed directly into the ALD reactor when selectivity wains (after etching away accumulated NGS Al2O3/TMA and reforming the halogen-reactive Si–H surface using either a vapor-phase, plasma-based, or atomic layer etching (ALE) method of Si–OH (75−79)), the halogenated substrates also exhibit a higher degree of ALD inhibition than that of H–Si(100).

Figure 5

Figure 5. (A) Schematic illustration of the traditional ALD cycle of Al2O3 onto OH-Si(100), H-Si(100), and Hal(H)-Si(100) surfaces. In step 1, the dosed Al(CH3)3 precursor readily adsorbs onto the OH-Si(100) surface, while H-Si(100) and Hal(H)-Si(100) surfaces exhibit total and partial blocking of the same molecule, respectively. In step 2, the H2O coreactant binds with the adsorbed metal precursor to form a complete metal oxide film on OH-Si(100) and a metal oxide island on Hal(H)-Si(100). Only H-Si(100) retains its original surface, but it must be maintained under high vacuum and temperature. (B) Histogram showing the quantitative XPS characterization of Al 2p region scan for all three halogenated surfaces and reference H-Si(100) and OH-Si(100) surfaces.

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Table 3. Characterization of Al2O3 Thin Films Deposited onto Sample Surfaces after 20 ALD Cycles Included Thickness Calculations from ARXPS and XPS Measurements and AFM Roughness Measurementsa
surfacethickness (nm) (based on XPS)ALD growth rate (nm/cycle)selectivity (%) (based on XPS)AFM RMS roughness (nm)
OH–Si(100)2.160.11--0.49
H-Si(100)1.490.0718.50.53
Cl(H)–Si(100)1.160.0630.00.21
Br(H)–Si(100)1.230.0627.60.76
I(H)–Si(100)1.320.0724.20.78
a

Selectivity is defined as a proportion between the surface concentration of Al atoms on the OH–Si(100) reference and the surface concentration of Al atoms on the Hal-Si(100) surfaces, all values found using XPS and normalized to the Si 2p signal.

selectivity(%)=[AlSi−OHnorm−AlSi−Halnorm]AlSi−OHnorm+AlSi−Halnorm,whereAlsubstratenorm=Al2psubstrateXPSSi2psubstrateXPS
The inhibiting character of the halogenated surfaces can also be defined by the degree of conformation of the deposited thin films. For example, in Figure 6, three-dimensional AFM roughness topographies are displayed for the OH–Si(100) and Br(H)–Si(100) surfaces post ALD. The OH–Si(100) surface exhibits both a lower RMS roughness measurement and a smoother topography compared to that of the Br(H)–Si(100) surface. This is as expected since the brominated monolayer does not promote homogeneous nucleation of the precursor molecules and thus the gradual Al2O3 film growth should remain uneven. And this phenomenon is observed in the surface topography for the Br(H)–Si(100) surface where there is a greater number of defects scattered across the entire area of measurement, whereas OH–Si(100) exhibits a more homogeneous surface.

Figure 6

Figure 6. Three-dimensional AFM roughness topographies taken for the (a) OH–Si(100) and (b) Br(H)–Si(100) surfaces post ALD.

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Angle-resolved XPS (ARXPS) measurements were used to calculate the thickness of the deposited Al2O3 film on an OH–Si(100) GS. (80−84) The ARXPS measurements were inputted into eq 2SI, which describes the relationship between the XPS area intensity of the substrate electrons, the electron collection angle, and the thickness of the film that covers the substrate. The values for the mean free path of Si 2p electrons in the SiO2 and Al2O3 layers were calculated using the computational NIST model. The ARXPS thickness for the surface layer system comprising both a native SiO2 base layer and the top Al2O3 ALD film was calculated to be 4.26 nm. A ellipsometry measurement for the native SiO2 base layer shown in Figure 6SI demonstrates that the thickness of this layer is approximately 2.10 nm. Thus, the ARXPS measured thickness of the Al2O3 film on an OH–Si(100) after 20 cycles was determined to be 2.16 nm, as reported in Table 3.
The Al2O3 film thickness on the OH–Si(100) surface was used to correlate measured Al 2p/Si 2p XPS peak ratios on Si-OH, Si-H, and Si-Hal substrates with the thicknesses of the deposited alumina layers on these substrates (ARXPS method was not applied due to the uncertainty of how the ALD chemistry alters the thickness of the underlying halogen sublayers). The resulting film thicknesses on the NGS are reported in Table 3, which shows that the thinnest Al2O3 film was observed on Cl(H)–Si(100), followed by Br(H)–Si(100) and then I(H)–Si(100). This trend in film thickness mirrors that of the XPS halogen-to-silicon signal ratios, halogen coverage values, water contact angle, and blocking ability determined from XPS for all three surfaces. All three halogenated surfaces exhibited ALD film thicknesses lower than H-Si(100). Despite the three halogenated surfaces exhibiting similar Al-to-Si XPS ratios, when accounting for a higher 24 h air stability observed on Cl-Si(100), this material appears to be a more suitable candidate for Al2O3 ALD surface blocking. Overall, the reduced reactivity that each halogenated surface showed toward the ALD chemistry demonstrates that they are each suitable candidates for effective ALD resists and when paired with an ALD growth material, such as OH–Si(100), can participate in chemoselective processing schemes such as AS-ALD.

Conclusions

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In this study, XPS, ellipsometry, and contact angle goniometry measurements were used to demonstrate the covalent bonding of halogenated monolayers to a H-Si(100) surface prepared via a dry reaction process. NCS, NBS, and NIS were all found to be effective halogenating agents of H-Si(100). However, chlorination resulted in the highest halogen surface coverage by a significant margin, followed by bromination and then iodination. This approach exhibited exclusive bonding of halogen atoms to silicon while maintaining a low rate of oxidation of the underlying silicon interface, especially for chlorination and bromination. Stability tests in air were then undertaken to determine how long each surface could resist degradation and oxidation. Over the course of 24 h, Cl(H)–Si(100) demonstrated the strongest resistance to both halogen deterioration and SiO2 growth, followed by Br(H)–Si(100) and then I(H)–Si(100). At the end of 72 h, each surface more or less resembled each other with respect to organic and oxide concentration; however, Cl(H)–Si(100) was able to retain about a quarter of its original halogen coverage, something the other two surfaces did not achieve. Surfaces halogenated via a vapor-phase reaction can more feasibly be implemented into vacuum-based processes such as ALD. In such a process, the halogenating molecule can be dosed into the reactor chamber in the same manner as the ALD chemistry. Applying inhibiting molecules to a NGS on a sample surface will allow for patterned deposition of the desired thin film, using atoms as building blocks for synthesizing materials from the bottom-up. As a proof of principle, surfaces halogenated following our enumerated protocol underwent traditional ALD in order to examine the newly formed surface’s blocking ability against a metal oxide precursor. Consequently, SE and AFM data demonstrated the improved shielding ability of the halogenated monolayers relative to those of H-Si(100) and OH–Si(100). Once again, Cl(H)–Si(100) demonstrated the most effective blocking ability against the ALD chemistry, followed by bromination and then iodination. However, the reduced reactivity that each halogenated surface showed with the ALD chemistry demonstrates that they are each suitable candidates for effective ALD resists and when paired with an ALD growth material, such as OH–Si(100), can participate in chemoselective processing schemes such as AS-ALD.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.3c13269.

  • AFM images of the Si-H and Si-OH substrates, Haber and Lewis’s substrate-overlayer model equation, water contact angle measurement of the halogenated substrates, XPS spectra of all substrates, ARXPS Al2O3 film thickness measurement on the Si-OH substrate, and ellipsometry topographies of the Si-OH substrate (PDF)

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Author Information

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  • Corresponding Author
  • Authors
    • Patrick R. Raffaelle - Department of Chemical Engineering, Hajim School of Engineering and Applied Sciences, University of Rochester, Rochester, New York 14627, United States
    • George T. Wang - Sandia National Laboratories, Albuquerque, New Mexico 87185, United States;  Orcidhttps://orcid.org/0000-0001-9007-0173
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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The project is funded by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under Contract No. DE-NA-0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government. This article has been authored by an employee of National Technology & Engineering Solutions of Sandia, LLC. under Contract No. DE-NA-0003525 with the U.S. Department of Energy (DOE). The employee owns all right, title, and interest in and to the article and is solely responsible for its contents. The publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this article or allow others to do so, for United States Government purposes. The DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan https://www.energy.gov/downloads/doe-public-access-plan. This work was also supported by the National Science Foundation CMMI division under Grant No. 2225896.

Abbreviations

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(AS-ALD)

area-selective atomic layer deposition

(GS)

growth surface

(NGS)

nongrowth surface

(H-Si(100))

hydrogen-terminated silicon

(OH–Si(100))

hydroxyl-terminated silicon

(UHV)

ultrahigh vacuum

(Hal-Si(100))

halogenated Si(100)

(Cl-Si(100))

Cl-terminated Si(100) surface

(Br-Si(100))

Br-terminated surface

(H-SiQDs)

H-terminated silicon quantum dots

(NCS)

N-chlorosuccinimide

(NBS)

N-bromosuccinimide

(NIS)

N-iodosuccinimide

(XPS)

X-ray photoelectron spectroscopy

(ARXPS)

angle-resolved X-ray photoelectron spectroscopy

(SE)

spectroscopic ellipsometry

(SEM)

secondary electron microscopy

(STM)

scanning tunneling microscopy

(AFM)

atomic force microscopy

(BE)

binding energy

(SAMs)

self-assembled monolayers

(DFT)

density functional theory

(ASF)

atomic sensitivity factors

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    ACS Nano (2020), 14 (12), 17262-17272CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    There is an increasing interest in additive nanomanufg. processes, which enable customizable patterning of functional materials and devices on a wide range of substrates. However, there are relatively few techniques with the ability to directly 3D print patterns of functional materials with sub-micron resoln. In this study, we demonstrate the use of additive electrohydrodynamic jet (e-jet) printing with an av. line width of 312 nm, which acts as an inhibitor for area-selective at. layer deposition (AS-ALD) of a range of metal oxides. We also demonstrate subtractive e-jet printing with solvent inks that dissolve polymer inhibitor layers in specific regions, which enables localized AS-ALD within those regions. The chem. selectivity and morphol. of e-jet patterned polymers towards binary and ternary oxides of ZnO, Al2O3, and SnO2 were quantified using XPS, at. force microscopy, and Auger electron spectroscopy. This approach enables patterning of functional oxide semiconductors, insulators, and transparent conducting oxides with tunable compn., Å-scale control of thickness, and sub-μm resoln. in the x-y plane. Using a combination of additive and subtractive e-jet printing with AS-ALD, a thin-film transistor was fabricated using zinc-tin-oxide for the semiconductor channel and aluminum-doped zinc oxide as the source and drain elec. contacts. In the future, this technique can be used to print integrated electronics with sub-micron resoln. on a variety of substrates.
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  11. 11
    Deminskyi, P.; Haider, A.; Eren, H.; Khan, T. M.; Biyikli, N. Area-selective atomic layer deposition of noble metals: Polymerized fluorocarbon layers as effective growth inhibitors. J. Vac. Sci. Technol., A 2020, 39 (1), 022402  DOI: 10.1116/6.0000701
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  12. 12
    Krishtab, M.; Armini, S.; Meersschaut, J.; De Gendt, S.; Ameloot, R. Cyclic Plasma Halogenation of Amorphous Carbon for Defect-Free Area-Selective Atomic Layer Deposition of Titanium Oxide. ACS Appl. Mater. Interfaces 2021, 13 (27), 32381– 32392,  DOI: 10.1021/acsami.1c04405
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    12
    Cyclic plasma halogenation of amorphous carbon for defect-free area-selective atomic layer deposition of titanium oxide
    Krishtab, Mikhail; Armini, Silvia; Meersschaut, Johan; De Gendt, Stefan; Ameloot, Rob
    ACS Applied Materials & Interfaces (2021), 13 (27), 32381-32392CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    As crit. dimensions in integrated circuits continue to shrink, the lithog.-based alignment of adjacent patterned layers becomes more challenging. Area-selective at. layer deposition (ALD) allows circumventing the alignment issue by exploiting the chem. contrast of the exposed surfaces. In this work, we investigate the selective deposition of TiO2 by plasma halogenation of amorphous carbon (a-C:H) acting as a growth-inhibiting layer. On a-C:H, a CF4 or Cl2 plasma forms a thin halogenated layer that suppresses the growth of TiO2, while nucleation remains unaffected on plasma-treated SiO2. The same halogenating plasmas preferentially etch TiO2 nuclei over films and thus enable the restoration of the halogenated surface of amorphous carbon. By embedding the intermediate plasma treatments in the ALD TiO2 sequence, an 8 nm TiO2 layer could be deposited with a selectivity of 0.998. The application of the cyclic process on a 60 nm half-pitch line pattern resulted in the defect-free deposition of TiO2 at the bottom of the trenches. Cyclic fluorination demonstrated better growth inhibition compared to chlorination due to more efficient defect removal and retention of the favorable surface compn. during plasma exposure. While exploring the TiO2 nucleation defects at the limit of detection for conventional elemental anal. techniques (<1 x 1014 at/cm2), we addnl. highlight the value of imaging techniques such as at. force microscopy for understanding defect formation mechanisms and accurately assessing growth selectivity.
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  13. 13
    Miyajima, C.; Ito, S.; Nakagawa, M. Selective dry etching of UV-nanoimprinted resin passivation masks for area selective atomic layer deposition of aluminum oxide. J. Vac. Sci. Technol., B: Nanotechnol. Microelectron.: Mater., Process., Meas., Phenom. 2021, 39 (5), 052804  DOI: 10.1116/6.0001250
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    13
    Selective dry etching of UV-nanoimprinted resin passivation masks for area selective atomic layer deposition of aluminum oxide
    Miyajima, Chiaki; Ito, Shunya; Nakagawa, Masaru
    Journal of Vacuum Science & Technology, B: Nanotechnology & Microelectronics: Materials, Processing, Measurement, & Phenomena (2021), 39 (5), 052804CODEN: JVSTCN; ISSN:2166-2746. (American Institute of Physics)
    To demonstrate area selective at. layer deposition (ALD) using UV-nanoimprinted resin patterns as phys. passivation masks, we investigated the removal of UV-cured resin films subjected to sequential mutual doses of trimethylaluminum (TMA) and H2O by using dry etching procedures. On the basis of the removal of a residual layer characteristic from imprint resin patterns by anisotropic oxygen reactive ion etching (O2 RIE), oxidatively etched UV-cured films were modified with TMA and H2O in an ALD-like cyclic manner. Atomic force microscopy and time-of-flight secondary ion mass spectrometry [time-of-flight secondary ion mass spectrometry (TOF-SIMS)] anal. suggested that the combination of phys. Ar ion milling and subsequent chem. O2 RIE enabled the elimination of oxidized UV-cured resin masks modified with 5-cycle TMA doses. By contrast, Ar ion milling or O2 RIE left org. or inorg. residues on silicon surfaces, resp. A TMA-modified hybridized resin layer was etched by phys. Ar ion milling; subsequently, the org. residual resin layer was removed by chem. O2 RIE in the case of 5-cycle modification with TMA. The mapping image of Al+ visualized by TOF-SIMS suggested that line patterns of aluminum oxide were left selectively on unmasked silicon substrate surfaces by site-selective dry etching of TMA-modified imprint resin passivation masks with 500 nm linewidth. (c) 2021 American Institute of Physics.
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  14. 14
    Papananou, H.; Katsumata, R.; Neary, Z.; Goh, R.; Meng, X.; Limary, R.; Segalman, R. A. Dopamine-Mediated Polymer Coating Facilitates Area-Selective Atomic Layer Deposition. ACS Appl. Polym. Mater. 2021, 3 (10), 4924– 4931,  DOI: 10.1021/acsapm.1c00692
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    14
    Dopamine-Mediated Polymer Coating Facilitates Area-Selective Atomic Layer Deposition
    Papananou, Hellen; Katsumata, Reika; Neary, Zachary; Goh, Rubayn; Meng, Xiangxi; Limary, Ratchana; Segalman, Rachel A.
    ACS Applied Polymer Materials (2021), 3 (10), 4924-4931CODEN: AAPMCD; ISSN:2637-6105. (American Chemical Society)
    Area-selective at. layer deposition (ALD) has the potential to significantly improve current fabrication approaches by introducing a bottom-up process in which robust and conformal thin films are selectively deposited onto patterned substrates. This bottom-up approach requires selective areas of the substrates to be masked to inhibit deposition. Spontaneous self-assembly and organization of a mask, incorporating adhesion and other functions, are particularly attractive for this role as they do not require a sep. patterning step. Here, we make use of the pH/light tunability of catechol adhesion to develop a catechol-functionalized polymer that exhibits tunable adhesion strengths on different materials based on their specific chem. Tunable selective deposition was shown between metal/metal oxide substrates by controlling the local pH. Moreover, by controlling the adhesion strength through UV light, the deposition of hafnium oxide (HfO2) during ALD was successfully inhibited.
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  15. 15
    Chou, C.-Y.; Lee, W.-H.; Chuu, C.-P.; Chen, T.-A.; Hou, C.-H.; Yin, Y.-T.; Wang, T.-Y.; Shyue, J.-J.; Li, L.-J.; Chen, M.-J. Atomic Layer Nucleation Engineering: Inhibitor-Free Area-Selective Atomic Layer Deposition of Oxide and Nitride. Chem. Mater. 2021, 33 (14), 5584– 5590,  DOI: 10.1021/acs.chemmater.1c00823
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    15
    Atomic layer nucleation engineering: Inhibitor-free area-selective atomic layer deposition of oxide and nitride
    Chou, Chun-Yi; Lee, Wei-Hao; Chuu, Chih-Piao; Chen, Tse-An; Hou, Cheng-Hung; Yin, Yu-Tung; Wang, Ting-Yun; Shyue, Jing-Jong; Li, Lain-Jong; Chen, Miin-Jang
    Chemistry of Materials (2021), 33 (14), 5584-5590CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Area-selective at. layer deposition (AS-ALD) has attracted attention due to the process demand for semiconductor device scaling. Here, we propose the at. layer nucleation engineering (ALNE) technique, an inhibitor-free AS-ALD of an oxide (Al2O3) and a nitride (AlN) with nearly 100% selectivity between the dielec. (SiO2) and the metal (Pt). The key is to add a radio-frequency substrate bias after precursor exposure and purge in each ALD cycle, where the energy from the ignited plasma selectively removes the precursors on the metal owing to the relatively lower binding energy compared to those on the dielec., thereby inhibiting the film growth on the metal. This crit. step enables the AS-ALD without selectivity loss up to 100 ALD cycles, leading to significant thickness differences of ~ 14.9 and ~ 8.7 nm for Al2O3 and AlN between the dielec. and metal surfaces. The realization of AS-ALD of Al2O3 and AlN by ALNE is also confirmed on the Pt/SiO2 patterned substrate. The ALNE offers a novel concept and approach to achieve high-selectivity AS-ALD, which is crit. to further extension of Moore's law.
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  16. 16
    Gasvoda, R. J.; Xu, W.; Zhang, Z.; Wang, S.; Hudson, E. A.; Agarwal, S. Selective Gas-Phase Functionalization of SiO2 and SiNx Surfaces with Hydrocarbons. Langmuir 2021, 37 (13), 3960– 3969,  DOI: 10.1021/acs.langmuir.1c00212
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    16
    Selective Gas-Phase Functionalization of SiO2 and SiNx Surfaces with Hydrocarbons
    Gasvoda, Ryan J.; Xu, Wanxing; Zhang, Zhonghao; Wang, Scott; Hudson, Eric A.; Agarwal, Sumit
    Langmuir (2021), 37 (13), 3960-3969CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    Selective functionalization of dielec. surfaces is required for area-selective at. layer deposition and etching. We have identified precursors for the selective gas-phase functionalization of plasma-deposited SiO2 and SiNx surfaces with hydrocarbons. The corresponding reaction mechanism of the precursor mols. with the two surfaces was studied using in situ surface IR spectroscopy. We show that at a substrate temp. of 70°C, cyclic azasilanes preferentially react with an -OH-terminated SiO2 surface over a -NHx-terminated SiNx surface with an attachment selectivity of ~ 5.4, which is limited by the partial oxidn. of the SiNx surface. The cyclic azasilane undergoes a ring-opening reaction where the Si-N bond cleaves upon the reaction with surface -OH groups forming a Si-O-Si linkage. After ring opening, the backbone of the grafted hydrocarbon is terminated with a secondary amine, -NHCH3, which can react with water to form an -OH-terminated surface and release CH3NH2 as the product. The surface coverage of the grafted cyclic azasilane is calcd. as ~ 3.3 x 1014 cm-2, assuming that each reacted -OH group contributes to one hydrocarbon linkage. For selective attachment to SiNx over SiO2 surfaces, we detd. the reaction selectivity of aldehydes. We demonstrate that aldehydes selectively attach to SiNx over SiO2 surfaces, and for the specific branched aliph. aldehyde used in this work, almost no reaction was detected with the SiO2 surface. A fraction of the aldehyde mols. reacts with surface -NH2 groups to form an imine (Si-N = C) surface linker with H2O released as the byproduct. The other fraction of the aldehydes also reacts with surface -NH2 groups but do not undergo the water-elimination step and remains attached to the surface as an aminoalc. (Si-NH-COH-). The surface coverage of the grafted aldehyde is calcd. as ~ 9.8 x 1014 cm-2 using a known IR absorbance cross-section for the -C(CH3)3 groups.
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  17. 17
    Kim, H.-M.; Lee, J.-H.; Lee, S.-H.; Harada, R.; Shigetomi, T.; Lee, S.; Tsugawa, T.; Shong, B.; Park, J.-S. Area-Selective Atomic Layer Deposition of Ruthenium Using a Novel Ru Precursor and H2O as a Reactant. Chem. Mater. 2021, 33 (12), 4353– 4361,  DOI: 10.1021/acs.chemmater.0c04496
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    17
    Area-selective atomic layer deposition of ruthenium using Ru precursor and H2O as reactant
    Kim, Hye-Mi; Lee, Jung-Hoon; Lee, Seung-Hwan; Harada, Ryosuke; Shigetomi, Toshiyuki; Lee, Seungjoon; Tsugawa, Tomohiro; Shong, Bonggeun; Park, Jin-Seong
    Chemistry of Materials (2021), 33 (12), 4353-4361CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Ruthenium (Ru) has drawn attention in the field of future semiconductor processing as a diffusion barrier layer and an electrode material. Here, ruthenium films are deposited by at. layer deposition (ALD) using a novel precursor, Ru2{μ2-η3-N(tBu)-C(H)-C(iPr)}(CO)6 (T-Rudic), and two different co-reagents, i.e., H2O and O2. Ru films are deposited at 0.1 Å/cycle at 150 °C with H2O and 0.8 Å/cycle at 200 °C with O2. The H2O reactant set exhibits ALD satn. between 150 and 200 °C. However, the O2 reactant set shows a linear incremental growth rate over 200 °C and nongrowth under 175 °C. Film growth preference is obsd. on various substrates (e.g., Si, SiO2, Al2O3, and graphitic carbon) when the H2O reactant is applied at 150 °C. Both exptl. data and d. functional theory calcns. indicate that preferential growth occurs on a hydrogen-terminated surface (Si) rather than a hydroxyl-terminated surface (SiO2). The Auger electron spectroscopy mapping image of a selectively deposited Ru film on a patterned Si and SiO2 substrate supports that this selective deposition mechanism also occurs in a square-patterned substrate.
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  18. 18
    Lee, J.; Lee, J.-M.; Oh, H.; Kim, C.; Kim, J.; Kim, D. H.; Shong, B.; Park, T. J.; Kim, W.-H. Inherently Area-Selective Atomic Layer Deposition of SiO2 Thin Films to Confer Oxide Versus Nitride Selectivity. Adv. Funct. Mater. 2021, 31 (33), 2102556  DOI: 10.1002/adfm.202102556
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    18
    Inherently Area-Selective Atomic Layer Deposition of SiO2 Thin Films to Confer Oxide Versus Nitride Selectivity
    Lee, Jinseon; Lee, Jeong-Min; Oh, Hongjun; Kim, Changhan; Kim, Jiseong; Kim, Dae Hyun; Shong, Bonggeun; Park, Tae Joo; Kim, Woo-Hee
    Advanced Functional Materials (2021), 31 (33), 2102556CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Area-selective at. layer deposition (AS-ALD) offers tremendous advantages in comparison with conventional top-down patterning processes that at.-level selective deposition can achieve in a bottom-up fashion on pre-defined areas in multi-dimensional structures. In this work, a method for exploiting substrate-dependent selectivity of aminosilane precursors for oxides vs. nitrides through chemo-selective adsorption is reported. For this purpose, AS-ALD of SiO2 thin films on SiO2 substrates rather than on SiN substrates are investigated. Theor. screening using d. functional theory (DFT) calcns. are performed to identify Si precursors that maximize adsorption selectivity; results indicate that di(isopropylamino)silane (DIPAS) has the potential to function as a highly chemo-selective precursor. Application of this precursor to SiN and SiO2 substrates result in inherent deposition selectivity of ≈4 nm without the aid of surface inhibitors. Furthermore, deposition selectivity is enhanced using an ALD-etch supercycle in which an etching step inserts periodically after a certain no. of ALD SiO2 cycles. Thereby, enlarged deposition selectivity greater than ≈10 nm is successfully achieved on both blanket- and SiO2/SiN-patterned substrates. Finally, area-selective SiO2 thin films over 4-5 nm are demonstrated inside 3D nanostructure. This approach for performing inherent AS-ALD expands the potential utility of bottom-up nanofabrication techniques for next-generation nanoelectronic applications.
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  19. 19
    Li, Y.-C.; Cao, K.; Yu-Xiao, L.; Jing-Ming, Z.; Gong, M.; Yan-Wei, W.; Shan, B.; Chen, R. Inherently Area-Selective Atomic Layer Deposition of Manganese Oxide through Electronegativity-Induced Adsorption. Molecules 2021, 26 (10), 3056  DOI: 10.3390/molecules26103056
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    19
    Inherently area-selective atomic layer deposition of manganese oxide through electronegativity-induced adsorption
    Li, Yi-Cheng; Cao, Kun; Lan, Yu-Xiao; Zhang, Jing-Ming; Gong, Miao; Wen, Yan-Wei; Shan, Bin; Chen, Rong
    Molecules (2021), 26 (10), 3056CODEN: MOLEFW; ISSN:1420-3049. (MDPI AG)
    Manganese oxide (MnOx) shows great potential in the areas of nano-electronics, magnetic devices and so on. Since the characteristics of precise thickness control at the at. level and self-align lateral patterning, area-selective deposition (ASD) of the MnOx films can be used in some key steps of nanomanufg. In this work, MnOx films are deposited on Pt, Cu and SiO2 substrates using Mn(EtCp)2 and H2O over a temp. range of 80-215°C. Inherently area-selective at. layer deposition (ALD) of MnOx is successfully achieved on metal/SiO2 patterns. The selectivity improves with increasing deposition temp. within the ALD window. Moreover, it is demonstrated that with the decrease of electronegativity differences between M (M = Si, Cu and Pt) and O, the chemisorption energy barrier decreases, which affects the initial nucleation rate. The inherent ASD aroused by the electronegativity differences shows a possible method for further development and prediction of ASD processes.
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  20. 20
    Bobb-Semple, D.; Zeng, L.; Cordova, I.; Bergsman, D. S.; Nordlund, D.; Bent, S. F. Substrate-Dependent Study of Chain Orientation and Order in Alkylphosphonic Acid Self-Assembled Monolayers for ALD Blocking. Langmuir 2020, 36 (43), 12849– 12857,  DOI: 10.1021/acs.langmuir.0c01974
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    20
    Substrate-Dependent Study of Chain Orientation and Order in Alkylphosphonic Acid Self-Assembled Monolayers for ALD Blocking
    Bobb-Semple, Dara; Zeng, Li; Cordova, Isvar; Bergsman, David S.; Nordlund, Dennis; Bent, Stacey F.
    Langmuir (2020), 36 (43), 12849-12857CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    For years, many efforts in area selective at. layer deposition (AS-ALD) have focused on trying to achieve high-quality self-assembled monolayers (SAMs), which have been shown by a no. of studies to be effective for blocking deposition. Herein, we show that in some cases where a densely packed SAM is not formed, significant ALD inhibition may still be realized. The formation of octadecylphosphonic acid (ODPA) SAMs was evaluated on four metal substrates: Cu, Co, W, and Ru. The mol. orientation, chain packing, and relative surface coverage were evaluated using near-edge X-ray absorption fine structure (NEXAFS), Fourier transform IR (FTIR) spectroscopy, and electrochem. impedance spectroscopy (EIS). ODPA SAMs formed on Co, Cu, and W showed strong angular dependence of the NEXAFS signal whereas ODPA on Ru did not, suggesting a disordered layer was formed on Ru. Addnl., EIS and FTIR spectroscopy confirmed that Co and Cu form densely packed, "crystal-like" SAMs whereas Ru and W form less dense monolayers, a surprising result since W-ODPA was previously shown to inhibit the ALD of ZnO and Al2O3 best among all the substrates. This work suggests that multiple factors play a role in SAM-based AS-ALD, not just the SAM quality. Therefore, metrol. averaging techniques (e.g., WCA and FTIR spectroscopy) commonly used for evaluating SAMs to predict their suitability for ALD inhibition should be supplemented by more atomically sensitive methods. Finally, it highlights important considerations for describing the mechanism of SAM-based selective ALD.
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  21. 21
    de Paula, C.; Bobb-Semple, D.; Bent, S. F. Increased selectivity in area-selective ALD by combining nucleation enhancement and SAM-based inhibition. J. Mater. Res. 2021, 36 (3), 582– 591,  DOI: 10.1557/s43578-020-00013-4
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    21
    Increased selectivity in area-selective ALD by combining nucleation enhancement and SAM-based inhibition
    de Paula, Camila; Bobb-Semple, Dara; Bent, Stacey F.
    Journal of Materials Research (2021), 36 (3), 582-591CODEN: JMREEE; ISSN:2044-5326. (Springer International Publishing AG)
    An area-selective at. layer deposition (AS-ALD) process is developed that achieves increased selectivity by combining two strategies: (i) selective enhancement using a small mol. activator and (ii) self-assembled monolayer (SAM)-based inhibition. Specifically, we show that Pt can be selectively deposited on SiO2 over Co. In this process, Co, which serves as the non-growth surface, is protected by an octadecylphosphonic acid (ODPA) SAM, while the subsequent nucleation and growth of Pt on SiO2 is enhanced using a trimethylaluminum (AlMe3) pretreatment. This combination of enhancement and inhibition yields 3-6 times higher Pt coverage on the growth surface (SiO2) while maintaining selectivity of at least 0.98 after 100 Pt ALD cycles. Pt is used here as a model system, but this process can be extended for AS-ALD of other materials.
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  22. 22
    Liu, T.-L.; Bent, S. F. Area-Selective Atomic Layer Deposition on Chemically Similar Materials: Achieving Selectivity on Oxide/Oxide Patterns. Chem. Mater. 2021, 33 (2), 513– 523,  DOI: 10.1021/acs.chemmater.0c03227
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    22
    Area-selective atomic layer deposition on chemically similar materials: Achieving selectivity on oxide/oxide patterns
    Liu, Tzu-Ling; Bent, Stacey F.
    Chemistry of Materials (2021), 33 (2), 513-523CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Area-selective at. layer deposition (AS-ALD) is attracting increasing interest, but the process usually requires substrate materials with substantially different chem. properties. We introduce a process that expands the application to more general material systems by demonstrating AS-ALD on patterns with chem. similar materials. The substrate materials investigated are Al2O3, HfO2, TiO2, Ta2O5, and SiO2. By taking advantage of differential reactivity of octadecylphosphonic acid (ODPA) self-assembled monolayers (SAMs) on the various dielec. surfaces, we use the SAMs as ALD inhibitors to achieve selective ALD of both ZnO and Al2O3. With SiO2 as the growth surface, the best blocking performance against ZnO and Al2O3 ALD is achieved on ODPA-protected Al2O3 and HfO2 substrates which reach selectivities above 0.9 after 14 nm ZnO and 2.5 nm Al2O3 growth, resp., on control Si wafers. Selectivity between different metal oxides is also explored, including HfO2/Al2O3 patterns. With the optimization of solvent and ODPA SAM deposition time, selectivity above 0.9 can be achieved for at least 4 nm ZnO ALD on a HfO2 growth surface, while preventing growth on an Al2O3 nongrowth surface. This study introduces a strategy for achieving more general selectivity and opens up the possibility for new applications in next generation electronic devices.
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  23. 23
    Liu, T.-L.; Zeng, L.; Nardi, K. L.; Hausmann, D. M.; Bent, S. F. Characterizing Self-Assembled Monolayer Breakdown in Area-Selective Atomic Layer Deposition. Langmuir 2021, 37 (39), 11637– 11645,  DOI: 10.1021/acs.langmuir.1c02211
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    23
    Characterizing self-assembled monolayer breakdown in area-selective atomic layer deposition
    Liu, Tzu-Ling; Zeng, Li; Nardi, Katie L.; Hausmann, Dennis M.; Bent, Stacey F.
    Langmuir (2021), 37 (39), 11637-11645CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    To enable area-selective at. layer deposition (AS-ALD), self-assembled monolayers (SAMs) have been used as the surface inhibitor to block a variety of ALD processes. The integrity of the SAM throughout the ALD process is crit. to AS-ALD. Despite the demonstrated effectiveness of inhibition by SAMs, nucleation during ALD eventually occurs on SAM-protected surfaces, but its impact on SAM structures is still not fully understood. In this study, we chose the octadecyltrichlorosilane (ODTS) SAM as a model system to investigate the evolution of crystallinity and structure of SAMs before and after ALD. The breakdown behavior of SAMs when exposed to ZnO and Al2O3 ALD was systematically studied by combining synchrotron X-ray techniques and electron microscopy. We show that the crystallinity and structure of ODTS SAMs grown on Si substrates remain intact until a significant amt. of material deposition takes place. In addn., the undesired ALD materials that grow on ODTS SAMs present contrasting morphologies: dispersed nanoparticles for ZnO while relatively continuous film for Al2O3. Lastly, substrate dependency was explored by comparing a Si substrate to single-crystal sapphire. Similar results in the evolution of SAM crystallinity and formation of ALD nuclei on top of SAM are obsd. in the ODTS-sapphire system. This study provides an in-depth view of the influence of ALD processes on the SAM structure and the nucleation behavior of ALD on SAM-protected surfaces.
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  24. 24
    Hashemi, F. S. M.; Prasittichai, C.; Bent, S. F. Self-Correcting Process for High Quality Patterning by Atomic Layer Deposition. ACS Nano 2015, 9 (9), 8710– 8717,  DOI: 10.1021/acsnano.5b03125
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  25. 25
    Liu, T. L.; Bent, S. F. Area-Selective Atomic Layer Deposition on Chemically Similar Materials: Achieving Selectivity on Oxide/Oxide Patterns. Chem. Mater. 2021, 33 (2), 513– 523,  DOI: 10.1021/acs.chemmater.0c03227
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    25
    Area-selective atomic layer deposition on chemically similar materials: Achieving selectivity on oxide/oxide patterns
    Liu, Tzu-Ling; Bent, Stacey F.
    Chemistry of Materials (2021), 33 (2), 513-523CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Area-selective at. layer deposition (AS-ALD) is attracting increasing interest, but the process usually requires substrate materials with substantially different chem. properties. We introduce a process that expands the application to more general material systems by demonstrating AS-ALD on patterns with chem. similar materials. The substrate materials investigated are Al2O3, HfO2, TiO2, Ta2O5, and SiO2. By taking advantage of differential reactivity of octadecylphosphonic acid (ODPA) self-assembled monolayers (SAMs) on the various dielec. surfaces, we use the SAMs as ALD inhibitors to achieve selective ALD of both ZnO and Al2O3. With SiO2 as the growth surface, the best blocking performance against ZnO and Al2O3 ALD is achieved on ODPA-protected Al2O3 and HfO2 substrates which reach selectivities above 0.9 after 14 nm ZnO and 2.5 nm Al2O3 growth, resp., on control Si wafers. Selectivity between different metal oxides is also explored, including HfO2/Al2O3 patterns. With the optimization of solvent and ODPA SAM deposition time, selectivity above 0.9 can be achieved for at least 4 nm ZnO ALD on a HfO2 growth surface, while preventing growth on an Al2O3 nongrowth surface. This study introduces a strategy for achieving more general selectivity and opens up the possibility for new applications in next generation electronic devices.
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  26. 26
    Merkx, M. J. M.; Jongen, R. G. J.; Mameli, A.; Lemaire, P. C.; Sharma, K.; Hausmann, D. M.; Kessels, W. M. M.; Mackus, A. J. M. Insight into the removal and reapplication of small inhibitor molecules during area-selective atomic layer deposition of SiO2. J. Vac. Sci. Technol.. A 2021, 39 (1), 012402  DOI: 10.1116/6.0000652
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    26
    Insight into the removal and reapplication of small inhibitor molecules during area-selective atomic layer deposition of SiO2
    Merkx, Marc J. M.; Jongen, Rick G. J.; Mameli, Alfredo; Lemaire, Paul C.; Sharma, Kashish; Hausmann, Dennis M.; Kessels, Wilhelmus M. M.; Mackus, Adriaan J. M.
    Journal of Vacuum Science & Technology, A: Vacuum, Surfaces, and Films (2021), 39 (1), 012402CODEN: JVTAD6; ISSN:0734-2101. (American Institute of Physics)
    As the semiconductor industry progresses toward more complex multilayered devices with ever smaller features, accurately aligning these layers with respect to each other has become a bottleneck in the advancement to smaller transistor nodes. To avoid alignment issues, area-selective at. layer deposition (ALD) can be employed to deposit material in a self-aligned fashion. Previously, we demonstrated area-selective ALD of SiO2 using three-step (i.e., ABC-type) ALD cycles comprising an acetylacetone (Hacac) dose (step A), a bis(diethylamino)silane precursor dose (step B), and an O2 plasma exposure (step C). In this work, the mechanisms of the removal and reapplication of the inhibitor mols. during area-selective ALD were studied, with the aim of enhancing the selectivity of the process. In situ IR spectroscopy shows that the O2 plasma exposure does not completely remove the adsorbed Hacac species (i.e., acac adsorbates) at the end of the cycle. The persisting species were found to contain fragments of Hacac mols., which hinder subsequent inhibitor adsorption in the next ALD cycle, and thereby contribute to a loss in selectivity. Alternatively, it was found that an H2 plasma is able to completely remove all acac species from the surface. An improvement in selectivity was achieved by using a four-step ALD cycle that includes an H2 plasma step, allowing the nucleation delay to be prolonged from 18 2 to 30 ± 3 ALD cycles. As a result, 2.7 ± 0.3 nm SiO2 can be deposited with a selectivity of 0.9, whereas only 1.6 ± 0.2 nm can be achieved without the H2 plasma step. This work shows that the addn. of a dedicated inhibitor removal step before the reapplication of the inhibitors can significantly improve the selectivity. (c) 2021 American Institute of Physics.
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  27. 27
    Rozyyev, V.; Murphy, J. G.; Barry, E.; Mane, A. U.; Sibener, S. J.; Elam, J. W. Vapor-phase grafting of a model aminosilane compound to Al2O3, ZnO, and TiO2 surfaces prepared by atomic layer deposition. Appl. Surf. Sci. 2021, 562, 149996  DOI: 10.1016/j.apsusc.2021.149996
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    27
    Vapor-phase grafting of a model aminosilane compound to Al2O3, ZnO, and TiO2 surfaces prepared by atomic layer deposition
    Rozyyev, Vepa; Murphy, Julia G.; Barry, Edward; Mane, Anil U.; Sibener, S. J.; Elam, Jeffrey W.
    Applied Surface Science (2021), 562 (), 149996CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
    Atomic layer deposition (ALD) is a highly versatile surface functionalization technique that can conformally coat both planar and porous substrates. Here we use ALD metal oxide layers to establish a well-defined starting surface for vapor-phase surface org. modification. Vapor-phase (3-aminopropyl)triethoxysilane (APTES) surface silanization of ALD Al2O3, ZnO and TiO2 surfaces were studied at 100°C, 150°C and 200°C. In situ quartz crystal microbalance (QCM) and Fourier-transform IR (FTIR) spectroscopy measurements, and ex situ at. force microscopy (AFM) and XPS measurements showed uniform monolayer silane formation through self-limiting APTES reaction. We obsd. a higher surface d. of grafted APTES species following silanization at 100°C compared to 200°C, and we attribute this to the temp.-dependent reactivity of the surface hydroxyls and changes in the mode of APTES reaction. The FTIR and XPS measurements revealed that APTES reacts with Al2O3 and ZnO exclusively through metal siloxy bond formation. However, APTES reacts with TiO2 through both siloxy bond formation and ammonium salt formation via the amine group.
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  28. 28
    Vos, M. F. J.; Chopra, S. N.; Ekerdt, J. G.; Agarwal, S.; Kessels, W. M. M.; Mackus, A. J. M. Atomic layer deposition and selective etching of ruthenium for area-selective deposition: Temperature dependence and supercycle design. J. Vac. Sci. Technol., A 2021, 39 (3), 032412  DOI: 10.1116/6.0000912
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    28
    Atomic layer deposition and selective etching of ruthenium for area-selective deposition: Temperature dependence and supercycle design
    Vos, Martijn F. J.; Chopra, Sonali N.; Ekerdt, John G.; Agarwal, Sumit; Kessels, Wilhelmus M. M.; Mackus, Adriaan J. M.
    Journal of Vacuum Science & Technology, A: Vacuum, Surfaces, and Films (2021), 39 (3), 032412CODEN: JVTAD6; ISSN:0734-2101. (American Institute of Physics)
    For future sub-5 nm technol. nodes, the fabrication of semiconductor devices will likely involve the use of area-selective at. layer deposition (ALD). While area-selective ALD processes have been reported for a variety of materials, most approaches yield a limited selectivity, for example, due to growth initiation at defects or impurities on the non-growth area. Recently, we demonstrated that Ru ALD can be combined with selective etching to achieve area-selective ALD of metal-on-metal with high selectivity. Cycles consisting of an O2 plasma and an H2 gas dose were integrated in an ALD-etch supercycle recipe to remove unwanted nuclei on the SiO2 non-growth area, while obtaining deposition on the Pt or Ru growth area. The current work discusses the challenging compromise that needs to be made between selectivity and net deposition, considering that the material is also removed from the growth area. After investigating deposition between 100 and 200°C on SiO2, Al2O3, Pt, and Ru in terms of selectivity and net deposition, a substrate temp. of 150°C was selected since the difference in Ru thickness on Pt and SiO2/Al2O3 was max. at this temp., even though still some deposition occurred on the SiO2 and Al2O3 non-growth areas. Different ALD-etch supercycles were studied, using varying O2 plasma etch times and etch frequencies. The amt. of the (undesired) material deposited on the SiO2 non-growth area was quantified, demonstrating that the selectivity improved for longer O2 plasma times. On the basis of the results, a simple math. description of the nucleation, growth, and etching effects during ALD-etch supercycles is discussed, which can assist the design of future area-selective deposition processes. Overall, this work illustrates how ALD and etch processes can be tuned to simultaneously obtain a high selectivity and a high net deposition of the material at the desired locations. (c) 2021 American Institute of Physics.
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    Hong, J.; Porter, D. W.; Sreenivasan, R.; McIntyre, P. C.; Bent, S. F. ALD resist formed by vapor-deposited self-assembled monolayers. Langmuir 2007, 23 (3), 1160– 1165,  DOI: 10.1021/la0606401
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    ALD Resist Formed by Vapor-Deposited Self-Assembled Monolayers
    Hong, Junsic; Porter, David W.; Sreenivasan, Raghavasimhan; McIntyre, Paul C.; Bent, Stacey F.
    Langmuir (2007), 23 (3), 1160-1165CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    A new process of applying mol. resists to block HfO2 and Pt at. layer deposition (ALD) has been investigated. Monolayer films are formed from octadecyltrichlorosilane (ODTS) or tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS) and water vapor on native silicon oxide surfaces and from 1-octadecene on hydrogen-passivated silicon surfaces through a low-pressure chem. vapor deposition process. XPS data indicates that surfaces blocked by these monolayer resists can prevent at. layer deposition of both HfO2 and Pt successfully. Time-dependent studies show that the ODTS monolayers continue to improve in blocking ability for as long as 48 h of formation time, and IR spectroscopy measurements confirm an evolution of packing order over these time scales.
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  30. 30
    Halls, M. D.; Raghavachari, K. Atomic layer deposition of Al2O3 on H-passivated Si.: I.: Initial surface reaction pathways with H/Si(100)-2 × 1. J. Chem. Phys. 2003, 118 (22), 10221– 10226,  DOI: 10.1063/1.1571513
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    Atomic layer deposition of Al2O3 on H-passivated Si. I. Initial surface reaction pathways with H/Si(100)-2×1
    Halls, Mathew D.; Raghavachari, Krishnan
    Journal of Chemical Physics (2003), 118 (22), 10221-10226CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    Aluminum oxide (Al2O3) grown by at. layer deposition (ALD) is currently under investigation for use as a high-k gate dielec. alternative to SiO2. Cluster calcns. employing hybrid d. functional theory have been carried out to examine the chem. reaction pathways between the ALD precursors, trimethylaluminum (TMA) and H2O, with the H/Si(100)-2×1 surface. Results obtained using Si9H14 and Si15H20, dimer and double dimer clusters to represent the surface active site are in good agreement, providing a consistent view of reaction energetics on the H/Si(100)-2×1 surface. The adsorption energies for TMA and H2O on the surface are calcd. to be 0.02 and 0.15 eV, resp. For the reaction between H2O and the H/Si(100)-2×1 surface, hydroxylation of the surface accompanied by loss of H2 was found to be the preferred pathway having an activation energy and overall reaction enthalpy of 1.60 eV and -0.75 eV, both of which are ≥0.70 eV lower than the corresponding values for the possible H/D exchange reaction. TMA exposure of the H/Si(100)-2×1 surface favors the deposition of -Al(CH3)2 with loss of CH4, having a barrier height of 1.30 eV and reaction enthalpy of -0.31 eV, which are 0.10 and 0.40 eV lower than the surface methylation pathway (H/CH3 exchange) and 2.64 and 0.45 eV lower in energy than the H2 loss reaction, which results in the deposition of -CH2-Al(CH3)2 to the surface. Therefore, the dominant reactions identified in this work are those with direct implication in the Al2O3 ALD growth mechanism, leading to the formation of Si-O and Si-Al species on the H/Si(100)-2×1 surface.
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  31. 31
    Tai, T. B.; Cao, L. A.; Mattelaer, F.; Rampelberg, G.; Hashemi, F. S. M.; Dendooven, J.; van Ommen, J. R.; Detavernier, C.; Reyniers, M. F. Atomic Layer Deposition of Al2O3 Using Aluminum Triisopropoxide (ATIP): A Combined Experimental and Theoretical Study. J. Phys. Chem. C 2019, 123 (1), 485– 494,  DOI: 10.1021/acs.jpcc.8b09198
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    Atomic Layer Deposition of Al2O3 Using Aluminum Triisopropoxide (ATIP): A Combined Experimental and Theoretical Study
    Tai, Truong Ba; Cao, LiAo; Mattelaer, Felix; Rampelberg, Geert; Hashemi, Fatemeh S. M.; Dendooven, Jolien; van Ommen, J. Ruud; Detavernier, Christophe; Reyniers, Marie-Francoise
    Journal of Physical Chemistry C (2019), 123 (1), 485-494CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    The aluminum precursor plays a crucial role in the Al2O3 at. layer deposition (ALD) process. To date, trimethylaluminum (TMA) is 1 of the most widely used precursors in exptl. and theor. studies. However, its application at industrial scale can pose safety risks since it is pyrophoric and extremely reactive with water. Aluminum alkoxides offer a promising alternative, but have received far less attention. A combined theor. and exptl. investigation is carried out on the Al2O3 ALD process using aluminum triisopropoxide (ATIP) as a prototypical example of Al-alkoxide precursors. The thermal ALD process using ATIP and water has a maximal growth per cycle (GPC) of 1.8 Å/cycle at 150-175°. On the basis of the in situ mass spectrometry anal. and DFT calcns., the formation of the alumina film mainly occurs during the water pulse by ligand exchange reactions between water and adsorbed precursors, while during the ATIP pulse only adsorption of ATIP and/or its dissocn. occur. Design of heteroleptic precursors contg. alkoxide group as basic ligand is challenging, but greatly promising for future industrial scale Al2O3 ALD.
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    Perrine, K. A.; Teplyakov, A. V. Reactivity of selectively terminated single crystal silicon surfaces. Chem. Soc. Rev. 2010, 39 (8), 3256– 3274,  DOI: 10.1039/b822965c
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    Reactivity of selectively terminated single crystal silicon surfaces
    Perrine, Kathryn A.; Teplyakov, Andrew V.
    Chemical Society Reviews (2010), 39 (8), 3256-3274CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. As the cornerstone of multiple practical applications, silicon single crystal surfaces have attracted the interest of scientific and engineering communities for several decades. The most recent advances employ the surfaces precovered with a specific functionality to extend into the realm of org. and metal-org. films with well-defined interfaces, to protect the surfaces from oxidn. and other contaminations, and to build the components of present and future mol. electronics and sensing devices. This crit. review will focus on the reactivity of the selectively terminated Si(100) and Si(111) surfaces. The hydrogen and halogen-terminated surfaces are the most widely used and most heavily reviewed previously, thus only a brief summary will be given here with the emphasis of the most recent thermal approaches to functionalization of hydrogen-terminated silicon. The silicon surfaces precovered with NHx functionality are emerging as a very likely candidate both for the prodn. of sharp interfaces and for coadsorption, co-assembly, and potential mol. templating of patterns on single cryst. surfaces. A brief overview of recent advances in achieving control over the hydroxyl-termination of silicon will be given. Some future directions for further development of chem., reactivity, and assembly on these surfaces, as well as potential applications, are highlighted in the last section (152 refs.).
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    Clark, R.; Tapily, K.; Yu, K. H.; Hakamata, T.; Consiglio, S.; O’Meara, D.; Wajda, C.; Smith, J.; Leusink, G. Perspective: New process technologies required for future devices and scaling. APL Mater. 2018, 6 (5), 058203  DOI: 10.1063/1.5026805
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    Perspective: New process technologies required for future devices and scaling
    Clark, R.; Tapily, K.; Yu, K.-H.; Hakamata, T.; Consiglio, S.; O'Meara, D.; Wajda, C.; Smith, J.; Leusink, G.
    APL Materials (2018), 6 (5), 058203/1-058203/12CODEN: AMPADS; ISSN:2166-532X. (American Institute of Physics)
    This paper presents an overview and perspective on processing technologies required for continued scaling of leading edge and emerging semiconductor devices. We introduce the main drivers and trends affecting future semiconductor device scaling and provide examples of emerging devices and architectures that may be implemented within the next 10-20 yr. We summarize multiple active areas of research to explain how future thin film deposition, etch, and patterning technologies can enable 3D (vertical) power, performance, area, and cost scaling. Emerging and new process technologies will be required to enable improved contacts, scaled and future devices and interconnects, monolithic 3D integration, and new computing architectures. These process technologies are explained and discussed with a focus on opportunities for continued improvement and innovation. (c) 2018 American Institute of Physics.
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    He, J.; Patitsas, S. N.; Preston, K. F.; Wolkow, R. A.; Wayner, D. D. M. Covalent bonding of thiophenes to Si(111) by a halogenation/thienylation route. Chem. Phys. Lett. 1998, 286 (5–6), 508– 514,  DOI: 10.1016/S0009-2614(98)00128-6
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    Covalent bonding of thiophenes to Si(111) by a halogenation/thienylation route
    He, J.; Patitsas, S. N.; Preston, K. F.; Wolkow, R. A.; Wayner, D. D. M.
    Chemical Physics Letters (1998), 286 (5,6), 508-514CODEN: CHPLBC; ISSN:0009-2614. (Elsevier Science B.V.)
    Thienyl monolayers covalently bonded to a Si(111) surface were prepd. by a wet chem. process in which a Si(111)-H surface was brominated to form Si(111)-Br and further reacted with lithiated thiophenes. Both N-bromosuccinimide and bromochloroform were found to be effective brominating reagents. The derivatized Si(111) surfaces were characterized by XPS, AES, ATR-FTIR and NEXAFS.
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    Yu, W. H.; Kang, E. T.; Neoh, K. G.; Zhu, S. P. Controlled grafting of well-defined polymers on hydrogen-terminated silicon substrates by surface-initiated atom transfer radical polymerization. J. Phys. Chem. B 2003, 107 (37), 10198– 10205,  DOI: 10.1021/jp034330s
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    Controlled grafting of well-defined polymers on hydrogen-terminated silicon substrates by surface-initiated atom transfer radical polymerization
    Yu, W. H.; Kang, E. T.; Neoh, K. G.; Zhu, Shiping
    Journal of Physical Chemistry B (2003), 107 (37), 10198-10205CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
    Controlled grafting of well-defined polymer brushes on the hydrogen-terminated Si(100) substrates (the Si-H substrate) was carried out via the surface-initiated atom transfer radical polymn. (ATRP). Surface initiators were immobilized on the Si-H substrates in three consecutive steps: (i) coupling of an ω-unsatd. alkyl ester to the Si-H surface under UV irradn., (ii) redn. of the ester groups by LiAlH4, and (iii) esterification of the surface-tethered hydroxyl groups with 2-bromoisobutyrate bromide. Homopolymer brushes of Me methacrylate (MMA), (2-dimethylamino)ethyl methacrylate (DMAEMA), and poly(ethylene glycol) monomethacrylate (PEGMA) were prepd. by ATRP from the α-bromoester functionalized silicon surface. The chem. compn. and topog. of the graft-functionalized silicon surfaces were characterized by XPS and at. force microscopy (AFM), resp. Kinetic studies revealed a linear increase in polymer film thickness with reaction time, indicating that chain growth from the surface was a controlled process with a "living" characteristic. Diblock copolymer brushes consisting of PMMA and PDMAEMA blocks were obtained by using the homopolymer brushes as the macroinitiators for the ATRP of the second monomer, providing further evidence to the existence of "living" chain ends. ATRP from the Si-H surfaces allowed the prepn. of polymeric-inorg. hybrid materials with well-structured surface and interface.
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    Coffinier, Y.; Piret, G.; Das, M. R.; Boukherroub, R. Effect of surface roughness and chemical composition on the wetting properties of silicon-based substrates. C. R. Chim. 2013, 16 (1), 65– 72,  DOI: 10.1016/j.crci.2012.08.011
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    Effect of surface roughness and chemical composition on the wetting properties of silicon-based substrates
    Coffinier, Yannick; Piret, Gaelle; Das, Manash R.; Boukherroub, Rabah
    Comptes Rendus Chimie (2013), 16 (1), 65-72CODEN: CRCOCR; ISSN:1631-0748. (Elsevier Masson SAS)
    The article reports on the wetting properties of Si-based materials as a function of their roughness and chem. compn. The studied surfaces consist of H-terminated and chem. modified atomically flat cryst. Si, porous Si and Si nanowires. The hydrogenated surfaces are functionalized with 1-octadecene or undecylenic acid under thermal conditions. The changes occurring upon surface functionalization are characterized using FTIR spectroscopy, XPS spectroscopy and H2O contact angle measurements. By increasing the surface roughness, the static H2O contact angle increases. The combination of high surface roughness with chem. functionalization with H2O repellent coating (1-octadecene) enables reaching superhydrophobicity (water contact angle >150°) for Si nanowires.
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    Frederick, E.; Dwyer, K. J.; Wang, G. T.; Misra, S.; Butera, R. E. The stability of Cl-, Br-, and I-passivated Si(100)-(2 × 1) in ambient environments for atomically-precise pattern preservation. J. Phys.: Condens. Matter 2021, 33 (44), 444001  DOI: 10.1088/1361-648x/ac1aa4
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    The stability of Cl-, Br-, and I-passivated Si(100)-(2 x 1) in ambient environments for atomically-precise pattern preservation
    Frederick, E.; Dwyer, K. J.; Wang, G. T.; Misra, S.; Butera, R. E.
    Journal of Physics: Condensed Matter (2021), 33 (44), 444001CODEN: JCOMEL; ISSN:0953-8984. (IOP Publishing Ltd.)
    Atomic precision advanced manufg. (APAM) leverages the highly reactive nature of Si dangling bonds relative to H- or Cl-passivated Si to selectively adsorb precursor mols. into lithog. defined areas with sub-nanometer resoln. Due to the high reactivity of dangling bonds, this process is confined to ultra-high vacuum (UHV) environments, which currently limits its commercialization and broad-based appeal. In this work, we explore the use of halogen adatoms to preserve APAM-derived lithog. patterns outside of UHV to enable facile transfer into real-world com. processes. Specifically, we examine the stability of H-, Cl-, Br-, and I-passivated Si(100) in inert N2 and ambient environments. Characterization with scanning tunneling microscopy and XPS confirmed that each of the fully passivated surfaces were resistant to oxidn. in 1 atm of N2 for up to 44 h. Varying levels of surface degrdn. and contamination were obsd. upon exposure to the lab. ambient environment. Characterization by ex situ XPS after ambient exposures ranging from 15 min to 8 h indicated the Br- and I-passivated Si surfaces were highly resistant to degrdn., while Cl-passivated Si showed signs of oxidn. within minutes of ambient exposure. As a proof-of-principle demonstration of pattern preservation, a H-passivated Si sample patterned and passivated with independent Cl, Br, I, and bare Si regions was shown to maintain its integrity in all but the bare Si region post-exposure to an N2 environment. The successful demonstration of the preservation of APAM patterns outside of UHV environments opens new possibilities for transporting atomically-precise devices outside of UHV for integrating with non-UHV processes, such as other chemistries and com. semiconductor device processes.
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    Rogozhina, E.; Belomoin, G.; Smith, A.; Abuhassan, L.; Barry, N.; Akcakir, O.; Braun, P. V.; Nayfeh, M. H. Si-N linkage in ultrabright, ultrasmall Si nanoparticles. Appl. Phys. Lett. 2001, 78 (23), 3711– 3713,  DOI: 10.1063/1.1377619
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    Si-N linkage in ultra-bright, ultrasmall Si nanoparticles
    Rogozhina, E.; Belomoin, G.; Smith, A.; Abuhassan, L.; Barry, N.; Akcakir, O.; Braun, P. V.; Nayfeh, M. H.
    Applied Physics Letters (2001), 78 (23), 3711-3713CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    Ultra-bright ultrasmall (∼1 nm) blue luminescent Si29 nanoparticles are chlorinated by reaction with Cl2 gas. A Si-N linkage is formed by the reaction of the chlorinated particles with the functional amine group in butylamine. FTIR spectroscopy and x-ray photo-spectroscopy measurements confirm the N linkage and the presence of the Bu group, while emission, excitation, and autocorrelation femtosecond optical spectroscopy show that, after the linkage formation, the particles with the ultra-bright blue luminescence remain, but with a red shift of 40 nm.
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    Ferng, S. S.; Wu, S. T.; Lin, D. S.; Chiang, T. C. Mediation of chain reactions by propagating radicals during halogenation of H-masked Si(100): Implications for atomic-scale lithography and processing. J. Chem. Phys. 2009, 130 (16), 164706  DOI: 10.1063/1.3122987
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    Mediation of chain reactions by propagating radicals during halogenation of H-masked Si(100): Implications for atomic-scale lithography and processing
    Ferng, Shyh-Shin; Wu, Shiao-Ting; Lin, Deng-Sung; Chiang, Tai C.
    Journal of Chemical Physics (2009), 130 (16), 164706/1-164706/5CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    Scanning tunneling microscopy reveals a free radical-induced surface chain reaction in the chlorination of nanoscale patterns on an otherwise H-passivated (masked) Si(100). While scanning probe methods can be used to pattern active surface regions with single-bond precision, follow-up selective chem. vapor deposition with polyat. mols. can produce various filling characteristics. On active surface regions, mol. Cl2 undergoes an atom abstraction reaction in which a Si dangling bond abstrs. one atom of the incident Cl2 mol. while the complementary Cl atom is scattered away from the initial abstraction site either back into the vacuum or to be captured by a second dangling bond and adsorbed there, or to react with a nearby adsorbed H atom to form volatile HCl. In contrast, I2 undergoes only dissociative adsorption on two immediately neighboring dangling bonds, whereby two I-Si bonds are formed simultaneously upon cleavage of the I2 bond. The different chemisorption processes of the two model diat. mol. gases place intrinsic limitations on at.-scale lithog. and processing: adsorption of Cl2 results in spillage over the prepatterned regions of active bonds. In contrast, adsorption of I2 is a pair process and results in under-filling. (c) 2009 American Institute of Physics.
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  40. 40
    Rivillon, S.; Brewer, R. T.; Chabal, Y. J. Water reaction with chlorine-terminated silicon (111) and (100) surfaces. Appl. Phys. Lett. 2005, 87 (17), 173118  DOI: 10.1063/1.2119426
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    Water reaction with chlorine-terminated silicon (111) and (100) surfaces
    Rivillon, Sandrine; Brewer, Rhett T.; Chabal, Yves J.
    Applied Physics Letters (2005), 87 (17), 173118/1-173118/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    Hydroxylation of chlorine-terminated silicon (111) and (100) by water vapor exposure has been studied as a function of substrate temp. using in situ IR absorption spectroscopy. No hydroxyl is obsd., as would have been expected from the surface reaction: Si-Cl(ads)+H2O(g) Si-OH(ads)+HCl(g) (ads referring to adsorbed surface species). Instead, silicon oxide is formed upon removal of the Si-Cl bond at ∼325 °C. This indicates that, while hydroxylation of the Cl-terminated silicon surface may occur, the hydroxylated surface formed by this reaction is not stable at the temp. necessary for the reaction.
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    Dumas, P.; Chabal, Y. J.; Jakob, P. Morphology of Hydrogen-Terminated Si(111) and Si(100) Surfaces Upon Etching in Hf and Buffered-Hf Solutions. Surf. Sci. 1992, 269-270, 867– 878,  DOI: 10.1016/0039-6028(92)91363-G
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    Morphology of hydrogen-terminated silicon(111) and Si(100) surfaces upon etching in hydrofluoric acid and buffered-HF solutions
    Dumas, P.; Chabal, Y. J.; Jakob, P.
    Surface Science (1992), 269-270 (Pt. B), 867-78CODEN: SUSCAS; ISSN:0039-6028.
    High resoln. EELS and IR absorption spectroscopy (IRAS) were used to characterize Si(111) and Si(100) surfaces after chem. etching in solns. of HF and buffered HF. The EELS spectra confirm that the HF-etched Si surfaces are terminated completely by H, and display essentially no loss features attributable to at. or mol. impurities. IRAS and specular beam EELS measurements show that Si(111) surfaces become flatter as the pH of the etching solns. increases from 1 (concd. HF) to 7.8 (NH4F soln.). For high pH, the (111) surfaces are atomically flat and ideally H-terminated. In contrast, the Si(100) surfaces remain rough for all pH. The surface morphol., however, depends critically on the pH and varies most for pH between 5 and 7. The EELS spectra are dominated by impact scattering and the loss features show no measurable dispersion except for the atomically smooth, ideally H-terminated Si(111) surface.
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    Layadi, N.; Donnelly, V. M.; Lee, J. T. C. Cl-2 plasma etching of Si(100): Nature of the chlorinated surface layer studied by angle-resolved x-ray photoelectron spectroscopy. J. Appl. Phys. 1997, 81 (10), 6738– 6748,  DOI: 10.1063/1.365216
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    Cl2 plasma etching of Si(100): nature of the chlorinated surface layer studied by angle-resolved x-ray photoelectron spectroscopy
    Layadi, N.; Donnelly, V. M.; Lee, J. T. C.
    Journal of Applied Physics (1997), 81 (10), 6738-6748CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
    The interaction of a Cl2 plasma with a Si(100) surface has been investigated by angle resolved XPS (XPS). It was found that the amt. of chlorine incorporated into the near-surface region of Si increases with ion energy, and does not change with long exposure to the plasma. Chlorine is present as SiClx (x=1-3) with av. relative coverages (integrated over depth) of [SiCl]:[SiCl2]:[SiCl3]≃1:0.33.0.13 at -240 V dc bias (mean ion energy ≈280 eV) and 1.0.34:0.087 at 0 V dc bias (mean ion energy ≈40 eV), at XPS (XPS) binding energies of 100.2, 101.2 and 102.3 eV, resp. Moreover, there is a substantial amt. of disordered Si within the chlorinated layer at high ion energy, reflected in a broadening of the 99.4 eV Si peak and the appearance of a shoulder at 98.8 eV, ascribed to Si with a dangling bond. In addn., bulk Si plasmon loss assocd. with the Cl(2p) and Cl(2s) core levels indicate that roughly one-third of the Cl in the near-surface region is surrounded by bulklike Si at the high ion energy. Modeling of the dependence of the relative concn. of Cl on the take-of angle was used to est. the Cl content and thickness of the surface layer. From an inversion of the obsd. take-off angle dependence of the relative Cl and Si XPS signals, depth profiles were derived for the near-surface region. Cl content falls off in a graded fashion, over a depth of about 25 and 13 Å for a mean ion energies of 280 and 40 eV, resp. The Cl areal d. (coverage integrated throughout the layer) increases with increasing mean ion energy from 1.8×1015 Cl/cm2 at 40 eV to 3.5×1015 Cl/cm2 at 280 eV. From a similar inversion of the take-off angle dependence of the SiClx signals, SiCl2 and SiCl3 are found to be largely confined at the top ∼5 Å, while below the surface, disordered Si and SiCl are present.
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    Butera, R. E.; Suwa, Y.; Hashizume, T.; Weaver, J. H. Adsorbate-mediated step transformations and terrace rearrangement of Si(100)-(2 × 1). Phys. Rev. B 2009, 80 (19), 193307  DOI: 10.1103/physrevb.80.193307
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    Adsorbate-mediated step transformations and terrace rearrangement of Si(100)-(2 × 1)
    Butera, R. E.; Suwa, Yuji; Hashizume, Tomihiro; Weaver, J. H.
    Physical Review B: Condensed Matter and Materials Physics (2009), 80 (19), 193307/1-193307/4CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    Scanning tunneling microscopy and d.-functional theory have been combined to demonstrate structural transformations of steps of Si(100)-(2×1) induced by nondangling bond-terminated Cl adsorbates. We identify a stable, bridge-bonded step adsorption site and show that supersatn. facilitates the population of those sites, leading to rebonded atom etching, step retreat, and extensive terrace rearrangement from the diffusion of resultant at. vacancy lines across the supersatd. surface. Similarities to H-Si(100) are briefly discussed.
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    Aldao, C. M.; Agrawal, A.; Butera, R. E.; Weaver, J. H. Atomic processes during Cl supersaturation etching of Si(100)-(2 × 1). Phys. Rev. B 2009, 79 (12), 125303  DOI: 10.1103/physrevb.79.125303
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    Atomic processes during Cl supersaturation etching of Si(100)-(2×1)
    Aldao, C. M.; Agrawal, Abhishek; Butera, R. E.; Weaver, J. H.
    Physical Review B: Condensed Matter and Materials Physics (2009), 79 (12), 125303/1-125303/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    Supersatn. etching starts with Cl insertion into Si-Si bonds of Si(100) and leads to the desorption of SiCl2 pairs. During etching, insertion occurs through a Cl2 dissociative chemisorption process mediated by single dangling bond sites created by phonon-activated electron-stimulated desorption of at. Cl. Based on scanning tunneling microscopy results, the authors identify a surface species, describe its involvement in supersatn. etching, and explore the energetics that control this process. In doing so, insertion occurs at room temp. and paired dangling bonds of bare dimers also mediate this process.
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    Biswas, S.; Narasimhan, S. Bromine as a Preferred Etchant for Si Surfaces in the Supersaturation Regime: Insights from Calculations of Atomic Scale Reaction Pathways. J. Phys. Chem. C 2016, 120 (28), 15230– 15234,  DOI: 10.1021/acs.jpcc.6b04450
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    45
    Bromine as a Preferred Etchant for Si Surfaces in the Supersaturation Regime: Insights from Calculations of Atomic Scale Reaction Pathways
    Biswas, Sananda; Narasimhan, Shobhana
    Journal of Physical Chemistry C (2016), 120 (28), 15230-15234CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Etching of semiconductors by halogens is of vital importance in device manuf. A greater understanding of the relevant processes at the atomistic level can help det. optimal conditions for etching to be carried out. Supersatn. etching is a seemingly counterintuitive process where the coverage of the etchant mols. on the surface to be etched is >1. Here we use d. functional theory computations of reaction pathways and barriers to suggest that supersatn. etching of Si(001) by Br2 should be more effective than conventional etching by Br2, as well as both conventional and supersatn. etching by Cl2. Anal. of our results shows that this is due in part to the larger size of bromine atoms, and partly due to Br-Si bonds being weaker than Cl-Si bonds. We also show that, for both conventional and supersatn. etching, the barrier for the rate-limiting step of desorption of SiX2 units is lower when the halogen X is Br rather than Cl. This contributes to the overall reaction barrier for supersatn. etching being lower for Br2 than for Cl2.
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    Pavlova, T. V.; Shevlyuga, V. M.; Andryushechkin, B. V.; Eltsov, K. N. Chlorine insertion and manipulation on the Si(100)-2 × 1-Cl surface in the regime of local supersaturation. Phys. Rev. B 2020, 101 (23), 235410  DOI: 10.1103/physrevb.101.235410
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    Chlorine insertion and manipulation on the Si(100)-2x1-Cl surface in the regime of local supersaturation
    Pavlova, T. V.; Shevlyuga, V. M.; Andryushechkin, B. V.; Eltsov, K. N.
    Physical Review B (2020), 101 (23), 235410CODEN: PRBHB7; ISSN:2469-9969. (American Physical Society)
    We insert and manipulate a single chlorine atom in chlorine monolayer on a Si(100)-2x1 surface using a scanning tunneling microscope. Two objects were created-a Cl atom in a groove between two dimer rows, and bridge-bonded Cl on a silicon dimer. Changing the voltage polarity leads to conversion of the objects into each other. Anisotropic movement of the objects at 77 K is mediated by two different diffusion mechanisms: hopping and crowdion-like motion. Insertion of a Cl atom in a groove between two dimer rows leads to the formation of a dangling bond on a third-layer Si atom. At pos. sample voltage bias, the first object is pos. charged while the second object can be neutral or neg. charged depending on silicon sample doping.
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    Rivillon, S.; Chabal, Y. J.; Webb, L. J.; Michalak, D. J.; Lewis, N. S.; Halls, M. D.; Raghavachari, K. Chlorination of hydrogen-terminated silicon(111) surfaces. J. Vac. Sci. Technol., A 2005, 23 (4), 1100– 1106,  DOI: 10.1116/1.1861941
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    Chlorination of hydrogen-terminated silicon (111) surfaces
    Rivillon, Sandrine; Chabal, Yves J.; Webb, Lauren J.; Michalak, David J.; Lewis, Nathan S.; Halls, Mathew D.; Raghavachari, Krishnan
    Journal of Vacuum Science & Technology, A: Vacuum, Surfaces, and Films (2005), 23 (4), 1100-1106CODEN: JVTAD6; ISSN:0734-2101. (American Institute of Physics)
    IR absorption spectroscopy was used to investigate the chlorination of H-terminated Si(111) surfaces by 3 different methods: (a) exposure to a satd. soln. of PCl5 in chlorobenzene; (b) exposure to Cl gas, Cl2(g), and (c) exposure to Cl2(g) under UV illumination. XPS and first principles model (clusters) calcns. were used to explore the structure and dynamics of these surfaces. The IR spectra exhibited sharp Cl-related vibrations at 586 and 527 cm-1. The narrow full width at half max. of these vibrations for all 3 prepn. methods indicated that all functionalization schemes produced a nearly complete monolayer of Cl with little surface roughening or introduction of step edges. The 527 cm-1 mode was at a much higher frequency than might be expected for the bending vibration of Si monochloride. Theor. calcns. show, however, that this vibration involves the displacement of the top Si atom parallel to the surface, subject to a relatively stiff potential, shifting its frequency to a value fairly close to that of the Si-Cl stretching mode on a Si(111) surface.
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    Solares, S. D.; Yu, H. B.; Webb, L. J.; Lewis, N. S.; Heath, J. R.; Goddard, W. A. Chlorination-methylation of the hydrogen-terminated silicon(111) surface can induce a stacking fault in the presence of etch pits. J. Am. Chem. Soc. 2006, 128 (12), 3850– 3851,  DOI: 10.1021/ja055408g
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    Chlorination-Methylation of the Hydrogen-Terminated Silicon(111) Surface Can Induce a Stacking Fault in the Presence of Etch Pits
    Solares, Santiago D.; Yu, Hongbin; Webb, Lauren J.; Lewis, Nathan S.; Heath, James R.; Goddard, William A., III
    Journal of the American Chemical Society (2006), 128 (12), 3850-3851CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Recently, we reported STM images of the methylated Si(111) surface [prepd. through chlorination-alkylation of the Si(111)-H surface] taken at 4.7 K, indicating that the torsion angle of the Me group with respect to the subsurface silicon layer is φ = 23 ± 3°. Repulsions between H atoms in adjacent Me groups are minimized at 30°, while repulsions between H atoms and second layer Si atoms are minimized at 60°. The exptl. result of 23° is surprising because it suggests a tendency of the Me group toward the eclipsed configuration (0°) rather than staggered (60°). In contrast, extensive fully periodic quantum mech. D. Functional Theory studies of this surface give an equil. torsion angle of 37.5°, indicating a tendency toward the staggered configuration. This discrepancy can be resolved by showing that the CH3 on the step edges and etch pits interacts repulsively with the CH3 on the surface terraces unless a stacking fault is introduced between the first and second silicon layers of the Si(111)-CH3 surface terraces. We propose that this could occur during the chlorination-alkylation of the Si(111)-H surface. This stacking fault model predicted φ = 22.5° measured with respect to the bulk (corresponding to φ = 37.5° with respect to the second layer Si atoms). This model can be tested by measuring the orientation of the CH3 within the etch pits, which should have φ = 37.5°, or by making a surface without etch pits, which should have φ = 37.5°.
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    Kornev, A. N. Tris(trimethylsilyl)silyl group in organic, coordination and organometallic chemistry. Russ. Chem. Rev. 2004, 73 (11), 1155– 1180
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    Suarez, D.; Laval, G.; Tu, S. M.; Jiang, D.; Robinson, C. L.; Scott, R.; Golding, B. T. Benzylic Brominations with N-Bromosuccinimide in (Trifluoromethyl)benzene. Synthesis 2009, 2009 (11), 1807– 1810,  DOI: 10.1055/s-0029-1216793
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    Parke, T.; Silva-Quinones, D.; Wang, G. T.; Teplyakov, A. V. The Effect of Surface Terminations on the Initial Stages of TiO2 Deposition on Functionalized Silicon. ChemPhysChem 2023, 24, e202200724  DOI: 10.1002/cphc.202200724
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    The Effect of Surface Terminations on the Initial Stages of TiO2 Deposition on Functionalized Silicon
    Parke, Tyler; Silva-Quinones, Dhamelyz; Wang, George T.; Teplyakov, Andrew V.
    ChemPhysChem (2023), 24 (7), e202200724CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)
    As at. layer deposition (ALD) emerges as a method to fabricate architectures with at. precision, emphasis is placed on understanding surface reactions and nucleation mechanisms. ALD of titanium dioxide with TiCl4 and water has been used to investigate deposition processes in general, but the effect of surface termination on the initial TiO2 nucleation lacks needed mechanistic insights. This work examines the adsorption of TiCl4 on Cl-, H-, and HO- terminated Si(100) and Si(111) surfaces to elucidate the general role of different surface structures and defect types in manipulating surface reactivity of growth and non-growth substrates. The surface sites and their role in the initial stages of deposition are examd. by XPS and at. force microscopy (AFM). D. functional theory (DFT) computations of the local functionalized silicon surfaces suggest oxygen-contg. defects are primary drivers of selectivity loss on these surfaces.
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    Bell, J. P.; Cloud, J. E.; Cheng, J. F.; Ngo, C.; Kodambaka, S.; Sellinger, A.; Williams, S. K. R.; Yang, Y. A. N-Bromosuccinimide-based bromination and subsequent functionalization of hydrogen-terminated silicon quantum dots. RSC Adv. 2014, 4 (93), 51105– 51110,  DOI: 10.1039/C4RA08477B
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    N-Bromosuccinimide-based bromination and subsequent functionalization of hydrogen-terminated silicon quantum dots
    Bell, Jacob P.; Cloud, Jacqueline E.; Cheng, Jifang; Ngo, Chilan; Kodambaka, Suneel; Sellinger, Alan; Ratanathanawongs Williams, S. Kim; Yang, Yongan
    RSC Advances (2014), 4 (93), 51105-51110CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
    We report a mild, effective, room-temp. method for brominating and functionalizing colloidal hydrogen-terminated silicon quantum dots (H-SiQDs) using N-bromosuccinimide (NBS) as the bromination reagent. This post-synthesis bromination overcomes a long-standing challenge of producing emissive SiQDs through the functionalization of directly synthesized halogen-terminated colloidal SiQDs.
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    Baldwin, R. K.; Pettigrew, K. A.; Ratai, E.; Augustine, M. P.; Kauzlarich, S. M. Solution reduction synthesis of surface stabilized silicon nanoparticles. Chem. Commun. 2002, (17), 1822– 1823,  DOI: 10.1039/b205301b
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    Solution reduction synthesis of surface stabilized silicon nanoparticles
    Baldwin, Richard K.; Pettigrew, Katherine A.; Ratai, Eva; Augustine, Matthew P.; Kauzlarich, Susan M.
    Chemical Communications (Cambridge, United Kingdom) (2002), (17), 1822-1823CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    This paper describes the prepn. of air and moisture stable octanol derivatized cryst. silicon nanoparticles by room temp. sodium naphthalenide redn. of silicon halides.
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    Zou, J.; Baldwin, R. K.; Pettigrew, K. A.; Kauzlarich, S. M. Solution synthesis of ultrastable luminescent siloxane-coated silicon nanoparticles. Nano Lett. 2004, 4 (7), 1181– 1186,  DOI: 10.1021/nl0497373
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    Solution Synthesis of Ultrastable Luminescent Siloxane-Coated Silicon Nanoparticles
    Zou, Jing; Baldwin, Richard K.; Pettigrew, Katherine A.; Kauzlarich, Susan M.
    Nano Letters (2004), 4 (7), 1181-1186CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Silicon nanoparticles (NPs) of ∼4.5(1.10) nm from a room-temp. soln. route are terminated by a silanization method for the first time. Energy-selected emission is obsd., consistent with the distribution of sizes obtained by this route. The NPs are photochem. stable in nonpolar org. solvents and when exposed to air/water under ambient conditions for up to 1 yr. The nanoparticles were characterized by TEM, HRTEM, EDX, SAED, FTIR, 1H/13C NMR, UV-vis, and photoluminescence (PL) spectroscopy.
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    Rogozhina, E. V.; Eckhoff, D. A.; Gratton, E.; Braun, P. V. Carboxyl functionalization of ultrasmall luminescent silicon nanoparticles through thermal hydrosilylation. J. Mater. Chem. 2006, 16 (15), 1421– 1430,  DOI: 10.1039/b509868h
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    Carboxyl functionalization of ultrasmall luminescent silicon nanoparticles through thermal hydrosilylation
    Rogozhina, Elena V.; Eckhoff, Dean A.; Gratton, Enrico; Braun, Paul V.
    Journal of Materials Chemistry (2006), 16 (15), 1421-1430CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)
    Here, we report one of the first examples of thermal hydrosilylation between a bi-functional alkene and ultrasmall (∼1 nm) H-passivated silicon nanoparticles (Si-np-H) to prep. strongly luminescent, water stable, carboxyl functionalized nanoparticles (Si-np-COOH). NMR, IR absorption spectroscopy (FTIR), size exclusion chromatog. (SEC), and photoluminescence spectroscopy are used to characterize the Si-np dispersions. Based on the SEC and FTIR data, a reaction scheme is proposed to account for side products formed through a free radical crosslinking mechanism. The Si-np-COOH may find use in applications such as biomol. labeling and biol. imaging.
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    Dasog, M.; Veinot, J. G. C. Size independent blue luminescence in nitrogen passivated silicon nanocrystals. Phys. Status Solidi A 2012, 209 (10), 1844– 1846,  DOI: 10.1002/pssa.201200273
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    Size independent blue luminescence in nitrogen passivated silicon nanocrystals
    Dasog, Mita; Veinot, Jonathan G. C.
    Physica Status Solidi A: Applications and Materials Science (2012), 209 (10), 1844-1846CODEN: PSSABA; ISSN:1862-6300. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The photoluminescent properties of allylamine terminated silicon nanocrystals (Si-NCs) are investigated. Chloride surface terminated Si-NCs of different sizes react with allylamine, yielding NCs that exhibit size independent blue luminescent NCs. NCs were characterized using X-ray diffraction, Fourier transformed IR spectroscopy, photoluminescence spectroscopy, and dynamic light scattering.
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    Lee, J. C.; Bae, Y. H.; Chang, S. K. Efficient α-halogenation of carbonyl compounds by N-bromosuccinimide and N-chlorosuccinimde. Bull. Korean Chem. Soc. 2003, 24 (4), 407– 408,  DOI: 10.5012/bkcs.2003.24.4.407
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    Efficient α-halogenation of carbonyl compounds by N-bromosuccinimide and N-chlorosuccinimide
    Lee, Jong Chan; Bae, Yong Hun; Chang, Suk-Kyu
    Bulletin of the Korean Chemical Society (2003), 24 (4), 407-408CODEN: BKCSDE; ISSN:0253-2964. (Korean Chemical Society)
    Arom. ketones and 1,3-dicarbonyl compds. are efficiently α-halogenated by systems contg. N-bromosuccinimide or N-chlorosuccinimide, p-toluenesulfonic acid, and MeCN. The protocol is operationally simple and requires only readily available starting materials.
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    Bergstrom, M.; Suresh, G.; Naidu, V. R.; Unelius, C. R. Iodosuccinimide (NIS) in Direct Aromatic Iodination. Eur. J. Org. Chem. 2017, 2017 (22), 3234– 3239,  DOI: 10.1002/ejoc.201700173
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    Zhao, S.; Liu, W. K. Methods for Brominations at Benzylic Positions. Curr. Org. Chem. 2019, 22 (25), 2444– 2459,  DOI: 10.2174/1385272822666181031094702
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    Bera, S. K.; Mal, P. Mechanochemical-Cascaded C-N Cross-Coupling and Halogenation Using N-Bromo- and N-Chlorosuccinimide as Bifunctional Reagents. J. Org. Chem. 2021, 86 (20), 14144– 14159,  DOI: 10.1021/acs.joc.1c01742
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    Mechanochemical-Cascaded C-N Cross-Coupling and Halogenation Using N-Bromo- and N-Chlorosuccinimide as Bifunctional Reagents
    Bera, Shyamal Kanti; Mal, Prasenjit
    Journal of Organic Chemistry (2021), 86 (20), 14144-14159CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
    Direct synthesis of halo-substituted phenanthridinone derivs. I [R = Cl, Br, I; R1 = H, 3-Me, 3-F, etc.; R2 = H, 8-Me; R3 = OMe, Ph] was achieved via cascade C-N bond formation and subsequent halogenation reactions of N-halosuccinimides with N-methoxy-[1,1'-biphenyl]-2-carboxamides. During the reactions, NBS/NCS first assisted the oxidative C-N coupling reaction and subsequently promoted a halogenation reaction. Thus, the role of NBS/NCS was established to be bifunctional. This protocol offered a mild, solvent-free, convenient, one-pot synthesis of compds. I.
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    O’Leary, L. E.; Rose, M. J.; Ding, T. X.; Johansson, E.; Brunschwig, B. S.; Lewis, N. S. Heck Coupling of Olefins to Mixed Methyl/Thienyl Monolayers on Si(111) Surfaces. J. Am. Chem. Soc. 2013, 135 (27), 10081– 10090,  DOI: 10.1021/ja402495e
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    Heck Coupling of Olefins to Mixed Methyl/Thienyl Monolayers on Si(111) Surfaces
    O'Leary, Leslie E.; Rose, Michael J.; Ding, Tina X.; Johansson, Erik; Brunschwig, Bruce S.; Lewis, Nathan S.
    Journal of the American Chemical Society (2013), 135 (27), 10081-10090CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The Heck reaction has been used to couple olefins to a Si(111) surface that was functionalized with a mixed monolayer comprised of Me and thienyl groups. The coupling method maintained a conjugated linkage between the surface and the olefinic surface functionality, to allow for facile charge transfer from the silicon surface. While a Si(111) surface terminated only with thienyl groups displayed a surface recombination velocity, S, of 670 ± 190 cm s-1, the mixed CH3/SC4H3-Si(111) surfaces with a coverage of θSC4H3 = 0.15 ± 0.02 displayed a substantially lower value of S = 27 ± 9 cm s-1. Accordingly, CH3/SC4H3-Si(111) surfaces were brominated with N-bromosuccinimide, to produce mixed CH3/SC4H2Br-Si(111) surfaces with coverages of θBr-Si < 0.05. The resulting aryl halide surfaces were activated using [Pd(PPh3)4] as a catalyst. After activation, Pd(II) was selectively coordinated by oxidative addn. to the surface-bound aryl halide. The olefinic substrates 4-fluorostyrene, vinylferrocene, and protoporphyrin IX di-Me ester were then coupled (in DMF at 100°C) to the Pd-contg. functionalized Si surfaces. The porphyrin-modified surface was then metalated with Co, Cu, or Zn. The vinylferrocene-modified Si(111) surface showed a linear dependence of the peak current on scan rate in cyclic voltammetry, indicating that facile electron transfer had been maintained and providing evidence of a robust linkage between the Si surface and the tethered ferrocene. The final Heck-coupled surface exhibited S = 70 cm s-1, indicating that high-quality surfaces could be produced by this multistep synthetic approach for tethering small mols. to silicon photoelectrodes.
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    Lauerhaas, J. M.; Sailor, M. J. Chemical Modification of the Photoluminescence Quenching of Porous Silicon. Science 1993, 261 (5128), 1567– 1568,  DOI: 10.1126/science.261.5128.1567
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    Chemical modification of the photoluminescence quenching of porous silicon
    Lauerhaas, Jeffrey M.; Sailor, Michael J.
    Science (Washington, DC, United States) (1993), 261 (5128), 1567-8CODEN: SCIEAS; ISSN:0036-8075.
    The photoluminescence of porous silicon can be quenched by adsorbates, and the degree of quenching can be tuned by chem. derivatization of the porous silicon surface. Thus, as-prepd. porous silicon has a hydrophobic, hydrogen-terminated surface, and the photoluminescence is strongly quenched by ethanol and weakly quenched by water. Mild chem. oxidn. (iodine followed by hydrolysis) produces a hydrophilic porous silicon surface. Photoluminescence from this hydrophilic material is quenched to a lesser extent by ethanol and to a greater extent by water, relative to the original surface. This demonstrates that the visible luminescence from porous silicon is highly surface-sensitive, and the surface interactions can be tuned by specific chem. transformations.
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    Silva-Quinones, D.; He, C.; Dwyer, K. J.; Butera, R. E.; Wang, G. T.; Teplyakov, A. V. Reaction of Hydrazine with Solution- and Vacuum-Prepared Selectively Terminated Si(100) Surfaces: Pathways to the Formation of Direct Si-N Bonds. Langmuir 2020, 36 (43), 12866– 12876,  DOI: 10.1021/acs.langmuir.0c02088
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    Reaction of Hydrazine with Solution- and Vacuum-Prepared Selectively Terminated Si(100) Surfaces: Pathways to the Formation of Direct Si-N Bonds
    Silva-Quinones, Dhamelyz; He, Chuan; Dwyer, Kevin J.; Butera, Robert E.; Wang, George T.; Teplyakov, Andrew V.
    Langmuir (2020), 36 (43), 12866-12876CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    The reactivity of liq. hydrazine (N2H4) with respect to H-, Cl-, and Br-terminated Si(100) surfaces was investigated to uncover the principles of nitrogen incorporation into the interface. This process has important implications in a wide variety of applications, including semiconductor surface passivation and functionalization, nitride growth, and many others. The use of hydrazine as a precursor allows for reactions that exclude carbon and oxygen, the primary sources of contamination in processing. In this work, the reactivity of N2H4 with H- and Cl-terminated surfaces prepd. by traditional solvent-based methods and with a Br-terminated Si(100) prepd. in ultrahigh vacuum was compared. The reactions were studied with XPS, at. force microscopy, and scanning tunneling microscopy, and the observations were supported by computational investigations. The H-terminated surface led to the highest level of nitrogen incorporation; however, the process proceeds with increasing surface roughness, suggesting possible etching or replacement reactions. In the case of Cl-terminated (predominantly dichloride) and Br-terminated (monobromide) surfaces, the amt. of nitrogen incorporation on both surfaces after the reaction with hydrazine was very similar despite the differences in prepn., initial structure, and chem. compn. D. functional theory was used to propose the possible surface structures and to analyze surface reactivity.
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    Wagner, C. D.; V N, A.; Kraut-Vass, A.; Allison, J. W.; Powell, C. J.; R, J., Jr. NIST Standard Reference Database 20, Version 3.4.
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    Haber, J. A.; Lewis, N. S. Infrared and X-ray photoelectron spectroscopic studies of the reactions of hydrogen-terminated crystalline Si(111) and Si(100) surfaces with Br-2, I-2, and ferrocenium in alcohol solvents. J. Phys. Chem. B 2002, 106 (14), 3639– 3656,  DOI: 10.1021/jp0102872
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    Infrared and X-ray Photoelectron Spectroscopic Studies of the Reactions of Hydrogen-Terminated Crystalline Si(111) and Si(100) Surfaces with Br2, I2, and Ferrocenium in Alcohol Solvents
    Haber, Joel A.; Lewis, Nathan S.
    Journal of Physical Chemistry B (2002), 106 (14), 3639-3656CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)
    The reaction chem. of H-terminated cryst. Si(111) and Si(100) surfaces in MeOH, CD3OD, CF3(CH2)3OH, BuOH, and C4D9OD solns. contg. ferrocenium (Fc+)-BF4, I2, or Br2 was monitored using x-ray photoelectron (XP) spectroscopy and IR spectroscopy. Addn. of the 1-electron oxidant Fc+, or addn. of the oxidizing species I2 or Br2, produced diagnostic changes in the IR spectra that clearly indicated formation of surficial Si-OR groups. XPS data confirmed the conclusions of the IR studies. Under the authors' reaction conditions, no detectable reaction occurred without the presence of the oxidant. The data are consistent with oxidative activation of the surficial Si-H bonds toward nucleophilic attack by the alcs. The reaction chem. was generally similar on (111)- and (100)-oriented Si surfaces, although some differences were obsd. in the ratio of reaction products on the two different surface orientations. Alkoxylated surfaces were also prepd. by a two-step process in which the surface was 1st chlorinated and then reacted with LiOCH3, LiOCD3, or LiO(CH2)3CF3. The data indicate that formation of Si-halogen bonding alone is not sufficient to provide a robust correlation between the electronic and chem. properties of such cryst. Si surfaces and that formation of Si-alkoxyl bonds is a common motif for surfaces often used in electronic and electrochem. studies of Si.
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    Hinckley, A. P.; Driskill, M. M.; Muscat, A. J. Dense Organosilane Monolayer Resist That Directs Highly Selective Atomic Layer Deposition. ACS Appl. Nano Mater. 2020, 3 (4), 3185– 3194,  DOI: 10.1021/acsanm.9b02128
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    Dense Organosilane Monolayer Resist That Directs Highly Selective Atomic Layer Deposition
    Hinckley, Adam P.; Driskill, Madison M.; Muscat, Anthony J.
    ACS Applied Nano Materials (2020), 3 (4), 3185-3194CODEN: AANMF6; ISSN:2574-0970. (American Chemical Society)
    Organosilane monolayers are part of many process flows in nanoelectronics and biotechnol. because of their versatility. Monolayers that inhibit reactions on silicon/silicon oxide surfaces are needed to create patterns that direct the deposition of mols. and realize some of these applications. Organosilane monolayers on silicon oxide are typically deposited from the liq. phase by repeated deposition and cleaning cycles. Cleaning consists of solvent extn., which removes weakly bound aggregates that physisorb in or on the layer during deposition. Adding a short immersion in an aq. oxidizing base such as Std. Clean 1 (SC-1), which is a particle removal method in semiconductor manufg., reduced the time from 48 to 2 h to deposit an inhibiting monolayer. The SC-1 not only removed agglomerates but also rehydroxylated the siloxane bridges at the interface between the monolayer and the silicon oxide surface based on XPS measurements of the hydroxyl group concn. A line and space pattern in the organosilane monolayer made by conductive at. force microscopy (C-AFM) was used to direct the precursors titanium tetrachloride (TiCl4) and water vapor to deposit titanium dioxide (TiO2) by at. layer deposition (ALD) with a selectivity greater than 0.999. The titanium dioxide lines were about 170 nm wide, 9 nm high, and 20μm long. The monolayer deposition procedure was done in a conventional lab. using the common deposition solvent toluene and could be used to make versatile structures for nanodevice fabrication.
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    Ott, J.; Pasanen, T. P.; Gadda, A.; Garin, M.; Rosta, K.; Vahanissi, V.; Savin, H. Impact of doping and silicon substrate resistivity on the blistering of atomic-layer-deposited aluminium oxide. Appl. Surf. Sci. 2020, 522, 146400  DOI: 10.1016/j.apsusc.2020.146400
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    Impact of doping and silicon substrate resistivity on the blistering of atomic-layer-deposited aluminum oxide
    Ott, Jennifer; Pasanen, Toni P.; Gadda, Akiko; Garin, Moises; Rosta, Kawa; Vahanissi, Ville; Savin, Hele
    Applied Surface Science (2020), 522 (), 146400CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
    Aluminum oxide (Al2O3) thin films grown at low temps. using at. layer deposition (ALD) are known to often suffer from local delamination sites, referred to as "blisters", after post-deposition annealing during device processing. In this work, the authors report their observation that doping of the silicon substrate has an effect on blister formation. The introduction of a highly doped layer by diffusion or implantation is found to significantly reduce blistering, compared to the non-doped regions in the immediate vicinity. Similar behavior is obsd. for both phosphorus and boron doping. Further investigation of this phenomenon using substrates with different resistivities reveals that even when introduced already during silicon crystal growth, doping affects the blistering of aluminum oxide films. Changes in several properties of silicon affected by doping, most importantly surface terminating groups, native oxide growth, and passivation of defects with hydrogen, are discussed as potential reasons behind the obsd. effect on blistering.
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    Hashemi, F. S. M.; Bent, S. F. Sequential Regeneration of Self-Assembled Monolayers for Highly Selective Atomic Layer Deposition. Adv. Mater. Interfaces 2016, 3 (21), 1600464  DOI: 10.1002/admi.201600464
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    Mameli, A.; Merkx, M. J. M.; Karasulu, B.; Roozeboom, F.; Kessels, W. M. M.; Mackus, A. J. M. Area-Selective Atomic Layer Deposition of SiO2 Using Acetylacetone as a Chemoselective Inhibitor in an ABC-Type Cycle. ACS Nano 2017, 11 (9), 9303– 9311,  DOI: 10.1021/acsnano.7b04701
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    69
    Area-selective atomic layer deposition of SiO2 using acetylacetone as a chemoselective inhibitor in an ABC-type cycle
    Mameli, Alfredo; Merkx, Marc J. M.; Karasulu, Bora; Roozeboom, Fred; Kessels, Wilhelmus M. M.; Mackus, Adriaan J. M.
    ACS Nano (2017), 11 (9), 9303-9311CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Area-selective at. layer deposition (ALD) is rapidly gaining interest because of its potential application in self-aligned fabrication schemes for next-generation nanoelectronics. Here, we introduce an approach for area-selective ALD that relies on the use of chemoselective inhibitor mols. in a three-step (ABC-type) ALD cycle. A process for area-selective ALD of SiO2 was developed comprising acetylacetone inhibitor (step A), bis(diethylamino)silane precursor (step B), and O2 plasma reactant (step C) pulses. Our results show that this process allows for selective deposition of SiO2 on GeO2, SiNx, SiO2, and WO3, in the presence of Al2O3, TiO2, and HfO2 surfaces. In situ Fourier transform IR spectroscopy expts. and d. functional theory calcns. underline that the selectivity of the approach stems from the chemoselective adsorption of the inhibitor. The selectivity between different oxide starting surfaces and the compatibility with plasma-assisted or ozone-based ALD are distinct features of this approach. Furthermore, the approach offers the opportunity of tuning the substrate-selectivity by proper selection of inhibitor mols.
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    Hinckley, A. P.; Muscat, A. J. Detecting and Removing Defects in Organosilane Self-Assembled Monolayers. Langmuir 2020, 36 (10), 2563– 2573,  DOI: 10.1021/acs.langmuir.9b02753
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    Detecting and Removing Defects in Organosilane Self-Assembled Monolayers
    Hinckley, Adam P.; Muscat, Anthony J.
    Langmuir (2020), 36 (10), 2563-2573CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    Defects occur as self-assembled monolayers form, and the no. and type of defects depend on the surface prepn. and deposition solvent, among other parameters. Indirect measures to detect defects using a layer property, such as the thickness or bond vibrational frequency, are used routinely for process development but often lack sensitivity. Direct measures using an at. probe offer a glimpse of defect structures but over a small fraction of the layer. Direct detection after reacting defects by etching or deposition is more common, and this approach has advanced our understanding of how monolayers form and has led to improved monolayers for a variety of applications. Here we show that a series of TiCl4 gas pulses reacts with defects in organosilane layers on SiO2 depositing TiO, which was measured by XPS. The defects were silanol groups and siloxane bridge bonds at the interface between the layer and the SiO2 surface and on agglomerates physisorbed to the layer. As the TiO satn. coverage or the total no. of defects decreased, the incubation period in which no TiO was detected became longer. Cleaning the layer by solvent extn. to remove nonpolar agglomerates followed by an aq. mixt. of ammonium hydroxide and hydrogen peroxide, which is Std. Clean 1, a common particle removal step for silicon surfaces, produced an organosilane monolayer without agglomerates based on at. force microscopy. After a second organosilane immersion, the monolayer d. rose to 3.8 mols./nm2. This monolayer inhibited the deposition of TiO on the SiO2 surface for 250 pulses of TiCl4 and 200 complete TiO2 at. layer deposition cycles using TiCl4 and water vapor, and it failed at 300 complete cycles. The Std. Clean 1 soln. not only removed defects left by solvent extn. but also led to the reorganization of the organosilane layer.
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    Ulman, A. Formation and structure of self-assembled monolayers. Chem. Rev. 1996, 96 (4), 1533– 1554,  DOI: 10.1021/cr9502357
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    Formation and Structure of Self-Assembled Monolayers
    Ulman, Abraham
    Chemical Reviews (Washington, D. C.) (1996), 96 (4), 1533-1554CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review on the organization of complex, semiflexible org. mols. within quasi-2-D assemblies due to the delicate interplay between substrate-adsorbate interactions, nonbonded interactions between adsorbates, electrostatic and VDW forces, and intramol. interactions (e.g., bond stretches, angle bends, and torsions). Surface reorganization contributes to the final equil. structure of the assembly. Structural factors controlling the formation of self-assembled monolayers (SAMs) are discussed. Different SAMs with unique properties and potential applications are considered. An attempt is made to provide a general picture of self-assembly on solid surfaces as it emerges from a consideration of the interplay of different forces that control this process. 273 Refs.
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    Hutchins, D. O.; Acton, O.; Weidner, T.; Cernetic, N.; Baio, J. E.; Ting, G.; Castner, D. G.; Ma, H.; Jen, A. K. Y. Spin cast self-assembled monolayer field effect transistors. Org. Electron. 2012, 13 (3), 464– 468,  DOI: 10.1016/j.orgel.2011.11.025
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    Spin cast self-assembled monolayer field effect transistors
    Hutchins, Daniel O.; Acton, Orb; Weidner, Tobias; Cernetic, Nathan; Baio, Joe E.; Ting, Guy; Castner, David G.; Ma, Hong; Jen, Alex K.-Y.
    Organic Electronics (2012), 13 (3), 464-468CODEN: OERLAU; ISSN:1566-1199. (Elsevier B.V.)
    Top-contact self-assembled monolayer field-effect transistors (SAMFETs) were fabricated through both spin-coating and soln. assembly of a semiconducting phosphonic acid-based mol. (11-(5''''-butyl-[2,2';5',2'';5'',2''';5''',2'''']quinquethiophen-5-yl)undecylphosphonic acid) (BQT-PA). The field-effect mobilities of both spin-cast and soln. assembled SAMFETs were 1.1-8.0 × 10-6 cm2 V-1 s-1 for a wide range of channel lengths (between 12-80 μm). The mol. monolayers were characterized by AFM, attenuated total reflectance-Fourier transform IR spectroscopy (ATR-FTIR), and NEXAFS spectroscopy. The BQT-PA monolayer films exhibit dense surface coverage, bidentate binding, and tilt angles of ∼32° and ∼44° for the thiophene rings and alkyl chain, resp. These results indicate that rapid throughput of fabricating SAMFETs is possible even by spin-coating.
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    Fang, M.; Ho, J. C. Area-Selective Atomic Layer Deposition: Conformal Coating, Subnanometer Thickness Control, and Smart Positioning. ACS Nano 2015, 9 (9), 8651– 8654,  DOI: 10.1021/acsnano.5b05249
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    Area-Selective Atomic Layer Deposition: Conformal Coating, Subnanometer Thickness Control, and Smart Positioning
    Fang, Ming; Ho, Johnny C.
    ACS Nano (2015), 9 (9), 8651-8654CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    A review. Transistors have already been made three-dimensional (3D), with device channels (i.e., fins in trigate field-effect transistor (FinFET) technol.) that are taller, thinner, and closer together to enhance device performance and lower active power consumption. As device scaling continues, these transistors will require more advanced, fabrication-enabling technologies for the conformal deposition of high-κ dielec. layers on their 3-dimensional channels with accurate position alignment and thickness control down to the subnanometer scale. Among many competing techniques, area-selective at. layer deposition (AS-ALD) is a promising method that is well suited to the requirements without the use of complicated, complementary metal-oxide semiconductor (CMOS)-incompatible processes. However, further progress is limited by poor area selectivity for thicker films formed via a higher no. of ALD cycles as well as the prolonged processing time. In this issue of ACS Nano, Professor Stacy Bent and her research group demonstrate a straightforward self-correcting ALD approach, combining selective deposition with a postprocess mild chem. etching, which enables selective deposition of dielec. films with thicknesses and processing times at least 10 times larger and 48 times shorter, resp., than those obtained by conventional AS-ALD processes. These advances present an important technol. breakthrough that may drive the AS-ALD technique a step closer toward industrial applications in electronics, catalysis, and photonics, etc. where more efficient device fabrication processes are needed.
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    Longo, R. C.; McDonnell, S.; Dick, D.; Wallace, R. M.; Chabal, Y. J.; Owen, J. H. G.; Ballard, J. B.; Randall, J. N.; Cho, K. Selectivity of metal oxide atomic layer deposition on hydrogen terminated and oxidized Si(001)-(2 × 1) surface. J. Vac. Sci. Technol., B: Nanotechnol. Microelectron.: Mater., Process., Meas., Phenom. 2014, 32 (3), 03D112  DOI: 10.1116/1.4864619
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    Montaño-Miranda, G.; Muscat, A. Etching of silicon dioxide with gas phase HF and water:: Initiation, bulk etching, and termination. Solid State Phenom. 2008, 134, 3– 6,  DOI: 10.4028/www.scientific.net/ssp.134.3
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    Etching of silicon dioxide with gas phase HF and water: initiation, bulk etching, and termination
    Montano-Miranda, Gerardo; Muscat, Anthony
    Diffusion and Defect Data--Solid State Data, Pt. B: Solid State Phenomena (2008), 134 (Ultra Clean Processing of Semiconductor Surfaces VIII), 3-6CODEN: DDBPE8; ISSN:1012-0394. (Trans Tech Publications Ltd.)
    The SiO2 etching process was studied to explain the initiation mechanism and reaction kinetics of the SiO2 etching process and the surface termination on the resulting Si surface. The data showed that the induction time can be defined as the time required for a sufficient no. of HF/water clusters to adsorb on the SiO2 surface and produce the first SiF4 mols. Also, it was revealed that the etching rates are almost two orders of magnitude lower than those achieved with a detectable water layer. Furthermore, a gas/solid reaction without a liq. water layer may be advantageous for etching metal oxide films on high mobility semiconductor surfaces with narrow band gaps, which are prone to oxidn. in the presence of water.
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    Garín, M.; Khoury, R.; Martin, I.; Johnson, E. V. Direct etching at the nanoscale through nanoparticle-directed capillary condensation. Nanoscale 2020, 12 (16), 9240– 9245,  DOI: 10.1039/C9NR10217E
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    Direct etching at the nanoscale through nanoparticle-directed capillary condensation
    Garin, M.; Khoury, R.; Martin, I.; Johnson, E. V.
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    We report a method to locally deliver a chem. etchant at the nanoscale in the vapor phase by capillary condensation forming a meniscus at the nanoparticle/substrate interface. The process is simple, scalable and does not require functionalization of the nanoparticles. Furthermore, it does not rely on any specific chem. properties of the materials other than the soln. being aq. and the wettability properties of the surfaces involved, which should enable its application to other material and chem. combinations. In particular, in this work we demonstrate the proposed process by periodically pattering a SiO2 layer using a self-assembled monolayer of polystyrene particles exposed to HF vapors. The patterned SiO2 layer is then used as a mask to etch a pattern of inverted nanopyramids on Si. The silicon nanopatterning has been demonstrated for particles sizes ranging from 800 nm down to 100 nm, providing pyramids with a size down to 50 nm for 100 nm nanoparticles.
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  1. Patrick R. Raffaelle, George T. Wang, Alexander A. Shestopalov. Light-Mediated Contact Printing of Phosphorus Species onto Silicon Using Carbene-Based Molecular Layers. Langmuir 2024, 40 (23) , 12027-12034. https://doi.org/10.1021/acs.langmuir.4c00763
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  • Abstract

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    Figure 1

    Figure 1. Schematic procedure of reaction steps and process conditions for the vapor-phase halogenation of H–Si(100) and OH–Si(100) with N-Hal-succinimides. (1) Si(100) is cleaned and oxidized in Nano-Strip solution before (1 ⇒ 3) direct exposure to an N-Cl/Br/I-succinimide molecule in the vapor phase, alternatively (1 ⇒ 2) the new oxide is re-etched in HF and then (2 ⇒ 3) exposed to the N-Cl/Br/I-succinimide molecules.

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    Figure 2

    Figure 2. Comparison of XPS spectra from Hal(H)–Si(100) and Hal(OH)–Si(100) surfaces postreaction and an OH–Si(100) standard. Region scans for each respective halogen (Cl 2p, Br 3d, and I 3d) are depicted from left to right.

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    Figure 3

    Figure 3. Comparison of XPS region scans of C 1s, O 1s, and SiO2 (from Si 2p) spectra depicted from left to right for OH–Si(100), H–Si(100), Cl(H)–Si(100), Br(H)–Si(100), and I(H)–Si(100) surfaces. In the bottom row is histograms showing the quantitative XPS characterization of region scans (C 1s, O 1s, SiO2 from Si 2p) for each Hal(H)–Si(100) surface and reference unreacted OH–Si(100) and H–Si(100) surfaces, all normalized by the Si 2p peak intensity which includes contributions from both the bulk Si (SiB) and surface oxide (SiOx) interfaces (the values in the SiOx histogram were normalized by only SiB).

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    Figure 4

    Figure 4. Stability study consisting of histograms showing the quantitative XPS characterization of halogen, C 1s, O 1s, and SiO2 (from Si 2p) region scans shown from top to bottom, respectively, for I–Si(100), Br–Si(100), and Cl–Si(100) surfaces shown from left to right, respectively, over a 72 h period of air exposure.

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    Figure 5

    Figure 5. (A) Schematic illustration of the traditional ALD cycle of Al2O3 onto OH-Si(100), H-Si(100), and Hal(H)-Si(100) surfaces. In step 1, the dosed Al(CH3)3 precursor readily adsorbs onto the OH-Si(100) surface, while H-Si(100) and Hal(H)-Si(100) surfaces exhibit total and partial blocking of the same molecule, respectively. In step 2, the H2O coreactant binds with the adsorbed metal precursor to form a complete metal oxide film on OH-Si(100) and a metal oxide island on Hal(H)-Si(100). Only H-Si(100) retains its original surface, but it must be maintained under high vacuum and temperature. (B) Histogram showing the quantitative XPS characterization of Al 2p region scan for all three halogenated surfaces and reference H-Si(100) and OH-Si(100) surfaces.

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    Figure 6

    Figure 6. Three-dimensional AFM roughness topographies taken for the (a) OH–Si(100) and (b) Br(H)–Si(100) surfaces post ALD.

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  • References

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    6. 6
      Parsons, G. N.; Clark, R. D. Area-Selective Deposition: Fundamentals, Applications, and Future Outlook. Chem. Mater. 2020, 32 (12), 4920– 4953,  DOI: 10.1021/acs.chemmater.0c00722
      6
      Area-Selective Deposition: Fundamentals, Applications, and Future Outlook
      Parsons, Gregory N.; Clark, Robert D.
      Chemistry of Materials (2020), 32 (12), 4920-4953CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      A review. This review provides an overview of area-selective thin film deposition (ASD) with a primary focus on vapor-phase thin film formation via chem. vapor deposition (CVD) and at. layer deposition (ALD). Area-selective deposition has been successfully implemented in microelectronic processes, but most approaches to date rely on high-temp. reactions to achieve the desired substrate sensitivity. Continued size and performance scaling of microelectronics, as well as new materials, patterning methods, and device fabrication schemes are seeking solns. for new low-temp. ( < 400°C) ASD methods for dielecs., metals, and org. thin films. To provide an overview of the ASD field, this article critically reviews key challenges that must be overcome for ASD to be successful in microelectronics and other fields, including descriptions of current process application needs. We provide an overview of basic mechanisms in film nucleation during CVD and ALD and summarize current known ASD approaches for semiconductors, metals, dielecs., and org. materials. For a few key materials, selectivity is quant. compared for different reaction precursors, giving important insight into needs for favorable reactant and reaction design. We summarize current limitations of ASD and future opportunities that could be achieved using advanced bottom-up at. scale processes.
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    7. 7
      George, S. M. Atomic Layer Deposition: An Overview. Chem. Rev. 2010, 110 (1), 111– 131,  DOI: 10.1021/cr900056b
      7
      Atomic Layer Deposition: An Overview
      George, Steven M.
      Chemical Reviews (Washington, DC, United States) (2010), 110 (1), 111-131CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. A review on the at. layer deposition and its application to the fabrication of semiconductor device and nanodevices. The nucleation and growth mechanism during at. layer deposition are discussed.
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    8. 8
      Mackus, A. J. M.; Merkx, M. J. M.; Kessels, W. M. M. From the Bottom-Up: Toward Area-Selective Atomic Layer Deposition with High Selectivity. Chem. Mater. 2019, 31 (1), 2– 12,  DOI: 10.1021/acs.chemmater.8b03454
      8
      From the bottom-up: Toward area-selective atomic layer deposition with high selectivity
      Mackus, Adriaan J. M.; Merkx, Marc J. M.; Kessels, Wilhelmus M. M.
      Chemistry of Materials (2019), 31 (1), 2-12CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      A review. Bottom-up nanofabrication by area-selective at. layer deposition (ALD) is currently gaining momentum in semiconductor processing, because of the increasing need for eliminating the edge placement errors of top-down processing. Moreover, area-selective ALD offers new opportunities in many other areas such as the synthesis of catalysts with at.-level control. This Perspective provides an overview of the current developments in the field of area-selective ALD, discusses the challenge of achieving a high selectivity, and provides a vision for how area-selective ALD processes can be improved. A general cause for the loss of selectivity during deposition is that the character of surfaces on which no deposition should take place changes when it is exposed to the ALD chem. A soln. is to implement correction steps during ALD involving for example surface functionalization or selective etching. This leads to the development of advanced ALD cycles by combining conventional two-step ALD cycles with correction steps in multistep cycle and/or supercycle recipes.
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    9. 9
      Lee, H.-B.-R.; Bent, S. Nanopatterning by Area-Selective Atomic Layer Deposition. At. Layer Deposition Nanostruct. Mater. 2011, 193– 225,  DOI: 10.1002/9783527639915.ch9
      There is no corresponding record for this reference.
    10. 10
      Cho, T. H.; Farjam, N.; Allemang, C. R.; Pannier, C. P.; Kazyak, E.; Huber, C.; Rose, M.; Trejo, O.; Peterson, R. L.; Barton, K.; Dasgupta, N. P. Area-Selective Atomic Layer Deposition Patterned by Electrohydrodynamic Jet Printing for Additive Manufacturing of Functional Materials and Devices. ACS Nano 2020, 14 (12), 17262– 17272,  DOI: 10.1021/acsnano.0c07297
      10
      Area-Selective Atomic Layer Deposition Patterned by Electrohydrodynamic Jet Printing for Additive Manufacturing of Functional Materials and Devices
      Cho, Tae H.; Farjam, Nazanin; Allemang, Christopher R.; Pannier, Christopher P.; Kazyak, Eric; Huber, Carli; Rose, Mattison; Trejo, Orlando; Peterson, Rebecca L.; Barton, Kira; Dasgupta, Neil P.
      ACS Nano (2020), 14 (12), 17262-17272CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      There is an increasing interest in additive nanomanufg. processes, which enable customizable patterning of functional materials and devices on a wide range of substrates. However, there are relatively few techniques with the ability to directly 3D print patterns of functional materials with sub-micron resoln. In this study, we demonstrate the use of additive electrohydrodynamic jet (e-jet) printing with an av. line width of 312 nm, which acts as an inhibitor for area-selective at. layer deposition (AS-ALD) of a range of metal oxides. We also demonstrate subtractive e-jet printing with solvent inks that dissolve polymer inhibitor layers in specific regions, which enables localized AS-ALD within those regions. The chem. selectivity and morphol. of e-jet patterned polymers towards binary and ternary oxides of ZnO, Al2O3, and SnO2 were quantified using XPS, at. force microscopy, and Auger electron spectroscopy. This approach enables patterning of functional oxide semiconductors, insulators, and transparent conducting oxides with tunable compn., Å-scale control of thickness, and sub-μm resoln. in the x-y plane. Using a combination of additive and subtractive e-jet printing with AS-ALD, a thin-film transistor was fabricated using zinc-tin-oxide for the semiconductor channel and aluminum-doped zinc oxide as the source and drain elec. contacts. In the future, this technique can be used to print integrated electronics with sub-micron resoln. on a variety of substrates.
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    11. 11
      Deminskyi, P.; Haider, A.; Eren, H.; Khan, T. M.; Biyikli, N. Area-selective atomic layer deposition of noble metals: Polymerized fluorocarbon layers as effective growth inhibitors. J. Vac. Sci. Technol., A 2020, 39 (1), 022402  DOI: 10.1116/6.0000701
      There is no corresponding record for this reference.
    12. 12
      Krishtab, M.; Armini, S.; Meersschaut, J.; De Gendt, S.; Ameloot, R. Cyclic Plasma Halogenation of Amorphous Carbon for Defect-Free Area-Selective Atomic Layer Deposition of Titanium Oxide. ACS Appl. Mater. Interfaces 2021, 13 (27), 32381– 32392,  DOI: 10.1021/acsami.1c04405
      12
      Cyclic plasma halogenation of amorphous carbon for defect-free area-selective atomic layer deposition of titanium oxide
      Krishtab, Mikhail; Armini, Silvia; Meersschaut, Johan; De Gendt, Stefan; Ameloot, Rob
      ACS Applied Materials & Interfaces (2021), 13 (27), 32381-32392CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      As crit. dimensions in integrated circuits continue to shrink, the lithog.-based alignment of adjacent patterned layers becomes more challenging. Area-selective at. layer deposition (ALD) allows circumventing the alignment issue by exploiting the chem. contrast of the exposed surfaces. In this work, we investigate the selective deposition of TiO2 by plasma halogenation of amorphous carbon (a-C:H) acting as a growth-inhibiting layer. On a-C:H, a CF4 or Cl2 plasma forms a thin halogenated layer that suppresses the growth of TiO2, while nucleation remains unaffected on plasma-treated SiO2. The same halogenating plasmas preferentially etch TiO2 nuclei over films and thus enable the restoration of the halogenated surface of amorphous carbon. By embedding the intermediate plasma treatments in the ALD TiO2 sequence, an 8 nm TiO2 layer could be deposited with a selectivity of 0.998. The application of the cyclic process on a 60 nm half-pitch line pattern resulted in the defect-free deposition of TiO2 at the bottom of the trenches. Cyclic fluorination demonstrated better growth inhibition compared to chlorination due to more efficient defect removal and retention of the favorable surface compn. during plasma exposure. While exploring the TiO2 nucleation defects at the limit of detection for conventional elemental anal. techniques (<1 x 1014 at/cm2), we addnl. highlight the value of imaging techniques such as at. force microscopy for understanding defect formation mechanisms and accurately assessing growth selectivity.
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    13. 13
      Miyajima, C.; Ito, S.; Nakagawa, M. Selective dry etching of UV-nanoimprinted resin passivation masks for area selective atomic layer deposition of aluminum oxide. J. Vac. Sci. Technol., B: Nanotechnol. Microelectron.: Mater., Process., Meas., Phenom. 2021, 39 (5), 052804  DOI: 10.1116/6.0001250
      13
      Selective dry etching of UV-nanoimprinted resin passivation masks for area selective atomic layer deposition of aluminum oxide
      Miyajima, Chiaki; Ito, Shunya; Nakagawa, Masaru
      Journal of Vacuum Science & Technology, B: Nanotechnology & Microelectronics: Materials, Processing, Measurement, & Phenomena (2021), 39 (5), 052804CODEN: JVSTCN; ISSN:2166-2746. (American Institute of Physics)
      To demonstrate area selective at. layer deposition (ALD) using UV-nanoimprinted resin patterns as phys. passivation masks, we investigated the removal of UV-cured resin films subjected to sequential mutual doses of trimethylaluminum (TMA) and H2O by using dry etching procedures. On the basis of the removal of a residual layer characteristic from imprint resin patterns by anisotropic oxygen reactive ion etching (O2 RIE), oxidatively etched UV-cured films were modified with TMA and H2O in an ALD-like cyclic manner. Atomic force microscopy and time-of-flight secondary ion mass spectrometry [time-of-flight secondary ion mass spectrometry (TOF-SIMS)] anal. suggested that the combination of phys. Ar ion milling and subsequent chem. O2 RIE enabled the elimination of oxidized UV-cured resin masks modified with 5-cycle TMA doses. By contrast, Ar ion milling or O2 RIE left org. or inorg. residues on silicon surfaces, resp. A TMA-modified hybridized resin layer was etched by phys. Ar ion milling; subsequently, the org. residual resin layer was removed by chem. O2 RIE in the case of 5-cycle modification with TMA. The mapping image of Al+ visualized by TOF-SIMS suggested that line patterns of aluminum oxide were left selectively on unmasked silicon substrate surfaces by site-selective dry etching of TMA-modified imprint resin passivation masks with 500 nm linewidth. (c) 2021 American Institute of Physics.
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    14. 14
      Papananou, H.; Katsumata, R.; Neary, Z.; Goh, R.; Meng, X.; Limary, R.; Segalman, R. A. Dopamine-Mediated Polymer Coating Facilitates Area-Selective Atomic Layer Deposition. ACS Appl. Polym. Mater. 2021, 3 (10), 4924– 4931,  DOI: 10.1021/acsapm.1c00692
      14
      Dopamine-Mediated Polymer Coating Facilitates Area-Selective Atomic Layer Deposition
      Papananou, Hellen; Katsumata, Reika; Neary, Zachary; Goh, Rubayn; Meng, Xiangxi; Limary, Ratchana; Segalman, Rachel A.
      ACS Applied Polymer Materials (2021), 3 (10), 4924-4931CODEN: AAPMCD; ISSN:2637-6105. (American Chemical Society)
      Area-selective at. layer deposition (ALD) has the potential to significantly improve current fabrication approaches by introducing a bottom-up process in which robust and conformal thin films are selectively deposited onto patterned substrates. This bottom-up approach requires selective areas of the substrates to be masked to inhibit deposition. Spontaneous self-assembly and organization of a mask, incorporating adhesion and other functions, are particularly attractive for this role as they do not require a sep. patterning step. Here, we make use of the pH/light tunability of catechol adhesion to develop a catechol-functionalized polymer that exhibits tunable adhesion strengths on different materials based on their specific chem. Tunable selective deposition was shown between metal/metal oxide substrates by controlling the local pH. Moreover, by controlling the adhesion strength through UV light, the deposition of hafnium oxide (HfO2) during ALD was successfully inhibited.
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    15. 15
      Chou, C.-Y.; Lee, W.-H.; Chuu, C.-P.; Chen, T.-A.; Hou, C.-H.; Yin, Y.-T.; Wang, T.-Y.; Shyue, J.-J.; Li, L.-J.; Chen, M.-J. Atomic Layer Nucleation Engineering: Inhibitor-Free Area-Selective Atomic Layer Deposition of Oxide and Nitride. Chem. Mater. 2021, 33 (14), 5584– 5590,  DOI: 10.1021/acs.chemmater.1c00823
      15
      Atomic layer nucleation engineering: Inhibitor-free area-selective atomic layer deposition of oxide and nitride
      Chou, Chun-Yi; Lee, Wei-Hao; Chuu, Chih-Piao; Chen, Tse-An; Hou, Cheng-Hung; Yin, Yu-Tung; Wang, Ting-Yun; Shyue, Jing-Jong; Li, Lain-Jong; Chen, Miin-Jang
      Chemistry of Materials (2021), 33 (14), 5584-5590CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Area-selective at. layer deposition (AS-ALD) has attracted attention due to the process demand for semiconductor device scaling. Here, we propose the at. layer nucleation engineering (ALNE) technique, an inhibitor-free AS-ALD of an oxide (Al2O3) and a nitride (AlN) with nearly 100% selectivity between the dielec. (SiO2) and the metal (Pt). The key is to add a radio-frequency substrate bias after precursor exposure and purge in each ALD cycle, where the energy from the ignited plasma selectively removes the precursors on the metal owing to the relatively lower binding energy compared to those on the dielec., thereby inhibiting the film growth on the metal. This crit. step enables the AS-ALD without selectivity loss up to 100 ALD cycles, leading to significant thickness differences of ~ 14.9 and ~ 8.7 nm for Al2O3 and AlN between the dielec. and metal surfaces. The realization of AS-ALD of Al2O3 and AlN by ALNE is also confirmed on the Pt/SiO2 patterned substrate. The ALNE offers a novel concept and approach to achieve high-selectivity AS-ALD, which is crit. to further extension of Moore's law.
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    16. 16
      Gasvoda, R. J.; Xu, W.; Zhang, Z.; Wang, S.; Hudson, E. A.; Agarwal, S. Selective Gas-Phase Functionalization of SiO2 and SiNx Surfaces with Hydrocarbons. Langmuir 2021, 37 (13), 3960– 3969,  DOI: 10.1021/acs.langmuir.1c00212
      16
      Selective Gas-Phase Functionalization of SiO2 and SiNx Surfaces with Hydrocarbons
      Gasvoda, Ryan J.; Xu, Wanxing; Zhang, Zhonghao; Wang, Scott; Hudson, Eric A.; Agarwal, Sumit
      Langmuir (2021), 37 (13), 3960-3969CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      Selective functionalization of dielec. surfaces is required for area-selective at. layer deposition and etching. We have identified precursors for the selective gas-phase functionalization of plasma-deposited SiO2 and SiNx surfaces with hydrocarbons. The corresponding reaction mechanism of the precursor mols. with the two surfaces was studied using in situ surface IR spectroscopy. We show that at a substrate temp. of 70°C, cyclic azasilanes preferentially react with an -OH-terminated SiO2 surface over a -NHx-terminated SiNx surface with an attachment selectivity of ~ 5.4, which is limited by the partial oxidn. of the SiNx surface. The cyclic azasilane undergoes a ring-opening reaction where the Si-N bond cleaves upon the reaction with surface -OH groups forming a Si-O-Si linkage. After ring opening, the backbone of the grafted hydrocarbon is terminated with a secondary amine, -NHCH3, which can react with water to form an -OH-terminated surface and release CH3NH2 as the product. The surface coverage of the grafted cyclic azasilane is calcd. as ~ 3.3 x 1014 cm-2, assuming that each reacted -OH group contributes to one hydrocarbon linkage. For selective attachment to SiNx over SiO2 surfaces, we detd. the reaction selectivity of aldehydes. We demonstrate that aldehydes selectively attach to SiNx over SiO2 surfaces, and for the specific branched aliph. aldehyde used in this work, almost no reaction was detected with the SiO2 surface. A fraction of the aldehyde mols. reacts with surface -NH2 groups to form an imine (Si-N = C) surface linker with H2O released as the byproduct. The other fraction of the aldehydes also reacts with surface -NH2 groups but do not undergo the water-elimination step and remains attached to the surface as an aminoalc. (Si-NH-COH-). The surface coverage of the grafted aldehyde is calcd. as ~ 9.8 x 1014 cm-2 using a known IR absorbance cross-section for the -C(CH3)3 groups.
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    17. 17
      Kim, H.-M.; Lee, J.-H.; Lee, S.-H.; Harada, R.; Shigetomi, T.; Lee, S.; Tsugawa, T.; Shong, B.; Park, J.-S. Area-Selective Atomic Layer Deposition of Ruthenium Using a Novel Ru Precursor and H2O as a Reactant. Chem. Mater. 2021, 33 (12), 4353– 4361,  DOI: 10.1021/acs.chemmater.0c04496
      17
      Area-selective atomic layer deposition of ruthenium using Ru precursor and H2O as reactant
      Kim, Hye-Mi; Lee, Jung-Hoon; Lee, Seung-Hwan; Harada, Ryosuke; Shigetomi, Toshiyuki; Lee, Seungjoon; Tsugawa, Tomohiro; Shong, Bonggeun; Park, Jin-Seong
      Chemistry of Materials (2021), 33 (12), 4353-4361CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Ruthenium (Ru) has drawn attention in the field of future semiconductor processing as a diffusion barrier layer and an electrode material. Here, ruthenium films are deposited by at. layer deposition (ALD) using a novel precursor, Ru2{μ2-η3-N(tBu)-C(H)-C(iPr)}(CO)6 (T-Rudic), and two different co-reagents, i.e., H2O and O2. Ru films are deposited at 0.1 Å/cycle at 150 °C with H2O and 0.8 Å/cycle at 200 °C with O2. The H2O reactant set exhibits ALD satn. between 150 and 200 °C. However, the O2 reactant set shows a linear incremental growth rate over 200 °C and nongrowth under 175 °C. Film growth preference is obsd. on various substrates (e.g., Si, SiO2, Al2O3, and graphitic carbon) when the H2O reactant is applied at 150 °C. Both exptl. data and d. functional theory calcns. indicate that preferential growth occurs on a hydrogen-terminated surface (Si) rather than a hydroxyl-terminated surface (SiO2). The Auger electron spectroscopy mapping image of a selectively deposited Ru film on a patterned Si and SiO2 substrate supports that this selective deposition mechanism also occurs in a square-patterned substrate.
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    18. 18
      Lee, J.; Lee, J.-M.; Oh, H.; Kim, C.; Kim, J.; Kim, D. H.; Shong, B.; Park, T. J.; Kim, W.-H. Inherently Area-Selective Atomic Layer Deposition of SiO2 Thin Films to Confer Oxide Versus Nitride Selectivity. Adv. Funct. Mater. 2021, 31 (33), 2102556  DOI: 10.1002/adfm.202102556
      18
      Inherently Area-Selective Atomic Layer Deposition of SiO2 Thin Films to Confer Oxide Versus Nitride Selectivity
      Lee, Jinseon; Lee, Jeong-Min; Oh, Hongjun; Kim, Changhan; Kim, Jiseong; Kim, Dae Hyun; Shong, Bonggeun; Park, Tae Joo; Kim, Woo-Hee
      Advanced Functional Materials (2021), 31 (33), 2102556CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Area-selective at. layer deposition (AS-ALD) offers tremendous advantages in comparison with conventional top-down patterning processes that at.-level selective deposition can achieve in a bottom-up fashion on pre-defined areas in multi-dimensional structures. In this work, a method for exploiting substrate-dependent selectivity of aminosilane precursors for oxides vs. nitrides through chemo-selective adsorption is reported. For this purpose, AS-ALD of SiO2 thin films on SiO2 substrates rather than on SiN substrates are investigated. Theor. screening using d. functional theory (DFT) calcns. are performed to identify Si precursors that maximize adsorption selectivity; results indicate that di(isopropylamino)silane (DIPAS) has the potential to function as a highly chemo-selective precursor. Application of this precursor to SiN and SiO2 substrates result in inherent deposition selectivity of ≈4 nm without the aid of surface inhibitors. Furthermore, deposition selectivity is enhanced using an ALD-etch supercycle in which an etching step inserts periodically after a certain no. of ALD SiO2 cycles. Thereby, enlarged deposition selectivity greater than ≈10 nm is successfully achieved on both blanket- and SiO2/SiN-patterned substrates. Finally, area-selective SiO2 thin films over 4-5 nm are demonstrated inside 3D nanostructure. This approach for performing inherent AS-ALD expands the potential utility of bottom-up nanofabrication techniques for next-generation nanoelectronic applications.
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    19. 19
      Li, Y.-C.; Cao, K.; Yu-Xiao, L.; Jing-Ming, Z.; Gong, M.; Yan-Wei, W.; Shan, B.; Chen, R. Inherently Area-Selective Atomic Layer Deposition of Manganese Oxide through Electronegativity-Induced Adsorption. Molecules 2021, 26 (10), 3056  DOI: 10.3390/molecules26103056
      19
      Inherently area-selective atomic layer deposition of manganese oxide through electronegativity-induced adsorption
      Li, Yi-Cheng; Cao, Kun; Lan, Yu-Xiao; Zhang, Jing-Ming; Gong, Miao; Wen, Yan-Wei; Shan, Bin; Chen, Rong
      Molecules (2021), 26 (10), 3056CODEN: MOLEFW; ISSN:1420-3049. (MDPI AG)
      Manganese oxide (MnOx) shows great potential in the areas of nano-electronics, magnetic devices and so on. Since the characteristics of precise thickness control at the at. level and self-align lateral patterning, area-selective deposition (ASD) of the MnOx films can be used in some key steps of nanomanufg. In this work, MnOx films are deposited on Pt, Cu and SiO2 substrates using Mn(EtCp)2 and H2O over a temp. range of 80-215°C. Inherently area-selective at. layer deposition (ALD) of MnOx is successfully achieved on metal/SiO2 patterns. The selectivity improves with increasing deposition temp. within the ALD window. Moreover, it is demonstrated that with the decrease of electronegativity differences between M (M = Si, Cu and Pt) and O, the chemisorption energy barrier decreases, which affects the initial nucleation rate. The inherent ASD aroused by the electronegativity differences shows a possible method for further development and prediction of ASD processes.
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    20. 20
      Bobb-Semple, D.; Zeng, L.; Cordova, I.; Bergsman, D. S.; Nordlund, D.; Bent, S. F. Substrate-Dependent Study of Chain Orientation and Order in Alkylphosphonic Acid Self-Assembled Monolayers for ALD Blocking. Langmuir 2020, 36 (43), 12849– 12857,  DOI: 10.1021/acs.langmuir.0c01974
      20
      Substrate-Dependent Study of Chain Orientation and Order in Alkylphosphonic Acid Self-Assembled Monolayers for ALD Blocking
      Bobb-Semple, Dara; Zeng, Li; Cordova, Isvar; Bergsman, David S.; Nordlund, Dennis; Bent, Stacey F.
      Langmuir (2020), 36 (43), 12849-12857CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      For years, many efforts in area selective at. layer deposition (AS-ALD) have focused on trying to achieve high-quality self-assembled monolayers (SAMs), which have been shown by a no. of studies to be effective for blocking deposition. Herein, we show that in some cases where a densely packed SAM is not formed, significant ALD inhibition may still be realized. The formation of octadecylphosphonic acid (ODPA) SAMs was evaluated on four metal substrates: Cu, Co, W, and Ru. The mol. orientation, chain packing, and relative surface coverage were evaluated using near-edge X-ray absorption fine structure (NEXAFS), Fourier transform IR (FTIR) spectroscopy, and electrochem. impedance spectroscopy (EIS). ODPA SAMs formed on Co, Cu, and W showed strong angular dependence of the NEXAFS signal whereas ODPA on Ru did not, suggesting a disordered layer was formed on Ru. Addnl., EIS and FTIR spectroscopy confirmed that Co and Cu form densely packed, "crystal-like" SAMs whereas Ru and W form less dense monolayers, a surprising result since W-ODPA was previously shown to inhibit the ALD of ZnO and Al2O3 best among all the substrates. This work suggests that multiple factors play a role in SAM-based AS-ALD, not just the SAM quality. Therefore, metrol. averaging techniques (e.g., WCA and FTIR spectroscopy) commonly used for evaluating SAMs to predict their suitability for ALD inhibition should be supplemented by more atomically sensitive methods. Finally, it highlights important considerations for describing the mechanism of SAM-based selective ALD.
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    21. 21
      de Paula, C.; Bobb-Semple, D.; Bent, S. F. Increased selectivity in area-selective ALD by combining nucleation enhancement and SAM-based inhibition. J. Mater. Res. 2021, 36 (3), 582– 591,  DOI: 10.1557/s43578-020-00013-4
      21
      Increased selectivity in area-selective ALD by combining nucleation enhancement and SAM-based inhibition
      de Paula, Camila; Bobb-Semple, Dara; Bent, Stacey F.
      Journal of Materials Research (2021), 36 (3), 582-591CODEN: JMREEE; ISSN:2044-5326. (Springer International Publishing AG)
      An area-selective at. layer deposition (AS-ALD) process is developed that achieves increased selectivity by combining two strategies: (i) selective enhancement using a small mol. activator and (ii) self-assembled monolayer (SAM)-based inhibition. Specifically, we show that Pt can be selectively deposited on SiO2 over Co. In this process, Co, which serves as the non-growth surface, is protected by an octadecylphosphonic acid (ODPA) SAM, while the subsequent nucleation and growth of Pt on SiO2 is enhanced using a trimethylaluminum (AlMe3) pretreatment. This combination of enhancement and inhibition yields 3-6 times higher Pt coverage on the growth surface (SiO2) while maintaining selectivity of at least 0.98 after 100 Pt ALD cycles. Pt is used here as a model system, but this process can be extended for AS-ALD of other materials.
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    22. 22
      Liu, T.-L.; Bent, S. F. Area-Selective Atomic Layer Deposition on Chemically Similar Materials: Achieving Selectivity on Oxide/Oxide Patterns. Chem. Mater. 2021, 33 (2), 513– 523,  DOI: 10.1021/acs.chemmater.0c03227
      22
      Area-selective atomic layer deposition on chemically similar materials: Achieving selectivity on oxide/oxide patterns
      Liu, Tzu-Ling; Bent, Stacey F.
      Chemistry of Materials (2021), 33 (2), 513-523CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Area-selective at. layer deposition (AS-ALD) is attracting increasing interest, but the process usually requires substrate materials with substantially different chem. properties. We introduce a process that expands the application to more general material systems by demonstrating AS-ALD on patterns with chem. similar materials. The substrate materials investigated are Al2O3, HfO2, TiO2, Ta2O5, and SiO2. By taking advantage of differential reactivity of octadecylphosphonic acid (ODPA) self-assembled monolayers (SAMs) on the various dielec. surfaces, we use the SAMs as ALD inhibitors to achieve selective ALD of both ZnO and Al2O3. With SiO2 as the growth surface, the best blocking performance against ZnO and Al2O3 ALD is achieved on ODPA-protected Al2O3 and HfO2 substrates which reach selectivities above 0.9 after 14 nm ZnO and 2.5 nm Al2O3 growth, resp., on control Si wafers. Selectivity between different metal oxides is also explored, including HfO2/Al2O3 patterns. With the optimization of solvent and ODPA SAM deposition time, selectivity above 0.9 can be achieved for at least 4 nm ZnO ALD on a HfO2 growth surface, while preventing growth on an Al2O3 nongrowth surface. This study introduces a strategy for achieving more general selectivity and opens up the possibility for new applications in next generation electronic devices.
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    23. 23
      Liu, T.-L.; Zeng, L.; Nardi, K. L.; Hausmann, D. M.; Bent, S. F. Characterizing Self-Assembled Monolayer Breakdown in Area-Selective Atomic Layer Deposition. Langmuir 2021, 37 (39), 11637– 11645,  DOI: 10.1021/acs.langmuir.1c02211
      23
      Characterizing self-assembled monolayer breakdown in area-selective atomic layer deposition
      Liu, Tzu-Ling; Zeng, Li; Nardi, Katie L.; Hausmann, Dennis M.; Bent, Stacey F.
      Langmuir (2021), 37 (39), 11637-11645CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      To enable area-selective at. layer deposition (AS-ALD), self-assembled monolayers (SAMs) have been used as the surface inhibitor to block a variety of ALD processes. The integrity of the SAM throughout the ALD process is crit. to AS-ALD. Despite the demonstrated effectiveness of inhibition by SAMs, nucleation during ALD eventually occurs on SAM-protected surfaces, but its impact on SAM structures is still not fully understood. In this study, we chose the octadecyltrichlorosilane (ODTS) SAM as a model system to investigate the evolution of crystallinity and structure of SAMs before and after ALD. The breakdown behavior of SAMs when exposed to ZnO and Al2O3 ALD was systematically studied by combining synchrotron X-ray techniques and electron microscopy. We show that the crystallinity and structure of ODTS SAMs grown on Si substrates remain intact until a significant amt. of material deposition takes place. In addn., the undesired ALD materials that grow on ODTS SAMs present contrasting morphologies: dispersed nanoparticles for ZnO while relatively continuous film for Al2O3. Lastly, substrate dependency was explored by comparing a Si substrate to single-crystal sapphire. Similar results in the evolution of SAM crystallinity and formation of ALD nuclei on top of SAM are obsd. in the ODTS-sapphire system. This study provides an in-depth view of the influence of ALD processes on the SAM structure and the nucleation behavior of ALD on SAM-protected surfaces.
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    24. 24
      Hashemi, F. S. M.; Prasittichai, C.; Bent, S. F. Self-Correcting Process for High Quality Patterning by Atomic Layer Deposition. ACS Nano 2015, 9 (9), 8710– 8717,  DOI: 10.1021/acsnano.5b03125
      There is no corresponding record for this reference.
    25. 25
      Liu, T. L.; Bent, S. F. Area-Selective Atomic Layer Deposition on Chemically Similar Materials: Achieving Selectivity on Oxide/Oxide Patterns. Chem. Mater. 2021, 33 (2), 513– 523,  DOI: 10.1021/acs.chemmater.0c03227
      25
      Area-selective atomic layer deposition on chemically similar materials: Achieving selectivity on oxide/oxide patterns
      Liu, Tzu-Ling; Bent, Stacey F.
      Chemistry of Materials (2021), 33 (2), 513-523CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Area-selective at. layer deposition (AS-ALD) is attracting increasing interest, but the process usually requires substrate materials with substantially different chem. properties. We introduce a process that expands the application to more general material systems by demonstrating AS-ALD on patterns with chem. similar materials. The substrate materials investigated are Al2O3, HfO2, TiO2, Ta2O5, and SiO2. By taking advantage of differential reactivity of octadecylphosphonic acid (ODPA) self-assembled monolayers (SAMs) on the various dielec. surfaces, we use the SAMs as ALD inhibitors to achieve selective ALD of both ZnO and Al2O3. With SiO2 as the growth surface, the best blocking performance against ZnO and Al2O3 ALD is achieved on ODPA-protected Al2O3 and HfO2 substrates which reach selectivities above 0.9 after 14 nm ZnO and 2.5 nm Al2O3 growth, resp., on control Si wafers. Selectivity between different metal oxides is also explored, including HfO2/Al2O3 patterns. With the optimization of solvent and ODPA SAM deposition time, selectivity above 0.9 can be achieved for at least 4 nm ZnO ALD on a HfO2 growth surface, while preventing growth on an Al2O3 nongrowth surface. This study introduces a strategy for achieving more general selectivity and opens up the possibility for new applications in next generation electronic devices.
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    26. 26
      Merkx, M. J. M.; Jongen, R. G. J.; Mameli, A.; Lemaire, P. C.; Sharma, K.; Hausmann, D. M.; Kessels, W. M. M.; Mackus, A. J. M. Insight into the removal and reapplication of small inhibitor molecules during area-selective atomic layer deposition of SiO2. J. Vac. Sci. Technol.. A 2021, 39 (1), 012402  DOI: 10.1116/6.0000652
      26
      Insight into the removal and reapplication of small inhibitor molecules during area-selective atomic layer deposition of SiO2
      Merkx, Marc J. M.; Jongen, Rick G. J.; Mameli, Alfredo; Lemaire, Paul C.; Sharma, Kashish; Hausmann, Dennis M.; Kessels, Wilhelmus M. M.; Mackus, Adriaan J. M.
      Journal of Vacuum Science & Technology, A: Vacuum, Surfaces, and Films (2021), 39 (1), 012402CODEN: JVTAD6; ISSN:0734-2101. (American Institute of Physics)
      As the semiconductor industry progresses toward more complex multilayered devices with ever smaller features, accurately aligning these layers with respect to each other has become a bottleneck in the advancement to smaller transistor nodes. To avoid alignment issues, area-selective at. layer deposition (ALD) can be employed to deposit material in a self-aligned fashion. Previously, we demonstrated area-selective ALD of SiO2 using three-step (i.e., ABC-type) ALD cycles comprising an acetylacetone (Hacac) dose (step A), a bis(diethylamino)silane precursor dose (step B), and an O2 plasma exposure (step C). In this work, the mechanisms of the removal and reapplication of the inhibitor mols. during area-selective ALD were studied, with the aim of enhancing the selectivity of the process. In situ IR spectroscopy shows that the O2 plasma exposure does not completely remove the adsorbed Hacac species (i.e., acac adsorbates) at the end of the cycle. The persisting species were found to contain fragments of Hacac mols., which hinder subsequent inhibitor adsorption in the next ALD cycle, and thereby contribute to a loss in selectivity. Alternatively, it was found that an H2 plasma is able to completely remove all acac species from the surface. An improvement in selectivity was achieved by using a four-step ALD cycle that includes an H2 plasma step, allowing the nucleation delay to be prolonged from 18 2 to 30 ± 3 ALD cycles. As a result, 2.7 ± 0.3 nm SiO2 can be deposited with a selectivity of 0.9, whereas only 1.6 ± 0.2 nm can be achieved without the H2 plasma step. This work shows that the addn. of a dedicated inhibitor removal step before the reapplication of the inhibitors can significantly improve the selectivity. (c) 2021 American Institute of Physics.
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    27. 27
      Rozyyev, V.; Murphy, J. G.; Barry, E.; Mane, A. U.; Sibener, S. J.; Elam, J. W. Vapor-phase grafting of a model aminosilane compound to Al2O3, ZnO, and TiO2 surfaces prepared by atomic layer deposition. Appl. Surf. Sci. 2021, 562, 149996  DOI: 10.1016/j.apsusc.2021.149996
      27
      Vapor-phase grafting of a model aminosilane compound to Al2O3, ZnO, and TiO2 surfaces prepared by atomic layer deposition
      Rozyyev, Vepa; Murphy, Julia G.; Barry, Edward; Mane, Anil U.; Sibener, S. J.; Elam, Jeffrey W.
      Applied Surface Science (2021), 562 (), 149996CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
      Atomic layer deposition (ALD) is a highly versatile surface functionalization technique that can conformally coat both planar and porous substrates. Here we use ALD metal oxide layers to establish a well-defined starting surface for vapor-phase surface org. modification. Vapor-phase (3-aminopropyl)triethoxysilane (APTES) surface silanization of ALD Al2O3, ZnO and TiO2 surfaces were studied at 100°C, 150°C and 200°C. In situ quartz crystal microbalance (QCM) and Fourier-transform IR (FTIR) spectroscopy measurements, and ex situ at. force microscopy (AFM) and XPS measurements showed uniform monolayer silane formation through self-limiting APTES reaction. We obsd. a higher surface d. of grafted APTES species following silanization at 100°C compared to 200°C, and we attribute this to the temp.-dependent reactivity of the surface hydroxyls and changes in the mode of APTES reaction. The FTIR and XPS measurements revealed that APTES reacts with Al2O3 and ZnO exclusively through metal siloxy bond formation. However, APTES reacts with TiO2 through both siloxy bond formation and ammonium salt formation via the amine group.
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    28. 28
      Vos, M. F. J.; Chopra, S. N.; Ekerdt, J. G.; Agarwal, S.; Kessels, W. M. M.; Mackus, A. J. M. Atomic layer deposition and selective etching of ruthenium for area-selective deposition: Temperature dependence and supercycle design. J. Vac. Sci. Technol., A 2021, 39 (3), 032412  DOI: 10.1116/6.0000912
      28
      Atomic layer deposition and selective etching of ruthenium for area-selective deposition: Temperature dependence and supercycle design
      Vos, Martijn F. J.; Chopra, Sonali N.; Ekerdt, John G.; Agarwal, Sumit; Kessels, Wilhelmus M. M.; Mackus, Adriaan J. M.
      Journal of Vacuum Science & Technology, A: Vacuum, Surfaces, and Films (2021), 39 (3), 032412CODEN: JVTAD6; ISSN:0734-2101. (American Institute of Physics)
      For future sub-5 nm technol. nodes, the fabrication of semiconductor devices will likely involve the use of area-selective at. layer deposition (ALD). While area-selective ALD processes have been reported for a variety of materials, most approaches yield a limited selectivity, for example, due to growth initiation at defects or impurities on the non-growth area. Recently, we demonstrated that Ru ALD can be combined with selective etching to achieve area-selective ALD of metal-on-metal with high selectivity. Cycles consisting of an O2 plasma and an H2 gas dose were integrated in an ALD-etch supercycle recipe to remove unwanted nuclei on the SiO2 non-growth area, while obtaining deposition on the Pt or Ru growth area. The current work discusses the challenging compromise that needs to be made between selectivity and net deposition, considering that the material is also removed from the growth area. After investigating deposition between 100 and 200°C on SiO2, Al2O3, Pt, and Ru in terms of selectivity and net deposition, a substrate temp. of 150°C was selected since the difference in Ru thickness on Pt and SiO2/Al2O3 was max. at this temp., even though still some deposition occurred on the SiO2 and Al2O3 non-growth areas. Different ALD-etch supercycles were studied, using varying O2 plasma etch times and etch frequencies. The amt. of the (undesired) material deposited on the SiO2 non-growth area was quantified, demonstrating that the selectivity improved for longer O2 plasma times. On the basis of the results, a simple math. description of the nucleation, growth, and etching effects during ALD-etch supercycles is discussed, which can assist the design of future area-selective deposition processes. Overall, this work illustrates how ALD and etch processes can be tuned to simultaneously obtain a high selectivity and a high net deposition of the material at the desired locations. (c) 2021 American Institute of Physics.
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    29. 29
      Hong, J.; Porter, D. W.; Sreenivasan, R.; McIntyre, P. C.; Bent, S. F. ALD resist formed by vapor-deposited self-assembled monolayers. Langmuir 2007, 23 (3), 1160– 1165,  DOI: 10.1021/la0606401
      29
      ALD Resist Formed by Vapor-Deposited Self-Assembled Monolayers
      Hong, Junsic; Porter, David W.; Sreenivasan, Raghavasimhan; McIntyre, Paul C.; Bent, Stacey F.
      Langmuir (2007), 23 (3), 1160-1165CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      A new process of applying mol. resists to block HfO2 and Pt at. layer deposition (ALD) has been investigated. Monolayer films are formed from octadecyltrichlorosilane (ODTS) or tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS) and water vapor on native silicon oxide surfaces and from 1-octadecene on hydrogen-passivated silicon surfaces through a low-pressure chem. vapor deposition process. XPS data indicates that surfaces blocked by these monolayer resists can prevent at. layer deposition of both HfO2 and Pt successfully. Time-dependent studies show that the ODTS monolayers continue to improve in blocking ability for as long as 48 h of formation time, and IR spectroscopy measurements confirm an evolution of packing order over these time scales.
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    30. 30
      Halls, M. D.; Raghavachari, K. Atomic layer deposition of Al2O3 on H-passivated Si.: I.: Initial surface reaction pathways with H/Si(100)-2 × 1. J. Chem. Phys. 2003, 118 (22), 10221– 10226,  DOI: 10.1063/1.1571513
      30
      Atomic layer deposition of Al2O3 on H-passivated Si. I. Initial surface reaction pathways with H/Si(100)-2×1
      Halls, Mathew D.; Raghavachari, Krishnan
      Journal of Chemical Physics (2003), 118 (22), 10221-10226CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      Aluminum oxide (Al2O3) grown by at. layer deposition (ALD) is currently under investigation for use as a high-k gate dielec. alternative to SiO2. Cluster calcns. employing hybrid d. functional theory have been carried out to examine the chem. reaction pathways between the ALD precursors, trimethylaluminum (TMA) and H2O, with the H/Si(100)-2×1 surface. Results obtained using Si9H14 and Si15H20, dimer and double dimer clusters to represent the surface active site are in good agreement, providing a consistent view of reaction energetics on the H/Si(100)-2×1 surface. The adsorption energies for TMA and H2O on the surface are calcd. to be 0.02 and 0.15 eV, resp. For the reaction between H2O and the H/Si(100)-2×1 surface, hydroxylation of the surface accompanied by loss of H2 was found to be the preferred pathway having an activation energy and overall reaction enthalpy of 1.60 eV and -0.75 eV, both of which are ≥0.70 eV lower than the corresponding values for the possible H/D exchange reaction. TMA exposure of the H/Si(100)-2×1 surface favors the deposition of -Al(CH3)2 with loss of CH4, having a barrier height of 1.30 eV and reaction enthalpy of -0.31 eV, which are 0.10 and 0.40 eV lower than the surface methylation pathway (H/CH3 exchange) and 2.64 and 0.45 eV lower in energy than the H2 loss reaction, which results in the deposition of -CH2-Al(CH3)2 to the surface. Therefore, the dominant reactions identified in this work are those with direct implication in the Al2O3 ALD growth mechanism, leading to the formation of Si-O and Si-Al species on the H/Si(100)-2×1 surface.
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    31. 31
      Tai, T. B.; Cao, L. A.; Mattelaer, F.; Rampelberg, G.; Hashemi, F. S. M.; Dendooven, J.; van Ommen, J. R.; Detavernier, C.; Reyniers, M. F. Atomic Layer Deposition of Al2O3 Using Aluminum Triisopropoxide (ATIP): A Combined Experimental and Theoretical Study. J. Phys. Chem. C 2019, 123 (1), 485– 494,  DOI: 10.1021/acs.jpcc.8b09198
      31
      Atomic Layer Deposition of Al2O3 Using Aluminum Triisopropoxide (ATIP): A Combined Experimental and Theoretical Study
      Tai, Truong Ba; Cao, LiAo; Mattelaer, Felix; Rampelberg, Geert; Hashemi, Fatemeh S. M.; Dendooven, Jolien; van Ommen, J. Ruud; Detavernier, Christophe; Reyniers, Marie-Francoise
      Journal of Physical Chemistry C (2019), 123 (1), 485-494CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      The aluminum precursor plays a crucial role in the Al2O3 at. layer deposition (ALD) process. To date, trimethylaluminum (TMA) is 1 of the most widely used precursors in exptl. and theor. studies. However, its application at industrial scale can pose safety risks since it is pyrophoric and extremely reactive with water. Aluminum alkoxides offer a promising alternative, but have received far less attention. A combined theor. and exptl. investigation is carried out on the Al2O3 ALD process using aluminum triisopropoxide (ATIP) as a prototypical example of Al-alkoxide precursors. The thermal ALD process using ATIP and water has a maximal growth per cycle (GPC) of 1.8 Å/cycle at 150-175°. On the basis of the in situ mass spectrometry anal. and DFT calcns., the formation of the alumina film mainly occurs during the water pulse by ligand exchange reactions between water and adsorbed precursors, while during the ATIP pulse only adsorption of ATIP and/or its dissocn. occur. Design of heteroleptic precursors contg. alkoxide group as basic ligand is challenging, but greatly promising for future industrial scale Al2O3 ALD.
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    32. 32
      Perrine, K. A.; Teplyakov, A. V. Reactivity of selectively terminated single crystal silicon surfaces. Chem. Soc. Rev. 2010, 39 (8), 3256– 3274,  DOI: 10.1039/b822965c
      32
      Reactivity of selectively terminated single crystal silicon surfaces
      Perrine, Kathryn A.; Teplyakov, Andrew V.
      Chemical Society Reviews (2010), 39 (8), 3256-3274CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. As the cornerstone of multiple practical applications, silicon single crystal surfaces have attracted the interest of scientific and engineering communities for several decades. The most recent advances employ the surfaces precovered with a specific functionality to extend into the realm of org. and metal-org. films with well-defined interfaces, to protect the surfaces from oxidn. and other contaminations, and to build the components of present and future mol. electronics and sensing devices. This crit. review will focus on the reactivity of the selectively terminated Si(100) and Si(111) surfaces. The hydrogen and halogen-terminated surfaces are the most widely used and most heavily reviewed previously, thus only a brief summary will be given here with the emphasis of the most recent thermal approaches to functionalization of hydrogen-terminated silicon. The silicon surfaces precovered with NHx functionality are emerging as a very likely candidate both for the prodn. of sharp interfaces and for coadsorption, co-assembly, and potential mol. templating of patterns on single cryst. surfaces. A brief overview of recent advances in achieving control over the hydroxyl-termination of silicon will be given. Some future directions for further development of chem., reactivity, and assembly on these surfaces, as well as potential applications, are highlighted in the last section (152 refs.).
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    33. 33
      Clark, R.; Tapily, K.; Yu, K. H.; Hakamata, T.; Consiglio, S.; O’Meara, D.; Wajda, C.; Smith, J.; Leusink, G. Perspective: New process technologies required for future devices and scaling. APL Mater. 2018, 6 (5), 058203  DOI: 10.1063/1.5026805
      33
      Perspective: New process technologies required for future devices and scaling
      Clark, R.; Tapily, K.; Yu, K.-H.; Hakamata, T.; Consiglio, S.; O'Meara, D.; Wajda, C.; Smith, J.; Leusink, G.
      APL Materials (2018), 6 (5), 058203/1-058203/12CODEN: AMPADS; ISSN:2166-532X. (American Institute of Physics)
      This paper presents an overview and perspective on processing technologies required for continued scaling of leading edge and emerging semiconductor devices. We introduce the main drivers and trends affecting future semiconductor device scaling and provide examples of emerging devices and architectures that may be implemented within the next 10-20 yr. We summarize multiple active areas of research to explain how future thin film deposition, etch, and patterning technologies can enable 3D (vertical) power, performance, area, and cost scaling. Emerging and new process technologies will be required to enable improved contacts, scaled and future devices and interconnects, monolithic 3D integration, and new computing architectures. These process technologies are explained and discussed with a focus on opportunities for continued improvement and innovation. (c) 2018 American Institute of Physics.
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    34. 34
      He, J.; Patitsas, S. N.; Preston, K. F.; Wolkow, R. A.; Wayner, D. D. M. Covalent bonding of thiophenes to Si(111) by a halogenation/thienylation route. Chem. Phys. Lett. 1998, 286 (5–6), 508– 514,  DOI: 10.1016/S0009-2614(98)00128-6
      34
      Covalent bonding of thiophenes to Si(111) by a halogenation/thienylation route
      He, J.; Patitsas, S. N.; Preston, K. F.; Wolkow, R. A.; Wayner, D. D. M.
      Chemical Physics Letters (1998), 286 (5,6), 508-514CODEN: CHPLBC; ISSN:0009-2614. (Elsevier Science B.V.)
      Thienyl monolayers covalently bonded to a Si(111) surface were prepd. by a wet chem. process in which a Si(111)-H surface was brominated to form Si(111)-Br and further reacted with lithiated thiophenes. Both N-bromosuccinimide and bromochloroform were found to be effective brominating reagents. The derivatized Si(111) surfaces were characterized by XPS, AES, ATR-FTIR and NEXAFS.
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    35. 35
      Yu, W. H.; Kang, E. T.; Neoh, K. G.; Zhu, S. P. Controlled grafting of well-defined polymers on hydrogen-terminated silicon substrates by surface-initiated atom transfer radical polymerization. J. Phys. Chem. B 2003, 107 (37), 10198– 10205,  DOI: 10.1021/jp034330s
      35
      Controlled grafting of well-defined polymers on hydrogen-terminated silicon substrates by surface-initiated atom transfer radical polymerization
      Yu, W. H.; Kang, E. T.; Neoh, K. G.; Zhu, Shiping
      Journal of Physical Chemistry B (2003), 107 (37), 10198-10205CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
      Controlled grafting of well-defined polymer brushes on the hydrogen-terminated Si(100) substrates (the Si-H substrate) was carried out via the surface-initiated atom transfer radical polymn. (ATRP). Surface initiators were immobilized on the Si-H substrates in three consecutive steps: (i) coupling of an ω-unsatd. alkyl ester to the Si-H surface under UV irradn., (ii) redn. of the ester groups by LiAlH4, and (iii) esterification of the surface-tethered hydroxyl groups with 2-bromoisobutyrate bromide. Homopolymer brushes of Me methacrylate (MMA), (2-dimethylamino)ethyl methacrylate (DMAEMA), and poly(ethylene glycol) monomethacrylate (PEGMA) were prepd. by ATRP from the α-bromoester functionalized silicon surface. The chem. compn. and topog. of the graft-functionalized silicon surfaces were characterized by XPS and at. force microscopy (AFM), resp. Kinetic studies revealed a linear increase in polymer film thickness with reaction time, indicating that chain growth from the surface was a controlled process with a "living" characteristic. Diblock copolymer brushes consisting of PMMA and PDMAEMA blocks were obtained by using the homopolymer brushes as the macroinitiators for the ATRP of the second monomer, providing further evidence to the existence of "living" chain ends. ATRP from the Si-H surfaces allowed the prepn. of polymeric-inorg. hybrid materials with well-structured surface and interface.
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    36. 36
      Coffinier, Y.; Piret, G.; Das, M. R.; Boukherroub, R. Effect of surface roughness and chemical composition on the wetting properties of silicon-based substrates. C. R. Chim. 2013, 16 (1), 65– 72,  DOI: 10.1016/j.crci.2012.08.011
      36
      Effect of surface roughness and chemical composition on the wetting properties of silicon-based substrates
      Coffinier, Yannick; Piret, Gaelle; Das, Manash R.; Boukherroub, Rabah
      Comptes Rendus Chimie (2013), 16 (1), 65-72CODEN: CRCOCR; ISSN:1631-0748. (Elsevier Masson SAS)
      The article reports on the wetting properties of Si-based materials as a function of their roughness and chem. compn. The studied surfaces consist of H-terminated and chem. modified atomically flat cryst. Si, porous Si and Si nanowires. The hydrogenated surfaces are functionalized with 1-octadecene or undecylenic acid under thermal conditions. The changes occurring upon surface functionalization are characterized using FTIR spectroscopy, XPS spectroscopy and H2O contact angle measurements. By increasing the surface roughness, the static H2O contact angle increases. The combination of high surface roughness with chem. functionalization with H2O repellent coating (1-octadecene) enables reaching superhydrophobicity (water contact angle >150°) for Si nanowires.
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    37. 37
      Frederick, E.; Dwyer, K. J.; Wang, G. T.; Misra, S.; Butera, R. E. The stability of Cl-, Br-, and I-passivated Si(100)-(2 × 1) in ambient environments for atomically-precise pattern preservation. J. Phys.: Condens. Matter 2021, 33 (44), 444001  DOI: 10.1088/1361-648x/ac1aa4
      37
      The stability of Cl-, Br-, and I-passivated Si(100)-(2 x 1) in ambient environments for atomically-precise pattern preservation
      Frederick, E.; Dwyer, K. J.; Wang, G. T.; Misra, S.; Butera, R. E.
      Journal of Physics: Condensed Matter (2021), 33 (44), 444001CODEN: JCOMEL; ISSN:0953-8984. (IOP Publishing Ltd.)
      Atomic precision advanced manufg. (APAM) leverages the highly reactive nature of Si dangling bonds relative to H- or Cl-passivated Si to selectively adsorb precursor mols. into lithog. defined areas with sub-nanometer resoln. Due to the high reactivity of dangling bonds, this process is confined to ultra-high vacuum (UHV) environments, which currently limits its commercialization and broad-based appeal. In this work, we explore the use of halogen adatoms to preserve APAM-derived lithog. patterns outside of UHV to enable facile transfer into real-world com. processes. Specifically, we examine the stability of H-, Cl-, Br-, and I-passivated Si(100) in inert N2 and ambient environments. Characterization with scanning tunneling microscopy and XPS confirmed that each of the fully passivated surfaces were resistant to oxidn. in 1 atm of N2 for up to 44 h. Varying levels of surface degrdn. and contamination were obsd. upon exposure to the lab. ambient environment. Characterization by ex situ XPS after ambient exposures ranging from 15 min to 8 h indicated the Br- and I-passivated Si surfaces were highly resistant to degrdn., while Cl-passivated Si showed signs of oxidn. within minutes of ambient exposure. As a proof-of-principle demonstration of pattern preservation, a H-passivated Si sample patterned and passivated with independent Cl, Br, I, and bare Si regions was shown to maintain its integrity in all but the bare Si region post-exposure to an N2 environment. The successful demonstration of the preservation of APAM patterns outside of UHV environments opens new possibilities for transporting atomically-precise devices outside of UHV for integrating with non-UHV processes, such as other chemistries and com. semiconductor device processes.
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    38. 38
      Rogozhina, E.; Belomoin, G.; Smith, A.; Abuhassan, L.; Barry, N.; Akcakir, O.; Braun, P. V.; Nayfeh, M. H. Si-N linkage in ultrabright, ultrasmall Si nanoparticles. Appl. Phys. Lett. 2001, 78 (23), 3711– 3713,  DOI: 10.1063/1.1377619
      38
      Si-N linkage in ultra-bright, ultrasmall Si nanoparticles
      Rogozhina, E.; Belomoin, G.; Smith, A.; Abuhassan, L.; Barry, N.; Akcakir, O.; Braun, P. V.; Nayfeh, M. H.
      Applied Physics Letters (2001), 78 (23), 3711-3713CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      Ultra-bright ultrasmall (∼1 nm) blue luminescent Si29 nanoparticles are chlorinated by reaction with Cl2 gas. A Si-N linkage is formed by the reaction of the chlorinated particles with the functional amine group in butylamine. FTIR spectroscopy and x-ray photo-spectroscopy measurements confirm the N linkage and the presence of the Bu group, while emission, excitation, and autocorrelation femtosecond optical spectroscopy show that, after the linkage formation, the particles with the ultra-bright blue luminescence remain, but with a red shift of 40 nm.
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    39. 39
      Ferng, S. S.; Wu, S. T.; Lin, D. S.; Chiang, T. C. Mediation of chain reactions by propagating radicals during halogenation of H-masked Si(100): Implications for atomic-scale lithography and processing. J. Chem. Phys. 2009, 130 (16), 164706  DOI: 10.1063/1.3122987
      39
      Mediation of chain reactions by propagating radicals during halogenation of H-masked Si(100): Implications for atomic-scale lithography and processing
      Ferng, Shyh-Shin; Wu, Shiao-Ting; Lin, Deng-Sung; Chiang, Tai C.
      Journal of Chemical Physics (2009), 130 (16), 164706/1-164706/5CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      Scanning tunneling microscopy reveals a free radical-induced surface chain reaction in the chlorination of nanoscale patterns on an otherwise H-passivated (masked) Si(100). While scanning probe methods can be used to pattern active surface regions with single-bond precision, follow-up selective chem. vapor deposition with polyat. mols. can produce various filling characteristics. On active surface regions, mol. Cl2 undergoes an atom abstraction reaction in which a Si dangling bond abstrs. one atom of the incident Cl2 mol. while the complementary Cl atom is scattered away from the initial abstraction site either back into the vacuum or to be captured by a second dangling bond and adsorbed there, or to react with a nearby adsorbed H atom to form volatile HCl. In contrast, I2 undergoes only dissociative adsorption on two immediately neighboring dangling bonds, whereby two I-Si bonds are formed simultaneously upon cleavage of the I2 bond. The different chemisorption processes of the two model diat. mol. gases place intrinsic limitations on at.-scale lithog. and processing: adsorption of Cl2 results in spillage over the prepatterned regions of active bonds. In contrast, adsorption of I2 is a pair process and results in under-filling. (c) 2009 American Institute of Physics.
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    40. 40
      Rivillon, S.; Brewer, R. T.; Chabal, Y. J. Water reaction with chlorine-terminated silicon (111) and (100) surfaces. Appl. Phys. Lett. 2005, 87 (17), 173118  DOI: 10.1063/1.2119426
      40
      Water reaction with chlorine-terminated silicon (111) and (100) surfaces
      Rivillon, Sandrine; Brewer, Rhett T.; Chabal, Yves J.
      Applied Physics Letters (2005), 87 (17), 173118/1-173118/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      Hydroxylation of chlorine-terminated silicon (111) and (100) by water vapor exposure has been studied as a function of substrate temp. using in situ IR absorption spectroscopy. No hydroxyl is obsd., as would have been expected from the surface reaction: Si-Cl(ads)+H2O(g) Si-OH(ads)+HCl(g) (ads referring to adsorbed surface species). Instead, silicon oxide is formed upon removal of the Si-Cl bond at ∼325 °C. This indicates that, while hydroxylation of the Cl-terminated silicon surface may occur, the hydroxylated surface formed by this reaction is not stable at the temp. necessary for the reaction.
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    41. 41
      Dumas, P.; Chabal, Y. J.; Jakob, P. Morphology of Hydrogen-Terminated Si(111) and Si(100) Surfaces Upon Etching in Hf and Buffered-Hf Solutions. Surf. Sci. 1992, 269-270, 867– 878,  DOI: 10.1016/0039-6028(92)91363-G
      41
      Morphology of hydrogen-terminated silicon(111) and Si(100) surfaces upon etching in hydrofluoric acid and buffered-HF solutions
      Dumas, P.; Chabal, Y. J.; Jakob, P.
      Surface Science (1992), 269-270 (Pt. B), 867-78CODEN: SUSCAS; ISSN:0039-6028.
      High resoln. EELS and IR absorption spectroscopy (IRAS) were used to characterize Si(111) and Si(100) surfaces after chem. etching in solns. of HF and buffered HF. The EELS spectra confirm that the HF-etched Si surfaces are terminated completely by H, and display essentially no loss features attributable to at. or mol. impurities. IRAS and specular beam EELS measurements show that Si(111) surfaces become flatter as the pH of the etching solns. increases from 1 (concd. HF) to 7.8 (NH4F soln.). For high pH, the (111) surfaces are atomically flat and ideally H-terminated. In contrast, the Si(100) surfaces remain rough for all pH. The surface morphol., however, depends critically on the pH and varies most for pH between 5 and 7. The EELS spectra are dominated by impact scattering and the loss features show no measurable dispersion except for the atomically smooth, ideally H-terminated Si(111) surface.
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    42. 42
      Layadi, N.; Donnelly, V. M.; Lee, J. T. C. Cl-2 plasma etching of Si(100): Nature of the chlorinated surface layer studied by angle-resolved x-ray photoelectron spectroscopy. J. Appl. Phys. 1997, 81 (10), 6738– 6748,  DOI: 10.1063/1.365216
      42
      Cl2 plasma etching of Si(100): nature of the chlorinated surface layer studied by angle-resolved x-ray photoelectron spectroscopy
      Layadi, N.; Donnelly, V. M.; Lee, J. T. C.
      Journal of Applied Physics (1997), 81 (10), 6738-6748CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
      The interaction of a Cl2 plasma with a Si(100) surface has been investigated by angle resolved XPS (XPS). It was found that the amt. of chlorine incorporated into the near-surface region of Si increases with ion energy, and does not change with long exposure to the plasma. Chlorine is present as SiClx (x=1-3) with av. relative coverages (integrated over depth) of [SiCl]:[SiCl2]:[SiCl3]≃1:0.33.0.13 at -240 V dc bias (mean ion energy ≈280 eV) and 1.0.34:0.087 at 0 V dc bias (mean ion energy ≈40 eV), at XPS (XPS) binding energies of 100.2, 101.2 and 102.3 eV, resp. Moreover, there is a substantial amt. of disordered Si within the chlorinated layer at high ion energy, reflected in a broadening of the 99.4 eV Si peak and the appearance of a shoulder at 98.8 eV, ascribed to Si with a dangling bond. In addn., bulk Si plasmon loss assocd. with the Cl(2p) and Cl(2s) core levels indicate that roughly one-third of the Cl in the near-surface region is surrounded by bulklike Si at the high ion energy. Modeling of the dependence of the relative concn. of Cl on the take-of angle was used to est. the Cl content and thickness of the surface layer. From an inversion of the obsd. take-off angle dependence of the relative Cl and Si XPS signals, depth profiles were derived for the near-surface region. Cl content falls off in a graded fashion, over a depth of about 25 and 13 Å for a mean ion energies of 280 and 40 eV, resp. The Cl areal d. (coverage integrated throughout the layer) increases with increasing mean ion energy from 1.8×1015 Cl/cm2 at 40 eV to 3.5×1015 Cl/cm2 at 280 eV. From a similar inversion of the take-off angle dependence of the SiClx signals, SiCl2 and SiCl3 are found to be largely confined at the top ∼5 Å, while below the surface, disordered Si and SiCl are present.
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    43. 43
      Butera, R. E.; Suwa, Y.; Hashizume, T.; Weaver, J. H. Adsorbate-mediated step transformations and terrace rearrangement of Si(100)-(2 × 1). Phys. Rev. B 2009, 80 (19), 193307  DOI: 10.1103/physrevb.80.193307
      43
      Adsorbate-mediated step transformations and terrace rearrangement of Si(100)-(2 × 1)
      Butera, R. E.; Suwa, Yuji; Hashizume, Tomihiro; Weaver, J. H.
      Physical Review B: Condensed Matter and Materials Physics (2009), 80 (19), 193307/1-193307/4CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      Scanning tunneling microscopy and d.-functional theory have been combined to demonstrate structural transformations of steps of Si(100)-(2×1) induced by nondangling bond-terminated Cl adsorbates. We identify a stable, bridge-bonded step adsorption site and show that supersatn. facilitates the population of those sites, leading to rebonded atom etching, step retreat, and extensive terrace rearrangement from the diffusion of resultant at. vacancy lines across the supersatd. surface. Similarities to H-Si(100) are briefly discussed.
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    44. 44
      Aldao, C. M.; Agrawal, A.; Butera, R. E.; Weaver, J. H. Atomic processes during Cl supersaturation etching of Si(100)-(2 × 1). Phys. Rev. B 2009, 79 (12), 125303  DOI: 10.1103/physrevb.79.125303
      44
      Atomic processes during Cl supersaturation etching of Si(100)-(2×1)
      Aldao, C. M.; Agrawal, Abhishek; Butera, R. E.; Weaver, J. H.
      Physical Review B: Condensed Matter and Materials Physics (2009), 79 (12), 125303/1-125303/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      Supersatn. etching starts with Cl insertion into Si-Si bonds of Si(100) and leads to the desorption of SiCl2 pairs. During etching, insertion occurs through a Cl2 dissociative chemisorption process mediated by single dangling bond sites created by phonon-activated electron-stimulated desorption of at. Cl. Based on scanning tunneling microscopy results, the authors identify a surface species, describe its involvement in supersatn. etching, and explore the energetics that control this process. In doing so, insertion occurs at room temp. and paired dangling bonds of bare dimers also mediate this process.
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    45. 45
      Biswas, S.; Narasimhan, S. Bromine as a Preferred Etchant for Si Surfaces in the Supersaturation Regime: Insights from Calculations of Atomic Scale Reaction Pathways. J. Phys. Chem. C 2016, 120 (28), 15230– 15234,  DOI: 10.1021/acs.jpcc.6b04450
      45
      Bromine as a Preferred Etchant for Si Surfaces in the Supersaturation Regime: Insights from Calculations of Atomic Scale Reaction Pathways
      Biswas, Sananda; Narasimhan, Shobhana
      Journal of Physical Chemistry C (2016), 120 (28), 15230-15234CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Etching of semiconductors by halogens is of vital importance in device manuf. A greater understanding of the relevant processes at the atomistic level can help det. optimal conditions for etching to be carried out. Supersatn. etching is a seemingly counterintuitive process where the coverage of the etchant mols. on the surface to be etched is >1. Here we use d. functional theory computations of reaction pathways and barriers to suggest that supersatn. etching of Si(001) by Br2 should be more effective than conventional etching by Br2, as well as both conventional and supersatn. etching by Cl2. Anal. of our results shows that this is due in part to the larger size of bromine atoms, and partly due to Br-Si bonds being weaker than Cl-Si bonds. We also show that, for both conventional and supersatn. etching, the barrier for the rate-limiting step of desorption of SiX2 units is lower when the halogen X is Br rather than Cl. This contributes to the overall reaction barrier for supersatn. etching being lower for Br2 than for Cl2.
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    46. 46
      Pavlova, T. V.; Shevlyuga, V. M.; Andryushechkin, B. V.; Eltsov, K. N. Chlorine insertion and manipulation on the Si(100)-2 × 1-Cl surface in the regime of local supersaturation. Phys. Rev. B 2020, 101 (23), 235410  DOI: 10.1103/physrevb.101.235410
      46
      Chlorine insertion and manipulation on the Si(100)-2x1-Cl surface in the regime of local supersaturation
      Pavlova, T. V.; Shevlyuga, V. M.; Andryushechkin, B. V.; Eltsov, K. N.
      Physical Review B (2020), 101 (23), 235410CODEN: PRBHB7; ISSN:2469-9969. (American Physical Society)
      We insert and manipulate a single chlorine atom in chlorine monolayer on a Si(100)-2x1 surface using a scanning tunneling microscope. Two objects were created-a Cl atom in a groove between two dimer rows, and bridge-bonded Cl on a silicon dimer. Changing the voltage polarity leads to conversion of the objects into each other. Anisotropic movement of the objects at 77 K is mediated by two different diffusion mechanisms: hopping and crowdion-like motion. Insertion of a Cl atom in a groove between two dimer rows leads to the formation of a dangling bond on a third-layer Si atom. At pos. sample voltage bias, the first object is pos. charged while the second object can be neutral or neg. charged depending on silicon sample doping.
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    47. 47
      Rivillon, S.; Chabal, Y. J.; Webb, L. J.; Michalak, D. J.; Lewis, N. S.; Halls, M. D.; Raghavachari, K. Chlorination of hydrogen-terminated silicon(111) surfaces. J. Vac. Sci. Technol., A 2005, 23 (4), 1100– 1106,  DOI: 10.1116/1.1861941
      47
      Chlorination of hydrogen-terminated silicon (111) surfaces
      Rivillon, Sandrine; Chabal, Yves J.; Webb, Lauren J.; Michalak, David J.; Lewis, Nathan S.; Halls, Mathew D.; Raghavachari, Krishnan
      Journal of Vacuum Science & Technology, A: Vacuum, Surfaces, and Films (2005), 23 (4), 1100-1106CODEN: JVTAD6; ISSN:0734-2101. (American Institute of Physics)
      IR absorption spectroscopy was used to investigate the chlorination of H-terminated Si(111) surfaces by 3 different methods: (a) exposure to a satd. soln. of PCl5 in chlorobenzene; (b) exposure to Cl gas, Cl2(g), and (c) exposure to Cl2(g) under UV illumination. XPS and first principles model (clusters) calcns. were used to explore the structure and dynamics of these surfaces. The IR spectra exhibited sharp Cl-related vibrations at 586 and 527 cm-1. The narrow full width at half max. of these vibrations for all 3 prepn. methods indicated that all functionalization schemes produced a nearly complete monolayer of Cl with little surface roughening or introduction of step edges. The 527 cm-1 mode was at a much higher frequency than might be expected for the bending vibration of Si monochloride. Theor. calcns. show, however, that this vibration involves the displacement of the top Si atom parallel to the surface, subject to a relatively stiff potential, shifting its frequency to a value fairly close to that of the Si-Cl stretching mode on a Si(111) surface.
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    48. 48
      Solares, S. D.; Yu, H. B.; Webb, L. J.; Lewis, N. S.; Heath, J. R.; Goddard, W. A. Chlorination-methylation of the hydrogen-terminated silicon(111) surface can induce a stacking fault in the presence of etch pits. J. Am. Chem. Soc. 2006, 128 (12), 3850– 3851,  DOI: 10.1021/ja055408g
      48
      Chlorination-Methylation of the Hydrogen-Terminated Silicon(111) Surface Can Induce a Stacking Fault in the Presence of Etch Pits
      Solares, Santiago D.; Yu, Hongbin; Webb, Lauren J.; Lewis, Nathan S.; Heath, James R.; Goddard, William A., III
      Journal of the American Chemical Society (2006), 128 (12), 3850-3851CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Recently, we reported STM images of the methylated Si(111) surface [prepd. through chlorination-alkylation of the Si(111)-H surface] taken at 4.7 K, indicating that the torsion angle of the Me group with respect to the subsurface silicon layer is φ = 23 ± 3°. Repulsions between H atoms in adjacent Me groups are minimized at 30°, while repulsions between H atoms and second layer Si atoms are minimized at 60°. The exptl. result of 23° is surprising because it suggests a tendency of the Me group toward the eclipsed configuration (0°) rather than staggered (60°). In contrast, extensive fully periodic quantum mech. D. Functional Theory studies of this surface give an equil. torsion angle of 37.5°, indicating a tendency toward the staggered configuration. This discrepancy can be resolved by showing that the CH3 on the step edges and etch pits interacts repulsively with the CH3 on the surface terraces unless a stacking fault is introduced between the first and second silicon layers of the Si(111)-CH3 surface terraces. We propose that this could occur during the chlorination-alkylation of the Si(111)-H surface. This stacking fault model predicted φ = 22.5° measured with respect to the bulk (corresponding to φ = 37.5° with respect to the second layer Si atoms). This model can be tested by measuring the orientation of the CH3 within the etch pits, which should have φ = 37.5°, or by making a surface without etch pits, which should have φ = 37.5°.
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    49. 49
      Kornev, A. N. Tris(trimethylsilyl)silyl group in organic, coordination and organometallic chemistry. Russ. Chem. Rev. 2004, 73 (11), 1155– 1180
      There is no corresponding record for this reference.
    50. 50
      Suarez, D.; Laval, G.; Tu, S. M.; Jiang, D.; Robinson, C. L.; Scott, R.; Golding, B. T. Benzylic Brominations with N-Bromosuccinimide in (Trifluoromethyl)benzene. Synthesis 2009, 2009 (11), 1807– 1810,  DOI: 10.1055/s-0029-1216793
      There is no corresponding record for this reference.
    51. 51
      Parke, T.; Silva-Quinones, D.; Wang, G. T.; Teplyakov, A. V. The Effect of Surface Terminations on the Initial Stages of TiO2 Deposition on Functionalized Silicon. ChemPhysChem 2023, 24, e202200724  DOI: 10.1002/cphc.202200724
      51
      The Effect of Surface Terminations on the Initial Stages of TiO2 Deposition on Functionalized Silicon
      Parke, Tyler; Silva-Quinones, Dhamelyz; Wang, George T.; Teplyakov, Andrew V.
      ChemPhysChem (2023), 24 (7), e202200724CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)
      As at. layer deposition (ALD) emerges as a method to fabricate architectures with at. precision, emphasis is placed on understanding surface reactions and nucleation mechanisms. ALD of titanium dioxide with TiCl4 and water has been used to investigate deposition processes in general, but the effect of surface termination on the initial TiO2 nucleation lacks needed mechanistic insights. This work examines the adsorption of TiCl4 on Cl-, H-, and HO- terminated Si(100) and Si(111) surfaces to elucidate the general role of different surface structures and defect types in manipulating surface reactivity of growth and non-growth substrates. The surface sites and their role in the initial stages of deposition are examd. by XPS and at. force microscopy (AFM). D. functional theory (DFT) computations of the local functionalized silicon surfaces suggest oxygen-contg. defects are primary drivers of selectivity loss on these surfaces.
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    52. 52
      Bell, J. P.; Cloud, J. E.; Cheng, J. F.; Ngo, C.; Kodambaka, S.; Sellinger, A.; Williams, S. K. R.; Yang, Y. A. N-Bromosuccinimide-based bromination and subsequent functionalization of hydrogen-terminated silicon quantum dots. RSC Adv. 2014, 4 (93), 51105– 51110,  DOI: 10.1039/C4RA08477B
      52
      N-Bromosuccinimide-based bromination and subsequent functionalization of hydrogen-terminated silicon quantum dots
      Bell, Jacob P.; Cloud, Jacqueline E.; Cheng, Jifang; Ngo, Chilan; Kodambaka, Suneel; Sellinger, Alan; Ratanathanawongs Williams, S. Kim; Yang, Yongan
      RSC Advances (2014), 4 (93), 51105-51110CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
      We report a mild, effective, room-temp. method for brominating and functionalizing colloidal hydrogen-terminated silicon quantum dots (H-SiQDs) using N-bromosuccinimide (NBS) as the bromination reagent. This post-synthesis bromination overcomes a long-standing challenge of producing emissive SiQDs through the functionalization of directly synthesized halogen-terminated colloidal SiQDs.
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    53. 53
      Baldwin, R. K.; Pettigrew, K. A.; Ratai, E.; Augustine, M. P.; Kauzlarich, S. M. Solution reduction synthesis of surface stabilized silicon nanoparticles. Chem. Commun. 2002, (17), 1822– 1823,  DOI: 10.1039/b205301b
      53
      Solution reduction synthesis of surface stabilized silicon nanoparticles
      Baldwin, Richard K.; Pettigrew, Katherine A.; Ratai, Eva; Augustine, Matthew P.; Kauzlarich, Susan M.
      Chemical Communications (Cambridge, United Kingdom) (2002), (17), 1822-1823CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      This paper describes the prepn. of air and moisture stable octanol derivatized cryst. silicon nanoparticles by room temp. sodium naphthalenide redn. of silicon halides.
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    54. 54
      Zou, J.; Baldwin, R. K.; Pettigrew, K. A.; Kauzlarich, S. M. Solution synthesis of ultrastable luminescent siloxane-coated silicon nanoparticles. Nano Lett. 2004, 4 (7), 1181– 1186,  DOI: 10.1021/nl0497373
      54
      Solution Synthesis of Ultrastable Luminescent Siloxane-Coated Silicon Nanoparticles
      Zou, Jing; Baldwin, Richard K.; Pettigrew, Katherine A.; Kauzlarich, Susan M.
      Nano Letters (2004), 4 (7), 1181-1186CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Silicon nanoparticles (NPs) of ∼4.5(1.10) nm from a room-temp. soln. route are terminated by a silanization method for the first time. Energy-selected emission is obsd., consistent with the distribution of sizes obtained by this route. The NPs are photochem. stable in nonpolar org. solvents and when exposed to air/water under ambient conditions for up to 1 yr. The nanoparticles were characterized by TEM, HRTEM, EDX, SAED, FTIR, 1H/13C NMR, UV-vis, and photoluminescence (PL) spectroscopy.
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    55. 55
      Rogozhina, E. V.; Eckhoff, D. A.; Gratton, E.; Braun, P. V. Carboxyl functionalization of ultrasmall luminescent silicon nanoparticles through thermal hydrosilylation. J. Mater. Chem. 2006, 16 (15), 1421– 1430,  DOI: 10.1039/b509868h
      55
      Carboxyl functionalization of ultrasmall luminescent silicon nanoparticles through thermal hydrosilylation
      Rogozhina, Elena V.; Eckhoff, Dean A.; Gratton, Enrico; Braun, Paul V.
      Journal of Materials Chemistry (2006), 16 (15), 1421-1430CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)
      Here, we report one of the first examples of thermal hydrosilylation between a bi-functional alkene and ultrasmall (∼1 nm) H-passivated silicon nanoparticles (Si-np-H) to prep. strongly luminescent, water stable, carboxyl functionalized nanoparticles (Si-np-COOH). NMR, IR absorption spectroscopy (FTIR), size exclusion chromatog. (SEC), and photoluminescence spectroscopy are used to characterize the Si-np dispersions. Based on the SEC and FTIR data, a reaction scheme is proposed to account for side products formed through a free radical crosslinking mechanism. The Si-np-COOH may find use in applications such as biomol. labeling and biol. imaging.
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    56. 56
      Dasog, M.; Veinot, J. G. C. Size independent blue luminescence in nitrogen passivated silicon nanocrystals. Phys. Status Solidi A 2012, 209 (10), 1844– 1846,  DOI: 10.1002/pssa.201200273
      56
      Size independent blue luminescence in nitrogen passivated silicon nanocrystals
      Dasog, Mita; Veinot, Jonathan G. C.
      Physica Status Solidi A: Applications and Materials Science (2012), 209 (10), 1844-1846CODEN: PSSABA; ISSN:1862-6300. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The photoluminescent properties of allylamine terminated silicon nanocrystals (Si-NCs) are investigated. Chloride surface terminated Si-NCs of different sizes react with allylamine, yielding NCs that exhibit size independent blue luminescent NCs. NCs were characterized using X-ray diffraction, Fourier transformed IR spectroscopy, photoluminescence spectroscopy, and dynamic light scattering.
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    57. 57
      Lee, J. C.; Bae, Y. H.; Chang, S. K. Efficient α-halogenation of carbonyl compounds by N-bromosuccinimide and N-chlorosuccinimde. Bull. Korean Chem. Soc. 2003, 24 (4), 407– 408,  DOI: 10.5012/bkcs.2003.24.4.407
      57
      Efficient α-halogenation of carbonyl compounds by N-bromosuccinimide and N-chlorosuccinimide
      Lee, Jong Chan; Bae, Yong Hun; Chang, Suk-Kyu
      Bulletin of the Korean Chemical Society (2003), 24 (4), 407-408CODEN: BKCSDE; ISSN:0253-2964. (Korean Chemical Society)
      Arom. ketones and 1,3-dicarbonyl compds. are efficiently α-halogenated by systems contg. N-bromosuccinimide or N-chlorosuccinimide, p-toluenesulfonic acid, and MeCN. The protocol is operationally simple and requires only readily available starting materials.
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    58. 58
      Bergstrom, M.; Suresh, G.; Naidu, V. R.; Unelius, C. R. Iodosuccinimide (NIS) in Direct Aromatic Iodination. Eur. J. Org. Chem. 2017, 2017 (22), 3234– 3239,  DOI: 10.1002/ejoc.201700173
      There is no corresponding record for this reference.
    59. 59
      Zhao, S.; Liu, W. K. Methods for Brominations at Benzylic Positions. Curr. Org. Chem. 2019, 22 (25), 2444– 2459,  DOI: 10.2174/1385272822666181031094702
      There is no corresponding record for this reference.
    60. 60
      Bera, S. K.; Mal, P. Mechanochemical-Cascaded C-N Cross-Coupling and Halogenation Using N-Bromo- and N-Chlorosuccinimide as Bifunctional Reagents. J. Org. Chem. 2021, 86 (20), 14144– 14159,  DOI: 10.1021/acs.joc.1c01742
      60
      Mechanochemical-Cascaded C-N Cross-Coupling and Halogenation Using N-Bromo- and N-Chlorosuccinimide as Bifunctional Reagents
      Bera, Shyamal Kanti; Mal, Prasenjit
      Journal of Organic Chemistry (2021), 86 (20), 14144-14159CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
      Direct synthesis of halo-substituted phenanthridinone derivs. I [R = Cl, Br, I; R1 = H, 3-Me, 3-F, etc.; R2 = H, 8-Me; R3 = OMe, Ph] was achieved via cascade C-N bond formation and subsequent halogenation reactions of N-halosuccinimides with N-methoxy-[1,1'-biphenyl]-2-carboxamides. During the reactions, NBS/NCS first assisted the oxidative C-N coupling reaction and subsequently promoted a halogenation reaction. Thus, the role of NBS/NCS was established to be bifunctional. This protocol offered a mild, solvent-free, convenient, one-pot synthesis of compds. I.
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    61. 61
      O’Leary, L. E.; Rose, M. J.; Ding, T. X.; Johansson, E.; Brunschwig, B. S.; Lewis, N. S. Heck Coupling of Olefins to Mixed Methyl/Thienyl Monolayers on Si(111) Surfaces. J. Am. Chem. Soc. 2013, 135 (27), 10081– 10090,  DOI: 10.1021/ja402495e
      61
      Heck Coupling of Olefins to Mixed Methyl/Thienyl Monolayers on Si(111) Surfaces
      O'Leary, Leslie E.; Rose, Michael J.; Ding, Tina X.; Johansson, Erik; Brunschwig, Bruce S.; Lewis, Nathan S.
      Journal of the American Chemical Society (2013), 135 (27), 10081-10090CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The Heck reaction has been used to couple olefins to a Si(111) surface that was functionalized with a mixed monolayer comprised of Me and thienyl groups. The coupling method maintained a conjugated linkage between the surface and the olefinic surface functionality, to allow for facile charge transfer from the silicon surface. While a Si(111) surface terminated only with thienyl groups displayed a surface recombination velocity, S, of 670 ± 190 cm s-1, the mixed CH3/SC4H3-Si(111) surfaces with a coverage of θSC4H3 = 0.15 ± 0.02 displayed a substantially lower value of S = 27 ± 9 cm s-1. Accordingly, CH3/SC4H3-Si(111) surfaces were brominated with N-bromosuccinimide, to produce mixed CH3/SC4H2Br-Si(111) surfaces with coverages of θBr-Si < 0.05. The resulting aryl halide surfaces were activated using [Pd(PPh3)4] as a catalyst. After activation, Pd(II) was selectively coordinated by oxidative addn. to the surface-bound aryl halide. The olefinic substrates 4-fluorostyrene, vinylferrocene, and protoporphyrin IX di-Me ester were then coupled (in DMF at 100°C) to the Pd-contg. functionalized Si surfaces. The porphyrin-modified surface was then metalated with Co, Cu, or Zn. The vinylferrocene-modified Si(111) surface showed a linear dependence of the peak current on scan rate in cyclic voltammetry, indicating that facile electron transfer had been maintained and providing evidence of a robust linkage between the Si surface and the tethered ferrocene. The final Heck-coupled surface exhibited S = 70 cm s-1, indicating that high-quality surfaces could be produced by this multistep synthetic approach for tethering small mols. to silicon photoelectrodes.
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    62. 62
      Lauerhaas, J. M.; Sailor, M. J. Chemical Modification of the Photoluminescence Quenching of Porous Silicon. Science 1993, 261 (5128), 1567– 1568,  DOI: 10.1126/science.261.5128.1567
      62
      Chemical modification of the photoluminescence quenching of porous silicon
      Lauerhaas, Jeffrey M.; Sailor, Michael J.
      Science (Washington, DC, United States) (1993), 261 (5128), 1567-8CODEN: SCIEAS; ISSN:0036-8075.
      The photoluminescence of porous silicon can be quenched by adsorbates, and the degree of quenching can be tuned by chem. derivatization of the porous silicon surface. Thus, as-prepd. porous silicon has a hydrophobic, hydrogen-terminated surface, and the photoluminescence is strongly quenched by ethanol and weakly quenched by water. Mild chem. oxidn. (iodine followed by hydrolysis) produces a hydrophilic porous silicon surface. Photoluminescence from this hydrophilic material is quenched to a lesser extent by ethanol and to a greater extent by water, relative to the original surface. This demonstrates that the visible luminescence from porous silicon is highly surface-sensitive, and the surface interactions can be tuned by specific chem. transformations.
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    63. 63
      Silva-Quinones, D.; He, C.; Dwyer, K. J.; Butera, R. E.; Wang, G. T.; Teplyakov, A. V. Reaction of Hydrazine with Solution- and Vacuum-Prepared Selectively Terminated Si(100) Surfaces: Pathways to the Formation of Direct Si-N Bonds. Langmuir 2020, 36 (43), 12866– 12876,  DOI: 10.1021/acs.langmuir.0c02088
      63
      Reaction of Hydrazine with Solution- and Vacuum-Prepared Selectively Terminated Si(100) Surfaces: Pathways to the Formation of Direct Si-N Bonds
      Silva-Quinones, Dhamelyz; He, Chuan; Dwyer, Kevin J.; Butera, Robert E.; Wang, George T.; Teplyakov, Andrew V.
      Langmuir (2020), 36 (43), 12866-12876CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      The reactivity of liq. hydrazine (N2H4) with respect to H-, Cl-, and Br-terminated Si(100) surfaces was investigated to uncover the principles of nitrogen incorporation into the interface. This process has important implications in a wide variety of applications, including semiconductor surface passivation and functionalization, nitride growth, and many others. The use of hydrazine as a precursor allows for reactions that exclude carbon and oxygen, the primary sources of contamination in processing. In this work, the reactivity of N2H4 with H- and Cl-terminated surfaces prepd. by traditional solvent-based methods and with a Br-terminated Si(100) prepd. in ultrahigh vacuum was compared. The reactions were studied with XPS, at. force microscopy, and scanning tunneling microscopy, and the observations were supported by computational investigations. The H-terminated surface led to the highest level of nitrogen incorporation; however, the process proceeds with increasing surface roughness, suggesting possible etching or replacement reactions. In the case of Cl-terminated (predominantly dichloride) and Br-terminated (monobromide) surfaces, the amt. of nitrogen incorporation on both surfaces after the reaction with hydrazine was very similar despite the differences in prepn., initial structure, and chem. compn. D. functional theory was used to propose the possible surface structures and to analyze surface reactivity.
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    64. 64
      Wagner, C. D.; V N, A.; Kraut-Vass, A.; Allison, J. W.; Powell, C. J.; R, J., Jr. NIST Standard Reference Database 20, Version 3.4.
      There is no corresponding record for this reference.
    65. 65
      Haber, J. A.; Lewis, N. S. Infrared and X-ray photoelectron spectroscopic studies of the reactions of hydrogen-terminated crystalline Si(111) and Si(100) surfaces with Br-2, I-2, and ferrocenium in alcohol solvents. J. Phys. Chem. B 2002, 106 (14), 3639– 3656,  DOI: 10.1021/jp0102872
      65
      Infrared and X-ray Photoelectron Spectroscopic Studies of the Reactions of Hydrogen-Terminated Crystalline Si(111) and Si(100) Surfaces with Br2, I2, and Ferrocenium in Alcohol Solvents
      Haber, Joel A.; Lewis, Nathan S.
      Journal of Physical Chemistry B (2002), 106 (14), 3639-3656CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)
      The reaction chem. of H-terminated cryst. Si(111) and Si(100) surfaces in MeOH, CD3OD, CF3(CH2)3OH, BuOH, and C4D9OD solns. contg. ferrocenium (Fc+)-BF4, I2, or Br2 was monitored using x-ray photoelectron (XP) spectroscopy and IR spectroscopy. Addn. of the 1-electron oxidant Fc+, or addn. of the oxidizing species I2 or Br2, produced diagnostic changes in the IR spectra that clearly indicated formation of surficial Si-OR groups. XPS data confirmed the conclusions of the IR studies. Under the authors' reaction conditions, no detectable reaction occurred without the presence of the oxidant. The data are consistent with oxidative activation of the surficial Si-H bonds toward nucleophilic attack by the alcs. The reaction chem. was generally similar on (111)- and (100)-oriented Si surfaces, although some differences were obsd. in the ratio of reaction products on the two different surface orientations. Alkoxylated surfaces were also prepd. by a two-step process in which the surface was 1st chlorinated and then reacted with LiOCH3, LiOCD3, or LiO(CH2)3CF3. The data indicate that formation of Si-halogen bonding alone is not sufficient to provide a robust correlation between the electronic and chem. properties of such cryst. Si surfaces and that formation of Si-alkoxyl bonds is a common motif for surfaces often used in electronic and electrochem. studies of Si.
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    66. 66
      Hinckley, A. P.; Driskill, M. M.; Muscat, A. J. Dense Organosilane Monolayer Resist That Directs Highly Selective Atomic Layer Deposition. ACS Appl. Nano Mater. 2020, 3 (4), 3185– 3194,  DOI: 10.1021/acsanm.9b02128
      66
      Dense Organosilane Monolayer Resist That Directs Highly Selective Atomic Layer Deposition
      Hinckley, Adam P.; Driskill, Madison M.; Muscat, Anthony J.
      ACS Applied Nano Materials (2020), 3 (4), 3185-3194CODEN: AANMF6; ISSN:2574-0970. (American Chemical Society)
      Organosilane monolayers are part of many process flows in nanoelectronics and biotechnol. because of their versatility. Monolayers that inhibit reactions on silicon/silicon oxide surfaces are needed to create patterns that direct the deposition of mols. and realize some of these applications. Organosilane monolayers on silicon oxide are typically deposited from the liq. phase by repeated deposition and cleaning cycles. Cleaning consists of solvent extn., which removes weakly bound aggregates that physisorb in or on the layer during deposition. Adding a short immersion in an aq. oxidizing base such as Std. Clean 1 (SC-1), which is a particle removal method in semiconductor manufg., reduced the time from 48 to 2 h to deposit an inhibiting monolayer. The SC-1 not only removed agglomerates but also rehydroxylated the siloxane bridges at the interface between the monolayer and the silicon oxide surface based on XPS measurements of the hydroxyl group concn. A line and space pattern in the organosilane monolayer made by conductive at. force microscopy (C-AFM) was used to direct the precursors titanium tetrachloride (TiCl4) and water vapor to deposit titanium dioxide (TiO2) by at. layer deposition (ALD) with a selectivity greater than 0.999. The titanium dioxide lines were about 170 nm wide, 9 nm high, and 20μm long. The monolayer deposition procedure was done in a conventional lab. using the common deposition solvent toluene and could be used to make versatile structures for nanodevice fabrication.
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    67. 67
      Ott, J.; Pasanen, T. P.; Gadda, A.; Garin, M.; Rosta, K.; Vahanissi, V.; Savin, H. Impact of doping and silicon substrate resistivity on the blistering of atomic-layer-deposited aluminium oxide. Appl. Surf. Sci. 2020, 522, 146400  DOI: 10.1016/j.apsusc.2020.146400
      67
      Impact of doping and silicon substrate resistivity on the blistering of atomic-layer-deposited aluminum oxide
      Ott, Jennifer; Pasanen, Toni P.; Gadda, Akiko; Garin, Moises; Rosta, Kawa; Vahanissi, Ville; Savin, Hele
      Applied Surface Science (2020), 522 (), 146400CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
      Aluminum oxide (Al2O3) thin films grown at low temps. using at. layer deposition (ALD) are known to often suffer from local delamination sites, referred to as "blisters", after post-deposition annealing during device processing. In this work, the authors report their observation that doping of the silicon substrate has an effect on blister formation. The introduction of a highly doped layer by diffusion or implantation is found to significantly reduce blistering, compared to the non-doped regions in the immediate vicinity. Similar behavior is obsd. for both phosphorus and boron doping. Further investigation of this phenomenon using substrates with different resistivities reveals that even when introduced already during silicon crystal growth, doping affects the blistering of aluminum oxide films. Changes in several properties of silicon affected by doping, most importantly surface terminating groups, native oxide growth, and passivation of defects with hydrogen, are discussed as potential reasons behind the obsd. effect on blistering.
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    68. 68
      Hashemi, F. S. M.; Bent, S. F. Sequential Regeneration of Self-Assembled Monolayers for Highly Selective Atomic Layer Deposition. Adv. Mater. Interfaces 2016, 3 (21), 1600464  DOI: 10.1002/admi.201600464
      There is no corresponding record for this reference.
    69. 69
      Mameli, A.; Merkx, M. J. M.; Karasulu, B.; Roozeboom, F.; Kessels, W. M. M.; Mackus, A. J. M. Area-Selective Atomic Layer Deposition of SiO2 Using Acetylacetone as a Chemoselective Inhibitor in an ABC-Type Cycle. ACS Nano 2017, 11 (9), 9303– 9311,  DOI: 10.1021/acsnano.7b04701
      69
      Area-selective atomic layer deposition of SiO2 using acetylacetone as a chemoselective inhibitor in an ABC-type cycle
      Mameli, Alfredo; Merkx, Marc J. M.; Karasulu, Bora; Roozeboom, Fred; Kessels, Wilhelmus M. M.; Mackus, Adriaan J. M.
      ACS Nano (2017), 11 (9), 9303-9311CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Area-selective at. layer deposition (ALD) is rapidly gaining interest because of its potential application in self-aligned fabrication schemes for next-generation nanoelectronics. Here, we introduce an approach for area-selective ALD that relies on the use of chemoselective inhibitor mols. in a three-step (ABC-type) ALD cycle. A process for area-selective ALD of SiO2 was developed comprising acetylacetone inhibitor (step A), bis(diethylamino)silane precursor (step B), and O2 plasma reactant (step C) pulses. Our results show that this process allows for selective deposition of SiO2 on GeO2, SiNx, SiO2, and WO3, in the presence of Al2O3, TiO2, and HfO2 surfaces. In situ Fourier transform IR spectroscopy expts. and d. functional theory calcns. underline that the selectivity of the approach stems from the chemoselective adsorption of the inhibitor. The selectivity between different oxide starting surfaces and the compatibility with plasma-assisted or ozone-based ALD are distinct features of this approach. Furthermore, the approach offers the opportunity of tuning the substrate-selectivity by proper selection of inhibitor mols.
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    70. 70
      Hinckley, A. P.; Muscat, A. J. Detecting and Removing Defects in Organosilane Self-Assembled Monolayers. Langmuir 2020, 36 (10), 2563– 2573,  DOI: 10.1021/acs.langmuir.9b02753
      70
      Detecting and Removing Defects in Organosilane Self-Assembled Monolayers
      Hinckley, Adam P.; Muscat, Anthony J.
      Langmuir (2020), 36 (10), 2563-2573CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      Defects occur as self-assembled monolayers form, and the no. and type of defects depend on the surface prepn. and deposition solvent, among other parameters. Indirect measures to detect defects using a layer property, such as the thickness or bond vibrational frequency, are used routinely for process development but often lack sensitivity. Direct measures using an at. probe offer a glimpse of defect structures but over a small fraction of the layer. Direct detection after reacting defects by etching or deposition is more common, and this approach has advanced our understanding of how monolayers form and has led to improved monolayers for a variety of applications. Here we show that a series of TiCl4 gas pulses reacts with defects in organosilane layers on SiO2 depositing TiO, which was measured by XPS. The defects were silanol groups and siloxane bridge bonds at the interface between the layer and the SiO2 surface and on agglomerates physisorbed to the layer. As the TiO satn. coverage or the total no. of defects decreased, the incubation period in which no TiO was detected became longer. Cleaning the layer by solvent extn. to remove nonpolar agglomerates followed by an aq. mixt. of ammonium hydroxide and hydrogen peroxide, which is Std. Clean 1, a common particle removal step for silicon surfaces, produced an organosilane monolayer without agglomerates based on at. force microscopy. After a second organosilane immersion, the monolayer d. rose to 3.8 mols./nm2. This monolayer inhibited the deposition of TiO on the SiO2 surface for 250 pulses of TiCl4 and 200 complete TiO2 at. layer deposition cycles using TiCl4 and water vapor, and it failed at 300 complete cycles. The Std. Clean 1 soln. not only removed defects left by solvent extn. but also led to the reorganization of the organosilane layer.
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    71. 71
      Ulman, A. Formation and structure of self-assembled monolayers. Chem. Rev. 1996, 96 (4), 1533– 1554,  DOI: 10.1021/cr9502357
      71
      Formation and Structure of Self-Assembled Monolayers
      Ulman, Abraham
      Chemical Reviews (Washington, D. C.) (1996), 96 (4), 1533-1554CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review on the organization of complex, semiflexible org. mols. within quasi-2-D assemblies due to the delicate interplay between substrate-adsorbate interactions, nonbonded interactions between adsorbates, electrostatic and VDW forces, and intramol. interactions (e.g., bond stretches, angle bends, and torsions). Surface reorganization contributes to the final equil. structure of the assembly. Structural factors controlling the formation of self-assembled monolayers (SAMs) are discussed. Different SAMs with unique properties and potential applications are considered. An attempt is made to provide a general picture of self-assembly on solid surfaces as it emerges from a consideration of the interplay of different forces that control this process. 273 Refs.
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    72. 72
      Hutchins, D. O.; Acton, O.; Weidner, T.; Cernetic, N.; Baio, J. E.; Ting, G.; Castner, D. G.; Ma, H.; Jen, A. K. Y. Spin cast self-assembled monolayer field effect transistors. Org. Electron. 2012, 13 (3), 464– 468,  DOI: 10.1016/j.orgel.2011.11.025
      72
      Spin cast self-assembled monolayer field effect transistors
      Hutchins, Daniel O.; Acton, Orb; Weidner, Tobias; Cernetic, Nathan; Baio, Joe E.; Ting, Guy; Castner, David G.; Ma, Hong; Jen, Alex K.-Y.
      Organic Electronics (2012), 13 (3), 464-468CODEN: OERLAU; ISSN:1566-1199. (Elsevier B.V.)
      Top-contact self-assembled monolayer field-effect transistors (SAMFETs) were fabricated through both spin-coating and soln. assembly of a semiconducting phosphonic acid-based mol. (11-(5''''-butyl-[2,2';5',2'';5'',2''';5''',2'''']quinquethiophen-5-yl)undecylphosphonic acid) (BQT-PA). The field-effect mobilities of both spin-cast and soln. assembled SAMFETs were 1.1-8.0 × 10-6 cm2 V-1 s-1 for a wide range of channel lengths (between 12-80 μm). The mol. monolayers were characterized by AFM, attenuated total reflectance-Fourier transform IR spectroscopy (ATR-FTIR), and NEXAFS spectroscopy. The BQT-PA monolayer films exhibit dense surface coverage, bidentate binding, and tilt angles of ∼32° and ∼44° for the thiophene rings and alkyl chain, resp. These results indicate that rapid throughput of fabricating SAMFETs is possible even by spin-coating.
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    73. 73
      Fang, M.; Ho, J. C. Area-Selective Atomic Layer Deposition: Conformal Coating, Subnanometer Thickness Control, and Smart Positioning. ACS Nano 2015, 9 (9), 8651– 8654,  DOI: 10.1021/acsnano.5b05249
      73
      Area-Selective Atomic Layer Deposition: Conformal Coating, Subnanometer Thickness Control, and Smart Positioning
      Fang, Ming; Ho, Johnny C.
      ACS Nano (2015), 9 (9), 8651-8654CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      A review. Transistors have already been made three-dimensional (3D), with device channels (i.e., fins in trigate field-effect transistor (FinFET) technol.) that are taller, thinner, and closer together to enhance device performance and lower active power consumption. As device scaling continues, these transistors will require more advanced, fabrication-enabling technologies for the conformal deposition of high-κ dielec. layers on their 3-dimensional channels with accurate position alignment and thickness control down to the subnanometer scale. Among many competing techniques, area-selective at. layer deposition (AS-ALD) is a promising method that is well suited to the requirements without the use of complicated, complementary metal-oxide semiconductor (CMOS)-incompatible processes. However, further progress is limited by poor area selectivity for thicker films formed via a higher no. of ALD cycles as well as the prolonged processing time. In this issue of ACS Nano, Professor Stacy Bent and her research group demonstrate a straightforward self-correcting ALD approach, combining selective deposition with a postprocess mild chem. etching, which enables selective deposition of dielec. films with thicknesses and processing times at least 10 times larger and 48 times shorter, resp., than those obtained by conventional AS-ALD processes. These advances present an important technol. breakthrough that may drive the AS-ALD technique a step closer toward industrial applications in electronics, catalysis, and photonics, etc. where more efficient device fabrication processes are needed.
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    74. 74
      Longo, R. C.; McDonnell, S.; Dick, D.; Wallace, R. M.; Chabal, Y. J.; Owen, J. H. G.; Ballard, J. B.; Randall, J. N.; Cho, K. Selectivity of metal oxide atomic layer deposition on hydrogen terminated and oxidized Si(001)-(2 × 1) surface. J. Vac. Sci. Technol., B: Nanotechnol. Microelectron.: Mater., Process., Meas., Phenom. 2014, 32 (3), 03D112  DOI: 10.1116/1.4864619
      There is no corresponding record for this reference.
    75. 75
      Montaño-Miranda, G.; Muscat, A. Etching of silicon dioxide with gas phase HF and water:: Initiation, bulk etching, and termination. Solid State Phenom. 2008, 134, 3– 6,  DOI: 10.4028/www.scientific.net/ssp.134.3
      75
      Etching of silicon dioxide with gas phase HF and water: initiation, bulk etching, and termination
      Montano-Miranda, Gerardo; Muscat, Anthony
      Diffusion and Defect Data--Solid State Data, Pt. B: Solid State Phenomena (2008), 134 (Ultra Clean Processing of Semiconductor Surfaces VIII), 3-6CODEN: DDBPE8; ISSN:1012-0394. (Trans Tech Publications Ltd.)
      The SiO2 etching process was studied to explain the initiation mechanism and reaction kinetics of the SiO2 etching process and the surface termination on the resulting Si surface. The data showed that the induction time can be defined as the time required for a sufficient no. of HF/water clusters to adsorb on the SiO2 surface and produce the first SiF4 mols. Also, it was revealed that the etching rates are almost two orders of magnitude lower than those achieved with a detectable water layer. Furthermore, a gas/solid reaction without a liq. water layer may be advantageous for etching metal oxide films on high mobility semiconductor surfaces with narrow band gaps, which are prone to oxidn. in the presence of water.
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    76. 76
      Garín, M.; Khoury, R.; Martin, I.; Johnson, E. V. Direct etching at the nanoscale through nanoparticle-directed capillary condensation. Nanoscale 2020, 12 (16), 9240– 9245,  DOI: 10.1039/C9NR10217E
      76
      Direct etching at the nanoscale through nanoparticle-directed capillary condensation
      Garin, M.; Khoury, R.; Martin, I.; Johnson, E. V.
      Nanoscale (2020), 12 (16), 9240-9245CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
      We report a method to locally deliver a chem. etchant at the nanoscale in the vapor phase by capillary condensation forming a meniscus at the nanoparticle/substrate interface. The process is simple, scalable and does not require functionalization of the nanoparticles. Furthermore, it does not rely on any specific chem. properties of the materials other than the soln. being aq. and the wettability properties of the surfaces involved, which should enable its application to other material and chem. combinations. In particular, in this work we demonstrate the proposed process by periodically pattering a SiO2 layer using a self-assembled monolayer of polystyrene particles exposed to HF vapors. The patterned SiO2 layer is then used as a mask to etch a pattern of inverted nanopyramids on Si. The silicon nanopatterning has been demonstrated for particles sizes ranging from 800 nm down to 100 nm, providing pyramids with a size down to 50 nm for 100 nm nanoparticles.
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    77. 77
      Salimian, S.; Delfino, M. Removal of Native Silicon-Oxide with Low-Energy Argon Ions. J. Appl. Phys. 1991, 70 (7), 3970– 3972,  DOI: 10.1063/1.349160
      77
      Removal of native silicon oxide with low-energy argon ions
      Salimian, S.; Delfino, M.
      Journal of Applied Physics (1991), 70 (7), 3970-2CODEN: JAPIAU; ISSN:0021-8979.
      Electron cyclotron resonance argon plasmas have been used to clean native silicon oxide at low (≈100 eV) ion energies. There is complete and rapid removal of chem. bound O to Si and the presence of small levels of adsorbed or interstitially implanted O.
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    78. 78
      Metzler, D.; Li, C.; Lai, C. S.; Hudson, E. A.; Oehrlein, G. S. Investigation of thin oxide layer removal from Si substrates using an SiO atomic layer etching approach: the importance of the reactivity of the substrate. J. Phys. D: Appl. Phys. 2017, 50 (25), 254006  DOI: 10.1088/1361-6463/aa71f1
      78
      Investigation of thin oxide layer removal from Si substrates using an SiO2 atomic layer etching approach: the importance of the reactivity of the substrate
      Metzler, Dominik; Li, Chen; Lai, C. Steven; Hudson, Eric A.; Oehrlein, Gottlieb S.
      Journal of Physics D: Applied Physics (2017), 50 (25), 254006/1-254006/9CODEN: JPAPBE; ISSN:0022-3727. (IOP Publishing Ltd.)
      The evaluation of a plasma-based at. layer etching (ALE) approach for native oxide surface removal from Si substrates is described. Objectives include removal of the native oxide while minimizing substrate damage, surface residues and substrate loss. Oxide thicknesses were measured using in situ ellipsometry and surface chem. was analyzed by XPS. The cyclic ALE approach when used for removal of native oxide SiO2 from a Si substrate did not remove native oxide to the extent required. This is due to the high reactivity of the silicon substrate during the low-energy (<40 eV) ion bombardment phase of the cyclic ALE approach which leads to reoxidn. of the silicon surface. A modified process, which used continuously biased Ar plasma with periodic CF4 injection, achieved significant oxygen removal from the Si surface, with some residual carbon and fluorine. A subsequent H2/Ar plasma exposure successfully removed residual carbon and fluorine while passivating the silicon surface. The combined treatment reduced oxygen and carbon levels to about half compared to as received silicon surfaces. A generic insight of this work is the importance of the substrate and final surface chem. in addn. to precise etch control of the target film for ALE processes. By a fluorocarbon-based ALE technique, thin SiO2 layer removal at the Ångstrom level can be precisely performed from an inert substrate, e.g. a thick SiO2 layer.
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    79. 79
      Hennessy, J.; Moore, C. S.; Balasubramanian, K.; Jewell, A. D.; France, K.; Nikzad, S. Enhanced atomic layer etching of native aluminum oxide for ultraviolet optical applications. J. Vac. Sci. Technol., A 2017, 35 (4), 041512  DOI: 10.1116/1.4986945
      79
      Enhanced atomic layer etching of native aluminum oxide for ultraviolet optical applications
      Hennessy, John; Moore, Christopher S.; Balasubramanian, Kunjithapatham; Jewell, April D.; France, Kevin; Nikzad, Shouleh
      Journal of Vacuum Science & Technology, A: Vacuum, Surfaces, and Films (2017), 35 (4), 041512/1-041512/9CODEN: JVTAD6; ISSN:0734-2101. (American Institute of Physics)
      The authors report on the development and application of an at. layer etching (ALE) procedure based on alternating exposures of trimethylaluminum and anhyd. hydrogen fluoride (HF) implemented to controllably etch aluminum oxide. The ALE process utilizes the same chem. previously demonstrated in the at. layer deposition of aluminum fluoride thin films, and can therefore be exploited to remove the surface oxide from metallic aluminum and replace it with thin fluoride layers in order to improve the performance of UV aluminum mirrors. This ALE process is modified relative to existing methods through the use of a chamber conditioning film of lithium fluoride, which is shown to enhance the loss of fluorine surface species and results in conformal layer-by-layer etching of aluminum oxide films. Etch properties were explored over a temp. range of 225-300 °C with the Al2O3 etch rate increasing from 0.8 to 1.2 Å per ALE cycle at a fixed HF exposure of 60 ms per cycle. The effective etch rate has a dependence on the total HF exposure, but the process is shown to be scalable to large area substrates with a postetch uniformity of better than 2% demonstrated on 125 mm diam. wafers. The efficacy of the ALE process in reducing interfacial native aluminum oxide on evapd. aluminum mirrors is demonstrated using characterization by XPS and measurements of UV reflectance at wavelengths down to 120 nm. (c) 2017 American Institute of Physics.
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    80. 80
      Briggs, D.; Wootton, A. B. Analysis of Polymer Surfaces by Sims. 1. An Investigation of Practical Problems. Surf. Interface Anal. 1982, 4 (3), 109– 115,  DOI: 10.1002/sia.740040306
      80
      Analysis of polymer surfaces by SIMS. 1. An investigation of practical problems
      Briggs, D.; Wootton, A. B.
      Surface and Interface Analysis (1982), 4 (3), 109-15CODEN: SIANDQ; ISSN:0142-2421.
      XPS was used simultaneously with secondary ion mass spectroscopy (SIMS) in an attempt to sep. the effects of surface drift potential and ion beam damage on relative peak intensity changes with time in surface anal. of polymers. SIMS studies of polystyrene [9003-53-6], polytetrafluoroethylene [9002-84-0] and paraffin wax (as a model compd.) were reported.
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    81. 81
      Shircliff, R. A.; Stradins, P.; Moutinho, H.; Fennell, J.; Ghirardi, M. L.; Cowley, S. W.; Branz, H. M.; Martin, I. T. Angle-Resolved XPS Analysis and Characterization of Mono layer and Multi layer Si lane Films for DNA Coupling to Silica. Langmuir 2013, 29 (12), 4057– 4067,  DOI: 10.1021/la304719y
      81
      Angle-Resolved XPS Analysis and Characterization of Monolayer and Multilayer Silane Films for DNA Coupling to Silica
      Shircliff, Rebecca A.; Stradins, Paul; Moutinho, Helio; Fennell, John; Ghirardi, Maria L.; Cowley, Scott W.; Branz, Howard M.; Martin, Ina T.
      Langmuir (2013), 29 (12), 4057-4067CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      The authors measure silane d. and Sulfo-EMCS crosslinker coupling efficiency on aminosilane films by high-resoln. XPS and at. force microscopy (AFM) measurements. The authors then characterize DNA immobilization and hybridization on these films by 32P-radiometry. The silane film structure controls the efficiency of the subsequent steps toward DNA hybridization. A self-limited silane monolayer produced from 3-aminopropyldimethylethoxysilane (APDMES) provides a silane surface d. of ∼3 nm-2. Thin (1 h deposition) and thick (19 h deposition) multilayer films were generated from 3-aminopropyltriethoxysilane (APTES), resulting in surfaces with increased roughness compared to the APDMES monolayer. Increased silane surface d. is estd. for the 19 h APTES film, due to a ∼ 32% increase in surface area compared to the APDMES monolayer. High crosslinker coupling efficiencies were measured for all three silane films. DNA immobilization densities are similar for the APDMES monolayer and 1 h APTES. However, the DNA immobilization d. is double for the 19 h APTES, suggesting that increased surface area allows for a higher probe attachment. The APDMES monolayer has the lowest DNA target d. and hybridization efficiency. This is attributed to the steric hindrance as the random packing limit is approached for DNA double helixes (dsDNA, diam. ≥ 2 nm) on a plane. The heterogeneity and roughness of the APTES films reduce this steric hindrance and allow for tighter packing of DNA double helixes, resulting in higher hybridization densities and efficiencies. The low steric hindrance of the thin, one to two layer APTES film provides the highest hybridization efficiency of nearly 88%, with 0.21 dsDNA/nm2. The XPS data also reveal water on the crosslinker-treated surface that is implicated in device aging.
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    82. 82
      Lockett, V.; Sedev, R.; Bassell, C.; Ralston, J. Angle-resolved X-ray photoelectron spectroscopy of the surface of imidazolium ionic liquids. Phys. Chem. Chem. Phys. 2008, 10 (9), 1330– 1335,  DOI: 10.1039/b713584j
      82
      Angle-resolved X-ray photoelectron spectroscopy of the surface of imidazolium ionic liquids
      Lockett, Vera; Sedev, Rossen; Bassell, Chris; Ralston, John
      Physical Chemistry Chemical Physics (2008), 10 (9), 1330-1335CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      The surfaces of 3 imidazolium based ionic liqs. with a common anion were studied with angle-resolved XPS. The room temp. ionic liqs. (RTILs): 1-butyl-3-methylimidazolium (bmim), 1-hexyl-3-methylimidazolium (hmim), and 1-octyl-3-methylimidazolium (omim) tetrafluoroborates, were meticulously purified and dried under vacuum. Survey and high-resoln. spectra were obtained at different take-off angles (0-84°), thus increasing the surface sensitivity of the measurement. No impurities were detected and the survey spectra at normal emission (0°) confirmed the stoichiometric compn. of the liqs. However, the spectra at take-off angles of 60, 70, 80 and 84° indicated a higher amt. of C. High resoln. spectra of C1s, at these angles, showed an increased amt. of aliph. C when compared to the spectra at normal emission. The longer the side chain (R) of the imidazolium cation (Rmim), the larger was the amt. of aliph. C detected. Previous studies with other surface sensitive techniques have yielded contradictory conclusions about the surface orientation of the Rmim. The authors conclude unequivocally that the alkyl chain of the imidazolium ring of the studied RTILs is oriented away from the liq. Study demonstrates the ability of XPS to probe the structure, along with the compn., of the free liq. surface by comparing signals from different penetration depths.
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    83. 83
      Laibinis, P. E.; Bain, C. D.; Whitesides, G. M. Attenuation of Photoelectrons in Monolayers of Normal-Alkanethiols Adsorbed on Copper, Silver, and Gold. J. Phys. Chem. A 1991, 95 (18), 7017– 7021,  DOI: 10.1021/j100171a054
      83
      Attenuation of photoelectrons in monolayers of n-alkanethiols adsorbed on copper, silver, and gold
      Laibinis, Paul E.; Bain, Colin D.; Whitesides, George M.
      Journal of Physical Chemistry (1991), 95 (18), 7017-21CODEN: JPCHAX; ISSN:0022-3654.
      The attenuation length, λ, of photoelectrons with kinetic energies in the range 500-1500 eV in hydrocarbon films was measured with self-assembled monolayers (SAMs) of n-alkanethiols adsorbed on copper and silver surfaces. This work extends a previous study using SAMs on gold. The following values were detd. for λ: on Ag, 37 Å at 1390 eV, 36 Å at 1119 eV, 35 Å at 1113 eV, 30 Å at 914 eV, 29 Å at 883 eV, and 24 Å at 768 eV; on Cu, 40 Å at 1410 and 1364 eV, 28 Å at 918 eV, and ∼22 Å at 554 eV. Ests. of λ obtained by using SAMs as scattering layers are more consistent than those obtained by using thin org. films fabricated by other methods. The relationship between λ and the kinetic energy (KE) of photoelectrons, over the energy range studied by using SAMs, can be fit equally well by the expressions λ = 9.0 + 0.022KE or λ /idn kEp where p = 0.67 ± 0.11. Bethe's equation for electron scattering in matter also relates λ to KE.
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    84. 84
      Li, X. Z.; Ma, W. C.; Shestopalov, A. A. Vapor-Phase Carbenylation of Hard and Soft Material Interfaces. Langmuir 2016, 32 (44), 11386– 11394,  DOI: 10.1021/acs.langmuir.6b02471
      84
      Vapor-Phase Carbenylation of Hard and Soft Material Interfaces
      Li, Xunzhi; Ma, Wenchuan; Shestopalov, Alexander A.
      Langmuir (2016), 32 (44), 11386-11394CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      This study describes the formation of functional org. monolayers on hard and soft interfaces via a vapor-phase carbene insertion into Si-H and C-H bonds. We demonstrate that functional diazirine mols. can be used to form monomol. coatings on silicon, silicon nitride, and urethane-acrylate polymers under mild vacuum conditions and exposure to UV light. We investigate the mol. coverage and the long-term stability of the resulting monolayers in air, isopropanol, and water. Our results suggest that vapor-phase carbenylation can be used as a complementary technol. to the traditional self-assembly, permitting functionalization of various passivated substrates with stable and functional mol. coatings under mild and scalable conditions.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.3c13269.

    • AFM images of the Si-H and Si-OH substrates, Haber and Lewis’s substrate-overlayer model equation, water contact angle measurement of the halogenated substrates, XPS spectra of all substrates, ARXPS Al2O3 film thickness measurement on the Si-OH substrate, and ellipsometry topographies of the Si-OH substrate (PDF)


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