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Ru Passivation Layer Enables Cu–Cu Direct Bonding at Low Temperatures with Oxidation Inhibition

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    Surfaces, Interfaces, and Applications

    Ru Passivation Layer Enables Cu–Cu Direct Bonding at Low Temperatures with Oxidation Inhibition
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    • Chansu Jeon
      Chansu Jeon
      Department of Material Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
      More by Chansu Jeon
    • Sukkyung Kang
      Sukkyung Kang
      Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
      More by Sukkyung Kang
    • Myeong Eun Kim
      Myeong Eun Kim
      Department of Material Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
      More by Myeong Eun Kim
    • Juseong Park
      Juseong Park
      Department of Material Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
      More by Juseong Park
      Orcidhttps://orcid.org/0000-0002-9568-5991
    • Daehee Kim
      Daehee Kim
      Department of Material Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
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    • Sanha Kim*
      Sanha Kim
      Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
      * E-mail: [email protected]
      More by Sanha Kim
      Orcidhttps://orcid.org/0000-0002-3548-6173
    • Kyung Min Kim*
      Kyung Min Kim
      Department of Material Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
      * E-mail: [email protected]
      More by Kyung Min Kim
      Orcidhttps://orcid.org/0000-0002-0190-4226
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    ACS Applied Materials & Interfaces

    Cite this: ACS Appl. Mater. Interfaces 2024, 16, 36, 48481–48487
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    https://doi.org/10.1021/acsami.4c08390
    Published August 27, 2024
    Copyright © 2024 American Chemical Society
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    Abstract

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    Stacking semiconductor chips allows for increased packing density within a given footprint and efficient communication between different functional layers of the chip, leading to higher performance, improved speed, and reduced power consumption. In such vertical stacking, achieving homogeneous electrical and mechanical bonding between heterogeneous chips is crucial, which is termed Cu to Cu direct bonding (CCDB) technology. However, conventional CCDB required a high temperature of over 250 °C to allow Cu diffusion and a vacuum condition for inhibiting Cu oxidation, limiting its practical utilization. Here, we propose that the covering of the Ru layer enables a reliable CCDB as low as 200 °C without concerns regarding oxidation. The bonding strength was as high as 2.24 MPa, and it was endurable at the −45 and 125 °C temperature cycle test for 500 cycles. Through microscopic analysis, we have identified that Cu diffuses through the intercluster boundaries of the Ru layer and moves to the surface, and these atomic Cu ions are recrystallized at the bonding interface, enabling stable bonding at lower temperatures. Specifically, we observed a trade-off between Cu diffusion distance and oxidation inhibition capability depending on the thickness of Ru and found that a 6 nm-thick Ru is optimal, balancing these factors.

    Copyright © 2024 American Chemical Society

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    Supporting Information

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    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.4c08390.

    • Details of the cross-sectional images of Ru-passivated Cu sample after TCB, profile of temperature cycle test, contact resistance measurement methods, and TEM/EDS images (PDF)

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    ACS Applied Materials & Interfaces

    Cite this: ACS Appl. Mater. Interfaces 2024, 16, 36, 48481–48487
    Click to copy citationCitation copied!
    https://doi.org/10.1021/acsami.4c08390
    Published August 27, 2024
    Copyright © 2024 American Chemical Society
    Request reuse permissions

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