Boundary Layer Chemistry Probed by in Situ Infrared Spectroscopy during SiO₂ Deposition at Atmospheric Pressure from Tetraethylorthosilicate and Ozone

The deposition of silicon dioxide films at 450 °C was studied in quasi real time by probing the thermally activated boundary layer region near the growing surface during atmospheric pressure chemical vapor deposition (APCVD). Potential tetraethylorthosilicate (TEOS)/O₃ reaction products have been investigated in an attempt to clarify the reaction mechanism leading to the observed silanol deposition intermediates and delineate the film formation process. The organic products formed during the TEOS/O₃ reaction are acetic acid, formic acid, formaldehyde, carbon monoxide, carbon dioxide, and water. Quantitative methods are developed using FT-IR (Fourier transform infrared) spectroscopy during ozonation of TEOS at elevated temperatures. The measurement of gaseous alcohols of silicon alkoxides by FT-IR is demonstrated by application of an in situ methodology that probes the high-temperature region within the CVD environment. Partial least squares (PLS) Beer's law absorption models are used in determining relative TEOS, ozone, and ethoxysilanol levels during the reaction. The reaction order in TEOS is measured at 1.65 ± 0.02 over a 0.9 Torr pressure range. Similarly, the ratio of ethoxysilanol formed versus the amount of ozone consumed is ca. 1:3. A radical chain oxidative mechanism involving direct reaction of TEOS and ozone is proposed for formation of highly reactive silanol film growth intermediates.