Enthalpies of Formation and Reaction for Primary Reactions of Methyl‐ and Methylmethoxysilanes from Density Functional Theory

Summary: The enthalpies of formation and enthalpies of reaction at 298 K for a set of Si:C:O:H species derived from methylsilanes and methylmethoxysilanes were computed using the B3LYP density functional theory. Total energies were calculated at the B3LYP/6‐311+G(3df,2p)//B3LYP/6‐311+G(d) level. Zero point energies and thermal corrections were calculated using B3LYP/6‐311+G(d)//B3LYP/6‐311+G(d) vibrational energies scaled by a factor of 0.96. The average absolute deviation of enthalpies of formation and reaction were 3.89 and 1.86 kcal/mol, respectively. Bond strengths and reactions with O atom and H atom are examined in the context of understanding the initial reactions in chemical vapor deposition. The SiH bond was calculated to be 8.4 kcal/mol stronger than the SiC bond in methylsilanes and to increase by 0.6 kcal/mol with increased methylation; however, the thermochemistry of methylsilane reactions with O atom favors scission of the SiH bond to produce hydroxyl and methylsilyl radicals. Thermodynamic control over the reaction pathways of methylmethoxysilanes is possible only when considering the reaction with H atom for which methylmethoxysilanol formation is favored. This illuminates a conceivable strategy to control the SiOSi bonding network while retaining methyl functionality in a CVD thin film by controlling the ratio of methoxy functionality and free hydrogen in the reactor. Density functional theory is a useful tool in understanding and subsequently controlling the initial chemistry in the CVD process. Representation of the reaction of methyltrimethoxysilane with hydrogen atoms to produce the favored products, dimethylmethoxysilanol and methyl radicals. magnified image Representation of the reaction of methyltrimethoxysilane with hydrogen atoms to produce the favored products, dimethylmethoxysilanol and methyl radicals.