Ab initio chemical kinetic study for reactions of H atoms with SiH ₄ and Si₂H₆: Comparison of theory and experiment

The reactions of hydrogen atom with silane and disilane are relevant to the understanding of catalytic chemical vapor deposition (Cat-CVD) and plasma enhanced chemical vapor deposition (PECVD) processes. In the present study, these reactions have been investigated by means of ab initio molecular-orbital and transition state theory calculations. In both reactions, the most favorable pathway was found to be the H abstraction leading to the formation of SiH ₃ and Si₂H₅ products, with 5.1 and 4.0 kca/mol barriers, respectively. For H + Si₂H₆, another possible reaction pathway giving SiH₃ + SiH₄ may take place with two different mechanisms with 4.3 and 6.7 kcal/mol barriers for H-atom attacking side-way and end-on, respectively. To validate the calculated energies of the reactions, two isodesmic reactions, SiH₃+CH₄→ SiH₄+CH₃ and Si₂H₅+C ₂H₆→ Si₂H₆+C₂H ₅ were employed; the predicted heats of the formation for SiH ₃ (49.0 kcal/mol) and Si₂H₅ (58.6 kcal/mol) were found to agree well with the experimental data. Finally, rate constants for both H-abstraction reactions predicted in the range of 290-2500 K agree well with experimental data. The result also shows that H+Si₂H₆ producing H₂+Si₂H₅ is more favorable than SiH₃+SiH₄