Radical chain reaction of methyltrichlorosilane with hydrogen and its role in chemical vapor deposition of stoichiometric SiC films

The role of hydrogen (H₂) in reaction with methyltrichlorosilane (MTS) in a hot-wall tubular chemical vapor deposition reactor to form stoichiometric SiC films was elucidated for the first time. Deposition experiments conducted at 1273 K showed that increasing the [H₂]/[MTS] concentration ratio from 2.5 to 18.2 accelerates the film growth rate by 22 %. Kinetic analysis of the film growth rate profile along the gas flow direction in a tubular reactor revealed a stepwise reaction mechanism in which MTS and H₂ form at least two consecutive intermediate species contributing to the film growth. By employing density functional theory calculations to compare the energy barriers of plausible reaction pathways with the experimental activation energy values derived from film growth rate data, we found that the first step of the stepwise reaction is most plausibly the gas-phase reaction of MTS, which dissociates HCl to form 1,1-dichlorosilaethylene (CH₂SiCl₂) as the first intermediate species to correspond a sticking probability of 4.6 × 10^–4. Subsequently, CH₂SiCl₂ initiates a radical chain reaction with H₂ to produce CH₂SiCl· as the second intermediate species. This radial species exhibits a higher sticking probability of 5.1 × 10^–2 and is responsible for the increased film growth rate at high H₂ concentrations. Most importantly, both intermediate species maintain a Si to C atomic ratio of 1:1, thereby facilitating the deposition of stoichiometric SiC films.