ON THE MECHANISM OF HOMOGENEOUS DECOMPOSITION OF THE CHLORINATED SILANES - CHAIN-REACTIONS PROPAGATED BY DIVALENT SILICON SPECIES

A mechanism for the homogeneous gas-phase decomposition of SiHCl3, SiH 2Cl2, and SiH3Cl in hydrogen is derived from the results of ab initio molecular-orbital studies. It consists of 39 reversible elementary rea ctions among 25 species, including pressure-dependent unimolecular dec omposition of the chlorinated silanes and secondary chemistry due to r eactions of SiH2, SiHCl, and SiCl2 with one another and with the chlor inated silanes. Rate parameters in the mechanism have been calculated based on results of ab initio studies using transition-state theory an d unimolecular rate theories. This allows us to construct a reasonably complete mechanism that provides qualitative explanations for several features of dichlorosilane decomposition that have been presented in the literature, including observations on the presence and concentrati ons of SiCl2, SiHCl, and Si atoms. Several chain reactions in which th e chain carriers are divalent silicon species have been identified.