The Decomposition Pathways of CH2SiCl3, CH3SiCl2 and CH2SiCl2 in CVD of SiC from MTS/H2 System

The decomposition pathways in CVD preparing SiC with CH3SiCl3-H2 precursors was searched theoretically, which involves 54 well-defined transition states. The geometries of the species were optimized by employing the B3PW91/6-311G(d,p) method. The transition states as well as their linked intermediates were confirmed with frequency and the intrinsic reaction coordinates analyses. The energy barriers and the reaction energies were evaluated with the accurate model chemistry method at G3(MP2) level after a non-dynamical electronic correlation detection. The heat capacities and entropies were obtained with statistical thermodynamics. The Gibbs free energies at 298.15 K and 1200 K for all of the reactions were reported. The energies at any temperature could be derived classically by using the analytical heat capacities. All the possible elementary reactions, including both direct decomposition and the radical attacking dissociations for CH2SiCl3, CH3SiCl2 and CH2SiCl2 were examined. A free radical reaction mechanism was proposed.