KINETIC PROCESSES IN THE CVD OF SIC FROM CH3SICL3-H-2 IN A VERTICAL HOT-WALL REACTOR

The chemical vapour deposition of SiC-based ceramics from the CH3SiCl3-H-2 precursor is investigated on the basis of large scale experimental and theoretical approaches. The use of a vertical cylindrical hot-wall LPCVD reactor permits to get a wide isothermal reaction zone with a creeping laminar flow around the substrate and a largely chemical control of the kinetics, which favours a high supersaturation and a nucleation regime. A calculation of the coverage of C(111) or Si(111) planes of SiC points out the importance of the chemisorption of SiCl3 and H radicals on C atoms and of CH3 and Cl radicals on Si atoms. On the basis of kinetic experiments and of chemical and structural investigations of the deposits, several domains of conditions are defined with different mechanisms for the formation of SiC-based ceramics. For low temperatures and low pressures, a regime of growth of stoichiometric SiC microcrystals occurs from reaction of CH3 and SiCl3 intermediates. Higher pressures in the chemical control kinetic domain, favour a regime of nucleation of nanocrystals with an excess of silicon resulting from SiCl3/SiCl2 effective silicon precursor.