Kinetic Processes in the CVD of SiC from CH₃SiCl₃-H₂ in a Vertical Hot-Wall Reactor

Abstract
The chemical vapour deposition of SiC-based ceramics from the CH₃SiCl₃-H₂ precursor is investigated on the basis of large scale experimental and theoretical approaches. The use of a vetirtical cylindrical hot-wall LPCVD reactor permits to get a wide isothemal 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 rnechanisms 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 knetic domain, favour a regime of nucleation of nanocrystals with an excess of silicon resulting from SiCl₃/SiCl₂ silicon precursor.