Multiplicity of steady states in the codeposition of silicon carbide and carbon

Abstract

AbstractPast studies have suggested that the process of chemical vapor deposition of SiC and C from mixtures of methyltrichlorosilane (CH3 SiCl3, MTS), ethylene and hydrogen may exhibit multiple steady states in some regions of its space of operating parameters and conditions. This phenomenon was studied systematically and experimentally in a hot‐wall chemical‐vapor deposition reactor, in which small substrates hung from the sample arm of a sensitive microbalance are used for continuous monitoring of the deposition rate. Multiplicity of steady states occurs in a wide region of the space of process operating parameters, which covers a considerable portion of the range of conditions where deposition of SiC from MTS usually occurs. All cases studied manifest themselves as two stable (observable) deposition states at the same condition, differing by at least one order of magnitude. Various experimental observations and results of the thermochemical equilibrium analysis in the gas phase of the deposition system prove that the appearance of multiplicity in the MTS–C2H4–H2 system manifests the heterogeneous chemistry of the deposition process, not of the homogeneous chemistry or the interactions of the transport and reaction processes. The composition analysis of the deposits reveals that sudden changes of the composition from almost pure carbon at the low deposition rate branch to SiC with excess carbon at the high deposition branch take place at the two limits of the multiplicity region. It indicates that one must operate outside the range of multiple steady states to obtain deposit compositions over the whole range from C to SiC.