Mathematical Modeling of the Gas-Phase Chemistry in the Decomposition of Chlorosilanes in Mixtures of Carbon Dioxide and Hydrogen at High Temperatures

A detailed kinetic model is formulated for the decomposition of chlorosilanes [ e.g. , silicon tetrachloride and methyltrichlorosilane MTS)] in mixtures of and under conditions encountered when these mixtures are used to deposit on solid substrates or to form powders in the gas phase. A complete mechanistic model for the water gas-shift reaction is included as a subset in the overall homogeneous mechanism. The kinetic model is introduced into the transport and reaction model of a plug-flow reactor, and the overall model is used to investigate the sensitivity of gas-phase composition on the operating conditions, the residence time in the reactor, and some key steps in the pathways of the homogeneous chemistry of the process. Two sources of silicon are used in the computations, namely, silicon tetrachloride and methyltrichlorosilane. The results of the computations reveal that at the same conditions the major components of the gas phase reach partial equilibrium at shorter residence times in the MTS system. In both systems, the gas phase approaches equilibrium at residence times that are much greater than those typically encountered in chemical vapor deposition reactors. The concentrations of compounds and water vapor are much higher in the MTS system. In agreement with past experimental observations, this result suggests that silica should be deposited at higher rates from mixtures containing MTS.