CVD of SiC from Methyltrichlorosilane. Part II: Composition of the Gas Phase and the Deposit

Part I of the paper was concerned with the influence of the surface area/volume ratio, [AS/VR], temperature, and residence time on the deposition rate of silicon carbide from a 1:4 methyltrichlorosilane (MTS)/hydrogen mixture. In Part II, the composition of the gas phase and the deposit are investigated. It is shown that deposition rate maxima at about 900 °C and 1025 °C, frequently reported in the literature, result from a temperature-selective deposition of both SiC and Si. This selectivity is determined by the [AS/VR] ratio because it controls the interaction of the gas phase and surface reactions. At a sufficiently high [AS/VR] ratio, deposition of free silicon is completely suppressed and the rate maxima disappear simultaneously. Increasing the temperature generally favors deposition of stoichiometric silicon carbide. Results for the gas phase composition are used to discuss changes of gas phase chemistry responsible for the deposition of free silicon, as well as of stoichiometric silicon carbide. Higher chlorosilanes, as well as carbochlorosilanes, are postulated as intermediates of silicon and silicon carbide deposition, respectively.