STEADY-STATE MULTIPLICITY PHENOMENA IN THE DEPOSITION OF SILICON-CARBIDE

An experimental investigation of the occurrence of multiple steady sta tes in the chemical vapor deposition of silicon carbide from methyltri chlorosilane, hydrogen, and hydrogen chloride mixtures is presented in this study. Experiments have been carried out over broad temperature, pressure, and composition ranges in a hot-wall chemical vapor deposit ion reactor coupled with an electronic microbalance. It has been found that in the absence of hydrogen chloride in the feed, multiple steady states appear at temperatures around 850 degrees C, and that the addi tion of HCl moves the multiplicity region toward higher temperatures. Multiple steady states have been observed over the whole temperature ( 800-1400 degrees C) and pressure (20-760 Torr) region covered in our e xperiments, with the difference in the deposition rate between the upp er and lower stable branches exceeding in some eases two orders of mag nitude. Since the key parameter involved in the appearance of multiple steady states is the concentration of hydrogen chloride, which depend s on the residence time of the reacting mixture in the reactor; the te mperature profile, and the reactor geometry, the poor agreement among deposition rate data reported in the literature by different groups ma y be partly due to the multiple steady-states phenomenon. The appearan ce of multiplicity is explained qualitatively in terms of a simplified model of SiC deposition.