LOCAL EQUILIBRIUM PHASE-DIAGRAMS - SIC DEPOSITION IN A HOT-WALL LPCVDREACTOR

Traditional CVD phase diagrams, which neglect the depletion effects in a hot wall reactor and assume the gaseous species concentrations at t he substrate are the same as input concentrations, are at best valid f or a cold wall reactor. Due to the constant change of gaseous species concentration along the length of the reactor, traditional CVD phase d iagrams do not accurately predict the phases in the deposit on the sub strate in a hot wall CVD system. In this paper, a new approach to calc ulate the local equilibrium CVD phase diagrams at the substrate is pre sented by coupling the depletion effects in a hot wall reactor to the equilibrium thermodynamic computer codes SOLGASMIX-PV. The deposition of SiC using the gas system of methyltrichlorosilane (MTS)-hydrogen (H -2) under low pressure was chosen for this study. Differences between the new CVD phase diagrams and the traditional phase diagrams for this gas system are discussed. The calculated CVD phase diagrams are also compared with the experimental data both from our own experiment and f rom the literature. The local equilibrium phase diagrams predicted the deposition of a single phase of SiC much better than those without th e consideration of the depletion effects. The experimental regions for depositing single phase SiC are larger than the calculated local phas e diagrams. This is attributed to the higher linear velocity of the ga s flux under low pressure and the polarity of the Si carrying intermed iate species.