Kinetic investigation of the chemical vapor deposition of silicon carbide through thermal decomposition of methyltrichlorosilane

• Main Author: Papasouliotis, George D
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1998
• Subjects: Chemical engineering
• ISBN: 0591730863; 9780591730869

A comprehensive investigation of the deposition kinetics of silicon carbide through the thermal decomposition of methyltrichlorosilane in hydrogen is the objective of this study. Experiments are performed in a tubular, hot-wall reactor coupled to an electronic microbalance. The effects of process parameters on deposition rate, film stoichiometry, and film morphology are examined over a wide range of process conditions typically encountered in SiC chemical vapor deposition reactors. Our experimental results reveal complex dependence of reaction rate and film stoichiometry not only on process conditions, such as temperature, pressure, mixture flow rate, and composition, but on residence time as well. It is shown that the dramatic variation of reaction rate with residence time, which is among the main factors contributing to the wide discrepancies in the conclusions of past studies on silicon carbide deposition, is caused by the variation of gas phase composition with residence time in the reactor, and the severe inhibitory effect of reaction by-products on the deposition process. Several kinetic expressions are used to reproduce the dependence of reactivity on process conditions and the gas-phase concentrations of deposition precursor gases and by-products. Results on the existence of multiple steady states in the deposition of silicon carbide films as temperature and mixture composition vary are reported, and their origin is traced to interactions of elementary chemical steps in the deposition mechanism. A detailed kinetic mechanism for the homogeneous decomposition of methyltrichlorosilane and the deposition of silicon carbide, silicon, and carbon from the resulting gas-phase compounds is proposed. The mechanism encompasses all compounds identified in significant quantities in the gas phase of the system, and its constituent reactions, homogeneous and surface, are treated as reversible in a thermodynamically consistent manner. The kinetic mechanism is incorporated into the reaction and transport model of a plug flow reactor, and its capability to account for fundamental attributes of the MTS/SiC reactive system, such as the variation of deposition rate and film stoichiometry with process conditions and residence time, is demonstrated.