| A fundamental study of radio-frequency thermal plasma chemical vapor deposition of silicon carbide films was performed experimentally and numerically. A completely new thermal plasma chemical vapor deposition system, including a customized deposition chamber and a reactant delivery system, was designed and constructed for silicon carbide film deposition. Deposition experiments were conducted to understand the effects of operating parameters such as substrate temperature, reactant and plasma gas flow rates, and pulsed reactant delivery. The deposition process was mass diffusion limited. With an input CH4/SiCl4 ratio near unity, the film growth rate was proportional to the flow rate of SiCl4, from about 50 mum/hour at a SiCl4 flow rate of 16sccm to about 430 mum/hour at a SiCl 4 flow rate of 140sccm, as measured from the cross-section SEM images. Film morphology, microstructure, composition, and hardness were characterized by various methods. Nanocrystalline beta-SiC films with carbon enrichment were deposited, with the size of crystallites varying with process parameters. The films had high hardness and modulus, especially when the substrate temperature was high. A hardness of about 53 GPa was obtained for a film produced at a substrate temperature of 1215°C and a growth rate of 240 mum/hour. Proper hydrogen flow rate and choice of reactant delivery method significantly improved film morphology. A chemistry model containing 97 gas-phase reactions, 46 surface reactions and 38 chemical species was developed and verified by experiments to accurately predict SiC film growth rates. Thermochemical calculations of the Si-C-Cl-H system based on ab initio methods were performed to provide complementary thermodynamic information for the modeling. Numerical simulations identified the most significant species in the deposition process to be atomic silicon and carbon, while SiCl2, C2H 2, SiC2, Si2, and SiC also become important under different conditions. |
