A study of chemical vapor deposition diamond morphology: Gas phase chemistry and substrate temperature effects

Diamond films were grown by chemical vapor deposition (CVD) using a radiofrequency inductively-coupled thermal plasma operated at 200 torr or 1 atm. Depending on the deposition conditions, it was found that high substrate temperature favored either {100} or {111} morphology. It was postulated that this change in morphology trend with substrate temperature was caused by changes in the chemical environment at the growing diamond surface. This chemical environment was studied using a combined experiment-modeling research program.;Gas chromatograph (GC) measurements were made of gas sampled through a micro-orifice drilled in the center of the diamond growth substrate. The GC measurements of argon, hydrogen and stable hydrocarbons were used to validate a detailed numerical model of the deposition system. Simulation predictions of CH4, C2H2, C2H6, and C2H4 were in good agreement with the GC measurements over a broad range of process parameters.;The validated model was then used to investigate the gas phase composition of C, CH3, H, and C2H2 at the growth surface. It was found that the gas phase composition ratio C2H2 C+ CH3 at the growth surface correlated with the reversal of the morphology trend with substrate temperature.;Based on these results and a simple diamond growth mechanism, a correlation equation was developed that predicts the changes in diamond morphology as substrate temperature and gas composition at the growing diamond surface vary. This expression indicates that for acetylene-enriched diamond CVD growth environments, acetylene plays a crucial role for diamond morphological development.