Gas Phase Reactions for the CVD of Diamond Films.

The study of the gas phase chemical and physical reactions that occur in the chemical vapor deposition CVD of diamond was the goal of ARO grants DAAH04-93-G-0260 and DAAH04-93-0185. We have developed an ultra-sensitive white light absorption spectroscopy technique and have used it together with absorption spectroscopy at the SRC synchrotron to determine the density of CH4, CH3, CH2, CH, C, and C2H2 and the dissociation fraction HH2in various CVD reactors under diamond growth conditions. We have developed models to understand the gas phase reactions. We have found for different input gases with the same carbon fraction that the CH3 and CH densities are nearly the same in a microwave CVD reactor. Gas phase reactions rapidly scramble the system. We have also found that the HH2 ratio is determined by the dissociation fraction at the filament and that the C, CH, CH2, CH3 and CH4 species are in equilibrium at the HH2 ratio and the temperature. We have developed methods to measure the gas phase temperature in CVD reactors.