Diamond growth with locally supplied methane and acetylene

Experiments have been conducted to examine the relative importance of different gas feed geometries and molecular species in the hot filament assisted vapor phase deposition of diamond. Remote and local (relative to the substrate) gas feeds of methane and acetylene were tested and it was found that although dramatic effects on uniformity and rate of deposition can be observed using a gas feed of methane local to the substrate surface, little or no variation in growth rate or deposition uniformity was produced by feeding acetylene locally. The growth rate observed on a defined area of the substrate using a local gas feed of methane was 0.50 mgms/h versus 0.17 mgms/h for a local feed of acetylene. These results, as well as the patterns of deposition observed, suggest that the major species contributing to growth in the hot filament assisted CVD of diamond is the methyl radical. This species is readily formed in the gas phase from methane and atomic hydrogen by hydrogen abstraction. It is, however, further suggested that numerous different hydrocarbon species may be of importance, with the nature of the species contributing most to the growth dependent on the method used.