GAS-PHASE PROCESSES IN DIAMOND SYNTHESIS BY HOT-FILAMENT CVD

Diamond films were synthesized by the hot-filament CVD method and the relation between the composition of the outlet gas and the crystallinity of the deposit were investigated. CH4 and C2H2 were used as the carbon source. It was found for the first time that at a constant feed C/H ratio a C2H2-rich ambience was favorable for the growth of diamond with high crystallinity. The results of gas analysis indicated that chemical equilibrium was achieved near the filament (∼2000K) and that both forward and backward reactions of CH4⇄C2H2 were important. Furthermore, the evolution of gas-phase species was calculated on the basis of a reaction model to show that the composition of radicals changed as fast as H radicals diffused from the filament. Factors determining the crystallinity of deposited diamond are discussed, based on the present results. © 1990, The Society of Chemical Engineers, Japan. All rights reserved.