EFFICIENCY OF METHANE AND ACETYLENE IN FORMING DIAMOND BY MICROWAVE PLASMA ASSISTED CHEMICAL VAPOR-DEPOSITION

Diamond films were grown by microwave plasma assisted chemical vapor deposition using mixtures of 1% (CH4)-C-13 and 0.5% (C2H2)-C-12 in H-2, and stable gaseous products were analyzed by mass spectrometry. The major gaseous products are methane and acetylene, and scrambling of the C-13 label can be controlled at relatively high gas flow rates. At the highest flow rate studied a diamond film was grown with 77% C-13 incorporation, while the methane in the reactor exhaust gas at this flow rate contained 83% C-13. By comparing gaseous C-13 compositions with that of the films, the efficiency of diamond growth from methane (possibly via the methyl radical) is estimated to be about ten times higher than that for acetylene.