Modeling of the gas-phase chemistry in C-H-O gas mixtures for diamond chemical vapor deposition

The boundaries of the diamond deposition region in the C-H-O (Bachmann) ato mic phase composition diagram have been reproduced successfully for 38 diff erent C, H, and O containing gas mixtures using the CHEMKIN computer packag e, together with just two criteria-a minimum mole fraction of methyl radica ls [CH3] and a limiting value of the [H]/[C2H2] ratio. The diamond growth/n o-growth boundary coincides with the line along which the input mole fracti ons of C and O are equal. For every gas mixture studied, no-growth regions are found to coincide with a negligible (< 10(-10)) mole fraction of CH3 ra dicals, while for gas mixtures lying within the diamond growth region the C H3 mole fraction is similar to 10(-7). Each no-growth --> diamond growth bo undary is seen to be accompanied by a 2-3 order of magnitude step in CH3 mo le fraction. The boundary between diamond and nondiamond growth is less cle arly defined, but can be reproduced by assuming a critical, temperature dep endent [H]/[C2H2] ratio (0.2, in the case that T-gas=2000 K) that reflects the crucial role of H atoms in the etching of nondiamond phases. The analys is allows prediction of the composition process window for good quality dia mond growth for all stable input gas mixtures considered in this study. (C) 2001 American Institute of Physics.