Construction and analysis of C-H-N phase diagram for diamond chemical vapor deposition by simulation of gas-phase chemistry

According to roles of atomic hydrogen, methyl and acetylene in diamond film chemical vapor deposition (CVD) in C-H and C-H-O systems, two micro parameters and their criteria were established, viz., methyl mole fraction [CH3] and ratio of atomic hydrogen mole fraction to acetylene [H] / [C2H2], corresponding to the growth of diamond and etching of non-diamond carbon, respectively. By simulating gas-phase chemistry in C-H-N environment, equilibrium compositions for various nitrogenous mixtures were obtained. A C-H-N ternary phase diagram for diamond chemical vapor deposition under low pressure was constructed and influence of activation temperature on diamond domain was calculated. They were proved basically logical by over eighty experimental points in literatures, confirming the dominant roles of H, CH3 and C2H2. It is indicated that atomic hydrogen is not replaced by atomic nitrogen in preferably etching non-diamond carbon and generating surface growth sites. Further calculation and discussion reveals that nitrogen addition not only influences the concentrations of atomic hydrogen, methyl and acetylene, but also produces CN radicals, which actively participate in surface reactions, resulting in strong dependence of deposition rate and quality on nitrogen addition amount.