Gas-phase chemistry in chlorine-containing nonequilibrium plasmas relevantfor diamond synthesis

We have investigated the plasma chemistry of process gases consisting of hy drogen with a small admixture of chlorinated hydrocarbons by kinetic modeli ng. The simulations show a very fast decomposition of the chlorinated hydro carbons to the main stable species, namely, hydrogen chloride, methane, and acetylene. Chlorinated methyl radicals, which are possible diamond growth species, are created during the decomposition process. However, they decomp ose so quickly that they occur only within less than five milliseconds afte r the initial contact of the feed stock gas with the plasma. The simulation has shown that atomic chlorine is, besides atomic hydrogen and the methyl radical, the third most important radical in the gas phase at the steady st ate. Atomic chlorine acts in a manner very similar to atomic hydrogen in th e gas phase and it is responsible for a change of the species distribution within the C, and C, hydrocarbons. Most pronounced is the increase in the m ethyl radical concentration at lower gas temperatures. As the most abundant radicals in the gas phase are also those that dominate the interaction wit h the surface of the growing diamond film, growth rate as well as diamond q uality is determined by the atomic hydrogen, methyl radical and atomic chlo rine concentration.