Investigation of the plasma chemistry relevant for diamond deposition with chlorinated hydrocarbons

Abstract

We have investigated the plasma chemistry of process gases consisting of hydrogen with a small admixture of chlorinated methanes in a pulsed r.f. discharge. The temporal development of certain species in the plasma was explored by experiment and simulation. Experiment and simulation are in good agreement and show a very fast decomposition of the chlorinated methanes to the main stable species hydrogen chloride, methane, and acetylene. Chlorinated methyl radicals, which are possible diamond growth species, are created during the decomposition process. However, they decompose so quickly that they occur only within a few ms after the first contact of the feed stock gas with the plasma. The simulation showed that atomic chlorine is, besides atomic hydrogen and the methyl radical, the third most important radical in the gas phase. Chlorine in the gas phase increases the methyl radical concentration at lower temperatures. As atomic chlorine generates active surface sites more efficiently than atomic hydrogen and higher methyl radical concentrations are present at lower temperatures, higher growth rates are possible with chlorinated process gas mixtures.