KINETICS OF CHEMICAL-REACTIONS IN HYDROCARBON-HYDROGEN PLASMAS FOR DIAMOND DEPOSITION

A previous paper has outlined the basis of a kinetic model applied to the growth of diamond layers using microwave plasmas. The present work deals with the influence on the gas phase composition of the discharge, of some externally controlled parameters such as the methane concentration in hydrogen-methane mixtures, the gas temperature, the nature of the inlet hydrocarbon gas (CH4 or C2H2), and the total flow rate. The importance of the relative concentrations of hydrocarbon neutrals and H atoms at the substrate interface has already been pointed out qualitatively; here, it is proposed that the calculated species concentrations in the discharge can be linked to the nature and deposition rates of the carbon layers. In order to do this, sticking coefficients have been assigned to different neutrals and the influence on the initial plasma composition of this "deposition loss rate" for these species has been taken into account. The relative importance of various species to diamond growth is thus deduced.