Experimental and kinetic studies of C–H–O plasmas for polycrystalline and nano-smooth diamond deposition

CO2–CH4 and CO–H2 plasmas were studied by optical emission spectroscopy, microwave interferometry, Langmuir probing and molecular beam mass spectrometry. The variations of the plasma parameters as well as the concentration variations of both stable species and radicals were obtained as a function of the inlet composition. A modelling of the plasma kinetics taking into account the coupled hydrodynamics of the gaseous species and the gas phase chemistry including electron dissociation and surface recombination at the reactor wall was carried out. These experimental and modelling studies were used for correlating the influence of the relative concentration of important gaseous species in the plasma to the deposition domain, the structure (polycrystalline or nano-smooth) and the quality of diamond films which are deposited at moderate temperature. The influence of the concentrations of both hydrocarbon radicals and H and OH species is especially evidenced. The growth of nano-smooth diamond films relatively to polycrystalline ones is explained.