Gaseous precursors of diamond-like carbon films: Chemical composition of CH4/Ar plasmas

We have implemented a gas-phase chemistry numerical simulation of a typical radio frequency, low-pressure plasma. We have applied it to the study of CH4/Ar plasmas used For the deposition of diamond and diamond-like carbon films. Our results show that CH3 is the most abundant carbon-containing radical in pure methane discharges and in CH4/Ar mixtures at low argon concentrations, indicating that the gaseous precursor of the film is CH3. On the contrary, in discharges of methane highly diluted by argon, we find evidence of a transition in the gas-phase composition. Since the most abundant carbon-containing radical becomes the carbon dimer C-2, while CH3 gets completely removed from the gas phase, we are led to the conclusion that an alternative growth mechanism should act in highly diluted CH4/Ar plasmas, where the role of the gaseous precursor of the film is played by C-2 radicals. (C) 2001 Elsevier Science Ltd. All rights reserved.