COMPUTER-SIMULATION OF A CARBON-DEPOSITION PLASMA IN CH4

A transport and reaction model of a low-pressure, high-frequency (13.56 MHz) CH4 plasma used for diamondlike carbon (a-C : H) deposition was developed. The model includes reactions among four molecular species (CH4, C2H6, C2H4, and H2), five radicals and atom (CH3, CH2, CH, C2H5, and H), and four ions (CH4+, CH3+, CH5+, and C2H5+). It also accounts for the influence of the sticking coefficient of species at the walls. Calculated values of the dissociation degree for several flow rates are in good agreement with experimental measurements made by quadrupole mass spectroscopy. A simple surface-model based on the hydrogen coverage of surface and ion flux and energy at the substrate surface was established. This model permitted the calculation of the deposition rate on the powered electrode as a function of the power applied to this electrode. Good agreement between experimental and calculated growth rates was obtained when CH3, C2H5, and CH2 were assumed to participate in film formation, and when hydrogen removal by ion bombardment with variable energy as a function of the power was included in the model.