A particle-in-cell Monte Carlo simulation of an rf discharge in methane: frequency and pressure features of the ion energy distribution function

A one-dimensional particle-in-cell Monte Carlo (PIC-MC) model for a capacitively coupled rf discharge in methane with the kinetic approach of electron and ion behaviour is presented. To make a computation reasonably fast only two main ion species, CH4+ and CH5+, have been taken into consideration. The ion energy distribution functions (IEDF) near the substrate have been calculated for different discharge parameters. The IEDF of CH4+ differs substantially from the IEDF of CH5+ at low frequency because of the resonant charge transfer for CH4+ . The elastic scattering of ions on different neutral products originating in the plasma becomes essential for ion spectra at high frequencies. It was shown that the discharge frequency has an influence on the electron density and the electron energy as well as on the dissociation rate. The ion and radical fluxes to the substrate have been calculated for different gas pressures and discharge frequencies. The results of the present model were compared with the data calculated by means of the hybrid PIC-MC-fluid model (Ivanov et al 2002 J. Appl. Phys. 91 6296) in which for the ions the drift-diffusion approximation is being used. It is shown that the kinetic approach for the ion motion results in a decrease in the charge fluxes to the substrate. A correlation between the IEDF and the experimental deposition rate of diamond-like carbon films has been analysed