Similarities and differences between direct current and radio-frequency glow discharges: a mathematical simulation

A comprehensive three-dimensional modeling network has been developed both for argon glow discharges operating in the direct current (dc) and in the radio-frequency (rf) mode. The model network consists of various Monte Carlo, fluid and collisional-radiative models to describe the behavior of the electrons, argon atoms, argon ions, fast argon atoms, argon atoms in various excited levels, sputtered copper atoms and the corresponding ions, both in the ground state and in various excited levels. Typical results of the simulations comprise the electrical characteristics of the glow discharge, the densities, fluxes and energies of the various plasma species, information about collisions in the plasma, optical emission intensities and erosion rates due to sputtering. The results for the dc and the rf discharges have been compared. It is found that for the same input power (i.e., power effectively going into the plasma) and pressure, the rf discharge requires lower voltages than the dc discharge, in agreement with experimental data. The erosion rates and optical emission intensities are, however, rather similar in both operation modes, which is also in agreement with experiment.