Global model of Ar, O2, Cl2, and Ar/O2 high-density plasma discharges

Abstract

We develop a global (volume averaged) model of high-density plasma discharges in molecular gases. For a specified discharge length and diameter, absorbed power, pressure, and feed gas composition, as well as the appropriate reaction rate coefficients and surface recombination constants, we solve the energy and particle balance equations to determine all species densities and the electron temperature. We use an expression for charged particle diffusive loss that is valid for low and high pressures and for electropositive and electronegative plasmas. We apply the model to Ar, O2, Cl2, and Ar/O2 discharges and compare with available experimental data. In Ar, we find that the ion density increases monotonically with increasing pressure, while for O2 and Cl2, the total positive ion density increases initially, then decreases as pressure is further increased. For a pure Cl2 discharge, we find that surface recombination processes are important in affecting the degree of dissociation and the negative-ion density of the system. For mixtures of Ar and O2, we find that at a fixed ratio of Ar to O2 flowrates, the dominant ionic species changes from Ar+ to O+ as pressure is increased. When a small amount of Ar is added to a pure O2 discharge, the overall positive-ion density increases, whereas the ratio of negative ion to electron density decreases.