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.

The gas-phase kinetics and plasma chemistry of high density oxygen discharges are studied. A self-consistent spatially averaged model is developed to determine positive ion, negative ion, and electron densities, ground state and metastable free radical densities, and electron temperature as functions of gas pressure, microwave input power, and cylindrical source diameter and length. For an electron cyclotron resonance discharge, the reduction in radial transport due to the confining magnetic field is also modeled. The kinetic scheme includes excitation, dissociation, and ionization of neutrals due to electron impact, electron attachment and detachment, and ion-ion neutralization. In addition, ion neutralization at the reactor walls is included. Model results show that for a low neutral pressure, high plasma density discharge, oxygen molecules are almost completely dissociated to form oxygen atoms, and the dominant positive ion is O § rather than Q. The metastable species are not important for the pressure range studied (0.5 to 100 mTorr), and the confining magnetic field significantly affects the plasma chemistry, the total positive ion density, and the electron temperature. Comparisons are made with experimental data, and qualitative agreement between experiment and model is observed.