Characterization of neutral, positive, and negative species in a chlorine high-density surface-wave plasma

Abstract

This article reports an experimental study of the influence of the plasma parameters on the concentration of neutral and ion species in a chlorine high-density plasma sustained by surface waves. The investigation focuses on the dependence of the concentrations of Cl, Cl2, Cl+, Cl2+, Cl−, and electrons on the gas pressure in the 0.1 to 10 mTorr range, and on the intensity of a confinement magnetic field. The results show that a high dissociation degree (up to 90%) can be achieved even with a very modest power level (250 W, power density of about 2 mW/cm3), provided the pressure is low enough (i.e., less than 1 mTorr). It was also found that Cl+ is the main positive ion and that electrons are the main negative charge carrier at lower pressure. When the gas pressure is higher than a few mTorr, Cl2+ becomes dominant with Cl− as the negative charge carrier. The behavior of the positive ion and neutral species concentrations is compared to the results of a simple model based on creation–losses rate equations for the various species. It is shown that for a given magnetic field intensity, there is a critical pressure above which diffusion can be neglected in comparison with ion–ion recombination and charge transfer.