Gas-phase parameters and densities of atomic species in Cl2 + O2 + Ar plasma: Effects of O2/Ar and Cl2/Ar mixing ratios

Abstract

In this work, we investigated the effects of Cl2/Ar (at the constant fraction of O2) and O2/Ar (at the constant fraction of Cl2) mixing ratios in Cl2 + O2 + Ar gas system on plasma parameters, gas-phase chemistry and steady-state densities of atomic species under the condition of inductively coupled RF (13.56 MHz) plasma. The combination of plasma diagnostics by Langmuir probes and optical emission spectroscopy together with 0-dimensional plasma modeling were applied to compare two different gas mixing regimes in respect to a) electrons- and ions-related plasma parameters; b) steady-state densities of plasma active species; and c) formation kinetics for Cl and O atoms. It was found that both gas mixing regimes are characterized by the domination of Cl2+ and Cl + over O2+ and O+ ions as well as by much higher densities of Cl− compared with O−. A decrease in Cl2/Ar ratio at constant fraction of O2 provides the stronger increase in the electron density (due to the deeper fall in plasma electronegativity) as well as influences both Cl and O atom densities. The latter is mostly due to the change in electron-impact kinetics while the role of stepwise processes involving ClO species is almost negligible due to their low density. Oppositely, the feature of the O2/Ar gas mixing regime is the possibility to adjust O atom density under the condition of [Cl] ≈ const. It was found that the model demonstrated the acceptable agreement with experiments in respect to both O and Cl atom densities.