Discharge kinetics of inductively coupled oxygen plasmas: experiment and model

Abstract

In this paper, neutral and charged particle dynamics in both the capacitive and inductive modes of an inductively coupled oxygen discharge are presented. Langmuir probes, laser-assisted photodetachment and two-photon laser-induced fluorescence are employed to measure plasma parameters in the 13.56 MHz system for a range of plasma powers and gas pressures. It is found that the capacitive mode is more electronegative with lower molecular dissociation compared with the inductive mode. However, the negative ion density in each mode is comparable. A maximum is observed in the negative ion density and fraction with pressure for both modes. The experimental measurements are supplemented by a global model, which includes capacitive and inductive coupling effects. The model and experiments demonstrate that negative ion loss is dominated by ion–ion recombination and electron detachment at low pressures (<10 mTorr), while it is dominated by detachment processes with the metastable molecule O2(a 1Δg) and oxygen atoms at higher pressures. These findings support recent global model predictions of oxygen discharges.