A global model for SF6 plasmas coupling reaction kinetics in the gas phase and on the surface of the reactor walls

Abstract

Gas phase and reactor wall-surface kinetics are coupled in a global model for SF6 plasmas. A complete set of gas phase and surface reactions is formulated. The rate coefficients of the electron impact reactions are based on pertinent cross section data from the literature, which are integrated over a Druyvesteyn electron energy distribution function. The rate coefficients of the surface reactions are adjustable parameters and are calculated by fitting the model to experimental data from an inductively coupled plasma reactor, i.e. F atom density and pressure change after the ignition of the discharge. The model predicts that SF6, F, F2 and SF4 are the dominant neutral species while and F− are the dominant ions. The fit sheds light on the interaction between the gas phase and the reactor walls. A loss mechanism for SFx radicals by deposition of a fluoro-sulfur film on the reactor walls is needed to predict the experimental data. It is found that there is a net production of SF5, F2 and SF6, and a net consumption of F, SF3 and SF4 on the reactor walls. Surface reactions as well as reactions between neutral species in the gas phase are found to be important sources and sinks of the neutral species.