FEATURES OF PLASMA COMPOSITION AND FLUORINE ATOM KINETICS IN CHF3 + O2 GAS MIXTURE

Abstract

The effects of initial composition of CHF3 + O2 gas mixture on electro-physical plasma parameters, steady-state densities of active species and fluorine atom kinetics were investigated under the condition of constant gas pressure and input power. The combination of plasma diagnostics by Langmuir probes and model-based analysis of plasma chemistry confirmed known from previous work features of plasma composition in the absence of oxygen (in particular, the domination of HF molecules in a gas phase) as well as demonstrated how the oxygen influences steady-state densities of neutral species through kinetics of both electron-impact and atom-molecular reactions. It was shown that the addition of O2 with a proportional decrease in the content of CHF3 a) results in noticeable changes in electrons- and ions-related plasma parameters (electron temperature, electron density, ion flux); b) provides the effective conversion of fluorocarbon radicals (CHFx, CFx) into such compounds as CFxO, FO and COx; and b) causes an increase in the fluorine atom density up to 50% O2. The last phenomenon contradicts with the change in the total F atom formation rate, but reflects a decrease of their loss frequency in the reaction family of CHFx + F → CFx + HF. The model-based analysis of heterogeneous process kinetics was carried out using the set of tracing parameters based on gas-phase plasma characteristics. It was found that the addition of oxygen lowers the plasma polymerizing ability through both decreasing flux of polymerizing species and accelerating the oxidative destruction of deposited polymer film.