Parameters of Plasma and Way of Etching Silicon in a CF4 + CHF3 + O2 Mixture

Abstract

The effect of the CF₄/CHF₃ ratio in a CF₄ + CHF₃ + 9% O₂ mixture on the parameters of the gaseous phase and kinetics of etching of silicon under the conditions of low-pressure inductively coupled plasma is investigated. It was found that substitution of CF₄ by CHF₃ at constant external parameters of the plasma (1) leads to a change of the temperature (average energy) and density of the electrons; (2) causes a decrease of the fluorine atom density followed by the majority of the molecules of HF; and (3) stimulates an increase of the rate of deposition and thickness of the fluorocarbon polymer film. By the analysis of the way of etching of silicon with the use of the calculated data on the fluxes of active particles, it was found that the observed change of the etching rate can be explained by heterogeneous reactions with the involvement of O, H, and HF. It was assumed that the process of etching silicon proceeds in the mode of limitation by the flux of chemically active particles F + HF and is characterized by the effective probability depending on the thickness of the fluorocarbon polymer film.