Specific features of intensification of silicon etching in CF4/O2 plasma

Abstract

On the basis of numerical modeling, the effect of oxygen concentration on the etching rate of silicon in a CF4/O2 plasma is investigated. The calculations are carried out with the use of an improved model of a nonisothermal reactor with multicomponent kinetics incorporating F, F2, CF2, CF3, CF4, C2F6, O, O2, CO, CO2, COF, and COF2; altogether, there are twelve reagents. The competition of processes of interaction of fluorine with silicon and oxygen chemisorption on the wafer surface is considered the central mechanism responsible for reducing the etching rate. An improved model for describing the competing processes of etching, chemisorption of O and CF2, and adsorption of CF2 and CF3 radicals on silicon is proposed. The effect of model parameters on the etching rate is investigated. The chemisorption of O on silicon dominates over the adsorption processes of the CF2 and CF3 radicals. It is shown that the ratio of sticking coefficients of the fluorine and oxygen atoms substantially affects the location of the maxima of the spontaneous etching rate and concentration of active particles depending on the oxygen concentration in the mixture. If these coefficients are equal, the peak value of the spontaneous etching rate is attained at an oxygen concentration 10–15% lower than the concentration of active fluorine in the reactor volume.