On the relationships between plasma chemistry, etching kinetics and etching residues in CF4+C4F8+Ar and CF4+CH2F2+Ar plasmas with various CF4/C4F8 and CF4/CH2F2 mixing ratios

Abstract

In this work, we investigated how the CF4/C4F8 and CF4/CH2F2 mixing ratios in CF4+C4F8+Ar and CF4+CH2F2+Ar inductively coupled plasmas influence plasma parameters, densities and fluxes of plasma active species and etching characteristics (process kinetics, etching rates and selectivities, etching residues) for both Si and SiO2. For this purpose, we employed surface diagnostics by x-ray photoelectron spectroscopy (XPS), plasma diagnostics by Langmuir probes and 0-dimensional plasma model. It was found that the substitution of CF4 for CH2F2 causes the stronger decreases in both F atom flux and ion energy flux compared with the effect of C4F8. Accordingly, the CF4+CH2F2+Ar mixture provides the deeper fall of both Si and SiO2 etching rates, leaves the higher amount of the fluorocarbon polymer on the etched surface (especially in the case of Si) and results in a bit higher SiO2/Si etching selectivity. It was shown also that, in both gas systems, the etching process appears in the steady-state regime. The mechanisms influencing the etching/polymerization balance were discussed based on the correlation between Si and SiO2 etching rates with fluxes of plasma active species.