Plasma Parameters and Etching Kinetics of Si/SiO₂ in Mixtures of Fluorocarbon Gases with Argon and Helium

A comparative study is carried out of the electrophysical parameters of plasma, concentrations of fluorine atoms, and kinetics of reactive ion etching of Si and SiO₂ in CF₄ + Ar/He, CHF₃ + Ar/He, and C₄F₈ + Ar/He mixtures of variable (0–45% He) initial composition. It is established that the substitution of Ar by He at a constant content of the fluorocarbon component (a) disturbs the characteristics of the electron component of the plasma; (b) it has practically no effect on the intensity of ion bombardment of the treated surface; and (c) it leads to a decrease in the etching rates of Si and SiO₂ against the background of a similar change in the concentration of fluorine atoms. It is shown that the dominant etching mechanism is always a heterogeneous chemical reaction, whose effective probability increases (in CF₄ plasma) or remains unchanged (in CHF₃ and C₄F₈ plasma) with an increase in the proportion of helium in the plasma-forming gas. Assumptions are made about the mechanisms of the processes that cause these effects.