Concentration of Fluorine Atoms and Kinetics of Reactive-Ion Etching of Silicon in CF4 + O2, CHF3 + O2, and C4F8 + O2 Mixtures

Abstract

A comparative study of the electrophysical parameters of the plasma, the fluorine atom concentra-tions, and the kinetics of reactive-ion etching of silicon in CF4 + O2, CHF3 + O2, and C4F8 + O2 mixtures of a variable (0–75% O2) initial composition is carried out. It is shown that the dominant etching mecha-nism is always the ion-stimulated chemical reaction Si + xF → SiFx, whose rate has a maximum in the region of 20–50% O2. Based on the results of plasma diagnostics, it is found that the similar behavior of the concen-tration of fluorine atoms is typical only for mixtures of CF4 + O2 and CHF3 + O2, while in the C4F8 + O2 mix-ture, there is a nonmonotonic change in the probability of the interaction. It is assumed that the latter effect is caused by the competition between the processes of reducing the thickness of the fluorocarbon polymer film and the oxidation of the silicon surface by oxygen atoms.