Properties of c-C4F8 inductively coupled plasmas. II. Plasma chemistry and reaction mechanism for modeling of Ar/c-C4F8/O2 discharges

Abstract

Gas mixtures containing Ar, c-C4F8, O2, and CO are often used for the plasma etching of silicon dioxide. Gas phase reaction mechanisms are required for first principles modeling of these systems to both provide insights to the plasma chemistry and to help optimize the process. In this article, results from computational and experimental investigations of the plasma chemistry of inductively coupled plasmas (ICPs) sustained in Ar, O2, Ar/c-C4F8 and O2/c-C4F8 gas mixtures with and without magnetic confinement are discussed. These results were used to develop a reaction mechanism for low-pressure and low-temperature plasmas sustained in mixtures initially consisting of any combination of Ar/c-C4F8/O2/CO. Predictions for ion saturation current and ion mass fractions were compared to experiments for validation. The consequences of charge exchange of fluorocarbon species with Ar+ and CO+ on the ratio of light to heavy fluorocarbon ion densities in Ar/c-C4F8/O2/CO plasmas are discussed. We found that the electron density and ion saturation current significantly increase with the addition of Ar to c-C4F8 but weakly depend on the addition of O2. The ratio of light to heavy fluorocarbon ion densities increases with power, especially for ICPs with magnetic confinement.