Chemisorption of fluorocarbon free radicals on silicon and SiO2

Abstract

We have investigated the interaction of CF₃ free radicals, produced by infrared multiple‐photon dissociation of C₂F₆, with Si(100) and SiO₂ surfaces. The CF₃ radicals initially undergo dissociative chemisorption on the Si surface to produce surface carbides and fluorosilyl species. At higher coverages, the fluorine transfer reaction is inhibited. Significantly smaller amounts of the CF₃ radical chemisorb on the oxide surfaces and those that do adsorb do not dissociate. Sputtering the oxide surface by argon ion bombardment increases the amount of radicals that can be adsorbed. Ion bombardment of the fluorocarbon overlayer on both surfaces results primarily in removal of the CF₃ groups. The radical reactions cannot by themselves account for SiO₂/Si selectivity in plasma reactive etching, but do appear to play an important role in anisotropic etching.