Chemisorption of fluorocarbon free radicals on silicon and SiO2

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.