A spectroscopic immersion ellipsometry study of SiO 2-Si interface roughness for electron cyclotron resonance plasma and thermally oxidized Si surfaces

Abstract

By immersing a film-covered substrate in a liquid whose refractive index matches that of the film, the sensitivity of ellipsometry to the film/substrate interface can be greatly enhanced. This spectroscopic immersion ellipsometry (SIE) technique was employed for the study of SiO 2-Si interface roughness for electron cyclotron resonance (ECR) plasma and thermally oxidized Si surfaces. The SIE results show that for an initially rough Si surface, oxidation reduces the interface roughness, while for an initially smooth Si surface, the interface roughens as the oxidation proceeds. These results were confirmed by atomic force microscopy measurements with fractal analysis. The results indicate that there are two competing mechanisms for the interface roughness evolution during oxidation. The smoothing is believed driven by the reduction of free energy dictated by the Kelvin equation, and enhanced by the external electric field during ECR oxidation. The roughening is possibly due to a chemical-reaction-enhanced roughening transition. The results also show that SIE emerges as a powerful technique to study interfaces non-destructively.