Spectroscopic Ellipsometric Analysis of Surface and Subsurface Damage in Chemical-Mechanical Polished Semiconductors

Abstract

ABSTRACTSpectroscopic ellipsometry (SE), with the added capability of variable angle of incidence, is a sensitive technique for nondestructive surface and interface analysis. In this work, we demonstrate the application of this technique to the quantitative characterization of surface and subsurface damage in Si and GaAs, induced by conventional chemical-mechanical polishing. We show that the optimum selection of angle of incidence and spectral range is of crucial importance for detecting and evaluating surface and subsurface quality. To adequately describe the measured SE data, a two-layer model (i.e. oxide overlayer/subsurface damage layer/substrate) was found to be necessary. In this model, the oxide overlayer and subsurface damage layer were each modeled as a simple physical mixture of the chosen constituents, using the Bruggeman effective medium approximation. SE analysis clearly indicated the presence of surface microscopic roughness and subsurface damage for all the samples investigated. Typical results for thickness were 2 to 3 nm of surface overlayer, and 15 to 40 nm of damage beneath it, containing about 1 ∼ 2% volume fraction of either oxide or voids. As verification, atomic force microscopy (for surface characterization) and wet chemical oxide stripping (for subsurface analysis) were used to substantiate the SE results.