Spectroscopic Ellipsometry of SIMOX (Separation by Implanted Oxygen): Thickness Distribution of Buried Oxide and Optical Properties of Top-Si Layer

Abstract

Spectroscopic ellipsometry has been used to characterize SIMOX (separation by implanted oxygen) wafers. High-dose SIMOX wafers with 450 nm thick buried SiO2 were measured using a four-zone null spectroscopic ellipsometer in a 230–840 nm range. The measured spectra of Ψ and Δ were analyzed based on a multilayer structure of air/surface- SiO2/top-Si/buried- SiO2/Si in which the optical constants of the top-Si layer were analyzed using the optical constants of bulk-Si and also using model dielectric functions proposed for Si. In the fitting of Ψ and Δ spectra, a thickness fluctuation of buried- SiO2 was considered with an arbitrary thickness distribution function. Measured Ψ and Δ spectra could be well fitted under the assumption of thickness distribution in the buried- SiO2. To examine the thickness dependence of the optical properties of the top-Si layer, the thickness of this layer was systematically reduced by repeating oxidation and etching with HF. It was found that the optical constants of the top-Si layer were equal to those of Si for a thickness above 5 nm.