SPECTROSCOPIC ELLIPSOMETRY OF SIMOX (SEPARATION BY IMPLANTED OXYGEN) - THICKNESS DISTRIBUTION OF BURIED OXIDE AND OPTICAL-PROPERTIES OF TOP-SI LAYER

Spectroscopic ellipsometry has been used to characterize SIMOX (separa tion by implanted oxygen) wafers. High-dose SIMOX wafers with 450 nm t hick buried SiO2 were measured using a four-zone null spectroscopic el lipsometer in a 230-840 nm range. The measured spectra of Psi and Delt a were analyzed based on a multilayer structure of air/surface-SiO2/to p-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 m odel dielectric functions proposed for Si. In the fitting of Psi and D elta spectra, a thickness fluctuation of buried-SiO2 was considered wi th an arbitrary thickness distribution function. Measured Psi and Delt a spectra could be well fitted under the assumption of thickness distr ibution in the buried-SiO2. To examine the thickness dependence of the optical properties of the top-Si layer, the thickness of this layer w as 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.