Study of Ellipsometric Applications and Examination of Optical Anisotropy in Aluminium and Silicon Oxides

Abstract

The ellipsometric technique was used to study optical anisotropy in aluminium and silicon oxides by rotating the samples about their normal surface. The optical anisotropy in the aluminium oxide was detected in a polycrystalline (as received) and electropolished single crystal. In silicon oxide, optical anisotropy was present only in thermally grown samples at a thickness higher than 400 nm. The anisotropy in the optical properties was attributed to the stress in the film, which arose from the differences in thermal expansion between the film and the substrate. Anisotropy was reduced by annealing the sample at a temperature lower than the oxidation temperature. A reduction in the range of 83% was obtained in aluminium oxide (as received) after it was annealed for four hours at 500°C. However, a 91% reduction was achieved in silicon oxide when it was annealed for 90 minutes at 950°C. The importance of using the correct refractive index for the film and substrate, using the same angle of incidence during the study, and the sensitivity of measuring Ψ and Δ angles was investigated in order to obtain the most accurate results. We then calculated the optimum angle of incidence for silicon nitride on silicon and aluminium.