<title>Spectroscopic ellipsometry investigation of influence of high-pressure high-temperature process on optical properties of SiO<formula><inf><roman>2</roman></inf></formula>-Si structures</title>

Abstract

In this paper, spectroscopic ellipsometry (SE) has been used to investigate SiO2-Si structures, which were subjected to annealing under a high hydrostatic pressure at high temperature (HPHT) processes. Temperature and pressure varied from 450 degrees Celsius to 1280 degrees Celsius and from 105 Pa to 1.2 GPa, respectively. Investigations have been carried out by variable angle spectroscopic ellipsometer VASE of J.A. Woollam Co Inc. Using the standard optical model of the SiO2-Si structure, no satisfying fit of measured and calculated (Psi) and (Delta) ellipsometric parameters characteristics can be obtained. This inconsistency, expressed by the MSE parameter (Mean Squared Error), is proportional to temperature, pressure and time of the HPHT process. Elongated convexities on SiO2 surface have been observed by scanning electron microscope (SEM). It was found that depolarization effect takes place as a result of non-uniformity of either chemical composition or SiO2 film thickness. A model consisting of upper SiO2 surface roughness, SiO2 layer and SiO2-Si interface has been used for data analysis. Application of this model allowed determination of changes in thickness and refractive index of SiO2 as a result of the HPHT process. An increase of refractive index and decrease of layer thickness can be ascribed to excessive stress in SiO2 layer. This stress has been probably caused by densification of silicon dioxide.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.