Stress Distribution in Ultra Thin SiO₂ Film/Si Substrate System Measured by a Low Level Birefringence Detection Technique

Abstract

In this work, a low level birefringence detection system was employed to study the stress distribution in Si substrate induced by thermally grown ultra-thin SiO₂ film. According to traditional bi-metallic strip theory, it is expected that the stress should show a linear dependence on depth with the zero stress plane located at the position of two third of the thickness of the substrate from the SiO₂/Si interface. The linear dependence of stress on depth in accordance with the bi-metallic strip theory was observed only in part of the substrate. For the region below the SiO₂/Si interface extending to a depth of about 1/5 of the thickness of the substrate, the magnitude of the stress was found to be significantly smaller than expected. The position of the zero stress plane was found to depend on the thickness of the SiO₂ film and the oxidation conditions. The zero stress plane seemed to move towards the bottom of the Si substrate as the thickness of the SiO₂ film became thinner and no zero stress plane was observed in the Si substrate when the SiO₂ films became sufficiently thin.