Intrinsic strain in SiO2 thin films

The oxidation of silicon to form SiO2 is accompanied by large changes in volume. Existing models of silicon oxidation indicate that almost all of this volume change takes place normal to the oxidation front. However, available experimental results clearly indicate that there exists a small component of expansion in the plane of oxidation, leading to what may be termed as intrinsic, in-plane strain in SiO2 films on silicon substrates. We reanalyze the experimental data of Kobeda and Irene (J. Vac. Sci. Technol. B 6, 720, 1986) to estimate this quantity, arriving at a value of approximately 2×10−3. The effect of this intrinsic strain upon the oxide film stresses is then examined for planar and nonplanar oxidation. Implications of these results for standard oxidation prediction schemes are discussed.