Abnormal oxidation characteristics of SiGe∕Si-on-insulator structures depending on piled-up Ge fraction at SiO2∕SiGe interface

Abstract

Oxidation characteristics of SiGe (Ge fraction of 0%–50%) layers grown on Si-on-insulator structures were investigated in a wide temperature range, for which different oxidation features were observed in low (<680°C), middle (700–800°C), and high (>800°C) temperature regions. In the low temperature region, enhanced oxidation dependent on the initial Ge fraction of the SiGe layers was observed. This is because the Ge fractions at the SiO2∕SiGe interfaces did not change from the initial Ge fractions in this region. In the high temperature region, the oxidation rates did not depend on the Ge fraction. This is because thick SiO2 (>200nm) formed in this region and, thus, oxidation rates were limited by the diffusion process of O atoms through the SiO2 layer. In the middle temperature region, an abnormal phenomenon was found; i.e., the oxidation rates did not depend on temperature for samples with high initial Ge fractions (>20%). Quantitative relations between the oxidation rate and fraction of Ge atoms piled up at the SiO2∕SiGe interfaces were obtained. Based on these findings, a model for temperature independent oxidation was proposed and it explains the contradicting oxidation rates, i.e. Ge enhanced oxidation and Ge retarded oxidation, in the literature.