Operando study of the preferential growth of SiO2 during the dry thermal oxidation of Si0.60Ge0.40(001) by ambient pressure x-ray photoelectron spectroscopy

Abstract

Controlling the grown oxide composition, the oxide/semiconductor interface properties, and the semiconductor surface composition is of interest for SiGe devices. We have used ambient-pressure x-ray photoelectron spectroscopy (AP-XPS) to study the initial stages of dry thermal oxidation of an epitaxial Si0.60Ge0.40(001) film on Si(001). Si 2p and Ge 3d chemical-state resolved AP-XPS was performed at 300 °C and O2 pressures (PO2) of 10−4, 10−2, and 1 mbar during oxide growth. The National Institute of Standards simulated electron spectra for surface analysis (SESSA) was used to analyze both the oxide composition and the thickness versus time for each pressure. At all three PO2, the SESSA analysis indicated that oxidation proceeds via three oxide growth rate regimes: an initial rapid regime, an intermediate transitionary regime, and finally a quasisaturation slow regime. The Si and Ge oxidation rates were found to be pressure dependent during the rapid regime with both rates decreasing monotonically with decreasing pressure. Results indicated that Ge was much more sensitive to changes in PO2 compared to Si. As a result, a decrease in PO2 resulted in significant suppression of GeO2 formation compared to SiO2. Using SESSA, we were able to quantify the grown oxide composition and the thickness, both of which were strongly dependent on O2 pressure. The Ge composition, in Si1−xGexO2, was found to decrease monotonically with decreasing PO2.