Experimental study of the oxidation of silicon germanium alloys

Abstract

We report on the in situ oxidation of a series of Si–Ge alloy layers grown epitaxially on a (100) Si substrate. The alloy compositions of the layers varied in Ge composition from 1.8% to a high of 16.8%. Oxidations were carried out in situ in a Scientia ESCA-300 system between 400 and 800 °C. In order to explore the transition from pure SiO2 to mixed SiO2−GeO2 films, dry oxidations were carried out under partial pressures which were varied by almost nine orders of magnitude. State of the art oxidations were also carried out in a double walled oxidation furnace at one atmosphere to compare with some of the published results. In situ oxidations and analyses were done at each stage of the process from initial cleaning to monolayer absorption and oxide formation. Films grown in the thin regime up to 10 nm were analyzed by angle resolved x-ray spectroscopy. These studies were carried out to explore the influence of alloy composition on the distribution of subbonded states of Si and their influence on interfacial properties. Comparisons were made between films that were grown as pure SiO2 and those that resulted in mixed SiO2−GeO2 with regard to the areal density of these states. In spite of the strong pileup of Ge at the interface during oxide growth, there was less than expected influence of alloy composition on the interface and some evidence that interfacial annealing was taking place. It was also confirmed that mixed oxide interfaces were poorer and more highly defective than those of pure SiO2 on the same alloy.