A COMPARISON OF THE BEHAVIOR OF SI0.5GE0.5 ALLOY DURING DRY AND WET OXIDATION

We have studied the oxidation behaviour of 350 nm thick films of Si0.5Ge0.5 alloy grown on Si(100) substrates by molecular beam epitaxy. The oxidation was performed at 1000-degrees-C in both dry and wet oxygen environments. As a reference, bulk silicon oxidation was also studied. Oxidation rates and atomic redistribution were measured using Rutherford backscattering. The formation of SiO2 bonding was indicated by IR transmission spectroscopy, and X-ray photoelectron spectroscopy was used to determine the silicon and germanium electronic states in the oxide layer. Two stages of oxide growth can be identified in our experiment. During the initial stage the dry oxidation rates for alloy and bulk silicon are the same whilst the wet oxidation rate for the alloy is about three times faster than that for the bulk. Germanium trapped in the near-surface region and accumulated at the oxide-alloy interface during wet and dry oxidation was observed at this stage. Longer oxidation times are characterized by similar growth rates for both alloy and bulk silicon during wet oxidation, but during dry oxidation a significantly lower rate for the alloy compared with bulk silicon. The accumulated germanium diffused away from the interface of the oxide layer in the case of dry oxidation and the alloy layer transformed to a germanium-rich layer during wet oxidation. The above results demonstrate that the presence of germanium increases the rate during wet oxidation, but decreases the rate during dry oxidation. We explain these phenomena in terms of the mass transport, of either silicon or oxygen atoms, to the oxide front.