Rate-limiting step, as well as self-limited oxidation of SiGe alloys is so far under controversy. Contrasting to the monoparabolic growth mode for oxidation of Si, a parabolic growth mode and self-limited oxidation of SiGe alloys at different temperature are clearly observed depending on the oxidation time. With modified Deal-Grove model, we extract the parabolic rate constants related to the oxygen diffusion at different temperature and the activation energy of oxygen diffusivity finding that oxygen diffusion is still the rate-limiting step. We attribute this oxidation behavior to the strain effects associated with the volume change in converting Si/SiGe to SiO(2)/mixed oxide at different oxidation stages. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3191382

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The oxidation behavior of a strained SiGe epitaxial layer on silicon substrate in both dry and wet ambient was investigated. We found that the oxide thickness at which oxidation saturation occurs increases with oxidation temperature and is larger for wet oxidation than dry oxidation at the same temperature, although Ge concentration at the oxidizing interface is much higher for wet oxidation. This observation shows that the oxidation saturation is not due to the thin, higher Ge-concentration layer at the oxidizing interface or the remaining strain of SiGe layer as reported previously. Different from the monotonous increase with oxidation time for the SiGe layer oxidized in dry oxygen, the degree of strain relaxation in the SiGe layer increases up to about 90% in a short time and then decreases slowly during wet oxidation at 1000°C. These results suggest that the expansion in volume due to the transformation of SiGe to oxide greatly contributes to the anomalous strain relaxation process for fast oxidation in wet ambient. In addition, higher density of threading dislocations was observed in the samples oxidized in wet ambient.

SiGe/silicon-on-insulator (SOI) prepared by epitaxial growth of SiGe layer on separation by implanted oxygen SOI wafer is used to fabricate the SiGe-on-insulator (SGOI) by the multistep Ge condensation technique. The SGOI with various Ge content is systematically studied by employing Auger electron spectroscopy, X-ray diffraction, Raman spectroscopy, and atomic force microscopy. During the condensation processes, the degree of strain relaxation increases at the very beginning through the generation of misfit dislocations at elevated temperature. And then, the degree of strain relaxation starts to decrease with the reduction of SiGe thickness on the insulator although Ge content continues to increase. At this stage, the increase of density of misfit dislocations cannot effectively relieve the strain and the strain relaxation is dominated by the reduced thickness. When the Ge content in the SGOI is up to 0.58, the surface roughening starts to play a role in relieving the strain accumulated in the thinner SiGe layer with higher Ge content.

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