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Oxidation of Epitaxial- and Polycrystalline-SiGe Alloys

  • Hiroshi Tsutsu (a1), William J. Edwards (a1), Dieter G. Ast (a1) and Theodore I. Kamins (a2)

Abstract

Epitaxial-SiGe (epi-SiGe) and polycrystalline-SiGe (poly-SiGe) films with Ge concentrations ranging from 5 to 30% were wet-oxidized with TCA at temperatures ranging from 700 to 1,000°C. The oxidation rate of epi-SiGe decreases with increasing Ge concentration for temperatures ≥900°C, but increases for temperatures ≤800°C. The oxidation of poly-SiGe, on the other hand, is found to depend only weakly on the Ge concentration for oxidation temperatures ≥ 800°C. At 700°C, the rate increases with Ge concentration and can exceed that at 800°C. RBS spectra show that in epi samples oxidized at ≥900°C, Ge is completely rejected from the oxide and Ge rejection results in a pile-up at the oxide/epi-SiGe interface. At 800°C, Ge is partially incorporated in the oxide for high Ge containing films and rejected for lower Ge containing films. At 700°C, Ge is fully incorporated in the oxide. On the other hand, in poly samples oxidized at ≥ 800°C, Ge is completely rejected from the oxide, resulting in a pile-up at the interface and diffusion into the poly-SiGe. At 700°C, however, Ge is partially incorporated into the growing oxide when layers with high Ge concentration (≥20%) are oxidized. Most of the Ge is still rejected from the oxide and diffuses into the poly-SiGe layer. Our results on both epi and poly samples can be explained by assuming that at low temperatures the diffusion of the oxidant through the growing oxide is rate limiting whereas at high temperatures the rate is determined by the concentration of Si at the oxide/alloy interface. In the low temperature limit, the Si to Ge ratio in the oxide is identical to that of the alloy. At high temperatures, SiO2 is formed. In the intermediate regime, the composition of the oxide depends on the degree to which Ge can be rejected from the oxide. The Ge removal rate from the interface of polycrystalline films exceeds that of single crystal films because of the enhanced diffusion of Ge along grain boundaries.

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Oxidation of Epitaxial- and Polycrystalline-SiGe Alloys

  • Hiroshi Tsutsu (a1), William J. Edwards (a1), Dieter G. Ast (a1) and Theodore I. Kamins (a2)

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