We have studied the kinetics and mechanism of oxidation of SiGe alloys deposited epitaxially onto Si substrates by low-temperature chemical vapor deposition. Ge is shown to enhance oxidation rates by a factor of about 3 in the linear regime, and to be completely rejected from the oxide so that it piles up at the SiO2/SiGe interface. We demonstrate that Ge plays a purely catalytic role, i.e., it enhances the reaction rate while remaining unchanged itself. Electrical properties of the oxides formed under these conditions are presented, as well as microstructures of the oxide/substrate, Ge-enriched/SiGe substrate, and SiGe/Si substrate interfaces, and x-ray photoemission studies of the early stages of oxidation. Possible mechanisms are discussed and compared with oxidation of pure silicon.
The high-temperature decomposition of thin ( ~ 100 A) Si02 layers on Si(001) under ultrahighvacuum annealing conditions has been studied by means of ion scattering and microscopy techniques. Si02 is removed from the Si surface by the formation and lateral growth of holes in the oxide, exposing regions of atomically clean Si, while the surrounding oxide retains its initial thickness. Surface diffusion of Si inside the holes supplies Si for reaction with Si02 at the periphery, so that a volatile product (presumably SiO) can be formed.
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