WET OXIDATION OF AMORPHOUS SI0.67GE0.25C0.08 GROWN ON (100)SI SUBSTRATES

Wet oxidation annealing of thin films of amorphous Si0.67Ge0.25C0.08 w as performed over the temperature range from 700 to 950 degrees C. Cha nges in composition and microstructure were assessed using Rutherford backscattering spectrometry and transmission electron microscopy. A ne arly pure layer of SiO2 with approximately 1 at. % carbon was formed, with Ge being rejected from the oxide at all temperatures. At low temp eratures, the oxide formed was very thin. Ge piled up at the oxide/fil m interface and the thin film microstructure remained amorphous. At hi gher temperatures, a network of nanocrystals was observed which was be lieved to provide a grain boundary diffusion path for Ge which had red istributed throughout the remaining layer. It is proposed that the Ge layer had inhibited oxidation at the lower temperatures, whereas its r emoval resulted in increased oxidation rates at higher temperatures. A nnealing at 950 degrees C for 5 and 6 h resulted in an epitaxial trans formation and a single crystal structure. This process occurred as a r esult of the silicon being removed from the substrate by the oxide fro nt which served as a sink. Germanium then diffused into the vacancies in the substrate forming a new epitaxial layer. (C) 1998 American Inst itute of Physics.