Photoemission studies of Si(100) oxidation process (abstract)

Abstract

Photoemission spectroscopy using synchrotron radiation is a powerful tool to investigate electronic states of solid surfaces. In the present study, the oxidation process of the Si(100) surface has been extensively examined. Experiments were carried out with soft x-rays monochromatized by the grazing incidence monochromator,1 at beamline 8A at the Photon Factory. The energy resolution, including both the electron energy analyzer (a double-pass type CMA) and the monochromator, was estimated from the Au Fermi edge. The Au foil was sputter cleaned by Ar ions. For the photon energy between 40 and 200 eV, the resolution is about 0.3 eV with electron pass energy of 10 eV and monochromator exit slit width of 10 μm. The oxidation process of a Si(100) surface has been examined in situ at the base pressure of 5×10−8 Pa. The Si(100) clean surface is obtained by repeating Ar ion sputtering and annealing. We have measured the Si 2p photoelectron spectra of the Si(100) surface exposed to oxygen. At the early stage of 20–1000 ℓ oxygen exposure at room temperature, outermost Si atoms are partially oxidized and an energy shift of 1–2 eV is observed. The oxidation proceeds much faster when the surface is heated at 300–400 °C during oxygen exposure. In this case, three intermediary components (SiOx x<2) and SiO2 are detected. By further oxidation (104 ℓ oxygen exposure) at 700 °C, a thin SiO2 layer is formed. In addition, valence band and Si L2,3 XANES spectra have been taken for the surface. The results support the oxidation process clarified by the present method.