Mechanisms of concurrent SiO desorption with oxide layer formation at Si(001) surface

Oxidation reactions at Si(001) surfaces have been studied via real-time in situ photoemission spectroscopy with synchrotron radiation for chemical bonding states of Si and O atoms and mass spectrometry for desorption of SiO molecules with supersonic O-2 molecular beams in a temperature region from 900 K to 1300 K. In our previous studies, the SiO desorption yield decreased with increasing incident energy in a temperature region from 900 K to 1000 K. In that case, the time evolutions of Si 2p photoemission spectra showed that SiO2 structure on the surface was easily formed by the action of larger incident energy and the increased SiO2 coverage correlated with the decreased SiO desorption yield. In this study, simultaneous measurements of Si 2p photoemission spectra and SiO desorption yield revealed that the decrease of SiO correlated with the increase of Si2+ component, and the SiO desorption was terminated at the oxide thickness of 0.22 nm. These facts suggest that the SiO desorption takes place at the topmost Si dimcrs and a precursor for SiO desorption is a so-called T site, in which O atoms are bonding with the dangling bonds of the dimers. Consequently, M1 and M2 in the Dual-Oxide-Species (DOS) model have been clarified to be a T site and a Si2+ state, respectively. (c) 2008 Wiley Periodicals, Inc.