Si-2p and O-1s photoemission spectroscopy during initial oxidation of Si[001] induced by supersonic O/sub 2/ molecular beams at 860 K to 1300 K

The control of Si oxidation with the atomic scale is necessary for nano-scale fabrication of ultra-thin gate-oxide layers in Si-based electronic devices such as MOSFETs. Dissociative chemisorption Of O/sub 2/ molecules takes place on the Si[001] surface even at room temperature (passive oxidation) and thermal desorption of SiO molecules occurs at surface temperature (T/sub s/) higher than 1000 K (active oxidation). The translational kinetic energy (E/sub t/) of incident O/sub 2/ molecules affects the passive and active oxidation reactions. The determination of E/sub t/ roles is an area of current interest from an application viewpoint as well as pure surface reaction dynamics studies. Current data concerning E/sub t/-dependent oxidation, however, is not sufficient to obtain complete understanding of E/sub t/ roles. Therefore, we have performed Si/sup 18/O (m/z:46) desorption yield measurements using supersonic seed molecular beams (SSMEBs) of the isotope /sup 18/O/sub 2/. We found out a singular phenomenon, that is, the increase of Si/sup 18/O desorption yield with decreasing the E/sub t/ at T/sub s/ lower than 1000 K. In order to analyze the surface, we have performed real-time in-situ photoemission spectroscopy (PES) of Si-2p and O-1s core levels to obtain uptake curves of oxygen and information about time evolution of Si sub-oxides. The O-1s uptake curves and Si-2p PES spectra revealed the coexistence of the passive and active oxidation reactions. In this report, the E/sub t/ effects for the Si[001] initial oxidation in the high T/sub s/ region in conjunction with the coexistence issue of the passive and active oxidation reactions is discussed on the basis of time evolution of Si-2p and O-1s photoemission spectra as well as the mass spectrometry of desorbed SiO molecules.