EFFECT OF ANISOTROPIC COULOMB FIELD ON SI 2P CORE LEVELS IN OXIDIZED SILICON

Variation in the level structure of Si 2p states upon oxidation has been theoretically investigated. The 2p core levels at various Si sites in the vicinity of oxidized Si(100) surfaces and SiO2/Si(100) interfaces have been calculated by a perturbation theory based on ab initio results for the atomic and electronic structures of the oxidized silicon. Contrary to the understanding prevailing in the usual analysis in x-ray photoemission spectroscopy (XPS), (1) splitting of the Si 2p orbitals due to the anisotropic Coulomb field arising from the oxidized area is comparable to the shift due to charge transfer, and (2) the Si 2p1/2 and 2p3/2 spin-orbit-split states are thereby hybridized to each other. A possibility of determination of the atomic structures by using XPS with linearly polarized light is discussed.