XPS study on the early stages of oxidation of Si(100) by atomic oxygen

Abstract

Clean Si(100) surfaces were oxidized at room temperature by N 2O exposure and by the successive exposure of atomic oxygen formed via the photochemical decomposition of N 2O. X-ray photoelectron spectroscopy (XPS) was employed to study the oxidation step by atomic oxygen. The O(1s) XPS spectra consist of two bands; the higher binding energy component was ascribed to oxygen bonded to the dangling bond of the top-most Si atom and the lower binding energy component to oxygen bridging two Si atoms. The binding energy (BE) of oxygen showed an abrupt shift for very thin oxide films. This abrupt BE shift may be explained in terms of charge transfer from Si to O in the ground state rather than in the final hole state. Some evidence for layer-by-layer oxidation was obtained in the BE shift, oxide thickness, and the evolution of the suboxide species. The oxidation process by atomic oxygen was simulated, based on a random bonding layer-by-layer mechanism for the 2 × 1 reconstructed surface with Si-Si dimer bonds. Among Si(111) and Si(100), there was no essential difference in the oxidation process by atomic oxygen.