Depth Profiling of Si Oxidation States in Si-Implanted SiO2Films by X-Ray Photoelectron Spectroscopy

Thin SiO2 films containing Si nanocrystals (nc-Si) prepared by low-energy Si ion implantation and high-temperature annealing, which are used in the application of single-electron memory devices, are studied by X-ray photoelectron spectroscopy (XPS). XPS analysis shows the existence of five Si oxidation states Sin+ (n =0, 1, 2, 3, and 4) in the SiO2 films, indicating that not all of the implanted Si atoms are converted to nanocrystals during annealing and some of them form Si suboxides corresponding to the three oxidation states Sin+ (n =1, 2 and 3). The relative concentration of each oxidation state at various depths is determined quantitatively by XPS analysis. In addition, the effects of annealing on both the oxidation states and their depth distributions are also studied.