In this paper the effect of the iron ion implantation on the oxide surface and SiO2-Si interface of MOS structure was studied by X-ray photo-electron spectroscopy （XPS）

and the chemical states of compounds formed were examined. The results obtained show that in the surface layers of SiO2 the pure Si micro-regions are formed under the implantation and the interface thickness is almost doubled that leads to failure of MOS capacitors. The physical and chemical mechanisms of MOS structure change by Fe+ ion implantation are also discussed and analyzed.