Ti ion valence variation induced by ionizing radiation at TiO2/Si interface

Titanium oxide films are prepared on silicon substrates by the DC reactive sputtering method. The TiO2/Si structures with different TiO2 film thickness are irradiated by electron beams and γ-rays. It is found after irradiation that the shift of flat-band voltage ΔVFB of MOS structures is very small. There is no evident distortion in the HF C–V curves in comparison with pre irradiation cases. By the XPS analysis, it is found that, after irradiation, the valence of the Ti ion varies; the Ti3+ ion increases and the Ti4+ ion clearly decreases at the TiO2/Si interface. The variation comes mainly from the transition layer between the titanium oxide film and silicon substrate. The mechanism has been discussed in detail.