XPS study of TiOx thin films prepared by d.c. magnetron sputtering in Ar-O2 gas mixtures

Abstract

Titanium oxide films have been deposited, at a pressure of 5 mTorr and a discharge current of 500 mA, on borosilicate glass substrates. We have studied in situ by XPS the dependence of film composition on oxygen partial pressure. All the experiments have been performed under high vacuum; there is no air contamination of film surfaces before XPS analysis. The ions produced in the plasma have been analyzed by glow discharge mass spectrometry (GDMS). The stoichiometry of the films is compared to the plasma composition. The XPS results show that for an increasing oxygen partial pressure four regimes are observed. At very low oxygen concentration (<2%), the film is mainly metallic (zone I). For an oxygen concentration between 2% and 6%, a mixture of Ti, TiO, Ti2O3 and TiO2 is observed (zone II). In this zone the concentration of Ti decreases but the concentration of the three titanium oxides grows. In zone III (6% 15% (zone IV) a pure TiO2 film is obtained. When zone IV starts, the Ti+ mass spectrometric signal is still higher than the TiO+ signal, showing that a pure TiO2 phase is occurring at the substrate while the sputtering mode is still partially metallic.