Compositional and Structural Properties of TiO_2-xN_x Thin Films Deposited by Radio-Frequency Magnetron Sputtering

TiO_2-xN_x thin films are deposited onto Si(100) and quartz substrates by a rf magnetron sputtering method using a titanium metal disc as a target in Ar, N₂, and O₂ atmospheres. The substrate temperature is kept at 300°C. The O₂ and Ar gas flow rates are kept to be constants and the N gas flow rate is varied. TiO_2-xN_x films with different N contents are characterized by x-ray diffraction and x-ray photoelectron spectroscopy. The results indicate that the TiO_2-xN_x thin films can be obtained at 13% N and 15% N contents in the film, and the films with mixed TiO₂ and TiN crystal can be obtained at 13% N and 15% N contents in the film. In terms of the results of x-ray photoelectron spectroscopy, N 1s of β-N (396eV) is the main component in the TiO_2-xN_x thin films. Because the energy level of β-N is positioned above the valence-band maximum of TiO₂, an effective optical-energy gap decreases from 2.8eV (for pure TiO₂ film deposited by the same rf sputtering system) to 2.3eV, which is verified by the optical-absorption spectra.