Influence of nitrogen content on properties of direct current sputtered TiO(x)N(y) films

The deposition of optical functional coatings with large rates yet also high refractive index and excellent transparency over a wide spectral range is of paramount importance for many applications. In this study we will demonstrate that TiO(x)N(y) films can meet these requirements. The films were deposited by reactive dc magnetron sputtering from a metallic titanium target. The sputtering atmosphere consisted of both Ar as well as oxygen and nitrogen. The starting oxygen partial pressure was 1.14 x 10(-1) Pa which corresponds to the oxidic mode of the Ti target. Then oxygen was being replaced stepwise by nitrogen. Even for high nitrogen partial pressures, only a very small amount of nitrogen incorporation in the films was observed by Rutherford Backscattering Spectroscopy and Secondary Neutral Mass Spectroscopy. This result was compared with simulations based upon thermodynamics, which however showed a significant deviation from experiment that could be explained incorporating kinetic aspects. X-ray reflectometry showed that the density and the deposition rate increase with increasing nitrogen partial pressure. X-ray diffraction revealed that the amount of incorporated oxygen tailors the crystal structure of the TiO(x)O(y) films. The optical properties were measured using optical spectroscopy and spectroscopic ellipsometry. The optical band gap was found to decrease from 3.29 to 2.11 eV with increasing nitrogen content in the sputtering gas, while the refractive index was found to increase by 15%. The detected intrinsic stresses in TiO(x)N(y) were compressive and had values similar to titanium oxide.