Thin films of zirconium oxide have been deposited onto glass and Si(100) substrates at room temperature by reactive dc magnetron sputtering of a metallic Zr target in an argon–oxygen atmosphere. The films were characterized by Rutherford backscattering spectroscopy, x-ray diffraction, x-ray reflectometry, atomic force microscopy, and optical spectroscopy to investigate the variation of stoichiometry, structure, density, and optical properties upon increasing oxygen partial pressure. The Zr target shows a well-defined hysteresis upon varying the oxygen pressure as determined by quartz crystal microbalance measurements. Rutherford backscattering experiments reveal that the films are metallic with a small amount of oxygen incorporation at oxygen flows well below 2.7 sccm. Stoichiometric ZrO2 films, however, are formed above 2.8 sccm O2 flow (oxidic mode). Grazing angle incidence x-ray diffraction studies show that crystalline ZrO2 films with monoclinic structure grow in this oxygen flow regime. X-ray reflectivity studies determine a constant density of 6.5 g/cm3 and a deposition rate of approximately 1.5 nm/s in the metallic mode. The transition to the oxidic mode is accompanied by a decrease of film density and a reduction in deposition rate to below 0.2 nm/s for a constant cathode current of 900 mA. In this oxygen flow regime a density of 5.2 g/cm3 is determined, which is approximately 90% of the bulk density of monoclinic ZrO2. With increasing O2 flow in the oxidic sputtering regime the surface roughness of the films increases as is also confirmed by atomic force microscopy. For these O2 flow rates fully transparent ZrO2 films are grown. From measurements of the optical transmittance and reflectance we have determined the optical constants such as the band gap Eg, refractive index n, and extinction coefficient k as well as the film thickness. While the refractive index of the films decreases upon increasing O2 flow, the band gap Eg increases simultaneously from 4.52 to 4.67 eV.

The effect of annealing temperature on the structural and optical properties of sputtered niobium–oxide films has been investigated. The temperature dependence of structure, density, and optical constants has been studied by Rutherford backscattering, x-ray diffraction, x-ray reflection, optical spectroscopy, and variable angle spectroscopic ellipsometry techniques. Rutherford backscattering measurements show no variation in the stoichiometry of the films upon annealing of amorphous Nb2O5 films, while amorphous NbO is oxidized to Nb2O5. X-ray diffraction studies show that as-deposited films are amorphous and only crystallize at around 500 °C. X-ray reflectivity studies reveal a continuous increase of film density with increasing annealing temperature. Optical spectroscopy and spectroscopic ellipsometry confirm that the refractive index n and the band gap Eg increase upon increasing annealing temperature. The variation of the refractive index with density of the niobium–oxide films is observed to follow the Clausius–Mossotti relation and the molecular electronic polarizability has been deduced from the straight line fit of Lorentz–Lorentz law.

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 × 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 N 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.

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