Structural and optical evaluation of WOxNy films deposited by reactive magnetron sputtering

Thin films of tungsten oxynitrides were deposited on substrates preheated at 300 °C from metallic tungsten target using reactive pulsed d.c. magnetron sputtering. The deposition was carried out at different nitrogen to total reactive gas partial pressures ratios. The energy dispersive analysis of X-ray showed that significant incorporation of nitrogen occurred only when the nitrogen partial pressure exceeded 74% of the total reactive gas pressure. X-ray diffraction analysis revealed that the formation of a specific crystalline phase is affected by the composition and the possibility of competitive growth of different phases. The increase of nitrogen content into the films increases the optical absorption and decreases the optical band gap. The refractive index was determined from the transmittance spectra using Swanepoel's method. It was found that the refractive index increases with increasing nitrogen content over the entire spectral range. The values of the tungsten effective coordination number, N_c, was estimated from the analysis of the dispersion of the refractive index, and an increase in N_c with increasing nitrogen content was observed.