Structural, optical and electrical properties of WOxNy films deposited by reactive dual magnetron sputtering

Thin films of tungsten oxynitrides were prepared by dual magnetron sputtering of tungsten using argon/oxygen/nitrogen gas mixtures with various nitrogen/oxygen ratios. The presence of even relatively small amounts of oxygen led to close-to-stoichiometric WO₃, with little incorporation of nitrogen, therefore the films were labeled as WO_x(N_y). Oxygen had a great effect not only on the composition but on the structure of WO_x(N_y) films, as shown by Rutherford backscattering and X-ray diffraction, respectively. Significant incorporation of nitrogen occurred only when the nitrogen partial pressure exceeded 89% of the total reactive gas pressure. Sharp changes in the stoichiometry, deposition rate, room temperature resistivity, electrical activation energy and optical band gap were observed when the nitrogen/oxygen ratio was high. The deposition rate increased from 0.31 to 0.89 nm/s, the room temperature resistivity decreased from 1.65 × 10⁸ to 1.82 × 10^{− 2} Ω cm, the electrical activation energy decreased from 0.97 to 0.067 eV, and the optical band gap decreased from 3.19 to 2.94 eV upon nitrogen incorporation into the films. WO_x(N_y) films were highly transparent as long as the nitrogen incorporation was low, and were brownish (absorbing) and partially reflecting as nitrogen incorporation became significant.