Characterization of sputtered and annealed niobium oxide films using spectroscopic ellipsometry, Rutherford backscattering spectrometry and X-ray diffraction

Niobium oxide films were prepared by radio frequency sputtering using Nb2O5 crystalline powder. The thickness and the complex dielectric functions of the as-prepared films were determined by spectroscopic ellipsometry using the Tauc–Lorentz oscillator model. The as-deposited films were amorphous, their refractive index varies between 2.26 and 2.30 at wavelength of 550 nm and the optical band gap varies between 3.29 and 3.46 eV depending on the sputtering conditions. The composition of the layers was studied using Rutherford backscattering spectrometry with 2 MeV 4He+ ion beam. The Nb/O ratio was found in the close vicinity of the stoichiometric one. The films contained small amount of argon. Annealing in air (500 °C, 24 h) causes crystallization and changes in the refractive index and in the extinction coefficient of the film. The optical properties of the sputtered films were compared with those of layers prepared by plasma enhanced chemical vapor deposition, reactive dc sputtering and low frequency magnetron sputtering in other laboratories.