Fine Control of Optical Properties of Nb2O5 Film by Thermal Treatment

Thermal treatment is a common method to improve the properties of optical thin films, but improper thermal treatment processing will result in the degradation of the optical properties of the optical thin film. The thermal stability of niobium oxide (Nb₂O₅) thin films prepared by magnetron sputtering was systematically studied by analyzing the roughness and morphology of the film under different thermal treatment processes. The results show that the amorphous stability of the Nb₂O₅ thin film can be maintained up to 400 °C. Before crystallization, with an increase in annealing temperature, the surface roughness of the film has no obvious change, the refractive index decreases, and the elastic modulus and hardness increase. The residual stress was measured by a laser interferometer. The results show that the residual compressive stress is present in the film, and the residual stress decreases with an increase in thermal treatment temperature. Considering the residual stress state, phase composition, mechanical properties, and optical properties of Nb₂O₅ films at different thermal treatment temperatures, we believe that the spectral position of the optical thin film device can be finely controlled within a 1.6% wavelength, and the thermal treatment temperature of Nb₂O₅ films prepared by magnetron sputtering should not exceed 400 °C.