Enhancement of the stability of ion-beam assisted TiO2 thin films by using re-annealing with different substrate temperatures

Abstract

Titanium oxide (TiO2) thin films were prepared by ion-beam-assisted deposition(IAD) on glass substrates at different substrate temperatures. The effect of the stabilities of the optical properties, residual stress and surface roughness by re-annealing were investigated. Thermal annealing is a very useful process to improve the stoichiometry of optical oxide films, particularly for titanium oxide. The evolution of oxidation and the reason of the change in stress during annealing have been discussed. XRD revealed that all films were amorphous at as-deposited. As the substrate temperature increased from 150oC, 200oC to 250oC, the re-crystallization temperature fell from 300oC, through 250oC to 200oC during annealing process. In the re-annealing process, the films would be annealing again and stop the annealing at the temperature of re-crystallization. The refractive indices and extinction coefficients didn't have large fluctuations during the re-annealing process for all films deposited at different substrate temperatures. At substrate temperatures of 200oC and 250oC had the high refraction indices and low extinction coefficients than substrate temperature of 150oC during re-annealing processes. The residual stress had small variations during the re-annealing process. The situation also appeared on the surface roughness. However, the substrate temperature of 150oC had a great transform than 200oC and 250oC during the re-annealing process. Therefore, these results all reveal that the TiO2 films after thermal annealing became more stable than as-deposited, and it was especially useful for the films deposited at substrate temperature of 150oC.