Investigation of thermally induced changes on structure, morphology and stoichiometry of sputter deposited titanium oxide thin films

We report here tailoring the properties of amorphous titanium oxide (a-TiOx) thin films by changing substrate heating as well as post-annealing. The a-TiOx thin films have been deposited on silicon substrates by direct current magnetron sputtering at a sputter power of 50 W without and with substrate heating (200°C) with no additional oxygen sources. After deposition, the films were annealed in vacuum for 1 hour at 300°C, 400°C, and 500°C. The influence of substrate heating and post-deposition annealing on the structure and surface morphology of the films along with their chemical states has been investigated. X-ray reflectivity analysis revealed that films deposited at 200°C were denser and thinner with low roughness than those deposited without substrate heating. Grazing incidence X-ray diffraction analyses showed that the films before and after annealing were amorphous; except for the ones deposited without substrate heating and were annealed at 500°C which showed slight crystallinity. From field emission scanning electron microscopy and atomic force microscopy images, distinct variations in the morphology of the films were also observed when films were deposited at 200°C X-ray photoelectron spectroscopy analysis showed that the a-TiOx films were oxygen deficient. It was observed that Ti was found in Ti4+ and Ti3+ states in the films and that the proportion of Ti4+ increased when the films were annealed at 500°C. Therefore, the structure, morphology, and chemical states of a-TiOx thin films can be tailored with substrate heating and post-annealing.