Effect of substrate temperature and annealing on the growth of TiO2-x thin films deposited by using DC-magnetron sputtering technique

In this study, the effect of annealing on the structural, surface morphology and chemical structure of titanium suboxide (TiO_2-x) thin films has been investigated. TiO_2-x films had been grown on Si substrates by DC-magnetron sputtering with different sputter powers (75 and 100 W) at room temperature (RT) and 200°C substrate temperature (ST). The films were subsequently annealed for 1 h at 300, 400 and 500°C in vacuum. The impact of ST, post-annealing and sputter power on crystallinity, surface morphology and chemical state of the films were studied. Grazing incidence X-ray diffraction (GIXRD) data revealed that the films were amorphous or exhibited a very low crystalline structure while deposited at RT and even after annealing. Moreover, the films showed crystallinity while deposited at ST and exhibited an anatase-rutile (A-R) mix phase from anatase (A) annealed at 300°C (75 W at ST). X-ray reflectivity (XRR) data showed that the mass density of the films increased with the annealing temperature. Images obtained using atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) revealed that post-annealing increased the surface roughness of the films. X-ray photoelectron spectroscopy (XPS) analysis indicated the films were sub stoichiometric. It was also indicated that Ti was in the form of Ti⁴⁺ and Ti³⁺ states in all films, and the proportion of Ti⁴⁺ slightly increased after post-annealing at 500°C. The findings showed that post-annealing, ST and sputtering power can all affect the growth of TiO_2-x films.