Effects of plasma exposure on structural and optical properties of TiO2 films deposited by off-axis target sputtering

TiO 2 films with thickness of about 800–2300 nm have been reactively deposited on glass-slide substrates at an atmosphere of Ar and O2 mixture, using the off-axis target sputtering method. The maximum deposition rate of the film was 12.8 nm/min. The optical properties and the crystal structure of the films were measured using spectrophotometry, Raman spectroscopy, and x-ray diffractometry, respectively. Most of the films deposited in this study were transparent and had anatase crystal structure, while some of them were semitransparent. The A(101), A(112), A(211) and A(220) peaks were observed in the x-ray diffraction patterns, where A shows the anatase phase of TiO2. With increasing plasma exposure, the x-ray peak intensities IP of A(101) and A(112) gradually decreased, while the IP of A(211) and A(220) gradually increased. The IP depended strongly on the substrate position in this study. Moreover, the A(220) peak was significantly higher than other peaks when the TiO2 crystallites became larger. The anatase phase of the TiO2 films was also revealed in the Raman spectra with a Raman shift of 145 cm−1. With decreasing plasma exposure, the changes in the optical transmittance spectra of TiO2 films were very small at the wavelength of 350–900 nm. However, the transmittance spectra significantly depended on the wavelength with increasing plasma exposure. Consequently, it was found that the crystal structure and the optical properties of as-deposited TiO2 films were strongly affected by plasma exposure during film deposition.