Nano-organization of thin titanium films by an electrical field during vacuum arc deposition

Ti films were deposited onto 25×76 mm glass substrates using vacuum arc deposition under the following conditions: arc current of 170 A, residual gas pressure of approximately 10^-2 Pa, coating duration of 10 s, and a coating rate of 3-4.5 nm/s. A voltage of U = 0-100 V d.c. was applied during deposition between 25×5-mm silver paint electrodes, separated by 20 mm, on the exposed surface of the substrates. The films were examined by atomic force microscopy (AFM), X-ray photo-electron spectroscopy (XPS), and grazing incidence X-ray reflectometry (GIXR). AFM showed that the surface of films deposited with applied voltage consisted of rows of titanium `hills' separated by troughs or quasi-`valleys'. The rows had tendency to be orientated approximately parallel to the direction of the electric field which was applied during deposition. The surface structure was more regular and finer at U = 20 V than at U = 0 and 40 V. The film resistance was 60, 38 and 50 Ω at U = 0, 20 and 40 V, respectively. After deposition, the samples were annealed at 450 °C in air for 19 h. XPS showed that upper layer of the annealed samples was composed of TiO₂. AFM showed that the titanium oxide layer grown during annealing on the Ti film deposited at U = 20 V was more homogeneous than the oxide layers grown on the Ti films deposited at U = 0 and 40 V. The size of the titanium oxide grains increased with U = 0.2, 0.3 and 0.6 μm at 0, 20 and 40 V, respectively. GIXR before and after annealing indicated that the maximum film thickness and the minimum roughness of all interfaces (air-titanium oxide, titanium oxide-titanium and titanium-glass substrate) were obtained at U = 20 V.