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

Abstract

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 ∼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 TiO 2. 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.