Some properties of TiO2 layers prepared by medium frequency reactive sputtering

One of the most extensively used coating materials with a high index of refraction is titania (TiO2). It is transparent in the visible range and has good mechanical properties and chemical stability. Among the several crystal structures of this oxide, rutile has the highest density and microhardness, the highest index of refraction and the highest temperature stability. For TiO2, it is known that different types of deposition techniques create films with different properties. The aim of this work was to analyze the properties of TiO2 films prepared by twin magnetron sputtering. The films were prepared by medium frequency (MF) twin magnetron reactive sputtering. This method offers two special properties which may strongly influence the growth of the film. First, the substrate is continuously bombarded by positively charged ions of high energy. The values obtained are up to 200 eV. Second, using this method it is possible to prepare transparent TiO2 films in the metallic or transition mode of the cathode characteristic with a very high deposition rate. X-ray diffraction patterns show that, depending on the preparation conditions, the films contain different amounts of rutile, mixed with anatase and amorphous phases. The film morphology, i.e. microstructure and surface roughness, was investigated by scanning electron microscopy (SEM). It was shown that samples with a highly homogenous microstructure and with a very smooth surface could be produced. The optical constants were calculated from the measured optical transmission and reflection spectra. The film density was determined by weighing. The values obtained were around 90% of the density of bulk TiO2 with rutile structure. All films showed a compressive stress. The microhardness was measured by the Vickers method. (C) 1999 Elsevier Science S.A. All rights reserved.