Properties of titanium oxide films obtained by PECVD

Amorphous TiO2 films containing carbon and excess oxygen were deposited from glow discharge plasmas of titanium tetraisopropoxide Ti(OC3H7)4, helium, oxygen and argon mixtures. The discharge was generated in a stainless steel vacuum chamber by two parallel-plate electrodes connected to a 13.56 MHz power supply. A substrate holder, to which a d.c. bias voltage could be applied, was positioned outside the region between the two electrodes, i.e. in a region of lower plasma density. The substrate voltage bias, VB, and the ratio of the partial pressures of O2 to Ti(OC3H7)4 [oxygen to precursor (OTP) ratio] in the chamber were adopted as the principal deposition parameters. Details of the molecular structure of the films were investigated by infrared spectroscopy and X-ray photoelectron spectroscopy. The latter was also used to determine the O/Ti and C/Ti atomic ratios at the film surface. The total (surface and bulk) O/Ti and C/Ti atomic ratios were determined using Rutherford backscattering spectroscopy. While neither the surface nor the total O/Ti ratio varied significantly with VB and the OTP ratio, both the surface and total C/Ti ratios varied strongly with these parameters. The refractive index, determined by ultraviolet-visible spectroscopy, and the electrical conductivity, measured by a two-point probe, were influenced by the polarity and magnitude of VB.