THICKNESS-DEPENDENT CRYSTALLINITY OF SPUTTER-DEPOSITED TITANIA

In this study, we sputter deposited titania films of thickness ranging from 256 to 705 nm on unheated substrates and studied changes in phas e constituency as a function of film thickness. X-ray diffraction, and infrared spectroscopy were used for post-deposition analysis. The res ults show that the thinnest films consisted of anatase, rutile, and an amorphous structure. As film thickness increased, anatase formed at t he expense of the amorphous constituent, whereas the amount of rutile per unit film Volume remained constant. We hypothesized,that if the th ickness-related crystallographic changes were caused by bulk annealing effects due to in situ plasma heating during deposition, then it shou ld be possible to reproduce these changes, ex situ, by furnace anneali ng. The thinnest films were annealed at three temperatures: 300, 500, and 700 degrees C. There was no change in phase composition at 300 OC. Metallurgical recovery of both crystalline phases occurred at 500 deg rees C. At 700 degrees C, rutile grew at the expense of anatase, which completely,disappeared. The results showed that post-deposition annea ling caused crystallographic changes that were inconsistent with the t hickness-dependent crystallographic changes in the as-grown films. We suggested that the latter was caused by enhanced surface, not bulk dif fusion, possibly due to an increase in substrate temperature during de position. (C) 1998 American Vacuum Society.