SPECTROSCOPIC MEASUREMENTS OF STRESS-RELAXATION DURING THERMALLY INDUCED CRYSTALLIZATION OF AMORPHOUS TITANIA FILMS

Amorphous TiO2 optical films transform irreversibly to a crystalline phase when subjected to temperatures in excess of 573 K. The transformation is accompanied by film densification and a marked change in the intrinsic film stress. Work reported here involves the application of real-time Raman spectroscopy to follow the transformation dynamics and to evaluate transient stresses which evolve during thermally induced crystallization of amorphous sol-gel deposited films. Relative changes in vibrational mode intensities characteristic of the crystalline phase correlate with the degree of crystallinity in the film while mode frequency shifts also acquired in real time are used to estimate the film temperature and the magnitude of internal stress. A contour analysis method is presented whereby knowledge of two vibrational mode frequencies is sufficient to determine these quantities uniquely. Results suggest that both deposition temperature and crystallization temperature affect the intrinsic film stress. Advantages and limitations of this method for the evaluation of stress in dielectric films are discussed.