Determination of microstructure related optical constants of titanium dioxide thin films using optical methods

Titanium dioxide films prepared by a conventional electron beam deposition, an ion assisted deposition (IAD) and a radio frequency (RF) sputtering deposition is studied, where optical methods of transmission, spectroscopic ellipsometry (SE) and a quantum mechanical dispersion relation are involved. The complex dielectric function of TiO2 in film phase at the spectral range from 1.5 eV to 6.5 eV is obtained for the use of the reference data. From the SE analysis, it is found that IAD grown TiO2 films and RF sputter grown TiO2 films have lower void fraction (5 - 14%) compared to the conventional electron beam grown ones (19 - 24%). As the film thickness increases from 500 angstroms to 3200 angstroms, the packing density of TiO2 films monotonically rises from 87% to 95% when prepared on c-Si substrate, but it varies from 86% to the maximum value of 91% near 2000 angstroms when prepared on vitreous silica substrate. Surface microroughness of TiO2 films prepared by the conventional electron beam deposition is confirmed by atomic force microscopy images.