Optical constants of thin TiN films: thickness and preparation effects

The optical properties of reactively sputtered TiN films 5–80 nm thick are reported. The stoichiometry and purity of the films were verified with x-ray diffraction and Auger spectroscopy, respectively. The optical constants have been determined by combined R and T measurements at oblique incidence. It is found that deposition onto 400°C substrates significantly improves the optical quality of the films. In particular, the optical selectivity for heat mirror applications is increased, the refractive index in the visible is lowered, and the thickness variation of the optical constants is reduced. It is argued that a low refractive index in the visible is a sensitive measure of film quality. The Drude relaxation time was ~25% longer for the films prepared on heated substrates. Electrical measurements confirm the high quality of the films.