Spectroscopic ellipsometry (SE) is used to characterize amorphous and crystalline thin films of TiO2. Amorphous precursor films of TiO2 are deposited by radio frequency magnetron sputtering on fused silica and silicon substrates. Annealing the amorphous precursor films induces them to crystallize into either pure or mixed phases of the three crystal polymorphs of TiO2: rutile, brookite, and anatase. Previous research in our group has shown that TiO2 crystal polymorph formation post-annealing, in both pulsed-laser deposition (PLD) and radio frequency magnetron sputtered deposition, is dependent on the thickness of the deposited film, among other deposition parameters.
A set of thin film samples has been made at varying sputtered deposition parameters. SE was employed to estimate the thickness and optical constants of the TiO2 films. The samples were measured on the wavelength range of 200 – 1000 nm (ultraviolet to near-infrared) with a Woollam M-2000X spectroscopic ellipsometer. The modeling software CompleteEASE was used for data acquisition, and to fit the measured ᴪ & ∆ spectra with two different optical dispersion models. A Cauchy function models the films as transparent on the restricted wavelength range of 400 – 1000 nm. A Cody-Lorentz oscillator function models the dispersion of the films from 200 – 1000 nm, yielding an estimate of the bandgap energy. Results of fitting model parameters from the two different CompleteEASE models were compared to each other.