Simultaneous determination of refractive index, extinction coefficient, and void distribution of titanium dioxide thin film by optical methods.

The refractive index n(λ) and the extinction coefficient k(λ) of a TiO(2) film prepared by electron-beam evaporation are determined in the spectral region 1.5-5.5 eV. The transmission spectrum of the TiO(2) film on a vitreous silica specimen is inverted to get the k(λ) of TiO(2) in its interband transition region. Above 3.5 eV, k(λ) is used to get the coefficients of the quantum mechanically derived dispersion relation of an amorphous TiO(2). These coefficients and n(∞) are used to determine n(λ). The modeling procedure is applied to spectroscopic ellipsometry data of a TiO(2) film on a c-Si specimen, and the void distribution of the film is revealed. With spectroscopic ellipsometry data above the fundamental band gap, valuable information about surface roughness is obtained. The effective thickness of this rough surface layer is confirmed by an atomic force microscopy measurement.