Ex situ and in situ spectroscopic ellipsometry of MF and DC-sputtered TiO2 and SiO2 films for process control
Titanum oxide and silicon oxide films were deposited on floatglass substrates by magnetron sputtering employing both the DC and the MF (mid-frequency) technique. The films were grown at different working points between transition and oxide mode, target power densities up to 7.5 W/cm(2). Ex-situ ellipsometry at different angles of incidence was applied to study the optical properties and the morphology of the films. For modeling the spectra, the Lorentz model with one single oscillator was used within the spectral range between 380 and 850 nm. For SiO2, the ellipsometric data could be fitted using a model with one single homogeneous film. The ellipsometric investigation of TiO2 films with thicknesses below 150 nm show that, in general inhomogeneities of the refractive index in the growth direction have to be taken into account. It is concluded that both plasma heating as well as ion bombardment are responsible for these inhomogeneities. Refractive indices of 2.43 for DC sputtered films up to 2.58 for MF sputtered films are observed. A four-layer SiO2-TiO2 antireflective coating on glass was fabricated using both plasma and ellipsometric control. The reflectivity, calculated from the in situ ellipsometric analysis, is in a good agreement wih the measured reflectivity.