A spectroscopic ellipsometry study of TiO2 thin films prepared by dc reactive magnetron sputtering:: Annealing temperature effect

TiO2 thin Elms are obtained by dc reactive magnetron sputtering. A target of titanium (99.995%) and a mixture of argon and oxygen gases are used to deposit TiO2 films on to silicon wafers (100). The crystalline structure of deposited and annealed Elm are deduced by variable-angle spectroscopic ellipsometry (VASE) and supported by x-ray diffractometry, The optical properties of the Elms are examined by VASE. Measurements of ellipsometry are performed in the spectral range 0.72-3.55 eV at incident angle 75 degrees. Several SE models, categorized by physical and optical models, are proposed based on the 'simpler better' rule and curve-fits, which are generated and compared to the experimental data using the regression analysis. It has been found that the triple-layer physical model together with the Cody-Lorentz dispersion model offer the most convincing result. The as-deposited Elms are found to be inhomogeneous and amorphous, whereas the annealed Elms present the phase transition to anatase and rutile structures. The refractive index of TiO2 thin Elms increases with annealing temperature. A more detailed analysis further reveals that thickness of the top sub-layer increases, whereas the region of the bottom amorphous sub-layer shrinks when the Elms are annealed at 300 degrees C.