A Spectroscopic Ellipsometry Study of TiO₂ Thin Films Prepared by dc Reactive Magnetron Sputtering: Annealing Temperature Effect

TiO2 thin films 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 film are deduced by variable-angle spectroscopic ellipsometry (VASE) and supported by x-ray diffractometry. The optical properties of the films are examined by VASE. Measurements of ellipsometry are performed in the spectral range 0.72--3.55eV at incident angle 75°. 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 films are found to be inhomogeneous and amorphous, whereas the annealed films present the phase transition to anatase and rutile structures. The refractive index of TiO₂ thin films 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 films are annealed at 300°C.