Optical and structural characterization of as-deposited and annealed ZrO 2 thin films obtained by PIAD

During the recent years, there has been a growing interest on the physical properties of zirconium dioxide (ZrO 2 ) for its possible use as high-k material and its application in optical coatings technology as high-refractive index material. In the present work we study the optical and structural properties of ZrO 2 thin films obtained by plasma ion-assisted deposition (PIAD) on silicon wafers, in their as-deposited state and after annealing of the samples at different temperatures. The optical properties were studied by variable angle spectroscopic ellipsometry in the visible spectral range, while the structural properties were analyzed with grazing-incidence x-ray diffraction and x-ray reflectometry. The experimental results show a clear correlation between the optical properties and the variations of the structural properties due to the annealing. Thus, the as-deposited layers show a poor crystalline state, with a low refractive index and energy band-gap. As the annealing temperature was augmented, the degree of crystallinity was increased, as well as the refractive index and the band-gap. Moreover, the annealing also induced a reduction of the layer thickness and a slight increase of the surface roughness.