Ultraviolet Optical Properties and Structural Characteristics of Radio Frequency-Deposited HfO_2 Thin Films

Hafnium oxide (HfO_2) thin films were deposited on quartz substrate by radio frequency magnetron sputtering with power from 160 W to 240 W. The optical and microstructural properties of samples before and after annealing were characterized by XRD, XPS, UV-VIS-NIR spectrophotometer and ellipsometer. The results show optical transmittances with low absorption in wavelength range above \lambda=200 nm for all samples. The appropriate annealing can transfer the amorphous state of as-deposited films to the crystal film, contribute to the growth of nanocrystalline and compressive stress, optimize the stoichiometry of the film and systematically improve film density and the refractive index. In consideration of the stability of proper refractive index (> 2) and high optical transmittance in UV band, HfO_2 films deposited approximately at 220 W can be used in UV anti-reflection system.