Study of the structure, roughness and optical properties of HfO₂ coatings deposited on microscopic glass substrates

Abstract

In this work, we deposited HfO2 films on microscopic glasses by direct current (DC) magnetron sputtering for different deposition times, namely 120 min and 180 min. The phase composition of the coatings was assessed by X-ray diffraction (XRD). The surface roughness, the optical constants, the refractive index n, the extinction coefficient k and the thickness of the prepared HfO2 coatings were estimated by ellipsometric measurements. The XRD results pointed to the presence of a polycrystalline monoclinic phase. A slight difference was found in the surface roughness of the two HfO2 films, which was 5.1 nm and 5.7 nm, respectively, for the deposition times of 120 minutes and 180 minutes. The optical constants n and k were determined at the wavelength of 630 nm by using the Cauchy model. The results showed almost the same value of the refractive index for both films (1.88 and 1.89), but a higher extinction coefficient (0.01) for the film grown for 180 minutes, compared to a value of 0.007 for the one deposited for 120 minutes. The films thickness was 410 nm and 780 nm for deposition times of 120 minutes and 180 minutes, respectively. The deposited HfO2 films were transparent, with the longer deposition time corresponding to an improved reflection (57%), compared to the 28% reflection for the film deposited for 120 minutes.