Optical constants of off-stoichiometric aluminum oxide thin film in 6–20 nm soft-X-ray/extreme ultraviolet region

Abstract

In this study, the optical constants of a sputter-deposited aluminum oxide thin film are measured in the soft-X-ray wavelength region of 6–20 nm using an angle-dependent X-ray reflectivity technique at the Indus-1 synchrotron radiation source. The chemical composition of the aluminum oxide thin film is analyzed by an X-ray photoelectron spectroscopy technique. Grazing incidence X-ray reflectivity results indicate that the density of the film is lower (2.93 g·cm−3) than that of bulk alumina (3.97 g·cm−3). The experimentally obtained optical constants correlate with the film composition and density. It is found that the experimentally measured delta and beta values are 5–33% higher than the tabulated values except those near the Al L edge (17 nm) region, where the experimentally obtained beta values are 7–20% lower and the delta values are 50–120% higher. This large mismatch observed between the experimental values and Henke et al. data is attributed to the reduced film density and the presence of a mixed phase of AlOx and Al2O3, as evidenced by X-ray photoelectron spectroscopy.