High-kappa hafnium-oxide thin films have been fabricated by radio frequency (rf) reactive magnetron sputtering technique. To avoid formation of an undesired interfacial suboxide layer between Si and high-kappa film, prior to HfO2 deposition, a thin Hf buffer layer was deposited on p-type (100) Si substrate at room temperature. Effect of oxygen gas quantity in the O-2/Ar gas mixture was studied for the optical and structural properties of grown HfO2 high-kappa thin films. The grown thin oxide films were characterized optically using spectroscopic ellipsometer (SE) in detail. Crystal structure was studied by grazing incidence X-ray diffractometer (GIXRD) technique, while bonding structure was obtained by Fourier transform infrared spectroscopy (FTIR) analyses. In agreement with GIXRD and FTIR analyses, SE results show that any increment above ideal quantity of oxygen content in the gas mixture resulted in decrements in the refractive index and thickness of HfO2 dielectric film, while increments in SiO2 thickness. It is apparent from experimental results that oxygen to argon gas ratio needs to be smaller than 0.2 for a good film quality. The superior structural and optical properties for grown oxide film were obtained for O-2/Ar gas ratio of about 0.05-0.1 combined with similar to 30W constant rf sputtering power. (C) 2014 Elsevier B.V. All rights reserved.