High-rate reactive high-power impulse magnetron sputtering of hard and optically transparent HfO2 films

High-power impulse magnetron sputtering (HiPIMS) with a pulsed reactive gas (oxygen) flow control was used for high-rate reactive depositions of densified, highly optically transparent, stoichiometric HfO2 films onto floating substrates. The depositions were performed using a strongly unbalanced magnetron with a directly water-cooled planar Hf target of 100 mm diameter in argon-oxygen gas mixtures at the argon pressure of 2 Pa. The repetition frequency was 500 Hz at the deposition-averaged target power density from 29 W cm(-2) to 54 W cm(-2). The voltage pulse durations ranged from 50 mu s to 200 mu s. The target-to-substrate distance was 100 mm and the substrate temperatures were less than 165 degrees C. We showed that the HfO2 films can be prepared with very high deposition rates (up to 200 nm/min) at a deposition-averaged target power density of approximately 30 W cm(-2), which is relatively close to a target power density applicable in industrial HiPIMS systems. The films were nanocrystalline with a dominant monoclinic phase. They exhibited a hardness of 15-18 GPa, a refractive index of 2.07-2.12 and an extinction coefficient between <= 0.1 x 10(-3) and 0.6 x 10(-3) (both quantities at the wavelength of 550 nm). At 300 nm, the extinction coefficient was between 1.5 x 10(-3) and 7.0 x 10(-3). A simplified relation for the deposition rate of films prepared using a reactive HiPIMS was presented. (C) 2015 Elsevier B.V. All rights reserved.