Benefits of the controlled reactive high-power impulse magnetron sputtering of stoichiometric ZrO2 films

High-power impulse magnetron sputtering with a pulsed reactive gas (oxygen) flow control was used for high-rate reactive depositions of densified, highly optically transparent, stoichiometric ZrO2 films onto floating substrates. The depositions were performed using a strongly unbalanced magnetron with a directly water-cooled planar Zr 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 5 Wcm−2 to 53 Wcm−2. The voltage pulse durations ranged from 50 μs to 200 μs. The target-to-substrate distance was 100 mm. An optimized location of the oxygen gas inlets in front of the target and their orientation toward the substrate made it possible to improve the quality of the films due to minimized arcing at the sputtered target and to enhance their deposition rates up to 120 nm/min at the deposition-averaged target power density of 52 Wcm−2, a voltage pulse duration of 200 μs and a substrate temperature less than 120 °C. The films exhibited a hardness of 16 GPa, a refractive index of 2.19 and an extinction coefficient of 2 × 10−3 (both at the wavelength of 550 nm). Under these optimized conditions, we measured the highest (Zr+ + Zr2+) and (O2+ + O+) ion fractions in the total fluxes of positive ions, and a low population of high-energy O− ions at the substrate position.