Effects of power per pulse on reactive HiPIMS deposition of ZrO2 films: A time-resolved optical emission spectroscopy study

Abstract

Time-resolved optical emission spectroscopy was carried out during controlled reactive high-power impulse magnetron sputtering of ZrO2 films in argon–oxygen gas mixtures. The effects of increased target power density (up to 3.0 kW cm−2) applied in voltage pulses shortened from 200 to 50 μs were studied at a nearly constant deposition-averaged target power density (close to 50 W cm−2) and a fixed repetition frequency of 500 Hz. The trends in time evolution of the local ground-state densities of Zr, Ar, and O atoms and that of the Zr+, Zr2+, Ar+, and O+ ions during a voltage pulse were deduced from the time evolution of the corresponding excited-state populations and the excitation temperature. It was found that the sputtered Zr atoms are much more ionized (with a high fraction of Zr2+ ions) and the Ar atom density is more decreased near the target during the shorter (50 μs) high-power pulses. These shorter pulses produce a four times higher pulse-averaged target power density oscillating between 1.7 and 2.1 kW cm−2 during deposition. Under these conditions, much higher densities of O atoms and Zr2+ ions were measured in the plasma bulk. The higher backward flux of the Zr+ and Zr2+ ions onto the target during this high-power discharge regime contributed significantly to a 34% decrease in the efficiency of the magnetron sputter deposition of ZrO2 films.