Discharge characteristics and preparation for Al₂O₃thin films using liquid-target reactive high power impulse magnetron sputtering

To increase the deposition rate of Al₂O₃ thin films in the process of reactive magnetron sputtering, liquid -target reactive high power impulse magnetron sputtering (R-HiPIMS) is proposed in this study. Ion current curves and optical emission spectroscopy indicate that the density of aluminum ions in the R-HiPIMS process can be enhanced greatly by the liquid target. The peak ion currents in this process are approximately twice as high as those in the solid-target R-HiPIMS under the same sputtering voltage. Al₂O₃ thin films were deposited on Si (100) and SiO₂ substrates with various power densities, and the deposition rate of alumina films can reach 700 nm/h under a power density of 6.0 W/cm². X-ray photoelectron spectrometer analysis shows that a power density of 4.5–5.5 W/cm²was advantageous for depositing a close stoichiometric alumina film. Scanning electron microscopy reveals that the as-deposited alumina films exhibit smooth surfaces at higher power densities, suggesting that arc events during the liquid-target R-HiPIMS process can be virtually eliminated by proper power densities. The transmittance of the film attained at the power density of 5.5 W/cm²is close to that of the SiO₂ substrate. These results suggest that the liquid-target R-HiPIMS technique represents a straightforward and efficient means for the rapid deposition of alumina films.