Pressure dependence of (Ti, Al)N film growth on inner walls of small holes in high-power impulse magnetron sputtering

Publication date: 28 February 2017
Source:Thin Solid Films, Volume 624
Author(s): Tetsuhide Shimizu, Hidetoshi Komiya, Yoshikazu Teranishi, Kazuo Morikawa, Hiroshi Nagasaka, Ming Yang
(Ti, Al)N films were deposited inside 1mm scale small holes from a Ti0.33Al0.67 alloy target by high-power impulse magnetron sputtering (HiPIMS). To investigate the transport behavior of sputtered and gas species of ternary nitride into the small hole structure and its effect on the chemical and phase compositions of the films grown on the inner side walls, the deposition was performed under inert working gas pressures of 0.5, 1, and 2Pa with a fixed pulse length of 50μs and a frequency of 1kHz. Optical emission spectra revealed the pressure dependence of the ion-to-neutral fraction for titanium, showing an increasing fraction at a higher working pressure. The highest fraction of Al/(Al+Ti) was obtained at 0.5Pa, while the lowest value was obtained at 1Pa. This pressure dependence is discussed by considering the degree of thermalization from the viewpoint of mass differences between Al, Ti and the gas species. Under ballistic transport at 0.5Pa, the high degree of ionization of the HiPIMS discharge further enhances the film coverage at a greater depth, resulting with an aspect ratio of 2.7, and a higher Al fraction was obtained even at a greater depth of 2mm. The films deposited at 0.5Pa had a high Al content with mixed cubic and wurtzite phases of (Ti, Al)N and exhibited a hardness of 35GPa even on the inner walls of the small holes. The influence of the degrees of ionization and thermalization of the sputtered species in the growth of ternary nitride films on a high aspect ratio geometry was demonstrated.