Effect of N2 and Ar gas on DC arc plasma generation and film composition from Ti-Al compound cathodes

Abstract

Articles you may be interested inEffect of Ti-Al cathode composition on plasma generation and plasma transport in direct current vacuum arc J. Appl. Phys. 115, 123301 (2014); 10.1063/1.4869199Ion velocities in direct current arc plasma generated from compound cathodes J. Appl. Phys. 114, 213302 (2013) DC arc plasma from Ti, Al, and Ti 1Àx Al x (x ¼ 0.16, 0.25, 0.50, and 0.70) compound cathodes has been characterized with respect to plasma chemistry (charged particles) and charge-stateresolved ion energy for Ar and N 2 pressures in the range 10 À6 to 3 Â 10 À2 Torr. Scanning electron microscopy was used for exploring the correlation between the cathode and film composition, which in turn was correlated with the plasma properties. In an Ar atmosphere, the plasma ion composition showed a reduction of Al of approximately 5 at. % compared to the cathode composition, while deposited films were in accordance with the cathode stoichiometry. Introducing N 2 above $5 Â 10 À3 Torr, lead to a reduced Al content in the plasma as well as in the film, and hence a 1:1 correlation between the cathode and film composition cannot be expected in a reactive environment. This may be explained by an influence of the reactive gas on the arc mode and type of erosion of Ti and Al rich contaminations, as well as on the plasma transport. Throughout the investigated pressure range, a higher deposition rate was obtained from cathodes with higher Al content. The origin of generated gas ions was investigated through the velocity rule, stating that the most likely ion velocities of all cathode elements from a compound cathode are equal. The results suggest that the major part of the gas ions in Ar is generated from electron impact ionization, while gas ions in a N 2 atmosphere primarily originate from a nitrogen contaminated layer on the cathode surface. The presented results provide a contribution to the understanding processes of plasma generation from compound cathodes. It also allows for a more reasonable approach to the selection of composite cathode and experimental conditions for thin film depositions. V C 2015 AIP Publishing LLC.

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