The use of segmented cathodes to determine the spoke current density distribution in high power impulse magnetron sputtering plasmas

Poolcharuansin, Phitsanu, Estrin, Francis Lockwood and Bradley, James W (2015) The use of segmented cathodes to determine the spoke current density distribution in high power impulse magnetron sputtering plasmas. JOURNAL OF APPLIED PHYSICS, 117 (16). p. 163304.

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Abstract

The localized target current density associated with quasi-periodic ionization zones (spokes) has been measured in a high power impulse magnetron sputtering (HiPIMS) discharge using an array of azimuthally separated and electrical isolated probes incorporated into a circular aluminum target. For a particular range of operating conditions (pulse energies up to 2.2-J and argon pressures from 0.2 to 1.9-Pa), strong oscillations in the probe current density are seen with amplitudes up to 52% above a base value. These perturbations, identified as spokes, travel around the discharge above the target in the E×B direction. Using phase information from the angularly separated probes, the spoke drift speeds, angular frequencies, and mode number have been determined. Generally, at low HiPIMS pulse energies Ep-<-0.8-J, spokes appear to be chaotic in nature (with random arrival times), however as Ep increases, coherent spokes are observed with velocities between 6.5 and 10-km s-1 and mode numbers m-=-3 or above. At Ep->-1.8-J, the plasma becomes spoke-free. The boundaries between chaotic, coherent, and no-spoke regions are weakly dependent on pressure. During each HiPIMS pulse, the spoke velocities increase by about 50%. Such an observation is explained by considering spoke velocities to be determined by the critical ionization velocity, which changes as the plasma composition changes during the pulse. From the shape of individual current density oscillations, it appears that the leading edge of the spoke is associated with a slow increase in local current density to the target and the rear with a more rapid decrease. The measurements show that the discharge current density associated with individual spokes is broadly spread over a wide region of the target.

Item Type:	Article
Subjects:	?? QC ??
Depositing User:	Symplectic Admin
Date Deposited:	14 Aug 2015 08:02
Last Modified:	16 Dec 2022 16:17
DOI:	10.1063/1.4918720
Related URLs:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/2020399