Evidence for breathing modes in direct current, pulsed, and high power impulse magnetron sputtering plasmas

Yang, Yong‐Hua; Zhou, Xue; Liu, Jason X.; Anders, André

doi:10.1063/1.4939922

Cited by 24 publications

(23 citation statements)

References 21 publications

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“…The rotation direction exhibits a strong dependence on power density and pressure, as measured by Yang et al [29], illustrated in figure 5. The exact values of power and pressure where the rotation direction changes depend on the geometry of the magnetron, with the shape and magnitude of the magnetic field having the most significant influence.…”

Section: Spoke Rotation Directionmentioning

confidence: 59%

Spokes in high power impulse magnetron sputtering plasmas

Hecimovic

Keudell²

2018

J. Phys. D: Appl. Phys.

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High power impulse magnetron sputtering (HiPIMS) is a deposition technique where a metal magnetron target is sputtered in a high density plasma to synthesize thin layers with superior properties on a substrate material. These plasmas are characterised by short pulses in the range of 50 µs to 200 µs and very high peak powers in the range of several kW/cm 2 per target area. The understanding of these dynamic plasmas is of upmost interest for the further development of this coating technique. Fast camera measurements revealed the formation of localised ionisation zones in these plasmas that propagate with a velocity of the order km/s. In the case of a circular magnetron, the movement of these ionisation zones appears like the movement of a set of spokes, which led to this common expression spoke to illustrate the pattern formation in these high density plasmas. The analysis and understanding of the spoke phenomenon is still a matter of an open debate, because the analysis and the theoretical description is hampered by the inherent complexity of these plasmas. In this paper, we review the experimental observations of the spoke phenomenon and highlight several approaches for their theoretical explanation.

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Section: Spoke Rotation Directionmentioning

confidence: 59%

Spokes in high power impulse magnetron sputtering plasmas

Hecimovic

Keudell²

2018

J. Phys. D: Appl. Phys.

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“…In contrast, there are several traveling ionization zones in HiPIMS discharges affecting each other (self-organization) 5,47 and growing/decaying in a more-or-less chaotic manner producing different ionization zone patterns from pulse to pulse. 9 We therefore focused here on DCMS discharges and anticipate that the findings will provide much insight when interpreting the more complicated case of HiPIMS discharges. 48,49 B.…”

Section: Discussionmentioning

confidence: 99%

“…[4][5][6] Conditions for stochastic versus regular patterns depend on many factors and have been explored in recent publications. 8,9 Generally, the pattern of ionization zones in DCMS tend to be periodic, which was one of the main reasons to utilize DCMS for the current study.…”

Section: Introductionmentioning

confidence: 99%

Plasma potential of a moving ionization zone in DC magnetron sputtering

Panjan

Anders

2017

Journal of Applied Physics

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Using movable emissive and floating probes, we determined the plasma and floating potentials of an ionization zone (spoke) in a direct current magnetron sputtering discharge. Measurements were recorded in a space and time resolved manner, which allowed us to make a three-dimensional representation of the plasma potential. From this information we could derive the related electric field, space charge, and the related spatial distribution of electron heating. The data reveal the existence of strong electric fields parallel and perpendicular to the target surface. The largest E-fields result from a double layer structure at the leading edge of the ionization zone. We suggest that the double layer plays a crucial role in the energization of electrons since electrons can gain several 10 eV of energy when crossing the double layer. We find sustained coupling between the potential structure, electron heating, and excitation and ionization processes as electrons drift over the magnetron target. The brightest region of an ionization zone is present right after the potential jump, where drifting electrons arrive and where most local electron heating occurs. The ionization zone intensity decays as electrons continue to drift in the Ez × B direction, losing energy by inelastic collisions; electrons become energized again as they cross the potential jump. This results in the elongated, arrowhead-like shape of the ionization zone. The ionization zone moves in the –Ez × B direction from which the to-be-heated electrons arrive and into which the heating region expands; the zone motion is dictated by the force of the local electric field on the ions at the leading edge of the ionization zone. We hypothesize that electron heating caused by the potential jump and physical processes associated with the double layer also apply to magnetrons at higher discharge power, including high power impulse magnetron sputtering.

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“…Although perturbing to the plasma, they can yield local values of the plasma electron density (n e ), electron temperature T e , floating potential V f and plasma potential V p and in some cases the electron velocity distribution function f e (v). Electrical probes have used to detect the presence of spokes in a number of recent HiPIMS studies, including the use of single cylindrical Langmuir probes to identify spokes in the floating potential V f [29] and the ion saturation current I isat [30]. An array of radially separated planar (single) probes placed around the target was used to detect variations in V f [14].…”

Section: Introductionmentioning

confidence: 99%

Triple probe interrogation of spokes in a HiPIMS discharge

Estrin

Karkari

Bradley

2017

J. Phys. D: Appl. Phys.

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Using a triple probe situated above the racetrack and inside the magnetic trap of a magnetron, rotating spokes-like structures have been clearly identified in a single HiPIMS pulse as periodic modulations in the electron temperature T e , electron density n e , ion saturation current I isat , floating potential V f and plasma potential V p. The spokes rotate in the E x B direction with a velocity of ~ 8.8 km/s. Defining the spoke shape from the footprint of ion current they deliver to flush mounted probes embedded in the target, each spoke can be characterised by a dense but cool leading edge (n e ~ 2.0 x 10 19 m-3 , T e ~ 2.1 eV) and relatively hotter but more rarefied trailing edge (n e ~ 1 x 10 19 m-3 , T e ~ 3.9 eV). Measurements of V p show a potential hump towards the rear of spoke, separated from regions of highest density, with plasma potentials up to 8 V more positive than the inter-spoke regions. Azimuthal electric fields of ~1kV/m associated with these structures are calculated.

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Evidence for breathing modes in direct current, pulsed, and high power impulse magnetron sputtering plasmas

Cited by 24 publications

References 21 publications

Spokes in high power impulse magnetron sputtering plasmas

Spokes in high power impulse magnetron sputtering plasmas

Plasma potential of a moving ionization zone in DC magnetron sputtering

Triple probe interrogation of spokes in a HiPIMS discharge

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