Analytic model of the energy distribution function for highly energetic electrons in magnetron plasmas

Gallian, Sara; Trieschmann, Jan; Mussenbrock, Thomas; Brinkmann, Ralf Peter; Hitchon, W. N. G.

doi:10.1063/1.4905943

Cited by 19 publications

(25 citation statements)

References 23 publications

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“…This assumption is largely supported by a body of experimental work undertaken on dc and pulsed-dc magnetrons which shows the eedf is usually well fitted by a Maxwellian in the vicinity of the cathode (inside the magnetic trap region) and by a bi-Maxwellian further away from it [41]- [43]. In dense HiPIMS plasmas (n e > 5 x 10 18 m -3 ) with long on-times (> 10's of microseconds) there is sufficient time for the eedf's of electrons in the magnetic trap to reach a steady state configuration, as discussed by Gallian et al [44] in a kinetic modelling study of a HiPIMS plasma operating with an aluminium target. Energetic secondary electrons liberated from the cathode will Maxwellianize in that region, in a few 10's of nanoseconds.…”

Section: Introductionmentioning

confidence: 94%

“…Energetic secondary electrons liberated from the cathode will Maxwellianize in that region, in a few 10's of nanoseconds. The predictions for the eedf in Ref [44] show that inside the magnetic trap, the vast majority of electrons do relax to form a cold Maxwellian distribution, however with a hot tail of electrons emerging for electron energies above ~30 eV. This energetic group, originating from the interaction of sheath-accelerated secondary electrons with heavy gas and metal species is four orders of magnitude smaller than the main group.…”

Section: Introductionmentioning

confidence: 97%

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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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Section: Introductionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 97%

Triple probe interrogation of spokes in a HiPIMS discharge

Estrin

Karkari

Bradley

2017

J. Phys. D: Appl. Phys.

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“…The energy distribution of the electrons in a HiPIMS plasma has been also obtained, both experimentally [21] and by modelling [22]. It has been found to be predominantly Maxwellian with a high energy tail from about 30 eV to the energy corresponding to the value of the cathode potential.…”

Section: Introductionmentioning

confidence: 97%

First measurements of the temporal evolution of the plasma density in HiPIMS discharges using THz time domain spectroscopy

Meier

Hecimovic

Tsankov

et al. 2018

Plasma Sources Sci. Technol.

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In this paper the novel technique of THz time domain spectroscopy has been applied to obtain time-resolved measurements of the plasma density in the active zone of a HiPIMS discharge with a titanium target. The obtained peak values are in the range of 10 12 -10 13 cm −3 for discharge current densities of 1 to 4 A/cm 2 at 0.5 and 2 Pa argon pressure. The measured densities show good correlation with the discharge current and voltage and the intensity of various atomic and ionic lines. The well known phases of the discharge have been identified and related to the variation of the electron density. The measurement results show that the plasma density remains nearly constant during the runaway/self-sputtering phase. Based on that it is conjectured that singly charged titanium ions are the dominant ion species during this phase.

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“…According to an analytical model these electrons are cooled by inelastic ionization and excitation collisions with neutral species, and by elastic Coulomb interactions with the cold Maxwellian electron population [48]. One important aspect of HiPIMS is the natural occurence of high energetic ions of sputtered species [49].…”

Section: Electron and Ion Energy Distribution Functionsmentioning

confidence: 99%

Scaling and laws of DC discharges as pointers for HiPIMS plasmas

Maszl¹,

Laimer²,

Keudell³

et al. 2015

Preprint

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Scaling or smiliarity laws of plasmas are of interest if lab size plasma sources are to be scaled for industrial processes. In the case of direct current (DC) magnetron sputtering the scales can range from few centimeters in the lab to several meters if one takes the flat glass industry as one example. Ideally, the discharge parameters of the scaled plasmas are predictable and the fundamental physical processes are unaltered. Naturally, there are limitations and ranges of validity. Scaling laws for direct current glow discharges are well known. If a well diagnosed discharge is scaled, the field strength in the positive column, the gas amplification and the normal current density can easily be estimated. For non-stationary high power discharges like high power impulse magnetron sputtering (HiPIMS) plasmas, scaling is not as straight forward. Here, one deals with a non-stationary complex system with strong changes in plasma chemistry and symmetry breaks during the pulses. Because of the huge parameter space no good parameters are available to define these kind of discharges unambiguous at the moment. In this contribution we will discuss the scaling laws for DC glow discharges briefly and present experimental results for a discharge with copper electrodes and helium as plasma forming gas. This discharge was operated in a pressure range from 200 to 1600 hPa with three different electrode diameters (D = 2.1, 3.0 and 4.3 mm). Results from breakdown voltage measurements indicate that the pressure and electrode distance cannot be varied independently. Also limitations of the theoretical Paschen curves will be adressed. Effects of the scaling on the reduced normal current density, the reduced normal electric field in the positive column and discharge temperature will be discussed and limitations highlighted. Compared with these results the added complexity of HiPIMS plasmas will be described. Suggestions in the community how to obtain experimental finger prints of the plasmas will be reviewed and implications from the experiences with DC discharges on the development of similarity laws for HiPIMS plasmas will be discussed.

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Analytic model of the energy distribution function for highly energetic electrons in magnetron plasmas

Cited by 19 publications

References 23 publications

Triple probe interrogation of spokes in a HiPIMS discharge

Triple probe interrogation of spokes in a HiPIMS discharge

First measurements of the temporal evolution of the plasma density in HiPIMS discharges using THz time domain spectroscopy

Scaling and laws of DC discharges as pointers for HiPIMS plasmas

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