Localized heating of electrons in ionization zones: Going beyond the Penning-Thornton paradigm in magnetron sputtering

Anders, André

doi:10.1063/1.4904713

Cited by 56 publications

(39 citation statements)

References 34 publications

(40 reference statements)

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“…39. The measurements of potential distribution together with obtained electric field, space charge, and electron energization distributions presented in this work therefore provide a greater insight into the dynamics, sustainability, and mechanism of localized electron heating 46 in moving ionization zones. The choice of investigating the ionization zones in DCMS offers a great advantage as opposed to the investigating zones in HiPIMS.…”

Section: Discussionmentioning

confidence: 99%

“…In that sense, the here-described electron energization in a double layer is Ohmic heating. Following the prior work, 46 Ohmic heating appears to be highly localized involving electrons going to a higher potential, where the potential difference exceeds the ionization energy. Ohmic heating as viewed in this work thus includes two mechanisms: a collisionless mechanism where electrons gain energy from the potential jump (i.e., electric field of the double layer), and a collisional heating mechanism in which electrons gain energy via collisions when moving from lower to higher equipotential lines.…”

Section: -12mentioning

confidence: 99%

“…More recently, this global ionization region model was reevaluated in light of azimuthally non-uniform plasma, and it was suggested that an underlying physical mechanism for the electron heating is related to the potential structure of the ionization zone. 46 More specifically, it was suggested that electrons gain energy when crossing from the lowpotential side of the ionization zone to the high-potential side. These concepts have been so far supported by particle energy measurements 56 and by spectroscopically resolved snapshot-images of ionization zones.…”

Section: -12mentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 99%

Section: -12mentioning

confidence: 99%

Section: -12mentioning

confidence: 99%

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Plasma potential of a moving ionization zone in DC magnetron sputtering

Panjan

Anders

2017

Journal of Applied Physics

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“…presented a model that is based on the localised generation of secondary electrons [15]. The configuration of the electric field along the target's racetrack was first discussed by Brenning et al [16] and later modified by Anders et al [17,18]. In the latter publication it is argued that for a closed racetrack, the potential needs to be reproduced when returning to the same location.…”

Section: Introductionmentioning

confidence: 99%

Influence of ionisation zone motion in high power impulse magnetron sputtering on angular ion flux and NbO_xfilm growth

Franz

Clavero

Kolbeck

et al. 2016

Plasma Sources Sci. Technol.

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The ion energies and fluxes in the high power impulse magnetron sputtering plasma from a Nb target were analysed angularly resolved along the tangential direction of the racetrack. A reactive oxygen-containing atmosphere was used as such discharge conditions are typically employed for the synthesis of thin films. Asymmetries in the flux distribution of the recorded ions as well as their energies and charge states were noticed when varying the angle between mass-energy analyser and target surface. More positively charged ions with higher count rates in the medium energy range of their distributions were detected in +E × B than in −E × B direction, thus confirming the notion that ionisation zones (also known as spokes or plasma bunches) are associated with moving potential humps. The motion of the recorded negatively charged high-energy oxygen ions was unaffected. NbO x thin films at different angles and positions were synthesised and analysed as to their structure and properties in order to correlate the observed plasma properties to the film growth conditions. The chemical composition and the film thickness varied with changing deposition angle, where the latter, similar to the ion fluxes, was higher in +E × B than in −E × B direction.

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“…The predictive power of equation 1 is, however, limited since any change of the plasma is affecting all parameters simultaneously. A more recent modification of equation 1 has been proposed by Anders [13] on the basis of Ohmic heating in the magnetic presheath of the HiPIMS plasma, as proposed by Huo et al [14], who found a very good agreement between measured currents and a global model of the plasma. The connection between current and voltage is usually expressed in the form of a power law with the current I proportional to the voltage V as I ∝ V n .…”

Section: Introductionmentioning

confidence: 99%

Control of High Power Pulsed Magnetron Discharge by Monitoring the Current Voltage Characteristics

Keudell

Hecimovic

Maszl

2016

Contrib. Plasma Phys.

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Key words High power pulsed magentron sputtering, plasma control.Discharge current voltage (IV) curves are directly measured at the target of a high impulse power magnetron sputtering (HiPIMS) plasma for the target materials aluminium, chromium, titanium and copper. These discharge IV curves have been correlated with ICCD camera images of the plasma torus. A clear connection between the change in the discharge IV curve slopes at specific currents and the appearance of localized ionization zones, so-called spokes, in a HiPIMS plasma is identified. These spokes appear above typical target current densities of 2 A/cm 2 . The slope of the discharge IV curves, at current densities when spokes are formed, depends on the mass of the target atoms with a higher plasma conductivity for higher mass target materials. This is explained by the momentum transfer from the sputter wind to the argon background gas, which leads to higher plasma densities for heavier target materials. The change in the VI curve slope can be used to identify the spokes regime for HiPIMS plasmas, as being mandatory for deposition of good quality materials by HiPIMS. Consequently, the discharge IV curve slope monitoring can be regarded an essential control approach of any industrial HiPIMS process, where discharge IV curves are much easier accessible compared to more complex diagnostics such as time and space resolved ICCD camera measurements.

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Localized heating of electrons in ionization zones: Going beyond the Penning-Thornton paradigm in magnetron sputtering

Cited by 56 publications

References 34 publications

Plasma potential of a moving ionization zone in DC magnetron sputtering

Plasma potential of a moving ionization zone in DC magnetron sputtering

Influence of ionisation zone motion in high power impulse magnetron sputtering on angular ion flux and NbO_xfilm growth

Control of High Power Pulsed Magnetron Discharge by Monitoring the Current Voltage Characteristics

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Localized heating of electrons in ionization zones: Going beyond the Penning-Thornton paradigm in magnetron sputtering

Cited by 56 publications

References 34 publications

Plasma potential of a moving ionization zone in DC magnetron sputtering

Plasma potential of a moving ionization zone in DC magnetron sputtering

Influence of ionisation zone motion in high power impulse magnetron sputtering on angular ion flux and NbOxfilm growth

Control of High Power Pulsed Magnetron Discharge by Monitoring the Current Voltage Characteristics

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Product

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Influence of ionisation zone motion in high power impulse magnetron sputtering on angular ion flux and NbO_xfilm growth