Spoke-resolved electron density, temperature and potential in direct current magnetron sputtering and HiPIMS discharges

  • Spokes are long wavelength oscillations observed in the magnetized region of direct current magnetron sputtering (DCMS), high power impulse magnetron sputtering (HiPIMS), as well as other \(\vec{E} \times \vec{B}\) discharges. Spokes rotate in front of the cathode with velocities between about 2 km s\(^{−1}\) and 15 km s\(^{−1}\), making it difficult to perform quantitative measurements. This is overcome by synchronizing Langmuir probe measurements to the movement of spokes in DCMS to obtain the probe current–voltage (\(\it I–V\)) characteristic without averaging out the spoke influence. The \(\it I–V\) curves are then evaluated using magnetized probe theory, revealing the strong plasma parameter modulations, caused by the spokes. The plasma density was found to oscillate between 2.5 × 10\(^{16}\) m\(^{-3}\) and 1.7 × 10\(^{17}\) m\(^{-3}\), which corresponds to a modulation strength of more than 70% or an almost seven times increase of density. In good agreement with previous work, a plasma potential minimum of −55 V is found ahead of the spoke followed by a sudden increase to about 2 V inside the spoke. The electron temperature was found to oscillate between 3 eV and 7 eV. On top of that oscillation, electrons experience a sudden energy increase as they move inside the spoke, crossing the potential jump at the leading edge for the spoke. On basis of these observations a model is presented to explain spokes in DCMS. These results are then compared to HiPIMS spokes under otherwise similar conditions. The plasma parameter modulation found for HiPIMS is much weaker than for DCMS, which is explained by the higher collision frequency for electrons in HiPIMS plasmas.

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Author:Julian HeldORCiDGND, Mathews GeorgeGND, Achim von KeudellORCiDGND
Parent Title (English):Plasma sources science and technology
Publisher:IOP Publishing
Place of publication:Bristol, Vereinigtes Königreich
Document Type:Article
Date of Publication (online):2024/02/02
Date of first Publication:2022/09/07
Publishing Institution:Ruhr-Universität Bochum, Universitätsbibliothek
Tag:DCMS; EEDF; Langmuir probe; ionization zones; magnetron sputtering; spokes
Issue:8, Artikel 085013
First Page:085013-1
Last Page:085013-12
Institutes/Facilities:Institut für Experimentalphysik II
Dewey Decimal Classification:Naturwissenschaften und Mathematik / Physik
open_access (DINI-Set):open_access
faculties:Fakultät für Physik und Astronomie
Licence (English):License LogoCreative Commons - CC BY 4.0 - Attribution 4.0 International