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Plasma properties in high power impulse magnetron sputtering
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
2008 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The work presented in this thesis involves experimental and theoretical studies related to plasma properties in high power impulse magnetron sputtering (HiPIMS), and more specifically plasma transport. HiPIMS is an ionized PVD method based on conventional direct current magnetron sputtering (dcMS). In dcMS very little of the sputtered material is ionized since the plasma power density is not high enough. This is not the case for HiPIMS, where a substantial part is ionized, and thus presents many new opportunities for thin film growth. Understanding the dynamics of the charged species in the HiPIMS discharge is therefore of essential value when producing high-quality thin film coatings.

In the first part of the work a new type of anomalous electron transport was found. Investigations of the transport resulted in the discovery that this phenomenon could quantitatively be described as being related and mediated by highly nonlinear waves, likely due to the modified two-stream instability (MTSI), resulting in electric field oscillations in the MHz-range (the so-called lower hybrid frequency). Measurements in the plasma confirmed these oscillations as well as trends predicted by the theory of these types of waves. The degree of anomalous transport in the plasma could also be determined by measuring the current density ratio between the azimuthal current density (of which the Hall current density is one contribution) and the discharge current density, Jφ / JD. The results provided important insights into understanding the mechanism behind the anomalous transport.

It was furthermore found that the current ratio Jφ / JD is inversely proportional to the transverse resistivity, eta_perpendicular , which governs how well momentum is transferred from the electrons to the ions in the plasma. By looking at the forces involved in the charged particle transport it was expected that the azimuthally rotating electrons would exert a volume force on the ions tangentially outwards from the circular race track region. The effect of having an anomalous transport would therefore be a large fraction of highly energetic ions being transported sideways and lost to the walls. In a series of experiments, deposition rates as well as incoming ion energy distributions were measured directly at the side of the magnetron. It was found that a substantial fraction of sputtered material is transported radially away from the cathode and lost to the walls in HiPIMS as well as dcMS, but more so for HiPIMS giving one possible explanation to why the deposition rate for substrates placed in front of the target is lower for HiPIMS compared to dcMS. Furthermore, the recorded, incoming ion energy distributions confirmed theoretical estimations on this type of transport regarding energy and direction.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi , 2008. , 46 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1358
Keyword [en]
HiPIMS, HPPMS, plasma, plasma transport, plasma instabilities
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:liu:diva-11621ISBN: 978-91-7393-932-4 (print)OAI: oai:DiVA.org:liu-11621DiVA: diva2:18040
Presentation
2008-05-15, Planck, Fysikhuset, Campus Valla, Linköping university, Linköping, 00:00 (English)
Opponent
Supervisors
Available from: 2008-04-28 Created: 2008-04-28 Last updated: 2013-10-30
List of papers
1. Anomalous electron transport in high power impulse magnetron sputtering
Open this publication in new window or tab >>Anomalous electron transport in high power impulse magnetron sputtering
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2008 (English)In: Plasma Sources Science and Technology, ISSN 0963-0252, Vol. 17, no 2, 025007- p.Article in journal (Refereed) Published
Abstract [en]

Oscillating electric fields in the megahertz range have been studied in a high power impulse magnetron sputtering (HIPIMS) plasma with the use of electric field probe arrays. One possible reason for these oscillations to occur is charge perturbation—or so-called modified two-stream instabilities (MTSIs). It is known that MTSIs give rise to acceleration of the charged plasma species and can give a net transport of electrons across the magnetic field lines. Measurements of these oscillations confirm trends, specifically of the frequency dependence on ion mass and magnetic field strength as expected from the theory of MTSI waves. These results help to explain the previously reported anomalous fast electron transport in HIPIMS discharges, where classical theory of diffusion using collisions to transport electrons has failed.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13208 (URN)10.1088/0963-0252/17/2/025007 (DOI)
Note
Original Publication: Daniel Lundin, Ulf Helmersson, Scott Kirkpatrick, Suzanne Rohde and Nils Brenning, Anomalous electron transport in high power impulse magnetron sputtering, 2008, Plasma Sources Science and Technology, (17), 2, 025007. http://dx.doi.org/10.1088/0963-0252/17/2/025007 Copyright: IOP Publishing http://www.iop.org/ Available from: 2009-02-22 Created: 2009-02-17 Last updated: 2013-10-30Bibliographically approved
2. Cross-field ion transport during high power impulse magnetron sputtering
Open this publication in new window or tab >>Cross-field ion transport during high power impulse magnetron sputtering
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2008 (English)In: Plasma Sources Science and Technology, ISSN 0963-0252, Vol. 17, no 035021Article in journal (Refereed) Published
Abstract [en]

In this study, the effect on thin film growth due to an anomalous electron transport, found in high power impulse magnetron sputtering (HiPIMS), has been investigated for the case of a planar circular magnetron. An important consequence of this type of transport is that it affects the way ions are being transported in the plasma. It was found that a significant fraction of ions are transported radially outwards in the vicinity of the cathode, across the magnetic field lines, leading to increased deposition rates directly at the side of the cathode (perpendicular to the target surface). Furthermore, this mass transport parallel to the target surface leads to that the fraction of sputtered material reaching a substrate placed directly in front of the target is substantially lower in HiPIMS compared with conventional direct current magnetron sputtering (dcMS). This would help to explain the lower deposition rates generally observed for HiPIMS compared with dcMS. Moreover, time-averaged mass spectrometry measurements of the energy distribution of the cross-field transported ions were carried out. The measured distributions show a direction-dependent high-energy tail, in agreement with predictions of the anomalous transport mechanism.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13209 (URN)10.1088/0963-0252/17/3/035021 (DOI)
Note
Original Publication: Daniel Lundin, Petter Larsson, Erik Wallin, Martina Lattemann, Nils Brenning and Ulf Helmersson, Cross-field ion transport during high power impulse magnetron sputtering, 2008, Plasma Sources Science and Technology, (17), 035021. http://dx.doi.org/10.1088/0963-0252/17/3/035021 Copyright: Iop Publishing http://www.iop.org/ Available from: 2009-02-26 Created: 2009-02-26 Last updated: 2013-10-30Bibliographically approved

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