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On the film density using high power impulse magnetron sputtering
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Royal Institute of Technology.
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2010 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 205, no 2, 591-596 p.Article in journal (Refereed) Published
Abstract [en]

The influence on thin film density using high power impulse magnetron sputtering (HIPIMS) has been investigated for eight different target materials (Al, Ti, Cr. Cu, Zr, Ag, Ta, and Pt). The density values as well as deposition rates have been compared to results obtained from thin films grown by direct current magnetron sputtering (DCMS) under the same experimental conditions. Overall, it was found that the HIPIMS deposited coatings were approximately 5-15% denser compared to the DCMS deposited coatings This could be attributed to the increased metal ion bombardment commonly seen in HIPIMS discharges, which also was verified using a global plasma model to assess the degree of ionization of sputtered metal One key feature is that the momentum transfer between the growing film and the incoming metal ions is very efficient due to the equal mass of film and bombarding species, leading to a less pronounced columnar microstructure As expected the deposition rates were found to be lower for HiPIMS compared to DCMS For several materials this decrease is not as pronounced as previously reported in the literature, which is shown in the case of Ta. Pt, and Ag with rate(HIPIMS)/rate(DCMS)-70-85%. while still achieving denser coatings

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam. , 2010. Vol. 205, no 2, 591-596 p.
Keyword [en]
HIPIMS, HPPMS, DCMS, Density, RBS, Global plasma model
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-60690DOI: 10.1016/j.surfcoat.2010.07.041ISI: 000282542300053OAI: oai:DiVA.org:liu-60690DiVA: diva2:359877
Available from: 2010-11-01 Created: 2010-10-22 Last updated: 2017-12-12Bibliographically approved
In thesis
1. High power impulse magnetron sputtering under industrial conditions
Open this publication in new window or tab >>High power impulse magnetron sputtering under industrial conditions
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, the recent development step of magnetron sputtering, termed high power impulse magnetron sputtering (HiPIMS) has been studied. Compared to conventional magnetron sputtering HiPIMS provides a higher plasma density which can ionise the sputtered material. The beneficial influence of the coating properties due to this ionisation has been extensively shown in academic publications. Here, industrial conditions, i.e. no substrate heating and high vacuum conditions have been used during the studies, of which one was performed in an industrial deposition system.

For eight metallic targets, films were deposited with HiPIMS and conventional sputtering. The films were evaluated by Rutherford back scattering analysis, scanning electron microscopy, and profilometry. It was found that the density of the HiPIMS grown films exhibited a statistically significant higher density of approximately 5-15% in comparison to films deposited using DCMS under identical conditions. A global plasma model was employed to evaluate the degree of ionisation for some of the target materials, and process conditions used in the study. Conformity between density increase and degree of ionisation as assessed by the plasma model was confirmed.

The influence of using HiPIMS during reactive sputtering of TiC was also studied. A metallic Ti target was sputtered in a gas mixture of Ar and C2H2. The coatings were evaluated by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, 4 point probe resistivity measurements, and nanoindentation. The coatings were found to be nanocomposite TiC/a-C:H. For the HiPIMS process the transition zone between metallic and compound target states was found to be significantly expanded over a wide reactive gas flow range. The implications of choice of deposition method for coating composition, chemical structure, as well as electrical and mechanical properties were evaluated for DCMS and HiPIMS. The process behaviour was suggested to be due to the pulsed nature of the HiPIMS, the high plasma density, and ion content of the particles reaching the substrate.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2011. 45 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1477
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-67487 (URN)LIU-TEK-LIC-2011:16 (Local ID)978-91-7393-194-6 (ISBN)LIU-TEK-LIC-2011:16 (Archive number)LIU-TEK-LIC-2011:16 (OAI)
Presentation
2011-05-17, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:00 (English)
Opponent
Supervisors
Available from: 2011-04-14 Created: 2011-04-14 Last updated: 2013-10-30Bibliographically approved
2. The HiPIMS Process
Open this publication in new window or tab >>The HiPIMS Process
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The work presented in this thesis involves experimental and theoretical studies related to a thin film deposition technique called high power impulse magnetron sputtering (HiPIMS), and more specifically the plasma properties and how they influence the coating. HiPIMS is an ionized physical vapor deposition technique based on conventional direct current magnetron sputtering (DCMS). The major difference between the two methods is that HiPIMS has the added advantage of providing substantial ionization of the sputtered material, and thus presents many new opportunities for the coating industry. Understanding the dynamics of the charged species and their effect on thin film growth in the HiPIMS process is therefore essential for producing high-quality coatings.

In the first part of the thesis 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, resulting in electric field oscillations in the MHz-range (the lower hybrid frequency). Measurements in the plasma confirmed these oscillations as well as trends predicted by the theory of these types of waves. Using electric probes, 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 were verified in another series of measurements using Rogowski probes to directly gain insight into the internal currents in the HiPIMS discharge. The results provided important insights into understanding the mechanism behind the anomalous transport.

It was furthermore demonstrated that the current ratio Jϕ / JD is inversely proportional to the transverse resistivity, η , which governs how well momentum in the direction of the current 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 that the ions were transported across the magnetic field lines and to a larger extent deflected sideways, instead of solely moving from the target region towards a substrate placed in front of the target some distance away. From the experiments it was confirmed that a substantial fraction of sputtered material is transported radially away from the cathode and lost to the walls in HiPIMS as well as in DCMS, but more so for HiPIMS giving one possible explanation to why the deposition rate is lower for HiPIMS compared to DCMS. Moreover, in a separate investigation on the energy flux it could be determined that the heating due to radial energy flux reached as much as 60 % of the axial energy flux, which is likely a result of the anomalous transport of charged species present in the HiPIMS discharge. Also, the recorded ion energy flux confirmed theoretical estimations on this type of transport regarding energy and direction.In order to gain a better understanding of the complete discharge regime, as well as providing a link between the HiPIMS and DCMS processes, the current and voltage characteristics were investigated for discharge pulses longer than 100 μs. The current behavior was found to be strongly correlated with the chamber gas pressure. Based on these experiments it was suggested that high-current transients commonly seen in the HiPIMS process cause a depletion of the working gas in the area in front of the target, and thereby a transition to a DCMS-like high voltage, lower current regime, which alters the deposition conditions.

In the second part of the thesis, using the results and ideas from the fundamental plasma investigations, it was possible to successfully implement different coating improvements. First, the concept of sideways deposition of thin films was examined in a dual-magnetron system providing a solution for coating complex shaped surfaces. Here, the two magnetrons were facing each other having opposing magnetic fields forcing electrons, and thereby also ionized material to be transported radially towards the substrate. In this way deposition inside tubular substrates can be made in a beneficial way.

Last, the densification process of thin films using HiPIMS was investigated for eight different materials (Al, Ti, Cr, Cu, Zr, Ag, Ta, and Pt). Through careful characterization of the thin film properties it was determined that the HiPIMS coatings were approximately 5-15 % denser compared to the DCMS coatings. This could be attributed to the increased ion bombardment seen in the HiPIMS process, where the momentum transfer between the growing film and the incoming ions is very efficient due to the equal mass of the atoms constituting the film and the bombarding species, leading to a less pronounced columnar microstructure. The deposition conditions were also examined using a global plasma model, which was in good agreement with the experimental results.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2010. 72 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1305
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-56748 (URN)978-91-7393-419-0 (ISBN)
Public defence
2010-05-27, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2010-06-02 Created: 2010-06-02 Last updated: 2013-10-30Bibliographically approved
3. Fundamental aspects of HiPIMS under industrial conditions
Open this publication in new window or tab >>Fundamental aspects of HiPIMS under industrial conditions
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fundamental aspects of the high power impulse magnetron sputtering (HiPIMS) process and its implication for film growth under industrial conditions have been studied. The emerging HiPIMS technique exhibits a higher plasma density and an enhanced degree of ionisation of sputtered material as compared to conventional direct current magnetron sputtering (DCMS). The increased ionisation permits control of the deposition flux and facilitates an intense ion bombardment of the growing films. The latter allows for growth of well adherent, smooth, and dense thin films. Moreover, the technique offers increased stability of reactive processes, control of film phase constitution as well as tailoring of e.g. optical and mechanical properties.

In the present work, it was shown, for eight different metals (Al, Ti, Cr, Cu, Zr, Ag, Ta, and Pt), that films grown using HiPIMS exhibit a 5-15% higher density than films grown using DCMS under otherwise identical conditions. Through simulations of the fundamental ionisation processes in the plasma discharge, a correlation between high ionisation degree and film densification was established. The densification was suggested to be a consequence of increased ion irradiation of the growing films in the HiPIMS case. This knowledge was used to investigate the degree of ionisation in the deposition flux required for film modifications. Using a hybrid process, where DCMS and HiPIMS were combined on a single Cr cathode, independent control of the degree of ionisation from other experimental parameters was achieved. The results showed that the majority of the ion irradiation induced modifications of surface related film properties occurred when ~40% of the total average power was supplied by the HiPIMS generator. Under such conditions, the power normalised deposition rate was found to be ~80% of that of DCMS. This was attributed to a reduction in back-attracted ionised sputtered material, which is considered to be the main reason for the low deposition rate of HiPIMS. Thus, enhanced film properties were attainable largely without sacrificing deposition rate.

Compound carbide and boride films were synthesised using both reactive processes and compound sources. Reactive deposition of TiC/a-C:H thin films using C2H2 as reactive gas, i.e. carbon source, was demonstrated. It was found that the high plasma density processes (i.e. HiPIMS) facilitated growth conditions for the film structure formation closer to thermodynamic equilibrium than did processes exhibiting lower plasma densities (i.e. DCMS). This was manifested in a high stoichiometry of the carbide phase, whilst excess a-C was removed by physical sputtering. Moreover, the feasibility of using HiPIMS for thin film growth from a compound source, obtaining the same composition in the films as the sputtering source, was demonstrated through synthesis of ZrB2 films.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 52 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1461
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-79306 (URN)978-91-7519-856-9 (ISBN)
Public defence
2012-08-16, Planck, Fysikhuset, Campus Valla, Linköpings univeristet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2012-07-09 Created: 2012-07-09 Last updated: 2013-10-30Bibliographically approved

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Samuelsson, MattiasLundin, DanielJensen, JensHelmersson, Ulf

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