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Reactive High Power Impulse Magnetron Sputtering of Metal Oxides
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The work presented in this thesis deals with reactive magnetron sputtering processes of metal oxides with a prime focus on high power impulse magnetron sputtering (HiPIMS). The aim of the research is to contribute towards understanding of the fundamental mechanisms governing a reactive HiPIMS process and to investigate their implications on the film growth.

The stabilization of the HiPIMS process at the transition zone between the metal and compound modes of Al-O and Ce-O was investigated for realizing the film deposition with improved properties and higher depositionrate and the results are compared with direct current magnetron sputtering (DCMS) processes. The investigations were made for different sputtering conditions obtained by varying pulse frequency, peak power and pumping speed. For the experimental conditions employed, it was found that reactive HiPIMS can eliminate/suppress the hysteresis effect for a range of frequency, leading to a stable deposition process with a high deposition rate. The hysteresis was found to be eliminated for Al-O while for Ce-O, it was not eliminated but suppressed as compared to the DCMS. The behavior of elimination/suppression of the hysteresis may be influenced by high erosion rate during the pulse, limited target oxidation between the pulses and gas rarefaction effects in front of the target. Similar investigations were made for Ti-O employing a larger target and the hysteresis was found to be suppressed as compared to the respective DCMS, but not eliminated. It was shown that the effect of gas rarefaction is a powerful mechanism for preventing oxide formation upon the target surface. The impact of this effect depends on the off-time between the pulses. Longer off-times reduce the influence of gas rarefaction.

To gain a better understanding of the discharge current-voltage behavior in a reactive HiPIMS process of metal oxides, the ion compositions and ion energy distributions were measured for Al-O and Ti-O using time averaged and time-resolved mass spectrometry. It was shown that the different discharge current behavior between non-reactive and reactive modes couldn’t be explained solely by the change in the secondary electron emission yield from the sputtering target. The high fluxes of O1+ ions contribute substantially to the discharge current giving rise to an increase in the discharge current in the oxide mode as compared to the metal mode. The results also show that the source of oxygen in the discharge is both, the target surface (via sputtering) as well as the gas phase.

The investigations on the properties of HiPIMS grown films were made by synthesizing metal oxide thin films using Al-O, Ti-O and Ag-Cu-O. It was shown that Al2O3 films grown under optimum condition using reactive HiPIMS exhibit superior properties as compared to DCMS. The HiPIMS grown films exhibit higher refractive index as well as the deposition rate of the film growth was higher under the same operating conditions. The effect of HiPIMS peak power on TiO2 film properties was investigated and the results are compared with the DCMS. The properties of TiO2 films such as refractive index, film density and phase structure were experimentally determined. The ion composition during film growth was investigated and an explanation on the correlation of the film properties and ion energy was made. It was found that energetic and ionized sputtered flux in reactive HiPIMS can be used to tailor the phase formation of the TiO2 films with high peak powers facilitating the rutile phase while the anatase phase can be obtained using low peak powers. These phases can be obtained at room temperature without external substrate heating or post-deposition annealing which is in contrast to the reactive DCMS where both, anatase and rutile phases of TiO2 are obtained at either elevated growth temperatures or by employing post deposition annealing. The effect of HiPIMS peak power on the crystal structure of the grown films was also investigated for ternary compound, Ag-Cu-O, for which films were synthesized using reactive HiPIMS as well as reactive DCMS. It was found that the stoichiometric Ag2Cu2O3 can be synthesized by all examined pulsing peak powers. The oxygen gas flow rate required to form stoichiometric films is proportional to the pulsing peak power in HiPIMS. DCMS required low oxygen gas flow to synthesis the stoichiometric films. The HiPIMS grown films exhibit more pronounced crystalline structure as compared to the films grown using DCMS. This is likely an effect of highly ionized depositing flux which facilitates an intense ion bombardment during the film growth using HiPIMS. Our results indicate that Ag2Cu2O3film formation is very sensitive to the ion bombardment on the substrate as well as to the backattraction of metal and oxygen ions to the target.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. , 51 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1519
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-91259ISBN: 978-91-7519-622-0 (print)OAI: oai:DiVA.org:liu-91259DiVA: diva2:616688
Public defence
2013-05-17, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2013-04-18 Created: 2013-04-18 Last updated: 2013-10-30Bibliographically approved
List of papers
1. Hysteresis and process stability in reactive high power impulse magnetron sputtering of metal oxides
Open this publication in new window or tab >>Hysteresis and process stability in reactive high power impulse magnetron sputtering of metal oxides
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2011 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 22, 7779-7784 p.Article in journal (Refereed) Published
Abstract [en]

In the further development of reactive sputter deposition, strategies which allow for stabilization of the transition zone between the metallic and compound modes, elimination of the process hysteresis, and increase of the deposition rate, are of particular interest. In this study, the hysteresis behavior and the characteristics of the transition zone during reactive high power impulse magnetron sputtering (HiPIMS) of Al and Ce targets in an Ar-O(2) atmosphere as a function of the pulsing frequency and the pumping speed are investigated. Comparison with reactive direct current magnetron sputtering (DCMS) reveals that HiPIMS allows for elimination/suppression of the hysteresis and a smoother transition from the metallic to the compound sputtering mode. For the experimental conditions employed in the present study, optimum behavior with respect to the hysteresis width is obtained at frequency values between 2 and 4 kHz, while HiPIMS processes with values below or above this range resemble the DCMS behavior. Al-O films are deposited using both HiPIMS and DCMS. Analysis of the film properties shows that elimination/suppression of the hysteresis in HiPIMS facilitates the growth of stoichiometric and transparent Al(2)O(3) at relatively high deposition rates over a wider range of experimental conditions as compared to DCMS.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
Reactive sputtering, High power impulse magnetron sputtering, Aluminum oxide, Cerium oxide, Hysteresis, Process stability
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-71797 (URN)10.1016/j.tsf.2011.06.021 (DOI)000295057000027 ()
Note

Funding Agencies|Swedish Research Council (VR)|621-2008-3222|Strategic Research Center in Materials Science for Nanoscale Surface Engineering (MS2E)||Ministry of Science and Technology, Thailand||VR|623-2009-7348|

Available from: 2011-11-04 Created: 2011-11-04 Last updated: 2017-12-08
2. Studies of hysteresis effect in reactive HiPIMS deposition of oxides
Open this publication in new window or tab >>Studies of hysteresis effect in reactive HiPIMS deposition of oxides
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2011 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 205, S303-S306 p.Article in journal (Refereed) Published
Abstract [en]

igh power impulse magnetron sputtering (HiPIMS) has proven to be capable of substantial improvement of the quality of deposited coatings. Lately, there have been a number of reports indicating that the hysteresis effect may be reduced in HiPIMS mode resulting in an increase of the deposition rate of stoichiometric compound as compared to a direct current magnetron sputtering process in oxide mode. In this contribution, we have studied the hysteresis behaviour of Ti metal targets sputtered in Ar + O(2) mixtures. For fixed pulse on time and a constant average power, there is an optimum frequency minimizing the hysteresis. The effect of gas dynamics was analyzed by measurements of the gas refill time and rarefaction. Results indicate that the gas rarefaction may be responsible for the observed hysteresis behaviour. The results are in agreement with a previous study of Al oxide reactive process.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2011
Keyword
Magnetron sputtering, Reactive sputtering, HiPIMS, Hysteresis, Oxides deposition
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-69986 (URN)10.1016/j.surfcoat.2011.01.019 (DOI)000293258600065 ()
Available from: 2011-08-12 Created: 2011-08-12 Last updated: 2017-12-08
3. Understanding the discharge current behavior in reactive high power impulse magnetron sputtering of oxides
Open this publication in new window or tab >>Understanding the discharge current behavior in reactive high power impulse magnetron sputtering of oxides
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2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 13Article in journal (Refereed) Published
Abstract [en]

The discharge current behavior in reactive high power impulse magnetron sputtering (HiPIMS) of Ti-O and Al-O is investigated. It is found that for both metals, the discharge peak current significantly increases in the oxide mode in contrast to the behavior in reactive direct current magnetron sputtering where the discharge current increases for Al but decreases for Ti when oxygen is introduced. In order to investigate the increase in the discharge current in HiPIMS-mode, the ionic contribution of the discharge in the oxide and metal mode is measured using time-resolved mass spectrometry. The energy distributions and time evolution are investigated during the pulse-on time as well as in the post-discharge. In the oxide mode, the discharge is dominated by ionized oxygen, which has been preferentially sputtered from the target surface. The ionized oxygen determines the discharge behavior in reactive HiPIMS.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2013
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-91256 (URN)10.1063/1.4799199 (DOI)000317238000006 ()
Available from: 2013-04-18 Created: 2013-04-18 Last updated: 2017-12-06
4. Effect of peak power in reactive high power impulse magnetron sputtering of titanium dioxide
Open this publication in new window or tab >>Effect of peak power in reactive high power impulse magnetron sputtering of titanium dioxide
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2011 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 205, no 20, 4828-4831 p.Article in journal (Refereed) Published
Abstract [en]

The effect of peak power in a high power impulse magnetron sputtering (HiPIMS) reactive deposition of TiO(2) films has been studied with respect to the deposition rate and coating properties. With increasing peak power not only the ionization of the sputtered material increases but also their energy. In order to correlate the variation in the ion energy distributions with the film properties, the phase composition, density and optical properties of the films grown with different HiPIMS-parameters have been investigated and compared to a film grown using direct current magnetron sputtering (DCMS). All experiments were performed for constant average power and pulse on time (100W and 35 mu s, respectively), different peak powers were achieved by varying the frequency of pulsing. Ion energy distributions for Ti and O and its dependence on the process conditions have been studied. It was found that films with the highest density and highest refractive index were grown under moderate HiPIMS conditions (moderate peak powers) resulting in only a small loss in mass-deposition rate compared to DCMS. It was further found that TiO2 films with anatase and rutile phases can be grown at room temperature without substrate heating and without post-deposition annealing.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2011
Keyword
HiPIMS; Titanium dioxide; Rutile; Anatase; Reactive sputtering; TiO(2)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-69795 (URN)10.1016/j.surfcoat.2011.04.071 (DOI)000292361400013 ()
Note

Original Publication: Montri Aiempanakit, Ulf Helmersson, Asim Aijaz, Petter Larsson, Roger Magnusson, Jens Jensen and Tomas Kubart, Effect of peak power in reactive high power impulse magnetron sputtering of titanium dioxide, 2011, Surface & Coatings Technology, (205), 20, 4828-4831. http://dx.doi.org/10.1016/j.surfcoat.2011.04.071 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/

Available from: 2011-08-10 Created: 2011-08-08 Last updated: 2017-12-08
5. Ag2Cu2O3 thin films deposited by reactive high power impulse magnetron sputtering
Open this publication in new window or tab >>Ag2Cu2O3 thin films deposited by reactive high power impulse magnetron sputtering
2013 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Ag2Cu2O3 thin films were prepared by reactive high power impulse magnetron sputtering (HiPIMS) from an alloy silver-copper (Ag0.5Cu0.5) target on silicon and glass substrates. The effects of the oxygen gas flow and the peak power on the structural properties of the films were investigated. Structural characterization by grazing incidence X-ray diffraction measurements show that the structure of Ag2Cu2O3 is related to the oxygen flow and the peak power. Films grown with high peak power required higher oxygen flow rate in order to get stoichiometric Ag2Cu2O3 thin films. It was further found that using HiPIMS, polycrystalline Ag2Cu2O3 films can be grown at room temperature without substrate heating or post-deposition annealing, while films deposited by DCMS exhibit poor crystallinity under the same process conditions.

Keyword
Silver-copper oxide, HiPIMS, Reactive sputtering, film structure
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-91258 (URN)
Available from: 2013-04-18 Created: 2013-04-18 Last updated: 2013-10-30Bibliographically approved

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