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Mechanisms for compositional variations of coatings sputtered from a WS2 target
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. (tunnfilmsgruppen)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
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2014 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 252, 186-190 p.Article in journal (Refereed) Published
Abstract [en]

Magnetron sputtering fromcompound targets is widely used for the deposition of compound films since it is easyto scale up and it exhibits a high reproducibility. Controlling film stoichiometry is crucial for obtaining filmswithdesired properties. However, the process is rather complex and sputtering from a compound target frequentlyresults in film compositions that deviate significantly from that of the target. This is due to a number of effectsrelated to the nature of the sputtering process which include preferential re-sputtering due to energetic particlebombardment at the substrate, different take-off angles, scattering in the gas phase, and different stickingcoefficients.

In this work, we have investigated how sputtering from aWS2 target results in different film compositions as afunction of the position in the chamber, for different processing conditions. Hence, the films have not been characterizedwith respect to structural or morphological properties. A Monte-Carlo based software, accounting fordifferent take-off angles and scattering in the gas phase, was developed to simulate the compositional variationsat various positions in the chamber. Further, a number of experimentswere performed by varying the target voltage,process pressure, as well as the location of the substrate (on and off axis). Simulations and experiments revealsignificant compositional variations for different processing conditions. Experiments show that thesevariations are only slightly affected by the target voltage, while the most significant variations result from theprocessing pressure and position on the chamber. From the qualitatively good agreement between experimentsand simulations it is clear that gas phase scattering must be taken into account to explain the observed compositionaltrends, while the other effects are less important and sticking coefficients effectsmay even be negligible.It is therefore concluded that themajor effect responsible for the compositional variation of the film is the differentscattering behaviour of S andWin the gas phase.

Place, publisher, year, edition, pages
2014. Vol. 252, 186-190 p.
Keyword [en]
Magnetron sputtering, gas phase scattering, deposition profile
National Category
Other Physics Topics Engineering and Technology
Research subject
Engineering Science with specialization in Electronics; Engineering Science with specialization in Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-229203DOI: 10.1016/j.surfcoat.2014.04.066ISI: 000338620100025OAI: oai:DiVA.org:uu-229203DiVA: diva2:736164
Funder
Swedish Foundation for Strategic Research
Available from: 2014-08-05 Created: 2014-08-05 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Sputtering and Characterization of Complex Multi-element Coatings
Open this publication in new window or tab >>Sputtering and Characterization of Complex Multi-element Coatings
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The thin film technology is of great importance in modern society and is a key technology in wide spread applications from electronics and solar cells to hard protective coatings on cutting tools and diffusion barriers in food packaging. This thesis deals with various aspects of thin film processing and the aim of the work is twofold; firstly, to obtain a fundamental understanding of the sputter deposition and the reactive sputter deposition processes, and secondly, to evaluate sputter deposition of specific material systems with low friction properties and to improve their performance.From studies of the reactive sputtering process, two new methods of eliminating the problematic and undesirable hysteresis effect were found. In the first method it was demonstrated that an increased process pressure caused a reduction and, in some cases, even elimination of the hysteresis. In the second method it was shown that sufficiently high oxide content in the target will eliminate the hysteresis.

Further studies of non-reactive magnetron sputtering of multi-element targets at different pressures resulted in huge pressure dependent compositional gradients over the chamber due to different gas phase scattering of the elements. This has been qualitatively known for a long time but the results presented here now enable a quantitative estimation of such effects. For example, by taking gas phase scattering into consideration during sputtering from a WS2 target it was possible to deposit WSx films with a sulphur content going from sub-stoichiometric to over-stoichiometric composition depending on the substrate position relative the target.

By alloying tungsten disulphide (WS2) with carbon and titanium (W-S-C-Ti) its hardness was significantly increased due to the formation of a new titanium carbide phase (TiCxSy). The best sample increased its hardness to 18 GPa (compared to 4 GPa for the corresponding W-S-C coating) while still maintaining a low friction (µ=0.02) due to the formation of easily sheared WS2 planes in the wear track. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 74 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1162
Keyword
thin film, coating, magnetron sputtering, modelling, tribofilm, tungsten disulphide
National Category
Other Physics Topics
Identifiers
urn:nbn:se:uu:diva-229207 (URN)978-91-554-8997-7 (ISBN)
Public defence
2014-09-26, Polhemsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research , 30003
Available from: 2014-09-02 Created: 2014-08-05 Last updated: 2014-09-08

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Särhammar, ErikSundberg, JillNyberg, HaraldKubart, TomasJacobson, StaffanJansson, UlfNyberg, Tomas

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