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Synthesis of Carbon-based and Metal-Oxide Thin Films using High Power Impulse Magnetron Sputtering
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0001-9126-6004
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The work presented in this thesis deals with synthesis of carbon-based as well as metal-oxide thin films using highly ionized plasmas. The principal deposition method employed was high power impulse magnetron sputtering (HiPIMS). The investigations on plasma chemistry, plasma energetics, plasma-film interactions and its correlation to film growth and resulting film properties were made. The thesis is divided into two parts: (i) HiPIMS-based deposition of carbon-based thin films and (ii) HiPIMS-based deposition of metal-oxide thin films.

In the first part of the thesis, HiPIMS based strategies are presented that were developed to address the fundamental issues of low degree of carbon ionization and low deposition rates of carbon film growth in magnetron sputtering. In the first study, a new strategy was introduced for increasing the degree of ionization of sputtered carbon via increasing the electron temperature in the discharge by using a higher ionization potential buffer gas (Ne) in place of commonly used Ar. A direct consequence of enhanced electron temperatures was observed in the form of measured large fluxes of ionized carbon at the substrate position. Consequently, high mass densities of the resulting amorphous carbon (a-C) thin films reaching 2.8 g/cm3 were obtained.

In another study, feasibility of HiPIMS-based high density discharges for high-rate synthesis of dense and hard a-C thin films was explored. A strategy was compiled and implemented that entailed coupling a hydrocarbon precursor gas (C2H2) with high density discharges generated by the superposition of HiPIMS and direct current magnetron sputtering (DCMS). Appropriate control of discharge density (by tuning HiPIMS/DCMS power ratio), gas phase composition and energy of the ionized depositing species lead to a route capable of providing ten-fold increase in the deposition rate of a-C film growth compared to that obtained using HiPIMS Ar discharge in the first study. The increased deposition rate was achieved without significant incorporation of H (<10 %) and with relatively high hardness (>25 GPa) and mass density (~2.32 g/cm3). The knowledge gained in this work was utilized in a subsequent work where the feasibility of adding high ionization potential buffer gas (Ne) to increase the electron temperature in an Ar/C2H2 HiPIMS discharge was explored. It was found that the increased electron temperature lead to enhanced dissociation of hydrocarbon precursor and an increased H incorporation into the growing film. The resulting a-C thin films exhibited high hardness (~ 25 GPa), mass densities in the order of 2.2 g/cm3 and H content as low as about 11%. The striking feature of the resulting films was low stress levels where the films exhibited compressive stresses in the order of 100 MPa.

In the second part of the thesis, investigations on reactive HiPIMS discharge characteristics were made for technologically relevant metal-oxide systems. In the first study, the discharge characteristics of Ti-O and Al-O were investigated by studying the discharge current characteristics and measuring the ion flux composition. Both, Ti-O and Al-O discharges were dominated by large fluxes of ionized metallic as well as sputtering and reactive gases species. The generation of large ionized fluxes influenced the discharge characteristics consequently surpassing the changes in the secondary electron emission yields which, in the case of DCMS discharges entail contrasting behavior of the discharge voltage for the two material systems. The study also suggested that the source of oxygen ions in the case of reactive HiPIMS is both, the target surface (via sputtering) as well as gas phase.

In a subsequent study, the knowledge gained from the studies on metal-oxide HiPIMS discharges was utilized for investigating the behavior of reactive HiPIMS discharges related to ternary compound thin film growth. In this work Al-Si-O system, which is a promising candidate for anti-reflective and solar thermal applications, was employed to carry out the investigations under varied target compositions (Al, Al0.5Si0.5, and Al0.1Si0.9). It was found that the discharge current behavior of metal and oxide modes of Al-Si-O HiPIMS discharges were similar to those of Al-O and were independent of the target composition. The influence of energy and composition of the ionized depositing fluxes on the film growth was also investigated. It was shown that stoichiometric Al-Si-O thin films exhibiting a refractive index below 1.6 (which is desired for anti-reflective applications) can be grown. Furthermore, the refractive index and chemical composition of the resulting films were found to be unchanged with respect to the energy of the depositing species.

The effect of ionized deposition fluxes that are generated in metal-oxide HiPIMS discharges was also investigated for the phase composition and optical properties of TiO2 thin films. 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. It was also demonstrated that using HiPIMS, these phases can be obtained at room temperature without external substrate heating or  post-deposition annealing. The results on plasma and film properties were also compared with DCMS.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. , 72 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1572
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-104265DOI: 10.3384/diss.diva-104265ISBN: 978-91-7519-408-0 (print)OAI: oai:DiVA.org:liu-104265DiVA: diva2:696231
Public defence
2014-03-17, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-02-13 Created: 2014-02-13 Last updated: 2014-02-13Bibliographically approved
List of papers
1. A strategy for increased carbon ionization in magnetron sputtering discharges
Open this publication in new window or tab >>A strategy for increased carbon ionization in magnetron sputtering discharges
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2012 (English)In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 23, 1-4 p.Article in journal (Refereed) Published
Abstract [en]

A strategy that facilitates a substantial increase of carbon ionization in magnetron sputtering discharges is presented in this work. The strategy is based on increasing the electron temperature in a high power impulse magnetron sputtering discharge by using Ne as the sputtering gas. This allows for the generation of an energetic C+ ion population and a substantial increase in the C+ ion flux as compared to a conventional Ar-HiPIMS process. A direct consequence of the ionization enhancement is demonstrated by an increase in the mass density of the grown films up to 2.8 g/cm3; the density values achieved are substantially higher than those obtained from conventional magnetron sputtering methods.

Place, publisher, year, edition, pages
Elsevier, 2012
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-74315 (URN)10.1016/j.diamond.2011.12.043 (DOI)000302887600001 ()
Funder
Swedish Research Council, 621-2008-3222 623-2009-7348
Available from: 2012-01-24 Created: 2012-01-24 Last updated: 2017-12-08Bibliographically approved
2. Principles for designing sputtering-based strategies for high-rate synthesis of dense and hard hydrogenated amorphous carbon thin films
Open this publication in new window or tab >>Principles for designing sputtering-based strategies for high-rate synthesis of dense and hard hydrogenated amorphous carbon thin films
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2014 (English)In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 44, 117-122 p.Article in journal (Refereed) Published
Abstract [en]

In the present study we contribute to the understanding that is required for designing sputtering-based routes for high rate synthesis of hard and dense amorphous carbon (a-C) films. We compile and implement a strategy for synthesis of a-C thin films that entails coupling a hydrocarbon gas (acetylene) with high density discharges generated by the superposition of high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS). Appropriate control of discharge density (by tuning HiPIMS/DCMS power ratio), gas phase composition and energy of the ionized depositing species leads to a route capable of providing ten-fold increase in the deposition rate of a-C film growth compared to HiPIMS Ar discharge (Aijaz et al. Diamond and Related Materials 23 (2012) 1). This is achieved without significant incorporation of H (< 10 %) and with relatively high hardness (> 25 GPa) and mass density (~2.32 g/cm3). Using our experimental data together with Monte-Carlo computer simulations and data from the literature we suggest that: (i) dissociative reactions triggered by the interactions of energetic discharge electrons with hydrocarbon gas molecules is an important additional (to the sputtering cathode) source of film forming species and (ii) film microstructure and film hydrogen content are primarily controlled by interactions of energetic plasma species with surface and sub-surface layers of the growing film.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Hydrogenated amorphous carbon, DLC, HiPIMS, reactive sputtering
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-104261 (URN)10.1016/j.diamond.2014.02.014 (DOI)000335272800017 ()
Available from: 2014-02-13 Created: 2014-02-13 Last updated: 2017-12-06Bibliographically approved
3. Synthesis of amorphous carbon thin films using acetylene-based high power impulse magnetron sputtering discharges
Open this publication in new window or tab >>Synthesis of amorphous carbon thin films using acetylene-based high power impulse magnetron sputtering discharges
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2013 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Amorphous carbon (a-C) thin films are synthesized using high power impulse magnetron sputtering (HiPIMS) based Ne-Ar/C2H2 discharges. Plasma properties and film growth are investigated under different gas phase composition and operating pressures. Film mass densities, H content, hardness and compressive stresses are measured. Mass densities in the order of 2.2 g/cm3, hardness close to 25 GPa and H content as low as 11% are obtained. The film properties manifest a dependence on energy and flux of the depositing species and energetic ion bombardment driven structural changes in the films are found to govern the resulting film properties.

Keyword
Diamond-like carbon, hydrogenated amorphous carbon, HiPIMS, Reactive sputtering
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-104263 (URN)
Available from: 2014-02-13 Created: 2014-02-13 Last updated: 2014-02-13Bibliographically approved
4. 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
5. Exploring the potential of high power impulse magnetron sputtering for the synthesis of scratch resistant, antireflective coatings
Open this publication in new window or tab >>Exploring the potential of high power impulse magnetron sputtering for the synthesis of scratch resistant, antireflective coatings
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2013 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Broad band anti-reflective multilayer coatings require the use of a low-index material as a top layer. Normally SiO2 is used which exhibits sufficiently low refractive index (~1.5 at 550 nm) yet its low hardness (~10 GPa) hinders its application in abrasive environments. A strategy to circumnavigate these limitations is the synthesis of multicomponent materials that combine good mechanical and optical performance. In this work we synthesize Al-Si-O thin films seeking to combine the low refractive index of SiO2 and the relatively high hardness of Al2O3. The potential of reactive high power impulse magnetron sputtering (HiPIMS) for synthesizing Al-Si-O suitable for top-layers in anti-reflective coating stacks is explored by depositing films in an Ar+O2 ambient under varied target compositions (Al0.5Si0.5 and Al0.1Si0.9). The behavior of discharge current in metal and oxide mode is correlated with the plasma composition, plasma energetics as well as target surface composition in order to obtain information about the chemical nature and the energy of the film forming species. Plasma composition and plasma energetics are investigated by measuring electron density, electron temperature as well as energy distributions and as fluxes of Ar+, Al+, Si+ and O+ ions. Monte-Carlo based computer simulations are employed to assess the ion-target surface interactions to gain insight into the discharge characteristics as well as film growth. The properties of the grown films (chemical composition, mechanical and optical properties) are investigated and an understanding of the reactive HiPIMS-based growth of anti-reflective Al-Si-O thin films is established. For reference, the plasma and film properties of Al-O are also studied.

Keyword
Al-Si-O, anti-reflective coatings, optical coatings, HiPIMS, reactive sputtering
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-104264 (URN)
Available from: 2014-02-13 Created: 2014-02-13 Last updated: 2014-02-13Bibliographically approved
6. 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

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