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Principles for designing sputtering-based strategies for high-rate synthesis of dense and hard hydrogenated amorphous carbon thin films
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0001-9126-6004
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0003-2864-9509
Chimie des Interactions Plasma-Surface (ChIPS), University of Mons, Belgium.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
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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. Vol. 44, 117-122 p.
Keyword [en]
Hydrogenated amorphous carbon, DLC, HiPIMS, reactive sputtering
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-104261DOI: 10.1016/j.diamond.2014.02.014ISI: 000335272800017OAI: oai:DiVA.org:liu-104261DiVA: diva2:696190
Available from: 2014-02-13 Created: 2014-02-13 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Synthesis of Carbon-based and Metal-Oxide Thin Films using High Power Impulse Magnetron Sputtering
Open this publication in new window or tab >>Synthesis of Carbon-based and Metal-Oxide Thin Films using High Power Impulse Magnetron Sputtering
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:nbn:se:liu:diva-104265 (URN)10.3384/diss.diva-104265 (DOI)978-91-7519-408-0 (ISBN)
Public defence
2014-03-17, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
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Available from: 2014-02-13 Created: 2014-02-13 Last updated: 2014-02-13Bibliographically approved

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Aijaz, AsimSarakinos, KostasJensen, JensHelmersson, Ulf

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