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A strategy for increased carbon ionization in magnetron sputtering discharges
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
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
Royal Institute of Technology.
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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. Vol. 23, 1-4 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-74315DOI: 10.1016/j.diamond.2011.12.043ISI: 000302887600001OAI: oai:DiVA.org:liu-74315DiVA: diva2:482751
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
In thesis
1. HiPIMS-based Novel Deposition Processes for Thin Films
Open this publication in new window or tab >>HiPIMS-based Novel Deposition Processes for Thin Films
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this research, high power impulse magnetron sputtering (HiPIMS) based new deposition processes are introduced to address; the issue of low degree of ionization of C in magnetron sputtering discharges, and the difficulty encountered in thin film deposition on complex-shaped surfaces. The issue of low degree of C ionization is addressed by introducing a new strategy which is based on promoting the electron impact ionization ofC by increasing the electron temperature in the plasma discharge using Ne, instead of conventionally used Ar. The Ne-based HiPIMS process provides highly ionized C fluxes which are essential for the synthesis of high-density and sp3 rich amorphous carbon (a-C) thin films such as diamond-like carbon (DLC) and tetrahedral a-C (ta-C). The feasibility of coating complex-shaped surfaces is demonstrated by using the dual-magnetron approach in an open-field (magnetic field of the magnetrons) configuration and performing sideways deposition of Ti films. The HiPIMS-based open-field configuration process enhances the sideways transport of the sputtered flux — an effect which is observed in the case of HiPIMS.

The characterization of the Ne-HiPIMS discharge using a Langmuir probe and mass spectrometry shows that it provides an increase in the electron temperature resulting in an order of magnitude decrease in the mean ionization length of the sputtered C as compared to the conventional Ar-HiPIMS discharge. The C1+ ion energy distribution functions exhibit the presence of an energetic C1+ ion population and a substantial increase in the total C1+ ion flux. The higher C1+ ion flux facilitates the growth of sp3 rich carbon films with mass densities, measured by x-ray reflectometry, reaching as high as approx. 2.8 gcm-3.

The dual-magnetron open-field configuration process is operated in DCMS as well as in HiPIMS modes. The plasma characterization, performed by Langmuir probe measurements and optical emission spectroscopy, shows that the plasma density in the Ti-HiPIMS discharge is higher than that of the Ti-DCMS discharge. This results in the higher ionized fraction of the sputtered Ti in the case of HiPIMS. The film uniformity and the deposition rate of the film growth, obtained by employing scanning electron microscopy, demonstrate that the sideways deposition approach can be used for depositing thin films on complex-shaped surfaces.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 49 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1537
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-78728 (URN)LIU-TEK-LIC-2012:22 (Local ID)978-91-7519-870-5 (ISBN)LIU-TEK-LIC-2012:22 (Archive number)LIU-TEK-LIC-2012:22 (OAI)
Supervisors
Available from: 2012-06-19 Created: 2012-06-19 Last updated: 2013-10-30Bibliographically approved
2. 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)
Opponent
Supervisors
Available from: 2014-02-13 Created: 2014-02-13 Last updated: 2014-02-13Bibliographically approved

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Aijaz, AsimSarakinos, KostasLundin, DanielHelmersson, Ulf

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