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Reactive High Power Impulse Magnetron Sputtering of CFx Thin Films in Mixed Ar/CF4 and Ar/C4F8 Discharges
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-9464-5111
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0001-9402-1491
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The reactive high power impulse magnetron sputtering (HiPIMS) processes of C in Ar/tetrafluoromethane CF4 and Ar/octafluorocyclobutane (c-C4F8) have been characterized. Amorphous carbon fluoride (CFx) films were synthesized at deposition pressure and substrate temperature of 400 mPa and 110 oC, respectively. The CFx film composition was controlled in the range of 0.15 < x < 0.35 by varying the partial pressure of the F-containing gases from 0 mPa to 110 mPa. The reactive plasma was studied employing time averaged positive ion mass spectrometry and the resulting thin films were characterized regarding their composition, chemical bonding and microstructure as well as mechanical properties by elastic recoil detection analysis, X-ray photoelectron spectroscopy, transmission electron microscopy, nanoindentation, and water droplet contact angle measurements, respectively. The experimental results were compared to results obtained by first-principles calculations based on density functional theory.

The modeling of the most abundant precursor fragment from the dissociation of CF4 and C4F8 provided their relative stability, abundance, and reactivity, thus permitting to evaluate the role of each precursor during film growth. Positive ion mass spectrometry of both F plasmas show an abundance of CF+, C+, CF⁺₂, and CF⁺₃ (in this order) as corroborated by first-principles calculations. Only CF⁺₃ exceeded the Ar+ signal in a CF4 plasma. Two deposition regimes are found depending on the partial pressure of the F-containing reactive gas, where films with fluorine contents below 24 at% exhibit a graphitic nature, whereas a polymeric structure applies to films with fluorine contents exceeding 27 at%. Moreover, abundant precursors in the plasma are correlated to the mechanical response of the different CFx thin films. The decreasing hardness with increasing F content can be attributed to the abundance of CF⁺₃ precursor species, weakening the C matrix.

Keyword [en]
c-C4F8, CF4, fluorine containing carbon thin films, HiPIMS, CFx, first principle calculations, XPS, TEM, positive ion mass spectrometry
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-90908OAI: oai:DiVA.org:liu-90908DiVA: diva2:615007
Available from: 2013-04-08 Created: 2013-04-08 Last updated: 2017-05-05Bibliographically approved
In thesis
1. Carbon Nitride and Carbon Fluoride Thin Films Prepared by HiPIMS
Open this publication in new window or tab >>Carbon Nitride and Carbon Fluoride Thin Films Prepared by HiPIMS
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis focuses on carbon based thin films prepared by high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS). Carbon nitride (CNx: 0 < x < 0.20) as well as carbon fluoride (CFx: 0.16 < x < 0.35) thin films were synthesized in an industrial deposition chamber by reactive magnetron sputtering of graphite in Ne/N2, Ar/N2, Kr/N2, Ar/CF4, and Ar/C4F8 ambients. In order to increase the understanding of the deposition processes of C in the corresponding reactive gas mixture plasmas, ion mass spectroscopy was carried out. A detailed evaluation of target current and target voltage waveforms was performed when graphite was sputtered in HiPIMS mode. First principle calculations targeting the growth of CFx thin films revealed most probable film forming species as well as CFx film structure defining defects. In order to set different process parameters into relation with thin film properties, the synthesized carbon based thin films were characterized with regards to their chemical composition, chemical bonding, and microstructure. A further aspect was the thin film characterization for possible applications. For this, mainly nanoindentation and contact angle measurements were performed. Theoretical calculations and the results from the characterization of the deposition processes were successfully related to the thin film properties.

The reactive graphite/N2/inert gas HiPIMS discharge yielded high ion energies as well as elevated C+ and N+ abundances. Under such conditions, amorphous CNx thin films with hardnesses of up to 40 GPa were deposited. Elastic, fullerene like CNx thin films, on the other hand, were deposited at increased substrate temperatures in HiPIMS discharges exhibiting moderate ion energies. Here, a pulse assisted chemical sputtering at the target and the substrate was found to support the formation of a fullerene-like microstructure.

CFx thin films were found to have surface energies equivalent to super-hydrophobic materials for x > 0.26 while such films were polymeric in nature accounting for hardnesses below 1 GPa. Whereas, an amorphous structure for carbon-based films with fluorine contents ranging between 16 % and 23 % was observed. For those films, the hardness increased with decreasing fluorine content and ranged between 16 GPa and 4 GPa. The HiPIMS process in fluorinecontaining atmosphere was found to be a powerful tool in order to change the surface properties of carbon based thin films.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 82 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1512
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-90912 (URN)978-91-7519-642-8 (ISBN)
Public defence
2013-05-08, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2013-04-08 Created: 2013-04-08 Last updated: 2016-08-31Bibliographically approved
2. Nanostructured carbon-based thin films: prediction and design
Open this publication in new window or tab >>Nanostructured carbon-based thin films: prediction and design
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Carbon-based thin films are a vast group of materials of great technological importance. Thanks to the different bonding options for carbon, a large variety of structures (from amorphous to nanostructured) can be achieved in the process of film synthesis. The structural diversity increases even more if carbon is combined with relatively small quantities of atoms of other elements. This results in a set of materials with many different interesting properties for a wide range of technological applications.

This doctoral thesis is about nanostructured carbon-based thin films. In particular, the focus is set on theoretical modeling, prediction of structural features and design of sulfo carbide (CSx) and carbon fluoride (CFx) thin films.

The theoretical approach follows the synthetic growth concept (SGC) which is based on the density functional theory. The SGC departure point is the fact that the nanostructured films of interest can be modeled as assemblies of low dimensional units (e.g., finite graphene-like model systems), similarly to modeling graphite as stacks of graphene sheets. Moreover, the SGC includes a description of the groups of atoms that act as building blocks (i.e., precursors) during film deposition, as well as their interaction with the growing film.

This thesis consists of two main parts:

Prediction: In this work, I show that nanostructured CSx thin films can be expected for sulfur contents up to 20 atomic % with structural characteristics that go from graphite-like to fullerene-like (FL). In the case of CFx thin films, a diversity of structures are predicted depending on the fluorine concentration. Short range ordered structures, such as FL structure, can be expected for low concentrations (up to 5 atomic %). For increasing fluorine concentration, diamond-like and polymeric structures should predominate. As a special case, I also studied the ternary system CSxFy. The calculations show that CSxFy thin films with nanostructured features should be possible to synthesize at low sulfur and fluorine concentrations and the structural characteristics can be described and explained in terms of the binaries CSx and CFx.

Design: The carbon-based thin films predicted in this thesis were synthesized by magnetron sputtering. The results from my calculations regarding structure and composition, and analysis of precursors (availability and role during deposition process) were successfully combined with the experimental techniques in the quest of obtaining films with desired structural features and understanding their properties.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 79 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1696
Keyword
carbon, carbon-based, thin films, fullerene-like, modeling, dft
National Category
Condensed Matter Physics Nano Technology
Identifiers
urn:nbn:se:liu:diva-121021 (URN)10.3384/diss.diva-121021 (DOI)978-91-7685-976-6 (ISBN)
Public defence
2015-10-16, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2015-09-04 Created: 2015-09-02 Last updated: 2016-08-31Bibliographically approved

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Schmidt, SusannGoyenola, CeciliaGueorguiev, Gueorgui KostovJensen, JensGreczynski, GrzegorzIvanov, Ivan GueorguievHultman, Lars

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Thin Film PhysicsThe Institute of TechnologySemiconductor Materials
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