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Thin Film Growth using Pulsed and Highly Ionized Vapor Fluxes
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0003-4811-478X
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Microstructure and morphology of thin films are decisive for many of their resulting properties. To be able to tailor these properties, and thus the film functionality, a fundamental understanding of thin film growth needs to be acquired. Film growth is commonly performed using continuous vapor fluxes with low energy, but additional handles to control growth can be obtained by instead using pulsed and energetic ion fluxes. In this licentiate thesis the physical processes that determine microstructure and morphology of thin films grown using pulsed and highly ionized vapor fluxes are investigated.

The underlying physics that determines the initial film growth stages (i.e., island nucleation, island growth and island coalescence) and how they can be manipulated individually when using pulsed vapor fluxes have previously been investigated. Their combined effect on film growth is, however, paramount to tailor film properties. In the thesis, a route to generate pulsed vapor fluxes using the vapor-based technique high power impulse magnetron sputtering (HiPIMS) is established. These fluxes are then used to grow Ag films on SiO2 substrates. For fluxes with constant energy and deposition rate per pulse it is demonstrated that the growth evolution is solely determined by the characteristics of the vapor flux, as set by the pulsing frequency, and the average time required for coalescence to be completed.

Highly ionized vapor fluxes have previously been used to manipulate film growth when deposition is performed both normal and off-normal to the substrate. For the latter case, the physical mechanisms that determine film microstructure and morphology are, however, not fully understood. Here it is shown that the tilted columnar microstructure obtained during  off-normal film growth is positioned closer to the substrate normal as the ionization degree of the flux increases, but only if certain nucleation characteristics are present.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. , 53 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1641
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-103921DOI: 10.3384/lic.diva-103921ISBN: 978-91-7519-426-4 (print)OAI: oai:DiVA.org:liu-103921DiVA: diva2:693025
Presentation
2014-02-28, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Note

The series name "Linköping studies in science and technology. Licentiate Thesis" is incorrect. The correct series name is "Linköping studies in science and technology. Thesis".

Available from: 2014-02-03 Created: 2014-02-03 Last updated: 2014-02-04Bibliographically approved
List of papers
1. Time-domain and energetic bombardment effects on the nucleation and coalescence of thin metal films on amorphous substrates
Open this publication in new window or tab >>Time-domain and energetic bombardment effects on the nucleation and coalescence of thin metal films on amorphous substrates
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2013 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 46, no 21, 215303Article in journal (Refereed) Published
Abstract [en]

Pulsed, ionized vapour fluxes, generated from high power impulse magnetron sputtering (HiPIMS) discharges, are employed to study the effects of time-domain and energetic bombardment on the nucleation and coalescence characteristics during Volmer–Weber growth of metal (Ag) films on amorphous (SiO2) substrates. In situ monitoring of the film growth, by means of wafer curvature measurements and spectroscopic ellipsometry, is used to determine the film thickness where a continuous film is formed. This thickness decreases from ~210 to ~140 Å when increasing the pulsing frequency for a constant amount of material deposited per pulse or when increasing the amount of material deposited per pulse and the energy of the film forming species for a constant pulsing frequency. Estimations of adatom lifetimes and the coalescence times show that there are conditions at which these times are within the range of the modulation of the vapour flux. Thus, nucleation and coalescence processes can be manipulated by changing the temporal profile of the vapour flux. We suggest that other than for elucidating the atomistic mechanisms that control pulsed growth processes, the interplay between the time scales for diffusion, coalescence and vapour flux pulsing can be used as a tool to determine characteristic surface diffusion and island coalescence parameters.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-95508 (URN)10.1088/0022-3727/46/21/215303 (DOI)000319116300009 ()
Note

Funding Agencies|Swedish Research Council|VR 621-2011-4280|COST Action Highly Ionized Pulsed Plasmas|MP0804|Linkoping University via the LiU Research Fellows program||.

The previous status of the article was Manuscript and the working title was Time-domain and energetic bombardment effects on the nucleation and post-nucleation characteristics during none-quilibrium film synthesis.

Available from: 2013-07-05 Created: 2013-07-05 Last updated: 2017-12-06Bibliographically approved
2. Unravelling the Physical Mechanisms that Determine Microstructural Evolution of Ultrathin Volmer-Weber Films
Open this publication in new window or tab >>Unravelling the Physical Mechanisms that Determine Microstructural Evolution of Ultrathin Volmer-Weber Films
2014 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 4, 044302- p.Article in journal (Refereed) Published
Abstract [en]

The initial formation stages (i.e., island nucleation, island growth, and island coalescence) set characteristic length scales during growth of thin films from the vapour phase. They are, thus, decisive for morphological and microstructural features of films and nanostructures. Each of the initial formation stages has previously been well-investigated separately for the case of Volmer-Weber growth, but knowledge on how and to what extent each stage individually and all together affect the microstructural evolution is still lacking. Here we address this question using growth of Ag on SiO2 from pulsed vapour fluxes as a case study. By combining in situ growth monitoring, ex situ imaging and growth simulations we systematically study the growth evolution all the way from nucleation to formation of a continuous film and establish the effect of the vapour flux time domain on the scaling behaviour of characteristic growth transitions (elongation transition, percolation and continuous film formation). Our data reveal a pulsing frequency dependence for the characteristic film growth transitions, where the nominal transition thickness decreases with increasing pulsing frequency up to a certain value after which a steady-state behaviour is observed. The scaling behaviour is shown to result from differences in island sizes and densities, as dictated by the initial film formation stages. These differences are determined solely by the interplay between the characteristics of the vapour flux and time required for island coalescence to be completed. In particular, our data provide evidence that the steady-state scaling regime of the characteristic growth transitions is caused by island growth that hinders coalescence from being completed, leading to a coalescence-free growth regime.

National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-103920 (URN)10.1063/1.4890522 (DOI)000340710700078 ()
Available from: 2014-02-03 Created: 2014-02-03 Last updated: 2017-12-06
3. Tilt of the columnar microstructure in off-normally deposited thin films using highly ionized vapor fluxes
Open this publication in new window or tab >>Tilt of the columnar microstructure in off-normally deposited thin films using highly ionized vapor fluxes
2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 17, 7 pages- p.Article in journal (Refereed) Published
Abstract [en]

The tilt of the columnar microstructure has been studied for Cu and Cr thin films grown off-normally using highly ionized vapor fluxes, generated by the deposition technique high power impulse magnetron sputtering. It is found that the relatively large column tilt (with respect to the substrate normal) observed for Cu films decreases as the ionization degree of the deposition flux increases. On the contrary, Cr columns are found to grow relatively close to the substrate normal and the column tilt is independent from the ionization degree of the vapor flux when films are deposited at room temperature. The Cr column tilt is only found to be influenced by the ionized fluxes when films are grown at elevated temperatures, suggesting that film morphology during the film nucleation stage is also important in affecting column tilt. A phenomenological model that accounts for the effect of atomic shadowing at different nucleation conditions is suggested to explain the results.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-94608 (URN)10.1063/1.4804066 (DOI)000319292800398 ()
Available from: 2013-06-27 Created: 2013-06-27 Last updated: 2017-12-06Bibliographically approved

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