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Time-domain and energetic bombardment effects on the nucleation and coalescence of thin metal films on amorphous substrates
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0003-0099-5469
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0003-4811-478X
Institut P', Département Physique et Mécanique des Matériaux, Université de Poitiers-CNRS-ENSMA, SP2MI, Téléport 2, Bd M. et P. Curie, F-86962 Chasseneuil-Futuroscope, France.
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-1744-7322
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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. Vol. 46, no 21, 215303
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-95508DOI: 10.1088/0022-3727/46/21/215303ISI: 000319116300009OAI: oai:DiVA.org:liu-95508DiVA: diva2:635742
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
In thesis
1. Thin Film Growth using Pulsed and Highly Ionized Vapor Fluxes
Open this publication in new window or tab >>Thin Film Growth using Pulsed and Highly Ionized Vapor Fluxes
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:nbn:se:liu:diva-103921 (URN)10.3384/lic.diva-103921 (DOI)978-91-7519-426-4 (ISBN)
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
2. Fundamental processes in thin film growth: The origin of compressive stress and the dynamics of the early growth stages
Open this publication in new window or tab >>Fundamental processes in thin film growth: The origin of compressive stress and the dynamics of the early growth stages
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Fundamentala processer under tunnfilmstillväxt : Tryckspänningars ursprung och dynamiska processer i de tidiga tillväxtstegen
Abstract [en]

The fundamental mechanisms behind the generation of compressive stresses in polycrystalline thin films, the effects of pulsed deposition fluxes on the dynamics of the early growth stages as well as the generation of energetic Ar+ ions in high power impulse magnetron sputtering (HiPIMS) discharges has been studied in this thesis.

It was found that compressive film stresses in Mo films deposited using energetic vapor fluxes are correlated with high film densities while only a slight lattice expansion compared to relaxed Mo was found. This implies that the stress is caused by grain boundary densification and not defect creation in the grain bulk. The compressive stress magnitude should scale with the grain boundary length per unit area, or the inverse grain size, if the stress originates in the grain boundaries. This was found to be the case for dense Mo films confirming that the observed compressive stresses originate in the grain boundaries. Similarly to what has been suggested for conditions where adatoms are highly mobile we suggest that atom insertion into grain boundaries is the cause of the compressive stresses observed in the Mo films.

Island nucleation, growth and coalescence are the dynamic processes that decide the initial microstructure of thin films growing in a three dimensional fashion. Using Ag on SiO2 as a model system and estimations of adatom life times and coalescence time it was shown that the time scales of island nucleation and coalescence are in the same range as the time scale of the vapor flux modulation in HiPIMS and other pulsed deposition methods. In situ real time measurements were used to demonstrate that it is possible to decrease the thickness at which a continuous film is formed from 21 to 15 nm by increasing the flux modulation frequency. A more in depth study where in situ real time monitoring was coupled with ex situ imaging and kinetic Monte Carlo simulations showed that this behavior is due to the interplay of the pulsed deposition flux and island coalescence where island coalescence is hindered at high pulsing frequencies.

The generation of energetic Ar+ ions was investigated by ion mass spectrometry and Monte Carlo simulations of gas transport. It was shown that the energetic Ar+ ions originate from Ar atoms backscattered from the target that are ionized in the plasma by correlating the length of the high energy tail in the ion energy distribution functions with the atomic mass of the Cr, Mo and W sputtering targets. 

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 116 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1592
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-105791 (URN)19.3384/diss.diva-105791 (DOI)978-91-7519-352-6 (ISBN)
Public defence
2014-05-16, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-04-08 Created: 2014-04-07 Last updated: 2017-01-16Bibliographically approved
3. Nanoscale structure forming processes: Metal thin films grown far-from-equilibrium
Open this publication in new window or tab >>Nanoscale structure forming processes: Metal thin films grown far-from-equilibrium
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Thin film growth from the vapor phase has for a long time intrigued researchers endeavouring to unravel and understand atomistic surface processes that govern film formation. Their motivation has not been purely scientific, but also driven by numerous applications where this understanding is paramount to knowledge-based design of novel film materials with tailored properties.

Within the above framework, this thesis investigates growth of metal films on weakly bonding substrates, a combination of great relevance for applications concerning e.g., catalysis, graphene metallization and architectural glazing. When metal vapor condenses on weakly bonding substrates three dimensional islands nucleate, grow and coalesce prior to forming a continuous film. The combined effect of these initial growth stages on film formation and morphology evolution is studied using pulsed vapor fluxes for the model system Ag/SiO2. It is shown that the competition between island growth and coalescence completion determines structure evolution. The effect of the initial growth stages on film formation is also examined for the tilted columnar microstructure obtained when vapor arrives at an angle that deviates from the substrate surface normal. This is done using two metals with distinctly different nucleation behaviour, and the findings suggest that the column tilt angle is set by nucleation conditions in conjunction with shadowing of the vapor flux by adjacent islands. Vapor arriving at an angle can in addition result in films that exhibit preferred crystallographic orientations, both out-of-plane and in-plane. Their emergence is commonly described by an evolutionary growth model, which for some materials predict a double in-plane alignment that has not been observed experimentally. Here, an experiment is designed to replicate the model’s growth conditions, confirming the existence of double in-plane alignment.

New and added film functionalities can further be unlocked by alloying. Properties are then largely set by chemistry and atomic arrangement, where the latter can be affected by thermodynamics, kinetics and vapor flux modulation. Their combined effect on atomic arrangement is here unravelled by presenting a research methodology that encompasses high resolution vapor flux modulation, nanoscale structure v vi probes and growth simulations. The methodology is deployed to study the immiscible Ag-Cu and miscible Ag-Au model systems, for which it is shown that capping of Cu by Ag atoms via near surface diffusion processes and rough morphology of the Ag-Au growth front are the decisive structure forming processes in each respective system.

The results generated in this thesis are of relevance for tuning structure of metal films grown on weakly bonding substrates. They also indicate that improved growth models are required to accurately describe structure evolution and emergence of a preferred in-plane orientation in films where vapor arrives at an angle that deviates from the substrate surface normal. In addition, this thesis presents a methodology that can be used to identify and understand structure forming processes in multicomponent films, which may enable tailoring of atomic arrangement and related properties in technologically relevant material systems.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2016. 71 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1804
National Category
Inorganic Chemistry Other Materials Engineering Other Physics Topics Materials Chemistry Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-132895 (URN)10.3384/diss.diva-132895 (DOI)9789176856390 (ISBN)
Public defence
2017-01-20, Planck, Fysikhuset, Campus Valla, Linköping, 09:15 (English)
Opponent
Supervisors
Available from: 2016-11-30 Created: 2016-11-30 Last updated: 2016-11-30Bibliographically approved
4. Nucleation and stress generation in thin films deposited with a pulsed energetic deposition flux
Open this publication in new window or tab >>Nucleation and stress generation in thin films deposited with a pulsed energetic deposition flux
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents fundamental mechanisms of nucleation and early growth of and stress generation in thin polycrystalline metal films deposited using pulsed energetic deposition fluxes. The effects of a pulsed deposition flux and energetic bombardment on film nucleation was investigated using in situ stress measurements and in situ ellipsometry to determine the film thickness at which the films become continuous. Ag films where deposited using high power impulse magnetron sputtering (HiPIMS) in two series - one with constant low pulse power to minimize energetic bombardment while varying the pulse frequency and one with a constant pulse frequency while varying the pulse power, resulting in different amounts of energetic bombardment and different deposition rates - to separate the effects of a pulsed deposition flux and energetic bombardment. The thickness at which the film becomes continuous was found to decrease both with increasing pulse frequency and increasing pulse power. The effects of the increased energetic bombardment and deposition rate cannot be separated due to their coupling. Adatom lifetimes and the coalescence times for islands where calculated for different coverages and island sizes and compared to the time between pulses. It was found that the time between pulses was lower than the adatom lifetimes for certain conditions; this leads to an increase in the adatom density and therefore an increase of the nucleation density resulting in smaller thicknesses for the formation of continuous film. It was also found that the coalescence time for clusters becomes longer than the time between pulses, retarding the coalescence process; this leads to formation of long lived elongated clusters also resulting in a decrease of the thickness at which the films become continuous.

Energetic bombardment during growth of Mo films using HiPIMS is found to result in large compressive stresses without the commonly observed defect induced associated lattice expansion seen when depositing films using energetic bombardment. This and a correlation between the magnitude of the compressive stress and the film density allow us to conclude that the compressive stress is generated by grain boundary densification. Two mechanisms leading to grain boundary densification and thus generation of compressive stresses are proposed.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 49 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1570
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-86472 (URN)LIU-TEK-LIC-2013:4 (Local ID)978-91-7519-706-7 (ISBN)LIU-TEK-LIC-2013:4 (Archive number)LIU-TEK-LIC-2013:4 (OAI)
Presentation
2013-01-24, Plack, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2012-12-17 Created: 2012-12-17 Last updated: 2017-01-16Bibliographically approved

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