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Atom insertion into grain boundaries and stress generation in physically vapor deposited films
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0003-0099-5469
University of Poitiers, France.
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0003-2864-9509
2013 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 5Article in journal (Refereed) Published
Abstract [en]

We present evidence for compressive stress generation via atom insertion into grain boundaries in polycrystalline Mo thin films deposited using energetic vapor fluxes (<∼120 eV). Intrinsic stress magnitudes between −3 and +0.2 GPa are obtained with a nearly constant stress-free lattice parameter marginally larger (0.12%) than that of bulk Mo. This, together with a correlation between large compressive film stresses and high film densities, implies that the compressive stress is not caused by defect creation in the grains but by grain boundary densification. Two mechanisms for diffusion of atoms into grain boundaries and grain boundary densification are suggested.

Place, publisher, year, edition, pages
American Institute of Physics (AIP) , 2013. Vol. 103, no 5
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-98154DOI: 10.1063/1.4817669ISI: 000322723000036OAI: oai:DiVA.org:liu-98154DiVA: diva2:652279
Note

Funding Agencies|COST Action|MP0804|Linkoping University.

The previous status of this article was Manuscript and the working title was Atomistic mechanisms leading to adatom insertion into grain boundaries and stress generation in physically vapor deposited films.

Available from: 2013-09-30 Created: 2013-09-30 Last updated: 2017-12-06
In thesis
1. 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
2. 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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Magnfält, DanielSarakinos, Kostas

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