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Compressive intrinsic stress originates in the grain boundaries of dense refractory polycrystalline thin films
Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska fakulteten.ORCID-id: 0000-0003-0099-5469
University of Poitiers, France; INSA Rennes, France.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska fakulteten.ORCID-id: 0000-0002-6602-7981
Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska fakulteten.ORCID-id: 0000-0002-1744-7322
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2016 (Engelska)Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, nr 5, s. 055305-Artikel i tidskrift (Refereegranskat) Published
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Text
Abstract [en]

Intrinsic stresses in vapor deposited thin films have been a topic of considerable scientific and technological interest owing to their importance for functionality and performance of thin film devices. The origin of compressive stresses typically observed during deposition of polycrystalline metal films at conditions that result in high atomic mobility has been under debate in the literature in the course of the past decades. In this study, we contribute towards resolving this debate by investigating the grain size dependence of compressive stress magnitude in dense polycrystalline Mo films grown by magnetron sputtering. Although Mo is a refractory metal and hence exhibits an intrinsically low mobility, low energy ion bombardment is used during growth to enhance atomic mobility and densify the grain boundaries. Concurrently, the lateral grain size is controlled by using appropriate seed layers on which Mo films are grown epitaxially. The combination of in situ stress monitoring with ex situ microstructural characterization reveals a strong, seemingly linear, increase of the compressive stress magnitude on the inverse grain size and thus provides evidence that compressive stress is generated in the grain boundaries of the film. These results are consistent with models suggesting that compressive stresses in metallic films deposited at high homologous temperatures are generated by atom incorporation into and densification of grain boundaries. However, the underlying mechanisms for grain boundary densification might be different from those in the present study where atomic mobility is intrinsically low. (C) 2016 AIP Publishing LLC.

Ort, förlag, år, upplaga, sidor
AMER INST PHYSICS , 2016. Vol. 119, nr 5, s. 055305-
Nationell ämneskategori
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Identifikatorer
URN: urn:nbn:se:liu:diva-125810DOI: 10.1063/1.4941271ISI: 000369900600028OAI: oai:DiVA.org:liu-125810DiVA, id: diva2:910251
Anmärkning

Funding Agencies|COST Action "Highly Ionized Pulsed Plasmas" [MP0804]; Swedish Research Council VR [621-2014-4882]; Linkoping University via the "LiU Research Fellows" program.

The previous status of this article was Manuscript and the working title was Atom insertion into grain boundaries generates compressive intrinsic stress in polycrystalline thin films.

Tillgänglig från: 2016-03-08 Skapad: 2016-03-04 Senast uppdaterad: 2017-11-30Bibliografiskt granskad
Ingår i avhandling
1. Fundamental processes in thin film growth: The origin of compressive stress and the dynamics of the early growth stages
Öppna denna publikation i ny flik eller fönster >>Fundamental processes in thin film growth: The origin of compressive stress and the dynamics of the early growth stages
2014 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Alternativ titel[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. 

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2014. s. 116
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1592
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:liu:diva-105791 (URN)10.3384/diss.diva-105791 (DOI)978-91-7519-352-6 (ISBN)
Disputation
2014-05-16, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2014-04-08 Skapad: 2014-04-07 Senast uppdaterad: 2019-11-19Bibliografiskt granskad

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Magnfält, DanielBoyd, RobertHelmersson, UlfSarakinos, Kostas

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