Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
High-resolution characterization of TiN diffusion barrier layers
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0001-7347-5371
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Titanium nitride (TiN) films are widely applied as diffusion barrier layers in microelectronic devices. The continued miniaturization of such devices not only poses new challenges to material systems design, but also puts high demands on characterization techniques. To gain understanding of diffusion processes that can eventually lead to failure of the barrier layer and thus of the whole device, it is essential to develop routines to chemically and structurally investigate these layers down to the atomic scale. In the present study, model TiN diffusion barriers with a Cu overlayer acting as the diffusion source were grown by reactive magnetron sputtering on MgO(001) and thermally oxidized Si(001) substrates. Cross-sectional transmission electron microscopy (XTEM) of the pristine samples revealed epitaxial, single-crystalline growth of TiN on MgO(001), while the polycrystalline TiN grown on Si(001) exhibited a [001]-oriented columnar microstructure. Various annealing treatments were carried out to induce diffusion of Cu into the TiN layer. Subsequently, XTEM images were recorded with a high-angle annular dark field detector, which provides strong elemental contrast, to illuminate the correlation between the structure and the barrier efficiency of the single- and polycrystalline TiN layers. Particular regions of interest were investigated more closely by energy dispersive X-ray (EDX) mapping. These investigations are completed by atom probe tomography (APT) studies, which provide a three-dimensional insight into the elemental distribution at the near-interface region with atomic chemical resolution and high sensitivity. In case of the single-crystalline barrier, a uniform Cu-enriched diffusion layer of 12 nm could be detected at the interface after an annealing treatment at 1000 °C for 12 h. This excellent barrier performance can be attributed to the lack of fast diffusion paths such as grain boundaries. Moreover, density-functional theory calculations predict a stoichiometry-dependent atomic diffusion mechanism of Cu in bulk TiN, with Cu diffusing on the N-sublattice for the experimental N/Ti ratio. In comparison, the polycrystalline TiN layers exhibited grain boundaries reaching from the Cu-TiN interface to the substrate, thus providing direct diffusion paths for Cu. However, the microstructure of these columnar layers was still dense without open porosity or voids, so that the onset of grain boundary diffusion could only be found after annealing at 900 °C for 1 h.

The present study shows how to combine two high resolution state-of-the-art methods, TEM and APT, to characterize model TiN diffusion barriers. It is shown how to correlate the microstructure with the performance of the barrier layer by two-dimensional EDX mapping and three-dimensional APT. Highly effective Cu-diffusion barrier function is thus demonstrated for single-crystal TiN(001) (up to 1000 °C) and dense polycrystalline TiN (900 °C).

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. , 61 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1720
Keyword [en]
Diffusion, TiN, Microstructure, Transmission electron microscopy, TEM, Atom probe tomography, APT
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-120394DOI: 10.3384/lic.diva-120394ISBN: 978-91-7685-994-0 (print)OAI: oai:DiVA.org:liu-120394DiVA: diva2:844272
Presentation
2015-08-28, Schrödinger, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:00 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation
Available from: 2015-08-25 Created: 2015-08-04 Last updated: 2016-08-31Bibliographically approved
List of papers
1. Copper diffusion into single-crystalline TiN studied by transmission electron microscopy and atom probe tomography
Open this publication in new window or tab >>Copper diffusion into single-crystalline TiN studied by transmission electron microscopy and atom probe tomography
Show others...
2015 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 574, 103-109 p.Article in journal (Refereed) Published
Abstract [en]

TiN/Cu bilayers were grown by unbalanced DC magnetron sputter deposition on (001)-oriented MgO substrates. Pole figures and electron back-scatter diffraction orientation maps indicate that both layers in the as-deposited state are single-crystalline with a cube-on-cube epitaxial relationship with the substrate. This is confirmed by selected area electron diffraction patterns. To study the efficiency of the TiN barrier layer against in-diffusion of Cu, we annealed samples at 900 degrees C for 1 h in vacuum and at 1000 degrees C for 12 h in Ar atmosphere. The single-crystalline structure of the TiN layer is stable up to annealing temperatures of 1000 degrees C as shown by high resolution transmission electron microscopy. While no Cu diffusion was evident after annealing at 900 degrees C, scanning transmission electron microscopy images and energy-dispersive X-ray spectrometry maps show a uniform diffusion layer of about 12 nm after annealing at 1000 degrees C for 12 h. Concentration depth profiles obtained from 3D atom probe tomography reconstructions confirm these findings and reveal that the TiN film is slightly substoichiometric with a N/Ti ratio of 0.92. Considering this composition, we propose a lattice diffusion mechanism of Cu in TiN via the formation of Cu-N vacancy complexes. The excellent diffusion barrier properties of single-crystalline TiN are further attributed to the lack of fast diffusion paths such as grain boundaries.

Place, publisher, year, edition, pages
Elsevier, 2015
Keyword
Titanium nitride; Copper; Diffusion; Transmission electron microscopy; Atom probe tomography
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-114436 (URN)10.1016/j.tsf.2014.11.084 (DOI)000348044700017 ()
Note

Funding Agencies|Austrian Federal Government; Bundesministerium fur Verkehr, Innovation und Technologie; Bundesministerium fur Wirtschaft, Familie und Jugend; Styrian and the Tyrolean Provincial Government; Swedish Research Council [2013-4018]; Knut and Alice Wallenberg Foundation for the Electron Microscopy Laboratory at Linkoping University

Available from: 2015-03-02 Created: 2015-02-20 Last updated: 2017-12-04
2. Cu diffusion in single-crystal and polycrystalline TiN barrier layers: A high-resolution experimental study supported by first-principles calculations
Open this publication in new window or tab >>Cu diffusion in single-crystal and polycrystalline TiN barrier layers: A high-resolution experimental study supported by first-principles calculations
Show others...
2015 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, no 8, 085307Article in journal (Refereed) Published
Abstract [en]

Dense single-crystal and polycrystalline TiN/Cu stacks were prepared by unbalanced DC magnetron sputter deposition at a substrate temperature of 700 °C and a pulsed bias potential of -100 V. The microstructural variation was achieved by using two different substrate materials, MgO(001) and thermally oxidized Si(001), respectively. Subsequently, the stacks were subjected to isothermal annealing treatments at 900 °C for 1 h in high vacuum to induce the diffusion of Cu into the TiN. The performance of the TiN diffusion barrier layers was evaluated by cross-sectional transmission electron microscopy in combination with energy-dispersive X-ray spectrometry mapping and atom probe tomography. No Cu penetration was evident in the single-crystal stack up to annealing temperatures of 900 °C, due to the low density of line and planar defects in single-crystal TiN. However, at higher annealing temperatures when diffusion becomes more prominent, density-functional theory calculations predict a stoichiometry-dependent atomic diffusion mechanism of Cu in bulk TiN, with Cu diffusing on the N sublattice for the experimental N/Ti ratio. In comparison, localized diffusion of Cu along grain boundaries in the columnar polycrystalline TiN barriers was detected after the annealing treatment. The maximum observed diffusion length was approximately 30 nm, yielding a grain boundary diffusion coefficient of the order of 10‑16 cm2s-1 at 900 °C. This is 10 to 100 times less than for comparable underdense polycrystalline TiN coatings deposited without external substrate heating or bias potential. The combined numerical and experimental approach presented in this paper enables the contrasting juxtaposition of diffusion phenomena and mechanisms in two TiN coatings, which differ from each other only in the presence of grain boundaries.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2015
Keyword
Diffusion, TiN, Microstructure, Transmission electron microscopy, TEM, Atom probe tomography, APT
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-120391 (URN)10.1063/1.4929446 (DOI)000360658600039 ()
Funder
Swedish Research Council, 2013-4018Knut and Alice Wallenberg Foundation
Available from: 2015-08-04 Created: 2015-08-04 Last updated: 2017-12-04Bibliographically approved

Open Access in DiVA

fulltext(3342 kB)717 downloads
File information
File name FULLTEXT01.pdfFile size 3342 kBChecksum SHA-512
3f5748755a2b5e34f725cdc4148024acff95fcc9f12095a94205f5d52d61ac87bbea0872c0c599b5295c02c236085ed1b877d86c936b3f1552ad45d4d090cfb4
Type fulltextMimetype application/pdf
omslag(123 kB)11 downloads
File information
File name COVER01.pdfFile size 123 kBChecksum SHA-512
9b0e8fa02446a925231579b0d4eeda1bbfab6cb21d0bd923ee0fc1e0a60ace5a5cdb32b1023bc5fc9d4a457fd0011acad07fba9d951a5a1cbf7ad7ae4db5d47d
Type coverMimetype application/pdf

Other links

Publisher's full text

Search in DiVA

By author/editor
Mühlbacher, Marlene
By organisation
Thin Film PhysicsFaculty of Science & Engineering
Materials Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 717 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

doi
isbn
urn-nbn

Altmetric score

doi
isbn
urn-nbn
Total: 1387 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf