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Electromigration behavior of Cu metallization interfacing with Ta versus TaN at high temperatures
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
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2016 (English)In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 34, 060603Article in journal (Refereed) Published
Abstract [en]

High-temperature stability of Cu-based interconnects is of technological importance for electronic circuits based on wide band gap semiconductors. In this study, different metal stack combinations using Ta or TaN as capping- and/or barrier-layer, in the configuration cap/Cu/barrier, are evaluated electrically and morphologically prior to and after high-temperature treatments. The symmetric combinations Ta/Cu/Ta and TaN/Cu/TaN are characterized by a low and stable sheet resistance after annealing up to 700 °C. Asymmetric combinations of Ta/Cu/TaN and TaN/Cu/Ta, however, display an increase in sheet resistance values after annealing at 500 °C and above. This increase in sheet resistance is considered to result from Ta diffusion into the grain boundaries of the Cu film. The preliminary electromigration studies on the TaN/Cu/Ta and TaN/Cu/TaN structures show a twofold higher activation energy and a tenfold longer lifetime for the former, thus suggesting an important role of the interface between Cu and the cap and/or barrier.

Place, publisher, year, edition, pages
2016. Vol. 34, 060603
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:uu:diva-300795DOI: 10.1116/1.4967372OAI: oai:DiVA.org:uu-300795DiVA: diva2:952462
Funder
Swedish Foundation for Strategic Research , RE10-0011Swedish Foundation for Strategic Research , RIF-14-0053
Available from: 2016-08-13 Created: 2016-08-13 Last updated: 2016-11-25Bibliographically approved
In thesis
1. Copper and Silver Metallization for High Temperature Applications
Open this publication in new window or tab >>Copper and Silver Metallization for High Temperature Applications
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

High-temperature electrical- and morphological-stability of interconnect is critical for electronic systems based on wide band gap (WBG) semiconductors. In this context, the thermal stability of both Ag and Cu films with Ta and TaN films as diffusion barriers and/or surface-capping layers at high temperatures up to 800 oC is investigated in this thesis.

The investigation of un-capped Ag films with either Ta or TaN diffusion barrier layers shows electrical stability upon annealing up to 600 °C. Degradation occurs above 600 °C mainly as a result of void formation and Ag agglomeration. Sandwiching Ag films between Ta and/or TaN layers is found to electrically and morphologically stabilize the Ag metallization up to 800 °C. The barrier layer plays a key role; the β-to-α phase transition in the underlying Ta barrier layer is identified as the major cause for the morphological instability of the film above 600 °C. This phase transition can be avoided using a stacked Ta/TaN barrier. Furthermore, no observable Ta diffusion in Ag films is found.

Copper films with a Ta diffusion barrier show clearly different behaviors. In the Cu/Ta sample, Ta starts to diffuse up to the surface via fast-diffusing grain boundaries (GBs) after annealing at 500 °C. The activation energy for the GB diffusion is 1.0+0.3 eV. Un-capped Cu is electrically stable up to 800 °C. An appreciable increase in sheet resistance occurs above 600 °C for the asymmetric combinations Ta/Cu/TaN and TaN/Cu/Ta. This degradation is closely related to a substantial diffusion of Ta across the Cu film and on to the TaN layer, where Ta1+xN forms. The symmetrical combinations Ta/Cu/Ta and TaN/Cu/TaN show only small changes in sheet resistance even after annealing at 800 °C. No Ta diffusion can be found in the Ta/Cu/Ta and TaN/Cu/TaN stacks.

Finally, the influence of barrier and cap, their interfaces to Cu and Ta diffusion and segregation in the Cu GBs on electromigration is studied. Our preliminary results with the TaN/Cu/Ta and TaN/Cu/TaN structures report a 2-fold higher activation energy and a 10-fold longer lifetime for the former, thus confirming an important role of the interface between Cu and the cap and/or barrier.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 68 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1406
Keyword
Metallization, Copper, Silver, Tantalum, High tempreture, Diffussion, Electromigration, Stability
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-300796 (URN)978-91-554-9656-2 (ISBN)
External cooperation:
Public defence
2016-09-30, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research , RE10-0011Swedish Foundation for Strategic Research , RIF-140053
Available from: 2016-09-08 Created: 2016-08-13 Last updated: 2016-09-13

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Mardani, ShabnamNorström, HansSmith, UlfGustavsson, FredrikOlsson, JörgenZhang, Shi-Li
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