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Grain structure effect on electromigration reliability of Cu interconnects with CoWP capping

: Zhang, L.J.; Ho, P.S.; Aubel, O.; Hennesthal, C.; Zschech, E.


Journal of Materials Research 26 (2011), No.21, pp.2757-2760
ISSN: 0884-2914
ISSN: 2044-5326
Journal Article
Fraunhofer IZFP, Institutsteil Dresden ( IKTS-MD) ()

This article investigates the effect of grain structure on electromigration (EM) reliability of dual-damascene Cu interconnects with a CoWP capping layer, including the lifetime and statistics. Downstream EM tests were performed on two sets of CoWP-capped Cu interconnects with different grain sizes. Compared to Cu interconnects with the standard SiCN cap layer, the CoWP capping clearly improved the EM lifetime by similar to 24 x for the small grain structure and by another similar to 14 x for the large grain structure. Here, the effect of grain structure on EM lifetime was attributed to the grain boundary contribution to mass transport. The lifetime improvement, however, was accompanied with an increase in the statistical deviation, increasing from 0.27 for the SiCN cap to 0.53 for the small grain structure and to 0.88 for the large grain structure with the CoWP cap. This was attributed to the effect of grain structure in changing the statistical distribution of flux divergence sites and thus the failure statistics.