In-situ TEM studies of damage formation under electromigration in Al interconnects

Abstract

Both depth- and in-plane-resolved information is essential for analysis of electromigration (EM) in layered interconnect lines. We demonstrate the usefulness of a combination of in situ side-view TEM, SEM and EPMA for this purpose. We have analyzed EM in Al-2 wt%Cu bamboo-grain drift lines using these techniques. The analysis leads to the conclusions that large precipitates near the cathode end cause voiding when Ca depletes from them, and that the variation in precipitate sites may be one of the causes of the variation of voiding sites in the cathode area, which have a strong influence on the EM reliability. It was also clarified that Cu that migrated from upstream mostly accumulated at preexisting precipitates at the anode, and no new precipitate formation was observed.