Microstructural void environment characterization by electron imaging in 45 nm technology node to link electromigration and copper microstructure

The work presented in this paper illustrates the link between electromigration (EM) and microstructure in copper interconnects. For this study, 70 nm wide copper interconnects from 45 nm technology node are considered. Microstructure and grain orientation have been obtained in the vicinity of EM induced voids at early stage. Electron Backscattered Diffraction (EBSD) characterization is used to get microstructure and grain orientation. Then Transmission Electronic Microscope (TEM) imaging provides unambiguous location of void on EBSD map. Finally, the comparison of EBSD technique with its equivalent in TEM (commercialized as ASTAR by NanoMEGAS) shows that EBSD limitations are reached and that TEM should soon replace EBSD for local analyses. The results confirm that EM voids are nucleated at high angle misoriented grain boundaries (grain boundary with misorientation higher than 15°) and does not show link between grain orientation and electromigration phenomenon.

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