Grain boundary as relevant microstructure feature for electromigration in advanced technology studied by Electron BackScattered Diffraction

The work presented in this paper shows the links between electromigration (EM) in copper interconnects and microstructure of copper. Metal lines of 70 nm width corresponding to minimum width of 45-40 nm technology node are aged by electromigration (EM) test. Electron Backscattered Diffraction (EBSD) technique is then used to characterize microstructure and orientation of copper grains around void(s) resulting from EM. Advanced TEM and STEM characterization have also been used to assess reliability of EBSD technique (void localization, texture determination) applied to very small dimensions. Finally, the influence of cobalt (Co) as capping or sidewall liner and Aluminum-Copper alloy (CuAl) seed layer were investigated by EM tests and physical characterization. Our results confirm that critical microstructure parameter for electromigration phenomena in copper is grain boundary and in particular high angle misoriented grain boundaries.