Microstructure and electromigration in copper damascene lines

Grain sites and crystallographic orientations of Cu were analyzed versus linewidth in damascene Cu interconnects. Pure bamboo lines were not obtained because grain size decreased as line width was reduced. Comparison of electromigration results, for wide line CVD-Cu (3 mu m) polycrystalline structure, and narrow lines (0.5 mu m) quasi-bamboo structure, provided almost the same activation energy Ea similar to 0.65 eV, even though the (200) texture has rotated in the film plane for the narrow damascene lines. These results are in agreement with copper diffusion involving a slow self surface diffusion or located at the interface between Cu and SiO2. On the contrary, PVD-Cu samples showed a better activation energy value Ea = 1.02 eV.