Grain structure analysis and implications on electromigration reliability for Cu interconnects

A recently developed precession electron diffraction (PED) technique in transmission electron microscopy (TEM) was employed to characterize the grain orientation and grain boundaries for Cu interconnects of the 45 nm node. The results showed a strong <;111>; and <;110>; textures along the width and the thickness of the line, respectively and a low fraction of coherent twin boundaries. The microstructure characteristics were applied to evaluate the grain structure effect on electromigration (EM) reliability. We first extracted the interfacial diffusivity components for (111), (110), and (100) surfaces and the averaged grain boundary diffusivity by analyzing the resistance traces observed in EM tests. Then the flux divergence at the triple points of grain boundary intersecting the interface was calculated to identify potential voiding sites. Similar analysis was extended to via/line regions to evaluate the flux divergence for slit void formation and to assess the probability of EM early failure.