Analysis of grain structure by precession electron diffraction and effects on electromigration reliability of Cu interconnects

In this paper, a recently developed high resolution electron diffraction technique is employed to characterize the grain orientation and grain boundaries for 45 nm node Cu interconnects with SiCN capping. The results are applied to evaluate the grain structure effect on electromigration (EM) reliability. We first calculate the flux divergence for void formation using interfacial and grain boundary diffusivities extracted from the resistance evolution of test structures observed during EM tests. To further correlate grain structure statistics with EM failure statistics, the EM lifetime distribution for Cu interconnects with CoWP capping is analyzed using a microstructure-based statistical model.