In situ X-ray Microscopy Studies of Electromigration in Copper Interconnects

Abstract

Real‐time X‐ray microscopy is applied for degradation studies to understand electromigration‐induced transport processes in on‐chip copper interconnects. The material transport in inlaid Cu line/via structures is observed with about 40 nm lateral resolution. The image sequences show void formation, migration and nucleation processes. Correlation of the real‐time X‐ray images with post‐mortem SEM micrographs is used to discuss degradation mechanisms in inlaid copper interconnects. Due to the high penetration power of X‐rays through matter and its high spatial resolution, X‐ray microscopy (XRM) overcomes several limitations of conventional microscopic techniques. It utilizes the natural absorption contrast between the structures of interest, i.e. for on‐chip copper interconnects embedded in dielectrics. Due to their different X‐ray absorption characteristics at 0.52 keV, even different silicon compounds like Si, SiO2, and Si3N4 can be distinguished in X‐ray images of thinned layers as demonstrated. For failure analysis of thicker layers, phase contrast microscopy in the multi‐keV photon energy range is proposed.