Electromigration (EM) in sub-micron metal interconnects depends on interface bonding and metal microstructure. The process of EM-induced degradation in on-chip interconnects as observed from both in-situ scanning electron microscopy (SEM) experiments at embedded inlaid copper interconnect structures and numerical simulations based on a physical model is explained based on transmission electron microscopy (TEM) brightfield images. Interface strengthening results in completely changed degradation and failure mechanisms. The changed void evolution for interconnects with strengthened interfaces, e.g. caused by additional metal coating like CoWP or self-assembled monolayers (SAMs) on top of the polished copper lines, is explained with increased atomic order and stronger bonding compared to standard CU/SiN interfaces. (c) 2005 Elsevier B.V All rights reserved.