Geometry and Microstructure Effect on EM-Induced Copper Interconnect Degradation

Statistical analysis of electromigration (EM) lifetimes of inlaid copper interconnects, in situ microscopy experiments at embedded inlaid copper interconnect structures, and numerical simulations of grain growth and EM degradation processes are necessary for future on-chip interconnect systems with high immunity to EM-induced failure. Experimental results, i.e., statistics of lifetime and void distributions, copper microstructure data from electron backscatter diffraction studies, as well as in situ scanning electron microscopy and transmission X-ray microscopy studies of EM degradation processes, are discussed for inlaid interconnect structures, varying geometry and process conditions. EM failure statistics for a large number of interconnects and in situ studies for a selected number of samples, which allow to visualize the time-dependent evolution of voids, demonstrate that interconnect degradation and, eventually, interconnect failure depend on interface bonding and the copper microstructure. With decreasing interconnect dimensions, the copper microstructure will become more critical for interconnect reliability.