Linewidth influence on electromigration tests at wafer level on TiN/AlCu/TiN/Ti metal lines

Today, electromigration-the transport of metal caused by electrical current-is one of the major reliability problem. It is well known, the grain boundary is the main diffusion path in polycrystalline lines, but do not exist in bamboo lines. The new metallizations using barrier and cap layers generate a new diffusion path at the metal interfaces. In this paper, wafer-level electromigration tests were performed on TiN/AlCu/TiN/Ti lines. The activation energy and the lifetime are extracted for three linewidths with bamboo (0.7 micrometers ) and non-bamboo structures (3 micrometers and 5 micrometers ). The values are ranged between 0.91 eV (0.7 micrometers wide line) highlighting the interfacial diffusion and 0.67 eV (3 micrometers wide line) revealing the grain boundary diffusion. The extrapolated lifetimes are calculated. The bamboo line shows a lifetime dramatically higher than the non-bamboo lines. Finally, the failure locations are determined. They are randomly distributed for the widest lines, but the failures are always located near the cathode end segment in the bamboo line. This failure location is explained by the relation between the main diffusion path and the ion flux divergence.