Electromigration in copper damascene interconnects: reservoir effects and failure analysis

Electromigration in dual damascene copper interconnects was investigated using package level electromigration tests and failure analysis techniques. Interface diffusion along Cu/Si3N4 interface was found to be the dominant electromigration path. Effect of reservoir at the copper via region on electromigration performance was studied using via-fed two-layer test structures with various extension lengths above the via. Improvement in electromigration failure times was observed with increasing reservoir length, consistent with the mechanism of vacancy movement along the Cu/Si3N4 interface. Electromigration mechanism and the reservoir effect are discussed in detail.