Electromigration failure modes in damascene copper interconnects

Electromigration experiments were performed on passivated damascene copper interconnects with 1 μm linewidth. A wide range of activation energy values were obtained depending upon barrier layer (Ti or TiN), Cu deposition technique (PVD or CVD process) and grain size. An activation energy of 1.1 eV was measured in PVD-Cu layers leading to significant improvement over AlCu technology: lifetime at 140°C was about 2 orders of magnitude longer. Furthermore, SEM pictures after line failure emphasized interface diffusion mechanisms which occurred in these structures for both Cu CVD and PVD deposition processes.