Electromigration design rules for bidirectional current

Electromigration reliability of different metallization systems and structures under bidirectional current stress is studied in a wide frequency range (from mHz to 200 MHz). The experimental results show that at very low frequencies, the damage healing factor and lifetime under AC stress increases with increasing frequency. At high frequencies, the pure AC lifetime was found to be determined by the thermal migration instead of electromigration. All the observations are in agreement with an average current model indicating that while AC current contributes to self-heating, only the average (DC) current contributes to electromigration in all practical cases for interconnects and vias. The conclusion applies to all materials and geometries tested.