Experimental investigation on the impact of stress free temperature on the electromigration performance of copper dual damascene submicron interconnect

Electromigration experiments are conducted for submicron dual damascene copper lower level interconnect samples of different stress free temperatures. The electromigration life-time is found to be strongly depend on the stress state of the metallization and the stress gradient that exist due to thermal mismatch of various materials surrounding the copper metallization. It is found that by reducing the stress free temperature, electromigration lifetime can be improved. In order to explain the life-time behavior, an atomic flux divergence based coupled field finite element model is developed. The model predicts a reduction in the atomic flux divergence at the electromigration test condition due to the reduction in the stress free temperature as the key factor responsible for longer electromigration life-time observed experimentally.