Dynamic study of the physical processes in the intrinsic line electromigration of deep-submicron copper and aluminum interconnects

Various physical mechanisms are involved in an electromigration (EM) process occurring in metal thin film. These mechanisms are electron-wind force induced migration, thermomigration due to temperature gradient, stressmigration due to stress gradient, and surface migration due to surface tension in the case where free surface is available. In this work, a finite element model combining all the aforementioned massflow processes was developed to study the behaviors of these physical mechanisms and their interactions in an EM process for both Al and Cu interconnects. The simulation results show that the intrinsic EM damage in Al is mainly driven by the electron-wind force, and thus the electron-wind force induced flux divergence is the dominant cause of Al EM failure. On the other hand, the intrinsic EM damage in Cu is driven initially by the thermomigration, and the electron-wind force dominates the EM failure only at a latter stage. This shows that the early stage of void growth in Cu interconnects is more prone to thermomigration than Al.