Electromigration threshold in copper interconnects and consequences on lifetime extrapolations

Electromigration in interconnects is a major reliability concern for integrated circuits, which leads to aggressive design rules. These rules can be lightened by taking advantage of the Blech effect in extrapolated lifetimes. In the present paper is reported the critical product (jL)_c for copper-oxide interconnects measured at 250°C, 300°C and 350°C from electron-migration lifetime tests. The existence of this threshold product implies an increase of n values from Black´s model with decreasing (current density-line length) products. This increase significantly changes the extrapolated lifetime at operating conditions.