Simulation of Electromigration Test Structures with and without Extrusion Monitors

The thermal-electrical behavior of metallization structures with and without extrusion monitors has been investigated by finite element method (FEM) simulations. The explanation of changes in stress conditions (line temperature, spatial temperature distributions) has been proven to be helpful for the interpretation of electromigration test results. The simulation results of metallization structures with and without extrusion monitors are then compared to corresponding results from standard wafer-level electromigration accelerated test (SWEAT) and isothermal electromigration tests. The detected failure mode has been verified by optical observation of the metallization structures during and after electromigration stress. The investigations performed on a 0.35 um metallization process suggest that it is necessary to use optimized test structure layouts featuring extrusion monitors to obtain accurate electromigration results.