Impact of test structure design on electromigration of metal interconnect

The impact of test structure design on the electromigration (EM) lifetime of metal interconnects has been investigated using high resolution resistance measurement (HRRM). The metal stripe in the test structure is of bamboo structure and multiple vias are added at both ends of the line to enhance the via effect. The resistance change of the test structure clearly shows two stages in the EM test. The values of activation energy E_a in stage II are found to be much smaller than that of bulk diffusion; rather, they are quite close to those obtained in wide polycrystalline stripes. Moreover, line electromigration becomes easier when more vias are added at the end of the line. These results indicate that W-plug vias not only cause discontinuity at the interface between metal and W-plug, but also make metal stripes near W-plug vias much more vulnerable to electromigration, which further reduces the electromigration lifetime of the metal stripe