Electromigration performance of laser planarized aluminum alloy films

An excimer laser was used to melt aluminum alloy films so as to obtain contact filling and local planarization. The objective was to obtain a film that had a wide process window for planarization and exhibited good electromigration performance. The results of wafer-level (accelerated) and package-level (conventional) electromigration testing on metal line structures over flat and topographical areas for control and planarized samples are discussed. Accelerated test data indicate that the control samples are superior to the planarized samples. However, conventional test data indicate that planarization improves the electromigration characteristics. Three mechanisms are proposed to explain this discrepancy. Scanning electron microscopy (SEM) analysis was performed, indicating that electromigration failure is localized and catastrophic on the planarized samples. Control samples exhibit traditional electromigration voiding dispersed throughout the metal line. This is attributed to the difference in microstructure of the films