Electromigration failure mechanism investigation between wafer level and plackage level reliability test in AL interconects

Abstract

Wafer level reliability (WLR) and package level reliability (PLR) test methods are widely used for Electromigration (EM) accelerated lifetime test. Both methods on different via and metal line structures are studied in this paper. The experimental result shows single via terminated EM structure lifetime is comparable between WLR and PLR methods based on Black's equation; while stack via terminated structure and metal line structure lifetime shows difference between the two methods. By physical failure analysis (PFA), we also find different failure mechanisms between WLR and PLR methods on stack via terminated structure and metal line structure. The hypothesis is that for stack via terminated structure, large joule heating is produced at stack via area due to W-via high resistivity and WLR high stress current. The temperature even is high enough to make the small aluminum plate between stack vias melt or burnt out. But the single via terminated structure can emit heating along the long metal line and then into the oxide and cause less temperature flux. And for metal line structure, the WLR stress current is even much higher than via structures which will make the metal line over stressed and get burnt out near the line end area.