The Enhancement in the Reliability of Nanotwinned Cu Redistribution Lines Passivated with Immersion Sn and Ag

The oxidation of redistribution layers (RDLs) plays a crucial role in the lifetime of electromigration as the line width of RDLs is decreasing. Polyimide, a common material of the passivation layer, still leads to the generation of oxide because of the remaining void after the curing process. We capped the nanotwinned Cu (NT-Cu) RDLs with immersion Ag or immersion Sn and then conducted the temperature cycling test (TCT) to observe the ability of anti-oxidation. The result shows that these two materials could inhibit the formation of oxide layers and thus serve as a good passivation layer, but the performance of the Ag capping layers is better than that of the Sn layer.