Improving Electromigration Resistance of Fine-Pitch Redistributed Layer Using Graphene-Doped Twinned Copper Composites

The electromigration (EM) behavior of graphene-doped twinned copper composite (GC-Cu) and nanotwinned copper (NT-Cu) redistributed layers (RDLs) are investigated. Firstly, the GC-Cu has longer lifetimes under various test conditions. For example, the GC-Cu RDL took 291 h to reach a 20% resistance increase, while the NT-Cu RDL took 117 h under the same condition of 120 degrees C and 106 A cm-2. Secondly, thinner oxidation layer and slighter voiding phenomena are detected on GC-Cu RDLs. When the line width and spacing (L/S) of RDL decreased from 20/20 mu m to 10/10 mu m, new failure modes, i.e., fracture of oxide layer, separation between the oxide layer and copper matrix are also detected, demonstrating the increasing thermal mismatch. Combined with the finite element analysis (FEA), there is simultaneous current aggregation and stress concentration around the voids, which should further cause the degradation of RDL. Above all, this study gives insights into the material design in the fine-pitch RDL structure. The electromigration (EM) resistance of three different copper redistributed layers (RDLs), including nanotwinned copper (NT-Cu) and graphene-doped copper composite (GC-Cu) are compared. The result reveals that both increasing twin density and adding graphene can improve the EM performance. Especially, the GC-Cu have longer lifetimes, thinner oxidation layers, and slighter voiding phenomena.image (c) 2024 WILEY-VCH GmbH