Cu Barrier Seed Innovation for EM Improvement

Cu barrier seed is a key process in Cu interconnect. Continuous improvement in Cu barrier and seed processes and hardware has enabled improvement in Cu gap fill and effective suppression of Cu diffusion and EM (electron migration). This paper addresses innovations in Cu barrier and seed aimed at suppressing EM. Both barrier and seed processes are crucial for EM qualification. In vias, a robust and continuous barrier reduces Cu diffusion at the interface; robust punch through helps via clean; and the resputtering process can optimize via profile and current distribution. Most early failures in the via could be fixed by the PVD (physical vapor deposition) Ta(N) process. Cu alloy seed was later developed to increase EM life time. CuAl alloy can retard Cu migration at the grain boundary and interface; CuMn alloy can create a self-formed barrier. Co wetting and capping layers are the newest approaches for suppressing EM failures at 32nm and below. The entire Cu line can be encapsulated by a Co layer, leaving no weak spots in the top and sidewall interface and blocking the rapid diffusion path of Cu. Compared to CuMn, the Co solution also offers advantages for gap fill and Rc reduction.