Study of upstream electromigration bimodality and its improvement in Cu low-k interconnects

The bimodality of upstream electromigration (EM) failures in the dual damascene structure of 45 nm Cu interconnection process with low-k material is investigated, and the improvement is demonstrated. Two major early failure modes with voids forming in via or at the chamfer of via-trench transition area are revealed and attributed to liner process weakness at the respective locations, which can be reduced and eliminated with optimized via and chamfer aspect ratios (ARs) defined by the dual damascene profile. Dielectric thickness, trench etch depth, via critical dimension (CD), chamfer of via-trench transition profile etc. can serve as the tuning factors for the upstream EM bimodality improvement. However, a balance between EM, time-dependent dielectric breakdown (TDDB) and resistance-capacitance (RC) performance need to be achieved.