Fracture Toughness Assessment of Patterned Cu-Interconnect Stacks by Dual-Cantilever-Beam (DCB) Technique

Dual cantilever beam (DCB) mechanical testing is applied to two kinds of chips, manufactured in the 45 nm technology node. Both chips consist of different numbers of ultra low-k (ULK) dielectric layers, however, they have similarly designed crack-stop structures. It is shown that in all cases, cohesive cracking occurred in the upper ULK layers. The crack-stops hamper the crack propagation, and cracks are deflected outside the interconnect stack. The paths of the deflected crack fronts are FIB-sectioned and imaged in SEM. The increasing number of ULK layers leads to decrease in effective Gc of the stack.