Post electrochemical Cu deposition anneal impact on stress-voiding in individual vias

Stress-voiding is a critical reliability issue in Cu dual-damascene interconnects which could induce via openings. In our case, voids are typically observed at the edges at the bottom of vias. This location is correlated to a local delamination at Cu/Ta interface [E.T. Ogawa, J.W. McPherson, J.A. Rosal, M.J. Dickerson, T.-C. Chiu, L.Y. Tsung, M.K. Jain, T.D. Bonifield, J.C. Ondrusek, W.R. McKee, IEEE Int. Rel. Phys. Symp. Proc. (2002) 312–321; Y.K. Lim et al., Stress-induced voiding in multi-level copper/low-k interconnects, IEEE Int. Rel. Phys. Symp. Proc. (2004) 240–245]. Then, Cu/Ta interface properties at the bottom of via seem to be in the critical path for stress-voiding. In this paper, stress-voiding on 300 mm wafers in individual vias for different post electrochemical Cu deposition (ECD) anneals is studied. Electrical results show the clear benefit of hot plate and short furnace annealings. Microstructural characterizations indicate that impurities accumulation at Cu/Ta interface during long annealings could drive preferred void nucleation.