Nitrogen passivation formation on Cu surface by Ar–N2 plasma for Cu-to-Cu wafer stacking application

Abstract

Wafer stacking technology provides reduced interconnect delay, improved bandwidth, reduced form factor, and decreased cost. Solder-based metallic die bonding is presently utilized in high-volume manufacturing, but Cu-based metallic wafer bonding is quickly becoming a key bonding technique for next generation 3D IC and heterogeneous stacking applications. In this study, Ar–N2 plasma treatment on Cu surface was investigated to passivate Cu surface with nitrogen and to enhance the bonding quality of Cu-to-Cu wafer bonding. The Ar–N2 plasma treatment was performed by conventional DC sputtering under 5 mTorr working pressure with different Ar–N2 partial pressures. Then, the effect of Ar–N2 plasma treatment on Cu surface was evaluated structurally and electrically. It was observed that the Ar–N2 plasma treatment with high nitrogen partial pressure over a sufficient plasma treatment time provided activated Cu surface, reduction of copper oxide and chemisorbed nitrogen, and copper nitride passivation. The Ar–N2 plasma treatment of Cu surface was found to be a potential pretreatment method for Cu-to-Cu bonding.