A Study on the Breakdown Mechanism of an Electroless-Plated Ni(P) Diffusion Barrier for Cu/Sn/Cu 3D Interconnect Bonding Structures

This study examined the thermal stability of an electroless-plated Ni(P) barrier layer inserted between Sn and Cu in the bonding structure of Cu/Sn/Cu for three-dimensional (3D) interconnect applications. A combination of transmission electron microscopy (TEM) and scanning electron microscopy allowed us to fully characterize the bonding morphology of the Cu/Ni(P)/Sn/Ni(P)/Cu joints bonded at various temperatures. The barrier suppressed Cu and Sn interdiffusion very effectively up to 300°C; however, an interfacial reaction between Ni(P) and Sn led to gradual decomposition into Ni₃P and Ni₃Sn₄. Upon 350°C bonding, the interfacial reaction brought about complete disintegration of the barrier in local areas, which allowed unhindered interdiffusion between Cu and Sn.