Effects of Surface Composition on Bonding Strength for Direct Cu-Cu Bonding with Passivation Layer

Cu bonding with an addition of a thin interfacial layer has been gaining attention for providing low-temperature bonding solutions for direct Cu bonding in advanced packaging. In this paper, Cu surfaces with an Au thin film passivation layer were exposed to various dry surface treatments and analyzed to understand the effects of carbon contaminants on bonding strength. We have shown that Vacuum Ultraviolet (VUV) N2 treated samples improved the bonding strength and yield significantly compared to the bare, Plasma Ar and VUV O3 treated samples as CO groups were removed from the bonding interface without affecting the roughness of the surface.