Ultrafine Pitch (6 $\mu\hbox {m}$ ) of Recessed and Bonded Cu–Cu Interconnects by Three-Dimensional Wafer Stacking

In this letter, an evolution of high-density (>; 10⁶ cm-2) bonded Cu-Cu interconnects of 6-μm pitch is successfully demonstrated using wafer-on-wafer thermocompression bonding. Cu sealing frame with excellent hermeticity is integrated to the bonded structures to promote bond reliability. Additionally, temporary passivation of Cu surface using self-assembled monolayer enhances the resistance against oxidation, which, in turn, enables moderately low-temperature bonding process at 300°C. Finally, thermal cycling test confirms the thermal stability of the 6-μm-pitch Cu-Cu daisy chain structure up to 1000 cycles. This work opens up new opportunity for wafer-level integration of bumpless Cu-Cu bonding to enable future high-bandwidth 3-D integrated circuit applications.