Single-Grain Cu μ-Joint Formation Induced by Selective Under-Seed-Metallurgy for Hybrid Bonding

SINGLE-grain Cu μ-joint which is completely free of Cu-Cu bonding-interface was realized in the direct-bonded wafers/ chips by employing prospective under-seed-metal (USM) layer. Both the in-plane as well as the out-of-plane inverse pole figure maps derived from electron backscatter diffraction confirm that one of the under-seed-material, USM-C did induce grain orientation and facilitating the grain-growth across top and bottom Cu bond-pads/electrodes. This kind of bonding-interface free single grain μ-joints are highly important to bring down the electrical resistance of these nano-scale Cu interconnects, which in turn is extremely important not only to improve the EM reliability of these interconnects, but also to enhance the hybrid bonding yield as well.