2 μm Pitch Direct Die-to-Wafer Hybrid Bonding Using Surface Protection During Wafer Thinning and Die Singulation

To preserve the bonding surface quality, this paper proposes and demonstrates the feasibility of incorporating an inorganic protective layer in the direct die-to-wafer (D2W) hybrid bonding flow. The bonding surface is found well preserved even after wafer thinning and die singulation: Cu recess is kept ~2 nm, which is comparable to 1.5 nm after the initial CMP. Transmission electron microscopy (TEM) inspection at the bonding interface confirms seamless bonding of SiCN-SiCN and Cu-Cu. The best electrical results of the 2 μm pitch structures show Kelvin yield > 95% and the daisy chain yield > 80%, indicating effective surface protection.