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Hybrid bonding technology with Cu-Cu/adhesives for high density 2.5D/3D integration

We have developed Cu-Cu/adhesives hybrid bonding technique by using collective cutting of Cu bumps and adhesives in order to achieve high density 2.5D/3D integration. It is considered that progression of high density interconnection leads to lower height of bonding electrodes, resulting in narrow gap between ICs. Therefore, it is difficult to fill in adhesive to such a narrow gap ICs after bonding. Thus, we consider that hybrid bonding of pre-applied adhesives and Cu-Cu thermocompression bonding must be advantageous, in terms of void less bonding and minimizing bonding stress by adhesives and also low electricity by Cu-Cu solid diffusion bonding. In the present study, we adapted the following process; at first adhesives were spin coated on the wafer with Cu post and then pre-baked. After that, pre-applied adhesives and Cu bumps were simultaneously cut by single crystal diamond bite. We found that both adhesives and Cu post surfaces after cutting have highly smooth surface less than 10nm, and dishing phenomena, which might be occurred in typical CMP process, could not be seen on the cut Cu post/ adhesives surfaces.