Hybrid Bonding Methods Using Ultra Precision Cutting for 3D-SIC

Abstract

We have developed Cu-Cu/adhesives hybrid bonding technique by using collective cutting of Cu bumps and adhesives in order to achieve high density 3D-SIC. It is considered that progression of fine pitch interconnection leads to lower height of bonding electrodes, resulting in narrow gap between 3D-SICs. Therefore, it is difficult to fill in adhesive to such a narrow gap 3D-SICs after bonding, so 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 successfully cut by single crystal diamond bite. Typical adhesives may cause bite damage with continuous cutting, but in this research, we selected low damage adhesive against continuous cutting, which is important properties to commercial uses. Then, chips with adhesives were attached to substrates and Cu oxidation layer was removed by exposing formic acid atmosphere. Finally permanent bonding was done at 225 degree C for 30 minutes. We concluded that solid diffusion between bonded Cu bumps could be achieved and no adhesive residue could be seen between bonded interfaces by TEM/EDX analysis.