Cu/Adhesive Hybrid Bonding at 180 °C in H-Containing HCOOH Vapor Ambient for 2.5D/3D Integration

Bump-less Cu/adhesive hybrid bonding is a promising technology for 2.5D/3D integration. The remaining issues of this technology include high Cu-Cu bonding temperature, long thermal-compression time (low throughput), and large thermal stress. In this paper, we investigate a Cu-first hybrid bonding process in hydrogen(H)-containing formic acid (HCOOH) vapor ambient, lowering the bonding temperature to 180 °C and shortening the thermal-compression time to 600 s. We find that the H-containing HCOOH vapor pre-bonding treatment is effective for Cu surface activation and friendly to adhesives at treatment temperature of 160-200 °C. The effects of surface activation (temperature and time) on Cu-Cu bonding and cyclo-olefin polymer (COP) adhesive bonding are studied by shear tests, fracture surface observations, and interfacial observations. Cu/adhesive hybrid bonding was successfully demonstrated at a bonding temperature of 180 °C with post-bonding adhesive curing at 200 °C.