A hybrid bonding interconnection with a novel low-temperature bonding polymer system

The heterogeneous integrated package structure and process development for multi-chip and high-density interconnection structures have become a hot topic due to their ability to obtain high performance and high bandwidth density. To meet the different requirements of various heterogeneous chips, a new chip stacking technology is needed to simplify and reduce the packaging structure. Hybrid bond interconnection is one of the key technologies for achieving this kind of chiplet integration. The current hybrid bond is also called bumpless interconnection. Its interface includes copper metal pads and SiO2 dielectric material without Cu pillar bumps and underfills encapsulation. Bonding surface requirements include excellent flatness and ultralow roughness to obtain ultrafine pitch Cu pads under 10 Pm. However, thermal annealing of the bonding interface to allow Cu/Cu surface interdiffusion still requires temperatures above 350 °C. This thermal requirement results in some chips losing their device characteristics when processed at elevated temperatures. Therefore, metal pads and dielectric materials require some research to attain a lower bonding or annealing temperature. Polymeric materials have the potential to be a low-temperature bonding dielectric layer, such as benzocyclobutene, non-conductive films, and polyimide. In our study, a novel photo-imageable dielectric is applied in the test vehicle and SiO2/polymer bonding interface and is used to evaluate bond feasibility with a lower-temperature bonding process. Finally, bonding can be done at room temp. After annealing at 200 ºC for 1 hour, the bonding strength of the material can be improved significantly.