Electrically yielding Collective Hybrid Bonding for 3D stacking of ICs

The production of non-monolithic 3D-systems by stacking and interconnecting components through substrate vias (TSVs) is intrinsically limited to the stacking of thin dies, typically ranging from 100 mum down to 15 mum. Since dies or wafers of such thickness are no longer rigid, it is an important requirement that the bond guarantees mechanical stability and rigidity to the thin stacked die or wafer. The route followed here combines the fixation of a thin wafer or die by means of a dielectric adhesive with the formation of a metallic interconnect. This process is called Hybrid Bonding. The introduction of a tacky polymer as an intermediate glue layer in the direct bonding scheme offers the possibility for die-to-wafer throughput optimization: the opportunity lies in the separation of die pick-and-place and bonding operations. This process is called Collective Hybrid Bonding. Two polymers have been selected (so called polymer A and polymer B) according to their reflowing and bonding properties, and a die pick and place procedure has been defined and optimized for each of them, allowing a fast and reliable operation. Moreover, electrical measurements of daisy chains showed a comparable and reproducible yield of 80% working chains up to 1000 TSVs.