Wafer Level Fine-Pitch Hybrid Bonding: Challenges and Remedies

Fine-pith hybrid bonding has been demonstrated using 3μm Cu pad size and 6μm pitch. TEOS SiO2 is used as a dielectric material. Oxide films were characterized in terms of porosities. A good correlation has been established between the % of porosity in the oxide film and the bonding energy. Chemical-mechanical polishing (CMP) process control challenges in order to achieve a narrow Cu dishing range has also been discussed. It has been recommended that the post-bond annealing temperature needs to be appropriately adjusted in order to achieve good diffusion bonding at the Cu-Cu interface and at the same time mitigate generation of peeling stresses. Disparity in misalignment is observed within the same bonded wafer. To resolve this, a novel solution of designing mating Cu pads of different dimensions is being proposed. Through this design approach, misalignment could be successfully offset and better Cu pad connectivity could be achieved.