Low Temperature (250°C) and Fine Pitch (≤4 μ m) New Nanocrystalline Cu/SiO₂ Chip-on-Wafer Hybrid Bonding for 3D Chip Integration

With the advancement of 3D packaging technology, the demand for low-temperature fine-pitch hybrid bonding has increased drastically. In this research, we developed 250°C low-temperature C2W (chip-to-wafer) nano-crystalline copper hybrid bonding with a chip including 2μm, 3μm, and 5μm different pad sizes. The fine-pitch (4 μm) daisy chain with a maximum of 672,150 bonding nodes was successfully connected, having an interlayer interconnect density of 6.26 × 10 6 cm −2 . The microstructure, electrical, and mechanical properties of Cu-Cu hybrid bonding were evaluated, showing superior reliability following thermal cycling tests. With the alignment accuracy <0.5μm, the maximum bonding strength reached 9.01 MPa. Through EBSD analysis, nano-crystalline copper is beneficial for the development of low-temperature (<250°C) fine-pitch hybrid bonding. By conducting nano-crystalline copper, the present study exhibits a significant step forward in the development of hybrid bonding technology for high-density and low-temperature applications.