A Novel Low- Temperature Cu/SiO₂ Hybrid Bonding Based on Functional Group Selective Construction

Hybrid bonding technology is a high-density 3D integration technology that can significantly reduce the interconnect distance, allowing multifunctional chips to be processed independently. Therefore, it can enhance the flexibility of chip processing and mitigate production costs. However, in order to take into account the different degrees of high temperature tolerance of various heterogeneous chips and avoid the problems of wafer warping and device failure caused by inconsistent thermal expansion coefficients, it is urgent to develop a low temperature hybrid bonding process. At present, Cu and SiO₂ remain the prevailing choices for interconnect materials in hybrid bonding technology. The key to achieving Cu/SiO₂ low temperature hybrid bonding is to simultaneously obtain an oxide-free Cu surface and a hydroxy-enriched SiO₂ surface using the same surface activation process. Therefore, a novel approach for synergistic activation bonding has been devised and implemented, which involves the utilization of Ar/H2 plasma activation and citric acid immersion. By this way, strong Cu/Cu and SiO₂/SiO₂ bonding pairs can be simultaneously achieved at 200°C. The evaluations through tensile testing and scanning electron microscopy reveal that both Cu/Cu and SiO₂/SiO₂ exhibit sufficient strength to endure mechanical polishing without any interface defects. In summary, our method presents a promising solution for the low-temperature hybrid bonding of Cu/SiO₂, which promotes the future development of multifunctional chips 3D integration.