HF-Assisted Binary Synergistic Activation Strategy for Large-Dishing Cu/SiO₂ Low-Temperature Hybrid Bonding

Cu/SiO 2 hybrid bonding technology enables low-power, low-latency, and high-density three-dimensional (3D) integration among multifunctional chips and has emerged as a prominent research focus in the post-Moore era. However, due to the significant differences in material properties between Cu and SiO 2, a large Cu dishing often occurs during the planarization process. To ensure stable electrical transmission in Cu/Cu interconnects, a relatively high bonding temperature is generally required, which poses particular challenges for low-temperature Cu/SiO 2 hybrid bonding. In this study, we propose a hydrofluoric acid (HF)-assisted binary synergistic activation low-temperature bonding process. By combining argon and hydrogen gas mixture (Ar/H 2 ) plasma activation, citric acid activation, and introducing an appropriate amount of diluted HF aqueous solution at the interface, prebonding is achieved at room temperature. Furthermore, a multistep thermal compression bonding process is utilized to simultaneously achieve reliable Cu/Cu and SiO 2 /SiO 2 connections under a low thermal budget (200 °C), with the SiO 2 /SiO 2 bonding strength reaching 19 MPa. More interestingly, the addition of HF effectively reduces the surface hardness of SiO 2, which is conducive to reducing the influence of Cu dishing. Additionally, HF further facilitates the formation of highly reactive hydroxyl groups (−OH) on the SiO 2 surface while maintaining a pure Cu surface, thereby enabling low-temperature hybrid bonding of large-dishing Cu/SiO 2 . Due to the low concentration of HF used, no residual F atoms were detected at the bonding interface. This technology is expected to promote the cost-effective development and application of Cu/SiO 2 hybrid bonding in the field of 3D integration.