Low-temperature Cu/SiO2 hybrid bonding using a novel two-step cooperative surface activation

Compared with continuous node scaling in a two-dimensional (2D) plane, advanced three-dimensional (3D) integration finds a new pathway to expand Moore's Law in the vertical direction. The essence of advanced 3D integration technology relies on the dense vertical interconnection, and state-of-the-art metal/oxide hybrid bonding provides such an ideal fine-pitch structure (≤ 1 µm) by eliminating microbump and underfill. Of the various hybrid bonding platform, Cu/SiO2hybrid bonding structure is the most promising candidate due to the excellent electrical and mechanical properties of Cu and SiO2, respectively.

However, the feasible Cu/SiO2hybrid bonding technology often requires high temperature (-400°C) currently, which is not desirable for temperature-sensitive chips. Here, we develop a novel two-step cooperative surface activation method to overcome this bottleneck. Based on the combination of plasma activation and acid treatment of this cooperative surface activation, the atomic smooth Cu and SiO2surface with hydrophilic layers were obtained, and the strong homogeneous bonding of Cu-Cu and SiO2-SiO2was realized at 200°C.

Eventually, the Cu/SiO2hybrid bonding device was successfully achieved, which void-free and atomically interconnected Cu-Cu, SiO2-SiO2, and even Cu-SiO2interfaces were obtained simultaneously. This hybrid bonding structure realized by cooperative surface activation brings unprecedented 3D integration feasibility and flexibility.