Development of low temperature Cu[sbnd]Cu bonding and hybrid bonding for three-dimensional integrated circuits (3D IC)

Thermal-compression bonding (TCB) is the key technology to ensure vertical chip (or wafer) stacking in three-dimensional (3D) integration with higher I/O density than conventional soldering technology. For different TCB approaches, copper (Cu) to Cu bonding has always been the preferred candidate due to the excellent electrical and thermal properties of Cu, high mechanical strength of bonding interface, as well as compatibility and cost consideration in the packaging fabrication. However, high thermal budget of the bonding process caused by oxidation of Cu leads to issue of wafer warpage, bonding misalignment, and compatibility with back-end-of-line process. Therefore, this review paper first presents an extensive survey on the advance of low temperature Cu-based bonding technologies. In addition, the feasibility of Cu[sbnd]Cu bonding in the fine pitch applications is challenged by coplanarity issue of Cu pillars and insufficient gaps for filling. Accordingly, based on the progress of low temperature Cu[sbnd]Cu bonding, low temperature Cu/SiO₂ hybrid bonding will be introduced as an emerging bonding technology to solve the coplanarity and filling issue, which can provide the great potential for 3D integration with ultra-high density of interconnection.