Facilitating Small-Pitch Interconnects With Low-Temperature Solid-Liquid Interdiffusion Bonding

The trend for 3-D heterogeneous integration drives the need for a low-temperature bonding process for high-density interconnects (HDIs). The Cu-Sn–In-based solid-liquid interdiffusion (SLID) is a promising option as a low-temperature bonding technique that offers better processing flexibility and relatively lower costs for chip-sized substrates when compared with hybrid bonding. In this letter, the low-temperature process was applied in a chip-to-chip bonding process. The test structures contain microbumps with 5- $\mu $ m width and 15- $\mu $ m pitch, mimicking state-of-the-art small-pitch interconnects. At the bonding temperature of 170°C, the process was completed within 5 min, while at 150°C extended bonding time was required to completely transform low-melting materials into intermetallic phases. Electrical characterization, performed using three test structures, estimated a single interconnect resistivity as low as 1.3e $^{-7}~\Omega $ m. This letter showcases the potential of the low-temperature SLID bond process for HDI applications.