Demonstrating 170 °C Low-Temperature Cu-In-Sn Wafer-Level Solid Liquid Interdiffusion Bonding

The wafer-level solid liquid interdiffusion (SLID) bonds carried out for this work take advantage of the Cu-In-Sn ternary system to achieve low-temperature interconnections. The 100-mm Si wafers had mu-bumps from 250 mu m down to 10 mu m fabricated by consecutive electrochemical deposition of Cu, Sn, and In layers. The optimized wafer-level bonding processes were carried out by EV Group and Aalto University across a range of temperatures from 250 degrees C down to 170 degrees C. Even though some quality-related process challenges were observed, it could be verified that high strength bonds with low defect content can be achieved even at a low bonding temperature of 170 degrees C with an acceptable 1-h wafer-level bonding duration. The microstructural analysis revealed that the bonding temperature significantly impacts the obtained phase structure as well as the number of defects. A higher (250 degrees C) bonding temperature led to the formation of Cu3Sn phase in addition to Cu-6(Sn,In)(5) and resulted in several voids at Cu3Sn vertical bar Cu interface. On the other hand, with lower (200 degrees C and 170 degrees C) bonding temperatures, the interconnection microstructure was composed purely of void-free Cu-6(Sn,In)(5). The mechanical testing results revealed the clear impact of bonding quality on the interconnection strength.

Automated summary

The study demonstrates the use of the Cu-In-Sn ternary system for low-temperature solid liquid interdiffusion (SLID) bonding. Through optimized processes, high strength bonds with low defect content can be achieved at a bonding temperature as low as 170 degrees C. The bonding temperature significantly affects the phase structure and number of defects, with lower temperatures resulting in purer interconnection structures. The bonding quality has a clear impact on the interconnection strength.