Novel low-temperature interconnects for 2.5/3D MEMS integration: demonstration and reliability

To meet the essential demands for high-performance microelectromechanical system (MEMS) integration, this study developed a novel Cu-Sn-based solid-liquid interdiffusion (SLID) interconnect solution. The study utilized a metallization stack incorporating a Co layer to interact with low-temperature Cu-Sn-In SLID. Since Cu6(Sn,In)5 forms at a lower temperature than other phases in the Cu-Sn-In SLID system, the goal was to produce single-phase (Cu,Co)6(Sn,In)5 interconnects. Bonding conditions were established for the Cu-Sn-In/Co system and the Cu-Sn/Co system as a reference. Thorough assessments of their thermomechanical reliability were conducted through high-temperature storage (HTS), thermal shock (TS), and tensile tests. The Cu-Sn-In/Co system emerged as a reliable low-temperature solution with the following key attributes: 1) a reduced bonding temperature of 200 °C compared to the nearly 300 °C required for Cu-Sn SLID interconnects to achieve stable phases in the interconnect bondline; 2) the absence of the Cu3Sn phase and resulting void-free interconnects; and 3) high thermomechanical reliability with tensile strengths exceeding the minimum requirements outlined in the MIL-STD-883 method 2027.2, particularly following the HTS test at 150 °C for 1000 h.