Aluminum-Germanium eutectic bonding for 3D integration

Low-temperature Aluminum-Germanium (Al-Ge) eutectic bonding has been investigated for monolithic three-dimensional integrated circuits (3DIC) applications. Successful bonds using Al-Ge bilayer films as thin as 157 nm were achieved at temperatures as low as 435 °C, when applying 200 kPa down-pressure for 30 minutes. The liquid phase of the eutectic composition ensured a seamless and void-free bond. The fracture energy of the Al-Ge bond (630 nm thick) was measured to be G c = 50.5 ± 12.7 J/m 2 , using double cantilever beam thin-film adhesion measurement technique. An array of silicon islands was attached onto an amorphous SiO 2 wafer using low-temperature Al-Ge bonding. These islands could be used to form devices on upper layers of monolithically integrated 3DICs.