Low-temperature Al-Ge bonding for 3D integration

Low-temperature aluminum-germanium (Al-Ge) bonding has been investigated for monolithic three-dimensional integrated circuit (3DIC) applications. As upper layer devices of a monolithic 3DIC are fabricated in situ, a suitable technique for providing high-quality semiconducting material without inflicting damage to underlying circuits below is needed. Here, the authors demonstrate a method of attaching high-quality single-crystal Si (100) and Ge (100) islands (3-3000 mu m in size) onto amorphous SiO2 substrates using both eutectic (435 degrees C) and subeutectic (400 degrees C) Al-Ge bonding. The 30 min, 3DIC compatible process utilizes Al-Ge bilayer films as thin as 157 nm to form void-free bonds strong enough to withstand SmartCut (R) hydrogen splitting of the donor wafer. The fracture energy of the Al-Ge bond was measured to be G(C)=50.5 +/- 12.7 J/m(2), as measured by the double cantilever beam thin-film adhesion measurement technique. (C) 2012 American Vacuum Society. [http://dx.doi.org/10.1116/1.4762844]