Study on crystallization mechanism of GeSn interlayer for low temperature Ge/Si bonding

Low temperature bonding technologies is necessary in next-generation photonic integrated circuits, such as flexible optoelectronic devices, low dark current Ge/Si devices and so on. Since Germanium-Tin (GeSn) alloy has lower crystallization temperature, in this work, amorphous GeSn with 5% Sn alloy by magnetron sputtering is introduced as an intermediate layer for wafer bonding innovatively. And high strength Ge/Si heterojunction with a crystal GeSn layer is realized without any surface activation process. Two mechanisms in the interlayer crystallization are put forward and substantiated experimentally and theoretically: (1) the a-GeSn turns to be poly-GeSn due to the induction of the c-Ge substrate. (2) Stress between Si wafer and interlayer due to thermal mismatch contributes to the crystallization. It is concluded that GeSn semiconductor interlayer bonding would be one of the potential technologies for bonding process.