Interface characteristics of different bonded structures fabricated by low-temperature a-Ge wafer bonding and the application of wafer-bonded Ge/Si photoelectric device

摘要

We report the interface characteristics of Si/Si, Si/SiO2, SiO2/SiO2, Ge/Si, Ge/Ge, and Ge/SiO2 bonded wafers based on an amorphous germanium (a-Ge) intermediate layer. The crystallization of a-Ge and the atom migration mechanism at different bonded structures are very different. The a-Ge turns into polycrystalline Ge (poly-Ge) at Si/Si bonded interface, while it exhibits amorphous phase at Si/SiO2 and SiO2/SiO2 interfaces after post-annealing. This is due to the change of the stress field when SiO2 is introduced. Thanks to the crystallization of a-Ge, serious atom migration appears at Si/Si bonded interface, leading to the decomposition of the interface oxide layer formed by the hydrophilic reaction. Interestingly, the a-Ge at Ge/Si, Ge/Ge, and Ge/SiO2 interface becomes single-crystal Ge after post-annealing. The a-Ge crystallization starts from a-Ge/Ge interface. Similarly, the interface Ge oxide layer also decomposes after the crystallization of a-Ge. This results from the atom redistribution triggered by Ge-induced crystallization under high thermal stress. More importantly, the threading dislocations are not observed at Ge/Si and Ge/SiO2 interface. The Si/Si, Si/SiO2, SiO2/SiO2, and Ge/SiO2 bonded interface is demonstrated to be bubble-free. The transferring of the interface by-products (H2O and H-2) by SiO2 and poly-Ge can be responsible for this phenomenon. Finally, a wafer-bonded Ge/Si heterojunction photodiode is fabricated to verify the application of a-Ge wafer bonding technique in photoelectric devices.