High-quality Ge/Si hetero-bonding by sputtered microcrystalline Ge interlayer

We report a high-quality germanium (Ge) and silicon (Si) wafer bonding based on an intermediate layer of 5 nm-thick microcrystalline Ge. The bubble evolution, crystalline state evolution, and oxide layer evolution at the wafer-bonded interface are investigated. The mechanisms of bubble elimination and oxide layer disappearance are systematically analyzed. The sputtered microcrystalline Ge film consists of an amorphous Ge (a-Ge) layer and a low-quality single-crystal Ge (c-Ge) layer. The bubbles can be eliminated by the loose structure of the low-quality c-Ge at the bonded interface. Thus, the bubble-free bonded interface can be obtained. Besides, the bonding strength decreases with the increase of the sputtering temperature. The pressure on the bonded wafers before post-annealing can eliminate large bubbles and improve bonding strength. It is worth mentioning that the oxide layer and the threading dislocations are not observed at the bonded interface. This study can give a guidance for the subsequent manufacture of high-performance Si-based Ge optoelectronic devices.