Germanium surface hydrophilicity and low-temperature Ge layer transfer by Ge–SiO2 bonding

Wafer bonding and layer transfer are two fundamental technologies in the fabrication of advanced microsystems. In the authors’ experiments, prior to Ge wafer bonding, the hydrophilicity of the germanium surface after wet chemical treatment and O2/N2 plasma activation is evaluated by contact angle measurement. The effects and mechanism of wet or dry treatments on the Ge surface roughness are also characterized. The results are used to tailor the Ge–SiO2 direct bonding process. Finally, oxygen plasma activation for 10 s and B+/H+ coimplantation are employed to facilitate Ge–SiO2 direct bonding and Ge layer transfer at a low temperature. In comparison with hydrogen only ion implantation using the same fluence, coimplantation of B+ and H+ decreases the layer transfer temperature from over 400–320 °C.