Epitaxial Germanium on SOI Substrate and Its Application of Fabricating High ${\rm I}_{\rm ON}/{\rm I}_{\rm OFF}$ Ratio Ge FinFETs

Integrating germanium (Ge) thin film on silicon-on-insulator (SOI) substrate and fabricating Ge fin field-effect transistors (FinFETs) are demonstrated in this paper. Directly grown Ge film on a high-resistivity thin SOI substrate provides a good platform for fabricating advanced Ge devices. The SOI structure could effectively suppress junction leakage; therefore, high I_ON/I_OFF ratio (~5×10⁵, at VD=0.1 V) of the drain current is achieved. Tri-gate structure provides better short-channel control abilities for the Ge FinFETs, and the drain-induced barrier lowering and threshold voltage (V_TH) shift can be maintained at the level of ~110 mV/V and ~ 0.1 V, respectively, for Ge n-channel FinFET with L_channel=120 nm and W_Fin=40 nm. Multifin Ge FinFET with L_channel=170 nm and W_Fin=50 nm is also illustrated. Both N- and P-FinFETs possess high I_ON/I_OFF ratio over 10⁴. Besides, the subthreshold swing could be reduced around 25% after forming gas annealing.