Fin field-effect transistor and preparation method therefor

The invention discloses a fin field-effect transistor and a preparation method therefor. When the preparation method for the fin field-effect transistor (FinFET) is adopted to prepare a FinFET device, silicon fin parts and isolation parts are formed firstly; then the silicon fin parts are etched in an in-situ manner to a reserved space for formation of silicon germanium fins and germanium fins; and finally, the silicon germanium fins and the germanium fins are formed through epitaxial growth in sequence. Since that the silicon germanium fins are between a silicon substrate and the germanium fins, an effect of a strain buffer layer is played, thereby reducing the lattice mismatch degree between germanium and silicon; and therefore, a precondition is established for the formation of the germanium fins; and a condition that the reliability of the FinFET device is lowered caused by morphological defects of the germanium fins due to the fact that the small-dimensional gaps between the isolation parts cannot be filled with germanium when the germanium material is directly used for filling the gaps is avoided.