In this work, the ferroelectricity of hafnium zirconium oxide (Hf0.5Zr0.5O2, HZO) is enhanced by fluorine (F)-plasma treatment, which is used to fabricate MoS2 negative-capacitance field-effect transistor. Measurements show that the subthreshold swing of the transistor is significantly reduced to 17.8 mV dec-1 over almost four orders of output current, as compared to its counterpart without the F-plasma treatment (37.4 mV dec-1). The involved mechanism is that during the F-plasma treatment, F atoms can be incorporated into the HZO bulk to passive its oxygen vacancies and interface traps, thus forming robust Zr-F and Hf-F bonds. Therefore, the F-plasma-treated HZO film exhibits much less oxygen vacancies than the untreated HZO film, which is beneficial to enhancing the amplification effect on the surface potential of the MoS2 channel during the NC operation.