This work studied plasma effects on the resistivity, effective free carrier concentration, and mobility of As (+)-doped, F-implanted polycrystalline silicon (polysilicon) thin films of various thicknesses. It was found that the resistivity of the polysilicon thin film increases with the decrease of the thickness of the film. This is mainly due to the decrease of the effective carrier concentration and mobility through the decrease of the grain size which is limited by the thickness of the him. Hydrogen and NH3 plasma treatments decrease the effective carrier concentration of the film through neutralization of As ions. This effect is more evident for the thinner films (< 60 nm). The mobility of the high F-dose sample (3 x 10(15) cm(-2)) is larger than that of the low F-dose samples (1 x 10(15) cm(-2)), because the implanted F atoms passivate trapping states of the polysilicon thin film. Through the use of the F implantation passivation and the NH3-plasma treatment, a polysilicon film of a high mobility can be obtained.