A method is provided for performing plasma immersion ion implantation with a highly uniform seasoning film on the interior of a reactor chamber having a ceiling and a cylindrical side wall and a wafer support pedestal facing the ceiling. The method includes providing a gas distribution ring with plural gas injection orifices on a periphery of a wafer support pedestal, the orifices facing radially outwardly from the wafer support pedestal. Silicon-containing gas is introduced through the gas distribution orifices of the ring to establish a radially outward flow pattern of the silicon-containing gas. The reactor includes pairs of conduit ports in the ceiling adjacent the side wall at opposing sides thereof and respective external conduits generally spanning the diameter of the chamber and coupled to respective pairs of the ports. The method further includes injecting oxygen gas through the conduit ports into the chamber to establish an axially downward flow pattern of oxygen gas in the chamber. RF power is coupled into the interior of each of the conduits to generate a toroidal plasma current of SixOy species passing through the chamber to deposit a seasoning layer of a SixOy material on surfaces within the chamber, while leaving the pedestal without a wafer so as to expose a wafer support surface of the pedestal.