A gas injection system for an ion beam device, the gas injection system including an extraction plate, an extraction aperture formed in the extraction plate for allowing passage of an ion beam, a first gas distributor removably fastened to the extraction plate on a first side of the extraction aperture, the first gas distributor having a gas orifice formed therein, a second gas distributor removably fastened to the extraction plate on a second side of the extraction aperture opposite the first side, the second gas distributor having a gas orifice formed therein, a first gas conduit extending through the extraction plate between the first gas distributor and a gas manifold mounted to the extraction plate, and a second gas conduit extending through the extraction plate between the second gas distributor the gas manifold, and a residue removal gas source connected to the gas manifold.