An apparatus to treat a substrate. The apparatus may include a reactive gas source having a reactive gas outlet disposed in a process chamber, the reactive gas outlet to direct a first reactive gas to the substrate; a plasma chamber coupled to the process chamber and including an extraction plate having an extraction aperture extending along a first direction, disposed within the process chamber and movable along a second direction perpendicular to the first direction between a first position facing the reactive gas source and a second position facing the extraction aperture; and a gas flow restrictor disposed between the reactive gas outlet and the extraction aperture, the gas flow restrictor defining a differential pumping channel between at least the plasma chamber and substrate stage.