A method and apparatus for processing a semiconductor substrate are described herein. A process system described herein includes a plasma source and a flow distribution plate. A method described herein includes generating fluorine radicals or ions, delivering the fluorine radicals or ions through one or more plasma blocking screens to a volume defined by the flow distribution plate and one of one or more plasma blocking screens, delivering oxygen and hydrogen to the volume, mixing the oxygen and hydrogen with fluorine radicals or ions to form hydrogen fluoride, flowing hydrogen fluoride through the flow distribution plate, and etching a substrate using bifluoride. The concentration of fluorine radicals or ions on the surface of the substrate is reduced to less than about two percent.