A plasma processing system includes a radical source chamber including a gas inlet, an electrode coupled to a radio frequency (RF) power source, where the electrode is configured to generate radicals within the radical source chamber, and an exit for radicals generated within the radical source chamber; a plenum attached to the exit of the radical source chamber, where the plenum is made of a first thermal conductor, and where the walls of the plenum include openings for gas flow; and a process chamber connected to the radical source chamber through the plenum. The process chamber includes a substrate holder disposed below the plenum; a gas outlet below the substrate holder; and process chamber walls including a second thermal conductor, where the process chamber walls of the process chamber are thermally coupled to the walls of the plenum.