In one example, a process chamber comprises a lid assembly, a first gas supply, second gas supply, a chamber body, and a substrate support. The lid assembly comprises a gas box, a gas conduit passing through the gas box, a blocker plate, and a showerhead. The gas box comprises a gas distribution plenum, and a distribution plate comprising a plurality of holes aligned with the gas distribution plenum. The blocker plate is coupled to the gas box forming a first plenum. The showerhead is coupled to the blocker plate forming a second plenum. The first gas supply is coupled to the gas distribution plenum, and the second gas supply system is coupled to the gas conduit. The chamber body is coupled to the showerhead, and the substrate support assembly is disposed within an interior volume of the chamber body, and is configured to support a substrate during processing.