gas outlet and a first valve seat assembly the first purge line comprises a first purge gas inlet and a first purge gas outlet the first purge gas outlet of the first purge line is in communication with the first delivery line downstream of the first valve seat assembly the second valve includes a second delivery line and a second purge line the second delivery line comprises a second reactant gas inlet a second reactant gas outlet and a second valve seat assembly the second purge line comprises a second purge gas inlet and a second purge gas outlet the second purge gas outlet of the second purge line is in communication with the second delivery line downstream of the second valve seat assembly the reactor chamber could also comprise a substrate support having a substrate receiving surface the chamber further includes a chamber lid having a passageway at a central portion of the chamber lid and a tapered bottom surface extending from the passageway to a peripheral portion of the chamber lid the bottom surface of the chamber lid is shaped and sized to substantially cover the substrate receiving surface one or more valves are coupled to the passageway and one or more gas sources are coupled to each valve in one aspect the bottom surface of the chamber lid may be tapered in another aspect a reaction zone defined between.