Disclosed embodiments generally relate to a processing chamber that includes a perforated lid, a gas blocker disposed on the perforated lid, and a substrate support disposed below the perforated lid. The gas blocker includes a gas manifold, a central gas channel formed in the gas manifold, a first gas distribution plate that includes inner and outer trenches surrounding the central gas channel, and a first and second gas channels formed in the gas manifold. The first gas channel is in fluid communication with a first gas source and the inner trench, and the second gas channel is in fluid communication with the first gas source and the outer trench and a second gas distribution plate The first gas channel is in further fluid communication with a third gas distribution plate that is disposed below the second gas distribution plate, and a plurality of pass-through channels that are disposed between the second gas distribution plate and the third gas distribution plate. The second gas distribution plate includes a plurality of through holes formed through a bottom of the second gas distribution plate as well as a central opening in fluid communication with the central gas channel The second gas distribution plate further includes a recess region formed in a top surface of the second gas distribution plate, and the recess region surrounds the central opening.