In one embodiment, an apparatus for performing an atomic layer deposition process is provided which includes a chamber body having a substrate support, a lid assembly attached to the chamber body, and delivery sub-assemblies coupled to the lid assembly and configured to deliver process gases into a centralized expanding conduit, which extends through the lid assembly and expands radially outward. The first gas delivery sub-assembly contains an annular mixing channel encircling and in fluid communication with the centralized expanding conduit, wherein the annular mixing channel is adapted to deliver a first process gas through a plurality of passageways and nozzles and into the centralized expanding conduit. A first gas inlet may be coupled to the annular mixing channel and positioned to provide the first process gas to the annular mixing channel. The second gas delivery sub-assembly contains a second gas inlet in fluid communication to the centralized expanding conduit.