Gas control in process chamber

A process chamber comprising:

• a sidewall;
• a substrate support including a plurality of substrate holders disposed at different angular locations around the substrate support, the substrate support rotatable around an interior region of the process chamber;
• an exhaust vent disposed above each substrate holder in the process chamber, wherein a processing region is formed between each exhaust vent and the substrate support, and each exhaust vent is coupled to an exhaust device configured to create a low pressure at the exhaust vent relative to the processing region;
• and
• a gas ring comprising:
• an annular shaped body having an inner surface that circumscribes an annular region;
• a plurality of first nozzles for coupling to a first gas source and configured to deliver a first gas to the processing region, wherein the plurality of first nozzles are formed in the annular shaped body in a first circular array;
• and
• a plurality of second nozzles for coupling to a second gas source and configured to deliver a second gas to the processing region, wherein the plurality of second nozzles are formed in the annular shaped body in a second circular array.