Chemical control features in wafer process equipment

A gas distribution assembly, comprising:

• an annular body comprising:
• an inner annular wall located at an inner diameter, an outer annular wall located at an outer diameter, an upper surface, and a lower surface;
• an upper plate coupled with the annular body, wherein the upper plate defines a plurality of first apertures;
• an intermediate plate coupled with the upper plate, wherein the intermediate plate defines a plurality of second and third apertures, and wherein the second apertures align with the first apertures of the upper plate;
• and
• a lower plate coupled with the annular body and the intermediate plate, comprising:
• a plurality of fourth apertures defined therein that align with the first apertures of the upper plate and the second apertures of the intermediate plate to form a first set of fluid channels through the plates,
• a plurality of fifth apertures defined therein that align with the third apertures of the intermediate plate to form a second set of fluid channels through the intermediate and lower plates, wherein the second set of fluid channels are fluidly isolated from the first set of fluid channels, and
• a plurality of sixth apertures defined therein that form a third set of fluid channels through the lower plate, wherein the third set of fluid channels are fluidly isolated from the first and second set of fluid channels.