US Patent 10354843 Chemical control features in wafer process equipment

Gas distribution assemblies are described including an annular body, an upper plate, and a lower plate. The upper plate may define a first plurality of apertures, and the lower plate may define a second and third plurality of apertures. The upper and lower plates may be coupled with one another and the annular body such that the first and second apertures produce channels through the gas distribution assemblies, and a volume is defined between the upper and lower plates.