Patent ID: 8475625

Claim:
A processing chamber comprising: a chamber body assembly having an interior volume; a showerhead assembly coupled to a ceiling of the chamber body and having at least two fluidly isolated plenums formed therein, a region transmissive to an optical metrology signal defined through a ceramic plug, a first plurality of gas passages formed through the showerhead assembly fluidly coupling a first plenum of the at least two fluidly isolated plenums to the interior volume of the chamber body, wherein the first gas passages are distributed at a plurality radial distances from a center of the showerhead assembly, and a second plurality of gas passages formed through the showerhead assembly fluidly coupling a second plenum of the at least two fluidly isolated plenums to the interior volume of the chamber body, wherein the second gas passages are distributed at a plurality radial distances from the center of the showerhead assembly, wherein the showerhead assembly further includes a gas distribution plate facing the substrate support assembly fabricated from bulk Yttrium, the gas distribution plate having a plurality of apertures aligned with a plurality of apertures formed in the ceramic plug; and a substrate support assembly disposed in the chamber body.