Patent ID: 8440049

Claim:
A showerhead assembly, comprising: a gas distribution plate having an outer set of gas flow holes, an inner set of gas flow holes, and a set of optical metrology holes; an upper section coupled to the gas distribution plate and having a first plenum fluidly coupled to the outer set of gas flow holes and a second plenum fluidly coupled to the inner set of gas flow holes, the plenums being fluidly isolated within the upper section, wherein the upper section further comprises: a base having a stepped recess; a first plate disposed in the recess; a second plate disposed in the recess between the first plate and the base; and a barrier wall disposed between the first and second plates and separating the first and second plenums; concentric rings of adhesive coupling the gas distribution plate to the upper section, wherein the concentric rings maintaining the gas distribution plate spaced from the upper section to form radially isolated concentric plenums defined between the gas distribution plate and the upper section; beads of adhesive disposed between the concentric rings of adhesive, wherein gases present between the gas distribution plate, the upper section and a pair of adhesive rings may flow around the beads; and a ceramic plug disposed within the upper section and having an optically transmissive region having a plurality of passages aligned with the optical metrology holes; wherein a window disposed through the upper section and aligned with the plug; and wherein the gas distribution plate covers the stepped recess, and the window is disposed in the stepped recess.