Patent ID: 8236133

Claim:
A ceiling gas distribution assembly for use in a plasma reactor for processing a semiconductor substrate, comprising: a planar gas injection orifice plate comprising concentric inner, intermediate and outer annular zones of gas injection orifices; a central gas receiving hub overlying said orifice plate, said hub comprising three gas supply ports and having a hub bottom surface and three concentric hub channels formed in said hub bottom surface and internally coupled to respective ones of said three gas supply ports; a translation gas manifold underlying said hub and comprising three sets of internal gas flow channels associated with said inner, intermediate and outer zones, respectively, each of said internal gas flow channels comprising: (a) a gas input opening at a top surface of said translation gas manifold in registration with a respective one of said concentric hub channels and (b) a gas output opening at a bottom surface of said translation gas manifold at a radius corresponding to a respective one of said inner, intermediate and outer zones; an equal path length (EPL) manifold between said translation gas manifold and said orifice plate and providing gas flow paths of equal path lengths from the gas output openings of individual ones of said zones to the gas injection orifices of the same zones; wherein said gas flow paths of equal path lengths comprise a hierarchy of radial channels and a hierarchy of circumferential channels, said radial channels coupling between successive circumferential channels; and wherein circumferential channels are configured as arcs corresponding to fractions of circles.