Patent ID: 8328939

Claim:
A gas distribution plate assembly, comprising: a diffuser plate element having an upstream side, a downstream side, a first edge to be disposed adjacent a slit valve in a processing chamber, a center, and a second edge; and a plurality of gas passages passing between the upstream side and the downstream side, each gas passage having a choke and a hollow cathode cavity with the chokes of the gas passages being substantially identical, the plurality of gas passages comprise: a first gas passage having a first hollow cathode cavity disposed adjacent the first edge of the diffuser plate element; a second gas passage having a second hollow cathode cavity disposed adjacent the center of the diffuser plate element; and a third gas passage having a third hollow cathode cavity disposed adjacent the second edge, wherein the first hollow cathode cavity, second hollow cathode cavity, and third hollow cathode cavity have different volumes, wherein the third hollow cathode cavity volume is greater than the first hollow cathode cavity volume and the second hollow cathode cavity volume.