Patent ID: 8083853

Claim:
A gas distribution plate assembly for a plasma processing chamber, comprising: a planar diffuser plate element having an edge, a center, an upstream side and a downstream side, wherein the upstream side and the downstream side are parallel; and inner and outer gas passages passing between the upstream and downstream sides of the diffuser plate element from the center to the edge of the diffuser plate element, each gas passage having: an orifice hole having a first diameter; and a hollow cathode cavity that is downstream of the orifice hole and is at the downstream side, the hollow cathode cavity having a cone or cylinder shape and a second diameter at the downstream side that is greater than the first diameter, the second diameters or the depths or a combination of both of the cones or cylinders increases from the center to the edge of the diffuser plate element, the first diameters are substantially uniform from the center to the edge of the diffuser plate element, and the size of the hollow cathode cavities of the inner gas passages is less than the size of the hollow cathode cavities of the outer gas passages.