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A showerhead electrode assembly of a plasma processing apparatus includes a thermal control plate attached to a showerhead electrode, and a top plate attached to the thermal control plate. At least one thermal bridge is provided between opposed surfaces of the thermal control plate and the top plate

A showerhead electrode assembly of a plasma processing apparatus includes a thermal control plate attached to a showerhead electrode, and a top plate attached to the thermal control plate. At least one thermal bridge is provided between opposed surfaces of the thermal control plate and the top plate to allow electrical and thermal conduction between the thermal control plate and top plate. A lubricating material between the thermal bridge and the top plate minimizes galling of opposed metal surfaces due to differential thermal expansion between the top plate and thermal control plate. A heater supported by the thermal control plate cooperates with the temperature controlled top plate to maintain the showerhead electrode at a desired temperature.

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What is claimed is: 1. A showerhead electrode assembly of a semiconductor substrate processing apparatus, comprising: a top plate; a showerhead electrode comprising a plate; a backing plate including a bottom surface attached to an upper surface of the plate; a thermal control plate including a cen

What is claimed is: 1. A showerhead electrode assembly of a semiconductor substrate processing apparatus, comprising: a top plate; a showerhead electrode comprising a plate; a backing plate including a bottom surface attached to an upper surface of the plate; a thermal control plate including a central portion, an outer portion and a flexure portion extending from and connecting the outer portion to the central portion, the central portion being attached to a top surface of the backing plate and to the top plate such that the central portion of the thermal control plate is movable relative to the top plate, the outer portion being attached to the top plate, and the flexure portion being configured to accommodate differential thermal expansion between the top plate and the thermal control plate; a heater on the central portion of the thermal control plate adapted to heat the thermal control plate; and at least two laterally spaced apart thermal bridges between the central portion of the thermal control plate and the top plate, the thermal bridges providing a thermal and electrical path between the showerhead electrode and the top plate. 2. The showerhead electrode assembly of claim 1, wherein each of the thermal bridges comprises a layer of graphite material providing thermal and electrical conductivity between the thermal control plate and the top plate, the graphite material being located within a vacuum seal comprising at least one O-ring. 3. The showerhead electrode assembly of claim 2, wherein each of the layers of graphite material has an annular configuration and a width of from about 0.75 inch to about 1.25 inch. 4. The showerhead electrode assembly of claim 1, wherein the heater is a three-phase heater. 5. The showerhead electrode assembly of claim 1, wherein the heater comprises a laminate including a resistive heating material between opposed layers of a dielectric material. 6. The showerhead electrode assembly of claim 1, wherein the top plate includes at least one flow passage through which a heat transfer fluid is flowed to control the temperature of the top plate. 7. The showerhead electrode assembly of claim 1, wherein the backing plate is a graphite backing plate, the plate of the showerhead electrode is a silicon plate, the backing plate and silicon plate are attached by an elastomer bond. 8. The showerhead electrode assembly of claim 1, wherein the thermal control plate is a machined piece of aluminum or an aluminum alloy. 9. The showerhead electrode assembly of claim 1, wherein the top plate is attached to the thermal control plate with fasteners which extend through openings in the top plate, the showerhead electrode assembly optionally including a cover plate attached to a top side of the top plate and sealing the openings such that the fasteners are exposed to vacuum pressure in the processing apparatus. 10. The showerhead electrode assembly of claim 1, wherein the top plate is attached to the thermal control plate with fasteners which extend through oversized openings in the top plate and are screwed into threaded openings in the at least two thermal bridges, each of the thermal bridges comprising at least one O-ring which provides a vacuum seal between the thermal control plate and the top plate such that the fasteners are exposed to atmospheric pressure. 11. The showerhead electrode assembly of claim 1, wherein the top plate is attached to the thermal control plate with fasteners which extend through openings in the top plate, the openings having diameters larger than diameters of the fasteners to accommodate differential thermal expansion between the top plate and the thermal control plate. 12. The showerhead electrode assembly of claim 1, wherein the at least two thermal bridges comprises two spaced apart annular projections on the thermal control plate, the top plate is attached to the thermal control plate with fasteners which extend through oversized openings in the top plate and into each of the thermal bridges, and the thermal control plate includes laterally extending gas passages through the projections and axially extending gas passages between opposed surfaces of the thermal control plate located laterally inwardly and outwardly of the thermal bridges.