Clamped monolithic showerhead electrode
An electrode assembly for a plasma reaction chamber used in semiconductor substrate processing. The assembly includes an upper showerhead electrode which is mechanically attached to a backing plate by a series of spaced apart cam locks. A guard ring surrounds the backing plate and is movable to positions at which openings in the guard ring align with openings in the backing plate so that the cam locks can be rotated with a tool to release locking pins extending from the upper face of the electrode.
1. A method of replacing a showerhead electrode of a showerhead electrode assembly comprising a showerhead electrode having:
a central portion and a peripheral portion defined by upper and lower faces of the showerhead electrode, the upper face including a planar surface extending across the central portion and part way across the peripheral portion, the upper face including an annular recess outward of the planar surface, the lower face defined by a planar inner surface extending across the central portion and a stepped outer surface extending across the peripheral portion, the stepped outer surface including an annular planar surface defining an area of increased thickness of the showerhead electrode;
a plurality of gas outlets in the central portion of the electrode through which process gas can be delivered to a gap between the showerhead electrode and a lower electrode on which a wafer is supported;
a plurality of circumferentially spaced apart pockets in the annular recess, the pockets configured to received cam locks therein adapted to clamp the showerhead electrode to a backing plate;
a backing plate including axially extending bores aligned with the pockets in the showerhead electrode and radially extending bores communicating with the axially extending bores;
rotatable camshafts mounted in the radially extending bores;
locking pins located in the pockets in the showerhead electrode, the locking pins including enlarged heads at free ends thereof, the camshafts including cutouts adapted to engage and lock the heads of the locking pins so as to mechanically clamp the showerhead electrode to the backing plate, comprising releasing the cam locks to disengage the cam locks from the locking pins, removing the showerhead electrode, aligning locking pins of a new or refurbished showerhead electrode with the axial bores in the backing plate, and rotating the cam locks to engage the heads of the locking pins.
2. The method of claim 1 , wherein the showerhead electrode includes alignment pin bores in the upper face, the alignment pin bores being mated with alignment pins extending into the backing plate.
3. The method of claim 1 , wherein the locking pins are movable axially and laterally in the sockets to accommodate differential thermal expansion of the backing plate and the showerhead electrode.
4. The method of claim 1 , wherein the showerhead electrode is a plate of polycrystalline silicon, single crystal silicon, silicon carbide, aluminum, anodized aluminum or yttria coated aluminum and the backing plate is a plate of aluminum.
5. The method of claim 1 , wherein the backing plate is free of thermal control coolant passages and heating elements.
6. The method of claim 1 , wherein a gas seal is located between the backing plate and the showerhead electrode, the gas seal being located outwardly of the gas passages.