Clamped monolithic showerhead electrode

A method of treating a semiconductor substrate in a plasma chamber, said method comprising the steps of:

• supporting the semiconductor substrate on a bottom electrode in the chamber;
• supplying process gas to the chamber;
• forming a plasma adjacent an exposed surface of an upper electrode;
• and
• processing the semiconductor substrate with the plasma;
• wherein the upper electrode comprises a showerhead electrode comprising:
• 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.