Patent ID: 8796153

Claim:
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, the upper electrode comprising 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, 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 the semiconductor substrate is supported; and a plurality of circumferentially spaced apart pockets in the upper face, the pockets configured to receive cam locks therein adapted to clamp the showerhead electrode to a backing plate; heating the showerhead electrode and backing plate to an elevated temperature which causes differential thermal expansion of the showerhead electrode and the backing plate, and accommodating the thermal expansion by movement of locking pins; and processing the semiconductor substrate with the plasma.