Plasma apparatus including dielectric window for inducing a uniform electric field in a plasma chamber

An apparatus for plasma etching or plasma deposition, comprising:

• a housing having a chamber in which a wafer can be treated with plasma, the housing including at least one inlet port connected to an interior of the chamber through which process gas can be supplied to the chamber;
• a radiofrequency energy source comprising a plasma generating electrode arranged to pass radiofrequency energy into the chamber and induce plasma in the interior of the chamber by activating, with an electric field induced by the radiofrequency energy source, process gas supplied to the chamber through the inlet port the plasma generating electrode inducing a flow of electrons within a planar region in the chamber;
• and
• a dielectric window having an inner surface thereof forming part of an inner wall of the chamber, radiofrequency energy passing from the radiofrequency energy source to the interior of the chamber through the dielectric window, the dielectric window having a thickness which varies at different points along the inner surface thereof such that the thickness is largest at a central portion of the dielectric window, the dielectric window being effective to decrease the induced electric field in the interior of the chamber near the central portion of the dielectric window.