An apparatus for producing a plasma suitable for semiconductor processing at pressures in the low millitorr range. The apparatus includes a vacuum chamber with a dielectric window, a generally planar coil disposed adjacent the window outside the chamber and coupled to an appropriate power source, and a plasma initiator disposed within the chamber. Once the plasma is initiated, the planar coil sustains the plasma by inductive power coupling. In one embodiment the plasma initiator is a secondary electrode disposed within the chamber and coupled to a second RF power source. In an alternative embodiment both the secondary electrode and a target pedestal are coupled to the secondary RF power source through a power splitter. In an alternative embodiment, the plasma initiator is used to ionize a portion of the process gas and provide a plasma that may then inductively couple with the planar coil. Initial ionization of the process gas may be achieved by use of an ultraviolet light source, an ultraviolet laser, a high voltage power source such as a tesla coil, or an electrical arc forming device such as a spark plug. A further aspect of the invention concerns introducing optical energy of preselected frequencies or wavelengths into a semiconductor processing plasma to induce changes in the composition or character of reactive species within the plasma.