Patent ID: 7276135

Claim:
A vacuum plasma processor comprising: a vacuum plasma chamber for processing a workpiece, the chamber including a first electrode assembly arranged to be electrically coupled with gas in the chamber and a second electrode assembly arranged to be electrically coupled with gas in the chamber, the first electrode assembly including a first electrode, the second electrode assembly including second and third electrodes spaced from each other; an AC electric source arrangement connected to at least one of said electrodes, the AC source arrangement having sufficient power to excite the gas in the chamber to a plasma; the chamber and the electrode assemblies being arranged for causing (a) plasma exciting AC electric fields at a frequency of the source arrangement to subsist between the first and second electrode assemblies and (b) a DC bias voltage to be developed on at least one of said electrodes in response to the gas in the chamber being excited to a plasma; a detector for the DC bias voltage; and circuitry connected to be responsive to the detector for controlling the plasma exciting AC electric fields; the first assembly including a fourth electrode at least substantially surrounding the first electrode; the fourth electrode being coaxial with the first, second and third electrodes and having a circular periphery and being substantially coplanar with the first electrode; the chamber and electrode assemblies being arranged for causing third electric field lines at an AC frequency of the source arrangement to subsist between the first and fourth electrodes; the chamber, electrode assemblies and the circuitry being arranged for causing the circuitry to affect the third electric field lines in response to the detected DC bias voltage.