Methods and apparatus for improving an RF excited reactive gas plasma

Claim 1

Apparatus for controlling the plasma etching of at least one surface of a workpiece which comprises: a hermetically-sealed reaction chamber; first and second, spaced-apart, electrodes positioned within said chamber, said workpiece being supported by at least said second electrode for exposure to the plasma; means for supplying at least one gas species to said reaction chamber; means for maintaining a predetermined level of vacuum within said chamber, said means also serving to exhaust spend gases and reaction by-products from the chamber; a source of RF energy for establishing an alternating field between said first and second electrodes thereby to excite said gas species to form an RF reactive gas plasma; a DC blocking capacitor intermediate the output of said source of RF energy and said first electrode; a variable source of DC potential; an RF-choke interconnecting a first output terminal of said variable source of DC potential and said first electrode; a voltage-controlled-resistor having a control electrode connected intermediate a second output terminal of said variable DC source and ground; and an RF-choke interconnecting the control electrode of said voltage-controlled-resistor and said second electrode.