[54] ELECTROSTATIC WAFER CLAMP
[75] Inventor: William A. Frutiger, Beverly, Mass.
[73] Assignee: Varian Associates, Inc., Palo Alto, Calif.
[21] Appl. No.: 383,554
[22] Filed: Jan. 31, 1995
Related U.S. Application Data
[63] Continuation of Ser. No. 972,617, Nov. 6, 1992, abandoned, which is a continuation-in-part of Ser. No. 535,384, Jun. 8, 1990, abandoned.
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Apparatus for electrostatic clamping of a semiconductor wafer in a vacuum processing chamber wherein an ion beam is applied to the wafer. In a first embodiment, the apparatus includes an electrically conductive platen, a resilient, thermally-conductive dielectric layer affixed to the platen and one or more conductive wires positioned on the clamping surface. A clamping voltage is applied between the wires and the platen to firmly clamp the wafer against the clamping surface and depress the wires into the resilient dielectric layer. In a second embodiment, a three-phase wafer clamping apparatus includes a platen divided into three electrically isolated sections. One phase of a three-phase clamping voltage is connected to each of the platen sections. In the three-phase configuration, the wafer charging current is very small, and the clamping force is essentially constant. In a third embodiment, a six phase wafer clamping apparatus includes a platen having six symmetrically located electrodes. Voltages with six different phases are applied to the electrodes, with the voltages applied to electrodes on opposite sides of the platen being one-half cycle out of phase. The applied voltages are preferably bipolar square waves.
39 Claims, 11 Drawing Sheets
SIX POLE E-CLAMP
