Electrostatic wafer clamp

Abstract

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.

What is claimed is:  
     
         1 . Apparatus for electrostatic clamping of a workpiece, comprising: 
 a platen including at least two platen sections, said at least two platen sections comprising a conductive material and being electrically isolated from each other;    a dielectric material disposed on said at least two platen sections, said dielectric material having a clamping surface for receiving a workpiece; and    means for applying a polyphase clamping voltage to said platen, one phase of said polyphase clamping voltage being applied to each of said at least two platen sections so that the workpiece is electrostatically clamped in a fixed position on said clamping surface, wherein each phase of said polyphase clamping voltage comprises a bipolar square wave voltage.