Clamping a workpiece utilizing polyphase clamping voltage

Abstract

Abstract Apparatus for electrostatic clamping of a workpiece such as a semiconductor wafer in a vacuum processing chamber wherein an ion beam is applied to the wafer is provided. In one 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. The wires protrude at least slightly above the clamping surface except when the wafer is clamped thereon. 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. The clamping voltage preferably comprises a bipolar square wave in the frequency range of less than one Hz to 300 Hz and having a switching rate of about 1000 volts per millisecond or less to limit charging current to the wafer and thereby prevent arcing. In another 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.

Inventors

• 👤 William A. Fritiger

Bibliographic Details