Electrostatic wafer clamp having electrostatic seal for retaining gas

摘要

Methods and apparatus are provided for holding a workpiece, such as a semiconductor wafer, during processing. The apparatus includes a platen assembly, a gas source and voltage source. The platen assembly includes a dielectric element that defines an electrically insulating clamping surface for receiving a workpiece and electrodes underlying the clamping surface. The electrodes include sealing electrodes at or near a periphery of the clamping surface. The gas source provides a gas in a region between the workpiece and the clamping surface for conducting thermal energy between the workpiece and the clamping surface. The voltage source applies sealing voltages to the sealing electrodes for producing an inwardly moving wave in the workpiece. Gas is transported inwardly away from the periphery of the clamping surface by the inwardly moving wave. The sealing electrodes may have the form of concentric rings at or near the periphery of the clamping surface.