Patent ID: 7385799

Claim:
A method for clamping a workpiece, the method comprising: providing a clamping system comprising a multi-polar electrostatic clamp and a power source, wherein the multi-polar electrostatic clamp comprises a clamping plate and a plurality of electrodes; placing the workpiece on a surface of the clamping plate; applying a plurality of phases of an AC clamping voltage to the plurality of electrodes via the power source, wherein at least one of the plurality of phases of the AC clamping voltage applied to at least one of the plurality of electrodes is shifted with respect to the remaining of the plurality of phases by an offset phase shift; determining a fluctuation in clamping force between the clamping plate and the workpiece during a cycle of the AC clamping voltage; and controlling the offset phase shift, based; at least in part, on the determined fluctuation in clamping force, an RC time constant of the clamping system, and a set of performance criteria.