Offset phase operation on a multiphase AC electrostatic clamp
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United States of America Patent
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Jun 10, 2008
Grant Date -
N/A
app pub date -
Feb 7, 2007
filing date -
Feb 7, 2007
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A method for clamping a workpiece is provided, wherein a workpiece is placed on a surface of a clamping plate of a multi-polar electrostatic clamp having a plurality of electrodes. A plurality of phases of the AC clamping voltage are applied to the plurality of electrodes, 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 plurality of phases by an offset phase shift. A fluctuation in clamping force between the clamping plate and the workpiece during a cycle of the at least one of the plurality of phases of AC clamping voltage is determined, and the offset phase shift is controlled, 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.
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