Electrostatic wafer clamp
First Claim
1. Apparatus for electrostatic clamping of a workpiece, comprising:
- a platen having a substantially circular, electrically insulating clamping surface for receiving a workpiece and at least six platen sectors each having a conductive electrode underlying and electrically isolated from said clamping surface said electrodes being configured in pairs symmetrically disposed about a center of said clamping surface, said clamping surface comprising a dielectric material selected to avoid sticking of the workpiece thereto after clamping; and
clamping control means for applying AC voltages to said electrodes when clamping of the workpiece is desired, the workpiece being electrostatically clamped in a fixed position on said clamping surface when said AC voltages are applied to said electrodes, said clamping control means comprising means for generating at least six bipolar square wave voltages having relative phases of 0°
, 60°
, 120°
, 180°
, 240° and
300°
, said square wave voltages defining a first set having phases 0° and
180°
, a second set having phases 60° and
240°
, and a third set having phases 120° and
300°
each of said sets including positive and negative, equal amplitude, bipolar square wave voltages that are one half cycle out of phase, each of said bipolar square wave voltages having a predetermined switching speed selected to limit transients which could potentially damage the workpiece, and means for coupling said sets of square wave voltages to said Symmetrically disposed electrode pairs so as to provide symmetrical clamping of said workpiece to said clamping surface providing reliable high speed clamping with reduced risk of damage to said workpiece.
1 Assignment
0 Petitions
Accused Products
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.
113 Citations
39 Claims
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1. Apparatus for electrostatic clamping of a workpiece, comprising:
-
a platen having a substantially circular, electrically insulating clamping surface for receiving a workpiece and at least six platen sectors each having a conductive electrode underlying and electrically isolated from said clamping surface said electrodes being configured in pairs symmetrically disposed about a center of said clamping surface, said clamping surface comprising a dielectric material selected to avoid sticking of the workpiece thereto after clamping; and clamping control means for applying AC voltages to said electrodes when clamping of the workpiece is desired, the workpiece being electrostatically clamped in a fixed position on said clamping surface when said AC voltages are applied to said electrodes, said clamping control means comprising means for generating at least six bipolar square wave voltages having relative phases of 0°
, 60°
, 120°
, 180°
, 240° and
300°
, said square wave voltages defining a first set having phases 0° and
180°
, a second set having phases 60° and
240°
, and a third set having phases 120° and
300°
each of said sets including positive and negative, equal amplitude, bipolar square wave voltages that are one half cycle out of phase, each of said bipolar square wave voltages having a predetermined switching speed selected to limit transients which could potentially damage the workpiece, and means for coupling said sets of square wave voltages to said Symmetrically disposed electrode pairs so as to provide symmetrical clamping of said workpiece to said clamping surface providing reliable high speed clamping with reduced risk of damage to said workpiece. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. Apparatus for electrostatic clamping of a workpiece, comprising:
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a platen having an electrically insulating clamping surface for receiving a workpiece and 2n conductive electrodes, where n is an integer equal to or greater than three, underlying and electrically isolated from said clamping surface; and clamping control means for applying AC voltage to said electrodes when clamping of the workpiece is desired, the workpiece being electrostatically clamped in a fixed position on said clamping surface when said AC voltages are applied to said electrodes, said clamping control means comprising means for generating 2n bipolar square wave voltages having equally shifted relative phases, said square wave voltages defining n sets of square wave voltages, each of said sets including positive and negative, bipolar square wave voltages that are one half cycle out of phase, each of said bipolar square wave voltages having a predetermined switching speed selected to limit transients which could potentially damage the workpiece, and means for coupling said sets of square wave voltages to said electrodes so as to provide symmetrical clamping of the workpiece to said clamping surface. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33, 34, 35)
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36. Apparatus for electrostatic clamping of a workpiece in a vacuum chamber, comprising:
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a platen having a circular, electrically insulating clamping surface for receiving a workpiece, said clamping surface being defined by six dielectric insulators, said platen further including six electrodes underlying said dielectric insulators and an insulating substrate for supporting said electrodes and said dielectric insulators; clamping control means for applying AC voltages to said electrodes when clamping of the workpiece is desired, the workpiece being electrostatically clamped in a fixed position on said clamping surface when said AC voltages are applied to said electrodes, said clamping control means comprising means for generating six bipolar square wave voltages having relative phases of 0°
, 60°
, 120°
, 180°
, 240° and
300°
, said square wave voltages defining first, second and third sets of square wave voltages, each of said sets including positive and negative, equal amplitude, bipolar square wave voltages that are one half cycle out of phase, each of said bipolar square wave voltages having a predetermined switching speed selected to limit transients which could potentially damage the workpiece, and means for coupling said sets of square wave voltages to said electrodes so as to provide symmetrical clamping of the workpiece to said clamping surface;means for introducing a gas into a region between said workpiece and said clamping surface for conducting thermal energy between said workpiece and said clamping surface; and means for cooling said platen. - View Dependent Claims (37)
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38. Apparatus for electrostatic clamping of a workpiece, comprising:
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a platen having an electrically insulating clamping surface for receiving a workpiece and 2n conductive electrodes, where n is an integer equal to or greater than three, underlying and electrically isolated from said clamping surface; and clamping control means for applying AC voltages to said electrodes when clamping of the workpiece is desired, the workpiece being electrostatically clamped in a fixed position on said clamping surface when said AC voltages are applied to said electrodes, said clamping control means comprising means for generating six bipolar square wave voltages having relative phases of 0°
, 60°
, 120°
, 180°
, 240° and
300°
, said square wave voltages defining first, second and third sets of square wave voltages, each of said sets including positive and negative, equal amplitude, bipolar square wave voltages that are one-half cycle out of phase, each of said bipolar square wave voltages having a predetermined switching speed selected to limit transients which could potentially damage the workpiece, and means for coupling said sets of square wave voltages to said electrodes so as to provide symmetrical clamping of the workpiece to said clamping surface. - View Dependent Claims (39)
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Specification