Apparatus and method for actively controlling the DC potential of a cathode pedestal
First Claim
1. Apparatus for controlling a DC potential on a cathode pedestal used to support a workpiece, comprising:
- a variable DC power supply coupled to said cathode pedestal;
a cathode bias control unit, coupled to said variable DC power supply, for generating a control signal that causes said DC power supply to produce a particular DC voltage, said control signal being generated in response to indicia of arcing potential between said workpiece and said cathode pedestal.
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Abstract
A method and apparatus for actively controlling the DC cathode potential of a wafer support pedestal within a semiconductor wafer processing system. The apparatus contains a variable DC power supply coupled through an RF filter to a cathode pedestal. The variable DC power supply is actively controlled by a control signal generated by a cathode bias control unit, e.g., a computer or other control circuitry. The cathode bias control unit can be as simple as an operator adjustable control signal, e.g., a rheostat. However, for more accurate control of the DC power supply, a feedback circuit is used that generates a control signal that is proportional to the peak-to-peak voltage on a cathode pedestal. The application of the DC bias to the pedestal reduces the DC potential difference between the wafer and the cathode and, thereby avoids arcing from the wafer to the pedestal.
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Citations
13 Claims
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1. Apparatus for controlling a DC potential on a cathode pedestal used to support a workpiece, comprising:
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a variable DC power supply coupled to said cathode pedestal; a cathode bias control unit, coupled to said variable DC power supply, for generating a control signal that causes said DC power supply to produce a particular DC voltage, said control signal being generated in response to indicia of arcing potential between said workpiece and said cathode pedestal. - View Dependent Claims (2, 3, 4, 5, 6, 8)
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7. Apparatus for controlling a DC potential on a cathode pedestal used to support a workpiece, comprising:
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a variable DC power supply, coupled to said cathode pedestal, for applying a DC voltage to the cathode pedestal in response to a control voltage; an RF probe, coupled to said cathode pedestal, for generating an AC voltage signal; a positive peak detector, coupled to said RF probe, for producing a positive peak voltage; a negative peak detector, coupled to said RF probe, for producing a negative peak voltage; a differential amplifier, coupled to said positive peak detector and said negative peak detector, for producing a peak-to-peak value of said AC voltage signal; and a transfer function generator, coupled to said differential amplifier, for producing said control signal in response to said peak-to-peak value.
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9. A method of controlling a DC potential on a cathode pedestal used to support a workpiece, comprising the steps of:
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detecting an indicia of arcing between the workpiece and pedestal; generating, in response to said indicia of arcing, a DC voltage having a magnitude that reduces the probability of arcing; and applying said DC voltage to said cathode pedestal. - View Dependent Claims (10, 11, 12, 13)
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Specification