Electrostatic charge measurement on semiconductor wafers

• US 6,781,205 B1
• Filed: 10/11/2002
• Issued: 08/24/2004
• Est. Priority Date: 10/11/2002
• Status: Expired due to Term

• Current Assignee: Illinois Tool Works Inc.
• Original Assignee: Ion Systems Inc (Illinois Tool Works Inc.)
• Inventors: Ignatenko, Alexander, Levit, Lawrence B.
• Primary Examiner(s): Nadav, Ori
• Application Number:
  US10/269,426
• Time in Patent Office: 683 Days
• Field of Search: 257/355-363, 206/701, 206/706, 206/709-712
• US Class Current: 257/355
• CPC Class Codes: H01L 21/67253 Process monitoring, e.g. flow or thickness monitoring

Abstract

An enclosure for transporting semiconductor wafers includes a pair of sensors that are responsive to electrostatic fields mounted on conductive grounded plates in facing orientations on opposite sides of a position within the enclosure at which a semiconductor wafer is to be located. Electronic circuitry within the enclosure in communication with the sensors supplies monitoring signals to remote circuitry external to the enclosure that isolates sources of contaminants and provides remote balance and gain adjustments. Calibration of the balance and gain adjustments uses a grounded plate for zero balance reference, and uses a plate of insulating material that is charged to a known potential for referencing gain adjustments to produce related outputs.

Claims

1. Apparatus for monitoring electrostatic fields on a semiconductor wafer, comprising:

an enclosure including side walls having a plurality slots for supporting at least one semiconductor wafer therein;

at least one conductive layer supported within the enclosure in substantially plane-parallel, spaced orientation relative to a semiconductor wafer supported therein;

a sensor responsive to electrostatic field disposed on the conductive layer on a side thereof facing a position at which a semiconductor wafer is to be supported within the enclosure;

electronic circuitry communicating with the sensor and mounted within the enclosure for producing a monitoring signal indicative of the sensor response to electrostatic field; and

remote circuitry disposed external to the enclosure and communicating with the electronic circuitry for producing an output signal representative of the monitoring signal from the electronic circuitry.

2. Apparatus as in claim 1 including a pair of the conductive layers disposed within the enclosure on opposite sides of a semiconductor wafer supported therein;

a pair of said sensors, each mounted on one of the conductive layers on facing sides thereof;

electronic circuitry for each of the sensors mounted within the enclosure and communicating with a respective one of the pair of sensors, each for producing the monitoring signal indicative of the respective sensor response to electrostatic field; and

the remote circuitry communicates with the electronic circuitry for the pair of sensors for producing output signals representative of the monitoring signals from the electronic circuitry for each of the pair of sensors.

3. Apparatus according to claim 1 in which the conductive layer is grounded;

and

the sensor responds to electrostatic field associated with charge on a semiconductor wafer transferred into or out of the enclosure.

4. Apparatus according to claim 1 in which the remote circuitry alters balance and gain of the monitoring signal to produce the output signal therefrom.

5. Apparatus according to claim 3 in which the sensor is mounted near a forward edge of the conductive layer in position to sense electrostatic field along a segment of a semiconductor wafer transferred into or out of the enclosure.

6. Apparatus according to claim 1 in which the remote circuitry alters balance level of the monitoring signal relative to ground potential, and alters gain of the output signal relative to the monitoring signal.

7. A method for calibrating field-sensing apparatus including a field sensor and monitoring circuitry disposed to sense electrostatic field associated with charge on a semiconductor wafer that is supportable within an enclosure, the method comprising:

processing a signal produced in response to the sensor sensing electrostatic field associated with charge to produce an output;

altering the processing of the signal to produce zero output in response to the sensor sensing ground reference potential; and

altering the processing of the signal to produce an output directly proportional to the sensor sensing electrostatic field associated with a known potential.

8. The method of claim 7 including a field sensor on each side of a semiconductor wafer that is supportable within an enclosure, the method comprising:

processing signals produced in response to each sensor sensing electrostatic field to produce outputs therefrom;

altering the processing of each signal to produce zero outputs in response to the sensors sensing ground reference potential; and

altering the processing of each signal to produce outputs directly related to the sensors sensing electrostatic fields associated with known potentials.

9. The method according to claim 7 in which a grounded conductive plate is disposed at a location near the sensor at which a semiconductor wafer is to be located for altering the processing to produce zero output on ground reference potential.

10. The method according to claim 7 in which an insulated plate is charged to a known potential and is disposed at a location near the sensor at which a semiconductor wafer is to be located for altering the processing to produce the output related to the known potential.

11. The method according to claim 8 in which a grounded conductive plate is disposed at a location intermediate the sensors at which a semiconductor wafer is to be located for altering the processing to produce zero outputs on ground reference potential.

12. The method according to claim 8 in which an insulated plate is charged to a known potential and is disposed at a location intermediate the sensors at which a semiconductor wafer is to be located for altering the processing to produce the outputs related to the known potential.

13. A method of sensing electrostatic field on a substrate wafer including electrically insulating material upon transfer to or from a housing, the method comprising:

positioning an isopotential surface at least on one side adjacent a position in the housing for receiving a substrate wafer; and

sensing field on an adjacent surface of a substrate wafer relative to the isopotential surface during transfer of the substrate wafer into or out of the housing.

14. The method according to claim 13 in which positioning includes positioning electrically conductive plates spaced apart an opposite sides of the position in the housing for receiving a substrate wafer;

and

sensing includes sensing electrostatic fields associated with charge along paths of relative movement between locations on the plates and a substrate wafer during transfer thereof into or out of the housing to produce electrical outputs indicative of the field sensed on opposite sides of the substrate wafer.

15. The method according to claim 13 in which the isopotential surface is grounded.

16. The method according to claim 14 in which field sensing is performed from said locations that are disposed near forward edges of the plates.