SEMICONDUCTOR WAFER METROLOGY APPARATUS AND METHOD

• US 20100206098A1
• Filed: 09/30/2008
• Published: 08/19/2010
• Est. Priority Date: 10/04/2007
• Status: Active Grant

• Current Assignee: Metryx Limited (Lam Research Corporation)
• Original Assignee: Metryx Limited (Lam Research Corporation)
• Inventors: Wilby, Robert John
• Granted Patent: US 8,683,880 B2
• Time in Patent Office: Days
• US Class Current: 73/865
• CPC Class Codes: G01G 21/22 Weigh pans or other weighing receptacles; Weighing platforms
• CPC Class Codes: G01G 23/00 Auxiliary devices for weighing apparatus
• CPC Class Codes: G01G 23/14 Devices for determining tare weight or for cancelling out the tare by zeroising, e.g. mechanically operated in connection with automatic loading G01G13/14
• CPC Class Codes: G01G 9/00 Methods of, or apparatus for, the determination of weight, not provided for in groups G01G1/00 - G01G7/00
• CPC Class Codes: H01L 21/67253 Process monitoring, e.g. flow or thickness monitoring

Abstract

A semiconductor wafer metrology technique which corrects for the effect of electrostatic forces on an atmospheric buoyancy compensated weight force measurement of a semiconductor wafer. In one aspect a wafer is weighed in a faraday cage whose is measured independently. A change in the measured weight of the faraday cage can be used to correct the measure weight the wafer. In another aspect a direct electrostatic measurement can be converted into a weight correction using a predetermined correlation between an electrostatic charge measured by the charge meter and a weight error force. In another aspect the electrostatic measurement may be indirect, e.g. derived from varying the distance between the wafer and a grounded plate parallel to the wafer to effect a change in an electrostatic force between the grounded plate and the wafer.

Claims

1. A method of measuring the mass of a semiconductor wafer, the method including:

placing the wafer on a sensing element of a first weighing instrument, the sensing element of the first weighing instrument being inside a grounded faraday cage which is on a sensing element of a second weighing instrument whereby the weight of the faraday cage is measurable independently of the weight of the wafer;

determining a change in a measured weight of the faraday cage indicated by the second weighing instrument when the wafer is placed inside the faraday cage; and

correcting a measured weight of the wafer indicated by the first weighing instrument using the determined change in measured weight.

2. A method according to claim 1, including compensating for buoyancy exerted on the wafer by the atmosphere in the faraday cage.

3. A method according to claim 1, including obtaining a baseline measured weight of the faraday cage indicated by the second weighing instrument immediately before the wafer is placed inside the faraday cage, wherein the change in measured weight of the faraday cage is determined by calculating a difference between a weight indicated by the second weighing instrument after the wafer is placed inside the faraday cage and the baseline measured weight.

4. A method according to claim 1, wherein the measured weight of the wafer is corrected by subtracting the determined change in measured weight indicated by the second weighing instrument from the measured weight of the wafer indicated by the first weighing instrument.

6. A method according to claim 1, including positioning the wafer substantially equidistant between two parallel grounded conductive plates.

5. (canceled)

7. (canceled)

8. Apparatus for measuring the mass of a semiconductor wafer, the apparatus having:

a first weighing instrument for measuring the weight of the wafer;

a faraday cage for containing the wafer during measurement; and

a second weighing instrument for measuring the weight of the faraday cage independently from the wafer when the wafer is contained within the faraday cage.

9. Apparatus according to claim 8, having monitoring means arranged to determine the buoyancy exerted on the wafer by the atmosphere in the cage.

12. Apparatus according to claim 8, wherein the first weighing instrument includes a weighing pan for supporting the wafer during weight measurement, the weighing pan being made from or having a surface layer made from an electrically insulating material.

16. Apparatus according to claim 8, including two parallel grounded conductive plates locatable equidistant from a wafer when its weight is measured by the first weighing instrument.

17. Apparatus according to claim 8, including a grounded conductive guard ring locatable around a periphery of a wafer when its weight is measured by the first weighing instrument.

10-11. -11. (canceled)

13-15. -15. (canceled)

18. (canceled)

19. A method of measuring the mass of a semiconductor wafer, the method including:

placing the wafer on a weighing instrument;

measuring an electrostatic charge in or on the wafer; and

using a predetermined correlation between measured electrostatic charge and weight error force experienced by the weighing instrument to correct the weight of the wafer measured by the weighing instrument.

21. A method according to claim 19, wherein the electrostatic charge is measured by a charge meter that is operable to measure the electric field strength created by the wafer'"'"'s charge.

20. (canceled)

22-29. -29. (canceled)

30. Apparatus for measuring the mass of a semiconductor wafer, the apparatus having:

a weighing instrument for measuring the weight of the wafer;

a charge meter for measuring the electrostatic charge in and/or on the wafer; and

a processor arranged to correct the weight of the wafer measured by the weighing instrument by using a predetermined correlation between an electrostatic charge measured by the charge meter and a weight error force experienced by the weighing instrument.

31-43. -43. (canceled)

44. A method of measuring the mass of a semiconductor wafer, the method including:

placing the wafer on a sensing element of a weighing instrument;

varying the distance between the wafer and a grounded plate parallel to the wafer to effect a change in an electrostatic force between the grounded plate and the wafer;

determining a relationship between weight measurement indicated by the weighing instrument and distance between the wafer and the grounded plate; and

based on the relationship, obtaining a weight measurement which compensates for the electrostatic force.

45. (canceled)

46. Apparatus for measuring the mass of a semiconductor wafer, the apparatus having:

a weighing instrument for measuring the weight of the wafer;

a grounded plate locatable parallel to the wafer and movable in order to vary a distance between the grounded plate and the wafer to effect a change in an electrostatic force between the grounded plate and wafer; and

a processor arranged to determine a relationship between weight measurement indicated by the weighing instrument and distance between the wafer and the grounded plate, and to use the determined relationship to obtain a weight measurement which compensates for the electrostatic force.

47-55. -55. (canceled)