Multi-axis interferometer with procedure and data processing for mirror mapping

• US 20060215173A1
• Filed: 03/17/2006
• Published: 09/28/2006
• Est. Priority Date: 03/18/2005
• Status: Active Grant

• Current Assignee: Zygo Corporation (Ametek Incorporated)
• Original Assignee: Zygo Corporation (Ametek Incorporated)
• Inventors: Hill, Henry A., Womack, Gary
• Granted Patent: US 7,433,049 B2
• Time in Patent Office: Days
• US Class Current: 356/500
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02018 Multipass interferometers, e.g. double-pass
• CPC Class Codes: G01B 9/02019 contacting different points on same face of object
• CPC Class Codes: G01B 9/02021 contacting different faces of object, e.g. opposite faces
• CPC Class Codes: G01B 9/02059 Reducing effect of parasitic reflections, e.g. cyclic errors
• CPC Class Codes: G03F 7/70775 Position control, e.g. interferometers or encoders for determining the stage position

Abstract

In general, in one aspect, the invention features methods that include locating a plurality of alignment marks on a moveable stage, interferometrically measuring a position of a measurement object along an interferometer axis for each of the alignment mark locations, and using the interferometric position measurements to derive information about a surface figure of the measurement object. The position of the measurement object is measured using an interferometry assembly and either the measurement object or the interferometry assembly are attached to the stage.

Claims

1. A method, comprising:

locating a plurality of alignment marks on a moveable stage;

interferometrically measuring a position of a measurement object along an interferometer axis for each of the alignment mark locations; and

using the interferometric position measurements to derive information about a surface figure of the measurement object,

wherein the position of the measurement object is measured using an interferometry assembly and either the measurement object or the interferometry assembly are attached to the stage.

2. The method of claim 1 wherein the information comprises information related to a certain spatial frequency component of the surface figure of the measurement object.

3. The method of claim 1 further comprising using the information to determine the surface figure of the measurement object.

4. The method of claim 3 wherein the surface figure of the measurement object is determined based on values of a parameter associated with a displacement of the measurement object along three different measurement axes in addition to the information.

5. The method of claim 4 wherein the parameter values are determined by interferometrically monitoring the displacement of the measurement object along each of the three different interferometer axes while moving the measurement object relative to the interferometry assembly;

and

determining the parameter values for different positions of the measurement object from the monitored displacements, wherein for a given position the parameter is based on the displacements of the measurement object along each of the three different interferometer axes at the given position.

6. The method of claim 5 wherein the surface figure of the measurement object is determined based on a frequency transform of the parameter values.

7. The method of claim 6 wherein the frequency transform is a Fourier transform.

8. The method of claim 6 wherein the information comprises information related to a certain spatial frequency component of the surface figure of the measurement object at which the frequency transform of the parameter values is substantially insensitive.

9. The method of claim 4 wherein the parameter is a second difference parameter.

10. The method of claim 1 wherein the plurality of alignment marks comprises a linear array of alignment marks.

11. The method of claim 10 wherein the linear array of the alignment marks are nominally parallel to the measurement object during the measuring.

12. The method of claim 10 wherein adjacent alignment marks in the linear array are separated by a distance, d_a, and the information about the surface figure of the measurement object is related to a spatial frequency component of the surface figure having a spatial wavelength Λ

greater than d_a.

13. The method of claim 12 wherein Λ

=4d_a.

14. The method of claim 1 wherein the alignment marks are located on the surface of an object supported by the moveable stage, and locating the alignment marks includes locating the alignment marks for at least two different positions of the object.

15. The method of claim 14 wherein the two different object positions include a first position and a second position where the object is rotated 180°

with respect to the first position.

16. The method of claim 14 wherein the two different object positions include a first position and a second position where the object is translated relative to the first position.

17. The method of claim 16 wherein the translation is by an amount related to a spacing of the alignment marks.

18. The method of claim 1 further comprising using the information about the surface figure of the measurement object to improve the accuracy of measurements made using the interferometry assembly and the measurement object.

19. The method of claim 1 further comprising using a lithography tool to expose a substrate supported by the moveable stage with a radiation pattern while interferometrically monitoring a distance between the interferometry assembly and the measurement object, wherein the position of the substrate relative to a reference frame is related to the distance between the interferometry assembly and the measurement object.

20. A lithography method for use in fabricating integrated circuits on a wafer, the method comprising:

supporting the wafer on a moveable stage;

imaging spatially patterned radiation onto the wafer;

adjusting the position of the stage; and

monitoring the position of the stage using a measurement object and information about the surface figure of the measurement object derived using the method of claim 1 to improve the accuracy of the monitored position of the stage.

21. A lithography method for use in the fabrication of integrated circuits comprising:

directing input radiation through a mask to produce spatially patterned radiation;

positioning the mask relative to the input radiation;

monitoring the position of the mask relative to the input radiation using a measurement object and information about the surface figure of the measurement object derived using the method of claim 1 to improve the accuracy of the monitored position of the mask; and

imaging the spatially patterned radiation onto a wafer.

22. A lithography method for fabricating integrated circuits on a wafer comprising:

positioning a first component of a lithography system relative to a second component of a lithography system to expose the wafer to spatially patterned radiation; and

monitoring the position of the first component relative to the second component using a measurement object and using information about the surface figure of the measurement object derived using the method of claim 1 to improve the accuracy of the monitored position of the first component.

23. A method for fabricating integrated circuits comprising:

applying a resist to a wafer;

forming a pattern of a mask in the resist by exposing the wafer to radiation using the lithography method of claim 20;

and

producing an integrated circuit from the wafer.

24. A method for fabricating integrated circuits comprising:

applying a resist to a wafer;

forming a pattern of a mask in the resist by exposing the wafer to radiation using the lithography method of claim 21;

and

producing an integrated circuit from the wafer.

25. A method for fabricating integrated circuits comprising:

applying a resist to a wafer;

forming a pattern of a mask in the resist by exposing the wafer to radiation using the lithography method of claim 22;

and

producing an integrated circuit from the wafer.

26. A system, comprising:

a moveable stage;

an alignment sensor configured to locate alignment marks associated with the moveable stage;

a interferometer assembly configured to produce three output beams each including interferometric information about a distance between the interferometer and a measurement object along a respective axis, the interferometer assembly or the measurement object being attached to the moveable stage; and

an electronic processor configured to derive information about a surface figure of the measurement object based on data acquired by locating the plurality of alignment marks with the alignment sensor and measuring the position of the measurement object along one of the respective axes of the interferometer assembly for each of the alignment mark locations.

27. The system of claim 26 wherein the measurement object is a plane mirror.

28. The system of claim 26 wherein a surface of the stage includes the alignment marks.

29. The system of claim 26 wherein the stage is configured to support an object that includes the alignment marks.

30. The system of claim 26 wherein the alignment sensor is an optical alignment sensor.

31. The system of claim 26 wherein the optical alignment sensor comprises a microscope.

32. A lithography system for use in fabricating integrated circuits on a wafer, the system comprising:

the system of claim 26;

an illumination system for imaging spatially patterned radiation onto a wafer supported by the moveable stage; and

a positioning system for adjusting the position of the stage relative to the imaged radiation;

wherein the interferometer assembly is configured to monitor the position of the wafer relative to the imaged radiation and electronic processor is configured to use the information about the surface figure of the measurement object to improve the accuracy of the monitored position of the wafer.

33. A method for fabricating integrated circuits comprising:

applying a resist to a wafer;

forming a pattern of a mask in the resist by exposing the wafer to radiation using the lithography system of claim 32;

and

producing an integrated circuit from the wafer.

34. A beam writing system for use in fabricating a lithography mask, the system comprising:

the system of claim 26;

a source providing a write beam to pattern a substrate supported by the moveable stage;

a beam directing assembly for delivering the write beam to the substrate;

a positioning system for positioning the stage and beam directing assembly relative one another;

wherein the interferometer assembly is configured to monitor the position of the stage relative to the beam directing assembly and electronic processor is configured to use the information about the surface figure of the measurement object to improve the accuracy of the monitored position of the stage.

35. A method for fabricating a lithography mask comprising:

directing a beam to a substrate using the beam writing system of claim 34;

varying the intensity or the position of the beam at the substrate to form a pattern in the substrate; and

forming the lithography mask from the patterned substrate.