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Coherent gradient sensing ellipsometer

Imported: 23 Feb '17 | Published: 22 Oct '02

David A. Boyd, Ares J. Rosakis, David M. Owen

USPTO - Utility Patents

Abstract

Systems and techniques for integrating an optical coherent gradient sensing (CGS) module and another optical sensing module to simultaneously measure the curvature and another property of a specularly reflective surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the optical layout of an optical coherent gradient sensing (CGS) ellipsometer according to one embodiment.

FIG. 2 illustrates the operation of the coherent gradient sensing module for extracting curvature information from the reflected beam by using two identical gratings aligned parallel to each other.

FIG. 3 shows another embodiment of the CGS detector having two optical arms for two different shearing directions.

Claims

1. A system, comprising:

2. The system as in claim 1, wherein said first detector module includes two optical gratings disposed process said first reflected probe beam and a first optical detector to receive an output from said two optical gratings.

3. The system as in claim 2, wherein said input module is configured so that said input probe beam is polarized, and wherein said second detector module includes a polarization analyzer to receive said second reflected probe beam and an optical sensing array with a plurality of optical sensing pixels to receive transmission of said polarization analyzer.

4. The system as in claim 3, further comprising a processing circuit coupled to receive output signals from said first and said second detector modules and operable to process information from said second detector module based on said measured curvature from said first detector module to extract information of the sample at each location that is associated with curvature at said each location.

5. The system as in claim 3, further comprising a rotating device engaged to said polarization analyzer to rotate said analyzer.

6. The system as in claim 3, wherein said input module includes an optical retardation element operable to produce a time-varying phase retardation on said input probe beam.

7. The system as in claim 1, wherein said input module and said second detector module are configured to form an ellipsometer to measure a change in a state of polarization of said input probe beam.

8. The system as in claim 7, wherein said ellipsometer is a null ellipsometer.

9. The system as in claim 7, wherein said ellipsometer is photometric ellipsometer.

10. The system as in claim 7, wherein said first detector module includes:

11. The system as in claim 10, further comprising a signal processor connected to receive said electrical signal and configured to extract a spatial gradient information on the wavefront of said reflected probe beam caused by a curvature of the reflective surface, wherein said signal processor determines said curvature of the reflective surface according to said spatial gradient information and processes information from said second detector module based on said curvature to determine a property of the sample.

12. A system, comprising:

13. The system as in claim 12, wherein said optical phase compensator is configured to produce a time-varying retardation on said second reflected probe beam.

14. The system as in claim 12, wherein said polarization analyzer is configured to rotate.

15. The system as in claim 12, wherein said first and second gratings are spaced relative to each other in an optical path of said first reflected probe beam and configured to produce a predetermined phase manipulation on a wavefront of said first reflected probe beam, wherein said first detector module further includes:

16. A method, comprising:

17. The method as in claim 16, wherein a change in polarization of said reflected probe beam is measured in processing said second portion.

18. The method as in claim 17, wherein said another property of said sample includes a thickness of a film formed said sample surface.

19. The method as in claim 17, wherein said another property of said sample includes a refractive index.

20. The method as in claim 17, wherein said another property of said sample includes an optical absorption coefficient.

21. The method as in claim 17, wherein said another property of said sample includes a stress.

22. The method as in claim 16, wherein the processing of said second portion includes:

23. The method as in claim 16, wherein said sample surface is a flat mirror, and further comprising using an error in a measurement of said property to determine a degree of collimation of said probe beam.

24. A method, comprising:

25. The method as in claim 24, wherein said property includes a thickness of a film formed on said sample.

26. The method as in claim 24, wherein said property includes a stress on said sample.

27. The method as in claim 24, further comprising using said ellipsometric measurement to determine a degree of collimation of said probe beam.

28. The method as in claim 24, wherein said curvature is measured by diffracting said second portion of said reflected probe beam through two optical gratings and measuring an interference signal produced by combining two selected diffracted signals.

29. The method as in claim 24, further comprising measuring an optical property of said first portion of said reflected probe beam to infer whether a location on said sample surface is concave or convex.