Combined spatial filter and relay systems

• US 7,317,530 B2
• Filed: 03/22/2005
• Issued: 01/08/2008
• Est. Priority Date: 08/28/2003
• Status: Active Grant

• Current Assignee: J.A. Woollam Co., Inc.
• Original Assignee: J.A. Woollam Co., Inc.
• Inventors: Liphardt, Martin M., He, Ping
• Primary Examiner(s): Chowdhury; Tarifur
• Assistant Examiner(s): Akanbi; Isiaka O
• Application Number:
  US11/085,450
• Publication Number:
  US 20060268271A1
• Time in Patent Office: 1,022 Days
• Field of Search: 356/317, 356/369
• US Class Current: 356/369
• CPC Class Codes: G01J 3/02 Details
• CPC Class Codes: G01J 3/0208 using focussing or collimating elements, e.g. lenses or mirrors; performing aberration correction
• CPC Class Codes: G01J 3/021 using plane or convex mirrors, parallel phase plates, or particular reflectors
• CPC Class Codes: G01J 3/0229 using masks, aperture plates, spatial light modulators or spatial filters, e.g. reflective filters
• CPC Class Codes: G01J 3/0243 having a through-hole enabling the optical element to fulfil an additional optical function, e.g. a mirror or grating having a throughhole for a light collecting or light injecting optical fiber
• CPC Class Codes: G01J 4/00 Measuring polarisation of light
• CPC Class Codes: G01N 21/211 Ellipsometry optical thickness measurement G01B11/06
• CPC Class Codes: G02B 17/008 Systems specially adapted to form image relays or chained systems

Abstract

Low aberration relay systems modified to perform as spatial filters in reflectometer, spectrophotometer, ellipsometer, polarimeter and the like systems.

Claims

1. A combined spatial filter and relay system comprising three elements:

a) a concave spherical mirror having at least one concave spherical surface and an aperture hole therethrough;

b) a flat mirror; and

c) a convex spherical mirror having at least one convex spherical surface;

said elements being arranged such that electromagnetic radiation caused to approach the concave spherical mirror passes through said aperture hole thereby forming an effective point source of electromagnetic radiation thereat, then proceeds as an expanding electromagnetic beam and reflects from said flat mirror onto a first location of a concave surface of said concave spherical mirror, then reflects from said first location onto a convex spherical surface of said convex spherical mirror and reflects therefrom onto a second location of said concave surface of said concave spherical mirror from which it reflects as a converging beam of electromagnetic radiation.

2. A system for investigating a sample as in claim 1 which further comprises a coating on at least one of the concave, convex and flat mirrors which changes the intensity vs. wavelength plot of a reflected electromagnetic beam relative to an incident beam.

3. A system for investigating a sample as in claim 1, in which said aperture hole is actually or effectively non-circular.

4. A combined spatial filter and relay system comprising:

a) an aperture;

b) a flat mirror;

c) a concave spherical mirror having at least one concave spherical surface; and

d) a convex spherical mirror having at least one convex spherical surface;

said elements being arranged such that electromagnetic radiation caused to approach from said aperture forms an effective point source of electromagnetic radiation thereat, then proceeds as an expanding electromagnetic beam and is caused to approach the flat mirror and reflect therefrom onto a first location of a concave surface of said concave spherical mirror, reflect from said first location onto a convex spherical surface of said convex spherical mirror and reflect therefrom onto a second location of said concave surface of said concave spherical mirror from which it reflects as a converging beam of electromagnetic radiation.

5. A combined spatial filter and relay system as in claim 4, which further comprises a second flat mirror positioned to intercept and reflect electromagnetic radiation reflected from said second location of said concave surface of said concave spherical mirror as a converging beam of electromagnetic radiation.

6. A system for investigating a sample as in claim 4 which further comprises a coating on at least one of the concave, convex and flat mirrors which changes the intensity vs. wavelength plot of a reflected electromagnetic beam relative to an incident beam.

7. A system for investigating a sample as in claim 4, in which said aperture is actually or effectively non-circular.

8. A combined spatial filter and relay system comprising five elements:

a) an aperture;

b) a first flat mirror;

c) a concave spherical mirror having at least one concave spherical surface;

d) a convex spherical mirror having at least one convex spherical surface; and

e) a second flat mirror;

said elements being arranged such that electromagnetic radiation caused to approach said aperture forms an effective point source of electromagnetic radiation thereat, then proceeds as an expanding electromagnetic beam and is caused to approach the first flat mirror and reflect therefrom onto a first location of a concave surface of said concave spherical mirror, reflect from said first location onto a convex spherical surface of said convex spherical mirror and reflect therefrom onto a second location of said concave surface of said concave spherical mirror from which it reflects onto said second flat mirror positioned to intercept and reflect electromagnetic radiation reflected from said second location of said concave surface of said concave spherical mirror as a converging beam of electromagnetic radiation.

9. A combined spatial filter and relay system as in claim 8 wherein electromagnetic radiation from said aperture is caused to approach the first flat mirror at a 45 degree angle, and reflect from said second flat mirror at a 45 degree angle.

10. A system for investigating a sample as in claim 8 which further comprises a coating on at least one of the concave, convex, first flat and second flat mirrors which changes the intensity vs. wavelength plot of a reflected electromagnetic beam relative to an incident beam.

11. A system for investigating a sample as in claim 8, in which said aperture is actually or effectively non-circular.

12. A system for investigating a sample comprising:

a source of electromagnetic radiation;

an aperture;

first and second relay systems, each thereof comprising four elements;

a) a first flat mirror;

b) a concave spherical mirror having at least one concave spherical surface;

c) a convex spherical mirror having at least one convex spherical surface; and

d) a second flat mirror;

said elements being arranged such that electromagnetic radiation is caused to approach the first flat mirror and reflect therefrom onto a first location of a concave surface of said concave spherical mirror, reflect from said first location onto a convex spherical surface of said convex spherical mirror and reflect therefrom onto a second location of said concave surface of said concave spherical mirror from which it reflects onto said second flat mirror positioned to intercept and reflect electromagnetic radiation reflected from said second location of said concave surface of said concave spherical mirror as a converging beam of electromagnetic radiation;

and a detector;

said sample being positioned between said first and second relay systems;

said first relay system being positioned to relay electromagnetic radiation from the source thereof, as it passes through said aperture, and direct it onto a surface of said sample at an oblique angle of incidence, and said second relay system being positioned to receive electromagnetic radiation reflected from the sample and pass it on to said detector;

the propagation direction of electromagnetic radiation entering and exiting each of said first and second relay systems being substantially unchanged by passing therethrough;

said system being further characterized in that a plane formed by the locus of the electromagnetic radiation passing through the first relay system is oriented 90 degrees to a plane formed by the locus of the electromagnetic radiation passing through the second relay system, the purpose being to minimize effects of said first and second relay systems on a polarization state of said electromagnetic radiation which passes through both thereof.

13. A system for investigating a sample as in claim 12 which further comprises:

a) a polarizer between said source and sample; and

b) an analyzer between said sample and detector;

wherein said system is an ellipsometer.

14. A system for investigating a sample as in claim 13 which further comprises at least one compensator between said source and detector.

15. A system for investigating a sample as in claim 12 which further comprises a coating on at least one of the concave, convex, first flat and second flat mirrors which changes the intensity vs. wavelength plot of a reflected electromagnetic beam relative to an incident beam.

16. A system for investigating a sample as in claim 12, in which said aperture is actually or effectively non-circular.

17. A system for investigating a sample comprising:

a source of electromagnetic radiation;

an aperture;

first and second relay systems, each thereof comprising four elements;

a) a first flat mirror;

b) a concave spherical mirror having at least one concave spherical surface;

c) a convex spherical mirror having at least one convex spherical surface; and

d) a second flat mirror;

said elements being arranged such that electromagnetic radiation is caused to approach the first flat mirror and reflect therefrom onto a first location of a concave surface of said concave spherical mirror, reflect from said first location onto a convex spherical surface of said convex spherical mirror and reflect therefrom onto a second location of said concave surface of said concave spherical mirror from which it reflects onto said second flat mirror positioned to intercept and reflect electromagnetic radiation reflected from said second location of said concave surface of said concave spherical mirror as a converging beam of electromagnetic radiation;

and a detector;

said first and second relay systems being positioned on the same side of the sample;

the propagation direction of electromagnetic radiation entering and exiting each of said first and second relay systems being substantially unchanged by passing therethrough;

said system being further characterized in that a plane formed by the locus of the electromagnetic radiation passing through the first relay system is oriented 90 degrees to a plane formed by the locus of the electromagnetic radiation passing through the second relay system, the purpose being to minimize effects of said first and second relay systems on a polarization state of said electromagnetic radiation which passes through both thereof.

18. A system for investigating a sample as in claim 17 which further comprises:

a) a polarizer between said source and sample; and

b) an analyzer between said sample and detector;

wherein said system is an ellipsometer.

19. A system for investigating a sample as in claim 18 which further comprises at least one compensator between said source and detector.

20. A system for investigating a sample as in claim 17 which further comprises a coating on at least one of the concave, convex, first flat and second flat mirrors which changes the intensity vs. wavelength plot of a reflected electromagnetic beam relative to an incident beam.

21. A system for investigating a sample as in claim 17, in which said aperture is actually or effectively non-circular.

22. A system for investigating a sample comprising:

a source of electromagnetic radiation;

an aperture;

a relay system comprising three elements;

a) a flat mirror;

b) a concave spherical mirror having at least one concave spherical surface;

c) a convex spherical mirror having at least one convex spherical surface;

said elements being arranged such that electromagnetic radiation is caused to approach said aperture and form an effective point source of electromagnetic radiation thereat, then proceed as an expanding electromagnetic beam toward the flat mirror and reflect therefrom onto a first location of a concave surface of said concave spherical mirror, reflect from said first location onto a convex spherical surface of said convex spherical mirror and reflect therefrom onto a second location of said concave surface of said concave spherical mirror from which it reflects as a converging beam of electromagnetic radiation;

a sample; and

a detector.

23. A system for investigating a sample as in claim 22 in which said aperture is in said concave spherical mirror.

24. A system for investigating a sample as in claim 22 which further comprises:

a) a polarizer between said source and sample; and

b) an analyzer between said sample and detector;

wherein said system is an ellipsometer.

25. A system for investigating a sample as in claim 22 which further comprises at least one compensator between said source and detector.

26. A system for investigating a sample as in claim 22 which further comprises a coating on at least one of the concave, convex, first flat and second flat mirrors which changes the intensity vs. wavelength plot of a reflected electromagnetic beam relative to an incident beam.

27. A system for investigating a sample as in claim 22, in which said aperture is actually or effectively non-circular.