OPTICAL IMAGING SYSTEM WITH CATOPTRIC OBJECTIVE; BROADBAND OBJECTIVE WITH MIRROR; AND REFRACTIVE LENSES AND BROADBAND OPTICAL IMAGING SYSTEM HAVING TWO OR MORE IMAGING PATHS

• US 20110242528A1
• Filed: 03/30/2010
• Published: 10/06/2011
• Est. Priority Date: 10/02/2007
• Status: Active Grant

• Current Assignee: KLA-Tencor Corporation (KLA Corporation)
• Original Assignee: KLA-Tencor Corporation (KLA Corporation)
• Inventors: Hudyma, Russell, Shafer, David, Jeong, Hwan J., Kirk, Gregory L., Hwang, Shiow-Hwei
• Granted Patent: US 9,052,494 B2
• Time in Patent Office: Days
• US Class Current: 356/237.2
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G02B 17/084 on-axis systems with at least one of the mirrors having a central aperture
• CPC Class Codes: G03F 1/84 Inspecting

Abstract

An optical system may include an objective having at least four mirrors including an outermost mirror with aspect ratio <20:1 and focusing optics including a refractive optical element. The objective provides imaging at numerical aperture >0.7, central obscuration <35% in pupil. An objective may have two or more mirrors, one with a refractive module that seals off an outermost mirror'"'"'s central opening. A broad band imaging system may include one objective and two or more imaging paths that provide imaging at numerical aperture >0.7 and field of view >0.8 mm. An optical imaging system may comprise an objective and two or more imaging paths. The imaging paths may provide two or more simultaneous broadband images of a sample in two or more modes. The modes may have different illumination and/or collection pupil apertures or different pixel sizes at the sample.

Claims

1. An optical system for sample inspection comprising:

an objective comprising at least four mirrors including an outermost mirror; and

focusing optics optically coupled to the objective, wherein the focusing optics include one or more refractive optical elements,

wherein the objective is configured to provide imaging at a numerical aperture greater than 0.7, central obscuration less than 35% in pupil, and wherein an aspect ratio of outermost mirror at a sample side is no more than 20;

1.

2. The optical system of claim 1 wherein the focusing optics include a relay module configured to relay an aperture stop inside the objective to a pupil plan located outside the objective.

3. The optical system of claim 1 wherein the focusing optics are configured to provide variable magnification.

4. The optical system of claim 1, further comprising a refractive element disposed in a central opening in an outermost mirror of the objective to seal off a central obscuration at the outermost mirror.

5. The optical system of claim 4, further comprising one or more additional refractive elements inside the objective, wherein the one or more additional refractive elements are configured to provide color correction for the refractive element disposed in the central opening in the outermost mirror.

6. The optical system of claim 1 wherein objective is characterized by a negative field curvature.

7. The optical system of claim 6, wherein the focusing optics are characterized by a Petzval curvature that compensates for the field curvature of the objective.

8. The optical system of claim 1 wherein the objective is characterized by a sample field size that is greater than 0.5 mm.

9. The optical system of claim 1 wherein the objective includes six mirrors and is configured to provide imaging of infinite conjugate.

10. The optical system of claim 9 wherein objective includes an outermost mirror module that generates an intermediate field characterized by negative spherical aberration.

11. The optical system of claim 10 wherein the objective includes more than one convex mirror.

12. The optical system of claim 1, further comprising one or more optical elements configured to compensate for optical aberrations between the objective and the focusing optics.

13. An imaging objective, comprising:

two or more mirrors, at least one of which contains a refractive module that seals off a central opening of an outermost mirror of the two or more mirrors in order to substantially isolate an atmosphere inside the objective from a sample atmosphere.

14. The imaging objective of claim 13 wherein the refractive module and one or more mirrors are configured such that light passing through the objective is incident on an optical surface of the refractive module at an angle of incidence that is less than about 25 degrees.

15. The imaging objective of claim 13 wherein the refractive module includes an optical element that is flat or nearly flat.

16. The imaging objective of claim 13 wherein the refractive module is configured to provide a field curvature that is opposite to the field curvature generated by the two or more mirrors.

17. The imaging objective of claim 13 wherein the refractive optical element is configured to compensate for an optical aberration of one or more of the one or more mirrors.

18. The imaging objective of claim 13 wherein the two or more mirrors includes one or more mirrors, other than the outermost mirror, having a body with a central opening and a refractive optical element disposed in the central opening.

19. The imaging objective of claim 18 wherein the refractive optical element is configured to provide color correction.

20. The imaging objective of claim 13 wherein the two or more mirrors include at least four mirrors.

21. The imaging objective of claim 13 wherein the two or more mirrors include at most six mirrors.

22. The imaging objective of claim 21, including six mirrors, wherein said objective is infinite conjugate;

and said objective has a flat Petzval field.

23. The imaging objective of claim 22, wherein said six mirrors include a two-mirror relay group adjacent a convex mirror, the two-mirror relay group including the outermost mirror and another mirror disposed between the convex mirror and the outermost mirror, wherein said two-mirror relay group has a magnification close to one, and wherein said two-mirror relay group has a negative spherical aberration.

24. The imaging objective of claim 23, wherein said slight negative spherical aberration less than two times a distance between a reflective surfaces of the relay mirror and a reflective surface of the convex mirror.

25. A optical imaging system comprising a single objective and two or more broadband imaging paths optically coupled to the objective, wherein the objective and imaging paths are configured to provide broadband imaging at a numerical aperture greater than 0.7 and a field of view greater than 0.8 mm

26. The system of claim 25 wherein each of said two or more imaging paths contains a separate independently accessible pupil.

27. The system of claim 26 wherein the two or more imaging paths are configured to enable simultaneous inspection of a surface of a sample proximate the objective with a plurality of inspection modes.

28. The system of claim 27 wherein said plurality of inspection modes comprises a bright field mode and a dark field mode.

29. The system of claim 28 wherein said plurality of inspection modes comprises two different wavelength bands each wavelength band having a field on the sample and resulting in an image transmitted to a sensor.

30. The system of claim 29, further comprising different sensors coupled to each of said two or more imaging paths for detecting said different wavelength bands.

31. The system of claim 29 wherein said two different wavelength bands include a first band characterized by vacuum wavelengths less than about 250 nm;

and a second band characterized by vacuum wavelengths between about 250 nm and about 450 nm.

32. The system of claim 29 wherein said two different wavelength bands include a first band that is at least 10 nm wide and includes vacuum wavelengths less than 250 nm.

33. The system of claim 32 wherein said two different wavelength bands further include a second band that is greater than 100 nm wide.

34. The system of claim 32, wherein said pupil relay is comprised of refractive elements.

35. The system of claim 34, wherein a single pupil relay is shared between a plurality of said imaging paths.

36. The system of claim 34, wherein each of said two or more imaging paths has a separate pupil relay.

37. The system of claim 29 wherein said two different wavelength bands include a first band that is at least 10 nm wide and includes vacuum wavelengths less than 270 nm.

38. The system of claim 37 wherein the optical components of the imaging paths include one or more refractive optical elements downstream of a split between the two imaging paths.

39. The system of claim 25 wherein the objective comprises at least four mirrors including an outermost mirror, wherein the objective is configured to provide imaging at a numerical aperture greater than 0.7, central obscuration less than 35% in pupil, and wherein an aspect ratio of outermost mirror at a sample side is no more than 20:

1.

40. The system of claim 25 wherein the objective comprises two or more mirrors, at least one of which contains a refractive module that seals off a central opening of an outermost mirror of the two or more mirrors in order to substantially isolate an atmosphere inside the objective from a sample atmosphere.

41. The system of claim 25, wherein each of said two or more imaging paths includes:

a pupil relay;

a pupil; and

a zoom/variable magnification module.

42. The system of claim 25, wherein each of said two or more imaging paths includes a variable magnification module operable to provide a plurality of magnifications that map into a plurality of pixel sizes.

43. The system of claim 25, wherein said two or more imaging paths have independent alignment and magnification adjustment.

44. The system of claim 25, wherein each of said imaging paths includes a sensor having a data rate, and wherein said data rate of each said sensor can be set independently.

45. The system of claim 25, further including a plurality of illumination paths.

46. The system of claim 45, wherein an optical spectrum, output power, and illumination configuration are independently chosen and adjusted for each of said illumination paths.

47. The system of claim 46, wherein said illumination configuration includes:

numerical aperture, illumination aperture, polarization, light power, and illumination location on the sample.

48. The system of claim 25 wherein the at least one of said imaging paths includes a long range optical trombone.

49. An optical imaging system, comprising an objective configured to collect light from a sample located proximate the objective and two or more imaging paths optically coupled to the objective, wherein the two or more imaging paths are configured to provide a corresponding two or more simultaneous images of the sample in a corresponding two or more modes, wherein each mode of the two or more modes is characterized by an illumination pupil aperture and/or a collection pupil aperture and wherein each of the two or more simultaneous images is a broad band image.

50. An optical imaging system, comprising an objective configured to collect light from a sample located proximate the objective and two or more imaging paths optically coupled to the objective, wherein the two or more imaging paths are configured to provide a corresponding two or more simultaneous images of the sample in a corresponding two or more modes, wherein each mode of the two or more modes is characterized by a different pixel size at the sample.

51. A optical imaging system comprising a single objective and two or more imaging paths optically coupled to the objective, wherein the imaging paths are configured to transmit two different wavelength bands, wherein at least one wavelength band is a broadband wavelength band have a wavelength bandwidth greater than 10 nm in width, wherein illumination for the two different wavelength bands is coupled to a sample through the objective, wherein the objective and imaging paths are configured to provide imaging at a numerical aperture greater than 0.7 and a field of view greater than 0.8 mm.