Variable annular illuminator for photolithographic projection imager

• US 5,452,054 A
• Filed: 11/21/1994
• Issued: 09/19/1995
• Est. Priority Date: 03/01/1993
• Status: Expired due to Term

• Current Assignee: Ultratech Stepper East, Inc. (Veeco Instruments Incorporated), Ultratech Stepper, Inc. (Veeco Instruments Incorporated)
• Original Assignee: General Signal Corporation (SPX Corporation)
• Inventors: Partlo, William N., Dewa, Paul G., Michaloski, Paul F., Tompkins, Paul J.
• Primary Examiner(s): Yeung, James C.
• Assistant Examiner(s): Sember, Thomas M.
• Application Number:
  US08/342,787
• Time in Patent Office: 302 Days
• Field of Search: 355/67, 355/53, 355/70, 355/71, 355/77, 362/332, 362/281, 362/268, 362/277, 362/28, 353/201, 353/203, 359/385, 359/789
• US Class Current: 355/67
• CPC Class Codes: G03F 7/70108 Off-axis setting using a light-guiding element, e.g. diffractive optical elements [DOEs] or light guides
• CPC Class Codes: G03F 7/70141 Illumination system adjustment, e.g. adjustments during exposure or alignment during assembly of illumination system
• CPC Class Codes: G03F 7/702 Reflective illumination, i.e. reflective optical elements other than folding mirrors, e.g. extreme ultraviolet [EUV] illumination systems

Abstract

The illumination of a photolithographic projection imager is given a variable annular intensity profile by using diverging and counter diverging elements that are movable relative to each other in the illumination path. An upstream element diverges the illumination into an annular configuration, the radius of which is set by the distance downstream to the counter diverging element. Convex and concave conical surfaces on the movable elements can accomplish this.

Claims

1. A combination of an illuminator and a photolithographic projection imager, the combination comprising:

a. an illuminator optical system for directing illumination from a source to a pupil of the illuminator from which a reticle is illuminated to be imaged on a wafer by an objective imaging system;

b. the illuminator in a collimated region of illumination upstream of the illuminator pupil having a pair of refractive elements having conical surfaces that are respectively concave and convex; and

c. said elements being arranged so that an upstream one of said elements diverges the illumination into a single beam having an annular configuration of intensity and a downstream one of said elements counters the divergence caused by the upstream element, to give the illumination an annular intensity profile of the single beam at the pupil of the illuminator.

2. The combination of claim 1 wherein the distance between said elements is variable, to vary the radius of said annular intensity profile to accommodate characteristics of the reticle.

3. The combination of claim 2 wherein said distance between said elements can be reduced enough to counter said divergence approximately at its source to keep said intensity configuration from becoming annular.

4. The combination of claim 1 wherein said upstream element has said concave conical surface and said downstream element has said convex conical surface.

5. The combination of claim 1 wherein a mask is positionable at said pupil within said annular intensity profile.

6. The combination of claim 1 wherein said concave and convex conical surfaces have the same conic angle.

7. The combination of claim 1 wherein said elements are separated by an air gap.

8. The combination of claim 1 wherein said conical surfaces are arranged to confront each other.

9. The combination of claim 8 wherein the distance between said elements is variable, to vary the radius of said annular intensity profile to accommodate characteristics of the reticle.

10. The combination of claim 8 wherein said conical surfaces can be moved into proximity for countering said divergence to keep said intensity configuration from becoming annular.

11. The combination of claim 10 wherein a mask of variable size is positionable downstream of said conical surfaces within said annular intensity profile.

12. The combination of claim 1 wherein said refractive elements are faceted.

13. In an illuminator for a photolithographic projection imager, the improvement comprising:

a. a first refractive element arranged in a collimated region of an illumination path of said illuminator upstream of a pupil of said illuminator so that a conical surface of said first refractive element diverges the illumination into a single beam having an annular configuration of intensity;

b. a second refractive element arranged to receive diverged illumination from said first refractive element, and said second refractive element having a conical surface arranged for countering the illumination divergence caused by said first refractive element, to fix the radius of the divergence of the single beam of said illumination; and

c. the radius of divergence of the illumination output from the second refractive element appearing as an annular intensity profile of illumination at the pupil region of the illuminator causing illumination with an annular intensity profile to illuminate a reticle that is imaged onto a wafer by an objective imaging system of the photolithographic projection imager.

14. The improvement of claim 13 wherein said conical surface of said first refractive element is concave, and said conical surface of said second refractive element is convex.

15. The improvement of claim 13 wherein said first and second refractive elements are separated by an air gap.

16. The improvement of claim 13 wherein a distance between said refractive elements is variable for varying said radius of illumination divergence to accommodate characteristics of the reticle.

17. The improvement of claim 16 wherein a minimum of said variable distance between said refractive elements results in said second element countering the illumination divergence so that the configuration of illumination intensity does not become annular.

18. The improvement of claim 16 including a variable size mask arranged for blocking illumination within said annular configuration of intensity.

19. The improvement of claim 13 wherein said conic surfaces of said first and second refractive elements have the same conic angle.

20. The improvement of claim 13 wherein said conic surfaces of said first and second refractive elements confront each other.

21. The improvement of claim 20 wherein a distance between said refractive elements is variable for varying said radius of illumination divergence to accommodate characteristics of the reticle.

22. The improvement of claim 21 wherein said illumination divergence is substantially eliminated by moving said conic surfaces into proximity.

23. The improvement of claim 21 wherein illumination within said annular configuration of intensity is blocked by a mask.

24. The improvement of claim 13 wherein said conic surfaces of said first and second refractive elements face away from each other.

25. The improvement of claim 13 wherein said refractive elements are faceted.

26. An illuminator combined with a photolithographic projection imager, the combination comprising:

a. the illuminator having an optical system for directing illumination along an optical axis of the illuminator upstream of a pupil of the illuminator so that an intensity profile of the illumination at the illuminator pupil is directed to a reticle that is imaged on a wafer by an objective imaging system of the photolithographic projection imager;

b. a diverging element arranged in a collimated region of the illumination path of said illuminator upstream of the illuminator pupil for diverging said illumination into a single beam having an annular configuration of intensity;

c. a counter diverging element arranged in said illumination path at a variable distance from said diverging element for receiving said diverging illumination;

d. said counter diverging element being arranged for countering the divergence of said illumination and fixing the radius of said annular configuration of intensity of the single beam as a function of the distance between said elements; and

e. the annular configuration of illumination intensity output from the counter diverging element appearing as an annular intensity profile of the single beam of illumination at the illuminator pupil and at the reticle so that the radius of the annular intensity profile accommodates characteristics of the reticle.

27. The combination of claim 26 wherein said elements are refractive and have faceted surfaces.

28. The combination of claim 26 wherein said elements are concentrically diffractive.

29. The combination of claim 26 wherein said elements are reflective and have conical surfaces,

30. The combination of claim 26 wherein said elements are refractive and have conical surfaces,

31. The combination of claim 30 wherein said conical surfaces are concave on one of said elements and convex on another of said elements.

32. The combination of claim 31 wherein said concave and convex conical surfaces confront each other.

33. The combination of claim 32 wherein said counter diverging element can be positioned for countering said diverging illumination so that the illumination intensity profile does not become annular.

34. The combination of claim 31 wherein said concave and convex conical surfaces face away from each other,

35. The combination of claim 26 wherein said diverging element is refractive and has a concave conical surface,

36. The combination of claim 37 wherein said counter diverging element is refractive and has a convex conical surface.

37. The combination of claim 26 wherein said counter diverging element can be positioned for countering said diverging illumination so that said intensity configuration does not become annular.

38. The combination of claim 26 including a variable size mask positioned to block illumination within said annular configuration.