Lithographic apparatus and device manufacturing method

• US 20050012915A1
• Filed: 08/18/2004
• Published: 01/20/2005
• Est. Priority Date: 10/19/2001
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Neijzen, Jacobus Hermanus Maria, Monshouwer, Rene
• Granted Patent: US 7,312,846 B2
• Time in Patent Office: Days
• US Class Current: 355/53
• CPC Class Codes: G03F 9/7049 Technique, e.g. interferometric
• CPC Class Codes: G03F 9/7076 Mark details, e.g. phase grating mark, temporary mark
• CPC Class Codes: G03F 9/7088 Alignment mark detection, e.g. TTR, TTL, off-axis detection, array detector, video detection

Abstract

An off-axis alignment system in a lithographic projection apparatus uses broadband radiation to illuminate a phase grating on the wafer. The broadband radiation source may include fluorescent materials, e.g. Yag:Ce or ND:Yag crystals illuminated by excitation light.

Claims

1-14. -14. (Cancelled).

15. An alignment system for aligning a substrate in a lithographic apparatus comprising:

an illumination system configured to illuminate a phase grating on the substrate; and

an imaging system configured to image diffracted light from said phase grating onto a reference grating substantially correctly at at least two distinct wavelengths.

16. An alignment system according to claim 15, wherein the illumination system is configured to illuminate the phase grating with a numeric aperture greater than about 0.01.

17. An alignment system according to claim 15, wherein the imaging system has an aperture greater than about 0.7.

18. An alignment system according to claim 15, further comprising a radiation system configured to supply the illumination system with a radiation.

19. An alignment system according to claim 15, wherein said radiation system includes a broadband source with a low etendue configured to emit broadband radiation in the visible spectrum.

20. An alignment system according to claim 15, wherein said illumination system includes an optical system configured to image said phase grating onto a first intermediate plane where a field stop is located.

21. An alignment system according to claim 20, wherein said field stop is arranged to act as a field stop for the imaging system and the illumination system.

22. An alignment system according to claim 15, further comprising a spatial filter located at a pupil plane of said imaging system.

23. An alignment system according to claim 22, wherein said spatial filter includes apertures in a first and second direction, said spatial filter being configured to select orders diffracted in said first and second direction.

24. An alignment system according to claim 22, wherein said spatial filter is configured to block zero order diffracted light.

25. An alignment system according to claim 15, wherein said imaging system includes optical components mounted on a reference frame of said lithographic apparatus.

26. An alignment system according to claim 15, wherein said phase grating is a two dimensional phase grating having diamond shaped unit cells.

27. An alignment system according to claim 15, further comprising a field stop substantially positioned at a location of said phase grating.

28. An alignment system according to claim 15, further comprising a detection system configured to measure an intensity of the light transmitted through said phase grating.

29. An alignment system according to claim 28, wherein said detection system comprises a main signal detection branch and an alternative signal detection branch, said alternative signal detection branch being configured to measure a low intensity of said transmitted light.

30. An alignment system according to claim 29, wherein said alternative signal detection branch includes a photomultiplier.

31. An alignment system according to claim 28, wherein said detection system includes a cell detector comprising a plurality of cells, each of said plurality of cells being configured to simultaneously detect a portion of the light transmitted through said phase grating.

32. An alignment system according to claim 31, wherein each of said plurality of cells includes a silicon photodiode.

33. An alignment system according to claim 31, wherein the intensity detected by said plurality of cells is a sine function of substrate table position.

34. An alignment system according to claim 31, wherein said plurality is four.

35. An alignment system according to claim 28, wherein said detection system includes a camera branch configured to provide images of a pupil plane of said imaging system and images of said phase grating.

36. An alignment system according to claim 35, wherein said camera branch includes a CCD camera.

37. An alignment system according to claim 35, wherein said detection system is further configured to detect a focus signal of said lithographic apparatus.

38. An alignment system according to claim 15, wherein said phase grating is illuminated with a modulated light.

39. A method of aligning a substrate in a lithographic apparatus comprising:

illuminating a phase grating on a substrate;

imaging light diffracted by said phase grating onto a reference grating substantially correctly at at least two distinct wavelengths; and

detecting light transmitted through said reference grating.