SYSTEM AND METHOD FOR COMPENSATING INSTABILITY IN AN AUTOFOCUS SYSTEM

• US 20140233011A1
• Filed: 02/18/2014
• Published: 08/21/2014
• Est. Priority Date: 03/31/2009
• Status: Active Grant

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Goodwin, Eric Peter, Smith, Daniel Gene, Sogard, Michael
• Granted Patent: US 9,097,851 B2
• Time in Patent Office: Days
• US Class Current: 356/4.05
• CPC Class Codes: G01B 11/02 for measuring length, width or thickness G01B11/08 takes precedence
• CPC Class Codes: G02B 27/40 Optical focusing aids
• CPC Class Codes: G02B 7/28 Systems for automatic generation of focusing signals

Abstract

An autofocus system and method designed to account for instabilities in the system, e.g. due to instabilities of system components (e.g. vibrating mirrors, optics, etc) and/or environmental effects such as refractive index changes of air due to temperature, atmospheric pressure, or humidity gradients, is provided. An autofocus beam is split into a reference beam component (the split off reference channel) and a measurement beam component, by a beam splitting optic located a predetermined distance from (and in predetermined orientation relative to) the substrate, to create a first space between the beam splitting optic and the substrate. A reflector is provided that is spaced from the beam splitting optic by the predetermined distance, to create a second space between the reflector and the beam splitting optic. The measurement beam component is directed at the substrate and a reflected measurement beam component through the first space between the substrate and the beam splitting optic, while the reference beam component is directed at the reflector and a reflected reference beam component is directed from the reflector through the second space between the beam splitting optic and the reflector. The reflected reference and measurement beam components are returned to the beam splitting optic, and emerge substantially collinear from the beam splitting optic. The reference and measurement beam components are then detected, and provide information that enables compensation for changes in the z position of the substrate that are due to instabilities in the autofocus system components and/or environmental factors.

Claims

1-24. -24. (canceled)

25. A method for compensating instability in an optical autofocus system, which optical autofocus system uses light directed at and reflected from a substrate to determine changes in the height position of the substrate, the method comprising

a. deflecting a reference beam component by a beam-deflecting optic located a predetermined distance from the substrate to form a deflected reference beam, said predetermined distance defining a first space;

b. providing a reflector, spaced from the beam-deflecting optic by a predetermined distance, to create a second space between the reflector and the beam-deflecting optic;

c. directing a measurement beam component at the substrate and directing a reflected measurement beam component through the first space between the substrate and the beam-deflecting optic, while directing the reference beam component at the reflector and directing a reflected reference beam component from the reflector through the second space between the beam-deflecting optic and the reflector;

d. returning the reflected reference and measurement beam components such that the reference and measurement beam components emerge substantially collinearly from the beam deflecting optic;

e. detecting the reference and measurement beam components and producing from detected reference and measurement beam components information enabling compensation for changes, in the height position of the substrate, that are due to instabilities in at least one of the system and environmental factors; and

f. propagating the deflected reference beam component by the beam-deflecting optic and the reflected reference beam component by the reflector along a first plane, which first plane crosses a second plane along which the measurement beam component at the substrate and the a reflected measurement beam component propagate.

26. The method of claim 25, wherein the providing a reflector includes providing a reflector position and orientation of which relative to the beam -deflecting optic is maintained substantially fixed.

27. The method of claim 25, wherein the optical autofocus system is of the slit detection type,

wherein light reflected from the substrate is passed through a slit before impinging on a slit detector, and

wherein said detecting of the reflected reference and measurement beam components comprises directing the reflected reference and measurement beam components through a beam splitter disposed between the slit and respective detectors for the reflected reference beam component and the reflected measurement beam component.

28. The method of claim 25, wherein the substrate is moveable in a first direction and said providing a reflector includes providing the reflector that has a reflective surface in a plane oriented substantially transversely to the first direction.

29. The method of claim 25, wherein the substrate is moveable in a first direction and said providing a reflector includes providing the reflector that has a reflective surface in a plane oriented substantially parallel to the first direction.

30. The method of claim 29, wherein said deflecting a reference beam includes deflecting a reference bean with the beam-deflecting optic that comprises a pair of adjacent 30-60-90 degree prisms with respective sides that are adjacent and offset from each other in a direction transverse to the first direction.

31. The method of claim 25, wherein the first and second air spaces between the substrate and the beam-deflecting optic and between the reflector and the beam-deflecting optic are non-common, and further comprising adjusting for index differences in said non-common first and second air spaces.

32. The method of claim 31, wherein said adjusting for index differences comprises directing a dedicated air supply to the non-common first and second air spaces.

33. The method of claim 25, wherein the first and second air spaces between the substrate and the beam-deflecting optic and between the reflector and the beam-deflecting optic are non-common, and further comprising adjusting for index gradients in said non-common first and second air spaces.

34. The method of claim 33, wherein the optical autofocus system is of a slit detection type, wherein light reflected from the substrate is passed through a slit before impinging on a slit detector, wherein the reference and measurement beams are detected by means of respective detection slits, and wherein said adjusting for index gradients in said non-common first and second non common air spaces includes changing orientations of the respective detection slits.

35. The method of claim 34, further including adjusting for changes in index gradients with time in said non-common first and second air spaces.

36. The method of claim 35, wherein said adjusting for changes in index gradients with time comprises adjusting sizes of the respective detection slits for the reflected measurement beam and the reflected reference beam.

37. The method of claim 25, including adjusting for changes in index gradients with time in the non common air spaces between the reflector and the beam splitting optic and between the substrate and the beam splitting optic.

38. The method of claim 37, wherein the optical autofocus system is of the slit detection type, wherein light reflected from the substrate is passed through a slit before impinging on a slit detector, and said adjusting for changes in index gradients with time includes adjusting sizes of respective detection slits for the reflected measurement and reference beams.

39. An optical autofocus system that uses light directed at and reflected from a substrate to determine changes in a height position of the substrate, said system comprising:

a beam-deflecting optic located a predetermined distance from the substrate, said predetermined distance creating a first space between the beam-deflecting optic and the substrate;

a reflector spaced from the beam-deflecting optic by the predetermined distance and creating a second space between the beam-deflecting optic and the reflector,

wherein the beam-deflecting optic deflects a reference beam component to the reflector to form a deflected reference beam component,

wherein the deflected reference beam component and a reflected reference beam component from the reflector propagate along a first plane, and

wherein a measurement beam component at the substrate and a reflected measurement beam component from the substrate propagate along a second plane which intersects the first plane,

detectors that respectively detect the reference and measurement beam components; and

a processing device configured to produce, from the reference and measurement beam components detected by the detectors, information to enable compensation for changes, in the height position of the substrate, that are due to instabilities in at least one of system components and environmental factors.

40. The optical autofocus system of claim 39, wherein position and orientation of the reflector relative to the beam splitting optic is maintained substantially fixed.

41. The optical autofocus system of claim 39, wherein the optical autofocus system is of a slit detection type, wherein light reflected from the substrate is passed through a slit before impinging on a slit detector, and wherein detection of reflected reference beam components and measurement beam components by the detectors comprises directing said beam components through a beam splitter disposed between the slit and respective detectors for the reflected reference beam component and the reflected measurement beam component.

42. The optical autofocus system of claim 39, wherein the substrate is moveable in a first direction and the reflector has a reflective surface in a plane oriented substantially transversely to the first direction.

43. The optical autofocus system of claim 39, wherein the substrate is moveable in a first direction and the reflector has a reflective surface in a plane oriented substantially parallel to the first direction.

44. The optical autofocus system of claim 43, wherein the beam splitting optic comprises a pair of adjacent 30-60-90 degree prisms with respective sides that are adjacent and offset from each other in a direction transverse to the first direction.

45. The optical autofocus system of claim 39, wherein the first and second air spaces between the substrate and beam splitting optic and between the reflector and the beam splitting optic are non-common, and further including one or more fluid conduits provided for directing a dedicated air supply to said non-common first and second spaces to minimize index differences in said non-common first and second spaces.

46. The optical autofocus system of claim 45, wherein the optical autofocus system is of a slit detection type, wherein light reflected from the substrate is passed through a slit before impinging on a slit detector, wherein the detectors comprise respective slit detectors for the measurement and reference beams, and respective detection slits are oriented such as to reduce sensitivity to index gradients in the non-common first and second air spaces.

47. The optical autofocus system of claim 46, wherein sizes of the respective detection slits are adjustable to adjust for changes in index gradients with time in the non-common first and second spaces.

48. The optical autofocus system of claim 39, wherein the optical autofocus system is of the slit detection type, wherein the first and second air spaces between the substrate and beam splitting optic and between the reflector and the beam splitting optic are non-common, wherein light reflected from the substrate is passed through a slit before impinging on a slit detector, wherein respective detection slits are provided for the measurement and reference beams, and sizes said of the respective detection slits are adjustable to adjust for changes in index gradients with time in the non-common first and second spaces.