Method for evaluating and improving pupil luminance distribution, illumination optical system and adjustment method thereof, exposure apparatus, exposure method, and device manufacturing method

• US 9,581,811 B2
• Filed: 04/30/2013
• Issued: 02/28/2017
• Est. Priority Date: 05/02/2012
• Status: Active Grant

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Kita, Naonori
• Primary Examiner(s): Chowdhury, Tarifur
• Assistant Examiner(s): AKANBI, ISIAKA O
• Application Number:
  US14/398,245
• Publication Number:
  US 20150323786A1
• Time in Patent Office: 1,400 Days
• Field of Search: 356/121, 356/237.2, 348/280, 348/302, 348/349, 355/67
• US Class Current: 1/1
• CPC Class Codes: G01M 11/02 Testing optical properties
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 27/0012 Optical design, e.g. procedures, algorithms, optimisation routines
• CPC Class Codes: G02B 27/0927 Systems for changing the beam intensity distribution, e.g. Gaussian to top-hat
• CPC Class Codes: G02B 27/0933 Systems for active beam shaping by rapid movement of an element
• CPC Class Codes: G03F 7/40 Treatment after imagewise removal, e.g. baking
• CPC Class Codes: G03F 7/70116 Off-axis setting using a programmable means, e.g. liquid crystal display [LCD], digital micromirror device [DMD] or pupil facets
• CPC Class Codes: G03F 7/70133 Measurement of illumination distribution, in pupil plane or field plane
• 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 7/70216 Mask projection systems

Abstract

Improvement of pupil luminance distribution includes: a fifth process in which an index value obtained from the illumination pupil, using evaluation method of a first process to fourth process; a sixth process wherein a unit change amount of the index value in the discrete data acquired in the previous process is acquired for each unit pupil area; a seventh process wherein discrete data modulated by an improving technique using the unit change amount so that the index value nears a target index value is acquired; and an eighth process wherein an index value obtained corresponding to the modulated discrete data in the seventh process is acquired, using the evaluation method of the first process to the fourth process, and by repeatedly performing the sixth process to eighth process so an error of the index value obtained corresponding to the modulated discrete data falls within permissible range.

Claims

1. An adjustment method of an illumination optical system, the illumination optical system illuminating an irradiation target surface by light from a light source and supplying illumination light to an image-forming optical system that forms an image of a pattern placed on a first plane on a second plane, the method comprising:

adjusting a pupil luminance distribution to be formed on an illumination pupil of the illumination optical system; and

changing the pupil luminance distribution to be formed on the illumination pupil, with the adjusted pupil luminance distribution serving as a target, wherein

the adjusting comprises;

a process of acquiring an index value obtained from a pupil luminance distribution formed on the illumination pupil with a standard pupil luminance distribution serving as a target, using a predetermined evaluation method, wherein

the evaluation method includes;

preparing a variation table that shows a variation of an intensity distribution of the image of the pattern with respect to a change in a pupil luminance for each of a plurality of unit pupil areas, the preparing including a first process of acquiring, for each unit pupil area, a unit intensity distribution formed on the second plane by light of a unit luminance level supplied from each unit pupil area, the plurality of unit pupil areas being obtainable by virtually dividing the illumination pupil;

calculating, by using luminance for each of the plurality of unit pupil areas of the pupil luminance distribution subject to evaluation and the variation table, the intensity distribution of the image of the pattern that is formed on the second plane with light from the pupil luminance distribution subject to evaluation, the calculating including a second process of acquiring discrete data of the pupil luminance distribution wherein each area of the plurality of unit pupil areas is approximated according to a three-dimensional model having a luminance level expressed by a multiple of the unit luminance level, and a third process of acquiring a light intensity distribution of an aerial image formed on the second plane from the pupil luminance distribution, based on a plurality of the unit intensity distributions acquired for each unit pupil area in the first process, and the discrete data acquired in the second process; and

acquiring, by using the calculated intensity distribution of the image, an index value of image-forming property obtained according to the pupil luminance distribution subject to evaluation, the acquiring including a fourth process of acquiring an index value of image-forming property obtained from the pupil luminance distribution, based on the light intensity distribution of the aerial image acquired in the third process, and

the adjusting further comprises;

a process of acquiring a unit change amount of the index value for each unit pupil area when a luminance level of one unit pupil area changes only by a unit luminance level in the discrete data acquired in a preceding process;

a process of acquiring discrete data modulated from the discrete data acquired in the preceding process, by an adjusting technique using the unit change amounts of a plurality of the index values that have been acquired, so as to make an index value obtained from the modulated discrete data approach a target index value; and

a process of acquiring an index value obtained corresponding to the modulated discrete data that has been acquired, using the evaluation method, wherein

by repeatedly performing the process of acquiring the unit change amount of the index value for each unit pupil area, the process of acquiring the discrete data modulated and the process of acquiring the index value until a difference between the index value obtained corresponding to the modulated discrete data and the target index value falls within a permissible range, the pupil luminance distribution to be formed on the illumination pupil is adjusted.

2. The adjustment method according to claim 1, wherein

in the first process, by virtually dividing the illumination pupil along two directions that are orthogonal to each other in the illumination pupil, the plurality of unit pupil areas is obtained in rectangular shapes.

3. The adjustment method according to claim 1, wherein

in the second process, a pupil luminance distribution formed on the illumination pupil is measured, and the discrete data is acquired based on a result of the measurement.

4. The adjustment method according to claim 1, wherein

in the third process, the light intensity distribution of the aerial image is acquired by linear combination of the plurality of unit intensity distributions, with the luminance level of each unit pupil area serving as a coefficient.

5. The adjustment method according to claim 1, wherein

in the fourth process, as the index value, line width of a pattern obtained from the pupil luminance distribution is acquired.

6. The adjustment method according to claim 1, wherein

in the fourth process, as the index value, an OPE value obtained from the pupil luminance distribution is acquired.

7. The adjustment method according to claim 1, wherein

in the process of acquiring the unit change amount of the index value for each unit pupil area, the unit change amount of the index value when the luminance level changes only by the unit luminance level is acquired for each unit pupil area, for a selected plurality of unit pupil areas.

8. The adjustment method according to claim 7, wherein

the selected plurality of unit pupil areas is a first group of unit pupil areas having a luminance level that is equal to or more than the unit luminance level, and a second group of unit pupil areas adjacent to the first group of unit pupil areas.

9. The adjustment method according to claim 1, wherein

in the process of acquiring the discrete data modulated, the modulated discrete data is acquired by a steepest descent method that refers to mutual ratio of the unit change amount of the index value acquired for each unit pupil area.

10. The adjustment method according to claim 5, wherein

a light intensity distribution in a surface optically conjugate to the illumination pupil is measured based on the light having passed through the irradiation target surface, when changing the pupil luminance distribution formed on the illumination pupil with the adjusted pupil luminance distribution serving as a target.

11. The adjustment method according to claim 1, wherein

a light intensity distribution in a surface optically conjugate to the illumination pupil is measured based on the light proceeding toward the irradiation target surface, when changing the pupil luminance distribution formed on the illumination pupil with the adjusted pupil luminance distribution serving as a target.

12. The adjustment method according to claim 10, wherein

an index value difference corresponding to a difference between discrete data of the adjusted pupil luminance distribution and discrete data of a measurement result of the light intensity distribution is acquired, when changing the pupil luminance distribution formed on the illumination pupil with the adjusted pupil luminance distribution serving as a target.

13. The adjustment method according to claim 12, wherein

the index value difference corresponding to the difference is acquired by acquiring a unit change amount of an index value when a luminance level of one unit pupil area changes by only a unit luminance level in the discrete data of the adjusted pupil luminance distribution for each unit pupil area, and using a plurality of the unit change amounts of the index values acquired for each unit pupil area.

14. The adjustment method according to claim 12, wherein

a light intensity distribution of the aerial image obtained on the second plane corresponding to the discrete data of the measurement result of the light intensity distribution is acquired, based on the discrete data of the measurement result of the light intensity distribution and the unit intensity distribution acquired for each of the unit pupil areas, and based on the light intensity distribution of the aerial image acquired, the index value difference corresponding to the difference is acquired.

15. The adjustment method according to claim 1, wherein

by controlling a spatial light modulator that is equipped in the illumination optical system and also forms the pupil luminance distribution on the illumination pupil, the pupil luminance distribution formed on the illumination pupil is changed with the adjusted pupil luminance distribution serving as a target.

16. An illumination optical system, wherein

adjustment is performed by the adjustment method according to claim 1.

17. An exposure apparatus, comprising:

the illumination optical system according to claim 16 to illuminate a predetermined pattern, the apparatus exposing the predetermined pattern on a photosensitive substrate.

18. The exposure apparatus according to claim 17, comprising:

a projection optical system that forms an image of the predetermined pattern on the photosensitive substrate, wherein the illumination pupil is a position optically conjugate to an aperture stop of the projection optical system.

19. The exposure apparatus according to claim 18, wherein

the standard pupil luminance distribution is a pupil luminance distribution used in another exposure apparatus, and the target index value is an index value obtained from the standard pupil luminance distribution in the another exposure apparatus.

20. The exposure apparatus according to claim 17, wherein

the standard pupil luminance distribution is a designed pupil luminance distribution, and the target index value is an index value that should be achieved by the designed pupil luminance distribution.

21. A device manufacturing method comprising:

exposing the predetermined pattern on the photosensitive substrate, using the exposure apparatus according to claim 17;

developing the photosensitive substrate on which the predetermined pattern is transferred, and forming a mask layer with a shape corresponding to the predetermined pattern on a surface of the photosensitive substrate; and

processing the surface of the photosensitive substrate via the mask layer.

22. An exposure method in which a predetermined pattern is illuminated by an illumination optical system adjusted by the adjustment method according to claim 1, and the predetermined pattern is exposed on a photosensitive substrate via a projection optical system, wherein

at least one of a numerical aperture of the projection optical system, a defocus amount of the photosensitive substrate with respect to the projection optical system, and a wavefront aberration of the projection optical system is adjusted so that an index value of image-forming property nears the target index value.

23. An adjustment method of an illumination optical system, the illumination optical system illuminating an irradiation target surface by light from a light source and supplying illumination light to an image-forming optical system that forms an image of a pattern placed on a first plane on a second plane, the method comprising:

evaluating a pupil luminance distribution formed on an illumination pupil of the illumination optical system; and

adjusting the pupil luminance distribution formed on the illumination pupil based on a result of the evaluating, wherein

the evaluating comprises;

preparing a variation table that shows a variation of an intensity distribution of the image of the pattern with respect to a change in a pupil luminance for each of a plurality of unit pupil areas on the illumination pupil, the preparing including a first process of acquiring, for each of a plurality of unit pupil areas, a unit intensity distribution formed on the second plane by light of a unit luminance level supplied from each unit pupil area, the plurality of unit pupil areas being obtained by virtually dividing the illumination pupil,

calculating, by using luminance for each of the plurality of unit pupil areas of the pupil luminance distribution subject to evaluation and the variation table, the intensity distribution of the image of the pattern that is formed on the second plane with light from the pupil luminance distribution subject to evaluation, the calculating including a second process of acquiring discrete data of a standard pupil luminance distribution, according to a three-dimensional model in which each area of the plurality of unit pupil areas has a luminance level expressed by a multiple of the unit luminance level, and a third process of acquiring a light intensity distribution of an aerial image formed on the second plane from the standard pupil luminance distribution, based on the plurality of the unit intensity distributions acquired for each unit pupil area in the first process and the discrete data of the standard pupil luminance distribution acquired in the second process;

acquiring, by using the calculated intensity distribution of the image, an index value of image-forming property obtained according to the pupil luminance distribution subject to evaluation, the acquiring including a fourth process of acquiring an index value of image-forming property obtained from the standard pupil luminance distribution, based on the light intensity distribution of the aerial image acquired in the third process; and

acquiring, for each unit pupil area, a unit change amount of the index value obtained when the luminance level of one unit pupil area changes only by a unit luminance level in the discrete data of the standard pupil luminance distribution.

24. The adjustment method according to claim 23, wherein

in the first process, by virtually dividing the illumination pupil along two directions that are orthogonal to each other in the illumination pupil, the plurality of unit pupil area is obtained in rectangular shapes.

25. The adjustment method according to claim 23, wherein

in the third process, by a linear combination of the plurality of unit intensity distributions with a luminance level of each unit pupil area serving as a coefficient, the light intensity distribution of the aerial image is acquired.

26. The adjustment method according to claim 23, wherein

in the fourth process, as the index value, line width of a pattern obtained from the standard pupil luminance distribution is acquired.

27. The adjustment method according to claim 23, wherein

in the acquiring, for each unit pupil area, the unit change amount of the index value, the unit change amount of the index value when the luminance level changes only by a unit luminance level is acquired for each unit pupil area, for a selected plurality of unit pupil areas.

28. The adjustment method according to claim 23, wherein

the evaluating further comprises measuring the pupil luminance distribution formed on the illumination pupil, and acquiring discrete data of the measured pupil luminance distribution based on a result of the measuring and the three-dimensional model.

29. The adjustment method according to claim 28, wherein

the evaluating further comprises acquiring, for each unit pupil area, a difference between discrete data of the standard pupil luminance distribution and discrete data of the measured pupil luminance distribution, and acquiring, for each unit pupil area, a change amount of the index value corresponding to the difference.

30. The adjustment method according to claim 29, wherein

in the acquiring, for each unit pupil area, the change amount of the index value, based on the unit change amount of the index value acquired for each unit pupil area and the difference acquired for each unit pupil area, the change amount of the index value corresponding to the difference is acquired for each unit pupil area.

31. The adjustment method according to claim 29, wherein

the evaluating further comprises from a total sum of the change amount of the index value corresponding to the difference acquired for each unit pupil area, acquiring an error from a target index value of an index value obtained corresponding to the measured pupil luminance distribution.

32. The adjustment method according to claim 23, wherein

the evaluating further comprises:

measuring the pupil luminance distribution formed on the illumination pupil, and acquiring discrete data of the measured pupil luminance distribution, based on a result of the measuring and the three-dimensional model,

acquiring, for each unit pupil area, a difference between discrete data of the standard pupil luminance distribution and the discrete data of the measured pupil luminance distribution, and acquiring, for each unit pupil area, a change amount of the index value corresponding to the difference; and

from a total sum of the change amount of the index value corresponding to the difference acquired for each unit pupil area, acquiring an error from a target index value of an index value obtained corresponding to the measured pupil luminance distribution, and the adjusting comprises

a discrete data acquiring process of setting a modulation model that is defined by a plurality of modulation parameters, and acquiring discrete data of the pupil luminance distribution modulated for each modulation parameter from the discrete data of the measured pupil luminance distribution,

a change amount acquiring process of acquiring, for each unit pupil area, a difference between the discrete data of the standard pupil luminance distribution and the discrete data of the pupil luminance distribution modulated for each modulation parameter, and acquiring, for each unit pupil area, a change amount of the index value corresponding to the difference;

an error acquiring process of acquiring from a total sum of the change amount of the index value corresponding to the difference acquired for each unit pupil area, an error from a target index value of an index value obtained corresponding to the pupil luminance distribution modulated for each modulation parameter;

a value acquiring process of acquiring values of the plurality of modulation parameters so that the error from the target index value of the index value obtained corresponding to the pupil luminance distribution modulated from the measured pupil luminance distribution becomes smaller than the error from the target index value of the index value obtained corresponding to the measured pupil luminance distribution; and

an adjustment process of adjusting the pupil luminance distribution formed on the illumination pupil, with the pupil luminance distribution modulated from the measured pupil luminance distribution based on the values of the plurality of modulation parameters serving as a target.

33. The adjustment method according to claim 32, wherein

the plurality of modulation parameters include a modulation parameter corresponding to a transmittance distribution.

34. The adjustment method according to claim 32, wherein

the plurality of modulation parameters include a modulation parameter corresponding to aberration.

35. The adjustment method according to claim 34, wherein

as the modulation parameter corresponding to the aberration, a modulation parameter corresponding to deformation of the pupil luminance distribution is used.

36. The adjustment method according to claim 32, wherein

the plurality of modulation parameters include a modulation parameter corresponding to blurring effect.

37. The adjustment method according to claim 32, wherein

the plurality of modulation parameters include a modulation parameter corresponding to flare light.

38. The adjustment method according to claim 32, wherein

when adjusting the pupil luminance distribution formed on the illumination pupil with the modulated pupil luminance distribution serving as a target, a light intensity distribution in a surface optically conjugate to the illumination pupil is measured, based on light that has passed through the irradiation target surface.

39. The adjustment method according to claim 32, wherein

by controlling a spatial light modulator equipped in the illumination optical system that forms the pupil luminance distribution on the illumination pupil, the pupil luminance distribution formed on the illumination pupil is adjusted, with the modulated pupil luminance distribution serving as a target.

40. The adjustment method according to claim 23, wherein

as the index value, line width of a pattern obtained from the pupil luminance distribution is acquired.

41. An illumination optical system, wherein

adjustment is performed by the adjustment method according to claim 23.

42. An exposure method in which a predetermined pattern is illuminated by an illumination optical system adjusted by the adjustment method according to claim 23, and the predetermined pattern is exposed on a photosensitive substrate via a projection optical system, wherein

at least one of a numerical aperture of the projection optical system, a defocus amount of the photosensitive substrate with respect to the projection optical system, and a wavefront aberration of the projection optical system is adjusted so that an index value of image-forming properties nears the target index value.

43. A device manufacturing method comprising:

exposing the predetermined pattern on the photosensitive substrate, using the exposure method according to claim 42;

developing the photosensitive substrate on which the predetermined pattern is transferred, and forming a mask layer with a shape corresponding to the predetermined pattern on a surface of the photosensitive substrate; and

processing the surface of the photosensitive substrate via the mask layer.

44. An illumination optical system that illuminates an irradiation target surface by light from a light source, and supplies illumination light to an image-forming optical system that forms an image of a pattern placed on a first plane on a second plane, the system comprising:

a pupil distribution measurement device that measures a pupil luminance distribution formed on an illumination pupil of the illumination optical system;

a pupil adjustment device that adjusts the pupil luminance distribution formed on the illumination pupil; and

a controller that controls the pupil adjustment device to change the pupil luminance distribution formed on the illumination pupil with the pupil luminance distribution adjusted using an adjustment method, as a target, the adjustment method adjusting a pupil luminance distribution to be formed on the illumination pupil of the illumination optical system, wherein

the adjustment method comprises;

a process of acquiring an index value obtained from a pupil luminance distribution formed on the illumination pupil with a standard pupil luminance distribution serving as a target, using a predetermined evaluation method, wherein

the evaluation method includes;

preparing a variation table that shows a variation of an intensity distribution of the image of the pattern with respect to a change in a pupil luminance for each of a plurality of unit pupil areas, the preparing including a first process of acquiring, for each unit pupil area, a unit intensity distribution formed on the second plane by light of a unit luminance level supplied from each unit pupil area, the plurality of unit pupil areas being obtainable by virtually dividing the illumination pupil;

calculating, by using luminance for each of the plurality of unit pupil areas of the pupil luminance distribution subject to evaluation and the variation table, the intensity distribution of the image of the pattern that is formed on the second plane with light from the pupil luminance distribution subject to evaluation, the calculating including a second process of acquiring discrete data of the pupil luminance distribution wherein each area of the plurality of unit pupil areas is approximated according to a three-dimensional model having a luminance level expressed by a multiple of the unit luminance level, and a third process of acquiring a light intensity distribution of an aerial image formed on the second plane from the pupil luminance distribution, based on a plurality of the unit intensity distributions acquired for each unit pupil area in the first process, and the discrete data acquired in the second process; and

acquiring, by using the calculated intensity distribution of the image, an index value of image-forming property obtained according to the pupil luminance distribution subject to evaluation, the acquiring including a fourth process of acquiring an index value of image-forming property obtained from the pupil luminance distribution, based on the light intensity distribution of the aerial image acquired in the third process, and

the adjustment method further comprises;

a process of acquiring a unit change amount of the index value for each unit pupil area when a luminance level of one unit pupil area changes only by a unit luminance level in the discrete data acquired in a preceding process;

a process of acquiring discrete data modulated from the discrete data acquired in the preceding process by an adjusting technique using the unit change amounts of a plurality of the index values that have been acquired so as to make an index value obtained from the modulated discrete data approach a target index value; and

a process of acquiring an index value obtained corresponding to the modulated discrete data that has been acquired, using the evaluation method, wherein

by repeatedly performing the process of acquiring the unit change amount of the index value for each unit pupil area, the process of acquiring the discrete data modulated and the process of acquiring the index value until a difference between the index value obtained corresponding to the modulated discrete data and the target index value falls within a permissible range, the pupil luminance distribution to be formed on the illumination pupil is adjusted.

45. An illumination optical system that illuminates an irradiation target surface by light from a light source, and supplies illumination light to an image-forming optical system that forms an image of a pattern placed on a first plane on a second plane, the system comprising:

a pupil distribution measurement device that measures a pupil luminance distribution formed on an illumination pupil of the illumination optical system;

a pupil adjustment device that adjusts the pupil luminance distribution formed on the illumination pupil; and

a controller that controls the pupil adjustment device to adjust the pupil luminance distribution formed on the illumination pupil using a predetermined adjustment method, wherein

the adjustment method comprises;

a process of adjusting the pupil luminance distribution formed on the illumination pupil of the illumination optical system based on a result of evaluating the pupil luminance distribution formed on the illumination pupil using a predetermined evaluation method, wherein

the evaluation method includes;

preparing a variation table that shows a variation of an intensity distribution of the image of the pattern with respect to a change in a pupil luminance for each of a plurality of unit pupil areas, the preparing including a first process of acquiring, for each unit pupil area, a unit intensity distribution formed on the second plane by light of a unit luminance level supplied from each unit pupil area, the plurality of unit pupil areas being obtained by virtually dividing the illumination pupil;

calculating, by using luminance for each of the plurality of unit pupil areas of the pupil luminance distribution subject to evaluation and the variation table, the intensity distribution of the image of the pattern that is formed on the second plane with light from the pupil luminance distribution subject to evaluation, the calculating including a second process of acquiring discrete data of a standard pupil luminance distribution, according to a three-dimensional model in which each area of the plurality of unit pupil areas has a luminance level expressed by a multiple of the unit luminance level, and a third process of acquiring a light intensity distribution of an aerial image formed on the second plane from the standard pupil luminance distribution, based on the plurality of the unit intensity distributions acquired for each unit pupil area in the first process and the discrete data of the standard pupil luminance distribution acquired in the second process;

acquiring, by using the calculated intensity distribution of the image, an index value of image-forming property obtained according to the pupil luminance distribution subject to evaluation, the acquiring including a fourth process of acquiring an index value of image-forming property obtained from the standard pupil luminance distribution, based on the light intensity distribution of the aerial image acquired in the third process; and

acquiring, for each unit pupil area, a unit change amount of the index value obtained when the luminance level of one unit pupil area changes only by a unit luminance level in the discrete data of the standard pupil luminance distribution.

46. The illumination optical system according to claim 45, wherein

the pupil distribution measurement device measures a light intensity distribution in a surface optically conjugate to the illumination pupil, based on light that has passed through the irradiation target surface.

47. The illumination optical system according to claim 45, wherein

the pupil distribution measurement device measures a light intensity distribution in a surface optically conjugate to the illumination pupil, based on light proceeding toward the irradiation target surface.

48. The illumination optical system according to claim 45, wherein

the pupil adjustment device has a spatial light modulator that has a plurality of optical elements arranged on a predetermined plane that are individually controlled and variably forms a pupil luminance distribution on the illumination pupil, and

the controller controls the plurality of optical elements of the spatial light modulator.

49. The illumination optical system according to claim 48, wherein

the spatial light modulator has the plurality of mirror elements arranged two-dimensionally in the predetermined plane, and a driving section that controls and drives an attitude of the plurality of mirror elements individually.