Illumination optical system, exposure apparatus, and exposure method

• US 20080074632A1
• Filed: 11/05/2007
• Published: 03/27/2008
• Est. Priority Date: 12/03/2002
• Status: Active Grant

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Tanaka, Hirohisa, Tanitsu, Osamu, Muramatsu, Kenichi, Matsuyama, Tomoyuki, Komine, Norio, Kudo, Takehito, Nishinaga, Hisashi
• Granted Patent: US 7,515,248 B2
• Time in Patent Office: Days
• US Class Current: 355/71
• CPC Class Codes: G03B 27/42 for automatic sequential copying of the same original G03B27/34, G03B27/53 take precedence
• CPC Class Codes: G03F 7/70091 Illumination settings, i.e. intensity distribution in the pupil plane or angular distribution in the field plane; On-axis or off-axis settings, e.g. annular, dipole or quadrupole settings; Partial coherence control, i.e. sigma or numerical aperture [NA]
• CPC Class Codes: G03F 7/70566 Polarisation control

Abstract

An illumination optical system for, when installed in an exposure system, realizing a suitable illumination condition by varying the polarized state of the illumination light according to the pattern characteristics of the mask while suppressing the loss of the intensity of the light. The illumination optical system has a light source unit for supplying a linearly polarized light for illuminating surfaces to be illuminated therewith, and a polarized state changing device for changing the polarized state of the illuminating light from a predetermined polarized state to a nonpolarized state and vice versa. The polarized state changing device is arranged in the optical path between the light source unit and the surfaces to be illuminated. The polarized state changing device can be removed from the illumination optical path and has a depolarizer for selectively depolarizing the incident linearly polarized light.

Claims

1. A method for adjusting an illumination optical system that illuminates an illuminated surface with light including a predetermined polarized state supplied from a light source, comprising:

setting a quarter-wave plate in an illumination light path of the illumination optical system such that a crystal optic axis of the quarter-wave plate is set at a predetermined angular position, and sets a half-wave plate in the illumination light path such that a crystal optic axis of the half-wave plate is set at a predetermined angular positioned, wherein

based on a result of detection of the polarized state of the light in the light path between a polarized state switching device and the illuminated surface when the crystal optic axes of the quarter-wave plate and the half-wave plate are respectively changed, the wavelength plate setting step sets the crystal optic axis of the quarter-wave plate at a desired position for converting incident elliptically polarized light into linearly polarized light, and the crystal optic axis of the half-wave plate at a standard position for converting incident linearly polarized light into linearly polarized light that includes a polarized plane in a predetermined direction.

2. The adjustment method of claim 1, wherein

the crystal optic axis of the quarter-wave plate is set at a first angular position, at which a contrast for changes in an S1 component of a Stokes parameter becomes substantially maximum in the detection result, and

the crystal optic axis of the half-wave plate is set at a second angular position, at which the S1 component of the Stokes parameter becomes substantially maximum or substantially minimum in the detection result while the crystal optic axis of the quarter-wave plate is set at the first angular position.

3. The adjustment method of claim 1, further comprising:

forming a predetermined light intensity distribution on or adjacent to a pupil plane of the illumination optical system by the light from the light source,

changing at least one of a shape and a size of the predetermined light intensity distribution, and

resetting at least one of the crystal optic axes of the quarter-wave plate and the half-wave plate.

4. An exposure apparatus, comprising the illumination optical system adjusted by the adjustment method of claim 1.

5. The exposure apparatus of claim 4, further comprising:

a projection optical system positioned in the light path between a first plane at which the mask is positioned, and a second plane at which the photosensitive substrate is positioned, the projection optical system forming an image of a pattern on the mask onto the second plane;

a pupil intensity distribution forming device that forms a predetermined light intensity distribution at a position conjugate to a pupil of the projection optical system or a position adjacent thereto; and

a pupil intensity distribution changing device that changes at least one of a shape and a size of the predetermined light intensity distribution.

6. The exposure apparatus of claim 5, further comprising a polarized state changing device that is positioned in the light path between the light source and the illuminated surface and changes the polarized state of the light that illuminates the illuminated surface, wherein

the pupil intensity distribution changing device changes at least one of the shape and the size of the predetermined light intensity distribution in accordance with pattern characteristics of the mask, and

the polarized state changing device changes the polarized state of the light that illuminates the illuminated surface in accordance with at least one of the shape and the size of the predetermined light intensity distribution.

7. The exposure apparatus of claim 6, wherein

the polarized state changing device comprises a polarized state switching device that switches the polarized state of the light that illuminates the illuminated surface between a predetermined polarized state and a nonpolarized state, and

the polarized state switching device switches between the predetermined polarized state and the nonpolarized state in accordance with a change in at least one of the shape and the size of the predetermined light intensity distribution.

8. The exposure apparatus of claim 6, wherein

the pupil intensity distribution forming device forms two areas including a high light intensity distribution that are spaced away from each other along a pitch direction of a line-and-space pattern formed on the mask, and

the polarized state changing device sets the polarized state of the light that illuminates the illuminated surface from the two areas including a high light intensity distribution to a linearly polarized state that includes a polarization plane in a direction orthogonal to the pitch direction.

9. The exposure apparatus of claim 8, wherein the two areas including a high light intensity distribution are formed symmetrically about the optical axis of the illumination optical system, and

a value σ

o defined by a ratio φ

o/φ

p satisfies the following condition;

0.7≦

σ

o

where φ

o is a diameter of a circle about the optical axis that circumscribes the two areas including a high light intensity distribution, and φ

p is a diameter of the pupil plane.

10. The exposure apparatus of claim 8, wherein the two areas including a high light intensity distribution are formed symmetrically about the optical axis of the illumination optical system, and

a value σ

o defined by a ratio φ

o/φ

p and σ

i defined by a ratio φ

i/φ

p satisfy the following condition;

0.5≦

σ

o/σ

i

where φ

o is a diameter of a circle about the optical axis that circumscribes the two areas including a high light intensity distribution, φ

p is a diameter of the pupil plane, and φ

i is a diameter of a circle about the optical axis that inscribes the two areas including a high light intensity distribution.

11. The exposure apparatus of claim 6, wherein

the pupil intensity distribution forming device forms one area including a high light intensity distribution substantially about the optical axis of the illumination optical system, and

the polarized state changing device sets the polarized state of the light that illuminates the illuminated surface from the one area including a high light intensity distribution to the linearly polarized state that includes a polarization plane in a direction substantially orthogonal to the pitch direction of the line-and-space pattern formed on a phase shift mask as the mask.

12. The exposure apparatus of claim 11, wherein a value σ

that is defined by a ratio φ

o/φ

p satisfies the following condition;

σ

≦

0.4

where φ

is a size of the one area including a high light intensity distribution, and φ

p is a diameter of the pupil plane.

13. An exposure method, comprising:

illuminating a mask through the illumination optical system adjusted in accordance with the adjustment method of claim 1;

and

exposing an image of a pattern on the mask onto the photosensitive substrate positioned on the illuminated surface.

14. The exposure method of claim 13, further comprising:

forming the image of the pattern on the mask using a projection optical system;

forming a predetermined light intensity distribution at a position conjugate to a pupil of the projection optical system or a position adjacent thereto; and

changing at least one of a shape or a size of the predetermined light intensity distribution.

15. The exposure method of claim 14, wherein

the changing at least one of a shape or a size of the predetermined light intensity distribution changes at least one of the shape and the size of the predetermined light intensity distribution in accordance with pattern characteristics of the mask;

the exposure method further comprises changing a polarized state of the light that illuminates the illuminated surface in accordance with a change in the at least one of the shape and the size of the predetermined light intensity distribution.

16. The exposure method of claim 15, wherein the forming the predetermined light intensity distribution forms two areas including a high light intensity distribution spaced away from each other along a pitch direction of a line-and-space pattern formed on the mask, the exposure method further comprising setting the polarized state of the light that illuminates the illuminated surface from the two areas including a high light intensity distribution to a linearly polarized state that includes a polarization plane in a direction substantially orthogonal to the pitch direction.

17. The exposure method of claim 16, wherein

the two areas including a high light intensity distribution are formed symmetrically about the optical axis of the illumination optical system, and

a value σ

o defined by a ratio φ

o/φ

p satisfies the following condition;

0.7≦

σ

o

where φ

o is a diameter of a circle about the optical axis that circumscribes the two areas including a high light intensity distribution, and φ

p is a diameter of the pupil plane.

18. The exposure method of claim 16, wherein

the two areas including a high light intensity distribution are formed symmetrically about the optical axis of the illumination optical system, and

a value σ

o defined by a ratio φ

o/φ

p and σ

i defined by a ratio φ

i/φ

p satisfy the following condition;

0.5≦

σ

i/σ

o

where φ

o is a diameter of a circle about the optical axis that circumscribes the two areas including a high light intensity distribution, φ

p is a diameter of the pupil plane, and φ

i is a diameter of a circle about the optical axis that inscribes the two areas including a high light intensity distribution.