Acousto-optic modulator, position detector using it, and projection exposure apparatus

• US 5,801,389 A
• Filed: 07/31/1996
• Issued: 09/01/1998
• Est. Priority Date: 05/30/1995
• Status: Expired due to Fees

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Mizutani, Hidoe, Ota, Kazuya
• Primary Examiner(s): Allen, Stephone B.
• Application Number:
  US08/688,800
• Time in Patent Office: 762 Days
• Field of Search: 250/548, 250/226, 356/399-401, 356/351, 356/356, 356/363
• US Class Current: 250/548
• 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

Abstract

In a position detecting apparatus, a light beam from a white light source is guided through a collimator lens etc. to be converted into a parallel beam, and this parallel beam is incident to a first acousto-optic modulator (AOM) and a second acousto-optic modulator positioned with a spacing by which a phase difference between diffracted light is approximately m.sup.π (where m is an integer). Traveling waves of slightly different frequencies opposite to each other are supplied in opposite directions to the two acousto-optic modulators, and the position detecting apparatus executes position detection by the heterodyne interference method as guiding a beam comprised of +first-order diffracted light from the acousto-optic modulators and a beam comprised of -first-order diffracted light from the acousto-optic modulators through an objective lens to project them with a predetermined intersecting angle onto a diffraction grating mark.

Claims

1. An acousto-optic modulator for splitting a light beam incident thereinto into two light beams of mutually different frequencies, comprising:

an acousto-optic medium; and

an ultrasonic generator for generating two progressive waves of mutually different frequencies in an ultrasonic acting area in said acousto-optic medium.

2. An acousto-optic modulator according to claim 1, wherein said two progressive waves travel in a superimposed manner in said ultrasonic acting area.

3. An acousto-optic modulator according to claim 1, wherein said two progressive waves travel in first and second regions separately present in said ultrasonic acting area.

4. An acousto-optic modulator according to claim 3, wherein said first and second regions are present in a same acousto-optic medium.

5. An acousto-optic modulator according to claim 3, wherein said first and second regions are present in separate acousto-optic media.

6. An acousto-optic modulator according to claim 1, wherein traveling directions of said two progressive waves are opposite to each other.

7. An acousto-optic modulator according to claim 1, wherein traveling directions of said two progressive waves are coincident with each other.

8. An acousto-optic modulator according to claim 1, wherein said ultrasonic generator comprises:

a transducer disposed on a first surface of said acousto-optic medium, for generating an ultrasonic wave; and

a sound absorbing member disposed on a second surface of said acousto-optic medium which is opposite to said first surface with respect to said acousto-optic medium.

9. A position detecting apparatus comprising:

a light source system for supplying a light beam of a single wavelength or a light beam containing light of a plurality of wavelengths;

an acousto-optic medium into which the light beam from said light source system is incident;

an ultrasonic generator for generating two progressive waves of mutually different frequencies in an ultrasonic acting area in said acousto-optic medium, splitting a light beam incident into said acousto-optic medium into two light beams of mutually different frequencies, and making the two light beams thus split emergent from said acousto-optic medium;

an objective optical system for condensing the two light beams emergent from said acousto-optic medium and applying the two light beams thus condensed to a diffraction-grating-like mark on a measured object in two predetermined directions;

a photoelectric detector for photoelectrically detecting interference light formed by a plurality of diffracted light beams appearing from said diffraction-grating-like mark; and

a processing apparatus for detecting a position of the measured object, based on a detection signal from said photoelectric detector.

10. A position detecting apparatus according to claim 9, wherein traveling directions of the two progressive waves generated in said ultrasonic acting area are opposite to each other.

11. A position detecting apparatus according to claim 9, wherein said two progressive waves are generated in first and second regions in said ultrasonic acting area, said first and second regions are adjacent to each other, and traveling directions of said two progressive waves are coincident with each other.

12. A projection exposure apparatus comprising:

an illumination optical system for supplying an illumination light beam;

a first stage for supporting an illuminated object illuminated by the light beam from said illumination optical system;

a second stage for supporting an exposed object;

a projection optical system for making a position on the illuminated object supported by said first stage conjugate with a position on the exposed object supported by said second stage;

a light source system for supplying a light beam of a single wavelength or a light beam containing light of a plurality of wavelengths;

an acousto-optic medium into which the light beam from said light source system is incident;

an ultrasonic generator for generating two progressive waves of mutually different frequencies in an ultrasonic acting area in said acousto-optic medium, splitting the light beam incident into said acousto-optic medium into two light beams of mutually different frequencies, and making the two light beams thus split emergent from said acousto-optic medium;

an objective optical system for condensing the two light beams emergent from said acousto-optic medium and applying the two light beams thus condensed to a diffraction-grating-like mark on the illuminated object or on the exposed object in two predetermined directions;

a photoelectric detector for photoelectrically detecting interference light formed by a plurality of diffracted light beams appearing from said diffraction-grating-like mark; and

a processing apparatus for detecting a position of the illuminated object or the exposed object provided with said diffraction-grating-like mark, based on a detection signal from said photoelectric detector.

21. A projection exposure apparatus according to claim 12, wherein said two progressive waves of mutually different frequencies travel alternately in opposite directions.

22. A projection exposure apparatus according to claim 12, wherein said two progressive waves of mutually different frequencies are separated in said acousto-optic medium from each other so that the separated waves progress to first and second regions, respectively.

23. A projection exposure apparatus according to claim 22, wherein said acousto-optic medium comprises a first medium element and a second medium element which are separated from each other, said first region being on said first medium element and said second region being on said second medium element.

24. A projection exposure apparatus according to claim 23, wherein progressive waves respectively traveling on said first medium element and said second medium element travel alternately in opposite directions.

41. A method of manufacturing a semiconductor device or a liquid display apparatus using the projection exposure apparatus according to claim 12, said method comprising the steps of:

illuminating said illuminated object by said illumination optical system; and

transferring an image of said illuminated object on an exposure object.

42. A method of manufacturing a semiconductor device or a liquid display apparatus using the projection exposure apparatus according to claim 24, said method comprising the steps of:

illuminating said illuminated object by said illumination optical system; and

transferring an image of said illuminated object on an exposure object.

13. A position detecting apparatus having two-beam generating means for generating two beams having mutually different frequencies, an objective optical system for condensing the two beams from said two-beam generating means to project said two beams in two predetermined directions to a diffraction grating mark formed on a detected object, and a photoelectric detector for photoelectrically detecting interference light consisting of a plurality of diffracted light occurring from said diffraction grating mark, which is arranged to detect a position of said detected object, based on a detection signal of said photoelectric detector,

wherein said two-beam generating means comprises light source means for generating a beam containing light of plural wavelengths or a beam of a single wavelength, and a plurality of acousto-optic elements for generating two beams of mutually different frequencies from the beam from said light source means,

wherein traveling directions of ultrasonic waves in said plurality of acousto-optic elements are set to be alternately opposite to each other, and wherein a spacing in a traveling direction of said beam between ultrasonic acting regions of two adjacent acousto-optic elements out of said plurality of acousto-optic elements is set so that a phase difference .o slashed. between diffracted light in a same direction from the ultrasonic acting regions of said two adjacent acousto-optic elements is within the following range, using an integer m:

space="preserve" listing-type="equation">(m-1/3).sup.π

<

.o slashed.<

(m+1/3).sup.π

.

14. The position detecting apparatus according to claim 13, wherein the spacing s, calculated as a value in the air in the traveling direction of said beam between the ultrasonic acting regions of the two adjacent acousto-optic elements out of said plurality of acousto-optic elements, is within the range expressed by:

space="preserve" listing-type="equation">(m-1/3)Λ

.sup.2 /λ

<

s<

(m+1/3)Λ

.sup.2 /λ

or,

space="preserve" listing-type="equation">(m-1/3)v.sup.2 /(λ

f.sup.2)<

s<

(m+1/3)v.sup.2 /(λ

f.sup.2)

where λ

is an average wavelength in the air of said two beams having the mutually different frequencies, Λ

is an average wavelength of the ultrasonic waves in said two adjacent acousto-optic elements, v is a sound velocity of said ultrasonic waves, f is an average frequency of said ultrasonic waves, and m is an integer.

15. The position detecting apparatus according to claim 13, wherein a relay optical system is positioned in two, predetermined, adjacent, acousto-optic elements out of said plurality of acousto-optic elements and wherein the ultrasonic acting regions in said two, predetermined, adjacent, acousto-optic elements are located at positions conjugate with each other with respect to said relay optical system.

16. The position detecting apparatus according to claim 13, wherein a field stop for interrupting noise light in a peripheral region of said two beams having the mutually different frequencies is provided at a position substantially conjugate with a middle point in the traveling direction of said beam between the ultrasonic acting regions of said plurality of acousto-optic elements.

17. An acousto-optic modulator for generating two beams having mutually different frequencies from a beam containing light of plural wavelengths or a beam of a single wavelength incident therein, comprising:

a plurality of acousto-optic elements for generating two beams of mutually different frequencies from the beam from said light source means,

wherein traveling directions of ultrasonic waves in said plurality of acousto-optic elements are set to be alternately opposite to each other, and wherein a spacing in a traveling direction of said beam between ultrasonic acting regions of two adjacent acousto-optic elements out of said plurality of acousto-optic elements is set so that a phase difference .o slashed. between diffracted light in a same direction from the ultrasonic acting regions of said two adjacent acousto-optic elements is within the following range, using an integer m;

space="preserve" listing-type="equation">(m-1/3).sup.π

<

.o slashed.<

(m+1/3).sup.π

.

18. The acousto-optic modulator according to claim 17, wherein the spacing s, calculated as a value in the air in the traveling direction of said beam between the ultrasonic acting regions of the two adjacent acousto-optic elements out of said plurality of acousto-optic elements, is within the range expressed by:

space="preserve" listing-type="equation">(m-1/3)Λ

.sup.2 /λ

<

s<

(m+1/3)Λ

.sup.2 /λ

or,

space="preserve" listing-type="equation">(m-1/3)v.sup.2 /(λ

f.sup.2)<

s<

(m+1/3)v.sup.2 /(λ

f.sup.2)

where λ

is an average wavelength in the air of said two beams having the mutually different frequencies, Λ

is an average wavelength of the ultrasonic waves in said two adjacent acousto-optic elements, v is a sound velocity of said ultrasonic waves, f is an average frequency of said ultrasonic waves, and m is an integer.

19. The acousto-optic modulator according to claim 17, further comprising a relay optical system positioned in two, predetermined, adjacent, acousto-optic elements out of said plurality of acousto-optic elements and wherein the ultrasonic acting regions in said two, predetermined, adjacent, acousto-optic elements are located at positions conjugate with each other with respect to said relay optical system.

20. The position detecting apparatus according to claim 17, further comprising a field stop for interrupting noise light in a peripheral region of said two beams having the mutually different frequencies which is provided at a position substantially conjugate with a middle point in the traveling direction of said beam between the ultrasonic acting regions of said plurality of acousto-optic elements.

25. A position detecting apparatus comprising:

a light source for supplying light of a single wavelength or a light of a plurality of wavelengths;

two-beam generating system including an acousto-optic medium for generating two beams having mutually different frequencies based on light from said light source;

an objective optical system for condensing the two beams from said two-beam generating system to project said two beams to a diffraction grating like mark formed on a detected object;

a detector for photo-electrically detecting diffracted light from said diffraction grafting like mark;

a processing system for detecting a position of said detected object based on a detection signal from said detector; and

a progressive wave generator for applying two progressive waves having mutually different frequencies to an ultrasonic acting area of said acousto-optic medium to cause a predetermined frequency difference in said two beams guided from said objective optical system.

26. A position detecting apparatus according to claim 25, wherein said two beam generating system includes a dividing member for dividing the light from said light source into two beams to guide the divided beams to said acousto-optic medium.

27. A position detecting apparatus according to claim 25, wherein said two progressive waves of mutually different frequencies travel alternately in opposite directions.

28. A position detecting apparatus according to claim 26, wherein said two progressive waves have mutually different frequencies which travel alternately in opposite directions.

29. A position detecting apparatus according to claim 25, wherein said two progressive waves having mutually different frequencies travel in first and second regions which separately exist on said acousto-optic medium.

30. A position detecting apparatus according to claim 29, wherein said two progressive waves of mutually different frequencies are separated in said acousto-optic medium from each other so that the separated waves progress to first and second regions, respectively.

31. A projection exposure apparatus according to claim 29, wherein said acousto-optic medium includes a first medium element and a second medium element which are separated from each other, said first region being on said first medium element and said second region being on said second medium element.

32. A projection exposure apparatus according to claim 31, wherein said two progressive waves respectively travelling on said first medium element and said second medium element travel alternately in opposite directions.

33. An exposure apparatus comprising:

a illumination unit for illuminating a reticle on which a predetermined pattern image is formed, with a light for exposure;

a first stage for holding said reticle;

a projection system for projecting said predetermined pattern image on said reticle on a substrate;

a second stage for holding said substrate; and

a position detecting apparatus for detecting a position of a positioning mark formed on either one of said reticle and said substrate,

said position detecting apparatus including;

a light source for supplying light of a single wavelength or light of a plurality of wavelengths;

a two-beam generating system including an acousto-optic medium for generating two beams having mutually different frequencies based on said light from said light source;

an objective optical system for condensing the two beams from said two-beam generating system to project said two beams to a diffraction grating mark formed on a detected object;

a detector for photo-electrically detecting diffracted light from said diffraction grating mark;

a processing system for detecting a position of said detected object based on a detection signal from said detector; and

a progressive wave generator for applying two progressive waves having mutually different frequencies to an ultrasonic acting area of said acousto-optic medium to cause a predetermined frequency difference in said two beams guided from said objective optical system.

34. An exposure apparatus according to claim 33, wherein said two beam generating system includes a dividing member for dividing the light from said light source into two beams to guide the divided beams to said acousto-optic medium.

35. An exposure apparatus according to claim 34, wherein said two progressive waves of mutually different frequencies travel alternately in opposite directions.

36. An exposure apparatus according to claim 33, wherein said two progressive waves have mutually different frequencies which travel alternately in opposite directions.

37. An exposure apparatus according to claim 33, wherein said acousto-optic medium includes a first medium element and a second medium element which are separated from each other, said first region being on said first medium element and said second region being on said second medium element.

38. An exposure apparatus according to claim 37, wherein said two progressive waves of mutually different frequencies travel alternately in opposite directions.

39. An exposure apparatus according to claim 37, wherein said acousto-optic medium includes a first medium element and a second medium element which are separated from each other, said first region being on said first medium element and said second region being on said second medium element.

40. An exposure apparatus according to claim 39, wherein progressive waves respectively travel on said first medium element and said second medium element travel alternately in opposite directions.

43. A method of manufacturing a semiconductor device or a liquid display apparatus using the exposure apparatus according to claim 33, said method comprising the steps of:

illuminating said reticle by said illumination optical system; and

transferring said image of the said reticle on said substrate.

44. A method of manufacturing a semiconductor device or a liquid display apparatus using the exposure apparatus according to claim 34, said method comprising the steps of:

illuminating said reticle by said illumination optical system; and

transferring said image of the said reticle on said substrate.

45. A method of manufacturing a semiconductor device or a liquid display apparatus using the exposure apparatus according to claim 40, said method comprising the steps of:

illuminating said reticle by said illumination optical system; and

transferring said image of the said reticle on said substrate.