Projection objective having a high aperture and a planar end surface

• US 20060012885A1
• Filed: 06/14/2005
• Published: 01/19/2006
• Est. Priority Date: 12/15/2003
• Status: Active Grant

• Current Assignee: CARL Zeiss SMT GmbH (Carl-Zeiss-Stiftung)
• Original Assignee: Carl Zeiss AG (Carl-Zeiss-Stiftung)
• Inventors: Singer, Wolfgang, Beder, Susanne, Schuster, Karl-Heinz
• Granted Patent: US 7,466,489 B2
• Time in Patent Office: Days
• US Class Current: 359/649
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: G02B 17/0804 using two curved mirrors G02B17/0864, G02B17/0896 takes precedence
• CPC Class Codes: G02B 17/0812 off-axis or unobscured systems in which all of the mirrors share a common axis of rotational symmetry
• CPC Class Codes: G02B 17/0892 specially adapted for the UV
• CPC Class Codes: G03F 7/70225 Optical aspects of catadioptric systems, i.e. comprising reflective and refractive elements
• CPC Class Codes: G03F 7/70325 Resolution enhancement techniques not otherwise provided for, e.g. darkfield imaging, interfering beams, spatial frequency multiplication, nearfield lenses or solid immersion lenses
• CPC Class Codes: G03F 7/70341 Details of immersion lithography aspects, e.g. exposure media or control of immersion liquid supply chemical composition of immersion liquids G03F7/2041
• CPC Class Codes: G03F 7/70958 Optical materials or coatings, e.g. with particular transmittance, reflectance or anti-reflection properties

Abstract

A projection objective for imaging a pattern provided in an object plane of the projection objective onto an image plane of the projection objective suitable for microlithography projection exposure machines has a plurality of optical elements transparent for radiation at an operating wavelength of the projection objective. At least one optical element is a high-index optical element made from a high-index material with a refractive index n≧1.6 at the operating wavelength.

Claims

23. Projection objective having an image plane and a lens furthest therefrom and starting from which there is a convergent beam path up to the image plane, in which a pupil plane or system aperture is arranged at a distance of at least 10 mm on the image side of said lens.

27. Microlithography projection exposure method for imaging a pattern provided on a mask positioned in an object plane of a projection objective onto a substrate provided in an image plane of the projection objective, in which an image-side last optical element of a projection objective being used is wrung or pressed onto the object to be exposed comprising the following steps in the given sequence:

positioning the projection objective and the substrate to be exposed relative to one another;

contacting the exit surface of the projection objective and an incoupling surface of the substrate; and

aligning the mask relative to the projection objective such that a desired pattern region of the mask is imaged onto a target area of the substrate in contact with the exit surface of the projection objective.

28. Method according to claims 27, wherein the steps are repeated for a number of juxtaposed target areas on the substrate.

29. Method according to claim 27, wherein a thin transparent membrane is placed between the substrate to be exposed and the exit surface of the projection objective.

31. Microlithography projection exposure method for imaging a pattern provided on a mask positioned in an object plane of a projection objective onto a substrate provided in an image plane of the projection objective, in which a microlithography projection objective is used and an immersion fluid is introduced between a last lens of the microlithography projection objective and the substrate to be exposed, wherein Cyclohexane is used as immersion fluid.

66. A projection objective for imaging a pattern provided in an object plane of the projection objective onto an image plane of the projection objective comprising:

a plurality of optical elements transparent for radiation at an operating wavelength of the projection objective and including a plurality of aspheric lenses having at least one aspheric lens surface,

where an aspheric lens surface is represented by Zernike coefficients K_i and Zernike polynomials Z_i according to

$p<br><br>\left(h\right)=\frac{h_n^2}{R\left(1+\sqrt{1-\frac{h^2}{R^2}}\right)}+\mathrm{K0}+\mathrm{K4}·<br><br>\mathrm{Z4}+\mathrm{K9}·<br><br>\mathrm{Z9}+\mathrm{K16}·<br><br>\mathrm{Z16}+\mathrm{K25}·<br><br>\mathrm{Z25}+\mathrm{K36}·<br><br>\mathrm{Z36}+\mathrm{K49}·<br><br>\mathrm{Z49}+\mathrm{K64}·<br><br>\mathrm{Z64}+\mathrm{K81}·<br><br>\mathrm{Z81}+\mathrm{K100}·<br><br>\mathrm{Z100}$

where the sagitta p of a point on an aspherical surface is represented as a function of a normalized radial distance h from the optical axis and the radius R of the aspheric lens surface is fixed such that K4=0, where

Z4=2·

h²−

1
Z9=6·

h⁴−

6·

h²+1
Z16=20·

h⁶−

30·

h⁴+12·

h²−

1
Z25=70·

h⁸−

140−

h⁶+90−

h⁴−

20·

h²+1
Z36=252·

h¹⁰−

630−

h⁸+560·

h⁶−

210·

h⁴+30·

h²−

1
Z49=924·

h¹²−

2772h¹⁰+3150·

h⁸−

1680·

h⁶+420·

h⁴−

42·

h²+1
Z64=3432·

h¹⁴·

12012·

h¹²+16632·

h¹⁰−

11550·

h⁸+4200·

h⁶−

756·

h⁴+56·

h²−

1
Z81=12870·

h¹⁶−

51480·

h¹⁴+84084·

h¹²−

72072·

h¹⁰+34650·

h⁸−

9240·

h⁶+1260·

h⁴−

72·

h²+1

Z100=48620·

h¹⁸−

218790·

h¹⁶+411840·

h¹⁴−

420420·

h¹²+252252·

h¹⁰−

90090·

h⁸+18480·

h⁶−

1980·

h⁴+90·

h²−

1

and where the normalized radius h with 0<

h≦

1 is defined as;

$h=\frac{\mathrm{distance}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{from}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{optical}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{axis}}{1/2<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{lens}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{diameter}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{the}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{aspheric}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{surface}};<br><br>$

a last optical element arranged closest to the image plane, where the last optical element has refractive power and a refractive index n_LOE;

an image-side numerical aperture NA; and

a geometrical aperture sin α

within the last optical element;

wherein the projection objective is used at high image-side numerical aperture NA≧

1.3 in an optical limit range where the aperture sin α

within the last optical element corresponding to the ratio NA/n_LOE obeys the condition

sin α

≧

0.8.

1. Projection objective for imaging a pattern provided in an object plane of the projection objective onto an image plane of the projection objective suitable for microlithography projection exposure machines comprising:

a plurality of optical elements transparent for radiation at an operating wavelength of the projection objective;

wherein at least one optical element is a high-index optical element made from a high-index material with a refractive index n≧

1.6 at the operating wavelength.

2. Projection objective according to claim 1, wherein the high-index material has a refractive index n≧

1.8 at the operating wavelength.

3. Projection objective according to claim 1, wherein the high-index material is sapphire.

4. Projection objective according to claim 1, wherein the high-index material is germanium dioxide.

5. Projection objective according to claim 1, wherein an object-side numerical aperture NA_Obj is greater than 0.3.

6. Projection objective according to claim 5, wherein the object-side numerical aperture NA_Obj >

0.36 in conjunction with an absolute reduction ratio of |β

|≦

0.25.

7. Projection objective according to claim 1, having a first high-index optical element and at least one second high-index optical element.

8. Projection objective according to claim 7, wherein the first high-index optical element and the second high-index optical element are each made from a high-index material exhibiting birefringence defining an orientation of birefringence of each optical element, where the first and second high-index optical elements are installed differently with regard to the orientation of the birefringence such that effects of birefringence caused by the high-index optical elements are at least partly compensated.

9. Projection objective according to claim 1, wherein the projection objective has a last optical element closest to the image plane and wherein the last optical element is at least partly made of a high-index material with refractive index n>

1.6.

10. Projection objective according to claim 9, wherein the last optical element is a monolithic plano-convex lens made of a high-index material with refractive index n>

1.6.

11. Projection objective according to claim 9, wherein the last optical element consists of at least two optical elements in optical contact with each other along a splitting interface, where at least one of the optical elements forming the last optical element consists of a high-index material with refractive index n>

1.6.

12. Projection objective according to claim 9, wherein the last optical element consists of an entry side plano-convex lens element having a curved entry side and a planar exit side and an exit side plane parallel plate in optical contact with the plano-convex lens element along a planar splitting surface.

13. Projection objective according to claim 12, wherein the plano-convex lens element consists of a high-index material with a refractive index n>

1.6 and wherein the exit side plane parallel plate consists of fused silica.

14. Projection objective according to claim 12, wherein the plano-convex lens element consists of fused silica and wherein the exit side plane parallel plate consists of a high-index material with a refractive index n>

1.6.

15. Projection objective according to claim 11, wherein the last optical element is shaped as a plano-convex lens and a splitting surface is curved such that both optical elements contacted at the splitting surface are lens parts with similar refractive power.

16. Projection objective according to claim 1, wherein the projection objective is designed as an immersion objective adapted with reference to aberrations such that an image side working distance between a last optical element and the image plane is filled up with an immersion medium with a refractive index substantially greater than 1.

17. Projection objective according to claim 16, wherein the projection objective is adapted to an immersion fluid which has a refractive index greater than 1.4 at the operating wavelength.

18. Projection objective according to claim 17, wherein the projection objective is designed for 193 nm operating wavelength and wherein the immersion fluid is cyclohexane.

19. Projection objective according to one claim 1, wherein the projection objective is designed as a solid immersion objective having a finite image side working distance in the order of the operating wavelength or below such that evanescent fields exiting from an image side exit surface of the projection objective can be used for imaging.

20. Projection objective according to claim 1, wherein the projection objective is designed for solid immersion lithography where an image side exit surface of the projection objective is in mechanical contact with an incoupling surface associated with a substrate to be exposed.

21. Projection objective according to claim 1, wherein an image side numerical aperture NA is greater than 1.3.

22. Projection objective according to claim 1, wherein a pupil surface positioned closest to the image plane is positioned in a region of convergent beam between a region of a local maximum of beam diameter closest to the image plane and the image plane.

24. Microlithography projection exposure method for imaging a pattern provided on a mask positioned in an object plane of a projection objective onto a substrate provided in an image plane of the projection objective, in which a microlithography projection objective according to claim 1 is used and an immersion fluid is introduced between a last lens of the microlithography projection objective and the substrate to be exposed.

25. Method according to claim 24, in which an immersion fluid is used which has a refractive index greater than 1.4 at an operating wavelength of the projection objective.

26. Method according to claim 25, in which the immersion fluid has a refractive index greater than 1.5 at the operating wavelength.

30. Method according to claim 24, in which a microlithography projection objective according to claim 1 is used.

32. Projection objective according to claim 9, wherein the last optical element includes a plano-convex composite lens having an image-side plano-convex second lens element having a curved entry surface and an essentially planar exit surface, and an object-side first lens element having a curved entry surface and a curved exit surface in optical contact with the curved entry surface of the first lens element, where a first curvature radius R1 of the curved entry surface of the first lens element is larger than a second curvature radius R2 of the entry surface of the second lens element.

33. Projection objective according to claim 32, wherein the first lens element has a first refractive index n1 which is smaller than the second refractive index n2 of the second lens element such that the condition Δ

n≧

0.25 holds for a refractive index difference Δ

n=n2−

n1.

34. Projection objective according to claim 32, wherein the second lens element is made from a high-index crystalline material and the first lens element is made from a glassy material.

35. Projection objective according to claim 34, wherein the crystalline material is chosen from the group consisting of aluminum oxide (Al₂O₃), beryllium oxide (BeO), magnesium aluminum oxide (MgAlO₄, spinell), magnesium oxide (MgO), yttrium aluminum oxide (Y₃Al₅O₁₂), yttrium oxide (Y₂O₃) and lanthanum fluoride (LaF₃).

36. Projection objective according to claim 34, wherein the first lens element is made from silicon dioxide (SiO₂).

37. Projection objective according to claim 9, wherein the last optical element includes a plano-convex composite lens having an image-side plano-convex second lens element having a curved entry surface and an essentially planar exit surface, and an object-side first lens element having a curved entry surface and a curved exit surface in optical contact with the curved entry surface of the first lens element, wherein an immersion medium having refractive index n₁ is disposed in a gap between the exit surface of the first lens element and the entry surface of the second lens element.

38. Projection objective according to claim 37, wherein the first lens element has a first refractive index n1 which is smaller than the second refractive index n2 of the second lens element such that the condition Δ

n≧

0.25 holds for a refractive index difference Δ

n=n2−

n1 and wherein the immersion medium has a refractive index in the range 1.3≦

n₁≦

1.6.

39. Projection objective according to claim 37, wherein the gap has a maximum gap width GW in the range 50 μ

m≦

GW≦

2 mm.

40. Projection objective according to claim 9, wherein the last optical element includes a hyper-hemispherical lens having a curved entry surface with curvature radius R2, an essentially planar exit surface, and an axial lens thickness T defined as a distance between the entry surface and the exit surface measured along the optical axis of the lens, where T>

R2.

41. Projection objective according to claim 40, wherein the projection objective has an image-side numerical aperture 1.7≦

NA≦

1.8

42. Projection objective according to claim 40, wherein a shape of the hyper-hemispherical lens is a combination of a hemispherical section and a cylindrical section having a radius equal to the radius of curvature of the hemispherical section.

43. Projection objective according to claim 40, wherein the hyper-hemispherical lens has a spherical entry surface extending spherically beyond a central section plane through the center of curvature of the spherical entry surface and aligned perpendicular to the optical axis of the lens.

44. Projection objective according to claim 40, wherein the hyper-hemispherical lens forms an image-side second lens element of a composite plano-convex last optical element.

45. Projection objective according to claim 1, wherein the projection objective includes at least one aspheric lens group consisting of a number N_ASPL of at least two immediately consecutive aspheric lenses providing a number N_ASP of aspheric lens surfaces, where the condition AR>

1 holds for an asphere ratio AR=N_ASP/N_ASPL.

46. Projection objective according to claim 45, wherein N_ASPL≧

3 and AR≧

1.5

47. Projection objective according to claim 45, wherein N_ASPL is selected from the group consisting of 3, 4, 5, 6.

48. Projection objective according to claim 45, wherein the aspherical lens group includes at least one of three, four, five and six immediately consecutive aspheric surfaces.

49. Projection objective according to claim 45, wherein exactly one spherical surface is present within the aspherical lens group such that the condition N_ASP=2·

N_ASPL−

1 is fulfilled, where N_ASPL≧

3.

50. Projection objective according to claim 49, wherein N_ASPL is selected from the group consisting of 3, 4, 5.

51. Projection objective according to claim 9, wherein an image-side aspheric lens group is arranged immediately upstream of the last optical element consisting of a number N_ASPL of at least two immediately consecutive aspheric lenses providing a number N_ASP of aspheric lens surfaces, where the condition AR>

1.5 holds for an asphere ratio AR=N_ASP/N_ASPL.

52. Projection objective according to claim 51, wherein N_ASPL=2

53. Projection objective according to claim 9, wherein at least three immediately consecutive aspheric lens surfaces are provided immediately upstream of the last optical element.

54. Projection objective according to claim 51, wherein the image-side aspheric lens group includes at least two consecutive positive meniscus lenses having a concave lens surface facing the image surface.

55. Projection objective according to claim 1, wherein an object-side aspheric lens group is arranged immediately downstream of the object plane consisting of a number N_ASPL of at least two immediately consecutive aspheric lenses providing a number N_ASP of aspheric lens surfaces, where the condition AR>

1.5 holds for an asphere ratio AR=N_ASP/N_ASPL.

56. Projection objective according to claim 55, wherein N_ASPL is one of 3, 4 and 5.

57. Projection objective according to claim 55, wherein the object-side aspheric lens group includes an aspheric lens surface having a vertex radius of curvature, R_V, on the optical axis and an edge radius of curvature, R_E, at the edge of the lens surface, where R_E ≦

0.7·

R_V

58. Projection objective according to claim 1, having a first, refractive objective part for imaging the pattern provided in the object plane into a first intermediate image;

a second objective part including at least one concave mirror for imaging the first intermediate image into a second intermediate image; and

a third objective part for imaging the second intermediate image onto the image plane.

59. Projection objective according to claim 58, where pupil surfaces are formed between the object plane and the first intermediate image, between the first and the second intermediate image and between the second intermediate image and the image plane;

and

wherein at least one biaspherical lens having an aspheric entry surface and an aspheric exit surface is positioned between the object surface and a first pupil surface in a region close to the first pupil surface at a distance from that pupil surface smaller than or equal to a diameter of the pupil at that pupil surface.

60. Projection objective according to claim 58, wherein a meniscus group having at least one meniscus lens having an object-side concave lens surface is arranged immediately downstream of a first pupil surface in the first objective part, where a thickness of that meniscus lens does not exceed 0.6 times the diameter of the meniscus lens.

61. Projection objective according to claim 60, wherein aspheric lens surfaces of the meniscus group have local radii of curvature, R_C smaller than 1.2 D, where D is the free diameter of the meniscus lens.

62. Projection objective according to claim 58, where a lens group immediately upstream of the first intermediate image has at least one lens having an entry side radius of curvature R1 and an entry side radius of curvature R2 defining a mean radius of curvature R_m =1/(1/R1+1/R2), where the mean radius of curvature has a center on the image-side of the lens.

63. Projection objective according to claim 58, wherein a lens group immediately upstream of the first intermediate image includes at least one biaspherical lens.

64. Projection objective according to claim 58, wherein a lens group immediately downstream of the second intermediate image includes at least one positive meniscus lens having an image-side concave lens surface.

65. Projection objective according to claim 58, wherein the third objective part includes a negative lens group between the second intermediate image and an image-side pupil surface having at least three consecutive aspheric lens surfaces.

67. Projection objective according to claim 66, wherein NA≧

1.4 and sin α

≧

0.9.

68. Projection objective according to claim 66, wherein an object-side aspheric lens group formed by lenses immediately downstream of the object plane has at least three immediately consecutive aspheric lens surfaces and a first surface of that object-side aspheric lens group closest to the object plane observes at least one of the following conditions:

−

14≧

K9/K16≧

−

25
+2≦

K16/K25≦

8.

69. Projection objective according to claim 68, wherein a second aspheric surface following the first aspheric surface of the object-side aspheric lens group obeys at least one of the following conditions:

−

3.5≧

K9/K16≧

−

7.5
+7≦

K16/K25≦

+25.

70. Projection objective according to claim 66, wherein an object-side aspheric lens group formed by lenses immediately downstream of the object plane includes at least four immediately consecutive aspheric lens surfaces and at least one of the following conditions holds for a fourth aspheric lens surface following the first, second and third aspheric lens surface:

3≦

K9/K16≦

5
5≦

K9/K16≦

15.

71. Projection objective according to claim 66, wherein an object-side aspheric lens group formed by lenses immediately downstream of the object plane has one of three, four, five and six immediately consecutive aspheric lens surfaces, and a surface curvature at the vertex is oriented such that the local radius of curvature has its center on the image-side for all the aspheric lens surfaces.

72. Projection objective according to claim 66, wherein an object-side aspheric lens group formed by lenses immediately downstream of the object plane has one of three, four, five and six immediately consecutive aspheric lens surfaces, and a center of curvature of an envelope sphere to an aspheric surface is on the image-side for all the aspheric lens surfaces of the object-side aspheric lens group.

73. Projection objective according to claim 66, wherein a second lens group is defined as the lens group starting with the first lens surface having the center of curvature on the object-side and at least one of the center of curvature of the first aspheric surface of the second group and the second aspheric lens surface of that second group lies on the object-side.

74. Projection objective according to claim 73, wherein the shape of a first asphere of the second group obeys the following condition:

9≦

K9/K16≦

20.

75. Projection objective according to claim 66, wherein a lens group including negative lenses and designed to form a constriction of the beam diameter between the object plane and the image plane has a first aspheric lens surface obeying at least one of the following conditions:

3≦

K9/K16≦

5
3≦

K16/K25≦

5.

76. Projection objective according to claim 66, wherein a lens group including negative lenses and designed to form a constriction of the beam diameter between the object plane and the image plane includes at least three and at most five consecutive aspheric lens surfaces and at least one of the following condition holds:

a first aspheric lens surface of that group obeys at least one of the following conditions;

−

3≧

K9/K25≧

−

5
+5≦

K16/K25≦

+7;

a second aspheric lens surface of that lens group obeys at least one of the following conditions;

0.3≦

K9/K16≦

0.5
3.0≦

K16/K25≦

5.0;

a third aspheric lens surface of that lens group obeys at least one of the following conditions;

3≦

K9/K16≦

5
−

25≧

K16/K25≧

−

40;

a fourth aspheric lens surface of that lens group obeys at least one of the following conditions;

+5≦

K9/K16≦

+7
−

3≦

K16/K25≦

−

5;

a fifth aspheric lens surface of that lens group obeys at least one of the following conditions;

2.0≦

K9/K16≦

3
10.0≦

K16/K25≦

15.0

77. Projection objective according to claim 66, wherein a lens group immediately upstream of a last optical element is primarily or exclusively composed of positive lenses and a first aspheric lens surface on a positive lens of this lens group obeys at least one of the following conditions:

500≦

K9/K16≦

700

0.2≦

K16/K25≦

0.3.

78. Projection objective according to claim 77, wherein a second aspheric lens surface following the first aspheric surface obeys at least one of the following conditions:

−

7.0≧

K9/K16≧

−

10.0
1.3≦

K16/K25≦

1.8.

79. Projection objective according to claim 66, wherein a lens group immediately upstream of a last optical element includes an aspheric lens surface in the region of maximum beam diameter which obeys at least one of the following conditions:

6≦

K9/K16≦

9
12≦

K16/K25≦

17.

80. Projection objective according to claim 66, wherein a lens group immediately upstream of a last optical element includes at least three and at most five consecutive aspheric lens surfaces in the region of a convergent beam and a first aspheric lens surface of that lens group obeys at least one of the following conditions:

7.0≦

K9/K16≦

12
−

2.5≧

K16/K25≧

5.0.

81. Projection objective according to claim 66, wherein at least one of a third aspheric lens surface of a lens group immediately upstream of the last optical element and a penultimate aspheric lens surface of that lens group obeys at least one of the following conditions:

3≦

K9/K16≦

5
10≦

K16/K25≦

15.

82. Projection objective according to claim 66, wherein at least one of a last aspheric surface of a lens group immediately upstream of the last optical element and a last aspheric surface of the projection objective upstream the image plane obeys at least one of the following conditions:

+25≦

K9/K16≦

40
−

2≧

K16/K25≧

−

4.

83. Projection objective according to claim 66, wherein a last aspheric lens surface of the projection objective upstream the image plane obeys at least one of the following conditions:

−

1.8≦

K9/K16≦

2.5
+1.3≦

K16/K25≦

1.7
+2.5≦

K25/K36≦

4.0
+3.5≦

K36/K49≦

5.0
+4.5≦

K49/K64≦

7.0.

84. Projection objective according to claim 83, wherein the projection is designed to generate at least two real intermediate images.

83-1. Projection objective according to claim 66, wherein the projection objective is designed to generate at least one real intermediate image.