JPH10284365A - Cata-dioptric system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cata-dioptric system which is compact and has superior imaging performance in spite of about the same number of lenses as a conventional one. SOLUTION: In this optical system, an intermediate image C of a first face R is formed with a first imaging optical system A having a concave mirror M1, and then the intermediate image C is imaged on a second face W with a second imaging optical system B having an aperture stop S. In this case, a first aspheric member P is positioned in the vicinity of the intermediate image C, and a second aspheric member Q is positioned in the vicinity of the concave mirror M1 or the aperture stop S, or the concave mirror M1 is shaped into an aspheric surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system of a reduction exposure apparatus such as a stepper used in the manufacture of semiconductors.
It relates to a / 5-fold catadioptric optical system.

[0002]

2. Description of the Related Art In recent years, an exposure apparatus for printing a pattern of a semiconductor device has been required to have a higher resolution. In order to satisfy this requirement, the wavelength of the light source must be shortened and the NA (numerical aperture of the optical system) must be increased. In order to meet this demand, various techniques have been proposed in which a reduction projection optical system is constituted by a so-called catadioptric system that combines a reflection system and a refraction system made of optical glass usable for a used wavelength.

[0003] Among them, various types have been proposed so far for a type in which an intermediate image is formed at least once in the middle of an optical system. JP-B-5-25170, JP-A-63-163
No. 319, JP-A-4-234722, USP-4,7
No. 79,966.

[0004]

In the above prior art,
One in which only one concave mirror is used is disclosed in Japanese Patent Laid-Open No. 4-234.
No. 722 and U.S. Pat. No. 4,779,966. In these optical systems, only a negative lens is employed in a reciprocating optical system constituted by a concave mirror, and an optical system having a positive refractive power is not used. Therefore, the light beam spreads and enters the concave mirror, so that the diameter of the concave mirror tends to increase.

[0005] In particular, in the catadioptric optical system disclosed in US Pat. No. 4,779,966, the second optical system is located behind the intermediate image.
A concave mirror is used for the imaging optical system. Therefore, in order to ensure the required brightness of the optical system, the light beam spreads and enters the concave mirror, making it difficult to reduce the size of the concave mirror. In view of the above problems, it is an object of the present invention to provide a catadioptric optical system that is small in size and excellent in image forming performance, although the number of lenses is almost the same as in the conventional example.

[0006]

In order to achieve the above object, according to the present invention, a first imaging optical system A having a concave mirror M1 is provided.
To form an intermediate image C of the first surface R, and the second image forming optical system B having the aperture stop S converts the image of the intermediate image C to a second image.
In the catadioptric optical system formed on the surface W, a first aspherical member P is disposed near the intermediate image C, and the concave mirror M1 is provided.
A catadioptric optical system is provided in which a second aspherical member Q is disposed in the vicinity or near the aperture stop S, or the concave mirror M1 is formed as an aspherical surface.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, description will be made with reference to FIG. In the present invention, a so-called two-time imaging optical system that once forms an intermediate image C is employed in the optical system that projects the first surface R onto the second surface W. The reason why the two-time imaging optical system using the concave mirror is employed is to favorably correct Petzval sum and chromatic aberration. Here, in the present invention, the aspherical member is provided at a specific position in order to further improve aberration correction.

Here, when the second aspherical member Q is arranged near the aperture stop S, spherical aberration and coma aberration are hardly affected on the angle of view (for example, distortion and astigmatism). Can be corrected. This is because the chief ray of the light beam passes through the center of the stop, and the chief ray is not affected by the aspheric shape regardless of the aspheric shape. Conversely, all light beams emitted from on-axis and off-axis on the first surface R always pass through the entire aperture stop S, so all light beams emitted from on-axis and off-axis on the first surface R are Becomes evenly refracted.

[0009] In addition to the vicinity of the aperture stop S of the second imaging optical system B, the vicinity of the concave mirror M1 of the first imaging optical system A can be corrected independently of the aberration relating to the incident height. . When an aspherical member is arranged near the concave mirror M1 of the first imaging optical system A, a parallel plane plate whose surface is processed into an aspherical surface or one independent aspherical lens can be considered. Further, the concave mirror M1 itself may be an aspherical concave mirror without disposing an aspherical member near the concave mirror M1 of the first imaging optical system A.

Next, when the first aspherical member P is disposed near the intermediate image C, distortion and astigmatism are hardly affected by aberrations relating to the incident height (for example, spherical aberration and coma). Can be corrected. this is,
This is because the luminous flux converges near the intermediate image C, and the on-axis and off-axis peripheral luminous fluxes on the first surface R are not affected by the shape of the aspheric surface in the vicinity. Conversely, all chief rays undergo refraction due to the aspherical shape.

Here, the first aspherical member P is located near the intermediate image C.
In this case, a single independent aspherical lens may be used, or an end surface of a prism and a plane of a parallel flat plate arranged in the vicinity may be processed into an aspherical surface. In addition, the reflection surface of the light beam separating mirror or the prism disposed in the vicinity may be processed to be an aspheric surface. Further, the aspherical member in the present invention,
Not only a parallel plate but also a general lens may be used.
When the first aspherical member P is provided with the second reflecting surface M2 for deflecting the optical path, the first aspherical member P may be a prism.

In order to make the entire two-time imaging optical system more compact, it is preferable to provide a second reflection surface M2 for deflecting the optical path at or near the position where the intermediate image C is formed. At this time, the second reflection surface M2 may be a reflection surface of a mirror or a prism. Further, the first imaging optical system A includes a forward optical system A11 that only allows incident light to the concave mirror M1 to pass, and both the incident light to the concave mirror M1 including the concave mirror M1 and the reflected light from the concave mirror M1 pass. And a reciprocating optical system A12. This means that the first imaging optical system A is not used at the same magnification, and thereby the distortion and coma generated in the second imaging optical system B are favorably corrected.

At this time, it is preferable that the outward optical system A11 has a negative refractive power. This is because the light beam entering the reciprocating optical system A12 and the light beam exiting from the reciprocating optical system A12 are:
This is so as not to overlap. Further, a third reflecting surface M3 for deflecting the optical path is provided between the second reflecting surface M2 and the second imaging optical system B, and the first surface R and the second surface W are arranged in parallel. Is preferred. By providing the third reflecting surface M3, the optical system itself can be bent twice, so that the size can be further reduced. At this time, by arranging the first surface R and the second surface W in parallel, the second reflection surface M2 and the third reflection surface M
Since the optical axis directions of the optical members disposed other than the position 3 coincide with each other, asymmetric deformation does not occur in the optical members, and an optical system with higher precision in manufacturing can be achieved. Further, in each embodiment according to the present invention, since no optical member exists between the second reflecting surface M2 and the third reflecting surface M3, the optical axis directions of all the optical members match. Therefore, a highly accurate optical system can be expected in manufacturing.

Further, the aspherical surface of the first aspherical member P is
It is preferable to use any of a rotationally symmetric aspheric surface, a toric aspheric surface, and a completely asymmetric aspheric surface. The aspheric surface of the second aspherical member Q is preferably a rotationally symmetric aspherical surface.

[0015]

Examples of the present invention will be described below. Further, SiO ₂ used as a glass material has a refractive index of 1.5 at a wavelength of 248 nm.
0839. In each embodiment, only SiO ₂ was used as the glass material, but CaF ₂ can also be used as the glass material. [First Embodiment] FIG. 2 is an optical path diagram of a catadioptric optical system in this embodiment, and Table 1 is a lens data table of the catadioptric optical system in this embodiment. The description will be made below with reference to this figure and table. In Table 1, a surface number, a radius of curvature, a surface interval, a glass material, and a symbol according to the present invention are described in order from the left. The catadioptric optical system in the present embodiment has a first surface R
In the order in which light rays pass from above the reticle, a forward optical system A11 consisting of one refracting lens, six lenses, a concave mirror M1, and one parallel flat plate processed into an aspheric surface as the first aspherical member P And a first imaging optical system A composed of a reciprocating optical system A12. In addition, the light beam
After passing through the imaging optical system A, it is reflected by the light beam separating mirror as the second reflecting surface M2 and the bending mirror as the third reflecting surface M3, and includes five lenses, a diaphragm, and a second aspherical member Q. The light passes through a second imaging optical system composed of one parallel flat plate processed into an aspherical surface, and reaches a wafer as a second surface. An intermediate image C of the reticle is formed near the light beam splitting mirror.

Here, this optical system has a reduction magnification of 1/4.
, The numerical aperture NA on the image side is 0.6, and the maximum object height is 52.8.
It is possible to perform scanning and exposure with a rectangular aperture having an exposure size of 55 × 90 or the like.

[0017]

TABLE 1 Surface number curvature radius spacing glass materials 0 0.00000 60.000 R 1 -639.93122 10.935 SiO 2 A A11 2 638.79323 63.097 3 772.20352 30.000 SiO 2 A12 4 -534.73642 0.081 5 285.29345 30.000 SiO 2 6 -5948.04836 206.478 7 501.06370 30.000 SiO 2 8 -309.92623 5.000 9 -251.33100 11.810 SiO ₂ 10 168.56869 117.942 11 321.57847 30.000 SiO ₂ 12 -464.57044 115.331 13 -161.47861 12.000 SiO ₂ 14 765.45803 20.000 15 -244.06677 -20.000 Reflection surface M1 16 765.45803 -12.000 SiO ₂ 17 -161. 18 -464.57044 -30.000 SiO ₂ 19 321.57847 -117.942 20 168.56869 -11.811 SiO ₂ 21 -251.33100 -5.000 22 -309.92623 -30.000 SiO ₂ 23 501.06370 -206.478 24 -5948.04836 -30.000 SiO ₂ 25 285.29345 -0.081 26 -534.73642 -30.000 SiO ₂ 27 772.20352 -0.100 28 0.00000 -7.000 SiO ₂ P Aspherical data K 1 A 0.645652210378e-8; B -0.254015221025e-13; C 0.152056034342e-16; -0.158200516208e-20 28 0.00000 -0.100 29 0.00000 267.300 Reflective surface M2 30 0.00000 -346.376 Reflective surface M3 31 -197.49176 -3 0.000 SiO ₂ B 32 17530.15232 -67.213 33 0.00000 -5.000 S 34 0.00000 -7.000 SiO ₂ Q Aspherical data K 1 A 0.131379214487e-7; B 0.333184500674e-12; C -0.250435601016e-17; 0.20950464532e-20 35 0.00000 -0.100 36 -147.90421 -25.000 SiO ₂ 37 -414.36719 -69.235 38 -91.80571 -35.000 SiO ₂ 39 -1272.56390 -0.100 40 -147.96775 -15.000 SiO ₂ 41 -63.01133 -3.000 42 -63.15395 -43.894 SiO ₂ 43 772.99694 -15.000 45 0.00000 W As shown in FIG. 2, the effective diameter of the lens used is 170 or less, and the distance between the object and the image is 741. It can be seen that the effective diameter of the lens is about ／ of that of the refractive spherical optical system normally used in this specification. Further, despite the downsizing of the effective diameter of the lens and the entire optical system, the number of lenses used is almost the same as that of the conventional optical system.

FIG. 3 is a lateral aberration diagram of the catadioptric optical system in this embodiment, and FIG. 4 is an astigmatism diagram and a distortion diagram. From these, the UV excimer laser 2
It can be seen that the optical system of the present invention provides excellent performance in which spherical aberration, coma, astigmatism, and distortion at a single wavelength of 48 nm have been well corrected to almost no aberration. [Second Embodiment] FIG. 5 is an optical path diagram of a catadioptric optical system in this embodiment, and Table 2 is a lens data table of the catadioptric optical system in this embodiment. The description will be made below with reference to this figure and table. In Table 1, a surface number, a radius of curvature, a surface interval, a glass material, and a symbol according to the present invention are described in order from the left.

The catadioptric optical system according to the present embodiment has a first
A first imaging optical system A including a forward optical system A11 including one refracting lens and a reciprocating optical system A12 including eight lenses and a concave mirror M1 in the order in which light beams pass from the reticle serving as the surface R. It has a light beam splitting prism. After passing through the first image-forming optical system A and the light beam splitting prism, the light beam has five lenses, an aperture stop S, and a parallel plane plate processed into one aspherical surface as a second aspherical member Q. And reaches the wafer which is the second surface W. Here, the light beam splitting prism has an incident surface processed into an aspherical surface, and is itself a first aspherical member P,
It has a second reflecting surface M2 and a third reflecting surface M3.

Here, this optical system has a reduction magnification of 1/4.
The numerical aperture NA on the image side is 0.6, the maximum object height is 70, and it is possible to perform scanning and exposure with a rectangular aperture having an exposure size of 24 × 120 or the like.

[0021]

TABLE 2 97.329 Surface number curvature radius spacing glass materials 0 0.0 000 R 1 -852.84892 10.935 SiO 2 A A11 2 427.78583 60.827 3 663.60250 40.000 SiO 2 A12 4 -351.03784 0.081 5 257.40324 34.550 SiO 2 6 2438.07789 216.095 7 502.34945 40.000 SiO 2 8 -262.00938 0.775 9 -244.76524 11.810 SiO ₂ 10 159.40009 37.191 11 953.44172 20.000 SiO ₂ 12 -747.74093 23.298 13 -127.21946 15.000 SiO ₂ 14 -225.24650 1.495 15 270.26506 40.000 SiO ₂ 16 -212.42840 44.058 17 -136.12200 12.000 SiO ₂ 18 300.22202 20 19 -209.22265 -20.000 Reflective surface M1 20 300.22202 -12.000 SiO ₂ 21 -136.12200 -44.058 22 -212.42840 -40.000 SiO ₂ 23 270.26506 -1.495 24 -225.24650 -15.000 SiO ₂ 25 -127.21946 -23.298 26 -747.74094 -20.000 SiO ₂ 27 953.44172 -37.191 28 159.40009 -11.810 SiO ₂ 29 -244.76524 -0.775 30 -262.00938 -40.000 SiO ₂ 31 502.34945 -216.095 32 2438.07789 -34.550 SiO ₂ 33 257.40324 -0.081 34 -351.03784 -40.000 SiO ₂ 35 663.60250 -3.000 36 0.00000 3.000 SiO ₂ P Aspheric data K 1 A 0.8873 90809767e-8; B 0.169993245617e-13; C -0.191633424206e-19; -0.177186383906e-22 37 0.00000 267.300 Reflective surface M2 38 0.00000 -16.200 Reflective surface M3 39 0.00000 -290.000 40 -147.64203 -30.000 SiO ₂ 41 191842.92952 -32.911 42 0.00000 -5.000 S 43 0.00000 -20.000 SiO ₂ Q 44 0.00000 -27.384 Aspherical data K 1 A 0.669401563554e-8; B 0.390599494004e-12; C 0.312995771257e-16; D -0.592108763547e-20 45 -135.93921 -26.306 SiO ₂ 46 -499.74670 -4.092 47 -107.66763 -43.000 SiO ₂ 48 -64.44984 -2.000 49 -66.18404 -30.000 SiO ₂ 50 -574.11841 -0.073 51 -114.99848 -29.315 SiO ₂ 52 252.71212 -15.000 53 0.00000 W As can be seen from FIG. In addition, the effective diameter of some lenses is 22
Other lens effective diameters are as small as 150 or less, and the object-image distance is as small as 790. Further, despite the downsizing of the effective diameter of the lens and the entire optical system, the number of lenses used is almost the same as that of the conventional optical system.

FIG. 6 is a lateral aberration diagram of the catadioptric optical system in this embodiment, and FIG. 7 is an astigmatism diagram and a distortion diagram. As a result, an optical system with excellent performance in which spherical aberration, coma, astigmatism, and distortion at a single wavelength of 248 nm of an ultraviolet excimer laser are satisfactorily corrected to almost no aberration is provided. I understand.

[0023]

As described above, in the present invention, the first aspherical member P is arranged near the intermediate image C, and the second aspherical member P is arranged near the concave mirror M1 or near the aperture stop S. Alternatively, by forming the concave mirror as an aspherical surface, it is possible to provide a catadioptric optical system which is small in size and excellent in image forming performance, although the number of lenses is almost the same as that of the conventional example.

As described above, according to the present invention, the maximum effect can be obtained while using the minimum aspherical element.
Of course, by using an additional aspherical surface, an optical system with a smaller size and a smaller number of lenses can be used.

[Brief description of the drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is an optical path diagram of the catadioptric optical system of the first embodiment.

FIG. 3 is a lateral aberration diagram of the first example.

FIG. 4 is a diagram illustrating a field curvature and a distortion diagram according to the first embodiment.

FIG. 5 is an optical path diagram of a catadioptric optical system according to a second embodiment.

FIG. 6 is a lateral aberration diagram of the second embodiment.

FIG. 7 shows a field curvature diagram and a distortion diagram of the second embodiment.

[Explanation of symbols]

 R first surface A first imaging optical system A11 forward optical system A12 reciprocating optical system M1 concave mirror M2 second reflection surface M3 third reflection surface C intermediate image B second imaging optical system S aperture stop W second surface P 1 Aspherical member Q 2nd aspherical member

Claims (9)

[Claims] 1. A reflection for forming an intermediate image on a first surface by a first imaging optical system having a concave mirror and forming an image of the intermediate image on a second surface by a second imaging optical system having an aperture stop. In the refractive optical system, a first aspherical member is arranged near the intermediate image, and a second aspherical member is arranged near the concave mirror or near the aperture stop, or the concave mirror is formed as an aspherical surface. Characteristic catadioptric system. 2. The optical system according to claim 1, wherein the first imaging optical system includes an outward optical system that only allows the light incident on the concave mirror to pass therethrough, and includes the concave mirror, wherein the light incident on the concave mirror and the light reflected from the concave mirror are combined. 2. A catadioptric optical system according to claim 1, comprising a reciprocating optical system through which both pass. 3. The catadioptric optical system according to claim 2, wherein said outward optical system has a negative refractive power. 4. The aspherical surface of the first aspherical member is formed on a plane, and the aspherical surface of the second aspherical member is formed on a plane. Catadioptric system. 5. The catadioptric optical system according to claim 1, wherein the first aspherical member is a plane parallel plate or a prism, and the second aspherical member is a plane parallel plate. . 6. The catadioptric optical system according to claim 1, further comprising a second reflecting surface for deflecting an optical path at or near a position where said intermediate image is formed. 7. A third reflecting surface for deflecting an optical path is provided between the second reflecting surface and the second imaging optical system, and the first surface and the second surface are arranged in parallel. 7. The catadioptric optical system according to claim 6, wherein 8. The catadioptric system according to claim 1, wherein the aspherical surface of the first aspherical member is a rotationally symmetric aspherical surface, a toric aspherical surface, or a completely asymmetrical aspherical surface. 9. The catadioptric optical system according to claim 1, wherein the aspherical surface of said second aspherical member is a rotationally symmetric aspherical surface.