JPH0821955A - Catadioptric reduction projection optical system - Google Patents

Abstract

(57) [Abstract] [Objective] Catadioptric reduction projection optics having a large numerical aperture while having a simple structure, while correcting chromatic aberration in a wide band and having excellent imaging performance as an optical system for semiconductor manufacturing. Provide the system. A primary image of an object having a first lens group G ₁ having a positive refractive power, a second lens group G ₂ having a negative refractive power, and a first concave reflecting mirror M _{1 in} order from the light incident side. Forming the first partial optical system, the second concave reflecting mirror M ₂ and the fourth lens group G ₄ having a positive refractive power.
And a second partial optical system for forming a secondary image of an object based on light from the primary image, and a first concave reflecting mirror M ₁ and a second concave reflecting mirror having positive or negative refractive power. The third lens group G ₃ is disposed in the optical path between the mirror M ₂ and the mirror M ₂ . The first to fourth lens groups are composed of at least one of quartz glass and fluorite. Here, the magnification β of the first concave reflecting mirror M _1
M1 is -1.0 <β _M1 <-0.7, and the second concave reflecting mirror M ₂
The magnification β _M2 of the above satisfies −2.5 <β _M2 <−1.2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catadioptric optical system having a reflecting surface and a refracting surface, and more particularly to an image forming optical system for performing reduction projection.

[0002]

2. Description of the Related Art Conventionally, various optical systems suitable for projecting and exposing a mask pattern on a photoresist on a wafer when manufacturing an integrated circuit such as an LSI have been proposed. For example, it is known that the Dyson-type catadioptric optical system can satisfactorily correct aberrations at a relatively large numerical aperture.
However, since the Dyson type catadioptric optical system has the same imaging magnification, there is a limit in transferring a fine pattern. Furthermore, since it is not corrected for chromatic aberration, it cannot be practically used in a light source with a wide band.

Therefore, as an optical system having a reduction magnification suitable for manufacturing a semiconductor having a finer pattern, an optical system obtained by modifying the Dyson type catadioptric optical system is disclosed, for example, in Japanese Patent Laid-Open No. 63-163319 and Japanese Patent Laid-Open No. 63-163319. It is proposed in Japanese Patent Laid-Open No. 2-66510.

[0004]

However, according to the optical system disclosed in Japanese Unexamined Patent Publication No. 63-163319, which enables reduction projection, it is possible to form an image at a reduction magnification having an annular field. However, basically, it has three concave mirrors and one convex mirror, and in order to use it as an exposure apparatus for microlithography, it was inevitable to have an extremely complicated structure by combining a large number of lenses.

Further, the reduction optical system proposed in the above-mentioned Japanese Patent Application Laid-Open No. 2-66510 has a construction in which one concave reflecting mirror, a lens system and a beam splitter are combined.
However, with this beam splitter, attenuation of the light quantity, aberration at the reference wavelength due to the angle characteristics of the wave plate,
It has problems such as limitation of wavelength range due to wavelength characteristics.

Therefore, the present invention has a simple structure and has excellent imaging performance as an optical system for semiconductor manufacturing while correcting chromatic aberration in a wide band, and catadioptric reduction projection optical system having a large numerical aperture. The purpose is to provide a system.

[0007]

In order to achieve the above object, a catadioptric reduction projection optical system according to the present invention has the following configuration. For example, as shown in FIG. 1, a catadioptric reduction projection optical system according to the present invention forms a secondary image of an object based on light from the first partial optical system that forms a primary image of the object and the primary image. A second partial optical system, and the first partial optical system includes a first lens group G ₁ having a positive refractive power in order from the incident side,
It has a second lens group G ₂ having a negative refractive power and a first concave reflecting mirror M _1, and the second partial optical system is a second concave reflecting mirror M ₂ and a fourth lens group having a positive refractive power. G ₄ and a third lens group G ₃ having a positive or negative refractive power is arranged in the optical path between the first concave reflecting mirror M ₁ and the second concave reflecting mirror M ₂ . 1
The fourth lens group is composed of at least one of quartz glass and fluorite, and when the magnification of the first concave reflecting mirror M ₁ is β _M1 and the magnification of the second concave reflecting mirror M ₂ is β _M2 , − It is configured to satisfy the condition of 1.0 <β _M1 <-0.7 -2.5 <β _M2 <-1.2.

[0008]

In the catadioptric reduction projection optical system according to the present invention having the above-described structure, the first and second partial optical systems each have a concave reflecting mirror having a main refracting power and a lens group (first refracting power). By having the first lens group G ₁ and the fourth lens group G ₄ ), reduction imaging can be performed together, so that the partial optical system does not impose a large burden on aberration correction, and a predetermined amount is set as the entire system. The reduction ratio can be obtained. Therefore, it is possible to achieve excellent imaging performance with a simple configuration. Also, it is an advantageous condition for correction of chromatic aberration and Petzval sum to obtain a positive refractive power as much as possible with a concave reflecting mirror.

With the above arrangement, in the catadioptric reduction projection optical system according to the present invention, it is possible to correct a chromatic aberration in a wide band while maintaining a large numerical aperture and keeping various other aberrations satisfactorily. , It is difficult to give a reflecting mirror a large refractive power. Since it is necessary for the refracting member to have a certain degree of refracting power, it is preferable that the refracting member be made of two types of glass, fluorite and quartz glass. In addition,
When the wavelength used by the light source is on the short wavelength side, especially 250 nm
The following cases are advantageous in terms of transmittance.

In the catadioptric reduction projection optical system according to the present invention, when the magnification of the first concave reflecting mirror M ₁ is β _M1 , -1.0 <β _M1 <-0.7 (1) It is better to satisfy the condition of. This condition defines an appropriate magnification of the first concave reflecting mirror M ₁ . As a result, a catadioptric reduction projection optical system with excellent optical performance can be realized, and a physically realizable catadioptric reduction projection optical system can be obtained. It should be noted that the physically realizable optical system is an optical system in which the respective optical members do not interfere with each other when the optical members constituting the catadioptric reduction projection optical system are arranged.

[0011] Here, beta _M1 is when exceeded the upper limit of the above conditions (1), the refractive power of the first concave reflecting mirror M ₁ is increased, generated in the first concave reflector M ₁ Aberrations, especially spherical and coma, increase. Then, the refracting optical system must strengthen the negative refracting power in order to cancel out these aberrations, and it becomes difficult to satisfactorily correct the aberrations. Therefore, the upper limit of β _M1 is more preferably −0.8.
Is desirable.

Further, β_M1Is below the lower limit of condition (1) above
When turned, the first concave reflecting mirror M ₁Has a low refractive power
Therefore, the refracting power of that amount will be supplemented by the refracting optical system.
It Refractive system becomes more complicated to correct various aberrations
Is not preferable. Especially for chromatic aberration,
In order to achieve achromatism in lens groups, refraction systems
Not only becomes more complicated, but also increases in secondary spectrum and colors
Due to the coma aberration, it is difficult to correct it.
Therefore, β_M1The lower limit of -1.0 is desirable.
Yes.

Further, in the catadioptric reduction projection optical system according to the present invention, when the magnification of the second concave reflecting mirror M ₂ is β _M2 , -2.5 <β _M2 <-1.2 (2 It is better to satisfy the condition of. This condition defines an appropriate magnification of the second concave reflecting mirror M ₂ , whereby a catadioptric reduction projection optical system with excellent optical performance can be realized, and catadioptric reduction projection physically realizable. The configuration of the optical system can be obtained.

[0014] Here, beta _M2 is when exceeded the upper limit of the above condition (2), the refractive power of the second concave reflector M ₂ is increased, generated in the second concave reflecting mirror M ₂ Aberrations, especially spherical and coma, increase. Further, the refracting optical system must strengthen the negative refracting power in order to cancel these aberrations, and it is difficult to correct the aberrations satisfactorily, which is not preferable. Therefore, more preferably β _M2
The upper limit of is preferably -1.5.

Further, β_M2Is below the lower limit of condition (2) above
When turned, the second concave reflecting mirror M ₂Has a low refractive power
Therefore, the refracting power of that amount will be supplemented by the refracting optical system.
It Refractive system becomes more complicated to correct various aberrations
Is not preferable. Especially for chromatic aberration,
The refraction system is made more complicated in order to achieve achromaticity of the lens group.
In addition to the increase in secondary spectrum and color
Ma aberration and the like occur, and it is difficult to correct it. That
Therefore, β is more desirable_M2Lower limit of -2.3
Is desirable.

In the catadioptric reduction projection optical system according to the present invention, the magnification of the fourth lens group G ₄ having a positive refractive power is set to β.
_{When G4} , it is desirable that the condition of 0.05 <β _G4 <0.3 (3) is satisfied. This condition defines an appropriate magnification of the fourth lens group G ₄ , and thereby a catadioptric reduction projection optical system with excellent optical performance can be realized, and catadioptric reduction projection optics that can be physically realized. The configuration of the system can be obtained. Here, when β _G4 exceeds the upper limit of the above condition (3), the refracting power of the fourth lens group G ₄ becomes small, and the refracting power corresponding to that is placed before G _{4 in the} optical path. It will be compensated by the optical system. Especially the first,
Also, the second concave reflecting mirror has a strong tendency to supplement its refracting power, and it becomes impossible to correct the aberration generated there. Further, there is a tendency that the light flux before and after entering the second concave reflecting mirror or the lenses on the incident side and the exit side interfere with each other, which makes it difficult to achieve a feasible optical arrangement. Considering these things, it is more preferable that the upper limit of β _G4 is 0.2.

Further, β_G4Is below the lower limit of condition (3) above
When turned, the second concave reflecting mirror M ₂Has a large refractive power
And this fourth lens group G_FourAberrations caused by
Surface aberration, coma and chromatic aberration increase. Especially color
As for aberrations, achromatization should be performed in each lens group of the refraction system.
Not only does the refraction system become more complex to achieve
Increase in secondary spectrum and coma aberration due to color
It will be difficult to correct. Therefore, I want more
Ku β_G4The lower limit of is preferably 0.1.

Next, catadioptric reduction projection optics according to the present invention
The aberration balance of each lens group in the system will be explained.
It First lens group G₁Is located near the object and
It has the function of maintaining the trickiness and corrects distortion.
It is carried out. Second lens group G ₂Is a concave mirror and a convex lens.
Mainly correcting spherical aberration and coma by the lens group
There is. Third lens group G₃And the fourth lens group G_FourIs a reduced image
And the correction of Petzval sum
I do. In particular, the third lens group G₃Is the so-called field ren
And the first concave reflecting mirror M.₁Light of
Allows light flux from near the axis to pass. By this, the second concave surface
Reflector M₂So that the light flux also passes near the optical axis
This second concave reflecting mirror M can be constructed.₂Aberration at
Can be prevented.

[0019]

Embodiments of the present invention will be described below. FIG. 1 is an optical path diagram showing the configuration of the first embodiment according to the present invention. As shown in the figure, the light flux from the object plane passes through the first lens group G ₁ having a positive refractive power, the optical path is bent by the plane reflecting mirror M ₃ and the second lens group G ₂ , and the reduction magnification is slightly reduced. It is reflected by the first concave reflecting mirror M ₁ that it has.

The first lens group G ₁ includes a plano-convex positive lens L ₁₁ having a flat surface facing the object surface, a positive meniscus lens L ₁₂ having a convex surface facing the object surface, and a negative meniscus lens having a convex surface facing the object side. It is composed of a lens L ₁₃ and a positive meniscus lens L ₁₄ having a concave surface facing the incident side. The plane reflecting mirror M ₃ is arranged between the positive meniscus lens L ₁₂ and the negative meniscus lens L ₁₃ .

The second lens group G ₂ is arranged between the first lens group G ₁ and the first concave reflecting mirror M ₁ and has a negative meniscus lens L with its convex surface facing the first concave reflecting mirror M _{1. It} consists of ₂₁ . Here, the first lens group G ₁ mainly corrects distortion and maintains telecentricity. The second lens group G ₂ corrects higher-order coma aberrations generated by the first concave reflecting mirror M ₁ and the second concave reflecting mirror M ₂ .

Next, the first concave reflecting mirror M₁Reflected in
The luminous flux is again the second lens group G₂Through the negative meniscus
Lens L₃₂And positive meniscus lens L₃₃Is reduced between
Primary image I₁Is formed. Third lens group G₃Is the first
Concave reflector M₁Positive meniscus lens with convex side facing
L₃₁And the primary image I₁Negative plano-concave lens with concave surface facing side
Z L₃₂And the primary image I₁Weak refractive power with concave surface facing side
Meniscus lens L ₃₃Consists of Third lens group G₃
Is the correction of distortion, field curvature and field lens
It works.

The light beam emitted from the third lens group G ₃ is reflected by the second concave reflecting mirror M ₂ after the optical path is bent by the flat reflecting mirror M ₄ . Further, the light reflected by the second concave reflecting mirror M ₂ enters the fourth lens group G ₄ having a positive refractive power. The fourth lens group G ₄ includes, in order from the light incident side, positive meniscus lenses L ₄₁ and L ₄₂ having convex surfaces facing the second concave reflecting mirror M ₂ , a biconvex lens L _43, and a biconcave lens L ₄₄ . , A biconvex lens L ₄₅ and a second concave reflecting mirror M
A negative meniscus lens L ₄₆ having a convex surface directed toward the _second side, and a second
Positive meniscus lens L with the convex surface facing the concave reflecting mirror M ₂ side
₄₇ , and forms a secondary image I ₂ having a reduction ratio higher than that of the primary image I ₁ .

At this time, the negative meniscus lens L ₁₃ and the positive meniscus lens L _{14 of} the first lens group G ₁
The positive meniscus lens L ₃₁ and the negative meniscus lens L _{32 of the} lens group G ₃ have a shape in which a part of the lens is used so as not to block the other optical path. Further, since the positive meniscus lens L ₃₃ of the third lens group does not block the light flux after being bent by the plane reflecting mirror M ₄ , the negative meniscus lens L ₁₃ , the positive meniscus lens L ₁₄ , and the positive meniscus lens L ₃₃ are included. Like the lens L ₃₁ and the negative meniscus lens L ₃₂ , a part of the lens is used.

In the first embodiment, the overall reduction ratio is +
It has a reduction ratio of 0.25, that is, a quarter, and achieves a numerical aperture (NA) of 0.45 in a ring-shaped visual field with a radius of 20 mm centered on the optical axis on the wafer. Furthermore, the central wavelength of the light source used for illumination and its spread are λ = 217
± 4 nm. Table 1 below shows specifications of the first embodiment.

In the table, it is assumed that the signs of the refractive index and the surface spacing are inverted by the reflection on the concave reflecting mirror. The refractive index of the glass material indicates the refractive index at the center wavelength (217 nm). The positions of the plane reflecting mirrors M ₃ and M ₄ for bending the optical path are omitted because they are not essential in the optical design.

[0027]

[Table 1] [Specifications of the first embodiment] No. Radius of curvature Surface spacing Refractive index (object surface) 195.426 1.0000 1 ∞ 28.240 1.53126 (quartz) L ₁₁ 2 -357.547 0.100 1.0000 3 230.557 40.000 1.53126 (quartz) L ₁₂ 4 511.280 127.690 1.0000 5 878.395 15.000 1.53126 (Quartz) L ₁₃ 6 147.119 30.000 1.0000 7 -460.235 21.395 1.53126 (Quartz) L ₁₄ 8 -331.076 503.034 1.0000 9 -249.818 20.000 1.53126 (Quartz) L ₂₁ 10 -339.471 197.664 1.0000 11 -788.338 -197.664 -1.0000 M ₁ 12 -339.471 -20.000 -1.53126 (quartz) L ₂₁ 13 -249.818 -476.065 -1.0000 14 -190.475 -35.000 -1.53126 (quartz) L ₃₁ 15 -519.430 -34.164 -1.0000 16 -5178.591 -15.000- 1.48295 (fluorite) L ₃₂ 17 -168.466 -237.584 -1.0000 18 210.704 -9.790 -1.53126 (quartz) L ₃₃ 19 200.000 -800.100 -1.0000 20 1107.209 800.100 1.0000 M ₂ 21 198.147 14.809 1.48295 (fluorite) L ₄₁ 22 372.888 0.100 1.0000 23 129.330 25.653 1.53126 (Quartz) L ₄₂ 24 557.405 0.100 1.0000 25 444.552 14.301 1.48 295 (fluorite) L ₄₃ 26 -3249.866 7.298 1.0000 27 -295.228 8.000 1.53126 (quartz) L ₄₄ 28 206.396 0.100 1.0000 29 206.202 25.530 1.48295 (fluorite) L ₄₅ 30 -284.380 0.100 1.0000 31 141.752 45.000 1.53126 (quartz) L ₄₆ 32 72.518 1.447 1.0000 33 80.818 40.000 1.53126 (Quartz) L ₄₇ 34 -1726.119 15.000 1.0000 《Condition corresponding value》 β _{M1 =} −0.959 β _M2 = −1.646 β _G4 = 0.178 Result of the first embodiment Fig. 2 shows coma aberration to show image performance.
Shown in This aberration diagram shows coma aberrations in the meridional direction and the sagittal direction at the center of the annular visual field. 21
A coma aberration at 3 nm is shown by a broken line, a coma aberration at 217 nm is shown by a solid line, and a coma aberration at 221 nm is shown by a dotted line. It can be seen from FIG. 2 that the catadioptric reduction projection optical system according to the first embodiment has an excellent imaging performance because the aberration is corrected in this range.

Next, referring to FIG. 3, the second embodiment of the present invention will be described.
An example will be described. In FIG. 3, the light flux from the object plane passes through the first lens group G ₁ having a positive refractive power, the optical path is bent by the plane reflecting mirror M ₃ , passes through the second lens group G _{2, and} has a slightly reduced magnification. It is reflected by the first concave reflecting mirror M ₁ that it has. The first lens group G ₁ is composed of a plano-convex positive lens L ₁₁ having a flat surface facing the object plane, a biconvex positive lens L _12, and a biconcave negative lens L ₁₃ . The second lens group G ₂ includes the first lens group G
₁ is disposed between the first concave reflecting mirror M ₁ and the plano-convex positive lens L ₂₁ having a convex surface facing the plane reflecting mirror M ₃ side, and a negative lens having a convex surface facing the first concave reflecting mirror M ₁ side. Meniscus lens L ₂₂
Consists of

The first lens group G ₁ mainly corrects distortion and maintains telecentricity. The second lens group G ₂ includes the first concave reflecting mirror M ₁ and the second concave mirror M ₁ .
The high-order coma aberration generated by the concave reflecting mirror M ₂ is corrected. Next, the light flux reflected by the first concave reflecting mirror M ₁ is
After passing through the second lens group G ₂ again and the third lens group G ₃ , a reduced primary image I ₁ is formed. The third lens group G ₃ includes a positive meniscus lens L ₃₁ having a convex surface facing the first concave reflecting mirror side, a negative meniscus lens L ₃₂ having a concave surface facing the _primary image I ₁ image side, and a biconvex lens L 3. It consists of ₃₃ and. The third lens group G ₃ serves to correct distortion, curvature of field and act as a field lens.

The third lens group G₃Light emitted from
The bundle is a plane mirror M_FourSecond concave after the optical path is bent at
Surface reflector M₂The fourth lens, which has a positive refractive power, is reflected by
Group G_FourIncident on. This fourth lens group G_FourOf the rays
The second concave reflecting mirror M in order from the incident side₂With the convex side facing
Positive meniscus lens L₄₁And the second concave reflecting mirror M₂On the side
Negative meniscus lens L with concave surface₄₂And a biconvex lens
L₄₃And a biconcave lens L ₄₄And the second concave reflecting mirror M₂Convex to the side
Positive meniscus lens L facing the surface₄₅And the second concave reflection
Mirror M₂Negative meniscus lens L with convex surface facing side₄₆When,
Second concave reflecting mirror M₂Positive meniscus ray with convex side facing
L₄₇And the primary image I ₁Shrink more than
Secondary image I with a high rate₂To form

At this time, the biconcave lens L ₁₃ and the plane reflecting mirror M _{3 of} the first lens group G ₁ have a shape in which a part of the lens is used so as not to block the other optical path. This second embodiment has a reduction ratio of +0.25 as a whole, that is, a reduction ratio of 1/4, and a numerical aperture (NA) in a ring-shaped visual field centered on the optical axis and having a radius of 20 mm on the wafer. 0.45
Has been achieved. Further, the center wavelength of the light source used for illumination and its spread are λ = 217 ± 4 nm.

Table 2 below shows the specifications of the second embodiment. In the table, it is assumed that the signs of the refractive index and the surface spacing are inverted due to the reflection by the concave reflecting mirror. The refractive index of the glass material is
The refractive index at the central wavelength (217 nm) is shown.
The positions of the plane reflecting mirrors M ₃ and M ₄ for bending the optical path are omitted because they are not essential in the optical design.

[0033]

[Table 2] [Specifications of the second embodiment] No. Radius of curvature Surface spacing Refractive index (object surface) 326.189 1.0000 1 ∞ 40.000 1.53126 (quartz) L ₁₁ 2 -509.905 0.500 1.0000 3 290.348 57.790 1.53126 (quartz) L ₁₂ 4 -302.026 1.115 1.0000 5 -297.387 15.000 1.53126 (Quartz) L ₁₃ 6 291.877 584.373 1.0000 7 900.000 30.000 1.53126 (Quartz) L ₂₁ 8 ∞ 50.000 1.0000 9 -225.015 20.000 1.53126 (Quartz) L ₂₂ 10 -550.380 155.364 1.0000 11 -714.562 -155.364 -1.0000 M ₁ 12 -550.380 -20.000 -1.53126 (Quartz) L ₂₂ 13 -225.015 -50.000 -1.0000 14 ∞ -30.000 -1.53126 (Quartz) L ₂₁ 15 900.000 -481.784 -1.0000 16 -257.121 -35.000 -1.48295 ( Quartz) L ₃₁ 17 -306.348 -34.164 -1.0000 18 -238.821 -15.000 -1.53126 (Quartz) L ₃₂ 19 -202.203 -24.613 -1.0000 20 -94514.655 -14.817 -1.53126 (Quartz) L ₃₃ 21 1000.000 -965.156 -1.0000 22 1192.217 800.500 1.0000 M ₂ 2 3 239.014 13.881 1.48295 (fluorite) L ₄₁ 24 701.943 14.547 1.0000 25 -221.419 40.000 1.4 8295 (quartz) L ₄₂ 26 -252.472 0.500 1.0000 27 138.449 40.079 1.48295 (fluorite) L ₄₃ 28 -253.108 0.500 1.0000 29 -249.340 21.997 1.53126 (quartz) L ₄₄ 30 313.176 0.499 1.0000 31 335.839 13.623 1.48295 (fluorite) L ₄₅ 32 22383.397 0.500 1.0000 33 94.117 45.000 1.53126 (Quartz) L ₄₆ 34 63.412 4.289 1.0000 35 79.601 40.000 1.48295 (Fluorite) L ₄₇ 36 775.688 26.439 1.0000 《Condition corresponding value》 β _M1 = −0.828 β _M2 = -2.242 β _G4 = 0.120 FIG. 4 shows the coma aberration for showing the image forming performance of the second embodiment.
Shown in This aberration diagram shows coma aberrations in the meridional direction and the sagittal direction at the center of the annular visual field. 21
A coma aberration at 3 nm is shown by a broken line, a coma aberration at 217 nm is shown by a solid line, and a coma aberration at 221 nm is shown by a dotted line. It can be seen from FIG. 4 that the catadioptric reduction projection optical system according to the second embodiment corrects aberrations in this range and has excellent imaging performance.

Next, a third embodiment will be described with reference to FIG. FIG. 5 is an optical path diagram showing the configuration of the third embodiment according to the present invention. As shown in the figure, the light flux from the object plane passes through the first lens group G ₁ having a positive refractive power, the optical path is bent by the plane reflecting mirror M ₃ , passes through the second lens group G _{2, and} has a slightly reduced magnification. It is reflected by the first concave reflecting mirror M ₁ that it has. First
The lens group G ₁ is a plano-convex positive lens L having a plane facing the object plane.
₁₁ and a positive meniscus lens L ₁₂ with a convex surface facing the object surface.
And a negative meniscus lens L ₁₃ having a convex surface facing the object side. The plane reflecting mirror M ₃ is a positive meniscus lens L ₁₂
It is disposed between the negative meniscus lens L ₁₃ with.

Second lens group G₂Is the first lens group G₁When
First concave mirror M₁Is disposed between the first concave reflecting mirror
M₁Negative meniscus lens L with convex surface facing side_{twenty one}Empty
It Here, the first lens group G₁Mainly compensates for distortion.
Positive and maintaining telecentricity. First
2 lens group G₂Is the first concave reflecting mirror M₁And the second concave reflection
Mirror M₂It corrects the higher-order coma aberration that occurs in. Next
And the first concave mirror M ₁The light flux reflected at
2 lens group G₂Through the third lens group G₃Through
Primary image I reduced after passing₁Is formed.

The third lens group G ₃ includes a positive meniscus lens L ₃₁ having a convex surface facing the first concave reflecting mirror side and a primary image I ₁
Negative substantially plano-concave lens L ₃₂ having a concave surface directed to the side and the primary image I
_It is composed of a positive meniscus lens L ₃₃ having a weak refractive power and having a convex surface facing the _1st side. The third lens group G ₃ has a distortion aberration,
It serves to correct field curvature and act as a field lens.

The third lens group G₃Light emitted from
The bundle is a plane mirror M_FourSecond concave after the optical path is bent at
Surface reflector M₂Is reflected at. Furthermore, it has a positive refractive power
4th lens group G_FourIncident on. Fourth lens group G_FourIs
Biconvex lens L in order from the incident side of the light beam₄₁And a biconcave lens
L₄₂And the second concave reflecting mirror M₂Positive menis with convex side
Scus lens L₄₃And a biconcave lens L₄₄And a biconvex lens L
₄₅And a negative meniscus with the convex surface facing the second concave reflecting mirror side.
Lens L₄₆And a positive lens with the convex surface facing the second concave reflecting mirror side.
Varnish lens L₄₇And the primary image I₁Yo
Secondary image I with a reduction ratio₂To form This and
First lens group G₁Negative meniscus lens L₁₃as well as
Flat mirror M₃And the third lens group G₃The positive meniscus
Lens L ₃₁And negative plano-concave lens L₃₂And the other on the other
With a shape that uses a part of the lens so as not to block the optical path of
Become.

In the third embodiment, the overall reduction ratio is +
It has a reduction ratio of 0.25, that is, a quarter, and achieves a numerical aperture (NA) of 0.45 in a ring-shaped field of view with a radius of 20 mm centered on the optical axis on the wafer. Furthermore, the central wavelength of the light source used for illumination and its spread are λ = 217
± 4 nm. . Table 3 below shows specifications of the third embodiment.

In the table, it is assumed that the signs of the refractive index and the surface spacing are reversed by the reflection from the concave reflecting mirror. The refractive index of the glass material indicates the refractive index at the center wavelength (217 nm). The positions of the plane reflecting mirrors M ₃ and M ₄ for bending the optical path are omitted because they are not essential in the optical design.

[0040]

[Table 3] [Specifications of the third embodiment] No. Radius of curvature Surface spacing Refractive index (object surface) 183.527 1.0000 1 ∞ 37.138 1.53126 (quartz) L ₁₁ 2 -339.043 0.500 1.0000 3 256.545 17.073 1.53126 (quartz) L ₁₂ 4 429.175 155.427 1.0000 5 314.370 15.000 1.53126 (Quartz) L ₁₃ 6 154.417 504.109 1.0000 7 -236.577 20.000 1.48295 (Fluorite) L ₂₁ 8 -369.351 266.233 1.0000 9 -799.568 -266.233 -1.0000 M ₁ 1 0 -369.351 -20.000 -1.48295 (Fluorite) L ₂₁ 11 -236.577 -491.460 -1.0000 12 -216.826 -35.000 -1.53126 (Quartz) L ₃₁ 13 -536.198 -34.164 -1.0000 14 -1123.930 -15.000 -1.48295 (Fluorite) L ₃₂ 15 -199.354 -199.805 -1.0000 16 1488.012 -21.214 -1.53126 (quartz) L ₃₃ 17 1000.000 -880.000 -1.0000 18 1143.371 802.383 1.0000 M ₂ 19 222.215 22.128 1.48295 (fluorite) L ₄₁ 20 -929.491 0.500 1.0000 21 -1000.000 7.500 1.53126 (quartz) L ₄₂ 22 1221.490 0.500 1.0000 23 116.974 36.073 1.48295 (fluorite) L ₄₃ 24 1474.680 7.516 1.0000 25 -407.993 19.06 3 1.53126 (quartz) L ₄₄ 26 852.730 0.782 1.0000 27 1302.010 19.232 1.48295 (fluorite) L ₄₅ 28 -376.270 0.500 1.0000 29 145.377 45.000 1.53126 (quartz) L ₄₆ 30 66.088 1.158 1.0000 31 71.786 40.000 1.48295 (fluorite) L ₄₇ 32 2939.734 15.769 1.0000 << Corresponding value >> β _M1 = −0.988 β _M2 = −2.008 β _G4 = 0.142 The coma aberration for showing the image forming performance of the third embodiment is shown in FIG.
Shown in This aberration diagram shows coma aberrations in the meridional direction and the sagittal direction at the center of the annular visual field. 21
A coma aberration at 3 nm is shown by a broken line, a coma aberration at 217 nm is shown by a solid line, and a coma aberration at 221 nm is shown by a dotted line. It can be seen from FIG. 6 that the catadioptric reduction projection optical system according to the third example has aberrations corrected in this range and has excellent image forming performance.

[0041]

As described above, while the present invention has a relatively simple structure, it corrects chromatic aberration in a wide band,
It is possible to obtain a catadioptric reduction projection optical system which has excellent imaging performance as an optical system for semiconductor manufacturing and has a large numerical aperture.

[Brief description of drawings]

FIG. 1 is an optical path diagram showing the configuration of a first embodiment of a catadioptric reduction projection optical system according to the present invention.

FIG. 2 is a coma aberration diagram of the first embodiment.

FIG. 3 is an optical path diagram showing a configuration of a second embodiment of a catadioptric reduction projection optical system according to the present invention.

FIG. 4 is a coma aberration diagram of the second embodiment.

FIG. 5 is an optical path diagram showing the configuration of a third embodiment of a catadioptric reduction projection optical system according to the present invention.

FIG. 6 is a coma aberration diagram of the third embodiment.

[Explanation of symbols for main parts]

 M1 ... 1st concave reflecting mirror M2 ... 2nd concave reflecting mirror M3 ... Planar reflecting mirror M4 ... Planar reflecting mirror G1 ... 1st lens group G2 ... 2nd lens group G3 ... .... Third lens group G4 ... fourth lens group

Claims (4)

[Claims] 1. A catadioptric reduction projection having a first partial optical system for forming a primary image of an object and a second partial optical system for forming a secondary image of the object based on light from the primary image. In the optical system, the first partial optical system includes, in order from the light incident side, a first lens group G ₁ having a positive refractive power and a second lens group G ₂ having a negative refractive power.
And a first concave reflecting mirror M ₁ and the second partial optical system has a second concave reflecting mirror M ₂ and a fourth lens group G ₄ having a positive refractive power, A third lens group G ₃ having a positive or negative refractive power is arranged in the optical path between the concave reflecting mirror M ₁ and the second concave reflecting mirror M _2, and the first to fourth lens groups are , Quartz glass and / or fluorite. When the magnification of the first concave reflecting mirror M ₁ is β _M1 and the magnification of the second concave reflecting mirror M ₂ is β _M2 , −1.0 < A catadioptric reduction projection optical system which satisfies the condition of β _M1 <−0.7 −2.5 <β _M2 <−1.2. 2. The catadioptric reduction projection according to claim 1, wherein the condition of 0.05 <β _G4 <0.3 is satisfied when the magnification of the fourth lens group G ₄ is β _M4. Optical system. 3. The third lens group G ₃ has at least one positive lens made of quartz glass and at least one negative lens made of fluorite.
3. The catadioptric reduction projection optical system according to claim 1, wherein the lens group G ₄ has at least two positive lenses made of fluorite and at least one negative lens made of quartz glass. system. 4. The catadioptric reduction according to claim 1, wherein the second lens group G ₂ is composed of a single lens having a negative refractive power, and the glass material of the single lens is fluorite. Projection optics.