JPH0588088A - Reflective and refractive reduction projection optical system - Google Patents

Abstract

PURPOSE:To employ constitution wherein a reflection and refraction system uses luminous flux on an optical axis and to eliminate deterioration in resolving power. CONSTITUTION:This optical system has a 1st lens group G1 which has negative refracting power and diffuses luminous flux from a reticle 1, a half-mirror 5 which transmits luminous flux from this 1st lens group G1, three parallel plane plates 2, 3, and 4 which are arranged between the 1st lens group G1 and half-mirror 5 slantingly to the optical axis and compensate aberration due to the half-mirror 5, a concave surface reflecting mirror 7 which returns luminous flux projected by the half-mirror 5 to the half-mirror 5 while converting it, and a 2nd lens group G3 which has positive refracting power and converges luminous flux returned to the half-mirror 5 and reflected by the half-mirror 5 to form a reduced image of a pattern on its reticle 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for catadioptric reduction when applied to an optical system used for, for example, an exposure apparatus for manufacturing a semiconductor device for reducing and projecting a pattern which is larger than the pattern of an actual device. Projection optical system.

[0002]

2. Description of the Related Art Semiconductor integrated circuits are becoming finer and finer, and an exposure apparatus for printing a pattern thereof is required to have a higher resolution. In order to satisfy this requirement, it is necessary to shorten the wavelength of the light source and increase the numerical aperture (NA) of the optical system. However, as the wavelength becomes shorter, the glass materials that can be used practically are limited due to the absorption of light. When the wavelength is 300 nm or less, only synthetic quartz and fluorite (calcium fluoride) can be practically used. In addition, fluorspar has poor temperature characteristics and cannot be used in large quantities. Therefore, it is extremely difficult to make a projection lens using only the refraction system. Further, it is difficult to make a projection optical system having a large numerical aperture only with a reflective system because of the difficulty of aberration correction.

Therefore, various techniques for forming a projection optical system by combining a reflective system and a refraction system have been proposed. One example thereof is a ring-field optical system as disclosed in JP-A-63-163319. This optical system uses an off-axis light beam so that the incident light and the reflected light do not interfere with each other, and is configured to expose only the off-axis ring zone.

As another example, a projection exposure apparatus including a catadioptric system that projects an image of a reticle (mask) at once by arranging a beam splitter in the projection optical system, for example, is used. Japanese Patent Publication 51-271
No. 16 and Japanese Patent Laid-Open No. 2-66510.

FIG. 8 schematically shows the optical system disclosed in Japanese Patent Laid-Open No. 2-66510. In FIG. 8, the light flux from the reticle 21 on which the pattern to be reduced and transferred is drawn is the lens group 2 having a positive refractive power.
It is converted into a substantially parallel light beam by 2 and is irradiated on a prism type beam splitter (beam splitter cube) 23. Bonding surface 23a of this beam splitter 23
The light flux that has passed through is a correction lens group 24 having a negative refractive power.
Is reflected by the concave reflecting mirror 25. The light flux reflected by the concave reflecting mirror 25 passes through the correction lens group 24 again, is reflected by the cemented surface 23a of the beam splitter 23, and then is focused on the wafer 27 by the lens group 26 having a positive refractive power. A reduced image of the reticle pattern is formed on the wafer 27. An example in which a half mirror made of a plane parallel plate is used instead of the prism type beam splitter 23 is also disclosed.

[0006]

However, it is difficult to increase the numerical aperture in the ring-field optical system among the conventional examples. Moreover, since it is not possible to perform exposure in a lump, it is necessary to perform exposure while moving the reticle and the wafer at different speeds according to the reduction ratio of the optical system, which causes the inconvenience that the configuration of the mechanical system becomes complicated. It was

Further, in the structure disclosed in Japanese Patent Publication No. 51-27116, there is a problem that there is a large amount of flare due to reflection on the refracting surface of the optical system after the beam splitter. Furthermore, because the characteristics of the beam splitter such as uneven reflectance, absorption and phase change are not taken into consideration, the resolution is low and the magnification of the entire system is the same. For the next-generation semiconductor manufacturing that requires higher resolution. It cannot be used as an exposure apparatus at all.

Further, among the projection optical systems disclosed in Japanese Patent Laid-Open No. 2-66510, the optical system shown in FIG. 8 has a disadvantage that the resolution is deteriorated due to nonuniformity of a large-sized prism material for the beam splitter 23. In addition, there is no adhesive that can withstand use in a wavelength range of about 300 nm or less, and it is difficult to construct a beam splitter by bonding two blocks together. Further, in the example in which the half mirror is used instead of the beam splitter 23 of the optical system in FIG. 8, there is a disadvantage that the resolution is deteriorated as a whole due to the aberration caused by the half mirror. The present invention has been made in view of the above problems, and an object of the present invention is to provide a reduction projection optical system that uses an axial light beam in a catadioptric system and does not deteriorate resolution.

[0009]

A catadioptric reduction projection optical system according to the present invention has a first surface (1) as shown in FIG. 1, for example.
Is an optical system for reducing and projecting the pattern of No. 2 on the second surface (8), and has a negative or positive refractive power, and its first surface (1)
First lens group G ₁ for diffusing or converging the light flux from the first lens group, a half mirror (5) for transmitting the light flux from the first lens group G ₁ , the first lens group G ₁ and the half mirror (5) thereof And three parallel plane plates (2, 3, 4) that are arranged obliquely with respect to the optical axis and correct the aberration caused by the half mirror (5), and are emitted from the half mirror (5). The concave reflecting mirror (7) that focuses the light flux that returns to the half mirror (3) and the light flux that has a positive refractive power and that is returned to the half mirror (5) and that is reflected by the half mirror (5) The second lens group G ₃ which focuses and forms a reduced image of the pattern of the first surface (1) on the second surface (8)
And have.

In this case, the radius of curvature of the concave reflecting mirror (7) is preferably set within the range of 17 to 25 times the diameter of the exposure area (image circle) on the second surface (8). .. Further, the inclination of the off-axis chief ray incident on the concave reflecting mirror (7) with respect to the optical axis is preferably 6 degrees or less.

Further, in the present invention, it is preferable to dispose a quarter-wave plate (6) between the half mirror (5) and the concave reflecting mirror (7). The quarter-wave plate (6) is preferably formed of a uniaxial crystal (eg, quartz) having a thickness of 100 μm or less.

[0012]

According to the present invention, the on-axis light flux is used to collectively expose a large area in a structure in which the reflection system and the refraction system are combined. Further, since the reflective system has no chromatic aberration, most of the refracting power of the entire system is given to the concave reflecting mirror (7) to suppress the occurrence of chromatic aberration. The half mirror (5) separates the incident light and the reflected light. The half mirror is used because it does not require a large glass material as compared with the prism type beam splitter, it does not require an adhesive as it is a single body, and the surface accuracy may be poor by the refractive index.

However, astigmatism and coma are generated by using the half mirror (5). In order to prevent this, it is necessary to completely collimate the light flux passing through the half mirror (5). However, it is impossible to realize a perfect parallel light flux for all image heights. Therefore, in order to eliminate the aberration caused by the half mirror (5), three parallel plane plates (2, 3, 4) are obliquely arranged on the optical axis between the half mirror (5) and the first lens group G ₁ . In this case, the plane parallel plates (2, 3, 4) are made equal in thickness to the half mirror (5) and are inclined by 45 degrees with respect to the optical axis. Further, as shown in FIG. 1, the planes of parallel plane plates (4), (3), and (2) are rotated by 90 degrees, 180 degrees, and 270 degrees from the direction of the half mirror (5), respectively. Astigmatism and coma due to (5) are completely corrected.

An additional lens group G ₂ having a negative refractive power may be arranged between the half mirror (5) and the concave reflecting mirror (7). As a result, the chromatic aberration of the second lens group G _{3 having} a positive refractive power can be better corrected, and the spherical aberration of the concave reflecting mirror (7) can be better corrected.

Next, the radius of curvature of the concave reflecting mirror (7) is the second
1 of the diameter of the exposure area (image circle) on the surface (8)
The reason why 7 to 25 times is preferable will be described. In the concave reflecting mirror, it is possible to achieve a certain reduction magnification due to its converging action, and since it affects Petzval sum, astigmatism, and distortion, refraction consisting of the first lens group G ₁ and the second lens group G ₃ It is possible to maintain a good aberration balance with the system. That is, when the radius of curvature of the concave reflecting mirror (7) is less than 17 times the diameter of the image circle of the second surface (8), it is advantageous for the correction of chromatic aberration, but the Petzval sum increases in the positive direction. Astigmatism and distortion also increase.

The reason is that when the radius of curvature of the concave reflecting mirror becomes small and the refracting power becomes large, the spherical aberration due to the concave reflecting mirror (7) becomes large, but in order to correct the spherical aberration, the second lens group G ₃ It is necessary to increase the positive refractive power of. However, since the second lens group G ₃ is arranged at a position close to the second surface (8) as an image surface, a large refracting power is required for aberration correction and the Petzval sum remarkably increases. Will end up. Therefore, in order to satisfactorily correct various aberrations, the radius of curvature of the concave reflecting mirror (7) is preferably about 19 times or more the diameter of the image circle of the reduced image.

On the contrary, if the radius of curvature of the concave reflecting mirror (7) exceeds 25 times the diameter of the image circle of the reduced image and becomes large, it is advantageous for correction of astigmatism and distortion, It becomes difficult to obtain a desired reduction magnification, and correction of chromatic aberration becomes insufficient, which is not very practical.

Next, the reason why the inclination of the off-axis chief ray incident on the concave reflecting mirror (7) with respect to the optical axis is preferably 6 degrees or less will be explained. If not limited, the astigmatism and the like at the concave reflecting mirror (7) will become too large. Also, half mirror (5)
Since the inclination of the off-axis chief ray incident on is also limited, the transmittance and reflectance of the half mirror (5) are stable. Therefore, by limiting the inclination of the off-axis chief ray with respect to the optical axis, the imaging performance is improved as a whole.

The effect of the quarter wave plate (6) disposed between the half mirror (5) and the concave reflecting mirror (7) will be described. A dielectric film, which is generally used as a semi-transparent surface of a half mirror, has a strong polarization characteristic, and a semi-transparent surface (5a) of a half mirror (5) has a light beam (p-polarized light) polarized parallel to the plane of FIG. Is easily transmitted, and a light beam (s-polarized light) polarized perpendicularly to the paper surface of FIG. 1 is easily reflected. In this case, the p-polarized light component transmitted through the semi-transparent surface (5a) is transmitted through the quarter-wave plate (6) to become circularly polarized light, and this circularly polarized light beam is reflected by the concave reflecting mirror (7). It becomes circularly polarized light in the opposite direction. The reverse circularly polarized reflected light becomes s-polarized light by passing through the quarter-wave plate (6), and most of the s-polarized light flux is the half mirror (5).
It is reflected by the semi-transparent surface (5a) and goes toward the second surface (8).
Therefore, not only the quarter-wave plate (6) can reduce the loss of the amount of light in the half mirror (5), but also it becomes difficult for excess reflected light to return to the second surface (8), and flare is prevented. Can be reduced.

Further, it is desirable to use a thin uniaxial crystal (quartz, for example) as the quarter-wave plate (6). The reason is that if the light beam that passes through the quarter-wave plate deviates from the parallel light beam, astigmatism occurs for the extraordinary light beam. This astigmatism cannot be corrected by a method of laminating two crystals by rotating their optical axes 90 degrees with respect to each other, as is usually done with a wave plate. That is, astigmatism occurs in both ordinary rays and extraordinary rays.

[0021] as represented by the astigmatism amount wavefront aberration W, the difference in refractive index between the (n _o -n _e) between the ordinary ray and the extraordinary ray, the thickness of d of the crystals, theta and from collimated light If the deviation, that is, the divergence (or focusing) angle of the light beam, the wavefront aberration W is expressed by the following equation. W = (n _o -n _e) the d [theta] ^2/2 for example a quarter-wave plate when configuring in crystal, (n
_o −n _e ) = 0.01, and the divergent (focused) state of the light beam is θ = 14 degrees. When the wavelength used is λ, it is preferable to maintain the wavefront aberration W at a quarter wavelength, that is, λ / 4 or less, in order to maintain sufficiently good imaging performance. For that purpose, the wavelength λ should be set to, for example, 248 nm, and d <100 μm must be satisfied from the above equation.

[0022]

Embodiments of the catadioptric reduction projection optical system according to the present invention will be described below with reference to FIGS. In this example, the present invention is applied to an optical system of an exposure apparatus having a wavelength of 248 nm and a reduction ratio of 1/5 for semiconductor manufacturing. FIG. 1 shows a schematic configuration of the optical system of this example.
In the figure, 1 is a reticle on which a pattern for an integrated circuit is formed. A first lens group G ₁ having a negative or positive refractive power, a first parallel plane plate 2, a second parallel plane plate 3, and a third parallel plane plate 4 are arranged in this order on an optical axis perpendicular to the reticle 1. , The half mirror 5, the quarter-wave plate 6, the additional lens group G ₂ having a negative refractive power, and the concave reflecting mirror 7 are arranged.
The second lens group G ₃ having a positive refracting power and the wafer 8 are arranged in order in the direction in which the light reflected by the semi-transparent surface 5a of the half mirror 5 is reflected.

The plane-parallel plates 2 to 4 and the half mirror 5 are inclined at 45 ° with respect to the optical axis, and the thickness of the plane-parallel plates 2 to 4 is made equal to the thickness of the half mirror 3, respectively. Further, the orientations of the plane-parallel plates 4, 3 and 2 are rotated by 90 °, 180 ° and 270 ° from the orientation of the half mirror 5, respectively. Astigmatism and coma due to the half mirror 5 are completely corrected by these plane parallel plates 2 to 4.
Incidentally, in FIG. 1, the additional lens group G ₂ can be omitted.

Then, the reticle 1 is illuminated by an illumination optical system (not shown), and the luminous flux emitted from the reticle 1 is
The plane parallel plate 2 diffused or focused by the first lens group G1
The light is made incident on the half mirror 5 through. The light flux transmitted through the semi-transparent surface 5a of the half mirror 5 is converted into a quarter wave plate 6
Then, the light is made incident on the concave reflecting mirror 7 via the additional lens group G ₂ . The radius of curvature of the concave reflecting mirror 7 is about 400 mm. The light flux reflected by the concave reflecting mirror 7 passes through the additional lens group G ₂ and the quarter-wave plate 6 while converging, and again faces the half mirror 5, and is reflected by the semi-transparent surface 5 a of the half mirror 5. To the wafer 8 by the second lens group G ₃ having a positive refractive power.
Focus on top. As a result, a reduced image of the pattern on the reticle 1 is formed on the wafer 8.

Further, it is efficient to use a luminous flux (p-polarized light) polarized in parallel to the paper surface of FIG. 1 as the illuminating light, but ordinary random polarized illuminating light may be used. In any case,
Most of the p-polarized component in the illumination light is transmitted through the semi-transparent surface 5a due to the polarization characteristics of the half mirror 5, and this transmitted light is further reduced to 1 /
Circularly polarized light is obtained by passing through the four-wave plate 4. This circularly polarized light beam is reflected by the concave reflecting mirror 7 to become counterclockwise circularly polarized light, but the counterclockwise circularly polarized light beam is again converted into the quarter-wave plate 6.
, The polarization state becomes linearly polarized light which is perpendicular to the paper surface of FIG. Due to the polarization characteristics of the half mirror 5, most of the light flux polarized in the direction perpendicular to the paper surface of FIG. 1 is reflected by the semi-transparent surface 5 a and travels toward the wafer 8. As a result, the reduction of light in the half mirror 5 is prevented and the return light to the reticle 1 is reduced, so that the effective use of the light flux and the reduction of flare are achieved.

Further, as the quarter-wave plate 6, a thin uniaxial crystal (for example, quartz) is used to prevent the generation of astigmatism. Specifically, if quartz is used and the wavelength λ used is 248 nm, and the wavefront aberration due to the quarter-wave plate 6 is suppressed to λ / 4 or less, the thickness of the quarter-wave plate 6 is 100 μm or less. There is a need to.

If the semi-transmissive surface 5a of the half mirror 5 is positively provided with a polarization characteristic such as a polarization beam splitter, the reflectivity and the transmissivity are further improved in combination with the quarter wavelength plate 6. be able to. However, even with a normal half mirror, for example, since the dielectric film has a strong polarization characteristic, the reflectance and the transmittance can be improved by combining it with the quarter-wave plate 6.

A specific example of the configuration of the optical system shown in FIG. 1 will be described below. In order to represent the shapes and the intervals of the lenses in the following examples, the reticle 1 is used as a first surface, and the surface through which the light emitted from the reticle 1 passes until it reaches the wafer 8 is sequentially the i-th surface (i = 2. 3, ...) And
The sign of the curvature radius r _i of the i-th surface is positive between the reticle 1 and the concave reflecting mirror 7 when it is convex with respect to the reticle 1, and between the semi-transparent surface 5 a of the half mirror 5 and the wafer 8. The case where the semi-transparent surface is convex is taken to be positive. The sign of the surface distance d _i between the i-th surface and the (i + 1) -th surface is negative in the area where the reflected light from the concave reflecting mirror 7 passes to the semi-transparent surface 5a of the half mirror 5, and is negative in other areas. Take exactly. Also,
As the glass material, CaF ₂ represents fluorite and SiO ₂ represents quartz glass. Standard wavelength of quartz glass and fluorite (2
The refractive index for 48 nm) is as follows. Quartz glass: 1.50855 Fluorite: 1.46799

[First Embodiment] FIG. 2 is a lens configuration diagram of the first embodiment. As shown in FIG. 2, the first lens group G is used.
₁ includes a biconcave lens L ₁₁ , a biconvex lens L ₁₂ , a biconvex lens L ₁₃ , a negative meniscus lens L ₁₄ having a convex surface facing the reticle 1 and a biconcave lens L ₁₅ in this order from the reticle 1 side. Further, in this example, the additional lens group G ₂ is not used. Further, the third lens group G ₃ has, in order from the half mirror 5 side, a positive meniscus lens L ₃₁ having a convex surface facing the half mirror 5 side, a biconcave lens L ₃₂ , a biconvex lens L ₃₃ , and a convex surface facing the half mirror 5 side. The negative meniscus lens L ₃₄ , the biconvex lens L _35, and the positive meniscus lens L ₃₆ having a convex surface facing the half mirror 5 are arranged. However, since the quarter-wave plate 6 in FIG. 1 is thin and can be ignored, it is omitted in FIG. The radius of curvature r in the first embodiment of FIG.
Table 1 below shows _i , the surface distance d _i, and the glass material.

[0030]

[Table 1] Specifications of the first embodiment i r _i d _i glass material i r _i d _i glass material 1 ∞ 51.910 21 ∞ 64.691 2 -223.371 20.000 CaF ₂ 22 72.100 17.000 CaF ₂ 3 232.874 6.000 23 329.873 9.000 4 257.055 32.000 SiO ₂ 24 -239.781 11.000 SiO ₂ 5 -146.386 16.818 25 91.969 5.300 6 376.776 20.000 SiO ₂ 26 166.797 13.800 CaF ₂ 7 -188.260 1.000 27 -374.866 0.200 8 131.915 16.000 CaF ₂ 28 93.741 11.096 SiO ₂ 9 100.367 30.000 29 40.662 1.000 10- 122.526 18.000 SiO ₂ 30 40.807 19.000 CaF ₂ 11 182.282 50.000 31 -181.965 1.200 12 ∞ 20.000 SiO ₂ 32 104.781 12.800 CaF ₂ 13 ∞ 70.000 33 148.726 17.381 14 ∞ 20.000 SiO ₂ 15 ∞ 90.000 16 ∞ 20.000 SiO ₂ 17 ∞ 94.000 18 ∞ 20.000 SiO ₂ 19 ∞ 75.435 20 -392.660 -75.435

In the embodiment of FIG. 2, the reduction ratio is ⅕, the numerical aperture is 0.4, and the diameter d of the effective exposure area (image circle) on the wafer 8 is 20 mm. The radius of curvature r of the concave reflecting mirror 5 is 392.66 mm, and the radius of curvature r is about 19.6 times the diameter d thereof. Further, marginal rays (land rays) from the on-axis object point incident on the concave reflecting mirror 7
The maximum value of the inclination with respect to the optical axis is 6.18 °, and the maximum value of the inclination of the off-axis chief ray incident on the concave reflecting mirror 7 with respect to the optical axis is 3.44 °. Incidentally, the maximum value of the inclination of the land ray emitted from the concave reflecting mirror 7 with respect to the optical axis is 10.70 °.

A longitudinal aberration diagram of the first embodiment of FIG. 2 is shown in FIG. 3, and a lateral aberration diagram is shown in FIG. In these aberration diagrams,
The curve J, the curve P and the curve Q each have a wavelength of 24.
It is 8.4 nm, 247.9 nm and 248.9 nm. From these aberration diagrams, it can be seen that in this example, the numerical aperture is 0.40, and that various aberrations are well corrected in the wide image circle area. Also, the chromatic aberration is well corrected when the wavelength λ is between 248 nm and 249 nm.

[Second Embodiment] FIG. 5 is a lens configuration diagram of the second embodiment. As shown in FIG. 5, the first lens group G is used.
₁ includes a biconcave lens L ₁₁ , a biconvex lens L ₁₂ , a biconvex lens L ₁₃ , a negative meniscus lens L ₁₄ having a convex surface facing the reticle 1 and a biconcave lens L ₁₅ in this order from the reticle 1 side. Further, in this example, the additional lens group G ₂ is composed of only the negative meniscus lens L ₂₀ having a concave surface facing the reticle 1. Further, the third lens group G ₃ has, in order from the half mirror 5 side, a positive meniscus lens L ₃₁ having a convex surface facing the half mirror 5 side, a biconcave lens L ₃₂ , a biconvex lens L ₃₃ , and a convex surface facing the half mirror 5 side. Negative negative meniscus lens L ₃₄ ,
Positive meniscus lens L with convex surface facing the half mirror 5 side
₃₅ and a positive meniscus lens L ₃₆ having a convex surface facing the half mirror 5 side. However, 1/4 in FIG.
Since the wave plate 6 has a small thickness and can be ignored, it is omitted in FIG. Table 2 below shows the radius of curvature r _i , the surface distance d _i and the glass material in the second embodiment of FIG.

[0034]

[Table 2] Specifications of the second embodiment i r _i d _i glass material i r _i d _i glass material 1 ∞ 71.910 21 -184.047 2.000 2 -331.269 20.000 CaF ₂ 22 -414.280 -2.000 3 247.759 4.000 23 -184.047 -22.000 SiO ₂ 4 242.788 32.000 SiO ₂ 24 -161.300 -75.435 5 -149.834 16.818 25 ∞ 64.691 6 381.244 20.000 SiO ₂ 26 72.301 17.000 CaF ₂ 7 -251.080 1.000 27 150.614 11.000 8 181.255 16.000 CaF ₂ 28 -159.386 11.000 SiO ₂ 9 111.725 30.000 29 7177.924 3.300 10 -116.618 18.000 SiO ₂ 30 161.829 13.800 CaF ₂ 11 374.749 50.000 31 -197.510 0.200 12 ∞ 20.000 SiO ₂ 32 124.113 11.096 SiO ₂ 13 ∞ 70.000 33 33.879 1.000 14 ∞ 20.000 SiO ₂ 34 34.202 19.000 CaF ₂ 15 ∞ 90.000 196.355 1.200 16 ∞ 20.000 SiO ₂ 36 92.275 12.800 CaF ₂ 17 ∞ 94.000 37 310.070 17.381 18 ∞ 20.000 SiO ₂ 19 ∞ 75.435 20 -161.300 22.000 SiO ₂

In the embodiment of FIG. 5, the reduction ratio is 1/5, the numerical aperture is 0.4, and the diameter d of the effective exposure area (image circle) on the wafer 8 is 20 mm. The radius of curvature r of the concave reflecting mirror 5 is 414.28 mm, and the radius of curvature r is about 20.7 times the diameter d thereof. Further, marginal rays (land rays) from the on-axis object point incident on the concave reflecting mirror 7
The maximum value of the inclination with respect to the optical axis is 6.08 °, and the maximum value of the inclination of the off-axis chief ray incident on the concave reflecting mirror 7 with respect to the optical axis is 3.34 °. Incidentally, the maximum value of the inclination of the land ray emitted from the concave reflecting mirror 7 with respect to the optical axis is 10.47 °.

FIG. 6 shows a longitudinal aberration diagram of the second embodiment of FIG. 5, and FIG. 7 shows a lateral aberration diagram. In these aberration diagrams,
The curve J, the curve P and the curve Q each have a wavelength of 24.
It is 8.4 nm, 247.9 nm and 248.9 nm. From these aberration diagrams, it can be seen that in this example, the numerical aperture is 0.40, and that various aberrations are well corrected in the wide image circle region. Also, the chromatic aberration is well corrected when the wavelength λ is between 248 nm and 249 nm. It should be noted that the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various configurations can be adopted without departing from the gist of the present invention.

[0037]

According to the present invention, since the half mirror is used, the resolution is not deteriorated due to the nonuniformity of the large prism material. Further, since the three parallel plane plates are arranged between the first lens group and the half mirror, astigmatism and coma aberration due to the half mirror can be corrected well. Therefore, as a whole, there is an advantage that the deterioration of the resolution is small.

When the radius of curvature of the concave reflecting mirror is 17 to 25 times the diameter of the exposure area of the second surface, astigmatism and distortion can be easily corrected and a predetermined reduction magnification can be easily obtained. There are advantages. Further, when the inclination of the off-axis chief ray incident on the concave reflecting mirror with respect to the optical axis is limited to 6 degrees or less, the amount of aberration such as astigmatism can be suppressed within a predetermined range, and the overall resolving power can be reduced. There is an advantage that it can be further increased and the variations in reflectance and transmittance in the half mirror can be reduced.

Further, when the quarter-wave plate is arranged between the half mirror and the concave reflecting mirror, the reflectance of the half mirror can be increased and flare can be reduced. Especially, the quarter wavelength plate has a thickness of 100 μm.
Forming from the following uniaxial crystal has an advantage that deterioration of astigmatism is negligible.

[Brief description of drawings]

FIG. 1 is a sectional view showing a basic configuration of an embodiment of a catadioptric reduction projection optical system according to the present invention.

FIG. 2 is a lens configuration diagram showing a first example which is a specific configuration example of the optical system of FIG.

FIG. 3 is a longitudinal aberration diagram for the first embodiment of FIG.

FIG. 4 is a lateral aberration diagram for the first example of FIG.

5 is a lens configuration diagram showing a second example which is a specific configuration example of the optical system of FIG.

FIG. 6 is a longitudinal aberration diagram for the second example of FIG.

FIG. 7 is a lateral aberration diagram for the second example of FIG.

FIG. 8 is a sectional view showing a basic configuration of a conventional catadioptric reduction projection optical system.

[Explanation of symbols]

1 Reticle G ₁ First lens group 2, 3, 4 Parallel plane plate 5 Half mirror 6 1/4 wave plate G ₂ Additional lens group 7 Concave reflecting mirror G ₃ Second lens group 8 Wafer

Claims (5)

[Claims] 1. An optical system for reducing and projecting a pattern of a first surface onto a second surface, the first lens having a negative or positive refractive power and diffusing or converging a light beam from the first surface. A group, a half mirror that transmits the light flux from the first lens group, and an oblique arrangement with respect to the optical axis between the first lens group and the half mirror, and correct aberrations caused by the half mirror. Three parallel plane plates, a concave reflecting mirror that converges the light flux emitted from the half mirror and returns it to the half mirror, and has a positive refractive power, is returned to the half mirror and is reflected by the half mirror. A catadioptric reduction projection optical system comprising: a second lens group that focuses the light flux to form a reduced image of the pattern of the first surface on the second surface. 2. The radius of curvature of the concave reflecting mirror is the second radius.
2. The catadioptric reduction projection optical system according to claim 1, wherein the diameter is 17 to 25 times the diameter of the exposure area on the surface. 3. The catadioptric reduction projection optical system according to claim 1, wherein the inclination of the off-axis chief ray incident on the concave reflecting mirror with respect to the optical axis is 6 degrees or less. 4. A quarter-wave plate is arranged between the half mirror and the concave reflecting mirror.
The catadioptric reduction projection optical system described. 5. The quarter wavelength plate has a thickness of 100 μm.
5. It is formed from the following uniaxial crystal.
The catadioptric reduction projection optical system described.