JPH0130125B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an optical system for forming an image of an object with a magnification of 1, and more particularly to such a system with a large spectral band. Optical systems formed in accordance with the concepts of the present invention are used to expose photoresist-coated semiconductor wafers during integrated circuit manufacturing, among many other possible applications. The present invention is closely related to annular projection systems of the type shown in Patent No. 3,748,015, issued July 24, 1973 by the applicant. This patent discloses a reflective optical system that has high resolution and forms the details of an image of an object with microscopic precision at 1x magnification, and is characterized by the fact that the centers of curvature of convex and concave spherical mirrors coincide at one point. It is. The mirror is arranged in such a way that it causes at least three reflections in the system, and has an on-axis conjugate point in the system at the above point, and two off-axis magnifications of 1x in the plane containing the center of curvature. They are arranged to obtain a conjugate area, and the axis of the system is an axis perpendicular to this conjugate plane and passing through the conjugate point. Although this optical system has many features and advantages, the present invention aims to improve it. Other related patents are U.S. Patent No. 3821763, published June 28, 1974, and U.S. Patent No.
No. 3951546 and U.S. Patent Application No. 9 March 1973
This is US Patent Application No. 534465, dated December 19, 1974, which is an addition to No. 339860. To achieve the desired results, the present invention provides a new and improved annular field optical system for use in an apparatus in which an image receiving surface is photographically exposed to a light image of an object. The optical system includes at least one convex mirror and a concave mirror arranged substantially concentrically along the optical axis. The system is arranged so as to form a conjugate plane perpendicular to this axis, about which the system has a magnification of 1. Additionally, the system includes at least one set of symmetrically arranged, substantially concentric meniscuses, the convex radius of which is greater than the concave radius, and the thickness of which is greater than the difference between the convex and concave radii. According to one aspect of the invention, a color correction device is inserted between the mirror and the object and image position, the device being arranged in a substantially parallel plane supported perpendicularly to the optical axis of the mirror. It is a board. In particular, one surface of the plane-parallel plate is formed aspherically, or the plate is a meniscus element supported perpendicular to the mirror optical axis. According to another aspect of the invention, the concave and convex mirrors are supported with a distance between the centers of curvature that is less than about 2% of the length of the short radius, and according to another aspect, the mirrors are arranged three times from the concave mirror. and two reflections from the convex mirror. One aspect of the present invention provides a new and improved annular field optical system for use in apparatus that photographically exposes an image receiving surface to a light image of an object, the system having an optical axis and an optical axis, respectively. The first and second halves include a unit optical system having a conjugate plane approximately perpendicular to the axis, about which the magnification of the system is 1x. These two halves are placed in back-to-back relationship so that the conjugate planes overlap on at least one side of the optical system to form an intermediate image position and provide distant object and image positions on the other side of the optical system. There are means to obtain it. According to one aspect of the invention, each half of the optical system includes a substantially concentric meniscus element, the convex radius of which is greater than the concave radius, the thickness of which is greater than the difference between the convex radius and the concave radius, and According to one aspect, at least one color correction element is provided within the system. According to one implementation, each unit optical system has a concave spherical mirror and a convex spherical mirror facing the concave mirror, and these mirrors are supported so that their centers of curvature substantially coincide. Means are provided for determining the position of the object such that the image of the object is a real image in a second position, wherein the convex mirror directs a ray from the object position, which is initially reflected from the concave mirror to the convex mirror, to the concave mirror. The light rays from the object location are reflectively arranged so that the light rays from the object location are reflected at least twice on the concave mirror and at least once on the convex mirror before being imaged to the second location. Small aberrations resulting from differences in the concentricity of the meniscus are compensated for by introducing small differences in the concentricity of the mirror sets. That is, in each half of the optical system, concave and convex mirrors are supported with a distance between their centers of curvature that is less than about 2% of the length of the small radius of curvature. In particular, the color correction element is a plane-parallel plate supported perpendicular to the optical axis of the mirror. According to one version of the invention, a parallel plane color correction plate is supported at an intermediate image position, and according to another version, a color correction plate is supported in each half of the system. According to the mode of implementation of the invention, the two halves of the optical system are arranged coaxially and back-to-back, so that the conjugate planes overlap on both sides of the system, with intermediate image positions on one side and objects on the other side. Form a position where the images overlap.
Means such as reflective mirrors are provided to separate the object and image positions, allowing access to these positions with the actual device. According to another implementation, the two halves of the optical system are placed coaxially in back-to-back relationship, forming an intermediate image position on one side of the optical system and a remote position of the object and image on the other side. be done. For this purpose, the intermediate image is axially separated from the other conjugate plane in at least one half of the system. According to one implementation, the distances from the two mirror components to the intermediate image are in at least one half greater than the distances to the other conjugate positions, so that the object and image positions are separated from each other. According to a further embodiment, the distances from the two mirror components to the intermediate image are at least half smaller than the distances to the other conjugate positions, so that intersecting object and image planes are formed. In this case a reflection device is inserted between the object position and the image position, making it possible to physically approach these positions. A necessary condition for eliminating field curvature (i.e., a flat field) in a composite system is that the arithmetic sum of the refractive power of each surface divided by its refractive index is zero;
At this time, the refractive index of the reflective surface is defined as negative in this calculation. Since the meniscus refractive element, which is a main component of the optical system according to the present invention, causes a change depending on the color of the above-mentioned sum, the curvature of field of the composite system changes depending on the color even if the sum is approximately zero. According to the invention, the focal position is made constant over a wide spectral band by the introduction of axial chromatic aberration that compensates for chromatic variations in field curvature within the annular field of the optical system. Next, the present invention will be explained with reference to the drawings. According to an embodiment of the invention shown in FIG. 1, a new and improved optical system, generally designated 10, has three
Two spherical mirrors, a convex mirror 12 and a concave mirror 14, arranged to obtain a reflection of
has. The mirror is arranged such that its center of curvature has a conjugate plane along the axis SA of the system, away from the axis centered at points O and I. Points O and I are each at a distance H in opposite directions from the reference axis SA. In the case of the optical system shown in FIG. 2 of Japanese Patent No. 3748015, a concave mirror forms an image of an object O at I. The convex mirror forms a virtual image of point I at point O, and this image is reimaged onto I by the concave mirror. It is pointed out that the corrected annulus width achieved with the optical system of this patent is limited by the fifth order astigmatism inherent in this design. Higher-order astigmatism is based on the spherical aberration of the principal ray of this system. It is clear that meniscus elements can be used to reduce or eliminate the spherical aberration of the chief ray parallel to the optical axis. If the meniscus element is concentric with the mirror, the meniscus element will not introduce third-order aberrations other than field curvature if the conjugate point is at a common center of curvature. A set of meniscus elements 16 as shown in FIG.
are arranged symmetrically to reduce the spherical aberration of the chief ray. Note that the meniscus element is also effective for reducing the spherical aberration of the principal ray when it is placed very close to the convex mirror 12 so that the surface of the mirror 12 and the convex surface of the meniscus element 16 form part of the same spherical surface. be done. It is clear that an order of magnitude increase in the width of the corrected annulus results in a significant reduction in higher order astigmatism. The necessary condition for obtaining a flat image surface with no field curvature in a composite system is that the arithmetic sum of the quotients of the refractive power divided by the refractive index of each surface is approximately zero.
At this time, the refractive index of the reflective surface is defined as negative in this calculation. Since the refractive index of the meniscus element changes with the wavelength of the light beam forming the image, inserting this element into the optical system causes a change in the field curvature with wavelength. Therefore, as shown in FIG. 9, the focal position changes as a function of the distance from the axis and as a function of the wavelength of the light beam forming the image. In the case of annular field optics, variation with distance from the axis is effectively eliminated by restricting the field of view to an annular zone whose distance from the axis is constant. A change in field curvature with wavelength in such a system results in a change in focal position with wavelength, which can be compensated for by introducing chromatic aberration of the opposite sign. To achieve this, according to the invention, the refractive meniscus departs from exact concentricity by having a radius of curvature of the convex surface that is smaller than the radius of curvature of the concave surface plus the thickness. That is, its thickness is greater than the difference between the radii of the convex and concave surfaces. Next, the function of this system will be explained. The change in field curvature with wavelength introduced by a nearly concentric meniscus of negative refractive power is such that the back focal length changes more for short wavelengths than for long wavelengths. A concentric meniscus with a conjugate point at the center of curvature does not introduce longitudinal chromatic aberration.
The same is true for a meniscus that has a conjugate point near the center of curvature. The addition of a positive lens to such a meniscus introduces axial chromatic aberration in the direction necessary to compensate for wavelength variations in focus due to wavelength variations in field curvature (due to the meniscus). This is accomplished by making the radius of the convex side of the meniscus smaller than the radius of its concave side plus its thickness. This meniscus then consists of a virtual concentric meniscus lens with a convex radius equal to the sum of the concave radius and the thickness, and a zero thickness where the concave radius is the convex radius of the virtual meniscus and the convex radius is the convex radius of the actual meniscus. is equivalent to two positive meniscus lenses. In a nearly concentric meniscus of concave radius R ₁ , convex radius R ₂ , thickness t and refractive index N: R ₂ >R ₁ tR ₂ −R ₁ +(H ² /2N ² )(1/R ₁ −1/ _R2 )
If (1), the axial chromatic aberration compensates for the change in focus due to the change in field curvature with wavelength within the ring zone of radius H. By introducing a set of menisci whose parameters substantially satisfy equation (1) into the optical system of the type described in the above-mentioned U.S. Pat. No. 3,748,015, along with the improvements described below, higher-order astigmatism can be reduced over a wide spectral band. It became clear that this could be achieved. The synthetic system can be significantly improved by changing the meniscus such that its thickness is greater than the value given by equation (1). The focal point of the annular viewing system is thereby changed in a similar manner, which can be compensated for by the introduction of a plane-parallel plate of appropriate thickness, indicated at 18 in FIG. The greater degree of freedom afforded by the additional elements allows even greater degrees of correction. Further improvements are achieved by modifying the plane-parallel plate in one of two ways: (1) Making one surface of the plane-parallel plate aspheric. (2) Bending parallel planes to form a meniscus element. The highest degree of correction is obtained by a system in which the meniscus thickness is greater than the value given by equation (1) and in which color correction is performed by using a parallel plane plate modified by one of the two methods mentioned above. achieved. Small aberrations due to the out-of-concentricity of the meniscus element 16 are compensated for by the small out-of-concentricity of the mirrors 12 and 14. That is, concave mirror 14 and convex mirror 12 are supported with a distance between their centers of curvature that is less than about 2% of the length of the small radius. Table 1 shows an example of configuration data of the annular viewing optical system shown in FIG. As is well known, a positive sign indicates that the surface is convex to the object and the distance is measured from left to right, and a negative sign indicates that the surface is concave to the object and the distance is measured from right to left. Indicates that the

[Table] Table 2 is a performance table in which RMS wavefront aberrations at various annular radii are calculated for the annular viewing optical system in Table 1 over the spectral range of 2800 Å to 5461 Å. The width of the usable annulus is the difference between the values of the upper and lower radii whose performance is suitable for use.
Systems with RMS wavefront aberrations less than 0.07 are commonly referred to as "diffraction limited" or "aperture limited" systems. For scanning systems, the RMS wavefront aberration may be as large as 0.09 or 0.1 at each end of the annulus.

[Table] As mentioned above, the annular field optical system of the present invention has at least one convex and one concave mirror, these mirrors are arranged substantially concentrically along the optical axis, and have a conjugate plane perpendicular to the optical axis. , and the magnification of the system is 1 with respect to this conjugate plane. FIG. 1 shows one suitable arrangement of convex and concave mirrors; other suitable arrangements are described in the aforementioned Patent No. 3,748,015. According to the arrangement shown in FIG. 8 of the present invention, the convex mirror 12l and the concave mirror 14l are arranged substantially concentrically along the optical axis SA, and a total of five reflections are utilized in the system, three of which are reflected by the concave mirror. It is reflected twice from the mirror 14l and twice from the convex mirror 12l.
According to this embodiment, if the radius of the convex mirror 12l is 2/3 of the radius of the concave mirror 14l, the arithmetic sum of the refractive powers of the reflective surfaces is zero. Similar to that described with reference to FIG. 1, the system of FIG. 8 includes a meniscus element 16l and a color correction plate 18l having the functions described above. It is pointed out that annular field optics of the type described above are normally used in scanning mode. Because of this orientation, the orientation of object and image is the same and their physical supports can be maintained in a fixed relationship to each other while moving relative to the optical system for scanning, thereby controlling the scanning motion. It is particularly desirable that the requirements for accuracy be reduced. An arrangement for achieving this by adding three plane mirrors to the optical system is disclosed in the above-mentioned U.S. Patent No.
It is shown in specification No. 3951546. Another means of achieving this effect is shown in FIG. 2, in which two optical systems 10 and 10', each of the type shown in FIG. . The optical system 10 thus includes two spherical mirrors 12 and 14, a set of meniscus elements 16 and a color correction plate 18, and the symmetric optical system 1
0' includes two spherical mirrors 12' and 14', a set of meniscus elements 16' and a color correction plate 18'. The physical separation of the object and the final image required in the actual device is achieved by the addition of reflective mirrors 20 and 20', which move the actual object and image to O' and I', respectively, as shown in dashed lines in FIG. will be achieved.
In this arrangement the distance between the reflecting mirrors must be sufficient to provide scanning space. Of course, other arrangements of reflective mirrors that maintain relative object-image relationship are clearly within the scope of the invention. According to the optical system of FIG. 2, the intermediate image shown at 22 is formed by the optical system 10 of FIG. 1 and is therefore highly corrected. In this arrangement each half 10 and 10' is symmetrical about the longitudinal axis and can therefore be reversed. Since a high degree of correction of the intermediate image is not required for many applications, the system can be simplified by removing the requirement that each half be symmetrical. As shown in FIG. 3, it is therefore possible to maintain the system, or at least its refractive component, as a whole symmetrically, thereby reducing the number of compensation menisci and corrector plates to two each. One half of the optical system 10a thus consists of two spherical mirrors 12 and 14, one meniscus element 16a arranged on the side of the intermediate image 22 and one color correction plate 18a, all of which are connected to the optical axis. They are arranged symmetrically with respect to SA (the meniscus element 16a and the color correction plate 18a are half removed; the same applies hereinafter). The other half of the optical system, designated 10a', includes two spherical mirrors 12' and 14';
Meniscus element 16 arranged on the intermediate image 22 side
a' and color correction plate 18a', and all these elements are arranged symmetrically with respect to the optical axis SA.
In order to move the actual object and the final image to O' and I', respectively, for the same reasons mentioned above, each half of the optical system is equipped with reflective mirrors 20 and 2, shown in dashed lines in FIG.
0'. According to FIG. 4, a system having an intermediate image indicated at 22 can then be obtained by converting the two color correction plates 18 and 18a' of FIG. 3 into one element of the same shape, indicated at 18b in FIG. further simplified. One color correction plate 18b at the position of the intermediate image 22 or a position close to it.
Symmetry is maintained by placing . Further, the reflecting mirrors 20 and 20' in FIG. 3 also include two mirror elements 12b, 14b and 12b', 14
It can be removed by making at least one conjugate distance of b' unequal. That is, the distances from the intermediate image to the two mirror components are made greater than the distances from the object and/or image, so that the final image I is separated from the object O. In this system, the color correction plate 18b at the intermediate image position may be a completely parallel plane. For a true afocal system, the magnification is the same for all conjugate positions. However, this desirable feature is not achieved in practical applications because practical systems generally do not remain truly afocal for all viewing positions. For example, if we move object O and image I by 1 mm in the vertical direction using the 1x magnification system in Figure 4, we get
The magnification of the 4mm radial ring is 1x to ±0.00032
Change. This variation, which causes tracking smear during scanning, can be reduced to ±0.00001 by making one of the surfaces of color correction plate 18b aspherical. One variation of the FIG. 4 optical system is shown in FIG. 5, in which the correction meniscus is moved from the intermediate image side of the system to the object-image side. According to the embodiment of FIG. 5, one half of the system comprises two spherical mirrors 12b, 14b and a meniscus element 16c arranged symmetrically with respect to the axis SA of the system on the object-image side, and the other half of the system It comprises two spherical mirrors 12b', 14b' and a meniscus element 16c' arranged symmetrically with respect to the system axis SA on the object-image side. one color correction plate 18
b is located symmetrically with respect to the axis SA of the system at or in the vicinity of the intermediate image. As in the example of FIG. 4, one surface of this plate is aspheric. Furthermore, the fourth
As in the illustrated example, the distances from the intermediate image to the two mirror components are made greater than the distances from the object and the image, so that the final image I is separated from the object I for scanning purposes. Table 3 is an example showing the configuration data of the annular viewing optical system shown in FIG.

[Table] Table 4 shows a wide spectral band (2800 Å to 5461 Å) expressed by RMS wavefront aberration at various annular radii.
3 is a calculated performance table of the annular viewing optical system of Table 3 over the range of . The width of the annulus that can be used is the difference in the values of the upper and lower radii whose performance is suitable for use.

An optical system in which the distance from intermediate image 22 to two mirror components 12d-14d and 12d'-14d' is smaller than the distance from object O and final image I is shown in FIG. In the embodiment of FIG. 6, one half of the system includes two spherical mirrors 12d, 14d and a meniscus element 16a arranged symmetrically with respect to the axis SA of the system on the intermediate image side, and the other half of the system includes two It includes spherical mirrors 12d', 14d' and a meniscus element 16a' arranged symmetrically with respect to the system axis SA on the intermediate image side. One color correction plate 18b is placed at or near the intermediate image 22. As in the systems of Figures 2 and 3, a parallel reflective surface is introduced between the two intersecting conjugate points O and I, making it possible to approach them for scanning. However, in the embodiment of FIG. 6, the two reflective surfaces are the front and back surfaces of a plane-parallel plate 20d, the thickness of which is determined by the considerations for the apparatus of FIGS. 2 and 3 that determine the separation between the reflective surfaces. is determined by mechanical considerations. Thus, in the embodiment of FIG. 6, the front and back surfaces of the plate 20d serve to deflect the object O to O' and the final image I to I', thereby providing the necessary object and image separation for scanning. You get the space in between. Another implementation of the invention that utilizes intersecting object and image planes is shown in FIG.
Only one color correction plate 18b shown at the intermediate image position in the figure
two separate color correction plates 18e and 18 instead of
e' is placed on the object-image side of the system. In this embodiment, substantially parallel plane plates are bent to form meniscus elements. The rest of the system in FIG. 7 is the same as in FIG. That is, one half of the system includes two spherical mirrors 12d, 14d and a meniscus element 16a arranged on the intermediate image side, and the other half of the system contains two spherical mirrors 12d', 14d' and likewise arranged on the intermediate image side. including a meniscus element 16a'. As mentioned in connection with the example of FIG. 6, the plate 20d with the mirror front and rear surfaces
O', which serves to move the final image I to I', achieving the physical separation of object and image required in a practical device. Table 5 is an example showing the configuration data of the annular viewing optical system shown in FIG.

[Table] Table 6 shows a wide spectral band (2800 Å to 5461 Å) expressed by RMS wavefront aberration at various annular radii.
5 is a calculated performance table of the annular viewing optical system of Table 5 over the range of . The width of the annulus that can be used is the difference between the upper and lower radii whose performance is suitable for use.

Table: For the devices of FIGS. 7 and 5, refractive or meniscus elements 18e, 18e', 16c and 16
It is pointed out that c' can be used as a window for sealing parts of the optical system between them. FIG. 10 shows yet another embodiment of the invention. This embodiment is similar to the embodiment shown in FIG. 7, except that the mirror plate 20d having reflective mirrors on the front and back surfaces is removed. This is achieved by making the conjugate distances of at least one of the two mirror elements 12b, 14b and 12b', 14b' unequal. That is, the intermediate image distance for the two mirror elements is made larger than the object and/or image distance, so that the final image I is separated from the object O. Thus, one half 10f of the system of FIG. 10 includes two spherical mirrors 12b and 14b, a meniscus element 16a on the intermediate image side of the system, and a color correction plate 18e on the object-image side. The other half of the system 10f' includes two spherical mirrors 13b' and 14b', a meniscus element 16a' on the intermediate image side of the system, and a color correction plate 18e' on the object-image side. As in the embodiment of FIG. 7, the color correction element is a meniscus. Meniscus element 18e
and 18e' have improved bending of parallel plane plates, and their function is that of meniscus elements 16a and 1.
The purpose is to correct the undercorrected longitudinal chromatic aberration caused by 6a' to the value necessary to compensate for the overcorrected focal difference of the off-axis image based on the Petzval sum color variation of the refractive element. All these elements are arranged symmetrically along the optical axis SA. Table 7 shows an example of the configuration data of the annular viewing optical system shown in FIG.

TABLE The system defined in Table 7 was designed for use with a numerical aperture of 0.17 in both object and image in the spectral band 240-365 nm. For this spectral band, the change in focus due to the variation of the Petzval sum with wavelength is 0.017 mm in the overcorrection direction at a distance of 100 mm from the axis, ie the back focus of the 240 nm ray is longer than the back focus of the 365 nm ray. The undercorrected vertical chromatic aberration is 0.074 mm, so from the axis based on the difference due to Pettuval sum color.
Differences due to focus color at 100mm are almost corrected. Almost concentric menisci 16a and 16
The thickness of a' (Surface Nos. 6, 7, 8 and 9 in Table 7) is determined by equation (1), which is necessary to keep the color-related change in astigmatism small in a system using a numerical aperture of 0.17. Significantly larger than the required 5.30 mm, as in other examples of the invention, the additional longitudinal chromatic aberration undercorrection based on this is due to color correction elements 18e, 18e' (surfaces No. 1, 2 and 13 of Table 7). , 14), the radii of the concave and convex surfaces of elements 18e and 18e' are so different that they cannot be considered as bent parallel plane plates. Its contribution to the color variation of the Pettuval sum is meniscus 16a and 1
approximately 0.4 in the same direction of the amount achieved by 6a'. These elements contribute slightly to the chromatic variation of astigmatism in the opposite direction to the residual chromatic variation of astigmatism achieved by menisci 16a and 16a'. The main function of the color correction element is the meniscus 16
This is a reduction in the undercorrected longitudinal chromatic aberrations of a and 16a'. Although the functional separation of the two sets of meniscus elements is not as perfect as in other examples, their combined effect in the optical system is the same, i.e. the chromatic change in focus at the center of the restricted off-axis field of view is Compensated by having equal and opposite changes in focus due to chromatic aberration. Thus, embodiments of the invention may take equivalent forms. The functional separation of the nearly concentric meniscus and color correction elements is conceptually convenient, and equivalent means of achieving the same type of color correction within a limited off-axis field of view will be apparent to those skilled in the art. Convex mirrors 12b and 12 as in other examples
b' is symmetrical with respect to the concave mirrors 14b and 14b', and the optical path parallel to the optical axis from the object O is the center point 2 of the system.
2 and the final image I. That is, in this reversible optical system, light rays parallel to the axis from the object O pass through the system symmetrically. In this case, the concave mirror and the convex mirror are approximately concentric. The centers of curvature of each convex mirror are 3.07 mm apart from the center of curvature of the nearest concave mirror. The distance from the concentricity is 1.2% of this short (convex) radius. Because there are an infinite number of systems that can be constructed along the lines shown in FIGS. 1-8 and 10, no precise limit can be established on the distance between the centers of the concave and convex mirrors. However, it has been found that in these systems this distance does not exceed 3% of the radius of the convex mirror. Table 8 is a calculated performance table of the annular field optics of Table 7 over an expanded spectral band. Although the system was designed for the 240-365 nm spectral band, the degree of correction measured in wavelength units is comparable or better at 546 nm.
This is because both the chromatic variation of the Petzval sum and the longitudinal chromatic aberration correction occur as a result of the wavelength variation of the refractive index of a single material.

Table 10a shows an example of one means of limiting the off-axis field of view. Although this system is shown for application to the embodiment of FIG. 10, it is equally applicable to other embodiments of the invention illustrated. A mask 28 having a curved slit 30 of radius H as shown in FIG. 10a is arranged with its center of curvature in the optical axis SA and in the object plane O shown in FIG. limited to the exposed area. This portion of the object plane images point-to-point onto a similarly curved surface in image plane I. This is because all parts of the object and image within the slit or within the image of the slit are at approximately the same distance H from the optical axis SA, and the system is corrected at this distance. A mask 28 can be provided in the image plane I, a mask can be provided in each side, or a mask can be arranged so that its image is in the image plane I. Additionally, when the system is used to expose a photoresist-coated semiconductor wafer in a scanning mode, an object such as a transparent slide is moved through the slit 30 in the direction of arrow 32 so that approximately the portion of the object exposed by the slit is An image with a magnification of 1x is formed on I,
Moving past I in the direction indicated by arrow 34. As a result, when the wafer is placed at image point I and moved synchronously with the transparent slide, the wafer is exposed to the image over its entire surface. The present invention provides a new and improved optical system for use in applications where spatial relationships must be reproduced with great accuracy and can be corrected over both a wide annulus and a wide spectral band. It is clear that

[Brief explanation of drawings]

Figure 1 is an optical system showing the concept of the present invention, Figure 2 is a compound optical system in which the optical system in Figure 1 is placed back to back, and Figure 3 is an optical system that simplifies the object-image side of the system in Figure 2. 4 shows an optical system in which the two color correction elements shown in FIG. 3 are combined into one; FIGS. 5 to 7 show other embodiments of the optical system according to the present invention; Another similar embodiment is shown in cross section, and FIG. 9 is a graph showing the focal point position as a function of wavelength and distance from the optical axis. FIG. 10 shows yet another embodiment of an optical system similar to FIG. 7, and FIG. 10a is a diagram of an embodiment of a mask limiting the field of view. 12, 14... Spherical mirror, 16... Meniscus element, 18... Color correction plate, O... Object, I...
image.

Claims (1)

[Scope of Claims] 1. At least one convex mirror and a concave mirror disposed substantially concentrically along an optical axis and a refractive element, the convex mirror having an object position that is initially reflected from the concave mirror to the convex mirror. a wide spectral band arranged to reflect light onto a concave mirror such that light from an object location is reflected twice off the concave mirror and at least once off the convex mirror before being imaged to a second location; , in a restricted off-axis field optical system, the restricted off-axis field is an annular field, the optical system is constructed and arranged such that the Petzval sum is approximately zero, and the refractive element is a Petzval sum based on color change. The effect of the change in sum is corrected by introducing longitudinal chromatic aberration in the opposite direction so that the position of the focal point in the annular field remains approximately constant; at least one set of meniscus elements with substantially concentric convex and concave meniscus surfaces disposed between final or intermediate image positions, the set of elements including the intermediate image point and perpendicular to the optical axis or the optical axis; arranged symmetrically with respect to a plane perpendicular to this plane, each characterized in that the radius of the convex surface of the meniscus element is greater than the radius of the concave surface, and that its axial thickness is greater than the difference between the radii of its convex and concave surfaces. off-axis viewing optical system. 2. The optical system according to claim 1, wherein the refractive element is made of one optical material. 3. A device for correcting changes in field curvature due to color in the annular field by introducing longitudinal chromatic aberration in opposite directions consists of a pair of symmetrically arranged approximately concentric meniscus elements and a color correction element, each of which 2. The optical system according to claim 1, wherein the radius of the convex surface is larger than the radius of the concave surface, and the axial thickness thereof is larger than the difference between the radii of the convex and concave surfaces. 4. The optical system according to claim 3, in which all refractive elements are made of a single optical material. 5. The optical system according to claim 1, wherein the mirrors are arranged so that there are three reflections from the concave mirror and two reflections from the convex mirror. 6. A device for correcting the effects of changes in the Petzval sum due to color changes comprises at least one set of meniscus elements having substantially concentric convex and concave meniscus surfaces disposed between the convex mirror and the object or final image or intermediate image position. This set of elements is arranged symmetrically with respect to a plane containing the intermediate image point and perpendicular to the optical axis, or a plane containing the optical axis and perpendicular to this plane, and the radius of the convex surface of each meniscus element is larger than the radius of the concave surface. The relationship between the properties of a meniscus lens that is large, and whose axial thickness is greater than the difference between the radii of its convex and concave surfaces and approximately concentric with the annular radius of the system is expressed by the formula: R ₂ > R ₁ and tR ₂ −R ₁ + (H ² /2N ² ) (1/R ₁ −
1/R ₂ ) [Here, H = ring radius of the system, R ₁ = concave radius of the meniscus lens, R ₂ = convex radius of the meniscus lens, t = thickness of the meniscus lens, N = refractive index of the meniscus lens. be. ] Claims 1 or 5 determined by
Optical system described in section. 7. The device for correcting the effects of changes in the Petzval sum due to color changes comprises at least one set of meniscus elements with substantially concentric convex and concave meniscus surfaces disposed between the convex mirror and the object or final image or intermediate image position; A set of color correction elements arranged symmetrically with respect to a plane containing the intermediate image point and perpendicular to the optical axis or a plane containing the optical axis and perpendicular to this plane, each with a radius of the convex surface of the meniscus element. The relationship between the properties of a meniscus lens larger than the radius of its concave surface and whose axial thickness is larger than the difference between the radii of its convex and concave surfaces and approximately concentric with the annular radius of the system is expressed by the formula: R ₂ > R ₁ and tR ₂ −R ₁ + (H ² /2N ² ) (1/R ₁ −
1/R ₂ ) [Here, H = ring radius of the system, R ₁ = concave radius of the meniscus lens, R ₂ = convex radius of the meniscus lens, t = thickness of the meniscus lens, N = refractive index of the meniscus lens. be. ] Claims 1 or 5 determined by
Optical system described in section. 8. Claim 7, wherein the color correction element is a substantially parallel plane plate mounted at right angles to the optical axis of the mirror.
Optical system described in section. 9. The optical system according to claim 7, wherein the color correction element is a plate having an aspherical surface. 10. The optical system of claim 7, wherein the color correction element is a weak meniscus element mounted perpendicular to the optical axis of the mirror. 11. The optical system according to claim 7, wherein a color correction element is inserted between the mirror and the object and image position. 12. The optical system according to claim 7, wherein the color correction element is inserted between the meniscus element and the mirror. 13. The optical system according to claim 10, having the following configuration data: [Table]. 14 The optical system consists of a first half and a second half, each half has an optical system each having one optical axis and a conjugate plane perpendicular to the optical axis, and the first half and the second half are arranged coaxially in back-to-back relationship such that the conjugate surfaces overlap on at least one side of the optical system, and include means for separating the object and final image positions on the other side of the optical system. The optical system according to item 1. 15. An apparatus for correcting the effect of changes in the Petzval sum due to color changes includes substantially concentric meniscus elements symmetrically arranged in a first half and a second half,
15. The optical system according to claim 14, wherein the convex radius is greater than the concave radius and the thickness is greater than the difference between the convex and concave radii. 16. The optical system of claim 15, wherein each of the first and second halves further comprises a color correction element. 17. The optical system according to claim 16, wherein the color correction element is a parallel plane plate supported substantially perpendicular to the optical axis. 18. The optical system according to claim 16, wherein the color correction element is a plate having an aspherical surface. 19. The optical system according to claim 16, wherein the color correction element is a weak meniscus element supported perpendicular to the optical axis. 20. Claims 14, 15, and 17 through 20, wherein the first and second halves each include a concave mirror and a convex mirror, the mirrors being supported with substantially coincident centers of curvature. The optical system according to any one of items 19 to 19. 21. The optical system of claim 16, wherein the first and second halves each have a concave mirror and a convex mirror, the mirrors being supported with substantially coincident centers of curvature. 22 Claim 16 or 21, wherein the device for separating the object from the final image is a reflecting mirror.
Optical system described in section. 23. The optical system according to claim 16 or 21, wherein the first half and the second half are substantially symmetrical about an axis in the conjugate plane. 24. Any one of claims 14, 15, 16, and 21, wherein the first half optical system and the second half optical system are each optical systems with a magnification of approximately 1. Optical system described. 25. The optical system according to claim 21, wherein the meniscus element is inserted between the mirror and the object position and the image position, respectively. 26. Claim 21, in which a meniscus element is inserted between the mirror and the intermediate image position, respectively.
Optical system described in section. 27. The optical system according to claim 21, wherein the color correction element comprises two elements each inserted between the mirror and the intermediate image position. 28. The optical system according to claim 21, wherein the color correction element includes two elements inserted between the mirror and the object position and the final image position, respectively. 29 Only one color correction element placed at the intermediate image position
22. An optical system according to claim 21, which comprises two elements. 30 Each half has a concave mirror and a convex mirror facing this concave mirror, these mirrors are arranged approximately concentrically along the axis, and the distance of the two mirror elements from the conjugate position on the other side of the optical system differs from the distance to the intermediate image position in at least one half,
15. Optical system according to claim 14, whereby a remote object and final image position is obtained. 31 A device for correcting the effect of changes in the Petzval sum due to color changes has approximately concentric meniscus elements in the first and second halves, the convex radius being greater than the concave radius, and the thickness of the convex and concave 31. The optical system according to claim 30, wherein the difference in radius is greater than the difference in radius. 32. The optical system of claim 31, wherein a meniscus element is inserted between the mirror and each of the object and final image positions. 33. Claim 31, wherein a meniscus element is inserted between the mirror and the intermediate image position, respectively.
Optical system described in section. 34. The optical system according to any one of claims 31 to 33, wherein the optical system further comprises a color correction element arranged approximately at the intermediate image position. 35. The optical system according to claim 31, wherein the optical system further comprises a parallel plane plate supported substantially perpendicular to the optical axis and at substantially an intermediate image position. 36. Claims 31 to 33, wherein the optical system further includes a plane-parallel plate supported substantially perpendicular to the optical axis at an approximately intermediate image position, and one surface of the plane-parallel plate is an aspherical surface. The optical system according to any one of the preceding items. 37. An optical system according to any one of claims 31 to 33, wherein the optical system further comprises a weak meniscus element supported substantially perpendicular to the optical axis of the mirror and in substantially an intermediate image position. 38 Claim 3, wherein the first half and the second half are substantially symmetrical about an axis passing through the intermediate image position
The optical system according to any one of items 0 to 33. 39 Each half has a concave mirror and a convex mirror facing the concave mirror, these mirrors are arranged approximately concentrically along the optical axis, and the distance of the two mirror elements from the intermediate image is such that the distance from the other conjugate position The first and second halves are at least one half larger than the distance to the two mirror elements, whereby the object position and the image position are spaced apart from each other, and a device for correcting the effects of changes in the Petzval sum due to color changes is provided in the first and second halves. has a meniscus element inserted between the mirror and the intermediate image position in which the meniscus element is approximately concentric but has a radius difference in the meniscus surfaces that is less than its thickness, and therefore is not exactly concentric and its refractive power 15. The optical system according to claim 14, wherein is negative and the color correction element is arranged substantially at an intermediate image position perpendicular to the optical axis of the mirror. 40. The optical system according to claim 39, having the following configuration data: [Table]. 41. the intermediate image position is axially offset from the other conjugate plane such that the distance from the intermediate image to the two mirror elements is at least one half smaller than the distance from the other conjugate position to the two mirror elements; 15. Optical system as claimed in claim 14, in which a reflecting device is inserted between the object and the final image position in order to reposition these positions and make it possible to approach these positions. 42. The optical system of claim 41, wherein the first half and the second half each have a concave mirror and a convex mirror facing the concave mirror. 43 A device for correcting the effect of changes in the Petzval sum due to color changes has approximately concentric meniscus elements in the first and second halves, the convex radius being greater than the concave radius, and the thickness of the convex and concave 43. The optical system according to claim 42, wherein the radius difference is greater than the radius difference. 44. Claim 43, in which a meniscus element is inserted between the mirror and the intermediate image position, respectively.
Optical system described in section. 45. The optical system according to claim 44, wherein the optical system further comprises correction elements disposed approximately at intermediate image positions. 46. The optical system of claim 44, wherein the first half and the second half each further include a color correction element. 47. Claim 44, wherein the first and second halves each have a color correction element inserted between the mirror and the object and the final image position, respectively, this element being perpendicular to the optical axis of the mirror. optical system. 48. The optical system according to claim 47, wherein one of the surfaces of the color correction element is an aspherical surface. 49. Claim 4 in which a concave mirror and a convex mirror are supported in each half of the system with a distance between the centers of curvature of less than 2% of the length of the short radius.
Optical system according to item 2. 50 Claim 47, wherein the first half and the second half are substantially symmetrical about an axis passing through the intermediate image position
Optical system described in section. 51 The following configuration data: [Table]
The optical system according to claim 47, having the following table. 52 Each half has a concave mirror and a convex mirror facing the concave mirror, the mirrors are supported with approximately coincident centers of curvature, and the distance from the intermediate image to the two mirror elements is at least one half and the other greater than the distance from the conjugate position to the two mirror elements, thereby separating the object position and the final image position from each other, and providing elements in the first and second halves to correct the effect of changes in the Petzval sum due to color changes. having a meniscus element inserted between the mirror and the intermediate image position, the meniscus elements being arranged symmetrically and approximately concentrically, with a convex radius greater than the concave radius, and a thickness greater than the difference between the convex and concave radii. An optical system according to claim 14.