Measuring arrangement for the interferometric determination of the surface shape of a test specimen, as well as a method for manufacturing an optical element for such a measuring arrangement

Abstract

The invention relates to a measuring arrangement for the interferometric determination of the surface shape of a test object, wherein a test wave generated from electromagnetic radiation and reflected at the test object can be superimposed with a reference wave not reflected at the test object, with a reference element (110, 210, 310, 410) having a reference surface (112, 212, 312, 412) which, in the optical beam path, splits off the reference wave from the test wave before it strikes the test object (120, 220, 320, 420) by reflection, and at least one beam shaping surface (111, 211, 311, 411, 413, 414) located in the optical beam path in front of the reference surface, wherein this beam shaping surface is designed as an aspherical distortion correction surface such that a distortion occurring in a predetermined reference plane of the measuring arrangement is reduced. The invention further relates to a method for manufacturing an optical element for such a measuring arrangement.

Description

BACKGROUND OF THE INVENTION Area of ​​the invention

[0001] The invention relates to a measuring arrangement for the interferometric determination of the surface shape of a test specimen, and to a method for manufacturing an optical element for such a measuring arrangement. The test specimen can, in particular, be an optical element for microlithography, especially an optical element of a microlithographic projection exposure system. State of the art

[0002] Microlithography is used to manufacture microstructured components, such as integrated circuits or LCDs. The microlithography process is carried out in a projection exposure system, which includes an illumination unit and a projection lens. The image of a mask (= reticulum) illuminated by the illumination unit is projected by the projection lens onto a substrate (e.g., a silicon wafer) coated with a photosensitive layer (photoresist) and positioned in the image plane of the projection lens. This transfers the mask structure onto the photosensitive coating of the substrate.

[0003] In projection lenses designed for the EUV range, i.e., at wavelengths of, for example, approximately 13 nm or approximately 7 nm, mirrors are used as optical components for the imaging process due to the lack of suitable translucent refractive materials. Typical EUV projection lenses, such as those known from US 2016 / 0085061 A1, can, for example, have an image-side numerical aperture (NA) in the range of NA = 0.55 and project an object field (e.g., ring-segment-shaped) onto the image plane or wafer plane.

[0004] Increasing the image-side numerical aperture (NA) typically necessitates an increase in the required mirror surface area of ​​the mirrors used in the projection exposure system. Given the high accuracy requirements in microlithography, this means that, in addition to manufacturing, the inspection of the surface shape, especially of EUV mirrors, presents a significant challenge. For high-precision mirror inspection, interferometric measurement methods are employed, for example, using diffractive optical elements such as computer-generated holograms (CGH). The determination of the surface shape of the respective mirror or test specimen is based on the interferometric superposition of a test wave, generated (e.g.) by the CGH and reflected from the test specimen, with a wavefront adapted to the desired surface shape of the test specimen, and a reference wave that is not reflected from the test specimen.

[0005] There are various approaches to generating the reference wave, such as placing a reference mirror in the optical beam path of a so-called reference mirror interferometer or using a Fizeau element in a Fizeau interferometer. Another approach, also known as "matrix testing," involves generating the reference wave required for interferometric measurement or superposition with the test wave reflected from the test specimen by means of a splitting of the test wave via a reference surface (also called a "matrix") located in the optical beam path in front of the test specimen.

[0006] As the size of the mirror to be tested increases, the need arises to produce ever larger CGHs (e.g., with diameters of several tens of centimeters). With conventional electron lithography, this requires extremely long writing times as well as the costly development or adaptation of the machine components used for production.

[0007] Another problem encountered in practice regarding the most reliable and accurate interferometric determination of mirror surfaces is distortion in the interferogram or camera image generated by the interferometer camera in the measurement setup. This distortion can be intrinsically caused by the optical system, particularly when imaging a non-spherical test object surface, if a non-spherical wave originating from such a surface (e.g., a freeform surface) is projected onto the interferometer camera. The result is a resolution that varies depending on the location on the interferometer camera, leading to an inaccurate determination of the surface shape, potentially resulting in incorrect processing of the test object and ultimately impairing the performance of the optical system using this mirror.the projection exposure system.

[0008] For examples of the state of the art, reference is made only to DE 10 2022 209 651 A1, DE 10 2011 004 376 B3, DE 10 2021 202 909 A1, US 6,312,373 B1, EP 1 682 851 B1 and the publication by X. Qiao et al.: “Measurement and correction of lateral distortion in a Fizeau interferometer based on the self-calibration technique”, Optics Express, Vol. 30, No. 20, pages 36134-36143, https: / / doi.org / 10.1364 / OE.467554. SUMMARY OF THE INVENTION

[0009] Against the above background, it is an object of the present invention to provide a measuring arrangement for the interferometric determination of the surface shape of a test specimen and a method for producing an optical element for such a measuring arrangement, which enables reliable testing even of comparatively large - especially raised - mirror surfaces.

[0010] This problem is solved by the features of independent patent claims.

[0011] The invention relates in particular to a measuring arrangement for the interferometric determination of the surface shape of a test object, wherein a test wave generated from electromagnetic radiation and reflected at the test object can be superimposed with a reference wave not reflected at the test object, with - a reference element with a reference surface which, in the optical beam path, splits off the reference wave from the test wave by reflection before it strikes the test object; and - at least one beam-shaping surface located in the optical beam path in front of the reference surface; - wherein this beam shaping surface is designed as an aspherical distortion correction surface such that distortion occurring in a given reference plane of the measuring arrangement is reduced.

[0012] In accordance with common terminology, "distortion" is understood here as a generally undesirable variation in the respective area of ​​pixels generated by the imaging process in a reference plane. This imaging process is based on a Cartesian grid of pixels (with identical areas) on the object plane of the imaging process (i.e., in this case, the surface of the test specimen). Distortion can be defined, for example, as the ratio between the maximum area of ​​a pixel and the minimum area of ​​a pixel in the reference plane. The reference plane can be located, for example, in the area of ​​a CGH (constant wave generator) used to generate the test wave or in the area of ​​the interferometer camera.

[0013] For the purposes of the present application, an “aspherical surface” (i.e., in particular the aspherical distortion correction surface provided for in the invention) is understood to be a surface that deviates from a sphere, whereby this surface may, but need not, have rotational symmetry.

[0014] The invention initially starts from the known approach of generating, in a measuring arrangement for the interferometric determination of the surface shape of a test object (in particular EUV mirrors), the reference wave required for the interferometric measurement or the superposition with a test wave reflected from the test object by means of a splitting from the test wave achieved by reflection via a reference surface located in the optical beam path in front of the test object. By designing said reference surface similarly to the surface of the test object, it is ensured that the wavefronts of the test wave and the reference wave are configured similarly or identically to each other. In this approach, the invention initially differs from "reference mirror arrangements" such as those known from DE 10 2015 209 490 A1, in which the reference wave required for the interferometric superposition is already generated by the diffractive optical element.CGHs are generated and from there directed in a direction different from the test wave towards a reference mirror located at a specific distance and typically planar. This difference initially offers the advantage (with the test wave typically generated by diffraction at a diffractive optical element or CGH) that structural defects located in the diffractive optical element affect both the test wave and the reference wave equally, thus eliminating the need for separate functionalities of the CGH (such as a corresponding complex coding for generating both the reference wave and the test wave). Furthermore, the placement of the reference surface according to the invention can result in a cavity or...The gap length (corresponding to the remaining path to be traveled by the electromagnetic radiation between the reference surface and the test specimen) is kept comparatively small, with the result that pressure or temperature fluctuations (especially refractive index inhomogeneities occurring in the form of "air streaks" when measuring in air) only play a subordinate role.

[0015] Starting from the approach chosen according to the invention, also referred to as "matrix testing technique," the invention is based in particular on the concept of designing a beam-shaping surface located in the optical beam path in front of the aforementioned reference surface as an aspherical distortion correction surface, by which a distortion occurring in a predetermined reference plane of the measuring arrangement is reduced. The aforementioned reference plane can, in principle, be located at any position within the measuring arrangement, in particular, for example, in the area of ​​a CGH (constant wave generator) that may be present for generating the test wave, or also in the area of ​​the interferometer camera. Furthermore, the beam-shaping surface designed aspherically according to the invention can, in particular, reduce the distortion generated by the aforementioned CGH, but also, depending on the embodiment, distortion occurring in the rest of the optical beam path.Distortion generated along the light path of the measurement setup up to the interferometer camera is corrected. It should be noted that the CGH structure must then be adapted according to the design of the distortion correction surface (e.g., within optimization steps).

[0016] The invention is based, among other things, on the consideration that a beam-shaping surface located in the optical beam path in front of the reference surface (and thus outside the "cavity" defined by said reference surface and the surface of the test specimen) is comparatively uncritical with regard to its surface accuracy and the applicable tolerance values, since the beam-shaping surface in question is traversed equally by both the test wave reflected back from the test specimen and the reference wave split off by reflection from the reference surface. In other words, according to the invention, the beam-shaping surface is used to a particularly advantageous extent as an additional degree of freedom for distortion correction.

[0017] In addition to the greater accuracy achievable according to the invention as a result of the distortion correction, a further advantage of the inventive design is that even when testing comparatively large test specimen or mirror surfaces, the diffractive optical element or CGH used to generate the corresponding test wave can be designed to be comparatively small, since, as described below, the particularly effective beam shaping via the inventively aspherically designed beam shaping surface can be used to adapt the optical beam path accordingly. This avoids the problems (e.g., manufacturing-related) that arise when using comparatively large CGHs, as described in the introduction.

[0018] Furthermore, according to the invention, it is also possible to test different types of test objects or mirrors simply by exchanging the reference element and the diffractive optical element (e.g. CGHs) used to generate the test wave, while otherwise maintaining the same distance between the CGH and the reference element providing the reference surface (referred to as "matrix"), thus ultimately using a uniform design of the test tower.

[0019] The inventive concept of distortion correction via the targeted aspherical design of a beam shaping surface located in the optical beam path in front of the reference surface has the further advantage over a possible computational distortion correction that an undesirable variation in resolution (as is not eliminated in said computational distortion correction) is avoided.

[0020] According to one embodiment, the beam shaping surface is designed as an aspherical distortion correction surface such that the distortion occurring in the given reference plane of the measuring arrangement is reduced compared to a corresponding measuring arrangement with the beam shaping surface designed as a sphere.

[0021] According to one embodiment, the beam shaping surface is designed as an aspherical distortion correction surface such that the distortion occurring in the given reference plane of the measuring arrangement is reduced compared to a corresponding measuring arrangement with the beam shaping surface designed as a sphere best adapted to the aspherical distortion correction surface.

[0022] According to one embodiment, the relationship V2=1+(1−p)⋅(V1−1) with p ≥ 0.2, where V2 specifies the distortion occurring in a given reference plane of the measuring arrangement, and where V1 specifies the distortion occurring in a corresponding measuring arrangement with the beam shaping surface configured as a sphere best adapted to the aspherical distortion correction surface.

[0023] According to one embodiment, the aforementioned relationship (1) is satisfied with p ≥ 0.4, in particular with p ≥ 0.5, and further in particular with p ≥ 0.6.

[0024] According to one embodiment, the beam shaping surface is a freeform surface without rotational symmetry.

[0025] According to one embodiment, the beam shaping surface deviates from a best-fit sphere by more than 100 µm.

[0026] According to one embodiment, the beam shaping surface is arranged on the side of the reference element facing away from the reference surface.

[0027] According to one embodiment, the measuring arrangement features a computer-generated hologram (CGH) which generates the test wave by diffraction of electromagnetic radiation.

[0028] According to one embodiment, the CGH has an optically effective surface whose area is at least 1.2 times smaller, in particular at least 2 times smaller, and further, in particular at least 5 times smaller, than the area of ​​a surface of the test specimen to be tested in the measuring arrangement. The beam shaping surface, designed according to the invention as an aspherical distortion correction surface, is used to achieve a significantly smaller dimension for the CGH compared to the test specimen (or the reference element), whereby the particularly effective beam shaping is utilized via the beam shaping surface according to the invention.

[0029] According to one embodiment, the distance between the CGH and the surface of the test specimen is greater than the minimum cavity radius of the test specimen. The minimum cavity radius is sometimes also referred to as the "caustic distance".

[0030] According to one embodiment, at least one further refractive optical element is arranged between the CGH and the reference element. This design has the advantage that the refractive power required in the optical beam path of the measuring arrangement for beam shaping or adaptation to a CGH that may be used to generate the test wave can be distributed across several optical elements.

[0031] According to one embodiment, the minimum distance between the reference surface and the test specimen is less than 10 mm.

[0032] According to one embodiment, there is no optical medium with a refractive index n greater than 1.1 between the reference surface and the test specimen.

[0033] According to one embodiment, the test specimen to be characterized with regard to its surface shape has an optical effective surface in the form of a freeform surface without rotational symmetry.

[0034] According to one embodiment, the test object is a mirror or a lens.

[0035] According to one embodiment, the test specimen is designed for a working wavelength of less than 30 nm, in particular less than 15 nm.

[0036] According to one embodiment, the surface shape of the reference surface is at least substantially inverse to the surface shape of the test specimen.

[0037] According to one embodiment, the test object is an optical element for microlithography, in particular for a microlithographic projection exposure system.

[0038] The invention further relates to an optical element for use in a measuring arrangement with the features described above, wherein the optical element has a beam shaping surface designed as an aspherical distortion correction surface such that distortion occurring in a predetermined reference plane of the measuring arrangement is reduced.

[0039] According to one embodiment, the beam shaping surface is designed as an aspherical distortion correction surface such that the distortion occurring in the given reference plane of the measuring arrangement is reduced compared to a corresponding measuring arrangement with the beam shaping surface designed as a sphere.

[0040] According to one embodiment, the beam shaping surface is designed as an aspherical distortion correction surface such that the distortion occurring in the given reference plane of the measuring arrangement is reduced compared to a corresponding measuring arrangement with the beam shaping surface designed as a sphere best adapted to the aspherical distortion correction surface.

[0041] According to one embodiment, the optical element is a reference element having the reference surface, wherein the beam shaping surface is formed on the side of the reference element facing away from the reference surface.

[0042] According to one embodiment, the surface shape of the reference surface is at least substantially inverse to the surface shape of the test specimen.

[0043] The invention further relates to a method for manufacturing an optical element for a measuring arrangement with the features described above, wherein a beam shaping surface is formed on the optical element as an aspherical distortion correction surface in such a way that a distortion occurring in a predetermined reference plane of the measuring arrangement is reduced.

[0044] According to one embodiment, this beam shaping surface is designed as an aspherical distortion correction surface such that the distortion occurring in the given reference plane of the measuring arrangement is reduced compared to a corresponding measuring arrangement with the beam shaping surface designed as a sphere.

[0045] According to one embodiment, the beam shaping surface is designed as an aspherical distortion correction surface such that the distortion occurring in the given reference plane of the measuring arrangement is reduced compared to a corresponding measuring arrangement with the beam shaping surface designed as a sphere best adapted to the aspherical distortion correction surface.

[0046] According to one embodiment, the optical element is manufactured as a reference element having the reference surface, wherein the beam shaping surface is formed on the side of this reference element facing away from the reference surface.

[0047] Further embodiments of the invention can be found in the description and the dependent claims.

[0048] The invention is explained in more detail below with reference to exemplary embodiments shown in the accompanying figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] They show: Fig. 1 a schematic representation to illustrate the concept of the invention in an exemplary embodiment; Fig. 2-4 schematic diagrams to illustrate further possible embodiments; Fig. 5 a schematic representation to illustrate a possible setup for a measuring arrangement for the interferometric determination of the surface shape of a test specimen; and Fig. 6 a schematic representation of a projection exposure system designed for operation in the EUV. DETAILED DESCRIPTION OF PREFERRED EXECUTION FORMS

[0050] Fig. Figure 5 shows a schematic representation illustrating a possible setup for interferometrically determining the surface shape of a test specimen. Electromagnetic radiation generated by a light source 501 travels via an optical fiber 502 to a beam splitter 503 and from there via a deflecting mirror 504 to a diffractive optical element in the form of a CGH 505. The CGH 505, with a diffractive structure 505a located on it, generates a test wave for examining the surface shape of a test specimen 520, where this test specimen 520 can, in particular, have an optical surface or test specimen surface 521 in the form of a freeform surface without rotational symmetry.

[0051] The radiation passes through according to Fig. On the path from the CGH 505 to the test specimen 520, a reference element 510 is present, which has an inlet surface 511 and an outlet surface 512. At said outlet surface 512, a reference wave is split off from the test wave by reflection. Unlike the test wave, this reference wave is not reflected at the test specimen 520, but travels back along the original beam path without reflection. The outlet surface of the reference element 510 is therefore hereinafter also referred to as the "reference surface" 512.

[0052] The reference surface 512 and the test specimen surface 521 are "similar surfaces" in that a beam exiting the test specimen surface 521 perpendicularly also strikes the reference surface 512 perpendicularly. The test specimen shaft and the reference shaft run according to Fig. 5 follows the original beam path of the test wave back through the reference element 510, the deflecting mirror 504, and the beam splitter 503. From this beam splitter 503, the reference wave and the test wave pass through an aperture 507 and an eyepiece 508 to an interferometer camera 509. The interferometer camera 509 records an interferogram generated by the interfering waves, from which the surface shape of the test specimen 520 is determined by an evaluation unit (not shown).

[0053] Starting from the known setup of an interferometric measuring arrangement according to Fig. 5. Different embodiments of the invention will now be described with reference to the merely schematic representations of Fig. 1-4 described.

[0054] These exemplary and simplified embodiments all share the common feature that at least one beam-shaping surface located in the beam path in front of the reference surface is designed as an aspherical distortion correction surface in such a way that any distortion occurring in a given reference plane of the measuring arrangement is reduced. In particular, the beam-shaping surface can be designed as an aspherical distortion correction surface in such a way that the distortion occurring in the given reference plane of the measuring arrangement is reduced compared to a corresponding measuring arrangement with the beam-shaping surface configured as a sphere, and / or that the distortion occurring in the given reference plane of the measuring arrangement is reduced compared to a corresponding measuring arrangement with the beam-shaping surface configured as a sphere best adapted to the aspherical distortion correction surface.

[0055] Referring first to Fig. Figure 1 shows on the left a possible conventional setup and optical beam path for that section of the interferometric measuring arrangement which includes a CGH 55 with CGH structure 55a, a reference element 60 with spherical beam shaping surface 61 and reference surface 62 and a test specimen 70 with test specimen surface 71.

[0056] Right in Fig. Figure 1, in contrast, shows an embodiment according to the invention, wherein, compared to the conventional arrangement shown on the left, analogous components are designated with reference numerals increased by "50". In contrast to the conventional embodiment, in the embodiment according to the invention, on the right... Fig. 1 The beam shaping surface 111 of the reference element 110 is designed as an aspherical distortion correction surface with the result that a left in Fig. 1. Any visible distortion that occurs in the area of ​​the CGH 50 or in a reference plane located there is eliminated.

[0057] As from Fig. 1 (as well as in Fig. As can be seen in 2-4), the surface shape of the reference surface 62 or 112 can be at least essentially inverse to the surface shape of the test specimen 70 or 120.

[0058] According to one embodiment, the relationship V2=1+(1−p)⋅(V1−1) with p ≥ 0.2, where V2 specifies the distortion occurring in a given reference plane of the measuring arrangement, and where V1 specifies the distortion occurring in a corresponding measuring arrangement with the beam shaping surface configured as a sphere best adapted to the aspherical distortion correction surface.

[0059] In embodiments, the aforementioned relationship (1) can be satisfied in particular with p ≥ 0.4, in particular with p ≥ 0.5, and further in particular with p ≥ 0.6.

[0060] To optimize the distortion correction surface according to the invention (which may in particular be a freeform surface, e.g. on the rear surface of the reference element 110 facing away from the reference surface 112), the following procedure can be used: a) Specification of pixels with a regular Cartesian grid on a first reference plane on the test object 120 (e.g. mirror); this first reference plane can be defined in its position by the centroid of the test object surface 121 and in its orientation by the mean surface normal; b) Establishment or selection of a second reference plane (e.g. at the location of the CGH 105); this second reference plane can be defined perpendicular to a reference ray emanating from the centroid of the test specimen surface 121 and with a direction corresponding to the direction of the above mean surface normal on the test specimen surface 121 and at the intersection of this reference ray with the surface of the CGH 105 having the CGH structure 105a; c) Calculating rays in the normal direction on the test object surface 121 and starting from this test object surface 121; d) Determination of the beam penetration points on the aforementioned second reference plane (e.g. at CGH 105); e) Determination of the local imaging scales when imaging between the first (test object) reference plane and the aforementioned second reference plane (e.g., on the CGH 105) in two sections (x and y directions); and f) Optimization of the polynomial coefficients of the distortion correction surface or freeform surface (= beam shaping surface 111) such that the ratio of the imaging scales between the first (test object) reference plane and the above second reference plane (e.g. at CGH 105) is as homogeneous as possible everywhere.

[0061] Fig. Figure 2 shows, again in a schematic and simplified representation, another embodiment, in comparison to the one on the right in Fig. In the arrangement shown in Figure 1, analogous or essentially functionally identical components are designated with reference numerals increased by "100". As shown in Figure 1, Fig. As can be seen in Figure 2, the beam shaping surface 211, which according to the invention is again designed as an aspherical distortion correction surface, is additionally used to realize a significantly smaller dimension of the CGH 205 compared to the test specimen 220 or the reference element 210, whereby the particularly effective beam shaping via the beam shaping surface 211 according to the invention is utilized.

[0062] The invention is not fundamentally limited to the use of a CGH to generate the test wave. Fig. Figure 3 shows a possible further embodiment with generation of the test wave via a refractive optical element 305, wherein its light-emitting surface 305a is also designed as an aspherical surface, in particular a freeform surface. In the exemplary embodiment of Fig. 3 The distortion correction according to the invention is thus achieved by two beam shaping surfaces, namely the light exit surface 305a of the refractive optical element 305 and the beam shaping surface 311 of the reference element 310.

[0063] Fig. Figure 4 shows another possible embodiment, again in comparison to Fig. One analogous or essentially functionally identical component is designated with reference numerals increased by "300". This is in accordance with... Fig. 4 in contrast to Fig. 1. An additional refractive optical element 410a is arranged in front of the reference element 410, which has the reference surface 412, with respect to the optical beam path. This design has the advantage that the refractive power required for beam shaping or adaptation to the CGH 405 can be distributed between both optical elements 410 and 410a. In the exemplary embodiment of Fig. 4. The distortion correction according to the invention is implemented via the light-entry surface 411 of the refractive optical element 410a, whereas the light-emission surface 413 of this element 410a, as well as the light-entry surface 414 of the reference element 410, are spherically shaped. In further embodiments (not shown), the distortion correction according to the invention can also be implemented on another surface (e.g., the light-emission surface 413 of the element 410a). Furthermore, analogously to Fig. 4. The refractive power can also be divided among more than two optical elements.

[0064] Fig. Figure 6 schematically shows, in meridional section, the possible setup of a microlithographic projection exposure system designed for operation in EUV, which includes mirrors that can be tested using a method according to the invention. For example, a test specimen examined with regard to its surface shape within the scope of the invention can be any mirror of this projection exposure system 1. However, the invention is not limited to this and is also advantageously applicable for determining the surface shape of other elements. In particular, the invention can also be used to determine the surface shape of optical elements (e.g., mirrors or lenses) in a system designed for operation in DUV (i.e., at wavelengths of less than 250 nm, in particular less than 200 nm) or of other elements.

[0065] According to Fig. 6. The projection exposure system 1 comprises a lighting device 2 and a projection lens 10. In one embodiment of the lighting device 2 of the projection exposure system 1, in addition to a light or radiation source 3, there is a lighting optic 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a separate module from the rest of the lighting device. In this case, the lighting device does not include the light source 3.

[0066] In this process, a reticule 7 arranged in the object field 5 is exposed. The reticule 7 is held by a reticule holder 8. The reticule holder 8 can be moved, particularly in one scanning direction, via a reticule displacement drive 9. Fig. Figure 6 shows a Cartesian xyz coordinate system for illustrative purposes. The x-direction runs perpendicular to the plane of the drawing. The y-direction runs horizontally, and the z-direction runs vertically. The scan direction runs in Fig. 6 along the y-direction. The z-direction runs perpendicular to the object plane 6.

[0067] The projection lens 10 serves to image the object field 5 onto an image field 11 in an image plane 12. A structure on the reticulum 7 is imaged onto a light-sensitive layer of a wafer 13 located in the image field 11 within the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be moved, particularly along the y-direction, via a wafer transfer drive 15. The movement of the reticulum 7 via the reticulum transfer drive 9 and of the wafer 13 via the wafer transfer drive 15 can be synchronized.

[0068] The radiation source 3 is an EUV radiation source. In particular, the radiation source 3 emits EUV radiation, which is also referred to below as useful radiation or illumination radiation. The useful radiation has a wavelength in the range between 5 nm and 30 nm. The radiation source 3 can be, for example, a plasma source, a synchrotron-based radiation source, or a free-electron laser (FEL). The illumination radiation 16 emanating from the radiation source 3 is focused by a collector 17 and propagated through an intermediate focus in an intermediate focal plane 18 into the illumination optics 4. The illumination optics 4 has a deflecting mirror 19 and, downstream in the beam path, a first faceted mirror 20 (with facets 21 shown schematically) and a second faceted mirror 22 (with facets 23 shown schematically).

[0069] The projection lens 10 has a plurality of mirrors Mi (i = 1, 2, ...) which are numbered according to their arrangement in the beam path of the projection exposure system 1. In the case of the Fig. In the example shown in Figure 6, the projection lens 10 has six mirrors M1 to M6. Alternatives with four, eight, ten, twelve, or any other number of mirrors Mi are also possible. The penultimate mirror M5 and the last mirror M6 each have an aperture for the illumination radiation 16. The projection lens 10 is a double-obscured optical system. The projection lens 10 has an image-side numerical aperture that is greater than 0.5 and can also be greater than 0.6, for example, 0.7 or 0.75.

[0070] Even though the invention has been described with reference to specific embodiments, numerous variations and alternative embodiments are apparent to the person skilled in the art, for example, through the combination and / or exchange of features of individual embodiments. Accordingly, it is understood to the person skilled in the art that such variations and alternative embodiments are included in the present invention and that the scope of the invention is limited only to the extent of the appended claims and their equivalents. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2016 / 0085061 A1

[0003] DE 10 2022 209 651 A1

[0008] DE 10 2011 004 376 B3

[0008] DE 10 2021 202 909 A1

[0008] US 6,312,373 B1

[0008] EP 1 682 851 B1

[0008] DE 10 2015 209 490 A1

[0014] Cited Non-Patent Literature

[0000] X. Qiao et al.: "Measurement and correction of lateral distortion in a Fizeau interferometer based on the self-calibration technique", Optics Express, Vol. 30, no. 20, Pages 36134-36143, https: / / doi.org / 10.1364 / OE.467554

[0008]

Claims

[1] Measuring arrangement for the interferometric determination of the surface shape of a test object, wherein a test wave generated from electromagnetic radiation and reflected by the test object can be superimposed with a reference wave not reflected by the test object, with • a reference element (110, 210, 310, 410) with a reference surface (112, 212, 312, 412) which, in the optical beam path, reflects the reference wave from the test wave before it strikes the test specimen (120, 220, 320, 420); and • at least one beam shaping surface (111, 211, 311, 411, 413, 414) located in the optical beam path in front of the reference surface (112, 212, 312, 412); • wherein this beam shaping surface (111, 211, 311, 411, 413, 414) is designed as an aspherical distortion correction surface such that distortion occurring in a given reference plane of the measuring arrangement is reduced. [2] Measuring arrangement according to claim 1,characterized by , that this beam shaping surface is designed as an aspherical distortion correction surface such that the distortion occurring in the given reference plane of the measuring arrangement is reduced compared to a corresponding measuring arrangement with the beam shaping surface designed as a sphere. [3] Measuring arrangement according to claim 1 or 2, characterized by , that this beam shaping surface is designed as an aspherical distortion correction surface such that the distortion occurring in the given reference plane of the measuring arrangement is reduced compared to a corresponding measuring arrangement with the beam shaping surface designed as a sphere best adapted to the aspherical distortion correction surface. [4] Measuring arrangement according to one of claims 1 to 3, characterized by that the relationship V2=1+(1−p)⋅(V1−1) with p ≥ 0.2, where V2 specifies the distortion occurring in a given reference plane of the measuring arrangement, and where V1 specifies the distortion occurring in a corresponding measuring arrangement with the beam shaping surface configured as a sphere best adapted to the aspherical distortion correction surface. [5] Measuring arrangement according to claim 4, characterized by , that the relation (1) is satisfied with p ≥ 0.4, in particular with p ≥ 0.5, and further in particular with p ≥ 0.

6. [6] Measuring arrangement according to one of the preceding claims, characterized by , that the beam shaping surface (111, 211, 311, 411, 413, 414) is a freeform surface without rotational symmetry. [7] Measuring arrangement according to one of the preceding claims, characterized by , that the beam shaping surface (111, 211, 311, 411, 413, 414) deviates from a best-fit sphere by more than 100 µm. [8] Measuring arrangement according to one of the preceding claims, characterized by, that the beam shaping surface (111, 211, 311) is arranged on the side of the reference element (110, 210, 310) facing away from the reference surface (112, 212, 312). [9] Measuring arrangement according to one of the preceding claims, characterized by , that it has a computer-generated hologram (CGH) (105, 205, 405) which generates the test wave by diffraction of electromagnetic radiation. [10] Measuring arrangement according to claim 9, characterized by , that the CGH (105, 205, 405) has an optically effective area whose area is at least by a factor of 1.2, in particular at least by a factor of 2, and further in particular at least by a factor of 5, smaller than the area of ​​a surface of the test specimen (120, 220, 320, 420) to be tested in the measuring arrangement. [11] Measuring arrangement according to claim 9 or 10, characterized by, that a distance between the CGH (105, 205, 405) and the surface (121, 221, 421) of the test specimen (120, 220, 320, 420) to be tested is greater than a minimum hollow radius of the test specimen (120, 220, 420). [12] Measuring arrangement according to one of the preceding claims, characterized by , that at least one further refractive optical element (410a) is arranged between the CGH (405) and the reference element (410). [13] Measuring arrangement according to one of the preceding claims, characterized by , that a minimum distance between reference surface (112, 212, 312, 412) and test specimen (120, 220, 320, 420) is less than 10 mm. [14] Measuring arrangement according to one of the preceding claims, characterized by , that there is no optical medium with a refractive index n greater than 1.1 between the reference surface (112, 212, 312, 412) and the test specimen (120, 220, 320, 420). [15] Measuring arrangement according to one of the preceding claims, characterized by, that the test specimen (120, 220, 320, 420) to be characterized with regard to its surface shape has an optical effective surface in the form of a freeform surface without rotational symmetry. [16] Measuring arrangement according to one of the preceding claims, characterized by , that the test subject (120, 220, 320, 420) is a mirror or a lens. [17] Measuring arrangement according to one of the preceding claims, characterized by , that the test specimen (120, 220, 320, 420) is designed for a working wavelength of less than 30 nm, in particular less than 15 nm. [18] Measuring arrangement according to one of the preceding claims, characterized by , that the surface shape of the reference surface (112, 212, 312, 412) is at least substantially inverse to the surface shape of the test specimen (120, 220, 320, 420). [19] Measuring arrangement according to one of the preceding claims, characterized by, that the test item (120, 220, 320, 420) is an optical element for microlithography, in particular a microlithographic projection exposure system (1). [20] Optical element for use in a measuring arrangement according to one of claims 1 to 19, wherein the optical element has a beam shaping surface (111, 211, 311, 411, 413, 414) designed as an aspheric distortion correction surface such that distortion occurring in a predetermined reference plane of the measuring arrangement is reduced. [21] Optical element according to claim 20, characterized by , that this beam shaping surface is designed as an aspherical distortion correction surface such that the distortion occurring in the given reference plane of the measuring arrangement is reduced compared to a corresponding measuring arrangement with the beam shaping surface designed as a sphere. [22] Optical element according to claim 20 or 21, characterized by, that this beam shaping surface is designed as an aspherical distortion correction surface such that the distortion occurring in the given reference plane of the measuring arrangement is reduced compared to a corresponding measuring arrangement with the beam shaping surface designed as a sphere best adapted to the aspherical distortion correction surface. [23] Optical element according to one of claims 20 to 22, characterized by , that the optical element is a reference element having the reference surface (112, 212, 312, 412), wherein the beam shaping surface (111, 211, 311) is formed on the side of the reference element (110, 210, 310) facing away from the reference surface (112, 212, 312). [24] Optical element according to any one of claims 20 to 23, characterized by , that a surface shape of the reference surface (112, 212, 312, 412) is formed at least substantially inversely to the surface shape of the test specimen (120, 220, 320, 420). [25] Method for manufacturing an optical element for a measuring arrangement according to one of claims 1 to 19, wherein a beam shaping surface (111, 211, 311, 411, 413, 414) is formed on the optical element as an aspherical distortion correction surface such that a distortion occurring in a predetermined reference plane of the measuring arrangement is reduced. [26] Method according to claim 25, characterized by , that this beam shaping surface is designed as an aspherical distortion correction surface such that the distortion occurring in the given reference plane of the measuring arrangement is reduced compared to a corresponding measuring arrangement with the beam shaping surface designed as a sphere. [27] Method according to claim 25 or 26, characterized by, that this beam shaping surface is designed as an aspherical distortion correction surface in such a way that the distortion occurring in the given reference plane of the measuring arrangement is reduced compared to a corresponding measuring arrangement with the beam shaping surface designed as a sphere best adapted to the aspherical distortion correction surface. [28] Method according to any one of claims 25 to 27, characterized by , that the optical element is manufactured as a reference element (110, 210, 310) having the reference surface (112, 212, 312), wherein the beam shaping surface (111, 211, 311) is formed on the side of this reference element (110, 210, 310) facing away from the reference surface (112, 212, 312).

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