Interferometric test setup for testing the surface shape of a test object

Abstract

The invention relates to an interferometric testing arrangement for testing the surface shape of a test object, comprising a lighting device (105, 205, 305) for generating an input wave from electromagnetic radiation produced by a light source and an interferometer (150) in which, after splitting the input wave into at least one test wave directed towards the test object (170) and a reference wave, testing the surface shape of at least a partial surface of the test object (170) can be carried out by interferometric superposition of the at least one test wave and the reference wave, wherein a diffuser (130, 230, 330) is arranged in the lighting device, wherein the lighting device has a first optical path (110, 210, 310) and a separate second optical path (120, 220, 320), and wherein the input wave is transmitted via both the first optical path (110, 210, 310) and the second optical path (120, 220, 320). 220,320) can be coupled into the interferometer (150).

Description

BACKGROUND OF THE INVENTION Area of ​​the invention

[0001] The invention relates to an interferometric testing arrangement for testing the surface shape of a test object. 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 system. This, in turn, means that in addition to manufacturing, verifying the surface shape of the mirrors presents a significant challenge. For high-precision mirror testing, interferometric measurement methods using diffractive optical elements, such as computer-generated holograms (CGH), are employed.

[0005] A problem that arises in practice, particularly when testing EUV mirrors with correspondingly high requirements for measurement accuracy, is that the achievable measurement accuracy is limited by a number of effects. For example, defects present on the optical surfaces of the interferometric test setup lead to measurement disturbances and ultimately to an incorrect characterization of the surface shape of the test object or mirror. One critical effect is the appearance of speckle patterns, which are due to the spatial coherence of the light generated by the light source used.

[0006] To limit or minimize the speckle patterns mentioned above and the associated measurement disturbances, the use of a (possibly rotatable) diffuser in the illumination device – which generates the respective input wave for the interferometer in the interferometric test setup – is known, whereby a reduction in measurement errors is achieved during the test specimen measurement by blurring the image of existing defects.

[0007] Furthermore, it is known to perform an adjustment before the actual test specimen measurement, in which, for example, a cat's eye optic is inserted into the optical beam path of the interferometer instead of the test specimen. In practice, depending on whether an adjustment or the actual test specimen measurement is being carried out, the diffuser in the illumination device needs to be illuminated differently, with a larger spatial extent of the light spot generated on the diffuser being required for the test specimen measurement compared to the adjustment.

[0008] For the state of the art, reference is made only by way of example to DE 10 2022 201 462 A1, DE 10 2019 216 447 A1, DE 10 2016 213 237 A1 and US 6,643,024 B2. SUMMARY OF THE INVENTION

[0009] Against the above background, it is an object of the present invention to provide an interferometric testing arrangement for testing the surface shape of a test object, which enables both the actual measurement of the test object and the performance of an adjustment in a flexible and as error-free a manner as possible.

[0010] This problem is solved by the interferometric testing arrangement according to the features of independent claim 1.

[0011] According to one aspect of the invention, an interferometric test arrangement for testing the surface shape of a test object comprises - a lighting device for generating an input wave from electromagnetic radiation produced by a light source; and - an interferometer in which, after splitting the input wave into at least one test wave directed towards the test object and a reference wave, a test of the surface shape of at least one partial surface of the test object can be carried out by interferometric superposition of the at least one test wave and the reference wave; - wherein a diffuser is arranged in the lighting device; - wherein the lighting device has a first optical path and a separate second optical path; and - where the input wave can be coupled into the interferometer via both the first optical path and the second optical path.

[0012] The formulation stating that the input wave can be coupled into the interferometer via both the first optical path and the second optical path includes scenarios in which, as described below, the electromagnetic radiation generated by the light source passes through either only the first optical path or only the second optical path, as well as scenarios in which the electromagnetic radiation generated by the light source passes through both optical paths at least temporarily.

[0013] The invention is based in particular on the concept of realizing variable illumination of a diffuser in a lighting device of an interferometric test arrangement in a particularly advantageous manner by enabling flexible switching between different optical paths, along which the input wave can be coupled into the interferometer of the test arrangement, depending on whether an adjustment or the actual test specimen measurement is currently being carried out.

[0014] In this context, the following refers to the embodiments of Fig. The inventive realization of said variable illumination of a diffuser described in 1a-4c, compared to the fundamentally also possible and further explained by means of Fig. The implementation described in more detail in 5a-5b using a movable lens in the lighting device has the advantage that, according to the invention, the illumination of the diffuser varies over a comparatively large range with regard to the diameter of the light spot generated on the diffuser.

[0015] Furthermore, the illumination of the diffuser can be implemented telecentrically in both the first operating mode (adjustment) and the second operating mode (test object measurement). Telecentric illumination of the diffuser means that all light cones striking the diffuser are perpendicular to it, thus avoiding measurement errors associated with non-perpendicular light coupling into the interferometer of the interferometric measuring setup following the illumination device.

[0016] According to one embodiment, when the input wave is coupled via the first optical path, a light spot generated on the diffuser has a first diameter (D1), and when the input wave is coupled via the second optical path, a light spot generated on the diffuser has a second diameter (D2), wherein the second diameter differs from the first diameter.

[0017] According to one embodiment, the second diameter is larger than the first diameter by at least a factor of 10, in particular by at least a factor of 100, and further in particular by at least a factor of 1000.

[0018] According to one embodiment, the first diameter is less than 10 µm, in particular less than 5 µm.

[0019] According to one embodiment, the second diameter is at least 0.05 mm, in particular at least 0.5 mm, and further in particular at least 5 mm.

[0020] According to one embodiment, a numerical aperture (NA2) present when the input wave is coupled to the diffuser via the first optical path differs from a numerical aperture (NA1) present when the input wave is coupled to the diffuser via the second optical path.

[0021] According to one embodiment, the numerical aperture (NA2) present when the input wave is coupled to the diffuser via the first optical path is at least two times larger than the numerical aperture (NA1) present when the input wave is coupled to the diffuser via the second optical path.

[0022] According to one embodiment, a spatial light modulator is arranged in the second optical path. By providing two separate optical paths for the two operating modes described above, the requirements placed on this spatial light modulator are significantly reduced compared to an arrangement in which both the comparatively large light spot for measuring the test specimen and the comparatively small light spot for adjustment have to be generated with only one optical path and via one and the same spatial light modulator.

[0023] According to one embodiment, this spatial light modulator is configured as a phase modulator. However, the invention is not limited to this, and in further embodiments the spatial light modulator can also be configured as an intensity modulator.

[0024] According to one embodiment, the input wave coupled into the interferometer via the first optical path and the input wave coupled into the interferometer via the second optical path are identical with respect to their wavelength.

[0025] According to one embodiment, the electromagnetic radiation has a wavelength greater than 500 nm.

[0026] According to one embodiment, the first optical path and the second optical path differ from each other with respect to the polarization of the electromagnetic radiation passing through the respective optical path. In this way, as described below, undesirable light losses at a beam splitter present in the lighting device can be significantly reduced.

[0027] According to one embodiment, at least one intermediate image plane is present in the first optical path and / or in the second optical path. This design is advantageous insofar as it allows the placement of apertures in the optical beam path, as described below.

[0028] According to one embodiment, at least one aperture is arranged in the first optical path and / or in the second optical path. In this way, unwanted stray light can be eliminated from the optical beam path, and an excessive spatial extent of the light spot generated on the diffuser and the associated loss of contrast can be avoided.

[0029] According to one embodiment, the test object is an optical element, particularly for microlithography.

[0030] According to one embodiment, the test object is a mirror, in particular a mirror designed for operation under EUV conditions.

[0031] The invention further relates to a method for testing the surface shape of a test object using a test arrangement with the features described above.

[0032] Further embodiments of the invention can be found in the description and the dependent claims.

[0033] The invention is explained in more detail below with reference to exemplary embodiments shown in the accompanying figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] They show: Fig. 1a-1c schematic representations to illustrate a possible embodiment of an interferometric test arrangement according to the invention; Fig. 2-4c schematic representations to explain further embodiments of a lighting device present in an interferometric test arrangement according to the invention; Fig. 5a-5b a schematic representation to illustrate another possible setup of a lighting device present in an interferometric test setup; and Fig. 6 a schematic representation of a projection exposure system designed for operation in the EUV. DETAILED DESCRIPTION OF PREFERRED EXECUTION FORMS

[0035] Fig. Figure 6 shows a schematic representation of an exemplary projection exposure system designed for operation in the EUV, which has mirrors that can be tested with a device according to the invention.

[0036] According to Fig. Figure 6 comprises a field faceted mirror 603 and a pupil faceted mirror 604 in a projection exposure system 610 designed for EUV. The light from a light source unit, which includes a plasma light source 601 and a collector mirror 602, is directed onto the field faceted mirror 603. A first telescope mirror 605 and a second telescope mirror 606 are arranged in the light path after the pupil faceted mirror 604. A deflecting mirror 607 is arranged further down the light path, which directs the incident radiation onto an object field in the object plane of a projection lens comprising six mirrors 621-626. At the location of the object field, a reflective structure-bearing mask 631 is arranged on a mask table 630, which is imaged into an image plane by means of the projection lens, in which a substrate 641 coated with a light-sensitive layer (photoresist) is located on a wafer table 640.

[0037] The test object tested in a test arrangement according to the invention described below can be, for example, any mirror of the projection exposure system 610.

[0038] In the following, embodiments of an interferometric test arrangement according to the invention are described with reference to the schematic figures in Fig. 1a-1c, Fig. 2 and Fig. 3 described. In each case, to test the surface shape of a test object such as an EUV mirror, an interferometric superposition of a test wave reflected by the test object or mirror and a reference wave not reflected by the test object or mirror is generated.

[0039] The following, with reference to Fig. 1a-1c, Fig. 2 and Fig. The three described embodiments have in common that the lighting device (in Fig. 1a-1c with “105” and in Fig. 2 and Fig. 3 (designated with “205” or “305”) has a first optical path 110 (or 210 or 310) and a separate second optical path 120 (or 220 or 320). During operation, the test setup selectively switches between a first operating mode, in which the input wave is coupled into the interferometer 150 via the first optical path 110 (or 210 or 310), and a second operating mode, in which the input wave is coupled into the interferometer 150 via the second optical path 120 (or 220 or 320).

[0040] Referring first to Fig. Figures 1a-1c describe a lighting device 105 for generating an input wave from electromagnetic radiation produced by a light source (not shown), wherein the light source can be configured in particular as a neodymium-YAG laser for generating electromagnetic radiation with a wavelength of 532 nm or as a helium-neon laser for generating electromagnetic radiation with a wavelength of 633 nm. The invention is not limited to implementations with a wavelength greater than 500 nm. In further embodiments, the electromagnetic radiation can also have a different wavelength in the visible or UV range.

[0041] Fig. Figure 1a shows an enlarged schematic representation of the lighting device 105, whereas in Fig. 1b and Fig. Figure 1c also shows the interferometer 150, into which the input wave generated by the illumination device 105 is coupled. This shows Fig. 1c the previously described scenario of the actual test specimen measurement, whereas Fig. 1b shows the previously mentioned adjustment scenario. According to Fig. 1b is replaced in this adjustment in the optical beam path of the interferometer 150 by the test specimen 170. Fig. 1c a cat's eye optic, merely schematically indicated and labelled "160".

[0042] The lighting device 105 has a diffuser 130 in a manner known per se, which in the exemplary embodiment is rotatable. The electromagnetic radiation from the lighting system 105 or the diffuser 130 is emitted according to Fig. 1c as input wave into an interferometer designated "150". The invention is not limited to a rotatable design of the diffusing disk 130. Rather, in further embodiments, a movable diffusing disk (to realize a back-and-forth movement) or, if necessary, a stationary diffusing disk can also be used.

[0043] This interferometer 150 is according to Fig. 1c is implemented as a so-called Fizeau arrangement only by way of example (and without limiting the invention thereto). Here, the electromagnetic radiation strikes a Fizeau plate 153 via a beam splitter 151 and a collimator 152, whereby a reference wave is generated by reflection at the Fizeau plate 153 and a test wave is generated by transmission from the Fizeau plate 153, wherein the test wave according to Fig. 1c is reflected at the test object 170. The reference wave and the test wave pass via the beam splitter 151 and via an interferometer aperture 155 and an eyepiece lens 156 onto a detector 157 (e.g. in the form of a CCD camera) and interfere with each other there, so that an interferogram of the respective test object 170 is recorded with the detector 157 or the CCD camera.

[0044] In further embodiments, the interferometer can also be designed as a so-called "reference mirror arrangement", in which the reference wave is generated by reflection at a reference mirror in a manner known per se. Reference is made to DE 10 2019 216 447 A1 by way of example.

[0045] How best to Fig. As can be seen in Figure 1a, the lighting device 105 has two separate optical paths 110 and 120, along which the electromagnetic radiation supplied from the (not shown) light source via a first optical fiber 111 and a second optical fiber 121 respectively can be supplied to the diffuser 130.

[0046] In the first optical path 110, the electromagnetic radiation from the first optical fiber 111 passes through a collimator lens 112 and a beam splitter 113 to a focusing lens 114, where it is focused by this focusing lens 114 with a comparatively large numerical aperture (NA2 = 0.2 in the exemplary embodiment) onto the diffuser 130. The diffraction pattern shown here is... Fig. 1b on the diffuser 130, the light spot produced has a comparatively small spatial extent (in the exemplary embodiment with a first diameter D1= 3 µm).

[0047] In the second optical path 120, however, a second operating mode is reached according to the one described in Fig. In the test specimen measurement shown in Figure 1c, electromagnetic radiation from the second optical fiber 121 is directed via a collimator lens 122 to a spatial light modulator 123 (SLM), which in this embodiment is designed as a phase modulator and is arranged in a Fourier plane of the diffuser 130. The spatial light modulator 123 imprints a defined phase pattern upon reflection of the incident electromagnetic radiation. In further embodiments, the spatial light modulator 123 can alternatively or additionally be designed as an intensity modulator to imprint an intensity pattern onto the incident electromagnetic radiation.

[0048] The radiation emanating from the spatial light modulator 123 is then reflected at the beam splitter 113 and passes through the focusing lens 114 to the diffuser 130. It should be noted that in Fig. 1a For the corresponding beam path along the second optical path 120, both the dotted and the dashed marginal ray are shown, whereby, in addition to these extremal rays or ray directions shown, the intermediate rays or ray directions can also be generated via the spatial light modulator 123. The angular distribution generated by the spatial light modulator 123 corresponds in turn to an intensity distribution on the diffuser 130, whereby the light spot generated on the diffuser 130 in the second operating mode, according to the scenario of the test specimen measurement, has a comparatively large spatial extent (in the exemplary embodiment with a second diameter D2 = 6 mm). The numerical aperture in this second operating mode has a comparatively low value (which, by way of example, can be NA1 = 0.02 in the exemplary embodiment).

[0049] Fig. Figures 5a-5b show, in a purely schematic representation, a fundamentally possible embodiment of a lighting device 505, wherein lenses 512, 513 are provided, of which different diameters D1 ( Fig. 5a) and D2 ( Fig. 5b) on a site as shown in the example according to Fig. 5a-5b also includes a rotatable diffuser 530, and the lens 513 is movable. “511” designates an optical fiber.

[0050] The based on Fig. 1a-1c described selective switching between first optical path 110 according to Fig. 1b and second optical path 120 according to Fig. 1c enables, according to the invention - in contrast to an embodiment according to Fig. 5a-5b - ensuring telecentric illumination of the diffuser 130, the flexible switching between one for adjustment according to Fig. 1b on the diffuser 130 produced a comparatively small light spot and one for the actual test specimen measurement according to Fig. The invention provides two separate optical paths for the two operating modes described above, thus significantly reducing the requirements placed on the spatial light modulator 123 compared to an arrangement where both the relatively large light spot for measuring the test specimen and the relatively small light spot for adjustment are generated using only one optical path and the same spatial light modulator.

[0051] In a calculation example, in the last-mentioned (non-inventive) scenario of using a spatial light modulator in a single optical path for both applications (i.e., test specimen measurement and adjustment), with a typical pixel count of 2000*2000 pixels for a numerical aperture NA= 0.2, the maximum diameter of the light spot generated on the diffuser would only be 1.2 mm, whereas for a diameter of the light spot on the diffuser of 6 mm, a much higher pixel count of 10000*10000 pixels would already be required.

[0052] Although the selective coupling of electromagnetic radiation according to the invention can alternatively be into the first optical path 110 or into the second optical path 120 in both embodiments of Fig. 1a-1c as well as in the further embodiments described below of Fig. 2 to Fig. The invention is not limited to the fact that, although the operation is implemented via separate optical fibers, as described in section 3, selective activation of the optical paths can also be achieved in further embodiments via any other suitable coupling optic, e.g., using a tiltable mirror.

[0053] Fig. Figure 2 shows a schematic representation to illustrate a further embodiment, wherein in comparison to Fig. 1a-1c are analogous or essentially functionally identical components with reference digits increased by “100”.

[0054] According to the embodiment of Fig. 2 is located in contrast to the embodiment of Fig. In the optical beam path of the second optical path 220, an additional intermediate image plane is provided by collimator lenses 224, 225 arranged in the optical beam path between the spatial light modulator 223 and the beam splitter 213. An aperture 226 is arranged at a position optically conjugate to the diffuser 230 in the optical far field of the spatial light modulator 223. This circular aperture 226 blocks unwanted stray light generated by the spatial light modulator 223 in higher diffraction orders, thereby also limiting the maximum diameter of the light spot generated on the diffuser 230.

[0055] Another aperture of 227 is located according to Fig. 2 in the optical beam path between the collimator lens 225 and the beam splitter 213 at a position optically conjugate to the spatial light modulator 223 and clips the typically Gaussian illumination in this area. As in Fig. As shown schematically in Figures 4a-4c, the displacement of this aperture 227 enables the adjustment of telecentric illumination of the diffuser 230, in which all light cones incident on the diffuser 230 strike it perpendicularly. In this way, undesirable measurement errors associated with non-perpendicular light coupling into the interferometer of the interferometric measuring arrangement following the illumination device 205 can be avoided.

[0056] With reference to Fig. 4a-4c represents the schematic representation of Fig. 4a the scenario of a point illumination of the diffuser 430, whereas Fig. Figures 4b-4c each represent the scenario of a “disc-shaped” illumination of the diffuser 430 corresponding to a comparatively large spatial extent of the light spot generated on the diffuser 430.

[0057] While according Fig. 4a for the electromagnetic radiation emanating from the diffusing disk 430, the source point lies in the diffusing disk plane of the diffusing disk 430, the relevant source point is according to Fig. 4b is shifted by a distance dz because the fact that different locations on the diffuser 430 are illuminated differently suggests a point light source corresponding to the light cone. This source shift undesirably results in non-perpendicular light coupling into the interferometer of the interferometric measuring arrangement following the illumination device, which in turn leads to undesirable measurement errors.

[0058] According to Fig. In 4c, however, the source in question is located in the plane of the diffusing disk 430, with all incident light cones striking the diffusing disk 430 perpendicularly in a telecentric beam path. This can, as shown in Fig. As indicated in Figure 4b, this can be achieved by moving aperture 427 along the direction of light propagation (corresponding to the z-direction in the plotted coordinate system). By moving aperture 427 perpendicular to the z-direction (i.e., in the x-direction in the plotted coordinate system), the angle of incidence of all rays is changed equally.

[0059] Fig. Figure 3 shows a schematic representation to illustrate a further embodiment, wherein in comparison to Fig. Two analogous or essentially functionally identical components are designated with reference digits increased by "100".

[0060] The embodiment according to Fig. 3 differs from the one from Fig. 2 firstly, by replacing the (intensity) beam splitter 213 with Fig. 2. A polarization beam splitter 313 is provided, which reflects electromagnetic radiation of a given polarization direction almost 100% and transmits electromagnetic radiation with an orthogonal polarization direction almost 100%. Furthermore, according to... Fig. 3 Additional polarization-influencing optical elements are arranged in the optical beam path of both the first optical path 310 and the second optical path 320. Specifically, according to Fig. 3. Between the collimator lens 312 and the polarization beam splitter 313 in the first optical path 310, there is a p-polarizer 315, and between the spatial light modulator 323 and the collimator 324 in the second optical path 320, there is an s-polarizer 328. "329" denotes the s-polarization of the radiation emerging from the s-polarizer 328. Furthermore, a lambda / 4 plate 316 is located in the optical beam path between the polarization beam splitter 313 and the focusing lens 314.

[0061] Because in the embodiment of Fig. 3. If the polarization beam splitter 313 is supplied with p-polarized light via the first optical path 310, i.e. in transmission, whereas the polarization emitter 313 is supplied with s-polarized light via the second optical path 320, i.e. in reflection, a significant reduction in light losses at the polarization beam splitter 313 is achieved (compared to the use of an intensity beam splitter according to the embodiments described above).

[0062] The according to Fig.The lambda / 4 plate 316, arranged in the optical beam path between the polarizing beam splitter 313 and the focusing lens 314, is generally optional and serves to convert the linearly (s- or p-) polarized light emanating from the polarizing beam splitter 313 into (right- or left-) circularly polarized light. In further embodiments, a lambda / 2 plate can also be used instead of the lambda / 4 plate 316 in order to be able to adjust the polarization direction as desired (by correspondingly rotating the lambda / 2 plate) while the electromagnetic radiation incident on the diffuser 330 is again linearly polarized.

[0063] 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 scope 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 201 462 A1

[0008] OF 10 2019 216 447 A1 [0008, 0044] DE 10 2016 213 237 A1

[0008] US 6,643,024 B2

[0008]

Claims

[1] Interferometric test setup for testing the surface shape of a test object, comprising: • a lighting device (105, 205, 305) for generating an input wave from electromagnetic radiation produced by a light source; and • an interferometer (150) in which, after splitting the input wave into at least one test wave directed towards the test object (170) and a reference wave, a test of the surface shape of at least one partial surface of the test object (170) can be carried out by interferometric superposition of the at least one test wave and the reference wave; • wherein a diffuser (130, 230, 330) is arranged in the lighting device (105, 205, 305); • wherein the lighting device (105, 205, 305) has a first optical path (110, 210, 310) and a separate second optical path (120, 220, 320); and • wherein the input wave can be coupled into the interferometer (150) via both the first optical path (110, 210, 310) and the second optical path (120, 220, 320). [2] Interferometric test setup according to claim 1, characterized by , that during operation of the test arrangement it is possible to selectively switch between a first operating mode, in which the input wave is coupled into the interferometer (150) via the first optical path (110, 210, 310), and a second operating mode, in which the input wave is coupled into the interferometer (150) via the second optical path (120, 220, 320). [3] Interferometric test setup according to claim 1 or 2, characterized by, that when the input wave is coupled via the first optical path (110, 210, 310) a light spot generated on the diffuser (130, 230, 330) has a first diameter (D1), and when the input wave is coupled via the second optical path (120, 220, 320) a light spot generated on the diffuser (130, 230, 330) has a second diameter (D2) which differs from the first diameter (D1). [4] Interferometric test setup according to claim 3, characterized by , that the second diameter (D2) is at least by a factor of 10, in particular at least by a factor of 100, and further in particular at least by a factor of 1000, larger than the first diameter (D1). [5] Interferometric test setup according to claim 3 or 4, characterized by , that the first diameter (D1) is less than 10 µm, in particular less than 5 µm. [6] Interferometric test setup according to any one of claims 3 to 5, characterized by , that the second diameter (D2) is at least 0.05 mm, in particular at least 0.5 mm, and further in particular at least 5 mm. [7] Interferometric test setup according to one of the preceding claims, characterized by , that a numerical aperture (NA2) present when the input wave is coupled via the first optical path (110, 210, 310) at the diffuser disk (130, 230, 330) differs from a numerical aperture (NA1) present when the input wave is coupled via the second optical path (120, 220, 320). [8] Interferometric test setup according to claim 7, characterized by, that the numerical aperture (NA2) present when the input wave is coupled to the scattering disk (130, 230, 330) via the first optical path (110, 210, 310) is at least two times larger than the numerical aperture (NA1) present when the input wave is coupled to the scattering disk (130, 230, 330) via the second optical path (120, 220, 320). [9] Interferometric test setup according to one of the preceding claims, characterized by , that a spatial light modulator (123, 223, 323) is arranged in the second optical path (120, 220, 320). [10] Interferometric test setup according to claim 9, characterized by , that this spatial light modulator (123, 223, 323) is designed as a phase modulator. [11] Interferometric test setup according to one of the preceding claims, characterized by, that the input wave coupled into the interferometer (150) via the first optical path (110, 210, 310) and the input wave coupled into the interferometer (150) via the second optical path (120, 220, 320) are identical in wavelength. [12] Interferometric test setup according to one of the preceding claims, characterized by that the electromagnetic radiation has a wavelength greater than 500 nm. [13] Interferometric test setup according to one of the preceding claims, characterized by , that the first optical path (310) and the second optical path (320) differ from each other with respect to the polarization of the electromagnetic radiation passing through the respective optical path (310, 320). [14] Interferometric test setup according to one of the preceding claims, characterized by, that at least one intermediate image plane is present in the first optical path (210, 310) and / or in the second optical path (220, 320). [15] Interferometric test setup according to one of the preceding claims, characterized by , that at least one aperture (226, 227, 326, 327, 426, 427) is arranged in the first optical path (210, 310) and / or in the second optical path (220, 320). [16] Interferometric test setup according to one of the preceding claims, characterized by , that the test object (170) is an optical element, especially for microlithography. [17] Interferometric test setup according to one of the preceding claims, characterized by , that the test object (170) is a mirror, in particular a mirror designed for operation under EUV conditions. [18] Method for characterizing the surface shape of a test object using an interferometric test setup according to one of the preceding claims.

Images