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

Abstract

The invention relates to an interferometric test arrangement for testing the surface shape of a test object, comprising an illumination device (105, 205, 305) for generating an input wave from electromagnetic radiation generated by a light source, and an interferometer (150) in which, after the input wave has been split into at least one test wave directed onto the test object (170) and a reference wave, the surface shape of at least one partial surface of the test object (170) can be tested by interferometrically superimposing the at least one test wave and the reference wave, wherein a diffusing plate (130, 230, 330) is arranged in the illumination device, wherein the illumination device has a first optical path (110, 210, 310) and, separate therefrom, a second optical path (120, 220, 320), wherein the input wave can be coupled into the interferometer via both the first optical path and the second optical path, wherein, when the input wave is coupled in via the first optical path, a light spot generated on the diffusing plate has a first diameter (D1), and wherein, when the input wave is coupled in via the second optical path, a light spot generated on the diffusing plate has a second diameter (D2) which differs from the first diameter (D1). (Figure 1a)

Description

[0001]

[0002] Interferometric test setup for testing the surface shape of a test object

[0003] The present application claims priority over German patent application DE 10 2024 208 940.0, filed on September 18, 2024. The content of that DE application is incorporated into the present application text by reference.

[0004] BACKGROUND OF THE INVENTION

[0005] Field of invention

[0006] The invention relates to an interferometric testing arrangement for testing the surface shape of a test object.

[0007] State of the art

[0008] 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. In projection lenses designed for the EUV range, i.e., at wavelengths of approximately 13 nm or 7 nm, mirrors are used as optical components for the imaging process due to the lack of suitable translucent refractive materials.Typical projection lenses designed for EUV, 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.

[0009] Increasing the image-side numerical aperture (NA) typically necessitates a larger mirror surface area in the projection system. This, in turn, makes both manufacturing and surface inspection of the mirrors a significant challenge. High-precision inspection of the mirrors is achieved primarily through interferometric measurement techniques using diffractive optical elements such as computer-generated holograms (CGH).

[0010] 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.

[0011] 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.

[0012] 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.

[0013] For examples of the state of the art, reference is made only 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.

[0014] SUMMARY OF THE INVENTION

[0015] 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.

[0016] This problem is solved by the interferometric testing arrangement according to the features of independent claim 1.

[0017] According to one aspect of the invention, an interferometric testing arrangement for testing the surface shape of a test object comprises an illumination 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 at the test object and a reference wave, testing the surface shape of at least a 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 illumination device; wherein the illumination device has a first optical path and a separate second optical path; and wherein the input wave can be coupled into the interferometer via both the first optical path and the second optical path;wherein, when the input wave is coupled via the first optical path, a light spot generated on the diffuser has a first diameter (D1 ), and wherein, when the input wave is coupled via the second optical path, a light spot generated on the diffuser has a second diameter (D2) which differs from the first diameter (D1 ).

[0018] 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.

[0019] The invention is based in particular on the concept of implementing 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. The implementation of said variable illumination of a diffuser according to the invention, described below with reference to the embodiments of Figs. 1a-4c, has advantages over the fundamentally also possible implementation shown below with reference to Figs.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.

[0020] 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.

[0021] According to the invention, 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.

[0022] 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.

[0023] According to one embodiment, the first diameter is less than 10 pm, in particular less than 5 pm. 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.

[0024] According to a further aspect of the disclosure, an interferometric testing arrangement for examining the surface shape of a test object comprises an illumination 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 at the test object and a reference wave, an examination of the surface shape of at least a 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 illumination device; wherein the illumination device has a first optical path and a separate second optical path; and wherein the input wave can be coupled into the interferometer via both the first optical path and the second optical path.

[0025] 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.

[0026] According to one embodiment, the numerical aperture (NA2) present at the diffuser when the input wave is coupled via the first optical path is at least two times larger than the numerical aperture (NA1) present at the diffuser when the input wave is coupled via the second optical path. According to another 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.

[0027] 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.

[0028] 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.

[0029] According to one embodiment, the electromagnetic radiation has a wavelength greater than 500 nm.

[0030] 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.

[0031] According to one embodiment, at least one intermediate image plane is present in the first optical path and / or the second optical path. This design is advantageous insofar as it allows the placement of apertures in the optical beam path, as described below. According to one embodiment, at least one aperture is arranged in the first optical path and / or 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.

[0032] According to one embodiment, the test object is an optical element, particularly for microlithography.

[0033] According to one embodiment, the test object is a mirror, in particular a mirror designed for operation under EUV conditions.

[0034] 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.

[0035] Further embodiments of the invention can be found in the description and the dependent claims.

[0036] The invention is explained in more detail below with reference to exemplary embodiments shown in the accompanying figures.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038] They show:

[0039] Figures 1a-1c are schematic representations to illustrate one possible embodiment of an interferometric test arrangement according to the invention; Figures 2-4c are schematic representations to illustrate further embodiments of a lighting device present in an interferometric test arrangement according to the invention;

[0040] Figures 5a-5b show a schematic representation to illustrate another possible setup of a lighting device present in an interferometric test arrangement; and

[0041] Figure 6 shows a schematic representation of a projection exposure system designed for operation in the EUV.

[0042] DETAILED DESCRIPTION OF PREFERRED EXECUTION FORMS

[0043] Fig. 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.

[0044] According to Fig. 6, a lighting device in a projection exposure system 610 designed for EUV has a field facet mirror 603 and a pupil facet mirror 604. The light from a light source unit, which comprises a plasma light source 601 and a collector mirror 602, is directed onto the field facet mirror 603. In the light path after the pupil facet mirror 604, a first telescope mirror 605 and a second telescope mirror 606 are arranged. Further down the light path is a deflecting mirror 607, 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.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.

[0045] In the following, embodiments of an interferometric test arrangement according to the invention are described with reference to the schematic figures in Figs. 1a-1c, 2 and 3. In each case, for testing 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.

[0046] The embodiments described below with reference to Figs. 1a-1c, 2 and 3 have in common that the illumination device (designated as "105" in Figs. 1a-1c and as "205" and "305" respectively in Figs. 2 and 3) has a first optical path 110 (or 210 or 310) and a separate second optical path 120 (or 220 or 320). During operation of the test arrangement, the device 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).

[0047] Referring initially to Figs. 1a-1c, a lighting device 105 serves to generate an input wave from electromagnetic radiation produced by a (not shown) light source, 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 of more than 500 nm. Thus, in further embodiments, the electromagnetic radiation can also have a different wavelength in the visible or UV range. Fig. 1a shows an enlarged schematic representation of the lighting device 105, whereas Fig. 1b and Fig. 1c show a more detailed representation.Figure 1c also shows the interferometer 150, into which the input wave generated by the illumination device 105 is coupled. Figure 1c depicts the previously described scenario of the actual test specimen measurement, whereas Figure 1b shows the previously mentioned scenario of the adjustment. According to Figure 1b, this adjustment takes place in the optical beam path of the interferometer.

[0048] 150 instead of the test specimen 170 of Fig. 1 c a cat's eye optic, only schematically indicated and labelled "160", was arranged.

[0049] The lighting device 105 comprises 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 rather the diffuser 130, enters an interferometer designated "150" as an input wave, as shown in Fig. 1c. The invention is not limited to a rotatable design of the diffuser 130. Rather, in further embodiments, a movable diffuser (to achieve a reciprocating motion) or, if necessary, a stationary diffuser can also be used.

[0050] This interferometer 150, as shown in Fig. 1c, is implemented as a so-called Fizeau arrangement only by way of example (and without limiting the invention to this arrangement). In this arrangement, the electromagnetic radiation meets the beam via a beam splitter.

[0051] 151 and a collimator 152 onto a Fizeau plate 153, wherein 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, the test wave being reflected at the test object 170 according to Fig. 1c. 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. In further embodiments, the interferometer can also be designed as a so-called "reference mirror arrangement", wherein the reference wave is then generated by reflection at a reference mirror in a manner known per se. For this purpose, reference is made only to DE 10 2019 216 447 A1 as an example.

[0052] As can best be seen from Fig. 1 a, 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.

[0053] 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, and 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 resulting light spot on the diffuser 130, as shown in Fig. 1b, has a comparatively small spatial extent (with a first diameter D1 = 3 pm in the exemplary embodiment).

[0054] In the second optical path 120, in a second operating mode corresponding to the test specimen measurement shown in Fig. 1c, electromagnetic radiation from the second optical fiber 121 passes through 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 onto the incident electromagnetic radiation upon reflection. 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. The radiation emitted by 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, both the dotted and dashed marginal rays are shown for the corresponding beam path along the second optical path 120. In addition to these extremal rays and beam directions shown, the spatial light modulator 123 can also generate the intermediate rays and beam directions. The angular distribution generated by the spatial light modulator 123 corresponds to an intensity distribution on the diffuser 130. The light spot generated on the diffuser 130 in the second operating mode, corresponding to the test specimen measurement scenario, 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 is NA1 = 0, shown only as an example in the exemplary embodiment).(can be 02).

[0055] 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 lens 513 is movable on a diffuser 530, which in the example according to Figures 5a-5b is also rotatable, in order to achieve different diameters D1 (Fig. 5a) and D2 (Fig. 5b). "511" denotes an optical fiber.

[0056] The selective switching between the first optical path 110 according to Fig. 1b and the second optical path 120 according to Fig. 1c, as described in Fig. 1a-1c, enables, according to the invention – in contrast to an embodiment according to Fig. 5a-5b – the flexible switching between a comparatively small light spot generated on the diffuser 130 for the adjustment according to Fig. 1b and a comparatively large light spot generated on the diffuser 130 for the actual test specimen measurement according to Fig. 1c, while ensuring telecentric illumination of the diffuser 130, without placing excessive demands on the spatial extent, number and size of pixels of the spatial light modulator 123 located in the second optical path 120.In other words, by providing two separate optical paths for the two operating modes described above according to the invention, the requirements placed on the spatial light modulator 123 are significantly relaxed 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.

[0057] 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 and 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.

[0058] Although the selective coupling of electromagnetic radiation according to the invention is alternatively realized in the first optical path 110 or in the second optical path 120 via separate optical fibers, both in the embodiment of Fig. 1a-1c and in the further embodiments described below in Fig. 2 to Fig. 3, the invention is not limited to this. In further embodiments, selective coupling of the optical paths can also be achieved via any other suitable coupling optic, e.g., using a tiltable mirror.

[0059] Fig. 2 shows a schematic representation to illustrate a further embodiment, in which, compared to Fig. 1 a-1 c, analogous or essentially functionally identical components are designated with reference numerals increased by 100. According to the embodiment of Fig. 2, in contrast to the embodiment of Fig. 1 a-1 c, an additional intermediate image plane is located in the optical beam path of the second optical path 220. This 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 in the optical far field of the spatial light modulator 223 that is optically conjugate to the diffuser 230.This circular aperture 226 can block 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.

[0060] As shown in Fig. 2, a further aperture 227 is located in the optical beam path between the collimator lens 225 and the beam splitter 213 at a position optically conjugated to the spatial light modulator 223 and clips the typically Gaussian illumination in this area. As schematically illustrated in Figs. 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.

[0061] With reference to Fig. 4a-4c, the schematic representation of Fig. 4a represents the scenario of a point illumination of the diffuser 430, whereas Fig. 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.

[0062] While, according to Fig. 4a, the source point of the electromagnetic radiation emanating from the diffuser 430 lies in the plane of the diffuser 430, according to Fig. 4b, the corresponding source point is shifted by a distance dz. This is 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 results in an undesirable non-perpendicular coupling of the light into the interferometer of the interferometric measuring arrangement following the illumination device, which in turn leads to undesirable measurement errors.

[0063] According to Fig. 4c, 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. As indicated in Fig. 4b, this can be achieved by moving the aperture 427 along the direction of light propagation (corresponding to the z-direction in the coordinate system shown). Moving the aperture 427 perpendicular to the z-direction (i.e., in the x-direction in the coordinate system shown) changes the angle of incidence of all rays equally.

[0064] Fig. 3 shows a schematic representation to illustrate a further embodiment, wherein, in comparison to Fig. 2, analogous or essentially functionally identical components are designated with reference numerals increased by “100”.

[0065] The embodiment according to Fig. 3 differs from that of Fig. 2 in that, firstly, instead of the (intensity) beam splitter 213 of Fig. 2, a polarization beam splitter 313 is provided, which reflects electromagnetic radiation of a predetermined 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, a p-polarizer 315 is located between the collimator lens 312 and the polarization beam splitter 313 in the first optical path 310, and an s-polarizer 328 is located between the spatial light modulator 323 and the collimator 324 in the second optical path 320. “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.

[0066] In the embodiment of Fig. 3, by supplying the polarization beam splitter 313 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).

[0067] The lambda / 4 plate 316, arranged in the optical beam path between the polarizing beam splitter 313 and the focusing lens 314 as shown in Fig. 3, 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.

[0068] 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.

Claims

Patent claims 1. Interferometric test setup for testing the surface shape of a test object, including: • 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); • 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); • wherein 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 wherein 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 ).

2. Interferometric test arrangement according to claim 1, characterized in that during operation of the test arrangement a selective choice is made between a first The operating mode in which the input wave is coupled into the interferometer (150) via the first optical path (110, 210, 310) is switchable, 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 arrangement according to claim 1 or 2, characterized in that the second diameter (D2) is larger than the first diameter (D1) by at least a factor of 10, in particular at least a factor of 100, and further in particular at least a factor of 1000.

4. Interferometric test arrangement according to one of claims 1 to 3, characterized in that the first diameter (D1 ) is less than 10 pm, in particular less than 5 pm.

5. Interferometric test arrangement according to one of the preceding claims, characterized in 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.

6. Interferometric test arrangement according to one of the preceding claims, characterized in that a numerical aperture (NA2) present when the input wave is coupled via the first optical path (1 10, 210, 310) at the diffuser (130, 230, 330) differs from a numerical aperture (NA1) present when the input wave is coupled via the second optical path (120, 220, 320).

7. Interferometric test arrangement according to claim 6, characterized in that the numerical aperture (NA2) present at the diffuser (130, 230, 330) when the input wave is coupled via the first optical path (110, 210, 310) is at least two times larger than that when the input wave is coupled via the second optical path. (120, 220, 320) numerical aperture (NA1) present on the diffuser (130, 230, 330).

8. Interferometric test arrangement according to one of the preceding claims, characterized in that a spatial light modulator (123, 223, 323) is arranged in the second optical path (120, 220, 320).

9. Interferometric test arrangement according to claim 8, characterized in that this spatial light modulator (123, 223, 323) is designed as a phase modulator.

10. Interferometric test arrangement according to one of the preceding claims, characterized in 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 with respect to their wavelength.

11. Interferometric test arrangement according to one of the preceding claims, characterized in that the electromagnetic radiation has a wavelength greater than 500 nm.

12. Interferometric test arrangement according to one of the preceding claims, characterized in 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).

13. Interferometric test arrangement according to one of the preceding claims, characterized in 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). 21 14. Interferometric test arrangement according to one of the preceding claims, characterized in 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).

15. Interferometric test setup according to any one of the preceding claims, characterized in that the test object (170) is an optical element, in particular for microlithography.

16. Interferometric test setup according to any one of the preceding claims, characterized in that the test object (170) is a mirror, in particular a mirror designed for operation under EUV conditions.

17. Method for characterizing the surface shape of a test object using an interferometric test setup according to any one of the preceding claims.

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