Measurement arrangement, ranging device, optical measurement system and method for detecting distance between two elements

Abstract

The invention relates to a measurement arrangement (1) for determining at least one distance between a first and a second optical element (2, 3), the first element (2) being designed in a light-transmissive manner as a measurement array and having a partially reflective first surface (7), the second optical element (3) being designed as an EUV mirror and having an at least partially reflective second surface (8), and the distance between the first element (2) and the second optical element (3) being determined. The first surface (7) and the second surface (8) face each other at a distance to be detected, having a light source (13) and a light sensor (21), light (14) generated by the light source (13) being coupled into the first optical element (2) via a surface (11) different from the first surface (7) in such a way that the light sensor (21) is coupled into the first optical element (2) via a surface (11) different from the first surface (7). The light sensor (21) is arranged such that a first partial light beam (19) is reflected back into the first optical element (2) by the first surface (7) and a second partial light beam (116) penetrating the first surface (7) is reflected back into the first optical element (2) by the second surface (8), and wherein the light sensor (21) is arranged such that it detects the two partial light beams (19, 16) in order to determine the distance from the detected partial light beams (19, 16).

Description

[0001] This application claims the priority of German patent application No. DE 10 2022 207 358.4, which was filed on July 19, 2022, the contents of which are hereby incorporated by reference in their entirety into the present application.

[0002] The invention relates to a measuring arrangement for determining at least one distance between a first and a second optical element, wherein the first element is designed as a measuring array in a light-transmissive manner and has a first, partially reflective surface, wherein the second optical element is designed as an EUV mirror and has a second, at least partially reflective surface, and wherein the first surface is situated opposite the second surface at a distance to be detected.

[0003] The invention also relates to a distance measuring device and an optical measuring system having at least one measuring arrangement as described above.

[0004] The invention also relates to a method for determining said distance between said two elements.

[0005] In optical systems or devices in which one or more light rays are deflected and / or manipulated by a plurality of optical elements, it is important that the distances between these elements are within predetermined tolerances. In particular, in devices for measuring the shape of surfaces by means of optical arrays, such devices are described, for example, in the applicant's as yet unpublished patent application DE 10 2021 202 909.4, the distances between the optical elements must be strictly adhered to. On the one hand, this is to avoid falsification of the measurement results, and on the other hand, to avoid collisions of the optical elements with one another.

[0006] Measuring devices for contactless detection of distances are known from the prior art. In the prior art, a large number of laser measuring instruments that can determine distances can be found. However, the distance that can be detected by these instruments is usually the distance between the laser measuring instrument itself and the inspection object. In order to use this type of laser measuring device in an optical device, such as an array measuring device, the device must be completely modified, because the laser measuring instrument itself requires a large installation space. In other known solutions, the following laser measuring devices are used, by which the thickness and / or the distance of the elements relative to each other can be detected by reflection on the optical element. For example, a corresponding solution is provided by Opto-Alignment Technology Inc., named "Fogale Nanotech Lenscan system". However, in-situ measurements cannot be performed with this system, because, in order to perform the measurement, the measuring instrument must be arranged in the working light path of the optical element.

[0007] The object of the present invention is therefore to provide a measuring arrangement which is designed to save installation space and which also allows a reliable in-situ determination of the distance of two elements relative to one another.

[0008] The technical problem to be solved by the present invention is solved by a measuring arrangement having the features of claim 1. The measuring arrangement has the advantage that the distance to be detected can be reliably determined with only one light source and only one light sensor by only one measuring process. In addition, the light source and the light sensor can be integrated in a measuring system, for example, having the two elements, in a space-saving manner, which enables distance measurement during operation of the measuring device itself, i.e. in-situ distance determination.

[0009] According to the invention, this is achieved in the following manner, that is, the measuring arrangement has a light source and a light sensor, wherein the light generated or can be generated by the light source is deflected by a lens so that the light is coupled into the first optical element through a surface different from the first surface and is focused on the first surface to a focus point, so that the first sub-light is reflected back into the first optical element by the first surface and the second sub-light penetrating the first surface is reflected back into the first optical element by the second surface, and wherein the light sensor is arranged so that the light sensor detects the two sub-lights in order to detect the distance according to the detected sub-lights. In particular, the light source and the light sensor are arranged fixedly relative to the first element. By means of this advantageous measuring arrangement, the light of the light source is therefore reflected both at the first surface and at the second surface and is respectively guided back to the light sensor through the first element. Therefore, both the light source and the light sensor can be arranged on the side of the first optical element facing away from the second optical element and in particular also outside the working light path. It can thus be integrated into a measuring device having the element, the integration does not impair the operation of the measuring device, and thus the distance can also be determined during the ongoing operation of the measuring device having the element. Since the light penetrates the first surface and is also reflected at the second surface, the light is divided into at least two sub-lights, and the light paths of the two sub-lights are different from each other due to the distance between the surfaces. Because the distance between the reflection positions at the first surface and the second surface causes the reflected sub-lights to be spaced apart from each other laterally. The displacement of the sub-lights relative to each other in the reflection section therefore corresponds to the distance between the two elements. The displacement is detected by a light sensor and analyzed to determine the distance. Therefore, in-situ measurement can be achieved by simple and space-saving means, and the distance between the elements can be accurately determined by the in-situ measurement. The first optical element is a measurement array, especially a measurement array as described in the aforementioned earlier patent application DE 10 2021202 909.4 of the applicant. Therefore, the first element is light-transmissive and partially reflective at the first surface, so that a part of the light continues to pass to the second surface to be reflected there. Here, the first surface is designed so that the sub-light reflected back by the second surface is re-coupled into the first element and guided to the light sensor through the first element. Preferably, the curvature of the surface of the first optical element or the measuring array and the curvature of the surface of the second optical element or the EUV mirror are designed inversely relative to one another, so that the two surfaces extend parallel to one another. In addition, the second optical element is an EUV mirror (EUV=extreme ultraviolet radiation). By means of an advantageous design of the measuring arrangement, the EUV mirror can be measured with and without a highly reflective coating.

[0010] According to a preferred embodiment of the invention, the measuring arrangement has a first focusing device, which has at least one first lens and / or at least one mirror, which is arranged between the light source and the first element and is designed in such a way that the first focusing device focuses the light on the first surface to a first focus point. The measurement quality is thereby optimized or the measurement accuracy with respect to the detected distance is increased. In particular, it is ensured that the light is not scattered before reaching the first surface, which would otherwise generate sub-beams that are reflected back to the light sensor and which could distort the measurement result. The focusing ensures that all sub-beams emerge from a focus point on the first surface and thus allows an accurate distance determination.

[0011] Particularly preferably, the light source and the first focusing device, in particular the lens, are arranged and designed such that the focused light impinges on the first surface at an angle (relative to the first surface) different from 90°.

[0012] Furthermore, it is preferably provided that the light source and the light sensor are arranged on the side of the first element facing away from the second element. This ensures that the light is reliably reflected at both surfaces and guided to the light sensor via the first optical element. Furthermore, this enables advantageous integration into existing measuring systems.

[0013] According to a preferred embodiment of the present invention, the light source and the first focusing device, in particular the lens of the first focusing device, are arranged and designed so that the light from the light source is coupled into the first optical element through the surface at an angle different from 90° relative to the surface at the coupling-in position.

[0014] The light is coupled into the first optical element via the surface at an angle relative to the surface which is preferably less than 75°, preferably less than 45° and particularly preferably less than 30°.

[0015] Preferably, the light source is arranged laterally next to a (virtual) axis oriented perpendicularly to the surface. The axis can be the axis of symmetry of the first optical element. This makes it possible to integrate the measuring arrangement into an existing measuring system without affecting the optics of the measuring system. The light source is arranged opposite the test object, in particular opposite the surface or laterally next to the surface, or the light source is laterally next to the test object. Preferably, the light sensor is also arranged laterally, in particular laterally next to an axis oriented perpendicularly to the surface, wherein the light source and the light sensor are preferably arranged on opposite sides of the (virtual) axis, i.e. separated by the (virtual) axis.

[0016] In this context, it is provided in particular that the angle between the light source and the axis is less than 120°, preferably less than 90° and particularly preferably less than 45°.

[0017] Furthermore, it is preferred that the light source is arranged, in particular laterally, such that the beam emitted by the light source impinges on the surface at an angle α, wherein the angle α is smaller than 75°, preferably smaller than 45° and particularly preferably smaller than 30°.

[0018] Preferably, the first lens of the first focusing device and / or the second focusing device is designed in such a way that the refraction effect of the light at the surface through which the light is coupled into the first element is corrected or compensated. In particular, the lens has a shape provided for this purpose. Preferably, the lens is designed to be non-rotationally symmetrical for this purpose and deviates in particular from a rotationally symmetrical lens for this purpose by more than 1 μm. Alternatively or additionally, the lens is preferably tilted about an axis oriented in particular perpendicular to the main ray direction of the light in order to perform the correction or compensation. Optionally, the lens is composed of a plurality of lenses and / or mirrors, wherein at least one lens deviates from the rotational symmetry by more than 1 μm.

[0019] According to a preferred extended design of the present invention, at least one second focusing device is arranged between the first element and the light sensor, and the second focusing device has at least one second lens and / or has at least one mirror, and the reflected sub-light is deflected to the light sensor through the second focusing device. Therefore, the light sensor can reliably detect the sub-light by means of the second focusing device, especially the second lens. Optionally, the first and / or second lens are respectively configured with at least one other optical element, especially another lens or mirror, of the corresponding focusing device, and the light and / or sub-light are deflected by the other optical element, so that the light source and / or the light sensor can be flexibly arranged relative to the optical element.

[0020] Preferably, the second lens or the lens of the second focusing device is designed and arranged to focus the sub-light beams onto the light sensor so that each sub-light beam has its own focal point, which can be detected by the light sensor. In particular, the light sensor is designed to detect the position of the focal points of the sub-light beams so as to determine the distance of the focal points relative to each other based on the detected position. Since the distance between the focal points corresponds to the distance between the elements, an advantageous determination of the distance between the elements is ensured. By forming the focal points of the sub-light beams, the corresponding distance can be determined particularly accurately. Preferably, the light sensor is designed as a camera sensor or a line scanner in order to detect the focal points of the sub-light beams. By preferably focusing both on the first surface or the gap area and on the light sensor, on the one hand, an accurate determination of the distance is ensured. On the other hand, a tilting of the first and / or second optical element does not lead to an erroneous distance signal.

[0021] According to a preferred embodiment of the present invention, the light sensor has a flat sensor surface, wherein at least one second lens is designed and arranged to focus the sub-light beam onto the sensor surface. Therefore, the focal point of the sub-light beam is located on the sensor surface and is detected with high precision. The smaller the focal point, the more accurately the position of the corresponding sub-light beam on the sensor surface is determined. In particular, the light sensor or the controller of the measuring arrangement structure is designed to determine the distance of the elements relative to each other based on the position of the focal point of the sub-light beam on the sensor surface. Here, the following fact is used, that is, as the distance changes, the position of the focal point of the sub-light beam on the sensor surface also moves. Therefore, there is a direct geometric connection between the distance to be detected and the position of the focal point on the sensor surface, and the distance is determined by using this geometric connection.

[0022] In a preferred embodiment, the light source and the first lens or the lens of the first focusing device are arranged so that the generated light is coupled into the first element via the surface of the first element opposite the first surface. In this case, the refractive index at the further surface is taken into account by the design of the first lens, so that the focusing point of the light is located on the first surface. Therefore, the first lens is designed according to the refractive index, the angle of incidence of the light on the further surface and the geometry of the first element.

[0023] According to an alternative embodiment, the light source and the first lens are arranged so that the generated light is coupled into the first element through another surface of the first element arranged laterally relative to the first surface. As a result, the measuring arrangement is designed to be flatter in its construction (relative to the working light path of the first element). Therefore, the integration of the measuring arrangement in an existing measuring system or optical device can be further simplified. In addition, for example, a plurality of measuring arrangements according to the present invention can be provided, and the light of these measuring arrangements is coupled into the first element at different positions and different surfaces, so that the corresponding light sensor only detects the sub-light of the light source corresponding to it and reliably avoids erroneous measurements. The surface arranged laterally can be located next to the surface in the continuation of the surface, or can be oriented at an angle of, for example, 30° to 120°, especially 90°, relative to the surface.

[0024] Preferably, the surface of the second element or the EUV mirror is designed to be aspherical, in particular to be an aspherical surface, or to be a free-form surface (or a free-form curved surface).

[0025] If the second element has at least one coating on the second surface, the coating effect makes the sub-light be reflected both at the coating surface and at the boundary surface below it relative to the second optical element, then two other sub-lights are formed by the sub-light, and the two other sub-lights are reflected and coupled back into the first element and guided to the light sensor through the first element. It is therefore possible to detect the height of the second distance or coating. Here, when the coating height is known, the coating height is preferably used as a reference to calibrate the light sensor to determine the distance between the elements. Alternatively, multiple distances, such as the distance of the first surface relative to the surface coating and the distance relative to the boundary surface or relative to another boundary surface in the second element are detected by the light sensor. Preferably, at least one coating has a layer height of 10nm to several microns, so that the layer effect is small in some cases during the measurement process or can no longer be detected due to inaccurate measurement. However, the measurement data can still be corrected based on the known layer thickness. Through a favorable measurement arrangement structure, at least the center of gravity can be corrected.

[0026] The distance measuring device according to the invention having the features of claim 14 is characterized in that at least one measuring arrangement according to the invention as described above is provided. This results in the advantages already mentioned. In particular, the distance measuring device has a housing in which the light source and the light sensor and optionally the first lens and the second lens are arranged.

[0027] Particularly preferably, the distance measuring device has two, three or six measuring arrangements according to the present invention as described above, wherein the focal points of the light rays are located on the first surface of the first optical element at intervals from one another. The distance between the two elements at different positions is thus detected so as to thereby determine the orientation of the two elements relative to one another. In particular, it is determined by three measuring arrangements whether the two elements are arranged parallel to one another or arranged in a desired orientation relative to one another. For a distinct free-form surface, six measuring arrangements are preferably used. Therefore, these measuring arrangements are not only used to detect distances, but also to detect orientations. Preferably, the distance measuring device has a controller, which is designed to control one or more light sources and to determine one or more detected distances by analyzing sensor signals of one or more light sensors.

[0028] The optical measuring system according to the invention with the features of claim 16 is characterized in that it is provided with a distance measuring device according to the invention. This results in the advantages already mentioned. In particular, the measuring system has at least one actuator, which is designed and / or arranged to adjust or change the distance between surfaces or between optical elements and / or the orientation of optical elements relative to each other. The optical measuring system has in particular at least one own measuring light source and at least one own measuring sensor for detecting the light generated by the measuring light source, which light is reflected in particular at the test object to be measured in order to in particular detect the shape or surface shape of the test object. The path of this light is also referred to as the working light path of the measuring system. In other words, the measuring system has a separate measuring light source, and the distance measuring device in turn has at least one own, separate (additional) light source.

[0029] Particularly preferably, the light path of the corresponding light of at least one measuring arrangement structure is different from the working light path of the measuring system for surface shape measurement, for which preferably, the coupling-in position of the light input into the first element of the distance measuring device and / or one / more coupling-out positions of the sub-light output from the first element are located outside the working light path. Therefore, the light path of the distance measuring device is at least partially, preferably completely, located outside the working light path. It is achieved thereby that the distance of the first optical element relative to the second optical element can also be determined in situ in the inspection system, for example, in particular in the optical measuring system in the above-mentioned DE 102021 202 909A1, i.e., determined during the ongoing operation of the measuring system. Particularly preferably, the coupling-in position and one / more coupling-out positions are both located outside the working light path. Alternatively or additionally, the light source and optionally the first lens and / or the light sensor and optionally the second lens are preferably arranged outside the working light path of the measuring system relative to at least one, preferably each measuring arrangement structure of the distance measuring device. According to one embodiment, the light source, the coupling-in position and the first lens as well as the light sensor, the coupling-out position(s) and the second lens are all located outside the working light path, thereby avoiding overall influence on the measuring system when detecting the distance. According to an alternative embodiment, the coupling-in position or the coupling-out position(s) or the coupling-in position and the coupling-out position(s) are located within the working light path. Thus, the light generated by the light source extends at least in sections through the working light path of the measuring system. This makes it possible, for example, to achieve a particularly space-saving variant of the measuring system.

[0030] The method according to the invention with the features of claim 21 is characterized in that the light source is controlled in such a way that the light is coupled into the first optical element via a surface different from the first surface of the first element, so that a first sub-light beam is reflected back into the first optical element by the first surface and a second sub-light beam penetrating the first surface is reflected back into the first optical element by the second surface, and wherein the two sub-light beams are detected and the distance of the first and second surfaces relative to one another is determined based on the detected sub-light beams. This results in the advantages already mentioned.

[0031] Preferably, the light is focused by the first lens in such a way that the focal point of the light is located at the first surface. Furthermore, preferably, the second lens is arranged and designed in the light path between the first element and the light sensor in such a way that the partial light beams are conveyed to the light sensor and are in particular focused respectively onto the sensor surface of the light sensor.

[0032] Further advantages and preferred features and feature combinations are particularly apparent from the claims and the preceding description. The invention is explained in detail below with reference to the accompanying drawings. In the drawings:

[0033] Figure 1 An advantageous measuring arrangement according to a first embodiment is shown;

[0034] FIG. 2A and FIG. 2B show Figure 1 Detailed view of the measurement arrangement in ;

[0035] Figure 3 A simplified diagram showing an optical measurement system having an advantageous measurement arrangement; and

[0036] Figure 4 A flow chart is shown which explains a method for operating a measuring arrangement.

[0037] Figure 1 A simplified side view of an advantageous measuring arrangement 1 is shown, which is designed for detecting the distance between two optical elements 2, 3. In the present example, the optical elements 2, 3 are a test object 5 and a measuring array 6, wherein the measuring array 6 has a reference shape for optically checking the surface shape of the test object 5 or the elements 3. In this case, the first element 2 has a first surface 7, which is spaced opposite to a second surface 8 of the second element 3.

[0038] The element 2 is therefore part of an optical measuring system 4 or an array measuring system, which is only partially shown here, by which the test object can be checked. The measuring system 4 is in particular a measuring system for performing interferometric shape measurements on the test object 5. Such a measuring system 4 is described, for example, in the patent application DE 10 2021 202 909 A1.

[0039] The test object 5 or the optical element 3 is an EUV mirror for EUV lithography or microlithography, for which the surface 8 is particularly designed as an aspherical, particularly as an aspherical surface or as a free-form surface to reflect EUV radiation, particularly EUV radiation with a wavelength of less than 100 nm. The surface 8 is designed to be uncoated, coated and / or highly reflective. The surface 8 optionally has one or more coatings, by which the reflection quality and the reflection quantity are improved.

[0040] In order to test the functionality of the mirror element, the surface 8 of the test object 5 facing the measuring array 6 is checked by the measuring system 4 to see whether it has the required desired shape.

[0041] The deviation of the actual shape of the surface 8 from the desired shape is determined as a result of the shape measurement. The desired shape can be related to a reference shape or surface 7. In particular, the desired shape corresponds to the reference surface or first surface 7, so that the surfaces 7, 8 are designed inversely relative to each other or extend parallel to each other. Alternatively, the desired shape deviates from the reference surface.

[0042] In order to measure the surface shape, for example, laser light is coupled into the element 2 via a further surface 11 facing away from the first surface 7, so that the laser light penetrates the element and is partially reflected at the surface 8, so that one sub-beam is reflected at the surface 7 and one sub-beam is reflected at the surface 8. For this purpose, Figure 1 1 and 2 are schematically shown by dashed lines in the figure, showing the working beam path 12 of the measuring system 4. By means of an interferometric analysis of the reflected partial beams, a measuring signal provides the distance between the surface 7 and the surface 8.

[0043] By means of the advantageous measuring arrangement 1, the distance between the elements 2 and 3 can also be determined in situ in the measuring system 4. This is particularly advantageous in cases where, for example, a reference object, in this case the element 2, is movably mounted in order to carry out a test process. Due to this movably mounted mounting, an exact arrangement of the element 2 relative to the element 3 is necessary so that the surfaces 7 and 8 lie opposite one another in the desired orientation and extend, for example, parallel to one another. In order to be able to adjust this orientation exactly and to prevent the element 2 from hitting the element 3, the distance is advantageously detected and monitored by the measuring arrangement 1. The element 2 and the element 3 preferably each have a simple spherical geometry.

[0044] For this purpose, the measuring arrangement 1 has a light source 13, in particular a light source 13 separate from the measuring system 4, which is designed to generate light 14. The light source 13 is designed for this purpose, for example, as an LED device, a fiber laser or a laser device or as another light source for generating structured light.

[0045] The light source 13 is assigned a first lens 15, through which the generated light 14 is focused before it is irradiated onto the first element 2. The light source 13 and the lens 15 are arranged and designed in such a way that the light 14 is coupled into the element 2 via the surface 11. The light source 13 and the lens 15 are also arranged and designed in such a way that the light 14 focused by the lens 15 has its focus point F at the surface 7. 14 The light 14 is also coupled obliquely into the optical element 2 via the surface 11, so that the light 14 is directed at an angle different from 90° to the surface at the coupling location.

[0046] Preferably, the first lens 15 is designed in such a way that the refraction effect of the light 14 at the surface 11, through which the light 14 is coupled into the first element 2, is corrected or compensated. In particular, the lens 15 has a shape provided for this purpose. Preferably, the lens 15 deviates from a rotationally symmetrical lens by more than 1 μm for this purpose. Alternatively or additionally, the lens 15 is preferably tilted about an axis which is oriented, in particular, perpendicular to the main ray direction of the light or perpendicular to the plane of the image, in order to perform the correction or compensation. Optionally, the lens 15 is composed of a plurality of lenses and / or mirrors, wherein at least one of the lenses 15 deviates from the rotational symmetry by more than 1 μm.

[0047] The light source 13 is arranged laterally, in particular, outside the working light path 12. In particular, the light source 13 is arranged laterally next to an axis oriented perpendicularly to the surface 11, which axis in particular extends through the coupling-in location. The angle between the light source 13, in particular the light or light bundle emitted by the light source 13, and the axis is less than 120°, preferably less than 90° and particularly preferably less than 45°.

[0048] Alternatively or additionally, the light source 13 can also be arranged such that the light beam emitted by the light source 13 impinges on the surface 11 at an angle α, wherein the angle α is smaller than 75°, preferably smaller than 45° and particularly preferably smaller than 30°.

[0049] FIG2A shows that Figure 1 Detailed view of the area marked by the dashed box K1 in FIG. In this area, the focus point F of the light 14 14 Located at the first surface 7 of the element 2. Preferably, the wavelength of the light 14 differs from the useful wavelength of the measuring system by more than 10 nm. The surface 7 is designed to be partially reflective, so that the light 14 is reflected back at the surface 7 in the sub-light 19 in the direction of the surface 11. Figure 1As shown, another sub-light 16 from the light 14 penetrates the surface 7 and hits the surface 8 and is reflected by the surface back in the direction of the element 2, where the sub-light 16 is coupled back into the element 2 through the surface 7 and is redirected toward the surface 11. Since the sub-light 16 and the sub-light 19 are fan-shaped due to reflection, Figure 1 FIG. 2B shows a plurality of fan-shaped rays for the respective partial light beams 16 , 19 .

[0050] exist Figures 1 to 3 2 and 3 are shown by way of example at a plurality of distances of the elements 2 and 3 relative to one another, wherein the smaller distance of the surface 8 of the second element 3 relative to the surface 7 is provided with the reference numeral 9 and the smaller distance relative to the surface 7 is provided with the reference numeral 10. Depending on the distance, the obliquely incident sub-ray 16 is reflected at different positions. Thus, the sub-ray 16 is reflected as the sub-ray 18 according to the smaller distance defined by the surface 9, and the sub-ray 16 impinging on the surface 10 is reflected as the sub-ray 17. The sub-rays 17, 18 are also reflected back to the element 2, coupled in via the surface 7 and coupled out via the surface 11.

[0051] The measuring arrangement 1 further comprises a second lens 20 and a light sensor 21. The light sensor 21 comprises a sensor surface 22 which is in particular of planar design and to which the lens 20 deflects the partial light beam 19 and the corresponding partial light beams 16, 17 or 18 in such a way that (depending on the current distance between the elements 2, 3) a focus point F is respectively present on the sensor surface 22. 19 and F 16 、F 17 or F 18 The light sensor 21 is, for example, a camera sensor, in particular a line scanner, wherein the sensor surface 22 is formed by the sensor.

[0052] In this example, lens 15 forms a first focusing device and lens 20 forms a second focusing device. Optionally, at least one of these focusing devices has at least one further optical element, such as, in particular, a lens and / or a mirror, in order to advantageously focus the corresponding light beam or partial light beam.

[0053] By focusing the sub-rays onto the sensor surface 22, they can be positioned on the sensor surface 22 by the camera sensor or the light sensor 21. According to this embodiment, the distances of the light source 13, the lens 15, the lens 20 and the light sensor 21 relative to the element 2 are always the same or fixed. Only the element 3 is moved to a measuring position close to the element 2.

[0054] In this regard, FIG. 2B shows Figure 1Detailed view of the dashed box K2 in FIG. 2 . The lens 20 is designed in such a way that it focuses the partial light rays 16 to 19 coupled out of the surface 11 or the element 2 onto the sensor surface 22 .

[0055] Due to the geometrical conditions and the known material and the resulting refractive index, the focal point F 19 and F 16 The displacement or distance relative to each other corresponds to the distance of the surfaces 7 and 8 relative to each other. 19 Relative to the focal point F 17 The displacement of corresponds to the distance of the surface 7 relative to the surface 10 or the minimum distance of the elements 2, 3 relative to each other in this example. 19 Relative to the focal point F 18 The distance corresponds to the distance of surface 7 relative to surface 9 or the intermediate distance shown.

[0056] Thus, the distance between the surfaces 7, 8 and the distance between the reflective surfaces or boundary surfaces of the coatings 9 and 10 can be detected by the measuring arrangement 1. Assuming that the coatings 9 and 10 have known thicknesses, the focal point F 17 、F 16 and F 18 The distances relative to one another can be used as reference values ​​for calibrating the light sensor 21 in order to determine the correct dimension for evaluating the distance of the surface 7 relative to the surface 8 .

[0057] The lenses 15 and 20 have, in particular, an xy polynomial description on one side, ie they are not rotationally symmetrical aspherical surfaces. Aberrations caused by the oblique coupling into the element 2 are advantageously corrected by the violation of symmetry.

[0058] Advantageous measuring arrangement 1 allows distance measurement accuracies of up to 1 μm to be achieved within a measuring range of up to 10 mm. If light sensor 21 is designed as a line scan camera, the measurement is performed in a measuring time of less than 10 μs.

[0059] By means of the advantageous design of the measuring arrangement 1, the transmitter, i.e. the light source 13 and the first lens 15, and the receiver, i.e. the light sensor 21 and the second lens 20, are arranged outside the working light path 12, in particular laterally relative to the axis perpendicular to the surface 7. Alternatively, however, only the light source 13 and optionally the first lens 15 or only the receiver can be arranged outside the working light path 12, in particular laterally relative to the axis perpendicular to the surface 7. Thus, the transmitter and the receiver together with the optical element 2 form an advantageous distance measuring device 23. The measuring arrangement 1 or the distance measuring device is thereby advantageously integrated into the measuring system 4, thereby also ensuring in-situ measurement of the distance.

[0060] According to the present embodiment, light is coupled in and coupled out via a surface 11, which is designed on the side of the element 2 facing away from the surface 7. In the present embodiment, the coupling-in position and the coupling-out position are located within the working light path 12. According to other embodiments, at least the coupling-in position or the coupling-out position is located outside the working light path 12. The coupling-in position and the coupling-out position can also both be located outside the working light path 12. Optionally, the surfaces 7 and 11 are provided with a coating with a predetermined refractive index in the region of the corresponding coupling position, by which the coupling-in and coupling-out are improved.

[0061] Figure 3 A further embodiment of a measuring arrangement 1 in a measuring system 4 is shown. In this case, the distance measuring device 23 has two measuring arrangements 1, namely a measuring arrangement 1A and a measuring arrangement 1B. The measuring arrangements 1A and 1B are at least substantially based on Figure 1 The measurement arrangement structure 1 is designed with the differences described below, and these differences can also be described separately or in combination in Figure 1 Identical elements are provided with the same reference numerals, wherein the corresponding reference numerals are additionally provided with A or B in order to distinguish between the measuring arrangements 1A and 1B.

[0062] The measuring arrangement 1A differs from the measuring arrangement 1 in that the light source 13A and the lens 15A are arranged and oriented in such a way that the light 14A of the first measuring arrangement 1A is not coupled into the element 2 via the surface 11, but via the surface 24 or the side arranged laterally relative to the surface 7. The reflected partial light beams 15A and 16A are coupled out from the surface 11 in the region of the working light beam path 12, so that, as described above, they strike a receiver consisting of the lens 20 and the light sensor 21, in particular a line array camera. As a result, the light 14A is coupled into the element 2 outside the working light beam 12 and is coupled out within the working light beam 12.

[0063] The measuring arrangement 1B differs from the measuring arrangement 1 in that the light 14B generated by the light source 13B is coupled into the element 2 via the surface 11 by means of the lens 15 and is reflected on the surfaces 7, 8 as described above. However, in contrast to the previous embodiment, the reflected sub-light beams 19B and 16B are not coupled out of the element 2 in the region of the working light beam path 12 but in a section of the surface 11 spaced apart and adjacent thereto and are conveyed to the second lens 20B and the second light sensor 21B. Thus, the light 14 is coupled into the element 2 within the working light beam 12 and is coupled out outside the working light beam 12. In this case, not only the distance of the elements 2 and 3 relative to each other but also their orientation can be easily determined in one measuring process by the distance measuring device 23.

[0064] Preferably, the measuring device has at least one further measuring arrangement 1C, which is designed to correspond to the measuring arrangement 1, 1A or 1B or a combination thereof. The three measuring arrangements 1A, 1B and 1C are designed in such a way that they detect the distance between the elements 2 and 3 or between the surfaces 7 and 8 at three different positions that are not in a line, so that the three-dimensional orientation of the elements 2 and 3 relative to each other can be detected.

[0065] Optionally, at least one of the measuring arrangements 1A, 1B and / or 1C, a plurality of the measuring arrangements 1A to 1C or each of the measuring arrangements 1A to 1C is designed in such a way that the corresponding light is coupled into the element 2 outside the working light path 12 and coupled out from the element 2 outside the working light path 12. The relevant light is coupled in, for example, via side walls spaced apart from the surface 11 and coupled out from the side walls, in particular as partial light, wherein the side walls are each oriented laterally, in particular at an angle of, for example, 45° to 90°, relative to the surface 11. The measuring arrangements 1A to 1C can be designed identically or differently in relation to the working light path 12.

[0066] Optionally, the measuring system 4 has a controllable actuator 25, by means of which the measuring array 6 or the element 2 can be moved relative to the test object 5 or the element 3, for example in order to adjust the orientation of the surfaces 7, 8 relative to one another. Thus, in conjunction with the measuring arrangement 1 and / or 1A, 1B and 1C or with the distance measuring device 23, an orientation of the test object and the array relative to one another can be achieved without them colliding by controlling the actuator 25 as a function of the measurement results.

[0067] Figure 4 An advantageous operating method for operating the measuring system 4 is shown. In a first step S1, the measuring process is started and the corresponding light source 13 or 13A, 13B and / or 13C is activated. In a subsequent step S2, the focus point F is detected by a light sensor, in particular a line scan camera. 19 And depending on the distance formed by adjustment, the focus point F is detected 16 、F 18 or F 17 , and determine the distances of these focus points relative to each other on the corresponding sensor surface 22 or 22A, 22B, 22C.

[0068] In a subsequent step S3 , the distance of the surface 7 relative to the surface 8 at the reflection point is calculated from the detected distances of the focus points relative to one another, wherein the geometry and the refractive index of the distance measuring device 23 are taken into account.

[0069] In a subsequent step S4, it is checked whether one or more of the detected distances falls below or exceeds a predefined limit value and / or whether the orientation of the surface 7 relative to the surface 8 corresponds to a desired orientation. If this is not the case (n), in a step S5, the actuator 25 is actuated to change the orientation of the measuring array 6 to correct the distance and / or orientation. In the process, it is ensured by determining the one or more distances that the actuator is actuated in such a way that the measuring array 6 does not strike the test object 5. As soon as the distance and / or orientation corresponds to the desired value (j), the method is terminated in a step S6 and the measuring system 4 can start the actual form measurement of the surface 8 of the test object 2.

[0070] For spherical or nearly spherical surfaces, three measuring positions or three measuring arrangements are sufficient to avoid mutual collisions of the elements 2, 3. The deviation from the spherical shape must be less than the permissible minimum distance. For clearly free-form surfaces, preferably six measuring arrangements or measuring positions are present in order to determine all six degrees of freedom (x, y, z displacements and rotations about the x, y, z axes) and thus reliably avoid collisions.

Claims

1. A measuring arrangement (1) for determining at least one distance between a first and a second optical element (2, 3), wherein: The first element (2) is designed as a measuring array (6) in a light-transmissive manner and has a partially reflective first surface (7), wherein the second optical element (3) is designed as an EUV mirror and has an at least partially reflective second surface (8), and wherein the first surface (7) and the second surface (8) are opposite each other at a distance to be detected, and the measuring arrangement has a light source (13) and a light sensor (21), wherein the light (14) generated by the light source (13) is coupled into the first optical element (2) via a surface (11) different from the first surface (7) in such a way that a first sub-light beam (19) is reflected back into the first optical element (2) by the first surface (7) and a second sub-light beam (16) penetrating the first surface (7) is reflected back into the first optical element (2) by the second surface (8), and wherein the light sensor (21) is arranged in such a way that it detects the two sub-light beams (19, 16) in order to determine the distance based on the detected sub-light beams (19, 16).

2. The measuring arrangement according to claim 1, characterized in that A first focusing device having at least one lens (15) and / or a mirror is arranged between the light source (21) and the first element (2) and is designed such that the first focusing device focuses the light (14) on the first surface (7) to a first focusing point (F14).

3. The measuring arrangement according to claim 2, characterized in that The light source (13) and the lens (15) are arranged and designed in such a way that the focused light (14) impinges on the first surface (7) at an angle different from 90°.

4. The measuring arrangement according to any one of the preceding claims, characterized in that The light source (13) and the light sensor (21) are arranged on a side of the first element (2) facing away from the second element (3).

5. The measuring arrangement according to any one of the preceding claims, characterized in that The light source (13) and the first focusing device, in particular the lens (15), are arranged and designed in such a way that the light (14) of the light source (13) is coupled into the first optical element (2) via the surface (11) obliquely, in particular at an angle different from 90° relative to the surface at the coupling-in position.

6. The measuring arrangement according to claim 5, characterized in that The angle is less than 75°, preferably less than 45° and particularly preferably less than 30°.

7. The measuring arrangement according to any one of the preceding claims, characterized in that At least one second focusing device having at least one lens (20) and / or at least one mirror is arranged between the first element (2) and the light sensor (21), by means of which the partial light beams (19, 16) are directed toward the light sensor (21).

8. The measuring arrangement according to any one of the preceding claims, characterized in that At least one lens (15, 20) of the first and / or second focusing device is designed to be rotationally asymmetrical and in particular has a deviation from rotational symmetry of more than 1 μm, in particular more than 10 μm.

9. The measurement arrangement according to claim 7, characterized in that The lens (20) of the second focusing device is designed and arranged to focus the sub-light beams (19, 16) onto the light sensor (21) so that each sub-light beam (19, 16) has its own focusing point (F 19 、F 16 ), the focus point can be detected by the light sensor (21).

10. The measuring arrangement according to any one of the preceding claims, characterized in that The light sensor (21) has a flat sensor surface (22), and at least one second lens (20) is designed and arranged to focus the partial light beams (19, 16) onto the sensor surface (22).

11. The measuring arrangement according to any one of the preceding claims, characterized in that The light source (13) and the first lens (15) are arranged in such a way that the generated light (14) is coupled into the first element (2) via a surface (11) opposite the first surface (7).

12. The measuring arrangement according to any one of claims 2 to 11, characterized in that The light source (13) and the lens (15) of the first focusing device are arranged such that the generated light (14) is coupled into the first element (2) via a surface (24) of the first element (2) arranged laterally relative to the first surface (7).

13. The measuring arrangement according to any one of the preceding claims, characterized in that The surface (8) of the second element (2) is designed to be aspherical, in particular as an aspherical surface or as a free-form surface.

14. A distance measuring device (23) for detecting the distance between a first and a second element (2, 3), wherein: The first element (2) is designed to be light-transmissive and have a partially reflective first surface (7), wherein the second optical element (3) has an at least partially reflective second surface (8), wherein the first surface (7) and the second surface (8) are opposite each other at a distance to be detected, characterized in that at least one measuring arrangement structure (1; 1A, 1B, 1C) according to any one of claims 1 to 13 is provided.

15. The distance measuring device according to claim 14, characterized in that: Two, three or six measuring arrangements (1A, 1B, 1C) are provided according to any one of claims 1 to 13, wherein the focus (F 19 、F 16 ) are located on the first surface (7) of the first optical element (2) at a distance from each other.

16. An optical measuring system (4), in particular an array measuring system, for inspecting the shape of an optical surface of an inspection object (5) by means of an optical measuring array (6) as a first optical element (2), wherein: The test object (5) can be arranged as a second optical element (3) opposite to a measuring array (6), wherein optionally the distance and / or orientation of the first optical element (2) relative to the second optical element (3) can be changed by at least one actuator (25), characterized in that a distance measuring device (23) according to claim 14 or 15 is provided.

17. The optical measuring system (4) according to claim 16, characterized in that The beam path of a corresponding light beam (14) of at least one measuring arrangement (1, 1A, 1B, 1C) differs from the working beam path (12) of the measuring system (4) for surface form measurement.

18. The optical measuring system (4) according to claim 16 or 17, characterized in that The light source (13) and the first lens (15) and / or the light sensor (21) and the second lens (20) of at least one measuring arrangement (1, 1A, 1B, 1C) of the distance measuring device (23) are arranged outside the working light path (12) of the measuring system (4).

19. The optical measurement system according to any one of claims 16 to 18, characterized in that Light (14) of at least one measuring arrangement (1A, 1B, 1C) or at least one of the measuring arrangements (1A, 1B, 1C) is coupled into a first optical element (2) and / or coupled out of the first optical element outside a working light path (12) of a measuring system (4).

20. The optical measurement system according to any one of claims 16 to 19, characterized in that Light (14) of at least one measuring arrangement (1A, 1B, 1C) or at least one of the measuring arrangements (1A, 1B, 1C) is coupled into a first optical element (2) and / or coupled out of the first optical element within a working light path (12) of a measuring system (4).

21. A method for detecting the distance of a first optical element (2) relative to a second optical element (3), in particular by means of a distance measuring device (23) according to claim 13 or 14, wherein: The first element (2) is designed to be light-transmissive and have a partially reflective first surface (7), wherein the second optical element (3) has an at least partially reflective second surface (8), and wherein the first surface (7) and the second surface (8) are opposite each other at a distance to be detected, characterized in that the light source (13) is controlled in such a way that the light (14) is coupled into the first optical element (2) via a surface (11, 24) different from the first surface (7) of the first element (2), so that a first sub-light (19) is reflected back into the first optical element (2) by the first surface (7) and a second sub-light (16) that penetrates the first surface (7) is reflected back into the first optical element (2) by the second surface (8), wherein the two sub-lights (19, 16) are detected, and wherein the distance between the first and second surfaces (7, 8) relative to each other is determined based on the detected sub-lights (19, 16).

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