Measuring apparatus for interferometric shape measurement

Abstract

The present invention relates to a measuring apparatus (10) for measuring the interference shape of the surface (12) of a test object (14-1; 14-2), the measuring apparatus comprising: a diffractive optical element (26-1; 26-2) for generating a test wave (28) from a measurement radiation (18) that has been radiated into the test object, the test wave being configured to radiate onto the surface of the test object; a deflection element (22) upstream of the diffractive optical element in the beam path of the measurement radiation; and a holding device (24, 124) for holding the deflection element, the holding device being configured to change the position of the deflection element (22) by a combination of tilting motion and translational motion.

Description

[0001] This application claims priority to German patent application 10 2020 201 958.4, dated February 17, 2020. The entire disclosure of that patent application is incorporated herein by reference. Background Technology

[0002] This invention relates to a measuring apparatus and method for measuring the interference shape of the surface of a test object. For example, microlithography optical elements can be used as test objects. Due to the need for smaller structures, higher demands are placed on the optical properties of the optical elements used in microlithography. Therefore, the optical surface shape of these optical elements must be determined with the highest possible accuracy.

[0003] Interferometric apparatuses and methods using diffractive optical elements to generate test and reference waves from an input wave are known for high-accuracy interferometry of optical surfaces down to the sub-nanometer scale. Diffractive optical elements allow the wavefront of the test wave to be fitted to the target surface of the test object, such that the wavefront is incident substantially perpendicularly at every location on the target shape and reflected back to itself. The deviation from the target shape can then be determined using an interferogram formed by superimposing the reflected test wave onto the reference wave.

[0004] US 7,061,626 B2 describes an interferometric measuring apparatus having a Fizeau element as a reference element for generating a reference wave and a computer-generated hologram (CGH) for at least partially adapting the wavefront of a test wave to the surface to be measured. Furthermore, US2018 / 0106591A1 describes an alternative embodiment of the measuring apparatus mentioned in the introduction, wherein a complexly coded computer-generated hologram (CGH) is used as a diffractive optical element. From the input wave, the CGH generates a test wave pointing towards the surface to be measured and a plane reference wave traveling in separate reference arms. The reference wave is reflected back to the CGH by a reflective optical reference element.

[0005] When using measuring equipment to measure test objects with different target shapes, different CGHs are typically used. To measure new test objects of different types, the previous CGH used to measure the first test object is therefore replaced by a CGH adapted to the target shape of the new test object. If the angle of incidence on the CGH remains unchanged, the new CGH usually needs to change the position of the test object, and if applicable, the position of the reference element also needs to be changed. This results in high space requirements within the interferometer, making the compact design of the interferometer very difficult.

[0006] This problem is addressed in US 7,061,626 B1 by configuring the CGH in a manner that keeps the position of the test object substantially the same. However, such a CGH configuration implies that the CGH must be illuminated at different incident angles. In the aforementioned prior art, prisms with different configurations are used to generate different incident angles. In each case, the prism configured to generate the desired incident angle is arranged in the beam path upstream of the corresponding CGH.

[0007] However, the use of different prism configurations to generate different incident angles results in a significant amount of changeover work on the measuring equipment, thus making its operation inflexible. Furthermore, this process involves considerable cost, as prisms adapted to the corresponding CGH must be specially manufactured.

[0008] Purpose of the invention

[0009] The object of this invention is to provide a measuring device and method for solving the aforementioned problems. In particular, the object of this invention is to provide a measuring device and method that can measure test objects with different surface shapes without requiring major conversion work. Summary of the Invention

[0010] The above objective can be achieved, for example, by using a measuring device for measuring the interferometric shape of the surface of a test object according to the present invention, the device comprising: a diffractive optical element for generating a test wave from incident measurement radiation configured to radiate onto the surface of the test object; a deflection element upstream of the diffractive optical element in the beam path of the measurement radiation; and a holding device for holding the deflection element, configured to change the position of the deflection element by a combination of tilting and translational movements.

[0011] Such a combination of tilting and translational motions can occur by tilting the deflecting element, particularly rotating the deflecting element, and displacing the deflecting element independently of tilting, through an tilting axis extending within the deflecting element or substantially through its center of mass. Alternatively, the combination of tilting and translational motions can occur through rotation about a rotation axis located at a considerable distance from the center of mass of the deflecting element. The deflecting element is understood as a module for changing the direction of propagation of the measured radiation, particularly changing an angle of at least 20°, at least 40°, or at least 80°.

[0012] The present invention provides deflection elements that can be positioned at the different locations, allowing measurement of test objects with different surface shapes without significant reconfiguration of the measuring equipment and therefore without major conversion work. Due to the adjustability of the deflection element's position, the position of the test object can be kept substantially the same, and repositioning of the reference element can be avoided if necessary. Therefore, the measuring equipment can be designed to be compact. Simultaneously, there is no need to incorporate specially adapted beam-orientation elements, such as prisms specifically designed for them, for the corresponding test objects, thus allowing measurement of different surface shapes with relatively little effort.

[0013] According to one embodiment, the holding device is configured to shift the position of the deflection element by at least 2 mm, particularly at least 10 mm, through a translational movement.

[0014] According to one embodiment, the holding device is configured to change the tilt position of the deflecting element by at least 2 mrad, particularly at least 10 mrad, through a tilting motion. If the combination of the aforementioned tilting and translational motions is a rotation about a rotational axis located considerably far from the center of mass of the deflecting element, then when the rotational motion is performed, the deflecting element simultaneously experiences a change in its orientation and its spatial position; that is, the aforementioned positional change of the deflecting element can already be caused by performing the rotational motion, but a translational motion can also occur if necessary.

[0015] The combination of changing the orientation of the deflection element and changing its spatial position allows the angle incident on the diffractive optical element to be changed without altering the spatial position of the diffractive optical element during the process.

[0016] According to other embodiments, the holding device is configured to change the position of the deflection element such that the center incident point of the measured radiation on the deflection element is shifted by at least 2 mm, particularly by at least 10 mm.

[0017] According to other embodiments, the holding device includes a tilt actuator for performing tilting motion and a separate displacement actuator for performing translational motion.

[0018] According to other embodiments, the retaining device has a curved guide rail. In particular, the guide rail is designed in the form of an arc segment. According to a variation of the embodiment, a deflection element is attached to a guide portion for performing reciprocating motion within the guide rail.

[0019] According to other embodiments, the combination of tilting and translational motions is achieved through rotational motion relative to a rotational axis, wherein the rotational axis is at least 2 mm, particularly at least 5 mm, from the geometric center of mass of the deflecting element. Specifically, the rotational axis is located outside the deflecting element.

[0020] According to other embodiments, the combination of tilting and translational motion is achieved through rotational motion relative to a rotational axis, wherein the distance between the rotational axis and the central incident point of the radiation measured on the deflecting element is at least 2 mm, particularly at least 5 mm. According to other embodiments, the distance between the rotational axis and the geometric center of mass of the deflecting element is at least 2 mm, particularly at least 5 mm.

[0021] According to other embodiments, the rotation axis is arranged such that the intersection of the rotation axis and the beam plane is located in the beam plane on the same side as the diffractive optical element relative to the irradiation axis defined by the direction vector of the incident measurement radiation, which is spanned by the direction vector of the measurement radiation radiated onto the deflection element and the direction vector of the measurement radiation emitted by the deflection element. In other words, both the diffractive optical element and the intersection are arranged in the "upper hemisphere" relative to the irradiation axis defined by the incident measurement radiation.

[0022] According to other embodiments, the rotation axis is arranged such that the intersection of the rotation axis and the beam plane is located in a region on the opposite side of the irradiation axis with respect to the diffractive optical element. This region has a range of at most twice the distance between the diffractive optical element and the irradiation axis in the direction of the irradiation axis, and at most three times that distance in the direction perpendicular to the irradiation axis. According to other embodiments, this region has a range of at most one time the distance in both the irradiation axis and the direction transverse to the irradiation axis.

[0023] According to other embodiments, the holding device includes at least one actuator for performing at least one rotational motion. In particular, the holding device includes an additional actuator for performing a translational motion.

[0024] In other embodiments, the deflecting element includes a deflecting mirror. In alternative embodiments, the deflecting element includes a prism.

[0025] According to other embodiments, the measuring device has an interferometer cavity, and the deflection elements are arranged outside the interferometer cavity. The region in the interferometer where the test wave and the reference wave do not travel in the same beam path is called the interferometer cavity. In other words, the deflection elements are arranged in the beam path of the measured radiation even before the reference wave is split. In this case, the reference wave can be split using diffractive optical elements.

[0026] According to an alternative embodiment, the measuring device has an interferometer cavity and a deflection element is arranged inside the cavity.

[0027] Furthermore, according to the present invention, a method for measuring the interferometric shape of a corresponding surface of a test object is provided. The method includes the following steps: radiating measurement radiation onto a first diffractive optical element via a deflection element to generate a first test wave, and interferometrically measuring the surface shape of a first test object using the first test wave; changing the position of the deflection element via a combination of tilting and translational movements, and radiating measurement radiation onto a second diffractive optical element via the changed deflection element to generate a second test wave; and interferometrically measuring the surface shape of a second test object using the second test wave. Specifically, the position of the deflection element is moved by at least 2 mm during the translational movement, and more particularly by at least 10 mm.

[0028] According to one embodiment of the method of the invention, instead of the first optical element, a second diffractive optical element is arranged in the test wave generation section of the interferometric measuring apparatus before irradiating the measured radiation through a deflection element whose position has been changed. Specifically, the second diffractive optical element is arranged in a holding device for the test head of the diffractive optical element used for test wave generation. Specifically, this holding device can be tilted and / or displaced.

[0029] According to other embodiments, the second diffractive optical element is arranged at a rotational position offset from that of the first diffractive optical element. This offset is at least 2 mrad, and particularly at least 10 mrad. The respective rotational positions of the two diffractive optical elements can be selected such that the beam paths of the test wave and (if applicable) the reference wave are optimally adapted to the spatial conditions of the interferometric apparatus, particularly with respect to the corresponding geometry of the test object and the configuration of the test wave in question.

[0030] With respect to the features specified in the foregoing embodiments, exemplary embodiments and variations of the measuring device according to the invention can be correspondingly converted to the measuring method according to the invention. These and other features of the embodiments according to the invention will be explained in the description of the claims and drawings. Individual features may be implemented separately or in combination as embodiments of the invention. Furthermore, they may describe advantageous embodiments that can be protected independently, as well as protection claimed only during or after the period when this application is pending (if reasonable). Attached Figure Description

[0031] The above and other advantageous features of the invention are illustrated in the following detailed description of exemplary embodiments thereof, with reference to the accompanying schematic drawings. In the drawings:

[0032] Figure 1 A first embodiment of a measuring apparatus for measuring the interference shape of the surface of a test object by means of a deflection element, the deflection element being mounted by a holding device to make it tiltable and movable, wherein the measuring apparatus is arranged in a configuration for measuring the first test object.

[0033] Figure 2 The configuration for measuring the second test object is shown according to... Figure 1 Measuring equipment,

[0034] Figure 3 Other embodiments of a measuring apparatus for measuring the interferometric shape of a test object are shown, wherein alternative holding devices are used to tilt and move the deflecting element by rotating it about a rotation axis disposed outside the deflecting element.

[0035] Figure 4 An illustration shows a favorable area for the arrangement of the rotation axis.

[0036] Figure 5 Other embodiments of a measuring apparatus for measuring interference shapes are shown, wherein a holding device is used to rotate a deflecting element about a rotation axis disposed outside the deflecting element.

[0037] Figure 6 An alternative embodiment of the deflection element in the form of a reflecting prism is shown.

[0038] Figure 7 Other alternative embodiments of the deflection element of a prism that utilizes the refraction of light at the side surface are shown.

[0039] Figure 8 Other embodiments of a measuring apparatus for measuring the interferometric shape of a test object are shown, wherein a collimator is arranged upstream of a deflection element, and

[0040] Figure 9 Another embodiment of a measuring apparatus for measuring the interference shape of a test object surface is shown, which is designed as a Fizeau interferometer. Detailed Implementation

[0041] In the exemplary embodiments, examples, or variations thereof described below, elements that are functionally or structurally similar to each other are provided with the same or similar reference numerals wherever possible. Therefore, in order to understand the features of individual elements that define exemplary embodiments, reference should be made to the description of other exemplary embodiments of the invention or to the general description of the invention.

[0042] For ease of description, the Cartesian xyz coordinate system is indicated in the accompanying drawings, and the positional relationship of the components shown in the drawings with respect to this coordinate system is self-evident. Figure 1 In the figure, the y-direction extends perpendicularly to the plane in the figure and into the plane, the x-direction extends to the right and the z-direction extends upward.

[0043] Figure 1An exemplary embodiment of a measuring device 10 is shown, which performs interference shape measurements on the optical surface 12 of a test object 14-1. The measuring device 10 can be used in particular to determine the deviation between the actual shape of the surface 12 and a target shape. The provided test object 14-1 may be, for example, a mirror of a projection lens for EUV microlithography, having an aspherical surface that reflects EUV radiation with wavelengths less than 100 nm, particularly wavelengths of approximately 13.5 nm or approximately 6.8 nm. The aspherical surface of the mirror may, for example, be a freeform surface, having a deviation greater than 5 μm from each rotationally symmetric aspherical surface and a deviation of at least 1 mm from each sphere.

[0044] The measuring device 10 includes a frame 15, an illumination / detection module 16, a deflection element 22, a holding device 24 for holding the deflection element 22, a diffractive optical element 26-1, and a reference element 32. The illumination / detection module 16 includes a radiation source 17, a beam splitter 25, and an observation unit 36.

[0045] Radiation source 17 is used to provide sufficiently coherent measurement radiation 18 as an input wave. In this exemplary embodiment, radiation source 17 includes a waveguide 19 having an exit surface from which the input wave originates. Waveguide 19 is connected to radiation generation module 20, such as a laser. As an example, a helium-neon laser with a wavelength of approximately 633 nm could be provided for this purpose. However, the measurement radiation 18 may also have other wavelengths within the visible and invisible wavelength range of electromagnetic radiation.

[0046] The radiation source 17 with waveguide 19 is merely an example of a radiation source 17 that can be used in the measuring device 10. In alternative embodiments, in addition to waveguide 19, an optical arrangement with lens elements, mirror elements, etc., can be configured to provide a suitable input wave 18 from the measuring radiation 18.

[0047] The measured radiation 18 first passes through beam splitter 25, and is then deflected by deflector 22 onto diffractive optical element 26-1. Deflector 22... Figure 1 The illustrated embodiment is designed as a reflective optical element with a reflective surface 23, i.e., as a deflecting mirror. In other words, the deflecting element 22 is located upstream of the diffractive optical element 26-1 in the beam path 21 of the measurement radiation 18. The measurement radiation radiated onto the deflecting element 22... Figure 1 The reference numeral 18a indicates the measurement radiation 18 emitted by the deflection element, and reference numeral 18b indicates the measurement radiation 18 emitted by the deflection element. A diffractive optical element 26-1 is arranged in the test wave generation section 60 of the measuring device 10. This section forms a test head for generating a test wave 28 to radiate onto the surface 12 of the test object 14-1. According to... Figure 1In one embodiment, in addition to the test wave 28, the diffractive optical element 26-1 also generates a reference wave 30 from the incident measurement radiation 18b.

[0048] Furthermore, the measurement arrangement 10 includes a reference element 32 designed as a reflective optical element, having a reflective surface 33 for reflecting the reference wave 30 into a returning reference wave 30r. The diffractive optical element 26-1 is designed in the form of a complex coded CGH and contains a diffractive structure 34, according to... Figure 1 In the illustrated embodiment, the diffraction structure 34 forms two diffraction patterned structures that are arranged overlapping each other in a plane. The diffractive optical element 30 is therefore also referred to as a secondary complex coded computer-generated hologram (CGH). Alternatively, the diffraction structure may also have more than two overlapping diffraction patterned structures arranged in a plane—for example, five overlapping diffraction patterned structures—for additionally generating calibration waves.

[0049] according to Figure 1 The two diffraction structure patterns of the diffractive optical element 26-1 can be formed, for example, by a first structure pattern in the form of a bottom grating and a second diffraction structure pattern in the form of a top grating. One of the diffraction structure patterns is configured to generate a test wave 28, which is directed toward the test object 14-1 and has a wavefront that is at least partially adapted to the target shape of the optical surface 12. The test wave 28 is reflected at the optical surface 12 of the test object 14-1 and returns to the diffractive optical element 26-1 as a returning test wave 28r. Due to the wavefront adapted to the target shape of the optical surface 12, the test wave 34 is incident substantially perpendicularly at each location on the optical surface 12 and reflected back to itself.

[0050] Another diffraction pattern generates a reference wave 30, which is directed towards the reference element 32 and has a planar wavefront. In an alternative exemplary embodiment, a simple coded CGH with a diffraction pattern or another grating can be used instead of a complex coded CGH. The test wave 28 can be generated, for example, with first-order diffraction, and the reference wave 30 can be generated with zero-order or any other order diffraction at the diffraction pattern.

[0051] In this embodiment, the reflecting element 30 is designed as a plane mirror that reflects a reference wave 30 having a plane wavefront. In another embodiment, the reference wave 30 may have a spherical wavefront, and the reference element 32 may be designed as a spherical mirror.

[0052] The test wave 28r returning from surface 12 passes through the diffractive optical element 26-1 again and is diffracted again in the process. In this case, the returning test wave 28r is converted back into an approximately spherical wave, wherein the wavefront of the test wave 28r has a corresponding deviation from the spherical wavefront due to the deviation between the surface 12 of the test object and the target shape.

[0053] The returned reference wave 30r, reflected by the reflective surface of reference element 32, also passes through diffractive optical element 26-1 again and is diffracted again in the process. In this case, the returned reference wave 30r is transformed back into a spherical wave. In an alternative embodiment where a collimator in the beam path of the measurement radiation 18 radiating to diffractive optical element 26-1 is used to generate an input wave with a plane wavefront, the wavefront of the returned reference wave 30r does not need to be adjusted by diffractive optical element 30.

[0054] The region in which the test wave 28 or 28r and the reference wave 30 of the interferometer 10 do not travel in the same beam path is called the interferometer cavity. According to... Figure 1 In one embodiment, the interferometer cavity 35 includes a beam path for a test wave 28 or 28r between the diffractive optical element 26-1 and the object under test 14-1, and a beam path for a reference wave 30 or 30r between the diffractive optical element 26-1 and the reference element 32. According to... Figure 1 In an embodiment of the measuring device 10, as can be seen from the figure, the deflection element 22 is arranged outside the interferometer cavity 35.

[0055] The diffractive optical element 26-1 also helps to superimpose the returned test wave 28r with the returned reference wave 30r. The returned waves 28r and 30r then travel through the beam path 21 of the incident measurement radiation 18 via the deflection element 22 back to the beam splitter 25. The latter guides the combination of the returned test wave 28r and the returned reference wave 30r away from the beam path 21 of the incident measurement radiation 18 and directs it to the observation unit 36.

[0056] The returning test wave 28r and the returning reference wave 30r are incident as converging beams on the beam splitter 25 and thus reflected in the direction of the observation unit 36. Both converging beams pass through the aperture 38 and eyepiece 40 of the observation unit 36 ​​and are ultimately incident on the two-dimensional resolution detector 42 of the observation unit 36. The camera 42 can be designed as, for example, a CCD sensor and captures the interferogram generated by the interfering waves.

[0057] Furthermore, the measuring device 10 includes an evaluation unit 44 for determining the actual shape of the optical surface 12 of the test object 14-1 from the captured interferogram or multiple captured interferograms. For this purpose, the evaluation unit 44 has a suitable data processing unit and uses corresponding calculation methods known to those skilled in the art. Alternatively or additionally, the measuring device 10 may have a data storage or network interface, making it possible to determine the surface shape using interferograms stored or transmitted via a network through an external evaluation unit.

[0058] The aforementioned holding device 24 is configured to adjust the deflection element 22 at least with respect to its rotational position. According to... Figure 1In one embodiment, the holding device 24 allows the position of the deflecting element 22 to be both tilted and moved, that is, the position of the deflecting element 22 is changed by a combination of tilting and translational movements.

[0059] In the current situation, the tilt position of the deflection element 22 can be changed by performing a tilting motion 48. This tilting motion 48 occurs by rotation relative to a tilting axis 28, which is located at... Figure 1 The y-direction is oriented transversely to the propagation direction of the incident measurement radiation 18a. A tilt actuator 50 is provided to perform the tilting motion. Here, the tilt axis can be arranged on the reflecting surface 23 of the deflection element 23 or at a position slightly spaced away from the reflecting surface 23, such as... Figure 1 The configuration shown in the exemplary embodiment is illustrated. Figure 1 The deflection element 22 is shown in a first tilt position relative to the z-axis at a tilt angle φ1 (shown as a solid line) and a second tilt position at a tilt angle φ2 (shown as a dashed line). The tilt angle of the deflection element 22 (expressed by the difference angle Δφ = φ1 - φ2) is at least 2 mrad, particularly at least 10 mrad. Alternatively, or attached to the tilt axis 46, it can provide a propagation direction parallel to the incident measurement radiation 18a, or according to... Figure 1 An inclined axis is arranged in the x-direction.

[0060] The positional displacement of the deflection element 22 is provided for at least one translational degree of freedom 52. In the current case, the translational degree of freedom is parallel to the propagation direction of the incident measurement radiation 18a (i.e., according to...). Figure 1 Alignment (in the x-direction). Furthermore, for example, it can be provided transverse to the propagation direction of the incident measurement radiation 18a or according to... Figure 1 The translational degree of freedom is aligned in the y-direction. A displacement actuator 54 is provided to perform the displacement of the deflection element 22. Figure 1 The solid line indicates that the deflection element 22 is in the first displacement position, while the dashed line indicates that the deflection element 22 is in the second displacement position.

[0061] The displaceability of the deflecting element 22 is configured such that the position of the deflecting element 22 is displaced by at least 2 mm, and particularly at least 10 mm. This specifically results in the fact that, after displacement, the corresponding position of the geometric centroid 56 of the deflecting element 22 changes by a distance d1 (also referred to as displacement 55) in the direction of the translational degree of freedom in question, which is at least 2 mm, and particularly at least 10 mm. Alternatively or additionally, the displaceability allows the position of the central incident point 57 of the measuring radiation 18a on the deflecting element 22 to change by at least 2 mm, and particularly at least 10 mm, in the direction of the translational degree of freedom in question.

[0062] The degree of freedom in adjusting the tilt and translation position of the deflection element allows the measurement radiation 18b emitted by the deflection element 22 to radiate onto the diffractive optical element 26-1 with precise position and orientation. The position and orientation of the measurement radiation 18b can be specifically adjusted to the structure of the diffractive optical element 26 selected for measuring the relevant test object 14-1, as well as the position and orientation selected for this purpose.

[0063] In other words, in order to measure the surface 12 of the test object 14-1, a diffractive optical element 26-1 is manufactured that is specifically adapted to the target surface shape of the test object 14-1. The design of the diffraction structure 34 on the diffractive optical element 26-1 is chosen such that the test wave 28 generated therefrom is emitted with a wavefront corresponding to the target surface shape, and the reference wave 30 is emitted in a direction that allows the test object 14-1 and the reference element 32 to be compactly arranged within the measuring device 10.

[0064] Based on the selected design of the diffraction structure 34, a preferred orientation of the diffractive optical element 26-1 is present within the measuring device 10, which is tiltable relative to at least one tilting axis and / or displaceable relative to at least one translational degree of freedom via the holding device 58 of the test head. Figure 1 In the illustrated embodiment, the holding device 58 enables the diffractive optical element 26-1 to tilt relative to the y-axis and shift in the x-axis direction.

[0065] To measure the surface shape of the test object 14-1, the optical element 26-1 provided for this purpose is now arranged in a preferred orientation and position by means of the holding device 58. This results in a suitable angle of incidence of the measuring radiation 18b onto the diffractive optical element 34. This angle of incidence is now generated by appropriately setting the tilt angle and translation position of the deflection element 22 by means of the holding device 24. In particular, the tilt angle and translation position of the deflection element 22 are selected such that the measuring radiation 18b strikes the diffractive optical element 34 in a centered manner.

[0066] If the purpose is then to measure the surface shape of another test object 14-2, then according to Figure 2As illustrated in the diagram, the diffractive optical element 26-1 is replaced by another diffractive optical element 26-2 in the test head holding device 58. The diffraction structure 34 of the other diffractive optical element 26-2 is specifically designed for measuring the surface shape of another test object 14-2. This diffraction structure 34 is selected such that the resulting test wave 28 has a wavefront adapted to the target surface shape of the test object 14-2, and the beam path configuration of the test wave 28 and the reference wave 30 is adapted to the spatial conditions in the measuring device 10. Considering the spatial conditions in the measuring device 10, the preferred orientation and positioning of the diffractive optical element 26-2 are determined by the design of the diffraction structure 34 of the other diffractive optical element 26-2. This orientation and positioning are set by the test head holding device 58.

[0067] The appropriate incident angle of the measured radiation 18b onto the diffractive optical element 34 is obtained from this orientation and positioning of the diffractive optical element 26-2 (considering the design of the diffractive structure 34). This incident angle is now set by appropriately changing the position of the deflection element 22 using the holding device 24. Figure 2 The position of the deflection element 22 in the middle diagram corresponds to Figure 1 The location is indicated by a dashed line and has been described in more detail above.

[0068] The change in position of the deflection element 22 therefore includes a change in the tilt angle and translational position of the deflection element 22 held in the holding device 24. The change in the translational position of the deflection element 22 is essentially used to compensate for the changed tilt angle, ensuring that the incident point on the diffractive optical element 26-2 remains within the region of the test wave generation section 60. In other words, if the deflection element 22 were not translated, the position of the diffractive optical element 26-2 would have to be moved so that it is no longer within the region of the test wave generation section 60, or its position might not be compatible with the spatial conditions in the measuring device 10.

[0069] exist Figure 2 In the configuration of the measuring device 10 shown, the actual shape of the optical surface 12 of the test object 14-2 is generated from one or more interferograms, which are generated by superimposing the returned test wave 28r with the returned reference wave 30r, similar to the reference wave 30r. Figure 1 As described.

[0070] Other embodiments of the interferometric measuring device 10 are in Figure 3 The diagram in the middle shows this. This is consistent with... Figure 1 The difference between the measuring device 10 and the previous one lies only in the configuration of the holding device 24 for the deflection element 22. This holding device, according to... Figure 3 In embodiments, it is indicated by reference numeral 124. According to... Figure 3In the illustration, for clarity, the beam path for measuring radiation 18 is drawn with only one line instead of three lines in some beam segments.

[0071] The holding device 124 includes a curved guide rail 126 attached to the frame 15 for guiding the guide portion 128 attached to the deflection element 22. The curvature of the guide rail 126 extends along a circumferential segment 132. The latter is part of a circle in the plane of the figures, with the intersection of the axis of rotation 146 and the plane of the figures as the center 152. The deflection element 22 can be moved by the holding device 124 relative to the axis of rotation 146 with a rotational motion 148. The rotational motion 148 corresponds to a combination of tilting motion and translational motion. The plane of the figures is the plane spanned by the direction vector 118a of the incident measurement radiation 18a and the direction vector 118b of the emitted measurement radiation 18b. This plane is also referred to herein as the beam plane.

[0072] The rotation axis 146 is arranged such that its intersection with the plane of the attached drawing or the beam plane is located directly above the incident midpoint 57 of the incident measurement radiation 18a. The intersection mentioned in the beam plane is arranged in the upper hemisphere relative to the irradiation axis 120a defined by the direction vector 118a, and thus is on the same side as the diffractive optical element 26-1 relative to the irradiation axis 120a. Due to the above arrangement of the rotation axis 146, when the rotational movement 148 is performed, the position of the deflection element 22 is shifted by at least 2 mm, particularly by at least 10 mm (the translation component 148 of the rotational movement), and tilted by at least 2 mrad, particularly by a difference tilt angle Δφ of at least 10 mrad (the tilting portion of the rotational movement 148).

[0073] The holding device 124 includes an actuator 150 integrated into a module of the guide rail 126 for performing rotational movement relative to the rotation axis 146. In the illustrated embodiment, the actuator 150 pulls a pin-shaped pull element 130 of the guide portion 128 along a circumferential segment 132. In addition to the first position (shown in solid lines) of the deflection element 22 for the irradiation diffraction optical element 26-1 described above, the second position of the deflection element 22 is shown in dashed lines. Figure 3 In this position, the deflection element 22 is tilted by Δφ relative to the first position. The second position is used to measure the irradiation already performed by radiation 18b. Figure 2 The other diffractive optical element 26-2 shown in the figure has its direction vector 118b' tilted by 2Δφ relative to the direction vector 118b at the first position.

[0074] This specifically results in the fact that, after the rotational motion 148, the corresponding position of the geometric center of mass 56 of the deflecting element 22 changes by a distance d1 (also referred to as displacement 55) in the direction of the translational degree of freedom in question, which is at least 2 mm, and particularly at least 10 mm. Alternatively or additionally, the displaceability allows the position of the central incident point 57 of the measuring radiation 18a on the deflecting element 22 to change by at least 2 mm, and particularly at least 10 mm, in the direction of the translational degree of freedom in question.

[0075] Figure 4 Used to illustrate in accordance with Figure 3 In the embodiment of the interferometric arrangement 10 with curved guide rail 126, the advantageous area for the arrangement of the rotation axis 146 is described above. The center 152 of the circumferential segment 132 defined by the guide rail 126 corresponds to the intersection of the rotation axis 146 and the plane of the drawing.

[0076] A preferred region 154 of the center 152 of the guide rail 126 is defined by a rectangle having a range of 2h in the horizontal direction (i.e., parallel to the irradiation axis 120a) and a range of 3h in the vertical direction (i.e., perpendicular to the irradiation axis 120a). h is the distance of the diffractive optical element 26-1 from the irradiation axis 120, and more precisely, the distance of the central irradiation point 160 of the measuring radiation 16b on the diffractive optical element 26-1 from the irradiation axis 120. For at least one embodiment variant, the distance of the second diffractive optical element 26-1 remains unchanged. The rectangle defining the preferred region 154 relates to the area above the diffractive optical element 26-1 with dimensions of 2h × 3h, wherein the irradiation point 160 is located at the middle of the lower edge of the rectangle.

[0077] A particularly preferred region 156 for center 152 is defined by another rectangle having a range of 1h in both the horizontal and vertical directions. Region 156 is specifically arranged such that its center is at a distance h from the irradiation point 160 of the measured radiation on the diffractive optical element 26-1. Figure 4 The illustration shows a particularly advantageous embodiment variant in which the center 152 assigned to the curved guide rail 126 coincides with the center of region 156.

[0078] exist Figure 3 In the illustrated embodiment, center 152 is located within a particularly preferred region. Figure 5 Other embodiments are shown, which are consistent with those according to Figure 3 The only difference in the embodiment is that the center 152 assigned to the curved guide rail is located further to the right and further down. The center 152 is approximately located at a distance h to the right of the irradiation point 160 and at approximately the same height as the irradiation point 160 in the vertical direction, thus arranged according to... Figure 4 The preferred area is the lower right corner of region 154.

[0079] Figure 8 Another embodiment of the measuring device 10 is illustrated, which performs interference shape measurement on the optical surface 12 of the test object 14-1. This embodiment is related to... Figure 1 The only difference in this embodiment is that the collimator 62 is arranged upstream of the deflection element 22. Measurement radiation 18a and measurement radiation 18b are therefore not considered as... Figure 1 Instead of being an extended wave, it is incident as a plane wave onto the deflection element 22 or the diffractive optical element 26-1 in each case.

[0080] Figure 9 Another embodiment of the measuring device 10 is illustrated, which performs interference shape measurements on the optical surface 12 of the test object 14-1. According to... Figure 9 The measuring device 10 and according to Figure 8 The difference in the measuring device 10 is that, instead of the reference element 32 designed as a reflective optical element, a reference element 232 in the form of a Fizeau collimator is provided. Figure 8 The diffractive optical element 26-1, a Fizeau collimator, is used to generate a reference wave 30 from the measured radiation 18, wherein the reference wave has already returned during generation and is therefore denoted by the reference symbol 30r. The Fizeau collimator can also be replaced by a combination of a collimator and separate Fizeau elements.

[0081] A reference element 232, configured as a Fizeau collimator, is arranged in the beam path of the incident measurement radiation 18 upstream of the deflection element 22 and has a Fizeau surface 233 at which a portion of the incident measurement radiation 18 is reflected as a returning reference wave 30r. The Fizeau surface 233 is designed to be a flat surface. Figure 7 The measuring device 10 is therefore configured as a Fizeau interferometer. Since the reference wave 30 is no longer generated by the diffractive optical element 26-1, it can be implemented using a simply coded diffractive structure 34.

[0082] As described above, the region in interferometer 10 where the test wave 28 and the reference wave 30 do not travel in the same beam path is called the interferometer cavity. According to... Figure 9 In one embodiment, the interferometer cavity 235 includes the beam path of the measurement radiation 18a after passing through the Fizeau surface 233 and the beam path of the test wave 28 between the diffractive optical element 26-1 and the object under test 14-1. According to... Figure 9 In an embodiment of the measuring device 10, the deflection element 22 is arranged within the interferometer cavity 235, as is evident from the accompanying drawings.

[0083] In addition to the retaining device 24, according to Figure 3 Embodiments of the holding device 124 can be integrated into according to Figure 8 and9 In an embodiment of the measuring device 10.

[0084] An alternative embodiment of the deflection element 22 is illustrated in Figure 6 and 7 In the middle. And Figures 1 to 5 or Figure 8 and Figure 9 The diagram shows a different deflecting element 22 configured as a reflector; the deflecting element can also be configured as a prism 22-1 or 22-2. According to... Figure 6 In one embodiment, prism 22-1 is designed as a reflecting prism and arranged according to Figures 1 to 5 or Figure 8 and Figure 9 In a corresponding measuring device 10, the incident measuring radiation 18a is incident perpendicularly onto the irradiation prism surface 70. From there, the measuring radiation 18a travels inside the prism 22-1 to the reflecting prism surface 74, where it is reflected, and then continues inside the prism 22-1 until it is emitted from the prism 22-1 at the emitting prism surface 72 as the emitted measuring radiation 18b.

[0085] According to Figure 7 In one embodiment, prism 22-2 is configured to utilize refraction at the prism surface and is arranged according to... Figures 1 to 5 or Figure 8 and Figure 9 In one of the corresponding measuring devices 10, the incident measuring radiation 18a is incident at an oblique angle onto the irradiated surface 70. Upon incident on the prism 22-2, the measuring radiation 18a is refracted toward the vertical, travels through the interior of the prism 22-2, and, upon leaving the prism 22-2, is refracted again away from the vertical at the emitting prism surface 72, which is oriented differently from the irradiated prism surface 70.

[0086] When the position of the deflection element 22 is changed, when the geometric centroid 56 or the incident midpoint 57 is shifted, the above references are made. Figures 1 to 3 The dimensions explained are correspondingly applied to the respective geometric centroids 56 or incident midpoints 57 of prisms 22-1 and 22-2.

[0087] The exemplary embodiments, examples, or variations thereof described above should be considered as examples. This disclosure, thus achieved, firstly enables those skilled in the art to understand the invention and its associated advantages, and secondly covers obvious variations and modifications of the structures and methods described within the understanding of those skilled in the art. Therefore, all such variations and modifications, provided they fall within the scope of the invention as defined by the appended claims, and their equivalents, are intended to be covered by the claims.

[0088] List of reference numerals

[0089] 10. Measuring equipment

[0090] 12 Optical Surfaces

[0091] 14-1 Test Item

[0092] 15 Framework

[0093] 16 Lighting / Detection Module

[0094] 17 Radiation Sources

[0095] 18. Measuring radiation

[0096] 18a Incident Measurement Radiation

[0097] Measurement of radiation emitted by 18b

[0098] 19 Waveguides

[0099] 20 Radiation Generation Module

[0100] 21. Beam path for measuring radiation

[0101] 22 Deflection element

[0102] 22-1 Prism

[0103] 22-2 Prism

[0104] 23 Reflective surfaces

[0105] 24 Holding device

[0106] 25 beam splitter

[0107] 26-1 Diffractive optical elements

[0108] 26-2 Diffractive optical elements

[0109] 28 Test Waves

[0110] 28r Return to test wave

[0111] 30 Reference Wave

[0112] 30r Return to reference wave

[0113] 32 Reference Components

[0114] 33 Reflective Surface

[0115] 34 Diffraction Structure

[0116] 35 Interferometer cavity

[0117] 36 Observation Units

[0118] 48. Aperture

[0119] 40 eyepieces

[0120] 42 detectors

[0121] 44 Evaluation Device

[0122] 46 Inclined axis

[0123] 48. Tilting motion

[0124] 50 Tilting Actuator

[0125] 52 translational degrees of freedom

[0126] 54 Displacement Actuator

[0127] 55 Displacement

[0128] 56 Geometric centroid

[0129] 57. Midpoint of incidence

[0130] 58 Holding device

[0131] 60 Test wave generation section

[0132] 62 Collimator

[0133] 70 Irradiated prism surface

[0134] 72. Surface of the emission prism

[0135] 74. Surface of the reflecting prism

[0136] 118a Direction Vector

[0137] 118b Direction Vector

[0138] 118b' Direction Vector

[0139] 120a Irradiation Axis

[0140] 120B launch axis

[0141] 124 Holding device

[0142] 126 Curved Guide Rail

[0143] 128. Guiding Section

[0144] 130 Pulling element

[0145] 132 Circular Section

[0146] 146 Rotation axis

[0147] 148 Rotational motion

[0148] 150 actuator

[0149] 152 Center

[0150] 154 Preferred Areas

[0151] 156 Special Preferred Areas

[0152] 158 Center

[0153] 160 Central Irradiation Point

[0154] 232 Reference Element

[0155] 233 Fizzo surface

[0156] 235 Interferometer cavity

Claims

1. A measuring device for measuring the interference shape of the surface of a test object, comprising: - A diffractive optical element for generating a test wave from incident measurement radiation, the test wave being configured to radiate onto the surface of the test object. - A deflection element, upstream of the diffractive optical element in the beam path for measuring radiation, and - A holding device for holding the deflecting element, which is configured to change the position of the deflecting element by a combination of tilting and translational movements.

2. The measuring device according to claim 1, in, The holding device is configured to shift the position of the deflection element by at least 2 mm through the translational movement.

3. The measuring device according to claim 1 or 2, The holding device is configured to change the tilt position of the deflection element by at least 2 mrad through the tilting motion.

4. The measuring device according to claim 1 or 2, The holding device includes a tilt actuator for performing the tilting motion and a separate displacement actuator for performing the translational motion.

5. The measuring device according to claim 1 or 2, The retaining device described herein has a curved guide rail.

6. The measuring device according to claim 1 or 2, The combination of the tilting motion and the translational motion is achieved by a rotational motion relative to a rotational axis, wherein the rotational axis is located at a distance of at least 2 mm from the geometric center of mass of the deflection element.

7. The measuring device according to claim 6, The rotation axis is arranged such that the intersection of the rotation axis and the beam plane is located in the beam plane, on the same side as the diffractive optical element relative to the irradiation axis defined by the direction vector of the incident measurement radiation, the beam plane being spanned by the direction vector of the measurement radiation radiated onto the deflection element and the direction vector of the measurement radiation radiated by the deflection element.

8. The measuring device according to claim 7, The rotation axis is arranged such that the intersection of the rotation axis and the beam plane is located in a region on the opposite side of the irradiation axis with respect to the diffractive optical element. The region in the direction of the irradiation axis has a range of up to twice the distance of the diffractive optical element from the irradiation axis, and a range of up to three times the distance in the direction perpendicular to the irradiation axis.

9. The measuring device according to claim 8, The region therein has a range of at most one times the distance along the irradiation axis and in the direction transverse to the irradiation axis.

10. The measuring device according to claim 1 or 2, The holding device includes at least one actuator for performing at least one rotational motion.

11. The measuring device according to claim 1 or 2, The deflection element includes a deflecting mirror.

12. The measuring device according to claim 1 or 2, The deflection element mentioned above includes a prism.

13. The measuring device according to claim 1 or 2, It has an interferometer cavity, and the deflection element is arranged outside the interferometer cavity.

14. The measuring device according to claim 1 or 2, It has an interferometer cavity, and the deflection element is arranged inside the interferometer cavity.

15. A method for measuring the interference shape of a corresponding surface of a test object, comprising the following steps: - The measurement radiation is radiated onto a first diffractive optical element by a deflection element to generate a first test wave, and the surface shape of the first of the test objects is measured by interferometry using the first test wave. - The position of the deflection element is changed by a combination of tilting and translational movements, and - The measurement radiation is radiated onto a second diffractive optical element by a deflection element whose position has been changed to generate a second test wave, and the surface shape of the second of the test objects is measured by interferometry through the second test wave.

16. The method according to claim 15, in, Instead of the first diffractive optical element, the second diffractive optical element is arranged in the test wave generation section of the interferometric measuring device before the measured radiation is irradiated by the deflection element whose position has been changed.

17. The method according to claim 15 or 16, in, The second diffractive optical element is arranged in a rotational position that is offset from the rotational position of the first diffractive optical element.

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