MEASURING DEVICE FOR INTERFEROMETRIC MEASUREMENT OF A SURFACE SHAPE

Abstract

A measuring device (10) for interferometrically measuring the shape of a surface (12) of a test object (14) comprises a radiation generation module (22) for generating a measuring radiation (18) for irradiating the surface of the test object, a reference element (26) for splitting off a reference wave (28) from the measuring radiation before the measuring radiation passes through an interferometer cavity (25), and a laminar flow module (50) for generating a laminar air flow within the interferometer cavity.

Description

Background of the invention

[0001] The invention relates to a measuring device for interferometrically measuring the shape of a surface of a test object.

[0002] For the high-precision interferometric measurement of optical surfaces down to the subnanometer range, interferometric measuring devices and methods are known in which a reference element generates a test wave and a reference wave from an input wave. The wavefront of the test wave can be adapted to a target surface of the test object using a diffractive optical element in such a way that it impinges on the target shape essentially perpendicularly at every location and is reflected back into itself by the surface. Using the interferogram formed by superimposing the reflected test wave with the reference wave, deviations from the target shape can then be determined, thus measuring the fit of the test object.

[0003] US 2015 / 0198438A1 describes such an interferometric measuring device with a Fizeau element as the reference element for generating the reference wave. Any influencing factors that change the optical path length between the Fizeau element and the test object relative to the reference wave are crucial for measurement accuracy. When measuring in air, the refractive index of the air, which depends on pressure, temperature, and humidity, can vary, among other things. Changes in these variables are directly reflected in the fit measurement result, and it is not possible to differentiate whether deviations in the fit exist or environmental conditions are responsible. These changes in the refractive index reach a relevant magnitude if the surface shape is to be qualified in the picometer range.One way to minimize the influence of environmental conditions on the measurement result is to operate the interferometer in a vacuum, which entails considerable effort and costs. Underlying task

[0004] It is an object of the invention to provide a measuring device of the type mentioned at the outset, whereby the aforementioned problems are solved and preferably to improve the measuring accuracy of the shape measurement while avoiding excessive expenditure. Inventive solution

[0005] The aforementioned object can further be achieved, for example, with the measuring device described below for interferometrically measuring the shape of a surface of a test object. The measuring device according to the invention comprises a radiation generation module for generating measuring radiation for irradiation onto the surface of the test object, a reference element for splitting a reference wave from the measuring radiation before the measuring radiation passes through an interferometer cavity, and a laminar flow module for generating a laminar air flow within the interferometer cavity. The laminar flow module can be configured, in particular, as a so-called flushing cistern.

[0006] The inventive provision of the laminar flow module for generating a laminar air flow within the interferometer cavity ensures a spatially stable and homogeneous temperature and velocity distribution of the air in the region of the interferometer cavity. Since the interferometer cavity is the section of the measuring device in which refractive index fluctuations have a particularly significant impact on measurement accuracy, the inventive measure can significantly improve the measurement accuracy of the measuring device. The effort required for this measure is minimal, at least compared to operating the measuring device in a vacuum.

[0007] According to one embodiment, the laminar flow module comprises an inflow side, for example in the form of an inflow wall or an inlet surface of the laminar flow module, for the planar inflow of air into the interferometer cavity, and an exhaust side, for example in the form of an exhaust wall or an outlet surface of the laminar flow module, for the planar exhaust of air from the interferometer cavity. The exhaust side is preferably arranged opposite the inflow side, with the sides enclosing the interferometer cavity.

[0008] According to a further embodiment, the inflow side comprises a fine-mesh fabric for laminarizing the air flowing into the interferometer cavity. A fine-mesh fabric is understood, for example, to be a fabric with a mesh size of at most 200 µm, at most 100 µm, at most 50 µm, or at most 5 µm.

[0009] According to a further embodiment, the inflow side is supplied with air via an air supply pipe, wherein at least one perforated plate is arranged inside the air supply pipe for homogenizing or evenly distributing the air supplied to the inflow side. The air supply pipe preferably supplies the inflow side with air from a rear side facing away from the interferometer cavity.

[0010] According to a further embodiment, the inflow side is supplied with air via an air supply pipe, which preferably has a cross-sectional area corresponding to at least 20%, in particular at least 70%, of the outlet area of ​​the inflow side from which the air exits into the interferometer cavity. According to one embodiment, the air supply pipe is provided with thermal insulation.

[0011] According to a further embodiment, the supply air pipe comprises a main pipe section with a uniform cross-section and a connecting section with an increasing cross-section for connection to the inflow side, wherein the cross-sectional area, which corresponds to at least 20% of the outlet area of ​​the inflow side, is a cross-sectional area of ​​the main pipe section. The connecting section is designed, for example, funnel-shaped and serves to widen the cross-section at the transition from the main pipe section to the inflow side.

[0012] According to a further embodiment, at least one temperature adjustment device is arranged inside the supply air pipe. The temperature adjustment device is preferably designed as a cooling device. Alternatively, it can also be configured as a heating device.

[0013] According to a further embodiment, the measuring device comprises a frame structure for holding at least the test piece and the reference element, wherein the laminar flow module is arranged inside the frame structure. In particular, further elements of the measuring device, such as a test optics for wavefront adaptation of the measuring radiation to a desired shape of the test piece surface and / or the radiation generation device, can also be attached to the frame structure.

[0014] According to a further embodiment, the measuring device comprises a further laminar flow module for generating a laminar air flow, which encloses the first laminar flow module. According to one embodiment variant, the further laminar flow module encloses the frame structure.

[0015] According to a further embodiment, the further laminar flow module has a larger flow cross-section than the first laminar flow module. In particular, the area of ​​the flow cross-section of the further laminar flow module is at least twice, in particular at least four times, the area of ​​the flow cross-section of the first laminar flow module. For this purpose, the respective inflow walls of the laminar flow modules can be dimensioned differently accordingly, i.e., the inflow side of the further laminar flow module has an area at least twice as large as the inflow side of the first laminar flow module.

[0016] According to a further embodiment, the laminar flow modules are connected to a common supply air pipe system, which comprises a uniform air supply pipe and a branching section between the air supply pipe and the respective supply air pipe to the laminar flow modules, wherein at least one temperature adjustment device is arranged in the air supply pipe. The temperature adjustment device is preferably designed as a cooling device; alternatively, it can also be configured as a heating device. According to one embodiment, the supply air pipe system is provided with thermal insulation.

[0017] According to a further embodiment, the laminar flow modules are connected to a respective air supply pipe via a respective supply air pipe, wherein the supply air pipes each comprise an inflow sector extending in a respective inflow direction of the air into the interferometer cavity, as well as a bend, wherein at least one temperature adjustment device is arranged in each of the air supply pipes. Advantageously, the temperature adjustment device is designed as a cooling device; alternatively, it can also be configured as a heating device. By connecting the laminar flow modules to a respective air supply pipe, the laminar flow modules can be connected to separate ventilation units, whose volume flow and temperature offset can be controlled independently of one another.

[0018] According to a further embodiment, a thermal mass with flow channels is arranged inside the supply air pipe. Depending on the design, the thermal mass has an effective heat storage capacity of at least 50 kJ / K, at least 250 kJ / K, at least 500 kJ / K, or at least 1000 kJ / K.

[0019] According to another embodiment, the thermal mass comprises a stack of metal plates, for example, aluminum plates. These can be provided with spacers so that air can flow between the plates.

[0020] According to a further embodiment, the measuring device is configured to establish a temperature stability of 1 mK or less in the interferometer cavity.

[0021] The features specified with regard to the above-mentioned embodiments, exemplary embodiments, or variant embodiments, etc. of the measuring device according to the invention are explained in the description of the figures and the claims. The individual features can be implemented either separately or in combination as embodiments of the invention. Furthermore, they can describe advantageous embodiments that are independently protectable and whose protection may be claimed only during or after the filing of the application. Short description of the drawings

[0022] The above and other advantageous features of the invention are illustrated in the following detailed description of exemplary embodiments or embodiments or variants of the invention with reference to the attached schematic drawings. They show: Fig. 1 an embodiment of a measuring device for interferometrically measuring a shape of an optical surface of a test specimen with two laminar flow modules, Fig. 2 shows a further embodiment of a measuring device for interferometrically measuring a shape of an optical surface of a test specimen with two laminar flow modules, and Fig. 3 an embodiment of a projection exposure apparatus with one or more using the measuring device according to Fig. 1 or Fig. 2 manufactured optical elements. Detailed description of embodiments according to the invention

[0023] In the exemplary embodiments or embodiments or variants described below, functionally or structurally similar elements are provided with the same or similar reference numerals wherever possible. Therefore, to understand the features of the individual elements of a specific embodiment, reference should be made to the description of other embodiments or the general description of the invention.

[0024] To facilitate the description, a Cartesian xyz coordinate system is shown in the drawing, from which the respective positional relationship of the components shown in the figures results. Fig. 1 the y-direction runs perpendicular to the drawing plane, the x-direction to the right and the z-direction upwards.

[0025] In Fig. 1 illustrates an embodiment of a measuring device 10 for interferometrically measuring the shape of an optical surface 12 of a test piece 14. The measuring device 10 can be used, in particular, to determine a deviation of the actual shape of the surface 12 from a desired shape. The test piece 14 can be, for example, a mirror of a projection exposure system for EUV microlithography, such as the one shown in Fig. 3, with a non-spherical surface for reflecting EUV radiation with a wavelength of less than 100 nm, in particular a wavelength of approximately 13.5 nm or approximately 6.8 nm. The test object 14 can be, for example, the mirror 226 of the projection lens 216 of the projection exposure system 200 according to Fig. 3. The non-spherical surface of the mirror may, for example, have a freeform surface with a deviation from any rotationally symmetric asphere of more than 5 µm and a deviation from any sphere of at least 1 mm.

[0026] The measuring device 10 comprises an adjustable holder 15 for holding the test object 14. The holder 15 is fastened to a frame structure 46 of the measuring device 10. Furthermore, the measuring device 10 comprises an optical measuring module 11 with a radiation source 16 for providing a sufficiently coherent measuring radiation 18 as the input wave 23. In this exemplary embodiment, the radiation source 16 comprises a waveguide 20 with an exit surface at which the input wave 23 originates. The waveguide 20 is connected to a radiation generation module 22 shown, e.g., in the form of a laser. For this purpose, for example, a helium-neon laser with a wavelength of approximately 633 nm can be provided. However, the measuring radiation 18 can also have a different wavelength in the visible or non-visible wavelength range of electromagnetic radiation.The radiation source 16 with the waveguide 20 represents only one example of a radiation source 16 that can be used for the measuring device. In alternative embodiments, instead of the waveguide 20, an optical arrangement with lens elements, mirror elements or the like can be provided to provide a suitable input wave from the measuring radiation 18.

[0027] The optical measurement module 11 further comprises a beam splitter 24, a reference element 26, a test optics 30, and a detection device 36. The input wave 23 first passes through the beam splitter 24 and then strikes the reference element 26 in the form of a Fizeau element, which is configured here as a Fizeau collimator. The Fizeau collimator has a Fizeau surface 27, at which a portion of the incoming measurement radiation 18 is reflected as a reference wave 28, which travels back in the beam path of the input wave 23. The reference element 26 in the form of the Fizeau collimator is held by a holder that is attached to the frame structure 46.

[0028] The portion of the measurement radiation 18 passing through the Fizeau collimator is referred to as cavity radiation 29. This enters a so-called interferometer cavity 25 of the interferometric measuring device 10. The interferometer cavity 25 is the section of the measuring device 10 through which only the cavity radiation 29, i.e., the measurement radiation 18 after separation of the reference wave 28, passes. The interferometer cavity 25 extends between the reference element 26 in the form of the Fizeau collimator and the test piece 14.

[0029] The cavity radiation 29 is focused as it passes through the Fizeau collimator and, in the present embodiment, strikes a so-called K-system as a plane wave, which forms the aforementioned test optics 30 for generating a test wave 32 for irradiation onto the surface 12 of the test object 14. The test wave 32 generated by the test optics 30 has a wavefront that is at least partially adapted to a desired shape of the optical surface 12. The test wave 32 is reflected by the optical surface 12 of the test object 14 and travels back to the test optics 30 as a returning test wave 32r. Due to the wavefront adapted to the desired shape of the optical surface 12, the test wave 32 strikes the optical surface 12 essentially perpendicularly at every location on the optical surface 12 and is reflected back into itself.

[0030] In the present embodiment, the test optics 30 are formed by a diffractive optical element in the form of a CGH (computer-generated hologram) arranged in the beam path of the measuring radiation 18. The diffractive optical element serves to generate a test wave 32 from the incident plane wave 29, the wavefront of which is adapted to the desired shape of the optical surface 12. Optionally, two or more CGHs can also be arranged in the beam path of the measuring radiation 18.

[0031] Furthermore, the measuring device 10 contains the above-mentioned detection device 36 with the above-mentioned beam splitter 24 for leading the combination of the returning test wave 32r and the reference wave 28 out of the beam path of the input wave 23 and an observation unit 38 for detecting an interferogram generated by superimposing the test wave 32r with the reference wave 28.

[0032] The returning test wave 32r and the reference wave 28 impinge on the beam splitter 24 as convergent beams and are reflected by the beam splitter 24 toward the observation unit 38. Both convergent beams pass through an aperture 40 and an eyepiece 42 of the observation unit 38 and finally impinge on a two-dimensional detector 44 of the observation unit 38. The detector 44 can be configured, for example, as a CCD sensor and records an interferogram generated by the interfering waves.

[0033] Furthermore, the measuring device 10 comprises an evaluation device 45 for determining the actual shape of the optical surface 12 of the test object 14 from the acquired interferogram or multiple acquired interferograms. For this purpose, the evaluation device 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 can contain a data storage device or an interface to a network to enable an external evaluation unit to determine the surface shape using the interferogram stored or transmitted over the network.

[0034] As mentioned above, the test piece 14 and the reference element 26 are attached to the frame structure 46, ie, the test piece 14 and the reference element 26 are held by the frame structure 46. Furthermore, the test optics 30, the beam splitter 24 and the observation unit 38, and possibly also the radiation generation module 22, can also be attached to the frame structure.

[0035] In the present embodiment, the measuring device 10, as described, is of the Fizeau type; however, alternative interferometer types can also be used. Such alternative interferometer types include, for example, the Twyman-Green type, the Michelson type, and the Mach-Zehnder type, etc. Examples of such interferometers are described in Chapter 2 of the textbook by Daniel Malacara, Optical Shop Testing, 2nd edition, Wiley Interscience Publication (1992). Furthermore, the measuring device 10 can also have a configuration in which the reference wave is split off at a diffractive optical element into a reference arm, which is tilted relative to a measuring arm in which the test wave guided for measuring the test object 14 runs. Such a configuration is known to the person skilled in the art, for example, from US 10,337,850 B2.

[0036] Furthermore, the measuring device comprises a laminar flow module 50 for generating a laminar air flow 55 within the interferometer cavity 25. The laminar air flow 55 serves for the spatial stabilization and uniform distribution of the temperature and flow fields so that the refractive index of the air 51 in the region of the interferometer cavity 25 is as homogeneous as possible.

[0037] To generate the laminar air flow 55, the laminar flow module 50 comprises an inflow side 52, approximately in the form of an inflow wall, with a flat inflow element, and an extraction side 54, approximately in the form of an extraction wall, with a flat extraction element. The inflow side 52 serves for the flat inflow of air 51 into the interferometer cavity 25 and for this purpose has an exit surface 53 which extends rectangularly in the xz coordinate plane, wherein the extension in the z direction essentially covers the interferometer cavity 25, i.e. the area between the reference element 26 and the test piece 14. The flat extraction element of the extraction side 54 has an inlet surface 48, via which the air 51 is extracted flatly from the interferometer cavity 25. The inlet surface 48 is preferably configured corresponding to the outlet surface 53 of the inflow side 52. The entire laminar flow module 50, ieBoth the inflow side 52 and the exhaust side 54 are arranged inside the frame structure 46. This ensures that no significant air turbulence is generated within the interferometer cavity 25 by the frame structure 46.

[0038] The flat inflow element of the inflow side 54 is connected, with its side opposite the outlet surface 53, to an air supply pipe 56 and is supplied with air 51 via it. The air supply pipe 56 comprises a straight pipe section 70, bends 66 and 68, a main pipe section 64, and a connecting section 62. Along the entire outlet surface 53, the flat inflow element of the inflow side 52 contains a fine-mesh fabric 94, which, according to one embodiment, is double-meshed with a spacing of between 5 mm and 20 mm, in particular of approximately 10 mm. The air 51 flows through this fabric before flowing into the interferometer cavity, whereby the air 51 is laminarized, i.e., possible turbulence in the air 51 supplied by the air supply pipe 56 is minimized due to the passage through the fabric.

[0039] The air 51 is fed into the supply air pipe 56 via an air supply pipe 90. This occurs via a branching section 92 which connects the air supply pipe 90 to the supply air pipe 56 and another supply air pipe 78. The another supply air pipe 78 supplies another laminar flow module 72 with the air 51. Thus, the two supply air pipes 56 and 78, the common air supply pipe 90 and the branching section 92 form a common supply air pipe system 88. A supply air throttle valve 59 and 79 is arranged in each of the supply air pipes 56 and 78. This allows the volume flows of the air supplied to the laminar flow modules 50 and 72 to be adjusted separately. In the illustration according to Fig. 1, the supply air throttle valves 59 and 79 are each illustrated in the maximum opening position (solid lines), with a closed position also shown (dashed lines).

[0040] The measuring device 10 further comprises a housing 89, which encloses the arrangement of the optical measuring module 11, the first laminar flow module 50, the frame structure 46, and the further laminar flow module 72. The air supply pipe 90 and the branching section 92 are located outside the housing 89, with the supply air pipes 56 and 78 extending through a respective opening in the housing 89 and thus each establishing a connection to the interior of the housing 89. The housing 89 represents a spatial encapsulation of the test chamber, in particular the interferometer cavity 25, from the environment.

[0041] The first supply air pipe 56 comprises an inlet sector 60 and an inlet sector 58. The inlet sector 60 comprises the aforementioned straight pipe section 70, the aforementioned bend 68, which is configured as a right-hand bend, and the aforementioned bend 66, which is configured as a left-hand bend 66. The inlet sector 58 has the aforementioned main pipe section 64 and the aforementioned connecting section 62. The air coming from the branching section 92 flows via the inlet sector 60, the two bends 68 and 66, the main pipe section 64, and the connecting section 62 into the inlet side 52 of the first laminar flow module 50.

[0042] As mentioned above, the laminarization module 50 serves in particular to keep the temperature within the interferometer cavity 25 as stable as possible; preferably, a temperature stability of 1 mK or less should be achieved. This is achieved, on the one hand, by ensuring that the air flowing into the interferometer cavity 25 from the inflow side 52 exhibits as little turbulence as possible, i.e., by representing as laminar a flow as possible, whereby thermal energy generated during the measurement process on the optical elements in the interferometer cavity 25, i.e., the reference element 26, the elements of the test optics 30, and the test piece 14, is dissipated as evenly as possible.In order to generate a flow that is as laminar as possible and to ensure that the heat energy is dissipated from the optical elements of the interferometer cavity 25 as evenly as possible, the measuring device 10 is configured to provide the air 51 supplied to the inflow side 52 with the best possible temperature stability.

[0043] For this purpose, several temperature adjustment devices are arranged in the supply air pipe system 88, namely a cooling device 102 and a cooling or heating device 104 in the air supply pipe 90, as well as another cooling device 100 in the supply air pipe 56. The cooling device 100 serves, in particular, to stabilize the pressure and humidity of the air 51 in the interferometer cavity and to establish temporal stability of the temperature in the interferometer cavity, so that the refractive index of the air 51 in the region of the interferometer cavity remains as stable as possible. According to one embodiment, the temperature adjustment devices 100, 102, and 104 are controlled such that a temperature stability of 1 mK or less is achieved within the interferometer cavity 25.

[0044] The main pipe section 64 of the supply air pipe 56 has a uniform cross-section. This can be round, rectangular, square, or another suitable shape. In the illustrated embodiment, the cross-sectional area of ​​the supply air pipe 56 is at least 20% of the outlet area 53 of the inflow side 52.

[0045] The connecting section 62 adjoining the main pipe section 64 has, starting from the main pipe section 64, a cross-section that increases toward the inflow side 52. The cross-section at the end of the connecting section 62 adjoining the inflow side 52 can be at least 70%, in particular at least 90%, of the outlet area 53 of the inflow side.

[0046] In the connecting section 62, several perforated plates 57 are arranged perpendicular to the flow direction of the air 51. These plates function as a pre-pressure stage / throttle and serve to pre-homogenize the air 51 supplied to the inlet side 52 in order to further improve the laminarization of the air 51 exiting the inlet wall 52.

[0047] The assembly consisting of the inlet side 52 in the form of the inlet wall, the fine-mesh fabric 94, the connecting section 62, and the perforated plates can also be referred to as a cistern. The suction side 54 can also be referred to as an extraction module. In a variant not shown in the drawing, this can be designed identically to the cistern and thus also be referred to as a return-air cistern.

[0048] The second laminar flow module 72 encloses the first laminar flow module 50 and partially the frame structure 46 and is designed to create the best possible basic climate within the housing 89 for the frame structure 46. In other words, the laminar flow module 72 ensures climate stability within the housing 89, so that the optical measuring module 11, and in particular the interferometer cavity 25, is well thermalized and sources of interference are avoided or minimized.

[0049] For this purpose, the second laminar flow module 72 comprises an inflow side 74 arranged to the left of the frame structure 46 with a flat inflow element and an exhaust side 76 arranged to the right of the frame structure 46 with a flat exhaust element. The flat inflow element has an outlet surface 53 for the outlet of the supplied air, and the flat exhaust element has an inlet surface 48 for the inlet of the exhausted air. In other words, the inflow side 52 and the exhaust side 54 of the first laminar flow module 50 lie within the volume surrounded by the inflow side 74 and the exhaust side 76 of the second laminar flow module 72. The laminar flow module 72 has a larger flow cross-section than the first laminar flow module 50.For this purpose, the inflow side 74 and the exhaust side 76 of the second laminar flow module 72 have an area at least five times larger, in particular at least ten times larger or at least twenty times larger. The described arrangement of the second laminar flow module 72 further improves the uniformity of the air flow and thus the refractive index within the interferometer cavity 25.

[0050] The inflow side 74 of the second laminar flow module 72 is connected to the second supply air pipe 78 with the side opposite its outlet surface. This comprises a bend 86 connected to the branching section 92 and an inflow sector 84, which comprises a straight main pipe section 82 with a constant cross-section and a connecting section 80, which, analogous to the connecting section 62, has a cross-section that increases in the air flow direction. Analogous to the supply air pipe 56, a cooling device 100 is arranged in the supply air pipe 78. Furthermore, perforated plates 57 can be arranged in the connecting section 80, analogous to the supply air pipe 56.

[0051] The entire supply air piping system 88, i.e., the air supply pipe 90, the branch section 92, and the two supply air pipes 56 and 78, are provided with thermal insulation 112 in the form of a thermally insulating piping jacket. This is intended to prevent the formation of radial temperature gradients in the piping and thus the formation of air turbulence. In other words, the external energy input is to be minimized so that the achieved temperature stability of the supply air is not negatively affected.

[0052] The extraction sides 54 and 76 of the two laminar flow modules 50 and 72 are connected to an exhaust air pipe system 114 for discharging the air 51 after passing through the respective laminar flow module 50 and 72. This is designed analogously to the supply air pipe system 88 and comprises a first exhaust air pipe 116 and a second exhaust air pipe 118. The exhaust air pipes 116 and 118 are each connected to the side of the flat extraction element of the extraction side 54 and 76 that is opposite the respective inlet surface 48. Furthermore, the exhaust air pipe system 115 comprises a merging section 120, with which the exhaust air pipes 116 and 118 are combined to form a common air extraction pipe 122.

[0053] An exhaust air throttle valve 124 and 126, respectively, is arranged in the exhaust air ducts 116 and 118. This allows the volumetric flow rates of the air discharged from the laminar flow modules 50 and 72 to be adjusted separately. The settings of the exhaust air throttle valves 124 and 126 are preferably coordinated with the settings of the supply air throttle valves 59 and 79.

[0054] In Fig. 2 illustrates a further embodiment of a measuring device 10 for interferometrically measuring a shape of an optical surface of a test piece 14. This embodiment differs from the embodiment according to Fig. 1 in the following properties. Firstly, the two supply air pipes 56 and 78 are not, as per Fig. 1, are not connected to a common air supply pipe 90, but rather to a separate air supply pipe 96 or 98, respectively. Alternatively, the supply air pipe 56 and the air supply pipe 96 can be configured as a continuous supply air pipe. The same applies to the supply air pipe 78 and the air supply pipe 98. In the embodiment according to Fig. 2, the two laminar flow modules 50 and 72 can be connected to separate ventilation units, whose volume flow and temperature offset can be controlled independently of each other. This allows the supply air throttle dampers 59 and 79 from Fig. 1 can be waived.

[0055] The two supply air pipes 56 and 78 each comprise an inflow sector 58 or 84 extending in a respective inflow direction of the air 51 into the interferometer cavity 25 as well as a bend 66 or 86. Analogous to the embodiment according to Fig. 1, a temperature adjustment device in the form of a cooling device 100 is arranged in the supply air pipe 56 and in the supply air pipe 78, respectively.

[0056] Furthermore, the cross section of the supply air pipe 56 in the embodiment according to Fig. 2 is considerably larger than in the embodiment according to Fig. 1. The cross-sectional area of ​​the main pipe section 64 is as follows Fig. 2 at least 70% of the outlet area 53 of the inlet side 52.

[0057] Furthermore, a thermal mass 106 in the form of a stack of metal plates 110, for example, aluminum plates, is arranged in the main pipe section 64. Flow channels 108 for the air 51 are arranged between the metal plates 110. For this purpose, the metal plates 110 can be provided with spacers so that the resulting gaps between the plates function as the flow channels 108.

[0058] Fig. 3 shows in a simplified representation the above-mentioned projection exposure apparatus 200 for microlithography with the mirror 226, which serves as a component for the measurement by means of the measuring device 10 according to Fig. 1 or Fig. 2. The mirror 226 is mounted on a support structure not shown in the drawing, for example in the form of a reference frame or a housing of the projection lens 216 of the projection exposure system 200.

[0059] The projection exposure system 200 according to Fig. 3 is designed for operation with EUV exposure radiation 201. In this text, EUV radiation is understood to mean electromagnetic radiation with a wavelength of less than 100 nm, in particular a wavelength of approximately 13.5 nm or approximately 6.8 nm. However, the present invention is not limited to use in such a system, but can also be implemented in the measurement of optical elements of projection exposure systems with other operating wavelengths, for example, operating wavelengths in the VUV or DUV range. In further applications, the test object measured with the measuring device 10 according to the invention can also be an optical element of another optical system for microlithography, such as a mask inspection system or a wafer inspection system.The projection exposure system 200 has an exposure beam path 217 in which the exposure radiation 201 is guided through an illumination optics 205 and a projection lens 216.

[0060] According to the embodiment of Fig.3, the illumination optics 205 comprises a field facet mirror 202, a pupil facet mirror 204, and two telescope mirrors 210 and 212. The exposure radiation 201, which is generated by an EUV radiation source comprising a plasma radiation source 206 and a collector mirror 208, is first directed onto the field facet mirror 202 and from there onto the pupil facet mirror 204. The first telescope mirror 210 and the second telescope mirror 212 are arranged in the radiation path downstream of the pupil facet mirror 204. A deflecting mirror 214 is arranged downstream in the radiation path, which deflects the radiation incident on it onto an object field in an object plane of the projection lens 216, which comprises six mirrors 218, 220, 222, 224, 226 and 228.

[0061] At the location of the object carrier, a reflective structure-bearing mask 230 is arranged on a mask table 232, which is imaged by means of the projection lens 216 into an image plane in which a substrate 234 coated with a radiation-sensitive layer (photoresist) in the form of a wafer is located on a wafer table 236.

[0062] The above description of exemplary embodiments, embodiments, and variants is to be understood as exemplary. The disclosure thus made enables those skilled in the art, on the one hand, to understand the present invention and the associated advantages, and, on the other hand, also encompasses obvious variations and modifications of the described structures and methods within the understanding of those skilled in the art. Therefore, all such variations and modifications, insofar as they fall within the scope of the invention as defined in the appended claims, as well as equivalents, are intended to be covered by the claims. List of reference symbols 10 Measuring device 11 optical measuring module 12 optical surface 14 candidates 15 Bracket 16 Radiation source 18 Measuring radiation 20 waveguides 22 Radiation generation module 23 Input shaft 24 beam splitters 25 Interferometer cavity 26 Reference element 27 Fizeau area 28 Reference wave 29 Cavity radiation 30 test optics 32 test shaft 32r returning test wave 36 Recording device 38 observation unit 40 aperture 42 eyepiece 44 Detector 45 Evaluation device 46 Frame structure 48 entrance area 50 first laminar flow module 51 Air 52 Inlet side 53 Exit surface 54 Suction side 55 laminar air flow 56 first supply air pipe 57 perforated sheet 58 Inflow sector 59 first supply air throttle valve 60 supply sector 62 connecting section 64 Main pipe section 66 Bend 68 Bend 70 straight pipe section 72 second laminar flow module 74 Inlet side 76 Suction side 78 second supply air pipe 79 second supply air throttle valve 80 connecting section 82 Main pipe section 84 Inflow sector 86 Bend 88 Supply air pipe system 89 Enclosure 90 Air supply pipe 92 branching section 94 fine mesh fabric 96 first air supply pipe 98 second air supply pipe 100 cooling device 102 Cooling device 104 Cooling or heating device 106 thermal mass 108 Flow channel 110 metal plate 112 thermal insulation 114 Exhaust pipe system 116 first exhaust pipe 118 second exhaust pipe 120 Merging section 122 Air discharge pipe 124 first exhaust air throttle valve 126 second exhaust air throttle valve 200 projection exposure system for microlithography 201 Exposure radiation 202 field facet mirrors 204 Pupillary facet mirrors 205 Lighting optics 206 Plasma light source 208 collector mirrors 210 first telescope mirror 212 second telescope mirror 214 Deflecting mirror 216 Projection lens 217 Exposure beam path 218, 220, 222, 224, 228 Mirrors of the projection lens 226 mirror of the projection lens serving as a component to be measured 230 Mask 232 Mask table 234 Substrat 236 wafer table QUOTES CONTAINED IN THE DESCRIPTION

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

[0000] US 2015 / 0198438A1

[0003] US 10,337,850 B2

[0035]

Claims

[1] Measuring device (10) for interferometrically measuring a shape of a surface (12) of a test specimen (14) comprising: - a radiation generation module (22) for generating a measuring radiation (18) for irradiation onto the surface of the test object, - a reference element (26) for splitting off a reference wave (28) from the measuring radiation before the measuring radiation passes through an interferometer cavity (25), and - a laminar flow module (50) for generating a laminar air flow within the interferometer cavity. [2] Measuring device according to claim 1, wherein the laminar flow module comprises an inflow side (52) for the planar inflow of air into the interferometer cavity and a suction side (54) for the planar suction of the air from the interferometer cavity. [3] Measuring device according to claim 2, wherein the inflow side (52) comprises a fine-mesh fabric (94) for laminarizing the air flowing into the interferometer cavity. [4] Measuring device according to claim 2 or 3, in which the inflow side is supplied with air via an air supply pipe (56), wherein at least one perforated plate (57) is arranged inside the air supply pipe for laminarizing the air supplied to the inflow side. [5] Measuring device according to one of claims 2 to 4, in which the inflow side is supplied with the air via an air supply pipe (56) which preferably has a cross-sectional area which corresponds to at least 20%, in particular at least 70%, of an outlet area (53) of the inflow side from which the air exits into the interferometer cavity. [6] Measuring device according to claim 5, wherein the supply air pipe (56) comprises a main pipe section (64) with a uniform cross-section and a connecting section (62) with an increasing cross-section for connection to the inflow side, and wherein the cross-sectional area, which preferably corresponds to at least 20% of the outlet area of ​​the inflow side, is a cross-sectional area of ​​the main pipe section. [7] Measuring device according to claim 5 or 6, wherein at least one temperature adjustment device (100) is arranged in the interior of the supply air pipe (56). [8] Measuring device according to one of the preceding claims, which comprises a frame structure (46) for holding at least the test object (14) and the reference element (26), wherein the laminar flow module (50) is arranged inside the frame structure. [9] Measuring device according to one of the preceding claims, which comprises a further laminar flow module (72) for generating a laminar air flow, which encloses the first laminar flow module (50). [10] Measuring device according to claim 9, wherein the further laminar flow module (72) has a larger flow cross-section than the first laminar flow module (50). [11] Measuring device according to claim 9 or 10, wherein the laminar flow modules (50, 72) are connected to a common supply air pipe system (88) which comprises a uniform air supply pipe (90) and a branching section (92) between the air supply pipe and the respective supply air pipe (56, 78) to the laminar flow modules, wherein at least one temperature adjustment device (102, 104) is arranged in the air supply pipe. [12] Measuring device according to claim 9 or 10, wherein the laminar flow modules (50, 72) are connected to a respective air supply pipe (96, 98) via a respective supply air pipe (56, 78), wherein the supply air pipes each comprise an inflow sector (58, 84) extending in a respective inflow direction of the air into the interferometer cavity and a bend (66, 86), wherein at least one temperature adjustment device (100) is arranged in each of the air supply pipes. [13] Measuring device according to one of claims 5 to 12, in which a thermal mass (106) with flow channels (108) is arranged in the interior of the supply air pipe. [14] Measuring device according to claim 13, the thermal mass comprises a stack of metal plates (110). [15] Measuring device according to one of the preceding claims, which is configured to produce a temperature stability of 1 mK or less in the interferometer cavity (25).

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