Measuring arrangement for determining the position of a movable component

Abstract

A measuring arrangement (10) for determining the position of a movable component (526) in a system (500) comprises an optical resonator (26) with two resonator mirrors (28, 30) which enclose a resonator cavity (32), a movable measuring mirror (14) assigned to the component, which is arranged within the resonator cavity for deflecting a measuring radiation (18) back and forth between the resonator mirrors and is movable from a home position, and a focusing lens (34). The lens (34) is arranged immovably within the resonator cavity (32) such that the measuring mirror is arranged in a cat's eye position of the lens in the home position.

Description

Background of the invention

[0001] The invention relates to a measuring arrangement for determining the position of a movable component in a system. Furthermore, the invention relates to a projection exposure system for photolithography, an illumination optics system for a projection exposure system for photolithography, a projection lens system for a projection exposure system for photolithography, an inspection system, and a coordinate measuring machine, each comprising at least one measuring arrangement of the aforementioned type.

[0002] Photolithography is used to produce microstructured components, such as integrated circuits or LCDs. In this context, the term "microstructured components" refers in particular to components with microstructures and / or nanostructures. Photolithography is often also referred to as "microlithography", although this can also be used in particular for the production of nanostructures. The production of microstructured components takes place using a so-called projection exposure system, which comprises an illumination device and a projection lens. The image of a mask located on a reticle and illuminated by the illumination device is projected by means of the projection lens onto a substrate (e.g.a silicon wafer) to transfer the mask pattern onto the light-sensitive coating of the substrate.

[0003] When operating such projection lenses, where the mask and wafer are typically moved relative to each other during a scanning process, the positions of the mirrors, some of which are movable in all six degrees of freedom, must be adjusted and maintained with high precision, both relative to each other and relative to the mask or wafer, in order to avoid or at least reduce aberrations and the associated impairment of the imaging result. For this position determination, for example, in EUV lithography, length measurement accuracies in the picometer (pm) range may be required over a path length of 1 meter.

[0004] Various approaches are known in the prior art for measuring the position of the individual objective mirrors as well as the wafer or wafer stage and the reticle plane. In addition to interferometric measuring arrangements, frequency-based position measurement using an optical resonator is also known. A setup used for this purpose in DE 10 2012 212 663 A1 comprises a resonator in the form of a Fabry-Perot resonator with two resonator mirrors, of which the first resonator mirror is attached to a reference element in the form of a measurement frame firmly connected to the housing of the projection lens of the projection exposure system, and the second resonator mirror (as a so-called "measurement target") is attached to an EUV mirror whose position is to be measured.The actual distance measuring device comprises a radiation source whose optical frequency is tunable. This radiation source generates coupling radiation that passes through a beam splitter and is coupled into the optical resonator. The radiation source is controlled by a coupling device such that the optical frequency of the radiation source is tuned to the resonant frequency of the optical resonator and thus coupled to this resonant frequency. The coupling radiation coupled out via a beam splitter is analyzed with an optical frequency measuring device, which may include, for example, a frequency comb generator for highly accurate determination of the absolute frequency.If the position of the EUV mirror changes in the extension direction of the resonator, the resonance frequency of the optical resonator also changes with the distance between the resonator mirrors and thus - due to the coupling of the frequency of the tunable radiation source to the resonance frequency of the resonator - also the optical frequency of the coupling radiation, which in turn is directly registered with the frequency measuring device.

[0005] A key factor for the functionality of an optical resonator for distance measurement is, on the one hand, that the measuring beam can complete as many revolutions as possible within the optical resonator (without leaving the cavity formed by the resonator) so that eigenmodes can develop in the resonator. Another key factor is the ability to couple the external radiation field (= "coupling field") present at the entrance to the resonator path to the mode field of the optical resonator (= "resonator field"). The coupling efficiency characteristic of this coupling is defined by the overlap integral between the coupling field and the resonator field, so that to achieve high coupling efficiency, the coupling field and the resonator field must match as closely as possible in all relevant parameters.

[0006] In practice, when using an optical resonator for distance measurement when measuring the position of a component or a mirror, problems can arise from the fact that movements of the measuring target mounted on the mirror can occur not only along the actual measurement direction, but also in other of the six degrees of freedom. Such (parasitic) movements that do not occur along the measurement direction, e.g., intentional or unintentional tilting or lateral displacement of the measuring target, can lead to a "wandering" of the main beam, on which the resonator modes are "threaded," in position and angle, with the result that sufficient coupling of the resonator field to the coupling field is no longer ensured.

[0007] Given the high demands placed on the beam direction deviation (which may, for example, require that angular deviations in the beam vector of the main beam are less than 0.1 mrad), ensuring that tilting or lateral displacements of the measuring target do not have an effect on the position determination is a demanding challenge. Underlying task

[0008] It is an object of the invention to provide a measuring arrangement which solves the aforementioned problems and, in particular, enables highly accurate position determination with reasonable effort. Inventive solution

[0009] The aforementioned object can be achieved according to a first aspect of the invention, for example, with a measuring arrangement for determining the position of a movable component in a system. The measuring arrangement comprises an optical resonator with two resonator mirrors enclosing a resonator cavity, as well as a measuring mirror assigned to the component, which is arranged within the resonator cavity for deflecting a measuring radiation back and forth between the resonator mirrors and is movable from a home position. Furthermore, the measuring arrangement comprises a focusing lens, which is immovably arranged within the resonator cavity such that the measuring mirror is arranged in a cat's eye position of the lens in the home position. The system in which the movable component is contained can be, for example, an optical system for photolithography.

[0010] The arrangement of the measuring mirror in the cat's eye position of the lens means that in this arrangement, radiation irradiated onto the lens parallel to the optical axis of the lens is focused onto the measuring mirror in such a way that its focal point lies on a mirror surface of the measuring mirror. This means that all individual rays entering the lens parallel to the optical axis meet on the mirror surface. In other words, the focal point of the lens lies on the mirror surface. In yet other words, the lens and the measuring mirror in the basic position represent a cat's eye arrangement. The lens can also be referred to as a Fourier lens and the measuring mirror as a measuring target. According to one embodiment, the measuring mirror functions as a folding mirror for folding the beam path of the measuring radiation within the resonator cavity.According to one embodiment, the movable component is an optical component, in particular a lens or a mirror, such as an EUV mirror, a wafer table or a reticle table of a projection exposure system for photolithography.

[0011] The arrangement of the measuring mirror in the cat's eye position of the lens means that the focal point of the lens defines the starting and reference position for the measuring mirror in such a way that the main beam associated with the measuring radiation passes through it in the basic position.

[0012] The statement that the lens is arranged immovably within the resonator cavity means that, in contrast to the movable measuring mirror, it is arranged at a fixed position within the resonator cavity, for example in a fixed positional relationship to the first and / or second resonator mirror.

[0013] According to the first aspect of the invention, the concept underlying the invention is preferably to repeatedly traverse the distance to be covered by the measuring radiation in the optical resonator by providing the cat's eye arrangement formed by the lens and the measuring mirror. By utilizing the principle of the reversibility of the light path, this ensures that lateral displacements or tilts on the part of the component to be measured, which do not act solely in the measuring direction, have little or no effect on the position determination, or have no significant impact on the measurement result.

[0014] In other words, the inventive use of the lens / measuring mirror arrangement ensures that, regardless of lateral displacements or tilts of the measuring mirror assigned to the component to be measured, the measuring radiation is essentially reflected back into itself. The measuring radiation thus travels back over the measuring mirror along essentially the same path, with the result that variations in the degrees of freedom that do not act along the direction of the measuring arm (measuring axis) are completely or almost completely eliminated in their effects on the measurement.

[0015] Compared to, for example, the use of a cube-corner retroreflector or a complete cat's-eye array as a measurement target, the measurement arrangement according to the invention enables a significantly more compact design of the photolithographic optical system. The use of a complete cat's-eye array as a measurement target is understood to mean the assignment of a fixed arrangement of the lens and mirror of the cat's-eye array to the movable component.

[0016] Due to the inventive immobile arrangement of the focusing lens arranged in the cat's eye position within the resonator cavity, only the measuring mirror needs to be assigned to the movable component in the photolithographic optical system. The measuring mirror can be designed as a plane mirror, for example, which can be arranged very space-savingly on an EUV mirror of a projection exposure system. The focusing lens can then be attached, for example, to at least one of the resonator mirrors, which requires no additional installation space on the EUV mirror. Using a cube-corner retroreflector or a complete cat's eye arrangement as the measurement target, however, would require considerably more installation space on the EUV mirror.

[0017] Furthermore, the measuring arrangement according to the invention prevents temperature fluctuations at the component of the photolithographic optical system, which can often be very large in the case of EUV mirrors, from impairing the measurement accuracy of the measuring arrangement. Due to the stationary arrangement of the focusing lens, it can be positioned far enough away from the movable component so that no significant temperature increase occurs. The measuring mirror, on the other hand, can be designed to be very insensitive to temperature fluctuations, for example, by designing it as a plane mirror.

[0018] According to one embodiment, a working distance between a measuring head comprising at least the resonator mirrors and the measuring mirror is at least 100 mm, in particular at least 200 mm or at least 500 mm.

[0019] According to a further embodiment, the lens is further configured or a further lens is provided to deflect the measuring radiation coming from the second resonator mirror onto the measuring mirror in such a way that the main beam associated with the measuring radiation penetrates the focal point of the lens in the undeflected state.

[0020] According to a further embodiment, the lens is arranged such that the measurement radiation coming from the first resonator mirror passes through the lens in a decentralized manner. Thus, the beam comprising the measurement radiation is deflected upon passing through the lens. Advantageously, the measurement radiation coming from the other resonator mirror also passes through the lens in a decentralized manner, specifically such that the beam comprising the measurement radiation is deflected upon passing through. Preferably, the direction of the deflection is opposite to the deflection direction of the beam coming from the first resonator mirror.

[0021] According to a further embodiment, at least one of the resonator mirrors and the lens form a coherent optical module. According to one embodiment, both resonator mirrors and the lens form the coherent optical module. In particular, the coherent module can be designed as a single piece or monolithic.

[0022] According to a further embodiment, a distance of the lens from at least one of the resonator mirrors is at least one order of magnitude smaller than the focal length of the lens.

[0023] According to a further embodiment, a working distance between one of the resonator mirrors and the measuring mirror is at least 100 mm, in particular at least 200 mm or at least 500 mm.

[0024] According to a second aspect of the invention, a measuring arrangement for determining the position of a movable component in an optical system for photolithography is provided. The measuring arrangement comprises an optical resonator with a first resonator mirror for coupling measurement radiation into a resonator cavity and a second resonator mirror. Furthermore, the measuring arrangement comprises a lens arranged within the resonator cavity such that a length of a section of the resonator cavity located between the lens and the second resonator mirror is between 0.5 and 1.0 times the value of a focal length of the lens.

[0025] In particular, the lower limit for the length of the section lying between the lens and the second resonator mirror can be 0.7 times or 0.9 times the focal length of the lens. Furthermore, the upper limit for the length of the section lying between the lens and the second resonator mirror can be 0.8 times or 0.6 times the focal length of the lens. Preferably, the first and second resonator mirrors enclose the resonator cavity. According to one embodiment, the movable component is an optical component, in particular a lens or a mirror, such as an EUV mirror, a wafer stage, or a reticle stage of a projection exposure system for photolithography.

[0026] The parameter selection made according to the second aspect of the invention (the length of the section of the resonator cavity located between the lens and the second resonator mirror is between 0.5 and 1.0 times the focal length of the lens) results in an optimized coupling efficiency for coupling a measurement radiation into the resonator cavity. This means that the coupling losses during coupling are minimized. This relationship can be understood using a model presented in the further description. Due to the optimization of the coupling efficiency, highly accurate position determination of the movable component is possible with reasonable effort.

[0027] According to an embodiment according to the second aspect of the invention, the length of the section of the resonator cavity located between the lens and the second resonator mirror corresponds to the distance between the lens and the second resonator mirror. That is, in this embodiment, the resonator cavity between the lens and the second resonator mirror is not folded.

[0028] According to a further embodiment according to the second aspect of the invention, a distance of the lens from the first resonator mirror is smaller than the focal length of the lens.

[0029] According to a further embodiment according to the second aspect of the invention, the first resonator mirror and the lens form a continuous optical module. According to one embodiment, the continuous module is integral or monolithic.

[0030] According to a further embodiment according to the second aspect of the invention, a working distance between the lens and the second resonator mirror, in other words the working distance of the measuring arrangement, is at most 150 mm, in particular at most 100 mm or at most 10 mm.

[0031] According to one embodiment according to the first or second aspect of the invention, the measuring arrangement is designed for frequency-based length measurement. According to one embodiment variant, the connected optical module is designed as a single piece or monolithic. According to a further embodiment, the measuring arrangement further comprises beam-shaping optics assigned to the first resonator mirror for coupling a measuring radiation into the optical resonator, wherein the connected optical module further comprises the beam-shaping optics. The beam-shaping optics can have the function of a focusing lens. According to a further embodiment, the measuring arrangement further comprises a tunable laser stabilized to a resonator mode of the resonator. A tunable laser is understood to be a laser whose optical frequency is variable.

[0032] According to a further embodiment according to the first or second aspect of the invention, the system is an optical system for photolithography.

[0033] According to a further embodiment according to the first or second aspect of the invention, the system is a projection exposure apparatus for photolithography.

[0034] Furthermore, the invention provides a projection exposure system for photolithography, which comprises at least one movable component and at least one measuring arrangement in an embodiment according to the first or second aspect of the invention for determining the position of the movable component. The projection exposure system can, in particular, have an operating wavelength in the EUV wavelength range, i.e., it is a so-called EUV projection exposure system. According to one embodiment, the movable component is an optical component, in particular a lens or a mirror, such as an EUV mirror, a wafer stage, or a reticle stage.

[0035] Furthermore, according to the invention, an illumination system of a projection exposure apparatus for photolithography is provided, which comprises at least one movable component and at least one measuring arrangement in an embodiment according to the first or second aspect of the invention for determining the position of the movable component.

[0036] Furthermore, according to the invention, a projection lens of a projection exposure apparatus for photolithography is provided, which comprises at least one movable component and at least one measuring arrangement in an embodiment according to the first or second aspect of the invention for determining the position of the movable component.

[0037] Furthermore, the invention provides an inspection system for inspecting a surface of a substrate, which comprises at least one movable component and at least one measuring arrangement in an embodiment according to the first or second aspect of the invention for determining the position of the movable component. The substrate can be, for example, a mask or a wafer.

[0038] The movable component can be a component in an optical system of the inspection system. An example of such an inspection system for mask or wafer inspection (without the measuring system according to the invention) is known from document DE 102012205181A1, the entire content of which is incorporated into the present application by reference.

[0039] Furthermore, according to the invention, a coordinate measuring machine is provided which comprises at least one movable component and at least one measuring arrangement in an embodiment according to the first or second aspect of the invention for determining the position of the movable component.

[0040] The movable component can be a component in an optical system of the coordinate measuring machine. The coordinate measuring machine serves to determine a respective positional deviation of one or more measuring points on a test component from a respective target position. An example of such a coordinate measuring machine (without the measuring arrangement according to the invention) is known from document DE10 2019 213 794A1, the entire content of which is incorporated into the present application by reference.

[0041] The features specified with regard to the above-mentioned embodiments, exemplary embodiments, or variant embodiments, etc. of the measuring arrangement 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 application has been filed. Brief description of the drawings

[0042] The above and other advantageous features of the invention are illustrated in the following detailed description of exemplary embodiments of the invention with reference to the accompanying schematic drawings. They show: Fig. 1 shows an embodiment of a measuring arrangement according to a first aspect of the invention, which is configured for determining the position of a movable component, Fig. 2 a beam generation and evaluation device of the measuring arrangement according to Fig. 1, Fig. 3 shows an embodiment of a measuring arrangement according to a second aspect of the invention, which is configured for determining the position of a movable component, Fig. 4 shows a further embodiment of the measuring arrangement according to the second aspect of the invention, Fig. 5 shows a section of a projection exposure apparatus for photolithography with a movable component, the position of which can be determined by means of a measuring arrangement according to one of the Fig. 1, Fig. 3 or Fig. 4 can be determined, Fig. 6 an embodiment of the projection exposure system according to Fig. 5, and Fig. 7 an enlarged detailed view of the projection exposure system according to Fig. 6 with a measuring arrangement integrated therein according to one of the Fig. 1, Fig. 3 or Fig. 4. Detailed description of embodiments according to the invention

[0043] 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 exemplary embodiments or the general description of the invention.

[0044] 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 x-direction runs perpendicular to the drawing plane, the z-direction to the right and the y-direction upwards.

[0045] In Fig. 1 illustrates an embodiment of a measuring arrangement 10 according to a first aspect of the invention. This measuring device 10 is used to determine the position of a movable component of a Fig. 5 is configured for photolithography using the optical system 500 illustrated in sections. The measuring arrangement 10 according to Fig. 1 comprises a measuring head 12 and a measuring mirror 14, which can also be referred to as a measuring target and is attached to the movable component and thus associated with it. To determine the position of the movable component, the distance between the measuring head 12 and the measuring mirror 14 is determined using the measuring arrangement, as described in detail below.

[0046] Fig. 6 shows a simplified representation of the optical system 500 in the form of a projection exposure system for photolithography. Fig. 5 shows a section of the projection exposure apparatus according to Fig. 6 with a mirror 526, which here serves as the aforementioned movable component. In the illustrated embodiment, the movable component with the mirror 526 is a component of a projection lens 516 of the projection exposure system. Alternatively, the movable component can also be a component of the illumination system 515 of the projection exposure system.

[0047] As mentioned, in the present embodiment, the component is the mirror 526, which is mounted on a Fig. 5 or on a housing of the optical system 500. The support structure 502 or the housing is also referred to below as the reference frame. In order to monitor the position and / or orientation of the component 526 with respect to the reference frame during operation, i.e., in situ, the distance of selected measuring points M from the support structure 502 is determined.

[0048] According to the present embodiment, the position of six measuring points M1 to M6, in particular in a hexapod configuration as shown in Fig. 5 is shown as an example, in each case in relation to an associated reference point R1 to R6 on the support structure 502. Thus, six hexapod lengths L1 to L6 are determined. The determination of the respective position of the six measuring points M1 to M6 is carried out by measuring the lengths L1 to L6, in each case by means of an example of the above-mentioned measuring arrangement 10 or an example of the one described below with reference to the Fig. 3 and Fig. 4 described measuring arrangement 210.

[0049] The Fig. The photolithographic projection exposure system illustrated in Figure 6, serving as optical system 500, is designed for operation with EUV exposure radiation. EUV radiation, as used herein, refers to 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 projection exposure systems with other operating wavelengths, for example, operating wavelengths in the VUV or DUV range. In further applications, the invention can also be implemented in another optical system for photolithography, such as a mask inspection system or a wafer inspection system.

[0050] According to the embodiment of Fig. 6, the optical system 500 in the form of an EUV projection exposure system comprises a field facet mirror 503 and a pupil facet mirror 504. The light from a light source unit, which comprises a plasma light source 506 and a collector mirror 508, is directed onto the field facet mirror 503. A first telescope mirror 510 and a second telescope mirror 512 are arranged in the light path downstream of the pupil facet mirror 504. A deflection mirror 514 is arranged downstream in the light path, which deflects the radiation incident upon it onto an object field in the object plane of the projection lens 516, which comprises six mirrors 518, 520, 522, 524, 526, and 528. The collector mirror 508, the field facet mirror 503, the pupil facet mirror 504, the two telescope mirrors 510 and 512 as well as the deflection mirror 514 together form the illumination system 515 of the projection exposure system.The radiation of the plasma light source 506 passes through the illumination system 515 and then strikes the object field in the object plane, ie the illumination system 515 illuminates the object field.

[0051] At the location of the object carrier, a reflective structure-bearing mask 530 is arranged on a mask table 532, which is imaged by means of the projection lens 516 into an image plane in which a substrate 534 coated with a light-sensitive layer (photoresist) is located on a wafer table 536.

[0052] Fig. 7 shows an enlarged detailed view of the projection exposure system serving as optical system 500 from Fig. 6 in the area of ​​the mirror 526 of the projection lens 516, which serves as a movable component. Fig. 7 shows the measuring arrangement 10 or the one shown in the Fig. 3 and Fig. 4 is shown in simplified form. The mirror 526 is movably held, for example, by the support structure 502 on the housing or on the wafer table 536 and thus represents the movable component in this exemplary embodiment. The support structure 502 is not shown in detail for reasons of clarity. The measuring head 12 of the measuring arrangement 10 or the measuring head 212 of the measuring arrangement 210 is arranged in a stationary manner on the housing or, for example, on the mask table. The measuring mirror 14 or the corresponding measuring target of the measuring arrangement 210 is fastened to the underside of the mirror 526. Depending on the result of the position measurement by the measuring arrangement 10 or 210 and in particular according to the Fig. According to an exemplary embodiment, the position of the mirror 526 is adjusted by means of the further measuring arrangements 10 and 210 provided in the configuration illustrated in FIG. 5.

[0053] The Fig. 1 comprises a radiation generation and evaluation device 16 for generating and evaluating measuring radiation 18, optionally an optical fiber 20, a beam-shaping optic in the form of a coupling lens 22, an optical module in the form of a resonator module 24 and the measuring mirror 14 already mentioned above. The measuring head 12, also already mentioned above, comprises at least the optical resonator module 24 and the coupling lens 22. The beam generation and evaluation device 16 can also be part of the measuring head 12 or can be arranged outside of it, as in Fig. 1 illustrates.

[0054] The beam generation and evaluation device 16 is in Fig. 2 shows an exemplary embodiment in detail. This is based on the principle that a laser 42, whose optical frequency is tunable, follows a frequency of the optical resonator 26 via a suitable control loop (in the example shown, according to the Pound-Drever-Hall method), so that the length of the resonator 26 ultimately to be measured, and thus the distance between the measuring head 12 and the measuring mirror 14, is encoded as the frequency of the tunable laser 42. The laser 42 serves as a radiation source for the measuring radiation 18, which lies, for example, in the visible or infrared wavelength range.

[0055] The device 16 comprises a Faraday isolator 44, an electro-optical modulator 46, a polarization-optical beam splitter 48, a lambda / 4 plate 50, a photodetector 52 and a low-pass filter 54. The part of the measuring radiation 18 passing through the lambda / -plate 50 exits via the Fig. 1 into the measuring head 12. Referring again to Fig. 2, for frequency measurement, a portion of the measurement radiation 18 emitted by the tunable laser 42 is coupled out via a beam splitter 56 and fed to an analyzer 58 for frequency measurement. The actual frequency measurement in the analyzer 58 can be performed, for example, by comparison with a frequency reference, e.g., an fs frequency comb of a femtosecond laser. The resonator module according to Fig. 1. The measuring radiation 18 exiting the measuring head 12 re-enters the device 16 via the optical fiber 20 and is detected by the photodetector 52. For further details regarding the operation of the device 16, reference is made to DE 10 2018 208 147 A1. The current distance between the measuring head 12 and the measuring mirror 14, and thus the position of the movable component, is determined from the frequency measured in the analyzer, which changes accordingly when the resonator length changes.

[0056] The resonator module 24, in conjunction with the measuring mirror 14 serving as the measurement target, forms an optical resonator 26. The resonator module 24 comprises a first resonator mirror 28 and a second resonator mirror 30 of the resonator 26, which enclose a resonator cavity 32. In the embodiment shown, the first resonator mirror 28 has a curved mirror surface, and the second resonator mirror 30 has a flat mirror surface. The measuring mirror 14 is arranged to deflect the measuring radiation 18 back and forth between the two resonator mirrors 28 and 30, which are both aligned in the positive z-direction and thus in the same direction. In other words, the measuring mirror 14 functions as a folding mirror for folding the beam path of the measuring radiation 18 within the resonator cavity 32.

[0057] Furthermore, the optical resonator 26 comprises a focusing lens 34 whose diameter is sufficiently large that both the beam path of the measuring radiation 28 in the region of the first resonator mirror 28 and the beam path of the measuring radiation 18 in the region of the second resonator mirror 30 are encompassed by the focusing lens 34. In other words, the focusing lens 34 is configured such that the measuring radiation 18 reflected by the first resonator mirror 28 and the measuring radiation 18 reflected by the second resonator mirror 30 pass through the focusing lens 34. Both the measuring radiation 18 coming from the first resonator mirror 28 and the measuring radiation 18 coming from the second resonator mirror 30 pass through the focusing lens 34 in a decentralized manner.

[0058] This results in the measuring beam 19 formed by the measuring radiation 18 within the optical resonator 26 being deflected as it passes through the focusing lens 34, in such a way that the main beam 25 associated with the measuring beam 19 passes through a focal point 36 of the focusing lens 34. This applies both to the main beam 25 of the measuring radiation 18 emanating from the first resonator mirror 28 and to the main beam 25 of the measuring radiation 18 emanating from the second resonator mirror 30. The focal point 36 of the focusing lens 34 is understood to be the focal point of all individual beams irradiated onto the focusing lens 34 parallel to the optical axis of the focusing lens 34.

[0059] In other words, the measuring mirror 14 is in the Fig. 1, which is also referred to as the basic position, in a cat's eye position of the focusing lens 34. The arrangement of the measuring mirror 14 in the cat's eye position of the focusing lens 34 means that, in this arrangement, radiation irradiated onto the focusing lens parallel to the optical axis of the focusing lens is focused onto the measuring mirror 14 such that its focal point lies on a mirror surface of the measuring mirror 14. The arrangement of the focusing lens 34 and the measuring mirror 14 can also be referred to as a cat's eye arrangement.

[0060] The optical resonator 26 is in Fig. 1 with a dashed rectangle. The functional structure of the optical resonator 26 is shown below and designated by the reference numeral 26f. The optical elements of the resonator module 24, namely the resonator mirrors 28 and 39 as well as the focusing lens, can be separate elements or, as in the specific embodiment of the optical resonator according to Fig. 1. In the latter case, the resonator module 24 is a coherent optical module, which can in particular be designed in one piece or monolithically.

[0061] The course of the beam path of the measuring radiation 28 folded by the measuring mirror 14 within the optical resonator 26 corresponds to that of a Gaussian beam whose waist is located at the second resonator mirror 30, wherein the Gaussian beam is modified by the influence of the focusing lens 34 in such a way that the beam is deflected as it passes through the focusing lens 34.

[0062] Due to the deflection of the measuring radiation 18 coming from the first resonator mirror 28 when passing through the focusing lens 34, the focal point 36 of the focusing lens 34 on the measuring mirror 14 is offset by the distance u from the optical axis 29 of the first resonator mirror 28; this also applies analogously to the optical axis of the second resonator mirror 30. The distance u is at least half the beam diameter of the measuring radiation 18 radiating onto the focusing lens 34 from the first resonator mirror 30.

[0063] In the specific embodiment according to Fig. 1, the resonator module 24 is made of a lens material and has a curved surface 38 on its side facing into the interior of the resonator cavity 32 to provide the resonator module 24 with the function of a focusing lens 34. On the side facing away from the resonator cavity 32, i.e., on an outer surface 40, the resonator module 24 has respective reflective coatings to provide the function of the resonator mirrors 28 and 30.

[0064] The focal length of the focusing lens 34, which, taking into account the optical theory, leads to thick lenses, in the concrete design of the resonator module 24 according to Fig. 1 indicates the distance between a second principal plane H' assigned to the curved surface 38 and the focal plane, is denoted by F. The nominal distance between the focusing lens 34, specifically the principal plane H', and the measuring mirror 14 is denoted by B0 (reference numeral 33). The distance B0 represents a working distance of the measuring arrangement 10, which represents the distance between the measuring head 12 and the measuring mirror 14 serving as the measuring target during the measuring operation of the measuring arrangement 10. Due to the cat's eye functionality described above, the following applies: B0 = F. In the functional representation 26f, the focusing lens 34 is represented as an infinitely thin approximated lens, i.e. the two principal planes H and H' coincide.

[0065] During measuring operation, a displacement of the measuring mirror 14, starting from the Fig. 1, which is also referred to in this text as the basic position, is permitted in the z-direction by ±d, where |d| is at least a factor of 5, in particular at least a factor of 10 smaller than F (|d|«F). The real distance B between the focusing lens 34 and the measuring mirror 14 is thus B0±d, thus: B ≈ F. The respective distance of the first resonator mirror 28 and second resonator mirror 30 from the focusing lens 34 is generally designated by G' (reference symbol 37') and G'' (reference symbol 37''), respectively. In the specific embodiment according to Fig. 1, in which the two resonator mirrors 28 and 30 are arranged at the same distance from the focusing lens 34, the common distance is denoted by G (reference numeral 37). The distance G, or the distances G' and G'', is / are smaller than F by at least a factor of 10, in particular by at least a factor of 50 (G «F). The relationship between the distance G and the focal length F is defined by a design parameter γ (G = y F). The length of the optical resonator 26 is 2F + G' + G'' or 2F + 2G. The radius of curvature of the resonator mirror 28 is denoted by R (reference numeral 27).

[0066] The crucial optical property, which is indispensable for the functioning of an optical cavity suitable for distance measurement, such as the optical resonator 26, is that a beam can complete a high, in the limiting case infinite, number of revolutions within the cavity, which is limited by the size of its mirrors, without leaving the cavity, regardless of the parasitic deflections of the measuring target in the form of the measuring mirror 14. If this condition is met, the main beam, on which the modes of the resonator are, as it were, threaded, must not additionally migrate in its position and angle as a result of the parasitic movements leading to the parasitic deflections, to such an extent that sufficient coupling to the irradiated measuring radiation field is no longer ensured or the aforementioned coupling efficiency becomes too low.

[0067] In order to achieve high coupling efficiency, the measuring radiation field coupled into the optical resonator 26 at the entrance to the resonator path, i.e. at the first resonator mirror 30, must match the mode field of the resonator 26 as closely as possible, whereby the latter should vary or migrate as little as possible in its main beam due to parasitic movements. For modeling purposes, the parasitic movements are designated by the two tilt angles θx and θy, i.e. the tilt of the measuring mirror 14 serving as the measurement target with respect to tilt axes oriented perpendicular to the surface normal of the measuring mirror 14, specifically the x-axis and the y-axis. In the modeling explained below, maximum tilts of ±θmax are assumed in θx and θy.

[0068] Furthermore, the coupling efficiency is influenced by the displacement ±d of the measuring mirror 14 in the direction of the surface normal of the measuring mirror 14 during the measurement process. For the modeling, a maximum permissible value d max set.

[0069] According to one embodiment, the modeling is based on the well-known formalism of matrix optics. The essential conditions for optical resonators suitable for frequency-based distance measurement are derived from the matrix formalism of paraxial optics.

[0070] As a result of the modeling, the maximum coupling losses k max as follows: κmax≈1−exp(−Spos,max2−Ssize,max2)≈Spos,max2+Ssize,max2.

[0071] The following applies to the combined loss contributions Spos,max2 and Size,max2: Spos,max≈2qθmaxdmax+udmaxFam(q,γ)λF, Ssize,max≈2qq(2q+5γ−5)4(2γ+q−2)dmaxF.

[0072] Here, Spos and Ssize are quality measures regarding the respective sensitivity of the optical resonator 26 to the parasitic interference movements caused by changes in the tilt angles θx and θy. Spos indicates the sensitivity of the beam coupling at the resonator mirror 28, which acts as the coupling mirror, due to position variations of the mode field of the optical resonator 26 at the location of the resonator mirror 28 caused by the parasitic interference movements. S tiltdenotes the sensitivity of the beam coupling at the resonator mirror 28 due to inclination variations of the mode field of the optical resonator 26 at the location of the resonator mirror 28 caused by the parasitic interference movements. Finally, Ssize indicates the sensitivity of the beam coupling at the resonator mirror 28 due to beam size variations of the mode field of the optical resonator 26 at the location of the resonator mirror 28 caused by the parasitic interference movements. The quality measures Spos and Ssize indicate the aforementioned sensitivities as a function of the design parameter q.

[0073] In expressions (2), the parameter γ denotes the value defined above with reference to Fig. 1 explained relationship between the distance G and the focal length F. The parameter u denotes the also previously described with reference to Fig. 1, by which the focal point 36 on the measuring mirror 15 is offset from the optical axis 29 of the resonator mirror, ie, the parameter quantifies a corresponding decentration. The wavelength of the measuring radiation 18 is denoted by λ. The parameter a m represents a dimensionless auxiliary quantity and is defined as follows: am(q,γ)=214πq1−γ2γ+q−2.

[0074] In Fig. 3 illustrates an embodiment of a measuring arrangement 210 according to a second aspect of the invention. This measuring arrangement differs from the measuring arrangement 10 according to Fig. 1 only in the configuration of the optical resonator, which in the embodiment according to Fig. 3 is designated by reference numeral 226. The functional structure of the optical resonator 226 is shown below and designated by reference numeral 226f. The optical resonator 226 comprises an input mirror designed as a resonator mirror 228. This differs from the curved resonator mirror 28 according to Fig. 1 in that it is designed as a plane mirror. Analogous to the embodiment according to Fig. 1, the optical resonator 226 comprises Fig. 3 a second planar resonator mirror 230. A resonator cavity 232 is formed between the first resonator mirror 228 and the second resonator mirror 230.

[0075] Unlike the embodiment according to Fig. 1, the resonator mirrors 228 and 230 do not point in the same direction, but rather face each other; a folding mirror is not present. Instead, the second resonator mirror 230 represents the measurement target. The distance between the two resonator mirrors 228 and 230 corresponds to the length L of the resonator 226 or the resonator cavity 232.

[0076] In the measuring arrangement 210 according to Fig. 3, a focusing lens 229 is additionally arranged at a distance G (reference numeral 237) in front of the resonator mirror 228 within the resonator cavity 232. The focusing lens 229, which has the focal length F (reference numeral 235), assumes the function provided by the curvature of the resonator mirror 228 for forming the Gaussian beam within the resonator cavity 232 between the first resonator mirror 228 and the second resonator mirror 230, which represents the measurement target. The distance G between the first resonator mirror 228 and the focusing lens 229, which is approximated as infinitely thin, is smaller than F by at least a factor of 2, in particular by at least a factor of 5 (G < F).

[0077] The functional structure of the optical resonator 226 is shown below and designated by reference numeral 226f. The distance between the focusing lens, approximated as infinitely thin, and the second resonator mirror 230 is denoted by B, where B0 (reference numeral 233) is the nominal distance. Since a displacement of the second resonator mirror 230 in the z-direction by ±d is permitted during measurement operation, the actual distance between the focusing lens 229 and the second resonator mirror 230 is B=B0±d.

[0078] The coupling lens 22, together with the first resonator mirror 228 and the focusing lens 229, forms a measuring head 212. The distance B0 between the focusing lens 229 and the resonator mirror 230 represents a working distance of the measuring arrangement 210, which refers to the distance between the measuring head 212 and the resonator mirror 230 serving as the measurement target during the measurement operation of the measuring arrangement 210. The working distance of the measuring arrangement 210 is also referred to in this text as the working distance between the focusing lens 229 and the resonator mirror 230.

[0079] Another, in Fig. The embodiment of the measuring device 210 according to the second aspect of the invention illustrated in Figure 4 differs from the embodiment according to Fig. 3, the resonator mirror 228 and the focusing lens 229 form a coherent mirror module 239. This consists of a lens material that transmits the measuring radiation 18 and has an outward-facing surface 241 opposite the coupling lens 22 and an inward-facing surface 243 (into the resonator cavity 232). The outward-facing surface 241 has a reflective coating to provide the function of the first resonator mirror 228. The inward-facing surface 241 is convexly curved to provide the function of the focusing lens 229. The focal length F and the distance B0 are measured starting from the second principal plane H' of the mirror module 239, which is assigned to the inward-facing surface 243. The distance G, on the other hand, is measured between the outward-facing surface 241 and the first main plane H of the mirror module 239.

[0080] The distance B, in particular its nominal length B0, is according to an embodiment of the measuring arrangement 210 according to the invention Fig. 3 or Fig. 4 between 0.5 times and 1.0 times the focal length F of the focusing lens 229, ie using a design parameter β the following relationship applies: B0=β F with 0.5<β<1.0.

[0081] When selecting the design parameter β within the value range of 0.5 to 1.0 specified according to the embodiment of the invention, an operating point for the optical resonator 226 results at which the coupling efficiency for coupling the measurement radiation 18 into the optical resonator 226 is in an optimal range. This means that the coupling losses during the coupling of the measurement radiation 18 are minimized. According to a further embodiment, 0.6 < β < 0.9 applies. The advantageous nature of the specified value range for the design parameter β can be understood from the modeling of the coupling losses presented below.

[0082] The crucial optical property, which is indispensable for the functioning of an optical cavity suitable for distance measurement, such as the optical resonator 226, is that a beam can complete a high, in the limiting case infinite, number of revolutions within the cavity, which is limited by the size of its mirrors, without leaving the cavity, regardless of the parasitic deflections of the measurement target in the form of the resonator mirror 230. If this condition is met, the main beam, on which the modes of the resonator are, as it were, threaded, must not additionally migrate in its position and angle as a result of the parasitic movements leading to the parasitic deflections, to such an extent that sufficient coupling to the irradiated measurement radiation field is no longer ensured or the aforementioned coupling efficiency becomes too low.

[0083] In order to achieve high coupling efficiency, the measuring radiation field coupled into the optical resonator 226 at the entrance of the resonator path, i.e., at the first resonator mirror 228, must match the mode field of the resonator 226 as closely as possible, whereby the latter must vary or migrate as little as possible in its main beam due to parasitic movements. For modeling purposes, the parasitic movements are represented by the two tilt angles θ x and θ y , ie, the tilt of the resonator mirror 230 serving as the measurement target with respect to tilt axes oriented perpendicular to the surface normal of the resonator mirror 230, specifically the x-axis and the y-axis. In the modeling explained below, maximum tilts of ±θmax are assumed in θx and θy.

[0084] Furthermore, the coupling efficiency is influenced by the displacement ±d of the resonator mirror 230 in the direction of the surface normal of the resonator mirror 230 during the measurement process. Therefore, a maximum permissible value dmax is used for the displacement d for modeling purposes.

[0085] According to one embodiment, the modeling is based on the well-known formalism of matrix optics. The essential conditions for optical resonators suitable for frequency-based distance measurement are derived from the matrix formalism of paraxial optics.

[0086] As a result of the modeling, the maximum coupling losses k max as follows: κmax≈1−exp(−Spos,max2−Ssize,max2)≈Spos,max2+Ssize,max2. where Spos and Ssize are quality measures as a function of the design parameter β, the focal length F of the wavelength λ of the measuring radiation 18 and a further design parameter γ, defined by G = γ F, for which the following applies: Spos,max≈θmaxam(γ,β)Fλ, Ssize,max≈dmax4F1(1−β)(γ+β−βγ).

[0087] The quality measures Spos and Ssize indicate the respective sensitivity of the optical resonator 226 to the parasitic interference movements caused by changes in the tilt angles θx and θy. Spos indicates the sensitivity of the beam coupling at the resonator mirror 228, which acts as a coupling mirror, due to position variations of the mode field of the optical resonator 226 at the location of the resonator mirror 228 caused by the parasitic interference movements. Ssize indicates the sensitivity of the beam coupling at the resonator mirror 228 due to beam size variations of the mode field of the optical resonator 226 at the location of the resonator mirror 228 caused by the parasitic interference movements.

[0088] In the expressions (7), wm denotes the self-consistent beam size, which is as follows: wm=λ Fπ((1−γ)(β+γ−βγ)1−β)14=λ F am(γ,β).

[0089] This means that a mdefined as a dimensionless auxiliary quantity as follows: am(γ,β)=1π((1−γ)(β+γ−βγ)1−β)14.

[0090] 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 arrangement 12 measuring head 14 measuring mirrors 16 Radiation generation and evaluation device 18 Measuring radiation 19 Measuring beam 20 optical fibers 22 Coupling lens 24 Resonator module 25 Main beam 26 optical resonator 26f functional representation of the optical resonator 27 Radius of curvature R 28 resonator mirrors 29 optical axis of the resonator mirror 30 resonator mirrors 32 Resonator cavity 33 Working distance B0 34 Focusing lens 35 focal length F 36 Focus 37, 37', 37'' Distance G, G' or G'' 38 curved surface 40 outer surface 42 lasers 44 Faraday insulator 46 electro-optical modulator 48 polarization optical beam splitters 50 Lambda / 4 plate 52 photodetector 54 low-pass filters 56 beam splitters 58 Analyzer 210 Measuring arrangement 212 measuring head 226 optical resonator 226f functional representation of the optical resonator 228 resonator mirrors 229 Focusing lens 230 resonator mirrors 232 Resonator cavity 233 Distance B0 235 focal length F 237 Distance G 239 Mirror module 241 outward-facing surface 243 inward-facing surface 500 optical system 502 Support structure 503 Field facet mirror 504 Pupillary facet mirror 506 plasma light source 508 collector mirror 510 first telescope mirror 512 second telescope mirror 514 Deflecting mirror 515 lighting system 516 projection lens 518, 520, 522, 524, 526, 528 Mirror of the projection lens 530 Mask 532 Mask table 534 Substrat 536 wafer table 526 movable components 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] DE 10 2012 212 663 A1

[0004] DE 102012205181A1

[0038] DE 10 2019 213 794A1

[0040] DE 10 2018 208 147 A1

[0055]

Claims

[1] Measuring arrangement (10) for determining the position of a movable component (526) in a system (500), comprising: - an optical resonator (26) with two resonator mirrors (28, 30) which enclose a resonator cavity (32), - a measuring mirror (14) associated with the component, which is arranged within the resonator cavity for deflecting a measuring radiation (18) back and forth between the resonator mirrors and is movable from a basic position, and - a focusing lens (34) which is arranged immovably within the resonator cavity (32) such that the measuring mirror is arranged in a cat's eye position of the lens in the basic position. [2] Measuring arrangement according to claim 1, wherein a working distance between a measuring head (12) comprising at least the resonator mirrors (28, 30) and the measuring mirror (14) is at least 100 mm. [3] Measuring arrangement according to claim 1 or 2, in which the lens (34) is further configured or a further lens is provided to deflect the measuring radiation coming from the second resonator mirror (30) onto the measuring mirror (14) in such a way that the main beam associated with the measuring radiation penetrates the focal point (36) of the lens in the undeflected state. [4] Measuring arrangement according to one of the preceding claims, in which the lens (34) is arranged such that the measuring radiation (18) coming from the first resonator mirror (28) passes through the lens (34) in a decentralized manner. [5] Measuring arrangement according to one of the preceding claims, in which at least one of the resonator mirrors (28, 30) and the lens form a continuous optical module (24). [6] Measuring arrangement according to one of the preceding claims, in which a distance (37, 37', 37") of the lens (34) from at least one of the resonator mirrors (28, 30) is at least one order of magnitude smaller than the focal length (35) of the lens. [7] Measuring arrangement according to one of the preceding claims, in which a working distance (33) between one of the resonator mirrors (28, 30) and the measuring mirror (14) is at least 100 mm. [8] Measuring arrangement (210) for determining the position of a movable component (526) in a system (500) for photolithography, comprising: - an optical resonator (226) with a first resonator mirror (228) for coupling measuring radiation into a resonator cavity (232) and a second resonator mirror (230), and - a lens (229) arranged within the resonator cavity such that a length (233) of a section of the resonator cavity lying between the lens and the second resonator mirror is between 0.5 times and 1.0 times the value of a focal length (235) of the lens. [9] Measuring arrangement according to claim 8, wherein the length of the section of the resonator cavity (132) lying between the lens (229) and the second resonator mirror (230) corresponds to the distance (233) between the lens and the second resonator mirror. [10] Measuring arrangement according to claim 8 or 9, wherein a distance (237) of the lens (229) from the first resonator mirror (228) is smaller than the focal length (235) of the lens. [11] Measuring arrangement according to claim 9, wherein the first resonator mirror (228) and the lens (229) form a continuous optical module (239). [12] Measuring arrangement according to one of claims 8 to 11, wherein a working distance (233) between the lens (229) and the second resonator mirror (230) is at most 150 mm. [13] Measuring arrangement according to one of the preceding claims, which is designed for frequency-based length measurement. [14] Measuring arrangement according to one of the preceding claims, in which the system is an optical system for photolithography. [15] Measuring arrangement according to one of the preceding claims, in which the system is a projection exposure system (500) for photolithography. [16] Projection exposure system (500) for photolithography with at least one movable component (526) and at least one measuring arrangement (10; 210) according to one of the preceding claims for determining the position of the movable component. [17] Illumination system (515) of a projection exposure system (500) for photolithography with at least one movable component and at least one measuring arrangement (10; 210) according to one of claims 1 to 15 for determining the position of the movable component. [18] Projection lens (516) of a projection exposure system (500) for photolithography with at least one movable component and at least one measuring arrangement (10; 210) according to one of claims 1 to 15 for determining the position of the movable component. [19] Inspection system for inspecting a surface of a substrate, in particular a mask or a wafer, with at least one movable component and at least one measuring arrangement (10; 210) according to one of claims 1 to 13 for determining the position of the movable component. [20] Coordinate measuring machine with at least one movable component and at least one measuring arrangement (10; 210) according to one of claims 1 to 13 for determining the position of the movable component.

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