Measuring arrangement for determining the position of a movable component

Abstract

A measuring arrangement (10; 110, 210; 310) for determining the position of a movable component (526) in an optical system (500) for microlithography comprises: an optical resonator (26) with two resonator mirrors (28, 30) enclosing a resonator cavity (32), and a movable measuring mirror (14) associated with the component, which is arranged within the resonator cavity for directing a measuring beam back and forth between the resonator mirrors. The measuring mirror is arranged at a working distance (34) from one of the resonator mirrors, which has a curvature adapted to the measuring mirror such that its center point (31) is located on the measuring mirror or at most 10% of the working distance therefrom.

Description

Background of the invention

[0001] The invention relates to a measuring arrangement for determining the position of a movable component in an optical system for microlithography and to a projection exposure system for microlithography with at least one such measuring arrangement.

[0002] Microlithography is used to manufacture microstructured components, such as integrated circuits or LCDs. This is done 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 the projection lens onto a substrate (e.g., a silicon wafer) coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection lens, in order to transfer the mask structure to the light-sensitive coating of the substrate.

[0003] During operation of 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. This position determination can require very high levels of accuracy, particularly in EUV lithography.

[0004] Various approaches are known in the state of the art for measuring the position of individual objective mirrors, as well as the wafer or wafer stage and the reticle plane. In addition to interferometric measurement setups, frequency-based position measurement using an optical resonator is also known.

[0005] A according to Fig. The setup used for this purpose in US Pat. No. 3 of US Pat. No. 11,274,914B2 comprises a resonator with two resonator mirrors, a retroreflector in the form of a triple mirror, and a plane mirror serving as a measurement target, on which the beam path is folded. The resonator mirrors and the triple mirror constitute a measurement head that is firmly connected to the housing of the projection lens of the projection exposure system, and the measurement target is attached to an element of the projection exposure system whose position is to be measured. The actual distance measuring device comprises a radiation source whose optical frequency is tunable, which 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. Coupling radiation coupled out via a beam splitter is analyzed using an optical frequency measuring device, which may, for example, include a frequency comb generator for highly accurate determination of the absolute frequency. If the position of the component to be measured changes in the direction of extension of the resonator, the resonant frequency of the optical resonator changes along with the distance between the resonator mirrors, and thus - due to the coupling of the frequency of the tunable radiation source to the resonant frequency of the resonator - also the optical frequency of the coupling radiation, which in turn is directly recorded by the frequency measuring device.

[0006] The Fig. 3 of US11,274,914B2 is preferred over a triple mirror, which is also possible at this point, for optomechanical reasons, in particular to avoid a large number of reflections and to reduce the size of the structure.

[0007] However, if the plane mirror is slightly tilted during its axial displacement in measurement mode, this can lead to a lateral offset of the mode formed in the resonator on the resonator mirror serving as the coupling mirror. This reduces the efficiency of coupling the radiation field present at the entrance of the resonator path (= "coupling field") to the mode field of the optical resonator (= "resonator field"). If the coupling efficiency decreases beyond a certain tolerance limit, the accuracy of the position measurement suffers, potentially rendering the measurement unusable. Similar effects can also occur when using non-plane mirrors as measurement targets. Underlying task

[0008] It is an object of the invention to provide a measuring arrangement of the type mentioned at the outset, whereby the aforementioned problems are solved, and in particular to provide the measuring arrangement in a compact design with which a high measuring accuracy can be achieved in the position determination. Inventive solution

[0009] The aforementioned object can be achieved according to the invention, for example, with a measuring arrangement for determining the position of a movable component in an optical system for microlithography. The measuring arrangement comprises an optical resonator with two resonator mirrors which enclose a resonator cavity, and a movable measuring mirror which is assigned to the component and which is arranged within the resonator cavity for deflecting a measuring radiation back and forth between the resonator mirrors. The measuring mirror is arranged at a working distance from one of the resonator mirrors, which has a curvature matched to the measuring mirror such that its center, i.e. the center of curvature of said resonator mirror, is arranged on the measuring mirror or at most 20%, in particular at most 10%, at most 5% or at most 1%, of the working distance therefrom.

[0010] The statement that the center of curvature lies on the measuring mirror means that the center is arranged on a reflective surface used to deflect the measuring radiation back and forth. In other words, the measuring mirror is at most 10% of the working distance from the center of curvature of the first resonator mirror. The measuring mirror preferably serves to fold the beam path of the measuring radiation in the optical resonator. The working distance between the resonator mirror with the tuned curvature and the measuring mirror is understood to mean the length of the beam path of the measuring radiation between the resonator mirror and the measuring mirror in the case where the measuring mirror is tilted with respect to the aforementioned resonator mirror. The length of the beam path is measured along the axis of the beam path.

[0011] By matching the curvature of one of the resonator mirrors to the measuring mirror in such a way that its center is located on the measuring mirror or at most 20%, in particular at most 10%, at most 5%, or at most 1% of the working distance away from it, it is ensured that a tilt of the measuring mirror causes no or only a slight lateral displacement on the other resonator mirror, via which the measuring radiation is advantageously coupled into the resonator cavity. Thus, with the arrangement according to the invention, the coupling efficiency of the coupling field to the mode field of the resonator can be maintained high, thus achieving high measurement accuracy.

[0012] If the center of the first-mentioned resonator mirror is located on the measuring mirror, the beam position is perfectly stable when the measuring mirror is tilted on the other resonator mirror. This is because the position of the center of curvature of the first-mentioned resonator mirror, as seen from the other resonator mirror via the measuring mirror, remains unchanged even when the measuring mirror is tilted. If the center of curvature of the first-mentioned resonator mirror deviates from the position on the measuring mirror by no more than 20%, in particular no more than 10%, no more than 5%, or no more than 1% of the working distance, i.e., only slightly, then only a slight lateral shift of the resonator mode occurs on the other resonator mirror, the influence of which on the coupling efficiency and thus on the measurement accuracy can be tolerable.

[0013] According to one embodiment, one of the resonator mirrors is configured as a coupling mirror for coupling a measuring radiation into the resonator cavity and the other resonator mirror is configured as a counter mirror to the coupling mirror, wherein the resonator mirror with the curvature matched to the measuring mirror is the counter mirror.

[0014] According to a further embodiment, the optical resonator is configured to form a beam path with a beam waist for the measurement radiation, wherein the beam waist lies between the measurement mirror and the first resonator mirror with a curvature matched to the measurement mirror. A beam waist is the location of the beam path in the optical resonator where the beam has the smallest diameter or radius. According to one embodiment, the beam path within the resonator cavity is configured as a Gaussian beam.

[0015] According to a further embodiment, the beam waist is arranged at least 5% of the working distance from the measuring mirror and at least 5% of the working distance from the first resonator mirror. According to a further embodiment, the beam waist is arranged at least 10%, at least 20%, or at least 40% of the working distance from the measuring mirror and at least 10%, at least 20%, or at least 40% of the working distance from the first resonator mirror. According to a further embodiment, the beam waist is located centrally between the measuring mirror and the first resonator mirror.

[0016] According to a further embodiment, the further resonator mirror of the optical resonator, which together with the resonator mirror with the curvature matched to the measuring mirror, encloses the resonator cavity, has a curvature whose center lies on the side of the measuring mirror opposite the further resonator mirror and is at a distance from the measuring mirror of at least 10% of the working distance. Advantageously, the center is arranged at a distance from the measuring mirror of at least 10%, in particular at least 50% of the distance between the further resonator mirror and the measuring mirror. According to one embodiment, the radius of curvature of the further resonator mirror is matched to the length of the resonator cavity and the radius of curvature of the first resonator mirror in such a way that a Gaussian mode forms in the optical resonator.

[0017] According to a further embodiment, the further resonator mirror enclosing the resonator cavity together with the first resonator mirror has a curvature, wherein the following relationship applies between the radius of curvature R2 of the first resonator mirror, the radius of curvature R1 of the further resonator mirror and a relative distance a of the beam waist from the first resonator mirror with respect to the working distance: R1=R2(3+2−2+a) or there is a deviation from this relationship of no more than 10%.

[0018] According to a further embodiment, the measuring mirror is configured as a plane mirror.

[0019] According to a further embodiment, the optical resonator is configured such that the measuring radiation radiated onto the measuring mirror forms an angle of at most 100 mrad, in particular at most 20 mrad, with the measuring radiation reflected therefrom.

[0020] According to a further embodiment, the two resonator mirrors are arranged offset from one another with respect to the direction of incidence of the measurement radiation onto the measurement mirror. In other words, the two resonator mirrors are arranged axially offset from one another. The two resonator mirrors are arranged substantially in the same direction, i.e., the respective incidence directions of the measurement radiation onto the resonator mirrors differ from one another by less than 100 mrad, in particular less than 20 mrad.

[0021] According to one embodiment, the two resonator mirrors are offset by at least the thickness of one of the resonator mirrors. This allows edge regions of one of the resonator mirrors not intended for the beam path of the measurement radiation to be arranged in overlap with the other resonator mirror, thus reducing the tilt angle of the measurement mirror relative to the measurement radiation radiated onto it.

[0022] According to a further embodiment, the optical resonator is configured such that the measuring radiation radiated onto the measuring mirror forms an angle of at most 1 mrad with the measuring radiation reflected therefrom.

[0023] According to a further embodiment, a polarization beam splitter is arranged in the beam path of the optical resonator, and the beam path of the measurement radiation is deflected by this splitter between the measurement mirror and one of the resonator mirrors. The deflection is advantageously performed by approximately 90°. For this purpose, for example, a λ / 4 plate is arranged in the beam path between the measurement mirror and the aforementioned resonator mirror. This allows the measurement mirror to be positioned for direct backreflection of the incoming measurement radiation, i.e., the directions of the incoming and reflected measurement radiation are collinear.

[0024] According to a further embodiment, the resonator is operated in a Laguerre-Gaussian mode with an azimuthal index of at least one. For example, the azimuthal index can be three, and the radial index is preferably zero. According to one embodiment, the measuring arrangement comprises a diffractive optical element in the form of a CGH (computer-generated hologram) for beam shaping the measuring radiation coupled into the optical resonator such that a mode-pure coupling of the resonator cavity to the Laguerre-Gaussian mode can occur. Thus, the measuring mirror can be arranged for direct backreflection of the incoming measuring radiation, i.e., the directions of the incoming and reflected measuring radiation are collinear.

[0025] According to a further embodiment, one of the two resonator mirrors has a central recess in which the other resonator mirror is arranged. This allows the measuring mirror to be positioned for direct back-reflection of the incoming measuring radiation, i.e., the directions of the incoming and reflected measuring radiation are collinear.

[0026] According to a further embodiment, the working distance is at least 2 cm, in particular at least 10 cm, at least 20 cm or at least 50 cm.

[0027] Furthermore, the invention provides a projection exposure system for microlithography, which comprises at least one movable component and at least one measuring arrangement in one of the above-described embodiments or variants. According to one variant, the projection exposure system is configured for operation in the EUV wavelength range. Alternatively, the measuring arrangement can also be integrated into a mask inspection system or a wafer inspection system in one of the above-described embodiments or variants.

[0028] According to one embodiment, the projection exposure system comprises a plurality of optical elements for guiding exposure radiation in the projection exposure system, with one of the optical elements serving as the movable component. This optical element can be part of a projection lens or an illumination optics system of the projection exposure system. As is known to those skilled in the art, such an illumination optics system serves to illuminate the mask during an exposure process, and the projection lens serves to image mask structures onto a wafer.

[0029] The embodiments, exemplary embodiments, or embodiment variants, etc. of the measuring arrangement according to the invention listed above 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 only be claimed during or after the filing of the application. Brief description of the drawings

[0030] 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 shows an embodiment of a measuring arrangement according to the invention, which is configured for determining the position of a movable component and has a resonator cavity and a measuring mirror arranged therein, Fig. 2a the beam path of the resonator cavity of the measuring arrangement according to the invention according to Fig. 1 in a simplified representation, Fig. 2b the beam path of a resonator cavity of a comparative example of the measuring arrangement, Fig. 3 a beam generation and evaluation device of the measuring arrangement according to Fig. 1, Fig. 4 a Rayleigh length z R in the resonator cavity of the measuring arrangement according to Fig. 1 depending on a relative distance a of a steel waist in the resonator cavity with respect to a working distance of a measuring mirror, Fig. 5 the radius of curvature R1 of a resonator mirror defining the resonator cavity as a function of the relative distance a, Fig. 6 the dependence of different beam radii in the resonator cavity on the relative distance a, Fig. 7 shows a further embodiment of the measuring arrangement according to the invention for determining the position of a movable component, Fig. 8 shows a further embodiment of the measuring arrangement according to the invention for determining the position of a movable component, Fig. 9 shows a further embodiment of the measuring arrangement according to the invention for determining the position of a movable component, Fig. 10 shows a section of a projection exposure apparatus for microlithography 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. 7, Fig. 8 or Fig. 9 can be determined, Fig. 11 an embodiment of the projection exposure system according to Fig. 10, as well as Fig. 12 an enlarged detailed view of the projection exposure system according to Fig. 11 with a measuring arrangement integrated therein according to one of the Fig. 1, Fig. 7, Fig. 8 or Fig. 9. Detailed description of embodiments according to the invention

[0031] 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.

[0032] 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.

[0033] In Fig. 1 illustrates an embodiment 10 of a measuring arrangement according to the invention. This measuring device 10 is used for determining the position of a movable component of a Fig. 10 is configured for microlithography 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 MS (reference numeral 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 10, as described in detail below.

[0034] Fig. 11 shows a simplified representation of the optical system 500 in the form of a projection exposure system for microlithography. Fig. 10 shows a section of the projection exposure apparatus according to Fig. 11 with a mirror 526, which here serves as the above-mentioned movable component.

[0035] As mentioned, in the present embodiment, the component is the mirror 526, which is mounted on a Fig. 10 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.

[0036] According to the present embodiment, the position of six measuring points M1 to M6, in particular in a hexapod configuration as shown in Fig. 10 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. Measuring arrangements 110, 210 and 310 described in 7 to 9.

[0037] The Fig. The microlithographic projection exposure system shown in Figure 11 and serving as optical system 500 is designed for operation with EUV exposure radiation. EUV radiation is understood in this text 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 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 microlithography, such as a mask inspection system or a wafer inspection system.

[0038] According to the embodiment of Fig. 11, 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 a projection objective 516 comprising six mirrors 518, 520, 522, 524, 526, and 528.

[0039] 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.

[0040] Fig. 12 shows an enlarged detailed view of the projection exposure system serving as optical system 500 from Fig. 11 in the area of ​​the mirror 526 of the projection lens 516, which serves as a movable component. Fig. 12 shows, by way of example, the measuring arrangement 10 or the Fig. 7, Fig. 8 and Fig. 9. 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 here for reasons of clarity. The measuring head 12 of the measuring arrangement 10, 110, 210 or 310 is arranged in a stationary manner on the housing or, for example, on the mask table. The measuring mirror 14 is attached to the underside of the mirror 526, which is opposite the side 527 of the mirror 526 that reflects the exposure radiation of the projection exposure system 500. Depending on the result of the position measurement by the measuring arrangement 10 or 110, 210 or 310 and in particular according to the Fig. According to an exemplary embodiment, the mirror 526 is adjusted in its position in the further measuring arrangements 10, 110, 210 and 310 provided in the configuration illustrated in FIG. 10.

[0041] The Fig. The measuring arrangement 10 illustrated in Figure 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, two resonator mirrors S1 (reference numeral 28) and S2 (reference numeral 30), and the measuring mirror 14 already mentioned above. The two resonator mirrors 28 and 30 can be integrated into a resonator module, whereby they are fixed to one another. Together with the measuring mirror 14, the resonator mirrors 28 and 30 form an optical resonator 26. The measuring head 12, also already mentioned above, comprises at least the two resonator mirrors 28 and 30 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.

[0042] The beam generation and evaluation device 16 is in Fig. 3 shows an exemplary embodiment in detail. This is based on the principle that a laser 42 tunable with respect to the optical frequency 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 L of the resonator 26 ultimately to be measured is encoded as the frequency of the tunable laser 42. The laser 42 serves as the radiation source for the measuring radiation 18, which lies, for example, in the visible or infrared wavelength range.

[0043] The beam generation and evaluation 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 / 4 plate 50 exits via the Fig. 1 into the measuring head 12. Referring again to Fig. 3, 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 optical resonator 16 according to Fig. 1 The measuring radiation 18 leaving the measuring head 12 re-enters the beam generation and evaluation device 16 via the optical fiber 20 and is detected by the photodetector 52. For further details regarding the operation of the beam generation and evaluation device 16, reference is made to DE 10 2018 208 147 A1.

[0044] As already mentioned above, the resonator mirrors 28 and 30, in conjunction with the measuring mirror 14 serving as the measuring target, form the optical resonator 26. The resonator mirrors 28 and 30 enclose a resonator cavity 32. The resonator mirror 28 serves as a coupling mirror for coupling the measuring radiation 18 into the resonator cavity 32. The resonator mirror 30 serves as a counter mirror to the resonator mirror 28.

[0045] In the embodiment shown, the resonator mirror 28 serving as the coupling mirror has a curved mirror surface, wherein the radius of curvature R1 is greater than the distance between the resonator mirror 28 and the measuring mirror 14. Thus, the center of curvature m1 (reference numeral 29) of the resonator mirror 28 lies on the side of the measuring mirror 14 opposite the resonator mirror 28 and thus outside the resonator cavity 32.

[0046] The resonator mirror 30 serving as a counter mirror also has a curved mirror surface, with a center point m2 (reference numeral 31) of its curvature being arranged on the measuring mirror 14, i.e., on a reflective surface 15 of the measuring mirror. Alternatively, the center point m2 can be at a certain distance from the measuring mirror 14, which can be at most 10% of a working distance d M (reference number 34) of the resonator mirror 30 from the measuring mirror 14.

[0047] 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 arranged essentially in the positive z-direction and thus essentially aligned with each other. In the embodiment according to Fig. 1, the resonator mirrors 28 and 30 and the measuring mirror 14 are arranged such that the measuring radiation 18 radiated onto the measuring mirror 14, together with the measuring radiation 18 reflected therefrom, encloses a folding angle β (reference numeral 36) of, for example, less than 100 mrad, in particular less than 20 mrad. Thus, the alignment of the resonator mirrors 28 and 30 deviates from the exactly unidirectional alignment only by the angle β. In other words, the respective directions of incidence of the measuring radiation 18 onto the resonator mirrors 28 and 30 deviate from each other by the angle β. 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.

[0048] The advantageous effects of the configuration of the resonator mirror 30 such that its center of curvature m2 on the measuring mirror 14 or at most 10% of the working distance d Maway from it, on the measuring accuracy of the measuring arrangement 10 is explained below with reference to the Fig. 2a and Fig. 2b explained. In Fig. 2a, the beam path of the measuring radiation 18 in the resonator 26 of the measuring arrangement 10 is shown schematically with the central main beam 18h. Fig. Figure 2b illustrates the beam path of a comparative example of the measuring arrangement, in which the resonator mirror 60 (counter mirror) corresponding to the resonator mirror 30 is configured with the same curvature as the resonator mirror 28 acting as the coupling mirror. This means that the center of curvature m2 of the resonator mirror 60 is well over 10% of the working distance d M from the measuring mirror 14. If the measuring mirror 14 is tilted by a tilt angle φ, the main beam 18h tilts in the area between the measuring mirror 14 and the resonator mirror 30 or 60 serving as a counter mirror, both in the arrangement according to Fig. 2a as well as according to Fig. 2b, as shown by the dashed line.

[0049] In the comparison example according to Fig. 2b, the main beam 18h is also tilted in the area between the resonator mirror 28 and the measuring mirror 14, i.e., a lateral shift of the beam path of the measuring radiation 18 on the resonator mirror 28 occurs. This shift reduces the coupling efficiency of the coupling field of the measuring radiation 18 radiated onto the resonator mirror 28 via the coupling lens 22 with the mode field in the resonator 26, thereby reducing the measurement accuracy of the measuring arrangement. This effect can be mitigated by increasing the beam diameter of the measuring radiation 18 radiated onto the resonator mirror 28 to such an extent that the lateral offset remains below a limit of 0.1 beam radii. At the same time, however, this also means that the beam diameter on the measuring mirror 14 becomes significantly smaller, effectively resulting in a focusing on the measuring mirror 14.However, this is disadvantageous for metrological reasons, as it increases the sensitivity to the local surface topography of the measuring mirror 14. Furthermore, impractically large beam diameters would result on the coupling side if the working distance d. M Values ​​of more than 10 mm can be selected.

[0050] In the inventive embodiment of the measuring arrangement 10 according to Fig. 2a, however, due to the arrangement of the center point m2 of the curvature of the resonator mirror 30 on the measuring mirror 14, the lateral position of the main beam 18h on the resonator mirror 28 is perfectly stable. This is due to the fact that the position of the center point of curvature m2 of the resonator mirror 30, as seen from the resonator mirror 28 via the measuring mirror 14, remains unchanged even when the measuring mirror 14 is tilted. If the center point of curvature m2 of the resonator mirror 30 deviates, as in the embodiment according to Fig. 1, maximum 10% of the working distance dM , ie only slightly, from the position on the measuring mirror 14, only a slight lateral shift of the resonator mode on the resonator mirror 28 occurs, the influence of which on the coupling efficiency and thus on the measurement accuracy is tolerable.

[0051] The course of the beam path 18r of the measuring radiation 18 folded by the measuring mirror 14 within the optical resonator 26 corresponds in the embodiment according to Fig. 1 that of a Gaussian beam, whose beam waist T (reference numeral 38) is located in the illustrated embodiment centrally between the measuring mirror 14 and the resonator mirror 30. This means that a waist distance d T from the resonator mirror 30 is 50% of the working distance d M , ie a relative distance a = d T / d M is 0.5. The Fig. 1 The boundary lines drawn to represent the beam path 18r of the measuring radiation correspond in the cross-section of the beam path to the locations at which the intensity 1 / e 2 of the maximum intensity at the center of the beam path. The corresponding beam cross-section represented by these boundary lines has a beam radius r1 at mirror 28, a beam radius rm at measuring mirror 14, and a beam radius r2 at mirror 30.

[0052] The radius of curvature R1 of the resonator mirror 28 is selected according to the following design rule: R1=R2(3+2−2+a) - in Fig. 5 this relationship is shown for a fixed radius of curvature R2. In alternative embodiments, the value of R1 deviates from R2(3+2−2+a) but by a maximum of 10%.

[0053] The choice of a value for the distance a is based on the considerations explained below. For the Rayleigh length z R In the optical resonator 26, the following relationship to the relative distance a results for the condition that the center point m2 lies on the measuring mirror 14: zR=a−a2 - see Fig. 4.

[0054] As is known to the person skilled in the art, the Rayleigh length z R the distance along the optical axis that a laser beam needs to travel until its cross-sectional area, starting from its beam waist, doubles. As in Fig. 4, for a -> 0 and a -> 1 the Rayleigh length z R tends towards 0 and is maximal for a=0.5.

[0055] The beam radii r1, rm and r2 resulting from a are in Fig. 6. For a -> 0, the beam radii r1 and rm tend to infinity, while r2 tends to 0. For a -> 1, the beam radii r1 and r2 tend to infinity and rm tends to 0. In one embodiment, 0.05 ≤ a ≤ 0.95 applies, ie the distance d T the beam waist T from the resonator mirror 30 or the distance d M - d T the beam waist T from the measuring mirror is at least 5% of the working distance d MFor this dimensioning of a, the dimensions of the beam radii r1, r2, and rm lie within a range in which stable modes can form in the optical resonator 26 and the installation space required for the mirrors of the resonator 26 is manageable. The sum of the beam radii r1 and r2, which essentially determines the dimensioning of the measuring arrangement 10 in the y-direction, has a similar value for a=0.05 as for a=0.95. According to further embodiments, the following applies: 0.1 ≤ a ≤ 0.9 or 0.2 ≤ a ≤ 0.8. For these values, the measuring arrangement 10 can be designed more compactly, and the mode stability is further improved.

[0056] In Fig. Figure 7 illustrates a further embodiment 110 of a measuring arrangement according to the invention, which, like the measuring arrangement 10, is configured for determining the position of a movable component in an optical system 500 for microlithography. The measuring arrangement 110 differs from the measuring arrangement 10 only in that the resonator mirrors 28 and 30 are offset from one another in the z-direction, i.e., essentially with respect to the direction of incidence of the measuring radiation 18 onto the resonator mirrors 28 and 30, i.e., in the axial direction.

[0057] In the present example, the resonator mirror 30 is offset in the negative z-direction, so that the distance to the measuring mirror 14 increases. This allows the resonator mirror 30 to be slightly offset transversely to the incident radiation direction 18, specifically in such a way that edge regions 128r and 130r of the resonator mirrors 28 and 30, which are not intended for the beam path of the measuring radiation 18, are arranged to overlap one another. This allows the folding angle β to be reduced compared to the measuring arrangement 10. This allows the effect of an axial displacement of the measuring mirror 14, i.e. a displacement of the measuring mirror along the z-axis during measuring operation, on the position of the mode at the resonator mirrors 28 and 30 to be reduced. Seen from the resonator mirror 28 in reflection via the measuring mirror 14, an axial displacement of the measuring mirror 14 by Δz causes a lateral displacement of the center of curvature m2 with respect to the measuring mirror 14 by 2 β Δz.The lateral shift of the mode on the resonator mirror 28 is larger by a factor of R1 / (R1-R2) due to the "leverage effect." Thus, in the embodiment according to . Fig. 7 due to the reduction of the folding angle β, the lateral displacement of the measuring mirror 14 permitted during measuring operation can be set larger than in the embodiment according to Fig. 1.

[0058] In Fig. 8 illustrates a further embodiment 210 of a measuring arrangement according to the invention, which, like the measuring arrangement 10, is configured for determining the position of a movable component in an optical system 500 for microlithography. The measuring arrangement 210 differs from the measuring arrangement 10 in that polarized measuring radiation 218 is radiated onto the optical resonator 26, for example, by using an upstream polarizer 260, and in that a polarization beam splitter 262 and a λ / 4 plate 264 are arranged in the beam path of the measuring radiation 18 between the resonator mirror 28 and the measuring mirror 14. The measuring radiation 18 reflected back by the measuring mirror 14 is deflected by 90° by the polarization beam splitter 262. The resonator mirror 30 is arranged in a corresponding position oriented transversely to the resonator mirror 28 below the polarization beam splitter 262.

[0059] By decoupling the measuring radiation 18 directed at the resonator mirror 30 from the beam path between the resonator mirror 28 and the measuring mirror 14, the folding angle β can be reduced to less than 1 mrad, in particular to 0 mrad. Thus, the directions of the measuring radiation 18 incident on the measuring mirror 14 and the reflected measuring radiation 18 are collinear. Thus, the effect of an axial displacement of the measuring mirror 14, i.e., a displacement of the measuring mirror 14 along the z-axis during measurement operation, on the position of the mode at the resonator mirrors 28 and 30 can be further reduced, and thus the permissible axial displacement of the measuring mirror 14 can be further increased.

[0060] In Fig. 9 illustrates a further embodiment 310 of a measuring arrangement according to the invention, which, like the measuring arrangement 10, is configured for determining the position of a movable component in an optical system 500 for microlithography. In the measuring arrangement 310, as in the measuring arrangement 210 according to Fig. 8, the directions of the measuring radiation 18 incident on the measuring mirror 14 and the reflected measuring radiation 18 are collinear.

[0061] The measuring arrangement 310 differs from the measuring arrangement 10 according to Fig. 1 in that the resonator 26 is operated in a Laguerre-Gaussian mode with an azimuthal index of at least one; in the present case, a Laguerre-Gaussian mode 366 with an azimuthal index of 3 and a radial index of 0 is generated. The coupling to the mode 366 can be carried out with suitable beam shaping, e.g., by means of a CGH (not shown in the drawing). By generating the mode 366 in the optical resonator 26, which essentially defines a ring-shaped intensity distribution, it is possible to use the resonator mirror 330 serving as a counter mirror (analogous to the resonator mirror 30 according to Fig. 1) in a central recess 368 of the resonator mirror 328 serving as a coupling mirror (analogous to the resonator mirror 28 according to Fig. 1) to be arranged.

[0062] Analogous to embodiment 210 according to Fig.8, in the embodiment 310, due to the collinear beam arrangement, the effect of an axial displacement of the measuring mirror 14, ie a displacement of the measuring mirror 14 along the z-axis during measuring operation, on the position of the mode at the resonator mirrors 328 and 330 can be reduced and thus the permissible axial displacement of the measuring mirror 14 can be increased.

[0063] 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 15 reflective surface 16 Radiation generation and evaluation device 18 Measuring radiation 18r Beam path of the measuring radiation in the resonator 18h central main beam of the measuring radiation in the resonator 20 optical fibers 22 Coupling lens 26 optical resonator 28 resonator mirrors 29 Center of curvature m1 30 resonator mirrors 31 Center of curvature m2 32 Resonator cavity 34 Working distance d M 36 folding angle β 38 frog waist T 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 110 Measuring arrangement 128r edge area 130r edge area 210 Measuring arrangement 218 polarized measuring radiation 260 Polarizer 262 polarization beam splitters 264 λ / 4 plates 310 Measuring arrangement 328 resonator mirrors 330 resonator mirrors 366 Laguerre-Gaussian mode 368 central recess 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 516 projection lens 518, 520, 522, 524, 528 Mirror of the projection lens 526 Mirror of the projection lens as a movable component 527 reflective side 530 Mask 532 Mask table 534 Substrat 536 wafer table R1 radius of curvature of the resonator mirror S1 R2 radius of curvature of the resonator mirror S2 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 11,274,914B2 [0005, 0006] DE 10 2018 208 147 A1

[0043]

Claims

[1] Measuring arrangement (10; 110, 210; 310) for determining the position of a movable component (526) in an optical system (500) for microlithography, comprising: - an optical resonator (26) with two resonator mirrors (28, 30) which enclose a resonator cavity (32), and - a movable measuring mirror (14) assigned to the component, which is arranged within the resonator cavity for deflecting a measuring radiation back and forth between the resonator mirrors, wherein the measuring mirror is arranged at a working distance (34) from one of the resonator mirrors, which has a curvature matched to the measuring mirror such that its center point (31) is arranged on the measuring mirror or at most 20% of the working distance away therefrom. [2] Measuring arrangement according to claim 1, in which one (28) of the resonator mirrors is configured as a coupling mirror for coupling a measuring radiation (18) into the resonator cavity and the other resonator mirror (30) is configured as a counter mirror to the coupling mirror, wherein the resonator mirror (30) with the curvature matched to the measuring mirror is the counter mirror. [3] Measuring arrangement according to claim 1 or 2, wherein the optical resonator (26) is configured to form a beam path with a beam waist (38) for the measuring radiation (18), wherein the beam waist lies between the measuring mirror (14) and the first resonator mirror (30) with the curvature matched to the measuring mirror. [4] Measuring arrangement according to claim 3, wherein the beam waist (38) is arranged at least 5% of the working distance (34) from the measuring mirror (14) and at least 5% of the working distance (34) from the first resonator mirror (30). [5] Measuring arrangement according to one of the preceding claims, in which the further resonator mirror (28) of the optical resonator, which together with the resonator mirror (30) with the curvature matched to the measuring mirror (14) encloses the resonator cavity (32), has a curvature whose center (29) lies on the side of the measuring mirror opposite the further resonator mirror and is at a distance from the measuring mirror of at least 10% of the working distance (34). [6] Measuring arrangement according to claim 3 or 4, in which the further resonator mirror (28) enclosing the resonator cavity (32) together with the first resonator mirror (30) has a curvature, the following relationship being valid between the radius of curvature R2 of the first resonator mirror, the radius of curvature R1 of the further resonator mirror and a relative distance a of the beam waist from the first resonator mirror with respect to the working distance (34): R1=R2(3+2−2+a) or there is a deviation from this relationship of no more than 10%. [7] Measuring arrangement according to one of the preceding claims, in which the measuring mirror is configured as a plane mirror. [8] Measuring arrangement according to one of the preceding claims, in which the optical resonator (26) is configured such that the measuring radiation (18) radiated onto the measuring mirror (14) encloses an angle of at most 100 mrad with the measuring radiation (18) reflected therefrom. [9] Measuring arrangement (110) according to claim 8, in which the two resonator mirrors are arranged offset from one another with respect to the direction of incidence of the measuring radiation onto the measuring mirror (14). [10] Measuring arrangement according to one of the preceding claims, in which the optical resonator is configured such that the measuring radiation radiated onto the measuring mirror forms an angle of at most 1 mrad with the measuring radiation reflected therefrom. [11] Measuring arrangement according to one of the preceding claims, in which a polarization beam splitter is arranged in the beam path of the optical resonator and the beam path of the measuring radiation is deflected thereon between the measuring mirror and one of the resonator mirrors. [12] Measuring arrangement according to one of claims 1 to 10, in which the resonator is operated in a Laguerre-Gaussian mode with an azimuthal index of at least 1. [13] Measuring arrangement according to one of claims 1 to 10 or according to claim 12, in which one of the two resonator mirrors has a central recess in which the other resonator mirror is arranged. [14] Measuring arrangement according to one of the preceding claims, in which the working distance is at least 2 cm. [15] Projection exposure system for microlithography with at least one movable component and at least one measuring arrangement according to one of the preceding claims. [16] Projection exposure apparatus according to claim 15, which comprises a plurality of optical elements for guiding an exposure radiation in the projection exposure apparatus, wherein one of the optical elements serves as the movable component.

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