Device for measuring telecentricity of an optical imaging system

Abstract

A measuring device (10) for measuring a telecentricity (68) of an optical imaging system (12) comprises an illumination device (22) configured to radiate a measuring radiation (32) onto an object plane (14) of the optical imaging system, an intensity detector (28) having a plurality of non-overlapping detection sections, arranged offset from an image plane (16) of the optical imaging system, and configured to detect angle-resolved intensity distributions (50) present at the field points for at least two field points (18-1, 18-2) in the image plane with a respective one of the detection sections (42-1, 42-2) of the intensity detector, a movement device (30) configured to set different measurement positions (54) by changing a relative position of the intensity detector to the optical imaging system in at least one rigid body degree of freedom,that the intensity distribution (50-2) of at least one of the field points before and after the relative position change can be detected with two different non-overlapping detection sections (42-2, 42-1) of the intensity detector, and an evaluation device (48) which is configured to determine the telecentricity (68) of the optical imaging system at each of the at least two field points on the basis of angle-resolved intensity distributions (50-1, 50-2) recorded at the different measuring positions (54).

Description

BACKGROUND OF THE INVENTIONThe invention relates to a device and a method for measuring a telecentricity of an optical imaging system, for example a projection objective of a microlithographically projected exposure apparatus.As is known, telecentricity determination serves to detect deviations from ideal telecentricity behavior of an optical imaging system, i.e., telecentricity errors. In an imaging system which is subject to telecentricity error, the main beam does not run parallel to the optical axis of the imaging system, as in the error-free case, for a respective field point, but instead tilts with respect to the latter, wherein the tilt angle represents a quantitative measure of telecentricity error. In other words, telecentricity denotes an energetic tilt of the beam cone of an optical imaging system about the focal point in the image or object plane. The telecentricity error is a 2-dimensional quantity that can be represented as two flip angles from the corresponding plane normal toward two orthogonal basis vectors in the corresponding plane. The telecentricity error can be field point dependent, that is to say dependent on the lateral position of the focal point in the corresponding plane. Telecentricity of microlithographically projecting objectives onto the image plane has effects on distortion in the lithography process due to 3D effects in the photoresist.An obvious approach for determining a telecentricity error is to measure the energetic position of the center of gravity of the image of a respective field point in an xy plane perpendicular to the optical axis at a plurality of measurement points which are displaced with respect to one another in the z direction of the optical axis and to calculate the tilt angle by triangulation therefrom. This is, however, counteracted by the difficulty that the energetic center of gravity position of the image of a respective field point in the xy-plane can also vary depending on the z-position due to other image aberrations with which imaging systems are typically involved, such as coma aberrations and image shell aberrations.To avoid these problems, U.S. Pat. No. 7,365,861 B2 proposes carrying out a wavefront measurement at various z positions on the optical imaging system by means of a shear interferometer and calculating the telecentricity on the basis of the Z2 and Z3 Zernike coefficients measured in this case. In shear interferometric measurement, a measuring unit comprising a diffraction grating and a detector unit arranged beneath it is arranged in the image plane of the optical imaging system. By superimposing one of the zeroth diffraction orders with the + / - 1st diffraction orders generated at the diffraction grating, an interference pattern is generated on the detector unit for different measurement channels arranged at different field points. The measurement unit is shifted stepwise in the xy plane so that the phase distribution of the interference patterns changes. This is also referred to as "phase shifting", wherein the shifting steps are so small that the measurement channels remain unchanged during the measurement, i.e. the detector sections assigned to the individual measurement channels do not change, and only the phase of the recorded interference patterns changes. However, it has been found that this measuring method also does not provide sufficiently accurate measured values for telecentricity. Reference is also made to the publication CN 114647154 A.Underlying ObjectIt is an object of the invention to provide an apparatus and a method of the type mentioned at the beginning, by means of which the aforementioned problems are solved and the accuracy of the telecentricity measurement is preferably improved.Solution according to the inventionThe aforementioned object can be achieved according to the invention, for example, with a measuring device for measuring a telecentricity of an optical imaging system. The measuring device according to the invention comprises an illumination device configured to irradiate a measurement radiation onto an object plane of the optical imaging system, and an intensity detector having a plurality of non-overlapping detection sections. The intensity detector is arranged offset from an image plane of the optical imaging system and is configured to detect angle-resolved intensity distributions present at the field points for at least two field points in the image plane with a respective one of the detection sections of the intensity detector. Furthermore, the measuring device according to the invention comprises a movement device which is configured to set different measurement positions by changing a relative position of the intensity detector to the optical imaging system in at least one rigid body degree of freedom such that the intensity distribution of at least one of the field points before and after the relative position change can be detected with two different ones of the non-overlapping detection sections of the intensity detector, and an evaluation device which is configured to determine the telecentricity of the optical imaging system at each of the at least two field points on the basis of angle-resolved intensity distributions recorded at the different measurement positions.The intensity detector may be part of a sensor head according to an embodiment. Telecentricity is to be understood as meaning an energetic tilting of one or more beam cones of the optical imaging system assigned to a respective field point about the focus point in the image plane or the object plane. This is referred to as the image-side telecentricity or the object-side telecentricity. In the present case, the telecentricity measurement preferably comprises the image-side telecentricity.The change of the relative position of the intensity detector to the optical imaging system is to be understood to mean that for this purpose the position of the intensity detector and / or the position of the optical imaging system is changed. The intensity distribution detected by the intensity detector is also referred to in this text as pupil image. The intensity detector is arranged offset from the image plane of the optical imaging system to such an extent that the angle-resolved intensity distributions present in the image plane, i.e. the pupil images assigned to the individual field points, are displayed on the detection surface of the detector.The angle-resolved intensity distributions recorded at the different relative positions of the intensity detector are intensity distributions which are generated on the detector by the above-explained change in the relative position of the intensity detector with respect to the optical imaging system. The angle-resolved intensity distribution at a field point corresponds to the intensity distribution in the pupil of the optical imaging system. The intensity detector is thus configured and arranged to detect the intensity distribution in a pupil or a pupil distribution of the optical imaging system at the relevant field points of the image plane. In other words, the relative position of the intensity detector is changed in such a way that the pupil distribution assigned to a specific field point is detected with another section of the intensity detector after the change in position, as before the change in position. In this case, the two sections are non-overlapping sections, i.e. sections of the detection detector which are in each case of their own.The inventive detection of angle-resolved intensity distributions at different field points in the image plane, i.e. the detection of pupil distributions assigned to the different field points, and the change of the relative position of the intensity detector in such a way that the intensity distribution of one of the field points before and after the relative position change can be detected with two different, non-overlapping sections of the intensity detector, makes it possible to determine the telecentricity with a high accuracy by mathematical evaluation of the intensity distributions detected at the different relative positions. The said relative position change enables the generation of sufficient redundancy in the measurements detected by the intensity detector in order to enable the mathematical evaluation for determining the telecentricity.In comparison with the above-mentioned determination of the telecentricity on the basis of a wavefront measurement according to U.S. Pat. No. 7,365,861 B2, in which the telecentricity is substantially equalized with a wavefront tilt which corresponds only approximately to the energetic tilt of the beam cone of an optical imaging system, the approach according to the invention enables the direct determination of the energetic tilt of the beam cone and thus the determination of the telecentricity with a higher accuracy.Although the mentioned shear-interferometric wavefront measurement likewise involves intensity distributions being recorded by a detector unit, these are, as already explained above, not angle-resolved intensity distributions present at the field points in the form of pupil distributions assigned to the field points, but rather interference patterns. Even if the + / -1 among these interference patterns is detected. If diffraction orders were calculated out, the resulting intensity distributions would still differ from the intensity distributions detected according to the invention by changing the relative position of the intensity detector. This is already due to the fact that the displacement of the measuring unit during the wavefront measurement takes place only in small steps which serve for phase shifting and are not large enough to detect one of the field points before and after the relative position change with two different, non-overlapping sections of the intensity detector.According to one embodiment, at least two different, non-overlapping detection sections of the intensity detector before the relative position change, in particular the aforementioned two different, non-overlapping detection sections, are used for measuring the intensity distributions of different field points.According to a further embodiment, the measuring device is configured to form measurement channels by the optical imaging system, which pass through the image plane at one of the field points to be measured in each case and strike different detection sections of a detection surface of the intensity detector, wherein the movement device is configured to change the relative position in such a way that a specific detection section is irradiated before and after the change in position of measurement radiation of different measurement channels.According to one embodiment variant, the measuring device further comprises a measurement mask arranged in the object plane and having measurement structures for forming the measurement channels. In other words, the measurement mask comprises an associated measurement structure for each of the field points of the image plane to be measured, said measurement structure forming a respective measurement channel. The measurement mask can optionally also be moved via a movement device which can be designed analogously to the movement device of the intensity detector.According to a further embodiment, the measuring device is configured to perform an alignment of the detector and, if applicable, of the measurement mask in all solid-state degrees of freedom with respect to the image and object plane. This can be done by an external measurement system or a wavefront or intensity measurement.According to one embodiment variant, in the case of more than two measurement masks, the distances of these measurement masks can be arranged on an equidistant grating in order to record identical measurement channels in the optical imaging system in the case of displacements by integer multiples of these distances in the object plane or image plane and / or in the case of correspondingly selected rotations relative to the optical imaging system.According to one embodiment variant, fewer measurement masks can be used than measurement channels of the optical imaging system in order to prevent superposition of the intensity images on the intensity detector. By serial measurement with different displacements and / or rotations of the intensity detector and the measurement masks relative to the optical imaging system, the remaining measurement channels can be realized.According to a further embodiment, the change of the relative position comprises a relative translation movement of the intensity detector with respect to the optical imaging system in a direction transverse or orthogonal to an optical axis of the optical imaging system, which is also referred to herein as "lateral direction".According to a further embodiment, the change in the relative position comprises a relative translation movement of the measurement mask arranged in the object plane with respect to the optical imaging system in a direction transverse to an optical axis of the optical imaging system. This can be done according to the relative translation movement of the intensity detector scaled with the imaging scale of the optical imaging system.According to a further embodiment, the position of the intensity detector and optionally of the measurement mask can be positioned via an external measurement system or via a wavefront- and / or intensity-based alignment with respect to the image plane or optionally with respect to the object plane of the optical imaging system.According to a further embodiment, the measuring device is configured to form measurement channels through the optical imaging system, which pass through the image plane at each of the field points to be measured, and wherein the change in the relative position comprises a relative translation movement of the intensity detector with respect to the optical imaging system in a lateral direction to an optical axis of the optical imaging system by at least one distance between two adjacent measurement channels. This is preferably the distance between the two adjacent measurement channels in the image plane.According to one embodiment variant, the evaluation device is configured to determine the telecentricity of the optical imaging system on the basis of angle-resolved intensity distributions which are recorded at three different measurement positions which differ by relative displacement of the intensity detector with respect to the optical imaging system along a degree of translational freedom.According to a further embodiment, the change in the relative position comprises a relative rotational movement of the intensity detector with respect to the optical imaging system about an axis of rotation aligned in the direction of the optical axis.The relative translation movement or the relative rotation movement is to be understood as a translation movement or rotation movement of the optical imaging system and / or of the sensor element. The lateral direction with respect to the optical axis is to be understood as a direction which is oriented perpendicularly to the optical axis or deviates up to 45°, in particular up to 30° or up to 10°, from the perpendicular direction. The alignment of the axis of rotation in the direction of the optical axis is to be understood as an exactly parallel alignment to the optical axis or an alignment deviating therefrom by up to 45°, in particular up to 30° or up to 10°.According to a further embodiment, the evaluation device is configured to determine a respective associated pupil image position from the recorded angle-resolved intensity distributions for each of the relative positions at all measured field points.According to one embodiment variant, the respective determined pupil image position comprises a displacement value of the relevant pupil image with respect to an associated standard pupil image, which would be present if telecentricity were not present, in at least one coordinate direction.According to a further embodiment variant, the evaluation device is configured to determine the displacement values by evaluating a system of equations containing the determined pupil image positions.According to a further embodiment variant, the evaluation device is configured to determine the determination of the pupil image positions in each case with subpixel accuracy, with respect to a pixel resolution of the intensity detector.According to a further embodiment variant, the evaluation device is configured to effect the determination of the pupil image positions by means of an edge edge fit of the recorded intensity distributions.According to a further embodiment, the respective marginal edge fit is carried out on the basis of intensity distributions averaged over different measurement positions of the intensity detector. The measurement positions may be shifted by a fraction, e.g. half, of a grating period of the diffraction grating. Alternatively, the measurement positions can also be shifted by more than half the grating period of the diffraction grating, for example by one, one and a half or two grating periods of the diffraction grating.According to a further embodiment, the evaluation device is configured to convert the determined pupil image positions into telecentricity angles of the optical imaging system. In this case, the pupil image positions are converted into beam cone angles in the substrate medium by conic section observations and the telecentricity angles of the optical imaging system are determined therefrom.According to a further embodiment, the evaluation device is configured to determine the numerical aperture at each of the field points from the recorded angle-resolved intensity distributions and to take it into account in the determination of the telecentricity. In other words: an NA field profile is determined. For determining the numerical aperture, a pupil radius is determined at each of the field points for each of the relative positions. The displacement values of the pupil image position have a dependence on the numerical aperture. By determining the numerical aperture, this influence can be taken into account in the determination of the telecentricity. In an alternative embodiment, it is ensured that the measurement of the intensity distributions takes place at full NA. In this case, the measurement of the NA field profile is not necessary, since it is already known in advance.According to a further embodiment, the measuring device is configured to partially measure the measurement channels in series by displacement of the intensity detector and, if applicable, of the measurement mask. A higher lateral resolution can thus be achieved than would be possible for the intensity detector without overlap of the pupil images.According to one embodiment, an NA aperture installed in a pupil plane in the microlithographic projection exposure objective can be partially closed in a defined manner in order to determine the telecentricity for corresponding application cases in a similar manner to the measurement at full NA.According to one embodiment, the optical imaging system is a projection objective of a microlithography projection exposure apparatus which is configured, for example, for DUV or EUV microlithography.Furthermore, according to the invention, a projection exposure apparatus for microlithography is provided, having a projection objective and a measurement arrangement according to one of the preceding embodiments or variant embodiments for measuring a telecentricity of the projection objective.The aforementioned object can furthermore be achieved, for example, by a method for measuring a telecentricity of an optical imaging system. The method comprises irradiating a measurement radiation onto an object plane of the optical imaging system, arranging an intensity detector having a plurality of non-overlapping detection sections in a plane offset from an image plane of the optical imaging system, and detecting angle-resolved intensity distributions which are present at at least two field points in the image plane, with a respective detection section of the intensity detector. Furthermore, the method comprises changing a relative position of the intensity detector to the optical imaging system in at least one rigid body degree of freedom for setting different measurement positions and detecting the intensity distribution of at least one of the field points before and after the relative position change with two different ones of the non-overlapping detection sections of the intensity detector, and determining the telecentricity of the optical imaging system on the basis of angle-resolved intensity distributions recorded at the different measurement positions at each of the at least two field points.According to one embodiment of the method according to the invention, a relative position of the intensity detector and of the measurement mask to the optical imaging system is changed in at least one rigid body degree of freedom in order to set the different measurement positions. The intensity distribution of at least one of the field points is then detected before and after the relative position change using two different ones of the non-overlapping detection sections of the intensity detector.According to one embodiment of the method according to the invention, the intensity detector is adjusted with respect to the optical imaging system before the detection of the angle-resolved intensity distributions, wherein a diffraction grating is arranged in the image plane and a wavefront measurement of the optical imaging system is therefore carried out by means of the intensity detector. On the basis of the wavefront measurement, the intensity detector can in turn be adjusted in the direction of the optical axis of the optical imaging system, i.e. with respect to the focus setting, and / or transversely thereto. The adjustment can take place in particular after each relative position change, i.e. before the detection of the intensity distributions following the respective relative position change.The features indicated with respect to the above-mentioned embodiments, exemplary embodiments or variant embodiments, etc. of the measuring device according to the invention can be transferred correspondingly to the measuring method according to the invention and vice versa. These and other features of the embodiments of the invention are explained in the description of the figures and the claims. The individual features can be realized either separately or in combination as embodiments of the invention. Furthermore, they can describe advantageous embodiments which are independently protectable and the protection of which is optionally claimed only during or after the pending application.Brief Description of the DrawingsThe above and further advantageous features of the invention are illustrated in the following detailed description of exemplary embodiments or embodiments or variant embodiments according to the invention with reference to the attached schematic drawings. The following are shown: FIG. 1 shows an exemplary embodiment of a measuring device for measuring a telecentricity of an optical imaging system at a plurality of field points in an image plane of the optical imaging system, having a sensor head in the form of an intensity detector, FIG. 2 shows an enlarged representation of the beam path in the region of a field point of a sensor head in the image plane of the optical imaging system, FIG. 3 shows an alternative exemplary embodiment of the sensor head, FIG. 4 shows a first embodiment, simplified to one dimension, of a method for operating the measuring device according to FIG. 1 for telecentricity measurement, FIG. 5 shows a second embodiment, simplified to one dimension, of the method for operating the measuring device according to FIG. 1 for telecentricity measurement, and FIG. 6 shows an exemplary embodiment of a projection exposure apparatus having a projection objective and a measuring device according to FIG. 1 integrated in the projection exposure apparatus for measuring the telecentricity of the projection objective.DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTIONIn the exemplary embodiments or embodiments or variant embodiments described below, functionally or structurally similar elements are provided with the same or similar reference numerals as far as possible. Therefore, for an understanding of the features of the individual elements of a particular embodiment, reference should be made to the description of other embodiments or the general description of the invention.For the purpose of facilitating the description, a Cartesian xyz-coordinate system is specified in the drawing, from which the respective positional relationship of the components illustrated in the figures results. In FIG. 1, the y-direction extends perpendicularly to the plane of the drawing into the latter, the x-direction extends to the right and the z-direction extends upward.FIG. 1 illustrates an exemplary embodiment of a measuring device 10 for measuring a telecentricity of an optical imaging system 12. The optical imaging system 12 can be an imaging system for microlithography, for example an optical imaging system 12 for a microlithography projection exposure apparatus, in particular a projection objective of a microlithography projection exposure apparatus. Alternatively, the optical imaging system 12 can also be a module of an illumination system of a microlithographically projected exposure apparatus or a module of a wafer inspection apparatus, etc. A microlithographically projected exposure apparatus is illustrated in FIG. 6 in an exemplary embodiment 100.The optical imaging system 12 has an optical axis 13, serves for imaging structures, for example structures of a lithography mask, from an object plane 14 into an image plane 16 and can be designed for exposure radiation of different wavelengths, such as e.g. for DUV radiation with a wavelength of approximately 248 nm or approximately 193 nm or for EUV radiation. Within the scope of this text, EUV radiation is understood to mean electromagnetic radiation having a wavelength of less than 100 nm, in particular a wavelength of approximately 13.5 nm or approximately 6.7 nm.As already mentioned above, the measuring device 10 serves for measuring the telecentricity of the optical imaging system 12. In an imaging system which is subject to telecentricity error, the main beam does not run parallel to the optical axis of the imaging system, as in the error-free case, for a respective field point, but instead tilts with respect to the latter, wherein the tilt angle represents a quantitative measure of telecentricity error. In other words, telecentricity denotes an energetic tilt of the beam cone of an optical imaging system about the focal point in the image or object plane. FIG. 2 shows, for an exemplary field point 18 in the image plane 16, such a main beam 20 tcomprising a telecentricity error, which is tilted by the tilt angle θ x in the x-z plane with respect to a standard main beam 20 nthat runs parallel to the optical axis of the imaging system 12 (without telecentricity error).The measuring device 10 comprises an illumination device 22 and a measurement mask 24 on the input side of the optical imaging system 12 and a sensor module 26 on the output side of the imaging system 12, which comprises a sensor head 27, here in the form of an intensity detector 28, a movement device 30 for changing a relative position of the intensity detector 28 to the optical imaging system 12 and an evaluation device 32.The measurement mask 24 is shown in FIG. 1 as an element in transmission, but can also be operated in reflection according to an alternative embodiment. The illumination device 22 is configured to generate a measurement radiation 32 and to irradiate it onto the measurement mask 24. The measurement radiation 32 may have the operating wavelength of the optical imaging system 12 to be tested or be in a similar wavelength range, according to an embodiment. For the case in which the optical imaging system 12 is designed as a projection objective of a microlithographically projected exposure apparatus, the wavelength of the measurement radiation 32 can thus be approximately in the DUV or in the EUV wavelength range.The measurement mask 24 comprises a two-dimensional point grid on measurement structures 34 (cf. measurement structures 34- 1 to 34- 4 according to FIG. 1 ). These are each configured as periodic structures, such as checkerboard structures, and serve to form measurement channels 36 through the optical imaging system 12, as illustrated in FIG. 1 with reference to the measurement channels 36- 1 through 36- 4. The beams contained in the measurement channels 36- 1 to 36- 4 pass through the optical imaging system 12 in different beam paths starting from the individual measurement structures 34- 1 to 34- 4, in this case pass through at least one pupil plane in which the maximum angular space is limited by geometric restrictions (e.g. mechanical diaphragm 40). This maximum angular space defines the pupil 38 of the optical imaging system 12. The pupil 38 is referred to in this context as the surface in the pupil plane through which the respective beams of all measurement channels 36- 1 to 36- 4 pass, i.e. the beams of the different measurement channels 36- 1 to 36- 4 each pass the same surface of the pupil plane. The rays passing through the pupil 38, i.e. the rays not absorbed by the diaphragm 40, propagate further and converge in the image plane 16 in a field point 18- 1 to 18- 4 to be measured in each case pass through the field point and strike different, non-overlapping detection sections 42 of a detection surface of the intensity detector 28. The field points 18- 1 to 18- 4 respectively adjacent to one another have a distance ΔK (reference sign 56). This is the distance of the corresponding adjacent measurement channels 36 in the image plane 16.In the embodiment illustrated in FIG. 1, the intensity detector 28 is illustrated with only two detection sections 42- 1 and 42- 2 adjoining one another in the x direction. In this embodiment, the intensity detector 28 serves for the partial serial measurement of the measurement channels, i.e. in a first measurement, for example the measurement channels 36- 1 and 36- 2 can be measured and then in a second measurement the measurement channels 36- 3 and 36- 4 can be measured. In FIGS. 4 and 5, the detection sections 42- 1 and 42- 2 are also denoted by the abbreviations DA 1 and DA 2. According to further embodiments, not shown in the drawing, the intensity detector 28 can also have a larger number of detection sections 42 adjoining one another in the x-direction, in particular just as many detection sections as measurement channels 36. Furthermore, the intensity detector 28 can have further detection sections 42 adjoining one another in the y direction, that is to say can comprise a two-dimensional grid of detection sections 42.The intensity detector 28 is arranged in a detection plane 44 offset in a defined manner from the image plane 16, which in the present case lies below the image plane 16, namely such that the intensity distribution assigned to the corresponding field point 18- 1 or 18- 2 is present in the pupil 38 of the optical imaging system 12 at the detection sections 42- 1 and 42- 2. These pupil intensity distributions correspond to the angle-resolved intensity distributions at the field points 18- 1 and 18- 2 in the image plane 16 and are also referred to in this text as pupil images 50 (cf. FIG. 2 ). In other words: The intensity detector 28 is arranged in such a way that the respective angle-resolved intensity distribution at the field points 18- 1 and 18- 2 can be detected by the detection sections 42- 1 and 42- 2.The intensity detector 28 is fastened to the aforementioned movement device 30, whereby the intensity detector 28 can be displaced in the x / y plane, i.e. in a lateral direction to the optical axis 13 of the optical imaging system 12 arranged in the z direction, and / or can be rotated about an axis of rotation 46 parallel to the optical axis 13. Alternatively, the optical imaging system 12, optionally together with the measurement mask 24, can also be mounted so as to be correspondingly displaceable and / or rotatable. Furthermore, the position of the intensity detector 28 can also be shifted with respect to the optical imaging system 12, while at the same time the position of the measurement mask 24 is carried along in accordance with the imaging scale of the optical imaging system 12, so that the assignment of the measurement structures 34 to the field points 18 remains.Importantly, the relative position of the intensity detector 28 to the imaging optical system can be varied by performing a relative translation motion in a lateral direction to the optical axis of the imaging optical system 12 and / or by performing a relative rotational motion about an axis of rotation oriented in the direction of the optical axis. By means of the corresponding relative position change of the intensity detector 28, it is possible to set various measurement positions 54, of which three measurement positions (1.MP, 2.MP and 3.MP) set by displacing the intensity detector 28 in the x direction are illustrated in FIG. 4, which is explained in more detail below, and two measurement positions (1.MP and 2.MP) set by 180° rotation of the intensity detector 28 are illustrated in FIG. 4, which is likewise explained in more detail below.Furthermore, the measuring device 10 comprises an evaluation device 48 which is configured, as explained in more detail below, to determine the telecentricity of the optical imaging system 12 at the different field points 18 on the basis of pupil images 50 recorded at the different relative positions of the intensity detector 28 for different field points 18.FIG. 2 shows the beam path during the recording of the pupil image 50 for an exemplary field point 18 in the image plane 16 in the presence of a telecentricity error, in which the main beam 20 tis tilted by the tilt angle θ x with respect to the standard main beam 20 nwithout telecentricity error. The measured pupil image 50 is shifted by a shift value Δ (reference sign 52) with respect to a standard pupil image 50 nillustrated with broken lines, which would be measurable without telecentricity errors.FIG. 3 shows an alternative embodiment of the sensor head 27, which can be used instead of the sensor head according to FIG. 1 comprising only the intensity detector 28. The sensor head according to FIG. 3 comprises a substrate 58, which is arranged with its upper side in the image plane 16, imaging optics 60 and the intensity detector 28. The layer 62 converts the wavelength of the measurement radiation 32 into a detection wavelength of the intensity detector 28. For example, the wavelength converting layer 62 is configured to convert EUV radiation into visible radiation. The imaging optics 60 is designed here in the form of a relay objective and serves to image the pupil image present in the detection plane 44 onto the intensity detector 28. In cases where reference is made in this text to a relative change in position of the intensity detector 28 with reference to the sensor head according to FIG. 1, the described relationship can be transferred to the sensor head 27 according to FIG. 3, wherein the entire sensor head 27 including the substrate 58, the imaging optics 60 and the intensity detector 28 then experiences the relative change in position.FIG. 4 illustrates a first exemplary embodiment of a method for measuring the telecentricity of the optical imaging system 12 by means of the measuring device 10 according to FIG. 1. In this method, the intensity detector 28 is arranged in three different measurement positions 54- 1 (1.MP), 54- 2 (2.MP) and 54- 3 (3.MP). The pupil images 50 present at the detection sections 42- 1 (DA 1) and 42- 2 (DA 2) are detected in each measurement position and an associated pupil image position 62 on the intensity detector 28, i.e. in the coordinate system 64 of the intensity detector 28, is determined for each pupil image 50.Specifically, in the first measurement position 54- 1, the intensity detector is located at the position illustrated in FIG. 1 below the field points 18- 1 and 18- 2, i.e. the measurement channels 36- 1 and 36- 2 irradiate the detection sections DA 1 and DA 2.For telecentricity at the field points 18- 1, 18- 2, 18- 3, and 18- 4, the tilt angles θ x1= +1,0 mrad, θ x2= +0,75 mrad, θ x3= +0,5 mrad, and θ x4= 0,25 mrad are set in FIG. 1 for illustration purposes. In the first measurement position 54- 1, a pupil image 50- 1 associated with the first field point 18- 1 or the first measurement channel MK 1 is obtained at the detection section DA 1, which pupil image is displaced by Δ 1 on account of the tilt angle θ x1 with respect to the corresponding standard pupil image 50 n, the center point of which has the x-coordinate x k1 in the coordinate system 64 of the intensity detector 28. At the detector section DA 2, a pupil image 50- 2 associated with the second field point 18- 2 or the second measurement channel MK 2 is obtained, which pupil image is displaced by Δ 2 by virtue of the tilt angle θ x2 with respect to the corresponding standard pupil image 50 n, the center point of which has the x-coordinate x k2 in the coordinate system 64 of the intensity detector 28.The evaluation device 48 determines the respective pupil image positions 62 from pupil images 50- 1 and 50- 2 acquired in the first measurement position 54- 1, these being the x-coordinates x p1-1 and x p2-1 of the center points of the pupil images 50- 1 and 50- 2 in the coordinate system 64 of the intensity detector 28 in the present case.According to an alternative embodiment of the measuring device 10, the sensor head according to FIG. 1 can further comprise a diffraction grating arranged in the image plane 16 in addition to the intensity detector 28. In this case, the intensity detector at the respective measurement position 54 does not record the relevant pupil image 50 or the angle-resolved intensity distribution present at the relevant field point 18 in the respective detector sections 42. Rather, a respective interference pattern formed by superposition of the zeroth order of diffraction, which corresponds to the relevant pupil image 50, with the + / - 1st order of diffraction is generated at the respective detector sections 42. In this embodiment, a plurality of interference patterns each having a slightly shifted phase are recorded, and then the interference patterns are averaged. Thus, about ten interference patterns can be recorded with a diffraction grating shifted by λ / 10 each. In the case of two-dimensional diffraction gratings, corresponding lateral displacements must be selected, so that the averaged image corresponds to the zeroth order of diffraction.By averaging the interference patterns, the DC component can be determined, which substantially corresponds to the pupil image 50. In other words, when a diffraction grating is used in the image plane 16, a special method is used with which + / -1. The diffraction orders can be calculated from the recorded intensity distribution and therefore only the angle-resolved intensity distributions present at the field points 18 can be determined in the form of the pupil images 50. From the pupil images 50 thus determined, first the x-coordinates x p1-1 and x p2-1 of the pupil image positions 62 are determined by means of edge edge fit, as described above.After recording the pupil images 50 in the first measurement position 54- 1, the intensity detector 28 is displaced by the distance ΔK between the measurement channels 36 in the x-direction and thus into the second measurement position 54- 2. Here, the pupil image 50- 2 assigned to the second measurement channel MK 2 is present at the detector section DA 1. That is, the pupil image 50- 2 is detectable in the two measurement positions 54- 1 and 54- 2 with two different detection sections, namely the detection section DA 2 in the first measurement position 54- 1 and the detection section DA 1 in the second measurement position 54- 2.The pupil image 50- 3 assigned to the third measurement channel MK 3 is in contact with the second detection section DA 2 in the second measurement position 54- 2. The pupil image 52- 2, as in the first measurement position 54- 1, is also displaced in the second measurement position 54- 2 by Δ 2 with respect to the standard pupil image 50 n, the center point of which has the x-coordinate x k1 in the coordinate system 64 of the intensity detector 28. The pupil image 52- 3, on the other hand, is displaced in the second measurement position 54- 2 by Δ 3 with respect to the corresponding standard pupil image 50 n, the center point of which has the x-coordinate x k2 in the coordinate system 64 of the intensity detector 28, on account of the tilt angle θ x3. From pupil images 50- 2 and 50- 3 acquired in second measurement position 54- 2, evaluation device 48 uses a marginal edge fit to determine respective pupil image positions 62, which in the present case are x-coordinates x p2-2 and x p3-2 of the center points of pupil images 50- 2 and 50- 3 in coordinate system 64 of intensity detector 28.After recording the pupil images 50 in the second measurement position 54- 2, the intensity detector 28 is again displaced by the distance ΔK between the measurement channels 36 in the x-direction and thus into the third measurement position 54- 3. Here, the pupil image 50- 3 assigned to the third measurement channel MK 3 is present at the detector section DA 1. The pupil image 50- 4 assigned to the fourth measurement channel MK 4 is in contact with the second detection section DA 2 in the third measurement position 54- 3. The pupil image 52- 3, as in the second measurement position 54- 2, is also displaced in the third measurement position 54- 3 by Δ 3 with respect to the standard pupil image 50 n, the center point of which has the x-coordinate x k1 in the coordinate system 64 of the intensity detector 28. The pupil image 52- 4, on the other hand, is displaced in the third measurement position 54- 3 by Δ 4 with respect to the corresponding standard pupil image 50 n, the center point of which has the x-coordinate x k2 in the coordinate system 64 of the intensity detector 28, on account of the tilt angle θ x4. From pupil images 50- 3 and 50- 4 acquired in third measurement position 54- 3, evaluation device 48 uses a marginal edge fit to determine respective pupil image positions 62, which in the present case are x-coordinates x p3-3 and x p4-3 of the center points of pupil images 50- 3 and 50- 4 in coordinate system 64 of intensity detector 28.The following relationships apply for the x-coordinates x p1-1 and x p2-1 determined in the first measurement position 54- 1: x p1-1= xk 1- Δ 1 and x p2-1= x k2- Δ 2: analogous relationships apply for x-coordinates x p2-2, x p3-2, x p3-3 and x p4-3. determined in the second measurement position 54- 2 and the third measurement position 54- 3: The following equation system 66- 1 can thus be established:This equation system from six equations has six unknowns with x k1, x k2, Δ 1, Δ 2, Δ 3 and Δ 4 which can be determined by solving the equation system. This is effected in the evaluation device 48. furthermore, the evaluation device 48 converts the displacement values Δ 1, Δ 2, Δ 3 and Δ 4 determined therewith into the relevant tilt angles θ x1, θ x2, θ x3 and θ x4( also referred to as telecentricity angles) via corresponding conic section considerations and thus determines a telecentricity field profile 68 in the x-coordinate direction at the field points 18- 1, 18- 2, 18- 3 and 18- 4. According to a further embodiment, the measuring device 10 is configured to determine the telecentricity field profile two-dimensionally, i.e. in the x- and y-direction, i.e. the tilt angles θ x and θ y are determined at the different field points 18.The relationship between a displacement value Δ of the pupil image and the associated telecentricity angle θ has a dependence on the numerical aperture (NA) of the imaging optical system 12. According to one embodiment, therefore, the numerical aperture is determined from the recorded pupil images 50 at the various field points 18 and taken into account in the determination of the telecentricity angles θ. According to a further embodiment, it is ensured that the pupil images 50 are measured at full numerical aperture. In this case, the numerical aperture is known in advance, so that the measurement of the NA field profile is not necessary.FIG. 5 illustrates a second exemplary embodiment of a method for measuring the telecentricity of the optical imaging system 12 by means of the measuring device 10 according to FIG. 1. In this method, the intensity detector 28 is arranged in two different measurement positions 54- 1 (1.MP) and 54- 4 (2.MP). The first measurement position 54- 1 corresponds to the first measurement position according to FIG. 4, while the second measurement position 54- 4 is effected not as in FIG. 4 by a displacement of the intensity detector 28, but by a 180° rotation of the intensity detector 28 about the axis of rotation 46.Analogously to the measuring method according to FIG. 4, in the measuring method according to FIG. 4, the pupil images 50 present at the detection sections 42- 1 (DA 1) and 42- 2 (DA 2) are detected in each of the measuring positions 54- 1 and 54- 4, and an associated pupil image position 62 on the intensity detector 28, i.e. in the coordinate system 64 of the intensity detector 28, is determined for each pupil image 50. The evaluation device 48 thus determines the respective pupil image positions 62 from pupil images 50- 1 and 50- 2 acquired in the first measurement position 54- 1, which in the present case are the x-coordinates x p1-1 and x p2-1 of the center points of the pupil images 50- 1 and 50- 2 in the coordinate system 64 of the intensity detector 28.In the second measurement position 54- 4, the pupil image 50- 1 assigned to the first measurement channel MK 1 is present at the detector section DA 2 and the pupil image 50- 2 assigned to the second measurement channel MK 2 is present at the detector section DA 1. That is, the pupil image 50- 1 is detectable in the two measurement positions 54- 1 and 54- 4 with two different detection sections, namely the detection section DA 1 in the first measurement position 54- 1 and the detection section DA 2 in the second measurement position 54- 4. The same applies analogously to the pupil image 50-2. The evaluation device 48 thus determines the respective pupil image positions 62 from the pupil images 50- 1 and 50- 2 acquired in the second measurement position 54- 4, these being the x-coordinates x p2-2 and x p2-2 of the center points of the pupil images 50- 1 and 50- 2 in the coordinate system 64 of the intensity detector 28 in the present case.From the relationships which apply to the x coordinates determined in the measurement positions 54- 1 and 54- 4, the following equation system 66- 2 can be established:This equation system of four equations has four unknowns with x k1, x k2, Δ 1, and Δ 2 which can be determined by solving the equation system. This is done in the evaluation device 48. furthermore, the evaluation device 48 converts the displacement values Δ 1 and Δ 2 determined therewith into the relevant tilt angles θ x1, and θ x2( also referred to as telecentricity angle) via corresponding conic section considerations and thus determines the telecentricity field profile 68 in the x-coordinate direction at the field points 18- 1 and 18- 2.FIG. 6 illustrates, in a simplified illustration, an exemplary embodiment of a projection exposure apparatus 100 having an optical imaging system 12 designed as a projection objective.The microlithographically projected exposure apparatus 100 illustrated in FIG. 6 is configured for operation with EUV exposure radiation. However, the present invention is not restricted to use in such an apparatus, but can also be used for measuring projection exposure apparatuses having other working wavelengths, for example working wavelengths in the VUV or DUV range.According to the exemplary embodiment of FIG. 6, the projection exposure apparatus 100 has a field facet mirror 103 and a pupil facet mirror 104. On the field facet mirror 103, the light of a light source unit comprising a plasma light source 106 and a collector mirror 108 is directed. In the light path downstream of the pupil facet mirror 104, a first telescope mirror 110 and a second telescope mirror 112 are arranged. Arranged in the light path downstream is a deflection mirror 114 which deflects the radiation impinging thereon to an object field in the object plane 14 of the projection objective 12 which comprises six mirrors 118, 120, 122, 124, 126 and 128.The projection exposure apparatus 100 further comprises a mask table 132 and a wafer table 136 for holding a wafer to be exposed during an exposure operation of the projection exposure apparatus 100. The measurement mask 24 of the measurement device 10 is arranged on the mask table 132. The sensor head 27 with the intensity detector 28 is integrated into the wafer table 136. In this case, the wafer table 136 is movable in the x and y directions. The sensor head 27 is attached to the wafer table by a rotation device 146 configured to rotate about the axis of rotation 46. Thus, the moving mechanism of the wafer stage 136 in conjunction with the rotating device serves as the moving device 30 according to FIG. 1.The above description of exemplary embodiments, embodiments or variants is to be understood as exemplary. The disclosure made thereby enables the person skilled in the art, on the one hand, to understand the present invention and the advantages associated therewith, and, on the other hand, also comprises alterations and modifications of the described structures and methods that are obvious in the understanding of the person skilled in the art. Therefore, all such alterations and modifications as come within the scope of the invention as defined in the appended claims, as well as equivalents, are intended to be covered by the protection of the claims.List of reference characters10 Measuring device 12 Optical imaging system 13 Optical axis 14 Object plane 16 Image plane 18 Field point 20 t Haupt beam with telecentricity error 20 nNormal main beam 22 Illumination device 24 Measuring mask 26 Sensor module 27 Sensor head 28 Intensity detector 30 Movement device 32 Measuring radiation 34 Measuring structures 36 Measuring channels 38 Pupil 40 Aperture 42 Detection sections 44 Detection plane 46 Axis of rotation 48 Evaluation device 50 Pupil image 50 nNormal pupil image 52 Displacement value Δ 54 Measuring positions 56 Distance between two adjacent measuring channels 58 Substrate 60 Imaging optical system 62 Pupil image position 64 Coordinate system of the intensity detector 66- 1, 66- 2 equation system 68 telecentricity field profile 100 projection exposure apparatus for microlithography 103 field facet mirror 104 pupil facet mirror 106 plasma light source 108 collector mirror 110 first telescope mirror 112 second telescope mirror 114 deflection mirrors 118, 120, 122, 124, 128 mirror of the projection objective 132 mask table 136 wafer table 146 rotation deviceReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedU.S. Pat. No. 7,365,861 B2 [0004, 0011]CN114647154 A

[0004]

Claims

Measuring device (10) for measuring a telecentricity (68) of an optical imaging system (12), comprising: - an illumination device (22) which is configured to emit a measurement radiation (32) onto an object plane (14) of the optical imaging system, - an intensity detector (28) which has a plurality of non-overlapping detection sections is arranged offset with respect to an image plane (16) of the optical imaging system and is configured to detect angle-resolved intensity distributions (50) present at the field points for at least two field points (18-1, 18-2) in the image plane with a respective one of the detection sections (42-1, 42-2) of the intensity detector, - a movement device (30) which is configured to set different measurement positions (54) by such a change of a relative position of the intensity detector to the optical imaging system in at least one rigid body degree of freedom, the intensity distribution (50-2) of at least one of the field points before and after the relative position change can be detected with two different ones of the non-overlapping detection sections (42-2, 42-1) of the intensity detector, and an evaluation device (48) which is configured to determine the telecentricity (68) of the optical imaging system at each of the at least two field points on the basis of angle-resolved intensity distributions (50-1, 50-2) recorded at the different measurement positions (54).Measuring device according to claim 1, wherein the two different, non-overlapping detection sections (42-2, 42-2) of the intensity detector before the relative position change serve for measuring the intensity distributions of different field points (18-1, 18-2).Measuring device according to claim 1 or 2, which is configured to form measuring channels (36) through the optical imaging system, which pass through the image plane (16) at one of the field points (18-1, 18-2, 18-3, 18-4) to be measured in each case and strike different detection sections (42-1, 42-2) of a detection surface of the intensity detector, wherein the movement device (30) is configured to change the relative position such that a specific detection section (42-1) is irradiated before and after the change in position of measuring radiation of different measuring channels (50-1, 50-2).Measuring device according to claim 3, further comprising a measuring mask (24) arranged in the object plane and having measuring structures (34) for forming the measuring channels (36).A measurement device according to any preceding claim, wherein the variation in relative position comprises a relative translation movement of the intensity detector (28) with respect to the imaging optical system (12) in a direction transverse to an optical axis (13) of the imaging optical system.Measuring device according to one of the preceding claims, in which the position of the intensity detector (28) can be positioned via an external measuring system or via a wavefront- and / or intensity-based alignment with the image plane of the optical imaging system.A measurement device according to any preceding claim, configured to form measurement channels (36) through the optical imaging system, each of which passes through the image plane (16) at a respective one of the field points (18) to be measured, and wherein the change in relative position comprises a relative translation movement of the intensity detector with respect to the optical imaging system in a lateral direction to an optical axis (13) of the optical imaging system by at least a distance (56) between two adjacent measurement channels.Measuring device according to claim 6 or 7, wherein the evaluation device (48) is configured to determine the telecentricity of the optical imaging system on the basis of angle-resolved intensity distributions which are recorded at three different measurement positions (54-1, 54-2, 54-3) which differ by relative displacement of the intensity detector with respect to the optical imaging system along a degree of translational freedom.A measuring device according to any preceding claim, wherein the variation in relative position comprises a relative rotational movement of the intensity detector with respect to the optical imaging system about an axis of rotation (46) oriented in the direction of the optical axis (13).Measuring device according to one of the preceding claims, in which the evaluation device (48) is configured to determine a respective associated pupil image position (62) from the recorded angle-resolved intensity distributions for each of the relative positions at all measured field points.Measuring device according to claim 10, wherein the respective determined pupil image position comprises a displacement value of the relevant pupil image (50) with respect to an associated standard pupil image (50n), which would be present if telecentricity were not present, in at least one coordinate direction.Measuring device according to claim 10 or 11, wherein the evaluation device is configured to determine the displacement values by evaluating a system of equations (66) containing the determined pupil image positions.Measuring device according to one of Claims 10 to 12, in which the evaluation device is configured to determine the determination of the pupil image positions (62) in each case with subpixel accuracy, based on a pixel resolution of the intensity detector (28).Measuring device according to one of Claims 10 to 13, in which the evaluation device is configured to bring about the determination of the pupil image positions (62) by means of an edge fit of the recorded intensity distributions (50).Measuring device according to claim 14, wherein the respective edge fit is based on intensity distributions averaged over different measuring positions (54) of the intensity detector.Measuring device according to one of Claims 10 to 15, in which the evaluation device (48) is configured to convert the determined pupil image positions (62) into telecentricity angles of the optical imaging system.Measuring device according to one of the preceding claims, in which the evaluation device (48) is configured to determine the numerical aperture at each of the field points (18) from the recorded angle-resolved intensity distributions (50) and to take it into account in the determination of the telecentricity.Measuring device according to one of the preceding claims 3 to 17, which is configured to measure the measurement channels partially serially by displacement of the intensity detector (28).A projection exposure apparatus for microlithography having a projection objective and a measuring arrangement according to one of the preceding claims for measuring a telecentricity of the projection objective.Method for measuring a telecentricity of an optical imaging system (12), comprising the steps: - irradiation of a measurement radiation (32) onto an object plane (14) of the optical imaging system, - arranging an intensity detector (28) having a plurality of non-overlapping detection sections (42) in a plane (44) offset from an image plane (16) of the optical imaging system and detecting angle-resolved intensity distributions (50) which are present at at at least two field points (18-1, 18-2) in the image plane, by means of a respective detection section (42-2, 42-2) of the intensity detector, changing a relative position of the intensity detector to the optical imaging system in at least one rigid body degree of freedom for setting different measurement positions (54) and detecting the intensity distribution of at least one of the field points before and after the relative position change with two different ones of the non-overlapping detection sections of the intensity detector, and determining the telecentricity of the optical imaging system on the basis of angle-resolved intensity distributions recorded at the different measurement positions at each of the at least two field points.

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