DE102023212214A1 - Device for measuring telecentricity of an optical imaging system - Google Patents

Abstract

A measuring device (10) for measuring a telecentricity (68) of an optical imaging system (12) comprises an illumination device (22) which is configured to radiate a measuring 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 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 measuring 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 in such a way that the intensity distribution (50-2) of at least one of the field points before and after the relative position change 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 invention

The invention relates to a device and a method for measuring a telecentricity of an optical imaging system, for example a projection lens of a microlithographic projection exposure system.

Telecentricity determination is known to detect deviations from the ideal telecentric behavior of an optical imaging system, i.e., telecentricity errors. In an imaging system affected by a telecentricity error, the chief ray for a given field point does not run parallel to the optical axis of the imaging system, as in the error-free case, but is tilted relative to it. The tilt angle represents a quantitative measure of the telecentricity error. In other words, telecentricity refers to an energetic tilt of the ray cone of an optical imaging system around the focal point in the image or object plane. The telecentricity error is a 2-dimensional quantity that can be represented as two tilt angles from the corresponding plane normal in the direction of two orthogonal basis vectors in the corresponding plane. The telecentricity error can be field-point-dependent, i.e., dependent on the lateral position of the focal point in the corresponding plane. The telecentricity of microlithographic projection lenses on the image plane affects the distortion in the lithography process through 3D effects in the photoresist.

An obvious approach for determining a telecentricity error is to measure the energetic center of gravity of the image of a particular field point in an xy-plane perpendicular to the optical axis at several measuring points offset from each other in the z-direction of the optical axis, and to trigonometrically calculate the tilt angle from this. However, this approach is challenged by the fact that the energetic center of gravity of the image of a particular field point in the xy-plane can vary depending on the z-position, also due to other image errors typically associated with imaging systems, such as coma and image shell errors.

To avoid this problem, US 7,365,861 B2 proposed performing a wavefront measurement on the optical imaging system at various z-positions using a shear interferometer and calculating the telecentricity based on the Z2 and Z3 Zernike coefficients measured in the process. In shear interferometric measurement, a measuring unit consisting of a diffraction grating and a detector unit arranged underneath 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 on the diffraction grating, an interference pattern is generated on the detector unit for various measuring channels arranged at different field points. The measuring unit is shifted step by step in the xy plane so that the phase distribution of the interference patterns changes. This is also referred to as "phase shifting", whereby the shift steps are so small that the measuring channels remain unchanged during the measurement, i.e. the detector sections assigned to the individual measuring channels do not change; only the phase of the recorded interference patterns changes. However, it has been found that this measurement method does not provide sufficiently accurate measurements for telecentricity. Furthermore, reference is made to the publication CN 114647154 A pointed out.

Underlying task

It is an object of the invention to provide a device and a method of the type mentioned at the outset, whereby the aforementioned problems are solved and preferably the accuracy of the telecentricity measurement is improved.

Inventive solution

The aforementioned object can be achieved according to the invention, for example, with a measuring device for measuring the telecentricity of an optical imaging system. The measuring device according to the invention comprises an illumination device configured to irradiate a measuring 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 configured to detect angle-resolved intensity distributions present at the field points for at least two field points in the image plane using a respective detection section of the intensity detector. Furthermore, the measuring device according to the invention comprises a movement device configured to set different measuring 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 using two different non-overlapping detection sections of the intensity detector, as well as a Evaluation device which is configured to determine the telecentricity of the optical imaging system at each of the at least two field points based on angle-resolved intensity distributions recorded at the different measuring positions.

According to one embodiment, the intensity detector can be part of a sensor head. Telecentricity is understood to mean an energetic tilt of one or more beam cones of the optical imaging system, assigned to a respective field point, around the focal point in the image plane or the object plane. This is referred to as image-side or object-side telecentricity. In the present case, the telecentricity measurement preferably includes image-side telecentricity.

Changing the relative position of the intensity detector to the optical imaging system means changing the position of the intensity detector and/or the position of the optical imaging system. The intensity distribution detected by the intensity detector is also referred to in this text as the pupil image. The intensity detector is offset from the image plane of the optical imaging system so 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 detector's detection surface.

The angle-resolved intensity distributions recorded at the different relative positions of the intensity detector are intensity distributions generated by the above-explained change in the relative position of the intensity detector to the optical imaging system on the detector. 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 such that the pupil distribution assigned to a specific field point is detected after the position change with a different section of the intensity detector than before the position change. The two sections are non-overlapping sections, i.e., each a separate section, of the detection detector.

The inventive acquisition of angle-resolved intensity distributions at different field points in the image plane, i.e., the acquisition of pupil distributions assigned to the different field points, and the changing of the relative position of the intensity detector such that the intensity distribution of one of the field points before and after the relative position change can be acquired with two different, non-overlapping sections of the intensity detector, makes it possible to determine telecentricity with high accuracy through mathematical evaluation of the intensity distributions acquired at the different relative positions. This relative position change enables the creation of sufficient redundancy in the measurements acquired by the intensity detector to enable the mathematical evaluation for determining telecentricity.

In comparison to the above-mentioned determination of telecentricity based on a wavefront measurement according to US 7,365,861 B2 , in which the telecentricity is essentially equated with a wavefront tilt, which only approximately corresponds to the energetic tilt of the beam cone of an optical imaging system, the procedure 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.

In the aforementioned shear interferometric wavefront measurement, intensity distributions are also recorded with a detector unit. However, as already explained above, these are 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 +/- 1st diffraction orders were subtracted from these interference patterns, the resulting intensity distributions would still differ from the intensity distributions recorded according to the invention by changing the relative position of the intensity detector. This is due to the fact that the displacement of the measuring unit during the wavefront measurement only occurs in small steps, which serve to phase shift 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, in particular the two different, non-overlapping detection sections mentioned above, serve to measure the intensity distributions of different field points before the relative position change.

According to a further embodiment, the measuring device is configured to form measuring channels through the optical imaging system, which pass through the image plane at one of the field points to be measured and impinge on different detection sections of a detection surface of the intensity detector, wherein the movement device is configured to change the relative position such that a specific detection section is irradiated by measuring radiation of different measuring channels before and after the change in position.

According to one embodiment, the measuring device further comprises a measuring mask arranged in the object plane with measuring structures for forming the measuring channels. In other words, the measuring mask comprises an associated measuring structure for each of the field points of the image plane to be measured, which structure forms a respective measuring channel. The measuring mask can also be moved, if necessary, 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, the measurement mask in all solid-state degrees of freedom to the image and object plane. This can be done using an external measuring system or a wavefront or intensity measurement.

According to one embodiment variant, if there are more than two measuring masks, the distances between these measuring masks can be arranged on an equidistant grid in order to detect identical measuring channels in the optical imaging system in the case of displacements by integer multiples of these distances in the object or image plane and/or in the case of correspondingly selected rotations relative to the optical imaging system.

According to one embodiment, fewer measurement masks can be used than measurement channels of the optical imaging system to prevent overlap of the intensity images on the intensity detector. The remaining measurement channels can be realized by serial measurements with different displacements and/or rotations of the intensity detector and the measurement masks relative to the optical imaging system.

According to a further embodiment, the change in the relative position comprises a relative translational 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 in this text as “lateral direction”.

According to a further embodiment, the change in the relative position comprises a relative translational 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 carried out according to the relative translational 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, if applicable, the measuring mask can be positioned via an external measuring system or via a wavefront and/or intensity-based alignment to the image plane or, if applicable, 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, each of which passes through the image plane at one of the field points to be measured, and wherein the change in the relative position comprises a relative translational 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 a 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 based on angle-resolved intensity distributions which are recorded at three different measuring positions which differ by the relative displacement of the intensity detector to the optical imaging system along a translational degree of 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 translational movement or relative rotational movement refers to a translational movement or rotational movement of the optical imaging system and/or the sensor element. The direction lateral to the optical axis refers to a direction that is perpendicular to the optical axis. deviates from the vertical direction by up to 45°, in particular up to 30° or up to 10°. The alignment of the rotation axis in the direction of the optical axis is understood to mean an alignment exactly parallel to the optical axis or an alignment deviating from it 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 pupil image in question compared to an associated standard pupil image, which would be present in the absence of telecentricity, in at least one coordinate direction.

According to a further embodiment, 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, the evaluation device is configured to determine the pupil image positions with subpixel accuracy, in each case based on a pixel resolution of the intensity detector.

According to a further embodiment, the evaluation device is configured to determine the pupil image positions by means of an edge fit of the recorded intensity distributions.

According to a further embodiment, the respective edge fit is performed based on intensity distributions averaged over various measurement positions of the intensity detector. The measurement positions can 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, e.g., 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. The pupil image positions are converted into beam cone angles in the substrate medium using conic section observations, and the telecentricity angles of the optical imaging system are determined from these.

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 this into account when determining the telecentricity. In other words, an NA field profile is determined. To determine the numerical aperture, a pupil radius is determined at each of the field points for each of the relative positions. The shift values of the pupil image position are dependent on the numerical aperture. By determining the numerical aperture, this influence can be taken into account when determining the telecentricity. In an alternative embodiment, it is ensured that the measurement of the intensity distributions takes place at full NA. In this case, measuring 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 measure the measurement channels partially serially by shifting the intensity detector and, if applicable, the measurement mask. This allows for a higher lateral resolution than would be possible with the intensity detector without overlapping the pupil images.

According to one embodiment, an NA diaphragm 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 applications analogously to the measurement at full NA.

According to one embodiment, the optical imaging system is a projection lens of a microlithographic projection exposure system, which is configured, for example, for DUV or EUV microlithography.

Furthermore, according to the invention, a projection exposure system for microlithography is provided with a projection objective and a measuring arrangement according to one of the preceding embodiments or embodiment variants for measuring a telecentricity of the projection objective.

The above-mentioned object can further be achieved, for example, with a method for measuring a telecentricity of an optical imaging system. The method comprises irradiating a measuring radiation onto an object plane of the optical imaging system, arranging an intensity detector having a plurality of non-overlapping detection sections in a Image plane of the optical imaging system offset from the image plane and detecting angle-resolved intensity distributions 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 to set 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, non-overlapping detection sections of the intensity detector, as well as determining the telecentricity of the optical imaging system based on 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, to set the different measurement positions, a relative position of the intensity detector and the measurement mask to the optical imaging system is changed in at least one rigid body degree of freedom. The intensity distribution of at least one of the field points is then recorded before and after the relative position change using two different non-overlapping detection sections of the intensity detector.

According to one embodiment of the method according to the invention, before the angle-resolved intensity distributions are acquired, the intensity detector is adjusted relative to the optical imaging system. A diffraction grating is arranged in the image plane, and a wavefront measurement of the optical imaging system is thus performed using the intensity detector. Based on 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 be performed, in particular, after each relative position change, i.e., before the acquisition of the intensity distributions following the respective relative position change.

The features specified with regard to the above-mentioned embodiments, exemplary embodiments, or embodiment variants, 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 according to the invention are explained in the description of the figures and the claims. The individual features can be implemented either separately or in combination as embodiments of the invention. Furthermore, they can describe advantageous embodiments that are independently protectable and whose protection may be claimed only during or after the application is filed.

Brief description of the drawings

• 1 ein Ausführungsbeispiel einer Messvorrichtung zur Messung einer Telezentrie eines optischen Abbildungssystems an einer Vielzahl an Feldpunkten in einer Bildebene des optischen Abbildungssystems mit einem Sensorkopf in Gestalt eines Intensitätsdetektors,
• 2 eine vergrößerte Darstellung des Strahlengangs im Bereich eines Feldpunktes eines Sensorkopfes in der Bildebene des optischen Abbildungssystems,
• 3 ein alternatives Ausführungsbeispiel des Sensorkopfes,
• 4 ein erstes, auf eine Dimension vereinfachtes, Ausführungsbeispiel eines Verfahrens zum Betrieb der Messvorrichtung gemäß 1 zur Telezentriemessung,
• 5 ein zweites, auf eine Dimension vereinfachtes, Ausführungsbeispiel des Verfahrens zum Betrieb der Messvorrichtung gemäß 1 zur Telezentriemessung, sowie
• 6 ein Ausführungsbeispiel einer Projektionsbelichtungsanlage mit einem Projektionsobjektiv sowie einer in der Projektionsbelichtungsanlage integrierten Messvorrichtung gemäß 1 zur Messung der Telezentrie des Projektionsobjektivs.

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:

• 1 an 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 with a sensor head in the form of an intensity detector,
• 2 an enlarged view of the beam path in the area of a field point of a sensor head in the image plane of the optical imaging system,
• 3 an alternative embodiment of the sensor head,
• 4 a first embodiment, simplified to one dimension, of a method for operating the measuring device according to 1 for telecentric measurement,
• 5 a second embodiment of the method for operating the measuring device according to 1 for telecentric measurement, as well as
• 6 an embodiment of a projection exposure system with a projection lens and a measuring device integrated in the projection exposure system according to 1 for measuring the telecentricity of the projection lens.

Detailed description of embodiments according to the invention

In the 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 particular embodiment, reference should be made to the description of other embodiments or the general description of the invention.

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

In 1 An exemplary embodiment of a measuring device 10 for measuring a telecentricity of an optical imaging system 12 is illustrated. The optical imaging system 12 can be an imaging system for microlithography, for example an optical imaging system 12 for a microlithographic projection exposure apparatus, in particular a projection lens of a microlithographic projection exposure apparatus. Alternatively, the optical imaging system 12 can also be a module of an illumination system of a microlithographic projection exposure apparatus or a module of a wafer inspection apparatus, etc. A microlithographic projection exposure apparatus is shown in an exemplary embodiment 100 in 6 shown.

The optical imaging system 12 has an optical axis 13, serves to image 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 DUV radiation with a wavelength of approximately 248 nm or approximately 193 nm, or EUV radiation. In the context of this text, EUV radiation is understood to mean electromagnetic radiation with a wavelength of less than 100 nm, in particular a wavelength of approximately 13.5 nm or approximately 6.7 nm.

As already mentioned above, the measuring device 10 serves to measure the telecentricity of the optical imaging system 12. Telecentricity is understood here to be a field distribution of a telecentricity error in the image plane 16 of the optical imaging system 12. In an imaging system that is affected by a telecentricity error, the main ray for a respective field point does not run parallel to the optical axis of the imaging system, as in the error-free case, but is tilted relative to it, with the tilt angle representing a quantitative measure of the telecentricity error. In other words, telecentricity refers to an energetic tilt of the beam cone of an optical imaging system around the focal point in the image or object plane. 2 For an exemplary field point 18 in the image plane 16, such a main ray 20t is shown, which is subject to a telecentricity error and which is tilted by the tilt angle θ _x in the xz plane relative to a standard main ray 20n (without telecentricity error) running parallel to the optical axis of the imaging system 12.

The measuring device 10 comprises an illumination device 22 and a measuring 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 measuring mask 24 is in 1 shown as an element in transmission, but according to an alternative embodiment can also be operated in reflection. The illumination device 22 is configured to generate a measuring radiation 32 and to radiate it onto the measuring mask 24. According to one embodiment, the measuring radiation 32 can have the operating wavelength of the optical imaging system 12 to be tested or can be in a similar wavelength range. In the case in which the optical imaging system 12 is designed as a projection objective of a microlithographic projection exposure system, the wavelength of the measuring radiation 32 can thus be approximately in the DUV or EUV wavelength range.

The measuring mask 24 comprises a two-dimensional dot matrix of measuring structures 34 (cf. measuring structures 34-1 to 34-4 according to 1 ). These are each configured as periodic structures, such as checkerboard structures, and serve to form measuring channels 36 through the optical imaging system 12, as shown in 1 illustrated using the measuring channels 36-1 to 36-4. The rays contained in the measuring channels 36-1 to 36-4, starting from the individual measuring structures 34-1 to 34-4, pass through the optical imaging system 12 in different beam paths, passing through at least one pupil plane in which the maximum angular space is limited by geometric restrictions (e.g. mechanical aperture 40). This maximum angular space defines the pupil 38 of the optical imaging system 12. In this context, the pupil 38 refers to the area in the pupil plane through which the respective rays of all measuring channels 36-1 to 36-4 pass, ie the rays of the different measuring channels 36-1 to 36-4 each pass through the same area of the pupil plane. The rays passing through the pupil 38, ie 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, pass through this point and arrive at different, non-overlapping detection sections 42 of a detection area of the intensity detector 28. The adjacent field points 18-1 to 18-4 are spaced apart by a distance ΔK (reference numeral 56). This is the distance between the corresponding adjacent measurement channels 36 in the image plane 16.

In the 1 In the illustrated embodiment, the intensity detector 28 is shown with only two detection sections 42-1 and 42-2 adjacent to each other in the x-direction. In this embodiment, the intensity detector 28 is used for the partially serial measurement of the measurement channels, ie in a first measurement, 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. 4 and 5 The detection sections 42-1 and 42-2 are also designated by the abbreviations DA1 and DA2. According to further embodiments not shown in the drawing, the intensity detector 28 can also have a larger number of detection sections 42 adjacent to one another in the x-direction, in particular as many detection sections as measuring channels 36. Furthermore, the intensity detector 28 can have further detection sections 42 adjacent to one another in the y-direction, i.e., comprise a two-dimensional grid of detection sections 42.

The intensity detector 28 is arranged in a detection plane 44 that is offset in a defined manner from the image plane 16, which in the present case lies below the image plane 16, in such a way that the intensity distribution in the pupil 38 of the optical imaging system 12 assigned to the corresponding field point 18-1 or 18-2 is present 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. 2 ). In other words, the intensity detector 28 is arranged such that the detection sections 42-1 and 42-2 can each detect the respective angle-resolved intensity distribution at the field points 18-1 and 18-2, respectively.

The intensity detector 28 is attached 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 rotated about a rotation axis 46 parallel to the optical axis 13. Alternatively, the optical imaging system 12, optionally together with the measurement mask 24, can be mounted so as to be displaceable and/or rotatable accordingly. Furthermore, the position of the intensity detector 28 can also be displaced relative to the optical imaging system 12, while simultaneously adjusting the position of the measurement mask 24 according to the image scale of the optical imaging system 12, so that the assignment of the measurement structures 34 to the field points 18 remains intact.

What is crucial is that the relative position of the intensity detector 28 to the optical imaging system can be changed, namely by performing a relative translational movement in a lateral direction to the optical axis of the optical imaging system 12 and/or by performing a relative rotational movement about a rotation axis aligned in the direction of the optical axis. By the corresponding relative position change of the intensity detector 28, various measurement positions 54 can be set, some of which are explained in more detail below. 4 three measuring positions (1.MP, 2.MP and 3.MP) adjusted by moving the intensity detector 28 in the x-direction and in the 4 two measurement positions (1.MP and 2.MP) adjusted by 180° rotation of the intensity detector 28 are illustrated.

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 various field points 18 on the basis of pupil images 50 recorded at the different relative positions of the intensity detector 28 for various field points 18.

In 2 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 ray 20t is tilted by the tilt angle θ _x relative to the standard main ray 20n without a telecentricity error, is shown. The measured pupil image 50 is shifted by a shift value Δ (reference numeral 52) relative to a standard pupil image 50n shown with dashed lines, which would be measurable without a telecentricity error.

In 3 an alternative embodiment of the sensor head 27 is shown, which instead of the sensor head comprising only the intensity detector 28 according to 1 The sensor head according to 3 comprises a substrate 58, which is arranged with its upper side in the image plane 16, an imaging optics 60 and the intensity detector 28. On an underside of the substrate 58, which forms the detection plane 44 in which the pupil image 50 to be recorded is generated, a wavelength-converting layer 62 or a quantum converter is applied. The layer 62 converts the wavelength of the measuring 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 lens and serves to image the pupil image present in the detection plane 44 onto the intensity detector 28. In the cases in which reference is made in this text to the sensor head according to 1 If a relative position change of the intensity detector 28 is mentioned, the described relationship can be applied to the sensor head 27 according to 3 transmitted, whereby the entire sensor head 27 including the substrate 58, the imaging optics 60 and the intensity detector 28 then experiences the relative position change.

In 4 is a first embodiment of a method for measuring the telecentricity of the optical imaging system 12 by means of the measuring device 10 according to 1 illustrated. In this method, the intensity detector 28 is arranged in three different measuring positions 54-1 (1st MP), 54-2 (2nd MP), and 54-3 (3rd MP). The pupil images 50 present at the detection sections 42-1 (DA1) and 42-2 (DA2) are acquired in each measuring position, and for each pupil image 50, an associated pupil image position 62 is determined on the intensity detector 28, i.e., in the coordinate system 64 of the intensity detector 28.

Specifically, the intensity detector is located in the first measuring position 54-1 at the 1 shown position below the field points 18-1 and 18-2, ie the measuring channels 36-1 and 36-2 irradiate the detection sections DA1 and DA2.

For the telecentricity at the field points 18-1, 18-2, 18-3 and 18-4, 1 For illustration purposes, the tilt angles θ _x ¹ = +1.0 mrad, θ _x ² = +0.75 mrad, θ _x ³ = +0.5 mrad and θ _x ⁴ = 0.25 mrad are used. In the first measuring position 54-1, a pupil image 50-1 assigned to the first field point 18-1 or the first measuring channel MK1 is obtained at the detection section DA1, which pupil image 50-1 is shifted by _{Δ 1} compared to the corresponding standard pupil image 50n, the center of which has the x-coordinate x _k1 in the coordinate system 64 of the intensity detector 28, due to the tilt angle θ x ¹ . At the detector section DA2, a pupil image 50-2 is produced which is assigned to the second field point 18-2 or the second measuring channel MK2 and which, due to the tilt angle θ _x ² , is shifted by Δ ₂ compared to the corresponding standard pupil image 50n, the center of which has the x-coordinate x _k2 in the coordinate system 64 of the intensity detector 28.

From pupil images 50-1 and 50-2 acquired in the first measuring position 54-1, the evaluation device 48 determines the respective pupil image positions 62; in the present case, these are the x-coordinates x _p1-1 and x _p2-1 of the centers of the pupil images 50-1 and 50-2 in the coordinate system 64 of the intensity detector 28. The pupil image positions 62 are determined with subpixel accuracy by means of an edge fit of the acquired pupil images 50, in each case based on the pixel resolution of the intensity detector 28.

According to an alternative embodiment of the measuring device 10, the sensor head can be 1 In addition to the intensity detector 28, the system may further comprise a diffraction grating arranged in the image plane 16. In this case, the intensity detector at the respective measuring position 54 in the respective detector sections 42 does not record the relevant pupil image 50 or the angle-resolved intensity distribution present at the relevant field point 18. Rather, a respective interference pattern is generated at the respective detector sections 42, formed by superimposing the zeroth diffraction order, which corresponds to the relevant pupil image 50, with the +/- 1st diffraction order. In this embodiment, a plurality of interference patterns are recorded, each with a slightly shifted phase, and the interference patterns are then averaged. Thus, approximately ten interference patterns can be recorded, each with a diffraction grating shifted by λ/10. For two-dimensional diffraction gratings, appropriate lateral shifts must be selected so that the averaged image corresponds to the zeroth diffraction order.

By averaging the interference patterns, the DC component can be determined, which essentially corresponds to the pupil image 50. In other words, when using a diffraction grating in the image plane 16, a special method is applied with which the +/-1st diffraction orders are subtracted from the recorded intensity distribution, and only then are the angle-resolved intensity distributions present at the field points 18 determined in the form of the pupil images 50. From the pupil images 50 thus determined, as described above, the x-coordinates x _p1-1 and x _p2-1 of the pupil image positions 62 are first determined by means of edge fitting.

After recording the pupil images 50 in the first measuring position 54-1, the intensity detector 28 is shifted by the distance ΔK between the measuring channels 36 in the x-direction and thus into the second measuring position 54-2. Here, the The pupil image 50-2 assigned to the second measuring channel MK2 is applied to the detector section DA1. This means that the pupil image 50-2 can be captured in the two measuring positions 54-1 and 54-2 with two different detection sections, namely the detection section DA2 in the first measuring position 54-1 and the detection section DA1 in the second measuring position 54-2.

The pupil image 50-3 assigned to the third measuring channel MK3 is located at the second detection section DA2 in the second measuring position 54-2. As in the first measuring position 54-1, the pupil image 52-2 is also shifted in the second measuring position 54-2 by Δ ₂ relative to the standard pupil image 50n, whose center has the x-coordinate x _k1 in the coordinate system 64 of the intensity detector 28. However, in the second measuring position 54-2, the pupil image 52-3 is shifted by _Δ ³ relative to the corresponding standard pupil image 50n, whose center has the x-coordinate x _k2 in the coordinate system 64 of the intensity detector 28, due to the tilt angle θ x ₃ . From pupil images 50-2 and 50-3 acquired in the second measuring position 54-2, the evaluation device 48 determines the respective pupil image positions 62 by means of a marginal edge fit; in the present case, these are the x-coordinates x _p2-2 and x _p3-2 of the centers of the pupil images 50-2 and 50-3 in the coordinate system 64 of the intensity detector 28.

After recording the pupil images 50 in the second measuring position 54-2, the intensity detector 28 is again shifted by the distance ΔK between the measuring channels 36 in the x-direction and thus into the third measuring position 54-3. Here, the pupil image 50-3 assigned to the third measuring channel MK3 is adjacent to the detector section DA1. The pupil image 50-4 assigned to the fourth measuring channel MK4 is adjacent to the second detection section DA2 in the third measuring position 54-3. As in the second measuring position 54-2, the pupil image 50-3 is also shifted in the third measuring position 54-3 by Δ ₃ relative to the standard pupil image 50n, whose center has the x-coordinate x _k1 in the coordinate system 64 of the intensity detector 28. In contrast, the pupil image 52-4 in the third measuring position 54-3 is shifted by _Δ ⁴ relative to the corresponding standard pupil image 50n, whose center point has the x-coordinate x _k2 in the coordinate system 64 of the intensity detector 28, due to the tilt angle θ x 4. From _the pupil images 50-3 and 50-4 acquired in the third measuring position 54-3, the evaluation device 48 determines the respective pupil image positions 62 by means of a peripheral edge fit. In this case, these are the x-coordinates x _p3-3 and x _p4-3 of the centers of the pupil images 50-3 and 50-4 in the coordinate system 64 of the intensity detector 28.

$${\text{x}}_{\text{p2}-1}={\text{x}}_{\text{k2}}-{\Delta }_2$$

$${\text{x}}_{\text{p2}-2}={\text{x}}_{\text{k1}}-{\Delta }_2$$

$${\text{x}}_{\text{p3}-2}={\text{x}}_{\text{k2}}-{\Delta }_3$$

$${\text{x}}_{\text{p3}-3}={\text{x}}_{\text{k1}}-{\Delta }_3$$

$${\text{x}}_{\text{p4}-3}={\text{x}}_{\text{k2}}-{\Delta }_4$$

The following relationships apply to the x-coordinates x _p1-1 and x _p2-1 determined in the first measuring position 54-1: x _p1-1 = Xk1 - Δ1 and x _p2-1 = x _k2 - Δ2. Analogous relationships apply to the x-coordinates x _p2-2 , x _p3-2 , x _p3-3 and x _{p4-3 determined in the second measuring position 54-2 and the third measuring position 54-3.} This allows the following system of equations 66-1 to be established: $${\text{x}}_{\text{p1}-1}={\text{x}}_{\text{k}1}-{\Delta }_1$$

$${\text{x}}_{\text{p2}-1}={\text{x}}_{\text{k2}}-{\Delta }_2$$

$${\text{x}}_{\text{p2}-2}={\text{x}}_{\text{k1}}-{\Delta }_2$$

$${\text{x}}_{\text{p3}-2}={\text{x}}_{\text{k2}}-{\Delta }_3$$

$${\text{x}}_{\text{p3}-3}={\text{x}}_{\text{k1}}-{\Delta }_3$$

$${\text{x}}_{\text{p4}-3}={\text{x}}_{\text{k2}}-{\Delta }_4$$

This system of six equations has six unknowns, x _k1 , x _k2 , Δ ₁ , Δ ₂ , Δ ₃ and Δ ₄ , which can be determined by solving the system of equations. This is done in the evaluation device 48. The evaluation device 48 then converts the displacement values Δ ₁ , Δ ₂ , Δ ₃ and Δ ₄ determined in this way into the relevant tilt angles θ _x ¹ , θ _x ² , θ _x ³ and θ _x ⁴ (also referred to as telecentric angles) using corresponding conic section considerations and thus determines a telecentric 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 telecentric field profile two-dimensionally, i.e. in the x and y directions, ie the tilt angles θ _x and θ _y are determined at the different field points 18.

The relationship between a shift value Δ of the pupil image and the associated telecentricity angle θ is dependent on the numerical aperture (NA) of the optical imaging system 12. According to one embodiment, the numerical aperture is therefore determined from the recorded pupil images 50 at the various field points 18 and taken into account when determining the telecentricity angle θ. According to another embodiment, it is ensured that the measurement of the pupil images 50 takes place at full numerical aperture. In this case, the numerical aperture is known in advance, thus eliminating the need to measure the NA field profile.

In 5 is a second embodiment of a method for measuring the telecentricity of the optical imaging system 12 by means of the measuring device 10 according to 1 In this method, the intensity detector 28 is positioned in two different measuring positions 54-1 (1.MP) and 54-4 (2.MP). The first measuring position 54-1 corresponds to the first measuring position according to 4 , while the second measuring position 54-4, not as in 4 by a displacement of the intensity detector 28, but by a 180° rotation of the intensity detector 28 around the axis of rotation 46.

Analogous to the measuring method according to 4 are measured in accordance with 4 the pupil images 50 present at the detection sections 42-1 (DA1) and 42-2 (DA2) are acquired in each of the measuring positions 54-1 and 54-4, and for each pupil image 50, an associated pupil image position 62 is determined on the intensity detector 28, i.e., in the coordinate system 64 of the intensity detector 28. From the pupil images 50-1 and 50-2 acquired in the first measuring position 54-1, the evaluation device 48 thus determines the respective pupil image positions 62; in the present case, these are the x-coordinates x _p1-1 and x _p2-1 of the centers of the pupil images 50-1 and 50-2 in the coordinate system 64 of the intensity detector 28.

In the second measuring position 54-4, the pupil image 50-1 assigned to the first measuring channel MK1 is located at the detector section DA2, and the pupil image 50-2 assigned to the second measuring channel MK2 is located at the detector section DA1. This means that the pupil image 50-1 can be captured in the two measuring positions 54-1 and 54-4 with two different detection sections, namely the detection section DA1 in the first measuring position 54-1 and the detection section DA2 in the second measuring position 54-4. The same applies to the pupil image 50-2. From the pupil images 50-1 and 50-2 acquired in the second measuring position 54-4, the evaluation device 48 thus determines the respective pupil image positions 62; in the present case, these are the x-coordinates x _p2-2 and x _p2-2 of the centers of the pupil images 50-1 and 50-2 in the coordinate system 64 of the intensity detector 28.

$${\text{x}}_{\text{p2}-1}={\text{x}}_{\text{k2}}-{\Delta }_2$$

$${\text{x}}_{\text{p1}-2}={\text{x}}_{\text{k2}}+{\Delta }_1$$

$${\text{x}}_{\text{p2}-2}={\text{x}}_{\text{k1}}+{\Delta }_2$$

From the relationships that apply to the x-coordinates determined in the measuring positions 54-1 and 54-4, the following system of equations 66-2 can be established: $${\text{x}}_{\text{p1}-1}={\text{x}}_{\text{k1}}-{\Delta }_1$$

$${\text{x}}_{\text{p2}-1}={\text{x}}_{\text{k2}}-{\Delta }_2$$

$${\text{x}}_{\text{p1}-2}={\text{x}}_{\text{k2}}+{\Delta }_1$$

$${\text{x}}_{\text{p2}-2}={\text{x}}_{\text{k1}}+{\Delta }_2$$

This system of four equations has four unknowns: x _k1 , x _k2 , Δ ₁ , and Δ ₂ , which can be determined by solving the system of equations. This is done in the evaluation device 48. Furthermore, the evaluation device 48 converts the displacement values Δ ₁ and Δ ₂ thus determined into the respective tilt angles θ _x ¹ and θ _x ² (also called telecentricity angles) using 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.

6 illustrates in a simplified representation an embodiment of a projection exposure apparatus 100 with an optical imaging system 12 designed as a projection lens. The measuring device 10 according to 1 is integrated in the projection exposure system 100 for measuring the projection lens 12.

The 6 The microlithographic projection exposure system 100 shown is designed for operation with EUV exposure radiation. However, the present invention is not limited to use in such a system, but can also be used for measuring projection exposure systems with other operating wavelengths, for example, operating wavelengths in the VUV or DUV range.

According to the embodiment of 6 The projection exposure system 100 has a field facet mirror 103 and a pupil facet mirror 104. The light from a light source unit, which comprises a plasma light source 106 and a collector mirror 108, is directed onto the field facet mirror 103. A first telescopic mirror 110 and a second telescopic mirror 112 are arranged in the light path downstream of the pupil facet mirror 104. A deflecting mirror 114 is arranged downstream in the light path, which deflects the radiation incident upon it onto 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 system 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 system 100. The measuring mask 24 of the measuring 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. 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 for rotation about the rotation axis 46. Thus, the movement mechanism of the wafer table 136 in conjunction with the rotation device serves as the movement device 30 according to 1 .

The above description of exemplary embodiments, embodiments or variants is to be understood as an example. The disclosure herein will enable one skilled in the art to understand the present invention and the associated advantages, and will also encompass variations and modifications of the described structures and methods that are obvious to 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, and equivalents, are intended to be covered by the claims.

List of reference symbols

10

measuring device

12

optical imaging system

13

optical axis

14

Object level

16

Image plane

18

Field point

20t

Main beam with telecentricity error

20n

Standard main beam

22

Lighting equipment

24

Measuring mask

26

Sensor module

27

Sensor head

28

Intensity detector

30

Movement device

32

Measuring radiation

34

Measurement structures

36

Measuring channels

38

pupil

40

aperture

42

Detection sections

44

Detection level

46

axis of rotation

48

Evaluation device

50

Pupil image

50n

Normal pupil image

52

Displacement value Δ

54

Measuring positions

56

Distance between two adjacent measuring channels

58

Substrat

60

Imaging optics

62

Pupillary image position

64

Coordinate system of the intensity detector

66-1, 66-2

system of equations

68

Telecentric field progression

100

Projection exposure system for microlithography

103

Field facet mirror

104

Pupillary facet mirror

106

Plasma light source

108

Collector mirror

110

first telescope mirror

112

second telescope mirror

114

Deflecting mirror

118, 120, 122, 124, 128

Mirror of the projection lens

132

Mask table

136

Wafer table

146

Rotation device

QUOTES CONTAINED IN THE DESCRIPTION

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

• US 7,365,861 B2 [0004, 0011]
• CN 114647154 A [0004]

Claims (20)

A measuring device (10) for measuring a telecentricity (68) of an optical imaging system (12), comprising: - 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 measuring 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 such that the intensity distribution (50-2) 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 based on angle-resolved intensity distributions (50-1, 50-2) recorded at the different measuring positions (54). Measuring device according to Claim 1 , wherein the two different, non-overlapping detection sections (42-2, 42-2) of the intensity detector serve to measure the intensity distributions of different field points (18-1, 18-2) before the relative position change. 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 and impinge on 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 in such a way that a specific detection section (42-1) is irradiated by measuring radiation from different measuring channels (50-1, 50-2) before and after the change in position. Measuring device according to Claim 3 which further comprises a measuring mask (24) arranged in the object plane with measuring structures (34) for forming the measuring channels (36). Measuring device according to one of the preceding claims, wherein the change in the relative position comprises a relative translational movement of the intensity detector (28) with respect to the optical imaging system (12) in a direction transverse to an optical axis (13) of the optical imaging 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 to the image plane of the optical imaging system. Measuring device according to one of the preceding claims, which is configured to form measuring channels (36) through the optical imaging system, which measuring channels pass through the image plane (16) at one of the field points (18) to be measured, and wherein the change in the relative position comprises a relative translational 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 one distance (56) between two adjacent measuring channels. Measuring device according to Claim 6 or 7 , in which 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 measuring positions (54-1, 54-2, 54-3) which differ by the relative displacement of the intensity detector to the optical imaging system along a translational degree of freedom. Measuring device according to one of the preceding claims, wherein 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 (46) aligned 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 has a shift value of the relevant pupil image (50) compared to an associated standard pupil image (50n), which would be present in the absence of telecentricity, in at least one coordinate direction. Measuring device according to Claim 10 or 11 , in which 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 the Claims 10 until 12 , in which the evaluation device is configured to determine the pupil image positions (62) with subpixel accuracy, in each case based on a pixel resolution of the intensity detector (28). Measuring device according to one of the Claims 10 until 13 , in which the evaluation device is configured to determine the pupil image positions (62) by means of an edge fit of the recorded intensity distributions (50). Measuring device according to Claim 14 , in which the respective edge fit is carried out on the basis of intensity distributions averaged over different measuring positions (54) of the intensity detector. Measuring device according to one of the Claims 10 until 15 , in which the evaluation device (48) is configured to convert the determined pupil image positions (62) into telecentric 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 this into account when determining the telecentricity. Measuring device according to one of the preceding Claims 3 until 17 which is configured to measure the measuring channels partially serially by shifting the intensity detector (28). Projection exposure system for microlithography with a projection lens and a measuring arrangement according to one of the preceding claims for measuring a telecentricity of the projection lens. A method for measuring telecentricity of an optical imaging system (12), comprising the steps of: - irradiating a measuring beam (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) present at at least two field points (18-1, 18-2) in the image plane with 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 to set different measuring 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 non-overlapping Detection sections of the intensity detector, and - Determining the telecentricity of the optical imaging system based on angle-resolved intensity distributions recorded at the different measurement positions at each of the at least two field points.