Method for determining the imaging quality of an optical assembly of an optical system

Abstract

To determine the imaging quality of an optical assembly of an optical system comprising an illumination optic for illuminating image structures of a target object, arranged in an object field (3), with illumination and imaging light (7), and an imaging optic for imaging the object field (3) into an image field in which a substrate can be arranged, a useful illuminance angle distribution of the illumination of the object field (3) with the illumination and imaging light (7) by the illumination optic is specified. Furthermore, a measurement illuminance angle distribution of the measurement light (39) for illuminating the object field (3) with the measurement light (39) is specified. The measurement illuminance angle distribution differs at least partially from the useful illuminance angle distribution.The image quality of the imaging optics is determined by illuminating and imaging measurement structures of a measurement object arranged in the object field with the measurement light (39). The measurement object is illuminated with the specified measurement illumination angle distribution. The measurement structures have a measurement structure size that is larger than the object structure size of the object structures of the target object. This results in an image quality determination method with which the image position of an imaged object relative to a reference image position can be determined as precisely as possible so that subsequent images, for example for the production of several superimposed layers of a multilayer semiconductor device, are aligned with each other within specified tolerance limits.

Description

[0001] The invention relates to a method for determining the imaging quality of an optical assembly of an optical system. Furthermore, the invention relates to an alignment method for aligning a wafer relative to a reticle using the determination method. Furthermore, the invention relates to a method for producing a micro- or nanostructured component using such an alignment method. Finally, the invention relates to a micro- or nanostructured component produced by such a method.

[0002] A projection exposure system with an optical system comprising beam guides for illuminating an object plane with illumination angle distributions along different beam paths is known from DE 10 2015 224 522 B4. Optical systems as components of projection exposure systems are known from EP 1 959 302 B1, WO 2019 / 145 126 A1, WO 2012 / 160 928 A1, US Pat. No. 8,325,324 B, and US Pat. No. 8,760,628 B.

[0003] It is an object of the present invention to provide an image quality determination method with which an image position of an imaged object relative to a reference image position can be determined as precisely as possible such that subsequent images, for example for producing several superimposed layers of a multilayer semiconductor component to be produced, are aligned with one another within predetermined tolerance limits.

[0004] This object is achieved according to the invention by a determination method having the features specified in claim 1.

[0005] According to the invention, it was recognized that it is not a disadvantage for determining image quality if the illumination angle distributions of a useful illumination on the one hand and a measurement illumination on the other hand differ at least partially from each other. Such a difference can be specifically exploited by the optical system, particularly by taking into account the different diffraction behavior of a finely structured useful object and a coarsely structured measurement object, for example, to approximate beam paths between a beam path of the useful illumination light on the one hand and the measurement light on the other.On the one hand, this can be used to adapt a measuring light beam path within the optical assembly whose imaging quality is to be determined, in particular within the imaging optics, to a useful illumination light beam path in such a way that a useful light image can actually be accurately reproduced with the measuring light. Alternatively or additionally, it is possible, particularly when using multiple measuring light illumination angle distributions, to use different sensitivities of the various measuring light illumination angle distributions for specific imaging contributions of the optical assembly whose imaging quality is to be determined, in particular the imaging optics, in such a way that an imaging behavior of the useful illumination light for a given useful illumination angle distribution can be simulated as approximately as possible using a linear combination of different measuring light illumination angle distributions.

[0006] The effective illumination angle distribution may deviate from at least one specified measured illumination angle distribution such that a correlation integral, which indicates a correlation between the effective illumination angle distribution and the respective measured illumination angle distribution, is less than 90%, less than 75%, and even less than 60%. Such a correlation integral is usually greater than 5%.

[0007] The determination method can be operated as a simulation method in which, using an optical image tracking program, for example a ray tracing program, the image is simulated for the respective specified illumination angle distribution and for the respective specified optical design of the optical system. Alternatively or additionally, the image quality can be determined using a measurement of the respective image quality. Such a measurement of the image quality can be carried out by measuring an exposure result in a photosensitive layer on the wafer. Such a photosensitive layer can be embodied as a photoresist. Such a measurement of the exposure result can be carried out using an electron microscope and / or scatterometry. Alternatively or additionally, an aerial image measurement can be carried out.To measure the aerial image, a detection device with at least one spatially resolving detector can be provided within the image field of the imaging optics. Such a detector can be implemented as a CCD detector or a CMOS detector.

[0008] The determination procedure can involve more than one measurement object. In particular, differently structured measurement structures can be used. This can be particularly useful for extracting individual functional contributions in a wavefront determination.

[0009] The object structures, on the one hand, and the measurement structures, on the other, can be located in different sections of the object field. The measurement structure size can be at least twice as large as an object structure size. The size ratio between the measurement structure size on the one hand and the object structure size on the other hand can be greater than 2, can be at least 5, can be at least 10, can be at least 20, can be at least 25, can be at least 50, and can even be at least 100. This size ratio is usually less than 10,000 or even less than 1,000.

[0010] Advantages of the method according to claim 2 have already been discussed above in the context of one of the possible method variants. In this embodiment of the determination method, a beam path of the measuring light through the optical assembly whose imaging quality is to be determined is approximated to a beam path of the useful light within specified tolerance limits. Optical surfaces of the optical assembly that contribute to the imaging quality then influence the measuring light on the one hand and the useful light on the other in the same way. Imaging quality deviations for the measuring light can then be translated into corresponding imaging quality contributions for the useful light, whereby wavelength influences and / or intensity influences can also be taken into account if necessary.

[0011] A method according to claim 3 specifically determines the diffraction behavior of the object structures for the subsequent possible, dependent specification of at least one measurement illumination distribution.

[0012] An approach according to claim 4 leads to the best possible overlap between the components of the optical system, on the one hand, by the useful illumination light and, on the other hand, by the measurement light. The pupil sub-areas can be larger than the extent of individual pupil spots assigned to the respective diffraction orders. The pupil sub-areas can thus result from the spatial superposition of several diffraction orders of the measurement light.

[0013] Structure sizes according to claims 5 and 6 have proven themselves in practice. Typically, there is at least one order of magnitude difference between the object structure size and the measurement structure size.

[0014] A wavelength difference according to claim 7 between the useful illumination light on the one hand and the measuring light on the other hand can be greater than 0.1 nm, can be greater than 0.5 nm and can also be significantly greater.

[0015] Alternatively, the wavelength deviation can be less than 1 nm, less than 0.5 nm, and less than 0.1 nm. The wavelengths can also be exactly identical.

[0016] A measurement light illumination step sequence according to claim 8 has proven particularly advantageous for precise image quality determination. Different measurement structures can be used for different measurement light illumination steps. When specifying the measurement illumination angle distribution, several different measurement illumination angle distributions are then specified in the form of differing measurement light intensity distributions.

[0017] The measuring light intensity distributions when carrying out the measuring light illumination steps regularly differ from a useful illumination angle distribution.

[0018] The measuring light intensity distributions in at least some of the measuring light illumination steps may differ from a diffraction intensity distribution of the useful illumination light taking into account the diffraction of the illumination light by the object structures.

[0019] The position of the diffraction orders and / or the image quality can be determined by decomposing a wavefront of the illumination and imaging light into linear combinations of a set of basis functions, for example, Zernike functions. This allows the influence of individual functional contributions to be extracted, which in turn can be used to determine an image offset for a useful illumination angle distribution, taking these extracted Zernike contributions into account.

[0020] In the determination procedure, several measurement illumination angle distributions can be specified. The measurement illumination angle distributions can be selected so that they have as different an influence as possible on the respective functional contributions. In this case, one of the measurement illumination angle distributions can also be identical to the effective illumination angle distribution.

[0021] A method according to claim 9 is particularly precise.

[0022] The method according to claim 10 allows for precise inference regarding an object image shift or an object image offset. The comparison of the object image shift with the measured image shift can be performed by measurement and / or by calculation or simulation.

[0023] An alignment method according to claim 11 enables the production of multilayer semiconductor components.

[0024] A manufacturing method according to claim 12 uses the alignment method according to claim 11 for manufacturing multilayer semiconductor devices.

[0025] The advantages of a micro- or nanostructured component according to claim 13 correspond to those already explained above with reference to the methods.

[0026] The lighting system can have a DUV (deep ultraviolet) light source (wavelengths, for example, in the range between 150 nm and 380 nm) or an EUV light source (extreme ultraviolet, wavelengths between 5 nm and 100 nm).

[0027] The projection exposure system can be used to produce, in particular, a micro- or nanostructured component, particularly a semiconductor chip, for example a memory chip.

[0028] A corresponding, alternative or additional method for aligning a wafer relative to a reticle is explained using the following numbered aspects: 1. Method for aligning an object in the form of a lithography mask in a projection exposure apparatus, for example in the form of a lithography scanner, wherein a second illumination spectrum I 2,Bel(kx, ky) of at least one measuring structure in the form of a reticle alignment structure noticeably from a first illumination spectrum I 1,Bel(kx, ky) of those reticle structures used to image functional components of the semiconductor device, wherein furthermore either at least two reticle marking structures differing from each other by more than 10% in their structure period are illuminated with this second illumination spectrum and their images are measured, or that at least two different illumination spectra are used for one or more similar or different reticle marking structure(s), wherein in the case of a single, differently illuminated reticle marking structure, illumination and associated measurement take place in temporal sequence (the case of several different reticle marking structures under several illumination spectra is also claimed). As a measure of the deviation, the integral Ikorr,Bel:=∫NAOdkxdkyI1,Bel(kx,ky)I2,Bel(kx,ky)∫NAOdkxdkyI1,Bel2(kxky)∫NAOdkxdkyI2,Bel2(kx,ky) across the illumination pupil for the product of a first illumination intensity for the reticle structures that carry functions with respect to the semiconductor component and a second illumination intensity for the reticle marking, which is normalized to the first and second illumination intensities averaged across the entrance pupil. Thus, this integral I korr,Bel preferably be below 90%, more preferably be less than 75% and most preferably be below 60%. 2. The method according to aspect 1, wherein the second illumination spectrum is provided by a second illumination system that physically differs from a first illumination system for the template of the semiconductor functional structures and can comprise, for example, a beam splitter for coupling out source light, a locally varying light-blocking plate, a locally varying gray filter, positioning mirrors, and / or an optical fiber. If the lithography objective is a pure mirror system, the second illumination system can include a separate light source whose wavelength differs from that of the source for the first illumination system by more than 0.1 nm or more than 0.5 nm.If, however, the lithography projection objective contains at least one lens, either decoupled source light of the first illumination system is used and / or a separate light source whose wavelength deviates from that of the first illumination system by less than 1 nm, preferably less than 0.5 nm and particularly preferably by less than 0.1 nm. 3. The method according to aspect 1, wherein both I 1,Bel (k x , k y ) as well as I 2,Bel (k x , k y ) are both provided by a first illumination system, said illumination system preferably comprising at least one module with MEMS mirrors. 4. Method according to one of the preceding aspects, wherein in a first step, a set of functional structures to be considered are selected together with an associated illumination, wherein this illumination can be selected individually for each structure (e.g., for MEMS illumination) or can be uniform for all these functional structures, that in a second step, for each combination of illumination and functional structure, a sensitivity to aberrations, in particular Zernike wavefront errors, is determined, e.g., by aerial image simulation according to methods known in the art and / or calibration measurements in the paint, whereupon, based on a predetermined first threshold, those sensitivities are selected whose magnitude for at least one structure / illumination combination exceeds this threshold, resulting in a first set of wavefront disturbances, that in a third step, a set of expected usage cases is determined,which may include, in particular, vibration and thermal influences, environmental factors such as air pressure or drift and aging influences, in a fourth step, for all of these use cases, a maximum value of the expected amplitude of the individual aberrations is determined by simulation, calibration measurement or comparison with similar systems, this maximum value is compared with a second threshold for the point at which these aberrations can exert a noticeable system influence, from this a second set of potentially relevant wavefront disturbances is derived, in a fifth step the intersection, z→ the first and second potentially relevant wavefront disturbances, which can be described, for example, via Zernike functions of the wavefront in the exit pupil, are formed, the number N' of which is determined after deducting the Zernike functions Z2 and Z3 (FRINGE notation), alternatively to forming this intersection set, the amount of the product of the expected maximum amplitude and imaging sensitivity of the functional structure(s) is formed for each wavefront disturbance, this amount is compared with a third threshold value for the product and the wavefront disturbance in question is included in the set z→ of the relevant wavefront disturbances is adopted precisely when the product value determined for this purpose exceeds this third threshold value, in a sixth step a number M≥1 of possibly different reticle marking structures and B≥1 of possibly different illuminations is selected, so that a relationship Z = M • B ≥ N' is satisfied for the total number Z of measurements, or in a case in which not all combinations of reticle marking structures and illuminations are measured, for the total number Z of measurements of the reticle marking structures that differ from each other in pairs at least in structure and / or illumination, the relationship Z ≥ N' is satisfied, wherein the selection is to be made in such a way that the sensitivity vectors of all used combinations illumination / reticle marking structure lie independently of each other in the aberration space, so that an invertible sensitivity matrix according to Δx→=S↔z→ can be formed, in a seventh step the image position changes of the M reticle marking structure(s) are measured during the B illumination(s), whereby either all combinations or only a sufficiently extensive subset of them can be measured, and a vector Δx→ these changes in position, in an eighth step from this vector Δx→ and the inverted S↔−1 the sensitivity matrix the relevant wavefront disturbances currently present in the system according to z→=S↔−1Δx→ be determined, in a ninth step, an average or suitably weighted image position change of the functional structures based on this vector zz→, whose individual image position sensitivities and resulting individual image position changes are determined and in a tenth step this average or suitably weighted image position change is completely or partially corrected in the system, in which in particular manipulators such as actuators on the reticle and semiconductor substrate table and / or optical elements are moved. 5. Method according to one of the preceding aspects, wherein the smallest feature size of at least one critical structure for the semiconductor component is at least a factor of 2, preferably a factor of 5, particularly preferably a factor of 10 smaller than the smallest feature size of a reticle marking structure.

[0029] Embodiments of the invention are explained in more detail below with reference to the drawings, in which: Fig.1 a schematic overview of a microlithography projection exposure system in a meridional section, comprising an illumination optics for illuminating an object field and a projection lens for imaging the object field into an image field; Fig. 2 also in meridional section and with reference to optical components in greater detail, a part of the illumination optics of the projection exposure system between a Rema intermediate image plane and the object field, wherein additionally a measuring light source is shown schematically, which is part of a measuring device of the projection exposure system for measuring an image quality of an optical assembly of an optical system of the projection exposure system, wherein the illumination optics and / or the projection lens of the projection exposure system belong to the optical system; Fig.3 a plan view of an object assembly that can be arranged in the object field, comprising a useful object with object structures to be imaged for the production of semiconductor components and a plurality of measurement objects with measurement structures to be imaged during operation of the measuring device; Fig. 4 a design of one of the measuring objects with two variants of measuring structures; Fig. 5 an embodiment of an illumination angle distribution which can be used in an image quality measurement method, in the form of a homogeneous illumination of an illumination pupil of the illumination optics; Fig. 6 schematically shows diffraction patterns when imaging object structures of the useful object in the form of a line structure of parallel lines with the illumination angle distribution according to Fig. 5, as a function of a line spacing or a structure period, with an entrance pupil of the projection lens highlighted in each case; Fig.7 exemplary diffraction patterns when imaging a line object structure with a small structure period using an illumination angle distribution in which a pupil or illumination spot is illuminated within the illumination pupil, i.e., a small pupil filling level is present, with a zeroth and a + / -1st diffraction order of an object structure being shown for two different illumination situations; Fig. 8 in one to Fig. 7 similar representation diffraction patterns, which with a corresponding illumination with a small pupil filling level when imaging measuring structures with compared to the structure period of the object structures according to Fig. 7 much larger structural period; Fig. 9 again in to Fig.7 shows, in a similar representation, the diffraction patterns for the small structural period of the object structures of the useful object, wherein a wavefront profile during imaging through the projection lens and a pupil partial area exposed to the illumination and imaging light are also illustrated; Fig. 10 in one to Fig. 9 similar representation a replica of a representation of the object structures of the useful object according to Fig. 9 used pupil area of ​​the entrance pupil when imaging measuring structures with measuring light with a correspondingly specified measuring illumination angle distribution; Fig.11 again the illumination pupil with a variant of an illumination angle distribution, which can be used as a useful illumination angle distribution and as a measuring illumination angle distribution, shown as an intensity distribution of useful or measuring light over the entrance pupil, in the form of an x-dipole illumination; Fig. 12 in one to Fig. 11 similar representation a measurement intensity distribution in the form of a conventional setting with a small maximum measurement illumination angle; Fig. 13 in a Fig. 11 similar representation a further measurement intensity distribution in the form of a measurement intensity distribution with compared to the Fig. 12 larger maximum illumination angle; Fig. 14 in a Fig. 11 similar representation a further measurement intensity distribution in the form of a measurement intensity distribution with compared to the Fig. 13 larger maximum illumination angle; Fig. 15 again the illumination pupil with a variant of a measurement illumination angle distribution, shown as a measurement intensity distribution of measuring light over the entrance pupil, in the form of an x-dipole illumination with compared to the Fig. 11 smaller pole extension and smaller maximum x-illumination angle; Fig. 16 another measurement intensity distribution according to Fig. 15 with a larger x-illumination angle in comparison; Fig. 17 another measurement intensity distribution according to Fig. 15 with compared to Fig. 16 larger x-illumination angle; Fig. 18 another measurement intensity distribution according to Fig. 15 with compared to Fig. 17 larger x-illumination angle; Fig. 19 another measurement intensity distribution according to Fig. 15 with compared to Fig.18 larger x-illumination angle.

[0030] To clarify positional relationships, a Cartesian xyz coordinate system is shown in the drawing. Fig. 1 the x-axis runs perpendicular to the plane of the drawing. The y-axis runs in the Fig. 1 upwards. The z-axis runs in the Fig. 1 to the left.

[0031] A microlithography projection exposure system 1 has an illumination system with illumination optics 2 for illuminating a defined illumination or object field 3 at the location of an object or reticle 4, which represents a template to be projected for the production of microstructured or microelectronic semiconductor components. Such a reticle is also referred to as a mask. The reticle 4 is held by a reticle holder (not shown).

[0032] A deep ultraviolet (DUV) laser serves as the light source 5 for the illumination system. This can be an ArF excimer laser. Other DUV sources are also possible. A variant of the light source 5 is described below using the Fig. 10 explained.

[0033] A beam expander 6, for example a mirror arrangement known from DE-A 41 24 311, serves to reduce coherence and to generate an expanded, collimated, rectangular cross-section of a beam of the illuminating light 7.

[0034] A first diffractive optical raster element (DOE) 8 is arranged in an object plane of a condenser 9. This DOE 8 is also referred to below as an intensity pre-fork element. The condenser 9 has an axicon pair 10 and a lens 11 with a positive focal length. The distance between the axicon elements of the axicon pair 10 and the position of the lens 11 are adjustable along an optical axis 12 of the illumination optics 2, as shown in the Fig. 1 is indicated by double arrows 13, 14. The condenser 9 therefore represents a zoom lens.

[0035] A further diffractive and / or refractive optical raster element (ROE) 16 is arranged in an exit pupil plane 15 of the condenser 9. If the raster element 16 is designed to be diffractive, it can be implemented, for example, as a computer-generated hologram (CGH). Alternatively or in addition to being designed as a diffractive optical element, the ROE 16 can be designed to be refractive, for example, as a refractive optical raster element, in particular as a microlens array. Although a diffractive design is also possible, the raster element 16 will be referred to below as an ROE.

[0036] The first DOE 8 sets a defined intensity distribution in the pupil plane 15 at the location of the ROE 16. This creates a predefined illumination setting, i.e., a defined distribution of illumination angles across the object field 3. The first DOE 8 therefore represents an illumination angle preset element for specifying an illumination angle distribution across the object field 3.

[0037] A coupling optics 17 arranged downstream of the ROE 16 transmits the illumination light to a frontal entrance surface 18 of a transparent optical rod in the form of a glass rod 19.

[0038] The optical rod 19 has a rectangular cross-section. This rod cross-section is generally polygonal and can also be square or hexagonal, for example.

[0039] The rod 19 mixes and homogenizes the illumination light by multiple internal reflections at the jacket walls of the rod 19. Immediately adjacent to an end-side exit surface 20 of the rod 19 opposite the entrance surface 18 is an intermediate field plane 20a in which a reticle masking system (REMA) 21, an adjustable field diaphragm, is arranged.

[0040] With the ROE 16, among other things, the cross-sectional shape of the illumination beam 7 is adapted to the rectangular shape of the entrance surface 18 of the rod 19.

[0041] The ROE 16 is also referred to below as the optical rod illumination specification element. The ROE 16 serves to specify the illumination of the entrance surface 18 of the rod 19 with the illumination light 7. This specification of the illumination of the entrance surface 18 is such that it specifies a distribution of the illumination intensity and, at the same time, the illumination angle distribution across the entrance surface 18. The specified illumination intensity distribution across the entrance surface 18 deviates from a homogeneous distribution, which will be explained in more detail below.

[0042] The DOE 8, i.e. the intensity specification element, is used to specify an illumination intensity distribution on the ROE 16, i.e. on the optical rod illumination specification element.

[0043] A condenser 22 is arranged downstream of the REMA 21. In an exit pupil plane 23 of the condenser 22, a diaphragm changing holder 24 with a plurality of diaphragms or filters can be arranged, of which in the Fig. 1, two diaphragms 25, 26 are shown. The diaphragm changing holder 24 carries the various diaphragms in the manner of a diaphragm carousel. For diaphragm changing, the carousel is driven by a drive shaft 27 of a drive motor 28, which is in signal communication with a central control device 28a of the projection exposure system 1. The diaphragms of the diaphragm changing holder 24 are divided into an even number of separate diaphragm sections. The diaphragm sections can be diaphragms that completely block the illumination light, gray filters that attenuate the illumination light by a predetermined amount, or polarization filters that linearly polarize the illumination light.

[0044] The pupil plane 23 downstream of the rod 19 is followed by another condenser with lens groups 29, 30. A 90° deflection mirror 31 for the illumination light is arranged between the two lens groups 29, 30. The condenser 22 and the further condenser with the two lens groups 29, 30 form an objective 31a, which images the intermediate field plane 20a of the REMA 21 onto the reticle 4. The pupil plane 23 represents an internal pupil plane of this objective 31a. A design of the objective 31a is known in principle from US 6,295,122 B1. A design of the objective 31a is described in Fig. 2 shows the optical components involved in more detail.

[0045] A projection lens 32 images the object field 3, which lies in an object plane 33, into an image field 34 in an image plane 35. Such a projection lens is known from US Pat. No. 8,970,964 B2.

[0046] The image field 34 is part of the surface of a wafer 36 to be exposed, which is provided with a coating sensitive to the illumination light. The wafer 36 is held by a wafer holder (not shown). During projection exposure, the reticle 4 and the wafer 36 are scanned synchronously with each other. Intermittent movement of the holders of the reticle 4 and the wafer 36, a so-called stepper operation, is also possible.

[0047] The various beam-guiding and beam-forming components of the projection exposure system 1, with the exception of the deflecting mirror 31, are indicated as refractive components. They can also be catadioptric or reflective components. The illumination optics 2, including the REMA lens 31a, and the projection lens 32, form an optical system of the projection exposure system 1.

[0048] The projection lens 32 has an image-side numerical aberration NA of 0.55.

[0049] The projection lens 32 has a magnification of 1:4. The projection lens 32 therefore reduces the image by a factor of 4.

[0050] Fig. 2 shows, in addition to the REMA lens 31a, a measuring light source 37, which is part of a measuring device 38, which in turn is part of the projection exposure system 1. The measuring light source 37 generates measuring light 39, which is coupled into the beam path of the illumination light 7 of the REMA lens 31a via the deflecting mirror 31, which is designed as a beam splitter, in particular as a dichroic beam splitter. This coupling is such that the measuring light 39 is guided in the beam path of the REMA lens 31a from the deflecting mirror 31 onwards, in terms of individual beam guidance and utilization of the pupil and field, in the same way as the illumination light 7.

[0051] Between the measuring light source 37 and the beam splitter 31, a pupil diaphragm 40 is arranged in a measuring pupil plane 41 of the measuring device 38 in the beam path of the measuring light 39. The function of the measuring pupil diaphragm 40 corresponds to that of the diaphragm 25. The measuring pupil diaphragm 40 specifies a measurement intensity distribution of the measuring light 39 in the measuring pupil plane 41 and thus an illumination angle distribution of the measuring light 39 across the object field 3. The measurement intensity distribution in the measuring pupil plane 41 is a measure of a measurement illumination angle distribution of an illumination of the object field 3 with the measuring light 39.

[0052] The measuring light 39 can be coupled into the beam path of the illumination light 7 near a field plane of the illumination light beam path, near a pupil plane of the illumination light beam path, or between a field plane and a pupil plane. Instead of a coupling mirror such as the deflection mirror 31, a beam splitter cube or a coupling foil can also be used.

[0053] A coupling effect can be based on an amplitude division, a polarization division or even a spatial, in particular a parceled, division.

[0054] The wavelength of the measuring light 39 may differ from that of the illumination light 7. Alternatively, an actinic measurement is also possible, i.e., a measurement in which the measuring light 39 and the illumination light 7 have the same wavelength. In any case, the light source 5 for the illumination light 7 can simultaneously represent the measuring light source 37. The measuring light 39 is then decoupled from the illumination light 7, or illumination light 7 that cannot be used for coupling into the beam path of the optical system of the projection exposure system 1 is used as the measuring light 39.

[0055] The measuring light source 37 can be a laser, a light-emitting diode or a mercury vapor lamp.

[0056] A locally varying stepped or alternatively or additionally a continuous grey filter can also be used as the measuring pupil diaphragm 40.

[0057] Part of a guide of the measuring light 39 can be at least one mirror and / or an optical fiber.

[0058] Using the projection exposure system 1, micro- or nanostructured semiconductor components are manufactured on the wafer 36. These are built layer by layer in steps that may include the application of a first material, followed by the application of a photosensitive resist, followed by an optical exposure during which useful object structures are imaged on the wafer 36, followed by thermal fixation of the resist, and followed by one or more etching processes. To structure a functional three-dimensional structure, the positions of superimposed layers must precisely match, so that, for example, vertical conductive connections connect to one another.For the purpose of such alignment, measuring structures on the reticle are used, which can be arranged both within the actual area filled with the functional structures, which are also referred to as useful object structures, and outside, close to the edge of this functional area.

[0059] Fig. Figure 3 shows one embodiment of such an arrangement of useful object structures 42 and measurement objects 43 with measurement structures 44 on the reticle 4. Since it comprises both a useful object 45 with the useful object structures 42 and the measurement objects 43 with the measurement structures 44, the reticle 4 is also referred to as an object assembly. The measurement structures 44 are also referred to as reticle alignment structures. The object structures 42 are also referred to as functional components or functional structures.

[0060] When executing according to Fig.3, the useful object structures 42 are present in a central, approximately rectangular section of the reticle 4 in the form of the useful object 45 as a functional area. The useful object structures 42 are designed, for example, as dense lines that extend in the y-direction (z-direction in the Fig. 1). A typical structural period of the useful object structures 42, i.e. a period running along the x-direction along which the y-lines of the useful object structures 42 follow one another, can be on the order of 10 nm.

[0061] When executing according to Fig. 3, a total of six measurement objects 43 are present between an outer edge of the useful object 45 of the reticle 4 and the outer edge of the reticle 4. The measurement objects 43 can be arranged in this edge region between the useful object 45 and the edge of the reticle 4 in a uniformly distributed or randomly distributed manner.

[0062] Fig.4 shows two variants of measuring structures 441, 442, which can be used for the respective measuring object 43.

[0063] The measuring structure 441 has a total of eight structural ribs 46 that extend radially from a center Z in an approximately star-shaped manner. Two of these structural ribs 46 run parallel to the x-direction and two parallel to the y-direction. The other four of the eight structural ribs 46 run in pairs parallel to the angle bisectors between the x- and y-coordinates. The angle between adjacent structural ribs 46 in the measuring structure 441 is 45°.

[0064] The measuring structure 442 has an approximately square envelope and is in turn divided into four structure areas 471, 472, 473 and 474 arranged as a 2x2 array, whose envelope is in the Fig.4 is indicated by dashed lines. The structural regions 471 and 474, which are located diagonally to each other in the array arrangement of the measuring structure 442, carry structural ribs 48 that run parallel to the y-direction. The other two structural regions 472 and 473 carry structural ribs 49 that run parallel to the x-direction.

[0065] A typical structural size of the structural ribs 46, 48, 49 of the measuring structures 441, 442, i.e. a transverse extension of these ribs, is in the range from 500 nm to 5 µm, for example in the range between 1 µm and 2 µm.

[0066] Compared to the useful object structures 42, the measurement structures 44 have a typical structure size that is approximately two orders of magnitude larger than a typical structure size of the useful object structures 42.

[0067] Fig.5 shows a variant of an illumination of an illumination pupil 50 of the illumination optics 2 in the exit pupil plane 23. The illumination pupil 50 has a round pupil boundary 51. Such a pupil boundary can also have a different shape, for example elliptical.

[0068] For simplicity, pupil coordinates will also be referred to as x- and y-coordinates. It is clear that pupil coordinates, on the one hand, and spatial coordinates, on the other, are not absolutely equivalent, at least in the physical sense.

[0069] Fig. Figure 6 illustrates diffraction ratios when imaging object structures running in the y-direction with the projection lens 32 as a function of a structure size SG, i.e. a measure of the distance between two adjacent y-lines. The structure size decreases in the Fig.6 from bottom to top. Due to the y-shape of the imaged structures, these lead to a diffraction of the illumination light 7, with the diffraction direction occurring in the + / - x direction depending on the diffraction order.

[0070] The Fig. Figure 6 shows a total of six diffraction patterns for the object structure size SG increasing upwards. An entrance pupil 52 of the projection lens 32 is shown centrally in each case.

[0071] Fig. Figure 6 shows, at the very bottom, a resolution limit of the projection lens 32, at which a plus first order of diffraction diffracted in the positive x-direction, on the one hand, and a minus first order of diffraction diffracted in the negative x-direction, on the other hand, just overlap with the entrance pupil 52 at a point at the edge of the entrance pupil 52. Structures with the corresponding structure size SG can just be imaged with the projection lens 32 at the given illumination setting.

[0072] With increasing object structure size SG, an x-distance between the diffracted pupils 53 and the entrance pupil 52, i.e. the zeroth diffraction order, decreases more and more, so that an overlap pupil area 54 between the diffracted pupils 53 and the entrance pupil 52 increases accordingly.

[0073] Fig. 6 shows in the third row from the bottom the situation in which the diffracted pupils 53 of the +- first diffraction order just touch in the center of the entrance pupil 52.

[0074] One line above is in the Fig. 6 shows the case in which the diffracted pupils of the +- second diffraction order also overlap with the entrance pupil 52 in overlap pupil areas 55.

[0075] The top line of the Fig. 6 shows a corresponding case in which this also applies to the diffracted pupils 53 of the +- third diffraction order (overlap pupil areas 56).

[0076] An effective diffraction distance, i.e. a distance between, for example, the zeroth and the + first diffraction order, takes in the Fig. 6 from bottom to top, i.e. with increasing structure size, continues to decrease.

[0077] The resulting intensity distribution in the pupil 52 including the diffraction orders arriving there is also called the illumination spectrum.

[0078] An object amplitude emanating from a respective object structure, i.e., from the useful object structure 42 or the measurement structure 44, is converted into a diffraction spectrum during the diffraction of light, i.e., the diffraction of the illumination and imaging light 7 or the diffraction of the measurement light 39. This diffraction spectrum can be understood as the Fourier transform of the object amplitude. A field distribution then arises in the pupil 52, which represents the product of the spectrum with a pupil function, which describes the blocking at the edge of the entrance pupil 52, and a phase function. The phase function results from the wavefront and the wavelength of the respective illumination light.

[0079] When imaged through projection lens 32, an image amplitude is created, which can be understood as the Fourier transform of the field distribution in pupil 52. Each illumination direction contributes to the image amplitude. An overall image is then a superposition of the image amplitudes from the various illumination directions and can depend on the wavefront via the phase function. As a rule, different illumination waves associated with different angles of incidence, i.e., different locations in the entrance pupil, are incoherent with each other. This leads to a superposition of the image intensities as the squared magnitudes of the image amplitudes of these different illumination waves.

[0080] Fig. 7 shows a comparison to the lower line of the Fig. 6 modified case, in which the illumination pupil 50 is not completely filled, thus a Fig.5 another illumination setting is selected, namely an x-dipole setting, in which the illumination pupil 50 and thus also the entrance pupil 52 are illuminated only at the location of two pupil spots 571, 572 spaced apart in the x-direction. In the illumination setting according to Fig. 7 is therefore an x-dipole lighting setting.

[0081] Shown in the Fig. 7 a zeroth diffraction order of these two pupil spots 571, 572 and a + first diffraction order 581 of the Fig. 7 left pupil spots 571 and a - first diffraction order 582 of the Fig. 7 right pupil spots 572. Arrows indicate the Fig. 7 also shows the respective diffraction effect, which acts in the positive x-direction in the case of diffraction spot 581 and in the negative x-direction in the case of diffraction spot 582. This diffraction effect, in turn, is achieved by useful object structures, which are designed as dense y-lines.

[0082] Fig. 8 shows a diffraction effect, starting from the same lighting setting as in the Fig. 7 for measurement structures with compared to the structure size of the useful object structures according to Fig. 7 much larger, for example, a factor of 50 larger, structure size SG. The diffraction spots 581 of the + first and + second diffraction orders, which arise from the diffraction of the pupil spot 571, are located very close to the pupil spot 571 and are only slightly displaced in the positive x-direction within the entrance pupil 52. The same applies to the position of the - first / - second diffraction spots 582, which arise from the diffraction of the pupil spot 572.

[0083] In principle, the different diffraction effects, on the one hand with regard to the dense useful object structures and, on the other hand, with regard to the measurement structures which are typically a factor of 100 less dense, lead to a different intensity exposure of the entrance pupil 52 with the same illumination setting. Normally, an image of the measurement structures 44 with the projection lens 32 therefore does not provide any reliable information as to whether an image of useful object structures behaves in the same way with regard to the resulting image quality, since the image of the measurement structures passes through different pupil areas and thus different surface sections of optical components of the projection lens 32 than the image of the useful object structures.

[0084] Fig. 9 and Fig.10 illustrate how, by adapting a measurement illumination setting to a useful illumination setting, the pupil areas used in the useful imaging by the projection lens 32 can be largely approximated by the measurement imaging.

[0085] When approximating the measurement intensity distribution according to Fig. 10 to the useful illumination angle distribution according to Fig. 9, those diffraction orders are considered that exhibit a diffraction efficiency above a specified limiting diffraction efficiency. For example, diffraction orders can be considered that result in a spot intensity of the respective diffraction spot, i.e., diffracted pupil spots, that is at least 1% of the spot intensity of the zeroth-order pupil spot.

[0086] Fig. 9 shows the figure comparable to Fig.7, again starting from an x-dipole setting, whereby again dense y-line structures are imaged.

[0087] It is indicated in the Fig. 9 also a course of a wavefront 59 over the x-coordinate of the entrance pupil 52. This wavefront course describes not only a tilt but also coma components.

[0088] Fig. 9 further shows those x-pupil sections 601, 602 or pupil sub-areas that are used in the imaging of the useful object structures according to Fig. 9 within the entrance pupil 52, i.e. in the beam path of the projection lens 32.

[0089] Fig. 10 shows an x-dipole illumination setting according to Fig. 9 adapted measurement intensity distribution over the entrance pupil 52, that including the diffraction at the less dense measurement structures, the same pupil areas 601 and 602 are used in the measurement light imaging as in the illumination setting according to Fig. 9 in the useful light image.

[0090] A measurement intensity distribution has Fig. 10 a total of four measuring pupil spots 611, 612, 613 and 614. Each of the measuring pupil spots 61 i (i = 1 to 4) has an extension in the y-direction which corresponds to the y-extension of the pupil spots 571 or 572 of the useful illumination setting according to Fig. 9. In the x-direction, the measuring pupil spot has an extension of 61 i by a factor of 2 to 5, so that an overall elliptical shape of the measuring pupil spot 61 i A different shape of the measurement pupil spot 61 i , which results in a corresponding aspect ratio, is possible, for example, a rectangular or stepped edge shape. A diamond-shaped edge shape, for example, is also possible.

[0091] Not shown to scale, but only roughly illustrated are the Fig. 10 also diffraction spots 62 i , which is due to a diffraction of the measuring pupil spots 61 i at the measurement structures. These diffraction spots 62 i are comparable to those in the Fig. 8 shown diffraction spots 581, 582 only slightly differ from the associated measuring pupil spots 61 i spaced apart, since the diffraction effect on the coarser measuring structures, i.e. an x-shift effect of the diffraction, is small.

[0092] The specification of the measurement intensity distribution according to Fig. 10 shows that including the diffraction spots 62 i Within the entrance pupil 52, practically the same pupil areas are exposed to light as in the useful imaging with the x-dipole setting according to Fig. 9. A measuring light image according to Fig.10 uses the same areas of optical surfaces of optical components of the projection lens 32 and thus allows a good conclusion about the quality of a useful light image after Fig. 9 to.

[0093] Although the specified measurement intensity distribution deviates significantly from the useful intensity distribution in the entrance pupil 52, a good approximation is obtained with regard to the pupil areas used, including the diffraction orders. The pupil sub-areas 601 and 602 used in the respective imaging are, as a comparison of the Fig. 9 and Fig. 10, practically the same. About the measurement with the Fig.10, an image offset of an image of the reticle 4 from a reference image position can be determined based on the determined imaging quality of the optical system. Based on this determined image offset, the reticle 4 can then be aligned relative to the wafer 36 to be exposed.

[0094] Typically, several such measurements are performed using different combinations of measurement structures and lighting settings. This allows more complex aberration patterns to be captured, which are incorporated into the results of the various measurement structure / lighting combinations with different weightings.

[0095] Based on the Fig.11 to 19, a set of intensity distributions across the entrance pupil 52 is described below, which can be specified by means of corresponding pupil diaphragms 25 of the illumination optics 2 and 40 of the measuring device 38 and via which a characterization of an imaging quality of an optical assembly of the optical system of the projection exposure apparatus 1, in particular of the projection lens 32, is possible. A resulting imaging quality determination method represents an alternative to the method of pupil approximation, which was described above with reference to the Fig. 9 and Fig.10. The aim of this alternative method is to generate a set of measurement intensity distributions, including the resulting diffraction spots, that is as independent as possible and which then approximates or simulates a pupil area actually used in the useful illumination by specifying corresponding, possibly weighted, linear combinations.

[0096] For the following example, the object structures running in the y-direction, i.e. corresponding structural ribs, of the useful object 45 have a structure size or structure period of 21 nm (rib width 8.5 nm, rib spacing 12.5 nm).

[0097] Fig. Figure 11 shows an x-dipole illumination setting for illuminating such useful object structures. The useful illumination setting according to Fig. 11 has two leaflet illumination poles 631, 632 corresponding to the pupil spots 571, 572 of the illumination setting according to Fig. 7. When setting the lighting according to Fig.11 is a useful illumination angle distribution of an illumination of the object field 3 with the illumination light 7.

[0098] Fig. 12 to 19 show measurement intensity distributions which, in combination, approximate the useful lighting setting according to Fig. 11 can be used. In addition, the intensity distribution according to Fig. 11, i.e. the intensity distribution corresponding to the useful illumination setting, are used as the measurement intensity distribution. The further measurement intensity distributions, i.e. the measurement illumination angle distributions of the measuring light 39 over the object field 3, according to the Fig. 12 to 19, deviate from the useful illumination angle distribution according to Fig. 11 off.

[0099] As a measure of the deviation between two illumination angle distributions to be compared according to the Fig. 11 to 19, an intensity correlation value I korr,Belwhich is calculated using the integral Ikorr,Bel:=∫NAOdkxdkyI1,Bel(kx,ky)I2,Bel(kx,ky)∫NAOdkxdkyI1,Bel2(kxky)∫NAOdkxdkyI2,Bel2(kx,ky) is calculated.

[0100] I 1,Bel (k x , k y ) and I 2,bel (k x , k y ) are the two illumination intensity distributions to be compared, for example the distributions according to the Fig. 11 and Fig. 12. Integration is performed over the entire pupil 52, which is referred to as NAO in the formula above. k x and k y are the pupil coordinates along x and y.

[0101] When determining the above correlation value, diffraction is taken into account, i.e. illumination intensity distributions in the form of diffraction spectra are compared with each other.

[0102] Fig.Figure 12 shows an illumination setting with a central measurement pupil spot 64 with a comparatively small maximum illumination angle. The diameter of the measurement pupil spot 64 is approximately 1 / 3 of the diameter of the entrance pupil 52.

[0103] Fig. Figure 13 shows another measurement intensity distribution, again with a central measurement pupil spot 65 with a larger maximum illumination angle. The measurement pupil spot 65 has a diameter approximately 60% of the diameter of the entrance pupil 52.

[0104] Fig. Figure 14 shows another measurement intensity distribution with a central measurement pupil spot 66 with an almost maximum illumination angle. The diameter of the measurement pupil spot 66 is approximately 90% of the diameter of the entrance pupil 52.

[0105] Fig.15 shows a further measurement intensity distribution, implemented as an x-dipole setting with two measurement dipole pupil spots 671, 672, which have an x-distance from each other that is approximately 40% of the diameter of the entrance pupil 52. A maximum x-extension of the respective measurement dipole pupil spots 671, 672 is less than 5% of the diameter of the entrance pupil 52. An x-extension of the measurement dipole pupil spots 671, 672 corresponds to an x-extension of the dipole pupil spots 631, 632 of the useful illumination setting according to Fig. 11.

[0106] Fig. 16 shows another measurement intensity distribution, again executed as an x-dipole setting with two measurement dipole pupil spots 681, 682. These measurement dipole pupil spots 681, 682 differ from those of the setting according to Fig. 15 only by their x-distance, which is set to Fig. 16 is about 55% of the diameter of the entrance pupil 52.

[0107] Fig.17 shows a further measurement intensity distribution, again implemented as an x-dipole setting with two measurement dipole pupil spots 691, 692, whose x-distance from each other is approximately 2 / 3 of the diameter of the entrance pupil 52.

[0108] Fig. 18 shows a further measurement intensity distribution, again implemented as an x-dipole setting with two measurement dipole pupil spots 701, 702, whose x-distance from each other is almost 80% of the diameter of the entrance pupil 52.

[0109] Fig. 19 shows a further measurement intensity distribution, again implemented as an x-dipole setting with two measurement dipole pupil spots 711, 712, whose x-distance from each other is almost 90% of the diameter of the entrance pupil 52.

[0110] To measure the imaging quality of the optical system of the projection exposure system 1, including the projection lens 32, an illumination angle distribution is first specified in the form of a useful illumination setting, for example the x-dipole illumination setting according to Fig. 11. With the aid of an algorithm simulating the effect of the projection lens 32, the optical image of the projection lens 32 is then determined, first without aberrations as a reference and then with deformations of the wavefront in a pupil of the projection lens 32, for example in the order of 0.1 nm for contributions of the Zernike polynomials of Z2, Z7, Z10, Z14, Z19, Z23, Z26 and Z30 in the fringe notation.

[0111] This wavefront deformation, added separately for each Zernike polynomial contribution, leads to a shift of the imaged structures in the x-direction in image field 34, which is tabulated.

[0112] Subsequently, the measurement intensity distributions, for example those described above in connection with the Fig. 12 to 19, are specified for each of the three wavelengths, and a corresponding simulation is performed, again as a reference without wavefront aberrations and for the respective Zernike contributions by specifying a corresponding wavefront deformation of 0.1 nm for the Zernike contributions Z2, Z7, Z10, Z14, Z19, Z23, Z26, and Z30, each separately. The resulting image shifts when imaging the measurement structures are also tabulated according to the Zernike contributions.

[0113] Table 1 illustrates a corresponding measurement result. Table 1a x-image shift in pm Zernike Z2 Z7 Z10 Z14 Useful object structure 42 Useful lighting setting acc. Fig. 11 -180 10 -80 -70 Measurement structures 44 Measurement lighting setting according to Fig. 11 -180 -260 -170 -140 Measurement structures 44 Measurement lighting setting according to Fig. 12 -180 160 -50 -120 Measurement structures 44 Measurement lighting setting acc. Fig. 13 -180 100 -30 -10 Measurement structures 44 Measurement lighting setting according to Fig. 14 -180 0 10 20 Measurement structures 44 Measurement lighting setting acc. Fig. 15 -180 50 -60 70 Measurement structures 44 Measurement lighting setting according to Fig. 16 -180 -10 -80 120 Measurement structures 44 Measurement lighting setting acc. Fig. 17 -180 -80 -110 130 Measurement structures 44 Measurement lighting setting acc. Fig. 18 -180 -170 -130 50 Measurement structures 44 Measurement lighting setting acc. Fig. 19 -180 -260 -170 -140 Table 1b x-image shift in pm Zernike Z19 Z23 Z26 Z30 Useful object structure 42 Useful lighting setting acc. Fig. 11 -20 60 -30 30 Measurement structures 44 Measurement lighting setting acc. Fig. 11 -150 -30 -100 -30 Measurement structures 44 Measurement lighting setting acc. Fig. 12 40 90 -20 -30 Measurement structures 44 Measurement lighting setting according to Fig. 13 0 -30 0 10 Measurement structures 44 Measurement lighting setting according to Fig. 14 0 20 0 0 Measurement structures 44 Measurement lighting setting according to Fig. 15 60 -100 -10 -50 Measurement structures 44 Measurement lighting setting according to Fig. 16 70 -70 -10 -20 Measurement structures 44 Measurement lighting setting according to Fig. 17 50 30 -20 40 Measurement structures 44 Measurement lighting setting acc. Fig. 18 -10 120 -40 90 Measurement structures 44 Measurement lighting setting according to Fig. 19 -140 10 -90 0

[0114] The first row of the table shows the respective Zernike contributions Z2, Z7, Z10, Z14, Z19, Z23, Z26 and Z30.

[0115] The second row of the table shows the image shifts when mapping the useful object structures 42 with the setting Fig. 11 at these respective Zernike contributions Z2 to Z30, specified in the unit pm (picometers) compared to a reference image position at the wavefront deformation 0. As long as a wavefront deformation of 0.1 nm is specified for the Zernike contribution Z2, this results in an image shift of -180 picometers (pm) compared to the reference image, i.e. of 180 picometers in the negative x-direction.

[0116] The following rows of Table 1 tabulate corresponding image shifts, this time for the measurement structures 44, for the measurement intensity distributions, i.e. the settings according to the Fig. 11 to 19.

[0117] These tabulated x-image shifts are also called sensitivities.

[0118] The measurement structure is also initially adjusted to the useful lighting setting Fig. 11 simulated.

[0119] Based on the data thus obtained, the image quality of the projection lens 32 can now be determined: With S↔ is the matrix of sensitivities for the measurement structure (in pm / 100 pm). z→ the vector of the Zernike components of the exit pupil (in pm) and Δx→ is the vector of structural displacements for the different illuminations in the horizontal direction (in pm).

[0120] It applies to small wavefront deformations, as expected in real operation: Δx→=S↔z→

[0121] This results in: z→=S↔−1Δx→

[0122] By determining the displacement of the image of the measurement structure as a function of the illumination setting, Zernike coefficients Zi of the wavefront can be reconstructed. The previously determined sensitivities for the target object structure then yield its image position change, which can be predicted, particularly for optimizing the positional conformance of a multilayer semiconductor device.

[0123] The resulting reconstructed waveform is, for example, a Zernike polynomial decomposition according to Table 2 below. Table 2 Zernike polynomial Z2 Z7 Z10 Z14 Z19 Z23 Z26 Z30 Zernike coefficient (pm) -100 200 -200 300 -50 50 100 -150

[0124] This results in an image shift or image storage for the measurement structures at the respective measurement intensity distributions according to the Fig. 12 to 17, the image shift Dx shown in Table 3 below: Table 3 Dx (pm) Setting nach Fig. 12 290 Setting nach Fig. 13 380 Setting nach Fig. 14 230 Setting nach Fig. 15 595 Setting nach Fig. 16 630 Setting nach Fig. 17 540 Setting nach Fig. 18 140 Setting nach Fig. 19 -435

[0125] For the mapping of the useful object structure, the Zernike vector z according to Table 2 results in the useful illumination setting according to Fig. 11 an image shift of 115 pm. By aligning the reticle relative to the wafer according to this resulting image shift, the superposition of object structures imaged in sequential imaging steps on the wafer can be optimized.

[0126] In extension of the simulation determination according to Table 1, in addition to wavefront deformations up to the Zernike polynomial Z30, wavefront deformations of higher Zernike polynomials can also be taken into account, for example the Zernike polynomials Z39, Z43, Z47, Z54, Z62, Z67, Z71, Z75, Z79, Z82, Z90, Z94, Z98, each again in the fringe notation.

[0127] By using different measuring structures, for example the measuring structures 441 on the one hand and 442 on the other hand according to Fig.4, the number of different measurements or simulations with different measurement intensity distributions can be reduced.

[0128] To specify the respective useful lighting setting in principle or to specify the respective measuring lighting setting, i.e. the measuring intensity distribution, alternatively to the above in connection with the Fig. The setting described in section 1 can also be specified using a honeycomb condenser comprising a field facet mirror and a pupil facet mirror, or alternatively using a specular reflector. It is also possible to specify an illumination setting using at least one MEMS module.

[0129] During the microlithographic production of a micro- or nanostructured component, an image shift of the useful object structure is first determined using the method explained above. The wafer 36 is coated at least in sections with a light-sensitive layer. Then, a structure on the reticle 4 is projected onto the wafer 36 using the projection exposure system 1. This is repeated for several structure layers if necessary, wherein the respectively determined image shift is used to optimize the overlay quality of the various structure layers. The reticle 4 and / or the wafer 36 are aligned to one another depending on the determined image storage or image shift. The exposed wafer 36 is then processed to form the microstructured component. A correspondingly micro- or nanostructured component can be produced.nanostructured semiconductor component, for example a microchip, in particular a memory chip. QUOTES CONTAINED IN THE DESCRIPTION

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

[0000] DE 10 2015 224 522 B4

[0002] EP 1 959 302 B1

[0002] WO 2019 / 145 126 A1

[0002] WO 2012 / 160 928 A1

[0002] US 8,325,324 B

[0002] US 8,760,628 B

[0002] DE-A 41 24 311

[0033] US 6,295,122 B1

[0044] US 8,970,964 B2

[0045]

Claims

[1] Method for determining an imaging quality of an optical assembly (32) of an optical system, comprising an illumination optics (2) for illuminating object structures (42) of a useful object (45) to be imaged, which are arranged in an object field (3), with illumination and imaging light (7) and an imaging optics (32) for imaging the object field (3) in an image field (34) in which a substrate (36) can be arranged, comprising the following steps: - specifying a useful illumination angle distribution (631, 632) of an illumination of the object field (3) with the illumination and imaging light (7) by the illumination optics (2), - Predetermining a measurement illumination angle distribution (631, 632; 64; 65; 66; 671, 672; 681, 682; 691, 692; 701, 702; 711, 712) of measuring light (39) for illuminating the object field (3) with the measuring light (39), wherein the measurement illumination angle distribution (64; 65; 66; 671, 672; 681, 682; 691, 692; 701, 702; 711, 712) differs at least partially from the useful illumination angle distribution (631, 632), - Determining the imaging quality of the imaging optics (32) when illuminating and imaging measurement structures (44) of a measurement object (43) arranged in the object field (3) with the measurement light (39), wherein the measurement object (43) is illuminated with the predetermined measurement illumination angle distribution (631, 632; 64; 65; 66; 671, 672; 681, 682; 691, 692; 701, 702; 711, 712) and wherein the measurement structures (44) have a measurement structure size that is larger than an object structure size of the object structures (42) of the useful object (45). [2] Method according to claim 1, characterized bythat when specifying the measurement illumination angle distribution, a measurement intensity distribution of the measurement light (39) in a pupil (52) of the optical system is specified which, taking into account diffraction effects on the measurement structures (44) and on the useful object structures (42), is approximated to a diffraction intensity distribution of the specified useful illumination angle distribution. [3] Method according to claim 2, wherein, in order to approximate the measurement intensity distribution to the diffraction intensity distribution, a position of diffraction orders of the illumination and imaging light (7) which is diffracted by the useful object structures (42) of the useful object (45) is determined as a diffraction intensity distribution of the illumination and imaging light (7) in the pupil (52) of the optical system, wherein the diffraction orders whose position is determined have a diffraction efficiency above a predetermined limit diffraction efficiency. [4] Method according to claim 3, characterized by that an approximation of the measuring intensity distribution to the diffraction intensity distribution is such that the measuring light (39) acts on the pupil (52) in predetermined pupil sub-regions (601, 602) in which the determined positions of the diffraction orders (571, 572, 581, 582) of the illuminating and imaging light (7) lie. [5] Method according to one of claims 1 to 4, characterized by that the object structure size of the object structures (42) of the useful object (45) is in the range between 1 nm and 500 nm. [6] Method according to one of claims 1 to 5, characterized by that the measuring structure size of the measuring structures (44) of the measuring object (43) is in the range between 500 nm and 500 µm. [7] Method according to one of claims 1 to 6, characterized by that the illuminating and imaging light (7) on the one hand and the measuring light (39) on the other hand differ in their wavelength. [8] Method according to one of claims 1 to 7, characterized by that when specifying the measurement illumination angle distribution and / or when determining the imaging quality, the measurement structures (44) are illuminated and imaged with the measurement light (39), divided into a sequence of measurement light illumination steps which differ in their respective measurement light intensity distribution in a pupil of the imaging optics (32). [9] Method according to claim 8, characterized by that the image quality is determined in all measurement light illumination steps. [10] Method according to claim 9, characterized bythat when determining the imaging quality, an object image shift of the object structures (42) of the useful object (45) when imaging with the predetermined illumination angle distribution is compared with a measurement image shift of the measurement structures (44) of the measurement object (43) when imaging with the different measurement light intensity distributions of the measurement light illumination steps. [11] Method for aligning a wafer (36) relative to a reticle (4), comprising object structures (42) to be imaged and imageable measurement structures (44), relative to an optical system of a projection exposure apparatus, comprising the following steps: - Providing the reticle (4) in a reticle holder, the projection exposure system, - Carrying out the determination method according to one of claims 1 to 10, - determining an image offset of an image of the object to be imaged (4) from a reference image position based on the determined image quality of the optical system, - Aligning an object (4) to be imaged and / or a wafer (36) to be exposed based on the determined image storage. [12] Process for producing a micro- or nanostructured component, comprising the following process steps: - providing a projection exposure system, an object (4) with object structures (42) to be imaged and a wafer (36) onto which the object structures are imaged by means of an imaging optics (32), - imaging the object structures (42) with the imaging optics (32) of the projection exposure system on the wafer (36) to produce an image layer, - correcting a position of the wafer (36) relative to the object (4) to be imaged by means of the imaging optics (32) using the alignment method according to claim 11, - imaging a further object structure (42) on the wafer (36) to produce a further image layer on the wafer (36), aligned with the initially produced image layer, - processing the multilayer exposed wafer (36) to form the micro- or nanostructured component. [13] Micro- or nanostructured component manufactured by a method according to claim 12.

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