MEASURING METHOD AND MEASURING ARRANGEMENT FOR AN IMAGING OPTICAL SYSTEM

Description

[0001] This application claims the priority of German patent application 10 2015 209 173.2 of May 20, 2015, the priority of German patent application 10 2015 220 588.6 of October 22, 2015, and the priority of German patent application 10 2016 203 562.2 of March 4, 2016. Background of the invention

[0002] The invention relates to a measuring arrangement for measuring an optical unit of a projection exposure system for microlithography. Furthermore, the invention relates to a measuring device and a method for interferometric shape measurement of optical surfaces. Furthermore, the invention relates to a method for measuring a wavefront error of an imaging optical system of a projection exposure system. The imaging optical system comprises a plurality of optical elements for imaging a pattern from an object plane into an image plane.

[0003] A projection exposure system is used in microlithography to expose a photosensitive material on a wafer with an image of structures on a mask or reticle. For this purpose, the projection exposure system typically contains an illumination system and a projection lens. The illumination system generates a desired radiation distribution to illuminate the structures of the mask, while the projection lens images the illuminated structures onto the photosensitive material of the wafer with very high resolution. To meet the imaging properties, the optical elements used in the projection exposure system must be manufactured and positioned with extremely high precision.For this purpose, during the manufacture or readjustment of projection exposure systems, both a measurement of a complete imaging optical system and of individual optical elements can currently be carried out.

[0004] Phase-shifting interferometry techniques, such as shearing interferometry or point diffraction interferometry, are particularly used to measure the imaging optical system of a projection exposure system. DE 103 16 123 A1 describes such a device for wavefront measurement of a projection lens for microlithography using shear interferometry.

[0005] For precise shape measurement of the surface of an optical element, diffractive optical arrangements, known as null optics, are often used as interferometric measuring devices. The wavefront of a test wave is adapted to a desired surface shape by a diffractive element, such as a computer-generated hologram (CGH). Deviations from the desired shape can be determined by superimposing the test wave reflected by the optical element with a reference wave. Such a measuring device is described, for example, in DE 10 2012 217 800 A1.

[0006] The constantly increasing demands on imaging optical systems in microlithography are leading to ever greater complexity of these systems. For example, projection lenses for microlithography with extreme ultraviolet radiation (EUV) use an increasing number of mirrors. As already mentioned, however, with the measuring devices and methods described above, an imaging optical system can only be measured as a whole or each optical element individually. When measuring a complex imaging optical system as a whole, it is difficult to assign the measured aberrations to individual optical elements. To measure an individual optical element, it may be necessary to disassemble the entire imaging optical system, which, due to the increasing complexity, is increasingly time-consuming. Underlying task

[0007] It is an object of the invention to provide a device and a method by which the aforementioned problems are solved and, in particular, the cause of a wavefront error of the imaging optical system can be determined with high accuracy and, at the same time, with little expenditure of time. Inventive solution

[0008] The invention is defined by the claims.

[0009] According to a first aspect of the invention, the object is achieved by the following measuring arrangement for measuring an optical unit of a projection exposure system for microlithography. The measuring device contains a wavefront measuring device configured to measure a wavefront error of an imaging optical system using a measuring radiation. Furthermore, the measuring arrangement contains at least one adaptation module configured to manipulate the wavefront of the measuring radiation such that the combination of the optical unit to be measured and the at least one adaptation module forms an imaging optical arrangement.The optical unit can, in particular, be one of the subassemblies described below within the scope of a measurement method according to the invention and thus a subassembly of an imaging optical system of a projection exposure system, such as an optical module of a projection lens of the projection exposure system. According to one embodiment, the projection exposure system can be an EUV projection exposure system.

[0010] Furthermore, the object can be achieved according to the first aspect of the invention by a method for measuring an optical unit of a projection exposure system for microlithography, which method comprises: arranging at least one adaptation module on the optical unit to be measured in such a way that the combination of the optical unit to be measured and the at least one adaptation module forms an imaging optical arrangement, and measuring a wavefront error of the imaging optical arrangement formed from the combination.

[0011] According to one embodiment, the optical unit to be measured is configured as a non-imaging optical system which, upon irradiation with a plane or spherical input wave having a wavelength λ, generates an output wave whose wavefront deviates from an ideal spherical wave at at least one point by at least λ, in particular at least 10 λ. Such an optical unit is also referred to in this description as a "non-stigmatic" optical system. An imaging optical arrangement is also referred to in this description as an optical arrangement which, upon irradiation with a plane or spherical input wave having a wavelength λ, generates an output wave whose wavefront deviates from an ideal spherical wave at no point by more than λ, in particular at no point by more than 10 λ.

[0012] According to one embodiment of the measuring arrangement, it is configured to measure the optical unit in the form of a non-imaging optic which, upon irradiation of a plane or a spherical input wave with a wavelength λ, generates an output wave whose wavefront deviates at least λ from an ideal spherical wave at at least one point. According to one embodiment, the optical unit is assigned to an imaging optical system comprising a plurality of optical elements of a projection exposure apparatus for microlithography, and the optical unit is formed by one of the optical elements of the imaging optical system or by a partial arrangement of the optical elements of the imaging optical system. A partial arrangement of the optical elements is an arrangement of optical elements, ieof at least two optical elements, wherein at least one optical element is missing compared to the imaging optical system. According to one embodiment, an imaging optical system of the projection exposure apparatus has a plurality of optical modules, each comprising at least two optical elements, and the optical arrangement comprises at least one of the optical modules and fewer than the plurality of optical modules.

[0013] According to a further embodiment, the optical unit is formed by a partial arrangement of the optical elements of the imaging optical system, wherein the partial arrangement of the optical elements differs from at least one section of the imaging optical system by the presence of a gap relating to at least one optical element.

[0014] According to a further embodiment, the adaptation module is configured to shorten a back focal length of the optical unit to be measured. According to one embodiment variant, the optical unit to be measured already forms an imaging optical system, but with an unwieldy large back focal length. This can be the lens-side and / or the image-side back focal length. In particular, the optical unit is an imaging optical system, in particular a projection lens of a projection exposure system for microlithography, but with a large back focal length. According to the aforementioned embodiment, the arrangement comprising the optical unit and the adaptation module forms an imaging optical arrangement with a back focal length that is shorter than that of the optical unit.

[0015] According to a further embodiment, the measuring arrangement further comprises a calibration unit having the optical function of the optical unit to be measured, which is configured to calibrate the at least one adaptation module by determining a wavefront error of an arrangement comprising the at least one adaptation module and the calibration unit before the measurement of the optical unit. The calibration unit can comprise one or more calibration modules. Thus, in a case in which the optical unit to be measured has a gap, the calibration unit can comprise a first calibration module having the function of the section of the optical unit arranged in front of the gap and a second calibration module having the function of the section of the optical unit arranged after the gap. According to one embodiment variant, the calibration unit comprises one or more diffractive structural patterns for manipulating the measuring radiation.

[0016] The wavefront measuring device and the adaptation module of the measuring arrangement can be designed according to the embodiment variants of a wavefront measuring device or an adaptation module described below with reference to the method for measuring a wavefront error according to the first aspect of the invention.

[0017] By providing the aforementioned adaptation module, the measuring arrangement according to the invention and the measuring method according to the invention enable separate measurement of individual optical modules of an imaging optical system, even in cases where the optical modules are not imaging optics. This enables the cause of a wavefront error in the imaging optical system to be determined with high accuracy and with less time expenditure compared to an individual measurement of any optical elements contained in the optical module. Furthermore, the separate measurement of individual optical modules enables the cause of a wavefront error to be determined prior to the measurement of the entire imaging optical system.

[0018] According to one embodiment of the measuring arrangement or the measuring method according to the invention described below, the adaptation module is arranged in the beam path of the wavefront measuring device upstream of the optical unit to be measured. In an alternative embodiment, the adaptation module is arranged in the beam path of the wavefront measuring device downstream of the optical unit to be measured.

[0019] According to a further embodiment, the at least one adaptation module comprises an input-side adaptation module for manipulating the measuring radiation, which is arranged in a beam path of the measuring radiation upstream of the optical unit to be measured, and an output-side adaptation module for manipulating the measuring radiation, which is arranged in the beam path of the measuring radiation downstream of the optical unit to be measured. Both adaptation modules contain at least one optical element. The optical elements of the adaptation modules are designed and arranged, for example, such that they form an imaging optical arrangement together with the optical unit to be measured.According to one embodiment of the measuring arrangement, the adaptation modules are configured such that the optical arrangement corresponds in its optical effect to an imaging optical system to be measured, wherein the optical unit is one of several optical modules of the optical system to be measured. In an alternative embodiment, the optical arrangement can also have other imaging properties, in particular a different focal length or a different imaging scale.

[0020] According to a further embodiment, the at least one adaptation module has one or more diffractive structure patterns used in reflection or transmission. For example, the at least one adaptation module contains one or more CGHs with diffractive structure patterns. According to one embodiment, at least one CGH is provided in the beam path of the wavefront measuring device before or after the module to be measured, or in each of both adaptation modules. In particular, two or more successively arranged diffractive structure patterns, such as CGHs each with a diffractive structure, can also be operated in reflection.

[0021] In one embodiment, the at least one adaptation module contains at least two diffractive structural patterns arranged superimposed on one another or one behind the other in a beam path of the measurement radiation. In particular, the diffractive structural patterns arranged one behind the other are each provided on a separate substrate, as described, for example, in US 2012 / 0127481 A1. According to one embodiment, two or more CGHs arranged one behind the other in the beam path are used. According to a further embodiment, the two superimposed structural patterns are arranged on a single substrate in the same plane, as disclosed, for example, in DE 10 2012 217 800 A1. For example, at least one complex-coded CGH with two or more diffractive structural patterns arranged superimposed on one another can be provided in the adaptation module.

[0022] Furthermore, according to the first aspect of the invention, the object is achieved by the method described below for measuring a wavefront error of an imaging optical system of a projection exposure system for microlithography. The optical system contains a plurality of optical elements for imaging a pattern from an object plane into an image plane. The method comprises a separate measurement of respective wavefront errors of different subarrangements of the optical elements.

[0023] A partial arrangement of optical elements is understood to mean an arrangement of a portion of the optical elements and thus comprises at least two optical elements each. The different partial arrangements each comprise a different combination of optical elements, with each combination lacking at least one optical element compared to the imaging optical system.

[0024] By measuring the different sub-arrangements separately according to the invention, in particular individual optical modules, the cause of a wavefront error in the imaging optical system can be narrowed down to one of the sub-arrangements. The next step can then be, for example, a measurement of the individual optical elements of this sub-arrangement. Furthermore, by cleverly configuring the measured sub-arrangements, a single optical element can be identified as the source of the error from the measurement results of the sub-arrangements. In any case, an individual measurement of all optical elements of the imaging optical system is not necessary. This keeps the time required to determine the cause of a wavefront error in the imaging optical system to a minimum without any loss of accuracy.Furthermore, by measuring the individual sub-assemblies separately, it is also possible to identify alignment errors of the optical elements of an optical module identified as the cause of the error, which cannot be determined by individual measurements and may be very difficult to determine by wavefront measurements of the imaging optical system as a whole.

[0025] According to one possible embodiment, one of the partial arrangements of the optical elements differs from at least one section of the imaging optical system by the presence of a gap relating to at least one optical element. A gap in the arrangement is characterized in that, in the beam path of the imaging optical system, at least one optical element is positioned upstream of the gap and at least one optical element is positioned downstream of the gap.

[0026] According to a further embodiment, the imaging optical system is provided with a plurality of optical modules, each comprising at least two of the optical elements, and the separate measurement of the respective wavefront errors of different sub-arrangements is carried out by separately measuring the respective wavefront errors of the individual optical modules. In other words, the different sub-arrangements are formed by the optical modules. In other words, the imaging optical system is divided into a plurality of modules. Each of the modules comprises at least two optical elements, preferably arranged one after the other in the beam path of the optical system. In particular, each optical module can be removed from the optical system as a whole and inserted back into it. According to one embodiment, adjustment means are provided for adjusting one or more modules in the optical system.

[0027] According to one embodiment, the imaging optical system is a projection objective of a projection exposure apparatus for microlithography. The imaging optical system can also be another imaging optical assembly from the exposure beam path of the projection exposure apparatus, such as an imaging optical assembly of an illumination system of the projection exposure apparatus. According to a further embodiment, the imaging optical system can be at least a part of either a projection objective or an illumination system of a projection exposure apparatus, i.e., either a part of the projection objective or the illumination system or the entire projection objective or the entire illumination system. According to a further embodiment, at least one of the sub-arrangements is not an imaging optical system, but rather a non-stigmatic optical system, as defined above, or, for example, an optical system with a defocusing or beam-expanding effect.According to a further embodiment, the sub-assemblies in the form of the optical modules of the imaging optical system are contained in a common housing during operation of the projection exposure apparatus.

[0028] According to one embodiment, the method according to the invention further comprises combining the measurement results for the individual sub-arrangements to form a result for the wavefront error of the entire imaging optical system. The wavefront error of the entire imaging optical system is thus measured by separately measuring the sub-arrangements and subsequently combining the measurement results to form an overall result. To measure the entire imaging optical system after post-processing or adaptation to specific requirements, only the respective processed sub-arrangement needs to be measured again. The modular design of the imaging optical system makes post-processing or adaptation significantly faster and more straightforward.

[0029] According to one embodiment, the imaging optical system is a projection lens of a projection exposure system for microlithography, in particular an EUV projection exposure system.

[0030] According to a further embodiment of the method according to the invention, the measurement of one of the sub-arrangements comprises arranging the sub-arrangement to be measured and at least one adaptation module in the beam path of a measuring radiation of a wavefront measuring device such that the combination of the sub-arrangement to be measured and the at least one adaptation module forms an imaging optical arrangement. Furthermore, the measurement comprises determining the wavefront error of the imaging optical arrangement by means of the wavefront measuring device. The wavefront error of the optical module to be measured can then be determined by subtracting a previously known wavefront error of the adaptation module from the determined wavefront error of the imaging optical arrangement.

[0031] In one embodiment, the imaging optical arrangement formed by combining the sub-array to be measured and the adaptation module can be configured such that its optical effect corresponds to the imaging optical system to be measured. Alternatively, the optical arrangement can also have different imaging properties, in particular a different focal length or a different imaging scale.

[0032] The adaptation module has at least one optical element. The optical element(s) of the adaptation module are designed and arranged such that, together with the sub-array to be measured, they form the aforementioned imaging optical array. Due to the imaging properties of the optical array, wavefront measuring devices for imaging optical systems, in particular, can be used to measure the sub-array.

[0033] According to one embodiment, a device for phase-shifting interferometry, in particular a device for shear interferometry or point diffraction interferometry, is used as the wavefront measuring device. For this purpose, the optical arrangement comprising the at least one adaptation module and the sub-array to be measured, in one embodiment, images an opening of a pinhole positioned in the object plane of the optical arrangement or a coherence mask of the wavefront measuring device onto a shear grating arranged in the image plane of the optical arrangement.

[0034] According to one embodiment, an adaptation module is arranged in the beam path of the wavefront measuring device upstream of the sub-array to be measured. Such an arrangement is particularly suitable for measuring a module that is provided last in the beam path of the imaging optical system, upstream of the image plane or another field plane. In a further embodiment, the adaptation module is arranged downstream of the sub-array to be measured in the beam path of the wavefront measuring device. This arrangement is advantageous for measuring a sub-array that is provided first in the beam path of the imaging optical system, downstream of the object plane or another field plane.

[0035] According to a further embodiment of the method, arranging the at least one adaptation module comprises arranging an input-side adaptation module for manipulating the measuring radiation upstream of the sub-arrangement to be measured, and arranging an output-side adaptation module for manipulating the measuring radiation downstream of the sub-arrangement to be measured. Both adaptation modules have at least one optical element. The optical element(s) of the adaptation modules are designed and arranged such that the two adaptation modules, together with the module to be measured, form an imaging optical arrangement. According to one embodiment of the inventive method, adaptation modules configured such that the optical arrangement corresponds in its optical effect to the imaging optical system to be measured.Alternatively, the optical arrangement can also have different imaging properties, in particular a different focal length or a different imaging scale. The arrangement of two adaptation modules is particularly suitable for measuring an optical module that is located between two other modules in the beam path of the imaging optical system or that is not directly upstream or downstream of a field plane of the optical system.

[0036] In one embodiment of the method according to the invention, at least one diffractive structural pattern is used in the at least one adaptation module to manipulate the wavefront of the measurement radiation. In particular, the diffractive structural pattern is operated in transmission. For example, a diffractive structural pattern of a computer-generated hologram (CGH) can be used as the diffractive structural pattern. A computer-generated hologram is generated by calculating a suitable line structure as a diffractive structure using a computer and suitable methods, such as ray tracing, and then writing the calculated line structure onto or into the surface of a substrate. The diffractive structural pattern can be arranged in the beam path of the wavefront measuring device, for example, before or after the partial arrangement to be measured.Furthermore, a diffractive structural pattern can also be arranged in each of the two adaptation modules described above.

[0037] According to a further embodiment of the method, the diffractive structural pattern is operated in reflection to manipulate the wavefront of the measurement radiation. For example, a diffractive structural pattern of a CGH is used as the diffractive structural pattern. In particular, two or more successively arranged diffractive structural patterns, such as CGHs each with a diffractive structure, can be operated in reflection. The CGH(s) are arranged in the beam path of the wavefront measuring device, for example, before or after the sub-array to be measured. Furthermore, in one embodiment, CGHs operated in reflection are used in both adaptation modules. CGHs operated in reflection enable, in particular, measurement of the sub-array with EUV radiation.

[0038] According to one embodiment of the method according to the invention, at least two diffractive structure patterns arranged consecutively in the beam path of the measuring radiation are used in the at least one adaptation module to manipulate the measuring radiation. In other words, the diffractive structure patterns are arranged such that the measuring radiation interacts sequentially with the two diffractive structure patterns. In particular, the first diffractive structure pattern and the second diffractive structure pattern are each arranged on a separate substrate. Such a diffractive arrangement is disclosed, for example, in patent application US 2012 / 0127481 A1. For example, two CGHs arranged consecutively in the beam path are used. Such an arrangement of diffractive structures, also referred to as "double CGH," enables a simultaneous change in the location and direction of a measuring beam.In this way, it is possible to adapt the imaging properties of the optical arrangement with the sub-array to be measured and the at least one adaptation module particularly well to the imaging properties of the optical system to be measured.

[0039] According to one embodiment of the invention, at least two diffractive structure patterns arranged superimposed on one another in the beam path are used in the at least one adaptation module to manipulate the measuring radiation. In particular, the two diffractive structure patterns are arranged superimposed on one another on a single substrate in the same plane. Such superimposed diffractive structure patterns for generating separate output waves with different propagation directions are described, for example, in DE 10 2012 217 800 A1. According to one embodiment, a complexly coded CGH with two or more diffractive structure patterns arranged superimposed on one another is used in an adaptation module. At one location of the diffractive structures, different measuring beams are thus deflected differently. This measure makes it possible, in particular, to deflect more than one field point, e.g.a pinhole array, in the object plane of the optical arrangement simultaneously imaged onto a shear grating in the image plane of the optical arrangement.

[0040] Furthermore, according to the first aspect of the invention, the method described below for measuring a wavefront error of an imaging optical system of a projection exposure system for microlithography is provided. The optical system contains a plurality of optical elements for imaging a pattern from an object plane into an image plane. The method comprises providing the imaging optical system with a plurality of optical modules, each comprising at least two of the optical elements. The method further comprises separately measuring the respective wavefront errors of the individual optical modules.

[0041] In other words, a plurality of modules are provided in the imaging optical system. Each of the modules comprises at least two optical elements, preferably arranged one after the other in the beam path of the optical system. In particular, each module can be removed from and reinserted into the optical system as a whole. According to one embodiment, adjustment means are provided for adjusting one or more modules in the optical system.

[0042] According to a second aspect of the invention, the object is achieved by the measuring device described below for the interferometric shape measurement of optical surfaces of a projection exposure system for microlithography. The measuring device contains a one-piece waveform element which has diffractive structures for generating a measuring radiation with a wavefront adapted to at least two adjacent, non-contiguous optical surfaces. The measuring device is configured to measure a relative positioning of the optical surfaces with respect to one another with respect to at least one rigid-body degree of freedom. Furthermore, the measuring device comprises an interferometer for the interferometric measurement of the measuring radiation after interaction with the optical surfaces.

[0043] The ability to measure the relative positioning of the optical surfaces with respect to one another with respect to at least one rigid-body degree of freedom allows the respective shape of the optical surfaces to be determined from the interferometric measurement result, taking into account the determined relative positioning. This enables the simultaneous shape measurement of both optical surfaces. This reduces the time required to measure some or all of the optical elements of an imaging optical system of the type described above with reference to the first aspect of the invention, such as a projection lens for microlithography. The time required to determine the cause of a wavefront error in the imaging optical system is thus reduced.

[0044] According to one embodiment, the measuring device according to the second aspect of the invention comprises an evaluation device for determining a respective shape of the optical surfaces from the interferometric measurement result, taking into account the determined relative positioning.

[0045] Furthermore, according to a second aspect of the invention, the object is achieved by the following method for the interferometric shape measurement of optical surfaces of a projection exposure system for microlithography. The method comprises the following steps: arranging at least two non-contiguous optical surfaces in a beam path of a measuring radiation generated by a one-piece waveform element having diffractive structures and a wavefront adapted to the optical surfaces; determining a relative positioning of the optical surfaces to one another with respect to at least one rigid body degree of freedom; and simultaneously interferometrically measuring the respective shape of the optical surfaces using the measuring radiation, taking into account the determined relative positioning.

[0046] In other words, in the measuring device and method according to the invention, the waveform element generates a measuring radiation by means of its diffractive structures, which is directed onto each of the optical surfaces. In addition, the wavefront of the measuring radiation reaching a surface is adapted to the shape of that surface. In particular, the diffractive structures can transform test radiation, provided for example by an interferometer, in such a way that a measuring wave with a correspondingly adapted wavefront is generated for each optical surface. The adaptation of the wavefront is preferably designed such that the wavefront at the location of each optical surface corresponds to the respective desired shape of the surface. In this way, a null optics is realized for each surface, in which a surface of the desired shape would reflect the measuring radiation back into itself.

[0047] For example, a CGH with diffractive structures arranged side by side on a substrate for each of the optical surfaces is used as a waveform element. Alternatively, a complex-encoded CGH with diffractive structures superimposed in one plane for two or more surfaces can be provided.

[0048] The measurement radiation is reflected back from the optical surfaces, passes through the one-piece waveform element, and is then measured in the interferometer by superimposing it with a reference wave. A characteristic interferogram is generated for each surface that deviates from the respective nominal shape. A Fizeau, Michelson, or Twyman-Green interferometer can be used as an interferometer, for example. The only essential element is the acquisition of an interferogram by superimposing the reflected measurement radiation with a reference wave. The acquisition of an interferogram can be achieved, for example, using a CCD camera.

[0049] In addition, the relative positioning of the optical surfaces to one another is determined. In this process, at least one relative position or tilt coordinate is determined as a relative rigid body degree of freedom. Interferometric methods, for example, can be used for this purpose. Finally, an evaluation device can determine the shape of each optical surface and their relative positioning to one another using the acquired interferograms and taking into account the at least one measured rigid body degree of freedom. Values ​​of additional rigid body degrees of freedom can be determined using the acquired values ​​and interferograms. Alternatively, the acquired interferograms and values ​​of relative rigid body degrees of freedom can be stored for later evaluation or transmission to an external evaluation unit.

[0050] According to one embodiment, the optical surfaces are part of a projection lens of a projection exposure system for microlithography, in particular an EUV projection exposure system. For example, the optical surfaces are reflective surfaces of mirrors of an EUV projection lens. The surfaces can be, for example, planar, spherical, or aspherical, with or without rotational symmetry.

[0051] An embodiment of the measuring device according to the invention is configured to measure the relative positioning of the optical surfaces to one another in a direction transverse to the optical surfaces. In particular, the relative positioning is measured in the direction of a mean propagation direction of the measuring radiation. According to one embodiment, the measuring device is configured to additionally measure the relative positioning of the optical surfaces to one another in one or both extension directions of the optical surfaces.

[0052] According to a further embodiment of the measuring device according to the invention, the waveform element has diffractive auxiliary measuring structures for generating auxiliary waves, which are each focused on one of the optical surfaces.

[0053] The auxiliary measurement structures, in particular, transform a portion of the measurement radiation into auxiliary waves. One or more diffractive auxiliary measurement structures can be provided for each optical surface. According to one embodiment, the auxiliary measurement structures are configured as additional diffractive structures on a CGH as a waveform element.

[0054] According to a further embodiment, the measuring device has a plurality of waveform elements or a waveform element with a plurality of diffractive structures for measuring a respective partial area of ​​at least one of the optical surfaces. In particular, the evaluation device is designed to combine partial measurements to form an overall measurement of the optical surfaces. In particular, the measuring device can be designed to use different waveform elements, for example designed as CGH, for the sequential measurement of different partial areas of one or more optical surfaces. Alternatively or additionally, a closure device, e.g. with one or more shutters, can be provided, which allows measurement radiation to pass only for selectable partial areas. Combining the partial measurements to form an overall measurement of the surfaces can be carried out, for example, by so-called stitching, which e.g.in WO 2005 / 114101 A1. This measure can also be used to measure surfaces where the reflected measurement radiation from two or more surfaces at least partially intersects. In such a case, which is also known to those skilled in the art as "causticity," the corresponding section of the interference pattern can no longer be clearly assigned to an optical surface. By measuring partial areas one after the other, such overlapping of the reflected measurement radiation can be avoided. Furthermore, this embodiment can also be used to completely measure very large optical surfaces.

[0055] In one embodiment of the method according to the invention for interferometric shape measurement of optical surfaces, the relative positioning of the optical surfaces to one another is measured using auxiliary waves generated from the measurement radiation using auxiliary measurement structures of the waveform element. The auxiliary measurement structures, in particular, transform a portion of the measurement radiation into auxiliary waves. According to one embodiment, one or more auxiliary waves are generated for each optical surface. The auxiliary measurement structures can be provided as additional diffractive structure patterns in a CGH as a wavefront element.

[0056] According to one embodiment of the method for shape measurement, partial areas of at least one of the optical surfaces are measured sequentially using different waveform elements or different diffractive structures of a waveform element. Subsequently, the partial measurements are combined to form an overall measurement of the optical surfaces. Depending on the corresponding embodiment of the measuring device, for example, different CGHs can be used sequentially for different partial areas, a shutter device can be used to block the measurement radiation for certain partial areas, or both. The combination of partial measurements is preferably carried out using the aforementioned stitching method.

[0057] Furthermore, according to one embodiment of the method for interferometric shape measurement of optical surfaces, the non-contiguous optical surfaces are arranged on a common substrate. In particular, the optical surfaces are positioned next to one another on one side of the substrate. The optical surfaces can be configured, for example, to reflect illumination radiation from the projection exposure system and thus represent a double mirror or multiple mirror. Using one substrate for multiple surfaces enables a particularly compact design.

[0058] According to an alternative embodiment, the non-contiguous optical surfaces are each arranged on separate substrates. This allows, for example, two or more adjacent mirrors to be measured simultaneously, such as two adjacent mirrors with a flat angle of incidence for a projection lens in EUV microlithography. In addition to their respective shapes, their relative positions to one another are also determined.

[0059] The features specified with regard to the above-mentioned embodiments, exemplary embodiments or embodiment variants, etc. of the measuring arrangement according to the invention according to the first aspect and the measuring device according to the second aspect can be transferred accordingly to the respective inventive method according to the first aspect or the second aspect, and vice versa. Furthermore, the features specified with regard to the above-mentioned embodiments, exemplary embodiments or embodiment variants, etc. of the inventive method and the measuring arrangement according to the invention according to the first aspect of the invention can be transferred to the inventive measuring device and the inventive method according to the second aspect of 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 filing of the application. Brief description of the drawings

[0060] The above and other advantageous features of the invention are illustrated in the following detailed description of exemplary embodiments of the invention with reference to the accompanying schematic drawings. Fig. 1 an embodiment of a projection lens for microlithography with optical elements arranged in optical modules in a schematic illustration, Fig. 2 a wavefront measuring device for an imaging optical system in a schematic illustration, Fig. 3 an embodiment of a measuring arrangement with an adaptation module arranged in the beam path after an optical module in a schematic illustration, Fig. 4 a further embodiment of a measuring arrangement with an adaptation module arranged in the beam path after an optical module in a schematic illustration, Fig. 5 an embodiment of a measuring arrangement with an adaptation module arranged in the beam path in front of an optical module in a schematic illustration, Fig. 6 an embodiment of a measuring arrangement with adaptation modules arranged in the beam path before and after an optical module in a schematic illustration, Fig. 7 an embodiment of a measuring arrangement with two diffractive structure patterns arranged one after the other in the beam path in a schematic illustration, Fig. 8 an embodiment of a measuring arrangement with two diffractive structure patterns arranged superimposed on each other in the beam path in a schematic illustration, Fig. 9 a further embodiment of a projection objective for microlithography with optical elements arranged in optical modules in a schematic illustration, Fig. 10 a further embodiment of a measuring arrangement with an adaptation module arranged in the beam path between two optical modules in a schematic illustration, Fig. 11 an illustration of a calibration of two adaptation modules using a calibration module, Fig. 12 a further embodiment of a measuring arrangement with an imaging optical system and an adaptation module for shortening an output-side back focus of the imaging optical system, Fig. 13 a further embodiment of a measuring arrangement with an imaging optical system and an adaptation module for shortening an input-side back focus of the imaging optical system, Fig. 14 an embodiment of a measuring device for interferometric shape measurement of optical surfaces in a schematic illustration, Fig. 15 the embodiment according to Fig. 14 with auxiliary waves for determining a relative position of the optical surfaces to each other in a schematic illustration, Fig. 16 another embodiment of a measuring device for interferometric shape measurement of different sub-areas of optical surfaces in a schematic illustration, as well as Fig. 17 the embodiment according to Fig. 14 when measuring the optical surfaces of two optical elements simultaneously. Detailed description of embodiments according to the invention

[0061] In the exemplary embodiments, specific embodiments, or variant embodiments described below, functionally or structurally similar elements are provided with the same or similar reference numerals wherever possible. Therefore, to understand the features of the individual elements of a specific embodiment, reference should be made to the description of other embodiments or the general description of the invention. To facilitate description, some drawings indicate a Cartesian xyz coordinate system, from which the respective positional relationship of the components illustrated in the figures can be derived.

[0062] The Figuren 1 bis 13 illustrate a first aspect of the invention. Fig. 1 shows an embodiment of a projection objective 10 of a projection exposure system for microlithography in a schematic representation. The projection objective 10 images a pattern of a mask or a reticle 12 onto a radiation-sensitive coating of a wafer 14. For this purpose, the pattern of the reticle 12 is arranged in an object plane, and the radiation-sensitive coating of the wafer 14 is arranged in an image plane of the projection objective 10. In this exemplary embodiment, the projection objective 10 is designed for microlithography with EUV radiation (extreme ultraviolet radiation) with a wavelength of less than 100 nm, in particular a wavelength of approximately 13.5 nm or approximately 6.8 nm, and therefore contains only optical elements operated in reflection mode. The EUV radiation provided by an illumination system (not shown) is also reflected at the reticle 12.In alternative embodiments, particularly for exposure radiation in a longer-wavelength spectral range, optical elements used in transmission, such as lenses or prisms, or even a transmission reticle, can also be used. For example, the optical system shown in . Fig. 9 illustrated embodiment of a projection lens 10 with optical elements in the form of lens elements.

[0063] The projection lens 10 according to Fig. 1 comprises six optical elements in the form of the mirrors E1, E2, E3, E4, E5 and E6, which are arranged successively in a beam path 16 of the projection lens 10, starting from the reticle 12. In Fig. 1 , the beam path 16 for a field point of the reticle 12 is shown as an example. The mirror E1 has a concave mirror surface and is arranged together with the essentially flat mirror E2 in a first optical module M1. Furthermore, the mirror E3 with a convex mirror surface is arranged together with the concave mirror E4 in a second optical module M2, and the convex mirror E5 is arranged together with the concave mirror E6 in a third optical module M3. The modules M1, M2, and M3 thus each contain 16 consecutive optical elements in the beam path. Each of the modules M1, M2, and M3 represents an optical unit in the form of a partial arrangement of the optical elements in the form of the mirrors E1 to E6 of the projection lens 10. In other words, each of the modules M1 to M3 comprises a part of the mirrors E1 to E6, specifically two of these mirrors in the present case.

[0064] Each module M1, M2, M3 can be individually removed from and reinserted into the projection lens 10. With appropriate adjustment devices, not only can the individual mirrors E1, E2, E3, E4, E5, E6 be adjusted, but also the individual modules M1, M2, M3, each as a whole, can be adjusted. This allows, on the one hand, the optical properties of the projection lens 10 to be quickly adapted to changing requirements by replacing one or more modules M1, M2, M3. On the other hand, reworking one of the optical elements of the projection lens 10 to correct imaging errors simply requires removing and, if necessary, disassembling the corresponding module M1, M2, or M3.

[0065] The described modules M1, M2, and M3 are merely examples of possible modules. In other embodiments of the projection lens 10, modules may contain more than two optical elements, such as three or four optical elements, or even just one optical element. Depending on the design, the projection lens 10 may also contain fewer or more than three modules and, in particular, may also contain optical elements not included in any module. Furthermore, a modular design of other components of a projection exposure system for microlithography is also possible, such as a modular illumination system for illuminating the mask.

[0066] During the manufacture of optical modules or the post-processing of individual modules or optical elements contained within a module, very precise measurement of the optical properties of the respective module is necessary. In particular, deviations from a desired wavefront change through the module must be determined with high precision. Such a measurement of the module's wavefront errors cannot generally be easily performed using the known devices for measuring projection lenses, since the individual modules generally do not constitute an imaging optical system.

[0067] In Fig. 2 A known wavefront measuring device 20 for measuring an imaging optical system 22 is schematically illustrated. The wavefront measuring device 20 is designed as a shear interferometer based on phase-shifting interferometry technology and is suitable, for example, for the very precise determination of imaging errors of a projection lens or other imaging optical system 22 in microlithography. The wavefront measuring device 20 contains a radiation source (not shown) which provides electromagnetic measuring radiation 24. The wavelength of the measuring radiation 24 preferably corresponds to the wavelength of the radiation used in the operation of the imaging optical system 22. In particular, EUV radiation serves as the measuring radiation 24. However, measuring radiation with a different wavelength in the visible or non-visible spectral range can also be provided.Furthermore, the wavefront measuring device 20 contains an opening of a pinhole 26 arranged in the object plane of the imaging optics 22 and a shear grating 28 arranged in the image plane of the imaging system 22. Instead of the pinhole 26, a pinhole grating or a coherence mask can also be used. The measuring radiation 24 passes through the opening of the pinhole 26 and then propagates with a spherical wavefront. The imaging optics 22 images the measuring radiation 24 onto the shear grating 28. The shear grating 28 represents a phase-shifting diffraction grating. A detector 30 of the wavefront measuring device 20 is arranged behind the shear grating 28.By laterally moving the shear grating 28 in the x- or y-direction, interference patterns are detected at the detector 30, from which the spatial derivative of the wavefront in the respective direction of movement and, from this, image aberration information of the imaging optics 22 can be determined with high precision. Such a wavefront measuring device is described, for example, in DE 103 16 123 A1.

[0068] A prerequisite for measuring an optic with the wavefront measuring device 20 is that the optic to be measured images the opening of the pinhole 26 onto the shear grating 28. As already mentioned above, however, this is the case with modules of an imaging optical system, such as the modules M1 to M3 of the projection lens 10 according to Fig. 1 , is generally not the case. In the following, various exemplary embodiments of a measuring arrangement 40 for measuring an optical unit which is not suitable for imaging the opening of the pinhole 26 onto the shear grating 28 are described, each together with corresponding methods. In particular, the measuring arrangement 40 is configured for measuring such an optical unit which has no imaging property at all, but is, for example, an optical system with a defocusing or beam-expanding effect. The measuring arrangement 40 according to the invention is therefore suitable for the respective measurement of the individual modules M1, M2 and M3 of the projection lens 10 according to Fig. 1 .

[0069] Fig. 3 schematically illustrates a first embodiment of a measuring arrangement 40 for measuring module M1 of the projection lens 10 according to Fig. 1 . The measuring arrangement 40 comprises the wavefront measuring device 20 according to Fig. 2 . Alternatively, any other wavefront measuring device for imaging optical systems based on phase-shifting interferometry, e.g. shear or point diffraction interferometry, or another technique can be used. Furthermore, the measuring arrangement 40 comprises an adaptation module 42, which is arranged together with a module M1 to be measured in the beam path 44 of the measuring radiation 24. In this exemplary embodiment, the adaptation module 42 is arranged in the beam path 44 after the module M1 and contains a CGH 46 operated in transmission with a diffractive structural pattern 48. The diffractive structural pattern 48 of the CGH 46 and thus also the adaptation module 42 are designed and arranged such that the opening of the pinhole 26 is imaged onto the shear grating 28 by the combination of the optical effect of the module M1 to be measured and the adaptation module 42.Alternatively or in addition to the CGH 46, the adaptation module 42 may also contain refractive or reflective optical elements, such as lenses or mirrors, in other embodiments.

[0070] In other words, the adaptation module 42 complements the module M1 to be measured to form an imaging optical arrangement 50. With the module M1 of the projection lens 10 according to Fig. 1 As an example of a module to be measured, the adaptation module 42 represents, in its optical effect, a replacement or an imitation of the other modules M2 and M3 of the projection lens 10. With the arrangement of the adaptation module 42 in the beam path 44 behind the module M1 to be measured, this exemplary embodiment is particularly suitable for measuring modules which are arranged in the beam path of an imaging system immediately after the object plane or another field plane. When the optical arrangement 50 is measured by the wavefront measuring device 20, a wavefront error of the optical arrangement 50 is determined with the aid of an evaluation device (not shown). From this, a wavefront error of the module M1 can in turn be determined very precisely, taking into account the known optical properties of the adaptation module 42 or the CGH 46.

[0071] In Fig. 4 A further embodiment of a measuring arrangement 40 is shown with an adaptation module 42 arranged in the beam path 44 after a module M1 to be measured. The measuring arrangement 40 essentially corresponds to the measuring arrangement according to Fig. 3 Instead of one CGH operated in transmission, however, the adaptation module 42 contains two CGHs 52, 54 operated in reflection, each with a diffractive structural pattern 48. The two CGHs 52, 54 are arranged one after the other in the beam path 44. Alternatively, the adaptation module 42 can contain only one or more than two CGHs used in reflection. The diffractive structural patterns 48 of the CGHs 52, 54 are configured such that, together with the module M1, they image the opening of the pinhole 26 onto the shear grating 28. Furthermore, additional diffractive, reflective, or refractive optical elements, such as CGHs operated in transmission, mirrors, or lenses, can also be provided in the adaptation module 42. By using CGHs in reflection, the module M1 can also be measured with an EUV measuring radiation 24.

[0072] In Fig. 5 A further embodiment of a measuring arrangement 40 is shown. The measuring arrangement 40 differs from the previous measuring arrangements by a different arrangement of the adaptation module 42 for measuring a module M3. The module M3 is a module arranged in the beam path of an imaging optical system as the last module in front of an image plane or another field plane, for example the module M3 of the projection lens 10 according to Fig. 1 The adaptation module 42 is arranged in the beam path 44 of the wavefront measuring device 20 in front of the module M3. It contains a CGH 46 operated in transmission with a diffractive structure 48. The diffractive structure 48 of the CGH 46 and thus also the adaptation module 42 are configured and arranged such that, together with the module M3, it represents an imaging optical arrangement 50. The optical arrangement 50 images, in particular, the opening of the pinhole 26 onto the shear grating 28. The adaptation module 42 thus replaces the modules M1 and M2 due to its optical effect, for example when measuring the module M3 of the projection lens 10. In other embodiments, the adaptation module 42 alternatively or additionally contains one or more refractive, reflective or reflection-operated diffractive optical elements.

[0073] Fig. 6 shows schematically an embodiment of a measuring arrangement 40 with a module M2 to be measured in the beam path 44, such as the optical module M2 of the projection lens 10 according to Fig. 1 , arranged first adaptation module 56 and a second adaptation module 58 arranged in the beam path 44 after the module M2. The adaptation modules 56, 58 each have a CGH 46, 60 operated in transmission with a diffractive structure pattern 48. The diffractive structures 48 of the two CGHs 46, 60 and thus also the two adaptation modules 56, 58 are configured such that, together with the module M2, they represent an imaging arrangement 50 for the opening of the pinhole 26. When measuring the module M2 of the projection lens 10 according to Fig. 1 Thus, the adaptation module 56 replaces the module M1 in its optical effect, and the adaptation module 58 replaces the module M3 in its optical effect. The measuring arrangement 40 is therefore particularly suitable for modules of an imaging optical system that are neither directly before nor directly after a field plane of the optical system. Alternatively or additionally, refractive, reflective, or reflection-operated diffractive optical elements can also be provided in one or both adaptation modules 56, 58.

[0074] Fig. 7 shows a further embodiment of a measuring arrangement 40. The measuring arrangement 40 basically corresponds to the measuring arrangement according to Fig. 6 , but provides in the adaptation module 58 two CGHs 60, 62 arranged one behind the other in the beam path 44 of the wavefront measuring device 20, each with a diffractive structure 48. Such an arrangement, also known as a "double CGH," is described, for example, in patent application US 2012 / 0127481 A1. In an alternative embodiment, one of the diffractive structures can be arranged on one side of a substrate and the other of the diffractive structures on another side.

[0075] A double CGH enables simultaneous change of the location and direction of a measurement beam. In this way, for some modules M2 to be measured, an imaging property of the optical arrangement 50 can be better achieved with the adaptation module and the module M2 to be measured. For example, when measuring the module M2 of the projection lens 10, the adaptation module 58 with the CGHs 60, 62 can achieve an optical effect that is more precisely adapted to the optical module M3 to be replaced.

[0076] In further embodiments, a double CGH is provided in the adaptation module 56 arranged in the beam path 44 upstream of the module M2, or in both adaptation modules 56, 58. Furthermore, two CGHs operated in reflection mode can also be used as a double CGH. In addition to the double CGH, further refractive, reflective, or diffractive optical elements can be arranged in one or both of the adaptation modules 56, 58.

[0077] In Fig. 8 Furthermore, an embodiment of a measuring arrangement 40 according to Fig. 6 with a complex-coded CGH 64 or 66 in the adaptation modules 56 and 58 and a second pinhole 68. Each of the complex-coded CGHs 64, 66 contains two diffractive structure patterns 70 arranged superimposed on one another in the beam path 44. The diffractive structure patterns 70 are in particular arranged superimposed on one another in a plane of the CGHs 64, 66. Such complex-coded CGHs are described, for example, in DE 10 2012 217 800 A1. The measuring radiation 44 from the opening of the pinhole 26 is transformed by one of the diffractive structures of the CGHs 64, 66, while a measuring radiation 72 from the opening of the second pinhole 68 is transformed by the other diffractive structure of the CGHs 64 and 66. In this way, the adaptation modules 56 and 58 together with the module M2 represent an optical arrangement 50 which simultaneously images the opening of the first pinhole 26 and the opening of the second pinhole 68 onto the shear grating 28.This allows two field points of the object plane of the optical arrangement 50 to be measured simultaneously.

[0078] In other versions, according to the measuring device according to Fig. 5 only an adaptation module 42 with a complex coded CGH in front of a module M3 to be measured, or analogous to the measuring device according to Fig. 3 An adaptation module with a complex-coded CGH may be provided downstream of a module M1 to be measured. In addition to the complex-coded CGHs 64, 66, further refractive, reflective, or diffractive optical elements may be arranged in one or both of the adaptation modules 56, 58 or in an adaptation module 42 upstream or downstream of the optical module to be measured.

[0079] Fig. 9 illustrates a further embodiment of a projection lens 10 of a projection exposure apparatus for microlithography. This differs from the embodiment according to Fig. 1 in that the projection lens 10 is designed for operation with UV radiation instead of EUV radiation, and thus the optical elements E1 to E5 are designed as lens elements. The projection lens 10 according to Fig. 9 comprises analogous to the embodiment according to Fig. 1 three optical modules M1, M2' and M3, wherein module M1 contains the optical elements E1 and E2, module M2' in the present case only the optical element E3 and module M3 the optical elements E4 and E5. In further embodiments, module M2' can also contain multiple optical elements. Each of the modules M1, M2' and M3 represents an optical unit of the projection lens 10. Modules M1 and M3 are each formed by a partial arrangement of the optical elements E1 to E5 of the projection lens 10 and module M2' by only the optical element E3.

[0080] In addition to a measurement of the individual modules M1, M2' and M3 analogous to the embodiments according to the Figuren 3 bis 8 A measurement of a combination of modules, such as modules M1 and M3, can also be considered, as in the Fig. 10 contained measuring arrangement 40. In this embodiment, the module M2' in the form of the optical element E3 is removed from the projection lens 10 according to Fig. 9 removed, so that the remaining modules M1 and M3 represent an optical unit formed by a partial arrangement of the optical elements E1 to E5, in which a gap 78 is present instead of the optical element E3. In the area of ​​the gap 78, an adaptation module 74 corresponding to the optical function of the module M2' in the form of the optical element E3 is arranged. The adaptation module 74 contains a CGH operated in transmission with a diffractive structure pattern 76. The optical arrangement 50 formed by the module M1, the adaptation module 74 and the module M3 is measured by means of the wavefront measuring device 20 according to Fig. 2 This measurement allows the wavefront error of the sub-array formed by the combination of modules M1 and M3, consisting of the optical elements E1, E2, E4, and E5, to be determined very precisely.

[0081] With the described embodiments of a measuring arrangement and a method, a measurement of all optical modules of an imaging optical system, for example in the form of the projection lens 10, and / or a measurement of various combinations of optical modules can be carried out in a similar manner Fig. 10 , or generally carry out a measurement of different sub-arrangements of the optical elements of the imaging optical system. According to one embodiment of the invention, one of the described methods comprises determining wavefront errors of an entire imaging optical system on the basis of the wavefront errors determined for each sub-arrangement, in particular the wavefront errors determined for each module of the optical system. Analogously, an embodiment of a measuring arrangement comprises a correspondingly designed evaluation device for determining wavefront errors of the imaging optical system based on the measurement results for each individual sub-arrangement of the optical system.

[0082] Fig. 11 illustrates the calibration of an arrangement of two adjustment modules. The two adjustment modules are an input-side adjustment module 56 and an output-side adjustment module 58 for measuring the measuring module M2' of the projection lens 10 according to Fig. 9 . In the embodiment shown, the measuring module M2' comprises only the optical element E3. The measuring arrangement is analogous to the measuring arrangement according to Fig. 6 built. In the Fig. 11 In the illustrated measurement setup, the input-side matching module 56 is configured as a CGH with the optical function of module M1, and the output-side matching module 58 is configured as a CGH with the optical function of module M3. Before the measurement process, the arrangement of the two matching modules 56 and 58 is first calibrated.

[0083] For this purpose, a calibration unit 80, which has the optical function of the optical unit to be measured in the form of the optical module M2', is arranged in place of the optical module M2' in the beam path 44 between the adaptation modules 56 and 58. The calibration unit 80 is configured as a CGH with a diffractive structure pattern 82. The calibration arrangement 82 consisting of the input-side adaptation module 56, the calibration unit 80, and the output-side adaptation module 58 is then measured using the wavefront measuring device 20. From the wavefront error determined in this process, the wavefront errors of the arrangement of the two adaptation modules 56 and 58 are determined as the calibration result, taking into account previously known wavefront errors of the calibration unit 80. To measure the optical module M2', the calibration module 80 is now replaced by the module M2', and the wavefront error determined in this process is corrected using the calibration result.

[0084] The Figuren 12 und 13 illustrate further embodiments of a measuring arrangement 40. In this embodiment, the measuring arrangement 40 is used to measure an optical unit in the form of an imaging optical system, such as a projection lens 10 of a projection exposure apparatus for microlithography. Fig. 12 The projection lens 10 shown is characterized by a very long output back focal length s 2 or focal length on the order of several meters, such as six meters. In order to reduce the installation space required for the measuring arrangement 40, the latter comprises, in addition to the wavefront measuring device 20, an adaptation module 84 in the form of a CGH with a diffractive structure pattern 86 arranged downstream of the projection lens 10. The adaptation module 84 significantly shortens the output back focal length s 2 to a reduced back focal length s 2 ', in particular by at least a factor of 2, 3, or 4.

[0085] Analogously, the measuring arrangement 40 is according to Fig. 13 Configured to measure a projection lens 10, which is characterized by a very long input-side back focal length s 1 or focal length on the order of several meters. To reduce the required installation space for the measuring arrangement 40, it has an adaptation module 88 in the form of a CGH with a diffractive structure pattern 90 positioned upstream of the projection lens 10. The adaptation module 88 significantly shortens the input-side back focal length s 1 to a reduced back focal length s 1 ', in particular by at least a factor of 2, 3, or 4.

[0086] The geometric shape of the diffractive structure patterns of the used adaptation modules in the form of CGHs, such as the adaptation modules 74, 56, 58, 84 or 88 according to the Figuren 10 bis 13 According to one embodiment, the adapters are adapted to the respective beam cross-section of the measuring radiation 44 present at the location of the adapter module. Thus, the surfaces described by the diffractive structural patterns can have, for example, a circular, elliptical, or crescent-shaped shape. For adapter modules arranged close to the field, separate surface areas of the aforementioned shape can be provided for each individual field point. For adapter modules arranged close to the pupil, the areas of the diffractive structural patterns assigned to the individual field points overlap.

[0087] The following Figuren 14 bis 17 relate to embodiments of a measuring device and a method for interferometric shape measurement of optical surfaces according to a second aspect of the invention. The embodiments of a measuring device are each described together with embodiments of a corresponding method.

[0088] Fig. 14 represents a first embodiment of a measuring device 100 for the interferometric shape measurement of optical surfaces. In particular, the measuring device 100 is suitable for the simultaneous measurement of at least two optical surfaces 102 and 104 arranged next to one another on a common substrate 106. In addition to a deviation of the actual shape of the respective surface 102 or 104 from a desired shape, the relative spatial position of the surfaces 102 and 104 to one another can also be determined. The optical surfaces 102 and 104 arranged on the same substrate 106 can, for example, assume the function of two mirror elements of a projection lens of a projection exposure system for EUV microlithography.

[0089] The measuring device 100 contains an interferometer 108 with a Fizeau element 110. The structure and operation of such a Fizeau interferometer are known to those skilled in the art. In particular, the interferometer 108 comprises a radiation source for generating electromagnetic illumination radiation 112 that is sufficiently coherent for an interferometric measurement. For this purpose, a laser, e.g., a helium-neon laser with a wavelength of approximately 633 nm, can be provided. The illumination radiation 112 can also have a different wavelength in the visible or non-visible wavelength range of electromagnetic radiation.

[0090] The illumination radiation 112 is formed, for example, by a collimator into a collimated beam with a substantially planar wavefront. In alternative embodiments, a divergent or convergent beam with a spherical wavefront can also be generated. The collimated beam impinges on the Fizeau element 110. A portion of the illumination radiation is reflected back in the form of a reference wave 114 by a Fizeau surface of the Fizeau element 110. A portion of the illumination radiation 112 passing through the Fizeau element 110 propagates further as test radiation 116 along the optical axis 118 of the interferometer 108 and impinges on a waveform element 120. By means of the waveform element 120, a measurement radiation 117 is generated from the incident test radiation 116, which measurement radiation is composed of two measurement waves 128 and 130.After interacting with the optical surfaces 102 and 104 arranged in the beam path of the measuring waves 128 and 130, respectively, and other optical elements provided in the beam path, the measuring radiation 117 travels back through the Fizeau element 110 into the interferometer 108, where it is superimposed with the reference wave 114. An interferogram thus generated at a detection plane is captured, for example, by a CCD sensor of an interferometer camera. In alternative embodiments, a Michelson interferometer, a Twyman-Green interferometer, or another suitable interferometer type can also be used as the interferometer.

[0091] The waveform element 120 contains a first diffractive structure 122 and a second diffractive structure 124, and in this exemplary embodiment is embodied as a CGH 126. The first and second diffractive structures 122, 124 are arranged side by side in a plane within the CGH 126. In alternative embodiments, more than two diffractive structures can be arranged side by side in a plane of a CGH, or a complex-encoded CGH with two or more diffractive structures arranged superimposed on one plane can be provided as the waveform element.

[0092] The first diffractive structure 122 is configured to generate a first measurement wave 128 directed toward the first optical surface 102 from a portion of the incident test radiation 116, with a wavefront adapted to a desired shape of the first surface 102. Accordingly, the second diffractive structure 124 is configured to generate a second measurement wave 130 directed toward the second optical surface 104 in the form of a measurement wave with a wavefront adapted to a desired shape of the second surface 104 from another portion of the test radiation 116 incident on the waveform element 120.

[0093] The wavefronts are adapted such that the wavefronts of the measuring waves 128 and 130 correspond to the respective desired shape of the surfaces 102 and 104 at the location of the optical surfaces 102 and 104. In this way, a null optic is realized for the first and second optical surfaces 102 and 104, respectively, in which a surface in the desired shape would reflect the measuring wave 128 and 130 back into itself. For the simultaneous measurement of more than two surfaces, additional diffractive structures on the CGH 126 or a complexly encoded CGH can be provided in further embodiments of the measuring device, each of which is configured to adapt the measuring radiation 117 accordingly for another optical surface.

[0094] The substrate 106 with the optical surfaces 102 and 104 to be measured is arranged in the beam path of the test radiation 116 by means of a holding device (not shown). The respective measuring wave 128 or 130 is reflected back from the optical surfaces 102 and 104, in turn passes through the one-piece waveform element 120, and is then measured in the interferometer 108 by superimposing it with the reference wave 114. In this case, an interferogram is created in a detection plane for each of the surfaces 102 and 104 in the event of a deviation from the respective desired shape, which is detected, for example, by a CCD sensor of an interferometer camera (not shown).

[0095] In addition to a simultaneous shape measurement of the two optical surfaces 102 and 104, the measuring device 100 also measures the relative positioning of the optical surfaces 102 and 104 to one another. This is described below with reference to Fig. 15 described in more detail. Finally, an evaluation device 158 determines the respective shape of surfaces 102 and 104 and their relative positions to one another. For this purpose, evaluation device 158 uses the acquired interferograms and a measured relative position value of optical surfaces 102 and 104 to one another for at least one rigid-body degree of freedom. Alternatively, the acquired interferograms and the position value can be stored for later evaluation or transmission to an external evaluation device.

[0096] Fig. 15 shows the embodiment according to Fig. 14 with auxiliary waves 132 and 136 for determining a relative position of the optical surfaces 102 and 104 to one another. To generate a first auxiliary wave 132, a first auxiliary measuring structure 134 is arranged in the CGH 126 of the waveform element 120 next to the diffractive structures 122 and 124. The first auxiliary measuring structure 134 contains a diffractive structure pattern configured to generate the first auxiliary wave 132, focused onto a target point 140 of the first surface 102, from a portion of the incident test radiation 116.

[0097] Furthermore, in the CGH 126, in addition to the diffractive structures 122 and 124 and the first auxiliary measurement structure 134, a second auxiliary measurement structure 138 is arranged. The second auxiliary measurement structure 138 contains a diffractive structure pattern, which is designed such that it generates a second auxiliary wave 136 focused on a target point 142 of the second surface 104 from a portion of the incident test radiation 116.

[0098] After a back reflection of the auxiliary waves 132 and 136 at the respective points 140 and 142 of the optical surfaces 102 and 104, they are interferometrically measured in the interferometer 108 by superimposing them with the reference wave 114. With the aid of the evaluation unit, a deviation of the optical surface 102 or 104 at the respective point 140 or 142 from the desired focal point is measured very precisely. Together with the angles determined by the auxiliary measuring structures 134 and 138 between the optical axis 118 of the interferometer 108 and the propagation directions of the auxiliary waves 132 and 136, for example, the relative z-coordinate of the optical surfaces 102 and 104 to each other with respect to the points 140, 142 is determined. The z-axis of the coordinate system describing the relative position of the surfaces 102, 104 to each other is here parallel to the optical axis 118 orarranged essentially parallel to the mean propagation direction of the measuring radiation 117 and thus transverse to the optical surfaces 102 and 104. The relative x-coordinate, y-coordinate, and tilt coordinates of the two optical surfaces 102 and 104 to each other are then determined by evaluating the measured reflected measuring waves of the surface measurement or the determined shapes of the surfaces 102 and 104, taking into account the known relative z-coordinate.

[0099] In other embodiments of the measuring device 100, additional auxiliary measurement structures for auxiliary waves can be provided on the waveform element in order to determine a deviation of additional points on the optical surfaces from a desired focus. Furthermore, additional planar or spherical adjustment structures can be arranged next to the optical surfaces on the substrate, whose spatial position is measured using auxiliary waves with a planar or spherical wavefront.

[0100] Fig. 16 shows a further embodiment of a measuring device 100 for the simultaneous shape measurement of adjacent optical surfaces 102 and 104. The measuring device 100 essentially corresponds to the measuring device according to Fig. 14 und Fig. 15 . In contrast to this, the first diffractive structure 122 of the CGH 126 of the waveform element 120 is configured such that it generates from a portion of the measuring radiation 116 a measuring wave 128 directed only onto a first partial region 144 of the first optical surface 102 with a wavefront adapted to a desired shape of the first partial region 144.

[0101] To measure a second partial area 146 of the first optical surface 102, a further waveform element 148 with a correspondingly configured diffractive structure 150 is provided in a CGH 152. To measure the second partial area 146, after measuring the first partial area 144 and the second optical surface 104 using the first waveform element 120, the waveform elements 120 and 148 are exchanged in the measuring device 100. For this purpose, the measuring device 100 can contain an exchange device (not shown). Subsequently, a measurement of the second partial area 146 is performed using the second waveform element 148. The partial measurement is combined to form an overall measurement of the optical surface 102 by the evaluation device 158 using a so-called stitching method or another suitable method.

[0102] In this way, even surfaces can be measured where, due to the shape of the surface, the reflected measuring radiation 116 at least partially intersects. In such a case, the corresponding section of the interferogram can no longer be assigned to the respective optical surface. By measuring partial areas one after the other, such overlapping of the reflected measuring radiation is prevented.

[0103] Accordingly, a measurement of two partial regions of the second surface 104 or a measurement of more than two partial regions of the surfaces 102 and 104 can also be provided one after the other using additional waveform elements. Alternatively or in addition to an exchange of waveform elements, the measuring device can also contain a closure device, e.g. with one or more shutters, which allows measuring radiation to pass only for selectable partial regions of the surfaces. In such an embodiment, the waveform element can contain a diffractive structure for each partial region. For example, on a CGH, several diffractive structures can be provided side by side as a waveform element, each for a partial region of a surface.

[0104] In Fig. 17 the embodiment of the measuring device 100 according to Fig. 14 during a simultaneous measurement of an optical surface 102 of a first optical element 154 and an optical surface 104 of a second optical element 156. Both optical elements 154 and 156 have their own substrate 106 and are adjustably fixed in their spatial position relative to one another by an adjustment device (not shown). The optical surfaces 102 and 104 are arranged next to one another in the beam path of the measuring radiation 117 comprising the measuring waves 128 and 130. Together with the adjustment device, the two optical elements 154 and 156, similar to the combination of substrate with the two optical surfaces 102 and 104 according to Fig. 14 , an overall module to be measured. For example, the optical elements 154 and 156 are two grazing incidence mirrors (G-mirrors) arranged next to one another for a projection lens or an illumination system of a projection exposure system for EUV microlithography. G-mirrors are mirrors that are illuminated under grazing incidence, i.e., at a flat angle of incidence. A flat angle of incidence in this context is understood to mean an angle of incidence that deviates by at least 45°, in particular at least 60° or at least 70°, from a surface normal of the irradiated mirror. With the measuring device 100 according to Fig. 14 or another measuring device described above, a measurement of both surfaces 102 and 104 and the relative positioning of the surfaces 102 and 104 to each other can be carried out simultaneously.

[0105] The foregoing description of exemplary embodiments is intended to be exemplary. The disclosure provided herein will enable those 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

[0106] 10Projection lens 12Reticle 14Wafer 16Beam path E1-E6Mirrors M1, M2, M2', M3Optical modules 20Wavefront measuring device 22Imaging optics 24Measuring radiation 26Pinhole 28Shear grating 30Detector 32Detection plane 40Measuring arrangement 42Adaptation module 44Beam path 46CGH 48Diffractive structure pattern 50Imaging optical arrangement 52, 54CGHs in reflection 56Input-side adaptation module 58Output-side adaptation module 60, 62CGHs in transmission 64, 66Complex encoded CGHs 68Second pinhole 70Superimposed diffractive structures 72Measuring radiation 74Adaptation module 76Diffractive structure pattern 78Gap 80Calibration unit 82Diffractive structure pattern 84Adaptation module 86Diffractive structure pattern 88Adaptation module 90Diffractive structure pattern 92Calibration arrangement 100Measuring device 102First optical surface 104Second optical surface 106Substrate 108Interferometer 110Fizeau element 112Illumination radiation 114Reference wave 116Test radiation 117Measurement radiation 118Optical axis120 Waveform element 122 First diffractive structure 124 Second diffractive structure 126 CGH 128 First measuring wave 130 Second measuring wave 132 First auxiliary wave 134 First auxiliary measuring structure 136 Second auxiliary wave 138 Second auxiliary measuring structure 140 Point of first surface 142 Point of second surface 144 First partial area 146 Second partial area 148 Second waveform element 150 Diffractive structure 152 CGH 154 First optical element 156 Second optical element 158 ​​Evaluation device

Claims

1. A measurement arrangement (40) for measuring an optical unit (M1; M2; M3; M1, M3, 10) of a microlithographic projection exposure apparatus, comprising: - a wavefront measurement apparatus (20) which is configured to measure, by means of phase-shifting interferometry, a wavefront aberration of imaging optics (22) by means of measurement radiation (72) and which comprises a pinhole or a coherence mask and a shearing grating, and - at least one adaptation module (42; 56, 58; 84) which is configured for such manipulation of the wavefront of the measurement radiation that the combination of the optical unit to be measured and the at least one adaptation module forms an imaging optical arrangement (50) which images an opening of the pinhole or the coherence mask on the shearing grating, wherein the measurement arrangement is furthermore configured to determine a wavefront aberration of the optical unit to be measured by removing an already known wavefront aberration of the adaptation module (42; 56; 58; 84) from a wavefront aberration, measured by means of the wavefront measurement apparatus, of the imaging optical arrangement formed by the combination.

2. The measurement arrangement according to Claim 1, wherein the optical unit is assigned to an imaging optical system (10), comprising a plurality of optical elements, of a microlithographic projection exposure apparatus, and the optical unit is formed by one of the optical elements of the imaging optical system, by a partial arrangement (M1; M2; M3; M1, M3) of the optical elements of the imaging optical system (10) or by the imaging optical system (10).

3. The measurement arrangement according to Claim 2, wherein the optical unit is formed by a partial arrangement of the optical elements of the imaging optical system, wherein the partial arrangement of the optical elements differs from at least one section of the imaging optical system by the presence of a gap (78) that relates to at least one optical element.

4. The measurement arrangement according to any of the preceding claims, wherein the adaptation module is configured to shorten a back focal length of the optical unit (10) to be measured.

5. The measurement arrangement according to any of the preceding claims, furthermore comprising a calibration unit (80) having the optical function of the optical unit to be measured, said calibration unit being configured to calibrate the at least one adaptation module (56, 58) before measuring the optical unit, the calibration being carried out by determining a wavefront aberration of an arrangement comprising the at least one adaptation module and the calibration unit.

6. The measurement arrangement according to any of the preceding claims, wherein the at least one adaptation module has one or more diffractive structures that are operated in reflection or in transmission.

7. The measurement arrangement according to any of the preceding claims, wherein the at least one adaptation module contains at least two diffractive structure patterns (70) that are superposed on one another, or arranged in succession, in a beam path of the measurement radiation.

8. A method for measuring an optical unit (M1; M2; M3; M1, M3, 10) of a projection lens (10) of a microlithographic projection exposure apparatus, comprising the following steps: - arranging at least one adaptation module (42; 56, 58; 84) on the optical unit to be measured, in such a way that the combination of the optical unit to be measured and the at least one adaptation module forms an imaging optical arrangement (50) which images an opening of a pinhole or a coherence mask on a shearing grating, - measuring, by means of phase-shifting interferometry, a wavefront aberration of the imaging optical arrangement formed by the combination, and - determining a wavefront aberration of the optical unit to be measured by removing an already known wavefront aberration of the adaptation module (42; 56; 58; 84) from the measured wavefront aberration of the optical arrangement formed by the combination.

9. The method according to Claim 8, wherein the optical unit to be measured is configured as non-imaging optics, which, if a plane or spherical input wave with a wavelength λ is radiated thereon, generate an output wave, the wavefront of which deviates by at least λ from an ideal spherical wave at at least one point.

10. A method for measuring a wavefront aberration of an imaging optical system (10) of a microlithographic projection exposure apparatus, comprising a plurality of optical elements (E1-E6) for imaging a pattern from an object plane into an image plane, wherein respective wavefront aberrations of different partial arrangements (M1; M2; M3; M1, M3) of the optical elements are measured separately.

11. The method according to Claim 10, wherein one of the partial arrangements of the optical elements differs from at least one section of the imaging optical system by the presence of a gap (78) that relates to at least one optical element.

12. The method according to Claim 10 or 11, wherein the imaging optical system is provided with a plurality of optical modules that respectively comprise at least two of the optical elements, and the separate measurement of the respective wavefront aberrations of different partial arrangements is effectuated by a separate measurement of respective wavefront aberrations of the individual optical modules (M1; M2; M3).

13. The method according to any of Claims 10 to 12, wherein the measurement of one of the partial arrangements comprises such arranging of the partial arrangement to be measured and of at least one adaptation module in the beam path of a measurement radiation (72) of a wavefront measurement apparatus (20) that the combination of the partial arrangement to be measured and the at least one adaptation module forms an imaging optical arrangement (50), and the measurement furthermore comprises determining the wavefront aberration of the imaging optical arrangement by means of the wavefront measurement apparatus.

14. The method according to Claim 13, wherein arranging the at least one adaptation module comprises arranging an input-side adaptation module (56) for manipulating the measurement radiation upstream of the partial arrangement to be measured, and arranging an output-side adaptation module (58) for manipulating the measurement radiation downstream of the partial arrangement to be measured.

15. The method according to Claim 13 or 14, wherein at least one diffractive structure pattern (48) for manipulating the wavefront of the measurement radiation is used in the at least one adaptation module.