Apparatus and method for characterizing microlithography masks

Abstract

The invention relates to an apparatus and a method for characterizing a microlithography mask. According to one aspect, the apparatus according to the invention comprises: at least one light source (105, 205, 405a, 405b, 605) emitting coherent light; an illumination optical unit (110, 210, 310, 311, 410, 510, 610, 710, 810) which generates a diffraction-limited light spot on a mask (120, 220, 620, 720, 820) from the coherent light of the at least one light source; and a scanning device, by which the diffraction-limited light spot can be realized. A light source for scanning a light spot controlled by the light source relative to a mask; a sensor unit (130, 230, 630, 730, 830); and an evaluation unit for evaluating light incident on the sensor unit and coming from the mask; an output coupling element (140, 240, 340) for coupling out a portion (145, 245) of coherent light emitted by at least one light source; and an intensity sensor (150, 250) for capturing the intensity of the output coupled portion (145, 245).

Description

[0001] This application claims the priority of German patent application DE 10 2020 207 566.2 filed on June 18, 2020. The contents of this application are incorporated herein by reference. Background of the Invention Technical Field

[0003] The present invention relates to an apparatus and a method for characterizing microlithography masks. Background Art

[0005] Microlithography is used, for example, for the production of microstructured components such as integrated circuits or LCDs. The microlithography process is carried out in an apparatus known as a projection exposure apparatus, which comprises an illumination device and a projection lens. In this case, an image of a mask (=reticle) illuminated by the illumination device is projected by the projection lens onto a substrate (e.g. a silicon wafer) coated with a photosensitive layer (photoresist) and arranged in the image plane of the projection lens, in order to transfer the mask structure to the photosensitive coating of the substrate.

[0006] In lithography processes, undesired defects on the mask have a particularly negative effect, since they reappear with each exposure step. An analysis of the imaging influence of possible defect locations directly is therefore desirable in order to minimize mask defects and in order to achieve successful mask repair. In principle, there is therefore a need to measure or characterize masks quickly and easily, as accurately as possible under the same conditions as actually present in a projection exposure apparatus, for example.

[0007] In this context, there are a number of methods for simulating a projection exposure tool within the scope of mask inspection (ie measuring the mask under conditions similar to those in the projection exposure tool, where possible).

[0008] Firstly, the practice of recording and evaluating aerial images of parts of a mask in a mask inspection device is known, wherein, for the purpose of recording the aerial image, the structures to be measured on the mask are illuminated by an amplifying illumination optical unit and the light from the mask is projected onto a detector unit via an imaging optical unit and detected by the detector unit.

[0009] In this process it is also known to illuminate the mask in the mask inspection apparatus in the same way as in the projection exposure apparatus, wherein in particular the same wavelength, the same numerical aperture and the same (if appropriate polarization) illumination settings are provided in the mask inspection apparatus.

[0010] Furthermore, methods are known in which the device for characterizing masks is configured as a scanning microscope for the purpose of simulating the conditions existing in a projection exposure apparatus. Fig. 9Schematic diagram of the invention, the prescribed illumination optical unit 910 for illumination of the mask 920 to be characterized with fully coherent light of the light source 905 is firstly designed such that it simulates the projection optical unit of a projection microlithography projection exposure apparatus. Secondly, the image recording or sensor arrangement 930 of the scanning microscope with a plurality of pixels 930-1, ..., 930-n is configured such that it simulates the illumination optical unit of a microlithography projection exposure apparatus.

[0011] With regard to the prior art, reference is made purely by way of example to DE 10 2010 063 337 B4 and US Pat. No. 7,821,714 B1. Summary of the invention

[0012] The object of the present invention is to provide an apparatus and a method for characterizing microlithographic masks which enable a rapid and reliable characterization taking into account the conditions given in the lithographic process.

[0013] This object is achieved by a device and a method according to the features as described below.

[0014] The apparatus for characterizing a microlithography mask according to the present invention comprises:

[0015] - at least one light source emitting coherent light,

[0016] - an illumination optical unit which generates a diffraction-limited light spot on the mask from the coherent light of the at least one light source,

[0017] a scanning device, by means of which a scanning movement of the diffraction-limited light spot relative to the mask can be achieved,

[0018] - sensor unit,

[0019] an evaluation unit for evaluating the light coming from the mask and incident on the sensor unit,

[0020] - an output coupling element for coupling out a portion of the coherent light emitted by the at least one light source, and

[0021] - an intensity sensor for capturing the intensity of the out-coupled portion.

[0022] The invention takes as its starting point a method (known per se from DE 10 2010 063 337 B4), according to which, in order to simulate the conditions existing in a projection exposure apparatus, a device for characterizing masks is configured as a scanning microscope, wherein firstly, the illumination optical unit of the scanning microscope is designed such that it simulates the projection optical unit of a microlithography projection exposure apparatus, and wherein secondly, the image recording or sensor unit of the scanning microscope is configured such that it simulates the illumination optical unit of a microlithography projection exposure apparatus. In other words, with regard to the simulation of a microlithography projection exposure apparatus in the device for characterizing masks according to the invention, the imaging optical unit and the illumination optical unit in a sense exchange their roles. With regard to the basic functionality of such a device or mask inspection device, reference is made to the aforementioned patent document DE 10 2010 063 337 B4.

[0023] Now, according to one aspect, the invention comprises the idea of ​​taking the above-described method as a starting point, outcoupling a portion of the coherent light emitted by at least one light source, and capturing the intensity or energy of this outcoupled portion. According to the invention, this allows determining energy fluctuations on a portion of the (at least one) light source, so that the image finally recorded by the sensor unit can be normalized with respect to the power of the at least one light source.

[0024] In this case, an advantageous result of the configuration according to the invention is that it is possible in particular to distinguish brightness changes occurring in the image recorded by the sensor unit, whether such brightness changes are caused by the currently characterized mask (e.g. due to a possible defect on the mask) or whether such brightness changes are caused by energy fluctuations of the utilized light source(s). In this way, erroneous conclusions about defects believed to be present on the mask can be avoided.

[0025] In this case, the invention can also make use of the fact that, with regard to the intensity or energy emitted by the at least one light source, only relative changes or fluctuations over time are of interest; that is to say that in particular no spatially resolved quantitative intensity measurement is required.

[0026] Furthermore, the invention can utilize the fact that a relatively small part of the light emitted by the at least one light source needs to be coupled out for said determining the relative change in energy or intensity over time, so that by far the main part of the light is still available for the actual mask characterization.

[0027] By the aforementioned consideration of variations in the energy or intensity of at least one light source, the present invention takes into account in particular the situation where, due to the high requirements in terms of accuracy in microlithography applications, already small variations (significantly of the order of less than one percent) are important for reliably identifying relevant defects in the mask.

[0028] According to one embodiment, the output coupling element is a reflective element.

[0029] The output coupling of a portion of the light generated by the at least one light source to the intensity sensor according to the invention can be realized in different ways here, as described in more detail below. Thus, in an embodiment, a reflector as an output coupling element can be arranged directly in the (usually collimated) beam path between the (multiple) light sources and the illumination optical unit. The average diameter of such a reflector can in particular be less than 0.5 mm, more in particular less than 0.1 mm. Furthermore, the average diameter of the reflector can be at least five times smaller, more in particular at least ten times smaller, than the average diameter of the coherent beam emitted by the at least one light source.

[0030] Hence, according to one embodiment, the outcoupling element is arranged between the at least one light source and the illumination optics unit.

[0031] According to a further embodiment, the outcoupling element is arranged in the illumination optics unit.

[0032] In this case, the back reflection of the illumination optical unit can be used for the outcoupling according to the invention. According to the invention, in this case, the situation can also be utilized in which the illumination optical unit represents only the beam shaping optical unit in the system according to the invention and can in particular consist of a single optical component such as a zone plate. In this case, in order to achieve the outcoupling according to the invention, for example, the reflectivity of the region of the component or the zone plate can be increased, and this can be achieved, for example, by coating with a suitable material, in particular a molybdenum (Mo)-silicon (Si) reflective layer stack.

[0033] Furthermore, it can be utilized according to the invention in this configuration that the relevant components or wave zone plates are in any case typically arranged in the beam path in an inclined manner (relative to the light beam emitted by at least one light source) so that the back reflections do not return to the light source and are therefore able to reach the intensity sensor according to the invention.

[0034] According to one embodiment, the outcoupling element is designed to outcouple a portion of the coherent light emitted by the at least one light source, the intensity proportion of which is less than 10%, in particular less than 5%, further in particular less than 1%.

[0035] According to one embodiment, the device further comprises an array of a plurality of optical elements which are adjustable independently of one another, for example in the form of an MMA ("micro mirror array"), said array being arranged in the optical path between the mask and the sensor unit.

[0036] This configuration is advantageous in particular in the device according to the invention, since the simulation of the illumination optical unit of the projection exposure device, which is implemented on one side of the image recording arrangement of the device conceived according to the invention, can also be realized without the use of a spatially resolving sensor unit, since the required elimination of individual pixels in the recorded image does not need to be realized in the sensor unit itself or during the evaluation of the relevant image, but can already be realized by a suitably arranged array of optical elements.

[0037] Furthermore, it is also possible to use an array of independently adjustable optical elements (in addition or as an alternative to the above-described selection of the pixels contributing to the image in the sensor unit) to intermittently - in particular during the advancement of the mask - set all adjustable optical elements in the array in such a way that light is no longer incident on the sensor unit, for example during a "step and repeat mode" (in which the mask remains in the same position during the illumination process and is only advanced one step after illumination).

[0038] In other words, the array of optical elements that are adjustable independently of one another can therefore also have the function of a "shutter", whereby an alternating activation and deactivation of the light source(s) can be avoided.

[0039] Furthermore, an array of optical elements that are adjustable independently of one another also offers the option of realizing grayscale values, since the corresponding exposure duration or exposure dose can be adjusted individually via individual optical elements or mirror elements, by means of which the relevant optical element is "deactivated" or tilted so that the light incident on this element no longer reaches the sensor unit after an individually specified duration (which is also shorter than the total exposure duration).

[0040] The above configuration is also advantageous independently of the above aspect of outcoupling a portion of the coherent light emitted by at least one light source and capturing the intensity or energy of the outcoupled portion. According to other aspects, the present invention therefore also relates to an apparatus for characterizing a mask for microlithography, comprising:

[0041] - at least one light source emitting coherent light,

[0042] - an illumination optical unit which generates a diffraction-limited light spot on the mask from the coherent light of the at least one light source,

[0043] a scanning device, by means of which a scanning movement of the diffraction-limited light spot relative to the mask can be achieved,

[0044] - a sensor unit, and

[0045] an evaluation unit for evaluating the light which has come from the mask and is incident on the sensor unit,

[0046] - wherein an array made of a plurality of optical elements which are independently adjustable from one another is arranged in the optical path between the mask and the sensor unit.

[0047] According to one embodiment, at least one light source is a HHG laser (HHG = "high-order harmonic generation"). Such a light source generates a quasi-continuous spectrum with a sufficient number of photons from which the desired wavelength or the desired wavelength range can be filtered out using suitable spectral elements. In this case, the electromagnetic radiation is already collimated and can therefore be focused on the mask in a relatively simple manner.

[0048] According to one embodiment, the device comprises a plurality of coherent light sources. This configuration is advantageous (particularly but not exclusively in combination with the above-described beam output coupling according to the invention) in order to take into account the typically quite significant limitations of the output power of suitable coherent light sources (e.g. HHG light sources), which output power may be in the milliwatt (mW) range, for example. Here, in the case of pulsed operation (e.g. assuming the case of an HHG laser source), the dead time remaining between the pulses of the light source can be used for pulsed light from one or more other light sources, respectively, wherein in this case the light beams generated by the light sources located at different positions can be combined by suitable switching optical units (e.g. a tiltable mirror or a mirror arrangement with one or more adjustable mirror elements). Thus, this can achieve multiplexing of a plurality of light sources.

[0049] The above configuration is also advantageous independently of the above aspect of outcoupling a portion of the coherent light emitted by at least one light source and capturing the intensity or energy of the outcoupled portion. According to other aspects, the present invention therefore also relates to an apparatus for characterizing a mask for microlithography, comprising:

[0050] - a plurality of light sources emitting coherent light,

[0051] - a switching optical unit for combining the light generated by these light sources,

[0052] - an illumination optical unit which generates a diffraction-limited light spot on the mask from the coherent light,

[0053] a scanning device, by means of which a scanning movement of the diffraction-limited light spot relative to the mask can be achieved,

[0054] - a sensor unit, and

[0055] - An evaluation unit for evaluating the light which has come from the mask and is incident on the sensor unit.

[0056] According to one embodiment, the illumination optical unit comprises at least one reflector, which is arranged such that an angle of incidence occurring at an optically active surface of the reflector during operation of the device is at least 70° relative to the respective surface normal.

[0057] In other words, according to this aspect, the illumination optical unit comprises at least one mirror operating at grazing incidence (GI = "grazing incidence"). This configuration is advantageous because, in the case of operation at grazing incidence, the high reflectivity required in principle can be obtained in the illumination optical unit in a manner largely independent of wavelength, so that the device according to the invention can also be used, for example, in another operating mode - for observing or checking the mask to be characterized at other working operating wavelengths utilized by the microlithography projection exposure device, which may also be in the EUV range in some cases.

[0058] In this case, a larger spectrum can be used in the other mode with the aim of achieving a greater throughput (e.g. by means of removing or replacing filters that are otherwise used in combination with the HHG light source), so that, for example, relatively large defects on the mask can be identified in this way, for which a detailed inspection at the actual (actinic) wavelength of the microlithography projection exposure apparatus is no longer necessary (e.g. because these relatively large defects should in any case be considered troublesome and should therefore be eliminated).

[0059] In other words, the configuration increases the functionality of the apparatus according to the present invention by facilitating switching between different operating modes with respect to corresponding operating wavelengths (e.g., (i) preliminary inspection for identifying relatively large defects using a broadband light source and (ii) actual inspection of remaining defects at an actinic wavelength).

[0060] The above configuration is also advantageous independently of the above aspect of outcoupling a portion of the coherent light emitted by at least one light source and capturing the intensity or energy of the outcoupled portion. According to other aspects, the present invention therefore also relates to an apparatus for characterizing a mask for microlithography, comprising:

[0061] - at least one light source emitting coherent light,

[0062] - an illumination optical unit which generates a diffraction-limited light spot on the mask from the coherent light of the at least one light source,

[0063] a scanning device, by means of which a scanning movement of the diffraction-limited light spot relative to the mask can be achieved,

[0064] - a sensor unit, and

[0065] an evaluation unit for evaluating the light which has come from the mask and is incident on the sensor unit,

[0066] wherein the illumination optical unit comprises at least one reflector, which is arranged such that an angle of incidence occurring at an optically active surface of the reflector during operation of the device is at least 70° relative to the corresponding surface normal.

[0067] According to one embodiment, the illumination optical unit comprises at least one reflector, which is arranged such that an angle of incidence occurring at an optically active surface of the reflector during operation of the device is at most 20° relative to the respective surface normal.

[0068] In other words, according to this configuration, the illumination optical unit comprises at least one mirror operating substantially at normal incidence (NI = "normal incidence"). Such a configuration of the illumination optical unit (e.g. a Schwarzschild optical unit) in the device according to the invention is advantageous compared to, for example, the above-mentioned zone plates, since in this case the placement of the illumination optical unit at a small distance from the mask (which is required when using a zone plate for reasons of minimizing chromatic aberrations) can be omitted, thus also facilitating the characterization or inspection of masks equipped with a protective film.

[0069] The above configuration is also advantageous independently of the above aspect of outcoupling a portion of the coherent light emitted by at least one light source and capturing the intensity or energy of the outcoupled portion. According to other aspects, the present invention therefore also relates to an apparatus for characterizing a mask for microlithography, comprising:

[0070] - at least one light source emitting coherent light,

[0071] - an illumination optical unit which generates a diffraction-limited light spot on the mask from the coherent light of the at least one light source,

[0072] a scanning device, by means of which a scanning movement of the diffraction-limited light spot relative to the mask can be achieved,

[0073] - a sensor unit, and

[0074] an evaluation unit for evaluating the light which has come from the mask and is incident on the sensor unit,

[0075] wherein the illumination optical unit comprises at least one reflector, which is arranged such that an angle of incidence arising at an optically active surface of the reflector during operation of the device is at most 20° relative to the corresponding surface normal.

[0076] According to one embodiment, the apparatus further comprises at least one phase shifter element in the optical path between the light source and the mask. Such a phase shifter element facilitates modification of the beam path by applying a phase shift, thus in case of a suitable configuration also emulating the projection exposure apparatus with respect to possible phase errors.

[0077] The above configuration is also advantageous independently of the above aspect of outcoupling a portion of the coherent light emitted by at least one light source and capturing the intensity or energy of the outcoupled portion. According to other aspects, the present invention therefore also relates to an apparatus for characterizing a mask for microlithography, comprising:

[0078] - at least one light source emitting coherent light,

[0079] - an illumination optical unit which generates a diffraction-limited light spot on the mask from the coherent light of the at least one light source,

[0080] a scanning device, by means of which a scanning movement of the diffraction-limited light spot relative to the mask can be achieved,

[0081] - a sensor unit, and

[0082] an evaluation unit for evaluating the light which has come from the mask and is incident on the sensor unit,

[0083] - wherein at least one phase shifter element is arranged in the light path between the light source and the mask.

[0084] The invention also relates to a method for characterizing a microlithography mask,

[0085] - wherein coherent light generated by at least one light source via an illumination optical unit generates a diffraction-limited light spot on the mask,

[0086] - a scanning movement of the light spot with respect to the mask in which the diffraction limitation is achieved, and

[0087] wherein light which has come from the mask and is incident on the sensor unit is evaluated;

[0088] - wherein a portion of the coherent light emitted by at least one light source is outcoupled and the intensity of the outcoupled portion is captured.

[0089] With regard to advantages and preferred embodiments of the method, reference is made to the above explanations in connection with the device according to the invention.

[0090] Other configurations of the present invention can be derived from the description.

[0091] The invention is explained in more detail below based on the exemplary embodiments shown in the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0092] In the attached figure:

[0093] Figure 1 A schematic diagram for explaining a possible arrangement of an apparatus for characterizing a mask according to the present invention in a first embodiment is shown;

[0094] Figure 2 shows a schematic diagram for explaining a possible arrangement of an apparatus for characterizing a mask according to the present invention in a second embodiment;

[0095] Figure 3a-3b shows a schematic diagram for explaining a possible configuration of an illumination optical unit present in a device according to the invention;

[0096] Figure 4 shows a schematic diagram for explaining the configuration of an apparatus using a plurality of light sources according to the present invention;

[0097] Figure 5a-Figure 5b shows schematic diagrams for explaining other configurations of the illumination optical unit present in the device according to the present invention;

[0098] Figure 6 shows schematic diagrams for explaining other configurations of the illumination optical unit present in the device according to the present invention;

[0099] Figure 7-Figure 8 A schematic diagram is shown for explaining the configuration of an apparatus for characterizing a mask according to other aspects of the present disclosure; and

[0100] Fig. 9 A schematic diagram for explaining a general setup of an apparatus for characterizing a mask is shown. DETAILED DESCRIPTION

[0101] As described below, embodiments of devices for characterizing microlithography masks have in common that - starting from the principle described in DE 102010063 337 B4 - the device or the mask inspection device is configured as a scanning microscope, in which fully coherent light from a light source is deflected via an illumination optical unit onto the mask to be characterized, so that only a single diffraction-limited spot is illuminated on the mask.

[0102] In this case, by appropriately selecting the pixels that contribute to the image in the sensor unit after the mask in the beam path, the illumination optical unit of the microlithography projection exposure apparatus is simulated on the image side in the apparatus according to the invention. Here, it is possible to use the embodiments described in the above-mentioned patent document or according to the embodiments to be referred to below. Figure 7 and Figure 8 The described embodiments perform the pixel selection in different ways.

[0103] Figure 1A first exemplary embodiment of a device according to the invention is shown in the purely schematic illustration. Figure 1 The device comprises a light source 105 for generating fully coherent light, wherein the light source 105 can be configured as a HHG laser in particular. However, the present invention is not limited thereto, and therefore other coherent sources (e.g., synchrotron or free electron laser) can also be used in other embodiments.

[0104] according to Figure 1 , the coherent light emitted from the light source 105 illuminates the illumination optical unit 110 in a collimated beam path, and the illumination optical unit focuses the illumination light on a diffraction-limited spot on the mask 120 to be characterized. In this case, the illumination optical unit 110 merely represents a beam shaping optical unit, which can in particular consist of a single optical component (e.g., according to Figure 3a The zone plate 310 is formed.

[0105] In order to check the imaging effect of the mask 120, a scanning movement of the diffraction-limited light spot relative to the mask 120 is realized, wherein the scanning process can be realized by moving only the illumination optical unit 120 or a component that generates the diffraction-limited light spot, by moving the illumination optical unit 110 and the sensor unit 130 while the mask remains fixed, or by moving only the mask 120 while the illumination optical unit 110 and the sensor unit 130 remain fixed.

[0106] In order to select pixels on a portion of the sensor unit 130 for the purpose of simulating the illumination device of a microlithography projection exposure apparatus, the sensor unit 130 can be configured as a spatially resolved sensor arrangement (e.g. a CCD camera) in a manner similar to the aforementioned DE 10 2010 063337 B4. In this case, depending on the respective illumination setting to be simulated, a limited portion of the pixels can remain out of consideration when evaluating the light incident on the sensor unit 130. However, the present invention is not limited thereto. Thus, non-spatially resolved sensors (e.g. simple photodiodes) can be used to detect light from other embodiments (e.g., such as based on a CCD camera). Figure 7 and Figure 8 ) in which the selection of pixels is then performed in different ways (e.g. using Figure 7 and Figure 8 An arrangement of optical elements that are independently adjustable from one another as described in ).

[0107] Reference again Figure 1 The device according to the invention further comprises an out-coupling element 140 in the form of a mirror for out-coupling a portion 145 of the coherent light emitted by the light source 105 , which out-coupled portion 145 is captured by the intensity sensor 150 .

[0108] Depending on the operating wavelength of the light source (eg approximately 13.5 nm), the reflector forming the output coupling element 140 may have a suitable coating, in particular a molybdenum (Mo)-silicon (Si) reflective layer stack.

[0109] By using an intensity sensor 150 in combination with the output coupling element 140, the invention allows energy fluctuations on a portion of the light source 105 to be determined, so that the image recorded by the sensor unit 130 can be normalized with respect to the power of the light source 105. In particular, this allows distinguishing whether brightness variations in the image recorded by the sensor unit 130 are caused by defects present on the mask 120 or by energy fluctuations of the light source 105, so that erroneous conclusions about the presence of defects on the mask can be avoided.

[0110] Figure 2 Schematic diagrams of other embodiments are shown, wherein Figure 1 Components that are similar or have substantially the same function are designated by reference numerals increased by "100". Figure 1 In contrast to the embodiment of Figure 2 The output coupling element 240 is a component of the illumination optical unit 210, so the back reflection of the illumination optical unit 210 is used for the output coupling according to the present invention. When the illumination optical unit 210 is configured as a zone plate, the area of ​​the zone plate 311 can have a shape according to Figure 3b and can therefore be used as output coupling element 340.

[0111] With regard to the generation of fully coherent light reaching the illumination optics unit, the invention is not limited to the use of a single light source. Figure 4 In a purely schematic and more simplified illustration, a configuration with two light sources (e.g. HHG lasers) 405a, 405b is shown. "406" is used to denote an adjustable mirror as a "switching optical unit" in order to redirect the light of one of the light sources (e.g. 405b) during a corresponding dead time (between consecutive pulses) of the corresponding other light source (e.g. 405a) towards the illumination device 410 and vice versa. In particular, the mirror 406 can be configured and arranged so that it operates at grazing incidence (GI = "grazing incidence") (wherein the angle of incidence occurring on the optically active surface of the mirror 406 is at least 70° relative to the corresponding surface normal), as a result of which intensity losses can be limited. In this case, the switching rate of the relevant mirror 406 can be selected in a suitable manner, for example, depending on the pulse rate of the light sources 405a, 405b and can, for example, lie in the kHz range.

[0112] By using more than one light source, the typically very significantly limited output power of a coherent light source or HHG laser can be taken into account. In other embodiments, more than two light sources for generating fully coherent light can also be provided for illuminating the illumination optical unit in combination with a suitable switching optical unit.

[0113] In a further embodiment, the apparatus according to the invention comprises at least one reflector which is arranged in the illumination optical unit at grazing incidence (i.e. the angle of incidence on the optically effective surface is at least 70° with respect to the corresponding surface normal). Such a configuration allows the use of the apparatus according to the invention to inspect masks at operating wavelengths other than 13.5 nm - since the reflectivity is substantially independent of the wavelength in the case of grazing incidence - and in particular makes it possible to also use light sources which provide coherent light with a larger spectrum, with the aim of achieving a greater throughput. As an example, such an additional operating mode can be used to identify relatively large defects which are in any case troublesome and should therefore be eliminated in advance, thereby already making their "actinic" inspection (i.e. at the actual operating wavelength of the microlithography projection exposure apparatus) superfluous.

[0114] As an example, in the additional operating mode multiple harmonics of the HHG source can be used for broadband illumination, wherein characterization at actinic wavelengths can be performed only after such preliminary checks and only insofar as it is still necessary (e.g. using only the first harmonic of the HHG source).

[0115] Figure 5a A possible configuration of such an illumination optical unit 510 is shown in purely schematic form, in which, starting from the principle of Walter optics, an arrangement of a combination of a plurality of parabolic reflectors 511 staggered concentrically with the optical axis OA and a plurality of hyperbolic reflectors 512 likewise staggered concentrically with the optical axis is used. In this way, as Figure 5a Indicated by the light source (at Figure 5a The collimated beam generated by the illumination optical unit 510 can be focused on the mask (also at Figure 5a The reflectivity is therefore essentially independent of wavelength.

[0116] The above implementation of the illumination optical unit under grazing incidence is not limited to the Figure 5a The specific embodiments described may rather be implemented in any suitable way. Figure 5b Other configurations of illumination optical units based on two elliptically curved cylindrical mirrors 513, 514 are shown only in an exemplary manner, which are arranged successively in the beam path in a perpendicular manner to each other. The two cylindrical mirrors 513, 514 have corresponding focal points, so the focal line of the first cylindrical mirror 513 coincides with the focal line of the second cylindrical mirror 514 perpendicular thereto.

[0117] Figure 6 Schematic diagram showing other configurations of an apparatus for characterizing a mask, wherein Figure 1 Components which are similar or have substantially the same function are designated by reference numerals with an increase of "500". According to this aspect, the illumination optical unit comprises at least one reflector which operates at substantially normal incidence (i.e., the angle of incidence on the optically effective surface is not greater than 20° relative to the corresponding surface normal). Figure 6 In the specified exemplary embodiment, the illumination optical unit 610 is configured as a Schwarzschild optical unit having a concave reflector 611 and a convex reflector 612 .

[0118] For example, with the use of Figure 3a-Figure 3b Compared with the implemented zone plate, Figure 6 The advantage of the configuration of the illumination optical unit 610 is that the illumination optical unit can be placed at a substantially greater distance from the mask 620 to be characterized, since in this case the limitations present during the use of a zone plate (in view of the chromatic aberrations to be avoided) are omitted. Figure 6 It is also possible to characterize a mask which is checked, for example due to the presence of a protective film (for protecting the mask 620 from dust or other particles), which protective film is then typically arranged at a distance of a few millimeters (mm) from the actual mask structure.

[0119] The above is based on Figure 6 The embodiments can be combined based on Figure 1 The described concept is implemented using an output coupling element and an intensity sensor; however, it can also be implemented independently thereof (e.g. Figure 6 as shown in the figure).

[0120] Although in the above-described exemplary embodiments and based on the principle of DE 10 2010 063 337 B4, a spatially resolving sensor unit is used to record images or to simulate an illumination optical unit of a projection exposure apparatus, the invention is not restricted thereto. Figure 7 and Figure 8 Each shows an embodiment having an array made of a plurality of optical elements that can be adjusted independently of one another, the array being arranged in the optical path between the mask 720 or 820 and the sensor unit 730 or 830. Here, the array is Figure 7 and Figure 8 They are represented by "760" and "860" respectively, wherein the illumination optical unit is represented by "710" or "810".

[0121] The array 760 or 860 allows the use of a simple non-spatially resolved sensor for recording the image, which only records the total intensity of the light incident on it, rather than spatially resolved ("pixelated") sensor cells. This is achieved by virtue of the fact that, for the purpose of simulating the illumination device of a microlithography projection exposure apparatus, the array 760 or 860 already allows the targeted elimination of individual pixels from the recording area. Thus, according to Figure 7 or Figure 8 , the sensor unit 730 or 830 may be configured as, for example, a simple photodiode.

[0122] according to Figure 7 , the array 760 includes a plurality of mirror elements ("micro-mirrors") that are independently adjustable and capable of selectively deflecting light incident thereon, respectively, so that the light is selectively incident on or not incident on the sensor unit 730. Figure 8 As shown, the array 860 operates in transmission to the extent that, depending on the tilt position of the individually adjustable elements of the array 860, light is either blocked (like a shutter) or transmitted to the sensor unit 830 or photodiode.

[0123] Based on the above Figure 7 and Figure 8 The described configuration can also be implemented in combination with the concept of using light outcoupling elements and intensity sensors, such as based on Figure 1 described, or can also be implemented independently thereof.

[0124] In further embodiments of the invention (and again in combination with or independently of the above configurations) a phase error may be imposed in the beam path by using a phase shifter element in order to emulate corresponding aberration characteristics of a microlithographic projection exposure apparatus.

[0125] Exemplary embodiments and suitable materials of such phase shifter elements are described in US 10,001,631 B2 and US 10,151,922 B2. In particular with regard to coupling and transmission changes of the wavefront, such a phase shifter element may consist of two separate films, whose shape and material are chosen such that the transmission loss at a given phase change may remain constant.

[0126] from Fig. 9Starting from the principle of DE 10 2010 063 337 B4 illustrated in FIG. 1 , the device for characterizing a mask can also be configured or operated such that a microlithography projection exposure apparatus comprising an anamorphic imaging system is simulated according to further aspects of the present disclosure. Anamorphic imaging is hereby understood to mean imaging that produces a distorted image of an object and is not an instance of similar imaging (i.e. it cannot be represented by a combination of displacement, rotation, mirroring and scaling). In a special case, such an anamorphic imaging system can be, for example, a projection lens with different imaging ratios along two mutually different axes.

[0127] In principle, it is now also desirable to characterize the mask with respect to the presence of defects for different defocus levels of a wafer in a microlithography projection exposure apparatus to be simulated, wherein the associated defocus of the wafer in the apparatus according to the invention in turn corresponds to the defocus of the reticle. Such defocus can now be taken into account by targeted addition of an aberration in the form of astigmatism in the beam path between the light source and the mask to be characterized. As an example, for this purpose, a phase shifter element can be inserted into the illumination beam path, or an illumination optical unit (e.g. a zone plate according to FIG. 3 , a projection exposure unit according to FIG. 4 ) can be inserted into the illumination beam path. Figure 6 Schwarzschild optical units, etc.) can be continuously deformed accordingly. DE 10 2018 201 495 A1 describes a suitable phase shifter element for use in the EUV range, which is continuously variable with respect to the phase shift and is based on the so-called Alvarez principle.

[0128] Although the present invention has been described based on specified embodiments, many variations and alternative embodiments will be apparent to those skilled in the art, for example by combining and / or exchanging features of individual embodiments. Therefore, it goes without saying that the present invention also encompasses such variations and alternative embodiments, and the scope of the present invention is limited only by the attached patent claims and their equivalents.

Claims

1. A device for characterizing microlithography masks, include: at least one light source (105, 205, 405a, 405b, 605) emitting coherent light; an illumination optical unit (110, 210, 310, 311, 410, 510, 610, 710, 810) which generates a diffraction-limited light spot on the mask (120, 220, 620, 720, 820) from the coherent light of the at least one light source (105, 205, 405a, 405b, 605); A scanning device, by which the scanning movement of the diffraction-limited light spot relative to the mask (120, 220, 620, 720, 820) can be achieved; Sensor unit (130, 230, 630, 730, 830); and an evaluation unit for evaluating light coming from the mask (120, 220, 620, 720, 820) and incident on the sensor unit (130, 230, 630, 730, 830); It is characterized in that The device also includes: an output coupling element (140, 240, 340) for coupling out a portion (145, 245) of the coherent light emitted by the at least one light source (105, 205, 405a, 405b, 605); an intensity sensor (150, 250) for capturing the intensity of the output coupling portion (145, 245), and At least one array of multiple optical elements that are independently adjustable and capable of selectively deflecting light respectively incident thereon so that the light is selectively incident on or not incident on the sensor unit, the array being arranged in an optical path between the mask (120, 220, 620, 720, 820) and the sensor unit (130, 230, 630, 730, 830).

2. The device according to claim 1, It is characterized in that The output coupling element (140, 240, 340) is a reflective element.

3. The device according to claim 1 or 2, It is characterized in that The output coupling element (140, 240, 340) is designed to output couple a portion (145, 245) of the coherent light emitted by the at least one light source (105, 205, 405a, 405b, 605), the intensity proportion of which is less than 10%.

4. The device according to claim 3, It is characterized in that The intensity ratio is less than 5%.

5. The device according to claim 3, It is characterized in that The intensity ratio is less than 1%.

6. The device according to claim 1 or 2, It is characterized in that The output coupling element (140) is arranged between the at least one light source (105) and the illumination optical unit (110).

7. The device according to claim 1 or 2, It is characterized in that The output coupling element (240, 340) is arranged in the illumination optical unit (210, 311).

8. The device according to claim 1 or 2, It is characterized in that The illumination optical unit (310, 311) includes a zone plate.

9. The device according to claim 8, It is characterized in that The output coupling element (340) is formed by a reflective region of the zone plate.

10. The device according to claim 1 or 2, It is characterized in that The at least one light source (105, 205, 405a, 405b, 605) is a HHG laser.

11. The device according to claim 1 or 2, It is characterized in that The apparatus comprises a plurality of coherent light sources (405a, 405b).

12. The device according to claim 1 or 2, It is characterized in that The illumination optical unit (510) comprises at least one reflector (511, 512, 513, 514) arranged such that during operation of the device an angle of incidence produced at an optically effective surface of the reflector (511, 512, 513, 514) is at least 70° relative to the corresponding surface normal.

13. The device according to claim 1 or 2, It is characterized in that The illumination optical unit (610) comprises at least one reflector (611, 612) arranged such that during operation of the device an incident angle produced at an optically active surface of the reflector (611, 612) is at most 20° relative to the corresponding surface normal.

14. The device according to claim 1 or 2, It is characterized in that The apparatus also includes at least one phase shifter element in the optical path between the light source (105, 205, 405) and the mask (120, 220, 620, 720, 820).

15. A method for characterizing a microlithography mask, - wherein a diffraction-limited light spot is generated on the mask (120, 220, 620, 720, 820) from the coherent light generated by at least one light source (105, 205, 405a, 405b, 605) by an illumination optical unit (110, 210, 310, 311, 410, 510, 610, 710, 810); - wherein a scanning movement of the diffraction-limited light spot is achieved relative to the mask (120, 220, 620, 720, 820); and - wherein light coming from the mask (120, 220, 620, 720, 820) and incident on a sensor unit (130, 230, 630, 730, 830) is evaluated; It is characterized in that out-coupling a portion (145, 245) of the coherent light emitted by the at least one light source (105, 205, 405a, 405b, 605) and capturing the intensity of the out-coupled portion (145, 245), and At least one array of multiple optical elements is arranged in the optical path between the mask (120, 220, 620, 720, 820) and the sensor unit (130, 230, 630, 730, 830), and the multiple optical elements are independently adjustable and can selectively deflect light respectively incident thereon, so that the light is selectively incident on or not incident on the sensor unit.

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