Method and apparatus for characterizing a microlithography mask - Patents.com

Abstract

The present invention relates to a method and an apparatus for characterizing a microlithography mask, in one embodiment of the method according to the invention, the mask (140, 240, 340, 740, 803) to be characterized is illuminated with light from a light source via an illumination optical unit (801), the light having a wavelength of less than 30 nm, the light passing through a used beam path from the light source (705) through the mask to a sensor unit (770, 806) is evaluated, a part of the light emitted from the light source is at least intermittently outcoupled from the used beam path using a mirror array (130, 230, 330, 630, 730) having a number of independently adjustable mirror elements, and all the light is intermittently outcoupled from the used beam path using the mirror array to establish a predetermined illumination time of the sensor unit.

Description

[Technical field]

[0001] This application claims priority to German patent application No. 102021113780.2, filed on May 27, 2021, the contents of which are incorporated herein by reference.

[0002] The present invention relates to a method and apparatus for characterizing a microlithography mask. [Background technology]

[0003] Microlithography is used, for example, in the production of finely structured components, such as integrated circuits or LCDs. The microlithography process is carried out in a so-called projection illumination system, which comprises an illumination device and a projection lens. The image of a mask (=reticle), illuminated by the illumination device, is then projected by the projection lens onto a substrate (for example a silicon wafer) coated with a photosensitive layer (photoresist), which is positioned in the image plane of the projection lens in order to transfer the mask structure onto the photosensitive coating of the substrate.

[0004] In the lithography process, undesired defects on the mask have a particularly detrimental effect, since they may be reproduced after every illumination step. Therefore, in order to minimize mask defects and to realize a successful mask repair, it is desirable to directly analyze the imaging influence of possible defect locations. Therefore, in principle, it is necessary to quickly and easily analyze or identify the mask, if possible, under the same conditions as actually exist in the projection illumination system.

[0005] In this context, there are various techniques for emulating a projection illuminator within the scope of mask inspection (ie measuring the mask under conditions as similar as possible to those of the projection illuminator).

[0006] Firstly, a method is known for recording and evaluating an aerial image of a part of a mask in a mask inspection apparatus, whereby to record the aerial image, the structure to be measured on the mask is illuminated using a magnifying illumination optical unit, and the light coming from the mask is projected via an imaging optical unit onto a detector unit and detected by the detector unit.

[0007] In this process, it is further known to illuminate the mask in the mask inspection apparatus in an identical manner to the illumination in the projection illumination apparatus, in particular providing the same wavelength, the same numerical aperture and also the same (if necessary polarized) illumination settings in the mask inspection apparatus.

[0008] With regard to the prior art, reference is made, purely by way of example, to DE 102010063337 A1, DE 102013212613 A1 and DE 102011086345 A1. Summary of the Invention

[0009] It is an object of the present invention to provide a method and apparatus for characterization of microlithography masks, which allows a fast and reliable characterization taking into account the conditions imposed by the lithography process.

[0010] This object is achieved by a method and a device, respectively, according to the features of the independent claims.

[0011] The present invention relates in one aspect to a method for characterizing a microlithography mask, comprising: the mask to be characterized is illuminated with light from a light source via an illumination optical unit, the light having a wavelength of less than 30 nm; - the light passing through the used beam path from the light source via the mask to the sensor unit is evaluated, - a portion of the light emitted by the light source is at least intermittently outcoupled from the used beam path using a mirror array having a multitude of independently adjustable mirror elements; - All light is intermittently outcoupled from the used beam path using the mirror array to establish a defined illumination time of the sensor unit.

[0012] The outcoupled light may be specifically directed to a beam trap.

[0013] This configuration takes into account the fact that on the one hand the light sources that can be used to generate EUV light, for example in particular plasma light sources, cannot be switched on and off on the short time scales required for the mask inspection process, while on the other hand the sensor devices used in the mask inspection process (for example CCD cameras) require precisely defined exposure times (usually of the order of 200 milliseconds). According to the invention, by all mirror elements of the mirror array used according to the invention and out-coupling the respective incoming light from the used beam path at a given end point of the respectively defined exposure time (and directing, for example, into a beam trap provided for the purpose), it is possible to achieve the same effect as switching off the light source (which is not feasible in the case of EUV light sources), while at the same time making unnecessary the use of a fast shutter, which would otherwise be conceivable for this purpose.

[0014] The invention in this case simultaneously takes advantage of the fact that, as a result of the pulsed operation, the remaining period between successive pulses (typically of the order of about 0.2 milliseconds) is available for the tilting movement required for each of the mirror elements.

[0015] In one embodiment, the intensity of the light components outcoupled from the used beam path by the mirror array is detected by an intensity sensor.

[0016] The invention takes into account, inter alia, the fact that in the case of EUV light, outcoupling cannot be performed using partially transparent mirrors, as in the case of UV light or light in the visible wavelength range, since such mirrors do not exist in the case of EUV. According to the above mentioned aspects, the invention includes the idea of ​​outcoupling a portion of the light emitted by at least one light source and detecting the intensity or energy of this outcoupled portion. According to the invention, this allows to ascertain energy variations on the side of the (at least one) light source, so that the image finally recorded by the sensor unit can be normalized to the energy of the at least one light source.

[0017] In this case, one advantageous result of the arrangement according to the invention is that it is possible to distinguish, with regard to brightness changes occurring in the image recorded by the sensor unit, whether such brightness changes are caused by the currently characterized mask (for example as a result of a defect that may be present on this mask) or whether such brightness changes are caused by energy fluctuations of the light source used. In this way, it may be possible to avoid drawing erroneous conclusions about defects recognized as being present on the mask.

[0018] The invention can also take advantage of the fact that in this case only the relative changes or fluctuations over time are of interest with respect to the intensity or energy emitted by the at least one light source. In other words, in particular no spatially resolved quantitative intensity measurements are necessary. The invention can further take advantage of the fact that for said determination of the relative changes in energy or intensity over time, only a relatively small part of the light emitted by the at least one light source needs to be outcoupled, so that a very large part of the light is still available for the characterization of the actual mask.

[0019] The present invention takes into account the above considerations regarding changes in the energy or intensity of at least one light source, particularly in microlithography applications where the demands on precision are high and therefore already small changes (on the order of significantly less than 1 percent) are important to reliably identify relevant defects in the mask.

[0020] It may also be advantageous to detect light components outcoupled from the used beam path by a mirror array with an intensity sensor, independent of its function as a fast shutter, as explained above.

[0021] The present invention therefore also relates, according to a further aspect, to a method for characterizing a microlithography mask, comprising: the mask to be characterized is illuminated with light from a light source via an illumination optical unit, the light having a wavelength of less than 30 nm; - the light passing through the used beam path from the light source via the mask to the sensor unit is evaluated, - a portion of the light emitted by the light source is at least intermittently outcoupled from the used beam path using a mirror array having a number of independently adjustable mirror elements; The intensity of the light components that are at least intermittently outcoupled from the used beam path by the mirror array is detected by an intensity sensor.

[0022] In one embodiment, greyscale adjustment is achieved by actuating at least some of the mirror elements such that light is outcoupled from the used beam path only during a portion of the illumination period of the sensor unit.

[0023] In this configuration, grey scale values ​​are achieved since, by utilising an array according to the invention of independently adjustable mirror elements, the respective exposure time or dose is individually adjusted via each individual mirror element by "switching off" or tilting the associated mirror element such that light incident on that mirror element does not reach the sensor unit after an individually predeterminable duration (shorter than the total exposure duration).

[0024] This configuration takes into account the fact that in the present invention's operation of a mask inspection system with EUV light, the inventive array of independently adjustable mirror elements cannot be utilized as a blazed diffraction grating (wherein the grayscale values ​​are established by the angle-dependent change in diffraction efficiency) since the wavelength is several orders of magnitude shorter than the dimensions and spacing of the mirror elements, and thus must ultimately be based on geometric optics units. Based on this consideration, the inventive grayscale values ​​are realized despite this fact, i.e., the fact that each mirror element is tilted to a position suitable for outcoupling light from the used beam path even after a portion of the respective exposure time (e.g., after a period of 50 milliseconds, and thus even after a quarter of the total exposure time of, e.g., 200 milliseconds).

[0025] This manner of establishing greyscale values ​​is advantageous even though it is independent of the above-described features of replacing a high speed shutter or out-coupling to feed an intensity sensor.

[0026] The invention therefore also relates to a method for characterizing a microlithography mask, comprising: the mask to be characterized is illuminated with light from a light source via an illumination optical unit, the light having a wavelength of less than 30 nm; - the light passing through the used beam path from the light source via the mask to the sensor unit is evaluated, - a portion of the light emitted by the light source is at least intermittently outcoupled from the used beam path using a mirror array having a number of independently adjustable mirror elements; Greyscale adjustment is achieved by actuating at least some of the mirror elements such that light is outcoupled from the used beam path only during a portion of the illumination period of the sensor unit.

[0027] In one embodiment, the settings of the mirror elements are selected in an intermittent manner such that a first group of mirror elements is in the illumination beam path from the light source to the mask and a second group of mirror elements is in the imaging beam path from the mask to the sensor unit.

[0028] This configuration takes into account the fact that in the inventive operation of a mask inspection system with EUV light, on the one hand, there is no available transmissive optical element acting as a beam splitter due to the lack of available transmissive material, but on the other hand, such a beam splitter function is necessary to separate the imaging beam path from the illumination beam path, for example to realize a mask inspection with normal incidence of light, which is desirable in certain applications. Based on this consideration, the invention therefore advantageously exploits the properties of the used array of a number of independently adjustable mirror elements, which, by suitable adjustment of the mirror elements, can contribute partly to the illumination beam path (from the light source to the mask) and partly to the imaging beam path (from the mask to the sensor arrangement).

[0029] In one embodiment, the settings of the mirror elements are selected so that the light strikes the mask in an intermittent manner at an angle of at least 85° relative to the mask surface, in particular at an angle of 90° (i.e. perpendicular to the mask surface).

[0030] In one embodiment, the light from the light source has a wavelength of less than 15 nm, particularly in the range of 13 nm to 14 nm.

[0031] In a further aspect, the present invention relates to an apparatus for characterizing a microlithography mask, the apparatus comprising: - a light source for generating light of a wavelength less than 30 nm; - an illumination optical unit for illuminating the mask to be characterized with light from a light source; a sensor unit; an evaluation unit for evaluating light passing through the used beam path from the light source via the mask to the sensor unit; a mirror array consisting of a number of independently adjustable mirror elements, by means of which at least a portion of the light can be outcoupled from the used beam path; - an actuation unit for actuating the mirror array; by means of which it is possible, by means of the mirror array, to intermittently outcouple all light from the used beam path in order to establish a predetermined illumination time of the sensor unit.

[0032] In one embodiment, the apparatus comprises a beam trap that receives light components outcoupled by the mirror array from the used beam path.

[0033] In one embodiment, the apparatus comprises an intensity sensor that detects the intensity of the light component outcoupled by the mirror array from the used beam path.

[0034] In a further aspect, the present invention relates to an apparatus for characterizing a mask for microlithography, the apparatus comprising: - a light source for generating light of a wavelength less than 30 nm; - an illumination optical unit for illuminating the mask to be characterized with light from a light source; a sensor unit; an evaluation unit for evaluating light passing through the used beam path from the light source via the mask to the sensor unit; a mirror array consisting of a number of independently adjustable mirror elements, by means of which at least a portion of the light can be outcoupled from the used beam path; an intensity sensor for detecting the intensity of the light component outcoupled from the used beam path by the mirror array; Equipped with.

[0035] In one embodiment, the apparatus is configured to carry out a method having the features described above.

[0036] Regarding the advantages and preferred configuration of the device, reference is made to the above explanations relating to the method according to the invention.

[0037] Further configurations of the invention can be seen from the description and the dependent claims.

[0038] The invention is explained in more detail below on the basis of exemplary embodiments shown in the attached drawings. [Brief description of the drawings]

[0039] [Figure 1a] FIG. 1a is a schematic diagram illustrating a possible structure and functioning approach of an inventive device for mask characterization in a first embodiment. [Figure 1b-1c] 1b and 1c are schematic diagrams illustrating a possible structural and functional approach of an inventive device for the characterization of a mask in a first embodiment. [Diagram 2] 5A-5C are schematic diagrams illustrating possible configurations of the device of the present invention in further embodiments. [Diagram 3] 5A-5C are schematic diagrams illustrating possible configurations of the device of the present invention in further embodiments. [Figure 4]1 is a schematic diagram illustrating a possible manner of functioning of the device of the invention; [Diagram 5] 1 is a schematic diagram illustrating a possible manner of functioning of the device of the invention; [Figure 6] 5A-5C are schematic diagrams illustrating possible configurations of the device of the present invention in further embodiments. [Figure 7a] 3A-3C are schematic diagrams illustrating the structure and possible functioning modes of the device of the invention in further embodiments. [Figure 7b] 3A-3C are schematic diagrams illustrating the structure and possible functioning modes of the device of the invention in further embodiments. [Figure 7c] 3A-3C are schematic diagrams illustrating the structure and possible functioning modes of the device of the invention in further embodiments. [Figure 7d] 3A-3C are schematic diagrams illustrating the structure and possible functioning modes of the device of the invention in further embodiments. [Figure 8] FIG. 1 is a schematic diagram illustrating the general structure of an apparatus for characterizing a mask. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] In a typical structure according to FIG. 8, the mask inspection system 800 comprises an illumination system 801 and a projection lens 805, where light from a light source (not shown in FIG. 1) enters the illumination system 801, a bundle of illumination rays 802 is directed to a mask 803 arranged in the object plane of the projection lens 805, and the illuminated area of ​​the mask 803 is imaged by a bundle of observation rays 804 using the projection lens 805 onto a sensor device 806, e.g. a CCD camera.

[0041] In mask inspection, in order to obtain the highest quality of reproducibility of the illumination conditions caused by the projection illumination system or scanner in the actual lithography process, it is also important to emulate the illumination settings used in the production illumination system or the irradiation device of the production illumination system in combination with the mask 803, i.e. the illumination settings including the partial coherence of the illumination light falling on the mask 803 that may be related to the illumination settings, for which purpose it is customary to use corresponding shutters in the illumination system of the mask inspection system 800 (i.e. quadrupole shutters with four cutouts that match the illumination poles, for example, if a quadrupole setting is used in the subsequent lithography process), so that the mask inspection system can perform partial coherent illumination. In addition, in the projection lens 805 of the mask inspection system 800, it is possible to emulate the beam path limitations, i.e. the NA, by using a suitable mask (typically with corresponding circular or elliptical cutouts) as well.

[0042] Various embodiments of the inventive apparatus for mask characterization will now be described with reference to the schematic diagrams of Figures 1a to 7d.

[0043] Common to these embodiments is that in each device operating with light from an EUV light source (i.e. light with wavelengths less than 30 nm, in particular less than 15 nm), a mirror array of a number of independently adjustable mirror elements is used to intermittently outcouple light for achieving various functions from the used beam path from the light source through the mask to the sensor device. Each mirror element of the mirror array is provided with a coating suitable for the wavelength used by the light source (e.g. around 13.5 nm), for example a stack of molybdenum (Mo)-silicon (Si) reflecting layers.

[0044] Referring first to Figure 1a, the EUV light from a light source (not shown in Figure 1a) passes through a shutter 110, via a mirror 120, to a mirror array 130, from which the EUV light can be directed, according to the settings of the respective mirror elements, via a mask 140 to a sensor arrangement (also not shown in Figure 1a) or otherwise outcoupled from the used beam path. As simply shown in Figure 1a, the light component outcoupled from the used beam path is directed to a beam trap, here identified as "150".

[0045] In a first function that can be realized with the structure of Fig. 1a, it is then possible to establish a predetermined illumination time of the sensor unit by suitably activating the mirror elements of the mirror array 130, i.e. by out-coupling all light from the used beam path via the mirror array 130 at the respective suitable connection points. This takes into account in particular the fact that the EUV light source itself cannot be cycled on and off on a short time scale. At the same time, said activation of the mirror elements of the mirror array 130 makes the use of a high-speed shutter unnecessary.

[0046] 1b and 1c show schematic diagrams illustrating the above-described functionality of mirror array 130. FIG.

[0047] According to Fig. 1c, all mirror elements of the mirror array 130 are tilted relative to a rest position before and after the respective desired exposure time, and reflect the illumination light coming from the light source towards the beam trap 150. In a further possible configuration according to Fig. 1b, all mirror elements of the mirror array 130 are in a rest position from the start to the end of the respective desired irradiation time, and reflect the illumination light coming from the light source towards the photomask.

[0048] If a combination of this function with the function of forming a specific illumination setting is desired, then the only mirror elements in a stationary position from the start to the end of each desired exposure time are those in the position where the desired illumination setting is bright, while all other mirror elements are tilted to direct light towards the beam trap 150 before, during, and after the desired exposure time.

[0049] FIG. 2 shows a schematic diagram illustrating a further embodiment of an apparatus of the present invention for characterizing a mask, where similar or substantially functionally identical components compared to FIG. 1a are designated with reference numerals increased by "100."

[0050] According to Fig. 2 the device further comprises an intensity sensor 260, which is able to detect the intensity of the light components outcoupled from the mirror array 230. In the present invention, the intensity sensor 260 is used in combination with the mirror array 230 to ascertain energy variations on the light source side, so that the image recorded by the sensor unit can be normalized to the energy of the light source. In particular, in case of brightness variations, for example, it is possible to distinguish whether such brightness variations in the image recorded by the sensor unit are caused by the currently characterized mask 240 (for example by any defect present in this mask 240) or by variations in the energy of the light source, thus avoiding erroneous conclusions about defects recognized as present on the mask.

[0051] Here, even a relatively small out-coupling of the light components is sufficient for the normalization, so that the predominant light components are still available for the actual mask characterization. Figure 4 shows an exemplary embodiment in which the mirror elements of the mirror arrangement 400, the hatched ones (two of which are identified as "402" as an example) direct the incident light to the intensity sensor, while the light from the other mirror elements (one of which is identified as "401" as an example) hits the mask.

[0052] The outcoupling of light described above with reference to Figures 2 and 4 has the advantage, in comparison with the detection of intensity outside the illuminated mask area, which is also possible in principle, that the light that is outcoupled in the direction of the intensity sensor for normalization purposes is outcoupled directly from the pupil and not from an area outside the pupil, thereby improving the measurement accuracy.

[0053] 5 shows a schematic diagram similar to FIG. 4 to illustrate another possible scenario, where the mirror elements that are not hatched and are not shown as dots (one of which is identified as “501” for example) each direct the incident light towards a mask, the mirror elements that are shown as dots (one of which is identified as “502” for example) each direct the incident light towards an intensity sensor for normalization purposes as described above, and the mirror elements that are shown as hatched (one of which is identified as “503” for example) direct the incident light towards a beam trap, so that in this way the desired illumination setting (in a specific embodiment, dipole illumination) is achieved.

[0054] FIG. 3 shows a schematic diagram illustrating a further embodiment of an apparatus of the present invention for characterizing a mask, where similar or substantially functionally identical components compared to FIG. 2 are designated by reference numerals increased by "100."

[0055] The embodiment according to Fig. 3 differs from the embodiment according to Fig. 2 in particular in the different arrangement of the mirror array 330 according to the optical beam path. In particular, the mirror array 330 is arranged according to the optical path upstream of the mirror 320 and upstream of the shutter 310, so that in the successive beam paths another mirror 325 is provided after the mirror 320. The arrangement of the mirror array 330 according to Fig. 3 is advantageous firstly in that, as a result of the mirror array 330 being arranged further away from the mask 340, a restriction of the available optical path between the mask 340 and the imaging optics or the sensor unit by the mirror array 330 is avoided, but also in that the available construction space is increased for cooling of the mirror array 330 (for example by connection with a cooling fluid) and for electronic and operating components.

[0056] In an embodiment of the invention, in addition to or as an alternative to the functions described above with reference to figures 1a to 5, it is also possible to implement a greyscale setting with the mirror array according to the invention. For this purpose, some of the mirror elements of the mirror array according to the invention can be actuated in each case for only a part of the illumination period of the sensor unit or CCD camera to outcouple light from the used beam path. This takes into account the fact that in the inventive configuration of a mask inspection system operating with EUV light, unlike DUV systems, an adjustment of the angle-dependent greyscale value by a change in the diffraction efficiency is not possible, since it must be based on geometrical optics when operating with EUV light, due to the wavelength being several orders of magnitude shorter compared to the dimensions and spacing of the mirror elements. Instead, the invention includes the principle of establishing different greyscale values ​​for the duration of the respective tilt of the mirror elements (or for the ratio of this duration to the overall illumination time) in order to achieve a greyscale value.

[0057] By way of example only, to achieve grey scale values, some of the mirror elements are tilted into a position suitable for out-coupling light from the used beam path even after a portion of the respective illumination time (e.g. after a quarter period of 50 milliseconds, thus of the total illumination time of e.g. 200 milliseconds).

[0058] 6a to 7d show schematic diagrams for illustrating further embodiments of an apparatus according to the invention for mask characterization, in which (in addition to or as an alternative to the functions described above) the further function of a beam splitter is implemented, in particular to separate the imaging beam path from the illumination beam path, in order to enable mask inspection with normal incidence of light.

[0059] This takes into account the fact that in the present invention's operation of a mask inspection system with EUV light, there is no transmissive optical element that can be directly used as a beam splitter due to the lack of available transmissive materials. In this respect, the present invention includes a further principle of suitably adjusting the mirror elements of a mirror array to ensure that the mirror array ultimately contributes to the illumination beam path and the imaging beam path.

[0060] Figures 6a-b first show a schematic diagram illustrating the underlying principle: according to figure 6a, in principle a beam splitter 601 is needed for perpendicular illumination of the mask 602 and to enable imaging at the sensor unit 603. Figure 6b shows a principle implementation of a mirror array 630 of the invention, where "611" indicates the illumination light incident on the mirror array 630 and "614" indicates the light that is directed by the mirror array 630 towards the imaging optics. "615" indicates the light component that is outcoupled in the direction of an additional intensity sensor, similar to the embodiment described above.

[0061] FIG. 7a shows a schematic diagram of a possible structure of a corresponding device according to the invention, in which all the functions described above are performed (i.e. realization of a fast shutter, outcoupling of light components in the direction of an intensity sensor for normalization or calibration purposes, establishment of gray scale values, and separation of illumination and imaging beam paths for mask characterization with normal incidence of light). Compared to FIG. 3, similar or substantially functionally identical components are here designated by reference numbers with the addition of "400". FIG. 7a further shows the positions of the (EUV) light source 705 and the sensor unit 770 (for example configured as a CCD camera). "715", "735", "745" and "755" respectively denote mirrors present for realizing the beam paths, which are curved in the example. "780" denotes a beam trap that receives light reflected by mirror elements of the mirror array 730 in their respective rest positions. “790” denotes a light trap for capturing the imaging light, which is reflected by a mirror element and used to outcouple the light component towards the intensity sensor 760.

[0062] Fig. 7b, with reference to an enlarged detail of the mirror array 730, illustrates a scenario which occurs when light hits the mirror array 730 for the first time in each case during operation of the device. For example, as shown in Fig. 7b, half of the mirror elements are in a rest position, thereby reflecting the incident illumination light towards the beam trap. In contrast, the other mirror elements of the mirror array 730 are redirected to reflect the incident illumination light towards the mask 740. Fig. 7c illustrates a further scenario which occurs when light hits the mirror array 730 for the second time during operation of the device. Here, the mirror elements in the rest position reflect the light coming from the mask 740 towards the sensor unit 770 or the CCD camera, while the other, redirected mirror elements reflect the light incident on the mask back to the light source 705.

[0063] FIG. 7 d illustrates a further scenario in which the apparatus is in operation, where two mirror elements of the mirror array 730 are tilted to direct the incoming illumination light towards the intensity sensor 760 .

[0064] Although the present invention has been described based on specific embodiments, numerous variations and alternative embodiments will become apparent to those skilled in the art, for example, by combining and / or substituting features of the individual embodiments. Accordingly, it will be apparent to those skilled in the art that such variations and alternative embodiments are also encompassed by the present invention, the scope of which is limited only by the scope of the appended claims and their equivalents.

Claims

1. 1. A method for characterizing a microlithography mask, comprising: the mask (140, 240, 340, 640, 740, 803) to be characterized is illuminated with light from a light source (705) via an illumination optical unit (801), said light having a wavelength of less than 30 nm; - the light passing through the used beam path from said light source (705) via said mask (140, 240, 340, 640, 740, 803) to a sensor unit (770, 806) is evaluated, a portion of the light emitted by the light source (705) is at least intermittently outcoupled from the used beam path by means of a mirror array (130, 230, 330, 630, 730) having a number of independently adjustable mirror elements, - all light is intermittently outcoupled from the used beam path by means of the mirror array (130, 230, 330, 630, 730) to establish a predetermined illumination time of the sensor unit (770, 806); method.

2. 2. The method of claim 1, wherein the outcoupled light is at least partially directed into a beam trap (150, 250).

3. 3. The method according to claim 1 or 2, characterized in that the intensity of light components outcoupled from the used beam path by the mirror array (230, 330) at least intermittently is detected by an intensity sensor (260, 360, 760).

4. 1. A method for characterizing a microlithography mask, comprising: the mask (240, 340, 740, 803) to be characterized is illuminated with light from a light source (705) via an illumination optical unit (801), said light having a wavelength of less than 30 nm; - the light passing through the used beam path from said light source (705) via said mask (240, 340, 740, 803) to a sensor unit (770, 806) is evaluated, a portion of the light emitted by the light source (705) is at least intermittently outcoupled from the used beam path by means of a mirror array (230, 330, 630, 730) having a number of independently adjustable mirror elements, at least intermittently, the intensity of the light components outcoupled from the used beam path by the mirror array (230, 330, 630, 730) is detected by an intensity sensor (260, 360, 760); method.

5. 5. The method according to claim 1, 2 or 4, characterized in that greyscale adjustment is achieved by actuating at least some of the mirror elements such that light is outcoupled from the used beam path only during a portion of the illumination period of the sensor unit (770, 806).

6. 1. A method for characterizing a microlithography mask, comprising: the mask (140, 240, 340, 740, 803) to be characterized is illuminated with light from a light source (705) via an illumination optical unit (801), said light having a wavelength of less than 30 nm; - the light passing through the used beam path from said light source (705) via said mask (140, 240, 340, 740, 803) to a sensor unit (770, 806) is evaluated, a portion of the light emitted by the light source (705) is at least intermittently outcoupled from the used beam path by means of a mirror array (230, 330, 630, 730) having a number of independently adjustable mirror elements, - greyscale adjustment is achieved by actuating at least some of the mirror elements such that light is outcoupled from the used beam path only during a portion of the illumination period of the sensor unit (806); method.

7. 7. The method according to claim 1, 2, 4 or 6, characterized in that the settings of the mirror elements are selected in an intermittent manner such that a first group of mirror elements is in an illumination beam path (611) leading from the light source (705) to the mask (640, 740) and a second group of mirror elements is in an imaging beam path (614) leading from the mask (640, 740) to the sensor unit (770).

8. 7. The method according to claim 1, 2, 4 or 6, characterized in that the settings of the mirror elements are selected such that light strikes the mask (640) in an intermittent manner at an angle of at least 85°, in particular at an angle of 90°, relative to the mask surface.

9. The method according to claim 1, 2, 4 or 6, characterized in that the light from the light source (705) has a wavelength of less than 15 nm, in particular in the range of 13 nm to 14 nm.

10. 1. An apparatus for characterizing a microlithography mask, comprising: a light source (705) for generating light of a wavelength less than 30 nm; an illumination optical unit (801) for illuminating the mask (140, 240, 340, 803) to be characterized with light from the light source (705); A sensor unit (770, 806), an evaluation unit for evaluating the light passing through the used beam path from the light source through the mask (140, 240, 340, 740, 803) to the sensor unit (770, 806); a mirror array (130, 230, 330, 630, 730) consisting of a number of independently adjustable mirror elements, by means of which at least a portion of said light can be outcoupled from said used beam path; an actuation unit for actuating said mirror array (130, 230, 330, 630, 730); and wherein said actuation to establish a predetermined illumination time of said sensor unit (770, 806) allows for intermittent outcoupling of all light from said used beam path using said mirror array (130, 230, 330, 630, 730). Device.

11. 11. The apparatus of claim 10, further comprising a beam trap (150, 250) for receiving light components outcoupled from the used beam path by the mirror array (230, 330).

12. 12. Apparatus according to claim 10 or 11, characterized in that it comprises an intensity sensor (260, 360) for detecting the intensity of a light component outcoupled from the used beam path by the mirror array (230, 330).

13. 1. An apparatus for characterizing a microlithography mask, comprising: a light source (705) for generating light of a wavelength less than 30 nm; an illumination optical unit (801) for illuminating the mask (140, 240, 340, 740, 803) to be characterized with light from the light source; A sensor unit (770, 806), an evaluation unit for evaluating the light passing through the used beam path from the light source (705) via the mask (140, 240, 340, 740, 803) to the sensor unit (770, 806); a mirror array (230, 330, 630, 730) consisting of a number of independently adjustable mirror elements, by means of which at least a portion of said light can be outcoupled from said used beam path; an intensity sensor (260, 360, 760) for detecting the intensity of the light component outcoupled from the used beam path by the mirror array (230, 330); An apparatus comprising:

14. Apparatus according to claim 10, 11 or 13, characterized in that the light from the light source (705) has a wavelength of less than 15 nm, in particular in the range of 13 nm to 14 nm.

15. An apparatus as described in claim 10, 11 or 13, characterized in that it is configured to carry out a method as described in claim 1, 2, 4 or 6.

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