Method for operating a mask inspection device, EUV camera, mask inspection device, computer program product

Abstract

Method for operating a mask inspection device, in which EUV radiation is directed onto a photomask (17) and in which EUV radiation reflected by the photomask (17) is directed via a projection lens (22) onto an image sensor (24) of an EUV camera (23), such that the photomask (17) is imaged onto the image sensor (24). The photomask (17) is moved in a scanning direction (32) while the image sensor (24) is exposed. Image data is acquired with the image sensor (24), which has a different resolution in the scanning direction (32) than in a cross-scanning direction (33). A compressed image (34) of the photomask (17) is generated from the image data. The invention also relates to a mask inspection device, an EUV camera, and a computer program product.

Description

[0001] The invention relates to a method for operating a mask inspection device, an EUV camera, a mask inspection device and a computer program product.

[0002] Photomasks are used in microlithographic projection exposure systems for the fabrication of integrated circuits with extremely small structures. The photomask, illuminated with very short-wavelength, extreme ultraviolet (EUV) radiation, is projected onto a lithography object to transfer the mask structure.

[0003] For high-quality images produced on lithographic objects, the photomask must be dimensionally accurate and free from impurities. It is known to inspect photomasks before use in a microlithographic projection exposure system or during downtime. This involves creating an aerial image of a section of the photomask, projecting the image not onto a lithographic object, but onto the image sensor of an EUV camera. Based on this image, an assessment can be made as to whether the photomask is free of defects and impurities.

[0004] During the operation of a mask inspection device, the image sensor generates significant amounts of data. This data volume can, for example, be on the order of several tens of gigabytes per second, resulting in considerable effort for data processing.

[0005] The invention is based on the objective of presenting a method for operating a mask inspection device, an EUV camera, a mask inspection device, and a computer program product, with which the aforementioned disadvantages are reduced. This objective is achieved by the features of the independent claims. Advantageous embodiments are specified in the dependent claims.

[0006] In the inventive method for operating a mask inspection device, EUV radiation is directed onto a photomask. EUV radiation reflected from the photomask is directed via a projection lens onto an image sensor of an EUV camera, so that the photomask is imaged onto the image sensor. While the image sensor is exposed, the photomask is moved in a scan direction. Image data is acquired by the image sensor, which has a different resolution in the scan direction than in a cross-scan direction. A compressed image of the photomask is generated from the image data.

[0007] The invention is based on the following consideration. There are microlithographic projection exposure systems in which the photomask is anamorphically imaged onto the lithographic object, meaning that the image scale in the scan direction does not correspond to the image scale in the cross-scan direction. A square structure of the photomask, whose sides are aligned parallel to the scan direction and the cross-scan direction, is then imaged as a rectangle onto the lithographic object. The scan direction and the cross-scan direction define a plane that corresponds to the plane of the photomask. The cross-scan direction forms a right angle with the scan direction.

[0008] With regard to mask inspection, it offers no advantage to analyze a photomask in the scan direction with the same resolution as in the cross-scan direction. A high resolution in the direction where the microlithographic projection exposure system has the smaller image scale would allow for the correction of errors in that dimension that are no longer correctable in the other dimension. However, this would not provide any added value because the overall quality of the structure on the lithographic object is limited by the larger of the two image scales of the microlithographic projection exposure system.

[0009] The invention proposes to account for this difference between the two dimensions of a photomask during the acquisition of image data from the photomask by acquiring the image data in the cross-scan direction at a different resolution than in the scan direction. This makes it possible to avoid image data that offers no added value for the subsequent use of the photomask in a microlithographic projection exposure system, thus preventing the significant effort required for processing acquired image data. The effort involved in further data processing is reduced because the amount of image data to be processed is smaller.

[0010] The anamorphic image scales of the microlithographic projection exposure system can be aligned such that a circular structure of the photomask is projected as an oval onto the lithographic object, with the oval having a larger extent in the cross-scan direction than in the scan direction. This means that a defect that is circular on the photomask has a greater effect in the cross-scan direction than in the scan direction. The inventive concept can be utilized in this case by ensuring that the image data acquired with the image sensor has a higher resolution in the cross-scan direction than in the scan direction. This would be the opposite if the anamorphic image scales of the microlithographic projection exposure system were inversely related to each other.

[0011] An image sensor is exposed when EUV radiation strikes it, and the sensor generates charge carriers based on the incident EUV radiation, which can then be read out to obtain image data. According to the invention, an image is generated from image data when the image data is provided in a form that allows inferences to be drawn about structures present on the photomask. Generating an image does not require that the image be physically produced or presented in a form perceptible to humans. An image is compressed if a structure that has the same extent in the scan direction and in the cross-scan direction on the photomask has a different extent in the scan direction than in the cross-scan direction.

[0012] The image sensor can comprise a large number of pixels. The pixels can form a pixel array aligned in the scan direction and cross-scan direction. The image sensor can comprise pixel rows extending in the scan direction. The cross-scan direction can be defined by a plurality of parallel pixel rows. It is also possible for the pixel rows to form an angle other than 0° with the scan direction. This angle can be less than 5°, preferably less than 2°, and more preferably less than 1°. The image sensor can be designed to be read out line by line.

[0013] The method can be implemented by shifting charge carriers generated by incident EUV radiation within the image sensor from pixel to pixel within a pixel row before the number of charge carriers is read out. The displacement speed of the charge carriers can be matched to the scan speed at which the photomask is moved in the scan direction. In particular, the displacement speed and the scan speed can be coordinated so that the speed at which the image of the photomask moves across the image sensor matches the displacement speed. This makes it possible to sum the charge carriers generated by the image over the duration of a scan, which has a beneficial effect on the accuracy and the signal-to-noise ratio of the acquired data.The image sensor can be designed as a CCD sensor (Charge Coupled Device) or as a CMOS sensor (Complementary Metal Oxide Semiconductor). In one embodiment, the image sensor is designed as a TDI sensor (Time Delay and Integration).

[0014] The term "scan direction" is used consistently to refer to the direction in which the photomask is moved relative to the projection lens, and the direction in which the image of the photomask moves relative to the image sensor. This use of the term "scan direction" is for clarity and does not imply that the direction of movement of the photomask and the direction of movement of the image must have a specific spatial arrangement relative to each other. In particular, it is not necessary for the image sensor to have an orientation in space that is parallel to the photomask.

[0015] The maximum resolution of an image sensor depends on the pixel density across its surface. The resolution of the image sensor in the cross-scan direction can be increased by reducing the spacing between adjacent pixel rows. The resolution of the image sensor in the scan direction can be increased by reducing the spacing between pixels within a pixel row. Since image sensors are generally designed so that adjacent pixels are directly connected, improving the resolution usually involves reducing the pixel size.

[0016] Image information can be obtained by determining the number of charge carriers in a pixel row segment, where the length of the pixel row segment is greater than the distance between two adjacent pixel rows. The number of charge carriers represents the amount of EUV radiation that fell on the corresponding pixel row segment during the exposure process. The image information can be supplied to a control unit, which can store the image information in a format that allows an image of the imaged photomask to be generated. For this purpose, the image information can be stored, for example, together with information about the pixel row from which the image information originates and together with information about the time at which the image information was read out. Image data according to the invention corresponds to a set of image information from which an image of the imaged photomask can be generated.

[0017] In one embodiment, the image sensor is equipped with pixels whose length is greater than their width. The length of the pixels can extend parallel to a pixel row of the image sensor. The length of the pixels can extend parallel to the scan direction. The width of a pixel extends perpendicular to this direction. In particular, the width of the pixel can extend in the cross-scan direction. Since the number of charge carriers within a pixel is determined when the image sensor is read out, the resolution relative to a direction decreases with the length of the pixel in that direction. The length of a pixel can be at least 1.3 times, preferably at least 1.5 times, and more preferably at least 1.8 times greater than the width of the pixel. The length of the pixel can be twice as large as the width of the pixel. These specifications can apply to at least 80%, preferably at least 90%, and more preferably 100% of the pixels of the image sensor.

[0018] The ratio between the length and width of the pixel can be matched to the ratio between the image scales of the anamorphic image produced by the microlithographic projection system. The two image scales, βx in the cross-scan direction and βy in the scan direction, can, for example, be (βx, βy) = (+ / - 0.25, + / - 0.125). An image scale β of 0.25 corresponds to a reduction ratio of 4:1, while an image scale β of 0.125 results in a reduction ratio of 8:1. A positive sign for the image scale β indicates an image without image inversion, a negative sign indicates an image with image inversion. With an image scale that is twice as large in the cross-scan direction as in the scan direction, the length of the pixel can be twice as large as its width.

[0019] The anamorphic imaging scales β x , β yThe microlithographic projection exposure system is reflected in the photomask. Structures that are intended to have the same size on the lithographic object in the scan direction and in the cross-scan direction are reproduced in a compressed form on the photomask 17. A photomask in which this is the case is called an anamorphic photomask. The method according to the invention can be carried out with an anamorphic photomask. The image of the photomask onto the image sensor can be non-anamorphic. In other words, the image of the photomask onto the image sensor can have the same image scale in the scan direction as in the cross-scan direction. The photomask can have an aspect ratio between 1:1 and 1:3, preferably between 1:1 and 1:2, and particularly preferably 1:1 or 1:2. The photomask can be substantially rectangular.The photomask can preferably be 5 to 7 inches (12.7 cm to 17.8 cm) long and wide, more preferably 6 inches (15.2 cm) long and wide. Alternatively, the photomask can be 5 to 7 inches (12.7 cm to 17.8 cm) long and 10 to 14 inches (25.4 cm to 35.6 cm) wide, more preferably 6 inches (15.2 cm) long and 12 inches (30.5 cm) wide.

[0020] A reduced image resolution in one direction can alternatively be achieved by adding the charge carriers of adjacent pixels in a pixel row when reading the image sensor. In particular, the number of charge carriers from each pair of adjacent pixels can be added. The charge carrier count can be performed before the total number of charge carriers is further processed as image information. In the inventive method, the number of charge carriers can first be read individually for each pixel and then added. It is also possible to read the charge carrier count of several pixels directly together. This approach can be applied to an image sensor whose pixels have a length and width that are identical. In particular, the image sensor can have square pixels.

[0021] The number of charge carriers thus obtained from one or more pixels corresponds to a single piece of image information. Image data suitable for generating an image can be derived from a multitude of such image information by storing the image information in such a way that it can be spatially assigned. Spatial assignment can be made possible, in particular, by assigning the image information to a pixel row and a specific point in time.

[0022] The EUV camera can comprise a first operating mode and a second operating mode. In the first operating mode, the charge carriers of more than one pixel are counted to generate image information, while in the second operating mode, image information is determined based on the number of charge carriers in each pixel. In the first operating mode, the charge carriers of adjacent pixels can be counted, in particular the charge carriers of two adjacent pixels.

[0023] The invention also relates to a mask inspection device comprising an EUV camera, a positioning device for a photomask, and a projection lens for imaging the photomask onto an image sensor of the EUV camera. The positioning device is designed to move the photomask in a scan direction while the image sensor is exposed. The EUV camera is designed to acquire image data that has a different resolution in the scan direction than in a cross-scan direction. The invention also encompasses EUV cameras comprising more than one image sensor.

[0024] The invention also relates to an EUV camera for such a mask inspection device. The EUV camera comprises an image sensor with a pixel array spanned by a plurality of pixel rows. The EUV camera is designed to acquire image information for an image of a photomask by determining the number of charge carriers in a pixel row segment, wherein the length of the pixel row segment is greater than the distance between two adjacent pixel rows.

[0025] The invention also relates to a computer program product or a set of computer program products comprising program parts which, when loaded into a computer or into interconnected computers connected to a mask inspection device according to the invention, are designed to carry out the method according to the invention.

[0026] The image data obtained according to the invention can be compared in a further step with dimensions of structures on the depicted section of the photomask. If it is found that a difference between the dimensions of structures on the section of the photomask, as represented in the image data, and the dimensions of structures on the section of the photomask is equal to or greater than a predetermined quality threshold, then structures on the section of the photomask can be modified to generate modified structures on the section of the photomask. Modifying the structures on the section of the photomask can include treating the photomask with an ion beam.One or more of the steps mentioned in this section can be repeated until a difference between the dimensions of the structures on the section of the photomask as represented in the image data and the dimensions for structures on the section of the photomask is less than the predetermined quality threshold, or until a termination criterion is met.

[0027] The disclosure includes further developments of the method with features that are described in connection with the mask inspection device or the EUV camera according to the invention. The invention includes further developments of the mask inspection device and further developments of the EUV camera that are described in connection with the method according to the invention.

[0028] The invention is described below by way of example with reference to the accompanying drawings and advantageous embodiments. The drawings show: Fig. 1: a schematic representation of a mask inspection device according to the invention; Fig. 2: a schematic representation of a photomask; Fig. 3: a perspective view of an EUV camera according to the invention; Fig. 4: A schematic representation of aspects of the EUV camera from Fig. 3; Fig. 5: a schematic representation of a photomask and an image of the photomask according to the invention; Fig. 6: a schematic representation of steps of the method according to the invention; Fig. 7, Fig. 8: Views accordingly Fig. 6 in alternative embodiments of the invention.

[0029] With a Fig. Microlithographic photomasks 17 can be examined using the mask inspection system shown in Figure 1.

[0030] Microlithographic photomasks 17 are generally intended for use in a microlithographic projection exposure system (not shown). In the microlithographic projection exposure system, the photomask 17 is illuminated with extreme ultraviolet (EUV) radiation with a wavelength of, for example, 13.5 nm to image a structure formed on the photomask 17 onto the surface of a lithographic object in the form of a wafer. The wafer is coated with a photoresist that reacts to the EUV radiation. The mask inspection device is used to check whether the photomask meets the specifications and is free of contaminants.

[0031] The mask inspection device is designed according to Fig. 1. The photomask 17 is arranged such that an EUV beam path 15 emanating from an EUV radiation source 14 is directed onto the photomask 17 via an illumination system 16. The illumination system 16 shapes the EUV radiation into a beam that illuminates an inspection area 20 on the surface of the photomask 17 with uniform brightness. The inspection area 20, which is small in relation to the area of ​​the photomask 17, is shown in a representation not to scale in Fig. Figure 2 illustrates this. The illuminated area 20 can, for example, have dimensions of 0.5 mm x 0.8 mm. The edge lengths of the photomask 17 can, for example, be between 100 mm and 200 mm. A field stop is arranged in the illumination system 16, which limits the illuminated area to the examination field 20 on the surface of the photomask 17. An XY positioner 26 allows the photomask to be moved in the XY plane to bring different examination fields 20 into the area of ​​the EUV beam path.

[0032] The EUV beam path 15, reflected at the photomask 17, continues via a projection lens 22 to an EUV camera 23, which is equipped with an image sensor 24. The projection lens maps the inspection field 20 of the photomask 17 onto the image sensor 24 of the EUV camera 23. The EUV radiation source 14, the illumination system 15, the photomask 17, the projection lens 22, and the EUV camera 23 are arranged in a vacuum housing 40, in which a negative pressure is maintained during operation of the mask inspection device.

[0033] The EUV radiation source 14 is a plasma radiation source in which EUV radiation with a wavelength of 13.5 nm is emitted from a plasma. Tin is a medium suitable for generating a plasma for emitting such EUV radiation. To generate the plasma, a droplet of the medium can be exposed to a laser beam.

[0034] The illumination system 16 and the projection lens 22 can include mirrors that reflect the EUV radiation. These mirrors can be designed as EUV mirrors, exhibiting particularly high reflectivity for EUV radiation. The optical surface of the EUV mirrors can be formed by a highly reflective coating. This can be a multilayer coating, in particular a multilayer coating with alternating layers of molybdenum and silicon. With such a coating, approximately 70% of the incident EUV radiation can be reflected.

[0035] The projection lens 22 has a magnification factor of more than 100. In order to fully capture the image generated by the examination field 20 of the photomask 17, the area of ​​the image sensor 24 is larger than the area of ​​the examination field 20, corresponding to the magnification factor. The image sensor 24 can, for example, have dimensions on the order of 100 mm to 200 mm. The image sensor 24 comprises a plurality of pixels 31, which span a pixel array 50 in a scan direction 32 and a cross-scan direction 33.

[0036] The EUV camera 23 includes, according to Fig. 4. A control unit 30 communicates with the image sensor 24. The control unit 30 controls the image sensor 24, among other things to determine the times at which the image sensor 24 is exposed to take an image. In each pixel 31, the amount of incident EUV radiation is then registered and converted into a corresponding number of free charge carriers. Image data can be obtained by reading the number of charge carriers for each pixel 31.

[0037] The image sensor 24 comprises a plurality of pixel rows 36, each pixel row 36 extending in the scan direction 32 over the entire length of the image sensor 24. The mutually parallel pixel rows 36 span the width of the image sensor 24 in the cross-scan direction 33.

[0038] The image sensor 24 is read out by moving the charge carriers generated by a pixel 31 in each pixel row 36 from pixel to pixel in the scan direction 32. With each movement step, the charge carriers from the last pixel of a pixel row 36 (in Fig. 4 (far left) is moved into a readout cell 37. The number of charge carriers is determined in readout cell 37. Information about the number of charge carriers in readout cell 37 is transmitted as image information to the control unit 30.

[0039] The image sensor 24 can be configured such that, in a single readout step, the charge carriers in all pixel rows 36 are simultaneously shifted by one pixel 31, so that charge carriers for each pixel row 36 are transferred to a corresponding readout cell 37. Image data can be acquired through a multitude of readout steps, from which an image spanned in the scan direction 32 and in the cross-scan direction 33 can be generated.

[0040] The EUV camera 23 is designed according to the invention to acquire image data from the photomask 17, which has a lower resolution in the scan direction 32 than in the cross-scan direction 33. Fig. Figure 5 shows a section 20 of the photomask 17 and an image taken of the section 20. The image was generated from image data 34 acquired with the image sensor 24. The image data 34 is not shown to scale; in reality, an image generated from the image data 34 is generally much larger than the depicted section 20 of the photomask 17. Fig. Figure 5 shows that the aspect ratio of the image generated from image data 34 does not match the depicted section 20. Since the image resolution in the scan direction 32 is lower than in the cross-scan direction 33, the section 20 and the structures 38 present in the section 20 are compressed in the scan direction 32.

[0041] The image sensor 24 is designed as a TDI sensor (Time Delay and Integration), as shown by Fig. Section 6 will be explained in more detail. Fig. Figure 6(A) shows a section of a pixel row 36 adjacent to the readout cell 37. In the two rightmost pixels 31, a number of charge carriers have accumulated, corresponding to a structure 38 on the photomask 17. The structure 38 is schematically indicated by a combination of a circle and a cross. During image acquisition, the photomask 17 is moved by the XY positioner 26 in a scan direction 32 that is parallel to the X direction. The movement of the photomask 17 relative to the projection lens 22 results in the image of the photomask 17 generated on the image sensor 24 also being moved relative to the image sensor 24. The direction in which the image on the image sensor 24 is moved when the photomask 17 is moved in the scan direction 32 is also referred to as the scan direction 32, even though the two directions are not necessarily parallel to each other in space.In the cross-scan direction 33, which forms a right angle with the scan direction 32 in the plane of the image sensor 24, the position of the image of the photomask 17 relative to the image sensor 24 remains unchanged.

[0042] The control unit 30 controls the image sensor 24 such that the speed at which the charge carriers are moved from pixel to pixel corresponds to the speed at which the image of the photomask 17 moves relative to the image sensor 24. Fig. Figure 6 shows the displacement of charge carriers from pixel to pixel in several steps (A) to (G). The exposure process continues over this time period, so the number of charge carriers increases continuously, which is indicated by a thickening line for the circle and the cross. In step (F), the first transfer of charge carriers belonging to structure 38 to the readout cell 37 takes place. The charge carriers are collected there for one step, so that in step (G), the charge carriers from the next pixel 31 are additionally transferred to the readout cell 37. Only the sum of the charge carriers from the two pixels 31 is transmitted to the control unit 30. This provides image information by determining the number of charge carriers in a pixel row segment 49 whose length is greater than the distance between two adjacent pixel rows 36.

[0043] The control unit 30 generates image data 34 based on the transmitted number of charge carriers by storing the number of charge carriers along with other information. This additional information includes the pixel row 36 in which the charge carriers were generated and the time at which the read cell 37 was read. The image data 34 is stored in a memory module 35 of the control unit 30. The amount of image data 34 is halved compared to a conventional method in which image information is stored individually for each pixel.

[0044] In Fig. Figure 7 shows a variant in which, in each step (A) to (G), the charge carriers transferred to the readout cell 37 are read out, and information about the number of charge carriers is transmitted to a digital module 39. In the digital module 39, the number of charge carriers determined in two successive readout processes is added together. Only the calculated sum is transmitted to the control unit 30. The amount of image data 34 to be processed can thus be reduced to the same extent as in a method in which the charge carriers from two pixels 31 are collected directly in the readout cell 37.

[0045] The control unit 30 can be configured to switch the EUV camera 23 between a first operating mode and a second operating mode. In the first operating mode, as described, a sum is calculated in the digital module 39 for each pair of pixels 31 before data is transmitted to the control unit 30. In the second operating mode, the digital module 39 can be deactivated, so that each number of charge carriers determined by a read cell 37 is transmitted to the control unit 30. This makes it possible, if required, to generate image data 34 whose resolution in the scan direction 32 is the same as the resolution in the cross-scan direction 33. In the second operating mode, it is accepted that the amount of data to be processed doubles compared to the first operating mode.

[0046] In the embodiment according to Fig. In the illustrated embodiment, pixels 31 are not square, but rectangular. The longer side of the rectangle is aligned parallel to the scan direction 32, and the shorter side of the rectangle is aligned parallel to the cross-scan direction 33. In the illustrated embodiment, the length 40 of a pixel 31 is twice the width 41 of the pixel.

[0047] Other aspect ratios between the length 40 and the width 41 of a pixel 31 are possible. In particular, the aspect ratio of the pixel 31 can be matched to the anamorphic imaging scales with which the photomask 17 is projected onto a lithographic object in an associated microlithographic projection exposure system.

[0048] The projection exposure system can achieve an image scale β in the scan direction. y have, which differs from the image scale β x differs in the cross-scan direction. In one embodiment, both imaging scales β are the same. x , β yof projection system 20 at (β x , β y ) = (+ / - 0.25, + / - 0.125). A magnification β of 0.25 corresponds to a reduction in the ratio of 4:1, while a magnification β of 0.125 results in a reduction in the ratio of 8:1. A positive sign for the magnification β indicates a magnification without image inversion, a negative sign indicates a magnification with image inversion.

[0049] In the example mentioned, the image scale in the cross-scan direction is twice as large as the image scale in the scan direction. A pixel 31 of the image sensor 24, tuned to the anamorphic image scales of the microlithographic projection exposure system, has a length 40 that is twice as large as its width 41. With a different ratio of the anamorphic image scales β x , β y The ratio of length 40 to width 41 of a correspondingly adapted pixel 31 changes accordingly.

[0050] The anamorphic imaging scales β x , β y The microlithographic projection exposure system is also reflected in the photomask 17. Structures that are intended to have the same size on the lithographic object in the scan direction and in the cross-scan direction are found on the photomask 17 in a compressed form. A photomask 17 in which this is the case is referred to as an anamorphic photomask 17. The method according to the invention can be carried out on an anamorphic photomask 17.

[0051] In Fig.Due to the rectangular shape of pixel 31, the structure 38 of the photomask 17, which in the preceding embodiments is mapped onto two pixels 31, fits onto a single pixel 31. The total number of charge carriers belonging to this structure 38 is transferred to the readout cell 37 in step (E). The number of image data 34 to be processed is reduced by half compared to a method in which the structure 38 is mapped onto two square pixels and the image data obtained with the pixels are stored individually.

Claims

[1] Method for operating a mask inspection device, wherein EUV radiation is directed onto a photomask (17) and wherein EUV radiation reflected from the photomask (17) is directed via a projection lens (22) onto an image sensor (24) of an EUV camera (23) so that the photomask (17) is imaged onto the image sensor (24), wherein the photomask (17) is moved in a scan direction (32) while the image sensor (24) is exposed, wherein image data are acquired with the image sensor (24) which have a different resolution in the scan direction (32) than in a cross-scan direction (33), and wherein a compressed image (34) of the photomask (17) is generated from the image data. [2] Method according to claim 1, wherein the image data obtained with the image sensor (24) have a higher resolution in cross-scan direction (33) than in scan direction (32). [3] Method according to claim 1 or 2, wherein charge carriers generated by incident EUV radiation in the image sensor (24) are moved within a pixel row (36) from pixel (31) to pixel (31) before the number of charge carriers is read out. [4] Method according to claim 3, wherein the pixel rows (36) of the image sensor (24) are aligned in the scanning direction (32). [5] Method according to claim 3 or 4, wherein the displacement speed at which the charge carriers are moved within the pixel row (36) is matched to the scan speed at which the photomask (17) is moved in the scan direction (32). [6] Method according to any one of claims 3 to 5, wherein image information is obtained by determining the number of charge carriers in a pixel row section (49), wherein the length of the pixel row section (49) is greater than the distance between two adjacent pixel rows (36). [7] Method according to any one of claims 1 to 6, wherein the image sensor (24) has a plurality of pixels (31) and wherein the length (40) of the pixels (31) is greater than the width (41) of the pixels (31). [8] Method according to claim 7, wherein the length (40) of the pixels (31) extends parallel to a pixel row (36) of the image sensor (24). [9] Method according to claim 7 or 8, wherein the length (40) of the pixels (31) is twice as large as the width (41) of the pixels (31). [10] Method according to any one of claims 1 to 9, wherein when reading the image sensor (24) the charge carriers of neighboring pixels (31) of a pixel row (36) are added. [11] Method according to any one of claims 1 to 9, wherein in a first operating mode of the EUV camera (23) image information is generated by counting the charge carriers of more than one pixel (31) of the image sensor (24) and wherein in a second operating mode image information is determined based on the number of charge carriers of individual pixels (31). [12] Method according to any one of claims 1 to 11, wherein an anamorphic photomask (17) is imaged onto the image sensor (24). [13] Method according to claim 12, wherein the anamorphic photomask (17) is non-anamorphically mapped onto the image sensor (24). [14] Mask inspection device comprising an EUV camera (23), a positioning device (26) for a photomask and a projection lens (22) for imaging the photomask (17) onto an image sensor (24) of the EUV camera (23), wherein the positioning device (26) is designed to move the photomask (17) in a scan direction (32) while the image sensor (24) is exposed, wherein the EUV camera (23) is designed to acquire image data which has a different resolution in the scan direction (32) than in a cross-scan direction (33). [15] Mask inspection device according to claim 14, wherein the image data obtained with the image sensor (24) in cross-scan direction (33) have a higher resolution than in scan direction (32). [16] Mask inspection device according to claim 14 or 15, wherein the pixel rows (36) of the image sensor (24) are aligned in the scan direction (32). [17] Mask inspection device according to one of claims 14 to 16, wherein image information is obtained by determining the number of charge carriers in a pixel row section (49), wherein the length of the pixel row section (49) is greater than the distance between two adjacent pixel rows (36). [18] Mask inspection device according to one of claims 14 to 17, wherein the image sensor (24) has a plurality of pixels (31) and wherein the length (40) of the pixels (31) is greater than the width (41) of the pixels (31). [19] Mask inspection device according to claim 18, wherein the length (40) of the pixels (31) extends parallel to a pixel row (36) of the image sensor (24). [20] Mask inspection device according to claim 18 or 19, wherein the length (40) of the pixels (31) is twice as large as the width (41) of the pixels (31). [21] Mask inspection device according to one of claims 14 to 20, wherein the EUV, (23) is designed to obtain image information by adding the charge carriers of neighboring pixels (31) of a pixel row (36) when reading the image sensor (24). [22] Mask inspection device according to one of claims 14 to 20, wherein the EUV camera (23) has a first operating mode and a second operating mode, wherein in the first operating mode image information is generated by counting the charge carriers of more than one pixel (31) of the image sensor (24), and wherein in the second operating mode image information is determined based on the number of charge carriers of individual pixels (31). [23] Mask inspection device according to one of claims 14 to 22, further comprising a photomask (17), wherein the photomask (17) is an anamorphic photomask (17). [24] Mask inspection device according to claim 23, wherein the projection lens (22) is designed to project the anamorphic photomask (17) non-anamorphically onto the image sensor (24). [25] EUV camera for a mask inspection device according to one of claims 14 to 24, comprising an image sensor (24) with a pixel array spanned by a plurality of pixel rows (36), wherein the EUV camera (23) is designed to obtain image information for an image of a photomask by determining the number of charge carriers in a pixel row section (49), wherein the length of the pixel row section (49) is greater than the distance between two adjacent pixel rows (36). [26] Computer program product or set of computer program products, comprising program parts which, when loaded into a computer or into interconnected computers connected to a mask inspection device according to any one of claims 14 to 24, are designed to carry out the method according to any one of claims 1 to 13.

Images