Filters for separating EUV useful light from stray light and / or particles carried along with the EUV useful light.

Abstract

A filter (8) serves to separate EUV useful light from stray light and / or particles carried along with the EUV useful light. The filter (8) has a filter body (24) designed as a carbon nanotube (CNT) membrane. The EUV transmission of the filter body (24) varies over a range (27) of the filter area of ​​the filter body (24) between a maximum and a minimum EUV transmission. The maximum EUV transmission is at least 10% greater than the minimum EUV transmission. This results in a filter that ensures improved guidance of EUV useful light for use, for example, in a mask inspection system.

Description

[0001] The invention relates to a filter for separating EUV useful light from stray light and / or particles carried along with the EUV useful light. The invention further relates to a method for manufacturing such a filter. It also relates to an optical system with such a filter and a metrology system with such an optical system.

[0002] Such a metrology system or mask inspection system is known from US 10,042,248 B2, DE 102 20 815 A1 and WO 2012 / 101269 A1.

[0003] It is an object of the present invention to improve the guidance of EUV useful light for use, for example, in a mask inspection system.

[0004] This problem is solved according to the invention by a filter having the features specified in claim 1.

[0005] According to the invention, it has been recognized that the use of a CNT membrane makes it possible, on the one hand, to ensure a high EUV throughput, while on the other hand, achieving the desired separation of the EUV useful or illumination light from stray light of a different wavelength, for example, from the pump light of a plasma light source, and / or from entrained particles. A maximum transmission of the CNT membrane in the range of more than 90% is achievable. In addition, CNT membranes can be designed with a longer service life compared to conventional filters when used to separate EUV useful light from stray light and / or particles. Stray light wavelengths can be in the DUV range, the UV range, or even the IR range.

[0006] The CNT membrane can exhibit diffraction properties. The CNT membrane can contain carbon nanotubes arranged in a lattice structure.

[0007] The maximum EUV transmission of the filter body can be at least 1% greater than the minimum EUV transmission across the entire range of filter area variations. Depending on the filter design, the maximum EUV transmission can also be at least 10% greater than the minimum EUV transmission. The difference between the maximum and minimum EUV transmissions across the entire range of filter area variations can be even greater.

[0008] The transmission variation range of the filter body allows for the adjustment of illumination parameters of the EUV (European Ultraviolet) light source across the object field, in particular the compensation of object-field-dependent illumination influences imposed on the EUV illumination light via an optical system to which the filter belongs. Specifically, a shift in illumination intensity across an object field coordinate—that is, a systematic object-field dependence of a variation in illumination intensity across an illumination pupil—can be corrected or compensated for by means of a corresponding transmission variation of the filter. For example, a desired balance between the illumination poles of a dipole or multipole illumination setup can be achieved in this way.

[0009] Alternatively or additionally, the transmission variation range of the filter body can be used to adjust the illumination parameters of the EUV useful light in an illumination pupil and / or in an imaging pupil of an optical system to which the filter belongs. For example, when using the filter in an optical system of a metrology system to examine an object, such as a lithography mask, the filter can be used in an illumination pupil plane and / or in an imaging pupil plane.

[0010] An embodiment according to claim 2 results in a variation range that exists at the filter location where it is used for compensation or correction purposes. In remaining areas of the filter surface beyond the variation range, the EUV transmission can then be constant. Several filter sections with a constant transmission profile across the surface can exist, and EUV transmissions can differ between these filter surfaces.

[0011] An area of ​​the filter surface through which the EUV illuminant passes can coincide with the variation range and, in particular, lie within the variation range. Alternatively, any filter sections beyond the variation range with constant EUV transmission can also be illuminated by the EUV illuminant.

[0012] Depending on the design of the filter, the range of variation can also cover the entire filter area, i.e., be as large as the entire filter area.

[0013] A gradient according to claim 3 can have a gradient direction that runs parallel or perpendicular to a meridional plane of an optical system in which the filter can be used. The gradient direction can lie in a fold plane of a mirror beam path of the optical system or run perpendicular to this fold plane. Such an orientation of the filter results in a particularly advantageous compensation or correction effect.

[0014] A gradient profile according to claim 4, which leads to a linear EUV transmission variation over the variation range of the filter area of ​​the filter, has proven to be particularly advantageous. Alternatively, the gradient can also have a different profile, resulting in a non-linear transmission dependence over the gradient direction.

[0015] Another task is to specify a manufacturing process for a filter according to the invention.

[0016] This further problem is solved according to the invention by a method with the features specified in claim 5.

[0017] The advantages of the method according to claim 5 correspond to those already explained above with reference to the filter.

[0018] In the manufacturing process according to claim 6, it was discovered that a variation in transmission can be achieved by varying the CNT deposition. The result of the varying CNT deposition can be a varying CNT surface density and / or a varying CNT volume density on the substrate.

[0019] During the manufacturing process, the CNT membrane can be separated from the carrier body.

[0020] The deposition variants according to claims 7 to 9, which may also be used in combination, ensure a correspondingly varying CNT deposition on the carrier body.

[0021] When using a movable metering element according to claim 8, its movement can be synchronized with a deposition application across the filter surface. For this purpose, a displacement drive that interacts with the metering element can be in signal communication with a CNT deposition system via a control device.

[0022] A deposition filter body can be designed like a mask with defined passage areas.

[0023] A varying coating according to claim 10 represents an alternative or additional variant for producing a varying EUV transmission.

[0024] The advantages of an optical system according to claim 11 and a metrology system according to claim 15 correspond to those already explained above with reference to the filter according to the invention and the manufacturing process. The optical system can, for example, also be used in a mask inspection system, in particular in an actinic system.

[0025] The object holder is specifically designed for scanning, particularly for line-by-line scanning, the repositioning of the object under investigation. The detector can be a CCD or a CMOS detector. The detector can include at least one TDI (Time Delay Integration) sensor.

[0026] The metrology or inspection system can be a system for actinic mask or wafer inspection.

[0027] An embodiment of the invention is explained in more detail below with reference to the drawing. This drawing shows: Fig. 1 schematically in a meridional section a mask inspection system for lithography masks for use with EUV illumination light with an illumination system comprising a filter for separating EUV useful light from false light carried with the EUV useful light and / or from particles carried with the EUV useful light; Fig. 2 a top view of the filter, illustrating a transmission profile of an EUV transmission from a filter body over a filter surface of the filter; Fig. 3 in a diagram showing the course of EUV transmission over a path in the Fig. 2 and Fig. 3 vertical position coordinates; Fig. 4 schematically depicting momentary situations A to E during the execution of a process for manufacturing the filter; Fig. 5 schematically the manufactured filter in a top view, with the location coordinate being that of the Fig. 2 and Fig. 3 corresponds to a density ρ of carbon nanotubes (CNTs) within the filter body designed as a carbon nanotube membrane, which is illustrated in a diagram; Fig. 6 a schematic top view of a grid with the position coordinate according to Fig. 5 varying mesh size or grid constant, which can be used in the manufacturing process to generate the EUV transmission of the filter that varies over this spatial coordinate; Fig. 7 schematically shows a section of a deposition nozzle and a movable metering body for generating a varying CNT deposition on the carrier body in a variant of the manufacturing process for the filter; Fig. 8 in one to Fig. 7. Similar representation: the deposition nozzle with a deposition filter body with a deposition filter aperture varying over a nozzle surface of the deposition nozzle to generate a [missing information] according to the spatial coordinate. Fig. 2, Fig. 3 and Fig. 5 varying deposition filter bandwidths; and Fig. 9 a transmission profile of the deposition filter body according to Fig. 8 for the CNTs, again depending on the location coordinates according to the Fig. 2, Fig. 3 and Fig. 5.

[0028] An illumination optic 1 is part of an optical system 2 of a mask inspection system or metrology system 2a for use with EUV illumination light 3. A beam path of the illumination light 3 is in the Fig. Figure 1 illustrates the illumination optics via marginal rays and a main ray. The illumination light 3 illuminates an object field or illumination field 4 of the mask inspection system 2a.

[0029] The illumination 3 is generated by an EUV light source 5 in a source area 6. The light source 5 can generate EUV useful radiation in a wavelength range between 2 nm and 30 nm, for example in the range between 2.3 nm and 4.4 nm or in the range between 5 nm and 30 nm, for example at 13.5 nm.

[0030] Light source 5 is designed as a plasma light source. This could be, for example, a laser-produced plasma (LPP) source or a discharge-produced plasma (DPP) source. Such plasma sources are generally known as light sources for EUV projection systems. The pulse frequency of light source 5 can be in the kHz range.

[0031] To facilitate spatial relationships, a Cartesian xyz coordinate system is used below. The x-axis is perpendicular to the drawing plane. Fig. 1 and runs into it. The y-axis runs in the Fig. 1 horizontally to the left and the z-axis runs in the Fig. 1 vertically upwards. A meridional plane of the optical system 2, which coincides with a fold plane of a beam path of the EUV illumination light 3, coincides with the yz plane.

[0032] After emission by the light source 5, the illumination light 3 first passes through a useful light filter 8, which in an operating position is arranged in the beam path of the illumination light 3 between the source volume 6 and a first ellipsoidal mirror IL1 of the illumination optics 1. Details of the filter 8 are described below with reference to the Fig. Section 2 ff. explains this further. The useful light filter 8 can be one of several filters that, for example, are stored in a filter magazine in the metrology system 2a. Another useful light filter can be arranged in a standby position outside the illumination light beam path of the illumination optics 1. The useful light filters 8 can have the same transmission characteristics, in which case a change between the useful light filters can be made if a degradation of the filter effect of the operating useful light filter 8 is observed. Alternatively, the useful light filters can also have different filter characteristics and, for example, transmit different useful light wavelength ranges into the subsequent illumination light beam path or be optimized to filter out different components of stray light.

[0033] The useful light filters are designed in such a way that they filter out, in particular, pump light carried in the illumination light beam path, which was used in the source volume 6 for useful light generation, and / or particles carried in the illumination light beam path that are generated during useful light generation.

[0034] After passing through filter 8 and mirror IL1, the illumination light 3 first passes through an aperture diaphragm 9, which limits the beam of the illumination light 3 at its edges. Following this, the illumination light beam 3 is directed towards a beam homogenizing element 11 of the illumination optics 1. Mirror IL1 serves as a coupling optic 10 for coupling the illumination light 3 into the beam homogenizing element 11. The beam homogenizing element 11 can be a mixed optic with at least one, and for example, two faceted mirrors arranged downstream of each other in the beam path of the EUV illumination light 3. Alternatively or additionally, the beam homogenizing element 11 can be designed as a hollow waveguide.

[0035] Between the source volume 6 and the beam homogenizing element 11, typically after the first mirror IL1 of the illumination optics 1, the illumination light 3 passes through an opening in a wall of a vacuum chamber VK, which is located in the Fig. 1 is indicated in the illumination light beam path between the mirror IL1 and the illumination light aperture diaphragm 9.

[0036] The aperture diaphragm 9 limits a numerical aperture of the illumination beam 3 emitted from the source area 6, also to a value of the numerical aperture in the range between 0.02 and 0.2, for example in the range between 0.07 and 0.15 or also in the range between 0.05 and 0.08. Alternatively or additionally to the aperture diaphragm 9, an aperture-limiting diaphragm can be arranged between the beam homogenizing element 11 and a subsequent optical component of the illumination optics 1, as shown in the Fig. 1 is indicated in 9b. It is also possible to arrange such a further aperture stop in the beam path of the illumination light 3 after the beam homogenizing element 11 between two downstream optical components of the illumination optics 1.

[0037] The ellipsoidal mirror IL1 serves to image the source region 6 of the EUV light source 5 into an entrance aperture 12 in an entrance plane 13 of the beam homogenizing element 11. A first focal point of the ellipsoidal mirror IL1 is thus located in the source region 6, and a second focal point of the ellipsoidal mirror IL1 is located in the entrance aperture 12. The ellipsoidal mirror IL1 focuses the illumination beam 3 into the entrance aperture 12 in the entrance plane 13 of the beam homogenizing element 11. The entrance-side numerical aperture of the illumination beam 3 at the entrance aperture 12 can be in the range of 0.02 to 0.2, for example, in the range of 0.05.

[0038] The angle of incidence of a central main ray of the illumination beam 3 on the coupling mirror IL1 can be in the range between 10° and 20°. The ellipsoidal mirror IL1 can be a normal incidence (NI) mirror, but can also be configured as a grazing incidence (GI) mirror.

[0039] The inlet opening 12 and an outlet opening 14 of the beam homogenizing element 11 are each square or rectangular with typical dimensions in the range of 0.5 mm to 5 mm, and, for example, between 0.5 mm and 2 mm, or between 0.5 mm and 1 mm. The aspect ratio of the inlet opening 12 and an equally sized outlet opening 14 of the beam homogenizing element 11 for the illuminating light 3 in an exit plane 15 is between 0.5 and 2. Typical sizes of the inlet opening 12 and the outlet opening 14 of the beam homogenizing element 11 are, for example, 0.5 mm x 1.0 mm, 0.75 mm x 0.75 mm, 1.0 mm x 2.0 mm, or 1.5 mm x 2.0 mm.

[0040] The beam homogenizing element 11 has a typical length perpendicular to the planes 13 and 15, i.e. along a principal beam direction of the illumination light 3, in the range between 50 mm and 500 mm, e.g. in the range between 50 mm and 150 mm, in particular in the range between 50 mm and 100 mm.

[0041] An angle between a normal to the entrance plane 13 of the beam homogenizing element 11 and the main beam of the illumination beam 3 incident into the entrance aperture 12 can be 0° or alternatively can be different from 0° and, for example, be in the range between 0° and 1.5°, for example between 0.25° and 0.75° and, in particular, in the range of 0.5°.

[0042] A ratio of the distance between the inlet plane 13 and the outlet plane 15, and a size or typical diameter of the inlet opening or outlet opening 12, 14, lies in the range between 50 and 1000 and can, for example, lie in the range between 50 and 200.

[0043] A downstream imaging output coupler optic 16 with two mirrors IL2, IL3, located after the beam homogenizing element 11, images the exit aperture 14 of the beam homogenizing element 11, which lies in the exit plane 15, into the illumination field 4 in an object plane 17. The image-side numerical aperture of this imaging can be in the range of 0.05 to 0.2.

[0044] In the illustrated embodiment, the output coupling mirror optic 16 has exactly two mirrors, namely mirrors IL2 and IL3. The aperture diaphragm described above, which may be used after the beam homogenizing element 11, can be arranged between the beam homogenizing element 11 and mirror IL2 or between mirrors IL2 and IL3.

[0045] The output coupler 16 is designed in the manner of a Wolter telescope, specifically a Wolter optic of type I. Such Wolter optics are described in J.D. Mangus and J.H. Underwood, "Optical Design of a Glancing Incidence X-ray Telescope," Applied Optics, Vol. 8, 1969, page 95, and the references cited therein. A hyperboloid can also be used in such Wolter optics instead of a paraboloid. Such a combination of an ellipsoidal mirror with a hyperboloid mirror also constitutes a Wolter optic of type I.

[0046] An embodiment of the output coupling mirror optics 16 is described in US 10,042,248 B2.

[0047] The imaging factor β1 of the input-coupling mirror optics 10 can range from 0.1 to 50, meaning it can reduce the image by a factor of 10 to magnify it by a factor of 50. The imaging factor β2 of the output-coupling mirror optics 16 can range from 0.02 to 10, meaning it can itself reduce the image by a factor of 50 to magnify it by a factor of 1. The product β1, β2 of the two imaging factors in the illumination optics 1 can range from 0.25 to 10.

[0048] In object plane 17, a reticle 18 to be inspected is arranged as the object or mask to be inspected, held by a reticle holder 19. The reticle holder 19 is mechanically connected to a reticle displacement drive 20, via which the reticle 18 is displaced along an object displacement direction y during a mask inspection. This enables a scanning displacement of the reticle 18 in object plane 17.

[0049] The illumination field 4 has a typical dimension in the object plane 17 that is less than 0.5 mm. In the illustrated embodiment, the extent of the illumination field 4 is 0.5 mm in the x-direction and 0.5 mm in the y-direction.

[0050] The x / y aspect ratio of the illumination field 4 matches the x / y aspect ratio of the exit aperture 14.

[0051] The illumination field 4, or a part of the illumination field 4 which then represents an object field, is projected by a projection optic PO onto an image field 21 in an image plane 22. The image field 21 can have a size in the range of 150 mm x 250 mm. The shorter image field extent runs along the scan direction y.

[0052] The projection optics PO have numbered mirrors M1 and M2 in the imaging beam path, thus comprising a total of two mirrors. Depending on the design of the projection optics PO, the number of mirrors can also be greater than two. An aperture diaphragm 9b is arranged in an entrance pupil plane EP of the projection optics PO, which lies in the imaging beam path of the illumination / imaging light between the reflecting reticle 18 and the first mirror M1. This aperture diaphragm 9b can also serve to define any internal obscuration of the projection optics PO.

[0053] The mirrors M1 and M2 of the projection optics PO are designed as NI mirrors with an angle of incidence of the illumination and imaging light 3 of less than 45°.

[0054] An illumination light beam path of illumination light 3 for illuminating reticulum 18 and an imaging light beam path of projection optic PO for imaging the object field 4 into the image field 21 intersect in a crossing region. This crossing region lies in the area of ​​the entrance pupil plane EP of projection optic PO. The imaging light beam path intersects here with the illumination light beam path between the exit aperture 14 and the mirror IL2 of illumination optic 1, as well as between the mirrors IL2 and IL3 of illumination optic 1.

[0055] As an alternative to the depicted two-mirror configuration of the projection optic PO, the number of mirrors in the projection optic PO can also be greater than 2 and can be, for example, 4 or 6. The object field 4 has a length of approximately 400 µm along the x-coordinate and approximately 300 µm along the y-coordinate.

[0056] The image field 21 is acquired by a detection device 23, e.g., by one or more CCD or CMOS cameras. For details of the imaging into the image field, reference is made to US 10,042,248 B2 and the references given in US 10,042,248 B2. The detection device 23 can also be implemented as a TDI (time delay integration) detection device with a plurality of TDI detectors. Such an implementation is explained in more detail below.

[0057] The mask inspection system 2a enables, for example, the inspection of a structure on reticulum 18. For this purpose, reticulum 18 can be scanned line by line in the xy-plane using the reticulum displacement device 20 until an entire surface of interest on reticulum 18 has been imaged by the projection optic PO of the mask inspection system 2a and inspected accordingly.

[0058] Fig. Figure 2 shows filter 8 in a top view. The x-coordinate of the Fig. 2 corresponds to that of the Fig. 1. The y-coordinate is the position coordinate spanning an arrangement plane of filter 8, which lies in the drawing plane of the Fig. 1 lies. A change of filter properties along this y-coordinate to Fig. 2 leads to a change in lighting properties along the object field coordinate y. Fig. 1. This object field coordinate y spans with the z-coordinate to Fig. 1. An incident plane of the EUV illumination light 3 upon reflection at the reticulum 18. The filter 8 has a filter base body 24, which is held by a filter frame 25.

[0059] The filter body 24 can, as in the Fig. As shown in section 2, the filter frame has a rounded edge contour. Other edge shapes are also possible. The filter frame 25 can, in turn, be used as shown in the Fig. 2 shown, have a square border, alternatively a rectangular or differently bordered border contour, for example a round border contour.

[0060] The filter body 24 is designed as a carbon nanotube (CNT) membrane. The CNTs are arranged along the y-coordinate with varying density ρ.

[0061] The filter base body 24 defines the total filter area of ​​the filter 8.

[0062] Overall, the basic filter body 24 is divided into three filter sections 26, 27, and 28, which follow each other in the y-direction. The two filter sections 26 and 28 located at the edges along the y-coordinate have a constant EUV transmission independent of the y-coordinate. This has the following properties in the Fig. 2. Field section 26 shown below has a minimum transmission value T. min (CNT density ρ maximum, absorption α for the EUV useful light maximum) and a maximum transmission value T via filter section 28 max (CNT density ρ minimal, absorption α for the EUV useful light 3 minimal). In the intermediate filter section 27, which represents a range of variation, there is a gradient of transmission between the values ​​T min at the transition to filter section 26 and T max at the transition to filter section 28.

[0063] The filter section 27, i.e. the range of variation, is smaller than the filter area 24.

[0064] This y-coordinate dependence for EUV transmission T and the associated parameters ρ and α is described in the Fig. Figure 3 illustrates this. Filter section 27 represents a range of variation of a filter surface of filter 8, in which the EUV transmission T ranges between the minimum EUV transmission T. min and the maximum EUV transmission T max varies. At the same time, over the variation range 27, the CNT density ρ varies between the maximum CNT density and the minimum CNT density ρ, and the EUV absorption varies concurrently between a maximum absorption and a minimum absorption α.

[0065] The maximum EUV transmission T max can, for example, be twice as large as the minimum EUV transmission T. min It is true that T max is at least 10% larger than T min Other relations in the range between 1.001 ≤ T max / T minValues ​​≤10 are possible, especially 1.01≤T max / T min ≤1.1.

[0066] Depending on the matching of the size of the variation range 27 to the size of a total beam diameter of the EUV illumination light 3 when passing through the filter 8, the area of ​​the filter surface 24 passed through by the EUV useful light 3 can coincide with the variation range 27 or lie within it, so that the image sections 26 and 28 with constant, gradient-free transmission profile are not affected by the EUV illumination light 3.

[0067] In variation range 27, the transmission gradient lies along a gradient direction that corresponds to the y-coordinate in the Fig. 2 and Fig. 3 agrees. This gradient direction y runs parallel to the yz meridional plane of optical system 2.

[0068] The transmission gradient over the variation range 27 is constant, so that there is a linear transmission profile between the values ​​T. max and T min in image section 27. In an alternative implementation of the filter 8, a non-linear transmission gradient can also be present over the variation range 27 in the gradient direction y, for example a parabolic transmission profile, a hyperbolic transmission profile, an exponential transmission profile or a logarithmic transmission profile.

[0069] Fig. 4 (4A to 4E) illustrates main steps A to E of a process for manufacturing a CNT membrane that is generally known from the prior art.

[0070] In step A, a carrier body 30 is prepared on which the CNTs are deposited during the further process.

[0071] In step B, CNTs 31 are depositioned using a CNT synthesis reactor 32, to which carbon-containing gas is supplied, via a deposition nozzle 33.

[0072] In step C, the CNT blanks 34 produced by deposition are removed from the carrier body 30.

[0073] In step D, the CNT blanks 34 are post-treated, for example by coating and / or irradiation and / or thermal treatment using a post-treatment device 35.

[0074] The result of the manufacturing process in step E is a self-supporting CNT membrane in the form of the filter body 24.

[0075] Fig. Figure 4 illustrates the course of a density ρ of the CNTs over the manufactured filter base body 24, with the three filter sections 26, 27 and 28 illustrated.

[0076] Fig. 6 shows in one of the Fig. 5 corresponding overhead view a grid 36 which is placed on the carrier body 30 in the area of ​​one of the filter base bodies 24 to be manufactured in the above step B of the manufacturing process.

[0077] The grid 36 has a varying mesh size d along the y-coordinate.

[0078] In grid section 26', where filter section 26 is produced during manufacturing, the mesh size d is the largest. In grid section 28', where filter section 28 is produced, the mesh size d is the smallest. In the intermediate grid section 27', there is a gradient of mesh size d between the maximum mesh size adjacent to grid section 26' and the minimum mesh size adjacent to grid section 28'. During CNT deposition in step B of the manufacturing process, grid 36 causes a CNT density ρ corresponding to the gradient shown. Fig. 5 results.

[0079] Fig. Figure 7 shows a variant of a disposition nozzle device 37, which in a variant of the manufacturing process according to Fig. 4 can be used. The deposition nozzle assembly 37 has a metering element 38 at the outlet of the deposition nozzle 33. This element can be displaced along the y-coordinate by means of a displacement drive 39. During manufacturing step B, the metering element 38 is moved by means of the displacement drive 39 synchronized to a deposition application over the filter base body 24, so that, for example, during deposition on the filter section 28, the metering element 38 throttles the deposition nozzle 33, whereas during CNT deposition on the filter section 26, a higher CNT density can reach the filter base body 24 due to the metering element 38 then releasing more of the deposition nozzle 33. The gradient profile of the CNT density ρ can be finely influenced, especially via the filter section 27, by means of a velocity profile of a displacement movement of the metering body 38 relative to the deposition nozzle 33.

[0080] Fig. Figure 8 shows another deposition nozzle assembly 40, which can be used in step B of a variant of the manufacturing process. A deposition filter body 41 is arranged in the area of ​​an outlet of the deposition nozzle 33 in the deposition nozzle assembly 40.

[0081] The deposition filter body 41 can be designed as a mask with defined passage areas for the passage of CNTs 31.

[0082] Fig. Figure 9 illustrates a transmission profile across the y-coordinate of the deposition filter body 41. This transmission profile can be achieved by varying the deposition filter aperture across filter sections of the deposition filter body 41. This transmission profile according to Fig. 9 is complementary to the one after Fig. 3, whereby in areas of low transmission of the deposition filter body 41, a high transmission of the useful light filter 8 ultimately results due to the resulting low CNT density ρ. Those filter sections 26' to 28' of the deposition filter body 41, which are used for the deposition production of the associated filter sections 26 to 28 of the filter base body 24, are in the Fig. 9 illustrates.

[0083] In another variant of the manufacturing process, particularly in the post-processing step D, a coating of the filter base body 24 can be applied, for example by means of a metal vapor, which varies in its transmission for the EUV useful light 3 over the variation range 27.

[0084] To prepare for operation of the mask inspection system 2a, a target transmission profile is specified for the EUV illumination light 3 via filter 8, depending on the desired object field illumination setting. Subsequently, a filter 8 is inserted into the beam path whose actual transmission profile corresponds to the specified target transmission profile. This target transmission profile can be used to compensate for a y-dependence of illumination parameters via the object field 4.

[0085] Subsequently, the object 18 is inspected with the EUV illumination light 3 and the object field 4, i.e. an illuminated section of the object 18, is imaged into the image plane 22 of the detection device 23 using the projection optics PO. QUOTES INCLUDED IN THE DESCRIPTION

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

[0000] US 10,042,248 B2 [0002, 0046, 0056] DE 102 20 815 A1

[0002] WO 2012 / 101269 A1

[0002] Cited non-patent literature

[0000] JD Mangus, JH Underwood “Optical Design of a Glancing Incidence X-ray Telescope”, Applied Optics, Vol. 8, 1969, page 95

[0045]

Claims

[1] Filter (8) for separating EUV useful light (3) from false light carried with the EUV useful light (3) and / or from particles carried with the EUV useful light (3), - with a filter body (24) designed as a carbon nanotube (CNT) membrane, - wherein an EUV transmission of the filter base body (24) varies over a variation range (27) of a filter surface of the filter base body (24) between a maximum EUV transmission and a minimum EUV transmission. [2] Filter according to claim 1, characterized in that the variation range (27) is smaller than the total filter area. [3] Filter according to claim 1 or 2, characterized by , that an EUV transmission profile over the variation range (27) exhibits a gradient along a gradient direction (y). [4] Filter according to claim 3, characterized by a constant gradient. [5] Method for manufacturing a filter according to any one of claims 1 to 4. [6] Method according to claim 5, characterized by , that to produce the filter base body (24) a deposition of CNTs on a carrier body (30) takes place which varies over the variation range (27) of the filter surface. [7] Method according to claim 6, characterized by , that the varying deposition is carried out using a grid (36) on the carrier body (30) with varying mesh size (d) of the grid (36). [8] Method according to one of claims 6 or 7, characterized by , that the varying deposition is carried out using a movable metering body (38) in the area of ​​a deposition nozzle (33) for the deposition of CNTs. [9] Method according to any one of claims 6 to 8, characterized by, that the varying deposition is carried out using a deposition filter body (41) in the area of ​​a deposition nozzle (33) for the deposition of the CNTs with a varying deposition filter aperture width over a nozzle area of ​​the deposition nozzle (33). [10] Method according to any one of claims 6 to 9, characterized by , that for the production of the filter base body (24) a coating of the filter base body (24) is applied which varies in its transmission for the EUV useful light (3) over the variation range (27) of the filter surface. [11] Optical system for guiding EUV useful light (3) between a light source (5) and downstream components, characterized by a filter (8) according to any one of claims 1 to 4. [12] Optical system according to claim 11, characterized by the EUV light source (5). [13] Optical system according to claim 11 or 12, characterized bya lighting optic (1) for guiding the EUV lighting light (3) to an object field (4) in which an object (18) to be illuminated with the EUV lighting light (3) can be arranged. [14] Optical system according to any one of claims 11 to 13, characterized by a projection optic for imaging an object field (4) into an image field (21) in which a detection device (23) can be arranged. [15] Metrology system - with an optical system according to one of claims 10 to 14, - with an object holder (19) for holding an object (18) to be examined in an object field (4), - with a detection device (23) arranged in an image field (21).

Images