Optical hollow waveguide component

Abstract

An optical hollow waveguide component (25), particularly for homogenizing EUV light, comprises two support elements (26) and two insert elements (28), which are particularly plate-shaped. The insert elements (28) are inserted between the support elements (26) such that a hollow waveguide (11) is formed between the insert elements (28). The hollow waveguide component (25) is particularly suitable for use in an illumination optic for a mask inspection system (1) for use with EUV illumination light. An optical system with such an illumination optic and a mask inspection system with the optical system are also described.

Description

[0001] The invention relates to an optical hollow waveguide component, in particular for homogenizing illumination light, for example EUV illumination light. The invention further relates to an illumination optic for a mask inspection system for use with EUV illumination light, comprising such a hollow waveguide component. The invention also relates to an optical system comprising such an illumination optic and a mask inspection system.

[0002] A mask inspection system is known, for example, from DE 10 2022 205 767 A1. EUV light used for illumination is homogenized using a hollow waveguide. The use of such hollow waveguides with EUV light is complicated by the requirements for the manufacturing precision of the hollow waveguide.

[0003] It is therefore the object of the present invention to improve an optical hollow waveguide, in particular with regard to its use for homogenizing EUV light, and in particular to provide an optical hollow waveguide that is easy and precise to manufacture.

[0004] This problem is solved according to the invention by an optical hollow waveguide component, in particular for homogenizing EUV light, with the features specified in claim 1.

[0005] The inventors recognized that inserting elements between support elements allows for more precise positioning of the insert elements. The hollow waveguide, and in particular its cross-section, is precisely defined. Specifically, the arrangement between the support elements enables planar contact between the support elements and the insert elements. This increases the angular accuracy of the relative positioning. Furthermore, holding forces are applied by the support elements primarily in a direction perpendicular to the support element surfaces that contact the insert elements, thus reducing lateral forces. The hollow waveguide component exhibits particularly high dimensional accuracy and is especially suitable for use with EUV light, for example, as a beam homogenizing element.

[0006] The hollow waveguide is formed as a cavity or space between the insert elements, in particular between the insert elements and the support elements. The hollow waveguide has an inlet opening arranged in an inlet plane and an outlet opening arranged in an outlet plane. The inlet plane and the outlet plane can, for example, be located in the region of the respective end faces of the insert elements. They are, in particular, parallel planes. The hollow waveguide extends along its longitudinal axis between the inlet opening and the outlet opening. The longitudinal axis of the hollow waveguide is, in particular, parallel to the direction of propagation of the beam of the illumination light to be homogenized. The longitudinal axis is, in particular, perpendicular to the inlet plane and the outlet plane.

[0007] The cross-section of the hollow waveguide is understood here and in the following as the cross-section perpendicular to the longitudinal axis of the hollow waveguide. The cross-section is defined by the insert elements, in particular by the insert elements and the support elements. Surfaces of the insert elements facing the hollow waveguide are also referred to here and in the following as boundary surfaces. The boundary surfaces of the insert elements delimit the hollow waveguide, in particular its cross-section.

[0008] The insert elements are arranged between the support elements. The insert elements are therefore to be understood as components inserted between the support elements. The support elements are thus spaced apart by the insert elements. The spacing between the support elements is precisely defined, in particular, by the insert elements.

[0009] The surfaces of the support elements facing the insert elements, and thus each other, are referred to here and in the following as facing support element surfaces or support element surfaces. These facing support element surfaces can partially define the cross-section of the hollow waveguide. In particular, the facing support element surfaces are parallel to each other.

[0010] The insert elements are arranged between the opposing surfaces of the support elements. The insert elements make contact with the surfaces of the support elements, particularly over a large area.

[0011] The confinement of the hollow waveguide between the end faces of the insert elements allows for a particularly simple and precise definition of the hollow waveguide geometry, especially its cross-section. An extent of the cross-section perpendicular to the opposing support element surfaces is determined, in particular, by the thickness of the insert elements in the region of their end faces. An extent of the cross-section parallel to the support element surfaces is determined, in particular, by the spacing of the end faces of the insert elements. The cross-section can, in particular, be rectangular.

[0012] A contour of the edge surfaces of the insert elements corresponds to at least a portion of a cross-sectional contour of the hollow waveguide. For example, the edge surfaces of the insert elements can form edge surfaces of the hollow waveguide. The edge surfaces bounding the hollow waveguide can run straight or otherwise along the respective cross-sectional contour regions, in particular they can be angled and / or curved.

[0013] The hollow waveguide can be bounded, in particular, by the edge surfaces of the insert elements and at least one of the support element surfaces. It is also possible that the hollow waveguide is bounded by the edge surfaces of the insert elements and the two opposing support element surfaces.

[0014] Because the hollow waveguide is bounded by the edge surfaces of the insert elements and, optionally, by at least one of the support element surfaces, any desired cross-sectional shape for the hollow waveguide can advantageously be realized. In particular, the hollow waveguide is not limited to rectangular cross-sections. The cross-section of the hollow waveguide can, for example, be triangular or polygonal, in particular triangular, square, pentagonal, or hexagonal. Curved cross-sectional contours are also possible.

[0015] For example, the edge surfaces of the insert elements can be parallel to each other. These parallel edge surfaces, together with the facing support element surfaces, can define a hollow waveguide with a rectangular cross-section. Alternatively, the edge surfaces can be perpendicular to the support element surfaces to form a rectangular hollow waveguide cross-section. The edge surfaces can also be at an angle of less than 90° to the support element surfaces, resulting in a hollow waveguide with a parallelogram-shaped cross-section.

[0016] It is also possible for the edge surfaces to be inclined to each other in a plane perpendicular to a longitudinal axis of the hollow waveguide. This allows, in particular, the formation of triangular or pentagonal cross-sections. For example, a triangular cross-section of the hollow waveguide can be formed by converging edge surfaces and one of the support element surfaces.

[0017] It is also possible for the edge surfaces to have one or more kinks or bends along the cross-sectional contour itself. For example, the edge surfaces, especially V-shaped ones, can have grooves. In this way, hexagonal or polygonal cross-sections can be easily created.

[0018] The flat application of the insert elements to the carrier element surfaces allows for particularly precise and stable manufacturing of transition areas between the edge surfaces and the carrier element surfaces. In particular, edge accuracy in the sub-micrometer range is achievable in the area of ​​the edge surfaces. The resulting transition areas do not impair transmission. This is especially advantageous for the homogenization of EUV light.

[0019] The fact that the insert elements rest against the surfaces of the support elements has the further advantage that the holding forces are distributed over a large area. Point-load application of holding forces, especially in the area of ​​the edges of the surface, and thus damage to these edges, is avoided.

[0020] Plate-shaped insert elements according to claim 2 offer the advantage of particularly simple and precise positioning. Transverse forces that could affect the distance between the edge surfaces are avoided. Preferably, the insert elements are plane-parallel plates. The opposing surfaces of the support elements are parallel to each other. The plate-shaped insert elements are also referred to here and in the following as plate elements.

[0021] Plate-shaped is understood to mean, in particular, that the insert elements have a significantly smaller extent in one direction than in the two directions perpendicular to it. The smallest extent is referred to here and in the following as the thickness of the plate elements. The thickness can be uniform across the entire plate element. Surfaces spaced apart by this thickness are, in particular, parallel to each other. Plate elements with two parallel surfaces spaced apart by a constant thickness are also referred to as plane-parallel plates.

[0022] Preferably, the plate-shaped insert elements are arranged between the support elements such that the support elements are spaced apart from each other by the thickness of the plate-shaped insert elements. This enables particularly good surface contact between the insert elements and the support elements.

[0023] The thickness of the plate elements corresponds in particular to an extension of the hollow waveguide cross-section in a direction perpendicular to the surfaces of the support elements.

[0024] The ratio of the width B of the insert elements to their thickness d according to claim 3 has proven to be particularly advantageous. The relatively large width ensures particularly precise positioning with a large contact area on the support element surfaces. Holding forces are distributed over a large area.

[0025] The main extent of the hollow waveguide cross-section according to claim 4 has proven particularly advantageous, especially with regard to the surface treatment of the edge surfaces. In practical applications of hollow waveguides, particularly in illumination optics for mask inspection systems, the cross-section of the hollow waveguide is rectangular with varying side lengths. The main extent corresponds to the longer side of the rectangle. By selecting the main extent according to the thickness of the insert elements, especially the thickness of plate-shaped insert elements, these elements exhibit the maximum possible thickness for the desired hollow waveguide cross-section in the area of ​​the side surface. This improves and simplifies the surface treatment in the area of ​​the edge surfaces. For example, coating the edge surfaces with an EUV-reflective material, especially ruthenium, is enhanced.The surfaces bounding the hollow waveguide, especially edges in the area of ​​the insert elements' boundary surfaces, can be manufactured with exceptional precision. The hollow waveguide component is particularly suitable for use with EUV light.

[0026] The positioning elements according to claim 5 ensure a particularly precise positioning of the insert elements relative to each other and especially also to the support elements.

[0027] The positioning elements can be arranged particularly in the area of ​​the outer surfaces of the hollow waveguide component, for example on the outer surfaces of the hollow waveguide component. For example, positioning grooves can be incorporated into the outer surfaces.

[0028] Alternatively or in addition to external positioning elements, positioning elements can also be integrated into the hollow waveguide being formed. For example, positioning spheres can be used, which are removed after positioning.

[0029] The arrangement of the positioning elements according to claim 6 on the end faces does not impair the contact of the insert elements with the surfaces of the support elements. The positioning elements are easily accessible. In this context, "end faces" refers in particular to the outer surfaces of the hollow waveguide component that are perpendicular to the longitudinal direction of the hollow waveguide.

[0030] Positioning grooves according to claim 7 are easy and precise to manufacture. The positioning grooves can have any groove cross-section perpendicular to a direction of travel of the groove. Preferably, the groove cross-section tapers from the opening of the groove to its bottom, in particular continuously.

[0031] V-shaped positioning grooves have proven particularly advantageous. These grooves feature a uniform taper in the cross-section, enabling exceptionally precise positioning. For example, positioning elements with a cross-section corresponding to the grooves, or with a round cross-section, can be inserted into the grooves to position the support elements and insert elements relative to each other. Specifically, the positioning grooves are designed to be integrated into the outer surfaces, particularly the end faces, of the support elements and / or insert elements in such a way that they form continuous grooves when assembled.

[0032] The support elements and / or the insert elements can be made of glass, quartz, ceramic and / or metal. The support elements and / or insert elements, especially those made of glass, quartz and / or metal, can have a coating of EUV-reflective material on their surface facing the hollow waveguide, in particular ruthenium, zirconium and / or molybdenum.

[0033] Manufacturing the support elements and / or the insert elements from metal according to claim 8 increases the stability of the respective elements. In particular, the support elements and / or insert elements are made entirely of metal, especially ruthenium. Because metal is ductile, especially compared to glass-like materials, holding forces can be absorbed more effectively. Damage, particularly in the area of ​​the edges of the surface, is avoided.

[0034] The use of metals also enables particularly high manufacturing precision, especially the precise manufacturing of the transition areas between the edge surfaces and the support element surfaces. In particular, high edge accuracy is possible.

[0035] The support elements and insert elements can be made of the same or different materials. In particular, different materials can be flexibly combined. For example, the insert elements can be made of metal, especially ruthenium. The support elements can be made of another metal, such as copper, or glass-like materials, such as glass. The surfaces of the support elements facing each other can be coated with a suitable material, especially ruthenium. Choosing the same materials for the support elements and the insert elements has the particular advantage of corresponding thermal expansion behavior.

[0036] Ruthenium has proven particularly suitable for reflecting UV light, especially EUV light. Other particularly suitable metals for this purpose are zirconium and / or molybdenum. For example, ruthenium, zirconium, and / or molybdenum can be used for manufacturing the support elements and / or the insert elements and / or for surface coatings on these elements.

[0037] The use of metal for the support elements and insert elements is a particularly independent aspect of the present invention, especially independent of the arrangement of the insert elements between mutually facing support element surfaces. In particular, differently arranged and / or designed support elements and / or insert elements for the hollow waveguide component can be used.

[0038] Insert elements according to claim 9 have proven to be particularly advantageous for use with EUV light. In particular, plate-shaped insert elements can be manufactured from ruthenium at comparatively low material costs. The manufacturing costs are significantly reduced, especially compared to the complex coating of surfaces with ruthenium and the surface treatment required for this purpose.

[0039] A contact plate according to claim 10 can, in particular, be configured as plate-shaped insert elements. In particular, the contact plate can be made of the same material as the insert elements. The contact plate can, for example, have the same thickness as the insert elements. The support elements can, for example, be configured as contact plates. Alternatively, the support elements can, in addition to the contact plate, also include a substrate. The substrate can be used, in particular, to stabilize thin contact plates.

[0040] The support elements according to claim 11 have proven to be particularly suitable for EUV light. The support elements, especially the contact plates of the support elements, and the insert elements made of ruthenium are particularly advantageous.

[0041] The support elements can be designed as single or multiple parts. A single-part design of the support elements has the advantage of a simple and stable arrangement.

[0042] The insert elements can be designed in one or more parts. A one-piece design, especially as a single-piece plate element, allows for easy arrangement between the support elements. The insert elements are particularly stable.

[0043] Insert elements according to claim 12 enable a particularly flexible design of the hollow waveguide, especially its cross-section. For example, the insert elements can comprise several insert element parts, which are arranged one above the other, particularly in the form of insert element plates, in the direction of a surface normal of the support element surface. Complex edge surface contours can be easily generated by different inclinations of the edge surfaces of the individual insert element parts, especially insert element plates. For example, the edge surfaces of different insert element parts can be inclined differently, resulting in a correspondingly polygonal shape of the edge surfaces.

[0044] The advantages of the lighting optics according to claim 13 correspond to those already explained above with reference to the hollow waveguide component.

[0045] The coupling mirror optic can include at least one mirror for grazing incidence (GI), particularly designed for an angle of incidence of the illumination light greater than 45°. The coupling mirror optic can include exactly one mirror or several mirrors, e.g., two mirrors.

[0046] An optic known, for example, from US 10,042,248 B2 can be used as the output coupling mirror optic.

[0047] The advantages of an optical system according to claim 14 and a mask inspection system according to claim 15 correspond to those already explained above with reference to the hollow waveguide component.

[0048] A wafer inspection system can be designed accordingly. The inspection system can include an object holder for the object to be inspected, which is mechanically coupled to an object displacement drive, enabling scanning and displacement of the object during illumination.

[0049] The inspection system could be a system for actinic mask inspection.

[0050] Further features, details and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings. These show: Fig. 1 schematically in a meridional section a mask inspection system for lithography masks for use with EUV illumination light with an illumination optic comprising a beam homogenizing element in the form of a hollow waveguide; Fig. 2 schematic angular relationships of an illumination light bundle at the entry into an entrance opening of the hollow waveguide and at the exit from an exit opening of the hollow waveguide; Fig. 3 a schematic, not to scale perspective of a hollow waveguide component for the realization of the hollow waveguide of the lighting optics, wherein the hollow waveguide component is shown as semi-transparent; Fig. 4 a schematic, not to scale cross-section through the hollow waveguide component; Fig. 5 A schematic, not to scale cross-section through a further embodiment of a hollow waveguide component for realizing the hollow waveguide of the lighting optics Fig. 6 to 9 schematic, not to scale cross-sections of further embodiments of a hollow waveguide component with different cross-sectional shapes of the hollow waveguide.

[0051] An illumination optic BO is part of an optical system 2 of a mask inspection system 1 for use with EUV illumination light 3. One beam path of the illumination light 3 is in the Fig. Figure 1 illustrates the illumination optics BO via marginal rays and a main ray. The illumination light 3 illuminates an illumination field 4 of the mask inspection system 1.

[0052] 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.

[0053] 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. Alternatively, light source 5 could also be a high-harmonic EUV source. The pulse frequency of light source 5 can be in the kHz range.

[0054] 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.

[0055] After emission by the light source 5, the illumination light 3 first passes through a useful light filter 8, which is positioned in an operating position in the beam path of the illumination light 3 between the source volume 6 and an ellipsoidal mirror 10 of the illumination optics BO. The useful light filter 8 can be a single filter or a plurality of filters, which, for example, are stored in a filter magazine in the mask inspection system 1. Another useful light filter 8 can be positioned in a standby position outside the illumination light beam path of the illumination optics BO. The useful light filters 8 can have the same transmission characteristics, and a change between the useful light filters 8 can then be made if a degradation of the filtering effect of one of the useful light filters 8 is detected.Alternatively, the useful light filters 8 can also have different filter characteristics and, for example, allow different useful light wavelength ranges to pass through into the subsequent illumination light beam path or be optimized to filter out different false light components.

[0056] The useful light filter 8 can be designed in such a way that it filters out, in particular, pump light carried in the illumination light beam path, which was used in the source volume 6 for useful light generation.

[0057] After passing through the useful light filter 8 and the ellipsoidal mirror 10, the illumination light 3 first passes through an aperture diaphragm 9, which limits a beam of the illumination light 3 at its edges. Subsequently, the illumination light beam 3 is directed towards a beam homogenizing element 11 in the form of a hollow waveguide of the illumination optics BO. The mirror 10 serves as a coupling optic for coupling the illumination light 3 into the beam homogenizing element 11.

[0058] Between the source volume 6 and the beam homogenizing element 11, typically after the ellipsoidal mirror 10 of the illumination optics BO, 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 ellipsoidal mirror 10 and the aperture diaphragm 9.

[0059] The aperture diaphragm 9 limits the numerical aperture of the illumination beam 3 emitted from the source area 6 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 BO. It is also possible to arrange such a further aperture diaphragm in the beam path of the illumination light 3 after the beam homogenizing element 11 between two downstream optical components of the illumination optics BO.

[0060] The ellipsoidal mirror 10 serves to focus 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 10 is thus located in the source region 6, and a second focal point of the ellipsoidal mirror 10 is located in the entrance aperture 12. The ellipsoidal mirror 10 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 upon entering the entrance aperture 12 can be in the range of 0.02 to 0.2, for example, in the range of 0.05.

[0061] The angle of incidence of a central main ray of the illumination beam 3 on the coupling mirror 10 can be in the range between 10° and 20°. The ellipsoidal mirror 10 can be a normal incidence (NI) mirror, but can also be configured as a grazing incidence (GI) mirror.

[0062] 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.

[0063] The beam homogenizing element 11 is designed as a hollow waveguide and is referred to here and in the following as hollow waveguide 11.

[0064] The beam homogenizing element 11 has a typical length perpendicular to the planes 13 and 15, i.e. along its longitudinal axis L 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.

[0065] An angle between a normal to the entrance plane 13 of the beam homogenizing element 11 and the main beam CR 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°.

[0066] 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.

[0067] A downstream imaging output coupler 16, located after the beam homogenizing element 11, images the exit aperture 14 of the beam homogenizing element 11, which lies in an 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.

[0068] The output coupler 16 can be designed as a Wolter telescope, specifically as 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. Instead of a paraboloid, a hyperboloid can also be used in such Wolter optics. Such a combination of an ellipsoidal mirror with a hyperboloid mirror also constitutes a Wolter optic of type I.

[0069] An embodiment of the output coupling mirror optics 16 is described in US 10,042,248 B2.

[0070] 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 BO can range from 0.25 to 10.

[0071] In object plane 17, a reticle 18 to be inspected is arranged as the object or mask to be inspected, in particular a photomask, and is held by a reticle holder 19. The reticle holder 19 is mechanically connected to a reticle displacement drive 20, by means of 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.

[0072] The mask to be inspected 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 mask can be substantially rectangular. The mask can preferably be 5 to 7 inches long and wide, and particularly preferably 6 inches long and wide. Alternatively, the photomask can be 5 to 7 inches long and 10 to 14 inches wide, and preferably 6 inches long and 12 inches wide.

[0073] 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.

[0074] The x / y aspect ratio of the illumination field 4 matches the x / y aspect ratio of the exit aperture 14.

[0075] 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.

[0076] The image field 21 is acquired by a detection device 23, e.g., by one or more CCD 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.

[0077] The mask inspection system 1 makes it possible to inspect, for example, a structure on reticulum 18.

[0078] Fig. Figure 2 schematically shows the effect of a principal beam angle α other than 0. CR of a main beam CR of the illumination light bundle 3, which enters the inlet opening 12 of the beam homogenizing element 11 designed as a hollow waveguide, to the longitudinal axis L of the hollow waveguide 11. Due to the angle α CRBoth the main beam CR and the other individual beams of the illumination beam 3 experience at least one reflection at the inner wall of the waveguide cavity of the hollow waveguide 11. This results in an influence on the angular distribution within the illumination beam 3 after exiting the exit aperture 14. This exit angle distribution is described in the Fig. 2 schematically indicated by a multitude of individual rays 24 of the illumination beam 3. This redistribution can be used to homogenize an intensity distribution within the illumination angles of the illumination beam 3.

[0079] For example, the illumination light 3 can have a main beam (α) running along the longitudinal axis L. CR= 0) is incident, with the illumination angle distribution of the incident illumination 3 preferably being symmetrical about the longitudinal axis L. The illumination beam 3 emerging from the hollow waveguide 11 then again has an illumination angle distribution centered about the longitudinal axis L, which corresponds to the angular distribution of the incident illumination beam 3 with respect to its angular variation. Due to reflections at the inner wall of the hollow waveguide 11, the illumination angles of the emerging illumination beam 3 are redistributed within the illumination angle variation of the incident illumination beam 3, but no new illumination angles arise.

[0080] With a main beam angle α CR A value of 0 results in a monopolistic illumination angle distribution. For main beam angles α CRDepending on the skin beam angle, dipole and multipole illumination angle distributions as well as mixtures thereof can be generated.

[0081] In the Fig. 3 and Fig. Figure 4 shows an embodiment of a hollow waveguide component 25 for realizing the hollow waveguide 11. The hollow waveguide component 25 has two support elements 26, which in the illustrated embodiment are essentially cuboid in shape.

[0082] Two insert elements 28 are arranged between two opposing support element surfaces 27. The insert elements 28 are designed as plane-parallel plates. The respective plate surfaces of the insert elements 28 abut the support element surfaces 27. The hollow waveguide 11 is formed between the insert elements 28 and the support element surfaces 27. A cross-section of the hollow waveguide 11 is bounded by the edge surfaces 29 of the insert elements 28 and the opposing support element surfaces 27. The hollow waveguide 11 has a rectangular cross-section whose aspect ratio corresponds to that of the illumination field 4.

[0083] The insert elements 28 and the support elements 26 have a length along the longitudinal axis L of the hollow waveguide 11 corresponding to the length of the hollow waveguide 11. A width b of the hollow waveguide 11, running parallel to the support element surfaces 27 and perpendicular to the longitudinal axis L, is determined by the spacing of the insert elements 28, in particular their edge surfaces 29, from one another. The height of the cross-section of the hollow waveguide 11 perpendicular to the width b is determined by the thickness d of the insert elements 28. The width b and the thickness d correspond in particular to the dimensions of the inlet opening 12 and the outlet opening 14 mentioned above. Preferably, the main extent of the cross-section is perpendicular to the support element surfaces 27, so that the main extent of the cross-section corresponds to the thickness d of the insert elements 28.Although this increases the thickness d and thus the material requirement for the insert elements 28, the increased thickness d also facilitates the surface treatment of the edge surfaces 29.

[0084] The insert elements 28 are designed as thin plates. A width B of the insert elements 28 perpendicular to the longitudinal axis L exceeds the thickness d. The following applies to the ratio of width B to thickness d: B / d ≥ 5, in particular B / d ≥ 10, in particular B / d ≥ 15; for example, the ratio B / d is approximately 20. A large width B results in a large contact area, thus reducing forces acting on edges in the region of the boundary surfaces 29. Furthermore, a large contact area enables precise positioning and reduces sensitivity to angular errors.

[0085] The thickness D of the support elements 26 can be flexibly selected. The thickness D can particularly influence the stability of the hollow waveguide component 25. An example thickness D could be approximately 15 mm.

[0086] A width T of the support elements 26 perpendicular to the longitudinal axis L preferably corresponds to the two widths B of the insert elements 28 plus the width b of the hollow waveguide 11. An exemplary width T can be approximately 40 mm.

[0087] For the relative positioning of the insert elements 28, corresponding positioning elements in the form of positioning grooves 30 are arranged on the end faces of the support elements 26 and the insert elements 28.

[0088] In the illustrated embodiment, each insert element 28 and each end face, i.e., on the side of the inlet opening 12 and on the side of the outlet opening 14, has a positioning groove 30. The positioning grooves 30 are V-shaped. During assembly, positioning elements, for example, round-rod-shaped positioning elements, can engage in the positioning grooves 30 to precisely position the support elements 26 and the insert elements 28 relative to each other in the lateral direction.

[0089] The insert elements 28 are held between the support elements 26. The support elements 26 exert a holding force F on the insert elements 28, which is schematically represented in Fig. 4 is shown.

[0090] There are various ways to connect the support elements 26 and the insert elements 28. One option is to glue the elements together, as shown schematically in Fig. Figure 3 shows that pockets are formed in the area of ​​the carrier element surfaces 27, each featuring an adhesive projection 31 and a surrounding degassing channel 32. The adhesive projections 31 are slightly recessed from the carrier element surface 27 to allow the application of an adhesive. The adhesive can degas via the degassing channels 32.

[0091] In addition to or as an alternative to bonding, the support elements 26 can be clamped to the insert elements 28. For this purpose, clamping receptacles 33 can be formed in the support elements 26 and, if necessary, in the insert elements 28 to receive clamping elements.

[0092] The support elements 26 and the insert elements 28 can be made of the same or different materials. In particular, material combinations are possible.

[0093] Preferably, the insert elements 28 and the support elements 26 are made of a metal. The metals exhibit increased ductility, particularly compared to glass, which simplifies the application of force. In particular, damage to the edges of the surface areas 29 is avoided. In a preferred embodiment, the insert elements 28 are made of ruthenium. Ruthenium has proven to be particularly suitable for the total internal reflection of EUV light. The use of plate-shaped insert elements 28 reduces the amount of ruthenium required. This lowers manufacturing costs, especially compared to ruthenium-coated components, for example, those made of glass.

[0094] The support elements 26 can be made of metal or glass. For example, the support elements 26 can also be made of ruthenium. It is also possible to manufacture the support elements 26 from another ductile material, for example, a metal, in particular copper. A coating, in particular of ruthenium, can be present on the surface of the support element 27.

[0095] Based on Fig. Section 5 describes a further embodiment of a hollow waveguide component 125. Components already mentioned in relation to the embodiment in the Fig. 3 and Fig. The items described in section 4 bear the same reference symbols and will not be explained again in detail.

[0096] The hollow waveguide component 125 differs from the previously described hollow waveguide component 25 only in the design of the support elements 126. The support elements 126 have contact plates 35 that form the mutually facing support element surfaces 27. The contact plates 35 make contact with the insert elements 28 over their entire surface. The contact plates 35 can, for example, be designed as plane-parallel plates. The contact plates 35 have, for example, the same thickness d as the insert elements 28.

[0097] Preferably, the contact plates 35 are made of ruthenium. Due to the small thickness of the contact plates 35, this is possible with relatively low material costs. Particularly preferably, the contact plates 35 are made of the same material, for example ruthenium, as the insert elements 28. The contact plates 35 and the insert elements 28 exhibit the same thermal expansion behavior.

[0098] The support elements 126 optionally have substrates arranged on the side of the contact plates 35 facing away from the insert elements 28. The substrates 36 can serve to stabilize the contact plates 35, especially if they have a small thickness d.

[0099] A particular advantage of using insert elements is that the cross-sectional shape of the hollow waveguide can be easily and flexibly adapted, as exemplified by the following: Fig. Sections 6 to 9 are described. Components already mentioned in relation to the exemplary embodiment in the Fig. 3 and Fig. The items described in section 4 bear the same reference symbols and will not be explained again in detail.

[0100] The hollow waveguide component 225 according to Fig. 6 has insert elements 228, the edge surfaces 229 of which are inclined towards each other. This creates a hollow waveguide 211 with a pentagonal cross-section.

[0101] In the case of the hollow waveguide component 325 according to Fig. 7 The mutually inclined edge surfaces 329 of the insert elements 328 touch, resulting in a triangular cross-section of the hollow waveguide 311. The hollow waveguide 311 is bounded by the side surfaces 329 and the support element surface 27 of one of the support elements, in this case the lower one.

[0102] The hollow waveguide component 425 according to Fig. 8 has insert elements 428, the edge surfaces 429 of which are parallel to each other but inclined at an angle of less than 90° to a surface normal of the support element surfaces 27. This creates a hollow waveguide 411 with a parallelogram-like cross-section.

[0103] In the case of the hollow shaft conductor component 525 according to Fig. 9. The insert elements 528 each consist of several, in this case two, insert element parts 540. The insert element parts 540 are designed as insert element plates, which are arranged one above the other in the direction of a surface normal of the carrier element surfaces 27. Due to the mutually obliquely running edge surfaces of the insert element parts 540, an edge surface 529 of the insert elements 528 is formed, which is V-shaped. Overall, this results in a hollow waveguide 511 with a hexagonal cross-section.

[0104] In the variant in Fig. 9. The insert elements 528 can also be formed in one piece. In the area of ​​the edge surfaces 529, a V-shaped groove can then be provided to realize the hexagonal cross-section of the hollow waveguide 511. Other contours of the edge surfaces are also possible. 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] DE 10 2022 205 767 A1

[0002] US 10,042,248 B2 [0046, 0069, 0076] 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

[0068]

Claims

[1] Optical hollow waveguide component (25; 125; 225; 325; 425; 525), in particular for homogenizing EUV light, comprising, - two support elements (26; 126) and - two insert elements (28; 228; 328; 428; 528) which are inserted between the support elements (26; 126) such that a hollow waveguide (11) is formed between the insert elements (28; 228; 328; 428; 528). [2] Hollow waveguide component (25; 125; 225; 325; 425; 525) according to claim 1, characterized by , that the insert elements (28; 228; 328; 428; 528) are plate-shaped, in particular plane-parallel plates. [3] Hollow waveguide component (25; 125; 225; 325; 425; 525) according to claim 1 or 2, characterized by, that the insert elements (28; 228; 328; 428; 528) have a thickness d corresponding to a minimum distance between the support elements (26; 126) and a width B perpendicular to the longitudinal axis (L) of the hollow waveguide (11) and perpendicular to the thickness d, wherein the following ratio of width B to thickness d applies: B / d ≥ 5, in particular B / d ≥ 10, in particular B / d ≥ 15. [4] Hollow waveguide component (25; 125; 228; 328; 428; 528) according to any of the preceding claims, characterized by , that a main extent of a cross-section of the hollow waveguide (11) perpendicular to the longitudinal axis (L) of the hollow waveguide (11) corresponds to a thickness d of the insert elements (28; 228; 328; 428; 528). [5] Hollow waveguide component (25; 125; 225; 325; 425; 525) according to any of the preceding claims, characterized byPositioning elements (30) on the support elements (26) and / or the insert elements (28; 228; 328; 428; 528) for the relative positioning of the insert elements (28; 228; 328; 428; 528) and / or support elements (26) to each other. [6] Hollow waveguide component (25; 125; 225; 325; 425; 525) according to claim 5, characterized by , that the positioning elements are arranged on the end faces of the support elements (26) and / or the insert elements (28; 228; 328; 428; 528). [7] Hollow waveguide component (25; 125; 225; 325; 425; 525) according to one of claims 5 or 6, characterized by , that the positioning elements are designed as positioning grooves (30), in particular V-shaped positioning grooves (30). [8] Hollow waveguide component (25; 125; 225; 325; 425; 525) according to any of the preceding claims, characterized by , that the support elements (26; 126) and / or the insert elements (28; 228; 328; 428; 528) are made of metal. [9] Hollow waveguide component (25; 125; 225; 325; 425; 525) according to claim 8, characterized by , that the insert elements (28) are made of ruthenium. [10] Hollow waveguide component (125) according to any one of the preceding claims, characterized by that the support elements (126) each have a contact plate (35) which contacts the insert elements. [11] Hollow waveguide component (25; 125; 225; 325; 425; 525) according to any of the preceding claims, characterized by , that the support elements (26; 126), in particular contact plates (35) of the support elements (126), are made of ruthenium. [12] Hollow waveguide component (525) according to any one of the preceding claims, characterized by that the insert elements (528) are designed in multiple parts, in particular consisting of several insert element plates (540) arranged one above the other. [13] Illumination optics (BO) for a mask inspection system (1) for use with EUV illumination light (3), - with a hollow waveguide component (25; 125; 225; 325; 425; 525) according to one of the preceding claims, - with a coupling mirror optic arranged upstream of one of the hollow waveguide components (25; 125; 225; 325; 425; 525) in the beam path of the illumination light (3) with at least one mirror (10) for imaging a source area (6) of an EUV light source (5) into an entrance aperture (12) of the hollow waveguide (11) and - with an output mirror optic (16) for imaging an exit aperture (14) of the hollow waveguide (11) into an illumination field. [14] Optical system (2) comprising an illumination optic (BO) according to claim 13 and an EUV light source (5) for the illumination light (3). [15] Mask inspection system (1) - with an optical system (2) according to claim 14, - with a projection optic (PO) for imaging the illumination field (4) into an image field (21) and - with a detection device (23) for detecting illumination light (3) incident on the image field (21).

Images