Illumination light guide, illumination optical unit and inspection apparatus

Abstract

To provide an improved illumination light guide which can be used particularly efficiently especially with respect to an installation space in an illumination optical unit, does not exert a negative influence on the beam path of an illumination light beam and is not particularly reduced.SOLUTION: An illumination light guide (32, 39, 49, 50) for guiding EUV or DUV illumination light (3) in an illumination optical unit (1), having a tubular conductor body (51), a conductor input (55) and a conductor output (56), wherein the conductor body (51) forms an interior for guiding the illumination light (3) along a longitudinal axis (L) from the conductor input (55) to the conductor output (56), An illumination light guide (32, 39, 49, 50), wherein the cross-sectional shape of the interior defined perpendicular to the longitudinal axis (L) varies along the longitudinal axis (L).SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The content of German Patent Application No. 10 2024 207 073.4 is incorporated herein by reference.

[0002] The present invention relates to an illumination light guide for an illumination optical unit, an illumination optical unit having such an illumination light guide, and an inspection device having such an illumination optical unit. [Background technology]

[0003] Based on prior use, the prior art discloses a wide variety of types of illumination light guides. Summary of the Invention

[0004] The problem addressed by the present invention is to provide an improved illumination light guide that can be used particularly efficiently, in particular in terms of installation space within an illumination optical unit, and that does not negatively affect, and in particular does not reduce, the beam path of the illumination light beam.

[0005] This problem is solved by an illumination light guide having the features set out in claim 1.

[0006] According to the invention, it has been recognized that an illumination light guide can be constructed particularly efficiently in terms of installation space if the internal cross-sectional shape varies along the longitudinal direction of the conductor body.

[0007] A further advantage resides in the fact that the varying cross-sectional shape allows optimal adaptation of the illumination light guide to various conditions and / or requirements in the area of ​​the conductor input and conductor output.

[0008] In this context, cross-sectional shape should be understood to mean the shape of the cross-sectional outline, regardless of the perimeter and / or surface area of ​​the internal cross-sectional area.

[0009] In particular, the longitudinal axis may represent an axis of symmetry of the tubular conductor body. In particular, the longitudinal axis may be oriented parallel to the direction of propagation of the illumination light, in particular of the chief ray of the illumination light.

[0010] The conductor body forms an interior for guiding illumination light, in particular the conductor body at least partially surrounds the interior, for example on the periphery or sides, in particular in a direction perpendicular to the longitudinal axis.

[0011] In particular, the conductor body may be in the form of a hollow body, for example, a tubular conductor body. The cross-sectional shape of the conductor body may vary in a manner equivalent to the cross-sectional shape of the interior, such that the wall thickness between the interior surface of the interior and the exterior surface of the conductor body is constant in the longitudinal direction. As a result, the illumination light guide may be integrated into the illumination optical unit in a manner that requires even less space. Material and manufacturing costs may be reduced.

[0012] The cross-sectional shape of the interior of the conductor body may vary continuously and / or in discrete increments. The cross-sectional shape preferably varies continuously. The interior surface of the conductor body facing the interior is particularly smooth.

[0013] In particular, the illumination light guide serves to transmit illumination light from a first optical component of the illumination optical unit to a second optical component of the illumination optical unit.

[0014] The first optical component may in particular be a hollow waveguide. The second optical component may take the form of an output-coupling mirror optical unit. The first optical component and / or the second optical component, and optionally further component parts arranged adjacent to the first optical component and / or the second optical component, may significantly reduce the installation space of the illumination light guide. Optimal use of this significantly reduced installation space may be made possible by using an illumination light guide according to the present invention.

[0015] At the same time, it has surprisingly been found that the beam path of the illumination light is not negatively affected, in particular not reduced, despite the change in the internal cross-sectional shape. The illumination light guide according to the invention can be efficiently integrated, in particular in an illumination optical unit, in terms of installation space, without any negative effects being foreseen regarding the illumination light and the associated defects of the illumination optical unit.

[0016] The conductor input and / or conductor output may be arranged in a plane perpendicular to the longitudinal direction, the conductor input may be arranged at a first end of the tubular body, and the conductor output may be arranged at an end opposite the first end in the longitudinal direction.

[0017] The illumination light guide according to claim 2 can be precisely adapted to the above requirements, in particular the installation space related conditions for arched illumination optical units in the region of the conductor input and / or conductor output.

[0018] The cross section of the conductor input and / or the cross section of the conductor output may have a cross-sectional area and / or cross-sectional shape.

[0019] In this case, the cross section of the conductor input and the cross section of the conductor output may refer to the respective cross sections of the interior of the illumination light guide at the conductor input and the conductor output, respectively.

[0020] The cross section of the conductor input and the cross section of the conductor output may refer to the respective cross sections of the outer surface of the illumination light guide at the conductor input and the conductor output, respectively.

[0021] In this case, the side ratio of a cross section, for example the input side ratio of a conductor input or the output side ratio of a conductor output, is understood to mean in particular the ratio between the length and the width of the smallest rectangle forming the envelope of the cross section, i.e. in particular the smallest rectangle whose area completely encompasses the cross section.

[0022] As a result of the different side ratios, the conductor input and / or the conductor output can be ideally adapted to the installation space predetermined by further optical components of the illumination optical unit and / or to the functional and / or mechanical coupling to these components.

[0023] The illumination light conductor according to claim 3 is particularly well-suited for the relevant practical applications, having a beam cross-section that is elliptical in particular and in which the illumination light has different extents in different spatial directions. As a result, the light, particularly for mask inspection, can be precisely guided.

[0024] The illumination light conductor according to claim 4 can be manufactured particularly easily. As a result of the input side ratio being substantially 1, preferably exactly 1, the conductor input has a number of symmetries, particularly rotational symmetry. The conductor input may particularly have a rotationally symmetric form. In general, manufacturing symmetric structural elements is easier.

[0025] Moreover, the symmetry of the conductor input enables the efficient integration of further functional components into the illumination light conductor, particularly the integration of upstream optical components, such as purging devices for hollow waveguides. This symmetry ensures a uniform embodiment and / or effect of the functional components, such as a uniform supply of purge gas.

[0026] The illumination light conductor according to claim 5 has proven its value in practice. As a result of the selected output side ratio, the illumination light conductor can be optimized, particularly with respect to the installation space, and integrated into an arc-shaped illumination optical unit.

[0027] In particular, for the output side ratio S2, it is possible to apply 1.2 < S2 < 1.8, particularly 1.3 < S2 < 1.7, particularly 1.4 < S2 < 1.6, and particularly S2 = 1.5.

[0028] The illumination light guide according to claim 6 allows for even more efficient use of the available installation space. Empirically, the installation space of an illumination optical unit is smaller in the region of the conductor output or in the region of the conductor input. The conical configuration of the tubular conductor body allows this to be taken into account when constructing the illumination optical unit.

[0029] The interior of the conductor body may also be conical in shape, and the wall thickness between the exterior surface of the conductor body and the interior surface of the interior may again be constant.

[0030] In particular, the cross-sectional area of ​​the conductor output can be larger than the cross-sectional area of ​​the conductor input, in which case the interior of the conductor body expands along the longitudinal axis in the direction of propagation of the illumination light, as a result of which illumination light with an expanding beam cross-section can be reliably guided without being damaged.

[0031] The illumination light guide according to claim 7 can be manufactured easily and precisely. By using a wide variety of production methods, component parts with circular contours can be produced. Furthermore, the conductor input has a particularly high degree of symmetry, which improves the arrangement and / or functional interaction with upstream components.

[0032] The conductor output according to claim 8 is particularly suitable for illumination light with an elliptical beam cross section.

[0033] The illumination light guide according to claim 9 can be particularly easily integrated into an illumination optical unit. In particular, the conductor input has a square cross-sectional shape. Optical components upstream of the illumination light guide, in particular hollow waveguides, may have a hollow waveguide cross-section that is, for example, rectangular, in particular square. A regular polygonal, in particular square, cross-sectional shape allows for good coupling and / or functional interaction between the upstream components and the illumination light guide. In the region of the conductor input, the illumination light guide has a high degree of symmetry.

[0034] Moreover, in particular the hollow waveguide may have a waveguide cavity with a substantially rectangular, in particular square, contour, in which case the illumination light may be transmitted particularly efficiently from the hollow waveguide to the illumination light guide.

[0035] An illumination light guide according to claim 10 can be integrated into an illumination optical unit particularly efficiently with regard to installation space. In particular, the cross-sectional shape can be rectangular, in particular with a side ratio not equal to 1.

[0036] The illumination light guide according to claim 11 can be used particularly flexibly: as a result of integrating further functional components into the illumination light guide, in particular into the conductor base of the illumination light guide, other component parts of the illumination optical unit, in particular optical components that are arranged immediately upstream of the illumination light guide, can be influenced in a targeted manner to ensure frictionless and efficient functionality of the illumination optical unit.

[0037] An illumination light guide according to claim 12 allows for efficient purging and / or cleaning of upstream optical components, in particular of upstream hollow waveguides. The purging device is in particular a waveguide purging device.

[0038] The illumination light guide may comprise a purge gas connector, in particular for supplying purge gas, in particular hydrogen gas, from a purge gas reservoir to upstream optical components in a targeted, more particularly controlled manner. As a result, the purge gas flow can be controlled particularly effectively. The purge gas connector can be positioned at a distance from sensitive optical components.

[0039] As an alternative to or in addition to the purge gas connector, further components of the purging device may be integrated into the illumination light guide, in particular into the conductor base, in particular a pressure chamber, an intermediate gap and / or a nozzle may be integrated into the illumination light guide, in particular into the conductor base.

[0040] It is also possible for the components of the purging device to be formed between the illumination light guide, in particular the conductor base, and the cover of an upstream optical component, in particular the cover of a hollow waveguide.

[0041] A further problem addressed by the present invention is that of improving the illumination optical unit.

[0042] This problem is solved by an illumination optical unit having the features set out in claim 13.

[0043] The illumination optical unit may be part of an inspection apparatus, for example, for inspecting photolithographic masks and / or photolithographic wafers.

[0044] An illumination optical unit according to claim 14 may provide and / or focus particularly homogeneous illumination light.

[0045] The illumination optical unit according to claim 15 is particularly compact. The components of the purging device may in particular be completely integrated into the illumination light guide, in particular into the conductor base, or may be formed between the illumination light guide, in particular the conductor base, and the cover of the hollow waveguide.

[0046] A further problem addressed by the present invention is that of improving inspection equipment.

[0047] This problem is solved by an inspection device having the features presented in claim 16.

[0048] In particular, the inspection system may be designed to inspect photolithographic masks and / or photolithographic wafers. In particular, the inspection system may take the form of an actinic inspection system, i.e., use light in the EUV wavelength range.

[0049] It is also possible that the inspection tool uses light from a different wavelength range, for example the DUV wavelength range.

[0050] In addition to the illumination optical unit, the inspection apparatus may also comprise a projection optical unit which serves to image light reflected from the inspected mask and / or from the inspected wafer into an image plane.

[0051] Exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings. [Brief explanation of the drawings]

[0052] [Figure 1] 1 is a schematic diagram illustrating an optical system having an illumination optical unit for a mask inspection system for use with EUV illumination light. [Figure 2] 1 is a schematic cross-sectional view of a first exemplary embodiment of a hollow waveguide assembly having a waveguide purging device and an illumination light guide. [Figure 3] 10 is a schematic cross-sectional view of a further exemplary embodiment of a hollow waveguide assembly having a waveguide purging device and an illumination light guide. [Figure 4] 10 is a schematic cross-sectional view of a third exemplary embodiment of a hollow waveguide assembly having a waveguide purging device and an illumination light guide. [Figure 5] 1 is a perspective view of an exemplary embodiment of an illumination light guide. [Figure 6] 6 is a cross-sectional view of the illumination light guide according to FIG. 5; [Figure 7] 6 is a schematic diagram of a conductor input of the illumination light guide according to FIG. 5; DETAILED DESCRIPTION OF THE INVENTION

[0053] The illumination optical unit 1 is a component of an illumination system 2 of a mask inspection system for use with EUV illumination light 3. In the drawing, the beam path of the illumination light 3 is indicated by marginal rays. An illumination field or object field 4 of the mask inspection system is illuminated by the illumination light 3.

[0054] The illumination light 3 is generated by an EUV light source 5 in a source region or source volume 6. The light source 5 may generate EUV radiation within a wavelength range of 2 nm to 30 nm, for example in the range of 2.3 nm to 4.4 nm or in the range of 5 nm to 30 nm, for example 13.5 nm.

[0055] The light source 5 may be embodied as a plasma light source. For example, the light source can be a laser plasma source (LPP; Laser Produced Plasma) or else a discharge source (DPP; Discharge Produced Plasma). It is also possible to use harmonic EUV sources. In principle, such plasma sources are known light sources of EUV projection exposure apparatus.

[0056] For ease of orientation, a Cartesian xyz coordinate system is used hereafter. The x-axis is perpendicular to the drawing surface of Figure 1. The y-axis extends horizontally to the right in Figure 1, and the z-axis extends vertically upwards in Figure 1.

[0057] The source region 6 has a generally elliptical shape and has a maximum extent, also referred to as the main extension direction, parallel to the y-axis. The main emission direction of the illumination light 3 from the source region 6 extends along this main extension direction, i.e., along the longest axis of the elliptical source region 6 when approximating an ellipse.

[0058] After emission of illumination light by the light source 5 , the illumination light 3 first passes through an aperture stop 9 which bounds the end of the beam of illumination light 3 .

[0059] The aperture stop 9 can be designed to be exchangeable. For example, an aperture wheel may be provided for this purpose, which stores various aperture stop embodiments that can be used alternately in the beam path of the illumination light 3. Different input apertures of the illumination light 3 can be specified by such an exchangeable aperture stop design.

[0060] The aperture stop 9 may be embodied so as to be exchangeable and / or adjustable and / or configurable with respect to its diaphragm edge. As a result, different diaphragm geometries of the aperture stop 9 can be realized and / or configured. For example, the specifiable diaphragm geometries may be circles with selectable diameters and / or ellipses with selectable ellipse sizes and, optionally, selectable ellipse semiaxial ratios. Such an ellipse semiaxial ratio specifiable by the aperture stop 9 may be 2:1.

[0061] Downstream of the aperture stop 9, the illumination light beam 3 is transmitted from an input coupling mirror 10 of the illumination optical unit 1 to a beam homogenizing device 11. As will be explained in more detail below, the input coupling mirror 10 may also be part of the beam homogenizing device 11. A beam homogenizing element, for example, in this case, a hollow waveguide 11a, may also be part of the beam homogenizing device 11. In other exemplary embodiments, the beam homogenizing device 11 may instead or in addition also comprise at least one facet mirror that serves to split the EUV illumination light 3 into multiple individual beams that are to be superimposed on one another for the purpose of homogenized mixing. In this case, the beam homogenizing device may also comprise, for example, two facet mirrors arranged in series.

[0062] The aperture stop 9 constrains the numerical aperture of the illumination light beam 3 emitted by the source region 6 to a numerical aperture value in the range of 0.02 to 0.3, for example, in the range of 0.02 to 0.1 or 0.05 to 0.08. A numerical aperture greater than 0.1, i.e., in the range of 0.1 to 0.3, as specified by the aperture stop 9, allows for a greater light yield in the illumination light beam path between the source volume 6 and the illuminated field 4.

[0063] An incoherent illumination setting may be used.

[0064] As an alternative to or in addition to the aperture stop 9, an aperture-limiting stop may be arranged between the hollow waveguide 11a and a downstream optical component of the illumination optical unit 1. It is also possible that such a further aperture stop is arranged in the beam path of the illumination light 3, downstream of the hollow waveguide 11a, between two downstream optical components of the illumination optical unit 1.

[0065] For example, the input coupling mirror 10 is embodied as an ellipsoidal mirror, which serves to image the source region 6 of the EUV light source 5 onto the waveguide input 12 in the entrance face 13 of the hollow waveguide 11a. Thus, a first focal point of the ellipsoidal mirror 10 is located within the source region 6, and a second focal point of the ellipsoidal mirror 10 is located within or in the region of the waveguide input 12. The ellipsoidal mirror 10 is used to focus the illumination light beam 3 onto the waveguide input 12 in the entrance face 13 of the hollow waveguide 11a. The entrance numerical aperture of the illumination light beam 3 when it enters the waveguide input 12 may be in the range of 0.02 to 0.2, and may be, for example, about 0.15, or about 0.05, or about 0.1.

[0066] In the embodiment of the illumination optical unit 1 according to FIG. 1, the ellipsoidal mirror 10 represents a mirror for grazing incidence (GI).

[0067] Depending on the embodiment of the input coupling optical unit, the input coupling optical unit may have exactly one input coupling mirror as depicted in FIG. 1, using the example of input coupling mirror 10, or may otherwise have multiple input coupling mirrors, for example two or three input coupling mirrors.

[0068] The waveguide input 12 and waveguide output 14 of the hollow waveguide 11a are in either a square or rectangular shape, with typical diameters ranging from 0.5 mm to 5 mm. The aspect ratio of the waveguide input 12 of the hollow waveguide 11a and the identically sized waveguide output 14 for the illumination light 3 in the exit face 15 is 0.25 to 4, for example 0.5 to 2. Typical dimensions of the waveguide input 12 and waveguide output 14 of the hollow waveguide 11a are 0.75 mm x 0.75 mm, 1.0 mm x 2.0 mm, or 1.5 mm x 2.0 mm.

[0069] The inner wall of the waveguide cavity of hollow waveguide 11a is provided with a highly reflective coating, for example a ruthenium coating, for the illumination light 3. The waveguide cavity is a rectangular parallelepiped according to the rectangular waveguide input 12 and waveguide output 14. The hollow waveguide 11a has a typical length in the beam direction of the illumination light 3 in the range of 10 to 500 mm, for example, 20 mm to 500 mm, 20 mm to 300 mm, or otherwise in the range of 20 mm to 80 mm.

[0070] The angle of incidence of the illumination light 3 on the inner wall of the waveguide cavity of the hollow waveguide 11a is, for example, greater than 60°. The illumination light 3 impinges on the inner wall at a small angle of incidence.

[0071] The angle between the longitudinal axis of the hollow waveguide 11a and the chief ray of the illumination light beam 3 incident on the waveguide input 12 may be 0° or, alternatively, may be different from 0°, for example in the range of 0° to 1.5°, for example 0.25° to 0.75°, in particular around 0.5°.

[0072] The ratio of the length of the hollow waveguide 11a, i.e., the distance between the entrance face 13 and the exit face 15, to the typical diameter of the hollow waveguide 11a, i.e., the typical dimension or typical diameter of the waveguide input 12 or the waveguide output 14, is in the range of 10 to 1000, and may be, for example, 10 to 500, 30 to 500, 30 to 300, or otherwise 30 to 80 or 200 to 500.

[0073] Such hollow waveguides 11a may be exposed to contamination as a result of material removal and / or external contamination. A purge gas device (not depicted in FIG. 1) serves to clean the hollow waveguides 11a and will be described in detail below on the basis of exemplary embodiment variants with reference to FIGS. 2 to 4.

[0074] Illumination light 3 can be delivered to the arcuate optical system by using an illumination light guide (not depicted in FIG. 1). Exemplary illumination light guides are described in detail below with reference to FIGS. 5-7.

[0075] An imaging output coupling mirror optical unit 16, depicted schematically in Figure 1 and positioned downstream of hollow waveguide 11a, images waveguide output 14, located in exit face 15 of hollow waveguide 11a, onto an illuminated field 4 in object plane 17. This imaging may have an image-side numerical aperture in the range of 0.1 to 0.3.

[0076] For example, two or more mirrors of the output-coupling mirror optical unit 16 may be embodied as mirrors for small angle incidence of the illumination light 3 .

[0077] The above-mentioned optional aperture stop downstream of the hollow waveguide 11a may be arranged between the hollow waveguide 11a and the first mirror of the output coupling mirror optical unit 16, or else between different mirrors of the output coupling mirror optical unit 16.

[0078] The output-coupling mirror optical unit 16 may be embodied in the style of a Wolter telescope, in particular in the style of a Type I Wolter optical unit. Such a Wolter optical unit is described in JD Mangus and JH Underwood, "Optical Design of a Glancing Incidence X-ray Telescope," Applied Optics, Vol. 8, 1969, p. 95, and references cited therein. In such a Wolter optical unit, a hyperbolic surface may also be used instead of a parabolic surface. Such a combination of an elliptical mirror and a hyperbolic mirror also constitutes a Type I Wolter optical unit.

[0079] Further exemplary embodiments of the output-coupling mirror optical unit 16 are described in U.S. Patent No. 10,042,248. Alternatively, the mirrors of the output-coupling mirror optical unit 16 may also include reflective surfaces in the form of freeform surfaces.

[0080] A reticle 18 to be inspected, held by a reticle holder 19, is arranged in the object plane 17. The reticle holder 19 is mechanically operatively connected to a reticle displacement drive 20, by means of which the reticle 18 is displaced in an object displacement direction y during mask inspection. In this way, a scanning displacement of the reticle 18 in the object plane 17 is possible.

[0081] The illuminated field 4 has typical dimensions in the object plane 17 that are less than 1 mm and may be less than 0.5 mm. In the illustrated embodiment, the illuminated field 4 extends 0.5 mm in the x direction and 0.5 mm in the y direction.

[0082] The x / y aspect ratio of the illumination field 4 may correspond to the x / y aspect ratio of the waveguide output 14 .

[0083] Using a projection optical unit, not depicted in FIG. 1, the illumination field 4 is imaged into an image field in an image plane.

[0084] The image file is detected by a detection device, such as a CCD camera or multiple CCD cameras. For details on imaging into the image field, reference is made to U.S. Patent No. 10,042,248 and the documents designated therein and in U.S. Patent No. 10,042,248.

[0085] For example, inspection of structures on reticle 18 is possible using a mask inspection system.

[0086] The imaging magnification β1 of the input coupling mirror optical unit 10 may be in the range of 0.1 to 50, i.e., the effect of the input coupling mirror optical unit may vary from a reduction of 1 / 10 to an enlargement of 50. The imaging magnification β2 of the output coupling mirror optical unit 16 may be in the range of 0.02 to 10, i.e., the effect of the output coupling mirror optical unit may vary from a reduction of 1 / 50 to an enlargement of 1. In the case of the illumination optical unit 1, the product of the two imaging magnifications β1, β2 may range from 0.25 to 10.

[0087] Three exemplary embodiments of an optical hollow waveguide assembly 11b having a hollow waveguide 11a with a purge gas device and an illumination light guide will be described in detail below with reference to Figures 2 to 4. First, the exemplary embodiment according to Figure 2 will be described in detail. Identical components of the exemplary embodiments according to Figures 3 and 4 described below retain the same reference numerals and will not be described in detail again.

[0088] The hollow waveguide 11a has a body 21. In particular, the body 21 may be formed from multiple parts. With regard to possible embodiments of the body 21 of the hollow waveguide 11a, reference is made to DE 10 2014 219 112 A1, in particular FIG. 3 and the relevant description therein, the disclosure of which is incorporated by reference in its entirety into the present application.

[0089] A waveguide cavity 22 is formed inside the body 21. In particular, the waveguide cavity 22 has an inner surface that is coated with a coating that is highly reflective to light in the EUV or DUV range, for example made from ruthenium.

[0090] The main body 21 is surrounded by a cover 23. The cover 23 mainly serves to protect the main body 21.

[0091] Moreover, the hollow waveguide assembly 11b comprises a waveguide purging device 26 having a purge gas connector 27 and a nozzle 28. The waveguide purging device 26 serves to purge the hollow waveguide 11a, particularly the waveguide cavity 22, with a purge gas 29. In particular, the hollow waveguide 11a can be continuously purged with the purge gas 29. In particular, hydrogen gas can be used as the purge gas 29.

[0092] 2, the cover 23 is attached to the body 21 such that an accumulation chamber 24 is formed in the area of ​​the waveguide output 14. An accumulation point 25 is formed within the accumulation chamber and substantially coincides with the waveguide output 14.

[0093] Purge gas 29 is first introduced into pressure chamber 30 of waveguide purging device 26 via purge gas connector 27. Pressure chamber 30 serves to reduce a first pressure P1 and a first velocity V1 at which the purge gas flows through purge gas connector 27.

[0094] In particular, the pressure P1 may be in the range of 30 Pa to 50 Pa. In particular, the velocity V1 may be in the range of 800 m / s to 900 m / s. An intermediate gap 31, through which the purge gas 29 flows out of the pressure chamber and into the nozzle 28 and is thus introduced into the accumulation chamber 24, is arranged between the pressure chamber 30 and the nozzle 28. As a result of the vortex generated when the purge gas 29 is introduced, the second pressure P2 and the second velocity V2 at the accumulation point 25 can be intentionally set. In particular, the second pressure P2 is in the range of 15 Pa to 25 Pa. In particular, the second velocity V2 is in the range of 20 m / s to 30 m / s.

[0095] As a result of pressure P2 at accumulation point 25, purge gas 29 flows into waveguide cavity 22 and exits waveguide cavity 22 at waveguide input 12. As it passes through waveguide cavity 22, purge gas 29 experiences a pressure loss ΔP as a result of friction, the inertia of purge gas 29, and the interaction of purge gas 29 with illumination light 3. Purge gas 29 has a third velocity V3 and a third pressure P3 within the waveguide cavity. Specifically, third velocity V3 may be in the range of 5 m / s to 10 m / s. Specifically, third pressure P3 may be in the range of 10 Pa to 15 Pa.

[0096] In particular, it is possible that the waveguide input and the waveguide output 14 are located at different heights in the Earth's gravitational field, which may affect, and in particular increase, the pressure loss ΔP3. In particular, the pressure loss ΔP3 may be in the range of 10 Pa to 15 Pa.

[0097] At the waveguide input, a fourth pressure P4 and / or a fourth velocity V4 is set. In particular, the fourth pressure P4 may be less than 10 Pa. In particular, the fourth velocity V4 is in the range of 4 m / s to 6 m / s.

[0098] As a result, it is possible to purge, in particular continuously purge, the hollow waveguide 11 a against the flow, in this context meaning that the propagation direction of the purge gas 29 extends antiparallel to the propagation direction of the illumination light 3.

[0099] A sensor 33 is attached to the waveguide input 12. In particular, the sensor 33 is capable of detecting pressure P4 and / or velocity V4. The sensor 33 may also measure properties of the illumination light 3, such as the intensity and / or energy of the illumination light. The sensor 33 may also take the form of a purge gas sensor 33 for detecting the flow rate of the purge gas 29. In particular, the waveguide purging device 26 allows the waveguide 11a, and in particular the waveguide cavity 22 of the waveguide, to be purged without compromising the positioning and / or function of the sensor 33 at the waveguide input 12.

[0100] Arranged at the waveguide output 14 is an illumination light guide 32 that serves to transmit the illumination light 3 from the hollow waveguide to the output coupling mirror optical unit 16. An exemplary illumination light guide 32 is described in detail below with reference to Figures 5-7.

[0101] Nozzle 28 is used to introduce purge gas 29 into waveguide output 14 indirectly via accumulation chamber 24. In the exemplary embodiment shown, at least parts of waveguide purging device 26, in particular pressure chamber 30, intermediate gap 31 and nozzle 28, are formed between the cover and a base of illumination light guide 32 facing hollow waveguide 11 a and the side of cover 23 facing illumination light guide 32. For example, suitable structures may be introduced into cover 23 and the base of illumination light guide 32 that form corresponding parts of waveguide purging device 26 when illumination light guide 32 is fixed to cover 23.

[0102] For example, the nozzle 28 may be formed between the cover 23 and the illumination light guide 32. As a result, the nozzle may be formed, for example, as an annular nozzle. It is also possible for multiple nozzles or nozzle openings to be formed between the cover and the illumination light guide.

[0103] In other exemplary embodiments, at least portions of the waveguide purging device 26, particularly the purge gas connector, the pressure chamber, the intermediate gap and / or one or more nozzles, may be fully integrated into the illumination light guide 32, particularly into the base of the illumination light guide.

[0104] As a result of introducing purge gas 29 into accumulation chamber 24, turbulence and / or vortices of the purge gas may be intentionally introduced into the accumulation chamber. This turbulence and / or these vortices may be particularly pronounced at accumulation point 25. This may increase the dynamic pressure at accumulation point 25, thereby improving purge gas flow through waveguide cavity 22.

[0105] 3 shows a further exemplary embodiment of an optical hollow waveguide assembly 11c in which purge gas 29 is introduced indirectly into the waveguide cavity 22 by using an accumulation chamber 40 and an accumulation point 41. Also depicted is a waveguide purging device 42 having a purge gas connector 43 and a nozzle 44 with multiple nozzle openings 45. The waveguide purging device 42 comprises a pressure chamber 47 and an intermediate gap 48.

[0106] By using two or more nozzle openings 45, it is possible to particularly deliberately influence the vortex flow in the accumulation chamber 40. As a result, the second pressure P2 and / or the second velocity V2 at the accumulation point 41 can be set particularly precisely.

[0107] The nozzle 44 may in particular comprise two nozzle openings 45, in particular at least three nozzle openings 45, in particular at least four nozzle openings 45. In particular, the nozzle openings 45 may be arranged symmetrically around the accumulation point 41.

[0108] The waveguide purging device 42 may be designed as part of the cover 23 or may be at least partially integrated into the cover 23 .

[0109] The optical hollow waveguide assembly 11c comprises an illumination light guide 49 that is formed as a separate component part from the waveguide purging device 42. In particular, the illumination light guide 49 may be connected to the waveguide purging device 42, and in particular fastened to the waveguide purging device 42. It is also possible for the individual components of the waveguide purging device to be integrated into the illumination light guide 42 and / or for these components to be formed between the cover and the illumination light guide 42.

[0110] 4 depicts an optical hollow waveguide assembly 11d having a waveguide purging device 34 with a purge gas connector 35 and a nozzle 36. Also according to the exemplary embodiment according to FIG. 4, the waveguide purging device 34 comprises a pressure chamber 37 and an intermediate gap 38.

[0111] 4 differs from the above-described exemplary embodiment mainly in that the purge gas 29 is introduced directly into the waveguide cavity 22. It is possible to omit the accumulation chamber 24 and the associated accumulation point 25. The nozzle 36 is arranged on the peripheral side of the cross section of the waveguide output 14 so that the purge gas 29 flows directly into the waveguide output 14.

[0112] FIG. 4 further depicts an illumination light guide 39 which is also designed as a separate component part from the waveguide purging device 34 .

[0113] 5 to 7 show exemplary embodiments of an illumination light guide 50. For example, the illumination light guide 50 may be used in the exemplary embodiments described above, in particular in the exemplary embodiment according to FIG.

[0114] In this case, the illumination light guide 50 comprises a conductor body 51 , a conductor base 52 and a conductor cover plate 53 .

[0115] The conductor base 52 serves to connect, in particular to the hollow waveguide 11a, and in particular to the hollow waveguide cover 23, in a fluid-tight manner. The conductor cover plate 53 serves to connect, in particular to a flange connection, the illumination light guide 50 to downstream components in the beam path of the illumination light 3.

[0116] The above-described waveguide purging device may be at least partially integrated into the conductor base 52. In the illustrated exemplary embodiment, the conductor base 52 is designed so that a fluid channel for forming the purging device is introduced on the side facing outward from the body 51. Following the fluid-tight connection of the conductor base 52 to the cover 27 of the hollow waveguide 11a, a fluid channel, e.g., a pressure chamber 30, is formed between the conductor base 52 and the cover. A purge gas connector 54 is integrated into the conductor base 52.

[0117] In another exemplary embodiment (not depicted in the drawings), the waveguide purging device is fully integrated into the conductor base 52. In particular, a nozzle is formed in the conductor base 52, which allows the purge gas 29 to flow directly or indirectly into the waveguide output 14. In particular, the conductor base 52 can act as part of the cover 23 of the hollow waveguide. In that case, it is possible to omit a separate cover, in particular in the region of the waveguide output 14.

[0118] In still further exemplary embodiments, the waveguide purging device may be separate from the illumination light guide 50. For example, the conductor base 52 may serve only to mechanically connect the illumination light guide 50 to the cover 23 in which the waveguide purging device is formed, or to a separate waveguide purging device.

[0119] Conductor base 52 allows illumination light guide 50 to be attached to hollow waveguide 11a such that conductor input 55 is arranged flush with waveguide output 14. Conductor input 55 serves as the entry point for illumination light 3 to exit waveguide output 14 of hollow waveguide 11a.

[0120] The conductor body 51 extends in particular parallel to the direction of propagation of the illumination light 3 and has a longitudinal axis L that in particular coincides with the direction of propagation of the illumination light 3 .

[0121] In that case, conductor input 55 and conductor output 56 lie in a plane perpendicular to longitudinal axis L and are located at respective ends of conductor body 51. Conductor body 52 takes the form of a hollow body enclosing an interior through which illumination light 3 is guided from conductor input 55 to conductor output 56. Conductor input 55 is formed in conductor base 52 and conductor output 56 is formed in conductor cover plate 53.

[0122] The interior has a cross-section defined perpendicular to the longitudinal axis L. The cross-section has a cross-sectional area and a cross-sectional shape. In this context, cross-sectional shape should be understood to mean the shape of the cross-sectional contour, regardless of the circumference and / or surface area of ​​the cross-sectional area of ​​the interior. In particular, different cross-sectional areas having the same surface area can have different cross-sectional shapes. Moreover, two cross-sections having different cross-sectional areas can have the same cross-sectional shape, for example, a circular or square cross-sectional shape.

[0123] The conductor input 55 has a different cross-sectional shape than the conductor output 56. At the conductor input 55 and the conductor output 56, the interior in each case has the same cross-sectional shape as the conductor input 55 and the conductor output 56, respectively. The cross-sectional shape of the interior cross section varies along the longitudinal axis L between the conductor input 55 and the conductor output 56. The cross-sectional shape varies, in particular, continuously along the longitudinal axis L. The cross-sectional shape of the interior may vary, in particular, smoothly along the longitudinal axis L, i.e., without corners and / or kinks. It is also possible for the cross-sectional shape of the interior to vary discontinuously.

[0124] In the exemplary embodiment shown, input conductor 55 has a circular cross-sectional shape, and output conductor 56 has an elliptical cross-sectional shape.

[0125] In other exemplary embodiments (not shown), conductor input 55 and conductor output 56 may also have polygonal cross-sectional shapes, particularly rectangular cross-sectional shapes. For example, the cross-sectional shape of conductor input 55 may be a regular polygon, particularly a square. The cross-sectional shape of conductor output 56 may be an irregular polygon, particularly a rectangle. Combinations of circular and polygonal cross-sectional shapes are also possible.

[0126] Upon emerging from the conductor output 56, the illumination light 3 has, in particular, a cross-sectional shape of the beam cross-section that corresponds to the cross-sectional shape of the conductor output 56.

[0127] 5-7, conductor output 56 has a larger cross-sectional area than conductor input 55. Conductor body 52 and the interior of conductor body 52 are conical in form. The cross-section of the interior increases particularly monotonically in cross-sectional area along longitudinal axis L, while simultaneously changing such that the initially circular cross-sectional shape of the interior eventually transitions to an elliptical cross-sectional shape.

[0128] In particular, the cross-sectional shape of the conductor input 55 has an input side ratio S1 substantially equal to 1. As a result of the input side ratio S1 being substantially equal to 1, the illumination light guide 50 can be particularly easily attached to the hollow waveguide 11a. The symmetrical area of ​​the conductor input 55 simplifies manufacturing. The purge gas supply is also improved and, in particular, becomes particularly uniform.

[0129] In particular, the input side ratio S1 may be defined as the ratio of the length to the width of the smallest rectangle forming the envelope of the cross section of the conductor input 55, i.e., the smallest rectangle whose area completely encompasses the cross section of the conductor input 55. For a circular cross section, such an enveloping rectangle takes the form of a square, resulting in an input side ratio S1 of 1. The diameter of the conductor input 55 having a circular cross section may in particular be in the range of 10 mm to 20 mm, and in particular may be in the order of about 15 mm.

[0130] The conductor output 56 has an output side ratio S2 that is not equal to 1. For the conductor output, the output side ratio S2 is defined analogously to the input side ratio S1 of the conductor input 55. For an elliptical cross-sectional shape, the output side ratio S2 corresponds to the quotient of the major axis and the minor axis of the ellipse. In particular, the major axis of the ellipse may have a length in the range of 30 mm to 60 mm, in particular about 45 mm. In particular, the minor axis of the ellipse may have a length in the range of 20 mm to 40 mm, in particular about 30 mm. In particular, for the output side ratio S2, 1.1

Claims

1. An illumination light guide (50) for guiding EUV or DUV illumination light (3) in an illumination optical unit (1), comprising: a conductor body (51), a conductor input (55), - conductor output (56) and Equipped with -- the conductor body (51) defines an interior for guiding the illumination light (3) along a longitudinal axis (L) from the conductor input (55) to the conductor output (56); -- an illumination light guide (50) in which the internal cross-sectional shape, defined perpendicular to the longitudinal axis (L), varies along the longitudinal axis (L).

2. The cross section of the conductor input (55) defined perpendicular to the longitudinal axis (L) has an input side ratio S 1 and a cross section of the conductor output (56) defined perpendicular to the longitudinal axis (L) has an output side ratio S 2 and S 1 and S 2 2. The illumination light guide (50) of claim 1, wherein the first and second electrodes are different from each other.

3. S 2 3. The illumination light guide (50) of claim 2, wherein is not equal to 1.

4. S 1 4. An illumination light guide (50) according to claim 2, wherein is substantially equal to 1.

5. S 2 For 1.1<S 2 An illumination light guide (50) according to any one of claims 2 to 4, characterized in that <1.9 applies.

6. An illumination light guide (50) according to any one of claims 1 to 5, characterized in that the conductor body (51) has a conical shape.

7. An illumination light guide (50) according to any one of claims 1 to 6, characterized in that the conductor input has a circular cross-sectional shape.

8. An illumination light guide (50) according to any one of claims 1 to 7, characterized in that the conductor output (56) has an elliptical cross-sectional shape.

9. An illumination light guide (50) according to any one of claims 1 to 6 or 8, characterized in that the cross-sectional shape of the conductor input (55) is a regular polygon.

10. An illumination light guide (50) according to any one of claims 1 to 7 or 9, characterized in that the cross-sectional shape of the conductor output (56) is an irregular polygon.

11. 11. An illumination light guide (50) according to any one of claims 1 to 10, characterized in that at least one functional component for influencing optical component parts arranged upstream in the illumination optical unit (1) is at least partially integrated into the illumination light guide (50) in the region of the conductor input (55).

12. 12. An illumination light guide (32, 39, 49, 50) according to claim 11, characterized in that a purging device for purging upstream optical components is at least partly integrated into the illumination light guide.

13. An illumination optical unit (1) comprising an illumination light guide (32, 39, 49, 50) according to any one of claims 1 to 12 and a light source (5).

14. 14. An illumination optical unit (1) according to claim 13, characterized by an optical hollow waveguide assembly (11b, 11c, 11d) comprising a hollow waveguide (11a) and a waveguide purging device (26, 34, 42).

15. 15. Illumination optical unit (1) according to claim 14, characterized in that the waveguide purging device (26, 34, 42) is at least partly integrated in the illumination light guide (50).

16. An inspection apparatus comprising the illumination optical unit according to any one of claims 13 to 15.

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