Lighting guidance, lighting optics and inspection system

Abstract

Illumination light guide (32; 39; 49; 50) for guiding EUV or DUV illumination light (5) in an illumination optic (1), comprising a tubular guide body (51), a guide inlet (55), and a guide outlet (50), wherein the guide body (51) forms an interior space for guiding the illumination light (3) from the guide inlet (55) to the guide outlet (56) along a longitudinal axis (L), and wherein a cross-sectional shape of the interior space defined perpendicular to the longitudinal axis (L) changes along the longitudinal axis (L).

Description

[0001] The present invention relates to an illumination light guide for an illumination optic, an illumination optic with such an illumination light guide and an inspection system with such an illumination optic.

[0002] Illumination guides are known in various forms from prior art. WO 03 / 050857 A1 discloses a reflective optical illumination element. DE 10 2013 213 564 A1 discloses an optical hollow waveguide assembly.

[0003] It is an object of the present invention to provide an improved illumination light guide which can be used in a particularly space-efficient manner in an illumination optic and which does not obstruct, in particular cut off, the beam path of an illumination light beam.

[0004] This problem is solved by an illumination light guide with the features listed in claim 1.

[0005] According to the invention, it was recognized that a lighting guide is designed to be particularly space-efficient if the cross-sectional shape of the interior changes along the longitudinal direction of the guide body.

[0006] It is also advantageous that the changing cross-sectional shape allows for optimal adaptation of the lighting guide to different conditions and / or requirements in the area of ​​the guide inlet and the guide outlet.

[0007] The cross-sectional shape is understood to mean the shape of the contour of the cross-section, independent of the perimeter and / or the area of ​​the cross-sectional surface of the interior space.

[0008] The longitudinal axis can, in particular, represent an axis of symmetry of the tubular guide body. The longitudinal axis can, in particular, be oriented parallel to the direction of propagation of the illumination light, especially a main beam of the illumination light.

[0009] The guide body forms an interior space for guiding the illumination light. In particular, the guide body encloses the interior space at least partially, especially in the direction perpendicular to the longitudinal axis, for example on its circumference or outer surface.

[0010] The guide body can be designed as a hollow body, for example, as a tubular guide body. The cross-sectional shape of the guide body can change in a manner equivalent to the cross-sectional shape of the interior, so that the wall thickness between an inner surface of the interior and an outer surface of the guide body remains constant along the longitudinal direction. This allows the lighting guide to be integrated into a lighting optic in a more space-saving manner. Material and manufacturing costs can be reduced.

[0011] The cross-sectional shape of the interior of the guide body can change continuously and / or in discrete steps. Preferably, the cross-sectional shape changes continuously. An inner surface of the guide body facing the interior is particularly smooth.

[0012] The illumination light guide serves in particular to transfer the illumination light from a first optical component of the illumination optics to a second optical component of the illumination optics.

[0013] The first optical component can, in particular, be a hollow waveguide. The second optical component can be designed as an output coupling mirror optic. The first and / or the second optical component, and optionally further components arranged with the first and / or second optical component, can significantly restrict the installation space for the illumination light guide. This significantly restricted installation space can be optimally utilized by means of an illumination light guide according to the invention.

[0014] At the same time, it was surprisingly found that despite the changing cross-sectional shape of the interior, the path of the illumination light is not obstructed and, in particular, not cut off. An illumination light guide according to the invention can be integrated into the lighting optics in a particularly space-efficient manner, without any negative effects on the illumination light and any associated deficiencies in the lighting optics.

[0015] The guide inlet and / or the guide outlet can be arranged, in particular, in planes orthogonal to the longitudinal direction. The guide inlet can be arranged, in particular, at a first end of the tubular base body. The guide outlet can be arranged, in particular, at an end opposite the first end with respect to the longitudinal direction.

[0016] A cross-section of the guide inlet defined perpendicular to the longitudinal axis has an inlet aspect ratio S1 and a cross-section of the guide outlet defined perpendicular to the longitudinal axis has an outlet aspect ratio S2, where S1 and S2 are different, and where for S2: 1.1 < S2 < 1.9.

[0017] This allows for precise adaptation to the requirements, especially the spatial conditions of the higher-level lighting optics, in the area of ​​the guide inlet and / or the guide outlet.

[0018] The side outlet ratio S2 has proven effective in practice. This selected outlet aspect ratio allows the lighting guide to be integrated into the overall lighting optics in a particularly space-saving manner.

[0019] In particular, it is possible that this applies to the outlet aspect ratio S2: 1.2 < S2 < 1.8, especially 1.3 < S2 < 1.7, especially 1.4 < S2 < 1.6 and especially S2 = 1.5.

[0020] The cross-section of the guide inlet and / or the cross-section of the guide outlet can have a cross-sectional area and / or a cross-sectional shape.

[0021] Here, the cross-section of the guide inlet or the cross-section of the guide outlet can refer to the cross-section of the interior of the lighting guide at the guide inlet or at the guide outlet, respectively.

[0022] It is also possible that the cross-section of the guide inlet or the cross-section of the guide outlet is defined as the cross-section of the outer surface of the lighting guide at the guide inlet or at the guide outlet, respectively.

[0023] In this context, the aspect ratio of a cross-section, for example the inlet-aspect ratio of the guide inlet or the outlet-aspect ratio of the guide outlet, shall be understood in particular as a ratio of a length and a width of the smallest rectangle that forms an envelope of the cross-section, i.e., in particular, the smallest rectangle whose area completely encompasses the cross-section.

[0024] Due to the different aspect ratios, the guide inlet and / or the guide outlet can be ideally adapted to the installation space defined by the other optical components of the lighting optics and / or a functional and / or mechanical coupling to these components.

[0025] The illumination light guide according to the invention is particularly well suited for the practically relevant application in which the illumination light has a beam cross-section that extends differently in different spatial directions, and which is particularly elliptical. This allows light to be guided precisely, especially for mask inspection.

[0026] An illumination guide according to claim 2 is particularly easy to manufacture. With an inlet aspect ratio of essentially 1, preferably exactly 1, the guide inlet exhibits a particularly high number of symmetries, especially rotational symmetries. The guide inlet can, in particular, be rotationally symmetrical. Symmetrical components are generally easier to manufacture.

[0027] The symmetry of the guide inlet also enables the efficient integration of further functional components into the illumination light guide, in particular a purging system for upstream optical components, for example, for a hollow waveguide. The symmetry ensures a uniform design and / or function of the functional components, such as a uniform supply of purging gas.

[0028] An illumination guide according to claim 3 enables even more efficient use of the available installation space. Experience has shown that the installation space in the illumination optics is smaller in the area of ​​the guide outlet or in the area of ​​the guide inlet. This can be taken into account in the design of the illumination optics by means of a conical design of the tubular guide body.

[0029] The interior of the guide body can also be conical. In this case, too, the wall thickness between the outer surface of the guide body and the inner surface of the interior can be constant.

[0030] It is particularly possible that the cross-sectional area of ​​the guide outlet is larger than the cross-sectional area of ​​the guide inlet. In this case, the interior of the guide body widens along its longitudinal axis in the direction of light propagation. This allows the light, which has a widening beam cross-section, to be reliably guided without impairment.

[0031] An illumination guide according to claim 4 is easy and precise to manufacture. Components with circular contours can be produced using a variety of manufacturing processes. Furthermore, the guide inlet exhibits a particularly high degree of symmetry, which improves the arrangement and / or functional interaction with upstream components.

[0032] A guide outlet according to claim 5 is particularly suitable for illumination light with an elliptical beam cross-section.

[0033] An illumination light guide according to claim 6 can be integrated into the illumination optics particularly easily. In particular, the guide inlet has a square cross-sectional shape. The optical component upstream of the illumination light guide, in particular the hollow waveguide, can, for example, have a rectangular and, in particular, a square hollow waveguide cross-section. The cross-sectional shape of a regular polygon, in particular a square, enables good coupling and / or functional interaction of the upstream component with the illumination light guide. The illumination light guide exhibits a high degree of symmetry in the region of the guide inlet.

[0034] Furthermore, the hollow waveguide, in particular, can have a waveguide cavity with a substantially rectangular, especially square, contour. In this case, the illumination light can be transferred from the hollow waveguide to the illumination guide with particular efficiency.

[0035] A lighting guide according to claim 7 can be integrated into a lighting optic in a particularly space-efficient manner. In particular, it is possible for the cross-sectional shape to be rectangular, especially with an aspect ratio other than 1.

[0036] An illumination light guide according to claim 8 is particularly flexible in its application. By integrating further functional components into the illumination light guide, in particular into a guide base of the illumination light guide, other components of the illumination optics, especially the optical component directly upstream of the illumination light guide, can be specifically influenced to ensure smooth and efficient operation of the illumination optics.

[0037] An illumination light guide according to claim 9 enables efficient rinsing and / or cleaning of the upstream optical component, in particular the upstream hollow waveguide. The rinsing device is in particular a waveguide rinsing device.

[0038] The illumination guide can, in particular, have a purge gas connection to supply purge gas, especially hydrogen gas, from a purge gas reservoir to the upstream optical component in a targeted and, in particular, controlled manner. This allows the purge gas flow to be controlled very effectively. The purge gas connection can be positioned at a distance from the sensitive optical components.

[0039] Alternatively or in addition to the purge gas connection, further components of the purge system can be integrated into the illumination / light guide, in particular the guide base. Specifically, pressure chambers, intermediate gaps, and / or nozzles can be integrated into the illumination / light guide, especially the guide base.

[0040] It is also possible that components of the flushing device are formed between the illumination light guide, in particular the guide base, and a cover of the upstream optical components, in particular a hollow waveguide.

[0041] Another objective of the invention is to improve lighting optics.

[0042] This problem is solved by a lighting optic having the features listed in claim 10.

[0043] The lighting optics can be part of an inspection system, for example for the inspection of photolithographic masks and / or photolithographic wafers.

[0044] A lighting optic according to claim 11 can provide and / or focus particularly homogeneous illumination light.

[0045] A lighting optic according to claim 12 is particularly compact. The components of the rinsing device can, in particular, be completely integrated into the lighting guide, especially the guide base, or be formed between the lighting guide, especially the guide base, and a cover of the hollow waveguide.

[0046] Another objective of the invention is to improve an inspection system.

[0047] This task is solved by an inspection system having the features listed in claim 13.

[0048] The inspection system can be specifically designed to inspect photolithographic masks and / or photolithographic wafers. The inspection system can be specifically designed as an actinic inspection system, i.e., using light in the EUV wavelength range.

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

[0050] In addition to the lighting optics, the inspection system may also include projection optics, which serve to image the light reflected from the mask and / or wafer to be inspected onto an image plane.

[0051] An embodiment of the invention is explained in more detail below with reference to the drawing. These show: Fig. 1 schematically an optical system with an illumination optic for a mask inspection system for use with EUV illumination light; Fig. 2 in schematic view a sectional view of a first embodiment of a hollow waveguide assembly with a waveguide cleaning device and an illumination light guide; Fig. 3 in schematic view a sectional view of a further embodiment of a hollow waveguide assembly with a waveguide cleaning device and an illumination light guide; Fig. 4 in schematic view a sectional view of a third embodiment of a hollow waveguide assembly with a waveguide cleaning device and an illumination light guide; Fig. 5 in perspective view an embodiment of an illumination light guide; Fig. 6 a sectional view of the lighting guide according to Fig. 5; and Fig. Figure 7 shows a schematic view of a guide inlet for a lighting guide according to Fig. 5.

[0052] An illumination optic 1 is part of an illumination system 2 of a mask inspection system for use with EUV illumination light 3. The beam path of the illumination light 3 is illustrated in the drawing via marginal rays. The illumination light 3 illuminates an illumination field or object field 4 of the mask inspection system.

[0053] The illumination 3 is generated by an EUV light source 5 in a source area or source volume 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.

[0054] Light source 5 can be implemented as a plasma light source. This could be, for example, a laser-produced plasma (LPP) source or a discharge-produced plasma (DPP) source. It is also possible to use a high-harmonic EUV source. Such plasma sources are generally known as light sources for EUV projection systems.

[0055] To facilitate spatial relationships, a Cartesian xyz coordinate system is used below. The x-axis is perpendicular to the drawing plane. Fig. 1. The y-axis runs in the Fig. 1 horizontally to the right and the z-axis runs in the Fig. 1 vertically upwards.

[0056] The source region 6 is approximately ellipsoidal in shape and has a greatest extent, also called the principal extent, parallel to the y-axis. A principal emission direction of the illumination light 3 from the source region 6 runs along this principal extent, i.e., with the ellipsoidal approximation, along one of the longest principal axes of the ellipsoidal source region 6.

[0057] After emission by the light source 5, the illumination light 3 first passes through an aperture diaphragm 9 which limits a bundle of the illumination light 3 at its edge.

[0058] The aperture diaphragm 9 can be designed to be interchangeable. For this purpose, for example, an aperture wheel can be provided which stores different aperture diaphragm configurations that can be selectively used in the beam path of the illumination light 3. Such an interchangeable aperture diaphragm design allows for the specification of different input apertures for the illumination light 3.

[0059] The aperture diaphragm 9 can be interchangeable and / or adjustable and / or have its aperture edge adjustable. This allows for the realization and / or adjustment of various aperture geometries for the aperture diaphragm 9. Predefinable aperture geometries can be, for example, round with a selectable diameter and / or elliptical with a selectable ellipse size and, if necessary, with a selectable semi-axis ratio of the ellipses. Such a semi-axis ratio of an ellipse predefinable via the aperture diaphragm 9 can be 2:1.

[0060] Following the aperture diaphragm 9, the illumination light beam 3 is transferred by a coupling mirror 10 to a beam homogenization device 11 of the illumination optics 1. As explained in more detail below, the coupling mirror 10 can also be part of the beam homogenization device 11. A beam homogenizing element, for example a hollow waveguide 11a, can be part of the beam homogenization device 11. In other embodiments, the beam homogenization device 11 can alternatively or additionally include at least one faceted mirror for splitting the EUV illumination light 3 into a plurality of individual beams that are superimposed to form a homogenizing mixture. In this case, the beam homogenization device can also include, for example, two faceted mirrors arranged one after the other.

[0061] The aperture diaphragm 9 limits the numerical aperture of the illumination beam 3 emitted from the source area 6 to a value between 0.02 and 0.03, for example, between 0.02 and 0.1 or between 0.05 and 0.08. A numerical aperture greater than 0.1, as determined by the aperture diaphragm 9, i.e., in the range between 0.1 and 0.3, allows for a greater luminous efficacy in the illumination beam path between the source volume 6 and the illumination field 4.

[0062] An incoherent lighting setting may be used.

[0063] Alternatively or additionally to the aperture diaphragm 9, an aperture-limiting diaphragm can be arranged between the hollow waveguide 11a and a subsequent optical component of the illumination optics 1. It is also possible to arrange such a further aperture diaphragm in the beam path of the illumination light 3 after the hollow waveguide 11a between two downstream optical components of the illumination optics 1.

[0064] The coupling mirror 10, for example, is designed as an ellipsoidal mirror and serves to image the source region 6 of the EUV light source 5 into a waveguide inlet 12 in an entry plane 13 of the hollow waveguide 11a. 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 in the waveguide inlet 12 or in the region of the waveguide inlet 12. The ellipsoidal mirror 10 focuses the illumination light beam 3 into the waveguide inlet 12 in the entry plane 13 of the hollow waveguide 11a. An entry-side numerical aperture of the illumination light bundle 3 at the entry into the waveguide inlet 12 can be in the range of 0.02 to 0.2, for example in the range of 0.15 or in the range of 0.05 or 0.1.

[0065] The ellipsoidal mirror 10 adjusts the illumination optics 1 according to Fig. 1 represents a mirror for grazing incidence (GI).

[0066] Depending on the design of the coupling optics, it has exactly one coupling mirror, as in the Fig. 1 is shown using the example of the coupling mirror 10, or several coupling mirrors, e.g. two or three coupling mirrors.

[0067] The waveguide inlet 12 and waveguide outlet 14 of the hollow waveguide 11a are each square or rectangular with typical dimensions in the range of 0.5 mm to 5 mm. The aspect ratio of the waveguide inlet 12 and an equally sized waveguide outlet 14 of the hollow waveguide 11a for the illumination 3 in an exit plane 15 is between 0.25 and 4, for example, between 0.5 and 2. Typical sizes of the waveguide inlet 12 and the waveguide outlet 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.

[0068] An inner wall of a waveguide cavity of the hollow waveguide 11a is provided with a highly reflective coating for the illumination light 3, for example, a ruthenium coating. Corresponding to the rectangular waveguide inlet and outlet 12, 14, the waveguide cavity is cuboidal. The hollow waveguide 11a has a typical length in the direction of the illumination light 3 in the range between 10 and 500 mm, for example, between 20 mm and 500 mm, between 20 mm and 300 mm, or between 20 mm and 80 mm.

[0069] 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 inner wall is illuminated by the illumination light 3 at a grazing angle.

[0070] An angle between a longitudinal axis of the hollow waveguide 11a and the main beam of the illumination beam 3 incident into the waveguide inlet 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 especially in the range of 0.5°.

[0071] A ratio of the length of the hollow waveguide 11a, i.e., the distance between the inlet plane 13 and the outlet plane 15, and a typical diameter of the hollow waveguide 11a, i.e., the typical size or diameter of the waveguide inlet 12 or the waveguide outlet 14, lies in the range between 10 and 1000 and can, for example, be between 10 and 500, between 30 and 500, between 30 and 300, or between 30 and 80 or between 200 and 500.

[0072] Due to material abrasion and / or external contamination, it is possible that such a hollow waveguide 11a may be exposed to contamination. A cleaning agent not included in the Fig. 1. Purge gas device shown, which is described below with reference to exemplary design variants. Fig. 2, Fig. 3 to Fig. 4 will be explained in more detail.

[0073] It is possible that the lighting light 3 is powered by means of a light that is not in the Fig. The illumination / lighting guide shown in Figure 1 is transferred to the higher-level optical system. An example illumination / lighting guide is described below with reference to the... Fig. 5, Fig. 6 to Fig. 7 explained in more detail.

[0074] One in the Fig. In a schematic representation of the imaging output coupler optic 16, located downstream of the hollow waveguide 11a, the waveguide outlet 14 of the hollow waveguide 11a, lying in an exit plane 15, images the illumination field 4 in an object plane 17. The image-side numerical aperture of this imaging can be in the range between 0.1 and 0.3.

[0075] The mirrors of the coupling mirror optics 16, for example two or more, can be designed as mirrors for grazing incidence of the illumination light 3.

[0076] The aperture stop described above, which may be used after the hollow waveguide 11a, can be arranged between the hollow waveguide 11a and a first mirror of the output coupling mirror optics 16 or between different mirrors of the output coupling mirror optics 16.

[0077] The output coupler 16 can be designed in the manner of a Wolter telescope, specifically as a Wolter optic of type I. Such Wolter optics are described in J.D. Mangus, 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.

[0078] Another embodiment of the output coupling mirror optics 16 is described in US 10,042,248 B2. Alternatively, mirrors of the output coupling mirror optics 16 can also have reflective surfaces in the form of freeform surfaces.

[0079] In object plane 17, a reticle 18 to be inspected is arranged and held by a reticle holder 19. The reticle holder 19 is mechanically connected to a reticle displacement drive 20, via which the reticle 18 is displaced along an object displacement direction y during a mask inspection. This enables scanning and displacement of the reticle 18 in object plane 17.

[0080] The illumination field 4 has a typical dimension in the object plane 17 that is less than 1 mm and can be 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.

[0081] The x / y aspect ratio of the illumination field 4 can match the x / y aspect ratio of the waveguide outlet 14.

[0082] Lighting field 4 is equipped with a [unclear] in the Fig. 1 projection optics not shown, projected into an image field in an image plane.

[0083] The image field is captured by a detection device, e.g., a CCD camera or multiple CCD cameras. For details of the imaging into the image field, refer to US 10,042,248 B2 and the references given here and in US 10,042,248 B2.

[0084] The mask inspection system makes it possible to inspect, for example, a structure on reticulum 18.

[0085] The imaging factor β1 of the input-coupling mirror optics 10 can range from 0.1 to 50, meaning it can reduce the image by a factor of 10 to magnify it by a factor of 50. The imaging factor β2 of the output-coupling mirror optics 16 can range from 0.02 to 10, meaning it can itself reduce the image by a factor of 50 to magnify it by a factor of 1. The product β1, β2 of the two imaging factors in the illumination optics 1 can range from 0.25 to 10.

[0086] The following will refer to the Fig. 2, Fig. 3 to Fig. 4 Three embodiments of an optical hollow waveguide assembly 11b comprising a hollow waveguide 11a, a purging gas device, and an illumination light guide are explained in more detail. First, an embodiment is described using the following examples: Fig. 2 explained in detail. Identical components in the embodiments to be explained later according to Fig. 3 and Fig. 4 have identical reference numbers and are not described again in detail.

[0087] The hollow waveguide 11a has a base body 21. The base body 21 can, in particular, be designed in multiple parts. Regarding a possible design of the base body 21 of the hollow waveguide 11a, reference is made to DE 10 2014 219 112 A1, in particular to that document. Fig. 3 and the accompanying description, the full disclosure of which is incorporated into this application by reference.

[0088] Inside the base body 21, a waveguide cavity 22 is formed. The waveguide cavity 22 has, in particular, an inner surface coated with a highly reflective coating, for example made of ruthenium, for light in the EUV or DUV range.

[0089] The base body 21 is enclosed by a cover 23. The cover 23 primarily serves to protect the base body 21.

[0090] The hollow waveguide assembly 11b also includes a waveguide purging device 26 with a purging gas connection 27 and a nozzle 28. The waveguide purging device 26 serves to purge the hollow waveguide 11a, in particular the waveguide cavity 22, with purging gas 29. The hollow waveguide 11a can be purged continuously with purging gas 29. Hydrogen gas can be used as the purging gas 29.

[0091] In the embodiment according to Fig. 2 The cover 23 is attached to the base body 21 in such a way that a stagnation chamber 24 is formed in the area of ​​the waveguide outlet 14. A stagnation point 25 forms within the stagnation chamber, which essentially coincides with the waveguide outlet 14.

[0092] The purge gas 29 is first introduced into a pressure chamber 30 of the waveguide purge device 26 via the purge gas connection 27. The pressure chamber 30 serves to reduce the initial pressure P1 and initial velocity V1 at which the purge gas flows in via the purge gas connection 27.

[0093] The pressure P1 can be in the range of 30 Pa to 50 Pa. The velocity V1 can be in the range of 800 m / s to 900 m / s. An intermediate gap 31 is arranged between the pressure chamber 30 and the nozzle 28, through which the purge gas 29 flows from the pressure chamber into the nozzle 28 and is thereby injected into the stagnation chamber 24. The turbulence created when the purge gas 29 is injected allows a second pressure P2 and a second velocity V2 to be selectively set at the stagnation point 25. The second pressure P2 is in the range of 15 Pa to 25 Pa. The second velocity V2 is in the range of 20 m / s to 30 m / s.

[0094] Due to the pressure P2 generated at stagnation point 25, the purge gas 29 flows into the waveguide cavity 22 and exits the waveguide cavity 22 at the waveguide inlet 12. As it traverses the waveguide cavity 22, the purge gas 29 experiences a pressure loss ΔP due to friction, inertia, and interaction with the illumination light 3. Within the waveguide cavity 22, the purge gas 29 exhibits a third velocity V3 and a third pressure P3. The third velocity V3 can be in the range of 5 m / s to 10 m / s. The third pressure P3 can be in the range of 10 Pa to 15 Pa.

[0095] It is particularly possible that the waveguide inlet and the waveguide outlet 14 are located at different heights in the Earth's gravitational field, which can influence, and especially increase, the pressure loss ΔP3. It is particularly possible that the pressure loss ΔP3 is in the range of 10 Pa to 15 Pa.

[0096] At the waveguide inlet, a fourth pressure P4 and / or a fourth velocity V4 is established. The fourth pressure P4 can be less than 10 Pa. The fourth velocity V4 is in the range of 4 m / s to 6 m / s.

[0097] This makes it possible to purge the hollow waveguide 11a in a counter-current direction, particularly continuously. "Counter-current direction" in this context means that the direction of propagation of the purge gas 29 is antiparallel to the direction of propagation of the illumination light 3.

[0098] Sensors 33 are attached to the waveguide inlet 12. These sensors can detect, in particular, the pressure P4 and / or the velocity V4. The sensors 33 can also measure properties of the illumination 3, such as its intensity and / or energy. It is also possible for the sensors 33 to be configured as purge gas sensors 33 to detect the flow rate of the purge gas 29. The waveguide purge device 26 enables, in particular, the purging of the waveguide 11a, especially its waveguide cavity 22, without affecting the positioning and / or function of the sensors 33 at the waveguide inlet 12.

[0099] An illumination light guide 32 is arranged at the waveguide outlet 14, which serves to transfer the illumination light 3 from the hollow waveguide to the output coupling mirror optics 16. An exemplary illumination light guide 32 is described in connection with the Fig. 5, Fig. 6 to Fig. 7 explained in more detail below.

[0100] The purge gas 29 is indirectly injected into the waveguide outlet 14 via the reservoir chamber 24 by means of the nozzle 28. In the illustrated embodiment, at least parts of the waveguide purge device 26, in particular the pressure chamber 30, the intermediate gap 31, and the nozzle 28, are formed between the cover and a base of the illumination guide 32 facing the hollow waveguide 11a and a side of the cover 23 facing the illumination guide 32. For example, corresponding structures can be incorporated into the cover 23 and the base of the illumination guide 32 which, when the illumination guide 32 is attached to the cover 23, form the corresponding parts of the waveguide purge device 26.

[0101] For example, the nozzle 28 can be formed between the cover 23 and the lighting guide 32. This allows the nozzle to be designed as a ring nozzle, for instance. It is also possible to form multiple nozzles or nozzle openings between the cover and the lighting guide.

[0102] In other embodiments, at least parts of the waveguide flushing device 26 can be fully integrated into the illumination light guide 32, in particular its base, especially a flushing gas connection, a pressure chamber, an intermediate gap and / or one or more nozzles.

[0103] By injecting the purge gas 29 into the storage chamber 24, turbulence and / or vortices of the purge gas can be selectively induced within the storage chamber. These turbulences and / or vortices are particularly pronounced at the stagnation point 25. This increases the dynamic pressure at the stagnation point 25, thereby improving the purge gas flow through the waveguide cavity 22.

[0104] In the Fig. Figure 3 shows a further embodiment of an optical hollow waveguide assembly 11c, in which the purge gas 29 is injected indirectly into the waveguide cavity 22 by means of a stagnation chamber 40 and a stagnation point 41. Also shown is a waveguide purge device 42 with a purge gas connection 43 and a nozzle 44 having a plurality of nozzle openings 45. The waveguide purge device 42 has a pressure chamber 47 and an intermediate gap 48.

[0105] By using more than one nozzle opening 45, it is possible to influence the turbulence in the stagnation chamber 40 in a particularly targeted manner. This allows the second pressure P2 and / or the second velocity V2 to be set very precisely at the stagnation point 41.

[0106] The nozzle 44 can, in particular, have two nozzle openings 45, in particular at least three nozzle openings 45, and in particular at least four nozzle openings 45. The nozzle openings 45 can, in particular, be arranged symmetrically around the stagnation point 41.

[0107] The waveguide flushing device 42 is designed as part of the cover 23, or at least partially integrated into the cover 23.

[0108] The optical hollow waveguide assembly 11c has an illumination light guide 49, which is designed as a separate component from the waveguide cleaning device 42. The illumination light guide 49 can, in particular, be connected to and, in particular, attached to the waveguide cleaning device 42. It is also possible to integrate individual components of the waveguide cleaning device into the illumination light guide 42 and / or to form them between the cover and the illumination light guide 42.

[0109] According to the exemplary embodiment Fig. Figure 4 shows an optical hollow waveguide assembly 11d with a waveguide purging device 34 having a purging gas connection 35 and a nozzle 36. Also according to the embodiment shown in Figure 4. Fig. 4 The waveguide flushing device 34 has a pressure chamber 37 and an intermediate gap 38.

[0110] The exemplary embodiment according to Fig. The embodiment 4 differs from previously described embodiments mainly in that the purge gas 29 is injected directly into the waveguide cavity 22. A stagnation chamber 24 and an associated stagnation point 25 are not required. The nozzle 36 is arranged circumferentially around a cross-section of the waveguide outlet 14 such that the purge gas 29 flows directly onto the waveguide outlet 14.

[0111] In the Fig. Figure 4 also shows an illumination light guide 39, which is designed as a separate component from the waveguide flushing device 34.

[0112] The Fig. 5, Fig. 6 to Fig. Figure 7 shows an embodiment of an illumination light guide 50. The illumination light guide 50 can be used, for example, in the embodiments described above, in particular in the embodiment according to Fig. 2.

[0113] The lighting guide 50 has a guide body 51, a guide base 52 and a guide cover plate 53.

[0114] The guide base 52 serves for a particularly fluid-tight connection to the hollow waveguide 11a, in particular its cover 23. The guide cover plate 53 serves for connecting, in particular flange-fitting, the illumination light guide 50 to components downstream in the beam path of the illumination light 3.

[0115] The guide base 52 can incorporate, at least partially, a previously described waveguide cleaning device. In the illustrated embodiment, the guide base 52 is designed such that fluid channels for forming the cleaning device are provided on the side facing away from the base body 51. After a fluid-tight connection of the guide base 52 to a cover 27 of the hollow waveguide 11a, fluid channels, for example the pressure chamber 30, are formed between the guide base 52 and the cover. The cleaning gas connection 54 is integrated into the guide base 52.

[0116] In other embodiments not shown in the figures, the waveguide cleaning device is fully integrated into the guide base 52. In particular, nozzles are formed in the guide base 52 to allow the cleaning gas 29 to flow directly or indirectly onto the waveguide outlet 14. It is particularly possible for the guide base 52 to function as part of the cover 23 of the hollow waveguide. In this case, a separate cover in the area of ​​the waveguide outlet 14 can be omitted.

[0117] In other embodiments, the waveguide cleaning device can be independent of the lighting guide 50. For example, the guide base 52 can serve only to mechanically connect the lighting guide 50 to a cover 23 in which the waveguide cleaning device is formed, or to a separate waveguide cleaning device.

[0118] The guide base 52 allows the illumination light guide 50 to be attached to the hollow waveguide 11a such that the guide inlet 55 is aligned with the waveguide outlet 14. The guide inlet 55 serves as the entry point for the illumination light 3, which exits from the waveguide outlet 14 of the hollow waveguide 11a.

[0119] The guide body 51 has a longitudinal axis L which runs in particular parallel to the direction of propagation of the illumination light 3 and in particular coincides with the direction of propagation of the illumination light 3.

[0120] The guide inlet 55 and the guide outlet 56 are located in planes orthogonal to the longitudinal axis L at respective ends of the guide base body 51. The guide base body 52 is designed as a hollow body enclosing an interior space in which the illumination light 3 is guided from the guide inlet 55 to the guide outlet 56. The guide inlet 55 is formed in the guide base 52, and the guide outlet 56 in the guide top plate 53.

[0121] The interior space has a defined cross-section perpendicular to the longitudinal axis L. This cross-section has a cross-sectional area and a cross-sectional shape. The cross-sectional shape refers to the contour of the cross-section, independent of the perimeter and / or the area of ​​the interior space's cross-sectional area. It is particularly possible for different cross-sectional areas of equal size to have different cross-sectional shapes. Furthermore, it is possible for two cross-sections with different cross-sectional areas to have the same cross-sectional shape, for example, a round or square cross-sectional shape.

[0122] The guide inlet 55 has a different cross-sectional shape than the guide outlet 56. At both the guide inlet 55 and the guide outlet 56, the interior space has the same cross-sectional shape as the guide inlet 55 and the guide outlet 56, respectively. The cross-sectional shape of the interior space changes along the longitudinal axis L between the guide inlet 55 and the guide outlet 56. The cross-sectional shape changes continuously along the longitudinal axis. The cross-sectional shape of the interior space can change smoothly along the longitudinal axis L, i.e., without edges and / or kinks. It is also possible for the cross-sectional shape of the interior space to change abruptly.

[0123] In the illustrated embodiment, the guide inlet 55 has a circular cross-sectional shape. The guide outlet 56 has an elliptical cross-sectional shape.

[0124] In other embodiments not shown in figures, the guide inlet 55 and the guide outlet 56 can also have a polygonal, in particular a rectangular, cross-sectional shape. For example, the cross-sectional shape of the guide inlet 55 can be a regular polygon, in particular a square. The cross-sectional shape of the guide outlet 56 can be an irregular polygon, in particular a rectangle. Combinations of round and polygonal cross-sectional shapes are also possible.

[0125] The illumination light 3, when exiting the guide outlet 56, has in particular a cross-sectional shape of the beam cross-section that corresponds to the cross-sectional shape of the guide outlet 56.

[0126] In the Fig. 5, Fig. 6 to Fig.In the embodiment shown in Figure 7, the guide outlet 56 has a larger cross-sectional area than the guide inlet 55. The interior of the guide base body 52 and the guide base body 52 are conically shaped. The cross-section of the interior changes such that the cross-sectional area increases along the longitudinal axis L, in particular monotonically, while at the same time the initially circular cross-sectional shape of the interior transitions into a final elliptical cross-sectional shape.

[0127] The cross-sectional shape of the guide inlet 55 features an inlet aspect ratio S1 that is essentially equal to 1. This aspect ratio S1, which is essentially equal to 1, allows the illumination guide 50 to be attached to a hollow waveguide 11a particularly easily. Manufacturing is simplified due to the symmetry in the area of ​​the guide inlet 55. Furthermore, the purge gas supply is improved, especially becoming more uniform.

[0128] The inlet aspect ratio S1 can be defined, in particular, as the ratio of the length and width of the smallest rectangle that forms an envelope of the cross-section of the guide inlet 55, i.e., in particular, the smallest rectangle whose area completely encompasses the cross-section of the guide inlet 55. For a circular cross-sectional shape, such an enveloping rectangle is designed as a square, resulting in an inlet aspect ratio S1 of 1. The diameter of the guide inlet 55 with a circular cross-sectional shape can be, in particular, in the range of 10 mm to 20 mm, and especially around 15 mm.

[0129] The guide outlet 56 has an outlet aspect ratio S2 that is not equal to 1. The outlet aspect ratio S2 for the guide outlet is defined analogously to the inlet aspect ratio S1 of the guide inlet 55. For an elliptical cross-sectional shape, the outlet aspect ratio S2 corresponds to the quotient of the major axis and the minor axis of the ellipse. The major semi-axis of the ellipse can, in particular, have a length in the range of 30 mm to 60 mm, especially approximately 45 mm. The minor semi-axis of the ellipse can, in particular, have a length in the range of 20 mm to 40 mm, especially approximately 30 mm. The outlet aspect ratio S2 can, in particular, be: 1.1 < S2 < 1.9 and, in particular, S2 = 1.5.

Claims

[1] Illumination light guide (32; 39; 49; 50) for guiding EUV or DUV illumination light (3) in an illumination optic (1), comprising - a guide body (51), - a guided tour entrance (55), and - a guide outlet (56), -- wherein the guide body (51) forms an interior space for guiding the illumination light (3) from the guide inlet (55) to the guide outlet (56) along a longitudinal axis (L), -- wherein a cross-sectional shape of the interior space defined perpendicular to the longitudinal axis (L) changes along the longitudinal axis (L), -- wherein a cross-section of the guide inlet (55) defined perpendicular to the longitudinal axis (L) has an inlet aspect ratio S1 and a cross-section of the guide outlet (56) defined perpendicular to the longitudinal axis (L) has an outlet aspect ratio S2, wherein S1 and S2 are different, and -- where for S2: 1.1 < S2 < 1.

9. [2] Lighting light guide (50) according to claim 1, characterized by , that S1 is essentially 1. [3] Lighting light guide (50) according to one of the preceding claims, characterized by , that the guide body (51) has a conical shape. [4] Lighting light guide (50) according to one of the preceding claims, characterized by that the guide inlet has a circular cross-sectional shape. [5] Lighting light guide (50) according to one of the preceding claims, characterized by , that the guide outlet (56) has an elliptical cross-sectional shape. [6] Lighting light guide (50) according to one of claims 1 to 3 or 5, characterized by , that the cross-sectional shape of the guide inlet (55) is a regular polygon. [7] Lighting light guide (50) according to one of claims 1 to 4 or 6, characterized by , that the cross-sectional shape of the guide outlet (56) is an irregular polygon. [8] Lighting light guide (32; 39; 49; 50) according to one of the preceding claims, characterized by , that in the area of ​​the guide inlet (55) at least one functional component for influencing optical components located upstream in the illumination optics (1) is at least partially integrated into the illumination light guide (50). [9] Lighting light guide (32; 39; 49; 50) according to claim 8, characterized by , that a rinsing device for rinsing upstream optical components is at least partially integrated into the lighting guide. [10] Lighting optics (1) comprising a lighting light guide (32; 39; 49; 50) according to one of the preceding claims and a light source (5). [11] Lighting optics (1) according to claim 10 characterized by an optical hollow waveguide assembly (11b; 11c; 11d) comprising a hollow waveguide (11a) and a waveguide cleaning device (26; 34; 42). [12] Lighting optics (1) according to claim 11, characterized by , that the waveguide flushing device (26;34; 42) is at least partially integrated into the lighting guide (50). [13] Inspection system with a lighting optic according to one of claims 10 to 12.

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