Assembly of optical system

Abstract

The invention relates to an assembly of an optical system, comprising at least one mirror having a mirror body (200, 300), in which there is a fluid channel arrangement having at least one fluid channel (206, 306) through which a fluid can flow, in which the fluid channel arrangement is coupled to a fluid line system via a detachable flange connection, wherein the flange connection comprises a flange interface (202, 302) formed on the mirror body and a flange (203, 303) mounted on the flange interface (202, 302) in a force-locking manner, and wherein a seal (207, 307) is formed between the flange (203, 303) and the flange interface (202, 302) in order to provide different vacuum.

Description

[0001] This application claims the priority of German patent application DE 10 2022 210 087.5 filed on September 23, 2022. The content of this DE application is incorporated into the text of the present application by reference. Technical Field

[0002] The invention relates to an assembly for an optical system. In particular, the optical system may be a beam guiding unit ("beamline") of a synchrotron or a free electron laser. Background Art

[0003] For optical applications in the EUV range (e.g. wavelengths below 30 nm) or the X-ray range (e.g. wavelengths below 0.1 nm), mirrors are used as optical components due to the lack of availability of suitable light-transmitting refractive materials. Examples include synchrotron mirrors and mirrors in illumination devices or projection lenses for microlithography projection exposure equipment.

[0004] The problem that arises in practice is that such mirrors are subject to heating and concomitant thermal expansion or deformation, in particular due to absorption of incident radiation. The temperature profile generated in the mirror substrate or on the optically active surface in the process can therefore (in particular in the case of a relatively strongly localized heat input of the incident electromagnetic radiation) have pronounced inhomogeneities over the optically used area, with the result that the thermally induced deformation profiles generated by the corresponding temperature profiles lead to optical aberrations which cannot be corrected or can be corrected only with difficulty during operation of the corresponding optical system.

[0005] In particular, this may be the case for synchrotron mirrors, where during operation of the synchrotron the current heat-affected zone corresponding to the current optically used area is usually relatively small in relation to the entire mirror surface and furthermore varies locally during operation, which may ultimately lead to impairment of the imaging properties of the optical system comprising the corresponding mirror.

[0006] Various methods are known for preventing surface deformations caused by heat input and the accompanying optical aberrations, for example active cooling using fluid channels, through which a (cooling) fluid can flow in each case.

[0007] In practice, however, further undesirable effects arise due to mechanical, thermal and / or dynamic loads, depending on the embodiment of the connection between the reflector and the cooling fluid supply system, and which limit the performance and the service life of the optical system. For example, in the event of a leak, complex repair processes or even replacement of the entire reflector may be necessary, resulting in considerable costs and, moreover, a reduction in the achievable production throughput due to the necessary operational downtime. Furthermore, in the event of a leak, there is also the risk that the optical system (which is usually operated under vacuum conditions) is contaminated by the escaping cooling fluid. Furthermore, the connection of the fluid channel device and its operation may cause parasitic forces and concomitant deformations of the reflector surface, which in turn lead to optical aberrations.

[0008] With regard to the prior art, reference is made to the following by way of example only:

[0009] US 10,955,595 B2 and US 2015 / 0083938 A1. Summary of the invention

[0010] The problem addressed by the present invention is to provide a component for an optical system that can effectively avoid thermally induced deformation while alleviating the above-mentioned problems.

[0011] This problem is solved according to the features of independent claim 1 .

[0012] The assembly for an optical system according to the present invention comprises:

[0013] at least one reflector having a reflector body, through which extends a fluid channel arrangement, the fluid channel arrangement having at least one fluid channel through which a fluid can flow;

[0014] - wherein the fluid channel device is coupled to the fluid line system via a releasable flange connection;

[0015] - wherein the flange connection comprises a flange interface formed on the reflector body and a flange frictionally mounted on the flange interface;

[0016] - wherein a seal is formed between said flange and said flange interface so as to provide a differential vacuum.

[0017] In particular, within the assembly of an optical system, the invention is based on the concept of coupling a fluid channel device to a fluid line system, the fluid channel device being used to avoid or reduce thermally induced deformations, the fluid channel device allowing a fluid to flow therethrough and the fluid channel device being present in the reflector body of the reflector without an integral joint (in particular "solderless") by a flange connection which is in principle releasable. In this case, by managing without implementing an integral joint (in particular without applying soldering technology), a relatively soft interface ("separation layer") along the joining area is avoided, thereby in turn avoiding the attendant problems of such a separation layer in terms of heat and strength. In addition, as a result of the releasable connection, the corresponding components can be easily replaced in the event of a leak. In the assembly according to the invention, maintenance work is also greatly simplified, since, if necessary, the flange can simply be unscrewed and screwed on again (for example after cleaning and optionally inserting a new seal), and the optical system can then be immediately put back into operation.

[0018] According to the invention, the following disadvantages are deliberately accepted in this context, firstly with regard to the installation space required for realizing the screw connection, which is increased compared to a welded connection, but secondly also with regard to the problem of introducing undesired mechanical stresses into the reflector. In principle, the connection according to the invention via the flange leads to an increase in the forces, in particular due to the attachment of corresponding masses for the flange, any threaded plate, etc., whereby the risk of fractures and the risk of deformations in the reflector body are increased again.

[0019] However, according to the invention, these disadvantages are intentionally accepted, firstly in order to achieve the above-mentioned advantages of the solderless connection, and secondly due to the consideration that the above-mentioned parasitic forces and the accompanying deformations can be significantly reduced or minimized by appropriate embodiments of the flange connection and, in particular, the flange interface formed on the reflector body.

[0020] According to the present invention, a seal is formed between the flange and the flange interface to provide a differential vacuum.

[0021] For the purposes of the present application, the term "differential vacuum" is understood in this case to mean a vacuum between a first vacuum and a second vacuum, the vacuum pressure of the differential vacuum having a value between the vacuum pressure present in the first vacuum and the vacuum pressure present in the second vacuum. In this case, the second vacuum may be present in the fluid channel device and the first vacuum may be present in the external surroundings of the reflector.

[0022] Quantitatively, in particular, the vacuum pressure present in the first vacuum or in the external surroundings of the mirror can be in the range of (10 -9 -10 -12) mbar, the vacuum pressure existing in the second vacuum or in the fluid channel device may be in the range of (0.1-10) bar, and the vacuum pressure existing in the differential vacuum may be in the range of (10 -3 -10 -4 ) in the range of mbar.

[0023] The differential vacuum (which may also be referred to as "support vacuum") allows monitoring of the tightness in the assembly according to the invention. As a result of the permanent monitoring of the differential vacuum, any leaks can be detected in real time. As soon as contamination of this vacuum is detected, the associated system or machine can be shut down. In particular, this allows taking into account the fact that when used as a synchrotron mirror, the mirror is exposed to a UHV environment (at 10 -10 mbar to 10 -12 mbar range) and for example with EUV applications (10 -9 mbar), the sealing requirements are even higher.

[0024] According to one embodiment, the seal is a seal according to the double O-ring principle. Within the meaning of the present application, the phrase "seal according to the double O-ring principle" shall also include seals in which at least one of the two sealing rings or O-rings is replaced by a molded seal. Furthermore, the term "O-ring" within the meaning of the present application shall also include seals having a polygonal cross-sectional profile.

[0025] According to one embodiment, a monitoring device is provided for monitoring the tightness of a flange connection with respect to fluid escape during operation of an optical system.

[0026] Furthermore, the invention relates to a component for an optical system, comprising:

[0027] at least one reflector having a reflector body, through which extends a fluid channel arrangement, the fluid channel arrangement having at least one fluid channel through which a fluid can flow;

[0028] - wherein the fluid channel device is coupled to the fluid line system via a releasable flange connection;

[0029] - wherein the flange connection comprises a flange interface formed on the reflector body and a flange frictionally mounted on the flange interface; and

[0030] - wherein a monitoring device is provided for monitoring the tightness of the flange connection with respect to fluid escape during operation of the optical system.

[0031] According to one embodiment, the monitoring device is configured to enable monitoring of the sealing of the flange connection without affecting the external vacuum environment of the reflector.

[0032] According to one embodiment, the monitoring device is configured to detect fluid entering the area between the flange and the flange interface.

[0033] According to one embodiment, the monitoring device comprises a mass spectrometer, a gas detector or a humidity sensor.

[0034] According to one embodiment, the assembly comprises, in addition to the flange connection, at least one further joint point, wherein a monitoring device is also provided for monitoring the tightness of the further joint point with respect to escaping fluid.

[0035] According to one embodiment, the flange interface takes the form of at least one decoupling structure for reducing the force transmission from the flange to the reflector body.

[0036] According to one embodiment, the decoupling structure is formed by a tapered portion of the flange interface.

[0037] According to one embodiment, the fluid channel extends in the tapered portion in an axial direction, wherein a ratio between the axial extent of the tapered portion and a wall thickness of the tapered portion facing the fluid channel is in the range of 1-5.

[0038] According to one embodiment, the flange is mounted on the flange interface by means of a screw connection.

[0039] According to one embodiment, this screw connection is implemented along a portion of the flange interface, wherein, for this portion, the ratio of its extent in a direction perpendicular to the screw direction to its extent in the screw direction is in the range of 2 to 10, in particular in the range of 2 to 4.

[0040] According to one embodiment, the reflector comprises a cover plate which is bonded to the reflector body and on which the reflective layer system is formed.In this context, the phrase "reflective layer system" shall include single layer and multilayer systems.

[0041] According to one embodiment, the cover plate is integrally connected to the reflector body by direct bonding or fusion bonding. These bonding processes can be managed without auxiliary materials and, due to the absence of physically separating joints, a monolithic component with optimized mechanical properties can be obtained.

[0042] According to one embodiment, the mirror body is made of a silicon-containing material, in particular of a material comprising single crystal silicon (Si), silicon dioxide (SiO 2 ) and titanium dioxide-doped quartz glass.

[0043] According to one embodiment, the mirror is designed for an operating wavelength of less than 30 nm, in particular less than 15 nm.

[0044] According to one embodiment, the mirror is designed for an operating wavelength of less than 0.1 nm.

[0045] According to one embodiment, the optical system is a beam guiding unit ("beamline") of a synchrotron or a free electron laser.

[0046] The invention also relates to an optical system having a component of the above-mentioned features.

[0047] According to one embodiment, the optical system is a synchrotron.

[0048] According to a further embodiment, the optical system is a projection lens or an illumination device of a microlithography projection exposure apparatus.

[0049] Further embodiments of the invention are apparent from the description and the dependent claims.

[0050] The invention is explained in detail hereinafter with reference to the exemplary embodiments shown in the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In the figure:

[0052] Figure 1 A schematic illustration is shown for explaining a possible application of the assembly according to the invention in a synchrotron;

[0053] Figure 2 A schematic illustration is shown for explaining a possible embodiment of the assembly according to the invention;

[0054] Figure 3a-3b shows a schematic diagram for explaining another possible embodiment of the assembly according to the invention; and

[0055] Figure 4 Schematic diagram showing a possible structure of a microlithography projection exposure apparatus designed for operation in EUV. DETAILED DESCRIPTION

[0056] According to the invention, within a component of an optical system, a fluid channel device for avoiding thermally induced deformation, allowing a cooling fluid to flow through and present in a reflector body of a reflector is connected to a fluid pipeline system by a releasable flange connection without the need for integral joining, in particular in a "solderless" manner.

[0057] The mirrors present in the assembly according to the invention can be used, for example, as deflection mirrors or beam guiding optics in a synchrotron, e.g. Figure 1 Schematically shown for the reflector 100. Figure 1, in such a synchrotron, electromagnetic radiation 150 (in the example in the form of a diverging X-ray beam) generated by the acceleration or deflection of an electron beam 170 is incident on a mirror 100. In particular, the mirror 100 can also be positioned in a so-called "beamline" on which the electromagnetic radiation generated in the synchrotron is incident. In this case, the elliptical "footprint" generated on the mirror 100 in this example is denoted by "101" as the optically used area, and the electromagnetic radiation (in the example in the form of a converging X-ray beam) emitted from the mirror 100 after reflection is denoted by "160". In this case, the optically used area or "footprint" in the scene shown is a relatively strongly localized area on the mirror surface, whose current position may, however, "migrate" or change on the mirror surface. The assembly according to the invention is used in particular to prevent or reduce deformations caused by electromagnetic radiation heat.

[0058] Figure 2 A purely schematic illustration is shown for explaining a possible embodiment of the assembly according to the invention. Figure 2 , the assembly comprises at least one reflector having a reflector body 200. In addition, the reflector comprises a cover plate 200a, which is bonded to the reflector body 200 and on which a reflective layer system (not shown here) is formed. Depending on the specific application scenario, the reflector can be a plane reflector or have any other (e.g. spherical or cylindrical) geometric shape.

[0059] In a specific exemplary embodiment, the reflector body 200 is made of single crystal silicon (Si), and the reflective layer system in the example includes a single layer of gold (Au), whose exemplary thickness is in the range of 20nm to 50nm. In other embodiments, the reflective layer can also be made of another noble metal, such as platinum (Pt), rhodium (Rh), silver (Ag), ruthenium (Ru), palladium (Pd), osmium (Os) or iridium (Ir). In addition, the reflective layer can also be made of organic materials, such as carbon (C), boron carbide (B 4 C) or silicon carbide (SiC).

[0060] Depending on the intended use, the mirror can be a mirror designed for operation at grazing incidence or a mirror designed for operation at normal incidence. As a reflective layer system, the mirror in the latter case usually comprises a multilayer system in the form of an alternating sequence of individual layers, for example made of at least two different layer materials. Furthermore, in further embodiments, the mirror body 200 or the mirror substrate can also be made of another substrate material, for example a substrate material which also contains silicon, for example silicon dioxide (SiO2) or Zerodur ® (SCHOTT). In addition, depending on the intended use, for example, Corning Incorporated sells ULE ® Commercially available titanium silicate glass can also be used as a substrate material.

[0061] Without suitable countermeasures, electromagnetic radiation incident on the mirror during operation leads to undesirable temperature distributions or deformation distributions (with possibly large gradients in the optical use region) and concomitant optical aberrations of the optical system comprising the mirror. In order to counteract such undesirable temperature distributions or deformation distributions, a fluid channel arrangement 205 having at least one fluid channel 206 through which a fluid (e.g. water) can flow extends through the mirror body 200, as shown in FIG. Figure 2 As shown. The fluid channel device 205 is connected to the fluid pipeline system through a releasable flange connection, which includes a flange interface 202 formed on the reflector body 200 and a flange 203 frictionally mounted on the flange interface 202. For example, the flange 203 can be made of stainless steel. In an exemplary embodiment, the releasable flange connection is implemented as a screw connection (but the present invention is not limited thereto). For this purpose, Figure 2 The screws indicated by "204" are secured to a threaded plate indicated by "208" (and also made of stainless steel in this embodiment).

[0062] Since the required connection between the fluid channel device (which extends in the reflector body 200) and the external fluid line system is achieved according to the invention, which is achieved by a releasable flange connection of the flange 203 on the flange interface 202, firstly the problems associated with a welded connection with regard to the thermal connection and the resulting leakage are avoided, and secondly maintenance work is also facilitated, as has been explained at the beginning. In the event of a leak, the affected releasably connected component can also be simply replaced.

[0063] However, in turn, according to the invention (as also mentioned at the beginning), the problems associated with the attachment of additional masses due to the flange 203, the flange interface 202 and the threaded plate 208 and also with the generation of additional (e.g. screwing or clamping) forces for producing the friction connection are accepted. In addition to the forces caused by the fluid flow in the fluid channel device, these forces act on the mirror as disturbing forces or parasitic forces and, without appropriate countermeasures, in turn lead to undesirable deformations of the optically active surface.

[0064] In order to reduce or minimize the influence of the generation of additional parasitic forces on the deformation of the mirror, which is accepted according to the invention, there is preferably a target embodiment of the flange connection according to the invention with a suitable design or optimization of the parameters described below.

[0065] In this case, it is assumed below (the present invention is not limited thereto) that the flange 203 is mounted on the flange interface 202 by a threaded connection. In other embodiments, the friction mounting of the flange 203 on the flange interface 202 can also be achieved in another suitable manner, in particular, for example, by a clamping connection.

[0066] Originally about reducing or minimizing the deformation caused by parasitic forces generated by threaded connections, Figure 2 The flange interface 202 in the embodiment of is implemented in certain areas to form a decoupling structure (or decoupling joint) 201. The decoupling structure 201 is formed by a conical portion of the flange interface 202. Figure 2 This is achieved by “cutting off” the flange interface 202 in the corresponding region 209 facing the reflector body 200, maintaining the wall thickness (h ) toward the fluid channel 206 compared to the remaining non-tapered portion of the flange interface 202 facing the flange 203. 1 Due to the thin wall in region 209 , the deformation or lateral shrinkage that occurs when flange 203 is screwed in is reduced in terms of its influence on the optically active surface of the reflector.

[0067] At the same time, the stiffness of the flange interface 202 in the “axial” direction (ie, in the x-direction of the drawn coordinate system) is increased by appropriately selecting a relatively large dimension t 2 Furthermore, this stiffness, which is mainly related to the influence of the prestressing force of the threaded connection, can also be increased by increasing the dimension h 2 To increase (thus the parameter h 2 In this respect, the parameter t 2 has a smaller effect). The ratio h 2 / t 2 It can be optimized according to the specific application scenario and is preferably in the range of 2 to 10, more preferably in the range of 2 to 4.

[0068] exist Figure 2 In an exemplary embodiment, the threaded connection is therefore implemented along a portion of the flange interface 202, wherein, for this portion, the ratio of its range in a direction perpendicular to the spiral direction to its range in the spiral direction is preferably in the range of 2 to 10 (but the present invention is not limited thereto), in particular in the range of 2 to 4.

[0069] The above-mentioned decoupling effect of the decoupling structure 201 in the x-direction of the drawn coordinate system can also be further enhanced by the dimension t 1 The appropriate expansion is achieved in order to influence the bending stiffness of the decoupling structure 201, but this parameter has a greater influence in this respect than the wall thickness (h 1 -d) / 2 is relatively small. The ratio t 1 / [(h 1 -d) / 2] can be optimized according to the specific application scenario and is preferably in the range of 1 to 5. In other words, according to Figure 2In an exemplary embodiment, the decoupling structure 201 is formed by a conical portion of the flange interface 202, wherein preferably (but the invention is not limited thereto), the ratio between the axial extent of the conical portion and the wall thickness of the conical portion facing the fluid channel is in the range of 1 to 5. In this case, the rupture risk increases with this ratio t 1 / [(h 1 -d) / 2] increases with increasing value of the ratio, while the stiffness of parasitic deformations on the optically effective surface and thus the punch-through increases with decreasing value of this ratio.

[0070] Furthermore, with regard to reducing or minimizing deformations caused by unavoidable forces within the fluid channel device due to the fluid flowing therethrough, this reduction or minimization can also be achieved by first appropriately reducing the wall thickness (h 1 Secondly, for a given force generated in the fluid channel device, the stiffness of the decoupling structure 201 can be determined by the parameter t 1 minimized by appropriate increase.

[0071] Within the scope of the above-mentioned dimensioning of the flange connection according to the invention and in particular of the flange interface, it must be noted that the stiffness of the decoupling structure 201 cannot be reduced to an absolute minimum. Depending on the specific load spectrum (pressure loads due to the fluid flowing in the fluid channel arrangement, external forces acting, for example, as a result of a fluid line system, etc.) and the fracture stress of the material used, the remaining wall thickness (h 1 -d) / 2 must still be large enough to ensure that the resulting mechanical stresses do not lead to damage of the mirror.

[0072] Another feature of the friction flange connection according to the invention is the differential vacuum, which still refers to Figure 3a-3b Detailed description and present in the entire assembly (including mirror body, cover plate, flange and fluid line system) in an embodiment of the invention. The differential vacuum is fed through the entire flange and passes at the interface between flange and mirror. This is achieved by means of an intermediate space between the two O-rings of the seal 207 according to the double O-ring principle. The differential vacuum (= "support vacuum") is used to monitor the tightness in an assembly according to the invention or to monitor the tightness of the mirror. As a result of the permanent monitoring of the differential vacuum, any leaks can be detected in real time. As soon as a contamination of this differential vacuum is detected, the associated system or machine can be shut down. This can take into account the fact that when used as a synchrotron mirror, the mirror is in a UHV environment (in conditions from 10 - 10 mbar to 10 -12 mbar range) and, for example, with EUV applications (10 -9 mbar), the sealing requirements are even higher.

[0073] Figure 3a-3b A schematic diagram is shown for explaining a possible embodiment of an assembly according to the invention. Figure 2 Components that are similar or have essentially the same function are denoted here by reference numerals which are increased by “100”.

[0074] according to Figure 3a-3b , "312a" and "312b" denote bores which extend in the reflector body 300 and the flange 303 and each extend as far as an intermediate space 313 located between two O-rings of the seal 307 (and substantially in a tubular manner around the fluid channel 306). In this case, the bore 312a provided in the reflector body 300 extends to a groove 311 (purely exemplarily formed with a rectangular cross section in the exemplary embodiment) which surrounds the fluid volume 310 receiving the fluid.

[0075] Quantitatively, the vacuum pressure existing in the external environment of the mirror (at Figure 3a denoted by "350" in (10 -9 -10 -12 ) mbar, the vacuum pressure existing in the fluid volume 310 may be in the range of (0.1-10) bar, and the vacuum pressure existing in the holes 312a, 312b, the intermediate space 313 and the groove 311 (ie, in a differential vacuum) may be in the range of (10 -3 -10 -4 ) in the range of mbar.

[0076] As a result of the above-described embodiment, in the event of a leak, the fluid escaping from the fluid channel 306 or the fluid volume 310 initially enters the region of the differential vacuum provided according to the invention, i.e. into the groove 311 or the intermediate space 313, depending on the location of the leak, before reaching the (ultra-high) vacuum present in the external environment of the reflector, and can thus be detected via a monitoring device 320 connected to the borehole 312 b. The monitoring device 320 can be implemented in any suitable manner and, for example, comprise a mass spectrometer, a gas detector or a humidity sensor. In the event of a corresponding detection of the fluid entering one of the above-described regions of differential vacuum, the entire system or the fluid supply connected to the fluid channel 306 can preferably be shut down and an undesired contamination of the (ultra-high) vacuum present in the external surrounding area of ​​the reflector can thus be reliably avoided.

[0077] In an embodiment, the assembly according to the invention can also comprise, in addition to the flange connection, at least one further joint point, wherein the monitoring device can then also be used to monitor the tightness of this / these further joint point(s) with respect to escaping fluid.

[0078] Although in the above-described embodiments reference has been made to synchrotron mirrors, the invention can also be implemented in other optical systems, in particular for example also in an illumination device or a projection lens of a microlithography projection exposure system.

[0079] In this regard, Figure 4 A possible structure of a microlithography projection exposure apparatus designed for operation in EUV is shown schematically in a meridional section. Figure 4 , the projection exposure device 1 comprises an illumination device 2 and a projection lens 10. An embodiment of the illumination device 2 of the projection exposure device 1 has, in addition to the light source or radiation source 3, an illumination optical unit 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a module separate from the rest of the illumination device. In this case, the illumination device does not include the light source 3. What is exposed here is a mask master 7 arranged in the object field 5. The mask master 7 is held by a mask master holder 8. The mask master holder 8 can be displaced by a mask master displacement drive 9, in particular in a scanning direction. For explanation purposes, Figure 4 A Cartesian xyz coordinate system is depicted in FIG. The x direction extends perpendicular to the plane of the drawing into the drawing. The y direction extends horizontally and the z direction extends vertically. The scanning direction is Figure 4 The z direction extends perpendicular to the object plane 6.

[0080] The projection lens 10 serves to image the object field 5 into an image field 11 in an image plane 12. The structures on the reticle 7 are imaged on a photosensitive layer of a wafer 13 arranged in the region of the image field 11 in the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be displaced, in particular in the y direction, by a wafer displacement drive 15. The displacement of the reticle 7, firstly by the reticle displacement drive 9, and secondly by the wafer 13, is synchronized with one another.

[0081] The radiation source 3 is an EUV radiation source. The radiation source 3 in particular emits EUV radiation, which is also referred to as used radiation or illumination radiation in the following text. In particular, the used radiation has a wavelength in the range between 5 nm and 30 nm. The radiation source 3 can be, for example, a plasma source, a synchrotron-based radiation source or a free electron laser (FEL). The illumination radiation 16 emitted from the radiation source 3 is focused by a light collector 17 and propagates through an intermediate focus in an intermediate focal plane 18 into the illumination optical unit 4. The illumination optical unit 4 comprises a deflection mirror 19 and a first facet mirror 20 (with schematically indicated facets 21) and a second facet mirror 22 (with schematically indicated facets 23) arranged downstream of the deflection mirror 19 in the beam path.

[0082] The projection lens 10 comprises a plurality of mirrors Mi (i=1, 2, . . . ), which are numbered consecutively according to their arrangement in the beam path of the projection exposure apparatus 1. Figure 4 In the example shown, the projection lens 10 comprises six mirrors M1 to M6. Alternative solutions with four, eight, ten, twelve or a different number of mirrors Mi are also possible. The penultimate mirror M5 and the last mirror M6 each have a through opening for the illumination radiation 16. The projection lens 10 is a doubly shielded optical unit. The projection lens 10 has an image-side numerical aperture which is greater than 0.5 and may also be greater than 0.6 and may be, for example, 0.7 or 0.75.

[0083] During operation of the microlithography projection exposure apparatus 1, electromagnetic radiation incident on the optically active surface of the mirror is partially absorbed and, as explained in the introduction, leads to heating and associated thermal expansion or deformation, which in turn can lead to impairment of the imaging properties of the optical system. Figure 4 Any desired mirrors of the microlithography projection exposure apparatus 1.

[0084] Furthermore, the invention can also advantageously be implemented in a projection exposure apparatus designed for operation in DUV, ie at a wavelength of less than 250 nm, in particular less than 200 nm, or in another optical system.

[0085] Although the present invention is also described by specific embodiments, those skilled in the art will appreciate that many variations and alternative embodiments are made, for example, by combining and / or exchanging the features of the various embodiments. Therefore, those skilled in the art will appreciate that these variations and alternative embodiments are also included in the present invention, and that the scope of the present invention is limited only by the appended claims and their equivalents.

Claims

1. A component for an optical system, comprising: • at least one reflector having a reflector body (200, 300) through which a fluid channel arrangement extends, the fluid channel arrangement having at least one fluid channel (206, 306) through which a fluid can flow; • wherein the fluid channel device is coupled to the fluid line system via a releasable flange connection; • wherein the flange connection comprises a flange interface (202, 302) formed on the reflector body (200, 300) and a flange (203, 303) frictionally mounted on the flange interface (202, 302); and • wherein a seal (207, 307) is formed between the flange (203, 303) and the flange interface (202, 302) to provide a differential vacuum.

2. The assembly according to claim 1, characterized in that The seal is a seal based on the double O-ring principle.

3. The assembly according to claim 1 or 2, characterized in that A monitoring device (320) is provided for monitoring the tightness of the flange connection with respect to fluid escape during operation of the optical system.

4. A component for an optical system, comprising: • at least one reflector having a reflector body (200, 300) through which extends a fluid channel arrangement, the fluid channel arrangement having at least one fluid channel (206, 306) through which a fluid can flow; • wherein the fluid channel device is coupled to the fluid line system via a releasable flange connection; • wherein the flange connection comprises a flange interface (202, 302) formed on the reflector body (200, 300) and a flange (203, 303) frictionally mounted on the flange interface (202, 302); and • wherein a monitoring device (320) is provided for monitoring the tightness of the flange connection with respect to fluid escape during operation of the optical system.

5. The assembly according to claim 3 or 4, characterized in that The monitoring device (320) is configured to monitor the sealing performance of the flange connection without affecting the external vacuum environment of the reflector.

6. The assembly according to any one of claims 3 to 5, characterized in that The monitoring device (320) is configured to detect fluid entering the area between the flange (203, 303) and the flange interface (202, 302).

7. An assembly according to any one of claims 4 to 6, characterized in that The monitoring device (320) includes a mass spectrometer, a gas detector or a humidity sensor.

8. An assembly according to any one of claims 3 to 7, characterized in that In addition to the flange connection, the assembly comprises at least one further joint, wherein the monitoring device (320) is also configured to monitor the tightness of the further joint with respect to escaping fluid.

9. Assembly according to any one of the preceding claims, characterized in that The flange interface (202) is in the form of at least one decoupling structure (201, 301), and the decoupling structure (201, 301) is used to reduce the force transmission from the flange (203, 303) to the reflector body (200, 300).

10. The assembly according to claim 9, characterized in that The decoupling structure (201, 301) is formed by a tapered portion of the flange interface (202, 302).

11. The assembly according to claim 10, wherein The fluid channel (206, 306) extends in the tapered portion in an axial direction, wherein a ratio between an axial extent of the tapered portion and a wall thickness of the tapered portion remaining toward the fluid channel (206, 306) is in the range of 1 to 5.

12. Assembly according to any one of the preceding claims, characterized in that The flange (203, 303) is mounted on the flange interface (202, 302) by means of screw connection.

13. The assembly according to claim 12, characterized in that The screw connection is implemented along a portion of the flange interface (202, 302), wherein, for this portion, the ratio of its extent in a direction perpendicular to the screw direction to its extent in the screw direction is in the range of 2 to 10, in particular in the range of 2 to 4.

14. Assembly according to any one of the preceding claims, characterized in that The reflector comprises a cover plate (200a, 300a), the cover plate (200a, 300a) being bonded to the reflector body (200, 300) and forming a reflective layer system on the cover plate (200a, 300a).

15. The assembly according to claim 14, characterized in that The cover plate (200a, 300a) is integrally connected to the reflector body (200, 300) by direct bonding or fusion bonding.

16. An assembly as claimed in any one of the preceding claims, characterised in that The mirror body (200, 300) is made of a silicon-containing material, in particular a material from the group comprising single-crystalline silicon (Si), silicon dioxide (SiO2) and titanium dioxide-doped quartz glass.

17. Assembly according to any one of the preceding claims, characterized in that The mirror is designed for an operating wavelength of less than 30 nm, in particular less than 15 nm.

18. Assembly according to any one of the preceding claims, characterized in that The mirrors are designed for operating wavelengths less than 0.1 nm.

19. Assembly according to any one of the preceding claims, characterized in that The optical system is the beam guiding unit ("beamline") of a synchrotron or a free electron laser.

20. An optical system comprising an assembly as claimed in any one of the preceding claims.

21. The optical system according to claim 20, characterized in that The optical system is a synchrotron.

22. The optical system according to claim 20, characterized in that The optical system is a projection lens (10) or an illumination device (2) of a microlithography projection exposure device (1).

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