OPTICAL SYSTEM AND PROJECTIONAL LIGHTING SYSTEM

Abstract

An optical system (100, 200) for a projection exposure system (1), comprising an optical element (104), and a pull-out socket (116, 204) which supports the optical element (104), wherein the pull-out socket (116, 204) has several pull-out elements (118, 120, 122, 206, 208, 210) which are connected to the optical element (104), wherein each pull-out element (118, 120, 122, 206, 208, 210) applies a pull-out force (F1, F2, F3) to the optical element (104), and wherein the pull-out forces (F1, F2, F3) are spatially oriented such that the pull-out forces (F1, F2, F3) compensate each other.

Description

[0001] The present invention relates to an optical system and a projection exposure system with such an optical system.

[0002] Microlithography is used to manufacture microstructured components, such as integrated circuits. The microlithography process is carried out using a lithography system, which includes an illumination system and a projection system. The image of a mask (reticule) illuminated by the illumination system is projected by the projection system onto a substrate, such as a silicon wafer, coated with a photosensitive layer (photoresist) and positioned in the image plane of the projection system. This transfers the mask structure onto the photosensitive coating of the substrate.

[0003] Driven by the pursuit of ever smaller structures in the fabrication of integrated circuits, EUV lithography systems are currently being developed that utilize light with wavelengths ranging from 0.1 nm to 30 nm, particularly 13.5 nm. Due to the high absorption of light of this wavelength by most materials, such EUV lithography systems require reflective optics, i.e., mirrors, instead of the previously used refracting optics, i.e., lenses.

[0004] As previously mentioned, optics, such as the lenses of a heating head, can be mounted using spring-loaded sockets. In this case, a spring might press the optic against a stop to position it. During operation, however, such optics can heat up, for example, due to the application of light radiation, leading to thermal expansion of both the optic and its socket. Since the optic and the socket are usually made of different materials, they expand to different degrees due to their differing coefficients of thermal expansion. This unequal expansion can cause the optic to shift position, potentially resulting in an undesirable change in its optical properties.

[0005] Against this background, one object of the present invention is to provide an improved optical system.

[0006] Accordingly, an optical system for a projection exposure system is proposed. The optical system comprises an optical element and a tensioning device that supports the optical element, the tensioning device having several tensioning elements connected to the optical element, each tensioning element applying a tensioning force to the optical element, and the tensioning forces being spatially oriented such that the tensioning forces compensate each other.

[0007] Because the tensile forces compensate for each other, it is possible that even if the optical element and the mounting differ in their thermal expansion, the tensile forces will change, but the central axis of the optical element will not shift from an optical axis of the optical system. Therefore, the optical properties of the optical system are not affected by heat input into the optical system.

[0008] The optical system is preferably a projection optic of the projection exposure system or part of such a projection optic. However, the optical system can also be an illumination system of the projection exposure system or part of such an illumination system. The optical system can also be part of a so-called mirror preheater or heating head, or part of such a heating head. The optical element is preferably a lens. However, the optical element can also be a mirror, in particular an EUV mirror. The optical system can be used for EUV lithography. However, the optical system can also be used for DUV lithography. The optical system can have any number of optical elements. Accordingly, the optical system can also have any number of pull-out sockets, with each pull-out socket being assigned an optical element. However, the following discussion focuses on only one optical element and only one pull-out socket.

[0009] In this context, a "tensile mount" is understood to be a mount designed to apply tensile forces to the optical element. These tensile forces are applied by means of the tensioning elements. The fact that the tensile mount "supports" the optical element means, in particular, that the tensile mount is connected to the optical element and, specifically, is capable of absorbing the weight of the optical element.

[0010] The pull-out mechanism can have any number of pull-out elements. However, it is particularly preferred that the pull-out mechanism has exactly three pull-out elements. The pull-out mechanism can also have fewer than three or more than three pull-out elements. The pull-out elements are preferably connected to the optical element in such a way that a positive-locking connection is established between the pull-out elements and the optical element. For this purpose, the optical element can have an annular groove running around a symmetry or central axis of the optical element, into which the pull-out elements engage positively. A positive-locking connection is created by the interlocking or overlapping of two elements, in this case, the respective pull-out element and the annular groove. All pull-out elements preferably engage in the same annular groove. This means, in particular, that the optical element has exactly one annular groove.Alternatively, the tension elements can also be connected to the optical element in any other way. For example, an adhesive bond can be used.

[0011] Each tension element is assigned a tensile force. The tension elements are spring-loaded in such a way that they already exert a tensile force on the optical element even when the optical system is not yet in operation. This means, in particular, that the tensile forces of the tension elements already act on the optical element when no heat has yet been introduced into the optical system. If heat is introduced into the optical system, the tensioning element expands, thereby increasing the tensile forces acting on the optical element. However, the tensile forces are arranged or oriented in such a way that they cancel each other out or compensate for each other. Preferably, the tensile forces are of the same magnitude but have different directions of action. The directions of action are oriented such that the tensile forces cancel each other out or compensate for each other.

[0012] According to one embodiment, the tensile forces are oriented perpendicular to an optical axis of the optical system.

[0013] Ideally, the optical axis coincides with the central axis of the optical element. The pull-out socket allows the central axis of the optical element and the optical axis to be kept coaxial. In this context, "perpendicular" refers in particular to an angle of 90° ± 10°, more preferably 90° ± 5°, more preferably 90° ± 3°, more preferably 90° ± 1°, and more preferably exactly 90°.

[0014] According to another embodiment, the tension elements are arranged evenly distributed around the optical axis.

[0015] Preferably, each tension element is assigned a plane of symmetry with which the respective tension element is mirror-symmetrical. The planes of symmetry of the tension elements are arranged such that they intersect at the optical axis of the optical system. The planes of symmetry are positioned rotated relative to each other about the optical axis such that the tension elements, and thus also the planes of symmetry, are evenly distributed around the optical axis. The tension forces are oriented along the planes of symmetry and perpendicular to the optical axis.

[0016] According to a further embodiment, the pull-out mechanism has a first pull element, a second pull element and a third pull element, wherein the first pull element, the second pull element and the third pull element are arranged rotated relative to each other by an angle of 120° with respect to the optical axis.

[0017] This means, in particular, that the planes of symmetry of the tension elements are positioned rotated by 120° relative to each other. Specifically, the first and second tension elements are offset by 120° from each other. Similarly, the second and third tension elements are also offset by 120° from each other. Likewise, the third and first tension elements are also offset by 120° from each other.

[0018] According to another embodiment, the traction elements are arranged next to each other when viewed along the optical axis.

[0019] This can mean, in particular, that the second tension element is arranged between the first and third tension elements. The tension elements are, in particular, stacked on top of each other and thus in contact with one another.

[0020] According to another embodiment, the pull fitting has a pull fitting housing, wherein the pull elements are connected to the pull fitting housing.

[0021] The pull-in housing is preferably at least partially hollow cylindrical or tubular. The optical element can be partially or completely enclosed within the pull-in housing. The pull-in elements can also be arranged within the pull-in housing. However, the pull-in elements can also be located outside the pull-in housing. The pull-in housing is preferably rotationally symmetrical about the optical axis of the optical system. The pull-in housing can, for example, have a cylindrical inner surface. The pull-in housing is preferably made of a metallic material, for example, stainless steel.

[0022] According to another embodiment, the tension elements are positively and / or force-fit connected to the tension holder housing.

[0023] For example, the tensioning elements can be hooked into the tensioning housing. In this case, a positive-locking connection is provided between the tensioning elements and the tensioning housing. Alternatively, the tensioning elements can also be pressed into the tensioning housing. In this case, a friction-locking connection is provided between the tensioning elements and the tensioning housing.

[0024] According to another embodiment, each pulling element has a connecting section by means of which the respective pulling element is positively connected to the pulling housing.

[0025] In particular, each connecting section has a bore or opening through which a fastener passes, which is connected to the pulley housing. Each pulley is associated with such a fastener. The fasteners can be, for example, bolts, screws, or rivets. For example, the pulleys can be screwed to the pulley housing.

[0026] According to another embodiment, the pull-type housing has a receiving section for receiving the pull elements and the optical element, wherein the pull elements are pressed into the receiving section.

[0027] In this case, the pulley housing can have a receiving section in the form of a stepped bore with a first inner surface and a second inner surface, between which a shoulder is arranged. The pulley elements can abut this shoulder. However, the shoulder is optional. In this case, the first inner surface extends through the entire receiving section. In particular, an interference fit is provided between the pulley elements and the first inner surface, so that the pulley elements are pressed into the receiving section. The material of the pulley elements and the material of the pulley housing are selected such that, when heat is applied to the pulley, the pulley housing does not expand to such an extent that the pulley elements lose contact with the first inner surface. Accordingly, the interference fit is always maintained, even when heat is applied to the pulley.

[0028] According to another embodiment, each traction element runs completely around the optical element.

[0029] The tensioning elements can be ring-shaped or at least partially ring-shaped. In particular, each tensioning element has a receiving section in the form of an opening in which the optical element is received. The tensioning elements then engage positively in the annular groove of the optical element.

[0030] According to another embodiment, each tension element has an outer ring section and an inner ring section arranged within the outer ring section, wherein the inner ring section is arranged eccentrically to the outer ring section.

[0031] The outer ring section preferably surrounds the optical element completely, whereas the inner ring section surrounds it only partially. The inner ring section can be connected to the outer ring section at connection points. The outer ring section is rotationally symmetrical about a central axis of symmetry. The inner ring section can also be rotationally symmetrical about a central axis of symmetry. The central axes of the outer ring section and the inner ring section are offset from each other. However, the two central axes lie on the plane of symmetry of the respective tensioning element. This eccentric or non-coaxial arrangement of the central axes allows for preloading of the tensioning elements when they are mounted in the tensioning housing.

[0032] According to another embodiment, the inner ring section has a lower stiffness than the outer ring section.

[0033] This can be achieved, in particular, by making the inner ring section narrower than the outer ring section. This allows the inner ring section to deform more easily due to its elasticity than the outer ring section. In this context, "stiffness" refers to the resistance of a body, specifically the inner or outer ring section, to elastic deformation. Stiffness depends on the geometry of the respective body and the material used.

[0034] According to another embodiment, a gap is arranged between the outer ring section and the inner ring section, which only partially surrounds the respective tension element.

[0035] The gap therefore only partially surrounds the optical element. The gap partially separates the outer ring section and the inner ring section from each other, although the inner and outer ring sections are connected at the interfaces.

[0036] According to another embodiment, the outer ring section and the inner ring section are joined together in one piece, in particular in one piece of material.

[0037] For example, the tension elements can be stamped sheet metal components. This makes the tension elements particularly easy to manufacture. "One-piece" or "one-part" in this context means that the outer ring section and the inner ring section are not two separate components, but rather form a single component, namely the respective tension element. "One-piece material" in this context means that the tension elements are manufactured entirely from the same material. For example, the tension elements are made of a metallic material, such as spring steel. The tension elements are preferably flat, i.e., not curved or bent. The tension elements can be plate-shaped or sheet-shaped.

[0038] Furthermore, a projection exposure system with such an optical system is proposed.

[0039] The projection exposure system can have any number of such optical systems. The projection exposure system can be an EUV lithography system. "EUV" stands for "Extreme Ultraviolet" and refers to a wavelength of the working light between 0.1 nm and 30 nm. The projection exposure system can also be a DUV lithography system. "DUV" stands for "Deep Ultraviolet" and refers to a wavelength of the working light between 30 nm and 250 nm.

[0040] The term "one" here is not necessarily to be understood as restricting the number to exactly one element. Rather, it can also refer to multiple elements, such as two, three, or more. Similarly, every other counter used here should not be interpreted as restricting the number to the exact number stated. Instead, numerical deviations, both higher and lower, are possible unless otherwise specified.

[0041] The embodiments and features described for the proposed optical system apply accordingly to the proposed projection exposure system and vice versa.

[0042] Other possible implementations of the invention also include combinations of features or embodiments described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. In such cases, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

[0043] Further advantageous embodiments and aspects of the invention are the subject of the dependent claims and the exemplary embodiments of the invention described below. The invention will be explained in more detail below with reference to preferred embodiments and the accompanying figures. Fig. Figure 1 shows a schematic meridional section of a projection exposure system for EUV projection lithography; Fig. Figure 2 shows a schematic perspective view of an embodiment of an optical system for the projection exposure system according to Fig. 1; Fig. Figure 3 shows a schematic top view of the optical system according to Fig. 2; Fig. Figure 4 shows a schematic partial sectional view of the optical system along section line IV-IV. Fig. 3; Fig. Figure 5 shows a schematic side view of an embodiment of an optical element for the optical system according to Fig. 2; Fig. Figure 6 shows a schematic top view of an embodiment of a tension element for the optical system according to Fig. 2; Fig. Figure 7 shows a schematic perspective view of another embodiment of an optical system for the projection exposure system according to Fig. 1; Fig. Figure 8 shows a schematic top view of the optical system according to Fig. 7; Fig. Figure 9 shows a schematic partial sectional view of the optical system according to section line IX-IX of the Fig. 8; and Fig. Figure 10 shows a schematic top view of an embodiment of a tension element for the optical system according to Fig. 7.

[0044] In the figures, identical or functionally equivalent elements have been labelled with the same reference symbols, unless otherwise indicated. Furthermore, it should be noted that the representations in the figures are not necessarily to scale.

[0045] Fig. Figure 1 shows an embodiment of a projection exposure system 1 (lithography system), in particular an EUV lithography system. One embodiment of the illumination system 2 of the projection exposure system 1 has, in addition to a light or radiation source 3, an illumination optic 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 separate module from the rest of the illumination system 2. In this case, the illumination system 2 does not include the light source 3.

[0046] A reticule 7 arranged in the object field 5 is exposed. The reticule 7 is held by a reticule holder 8. The reticule holder 8 can be moved, particularly in a scanning direction, via a reticule displacement drive 9.

[0047] In the Fig. Figure 1 shows a Cartesian coordinate system with an x-direction x, a y-direction y, and a z-direction z. The x-direction x runs perpendicular to the plane of the drawing. The y-direction y runs horizontally, and the z-direction z runs vertically. The scan direction runs in the Fig. 1 along the y-direction y. The z-direction z runs perpendicular to the object plane 6.

[0048] The projection exposure system 1 comprises a projection optic 10. The projection optic 10 serves to image the object field 5 onto an image field 11 in an image plane 12. The image plane 12 is parallel to the object plane 6. Alternatively, an angle other than 0° between the object plane 6 and the image plane 12 is also possible.

[0049] A structure on the reticulum 7 is imaged onto a photosensitive layer of a wafer 13 located in the image plane 12 within the image field 11. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be moved, particularly along the y-direction y, via a wafer transfer drive 15. The movement of the reticulum 7 via the reticulum transfer drive 9 and of the wafer 13 via the wafer transfer drive 15 can be synchronized.

[0050] Light source 3 is an EUV radiation source. Light source 3 emits, in particular, EUV radiation 16, which is also referred to below as useful radiation, illumination radiation, or illumination light. The illumination radiation 16 has a wavelength in the range between 5 nm and 30 nm. Light source 3 can be a plasma source, for example, an LPP source (Laser Produced Plasma) or a DPP source (Gas Discharged Produced Plasma). It can also be a synchrotron-based radiation source. Light source 3 can be a free-electron laser (FEL).

[0051] The illumination radiation 16 emanating from the light source 3 is focused by a collector 17. The collector 17 can be a collector with one or more ellipsoidal and / or hyperboloid reflective surfaces. The at least one reflective surface of the collector 17 can be illuminated by the illumination radiation 16 at grazing incidence (GI), i.e., with angles of incidence greater than 45°, or at normal incidence (NI), i.e., with angles of incidence less than 45°. The collector 17 can be structured and / or coated to optimize its reflectivity for the useful radiation and to suppress stray light.

[0052] After the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 can represent a separation between a radiation source module, comprising the light source 3 and the collector 17, and the illumination optics 4.

[0053] The illumination optics 4 comprise a deflecting mirror 19 and, downstream in the beam path, a first faceted mirror 20. The deflecting mirror 19 can be a planar deflecting mirror or, alternatively, a mirror with an effect that influences the beam shape beyond the mere deflection effect. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates a useful wavelength of the illumination radiation 16 from stray light of a different wavelength. If the first faceted mirror 20 is arranged in a plane of the illumination optics 4 that is optically conjugate to the object plane 6 as the field plane, it is also referred to as a field faceted mirror. The first faceted mirror 20 comprises a plurality of individual first facets 21, which can also be referred to as field facets. Of these first facets 21, the following are in the Fig. 1 only some examples are shown.

[0054] The first facets 21 can be designed as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or semicircular border contour. The first facets 21 can be designed as planar facets or alternatively as convexly or concavely curved facets.

[0055] As is known, for example, from DE 10 2008 009 600 A1, the first facets 21 can themselves each be composed of a plurality of individual mirrors, in particular a plurality of micromirrors. The first facet mirror 20 can in particular be designed as a microelectromechanical system (MEMS system). For details, reference is made to DE 10 2008 009 600 A1.

[0056] Between the collector 17 and the deflecting mirror 19, the illumination radiation 16 runs horizontally, i.e. along the y-direction y.

[0057] In the beam path of the illumination optics 4, a second faceted mirror 22 is arranged downstream of the first faceted mirror 20. If the second faceted mirror 22 is arranged in a pupil plane of the illumination optics 4, it is also referred to as a pupil faceted mirror. The second faceted mirror 22 can also be arranged at a distance from a pupil plane of the illumination optics 4. In this case, the combination of the first faceted mirror 20 and the second faceted mirror 22 is also referred to as a specular reflector. Specular reflectors are known from US 2006 / 0132747 A1, EP 1 614 008 B1, and US 6,573,978.

[0058] The second facet mirror 22 comprises a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets.

[0059] The second facets 23 can also be macroscopic facets, which may, for example, have round, rectangular, or hexagonal edges, or alternatively, facets composed of micromirrors. Reference is also made to DE 10 2008 009 600 A1 in this regard.

[0060] The second facets 23 can have planar or alternatively convex or concave curved reflective surfaces.

[0061] The illumination optics 4 thus form a double-faceted system. This basic principle is also known as a honeycomb condenser (English: Fly's Eye Integrator).

[0062] It can be advantageous not to arrange the second faceted mirror 22 exactly in a plane that is optically conjugate to a pupil plane of the projection optics 10. In particular, the second faceted mirror 22 can be arranged tilted relative to a pupil plane of the projection optics 10, as described, for example, in DE 10 2017 220 586 A1.

[0063] With the aid of the second faceted mirror 22, the individual first facets 21 are imaged into the object field 5. The second faceted mirror 22 is the last beam-shaping, or indeed the last, mirror for the illumination radiation 16 in the beam path before the object field 5.

[0064] In another embodiment of the illumination optics 4, not shown, a transmission optic can be arranged in the beam path between the second facet mirror 22 and the object field 5, which contributes in particular to imaging the first facets 21 into the object field 5. The transmission optic can have exactly one mirror, or alternatively two or more mirrors, arranged one behind the other in the beam path of the illumination optics 4. The transmission optic can, in particular, comprise one or two mirrors for normal incidence (NI mirrors) and / or one or two mirrors for grazing incidence (GI mirrors).

[0065] The lighting optics 4, in the version shown in the Fig. Figure 1 shows exactly three mirrors after the collector 17, namely the deflecting mirror 19, the first faceted mirror 20 and the second faceted mirror 22.

[0066] In a further embodiment of the lighting optics 4, the deflecting mirror 19 can also be omitted, so that the lighting optics 4 after the collector 17 can then have exactly two mirrors, namely the first faceted mirror 20 and the second faceted mirror 22.

[0067] The mapping of the first facets 21 by means of the second facets 23 or with the second facets 23 and a transmission optic into the object plane 6 is regularly only an approximate mapping.

[0068] The projection optics 10 comprise a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection exposure system 1.

[0069] In the Fig. In the example shown, the projection optics 10 comprise six mirrors M1 to M6. Alternatives with four, eight, ten, twelve, or any other number of mirrors Mi are also possible. The projection optics 10 is a doubly obscured optic. A penultimate mirror M5 and a final mirror M6 each have an aperture for the illumination radiation 16. The projection optics 10 has an image-side numerical aperture that is greater than 0.5 and can also be greater than 0.6, for example, 0.7 or 0.75.

[0070] The reflective surfaces of the mirrors Mi can be designed as freeform surfaces without an axis of rotational symmetry. Alternatively, the reflective surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflective surface shape. The mirrors Mi, like the mirrors of the illumination optics 4, can have highly reflective coatings for the illumination radiation 16. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0071] The projection optics 10 has a large object-image offset in the y-direction y between a y-coordinate of a center of the object field 5 and a y-coordinate of the center of the image field 11. This object-image offset in the y-direction y can be approximately as large as a z-distance between the object plane 6 and the image plane 12.

[0072] The projection optics 10 can be anamorphic. In particular, they have different image scales βx, βy in the x and y directions. The two image scales βx, By of the projection optics 10 are preferably (βx, βy) = (+ / - 0.25, + / - 0.125). A positive image scale β indicates a projection without image inversion. A negative sign for the image scale β indicates a projection with image inversion.

[0073] The projection optics 10 thus lead to a reduction in the x-direction x, that is, in the direction perpendicular to the scan direction, in a ratio of 4:1.

[0074] The projection optics 10 lead to a reduction of 8:1 in the y-direction y, that is, in the scan direction.

[0075] Other magnification ratios are also possible. Magnification ratios with the same sign and absolute value in the x and y directions (x, y), for example with absolute values ​​of 0.125 or 0.25, are also possible.

[0076] The number of intermediate image planes in the x and y directions x, y in the beam path between the object field 5 and the image field 11 can be the same or, depending on the design of the projection optics 10, different. Examples of projection optics with different numbers of such intermediate images in the x and y directions x, y are known from US 2018 / 0074303 A1.

[0077] Each of the second facets 23 is assigned to exactly one of the first facets 21 to form an illumination channel for illuminating the object field 5. This can result, in particular, in illumination according to Köhler's principle. The far field is divided into a multitude of object fields 5 with the help of the first facets 21. The first facets 21 generate a plurality of images of the intermediate focus on the second facets 23 assigned to each of them.

[0078] The first facets 21 are each superimposed on a corresponding second facet 23 to illuminate the object field 5 on the reticle 7. The illumination of the object field 5 is particularly homogeneous. It preferably exhibits a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

[0079] The illumination of the entrance pupil of the projection optics 10 can be geometrically defined by arranging the second facets 23. By selecting the illumination channels, in particular the subset of the second facets 23 that carry light, the intensity distribution in the entrance pupil of the projection optics 10 can be adjusted. This intensity distribution is also referred to as the illumination setting or illumination pupil filling.

[0080] Another preferred pupil uniformity in the area of ​​defined illuminated sections of an illumination pupil of the illumination optics 4 can be achieved by a redistribution of the illumination channels.

[0081] Further aspects and details of the illumination of the object field 5 and, in particular, the entrance pupil of the projection optics 10 are described below.

[0082] The projection optics 10 can, in particular, have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

[0083] The entrance pupil of the projection optics 10 cannot always be illuminated exactly by the second faceted mirror 22. When the projection optics 10 image the center of the second faceted mirror 22 telecentrically onto the wafer 13, the aperture rays often do not intersect at a single point. However, a surface can be found where the pairwise determined separation of the aperture rays is minimized. This surface represents the entrance pupil or a surface conjugate to it in real space. In particular, this surface exhibits a finite curvature.

[0084] The projection optics 10 may have different entrance pupil positions for the tangential and sagittal beam paths. In this case, an imaging element, in particular an optical component of the transmission optics, should be provided between the second faceted mirror 22 and the reticle 7. This optical element can accommodate the different positions of the tangential and sagittal entrance pupils.

[0085] During the Fig. In the arrangement of the components of the illumination optics 4 shown in Figure 1, the second faceted mirror 22 is arranged in a plane conjugate to the entrance pupil of the projection optics 10. The first faceted mirror 20 is arranged tilted relative to the object plane 6. The first faceted mirror 20 is arranged tilted relative to an arrangement plane defined by the deflecting mirror 19. The first faceted mirror 20 is arranged tilted relative to an arrangement plane defined by the second faceted mirror 22.

[0086] Fig. Figure 2 shows a schematic perspective view of an embodiment of an optical system 100 for the projection exposure system 1. Fig. Figure 3 shows a schematic top view of optical system 100. Fig. Figure 4 shows a schematic partial sectional view of the optical system 100. The following section refers to the Fig. 2 to 4 received simultaneously.

[0087] The optical system 100 can be a projection optic 10, as mentioned previously, or part of such a projection optic 10. Therefore, the optical system 100 can also be referred to as a projection optic. However, the optical system 100 can also be an illumination system 2, as explained previously, or part of such an illumination system 2. Therefore, the optical system 100 can also be referred to as an illumination system. Furthermore, the optical system 100 can be a so-called mirror preheater or heating head, or part of such a heating head. Therefore, the optical system 100 can also be referred to as a heating head. The optical system 100 is suitable for EUV lithography. However, the optical system 100 can also be suitable for DUV lithography.

[0088] Optical system 100 is associated with an optical axis 102. Optical system 100 includes an optical element 104. The optical element 104 can be a mirror or a lens. In this case, the optical element 104 is a lens.

[0089] One embodiment of the optical element 104 is described in the Fig. Figure 5 shows the optical element 104 having a symmetry or central axis 106. The optical element 104 can be rotationally symmetrical about the central axis 106. However, this is not mandatory. The central axis 106 can coincide with the optical axis 102. The optical element 104 has a first outer surface 108 and a second outer surface 110 facing away from the first outer surface 108. The outer surfaces 108 and 110 can be curved. However, the outer surfaces 108 and 110 can also be flat. For example, light can enter the first outer surface 108 and exit the second outer surface 110. Furthermore, the optical element 104 includes a cylindrical side surface 112. The side surface 112 is rotationally symmetrical about the central axis 106. An annular groove 114 is machined into the side surface 112, circumferencing the central axis 106. Optical element 104 can, for example, be made of glass.

[0090] Now returning to the Fig. Figures 2 to 4 show that the optical system 100 has a tensioning mount 116 in addition to the optical element 104. The tensioning mount 116 supports the optical element 104. This means that the tensioning mount 116 absorbs the weight of the optical element 104. The tensioning mount 116 has several tensioning elements 118, 120, 122. The tensioning elements 118, 120, 122 are connected to the optical element 104. In particular, the tensioning elements 118, 120, 122 engage positively in the annular groove 114 of the optical element 104. A positive connection is created by the interlocking or overlapping of two connecting partners, in this case the respective tensioning element 118, 120, 122 and the annular groove 114.

[0091] In particular, a first tension element 118, a second tension element 120, and a third tension element 122 are provided. This means, in particular, that preferably exactly three tension elements 118, 120, 122 can be provided. However, fewer than three or more than three tension elements 118, 120, 122 can also be provided. Viewed along the optical axis 102, the tension elements 118, 120, 122 are placed next to each other or one on top of the other.

[0092] Fig. Figure 6 shows a schematic top view of the first tension element 118. The tension elements 118, 120, and 122 are preferably identical in construction, so that all subsequent descriptions concerning the first tension element 118 are applicable to the tension elements 120 and 122, and vice versa. The first tension element 118 has an annularly closed gripping section 124, which has a central receiving section 126 in the form of an opening. The optical element 104 is received in the receiving section 126. The gripping section 124 engages in the annular groove 114 of the optical element 104.

[0093] The gripping section 124 has an arcuate, in particular circular, curved ring subsection 128. The ring subsection 128 has a symmetry or central axis 130. The ring subsection 128 is connected to a connecting subsection 136, oriented perpendicular to the side subsections 132, 134, by means of two straight side subsections 132, 134. The connecting subsection 136 transitions into the side subsections 132, 134 by means of two radii 138, 140. In plan view, the connecting subsection 136 is preferably narrower than the side subsections 132, 134 and the ring subsection 128.

[0094] A connecting section 142 is connected to the connecting subsection 136. The connecting section 142 is either tab-shaped or plate-shaped. The connecting section 142 is connected to the connecting subsection 136 by means of a coupling section 144. The coupling section 144 forms a constriction between the connecting section 142 and the connecting subsection 136. The connecting section 142 has a bore or opening 146. A fastening element, which will be explained later, can be passed through the opening 146.

[0095] The first tension element 118 is spring-elastic. In particular, the first tension element 118 is a spring element. If a tensile force is applied to the first tension element 118, the connecting subsection 136 deforms first, as it is the narrowest part. However, the side subsections 132, 134, the ring subsection 128 and / or the radii 138, 140 can also deform spring-elastically.

[0096] The first tensile element 118 can be a stamped sheet metal component. The first tensile element 118 can have a thickness of a few tenths of a millimeter to several millimeters. The first tensile element 118 is preferably flat. This means that the first tensile element 118 has no curvature or bulge. The first tensile element 118 is therefore plate-shaped. The tensile elements 118, 120, 122 are preferably made of a metallic material, for example, spring steel.

[0097] Now returning to the Fig. In sections 2 to 5, the pulley socket 116 has, in addition to the pulley elements 118, 120, 122, a pulley socket housing 148 to which the pulley elements 118, 120, 122 are connected. The pulley socket housing 148 is in the Fig. 2 not shown. In particular, the tension elements 118, 120, 122 can be connected to the tension housing 148 by means of their respective connecting sections 142. For example, the connecting sections 142 can be hooked into the tension housing 148.

[0098] The pull-in housing 148 is at least partially hollow cylindrical or tubular and comprises a receiving section 150 in which the optical element 104 is at least partially received. The receiving section 150 is an opening or a bore. The receiving section 150 has a cylindrical inner surface 152, which is rotationally symmetrical about the optical axis 102. Neither the optical element 104 nor the pull elements 118, 120, 122 contact the inner surface 152.

[0099] The pull-out housing 148 further comprises an end face 154, which surrounds the optical axis 102 in an annular fashion. The pull elements 118, 120, 122, or at least one of the pull elements 118, 120, 122, abut the end face 154. The end face 154 has bores, in particular threaded bores, into which fastening elements 156, 158, 160 are received. The fastening elements 156, 158, 160 can be, for example, screws, bolts, or rivets.

[0100] The fastening elements 156, 158, 160 are passed through the openings 146 of the connecting sections 142 of the tension elements 118, 120, 122 to connect the tension elements 118, 120, 122 to the tension housing 148. In this case, a positive-locking connection is provided in particular. However, a friction-locking connection can also be provided. The tension elements 118, 120, 122 can be hooked into the fastening elements 156, 158, 160. The tension housing 148 is preferably made of a metallic material, for example, stainless steel.

[0101] Each traction element 118, 120, 122 is assigned a plane of symmetry 162, 164, 166. Each traction element 118, 120, 122 is mirror-symmetrical with respect to its respective plane of symmetry 162, 164, 166. This means, in particular, that the central axes 130 of the traction elements 118, 120, 122 lie on their respective planes of symmetry 162, 164, 166. The planes of symmetry 162, 164, 166 intersect at the optical axis 102.

[0102] The tension elements 118, 120, 122 are arranged evenly distributed around the optical axis 102. Specifically, the tension elements 118, 120, 122 are arranged rotated 120° relative to each other with respect to the optical axis 102. This means, in particular, that an angle α1, α2, α3 of 120° is provided between each pair of symmetry planes 162, 164, 166. Viewed along the optical axis 102, the tension elements 118, 120, 122 are arranged side by side or one above the other. For example, the second tension element 120 is positioned between the first tension element 118 and the third tension element 122.

[0103] As previously explained, the pull elements 118, 120, 122 are hooked into the fastening elements 156, 158, 160 or connected to the pull-in housing 148 by means of the fastening elements 156, 158, 160. The gripping sections 124 of the pull elements 118, 120, 122 grip the optical element 104 by engaging in the annular groove 114 of the optical element 104.

[0104] The tension elements 118, 120, 122 are connected to the tension holder housing 148 such that each tension element 118, 120, 122 exerts a tensile force F1, F2, F3 on the optical element 104. The tension elements 118, 120, 122 are thus spring-loaded by means of the respective tensile force F1, F2, F3. This spring preload is already achieved during the assembly of the tension holder 116. During assembly, the tension elements 118, 120, 122 can be elongated or deformed elastically for this purpose. The tensile forces F1, F2, F3 are of equal magnitude, but have different directions of action. The directions of action of the tensile forces F1, F2, F3 are oriented along the planes of symmetry 162, 164, 166 and perpendicular to the optical axis 102.

[0105] The tensile forces F1, F2, F3 are oriented along the respective planes of symmetry 162, 164, 166 of the tensile elements 118, 120, 122. This means, in particular, that all tensile forces F1, F2, F3 point towards the optical axis 102. The tensile forces F1, F2, F3 act in the direction of the optical axis 102. The tensile forces F1, F2, F3 are oriented perpendicular to the optical axis 102. The tensile forces F1, F2, F3 are spatially oriented such that they cancel each other out or compensate for each other. The tensile forces F1, F2, F3 are inclined relative to each other at the previously mentioned angles α1, α2, α3.

[0106] If heat is introduced into the optical system 100 during operation, for example by the illumination radiation 16, the tensile socket housing 148 expands more due to the heat than the optical element 104, since the tensile socket housing 148 is made of a material with a higher coefficient of thermal expansion than the optical element 104. This increases the tensile forces F1, F2, F3. However, since the tensile forces F1, F2, F3 are always of equal magnitude and spatially oriented in such a way that they compensate for each other, this prevents the central axis 106 of the optical element 104 from shifting out of alignment with the optical axis 102 of the optical system 100. Therefore, the optical properties of the optical system 100 are advantageously not affected by the heat input.

[0107] Fig. Figure 7 shows a schematic perspective view of another embodiment of an optical system 200. Fig. Figure 8 shows a schematic top view of the optical system 200. Fig. Figure 9 shows a schematic partial sectional view of the optical system 200. The following section refers to the Fig. References to numbers 7 to 9 were made simultaneously.

[0108] The optical system 200 is essentially identical in functionality and design to the optical system 100. Therefore, only the differences between the two embodiments of the optical systems 100 and 200 will be discussed below.

[0109] The optical system 200 has an optical element 104, as previously mentioned, with a circumferential annular groove 114 (not shown). An optical axis 202 is associated with the optical system 200. In addition to the optical element 104, the optical system 200 includes a pull-out socket 204, which supports the optical element 104.

[0110] The pull-out mechanism 204 comprises several pull-out elements 206, 208, 210 which are connected to the optical element 104. In particular, the pull-out elements 206, 208, 210 engage positively in the annular groove 114 of the optical element 104. Specifically, a first pull-out element 206, a second pull-out element 208 and a third pull-out element 210 are provided.

[0111] Fig. Figure 10 shows a schematic top view of the first tension element 206. The tension elements 206, 208, and 210 are preferably identical in construction, so that all subsequent descriptions concerning the first tension element 206 are applicable to the tension elements 208 and 210, and vice versa. The first tension element 206 is particularly ring-shaped and includes a receiving section 212 in the form of an opening. The optical element 104 is received in the receiving section 212.

[0112] The first pulling element 206 has an outer ring section 214, which is ring-shaped. The outer ring section 214 runs completely around the optical element 104. The outer ring section 214 thus runs around the receiving section 212. The outer ring section 214 is rotationally symmetrical about a symmetry or central axis 216.

[0113] An inner ring section 218 is arranged within the outer ring section 214. The inner ring section 218 does not completely, but only partially, surround the receiving section 212. The inner ring section 218 comprises a symmetry or central axis 220, which is not identical to the central axis 216 of the outer ring section 214. In particular, the inner ring section 218 is arranged eccentrically to the outer ring section 214. For this purpose, the central axis 220 is oriented in the direction of Fig. 10 offset downwards from the central axis 216.

[0114] The inner ring section 218 is integrally connected to the outer ring section 214 at connection points 222, 224, in particular in one piece. "In one piece" or "one-piece" in this context means that the outer ring section 214 and the inner ring section 218 are not two separate components, but rather form a single component, namely the first tensile element 206. The first tensile element 206 can be a stamped sheet metal component. The first tensile element 206 can have a thickness ranging from a few tenths of a millimeter to several millimeters. The first tensile element 206 is preferably flat. This means that the first tensile element 206 has no curvature or bulge. The first tensile element 206 is thus plate-shaped. The tensile elements 206, 208, 210 are preferably made of a metallic material, for example, spring steel.

[0115] A gap 226 is provided between the outer ring section 214 and the inner ring section 218, which partially separates the outer ring section 214 from the inner ring section 218. The gap 226 does not extend completely around the central axes 216, 220.

[0116] In a top view, the inner ring section 218 is narrower than the outer ring section 214. This means, in particular, that the inner ring section 218 is more easily elastically deformed than the outer ring section 214. Accordingly, the inner ring section 218 has a lower stiffness than the outer ring section 214. In this context, "stiffness" refers specifically to the resistance of a body, in this case the outer ring section 214 or the inner ring section 218, to elastic deformation caused by an external load. Stiffness depends on the geometry of the body and the material used.

[0117] Now returning to the Fig. From 7 to 9, the pulley socket 204 has a pulley socket housing 228. The pulley socket housing 228 is in the Fig. Figure 7 not shown. The pull-in housing 228 is hollow cylindrical or tubular and rotationally symmetrical about the optical axis 202. The pull-in housing 228 includes a receiving section 230, which is configured as an opening or bore. The receiving section 230 accommodates the optical element 104 and the pull-in elements 206, 208, 210.

[0118] The receiving section 230 comprises a first inner surface 232 and a second inner surface 234. The first inner surface 232 has a larger diameter than the second inner surface 234. This means, in particular, that a shoulder 236 can be provided between the two inner surfaces 232 and 234. However, the shoulder 236 is optional. Alternatively, the first inner surface 232 can extend through the entire pull-out housing 228. The pull-out housing 228 is made of a metallic material, for example, stainless steel.

[0119] The tension elements 206, 208, 210 are pressed into the receiving section 230 with their respective outer ring sections 214. In particular, the tension elements 206, 208, 210 are pressed against the first inner surface 232. An interference fit may be provided for this purpose. This interference fit is designed such that, when heat is introduced into the tension holder 204, the tension holder housing 228 and the tension elements 206, 208, 210 do not expand differently to such an extent that the tension elements 206, 208, 210 lose contact with the first inner surface 232 with their outer ring sections 214.

[0120] Each traction element 206, 208, 210 is assigned a plane of symmetry 238, 240, 242, with which the respective traction element 206, 208, 210 is mirror-symmetrical. The two central axes 216, 220 each lie on the plane of symmetry 238, 240, 242 assigned to the corresponding traction element 206, 208, 210. The traction elements 206, 208, 210 are arranged rotated relative to each other around the optical axis 202 such that an angle β1, β2, β3 of 120° is provided between each pair of planes of symmetry 238, 240, 242.

[0121] To mount the pull-in holder 204, the pull-in elements 206, 208, 210 with their receiving sections 212 are inserted into the annular groove 114 of the optical element 104. The pull-in elements 206, 208, 210 are then pressed into the receiving section 230. Because the central axes 216, 220 are arranged eccentrically to each other, the inner ring sections 218 of the pull-in elements 206, 208, 210 are elongated or spring-deformed during assembly in the receiving section 230, so that a tensile force F1, F2, F3 is applied to the optical element 104 by each pull-in element 206, 208, 210. The spring-deformed inner ring sections 218 can bring the central axes 216, 220 into coaxiality.

[0122] The tensile forces F1, F2, F3 are oriented along the planes of symmetry 238, 240, 242. The tensile forces F1, F2, F3 are thus oriented at angles β1, β2, β3 of 120° to each other. The tensile forces F1, F2, F3 are arranged perpendicular to the optical axis 202. The tensile forces F1, F2, F3 act in the direction of the optical axis 202.

[0123] When heat is introduced into the optical system 200, the tensioning housing 228 expands together with the tensioning elements 206, 208, 210. The optical element 104 expands less due to the heat. As mentioned previously, the interference fit between the tensioning elements 206, 208, 210 and the first inner surface 232 is designed such that the tensioning elements 206, 208, 210 do not lose contact with the first inner surface 232 even when heat is introduced into the optical system 200. This expansion process increases the tensile forces F1, F2, F3. Since the equal tensile forces F1, F2, F3 cancel each other out or compensate for each other, the central axis 106 of the optical element 104 remains in the optical axis of the optical system 200. Therefore, the optical properties of the optical system 200 are advantageously not changed by heat input.

[0124] Although the present invention has been described using exemplary embodiments, it can be modified in many ways. REFERENCE MARK LIST 1 Projection exposure system 2 Lighting system 3 light source 4 Lighting optics 5 object field 6 Object level 7 reticles 8 label holders 9 Reticle displacement drive 10 Projection optics 11 Image field 12 Image plane 13 wafers 14 wafer holders 15 wafer transfer drive 16 Lighting radiation 17 Collector 18 Intermediate focus plane 19 deflecting mirrors 20 first faceted mirror 21 first facet 22 second faceted mirror 23 second facet 100 optical system 102 optical axis 104 optical element 106 Central axis 108 outdoor area 110 outdoor area 112 side surface 114 Ring groove 116 train grip 118 Pull element 120 pull element 122 Pull element 124 Reaching section 126 Recording section 128 Ring subsection 130 center axis 132 Page subsection 134 Page subsection 136 Connection subsection 138 Rounding 140 rounding 142 Connecting section 144 Coupling section 146 Breakthrough 148 cable housings 150 Recording section 152 interior surface area 154 Front surface 156 Fastening element 158 Fastening element 160 fastening element 162 Plane of symmetry 164 Plane of symmetry 166 Plane of symmetry 200 optical system 202 optical axis 204 train socket 206 Tension element 208 Pull element 210 Pull element 212 Recording section 214 Outer ring section 216 Center axis 218 Inner ring section 220 center axis 222 Connection area 224 Connection area 226 gap 228 cable housings 230 Recording section 232 interior surface area 234 interior surface area Paragraph 236 238 Plane of symmetry 240 Plane of symmetry 242 Plane of symmetry F1 traction F2 tractive force F3 traction M1 mirror M2 mirrors M3 mirror M4 mirrors M5 mirror M6 mirrors x x-direction y y-direction z z-direction α1 angle α2 angle α3 angle β1 angle β2 angle β3 angle QUOTES INCLUDED IN THE DESCRIPTION

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

[0000] DE 10 2008 009 600 A1 [0055, 0059] US 2006 / 0132747 A1

[0057] EP 1 614 008 B1

[0057] US 6,573,978

[0057] DE 10 2017 220 586 A1

[0062] US 2018 / 0074303 A1

[0076]

Claims

[1] Optical system (100, 200) for a projection exposure system (1), comprising an optical element (104), and a pull-out socket (116, 204) which carries the optical element (104), wherein the pull-out mechanism (116, 204) has several pull-out elements (118, 120, 122, 206, 208, 210) which are connected to the optical element (104), wherein each tensile element (118, 120, 122, 206, 208, 210) applies a tensile force (F1, F2, F3) to the optical element (104), and wherein the tensile forces (F1, F2, F3) are spatially oriented such that the tensile forces (F1, F2, F3) compensate each other. [2] Optical system according to claim 1, wherein the tensile forces (F1, F2, F3) are oriented perpendicular to an optical axis (102, 202) of the optical system (100, 200). [3] Optical system according to claim 2, wherein the traction elements (118, 120, 122, 206, 208, 210) are arranged uniformly distributed around the optical axis (102, 202). [4] Optical system according to claim 2 or 3, wherein the pull-out mechanism (116, 204) comprises a first pull-out element (118, 206), a second pull-out element (120, 208) and a third pull-out element (122, 210), and wherein the first pull-out element (118, 206), the second pull-out element (120, 208) and the third pull-out element (122, 210) are arranged rotated relative to each other by an angle (α1, α2, α3, β1, β2, β3) of 120° with respect to the optical axis (102, 202). [5] Optical system according to one of claims 2-4, wherein the traction elements (118, 120, 122, 206, 208, 210) are arranged side by side when viewed along the optical axis (102, 202). [6] Optical system according to one of claims 1-5, wherein the pull-in holder (116, 204) has a pull-in holder housing (148, 228), and wherein the pull elements (118, 120, 122, 206, 208, 210) are connected to the pull-in holder housing (148, 228). [7] Optical system according to claim 6, wherein the pull elements (118, 120, 122, 206, 208, 210) are positively and / or force-fit connected to the pull-in housing (148, 228). [8] Optical system according to claim 7, wherein each pull element (118, 120, 122) has a connecting section (142) by means of which the respective pull element (118, 120, 122) is positively connected to the pull housing (148). [9] Optical system according to one of claims 6-8, wherein the pull-in housing (228) has a receiving section (230) for receiving the pull elements (206, 208, 210) and the optical element (104), and wherein the pull elements (206, 208, 210) are pressed into the receiving section (230). [10] Optical system according to one of claims 1-9, wherein each traction element (118, 120, 122, 206, 208, 210) circumferentially completely around the optical element (104). [11] Optical system according to one of claims 1-10, wherein each traction element (206, 208, 210) has an outer ring section (214) and an inner ring section (218) arranged within the outer ring section (214), and wherein the inner ring section (218) is arranged eccentrically to the outer ring section (214). [12] Optical system according to claim 11, wherein the inner ring section (218) has a lower stiffness than the outer ring section (214). [13] Optical system according to claim 11 or 12, wherein a gap (226) is arranged between the outer ring section (214) and the inner ring section (218), which circumferentially only partially surrounds the respective pulling element (206, 208, 210). [14] Optical system according to one of claims 11-13, wherein the outer ring section (214) and the inner ring section (218) are joined together in one piece, in particular in one piece of material. [15] Projection exposure system (1) with an optical system (100, 200) according to one of claims 1-14.

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