Optical system and projection exposure apparatus

Abstract

An optical system (100) for a projection exposure apparatus (1) includes a first component (102), a second component (104) wherein the second component (104) is actuable within an actuation region (A) relative to the first component (102), and an end-stop device (106) that allows the second component (104) to move relative to the first component (102) within the actuation region (A) and blocks it outside the actuation region (A), wherein the end-stop device (106) includes a bending element (200, 200A, 200B, 200C) whose rigidity suddenly increases when the limit of the actuation region (A) is reached to block the movement of the second component (104) relative to the first component (102).

Description

Technical Field

[0001] This disclosure relates to an optical system for a projection exposure apparatus, and to a projection exposure apparatus incorporating the optical system.

[0002] The entire contents of priority application DE 10 2021 209 099.0 are incorporated herein by reference. Prior Technology

[0003] Lithography is used to produce microstructured components, such as integrated circuits. The lithography process is performed using lithography equipment with an illumination system and a projection system. In this case, the image of a photomask (reduced photomask) illuminated by the illumination system is projected onto a substrate, such as a silicon wafer, by the projection system. A photosensitive layer (photoresist) is coated on the substrate and positioned within the image plane of the projection system to transfer the photomask structure onto the photosensitive coating of the substrate.

[0004] Driven by the demand for smaller structures in integrated circuit manufacturing, EUV lithography equipment using light with wavelengths ranging from 0.1 nm to 30 nm, particularly 13.5 nm, is currently being developed. In the case of this EUV lithography equipment, since most materials highly absorb light with this wavelength, it is necessary to use reflective optical units, i.e., mirrors, instead of refractive optical units, i.e., lens elements, as previously used.

[0005] To prevent damage to the optical units of the projection system or other components such as a sensor frame due to vibration, a so-called end-point stop may be placed between the force frame and the sensor frame, defining the mobility between the force frame and the sensor frame. According to internal company findings, this end-point stop has a bolt connected to the force frame and a sleeve disposed on the sensor frame and adjustable to the bolt.

[0006] This movement allows the sensor frame to move relative to the force frame within the actuated area. Under strong vibration, the bolt contacts the sleeve. This firstly results in a large force acting on the sensor frame, and secondly, the direct contact between the metal bolt and the metal sleeve causes unwanted particulate wear. This needs to be improved. Summary of the Invention

[0007] In this context, one object of the present invention is to provide an improved optical system.

[0008] Therefore, an optical system for a projection exposure apparatus is proposed. The optical system includes a first component, a second component, wherein the second component is actuable within an actuation region relative to the first component, and an end-stop device that allows the second component to move relative to the first component within the actuation region and blocks it outside the actuation region, wherein the end-stop device includes a bending element whose rigidity suddenly increases upon reaching a limit in the actuation region to prevent movement of the second component relative to the first component.

[0009] Because the bending element can abruptly change its rigidity according to its deflection, the end-stop device can be designed to, for example, cause the bending element to harden under strong vibrations reaching the limit of the actuation region, thus preventing the movement of the second component relative to the first component. This prevents direct contact between the components of the end-stop device. Consequently, both the introduction of strong forces and the formation of multiple particles into these components can be prevented.

[0010] The optical system is, in particular, a projection lens or a projection optical unit, or part of such a projection optical unit, in a projection exposure apparatus. However, the optical system may also be part of an illumination optical unit. The first component and the second component may be any components of the optical system. For example, the first component may be a force frame, and the second component may be a sensor frame. However, these components may also include multiple optical elements, multiple measuring instruments, or the like.

[0011] The fact that the second component is actuable within an "actuation zone" relative to the first component, in this case, means that the second component can move relative to the first component in a specific area, for example, manageable by an actuator or actuator element. "Actuation," in this case, is understood to mean that the second component moves relative to the first component by means of the actuator or actuator element. Preferably, the second component is mounted using a weight-compensated support. This support may also be referred to as an active vibration isolation system (AVIS). This means that the second component can deflect in a stress-free manner.

[0012] Therefore, within the actuation zone, the end-stop device applies no force, or preferably almost no force, to the second component, allowing the latter to be freely actuated. Outside the permissible actuation zone, the end-stop device blocks the second component relative to the first component, thus preventing relative movement of multiple components relative to each other outside the actuation zone.

[0013] Specifically, the bending element allows the second component to move relative to the first component within the actuation region, wherein when the deflection of the bending element reaches the limit of the actuation region, the bending element automatically stiffens, thus preventing the second component from moving relative to the first component. That is, the rigidity of the bending element outside the actuation region is so high that movement of the second component relative to the first component is impossible, or only possible with increased force consumption. In this case, the "limit" of the actuation region should be understood as the point at which the bending element can reach the point where further deflection is no longer possible without moving beyond the actuation region. The rigidity of the bending element outside the actuation region is virtually infinite compared to within the actuation region.

[0014] The "sudden" increase in stiffness should be understood in particular as a significant increase in stiffness, for example, by a factor of several μm (micrometers), or less than 100 μm, in the deflection region of the bending element. This sudden increase in stiffness is achieved, in particular, solely through or solely through the appropriate geometry of the bending element. The bending element therefore does not possess linear characteristics, as is the case with cylindrical springs, for example. This behavior of the bending element can be termed a mechanical or kinematic singularity. A "singularity" is therefore understood to mean that the behavior of the bending element exhibits linear behavior until a certain point, for example, reaching the limit of the actuation region, and after said point exhibits nonlinear behavior, particularly the sudden increase in stiffness. This characteristic, or mechanical or kinematic singularity, is achieved, in particular, solely through the appropriate geometry of the bending element.

[0015] The end-stop device may include a plurality of bending elements. Preferably, within the actuation region, these bending elements are flexible, such that the actuation of the second component relative to the first component is unaffected or only minimally affected. Therefore, the bending elements do not exert any force on the second component, or only a very small force. In other words, the bending elements within the actuation region cannot transmit any or at least a very small amount of force from the first component to the second component.

[0016] Once the bending element deflects away from the actuation region or reaches its limit or periphery, the bending element automatically hardens. In this case, "automatically" or "self-hardening" means that the bending element, due to its structural design, can move from an unhardened state to a hardened state without an external actuator and without the introduction of external energy. Starting from the limit of the actuation region, or outside the actuation region, the bending element then hardens, thereby preventing the movement of the second component relative to the first component.

[0017] According to one embodiment, the rigidity of the bending element outside the actuation region is several times greater than the rigidity within the actuation region.

[0018] In this case, "multiple" is specifically understood to mean at least ten times. "Rigidity" in this example is generally understood to mean an object's resistance to force or torque. Here, rigidity depends on the object's geometry and the materials used. The greater the rigidity, the greater the object's resistance to deformation.

[0019] According to a further embodiment, the stiffness of the bending element increases abruptly within a deflection distance of less than 100 μm.

[0020] Depending on the structural design of the bending element, the deflection distance can be defined in any manner. Once the second component moves a distance of 100 µm relative to the first component when it reaches the limit of the actuation region, the bending element will suddenly stiffen, thus blocking the movement of the second component relative to the first component. That is, the sudden stiffening occurs within the deflection distance.

[0021] According to a further embodiment, the rigidity of the bending element outside the actuation region is 100 times or more than the rigidity within the actuation region.

[0022] The stiffness outside the actuation region can be 150 to 200 times that within the actuation region. In principle, the stiffness outside the actuation region is a multiple of the stiffness within the actuation region. However, compared to a conventional spring, the stiffness increases within a very short deflection distance, as mentioned above, which can be less than 100 µm.

[0023] According to a further embodiment, the bending element includes an arc-shaped first leaf spring portion and a precisely bent second leaf spring portion, wherein the first leaf spring portion and the second leaf spring portion are bent in opposite directions.

[0024] The first and second leaf spring portions can be curved in an arc shape in each case. In particular, the first and second leaf spring portions have the same curvature in opposite directions. The fact that the first and second leaf spring portions are "curved in opposite directions" means that the first and second leaf spring portions are oriented away from each other in a convex manner. In each case, these leaf spring portions are pre-stretched by the spring to form their arched geometry.

[0025] According to a further embodiment, the first leaf spring portion and the second leaf spring portion are connected to each other at each end by means of a first connecting portion and a second connecting portion.

[0026] For example, the connecting portions can be cubic. However, the connecting portions can have any geometric shape. In each case, one end of the first leaf spring portion and the second leaf spring portion are connected to each connecting portion. Starting from the two connecting portions, the first leaf spring portion and the second leaf spring portion are bent outward along a central direction between the connecting portions. The first leaf spring portion and the second leaf spring portion have the farthest distance between the centers of the connecting portions.

[0027] According to a further embodiment, since the first leaf spring portion and the second leaf spring portion are aligned parallel to each other, the rigidity of the bending element suddenly increases when it reaches the limit of the actuation region.

[0028] Here, a transition occurs from the flexible stiffness of the leaf springs to their tensile strength, which is twice the flexible stiffness. If the deflection of the bending element reaches the limit of the actuation region, the bending element stiffens, particularly due to the fact that the first and second leaf springs are aligned parallel to each other. That is, in particular, the arcuate curvature of the first and second leaf springs is flattened, so that the first and second leaf springs extend parallel to each other or directly abut against each other. Then, the leaf springs no longer have any spring action generated by their curvature.

[0029] According to a further embodiment, since the first leaf spring portion and the second leaf spring portion elastically deform as part of their arcuate curvature, the bending element allows the second component to move relative to the first component within the actuation region.

[0030] This specifically means that during the actuation of the second component relative to the first component, the curvature of the first leaf spring portion and the second leaf spring portion is changed, resulting in the second component being able to move within its actuation area.

[0031] According to a further embodiment, the endpoint stop device allows the second component to move relative to the first component in two degrees of freedom within the actuation region, and blocks movement in two degrees of freedom outside the actuation region.

[0032] Preferably, the second component has six degrees of freedom: three translational degrees of freedom along the x, y, and z directions, and three rotational or tilting degrees of freedom about the x, y, and z directions, respectively. Two of these degrees of freedom are assigned to each endpoint stop. Whether these two degrees of freedom are allowed or blocked depends on whether the second component is located within or outside the actuation region.

[0033] According to a further embodiment, the optical system also includes at least three endpoint stops, each of which is assigned two degrees of freedom.

[0034] However, the number of these end-stop devices is, in principle, arbitrary. For example, eight end-stop devices may also be provided.

[0035] According to a further embodiment, when the limit of the actuation region is reached, the rigidity of the bending element suddenly increases when a tensile force is applied to the bending element and when a compressive force is applied to the bending element, causing the bending element to block the movement of the second component relative to the first component.

[0036] Specifically, when the deflection of the bending element reaches the limit of the actuation region, the bending element stiffens, automatically preventing movement of the second component relative to the first component under both tensile and compressive forces. For this purpose, the bending element can have more than two leaf spring portions. For example, the bending element can have four leaf spring portions, wherein in each case, two leaf spring portions are connected to a common connecting portion at each end. Therefore, two non-interconnected connecting portions are provided at one end of these leaf spring portions. Facing away from these two connecting portions, all four leaf spring portions are connected to a common connecting portion. In this way, the bending element can absorb both compressive and tensile forces.

[0037] According to a further embodiment, the first component is coupled to the second component by means of the bending element.

[0038] "Coupled" here means that the first component is connected to the second component by means of the bending element. However, preferably, the connection is arranged in such a way that no force or only a very small force can be transmitted within the actuation region. Outside the actuation region, a larger force can therefore be transmitted.

[0039] According to a further embodiment, the first component is a force frame and the second component is a sensor frame.

[0040] However, as mentioned above, these elements may also be any other component of the projection exposure device or the projection optics unit.

[0041] According to a further embodiment, the bending element is a single-piece component, particularly a single-piece material component.

[0042] In this document, "single-piece" means that the bending element is a single component from beginning to end, rather than composed of different components. This means that the leaf springs and the connecting parts together form a common component. "Single-piece material" in this document means that the bending element is always made of the same material. For example, the bending element is made of steel, especially stainless steel.

[0043] Furthermore, a projection exposure device with this optical system is proposed.

[0044] The optical system may be a projection optics unit or part of a projection optics unit in the projection exposure apparatus. The projection exposure apparatus may include a plurality of optical systems. The projection exposure apparatus may be an EUV lithography apparatus. EUV stands for "Extreme Ultraviolet" and indicates that the wavelength of the working light is between 0.1 nm and 30 nm. The projection exposure apparatus may also be a DUV lithography apparatus. DUV stands for "Deep Ultraviolet" and indicates that the wavelength of the working light is between 30 nm and 250 nm.

[0045] In this context, "one; a" is not necessarily understood to be limited to a single element. Rather, multiple elements may be provided, such as, for example, two, three, or more. Any other number used herein should not be construed as a limitation on the precisely specified number of elements. Rather, unless otherwise stated, upward and downward numerical deviations are possible.

[0046] The embodiments and features described for this optical system are applicable to the proposed projection exposure device, and vice versa.

[0047] Further possible embodiments of the present invention also include combinations of any features or embodiments of the exemplary embodiments described above or below, not explicitly mentioned. In such cases, those skilled in the art will also add unique variations or supplements to the corresponding basic form of the invention.

[0048] Further advantageous improvements and features of the present invention are the subject of the claims following this document and the exemplary embodiments of the invention described below. Hereinafter, the invention will be explained in more detail based on preferred embodiments with reference to the accompanying drawings. Simple Explanation of the Diagram

[0049] Figure 1 shows a cross-sectional schematic diagram of one of the projection exposure devices used in this EUV projection lithography;

[0050] Figure 2 shows a partial cross-sectional schematic diagram of one embodiment of the optical system of the projection exposure apparatus according to Figure 1;

[0051] Figure 3 shows a schematic diagram of the stiffness distribution of a bending element of the optical system according to Figure 2 over the deflection distance of the bending element;

[0052] Figure 4 shows a perspective schematic diagram of one embodiment of the bending element used in the optical system according to Figure 2;

[0053] Figure 5 shows a side view of the bending element according to Figure 4;

[0054] Figure 6 shows a force-deflection distance diagram of the bending element according to Figure 4; and

[0055] Figure 7 shows a cross-sectional schematic diagram of a further embodiment of the optical system for the projection exposure apparatus of Figure 1. Implementation

[0056] Unless otherwise stated, identical or functionally equivalent components have the same component number in the drawings. It should also be noted that the illustrations in the drawings are not necessarily drawn to scale.

[0057] Figure 1 shows an embodiment of a projection exposure apparatus 1 (lithography apparatus), particularly an EUV lithography apparatus. One embodiment of the illumination system 2 of the projection exposure apparatus 1, in addition to having a light source or radiation source 3, also has an illumination optics unit 4 for illuminating the object field 5 in the object plane 6. In an alternative embodiment, the light source 3 may also be provided as a module separate from the rest of the illumination system 2. In this case, the illumination system 2 does not include the light source 3.

[0058] A zoom mask 7, positioned in the object field 5, is exposed. The zoom mask 7 is fixed by a mask carrier 8. The mask carrier 8 can be moved by a zoom mask displacement actuator 9, particularly in a scanning direction.

[0059] For illustrative purposes, 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 is perpendicular to the plane of the diagram. The y-direction y extends horizontally, and the z-direction z extends vertically. The scan direction in Figure 1 extends along the y-direction y. The z-direction z extends perpendicular to the object plane 6.

[0060] The projection exposure apparatus 1 includes a projection optics unit 10. The projection optics unit 10 is used 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, it may be an angle between the object plane 6 and the image plane 12 that is not equal to 0°.

[0061] The structure on the magnification mask 7 is imaged onto a photosensitive layer of a wafer 13, which is disposed in the region of the image field 11 in the image plane 12. The wafer 13 is supported by a wafer carrier 14. The wafer carrier 14 can be moved by a wafer displacement driver 15, particularly along the y-direction. On the one hand, the displacement of the magnification mask 7 by the magnification mask displacement driver 9, and on the other hand, the displacement of the wafer 13 by the wafer displacement driver 15 can be performed synchronously.

[0062] Light source 3 is an EUV radiation source. Specifically, light source 3 emits EUV radiation 16, hereinafter also referred to as operational radiation, illumination radiation, or illumination light. In particular, the operational radiation 16 has a wavelength in the range of 5 nm to 30 nm. Light source 3 can be a plasma source, such as an LPP (laser-generated plasma) source or a GDPP (gas discharge-generated plasma) source. It can also be a synchrotron-based radiation source. Light source 3 can be an FEL (free electron laser).

[0063] The illumination radiation 16 emitted from the light source 3 is focused by a concentrator 17. The concentrator 17 may be a concentrator having one or more elliptical and / or hyperboloidal reflective surfaces. The illumination radiation 16 may be incident on at least one reflective surface of the concentrator 17 with grazing incidence (GI), i.e., an angle of incidence greater than 45°, or perpendicular incidence (NI), i.e., an angle of incidence less than 45°. The concentrator 17 may be structured and / or coated, firstly to optimize its reflectivity to the radiation used, and secondly to suppress incoming light.

[0064] Downstream of the concentrator 17, the illumination radiation 16 propagates through a central focal point in an intermediate focal plane 18. The intermediate focal plane 18 can represent the separation between the radiation source module with the light source 3 and the concentrator 17 and the illumination optical unit 4.

[0065] The illumination optics unit 4 includes a deflector 19 and a first facet 20 disposed downstream of it in the beam path. The deflector 19 may be a planar deflector, or alternatively, a mirror with a beam-affecting effect beyond mere deflection. Alternatively or additionally, the deflector 19 may be in the form of a spectral filter that separates a wavelength of illumination radiation 16 from a wavelength deviating from the incoming light. If the first facet 20 is disposed in a plane of the illumination optics unit 4 serving as a field plane, and this plane is optically conjugate to the object plane 6, it is also called a field facet. The first facet 20 includes a plurality of individual first facets 21, which may also be called field facets. Only some of these first facets 21 are shown as examples in Figure 1.

[0066] The first facet 21 can be in the form of a macroscopic facet, particularly a rectangular facet or a facet with an arc-shaped outer contour or a portion of a circle. The first facet 21 can be in the form of a planar facet, or alternatively, it can be in the form of a convex or concave curved surface.

[0067] As can be seen, for example, from patent number DE 10 2008 009 600 A1, the first facet 21 itself can, in each case, be composed of a plurality of individual mirrors, particularly a plurality of micromirrors. The first facet 20 can, in particular, be formed as a microelectromechanical system (MEMS system). For further details, please refer to patent number DE 10 2008 009 600 A1.

[0068] Between the condenser 17 and the deflector 19, the illumination radiation 16 travels horizontally, that is, along the y-direction y.

[0069] In the beam path of the illumination optical unit 4, the second facet mirror 22 is positioned downstream of the first facet mirror 20. If the second facet mirror 22 is positioned in a pupil plane of the illumination optical unit 4, it is also called a pupil facet mirror. The second facet mirror 22 can also be positioned at a certain distance from a pupil plane of the illumination optical unit 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 is also called a specular reflector. Specular reflectors are known from several patents, including US 2006 / 0132747 A1, EP 1 614 008 B1, and US 6,573,978.

[0070] The second facet 22 comprises a plurality of second facets 23. In the case of a pupil facet 22, the second facet 23 is also called a pupil facet.

[0071] The second facet 23 can also be a macroscopic facet, which may, for example, have a circular, rectangular, or hexagonal perimeter, or alternatively, a facet composed of micromirrors. In this regard, see also patent number DE 10 2008 009 600 A1.

[0072] The second facet 23 may have a planar or alternatively convex or concave curved reflective surface.

[0073] The illumination optics unit 4 thus forms a biplane system. This basic principle is also known as a compound eye condenser (compound eye integrator).

[0074] It may be advantageous to not precisely position the second facet mirror 22 in a plane optically conjugate with the pupil plane of the projection optics unit 10. In particular, the second facet mirror 22 may be configured to be tilted relative to the pupil plane of the projection optics unit 10, as described, for example, in patent number DE 10 2017 220 586 A1.

[0075] With the aid of the second mirror 22, each of the first facets 21 is imaged into the object field 5. The second facet mirror 22 is the last beam shaping mirror, or in fact the last reflecting mirror of the illumination radiation 16 in the beam path upstream of the object field 5.

[0076] In a further embodiment of the illumination optics unit 4 (not shown in the figure), a transfer optics unit, particularly helpful in imaging the first facet 21 into the object field 5, may be disposed in the beam path between the second facet 22 and the object field 5. The transfer optics unit may have exactly one mirror, or alternatively, two or more mirrors, arranged sequentially in the beam path of the illumination optics unit 4. The transfer optics unit may particularly include one or two vertical incident mirrors (NI mirrors) and / or one or two grazing incident mirrors (GI mirrors).

[0077] In the embodiment shown in Figure 1, the illumination optical unit 4 has three mirrors downstream of the condenser 17, specifically the deflector 19, the first facet mirror 20, and the second facet mirror 22.

[0078] In a further embodiment of the illumination optical unit 4, the deflector 19 is not required. Therefore, the illumination optical unit 4 may have two mirrors, specifically the first facet mirror 20 and the second facet mirror 22, just downstream of the condenser 17.

[0079] Imaging the first plane 21 onto the object plane 6 using the second plane 23 or by using the second plane 23 with a transfer optical unit is usually only an approximate imaging.

[0080] The projection optical unit 10 includes a plurality of mirrors Mi, which are sequentially numbered according to their configuration in the beam path of the projection exposure device 1.

[0081] In the example shown in Figure 1, the projection optics unit 10 includes six mirrors M1 to M6. Alternatives using four, eight, ten, twelve, or any other number of mirrors M1 can be used. The projection optics unit 10 is a double-shielded optics unit. The penultimate mirror M5 and the last mirror M6 each have a through-hole for illumination radiation 16. The projection optics unit 10 has an image-side numerical aperture that is greater than 0.5, may also be greater than 0.6, and may be, for example, 0.7 or 0.75.

[0082] The reflecting surface of mirror Mi can be specifically implemented as a freeform surface without an axis of rotational symmetry. Alternatively, the reflecting surface of mirror Mi can be designed as an aspherical surface with exactly one axis of rotational symmetry in its shape. Like the reflecting mirror of illumination optics unit 4, mirror Mi can have a highly reflective coating for illumination radiation 16. These coatings can be designed as multilayer coatings, particularly with alternating molybdenum and silicon layers.

[0083] The projection optics unit 10 has a large object-image offset in the y-direction y between the y-coordinate of the center of the object field 5 and the y-coordinate of the center of the image field 11. In the y-direction y, this object-image offset can be approximately the same as the z-distance between the object plane 6 and the image plane 12.

[0084] Specifically, the projection optical unit 10 may have a modified form. In particular, it may have different imaging ratios βx and βy in the x and y directions. Preferably, the two imaging ratios βx and βy of the projection optical unit 10 are (βx, βy) = (+ / -0.25, + / -0.125). A positive imaging ratio β indicates imaging without image inversion. A negative sign for the imaging ratio β indicates imaging using image inversion.

[0085] Therefore, the projection optical unit 10 is reduced in size in the x-direction x, that is, in the direction perpendicular to the scanning direction, by a ratio of 4:1.

[0086] The projection optical unit 10 results in a size reduction of 8:1 in the y-direction, i.e., in the scanning direction.

[0087] Other imaging scales are also possible. Imaging scales with the same sign and the same absolute value in the x-direction (x) and y-direction (y) are also possible, for example, with absolute values ​​of 0.125 or 0.25.

[0088] The number of intermediate image planes in the x-direction x and y-direction y of the beam path between object field 5 and image field 11 may be the same or different, depending on the embodiment of projection optical unit 10. Examples of projection optical units with different numbers of these intermediate images in the x and y directions are known from US Patent No. 2018 / 0074303 A1.

[0089] In this case, one of the second planes 23 is assigned to exactly one of the first planes 21 to form illumination channels for the object field 5. This, in particular, produces illumination according to the Kohler principle. The far field is decomposed into a plurality of object fields 5 by means of the first plane 21. The first plane 21 produces a plurality of images with intermediate focal points on the second planes 23 to which it is assigned.

[0090] The first surface 21, through the assigned second surface 23, is imaged onto the photomask 7 in each case in a superimposed manner to illuminate the object field 5. The illumination of the object field 5 is particularly designed to be as uniform as possible. Preferably, it has a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

[0091] The full-area illumination of the entrance pupil of the projection optical unit 10 can be geometrically defined by the arrangement of the second facet 23. The intensity distribution in the entrance pupil of the projection optical unit 10 can be set by selecting the illumination channel, specifically a subset of the second facet 23 that guides the light. This intensity distribution is also referred to as illumination setting or illumination pupil filling.

[0092] A similarly improved pupil uniformity in multiple partial regions of the illumination pupil of the illumination optical unit 4, illuminated in a defined manner, can be achieved by redistributing the illumination channels.

[0093] The following describes other aspects and details of the illumination of the object field 5, and in particular the illumination of the entrance pupil of the projection optical unit 10.

[0094] Specifically, the projection optical unit 10 may have a concentric entrance pupil. The latter may be accessible, or it may be inaccessible.

[0095] The entrance pupil of the projection optics unit 10 is often not accurately illuminated by the second facet mirror 22. When the center of the second facet mirror 22 is telecentrically imaged onto the projection optics unit 10 on the wafer 13, the aperture rays typically do not intersect at a single point. However, a region can be found where the distance between pairs of defined aperture rays becomes minimal. This region represents the entrance pupil or a region in real space conjugate to it. In particular, this region has a finite curvature.

[0096] The entrance pupil positions for the tangential beam path and the sagittal beam path of the projection optical unit 10 can also be different. In this case, the imaging element, especially the optical components of the transfer optical unit, should be positioned between the second facet mirror 22 and the magnifying glass 7. With the help of this optical element, the different positions of the tangential entrance pupil and the sagittal entrance pupil can be considered.

[0097] In the component configuration of the illumination optical unit 4 shown in Figure 1, the second facet mirror 22 is disposed in the region conjugate with the entrance pupil of the projection optical unit 10. The first facet mirror 20 is configured to be tilted relative to the object plane 6. The first facet mirror 20 is configured such that it is tilted relative to a configuration plane defined by the deflector 19. The first facet mirror 20 is configured in an tilted manner relative to the configuration plane defined by the second facet mirror 22.

[0098] Figure 2 shows a partial cross-sectional schematic diagram of one embodiment of the optical system 100'. The optical system 100' is, or a part of, the projection optical unit 10 as described above. The optical system 100' includes a first component 102 and a second component 104. The first component 102 may be a so-called force frame. The second component 104 may be a so-called sensor frame. Both components 102 and 104 may be made of a ceramic material. Alternatively, only one of the two components 102 and 104 may be made of a ceramic material.

[0099] The second component 104 is mounted using a weight-compensated bracket (Active Vibration Isolation System, AVIS), thus allowing it to move in a powerless manner. The second component 104 has a specific actuation region or actuation area relative to the first component 102, within which it can move relative to the first component 102. The second component 104 may have six degrees of freedom: three translational degrees of freedom along the x-direction, y-direction, and z-direction, and three rotational or tilting degrees of freedom about the x-direction, y-direction, and z-direction, respectively.

[0100] To define a movement amplitude of the second component 104 relative to the first component 102, for example in the case of a tremor, an end-stop device 106 may be provided. The end-stop device 106 includes an end-stop portion 108 which is fixedly connected (e.g., threaded) to the first component 102. The end-stop portion 108 may be configured to rotate symmetrically relative to a central axis or axis of symmetry 110.

[0101] The end stop 108 includes a plate-shaped base 112, which is threadedly connected to the first assembly 102. A tapered connecting portion 114 connects to the base 112. A cylindrical contact portion 116 is located on the connecting portion 114. The end stop 108 is a single-piece component, particularly a monolithic element in terms of material. "Single-piece" in this context means that the end stop 108 is not composed of various parts, but forms a single component. "Single-piece material" in this context means that the end stop 108 is always made of the same material, such as steel.

[0102] In addition to the end-stop portion 108, the end-stop device 106 includes a socket or sleeve 118 in which an adjusting contact portion 116 is accommodated. The sleeve 118 can fit into a hole 120 disposed in the second assembly 104. The contact portion 116 can be translated relative to the sleeve 118 in the y-direction. Furthermore, a radially extending gap is provided between the sleeve 118 (particularly an inner wall 122 of the sleeve 118) and the contact portion 116. This gap allows the contact portion 116 to move slightly relative to the sleeve 118 in the x-direction and the z-direction, thus defining the actuation area.

[0103] This possible radial movement of the contact portion 116 relative to the sleeve 118 allows the second component 104 to be actuated relative to the first component 102 within the actuation region. At least three end-stop devices 106 are provided herein. Each of these end-stop devices 106 allows for a translational movement along one of the directions x, y, and z, and two smaller translational movements relative to the other two directions x, y, and z, until the contact portion 116 contacts the sleeve 118. If the limit of the actuation region is reached, the contact portion 116 contacts the sleeve 118.

[0104] During operation of the optical system 100' or projection optical unit 10, strong vibrations and accelerations of 2 to 3 g may occur, for example, caused by an earthquake. In the event of an earthquake, the end stop device 106 must absorb forces up to 50 kN. Due to the direct contact between the contact portion 116 and the sleeve 116, large forces can be transmitted to the second component 104. This can be a problem because the second component 104 and the reflectors M1 to M6 are made of ceramic material that will crack under excessive load.

[0105] Within the actuation region, that is, in the region where the contact portion 116 has not yet contacted the sleeve 118, the second component 104 is able to move in a weak manner because it is supported in a weight compensation device. Once a strong vibration acts on the optical system 100', the contact portion 116 contacts the sleeve 118, resulting in metal-to-metal contact. This has the effect of a large force acting on the end stop device 106 and causing the second component 104 to break, and the metal-to-metal contact can lead to unwanted friction and particle formation. This needs to be improved.

[0106] The challenge here is to limit the movement of the second component 104 outside the actuation area and minimize the impact of the end-stop device 106 within the actuation area. This can be achieved by designing a bending element with very low rigidity within the actuation area and very high rigidity outside the actuation area. This allows for a permanent connection between components 102 and 104 while preventing collisions.

[0107] Figure 3 shows a schematic diagram of the main functions of the bending element mentioned above. Rigidity is shown on the vertical axis. In Figure 3, rigidity is represented by the letter S. In this case, "rigidity" is generally understood to mean the resistance of a body to elastic deformation caused by force or moment. Rigidity depends on the geometry of the body and the material used. The greater the rigidity, the greater the force or moment required to deform the body.

[0108] The deflection distance w of the bending element is shown on the horizontal axis of Figure 3. As mentioned above, an actuation region A is provided. In actuation region A, the bending element has very low stiffness, which is preferably constant or nearly constant within actuation region A. Outside actuation region A or at the limits of actuation region A, the stiffness increases abruptly. Actuation region A can be, for example, 100 to 200 μm.

[0109] The second component 104 can move almost effortlessly within the actuation region A. Within actuation region A, the bending element requires only a few Newtons of force to deform. Outside actuation region A, the deformation force or stiffness increases abruptly over a very small deflection distance w. In conventional springs, this behavior requires a very long spring travel. Therefore, a linear spring cannot be used as a bending element. The bending element thus does not act linearly and has what is called a mechanical or movement singularity. This is understood in particular to mean that the bending element has linear characteristics before a certain point and no longer has linear characteristics after that point.

[0110] Figure 4 shows a perspective view of one embodiment of the bending element 200 as described above. The bending element 200 may be part of the end-stop device 106. In this case, the end-stop device 106 does not have the end-stop portion 108 and the sleeve 118. Instead, the bending element 200 couples components 102, 104 to each other. This means that the bending element 200 couples the second component 104 to the first component 102. The end-stop device 106 may include a plurality of bending elements 200.

[0111] The bending element 200 includes two bent or protruding leaf spring portions 202, 204. A first leaf spring portion 202 and a second leaf spring portion 204 are provided. In a no-load or unloaded state, the leaf spring portions 202, 204 bend outwards and away from each other, as shown in FIG4. The leaf spring portions 202, 204 are preloaded by springs. This means that the leaf spring portions 202, 204 abut against each other when compressed and automatically move back to the state shown in FIG4 when released.

[0112] At each end, the leaf spring portions 202 and 204 are interconnected by means of connecting portions 206 and 208 in each case. Connecting portions 206 and 208 may be cubical. The leaf spring portions 202 and 204 and the connecting portions 206 and 208 may be formed as a single piece, particularly from a single material. For example, the bending element 200 is made of steel, particularly stainless steel.

[0113] Figure 5 shows a side view of the bending element 200. Figure 6 shows the distribution of a force F (in N) acting on the bending element 200 along the deflection distance w (in μm) of the bending element 200.

[0114] In the direction shown in Figure 5, the bending element 200 is clamped at its connecting portion 206. In the direction to the right of Figure 5, the force F now acts on the connecting portion in the form of a tensile force. Figure 5 shows the bending element 200 initially in a weak or unsupported state, where the leaf spring portions 202 and 204 are bent apart or bent apart from each other.

[0115] Once a small force F, less than 1 N, is applied to the bending element 200 in this case, the leaf spring portions 202 and 204 move closer together, reducing their protrusion. The force F increases only slightly up to a deflection distance w of approximately 100 µm. Once the leaf spring portions 202 and 204 extend—that is, as long as they no longer have any protrusion and extend parallel to each other or abut against each other—the force F increases abruptly from the deflection distance w of approximately 100 µm, causing the bending element 200 to extend further to approximately 14 N. From the deflection distance w of approximately 100 µm, the stiffness of the bending element 200 increases approximately 100-fold.

[0116] The aforementioned end-stop device 106 may include one or more bending elements 200 as described above. Structurally, the bending element 200 may also be configured to function in both the tensile and compressive directions. That is, the bending element 200 stiffens when a tensile force, particularly the aforementioned force F, is applied, and also when a compressive force is applied. The aforementioned stiffening effect then occurs in both the tensile and compressive directions.

[0117] Figure 7 shows a cross-sectional schematic diagram of a further embodiment of the optical system 100 for the projection exposure apparatus 1. The optical system 100 includes a first component 102, which can be a force frame, and a second component 104, which can be a sensor frame. The optical system 100 in this example is observed in a simplified manner in two-dimensional space. That is, the second component 104 has three degrees of freedom relative to the first component 102, specifically a translational degree of freedom x along the x-direction x, a translational degree of freedom y along the y-direction y, and a rotational degree of freedom about the z-direction z.

[0118] The optical system 100 includes an end-stop device 106 as described above, having a plurality of (particularly three) bending elements 200A, 200B, and 200C. The second component 104 is coupled to the first component 102 by means of the bending elements 200A, 200B, and 200C. In this case, the x-direction x specifies a first bending element 200A. It is assumed that the first bending element 200A can absorb both tensile and compressive forces different from those described above. For the case where the first bending element 200A can only absorb tensile forces, two first bending elements 200A are provided, which are arranged on both sides of the second component 104 in the direction of FIG. 7. The first bending elements 200A produce an end-stop along the x-direction x.

[0119] A second bending element 200B and a third bending element 200C are designated for the y-direction y and the z-direction z, respectively. One of the bending elements 200B and 200C causes an endpoint stop along the y-direction y. Together, the two bending elements 200B and 200C produce an endpoint stop with respect to the rotational degree of freedom about the z-direction z. It is also assumed here that the bending elements 200B and 200C can absorb both tensile and compressive forces as previously described. For the case where the bending elements 200B and 200C can only absorb tensile forces, in each case two bending elements 200B and 200C are provided, which are arranged on the top and bottom sides of the second assembly 104 in the direction of FIG. 7.

[0120] Although the invention has been described based on exemplary embodiments, it can be modified in various ways.

[0121] 1: Projection exposure equipment 2: Lighting System 3: Light source 4: Illumination Optical Unit 5: Object Field 6: Object plane 7: Reduction Mask 8: Photomask vehicle 9: Reduction Mask Displacement Driver 10: Projection Optical Unit 11: Image Field 12: Image plane 13: Wafer 14: Wafer carrier 15: Wafer displacement driver 16: Lighting radiation 17: Concentrator 18: Intermediate focal plane 19: Deflecting Mirror 20: First Split Mirror 21: First facet 22: Second facet mirror 23: Second facet 100: Optical System 100': Optical System 102: First Component 104: Second Component 106: End-point stop device 108: End Stop 110: Axis of symmetry 112: Base 114: Connecting part 116: Contact Part 118: Sleeve 120: Hole 122: Inner wall 200: Bending element 200A: Bending element 200B: Bending element 200C: Bending element 202: Leaf Spring Section 204: Leaf Spring Section 206: Connecting part 208: Connecting part A: Actuation area F: Force M1: Reflector M2: Reflector M3: Reflector M4: Reflector M5: Reflector M6: Reflector S: Rigidity w: deflection distance x:x direction y:y direction z: z direction

Claims

1. An optical system (100) for a projection exposure apparatus (1), comprising: a first component (102); a second component (104), wherein the second component (104) is actuable relative to the first component (102) within an actuation region (A); and an end-stop device (106) that allows the second component (104) to move relative to the first component (102) within the actuation region (A) and blocks it outside the actuation region (A); wherein the end-stop device (106) includes a bending element (200, 200A, 200B, 200C) whose rigidity suddenly increases upon reaching a limit in the actuation region (A) to block the movement of the second component (104) relative to the first component (102); The bending element (200, 200A, 200B, 200C) includes a first leaf spring portion (202) with an arc-shaped bend and a second leaf spring portion (204) with an arc-shaped bend; wherein the first leaf spring portion (202) and the second leaf spring portion (204) are bent in opposite directions.

2. The optical system as claimed in claim 1, wherein the rigidity of the bending element (200, 200A, 200B, 200C) outside the actuation region (A) is several times greater than the rigidity inside the actuation region (A).

3. The optical system as claimed in claim 1 or 2, wherein the rigidity of the bending element (200, 200A, 200B, 200C) increases abruptly within a deflection distance (w) of less than 100 μm for the bending element (200, 200A, 200B, 200C).

4. The optical system as claimed in claim 1, wherein the rigidity of the bending element (200, 200A, 200B, 200C) outside the actuation region (A) is greater than one hundred times or more the rigidity inside the actuation region (A).

5. The optical system as claimed in claim 1, wherein the first leaf spring portion (202) and the second leaf spring portion (204) are connected to each other at each end via a first connecting portion (206) and a second connecting portion (208).

6. The optical system as claimed in claim 1, wherein the rigidity of the bending element (200, 200A, 200B, 200C) suddenly increases when the limit of the actuation region (A) is reached due to the action of the first leaf spring portion (202) and the second leaf spring portion (204) extending parallel to each other.

7. The optical system as claimed in claim 1, wherein the bending element (200, 200A, 200B, 200C) allows the second component (104) to move relative to the first component (102) within the actuation region (A) because the first leaf spring portion (202) and the second leaf spring portion (204) are spring-elastically deformed as part of their arcuate curvature.

8. The optical system as claimed in claim 1, wherein the end stop device (106) allows the second component (104) to move relative to the first component (102) with two degrees of freedom within the actuation region (A) and blocks the movement of the second component (104) with two degrees of freedom outside the actuation region (A).

9. The optical system as claimed in claim 8 further includes at least three endpoint stops (106), wherein each endpoint stop (106) is assigned two degrees of freedom in each case.

10. The optical system as claimed in claim 1, wherein the rigidity of the bending element (200, 200A, 200B, 200C) increases abruptly when the limit of the actuation region (A) is reached, in a manner that the bending element (200, 200A, 200B, 200C) blocks the movement of the second component (104) relative to the first component (102), whether a tensile force is applied to the bending element (200, 200A, 200B, 200C) or a compressive force is applied to the bending element (200, 200A, 200B, 200C).

11. The optical system as claimed in claim 1, wherein the first component (102) is coupled to the second component (104) by means of the bending element (200, 200A, 200B, 200C).

12. The optical system as claimed in claim 1, wherein the first component (102) is a force frame and the second component (104) is a sensor frame.

13. The optical system as claimed in claim 1, wherein the bending element (200, 200A, 200B, 200C) is a single-piece component, particularly a component made of a single piece of material.

14. A projection exposure apparatus (1) comprising an optical system (100) as described in any one of claims 1 to 13.

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