Optical system and projection exposure apparatus

Abstract

The invention relates to an optical system (100) for a projection exposure apparatus (1), comprising a first part (102), a second part (110), and a fastening device (118) by means of which the second part (110) is fastened to the first part (102), the fastening device (118) having a decoupling bushing (200A, 200B, 200C, 200D) for mechanically decoupling the second part (110) from the first part (102), and the decoupling bushing (200A, 200B, 200C, 200D) having a decoupling groove (228, 230), the invention relates to a decoupling bushing (200A, 200B, 200C, 200D) which reduces the stiffness of the decoupling bushing (200A, 200B, 200C, 200D)

Description

Field of the Invention

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

[0002] The content of priority application DE 10 2022 214 184.9 is hereby incorporated by reference in its entirety. Background of the Invention

[0003] Microlithography is used to produce microstructured devices, such as integrated circuits. A microlithography process is performed using a lithography apparatus, which includes an illumination system and a projection system. An image of a mask (mask blank) illuminated by the illumination system is projected onto a substrate (e.g., a silicon wafer) by the projection system. The substrate is coated with a photosensitive layer (photoresist) and is arranged in the image plane of the projection system in order to transfer the mask structure onto the photosensitive coating of the substrate.

[0004] Driven by the desire for smaller structures in integrated circuit production, EUV lithography apparatuses using light having a wavelength in the range of 0.1 nm to 30 nm (especially 13.5 nm) and DUV lithography apparatuses using light having a wavelength in the range of 30 nm to 250 nm are currently being developed. However, lithography apparatuses having larger wavelengths (e.g., 365 nm) are also possible. Especially in the case of such EUV lithography apparatuses, due to the high absorption of light of this wavelength by most materials, reflective optical elements (i.e., mirrors) must be used instead of the previous refractive optical elements (i.e., lens elements).

[0005] The projection system, as described above, may have a sensor frame on which an optical element in the form of a measurement target is mounted, and the optical element is measured, for example, using an interferometer. The optical element may be mounted on the sensor frame, and the interferometer may be mounted on another component part. In order to mount such an optical element on the sensor frame, a fastening device having a bushing adhesively bonded into the optical element may be used.

[0006] The fastening device has a spherical cap-shaped spacer for compensating for an angular error between the optical element and the sensor frame. The bushing adhesively bonded into the optical element has a contact surface that is also shaped as a spherical cap, and one of the spacers abuts against the contact surface. Due to adverse friction conditions or shape deviations caused by production, which unfavorably change the leverage ratio, it may be the case that the spacer does not slide into its optimal position, i.e., is not optimally positioned. Due to the misalignment generated between the optical element and the sensor frame, a torque may be generated, which may cause an undesired deformation of the optical element. Summary of the Invention

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

[0008] Accordingly, an optical system for a projection exposure apparatus is proposed. The optical system includes a first component, a second component, and a fastening device by means of which the second component is attached to the first component, wherein the fastening device has a decoupling bushing for mechanically decoupling the second component from the first component, and wherein the decoupling bushing has decoupling grooves that reduce the stiffness of the decoupling bushing.

[0009] Due to the fact that the decoupling bushing has decoupling grooves, the second component can be mechanically decoupled from the first component, such that parasitic forces or torques that can deform the second component in an undesired manner are not transmitted to the second component.

[0010] The optical system is preferably the projection optical unit of a projection exposure apparatus or a part of such a projection optical unit. However, the optical system can also be the illumination system of a projection exposure apparatus or a part of this illumination system. The first component is preferably a sensor frame and can thus also be referred to in this way. That is to say, in particular, the terms "first component" and "sensor frame" can be used interchangeably as required. However, the first component can also be any other support structure that supports the second component. Exactly one decoupling groove can be provided. More, for example two, decoupling grooves can also be provided.

[0011] The second component is preferably an optical element and can thus also be referred to in this way. Accordingly, the terms "second component" and "optical element" can be used interchangeably as required. In particular, the second component is a measurement target. The second component is made of, for example, glass ceramic. The second component in particular has an optically effective surface. The optically effective surface can be a mirror surface. The optically effective surface is configured to reflect light, in particular a laser beam. The optical system can have an interferometer that interacts with the optically effective surface of the second component.

[0012] A coordinate system having a first spatial direction or x-direction, a second spatial direction or y-direction, and a third spatial direction or z-direction is assigned to the optical system. The z-direction corresponds to or is parallel to the axis of symmetry or central axis of the fastening device or the decoupling bushing. The x-direction and the y-direction are each perpendicular to the central axis and perpendicular to each other. Accordingly, an "angular error" is understood herein to mean an inclination of the second component relative to the first component about the x-direction and / or the y-direction.

[0013] The second component has six degrees of freedom, namely three translational degrees of freedom along the x-direction, y-direction, and z-direction, and three rotational degrees of freedom about the x-direction, y-direction, and z-direction. This means that six degrees of freedom can be used to determine or describe the position and orientation of the second component.

[0014] The "position" of the second component is understood in particular as its coordinates with respect to the x-direction, y-direction, and z-direction. In particular, the "orientation" of the second component is understood to mean its inclination with respect to the three directions. This constitutes six degrees of freedom for the position and orientation of the second component. The "pose" of the second component includes its position and its orientation. Thus, the term "pose" can be replaced by the wording "position and orientation", and vice versa. For example, an interferometer can be used to detect the pose of the second component.

[0015] The fastening device connects the second component to the first component. In particular, the first component bears the second component. The fastening device is preferably constructed rotationally symmetrically about its central axis. Preferably, the fastening device includes a first sleeve and a second sleeve, which can be mounted at a perforation in the first component. The first sleeve and the second sleeve can be supported on the first component such that the first component is clamped between the first sleeve and the second sleeve. The first sleeve and the second sleeve can be screwed together.

[0016] Furthermore, the fastening device includes a threaded pin, which is screwed into the first sleeve. The threaded pin passes through a decoupling bushing. The second sleeve in particular has a spherical cap-shaped contact surface, against which the spherical cap-shaped first contact surface of a first spherical cap element abuts. The "spherical cap" herein is understood as a part of a sphere.

[0017] The first spherical cap element has, in addition to the first contact surface, a flat second contact surface facing away from the first contact surface. The second contact surface faces the flat first contact surface of the decoupling bushing. Between the second contact surface of the first spherical cap element and the first contact surface of the decoupling bushing, a spacer in the form of a washer can be provided. A plurality of spacers can also be provided. The spacer is a device for maintaining a distance. A plurality of different spacers can be provided between the first spherical cap element and the first contact surface of the decoupling bushing. For example, so-called coarse spacers and fine spacers can be provided. The first contact surface of the decoupling bushing is preferably an annular ring, which is located as far as possible on the outside with respect to the radial direction of the decoupling bushing. This results in a large lever arm, which leads to a greater torque allowing for improved positioning. This makes it easier to overcome the frictional force.

[0018] The threaded pin passes through the first spherical cap element and the spacer. A decoupling bushing is arranged between the first spherical cap element or the spacer and the second spherical cap element. The decoupling bushing preferably has a second contact surface facing away from the first contact surface, which second contact surface is shaped in the form of a spherical cap. The second spherical cap element abuts the second contact surface of the decoupling bushing with a first spherical cap-shaped contact surface. The second spherical cap element preferably has a flat second contact surface facing away from the first contact surface. A nut screwed onto the threaded pin abuts the second contact surface. The nut can be used to clamp together the two spherical cap elements, the decoupling bushing, the spacer and the sleeve. Here, torque-free screwing is carried out. The threaded pin is stretched during this process.

[0019] In particular, the second component has a perforation, and the decoupling bushing is at least partially received in the perforation. The decoupling bushing is in particular adhesively bonded into the perforation. The decoupling bushing is preferably made of a material different from that of the second component. For example, the decoupling bushing is made of a FeNi alloy.

[0020] In particular, the fact that the decoupling bushing "mechanically decouples" the first component and the second component from each other is understood herein to mean that the decoupling bushing prevents or at least reduces the transmission of force and / or torque from the first component to the second component and vice versa. This reliably prevents unwanted deformation of the second component.

[0021] The fact that the decoupling grooves "reduce" the stiffness of the decoupling bushing is understood herein in particular to mean that the decoupling bushing has a lower stiffness due to the decoupling grooves compared to a solid decoupling bushing. "Stiffness" is understood herein to mean the resistance of a body, in particular a decoupling bushing, to elastic deformation imposed on it by an external load, and conveys the relationship between the load on the body and its deformation. The rigidity is determined by the material of the body and its geometry. This means that by appropriately selecting the material used and the geometry of the decoupling grooves, the rigidity of the decoupling bushing can be varied within a wide range.

[0022] The compensating bushing can also at least partially compensate for or make up for the angular error between the first component and the second component. This means that the decoupling bushing "compensates" for the angular error between the first component and the second component. In particular, the decoupling bushing can be elastically deformed due to its reduced stiffness through the decoupling grooves, such that the angular error within the decoupling bushing itself is compensated. This can be achieved, for example, in such a way that different sections of the decoupling bushing, such as the connecting section and the fastening section, can move relative to each other. Thus, the second component can be moved into the target position without introducing force into the second component via the decoupling bushing. This reliably prevents unwanted deformation of the second component.

[0023] According to one embodiment, the decoupling grooves extend annularly around the central axis of the decoupling bushing.

[0024] This particularly means that the decoupling groove is an annular groove. Thus, the terms "decoupling groove" and "annular groove" can be used interchangeably as required. The central axis of the decoupling bushing can coincide with the central axis of the fastening device. The decoupling bushing is preferably rotationally symmetric with respect to its central axis. The decoupling groove preferably has a rectangular cross-section. However, the decoupling groove can also have a circular or rounded groove bottom. The decoupling groove extends along the central axis of the decoupling bushing. Exactly one decoupling groove can be provided. However, multiple decoupling grooves can also be introduced into the decoupling bushing. For example, a first decoupling groove and a second decoupling groove different from the first decoupling groove are provided.

[0025] According to another embodiment, the decoupling bushing has a first decoupling groove and a second decoupling groove, where the first decoupling groove extends from the first end face of the decoupling bushing in the direction of the second end face of the decoupling bushing, and where the second decoupling groove extends from the second end face in the direction of the first end face.

[0026] The end faces are positioned at the decoupling bushing so as to face away from each other. Thus, the decoupling grooves extend into the decoupling bushing from different end faces of the decoupling bushing. The two decoupling grooves are separated from each other by a bridging member that extends rotationally symmetrically around the axis of symmetry. This particularly means that the first decoupling groove and the second decoupling groove are not connected to each other. The first decoupling groove only partially and thus does not completely penetrate the decoupling bushing. The same applies to the second decoupling groove. The decoupling bushing is in particular cylindrical and has a cylindrical outer surface. The first end face and the second end face are provided on the front side of the decoupling bushing. The first decoupling groove penetrates the first end face but does not penetrate the second end face. Correspondingly, the second decoupling groove penetrates the second end face but does not penetrate the first end face.

[0027] According to another embodiment, when viewed in the radial direction of the decoupling bushing, the first decoupling groove is arranged within the second decoupling groove.

[0028] The radial direction is perpendicular to the central axis of the decoupling bushing and is directed away from the latter. Thereby, the first decoupling groove is placed within the second decoupling groove when viewed in the radial direction, and the second decoupling groove is positioned outside the first decoupling groove when viewed in the radial direction. The first decoupling groove and the second decoupling groove are thus staggered.

[0029] According to a further embodiment, the first decoupling groove and the second decoupling groove overlap when viewed along the central axis.

[0030] This particularly means that the first decoupling groove covers the second decoupling groove when viewed in the radial direction, and vice versa. Thus, in particular, the first decoupling groove and the second decoupling groove are at least sectionally placed side by side when viewed along the central axis, where the first decoupling groove and the second decoupling groove are separated from each other by the aforementioned bridging member.

[0031] According to another embodiment, the decoupling bushing has a connecting section connected to the first component and a fastening section connected to the second component, wherein a decoupling groove is arranged between the connecting section and the fastening section.

[0032] The decoupling groove particularly mechanically decouples the connecting section from the fastening section. "Mechanical decoupling" is particularly understood herein as meaning that no force or only a minimal force can be transmitted from the connecting section to the fastening section and vice versa. The connecting section is connected, in particular screwed, to the first component by means of two spherical cap elements, a spacer, two sleeves, a threaded pin and a nut. The fastening section is preferably adhesively bonded to the second component. In particular, the fastening section is adhesively bonded into a perforation in the second component. The fastening section and the connecting section are each tubular or hollow cylindrical. The decoupling groove is provided between the connecting section and the fastening section. The connecting section preferably has a central perforation, in particular a drilled hole, through which the threaded pin passes without contact.

[0033] According to another embodiment, the connecting section and the fastening section are connected to each other only by means of a bridging piece serving as a flexure element.

[0034] This particularly means that one or more decoupling grooves separate the connecting section from the fastening section. The connection between the connecting section and the fastening section is achieved only by means of the bridging piece. The bridging piece can be elastically deformed, in particular spring elastically. "Elastic deformation" is particularly understood herein as meaning that the bridging piece can be moved from a non-deformed state to a deformed state by applying a force or a torque. If the force or the torque no longer acts on the bridging piece, the bridging piece automatically returns from the deformed state to the non-deformed state. In the present case, a "flexure element" is particularly understood as a region of a component part which can achieve a relative movement between two rigid body regions by bending. In the present case, the fastening section and the connecting section serve as rigid body regions between which the bridging piece is arranged as an elastically deformable flexure element.

[0035] According to another embodiment, the bridging piece is sleeve-shaped.

[0036] The bridging piece can also be referred to as tubular or hollow cylindrical. The bridging piece preferably extends completely around the central axis of the decoupling bushing. In particular, the bridging piece also extends completely around the connecting section. The bridging piece is arranged in the radial direction, in particular between the connecting section and the fastening section.

[0037] According to a further embodiment, the bridging piece has a slit penetrating the bridging piece.

[0038] The slit preferably extends along the central axis of the decoupling bushing. Any desired number of slits can be present. The slits are preferably evenly distributed around the central axis of the decoupling bushing. The slits can be used, for example, to further reduce the rigidity of the bridging piece. Thus, the rigidity of the bridging piece can be changed, in particular reduced, by means of the slits. The slits can have a rectangular geometry.

[0039] According to another embodiment, the connecting section has a flat first contact surface and a spherical cap-shaped second contact surface facing away from the first contact surface.

[0040] As described above, the spacer or the first spherical cap element abuts against the first contact surface. The second spherical cap element abuts against the second contact surface.

[0041] According to a further embodiment, the decoupling bushing has a first centering ring and a second centering ring for centering the decoupling bushing in a perforation provided in the second component.

[0042] The first centering ring and the second centering ring preferably extend radially from the aforementioned outer surface of the decoupling bushing or the fastening section when viewed in the radial direction. The two centering rings are used to center the decoupling bushing in the perforation in the second component.

[0043] According to a further embodiment, the decoupling bushing has a first fastening ring and a second fastening ring for attaching the decoupling bushing to the perforation, wherein the first fastening ring and the second fastening ring are arranged between the first centering ring and the second centering ring.

[0044] In particular, when viewed along the central axis of the compensation bushing, the first fastening ring and the second fastening ring are arranged between the first centering ring and the second centering ring. With the first fastening ring and the second fastening ring, the decoupling bushing is bonded to the second component. For this purpose, an adhesive layer is provided between the two fastening rings and the second component respectively. The fastening rings are adhesively bonded to the perforation in the second component accordingly. In particular, the decoupling bushing or the fastening ring is adhesively bonded radially to the second component. Alternatively, axial adhesive bonding can also be achieved.

[0045] According to another embodiment, the decoupling bushing has exactly one fastening ring for attaching the decoupling bushing to the perforation, wherein the fastening ring is arranged between the first centering ring and the second centering ring.

[0046] In particular, when viewed along the central axis of the decoupling bushing, the fastening ring is arranged centrally between the first centering ring and the second centering ring. This is a particularly advantageous arrangement. The central arrangement of the fastening ring further reduces the introduction of force and / or torque into the second component. This is the result of a reduced lever arm.

[0047] According to another embodiment, the decoupling bushing is integrally formed, in particular integrally formed in terms of material, component.

[0048] "Integrally formed" or "one-piece" in this context particularly means that the decoupling bushing is not composed of different subordinate components, but rather the connecting section, the fastening section and the bridging piece form a common component, namely the decoupling bushing. The term "integrally formed in terms of material" means that the decoupling bushing is always made of the same material. As described above, for example, an iron-nickel alloy can be used for the decoupling bushing.

[0049] In addition, a projection exposure apparatus having such an optical system is proposed.

[0050] The optical system is preferably the projection optical unit of the projection exposure apparatus. However, the optical system can also be an illumination system. The projection exposure apparatus can be an EUV lithography apparatus. EUV stands for "extreme ultraviolet" and refers to a wavelength of working light between 0.1 nm and 30 nm. The projection exposure apparatus can also be a DUV lithography apparatus. DUV stands for "deep ultraviolet" and refers to a wavelength of working light between 30 nm and 250 nm. However, a lithography apparatus having a larger wavelength (e.g., 365 nm) is also possible.

[0051] In this case, "a" or "an" should not necessarily be construed as limiting to exactly one element. On the contrary, there can also be multiple elements, such as two, three, or more. Any other numbers used here should not be construed as limiting to the exactly stated number of elements. On the contrary, numerical deviations up and down are possible, unless otherwise stated.

[0052] The embodiments and features described for the optical system apply correspondingly to the proposed projection exposure apparatus, and vice versa.

[0053] Other possible embodiments of the present invention also include combinations of features or embodiments not explicitly mentioned above or below in connection with the exemplary embodiments. Those skilled in the art will also add individual aspects as improvements or supplements to the corresponding basic forms of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Further advantageous configurations and aspects of the present invention are the subject matter of the dependent claims and the subject matter of the exemplary embodiments of the present invention described below. The present invention will be explained in more detail below with reference to the accompanying drawings based on preferred embodiments.

[0055] Figure 1 Showing a schematic meridional cross-section of a projection exposure apparatus for EUV projection lithography;

[0056] Figure 2 Showing Figure 1 a schematic cross-sectional view of an embodiment of the optical system of a projection exposure apparatus according to

[0057] Figure 3 Showing an exemplary cross-sectional view of a decoupling bushing for an optical system according to Figure 2 ;

[0058] Figure 4 Showing Figure 3 a schematic plan view of a decoupling bushing according to

[0059] Figure 5 shows a schematic bottom view of a decoupling bushing according to Figure 3 ;

[0060] Figure 6 shows a schematic cross-sectional view of another embodiment of a decoupling bushing for an optical system according to Figure 2 ;

[0061] Figure 7 shows a schematic cross-sectional view of another embodiment of a decoupling bushing for an optical system according to Figure 2 ; and

[0062] Figure 8 shows a schematic cross-sectional view of another embodiment of a decoupling bushing for an optical system according to Figure 2 ;

[0063] In the figures, unless otherwise indicated, the same or functionally identical elements have the same reference numerals. It should also be noted that the illustrations in the figures are not necessarily drawn to scale. Detailed Description

[0064] Figure 1 Shows an embodiment of a projection exposure apparatus 1 (lithographic apparatus), in particular an EUV lithographic apparatus. In addition to a light source or radiation source 3, an embodiment of the illumination system 2 of the projection exposure apparatus 1 has an illumination optical unit 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a module separate from the rest of the illumination system 2. In this case, the illumination system 2 does not include the light source 3.

[0065] Exposes a mask blank 7 arranged in the object field 5. The mask blank 7 is held by a mask blank holder 8. The mask blank holder 8 can be displaced by a mask blank displacement driver 9, in particular in the scanning direction.

[0066] For purposes of explanation, 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 extends perpendicularly into the plane of the drawing. The y-direction y extends horizontally, and the z-direction z extends vertically. The scanning direction travels along the Figure 1 y-direction y in

[0067] The projection exposure apparatus 1 includes a projection optical unit 10. The projection optical unit 10 is for imaging the object field 5 into an image field 11 in an image plane 12. The image plane 12 extends parallel to the object plane 6. In an alternative, an angle other than 0° between the object plane 6 and the image plane 12 is also possible.

[0068] The structures on the reticle 7 are imaged onto a photosensitive layer of a wafer 13 arranged in the region of an image field 11 in an image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be displaced, in particular in the y direction y, by a wafer displacement drive 15. It can be achieved that firstly the reticle 7 is moved by the reticle displacement drive 9 and secondly the wafer 13 is moved by the wafer displacement drive 15 so as to be synchronized with each other.

[0069] The light source 3 is an EUV radiation source. The light source 3 in particular emits EUV radiation 16, which is also referred to below as used radiation, illumination radiation or illumination light. The used radiation 16 has in particular a wavelength in the range between 5 nm and 30 nm. The light source 3 can be a plasma source, such as an LPP (abbreviation: laser produced plasma) source or a DPP (abbreviation: gas discharge produced plasma) source. It can also be a synchrotron-based radiation source. The light source 3 can be a FEL (abbreviation: free electron laser).

[0070] The illumination radiation 16 emitted from the light source 3 is focused by a light collector 17. The light collector 17 may be a light collector having one or more elliptical and / or hyperbolic reflective surfaces. The illumination radiation 16 may impinge on at least one reflective surface of the light collector 17 at grazing incidence (abbreviated as: GI) (that is, an angle of incidence greater than 45°) or at normal incidence (abbreviated as: NI) (that is, an angle of incidence less than 45°). The light collector 17 may firstly be constructed and / or coated to optimize its reflectivity for the radiation used and secondly to suppress extraneous light.

[0071] Downstream of the light collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 may represent a separation between the radiation source module comprising the light source 3 and the light collector 17 and the illumination optics unit 4.

[0072] The illumination optical unit 4 comprises a deflection mirror 19 and a first facet mirror 20 which is arranged downstream of the deflection mirror 19 in the beam path. The deflection mirror 19 can be a plane deflection mirror or, in an alternative thereof, a mirror which has a beam influencing effect that goes beyond a pure deflection effect. Alternatively or additionally, the deflection mirror 19 can be in the form of a spectral filter which separates the used light wavelength of the illumination radiation 16 from external light of a different wavelength. If the first facet mirror 20 is arranged in a plane of the illumination optical unit 4 which is optically conjugate to the object plane 6 (which serves as a field plane), this facet mirror is also referred to as a field facet mirror. The first facet mirror 20 comprises a plurality of individual first facets 21 which can also be referred to as field facets. In Figure 1 Only some of these first facets 21 are shown by way of example.

[0073] The first partial facet 21 can be in the form of a macroscopic partial facet, in particular as a rectangular partial facet or a partial facet with an arcuate or partially circular edge profile. The first partial facet 21 can be in the form of a planar partial facet, or alternatively, in the form of a convex or concave curved partial facet.

[0074] As is known, for example, from DE 10 2008 009 600 A1, the first partial facet 21 itself can also be composed of a plurality of individual mirrors, in particular a plurality of micromirrors. In particular, the first partial facet mirror 20 can be in the form of a microelectromechanical system (MEMS system). For details, reference is made to DE 10 2008 009 600 A1.

[0075] The illumination radiation 16 propagates horizontally (i.e., in the y - direction y) between the condenser 17 and the deflection mirror 19.

[0076] In the beam path of the illumination optical unit 4, the second partial facet mirror 22 is arranged downstream of the first partial facet mirror 20. If the second partial facet mirror 22 is arranged in the pupil plane of the illumination optical unit 4, this partial facet mirror is also referred to as a pupil partial facet mirror. The second partial facet mirror 22 can also be spaced apart from the pupil plane of the illumination optical unit 4. In this case, the combination of the first partial facet mirror 20 and the second partial facet mirror 22 is also referred to as a mirror reflector. Mirror reflectors are known from US 2006 / 0132747 A1, EP 1 614 008 B1, and US 6,573,978.

[0077] The second partial facet mirror 22 includes a plurality of second partial facets 23. In the case of a pupil partial facet mirror, the second partial facets 23 are also referred to as pupil partial facets.

[0078] The second partial facets 23 can likewise be macroscopic partial facets, which can, for example, have a circular, rectangular, or hexagonal boundary, or alternatively, be partial facets composed of micromirrors. For details in this regard, reference is also made to DE 10 2008 009 600 A1.

[0079] The second partial facets 23 can have a planar surface, or alternatively, a convex or concave curved reflective surface.

[0080] The illumination optical unit 4 thus forms a two - partial - facet system. This basic principle is also known as a fly - eye integrator.

[0081] It can be advantageous to arrange the second partial facet mirror 22 imprecisely in a plane that is optically conjugate to the pupil plane of the projection optical unit 10. In particular, the second partial facet mirror 22 can be arranged inclined with respect to the pupil plane of the projection optical unit 10, as described, for example, in DE 10 2017 220 586 A1.

[0082] The second faceted mirror 22 serves to image the respective first facets 21 into the object field 5. The second faceted mirror 22 is the last beam shaping mirror in the beam path upstream of the object field 5 or is in fact the last mirror for the illumination radiation 16.

[0083] In a further embodiment of the illumination optical unit 4 (not shown), a transmission optical unit that is particularly useful for imaging the first facets 21 into the object field 5 can be arranged in the beam path between the second faceted mirror 22 and the object field 5. The transmission optical unit can have exactly one mirror, or alternatively, two or more mirrors, which are arranged one behind the other in the beam path of the illumination optical unit 4. The transmission optical unit can in particular include one or two normal incidence mirrors (NI mirrors) and / or one or two grazing incidence mirrors (GI mirrors).

[0084] In Figure 1 the illustrated embodiment, the illumination optical unit 4 has exactly three mirrors downstream of the collector 17, specifically the deflection mirror 19, the first faceted mirror 20, and the second faceted mirror 22.

[0085] In a further embodiment of the illumination optical unit 4, the deflection mirror 19 can also be omitted, and thus the illumination optical unit 4 can then have exactly two mirrors downstream of the collector 17, specifically the first faceted mirror 20 and the second faceted mirror 22.

[0086] The imaging of the first facet 21 into the object plane 6 by means of the second facet 23 or using the second facet 23 and the transmission optical unit is generally only approximate imaging.

[0087] The projection optical unit 10 includes a plurality of mirrors Mi, which are successively numbered according to their arrangement in the beam path of the projection exposure apparatus 1.

[0088] In Figure 1 the illustrated example, the projection optical unit 10 includes six mirrors M1 to M6. Alternatives with four, eight, ten, twelve, or any other number of mirrors Mi are equally possible. The projection optical unit 10 is a dual-masking optical unit. The penultimate mirror M5 and the last mirror M6 each have a channel opening for the illumination radiation 16. The projection optical unit 10 has an image-side numerical aperture that is greater than 0.5 and can also be greater than 0.6, and can for example be 0.7 or 0.75. However, the numerical aperture can also be less than 0.5.

[0089] The reflective surface of the mirror Mi can be in the form of a free-form surface without a rotational axis of symmetry. Alternatively, the reflective surface of the mirror Mi can be designed as an aspherical surface having exactly one axis of rotational symmetry of the reflective surface shape. Similar to the mirrors of the illumination optical unit 4, the mirror Mi can have a highly reflective coating for the illumination radiation 16. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0090] The projection optical 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. This object-image offset in the y-direction y can have a magnitude approximately the same as the z-distance between the object plane 6 and the image plane 12.

[0091] In particular, the projection optical unit 10 can have a deformable design. It has different imaging ratios βx, βy especially in the x-direction x and the y-direction y. The two imaging ratios βx, βy of the projection optical unit 10 are preferably (βx, βy) = (+ / -0.25, + / -0.125). A positive imaging ratio β means imaging without image inversion. A negative sign of the imaging ratio β means imaging with image inversion.

[0092] Thus, the projection optical unit 10 causes the size to be reduced by a factor of 4 in the x-direction x (i.e., in the direction perpendicular to the scanning direction).

[0093] The projection optical unit 10 causes the size to be reduced by a factor of 8 in the y-direction y (i.e., in the scanning direction).

[0094] Other imaging ratios are likewise possible. Imaging ratios with the same sign and the same absolute value in the x-direction x and the y-direction y are also possible, for example with an absolute value of 0.125 or 0.25.

[0095] The number of intermediate image planes in the x-direction x and the y-direction y in the beam path between the object field 5 and the image field 11 can be the same or different, depending on the embodiment of the projection optical unit 10. Examples of projection optical units with different numbers of such intermediate images in the x-direction x and the y-direction y are known from US 2018 / 0074303A1.

[0096] In each case, one of the second facets 23 is assigned to exactly one of the first facets 21 for forming an illumination channel for illuminating the object field 5 in each case. This can in particular produce illumination according to the Köhler principle. The far field is decomposed into a plurality of object fields 5 by means of the first facet 21. The first facet 21 produces a plurality of images of the intermediate foci on the second facets 23 assigned to them respectively.

[0097] The first sub-facets 21 are each imaged onto the mask blank 7 via the assigned second sub-facets 23 and overlap one another for the purpose of illuminating the object field 5. The illumination of the object field 5 is in particular as uniform as possible. It preferably has a uniformity error of less than 2%. The field uniformity can be achieved by overlapping different illumination channels.

[0098] The illumination of the entrance pupil of the projection optical unit 10 can be geometrically defined by the arrangement of the second sub-facets 23. The intensity distribution in the entrance pupil of the projection optical unit 10 can be set by selecting the illumination channels guiding the light, in particular a subset of the second sub-facets 23. This intensity distribution is also referred to as illumination setting or illumination pupil filling.

[0099] An equally preferred pupil uniformity in the region of the section of the illumination pupil of the illumination optical unit 4 illuminated in a defined manner can be achieved by redistributing the illumination channels.

[0100] Other aspects and details of the illumination of the object field 5 are described below, in particular other aspects and details of the illumination of the entrance pupil of the projection optical unit 10.

[0101] The projection optical unit 10 can in particular have a concentric entrance pupil. The latter can be accessible. It may also be inaccessible.

[0102] The entrance pupil of the projection optical unit 10 generally cannot be precisely illuminated with the second sub-facet mirror 22. In the case of the imaging process of the projection optical unit 10, which images the center of the second sub-facet mirror 22 telecentrically onto the wafer 13, the aperture rays generally do not intersect at a single point. However, a region can be found where the distance between pairwise determined aperture rays becomes minimal. This region represents the entrance pupil or the region conjugate to it in real space. In particular, this region exhibits a finite curvature.

[0103] It may be the case that the projection optical unit 10 has different entrance pupil attitudes for the tangential beam path and the sagittal beam path. In this case, an imaging element, in particular an optical structural element of the transmission optical unit, should be provided between the second sub-facet mirror 22 and the mask blank 7. With the aid of this optical element, the different attitudes of the tangential entrance pupil and the sagittal entrance pupil can be taken into account.

[0104] In Figure 1 In the arrangement of the components of the illustrated illumination optical element 4, the second sub-facet mirror 22 is arranged in the region conjugate to the entrance pupil of the projection optical unit 10. The first sub-facet mirror 20 is arranged inclined with respect to the object plane 6. The first sub-facet mirror 20 is arranged inclined with respect to the arrangement plane defined by the deflection mirror 19. The first sub-facet mirror 20 is arranged inclined with respect to the arrangement plane defined by the second sub-facet mirror 22.

[0105] Figure 2 Shows a schematic cross-sectional view of an embodiment of the optical system 100 of the projection exposure apparatus 1.

[0106] The optical system 100 can be part of the projection optical unit 10 as described above. However, the optical system 100 can also be part of the illumination optical unit 4 as described above. However, it is assumed below that the optical system 100 is part of such a projection optical unit 4. The optical system 100 is suitable for DUV lithography. However, the optical system 100 can also be suitable for EUV lithography.

[0107] The optical system 100 has a first component 102. The first component 102 is preferably a sensor frame and can thus also be referred to in this way. The first component 102 has a top side 104 and a bottom side 106 facing away from the top side 104. The perforation 108 penetrates the first component 102. The perforation 108 can be a drilled hole.

[0108] In addition to the first component 102, the optical system 100 also has a second component 110. The second component 110 is preferably an optical element and can thus also be so called. In particular, the second component 110 is a measurement target. The second component 110 is made of, for example, glass ceramic.

[0109] The second component 110 has an optically effective surface 112 that is oriented downward in the Figure 2 orientation. The optically effective surface 112 is a mirror surface. The optically effective surface 112 can be realized by a coating. The second component 110 has a back side 114 facing away from the optically effective surface 112. The back side 114 does not have a defined optical property. The back side 114 faces the bottom side 106 of the first component 102. The perforation 116 penetrates the second component 110. The perforation 116 can be a drilled hole.

[0110] The second component 110 is attached to the first component 102 by means of a fastening device 118. The fastening device 118 is provided with a symmetry axis or central axis 120, and the fastening device 118 has a rotationally symmetric structure with respect to the symmetry axis or central axis 120.

[0111] The fastening device 118 has a first sleeve 122 and a second sleeve 124. The first sleeve 122 abuts the top side 104 of the first component 102 and at least partially passes through the perforation 108. For example, the first sleeve 122 is made of stainless steel.

[0112] The second sleeve 124 abuts the bottom side 106 of the first component 102 and at least partially passes through the perforation 108. For example, the second sleeve 124 is made of an iron-nickel alloy. The second sleeve 124 has a spherical cap-shaped contact surface 126. "Spherical cap" is understood here to mean a part of a sphere. The first sleeve 122 and the second sleeve 124 are screwed together (not shown) so that the first component 102 is clamped between the two sleeves 122, 124. In particular, the first sleeve 122 is screwed into the second sleeve 124.

[0113] The fastening device 118 further has a threaded pin 128 which is screwed into the first sleeve 122. The threaded pin 128 passes through the second sleeve 124 and thus also through the through-hole 108 of the first component 102 and through the through-hole 116 of the second component 110. The threaded pin 128 may be made of stainless steel.

[0114] The first spherical cap element 130 abuts against the contact surface 126 of the second sleeve 124. The first spherical cap element 130 is preferably made of stainless steel. The threaded pin 128 passes centrally through the first spherical cap element 130. The first spherical cap element 130 has a spherical cap-shaped first contact surface 132, with which the first spherical cap element 130 abuts against the contact surface 126 of the second sleeve 124. Facing away from the first contact surface 132, the first spherical cap element has a flat second contact surface 134.

[0115] A spacer 136 abuts the second contact surface 134. The spacer 136 is preferably made of stainless steel. There may be a plurality of spacers 136 with various thicknesses. In particular, a coarse spacer and a fine spacer may be provided. The threaded pin 128 passes centrally through the spacer 136. By means of the spacer 136, the second component 110 may be positioned in the z-direction z.

[0116] The spacer 136 is placed between the first spherical cap element 130 and the decoupling bushing 200A of the fastening device 118. The decoupling bushing 200A is explained in detail below. The decoupling bushing 200A is adhesively bonded to the through hole 116 in the second component 110. Therefore, the decoupling bushing 200A can also be called an adhesive bushing. The threaded pin 128 passes centrally through the decoupling bushing 200A. The decoupling bushing 200A is made of an iron-nickel alloy, for example.

[0117] The second spherical cap element 138 abuts the decoupling bushing 200A. The second spherical cap element 138 is preferably made of stainless steel. The threaded pin 128 passes centrally through the second spherical cap element 138. The second spherical cap element 138 comprises a spherical cap-shaped first contact surface 140, by which the second spherical cap element 138 abuts the decoupling bushing 200A. Facing away from the first contact surface 140, the second spherical cap element 138 has a flat second contact surface 142.

[0118] The fastening device 118 also has a nut 144 screwed onto the threaded pin 128. The nut 144 is made of stainless steel, for example. The nut 144 abuts the second contact surface 142 of the second spherical cap element 138.

[0119] The optical system 100 includes an interferometer 146 that interacts with the optically effective surface 112 of the second component 110 via a laser beam 148.

[0120] Figure 3 A schematic cross-sectional view of the decoupling bushing 200A is shown. Figure 4 A schematic plan view of the decoupling bushing 200A is shown. Figure 5 A schematic bottom view of the decoupling bushing 200A is shown. In the following, reference is made simultaneously Figures 3 to 5 .

[0121] The decoupling bushing 200A has a symmetry axis or central axis 202, and the decoupling bushing 200A has a rotationally symmetric structure with respect to this symmetry axis or central axis. In addition, a radial direction R is assigned to the decoupling bushing 200A. The radial direction R is perpendicular to the central axis 202 and is directed away from the central axis 202. The decoupling bushing 200A is an integrally formed component, in particular an integrally formed component in terms of material. "Integrally formed" or "one-piece" herein means that the decoupling bushing 200A is not composed of various individual components, but forms a continuous component. In the present case. "Integrally formed in terms of material" means that the decoupling bushing 200A is always made of the same material.

[0122] The decoupling bushing 200A has a cylindrical fastening section 204 that is connected to, in particular adhesively bonded to, the second component 110. The fastening section 204 is adhesively bonded into a perforation 116 in the second component 110. The fastening section 204 is rotationally symmetric with respect to the central axis 202. The fastening section 204 has a cylindrical outer surface 206.

[0123] Viewed along the radial direction R, a first centering ring 208 and a second centering ring 210 extend from the outer surface 206. By means of the centering rings 208, 210, the decoupling bushing 200A is centered in the perforation 116 in the second component 110. The centering rings 208, 210 are annular and extend completely around the central axis 202.

[0124] Between two centering rings 208, 210, a first fastening ring 212 and a second fastening ring 214 are placed, which also extend from the outer surface 206 when observed in the radial direction R. The fastening rings 212, 214 are annular and extend completely around the central axis 202. Using the fastening rings 212, 214, the decoupling bushing 200A is adhesively bonded into the perforation 116 in the second component 110. The decoupling bushing 200A is radially adhesively bonded to the second component 110 by means of the fastening rings 212, 214. However, alternatively, an axial adhesive bond can also be provided. For an axial adhesive bond, a circumferential collar can be provided on the decoupling bushing 200A, which is adhesively bonded to the second component 110. The fastening section 204 has a first end face 216 and a second end face 218 facing away from the first end face 216.

[0125] A cylindrical connecting section 220 is arranged within the fastening section 204, which is rotationally symmetric with respect to the central axis 202. The connecting section 220 has a central perforation 222 through which the threaded pin 128 passes. The perforation 222 can be a drilled hole.

[0126] The connecting section 220 has a flat first contact surface 224 against which the spacer 136 abuts. Facing away from the first contact surface 224, the connecting section 220 has a spherical cap-shaped second contact surface 226. The first contact surface 140 of the second spherical cap element 138 abuts the second contact surface 226.

[0127] Between the fastening section 204 and the connecting section 220, a first undercut or first decoupling groove 228 is provided, which separates the fastening section 204 and the connecting section 220 from each other. The first decoupling groove 228 extends completely around the central axis 202. The first decoupling groove 228 is an annular groove and can thus also be so called. The first decoupling groove 228 extends in the direction from the first end face 216 towards the second end face 218. However, the first decoupling groove 228 does not completely break through the decoupling bushing 200A.

[0128] A second undercut or second decoupling groove 230 that separates the fastening section 204 and the connecting section 220 from each other is further provided between the fastening section 204 and the connecting section 220. The second decoupling groove 230 extends completely around the central axis 202. The second decoupling groove 230 is an annular groove and can thus also be so called. Contrary to the first decoupling groove 228, the second decoupling groove 230 extends in the direction from the second end face 218 towards the first end face 216. However, the second decoupling groove 230 does not completely break through the decoupling bushing 200A.

[0129] When observed in the radial direction R, the first decoupling groove 228 is arranged within the second decoupling groove 230, and the second decoupling groove 230 is arranged outside the first decoupling groove 228. When observed along the central axis 202, the decoupling grooves 228, 230 overlap each other such that the fastening section 204 and the connecting section 220 are connected to each other only by means of the bridging member 232. The bridging member 232 is sleeve-shaped or tubular.

[0130] By changing the wall thickness of the bridging member 232, the stiffness of the bridge 232 can be changed. In the present context, "stiffness" should be understood to mean the resistance of a body (specifically, the bridging member 232) to elastic deformation imposed on it by an external load, and to convey the relationship between the load on the body and its deformation. Stiffness is determined by the material of the body and its geometry.

[0131] The bridging member 232 serves as a flexure between the fastening section 204 and the connecting section 220. In the present context, a "flexure" should be understood as a region of a component that allows relative movement between two rigid body regions by bending. In the present case, the fastening section 204 and the connecting section 220 serve as rigid body regions between which the bridging member 232 is provided as an elastically deformable flexure.

[0132] The function of the fastening device 118 will be described below. To connect two components 102, 110, first the sleeves 122, 124 are mounted on the perforations 108 of the first component 102. Then the threaded pin 128 is screwed into the first sleeve 122.

[0133] The decoupling bushing 200A is adhesively bonded into the perforation 116 in the second component 110 using the fastening rings 212, 214. The first spherical cap element 130, the spacer 123, the decoupling bushing 200A and the second spherical cap element 138 are threadedly connected to the threaded pin 128. The nut 144 is screwed onto the threaded pin 128 but not yet tightened.

[0134] Using the spherical cap elements 130, 138, the angular errors of the two components 102, 110 can now be compensated relative to each other. In this process, the second component 110 can be tilted relative to the first component 102 about the x direction and / or the y direction y. The threaded pin 128 is held by a tool and stretched in a defined manner. Then, first the nut 144 is tightened by hand while continuing to stretch the threaded pin 128. For this purpose, the aforementioned tool for stretching the threaded pin 128 is used. After the nut 144 has been applied, the tool is removed. Thereby, no torque is introduced into the fastening device 118.

[0135] In the case where the decoupling bushing 200A does not have decoupling grooves 228, 230 that reduce the stiffness of the decoupling bushing 200A compared to a solid bushing (not shown), it is possible that, due to adverse friction conditions, the spherical cap elements 130, 138 do not slide into their optimal positions, i.e., are not optimally positioned. Due to the resulting misalignment, torque may be generated, which may lead to an undesired deformation of the second component 110, in particular the optically effective surface 112.

[0136] Such deformation can be introduced into the second component 110 via the aforementioned solid bushing and result in an undesired and uncompensable deformation of the optically effective surface 112. By providing the decoupling grooves 228, 230 or the bridging piece 232 that act as flexure elements, the torque or deformation is absorbed in the decoupling bushing 200A itself and cannot be transmitted to the second component 110. Thus, the optical system 100 becomes significantly more robust against friction effects, which are particularly disadvantageous under EUV conditions. Accordingly, there is no longer a dependence on the friction coefficient and performance of the second component 110. Even small shape deviations of the individual components of the fastening device 118 can be compensated for.

[0137] Figure 6 A schematic cross-sectional view showing another embodiment of the decoupling bushing 200B is presented.

[0138] The decoupling bushing 200B differs from the decoupling bushing 200A only in that instead of two fastening rings 212, 214, exactly one fastening ring 234 is provided, which is placed centrally between the centering rings 208, 210 when viewed along the central axis 202. All statements regarding the decoupling bushing 200A apply accordingly to the decoupling bushing 200B and vice versa.

[0139] Figure 7 A schematic cross-sectional view showing another embodiment of the decoupling bushing 200C is presented.

[0140] The decoupling bushing 200C differs from the decoupling bushing 200A only in that the bridging piece 232 has any number of perforations or slits 236, 238 that penetrate the bridging piece 232. The slits 236, 238 are preferably arranged evenly distributed around the central axis 202. By introducing the slits 236, 238, the stiffness of the bridging piece 232 can be reduced. Thus, the stiffness of the bridging piece 232 can be varied or adapted within a wide range by the size and number of the slits 236, 238. All versions regarding the decoupling bushings 200A, 200B can be used accordingly for the decoupling bushing 200C and vice versa.

[0141] Figure 8 A schematic cross-sectional view showing another embodiment of the decoupling bushing 200D is presented.

[0142] The decoupling bushing 200D differs from the decoupling bushing 200A only in that instead of two decoupling grooves 228, 230, only the first decoupling groove 228 is provided. In this case, the second decoupling groove 230 is optional. Alternatively, only the second decoupling groove 230 may be provided. In this case, the first decoupling groove 228 is optional. All versions regarding the decoupling bushings 200A, 200B, 200C can be correspondingly applied to the decoupling bushing 200D and vice versa.

[0143] Although the present invention has been described based on exemplary embodiments, the present invention can be modified in various ways.

[0144] List of reference numerals

[0145] 1 Projection exposure apparatus

[0146] 2 Illumination system

[0147] 3 Light source

[0148] 4 Illumination optical unit

[0149] 5 Object field

[0150] 6 Object plane

[0151] 7 Mask blank

[0152] 8 Mask blank holder

[0153] 9 Mask blank displacement driver

[0154] 10 Projection optical unit

[0155] 11 Image field

[0156] 12 Image plane

[0157] 13 Wafer

[0158] 14 Wafer holder

[0159] 15 Wafer displacement driver

[0160] 16 Illumination radiation

[0161] 17 Collector

[0162] 18 Intermediate focal plane

[0163] 19 Deflection mirror

[0164] 20 First faceted mirror

[0165] 21 First facet

[0166] 22 Second faceted mirror

[0167] 23 Second sub - surface

[0168] 100 Optical system

[0169] 102 Component

[0170] 104 Top side

[0171] 106 Bottom side

[0172] 108 Perforation

[0173] 110 Component

[0174] 112 Optically effective surface

[0175] 114 Back side

[0176] 116 Perforation

[0177] 118 Fastening device

[0178] 120 Central axis

[0179] 122 Sleeve

[0180] 124 Sleeve

[0181] 126 Contact surface

[0182] 128 Threaded pin

[0183] 130 Spherical cap element

[0184] 132 Contact surface

[0185] 134 Contact surface

[0186] 136 Spacer

[0187] 138 Spherical cap element

[0188] 140 Contact surface

[0189] 142 Contact surface

[0190] 144 Nut

[0191] 146 Interferometer

[0192] 148 Laser beam

[0193] 200A Decoupling bushing

[0194] 200B Decoupling bushing

[0195] 200C Decoupling bushing

[0196] 200D Decoupling bushing

[0197] 202 Central axis

[0198] 204 fastening section

[0199] 206 outer surface

[0200] 208 centering ring

[0201] 210 centering ring

[0202] 212 fastening ring

[0203] 214 fastening ring

[0204] 216 end face

[0205] 218 end face

[0206] 220 connection section

[0207] 222 perforation

[0208] 224 contact surface

[0209] 226 contact surface

[0210] 228 decoupling groove

[0211] 230 decoupling groove

[0212] 232 bridge piece

[0213] 234 fastening ring

[0214] 236 slit

[0215] 238 slit

[0216] Mirror M1

[0217] Mirror M2

[0218] Mirror M3

[0219] Mirror M4

[0220] Mirror M5

[0221] Mirror M6

[0222] Radial direction R

[0223] xx direction

[0224] yy direction

[0225] zz direction

Claims

1. An optical system (100) for a projection exposure apparatus (1), comprising: a first component (102), a second component (110), and fastening means (118) for attaching the second component (110) to the first component (102), wherein the fastening means (118) has decoupling bushings (200A, 200B, 200C, 200D) for mechanically decoupling the second component (110) from the first component (102), and wherein the decoupling bushings (200A, 200B, 200C, 200D) have decoupling grooves (228, 230) that reduce the stiffness of the decoupling bushings (200A, 200B, 200C, 200D).

2. The optical system according to claim 1, wherein, The decoupling grooves (228, 230) extend in a ring shape around a central axis (202) of the decoupling bushings (200A, 200B, 200C, 200D).

3. The optical system according to claim 2, wherein the decoupling bushings (200A, 200B, 200C) have a first decoupling groove (228) and a second decoupling groove (230), wherein the first decoupling groove (228) extends from a first end face (216) of the decoupling bushings (200A, 200B, 200C) in a direction of a second end face (218) of the decoupling bushings (200A, 200B, 200C), and wherein the second decoupling groove (230) extends from the second end face (218) in a direction of the first end face (216).

4. The optical system according to claim 3, wherein, When observed in a radial direction (R) of the decoupling bushings (200A, 200B, 200C), the first decoupling groove (228) is arranged within the second decoupling groove (230).

5. The optical system according to any one of claims 2-4, wherein, When observed along the central axis (202), the first decoupling groove (228) and the second decoupling groove (230) overlap.

6. The optical system according to any one of claims 1-5, wherein, The decoupling bushings (200A, 200B, 200C, 200D) have a connection section (220) connected to the first component (102) and a fastening section (204) connected to the second component (110), and wherein the decoupling grooves (228, 230) are arranged between the connection section (220) and the fastening section (204).

7. The optical system according to claim 6, wherein, The connection section (220) and the fastening section (204) are connected to each other only by a bridging piece (232) serving as a flexure.

8. The optical system according to claim 7, wherein, The bridging piece (232) is sleeve-shaped.

9. The optical system according to claim 7 or 8, wherein, The bridging piece (232) has slits (236, 238) penetrating the bridging piece (232).

10. The optical system according to any one of claims 6 to 9, wherein, The connection section (220) has a flat first contact surface (224) and a spherical cap-shaped second contact surface (226) facing away from the first contact surface (224).

11. The optical system according to any one of claims 1-10, wherein, The decoupling bushings (200A, 200B, 200C, 200D) have a first centering ring (208) and a second centering ring (210) for centering the decoupling bushings (200A, 200B, 200C, 200D) in a perforation (116) provided in the second component (110).

12. The optical system according to claim 11, wherein, The decoupling bushings (200A, 200C, 200D) have a first fastening ring (212) and a second fastening ring (214) for attaching the decoupling bushings (200A, 200C, 200D) to the perforation (116), and wherein the first fastening ring (212) and the second fastening ring (214) are arranged between the first centering ring (208) and the second centering ring (210).

13. The optical system according to claim 11, wherein, The decoupling bushing (200B) has exactly one fastening ring (234) for attaching the decoupling bushing (200B) to the perforation (116), and wherein the fastening ring (234) is arranged between the first centering ring (208) and the second centering ring (210).

14. The optical system according to any one of claims 1-13, wherein, The decoupling bushings (200A, 200B, 200C, 200D) are integrally formed components, in particular integrally formed components in terms of material.

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

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