Optical element for projection exposure system, optical system comprising such optical element, and projection exposure system comprising such optical element and / or such optical system

Abstract

The invention relates to an optical element (100, 200) for a projection exposure system (1), comprising: a mirror body (104, 204) having a mirror portion (124, 224) with an optically effective surface (102, 202) and a base (106, 206) arranged on a back side of the mirror portion (124, 224), and the base (106, 206) having a higher stiffness than the mirror portion (124, 224); and a reinforcing rib structure (156, 238) attached to a back side of the mirror portion (124, 224).

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The content of the priority application DE102022210171.5 is hereby incorporated in its entirety by reference. Technical Field

[0003] The invention relates to an optical element for a projection exposure apparatus, an optical system having such an optical element, and a projection exposure apparatus having such an optical element and / or such an optical system. Background Art

[0004] Microlithography is used to produce microstructured components, such as integrated circuits. The microlithography process is performed using a lithography apparatus, which comprises an illumination system and a projection system. The image of a mask (reticle) illuminated by the illumination system is projected by the projection system onto a substrate (e.g. a silicon wafer) which is coated with a photosensitive layer (photoresist) and arranged in the image plane of the projection system, so that the mask structure is transferred to the photosensitive coating of the substrate.

[0005] Driven by the demand for smaller and smaller structures in the production of integrated circuits, EUV lithography equipment using light in the wavelength band from 0.1 nm to 30 nm (particularly 13.5 nm) is currently being developed. In the case of such EUV lithography equipment, due to the high absorption rate of most materials for light of this wavelength, reflective optical units (i.e., mirrors) must be used to replace the previous refractive optical units (i.e., lens elements).

[0006] The trend for future EUV-band projection systems is towards high numerical apertures (NA). Therefore, it is expected that the optical surfaces, i.e. the mirrors, will become larger. This trend makes the goal of a high control bandwidth more difficult, since a high control bandwidth depends inter alia on the first internal natural frequency of the corresponding mirror body. Low natural frequencies cause the sensors required for closed-loop control to start vibrating in the low-frequency range. Therefore, rigid-body closed-loop control is already unstable at low frequencies.

[0007] It can be shown that the first natural frequency ω of a cylindrical mirror body is proportional to the thickness d of the corresponding mirror and inversely proportional to the square of the radius r of the optical surface. This is due to the fact that the mass is proportional to d*r 2 is proportional to d 3 / r 2 Therefore, if the first natural frequency cannot be reduced, and thus the control bandwidth of the reflector cannot be reduced, the volume of the reflector body required for an optically effective surface with radius r is proportional to r. 4 The need for high control bandwidth becomes increasingly expensive as material costs scale with substrate volume. This needs to be improved. Summary of the invention

[0008] Against this background, the problem addressed by the present invention is to provide an improved optical element.

[0009] Therefore, an optical element for a projection exposure apparatus is proposed. The optical element comprises: a reflector body, the reflector body comprising a reflector part having an optically effective surface and a base arranged on the back side of the reflector part, and the base has greater rigidity than the reflector part; a plurality of actuator connectors for connecting an actuator to the optical element, the actuator connectors being arranged on the base; and a reinforcing rib structure attached to the back side of the reflector part.

[0010] Since the base has a greater rigidity compared to the reflector part, the base can be used as a support for the actuator connector. Therefore, the reflector part can be implemented with thinner walls compared to the base, whereby a significant reduction in the weight of the optical element can be achieved.

[0011] The optical element is preferably a reflector. In particular, the optical element is part of a projection optical unit of a projection exposure apparatus. For example, the reflector body can be made of a ceramic material or a glass ceramic material. The optically effective surface is suitable for reflecting illumination radiation, in particular EUV radiation. The optically effective surface is in particular a reflective mirror surface. The optically effective surface can be applied to the reflector body, in particular to the reflector part, by means of a coating method. The optically effective surface can also be referred to as an optically active surface. The optically effective surface can be curved, in particular annularly curved.

[0012] The reflector part is preferably in the form of a panel or a flat plate. In particular, the reflector part has a thinner wall than the base. The base is preferably in the form of a block or cylindrical solid body, which is much heavier than the reflector part. As mentioned above, the reflector part is preferably in the form of a panel or a flat plate and has a significantly lower material strength than the base. Therefore, the reflector part is substantially softer or less rigid than the base.

[0013] In the present case, "stiffness" is generally understood to refer to the resistance of a body to elastic deformation due to force or torque. Stiffness may be affected by the geometry utilized and the materials utilized. In the present case, the reflector portion has a thinner wall than the base, whereby the reflector portion has a lower stiffness than the base.

[0014] The reflector part has an optically active surface, in particular on the front side. The reflector part comprises a back side facing away from the optically active surface. The base is arranged on the back side. In particular, the fact that the base is "arranged" on the back side of the reflector part in the present case means that the base extends from the back side of the reflector part. The base thus faces away from the optically active surface.

[0015] Preferably, the reflector body is a one-piece component. In the present case, "one-piece", "single-component" or "integral" means that the reflector part, the base and the actuator connector form a single component, in particular the reflector body, and do not consist of different components. Furthermore, the reflector body can also be configured to be one-piece in terms of material. In the present case, "one-piece in terms of material" means that the reflector body is always made of the same material.

[0016] In an alternative to this, the reflector body can also be a multi-component assembly. For example, in this case, the reflector body can include a plurality of different components in the form of a base, a reflector portion and / or an actuator connector. These components are connected together to form the reflector body. Thus, there is also the option of manufacturing the individual components of the reflector body from different materials. For example, materials with different thermal expansion coefficients can be used. For example, one component of the reflector body can be made of a material with a zero thermal expansion coefficient, and at least one other component can be made of a material suitable for lightweight construction, easy to process and cost-effective. For example, different ceramic materials can be used.

[0017] The optical element preferably has six degrees of freedom. In particular, the optical element has three degrees of freedom of translation in the x-direction, the y-direction and the z-direction. In addition, the optical element has three degrees of freedom of rotation about the x-direction, the y-direction and the z-direction, respectively. In the present case, the "position" of the optical element should be understood to mean the coordinates of its coordinates or the coordinates of the measuring points arranged on the optical element relative to the x-direction, the y-direction and the z-direction. In the present case, the "orientation" of the optical element should be understood to mean its tilt or the tilt of the measuring points about the x-direction, the y-direction and the z-direction. In the present case, the "pose" of the optical element should be understood to mean both the position and the orientation of the optical element. Therefore, the term "pose" can be replaced by the wording "position and orientation".

[0018] The pose of the optical element can be influenced or adjusted by means of an actuator coupled to the actuator connector. For example, the optical element can be moved from an actual pose to a target pose. Therefore, "adjusting" or "aligning" the optical element can be understood to mean moving the optical element from its actual pose to its target pose. For example, an actuator known as a Lorentz actuator can be used as actuator or actuating element and coupled to the actuator connector. In particular, a so-called actuator-sensor unit can be used as actuator.

[0019] In the present case, the fact that the actuator connector is "arranged" on the base means that, in particular, the actuator connector is firmly connected to the base. In this case, the actuator connector can be part of the base. In particular, the actuator connector can also be formed integrally with the base, in particular from one piece of material. The actuator connector preferably extends out of the base on the back side of the base. Preferably, exactly three actuator connectors are provided, and therefore also three actuators are provided. In particular, the actuator connectors are arranged in a triangular manner. Therefore, the actuator connectors can be offset by 120° from each other.

[0020] The optical element also includes a reinforcing rib structure attached to a back surface of the reflector portion.

[0021] The rib structure is preferably part of the reflector body. In particular, this means that the rib structure can be integral with the reflector body, in particular formed from one piece of material. However, this is not mandatory. The rib structure is preferably arranged on the back side of the reflector part. Thus, the rib structure extends in particular from the back side of the reflector part. By means of the rib structure, the reflector part can be at least partially strengthened and at the same time a low weight of the optical element can be achieved.

[0022] According to a further embodiment, the rib structure has a truss-like or honeycomb-like geometry.

[0023] In particular, this means that the rib structure can have a plurality of different ribs or rib parts, which merge with each other, intersect with each other or are connected to each other and thus form a truss-shaped or honeycomb-shaped area. In this case, the rib structure can have any desired geometry.

[0024] According to another embodiment, the rib structure supports the reflector portion on the base.

[0025] In particular, this means that the rib structure connects the reflector part to the base. Forces introduced into the reflector part can be introduced into the solid base via the rib structure.

[0026] According to another embodiment, the rib structure comprises a circumferential rib extending at least partially around the base and a plurality of connecting ribs connecting the base to the circumferential rib.

[0027] The circumferential ribs can be at least partially curved, in particular in the shape of a circular arc. The circumferential ribs can extend completely around the base. In an alternative, the circumferential ribs can only partially extend around the base. In the latter case, the circumferential ribs can start and end at the base. In a plan view, the circumferential ribs can be oval or elliptical. The connecting ribs and the surrounding ribs are preferably formed in one piece, in particular formed by one piece of material. The connecting ribs can extend away from the base in the direction of the circumferential ribs extending around the base in a star shape. In the process, the connecting ribs intersect with the circumferential ribs. The connecting ribs can extend through the circumferential ribs. In particular, this means that the connecting ribs do not end at the circumferential ribs, but extend beyond the outer side of the circumferential ribs away from the base.

[0028] According to a further embodiment, the actuator connector is mechanically decoupled from the base by means of a decoupling point.

[0029] Such a decoupling point can be assigned to each actuator connector. In an alternative, a corresponding decoupling point of this type can be assigned only to some of the actuator connectors. This means that multiple actuator connectors or at least one actuator connector without a decoupling point can also be provided. The decoupling point is preferably formed as a gap or cutout arranged between the actuator connector and the base. However, in this case, the decoupling point does not completely separate the actuator connector from the base, so the actuator connector is connected to the base by at least a certain material cross section. In the present case, "mechanical decoupling" should be understood to mean in particular that the decoupling point prevents the transmission of undesirable forces from the actuator connector to the optically effective surface. Preferably, the actuator connector is cylindrical and extends out of the base. Thus, a decoupling point is provided between the actuator connector and the base.

[0030] According to a further embodiment, the actuator connectors are connected to each other by means of a connecting portion.

[0031] Preferably, the actuator connectors are arranged in a triangular manner spaced apart from each other, with an angle of 120° between them. The connecting portion forms a triangular geometry connecting the actuator connectors to each other. The connecting portion may be part of the base. The connecting portion strengthens the actuator connector by means of the connecting portion connecting the actuator connectors to each other. The connecting portions may meet at a central joint area of ​​the base. The joint area is used to connect the measurement target to the optical element.

[0032] According to a further embodiment, the connecting part is mechanically decoupled from the base part by means of the cutout.

[0033] The cutout can be provided as a gap. The cutout can be introduced into the base, for example, by means of a milling method or an erosion method. However, the cutout does not completely separate the connecting part from the base, so the connecting part is still connected to the base.

[0034] According to a further embodiment, the optical element further comprises a plurality of measurement targets configured to interact with a measurement beam of the measuring instrument, wherein the measurement targets are arranged on the base.

[0035] In particular, the measurement target is attached to the aforementioned joining area. The measurement target may also be referred to as a measurement mark. Preferably, each measurement target comprises a reflector or a reflector surface suitable for reflecting the measurement beam back to the measuring instrument. There may be any desired number of measurement targets. However, six measurement targets are preferably provided. The measurement target is securely connected to the base, for example by screwing. The measurement target may also be adhesively bonded to the base. Since the measurement target is arranged on a rigid base, the rigid body movement of the optical element may be measured in the best possible manner and without interfering with natural vibrations. The measurement beam may be a laser beam.

[0036] According to a further embodiment, the engagement region of the base portion extends laterally beyond the reflector portion.

[0037] In the present case, "laterally" is understood to mean in a direction parallel to the back side of the reflector part. In particular, this means that the reflector part does not cover the joining area. The joining area is part of the base. Since the joining area extends laterally beyond the reflector part, an asymmetric structure of the reflector body or the optical element can be achieved. The joining area is thus easily accessible and can carry measurement targets. Preferably, at least some of the measurement targets are arranged in the joining area. However, it is particularly preferred that all measurement targets are attached to the joining area.

[0038] According to a further embodiment, at least one of the actuator connectors is arranged in the engagement area.

[0039] Preferably, exactly one of the actuator connectors is arranged in the engagement region.The actuator connector extends out of the engagement region on the back side.

[0040] According to a further embodiment, the mirror body is actively cooled.

[0041] For example, active cooling can be realized or implemented by means of an optical element or a reflector body having a cooling channel, through which a coolant (e.g. water) is guided in order to cool or heat the optical element or the reflector body. In this case, "active" means, in particular, that a coolant is pumped through the cooling channel by means of a pump or the like in order to extract heat from the optical element or the reflector body or to supply heat to the optical element or the reflector body. However, heat is preferably extracted from the optical element or the reflector body in order to cool the optical element or the reflector body.

[0042] According to a further embodiment, cooling channels are guided through the mirror body for active cooling of the mirror body.

[0043] For example, the cooling channels are arranged in the base of the reflector body. However, the cooling channels can also be arranged in the reflector part and / or the rib structure. Any desired number of cooling channels can be provided. The cooling channels are preferably connected to each other. The cooling channels preferably form a cooling circuit or are part of a cooling circuit. The cooling circuit can include the above-mentioned pump. The coolant circulates in the cooling circuit. The connections for the cooling circuit or for the cooling channels can be arranged in the aforementioned joining area. This makes these connections particularly accessible.

[0044] Furthermore, an optical system, in particular a projection optical unit, for a projection exposure apparatus is proposed, which has at least one such optical element and a plurality of actuators which are connected to an actuator connector for adjusting the at least one optical element.

[0045] The optical system may include a plurality of such optical elements. For example, the optical system may include six, seven or eight such optical elements. The actuator may be a so-called Lorentz actuator. In the present case and as described above, "adjusting" or "aligning" the optical element is understood to mean moving the optical element from its actual pose to its target pose. Preferably, the optical element is assigned three actuators, one of which is coupled to each actuator connector. All six degrees of freedom of the optical element can be adjusted by means of the three actuators. The actuator may be part of an adjustment device for the optical system. The adjustment device may include an open-loop and closed-loop control unit for controlling the actuator. The optical system may include a measuring instrument that interacts with a measurement target in order to capture the position of the optical element. For example, the measuring instrument may be an interferometer. For example, the actual pose of the optical element may be captured by means of the measuring instrument and the measurement target. Then, the optical element may be moved from the actual pose to its target pose by means of the actuator. Then, the open-loop and closed-loop control unit controls the actuator based on the measurement signal from the measuring instrument.

[0046] Furthermore, a projection exposure apparatus is proposed which has at least one such optical element and / or such an optical system.

[0047] The projection exposure apparatus may comprise any desired number of optical elements. In particular, the optical system is a projection optical unit of the projection exposure apparatus. However, the optical system may also be an illumination optical unit of the projection exposure apparatus. The projection exposure apparatus may be an EUV lithography apparatus. EUV stands for "extreme ultraviolet" and means that the wavelength of the working light is between 1.0 nm and 30 nm. The projection exposure apparatus may also be a DUV lithography apparatus. DUV stands for "deep ultraviolet" and means that the wavelength of the working light is between 30 nm and 250 nm.

[0048] In the present case, "one" or "an" should not be understood as being limited to just one element. On the contrary, there may also be a plurality of elements, for example two, three or more. Any other number used here should also not be understood as being limited to the stated number of elements. On the contrary, upward and downward numerical deviations are possible unless otherwise stated.

[0049] The embodiments and features described for the optical element apply correspondingly to the proposed optical system and / or the proposed projection exposure apparatus and vice versa.

[0050] Other possible embodiments of the present invention also include the non-explicitly mentioned combinations of features or embodiments described above or below with respect to 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

[0051] Further advantageous embodiments and aspects of the invention are the subject matter of the dependent claims and of the exemplary embodiments of the invention described below.The invention will be explained in detail below based on preferred embodiments with reference to the drawings.

[0052] Figure 1 shows a schematic meridional cross section of a projection exposure apparatus for EUV projection lithography;

[0053] Figure 2 Shown is the Figure 1 A schematic perspective view of an embodiment of an optical element of a projection exposure apparatus;

[0054] Figure 3 Shown according to Figure 2 Another schematic perspective view of an optical element of ;

[0055] Figure 4 Shown according to Figure 2 A schematic rear view of an optical element;

[0056] Figure 5 Shown according to Figure 1 A schematic perspective view of another embodiment of an optical element of a projection exposure apparatus;

[0057] Figure 6 Shown according to Figure 5 Another schematic perspective view of an optical element of ;

[0058] Figure 7 Shown according to Figure 5 Another schematic perspective view of an optical element of ;

[0059] Figure 8 Shown according to Figure 5 a schematic rear view of an optical element of; and

[0060] Fig. 9 Shown according to Figure 1 Schematic diagram of an embodiment of an optical system of a projection exposure apparatus.

[0061] Unless otherwise indicated, identical or functionally identical elements have the same reference numerals in the figures. It should also be noted that the illustrations in the figures are not necessarily drawn to scale. DETAILED DESCRIPTION

[0062] Figure 1 An embodiment of a projection exposure apparatus 1 (lithography apparatus), in particular an EUV lithography apparatus, is shown. An embodiment of an illumination system 2 of the projection exposure apparatus 1 has, in addition to a light source or radiation source 3, an illumination optical unit 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a module separate from the rest of the illumination system 2. In this case, the illumination system 2 does not comprise the light source 3.

[0063] A reticle 7 arranged in the object field 5 is exposed. The reticle 7 is held by a reticle holder 8. The reticle holder 8 can be displaced by a reticle displacement drive 9, in particular in a scanning direction.

[0064] Figure 1 By way of illustration, a Cartesian coordinate system is shown with an x-direction x, a y-direction y and a z-direction z. The x-direction x extends vertically into the plane of the drawing. The y-direction y extends horizontally and the z-direction z extends vertically. The scanning direction is Figure 1 The z direction z extends perpendicular to the object plane 6.

[0065] The projection exposure apparatus 1 comprises a projection optical unit 10. The projection optical unit 10 is used to image 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, the angle between the object plane 6 and the image plane 12 may also be different from 0°.

[0066] 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 means of a wafer displacement drive 15. The displacement of the reticle 7 can be effected firstly by means of the reticle displacement drive 9 and secondly by means of the wafer displacement drive 15, so as to be synchronized with one another.

[0067] The light source 3 is an EUV radiation source. The light source 3 in particular emits EUV radiation 16, which is hereinafter also referred to as used radiation, illumination radiation or illumination light. In particular, the used radiation 16 has a wavelength in the range between 5 nm and 30 nm. The light source 3 may be a plasma source, such as an LPP (laser produced plasma) source or a GDPP (gas discharge produced plasma) source. It may also be a synchrotron-based radiation source. The light source 3 may be a free electron laser (FEL).

[0068] The illumination radiation 16 emitted from the light source 3 is focused by the light collector 17. The light collector 17 may be a light collector having one or more ellipsoidal and / or hyperbolic reflective surfaces. The illumination radiation 16 may be incident on at least one reflective surface of the light collector 17 at grazing incidence (GI) (i.e. at an angle of incidence greater than 45°) or at normal incidence (NI) (i.e. at an angle of incidence less than 45°). The light collector 17 may be structured and / or coated to optimize its reflectivity for the radiation used and to suppress extraneous light.

[0069] 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 optical unit 4.

[0070] The illumination optical unit 4 comprises a deflection mirror 19 and a first facet mirror 20 arranged downstream of the deflection mirror 19 in the beam path. The deflection mirror 19 can be a plane deflection mirror or, in its alternative, a mirror with a beam influencing effect that goes beyond a pure deflection effect. In its alternative or in addition thereto, the deflection mirror 19 can be in the form of a spectral filter, which separates the used light wavelengths of the illumination radiation 16 from external light of different wavelengths. If the first facet mirror 20 is arranged in a plane of the illumination optical unit 4 that is optically conjugate to the object plane 6 (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.

[0071] The first facets 21 may be in the form of macro facets, in particular as rectangular facets or facets with an arcuate or partially circular edge profile. The first facets 21 may be in the form of planar facets or, as an alternative, in the form of convex or concave curved facets.

[0072] As known from DE102008009600A1, for example, the first facet 21 itself can also be composed of a plurality of individual mirrors, in particular a plurality of micromirrors. In particular, the first facet mirror 20 can be in the form of a microelectromechanical system (MEMS system). For details, reference can be made to DE102008009600A1.

[0073] The illuminating radiation 16 propagates horizontally (ie in the y-direction y) between the light collector 17 and the deflecting mirror 19 .

[0074] In the beam path of the illumination optical unit 4, the second facet reflector 22 is arranged downstream of the first facet reflector 20. Provided that the second facet reflector 22 is arranged in the pupil plane of the illumination optical unit 4, it is also referred to as a pupil facet reflector. The second facet reflector 22 can also be arranged at a distance from the pupil plane of the illumination optical unit 4. In this case, the combination of the first facet reflector 20 and the second facet reflector 22 is also referred to as a specular reflector. Specular reflectors are known from US 2006 / 0132747 A1, EP 1 614 008 B1 and US 6 573 978.

[0075] The second facet mirror 22 comprises a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also called pupil facets.

[0076] The second facets 23 can likewise be macroscopic facets, which can have, for example, circular, rectangular or hexagonal boundaries, or alternatively facets consisting of micromirrors. In this respect, reference is also made to DE 10 2008 009 600 A1.

[0077] The second facet 23 may have a planar reflecting surface or, as an alternative thereto, a convexly or concavely curved reflecting surface.

[0078] The illumination optical unit 4 thus forms a two-facet system. This basic principle is also known as a fly's eye integrator.

[0079] It may be advantageous to arrange the second facet mirror 22 not exactly in a plane optically conjugate to the pupil plane of the projection optical unit 10. In particular, the second facet mirror 22 may be arranged tilted relative to the pupil plane of the projection optical unit 10, as described, for example, in DE 10 2017 220 586 A1.

[0080] The individual first facets 21 are imaged into the object field 5 by means of the second facet mirror 22 . The second facet mirror 22 is the last beam-shaping mirror in the beam path upstream of the object field 5 or the actual last mirror for the illumination radiation 16 .

[0081] In a further embodiment (not shown) of the illumination optical unit 4, a transfer optical unit, which particularly helps to image the first facet 21 into the object field 5, can be arranged in the beam path between the second facet mirror 22 and the object field 5. The transfer 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 transfer optical unit can in particular comprise one or two normal incidence mirrors (NI mirrors) and / or one or two grazing incidence mirrors (GI mirrors).

[0082] exist Figure 1 In the embodiment shown, the illumination optical unit 4 has exactly three mirrors downstream of the light collector 17 , specifically a deflection mirror 19 , a first facet mirror 20 and a second facet mirror 22 .

[0083] In another embodiment of the illumination optical unit 4 , the deflection mirror 19 can also be omitted, so that the illumination optical unit 4 can have exactly two mirrors downstream of the light collector 17 , in particular a first facet mirror 20 and a second facet mirror 22 .

[0084] The imaging of the first facet 21 into the object plane 6 by the second facet 23 or using the second facet 23 and the transfer optics is usually only an approximate imaging.

[0085] The projection optical unit 10 comprises a plurality of mirrors Mi which are numbered consecutively according to their arrangement in the beam path of the projection exposure apparatus 1 .

[0086] exist Figure 1 In the example shown, the projection optical unit 10 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve or any other number of mirrors Mi are also possible. The projection optical unit 10 is a doubly shielded optical unit. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16. The projection optical unit 10 has an image-side numerical aperture which is greater than 0.5 and may also be greater than 0.6, for example, may be 0.7 or 0.75.

[0087] The reflective surface of the reflector Mi can be in the form of a free-form surface without an axis of rotational symmetry. In an alternative, the reflective surface of the reflector Mi can be designed as an aspherical surface with exactly one axis of rotational symmetry of the shape of the reflective surface. Just like the reflectors of the illumination optical unit 4, the reflector Mi can have a highly reflective coating for the illumination radiation 16. These coatings can take the form of multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0088] 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 approximately the same magnitude as the z distance between the object plane 6 and the image plane 12.

[0089] In particular, the projection optical unit 10 may have a deformed design. It has different imaging ratios βx, βy in particular 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.

[0090] The projection optical unit 10 thus enables a reduction in size in the x-direction x (ie in a direction perpendicular to the scanning direction) by a ratio of 4:1.

[0091] The projection optical unit 10 enables a reduction in size in the y-direction y (ie in the scanning direction) by a ratio of 8:1.

[0092] 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.

[0093] The number of intermediate image planes in the x-direction x and in the y-direction y in the beam path between the object field 5 and the image field 11 may be the same or may be 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 in the y-direction y are known from US 2018 / 0074303 A1.

[0094] In each case, one of the second facets 23 is assigned to exactly one first facet 21, in order to form in each case an illumination channel for illuminating the object field 5. This can in particular produce an illumination according to the Kohler principle. The far field is decomposed into a plurality of object fields 5 by means of the first facets 21. The first facets 21 produce a plurality of images of the intermediate focus on the second facets 23 respectively assigned to them.

[0095] The first facets 21 are respectively imaged onto the reticle 7 and overlap each other via the assigned second facets 23 for illuminating the object field 5. The illumination of the object field 5 is in particular as homogeneous as possible. It preferably has a homogeneity error of less than 2%. Field homogeneity can be achieved by superimposing different illumination channels.

[0096] The illumination of the entrance pupil of the projection optical unit 10 can be geometrically defined by the arrangement of the second facets 23. The intensity distribution in the entrance pupil of the projection optical unit 10 can be set by selecting the illumination channels, in particular the subset of the second facets 23, through which the light is guided. This intensity distribution is also referred to as illumination setting or illumination pupil filling.

[0097] An equally preferred pupil homogeneity in the region of a segment of the illumination pupil of the illumination optical unit 4 illuminated in a defined manner can be achieved by redistributing the illumination channels.

[0098] Further aspects and details of the illumination of the object field 5 , in particular of the entrance pupil of the projection optical unit 10 , are described below.

[0099] The projection optical unit 10 may in particular have a concentric entrance pupil. The concentric entrance pupil may be accessible. The concentric entrance pupil may also be inaccessible.

[0100] The entrance pupil of the projection optical unit 10 cannot usually be accurately illuminated with the second facet mirror 22. In the case of an imaging process of the projection optical unit 10 in which the center of the second facet mirror 22 is telecentrically imaged onto the wafer 13, the aperture rays usually do not intersect at a single point. However, a region can be found in which the spacing of the aperture rays determined in pairs becomes minimal. This region represents the entrance pupil or a region conjugate therewith in real space. In particular, this region exhibits a finite curvature.

[0101] It is possible that the projection optical unit 10 has different entrance pupil positions for the tangential beam path and the sagittal beam path. In this case, an imaging element, in particular an optical structural element of the transfer optical unit, should be arranged between the second facet mirror 22 and the reticle 7. With the help of this optical element, different tangential and sagittal entrance pupil positions can be taken into account.

[0102] exist Figure 1 In the arrangement of the components of the illumination optical unit 4 shown, the second facet mirror 22 is arranged in a region conjugate with the entrance pupil of the projection optical unit 10. The first facet mirror 20 is arranged obliquely with respect to the object plane 6. The first facet mirror 20 is arranged obliquely with respect to the arrangement plane defined by the deflection mirror 19. The first facet mirror 20 is arranged obliquely with respect to the arrangement plane defined by the second facet mirror 22.

[0103] Figure 2 A schematic perspective view of an embodiment of an optical element 100 is shown. Figure 3 Another schematic perspective view of an optical element 100 is shown. Figure 4 A schematic bottom view of the optical element 100 is shown. Figures 2 to 4 .

[0104] The development of projection exposure apparatuses 1 with high numerical apertures (NA) has a direct impact on the design of the mirrors M1 to M6 in the projection optical unit 10. The higher the NA value, the larger and heavier the mirrors M1 to M6 become. The manufacturing costs increase or decrease disproportionately with the size of the respective mirrors M1 to M6. However, in order to minimize the production costs of larger mirrors M1 to M6, the goal is to switch to a lightweight mirror design by saving material for the mirrors M1 to M6.

[0105] Therefore, the optical element 100 is one of the reflectors M1 to M6. The optical element 100 is included in Figures 2 to 4 The optically active or optically effective surface 102 is oriented downwards in an orientation of . The optically effective surface 102 is adapted to reflect the illumination radiation 16, in particular EUV radiation. The optically effective surface 102 is a mirror surface. The optically effective surface 102 may be curved, in particular annularly curved.

[0106] The optically effective surface 102 is arranged on the front side of the reflector body 104 of the optical element 100. The optically effective surface 102 can be made by coating. The reflector body 104 can also be called a reflector substrate. For example, the reflector body 104 element is made of ceramic or glass ceramic.

[0107] The reflector body 104 comprises a block-shaped base 106. The base 106 may have a cylindrical geometry with an elliptical or circular base. The base 106 may have any desired geometry. The base 106 is in the form of a solid body and therefore has a high rigidity. The base 106 may be arranged approximately centrally on the reflector body 104.

[0108] Due to the high rigidity of the base 106 compared to the remaining reflector body 104, the sensor or Figures 2 to 4 Objects shown, referred to as measurement targets 108, 110, 112, 114, 116, 118, may be attached to the base 106. Six measurement targets 108, 110, 112, 114, 116, 118 may be provided. The measurement targets 108, 110, 112, 114, 116, 118 may also be referred to as measurement marks. The measurement targets 108, 110, 112, 114, 116, 118 may include or may be reflectors.

[0109] For example, Figure 4As shown, based on the measurement target 110, the measurement beam 120 from the measurement instrument 122 can be steered toward the corresponding measurement targets 108, 110, 112, 114, 116, 118. The position and posture of the optical element 100 can be captured with the help of the measurement targets 108, 110, 112, 114, 116, 118 and the measurement instrument 122.

[0110] The optical element 100 preferably has six degrees of freedom. All six degrees of freedom can be captured by means of the measuring targets 108, 110, 112, 114, 116, 118. In particular, the optical element 100 has three degrees of freedom in translation in the x-direction x, the y-direction y and the z-direction z. In addition, the optical element 100 has three degrees of freedom in rotation about the x-direction x, the y-direction y and the z-direction z, respectively.

[0111] In the present case, the “position” of the optical element 100 is understood to mean its coordinates or the coordinates of the measuring points arranged on the optical element 100 relative to the x-direction x, the y-direction y and the z-direction z. In the present case, the “orientation” of the optical element 100 is understood to mean its tilt or the tilt of the measuring points relative to the x-direction x, the y-direction y and the z-direction z. In the present case, the “pose” of the optical element 100 is correspondingly understood to mean both the position and the orientation of the optical element 100.

[0112] In addition to the base 106, the optical element 100 also includes a flat plate or panel-shaped reflector portion 124. Considered in the z-direction z, the reflector portion 124 has a much lower material strength than the base 106. In a plan view, the reflector portion 124 can be, for example, elliptical or triangular. The reflector portion 124 can extend completely around the base 106.

[0113] The optically active surface 102 is disposed on the front side of the reflector portion 124. The reflector portion 124 has a back side 126 facing away from the optically active surface 102. The back side 126 has no reflective properties. Since the reflector portion 124 has thinner walls than the base 106, the reflector portion 124 is softer or less rigid.

[0114] The reflector part 124 and the base 106 are formed in one piece, in particular, from one piece of material. In this case, "single component" or "integrated" means that the reflector part 124 and the base 106 are not composed of different parts, but form a common part. In the present case, "formed from one piece of material" means that the reflector part 124 and the base 106 are always made of the same material. Therefore, the reflector body 104 is integral or can be referred to as integral. For example, the reflector body 104 is made by appropriate grinding of a substrate block.

[0115] In an alternative to this, the base 106 and the reflector part 124 can also be two separate parts or components of the optical element 100, which are firmly connected to each other. This advantageously makes it possible to manufacture the base 106 and the reflector part 124 from different materials. For example, materials with different coefficients of thermal expansion (CTE) can be used.

[0116] For example, one component of the optical element 100 may be constructed of a 0-CTE material, and at least one other component may be made of a material suitable for lightweight construction, easy to process, and cost-effective. In this case, ceramic materials are particularly suitable. In this case, active cooling may be provided to compensate for CTE differences between the various materials. The components to be joined may be bonded or adhesively bonded.

[0117] In addition, the optical element 100 can be composed of many simple individual parts. To this end, various bonding methods can be used. For example, adhesion, screen printing, laser bonding, surface activation bonding, anodic bonding, glass fusion bonding, adhesive bonding, eutectic bonding, reaction bonding, silicate bonding, etc. can be used.

[0118] Actuator interfaces or actuator connectors 128, 130, 132 may be provided on the base 106. For example, three actuator connectors 128, 130, 132 are provided and arranged in a triangular form, offset from each other by 120°. In particular, a first actuator connector 128, a second actuator connector 130, and a third actuator connector 132 are provided.

[0119] The actuator connectors 128, 130, 132 are cylindrical. An actuator element or actuator can be connected to the actuator connectors 128, 130, 132. The actuator connected to the actuator connectors 128, 130, 132 can be, for example, a known Lorentz actuator. However, other actuators, such as piezoelectric elements, etc., can also be used. The position and posture of the optical element 100 can be adjusted by means of the actuator.

[0120] The actuator connectors 128, 130, 132 are arranged on the base 106. The actuator connectors 128, 130, 132 are rigidly connected to each other by means of triangularly arranged connecting portions 134, 136, 138. The connecting portions 134, 136, 138 may be part of the base 106 or at least firmly connected to the base 106. The cutouts 140, 142, 144, 146, 148, 150 ( Figure 4) may be disposed between the connecting portions 134, 136, 138 and the base 106. The connecting portions 134, 136, 138 meet at a solid joining area 152, which is a part of the base 106. The measurement targets 108, 110, 112, 114, 116, 118 are connected to the joining area 152.

[0121] Each actuator connector 128, 130, 132 is assigned a cutout or decoupling point 154 ( Figure 3 ). By means of the decoupling point 154, the actuator connectors 128, 130, 132 and thus the actuator can be decoupled from the base 106. The decoupling point 154 is designed as a slot provided between the base 106 and the respective actuator connector 128, 130, 132.

[0122] A significant reduction in weight can be achieved by designing the mirror portion 124 to have thinner walls compared to the base 106. Vibrations resulting from the excitation of the natural modes of the mirror portion 124 will not impair the stability of the measurement targets 108, 110, 112, 114, 116, 118 arranged on the base 106. Furthermore, the actuator is advantageously connected to the base 106 by means of the actuator connectors 128, 130, 132 and the decoupling point 154 in order to allow decoupling of parasitic forces and torques.

[0123] In addition, the rib structure 156 can also be additionally provided and placed on the back side 126 of the reflector portion 124. As mentioned above, the rib structure 156, the base 106 and the reflector portion 124 can form an integral component, in particular formed from one piece of material. In addition, the rib structure 156, the base 106 and the reflector portion 124 can be a plurality of separate components connected to each other to form the optical element 100.

[0124] The rib structure 156 may be honeycomb, honeycomb, truss, or truss-shaped. For example, the rib structure 156 may include a circumferential rib 158 that extends around the base 106 and surrounds the base 106. In a plan view, the circumferential rib 158 may be oval or elliptical. In addition, the rib structure 156 includes a plurality of connecting ribs 160, only one of which is connected to the base 106. Figures 2 to 4 Each of the figures in the drawings is provided with a reference numeral. Therefore, only one connecting rib 160 is discussed below. Starting from the base 106, the connecting rib 160 extends outward and connects the omnidirectional circumferential ribs 158 to the base 106. The connecting rib 160 can protrude beyond the circumferential ribs 158 and extend to the edge of the reflector portion 124.

[0125] The rib structure 156 is supported by the base 106. The rib structure 156 can extend in the x-direction x, the y-direction y and / or the z-direction z as required and can also branch out as required. As mentioned above, the rib structure 156 can be honeycomb-shaped. The rib structure 156 ensures a certain amount of reinforcement of the reflector part 124 and therefore ensures a certain amount of reinforcement of the entire reflector body 104. The rib structure 156 is preferably part of the reflector body 104.

[0126] The rib structure 156 also provides the option of attaching tuned mass dampers (TMDs) in order to damp certain natural modes. If necessary, the individual actuator connectors 128, 130, 132 can also be reinforced by means of the rib structure 156. The rib structure 156 is preferably formed integrally with the base 106 and the reflector part 124. Using the optical element 100 explained above, a higher control bandwidth can be obtained with a lower mass reflector body 104 compared to known reflectors for projection optical units 10.

[0127] The optical element 100 may be actively cooled. For example, such active cooling may be achieved or implemented by means of the optical element 100 or the reflector body 104 including cooling channels 162, 164. Figure 4 Only two of the cooling channels 162, 164 are shown in a very schematic manner. Any desired number of cooling channels 162, 164 may be provided. The cooling channels 162, 164 may extend through the base 106. However, the cooling channels 162, 164 may also or in addition extend within the rib structure 156 and / or within the reflector portion 124.

[0128] In order to dissipate heat from the optical element 100 or to control the temperature of the optical element 100, a coolant (e.g., water) passes through the cooling channels 162, 164 to cool or heat the optical element 100. In particular, "controlling the temperature" means maintaining the optical element 100 at a certain temperature. To this end, heat can be supplied or dissipated.

[0129] In this case, "active" means that the coolant is pumped through the cooling channels 162, 164 by means of a pump or the like in order to extract heat from or supply heat to the optical element 100. However, preferably heat is extracted from the optical element 100 in order to cool the optical element. The cooling channels 162, 164 form or are part of a cooling circuit 166. The cooling circuit 166 may include the above-mentioned pump. The coolant circulates in the cooling circuit 166.

[0130] Figure 5 A schematic perspective view of another embodiment of an optical element 200 is shown. Figure 6 Another schematic perspective view of an optical element 200 is shown. Figure 7 Another schematic perspective view of an optical element 200 is shown. Figure 8 A schematic bottom view of the optical element 100 is shown. Figures 5 to 8 .

[0131] The optical element 200 may be one of the reflectors M1 to M6. The optical element 200 includes Figure 6 The optically active surface 202 is oriented upwards in an orientation of . The optically active surface 202 is adapted to reflect the illumination radiation 16, in particular EUV radiation. The optically active surface 202 is a mirror surface. The optically active surface 202 may be curved, in particular annularly curved.

[0132] The optically effective surface 202 is arranged on the front side of the reflector body 204 of the optical element 200. The optically effective surface 202 can be made by coating. The reflector body 204 can also be called a reflector substrate. For example, the reflector body 204 element is made of ceramic or glass ceramic.

[0133] The reflector body 204 comprises a block-shaped base 206. The base 206 is constructed in an asymmetrical manner. The base 206 can have any desired geometric shape. The base 206 is in the form of a solid body and therefore has a high rigidity. The base 206 can be arranged laterally on the reflector body 204.

[0134] Due to the high rigidity of the base 206 compared to the remaining reflector body 204, the sensor or Figures 4 to 6 and Figure 8 Objects shown, referred to as measurement targets 208, 210, 212, 214, 216, 218, may be attached to the base 206. Six measurement targets 208, 210, 212, 214, 216, 218 may be provided. The measurement targets 208, 210, 212, 214, 216, 218 may also be referred to as measurement marks. The measurement targets 208, 210, 212, 214, 216, 218 may include or may be reflectors.

[0135] For example, Figure 8 As shown, based on the measurement target 214, the measurement beam 220 from the measurement instrument 222 can be steered toward the corresponding measurement targets 208, 210, 212, 214, 216, 218. The position and posture of the optical element 200 can be captured with the help of the measurement targets 208, 210, 212, 214, 216, 218 and the measurement instrument 222.

[0136] In addition to the base 206, the optical element 200 also includes a flat plate-shaped or panel-shaped reflector portion 224. Considered in the z-direction z, the reflector portion 224 has a much lower material strength than the base 206. In a plan view, the reflector portion 224 can be, for example, elliptical or triangular. The reflector portion 224 can extend completely around the base 206. However, this is not mandatory.

[0137] The optically active surface 202 is disposed on the front side of the reflector portion 224. The reflector portion 224 has a back side 226 facing away from the optically active surface 202. The back side 226 has no reflective properties. Since the reflector portion 224 has thinner walls than the base 106, the reflector portion 224 is softer or less rigid.

[0138] The reflector part 224 and the base 206 are formed in one piece, in particular from one piece of material. Therefore, the reflector body 204 is monolithic or can be referred to as monolithic. For example, the reflector body 204 is made by appropriate grinding of a substrate block. In an alternative to this and as explained above with respect to the optical element 100, the base 206 and the reflector part 224 can also be two separate parts or components of the optical element 100, which are firmly connected to each other.

[0139] An actuator interface or actuator connector 228, 230, 232 can be provided on the base 206. For example, three actuator connectors 228, 230, 232 are provided and are arranged in the form of a triangle, offset from each other by 120°. In particular, a first actuator connector 228, a second actuator connector 230 and a third actuator connector 232 are provided. The actuator connectors 228, 230, 232 are cylindrical. As has been explained above with reference to the optical element 100, an actuator element or actuator can be connected to the actuator connectors 228, 230, 232. The position and posture of the optical element 200 can be adjusted by means of the actuator.

[0140] The actuator connectors 228, 230, 232 are disposed on the base 206. Each actuator connector 228, 230, 232 may be assigned a cutout or decoupling point 234 ( Figure 7 ). However, this is not mandatory. In the present case, only the actuator connectors 230, 232 are cut away and thus decoupled from the base 206. In this case, the first actuator connector 228 does not have such a decoupling point 234. However, all actuator connectors 228, 230, 232 may also have such a decoupling point 234.

[0141] The type of decoupling and the number of actuators to be decoupled can vary depending on the arrangement (reflected about the longitudinal axis) and the pose (centered or eccentric) of the actuators. Exactly one actuator or two actuators or all three actuators can be decoupled from the base 206. By means of the decoupling point 234, the actuator connectors 228, 230, 232 and thus the actuators can be decoupled from the base 206. The decoupling point 234 is designed as a gap or slot provided between the base 206 and the respective actuator connector 228, 230, 232.

[0142] As part of the base 206, a solid bonding area 236 extends laterally from the base 206. The bonding area 236 extends laterally beyond the reflector portion 224. The measurement targets 208, 210, 212, 214, 216, 218 are connected to the bonding area 236.

[0143] A significant reduction in mass can be achieved by designing the mirror portion 224 to have thinner walls compared to the base 206. Vibrations resulting from the excitation of natural modes of the mirror portion 224 will not impair the stability of the measurement targets 208, 210, 212, 214, 216, 218 arranged on the base 206, in particular on the engagement area 236. Furthermore, the actuator is advantageously connected to the base 206 by means of actuator connectors 228, 230, 232 and a decoupling point 234 in order to allow decoupling of parasitic forces and torques.

[0144] In addition, the rib structure 238 can also be additionally provided and placed on the back side 226 of the reflector portion 224. As mentioned above, the rib structure 238, the base 206 and the reflector portion 224 can form an integral component, in particular formed from one piece of material. In addition, the rib structure 238, the base 206 and the reflector portion 224 can be multiple separate components connected to each other to form the optical element 200.

[0145] The rib structure 238 can be truss-shaped or truss-like. For example, the rib structure 238 can include a circumferential rib 240 that extends at least partially around the base 206; in plan view, the circumferential rib 240 can be oval or elliptical. In addition, the rib structure 238 includes a plurality of connecting ribs 242, only one of which is connected at Figure 5 , Figure 7 and Figure 8 240. Therefore, only one connecting rib 242 is discussed below. Starting from the base 206, the connecting rib 242 extends outward and connects the omnidirectional circumferential ribs 240 to the base 206. The connecting rib 242 preferably terminates at the omnidirectional circumferential ribs 240.

[0146] The rib structure 238 is supported by the base 206. The rib structure 238 can extend in the x-direction x, the y-direction y and / or the z-direction z as required and can also branch out as required. The rib structure 238 ensures a certain amount of reinforcement of the reflector portion 224 and therefore ensures a certain amount of reinforcement of the entire reflector body 204. The rib structure 238 is part of the reflector body 204.

[0147] Similar to the optical element 100, the optical element 200 can be actively cooled by a coolant. For example, such active cooling can be achieved or implemented by means of the optical element 200 or the reflector body 204 including cooling channels 244, 246. Figure 8 Only two of the cooling channels 244, 246 are shown in a very schematic manner. Any desired number of cooling channels 244, 246 may be provided.

[0148] The cooling channels 244, 246 can extend through the base 206. However, the cooling channels 244, 246 can also or in addition extend within the rib structure 238 and / or within the reflector part 224. The cooling channels 244, 246 form a cooling circuit 248 or are part of a cooling circuit 248. The cooling circuit 248 can include a pump. A coolant circulates in the cooling circuit 248. Connections for the cooling circuit 248 or for the cooling channels 244, 246 can be provided in the joining region 236. This makes these connections particularly accessible.

[0149] By means of both embodiments of the optical element 100, 200, a lightweight mirror design can be achieved which, despite saving material, has good dynamics in terms of controlling the bandwidth and good optical performance in terms of wavefront aberrations. The optically active surface 102, 202 is supported by the rib structure 156, 238 in the process.

[0150] More material is attached to the base 106, 206 on the back side of the optical element 100, 200, thereby rigidly attaching the measurement target 108, 110, 112, 114, 116, 118, 208, 210, 212, 214, 216, 218 to the reflector body 104, 204. This rigid attachment is important in the closed loop control of the optical element 100, 200. Three actuator connectors 128, 130, 132, 228, 230, 232 are arranged 120° offset from each other and rigidly connected to the base 106, 206.

[0151] The lightweight mirror design can be refined, calculated and optimized in multiple iterative design cycles and calculation cycles. In this process, the actuator connectors 128, 130, 132, 228, 230, 232 are first changed relative to the center of the optical element 100, 200. Secondly, different reinforcement options are studied, and the orientation of the measurement targets 108, 110, 112, 114, 116, 118, 208, 210, 212, 214, 216, 218 is iteratively modified to find the best compromise between controllability and natural frequency. In addition, the arrangement and geometry of the rib structure 156, 238 are adapted, and the decoupling of the actuator connectors 128, 130, 132, 228, 230, 232 is incorporated into the optically effective surface 102, 202.

[0152] Compared to a solid reference mirror, the lightweight mirror design of the optical element 100, 200 has a higher first natural frequency and a high control bandwidth. Compared to the reference mirror, the mass of the optical element 100, 200 is estimated to be reduced by about 61%. In this method, the raw material requirement is reduced by about 44%. The material savings achieved by this lightweight mirror design significantly reduce the production cost for producing the optical element 100, 200.

[0153] A reduction in production costs is achieved by eliminating material from the optical element 100, 200. Material is omitted where possible and effective. As a result of the conversion to a lightweight reflector design, the optical element 100, 200, previously modeled as a solid block, now consists of a thin-walled panel in the form of a reflector portion 124, 224 and a base 106, 206, which is supported by a rigid rib structure 156, 238 on the back side 126, 226. The optically active surface 102, 202 is provided on the front side of the thin-walled reflector portion 124, 224.

[0154] Due to the thin-walled lightweight mirror design, an optimized concept has been developed regarding the connection of the measurement targets 108, 110, 112, 114, 116, 118, 208, 210, 212, 214, 216, 218 and the actuator connectors 128, 130, 132, 228, 230, 232. The measurement targets 108, 110, 112, 114, 116, 118, 208, 210, 212, 214, 216, 218 for measuring the optical element 100, 200 are combined in a common area or point, in particular an adjustment point in the form of a joint area 152, 236. That is, six measurement targets 108, 110, 112, 114, 116, 118, 208, 210, 212, 214, 216, 218 are attached to the back side of the optical element 100, 200 and are rigidly attached to the adjustment points.

[0155] The rigid connection of the measurement targets 108, 110, 112, 114, 116, 118, 208, 210, 212, 214, 216, 218 is achieved by filling the cavity in the base 106, 206 with material and connecting the measurement targets 108, 110, 112, 114, 116, 118, 208, 210, 212, 214, 216, 218 to the base 106, 206. The orientation of each measurement target 108, 110, 112, 114, 116, 118, 208, 210, 212, 214, 216, 218 is optimized with respect to the direction of the corresponding measurement beam 122, 222 and is selected such that the control bandwidth of the optical element 100, 200 is increased.

[0156] In order to ensure that the optical element 100, 200 can continue to be rigidly mounted (despite the greatly reduced mass), the actuator connectors 128, 130, 132, 228, 230, 232 are centrally located on the back side of the reflector body 104, 204 and are offset from each other by 120°. In addition, the connection of the actuator connectors 128, 130, 132, 228, 230, 232 to the base 106, 206 is strengthened.

[0157] The actuator connectors 128, 130, 132, 228, 230, 232 preferably have the same structure. The respective geometries of the actuator connectors 128, 130, 132, 228, 230, 232 are selected so that the induced deformation of the optically active surface 102, 202 caused by various effects (such as assembly, pressure changes, acceleration, gravity, etc.) is reduced.

[0158] Another decoupling measure is implemented by means of the decoupling points 154, 234 to decouple the optically active surface 102, 202 from the load introduction on the actuator connectors 128, 130, 132, 228, 230, 232. In a plane spanned by the x-direction x and the y-direction y, the actuator connectors 128, 130, 132, 228, 230, 232 are separated from the base 106, 206 in the lateral direction by means of the decoupling points 154, 234, whereby the force flow directly acting on the optically active surface 102, 202 is blocked.

[0159] The difference between the optical element 100, 200 and the previous reflector design according to the reference reflector is essentially the reduction of the reflector material. This can significantly reduce the production costs. From a dynamic point of view, another difference of the lightweight reflector design is the higher natural frequency (despite the reduced mass), which is due to the rigid connection of the measurement target 108, 110, 112, 114, 116, 118, 208, 210, 212, 214, 216, 218 and the actuator connector 128, 130, 132, 228, 230, 232 and the reduced material displacement at the edge of the reflector part 124, 224.

[0160] The higher natural frequency in turn leads to a high control bandwidth of the optical element 100, 200, which plays an important role in the controllability of the optical element 100, 200. In addition, the lightweight mirror design provides more latitude for the design of the actuator due to the significant reduction of its mass.

[0161] Finally, the actuator connectors 128, 130, 132, 228, 230, 232 of the optical elements 100, 200 have different sizes compared to the reference mirrors and are also decoupled from the optically active surfaces 102, 202, thereby reducing deformations caused in the optically active surfaces 102, 202 due to the significant reduction in mass and the associated loss of stiffness.

[0162] Fig. 9 A schematic diagram of an embodiment of an optical system 300 for a projection exposure apparatus 1 is shown.

[0163] The optical system 300 may be the projection optical unit 10 as described above or a part of this projection optical unit 10. Therefore, the optical system 300 may also be referred to as the projection optical unit 10. However, the optical system 300 may also be the illumination optical unit 4 as described above or a part of this illumination optical unit 4. Therefore, the optical system 300 may also be referred to as the illumination optical unit 4 alternatively. However, it is assumed below that the optical system 300 is the projection optical unit 10 or a part of this projection optical unit 10.

[0164] The optical system 300 may include a plurality of optical elements 100, 200. Fig. 9 Only one of the optical elements 100 is shown in FIG. 1 . Therefore, only reference is made to the optical element 100 below. All the following statements about the optical element 100 apply correspondingly to the optical element 200. This means that, in particular, the optical system 300 can include both the optical element 100 and the optical element 200.

[0165] exist Fig. 9In the orientation of , the optically active surface 102 faces upward. Actuator connectors 128, 130, 132 are disposed on the back of the optical element. The optical element 100 or the optically active surface 102 has six degrees of freedom, as mentioned previously, specifically three degrees of freedom of translation in the x-direction x, the y-direction y and the z-direction z, respectively, and three degrees of freedom of rotation about the x-direction x, the y-direction y and the z-direction z, respectively.

[0166] Fig. 9 The actual position IL of the optical element 100 or the optically effective surface 102 is shown in solid lines, and the target position SL of the optical element 100 or the optically effective surface 102 is shown in dashed lines, and reference numerals 100' and 102' are used. The optical element 100 can be brought from its actual position IL to the target position SL, and vice versa. For example, the optical element 100 in the target position SL meets a specific optical specification or requirement that the optical element 100 in the actual position IL does not meet.

[0167] In order to move the optical element 100 from the actual position IL to the target position SL, the optical system 300 comprises an adjustment device 302. The adjustment device 302 is configured to adjust the optical element 100. In the present case, "adjustment" or "alignment" of the optical element 100 is to be understood as a change in the position of the optical element 100 in particular. For example, the optical element 100 can be moved from the actual position IL to the target position SL, and vice versa, by means of the adjustment device 302. Therefore, the adjustment or alignment of the optical element 100 can be implemented in all the aforementioned six degrees of freedom by means of the adjustment device 302.

[0168] The adjustment device 302 includes a plurality of actuators or actuators 304, 306, 308, which are arranged in a Fig. 9 1 and 2. The optical element 100 is shown in a very schematic manner only. Each actuator connector 128, 130, 132 is assigned an actuator 304, 306, 308. In particular, this means that exactly three actuators 304, 306, 308 are provided. By using three actuators 304, 306, 308, adjustment of the optical element 100 in all six degrees of freedom is possible.

[0169] The first actuator 304 is assigned to the first actuator connector 128. The second actuator 306 is assigned to the second actuator connector 130. The third actuator 308 is assigned to the third actuator connector 132. The actuators 304, 306, 308 have the same configuration.

[0170] The actuators 304, 306, 308 may be coupled to a fixed world 310. The fixed world 310 may be a force frame or any other immovable structure. All actuators 304, 306, 308 are operably connected to an open-loop and closed-loop control unit 312, and thus the open-loop and closed-loop control unit 312 may adjust the optical element 100 in all six degrees of freedom by means of appropriate control of these actuators 304, 306, 308.

[0171] Although the present invention has been described with reference to exemplary embodiments, the present invention can be modified in various ways.

[0172] Reference numerals list

[0173] 1 Projection exposure equipment

[0174] 2 Lighting system

[0175] 3 Light Source

[0176] 4 Illumination optical unit

[0177] 5. Material Field

[0178] 6 Object Plane

[0179] 7. Mask Master

[0180] 8 Reticle Holder

[0181] 9 Mask Master Displacement Driver

[0182] 10 Projection Optics Unit

[0183] 11 Image Field

[0184] 12 Image planes

[0185] 13 chips

[0186] 14 Wafer Holder

[0187] 15 chip displacement driver

[0188] 16 Lighting Radiation

[0189] 17 light collector

[0190] 18 Intermediate focal plane

[0191] 19 Deflecting mirror

[0192] 20First facet reflector

[0193] 21 First facet

[0194] 22 Second facet reflector

[0195] 23 Second facet

[0196] 100 optical elements

[0197] 100' Optics

[0198] 102 Optically effective surface

[0199] 104 reflector body

[0200] 106 base

[0201] 108 Measurement Target

[0202] 110 Measurement Target

[0203] 112 Measurement Target

[0204] 114 Measurement Target

[0205] 116 Measurement Target

[0206] 118 Measurement Target

[0207] 120 Measurement beam

[0208] 122 Measuring instruments

[0209] 124 Reflector part

[0210] 126 Back

[0211] 128 Actuator connector

[0212] 130 Actuator connector

[0213] 132 Actuator connector

[0214] 134 Connection part

[0215] 136 Connection part

[0216] 138 Connection part

[0217] 140 Incision

[0218] 142 Incision

[0219] 144 Incision

[0220] 146 Incision

[0221] 148 Incision

[0222] 150 Incision

[0223] 152 Junction area

[0224] 154 Decoupling point

[0225] 156 Rib structure

[0226] 158 Circumferential rib

[0227] 160 Connecting ribs

[0228] 162 Cooling channels

[0229] 164 Cooling channels

[0230] 166 Cooling circuit

[0231] 200 Optical Components

[0232] 202 Optically effective surface

[0233] 204 reflector body

[0234] 206 base

[0235] 208 Measurement Target

[0236] 210 Measurement target

[0237] 212 Measurement Target

[0238] 214 Measurement Target

[0239] 216 Measurement Target

[0240] 218 Measurement Target

[0241] 220 Measurement beam

[0242] 222 Measuring instruments

[0243] 224 Reflector Part

[0244] 226 Back

[0245] 228 Actuator connector

[0246] 230 Actuator Connector

[0247] 232 Actuator Connector

[0248] 234 Decoupling point

[0249] 236 Junction Area

[0250] 238 Rib structure

[0251] 240 Circumferential Rib

[0252] 242 Connecting rib

[0253] 244 Cooling channels

[0254] 246 Cooling channels

[0255] 248 Cooling circuit

[0256] 300 Optical System

[0257] 302 Adjustment device

[0258] 304 Actuator

[0259] 306 Actuator

[0260] 308 Actuator

[0261] 310 Fixed World

[0262] 312 Open-loop and closed-loop control units

[0263] IL Actual pose

[0264] M1 Reflector

[0265] M2 Reflector

[0266] M3 Reflector

[0267] M4 Reflector

[0268] M5 Reflector

[0269] M6 Reflector

[0270] SL target pose

[0271] xx Direction

[0272] yy direction

[0273] zz direction

Claims

1. An optical element (100, 200) for a projection exposure apparatus (1), comprising: A reflector body (104, 204), the reflector body (104, 204) comprising a reflector portion (124, 224) having an optically effective surface (102, 202) and a base portion (106, 206) arranged on the back side of the reflector portion (124, 224), and the base portion (106, 206) having a higher rigidity than the reflector portion (124, 224), a plurality of actuator connectors (128, 130, 132, 228, 230, 232) for connecting an actuator to the optical element (100, 200), the actuator connectors (128, 130, 132, 228, 230, 232) being disposed on the base (106, 206), and A reinforcing rib structure (156, 238) is attached to the back surface of the reflector portion (124, 224).

2. The optical element according to claim 1, characterized in that The rib structure (156, 238) has a truss-like or honeycomb-like geometry.

3. The optical element according to claim 1 or 2, characterized in that: The rib structure (156, 238) supports the reflector portion (124, 224) on the base (106, 206).

4. The optical element according to any one of claims 1 to 3, characterized in that The rib structure (156, 238) includes a circumferential rib (158, 240) extending at least partially around the base (106, 206) and a plurality of connecting ribs (160, 242) connecting the base (106, 206) to the circumferential rib (158, 240).

5. The optical element according to any one of claims 1 to 4, characterized in that: The actuator connector (128, 130, 132, 228, 230, 232) is mechanically decoupled from the base (106, 206) by means of a decoupling point (154, 234).

6. The optical element according to any one of claims 1 to 5, characterized in that: The actuator connectors (128, 130, 132) are connected to each other by means of connecting portions (134, 136, 138).

7. The optical element according to claim 6, characterized in that The connecting portion (134, 136, 138) is mechanically decoupled from the base (106, 206) by means of a cutout (140, 142, 144, 146, 148, 150).

8. The optical element according to any one of claims 1 to 7, characterized in that: Also included are a plurality of measurement targets (108, 110, 112, 114, 116, 118, 208, 210, 212, 214, 216, 218), the plurality of measurement targets (108, 110, 112, 114, 116, 118, 208, 210, 212, 214, 216, 218) being configured to interact with a measurement beam (120, 220) of a measurement instrument (122, 222), and the measurement targets (108, 110, 112, 114, 116, 118, 208, 210, 212, 214, 216, 218) being disposed on the base (106, 206).

9. The optical element according to any one of claims 1 to 8, characterized in that The engagement region (236) of the base (206) extends laterally beyond the reflector portion (224).

10. The optical element according to claim 9, characterized in that At least one of the actuator connectors (128, 130, 132, 228, 230, 232) is disposed in the engagement region (236).

11. The optical element according to any one of claims 1 to 10, characterized in that: The reflector body (104, 204) is actively cooled.

12. The optical element according to claim 11, characterized in that Cooling channels (162, 164, 244, 246) are guided through the reflector body (104, 204) for actively cooling the reflector body (104, 204).

13. An optical system (300) for a projection exposure apparatus (1), in particular a projection optical unit (10), characterized in that The optical system (300) has at least one optical element (100, 200) according to any one of claims 1 to 12 and a plurality of actuators (304, 306, 308), the plurality of actuators being coupled to the actuator connectors (128, 130, 132, 228, 230, 232) for adjusting the at least one optical element (100, 200).

14. A projection exposure apparatus (1), characterized in that The invention comprises at least one optical element (100, 200) according to any one of claims 1 to 12 and / or an optical system (300) according to claim 13.

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