Optical assembly, projection exposure apparatus for semiconductor lithography, and method

Abstract

The present invention relates to an optical assembly (30) having an optical element (Mx, 117), the optical element (Mx, 117) including a body (31), at least one actuator (35) for deforming the body (31) being disposed on the back side of the body (31), the at least one actuator (35) being connected to the back side (33) of the body at a first connection surface and to a back plate (36) at a second connection surface, the back plate (36) being attached only via the actuator (35).

Description

Technical Field

[0001] This application claims the priority of German Patent Application No. 10 2022 116 700.3 filed on July 5, 2022, and the content thereof is incorporated herein by reference in its entirety.

[0002] The present invention relates to an optical assembly, a projection exposure apparatus for semiconductor lithography, and a method for manufacturing an optical assembly.

Background Art

[0003] In a projection exposure apparatus for semiconductor lithography, using the photolithography method, a fine structure is imaged from a mask as a template onto a photoresist-coated wafer with a significant reduction. In subsequent development and further processing steps, a desired structure such as a memory or logic element is created on the wafer and then singulated into individual chips used in electronic devices.

[0004] Since extremely small structures up to the nanometer range are created, extreme requirements are imposed on the optical unit of the projection exposure apparatus and thus on the optical elements used. Furthermore, aberrations that often occur due to fluctuations in environmental conditions such as temperature fluctuations in the optical unit occur regularly during the operation of the corresponding apparatus. Usually, in order to be able to correct the above aberrations during the operation of the apparatus, the optical elements used, such as lens elements or mirrors, have movable or deformable embodiments to address this problem. For this purpose, mechanical actuators that may be suitable for deforming the surface of the optical element used for imaging, i.e., the so-called optically effective surface, in a targeted manner are generally utilized. This deformation can be carried out from the back side of the body of the corresponding optical element. According to the prior art, the mechanical action of the actuator is usually made possible by the actuator being mechanically supported on a back plate in the rear region of the body. This back plate, especially its mounting, further causes parasitic deformations during the operation of the optical element. As a result, very large expenditures are required to meet the requirements imposed on the manufacturing tolerances and assembly tolerances of the actuator and the back plate. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The problem addressed by the present invention is to identify an optical assembly and projection exposure apparatus that reduces the adverse effects caused by a backplate connected to an actuator compared to the prior art. Another problem addressed by the present invention is to identify a method for manufacturing such an assembly. [Means for solving the problem]

[0006] This objective is achieved by apparatus and method having the features described in the independent claim. Dependent claims relate to advantageous developments and variations of the present invention.

[0007] The optical assembly according to the present invention comprises an optical element, the optical element including a body, and at least one actuator that deforms the body is located on the back side of the body. In this case, at least two actuators are connected to the back side of the body at a first connection surface and to a back plate at a second connection surface, and the back plate is attached only via the actuators.

[0008] In other words, the only connection between the backplate and the “fixed environment” is in at least two, or usually more, actuators. In particular, the actuators can be piezo actuators, or solid actuators such as magnetostrictive, electrostrictive, or thermal actuators. Therefore, uniform expansion, for example due to heat, of all solid actuators perpendicular to the connection surface will only lead to deformation of the backplate and will not affect the shape and orientation of the optically effective surface. Actuator creep often occurs, as is known, especially during the switch-on procedure, i.e., the actuator moves to the desired state without stabilizing immediately after switching on. However, since the actuators usually behave similarly at that time, this effect is generally compensated for by the free backplate, or unwanted deformation does not occur.

[0009] Furthermore, even if there is a constant temperature gradient across the optical assembly, it will only lead to tilting of the backplate and will not lead to displacement or deformation of the optically effective surface.

[0010] In addition to defects arising from uniform changes in all actuators, the solution according to the present invention can also suppress parasitic effects from the joining technique. In particular, this includes thermal or humid volume changes of the joining material perpendicular to the connection surface. In this regard, the joining material is understood to mean any material that establishes the joint between the actuator and the adjacent component (in this case, between the body and the backplate). Examples for this purpose include adhesives, glass frit, solder, welding filler materials, and reaction layers formed by reactive bonding.

[0011] Since many actuators cause not only the desired extension in the operating direction but also changes in the lateral actuator shape which can lead to parasitic deformation, in a particularly preferred embodiment, at least one separation element for lateral separation is placed between the actuator and at least the body and / or backplate.

[0012] This lateral separation makes it possible to compensate for the thermal expansion of the bonded material in the transverse direction and the shape changes caused by moisture in this direction. This also applies to volume changes due to pressure.

[0013] In an advantageous variant of the present invention, the back side of the body has at least one flat portion. The resulting flat joint allows for the use of simple manufacturing methods with good roughness and very good shape tolerance or flatness. Of particular note here are grinding, lapping, planar honing, and planar polishing. Thus, it is possible to use joining methods that only allow for compensation of small mechanical tolerances. In particular, this includes the joining methods described above.

[0014] In particular, the thickness of the main body can vary over its lateral range. For example, installation space requirements may necessitate manufacturing the main body to be locally thinner. In this case, the embodiments of each actuator and / or backplate may need to be appropriately adapted.

[0015] Similarly, the thickness of the backplate can vary across its lateral range. For example, compared to the inner region, the backplate may have increased thickness in the area near the edge to compensate for the reduction in backplate rigidity that occurs near the edge.

[0016] To save installation space, it may also be advisable for the backplate and / or body to have a notch in which the actuator is at least partially positioned.

[0017] In particular, for mirrors that are strongly curved as optical elements, it can be advantageous for the back of the main body to have multiple flat sections that do not extend parallel to each other. This limits the variation in the overall thickness of the main body, and therefore, changes in its mechanical properties over that range can be kept within a controllable range.

[0018] In this particular case, it is advantageous to have multiple flat backplates, each aligned parallel to the flat section.

[0019] In one advantageous embodiment of the present invention, the surface of the backplate facing the main body and the surface of the backplate facing away from the main body each extend a certain distance from the back side of the main body. For example, this makes it possible to obtain a backplate of a certain thickness. This modified form can also be considered when the optical element is embodied as a spherical mirror having a main body of a certain thickness. In this case, the backplate becomes a substantially similar mapping of the main body.

[0020] In particular, the present invention encompasses the case where at least one effective direction of the actuator occurs perpendicular to the connection surface of the actuator with the body. However, it is also applicable to the case where at least one effective direction of the actuator occurs perpendicular to the optically effective surface.

[0021] Particularly when the body is not formed with a uniform thickness, it may be advantageous to form at least two actuators with different characteristics. As a result, it is possible to take into account the mechanical characteristics of the body such as different rigidities in the lateral direction. Thereby, the actuators used can be adapted to the mechanical conditions of the body at each position, for example, with respect to their inherent rigidity, movement distance, or the maximum applicable force.

[0022] As already mentioned, the optical element can be a mirror, particularly a multilayer mirror. Similarly, the mirror can be a concave mirror with a radius of curvature of 180 mm to 260 mm, particularly about 220 mm. Such a mirror is particularly used for beam path folding in a DUV projection exposure apparatus.

[0023] In an advantageous variant of the present invention, the backplate is less rigid than the body and can, for example, be provided with at least one sensor. The sensor can be a strain sensor or a temperature sensor.

[0024] It is also conceivable that both the backplate and the body are provided with an additional sensor system or temperature control elements such as cooling channels.

[0025] As already described, as a result of being able to make the rigidity of the backplate lower than the rigidity of the main body, when controlling the actuator stem to obtain a desired deformation of the optically effective surface, the deformation of the backplate can be set larger compared to the deformation of the effective surface. This large deformation particularly favorably affects the signal-to-noise ratio of the strain measurement of the backplate using, for example, a fiber Bragg grating sensor. When the mechanical characteristics of the actuator, the main body, and the backplate are known, the corresponding deformation of the optically effective surface can be estimated based on a model from the local deformation of the backplate.

[0026] In yet another embodiment, the characteristics (the thermal expansion coefficient and thickness of the actuator used) can be selected so that a defined temperature profile (for example, the main thermal mode of the system) does not lead to parasitic deformation or parasitic displacement of the optically effective surface. For example, such parasitic deformation can result from the heating of the actuator affecting its efficiency, that is, its respective mechanical response to a change in the control voltage. Further, parasitic deformation can occur solely due to the normal thermal expansion or thermal contraction of the materials involved. By appropriately selecting the materials used and / or the design of each shape, it becomes possible to achieve at least partial mutual compensation of the above effects.

[0027] As already described, the present invention is particularly suitable for use in a projection exposure apparatus for semiconductor lithography.

[0028] A method for manufacturing a corresponding optical assembly according to the present invention comprises connecting an actuator to a backplate, determining the surface tolerance of the connection surface of the actuator facing away from the backplate, machining the connection surface, repeating the previous two steps until the surface tolerance is less than a predetermined threshold, connecting the actuator to the main body and including.

[0029] In this case, the optically effective surface can be machined after the actuator is assembled. This method is particularly advantageous when multiple actuators are arranged on a backplate and their connection surfaces can be machined together.

[0030] Exemplary embodiments and variations of the present invention will be described in detail below with reference to the drawings. [Brief explanation of the drawing]

[0031] [Figure 1] A schematic diagram of the meridian cross-section of a projection exposure apparatus for EUV projection lithography is shown. [Figure 2] A schematic diagram of the meridian cross-section of a projection exposure apparatus for DUV projection lithography is shown. [Figure 3] A schematic diagram of the first embodiment of the present invention is shown. [Figure 4] Further embodiments of the present invention are shown. [Figure 5] Further embodiments of the present invention are shown. [Figure 6] Further embodiments of the present invention are shown. [Figure 7a] Further embodiments of the present invention are shown. [Figure 7b] Further embodiments of the present invention are shown. [Figure 8a] Further details of another embodiment of the present invention are shown. [Figure 8b] Further details of another embodiment of the present invention are shown. [Figure 8c] Further details of another embodiment of the present invention are shown. [Figure 9] A schematic diagram of possible separation elements is shown. [Figure 10] This shows variations in the design of the backplate. [Figure 11] A flowchart of the manufacturing method according to the present invention is shown. [Modes for carrying out the invention]

[0032] The essential components of the microlithography projection exposure apparatus 1 will first be explained illustratively with reference to Figure 1. The description of the basic structure of the projection exposure apparatus 1 and its components should not be understood as non-exclusive.

[0033] One embodiment of the illumination system 2 of the projection exposure apparatus 1 includes, in addition to the radiation source 3, an illumination optical unit 4 that illuminates the object field of view 5 on the object surface 6. In an alternative embodiment, the light source 3 may be provided as a module separate from the rest of the illumination system. In this case, the illumination system does not include the light source 3.

[0034] A reticle 7 positioned in the object field of view 5 is illuminated. The reticle 7 is held by a reticle holder 8. The reticle holder 8 is displaceable, particularly in the scanning direction, by a reticle displacement drive 9.

[0035] For illustrative purposes, Figure 1 shows a Cartesian xyz coordinate system. The x-direction extends perpendicular to the plane of the figure. The y-direction extends horizontally, and the z-direction extends vertically. In Figure 1, the scanning direction extends in the y-direction. The z-direction extends perpendicular to the object plane 6.

[0036] The projection exposure apparatus 1 includes a projection optical unit 10. The projection optical unit 10 functions to form an image of the object field of view 5 onto the image field of view 11 of the image plane 12. The image plane 12 extends parallel to the object surface 6. Alternatively, angles other than 0° are possible between the object surface 6 and the image plane 12.

[0037] The structure on the reticle 7 is imaged onto the photosensitive layer of the wafer 13, which is positioned in the image field 11 region of the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 is displaceable, particularly in the y-direction, by a wafer displacement drive 15. Firstly, the displacement of the reticle 7 by the reticle displacement drive 9, and secondly, the displacement of the wafer 13 by the wafer displacement drive 15, can be performed in synchronous manner.

[0038] Radiation source 3 is an EUV radiation source. Radiation source 3 emits EUV radiation 16, which in particular is also referred to below as the radiation used, illumination radiation, or illumination light. In particular, the radiation used has a wavelength in the range of 5 nm to 30 nm. Radiation source 3 may be a plasma source, such as an LPP (laser-generated plasma) source or a GDPP (gas discharge plasma) source. It may also be a synchrotron-based radiation source. Radiation source 3 may be a free electron laser (FEL).

[0039] Illumination radiation 16 emitted from the radiation source 3 is focused by a collector 17. The collector 17 may be a collector having one or more elliptical and / or hyperbolic reflecting surfaces. Illumination radiation 16 may be incident on at least one reflecting surface of the collector 17 obliquely (GI), i.e., at an incident angle greater than 45° with respect to the direction of the normal to the mirror surface, or perpendicularly (NI), i.e., at an incident angle less than 45°. The collector 17 may be structured and / or coated, firstly to optimize reflectivity for the radiation used, and secondly to suppress external light.

[0040] Downstream of the collector 17, the illumination radiation 16 propagates through the intermediate focal point of the intermediate focal plane 18. The intermediate focal plane 18 can be a separation point between the radiation source module, which includes the radiation source 3 and the collector 17, and the illumination optical unit 4.

[0041] The illumination optical unit 4 comprises a deflection mirror 19 and a first facet mirror 20 positioned downstream of it in the beam path. The deflection mirror 19 may be a planar deflection mirror or a mirror having a beam influence effect beyond a pure deflection effect. Alternatively or additionally, the deflection mirror 19 may be embodied in the form of a spectral filter that separates the wavelength of light used by the illumination radiation 16 from external light of wavelengths outside of it. When the first facet mirror 20 is positioned on the plane of the illumination optical unit 4 that is optically conjugate to the object plane 6 as a field of view, this facet mirror is also referred to as a field of view facet mirror. The first facet mirror 20 includes a plurality of individual first facets 21, which are also referred to below as field of view facets. Figure 1 shows only some of these facets 21 as examples.

[0042] The first facet 21 can be embodied as a macroscopic facet, particularly as a rectangular facet, or as a facet having an arc-shaped edge contour or a partially circular edge contour. The first facet 21 can be embodied as a planar facet, or as a convex or concave curved facet.

[0043] For example, as is known from German Patent Application Publication No. 10 2008 009 600, the first facet 21 itself can also be composed of multiple individual mirrors, particularly multiple micromirrors. The first facet mirror 20 can be embodied in particular as a micro-electromechanical system (MEMS system). For further details, please refer to German Patent Application Publication No. 10 2008 009 600.

[0044] Between the collector 17 and the deflection mirror 19, the illumination radiation 16 travels horizontally, i.e., in the y-direction.

[0045] In the beam path of the illumination optical unit 4, a second facet mirror 22 is positioned downstream of the first facet mirror 20. When the second facet mirror 22 is positioned on the pupil plane of the illumination optical unit 4, it is also referred to as a pupil facet mirror. The second facet mirror 22 can also be positioned away from the pupil plane of the illumination optical unit 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 is also referred to as a specular reflector. Specular reflectors are known from U.S. Patent Application Publication No. 2006 / 0132747, European Patent No. 1614008, and U.S. Patent No. 6,573,978.

[0046] The second facet mirror 22 includes multiple second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets.

[0047] Similarly, the second facet 23 may be a macroscopic facet having, for example, circular, rectangular, or hexagonal edges, or it may be a facet composed of micromirrors. In this regard, see German Patent Application Publication No. 10 2008 009 600.

[0048] The second facet 23 may have a planar reflective surface or a curved reflective surface that is convex or concave.

[0049] Therefore, the illumination optical unit 4 forms a dual-facet system. This basic principle is also called a fly-eye condenser (fly-eye integrator).

[0050] It may be advantageous not to precisely position the second facet mirror 22 on a plane optically conjugate to the pupil plane of the projection optical unit 10. In particular, the pupil facet mirror 22 may be positioned at an angle to the pupil plane of the projection optical unit 10, for example, as described in German Patent Application Publication No. 10 2017 220 586.

[0051] The individual first facets 21 are imaged into the object field of view 5 using the second facet mirror 22. The second facet mirror 22 is the last beam shaping mirror or, in fact, the final mirror for the illumination radiation 16 in the beam path upstream of the object field of view 5.

[0052] In yet another embodiment of the illumination optical unit 4 (not shown), a transfer optical unit, which contributes particularly to the imaging of the first facet 21 onto the object field of view 5, can be positioned in the beam path between the second facet mirror 22 and the object field of view 5. The transfer optical unit may have exactly one mirror, or two or more mirrors arranged in continuity with the beam path of the illumination optical unit 4. The transfer optical unit may, in particular, include one or two perpendicular incidence mirrors (NI mirrors) and / or one or two oblique incidence mirrors (GI mirrors).

[0053] In the embodiment shown in Figure 1, the illumination optical unit 4 has exactly three mirrors downstream of the collector 17, specifically a deflection mirror 19, a field of view facet mirror 20, and a pupil facet mirror 22.

[0054] In yet another embodiment of the illumination optical unit 4, the deflection mirror 19 can be omitted, so the illumination optical unit 4 may have exactly two mirrors downstream of the collector 17, specifically a first facet mirror 20 and a second facet mirror 22.

[0055] The imaging of the first facet 21 onto the object surface 6 by the second facet 23, or by using the second facet 23 and the transfer optics unit, is usually only an approximate image.

[0056] The projection optical unit 10 includes a plurality of mirrors Mi, which are numbered sequentially according to their arrangement in the beam path of the projection exposure apparatus 1.

[0057] In the example shown in Figure 1, the projection optical unit 10 includes six mirrors M1 to M6. Substitution with four, eight, ten, twelve, or any other number of mirrors Mi is equally possible. The second-to-last mirror M5 and the last mirror M6 each have a through aperture for illumination radiation 16. The projection optical unit 10 is a double-shielded optical unit. The projection optical unit 10 has an image-side numerical aperture greater than 0.5 and may be greater than 0.6, for example, 0.7 or 0.75.

[0058] The reflective surface of mirror Mi can be realized as a free-form surface without an axis of rotational symmetry. Alternatively, the reflective surface of mirror Mi can be designed as an aspherical surface with exactly one axis of rotational symmetry of the reflective surface shape. Similar to the mirrors of illumination optical unit 4, mirror Mi can have a highly reflective coating for illumination radiation 16. These coatings can be designed in particular as multilayer coatings having alternating layers of molybdenum and silicon.

[0059] The projection optical unit 10 has a large object-image offset in the y-direction between the y-coordinate of the center of the object field of view 5 and the y-coordinate of the center of the image field of view 11. This object-image offset in the y-direction may be approximately the same magnitude as the z-distance between the object plane 6 and the image plane 12.

[0060] In particular, the projection optical unit 10 can have an anamorphic design. Specifically, it can have different imaging scales β in the x and y directions. x , β y It has two imaging scales β of the projection optical unit 10. x , β y Preferably (β x ,β y The image scale β is (+ / -0.25, + / -0.125). A positive image scale β means that there is no image inversion. A negative sign in the image scale β means that there is image inversion.

[0061] As a result, the projection optical unit 10 is reduced in size in the x-direction, i.e., in the direction perpendicular to the scanning direction, at a ratio of 4:1.

[0062] The projection optical unit 10 reduces its size in the y-direction, i.e., in the scanning direction, at a ratio of 8:1.

[0063] Other imaging scales are also possible. Imaging scales with the same sign and absolute value in the x and y directions, for example, 0.125 or 0.25 absolute value, are also possible.

[0064] The number of intermediate image planes in the x and y directions in the beam path between the object field of view 5 and the image field of view 11 may be the same or may differ depending on the design of the projection optical unit 10. An example of a projection optical unit with a different number of such intermediate images in the x and y directions is known from U.S. Patent Application Publication No. 2018 / 0074303.

[0065] Each pupil facet 23 is assigned to exactly one of the field of view facets 21 to form an illumination channel that illuminates the object field of view 5. This allows for illumination that conforms particularly to Köhler's principle. The distant field of view is decomposed into multiple object fields of view 5 using the field of view facets 21. Each field of view facet 21 generates multiple images at intermediate focal points in the pupil facet 23 assigned to it.

[0066] The field of view facets 21 are each imaged onto the reticle 7, overlapping with the assigned pupil facets 23, to illuminate the object field of view 5. The illumination of the object field of view 5 is particularly uniform, preferably with an error in uniformity of less than 2%. Field of view uniformity can be achieved by overlapping different illumination channels.

[0067] The illumination of the entrance pupil of the projection optical unit 10 can be geometrically defined by the arrangement of the pupil facets. By selecting the illumination channels to guide light, particularly a subset of the pupil facets, the intensity distribution in the entrance pupil of the projection optical unit 10 can be set. This intensity distribution is also referred to as the illumination setting.

[0068] Similarly desirable pupil uniformity in a defined illuminated area of ​​the illumination pupil of the illumination optical unit 4 can be achieved by redistributing the illumination channels.

[0069] Further aspects and details of the illumination of the object field of view 5, particularly the entrance pupil of the projection optical unit 10, will be described below.

[0070] The projection optics unit 10 may have a concentric entrance pupil, which can be made accessible or inaccessible.

[0071] The entrance pupil of the projection optical unit 10 cannot normally be accurately illuminated using the pupil facet mirror 22. When the projection optical unit 10 forms a telecentric image on the wafer 13 with the center of the pupil facet mirror 22, the aperture rays often do not intersect at a single point. However, it is possible to find a plane where the distance between pairs of aperture rays is minimized. This plane represents the entrance pupil or its conjugate plane in real space. In particular, this plane exhibits a finite curvature.

[0072] The projection optics unit 10 may have different entrance pupil positions for the tangential beam path and the sagittal beam path. In this case, an imaging element, particularly an optical component of the transfer optics unit, should be placed between the second facet mirror 22 and the reticle 7. This optical element can be used to account for the difference in positions between the tangential and sagittal entrance pupils.

[0073] In the arrangement of the components of the illumination optical unit 4 shown in Figure 1, the pupil facet mirror 22 is positioned on a plane conjugate to the entrance pupil of the projection optical unit 10. The field of view facet mirror 20 is positioned at an angle with respect to the object surface 6. The first facet mirror 20 is positioned at an angle with respect to the arrangement plane defined by the deflection mirror 19.

[0074] The first facet mirror 20 is positioned so as to be inclined with respect to the arrangement plane defined by the second facet mirror 22.

[0075] Figure 2 schematically shows a meridian cross-section of yet another projection exposure apparatus 101 for DUV projection lithography, in which the present invention can similarly be used.

[0076] The configuration and imaging principle of the projection exposure apparatus 101 are equivalent to those described in Figure 1. Identical components are indicated by reference numerals that are 100 higher than those in Figure 1, and therefore the reference numerals in Figure 2 begin with 101.

[0077] Unlike the EUV projection lithography apparatus 1 described in Figure 1, the wavelength of the DUV radiation 116 used as the light source is in the range of 100 nm to 300 nm, particularly large at approximately 193 nm. Therefore, refraction, diffraction, and / or reflection optical elements 117 such as lens elements, mirrors, prisms, and end plates can be used for imaging or illumination in the DUV projection lithography apparatus 101. In this case, the projection lithography apparatus 101 essentially comprises an illumination system 102, a reticle holder 108 that houses and accurately positions a reticle 107 having a structure that determines the subsequent structure on the wafer 113, a wafer holder 114 that holds, moves, and accurately positions the wafer 113, and a projection lens 110 having a plurality of optical elements 117. The optical elements 117 are held by mounts 118 on the lens housing 119 of the projection lens 110.

[0078] The illumination system 102 supplies DUV radiation 116 necessary for imaging the reticle 107 onto the wafer 113. Lasers, plasma sources, etc., can be used as sources for this radiation 116. The radiation 116 is shaped by optical elements in the illumination system 102 so that when incident on the reticle 107, the DUV radiation 116 has desired characteristics in terms of diameter, polarization, wavefront shape, etc.

[0079] Aside from the additional use of refractive optical elements 117 such as lens elements, prisms, and end plates, the structure of the downstream projection optical unit 110 having a lens housing 119 is not fundamentally different from the structure described in Figure 1, and therefore will not be described in further detail.

[0080] In the schematic diagram, Figure 3 shows an embodiment of the present invention, illustrating an optical assembly 30. The optical assembly 30 comprises an optical element designed as a mirror Mx, 117 and usable on one side of the projection exposure apparatus 1, 101 described in Figures 1 and 2, an actuator 35, and a support structure designed as a backplate 36. The mirror Mx, 117 includes a body 31 having an optically effective surface 32, the body 31 being mounted on a bearing 34, for example, on the frame of the projection exposure apparatus 1, 101. The actuator 35 is positioned between the body 31 and the backplate 36 and is connected to the body 31 on the back side 33 of the body 31 opposite the optically effective surface 32. The actuator 35 can be connected to the backplate 36 by an adhesive connection (not shown separately), but other types of connections, such as bonding or soldering, are also applicable.

[0081] A controller (also not shown) controls the actuator 35 so that the deflection of the actuator 35 causes deformation of the optically effective surface 32. As the degree of deflection of the actuators 35 differs, the backplate 36 deforms as a result, causing deformation of the body 31, and consequently deformation of the optically effective surface 32, in proportion to the ratio of the stiffness of the body 31 to the stiffness of the backplate 36. Thus, deformation can be caused by some of the actuators 35 securely holding the backplate in place, while other parts of the actuator 35 are supported on the backplate 36. In this case, the backplate 36 is attached only by the actuators 35 and is not connected to the frame, the body 31 of the mirror Mx, 117, or any other component. This is advantageous because a uniform effect acting similarly on all actuators 35, such as a temperature rise or drift in the control of the actuator 35, does not affect the optically effective surface 32 but only leads to the free displacement of the backplate 36. In the figure, three strain sensors 49, which measure the deformation of the backplate 37.3, are shown as an example on the backplate 37.3.

[0082] Figure 4 illustrates yet another embodiment of the present invention, illustrating an optical assembly 30 having an optical element designed as a mirror Mx, 117 and usable on one of the projection exposure apparatuses 1, 101 described in Figures 1 and 2. The mirror Mx, 117 includes a body 31 having a concave optically effective surface 32. The optical assembly 30 also includes a backplate 36 and an actuator 35 positioned between the backplate 36 and the back side 33 of the body 31. The back side 33 and the backplate 36 have a flat embodiment. This is advantageous because the actuator 35 is also positioned on a plane and can be post-processed to optimally fit the back side 33 after initial connection to the backplate 36. As a result, the adhesive gap of the adhesive connection between the actuator 35 and the body 31 can be configured such that the effect of the adhesive on the connection rigidity is negligible. The material thickness of the body 31 that varies laterally can be compensated for by different designs of actuators and control of the actuator 35.

[0083] Figure 5 illustrates yet another embodiment of the present invention, illustrating an optical assembly 30 having an optical element designed as a mirror Mx, 117 and usable on one of the projection exposure apparatuses 1, 101 described in Figures 1 and 2. The mirror Mx, 117 includes a body 31 having a concave optically effective surface 32. The optical assembly 30 further comprises three backplates 37.1, 37.2, 37.3, and an actuator 35 positioned between the backplates 37.1, 37.2, 37.3 and the back side 33 of the body 31. The body 31 is designed such that the difference in distance between the back side 33 of the body 31 and the optically effective surface 32 is minimized compared to the embodiment described in Figure 4. As already described in Figure 4, the backplates 37.1, 37.2, 37.3 are flat and therefore can be easily manufactured, and the actuator 35 may be in the form of a standard actuator.

[0084] Figure 6 illustrates yet another embodiment of the present invention, illustrating an optical assembly 30 having an optical element designed as a mirror Mx, 117 and usable on one side of the projection exposure apparatus 1, 101 described in Figures 1 and 2. The mirror Mx, 117 includes a body 31 having a concave optically effective surface 32. Unlike the body shown in Figure 5, the body 31 of the illustrated embodiment has a constant thickness, thereby obtaining a convex or spherical back side 33. The optical assembly 30 further includes a concave back plate 39 corresponding to the shape of the optically effective surface 32 and the body 31. The actuator 35 includes spherical bonding surfaces 38 on both sides to ensure a constant thickness bonding gap in the adhesive connection. The constant thickness of the back plate 39 and body 31 is advantageous because the rigidity of these parts is constant, and therefore all actuators need to apply equivalent force to produce the same deformation of the optically effective surface 32. This reduces manufacturing costs by increasing the number of similar parts.

[0085] Figures 7a and 7b illustrate yet another embodiment of the present invention in two operating states, illustrating an optical assembly 30 having an optical element designed as a mirror Mx, 117 and usable on one of the projection exposure apparatuses 1, 101 described in Figures 1 and 2. The mirror Mx, 117 includes a body 31 having a flat optically effective surface 32. Furthermore, the optical assembly 30 comprises four backplates 40.1, 40.2, 40.3, and 40.4. Two shear actuators 41, each performing a shear motion parallel to the optically effective surface 32 when a voltage is applied, are positioned between each backplate 40.1, 40.2, 40.3, and 40.4 and the back side 33 of the body 31.

[0086] In this case, Figure 7a shows the so-called zero state, where the optically effective surface 32 of the main body 31 is not deformed, i.e., it corresponds to its target surface shape. The shear actuator 41 bends from the zero position where no voltage is applied, and as a result, the main body 31 deforms in one direction from its zero position in accordance with the applied voltage. This is advantageous because the optically effective surface 32 can be completely machined before the assembly of the actuator 41.

[0087] Figure 7b shows the same optical assembly 30 in a flexed state. The actuator 41 positioned between the two central backplates 40.2 and 40.3 and the main body 31 flexes, causing deformation of the main body 31 and, consequently, deformation of the optically effective surface 32. In Figure 7b, both actuators on backplates 40.2 and 40.3 flex relative to each other, but it is also possible that only one actuator 41 on backplates 40.1, 40.2, 40.3, and 40.4 flexes, or that one actuator 41 flexes from each of two adjacently positioned backplates 40.1, 40.2, 40.3, and 40.4.

[0088] Figures 8a, 8b, and 8c show different embodiments of actuators 42, 44, and 46 that flex parallel to the optically effective surface 32.

[0089] Figure 8a shows an optical element embodied as a mirror Mx, 117, with an actuator 42 on its left side, the end face 43 of which is connected to the back side 33 of the main body 31. The magnetic field of the actuator 42 is generated perpendicular to the optically effective surface 32, whereas, as already mentioned above, the deflection is parallel to the optically effective surface 32. In contrast, the actuator 44 on the right side of the mirror Mx is connected to the main body 31 by its long side 45. The actuator 44 is designed as a stack actuator using piezoelectric material, and in the embodiment shown in Figure 8a, the electric field and deflection are generated parallel to the optically effective surface 32.

[0090] Figure 8b schematically shows the basic structure of a bimorph actuator 46, which includes a first actuator layer 47 and a second actuator layer 48. Since the two actuator layers 47 and 48 can bend in opposite directions (indicated by arrows in Figure 8b), deformation of the actuator 46 is caused when one actuator layer 47 stretches and the other actuator layer 48 contracts.

[0091] Figure 8c shows an optical element designed as a mirror Mx, 117 having a bimorph actuator 46 as described in Figure 8b. This is connected by adhesive to the back side 33 of the main body 31, which deforms when the bimorph actuator is bent. Its function is similar to that of an actuator positioned in the surface normal direction, which uses deformation resulting from the secondary effect of a shape change perpendicular to the main bending. However, it differs in that the main contribution of the deformation is caused by the deformation of the bimorph actuator 46 itself, as described in Figure 8b, and not by the shrinkage of the material of the main body 31 due to the shape change of the actuator.

[0092] Figure 9 shows an advantageous variant of the present invention utilizing the separation element 120. In this case, the main body 31 is connected to the free backplate 36 by the actuator 35 in the manner already described. In the illustrated example, mechanical separation in the connection region between the actuator 35 and the main body 31 is achieved by the separation element, which is embodied in the main body 31 as a slit 120. For example, if the actuator 35 is embodied as a cylindrical solid actuator, the separation element 120 can be realized as an annular groove extending around the entire circumference. In the illustrated example, the separation element 120 is formed only in the main body 31. It is obvious that corresponding measures can also be considered for the backplate 36.

[0093] Figure 10 shows an embodiment of the present invention in which the thickness of the backplate 36' is designed to vary laterally. Furthermore, the backplate 36' shows a notch 121 in which the actuator 35 is partially positioned. By varying the thickness of the backplate 36' laterally, the rigidity of the backplate 31' can be made equivalent in the edge region to the rigidity of the inner region. Furthermore, by positioning the actuator 35 within the notch 121, a certain amount of installation space can be saved. In this regard, it is not necessary to use the measures shown in Figure 10 in combination. Naturally, it is also possible to use only a backplate with laterally varying thickness or a backplate with a notch.

[0094] Figure 11 shows a possible method for manufacturing an optical assembly according to the present invention.

[0095] In step 51 of the first method, the actuator is connected to the backplate.

[0096] In step 52 of the second method, the surface tolerance of the actuator connection surface facing away from the backplate is determined.

[0097] In step 53 of the third method, the connecting surface is processed.

[0098] In step 54 of the fourth method, the previous two steps are repeated until the surface tolerance falls below a predetermined threshold.

[0099] In step 55 of the fifth method, the actuator is connected to the main body. [Explanation of symbols]

[0100] 1. Projection exposure apparatus 2. Lighting System 3 Radiation source 4. Illumination Optical Unit 5 Object field of view 6 Object plane 7 Reticle 8 Reticle holders 9. Reticle displacement drive 10 Projection Optical Unit 11 Image field 12 Image plane 13 wafers 14 Wafer holder 15 Wafer Displacement Drive 16 EUV radiation 17 Collector 18 Intermediate focal plane 19. Polarizing mirror 20 Faceted Mirror 21 Facets 22 Faceted Mirror 23 Facets 30 Optical Assembly 31 Main unit 32 Optically Effective Surface 33 Back of the main unit 34 Main body bearing 35 Actuators 36, 36' backplate 37.1~37.3 Divided backplate 38 Spherical bonding surface 39 Backplate 40.1~40.4 Divided backplate 41 Shear Actuator 42 Shear Actuator 43 End face 44 Vertical actuators 45 Long side 46 Bimorph Actuators 47 Actuator layer 1 48 Actuator layer 2 49. Strain Sensor 51 Method Step 1 52 Method Step 2 53 Method Step 3 54 Method Step 4 55 Method Step 5 101 Projection exposure apparatus 102 Lighting System 107 Reticle 108 Reticle Holder 110 Projection Optical Unit 113 wafers 114 Wafer Holder 116 DUV radiation 117 Optical elements 118 mount 119 Lens Housing M1~M6 Mirror 120 Annular groove 121 Notch

Claims

1. An optical assembly (30) having an optical element (117), wherein the optical element (Mx, 117) includes a body (31), and at least two actuators (35) that deform the body (31) are arranged on the back side of the body (31), the at least two actuators (35) are connected to the back side (33) of the body at a first connection surface and to a back plate (36) at a second connection surface, and the back plate (36) is attached only via the actuators (35), in the optical assembly (30), The optical assembly wherein the backplate (36) has a varying thickness over its lateral range, and at least one sensor (49) is provided on the backplate (36).

2. In the optical assembly (30) according to claim 1, An optical assembly in which at least one separation element for lateral separation is disposed between the actuator (35) and at least the main body (31) and / or the backplate (36).

3. In the optical assembly (30) according to claim 1 or 2, The back side (33) of the main body is an optical assembly having at least one flat portion.

4. In the optical assembly (30) according to claim 1 or 2, The aforementioned body (31) is an optical assembly whose thickness varies over its lateral range.

5. In the optical assembly (30) according to claim 1 or 2, The backplate (36) and / or the body (31) have a notch (121) in which the actuator (35) is at least partially positioned, in an optical assembly.

6. In the optical assembly (30) according to claim 1 or 2, The back side (33) of the main body has a plurality of flat portions that do not extend parallel to each other, forming an optical assembly.

7. In the optical assembly (30) according to claim 6, An optical assembly having a plurality of flat backplates (36), each aligned parallel to the aforementioned flat portion.

8. In the optical assembly (30) according to claim 1 or 2, An optical assembly in which at least one effective direction of the actuator (35) is perpendicular to the connection surface of the actuator (35) with the body (31).

9. In the optical assembly (30) according to claim 1 or 2, An optical assembly in which at least one effective direction of the actuator (35) is perpendicular to the optically effective surface (32).

10. In the optical assembly (30) according to claim 1 or 2, An optical assembly in which at least two actuators (35) with different characteristics are formed.

11. In the optical assembly (30) according to claim 1 or 2, The optical assembly is an optical element (Mx, 117) which is a mirror.

12. In the optical assembly (30) according to claim 11, The aforementioned mirror (Mx, 117) is a concave mirror with a radius of curvature of 180 mm to 260 mm, particularly about 220 mm, in an optical assembly.

13. In the optical assembly (30) according to claim 1 or 2, The backplate (36) is an optical assembly having lower rigidity than the main body (31).

14. In the optical assembly (30) according to claim 1, An optical assembly in which at least one sensor (49) is a strain sensor or a temperature sensor (49).

15. An optical assembly (30) having an optical element (117), wherein the optical element (Mx, 117) includes a body (31), and at least two actuators (35) that deform the body (31) are arranged on the back side of the body (31), the at least two actuators (35) are connected to the back side (33) of the body at a first connection surface and to a back plate (36) at a second connection surface, and the back plate (36) is attached only via the actuators (35), in the optical assembly (30), The optical assembly has a plurality of flat back plates (36) on the back side (33) of the main body, which have a plurality of flat portions that do not extend parallel to each other, and each of these flat portions is aligned parallel to the flat back plates.

16. In the optical assembly (30) according to claim 15, An optical assembly in which at least one separation element for lateral separation is disposed between the actuator (35) and at least the main body (31) and / or the backplate (36).

17. In the optical assembly (30) according to claim 15 or 16, The aforementioned body (31) is an optical assembly whose thickness varies over its lateral range.

18. In the optical assembly (30) according to claim 15 or 16, The backplate (36) and / or the body (31) have a notch (121) in which the actuator (35) is at least partially positioned, in an optical assembly.

19. An optical assembly (30) having an optical element (117), wherein the optical element (Mx, 117) includes a body (31), and at least two actuators (35) that deform the body (31) are arranged on the back side of the body (31), the at least two actuators (35) are connected to the back side (33) of the body at a first connection surface and to a back plate (36) at a second connection surface, and the back plate (36) is attached only via the actuators (35), in the optical assembly (30), An optical assembly in which the surface of at least one backplate (36) facing toward the main body (31) and the surface of at least one backplate (36) facing away from the main body (31) extend at a certain distance from the back side (33) of the main body.

20. In the optical assembly (30) according to claim 15 or 16, An optical assembly in which at least one effective direction of the actuator (35) is perpendicular to the first connection surface of the actuator (35) with the body (31).

21. In the optical assembly (30) according to claim 15 or 16, An optical assembly in which at least one effective direction of the actuator (35) is perpendicular to the optically effective surface (32).

22. In the optical assembly (30) according to claim 15 or 16, An optical assembly in which at least two actuators (35) with different characteristics are formed.

23. In the optical assembly (30) according to claim 15 or 16, The optical assembly is an optical element (Mx, 117) which is a mirror.

24. In the optical assembly (30) according to claim 23, The aforementioned mirror (Mx, 117) is a concave mirror with a radius of curvature of 180 mm to 260 mm, particularly about 220 mm, in an optical assembly.

25. In the optical assembly (30) according to claim 15 or 16, The backplate (36) is an optical assembly having lower rigidity than the main body (31).

26. In the optical assembly (30) according to claim 15 or 16, An optical assembly in which at least one sensor (49) is provided on the back plate (36).

27. In the optical assembly (30) according to claim 26, An optical assembly in which at least one sensor (49) is a strain sensor or a temperature sensor (49).

28. A projection exposure apparatus (1,101) for semiconductor lithography, comprising an optical assembly (30) according to claim 1, 2, 15, or 16.

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