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, the content of which 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 a 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 regularly occur 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, as desired 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 high expenditures are required to meet the requirements imposed on the manufacturing tolerances and assembly tolerances of the actuator and the back plate.

SUMMARY OF THE INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

[0005] The problem addressed by the present invention is to identify an optical assembly and a projection exposure apparatus that reduce the adverse effects caused by a backplate connected to an actuator as 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 object is achieved by an apparatus and a method having the features set forth in the independent claims. The dependent claims relate to advantageous developments and variants of the present invention.

[0007] The optical assembly according to the present invention comprises an optical element, the optical element includes a body, and at least one actuator that functions to deform the body is disposed 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 backplate at a second connection surface, and the backplate is attached only via the actuators.

[0008] In other words, the only connection between the backplate and the "fixed environment" is at at least two actuators or usually a plurality of actuators. In particular, the actuator can be a piezo actuator or a solid actuator such as a magnetostrictive, electrostrictive, or thermal actuator. Therefore, the uniform expansion of all solid actuators perpendicular to the connection surface, for example due to heat, only leads to deformation of the backplate and does not affect the shape and orientation of the optically effective surface. Creep of the actuator, as is known, often occurs especially during the switch-on procedure, that is, the actuator does not stabilize immediately after switch-on and moves to the desired state. However, since the actuators usually behave similarly in this case, this effect is generally corrected by a free backplate or no unwanted deformation occurs.

[0009] Furthermore, even if there is a certain temperature gradient across the optical assembly, it only leads to an inclination of the backplate and does not lead to displacement or deformation of the optically effective surface.

[0010] In addition to the defects resulting from uniform changes in all actuators, the solution according to the invention can also suppress parasitic effects from the joining technology. In particular, this includes volume changes due to heat or moisture of the joining material in a direction perpendicular to the connection surface. In this regard, the joining material is understood to mean any material that establishes the joining of the actuator with an adjacent component (in this case the body and the backplate). Examples for this purpose are adhesives, glass frits, solders, welding filler metals, reaction layers formed by reaction bonding, etc.

[0011] Since many actuators cause not only the desired elongation in the operating direction but also a change in the actuator shape in the transverse direction that can lead to parasitic deformations, in a particularly preferred embodiment, at least one separating element for transverse separation is arranged between the actuator and at least the body and / or the backplate.

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

[0013] In an advantageous variant of the invention, the back side of the body has at least one flat portion. The resulting flat joining points enable the use of a simple manufacturing method with good roughness and very good shape tolerances or flatness. Particularly to be mentioned here are grinding, lapping, surface honing, and surface polishing. Therefore, it is possible to use joining methods that only allow compensation of small mechanical tolerances. In particular, this includes the joining methods mentioned above.

[0014] In particular, the body can vary in thickness across its lateral extent. For example, due to installation space requirements, it may be necessary to manufacture the body to be locally thinner. In this case, it may be necessary to adapt the embodiments of each actuator and / or backplate as appropriate.

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

[0016] To save installation space, it may also be a good idea for the backplate and / or the body to have cutouts in which the actuators are at least partially arranged.

[0017] In particular, in the case of a mirror that is strongly curved as an optical element, it may be advantageous for the back side of the body to have a plurality of flat portions that do not extend parallel to each other. Thereby, the variation in the total thickness of the body is limited, so that the variation in its mechanical properties across that range can also be kept within a controllable range.

[0018] In particular, in this case, it is advantageous to have a plurality of flat backplates each aligned parallel to the flat portion.

[0019] In an advantageous embodiment of the present invention, the surface of the backplate facing the body and the surface of the backplate facing away from the body extend at a constant distance from the back side of the body, respectively. For example, thereby, a backplate of a constant thickness can be obtained. This variant is also conceivable when the optical element is embodied as a spherical mirror having a body of constant thickness. In this case, the backplate is a substantially similar mapping of the 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] In particular, 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 consider 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 with respect to, for example, their intrinsic rigidity, moving distance, or applicable maximum 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 folding the beam path 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 be provided with, for example, 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 back plate 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 back plate 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 back plate using, for example, a fiber Bragg grating sensor. When the mechanical characteristics of the actuator, the main body, and the back plate are known, the corresponding deformation of the optically effective surface can be estimated based on a model from the local deformation of the back plate.

[0026] In yet another embodiment, the characteristics (the thermal expansion coefficient and thickness of the actuator used) can be selected so that a specified 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 be due to 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 back plate, determining the surface tolerance of the connection surface of the actuator facing away from the back plate, machining the connection surface, repeating the previous two steps until the surface tolerance becomes less than a predetermined threshold, connecting the actuator to the main body and.

[0029] At that time, the optically effective surface can be processed after the actuator is assembled. This method can be implemented particularly advantageously when a plurality of actuators are arranged on the back plate and their connection surfaces can be processed together.

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

Brief Description of the Drawings

[0031]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7a

Figure 7b

Figure 8a

Figure 8b

Figure 8c

Figure 9

Figure 10

Figure 11

Modes for Carrying Out the Invention

[0032] The essential components of the microlithographic projection exposure apparatus 1 will first be exemplarily described with reference to FIG. 1. It should not be understood here that the description of the basic structure of the projection exposure apparatus 1 and its components is non-limiting.

[0033] One embodiment of the illumination system 2 of the projection exposure apparatus 1 has, in addition to the radiation source 3, an illumination optical unit 4 that illuminates the object field 5 of the 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. In this case, the illumination system does not include the light source 3.

[0034] The reticle 7 arranged in the object field 5 is illuminated. The reticle 7 is held by a reticle holder 8. The reticle holder 8 is displaceable, in particular in the scanning direction, by a reticle displacement drive 9.

[0035] For the sake of explanation, a Cartesian xyz coordinate system is shown in FIG. 1. The x-direction extends perpendicular to the plane of the figure. The y-direction extends horizontally and the z-direction extends vertically. In FIG. 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 comprises a projection optical unit 10. The projection optical unit 10 serves to image the object field 5 onto the image field 11 of the image plane 12. The image plane 12 extends parallel to the object plane 6. Alternatively, an angle other than 0° is also possible between the object plane 6 and the image plane 12.

[0037] The structure on the reticle 7 is imaged onto the photosensitive layer of the wafer 13 arranged in the region of the image field 11 of the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 is displaceable, in particular in the y-direction, by a wafer displacement drive 15. The displacement of the reticle 7 by the reticle displacement drive 9 and the displacement of the wafer 13 by the wafer displacement drive 15 can be implemented to be synchronized with each other.

[0038] The radiation source 3 is an EUV radiation source. The radiation source 3 emits EUV radiation 16, which is also particularly referred to as the radiation for use, illumination radiation, or illumination light hereinafter. In particular, the radiation for use has a wavelength in the range of 5 nm to 30 nm. The radiation source 3 can be a plasma source, such as an LPP (laser-produced plasma) source or a GDPP (gas-discharge plasma) source. This can also be a synchrotron-based radiation source. The radiation source 3 can be a free electron laser (FEL).

[0039] The illumination radiation 16 emitted from the radiation source 3 is focused by the collector 17. The collector 17 can be a collector having one or more elliptical reflecting surfaces and / or hyperbolic reflecting surfaces. The illumination radiation 16 can be incident on at least one reflecting surface of the collector 17 at a grazing incidence (GI), that is, at an incident angle greater than 45° with respect to the direction of the normal to the mirror surface, or at a normal incidence (NI), that is, at an incident angle less than 45°. The collector 17 can be structured and / or coated in order to optimize the reflectivity with respect to the radiation for use first and to suppress the extraneous light second.

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

[0041] The illumination optical unit 4 includes a deflection mirror 19 and a first facet mirror 20 arranged downstream thereof in the beam path. The deflection mirror 19 can be a planar deflection mirror or a mirror having a beam influence effect exceeding the pure deflection effect. Alternatively or additionally, the deflection mirror 19 can be embodied in the form of a spectroscopic filter that separates the illumination radiation 16 from extraneous light having a wavelength deviated from the wavelength of the light wave for use. When the first facet mirror 20 is arranged in the plane of the illumination optical unit 4 that is optically conjugate to the object plane 6 as the field plane, this facet mirror is also referred to as the field facet mirror. The first facet mirror 20 includes a plurality of individual first facets 21, which are also referred to as field facets hereinafter. FIG. 1 shows only some of the facets 21 as an example.

[0042] The first facet 21 can be embodied as a macroscopic facet, in particular as a rectangular facet, or as a facet having an arcuate edge contour or a partial circular edge contour. The first facet 21 can be embodied as a planar facet or as a facet curved convexly or concavely.

[0043] As is known, for example, from German Patent Application Publication No. 10 2008 009 600, the first facet 21 itself can also be composed of a plurality of individual mirrors, in particular a plurality of micromirrors. The first facet mirror 20 can be embodied in particular as a microelectromechanical system (MEMS system). For details, reference is made 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 arranged downstream of the first facet mirror 20. When the second facet mirror 22 is arranged at 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 arranged 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 US Patent Application Publication No. 2006 / 0132747, European Patent No. 1 614 008, and US Patent No. 6,573,978.

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

[0047] Similarly, the second facet 23 can be a macroscopic facet that can have edges, for example, in the shape of a circle, rectangle, or hexagon, or it can be a facet composed of micromirrors. In this regard, reference is also made to German Patent Application Publication No. 10 2008 009 600.

[0048] The second facet 23 can have a planar reflecting surface or a reflecting surface that is curved convexly or concavely.

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

[0050] It may be advantageous not to accurately place the second facet mirror 22 in a plane optically conjugate to the pupil plane of the projection optical unit 10. In particular, the pupil facet mirror 22 can be arranged inclined with respect to the pupil plane of the projection optical unit 10, as described, for example, in German Patent Application Publication No. 10 2017 220 586.

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

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

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

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

[0055] The imaging of the first facet 21 onto the object plane 6 by means of the second facet 23 or using the second facet 23 and the transfer optical unit is usually only an approximate imaging.

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

[0057] In the example shown in FIG. 1, the projection optical unit 10 includes six mirrors M1 to M6. Substitutions with 4, 8, 10, 12, or any other number of mirrors Mi are equally possible. The penultimate mirror M5 and the final mirror M6 each have a passage aperture for the illumination radiation 16. The projection optical unit 10 is a double shielding 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 reflecting surface of the mirror Mi can be embodied as a freeform surface without an axis of rotational symmetry. Alternatively, the reflecting surface of the mirror Mi can be designed as an aspherical surface with exactly one axis of rotational symmetry of the reflecting surface shape. Similar to the mirrors of the illumination optical unit 4, the mirror Mi can have a high-reflection coating for the 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 can 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. In particular, this means different imaging scales β in the x and y directions x , β y . The two imaging scales β of the projection optical unit 10 x , β y are preferably (β x , β y ) = (+ / -0.25, + / -0.125). A positive imaging scale β means imaging without image inversion. A negative sign of the imaging scale β means imaging with image inversion.

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

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

[0063] Other imaging scales are likewise possible. Imaging scales with the same sign and the same absolute value in the x and y directions, for example an absolute value of 0.125 or 0.25, 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 be different depending on the design of the projection optical unit 10. An example of a projection optical unit with different numbers of such intermediate images in the x and y directions is known from US Patent Application Publication No. 2018 / 0074303.

[0065] Each of the pupil facets 23 is assigned to exactly one of the field facets 21 to form an illumination channel for illuminating the object field 5. Thereby, illumination according to the Koehler principle can be obtained in particular. The far field is decomposed into a plurality of object fields 5 using the field facets 21. The field facets 21 generate a plurality of images of the intermediate focus for the pupil facets 23 assigned to each of them.

[0066] The field facets 21 are imaged onto the reticle 7 overlapping each other by the assigned pupil facets 23 to illuminate the object field 5. The illumination of the object field 5 is particularly uniform as much as possible. The uniformity error is preferably less than 2%. By superimposing different illumination channels, field uniformity can be obtained.

[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 a light-guiding illumination channel, in particular a subset of the pupil facets, the intensity distribution at 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 favorable pupil uniformity in the region of the defined illumination portion of the illumination pupil of the illumination optical unit 4 can be achieved by redistributing the illumination channels.

[0069] A further aspect and details of the illumination of the object field 5, in particular of the entrance pupil of the projection optical unit 10, will be explained below.

[0070] The projection optical unit 10 can in particular have a concentric entrance pupil. This can be made accessible. This can also be made inaccessible.

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

[0072] The projection optical unit 10 may have different entrance pupil positions in the tangential beam path and the sagittal beam path. In this case, the imaging element, particularly the optical components of the transfer optical unit, should be provided between the second facet mirror 22 and the reticle 7. Using this optical element, the difference in the positions of the tangential entrance pupil and the sagittal entrance pupil can be taken into account.

[0073] In the arrangement of the components of the illumination optical unit 4 shown in FIG. 1, the pupil facet mirror 22 is arranged on a plane conjugate to the entrance pupil of the projection optical unit 10. The field facet mirror 20 is arranged to be inclined with respect to the object plane 6. The first facet mirror 20 is arranged to be inclined with respect to the arrangement plane defined by the deflection mirror 19.

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

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

[0076] The configuration and imaging principle of the projection exposure apparatus 101 are equivalent to the configuration and procedure described in FIG. 1. The same components are denoted by reference numerals that are 100 more than those in FIG. 1. Thus, the reference numerals in FIG. 2 start from 101.

[0077] Unlike the EUV projection exposure apparatus 1 described with reference to FIG. 1, since the wavelength of the DUV radiation 116 used as the light to be used is in the range of 100 nm to 300 nm, particularly as large as about 193 nm, refractive, diffractive, and / or reflective optical elements 117 such as lens elements, mirrors, prisms, and end plates can be used for imaging or illumination in the DUV projection exposure apparatus 101. In this case, the projection exposure apparatus 101 essentially includes an illumination system 102, a reticle holder 108 that houses and accurately positions a reticle 107 provided with 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 a mount 118 in a lens housing 119 of the projection lens 110.

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

[0079] In addition to using additional refractive optical elements 117 such as lens elements, prisms, and end plates, the structure of the downstream projection optical unit 110 having the lens housing 119 is basically different from the structure described with reference to FIG. 1, and thus will not be described in further detail.

[0080] In the schematic diagram, FIG. 3 shows an embodiment of the present invention, in which an optical assembly 30 is illustrated. The optical assembly 30 includes an optical element designed as mirrors Mx, 117 and usable in one of the projection exposure apparatuses 1, 101 described with reference to FIGS. 1 and 2, an actuator 35, and a support structure designed as a backplate 36. The mirrors Mx, 117 include a body 31 having an optically effective surface 32, and the body 31 is mounted on bearings 34, for example, on the frame of the projection exposure apparatuses 1, 101. The actuator 35 is disposed 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 to 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] By a controller (not shown either), the actuator 35 is controlled such that the deflection of the actuator 35 causes deformation of the optically effective surface 32. Since the backplate 36 is deformed as a result of different degrees of deflection of the actuator 35, deformation of the body 31, and thus deformation of the optically effective surface 32, occurs according to the ratio of the rigidity of the body 31 to the rigidity of the backplate 36. Therefore, some of the actuators 35 can hold the backplate securely in its position, and another part of the actuator 35 can be supported on the backplate 36, thereby causing deformation. In this case, the backplate 36 is attached only by the actuator 35 and is not connected to the frame, the body 31 of the mirrors Mx, 117, or any other component. This is advantageous because a uniform effect acting equally on all the actuators 35, such as a temperature increase or a drift in the control of the actuator 35, does not affect the optically effective surface 32 and only leads to displacement of the free backplate 36. In the figure, three strain sensors 49, which function to measure the deformation of the backplate 37.3, are shown as an example on the backplate 37.3.

[0082] Figure 4 shows yet another embodiment of the present invention, and illustrates an optical assembly 30 having an optical element that is designed as a mirror Mx, 117 and can be used in one of the projection exposure apparatuses 1, 101 described with reference to FIGS. 1 and 2. The mirror Mx, 117 includes a body 31 having an optically effective surface 32 formed in a concave shape. The optical assembly 30 also includes a backplate 36 and an actuator 35 disposed 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 can also be disposed in a plane and can be post-processed to optimally conform to the back side 33 after an 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 influence of the adhesive on the connection rigidity is negligible. The laterally varying material thickness of the body 31 can be compensated by different designs of the actuator and the control of the actuator 35.

[0083] Figure 5 shows yet another embodiment of the present invention, and illustrates an optical assembly 30 having an optical element that is designed as a mirror Mx, 117 and can be used in one of the projection exposure apparatuses 1, 101 described with reference to FIGS. 1 and 2. The mirror Mx, 117 includes a body 31 having an optically effective surface 32 formed in a concave shape. The optical assembly 30 further includes three backplates 37.1, 37.2, 37.3 and an actuator 35 disposed 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 in the form of three flat surfaces and the optically effective surface 32 is minimized compared to the embodiment described with reference to FIG. 4. As already described with reference to FIG. 4, the backplates 37.1, 37.2, 37.3 are flat and can thus be easily manufactured, and the actuator 35 can be in the form of a standard actuator.

[0084] FIG. 6 shows yet another embodiment of the present invention, and illustrates an optical assembly 30 having an optical element that is designed as a mirror Mx, 117 and can be used in one of the projection exposure apparatuses 1, 101 described with reference to FIGS. 1 and 2. The mirror Mx, 117 includes a body 31 having an optically effective surface 32 formed in a concave shape. Different from the body shown in FIG. 5, the body 31 of the illustrated embodiment has a constant thickness, whereby a convex or spherical back side 33 is obtained. The optical assembly 30 further includes a concave back plate 39 corresponding to the shapes of the optically effective surface 32 and the body 31. The actuator 35 includes spherical joint surfaces 38 on both sides to ensure a constant thickness of the adhesive gap in the adhesive connection. The back plate 39 and the body 31 having a constant thickness are advantageous because the rigidity of these components is constant, and thus all actuators need to apply equal forces to bring about the same deformation of the optically effective surface 32. As a result, an increase in the number of similar components reduces the manufacturing cost.

[0085] FIGS. 7a and 7b show yet another embodiment of the present invention in two operating states, and illustrate an optical assembly 30 having an optical element that is designed as a mirror Mx, 117 and can be used in one of the projection exposure apparatuses 1, 101 described with reference to FIGS. 1 and 2. The mirror Mx, 117 includes a body 31 having a flat optically effective surface 32. Further, the optical assembly 30 includes four back plates 40.1, 40.2, 40.3, 40.4. Two shear actuators 41 each performing a shear motion parallel to the optically effective surface 32 when a voltage is applied are disposed between each of the back plates 40.1, 40.2, 40.3, 40.4 and the back side 33 of the body 31.

[0086] In this case, FIG. 7a shows a so-called zero state in which the optically effective surface 32 of the body 31 is not deformed, that is, corresponding to its target surface shape. The shear actuator 41 deflects from the zero position without voltage application, and as a result, the body 31 is deformed in one direction from its zero position according to the applied voltage. This is advantageous because the optically effective surface 32 can be fully processed before the assembly of the actuator 41.

[0087] Figure 7b shows the same optical assembly 30 in a flexed operating state. The actuator 41 disposed between the two central backplates 40.2, 40.3 and the body 31 flexes, causing deformation of the body 31 and thus deformation of the optically effective surface 32. In Figure 7b, the actuators of both backplates 40.2, 40.3 are flexed relative to each other, but only one actuator 41 of the backplates 40.1, 40.2, 40.3, 40.4 may flex, or one actuator 41 may flex from each of two adjacent backplates 40.1, 40.2, 40.3, 40.4.

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

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

[0090] Figure 8b schematically shows a schematic structure of a bimorph actuator 46 including a first actuator layer 47 and a second actuator layer 48. Since the two actuator layers 47, 48 can be flexed in opposite directions (indicated by arrows in Figure 8b), deformation of the actuator 46 is caused by one actuator layer 47 stretching and the other actuator layer 48 shrinking.

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

[0092] FIG. 9 shows an advantageous variant of the present invention that utilizes a separating element 120. In this case, the body 31 is connected to a free back plate 36 by an actuator 35 in the form as already described. In the illustrated example, the mechanical separation in the connection region between the actuator 35 and the body 31 is achieved by a separating element embodied as a cut 120 in the body 31. For example, when the actuator 35 is embodied as a cylindrical solid actuator, the separating element 120 can be realized as an annular groove extending over the entire circumference. In the illustrated example, the separating element 120 is formed only in the body 31. It is obvious that corresponding measures can also be considered for the back plate 36.

[0093] FIG. 10 shows an embodiment according to the present invention in which the thickness of the back plate 36' is designed to vary in the lateral direction. Further, the back plate 36' shows a notch 121 in which the actuator 35 is partially arranged. By varying the thickness of the back plate 36' in the lateral direction, the rigidity of the back plate 31' can be made equivalent to that of the inner region even in the edge region. Further, by arranging the actuator 35 in the notch 121, a certain installation space can be saved. In this regard, it is not necessary to necessarily use the measures shown in FIG. 10 in combination. Of course, it is also conceivable to use only a back plate with a thickness that varies in the lateral direction or a back plate having a notch.

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

[0095] In a first method step 51, an actuator is connected to a backplate.

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

[0097] In a third method step 53, the connection surface is machined.

[0098] In a fourth method step 54, the previous two steps are repeated until the surface tolerance is less than a predetermined threshold value.

[0099] In a fifth method step 55, the actuator is connected to the body.

Explanation of reference numerals

[0100] 1 Projection exposure apparatus 2 Illumination system 3 Radiation source 4 Illumination optical unit 5 Object field of view 6 Object plane 7 Reticle 8 Reticle holder 9 Reticle displacement drive 10 Projection optical unit 11 Image field of view 12 Image plane 13 Wafer 14 Wafer holder 15 Wafer displacement drive 16 EUV radiation 17 Collector 18 Intermediate focal plane 19 Deflection mirror 20 Facet mirror 21 Facet 22 Facet mirror 23 Facet 30 Optical assembly 31 Body 32 Optically effective surface 33 Back side of the body 34 Bearing of the body 35 Actuator 36, 36’ Back plate 37.1~37.3 Divided back plate 38 Spherical joint surface 39 Back plate 40.1~40.4 Divided back plate 41 Shearing actuator 42 Shearing actuator 43 End face 44 Vertical actuator 45 Long side 46 Bimorph actuator 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 Illumination system 107 Reticle 108 Reticle holder 110 Projection optical unit 113 Wafer 114 Wafer holder 116 DUV radiation 117 Optical element 118 Mount 119 Lens housing M1~M6 Mirrors 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 function to deform the body (31) are disposed 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 are connected 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 back plate (36') has a thickness that varies over its lateral extent.

2. In the optical assembly (30) according to Claim 1, An optical assembly, wherein at least one separating element for lateral separation is disposed between the actuator (35) and at least the body (31) and / or the back plate (36).

3. In the optical assembly (30) according to Claim 1 or 2, The optical assembly, wherein the back side (33) of the body has at least one flat portion.

4. In the optical assembly (30) according to any one of Claims 1 to 3, The optical assembly, wherein the body (31) has a thickness that varies over its lateral extent.

5. In the optical assembly (30) according to any one of Claims 1 to 4, The optical assembly, wherein the back plate (36') and / or the body (31) has a notch (121) in which the actuator (35) is at least partially disposed.

6. In the optical assembly (30) according to any one of Claims 1 to 5, The optical assembly, wherein the back side (33) of the body has a plurality of flat portions that do not extend parallel to each other.

7. In the optical assembly (30) according to Claim 6, The optical assembly, wherein there are a plurality of flat back plates (36) each aligned parallel to the flat portion.

8. In the optical assembly (30) according to any one of Claims 1 to 7, The optical assembly, wherein at least one effective direction of the actuator (35) occurs perpendicular to the connection surface of the actuator (35) with the body (31).

9. In the optical assembly (30) according to any one of Claims 1 to 8, An optical assembly in which at least one effective direction of the actuator (35) occurs perpendicular to the optically effective surface (32). **Claim 10** In the optical assembly (30) according to any one of claims 1 to 9, An optical assembly in which at least two actuators (35) having different characteristics are formed. **Claim 11** In the optical assembly (30) according to any one of claims 1 to 10, The optical element (Mx, 117) is a mirror, particularly a multilayer mirror, in the optical assembly. **Claim 12** In the optical assembly (30) according to claim 11, The mirror (Mx, 117) is a concave mirror having a radius of curvature of 180 mm to 260 mm, particularly about 220 mm, in the optical assembly. **Claim 13** In the optical assembly (30) according to any one of claims 1 to 12, The backplate (36) has lower rigidity than the main body (31) in the optical assembly. **Claim 14** In the optical assembly (30) according to any one of claims 1 to 13, At least one sensor (49) is provided on the backplate (36) in the optical assembly. **Claim 15** In the optical assembly (30) according to claim 14, The at least one sensor (49) is a strain sensor or a temperature sensor (49) in the optical assembly. **Claim 16** An optical assembly (30) having an optical element (117), wherein the optical element (Mx, 117) includes a main body (31), and at least two actuators (35) that function to deform the main body (31) are disposed on the back side of the main body (31), the at least two actuators (35) are connected to the back side (33) of the main body at a first connection surface and are connected to a backplate (36) at a second connection surface, and the backplate (36) is attached only via the actuator (35), in the optical assembly (30). The back side (33) of the main body has a plurality of flat portions that do not extend parallel to each other, and there are a plurality of flat backplates (36) each aligned parallel to the flat portion, in the optical assembly. **Claim 17** In the optical assembly (30) according to claim 16, At least one separating element for lateral separation is disposed between the actuator (35) and at least the main body (31) and / or the backplate (36) in the optical assembly. **Claim 18** In the optical assembly (30) according to claim 16 or 17, the body (31) has a thickness that varies across its lateral extent, the optical assembly.

19. In the optical assembly (30) according to any one of claims 16 to 18, the backplate (36') and / or the body (31) has a notch (121) in which the actuator (35) is at least partially disposed, the optical assembly.

20. In the optical assembly (30) according to any one of claims 16 to 19, the surfaces of at least one backplate (36) facing the body (31) and the surfaces of at least one backplate (36) facing away from the body (31) extend a certain distance from the back side (33) of the body, the optical assembly.

21. In the optical assembly (30) according to any one of claims 16 to 20, at least one effective direction of the actuator (35) occurs perpendicular to the connection surface of the actuator (35) with the body (31), the optical assembly.

22. In the optical assembly (30) according to any one of claims 16 to 21, at least one effective direction of the actuator (35) occurs perpendicular to the optically effective surface (32), the optical assembly.

23. In the optical assembly (30) according to any one of claims 16 to 22, at least two actuators (35) with different characteristics are formed, the optical assembly.

24. In the optical assembly (30) according to any one of claims 16 to 23, the optical element (Mx, 117) is a mirror, in particular a multilayer mirror, the optical assembly.

25. In the optical assembly (30) according to claim 24, the mirror (Mx, 117) is a concave mirror with a radius of curvature of 180 mm to 260 mm, in particular approximately 220 mm, the optical assembly.

26. In the optical assembly (30) according to any one of claims 16 to 25, the backplate (36) is less rigid than the body (31), the optical assembly.

27. In the optical assembly (30) according to any one of claims 16 to 26, at least one sensor (49) is provided on the backplate (36), the optical assembly.

28. In the optical assembly (30) according to claim 27, the at least one sensor (49) is a strain sensor or a temperature sensor (49), the optical assembly. **Claim 29** A projection exposure apparatus (1, 101) for semiconductor lithography, having the optical assembly (30) according to any one of claims 1 to 28. **Claim 30** A method of manufacturing an optical assembly (30) having an optical element (117), the optical element (Mx, 117) including a body (31) having an optically effective surface (32), at least one actuator (35) for deforming the optically effective surface (32), and a backplate (36), the actuator (35) being disposed between the body (31) and the backplate (36), the method comprising: connecting the actuator to the backplate; determining a surface tolerance of a 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; and connecting the actuator to the body. The method comprising. **Claim 31** In the method according to claim 30, the optically effective surface (32) is machined after assembly of the actuator (35), the method. **Claim 32** In the method according to claim 30 or 31, a plurality of actuators (35) are disposed on the backplate (36), the method.

Images