Optical Element for Semiconductor Lithography and Projection Exposure Apparatus

Abstract

The present invention relates to an optical element (Mx, 117) of a projection exposure apparatus (1, 101) for semiconductor lithography, comprising a main body (30) and at least one actuator (40) connected to the main body (30), wherein the actuator (40) is designed as a ring actuator. The present invention relates to a projection exposure apparatus for semiconductor lithography provided with the optical element, and to an optical element provided with a sensor for determining deformation of an optically effective surface, the sensor being designed to detect a signal correlated with the deformation of the optically effective surface.

Description

Technical Field

[0001] This application claims the priority of German Patent Application No. 10 2022 116 699.6 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 element described in the preamble of claim 1 and a projection exposure apparatus for semiconductor lithography including the optical element.

Background Art

[0003] In this type of projection exposure apparatus, using photolithography, a microscopic small structure is imaged from a mask as a template onto a wafer coated with photoresist. In subsequent development and further processing steps, a desired structure, such as a memory or logic element, is created on the wafer and then divided into individual chips used in electronic devices.

[0004] By creating very small structures down to the nanometer range, the requirements for the optical unit of the projection exposure apparatus, and thus the optical elements used, become extreme. Furthermore, imaging aberrations, which often occur during the operation of the apparatus due to changes in ambient conditions such as temperature changes in the optical unit, frequently occur.

[0005] This problem is usually addressed by designing the optical elements in use, such as lens elements or mirrors, to be movable or deformable in order to enable correction of the above imaging aberrations during the operation of the apparatus. For this purpose, for example, mechanical actuators that may be suitable for deforming the surface of the optical element used for imaging, that is, the so-called optically effective surface, in a targeted manner are generally utilized. This deformation can be performed from the back side of the main body of the optical element.

[0006] The usual problem regarding arranging the actuator on the back side of the main body is to form a reliable mechanical connection between the actuator and the main body, and first, to ensure simple productivity, and second, to minimize the adverse effect of the connection technology on the optical performance of the optical element.

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to identify an optical element for semiconductor lithography and a projection exposure apparatus in which a simple arrangement of an actuator for mechanically operating the optical element is implemented.

Means for Solving the Problems

[0008] This object is achieved by an apparatus having the features described in the independent claims. The dependent claims relate to advantageous developments and variants of the present invention.

[0009] The optical element according to the present invention for a projection exposure apparatus for semiconductor lithography includes a main body and at least one actuator connected to the main body, and the actuator is configured as a ring actuator. In this case, the ring actuator can be connected to the main body via a connecting shaped portion. The actuator can be configured as a solid actuator, for example, a piezo actuator or an electrostrictive actuator. This serves to deform the main body and thus deform the optically effective surface in order to generate a desired surface profile of the optically effective surface for achieving a corresponding optical effect in this case. The optical element can particularly be a multilayer mirror of a projection exposure apparatus for semiconductor lithography. In this case, it should be understood that the ring actuator is a ring-shaped actuator that can particularly have a substantially hollow cylindrical basic shape. This selection of the geometric shape of the actuator is quite advantageous with respect to the integration or connectability of the actuator with the main body.

[0010] In this regard, for example, the connecting shaped portion can be configured as a pin arranged on the main body, and the ring actuator can simply be press-fitted onto the pin.

[0011] The body and the pin can be configured, in particular, monolithically, i.e., integrally, but it is also conceivable to connect the body and the pin to each other in an integrally joined manner. Furthermore, meshing engagement and interference fit engagement are also conceivable.

[0012] In a variant of the present invention, the connecting shaped portion can be configured as a notch provided in the body, and the notch conforms to the geometric shape outside the ring actuator.

[0013] The contact area of the ring actuator with respect to the connecting shaped portion of the body can be configured in a conical shape, and the contact area of the connecting shaped portion of the body with respect to the ring actuator can also be configured in a conical shape. By this measure, the attachment of the actuator to the connecting shaped portion is simplified. The attachment itself can be performed by shrink fitting. Other attachment techniques such as pre-bending the actuator by applying a voltage are also conceivable.

[0014] What is advantageous regarding the selection of the conical shaped portion is, in particular, that in this case a certain degree of fitting can be achieved by axial displacement. This expands the possibility of frictionally engaging and thus fixing the ring actuator to the pin or notch, for example by pressing. By the described measures, it is possible in principle to connect the ring actuator without using an adhesive, but the use of additional integrally joined connections is not excluded.

[0015] The actuator effect can be further improved by the connecting shaped portion of the ring actuator including a suitably designed mechanical transmission region. In this case, in particular, the transmission region can be configured to reduce the rigidity acting on the deflection of the ring actuator, so that the force applied by the actuator side can be kept appropriate.

[0016] In an advantageous embodiment of the present invention, the ring actuator is arranged between the body and the support structure. In this case, the support structure can include a connecting shape corresponding to the ring actuator, so that the actuator can be simply connected to the support structure.

[0017] In particular, the ring actuator can be connected to a connecting shape configured as a pin or notch of the body and the support structure.

[0018] With the rear support of the ring actuator, the expansion of both actuators can contribute to the deformation of the optically effective surface.

[0019] Furthermore, there are various possibilities for fixing the body and the support structure. In this regard, firstly, the body can be connected to a fixed environment, and the support structure can be connected to the body only through the actuator. It is also conceivable to connect the support structure to the fixed environment and hold the body through the actuator. It is also conceivable to connect the body and the support structure to each other.

[0020] When the body is attached via the actuator, it is conceivable to achieve the translational displacement of the body by controlling all the actuators simultaneously and in the same manner. However, the lateral contraction of the related actuator is expected to lead to parasitic effects. However, such effects can be minimized by one-time or periodic calibration.

[0021] In yet another variant of the present invention, the ring actuator is integrated into the support structure. In this regard, for example, the entire support structure can be manufactured from a piezoelectric material, and the actuator can be realized by incorporating an appropriate electrode geometry into the support structure.

[0022] The preferred operating direction of the ring actuator can be defined by arranging the electrodes and the actuator material of the ring actuator in layers in the radial or axial direction.

[0023] In the present invention, but also generally, it is advantageous if the optical element comprises a sensor for determining a deformation of the optically effective surface of the optical element and the sensor is designed to detect a signal correlated with the deformation of the optically effective surface. In this case, it is not necessarily required to directly measure the deformation of the optically effective surface. It is sufficient to record a signal that allows the deformation of the optically effective surface to be estimated.

[0024] To obtain such a signal, it is advantageous if the sensor comprises an interferometer, in particular a Fabry-Perot interferometer. The interferometer is advantageously extremely accurate and at the same time offers the possibility of non-contact measurement. In this case, it is further advantageous if both the body and the connecting shaped part comprise a relatively precisely manufactured optical surface that can be used as a reflecting surface of the interferometer.

[0025] The measurement techniques described are, in principle, suitable for a wide variety of optical elements, in particular the optical elements described in the present application. Thus, the optical element can be, for example, a deformable mirror.

[0026] In this case, the deformable mirror can be a force-operated mirror.

[0027] Furthermore, the deformable mirror can be a mirror actuated by a solid actuator.

[0028] The operating direction of the actuator can be aligned perpendicular to the contact area of the actuator with the optical element. Additionally or alternatively, the operating direction of the actuator can also be aligned parallel to the contact area of the actuator with the optical element.

[0029] If a ring actuator is used, the geometric shape of such an actuator can be utilized such that the sensor detects the deformation of the optically effective surface through the center of the ring actuator. This results in the advantage that the measurement can be carried out relatively close to the area of interest.

[0030] In principle, the present invention can be realized, for example, by using a piezo actuator that can act in two directions, that is, the expansion and contraction directions can be changed when the polarity of the control signal changes. A piezo actuator made of single-crystal lithium niobate (LiNbO3) is suitable for such applications, for example.

[0031] Exemplary embodiments and variations of the present invention will be described in more detail below with reference to the drawings.

Brief Description of the Drawings

[0032]

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Embodiments for Carrying Out the Invention

[0033] The essential components of the microlithographic projection exposure apparatus 1 will first be exemplarily described below with reference to FIG. 1. It should be understood here that the description of the basic configuration of the projection exposure apparatus 1 and its components is non-limiting.

[0034] 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.

[0035] The reticle 7 disposed in the object field 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.

[0036] For the sake of explanation, a rectangular 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.

[0037] 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 on the image field of view 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.

[0038] The structure on the reticle 7 is imaged on the photosensitive layer of the wafer 13 disposed in the region of the image field of view 11 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. The displacement of the reticle 7 by the reticle displacement drive 9 first and the displacement of the wafer 13 by the wafer displacement drive 15 second can be performed in synchronization with each other.

[0039] The radiation source 3 is an EUV radiation source. The radiation source 3 emits EUV radiation 16, which is also particularly referred to as used radiation, illumination radiation, or illumination light hereinafter. In particular, the used radiation 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).

[0040] 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 obliquely (GI) on at least one reflecting surface of the collector 17, that is, at an incident angle greater than 45° with respect to the direction of the normal to the mirror surface, or normally incident (NI), that is, at an incident angle less than 45°. The collector 17 can be structured and / or coated, firstly, to optimize the reflectivity for the useful radiation and, secondly, to suppress the ambient light.

[0041] 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 the separation point between the radiation source module including the radiation source 3 and the collector 17 and the illumination optical unit 4.

[0042] 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 as a spectral filter that separates the useful wavelength of the illumination radiation 16 from the ambient light of wavelengths outside thereof. 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.

[0043] The first facet 21 can be embodied as a macroscopic facet, particularly 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 convexly or concavely curved facet.

[0044] 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 configured in particular as a microelectromechanical system (MEMS system). For details, reference may be made to German Patent Application Publication No. 10 2008 009 600.

[0045] Between the collector 17 and the deflection mirror 19, the illumination radiation 16 travels horizontally, i.e., in the y direction.

[0046] 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 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 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 mirror reflector. Mirror reflectors are known from US Patent Application Publication No. 2006 / 0132747, European Patent No. 1 614 008, and US Patent No. 6,573,978.

[0047] 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.

[0048] Similarly, the second facet 23 can be a macroscopic facet that may have, for example, a circular, rectangular, or hexagonal boundary, or a facet composed of micromirrors. In this regard, reference may also be made to German Patent Application Publication No. 10 2008 009 600.

[0049] The second facet 23 can have a planar reflecting surface, or a reflecting surface curved convexly or concavely.

[0050] Thus, the illumination optical unit 4 forms a dual-facets system. This basic principle is also referred to as a fly-eye condenser (fly-eye integrator).

[0051] It may be advantageous not to arrange the second facet mirror 22 exactly 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.

[0052] 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 actually the final mirror for the illumination radiation 16 in the beam path upstream of the object field of view 5.

[0053] In yet another embodiment (not shown) of the illumination optical unit 4, a transfer optical unit, which in particular 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 one after the other 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).

[0054] In the embodiment shown in FIG. 1, downstream of the collector 17, the illumination optical unit 4 has exactly three mirrors, specifically a deflection mirror 19, a field facet mirror 20, and a pupil facet mirror 22.

[0055] In yet another embodiment of the illumination optical unit 4, the deflection mirror 19 can also be omitted, so that in that case the illumination optical unit 4 can have exactly two mirrors, specifically a first facet mirror 20 and a second facet mirror 22, after the collector 17.

[0056] The imaging of the first facet 21 onto the object plane 6 by means of the second facet 23, or by means of the second facet 23 and the transfer optical unit, is generally only an approximate imaging.

[0057] The projection optical unit 10 includes a plurality of mirrors Mi, which are assigned consecutive numbers according to their arrangement in the beam path of the projection exposure apparatus 1.

[0058] 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 likewise 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 that is greater than 0.5, may be greater than 0.6, and can be, for example, 0.7 or 0.75.

[0059] The reflective surface of the mirror Mi can be embodied as a freeform surface without an axis of rotational symmetry. As an alternative, the reflective surface of the 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 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.

[0060] 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 5 and the y coordinate of the center of the image field 11. This object-image offset in the y direction can be approximately the same size as the z distance between the object plane 6 and the image plane 12.

[0061] In particular, the projection optical unit 10 can have an anamorphic configuration. In particular, this has different imaging scales βx, βy in the x- and y-directions. The two imaging scales βx, βy of the projection optical unit 10 are preferably (βx, βy) = (+ / -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.

[0062] 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.

[0063] The projection optical unit 10 reduces the size in the y-direction, i.e., by a factor of 8:1 in the scanning direction.

[0064] 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.

[0065] The number of intermediate image planes in the x- and y-directions in the beam path between the object field 5 and the image field 11 may be the same or may be different depending on the design of the projection optical unit 10. An example of a projection optical unit in which the number of such intermediate images in the x- and y-directions is different is known from US Patent Application Publication No. 2018 / 0074303.

[0066] 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. In particular, illumination according to Koehler's principle can thereby be obtained. 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 them.

[0067] The field facet 21 is imaged onto the reticle 7 in an overlapping manner by the assigned pupil facet 23 to illuminate the object field of view 5. The illumination of the object field of view 5 is particularly uniform as much as possible. The uniformity error is preferably less than 2%. The field uniformity can be obtained by overlapping different illumination channels.

[0068] 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 light - guiding illumination channels, particularly 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.

[0069] 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.

[0070] Further aspects and details of the illumination of the object field of view 5, particularly of the entrance pupil of the projection optical unit 10, will be described below.

[0071] The projection optical unit 10 can particularly have a concentric entrance pupil. This can be made accessible. This can also be made inaccessible.

[0072] The entrance pupil of the projection optical unit 10 generally cannot be accurately illuminated using the pupil facet mirror 22. In the case of imaging of the projection optical unit 10 that images the center of the pupil facet mirror 22 telecentrically onto the wafer 13, the aperture rays often do not intersect at a single point. However, it is possible to find the surface where the distance obtained for a pair of aperture rays is minimized. This surface represents the entrance pupil or the surface conjugate to it in real space. In particular, this surface exhibits a finite curvature.

[0073] The projection optical unit 10 may have different positions of the entrance pupil in the tangential beam path and the sagittal beam path. In this case, an optical element of the imaging device, particularly an optical component 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.

[0074] 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 so as to be inclined with respect to the object plane 6. The first facet mirror 20 is arranged so as to be inclined with respect to the arrangement plane defined by the deflection mirror 19.

[0075] The first facet mirror 20 is arranged so as to be inclined with respect to the arrangement plane defined by the second facet mirror 22.

[0076] 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 be similarly applied.

[0077] 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 with values increased by 100 from those in FIG. 1, that is, the reference numerals in FIG. 2 start from 101.

[0078] 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, end plates, etc. 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 whose structure is provided and 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.

[0079] The illumination system 102 supplies the DUV radiation 116 necessary for imaging the reticle 107 on the wafer 113. A laser, a plasma source, etc. 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.

[0080] In addition to using refractive optical elements 117 such as lens elements, prisms, end plates, etc. additionally, the configuration of the downstream projection optical unit 101 having the lens housing 119 is basically different from the configuration described with reference to FIG. 1, and thus will not be described in further detail.

[0081] Figure 3 shows a schematic view of the ring actuator 40 in three different operating states. At the top of Figure 3, the ring actuator 40 having a hollow cylindrical recess is shown in the zero state defined by half of the total possible deflection in the illustrated example. From this zero state, the ring actuator 40 can expand as shown at the lower left of Figure 3 or contract as shown at the lower right. As will be described in more detail later in Figure 15 in connection with the attachment and operation of the ring actuator 40, the zero state occurs in the case of a specific zero voltage of the zero state, and the expansion and contraction of the ring actuator 40 are caused by an increase or decrease in voltage by a controller (not shown). Alternatively, when an appropriate material is used, the zero state can also correspond to a zero voltage state. In this case, expansion is caused by the application of a voltage having a first polarity, and contraction is caused by the application of a voltage having the opposite polarity. Materials suitable for this are, for example, ceramic materials such as lead zirconate titanate (PZT), and further, for example, lithium niobate (LiNbO3) or lithium tantalate (LiTaO3).

[0082] Figures 4a and 4b show two different embodiments of the ring actuator 40 in which the arrangements of the electrodes 42 and the actuator material 41 with respect to the longitudinal axis of the ring actuator 40 are different.

[0083] Figure 4a shows the axial configuration of the layers of the actuator material 41 and the electrodes 42 connected to the controller 44 via the wire 43, which is known in the case of a rod actuator from the prior art. In the embodiment shown in Figure 4a, the electrode 42 is first arranged inside the ring actuator 40 and then outside the ring actuator 40, but it is also possible to contact both electrodes 42 only on the outside or only on the inside. The arrangement of the electrodes 42 can cause, for example, a primary deflection in the axial direction of the ring actuator 40, that is, perpendicular to the ring plane, and the radial expansion and contraction of the ring actuator 40 are only secondary effects.

[0084] Figure 4b shows the radial configuration of the ring actuator 40 in which the layers of the actuator material 41 and the electrodes 42 are configured radially. In this case, contact with the controller 44 is formed via the electric wires 43 on the upper and lower end faces of the ring actuator 40. As already explained in the case of Fig. 4a, an arrangement in which the contact of the electric wires 43 is only at the upper or lower part is also conceivable here. With this arrangement of the electrodes 42, a primary deflection in the radial direction of the ring actuator 40, that is, parallel to the ring plane, occurs, and the axial expansion and contraction of the ring actuator 40 are only secondary effects. In principle, it is advantageous that the ratio of expansion and contraction (the ratio of the change in radius to the change in the geometric shape along the axis of rotational symmetry) can be influenced by the selection of the electrostrictive material or piezoelectric material as well as the selection of the electrode positions. Thereby, it is possible to advantageously influence the deformation effect on the optically effective surface and thus the wavefront influence in the design.

[0085] Figure 5a shows a schematic view of a first embodiment of the present invention, showing an optical element applicable to one of the projection exposure apparatuses described with reference to Figs. 1 and 2 and configured as the mirror Mx, 117. Figure 5a shows the mirror Mx, 117 having the main body 30 with the optically effective surface 31 and the opposite back surface side 32, as seen from below, that is, from the back surface side 32 of the main body 30. The ring actuator 40 is arranged in the region corresponding to the optically effective surface 31, and the arrangement of the ring actuator 40 extends beyond the region of the optically effective surface 31 so as to be able to cause deformations having positive and negative gradients also in the edge region of the optically effective surface 31. This also requires the expansion and contraction of the ring actuator 40 from the so-called zero position. In principle, as long as the optically effective surface 31 is deformed when actuated, the ring actuator 40 can also be provided only in the edge region or in other places.

[0086] FIG. 5b shows yet another embodiment of the invention showing an optical element configured as mirrors Mx, 117, which mirrors comprise a body 30 having an optically effective surface 31, as do the mirrors Mx, 117 of FIG. 5b. The mirrors Mx, 117 are also shown in a perspective view seen from the back side. A connecting shaped part configured as a pin 45 for the ring actuator 40 is arranged on the back side 32. The ring actuator 40 is attached to the pin 45 by shrink fitting, as will be described in more detail later with reference to FIG. 14, although any other suitable technique, such as adhesive bonding or bonding, is also possible. The contraction or expansion of the ring actuator 40 leads to a constriction or expansion of the pin 45, which in turn causes a deformation of the optically effective surface 31. This deformation effect can be compared to that of an actuator acting parallel to the surface. In the case of the ring actuator 40, the axial component of the deflection is only a secondary contribution but contributes to the deformation. The resulting deformation of the optically effective surface 31 can be used to correct for the thermal expansion of the body 30 due to the absorption of electromagnetic radiation, or for correcting imaging aberrations occurring elsewhere in the projection exposure apparatus 1, 101.

[0087] FIG. 5c shows still another embodiment of the invention showing an optical element configured as a mirror Mx, 117, which mirror comprises a body 30 having an optically effective surface 31, as does the mirror Mx, 117 of FIG. 5b. The mirror Mx, 117 is also shown in a perspective view seen from the back side in this case. A connecting shaped portion configured as a notch 46 for the ring actuator 40 is arranged on the back side 32. The ring actuator 40 is attached to the notch 46 by shrink fitting, as will be described in more detail later with reference to FIG. 14, but other techniques such as adhesive bonding or bonding are also possible. The contraction or expansion of the ring actuator 40 leads to the contraction or expansion of the notch 46, which in turn causes deformation of the optically effective surface 31. This deformation effect can be compared with that of an actuator acting parallel to the surface. In the case of the ring actuator 40, the axial component of the deflection is only a secondary contribution but can contribute to the deformation. The resulting deformation of the optically effective surface 31 can be used for correcting the thermal expansion of the body 30 due to absorption of electromagnetic radiation, or for correcting imaging aberrations occurring at other locations of the projection exposure apparatus 1, 101.

[0088] FIGS. 6a and 6b show detailed views of the invention showing the ring actuator 40 shrink-fitted onto the pin 45 in two different operating states. Depending on the operating state of the ring actuator 40, the effect on the optically effective surface 31 of the body 30 is shown.

[0089] FIG. 6a shows the ring actuator 40 in a contracted operating state, where the pin causes an external deformation 47 of the optically effective surface 31.

[0090] FIG. 6b shows the ring actuator 40 in an expanded operating state, where the expansion of the pin 34 causes an internal deformation 47 of the optically effective surface 31.

[0091] FIG. 7a shows a first embodiment of a cylindrically configured pin 45. This has the advantage of simple manufacture and standard actuators can also be used for the ring actuator 40.

[0092] Figure 7b shows a second embodiment of pin 48, in which case the contact surface for the ring actuator is configured in a conical shape. This has the advantage that the ring actuator 40 can be at least partially fixed by covering the ring actuator 40 over the pin 48 and simply geometrically pushing it forward. Similar to the case of attachment to the cylindrical pin 45, the ring actuator 40 can likewise be configured in a hollow cylindrical shape, in which case the internal hollow cylindrical shape of the ring actuator 40 adapts to the conical external geometric shape of the pin 48 during shrink fitting by a local enlargement of the inner diameter of the ring actuator 40. The resulting prestress of the pin 48, which varies with the axial expansion of the ring actuator 40, can be taken into account in the control. Alternatively, the internal geometric shape of the ring actuator 40 can be configured to correspond to the pin 48 so that the contact area of the ring actuator 40 with respect to the pin 48 is configured in a conical shape. The advantages of the conical design in this case are the compensation of diameter tolerances and the possibility of axial press fitting.

[0093] Figures 8a and 8b show a connecting shape configured as notches 46, 48 in a variant of the present invention. What has been described with respect to Figures 7a and 7b also applies in principle to the embodiments shown in Figures 8a and 8b, in which case the description naturally relates to the corresponding inner surfaces of the notches and the outer surface of the ring actuator 40, and the ring actuator 40 is press-fitted axially or radially press-fitted or shrink-fitted using thermal expansion to a predetermined position.

[0094] Figs. 9a and 9b and Figs. 10a and 10b show modified forms of the present invention with respect to the connecting shaped portions configured as pins 45, 48 and described with reference to Figs. 7a and 7b, and the connecting shaped portions configured as notches 46, 49 and described with reference to Figs. 8a and 8b. This connecting shaped portion includes a mechanical transmission region including a recess 50, and this region will be described in detail below based on an embodiment configured as a cylindrical pin 45 as shown in Fig. 9a. The recess 50 is formed in the center of the pin 45 and extends beyond the pin to the body 30. First, since the recess 50 reduces the rigidity of the pin 45 and the body 30, even if the deflection of the ring actuator 40 is the same, the deformation of the optically effective surface 31 is advantageously and appropriately changed. Second, since the shape of the deformation of the optically effective surface 31 of the body can also be adjusted, in particular during the manufacture of the body 30 and the pins 45, 48 or the notches 46, 49 with additive manufacturing methods and the associated possible free geometric design, this can be adjusted in virtually any desired way. The effects of the recess 50 described with reference to Fig. 9a are also applicable to the embodiments shown in Figs. 9b, 10a, and 10b.

[0095] Figure 11a shows yet another embodiment of the present invention showing an optical element configured as mirrors Mx, 117. This mirror includes a body 30 having an optically effective surface 31, and also includes a support structure configured as a backplate 51, the backplate 51 including a conical pin 48 corresponding to the conical pin 48 configured on the body 30. Since the ring actuator 40 is configured in the form of a sleeve, it can be connected to both the pin 48 of the backplate 51 and the pin 48 of the body 30. The backplate 51 serves as a support structure and is connected to the body 30 or some other structure configured to absorb force, or is supported on the body 30 via the ring actuator 40. Support via the ring actuator 40 is possible because, in most cases, the ring actuator 40 that does not bend, rather than all ring actuators 40 bending in one direction, supports the backplate 51 due to the deformation of the optically effective surface 31. Figure 11b shows yet another embodiment of the present invention with a support structure configured as a backplate 51 as described in Figure 11a. This only differs in that the connecting shaped portion is configured as a conical notch 49. All other descriptions are consistent with that description, so please refer to them.

[0096] Figure 12 shows yet another embodiment of the present invention with a support structure having an integrated ring actuator 40. In this case, the backplate 54 of the support structure is manufactured from the actuator material 41, and electrodes 42 are formed only in the region of the ring actuator 40. Its function is the same as that of the embodiment described in Figure 11a.

[0097] FIG. 13a shows still another embodiment of the present invention, which is a detailed view of an optical element configured as mirrors Mx, 117 having a sensor 60. The mirrors Mx, 117 include a body 30 having an optically effective surface 31 and a ring actuator 40 shrink-fitted onto a conical pin 48. In the embodiment shown in FIG. 13a, the sensor 60 is configured like a Fabry-Perot interferometer. This interferometer includes a light source 61 that emits a light beam 62 in the direction of the back side of the body 30, and this light beam is perpendicularly incident on the back side. The sensor 60 uses the end face of the pin 48 that is partially transmissive to the wavelength of the light beam 62 as a first mirror surface 64, uses the optically effective surface 31 as a second mirror surface 65, and a detector 63 detects the superposition of reflections from the first mirror surface 64 and the second mirror surface 65. From the phase difference between the detected light beams caused by the deformation of the body, the change in the distance between the two mirror surfaces 64, 65 can be obtained, and from that, the deformation of the optically effective surface 31 can be obtained. One advantage of the configuration of the sensor 60 at the center of the ring actuator 40 is that the deformation caused by the ring actuator 40 can be directly detected at the location of generation from the back side of the body 30. The accessibility from the back side of the body 30 is significantly higher than the detection of deformation from the optically effective surface 31.

[0098] FIG. 13b shows still another embodiment of the present invention, which is a detailed view of an optical element configured as mirrors Mx, 117 having a sensor 60. The mirrors Mx, 117 include a support structure 51 as described in FIG. 11a and a sensor 60 configured like a Fabry-Perot interferometer in this case as well. Different from the arrangement described in FIG. 13a, the sensor 60 uses the two end faces of the conical pin 48 formed on the back plate 51 and the body 30 as a first mirror surface 64 and a second mirror surface 65. The deformation of the optical surface can be estimated using calibration data or model-based prediction, for example, FEM.

[0099] FIG. 14 shows a diagram for explaining a process of attaching a ring actuator to a connecting-shaped portion configured as a notch. The outer diameter of the ring actuator is shown on the vertical axis of the figure, and the control voltage is shown on the horizontal axis. In the illustrated embodiment, the ring actuator is controlled only with a positive voltage, and as the voltage increases, the diameter of the ring actuator decreases. For attachment, the ring actuator is controlled within a first voltage range S A such that the diameter is clearly smaller than the allowable diameter range T M of the notch. The voltage range S B for control during operation is less than the voltage range S M for attachment, and the voltage S A is less than the diameter at which the ring actuator becomes the maximum diameter tolerance T G of the notch. The voltage range S B for operation includes a so-called zero voltage S N corresponding to the voltage at which the optically effective surface has a predetermined surface shape. This can be achieved by reprocessing the optically effective surface after attaching the ring actuator, and all rings are controlled with the zero voltage S N . Alternatively, the deformation caused by the zero voltage S N can also be maintained during the manufacture of the optically effective surface.

Explanation of Signs

[0100] 1 Projection exposure apparatus 2 Illumination system 3 Radiation source 4 Illumination optical unit 5 Object field of view 6 Object surface 7 Reticle 8 Reticle holder 9 Reticle displacement drive 10 Projection optical unit 11 Image field of view 12 Image surface 13 Wafer 14 Wafer holder 15 Wafer displacement drive 16 EUV radiation 17 Collector 18 Intermediate focus plane 19 Deflection mirror 20 Facet mirror 21 Facet 22 Facet mirror 23 Facet 30 Body 31 Optically effective surface 32 Back side of the body 40 Ring actuator 41 Actuator material 42 Electrode 43 Electric wire 44 Controller 45 Pin 46 Notch 47 Deformation 48 Pin, conical 49 Notch, conical 50 Recess 51 Back plate 54 Integrated back plate 60 Sensor 61 Light source 62 Laser beam 63 Detector 64 First mirror surface 65 Second mirror surface 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 S N Voltage at zero point S M Voltage range for attachment S B Voltage range for operation S G Lower limit voltage of the tolerance range of the notch T A Tolerance of notch

Claims

1. An optical element (Mx, 117) of a projection exposure apparatus (1, 101) for semiconductor lithography, comprising a main body (30) and at least two actuators (40) connected to the main body (30), wherein the actuators are designed to deform the optically effective surface (31) of the optical element (Mx, 117). The optical element is characterized in that the at least two actuators (40) are configured as ring actuators.

2. In the optical element (Mx, 117) according to Claim 1, the optical element is characterized in that at least one of the ring actuators (40) is connected to the main body (30) via a connecting shaped portion (45, 46, 48, 49).

3. In the optical element (Mx, 117) according to Claim 2, the optical element is characterized in that the connecting shaped portion (45, 48) is configured as pins (45, 48) arranged on the main body (30).

4. In the optical element (Mx, 117) according to Claim 3, the optical element is characterized in that the main body (30) and the pins (45, 48) are configured monolithically.

5. In the optical element according to Claim 3, the optical element is characterized in that the main body (30) and the pins (45, 48) are connected to each other in an integrally joined manner.

6. In the optical element (Mx, 117) according to Claim 2, the optical element is characterized in that the connecting shaped portion (46, 49) is configured as notches (46, 49) arranged on the main body (30).

7. In the optical element (Mx, 117) according to any one of Claims 2 to 6, the optical element is characterized in that the contact area of at least one ring actuator (40) with the connecting shaped portion (48, 49) of the main body (30) is configured in a conical shape.

8. In the optical element (Mx, 117) according to any one of Claims 2 to 7, the optical element is characterized in that the contact area of the connecting shaped portion (48, 49) of the main body (30) with at least one ring actuator (40) is configured in a conical shape.

9. In the optical element (Mx, 117) according to any one of Claims 2 to 8, the optical element is characterized in that at least one ring actuator (40) is connected to the connecting shaped portion (48, 49) by shrink fitting.

10. In the optical element (Mx, 117) according to any one of claims 2 to 9, the connecting shaped portions (48, 49) of at least one ring actuator (40) include a mechanical transmission region (50), and the optical element is characterized by this.

11. In the optical element (Mx, 117) according to claim 10, the transmission region (50) is configured to reduce the rigidity acting on the deflection of the ring actuator (50), and the optical element is characterized by this.

12. In the optical element (Mx, 117) according to any one of claims 1 to 11, at least one ring actuator (40) is disposed between the main body (30) and the support structures (51, 54), and the optical element is characterized by this.

13. In the optical element (Mx, 117) according to claim 12, the support structure (51) includes connecting shaped portions (48, 49) corresponding to at least one ring actuator (40), and the optical element is characterized by this.

14. In the optical element (Mx, 117) according to claim 12 or 13, at least one ring actuator (40) is connected to a connecting shaped portion configured as a pin (48) or notch (49) of the main body (30) and the support structures (51, 54), and the optical element is characterized by this.

15. In the optical element (Mx, 117) according to claim 12, at least one ring actuator (40) is integrated with the support structure (54), and the optical element is characterized by this.

16. In the optical element (Mx, 117) according to any one of claims 1 to 15, the electrodes (42) and the actuator material (41) of at least one ring actuator (40) are arranged in layers in the radial direction or the axial direction, and the optical element is characterized by this.

17. An optical element (Mx, 117) of a projection exposure apparatus (1, 101) for semiconductor lithography, wherein the optical element (Mx, 117) includes a sensor (60) for obtaining the deformation of the optically effective surface (31) of the optical element (Mx, 117), and the sensor (60) is designed to detect a signal correlated with the deformation of the optically effective surface (31).

18. In the optical element (Mx, 117) according to claim 17, the sensor (60) includes an interferometer, and the optical element is characterized by this.

19. In the optical element (Mx, 117) according to claim 18, The sensor (60) is an optical element characterized by including a Fabry - Perot interferometer.

20. In the optical element (Mx, 117) according to any one of claims 17 to 19, An optical element characterized by being a deformable mirror.

21. In the optical element (Mx, 117) according to claim 20, The deformable mirror is an optical element characterized by being a force - actuated mirror.

22. In the optical element (Mx, 117) according to claim 20 or 21, The deformable mirror is an optical element characterized by being a mirror actuated by a solid actuator.

23. In the optical element (Mx, 117) according to any one of claims 17 to 22, An optical element characterized by being the optical element (Mx, 117) according to claims 1 to 16.

24. In the optical element (Mx, 117) according to claim 23, An optical element characterized in that the operating direction of at least one ring actuator (40) is aligned perpendicular to the contact area of the actuator (40) with the optical element (Mx, 117).

25. In the optical element (Mx, 117) according to claim 23 or 24, An optical element characterized in that the operating direction of at least one ring actuator (40) is aligned parallel to the contact area of the actuator (40) with the optical element (Mx, 117).

26. In the optical element (Mx, 117) according to any one of claims 23 to 25, The sensor (60) is an optical element characterized by detecting the deformation of the optical effective surface (31) through the center of at least one ring actuator (40).

27. A projection exposure apparatus (1, 101) having the optical element (Mx, 117) according to any one of claims 1 to 26.

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