Optical system and lithographic apparatus

Abstract

An optical system comprises at least one mirror having a mirror body and a mirror surface, and at least one actuator device coupled to the mirror body and for deforming the mirror surface. The actuator device comprises at least one electrostrictive actuator element for generating mechanical stresses in the mirror body for deforming the mirror surface depending on an electrical drive voltage, at least one electrostrictive sensor element for outputting a sensor signal depending on a deformation of the sensor element, wherein the at least one sensor element is arranged directly adjacent to the actuator element and / or is arranged such that the at least one sensor element is at least partially configured for transferring the mechanical stresses generated by the actuator element to the mirror body.

Description

Technical Field

[0001] The present invention relates to an optical system and to a lithographic apparatus having such an optical system.

[0002] The content of the priority application DE 10 2020 201724.7 is incorporated herein in its entirety by reference. Background Art

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

[0004] Mirrors are known whose mirror surfaces can be deformed in a targeted manner using suitably arranged actuators. This allows correction or compensation of optical imaging errors, also known as aberrations. Aberrations can have various sources. In particular, temperature fluctuations can lead to mechanical stresses, which can distort the optical element's support and / or the optical element itself, thereby changing the optical properties of the optical element in question. Such mirrors are used, for example, in astronomy, where the term adaptive optics has become established. Here, the mirror surface is scanned with measurement light, and deviations from the ideal shape are determined. A closed-loop control circuit can then be provided that drives the corresponding actuators based on the determined deviations, thereby bringing the mirror surface closer to its ideal shape.

[0005] Mirrors whose surfaces can be deformed by actuators are also used in lithographic apparatuses. However, known lithographic apparatuses have very limited installation space, as many functional units (e.g., active and passive components) must be accommodated within a small volume. Therefore, it is impractical to arrange additional optical measurement systems in the lithographic apparatus for scanning the mirror surface, as described above. Consequently, feedback control of the actuators has been impossible to date or has been implemented only with economically unjustifiable effort. Summary of the Invention

[0006] Against the above background, it is an object of the present invention to make available an improved optical system.

[0007] According to a first aspect, an optical system comprising at least one reflector is provided. The reflector comprises a reflector body and a reflector surface. At least one actuator device coupled to the reflector body is provided for deforming the reflector surface. The actuator device comprises at least one electrostrictive actuator element for generating a mechanical stress in the reflector body for deforming the reflector surface in dependence on an electrical drive voltage, and at least one electrostrictive sensor element for outputting a sensor signal in dependence on the deformation of the sensor. The at least one sensor element is arranged directly adjacent to the actuator element and / or on a side of the reflector body facing away from the reflector surface and is separated from the reflector body at least by the actuator element and / or is arranged such that it is at least partially configured to transfer the mechanical stress generated by the actuator element to the reflector body.

[0008] The advantage of this optical system is that it can detect the effects in the mirror body caused by the actuator element without directly scanning the mirror surface. Advantageously, this is possible within the physical domain, either mechanically or electrically, specifically by coupling an externally applied electric field with the polarization of the material that is affected by the deformation. This means that the actuator and sensor are not based on different physical mechanisms. In other words, the detection of deformation and actuation occurs via the same mechanism, for example electromechanically via the piezoelectric effect. This enables a unified description and processing of the effects that occur, which keeps the complexity of the optical system low. Since the actuator and sensor elements are made of the same material, the optical system can also be produced using a reduced number of different process steps. Furthermore, the optical system is therefore very robust, relatively inexpensive to produce, and less prone to defects.

[0009] The optical system is specifically designed as a projection optics unit for a lithographic apparatus. Furthermore, the optical system can be part of the beam shaping and illumination system of a lithographic apparatus. The optical system can also be used in other technical fields where high-precision beam guidance is required or desired, such as astronomy, scientific equipment, or military optics. Compared to known adaptive optics units, the optical system offers advantages particularly when available installation space is very limited, when a robust system is required, and / or when cost is a factor.

[0010] In particular, the optical system includes at least one mirror. Besides the mirror, the optical system may also include other mirrors, lens elements, gratings, apertures, filters, cavities, etc., but may also consist of a mirror with an actuator device. Furthermore, the optical system may include multiple mirrors with corresponding actuator devices. Other optically active elements of the optical system may also include additional or different actuators, such as electric heaters, coolers, etc.

[0011] The mirror surface of at least one mirror can have any geometric shape, such as flat, convex, concave, or the cross-section can vary. The mirror can be arranged at different positions in the beam path within the optical system, in particular in the area of ​​the pupil or hatch. Depending on the position in the beam path, different imaging errors or aberrations can be compensated by deformations of the mirror surface. Deformations are understood in particular to be deviations from the basic shape of the mirror surface. For example, the mirror assumes a basic shape when it is arranged stress-free in a support and orientation for operation. In this case, the basic shape can deviate from the ideal shape, for example due to the weight of the mirror itself, and the ideal shape is restored by deformations of the mirror surface. Deformations of the mirror surface are preferably understood to be deviations from the shape of the mirror surface when the actuator element is free of charge, current and voltage.

[0012] The actuator device comprises at least an actuator element and a sensor element. The actuator device also preferably includes a drive unit for driving the actuator element with a drive voltage. The drive voltage is predetermined, for example, by a control computer depending on the mechanical stress to be achieved. The mechanical stress directly determines the deformation of the mirror surface, with the functional relationship between mechanical stress and deformation depending, for example, on the material parameters of the mirror body and constraints such as geometric factors. Alternatively, the control computer may specify the mechanical stress to be achieved, and the drive unit itself may determine the required drive voltage.

[0013] An actuator arrangement is coupled to the mirror body of the mirror such that the mirror surface is deformable in dependence on an electrical driving voltage of the actuator element.

[0014] For example, the drive unit comprises a voltage or current source. Depending on the application, the actuator element can be operated using closed-loop voltage or charge control. Using closed-loop charge control for driving is particularly advantageous in dynamic applications where the attitude of the actuator element changes at high frequencies.

[0015] The actuator and sensor elements include electrostrictive materials, which are also understood to include, for example, piezoelectric materials. Electrostrictive materials have the property that, due to the interaction between an external electric field and the dipoles present in the material, mechanical stresses or forces can be generated in the material, resulting in deformation of the material. Conversely, deformation of the material results in a change in its polarization, which can be measured and used to draw conclusions about the magnitude of the deformation.

[0016] It is important to note that the terms force, mechanical stress, and deformation are used interchangeably.

[0017] Examples of electrostrictive materials are ceramic compounds containing the elements lead magnesium niobate (PMN) or lead zirconate titanate (PZT). These are preferably alloyed with platinum to improve the mechanical properties, with platinum reducing the dielectric properties, in particular the maximum polarization. Thus, the material composition of the alloy can be determined by the alloying factor x: PMNx -Pt 1-x or PZT x Pt 1-x To characterize.

[0018] In a preferred embodiment of the optical system, the electrostrictive material has a Curie temperature in the range of 0-40° C. At the Curie temperature, a phase transition occurs from a first crystal structure below the Curie temperature to a second crystal structure above the Curie temperature.

[0019] The actuator element preferably has an active region, such as a layer, made of an electrostrictive material, which is arranged between two electrodes, an anode and a cathode. By applying a drive voltage between the anode and the cathode, an electric field is formed in the active region, which causes mechanical stress.

[0020] The actuator element is mechanically coupled to the mirror body so that mechanical stresses of the actuator element are transferred to the mirror body, which manifests as corresponding deformations of the mirror body and thus the mirror surface. The extent of deformation achieved with a specific force depends on the strength of the material of the mirror body.

[0021] The sensor element preferably also has an active region arranged between two electrodes and made of an electrostrictive material, for example also having a layered structure. However, the sensor element and the actuator element may differ, for example, in their geometric dimensions and / or material composition.

[0022] The sensor element preferably has an associated measuring unit that determines the polarization of the active area of ​​the sensor element by means of a measuring alternating voltage applied between the cathode and anode of the sensor element. The sensor signal output by the sensor element specifically includes the polarization determined by the measuring unit. The deformation of the active area of ​​the sensor element can be derived from this. In particular, the amplitude of the measuring alternating voltage does not cause any significant mechanical stress in the active area. The measuring unit can constitute a separate unit of the actuator device, with the measuring unit and sensor element being associated with each other. Hereinafter, the term sensor element may refer to the entire sensor element or only to the active area of ​​the sensor element.

[0023] The sensor element is mechanically coupled to the actuator element and / or the mirror body such that the sensor element deforms when the actuator element deforms and / or the mirror body deforms, eg by mechanical stress applied by the actuator element.

[0024] In a preferred embodiment, the sensor element is arranged directly adjacent to the actuator element. Directly adjacent is understood to mean, for example, that there are no intermediate layers or additional materials between the actuator element and the sensor element. It can also be said that the sensor element and the actuator element are in contact.

[0025] In other preferred embodiments, the sensor element is arranged on the side of the mirror body facing away from the mirror surface and is separated from the mirror body by at least the actuator element. The sensor element is preferably arranged directly behind the actuator element, the rear side of the actuator element being the side facing away from the mirror body. It is also possible for additional layers to be present between the actuator element and the sensor element.

[0026] In other preferred embodiments, the sensor element is arranged so that it at least partially transfers the mechanical stress generated by the actuator element to the reflector body. It can also be said that the sensor element transfers the force from the actuator element to the reflector body, or it forms an operational connection between the actuator element and the reflector body. For example, the sensor element is arranged between the actuator element and the reflector body. Alternatively, the sensor element can be embedded in a matrix next to the actuator element, wherein the mechanical coupling between the sensor element, the actuator element and the matrix material causes the mechanical stress to propagate at the transition between the actuator element, the matrix material and the sensor element, at least substantially without interruption. In this case, it can also be said that the matrix containing the sensor element and the actuator element appears as a homogeneous body when observed from the outside.

[0027] This arrangement ensures a strong mechanical coupling between the sensor element and the mirror body and the actuator element, which is why a high measurement accuracy can be achieved.

[0028] The mechanical coupling between the actuator element, the sensor element and the mirror body is realized in particular by an interlocking connection, preferably by an adhesive connection, such as an adhesive bond.

[0029] The calibration measurement is preferably carried out before the optical system is put into operation. In this case, the mirror surface is illuminated with measuring light and the actuator device is caused to deform the mirror surface. The deformation of the mirror surface achieved at a specific drive voltage can be determined from the measuring light, so that a corresponding correlation can be established. In addition, if a sensor signal is detected at the same time, a correlation can also be established between the deformation of the mirror surface and the sensor signal. Since preferably only voltages with small absolute values ​​are applied to the sensor element, no hysteresis or the like occurs, so that the dielectric properties of the sensor element are constant. In contrast, the properties of the actuator element can change during operation, which is why precise control based on the correlation between the drive voltage and the deformation achieved during the calibration measurement is almost impossible. The sensor signal can be used during operation to check whether the deformation actually achieved corresponds to the desired deformation.

[0030] According to an embodiment of the optical system, the latter comprises a closed-loop control unit for controlling a drive voltage of the actuator element in dependence on a sensor signal output by the sensor element such that a predetermined mechanical stress in the mirror body is achieved.

[0031] The closed-loop control unit is advantageously configured to control the drive voltage as a function of the sensor signal output by the sensor element. This can be understood to mean that the closed-loop control unit includes, for example, an evaluation unit that evaluates the output sensor signal and derives the achieved mechanical stress therefrom. Alternatively, this step can be performed in the control computer. For example, the closed-loop control unit can be combined with the drive unit.

[0032] The closed-loop control unit can be implemented in the form of hardware and / or software. In the case of a hardware implementation, the closed-loop control unit can be designed as a computer or microprocessor, for example. In the case of a software implementation, the closed-loop control unit can be designed as a computer program product, a function, a routine, a portion of a program code, or an executable object.

[0033] Using an actuator arrangement, the mirror surface can thus be precisely deformed by the actuator element under closed-loop control. High accuracy of the closed-loop control is ensured by arranging the sensor element directly on the actuator element and / or on the rear side of the actuator element and / or in a direct operating path or force path from the actuator element to the mirror body.

[0034] According to further embodiments of the optical system, the at least one actuator element and the at least one sensor element are manufactured monolithically.

[0035] This specifically means that the actuator and sensor elements are made of materials from the same material class and that the same manufacturing technology is used for both elements. Furthermore, monolithic means that the actuator and sensor are based on the same operating mechanism. Both elements are preferably produced together, for example, in the same process. This has the advantage of using the same technology for both the actuator and sensor elements, thus keeping the complexity of the optical system low.

[0036] In particular, actuator-sensor arrangements in which, for example, actuation is performed electrically but measurement is performed optically are not monolithic. Nor are monolithic systems in which actuation is performed electrically by means of a magnetic field but measurement is performed electrically by means of a capacitance measurement, etc.

[0037] According to further embodiments of the optical system, the at least one actuator element and the at least one sensor element are integrated in a layer arranged on the mirror on a side of the mirror body facing away from the mirror surface.

[0038] The advantage of this embodiment is that it is not necessary to arrange separate actuator elements and separate sensor elements on the mirror body and attach them to the mirror body. Instead, a layer is produced in which the actuator elements and sensor elements are integrated, which is then applied as a whole to the rear side of the mirror, i.e. the side of the mirror body facing away from the mirror surface. The layer preferably covers the entire surface of the rear side of the mirror. Alternatively, a plurality of two-dimensional elements from the layer can also be arranged adjacent to each other on the rear side of the mirror. The fact that at least one actuator element and at least one sensor element are integrated in the layer should be understood to mean in particular that the active area of ​​the actuator element (the area that generates the mechanical stress) and the active area of ​​the sensor element (the area that detects the polarization) are integrated into the layer, wherein other elements, such as the measuring unit of the sensor element, are not integrated into the layer.

[0039] This layer preferably consists entirely of electrostrictive material, wherein the active regions (ie the actuator subregion and the sensor subregion) are formed by the arrangement of electrodes. The remaining material may be referred to as matrix material or passivation material.

[0040] According to further embodiments of the optical system, the at least one sensor element is at least partially arranged between the at least one actuator element and the mirror body in a direction along the surface normal of the mirror surface.

[0041] It can also be said that the actuator element and the sensor element partially or completely overlap. Due to this arrangement, the sensor element is arranged closer to the mirror body and therefore closer to the mirror surface than the actuator element. This is why the deformation or mechanical stress that can be derived from the sensor signal of the sensor element has a very high correlation with the mechanical stress in the mirror body and therefore the deformation of the mirror surface, which makes the closed-loop control more precise.

[0042] According to further embodiments of the optical system, the at least one actuator element and the at least one sensor element each comprise at least one layer of electrostrictive material.

[0043] In this context, a layer is preferably understood to mean a geometric shape having an aspect ratio of thickness to extent (i.e., length or width) of at least 1:5, preferably at least 1:10, preferably at least 1:100, and preferably up to 1:1000. It is assumed that the length and width are approximately of the same order of magnitude. For example, the layer may have a thickness between 10 μm and 500 μm and a length and width of 0.5-5 cm, or may be circular with a diameter in the range of 0.5-5 cm.

[0044] The advantage of the layer is that the effect achieved (i.e. the mechanical stress or deformation achieved in the plane of the layer at a specific drive voltage) is greater than the effect occurring in the perpendicular direction by a factor of the aspect ratio. Due to the electrostrictive effect, expansion in a first direction is always accompanied by a contraction in a second direction that differs from the first direction due to the incompressibility of the material.

[0045] Very thin layers also have the advantage that high deformations or forces can be achieved even at low driving voltages.

[0046] According to further embodiments of the optical system, the at least one actuator element has a plurality of layers made of electrostrictive material, wherein each layer of the plurality of layers has an assigned cathode and an assigned anode and is drivable with a respective drive voltage.

[0047] The advantage of a multilayer structure is that the force or mechanical stress achievable by the actuator element can be significantly increased compared to a single layer, as the sum of the forces achieved by the individual layers. Consequently, larger deformations are possible and the correction area that can effectively compensate for aberrations is expanded.

[0048] In an embodiment of the optical system, a cathode enclosed between two layers forms a common cathode for the adjacent layers, and an anode enclosed between two layers forms a common anode for the adjacent layers.

[0049] In this case, the electric field has opposite directions in adjacent layers. An advantage of this embodiment is that the proportion of active material in the actuator element can be maximized, since, for example, no insulating separation layer is required between two cathodes or anodes and since the amount of cathode material or anode material is also minimized.

[0050] In this embodiment, the electric field has opposite directions in adjacent layers. Therefore, it is advantageous to choose an electrostrictive material whose mechanical strain is proportional to the square of the polarization, because the opposite direction of the electric field has no effect on the direction of the force.

[0051] According to further embodiments of the optical system, the at least one actuator element and the at least one sensor element form a layer stack comprising at least two layers.

[0052] In this case, the sensor layer is applied directly to the actuator layer, for example, with a common electrode between them. This allows for a particularly compact design and maximizes the mechanical coupling between the sensor and actuator elements. The sensor element deforms in the same way as the actuator element, which is why the actuator drive voltage can be very precisely controlled in a closed loop.

[0053] According to further embodiments of the optical system, the actuator device has at least two sensor elements, wherein the material composition of the electrostrictive material of the at least two sensor elements is different, each of the at least two sensor elements being configured to output a sensor signal.

[0054] This embodiment is advantageous because, for example, temperature fluctuations can affect the polarization of the active material, which can lead to measurement errors. In the case of layers with different compositions, temperature fluctuations have different effects, allowing the temperature influence to be eliminated through calculation. This enables higher reliability and measurement accuracy. In this case, due to the small thickness of the layer stack consisting of the two sensor elements, it can be assumed that the two sensor elements have the same temperature, for example.

[0055] According to further embodiments of the optical system, a determination unit is provided which is configured to determine the temperature in the mirror body depending on sensor signals output by the at least two sensor elements.

[0056] By comparing two sensor signals from sensor elements with different compositions, mechanical stresses and temperatures can be determined by corresponding evaluation based on a physical model describing the underlying physics. This is particularly advantageous when optimal cooling of the mirror body in the desired area is not possible or can only be achieved with considerable effort. Mechanical stresses in the mirror body caused by temperature fluctuations or local temperature differences can then be taken into account when determining the current shape of the mirror surface and / or compensated for by the actuator arrangement. This can be advantageous without the need for additional systems.

[0057] The temperature that can be determined in this way relates to the temperature in the mirror body in the region of the two sensor elements, and is therefore in particular the local temperature.

[0058] According to further embodiments of the optical system, a measuring unit is provided for applying a measuring alternating voltage to at least two sensor elements to generate the sensor signal, wherein the frequency of the measuring alternating voltage is different for different sensor elements.

[0059] This has the advantage that crosstalk between different conductor tracks and the sensor element does not lead to measurement errors during the evaluation. Reference can also be made to frequency division multiplexing. The measuring unit can in particular be part of a closed-loop control unit or an actuator arrangement, but can also form a separate unit.

[0060] According to further embodiments of the optical system, the actuator arrangement has M actuator elements and a plurality, N, of sensor elements, wherein M and N are integers and the actuator elements and the sensor elements are arranged alternately.

[0061] Preferably, N>M, in particular N=M1, so that one sensor element is located on the outside in each case. For example, N=2 and M=1, where two sensor elements form a sandwiched structure with the actuator element. This advantageously allows for the determination of a two-dimensional deformation function, allowing for a more precise determination or prediction of the actual deformation in sections slightly further from the actuator element. This improves the accuracy of the closed-loop control. It can also be said that due to overdetermination, more precise closed-loop control is possible.

[0062] According to further embodiments of the optical system, the actuator arrangement comprises an assigning unit which is arranged to assign a value of an output sensor signal from the at least one sensor element to a deformation of the mirror surface achieved based on a calibration measurement, and wherein the closed-loop control unit is arranged for controlling the drive voltage depending on the assigned value and a predetermined deformation of the mirror surface.

[0063] In one embodiment, the assignment unit comprises a lookup table (LUT) in which sensor signal values ​​are assigned to the deformations of the mirror surface achieved. This embodiment is particularly simple and does not require high computing power. Intermediate values, i.e., values ​​of the deformation in the event that the sensor signal values ​​are not stored in the LUT, can be determined from the two closest values, for example by linear interpolation.

[0064] According to further embodiments of the optical system, a plurality of actuator devices are arranged at the at least one mirror, wherein each of the plurality of actuator devices is individually controllable.

[0065] Preferably, the entire area of ​​the mirror is covered, for example, with actuator devices, so that the mirror surface can be freely deformed in a variety of ways by appropriately driving the actuator devices. Each actuator device advantageously has a closed-loop control unit, so that each actuator device can be controlled independently of the other actuator devices using closed-loop control. Especially in the case of adjacent actuator devices, a deformation at the location of the first actuator device may also lead to a slight deformation at the location of the second actuator device due to the propagation of mechanical stresses throughout the entire mirror body. This deformation is also detected by the sensor element of the second actuator device, and the actuator element can be correspondingly controlled using closed-loop control to counteract the deformation, assuming that the deformation is undesirable in any case.

[0066] According to a second aspect, a lithographic apparatus comprising an optical system according to the first aspect or one of the embodiments is proposed.

[0067] This lithography apparatus has the advantage of being able to correct or compensate for imaging errors, as it includes a closed-loop control circuit for controlling the corresponding actuator elements. This means that aberrations can be corrected more accurately than without such a closed-loop control circuit. In lithography apparatuses, installation space is particularly limited, as the optical units used operate, for example, in a vacuum. This is why conventional adaptive optics solutions cannot be used.

[0068] The optical system preferably forms a beam shaping and illumination system or a projection system of a lithographic apparatus, or is part of such a system.

[0069] According to a third aspect, a method for using a mirror coupled to an actuator device in an optical system is proposed. The mirror has a mirror body and a mirror surface. The actuator device comprises at least one electrostrictive actuator element for generating a mechanical stress in the mirror body for deforming the mirror surface in accordance with an electrical drive voltage, and at least one electrostrictive sensor element for outputting a sensor signal depending on the deformation of the sensor element. The at least one sensor element is arranged directly adjacent to the actuator element and / or on a side of the mirror body facing away from the mirror surface and is separated from the mirror body at least by the actuator element and / or is arranged such that the at least one sensor element is at least partially configured to transfer the mechanical stress generated by the actuator element to the mirror body. The actuator device is coupled to the mirror body such that the mirror surface deforms depending on the electrical drive voltage.

[0070] A fourth aspect provides a method for operating an optical system having at least one mirror (the mirror having a mirror body and a mirror surface) and at least one actuator device coupled to the mirror body for deforming the mirror surface. In a first step, an electrostrictive actuator element of the actuator device is driven with an electrical drive voltage, so that a mechanical stress is generated in the mirror body and the mirror surface is deformed. In a second step, a sensor signal is detected by at least one electrostrictive sensor element of the actuator device, depending on the deformation of the sensor element. The at least one sensor element is arranged directly adjacent to the actuator element and / or on a side of the mirror body facing away from the mirror surface, and is separated from the mirror body at least by the actuator element and / or arranged such that the at least one sensor element is at least partially configured to transmit the mechanical stress generated by the actuator element to the mirror body. In a third step, the deformation of the mirror surface is determined based on the detected sensor signal.

[0071] In an embodiment, the optical system described above and below is arranged to carry out the method described above or to operate according to the method.

[0072] According to another aspect, a method for detecting deformations achieved on a mirror surface of an optical system according to the first aspect or one of the embodiments is provided. In a first step, at least one actuator element is driven by a drive voltage depending on a predetermined deformation of the mirror surface. For example, in the current state of the optical system, a control computer determines an ideal shape of the mirror surface that differs from the current actual shape of the mirror surface and, based on this, determines a drive voltage required for the actuator element, which is output to the actuator unit. In a second step, at least one sensor element outputs a sensor signal. This is achieved, in particular, by applying a measured alternating voltage to the active area of ​​the sensor element. The complex impedance of the sensor element allows the dielectric polarizability and, therefore, the polarization of the active area to be inferred. In a third step, the deformation of the sensor element is determined based on the output sensor signal, and thereby the achieved deformation of the mirror surface. The polarization of the active area of ​​the sensor element indicates the existing deformation of the sensor element. The deformation of the mirror surface can thus be determined using a mechanical model of the mirror. The deformation of the mirror surface that depends on the deformation of the sensor element is preferably predetermined during a calibration measurement and stored in a read-only table (LUT).

[0073] In an advantageous embodiment of the method, the drive voltage is controlled by means of a closed-loop control such that a predetermined deformation of the mirror surface is achieved.

[0074] The embodiments and features described for the optical system apply correspondingly to the proposed method.

[0075] The term "one" in the present case should not necessarily be understood as limiting to exactly one element. Of course, a plurality of elements, such as two, three, or more, may also be provided. Any other numerical values ​​used herein should not be understood as limiting to the number of elements precisely stated. On the contrary, unless otherwise indicated, upward and downward numerical deviations are possible.

[0076] Other possible implementations of the present invention also include any feature or embodiment described above or below with respect to the combination not clearly mentioned of exemplary embodiments. In this case, those skilled in the art will also add various aspects as improvements or supplements to the corresponding basic form of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Further advantageous configurations and aspects of the invention are the subject matter of the dependent claims and are also the subject matter of the exemplary embodiments of the invention described below.The invention is explained in detail below by means of preferred exemplary embodiments with reference to the drawings.

[0078] Figure 1 shows a schematic view of a first exemplary embodiment of an optical system;

[0079] Figure 2schematic view of a first exemplary embodiment of an arrangement of a mirror with an actuator device;

[0080] Figure 3 schematic view of a second exemplary embodiment of an arrangement of a mirror with an actuator device;

[0081] Figure 4 schematic view of a third exemplary embodiment of an arrangement of a mirror with an actuator device;

[0082] Figure 5 schematic view of a fourth exemplary embodiment of an arrangement of a mirror with an actuator device;

[0083] Figure 6 schematic view of a fifth exemplary embodiment of an arrangement of a mirror with an actuator device;

[0084] Figure 7 schematic view of a sixth exemplary embodiment of an arrangement of a mirror with an actuator device;

[0085] Figure 8 schematic view of a seventh exemplary embodiment of an arrangement of a mirror with an actuator device having two sensor elements;

[0086] Figure 9 schematic view of an exemplary embodiment of a construction of a driver element;

[0087] Figure 10 schematic view of an exemplary embodiment of a driver for a plurality of actuator elements and sensor elements in an actuator device;

[0088] Figure 11 three graphs showing the behavior of a physical variable as a function of a driving voltage;

[0089] Figure 12 is a graph showing a plurality of curves of the dielectric susceptibility as a function of the driving voltage;

[0090] Figure 13 schematic block diagram showing an exemplary embodiment of a closed loop control circuit.

[0091] Figure 14A schematic view of an embodiment of an EUV lithography apparatus;

[0092] Figure 14B schematic view of an embodiment of a DUV lithography apparatus; and

[0093] Figure 15A schematic block diagram illustrating an exemplary embodiment of a method for correction of aberrations in an optical system is shown.

[0094] Unless otherwise indicated, identical or functionally identical elements in the figures have the same reference numerals. It should also be noted that the illustrations in the drawings are not necessarily to scale. DETAILED DESCRIPTION

[0095] Figure 1 A schematic view illustrating a first exemplary embodiment of an optical system 200 is shown. The optical system 200 comprises here a light source LS, a lens element 128 collimating light incident thereon from the light source LS, two mirrors 110, 210, a further lens element 128 and a wafer 124 or object slide on which light from the further lens element 128 is focused. For example, the optical system 200 is an illumination system of a microscope or lithography apparatus 100A, 100B (see Figure 14A , 14B ).

[0096] The second mirror 210 of the optical system 200 is composed of a mirror body 212, a mirror surface 214 being arranged at the front side of the mirror body 212. An actuator device 220 is arranged at the rear side of the mirror body 212 and is configured to deform the mirror surface 214 by coupling mechanical stress into the mirror body 212. Without limiting the generality, only one actuator device 220 is shown here and in the following figures. However, it is not to be excluded that a plurality of such actuator devices 220 can be arranged at the mirror 210 in order to deform the mirror surface 214 in a targeted manner with high spatial resolution and / or to achieve an overall deformation of the mirror 210.

[0097] Due to the fact that the mirror surface 214 of the mirror 210 can be deformed, aberrations, i.e. imaging errors, can be compensated. In this case, the imaging errors depend in particular on the operating state of the optical system 200 and / or of further optical systems coupled to the optical system 200. For example, spatial and / or temporal temperature differences and / or temperature fluctuations can be compensated by the actuator device 220. The optical system 200 can thus also be described as an adaptive optical system, whose state is closed-loop controlled or kept constant with respect to a reference state. Preferably, the actuator device 220 comprises a closed-loop control circuit for controlling the actuator elements 222 (see Figure 2-8 , 10, 13, 14A or 14B).

[0098] The precise mode of operation of the actuator device 220 will be explained in detail with reference to the following figures.

[0099] Figure 2-7Schematic diagrams each show exemplary embodiments of an arrangement of a reflector 210 with an actuator device 220. The exemplary embodiments differ in the specific arrangement of the actuator device 220 and the reflector 210. Figure 1 、 14A Each exemplary embodiment may be used in an optical system 200 as shown in FIG. 14B .

[0100] Figure 2 An actuator device 220 is shown, arranged between the mirror body 212 and the mirror carrier 216. The mirror carrier 216 forms a mechanical fixing point, meaning it is rigid and stationary. The actuator device 220 comprises an actuator element 222 and a sensor element 224, wherein the sensor element 224 is in mechanical contact with the mirror body 212 and the actuator element 222 is supported on the mirror carrier 216. Furthermore, a drive unit 226 is present, which provides a drive voltage VS for driving the actuator element 222. In this example, the drive unit 226 also detects a sensor signal SS output by the sensor element 224. The drive unit 226 is preferably designed as a closed-loop control unit or includes a closed-loop control unit that controls the drive voltage VS as a function of the sensor signal SS.

[0101] In this arrangement, the actuation direction 223 is parallel to the surface normal of the mirror surface 214. When a drive voltage VS is applied to the actuator element 222, the actuator element 222 stretches or expands in the actuation direction 223. Because the mirror carrier 216 is fixed, the stretching of the actuator element 222 causes a bulge or displacement of the mirror surface 214 at the location of the actuator device 220. Here, the mirror body 212 can be supported on the mirror carrier 216 at one or more points by fixed connection elements (not shown). For example, such fixed connection elements, in their arranged position, fix the distance between the mirror body 212 and the mirror carrier 216.

[0102] Figure 3 An alternative embodiment of an actuator device 220 arranged between the mirror body 212 and the mirror carrier 216 is shown. In this case, the sensor element 224 is arranged directly laterally on the actuator element 222. In this arrangement, the sensor element 224 will accurately follow any deformation, in particular tension or compression, of the actuator element 222 in the actuation direction 223. The actual deformation of the actuator element 222 can therefore be determined very accurately from the sensor signal SS.

[0103] Figures 4 to 7 Each shows a different integration of the actuator device 220, wherein Figure 2 and Figure 3In contrast, a lateral actuation direction 223 is used, i.e. in the plane of the mirror body 212. Figure 4 and 5 In the embodiment, the actuator device 220 is adhesively bonded to the rear side of the reflector body 212 or is securely connected thereto in a similar manner. The sensor element 224 is arranged either between the actuator element 222 and the reflector body 212 ( Figure 4 ) or arranged on the rear side of the actuator element 222 ( Figure 5 ).exist Figure 4 In the arrangement shown, the sensor element 224 transfers any mechanical stresses generated by the actuator element 222 to the mirror body 212. In particular, the sensor element 224 experiences the same deformation as the areas of the actuator element 222 and the mirror body 212 that are in direct contact with the sensor element 224. The lateral actuation 223 (which may be a stretch or a contraction relative to the actuator element 222) generates mechanical stresses in the mirror body 212, and the mirror surface 214 deforms accordingly.

[0104] exist Figure 6 and Figure 7 In exemplary embodiments, the actuator elements 222 and the sensor elements 224 are embedded in a matrix MX. The matrix MX is typically composed of a material from the same material family as the actuator elements 222, and the sensor elements 224 are preferably composed of an electrostrictive ceramic material. Advantageously, the actuator elements 222, the sensor elements 224, and the matrix MX form a substantially uniform material layer 221 that is two-dimensionally affixed to the rear side of the mirror body 212, preferably over the entire surface. The active areas of the actuator elements 222 and the sensor elements 224 are defined by the electrode arrangement in the material MX. In these embodiments, the mechanical coupling of the actuator elements 222 to the mirror body 212 is particularly strong, which has a beneficial effect on the maximum achievable deformation of the mirror surface 214.

[0105] Figure 2-7 The exemplary embodiments shown in can also be combined with one another as required.

[0106] Figure 8 A schematic view of a fourth exemplary embodiment of an arrangement of a mirror 210 with an actuator device 220 is shown. The basic arrangement corresponds to Figure 7 , wherein actuator device 220 includes two sensor elements 224, which surround actuator element 222 in a sandwiched manner. The two sensor elements 224 advantageously have different chemical compositions, meaning they have different dependencies on temperature and deformation. Based on the two sensor signals SS, both the deformation and the temperature of the respective sensor element 224 can be determined. In the present case, this is accomplished by a determination unit 230 specifically provided for this purpose.

[0107] Figure 9 A schematic diagram of an exemplary embodiment of the construction of an actuator element 222 is shown, which consists of a plurality of individual layers L1-Ln. Electrode A1 is arranged on the uppermost layer L1 and serves here, for example, as an anode. Between the uppermost layer L1 and the layer L2 arranged adjacent thereto is arranged a further electrode K1, which operates here as a cathode. Anode A1 and cathode K1 can be said to surround the top layer L1 in a sandwiched manner. A drive voltage VS (see Figure 2-8 or 10-13) results in an electric field being formed in layer L1. In an embodiment, the roles of anode A1 and cathode K1 can also be interchanged, in which case the direction of the electric field is opposite.

[0108] The electrode A2 operating as an anode is again arranged between the second layer from the top L2 and the third layer from the top L3. Here it can be seen that the cathode K1 forms a common cathode for the adjacent layers L1 and L2. The anode A2 also forms a common anode for the adjacent layers L2 and L3.

[0109] In this example, this layered construction continues until the desired number of layers is reached. Disposed beneath the bottom layer Ln is the termination electrode Kn, which in this embodiment functions as a cathode. In this alternating configuration with common electrodes A1-An and K1-Kn, the electrostrictive material is typically one in which mechanical strain is proportional to the square of the polarization, so layers L1-Ln deform in the same direction despite the different directions of the electric field.

[0110] In other embodiments using electrostrictive materials in which mechanical strain is proportional to polarization, the electrodes A1-An, K1-Kn should be arranged and driven so that the electric field in all layers L1-Ln points in the same direction, otherwise the layers L1-Ln will oppose each other.

[0111] The thickness of each layer L1-Ln may be different. The thickness of the different layers L1-Ln is preferably substantially the same and is selected from the range of 10 μm to 500 μm. In this case, different material compositions can also be selected for each layer L1-Ln, for example, to obtain different electrostrictive properties.

[0112] In other embodiments, the sensor element 224 has Figure 9 The layered structure of the actuator element 222 is shown. In this case, the advantage of using different chemical compositions for the different layers L1-Ln is in particular that a comparison of the sensor signals SS of the individual layers L1-Ln allows conclusions to be drawn not only about the mechanical stresses, but also about other influencing variables, in particular the temperature in the layers L1-Ln.

[0113] Figure 10 A schematic diagram shows an exemplary embodiment of an actuator device 220 comprising a plurality of actuator elements 222, a plurality of sensor elements 224, and a drive unit 226. In this case, three sensor elements 224 and two actuator elements 222 are provided, forming a layer stack, wherein each actuator element 222 comprises three layers L1-L3, for example, made of electrostrictive material.

[0114] Two of the sensor elements 224 surround the entire layer stack in a sandwiched manner, and the third sensor element 224 divides the layer stack in the middle. In this example, the passive region is arranged between the sensor elements 224 and the actuator element 222. This can also be omitted in embodiments, in which the electrode arranged between the sensor element 224 and the actuator element 222 then constitutes a common electrode. In this case, the common electrode is preferably grounded, because the sensor elements advantageously operate without a bias voltage.

[0115] The drive unit 226 comprises a closed-loop controlled voltage source for providing a drive voltage VS to the actuator element 222, and three measuring units configured to generate sensor signals SS for the corresponding sensor elements 224 by measuring the alternating voltage VM. The measured alternating voltages VM preferably have different frequencies to avoid mutual interference. In other specific embodiments, multiple actuator elements 222 can also be operated with different drive voltages VS.

[0116] Figure 11 Three diagrams showing the behavior of the physical variables, mechanical stress σ, gradient of the deflection e achieved with respect to the driving voltage VS and the dielectric polarizability χ as a function of the driving voltage VS for an exemplary electrostrictive layer, which may be used for the actuator element 222 (see Figure 2-10 or 13) or sensor element 224 (see Figure 2-8 , 10 or 13). The variables σ, e and χ are expressed in arbitrary units. The unit volt is chosen as the scale of the driving voltage VS. The electrostrictive material is particularly PMN x Pt 1-x The curves shown relate to the mechanically free state of the layer, i.e. the state in which there is no mechanical prestressing and the layer is not embedded in a rigid material system.

[0117] The figure above shows the mechanical stress σ (unit: N / m 2, or Pa) is provided or generated by the layer driven by the drive voltage VS. For a drive voltage VS = 0, the layer does not generate any mechanical stress σ. It can also be seen that a low drive voltage VS only results in very small mechanical stress σ. For low drive voltages VS, the generated mechanical stress σ is, for example, proportional to the square of the drive voltage VS.

[0118] The middle diagram shows the gradient of the deflection e achieved relative to the drive voltage VS as a function of the drive voltage VS.

[0119] The figure below shows the dielectric polarizability χ as a function of the driving voltage VS. It can be seen that the dielectric polarizability χ has a maximum value when the driving voltage VS=0.

[0120] like Figure 12 As shown in FIG, the dielectric polarizability χ at the driving voltage VS=0 is also highly sensitive to mechanical stress. Figure 12 A graph shows multiple curves of the dielectric polarizability χ as a function of the drive voltage VS. The five curves 1-5 shown differ in terms of the deformation of the layer. For example, curve 3 corresponds to a mechanically free or stress-free state. For example, curves 1 and 2 correspond to layer tension in the ppm range, for example, curve 1 at 10 ppm and curve 2 at 5 ppm. For example, curves 4 and 5 correspond to layer compression in the ppm range, for example, curve 4 at 5 ppm and curve 5 at 10 ppm. Due to this maximum sensitivity of the dielectric polarizability χ, this physical variable is particularly suitable as a measured variable for determining layer deformation, particularly in sensor element 224. The dielectric polarizability χ can be determined by impedance measurement by measuring the alternating voltage VM.

[0121] Figure 13 Schematic block diagram of an exemplary embodiment of a closed-loop control circuit in an actuator device 220 is shown. In the present case, the drive unit 226 is designed as a closed-loop control unit. The closed-loop control unit 226 receives a predetermined mechanical target stress σ from the outside, for example via a control computer (not shown). s , which the actuator device 220 is intended to provide or generate by means of the actuator element 222. The closed-loop control unit 226 then drives the actuator element 222 with a drive voltage VS. The drive voltage VS is preferably selected such that under good conditions, it accurately achieves the mechanical target stress σ s , which is known, for example, from characterization measurements of the actuator element 222. However, due to hysteresis or various environmental influences, the actuator element 222 may slightly miss the target mechanical stress σ s .

[0122] Sensor element 224 is deformed by actuator element 222. The extent of this deformation can be determined as described above and is represented here by sensor signal SS. Sensor signal SS is, in particular, a characteristic of the deformation of sensor element 224 and, therefore, of the mechanical stress σ realized in sensor element 224. Due to the direct coupling between sensor element 222 and actuator element 224, the mechanical stress σ in sensor element 224 substantially corresponds to the mechanical stress σ in actuator element 222. Sensor signal SS is therefore suitable as a closed-loop control signal. Therefore, closed-loop control unit 226 readjusts drive voltage VS of actuator element 222 based on sensor signal SS.

[0123] The closed-loop control period may last, for example, in the range of 1 ms-100 ms, corresponding to a closed-loop control frequency between 10 Hz-1 kHz.

[0124] Figure 14A A schematic diagram of an EUV lithography apparatus 100A is shown, comprising a beam shaping and illumination system 102 and an optical system 200, implemented here as a projection system. In this context, EUV stands for "extreme ultraviolet" and refers to a wavelength of working light between 0.1 nm and 30 nm. The beam shaping and illumination system 102 and the projection system 200 are each housed in a vacuum housing (not shown), each of which is evacuated by means of an exhaust device (not shown). The vacuum housing is surrounded by a mechanical chamber (not shown), in which drive devices for mechanically moving or setting optical elements are provided. Furthermore, an electrical controller, etc., may also be provided in the mechanical chamber.

[0125] The EUV lithography apparatus 100A includes an EUV light source 106A. For example, a plasma source (or a synchrotron) can be provided as the EUV light source 106A, which emits radiation 108A in the EUV range (extreme ultraviolet range), that is, for example, in the wavelength range of 5 nm to 20 nm. In the beam shaping and illumination system 102, the EUV radiation 108A is focused and the desired operating wavelength is filtered out of the EUV radiation 108A. The EUV radiation 108A generated by the EUV light source 106A has a relatively low transmittance through air, so the beam guiding space in the beam shaping and illumination system 102 and in the projection system 200 is evacuated.

[0126] Figure 14AThe beam shaping and illumination system 102 shown in FIG. 1 has five mirrors 110, 112, 114, 116, and 118. After passing through the beam shaping and illumination system 102, the EUV radiation 108A is directed onto a photomask (reticle) 120. The photomask 120 is also designed as a reflective optical element and can be arranged outside the systems 102 and 104. Furthermore, the EUV radiation 108A can be directed onto the photomask 120 by means of a mirror 122. The photomask 120 has a structure that is imaged in a reduced manner onto a wafer 124 or the like by means of the projection system 200.

[0127] The projection system 200 (also referred to as a projection lens) has five mirrors M1 to M5 for imaging the photomask 120 onto the wafer 124. In this case, the individual mirrors M1 to M5 of the projection system 200 can be arranged symmetrically about the optical axis 126 of the projection system 200. It should be noted that the number of mirrors M1 to M5 of the EUV lithography apparatus 100A is not limited to the number shown. A greater or lesser number of mirrors M1 to M5 can also be provided. In addition, the mirrors M1 to M5 are typically curved at their front sides for beam shaping.

[0128] The projection system 200 also has a further reflector 210, on the rear side of which a plurality of actuator devices 220 are arranged, each of which can be designed as follows: Figure 2-8 , 10, or 13. Each actuator device 220 includes an assigned actuator element 222 and an assigned sensor element 224. A drive unit 226 is configured to drive the actuator element 222 with a drive voltage VS and apply a measurement alternating voltage VM to the sensor element 224 to generate a corresponding sensor signal SS. For clarity, only one drive unit 226 is shown here, which drives all actuator elements 222 and sensor elements 224. The front side of the mirror 210 can be deformed by the targeted drive of the actuator device 220, which can be used to correct optical aberrations to increase the resolution of the lithography process.

[0129] In an advantageous embodiment, the actuation is controlled by the actuator element 222 in a closed-loop control, by virtue of the fact that the actually achieved deformation is detected by the sensor element 224 and the drive voltage VS can therefore be controlled in a closed-loop control by evaluating the sensor signal SS. This closed-loop control is performed separately for each actuator device 220, wherein for the sake of clarity only one actuator device 220 and only one drive voltage VS, one measurement alternating voltage VM, and one sensor signal SS are shown.

[0130] The projection system 200 (or also the beam shaping and illumination system 102 ) can have a further mirror 210 with an assigned actuator device 220 .

[0131] Figure 14B A schematic view of a DUV lithography apparatus 100B is shown, comprising a beam shaping and illumination system 102 and an optical system 200 designed here as a projection system. In this case, DUV stands for "deep ultraviolet" and denotes a wavelength of working light between 30 nm and 250 nm. Figure 14A As already described, the beam shaping and illumination system 102 and the projection system 200 may be arranged in a vacuum housing and / or surrounded by a mechanical room with corresponding drive devices.

[0132] The DUV lithography apparatus 100B has a DUV light source 106B. As an example, an ArF excimer laser emitting radiation 108B in the DUV range of 193 nm may be provided as the DUV light source 106B.

[0133] exist Figure 14B The beam shaping and illumination system 102 shown in FIG directs DUV radiation 108B onto a photomask 120. The photomask 120 is formed as a transmissive optical element and can be arranged outside the systems 102, 104. The photomask 120 has a structure that is imaged in a reduced manner onto a wafer 124 or the like by means of a projection system 200.

[0134] The projection system 200 has a plurality of lens elements 128 and / or mirrors 130 for imaging the photomask 120 onto the wafer 124. In this case, the individual lens elements 128 and / or mirrors 130 of the projection system 104 can be arranged symmetrically about the optical axis 126 of the projection system 200. It should be noted that the number of lens elements 128 and mirrors 130 of the DUV lithography apparatus 100B is not limited to the number shown. A greater or lesser number of lens elements 128 and / or mirrors 130 can also be provided. In addition, the mirrors 130 are typically curved on their front sides for beam shaping.

[0135] The air gap between the last lens element 128 and the wafer 124 can be replaced by a liquid medium 132 having a refractive index greater than 1. Liquid medium 132 can be, for example, high-purity water. This configuration is also known as immersion lithography and has enhanced lithographic resolution. Medium 132 can also be referred to as an immersion liquid.

[0136] The projection system 200 further comprises a reflector 210, on the rear side of which an actuator device 220 is arranged, which can be designed as follows: Figure 2-8, 10, or 13. Without limiting generality, only one actuator device 220 is shown here, but it goes without saying that a plurality of actuator devices 220 are preferably present, each of which can be individually controlled via open-loop and / or closed-loop control. The actuator device 220 includes an assigned actuator element 222 and an assigned sensor element 224. A drive unit 226 is configured to drive the actuator element 222 with a drive voltage VS and to apply a measurement alternating voltage VM to the sensor element 224 in order to generate a corresponding sensor signal SS.

[0137] Figure 14B Also shown is the predetermined target mechanical stress σ s Specified externally, this will be achieved by the actuator element 222. The mechanical target stress σ s It is determined, for example, by a control computer based on a target deformation to be achieved for the mirror 210. The target deformation of the front side of the mirror 210 allows correction of optical aberrations to improve the resolution of the lithographic process.

[0138] In an advantageous embodiment, the actuation is controlled by the actuator element 222 via closed-loop control, by virtue of the fact that the actually achieved deformation is detected by the sensor element 224 and the drive voltage VS can therefore be controlled using closed-loop control by evaluating the sensor signal SS. This closed-loop control is performed separately for each actuator device 220, wherein for the sake of clarity only one actuator device 220 and only one drive voltage VS, one measurement alternating voltage VM, and one sensor signal SS are shown.

[0139] The projection system 200 (or also the beam shaping and illumination system 102 ) can have a further mirror 210 with an assigned actuator device 220 .

[0140] Figure 15 2. The mirror 210 (see FIG. Figure 1-8 or 14A, 14B) of the reflector surface 212 (see Figure 1-8 ) deformation to correct the optical system 200 in a targeted manner (e.g. Figure 1 Schematic block diagram of an exemplary embodiment of a method for analyzing aberrations in an optical system 200).

[0141] In a first step S1, at least one actuator element 222 (see Figure 2-8 or 13) by means of the drive voltage VS (see Figure 2-8 or 10-13) depending on the reflector surface 214 (see Figure 1-8 ) is driven by a specific deformation of the actuator element 222. Therefore, mechanical stress is generated in the actuator element 222, which is transmitted to the reflector body 212 of the reflector 210 (see Figure 1-8), which results in local deformation of the mirror surface 214.

[0142] In a second step S2, the sensor signal SS (see Figure 2-8 or 13) by at least one sensor element 224 (see Figure 2-8 For this purpose, a measuring alternating voltage VM is applied to the sensor element 224 , as already described above.

[0143] In a third step S3 , the deformation of sensor element 224 is determined as a function of detected sensor signal SS. From this, the deformation achieved by mirror surface 214 can be determined.

[0144] In an optional fourth step S4, the drive voltage VS is controlled by closed-loop control such that a predetermined deformation of the mirror surface 214 is achieved. For this purpose, for example, the predetermined deformation is compared with the achieved deformation, which shows whether the drive voltage VS needs to be higher or lower to achieve the predetermined deformation.

[0145] While the present invention has been described based on exemplary embodiments, it can be modified in a variety of ways. In particular, many of the physical variables used in the description can be interchanged with other variables. Instead of mechanical stress, force or mechanical strain or deformation can also be referred to. Furthermore, the sensor signal can be said to depend on dielectric polarizability, impedance, polarization, capacitance, and so on, all of which can be converted to each other as long as the respective material parameters are known.

[0146] In particular, the present invention allows for a large number of possible arrangements of the sensor element relative to the actuator element in the actuator device. Depending on the specific application, different positions may be advantageous. Furthermore, by combining different arrangements in one actuator element, detection accuracy can be improved.

[0147] Furthermore, without limiting the present invention in any particular manner, the closed-loop control circuit for controlling the driving voltage may be implemented or realized in various ways.

[0148] Reference Signs List

[0149] 1 Function Curve

[0150] 2 Function Curve

[0151] 3 Function Curves

[0152] 4 Function Curves

[0153] 5 Function Curve

[0154] 100A EUV lithography equipment

[0155] 100B DUV lithography equipment

[0156] 102 Beam Shaping and Illumination Systems

[0157] 106A EUV light source

[0158] 106B DUV light source

[0159] 108A EUV radiation

[0160] 108B DUV radiation

[0161] 110 reflector

[0162] 112 Reflector

[0163] 114 Reflector

[0164] 116 Reflector

[0165] 118 Reflector

[0166] 120 Photomask

[0167] 122 Reflector

[0168] 124 chips

[0169] 126 optical axis

[0170] 128 lens elements

[0171] 130 reflector

[0172] 132 Medium

[0173] 200 Optical System

[0174] 210 reflector

[0175] 212 reflector body

[0176] 214 mirror surface

[0177] 216 Mirror Carrier

[0178] 220 actuator device

[0179] 221st floor

[0180] 222 actuator element

[0181] 223 Actuation direction

[0182] 224 sensor elements

[0183] 226 drive unit

[0184] 230 Determine Unit

[0185] A1 Anode

[0186] A2 Anode

[0187] A3 Anode

[0188] An anode

[0189] K1 cathode

[0190] K2 cathode

[0191] K3 cathode

[0192] Kn cathode

[0193] L1 layer

[0194] L2 layer

[0195] L3 layer

[0196] Ln layer

[0197] LS light source

[0198] MX matrix

[0199] M1 reflector

[0200] M2 reflector

[0201] M3 reflector

[0202] M4 reflector

[0203] M5 reflector

[0204] S1 Method Steps

[0205] S2 Method Steps

[0206] S3 Method Steps

[0207] S4 Method Steps

[0208] SS sensor signal

[0209] VM measures alternating voltage

[0210] VS driving voltage

[0211] χ dielectric polarizability

[0212] σ Mechanical stress

[0213] σ s Mechanical stress

Claims

1. An optical system (200) having at least one mirror (210), the mirror (210) having a mirror body (212) and a mirror surface (214), and at least one actuator device (220) coupled to the mirror body (212) for deforming the mirror surface (214), wherein the actuator device (220) comprises: at least one electrostrictive actuator element (222) for generating mechanical stress in the mirror body (212) for deforming the mirror surface (214) in dependence on an electrical drive voltage (VS), at least one electrostrictive sensor element (224) for outputting a sensor signal (SS) depending on a deformation of the sensor element (224), wherein the at least one sensor element (224) is arranged directly adjacent to the actuator element (222) and / or is arranged on a side of the mirror body (212) facing away from the mirror surface (214) and is at least separated from the mirror body (212) by the actuator element (222) and / or is arranged such that the at least one sensor element (224) is at least partially provided for transferring mechanical stresses generated by the actuator element (222) to the mirror body (212), and wherein The actuator device (220) is coupled to the mirror body (212) such that the mirror surface (214) is deformable depending on an electrical drive voltage (VS) of the actuator element (222), wherein the actuator element (222) is arranged on a side of the mirror body (212) facing away from the mirror surface (214), The reflector body (212) has a front side and a rear side facing away from the front side, the reflector surface (214) is provided on the front side of the reflector body (212), and The at least one electrostrictive actuator element (222) is arranged on the rear side of the reflector body (212).

2. The optical system according to claim 1 further comprises a closed-loop control unit for controlling a drive voltage (VS) of the actuator element (222) depending on the sensor signal (SS) output by the sensor element (224) so ​​as to achieve a predetermined mechanical stress in the mirror body (212).

3. The optical system according to claim 1 or 2, wherein: The at least one actuator element (222) and the at least one sensor element (224) are monolithically fabricated.

4. The optical system according to claim 1 or 2, wherein: The at least one actuator element (222) and the at least one sensor element (224) are integrated in a layer (221) arranged on the mirror (210), on a side of the mirror body (212) facing away from the mirror surface (214).

5. The optical system according to claim 1 or 2, wherein: The at least one sensor element (224) is at least partially arranged between the at least one actuator element (222) and the mirror body (212) in the direction of the surface normal of the mirror surface (214).

6. The optical system according to claim 1 or 2, wherein: The at least one actuator element (222) and the at least one sensor element (224) each comprise at least one layer (L1, . . . , Ln) of electrostrictive material.

7. The optical system according to claim 6, wherein: The at least one actuator element (222) has a plurality of layers (L1, ..., Ln) of electrostrictive material, wherein each of the plurality of layers (L1, ..., Ln) has an assigned cathode (K1-Kn) and an assigned anode (A1-An) and is drivable with a corresponding drive voltage (VS).

8. The optical system according to claim 6, wherein: The at least one actuator element (222) and the at least one sensor element (224) form a layer stack (SL) comprising at least two layers (L1, . . . , Ln).

9. The optical system according to claim 1 or 2, wherein: The actuator device (220) has at least two sensor elements (224), wherein the electrostrictive materials of the at least two sensor elements (224) have different material compositions, wherein each of the at least two sensor elements (224) is configured to output a sensor signal (SS).

10. The optical system according to claim 9, wherein: A determination unit (230) is provided for determining the temperature in the mirror body (212) depending on the sensor signals (SS) output from the at least two sensor elements (224).

11. The optical system according to claim 9, wherein: A measuring unit is provided for applying a measuring alternating voltage (VM) to the at least two sensor elements (224) in order to generate the sensor signal (SS), wherein the frequency of the measuring alternating voltage (VM) is different for different sensor elements (224).

12. The optical system according to claim 1 or 2, wherein: The actuator device (220) has M actuator elements (222) and N sensor elements (224), wherein N and M are integers and the actuator elements (222) and the sensor elements (224) are arranged alternately.

13. The optical system according to claim 2, wherein: The actuator arrangement (220) comprises an assigning unit arranged to assign a value of an output sensor signal (SS) from the at least one sensor element (224) to a deformation of the mirror surface (214) achieved based on calibration measurements, and wherein the closed-loop control unit is arranged to control the drive voltage (VS) depending on the assigned value and a predetermined deformation of the mirror surface (214).

14. The optical system according to claim 1 or 2, wherein: A plurality of actuator devices (220) are arranged at the at least one reflector (210), and wherein each of the plurality of actuator devices (220) is individually controllable.

15. A lithographic apparatus (110A, 100B) having an optical system (200) according to any one of claims 1-13.

16. A method of using a mirror (210) coupled to an actuator device (220) in an optical system (200), wherein: The reflector (210) has a reflector body (212) and a reflector surface (214), and wherein the actuator device (220) comprises: at least one electrostrictive actuator element (222) for generating mechanical stress in the mirror body (212) for deforming the mirror surface (214) in dependence on an electrical drive voltage (VS), at least one electrostrictive sensor element (224) for outputting a sensor signal (SS) depending on a deformation of the sensor element (224), wherein the at least one sensor element (224) is arranged directly adjacent to the actuator element (222) and / or is arranged on a side of the mirror body (212) facing away from the mirror surface (214) and is at least separated from the mirror body (212) by the actuator element (222) and / or is arranged such that the at least one sensor element (224) is at least partially provided for transferring mechanical stresses generated by the actuator element (222) to the mirror body (212), and wherein The actuator device (220) is coupled to the mirror body (212) such that the mirror surface (214) is deformed in dependence on the electrical drive voltage (VS), wherein the actuator element (222) is arranged on a side of the mirror body (212) facing away from the mirror surface (214), The reflector body (212) has a front side and a rear side facing away from the front side, the reflector surface (214) is provided on the front side of the reflector body (212), and The at least one electrostrictive actuator element (222) is arranged on the rear side of the reflector body (212).

17. A method for operating an optical system (200), the optical system (200) having at least one mirror (210), the mirror (210) having a mirror body (212) and a mirror surface (214), and the optical system (200) having at least one actuator device (220) coupled to the mirror body (212) for deforming the mirror surface (214), the method comprising the following steps: driving an electrostrictive actuator element (222) of the actuator device (220) with an electrical drive voltage (VS) so that mechanical stress is generated in the reflector body (212) and the reflector surface (214) is deformed, wherein the actuator element (222) is arranged on a side of the reflector body (212) facing away from the reflector surface (214), detecting a sensor signal (SS) by means of at least one electrostrictive sensor element (224) of the actuator device (220) depending on the deformation of the sensor element (224), wherein the at least one sensor element (224) is arranged directly adjacent to the actuator element (222) and / or on a side of the mirror body (212) facing away from the mirror surface (214) and is at least separated from the mirror body (212) by the actuator element (222) and / or is arranged such that the at least one sensor element (224) is at least partially provided for transferring mechanical stresses generated by the actuator element (222) to the mirror body (212), and determining said deformation of said mirror surface (214) depending on the detected sensor signal (SS), in, The reflector body (212) has a front side and a rear side facing away from the front side, the reflector surface (214) is provided on the front side of the reflector body (212), and The at least one electrostrictive actuator element (222) is arranged on the rear side of the reflector body (212).

Images