EP4104020A1

EP4104020A1 - Optical system and lithography apparatus

Info

Publication number: EP4104020A1
Application number: EP21704249.8A
Authority: EP
Inventors: Matthias Manger; Markus Raab
Original assignee: Carl Zeiss SMT GmbH
Current assignee: Carl Zeiss SMT GmbH
Priority date: 2020-02-12
Filing date: 2021-02-08
Publication date: 2022-12-21
Also published as: JP2023513338A; WO2021160557A1; DE102020201724A1; CN115398344A; US20220382166A1

Abstract

An optical system (200) comprises at least one 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) and serving for deforming the mirror surface (214). The actuator device (220) comprises at least one electrostrictive actuator element (222) for generating a mechanical stress in the mirror body (212) for deforming the mirror surface (214) depending 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 in such a way that it is configured at least partly for transferring the mechanical stress generated by the actuator element (222) to the mirror body (212).

Description

OPTICAL SYSTEM AND LITHOGRAPHY SYSTEM

The present invention relates to an optical system and a lithography system with such an optical system.

The content of the priority application DE 10 2020 201 724.7 is fully incorporated by reference (incorporation by reference).

Microlithography is used to manufacture microstructured components such as integrated circuits. The microhythmia process is carried out with a lithography system which has a lighting system and a projection system. The image of a mask (reticle) illuminated by means of the illumination system is projected by means of the projection system onto a substrate, for example a silicon wafer, coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system, around the mask structure onto the light-sensitive coating of the substrate to be transferred.

Mirrors are known whose mirror surface can be deliberately deformed by means of appropriately arranged actuators. In this way, optical imaging errors, also called aberrations, can be corrected or compensated for. The aberrations can have different origins, in particular temperature fluctuations can lead to mechanical stresses which can warp a holder of an optical element and / or an optical element itself, as a result of which the optical properties of the respective optical element can change. Such mirrors are used, for example, in astronomy, whereby the term adaptive optics has become established. The mirror surface is scanned with a measuring light and a deviation from the ideal shape is determined. A control loop can therefore be set up which controls the corresponding actuators on the basis of the determined deviation, whereby the mirror surface is brought closer to its ideal shape.

Mirrors, the surface of which can be deformed with actuators, are also used in lithography systems. However, known lithography systems have a very cramped installation space, since many functional units, such as active or passive components, have to be arranged in a small volume. It is therefore not practical to arrange an additional optical measuring system in the lithography system in order to scan the mirror surface as explained above. A feedback control of the actuators has therefore not yet been possible or only with an economically unjustifiable effort.

Against this background, it is an object of the present invention to provide an improved optical system.

According to a first aspect, an optical system with at least one mirror is proposed. The mirror has a mirror body and a mirror surface. At least one actuator device coupled to the mirror body is provided for deforming the mirror surface. The actuator device comprises at least one electrostrictive actuator element for generating a mechanical tension in the mirror body for deforming the mirror surface as a function of an electrical control voltage and at least one electrostrictive sensor element for outputting a sensor signal as a function of a deformation of the Sensor element. The at least one sensor element is arranged directly adjacent to the actuator element and / or is arranged on a side of the mirror body facing away from the mirror surface and separated from the mirror body by at least the actuator element and / or is arranged such that it is at least partially set up to transfer the mechanical tension generated by the actuator element to the mirror body.

This optical system has the advantage that it is possible, without direct scanning of the mirror surface, to detect an effect achieved by the actuator element in the mirror body. In the present case, this is advantageously possible within a physical domain, mechanically or electrically, namely the coupling between an externally applied electrical field and the deformation-dependent polarization of the material, i.e. without the actuator and sensor having to operate on different physical mechanisms. men are based. One can say that the detection of the deformation and the actuation with the help of the same mechanism of action, such as electrome- mechanically via a piezo effect. This enables a uniform description and treatment of the occurring effects, which keeps the complexity of the optical system low. The optical system can also be manufactured with a reduced number of different process steps, since the actuator element and the sensor element have the same class of material. In addition, for this reason the optical system is very robust, can be manufactured comparatively cheaply and is less prone to defects.

The optical system is designed in particular as projection optics for a lithography system. Furthermore, the optical system can be part of a beam shaping and illumination system of a lithography system. The optical system can also be used in other technical areas in which high-precision beam guidance is required or desired, such as in astronomy, in scientific devices or in military optics. Compared to known adaptive optics, the optical system has advantages in particular when a tightly limited installation space is available, when a robust system is required and / or when costs play a role.

The optical system comprises at least one mirror. In addition to the mirror, the optical system can also have further mirrors, lenses, grids, diaphragms, filters, cavities and the like, but it can also consist of the mirror with the actuator device. Furthermore, the optical system can have a plurality of mirrors with a respective actuator device. Further optically effective elements of the optical system can also have additional or different actuators, such as electrical heating, cooling and the like.

The mirror surface of the at least one mirror can have an appropriate geometric shape, such as, for example, planar, convex, concave or also different in sections. The mirror can be arranged at different positions in a beam path within the optical system, in particular in the area of a pupil or a hatch. Depending on the position in the beam path, different imaging errors or aberrations can be compensated for by the deformation of the mirror surface. Under a deforma- tion is understood in particular as a deviation from a basic shape of the mirror surface. For example, the mirror assumes the basic shape when it is arranged without tension in a holder and orientation provided for operation. In this case, the basic shape can deviate from an ideal shape due to the mirror's own weight, for example, and the ideal shape is restored through the deformation of the mirror surface. A deformation of the mirror surface is preferably understood to mean a deviation from the shape of the mirror surface when the actuator element is without charge, current or voltage.

The actuator device comprises at least the actuator element and the sensor element. The actuator device preferably also comprises a control unit for controlling the actuator element with a control voltage. The control voltage is predetermined, for example, by a control computer as a function of the mechanical tension to be achieved. The mechanical stress directly determines the deformation of the mirror surface, with a functional relationship between the mechanical stress and the deformation depending, for example, on material parameters of the mirror body and on boundary conditions such as geometric factors. Alternatively, the control computer can specify the mechanical tension to be achieved and the control unit itself determines the control voltage required for this.

The actuator device is coupled to the mirror body of the mirror in such a way that the mirror surface can be deformed as a function of the electrical control voltage of the actuator element.

The control unit includes, for example, a voltage or current source. Depending on the application, the actuator element can be operated with voltage control or charge control. In particular in dynamic applications in which the position of the actuator element is changed at a high frequency, a charge-regulated control is advantageous.

The actuator element and the sensor element have electrostrictive material, which also includes, for example, piezoelectric materials become. Electrostrictive materials have the property that, due to an interaction between an external electric field and dipoles present in the material, a mechanical tension or force can be generated in the material, which is expressed in a deformation of the material. Conversely, a deformation of the material leads to a change in the polarization of the material, which can be recorded using measurement technology and allows conclusions to be drawn about the amplitude of the deformation.

It is pointed out that the terms force, mechanical tension or deformation can be used interchangeably.

Examples of the electrostrictive material are ceramic compounds that contain the elements lead magnesium niobate (PMN) or lead zirconate titanate (PZT). These are preferably alloyed with platinum to improve the mechanical properties, the platinum worsening the dielectric properties, in particular the maximum polarization. The alloys accordingly have a material composition that can be characterized by the alloy factor _{x: PMN X} _{-Pt 1 x} or PZT _x Pt _{1 x} .

In preferred embodiments of the optical system, the electrostrictive material has a Curie temperature which is in a range of 0-40 ° C. At the Curie temperature, there is a phase transition from a first crystal structure that prevails below the Curie temperature to a second crystal structure that prevails above the Curie temperature.

The actuator element preferably has an active region, for example a layer, made of the electrostrictive material, which is arranged between two electrodes, an anode and a cathode. When the control voltage is applied between the anode and cathode, an electric field is formed in the active area, which leads to the mechanical stress.

The actuator element is mechanically coupled to the mirror body, so that the mechanical tension of the actuator element is transmitted to the mirror body, which is expressed in a corresponding deformation of the mirror body and therefore the mirror surface. How big the deformation achieved at a certain force depends on the strength of the material of the mirror body.

The sensor element preferably also has an active area made of electrostrictive material and arranged between two electrodes, for example also a layer-like structure. The sensor element and the actuator element can, however, differ, for example, in their geometric dimensions and / or a material composition.

The sensor element preferably has an assigned measuring unit which determines the polarization of the active area of the sensor element by means of an alternating measuring voltage that is applied between the cathode and anode of the sensor element. The sensor signal output by the sensor element includes, in particular, the polarization determined by the measuring unit. A deformation of the active area of the sensor element can be derived from this. The measurement AC voltage has, in particular, an amplitude that does not lead to any appreciable mechanical stress in the active area. The measuring unit can represent an independent unit of the actuator device, the measuring unit and the sensor element being assigned to one another.

In the following, the term sensor element can relate to the sensor element as a whole or only to the active area of the sensor element.

The sensor element is mechanically coupled to the actuator element and / or to the mirror body in such a way that it is deformed when the actuator element is deformed and / or when the mirror body is deformed, for example by one of the actuator Element impressed mechanical tension.

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 is no intermediate layer or no additional material between the actuator element and the sensor element. One can also say that the sensor element and the actuator element touch. In a further preferred embodiment, the sensor element is arranged on a side of the mirror body facing away from the mirror surface and separated from the mirror body by at least the actuator element. The sensor element is preferably arranged directly on a rear side of the actuator element, the rear side of the actuator element being the side that points away from the mirror body. It is also possible for an additional layer to be present between the actuator element and the sensor element.

In a further preferred embodiment, the sensor element is arranged in such a way that it at least partially transmits the mechanical stress generated by the actuator element to the mirror body. One can also say that the sensor element transmits a force from the actuator element to the mirror body or it forms an operative connection between the actuator element and the mirror body. For example, the sensor element is arranged between the actuator element and the mirror body. Alternatively, the sensor element can be embedded in a matrix next to the actuator element, the mechanical coupling between the sensor element, the actuator element and a matrix material being such that there is a mechanical tension at the transitions between Actuator element, matrix material and sensor element, at least essentially, propagated uninterrupted. In this case, it can also be said that the matrix containing the sensor element and the actuator element, viewed from the outside, essentially appears like a homogeneous body.

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

A mechanical coupling between the actuator element, sensor element and mirror body takes place in particular by means of a form-fitting connection, preferably by means of a material connection, such as, for example, gluing. A calibration measurement is preferably carried out before the optical system is started up. The mirror surface is illuminated with measuring light and the actuator device is caused to deform the mirror surface. The measurement light can be used to determine the deformation of the mirror surface that is achieved with a specific control voltage and thus establish a corresponding correlation. In addition, when the sensor signal is detected at the same time, a correlation can be established between the deformation of the mirror surface and the sensor signal. Since the sensor element is preferably only subjected to voltages of small magnitude, there is no hysteresis or the like, 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 control voltage and the deformation achieved during the calibration measurement is hardly possible. The sensor signal can be used to check during operation whether the deformation actually achieved corresponds to the desired deformation.

According to one embodiment of the optical system, it comprises a control unit for regulating the control voltage for the actuator element as a function of the sensor signal output by the sensor element in such a way that a predetermined mechanical tension is achieved in the mirror body.

The regulating unit is advantageously set up to regulate the control voltage as a function of the sensor signal output by the sensor element. This can be understood to mean that the control unit has, for example, an evaluation unit which evaluates the output sensor signal and derives an achieved mechanical tension from it. Alternatively, this step can be carried out in a control computer. The control unit can be combined with the control unit, for example.

The control unit can be implemented in terms of hardware and / or software. In the case of a hardware implementation, the control unit can be designed, for example, as a computer or as a microprocessor. In the case of a software implementation, the control unit can be designed as a computer program product, as a function, as a routine, as part of a program code or as an executable object.

By means of the actuator device, the mirror surface can therefore be precisely deformed with a regulated actuator element. The arrangement of the sensor element directly on the actuator element and / or on the rear side of the actuator element and / or in the direct path of action or force path from the actuator element to the mirror body ensures a high level of control accuracy.

According to a further embodiment of the optical system, the at least one actuator element and the at least one sensor element are produced monolithically.

This is understood in particular to mean that the actuator element and the sensor element are made from a material of the same material class, the same manufacturing technology being used to manufacture both elements. Furthermore, monolithic is understood to mean that the actuator and the sensor are based on the same mechanism of action. The two elements are preferably produced together, for example in the same process. This has the advantage that one and the same technology is used for the actuator element and the sensor element, which keeps the complexity of the optical system low.

In particular, actuator-sensor arrangements in which actuation takes place electrically, for example, but measurement takes place optically, are not monolithic. A system in which the actuation takes place electrically by means of a magnetic field, but the measurement takes place electrically by means of a capacitance measurement or the like, is also not monolithic.

According to a further embodiment 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. This embodiment has the advantage that individual actuator elements and individual sensor elements do not have to be arranged and attached to the mirror body; The whole is attached to the back of the mirror, that is to say on the side of the mirror body facing away from the mirror surface. This layer preferably covers the entire surface of the rear side of the mirror. As an alternative to this, several flat elements from the layer can also be arranged next to one another on the rear side of the mirror. The fact that the at least one actuator element and the at least one sensor element are integrated in the layer is to be understood in particular as meaning that the active areas of the actuator element (the area from which the mechanical stress originates) and of the sensor element (the area whose polarization is detected) are integrated into the layer, further units, such as the measuring unit of the sensor element, not being integrated into the layer.

The layer preferably consists entirely of the electrostrictive material, the active areas, that is to say actuator subareas and sensor subareas, being formed by arranging electrodes. The remaining material can be referred to as matrix material or as passive material.

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

It can also be said that the actuator element and the sensor element partially or completely overlap. As a result of this arrangement, the sensor element is arranged closer to the mirror body and thus to the mirror surface than the actuator element, which is why the deformation or mechanical stress that can be derived from the sensor signal of the sensor element has a very high correlation the mechanical tension in the mirror body and thus the deformation of the mirror surface, whereby the control becomes more precise. According to a further embodiment of the optical system, the at least one actuator element and the at least one sensor element each comprise at least one layer made of electrostrictive material.

A layer is preferably understood here to mean a geometry in which an aspect ratio of thickness to extension, ie length or width, is at least 1: 5, preferably at least IGO, preferably at least L100, preferably up to L1000. It is assumed here that the length and width are approximately the same order of magnitude. For example, the layer is between 10 gm and 500 gm thick and has a length and width of 0.5-5 cm in each case or is circular with a diameter in the range of 0.5-5 cm.

A layer has the advantage that the effect achieved, ie the mechanical stress or deformation achieved at a certain control voltage in the plane of the layer is greater by the factor of the aspect ratio than the effect occurring in the direction perpendicular thereto. In the event of expansion due to the electrostrictive effect in a first direction, due to the incompressibility of the material, there is always a contraction in a second direction different from the first.

A very thin layer also has the advantage that high deformations or forces can be achieved even with low control voltages.

According to a further embodiment of the optical system, the at least one actuator element has a plurality of layers made of electrostrictive material, each layer of the plurality having an assigned cathode and an assigned anode and being controllable with a respective control voltage.

This multilayer structure has the advantage that a force or mechanical tension that can be achieved with the actuator element, as the sum of the force achieved by the individual layers, can be significantly increased compared to a single layer. Larger deformations are therefore possible, which is why a correction range in which aberrations can be effectively compensated for is expanded. In embodiments of the optical system, a cathode surrounded by two layers forms the common cathode of the adjoining layers and an anode surrounded by two layers forms the common anode of the adjoining layers.

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

In this embodiment, the electric field in adjacent layers has an opposite direction. An electrostrictive material is therefore advantageously chosen in which the mechanical expansion is proportional to the square of polarization, since the opposite direction of the electric field has no effect on one direction of force.

According to a further embodiment 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.

Here, the sensor layer is applied, for example, directly to the actuator layer, with a common electrode in between. This enables a particularly compact design to be implemented, and mechanical coupling between the sensor element and the actuator element is also maximized. The sensor element is deformed identically to the actuator element, which is why the control voltage of the actuator element can be regulated very precisely.

According to a further embodiment of the optical system, the actuator device has at least two sensor elements, a material composition of the electrostrictive material of the at least two sensor elements Elements is different, each of the at least two sensor elements being set up to output a sensor signal.

This embodiment is advantageous because, for example, temperature fluctuations can have an influence on the polarization of the active material, which can lead to measurement errors. In the case of layers of different composition, temperature fluctuations have different effects, so that the influence of temperature can be calculated out. This enables a higher level of reliability and measurement accuracy. Because of the small thickness of a layer stack made up of two sensor elements, it can be assumed, for example, that both sensor elements have the same temperature.

According to a further embodiment of the optical system, a determination unit is provided which is set up to determine a temperature in the mirror body as a function of the sensor signals output by the at least two sensor elements.

By comparing the two sensor signals of the sensor elements with different compositions, both the mechanical stress and the temperature can be determined by a corresponding evaluation based on a physical model that describes the underlying physics. This is particularly advantageous when optimal cooling of the mirror body in the required area is not possible or only possible with a great deal of effort. The mechanical stresses in the mirror body caused by temperature fluctuations or also local temperature differences can then be taken into account when determining the current shape of the mirror surface and / or compensated for by means of the actuator device. This is advantageously possible without an additional system.

The temperature that can be determined here relates to the temperature in the mirror body in the area of the two sensor elements, that is to say in particular a local temperature. According to a further embodiment of the optical system, a measuring unit is provided for applying a measuring alternating voltage to the at least two sensor elements to generate the sensor signal, a frequency of the measuring alternating voltage being different for different sensor elements.

This has the advantage that crosstalk between different conductor tracks to the sensor elements does not lead to a measurement error during the evaluation. One can also speak of frequency multiplexing. The measuring unit can in particular be part of the control unit or the actuator device, but can also form an independent unit.

According to a further embodiment of the optical system, the actuator device has a plurality of M actuator elements and a plurality of N sensor elements, where M and N are integers and the actuator elements and the sensor elements are arranged alternately are.

Preferably N> M, in particular N = M + 1, so that in each case one sensor element is on the outside. For example, N = 2 and M = 1, the two sensor elements forming a sandwich structure with the actuator element. A two-dimensional deformation function can advantageously be determined here, so that the actual deformation in a section somewhat remote from the actuator element can be determined or predicted more precisely, which increases the accuracy of the regulation. One can also say that a more precise regulation is possible due to an overdetermination.

According to a further embodiment of the optical system, the actuator device comprises an assignment unit which is set up to assign a value of the output sensor signal of the at least one sensor element to an achieved deformation of the mirror surface on the basis of a calibration measurement, and wherein the control unit is set up to regulate the control voltage as a function of the assigned value and a predetermined deformation of the mirror surface. In embodiments, the assignment unit comprises a look-up table (LUT) in which sensor signal values are assigned to an achieved deformation of the mirror surface. This embodiment is particularly simple and does not require any high computing power. Intermediate values, that is to say values for the deformation in the case of values of the sensor signal that are not stored in the LUT, can be determined from the two closest values, for example, by linear interpolation.

According to a further embodiment of the optical system, a plurality of actuator devices is arranged on the at least one mirror, each of the actuator devices of the plurality being individually controllable.

The mirror preferably has, for example, a full-surface cover with actuator devices, so that the mirror surface can be freely deformed in a variety of ways by appropriate control of the actuator devices. Each actuator device advantageously has a control unit, so that each actuator device can be controlled independently of the other actuator devices. In particular in the case of adjacent actuator devices, a deformation at the location of the first actuator device can lead to a slight deformation also at the location of the second actuator device, since the mechanical stresses spread throughout the mirror body. This deformation is also detected by the sensor element of the second actuator device and the actuator element can be regulated accordingly in order to counteract the deformation if this is not desired anyway.

According to a second aspect, a lithography system with an optical system according to the first aspect or one of the embodiments is proposed.

This lithography system has the advantage that imaging errors can be corrected or compensated for, with a closed control loop being available for controlling a respective actuator element. Correction of the aberrations can thus be carried out much more precisely than without such a control loop. In particular in the case of lithography systems, the installation space is very tight because the The optics used can be operated in a vacuum, for example, which is why classic solutions for adaptive optics cannot be used.

The optical system preferably forms a beam shaping and lighting system or a projection system of a lithography system or is part of such a system.

According to a third aspect, the use of 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 tension in the mirror body for deforming the mirror surface as a function of an electrical control voltage and at least one electrostrictive sensor element for outputting a sensor signal as a function of a deformation of the Sensor element. The at least one sensor element is arranged directly adjacent to the actuator element and / or is arranged on a side of the mirror body facing away from the mirror surface and separated from the mirror body by at least the actuator element and / or is arranged such that it is at least partially set up to transfer the mechanical tension generated by the actuator element to the mirror body. The actuator device is coupled to the mirror body in such a way that the mirror surface is deformed as a function of the electrical control voltage.

According to a fourth aspect, a method is proposed for operating an optical system with at least one mirror, which has a mirror body and a mirror surface, and with 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 controlled with an electrical control voltage, so that a mechanical tension is generated in the mirror body and the mirror surface is deformed. In a second step, a sensor signal is detected by means of at least one electrostrictive sensor element of the actuator device as a function of a deformation of the sensor element, the at least one sensor element being connected directly to the actuator element. is arranged adjacent and / or is arranged on a side of the mirror body facing away from the mirror surface and separated from the mirror body by at least the actuator element and / or is arranged in such a way that it is at least partially used to transmit the mechanical stress generated by the actuator element the mirror body is set up. In a third step, the deformation of the mirror surface is determined as a function of the detected sensor signal.

In embodiments, the optical system described above and below is set up to carry out the aforementioned method or to be operated according to the method.

According to a further aspect, a method for detecting an achieved deformation of a mirror surface of an optical system according to the first aspect or one of the embodiments is proposed. In a first step, the at least one actuator element is controlled by means of a control voltage as a function of a predetermined deformation of the mirror surface. For example, in a current state of the optical system, a control computer determines an ideal shape of the mirror surface that deviates from the current actual shape of the mirror surface and, as a function of this, determines the required control voltage for the actuator element which is at the actuator unit is output. In a second step, a sensor signal is output from the at least one sensor element. This takes place in particular in that the active area of the sensor element is subjected to a measuring alternating voltage. The dielectric susceptibility and thus the polarization of the active area can be deduced from the complex impedance of the sensor element. In a third step, a deformation of the sensor element is determined as a function of the output sensor signal and, from this, the deformation of the mirror surface achieved. The polarization of the active area of the sensor element is indicative of the existing deformation of the sensor element. The deformation of the mirror surface can be determined from this by means of a mechanical model of the mirror. The deformation of the mirror surface is preferably determined in advance in a calibration measurement as a function of the deformation of the sensor element and stored in an LUT. In advantageous embodiments of the method, the control voltage is regulated in such a way that the predetermined deformation of the mirror surface is achieved.

The embodiments and features described for the optical system apply accordingly to the proposed method.

In the present case, “a” is not necessarily to be understood as restricting to exactly one element. Rather, several elements, such as two, three or more, can also be provided. Every other counting word used here is also not to be understood to mean that there is a restriction to precisely the specified number of elements. Rather, numerical deviations upwards and downwards are possible, unless otherwise stated.

Further possible implementations of the invention also include combinations, not explicitly mentioned, of features or embodiments described above or below with regard to the exemplary embodiments. The person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

Further advantageous refinements and aspects of the invention are the subject matter of the subclaims and of the exemplary embodiments of the invention described below. The invention is explained in more detail below on the basis of preferred embodiments with reference to the attached figures.

Fig. 1 shows a schematic view of a first embodiment of an optical system;

2 shows a schematic view of a first exemplary embodiment of an arrangement of a mirror with an actuator device; 3 shows a schematic view of a second exemplary embodiment of an arrangement of a mirror with an actuator device;

4 shows a schematic view of a third exemplary embodiment of an arrangement of a mirror with an actuator device;

5 shows a schematic view of a fourth exemplary embodiment of an arrangement of a mirror with an actuator device;

6 shows a schematic view of a fifth exemplary embodiment of an arrangement of a mirror with an actuator device;

7 shows a schematic view of a sixth exemplary embodiment of an arrangement of a mirror with an actuator device;

8 shows a schematic view of a seventh exemplary embodiment of an arrangement of a mirror with an actuator device having two sensor elements;

9 shows a schematic view of an exemplary embodiment of a structure of an actuator element;

10 shows a schematic view of an exemplary embodiment of a control of several actuator elements and sensor elements in an actuator device;

11 shows three diagrams of a behavior of physical quantities as a function of a control voltage;

12 shows, in a diagram, several curves of the dielectric susceptibility as a function of a control voltage;

13 shows a schematic block diagram of an exemplary embodiment of a closed control loop; 14A shows a schematic view of an embodiment of an EUV lithography system

14B shows a schematic view of an embodiment of a DUV lithography system and

15 shows a schematic block diagram of an embodiment of a method for correcting an aberration in an optical system.

In the figures, elements that are the same or have the same function have been given the same reference symbols, unless stated otherwise. It should also be noted that the representations in the figures are not necessarily to scale.

1 shows a schematic view of a first exemplary embodiment of an optical system 200. The optical system 200 here comprises a light source LS, a lens 128 which collimates the light striking it from the light source LS, two mirrors 110, 210, one further lens 128 and a wafer 124 or slide on which the light from the further lens 128 is focused. For example, the optical system 200 is an illumination system of a microscope or a lithography system 100A, 100B (see FIGS. 14A, 14B).

The second mirror 210 of the optical system 200 consists of a mirror body 212, on the front side of which the mirror surface 214 is arranged. Arranged on the rear side of the mirror body 212 is an actuator device 220 which is set up to deform the mirror surface 214 by coupling a mechanical tension into the mirror body 212. Without restricting the generality, only one actuator device 220 is shown here and also in the following figures. It goes without saying, however, that a plurality of such actuator devices 220 can be arranged on the mirror 210 in order to deform the mirror surface 214 in a targeted manner with a high spatial resolution and / or to achieve an overall deformation of the mirror 210. Because the mirror surface 214 of the mirror 210 can be deformed, an aberration, that is to say an imaging error, can be output. The imaging error is in particular dependent on an operating state of the optical system 200 and / or other optical systems that are coupled to the optical system 200. For example, spatial and / or temporal temperature differences and / or fluctuations can be compensated for by the actuator device 220. One can therefore also speak of an adaptive optical system 200, the state of which is regulated or kept constant in relation to a reference state. The actuator device 220 preferably comprises a closed control loop for regulating the actuator element 222 (see FIGS. 2-8, 10, 13, 14A or 14B).

The exact mode of operation of the actuator device 220 is explained in detail with reference to the following figures.

2-7 each show a schematic view of an exemplary embodiment of an arrangement of a mirror 210 with an actuator device 220. The exemplary embodiments differ in the specific arrangement of actuator device 220 and mirror 210 optical system 200 as shown in FIG. 1, 14A or 14B can be used.

FIG. 2 shows an actuator device 220 which is arranged between the mirror body 212 and a mirror carrier 216. The mirror carrier 216 forms a mechanical fixed point, that is, it is rigid and fixed. The actuator device 220 has an actuator element 222 and a sensor element 224, the sensor element 224 making mechanical contact with the mirror body 212 and the actuator element 222 being supported on the mirror carrier 216. There is also a control unit 226 which provides the control voltage VS for controlling the actuator element 222. In this example, the control unit 226 also detects the sensor signal SS output by the sensor element 224. The control unit 226 is preferably designed as a control unit or comprises one that controls the control voltage VS as a function of the sensor signal SS. In this arrangement, the actuation direction 223 is parallel to a normal to the surface of the mirror surface 214. The actuator element 222 extends or elongates in the actuation direction 223 when a control voltage VS is applied to it. An extension of the actuator element 222 leads to a bulging or displacement of the mirror surface 214 at the location of the actuator device 220, since the mirror carrier 216 is fixed. It can be provided here that the mirror body 212 is supported at one or more points with a fixed connecting element (not shown) on the mirror carrier 216. Such a fixed connecting element fixes the distance between mirror body 212 and mirror carrier 216, for example, where it is arranged.

3 shows an alternative embodiment of an actuator device 220 which is arranged between the mirror body 212 and a mirror carrier 216. Here, the sensor element 224 is arranged laterally directly on the actuator element 222. In this arrangement, the sensor element 224 will exactly take part in every deformation, in particular expansion or compression, of the actuator element 222 along the actuation direction 223. The actual deformation of the actuator element 222 can therefore be determined very precisely from the sensor signal SS.

4 to 7 each show a different integration of the actuator device 220, in contrast to FIGS. 2 and 3, a transverse actuation direction 223, that is to say in the plane of the mirror body 212, being used. In FIGS. 4 and 5, the actuator device 220 is glued to the rear of the mirror body 212 or is firmly connected to it in a similar manner. The sensor element 224 is either arranged between the actuator element 222 and mirror body 212 (FIG. 4) or arranged on the rear side of the actuator element 222 (FIG. 5). In the arrangement shown in FIG. 4, the sensor element 224 transmits any mechanical stress generated by the actuator element 222 to the mirror body 212. In particular, the sensor element 224 experiences the same deformation as the actuator element 222 and the area of the mirror body 212 in direct contact with the sensor element 224. Through the transverse actuation 223, which can be an extension or a shortening in relation to the actuator element 222, A mechanical tension is created in the mirror body 212, as a result of which the mirror surface 214 is correspondingly deformed.

In the exemplary embodiments in FIGS. 6 and 7, the actuator element 222 and the sensor element 224 are embedded in a matrix MX. The matrix MX consists in particular of a material of the same material class as the actuator element 222 and the sensor element 224, preferably of an electrostatic ceramic material. The actuator element 222, the sensor element 224 and the matrix MX advantageously form an essentially homogeneous material layer 221 which is fixed flat, preferably over the entire area, on the rear side of the mirror body 212. The active areas of the actuator element 222 and the sensor element 224 are defined by the arrangement of electrodes in the material MX. In these embodiments, a mechanical coupling of the actuator element 222 to the mirror body 212 is particularly strong, which has an advantageous effect on the maximum achievable deformation of the mirror surface 214.

The exemplary embodiments shown in FIGS. 2-7 can also be combined with one another.

8 shows a schematic view of a fourth exemplary embodiment of an arrangement of a mirror 210 with an actuator device 220. The basic arrangement corresponds to that shown in FIG. 7, the actuator device 220 here having two sensor elements 224, which sandwich the actuator element 222. The two sensor elements 224 advantageously have a different chemical composition, so that they have different dependencies on the temperature and the deformation. Then not only the deformation of the respective sensor element 224, but also the temperature can be determined from the two sensor signals SS. In the present case, this is done by a determination unit 230 specially set up for this purpose.

9 shows a schematic view of an exemplary embodiment of a structure of an actuator element 222, which here consists of a plurality of individual layers L1-Ln. On the top layer L1 is an electrode A1 arranged, which is operated here for example as an anode. A further electrode K1, which is operated as a cathode, is arranged between the uppermost layer L1 and the layer L2 arranged adjacent below it. It can be said that the anode A1 and the cathode K1 sandwich the top layer L1. A control voltage VS applied between anode A1 and cathode K1 (see FIGS. 2-8 or 10-13) leads to the formation of an electric field in layer L1. The role of anode A1 and cathode K1 can also be reversed in embodiments, in which case the direction of the electric field is reversed.

An electrode A2, which is operated as an anode, is again arranged between the second layer from above L2 and the third layer from above L3. It can be seen here that the cathode K1 forms a common cathode for the adjoining layers L1 and L2. The anode A2 also forms a common anode for the adjacent layers L2 and L3.

This layer-like structure continues in this example until the desired number of layers is reached. A terminating electrode Kn, which in this embodiment is operated as a cathode, is arranged under the lowermost layer Ln. In this alternating structure with common electrodes A1-An, K1-Kn, the electrostrictive material is in particular one in which the mechanical expansion is proportional to the square of the polarization, so that the layers L1-Ln despite different directions of the electric field create a deformation in the same direction.

In other embodiments, in which an electrostrictive material is used, in which the mechanical expansion is proportional to the polarization, the electrodes A1-An, K1-Kn are to be arranged and controlled in such a way that the electric field in all layers L1-Ln points in the same direction, since the layers L1-Ln otherwise work against one another.

A layer thickness of the layers L1-Ln can be different for each layer L1-Ln. The layer thicknesses of the different layers L1-Ln are preferably essentially the same and are selected from a range of 10 gm-500 gm. A material composition can also be used for each of the layers L1-Ln can be selected differently, for example in order to achieve different electrostrictive properties.

In further embodiments, a sensor element 224 has such a layer-like structure as is shown in FIG. 9 for an actuator element 222. In particular, the use of different chemical compositions for different layers L1-Ln has the advantage that a comparison of the sensor signals SS of the individual layers L1-Ln can be used to infer other major influences besides the mechanical stress, in particular the temperature in the layers L1 - Ln.

10 shows a schematic view of an exemplary embodiment of an actuator device 220 which comprises a plurality of actuator elements 222, a plurality of sensor elements 224 and a control unit 226. Here three sensor elements 224 and two actuator elements 222 are provided, which form a layer stack, the actuator elements 222 here each comprising three layers L1-L3 made of electrostrictive material by way of example.

Two of the sensor elements 224 sandwich the entire layer stack and the third sensor element 224 divides the layer stack in the middle. In the present case, passive areas are in each case arranged between the sensor elements 224 and the actuator elements 222. These can also be omitted in embodiments, an electrode arranged between sensor element 224 and actuator element 222 then representing a common electrode. The common electrode in this case is preferably grounded, because the sensor element is advantageously operated without a bias voltage.

The control unit 226 here comprises a regulated voltage source for providing the control voltage VS for the actuator elements 222 and three measuring units which are set up to generate the sensor signal SS of a respective sensor element 224 by means of an AC measuring voltage VM. The measurement alternating voltages VM here preferably have different frequencies in order to avoid mutual interference. In further embodiments, the plurality of actuator elements 222 can also be operated with different control voltages VS. 11 shows three diagrams of the behavior of physical quantities, the mechanical voltage s, the gradient of the deflection e achieved in relation to the control voltage VS, and the dielectric susceptibility _X as a function of a control voltage VS for an exemplary electrostrictive layer which is in an actuator element 222 (see FIGS. 2-10 or 13) or a sensor element 224 (see FIGS. 2-8, 10 or 13 ) can be used. The sizes o, e and c are indicated in corrective units. Volts is selected as the scale for the control voltage VS. The electrostrictive material is, in particular, a material with a composition PMN _x Pt _{1 x.} The curves shown relate to a mechanically free state of the layer, that is, without mechanical pretension and without the layer being embedded in a rigid material system .

The upper diagram shows the mechanical stress o (unit: N / m ² or Pa), which the layer controlled with the control voltage VS provides or generates. With a control voltage VS = 0, the layer does not generate any mechanical stress o. It can also be seen that a small control voltage VS only causes a very low mechanical stress o. In the case of low control voltages VS, the mechanical stress o generated is, for example, proportional to the square of the control voltage VS.

The middle diagram shows the gradient of the deflection e achieved in relation to the control voltage VS as a function of the control voltage VS.

The lower diagram shows the dielectric susceptibility c as a function of the control voltage VS. It can be seen that the dielectric susceptibility c has a maximum at a control voltage VS = 0.

As shown in FIG. 12, the dielectric susceptibility _X at the control voltage VS = 0 also has a very high sensitivity with regard to mechanical stress. In FIG. 12, several curves of the dielectric susceptibility c as a function of a control voltage VS are shown in a diagram. The five curves 1 - 5 shown differ with regard to a deformation of the layer. For example, curve corresponds to 3 the mechanically free or untensioned state. Curves 1 and 2 correspond, for example, to a stretching of the layer in the ppm range, for example 10 ppm for curve 1 and 5 ppm for curve 2. Curves 4 and 5 correspond, for example, to compression of the layer in ppm Range, for example 5 ppm for curve 4 and 10 ppm for curve 5. Because of this sensitivity maximum of the dielectric susceptibility _X , this physical variable is particularly suitable as a measurement variable for deformation of the layer, especially in a sensor Element 224. The dielectric susceptibility x can be determined by an impedance measurement by means of the measurement alternating voltage VM.

13 shows a schematic block diagram of an exemplary embodiment of a closed control loop in an actuator device 220. In the present case, the control unit 226 is designed as a control unit. _{The control unit 226 receives a predetermined mechanical setpoint tension σ s} from the outside, for example by a control computer (not shown), which the actuator device 220 is intended to provide or generate by means of the actuator element 222. The control unit 226 then controls the actuator element 222 with the control voltage VS. The control voltage VS is preferably selected such that, under good conditions, it precisely _{achieves the mechanical setpoint voltage 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 can slightly miss _{the mechanical setpoint tension σ s.}

The sensor element 224 is deformed with the actuator element 222. The extent of the deformation can be determined as described above, which is represented here by the sensor signal SS. The sensor signal SS is particularly characteristic of the deformation of the sensor element 224 and thus also the mechanical stress o achieved in the sensor element 224. Due to the direct coupling of the sensor element 222 to the actuator element 224, the mechanical The voltage o in the sensor element 224 is essentially that in the actuator element 222. The sensor signal SS is therefore suitable as a control signal. The control unit 226 is therefore Readjust the control voltage VS for the actuator element 222 on the basis of the sensor signal SS.

A control cycle can last, for example, in the range of 1 ms - 100 ms, corresponding to a control frequency between 10 Hz - 1 kHz.

14A shows a schematic view of an EUV lithography system 100A, which comprises a beam shaping and illumination system 102 and an optical system 200, which is designed here as a projection system. EUV stands for “extreme ultraviolet” (EUV) and designates a wavelength of the work light between 0.1 nm and 30 nm. The beam shaping and lighting system 102 and the projection system 200 are each Provided in a vacuum housing (not shown), each vacuum housing being evacuated with the aid of an evacuation device (not shown). The vacuum housings are surrounded by a machine room, not shown, in which drive devices for mechanical movement or setting of optical elements are provided. Furthermore, electrical controls and the like can also be provided in this machine room.

The EUV lithography system 100A has an EUV light source 106A. A plasma source (or a synchrotron) can be provided as the EUV light source 106A, for example, which emits radiation 108A in the EUV range (extreme ultraviolet range), that is, for example, in the wavelength range from 5 nm to 20 nm. The EUV radiation 108A is bundled in the beam shaping and lighting system 102 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 transmissivity through air, which is why the beam guiding spaces in the beam shaping and lighting system 102 and in the projection system 200 are evacuated.

The beam shaping and illumination system 102 shown in FIG. 14A has five mirrors 110, 112, 114, 116, 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 as reflective optical element and can be arranged outside of the systems 102, 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 which is imaged on a wafer 124 or the like in a reduced size by means of the projection system 200.

The projection system 200 (also referred to as a projection objective) has five mirrors M1 to M5 for imaging the photomask 120 on the wafer 124. In this case, individual mirrors M1 to M5 of the projection system 200 can be arranged symmetrically to an optical axis 126 of the projection system 200. It should be noted that the number of mirrors M1 to M5 of the EUV lithography system 100A is not limited to the number shown. More or fewer mirrors M1 to M5 can also be provided. Furthermore, the mirrors M1 to M5 are generally curved on their front side to form the beam.

The projection system 200 furthermore has a further mirror 210, on the rear side of which a multiplicity of actuator devices 220 are arranged, each of which can be designed as on the basis of FIGS. 2-8, 10 or 13. Each actuator device 220 comprises an assigned actuator element 222 and an assigned sensor element 224. A control unit 226 is for controlling the actuator elements 222 with a control voltage VS and for applying the sensor elements 224 with an alternating measurement voltage VM set up to generate a respective sensor signal SS. For the sake of clarity, only one control unit 226 is shown here, which controls all of the actuator elements 222 and sensor elements 224. The front side of the mirror 210 can be deformed by targeted control of the actuator devices 220, which can be used to correct optical aberrations in order to increase the resolution of the lithography process.

In advantageous embodiments, the actuation takes place in a regulated manner by the actuator elements 222 in that an actually achieved deformation is detected by the sensor elements 224 and the control voltage VS can therefore be regulated by evaluating the sensor signal SS. This regulation takes place individually for each actuator device 220, for reasons of clarity only one actuator device 220 and only one control voltage VS, one measuring AC voltage VM and one sensor signal SS are shown.

The projection system 200 or also the beam shaping and lighting system 102 can have further mirrors 210 with an associated actuator device 220.

14B shows a schematic view of a DUV lithography system 100B, which comprises a beam shaping and lighting system 102 and an optical system 200, which is designed here as a projection system. DUV stands for “deep ultraviolet” (DUV) and designates a wavelength of the work light between 30 nm and 250 nm. The beam shaping and lighting system 102 and the projection system 200 can - as already described with reference to FIG 14A - arranged in a vacuum housing and / or surrounded by a machine room with corresponding drive devices.

The DUV lithography system 100B has a DUV light source 106B. An ArF excimer laser, for example, which emits radiation 108B in the DUV range at, for example, 193 nm, can be provided as the DUV light source 106B.

The beam shaping and illumination system 102 shown in FIG. 14B guides the DUV radiation 108B onto a photo mask 120. The photo mask 120 is designed as a transmissive optical element and can be arranged outside the systems 102, 104. The photomask 120 has a structure which is reduced by means of the projection system 200 onto a wafer 124 or the like.

The projection system 200 has a plurality of lenses 128 and / or mirrors 130 for imaging the photomask 120 on the wafer 124. Individual lenses 128 and / or mirrors 130 of projection system 104 can be arranged symmetrically to an optical axis 126 of projection system 200. It should be noted that the number of lenses 128 and mirrors 130 of the DUV lithography system 100B is not limited to the number shown. It More or fewer lenses 128 and / or mirrors 130 can also be provided. Furthermore, the mirrors 130 are generally curved on their front side for beam shaping.

An air gap between the last lens 128 and the wafer 124 can be replaced by a liquid medium 132 which has a refractive index> 1. The liquid medium 132 can be ultrapure water, for example. Such a structure is also referred to as immersion lithography and has an increased photolithographic resolution. The medium 132 can also be referred to as an immersion liquid.

The projection system 200 furthermore has a mirror 210, on the rear side of which an actuator device 220 is arranged, which can be designed as on the basis of FIGS. 2-8, 10 or 13. Without loss of generality, only one actuator device 220 is shown here, but it goes without saying that there is preferably a plurality of actuator devices 220, each of which can be individually controlled and / or regulated. The actuator device 220 comprises an assigned actuator element 222 and an assigned sensor element 224. A control unit 226 is used to control the actuator elements 222 with a control voltage VS and to apply a measurement to the sensor elements 224 AC voltage VM set up to generate a respective sensor signal SS.

In FIG. 14B it is also shown that a predetermined mechanical setpoint tension σ _{s is} specified from the outside, which is to be achieved by the actuator element 222. The mechanical target tension σ _s is determined, for example, by a control computer on the basis of a target deformation of the mirror 210 to be achieved. The targeted deformation of the front side of the mirror 210 allows optical aberrations to be corrected to increase the resolution of the lithography process.

In advantageous embodiments, the actuation takes place in a regulated manner by the actuator element 222 in that an actually achieved deformation is detected by the sensor element 224 and the control voltage VS can therefore be regulated by evaluating the sensor signal SS. This regulation takes place individually for each actuator device 220, only one actuator device 220 and only one control voltage VS, one measuring AC voltage VM and one sensor signal SS being shown for reasons of clarity.

15 shows a schematic block diagram of an exemplary embodiment of a method for correcting an aberration in an optical system 200, for example in the optical system 200 of FIG. 1, by using the mirror surface 212 (see FIGS. 1-8) of a mirror 210 ( see FIGS. 1-8 or 14A, 14B) of the optical system 200 is deliberately deformed.

In a first step S1, the at least one actuator element 222 (see FIGS. 2-8 or 13) is activated by means of a control voltage VS (see FIGS. 2-8 or 10-13) as a function of a predetermined deformation of the mirror surface 214 (see FIG . 1 - 8) controlled. As a result, a mechanical tension is generated in the actuator element 222, which tension is transmitted to the mirror body 212 (see FIGS. 1-8) of the mirror 210, which leads to a local deformation of the mirror surface 214.

In a second step S2, the at least one sensor element 224 (see FIGS. 2-8 or 13) outputs a sensor signal SS (see FIGS. 2-8 or 13). For this purpose, the sensor element 224 is acted upon with a measuring alternating voltage VM, as has already been described above.

In a third step S3, a deformation of the sensor element 224 is determined as a function of the detected sensor signal SS. An achieved deformation of the mirror surface 214 can be determined from this.

In a fourth, optional step S4, the control voltage VS is regulated in such a way that the predetermined deformation of the mirror surface 214 is achieved. For this purpose, for example, the predetermined deformation is achieved with the Deformation compared, from which it can be seen whether the drive voltage VS must be higher or lower in order to achieve the predetermined deformation.

Although the present invention has been described on the basis of exemplary embodiments, it can be modified in many ways. In particular, many of the physical quantities on the basis of which the description was made are interchangeable with other quantities. Instead of mechanical tension, it is also possible to speak of force or mechanical elongation or deformation. Furthermore, it can be said that the sensor signal depends on the dielectric susceptibility, on the impedance, on the polarization, on the capacitance or the like, which can all be converted into one another as long as the respective material parameters are known.

In particular, the invention allows a large number of possible arrangements of a sensor element in relation to an actuator element in an actuator

Establishment too. The different positions can be advantageous depending on the specific application. In addition, the combination of different arrangements in one actuator element increases the accuracy of the detection.

Furthermore, the control loop for regulating the control voltage can be implemented or realized in a variety of ways without the present invention being limited in a certain way.

REFERENCE LIST

1 Functional history

2 Functional history

3 Functional history

4 Functional history

5 Functional history

100A EUV lithography system

100B DUV lithography system

102 Beam shaping and lighting system

106A EUV light source

106B DUV light source

108A EUV radiation

108B DUV radiation

110 mirrors

112 mirror

114 mirrors

116 mirrors

118 mirrors

120 photo mask

122 mirrors

124 wafers

126 optical axis

128 lens

130 mirrors

132 medium

200 optical system

210 mirrors

212 mirror body

214 mirror surface

216 mirror supports

220 Actuator Setup

221 layer

222 actuator element

223 Actuating Direction 224 sensor element

226 control unit

230 Determination unit A1 anode

A2 anode

A3 anode

Cathode at anode K1

K2 cathode

K3 cathode

Kn cathode L1 layer

L2 layer

L3 layer

Ln layer

LS light source

MX matrix

Ml mirror

M2 mirror

M3 mirror

M4 mirror

M5 mirror

51 procedural step

52 Process step

53 procedural step

54 procedural step

55 Sensor signal VM measurement AC voltage VS control voltage

X dielectric susceptibility s mechanical stress σ _s mechanical stress

Claims

PATENT CLAIMS

1. Optical system (200) with at least one mirror (210), which has a mirror body (212) and a mirror surface (214), and with at least one actuator device (220) coupled to the mirror body (212) for deformation the mirror surface (214), wherein the actuator device (220) has: at least one electrostrictive actuator element (222) for generating a mechanical tension in the mirror body (212) for deforming the mirror surface (214) as a function of an electrical one Control voltage (VS), at least one electrostrictive sensor element (224) for outputting a sensor signal (SS) depending on a deformation of the sensor element (224), the at least one sensor element (224) being directly connected to the actuator - Element (222) is arranged adjacent and / or on a side of the mirror body (212) facing away from the mirror surface (214) and separated from the mirror body (212) by at least the actuator element (222) is ordered and / or is arranged in such a way that it is at least partially set up to transfer the mechanical stress generated by the actuator element (222) to the mirror body (212), and wherein the actuator device (220) is connected to the mirror body ( 212) is coupled so that the mirror surface (214) can be deformed as a function of the electrical control voltage (VS) of the actuator element (222).

2. Optical system according to claim 1, further comprising a control unit for regulating the control voltage (VS) for the actuator element (222) as a function of the sensor signal (SS) output by the sensor element (224) such that a predetermined mechanical tension is achieved in the mirror body (212).

3. 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 produced monolithically.

4. Optical system according to one of claims 1 to 3, wherein the at least one actuator element (222) and the at least one sensor element (224) in a side of the mirror body (212) facing away from the mirror surface (214) on the mirror (210) arranged layer (221) are integrated.

5. Optical system according to one of claims 1 to 4, wherein the at least one sensor element (224) is at least partially between the at least one actuator element (222) and the mirror body (212) in a direction along a surface normal of the mirror surface (214 ) is arranged.

6. Optical system according to one of claims 1 to 5, wherein the at least one actuator element (222) and the at least one sensor element (224) each have at least one layer (Ll, ..., Ln) made of electrostrictive material include.

7. Optical system according to claim 6, wherein the at least one actuator element (222) has a plurality of layers (Ll, ..., Ln) made of electrostrictive material, each layer (Ll, ..., Ln) the plurality has an assigned cathode (K1-Kn) and an assigned anode (A1-An) and can be controlled with a respective control voltage (VS).

8. Optical system according to one of claims 6 or 7, wherein the at least one actuator element (222) and the at least one sensor element (224) are a layer stack (SL) comprising at least two layers (Ll, ..., Ln) form.

9. Optical system according to one of claims 1-8, wherein the actuator device (220) has at least two sensor elements (224), wherein a material composition of the electrostrictive material of the at least two sensor elements (224) is different, each the at least two sensor elements (224) are set up to output a sensor signal (SS).

10. Optical system according to claim 9, wherein a determination unit (230) is provided for determining a temperature in the mirror body (212) as a function of the output sensor signals (SS) of the at least two sensor elements (224).

11. Optical system according to claim 9 or 10, wherein a measuring unit for applying the at least two sensor elements (224) with a measuring AC voltage (VM) for generating the sensor signal (SS) is provided, wherein a frequency of the measuring AC voltage ( VM) is different for different sensor elements (224).

12. Optical system according to one of claims 1-11, wherein the actuator device (220) has a plurality of M actuator elements (222) and a plurality of N sensor elements (224), where N and M are integers and the actuator elements (222) and the sensor elements (224) are arranged alternately.

13. Optical system according to one of claims 2 - 12, wherein the actuator device (220) comprises an assignment unit which is used to assign a value of the output sensor signal (SS) of the at least one sensor element (224) to an achieved deformation of the mirror surface (214) is set up on the basis of a calibration measurement, and wherein the control unit is set up to regulate the control voltage (VS) as a function of the assigned value and a predetermined deformation of the mirror surface (214).

14. Optical system according to one of claims 1-13, wherein a plurality of actuator devices (220) is arranged on the at least one mirror (210), and wherein each of the actuator devices (220) of the plurality is individually is controllable.

15. lithography system (110A, 100B) with an optical system (200) according to one of claims 1-13.

16. Use of a mirror (210) coupled to an actuator device (220) in an optical system (200), the mirror (210) having a mirror body (212) and a mirror surface (214), and wherein the actuator device (220) has: at least one electrostrictive actuator element (222) for generating a mechanical tension in the mirror body (212) for deforming the mirror surface (214) as a function of an electrical control voltage (VS), at least one electrostrictive sensor element (224) for outputting a sensor signal (SS) as a function of a deformation of the sensor element (224), the at least one sensor element (224) being arranged directly adjacent to the actuator element (222) and / or on one of the mirror surfaces surface of the mirror body (212) facing away from the surface (214) and separated from the mirror body (212) by at least the actuator element (222) and / or is arranged in such a way that it is at least partially used to transmit the from the actuator element ( 222) generated mechanical tension is set up on the mirror body (212), and wherein the actuator device (220) is coupled to the mirror body (212) in such a way that the mirror surface ( 214) is deformed depending on the electrical control voltage (VS).

17. A method for operating an optical system (200) with at least one mirror (210), which has a mirror body (212) and a mirror surface (214), and with at least one actuator coupled to the mirror body (212). Device (220) for deforming the mirror surface (214), with the steps:

Controlling an electrostrictive actuator element (222) of the actuator device (220) with an electrical control voltage (VS), so that a mechanical tension is generated in the mirror body (212) and the mirror surface (214) is deformed,

Detection of a sensor signal (SS) by means of at least one electrostrictive sensor element (224) of the actuator device (220) as a function of a deformation of the sensor element (224), the at least one sensor element (224) being directly connected to the actuator Element (222) is arranged adjacent and / or is arranged on a side of the mirror body (212) facing away from the mirror surface (214) and separated from the mirror body (212) by at least the actuator element (222) and / or is arranged in such a way that it is at least partially used to transmit the signals generated by the actuator element (222) generated mechanical stress is set up on the mirror body (212), and

Determining the deformation of the mirror surface (214) as a function of the detected sensor signal (SS).