Adaptive optical module for a microlithographic projection exposure system

Abstract

The invention relates to an adaptive optical module (38A) for a microlithographic projection exposure system (10; 210), comprising: an optical surface (32) for interacting with exposure radiation (14) of the projection exposure system; and a plurality of actuators (36n-1, 36n, 36n+1) for modifying a shape of the optical surface. The adaptive optical module comprises a dielectric medium (48) that can be deformed by applying an electric voltage (68), and each of the actuators comprises a separate control electrode (62n-1, 62n, 62n+1) which in each case is designed to generate an electric field in a layer of the dielectric medium. The control electrodes are connected to one another by means of a weakly conductive structure (60) having an electrical conductivity of at least 0.1 mS / m, and, in order to measure an impedance (86n-1, 86n, 86n+1) of at least one of the actuators, a measurement electrode (58n-1, 58n, 58n+1) is arranged between the control electrode of the actuator being measured and the dielectric medium.

Description

[0001] Adaptive optical module for a microlithographic projection exposure system

[0002] This application claims priority from German patent application 10 2023 210 952.2 filed on November 3, 2023. The entire disclosure of this patent application is incorporated by reference into the present description.

[0003] Background of the invention

[0004] The invention relates to an adaptive optical module for a microlithographic projection exposure apparatus having a plurality of actuators, a projection exposure apparatus for microlithography having such an adaptive optical module, and a method for determining a respective deflection of a plurality of actuators of an adaptive optical module of a microlithographic projection exposure apparatus.

[0005] To ensure the most precise possible imaging of the mask structures onto the wafer, a projection lens of a projection exposure system for microlithography with the lowest possible wavefront aberrations is required. Projection lenses are therefore equipped with manipulators that allow wavefront aberrations to be corrected by changing the state of individual optical elements of the projection lens. Examples of such a state change include a change in the position of one or more of the six rigid-body degrees of freedom of the respective optical element and a deformation of the optical element.

[0006] For the latter change of state, the optical element is typically integrated into an adaptive optical module of the type mentioned above. This module can incorporate one or more piezoelectric or electrostrictive actuators to actuate the optical surface. The functionality of such actuators is based on the deformation of a dielectric medium by applying an electric field. To determine the desired change of state, the aberration characteristics of the projection lens are typically measured regularly, and if necessary, changes in the aberration characteristics between individual measurements are determined by simulation. This allows, for example, lens or mirror heating effects to be computationally accounted for.

[0007] Problems often arise when using piezoelectric or electrostrictive adaptive optical elements because changes in relevant parameters in the actuator material, e.g. due to temperature variations, aging, defects, drifts, etc., can lead to considerable inaccuracies in the surface shape corrections performed by the adaptive optical element.

[0008] To correct or avoid these inaccuracies, DE 10 2020 212 743 A1, for example, proposes placing a measuring electrode for temperature measurement in the actuator material and making appropriate corrections based on the measurement results. However, this is an indirect measurement of the surface shape errors caused by actuator deviations, and the accuracy is often insufficient.

[0009] Underlying task

[0010] It is an object of the invention to provide an adaptive optical module and a method of the type mentioned above, with which the aforementioned problems can be solved, and in particular, a surface shape correction of the adaptive optical element can be carried out with improved accuracy. Inventive Solution

[0011] The above-mentioned object can be achieved according to a first aspect of the invention, for example, with an adaptive optical module for a microlithographic projection exposure apparatus. The adaptive optical module comprises an optical surface for interacting with exposure radiation of the projection exposure apparatus, as well as a plurality of actuators for changing a shape of the optical surface. Furthermore, the adaptive optical module has a dielectric medium that can be deformed by applying an electrical voltage, and each of the actuators comprises a separate control electrode, each of which is arranged to generate a respective electric field in a layer of the dielectric medium. Furthermore, the control electrodes are connected by means of a weakly conductive structure with an electrical conductivity of at least 0.1 mS / m, i.e. 10 -4S / m, and to measure the impedance of at least one of the actuators, a measuring electrode is arranged between the control electrode of the actuator being measured (i.e., the actuator with respect to which the impedance is being measured) and the dielectric medium. The measured actuator is understood to be the actuator whose impedance is being measured.

[0012] According to one embodiment, a respective measuring electrode for measuring an impedance of the respective actuator is arranged between the respective control electrode and the dielectric medium. The weakly conductive structure is to be understood as a weakly electrically conductive structure. The conductivity of the weakly conductive structure can, according to one embodiment, be at least 0.1 mS / m, i.e. 0.0001 Siemens / meter, and less than 1 kS / m. According to further embodiments, the conductivity of the weakly conductive structure is at least 1 mS / m, at least 0.01 S / m, at least 0.1 S / m or at least 10 S / m. The upper limit for the conductivity of the weakly conductive structure can, according to different embodiments, be 1 kS / m, 200 S / m or 100 S / m. The weakly conductive structure is formed, for example, as a layer, and the actuators are electrically coupled by means of the weakly conductive structure.In other words, the actuators can be used in coupled networks to smooth the deformation effect when controlling individual actuators. The use of the weakly conductive structure creates a gradient field between the actuator electrodes. The statement that each actuator has a separate control electrode means that each actuator has its own control electrode, meaning the actuators do not share a single control electrode.

[0013] The electric field in the layer of the dielectric medium is generated by applying an electrical voltage to the dielectric medium. This causes a deformation of the dielectric medium. The respective measuring electrode is arranged to measure the impedance of the respective actuator, i.e., the impedance of the actuator assigned to the respective control electrode. The impedance can be measured during operation of the projection exposure system or during exposure pauses.

[0014] The solution according to the first aspect of the invention enables the determination of a deflection of at least one of the actuators at at least one operating point based on an impedance measurement, i.e., an electrical measurement on the adaptive optical module. Compared to, for example, an interferometric measurement of the surface shape as a function of the operating voltage, the electrical measurement according to the invention can be performed at a high repetition rate, possibly even during the exposure operation of a microlithographic projection exposure system.

[0015] The inventive solution is further based on the finding that when using the control electrode of an actuator to be measured for impedance measurement, the connection of this control electrode to the control electrodes of neighboring actuators via the weakly conductive structure can lead to distortions in the measurement result. These distortions can be caused by leakage currents occurring between the control electrodes during the impedance measurement. To eliminate this source of error, according to the first aspect of the invention, at least one measuring electrode is arranged between the control electrode of the actuator being measured and the dielectric medium.This measuring electrode has no electrical connection to an electrode of a neighboring actuator, in particular to one of the control electrodes or to a further measuring electrode of a neighboring actuator. Thus, the adaptive optical module configured according to the first aspect of the invention enables a measurement of a deflection of at least one of the actuators with a high repetition rate and, at the same time, with high accuracy. This allows a surface shape correction of the adaptive optical element to be carried out with high accuracy. In this text, a neighboring actuator of a reference actuator is understood to mean any actuator whose control electrode is connected to the control electrode of the reference actuator via the weakly conductive layer. Thus, the term "neighboring actuator" includes both an actuator directly adjacent to the reference actuator, i.e.an actuator that is directly adjacent to the reference actuator, as well as a next-but-one or more distant actuator neighbor.

[0016] According to one embodiment, the weakly conductive structure is configured as a layer arranged between the drive electrodes of the actuators and the dielectric medium.

[0017] According to a further embodiment, the layer of the weakly conductive structure extends continuously along the control electrodes of the actuators.

[0018] According to a further embodiment, the adaptive optical module further comprises at least one base electrode, which is arranged as a counter electrode to the control electrodes and is configured to generate the respective electric field in the dielectric medium together with the respective control electrode. A common base electrode or multiple base electrodes can be provided for the various actuators.

[0019] The aforementioned object can be achieved according to a second aspect of the invention, for example, with an adaptive optical module for a microlithographic projection exposure system. The adaptive optical module comprises an optical surface for interacting with exposure radiation from the projection exposure system and a plurality of actuators for changing a shape of the optical surface. Furthermore, the adaptive optical module has a dielectric medium deformable by applying an electrical voltage, and each of the actuators comprises a separate control electrode, each of which is arranged to generate an electric field in a layer of the dielectric medium. Furthermore, the control electrodes are connected to one another by means of a weakly conductive structure with an electrical conductivity of at least 0.1 mS / m.Furthermore, the adaptive optical module has an evaluation device which is configured to calculate, when measuring an impedance of at least one of the actuators, an effect influencing the measurement result of a current flow caused by the weakly conductive structure between the control electrode of the measured actuator and at least one further control electrode from the measurement result.

[0020] The further control electrode is preferably a control electrode directly adjacent to the measured control electrode. According to one embodiment, for each measured impedance of the actuators, the respective current flow between the control electrode of the measured actuator and at least one further control electrode is calculated from the measurement result on the basis of at least one predetermined coupling resistance between the control electrodes. The current flows between the control electrodes occur substantially or entirely via the weakly conductive structure. According to one embodiment, a respective measuring electrode for measuring an impedance of the respective actuator is arranged between the respective control electrode and the dielectric medium. The weakly conductive structure is to be understood as a weakly electrically conductive structure. The conductivity of the weakly conductive structure can, according to one embodiment, be at least 0.1 mS / m, i.e.0.0001 Siemens / meter, and less than 1 kS / m. According to further embodiments, the conductivity of the weakly conductive structure is at least 1 mS / m, at least 0.01 S / m, at least 0.1 S / m, or at least 10 S / m. The upper limit for the conductivity of the weakly conductive structure can be 1 kS / m, 200 S / m, or 100 S / m, according to different embodiments.

[0021] The solution according to the second aspect of the invention, like the solution according to the first aspect of the invention, enables the determination of a deflection of at least one of the actuators at at least one operating point based on an impedance measurement, i.e., an electrical measurement on the adaptive optical module. The control electrode of an actuator to be measured can be used for the impedance measurement. As already explained above with reference to the solution according to the first aspect of the invention, such an electrical measurement can be performed at a high repetition rate, possibly even during the exposure operation of a microlithographic projection exposure system.

[0022] The inventive solution is further based on the finding that, due to the electrical connection of this control electrode to control electrodes of neighboring actuators via the weakly conductive structure, falsifications in the measurement result can occur due to leakage currents. According to the second aspect of the invention, these falsifications are avoided by subtracting from the measurement result an effect of a current flow caused by the weakly conductive structure between the control electrode of the measured actuator and at least one other of the control electrodes that influences the measurement result. Thus, the adaptive optical module configured according to the second aspect of the invention enables measurement of a deflection of at least one of the actuators at a high repetition rate and, at the same time, with high accuracy. This allows a surface shape correction of the adaptive optical element to be carried out with high accuracy.

[0023] According to an embodiment according to the second aspect of the invention, the adaptive optical module has at least one current measuring device for measuring the current flow between the control electrode of the measured actuator and the at least one further control electrode, wherein the evaluation device is configured to calculate the effect from the measurement result on the basis of the measured current flow.

[0024] According to a further embodiment according to the second aspect of the invention, the control electrode of the measured actuator is adjacent to, in particular directly adjacent to, at least four, in particular at least eight control electrodes of other actuators, and the adaptive optical module comprises a current measuring device for measuring the respective current flow between the control electrode of the measured actuator and each of the adjacent control electrodes. Furthermore, the evaluation device is configured to calculate the respective effect of the measured current flows from the measurement result.

[0025] According to a further embodiment according to the second aspect of the invention, the weakly conductive structure has a plurality of sections, wherein one of the sections is arranged on the control electrode of the actuator being measured and on the at least one further control electrode, and the two sections are electrically connected via the current measuring device. According to a further embodiment according to the second aspect of the invention, the sections of the weakly conductive structure are electrically insulated from one another, with the exception of the connection via the current measuring device, for example, by an insulating separating line.

[0026] According to a further embodiment according to the second aspect of the invention, one of the sections of the weakly conductive structure is arranged on the control electrode of the measured actuator and on the control electrodes of all actuators immediately adjacent to the measured actuator, and the section of the measured actuator is electrically conductively connected to each of the sections arranged on the immediately adjacent actuators via a separate current measuring device.

[0027] According to a further embodiment according to the second aspect of the invention, the evaluation device is further configured to calculate the effect based on at least one predetermined coupling resistance between the control electrode of the measured actuator and the at least one further control electrode from the measurement result. According to one embodiment, the control electrode of the measured actuator is adjacent to, in particular adjacent to, at least four, in particular at least eight, control electrodes of further actuators, and the evaluation device is configured to calculate the respective effect of predetermined coupling resistances between the control electrode of the measured actuator and the adjacent control electrodes from the measurement result.

[0028] According to a further embodiment according to the second aspect of the invention, the adaptive optical module comprises at least one current measuring device for measuring a current flow emerging from the further control electrode when a test voltage is applied to the control electrode of the actuator being measured. According to a further embodiment according to the second aspect of the invention, the adaptive optical element has at least one voltage source connected to at least one of the control electrodes, wherein the evaluation device is configured to calculate a line resistance from the voltage source to the control electrode from the measurement result when measuring the impedance of the at least one control electrode. In the general case, the adaptive optical module has an impedance measuring device configured to measure the impedance of the at least one control electrode.Such an impedance measuring device can also inject a current and measure the voltage instead of using a voltage source.

[0029] According to a further embodiment according to the second aspect of the invention, the adaptive optical module comprises an alternating voltage source configured to apply an alternating voltage to the at least one control electrode at such a high frequency in order to determine the line resistance of the at least one control electrode that an ohmic equivalent resistance of the actuator assigned to the control electrode drops to less than 10%, in particular to less than 5%, of the value of the line resistance. The frequency can, for example, be at least 10 kHz, in particular at least 100 kHz or at least 500 kHz. Here, too, the adaptive optical module can generally have an impedance measuring device that impresses an alternating current instead of a Weichsel voltage source.

[0030] According to a further embodiment according to the second aspect of the invention, the adaptive optical module further comprises a measuring device which is configured to measure a current flowing from the respective control electrode when measuring the respective impedance of the actuators. When measuring the impedance, an alternating voltage is applied to the respective control electrode, and the current flowing from the respective control electrode is measured. According to an embodiment according to the first or second aspect of the invention, the adaptive optical module further comprises an evaluation device which is configured to calculate an actuator deflection from a measured impedance of one of the actuators. This is done, for example, by determining a dielectric susceptibility of the actuator in question from the measured impedance and performing a linear mapping to determine the actuator deflection.

[0031] According to a further embodiment, the adaptive optical module further comprises a control unit which is configured to correct a control variable applied to the associated control electrode on the basis of the calculated actuator deflection.

[0032] According to a further embodiment according to the first or second aspect of the invention, the weakly conductive structure comprises a rare earth nickel oxide. Advantageously, the weakly conductive structure consists of at least 90% or entirely of the rare earth nickel oxide. According to one embodiment, the rare earth nickel oxide comprises LaNiOa, which can also be referred to as LNO.

[0033] Furthermore, according to the invention, a projection exposure system for microlithography is provided, which comprises at least one adaptive optical module according to one of the embodiments or embodiment variants according to the first or the second aspect of the invention.

[0034] Furthermore, according to the first aspect of the invention, a method is provided for determining a respective deflection of a plurality of actuators of an adaptive optical module of a microlithographic projection exposure apparatus, which actuators are configured to change a shape of an optical surface of the optical module.The adaptive optical module comprises a dielectric medium that can be deformed by means of an electrical voltage, each of the actuators has a separate control electrode for generating a respective electric field in a layer of the dielectric medium, the control electrodes are connected to one another by means of a weakly conductive structure with an electrical conductivity of at least 0.1 mS / m and the method comprises the steps of: measuring an impedance of at least one of the actuators by means of a measuring electrode arranged between the control electrode of the measured actuator and the dielectric medium and calculating the respective deflection of the actuators from the respective measured impedance.

[0035] Furthermore, according to the second aspect of the invention, a method is provided for determining a respective deflection of a plurality of actuators of an adaptive optical module of a microlithographic projection exposure apparatus, which actuators are configured to change a shape of an optical surface of the optical module.The adaptive optical module comprises a dielectric medium that can be deformed by means of an electrical voltage, each of the actuators has a separate control electrode for generating a respective electric field in a layer of the dielectric medium, the control electrodes are connected to one another by means of a weakly conductive structure with an electrical conductivity of at least 0.1 mS / m and the method comprises the steps of: measuring an impedance of at least one of the actuators, calculating an effect of a current flow caused by the weakly conductive structure from the measurement result of the impedance measurement, wherein the current flow occurs between the control electrode of the measured actuator and at least one further control electrode, and calculating the respective deflection of the actuators from the respective measured impedance.

[0036] According to an embodiment of the method according to the second aspect of the invention, the current flow caused by the weakly conductive structure is measured by means of a current measuring device and the effect is calculated from the measurement result of the impedance measurement on the basis of the measured current flow.

[0037] According to a further embodiment according to the second aspect of the invention, a coupling resistance between the control electrode of the measured actuator and the at least one further control electrode is determined, and the effect is calculated from the measurement result of the impedance measurement based on the determined coupling resistance. In other words, the coupling resistance is determined before the effect is calculated from the measurement result.

[0038] According to a further embodiment according to the second aspect of the invention, a line resistance of at least one electrical connection between at least one voltage source and at least one of the control electrodes is determined by applying an alternating voltage to the control electrode at such a high frequency that an ohmic equivalent resistance of the actuator associated with the control electrode drops to less than 10% of the line resistance value. Advantageously, the determined line resistance is subtracted from the measurement result when measuring the impedance of the control electrode.

[0039] According to a further embodiment according to the first or second aspect of the invention, the effect of a current flow caused by the weakly conductive structure is calculated from the impedance measurement result during operation of the projection exposure system for exposing a substrate. In other words, the calculation takes place in a period that begins with the exposure of a first field on the substrate, also referred to as a wafer, and ends with the exposure of the last field on the substrate. This means that the calculation can take place during the exposure of one or more fields or also in the short exposure pauses between the exposure of the fields.Advantageously, the entire method for determining a respective deflection of a plurality of actuators of an adaptive optical module according to the first or second aspect of the invention takes place during operation of the projection exposure apparatus for exposing a substrate.

[0040] The features specified with regard to the above-mentioned embodiments, exemplary embodiments or embodiment variants, etc. of the adaptive optical module according to the first or second aspect of the invention can be transferred correspondingly to the inventive method according to the first or second aspect of the invention, and vice versa. These and other features of the embodiments of the invention are explained in the description of the figures and the claims. The individual features can be implemented either separately or in combination as embodiments of the invention. Furthermore, they can describe advantageous embodiments that are independently protectable and whose protection may only be claimed during or after the application is filed.

[0041] Brief description of the drawings

[0042] The above and other advantageous features of the invention are illustrated in the following detailed description of exemplary embodiments of the invention with reference to the accompanying schematic drawings. It shows:

[0043] Fig. 1 shows an embodiment of an EUV projection exposure system for microlithography with an adaptive optical module,

[0044] Fig. 2 shows an embodiment of the adaptive optical module according to Fig. 1 in an initial state and a correction state, Fig. 3 shows an embodiment of the adaptive optical module according to a first aspect of the invention with an exemplary cross-sectional view of a layer structure with three actuators arranged next to one another and an electronic unit,

[0045] Fig. 4 shows an embodiment of the adaptive optical module according to a second aspect of the invention with an exemplary cross-sectional view of a layer structure with three actuators arranged next to one another and an electronic unit,

[0046] Fig. 5 shows the adaptive optical module according to Fig. 4 in a further sectional view, in which the respective control electrodes of the actuators are shown from above,

[0047] Fig. 6 is an equivalent circuit diagram of the actuators of an embodiment of the adaptive optical module shown in Fig. 8 according to the second aspect of the invention,

[0048] Fig. 7 the equivalent circuit diagram according to Fig. 6, in which additional line resistances are taken into account,

[0049] Fig. 8 shows a further embodiment of the adaptive optical module according to a second aspect of the invention with an exemplary cross-sectional view of a layer structure with three actuators arranged next to one another and an electronic unit,

[0050] Fig. 9 shows a view of a DUV projection exposure system for microlithography with the adaptive optical module. Detailed description of exemplary embodiments according to the invention

[0051] In the exemplary embodiments or embodiments or variants described below, functionally or structurally similar elements are provided with the same or similar reference numerals wherever possible. Therefore, to understand the features of the individual elements of a specific embodiment, reference should be made to the description of other exemplary embodiments or the general description of the invention.

[0052] To facilitate the description, a Cartesian xyz coordinate system is shown in the drawing, from which the respective positional relationships of the components shown in the figures are derived. In Fig. 1, the y-direction runs perpendicular to the plane of the drawing, the x-direction to the right, and the z-direction upward.

[0053] Fig. 1 shows an embodiment according to the invention of a projection exposure system 10 for microlithography. The present embodiment is designed for operation in the EUV wavelength range, i.e. with electromagnetic radiation having a wavelength of less than 100 nm, in particular a wavelength of approximately 13.5 nm or approximately 6.8 nm. Due to this operating wavelength, all optical elements are designed as mirrors. However, the invention is not limited to projection exposure systems in the EUV wavelength range. Further embodiments according to the invention are designed, for example, for operating wavelengths in the UV range, such as 365 nm, 248 nm or 193 nm. In this case, at least some of the optical elements are configured as conventional transmission lenses, as shown by way of example in Fig. 9 described further below.

[0054] The projection exposure system 10 according to Fig. 1 comprises an exposure radiation source 12 for generating exposure radiation 14. In the present case, the exposure radiation source 12 is embodied as an EUV source and can, for example, comprise a plasma radiation source. The exposure radiation 14 first passes through an illumination optics 16 and is directed by it onto a mask 18.

[0055] The mask 18 has mask structures that are imaged onto a substrate 24 in the form of a wafer during exposure operation of the projection exposure system 10, and is displaceably mounted on a mask shifting stage 20. The substrate 24 is displaceably mounted on a substrate shifting stage 26. The mask 18 can, as shown in Fig. 1, be designed as a reflection mask or, alternatively, particularly for UV lithography, can also be configured as a transmission mask. In the embodiment according to Fig. 1, the exposure radiation 14 is reflected by the mask 18 and then passes through a projection lens 22, which is configured to image the mask structures onto the substrate 24. The projection exposure system 10 can be designed as a so-called scanner or as a so-called stepper.The exposure radiation 14 is guided within the illumination optics 16 and the projection lens 22 by means of a plurality of optical elements, in this case in the form of mirrors.

[0056] In the illustrated embodiment, the illumination optics 16 comprises four optical elements in the form of mirror elements 30-1, 30-2, 30-3, and 30-4. The projection lens 22 also comprises four optical elements in the form of mirror elements 30-5, 30-6, 30-7, and 30-8. The mirror elements 30-1 to 30-8 are arranged to guide the exposure radiation 14 in an exposure beam path 28 of the projection exposure system 10.

[0057] In the embodiment shown, the mirror element 30-5 is part of an adaptive optical module 38, which can also be referred to as an adaptive optical element. The optical surface of the mirror element 30-5 serves as the active optical surface 32 of the adaptive optical module 38, the shape of which can be actively changed to correct local shape errors. In further embodiments, another one or more of the mirror elements 30-1, 30-2, 30-3, 30-4, 30-5, 30-6, 30-7, and 30-8 can each be configured as part of an adaptive optical module.

[0058] Furthermore, one or more of the mirror elements 30-1, 30-2, 30-3, 30-4, 30-6, 30-7, and 30-8, or the adaptive optical module 38 of the projection exposure system 10, can be movably mounted. For this purpose, a respective rigid-body manipulator is assigned to each of the movably mounted mirror elements. The rigid-body manipulators enable, for example, a tilting and / or a displacement of the assigned mirror elements substantially parallel to the plane in which the respective reflective surface of the optical elements lies. This allows the position of one or more of the mirror elements to be changed to correct imaging errors of the projection exposure system 10.

[0059] According to one embodiment, the projection exposure system 10 comprises a control device 41 for generating control signals 42 for the provided manipulation units, such as the aforementioned rigid-body manipulators, one or more adaptive optical modules, and / or optionally further manipulators. Fig. 1 illustrates, by way of example, the transmission of a control signal 42 to the adaptive optical module 38. According to one embodiment, for aberration correction of the projection lens 22, the control device 41 determines the control signals 42 based on wavefront deviations 46 of the projection lens 22 measured by a wavefront measuring device 44 using a feedforward control algorithm.

[0060] The adaptive optical module 38 is illustrated in one embodiment in Fig. 2. The illustration in the upper section of Fig. 2 shows the adaptive optical module 38 in an initial state, in which the shape of the optical surface 32 has an initial shape, in this case a planar shape. The illustration in the lower section of Fig. 2 shows the adaptive optical module 38 in a correction state, in which the shape of the optical surface 32 has a modified shape, in this case a convexly curved shape.

[0061] The adaptive optical module 38 comprises a support element 34 in the form of a backplate and the mirror element 30-5, the upper side of which forms the active optical surface 32 and serves to reflect the exposure radiation 14. A plurality of actuators 36, also called manipulators, are arranged along the underside of the mirror element 30-5. These are preferably positioned in both the x-direction and the y-direction, i.e., in a two-dimensional arrangement, along the underside of the mirror element 30-5. The actuators 36, of which only a few are provided with a reference numeral in Fig. 2 for reasons of readability, connect the support element 34 to the mirror element 30-5. The actuators 36 are configured to change their extent when actuated along their longitudinal direction. In the embodiment according to Fig. 2, the actuators 36 can be actuated transversely or perpendicularly to the optical surface 32.The actuators 36 are each controlled individually and can thus be actuated independently of one another. The adaptive optical module 38 can have more or fewer actuators 36 than shown in Fig. 2. In the correction state shown in the lower section of Fig. 2, the centrally arranged actuators 36 are increased in length by actuation, resulting in the convexly curved shape for the optical surface 32.

[0062] For the sake of simplicity, the following figures refer, by way of example, to three actuators 36n-i, 36n and 36n+i arranged one after the other. Here, n represents a counting variable for the actuators; in the illustration according to Fig. 2, n=4. In other words, the illustration of the actuators 36n-i, 36n and 36n+i in the following figures serves as an example to illustrate an adaptive optical module 38 with at least the three actuators mentioned, wherein additional actuators 36 are preferably present. Fig. 3 illustrates the adaptive optical element 38 according to Fig. 2 in an embodiment 38A according to a first aspect of the invention, by way of example with the three aforementioned actuators 36n-1, 36n and 36n+1. The adaptive optical element 38A comprises a dielectric medium 48 extending over the actuators 36n-1, 36n and 36n+1, which is deformable by applying an electric field.This can be a piezoelectric material or an electrostrictive material. In piezoelectric materials, the deformation is based on the piezoelectric effect, while in electrostrictive materials, it is based on the electrostrictive effect. In this text, the electrostrictive effect refers to the deformation of a dielectric medium as a function of an applied electric field, where the deformation is independent of the direction of the applied field and, in particular, proportional to the square of the electric field. In contrast, the linear response of the deformation to the electric field is referred to as the piezoelectric effect.

[0063] In the embodiment described below, the actuators 36 are embodied as ferroelectric actuators, in which the dielectric medium 48 comprises a perovskite-based ceramic, and are based on the electrostrictive effect, i.e., the deformation of the dielectric medium 48 caused by the application of an electric field is based on the electrostrictive effect. The ferroelectric actuators are particularly suitable for correcting the shape of the active optical surface 32, since they exhibit very low drift and low hysteresis.

[0064] The adaptive optical module 38A illustrated in Fig. 3 comprises a layer structure 39A and an electronics unit 40A. The layer structure 39A comprises the support element 34 in the form of a substrate, an actuator section 52 comprising the actuators 36n-1, 36n, and 36n+1, and the mirror element 30-5. The structure of the actuator section 52 comprises, starting from the support element 34, an insulator layer 54, a base electrode 56, the aforementioned dielectric medium 48, measuring electrodes 58, a weakly conductive structure 60, here in the form of an LNO layer, and control electrodes 62. The LNO layer has a conductivity of approximately 20 S / m at 30°C. In general, the weakly conductive layer has a conductivity of at least 0.1 mS / m, in particular of at least 1 mS / m, at least 0.01 S / m, at least 0.1 S / m or at least 10 S / m, but less than 1 kS / m, in particular of less than 200 S / m or less than 100 S / m.Advantageously, an insulating layer (not shown in the drawing) is arranged between the measuring electrodes 58 and the weakly conductive layer 60.

[0065] Each of the actuators 36n-1 , 36n and 36n+1 comprises a separate drive electrode 62. The drive electrodes 62 are also referred to as upper electrodes OE, wherein the actuator 36n-1 comprises the upper electrode OE n 1 (62n-1 ), the actuator 36n the upper electrode OE n (62n) and the actuator 36n+1 the upper electrode OE n+1(62n+1 ). In the embodiment shown, the base electrode 56 is grounded, serves as a counter electrode for the control electrodes 62, and in the present embodiment is also continuous, i.e., constructed in one piece. Alternatively, the base electrode 56 can also be divided into several individual electrodes, for example, one individual electrode per actuator 36. These individual electrodes can then be kept at the same electrical potential by means of wire connections. The combination of the respective control electrode 62 with the base electrode serves to generate an electric field in the dielectric medium 48 to change the respective expansion of the actuators 36.

[0066] The insulator layer 54 serves to electrically insulate the base electrode 56 from the support element 34. For this purpose, the insulator layer can be made of CNO (CNiOa), for example. The weakly conductive structure 60 in the form of the LNO layer is arranged below the control electrodes 62 and extends continuously along the control electrodes 62. It serves to smooth out the deformation effect when individual actuators 36 are controlled. In this context, one can speak of an arrangement of the actuators in coupled networks. Due to the weakly conductive LNO layer, when the control electrodes 62 are subjected to different voltages, leakage currents occur between the individual control electrodes 62, creating a gradient field. LNO stands for LaNiOa; this material has a conductivity of approximately 864 Siemens / cm.

[0067] Due to the aforementioned leakage currents, an impedance measurement of the actuators 36n-1, 36n, and 36n+1 performed at the control electrodes 62 would lead to falsifications. To avoid this, in the embodiment shown in Fig. 3, each of the actuators 36n-1, 36n, and 36n+1 further comprises a measuring electrode 58n-1, 58n, or 58n+1, respectively, used to measure the impedance of the respective actuator. The measuring electrodes 58 are each arranged directly below the LNO layer 60.

[0068] The mirror element 30-5 comprises a multilayer arrangement 64, also referred to as a multilayer layer, as well as a smoothing and insulating layer 65. The smoothing and insulating layer 65 is applied to the control electrodes 62 of the actuator section 52 and serves to create a smooth contact surface for the multilayer arrangement 64 and to electrically insulate the multilayer arrangement 64 from the control electrodes 62. The upper side of the multilayer arrangement 64 forms the active optical surface 32 of the adaptive optical module 38A.

[0069] The control electrodes 62n-1, 62n and 62n+1 are each connected to a voltage generator 66 of the electronic unit 40A, whereby a controllable working voltage 68 (U^ 1 , or opposite the base electrode 56. This means that the working voltage 68 is a direct voltage with a variable voltage value UA.

[0070] In addition to the voltage generators 66, the electronics unit 40A comprises a control unit 72, a measuring device 80 and an evaluation device 88A.

[0071] The electronics unit 40A or just some parts of the electronics unit 40A can, as in the embodiment described here, be part of the adaptive optical module 38A or can also be arranged outside the adaptive optical element 38A, for example, be part of the control device 41 of the projection exposure system 10.

[0072] The total change in the length (in the z-direction) of an individual actuator 36 when applying an operating voltage 68 other than 0 V is referred to as deflection S. The respective deflection S n-1 , S n or S n+1 (see also reference numerals 43n-1 , 43n and 43n+1 ) of the actuators 36n-1 , 36n and 36n+1 is visible on the top side of the multilayer arrangement 64. The deflections S n-1 , Sn or S n+1 lead to a changed topography 32s of the optical surface 32.

[0073] Before commissioning the adaptive optical module 38A, a reference characteristic curve 70 between the deflection S and the operating voltage UA is optionally measured in a so-called reference mode for each of the actuators 36n-1, 36n, and 36n+1. In the reference mode, different values ​​for the operating voltage UA, i.e., different operating points of the operating voltage UA, are set, and for each of these values, the corresponding deflection S of the optical surface 32 of the respective actuator 36 is measured using a reference measuring module in the form of an interferometer.

[0074] In a control mode 74, a target deflection vector Ss is read in by the control unit 72. The target deflection vector Ss (reference numeral 43s) is contained in the control signal 42 emitted by the control device 41 according to Fig. 1 and comprises target values ​​for the deflections S n-1 , S n and S n+1 . The information flow in control mode 74 is indicated by dashed lines in Fig. 3. The control unit 72 contains a conversion recipe 69 for determining a default vector UA for the individual working voltages or U +1from the specified target deflection vector Ss. The conversion recipe 69 can be formed, in particular, by curves of the operating voltage UA as a function of the target deflection Ss for the individual actuators 36. These curves are advantageously determined before commissioning of the adaptive optical module 38A from the reference characteristic curves 70 determined in the reference mode, which indicate the course of SR as a function of UA for the individual actuators 36. Alternatively, the conversion recipe 69 can be determined using a calibration mode 76 described in more detail below. During operation, the conversion recipe 69 is continuously corrected, as described in more detail below.

[0075] For the read-in target deflection vector Ss, the control device 41 determines corresponding control values ​​for the working voltage vector UA using the conversion recipe 69 and thus controls the voltage generators 66. By the working voltages applied by the voltage generators 66 to the control electrodes 62n-1, 62n and 62n+1 or U +1 will be the

[0076] Actuators 36n-1, 36n, and 36n+1 are deflected accordingly. Each time new operating voltages UA are set using the voltage generators 66, or at specific time intervals, a calibration mode 76 is applied to calibrate the conversion recipe 69. The information flow in calibration mode 76 is represented in Fig. 3 by a dash-dotted line.

[0077] To execute the calibration mode 76, the embodiment of the adaptive optical element 38A illustrated in Fig. 3 has the aforementioned measuring device 80, which is assigned to the illustrated actuators 36n-1, 36n, and 36n+1. The measuring device 80 comprises an alternating voltage source 82 applied between the measuring electrodes 58n-1, 58n, and 58n+1 and the base electrode 56 for generating an electrical measuring voltage 83 in the form of an alternating voltage Uw. According to a further embodiment, instead of a uniform alternating voltage source 82, separate alternating voltage sources can also be applied to the individual measuring electrodes 58n-1, 58n, and 58n+1.The measuring device 80 further comprises a plurality of current measuring devices 84, namely one current measuring device 84n-1 , 84n and 84n+1 for each of the measuring electrodes 58n-1 , 58n and 58n+1 for measuring the current intensity / ” flowing into the individual measuring electrodes 58 due to the applied alternating voltage Uw. -1 , and Iw +1 - Based on the alternating voltage Uw and the measured currents / ” - 1 , I and I^ + 1 the measuring device 80 determines the resulting impedance Z. This is done for a large number of working voltages UA, so that the result of the determination is a working voltage-dependent impedance Z n 1 (UA), Z M (UA) and Z n+1 (UA) (see reference numerals 86n-1, 86n, and 86n+1) for each of the actuators 36n-1, 36n, and 36n+1. The impedances 86n-1, 86n, and 86n+1 forming the vector Z(UA) are transmitted to the aforementioned evaluation device 88A.

[0078] In the evaluation device 88A, the impedances Z measured for the various actuators 36n- 1 , 36n and 36n+1 are n-1 (UA), Z M (UA) and Z n+1 (UA) into a respective deflection characteristic S n-1 (UA), S M (UA) and S n+1 (UA). The deflection characteristics S n-1 (UA), S M (UA) and S n+1 (UA) are shown in Fig. 3 together with the vector S(UA) (see reference numeral 90), one of which is shown as an example in a diagram 90d. Each of the deflection characteristics S n 1 (UA), S M (UA) and S n+1 (UA) represents the deflection 43n-1 , 43n or 43n+1 of the individual actuators 36n-1 , 36n and 36n+1 as a function of the working voltage UA. In other words, the evaluation device 88A is configured to calculate at least one actuator deflection from the measured impedances 86n-1 , 86n and 86n+1.

[0079] The evaluation device can, in addition to other algorithms known to the person skilled in the art, convert the measured Z n-1 (UA), Z M (UA) and Z M+1 (UA) into the deflection characteristics S n-1 (UA), S M (UA) and S n+1 (UA) is based on the following procedure: From the measured impedance Z, a capacitance C of the respective actuator 36 is calculated. For this purpose, the respective actuator 36 is represented by an equivalent circuit, for example, a series circuit consisting of a capacitor and an ohmic resistor. If the capacitance change due to a small deformation Ad is neglected, the susceptibility x can be directly derived from the capacitance C. From this, the polarization P in the dielectric medium and, from this, the deflection S of the actuator can be determined using the following relationships: P ~~ and S ~ P 2, where E is the electric field strength in the dielectric medium.

[0080] The deflection characteristics S(UA) are transmitted to a comparison module 91 of the control unit 72. This compares the deflection characteristics S(UA) with the reference characteristics 70 and, if any deviations are found, initiates a corresponding correction 92 of the conversion recipe 69 of the control unit 72. Alternatively, the control unit 72 calculates the conversion recipe 69 directly from the deflection characteristics S(UA). In any case, the control unit 72 determines the control value of the working voltage UA for the voltage generators 66 in control mode 74 based on the determined deflection characteristics S(UA). In other words, the control unit 72 is configured to determine, on the basis of the calculated actuator deflections in the form of the deflection characteristics S(UA), the respective control variables present at the assigned control electrodes 62n-1, 62n and 62n+1 in the form of the working voltages 1] or UA +1 TO correct.

[0081] Fig. 4 illustrates the adaptive optical element 38 according to Fig. 2 in an embodiment 38B according to a second aspect of the invention, exemplarily with three actuators 36n-1, 36n, and 36n+1. Embodiment 38B comprises a layer structure 39B and an electronics unit 40B. Layer structure 39B differs from the layer structure of embodiment 38A according to Fig. 3 in that no measuring electrodes 58 are provided in actuators 36n-1, 36n, and 36n+1, and in the configuration of the weakly conductive structure 60.

[0082] The electronics unit 40B is configured to carry out the impedance measurements of the actuators 36n-1, 36n and 36n+1 directly at the control electrodes 62n-1, 62n and 62n+1. The effect of the current flows caused by the weakly conductive structure 60, i.e., the aforementioned leakage currents, between adjacent control electrodes 62 on the measurement result is subtracted by the electronics unit 40B from the measurement result of the respective impedance measurement. In this text, a neighboring control electrode of a reference control electrode is understood to mean any control electrode that is connected to the control electrode of the reference control electrode via the weakly conductive layer. Thus, the term "neighboring control electrode" includes both a control electrode directly adjacent to the reference control electrode, i.e.a drive electrode that is directly adjacent to the reference drive electrode, as well as a drive electrode next to or further away.

[0083] For this purpose, the weakly conductive structure 60 is divided into sections, each assigned to one of the control electrodes 62, in the illustration according to Fig. 4 the sections 60n-1 , 60n and 60n+1 . This design is also shown in Fig. 5 in a sectional view parallel to the xy plane. As can be seen from Fig. 5, the sections of the weakly conductive structure in the illustrated embodiment each have a square shape with an area exceeding the area of ​​the respective control electrode 62 and are each arranged centered to the respective control electrode 62. Thus, the sections 60n-1 , 60n and 60n+1 are each assigned to the control electrode OE n-1 (Reference number 62n-1 ), OE n or OE n+1centered. Analogously, in a row of actuators in front of it, the sections 60m-1 , 60m and 60m+1 are connected to control electrodes OE m-1 , OE m or OE m+1 centered. The arrangement can be continued to the left, right, bottom, and top, as indicated by continuation points in Fig. 4.

[0084] The sections of the weakly conductive structure 60 are separated from the immediately adjacent sections; in particular, they are separated from the immediately adjacent sections by electrically insulating separating lines 93. Thus, separating lines 93 run around the section 60n, so that it is electrically insulated from the sections 60n-1, 60n+1, 60m, and any section adjoining it above. A respective current flow between these sections occurs solely via a respective current measuring device 94. This current flow between two sections is the aforementioned leakage current between the respective drive electrodes 62. In the embodiment described here, this leakage current can be precisely measured using the current measuring devices 94.

[0085] For this purpose, the current measuring devices 94 are connected to the respective sections via power lines 95 via contact points 61 arranged at the edge of the respective section of the weakly conductive structure 60. For example, the contact point 61 for measuring the leakage current I L serving current measuring device 94 is connected via respective power lines 95 to contact points 96 on the section 60n-1 and the section 60n.

[0086] The electronic unit 40B according to Fig. 4 differs from the electronic unit 40A according to Fig. 3 by the presence of the current measuring devices 94 for measuring the leakage currents 97 and in that the AC voltage source 82 and the current measuring devices 84 are not connected between the measuring electrodes 58 according to Fig. 3 and the base electrode 56, but between the control electrodes 62n-1, 62n and 62n+1 and the base electrode 56. The determination of the impedances Z carried out by the measuring device 80 n 1 (U A ), Z n (U A ) and Z n+1 (UA) is carried out analogously to the procedure described with reference to Fig. 4 using the alternating voltage Uw applied by the alternating voltage source 82 and the currents / determined by the current measuring devices 84n-1, 84n and 84n+1. - 1 , I and Iw +1 -

[0087] The functioning of the evaluation device 88B according to Fig. 4 differs from the evaluation device 88A according to Fig. 3 in that it takes into account the leakage currents 97 measured by the current measuring devices 94 when determining the deflection characteristics 90 from the working voltage-dependent impedances 86. The totality of the leakage currents 97 is designated in Fig. 4 by a leakage current vector II. The consideration of the leakage currents 97 in the evaluation device 88B is such that the respective effect of the leakage currents on the current flows measured by the current measuring devices 84, i.e. on the current intensities / " -1 , I and I^ + 1 etc. (see reference numerals 85n-1 , 85n, 85n+1 ) from the measurement result of the impedances Z n 1 (UA), Z n (UA) and Z n+1 (UA) etc. are subtracted. The impedances corrected in this way are then used to determine the deflection characteristics 90.

[0088] Fig. 8 illustrates the adaptive optical element 38 according to Fig. 2 in a further embodiment 38C according to the second aspect of the invention, exemplarily with three actuators 36n-1, 36n, and 36n+1. Embodiment 38C comprises a layer structure 39C and an electronics unit 40C. Layer structure 39C differs from the layer structure of embodiment 39B according to Fig. 4 only in that weakly conductive structure 60, as in embodiment 39A according to Fig. 3, is configured as a layer extending continuously along control electrodes 52.

[0089] The electronics unit 40C, like the electronics unit 40B according to Fig. 4, is configured to perform the impedance measurements of the actuators 36n-1, 36n, and 36n+1 directly at the control electrodes 62n-1, 62n, and 62n+1. Furthermore, the electronics unit 40C is also designed to calculate the effect of the leakage currents caused by the weakly conductive structure 60 between adjacent control electrodes 62 on the measurement result from the measurement result of the respective impedance measurement. In contrast to the electronics unit 40B, in which the calculation is based on measurements of the actually flowing leakage currents 97, the electronics unit 40C calculates the effect of the leakage currents based on predetermined coupling resistances RK (reference numeral 100) between the individual control electrodes 62 and the respective adjacent control electrodes 62.

[0090] In the embodiment shown in Fig. 8, current measuring devices 98 and a resistance determination device 99 for determining the aforementioned coupling resistances 100 are already integrated into the electronics unit 40C. As already mentioned, the coupling resistances 100 are determined before the operation of the adaptive optical module 38C in calibration mode 76, which is carried out as part of the exposure operation of the projection exposure system 10. The coupling resistances 100 are determined in a qualification mode 78, in which an electronics unit independent of the electronics unit 40C can also be used. Thus, in a further embodiment not shown in the drawing, the electronics unit 40C can be designed only to execute the control mode 74 and the calibration mode 76 and thus be configured without the current measuring devices 98 and the resistance determination device 99.

[0091] Fig. 6 shows an equivalent circuit diagram of the actuators 36n-1, 36n and 36n+1 of the adaptive optical module 38C to explain the procedure for determining the coupling resistances 100. Z n-1 , Z n and Z n+1 22, _ 1 / 22 the impedances of the actuators 36n-1 , 36n and 36n+1 and R K and j e Coupling resistances 100 between the control electrodes 62n-1 and 62n as well as the control electrodes 62n and 62n+1. To determine the , _ 1 / 22 TI / TI+ 1

[0092] Coupling resistances R K and R K In the qualification mode 78, a DC voltage U est applied to the drive electrode 62n and at the same time the voltage at the drive electrodes 62n-1 and 62n+1 and all other adjacent drive electrodes, if present, is set to 0V Well wer" the direct currents are measured by means of the current measuring devices 98 and I +1 measured, which corresponds to the leakage currents / ” - 1 as well as / " +1 through the coupling resistors and R K n,n+1 are equivalent to.

[0093] The resistance determination device then determines the leakage currents as follows: / ” - 1 and / +1 the coupling resistances and 7?^ n+1 : rn-1 / n y Test ■ r>n / n+l ^rest i, . ■ . x - . ,

[0094] R K = sowie = ■ Coupling resistances to other adjacent control electrodes 62 are calculated analogously.

[0095] The coupling resistances 100 thus determined (also shown as vector RK in Fig. 8) are passed on to the evaluation device 88C and stored there. The functioning of the evaluation device 88C according to Fig. 8 differs from the evaluation device 88B according to Fig. 4 in that, when determining the deflection characteristics 90 from the working voltage-dependent impedances 86, the latter takes into account the previously determined coupling resistances 100, instead of the directly measured leakage currents 97. The consideration of the coupling resistances 100 in the evaluation device 88B is such that the respective effect of the respective leakage currents resulting from the coupling resistances on the current flows measured by the current measuring devices 84 is derived from the measurement result of the impedances Z n-1 (U A ), Z n (U A ) and Z n+1 (U A), etc. are subtracted. The impedances corrected in this way are then used to determine the deflection characteristics 90.

[0096] The determination of the leakage currents from the coupling resistors 100 is carried out in the evaluation device 88C based on the equivalent circuit diagram shown in Fig. 6. For example, the current Izn of the actuator 36n results from this as follows:

[0097] Here, In are the currents of the neighboring actuators, Un are the voltages at the neighboring actuators and Ui is the voltage at actuator 36n.

[0098] Optionally, the evaluation device 88C can also be configured to measure line resistances Rw~ , Rw and / ? +1(see reference numeral 102) of the supply lines to the control electrodes 62n-1, 62n or 62n+1 are to be taken into account when determining the deflection characteristics 90 from the working voltage-dependent impedances 86. The line resistances 102 are taken into account in such a way that their respective effect on the measurement result of the impedances Z n - 1 (U A ), Z n (U A ) and Z n+1 (UA) etc. are subtracted. The impedances corrected in this way are then used to determine the deflection characteristics.

[0099] Among the line resistances R 1 , R and R^ + 1The resistances of the connecting lines between the voltage generators 66 and the AC voltage source 82 to the control electrodes 62n-1, 62n, and 62n+1 are to be understood, including the contact resistances that arise from the contacting of the control electrodes 62n-1, 62n, and 62n+1 by the connecting lines. The line resistances 102 are shown in an equivalent circuit diagram in Fig. 7.

[0100] To determine the line resistances 102, the frequency of the AC voltage source 82 is set to such a high frequency that a respective ohmic equivalent resistance of the actuators 36n-1, 36n, and 36n+1 approaches zero, i.e., the ohmic equivalent resistance is negligible compared to the value of the respective line resistance 102. This means that the respective ohmic equivalent resistance is less than 10%, in particular less than 5%, of the value of the respective line resistance. The frequency of the AC voltage source 82 set in this case can be, for example, at least 10 kHz, in particular at least 100 kHz. According to one embodiment, the frequency is in the range from 100 kHz to 1 MHz.

[0101] After setting the high frequency described above at the AC voltage source 82, test voltages U^est > Urest or [ / e + s t and by means of the current measuring devices 98 the respective resulting test currents , / est or l^ s measured. The resistance determination device 99 determines under jjn

[0102] Using the relationship = -p^ the line resistances Rw~ lTest

[0103] Rw and R” +1The measuring function of the line resistances 102 and their consideration in determining the deflection characteristics 90 can optionally also be integrated into the adaptive optical module 38B according to Fig. 4. In this embodiment, the optical module 38B, in addition to the configuration shown in Fig. 4, also includes the current measuring devices 98 illustrated in Fig. 8 and the resistance determination device with the function for determining the line resistances 102.

[0104] Fig. 9 shows a schematic view of a microlithographic projection exposure system 210 configured for operation in the DUV wavelength range, which comprises illumination optics in the form of a beam-shaping and illumination system 216 and a projection lens 222. DUV stands for "deep ultraviolet" (DUV) and denotes a wavelength of the exposure radiation 214 used in the projection exposure system 210 between 100 nm and 250 nm. The beam-shaping and illumination system 216 and the projection lens 222 can be arranged in a vacuum housing and / or surrounded by a machine room with corresponding drive devices.

[0105] The DUV projection exposure system 210 has a DUV exposure radiation source 212. For this purpose, an ArF excimer laser can be provided, for example, which emits exposure radiation 214 in the DUV range at, for example, approximately 193 nm.

[0106] The beam-shaping and illumination system 216 shown in Fig. 9 directs the exposure radiation 214 onto a photomask 218. The photomask 218 is designed as a transmissive optical element and can be arranged outside the systems 216 and 222. The photomask 218 has a structure that is imaged in reduced size onto a substrate 224 in the form of a wafer or the like by means of the projection lens 222. The substrate 224 is displaceably mounted on a substrate displacement stage 226. The projection lens 222 has a plurality of optical elements 230 in the form of lenses and / or mirrors for imaging the photomask 218 onto the substrate 224. In the illustrated embodiment, the optical elements 230 comprise lenses 230-1, 230-4 and 230-5, the mirror 230-3 and the further mirror 230-2 designed as an adaptive optical module 38.Individual lenses and / or mirrors of the projection lens 222 can be arranged symmetrically to an optical axis 223 of the projection lens 222. It should be noted that the number of lenses and mirrors of the DUV projection exposure system 210 is not limited to the number shown. More or fewer lenses and / or mirrors can also be provided. Furthermore, the mirrors are typically curved at their front side for beam shaping.

[0107] An air gap between the last lens 230-5 and the substrate 224 can be replaced by a liquid medium 231 having a refractive index > 1. The liquid medium 231 can be, for example, ultrapure water. Such a setup is also referred to as immersion lithography and features increased photolithographic resolution. The medium 231 can also be referred to as an immersion liquid.

[0108] In the embodiment shown in Fig. 9, the adaptive optical module 38 is designed analogously to the adaptive optical module 38 according to Fig. 1, although it naturally comprises a different mirror element than in Fig. 1. The adaptive optical module 38 is configured such that the shape of the surface 232 of the mirror 230-2 can be actively changed to correct local shape errors. The mirror surface is therefore also referred to as an active optical mirror surface 232. The adaptive optical module 38 according to Fig. 9 can be configured in one of the embodiments shown in Figs. 2, 3, 4 and 8. All statements made above with reference to Figs. 1 to 8 regarding the adaptive optical module 38 can thus be transferred to the adaptive optical module 38 according to Fig. 9. Analogous to the projection exposure system 10 according to Fig. 1, the adaptive optical module 38 according to Fig.9 is controlled by control signals 42, which are determined by a control device 41 on the basis of wavefront deviations 46 of the projection lens 222 measured by a wavefront measuring device 44. Without limiting the generality, only one actuator device is shown in Fig. 9; however, it is understood that preferably a plurality of actuator devices are present, each of which is individually controllable and / or adjustable.

[0109] The above description of exemplary embodiments, embodiments, and variants is to be understood as exemplary. The disclosure thus made enables those skilled in the art, on the one hand, to understand the present invention and the associated advantages, and, on the other hand, also encompasses obvious variations and modifications of the described structures and methods within the understanding of those skilled in the art. Therefore, all such variations and modifications, insofar as they fall within the scope of the invention as defined in the appended claims, as well as equivalents, are intended to be covered by the claims.

[0110] List of reference symbols

[0111] 10 projection exposure system

[0112] 12 Exposure radiation source

[0113] 14 Exposure radiation

[0114] 16 Lighting optics

[0115] 18 Mask

[0116] 20 mask transfer platform

[0117] 22 Projection lens

[0118] 24 Substrat

[0119] 26 Substrate transfer stage

[0120] 28 Exposure beam path

[0121] 30-1, 30-2, 30-3, 30-4, 30-5, 30-6, 30-7, 30-8 mirror elements

[0122] 32 active optical surfaces

[0123] 34 Support element

[0124] 36, 36n-1, 36n, 36n+1 actuator

[0125] 38, 38A, 38B, 38C adaptive optical module

[0126] 39A Layer structure

[0127] 39B Layer structure

[0128] 39C Layer structure

[0129] 40A electronic unit

[0130] 40B electronics unit

[0131] 40C electronics unit

[0132] 41 Control device

[0133] 42 Control signal

[0134] 43 Deflection

[0135] 43s Target deflection vector

[0136] 44 Wavefront measuring device

[0137] 46 wavefront deviations

[0138] 48 dielectric medium

[0139] 52 Actuator section

[0140] 54 Insulator layer 56 Base electrode

[0141] 58, 58n-1 , 58n, 58n+1 measuring electrode

[0142] 60 weakly conducting structure

[0143] 62, 62n-1 , 62n,62n+1 control electrode

[0144] 64 Multilayer arrangement

[0145] 65 Smoothing and insulating layer

[0146] 66 Voltage generator

[0147] 68 Working voltage

[0148] 69 Conversion recipe

[0149] 70 Reference characteristic curve

[0150] 72 Control unit

[0151] 74 Control mode

[0152] 76 Calibration mode

[0153] 78 Qualification mode

[0154] 80 measuring device

[0155] 82 AC voltage source

[0156] 83 Measuring voltage

[0157] 84, 84n-1 , 84n, 84n+1 current measuring device

[0158] 85n-1 , 85n, 85n+1 current

[0159] 86n-1 , 86n, 86n+1 Working voltage dependent impedance

[0160] 88A Evaluation device

[0161] 88B Evaluation device

[0162] 88C evaluation device

[0163] 90 deflection characteristics

[0164] 90d diagram of a deflection characteristic

[0165] 91 Comparison module

[0166] 92 Correction

[0167] 93 electrically insulating separating line

[0168] 94 Current measuring device

[0169] 95 power line

[0170] 96 contact points

[0171] 97 Leakage current Current measuring device Resistance measuring device Coupling resistance Line resistance Projection exposure system Exposure radiation source Exposure radiation Beam shaping and illumination system Photomask Projection lens Optical axis Substrate Substrate shift stage Optical element -1 , 230-4, 230-5 Lens -2 Adaptive optical module -3 Mirror Liquid medium Active optical mirror surface

Claims

Claims 1 . Adaptive optical module (38A) for a microlithographic projection exposure system (10;210) with an optical surface (32) for interacting with an exposure radiation (14) of the projection exposure apparatus and a plurality of actuators (36n-1, 36n, 36n+1) for changing a shape of the optical surface, wherein the adaptive optical module has a dielectric medium (48) that can be deformed by applying an electrical voltage (68), and each of the actuators comprises a separate control electrode (62n-1, 62n, 62n+1), which is each arranged to generate a respective electric field in a layer of the dielectric medium, wherein the control electrodes are connected to one another by means of a weakly conductive structure (60) with an electrical conductivity of at least 0.1 mS / m, and wherein for measuring an impedance (86n-1, 86n, 86n+1), at least one of the actuators has a measuring electrode (58n-1 , 58n, 58n+1 ) is arranged; 2. Adaptive optical module according to claim 1, wherein the weakly conductive structure (60) is configured as a layer which is arranged between the drive electrodes (62n-1, 62n, 62n+1) of the actuators and the dielectric medium (48).

3. Adaptive optical module according to claim 1 or 2, wherein the layer of the weakly conductive structure (60) extends continuously along the control electrodes (62n-1, 62n, 62n+1) of the actuators.

4. Adaptive optical module according to one of the preceding claims, which further comprises at least one base electrode (56) which is arranged as a counter electrode to the control electrodes (62n-1, 62n, 62n+1) and is configured to generate the respective electric field in the dielectric medium (48) together with the respective control electrode.

5. An adaptive optical module (38B; 38C) for a microlithographic projection exposure apparatus (10; 210) having an optical surface for interacting with an exposure radiation (14) of the projection exposure apparatus and a plurality of actuators (36n-1, 36n, 36n+1) for changing a shape of the optical surface, wherein the adaptive optical module has a dielectric medium (48) deformable by applying an electrical voltage (68), and each of the actuators comprises a separate control electrode (62n-1, 62n, 62n+1), each of which is arranged to generate an electric field in a layer of the dielectric medium, wherein the control electrodes are connected to one another by means of a weakly conductive structure (60) having an electrical conductivity of at least 0.1 mS / m, and wherein the adaptive optical module further comprises an evaluation device (88B, 88C) configured to is, when measuring an impedance (86n-1 ,86n, 86n+1 ) of at least one of the actuators to calculate from the measurement result an effect of a current flow (97) caused by the weakly conductive structure between the control electrode (62n) of the measured actuator and at least one further (62n+1 ) of the control electrodes, which influences the measurement result.

6. Adaptive optical module according to claim 5, which further comprises at least one current measuring device (94) for measuring the current flow (97) between the control electrode (62n) of the measured actuator and the at least one further (62n+1) of the control electrodes, wherein the evaluation device (88B) is configured to calculate the effect based on the measured current flow (97) from the measurement result.

7. Adaptive optical module according to claim 6, wherein the weakly conductive structure (60) has a plurality of sections (60n-1, 60n, 60n+1), wherein one of the sections is arranged on the control electrode (62n) of the measured actuator and on the at least one further control electrode (62n+1), and the two sections are electrically conductively connected via the current measuring device (94).

8. Adaptive optical module according to claim 6, wherein the sections (60n-1, 60n, 60n+1) of the weakly conductive structure are electrically isolated from each other except for the connection via the current measuring device (94).

9. Adaptive optical module according to claim 7 or 8, wherein one of the sections (60n-1, 60n, 60n+1) of the weakly conductive structure is arranged on the control electrode (62n) of the measured actuator and on the control electrodes of all actuators (62n-1, 62n+1, 62m) immediately adjacent to the measured actuator, and the section of the measured actuator is electrically conductively connected to each of the sections arranged on the immediately adjacent actuators via its own current measuring device (94).

10. Adaptive optical module according to claim 5, wherein the evaluation device (88C) is further configured to calculate the effect based on at least one predetermined coupling resistance (100) between the control electrode (62n) of the measured actuator and the at least one further control electrode (62n+1) from the measurement result. 11 . Adaptive optical module according to claim 10, which comprises at least one current measuring device (98) for measuring a current when applying a test voltage to the control electrode (62n) of the measured Actuator from the further control electrode (62n+1 ) exiting current flow.

12. Adaptive optical element according to one of claims 5 to 11, which has at least one voltage source (66, 82) which is connected to at least one of the control electrodes (62n-1, 62n, 62n+1), wherein the evaluation device (88b, 88C) is configured to calculate a line resistance (102) from the voltage source to the control electrode from the measurement result when measuring the impedance (86) of the at least one control electrode.

13. Adaptive optical element according to claim 12, which comprises an alternating voltage source (82) which is configured to apply an alternating voltage (83) to the at least one control electrode at such a high frequency in order to determine the line resistance (102) of the at least one control electrode that an ohmic equivalent resistance of the actuator assigned to the control electrode drops to less than 10% of the value of the line resistance (102).

14. Adaptive optical module according to one of claims 5 to 13, which further comprises a measuring device (80) which is configured to measure a current intensity (85n-1, 85n, 85n+1) flowing from the respective control electrode when measuring the respective impedance of the actuators.

15. Adaptive optical element according to one of the preceding claims, which further comprises an evaluation device (88A, 88B, 88C) which is configured to calculate an actuator deflection (90) from a measured impedance (86n-1, 86n, 86n+1) of one of the actuators.

16. Adaptive optical element according to claim 15, which further comprises a control unit (72) which is configured to correct a control variable (68) applied to the associated control electrode on the basis of the calculated actuator deflection.

17. Projection exposure system (10; 210) for microlithography with at least one adaptive optical module (38A, 38B, 38C) according to one of the preceding claims.

18. A method for determining a respective deflection of a plurality of actuators (36n-1, 36n, 36n+1) of an adaptive optical module (38A) of a microlithographic projection exposure apparatus (10; 210), which are configured to change a shape of an optical surface (32) of the optical module, wherein the adaptive optical module comprises a dielectric medium (48) deformable by means of an electrical voltage, each of the actuators has a separate control electrode (62n-1, 62n, 62n+1) for generating a respective electric field in a layer of the dielectric medium, the control electrodes are connected to one another by means of a weakly conductive structure (60) with an electrical conductivity of at least 0.1 mS / m, and the method comprises the steps: - measuring an impedance (86n-1, 86n, 86n+1) of at least one of the actuators by means of a measuring electrode (58n-1, 58n, 58n+1) arranged between the control electrode of the measured actuator and the dielectric medium, and - Calculate the respective deflection (43n-1 , 43n, 43n+1 ) of the actuators from the respective measured impedance.

19. Method for determining a respective deflection of a plurality of actuators of an adaptive optical module (38B; 38C) of a microlithographic projection exposure apparatus (10; 210), which actuators are configured to change a shape of an optical surface (32) of the optical module, wherein the adaptive optical module comprises a dielectric deformable by means of an electrical voltage. dielectric medium (48), each of the actuators has a separate drive electrode (62n-1, 62n, 62n+1) for generating a respective electric field in a layer of the dielectric medium, the drive electrodes are connected to one another by means of a weakly conductive structure (60) with an electrical conductivity of at least 0.1 mS / m, and the method comprises the steps: - Measuring an impedance (86n-1 , 86n, 86n+1 ) of at least one of the actuators, - calculating an effect of a current flow caused by the weakly conductive structure (60) from the measurement result of the impedance measurement, wherein the current flow occurs between the control electrode of the measured actuator and at least one further control electrode, and - Calculate the respective deflection (43n-1 , 43nm 43n+1 ) of the actuators from the respective measured impedance.

20. The method according to claim 19, wherein the current flow caused by the weakly conductive structure (60) is measured by means of a current measuring device (94) and the effect is calculated from the measurement result of the impedance measurement on the basis of the measured current flow (97).

21. The method according to claim 19, wherein a coupling resistance (100) between the control electrode (62n) of the measured actuator and the at least one further control electrode (62n+1) is determined and the effect is calculated from the measurement result of the impedance measurement on the basis of the determined coupling resistance.

22. Method according to one of claims 19 to 21, in which a line resistance (102) of at least one electrical connection between at least one voltage source and at least one of the control electrodes is determined by applying an alternating voltage (83) to the control electrode at such a high frequency that an ohmic equivalent resistance of the actuator assigned to the control electrode drops to less than 10% of the value of the line resistance (102).

23. Method according to one of claims 19 to 22, in which the effect of a current flow caused by the weakly conductive structure (60) is calculated out from the measurement result of the impedance measurement during operation of the projection exposure apparatus (10; 210) for exposing a substrate.

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