Adaptive optical module for a microlithographic projection exposure system

Abstract

An adaptive optical module (38A) for a microlithographic projection exposure system (10; 210) is provided, comprising an optical surface (32) for interacting with an exposure radiation (14) of the projection exposure system and several actuators (36n-1, 36n, 36n+1) for changing the shape of the optical surface. The adaptive optical module has a dielectric medium (48) that can be deformed by applying an electrical voltage (68), and each of the actuators includes a separate control electrode (62n-1, 62n, 62n+1), each of which is arranged to generate a respective electric field in a layer of the dielectric medium.The control electrodes are connected to each other by means of a weakly conductive structure (60) with an electrical conductivity of at least 0.1 mS / m and for measuring an impedance (86n-1, 86n, 86n+1) at least one of the actuators is arranged between the control electrode of the actuator being measured and the dielectric medium a measuring electrode (58n-1, 58n, 58n+1).

Description

Background of the invention

[0001] The invention relates to an adaptive optical module for a microlithographic projection exposure system with multiple actuators, a projection exposure system for microlithography with such an adaptive optical module, and a method for determining the respective deflection of multiple actuators of an adaptive optical module of a microlithographic projection exposure system.

[0002] To ensure the most precise possible imaging of the mask structures onto the wafer, a projection lens in a microlithography projection system is required with minimal wavefront aberrations. Projection lenses are therefore equipped with manipulators that allow wavefront errors to be corrected by changing the state of individual optical elements within the projection lens. Examples of such state changes include: a change in position in one or more of the six rigid-body degrees of freedom of the respective optical element, and a deformation of the optical element.

[0003] 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 operation 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 usually measured regularly, and changes in the aberration characteristics between individual measurements are determined by simulation, if necessary. For example, lens or mirror heating effects can be taken into account computationally.

[0004] Problems often arise when using piezoelectric or electrostrictive adaptive optical elements because changes in relevant parameters occurring in the actuator material, for example due to temperature variations, aging, defects, drifts, etc., can lead to significant inaccuracies in the surface shape corrections performed by the adaptive optical element.

[0005] To correct or avoid these inaccuracies, DE 10 2020 212 743 A1 proposes, for example, integrating a temperature measuring electrode into the actuator material and making corresponding corrections based on the measurement result. However, this is an indirect measurement of the surface form errors caused by actuator deviations, and its accuracy is often insufficient. Underlying task

[0006] 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

[0007] The aforementioned problem can be solved, according to a first 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 an exposure radiation from the projection exposure system and several actuators for changing the 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. The control electrodes are further connected by means of a weakly conductive structure with an electrical conductivity of at least 0.1 mS / m, i.e., 10 -4In a system where the actuators are connected to each other and 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 measured) and the dielectric medium, at least one of the actuators is connected to the other and a measuring electrode is arranged for measuring its impedance. The actuator being measured is understood to be the actuator whose impedance is being measured.

[0008] According to one embodiment, a measuring electrode for measuring the impedance of the respective actuator is arranged between the respective control electrode and the dielectric medium. The term "weakly conductive structure" refers to a structure with weak electrical conductivity. According to one embodiment, the conductivity of the weakly conductive structure can be at least 0.1 mS / m (i.e., 0.0001 Siemens / meter) and less than 1 kS / m. According to other 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.

[0009] The weakly conductive structure is, for example, designed as a layer, and the actuators are electrically coupled through this weakly conductive structure. In other words, the actuators can thus be used in coupled networks to smooth out the deformation effect when individual actuators are driven. The use of the weakly conductive structure creates a gradient field between the actuator electrodes. The statement that each actuator has a separate drive electrode means that each actuator has its own dedicated drive electrode; that is, the actuators do not share a single drive electrode.

[0010] The electric field in the dielectric medium layer is generated by applying an electrical voltage to the dielectric medium. This causes a deformation of the dielectric medium. The respective measuring electrode is positioned to measure the impedance of the respective actuator, i.e., the impedance of the actuator associated with the corresponding control electrode. The impedance can be measured during operation of the projection exposure system or during exposure breaks.

[0011] 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 at the adaptive optical module. In comparison, for example, to an interferometric measurement of the surface shape as a function of the operating voltage, the electrical measurement according to the invention can be performed with a high repetition rate, possibly even during the exposure operation of a microlithographic projection exposure system.

[0012] The solution according to the invention is further based on the understanding that when using the control electrode of an actuator under test 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 under test 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 another measuring electrode of a neighboring actuator. Thus, the adaptive optical module configured according to the first aspect of the invention enables the measurement of a deflection of at least one of the actuators with a high repetition rate and simultaneously with high accuracy. This allows for surface shape correction of the adaptive optical element 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 an actuator neighbor two steps away or further away.

[0013] According to one embodiment, the weakly conductive structure is configured as a layer located between the actuator control electrodes and the dielectric medium.

[0014] According to another embodiment, the layer of weakly conductive structure extends continuously along the control electrodes of the actuators.

[0015] 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 actuator electrodes and is configured to generate the respective electric field in the dielectric medium together with the respective actuator electrode. A common base electrode or several base electrodes can be provided for the different actuators.

[0016] The aforementioned problem can be solved, for example, according to a second aspect of the invention, with an adaptive optical module for a microlithographic projection exposure system. The adaptive optical module comprises an optical surface for interacting with the exposure radiation of the projection exposure system and several actuators for changing the 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 an electric field in a layer of the dielectric medium. The control electrodes are also connected to each other 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 subtract from the measurement result any effect on the measurement result of a current flow caused by the weakly conductive structure between the control electrode of the actuator being measured and at least one other control electrode.

[0017] The other control electrode is preferably one directly adjacent to the control electrode being measured. According to one embodiment, for each measured impedance of the actuators, the corresponding current flow between the control electrode of the actuator being measured and at least one other control electrode is calculated from the measurement result based on 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.

[0018] According to one embodiment, a measuring electrode for measuring the impedance of the respective actuator is arranged between the respective control electrode and the dielectric medium. The term "weakly conductive structure" refers to a structure with weak electrical conductivity. According to one embodiment, the conductivity of the weakly conductive structure can be at least 0.1 mS / m (i.e., 0.0001 Siemens / meter) and less than 1 kS / m. According to other 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.

[0019] 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 at 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 with a high repetition rate, optionally even during the exposure operation of a microlithographic projection exposure system.

[0020] The solution according to the invention is further based on the understanding that, due to the electrical connection of this control electrode to the control electrodes of neighboring actuators via the weakly conductive structure, leakage currents can cause distortions in the measurement result. According to the second aspect of the invention, these distortions are avoided by subtracting from the measurement result any effect of a current flow, caused by the weakly conductive structure, between the control electrode of the actuator being measured and at least one other control electrode. Thus, the adaptive optical module configured according to the second aspect of the invention enables the measurement of a deflection of at least one of the actuators with a high repetition rate and simultaneously high accuracy. This allows for highly accurate surface shape correction of the adaptive optical element.

[0021] 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 at least one further control electrode, wherein the evaluation device is configured to calculate the effect based on the measured current flow from the measurement result.

[0022] According to a further embodiment based on the second aspect of the invention, the control electrode of the actuator being measured is adjacent to, and in particular directly adjacent to, at least four, and 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 actuator being measured and each of the adjacent control electrodes. Furthermore, the evaluation unit is configured to subtract the respective effect of the measured current flows from the measurement result.

[0023] According to a further embodiment according to the second aspect of the invention, the weakly conductive structure has several sections, wherein one of the sections is arranged at the control electrode of the actuator being measured and at the at least one further control electrode, and the two sections are electrically connected via the current measuring device.

[0024] According to a further embodiment according to the second aspect of the invention, the sections of the weakly conductive structure are electrically isolated from each other, with the exception of the connection via the current measuring device, for example by an insulating dividing line.

[0025] According to a further embodiment according to the second aspect of the invention, one of the sections of the weakly conductive structure is arranged at the control electrode of the actuator being measured and at the control electrodes of all actuators immediately adjacent to the actuator being measured, and the section of the actuator being measured is electrically connected to each of the sections arranged at the immediately adjacent actuators via its own current measuring device.

[0026] According to a further embodiment according to the second aspect of the invention, the evaluation device is further configured to subtract from the measurement result the effect of at least one predetermined coupling resistance between the control electrode of the measured actuator and at least one other control electrode. According to one embodiment, the control electrode of the measured actuator is adjacent to at least four, in particular at least eight, control electrodes of other actuators, and the evaluation device is configured to subtract from the measurement result the respective effect of predetermined coupling resistances between the control electrode of the measured actuator and the adjacent control electrodes.

[0027] 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.

[0028] According to a further embodiment based on the second aspect of the invention, the adaptive optical element comprises at least one voltage source connected to at least one of the control electrodes, wherein the evaluation device is configured to subtract the 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 comprises an impedance measuring device configured to measure the impedance of the at least one control electrode. Such an impedance measuring device can also apply a current and measure the voltage instead of using a voltage source.

[0029] According to a further embodiment based on the second aspect of the invention, the adaptive optical module comprises an AC voltage source configured to apply an AC voltage with such a high frequency to the at least one control electrode, such that the equivalent ohmic resistance of the actuator associated with the control electrode falls to less than 10%, in particular less than 5%, of the value of the line resistance. The frequency can be, for example, 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 applies an alternating current instead of an AC voltage source.

[0030] According to a further embodiment based on the second aspect of the invention, the adaptive optical module further comprises a measuring device configured to measure the current flowing from the respective control electrode when measuring the impedance of the actuators. During the impedance measurement, an alternating voltage is applied to the respective control electrode, and the current flowing from the respective control electrode is measured.

[0031] According to an embodiment based on the first or second aspect of the invention, the adaptive optical module further comprises an evaluation unit configured to calculate an actuator displacement from a measured impedance of one of the actuators. This is done, for example, by determining the dielectric susceptibility of the actuator in question from the measured impedance and performing a linear mapping to determine the actuator displacement.

[0032] According to another embodiment, the adaptive optical module further comprises a control unit which is configured to correct a control variable applied to the associated control electrode based on the calculated actuator deflection.

[0033] According to a further embodiment based on the first or the 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 variant, the rare-earth nickel oxide comprises LaNiO3, which can also be referred to as LNO.

[0034] 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.

[0035] Furthermore, according to the first aspect of the invention, a method is provided for determining the respective deflection of several actuators of an adaptive optical module of a microlithographic projection exposure system, which are configured to change the shape of an optical surface of the optical module.The adaptive optical module comprises a dielectric medium deformable by means of an electrical voltage, each actuator has a separate control electrode for generating a respective electric field in a layer of the dielectric medium, the control electrodes are connected to each other by means of a weakly conductive structure with an electrical conductivity of at least 0.1 mS / m, and the method comprises the steps: measuring an impedance of at least one of the actuators by means of a measuring electrode arranged between the control electrode of the actuator being measured and the dielectric medium, and calculating the respective deflection of the actuators from the respective measured impedance.

[0036] Furthermore, according to the second aspect of the invention, a method is provided for determining the respective deflection of several actuators of an adaptive optical module of a microlithographic projection exposure system, which are configured to change the shape of an optical surface of the optical module.The adaptive optical module comprises a dielectric medium deformable by means of an electrical voltage, each actuator has a separate control electrode for generating a respective electric field in a layer of the dielectric medium, the control electrodes are connected to each other by means of a weakly conductive structure with an electrical conductivity of at least 0.1 mS / m, and the method comprises the steps: measuring an impedance of at least one of the actuators, subtracting the 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 other of the control electrodes, and calculating the respective deflection of the actuators from the respective measured impedance.

[0037] According to one 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 subtracted from the measurement result of the impedance measurement based on the measured current flow.

[0038] According to a further embodiment based on the second aspect of the invention, a coupling resistance is determined between the control electrode of the actuator being measured and at least one further control electrode, and the effect of the impedance measurement is subtracted from the measurement result based on this determined coupling resistance. In other words, the coupling resistance is determined before the effect is subtracted from the measurement result.

[0039] According to a further embodiment based on the second aspect of the invention, the 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 with such a high frequency to the control electrode that the equivalent ohmic resistance of the actuator associated with the control electrode falls to less than 10% of the line resistance. Advantageously, the determined line resistance is subtracted from the measurement result when measuring the impedance of the control electrode.

[0040] According to a further embodiment based on the first or second aspect of the invention, the effect of a current flow caused by the weakly conductive structure is subtracted from the impedance measurement result during operation of the projection exposure system for exposing a substrate. In other words, the subtraction takes place over 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. That is, the subtraction can take place during the exposure of one or more fields or even in the short exposure intervals between the exposures of the fields.Advantageously, the entire method for determining a respective deflection of several actuators of an adaptive optical module according to the first or the second aspect of the invention is carried out during the operation of the projection exposure system for exposure of a substrate.

[0041] The features of the adaptive optical module described above, including embodiments, exemplary embodiments, and variants, according to the first or second aspect of the invention, can be applied analogously to the method according to the first or second aspect of the invention, and vice versa. These and other features of the embodiments according to 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 patentable and whose protection may be claimed only during or after the filing of the application. Brief description of the drawings

[0042] The foregoing, as well as further 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. These show: Fig. 1 an embodiment of an EUV projection exposure system for microlithography with an adaptive optical module, Fig. 2 an embodiment of the adaptive optical module according to Fig. 1 in an initial state and a correction state, Fig. 3 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 side by side and an electronic unit, Fig. 4 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 side by side and an electronics unit, Fig. 5 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, Fig. 6. An equivalent circuit diagram of the actuators of a [system / assembly] Fig. 8 illustrated embodiment of the adaptive optical module according to the second aspect of the invention, Fig. 7 the equivalent circuit diagram according to Fig. 6, which also takes into account line resistances, Fig. 8 another 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 side by side and an electronics unit, Fig. 9 a view of a DUV projection exposure system for microlithography with the adaptive optical module. Detailed description of embodiments according to the invention

[0043] In the exemplary embodiments or variants described below, functionally or structurally similar elements are, as far as possible, provided with the same or similar reference numerals. Therefore, to understand the features of the individual elements of a particular exemplary embodiment, reference should be made to the description of other exemplary embodiments or to the general description of the invention.

[0044] To facilitate description, a Cartesian xyz coordinate system is shown in the drawing, from which the respective positional relationships of the components depicted in the figures can be derived. Fig. 1. The y-direction runs perpendicular to the plane of the drawing, into it, the x-direction to the right, and the z-direction upwards.

[0045] Fig. Figure 1 shows an embodiment of a projection exposure system 10 for microlithography according to the invention. The present embodiment is designed for operation in the EUV wavelength range, i.e., with electromagnetic radiation of 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 described below. Fig. 9 are shown as examples.

[0046] 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 designed as an EUV source and can, for example, comprise a plasma radiation source. The exposure radiation 14 first passes through an illumination optic 16 and is directed by it onto a mask 18.

[0047] The mask 18 has mask structures which are imaged onto a substrate 24 in the form of a wafer during the exposure operation of the projection exposure system 10, and is slidably mounted on a mask transfer stage 20. The substrate 24 is slidably mounted on a substrate transfer stage 26. The mask 18 can, as shown in Fig. 1 shown, can be designed as a reflection mask or alternatively, particularly for UV lithography, also configured as a transmission mask. The exposure radiation 14 is, in the embodiment according to Fig. The light 14 is reflected at 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 a so-called stepper. The exposure radiation 14 is guided within the illumination optics 16 and the projection lens 22 by means of a multitude of optical elements, in this case in the form of mirrors.

[0048] 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.

[0049] In the illustrated embodiment, 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, 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 also be configured as part of an adaptive optical module.

[0050] 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. Each of the movably mounted mirror elements is assigned a corresponding rigid-body manipulator. The rigid-body manipulators allow, for example, tilting and / or displacement of the assigned mirror elements essentially 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.

[0051] 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. Figure 1 illustrates the transmission of a control signal 42 to the adaptive optical module 38. According to one embodiment, the control unit 41 determines the control signals 42 for aberration correction of the projection lens 22 based on wavefront deviations 46 of the projection lens 22 measured by a wavefront measuring device 44 using a feedforward control algorithm.

[0052] The adaptive optical module 38 is in one embodiment in Fig. 2 illustrates. The illustration in the upper section of Fig. Figure 2 shows the adaptive optical module 38 in an initial state, where the shape of the optical surface 32 has a default form, here a planar form. The illustration in the lower section of Fig. Figure 2 shows the adaptive optical module 38 in a correction state in which the shape of the optical surface 32 has a changed shape, here a convex curved shape.

[0053] The adaptive optical module 38 comprises a support element 34 in the form of a backplate and the mirror element 30-5, the upper surface of which forms the active optical surface 32 and serves to reflect the illumination 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 along the underside of the mirror element 30-5 in both the x-direction and the y-direction, i.e., in a two-dimensional arrangement. The actuators 36, of which in Fig. 2 For the sake of readability, only some are marked with a reference symbol, connecting the support element 34 to the mirror element 30-5. The actuators 36 are configured to change their extension along their longitudinal direction when actuated. 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 therefore be actuated independently of one another. The adaptive optical module 38 can have more or fewer actuators 36 than in Fig. 2 shown. In the lower section of Fig. In the correction state shown in 2, centrally arranged actuators 36 are enlarged in length by actuation, resulting in the convex curved shape for the optical surface 32.

[0054] For the sake of simplicity, the following figures show, by way of example, three actuators arranged in succession 36 n-1, 36 n as well as 36 n+1 Reference is made to the above. Here, n represents a counter variable for the actuators, as shown in the representation according to... Fig. 2 is n=4. In other words, the representation of the actuators serves 36 n-1 , 36 n as well as 36 n+1 The following figures exemplify an adaptive optical module 38 with at least the three actuators mentioned, preferably including additional actuators 36.

[0055] Fig. Figure 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 actuators 36n-1, 36n and 36n+1 mentioned above. 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 medium can be a piezoelectric material or an electrostrictive material. In the case of a piezoelectric material, the deformation is based on the piezoelectric effect; in the case of an electrostrictive material, it is based on the electrostrictive effect. In this text, the electrostrictive effect is understood to mean the component of a deformation of a dielectric medium as a function of an applied electric field, in which 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 called the piezoelectric effect.

[0056] In the embodiment described below, the actuators 36 are designed as ferroelectric actuators in which the dielectric medium 48 comprises a perovskite-based ceramic and are based on the electrostrictive effect; that is, the deformation of the dielectric medium 48 caused by the application of an electric field is due to the electrostrictive effect. The ferroelectric actuators are particularly suitable for shape correction of the active optical surface 32, as they exhibit very low drift and low hysteresis.

[0057] The in Fig. The adaptive optical module 38A illustrated in Figure 3 comprises a layer structure 39A and an electronic unit 40A. The layer structure 39A includes 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, extending from the support element 34, comprises an insulating 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 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 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.

[0058] Each of the actuators 36n-1, 36n and 36n+1 includes a separate control electrode 62. The control electrodes 62 are also referred to as upper electrodes OE, with actuator 36n-1 including 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 illustrated embodiment, the base electrode 56 is grounded, serves as a counter electrode for the control electrodes 62, and is, in the present embodiment, a continuous, i.e., one-piece, component. Alternatively, the base electrode 56 can also be divided into several individual electrodes, for example, one individual electrode for each 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 dimensions of the actuators 36.

[0059] The insulating layer 54 serves to electrically insulate the base electrode 56 from the support element 34. For this purpose, the insulating layer can be made, for example, of CNO (CNiO3). The weakly conductive structure 60, in the form of the LNO layer, is located below the control electrodes 62 and extends continuously along them. It serves to smooth out the deformation effect when individual actuators 36 are activated. In this context, one can speak of an arrangement of the actuators in coupled networks. Due to the weakly conductive LNO layer, leakage currents occur when different voltages are applied to the individual control electrodes 62, creating a gradient field. LNO stands for LaNiO3, a material with a conductivity of approximately 864 Siemens / cm.

[0060] 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 inaccuracies. To avoid these, the following is included in the Fig. In the embodiment shown in Figure 3, each of the actuators 36n-1, 36n and 36n+1 further comprises a measuring electrode 58n-1, 58n or 58n+1 for measuring the impedance of the respective actuator. The measuring electrodes 58 are each arranged directly below the LNO layer 60.

[0061] 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 provide electrical insulation of the multilayer arrangement 64 from the control electrodes 62. The top surface of the multilayer arrangement 64 forms the active optical surface 32 of the adaptive optical module 38A.

[0062] The control electrodes 62n-1, 62n and 62n+1 are each connected to a voltage generator 66 of the electronic unit 40A, thereby providing a controllable operating voltage 68 designated by reference numeral 68. (UAn−1,UAn or UAn+1) can be generated relative to the base electrode 56. That is, the operating voltage 68 is a DC voltage with a variable voltage value U. A .

[0063] The electronic unit 40A comprises, in addition to the voltage generators 66, a control unit 72, a measuring device 80, and an evaluation unit 88A. The electronic unit 40A, or even just some parts of the electronic unit 40A, can be part of the adaptive optical module 38A, as in the embodiment described here, or it can be arranged outside the adaptive optical element 38A, for example, as part of the control device 41 of the projection exposure system 10.

[0064] The total change in the linear expansion (in the z-direction) of a single actuator 36 when a working voltage 68 other than 0 V is applied is called the displacement S. The respective displacement 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 upper side of the multilayer arrangement 64. The deflections s n-1 , S n or s n+1 lead to a changed topography 32s of the optical surface 32.

[0065] Before commissioning the adaptive optical module 38A, a reference characteristic curve 70 is optionally established in a so-called reference mode between the deflection S and the operating voltage U. A Measurements were taken for each of the actuators 36n-1, 36n, and 36n+1. Different values ​​for the operating voltage U were recorded in reference mode. A , i.e., different operating points of the operating voltage U A , set and for each of these values ​​the corresponding displacement S is measured using a reference measurement module in the form of an interferometer. R the optical surface 32 of the actuator 36 in question was measured.

[0066] In control mode 74, a target displacement vector S is defined. S Read in by control unit 72. The target displacement vector S S (Reference sign 43s) is in the one provided by the control unit 41 according to Fig. 1 outgoing control signal 42 contained and includes setpoints for the deflections S n-1 , S n as well as S n+1 The information flow in control mode 74 is described in Fig. 3 marked by dashed lines. Control unit 72 contains a conversion recipe 69 for determining a target vector U. A for the individual operating voltages UAn−1,UAn or UAn+1 from the specified target displacement vector S S saved.

[0067] Conversion formula 69 can be used in particular by means of curves of the operating voltage U. A depending on the target displacement S Sfor the individual actuators 36. These curves are advantageously determined from the reference characteristic curves 70 determined in reference mode before commissioning the adaptive optical module 38A, which describe the course of S R depending on U A Specify the conversion recipe 69 for each individual actuator. 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.

[0068] For the read-in target displacement vector S S The control unit 41 determines the corresponding control values ​​for the operating voltage vector U using the conversion recipe 69. A and thus controls the voltage generators 66. The operating voltages applied by the voltage generators 66 to the control electrodes 62n-1, 62n and 62n+1 UAn−1,UAn or UAn+1 The actuators 36n-1, 36n and 36n+1 are deflected accordingly. Each time new operating voltages U A The voltage generators 66 are set, or a calibration mode 76 is applied at certain time intervals to calibrate the conversion recipe 69. The information flow in calibration mode 76 is in Fig. 3 represented by a semicolon line.

[0069] To execute calibration mode 76, the [document / section] indicates Fig. Figure 3 illustrates the embodiment of the adaptive optical element 38A and the aforementioned measuring device 80, which is associated with the actuators 36n-1, 36n, and 36n+1 shown. The measuring device 80 comprises an AC voltage source 82 applied between each of the measuring electrodes 58n-1, 58n, and 58n+1 and the base electrode 56 to generate an electrical measuring voltage 83 in the form of an AC voltage Uw. According to a further embodiment, instead of a single AC voltage source 82, separate AC voltage sources can also be applied to each of the individual measuring electrodes 58n-1, 58n, and 58n+1.

[0070] The measuring device 80 further comprises several 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 flowing into the individual measuring electrodes 58 due to the applied alternating voltage Uw. Iwn−1,Iwn and Iwn+1. Based on the alternating voltage Uw and the measured currents Iwn−1,Iwn and Iwn+1 The measuring device 80 determines the resulting impedance Z in each case. This is done for a variety of operating voltages U. A , so that the result of the determination is a working voltage-dependent impedance Z n-1 (U A ), z n (U A ) as well as z n+1 (U A ) (cf. reference symbols 86n-1, 86n and 86n+1) for each of the actuators 36n-1, 36n and 36n+1. The vector Z(U A The impedances forming 86n-1, 86n and 86n+1 are transmitted to the aforementioned evaluation unit 88A.

[0071] The evaluation unit 88A displays the impedances Z measured for the various actuators 36n-1, 36n and 36n+1. n-1 (U A ), z n (U A ) as well as z n+1 (U A ) into a respective deflection characteristic curve S n-1 (UA ), s n (U A ) as well as S n+1 (U A ) converted. The deflection characteristics s n-1 (U A ), S n (U A ) as well as S n+1 (U A ) are in Fig. 3 with the vector S(U A ) (see reference numeral 90) are summarized, one of which is shown as an example in diagram 90d. Each of the deflection characteristic curves s n-1 (U A ), s n (U A ) as well as S n+1 (U A ) represents the deflection 43n-1, 43n and 43n+1 of the individual actuators 36n-1, 36n and 36n+1 as a function of the operating voltage U A In other words, the evaluation unit 88A is configured to calculate at least one actuator deflection from the measured impedances 86n-1, 86n and 86n+1.

[0072] The evaluation unit can use, among other algorithms known to those skilled in the art, to convert the measured Zn-1 (U A ), z n (U A ) as well as z n+1 (U A ) into the deflection characteristics s n-1 (U A ), s n (U A ) as well as s n+1 (U A The following procedure is used: The capacitance C of the respective actuator 36 is calculated from the measured impedance Z. For this purpose, the actuator 36 is represented by an equivalent circuit, for example, a series circuit consisting of a capacitor and a resistor. If the change in capacitance due to a small deformation Δd is neglected, the susceptibility χ can be directly derived from the capacitance C. From this, the polarization P in the dielectric medium and, consequently, the displacement S of the actuator can be determined using the following relationships: P = ∫ χ f0 dE and S ~ P 2 , where E denotes the electric field strength in the dielectric medium.

[0073] The deflection characteristics S(U A ) are transmitted to a comparison module 91 of the control unit 72. This performs a comparison of the deflection characteristics S(U). A ) with the reference characteristic curves 70 and, if 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 characteristic curves S(U A In any case, the control unit 72 determines the control value of the operating voltage U in control mode 74. A for the voltage generators 66 based on the determined deflection characteristics S(U A In other words, the control unit 72 is configured to, based on the calculated actuator deflections in the form of the deflection characteristic curves S(U), A ) the respective control variables applied to the assigned control electrodes 62n-1, 62n and 62n+1 in the form of the operating voltages UAn−1,UAn or UAn+1 to correct.

[0074] Fig. Figure 4 illustrates the adaptive optical element 38 according to Fig. 2 in an embodiment 38B according to a second aspect of the invention, exemplified by three actuators 36n-1, 36n and 36n+1. Embodiment 38B comprises a layer structure 39B and an electronic unit 40B. The layer structure 39B differs from the layer structure of embodiment 38A according to Fig. 3 such that no measuring electrodes 58 are provided in the actuators 36n-1, 36n and 36n+1, and in the configuration of the weakly conductive structure 60.

[0075] The electronic unit 40B is configured to perform the impedance measurements of the actuators 36n-1, 36n, and 36n+1 directly at the drive 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 drive electrodes 62 on the measurement result is factored out by the electronic unit 40B from the measurement result of the respective impedance measurement. In this text, an adjacent drive electrode of a reference drive electrode is understood to mean any drive electrode that is connected to the drive electrode of the reference drive electrode via the weakly conductive layer. Thus, the term "adjacent drive electrode" includes both a drive electrode directly adjacent to the reference drive electrode, i.e.,a control electrode that is directly adjacent to the reference control electrode, as well as a control electrode neighbor that is two steps away or further away.

[0076] For this purpose, the weakly conductive structure 60 is divided into sections assigned to each of the control electrodes 62, as shown in the representation according to Fig. 4. The sections 60n-1, 60n, and 60n+1 are divided. This design is also used in Fig. 5 is shown in a section view parallel to the xy-plane. As seen from Fig. As can be seen from Figure 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 on the respective control electrode 62. Thus, sections 60n-1, 60n and 60n+1 are each centered on the control electrode OE. n-1 (Reference number 62n-1), OE n or OE n+1centered. Similarly, in an upstream series of actuators, 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 accordingly to the left, right, down, and up, as shown in Fig. 4 indicated by continuation points.

[0077] The sections of the weakly conductive structure 60 are separated from their immediately adjacent sections, specifically from each other by electrically insulating separation lines 93. Separation lines 93 run around section 60n, so that it is electrically isolated from sections 60n-1, 60n+1, 60m, and any section that may be located above it. Any current flow between these sections occurs only via a respective current measuring device 94. This current flow between two sections is the aforementioned leakage current between the respective control electrodes 62. In the embodiment described here, this leakage current can be precisely measured by means of the current measuring devices 94.

[0078] For this purpose, the current measuring devices 94 are connected to the respective sections via current lines 95 through contact points 61 arranged at the edge of the relevant section of the weakly conductive structure 60. For example, the device used to measure the leakage current ILn−1 / n The power measuring device 94 is connected via respective power lines 95 to contact points 96 on section 60n-1 and section 60n.

[0079] 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 located between the measuring electrodes 58 according to Fig. 3 and the base electrode 56, but are connected between the control electrodes 62n-1, 62n and 62n+1 and the base electrode 56. The determination of the impedances Z by the measuring device 80 n-1 (U A ), z n (U A ) as well as z n+1 (U A ) is carried out analogously to the procedure with reference to Fig. 4 described procedure based on the alternating voltage Uw applied by the alternating voltage source 82 and the current intensities determined by the current measuring devices 84n-1, 84n and 84n+1 Iwn−1,Iwn and Iwn+1.

[0080] The operation of the evaluation unit 88B according to Fig. 4 differs from the evaluation unit 88A according to Fig. 3 such that, when determining the deflection characteristics 90 from the operating voltage-dependent impedances 86, the leakage currents 97 measured by the current measuring devices 94 are taken into account. The totality of the leakage currents 97 is in Fig. 4 with a leakage current vector I L The consideration of the leakage currents 97 in the evaluation unit 88B is carried out in such a way 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, is taken into account. Iwn−1,Iwn and Iwn+1 etc. (see reference symbols 85n-1, 85n, 85n+1) from the measurement result of the impedances z n-1 (U A ), z n (U A ) as well as Z n+1 (U A ) etc. is factored out. The impedances corrected in this way are then used to determine the deflection characteristics 90.

[0081] Fig. Figure 8 illustrates the adaptive optical element 38 according to Fig. 2 In a further embodiment 38C according to the second aspect of the invention, by way of example with three actuators 36n-1, 36n and 36n+1. Embodiment 38C comprises a layer structure 39C and an electronic unit 40C. The layer structure 39C differs from the layer structure of embodiment 39B according to Fig. 4 merely in that the weakly conductive structure 60, as in embodiment 39A according to Fig. 3, is configured as a layer extending continuously along the control electrodes 52.

[0082] The electronic unit 40C is, like the electronic unit 40B, according to Fig. 4, 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 electronic unit 40C is also designed to subtract the effect of the leakage currents between adjacent control electrodes 62 caused by the weakly conductive structure 60 from the measurement result of the respective impedance measurement. In contrast to the electronic unit 40B, where the subtraction is based on measurements of the actual leakage currents 97, the electronic unit 40C calculates the effect of the leakage currents based on predefined coupling resistances R. K (Reference sign 100) between the individual control electrodes 62 and the respective adjacent control electrodes 62.

[0083] In the Fig. In the embodiment shown in Figure 8, current measuring devices 98 and a resistance measurement device 99 for determining the coupling resistances 100 are already integrated into the electronic unit 40C. As mentioned previously, the coupling resistances 100 are determined before the adaptive optical module 38C is operated in calibration mode 76, which is carried out during the exposure operation of the projection exposure system 10. The coupling resistances 100 are determined in a qualification mode 78, in which an electronic unit independent of the electronic unit 40C can also be used. Thus, in a further embodiment not shown in the drawing, the electronic unit 40C can be designed solely for the execution of control mode 74 and calibration mode 76 and can therefore be configured without the current measuring devices 98 and the resistance measurement device 99.

[0084] In Fig. Figure 6 shows an equivalent circuit diagram of the actuators 36n-1, 36n and 36n+1 of the adaptive optical module 38C to illustrate the procedure for determining the coupling resistances 100. Z n-1 , Z n as well as Z n+1 the impedances of the actuators 36n-1, 36n and 36n+1 and RKn−1 / n and RKn / n+1 The coupling resistances 100 between the control electrodes 62n-1 and 62n, as well as between the control electrodes 62n and 62n+1, are shown. To determine the coupling resistances RKn−1 / n and RKn / n+1 In qualification mode 78, a DC voltage is generated using the corresponding voltage generator 66. UTestn applied to the control electrode 62n and simultaneously set the voltage to 0V at the control electrodes 62n-1 and 62n+1 as well as all other adjacent control electrodes, if present. (UTestn−1=0V,UTestn+1=0V). Now, the direct currents are measured using the current measuring devices 98. IGn−1 as well as IGn+1 measured which leakage currents ILn−1 as well as ILn+1 through the coupling resistances RKn−1 / n and RKn / n+1 are equivalent to.

[0085] The resistance measurement device then determines the following from the leakage currents. ILn−1 and ILn+1 the coupling resistances RKn−1 / n and RKn / n+1: RKn−1 / n=UTestnIn−1 and RKn / n+1=UTestnIn+1. Coupling resistances to other adjacent control electrodes 62 are calculated analogously.

[0086] The coupling resistances thus determined 100 (in Fig. 8 also as vector R KThe data shown (as displayed) is forwarded to the evaluation unit 88C and stored there. The operation of the evaluation unit 88C according to Fig. 8 differs from the evaluation unit 88B according to Fig. 4 such that, when determining the deflection characteristics 90 from the operating voltage-dependent impedances 86, the pre-determined coupling resistances 100 are taken into account instead of the directly measured leakage currents 97. The consideration of the coupling resistances 100 in the evaluation unit 88B is carried out 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 ) as well as Z n+1 (U A ) etc. is factored out. The impedances corrected in this way are then used to determine the deflection characteristics 90.

[0087] The determination of the leakage currents from the coupling resistors 100 is carried out in the evaluation unit 88C based on the in Fig. The equivalent circuit diagram shown in section 6 illustrates this. For example, the current I can be derived from this diagram. Zn of actuator 36n as follows: IZn=In−∑Un−UiRnimit i≠n

[0088] Here are I n the current strengths of the neighboring actuators, U n the stresses at the adjacent actuators and U i the voltage at actuator 36n.

[0089] Optionally, the 88C evaluation unit can also be configured to measure line resistances. Rwn−1,Rwn and Rwn+1 (cf. reference numeral 102) of the leads to the control electrodes 62n-1, 62n and 62n+1 must be taken into account when determining the deflection characteristics 90 from the operating voltage-dependent impedances 86. The lead 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 ) as well as z n+1 (U A ) etc. is factored out. The impedances corrected in this way are then used to determine the displacement characteristics.

[0090] Among the line resistances Rwn−1,Rwn and Rwn+1 The 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, including the contact resistances resulting from the contact between the control electrodes 62n-1, 62n and 62n+1 via the connecting lines, are to be understood as follows. The line resistances 102 are to be understood as follows: Fig. 7 is shown in an equivalent circuit diagram.

[0091] To determine the line resistances 102, the frequency of the AC voltage source 82 is set to such a high frequency that the respective equivalent ohmic resistance of the actuators 36n-1, 36n, and 36n+1 approaches zero, i.e., that the equivalent ohmic resistance is negligibly small compared to the value of the respective line resistance 102. This means that the respective equivalent ohmic resistance is less than 10%, and in particular less than 5%, of the value of the respective line resistance. The frequency of the AC voltage source 82 set for this purpose can, for example, be at least 10 kHz, and in particular at least 100 kHz. According to one embodiment, the frequency is in the range of 100 kHz to 1 MHz.

[0092] After setting the above-described high frequency at the AC voltage source 82, test voltages are successively applied to the individual control electrodes 62n-1, 62n and 62n+1 by means of the voltage generators 66. UTestn−1,UTestn or UTestn+1 set and the respective resulting test current strengths were determined using the current measuring devices 98. ITestn−1,ITestn or ITestn+1 measured. The resistance measuring device 99 determines using the relationship Rwn=UTestnITestn the line resistances Rwn−1,Rwn as well as Rwn+1.

[0093] The measurement function of the line resistances 102 and their consideration in the determination of the deflection characteristics 90 can optionally also be integrated into the adaptive optical module 38B according to Fig. 4 be integrated. In this embodiment, the optical module 38B comprises, in addition to the one in Fig. The configuration shown in 4 also includes the one in Fig. 8 illustrated current measuring devices 98 and the resistance determination device with the function for determining the line resistances 102.

[0094] Fig. Figure 9 shows a schematic view of a microlithographic projection exposure system 210 configured for operation in the DUV wavelength range, which includes an illumination optic in the form of a beam shaping and illumination system 216 and a projection lens 222. DUV stands for "deep ultraviolet" and refers to 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 appropriate drive devices.

[0095] The DUV projection exposure system 210 has a DUV exposure radiation source 212. For example, an ArF excimer laser can be provided for this purpose, which emits exposure radiation 214 in the DUV range at, for example, about 193 nm.

[0096] The in Fig. The beam shaping and illumination system 216 shown in Figure 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 which is imaged, reduced in 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 slidably mounted on a substrate transfer stage 226.

[0097] The projection lens 222 has several 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 additional mirror 230-2, which is designed as an adaptive optical module 38. Individual lenses and / or mirrors of the projection lens 222 can be arranged symmetrically about 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 generally curved on their front surface for beam shaping.

[0098] 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, highly purified water. Such a setup is also known as immersion lithography and exhibits increased photolithographic resolution. The medium 231 can also be referred to as the immersion fluid.

[0099] In the Fig. In the embodiment shown in 9, the adaptive optical module 38 is analogous to the adaptive optical module 38 according to Fig. 1 executed, whereby of course it uses a different mirror element than in Fig. 1 comprises. The adaptive optical module 38 is configured to actively change the shape of the surface 232 of the mirror 230-2 to correct local shape errors. The mirror surface is therefore also referred to as the active optical mirror surface 232. The adaptive optical module 38 can be configured according to Fig. 9 in one of the in the Fig. 2, Fig. 3, Fig. 4 and Fig. 8 embodiments are configured. All above with reference to the Fig. The statements made in sections 1 to 8 regarding the adaptive optical module 38 can thus be applied to the adaptive optical module 38 according to Fig. 9 transferred.

[0100] Analogous to the projection exposure system 10 according to Fig. 1 the adaptive optical module 38 according to Fig. 9 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 means of a wavefront measuring device 44. Without loss of generality, in Fig. 9 Here only one actuator device is shown, however it is understood that preferably a large number of actuator devices are present, each of which can be individually controlled and / or regulated.

[0101] The foregoing description of exemplary embodiments, embodiments, or variants is to be understood as illustrative. The disclosure thereby enables the person skilled in the art to understand the present invention and its associated advantages, and also encompasses, in the understanding of the person skilled in the art, obvious modifications and alterations of the described structures and methods. Therefore, all such modifications and alterations, insofar as they fall within the scope of the invention as defined in the appended claims, as well as equivalents, are to be covered by the protection of the claims. Reference symbol list 10 Projection exposure system 12. Exposure radiation source 14 Exposure radiation 16 Lighting optics 18 Mask 20 mask moving stage 22 Projection lens 24 substrate 26 Substrate transfer platform 28 Exposure beam path 30-1, 30-2, 30-3, 30-4, 30-5, 30-6, 30-7, 30-8 Mirror elements 32 active optical surfaces 34 Support element 36, 36n-1, 36n, 36n+1 actuator 38, 38A, 38B, 38C adaptive optical module 39A Layer structure 39B Layer structure 39C Layer structure 40A electronic unit 40B Electronic Unit 40C Electronic Unit 41 Control unit 42 Control signal 43 deflection 43s Target displacement vector 44 Wavefront measuring device 46 wavefront deviations 48 dielectric medium 52 Actuator section 54 Insulator layer 56 Base electrode 58, 58n-1, 58n, 58n+1 measuring electrode 60 weakly conducting structure 62, 62n-1, 62n,62n+1 Control electrode 64 Multi-layer arrangement 65 Smoothing and insulating layer 66 Voltage generator 68 Operating voltage 69 Conversion Recipe 70 Reference characteristic curve 72 Control unit 74 Control mode 76 Calibration mode 78 Qualification mode 80 Measuring device 82 AC voltage source 83 Measuring voltage 84, 84n-1, 84n, 84n+1 current measuring device 85n-1, 85n, 85n+1 Current 86n-1, 86n, 86n+1 Operating voltage-dependent impedance 88A Evaluation Unit 88B Evaluation Unit 88C Evaluation Unit 90 deflection characteristics 90d diagram of a deflection characteristic curve 91 Comparison module 92 Correction 93 electrically insulating dividing line 94 Current measuring device 95 Power line 96 Contact point 97 Leakage current 98 Current measuring device 99 Resistance Investigation Unit 100 coupling resistance 102 Line resistance 210 Projection exposure system 212 Exposure radiation source 214 Exposure radiation 216 Beam shaping and lighting system 218 Photomask 222 Projection lens 223 optical axis 224 Substrat 226 Substrate transfer platform 230 optical element 230-1, 230-4, 230-5 lens 230-2 adaptive optical module 230-3 mirror 231 liquid medium 232 active optical mirror surface QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2020 212 743 A1

[0005]

Claims

[1] Adaptive optical module (38A) for a microlithographic projection exposure apparatus (10; 210) having 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 comprises 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 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) of at least one of the actuators, a measuring electrode (58n-1, 58n, 58n+1) is arranged between the control electrode of the measured actuator and the dielectric medium. [2] The adaptive optical module of claim 1, wherein the weakly conductive structure (60) is configured as a layer disposed 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 drive 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 drive electrodes (62n-1, 62n, 62n+1) and is configured to generate the respective electric field in the dielectric medium (48) together with the respective drive electrode. [5] 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 comprises a dielectric medium (48) deformable by applying an electrical voltage (68), and each of the actuators comprises a separate drive 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) with an electrical conductivity of at least 0.1 mS / m, and wherein the adaptive optical module further comprises an evaluation device (88B, 88C) which is configured, when measuring an impedance (86n-1, 86n, 86n+1) of at least one of the actuators, to calculate from the measurement result an effect influencing the measurement result 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. [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 a separate 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 flow emerging from the further control electrode (62n+1) when a test voltage is applied to the control electrode (62n) of the measured actuator. [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, further comprising a measuring device (80) 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, further comprising a control unit (72) configured to correct a control variable (68) applied to the associated drive electrode based on 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] 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 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, - 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] 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] 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 out of 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 associated with 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 of the measurement result of the impedance measurement during operation of the projection exposure apparatus (10; 210) for exposing a substrate.

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