Adaptive Optics Module

Abstract

The adaptive optical module (38) includes at least one actuator (36-1) that changes the shape of the optical surface (32) of the optical module. The actuator includes a dielectric medium (48) that is deformable by an electric field (55) and an electrode (54) that generates an electric field in the dielectric medium by applying an operating voltage (60). The adaptive optical module further includes a measuring device (70) configured to measure the impedance (80) present at different values ​​of the operating voltage between the electrodes as a function of the frequency (76) of an AC voltage (74) applied to the electrodes for measurement, and an evaluation device (84) configured to derive from the measured impedance the approximate slope values ​​(86) of each characteristic curve representing the capacitance (81) of the actuator as a function of frequency for different values ​​of the operating voltage, and from there determine the deflection (42-1) of the actuator at at least one operating point of the operating voltage.

Description

Technical Field

[0001] This application claims priority to German Patent Application No. 10 2023 204 292.4 filed on May 10, 2023. The entire disclosure of the patent application is incorporated herein by reference.

[0002] The present invention relates to an adaptive optical module comprising at least one actuator for changing the shape of an optical surface, a microlithography projection exposure apparatus comprising at least one optical module of this type, and a method for deriving the deflection of the actuator of the adaptive optical module.

Background Art

[0003] To ensure the most precise imaging of the mask structure onto the wafer, a projection lens of a microlithography projection exposure apparatus with minimal wavefront aberration is required. Therefore, the projection lens is provided with a manipulator that enables correction of the wavefront error by changing the state of the individual optical elements of the projection lens. Examples of such state changes include changes in the orientation of one or more of the six rigid body degrees of freedom of the corresponding optical element, and deformation of the optical element.

[0004] In the case of the latter state change, the optical element is usually incorporated into an adaptive optical module of the type described above. The adaptive optical module may comprise one or more piezoelectric or electrostrictive actuators for actuating the optical surface. The functionality of such an actuator is based on the deformation of a dielectric medium by the application of an electric field. To determine the desired state change, the aberration characteristics of the projection lens are usually measured periodically, and, if appropriate, the change in the aberration characteristics between individual measurements is determined by simulation. Thus, it is possible to take into account, for example, lens or mirror heating effects computationally.

[0005] When using piezoelectric or electrostrictive adaptive optical elements, problems often arise because changes in the relevant parameters of the actuator material due to factors such as temperature changes, aging, defects, and drift can significantly inaccurate the surface shape correction performed by the adaptive optical element.

[0006] To avoid these inaccuracies, for example, Patent Document 1 proposes the arrangement of actuator material for measuring electrodes for measuring temperature, and the implementation of corrections based on the corresponding measurement results. However, this is merely an indirect measurement and often fails to capture surface shape errors caused by actuator misalignment with sufficient accuracy. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] German Patent Application Publication No. 10 2020 212 743 Specification [Overview of the project] [Problems that the invention aims to solve]

[0008] The problem addressed by the present invention is to provide an adaptive optical module and method of the type described above that can solve the above-mentioned problems and, in particular, can perform surface shape correction of adaptive optical elements with improved accuracy. [Means for solving the problem]

[0009] According to the present invention, the above-mentioned problems can be solved, for example, by an adaptive optical module equipped with at least one actuator that changes the shape of the optical surface of the optical module. The actuator includes a dielectric medium that can be deformed by an electric field and an electrode that generates an electric field in the dielectric medium by applying an operating voltage. Furthermore, the adaptive optical module includes a measuring device configured to measure the impedance present at different values ​​of the operating voltage between the electrodes as a function of the frequency of the AC voltage applied to the electrodes for measurement, and an evaluation device configured to derive approximate slope values ​​of each characteristic curve representing the capacitance of the actuator as a function of frequency for different values ​​of the operating voltage from the measured impedance, and from there determine the deflection of the actuator at at least one operating point of the operating voltage.

[0010] The adaptive optical module may have a mirror surface or a lens surface as its optical surface. In the case of a mirror surface, the adaptive optical module may also be called an adaptive mirror module or adaptive mirror. The deflection of the actuator at the relevant operating point should preferably be understood as the deflection of the actuator in a static or quasi-static state, i.e., the deflection at a frequency of 0 Hz. The actuator is preferably embodied as a ferroelectric actuator.

[0011] The solution according to the present invention makes it possible to determine the deflection of an actuator at at least one operating point based on electrical measurements at the electrodes. For example, compared to interference measurements of surface shape based on the operating voltage, the measurement according to the present invention at the electrodes can be performed at a high repetition rate, sometimes even during the exposure operation of a microlithography projection exposure apparatus. Basically, the measured impedance can be converted very easily to the susceptibility χ at the frequency f of the AC voltage on which the measurement is based. o or χ f0 That is, the susceptibility at f=0Hz or in a static state can be estimated from the susceptibility χ measured at different frequencies by interpolation. Based on this, the relationship P=∫χ f0 dE and S~P2 This allows us to determine the polarization P in the dielectric medium and the deflection S of the actuator from it, where E represents the electric field strength in the dielectric medium.

[0012] However, the baseline sensitivity χ obtained by interpolating the measured sensitivity χ f0 The estimation of the estimated baseline sensitivity χ² f0 This leads to inaccuracies. These inaccuracies can be avoided by determining the gradient value of the characteristic curve representing the capacitance of the actuator as a function of frequency according to the present invention. This is the basic susceptibility χ f0 Furthermore, the deflection of the actuator at the corresponding operating point of the operating voltage can be determined with high precision from the derived gradient value. This then enables similarly high-precision surface shape correction of the adaptive optical element.

[0013] According to one embodiment, the evaluation device is configured to determine the dependence of actuator deflection on operating voltage from the slope values ​​of characteristic curves derived for different operating voltage values. This dependence can be expressed by an analytical function of deflection as a function of operating voltage, or by a corresponding conversion table.

[0014] In yet another embodiment, the evaluation device is configured to determine the dependence of the actuator deflection on the operating voltage by integrating a characteristic variable derived from the gradient value of the characteristic curve over the electric field strength corresponding to the operating voltage. The characteristic variable derived from the gradient of the characteristic curve is an approximation of the susceptibility of the actuator in a static state. In one modified embodiment, the characteristic variable derived from the gradient of the characteristic curve differs from the gradient of the characteristic curve by a certain coefficient, for example. In particular, the variable derived from the gradient of the characteristic curve may be the susceptibility of the actuator.

[0015] In yet another embodiment, the characteristic variable obtained from the gradient is the susceptibility of the actuator in a static state, i.e., at an AC voltage frequency of 0 Hz.

[0016] In yet another embodiment, the evaluation device is configured to convert the gradient value of the characteristic curve into the gradient value of the actuator's susceptibility with respect to frequency in order to derive characteristic variables. The gradient value of susceptibility with respect to frequency should be understood as the gradient value of the characteristic curve representing susceptibility as a function of frequency. This means that the gradient of susceptibility at a given frequency is calculated using the gradient of capacitance at a particular frequency.

[0017] In yet another embodiment, the evaluation device is configured to derive a characteristic curve from impedance based on an equivalent circuit diagram of the actuator. The equivalent circuit diagram may include parallel and / or series connections of ohm resistors, capacitors, and / or inductive elements. In one modified embodiment, the equivalent circuit diagram includes a series connection of a capacitor and an ohm resistor. Thus, the capacitance of the capacitor is also referred to as the series capacitance. In particular, the equivalent circuit diagram further includes other series elements, and in one modified embodiment, also includes at least one parallel element. These elements may include at least one capacitive element, at least one inductive element, and / or at least one ohm resistor. In an alternative embodiment, the deriving of a characteristic curve from impedance can be performed based on an equivalent circuit diagram of the actuator including a parallel connection of a capacitor and an ohm resistor.

[0018] In yet another embodiment, the evaluation device is configured to derive the gradient value of each characteristic curve by fitting the corresponding characteristic curve. The fitting can be linear or nonlinear.

[0019] In yet another embodiment, the evaluation device is configured to derive the gradient values ​​of each characteristic curve by modal analysis of the corresponding characteristic curve. Alternatively, the gradient values ​​of each characteristic curve can be derived using an analytical solution or generally a model-based solution.

[0020] In yet another embodiment, the adaptive optical module is configured for use in a microlithography projection exposure apparatus. In particular, the projection exposure apparatus may be configured to operate in the EUV wavelength range. In an alternative embodiment, the optical module is configured as a telescope mirror, i.e., a mirror used in astronomy.

[0021] In yet another embodiment, the frequency range in which the impedance is measured is 20 Hz to 200 kHz.

[0022] Furthermore, the present invention provides a microlithography projection exposure apparatus comprising at least one adaptive optical module according to one of the above-described embodiments or modified embodiments.

[0023] According to one embodiment of the projection exposure apparatus, an evaluation device for an adaptive optical module is configured to determine the dependence of actuator deflection on the operating voltage from gradient values ​​derived for different operating voltages, and the projection exposure apparatus further includes a control unit configured to derive a control value for the operating voltage to control the actuator from a predetermined target deflection of the actuator based on the above dependence. In other words, the feedforward operation of the adaptive optical module is possible by using the gradient values ​​derived according to the present invention. Alternatively, the derived gradient values ​​can also be used to support the control loop.

[0024] The above-mentioned problems can also be solved, for example, by a method for deriving the deflection of an actuator in an adaptive optical module. The actuator is configured to change the shape of the optical surface of the optical module and includes a dielectric medium that is deformable by an electric field and an electrode that generates an electric field in the dielectric medium by applying an operating voltage. The method according to the present invention includes the steps of applying different values ​​of operating voltage and different frequencies of AC voltage to the electrode and measuring the impedance present at each value of the operating voltage as a function of the frequency of the AC voltage; and from the measured impedance, deriving the approximate slope values ​​of each characteristic curve that represents the capacitance of the actuator as a function of frequency for different values ​​of operating voltage, and determining the deflection of the actuator at at least one operating point of the operating voltage.

[0025] According to one embodiment of the method according to the present invention, impedance is measured at each value of the operating voltage for at least two, particularly at least five, at least ten, or at least twenty different values ​​of frequency. According to one modified embodiment, impedance is measured at each value of the operating voltage for up to 15 or up to 30 frequency values.

[0026] In yet another embodiment, the method according to the present invention is performed during the exposure operation of a microlithography projection exposure apparatus equipped with an adaptive optical module. Alternatively, the method according to the present invention may be performed outside of the exposure operation, for example, during the recovery phase of the projection exposure apparatus.

[0027] The features described above with respect to the embodiments, exemplary embodiments, or modified embodiments of the adaptive optical module according to the present invention can be appropriately applied to the methods according to the present invention, and vice versa. These and other features of embodiments according to the present invention are described in the description of the drawings and in the claims. Individual features can be implemented separately or in combination as embodiments of the present invention. Furthermore, these features may represent advantageous embodiments that are independently protectable and, in some cases, only seek protection during or after the pendency of this application.

[0028] The above-mentioned features and other advantageous features of the present invention are shown below in the detailed description of examples or embodiments of the present invention with reference to the attached schematic diagrams. [Brief explanation of the drawing]

[0029] [Figure 1] An embodiment of a microlithography projection exposure apparatus equipped with an adaptive optical module is shown. [Figure 2] A first embodiment of an adaptive optical element in its initial state and corrected state is shown. [Figure 3] Further embodiments of the adaptive optical element in its initial and corrected states are shown. [Figure 4] Figure 2 shows an embodiment of an adaptive optical element actuator, which includes a measuring device that measures impedance for each operating voltage and an evaluation device that derives the slope value of the characteristic curve derived from the impedance to determine the dependence of the actuator's deflection on the operating voltage. [Figure 5] Figure 4 shows an exemplary embodiment of the characteristic curve derived using the measuring device shown. [Modes for carrying out the invention]

[0030] In the exemplary embodiments, or embodiments or modifications described below, elements that are functionally or structurally similar to one another are denoted by the same or similar reference numerals whenever possible. Therefore, to understand the characteristics of individual elements in a particular exemplary embodiment, please refer to the descriptions or overviews of other exemplary embodiments of the present invention.

[0031] To facilitate explanation, an orthogonal xyz coordinate system is illustrated, from which the positional relationships of the components in the illustration become clear. In Figure 1, the y-direction extends perpendicular to the plane of the figure, the x-direction extends to the right, and the z-direction extends upward.

[0032] Figure 1 shows one embodiment of a microlithography projection exposure apparatus 10 according to the present invention. This embodiment is designed to operate in the EUV wavelength range, i.e., electromagnetic radiation with wavelengths less than 100 nm, particularly around 13.5 nm or about 6.8 nm. As a result of this operating wavelength, all optical elements are embodied as mirrors. However, the present invention is not limited to projection exposure apparatuses in the EUV wavelength range. Rather, the present invention can be used in other optical systems, particularly projection exposure apparatuses for UV or DUV wavelengths. For example, yet another embodiment of the present invention is designed for projection exposure apparatuses using operating wavelengths of 365 nm, 248 nm, or 193 nm. In this case, at least some of the optical elements are configured as conventional transmission lens elements.

[0033] The projection exposure apparatus 10 shown in Figure 1 includes an exposure radiation source 12 that generates exposure radiation 14. In this embodiment, the exposure radiation source 12 is embodied as an EUV source and may include, for example, a plasma radiation source. The exposure radiation 14 first passes through an illumination optical unit 16 and is thereby directed to the mask 18.

[0034] The mask 18 includes a mask structure that is imaged onto a substrate 24 in the form of a wafer during the exposure operation of the projection exposure apparatus 10, and is displaceably mounted on a mask displacement stage 20. The substrate 24 is displaceably mounted on a substrate displacement stage 26. As shown in Figure 1, the mask 18 may be embodied as a reflective mask, or alternatively, as a transmission mask, particularly in UV lithography. In the embodiment shown in Figure 1, exposure radiation 14 is reflected by the mask 18 and then passes through a projection lens 22 configured to image the mask structure onto the substrate 24. The substrate 24 is displaceably mounted on a substrate displacement stage 26. The projection exposure apparatus 10 may be embodied as a so-called scanner or so-called stepper. The exposure radiation 14 is guided within an illumination optical unit 16 and a projection lens 22, where multiple optical elements in the form of mirrors are used.

[0035] In the illustrated embodiment, four optical elements are included in the form of mirror elements 30-1, 30-2, 30-3, and 30-4. The projection lens 22 also includes 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 positioned in the exposure beam path 28 of the projection exposure apparatus 10 to guide the exposure radiation 14.

[0036] In the illustrated embodiment, the mirror element 30-5 is part of an adaptive optical module 38, which may also be called an adaptive optical element. In the adaptive optical module 30-5, the optical surface of the mirror element 30-5 acts as an active optical surface 32 whose shape can be actively changed to correct local shape errors. In further embodiments, different mirror elements or multiple mirror elements 30-1, 30-2, 30-3, 30-4, 30-5, 30-6, 30-7, and 30-8 may also be configured as part of the adaptive optical module.

[0037] Furthermore, one or more of the mirror elements 30-1, 30-2, 30-3, 30-4, 30-6, 30-7, and 30-8 of the projection exposure apparatus 10, or the adaptive module 38, can be movably mounted. For this purpose, each rigid manipulator is assigned to each of the movably mounted mirror elements. For example, each rigid manipulator allows the optical element to tilt and / or displace substantially parallel to the plane on which the reflective surface of each assigned optical element is located. Thus, the position of one or more mirror elements can be changed to correct the imaging aberration of the projection exposure apparatus 10.

[0038] According to one embodiment, the projection exposure apparatus 10 includes a control device 40 that generates control signals 42 to an operating unit and / or possibly other manipulators equipped with one or more adaptive optical modules such as the rigid manipulator described above. Figure 1 shows an example of the transmission of control signals 42 to an adaptive optical module 38. According to an embodiment for correcting aberrations of the projection lens 22, the control device 40 derives control signals 42 based on the wavefront deviation 46 of the projection lens 22 measured by a wavefront measuring device 44, using a feedforward control algorithm.

[0039] A first embodiment of the adaptive optical module 38 is shown in Figure 2. The upper part of Figure 2 shows the adaptive optical module 38 in its initial state, where the shape of the optical surface 32 is its initial shape, in this case a planar shape. The lower part of Figure 2 shows the adaptive optical module 38 in a corrected state, where the shape of the optical surface 32 has been changed, in this case a convex arch shape.

[0040] The adaptive optical module 38 includes a support element 34 in the form of a backplate and a mirror element 30-5 whose upper side forms an active optical surface 32 and reflects exposure radiation 14. A plurality of actuators 36, also referred to as manipulators, are arranged along the underside of the mirror element 30-5. In this case, it is preferable that they are positioned along the underside of the mirror element 30-5 in both the x and y directions, i.e., in a two-dimensional arrangement. For clarity, only a few actuators 36 are given reference numerals in Figure 2 and connect the support element 34 to the mirror element 38. The actuators 36 are configured to change size along their longitudinal direction when operated. In the embodiment shown in Figure 2, the actuators 36 can be actuated transversely or perpendicularly with respect to the optical surface 32. In this case, the actuators 36 can be driven individually and therefore independently of each other.

[0041] In the correction state shown at the bottom of Figure 2, the length of the actuator 36 located in the center is increased by its operation, resulting in a convex arch shape on the optical surface 32.

[0042] Figure 3 shows yet another embodiment of the adaptive optical module 38. Similar to Figure 2, the upper part of Figure 3 shows the adaptive optical module 38 in its initial state, where the shape of the optical surface 32 is planar as its initial shape. The lower part of Figure 3 shows the adaptive optical module 38 in its corrected state, where the shape of the optical surface 32 is convex arched, and therefore modified.

[0043] The adaptive optical module 38 shown in Figure 3 differs from the embodiment shown in Figure 2 in that the actuator 36 is positioned parallel to the optical surface 32 rather than transversely to the mirror element 30-5, and the actuator 36 is not supported by a rigid support element positioned parallel to the mirror element 30-5. That is, the actuator 36 can be deformed parallel to the optical surface 32 rather than transversely to the optical surface 32, as shown in Figure 2. As a result of the expansion and contraction of the individual actuators 36 parallel to the surface, a bending moment is introduced to the mirror element 30-5, deforming the mirror element 30-5 as shown in the lower part of Figure 3.

[0044] By driving each actuator 36, the profile of the mirror element 30-5 can be intentionally set in both the embodiment shown in Figure 2 and the embodiment shown in Figure 3, and as a result, the optical system of the projection exposure apparatus 10, particularly the projection lens 22 or illumination optical unit 16, can be corrected as optimally as possible. To drive the actuators 36 in this way, the control signal 42 includes target deflections for various actuators 36. The target deflection of one of the actuators 36-1 is shown in Figure 4 by reference numeral 42-1S.

[0045] Figure 4 shows a portion of the adaptive optical element 38 shown in Figure 2, equipped with one of the actuators 36, here denoted by reference numeral 36-1. As shown in Figure 4 for actuator 36-1 as an example, each actuator 36 of the adaptive optical module 38 includes a dielectric medium 48 that is deformable by the application of an electric field. This may be a piezoelectric material or an electrostrictive material. The deformation is based on the piezoelectric effect in the case of a piezoelectric material, and on the electrostrictive effect in the case of an electrostrictive material. In this specification, the electrostrictive effect is understood to mean the component of deformation of the dielectric medium due to the applied electric field, and this deformation does not depend on the direction of the applied electric field, but is in particular proportional to the square of the electric field. In contrast, the linear response of deformation to an electric field is called the piezoelectric effect.

[0046] In the modified embodiment described below, the actuator 36 is implemented as a ferroelectric actuator and is based on the electrostrictive effect. These are particularly suitable for correcting the shape of the active optical surface 32 because they exhibit very little drift and only slight hysteresis.

[0047] The actuator 36-1 shown in Figure 4 includes a dielectric medium 48 that contacts the back side of the mirror element 30-5, an electrode 54, wiring 56 for the electrode 54, and a voltage generator 58, as described above. The dielectric medium 48 has an integrated embodiment in the form of a ceramic component in which the electrode 54 is embedded or integrated. The integrated dielectric medium 48 is a continuous, seamless monolithic dielectric medium, which is formed, for example, by sintering.

[0048] In other words, the electrodes 54 are arranged in combination with an integrated dielectric medium 48. The electrodes 54 are housed in the dielectric medium 48 in the form of an electrode stack. In the illustrated embodiment, the electrode stack includes seven plate-shaped electrodes 54 arranged vertically. The entire area of ​​the dielectric medium 48 arranged between the electrodes 54 is referred to as the working volume 50 of the dielectric medium 48. The area of ​​the dielectric medium 48 located outside the electrode stack is therefore referred to as the non-working volume 52. In the illustrated embodiment, the non-working volume 52 completely encloses the working volume 50.

[0049] The wiring 56 of the electrode 54 alternately connects the electrode 54 to the positive and negative electrodes of the voltage generator 58, and between them, the voltage generator 58 generates a controllable operating voltage U indicated by the reference numeral 60. A That is, the operating voltage 60 is a DC voltage having a variable voltage value U A . The wiring 56 is configured such that the signs of the electric field strengths E (reference numeral 92) of the electric fields 55 respectively generated between two adjacent electrodes 50 by the applied operating voltage 60 alternate.

[0050] Since the dielectric medium 48 is an electrostrictive material in this embodiment, the expansion of the dielectric medium 48 caused by the electric field 55 does not depend on the direction of the electric field 55. That is, the change in the z - direction expansion of each layer of the dielectric medium 48 disposed between the electrodes 54 is in the same direction. The dielectric medium 48 can be configured as a single crystal or a polycrystal. At the same time, the dielectric medium contracts in the x - direction and the y - direction. Therefore, when the operating voltage 60 generated by the voltage generator 58 is applied, the length expansion of the active volume 50 of the dielectric medium 48 changes in the z - direction, and there are corresponding changes in the x - direction and the y - direction. The absolute value of the change in the length expansion changes according to the operating voltage 60 generated by the voltage generator 58. According to one embodiment, this value is proportional to the value U A of the operating voltage 60.

[0051] The overall change in the length expansion of the actuator 36 - 1 when an operating voltage 60 other than 0V is applied is called the deflection S, and in FIG. 4, the reference numeral 42 - 1 is provided.

[0052] Before the adaptive optical module 38 operates, a reference characteristic curve 68 between the deflection S and the operating voltage U A is arbitrarily measured in a so - called reference mode. In the reference mode, different values of the operating voltage U A , that is, different operating points of the operating voltage U A are set, and the corresponding deflections S R of the optical surface 32 of the actuator 36 - 1 are measured for each of these values by a reference measurement module in the form of an interferometer.

[0053] Furthermore, the embodiment of the adaptive optical element 38 shown in Figure 4 includes a control unit 62 assigned to the illustrated manipulator 36-1. This control unit 62 may be part of a control module that controls the multiple manipulators 36 of the adaptive optical element 38. Moreover, the control unit may be part of the adaptive optical element 38, or it may be located outside the adaptive optical element 38, for example, it may be part of the control device 40 of the projection exposure apparatus 10.

[0054] In control mode 64, the target deflection S of the manipulator 36-1 shown in Figure 4 is included in the control signal 42 output from the control device 40. S (Reference numeral 42-1s) is read by the control unit 62. The flow of information within the control module 64 is shown in Figure 4 using dashed lines. The specified target deflection S S Operating voltage U A A conversion formula 69 for deriving the default is stored in the control unit 62. In particular, the conversion formula 69 is for the target deflection S S Voltage U used as a function of A This can be formed by the curve of U, which is derived in reference mode before the operation of the adaptive optical element 30-5. A S as a function of R It is advantageous that the curve be derived from the reference characteristic curve 68. Alternatively, the conversion formula can be derived from the calibration mode 66, which is described in more detail below. During operation, the conversion formula 69 is continuously corrected, as will be described in more detail below.

[0055] Loaded target deflection S S In contrast, the control device 40 uses the voltage U based on the conversion formula 69. A The corresponding control value 65 is derived and used to control the voltage generator 58. New operating voltage U A Each time the voltage is set by the voltage generator 58, or at specific time intervals, the calibration module 66 that constitutes the conversion formula 69 is applied. The flow of information in the calibration module 66 is shown by a dashed line in Figure 4.

[0056] To perform the calibration module 66, the embodiment of the adaptive optical element 38 shown in Figure 4 includes a measuring device 70 assigned to the illustrated actuator 36. The measuring device is connected in series with a voltage generator 58 to generate an AC voltage U W It includes an AC voltage source 72 that functions to generate a measurement voltage 74 in the form of AC voltage U W Operating voltage U A Since these are superimposed, the operating voltage U A and AC voltage U W The sum of these is applied between adjacent electrodes 54 of actuator 36-1. AC voltage U W The frequency f (reference numeral 76) can be set variably by the AC voltage source 72. The measuring device 70 further includes an impedance measuring module 78 connected to the wiring 56 for measuring the impedance Z between the electrodes 54 at each frequency f.

[0057] During the measurement operation of the measuring device 70, different values ​​are set in the AC voltage source 72 for frequency f, and in particular, frequency f is adjusted continuously or in constant increments over a certain range of values. For each set frequency value, the resulting impedance Z (reference numeral 80) is derived by the impedance measurement module 78. This is used for multiple operating voltages U A It is executed against.

[0058] Furthermore, the embodiment of the adaptive optical element 38 shown in Figure 4 includes an evaluation device 84 assigned to the illustrated actuator 36-1. Various operating voltages U A The measured impedance Z values ​​derived by the impedance measurement module 78 for each related frequency f are sent to the evaluation device 84. The first evaluation unit 84-1 of the evaluation device 84 converts the impedance value Z into a capacitance value C.

[0059] This is carried out based on the equivalent circuit diagram 100 of actuator 36-1, which in this embodiment represents a series connection of capacitor 102 and ohm resistor 104. Therefore, the capacitance of capacitor 102 can also be referred to as the series capacitance. According to alternative embodiments, the equivalent circuit diagram 100 may further include other series elements, and according to one modified embodiment, it may also include at least one parallel element. According to yet another embodiment, the equivalent circuit diagram may also represent a parallel connection of capacitor and ohm resistor.

[0060] In this embodiment of the equivalent circuit diagram 100, which includes a series connection of a capacitor 102 having capacitance C and an ohm resistor 104 having resistance R, the capacitance C (reference numeral 81) of actuator 36-1 can be expressed as a function of Z as follows.

number

[0061] The first evaluation unit 84-1 converts the impedance value to a capacitance value C, thereby obtaining the characteristic curve C shown by reference numeral 82. U (f) is derived. These characteristic curves are shown as examples in Figure 4 for seven different values ​​U1 to U7 of the operating voltage 60, also indicated by reference numeral 82. The corresponding characteristic curve is C U1 ~C U7 These are shown, each representing a curve of capacitance C as a function of frequency f for each operating voltage 60.

[0062] Characteristic curve C U1 ~C U7 The characteristic curve is evaluated in evaluation interval 106, where the characteristic curve is approximately a straight line. Figure 5 shows the characteristic curve C in evaluation interval 106. U1 ~C U7 The curve is shown as an example with detailed resolution. Fitted line C fit U5 or C fit U7 However, each characteristic curve is shown using a dashed line. As can be seen from Figure 5, characteristic curve CU1 ~C U7 These have resonance at specific frequencies, some of which are indicated by reference numeral 108.

[0063] The second evaluation unit 84-2 of the evaluation device 84 performs linear fitting of the corresponding characteristic curve to C U1 ~C U7 We derive the respective gradient value p1 for each step. The underlying fitted line is described as follows:

number

[0064] As can be seen from Figure 5, the fitted line C fit U5 The gradient fits straight line C fit U7 The slope is greater than that of characteristic curve C, i.e., p1 is greater than that of characteristic curve C. U7 Characteristic curve C U5 The latter is larger. This relationship is also clear from the figure indicated by reference numeral 86 in Figure 4, where different operating voltages U A or a different characteristic curve C U1 ~C U7 The p1 value for this is shown.

[0065] The gradient value p1(U) is simply denoted as U below, and refers to the operating voltage U. A It depends on this and is sent to the third evaluation unit (84-3) of the evaluation device 84. From there, the basic susceptibility shown by reference numeral 88, i.e., the susceptibility χ of the actuator 36-1 in a stationary state, is obtained. f0 However, this is derived as a function of the operating voltage U. Susceptibility χ f0 In this specification, characteristic curve C U1 ~C U7 This is also called the characteristic variable derived from the gradient value p1.

[0066] susceptibility χ f0To find this, evaluation unit 84-3 uses the following relationship.

number

[0067] Sensitivity χ derived by evaluation unit 84-3 f0 (U) is shown as an example in the figure indicated by reference numeral 88 in Figure 4. In this example, the susceptibility χ f0 The first voltage used is U A As [the value] increases, it rises slightly to 1, and then effectively decreases to 0.

[0068] Furthermore, another evaluation unit 84-4 measures the susceptibility χ over the electric field intensity E. f0 By integrating (U), the operating voltage U A The polarization P in actuator 36-1, also shown as reference numeral 90 as a function of , is derived. The electric field strength E is given by the applied operating voltage U A It can be determined from the operating voltage U. A The polarization curve as a function of is shown in Figure 4, indicated by reference numeral 90.

[0069] Furthermore, another evaluation unit 84-5 uses polarization P to determine the operating voltage U A Dependence S of the deflection S of actuator 36-1 on (often simply denoted as U in this specification) f0 (U) is derived, and this dependency is shown by reference numeral 94. For this purpose, polarization P is squared. Dependency S f0 (U) is proportional to the square of P. S f0 ~P 2 (4)

[0070] Flex SF0 , in other words, the operating voltage U A The curve of the deflection S in a static or quasi-static state, shown by reference numeral 42-1 as a function of U, is shown in the figure shown by reference numeral 94 in Figure 4. In other words, the evaluation device 84 uses the measurement impedance 80 to obtain the operating voltage U A It is configured to determine the deflection 42-1 of the actuator at different operating points.

[0071] The functions of the evaluation units 84-1 to 84-5 described above can also be performed within the evaluation device 84 by fewer evaluation units or by only one evaluation unit.

[0072] Dependency S f0 (U) is sent to the comparison module 96 of the control unit 62. The control unit 62 compares the characteristic curve specified by dependency 94 with the reference characteristic curve 68 and, if a deviation is found, performs the corresponding correction 98 of the control unit's conversion formula 69. Alternatively, the control unit calculates the conversion formula 69 directly from dependency 94. In either case, in control mode 64, the control unit calculates the operating voltage U of the voltage generator 58 based on the determined dependency 94. A The control value of 65 is derived.

[0073] According to yet another embodiment of the evaluation unit 84-2, this is achieved by modal analysis of the corresponding characteristic curve 82 rather than linear fitting of the characteristic curve C U1 ~C U7 Derive the respective gradient values ​​p1 for each step.

[0074] In one embodiment of modal analysis, data relating to characteristic curves are supported by model dimensionality reduction. This allows for particularly stable extraction of the gradient value p1, and therefore the deflection 42-1. For this purpose, an optimal basis is extracted from the collected measurement data by singular value decomposition. According to the Eckert-Young theorem, these basis functions are the basis for the optimal rank n, which is determined with respect to the spectral norm and the Frobenius norm. In this case, n represents the dimensionality of the underlying data set or the reduced dimensionality. To support a sufficiently stable computation, the required rank and error of the model dimensionality reduction can be estimated.

[0075] According to one modified embodiment of the modal analysis, the gradient value p1 of the characteristic curve 82 can be determined using fewer than five basis functions, particularly only the first two basis functions of the modal analysis. According to yet another modified embodiment of the modal analysis, the extracted basis functions are smoothed using a Gaussian window. This suppresses the weighting of the resonance points. Furthermore, this makes it possible to mathematically formulate at which frequencies measurements should be performed.

[0076] The number of measurement conditions on the smoothed basis functions maps stably to the unsmoothed basis functions, and a region without resonance is automatically obtained. This is done by forming a matrix C and evaluating the traces of the eigenvalues. In one embodiment, the characteristic curve 82 evaluated by modal analysis each contains 10 to 15 measurement points, i.e., 5 to 15 different capacitance C measurements at different frequency values ​​f. In yet another embodiment, the characteristic curve contains more than 15 measurement points.

[0077] The above descriptions of exemplary embodiments, embodiments, or modified embodiments should be understood as illustrative examples. The disclosures made thereby include, firstly, changes and modifications of the described structures and methods that are obvious to those skilled in the art, and secondly, changes and modifications of the described structures and methods that are obvious to those skilled in the art. Accordingly, all such changes and modifications, and equivalents, insofar as they fall within the scope of the invention in accordance with the description of the appended claims, are intended to be subject to the protection of the claims. [Explanation of symbols]

[0078] 10 Projection exposure apparatus 12 Exposure radiation source 14. Exposure Radiation 16 Lighting Systems 18 masks 20 Mask displacement stage 22 Projection Lens 24 circuit boards 26 Substrate displacement stage 28 Exposure beam path 30-1~30-8 Mirror elements 32 Active optical surface 34 Support element 36 Actuators 38 Adaptive Optics Module 40 Control device 42 Control signals 42-1 Actuator deflection 42-1S Actuator target deflection 44 Wavefront measuring device 46 Wavefront deviation 48 hazard media 50 Working volume 52 Non-working volume 54 electrode 55 Electric field 56 Wiring 58 Voltage Generator 60 Operating voltage 62 Control Unit 64 control modes 65 Control Value 66 Calibration Mode 68 Reference characteristic curve 69 Conversion formula 70 Measuring device 72 AC voltage source 74 AC voltage 76 Frequencies 78 Impedance Measurement Module 80 Impedance 81 Capacitance C 82 Characteristic curve C U (f) 84 Evaluation device 84-1 Evaluation Unit 84-2 Evaluation Unit 84-3 Evaluation Unit 84-4 Evaluation Unit 84-5 Evaluation Unit 86 Gradient value p1 88 Sensitivity of an actuator in a static state χ f0 90-minute polarization 92 Electric field strength E 94 Dependency S f0 (U) 96 Comparison Module 98 Correction 100 Equivalent Circuit Diagram 102 Capacitors 104 ohm resistor 106 Evaluation intervals 108 Resonance

Claims

1. Adaptive optical module (38), An actuator (36-1) that changes the shape of the optical surface (32) of an optical module, comprising a dielectric medium (48) that can be deformed by an electric field (55), and an electrode (54) that generates the electric field in the dielectric medium by applying a working voltage (60), A measuring device (70) configured to measure the impedance (80) present at different values ​​of the operating voltage between the electrodes as a function of the frequency (76) of the AC voltage (74) applied to the electrodes for measurement, An evaluation device (84) is configured to derive from the measured impedance the approximate slope values ​​(86) of each characteristic curve (82) that represent the capacitance (81) of the actuator as a function of frequency for the different values ​​of the operating voltage, and from there determine the deflection (42-1) of the actuator at at least one operating point of the operating voltage. An adaptive optics module equipped with [specific features / features].

2. In the adaptive optical module according to claim 1, The evaluation device (84) is an adaptive optical module configured to determine the dependence (94) of the deflection (42-1) of the actuator on the operating voltage from the slope value (86) of the characteristic curve (82) derived for the different values ​​of the operating voltage (60).

3. In the adaptive optical module according to claim 2, The evaluation device (84-4, 84-5) is an adaptive optical module configured to determine the dependence (94) of the deflection of the actuator on the operating voltage by integrating a characteristic variable (88) derived from the gradient value of the characteristic curve over an electric field intensity (92) corresponding to the operating voltage.

4. In the adaptive optical module according to claim 3, The characteristic variable (88) derived from the gradient is an approximation of the susceptibility of the actuator in a static state, in an adaptive optical module.

5. In the adaptive optical module according to claim 3 or 4, The evaluation device (84-3) is an adaptive optical module configured to convert the gradient value (52) of the characteristic curve into the gradient value of the actuator's susceptibility with respect to the frequency in order to derive the characteristic variable (88).

6. In the adaptive optical module according to claim 5, The evaluation device (84-3) is an adaptive optical module configured to derive the characteristic curve (82) from the impedance based on the equivalent circuit diagram (100) of the actuator (36-1).

7. In the adaptive optical module according to any one of claims 1 to 6, The evaluation device (84-2) is an adaptive optical module configured to derive the gradient value (86) of each characteristic curve (82) by fitting the corresponding characteristic curve (82).

8. In the adaptive optical module according to any one of claims 1 to 7, The evaluation device is an adaptive optical module configured to derive the gradient values ​​of each characteristic curve (82) by modal analysis of the corresponding characteristic curve (82).

9. In the adaptive optical module according to any one of claims 1 to 8, An adaptive optical module configured for use in a microlithography projection exposure apparatus (10).

10. In the adaptive optical module according to any one of claims 1 to 9, The adaptive optical module is such that the frequency (76) at which the impedance (80) is measured is in the frequency range of 20 Hz to 200 kHz.

11. A microlithography projection exposure apparatus (10) comprising at least one adaptive optical module (38) according to any one of claims 1 to 10.

12. In the projection exposure apparatus according to claim 11, The projection exposure apparatus further comprises a control unit (62) configured to derive a control value (65) for the operating voltage (42-1) for controlling the actuator from a predetermined target deflection (42-1S) of the actuator, based on the dependency of the operating voltage (60), from a gradient value (86) derived for different values ​​of the operating voltage (60), and the projection exposure apparatus further comprises a control unit (62) configured to derive a control value (65) for the operating voltage to control the actuator from a predetermined target deflection (42-1S) of the actuator, based on the dependency.

13. A method for determining the deflection of an actuator (36-1) of an adaptive optical module (38), wherein the actuator is configured to change the shape of the optical surface (32) of the optical module and includes a dielectric medium (48) that is deformable by an electric field (55) and an electrode (54) that generates the electric field within the dielectric medium by applying a working voltage (60), The steps include applying different values ​​of the operating voltage and different frequencies (76) of the AC voltage to the electrodes, and measuring the impedance (80) present at each value of the operating voltage as a function of the frequency of the AC voltage, From the measured impedance, the approximate slope values ​​(86) of each characteristic curve (82) representing the capacitance (81) of the actuator as a function of frequency for the different values ​​of the operating voltage are derived, and the deflection (42-1) of the actuator at at least one operating point of the operating voltage is determined. Methods that include...

14. The method according to claim 13, wherein the impedance is measured for at least two different values ​​of the frequency (76) at each value of the operating voltage.

15. In the method according to claim 13 or 14, A method performed during exposure operation of a microlithography projection exposure apparatus (10) equipped with the adaptive optical module (38).

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