Method for operating a solid-state actuator in a microlithographic projection exposure system, adaptive optical element and projection exposure system

Abstract

The invention relates to a method for operating at least one solid-state actuator (100) of an optical element, said method comprising the following steps: - moving the solid-state actuator (100) to a working voltage (101), - requesting a target variable (102) for an expansion of the solid-state actuator (100), - moving the solid-state actuator (100) according to the target variable (102) within a control loop (103), - carrying out a charge measurement and a voltage measurement present at the electrodes of the solid-state actuator (100), by means of a measuring device (108), and - controlling the expansion s of the solid-state actuator (100) by determining a controlled variable Stot of the expansion based on the detected charge and the detected voltage, wherein the detected charge is included in the determination of the controlled variable Stot with a first weighting G1 and the detected voltage is included in same with a second weighting G2. The invention further relates to an adaptive optical element and to a projection exposure system.

Description

[0001] Method for operating a solid-state actuator in a microlithographic projection exposure system, adaptive optical element and projection exposure system

[0002] The invention relates to a method for operating at least one solid-state actuator of an optical element or an adaptive optical element, in particular for adjusting and / or deforming an optical element and / or its surface.The invention further relates to an adaptive optical element for a lithography system, in particular for a microlithographic projection exposure system, comprising at least one solid-state actuator for adjusting or changing an optical surface of the optical element, wherein the solid-state actuator has a dielectric medium which is deformable by means of an electric field, and electrodes for generating the electric field in the dielectric medium by applying an electrical operating voltage, comprising at least one measuring device configured to measure an electric charge and a voltage present on the electrodes when the operating voltage is applied, and a control unit. The invention further relates to a projection exposure system.

[0003] Projection exposure systems are used to create extremely fine structures, particularly on semiconductor devices or other microstructured components. The operating principle of these systems is based on the creation of ultra-fine structures down to the nanometer range by means of a generally reduced-size image of structures on a mask, a so-called reticle, onto a wafer, which is coated with photosensitive material. The minimum dimensions of the generated structures depend directly on the wavelength of the light used. This light is shaped in an illumination optic to optimally illuminate the reticle. Recently, light sources with emission wavelengths in the nanometer range, for example between 1 nm and 120 nm, particularly in the 13.5 nm range, have been increasingly used. This wavelength range is also known as the EUV range.

[0004] The microstructured components are manufactured not only using EUV systems but also with established DUV systems with wavelengths between 100 nm and 400 nm, particularly 193 nm. With the increasing demand for ever smaller structures, the requirements for optical correction in these systems have also risen. To reduce imaging errors, the optical elements of the microlithographic projection exposure system, such as lenses or mirrors, are adjusted, positioned, or their active surface is deformed by means of actuators. These actuators are preferably solid-state actuators, which, according to the present invention, are electrostrictive or piezoelectric actuators. The solid-state actuators are attached to the optical element, particularly to its back surface, and can actuate either perpendicular to or parallel to the surface.By controlling each individual actuator, the position or profile of the mirror can be specifically adjusted.

[0005] When controlling solid-state actuators, deviations between the specified or desired strain (setpoint) and the actual strain can occur, due to factors such as hysteresis, creep, and drift effects. Particularly when using feedforward control, high accuracy is required, making the control of at least one solid-state actuator using feedforward control a significant challenge.

[0006] Additionally, temporal changes in the actuation behavior, which can generally be categorized as aging effects, can lead to large and increasing actuation errors over the service life of the solid-state actuator. The actuation behavior of the solid-state actuator changes over time when it is operated at a setpoint voltage for an extended period (burn-in). The resulting change in the slope of the stress-strain curve is called the gain-dip effect. Since these changes can occur very locally, they can be particularly well identified in the first derivative of the strain of the solid-state actuator versus the stress.

[0007] In addition to feed-forward control, it is also possible to control the at least one solid-state actuator alternatively or additionally by measuring the charge present on the electrodes when the operating voltage is applied. This is described, for example, in DE 10 2023 202 040 A1.

[0008] It has been found that controlling the solid-state actuator solely via charge measurement as feedback control also leads to positioning errors or deviations between the desired strain and the actual strain with increasing operating time.

[0009] It is therefore the object of this invention to provide a method for operating at least one solid-state actuator, an adaptive optical element and a projection exposure system that overcomes or reduces the aforementioned disadvantages.

[0010] The problem relating to the method is solved by a method having the features of claim 1. The problem relating to the adaptive optical element is solved by an adaptive optical element having the features of claim 16, and the problem relating to the projection exposure system is solved by a projection exposure system having the features of claim 19. Advantageous embodiments with expedient further developments are specified in the dependent claims.

[0011] The inventive method for operating an adaptive optical element with at least one solid-state actuator comprises at least the following steps:

[0012] - Method of applying a solid-state actuator to a working voltage

[0013] - Requesting a target value for the strain of the solid actuator

[0014] - Method of the solid-state actuator according to the setpoint within a control loop - Performing a charge and a voltage measurement applied to the electrodes of the solid-state actuator using a measuring device and

[0015] - Control of the strain of the solid actuator by determining a controlled variable based on the detected charge and the detected voltage, whereby the detected charge is weighted first and the detected voltage is weighted second in the determination of the controlled variable.

[0016] Using the method according to the invention, the actual strain of the solid-state actuator can be detected and controlled by means of a feedback control system, whereby the control system, i.e., the determination of the controlled variable, takes into account both the detected charge and the detected voltage. Based on the detected voltage with a second weighting and the detected charge with a first weighting, the displacement, i.e., strain of the solid-state actuator, can be determined. For this purpose, a calibration curve exhibiting a charge-strain correlation can be generated, particularly before carrying out the method.

[0017] Similarly, a stress-strain correlation can be created as an additional correlation curve. Using this correlation(s), the strain of the solid-state actuator can be determined by measuring the stress and charge. Furthermore, a control unit can be configured to maintain the determined strain at the setpoint using the controlled variable and, if the measured strain deviates from the setpoint, to take appropriate measures to bring the actual strain into line with the setpoint. This can be done, for example, by adjusting the operating voltage of a voltage generator using a control signal based on the controlled variable. The measuring device includes at least one measuring capacitor and is configured to determine the electrical charge on the electrodes by measuring the voltage. For this purpose, the measuring device includes a voltage measuring unit configured to perform the voltage measurement across the measuring capacitor.The measuring device is specifically designed as a Sawyer tower circuit. The measuring device is configured to repeatedly, and in particular continuously, detect the charge and / or voltage. Furthermore, the method may include steps whereby an optical surface of the adaptive optical element is adjusted or locally deformed by means of the strain on the solid-state actuator.

[0018] Furthermore, it is advantageous if the weighting value is adjusted to the operating time of the solid-state actuator or the occurrence of an event. The two weightings can be temporarily equal. Preferably, the values ​​of the two weightings differ. In particular, the values ​​of the two weightings can change over the operating time of the solid-state actuator, or the weighting values ​​can change only intermittently, i.e., temporarily at a predetermined or predeterminable time and / or period. The weighting values ​​can behave periodically or repeatedly; that is, in a first period, the weighting values ​​are initial values, and in at least a second period, the weighting values ​​are second values ​​that differ from the initial values, with the first and second periods alternating.

[0019] Furthermore, it is advantageous if the value of one weighting is at least temporarily less than 10%, preferably less than 5%, and most preferably less than 2%. The weightings can also be temporarily 0%.

[0020] Furthermore, it is preferred that the value of the first weighting is greater than the value of the second weighting until a predetermined or predetermined time or the occurrence of an event, and that the value of the second weighting is at least temporarily greater than the value of the first weighting from the predetermined or predetermined time or the occurrence of the event. In particular, the value of one weighting is at least 60%, preferably at least 70%, and most preferably at least 80%.

[0021] The values ​​of the first and second weightings can exhibit a sudden increase, a step-like increase, or a continuous increase. Furthermore, the value of the first weighting can temporarily decrease, then increase at at least one predetermined or predeterminable time, or after the occurrence of an event, or increase abruptly to a value exceeding 50%, preferably exceeding 70%, and most preferably exceeding 80%. The value of the first weighting can subsequently decrease again—preferably continuously. It is particularly advantageous if the value of the first weighting decreases, at least temporarily, by the same amount as the value of the second weighting increases.This takes into account the surprising finding that control via charging has lower control errors than control via a detected voltage for short operating times, while control via charging can have a larger control error than control via the detected voltage for longer operating times.

[0022] Furthermore, it is advantageous to define a new reference point for the control system at a predetermined or predefinable time or upon the occurrence of an event. This new reference point is based predominantly or exclusively on the measured voltage, and the control system is then referenced to this new reference point using the measured charge. At a predetermined or predefinable time or upon the occurrence of an event, the system references the voltage measured at that time. This means that the measured voltage signal is considered error-free, and the determination of the controlled variable is temporarily or at a predetermined time based solely on the measured voltage. At this new reference point, the charge is measured again and defined as the new charge reference point. This means that the control error is set to zero at this charge level.

[0023] In this context, it is particularly preferred if, following the definition of the new reference point, the first weighting is greater than the second weighting when determining the controlled variable, or if the controlled variable is determined exclusively by means of the recorded charge.

[0024] In order to better take into account aging effects, hysteresis, creep, drift, gain-dip and / or temperature effects in the determination of the controlled variable, the procedure preferably includes the following steps:

[0025] - Determining a reference charge difference between a target position at a first operating point with a first charge-strain correlation and a reference operating point that differs from the first operating point using the measuring device

[0026] - Procedure of the solid-state actuator from the first operating point to the reference operating point, measuring the charge necessary for the procedure of the solid-state actuator,

[0027] - Retracting the solid actuator by the detected charge in the opposite direction to a new operating point that has the same charge-stretch correlation as the first operating point.

[0028] The reference operating point can be higher or lower than the operating point. These process steps shift the operating point such that hysteresis, gain dip, and creep effects are at least reduced. The solid-state actuator method ensures that the charge-strain correlation of the new operating point corresponds to that of the old operating point. Preferably, there is a voltage difference of at least 5 V, more preferably 10 V, and most preferably at least 20 V between the operating point and the reference operating point. It is particularly advantageous if the reference operating point is selected within a voltage range that is free of aging and / or drift effects. In this context, aging effects include effects such as hysteresis, creep, and gain dip.

[0029] Alternatively or additionally, the procedure includes the following steps:

[0030] - Method of the solid-state actuator at a predetermined or predeterminable event or time with a calibration signal and thereby detecting the charge and voltage using the measuring device and

[0031] - Considering the measured charge and voltage as an additional factor for determining the controlled variable.

[0032] At a predetermined or specifiable time or upon the occurrence of an event, a recalibration is performed by moving the solid-state actuator according to a predetermined or specifiable calibration signal, during which the charge and voltage are determined using the measuring device. These new calibration values ​​are taken into account when determining the controlled variable. The calibration signal is preferably an oscillating signal, in particular a trigonometric signal. Alternatively or additionally, it is preferred that at at least one predetermined or specifiable time or after the occurrence of an event, the charge and voltage are determined using the measuring device and compared with stored or storable setpoints as a disturbance variable observer. Preferably, the event is a wafer exchange or the end of an exposure time.

[0033] The method according to the invention can be used in particular for controlling a solid-state actuator configured to adjust a mirror.

[0034] The adaptive optical element is characterized in particular by the fact that the control unit is configured to control the at least one solid-state actuator by means of a control variable that takes into account the detected charge with at least a first weighting and the detected voltage with a second weighting. The adaptive optical element is specifically configured to carry out the method for operating a solid-state actuator. Alternatively, the adaptive optical element can also be designed as an optical element, the at least one of which has a solid-state actuator configured to adjust the optical element.

[0035] Based on the measured voltage and charge, the control unit is configured to determine the displacement (i.e., strain) of the solid-state actuator and compare it to the setpoint as the controlled variable, maintaining it at the setpoint. If necessary, if the measured strain deviates from the setpoint, a manipulated variable or correction variable based on the controlled variable can, for example, regulate a voltage generator that sets a working voltage. The measuring device includes at least one measuring capacitor and is configured to determine the electrical charge on the electrodes by measuring the voltage. For this purpose, the measuring device includes a voltage measuring unit configured to perform the voltage measurement across the measuring capacitor. The measuring device is specifically designed as a Sawyer tower circuit.A measuring device suitable for the method and the adaptive element is described in German patent application DE 10 2023 202 040.8, which is hereby fully incorporated into the present disclosure.

[0036] The advantages and embodiments mentioned for the method are also applicable to the adaptive optical element.

[0037] Furthermore, it is advantageous if the value of the weights is adjusted to the operating time of the solid-state actuator and / or the occurrence of an event, such as a wafer exchange or the end of an exposure time.

[0038] Furthermore, it is advantageous if the control unit includes a crossover network configured to reduce the value of the first weight by the increase in the value of the second weight. The crossover network can be configured as a high-pass and a low-pass filter. The low-pass filter is configured to reduce or suppress the weight value at times earlier than a predetermined or predefined time, while the high-pass filter is configured to reduce or suppress the weight value from the predetermined or predefined time onward, or upon the occurrence of an event.

[0039] The invention further relates to a projection exposure system with at least one adaptive element according to the invention.

[0040] The invention, that is, the method according to the invention and the adaptive optical element, can also be used in a lithography system, in a lighting system for a lithography system, in particular a microlithography system, or in a projection lens for a lithography system, in particular a microlithography system.

[0041] Further features, properties, and advantages of the present invention are described in more detail below with reference to embodiments and the accompanying figures. All features described so far and below are advantageous both individually and in any combination. The embodiments described below are merely examples and do not limit the scope of the invention. They show:

[0042] Figure 1a shows a schematic representation of a microlithographic projection exposure system designed for operation in the EUV,

[0043] Figure 1b shows a schematic representation of a microlithographic projection exposure system designed for operation in DUV,

[0044] Figure 2 shows a first schematic representation of the process,

[0045] Figure 3 shows a second schematic representation of the process,

[0046] Figure 4 shows a third schematic representation of the process.

[0047] Figure 5 shows a fourth schematic representation of the process, and

[0048] Figure 6 shows a fifth schematic representation of the process.

[0049] Figure 1a shows a schematic representation of an exemplary projection exposure system 600 designed for operation in the EUV, in which the present invention can be implemented.

[0050] According to Fig. 1a, a lighting device in a projection exposure system 600 designed for EUV has a field facet mirror 603 and a pupil facet mirror 604. The light from a light source unit, which comprises a plasma light source 601 and a collector mirror 602, is directed onto the field facet mirror 603. In the light path after the pupil facet mirror 604, a first telescope mirror 605 and a second telescope mirror 606 are arranged. Further down the light path is a deflecting mirror 607, which directs the incident radiation onto an object field in the object plane of a projection lens comprising six mirrors 651-656. At the location of the object field, a reflective structure-bearing mask 621 is arranged on a mask table 620, which is imaged into an image plane by means of the projection lens, in which a substrate 661 coated with a light-sensitive layer (photoresist) is located on a wafer table 660.One or more of the mirrors of the projection exposure system 600 designed for EUV can be formed as the (adaptive) optical element 100 according to the invention.

[0051] The invention can also be used in a DUV system, as shown in Figure 1b. A DUV system is fundamentally constructed like the EUV system described above in Figure 1a, except that mirrors and lenses can be used as optical elements in a DUV system, and the light source of a DUV system emits useful radiation in a wavelength range of 100 nm to 400 nm.

[0052] The DUV lithography system 700 shown in Figure 1b has a DUV light source 701. For example, an ArF excimer laser can be used as the DUV light source 701, which emits radiation 702 in the DUV range at, for example, 193 nm. A beam shaping and illumination system 703 directs the DUV radiation 702 onto a photomask 704. The photomask 704 is designed as a transmissive optical element and can be arranged outside the systems 703. The photomask 704 has a structure which is reduced in size and projected onto a wafer 706 or the like by means of the projection system 705. The projection system 705 has several lenses 707 and / or mirrors 708 for imaging the photomask 704 onto the wafer 706. Individual lenses 707 and / or mirrors 708 of the projection system 705 can be arranged symmetrically to the optical axis 709 of the projection system 705.It should be noted that the number of lenses 707 and mirrors 708 of the DUV lithography system 700 is not limited to the number shown. More or fewer lenses 707 and / or mirrors 708 may be used. In particular, the beam shaping and illumination system 703 of the DUV lithography system 700 has several lenses 707 and / or mirrors 708. Furthermore, the mirrors are typically curved on their front surface for beam shaping. An air gap 710 between the last lens 707 and the wafer 706 can be replaced by a liquid medium with a refractive index > 1. The liquid medium can be, for example, highly purified water. Such a setup is also called immersion lithography and offers increased photolithographic resolution.

[0053] Figure 2 shows a schematic representation of a control loop 103 for operating at least one solid-state actuator 100 of an (adaptive) optical element. First, the solid-state actuator 100 is moved to an operating voltage 101. A setpoint 102 for a strain of the solid-state actuator 100 is requested, and the solid-state actuator 100 is moved within the control loop 103 according to the setpoint 102. For feedback control of the at least one solid-state actuator, a charge and a voltage measurement applied to the electrodes of the solid-state actuator are performed using a measuring device 108. Preferably, the charge C and the voltage U are recorded repeatedly, and in particular continuously. The strain of the solid-state actuator 100 is controlled by a control unit 104, whereby a controlled variable Stot is determined, which in this case is a strain.The controlled variable Stot incorporates the measured charge with a first weight Gi and the measured voltage with a second weight G2. In other words, the measured voltage and charge are each converted into a charge-based polarization Pc and a voltage-based polarization Pu, respectively, which are then weighted G1 and G2 to form a total polarization Ptot. The resulting total polarization is proportional to the controlled variable Stot, i.e., the strain of the solid actuator 100.

[0054] Before carrying out the method for operating at least one (adaptive) optical element in a solid-state actuator 100, a calibration curve exhibiting a charge-strain correlation can preferably be generated. Likewise, a stress-strain correlation is generated as an additional correlation curve. Using these correlations, the strain of the solid-state actuator 100 can be determined by measuring the stress and charge. Furthermore, the control unit 104 is configured to maintain the determined strain at the setpoint using the control variable Stot. The control unit 104 is instructed to take action if the detected strain deviates from the setpoint 102 by a predetermined or predefinable value, in order to bring the setpoint strain into conformity with the actual strain. For example, a voltage generator 109 can be instructed to adjust an operating voltage Uo using a control signal based on the control variable Stot.The control unit 104 includes a conversion specification for determining a specification for the operating voltage Uo from the specified target strain 101.

[0055] The at least one solid-state actuator 100 has a dielectric medium which can be deformed by means of an electric field, as well as electrodes for generating the electric field in the dielectric medium by applying an electrical operating voltage.

[0056] Figure 2 also shows an embodiment of a measuring device 108 that may be used to carry out the method. The measuring device 108 is configured as a Sawyer tower circuit. The electrodes of the at least one solid-state actuator are connected to the voltage generator 109. The measuring device 108 is preferably connected between the solid-state actuator 100 and the voltage generator 109. The measuring device 108 includes at least one measuring capacitor CM and is configured to determine the electrical charge on the electrodes by measuring the voltage. For this purpose, the measuring device 108 includes a voltage measuring unit 110, which is configured to perform the voltage measurement at the measuring capacitor CM, i.e., to detect the voltage drop UM ZU across the measuring capacitor CM. An ohmic resistor RM can be connected in parallel with the measuring capacitor CM.Likewise, a further ohmic resistor RA, also known as a shunt resistor, can be connected in parallel to the electrode arrangement of the solid-state actuator 100. The measuring voltage UM corresponds to the difference between the operating voltage Uo and an actuator voltage UA. The measuring device is also configured to use the voltage drop UM across the measuring capacitor CM to determine the electric charge Q. This charge corresponds to the charge present on the electrodes of the solid-state actuator when the actuator voltage UA is applied. The charge QM is determined using the relationship Q. M = C M - U MThe measuring device 108 can also be connected downstream of the solid-state actuator 100, i.e., between the ground and one of the electrodes. The measuring device 108 is specifically designed to repeatedly, and in particular continuously, detect the charge and / or voltage. The charge QM determined by the measuring device 108 is converted into a strain S of the solid-state actuator. For this purpose, the charge QM is first converted into the polarization Pc on the electrodes. Pc is proportional to QM. The constant of proportionality can be determined by suitable calibration or by model-based calculation. The strain is then determined from the calculated polarization P, where the strain S is proportional to the square of the polarization (S ~ P). 2The determined voltage UM is also converted into a polarization Pu on the electrodes. The polarization Pc contributes to the total polarization Ptot with the first weighting Gi, and the polarization Pu contributes to the second weighting G2. The strain is then determined from the polarization Ptot thus calculated, where the strain S is proportional to the square of the polarization (S ~ P). 2 The proportionality constant can be determined through suitable calibration or model-based calculation.

[0057] The values ​​of the weights GI and G2 are preferably adapted to the operating time of the solid-state actuator 100 or to the occurrence of an event (for example, a wafer change). The two weights GI and G2 can be temporarily equal. Preferably, the values ​​of the two weights GI and G2 differ. In particular, the values ​​of the two weights GI and G2 can change over the operating time of the solid-state actuator 100, or the values ​​of the weights GI and G2 can change only intermittently, i.e., temporarily, especially at a predetermined or predeterminable time and / or period.The values ​​of the weights GI and G2 can behave periodically or repeatedly; that is, in a first period, the values ​​of the weights GI and G2 are the initial values, and in at least a second period, the values ​​of the weights GI and G2 are different from the initial values, with the first and second periods alternating. The value of one weight GI and G2 is at least temporarily less than 10%, preferably less than 5%, and most preferably less than 2%. The weights GI and G2 can also temporarily be 0%.

[0058] In one embodiment, the value of the first weighting G1 is greater than the value of the second weighting G2 until a predetermined or predeterminable time or the occurrence of an event. From the predetermined or predeterminable time or the occurrence of the event, the value of the second weighting G2 is at least temporarily greater than the value of the first weighting Gi. In particular, the value of one weighting GI,G2 is at least 60%, preferably at least 70%, and most preferably at least 80%.

[0059] The values ​​of the first and second weights GI,G2 can exhibit a discontinuous, step-like, or continuous profile. Furthermore, the value of the first weight GI can temporarily decrease, then increase at at least one predetermined or predeterminable time or after the occurrence of an event, or increase abruptly to a value exceeding 50%, preferably exceeding 70%, and most preferably exceeding 80%. The value of the first weight GI can subsequently decrease again—preferably continuously. In particular, the value of the first weight GI,G2 can decrease at least temporarily by the same amount by which the value of the second weight GI increases. In one embodiment, the controlled variable Stot is initially determined exclusively by charge measurement, i.e., by means of Pc, up to a predetermined or predeterminable time or the occurrence of an event.Once the time or event occurs, the controlled variable Stot is determined exclusively by means of voltage measurement, i.e., Pu.

[0060] This takes into account the surprising finding that control via charging has lower control errors than control via a detected voltage for short operating times, while control via charging can have a larger control error than control via the detected voltage for longer operating times.

[0061] In the embodiment shown in Figure 3, the control unit 104 can also include a crossover network configured to reduce the value of the first weighting Gi by the increase in the value of the second weighting G2ZU. The crossover network can be configured as a high-pass filter 111 and a low-pass filter 112. The low-pass filter is configured to filter frequency components of the measured charge and / or voltage such that Gi is greater than 50% for frequencies lower than a predetermined or predefinable frequency limit, i.e., for slow changes, where 100% = Gi + G2. The high-pass filter is configured to filter frequency components of the measured charge and / or voltage such that G2 is greater than 50% for frequencies greater than or equal to a predetermined or predefinable frequency limit, i.e., for fast changes, where 100% = Gi + G2.

[0062] The method according to Figure 4 differs in that, in addition to at least one predetermined or predefinable time or the occurrence of an event, a new reference point 105 is defined for the control, which is based predominantly or exclusively on the determined voltage, and that the control is referenced to the new reference point 105 using the detected charge. At a predetermined or predefinable time or the occurrence of an event (for example, a wafer exchange), the reference is therefore made to the voltage detected at that time; this means that the detected voltage signal is considered error-free and the determination of the controlled variable is temporarily or at a predetermined time based exclusively on the detected voltage.At this new reference point, the charge is again measured and defined as a new charge reference point. This means that the control error is set to zero at this charge. Following the definition of the new reference point 105, the first weighting G1 is greater than the second weighting G2 when determining the controlled variable. Alternatively, the controlled variable can be determined solely using the measured charge Pc. Preferably, a new voltage-based reference point 105 is referenced regularly over the operating lifetime of the solid-state actuator 100. This reduces the control error for charge-based control even over longer operating lifetimes.

[0063] The method according to Figure 5 differs by the following additional process steps: at at least one predetermined or predeterminable event or time, the solid-state actuator is moved by means of a calibration signal 106, preferably an oscillating, in particular trigonometric, calibration signal 106, and the charge and voltage are recorded by means of the measuring device 108. The charges and voltages thus recorded are taken into account as an additional quantity 107 when determining the controlled variable Stot. Consequently, at a predetermined or predeterminable time or upon the occurrence of an event, a recalibration is carried out by moving the solid-state actuator 100 according to a predetermined or predeterminable calibration signal, and the charge and voltage are determined by means of the measuring device. These new calibration values ​​are taken into account when determining the controlled variable.

[0064] Figure 6 shows a further embodiment of the method. To better account for aging effects, hysteresis, creep, drift, gain-dip and / or temperature effects of the solid-state actuator 100 when determining the controlled variable Stot, the method preferably comprises the following steps:

[0065] - Determining a reference charge difference between a target position at a first operating point 101a with a first charge-strain correlation and a reference operating point 101b that differs from the first operating point 101a by means of the measuring device 108,

[0066] - Procedure of the solid-state actuator 100 from the first operating point 101a to the reference operating point 101b and thereby measuring the charge Q necessary for the procedure (i.e. the adjustment) of the solid-state actuator 100,

[0067] - Retracting the solid actuator 100 by the detected charge -Q in the opposite direction to a new operating point 101c which has the same or approximately the same charge-strain correlation as the first operating point 101.

[0068] The reference operating point 101b can be larger or smaller than the operating point 101a. Using these process steps, the operating point 101 is shifted such that hysteresis, gain dip, and creep effects are at least reduced compared to the first operating point. The solid-state actuator 100 ensures that the charge-strain correlation of the new operating point 101c corresponds to that of the old operating point 101a, i.e., it is free of aging effects. Preferably, there is a voltage difference of at least 5V, preferably 10V, and particularly preferably at least 20V between the operating point 101a and the reference operating point 101b. The reference operating point 101b is selected within a voltage range that is free of aging and / or drift effects. In this context, aging effects include effects such as hysteresis, creep, and gain dip.

[0069] Alternatively or additionally, at least at a predetermined or predeterminable time or after the occurrence of an event, the charge and voltage can be determined using the measuring device and compared with stored or storeable target values ​​as a disturbance observer.

[0070] The method is preferably used to control a solid-state actuator 100 of an optical element in a lithography system, preferably an adaptive optical element. Preferably, the event is a wafer exchange or the end of the exposure time. The solid-state actuator 100 can adjust an optical element and / or deform its surface, at least locally.

[0071] REFERENCE MARK LIST

[0072] 100 solid-state actuators

[0073] 101 Operating voltage

[0074] 102 Target size

[0075] 103 Control loop

[0076] 104 Control unit

[0077] 105 Reference point

[0078] 106 Calibration signal

[0079] 107 additional size

[0080] 108 Measuring device

[0081] 109 Voltage generator

[0082] 110 voltage measuring unit

[0083] 111 High Pass

[0084] 112 Low-pass filter

[0085] 600 Projection exposure system

[0086] 601 Plasma light source

[0087] 602 Collector mirrors

[0088] 603 Field faceted mirror

[0089] 604 pupil facet mirrors

[0090] 605 first telescope mirror

[0091] 606 second telescope mirror

[0092] 607 Deflection mirror

[0093] 620 mask table

[0094] 621 Mask

[0095] 651 Mirror (projection lens)

[0096] 652 Mirror (projection lens)

[0097] 653 Mirror (projection lens)

[0098] 654 Mirror (projection lens)

[0099] 655 Mirror (projection lens)

[0100] 656 Mirror (projection lens)

[0101] 660 wafer table

[0102] 661 coated substrate

[0103] 700 DUV lithography system 701 DUV light source

[0104] 702 DUV radiation / beam path

[0105] 703 Beam shaping and illumination system (DUV)

[0106] 704 photomask 705 projection system

[0107] 706 wafers

[0108] 707 lens

[0109] 708 mirrors

[0110] 709 optical axis

Claims

REQUIREMENTS 1. Method for operating at least one solid-state actuator (100) of an optical element comprising the steps: - Method of applying the solid-state actuator (100) to a working voltage (101) - Requesting a setpoint (102) for an extension of the solid actuator (100), - Method of the solid-state actuator (100) according to the setpoint (102) within a control loop (103), - Performing a charge and a voltage measurement applied to the electrodes of the solid-state actuator (100) using a measuring device (108) and - Control of the strain s of the solid actuator (100) by determining a control variable Stot of the strain based on the detected charge and the detected stress, wherein the detected charge is included in the determination of the control variable Stot with a first weight Gi and the detected stress with a second weight G2.

2. Method according to claim 1, characterized in that the weights Gi, G2 differ from each other at least temporarily.

3. Method according to claim 1 or 2, characterized in that the value of the weighting Gi , G2 depends on an operating time of the solid-state actuator (100) or the occurrence of an event.

4. Method according to one of claims 1 to 3, characterized in that the value of one weighting Gi , G2 is at least temporarily less than 10%.

5. Method according to one of claims 1 to 4, characterized in that the value of the first weighting Gi is greater than the value of the second weighting G2 until a predetermined or predeterminable time or the occurrence of an event, and that the value of the second weighting G2 from at the given or foreseeable time or the occurrence of the event, the value of the first weight Gi is at least temporarily greater than the value of the first weighting.

6. Method according to claim 5, characterized in that the value of the first weighting Gi decreases at least temporarily by the amount by which the value of the second weighting G2 increases.

7. Method according to one of claims 1 to 6, characterized in that at a predetermined or predetermined time or upon the occurrence of an event a new reference point (105) for the control is defined, which is based predominantly or exclusively on the determined voltage, and that the control is referenced to the new reference point by means of the charge.

8. Method according to claim 7, characterized in that, following the definition of the new reference point (105), when determining the controlled variable Stot, the first weighting Gi is greater than the second weighting G2, or the controlled variable Stot is determined exclusively by means of the detected charge.

9. A method according to any one of claims 1 to 8, comprising the following steps: - Determining a reference charge difference between a target position at a first operating point (101 a) with a first charge-strain correlation and a reference operating point (101 b) that differs from the first operating point (101 a) using the measuring device (108), - Procedure of the solid-state actuator (100) from the first operating point (101 a) to the reference operating point (101 b) and measuring the charge necessary for the procedure of the solid-state actuator (100) and - Retracting the solid actuator (100) by the detected charge in the opposite direction to a new operating point (101 c) which has the same charge-strain correlation as the first operating point (101 a).

10. Method according to claim 9, characterized in that there is a voltage difference of at least 5V between the first operating point (101 a) and the reference operating point (101 b).

11. Method according to claim 9 or 10, characterized in that the reference operating point (101 b) is selected in a stress range that is free from aging and / or drift effects.

12. A method according to any one of claims 1 to 11 comprising the following steps - Method of the solid-state actuator (101) at a predetermined or predeterminable event or time with a calibration signal (106) and thereby detecting the charge and voltage by means of the measuring device (108) and - Considering the detected charge and voltage as an additional quantity (107) for determining the controlled variable Stot.

13. Method according to claim 12, characterized in that the calibration signal (106) is an oscillating signal.

14. Method according to claims 1 to 13, characterized in that at at least one predetermined or predetermined time or after the occurrence of an event, the charge and the voltage are determined by means of the measuring device (108) and compared with stored or storable target values ​​as a disturbance observer.

15. Method according to any one of claims 3 to 14, characterized in that the event is a wafer exchange or the end of an exposure time.

16. Adaptive optical element for a projection exposure system with at least one solid-state actuator (100) for changing an optical surface of the optical element, wherein the solid-state actuator has a dielectric medium which is deformed by means of an electric field. is mable, and has electrodes for generating the electric field in the dielectric medium by applying an electrical operating voltage, with at least one measuring device (108) which is configured to measure an electric charge and a voltage which is located on the electrodes when the operating voltage is applied, and with a control unit, characterized in that the control unit (104) is configured to control the at least one solid-state actuator (100) by means of a control variable Stot which takes into account at least the detected charge with a first weighting Gi and the detected voltage with a second weighting G2.

17. Adaptive optical element according to claim 16, characterized in that the value of the weights G1 , G2 depend on an operating time of the solid-state actuator (100) and / or the occurrence of an event.

18. Adaptive optical element according to claim 16 or 17, characterized in that the control unit (104) comprises a crossover network configured to reduce the value of the first weighting G1 by the increase in the value of the second weighting G2.

19. Projection exposure system with an adaptive optical element according to one of claims 16 to 18.

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