OPTICAL SYSTEM, LITHOGRAPHING PLANT AND METHOD FOR REDUCING VIBRATION-BASED DISTURBANCES

Abstract

An optical system (200) comprising: an optical element (N5); a sensor unit (202) configured to generate a position measurement signal (y) depending on the position of the optical element (N5). k ) to output; a controller unit configured to output a value depending on the position measurement signal (y) k ) to generate a controller control signal; a disturbance estimator unit configured to measure a periodic, externally excited disturbance (d k ) for a next time step, and based on this, a position of the optical element (N1 - N6) in the next time step as a function of the position measurement signal (y) k ) and a control signal (u k ) to estimate and, depending on the estimated position for the next time step, to output a pre-control position correction signal; an adding unit configured to combine the control signal (u k) by summing the controller control signal and the feedforward control correction signal; an actuator (208) configured to control the optical element (N5) depending on the control signal (u k ) to head towards.

Description

[0001] The present invention relates to an optical system, a lithography system having such an optical system, and a method for reducing vibration-based disturbances in an optical system and / or a lithography system.

[0002] Microlithography is used to manufacture microstructured components, such as integrated circuits. The microlithography process is carried out using a lithography system equipped with an illumination system and a projection system. The image of a mask (reticle) illuminated by the illumination system is projected by the projection system onto a substrate coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system, for example, a silicon wafer, in order to transfer the mask structure to the light-sensitive coating of the substrate.

[0003] Driven by the pursuit of ever smaller structures in the production of integrated circuits, EUV lithography systems are currently being developed that use light with a wavelength in the range of 0.1 nm to 30 nm, particularly 13.5 nm. Since most materials absorb light at this wavelength, such EUV lithography systems must use reflective optics, i.e., mirrors, instead of the refractive optics, i.e., lenses, as was previously the case.

[0004] So-called wafer stages are often used in the production of microstructured components. A wafer stage is a device in the semiconductor industry used to produce semiconductor discs, called wafers. The wafer stage is part of a wafer stepper and / or a lithography device, which is used to create microscopically small structures on the wafers. This wafer stage plays an important role in the production of semiconductor components, as it helps ensure that the structures on the wafer can be produced precisely and / or repeatably.

[0005] The wafer stage is a movable table on which the wafer is mounted. The table moves in the x, y, and z axes, allowing precise positioning of the wafer under the exposure system of the stepper and / or a lithography device. The wafer stage is controlled with high precision by a computer, which controls the precise positioning of the wafer according to the requirements of the exposure process.

[0006] During this movement of the wafer stage and the subsequent exposure process, vibration-related disturbances occur, which are among the largest contributors to the exposure errors observed on the microstructured component. Such disturbances are usually in the range below 100 Hz and result from the periodic movement of the wafer stage, often with high acceleration.

[0007] The vibrations and / or disturbances are transmitted through the air and / or the floor to components of the lithography system, particularly to the force frame of the optical elements, such as mirrors and / or lenses, and / or to sensors mounted on the sensor frame. Despite existing decoupling strategies, these components are excited to vibrate at the frequency of the wafer stage.

[0008] These excitations directly translate into a position error of the mirrors and / or lenses and thus into their respective line-of-sight (LoS) and / or into measurement errors of a sensor. The measured position error of the optical elements exhibits periodic characteristics whose frequencies coincide with the frequencies of the wafer stage movement / oscillation. Only the amplitudes and phase angles can differ. The control of the optical elements is usually limited to position feedback, which is designed to stabilize an operating point of the optical element and can thus react to absolute position errors through active control.

[0009] Another challenge is that the interference and / or frequency patterns caused by the wafer stage can vary depending on the microstructured component being manufactured. This inherently depends on which patterns are to be applied to the microstructured component. However, such patterns are often part of a manufacturer's trade secret and therefore not accessible for control engineering consideration before commissioning the lithography system. In addition, a wafer stage often runs several different patterns, which may change and / or vary after an exposure process. Therefore, it is not possible to precisely determine the interference frequencies that will occur in advance in order to counteract them through control engineering.

[0010] Against this background, it is an object of the present invention to provide an improved optical system and an improved method for reducing vibration-based disturbances.

[0011] Accordingly, an optical system is proposed. The optical system has an optical element. The optical system has a sensor unit configured to output a position measurement signal depending on a position of the optical element. The optical system has a controller unit configured to generate a controller actuating signal depending on the position measurement signal. The optical system has a disturbance estimator unit configured to estimate a periodic, externally excited disturbance for a next time step (preferably without actually measuring the disturbance), and based thereon, to estimate a position of the optical element in the next time step depending on the position measurement signal and an actuating signal, and to output a pre-control actuating correction signal depending on the position estimated for the next time step.The optical system comprises an adding unit configured to generate the control signal by summing the controller control signal and the pilot control correction signal. The optical system has an actuator configured to control the optical element as a function of the control signal, in particular to compensate for the position deviation caused by the periodic, externally excited disturbance. An advantage of the present optical system is that disturbance compensation is possible without the disturbance having to be detected by sensors or known. In this case, a time step can be determined, for example, by a cycle time of the disturbance estimation unit. Instead of the term "time step," the term "control time step" can also be used.

[0012] The "units" in this case can be implemented in hardware and / or software. A unit can thus be implemented, for example, as a control device with at least one processor and / or as a system-on-a-chip (SoC) on which at least one script and / or at least one algorithm and / or a database is stored and / or executable. Alternatively, a unit can also be implemented as a script and / or as a computer program and / or as a computer program product.

[0013] The sensor unit can preferably comprise a position measuring sensor. The position measuring sensor can be, for example, an encoder, in particular an optical encoder, and / or an interferometer and / or a potentiometer and / or a Hall sensor and / or a laser distance sensor. Depending on the type of sensor unit used, the position measuring signal generated by it can vary. The position measuring signal preferably indicates a position (actual position), in particular an absolute position, of the optical element per time step. Such a time step is preferably determined by a clock time of the sensor unit. The position measuring signal preferably indicates a relative position of the optical element to a target position over time. The position measuring signal can preferably be recorded interferometrically.

[0014] The controller unit is preferably a device or an algorithm that executes at least one control function to constantly change and / or adapt and / or maintain the respective actual position of the optical element, in particular per control time step, such that said position corresponds to a desired position of the optical element in the respective control time step. Particularly preferably, several degrees of freedom of movement (preferably all six degrees of freedom) of the optical element are controlled by the controller unit. The controller control signal generated by the controller unit preferably comprises at least one control instruction and / or control specification for at least one degree of freedom of movement of the optical element, depending on which the actuator adjusts a respective actual position of the optical element, in particular per control time step, to a respective desired position by initiating an adjusting movement of the optical element.The controller unit can be designed as a PID (amplifying, integrating, differentiating) controller.

[0015] The control signal is preferably formed in this case from a sum of control signals, namely from the controller control signal and the pilot control correction signal, if such a pilot control correction signal is present. In one embodiment, in an initial control time step, the control signal preferably corresponds to the controller control signal generated by the controller unit on the basis of the position measurement signal, since no pilot control correction signal is yet present in this initial step. In an alternative embodiment, the pilot control correction signal can be initialized so that the pilot control correction signal can already be used in the initial control time step. Only in the next control time step can a pilot control correction signal preferably be generated on the basis of the control signal from the previous control time step and summed to the controller control signal of this time step.Based on the control signal extended by the pilot control correction signal, the actuator preferably adjusts the position of the optical element to a respective target position for each control time step.

[0016] The periodic, externally excited disturbance comprises, for example, an oscillation in at least one frequency and / or frequency range, which is generated by an interference source and transmitted, for example, via the ground and / or the air, to components of the optical system. The disturbance excites the components, such as the optical element, to externally excited oscillation. This oscillation leads to a positional deviation of the optical element from a respective target position. This oscillation-induced positional deviation is at least partially compensated according to the invention.

[0017] The adding unit is preferably an electronic circuit configured to add two or more input signals to generate an output signal, in this case the control signal, which is the sum of the input signals.

[0018] The actuator can, for example, be an electrical and / or electromagnetic and / or mechanical actuator. For example, the actuator can comprise a servo motor or Lorenz actuator, by means of which the optical element can be adjusted in its position about at least one axis of movement and / or along at least one axis of movement. Particularly preferably, the optical system comprises at least one actuator for each degree of freedom of movement of the optical element, by means of which actuator the optical element can be moved in the respective degree of freedom of movement. The respective actuator is preferably controlled by the control signal in order to thereby bring about a change in the position of the optical element, preferably towards a desired position. The fact that the actuator controls the optical element means in particular that the actuator applies a force to the optical element.

[0019] Particularly preferably, the signal waveform of the pilot control correction signal corresponds essentially to a negative signal waveform of the periodic, externally excited disturbance. By superimposing the controller control signal with the pilot control correction signal, a control signal can be generated in which the periodic, externally excited disturbance is taken into account as a negative signal component. When the actuator is controlled as a function of the control signal, a position change of the optical element can be achieved in which the periodic, externally excited disturbance is compensated. If the pilot control correction signal is superimposed with the periodic, externally excited disturbance, these two signals preferably essentially cancel each other out, i.e., taking into account estimation-related tolerances.

[0020] In the present case, a disturbance estimator is preferably used to compensate for disturbances in an optical system and / or a projection exposure system, which can occur in particular as a result of or during a scanning process on an optical element. This improves the positional accuracy of the optical element in relation to its respective target position, since there are no or at least reduced positional deviations due to external disturbances. Instead, the disturbances can be filtered out and / or compensated for by corresponding counter-movement(s) of the optical element using the generated pilot control correction signal. This can improve the accuracy of the optical system. Furthermore, the disturbance estimator makes it unnecessary toto know the disturbance signal profile in advance, since the disturbance estimator can generate a feedforward correction signal, preferably in real time, which takes the respective disturbance signal profile into account in the respective time step. Thus, the present solution allows the utilization of the already existing position measurement signal of the optical element to improve controllability. This is achieved through a combination of feedback and feedforward control. Accordingly, disturbance-related position changes of the optical element, which lead to reduced accuracy of the optical system, can be compensated for in a simple and cost-effective manner.

[0021] According to one embodiment, the disturbance estimation unit comprises an estimation unit configured to execute a finite element model (FEM model) of the optical element and / or a model of the periodic, externally excited disturbance in order to estimate a respective position of the optical element as a function of the control signal for each state of the periodic, externally excited disturbance and / or per time step.

[0022] Particularly preferably, the model of the periodic, externally excited disturbance covers a frequency band that includes a frequency and / or a frequency range of the periodic, externally excited disturbance. For example, the model also includes disturbances that have a certain deviation in their frequency from a lower limit of the (known, for example, because empirically determined) frequency range of the periodic, externally excited disturbance and / or from an upper limit of the frequency range of the periodic, externally excited disturbance. The respective position change of the optical element preferably causes the respective position deviation. The disturbance variable estimator unit is preferably configured to generate the pre-control adjustment correction signal for each time step or control time step. This enables real-time control of the optical element to compensate for the disturbance.The disturbance estimation unit is preferably based on models by which a system dynamic, in particular one extended to include the periodic, externally excited disturbance, can be represented or simulated. In a prediction step carried out by the estimation unit, an actual position of the optical element reached by the control signal and a respective disturbance influence for a next time step or control time step are preferably predicted. The model of the periodic, externally excited disturbance preferably has a function superposition of several sine functions, each with different frequencies. The model of the periodic, externally excited disturbance is preferably based on the theory of Fourier transformation, which states that any periodic signal can be generated by a superposition of an infinite number of sine functions, each with different frequencies.The disturbance estimate from the disturbance estimator unit can preferably be used in the next control time step in the form of the pre-control correction signal to prevent and / or at least mitigate disturbance-related mispositioning of the optical element. Thus, the periodic, externally excited disturbance can preferably be compensated for by control technology at a particular moment or control time step in which it occurs, according to the invention.

[0023] According to one embodiment, the disturbance estimator unit comprises a correction unit configured to generate a correction signal for the respective estimated position for each "state" of the periodic, externally excited disturbance and / or per time step, depending on the position measurement signal; and to provide the correction signal to the estimator unit for estimating a respective position in a next state and / or in a next time step. The disturbance estimator unit is particularly preferably configured to generate the pre-control correction signal from the sum of the, in particular, state-by-state correction signals.

[0024] The correction signal preferably takes into account a deviation of the estimated position from an actual position, which is specified as a function of the position measurement signal. Because the correction signal is preferably determined per state and / or per control time step for at least two states, the pilot control correction signal is preferably generated based on these state-by-state determined correction signals per control time step. For this purpose, the correction unit can preferably have a further adding unit. It is understood that a periodic disturbance does not have states in the true sense. A sinusoidal signal, for example, has no "states", but is preferably a harmonic, periodic oscillation that is described by a sine function. A sinusoidal signal with a specific frequency ω can preferably be represented in a state space as x˙=[01−ω20]x.

[0025] Here, the state x is preferably two-dimensional, since the solution to the corresponding second-order differential equation is a sinusoidal signal. This signal is preferably defined by its amplitude and phase. While the frequency is assumed, the amplitude and phase are preferably determined via state estimation.

[0026] According to one embodiment, the disturbance estimation unit comprises a linear filter and / or a non-linear filter, in particular a Kalman filter.

[0027] A linear filter is preferably a signal processing unit that applies a linear transformation to an input signal to produce an output signal. A linear filter uses a mathematical operation to modify the input signal, with the output being proportional to the input. Linearity here preferably means that the filter's operation responds linearly to the input data, i.e., if the input signal is increased by a certain amount, the output signal is proportionally increased by the same amount. A linear filter can process various types of signals, including continuous-time or discrete-time, analog, or digital signals. There are different types of linear filters, including low-pass filters, high-pass filters, band-pass filters, band-rejection filters, and others.A nonlinear filter is a signal processing unit that preferably applies a nonlinear transformation to an input signal to produce an output signal. Unlike linear filters, a nonlinear filter preferably does not respond proportionally to changes in the input signal, but rather exhibits nonlinear distortion. Nonlinearity here means that the filter's output signal is preferably not proportional to the input variable. Instead, the output variable depends on the type of nonlinear transformation applied to the input signal. This results in more complex output signals compared to linear filters. There are different types of nonlinear filters, preferably including the median filter, the mean filter, the adaptive filter, the nonlinear low-pass filter, and the nonlinear high-pass filter.Each filter type preferably has a specific method for applying the nonlinear transformation to the input signal, such as the use of statistical methods, neural networks, or nonlinear functions. A Kalman filter preferably comprises at least two filtering steps. In the first filtering step, the prediction step, a temporally next state of an optical system or the optical element is preferably estimated and / or determined depending on the FEM model and / or another model of the optical system. In a second step, the correction step, this prediction is corrected depending on a (real) position measurement signal available from the optical element.

[0028] According to one embodiment, the optical system comprises an interference source configured to generate the periodic, externally excited interference. The interference source preferably comprises a wafer stage.

[0029] In principle, it can be a disturbance source that generates at least one periodic, externally excited disturbance due to its inherent dynamics and / or natural oscillation and / or natural movement. The disturbance can comprise various frequencies and / or amplitudes, which, for example, correspond to different natural frequencies of the disturbance source. The disturbance can preferably be represented on the signal side as an oscillation with various frequencies and / or amplitudes. The wafer table, also referred to as a wafer stage, is a movable table on which a wafer is arranged and / or fixed for processing. The table is movable in the x, y, and z directions and thus enables precise positioning of the wafer relative to an exposure system of a stepper and / or a lithography system. The wafer table is preferably controlled by a computer, which controls the precise positioning of the wafer according to the manufacturing requirements for wafer processing.

[0030] It is fundamentally conceivable that the periodic, externally excited disturbance can be detected at least partially and / or approximately and / or in sections in the form of a disturbance measurement signal by a disturbance sensor unit. The purely optional disturbance measurement signal can be provided to the disturbance estimator unit. This can be advantageous, for example, to enable verification of the estimate. The disturbance measurement signal can preferably be pre-filtered before it is made available to the disturbance estimator unit as an input signal. In this case, noise frequencies and / or other ambient frequencies can be filtered out, for example, so that the disturbance measurement signal describes the periodic, externally excited disturbance as accurately as possible. The disturbance sensor unit preferably comprises a vibration sensor. A vibration sensor is a sensor used to measure vibrations.Vibrations can be caused by mechanical, electrical, acoustic, or other types of energy transfer systems, and vibration sensors can be used to measure and analyze such vibrations. There are several types of vibration sensors, including piezoelectric sensors, capacitive sensors, magnetostrictive sensors, laser interferometry sensors, and acoustic sensors.

[0031] According to one embodiment, the optical element comprises a mirror and / or a lens.

[0032] The precise design and / or shape of such a lens and / or mirror is fundamentally arbitrary and depends in particular on the overall structure of the optical device. A "lens" is understood here to be a transparent, particularly disc-shaped element, of whose two surfaces at least one is curved. Passing light is deflected toward the center of the light beam (in the case of a converging lens) or scattered outward (in the case of a diverging lens). A "mirror" is understood to be an element with at least one reflective surface that has a predetermined roughness, so that reflected light retains its parallelism according to the law of reflection, thus allowing an image to be formed.

[0033] According to one embodiment, the periodic, externally excited disturbance has an oscillation frequency in a frequency range of 5 Hz to 150 Hz, preferably less than 100 Hz.

[0034] Particularly preferably, the periodic, externally excited disturbance is a low-frequency disturbance caused by the high mass inertia of the disturbance source. The disturbance can have multiple oscillation frequencies. Each of the oscillation frequencies, in turn, causes a disturbance in the position of the optical element, whereby an actual position deviation from the target position of the optical element is brought about by a superposition of the oscillation frequencies. This position deviation is compensated according to the invention by compensating for the disturbance with a corresponding pilot control correction signal. The pilot control correction signal preferably takes into account all, or at least several, oscillation frequencies of the disturbance that are significant in their respective amplitude. In this way, comprehensive compensation of the disturbance can be achieved.For example, the disturbance in the frequency range from 5 to 150 Hz can have several oscillation frequencies, each with a different intensity and / or amplitude.

[0035] According to one embodiment, the optical system comprises a support frame configured to hold the optical element and on which the actuator for controlling the optical element is preferably arranged. The support frame is preferably configured to absorb forces that occur during operation of the optical system, in particular due to the adjustment of the optical element relative to the support frame. Particularly preferably, the optical element is adjustable relative to the support frame by the actuator controlled according to the invention. By adjusting the positional deviation of the optical element from a desired position relative to the support frame can be adapted and / or corrected.

[0036] According to one embodiment, the optical system comprises a sensor frame configured to hold the sensor unit. The sensor frame is particularly preferably decoupled from the optional support frame by damping elements and, during operation of the optical system and / or a lithography system in which the optical system is used, absorbs only the forces resulting from holding the sensor unit—i.e., virtually no forces.

[0037] A lithography apparatus comprising an optical system according to any of the above embodiments is also proposed.

[0038] The optical system is preferably a projection optics system of the lithography system or a projection exposure system. However, the optical system can also be an illumination system. The projection exposure system can be an EUV lithography system. EUV stands for "Extreme Ultraviolet" and refers to a wavelength of the working light between 0.1 nm and 30 nm. The projection exposure system can also be a DUV lithography system. DUV stands for "Deep Ultraviolet" and refers to a wavelength of the working light between 30 nm and 250 nm.

[0039] Furthermore, a method for reducing vibration-based disturbances in an optical system and / or a lithography system is proposed. The method comprises the steps: a) outputting a position measurement signal as a function of a position of an optical element; b) generating a controller control signal as a function of the position measurement signal; c) estimating a periodic, externally excited disturbance (d k ) into a next time step and based thereon, estimating a position of the optical element in the next time step as a function of the position measurement signal and a control signal; d) outputting a pilot control correction signal as a function of the estimated position in the next time step; e) generating the control signal by summing the controller control signal and the pilot control correction signal; and f) controlling the optical element as a function of the control signal.

[0040] The structure in a), b), etc. does not exclude the possibility that the steps can be carried out in a different order.

[0041] The embodiments and features described for the optical system apply accordingly to the proposed method and vice versa.

[0042] "One" in this case is not necessarily limited to a single element. Rather, multiple elements, such as two, three, or more, may also be included. Any other counting term used here should not be understood as implying a limitation to the exact number of elements stated. Rather, numerical deviations upwards and downwards are possible, unless otherwise stated.

[0043] Further possible implementations of the invention also include combinations of features or embodiments described above or below with respect to the exemplary embodiments that are not explicitly mentioned. In this case, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

[0044] Further advantageous embodiments and aspects of the invention are the subject of the dependent claims and the exemplary embodiments of the invention described below. The invention will be explained in more detail below using preferred embodiments with reference to the accompanying figures. Fig. 1 shows a schematic meridional section of a projection exposure system for EUV projection lithography; Fig. 2 shows a schematic block diagram of an embodiment of an optical system according to the invention; Fig. 3 shows a detailed view of a section of the block diagram of the Fig. 2; Fig. 4 shows a detailed view of a section of the block diagram of the Fig. 3; Fig. 5(a) shows a displacement and / or offset in the x-direction and Fig. 5(b) a perturbation in the x-direction corresponding to this displacement; Fig. 5(c) shows a shift and / or offset in the y-direction and Fig. 5(d) a disturbance in the y-direction corresponding to this displacement; Fig. 5(e) shows a displacement and / or offset in the z-direction and Fig. (f) a perturbation in the z-direction corresponding to this displacement; Fig. 6(a) to 6(c) show Fourier transforms of position error signals in the x-direction ( Fig. 6(a)), the y-direction ( Fig. 6(b)) and the z-direction ( Fig. 6(c)); Fig. 7 a diagram of a disturbance spectrum of a periodic, externally excited disturbance; and Fig. 8 a flowchart of an embodiment of the method according to the invention.

[0045] In the figures, identical or functionally equivalent elements are provided with the same reference numerals unless otherwise indicated. Furthermore, it should be noted that the representations in the figures are not necessarily to scale.

[0046] Fig. 1 shows an embodiment of a projection exposure system 1 (lithography system), in particular an EUV lithography system. One embodiment of an illumination system 2 of the projection exposure system 1 has, in addition to a light or radiation source 3, an illumination optics 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a separate module from the rest of the illumination system 2. In this case, the illumination system 2 does not include the light source 3.

[0047] A reticle 7 arranged in the object field 5 is exposed. The reticle 7 is held by a reticle holder 8. The reticle holder 8 can be displaced via a reticle displacement drive 9, in particular in a scanning direction.

[0048] In the Fig. For illustrative purposes, Figure 1 shows a Cartesian coordinate system with an x-direction x, a y-direction y, and a z-direction z. The x-direction x runs perpendicular to the plane of the drawing. The y-direction y runs horizontally, and the z-direction z runs vertically. The scanning direction runs in the Fig. 1 along the y-direction y. The z-direction z runs perpendicular to the object plane 6.

[0049] The projection exposure system 1 comprises a projection optics 10. The projection optics 10 serves to image the object field 5 into an image field 11 in an image plane 12. The image plane 12 runs parallel to the object plane 6. Alternatively, an angle other than 0° between the object plane 6 and the image plane 12 is also possible.

[0050] A structure on the reticle 7 is imaged onto a light-sensitive layer of a wafer 13 arranged in the image plane 12 in the region of the image field 11. The wafer 13 is held by a wafer table 14. The wafer table 14 can be displaced, in particular along the y-direction y, via a wafer displacement drive 15. The displacement of the reticle 7, on the one hand, via the reticle displacement drive 9, and the displacement of the wafer 13, on the other hand, via the wafer displacement drive 15, can be synchronized with each other.

[0051] The light source 3 is an EUV radiation source. The light source 3 emits, in particular, EUV radiation 16, which is also referred to below as useful radiation, illumination radiation, or illumination light. The useful radiation 16 has, in particular, a wavelength in the range between 5 nm and 30 nm. The light source 3 can be a plasma source, for example, an LPP source (Laser Produced Plasma) or a DPP source (Gas Discharged Produced Plasma). It can also be a synchrotron-based radiation source. The light source 3 can be a free-electron laser (FEL).

[0052] The illumination radiation 16 emanating from the light source 3 is focused by a collector 17. The collector 17 can be a collector with one or more ellipsoidal and / or hyperboloidal reflection surfaces. The at least one reflection surface of the collector 17 can be exposed to the illumination radiation 16 at grazing incidence (GI), i.e., at angles of incidence greater than 45°, or at normal incidence (NI), i.e., at angles of incidence less than 45°. The collector 17 can be structured and / or coated, on the one hand, to optimize its reflectivity for the useful radiation and, on the other hand, to suppress stray light.

[0053] After the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 can represent a separation between a radiation source module, comprising the light source 3 and the collector 17, and the illumination optics 4.

[0054] The illumination optics 4 comprises a deflecting mirror 19 and, downstream of this in the beam path, a first facet mirror 20. The deflecting mirror 19 can be a flat deflecting mirror or, alternatively, a mirror with a beam-influencing effect beyond the pure deflection effect. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates a useful light wavelength of the illumination radiation 16 from stray light of a different wavelength. If the first facet mirror 20 is arranged in a plane of the illumination optics 4 that is optically conjugated to the object plane 6 as the field plane, it is also referred to as a field facet mirror. The first facet mirror 20 comprises a plurality of individual first facets 21, which can also be referred to as field facets. Of these first facets 21, Fig. 1 only some examples are shown.

[0055] The first facets 21 can be designed as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or partially circular edge contour. The first facets 21 can be designed as flat facets or, alternatively, as convexly or concavely curved facets.

[0056] As is known, for example, from DE 10 2008 009 600 A1, the first facets 21 themselves can also be composed of a plurality of individual mirrors, in particular a plurality of micromirrors. The first facet mirror 20 can, in particular, be designed as a microelectromechanical system (MEMS system). For details, reference is made to DE 10 2008 009 600 A1.

[0057] Between the collector 17 and the deflecting mirror 19, the illumination radiation 16 runs horizontally, i.e. along the y-direction y.

[0058] In the beam path of the illumination optics 4, a second facet mirror 22 is arranged downstream of the first facet mirror 20. If the second facet mirror 22 is arranged in a pupil plane of the illumination optics 4, it is also referred to as a pupil facet mirror. The second facet mirror 22 can also be arranged at a distance from a pupil plane of the illumination optics 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 is also referred to as a specular reflector. Specular reflectors are known from US 2006 / 0132747 A1, EP 1 614 008 B1, and US Pat. No. 6,573,978.

[0059] The second facet mirror 22 comprises a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets.

[0060] The second facets 23 can also be macroscopic facets, which can, for example, be round, rectangular, or hexagonal, or alternatively facets composed of micromirrors. Reference is also made to DE 10 2008 009 600 A1 in this regard.

[0061] The second facets 23 can have planar or alternatively convex or concave curved reflection surfaces.

[0062] The illumination optics 4 thus form a double-faceted system. This basic principle is also known as a fly's-eye integrator.

[0063] It may be advantageous to arrange the second facet mirror 22 not exactly in a plane that is optically conjugate to a pupil plane of the projection optics 10. In particular, the second facet mirror 22 can be arranged tilted relative to a pupil plane of the projection optics 10, as described, for example, in DE 10 2017 220 586 A1.

[0064] With the help of the second facet mirror 22, the individual first facets 21 are imaged into the object field 5. The second facet mirror 22 is the last beam-forming mirror or actually the last mirror for the illumination radiation 16 in the beam path before the object field 5.

[0065] In a further embodiment of the illumination optics 4 (not shown), a transmission optics can be arranged in the beam path between the second facet mirror 22 and the object field 5, which transmission optics contributes in particular to the imaging of the first facets 21 into the object field 5. The transmission optics can have exactly one mirror, but alternatively also two or more mirrors, which are arranged one behind the other in the beam path of the illumination optics 4. The transmission optics can in particular comprise one or two mirrors for normal incidence (NI mirrors, normal incidence mirrors) and / or one or two mirrors for grazing incidence (GI mirrors, grazing incidence mirrors).

[0066] The illumination optics 4 has in the version shown in the Fig. 1, after the collector 17 there are exactly three mirrors, namely the deflection mirror 19, the first facet mirror 20 and the second facet mirror 22.

[0067] In a further embodiment of the illumination optics 4, the deflection mirror 19 can also be omitted, so that the illumination optics 4 can then have exactly two mirrors after the collector 17, namely the first facet mirror 20 and the second facet mirror 22.

[0068] The imaging of the first facets 21 by means of the second facets 23 or with the second facets 23 and a transmission optics into the object plane 6 is usually only an approximate imaging.

[0069] The projection optics 10 comprises a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection exposure system 1.

[0070] In the Fig. In the example shown in Figure 1, the projection optics 10 comprises six mirrors M1 to M6. The mirrors M1 to M6 are each an optical element N1 to N6. Alternatives with four, eight, ten, twelve, or a different number of mirrors Mi are also possible. The projection optics 10 is a doubly obscured optic. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16. The projection optics 10 has an image-side numerical aperture that is greater than 0.5 and can also be greater than 0.6, for example, 0.7 or 0.75.

[0071] Reflection surfaces of the mirrors Mi can be designed as freeform surfaces without a rotational symmetry axis. Alternatively, the reflection surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one rotational symmetry axis of the reflection surface shape. The mirrors Mi, like the mirrors of the illumination optics 4, can have highly reflective coatings for the illumination radiation 16. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0072] The projection optics 10 has a large object-image offset in the y-direction y between a y-coordinate of a center of the object field 5 and a y-coordinate of the center of the image field 11. This object-image offset in the y-direction y can be approximately as large as a z-distance between the object plane 6 and the image plane 12.

[0073] The projection optics 10 can, in particular, be anamorphic. It has, in particular, different magnifications βx, βy in the x and y directions x, y. The two magnifications βx, βy of the projection optics 10 are preferably (βx, βy) = (+ / - 0.25, + / - 0.125). A positive magnification β means imaging without image inversion. A negative sign for the magnification β means imaging with image inversion.

[0074] The projection optics 10 thus leads to a reduction in the ratio 4:1 in the x-direction x, i.e. in the direction perpendicular to the scanning direction.

[0075] The projection optics 10 leads to a reduction of 8:1 in the y-direction y, i.e. in the scanning direction.

[0076] Other magnifications are also possible. Magnifications with the same sign and absolutely identical in the x and y directions (x, y), for example, with absolute values ​​of 0.125 or 0.25, are also possible.

[0077] The number of intermediate image planes in the x- and y-directions x, y in the beam path between the object field 5 and the image field 11 can be the same or can be different, depending on the design of the projection optics 10. Examples of projection optics with different numbers of such intermediate images in the x- and y-directions x, y are known from US 2018 / 0074303 A1.

[0078] Each of the second facets 23 is assigned to exactly one of the first facets 21 to form a respective illumination channel for illuminating the object field 5. This can, in particular, result in illumination according to the Köhler principle. The far field is divided into a plurality of object fields 5 using the first facets 21. The first facets 21 generate a plurality of images of the intermediate focus on the second facets 23 assigned to them.

[0079] The first facets 21 are each imaged onto the reticle 7 by an associated second facet 23, superimposed on one another, to illuminate the object field 5. The illumination of the object field 5 is, in particular, as homogeneous as possible. It preferably has a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

[0080] By arranging the second facets 23, the illumination of the entrance pupil of the projection optics 10 can be geometrically defined. By selecting the illumination channels, in particular the subset of the second facets 23 that guide light, the intensity distribution in the entrance pupil of the projection optics 10 can be adjusted. This intensity distribution is also referred to as the illumination setting or illumination pupil fill.

[0081] A likewise preferred pupil uniformity in the area of ​​defined illuminated sections of an illumination pupil of the illumination optics 4 can be achieved by redistributing the illumination channels.

[0082] Further aspects and details of the illumination of the object field 5 and in particular of the entrance pupil of the projection optics 10 are described below.

[0083] The projection optics 10 can, in particular, have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

[0084] The entrance pupil of the projection optics 10 cannot usually be precisely illuminated with the second facet mirror 22. When imaging the projection optics 10, which images the center of the second facet mirror 22 telecentrically onto the wafer 13, the aperture rays often do not intersect at a single point. However, a surface can be found in which the pairwise determined distance of the aperture rays is minimized. This surface represents the entrance pupil or a surface conjugate to it in spatial space. In particular, this surface exhibits a finite curvature.

[0085] It is possible that the projection optics 10 have different entrance pupil positions for the tangential and sagittal beam paths. In this case, an imaging element, in particular an optical component of the transmission optics, should be provided between the second facet mirror 22 and the reticle 7. With the help of this optical element, the different positions of the tangential entrance pupil and the sagittal entrance pupil can be taken into account.

[0086] In the Fig. In the arrangement of the components of the illumination optics 4 shown in Figure 1, the second facet mirror 22 is arranged in a surface conjugate to the entrance pupil of the projection optics 10. The first facet mirror 20 is arranged tilted relative to the object plane 6. The first facet mirror 20 is arranged tilted relative to an arrangement plane defined by the deflection mirror 19. The first facet mirror 20 is arranged tilted relative to an arrangement plane defined by the second facet mirror 22.

[0087] Fig. 2 shows an optical system 200 according to a first embodiment, which can be designed, for example, as the projection optics 10. With regard to Fig. 1 shows only a portion of the projection optics 10. More precisely, only the optical element N5 or the mirror M5 is shown. The following explanations also apply to the remaining optical elements Ni. The optical system 200 can also be used, for example, in a DUV lithography system.

[0088] The optical system 200 has a sensor unit 202. The sensor unit 202 is configured to generate a position measurement signal y depending on a position of the optical element N5. k(corresponding to the actual position of the optical element N5 in the respective current time step). The sensor unit 202 can preferably have a position measuring sensor 204. The position measuring sensor 204 can be an encoder, in particular an optical encoder, and / or an interferometer and / or a potentiometer and / or a Hall sensor and / or a laser distance sensor. The sensor unit 202 can be attached to a sensor frame 214 of the optical system 200 or the lithography system 1.

[0089] The optical system 200 comprises a controller 206 which is designed to operate in dependence on a control signal u k to control an actuator 208 which is designed to move the optical element N5 in dependence on the control signal u k to control its position relative to a target position P S to correct. The target position P Sof the optical element N5 is indicated by dashed lines. The actuator 208 can be designed, for example, as a Lorenz actuator. The actuator 208 is preferably supported on a support frame 216 of the optical system 200 or the lithography system 1. The support frame 216 and the sensor frame 214 are provided so as to be vibrationally decoupled from one another. The controller 206 can comprise at least one processor for executing program code and / or for executing at least one algorithm and / or a memory device for volatile and / or non-volatile (intermediate) storage of data and / or a working memory.

[0090] The position deviation of the optical element N5 from the target position P S can have different causes. One of these causes can be, for example, a periodic, externally induced disturbance of the kwhich is caused by the inertia of a moving disturbance source 210 of the optical system 200. The disturbance d generated by the disturbance source 210 k can be transmitted through the air and / or the ground to all components, such as the optical element N5, of the optical system 200 and, for example, excite them to oscillate at at least one oscillation frequency. The externally excited oscillation determines the positional deviation of the optical element N5 from the target position P S caused.

[0091] The disturbance source 210 can, for example, be the wafer table 14. The wafer table 14 can be provided in a vibrationally decoupled manner from the support frame 216 and / or the sensor frame 214, for example, by means of appropriate dampers. By displacing the wafer table along at least one movement axis by means of the wafer displacement drive 15, acceleration moments are generated that excite the wafer table 14 to oscillate at at least one oscillation frequency. As a result, the disturbance d k generated. Since the decoupling between the wafer table 14 and the support frame 216 or sensor frame 214 is imperfect, the disturbance d k partially passed through. The disruption of the k can exhibit vibration frequencies with directions of extension in multiple spatial directions. The vibration frequencies can exhibit longitudinal and / or transverse vibration patterns.

[0092] The periodic, externally excited disturbance of kcan optionally be at least partially detected by a disturbance sensor unit 212 of the optical system 200. The purely optional disturbance sensor unit 212 is configured to detect the periodic, externally excited disturbance d k in the form of a disturbance measurement signal and to provide the disturbance measurement signal to the controller 206.

[0093] Fig. 3 shows a detailed view of the block diagram of the Fig. 2, wherein the controller 206 is shown in more detail. The controller 206 comprises a controller unit 300 which is configured to, depending on the position measurement signal y k a controller control signal u c,k Furthermore, the controller 206 has a disturbance estimation unit 302, which is designed to estimate the periodic, externally excited disturbance d kfor a next time step (which follows the above-mentioned, current time step) and based on this, a position of the optical element N5 in the next time step as a function of the position measurement signal y k and the control signal u k and depending on the position estimated for the next time step, a feedforward control correction signal u d,k In addition, the controller 206 has an adding unit 304, which is designed to output the control signal u k by summing the controller control signal u c,k and the pilot control correction signal u d,k , to generate. The control signal u kis input as a feedforward signal to the disturbance estimator unit 302. The disturbance estimator unit 302 may comprise a linear filter and / or a non-linear filter. Particularly preferably, the disturbance estimator unit 302 comprises a Kalman filter, as described in detail in Fig. 4. A Kalman filter is preferably an estimator that observes non-measurable states of a system and reduces measurement noise for measurable states. For implementation, the system is temporally discretized with a sampling rate or time step rate of, for example, 2 kHz.

[0094] Fig. 4 shows a detailed view of the block diagram of the Fig. 3, wherein the disturbance estimation unit 302 is shown in more detail. The disturbance estimation unit 302 comprises an estimation unit 400 configured to generate a finite element model of the optical element N5 and / or a model of the periodic, externally excited disturbance d k to carry out for each state of the periodic, separately excited disturbance d k and / or per time step a respective position of the optical element N5 relative to the target position P S depending on the control signal u k The finite element model of the optical element N5 and / or the model of the periodic, externally excited disturbance d k is preferably implemented on the estimator unit 400 in the form of program code and / or in the form of an algorithm and is thereby executable.

[0095] The disturbance estimation unit 302 further comprises a correction unit 402 which is designed to, in particular, for each state of the periodic, externally excited disturbance d k and / or a state-dependent correction signal per time step x˜^k+1 to the respective estimated position depending on the position measurement signal y k to generate; and the correction signal x˜^k+1 the estimator unit 400 for estimating a respective position in a next state and / or in a next time step. For this purpose, the disturbance estimator unit 302 can have a time delay unit 404 or a delay unit. The disturbance estimator unit 302 is configured to provide the pre-control adjustment correction signal u d,k from the sum of the correction signals x˜^k+1 by generating the correction signals x˜^k+1 preferably summed per oscillation period.

[0096] The control signal u k = u c,k + u d,k preferably has two signals, namely the controller control signal and c,k , which is designed as a feedback signal, and the pilot control correction signal u d,k . In the feedback control by the controller control signal u c,k It is preferably assumed that a PID controller is used in combination with a decoupling matrix. However, the present methodology is fundamentally independent of the type of controller used. The decoupling is preferably based on a frequency approach and works particularly well for a specific frequency range in which the disturbance d k Outside this range, the system is not necessarily decoupled. The input tax regulation and d,kpreferably uses the results of the Kalman filter and includes the estimated states that correspond to the disturbance d k in the respective time step. The disturbance estimation unit 302 can be activated and deactivated to investigate the effects of using this control.

[0097] The functionality of the optical system 200 or the method can be verified, for example, by simulating a simplified oscillation system of the optical element N5. The results of such a verification are shown in the Fig. 5 and Fig. 6 shown.

[0098] For example, a single-mass oscillator whose oscillation is controlled by a PID controller can be used as a (FEM) model for the optical element N5. An additive, periodic input disturbance or the periodic, externally excited disturbance d kcan, for example, be applied to the single-mass oscillator to examine its vibration behavior with respect to the disturbance. Investigations have shown that the exact frequencies of the real disturbance d k must be included in the model of the disturbance estimation unit 302. Instead, it has been shown that it is sufficient to distribute frequencies evenly over a relevant frequency range. To arrive at this conclusion, a real disturbance spectrum of the disturbance d k This is then divided into individual subfrequencies using a Fourier transform. From this spectrum, for example, a predetermined number of the most dominant frequencies can be selected and used as interference with random amplitude and phase.

[0099] For example, in the disturbance estimation unit 302, a certain number of the most dominant frequencies is taken into account, which may be lower than the selected number. For example, only the three most dominant frequencies of the disturbance spectrum can be taken into account in the disturbance model in the disturbance estimation unit 302. For verification, for example, the frequencies 10, 50, and 100 Hz were chosen in order to cover the entire relevant disturbance spectrum. If one now compares the position error signals 500 of a feedforward control according to the invention by the disturbance estimation unit 302 with the position error signals 502 without such feedforward control, a significant improvement can be seen, as can be seen from Fig. 5. Examples are shown in the Fig. 5(a), Fig. 5(c), Fig. 5(e) shows the translational position error signals in the spatial directions x, z, y. In addition, the Fig. 5(b), Fig. 5 (d), Fig. 5(f) real interference signals 504 of the disturbance d k in the translational spatial directions x, y, z as well as their estimates 506 from the disturbance estimation unit 302. The disturbances are estimated very well and their use in a feedforward control leads to a drastic reduction of the position errors of the single-mass oscillator. The time t in seconds s is plotted on the respective ordinate. The respective position error for one spatial direction is plotted on the respective abscissa in Figs. (a), 5(c), 5(e). Fig. 5(b), Fig. 5 (d), Fig. 5(f) is the respective position deviation from the target position P S (here represented by the zero line) is plotted for one spatial direction each.

[0100] The reduction in the Fourier transform of the position error signals 600 without pre-control of the optical element 202 and in the Fourier transform of the position error signals 602 with pre-control is particularly clearly visible. This also shows that the exact frequencies of the real disturbance d k must be included in the disturbance estimation unit 302 to achieve good performance in compensating for the disturbance. At 10, 50, and 100 Hz, the disturbance is particularly well suppressed, but surrounding frequencies are also effectively filtered out. The respective position error signals 600, 602 are for the three spatial directions x, y, z in the Fig. 6(a) to 6(c). The frequency is plotted in Hz on the respective ordinate. The amplitude is plotted for a spatial direction, e.g., in %, on the respective abscissa.

[0101] In Fig. 7 is a real interference spectrum of the interference d kIt can be seen that the interference spectrum exhibits several significant interference frequencies that extend over a frequency range from 0 to 100 Hz. For example, the amplitudes at frequencies ~5 Hz, 20 Hz, ~24 Hz, 30 Hz, ~42 Hz, ~49 Hz, 60 Hz, ~73 Hz, 85 Hz, and ~94 Hz are significantly higher than the amplitudes at the remaining frequencies within the displayed frequency range. The frequency is plotted in Hz on the ordinate. The amplitude is plotted, for example, in % on the abscissa.

[0102] Fig. 8 shows a flowchart of an embodiment of the method according to the invention for reducing vibration-based disturbances in the optical system 200 and / or the lithography system 1. The method comprises the following steps: Outputting S1 of the position measurement signal y k depending on the position of an optical element N1 - N6; generating S2 of the controller control signal u c,kdepending on the position measurement signal y k ; Estimate S3 of a periodic, externally excited disturbance (d k ) in a next time step and based on this, estimating the position of the optical element N1 - N6 in the next time step depending on the position measurement signal y k and the control signal u k ; Output S4 of the pilot control correction signal u d,1 , depending on the estimated position in the next time step; generating S5 of the control signal u k by summing the controller control signal u c,k and the pilot control correction signal u d,k ; and controlling S6 of the optical element N1 - N6 depending on the control signal u k Preferably, the FEM model is generated in a step preceding step S1. For this purpose, measurements of disturbances in a known system and / or disturbance simulations are used, for example.

[0103] Although the present invention has been described using exemplary embodiments, it can be modified in many ways. LIST OF REFERENCE SYMBOLS 1 projection exposure system 2 Lighting system 3 Light source 4 Lighting optics 5 Object field 6 Object level 7 reticles 8 reticle holders 9 Reticle displacement drive 10 Projection optics 11 Image field 12 Image plane 13 wafers 14 wafer table 15 Wafer relocation drive 16 Illumination radiation 17 Collector 18 Intermediate focal plane 19 Deflecting mirrors 20 first facet mirror 21 first facet 22 second facet mirror 23 second facet 200 optical system 202 Sensor unit 204 Position measuring sensor 206 controllers 208 Actuator 210 Source of interference 212 Disturbance sensor unit 214 sensor frames 216 supporting frames 300 controller unit 302 Disturbance estimator unit 304 Adding unit 400 estimator unit 402 Correction Unit 404 Time Delay Unit 500 Position error signal with feedforward control 502 Position error signal without feedforward control 504 Interference signal 506 Estimation of the interference signal 600 Position error signal without feedforward control 602 Position error signal with feedforward control d k Disturbance M1 mirror M2 mirror M3 mirror M4 mirror M5 mirror M6 mirror N1 optical element N2 optical element N3 optical element N4 optical element N5 optical element N6 optical element P S Target position u k Control signal y k Position measurement signal QUOTES CONTAINED IN THE DESCRIPTION

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

[0000] DE 10 2008 009 600 A1 [0056, 0060] US 2006 / 0132747 A1

[0058] EP 1 614 008 B1

[0058] US 6,573,978

[0058] DE 10 2017 220 586 A1

[0063] US 2018 / 0074303 A1

[0077]

Claims

[1] Optical system (200), comprising: an optical element (N1 - N6); a sensor unit (202) which is designed to generate a position measurement signal (y k ) to be issued; a controller unit (300) which is designed to, depending on the position measurement signal (y k ) a controller control signal (u c,k ) to generate; a disturbance estimator unit (302) which is arranged to estimate a periodic, externally excited disturbance (d k ) for a next time step, and based thereon, a position of the optical element (N1 - N6) in the next time step as a function of the position measurement signal (y k ) and a control signal (u k ) and, depending on the position estimated for the next time step, a feedforward control correction signal (u d,k ) to be issued; an adding unit (304) which is arranged to add the control signal (u k ) by summing the controller control signal (u c,k ) and the pilot control correction signal (u d,k ) and an actuator (208) which is designed to move the optical element (N1 - N6) in dependence on the control signal (u k ) to control. [2] Optical system according to claim 1, wherein the disturbance estimation unit (302) comprises an estimation unit (400) which is configured to calculate a finite element model of the optical element (N1 - N6) and / or a model of the periodic, externally excited disturbance (d k ) to perform for each state of the periodic, externally excited disturbance (d k ) and / or per time step a respective position of the optical element (N1 - N6) depending on the control signal (u k ) to appreciate. [3] Optical system according to claim 2, wherein the disturbance estimation unit (302) comprises a correction unit (402) which is arranged to for each state of the periodic, externally excited disturbance (d k ) and / or a correction signal per time step (x˜^k+1) to the respective estimated position depending on the position measurement signal (y k ) and the correction signal (x˜^k+1) providing the estimator unit (400) for estimating a respective position in a next state and / or in a next time step; wherein the disturbance estimator unit (302) is preferably further configured to generate the pilot control correction signal (u d,k ) from the sum of the correction signals (x˜^k+1) to generate. [4] Optical system according to one of claims 1-3, wherein the disturbance estimation unit (302) comprises a linear filter and / or a non-linear filter, in particular a Kalman filter. [5] Optical system according to one of claims 1-4, wherein the optical system (200) comprises a disturbance source (210) which is arranged to generate the periodic, externally excited disturbance (d k ) to generate. [6] Optical system according to one of claims 5, wherein the interference source (210) comprises a wafer table (14). [7] Optical system according to one of claims 1-6, wherein the optical element (N1 - N6) comprises a mirror (M1 - M6) and / or a lens. [8] Optical system according to one of claims 1-7, wherein the periodic, externally excited disturbance (d k ) has an oscillation frequency in a frequency range of 5 Hz to 150 Hz, preferably less than 100 Hz. [9] Optical system according to one of claims 1-8, wherein the optical system (200) comprises a support frame (216) which is adapted to hold the optical element (N1 - N6) and on which the actuator (208) for controlling the optical element (N1 - N6) is arranged. [10] Optical system according to one of claims 1-9, wherein the optical system (200) comprises a sensor frame (214) adapted to hold the sensor unit (202). [11] Lithography system (1) with an optical system (200) according to one of claims 1 to 10. [12] Method for reducing vibration-based disturbances in an optical system (200) and / or a lithography system (1), comprising the steps: a) Output (S1) of a position measurement signal (y k ) depending on a position of an optical element (N1 - N6); b) Generating (S2) a controller control signal (u c,k ) depending on the position measurement signal (yk ) c) Estimation (S3) of a periodic, externally excited disturbance (d k ) in a next time step and based thereon, estimating a position of the optical element (N1 - N6) in the next time step as a function of the position measurement signal (y k ) and a control signal (u k ) d) Outputting (S4) a pilot control correction signal (u d,k ) depending on the estimated position in the next time step; e) Generating (S5) the control signal (u k ) by summing the controller control signal (u c,k ) and the pilot control correction signal (u d,k ); and f) Controlling (S6) the optical element (N1 - N6) depending on the control signal (u k ).

Images