WO2024256071A1 - Optical system, lithography system, and method for reducing oscillation-based interferences - Google Patents

Abstract

The invention relates to an optical system (200), comprising: an optical element (N5); a sensor unit (202) which is configured to output a position measurement signal (yk) depending on a position of the optical element (N5); a controller unit which is configured to generate a controller setting signal depending on the position measurement signal (yk); a interference value estimator unit which is configured to estimate a periodic, externally excited interference (dk) for a next time step, and based thereon to estimate a position of the optical element (N1 - N6) in the next time step depending on the position measurement signal (yk) and a setting signal (uk) and to output a precontrol setting correction signal depending on the position estimated for the next time step; an adding unit which is configured to generate the setting signal (uk) by summing the controller setting signal and the precontrol setting correction signal; an actuator (208) which is configured to actuate the optical element (N5) depending on the setting signal (uk).

Description

OPTICAL SYSTEM, LITHOGRAPHY DEVICE AND METHOD FOR REDUCING VIBRATION-BASED INTERFERENCE

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

The content of the priority application DE 10 2023 205 571.6 is incorporated in its entirety by reference.

Microlithography is used to produce microstructured components, such as integrated circuits. The microlithography process is carried out using a lithography system that has 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, such as a silicon wafer, that is coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system in order to transfer the mask structure onto the light-sensitive coating of the substrate.

Driven by the pursuit of ever smaller structures in the manufacture 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, in particular 13.5 nm. Since most materials absorb light of this wavelength, such EUV lithography systems must use reflective optics, i.e. mirrors, instead of - as previously - refractive optics, i.e. lenses. So-called wafer stages are often used in the manufacture of microstructured components. A wafer stage is a device in the semiconductor industry that is used to manufacture semiconductor discs, so-called wafers. The wafer stage is part of a so-called wafer stepper and/or a lithography device that is used to create microscopically small structures on the wafers. This wafer stage plays an important role in the manufacture of semiconductor components because it helps to ensure that the structures on the wafer can be manufactured precisely and/or repeatably.

The wafer stage is a movable table on which the wafer is mounted. The table moves in the x, y and z directions, allowing the 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 exact positioning of the wafer according to the requirements of the exposure process.

During this movement of the wafer stage and the subsequent exposure process, vibration-related disturbances occur, which make the largest contribution to the exposure errors recorded on the microstructured component. Such disturbances are usually in the range of less than 100 Hz and result from the periodic movement of the wafer stage with often high acceleration.

The vibrations and/or disturbances are transmitted via the air and/or the ground to components of the lithography system, in particular to the support frame (so-called 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, the above-mentioned components are excited to vibrate at the frequency of the wafer stage. These excitations are immediately converted 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 shows periodic characteristics whose frequencies match the frequencies of the wafer stage movement/oscillation. Only the amplitudes and the phase position can be different. 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.

Another challenge is that the interference and/or frequency patterns caused by the wafer stage can vary depending on the microstructured component to be manufactured. This inherently depends on which patterns are to be applied to the microstructured component. However, such patterns are often part of a trade secret of a respective manufacturer of microstructured components and are therefore not accessible for control-technical consideration before the lithography system is put into operation. In addition, a wafer stage is often used to run several different patterns, which may change and/or vary after an exposure process. It is therefore not possible to determine the interference frequencies that occur precisely in advance in order to counteract them with control technology.

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.

Accordingly, an optical system is proposed. The optical system has an optical element. The optical system has a sensor unit which is set up to output a position measurement signal depending on a position of the optical element. The optical system has a control unit which is set up to generate a controller actuating signal depending on the position measurement signal. The optical system has a disturbance estimator unit which is set up to estimate a periodic, externally excited disturbance for a next magazine (preferably without actually measuring the disturbance), and based thereon to estimate a position of the optical element in the next magazine depending on the position measurement signal and an actuating signal and to output a pilot control actuating correction signal depending on the position estimated for the next magazine. The optical system comprises an adding unit which is set up to generate the actuating signal by summing the controller actuating signal and the pilot control actuating correction signal. The optical system has an actuator that is designed to control the optical element depending on the control signal in order to compensate in particular for the position deviation caused by the periodic, externally excited disturbance. One 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 period can be determined, for example, by a cycle time of the disturbance estimator unit. Instead of the term “period”, the term “control time step” can also be used.

The "units" can be designed in terms of hardware and/or software. A unit can thus be designed, 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. A unit can alternatively also be designed as a script and/or as a computer program and/or as a computer program product. The sensor unit can preferably have 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 magazine. Such a magazine is preferably determined by a cycle 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.

The controller unit is preferably a device or an algorithm that carries out at least one control function in order to always change and/or adapt and/or keep the same a respective Isf position of the optical element, in particular per control time step, so that it corresponds to a target 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, in particular per control time step, of the optical element to a respective target position by initiating an adjustment movement of the optical element. The control unit can be designed as a PID (amplifying, integrating, differentiating) controller.

The control signal is preferably formed from a sum of control signals, namely the controller control signal and the pilot control correction signal formed when 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 in this initial step no pilot control correction signal is yet present. 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. On the basis of the control signal extended by the pilot control correction signal, a position adjustment of the optical element to a respective target position is preferably carried out by the actuator for each control time step.

The periodic, externally excited disturbance includes, 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 causes the components, such as the optical element, to oscillate externally. This oscillation leads to a position deviation of the optical element from a respective target position. This oscillation-related position deviation is at least partially compensated according to the invention.

The adding unit is preferably an electronic circuit which is designed 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.

The actuator can be, for example, 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 in its Position is adjustable about at least one movement axis and/or along at least one movement axis. 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 a movement of the optical element can take place 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 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.

Particularly preferably, the signal profile of the pilot control correction signal essentially corresponds to a negative signal profile of the periodic, externally excited disturbance. By superimposing the controller control signal with the pilot control correction signal, an actuating 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 depending on the actuating 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.

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 through or during a scanning process on an optical element. This improves the position accuracy of the optical element in relation to its respective target position, since there are no or at least reduced position deviations due to external disturbances. The disturbances can instead be filtered out and/or compensated for by corresponding countermovement(s) of the optical element can be compensated by the generated feedforward control correction signal. This can improve the accuracy of the optical system. The disturbance estimator also makes it unnecessary to know the disturbance or a signal curve of the disturbance in advance, since the disturbance estimator can generate a feedforward control correction signal, preferably in real time, which takes the respective signal curve of the disturbance into account in the respective period. The present solution thus allows the use of the already existing position measurement signal of the optical element to improve controllability. This is achieved by 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 in a simple and cost-effective manner.

According to one embodiment, the disturbance estimation unit has an estimation unit which is 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 actuating signal for each state of the periodic, externally excited disturbance and/or per magazine.

The model of the periodic, externally excited disturbance particularly preferably 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, because for example empirically recorded) 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 estimator unit is preferably designed to set up to generate the feedforward control 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 estimator unit is preferably based on models by means of which a system dynamic, in particular extended to include the periodic, externally excited disturbance, can be mapped or simulated. In a prediction step carried out by the estimator 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 each periodic signal can be generated by a superposition of an infinite number of sine functions, each with different frequencies. The estimate of the disturbance from the disturbance estimator unit can preferably be used in the next control time step in the form of the pre-control correction signal in order to avoid and/or at least reduce a disturbance-related incorrect positioning of the optical element. Thus, the periodic, externally excited disturbance can preferably be compensated for by control technology in accordance with the invention at a particular moment or control time step in which it occurs.

According to one embodiment, the disturbance estimator unit has a correction unit which is designed to generate a correction signal for each "state" of the periodic, externally excited disturbance and/or per magazine for the respective estimated position as a function of 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 magazine. The disturbance estimator unit is particularly preferably designed to to generate the pilot control correction signal from the sum of the particular state-wise correction signals.

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 in each case, the pilot control correction signal is preferably generated based on these correction signals determined per state per control time step. For this purpose, the correction unit can preferably have a further adding unit. It is understood that a periodic disturbance has no 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 sinusoidal function. A sinusoidal signal with a certain frequency a) can preferably be represented in a state space as

[ 0 11 = L-o 2 n 0J -

Here, the state x is preferably two-dimensional, since the solution of the associated 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 the state estimation.

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

A linear filter is preferably a signal processing unit that applies a linear transformation to an input signal to produce an output signal to produce. A linear filter uses a mathematical operation to modify the input signal, with the output magnitude being proportional to the input magnitude. Linearity here preferably means that the operation of the filter responds linearly to the input data, that is, if the input signal is increased by a certain amount, the output signal is increased proportionally 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 various types of linear filters, including the low-pass filter, high-pass filter, band-pass filter, band-stop filter, 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 output signal of the filter is preferably not proportional to the input magnitude. Instead, the output variable depends on the type of nonlinear transformation applied to the input signal. This leads to more complex output signals compared to linear filters. There are various types of nonlinear filters, including preferably 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 filter steps. In the first filter 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 made depending on a (real) position measurement signal available from the optical element.

According to one embodiment, the optical system has an interference source that is designed to generate the periodic, externally excited interference. The interference source preferably has a wafer table.

Basically, it can be a source of interference that generates at least one periodic, externally excited interference due to its own dynamics and/or natural oscillation and/or natural movement. The interference can comprise different frequencies and/or amplitudes, which correspond, for example, to different natural frequencies of the source of interference. The interference can preferably be represented on the signal side as an oscillation with different frequencies and/or amplitudes. The wafer table, which is also referred to as a wafer stage, is a movable table on which a wafer is arranged and/or fastened for processing. The table can be moved 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 in accordance with the production requirements for wafer processing.

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 a check 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. For example, noise frequencies and/or other ambient frequencies can be filtered out 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 various types of vibration sensors, including piezoelectric sensors, capacitive sensors, magnetostrictive sensors, laser interferometry sensors and acoustic sensors.

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

How exactly such a lens and/or such a mirror is designed and/or shaped is basically arbitrary and depends in particular on the overall structure of the optical device. In this case, a "lens" is understood to mean a transparent, in particular disk-shaped element, of whose two surfaces at least one is curved. Light passing through is deflected towards the center of the light beam (in the case of a converging lens) or scattered outwards (in the case of a diverging lens). A "mirror" is understood to mean 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 and thus an image can be created.

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. The periodic, externally excited disturbance is particularly preferably a low-frequency disturbance caused by the high mass inertia of the disturbance source. The disturbance can have several oscillation frequencies. Each of the oscillation frequencies in turn causes a disturbance in the position of the optical element, whereby a real 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 using 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. This makes it possible to achieve comprehensive compensation of the disturbance. For example, the disturbance can have several oscillation frequencies in the frequency range from 5 to 150 Hz, each with a different severity and/or amplitude.

According to one embodiment, the optical system has a support frame which is designed to hold the optical element and on which the actuator for controlling the optical element is preferably arranged. The support frame is preferably designed to absorb forces which occur during operation of the optical system, in particular due to the adjustment of the optical element relative to the support frame. The optical element is particularly preferably adjustable relative to the support frame by the actuator controlled according to the invention. By adjusting, the position deviation of the optical element from a target position to the support frame can be adjusted and/or corrected.

According to one embodiment, the optical system has a sensor frame which is designed to hold the sensor unit. The sensor frame is particularly preferably decoupled from the optional support frame by damping elements and takes up and/or a lithography system in which the optical system is used, only the forces resulting from holding the sensor unit, i.e. practically no forces.

A lithography apparatus with an optical system according to any of the above embodiments is also proposed.

The optical system is preferably a projection optics 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.

Furthermore, a method for reducing vibration-based disturbances in an optical system and/or a lithography system is proposed. The method comprises the steps of: 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 (dk) in 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. The structure in a), b), etc. does not exclude the possibility that the steps can be carried out in a different order.

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

In this case, "one" is not necessarily to be understood as being limited to just one element. Rather, several elements, such as two, three or more, can also be provided. Any other counting word used here is also not to be understood as meaning that there is a limitation to the exact number of elements mentioned. Rather, numerical deviations upwards and downwards are possible, unless otherwise stated.

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. The person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

Further advantageous embodiments and aspects of the invention are the subject of the subclaims and the embodiments of the invention described below. The invention is explained in more detail below using preferred embodiments with reference to the attached 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 Fig. 3;

Fig. 5(a) shows a displacement and/or offset in the x-direction and Fig. 5(b) shows a disturbance in the x-direction corresponding to this displacement!

Fig. 5(c) shows a displacement 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 an offset in the z-direction and Fig. (£) a disturbance 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 is a flow chart of an embodiment of the method according to the invention.

In the figures, identical or functionally identical elements have been given the same reference symbols, unless otherwise stated. It should also be noted that the representations in the figures are not necessarily to scale. Fig. 1 shows an embodiment of a projection exposure system 1 (lithography system), in particular an EUV lithography system. An 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 comprise the light source 3.

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.

For the purpose of explanation, a Cartesian coordinate system with an x-direction x, a y-direction y and a z-direction z is shown in Fig. 1. The x-direction x runs perpendicularly into the drawing plane. The y-direction y runs horizontally and the z-direction z runs vertically. The scanning direction in Fig. 1 runs along the y-direction y. The z-direction z runs perpendicular to the object plane 6.

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.

A structure on the reticle 7 is imaged onto a light-sensitive

Layer of a arranged in the area of the image field 11 in the image plane 12

wafer 13. The wafer 13 is held by a wafer table 14. The wafer table 14 can be displaced via a wafer displacement drive 15, in particular along the y-direction y. The displacement of the reticle 7 on the one hand via the reticle displacement drive 9 and the wafer 13 on the other hand via the wafer displacement drive 15 can be synchronized with one another.

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 (EnglJ Laser Produced Plasma, plasma generated with the aid of a laser) or a DPP source (EnglJ Gas Discharged Produced Plasma, plasma generated by means of gas discharge). It can also be a synchrotron-based radiation source. The light source 3 can be a free-electron laser (EnglJ Free-Electron-Laser, FEL).

The illumination radiation 16 that emanates from the light source 3 is bundled 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 in grazing incidence (Gl), i.e. with angles of incidence greater than 45°, or in normal incidence (NI), i.e. with 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.

After the collector 17, the illumination radiation 16 propagates through a

Intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 A separation between a radiation source module comprising the

light source 3 and the collector 17, and the illumination optics 4.

The illumination optics 4 comprise a deflection mirror 19 and a first facet mirror 20 arranged downstream of this in the beam path. The deflection mirror 19 can be a flat deflection mirror or alternatively a mirror with an effect that influences the bundle beyond the pure deflection effect. Alternatively or additionally, the deflection mirror 19 can be designed as a spectral filter that separates a useful wavelength of the illumination radiation 16 from false 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 a 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. Only a few of these first facets 21 are shown in Fig. 1 as examples.

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 convex or concave curved facets.

As is known, for example, from DE 10 2008 009 600 Al, 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 Al. Between the collector 17 and the deflection mirror 19, the illumination radiation 16 runs horizontally, i.e. along the y-direction y.

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 6,573,978.

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.

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

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

The illumination optics 4 thus form a double faceted system. This basic principle is also known as a honeycomb condenser (EnglJ Fly's Eye Integrator). It may be advantageous not to arrange the second facet mirror 22 exactly in a plane that is optically conjugated 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.

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

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 contributes in particular to the imaging of the first facets 21 in 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 vertical incidence (Ni mirrors, normal incidence mirrors) and/or one or two mirrors for grazing incidence (GF mirrors, grazing incidence mirrors).

In the embodiment shown in Fig. 1, the illumination optics 4 has exactly three mirrors after the collector 17, namely the deflection mirror 19, the first facet mirror 20 and the second facet mirror 22.

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. 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.

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.

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

Reflection surfaces of the mirrors Mi can be designed as free-form 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, just 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.

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 The y direction can be approximately as large as the z distance between the object plane 6 and the image plane 12.

The projection optics 10 can in particular be anamorphic. In particular, it has different image scales ßx, ßy in the x and y directions x, y. The two image scales ßx, ßy of the projection optics 10 are preferably (ßx, ßy) = (+/- 0.25, +/- 0.125). A positive image scale ß means an image without image inversion. A negative sign for the image scale ß means an image with image inversion.

The projection optics 10 thus leads to a reduction in the ratio 44 in the x-direction x, i.e. in the direction perpendicular to the scanning direction.

The projection optics 10 leads to a reduction of 84 in the y-direction y, i.e. in the scanning direction.

Other image scales are also possible. Image scales with the same sign and absolutely the same in the x and y directions x, y, for example with absolute values of 0.125 or 0.25, are also possible.

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 Al.

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

The first facets 21 are each imaged onto the reticle 7 by an associated second facet 23, superimposing 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%. The field uniformity can be achieved by superimposing different illumination channels.

By arranging the second facets 23, the illumination of the entrance pupil of the projection optics 10 can be defined geometrically. 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 set. This intensity distribution is also referred to as the illumination setting or illumination pupil filling.

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 a redistribution of the illumination channels.

In the following, 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.

The projection optics 10 can in particular have a homocentric entrance pupil. This can be accessible. It can also be inaccessible. The entrance pupil of the projection optics 10 cannot usually be illuminated precisely with the second facet mirror 22. When the projection optics 10 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 minimal. This surface represents the entrance pupil or a surface conjugated to it in spatial space. In particular, this surface shows a finite curvature.

It is possible that the projection optics 10 have different positions of the entrance pupil for the tangential and the sagittal beam path. 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.

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

Fig. 2 shows an optical system 200 according to a first embodiment, which can be designed, for example, as the projection optics 10. With respect to Fig. 1, only a part of the projection optics 10 is shown. More precisely, only the optical element N5 or the mirror M5 is shown. The statements made below naturally also apply to the remaining optical elements Ni. The optical system 200 can also be used, for example, in a DUV lithography system.

The optical system 200 has a sensor unit 202. The sensor unit 202 is designed to output a position measurement signal yk (corresponding to the actual position of the optical element N5 in the current magazine) depending on a position of the optical element N5. The sensor unit 202 can preferably have a position measurement sensor 204. The position measurement 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.

The optical system 200 comprises a controller 206, which is designed to control an actuator 208 as a function of a control signal U, which actuator is set up to control the optical element N5 as a function of the control signal uk in order to correct its position with respect to a target position Ps. The target position Ps of the optical element N5 is shown in dashed lines. The actuator 208 can be designed as a Lorenz actuator, for example. 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 decoupled from one another in terms of vibration technology. The controller 206 can comprise at least one processor for executing program code and/or for executing at least one algorithm and/or a storage device for volatile and/or non-volatile (intermediate) storage of data and/or a working memory.

The position deviation of the optical element N5 from the target position Ps can have different causes. One of these causes can be for example, a periodic, externally excited disturbance dk, which is caused by a mass inertia of a moving disturbance source 210 of the optical system 200. The disturbance dk generated by the disturbance source 210 can be transmitted via the air and/or the ground to all components, such as the optical element N5, of the optical system 200 and can, for example, excite them to oscillate at at least one oscillation frequency. The externally excited oscillation causes the position deviation of the optical element N5 from the target position Ps.

The source of interference 210 can be, for example, 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 axis of movement by means of the wafer displacement drive 15, acceleration moments are generated that excite the wafer table 14 to vibrate at at least one vibration frequency. This generates the interference dk. Since the decoupling between the wafer table 14 and the support frame 216 or sensor frame 214 is incomplete, the interference dk is partially passed through. The interference dk can have vibration frequencies with directions of extension in several spatial directions. The vibration frequencies can have longitudinal and/or transverse vibration patterns.

The periodic, externally excited disturbance dk can 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 designed to detect the periodic, externally excited disturbance dk in the form of a disturbance measurement signal and to provide the disturbance measurement signal to the controller 206.

Fig. 3 shows a detailed view of the block diagram of Fig. 2, where the controller

206 is shown in more detail. The controller 206 comprises a controller unit 300 which is designed to generate a controller actuating signal u _c ,k as a function of the position measurement signal yk. The controller 206 also has a disturbance estimator unit 302 which is designed to estimate the periodic, externally excited disturbance dk for a next period (which follows the above-mentioned, current period) and, based thereon, to estimate a position of the optical element N5 in the next period as a function of the position measurement signal yk and the actuating signal uk and to output a pilot control actuating correction signal ud,k as a function of the position estimated for the next period. The controller 206 also has an adding unit 304 which is designed to generate the actuating signal uk by summing the controller actuating signal u _c ,k and the pilot control actuating correction signal u .k. The actuating signal uk is input to the disturbance estimator unit 302 as a pilot control signal. The disturbance estimator unit 302 can have a linear filter and/or a non-linear filter. Particularly preferably, the disturbance estimator unit 302 has a Kalman filter, as shown in detail in Fig. 4. A Kalman filter is preferably an estimator that observes non-measurable states of a system and reduces the 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.

Fig. 4 shows a detailed view of the block diagram of Fig. 3, wherein the disturbance estimation unit 302 is shown in more detail. The disturbance estimation unit 302 has an estimation unit 400 which is designed to execute a finite element model of the optical element N5 and/or a model of the periodic, externally excited disturbance dk in order to estimate a respective position of the optical element N5 relative to the target position Ps for each state of the periodic, externally excited disturbance dk and/or per period as a function of the control signal uk. The finite element model of the optical element N5 and/or the model of the periodic, externally excited disturbance dk is preferably implemented on the estimation unit 400 in the form of program code and/or in the form of an algorithm and thus executable.

The disturbance estimator unit 302 further comprises a correction unit 402 which is designed to generate a state-dependent correction signal %k+i for the respective estimated position as a function of the position measurement signal yk, in particular for each state of the periodic, externally excited disturbance dk and/or per period, and to provide the correction signal %k+i to the estimator unit 400 for estimating a respective position in a next state and/or in a next period. For this purpose, the disturbance estimator unit 302 can comprise a time delay unit 404 or a delay unit. The disturbance estimator unit 302 is designed to generate the pre-control correction signal ud,k from the sum of the correction signals %k+i by summing the correction signals %k+i, preferably per oscillation period.

The control signal uk = u _c ,k + u .k preferably has two signals, namely the controller control signal u _c ,k, which is designed as a feedback signal, and the feedforward control correction signal Ud,k. The feedback control by the controller control signal u _c ,k is preferably assumed to be a PID controller 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 certain frequency range in which the disturbance dk is located. Outside this range, the system is not necessarily decoupled. The feedforward control u .k preferably uses the results of the Kalman filter and includes the estimated states that correspond to the disturbance dk in the respective period. The disturbance estimator unit 302 can be activated and deactivated to examine the effects of using this control. 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 Figs. 5 and 6.

For example, a single-mass oscillator can be used as a (FEM) model for the optical element N5, the oscillation of which is controlled by a PID controller. An additive, periodic input disturbance or the periodic, externally excited disturbance dk can, for example, be applied to the single-mass oscillator in order to examine its oscillation behavior with respect to the disturbance. Investigations have shown that the exact frequencies of the real disturbance dk do not necessarily have to be included in the model of the disturbance estimator unit 302. Instead, it has been shown that it is sufficient to distribute frequencies evenly over a relevant frequency range. In order to arrive at this conclusion, a real disturbance spectrum of the disturbance dk is preferably used, and this is divided into individual subfrequencies by a Fourier transformation. From this spectrum, for example, a predetermined number of the most dominant frequencies can be selected and used as a disturbance with a random amplitude and phase position.

For example, a certain number of the most dominant frequencies is taken into account in the disturbance estimator unit 302, which can be less than the selected number. For example, only the three most dominant frequencies of the disturbance spectrum can be taken into account in the model of the disturbance in the disturbance estimator 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 estimator unit 302 with the position error signals 502 without such a Feedforward control, a clear improvement can be seen, as is clear from Fig. 5. The translational position error signals in the spatial directions x, z, y are shown as examples in Figs. 5(a), 5(c), 5(e). In addition, real disturbance signals 504 of the disturbance dk in the translational spatial directions x, y, z and their estimates 506 from the disturbance estimation unit 302 are shown in Figs. 5(b), 5(d), 5(f). The disturbances are estimated very well and their use in feedforward control leads to a drastic reduction in 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). On the respective abscissa in Fig. 5(b), 5(d), 5(f), the respective position deviation from the target position Ps (here represented by the zero line) is plotted for one spatial direction.

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 can be seen particularly well. This also shows that the exact frequencies of the real disturbance dk do not have to be included in the disturbance estimator unit 302 in order to achieve good performance in compensating for the disturbance. At 10, 50 and 100 Hz, the disturbance is suppressed particularly well, but surrounding frequencies are also effectively filtered out. The respective position error signals 600, 602 are shown for the three spatial directions x, y, z in Figures 6(a) to 6(c). The frequency in Hz is plotted on the respective ordinate. The amplitude for each spatial direction, e.g. in %, is plotted on the respective abscissa.

Fig. 7 shows a real interference spectrum of the interference dk. It can be seen that the interference spectrum shows several significant interference frequencies that extend over a frequency range from 0 to 100 Hz. For example, the amplitudes at the frequencies ~5 Hz, 20 Hz, ~24 Hz, 30 Hz, ~42 Hz, ~49 Hz, 60 Hz, ~73 Hz, 85 Hz and ~94 Hz are pronounced compared to the amplitudes at the remaining frequencies within the frequency range shown. The ordinate shows the frequency in Hz. The abscissa shows the amplitude in %, for example.

Fig. 8 shows a flow chart 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 has the following steps: outputting S1 of the position measurement signal yk as a function of a position of an optical element NI - N6; generating S2 of the controller actuating signal u _c ,k as a function of the position measurement signal yk! estimating S3 a periodic, externally excited disturbance (dk) in a next magazine and based thereon, estimating the position of the optical element NI - N6 in the next magazine as a function of the position measurement signal yk and the actuating signal ui<; outputting S4 of the pilot actuating correction signal ud,k as a function of the estimated position in the next magazine; generating S5 of the actuating signal uk by summing the controller actuating signal u _c ,k and the pilot actuating correction signal ud.k! and controlling S6 the optical element N 1 - N6 depending on the control signal uk. Preferably, the FEM model is generated in a step preceding step S1. For this purpose, for example, measurements of disturbances in a known system and/or disturbance simulations are used.

Although the present invention has been described using exemplary embodiments, it can be modified in many ways. REFERENCE SYMBOL LIST

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 fields

12 image plane

13 wafers

14 wafer table

15 wafer displacement drive

16 Illumination radiation

17 collector

18 intermediate focal plane

19 deflection 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 government units

302 disturbance estimator unit

304 Adder unit

400 estimator units

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 dk fault

Ml Spiegel

M2 mirror

M3 mirror

M4 mirror

M5 mirror

M6 mirror

NI optical element

N2 optical element

N3 optical element

N4 optical element

N5 optical element

N6 optical element Ps target position uk control signal yk position measurement signal

Claims

PATENT CLAIMS 1. Optical system (200), comprising: an optical element (NI - N6); a sensor unit (202) which is configured to output a position measurement signal (yk) depending on a position of the optical element (NI - N6); a controller unit (300) which is configured to generate a controller actuating signal (u _c ,k) depending on the position measurement signal (yk); a disturbance estimator unit (302) which is configured to estimate a periodic, externally excited disturbance (dk) for a next magazine and, based thereon, to estimate a position of the optical element (NI - N6) in the next magazine depending on the position measurement signal (yk) and an actuating signal (uk) and to output a pilot control actuating correction signal (ua,k) depending on the position estimated for the next magazine; an adding unit (304) which is designed to generate the actuating signal (uü) by summing the controller actuating signal (u _c ,k) and the pilot control actuating correction signal (ud,k); and an actuator (208) which is designed to control the optical element (N 1 - N6) as a function of the actuating signal (uü). 2. Optical system according to claim 1, wherein the disturbance estimation unit (302) has an estimation unit (400) which is configured to execute a finite element model of the optical element (NI - N6) and/or a model of the periodic, externally excited disturbance (dk) in order to estimate a respective position of the optical element (NI - N6) as a function of the actuating signal (uü) for each state of the periodic, externally excited disturbance (dk) and/or per period. 3. Optical system according to claim 2, wherein the disturbance estimation unit (302) comprises a correction unit (402) which is arranged to to generate a correction signal (xk+i) for the respective estimated position as a function of the position measurement signal (yi) for each state of the periodic, externally excited disturbance (dk) and/or per magazine, and to provide the correction signal (xk+i) to the estimator unit (400) for estimating a respective position in a next state and/or in a next magazine; wherein the disturbance variable estimator unit (302) is preferably further configured to generate the pilot control correction signal (ua,k) from the sum of the correction signals (xk+i). 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) has an interference source (210) which is configured to generate the periodic, externally excited interference (dk). 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 (NI ■ N6) comprises a mirror (Ml - M6) and/or a lens. 8. Optical system according to one of claims 1 - 7, wherein the periodic, externally excited disturbance (dk) 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 support the optical element (NI - N6), and on which the actuator (208) for controlling the optical element (NI - 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 of: a) outputting (S1) a position measurement signal (yk) as a function of a position of an optical element (NI - N6); b) generating (S2) a controller actuating signal (u _c ,k) as a function of the position measurement signal (yk); c) estimating (S3) a periodic, externally excited disturbance (dk) in a next magazine and, based thereon, estimating a position of the optical element (NI ■ N6) in the next magazine as a function of the position measurement signal (yk) and an actuating signal (uk); d) outputting (S4) a pilot actuating correction signal (ua,k) as a function of the estimated position in the next magazine; e) generating (S5) the control signal (uk) by summing the controller control signal (u _c ,k) and the pilot control correction signal (ua,k); and f) controlling (S6) the optical element (NI - N6) depending on the control signal (uk).