Robust disturbance compensation control for MEMS mirrors

Abstract

The present invention comprises a method, a control device, a computer program, an optical system having the control device, and a lithography apparatus having the optical system for aligning a position-sensitive optical element of a lithography apparatus, comprising: determining a frequency-dependent amplitude of an amplification of a controlled system for controlling the position of the position-sensitive optical element; determining an amplitude of an amplification of a controller for counteracting a frequency-dependent drop in an amplitude of the amplification of the controlled system; applying the determined amplitude of the amplification of the controller in order to counteract the frequency-dependent drop in the amplitude of the amplification of the controlled system; and means for operating the controlled system in a phase stability range based at least in part on the determined amplitude of the amplification of the controller.

Description

[0001] Carl Zeiss SMT GmbH

[0002] 1

[0003] ROBUST DISTURBANCE COMPENSATION CONTROL FOR MEMS MIRRORS

[0004] The present invention relates to a method, a control device, a computer program, an optical system comprising the control device and a lithography system with the optical system for aligning a position-sensitive optical element of a lithography system.

[0005] The content of priority application DE 10 2025 106 275.7 is fully incorporated by reference.

[0006] Microlithography is used to manufacture microstructured components, such as integrated circuits. The microlithography process is carried out using a lithography system, which includes an illumination system and a projection system. The image of a mask (reticule) illuminated by the illumination system is projected by the projection system onto a substrate, such as a silicon wafer, coated with a photosensitive layer (photoresist) and positioned in the image plane of the projection system. This transfers the mask structure onto the photosensitive coating of the substrate.

[0007] 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 of this wavelength, such EUV lithography systems must use reflective optics, i.e., mirrors, instead of the previously used refracting optics, i.e., lenses.

[0008] Actuable optical elements can improve the imaging of the mask onto the substrate. For example, wavefront errors during exposure, which lead to magnified and / or blurred images, can be compensated for.

[0009] For example, a MEMS actuator (MEMS; Microelectromechanical System) or a PMN actuator (PMN; Lead-Magnesium Niobate) can be used. A PMN actuator enables positioning in the sub-micrometer or sub-nanometer range. The actuator, whose actuator elements are stacked on top of each other, experiences a force when a DC voltage is applied, which causes a specific linear expansion. Carl Zeiss SMT GmbH

[0010] 2

[0011] This is caused by the position set by the direct current (DC) voltage, which can be negatively affected by external electromechanical crosstalk at the inherent resonance points of the actuator driven by the DC voltage. MEMS mirrors and suitable actuators for driving them are described, for example, in DE 102016213025 A1.

[0012] Micromirror systems are known, for example, from WO 2016 / 146412 A1. The micromirror systems disclosed therein consist of a pivotable part (rotor) and a static part (stator). According to the micromirror system disclosed therein, corresponding mirrors can be tilted electrostatically by equipping both the rotor and the stator with interlocking comb electrodes. When a control voltage is applied to the comb electrodes, a desired tilting of the micromirror system can thus be achieved, based at least partially on an electrostatic interaction between the comb electrodes of the rotor and the comb electrodes of the stator, at least along one of, for example, at least two tilting axes. This drive concept for micromirror systems is also known as a capacitive actuator.

[0013] However, these arrangements often suffer from the disadvantage of non-linear behavior, meaning that the effective tilting stiffness, as seen from a moving mirror, decreases with increasing tilt of the micromirror system. This resulting non-linearity stems from the micromirror system itself, which, when a drive voltage is applied, exhibits an increasing negative stiffness with increasing tilt.

[0014] The reason for this can be seen in the fact that the comb electrodes of the capacitive actuator's rotor do not all move strictly parallel to the comb electrodes of the stator, but are also moved out of their planes; that is, the rotor's comb fingers can assume a non-parallel orientation to the stator's comb electrodes. This can cause the respective comb electrodes to approach each other if the mirror is tilted sufficiently. This parasitic (and undesirable) movement of the comb electrodes out of a relative, parallel alignment can result in a negative stiffness that increases with the tilt angle of the micromirror system (i.e., the relative alignment of the rotor's and stator's comb electrodes) and the drive voltage of the actuator used. This can lead to a variable Carl Zeiss SMT GmbH

[0015] 3

[0016] This leads to operating point-dependent negative stiffness, which depends on the design of the actuators, more precisely the comb fingers.

[0017] This operating-point-dependent stiffness can, in turn, be associated with different resonant frequencies of the mirror arrangement. When using a controller design that is solely focused on controlling a specific resonant frequency (and thus an associated stiffness), it cannot be guaranteed in all cases that a desired, uniform gain of a controlled system can be achieved across a considered frequency range.

[0018] Approaches to implementing operating point-dependent control prove to be mostly complex in this respect and require a comprehensive system characterization and thus a high degree of intervention by an operator of the system.

[0019] Due to the precise and high requirements for the accuracy of the alignment of a micromirror when used in a lithography system, it is also of particular importance to regulate the alignment of the micromirror over time and to maintain it at a required alignment value.

[0020] Therefore, there is a need to further improve the control of micromirrors, especially in the context of lithography.

[0021] Against this background, one object of the present invention is to provide an improved control of an alignment for a position-sensitive optical element, which at least partially overcomes the known disadvantages.

[0022] According to a first aspect, a method for aligning a position-sensitive optical element of a lithography system is proposed. The method can include determining a frequency-dependent gain amplitude of a control loop for position control of the position-sensitive optical element, as well as determining a gain amplitude of a controller to counteract a frequency-dependent decrease in the gain amplitude of the control loop. The method can further include applying the determined gain amplitude of the controller to counteract the frequency-dependent decrease in the gain amplitude of the control loop. Furthermore, the method can include operating the control loop in Carl Zeiss SMT GmbH.

[0023] 4

[0024] a phase stability range, at least partially based on the determined amplitude of the controller's gain.

[0025] The controller and the controlled system can each be contained within a control loop. In some examples, the control loop may include a proportional-integral-differential (PID) controller. In other cases, the control loop may include a proportional-integral (PI) controller.

[0026] In this context, frequency dependence can be understood as the dependence of the amplitude of the controller gain on the frequency of a signal fed to the controller. This frequency dependence can manifest itself as a change in the amplitude of the controller gain when the frequency fed to the controller changes.

[0027] In this context, counteracting can be understood as at least partially compensating for the drop in the amplitude of the controller gain.

[0028] Applying a specific gain amplitude to the controller can be understood here as changing an amplitude in the controller (e.g., increasing the amplitude) so that the resulting gain amplitude of the controller counteracts a decrease in the gain amplitude of the controlled system.

[0029] In this context, a phase stability region can be understood as a phase range within which a control loop can operate stably. This allows for the efficient compensation of a frequency-dependent gain in a controlled system by adjusting the gain amplitude of the controller (in a frequency-dependent manner). In particular, this efficiency is achieved because the present method does not rely on operating-point-dependent control of the orientation of the position-sensitive optical element, but instead pursues an approach that is independent of specific operating points.

[0030] According to one embodiment, the frequency-dependent decrease in the amplitude of the gain of the controlled system can decrease with increasing frequency.

[0031] The gain amplitude of the controlled system can decrease by at least -10 dB within an order of magnitude of frequency. In some examples, the gain amplitude of the controlled system can decrease by less than -10 dB per order of magnitude of frequency with increasing frequency. (Carl Zeiss SMT GmbH)

[0032] 5

[0033] For example, the gain amplitude of the controlled system can decrease by more than -10 dB per order of magnitude of frequency. An order of magnitude can be understood as the range between, for example, 1 Hz and 10 Hz, between 10 Hz and 100 Hz, or between 100 Hz and 1 kHz. Analogous conclusions can be drawn for frequencies in the kHz, MHz, GHz, and / or THz range.

[0034] In this way, the proposed method can prevent at least a partial reduction in the amplitude of the gain of the controlled system.

[0035] According to another embodiment, a decrease in the amplitude of the gain of the controlled system can be associated with an increasing stiffness with increasing frequency or an increase in the mass of the position-sensitive optical element with increasing frequency.

[0036] The amplitude of the gain of the controlled system, e.g., when considered as a spring-mass system, can vary across the frequency, for example, in the sense of the frequency response of a resonator. This can be the cause of the frequency-dependent decrease in the amplitude of the gain of the controlled system.

[0037] Unfavorable effects caused by an effective frequency dependence of the gain amplitude of the controlled system (e.g., an operating point-dependent change in a frequency response, where the stiffness of a considered system can change at each operating point, which in turn can cause a change in the frequency response (e.g., a decrease in the gain amplitude of the controlled system over the frequency of the frequency response)), which can be attributed, for example, to a frequency-dependent increase in the stiffness (or mass) of the position-sensitive optical element (and a possible actuator control), can therefore be at least partially overcome within the framework of the method presented herein.

[0038] According to another embodiment, operating the controlled system in the phase stability range can include determining a phase shift to increase the phase in a frequency range in which a decrease in the amplitude of the gain of the controlled system occurs.

[0039] Increasing the phase in a frequency range associated with a decrease in the amplitude of the control loop's gain can effectively increase the amplitude of the control loop's gain in that frequency range. Carl Zeiss SMT GmbH

[0040] 6

[0041] A phase shift can generally be understood as a measure of how far the first zero crossing of a sine function (with respect to a phase) is shifted to the left (i.e. towards a smaller phase) or to the right (i.e. towards a larger phase).

[0042] According to another embodiment, the phase stability region can be a phase lag region.

[0043] The frequency range associated with a phase-lag region can refer to a frequency response L(jω) of a gain within a control loop. Here, j indicates that the argument of the frequency response is complex-valued, while o represents the frequency for which a corresponding value of the frequency response is described.

[0044] The phase lag range can refer, for example, to the range of -540° - k • 360° < arg(L(jω)) < -180° - k • 380° with k GN.

[0045] The operation of the controlled system can be based, for example, on an implementation of a second-order low-pass filter to shift a resonance of the controlled system into the phase-lag stability range.

[0046] According to another embodiment, operating the controlled system in the phase stability range, based on the determined phase shift, can lead to a reduction of the phase in a frequency range in which a drop in the amplitude of the gain of the controlled system occurs.

[0047] Reducing the phase in a frequency range, which is associated with a decrease in the amplitude of the controller gain of the system, can be associated with an effective increase in the amplitude of the controller gain of the controller in the relevant frequency range.

[0048] This can efficiently counteract a decrease in the amplitude of the controller gain of the system.

[0049] According to another embodiment, the phase stability region can be a phase lead region.

[0050] The phase lead region can be defined as the region -180° < arg(L(jω)) < 180°. Carl Zeiss SMT GmbH

[0051] 7

[0052] According to another embodiment, the amplitude of the gain of the controlled system can decrease with increasing frequency both in an open control loop, preferably for individual system resonances, and in a closed control loop.

[0053] The individual system resonances can be associated with corresponding natural frequencies of operating points of the position-sensitive optical element.

[0054] An operating point can be understood as one or two parameters, each specifying a degree of tilt of the position-sensitive optical element about a corresponding tilt axis. The tilt axes can be defined, for example, by the x- and y-axes of a Cartesian coordinate system.

[0055] The closed control loop can be configured in such a way that, in its closed operation, the control loop counteracts system resonances and at least partially compensates for them.

[0056] According to a second aspect, a computer program is proposed. The computer program comprises instructions which, when executed by a computer, cause the computer to perform the procedure as described herein.

[0057] One or more of the algorithms / computer programs described here can be embodied directly in hardware, in a software module executed by a processor, or in a combination of both. A software module can reside in random-access memory (RAM), flash memory, read-only memory (ROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor so that the processor can read information from and write information to the storage medium. Alternatively, the storage medium can be integrated into the processor. The processor and the storage medium can be housed in an application-specific integrated circuit (ASIC).Alternatively, the processor and storage medium can be housed as discrete components within any component of a mobile computing platform. The computer program can also be executed, for example, on a Field Programmable Gate Array (FPGA). Carl Zeiss SMT GmbH.

[0058] 8

[0059] In some cases, the computer program can also be provided as a computer program product. A computer program product can be located on a memory card, a USB flash drive, a CD-ROM, a DVD, or as a file that can be downloaded from a server on a network. Such a file can be provided, for example, by transmitting the file containing the computer program product over a wireless communication network.

[0060] According to a third aspect, a control device for an optical element for aligning a position-sensitive optical element of a lithography system is proposed. The control device can include means for determining a frequency-dependent gain amplitude of a control loop for position control of the position-sensitive optical element, as well as means for determining a gain amplitude of a controller to counteract a frequency-dependent decrease in the gain amplitude of the control loop. Furthermore, the control device can include means for applying the determined gain amplitude of the controller to counteract the frequency-dependent decrease in the gain amplitude of the control loop. Finally, the control device can include means for operating the control loop in a phase-stability region, at least partially based on the determined gain amplitude of the controller.

[0061] According to one embodiment, a control loop associated with the controlled system and the controller can be designed for a dynamic range of at least 150 to 500 Hz.

[0062] According to another embodiment, the position-sensitive optical element can be a microelectromechanical MEMS mirror, preferably a MEMS mirror for extreme ultraviolet EUV lithography.

[0063] According to a further embodiment, the control device may comprise a first means for executing the computer program as described herein, and / or a second means for executing the method as described herein.

[0064] The first means of executing the computer program or the second means of executing the procedure can be a processor, a digital signal processor (DSP), a central processing unit (CPU), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a graphics processing unit (GPU), a tensor processing unit (TPU), a microcontroller, a Carl Zeiss SMT GmbH

[0065] 9

[0066] This includes transistor logic and / or other programmable logic devices, or partial combinations thereof. Analogous principles can also be applied to the other means described herein.

[0067] According to a fourth aspect, an optical system with a number of actuable optical elements is proposed, wherein each of the actuable optical elements of the number is assigned a plurality N of actuator elements of an actuator device, wherein each actuator device is assigned a control device as described herein.

[0068] According to a fifth aspect, a lithography system with the optical system as described herein is proposed.

[0069] The optical system is preferably a projection optic of the 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.

[0070] The term "one" here should not necessarily be understood as restricting the number to exactly one element. Rather, it can also refer to multiple elements, such as two, three, or more. Similarly, every other counter used here should not be interpreted as restricting the number to the exact number stated. Instead, numerical deviations, both higher and lower, are possible unless otherwise specified.

[0071] The embodiments and features described for the method apply accordingly to the proposed control device and vice versa.

[0072] Other possible implementations of the invention also include combinations of features or embodiments described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. In such cases, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

[0073] Further advantageous embodiments and aspects of the invention are the subject of the dependent claims and the embodiments of the invention described below. The invention will be further explained using the example of Carl Zeiss SMT GmbH.

[0074] 10

[0075] Preferred embodiments are explained in more detail with reference to the attached figures.

[0076] Fig. 1 shows a schematic meridional section of a projection exposure system for EUV projection lithography!

[0077] Fig. 2 shows an exemplary optical system!

[0078] Figures 3A and 3B show exemplary Bode diagrams, figure 3C shows a diagram of process sensitivity!

[0079] Figures 4A - 4J show exemplary characterization measurements of a conventional control loop!

[0080] Figures 5A - 5J show exemplary characterization measurements of a control loop operated in a phase-lag range;

[0081] Figs. 6A - 6J show exemplary characterization measurements of a control loop which is operated in a phase-lead region.

[0082] Fig. 7 shows a flowchart of a method for aligning a position-sensitive optical element!

[0083] Fig. 8 shows an exemplary control device for aligning a position-sensitive optical element!

[0084] Fig. 9 shows a system for aligning a position-sensitive optical element! and

[0085] Fig. 10 shows an optical system for aligning a position-sensitive optical element.

[0086] In the figures, identical or functionally equivalent elements have been labelled with the same reference symbols, unless otherwise indicated. Furthermore, it should be noted that the representations in the figures are not necessarily to scale.

[0087] 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 Carl Zeiss SMT GmbH

[0088] 11

[0089] Light or radiation source 3, a lighting optic 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 lighting system 2. In this case, the lighting system 2 does not include the light source 3.

[0090] A reticule 7 arranged in the object field 5 is exposed. The reticule 7 is held by a reticule holder 8. The reticule holder 8 can be moved, particularly in a scanning direction, via a reticule displacement drive 9.

[0091] Figure 1 illustrates 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. In Figure 1, the scan direction runs along the y-direction y. The z-direction z runs perpendicular to the object plane 6.

[0092] The projection exposure system 1 comprises a projection optic 10. The projection optic 10 serves to image the object field 5 onto 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.

[0093] A structure on the reticulum 7 is imaged onto a photosensitive layer of a wafer 13 located in the image plane 12 within the image field 11. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be moved, particularly along the y-direction y, via a wafer transfer drive 15. The movement of the reticulum 7 via the reticulum transfer drive 9 and of the wafer 13 via the wafer transfer drive 15 can be synchronized.

[0094] Light source 3 is an EUV radiation source. 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 a wavelength in the range between 5 nm and 30 nm. 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. Light source 3 is manufactured by Carl Zeiss SMT GmbH.

[0095] 12

[0096] It could be a free-electron laser (FEL).

[0097] 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 hyperboloid reflective surfaces. The at least one reflective surface of the collector 17 can be illuminated with the illumination radiation 16 at grazing incidence (Gl), i.e., with angles of incidence greater than 45°, or at normal incidence (NI), i.e., with angles of incidence less than 45°. The collector 17 can be structured and / or coated to optimize its reflectivity for the useful radiation and to suppress stray light.

[0098] 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.

[0099] The illumination optics 4 comprise a deflecting mirror 19 and, downstream in the beam path, a first faceted mirror 20. The deflecting mirror 19 can be a planar deflecting mirror or, alternatively, a mirror with a beam-shaping effect in addition to its deflecting function. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates a useful wavelength of the illumination radiation 16 from stray light of a different wavelength. If the first faceted mirror 20 is arranged in a plane of the illumination optics 4 that is optically conjugate to the object plane 6 as the field plane, it is also referred to as a field faceted mirror. The first faceted 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 as examples in Fig. 1.

[0100] The first facets 21 can be designed as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or semicircular edge contour. The first facets 21 can be designed as planar facets or alternatively as convexly or concavely curved facets.

[0101] As is known, for example, from DE 102008009600 Al, the first facets 21 themselves can each also consist of a multitude of individual mirrors, Carl Zeiss SMT GmbH

[0102] 13

[0103] in particular, it may be composed of a multitude of micromirrors. The first faceted mirror 20 may in particular be designed as a microelectromechanical system (MEMS system). For details, reference is made to DE 102008009600 A1.

[0104] Between the collector 17 and the deflecting mirror 19, the illumination radiation 16 runs horizontally, i.e. along the y-direction y.

[0105] In the beam path of the illumination optics 4, a second faceted mirror 22 is arranged downstream of the first faceted mirror 20. If the second faceted mirror 22 is arranged in a pupil plane of the illumination optics 4, it is also referred to as a pupil faceted mirror. The second faceted 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 faceted mirror 20 and the second faceted mirror 22 is also referred to as a specular reflector. Specular reflectors are known from US 2006 / 0132747 A1, EP 1614 008 B1, and US 6,573,978.

[0106] 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.

[0107] The second facets 23 can also be macroscopic facets, which may, for example, have round, rectangular, or hexagonal edges, or alternatively, facets composed of micromirrors. Reference is also made to DE 102008009600 Al in this regard.

[0108] The second facets 23 can have planar or alternatively convex or concave curved reflective surfaces.

[0109] The illumination optics 4 thus form a doubly faceted system. This basic principle is also known as a honeycomb condenser (EnglJ Fly's Eye Integrator).

[0110] It can be advantageous not to arrange the second faceted mirror 22 exactly in a plane that is optically conjugate to a pupil plane of the projection optics 10. In particular, the second faceted mirror 22 can be arranged tilted relative to a pupil plane of the projection optics 10, as described, for example, in DE 102017220586 A1. Carl Zeiss SMT GmbH

[0111] 14

[0112] With the aid of the second faceted mirror 22, the individual first facets 21 are imaged into the object field 5. The second faceted mirror 22 is the last beam-shaping or indeed the last mirror for the illumination radiation 16 in the beam path before the object field 5.

[0113] In another embodiment of the illumination optics 4, not shown, a transmission optic 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 into the object field 5. The transmission optic can have exactly one mirror, or alternatively two or more mirrors, which are arranged one behind the other in the beam path of the illumination optics 4. The transmission optic 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).

[0114] In the embodiment shown in Fig. 1, the lighting optics 4 has exactly three mirrors after the collector 17, namely the deflecting mirror 19, the first faceted mirror 20 and the second faceted mirror 22.

[0115] In a further embodiment of the lighting optics 4, the deflecting mirror 19 can also be omitted, so that the lighting optics 4 after the collector 17 can then have exactly two mirrors, namely the first faceted mirror 20 and the second faceted mirror 22.

[0116] The imaging of the first facets 21 by means of the second facets 23 or with the second facets 23 and a transmission optic into the object plane 6 is regularly only an approximate imaging.

[0117] The projection optics 10 comprise a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection exposure system 1.

[0118] In the example shown in Fig. 1, the projection optics 10 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve, or any other number of mirrors Mi are also possible. The projection optics 10 is a double-obscured optic. The penultimate mirror M5 and the last mirror M6 each have a transmission aperture 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. Carl Zeiss SMT GmbH

[0119] 15

[0120] The reflective surfaces of the mirrors Mi can be designed as freeform surfaces without an axis of rotational symmetry. Alternatively, the reflective surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflective 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.

[0121] 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.

[0122] The projection optics 10 can be anamorphic. In particular, they have different image scales βx, βy in the x and y directions. The two image scales βx, βy of the projection optics 10 are preferably (βx, βy) = (+ / - 0.25, + / - 0.125). A positive image scale β indicates an image without image inversion. A negative sign for the image scale β indicates an image with image inversion.

[0123] The projection optics 10 thus lead to a reduction in the x-direction x, that is, in the direction perpendicular to the scan direction, in a ratio of 4'1.

[0124] The projection optics 10 lead to a reduction of 8H in the y-direction y, that is, in the scan direction.

[0125] Other magnification ratios are also possible. Magnification ratios with the same sign and absolute value in the x and y directions (x, y), for example with absolute values ​​of 0.125 or 0.25, are also possible.

[0126] 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, depending on the design of the projection optics 10, different. Examples of projection optics with different numbers of such intermediate images in the x and y directions x, y are known from US Patent 2018 / 0074303, Carl Zeiss SMT GmbH.

[0127] 16

[0128] 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 Köhler's principle. The far field is divided into a multitude of object fields 5 with the help of the first facets 21. The first facets 21 generate a plurality of images of the intermediate focus on the second facets 23 assigned to each of them.

[0129] The first facets 21 are each superimposed on an associated second facet 23 to illuminate the object field 5 on the reticulum 7. The illumination of the object field 5 is particularly homogeneous. It preferably exhibits a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

[0130] The illumination of the entrance pupil of the projection optics 10 can be geometrically defined by the arrangement of the second facets 23. By selecting the illumination channels, in particular the subset of the second facets 23 that carry 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 filling.

[0131] Another 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.

[0132] Further aspects and details of the illumination of the object field 5 and, in particular, the entrance pupil of the projection optics 10 are described below.

[0133] The projection optics 10 can, in particular, have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

[0134] The entrance pupil of the projection optics 10 cannot regularly be illuminated exactly by the second faceted mirror 22. When the projection optics 10 image the center of the second faceted mirror 22 telecentrically onto the wafer 13, the aperture rays often do not intersect at a single point. However, a surface can be found where the pairwise determined distance between the aperture rays is minimized. This surface Carl Zeiss SMT GmbH

[0135] 17

[0136] represents the entrance pupil or a surface conjugate to it in spatial space. In particular, this surface exhibits a finite curvature.

[0137] The projection optics 10 may 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 faceted mirror 22 and the reticle 7. This optical element can then be used to account for the different positions of the tangential and sagittal entrance pupils.

[0138] In the arrangement of the components of the illumination optics 4 shown in Fig. 1, the second faceted mirror 22 is arranged in a plane conjugate to the entrance pupil of the projection optics 10. The first faceted mirror 20 is arranged tilted relative to the object plane 6. The first faceted mirror 20 is arranged tilted relative to an arrangement plane defined by the deflecting mirror 19. The first faceted mirror 20 is arranged tilted relative to an arrangement plane defined by the second faceted mirror 22.

[0139] Fig. 2 shows a schematic representation of an embodiment of an optical system 300 for a lithography system or projection exposure system 1, as shown, for example, in Fig. 1. Furthermore, the optical system 300 of Fig. 2 can also be used, for example, in a DUV lithography system.

[0140] The optical system 300 of Fig. 2 has a plurality of actuable optical elements 310. The optical system 300 is configured here as a micromirror array, wherein the optical elements 310 are micromirrors. Each micromirror 310 can be actuated by means of an associated actuator 200. For example, each micromirror 310 can be tilted about two axes and / or displaced in one, two, or three spatial axes by means of the associated actuator 200. For clarity, reference numerals are shown only for the top row of these elements.

[0141] The control device 100 controls the respective actuator 200, for example with a control voltage V2. This sets a position of the respective micromirror 310. The control device is described in particular with reference to Fig. 8. Carl Zeiss SMT GmbH

[0142] 18

[0143] Figures 3A and 3B show Bode plots to illustrate aspects of the present invention. Figure 3C shows a process sensitivity diagram.

[0144] Specifically, Fig. 3A shows a Bode plot of an exemplary controller gain (magnitude or amplitude of the controller gain, Fig. 3A, top) with respect to its transfer function plotted against a frequency, and relatedly, a phase of the control loop (Fig. 3A, bottom), plotted against the frequency.

[0145] Fig. 3A shows the operation of the controller.

[0146] Figure 3A shows that the amplitude of the controller gain decreases with increasing frequency. For frequencies greater than the -3 dB cutoff frequency f Tiefpass The amplitude of the controller gain even shows a steeper drop with increasing frequency than is observed for frequencies smaller than the cutoff frequency f. Tiefpass are.

[0147] In some cases, the system may include a position-sensitive element (such as a mirror) and associated control means. The system may have multiple operating points, where an operating point can result, for example, from the orientation of the position-sensitive element along an x-axis, a y-axis, and / or a z-axis. Each operating point can be associated with an operating-point-dependent stiffness of the system under consideration, and this operating-point-dependent stiffness may be associated with a corresponding operating-point-dependent resonant frequency of the system. Assuming a constant amplitude of a controller's gain over a frequency range, this can ultimately be reflected in an operating-point-dependent amplitude of the controlled system's gain due to the system's operating-point-dependent stiffness.According to the aspects described herein, this operating point-dependent amplitude of the gain of the controlled system can be at least partially compensated.

[0148] The use of a closed-loop control system is of particular importance to ensure the alignment of the position-sensitive optical element. The control loop is used especially to compensate for noise inputs such as actuator noise, quantization noise, sensor noise, and vibration noise (deterministic and stochastic). Carl Zeiss SMT GmbH

[0149] 19

[0150] where sensor noise can typically be considered the dominant noise source.

[0151] Fig. 3B, however, shows a Bode diagram for an open-loop control system (e.g., based on the multiplication of a controller by a controlled system).

[0152] The Bode diagram shown in Fig. 3B shows a multitude of resonance peaks 315, which decrease in amplitude (and thus in gain) with increasing frequency and which are to be compensated by a controller in the further course.

[0153] Figure 3B shows that the higher-frequency resonance peaks do not extend as far beyond the 0 dB line as the lower-frequency resonance peaks. Therefore, the higher-frequency resonance peaks are less affected by the control loop and receive correspondingly less amplification.

[0154] Fig. 3C finally shows a diagram of the behavior in the closed control loop.

[0155] The result of the controller design discussed above can be seen, for example, in the process sensitivity, in which the low-frequency resonances are damped significantly more than the higher-frequency resonances. From Fig.

[0156] 3C shows that higher-frequency resonances are damped less effectively, i.e., compensated less effectively, than lower-frequency resonances. Peaks at higher frequencies are therefore less suppressed than peaks at lower frequencies.

[0157] Figures 4A - 4J show exemplary characterization measurements of a conventionally used control loop.

[0158] In particular, Fig. 4A shows a Bode plot of a controller transfer function plotted against a corresponding frequency, analogous to the scenario shown in Fig. 3A. Fig. 4A also shows that the amplitude of the controller gain, expressed by the controller transfer function, decreases with increasing frequency.

[0159] Fig. 4B shows a representation of the controller zeros and poles. It illustrates the frequency and damping at which the controller zeros and poles were positioned. Carl Zeiss SMT GmbH

[0160] 20

[0161] Fig. 4C shows a Bode diagram of the open-loop control system (in analogy to Fig.

[0162] 3B). In particular, the resonant frequencies of the control loop become apparent from this, the corresponding amplitude of which of the controller gain decreases with increasing frequency.

[0163] Fig. 4D shows a Nichols diagram of the open-loop control system. This serves to illustrate the amplitude of the controller gain versus the phase of the control loop.

[0164] The Nichols diagram shows the stability range in which the resonances to be damped are placed (e.g., phase-lag or phase-lead). Furthermore, the robustness margin can be assessed based on the distance to the critical points (red crosses).

[0165] Fig. 4E shows a Nyquist plot for an open-loop control system. This represents the scenario shown in relation to Fig. 4D, but on a Cartesian plane.

[0166] Information regarding the existing stability margin can be extracted from the Nyquist plot. This can be indicated by the distance of a measurement point to the critical point at coordinates (-1,0).

[0167] Fig. 4F shows a diagram of the input sensitivity. Fig. 4F represents the singular values ​​(in dB) versus the frequency.

[0168] The representation shown in Fig. 4F can be used to determine a stability margin of the control loop, derivable from a maximum value of the sensitivity.

[0169] Fig. 4G shows a complementary sensitivity. The transfer function shown can represent a switching speed of the control loop as well as a transfer function via which sensor noise is transferred in the control loop for the sensors used in the control loop, where the sensor noise can be understood as one of the essential noise contributions to the control of the alignment of the position-sensitive optical element.

[0170] Fig. 4H shows a diagram of process sensitivity, based on Fig. 3C. The transfer function of the control loop for existing disturbances can be derived from this diagram. The transfer of existing vibrations can also be derived from the diagram shown in Fig. 4H. Carl Zeiss SMT GmbH

[0171] 21

[0172] Fig. 4I shows a diagram of the controller sensitivity. Fig. 4I represents the controller response behavior to a change in a controller setpoint.

[0173] Fig. 4J shows a diagram representing the pole-zero pairs of a closed-loop control system. From this representation, the damping ratio achieved in the closed-loop control system can be determined, for example. The damping ratio can correspond to the damping of the peaks in the process sensitivity diagram (Fig. 4H).

[0174] Figures 5A - 5J show the same diagrams that have already been described with reference to Figures 4A - 4J, but for the embodiment of a phase-lag approach.

[0175] In particular, the Bode diagram in Fig. 5A shows that by increasing the amplitude of the gain of the controller and operating the controller in the phase stability range (in this case in the phase lag range) an effective increase or stabilization of the amplitude of the gain of the controlled system can be achieved.

[0176] It should be noted that the lines shown in Figs. 5A-5I each represent a variable stiffness of the system under consideration, i.e., a variation of the operating point.

[0177] Figures 6A - 6J show the same diagrams that have already been described with reference to Figures 4A - 4J, but for the embodiment of a phase-lead approach.

[0178] Figure 6H also shows that the curves shown there are closer to the critical point (-1,0) than, for example, in the scenario shown in Figure 4H. This can be interpreted as an indication that implementing the approach presented here will achieve higher damping than previously used approaches.

[0179] This can also be seen, for example, in Fig. 6J, which shows the corresponding process sensitivities. Fig. 6J also shows (e.g., in comparison with 4J) that improved damping can be achieved using the control concept presented here. Carl Zeiss SMT GmbH

[0180] 22

[0181] It should be noted that the lines shown in Figs. 6A-6I each represent a variable stiffness of the system under consideration, i.e., a variation of the operating point.

[0182] Fig. 7 shows a flowchart of a method for aligning a position-sensitive optical element of a lithography system.

[0183] In step 710, a frequency-dependent amplitude of a gain of a control loop for position control of the position-sensitive optical element is determined.

[0184] In step 720, a phase shift is determined in the control loop to counteract a frequency-dependent decrease in the amplitude of a controller gain.

[0185] In step 730, the specified phase shift is applied to counteract the frequency-dependent decrease in the amplitude of the controller gain.

[0186] In step 740, the controlled system is operated in a phase stability range, at least partially based on the determined amplitude of the controller's gain.

[0187] Fig. 8 shows an exemplary control device 800 for an optical element for aligning a position-sensitive optical element of a lithography system. The control device comprises means for determining a frequency-dependent amplitude of a gain of a control system 810, means for determining an amplitude of a controller 820, means for applying the determined amplitude of the gain of the controller 830, and means for operating the control system in a phase stability range (840).

[0188] The means for determining a frequency-dependent amplitude of a gain of a control system 810 is configured to determine a frequency-dependent amplitude of a gain of a control system for position control of the position-sensitive optical element.

[0189] The means for determining the amplitude of a controller gain 820 is configured to determine the amplitude of a controller gain in order to counteract a frequency-dependent fall-off of the amplitude of the controlled system gain. Carl Zeiss SMT GmbH

[0190] 23

[0191] The means for applying the specific amplitude of the gain of the controller 830 is configured to apply the specific amplitude of the gain of the controller in order to counteract the frequency-dependent fall-off of the amplitude of the gain of the controlled system.

[0192] The means for operating the controlled system in a phase stability range 840 is configured to operate the controlled system in a phase stability range at least partially based on the determined amplitude of the controller's gain.

[0193] Fig. 9 shows a system 900 for aligning a position-sensitive optical element of a lithography system. The system 900 comprises a control device 910 and a computer program 920.

[0194] System 900 includes the control device 910, as described herein. The control device 910 can be configured like the control device 800.

[0195] System 900 includes the computer program 920 as described herein.

[0196] Fig. 10 shows an optical system 1000 which can represent a possible embodiment of the optical system 300, as described above with reference to Fig. 2. The optical system 1000 comprises a number of actuable optical elements 10101,..., 1010N, wherein each of the actuable optical elements 10101,..., 1010N is assigned a plurality N of actuator elements of an actuator device 1020 l,x, 1020 l,y,..., wherein each actuator device 10201, x, 10201, Y,... is assigned a control device 1030i,x, 1030i, Y as described herein.

[0197] Although the present invention has been described using exemplary embodiments, it can be modified in many ways. Carl Zeiss SMT GmbH

[0198] 24

[0199] REFERENCE MARK LIST

[0200] 1 Projection exposure system

[0201] 2 lighting systems

[0202] 3 light source

[0203] 4 Lighting optics

[0204] 5 object field

[0205] 6 Object level

[0206] 7 reticles

[0207] 8 label holders

[0208] 9 Reticle displacement drive

[0209] 10 Projection optics

[0210] 11 Image field

[0211] 12 Image plane

[0212] 13 wafers

[0213] 14 wafer holders

[0214] 15 wafer transfer drive

[0215] 16 Lighting radiation

[0216] 17 Collector

[0217] 18 Intermediate focus plane

[0218] 19 deflecting mirrors

[0219] 20 first faceted mirror

[0220] 21 first facet

[0221] 22 second faceted mirror

[0222] 23 second facet

[0223] 100 Control device

[0224] 200 actuator

[0225] 300 optical system

[0226] 310 optical elements

[0227] 315 resonance peaks

[0228] 700 procedures

[0229] 710 steps

[0230] 720 steps

[0231] 730 steps

[0232] 740 steps

[0233] 800 Control device

[0234] 810 Means of determining a frequency-dependent controller gain

[0235] 820 Means of Determining a Phase Shift

[0236] 830 Means of applying phase shift Carl Zeiss SMT GmbH

[0237] 25

[0238] 840 Means for operating the control system in a phase stability range

[0239] 900 System

[0240] 910 Control device

[0241] 920 computer program

[0242] 1000 optical system

[0243] IOION optical elements

[0244] 1020M, N actuator device

[0245] 1030M, N actuator device

[0246] ml mirror

[0247] M2 mirrors

[0248] M3 mirror

[0249] M4 mirrors

[0250] M5 mirror

[0251] M6 mirrors

[0252] V2 control voltage

Claims

Carl Zeiss SMT GmbH 26 PATENT CLAIMS 1. Method (700) for aligning a position-sensitive optical element of a lithography system, comprising: Determine (710) a frequency-dependent amplitude of a gain of a control system for position control of the position-sensitive optical element! Determining (720) an amplitude of a gain of a controller to counteract a frequency-dependent fall-off of the amplitude of the gain of the controlled system; Applying (730) the specified amplitude of the controller gain to counteract the frequency-dependent fall-off of the amplitude of the control loop gain; Operating (740) the controlled system in a phase stability range at least partially based on the determined amplitude of the gain of the controller.

2. Method according to claim 1, where the frequency-dependent decrease in the amplitude of the gain of the controlled system occurs with increasing frequency.

3. Method according to one of claims 1 or 2, where a decrease in the amplitude of the gain of the controlled system is associated with an increasing stiffness with increasing frequency or an increase in the mass of the position-sensitive optical element with increasing frequency.

4. Method according to one of claims 1-3, where operating the controlled system in the phase stability range includes determining a phase shift to increase the phase in a frequency range in which a decrease in the amplitude of the gain of the controlled system occurs.

5. Method according to any one of claims 1-4, where the phase stability region is a phase lag region.

6. Method according to one of claims 1-3, where operating the control system in the phase stability range, based on the determined phase shift, leads to a reduction of the phase in a Carl Zeiss SMT GmbH 27 Frequency range in which a decrease in the amplitude of the gain of the controlled system occurs.

7. Method according to one of claims 1-3 or 6, where the phase stability region is a phase lead region.

8. Method according to any one of claims 1-7, wherein the amplitude of the gain of the controlled system decreases with increasing frequency both in an open control loop, preferably for individual system resonances, and in a closed control loop.

9. Computer program comprising instructions which, when the program is executed by a computer, cause the computer to execute the method according to any one of claims 1-8.

10. Control device (800) for an optical element for aligning a position-sensitive optical element of a lithography system, comprising: Means for determining a frequency-dependent amplitude of a gain of a control system (810) for position control of the position-sensitive optical element! Means for determining an amplitude of a gain of a controller (820) to counteract a frequency-dependent fall-off of an amplitude of the gain of the controlled system; Means for applying the specified amplitude of the gain of the controller (830) to counteract the frequency-dependent fall-off of the amplitude of the gain of the controlled system; Means for operating the controlled system in a phase stability range (840) at least partially based on the determined amplitude of the gain of the controller.

11. Control device according to claim 10, wherein a control loop associated with the controlled system and the controller is designed for a dynamic range of at least 150 to 500 Hz.

12. Control device according to one of claims 10 or 11, wherein the position-sensitive optical element is a microelectromechanical MEMS mirror, preferably a MEMS mirror for extreme ultraviolet (EUV) lithography. Carl Zeiss SMT GmbH 28 13. Control device according to one of claims 10-12, further comprising: a first means for executing the computer program according to claim 9; and / or a second means for exporting the process according to one of claims 1'8.

14. Optical system (1000) with a number of actuable optical elements (10101,... 1010N), wherein each of the actuable optical elements (10101,... 1010N) is assigned a plurality N of actuator elements of an actuator device (10201, x, 10201, Y,.... 1020N, ​​X, 1020N, ​​Y), wherein each actuator device is assigned a control device (1030i,x, 1030I, Y,.... 1030N, X, 1030N, Y) according to one of claims 10 - 13.

15. Lithography system with the optical system according to claim 14.

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