Optical device, method for adjusting target deformation, and lithography system

Abstract

The invention relates to an optical device (1) for a lithography system (100, 200) comprising at least one optical element (2) having an optical surface (3) and one or more actuators (4) for deforming the optical surface (3). According to the invention, a strain gauge (5) is provided for determining the deformation of the optical surface (3), the strain gauge (5) comprising at least one optical fiber (6), the optical fiber (6) being polarization-preserving.

Description

[Technical Field]

[0001] This application claims priority from German Patent Application No. 10 2021 205 425.0, the content of which is incorporated herein by reference in its entirety.

[0002] The present invention relates to an optical device for a lithography system, comprising at least one optical element including an optical surface and one or more actuators for deforming the optical surface.

[0003] The invention further relates to a method for setting a target deformation of an optical surface of an optical element of a lithography system by means of one or more actuators.

[0004] Furthermore, the invention relates to a lithography system, in particular a projection exposure apparatus for semiconductor lithography, comprising an illumination system with a radiation source and an optical unit including at least one optical element. [Background technology]

[0005] Optical elements for guiding and shaping radiation in projection exposure apparatuses are known from the prior art. In known optical elements, surfaces of the optical element often guide and shape the light waves incident on the optical element. Therefore, precise control of the shape of the surfaces is particularly advantageous for generating precise wavefronts with the desired properties.

[0006] The prior art discloses lithography systems that use ultraviolet light, in particular DUV (deep ultraviolet) and / or EUV (extreme ultraviolet) light, to produce microlithographic structures with the highest precision, where the light of a radiation source is directed by a number of mirrors onto a wafer to be exposed, the arrangement, position and shape of the mirrors here decisively contributing to the exposure quality.

[0007] For example, existing lithography systems need to be further developed to accommodate ever-increasing numbers of transistors on a chip. A typical prior art technique teaches attaching actuators to mirrors, which shape the mirrors with as many degrees of freedom as possible.

[0008] Furthermore, the prior art describes various systems for actuating deformable mirrors.

[0009] The prior art discloses incorporating optical elements into optical devices that have actuators that generate forces to specifically shape optical surfaces that interact with light waves.

[0010] According to the prior art, the effect of an actuator on an optical surface is predicted, for example, based on modeling. However, effects that are ignored in the modeling can weaken the predictive power of the model.

[0011] Systems for deforming optical elements, as known from the prior art, use closed-loop control to deform an optical surface to set a target deformation. For this purpose, the deformation is measured by a sensor, coded in the form of an electrical signal within the closed-loop control, and output to an actuator. For lithography systems, the prior art does not allow sensors with sufficiently high measurement capabilities to be integrated into the lithography system or the optical element. For this reason, such optical devices operate in an open control chain or in a feedforward mode. Summary of the Invention [Problem to be solved by the invention]

[0012] A drawback of prior art optical devices is that, although maintaining the target deformation as accurately as possible is important to meet the increasing demand for precision, the measures known for this purpose to set the target deformation precisely are insufficient. [Means for solving the problem]

[0013] The present invention is based on the object of developing an optical device which avoids the drawbacks of the prior art and in particular allows precise shaping or precise setting of target deformations of optical surfaces.

[0014] According to the invention, this object is achieved by an optical device having the features of claim 1.

[0015] The invention is further based on the object of developing a method for setting a target deformation of an optical surface, which avoids the drawbacks of the prior art, in particular allowing precise shaping or precise setting of the target deformation of the optical surface.

[0016] This object is achieved by a method having the features of claim 16.

[0017] The invention is further based on the object of developing a lithography system which avoids the drawbacks of the prior art, in particular making it possible to form a precisely shaped wavefront of radiation.

[0018] According to the invention, this object is achieved by a lithography system having the features of claim 27 .

[0019] An optical apparatus according to the invention for a lithography system, in particular a projection exposure apparatus, comprises at least one optical element having an optical surface and one or more actuators for deforming the optical surface. According to the invention, a strain gauge device is provided for determining the deformation of the optical surface, the strain gauge device comprising at least one optical fiber, the optical fiber being polarization-preserving.

[0020] Within the scope of the present invention, strain may also be understood to mean contraction and / or compression.

[0021] Additionally, the mechanical deformation of the optical surface serves to shape the optical surface and / or set a target deformation.

[0022] The optical device according to the invention is advantageous because it allows for independent control of the actual deformation of the optical surface by the assumed strain gauges. Therefore, the optical device according to the invention allows for more precise and reliable deformation of the optical surface than prior art systems that do not allow for control of the actual deformation of the optical surface. This is particularly advantageous when actuators are used to effect the deformation or deformation, since the effect of the actuators on the precise shaping of the optical surface is often based on pure modeling. Using the optical device according to the invention, the modeling can be interpolated and / or replaced with empirical measurements of the actual deformation.

[0023] It is contemplated that at least one actuator may be in the form of an electrostrictive actuator, where embodiment as an electrostrictive actuator is advantageous as electrostrictive actuators have very little tendency to drift and are less prone to exhibiting hysteresis.

[0024] The optical device may comprise a plurality of actuators for deformation of the optical surface, and may be capable of driving individual actuators of the plurality of actuators.

[0025] By driving the actuators, it is possible to set the profile of the optical surfaces and / or optical elements, particularly the mirrors, as desired, and thus to correct the optical device or the lithography system in which the optical device is incorporated as much as possible.

[0026] The strain of the actuator can be described to a first approximation by equation (1), where M denotes the electrostrictive coefficient, which leads to strain S as a result of the application of an electric field E. As is evident from equation (1), the electrostrictive coefficient M varies with the temperature θ of the actuator. Furthermore, the strain S of the actuator varies with its stiffness s and the applied mechanical tension T. Furthermore, the thermal component of the strain can be obtained by multiplying the thermal expansion coefficient CTE by the difference between the temperature θ and the initial temperature θ0.

[0027]

number

[0028] For a precise and constant closed-loop control of the at least one actuator, it is advantageous if both strain losses and thermal strains of the at least one actuator based on the electrostrictive effect are compensated for. For this purpose, the at least one actuator is capable of using more than 80% of its working distance for self-compensation of thermal expansion or thermal effects.

[0029] It would therefore be advantageous to model and calibrate the electrostriction and thermal hysteresis and drift of the actuator along with temperature calibration to enable highly accurate positioning or deformation of optical surfaces.

[0030] Optical surfaces are often formed with highly complex coatings to enable reflection of EUV light, and controlling the effect of at least one actuator is particularly beneficial for such coatings, as overloading or excessive distortion of the optical surface can lead to damage or destruction of the complex coating disposed thereon.

[0031] The optical element may comprise a continuously and / or integrally formed optical surface and in particular may not be a field facet mirror, as a result of which the optical surface may form an at least approximately freeform surface.

[0032] It is understood that the optical device may be optimized for use in other applications than in a lithography system, for example the optical device may be provided for use as part of a space mirror.

[0033] It is understood that multiple strain gauge devices may be present as part of the optical system, and when there are multiple strain gauge devices, the multiple strain gauge devices may share other components of the optical system.

[0034] The use of optical fibers as part of a strain gauge device is advantageous because the optical fiber can be used to guide light to different locations in an optical device for measurement purposes. From these locations, light can be reflected and / or transmitted through the optical fiber, for example, to measure the properties of the light. In this regard, optical fibers are very reliable and precise light guides and are also available in very small diameters. The use of optical fibers is particularly advantageous when optical devices with very delicate components are used, and the optical fibers may have very delicate embodiments as well.

[0035] Distortion measurements based on impedance measurements known from the prior art often require a large number of electrical conductors which can limit the functionality of optical components.

[0036] Polarization-maintaining optical fiber allows for the separation or decoupling of effects on the deformation of an optical surface that may result from temperature changes from effects on the deformation of an optical surface that may result from distortion and / or warping of the optical device, thereby allowing for even more accurate and precise control of the deformation or precise shaping of the optical surface, since the various influences on the shape of the optical surface can be addressed and / or removed separately from each other.

[0037] Isolating the effect of temperature is particularly advantageous, since temperature fluctuations of optical surfaces can be one of the largest disturbances to the deformation of optical elements, especially when used in EUV lithography systems. In particular, the temperature of an optical surface or element can vary between 20°C and 40°C during operation.

[0038] In an advantageous development of the optical device according to the invention, at least one optical fiber may comprise one or more fiber Bragg gratings with respective fiber interference spectra.

[0039] When the optical fiber contains a fiber Bragg grating, this results in a fiber interference spectrum that is characteristic of the fiber Bragg grating, which in this regard should be understood to be the wavelength-dependent variation of radiation propagating through the fiber.

[0040] In particular, fiber Bragg gratings have a characteristic filter bandwidth, and radiation with wavelengths within the spectral range determined by the filter bandwidth is reflected by the fiber Bragg grating in the optical fiber. The reflected wavelengths propagate backward in the optical fiber in the opposite direction to their original direction and can, for example, be measured.

[0041] Alternatively, the fiber interference spectrum can be determined in a transmission configuration, resulting in a transmitted radiation spectrum in which the reflection ranges and filter bandwidths are discernible as notches.

[0042] In this case, the fiber interference spectrum and in particular the filter bandwidth varies depending on the geometrical properties of the fiber Bragg grating, in which the grating period of the fiber Bragg grating is the determining geometrical property of the fiber Bragg grating.

[0043] The use of fiber Bragg gratings is particularly advantageous for use in strain gauge devices because strain in the optical fiber, and therefore in the fiber Bragg grating, can also change its geometric properties. Changes in the geometric properties, particularly compression or stretching of the grating period, also result in changes in the fiber interference spectrum, particularly a change in the center wavelength of the filter bandwidth.

[0044] In this case, the center wavelength of the filter bandwidth is directly proportional to the grating period multiplied by twice the effective refractive index in the fiber Bragg grating.

[0045] The spectral width of the filter bandwidth varies depending on the length of the fiber Bragg grating and the degree of refractive index change between adjacent refractive index regions. These parameters can also be modified, for example, by stretching or compressing the fiber Bragg grating, and are therefore suitable for determining mechanical strain in the optical fiber and / or fiber Bragg grating.

[0046] Alternatively or in addition to optical fibers and fiber Bragg gratings, other optical sensors may be provided as part of the strain gauge device.

[0047] In particular, other optical waveguides and other optical interference filters, in particular Bragg gratings, may be provided. By way of example, alternative or additional optical interference filters may be line gratings and / or resonators and / or simple slit diaphragms. By way of example, alternative and / or additional waveguides may be rigidly formed optical channels that are not in the form of optical fibers. The optical waveguides or optical channels may be designed to maintain polarization. Furthermore, pure waveguides in the form of free beams may also be provided.

[0048] The use of a single-mode optical fiber as the optical fiber can be particularly advantageous as it results in a particularly well-defined structure of the fiber interference spectrum.

[0049] In particular, fiber Bragg gratings can be designed as periodic microstructures that selectively reflect wavelengths.

[0050] The fiber Bragg grating may be specifically designed to have a grating period such that the frequency shift when strained by the intended use of the at least one actuator is between 1 pm and 1 nm, preferably between 5 pm and 500 pm, particularly preferably between 20 pm and 100 pm.

[0051] The strain gauge device and / or fiber Bragg grating may be designed to have a strain resolution of 1 am to 1 nm, preferably 5 am to 1 pm, particularly preferably 0.5 fm to 50 fm.

[0052] In an advantageous development of the optical device according to the invention, the optical element may comprise a substrate element on which the optical surface is arranged.

[0053] In order to obtain particularly good shaping and guidance of the wavefront, it is advantageous if the optical surface is arranged or formed on a substrate element, and if the at least one actuator deforms the substrate element by applying its force, thereby also deforming the optical surface. Such an indirect action on the optical surface is advantageous in that, if the optical surface has a complex structure, it is protected from direct application of the actuator force, since it is applied through the substrate element.

[0054] Furthermore, the strain gauge device may include an optical capture device, e.g., a camera, that captures strain on the substrate element and / or optical surfaces based on, e.g., changes in the contour and / or optical properties, particularly on the backside of the substrate element. In such embodiments, the strain gauge device and the substrate element are mechanically decoupled, but the transfer of information regarding the strain state of the substrate element is obtained in different ways.

[0055] Furthermore, it is contemplated that fiber Bragg gratings can be fabricated such that changes in strain and / or temperature lead to changes in the reflected and / or transmitted fiber interference spectra.

[0056] The fiber Bragg grating may also be configured to measure temperature changes and / or temperatures in at least one measurement region.

[0057] As a result, temperature can be advantageously measured using strain gauge devices and / or fiber Bragg gratings.

[0058] In an advantageous development of the optical device according to the invention, the at least one actuator can be connected to the substrate element by means of a connection layer, which preferably comprises an adhesive.

[0059] In particular, it is intended that the optical surface may be formed on the substrate element, for example by coating and / or structuring.

[0060] To ensure the transmission of force between the at least one actuator and the substrate element, they can be connected to each other by a connecting layer. This is advantageous because the at least one actuator and the substrate element can be manufactured separately from each other and only need to be joined during the assembly of the optical device. The connecting layer connecting the at least one actuator to the substrate element is preferably made of or includes an adhesive. In this case, the use of an adhesive can increase flexibility during the assembly of the optical device.

[0061] Preferably, the at least one actuator may be located on the rear side opposite the optical surface.

[0062] In an advantageous development of the optical arrangement according to the invention, the strain gauge device can be arranged at least partially in the substrate element, preferably in a groove in the substrate element.

[0063] In this case, an embodiment of the optical arrangement in which the strain gauge device is arranged completely in the substrate element, preferably completely in a groove in the substrate element, is particularly advantageous.

[0064] When the strain gauge device includes a fiber Bragg grating, it is particularly advantageous if the fiber Bragg grating is located on the substrate element.

[0065] Locating the strain gauge device in a groove in the substrate element is advantageous because forming the groove, e.g., by cutting and / or milling, provides a suitable mounting space for the strain gauge device, which is particularly true when the strain gauge device includes an optical fiber and / or a fiber Bragg grating.

[0066] In terms of installation space, optical fibers are particularly suited to being fitted into grooves.

[0067] Furthermore, arranging the strain gauge device, and in this case especially the optical fiber and / or fiber Bragg grating, in the groove allows for a particularly strong mechanical coupling to the strains and / or distortions of the body in which the groove is formed. Therefore, if distortions and / or distortions occur in the substrate element in the above-mentioned cases, this strain can be particularly well transferred to the strain gauge device if the strain gauge device is embedded in the substrate element or arranged in the groove. As a result, the strains of the substrate element can be precisely mapped by the strain gauge device, which is particularly advantageous from a metrological point of view.

[0068] Locating the strain gauge device on the substrate element is further advantageous because the strain of the substrate element can be measured by the strain gauge device, and because the optical surface is located on the substrate element, and more particularly is directly mechanically coupled to the substrate element, the strain of the substrate element further allows for particularly meaningful predictions regarding the deformation of the optical surface.

[0069] By way of example, it is understood that the optical surface may be formed by a coating and / or structuring disposed on a substrate element, which in this regard may refer to an applied coating formed from a material different from the material of the substrate element and / or a structuring or coating formed from the material of the substrate element itself.

[0070] In such cases, the optical surface is physically connected directly and throughout to the substrate element, so that distortion of the substrate element, which may in particular be in the form of a single piece, directly leads to deformation of the optical surface, which is directly determined by distortions and distortions of the substrate element according to the laws of solid state physics.

[0071] In an advantageous development of the optical arrangement according to the invention, the strain gauge device can be arranged at least partially in the at least one actuator, preferably in a groove of the at least one actuator.

[0072] In this case, an embodiment of the optical arrangement in which the strain gauge device is arranged completely in the at least one actuator, preferably completely in the groove of the at least one actuator, is particularly advantageous.

[0073] Arranging a strain gauge device on the at least one actuator is advantageous as in this way the strain and deflection of the at least one actuator can be measured by the strain gauge device.

[0074] If the distortion of the at least one actuator is measured, it is advantageous to be able to determine the magnitude and / or type of force application by the at least one actuator that actually leads to a deformation of the optical surface.

[0075] A further advantage of disposing the strain gauge device on the at least one actuator is that such disposing can be performed during the manufacture of the at least one actuator, and thus the strain gauge device can be formed without the need for manipulation of substrate elements that may impair, for example, the mechanical and / or optical properties of the optical surface.

[0076] In an advantageous development of the optical arrangement according to the invention, the strain gauge device can be at least partially arranged, preferably inserted, in the connection layer.

[0077] In this case, embodiments of the optical arrangement in which the strain gauge device is completely arranged, preferably completely inserted, in the connection layer are particularly preferred.

[0078] Arranging the strain gauge device at least partially on the connection layer is advantageous because, firstly, the strain and distortion of both the at least one actuator and the substrate element can be measured by the strain gauge device, and secondly, no modification of the at least one actuator and / or the substrate element is required to arrange the strain gauge device.

[0079] Arranging the strain gauge device in the connection layer is particularly advantageous if the strain gauge device can be inserted, preferably completely, into the connection layer. For example, this is the case when the strain gauge device includes an optical fiber with a fiber Bragg grating and the connection layer is made of adhesive. In this case, the optical fiber with the fiber Bragg grating can be inserted into the connection layer and preferably encapsulated by the adhesive so that the formation of the connection layer by the adhesive is not impaired by the optical fiber of the strain gauge device.

[0080] In this case, it is particularly advantageous for the strain gauge device to be arranged on the connection layer in such a way that the strain gauge device can be mechanically coupled to the at least one actuator and / or substrate element, for example, if the strain gauge device is formed by adhesive, this can be made possible by the adhesive also adhesively bonding the optical fiber of the strain gauge device, thereby creating a mechanical coupling between the strain gauge device, the connection layer, the substrate element and the at least one actuator.

[0081] In particular, it is contemplated that portions of the strain gauge device may be disposed on the substrate element, at least one actuator, and at least one connection layer.

[0082] In an advantageous development of the optical device according to the invention, it is provided that the at least one fiber Bragg grating can also be arranged at least partially in the effective area of at least one of the at least one actuator.

[0083] In the context of the present invention, the effective area of the at least one actuator is understood to mean the area of the optical arrangement in which the strains caused by the at least one actuator can be measured with sufficient accuracy by means of a strain gauge device.

[0084] Preferably, each actuator may have a single, preferably path-related, effective area, and in particular the effective areas of adjacent actuators may overlap.

[0085] Positioning at least one fiber Bragg grating at least partially in at least one active area of at least one actuator is advantageous because strain induced by the at least one actuator can induce a change in the grating period of the fiber Bragg grating, thereby causing a change in the fiber interference spectrum that can provide information about the type and magnitude of the strain.

[0086] In particular, by arranging it in the effective area of at least one actuator, the strain determined by the fiber Bragg grating can be traced back to the actual effect of at least one actuator. In this case, it is particularly advantageous if the effective areas of several actuators are separable from one another. As a result, from the strain determined by the fiber Bragg grating, direct conclusions can be drawn about the effect of the actuator having an effective area in which at least one fiber Bragg grating is arranged.

[0087] Alternatively or additionally, the fiber Bragg grating may extend over the effective area of multiple actuators. As a result, the measured strain is composed of the effects of multiple actuators. For example, the actuators may be grouped as a result, which may result in cost savings, for example, by using only one fiber Bragg grating for multiple actuators.

[0088] Furthermore, at least one fiber Bragg grating may extend across the active area of the plurality of actuators, and strain in each active area may lead to a change in a different respective feature of the fiber interference spectrum of the fiber Bragg grating.

[0089] For example, the effective area of at least one actuator may include a portion of the backplane of the optical device. Therefore, at least one fiber Bragg grating may be disposed on the backplane of the optical device. Due to the principle of response, the strain in the backplane may be in the opposite direction to the strain in the substrate element disposed on the opposite side of the actuator. However, taking this opposite direction into account, the strain in the substrate element and / or the optical surface can be estimated from the strain in the backplane.

[0090] In an advantageous development of the optical device according to the invention, at least one fiber comprises a plurality of fiber Bragg gratings, and the fiber interference spectra of the individual fiber Bragg gratings can be designed to be distinguishable.

[0091] When at least one optical fiber contains multiple fiber Bragg gratings, by properly mounting the optical fibers, multiple effective areas can be measured by the strain gauge device using only one optical fiber. In particular, multiple effective areas of multiple actuators can be measured using only one optical fiber. In this case, it is particularly advantageous if the fiber interference spectra of the individual fiber Bragg gratings are formed so as to be distinguishable within the at least one optical fiber.

[0092] In this way, the distortion of the backreflection spectral range and / or the spectral range of the notch in the emission spectrum of an individual fiber Bragg grating, and therefore of an individual active area, can be distinguished from the distortion of other active areas of other fiber Bragg gratings in an optical fiber. As a result, multiple active areas can be monitored simultaneously while evaluating only one reflection and / or transmission spectrum.

[0093] Furthermore, the fiber Bragg gratings may be arranged in different spatial directions on the optical device, in particular on the substrate element and / or the connecting layer and / or at least one actuator, with respect to their extent, so that the distortions in the different spatial directions can be distinguished from one another.

[0094] The mutually distinguishable fiber interference spectra can be separated from each other by 1 nm to 100 nm, preferably 1 nm to 10 nm, and particularly preferably 3 nm to 5 nm.

[0095] In an advantageous development of the optical arrangement according to the invention, at least one spectrometer device can be provided for determining and / or characterizing the fiber interference spectrum.

[0096] One or more fiber interference spectra can be examined completely or partially by a spectrometer device.

[0097] In particular, the spectrometer device may be configured to determine and / or analyze reflected radiation within the fiber bandwidth of the fiber Bragg grating and / or transmitted fiber spectra having notches within the fiber bandwidth of the fiber Bragg grating. Thus, the spectrometer device need not be configured to resolve the complete fiber interference spectrum in its full spectral width, but rather the spectrometer device may be limited to determine and / or characterize particularly characteristic regions of the fiber interference spectrum.

[0098] In an advantageous development of the optical arrangement according to the invention, the at least one spectrometer device is configured to measure the frequency shift directly and / or may comprise a Mach-Zehnder interferometer.

[0099] Direct measurement of the frequency or wavelength shift of the reflected radiation and / or the notch in the transmitted radiation spectrum is advantageous as it allows a particularly fast and reliable analysis of the fiber interference spectrum by restricting it to such relevant parts of the spectrum.

[0100] If at least one spectrometer device comprises a Mach-Zehnder interferometer, the fiber interference spectrum can be measured and analyzed over its entire spectral width, and as a result, many properties of the fiber interference spectrum can be advantageously taken into account.

[0101] In an advantageous development of the optical device according to the invention, the optical fiber comprises a plurality of fiber Bragg gratings, extends in the form of a loop and can pass through the effective area of a plurality of actuators.

[0102] As a result of the optical fiber being extended in a loop, multiple active areas of multiple actuators can be recorded by a single optical fiber if the optical fiber is sized and configured so that a fiber Bragg grating is located in most of the active area, preferably in each active area. As a result of the loop, the optical fiber can individually address each active area of the measurement target without crossing.

[0103] Furthermore, multiple fiber Bragg gratings may be arranged in the same active area of the actuator, where the fiber Bragg gratings may, for example, be oriented differently and / or be arranged in different areas of the active area, resulting in particularly advantageous, accurate measurement of strain in the active area in three dimensions.

[0104] Alternatively, the optical fiber may have only one fiber Bragg grating, extend in a loop, and pass through the active area of multiple actuators.

[0105] In an advantageous development of the optical device according to the invention, at least one optical fiber is guided in a serpentine manner through the columns and / or rows of the plurality of active areas; and / or At least one fiber Bragg grating may be positioned in each of the multiple active areas.

[0106] The actuators and the associated effective areas can be arranged in a matrix, i.e., in particular in a grid, in the optical device, which firstly allows for an advantageous systematic application of forces by the actuators and secondly results in simplification of the production and thus cost savings.

[0107] In such a situation, it is particularly advantageous for at least one optical fiber to be guided in a serpentine manner through the rows and columns of the active areas. As a result of the serpentine extension, it is particularly advantageous to guide the optical fiber in the above-mentioned loop. In particular, in this regard, it is preferred that a fiber Bragg grating can be located in the active areas, preferably in most of the active areas, preferably in each active area.

[0108] In this case, fiber Bragg gratings are disposed in the individual active areas that are distorted or distorted by the respective assigned actuators. Between the active areas, optical fiber extends without fiber Bragg gratings disposed in these areas. This is advantageous in that, when the active areas are distorted, the optical fiber extending between the active areas can be cut or dimensioned to a length that allows the distortion of the active areas to be compensated for by the fiber profile length and can be used to advantageously maintain the beam-guiding qualities of the optical fiber. Thus, the individual active areas that are subject to distortion and the fiber Bragg gratings disposed therein or thereon are interconnected with play by the optical fiber, rather than being rigidly interconnected.

[0109] There may be a single optical fiber per row and / or column assigned to each row or column.

[0110] Preferably, at least one fiber Bragg grating may be disposed in each active area.

[0111] Furthermore, each actuator may only have one effective area.

[0112] In an advantageous development of the optical device according to the invention, a back plate is provided, and at least one actuator can be arranged between the back plate and the substrate element.

[0113] Embodiments of the optical device having a backplate as described are advantageous because the actuators can be actuated axially, and in particular because a support for distorting the optical surface and / or substrate elements is present in the form of the backplate. As a result, advantageously precise and predictable control or deformation of the optical surface can be achieved, since the overall profile of all actuators more or less directly defines the deformation of the optical surface.

[0114] Furthermore, the presence of the backplane allows for a particularly simple assembly of the optical device in a higher-level optical installation, in particular in a lithography system, such as a projection exposure apparatus.

[0115] Alternatively or additionally, the at least one actuator may be connected directly to the optical surface and / or substrate element without a backplane. In this case, an actuator with a preferably lateral effect may be used to cause a distortion or distortion of the substrate element and / or the optical surface. The advantage is that the optical device occupies smaller dimensions as a result of the absence of a backplane and can therefore be mounted in a space-saving manner.

[0116] In an advantageous development of the optical device according to the invention, the optical surfaces can be designed to be light-reflective, preferably EUV- and / or DUV-reflective.

[0117] If the surface is light reflective, especially EUV light reflective, the use of the optical device as a deformable mirror is possible.

[0118] The optical element is preferably a mirror, in particular a mirror of a projection exposure apparatus.

[0119] Alternatively or additionally, the optical surface may be designed as part of a transparent and deformable lens element.

[0120] Furthermore, the optical element may be a lens element, in particular a lens element of a DUV projection exposure apparatus.

[0121] The invention further relates to a method for setting a target deformation of an optical surface according to claim 16.

[0122] In a method for setting a target deformation of an optical surface of an optical element of a lithography system by means of one or more actuators, the actual deformation of the optical surface is determined by determining at least one actual distortion of at least one measurement area.

[0123] Within the scope of the present invention, measurement area is understood to mean an area of the optical device in which the real distortion, in particular the change in the real distortion relative to the original distortion, can be measured with sufficient accuracy.

[0124] In the present invention, it is preferred that each actuator has an effective area, and that the measurement area is assigned to the effective area of the actuator.

[0125] It is particularly advantageous if at least one measurement area is within at least one effective area of at least one actuator.

[0126] The method according to the invention is advantageous because the actual deformation of the optical surface is determined by a measurement method, in particular by determining the actual distortion of the measurement area, which makes it possible to avoid a prior modeling of the actual deformation of the optical surface from the effect of at least one actuator, which is particularly susceptible to model errors.

[0127] In particular, the target deformation is set by a closed control loop and the actual strain can serve as a feedback signal for driving and / or controlling the at least one actuator, so that the control loop can be particularly precisely adapted to the force application by the at least one actuator.

[0128] An embodiment of the method for determining the temperature of a measurement area may be advantageous.

[0129] In an advantageous development of the method according to the invention, the at least one measurement area can be selected in such a way that the actual deformation of the optical surface can be deduced from the actual distortion.

[0130] It is particularly advantageous if at least one measurement area is selected such that the real distortion determined in the measurement area indicates a real deformation of a physically present optical surface.

[0131] In particular, this can be made possible by the optical surface and the measurement area being mechanically coupled to one another in accordance with the laws of solid state physics and / or material mechanics, so that at least an approximate bijection between the real deformation of the optical surface and the real distortion of the measurement area is obtained.

[0132] In particular, the actual distortion of at least one measurement area may indicate only the actual deformation of a partial area of the optical surface, and in such a case, to obtain insight into the actual deformation of the entire optical surface, multiple measurement areas may be provided and multiple actual distortion determinations may be performed, for example, to determine the desired actual deformation of the entire optical surface.

[0133] However, in addition to the mechanical coupling of at least one measurement area, it is also possible to provide, for example, a thermal coupling, so that if heat transfer between the optical surface and the measurement area can be used for information exchange, the temperature-induced deformation of the optical surface can be deduced from the temperature-induced distortion of the measurement area.

[0134] In an advantageous development of the method according to the invention, the strain gauge device comprising at least one optical fiber with at least one fiber Bragg grating can be arranged in such a way that at least one fiber interference spectrum in at least one of the fiber Bragg gratings of the at least one optical fiber is influenced by the real strain in at least one measurement region.

[0135] If the strain gauge device comprises an optical fiber with at least one fiber Bragg grating, it is advantageous if the optical fiber and / or the fiber Bragg grating is arranged in or on the at least one measurement region such that the fiber interference spectrum of the fiber Bragg grating is affected by the strain in the at least one measurement region, in particular by the actual strain in the at least one measurement region.

[0136] The fiber interference spectrum of a fiber Bragg grating is crucially affected by the spatial physical properties of the fiber Bragg grating, and therefore by its geometry. The fiber interference spectrum can be affected by strain and / or compression of the portion of the optical fiber forming the fiber Bragg grating. This is particularly true when a mechanical coupling between at least one measurement region and the portion of the optical fiber forming the fiber Bragg grating is achieved.

[0137] In particular, at least one fiber Bragg grating can be placed in the measurement region to measure the actual strain, so that the measurement region is mechanically decoupled from the fiber Bragg grating or the fiber Bragg grating is not subjected to mechanical strain in the measurement region. For this purpose, it may be advantageous to have no mechanical coupling between the fiber Bragg grating and the measurement region. As a result, changes in the measured fiber interference spectrum are affected only by the inherent strain due to the temperature of the fiber Bragg grating. As a result, the temperature of the measurement region can be estimated.

[0138] This allows many high precision sensors to be integrated into the optical device with a small number of waveguides, especially with a small number of optical fibers and a small number of fiber Bragg gratings.

[0139] In an advantageous development of the method according to the invention, it is provided that the measurement radiation can be coupled into an optical fiber.

[0140] The coupled-in measurement radiation may be in broadband or narrowband form.

[0141] The use of broadband measurement radiation is advantageous because it allows the reflected fiber bandwidth and / or notch to be measured over a wide spectral range.

[0142] This allows the measurement of a large number of fiber interference spectra and / or the measurement of large spectral shifts in the fiber interference spectrum and / or characteristic regions of the fiber interference spectrum.

[0143] The measurement radiation is formed by a radiation source with a large bandwidth, and said measurement radiation can be introduced into a waveguide, in particular an optical fiber. If a fiber Bragg grating is also provided, only a very limited spectral bandwidth of the measurement radiation around the central wavelength or Bragg wavelength is reflected from the fiber Bragg grating. The remaining components of the measurement radiation continue to pass at least substantially unattenuated through the waveguide or optical fiber to the next fiber Bragg grating.

[0144] The fiber interference spectrum is preferably obtained by scanning irradiating the fiber Bragg with narrow-band measurement radiation, in particular laser radiation, having only a narrow wavelength range; and preferably sweeping or scanning a broad wavelength band as a result of varying the relative spectral position of a narrow wavelength band over time, e.g., by a tunable laser; and measuring the intensity of the transmitted and / or reflected radiation in a time-resolved manner, for example by means of a photodiode, synchronously with the change in wavelength range; and Determining a fiber interference spectrum, preferably over a broad wavelength band, by comparing the detected intensity of the measured radiation at different times with the wavelength of the measured radiation. It can be detected by

[0145] Such a scanning method for determining the fiber interference spectrum is particularly robust and accurate.

[0146] In particular, the fiber Bragg grating has a symmetrical design so that measurement radiation at or near the central wavelength or Bragg wavelength can be reflected, regardless of the side on which the measurement radiation is incident on the fiber Bragg grating.

[0147] Fiber bandwidth center wavelength or Bragg wavelength λ B is the period of the microstructure of the fiber Bragg grating, in particular the grating period Λ, and the refractive index of the waveguide core, in particular the fiber core, n ef Equation (2) is essentially defined as the Bragg wavelength λ B The location of the grating period Λ and the refractive index n ef Link to.

[0148]

number

[0149] Bragg wavelength λ B The strain dependence of is given by the Bragg wavelength λ according to equation (3). B In equation (3), k represents the sensitivity of the strain gauge device, and Δε represents the strain of the actuator.

[0150]

number

[0151] It is therefore possible to generate a sensor signal relating to the distortion of an optical surface or element, and thus to determine the actual physically present deformation of the optical surface, in particular of a mirror.

[0152] Furthermore, errors during application of, for example, optical devices can be detected.

[0153] By way of example, the in-coupling of the measurement radiation into the optical fiber can be achieved by means of a fiber coupler and / or a lens.

[0154] In an advantageous development of the method according to the invention, the fiber interference spectrum of at least one fiber Bragg grating of the strain gauge device can be determined.

[0155] By reading out the fiber interference spectrum, changes in the geometry of the at least one fiber Bragg grating can be measured with high precision from a metrological point of view. Generally, since the spectrum can be determined particularly reliably by interferometry, a particularly precise and accurate determination of the geometry of the at least one fiber Bragg grating is possible, and thus a particularly very precise determination of the actual strain in the at least one measurement area is possible.

[0156] By way of example, the fiber interference spectrum can be determined and / or analyzed using direct methods to determine frequency shift and / or interferometric methods, for example, using a Mach-Zehnder interferometer.

[0157] The measuring radiation used within the scope of the present invention may have a wavelength of 100 nm to 10,000 nm, preferably 300 nm to 3,000 nm, particularly preferably 1,500 nm to 1,600 nm.

[0158] The at least one fiber interference spectrum may have a wavelength between 100 nm and 10,000 nm, preferably between 300 nm and 3,000 nm, and particularly preferably between 1,500 nm and 1,600 nm.

[0159] In an advantageous development of the method according to the invention, the actual deformation of the optical surface can be determined in the lithography system and / or during reflection of radiation by the optical surface.

[0160] Since optical surfaces, especially in the case of deformable mirrors, have to meet specific requirements regarding accurate realization of surface shapes in lithography systems, the method is particularly advantageous if used to monitor actual deformations of optical surfaces in lithography systems.

[0161] It is particularly advantageous, especially in lithography systems, if the actual deformation of an optical surface is determined by the method during the operation of the mirror formed by the optical surface. The optical surface is subjected to high energy deposition during the reflection of radiation, in particular EUV radiation, which occurs in practice, thus increasing the risk of uncontrolled predicted distortions. Therefore, controlling the actual deformation of the optical surface is particularly advantageous in order to collectively fulfill the objective of guiding and shaping the reflected light when reflected by the optical surface during its operation.

[0162] In an advantageous development of the method according to the invention ,light The actual strain can be determined at one or more measurement areas in at least one substrate element in which the optical surface is arranged, preferably in a groove of the substrate element.

[0163] Determining the actual distortion at the substrate element on which the optical surface is arranged is advantageous since a particularly strong mechanical bond is formed between the substrate element and the optical surface, especially when the optical surface is embodied in the form of a coating and / or structuring of the underlying substrate element.

[0164] It is particularly advantageous here if the actual strain is determined in one or more measurement areas, which are preferably arranged in grooves in the substrate element. This results in a particularly strong mechanical connection between the substrate element and the measurement area, and thus, for example, the fiber Bragg grating. Thus, a strong mechanical connection is obtained between the fiber Bragg grating, the substrate element, and ultimately the optical surface.

[0165] In an advantageous development of the method according to the invention, the actual strain can be determined at one or more measuring areas on at least one actuator, preferably at a groove of the actuator.

[0166] Determining the actual strain of the at least one actuator is advantageous because it allows a direct measurement of the strain or distortion of the material of the actuator. Since the forces that lead to the deformation of the optical surface occur in the actuator itself, such an arrangement allows for particularly close direct monitoring of the force application by the at least one actuator.

[0167] It can also be said here that measurements carried out on the actuator, preferably on grooves introduced into the actuator, more particularly recessed grooves, give a particularly good indication as to the strain and distortion of the initial material of the actuator.

[0168] In an advantageous development of the method according to the invention, the actual strain can be determined in one or more measurement areas in at least one connection layer which connects the at least one actuator to the substrate element.

[0169] Determining the actual strain of the connection layer is advantageous because the at least one measurement area can be arranged particularly easily in the connection layer, especially when the connection layer is made of an adhesive material, and as a result, the measurement area can be easily formed in a newly introduced connection layer, so that the relative position of the at least one actuator and the substrate element remains virtually unchanged.

[0170] If the connection layer is further embodied as an adhesive, the adhesive can advantageously provide a mechanical bond between the at least one actuator and the measurement area and the substrate element.

[0171] In an advantageous development of the method according to the invention, the actual strain can be determined simultaneously in several measurement areas.

[0172] Advantageously, the actual deformation of the optical surface can be completely performed by synchronous determination of a plurality of actual distortions in a plurality of measurement areas.By means of a dense grid of measurement areas, the actual deformation of the optical surface is densely scanned.

[0173] The actual strain can be determined in time succession at several measurement areas, in particular the measurement areas can be read in a multiplexed manner.

[0174] In this case, it is particularly advantageous if the fiber interference spectra of fiber Bragg gratings arranged in multiple measurement areas are distinguishable from one another. As a result, synchronous determination of the fiber interference spectra and thus the actual strain is facilitated. In particular, multiple measurement areas can be monitored and controlled using a single optical fiber with multiple fiber Bragg gratings.

[0175] Furthermore, it is particularly advantageous if a shift in a number of fiber interference spectra is examined in this case, since if the mechanical coupling between the fiber Bragg grating and the measurement area is sufficient, a change in the actual strain in the measurement area will lead to a shift in the fiber interference spectrum, and the actual strain can be deduced from the shift in the fiber interference spectrum.

[0176] In particular, changes in the actual strain can lead to changes in the grating period of the fiber Bragg grating, such that the center wavelength of the fiber bandwidth of the fiber Bragg grating shifts in the spectrum proportional to the actual strain, resulting in, for example, a shift in the fiber bandwidth of the reflected light and / or the fiber bandwidth of the notch in the transmitted measurement radiation spectrum.

[0177] The frequency shift when strain occurs due to the intended use of the at least one actuator may be between 1 pm and 1 nm, preferably between 5 pm and 500 pm, particularly preferably between 20 pm and 100 pm.

[0178] The strain resolution in the measurement region can be 1 am to 1 nm, preferably 5 am to 1 pm, and particularly preferably 0.5 fm to 50 fm.

[0179] In an advantageous development of the method according to the invention, at least one optical fiber can be guided in a loop, preferably in a serpentine manner, through the columns and / or rows of the plurality of measurement areas, and / or at least one fiber Bragg grating can be arranged in each of the plurality of measurement areas.

[0180] If at least one optical fiber is guided in a serpentine manner through a matrix of multiple measurement areas, it is possible to control or monitor a large number of measurement areas, and therefore effective areas, using only a single optical fiber. Furthermore, arranging multiple measurement areas in a matrix allows for the control of optical surfaces, for example, in the form of a square lattice, which can lead to particularly advantageous systematic control of the realization of the optical surface.

[0181] If at least one fiber Bragg grating is located in each of several measurement regions, rather than just one, it is possible to control or monitor several measurement regions simultaneously. In particular, guiding the optical fiber in this way by embodying fiber Bragg gratings in various regions of the optical fiber allows defining the measurement regions in which the actual strain is to be determined already during the manufacture of the optical fiber.

[0182] Furthermore, guiding the optical fiber to the various measurement regions allows for an offset between the individual measurement regions and loose guiding of the optical fiber to avoid pinching of the fiber as a result of the offset of the measurement regions.

[0183] In particular, the at least one measurement area in the above embodiments of the method may correspond to at least one effective area of at least one actuator.

[0184] This is advantageous because the effective area of the actuator is particularly important for ascertaining the effect of a force application by at least one actuator, as the area in which the force application of the actuator leads at least indirectly to a change in the actual deformation of the optical surface.

[0185] For example, if the actual deformation is to be determined in a particular region of the optical surface, it is particularly advantageous if the actual distortion is measured in a region where the effect of the actuators on deforming the examined region of the optical surface can be measured.

[0186] Malfunctions of the optical device shall be determined based on the determined actual distortion and / or the determined actual deformation. If there is a malfunction during use of the optical device of the lithography system, the current process of the lithography system shall be terminated and / or an error shall be transmitted to a subsequent processing step, as the case may be. Furthermore, machine personnel shall be notified for analysis of the problem.

[0187] The invention further relates to a lithography system having the features set forth in claim 27.

[0188] A lithography system according to the invention, in particular a projection exposure apparatus for semiconductor lithography, comprises an illumination system with a radiation source and an optical unit comprising at least one optical element. According to the invention, at least one optical device according to the invention is provided, at least one of the optical elements being an optical element of an optical device according to the invention and / or at least one of the optical elements comprising an optical surface that can be deformed by the method according to the invention.

[0189] In this context, deformability is understood to mean the adjustability of the actual deformation of the optical surface.

[0190] The lithography system according to the invention is advantageous because the optical elements or optical surfaces used therein have particularly precisely controlled optical surfaces or shapes, as a result of which particularly reliable imaging can be achieved with the lithography system according to the invention, which leads to particularly good production results.

[0191] Advantageously, the features described in relation to one of the subject matters of the present invention, in particular those provided by the optical device according to the invention, the method according to the invention or the lithography system according to the invention, can also be implemented in the other subject matters of the present invention, and likewise, advantages indicated in relation to one of the subject matters of the present invention can also be realized in relation to the other subject matters of the present invention.

[0192] Furthermore, it should be noted that the use of terms such as "comprises," "has," or "includes" does not exclude other features or steps. Furthermore, the use of terms such as "a(n)" or "the" indicating a single step or feature does not exclude a plurality of features or steps and vice versa.

[0193] However, in a pure embodiment of the invention, the features introduced into the invention using the terms "comprises," "has," or "includes" may be an exhaustive list. Thus, one or more lists of features may be considered to be fully within the scope of the invention, for example, when considered separately for each claim. For example, the invention may consist only of the features recited in claim 1.

[0194] The use of designations such as "first" or "second" is primarily used to distinguish between features of each apparatus or method and is not intended to imply that the features are necessarily interrelated or related to one another.

[0195] Exemplary embodiments of the invention are explained in more detail below with reference to the drawings.

[0196] Each figure shows a preferred exemplary embodiment showing individual features of the present invention in combination with one another, and features of an exemplary embodiment can be implemented independently of other features of the same exemplary embodiment, or can be readily combined by those skilled in the art to form advantageous combinations and subcombinations with features of other exemplary embodiments, as appropriate.

[0197] In the figures, functionally identical elements are provided with the same reference numerals. [Brief explanation of the drawings]

[0198] [Figure 1] A meridian section of an EUV projection exposure tool is shown. [Figure 2] A DUV projection exposure tool is shown. [Figure 3] 1 shows a schematic diagram of the optical setup in a static state. [Figure 4] 4 shows a schematic diagram of the optical device shown in FIG. 3 in a deflected state. [Figure 5] 10 shows a schematic diagram of yet another possible embodiment of the optical device in a stationary state. [Figure 6] 6 shows a schematic diagram of the embodiment shown in FIG. 5 in a deflected state. [Figure 7] 1 shows a schematic diagram of possible strain profiles of the electrostrictive effect at different temperatures. [Figure 8] 1 shows a schematic diagram of possible profiles of thermal expansion of an electrostrictive actuator. [Figure 9] 1 shows a schematic diagram of a possible drift curve of an electrostrictive actuator. [Figure 10] 3 shows a schematic diagram of yet another possible embodiment of the optical device according to the invention; [Figure 11] 3 shows a schematic diagram of yet another possible embodiment of the optical device according to the invention; [Figure 12] 3 shows a schematic diagram of yet another possible embodiment of the optical device according to the invention; [Figure 13] 3 shows a schematic diagram of yet another possible embodiment of the optical device according to the invention; [Figure 14] 1 shows a schematic diagram of a fiber interference spectrum. DETAILED DESCRIPTION OF THE INVENTION

[0199] 1, the essential components of a microlithography EUV projection exposure apparatus 100 as an example of a lithography system are exemplarily described below. The description of the basic structure of the EUV projection exposure apparatus 100 and its components should not be construed as limiting here.

[0200] In addition to the radiation source 102, the illumination system 101 of the EUV projection exposure apparatus 100 also comprises an illumination optical unit 103 for illuminating an object field 104 in an object plane 105. Here, a reticle 106 arranged in the object field 104 is exposed. The reticle 106 is held by a reticle holder 107. The reticle holder 107 is displaceable, in particular in the scanning direction, by a reticle displacement drive 108.

[0201] To aid in illustration, Figure 1 shows a Cartesian xyz coordinate system. The x direction extends perpendicular to the plane of the figure. The y direction extends horizontally, and the z direction extends vertically. In Figure 1, the scanning direction extends in the y direction. The z direction extends perpendicular to the object plane 105.

[0202] The EUV projection exposure apparatus 100 comprises a projection optical unit 109. The projection optical unit 109 serves to image the object field 104 into an image field 110 in an image plane 111. The image plane 111 extends parallel to the object plane 105. Alternatively, an angle other than 0° between the object plane 105 and the image plane 111 is also possible.

[0203] Structures on the reticle 106 are imaged onto a photosensitive layer of a wafer 112, which is arranged in the region of an image field 110 of an image plane 111. The wafer 112 is held by a wafer holder 113. The wafer holder 113 is displaceable, in particular in the y-direction, by a wafer displacement drive 114. The displacement of the reticle 106 by the reticle displacement drive 108 on the one hand and the displacement of the wafer 112 by the wafer displacement drive 114 on the other hand can be performed synchronously with respect to one another.

[0204] The radiation source 102 is an EUV radiation source. The radiation source 102 in particular emits EUV radiation 115, also referred to below as working radiation or illumination radiation. In particular, the working radiation 115 has a wavelength in the range of 5 nm to 30 nm. The radiation source 102 may be a plasma source, for example an LPP source ("laser produced plasma") or a GDPP source ("gas discharge plasma"). It may also be a synchrotron-based radiation source. The radiation source 102 may be a free electron laser (FEL).

[0205] The illumination radiation 115 leaving the radiation source 102 is focused by the collector 116. The collector 116 may be a collector with one or more ellipsoidal and / or hyperbolic reflecting surfaces. The illumination radiation 115 may be incident on at least one reflecting surface of the collector 116 at grazing incidence (GI), i.e., at an angle of incidence greater than 45°, or at normal incidence (NI), i.e., at an angle of incidence smaller than 45°. The collector 116 may be structured and / or coated firstly to optimize its reflectivity for the used radiation 115 and secondly to suppress extraneous light.

[0206] Downstream of the collector 116, the illumination radiation 115 propagates through an intermediate focus in an intermediate focal plane 117. The intermediate focal plane 117 may represent the separation between the source module comprising the radiation source 102 and the collector 116 and the illumination optics unit 103.

[0207] The illumination optical unit 103 comprises a deflection mirror 118 and a first facet mirror 119 arranged downstream thereof in the beam path. The deflection mirror 118 may be a plane deflection mirror or a mirror with a beam-influencing effect beyond a pure deflection effect. Alternatively or additionally, the deflection mirror 118 may be in the form of a spectral filter that separates the used optical wavelength of the illumination radiation 115 from extraneous light of wavelengths deviating therefrom. If the first facet mirror 119 is arranged in a plane of the illumination optical unit 103 that is optically conjugate with the object plane 105 as the field plane, it is also referred to as a field facet mirror. The first facet mirror 119 comprises a plurality of individual first facets 120, also referred to as field facets in the following. Only some of these first facets 120 are shown exemplarily in FIG. 1 .

[0208] The first facet 120 may be in the form of a macroscopic facet, in particular a rectangular facet, or a facet with an arcuate or part-circular peripheral contour. The first facet 120 may be in the form of a planar facet, or a convexly or concavely curved facet.

[0209] The first facet 120 itself can also consist of a number of individual mirrors, in particular a number of micromirrors, as is known, for example, from DE 10 2008 009 600. The first facet mirror 119 can in particular be formed as a microelectromechanical system (MEMS system). See DE 10 2008 009 600 for further details.

[0210] Illumination radiation 115 travels horizontally, ie in the y-direction, between collector 116 and deflection mirror 118 .

[0211] A second facet mirror 121 is arranged downstream of the first facet mirror 119 in the beam path of the illumination optical unit 103. If the second facet mirror 121 is arranged in the pupil plane of the illumination optical unit 103, it is also referred to as a pupil facet mirror. The second facet mirror 121 can also be arranged away from the pupil plane of the illumination optical unit 103. In this case, the combination of the first facet mirror 119 and the second facet mirror 121 is also referred to as a specular reflector. Specular reflectors are known from US Patent Application Publication No. 2006 / 0132747, EP 1 614 008 and US 6,573,978.

[0212] The second facet mirror 121 includes a plurality of second facets 122. In the case of a pupil facet mirror, the second facets 122 are also referred to as pupil facets.

[0213] The second facet 122 may likewise be a macroscopic facet, which may have, for example, a circular, rectangular or hexagonal boundary, or may be a facet made up of a micromirror. In this respect, reference is also made to DE 10 2008 009 600 A1.

[0214] The second facet 122 may have a planar reflective surface or a convexly or concavely curved reflective surface.

[0215] The illumination optical unit 103 results in a dual facet system, this basic principle also being called a fly's eye integrator.

[0216] It may be advantageous not to position the second facet mirror 121 exactly in a plane that is optically conjugate with the pupil plane of the projection optical unit 109 .

[0217] The individual first facets 120 are imaged into the object field 104 using a second facet mirror 121. The second facet mirror 121 is the last beam-shaping mirror in the beam path upstream of the object field 104 or indeed the final mirror for the illumination radiation 115.

[0218] In yet another embodiment (not shown) of the illumination optical unit 103, a transfer optical unit, which in particular contributes to the imaging of the first facet 120 into the object field 104, can be arranged in the beam path between the second facet mirror 121 and the object field 104. The transfer optical unit can have exactly one mirror or two or more mirrors arranged one behind the other in the beam path of the illumination optical unit 103. In particular, the transfer optical unit can include 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).

[0219] In the embodiment shown in FIG. 1, the illumination optical unit 103 comprises exactly three mirrors downstream of the collector 116 , in particular a deflection mirror 118 , a field facet mirror 119 and a pupil facet mirror 121 .

[0220] In yet another embodiment of the illumination optical unit 103, the deflection mirror 118 can also be omitted, so that the illumination optical unit 103 then has exactly two mirrors downstream of the collector 116, specifically a first facet mirror 119 and a second facet mirror 121.

[0221] The imaging of the first facet 120 onto the object plane 105 by the second facet 122 or by means of the second facet 122 and the transfer optical unit is usually only an approximate imaging.

[0222] The projection optical unit 109 comprises a number of mirrors Mi, which are numbered according to their position in the beam path of the EUV projection exposure apparatus 100 .

[0223] 1, the projection optical unit 109 includes six mirrors M1 to M6. Four, eight, ten, twelve or any other number of mirrors Mi are equally possible. The penultimate mirror M5 and the final mirror M6 each have an aperture for the illumination radiation 115 to pass through. The projection optical unit 109 is a double-shielded optical unit. The projection optical unit 109 has an image-side numerical aperture that is greater than 0.5, may be greater than 0.6, and may be, for example, 0.7 or 0.75.

[0224] The reflective surface of the mirror Mi can be in the form of a freeform surface without an axis of rotational symmetry. Alternatively, the reflective surface of the mirror Mi can be designed as an aspheric surface, in which case the reflective surface shape has exactly one axis of rotational symmetry. Like the mirrors of the illumination optical unit 103, the mirror Mi can have a coating that is highly reflective with respect to the illumination radiation 115. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0225] Projection optical unit 109 has a large object-image offset in the y direction between the y coordinate of the center of object field 104 and the y coordinate of the center of image field 110. In the y direction, this object-image offset may be approximately the same size as the z distance between object plane 105 and image plane 111.

[0226] The projection optical unit 109 may have an anamorphic form in particular. In particular, it has different imaging scales βx, βy in the x- and y-directions. The two imaging scales βx, βy of the projection optical unit 109 are preferably (βx, βy)=(+ / -0.25, + / -0.125). A positive imaging scale β means imaging without image inversion. A negative sign for the imaging scale β means imaging with image inversion.

[0227] The projection optical unit 109 results in a size reduction in the x-direction, ie perpendicular to the scanning direction, by a ratio of 4:1.

[0228] The projection optical unit 109 reduces the size by 8:1 in the y-direction, ie the scanning direction.

[0229] Other imaging scales are possible as well, including imaging scales of the same sign and magnitude in the x and y directions, for example 0.125 or 0.25.

[0230] The number of intermediate image planes in the x and y directions in the beam path between the object field 104 and the image field 110 may be the same or may differ depending on the embodiment of the projection optical unit 109. An example of a projection optical unit with a different number of such intermediate images in the x and y directions is known from US Patent Application Publication No. 2018 / 0074303.

[0231] Each pupil facet 122 is assigned to exactly one of the field facets 120 to form a respective illumination channel that illuminates the object field 104. This makes it possible in particular to obtain illumination according to the Köhler principle. The far field is decomposed into a plurality of object fields 104 by means of the field facets 120. The field facets 120 generate a plurality of images of intermediate foci on the respectively assigned pupil facets 122.

[0232] By means of the respectively assigned pupil facets 122, the field facets 120 are imaged onto the reticle 106 in an overlapping manner in order to illuminate the object field 104. The illumination of the object field 104 is in particular as uniform as possible. Its uniformity error is preferably less than 2%. By overlapping the different illumination channels, field uniformity can be obtained.

[0233] The illumination of the entrance pupil of the projection optical unit 109 can be geometrically defined by the arrangement of the pupil facets. By selecting the illumination channels, and in particular the subset of pupil facets, that direct light, the intensity distribution at the entrance pupil of the projection optical unit 109 can be set. This intensity distribution is also referred to as the illumination setting.

[0234] A similarly favorable pupil uniformity in the region of a defined illuminated portion of the illumination pupil of the illumination optical unit 103 can be achieved by redistribution of the illumination channels.

[0235] Further aspects and details of the illumination of the object field 104, in particular the entrance pupil of the projection optical unit 109, are described below.

[0236] The projection optical unit 109 may in particular have a concentric entrance pupil. It may be accessible. It may also be inaccessible.

[0237] The entrance pupil of the projection optical unit 109 cannot usually be illuminated exactly by the pupil facet mirror 121. In the case of imaging by the projection optical unit 109, which telecentrically images the center of the pupil facet mirror 121 onto the wafer 112, the aperture rays often do not intersect at a single point. However, it is possible to find a surface where the distance determined by the pair of aperture rays is minimal. This surface represents the entrance pupil or a real space surface conjugate to it. In particular, this surface has a finite curvature.

[0238] The projection optical unit 109 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 transfer optical unit, should be provided between the second facet mirror 121 and the reticle 106. This optical component can be used to take into account the difference in the relative positions of the tangential and sagittal entrance pupils.

[0239] 1, the pupil facet mirror 121 is arranged in a plane conjugate with the entrance pupil of the projection optical unit 109. The first field facet mirror 119 is arranged at an angle relative to the object plane 105. The first facet mirror 119 is arranged at an angle relative to the plane of arrangement defined by the deflection mirror 118.

[0240] The first facet mirror 119 is disposed so as to be inclined with respect to the disposition plane defined by the second facet mirror 121 .

[0241] 2 shows an exemplary DUV projection exposure apparatus 200. The DUV projection exposure apparatus 200 comprises an illumination system 201, a device known as a reticle stage 202 that houses and precisely positions a reticle 203 that determines the subsequent structures on a wafer 204, a wafer holder 205 that holds, moves and precisely positions the wafer 204, and an imaging device, in particular a projection optical unit 206, that has a number of optical elements, in particular lens elements 207, which are held by mounts 208 in a lens housing 209 of the projection optical unit 206.

[0242] Alternatively or in addition to the illustrated lens element 207, various refractive, diffractive and / or reflective optical elements may also be provided, including mirrors, prisms, end plates, and the like, among others.

[0243] The basic functional principle of the DUV projection exposure tool 200 is that structures introduced on a reticle 203 are imaged onto a wafer 204 .

[0244] Illumination system 201 provides a projection beam 210 in the form of electromagnetic radiation required for imaging reticle 203 onto wafer 204. The source used for this radiation can be a laser, a plasma source, etc. The radiation is shaped in illumination system 201 by optical elements so that projection beam 210 has desired properties in terms of diameter, polarization, wavefront shape, etc. upon incidence on reticle 203.

[0245] An image of the reticle 203 is produced by the projection beam 210 and transferred in a suitable reduced form from the projection optical unit 206 onto the wafer 204. In this case, the reticle 203 and the wafer 204 can be moved synchronously so that each area of the reticle 203 is imaged onto a corresponding area of the wafer 204 virtually successively during a so-called scanning operation.

[0246] The air gap between the final lens element 207 and the wafer 204 can optionally be replaced with a liquid medium having a refractive index greater than 1.0. The liquid medium can be, for example, high-purity water. This configuration, also known as immersion lithography, provides high photolithographic resolution.

[0247] The use of the present invention is not limited to use in the projection exposure apparatus 100, 200, nor to a projection exposure apparatus having the specifically described configuration. The present invention is suitable for any lithography system, in particular a projection exposure apparatus having the described structure. The present invention is also suitable for EUV projection exposure apparatuses having smaller image-side numerical apertures than those described with reference to FIG. 1 and without the shielded mirror(s) M5 and / or M6. In particular, the present invention is also suitable for EUV projection exposure apparatuses having an image-side numerical aperture of 0.25-0.5, preferably 0.3-0.4, particularly preferably 0.33. The present invention and the following exemplary embodiments should not be understood as being limited to a particular design. The following figures illustrate the present invention very diagrammatically and by way of example only.

[0248] FIG. 3 shows a schematic diagram of the optical device 1.

[0249] The optical device 1 shown in the exemplary embodiment for a lithography system, in particular for a projection exposure apparatus 100, 200, comprises at least one optical element 2 with an optical surface 3 and a number of actuators 4 for deforming the optical surface 3. Furthermore, a strain gauge device 5 is provided or present for determining the deformation of the optical surface 3.

[0250] In one embodiment (not shown), there may be only one actuator 4 that deforms the optical surface 3. In this case, it is advantageous if the single actuator 4 is able to deform the optical surface 3 in all spatial directions, if possible.

[0251] The strain gauge device 5 includes at least one optical fiber 6 .

[0252] In this case, the optical fiber 6 is of the polarization maintaining type.

[0253] Furthermore, in the exemplary embodiment shown in FIG. 3, at least one optical fiber 6 of the optical device 1 includes a plurality of fiber Bragg gratings 7 having respective fiber interference spectra 8 (see FIG. 14).

[0254] 3, the optical element 2 comprises a substrate element 9 on which the optical surface 3 is disposed or formed. Furthermore, the actuator 4 is connected to the substrate element 9 by a connecting layer 10.

[0255] 3, the connecting layer 10 comprises an adhesive. In other embodiments, the connecting layer 10 can be formed from other materials.

[0256] In the exemplary embodiment shown in FIG. 3, the strain gauge device 5 is further at least partially disposed on the connection layer 10 .

[0257] In particular, in the exemplary embodiment shown in FIG. 3, the strain gauge device 5 is inserted into the connection layer 10 .

[0258] Furthermore, FIG. 3 shows an embodiment of the optical device 1 in which at least one fiber Bragg grating 7 is at least partially disposed in at least one active area 11 of the actuator 4 .

[0259] The fiber Bragg gratings 7 are preferably assigned to several, preferably most, particularly preferably all, of the active areas 11. In this case, each actuator 4 preferably forms an active area 11 dedicated to deforming or shaping the optical surface 3 of the optical element 2.

[0260] In the exemplary embodiment of the optical device 1 shown in Figure 3, a back plate 12 is preferably present. In this case, the actuators 4 are preferably located between the back plate 12 and the substrate element 9. In the exemplary embodiment shown in Figure 3, the back plate 12 allows support for the actuators 4 that move perpendicularly (orthogonally) to the optical surface 3.

[0261] The optical fiber 6 preferably includes a plurality of fiber Bragg gratings 7, the fiber interference spectra 8 of which (see FIG. 14) are preferably formed to be distinguishable.

[0262] In particular, in the illustrated exemplary embodiment, the fiber Bragg gratings 7 have different grating periods.

[0263] FIG. 3 also shows an embodiment of the optical apparatus 1 in which at least one spectrometer device 14 is present for determining and characterizing one or more fiber interference spectra 8 .

[0264] Furthermore, in the exemplary embodiment shown in Fig. 3, a closed-loop control device 14a is present, which is configured to set the target deformation by means of a closed control loop. In this case, the actual strain serves as a feedback signal for driving and / or controlling the at least one actuator 4. As a result, the control loop can be particularly precisely adapted to the force application by the at least one actuator 4. The actuation correction is indicated by a dashed line in Fig. 3.

[0265] The spectrometer device 14 is preferably configured to measure the direct frequency shift in the fiber interference spectrum 8. Alternatively or additionally, the spectrometer device 14 may include a Mach-Zehnder interferometer.

[0266] Furthermore, in the optical device 1 shown in FIG. 3, the optical surface 3 has a light-reflective, in particular EUV-light-reflective, embodiment.

[0267] In an alternative embodiment, the optical surface 3 may have a DUV light reflective embodiment.

[0268] 4 shows a schematic diagram of the optical device 1. In the embodiment shown, the optical surface 3 is deformed by the effect of an actuator 4. The actuator 4 is supported relative to a back plate 12 and operates in a direction extending substantially parallel to the surface normal of the optical surface 3.

[0269] As a result of the effect of the actuator 4, a strain is induced in the substrate element 9, which can be measured, for example, by a strain gauge device 5 (not shown in FIG. 4).

[0270] FIG. 5 shows a simplified schematic diagram of the optical device 1 , omitting the back plate 12 and with the actuator 4 having a direction of movement that extends at least approximately parallel to the optical surface 3 .

[0271] FIG. 6 shows the optical device 1 of FIG. 5 in a deflected state.

[0272] Figures 3 to 6 therefore show different systems for actuating a deformable optical surface 3, in particular a mirror surface, and Figures 3 and 4 therefore show actuation perpendicular (orthogonal) to the optical surface 3, while Figures 5 and 6 show actuation parallel to the optical surface 3.

[0273] 3 and 4, a plurality of actuators 4 can apply compressive forces to the optical element 2, thereby precisely deforming or shaping it. In the exemplary embodiment shown in Figures 5 and 6, distortion and / or contraction of the actuators 4 can introduce bending moments into the optical element 2 and / or optical surface 3, which can lead to deformation of the optical element and / or optical surface.

[0274] FIG. 7 shows a schematic diagram of different strain curves of the actuator 4.

[0275] The strain in the actuator 4 and / or the strain in the effective area 11 of the actuator 4 is shown on the longitudinal strain axis 15 .

[0276] In Figure 7, the field strength of the applied field is shown on the horizontal axis 16. The graph in Figure 7 shows four strain curves corresponding to different temperatures of the actuator 4. All four strain curves exhibit hysteresis.

[0277] In this case, the strain curve with the lowest profile corresponds to the highest temperature, and the strain curve with the highest profile corresponds to the lowest temperature of the actuator 4 .

[0278] The strain curve of the actuator 4 shown in Figure 7 reproduces the behavior of the actuator 4 according to equation (1). The hysteresis of the actuator 4 is evident here, and is of the order of <1% in the example shown.

[0279] Figure 8 shows a schematic diagram of the strain curve of actuator 4 under temperature changes. The strain axis 15 again represents the strain of actuator 4, and the horizontal axis 16 represents the temperature of actuator 4. The hysteresis of the strain curve as it is subjected to temperature cycling is evident.

[0280] The elongation of the actuator 4 in the case of a temperature change relative to room temperature, which is placed at the origin of the graph shown in Figure 8, is determined inter alia by the coefficient of thermal expansion CTE (see equation (1)). Thermal hysteresis of the strain is evident in the strain curve shown in Figure 8. In this case, the effect of hysteresis may not be reproducible.

[0281] 9 shows a schematic diagram of a drift curve for actuator 4. Strain axis 15 represents the strain of actuator 4, and horizontal axis 16 represents the passage of time. Actuator 4 is at an initial position, or origin, i.e., has an initial strain at the start of the time measurement, and receives a signal, preferably in the form of an applied voltage, to move to a target position, i.e., target strain. Over time, actuator 4 approaches or drifts toward the target position or target strain.

[0282] Furthermore, the drift shown in FIG. 9 may vary depending on the step height of the actuator 4.

[0283] FIG. 10 shows a schematic cross-sectional view of a possible embodiment of the optical device 1.

[0284] In this case, the optical fiber 6 includes a plurality of fiber Bragg gratings 7 , extends in a loop, and passes through the effective areas 11 of the plurality of actuators 4 .

[0285] 10, the optical fiber 6 is guided in a serpentine manner through a row of the active areas 11. In alternative exemplary embodiments, at least one optical fiber 6 may alternatively or additionally be guided in a serpentine manner through a column of the active areas 11.

[0286] In the exemplary embodiment shown in FIG. 10, a plurality of optical fibers 6 may be provided that extend in a serpentine manner.

[0287] Alternatively or additionally, in the exemplary embodiment shown in FIG. 10, a plurality of optical fibers 6 may be provided, each assigned to a column or row.

[0288] Furthermore, in the exemplary embodiment shown in FIG. 10, at least one optical fiber 6 is disposed in each of the multiple active areas 11 .

[0289] 11 shows a schematic diagram of yet another possible embodiment of the optical apparatus 1, in which the strain gauge device 5 is at least partially, preferably completely, arranged in the substrate element 9. In particular, in the illustrated exemplary embodiment, the strain gauge device 5 is arranged in the groove 17b.

[0290] The strain gauge device 5 may also be located on both the substrate element 9 and the connection layer 10 .

[0291] 11 shows a cross section of an actuator 10 and a substrate element 9 with a connecting layer 10. In the exemplary embodiment shown in FIG. 11, the actuator 4 extends on a connecting layer 10 that connects the actuator 4 and the substrate element 9.

[0292] In the exemplary embodiment shown in FIG. 11, the grooves 17b are preferably milled into the substrate element 9.

[0293] FIG. 12 shows yet another schematic view of an embodiment of the optical arrangement 1 in which the strain gauge device 5 is at least partially, preferably completely, arranged, in particular inserted, in the connection layer 10 .

[0294] FIG. 13 shows a schematic diagram of an embodiment of the optical apparatus 1, in which the strain gauge device 5 is at least partially arranged in at least one actuator 4, in particular in the groove 17a.

[0295] The strain gauge device 5 may also be arranged on both the at least one actuator 4 and the connection layer 10 .

[0296] The strain gauge device 5 may be disposed on both the substrate element 9 and the at least one actuator 4 .

[0297] The strain gauge device 5 may also be disposed on the substrate element 9 , the connection layer 10 and the at least one actuator 4 .

[0298] In the exemplary embodiment shown in FIG. 13, grooves 17 a are preferably milled into the actuator 4 .

[0299] The features described in the exemplary embodiment of Figures 3 to 13 can also be implemented in other exemplary embodiments, in particular using multiple optical fibers arranged in the optical element 2 as described with reference to Figures 11 and / or 12 and / or 13.

[0300] The exemplary embodiment of the optical device 1 shown in Figures 3 to 13 is also particularly suitable for carrying out a method for setting a target deformation of an optical surface 3 of an optical element 2 of a lithography system 100, 200 by means of one or more actuators 4. In this method, the actual deformation of the optical surface 3 is determined by determining at least one actual distortion of at least one measurement area 18. Furthermore, the at least one measurement area 18 is selected in such a way that the actual deformation of the optical surface 3 can be deduced from the actual distortion.

[0301] In an exemplary embodiment, the measurement area 18 is preferably selected so that a measurement area 18 is assigned to each effective area 11, at least to each effective area 11 to be measured or observed, and each measurement area 18 is preferably located or formed within the effective area 11.

[0302] Furthermore, to carry out this method, the strain gauge device 5 is preferably positioned such that the fiber interference spectrum 8 in the fiber Bragg grating 7 of the optical fiber 6 is affected by the actual strain in at least one measurement region 18 .

[0303] Furthermore, in order to carry out the method, broadband measurement radiation 19 is coupled into the optical fiber 6. That is to say, the method according to the invention preferably comprises the coupling of broadband measurement radiation 19.

[0304] The fiber interference spectrum 8 of the fiber Bragg grating 7 of the strain gauge device 5 can be determined using the measurement radiation.

[0305] Alternatively or additionally, narrowband measurement radiation 19 is coupled into the optical fiber 6 so that the fiber interference spectrum 8 can be determined by sweeping or scanning a sufficiently wide wavelength band in a scanning manner.

[0306] Furthermore, preferably, the actual deformation of the optical surface 3 is determined in the lithography systems 100, 200 shown in FIGS. 1 and 2 during reflection by the optical surface 3 of the operating radiation of the projection exposure apparatus 100, 200.

[0307] The embodiment of the optical device 1 shown in Figure 11 is particularly suitable for carrying out an embodiment of the method for determining the actual distortion of a plurality of measurement areas 18 in the substrate element 9 underlying the optical surface 3 at the groove 17b.

[0308] The exemplary embodiment of the optical device 1 shown in FIG. 12 is particularly well suited for carrying out an embodiment of a method for determining the actual strain of a plurality of measurement areas 18 in a connection layer 10 connecting the actuator 4 to a substrate element 9.

[0309] The exemplary embodiment of the optical device 1 shown in FIG. 13 is particularly well suited for carrying out an embodiment of the method for determining the actual strain of a plurality of measurement areas 18 on the actuator 4 in the grooves 17a.

[0310] Furthermore, the method preferably provides that the actual strains of the multiple measurement areas 18 are determined synchronously and / or in rapid succession in time.

[0311] 10 is particularly well suited for carrying out an embodiment of the method in which an optical fiber 6 is guided in a serpentine manner through a row of a plurality of measurement regions 18. Furthermore, in this embodiment, at least one fiber Bragg grating 7 is preferably arranged in each of the plurality of measurement regions 18.

[0312] Alternatively or additionally, the at least one optical fiber 6 may be guided in a serpentine manner through the row of measurement areas 18 .

[0313] Figure 14 shows a schematic diagram of a fiber interference spectrum 8. Wavelength is shown on the horizontal axis 16. The measured spectrum 8 of the back-reflected measurement radiation 19 is shown using a solid line on the intensity axis 20. The input spectrum of the illuminated measurement radiation 19 is shown using a dashed line. [Explanation of symbols]

[0314] 1 Optical device 2. Optical Elements 3 Optical surface 4 Actuators 5 Strain Gauge Devices 6. Optical Fiber 7 Fiber Bragg Grating 8 Fiber interference spectrum 9 Substrate elements 10 Connectivity Layer 11 Effective Area 12 Back plate 14 Spectrometer Devices 15 Distortion Axis 16 Horizontal axis 17a,b Groove 18 Measuring area 19 Measuring Radiation 20 Strength axis 100 EUV projection exposure equipment 101 Lighting System 102 Radiation source 103 Lighting optical unit 104 Object field of view 105 Object plane 106 Reticle 107 Reticle Holder 108 Reticle Displacement Drive 109 Projection Optical Unit 110 Image field 111 Image plane 112 wafers 113 Wafer holder 114 Wafer Displacement Drive 115 EUV / use / illumination radiation 116 Collector 117 Intermediate focal plane 118 Deflecting Mirror 119 First facet mirror / field facet mirror 120 First Facet / Field Facet 121 Second facet mirror / pupil facet mirror 122 Second Facet / Pupil Facet 200 DUV projection exposure equipment 201 Lighting 202 Reticle Stage 203 Reticle 204 wafers 205 wafer holder 206 Projection Optical Unit 207 Lens Elements 208 Mount 209 Lens Housing 210 Projection Beam Mi Mirror

Claims

1. An optical device (1) for a lithography system (100, 200) comprising at least one optical element (2) including an optical surface (3) and one or more actuators (4) for deforming said optical surface (3), 1. An optical arrangement comprising: a strain gauge device (5) for determining at least one actual strain of at least one actuator (4) in at least one measurement area (18), the strain gauge device (5) including at least one optical fiber (6), the optical fiber (6) being polarization-preserving, the strain gauge device (5) being configured to measure temperature changes and / or temperatures in the at least one measurement area (18).

2. 2. An optical device (1) according to claim 1, An optical device, characterized in that said at least one optical fiber (6) comprises one or more fiber Bragg gratings (7) with respective fiber interference spectra (8).

3. 2. An optical device (1) according to claim 1, An optical device, characterized in that the optical element (2) comprises a substrate element (9) on which the optical surface (3) is arranged.

4. 4. An optical device (1) according to claim 3, An optical device, characterized in that said at least one actuator (4) is connected to said substrate element (9) by a connecting layer (10) preferably comprising an adhesive.

5. 4. An optical device (1) according to claim 3, Optical arrangement, characterized in that the strain gauge device (5) is at least partially arranged in the substrate element (9), preferably in a groove (17b) of the substrate element (9).

6. 2. An optical device (1) according to claim 1, 10. An optical arrangement, characterized in that said strain gauge device (5) is at least partially arranged in said at least one actuator (4), preferably in a groove (17a) of said at least one actuator (4).

7. 5. An optical device (1) according to claim 4, Optical arrangement, characterized in that said strain gauge device (5) is at least partially arranged, preferably inserted, in said connection layer (10).

8. 3. An optical device (1) according to claim 2, The optical device is characterized in that the at least one optical fiber (6) includes a plurality of fiber Bragg gratings (7), and the fiber interference spectra (8) of the individual fiber Bragg gratings (7) are designed to be distinguishable.

9. 3. An optical device (1) according to claim 2, Optical arrangement, characterized in that it is provided with at least one spectrometer device (14) for determining and / or characterizing said fiber interference spectrum (8).

10. 10. An optical device (1) according to claim 9, 10. An optical arrangement, wherein the at least one spectrometer device (14) is configured to measure frequency shifts directly and / or comprises a Mach-Zehnder interferometer.

11. 4. An optical device (1) according to claim 3, An optical device comprising a back plate (12), said at least one actuator (4) being arranged between said back plate (12) and said substrate element (9).

12. 2. An optical device (1) according to claim 1, Optical device, characterized in that the optical surface (3) is designed to be light-reflective, preferably EUV-reflective and / or DUV-reflective.

13. 1. A method for setting a target deformation of an optical surface (3) of an optical element (2) of a lithography system (100, 200) by means of one or more actuators (4), comprising: determining an actual deformation of the optical surface (3) by determining at least one actual distortion of at least one of the actuators (4) in at least one measurement area (18); a strain gauge device (5) for determining an actual strain of at least one of the actuators (4) in the at least one measurement area (18), the strain gauge device (5) including at least one optical fiber (6), the optical fiber (6) being polarization-preserving, the strain gauge device (5) being configured to measure a temperature change and / or a temperature in the at least one measurement area (18).

14. 14. The method of claim 13, A method, characterized in that the at least one measurement area (18) is selected such that the actual deformation of the optical surface (3) can be deduced from the actual distortion.

15. 14. The method of claim 13, 1. A method for measuring strain in a measurement region of a fiber optic cable, comprising: a strain gauge device (5) including at least one optical fiber (6) having at least one fiber Bragg grating (7) arranged such that at least one fiber interference spectrum (8) in at least one of the fiber Bragg gratings (7) of the at least one optical fiber (6) is affected by the actual strain in the at least one measurement region (18).

16. 16. The method of claim 15, A method, characterized in that measurement radiation (19) is coupled into said optical fiber (6).

17. 16. The method of claim 15, A method, characterized in that the fiber interference spectrum (8) of the at least one fiber Bragg grating (7) of the strain gauge device (5) is determined.

18. 14. The method of claim 13, A method, characterized in that the actual deformation of the optical surface (3) is determined in the lithography system (100, 200) and / or during reflection of radiation by the optical surface (3).

19. 14. The method of claim 13, The method is characterized in that the actual distortion is determined in one or more measurement areas (18) in at least one substrate element (9) on which the optical surface (3) is arranged, preferably in a groove (17b) of said substrate element (9).

20. 14. The method of claim 13, 10. A method according to claim 9, wherein the actual strain is determined in one or more measurement areas (18) on the at least one actuator (4), preferably in a groove (17a) of said actuator (4).

21. 20. The method of claim 19, The method, characterized in that the actual strain is determined in one or more measurement areas (18) in at least one connection layer (10) connecting the at least one actuator (4) to the substrate element (9).

22. 14. The method of claim 13, The method, wherein the actual distortion is determined synchronously in a plurality of measurement regions (18).

23. A lithography system, in particular a projection exposure apparatus (100, 200) for semiconductor lithography, comprising an illumination system (101, 201) with a radiation source (102) and an optical unit (103, 109, 206) including at least one optical element (116, 118, 119, 120, 121, 122, Mi, 207), 22. A lithography system comprising at least one optical device (1) according to any one of claims 1 to 12, wherein at least one of the optical elements (116, 118, 119, 120, 121, 122, Mi, 207) is an optical element (2) of the at least one optical device (1) and / or at least one of the optical elements (116, 118, 119, 120, 121, 122, Mi, 207) comprises an optical surface (3) that can be deformed using a method according to any one of claims 13 to 22.

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