EP4348353A1

EP4348353A1 - Optical device, method for adjusting a setpoint deformation and lithography system

Info

Publication number: EP4348353A1
Application number: EP22732017.3A
Authority: EP
Inventors: Markus Raab; Stefan Troeger; Sascha Bleidistel; Thilo Pollak; Alexander Vogler; Klaus Gwosch; Andreas Koeniger; Matthias Manger
Original assignee: Carl Zeiss SMT GmbH
Current assignee: Carl Zeiss SMT GmbH
Priority date: 2021-05-27
Filing date: 2022-05-20
Publication date: 2024-04-10
Also published as: US20240085783A1; CN117377913A; DE102021205425A1; WO2022248369A1; JP2024518654A

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 a deformation of 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) maintaining polarization.

Description

Optical device, method for setting a target deformation and Lithoqrafiesvstem

The present application claims the priority of German patent application no. 10 2021 205 425.0, the content of which is incorporated herein by reference in its entirety.

The invention relates to an optical device for a lithography system, having at least one optical element having an optical surface and having one or more actuators for deforming the optical surface.

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

The invention also relates to a lithography system, in particular a projection exposure system for semiconductor lithography, having an illumination system with a radiation source and an optical system which has at least one optical element.

Optical elements for guiding and shaping radiation in projection exposure systems are known from the prior art. In the known optical elements, a surface of the optical element often guides and shapes the light waves incident on the optical element. Precise control of the shape of the surface is therefore of particular advantage in order to form an exact wavefront with the desired properties.

Lithography systems are known from the prior art which use ultraviolet radiation, in particular DUV (deep ultraviolet) and/or EUV (extreme ultraviolet) light, in order to produce microlithographic structures with the greatest precision. In this case, the light from a radiation source is directed via a number of mirrors to a wafer to be exposed. An arrangement, a position and a shape of the mirror make a decisive contribution to the quality of the exposure.

For example, in order to further increase the number of transistors on a chip, it is necessary to further develop existing lithography systems. In the general state of the art it is known to attach actuators to mirrors, which shape them with as many degrees of freedom as possible.

Various systems for actuating deformable mirrors are also described in the prior art.

It is known from the prior art to integrate optical elements in optical devices which have actuators for generating force in order to specifically shape the optical surface which interacts with the light waves. According to the prior art, an effect of the actuators on the optical surface is predicted, for example on the basis of modeling. However, influences not taken into account in the modeling can weaken the predictive power of the model.

Systems known from the prior art for the deformation of optical elements use a regulation for the deformation of the optical surface and for the setting of a target deformation. For this purpose, the deformation is detected by a sensor and sent to the actuators in a coded form as an electrical signal within a control system. In the context of lithography systems, it is not possible according to the prior art to integrate a sensor with a sufficiently high measurement performance into the lithography system or the optical element. For this reason, optical devices of this type are operated within an open control chain or in a feed-forward mode.

A disadvantage of optical devices according to the prior art is that, in order to meet the ever-increasing demands for increasing precision, it is crucial to adhere to the target deformation as precisely as possible, while the known measures for precisely setting the target deformation are insufficient.

The present invention is based on the object of creating an optical device which avoids the disadvantages of the prior art, in particular enabling precise shaping or precise setting of a target deformation of an optical surface.

According to the invention, this object is achieved by an optical device having the features specified in claim 1 .

The present invention is also based on the object of creating a method for setting a target deformation of an optical surface which avoids the disadvantages of the prior art, in particular precise and reliable shaping or precise setting of a target deformation of the optical surface allows.

This object is achieved by a method having the features specified in claim 16.

The present invention is also based on the object of creating a lithography system which avoids the disadvantages of the prior art, in particular enabling the formation of precisely shaped wavefronts of a radiation.

According to the invention, this object is achieved by a lithography system having the features specified in claim 27.

The optical device according to the invention for a lithography system, in particular a projection exposure system, comprises at least one optical element having an optical surface and a or multiple actuators for deformation of the optical surface. According to the invention, a strain gauge is provided for determining the deformation of the optical surface, wherein the strain gauge has at least one optical fiber and the optical fiber is polarization-preserving.

Within the scope of the invention, the term elongation can also be understood to mean contraction and/or compression.

Furthermore, the mechanical deformation of the optical surface serves to shape the optical surface and/or to set a target deformation.

The optical device according to the invention has the advantage that independent monitoring of an actual deformation of the optical surface is made possible by the strain measuring device provided. The optical device according to the invention thus enables a more precise and reliable deformation of the optical surface than systems according to the prior art, which do not allow the actual deformation of the optical surface to be checked. This is particularly advantageous when using the actuators for the deformation or for effecting the deformation, since their effect on the precise shaping of the optical surface is often based purely on modeling. With the optical device according to the invention, the modeling can be supplemented and/or replaced by empirical measurement of the actual deformation.

Provision can be made for the at least one actuator to be in the form of an electrostrictive actuator. An embodiment as an electrostrictive actuator has the advantage that electrostrictive actuators have a very low tendency to drift and a low tendency to hysteresis.

Provision can be made for the optics device to have a plurality of actuators for deforming the optical surface, each individual one of the plurality of actuators being controllable.

By controlling each individual actuator, it is possible to adjust profiles of the optical surface and/or the optical element, in particular a mirror, in a targeted manner and thus to correct the optical device or the lithography system in which the optical device is integrated in the best possible way.

An elongation of the actuators can be described in a first approximation by the formula (1). Here, M describes an electrostrictive coefficient, which leads to a strain S when an electric field E is applied. As can be seen from formula (1), the electrostrictive coefficient M depends on the temperature ϋ of the actuator. Furthermore, the elongation S of the actuator depends on its stiffness s and an applied mechanical stress T. Furthermore, a thermal component of the elongation results from multiplying the thermal expansion coefficient CTE with the difference between the temperature ϋ and an initial temperature ϋo. S(E, ΰ) = M ß ) E ² + s T + CTE ( ΰ - ΰ ₀ )

(1)

For high-precision and constant regulation of a position of the at least one actuator, it is advantageous if both a loss of expansion of the at least one actuator on the basis of the electrostrictive effect and the thermal expansion are corrected. For this purpose it can be provided that the at least one actuator uses more than 80% of its working distance for self-correction of thermal expansions or thermal effects.

Accordingly, it is advantageous if a highly precise positioning or deformation of the optical surface is made possible by modeling and calibrating an electrostrictive and thermal hysteresis and a drift of the actuator in addition to a temperature calibration.

To enable reflection of EUV light, highly complex coatings are often used to form the optical surface. Such coatings benefit to a particular degree from a control of the effect of the at least one actuator, since overdriving or excessive stretching of the optical surface can lead to damage and/or destruction of the complex coating arranged thereon.

It can be provided that the optical element has a continuous and/or one-piece optical surface and in particular is not a field facet mirror. As a result, the optical surface can form at least approximately a free-form surface.

It can be provided that the optics device is optimized for use in other application areas instead of for use in the lithography system. For example, the optics device can be intended for use as part of a space mirror.

It can be provided that several strain gauges are present as part of the optics device. If several strain gauges are present, it can be provided that the several strain gauges share other components of the optical device.

The use of an optical fiber as part of the strain gauge has the advantage that optical fibers can be used to guide light into different positions of the optical device for measurement purposes. From these positions, the light can be reflected and/or passed on through the optical fiber, for example in order to measure properties of the light. Optical fibers are very reliable and precise light guides, which are also available with very small diameters. In particular when used in optical devices which have very filigree components, the use of optical fibers, which can also be of very filigree design, is of particular advantage. Strain gauge arrangements known from the prior art, which are based on impedance measurements, often require a large number of electrical conductors, which can limit the function of an optical component.

By means of a polarization-maintaining optical fiber, those influences on the deformation of the optical surface that are due to a change in temperature can be separated from one another or reduced from those influences on the deformation of the optical surface that are due to stretching and/or distortion of the optical device . This enables an even more accurate and precise control of the deformation or the precise shaping of the optical surface, since the various factors influencing the shaping of the optical surface can be addressed and/or eliminated separately.

A separation of temperature-induced influences is of particular advantage, since one of the largest disturbance variables for the deformation of the optical element can be temperature fluctuations on the optical surface, in particular when used in EUV lithography systems. In particular, the temperature of the optical surface or of the optical element can be changed between 20° C. and 40° C. during operation.

In an advantageous development of the optical device according to the invention, it can be provided that the at least one optical fiber has one or more fiber Bragg gratings with respective fiber interference spectra.

If the optical fiber has a fiber Bragg grating, then a fiber interference spectrum that is characteristic of the fiber Bragg grating results. The fiber interference spectrum is to be understood as a wavelength-dependent change in radiation propagating through the fiber.

In particular, the fiber Bragg grating has a characteristic filter bandwidth. Radiation whose wavelength lies within a spectral range determined by the filter bandwidth is reflected by the fiber Bragg grating in the optical fiber. Radiation reflected in this way propagates backwards in the optical fiber opposite to the direction of origin and can be measured, for example.

Alternatively, the fiber interference spectrum can also be determined in a transmission configuration, resulting in a transmitted radiation spectrum in which the reflected area and the filter bandwidth can be seen as a notch.

The fiber interference spectrum and in particular the filter bandwidth are dependent on the geometric properties of the fiber Bragg grating. A crucial geometric property of the fiber Bragg grating is a grating period of the fiber Bragg grating. The use of a fiber Bragg grating is particularly advantageous for use in a strain gauge, since the geometric properties of the optical fiber and thus of the fiber Bragg grating can also be changed by stretching it. With the change in the geometric properties, in particular a compression or stretching of the grating period, there is also a change in the fiber interference spectrum and thus in particular in a center wavelength of the filter bandwidth.

The center wavelength of the filter bandwidth is in this case directly proportional to the grating period multiplied by twice an effective refractive index within the fiber Bragg grating.

A spectral width of the filter bandwidth depends on a length of the fiber Bragg grating and a magnitude of a refractive index change between adjacent refractive index ranges. These parameters can also be changed, for example, by stretching or compressing the fiber Bragg grating and are therefore suitable for determining mechanical expansion of the optical fiber and/or the fiber Bragg grating.

As an alternative or in addition to an optical fiber and a fiber Bragg grating, other optical sensors can also be provided as part of the strain gauge.

In particular, other optical waveguides and other optical interference filters, in particular Bragg gratings, can be provided. For example, an alternative or additional optical interference filter can be a line grating and/or a resonator and/or a simple slit diaphragm. The alternative and/or additional waveguide can be, for example, a fixed light channel that is not designed as an optical fiber. The optical waveguide or the light channel can be configured to maintain polarization. Furthermore, a puristic waveguide in the form of a free beam can also be provided.

The use of a single-mode optical fiber as the optical fiber can be particularly advantageous since this results in a particularly clear structure of the fiber interference spectrum.

In particular, it can be provided that the fiber Bragg grating is designed as a periodic microstructure which selectively reflects wavelengths.

Provision can be made for the fiber Bragg grating to be designed in such a way, in particular to have such a grating period, that a frequency shift in the event of an elongation caused by the intended use of the at least one actuator is 1 pm to 1 nm, preferably 5 pm to 500 pm, particularly preferably 20 pm to 100 pm. Provision can be made for the strain gauge and/or the fiber Bragg grating to be designed in such a way that a strain resolution is 1 μm to 1 nm, preferably 5 μm to 1 μm, particularly preferably 0.5 fm to 50 fm.

In an advantageous development of the optical device according to the invention, it can be provided that the optical element has a substrate element on which the optical surface is arranged.

In order to achieve particularly good shaping and guidance of wave fronts, it is advantageous if the optical surface is arranged or formed on a substrate element, with the at least one actuator deforming the substrate element through the action of its force and thereby also causing a deformation of the optical surface. Such an indirect effect on the optical surface has the advantage that in the case of complex structured optical surfaces, these are protected from a direct force effect of the actuator, since this is mediated by the substrate element.

Provision can furthermore be made for the strain measuring device to have an optical detection device, for example a camera, which detects a strain in the substrate element and/or the optical surface on the basis of a change, for example an outer contour and/or optical properties, in particular on a rear side of the substrate element. detected. In such an embodiment, the strain gauge and the substrate element are mechanically decoupled, but a transfer of information about the state of strain of the substrate element is achieved in a different way.

Furthermore, it can be provided that the fiber Bragg grating is also designed in such a way that changes in strain and/or temperature changes lead to changes in the reflected and/or the transmitted fiber interference spectrum.

It can be provided that the fiber Bragg grating is also set up to detect the temperature changes and/or a temperature of at least one measurement area.

As a result, the strain gauge and/or the fiber Bragg grating can advantageously be used for detecting the temperature.

In an advantageous development of the optical device according to the invention, it can be provided that the at least one actuator is connected to the substrate element by a connecting layer, preferably having an adhesive.

In particular, it can be provided that the optical surface is formed on the substrate element, for example by a coating and/or structuring.

In order to ensure power transmission between the at least one actuator and the substrate element, these can be connected with a connecting layer. This has the advantage that the at least one actuator and the substrate element can be manufactured separately and only assembled when the optical device is created. The connecting layer, which connects the at least one actuator to the substrate element, is preferably formed from an adhesive or has an adhesive. In this case, the use of an adhesive enables great flexibility in the assembly of the optical device.

The at least one actuator can preferably be arranged on a rear side facing away from the optical surface.

In an advantageous development of the optical device according to the invention, it can be provided that the strain measuring device is arranged at least partially in the substrate element, preferably in a groove of the substrate element.

An embodiment of the optical device in which the strain gauge is arranged completely in the substrate element, preferably completely in the groove of the substrate element, is particularly advantageous here.

If the strain gauge has the fiber Bragg grating, it is of particular advantage if the fiber Bragg grating is arranged in the substrate element.

An arrangement of the strain gauge in a groove of the substrate element has the advantage that a suitable installation space for the strain gauge is created by creating the groove, for example by a cutting and/or milling process. This applies in particular if the strain gauge has the optical fiber and/or the fiber Bragg grating.

In terms of their design, optical fibers are particularly suitable for laying in a groove.

Furthermore, arranging the strain gauge and in particular an optical fiber and/or a fiber Bragg grating in the groove enables particularly strong mechanical coupling to strains and/or distortions of the body on which the groove is formed. If, in the case described above, the substrate element is distorted and/or stretched, this stretching can be transferred particularly well to the strain gauge if the strain gauge is sunk in the substrate element or arranged in a groove. As a result, an elongation of the substrate element can be precisely imaged by the elongation measuring device in a particularly advantageous manner in terms of measurement technology.

An arrangement of the strain gauge on the substrate element also has the advantage that strains of the substrate element can be detected by the strain gauge. Strains of the substrate element in turn enable a particularly high predictive power over deformations optical surface, since the optical surface is arranged on the substrate element and, in particular, is mechanically directly coupled to it.

It can be provided, for example, that the optical surface is formed by a coating and/or structuring, which is arranged on the substrate element. This can involve applied coatings, which are formed from a material that is different from the substrate element and/or structuring or coatings, which are formed by the material of the substrate element itself.

In such cases there is a direct full-area physical connection of the optical surface with the substrate element. A stretching of the substrate element, which can in particular be embodied as a monolithic body, therefore leads directly to a deformation of the optical surface, which is determined directly by the physical laws of solid bodies through the stretching and straining of the substrate element.

In an advantageous development of the optical device according to the invention, it can be provided that the strain gauge is at least partially arranged in the at least one actuator, preferably in a groove of the at least one actuator.

An embodiment of the optical device in which the strain gauge is arranged completely in the at least one actuator, preferably completely in the groove of the at least one actuator, is particularly advantageous here.

An arrangement of the strain gauge in the at least one actuator has the advantage that in this way strains and distortions of the at least one actuator can be detected by the strain gauge.

If expansions of the at least one actuator are detected, then this has the advantage that an extent and/or a type of the force effect actually leading to the deformation of the optical surface can be detected by the at least one actuator.

Another advantage of arranging the strain gauge on the at least one actuator is that such an arrangement can be made when the at least one actuator is being manufactured. The strain gauge can thus be formed without having to manipulate the substrate element, which could, for example, impair mechanical and/or optical properties of the optical surface.

In an advantageous development of the optical device according to the invention, it can be provided that the strain gauge is at least partially arranged, preferably inserted, in the connecting layer. An embodiment of the optical device in which the strain gauge is arranged completely in the connecting layer, preferably completely inserted, is particularly advantageous here.

An at least partial arrangement of the strain gauge on the connecting layer has the advantage that on the one hand the strains and distortions of both the at least one actuator and the substrate element can be detected by means of the strain gauge and on the other hand no modification to the at least one actuator for the arrangement of the strain gauge and / or the substrate element must be made.

An arrangement of the strain gauge in the connecting layer is particularly advantageous if the strain gauge can be inserted into this, preferably completely. This is the case, for example, when the strain gauge comprises an optical fiber with a fiber Bragg grating, while the connecting layer is made of an adhesive. In this case, the optical fiber with the fiber Bragg grating can be placed in the connection layer and preferably cast around with the adhesive, so that the formation of the connection layer is not impaired by the adhesive through the optical fiber of the strain gauge.

It is particularly advantageous here if the strain gauge is arranged in the connecting layer in such a way that mechanical coupling of the strain gauge to the at least one actuator and/or the substrate element is made possible. For example, this can be made possible by the fact that when the connecting layer is formed by an adhesive, the adhesive also bonds the optical fiber of the strain gauge, resulting in a mechanical coupling between the strain gauge, the connecting layer, the substrate element and the at least one actuator.

In particular, it can be provided that the strain gauge is arranged in parts both in the substrate element and in the at least one actuator as well as in the at least one connecting layer.

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

In the context of the invention, the effective range of the at least one actuator is understood to mean that range of the optical device in which a strain caused by the at least one actuator can be detected by the strain gauge with sufficient accuracy. Provision can preferably be made for each actuator to have an individual, preferably path-related, effective range, in which case effective ranges, in particular of adjacent actuators, can also overlap.

An at least partial arrangement of the at least one fiber Bragg grating in at least one effective area of the at least one actuator has the advantage that expansions, which are triggered by the at least one actuator, can trigger changes in the grating period in the fiber Bragg grating and thus can cause a change in the fiber interference spectrum, which can provide information about the type and extent of the elongation.

In particular, an arrangement in the effective area of the at least one actuator makes it possible for a strain determined by the fiber Bragg grating to be traced back to an actual effect of the at least one actuator. It is of particular advantage here if the effective areas can be separated from one another in the case of several actuators. As a result, a strain determined by the fiber Bragg grating can be used to directly infer an effect of that actuator in whose effective range the at least one fiber Bragg grating is arranged.

Alternatively or additionally, it can be provided that the fiber Bragg grating extends over the effective ranges of a plurality of actuators. As a result, the measured strain is made up of the effects of the multiple actuators. For example, actuators can be grouped in this way, which can lead to a reduction in costs, for example, since only one fiber Bragg grating is used for a number of actuators.

Provision can also be made for the at least one fiber Bragg grating to extend over the effective ranges of a number of actuators and expansion of the respective effective ranges leads to a change in each case in different characteristics of the fiber interference spectrum of the fiber Bragg grating.

The effective area of the at least one actuator can, for example, also include a section of a back plate of the optical device. Accordingly, it can be provided that the at least one fiber Bragg grating is arranged in the back plate of the optics device. Due to the reaction principle, an expansion of the back plate can be directed in the opposite direction to an expansion of the substrate element arranged on an opposite side of the actuator. Taking into account this opposite direction, however, a stretching of the substrate element and/or the optical surface can be inferred from a stretching of the back plate.

In an advantageous development of the optical device according to the invention, it can be provided that the at least one optical fiber has a plurality of fiber Bragg gratings, with the fiber interference spectra of the individual fiber Bragg gratings being designed to be distinguishable. If the at least one optical fiber has a plurality of fiber Bragg gratings, a plurality of effective ranges can be detected by the strain gauge by suitably laying the optical fiber with only one optical fiber. In particular, a plurality of effective ranges of a plurality of actuators can be detected with only one optical fiber. In this case, it is of particular advantage if the fiber interference spectra of the individual fiber Bragg gratings are designed to be distinguishable within the at least one optical fiber.

A back-reflected spectral range and/or a spectral range of the incision in the radiation spectrum of an individual fiber Bragg grating and thus an expansion of an individual effective range can thus be distinguished from the expansions of the other effective ranges of the other fiber Bragg gratings of the one optical fiber. As a result, a number of effective areas can be monitored synchronously with the evaluation of only one reflection and/or transmission spectrum.

Provision can also be made for the fiber Bragg gratings to be arranged in their extension in different spatial directions on the optical device, in particular the substrate element and/or the connecting layer and/or the at least one actuator, so that expansions in different spatial directions can be distinguished from one another are.

Provision can be made for the fiber interference spectra to be differentiated to be spectrally separated from one another by 1 nm to 100 nm, preferably 1 nm to 10 nm, particularly preferably 3 nm to 5 nm.

In an advantageous development of the optical device according to the invention, it can be provided that at least one spectrometer device is provided for determining and/or characterizing the fiber interference spectra.

The one or more fiber interference spectrums can be examined in whole or in part by means of a spectrometer device.

In particular, it can be provided that the spectrometer device is set up to determine and/or analyze reflected radiation within the fiber bandwidth of the fiber Bragg grating and/or transmitted fiber spectra with notches within the fiber bandwidth of the fiber Bragg grating. Accordingly, the spectrometer device does not have to be set up to resolve the complete fiber interference spectrum in the full spectral width, but the spectrometer device can be limited to determining and/or characterizing particularly characteristic areas of the fiber interference spectra.

In an advantageous development of the optical device according to the invention, it can be provided that the at least one spectrometer device is set up to detect a direct frequency shift and/or has a Mach-Zehnder interferometer. Direct detection of the frequency shift or wavelength shift of the reflected radiation and/or the notch in the transmitted radiation spectrum has the advantage that a particularly fast and reliable analysis of the fiber interference spectra is made possible by limiting it to such a relevant part of the spectrum.

If the at least one spectrometer device has a Mach-Zehnder interferometer, the fiber interference spectrum can be recorded and analyzed in a full spectral width. In this way, many characteristics of the fiber interference spectra can advantageously be taken into account.

In an advantageous development of the optical device according to the invention, it can be provided that the optical fiber has a plurality of fiber Bragg gratings, runs in a loop and passes through the effective ranges of a plurality of actuators.

By running the optical fiber in a loop, several effective areas of several actuators can be covered by one optical fiber, provided that the optical fiber is dimensioned and set up in such a way that a fiber Bragg grating is located in a majority, preferably in each, effective area. Due to a loop-shaped course, the effective areas to be measured can each be addressed individually without the optical fiber crossing over itself.

Furthermore, it can be provided that several fiber Bragg gratings are arranged in one and the same effective range of an actuator. In this case, the fiber Bragg gratings can be oriented differently, for example, and/or can be arranged in different areas of the effective range. As a result, an expansion of the effective range in three-dimensional space can be precisely detected in a particularly advantageous manner.

Alternatively, it can be provided that the optical fiber has only one fiber Bragg grating, runs in a loop and passes through the effective ranges of a number of actuators.

In an advantageous development of the optical device according to the invention, it can be provided that the at least one optical fiber is routed in a meandering manner through rows and/or rows of several effective areas, and/or at least one fiber Bragg grating is arranged in a plurality of the effective areas.

Provision can be made for a plurality of actuators and with them a plurality of effective areas to be arranged in rows and lines, ie in particular in a chessboard-like manner, in the optical device. On the one hand, this allows for an advantageous systematic exertion of force by the plurality of actuators, and on the other hand, production-related simplifications and thus cost savings can be achieved as a result. In such a situation, it is of particular advantage if the at least one optical fiber is routed in a meandering manner through the lines and rows of the multiple effective areas. The above-described loop-shaped guidance of the optical fiber is made possible in a particularly efficient manner by the meandering course. In particular, provision can preferably be made here for a fiber Bragg grating to be located in a plurality, preferably a majority, preferably in each effective region.

In this case, the fiber Bragg gratings are arranged in the individual effective areas, which are stretched or strained by the respectively assigned actuators. The optical fiber runs between the effective areas without a fiber Bragg grating being arranged in these areas. This has the advantage that when the effective areas are stretched, the optical fiber running between the effective areas can be cut to length or dimensioned in such a way that a distortion of the effective area can be compensated for by a contour length of the fiber and an advantageous preservation of the beam guidance qualities of the optical fiber can be used. The individual areas of action to be expanded and the fiber Bragg gratings arranged in or on them are therefore not rigid but connected to one another with play through the optical fiber.

Provision can be made for each row and/or row to have a single optical fiber assigned to the respective row or row.

Provision can preferably be made for at least one fiber Bragg grating to be arranged in each of the effective areas.

Furthermore, it can be provided that each actuator has only one effective range.

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

The described embodiment of the optical device with a back plate has the advantage that the actuators can be operated axially and, in particular, there is an abutment for expansion of the optical surface and/or the substrate element in the form of the back plate. In this way, an advantageously precise and predictable control or deformation of the optical surface can be achieved, since a contour of the entirety of the actuators defines the deformations of the optical surface almost directly.

Furthermore, the presence of a back plate enables a particularly simple installation of the optics device in a superordinate optical system, in particular a lithography system, such as a projection exposure system. Alternatively or additionally, it can be provided that the at least one actuator is connected directly to the optical surface and/or the substrate element without using a back plate. In this case, preferably transversely acting actuators can be used in order to bring about a distortion or stretching of the substrate element and/or the optical surface. One advantage of this is that the optics device takes on smaller dimensions due to the lack of a back plate and can therefore be attached in a space-saving manner.

In an advantageous development of the optical device according to the invention, it can be provided that the optical surface is light-reflecting, preferably EUV-reflecting and/or DUV-reflecting.

If the surface is designed to be light-reflecting, in particular EUV light-reflecting, this enables the optical device to be used as a deformable mirror.

The optical element is preferably a mirror, in particular a mirror of a projection exposure system.

Alternatively or additionally, it can be provided that the optical surface is transparent and designed as part of a deformable lens.

Furthermore, the optical element can be a lens, in particular a lens of a DUV projection exposure system.

The invention also relates to a method for setting a target deformation of an optical surface according to claim 16.

The method for setting a target deformation of an optical surface of an optical element for a lithography system using one or more actuators provides that an actual deformation of the optical surface is determined by determining at least one actual strain of at least one measurement area.

Within the scope of the invention, the measurement area is understood to mean that area of the optical device in which the actual strain, in particular a change in the actual strain compared to an original strain, can be measured with sufficient accuracy.

Within the scope of the invention, each actuator preferably has an effective range, with the effective range of an actuator preferably being assigned a measuring range.

It is particularly advantageous if the at least one measuring range falls within at least one effective range of the at least one actuator. The method according to the invention has the advantage that the actual deformation of the optical surface is determined by a measurement method, specifically by determining the actual expansion of the measurement area. This makes it possible to avoid prior modeling of the actual deformation of the optical surface from the effect of the at least one actuator, which is particularly susceptible to model errors.

In particular, it can be provided that the target deformation is set by a closed control circuit, with the actual elongation serving as a feedback signal for the activation and/or regulation of the at least one actuator. As a result, a control loop can be matched particularly precisely to the force effect of the at least one actuator.

An embodiment of the method in which a temperature of the measurement area is determined can be advantageous.

In an advantageous development of the method according to the invention, it can be provided that the at least one measurement area is selected in such a way that the actual deformation of the optical surface can be inferred from the actual strain.

It is particularly advantageous if the at least one measurement area is selected in such a way that the actual strain determined in the measurement area provides information about the actual actual deformation of the optical surface.

This can be made possible in particular by the fact that the optical surface and the measuring area are mechanically coupled to one another in accordance with the laws of solid state physics and/or strength of materials in such a way that an at least approximately bijective mapping of the actual deformation of the optical surface onto the actual expansion of the measuring area results.

In particular, it can be provided that the actual expansion of the at least one measurement area only provides information about the actual deformation of a partial area of the optical surface. If knowledge of the actual deformation of the entire optical surface is to be obtained in such a case, several measurement areas and the determination of several actual strains can be provided, for example, in order to determine the desired actual deformation of the entire optical surface.

In addition to a mechanical coupling of the at least one measuring area, a thermal coupling can also be provided, for example, whereby a temperature-related expansion of the measuring area can be used to infer a temperature-related deformation of the optical surface, provided that a heat transfer between the optical surface and the measuring area is used for such an exchange of information can be. In an advantageous development of the method according to the invention it can be provided that a strain measuring device, having at least one optical fiber with at least one fiber Bragg grating, is arranged in such a way that in at least one of the fiber Bragg gratings of the at least one optical fiber at least one Fiber interference spectrum is influenced by the actual strain of at least one measurement area.

If the strain gauge has an optical fiber with at least one fiber Bragg grating, it is advantageous if the optical fiber and/or the fiber Bragg grating are arranged in or on the at least one measuring area in such a way that a strain of the at least one measurement area, in particular by the actual strain of the at least one measurement area, a fiber interference spectrum of the fiber Bragg grating is influenced.

The fiber interference spectrum of a fiber Bragg grating is decisively influenced by the spatial physical properties of the fiber Bragg grating and thus by its geometry. The fiber interference spectrum can be influenced by stretching and/or compressing the section of the optical fiber that forms the fiber Bragg grating. This is particularly successful when a mechanical coupling is achieved between the at least one measurement area and the section of the optical fiber that forms the fiber Bragg grating.

In particular, it can be provided that, for measuring the actual strain, at least one fiber Bragg grating is arranged in the measurement area in such a way that the measurement area is mechanically decoupled from the fiber Bragg grating or mechanical expansion of the measurement area from the fiber Bragg grating is not experienced. For this purpose, it can be advantageous if there is no mechanical coupling between the fiber Bragg grating and the measuring area. As a result, a detected change in the fiber interference spectrum is only influenced by a temperature-induced natural expansion of the fiber Bragg grating. This allows conclusions to be drawn about a temperature in the measuring range.

This makes it possible to integrate many high-precision sensors in the optical device using fewer waveguides, in particular using fewer optical fibers and fewer fiber Bragg gratings.

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

The coupled-in measurement radiation can be broadband or narrowband

The use of broadband measuring radiation has the advantage that reflected fiber bandwidths and/or cuts can be detected in a wide spectral range. This enables a large number of fiber interference spectra to be recorded and/or large spectral shifts in the fiber interference spectra to be recorded and/or characteristic ranges of the fiber interference spectra to be recorded.

It can be provided that the measurement radiation is formed by a radiation source with a large bandwidth and is introduced into a waveguide, in particular the optical fiber. If a fiber Bragg grating is also provided, only measurement radiation with a very limited spectral width around the center wavelength or Bragg wavelength is reflected on the fiber Bragg grating. Remaining portions of the measurement radiation continue their path through the waveguide or the optical fiber at least approximately without attenuation to a next fiber Bragg grating.

Provision can be made for the fiber interference spectrum to be detected by means of a raster method, in that preferably narrow-band measurement radiation, which only has a narrow wavelength range, in particular laser radiation, is radiated onto the fiber Bragg grating and a spectral position of the narrow wavelength range over time, for example by a tunable laser, whereby a wide wavelength band is preferably scanned or scanned, and synchronously with the variation of the wavelength range an intensity of the transmitted and/or reflected measurement radiation is recorded in a time-resolved manner, for example by means of a photodiode, and by a comparison the detected intensity of the measurement radiation with the wavelength of the measurement radiation at different points in time, the fiber interference spectrum is determined in the preferably broad wavelength band.

Such a raster method for determining the fiber interference spectrum is particularly reliable and precise.

In particular, it can be provided that the fiber Bragg grating is designed symmetrically and reflects the measurement radiation in the range of the medium wavelength or Bragg wavelength, regardless of the side from which the measurement radiation hits the fiber Bragg grating.

The center wavelength of the fiber bandwidth or the Bragg wavelength AB is essentially defined by a period of the microstructure of the fiber Bragg grating, in particular the grating period L, and a refractive index n _ef of a waveguide core, in particular the fiber core. Formula (2) links a position of the Bragg wavelength AB with the grating period L and the refractive index n _ef . l _B 2n _e fA

(2) An elongation dependency of the Bragg wavelength AB can be determined by differentiating the Bragg wavelength AB according to formula (3). In formula (3), k describes a sensitivity of the strain gauge and De describes a strain of the actuator.

Accordingly, it can be made possible to generate a sensor signal relating to the expansion of the optical surface or the optical element and thus to determine an actually existing deformation of the optical surface, in particular of a mirror.

Furthermore, for example, errors can be detected during use of the optical device.

The coupling of the measurement radiation into the optical fiber can be achieved, for example, by means of a fiber coupler and/or a lens.

In an advantageous development of the method according to the invention, it can be provided that the fiber interference spectrum of the at least one fiber Bragg grating of the strain gauge is determined.

Reading out the fiber interference spectrum enables the change in the geometry of the at least one fiber Bragg grating to be recorded with high-precision measurement technology. In general, spectra can be determined particularly reliably using interference methods and therefore allow a particularly precise and accurate determination of the geometry of the at least one fiber Bragg grating and thus in particular a very precise determination of the actual strain of the at least one measurement area.

Direct methods for determining a frequency shift and/or interferometric methods, for example using a Mach-Zehnder interferometer, can be used to determine and/or analyze the fiber interference spectrum.

It can be provided that the measuring radiation used within the scope of the invention has a wavelength of 100 nm to 10000 nm, preferably 300 nm to 3000 nm, particularly preferably 1500 nm to 1600 nm.

It can be provided that the at least one fiber interference spectrum has wavelengths of 100 nm to 10000 nm, preferably 300 nm to 3000 nm, particularly preferably 1500 nm to 1600 nm. In an advantageous development of the method according to the invention, it can be provided that the actual deformation of the optical surface is determined in the lithography system and/or during a reflection of a radiation through the optical surface.

The method is particularly advantageous when it is used to monitor the actual deformation of the optical surface in a lithography system, since optical surfaces, particularly in the case of deformable mirrors, in lithography systems must meet special requirements for a precise formation of the surface shape.

It is particularly advantageous if the actual deformation of the optical surface is determined by the method during operation of such a mirror formed by the optical surface, in particular in the lithography system. During a reflection of a radiation that is actually taking place, in particular an EUV radiation, the optical surface is exposed to an increased energy deposition and thus to an increased risk of foreseen and uncontrolled expansions. In order to completely fulfill the task of guiding and shaping the reflected light during the operation of the optical surface during a reflection, it is therefore particularly advantageous to monitor the actual deformation of the optical surface.

In an advantageous development of the method according to the invention, it can be provided that the actual strain is determined in one or more measurement areas in at least one substrate element on which the optical surface of the substrate element underlying the optical surface is arranged, preferably in a groove of the substrate element.

Determining the actual strain in the substrate element on which the optical surface is arranged has the advantage that a particularly strong mechanical coupling is formed between the substrate element and the optical surface. This applies in particular when the optical surface is formed in the form of a coating and/or structuring of the underlying substrate element.

It is particularly advantageous here if the actual strain is determined in one or more measurement areas, which are preferably arranged in a groove within the substrate element. This results in a particularly strong mechanical coupling between the substrate element and the measuring area and thus, for example, the fiber Bragg grating. Thus, a strong mechanical coupling is achieved between the fiber Bragg grating, the substrate element and ultimately with the optical surface.

In an advantageous development of the method according to the invention, it can be provided that the actual strain is determined in one or more measurement areas in the at least one actuator, preferably in a groove of the actuator. Determining the actual elongation in the at least one actuator has the advantage that an elongation or strain of the material of the actuator can be detected directly. Since force is generated on the actuator itself, which force is intended to lead to a deformation of the optical surface, such an arrangement enables the effect of the force to be monitored particularly closely and directly by the at least one actuator.

Here, too, it is true that a measurement carried out in the actuator, preferably in a groove made in the actuator, in particular a countersunk groove, enables a particularly good indication of expansions and strains in the starting material of the actuator.

In an advantageous development of the method according to the invention, it can be provided that the actual strain is determined in one or more measurement areas in at least one connection layer connecting the at least one actuator to the substrate element.

The determination or determination of the actual strain in the connecting layer has the advantage that the at least one measuring area can be arranged particularly easily in the connecting layer, in particular if the connecting layer is made of an adhesive material. As a result, a relative position of the at least one actuator and the substrate element can remain almost unchanged, since the measurement area can be easily formed in the newly introduced connection layer.

Furthermore, if the connecting layer is in the form of an adhesive, the adhesive can bring about an advantageously high mechanical coupling between the at least one actuator, the measuring area and the substrate element.

In an advantageous development of the method according to the invention, it can be provided that the actual elongation is determined synchronously in a number of measurement areas.

The actual deformation of the optical surface can advantageously be carried out completely by synchronously determining a number of actual strains in a number of measurement areas. A narrow grid of measurement areas results in dense sampling of the actual deformation of the optical surface.

Provision can be made for the actual elongation to be determined in a number of measurement areas in rapid chronological order. In particular, the measurement ranges can be read out using a multiplex method.

It is of particular advantage here if the fiber interference spectra of the fiber Bragg gratings arranged in the plurality of measurement areas can be distinguished from one another. This facilitates a synchronous determination of the fiber interference spectra and thus of the actual strains. In particular, a single optical fiber with multiple fiber Bragg gratings can be used to monitor and control multiple measurement areas. Furthermore, it is of particular advantage if a shift in the multiple fiber interference spectra is examined here. If there is sufficient mechanical coupling between the fiber Bragg grating and the measurement area, a change in the actual strain of the measurement area leads to a shift in the fiber interference spectrum, as a result of which the actual strain can be inferred from the shift in the fiber interference spectrum.

In particular, a change in the actual strain can lead to a change in a grating period of the fiber Bragg grating, as a result of which the center wavelength of the fiber bandwidth of the fiber Bragg grating shifts in a proportion proportional to the actual strain in the spectrum. This shifts, for example, the fiber bandwidth of the reflected light and/or the fiber bandwidth of the notch in the transmitted measurement radiation spectrum.

Provision can be made for the frequency shift to be 1 μm to 1 nm, preferably 5 μm to 500 μm, particularly preferably 20 μm to 100 μm when the at least one actuator is used as intended.

Provision can be made for a strain resolution capacity in the measurement range to be 1 μm to 1 nm, preferably 5 μm to 1 μm, particularly preferably 0.5 fm to 50 fm.

In an advantageous development of the method according to the invention, it can be provided that the at least one optical fiber is guided in a loop, preferably meandering, through rows and/or rows of a plurality of measurement areas, and/or at least one fiber Bragg grating is arranged in a plurality of the measurement areas .

If the at least one optical fiber is routed in a meandering manner through lines and rows of a plurality of measurement areas, a large number of measurement areas and thus effective areas can be checked or monitored using just one optical fiber. Furthermore, arranging the multiple measurement areas in rows and rows allows the optical surface to be checked, for example in the form of grid squares, which can lead to a particularly advantageous systematic control of the formation of the optical surface.

If at least one fiber Bragg grating is arranged in a plurality, ie not just in one, of the measurement areas, a plurality of measurement areas can be controlled or monitored at the same time. In particular, such a guidance of the optical fiber can already be determined during production of the optical fiber by the formation of fiber Bragg gratings in different areas of the optical fiber, in which of the measuring areas an actual strain is to be determined. Furthermore, guiding the optical fiber through the different measurement areas makes it possible for offsets between the individual measurement areas to be avoided by loosely guiding the optical fiber and tightening of the fiber due to the offset of the measurement areas.

In particular, it can be provided that in the above-described embodiments of the method the at least one measuring range corresponds to at least one effective range of the at least one actuator.

This is advantageous because the effective area of the actuator, as the area where exertion of force by the actuator at least indirectly leads to a change in the actual deformation of the optical surface, is of particular interest for checking the effect of the exertion of force by the at least one actuator.

For example, if the actual deformation is to be determined in a specific area of the optical surface, it is particularly advantageous if the actual strain is recorded in that area in which an effect of the actuator deforming the area of the optical surface to be examined can be recorded.

Provision can be made for a malfunction of the optical device to be determined on the basis of the determined actual strain and/or the determined actual deformation. If necessary, provision can be made for a current process of the lithography system to be aborted and/or for the error to be passed on to subsequent process steps if there is a malfunction when the optical device is used in a lithography system. Provision can also be made for a person responsible for the machine to be notified in order to analyze the problem.

The invention also relates to a lithography system having the features specified in claim 27 .

The lithography system according to the invention, in particular a projection exposure system for semiconductor lithography, has an illumination system with a radiation source and an optical system, which has at least one optical element. According to the invention, at least one optical device according to the invention is provided, with at least one of the optical elements being an optical element of the optical device according to the invention and/or at least one of the optical elements having an optical surface which can be deformed using a method according to the invention.

In this context, deformability is to be understood as the adjustability of the actual deformation of the optical surface.

The lithography system according to the invention has the advantage that the optical elements or optical surfaces used in it have a particularly precisely controlled optical surface or shape exhibit. As a result, particularly reliable imaging can be achieved with the lithography system according to the invention, which leads to particularly good production results.

Features that have been described in connection with one of the objects of the invention, specifically given 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 advantageously implemented for the other objects of the invention. Likewise, advantages that were mentioned in connection with one of the objects of the invention can also be understood in relation to the other objects of the invention.

In addition, it should be pointed out that terms such as "comprising", "having" or "with" do not exclude any other features or steps. Furthermore, terms such as "a" or "that" which indicate a singular number of steps or features do not exclude a plurality of features or steps - and vice versa.

In a puristic embodiment of the invention, however, it can also be provided that the features introduced in the invention with the terms “comprising”, “having” or “with” are listed exhaustively. Accordingly, one or more listings of features may be considered complete within the scope of the invention, e.g. considered for each claim. The invention can consist exclusively of the features mentioned in claim 1, for example.

It should be mentioned that designations such as "first" or "second" etc. are primarily used for reasons of distinguishing between respective device or method features and are not necessarily intended to indicate that features are mutually dependent or related to one another.

Exemplary embodiments of the invention are described in more detail below with reference to the drawing.

The figures each show preferred exemplary embodiments in which individual features of the present invention are shown in combination with one another. Features of an exemplary embodiment can also be implemented separately from the other features of the same exemplary embodiment and can accordingly easily be combined with features of other exemplary embodiments by a person skilled in the art to form further meaningful combinations and sub-combinations.

Elements with the same function are provided with the same reference symbols in the figures.

Show it:

FIG. 1 shows an EUV projection exposure system in meridional section;

FIG. 2 shows a DUV projection exposure system; FIG. 3 shows a schematic representation of an optical device in an idle state;

Figure 4 is a schematic representation of an optical device according to Figure 3 in a deflected

Condition;

FIG. 5 shows a schematic representation of a further possible embodiment of the optical device in an idle state;

Figure 6 is a schematic representation of an embodiment of Figure 5 in a deflected

Condition;

FIG. 7 shows a schematic representation of possible expansion curves of an electrostrictive effect at different temperatures;

FIG. 8 shows a schematic representation of a possible course of a thermal expansion of an electrostrictive actuator;

FIG. 9 shows a schematic representation of a possible drift curve of an electrostrictive actuator;

FIG. 10 shows a schematic representation of a further possible embodiment of the optical device according to the invention;

FIG. 11 shows a schematic representation of a further possible embodiment of the optical device according to the invention;

FIG. 12 shows a schematic representation of a further possible embodiment of the optical device according to the invention;

FIG. 13 shows a schematic representation of a further possible embodiment of the optical device according to the invention; and

Figure 14 is a schematic representation of a fiber interference spectrum.

The essential components of an EUV projection exposure system 100 for microlithography are described below as an example of a lithography system, initially with reference to FIG. The description of the basic structure of the EUV projection exposure system 100 and its components should not be understood as limiting here. In addition to a radiation source 102 , an illumination system 101 of the EUV projection exposure system 100 has illumination optics 103 for illuminating an object field 104 in an object plane 105 . In this case, 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 can be displaced via a reticle displacement drive 108, in particular in a scanning direction.

A Cartesian xyz coordinate system is shown in FIG. 1 for explanation. The x-direction runs perpendicularly into the plane of the drawing. The y-direction is horizontal and the z-direction is vertical. In FIG. 1, the scanning direction runs along the y-direction. The z-direction runs perpendicular to the object plane 105.

The EUV projection exposure system 100 includes projection optics 109. The projection optics 109 are used to image the object field 104 in an image field 110 in an image plane 111. The image plane 111 runs parallel to the object plane 105. Alternatively, there is also an angle other than 0° between the object plane 105 and the image plane 111 is possible.

A structure on the reticle 106 is imaged onto a light-sensitive layer of a wafer 112 arranged in the region of the image field 110 in the image plane 111. The wafer 112 is held by a wafer holder 113. The wafer holder 113 can be displaced via a wafer displacement drive 114, in particular along the y-direction. The displacement of the reticle 106 via the reticle displacement drive 108 on the one hand and the wafer 112 on the other hand via the wafer displacement drive 114 can be synchronized with one another.

The radiation source 102 is an EUV radiation source. The radiation source 102 emits in particular EUV radiation 115, which is also referred to below as useful radiation or illumination radiation. The useful radiation 115 has, in particular, a wavelength in the range between 5 nm and 30 nm a DPP ("Gas Discharged Produced Plasma") source. It can also be a synchrotron-based radiation source. The radiation source 102 can be a free-electron laser (FEL).

The illumination radiation 115 emanating from the radiation source 102 is bundled by a collector 116 . The collector 116 can be a collector with one or more ellipsoidal and/or hyperboloidal reflection surfaces. The at least one reflection surface of the collector 116 can in grazing incidence ("Grazing Incidence", Gl), i.e. with angles of incidence greater than 45°, or in normal incidence ("Normal Incidence", NI), i.e. with angles of incidence smaller than 45°, with of the illumination radiation 115 are applied. The collector 116 can be structured and/or coated on the one hand to optimize its reflectivity for the useful radiation 115 and on the other hand to suppress stray light. After the collector 116, the illumination radiation 115 propagates through an intermediate focus in an intermediate focal plane 117. The intermediate focal plane 117 can represent a separation between a radiation source module, comprising the radiation source 102 and the collector 116, and the illumination optics 103.

The illumination optics 103 includes a deflection mirror 118 and a first facet mirror 119 downstream of this in the beam path. The deflection mirror 118 can be a planar deflection mirror or alternatively a mirror with an effect that influences the bundle beyond the pure deflection effect. Alternatively or additionally, the deflection mirror 118 can be designed as a spectral filter, which separates a useful light wavelength of the illumination radiation 115 from stray light of a different wavelength. If the first facet mirror 119 is arranged in a plane of the illumination optics 103 which is optically conjugate to the object plane 105 as a field plane, it is also referred to as a field facet mirror. The first facet mirror 119 includes a multiplicity of individual first facets 120, which are also referred to below as field facets. A few of these facets 120 are shown in FIG. 1 only by way of example.

The first facets 120 can be embodied as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or part-circular edge contour. The first facets 120 can be embodied as planar facets or alternatively as convexly or concavely curved facets.

As is known, for example, from DE 10 2008 009 600 A1, the first facets 120 themselves can each also be composed of a multiplicity of individual mirrors, in particular a multiplicity of micromirrors. The first facet mirror 119 can be embodied in particular as a microelectromechanical system (MEMS system). Reference is made to DE 10 2008 009 600 A1 for details.

The illumination radiation 115 runs horizontally between the collector 116 and the deflection mirror 118, ie along the y-direction.

A second facet mirror 121 is arranged downstream of the first facet mirror 119 in the beam path of the illumination optics 103. If the second facet mirror 121 is arranged in a pupil plane of the illumination optics 103, it is also referred to as a pupil facet mirror. The second facet mirror 121 can also be arranged at a distance from a pupil plane of the illumination optics 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 2006/0132747 A1, EP 1 614 008 B1 and US Pat. No. 6,573,978.

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. The second facets 122 can also be macroscopic facets, which can have round, rectangular or hexagonal borders, for example, or alternatively facets composed of micromirrors. In this regard, reference is also made to DE 10 2008 009 600 A1.

The second facets 122 can have plane or alternatively convexly or concavely curved reflection surfaces.

The illumination optics 103 thus forms a double-faceted system. This basic principle is also called "Fly's Eye Integrator".

It can be advantageous not to arrange the second facet mirror 121 exactly in a plane which is optically conjugate to a pupil plane of the projection optics 109 .

The individual first facets 120 are imaged in the object field 104 with the aid of the second facet mirror 121 . The second facet mirror 121 is the last beam-forming mirror or actually the last mirror for the illumination radiation 115 in the beam path in front of the object field 104.

In a further embodiment of the illumination optics 103 that is not shown, transmission optics can be arranged in the beam path between the second facet mirror 121 and the object field 104 , which particularly contribute to the imaging of the first facets 120 in the object field 104 . The transmission optics can have exactly one mirror, but alternatively also have two or more mirrors, which are arranged one behind the other in the beam path of the illumination optics 103 . The transmission optics can in particular comprise one or two mirrors for normal incidence (NI mirror, "normal incidence" mirror) and/or one or two mirrors for grazing incidence (GI mirror, "gracing incidence" mirror).

In the embodiment shown in FIG. 1, the illumination optics 103 has exactly three mirrors after the collector 116, namely the deflection mirror 118, the field facet mirror 119 and the pupil facet mirror 121.

In a further embodiment of the illumination optics 103, the deflection mirror 118 can also be omitted, so that the illumination optics 103 can then have exactly two mirrors downstream of the collector 116, namely the first facet mirror 119 and the second facet mirror 121.

The imaging of the first facets 120 by means of the second facets 122 or with the second facets 122 and transmission optics in the object plane 105 is generally only an approximate imaging. The projection optics 109 includes a plurality of mirrors Mi, which are numbered consecutively according to their arrangement in the beam path of the EUV projection exposure system 100 .

In the example shown in FIG. 1, the projection optics 109 include six mirrors M1 to M6. Alternatives with four, eight, ten, twelve or another number of mirrors Mi are also possible. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 115. The projection optics 109 are doubly obscured optics. The projection optics 109 has an image-side numerical aperture which is greater than 0.5 and which can also be greater than 0.6 and which can be 0.7 or 0.75, for example.

Reflection surfaces of the mirrors Mi can be designed as free-form surfaces without an axis of rotational symmetry. Alternatively, the reflection surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. Just like the mirrors of the illumination optics 103, the mirrors Mi can have highly reflective coatings for the illumination radiation 115. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

The projection optics 109 has a large object-image offset in the y-direction between a y-coordinate of a center of the object field 104 and a y-coordinate of the center of the image field 110. This object-image offset in the y-direction can approximately as large as a z-distance between the object plane 105 and the image plane 111.

The projection optics 109 can in particular be anamorphic. In particular, it has different image scales βx, βy in the x and y directions. The two image scales βx, βy of the projection optics 109 are preferably at (βx, βy)=(+/−0.25, +/-0.125). A positive image scale ß means an image without image reversal. A negative sign for the imaging scale ß means imaging with image reversal.

The projection optics 109 thus leads to a reduction in the ratio 4:1 in the x-direction, ie in the direction perpendicular to the scanning direction.

The projection optics 109 lead to a reduction of 8:1 in the y-direction, ie in the scanning direction.

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

The number of intermediate image planes in the x-direction and in the y-direction in the beam path between the object field 104 and the image field 110 can be the same or, depending on the design of the projection optics 109, be different. Examples of projection optics with different numbers of such intermediate images in the x and y directions are known from US 2018/0074303 A1.

In each case one of the pupil facets 122 is assigned to precisely one of the field facets 120 in order to form a respective illumination channel for illuminating the object field 104 . In this way, in particular, lighting can result according to Köhler's principle. The far field is broken down into a large number of object fields 104 with the aid of the field facets 120 . The field facets 120 generate a plurality of images of the intermediate focus on the pupil facets 122 respectively assigned to them.

The field facets 120 are each imaged onto the reticle 106 by an associated pupil facet 122 in a superimposed manner in order to illuminate the object field 104 . In particular, the illumination of the object field 104 is as homogeneous as possible. It preferably has a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

The illumination of the entrance pupil of the projection optics 109 can be geometrically defined by an arrangement of the pupil facets. The intensity distribution in the entrance pupil of the projection optics 109 can be set by selecting the illumination channels, in particular the subset of the pupil facets that guide light. This intensity distribution is also referred to as an illumination setting.

A likewise preferred pupil uniformity in the area of defined illuminated sections of an illumination pupil of the illumination optics 103 can be achieved by redistributing the illumination channels.

Further aspects and details of the illumination of the object field 104 and in particular the entrance pupil of the projection optics 109 are described below.

The projection optics 109 can in particular have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

The entrance pupil of the projection optics 109 cannot regularly be illuminated exactly with the pupil facet mirror 121 . When imaging the projection optics 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, a surface can be found in which the distance between the aperture rays, which is determined in pairs, is minimal. This surface represents the entrance pupil or a surface conjugate to it in position space. In particular, this surface exhibits a finite curvature.

The projection optics 109 may have different positions of the entrance pupil for the tangential and for the sagittal beam path. In this case, an imaging element, in particular an optical component of the transmission optics, between the second facet mirror 121 and the Reticles 106 are provided. With the help of this optical component, the different positions of the tangential entrance pupil and the sagittal entrance pupil can be taken into account.

In the arrangement of the components of the illumination optics 103 shown in FIG. 1, the pupil facet mirror 121 is arranged in a surface conjugate to the entrance pupil of the projection optics 109 . The first field facet mirror 119 is arranged tilted to the object plane 105 . The first facet mirror 119 is tilted relative to an arrangement plane that is defined by the deflection mirror 118 .

The first facet mirror 119 is tilted relative to an arrangement plane that is defined by the second facet mirror 121 .

An exemplary DUV projection exposure system 200 is shown in FIG. The DUV projection exposure system 200 has an illumination system 201, a device called a reticle stage 202 for receiving and precisely positioning a reticle 203, through which the later structures on a wafer 204 are determined, a wafer holder 205 for holding, moving and precisely positioning the wafer 204 and an imaging device, namely projection optics 206, with a plurality of optical elements, in particular lenses 207, which are held in an objective housing 209 of the projection optics 206 via mounts 208.

As an alternative or in addition to the lenses 207 shown, various refractive, diffractive and/or reflective optical elements, including mirrors, prisms, end plates and the like, can be provided.

The basic functional principle of the DUV projection exposure system 200 provides that the structures introduced into the reticle 203 are imaged onto the wafer 204 .

The illumination system 201 provides a projection beam 210 in the form of electromagnetic radiation that is required for imaging the reticle 203 onto the wafer 204 . A laser, a plasma source or the like can be used as the source for this radiation. The radiation is shaped in the illumination system 201 via optical elements in such a way that the projection beam 210 has the desired properties in terms of diameter, polarization, shape of the wave front and the like when it strikes the reticle 203 .

An image of the reticle 203 is generated by means of the projection beam 210 and transmitted to the wafer 204 in a correspondingly reduced size by the projection optics 206 . The reticle 203 and the wafer 204 can be moved synchronously, so that areas of the reticle 203 are imaged onto corresponding areas of the wafer 204 practically continuously during a so-called scanning process.

Optionally, an air gap between the last lens 207 and the wafer 204 can be replaced by a liquid medium which has a refractive index greater than 1.0. The liquid medium can, for example be pure water. Such a structure is also referred to as immersion lithography and has an increased photolithographic resolution.

The use of the invention is not limited to use in projection exposure systems 100, 200, in particular not with the structure described. The invention is suitable for any lithography system, but in particular for projection exposure systems with the structure described. The invention is also suitable for EUV projection exposure systems which have a lower numerical aperture on the image side than that described in connection with FIG. 1 and no obscured mirror M5 and/or M6. In particular, the invention is also suitable for EUV projection exposure systems which have an image-side numerical aperture of 0.25 to 0.5, preferably 0.3 to 0.4, particularly preferably 0.33. Furthermore, the invention and the following exemplary embodiments are not to be understood as being restricted to a specific design. The following figures represent the invention only by way of example and in a highly schematic manner.

FIG. 3 shows a schematic representation of an optical device 1 .

The optics device 1 shown in the exemplary embodiment for a lithography system, in particular for a projection exposure system 100, 200, comprises at least one optical element 2, which has an optical surface 3, and a plurality of actuators 4 for a deformation of the optical surface 3. Furthermore, a strain gauge 5 for Determination of the deformation of the optical surface 3 provided or available.

In an embodiment that is not shown, it can be provided that there is only one actuator 4 for a deformation of the optical surface 3 . It is advantageous here if one actuator 4 can deform the optical surface 3 in all spatial directions as far as possible.

The strain gauge 5 has at least one optical fiber 6 .

In this case, the optical fiber 6 is polarization-maintaining.

Furthermore, in the exemplary embodiment illustrated in FIG. 3, the at least one optical fiber 6 of the optical device 1 has a plurality of fiber Bragg gratings 7 with respective fiber interference spectra 8 (see FIG. 14).

Furthermore, in the exemplary embodiment of the optical device 1 illustrated in FIG. 3, the optical element 2 has a substrate element 9 on which the optical surface 3 is arranged or formed. Furthermore, the actuators 4 are connected to the substrate element 9 by a connecting layer 10 . In the exemplary embodiment illustrated in FIG. 3, the connecting layer 10 has an adhesive. In other embodiments, the connecting layer 10 can also be formed from other materials.

In the exemplary embodiment illustrated in FIG. 3, the strain gauge 5 is also arranged at least partially in the connecting layer 10 .

In particular, the strain gauge 5 is inserted into the connecting layer 10 in the exemplary embodiment illustrated in FIG.

Furthermore, FIG. 3 shows an embodiment of the optical device 1 in which the at least one fiber Bragg grating 7 is at least partially arranged in at least one effective region 11 of the actuators 4 .

A fiber Bragg grating 7 is preferably assigned to a majority, preferably a majority, particularly preferably all effective areas 11 . Each actuator 4 preferably forms its own effective area 11 for deforming or shaping the optical surface 3 of the optical element 2 .

In the exemplary embodiment of the optical device 1 illustrated in FIG. 3, a back plate 12 is preferably present. The actuators 4 are preferably arranged between the back plate 12 and the substrate element 9 . The back plate 12 enables the actuators 4 working normal (orthogonal) to the optical surface 3 in the exemplary embodiment shown in Figure 3 to be supported.

The optical fiber 6 has a plurality of fiber Bragg gratings 7 whose fiber interference spectra 8 (see FIG. 14) are preferably designed to be distinguishable.

In particular, in the exemplary embodiment shown, the fiber Bragg gratings 7 have different grating periods.

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

Furthermore, in the exemplary embodiment illustrated in FIG. 3, a control device 14a is present and set up to set the target deformation by means of a closed control loop. In this case, the actual strain serves as a feedback signal for the activation and/or regulation of the at least one actuator 4 . Working connections are shown in Figure 3 by dashed lines. The spectrometer device 14 is preferably set up to detect a direct frequency shift in the fiber interference spectra 8 . Alternatively or additionally, it can be provided that the spectrometer device 14 has a Mach-Zehnder interferometer.

Furthermore, in the case of the optical device 1 illustrated in FIG. 3, the optical surface 3 is light-reflecting, in particular EUV light-reflecting.

In an alternative embodiment it can be provided that the optical surface 3 is designed to reflect DUV light.

FIG. 4 shows a schematic representation of the optical device 1 . In the exemplary embodiment shown, the optical surface 3 is deformed by the action of the actuators 4 . The actuators 4 are supported against the back plate 12 and work in a direction which runs approximately parallel to a surface normal of the optical surface 3 .

The effect of the actuators 4 results in expansions in the substrate element 9, which can be detected, for example, by means of the expansion measuring device 5 (not shown in FIG. 4).

FIG. 5 shows a simplified schematic representation of the optical device 1, with a back plate 12 being dispensed with and the actuators 4 having a working direction which runs at least approximately parallel to the optical surface 3.

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

Different systems for actuating deformable optical surfaces 3, in particular mirror surfaces, are therefore shown in FIGS. Figures 3 and 4 therefore show an actuation normal (orthogonal) to the optical surface 3 and Figures 5 and 6 an actuation parallel to the optical surface 3.

In the exemplary embodiment illustrated in FIGS. 3 and 4, a plurality of actuators 4 can exert a compressive force on the optical element 2 and thus deform or deform it precisely. In the exemplary embodiment illustrated in FIGS. 5 and 6, a bending moment is introduced into the optical element 2 and/or the optical surface 3 by expansion and/or contraction of the actuators 4, which can lead to deformation or deformation thereof.

Figure 7 shows a schematic representation of various expansion curves of the actuators 4.

An elongation of the actuator 4 and/or an elongation of the effective range 11 of the actuator 4 is plotted on a vertical elongation axis 15 . The field strength of an applied electric field is plotted on a horizontal axis 16 in FIG. The diagram in FIG. 7 shows four expansion curves which correspond to different temperatures of the actuator 4. All four strain curves show hysteresis.

In this case, the expansion curve with the lowest profile corresponds to the highest temperature, while the expansion curve with the highest profile corresponds to the lowest temperature of the actuator 4 .

The expansion curves of the actuator 4 shown in FIG. 7 reflect the behavior of the actuator 4 according to formula (1). A hysteresis of the actuator 4 can be seen here and is in a range of <1% in the example shown.

FIG. 8 shows a schematic representation of an expansion curve of the actuator 4 with a change in temperature. The expansion of the actuator 4 is again plotted on the expansion axis 15, while the temperature of the actuator 4 is plotted on the horizontal axis 16. A hysteresis of the expansion curve can be seen when running through a temperature cycle.

The expansion of the actuator 4 when the temperature changes compared to the normal temperature arranged at the origin of the diagram shown in FIG. 8 is determined in particular by the thermal expansion coefficient CTE (see formula (1)). A thermal hysteresis of the elongation can be seen in the elongation curve shown in FIG. The effects of the hysteresis cannot be reproduced here.

FIG. 9 shows a schematic representation of a drift curve of the actuator 4. The expansion of the actuator 4 is plotted on the expansion axis 15, while a time profile is plotted on the horizontal axis 16. At the origin, ie at the beginning of the time measurement, the actuator 4 is in an initial position or initial stretch and receives a signal, preferably in the form of an applied voltage, to assume a target position, ie a target stretch. In the course of time, the actuator 4 approaches the desired position or the desired elongation or drifts towards it.

Furthermore, the drift illustrated in FIG. 9 can be dependent on the respective jump height of the actuator 4.

FIG. 10 shows a schematic representation of a possible embodiment of the optical device 1 in a sectional view.

The optical fiber 6 has a number of fiber Bragg gratings 7, runs in a loop and passes through the effective areas 11 of a number of actuators 4.

Furthermore, in the exemplary embodiment illustrated in FIG. 10, the optical fiber 6 is guided in a meandering manner through rows of a plurality of effective regions 11 . In an alternative embodiment, be provided that additionally or alternatively, the at least one optical fiber 6 is guided in a meandering manner through rows of a plurality of effective areas 11 .

In the exemplary embodiment illustrated in FIG. 10, a plurality of optical fibers 6 running in a meandering manner can also be provided.

Alternatively or additionally, a plurality of optical fibers 6 can also be provided in the exemplary embodiment illustrated in FIG. 10, each of which is assigned to a line or row.

Furthermore, in the exemplary embodiment illustrated in FIG.

FIG. 11 shows a schematic representation of a further possible embodiment of the optical device 1, the strain measuring device 5 being arranged at least partially, preferably completely, in the substrate element 9. In particular, in the exemplary embodiment shown, the strain gauge 5 is arranged in a groove 17b.

The strain gauge 5 can also be arranged both in the substrate element 9 and in the connecting layer 10 .

FIG. 11 shows a section through an actuator 4 with a connection layer 10 and the substrate element 9 . In the exemplary embodiment illustrated in FIG. 11, the actuators 4 lie flat on the connecting layer 10, which connects the actuators 4 and the substrate element 9.

In the exemplary embodiment illustrated in FIG. 11, the groove 17b is preferably milled into the substrate element 9.

FIG. 12 shows a further schematic representation of the embodiment of the optical device 1, according to which the strain gauge 5 is at least partially, preferably completely, arranged in the connecting layer 10, in particular inserted.

FIG. 13 shows a schematic representation of an embodiment of the optical device 1, the strain measuring device 5 being arranged at least partially in the at least one actuator 4, in particular in the groove 17a.

The strain gauge 5 can also be arranged both in the at least one actuator 4 and in the connection layer 10 .

The strain gauge 5 can also be arranged both in the substrate element 9 and in the at least one actuator 4 . The strain gauge 5 can also be arranged both in the substrate element 9 and in the connecting layer 10 and in the at least one actuator 4 .

In the exemplary embodiment illustrated in FIG. 13, the groove 17a is preferably milled into the actuators 4.

Features that are mentioned in an embodiment of Figures 3 to 13 can also be implemented in the other embodiments. In particular, a plurality of optical fibers can also be used, which are arranged in the optical element 2 in the manner described with reference to FIGS. 11 and/or 12 and/or 13.

The exemplary embodiments of the optical device 1 shown in Figures 3 to 13 are also particularly suitable for carrying out a method for setting a target deformation of the optical surface 3 of the optical element 2 for a lithography system 100, 200 by means of one or more actuators 4 In the method, it is provided that an actual deformation of the optical surface 3 is determined by at least one actual elongation of at least one measurement area 18 being determined. Furthermore, the at least one measurement area 18 is selected in such a way that conclusions can be drawn about the actual deformation of the optical surface 3 from the actual strain.

In the exemplary embodiments, the measuring areas 18 are preferably selected in such a way that each effective area 11 , at least each effective area 11 , which is to be recorded or monitored, is assigned a measuring area 18 , with the respective measuring area 18 preferably being located or within the effective area 11 . trained there.

Furthermore, to carry out the method, the strain measuring device 5 is preferably arranged in such a way that the fiber interference spectrum 8 in the fiber Bragg gratings 7 of the optical fiber 6 is influenced by the actual strain of the at least one measuring region 18 .

Furthermore, a broadband measurement radiation 19 is coupled into the optical fiber 6 to carry out the method. This means that the method according to the invention preferably includes the coupling in of the broadband measurement radiation 19.

The fiber interference spectra 8 of the fiber Bragg gratings 7 of the strain gauge 5 can be determined using the measurement radiation 19 .

Alternatively or additionally, it can be provided that a narrow-band measurement radiation 19 is coupled into the optical fiber 6 and the fiber interference spectra 8 are determined in a grid method or scanning method by sweeping or scanning a sufficiently wide wavelength band. Furthermore, it is preferably provided that the actual deformation of the optical surface 3 in the lithography systems 100, 200 according to FIGS. 1 and 2 and during a reflection of a working radiation of the projection exposure system 100, 200 by the optical surface 3 is determined.

The embodiment of the optical device 1 shown in FIG. 11 is particularly suitable for carrying out an embodiment of the method according to which the actual strain is determined in a plurality of measurement areas 18 in the substrate element 9 on which the optical surface 3 is based in the groove 17b.

The exemplary embodiment of the optical device 1 shown in FIG. 12 is particularly suitable for carrying out an embodiment of the method according to which the actual strain is determined in a number of measurement areas 18 in the connecting layer 10 connecting the actuators 4 to the substrate element 9 .

The exemplary embodiment of the optical device 1 shown in FIG. 13 is particularly suitable for carrying out an embodiment of the method, according to which the actual strain is determined in a number of measuring areas 18 in the actuators 4 in the groove 17a.

Furthermore, it is preferably provided in the method that the actual elongation in the plurality of measurement areas 18 is determined synchronously and/or in quick succession over time.

The exemplary embodiment of the optical device 1 shown in FIG. 10 is particularly suitable for carrying out an embodiment of the method, according to which the optical fiber 6 is guided in a meandering manner through rows of a plurality of measuring regions 18 . Furthermore, at least one fiber Bragg grating 7 is preferably arranged in each case in a plurality of the measurement areas 18 in this embodiment.

Alternatively or additionally, it can be provided that the at least one optical fiber 6 is routed in a meandering manner through rows of a plurality of measurement regions 18 .

FIG. 14 shows a schematic representation of the fiber interference spectrum 8. The wavelength is plotted on the horizontal axis 16. The measurement spectrum 8 of a back-reflected measurement radiation 19 is plotted on an intensity axis 20 in a solid line. An input spectrum of the irradiated measuring radiation 19 is plotted in a dashed line. Reference List

1 optics device

2 optical element

3 optical surface

4 actuator

5 strain gauge

6 optical fiber

7 fiber Bragg gratings

8 fiber interference spectrum

9 substrate element

10 connection layer

11 Area of Effect

12 backplate

14 spectrometer setup

15 elongation axis

16 horizontal axis

17a,b grooves

18 measuring range

19 measuring radiation

20 intensity axis

100 EUV projection exposure system

101 lighting system

102 radiation source

103 illumination optics

104 object field

105 object level

106 reticle

107 reticle holder

108 reticle displacement drive

109 projection optics

110 field of view

111 image plane

112 wafers

113 wafer holder

114 wafer displacement drive

115 EUV / useful / illumination radiation

116 collector

117 intermediate focal plane 118 deflection mirrors

119 first facet mirror / field facet mirror

120 first facets / field facets

121 second facet mirror / pupil facet mirror 122 second facets / pupil facets

200 DUV projection exposure system

201 lighting system

202 reticle days

203 reticle 204 wafer

205 wafer holder

206 projection optics

207 lens

208 mount 209 lens body

210 projection beam Mi mirror

Claims

Patent Claims:

1. Optical device (1) for a lithography system (100,200), with at least one optical element (2) having an optical surface (3) and with one or more actuators (4) for a deformation of the optical surface (3), characterized in that that a strain gauge (5) is provided for determining the deformation of the optical surface (3), the strain gauge (5) having at least one optical fiber (6) and the optical fiber (6) is polarization-maintaining.

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

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

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

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

6. Optical device (1) according to one of claims 1 to 5, characterized in that the strain gauge (5) at least partially in the at least one actuator (4), preferably in a groove (17a) of the at least one actuator (4), arranged is.

7. Optical device (1) according to one of claims 4 to 6, characterized in that the strain gauge (5) is at least partially arranged in the connecting layer (10), preferably inserted.

8. Optical device (1) according to one of claims 2 to 7, characterized in that the at least one fiber Bragg grating (7) is arranged at least partially in at least one effective range (11) of the at least one actuator (4).

9. Optical device (1) according to one of claims 2 to 8, characterized in that the at least one optical fiber (6) has a plurality of fiber Bragg gratings (7), the fiber interference spectra (8) of the individual fiber Bragg gratings (7) are designed to be distinguishable.

10. Optical device (1) according to one of claims 2 to 9, characterized in that at least one spectrometer device (14) is provided for determining and/or characterizing the fiber interference spectra (8).

11. Optical device (1) according to claim 10, characterized in that the at least one spectrometer device (14) is set up to detect a direct frequency shift and/or has a Mach-Zehnder interferometer.

12. Optical device (1) according to one of claims 8 to 11, characterized in that the optical fiber (6) has a plurality of fiber Bragg gratings (7), runs in a loop and passes through the working areas (11) of a plurality of actuators (4). .

13. Optical device (1) according to one of claims 8 to 12, characterized in that the at least one optical fiber (6) is guided in a meandering manner through rows and/or rows of a plurality of working areas (11) and/or in a plurality of the working areas ( 11) at least one fiber Bragg grating (7) is arranged in each case.

14. Optical device (1) according to one of claims 3 to 13, characterized in that a back plate (12) is provided and the at least one actuator (4) is arranged between the back plate (12) and the substrate element (9).

15. Optical device (1) according to one of claims 1 to 14, characterized in that the optical surface (3) is light-reflecting, preferably EUV-reflecting and/or DUV is designed to be reflective.

16. A method for setting a target deformation of an optical surface (3) of an optical element (2) for a lithography system (100, 200) by means of one or more actuators (4), characterized in that an actual deformation of the optical surface (3 ) is determined in that at least one actual elongation of at least one measuring area (18) is determined.

17. The method according to claim 16, characterized in that the at least one measuring area (18) is selected in such a way that conclusions can be drawn from the actual strain to the actual deformation of the optical surface (3).

18. The method according to claim 16 or 17, characterized in that a strain gauge (5) having at least one optical fiber (6) with at least one fiber Bragg grating (7) is arranged such that in at least one of the fiber Bragg grating (7) of the at least one optical fiber (6) at least one fiber interference spectrum (8) is influenced by the actual strain of the at least one measurement area (18).

19. The method according to claim 18, characterized in that a measurement radiation (19) is coupled into the optical fiber (6).

20. The method according to claim 18 or 19, characterized in that the fiber interference spectrum (8) of the at least one fiber Bragg grating (7) of the strain gauge (5) is determined.

21. Method according to one of claims 16 to 20, characterized in that the actual deformation of the optical surface (3) is determined in the lithography system (100, 200) and/or during a reflection of a radiation through the optical surface (3).

22. The method according to any one of claims 16 to 21, characterized in that the actual strain 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 the substrate element (9) is determined.

23. The method according to any one of claims 16 to 22, characterized in that the actual strain is determined in one or more measurement areas (18) in the at least one actuator (4), preferably in a groove (17a) of the actuator (4). becomes.

24. The method according to claim 22 or 23, characterized in that the actual strain is determined in one or more measurement areas (18) in at least one connecting layer (10) connecting the at least one actuator (4) to the substrate element (9).

25. The method according to any one of claims 16 to 24, characterized in that the actual elongation is determined synchronously in a plurality of measurement areas (18).

26. The method according to any one of claims 18 to 25, characterized in that the at least one optical fiber (6) is guided in a loop shape, preferably in a meandering shape, through rows and/or rows of a plurality of measurement areas (18) and/or in a plurality of the measurement areas (18) in each case at least one fiber Bragg grating (7) is arranged.

27. Lithography system, in particular projection exposure system (100, 200) for semiconductor lithography, with an illumination system (101, 201) with a radiation source (102) and optics (103, 109, 206) which have at least one optical element (116, 118, 119, 120, 121, 122, Mi, 207), characterized in that at least one optical device (1) according to one of claims 1 to 15 is provided, 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) has an optical surface ( 3) which is deformable with a method according to any one of claims 16 to 26.