Mirror arrangement, in particular of a microlithographic projection exposure apparatus, and method for measuring the temperature of a mirror - Patents.com

Abstract

The present invention relates to a mirror device, particularly for a microlithography projection exposure apparatus, comprising a mirror (20), sensor units (41, 42, 44, 47, 49), and a control unit (38). The mirror (20) includes a mirror body (23) and a reflective surface (24) provided on the mirror body (23). The sensor units (41, 42, 44, 47, 49) include sensor elements (41, 49) and signal paths (50) extending to the control unit (38) for transmitting measurement signals representative of the temperatures of the sensor elements (41, 49). The sensor elements (41, 49) are provided on a substrate of the mirror body (23), and the sensor elements include a plurality of electrical conductor paths (41) integrated into the substrate of the mirror body (23), the conductor paths (41) forming a plurality of intersections (51), and the conductor paths (41) being electrically conductively connected to one another at the intersections (51). The present invention also relates to a method for measuring the temperature of a mirror (20).

Description

[Technical Field]

[0001] The invention relates in particular to a mirror arrangement in a microlithographic projection exposure apparatus and to a method for measuring the temperature of the mirror. [Background technology]

[0002] Microlithography projection exposure apparatus are used especially for the production of integrated circuits with small structures. A mask (reticle) illuminated with extremely short-wave deep ultraviolet or extreme ultraviolet radiation (DUV or EUV radiation) is imaged onto the lithography object in order to transfer the mask structure onto the lithography object.

[0003] Projection exposure apparatus comprise a number of mirrors that reflect radiation, the mirrors having a precisely defined shape and being accurately positioned so that the imaging of the mask onto the lithography object is of sufficient quality.

[0004] During operation, projection exposure apparatuses are subjected to actions that affect the imaging quality. For example, if the geometric shape of a mirror changes due to thermal expansion, the wavefront of the radiation reflected by the mirror changes. For proper operation of the projection exposure apparatus, it is useful to have information about the temperature of the mirror. The temperature information can be used to keep the temperature of the mirror at a constant value, for example by controlling a heating or cooling unit, or to adjust the projection exposure apparatus appropriately after a temperature change.

[0005] The temperature of the mirror can be estimated from a variable indirectly related to the mirror temperature, such as the temperature of the air adjacent to the mirror, or a temperature sensor located adjacent to the mirror can be used to record temperature measurements. Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to provide a mirror device and a method for measuring the temperature of a mirror which avoids these drawbacks. This object is achieved by the features of the independent claims. Advantageous embodiments are set forth in the dependent claims. [Means for solving the problem]

[0007] The above object is therefore achieved by a mirror device, particularly suitable for a microlithography projection exposure apparatus, comprising a mirror, a sensor unit, and a control unit. The mirror includes a mirror body and a reflective surface formed on the mirror body. The sensor unit includes a sensor element and a signal path extending to the control unit for transmitting a measurement signal representative of the temperature of the sensor element to the control unit. The sensor element is formed on a substrate of the mirror body. The sensor element includes a plurality of electrical conductor paths integrated into the substrate of the mirror body. The conductor paths form a plurality of intersections. The conductor paths are electrically conductively connected to one another at the intersections.

[0008] The invention is based on the concept of incorporating a sensor element, whose physical state changes depending on the temperature, directly into the substrate of the mirror body and translating this state change into a measurement signal that can be transmitted to a control unit. The sensor element formed in the substrate of the mirror body allows a direct thermal coupling between the material of the mirror body and the sensor element. In particular, by forming the sensor element as an integral part of the substrate of the mirror body, transmission losses can be avoided. Changes in the temperature of the mirror body directly affect the sensor element, so that a measurement signal can be obtained that directly represents the temperature of the mirror body in the area of ​​the sensor element.

[0009] In one embodiment, the sensor element includes an electrical conductor track integrated into the substrate of the mirror body. The electrical conductor track may be configured such that its electrical resistance varies depending on the temperature of the mirror body in the region of the conductor track. Suitable materials are known, both in the form of positive temperature coefficient (PTC) thermistors and negative temperature coefficient (NTC) thermistors. Preferably, the conductor track is made of a material that exhibits a substantially proportional relationship between temperature and electrical resistance.

[0010] By applying an electrical signal to the conductor path, the electrical resistance of the conductor path can be measured. The sensor unit can include a signal generator designed to apply the electrical signal to the conductor path. The sensor unit can include a closed electrical circuit extending from a first pole of the signal generator through the electrical conductor path to a second pole of the signal generator. Since changes in the electrical resistance of the conductor path affect the electrical signal, temperature changes in the area of ​​the electrical conductor path in the area of ​​the mirror body can be inferred from changes in the electrical signal. The relationship between the temperature of the conductor path and the electrical resistance can be known or can be calculated.

[0011] The conductor path may extend from the input end to the output end within the mirror body. A cable or similar conductor suitable for transmitting signals may be connected to the input end and the output end, and an electrical signal may be transmitted between the signal generator and the conductor path via the cable or similar conductor. The conductor path may include a first portion having a low temperature-dependent electrical resistance and a second portion having a high temperature-dependent electrical resistance. This allows accurate temperature measurement of a specific point on the mirror body. The second portion of the conductor path is introduced as a measurement point in an area of ​​the mirror body where measurement of the mirror body temperature is desired, and the first portion forms a kind of lead to the second portion.

[0012] In one embodiment, the cross section of the electrical conductor path is smaller in the second part than in the first part. Furthermore, the first and second parts can be homogeneous conductor paths, in particular those made of a homogeneous electrically conductive material. In this sense, the electrical conductor path can include a plurality of first and second parts. The second part of the conductor path can also be made of a different material from the first part, in which case the material of the second part has a higher temperature dependence of electrical resistance.

[0013] In an alternative embodiment, the electrical conductor path extends through the mirror body with a constant cross section. In this case, the electrical conductor path can be considered as a series connection of electrical resistances. The measurement signal obtained in this way provides temperature information in the form of an average value over the length of the electrical conductor path.

[0014] The substrate of the mirror body may include a region adjacent to the electrical conductor track and in which the material of the mirror body is non-conductive. In particular, the electrical conductor track may be electrically isolated from the reflective surface. The electrical conductor track may be electrically isolated from the back side of the mirror body, which is located opposite the reflective surface. In one embodiment, the electrical conductor track is surrounded on all sides by the non-conductive material of the mirror body.

[0015] The mirror body may include a plurality of electrical conductor paths, each forming a sensor element within the meaning of the present invention. From each of the conductor paths, a signal path may extend to a control unit. The mirror body includes a sensor layer extending parallel to the reflective surface, in which the conductor paths are arranged. The plurality of conductor paths makes it possible to obtain temperature information from different regions of the mirror body. Each of the conductor paths may have one or more of the above-mentioned characteristics.

[0016] The conductor tracks may be electrically isolated from one another within the mirror body, thus enabling each of the conductor tracks to obtain temperature information independently of the other conductor tracks. In one embodiment, one or more intersections are provided between the conductor tracks, where the conductor tracks are conductively connected to one another. The number of intersections may be greater than 10, preferably greater than 50, and more preferably greater than 100. By appropriate wiring of the electrical connections between the conductor tracks and the signal generator, it is possible to conduct electrical signals along different paths within the mirror body, thus obtaining temperature information from different regions of the mirror body.

[0017] Each conductor path may include a switch arranged between the input end and the signal generator, which establishes an electrical connection between the conductor path and the signal generator in a first switching state and breaks the electrical connection in a second switching state. Furthermore, each conductor path may include a corresponding switch arranged between the output end and the signal generator. These switches may be controlled so that one switch at the input end and one switch at the output end are closed, while all other switches are open. This allows an electrical path to extend between the input end of the first conductor path and the output end of the second conductor path, and through only one intersection between the first and second conductor paths. In one variant, there are two or more intersections between the first and second conductor paths. The sensor unit may be designed so that the switches rapidly switch between the switching states. The duration of each switching state may be, for example, 1 ms to 50 ms, preferably 2 ms to 20 ms. By appropriately evaluating the different measurement signals, temperature information of multiple regions of the mirror body can be obtained. For more precise setting of the current path, the conductor path may contain further electrical / electronic components with current-dependent properties. Such components may have negative and positive currents or may exhibit, for example, frequency dependence. In this way, the local resolution of the temperature information can be improved and / or the evaluation can be facilitated.

[0018] Another possibility for obtaining locally resolved temperature information is to form several separately controllable measurement points in each conductor path. For example, the measurement points can be designed for electrical signals of different frequencies. In one embodiment, each measurement point is configured as a combination of a temperature-dependent measurement resistor and a band-stop filter arranged in parallel with it. The band-stop filter has a high impedance for a defined frequency and therefore conducts electrical signals of that frequency through the measurement resistor. For other frequencies, the band-stop filter shorts out the measurement resistor.

[0019] In one embodiment, the electrical conductor path includes two different metals electrically connected to each other at a connection point. Based on the Seebeck effect, the voltage between the two ends of the conductor path changes depending on the temperature at the connection point. A sensor element based on two different metals thus forms a thermocouple. The thermocouple can be configured such that there are no transitions between the different metals within the mirror body other than the connection point. If there are additional transitions between the different metals within the mirror body, careful calibration of the thermocouple is required to obtain temperature information at the connection point. The sensor unit can include a voltmeter that measures the change in voltage between the ends of the conductor path.

[0020] In one embodiment, the first portion of the conductor path and the second portion of the conductor path are connected to two electrodes of a capacitor whose capacitance varies with temperature. The capacitor can be configured so that the electrode spacing varies with heating of the mirror body. The changed capacitance can be measured, from which a measurement signal can be derived that represents the temperature of the mirror body in the region of the capacitor. Additionally or alternatively, a dielectric having a temperature-dependent dielectric constant can be disposed between the two electrodes of the capacitor.

[0021] The capacitor can be fabricated in the form of a local capacitance near the reflecting surface. Alternatively, one electrode of the capacitor can be located near the reflecting surface and the second electrode can be located on the back side of the mirror body. In one embodiment, a continuous electrode surface is formed near the reflecting surface, forming a common ground for multiple measurement electrodes. The measurement electrodes can be located on the back side of the mirror body or can be housed within the mirror body.

[0022] The reflective surface of the mirror is usually formed by a layer system that is highly reflective to EUV and / or DUV radiation. Multilayer coatings, especially those with alternating layers of molybdenum and silicon, may be included. With such coatings, it is possible to reflect approximately 70% of the incident EUV radiation. The term EUV radiation refers to electromagnetic radiation in the extreme ultraviolet spectral range, with wavelengths between 5 nm and 100 nm, especially between 5 nm and 30 nm. DUV radiation is in the deep ultraviolet spectral range, with wavelengths between 100 nm and 300 nm.

[0023] The sensor element according to the invention can be arranged between the reflective surface of the mirror body and the main body. In the manufacture of the mirror according to the invention, the main body is usually the starting point. In one variant, further layers are applied to the main body by additive manufacturing until the mirror reaches its final state. In another variant, the manufacture of the mirror body includes a step of joining the main body to a second partial body. In all cases, the layer system forming the reflective surface can be applied to the mirror body by coating.

[0024] If the sensor element includes conductor paths, these may be applied by a coating process. The body or sub-body to which the conductor paths are applied may be non-conductive. The conductor paths can be produced by applying a conductive material along the conductor paths. The areas between the conductor paths can be filled with a non-conductive material. The layer disposed between the reflective surface and the body and on which the sensor element is disposed is referred to as the sensor layer. If the sensor element further includes other components, such as a material whose resistance changes depending on the temperature in the case of resistance measurements, or an electrode of a capacitor in the case of capacitance measurements, or a transition between two different metals in the case of a thermocouple, these components can also be applied by coating. All components of the sensor element can be disposed within the sensor layer. The sensor layer can be covered with a layer of a non-conductive material. Further layer structures can be formed thereon. If the layer structure includes a surface protection layer, the sensor layer can be disposed between the reflective surface and the surface protection layer or between the surface protection layer and the body.

[0025] If the mirror body includes a main body and a sub-body and the reflective surface is applied to the sub-body, the sensor layer can be arranged between the reflective surface and the sub-body. In another embodiment, the sensor layer is arranged between the main body and the sub-body. A sensor element arranged between the reflective surface and the main body of the mirror body is an independently inventive subject matter, even if it does not include a plurality of conductor tracks integrated into the substrate of the mirror body.

[0026] The sensor element may also include a grating structure written into the transparent material of the mirror body. The grating structure may be configured to affect an incident optical signal differently depending on the temperature, so that the temperature can be estimated from the reflected or transmitted portion of the optical signal. In the event of a temperature change, the transparent material undergoes thermal expansion, which is transmitted to the grating structure. The change in the grating structure can be measured by an appropriate optical signal. The sensor unit may include a signal generator that sends an optical signal into the transparent material of the mirror body and evaluates the portion of the optical signal that is transmitted or reflected by the grating structure to determine therefrom a measurement signal representative of the temperature of the mirror body in the region of the grating structure. The measurement signal may be transmitted as an electrical signal from the signal generator to a control unit of the mirror device. A sensor element including a grating structure written into the transparent material of the mirror body is independently inventive, even if it does not include a plurality of conductor tracks integrated into the substrate of the mirror body.

[0027] The grating structure may be a structure written into the transparent material of the mirror body using a laser, in particular a femtosecond laser. The grating structure may in particular be a periodic microstructure that reflects light wavelength-selectively. In particular, the grating structure may form a fiber Bragg grating. When an optical signal with a large bandwidth is directed to the grating structure, only light with a very limited spectral width is reflected by the grating structure. The wavelength of the reflected portion of the optical signal changes in the event of thermal expansion of the grating structure.

[0028] In addition to the grating structure, optical channels that guide optical signals to the grating structure can be written into the transparent material of the mirror body. The optical channels can be formed by processing the material around the channel with a laser that reflects the optical signal. As a result of processing with the laser, the material of the mirror body acquires a localized high refractive index. The processed material forms a kind of wall around the channel, so the optical channel acts like a light guide for the optical signal. The optical signal can be guided inside the optical channel, where it propagates to the grating structure.

[0029] The grating structure in this case acts like a fiber Bragg grating in the optical channel. The optical channel may be provided with multiple grating structures spaced apart along the length of the optical channel and reflecting different wavelengths of the optical signal. Only light of a very limited spectral width around the Bragg wavelength is reflected by each fiber Bragg grating. The other part of the light continues down the optical channel. Heating causes elongation of each grating structure. Based on the wavelength of the light reflected by the fiber Bragg grating, it is possible to generate a measurement signal representing the temperature of the mirror body in the region of the fiber Bragg grating. The light guide may be provided with three or more grating structures, preferably five or more, more preferably ten or more. The grating structures may be arranged equidistantly from one another within the light guide.

[0030] Instead of writing the optical channels into the transparent material of the mirror body, the optical channels can be formed as cavities within the mirror body. The cavities can extend to the area of ​​the mirror body where the lattice structure is formed. The cavities can be formed as perforations that extend from the edge of the mirror body to the immediate vicinity of the lattice structure. It is also possible to place the cavities at the junction between two components of the mirror body, and form depressions in one or both components that are shaped by the joining of the components to form closed channels.

[0031] A mirror device in which the sensor element is formed by a transparent optical channel provided with a fiber Bragg grating has an independent inventive subject matter, even if the sensor element is not formed in the substrate of the mirror body: the sensor element can also be inserted into a cavity of the mirror body in the form of a light guide provided with a fiber Bragg grating.

[0032] In order to minimize thermal deformation of the mirror despite the heat resulting from the absorbed radiation, the mirror arrangement may be equipped with a cooling system that keeps the temperature of the mirror as constant as possible. The cooling system may include a plurality of cooling channels extending into the mirror body along the reflective surface. The cooling system may include a coolant reservoir from which a coolant, in particular water, is supplied to the cooling channels. The fluid whose temperature is measured to estimate the temperature of the mirror body may be the coolant of the cooling system.

[0033] In many cases, the temperature of the mirror body in the region of the reflective surface is important. Therefore, the mirror body can be configured so that the sensor element is located near the reflective surface. The distance between the sensor element and the reflective surface can be smaller than the distance between the sensor element and the rear side of the mirror body located opposite the reflective surface, preferably by a factor of at least two, more preferably by a factor of at least five.

[0034] If cooling channels are formed in the mirror body, the temperature of the region of the mirror body located between the cooling channels and the reflective surface is particularly important. Therefore, it is preferable to arrange the sensor layer in this region of the mirror body. The sensor element according to the invention can be arranged in the mirror body so that the distance between the reflective surface and the sensor element is smaller than the distance between the sensor element and the cooling channels.

[0035] An embodiment of the present invention is described below in which the sensor element is formed from the material of the mirror body, and changes in the properties of the material are determined and used as a measure of temperature. For example, if the geometric shape of the mirror body changes due to a temperature change, this can be detected by ultrasound. For this purpose, ultrasound is directed at the material to excite ultrasonic vibrations in the material of the mirror body. To obtain information about the temperature of the mirror body, it is possible to determine the attenuation of the ultrasound or the time it takes for the ultrasound to re-emerge from the mirror body. In particular, reflections at the interface of the mirror body can affect the ultrasound, which is correlated with temperature and can therefore be used to generate a measurement signal. Additionally or alternatively, a correlation with temperature can be derived from the fact that the speed of sound in the material of the mirror body varies depending on the elastic modulus, Poisson's ratio, and density. If the dependence of these variables on temperature is known, the temperature can be estimated from the speed of sound. In all cases, the relationship between ultrasound measurements and temperature can be determined as a model-based correlation.

[0036] Alternatively, inelastic light scattering can excite acoustic waves in the material of the mirror body and / or in the material of components incorporated into the mirror body, such as optical fibers. For this purpose, laser light is directed into the material of the mirror body and / or the material of components incorporated into the mirror body, resulting in an interaction between the light wave and acoustic lattice vibrations (Brillouin scattering). This interaction can be used for elongation and / or temperature measurement by using the frequency detuning of the laser radiation as a measurement signal for obtaining information. For example, continuous and pulsed laser beams can be incident on the material of the mirror body, and the measurement location of the associated temperature can be deduced from the pulse propagation time of the pulsed laser beam. Alternatively, the Raman effect, based on the interaction of light waves with optical phonons instead of acoustic phonons, can also be used.

[0037] In yet another variant, eddy currents are induced in the conductive material of the mirror body by applying an alternating magnetic field. For this purpose, a conductive layer can be introduced into the mirror body, which otherwise consists of a non-conductive material. In particular, a metal layer in the layer structure of the reflective surface is considered. The eddy currents generate an electromagnetic field that can be measured. The strength of the eddy currents and the associated electromagnetic field generally varies depending on the electrical resistance and the geometric shape of the mirror body. By selecting an appropriate excitation frequency, a corresponding measurement signal can be generated. The temperature dependence of the measurement signal is due to the temperature-dependent change in the resistivity of the mirror body material and the change in distance to the measurement coil due to the thermal expansion of the mirror body.

[0038] The penetration depth of the eddy currents into the target depends, inter alia, on the frequency of the alternating magnetic field, as follows: δ=(2ρ / ω / μ)^0.5 where δ is the standard penetration depth, ρ is the electrical resistivity, μ is the magnetic permeability, and ω is the angular frequency of the excitation field. δ corresponds to the penetration depth at which the eddy current intensity still corresponds to 36.8% of the value at the surface of the target. At a depth of 5δ, the relative eddy current intensity is only 0.7%. Therefore, the penetration depth can be controlled by the excitation frequency. Measurements at different excitation frequencies allow the resistance measurement to be assigned to a depth within the mirror body. This allows for the depth at which the temperature is measured to be varied. To prevent magnetic field lines from exiting the back side of the target, the target thickness should be greater than 5δ if possible. Thin conductive measurement regions require high frequencies for the excitation field, e.g., 1 MHz or higher, preferably 10 MHz or higher, more preferably 100 MHz or higher, and more preferably 1 THz or higher.

[0039] The measurement can be performed by an excitation coil and a measurement coil. Both the excitation coil and the measurement coil can be embodied as wound coils. The coils can be planar or cylindrical, each embodied with or without a core. The coils can be made by a coating process and / or a patterning process. The coils can be single-layer or multi-layer designs.

[0040] The excitation coil and / or measurement coil can be located within the mirror body, for example forming an integral part of the sensor layer of the mirror body. In alternative embodiments, the excitation coil and / or measurement coil are located external to the mirror body, for example on the back side of the mirror, in a separate frame near the back side of the mirror, in a separate frame close to the mirror, or at the edge of the mirror. In one embodiment, the excitation coil is located as a separate component adjacent to the reflective surface, while the measurement coil is integrated into the sensor layer of the mirror body. The measurement coil can be fabricated by coating and patterning.

[0041] The present invention also relates to a projection lens of a projection exposure apparatus, in which a mask is imaged onto a lithography object by means of a plurality of mirror devices, at least one of the mirror devices being configured as a mirror device according to the invention. The projection lens may comprise two or more, preferably three or more, more preferably five or more mirror devices according to the invention. Temperature measurements obtained by a sensor unit according to the invention can be used in a control system of the projection lens to control operating parameters of the projection lens. In particular, the operating parameters can be controlled in a closed control loop using the temperature measurements. The present invention further relates to a projection exposure apparatus comprising such a projection lens.

[0042] The invention also relates to a method for measuring the temperature of a mirror of a microlithographic projection exposure apparatus, the mirror comprising a mirror body and a reflective surface formed on the mirror body, a sensor element formed on a substrate of the mirror body, and a measurement signal representative of the temperature of the sensor element being transmitted to a control system of the microlithographic projection exposure apparatus.

[0043] The present disclosure encompasses developments of a method having the features described in relation to the mirror device according to the invention.The present disclosure encompasses developments of a mirror device having the features described in relation to the method according to the invention.

[0044] The invention will now be described by way of example on the basis of advantageous embodiments with reference to the accompanying drawings, in which: FIG. [Brief explanation of the drawings]

[0045] [Figure 1] 1 shows a schematic diagram of a projection exposure apparatus according to the invention; [Figure 2] 1 shows a schematic diagram of a mirror device according to the present invention; [Figure 3] 3 shows a plan view of the mirror body from FIG. 2. [Figure 4] 3 shows a vertical cross section of the mirror body shown in FIG. 2. [Figure 5] 5 shows an enlarged detail from FIG. [Figure 6] 1 shows an embodiment of a sensor element according to the invention; [Figure 7] 7 shows the diagram shown in FIG. 6 for an alternative embodiment of the present invention. [Figure 8] 7 shows the diagram shown in FIG. 6 for an alternative embodiment of the present invention. [Figure 9] 3 shows an alternative embodiment of a sensor element according to the invention; [Figure 10] 10 shows an enlarged view of the fiber Bragg light guide from FIG. [Figure 11] A variation on FIG. 8 is shown. DETAILED DESCRIPTION OF THE INVENTION

[0046] 1 shows a schematic representation of a microlithography EUV projection exposure apparatus. The projection exposure apparatus comprises an illumination system 10 and a projection lens 22. An object field 13 in an object plane 12 is illuminated by means of the illumination system 10.

[0047] The illumination system 10 includes an exposure radiation source 14 that emits electromagnetic radiation in the EUV range, i.e. in particular having a wavelength between 5 nm and 30 nm. The illumination radiation emerging from the exposure radiation source 14 is initially focused by a collector 15 onto an intermediate focal plane 16.

[0048] The illumination system 10 comprises a polarizing mirror 17 which deflects the illumination radiation emitted by the exposure radiation source 14 onto a first facet mirror 18. A second facet mirror 19 is arranged downstream of the first facet mirror 18. The individual facets of the first facet mirror 18 are imaged into the object field 13 by the second facet mirror 19.

[0049] A projection lens 22 images the object field 13 onto an image plane 21 using a number of mirrors 20. A mask (also called a reticle) is placed in the object field 13, which is imaged onto a photosensitive layer of a wafer placed at the image plane 21.

[0050] Various mirrors in a projection exposure apparatus that reflect illumination radiation are configured as EUV mirrors. The EUV mirrors are provided with a highly reflective coating. This can include multi-layer coatings, in particular multi-layer coatings with alternating layers of molybdenum and silicon. The EUV mirrors reflect approximately 70% of the incident EUV radiation. The remaining approximately 30% is absorbed, leading to heating of the EUV mirror.

[0051] 2 shows a mirror arrangement in which a mirror body 23 of a mirror 20 is held on a frame structure 29 by actuators 28. The actuators 28 can be used to change the position of the mirror 20 relative to the frame structure 29 in order to align and position the mirror 20 within the rigid body degrees of freedom. A reflective surface 24 is formed on the mirror body 23 to reflect incident EUV radiation.

[0052] Cooling channels 27 are formed in and penetrate the mirror body 23. The cooling channels 27 belong to a cooling system that includes a coolant reservoir 33 filled with a cooling liquid and a pump 30. The pump 30 draws the coolant from the coolant reservoir 33 and directs it to the cooling channels 27 via a first connecting line 35 and the input manifold 25. The coolant is returned to the coolant reservoir 33 via the output manifold 26 adjacent to the cooling channel and a second connecting line 32. The coolant absorbs heat due to absorbed EUV radiation and dissipates this heat from the mirror body 23. At the transition between the frame structure 29 and the mirror body 23, the connecting lines 32, 35 are embodied as flexible hose lines so as not to interfere with mirror adjustment and alignment.

[0053] The cooling channels 27 are aligned along the horizontal extent of the mirror body 23. They extend linearly and parallel to one another. The distance between the cooling channels 27 and the reflective surface 24 is constant over the length of the cooling channels 27 and is approximately 5 mm. While only four parallel cooling channels 27 are shown in the schematic diagram of FIG. 2, in reality there are more cooling channels 27, as shown in the cross-section of FIG. 4. FIG. 3 shows a plan view of the reflective surface 24 of the mirror body 23. In the projection exposure apparatus of FIG. 1, each of the mirrors 20 of the projection lens 22 can be configured as a mirror arrangement as shown in FIG. 2.

[0054] The mirror apparatus comprises a control unit 38 which performs various control tasks of the mirror apparatus. In particular, the control unit 38 controls the actuators 28 to bring the mirror body 23 into a desired position and orientation relative to the frame structure 29, and controls the pump 30 of the cooling system to adjust the cooling capacity. One of the input variables processed by the control unit 38 when determining control commands for the actuators 28 is a temperature measurement value relating to the temperature of the mirror body 23, which the control unit 38 obtains from a sensor unit. The temperature measurement value is used as the basis for controlling operating parameters of the mirror apparatus, such as the actuators 28 or the cooling capacity of the cooling system or the capacity of a heating unit (not shown). The control may be performed within a closed control loop.

[0055] 5 shows an enlarged view of the structure of the mirror body 23 in the region between the cooling channels 27 and the reflective surface 24. The reflective surface 24 is formed by an optical layer system 40, which is made up of alternating layers of molybdenum and silicon. The optical layer system 40 is configured to reflect approximately 70% of the incident EUV radiation.

[0056] A sensor layer 45 is formed under the optical layer system 40 and determines the temperature of the mirror body 23 in the area of ​​the sensor layer 45, and therefore in the vicinity of the reflective layer 24. In the exemplary embodiment shown in FIG. 5, conductor tracks 41 are formed in the sensor layer 45 and consist of a material whose resistance changes with temperature. Suitable materials are known, both in the form of positive temperature coefficient (PTC) thermistors and negative temperature coefficient (NTC) thermistors. Preferably, the conductor tracks 41 consist of a material whose electrical resistance is substantially proportional to temperature. The sensor layer 45 is produced by additive manufacturing, in which a non-conductive material is applied between the conductor tracks 41. To provide a good base for the construction of the optical layer system 40, the upper side of the sensor layer 45 is preferably smooth, i.e., free of bumps caused by the conductor tracks 41.

[0057] 6, the sensor layer 45 includes a plurality of conductor tracks 41 that extend parallel to one another and parallel to the reflective surface 24 through the mirror body 23. In an exemplary embodiment, the conductor tracks 41 consist of an NTC thermistor material throughout their entire length within the mirror body 23. The mirror device includes a signal generator 42 designed to transmit an electrical signal to one of the conductor tracks 41 in order to obtain a measurement of the electrical resistance of the conductor track 41. Since the relationship between temperature and the electrical resistance of the conductor track 41 is known, the signal generator 42 can communicate a measurement signal in the form of a temperature measurement to the control unit 38.

[0058] The signal generator 42 is connected to the conductor tracks 41 via a switching unit 43, which is shown schematically in Figure 6, so that the resistance of each conductor track 41 can be measured individually depending on the state of the switching unit 43. The resistance of the conductor track 41 corresponds to the average value of the temperature of the mirror body 23 over the length of the conductor track 41.

[0059] 7, the conductor tracks 41 are configured as structured conductor tracks whose electrical properties vary over their length. Each conductor track 41 includes a measurement point 44 made of NTC thermistor material. Another portion 39 of the conductor track 41 consists of a material with a low electrical resistance and forms a lead to the measurement point 44. In contrast to FIG. 6, the temperature information obtained by the signal generator 42 can be assigned to a specific position in the sensor layer 45 and thus to a specific area of ​​the reflective surface 24.

[0060] 8, the sensor layer 45 includes ten horizontally arranged conductor paths 41 and ten vertically arranged conductor paths 41. The conductor paths 41 are conductively connected to one another at some of the intersections 51, thus resulting in multiple branch points within the sensor layer 45. The switching unit 43 is configured so that the input and output interfaces are closed one by one, while all other terminals of the conductor paths 41 are not connected to the signal generator 42. In this way, multiple electrical paths can be selected for the signal output by the signal generator 42 to flow through the sensor layer 45. Locally resolved temperature measurements can be obtained by successively measuring the resistances for the multiple electrical paths and appropriately forming appropriate differences between the measurements.

[0061] In the variant shown in Fig. 11, three conductor paths 41 are connected to each switch of the switching unit 43. If the switching unit 43 is activated so that one input interface and one output interface are closed, there is only one possible electrical path for the measurement signal. Other possible current paths are blocked by diodes 55, which only allow current to pass in one direction. Only one measuring point 56 is provided in each electrical path. By activating only three switches on the input side and three switches on the output side, temperature measurements can be obtained in nine different positions in this way.

[0062] In an alternative embodiment shown in Figure 9, the mirror body 23 is made of a material that is transparent to visible light. An optical channel 48 is written into the transparent material of the mirror body 23 and extends through the mirror body 23 into the sensor layer 45. The optical channel 48 can be formed by using a laser to process the material around the channel 48 so that the channel 48 acquires a localized high refractive index. The processed material forms a kind of wall around the optical channel 48, so that the optical channel 48 acts like a light guide. An optical signal introduced inside the optical channel 48 propagates through the optical channel 48 as in a light guide.

[0063] Grating structures in the form of fiber Bragg gratings 49 are written into the optical channel 48, and these are fabricated in the same way as the walls of the optical channel 48. The fiber Bragg gratings 49 are periodic microstructures written into the material of the mirror body 23 that reflect light wavelength-selectively. Within the optical channel 48, the fiber Bragg gratings 49 are equally spaced relative to one another. Each of the fiber Bragg gratings 49 reflects a different wavelength of light.

[0064] When a large bandwidth of light is introduced into the light guide 46, only a narrowly defined spectral width of the light is reflected by each of the fiber Bragg gratings 49. The other portion of the light continues down the light guide until a different wavelength of light is reflected by the next fiber Bragg grating 49. Heating of the mirror body 23 causes the fiber Bragg gratings 49 to elongate, resulting in a change in the wavelength of the light reflected by the fiber Bragg gratings 49. Based on the wavelength of the reflected light, a measurement signal can be generated that represents the temperature in the region of the fiber Bragg grating 49. By appropriate evaluation of the reflected light signal, temperature information for each of the fiber Bragg gratings 49 can be obtained.

[0065] The mirror device includes a signal generator 47 coupled to an optical channel 48 via a light guide 46. An optical signal generated by the signal generator 47 may be incident and coupled into the optical channel 48 via the light guide 46. From the reflected light portion, the signal generator 47 determines a temperature measurement and communicates it to the control unit 38 via a signal path 50.

Claims

1. A mirror device, in particular for a microlithography projection exposure apparatus, comprising a mirror (20), a sensor unit (41, 42, 44, 47, 49) and a control unit (38), wherein the mirror (20) comprises a mirror body (23) and a reflective surface (24) formed on the mirror body (23), and the sensor unit (41, 42, 44, 47, 49) receives a sensor element (41, 49) and a measurement signal representative of the temperature of the sensor element (41, 49). and a signal path (50) extending to the control unit (38) for transmission to the control unit (38), wherein the sensor elements (41, 49) are formed on a substrate of the mirror body (23), the sensor elements include a plurality of electrical conductor paths (41) incorporated in the substrate of the mirror body (23), the electrical conductor paths (41) forming a plurality of intersections (51), and the electrical conductor paths (41) being conductively connected to each other at the intersections (51).

2. 2. The mirror device according to claim 1, wherein the conductor path (41) comprises a first portion (39) having a low temperature dependency of electrical resistance and a second portion (44) having a high temperature dependency of electrical resistance.

3. 3. The mirror device according to claim 1, wherein the substrate of the mirror body (23) comprises an area adjacent to the electrical conductor track (41) and in which the material of the mirror body (23) is electrically non-conductive.

4. Mirror arrangement according to any one of claims 1 to 3, wherein the sensor element comprises a grating structure (49) written into a transparent material of the mirror body (23).

5. 5. The mirror device according to claim 4, wherein the sensor unit comprises a signal generator (47) which sends an optical signal into the transparent material of the mirror body (23) and evaluates the part of the optical signal that is transmitted or reflected by the grating structure (49) to determine therefrom a measurement signal that is representative of the temperature of the mirror body (23) in the region of the grating structure (49).

6. 6. The mirror device according to claim 4 or 5, wherein an optical channel (48) surrounding the grating structure (49) is written into the material of the mirror body (23).

7. 7. The mirror device according to claim 1, wherein the mirror body (23) includes a sensor layer (45) extending at least in an area parallel to the reflecting surface (24), and the sensor elements (41, 49) are arranged in the sensor layer.

8. 8. The mirror device according to claim 1, wherein the sensor element (41, 49) is arranged between the reflective surface (24) of the mirror body (23) and a main body.

9. 9. The mirror device according to claim 1, wherein the mirror body (23) includes a plurality of cooling channels (27), and the sensor element (41, 49) is arranged between the reflective surface (24) and the cooling channels (27).

10. 10. A projection lens (10, 22) of a microlithography projection exposure apparatus, in which a mask (13) is imaged onto a lithography object (21) by means of a plurality of mirror arrangements (20), at least one of the mirror arrangements being configured as a mirror arrangement according to any one of claims 1 to 9.

11. 1. A method for measuring the temperature of a mirror (20) of a microlithography projection exposure apparatus, the mirror (20) comprising a mirror body (23) and a reflective surface (24) formed on the mirror body (23), a sensor element (41, 49) formed on a substrate of the mirror body (23), the sensor element comprising a plurality of electrical conductor paths (41) integrated into the substrate of the mirror body (23), the electrical conductor paths (41) forming a plurality of intersections (51), the electrical conductor paths (41) being conductively connected to one another at the intersections (51), and a measurement signal representative of the temperature of the sensor element (41, 49) being transmitted to a control system of the microlithography projection exposure apparatus.

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