Mirror arrangement, in particular for microlithographic projection exposure system, and method for measuring temperature of mirror

Abstract

The invention relates to a mirror arrangement, in particular for a microlithographic projection exposure system, comprising a mirror (20), a sensor unit (41, 42, 44, 47, 49) and a control unit (38). The mirror (20) comprises a mirror body (23) and a reflective surface (24) provided on the mirror body (23). The sensor unit (41, 42, 44, 47, 49) comprises a sensor element (41, 49) and a signal path (50) extending to the control unit (38) in order to transmit a measurement signal representative of the temperature of the sensor element (41, 49) to the control unit (38). A sensor element (41, 49) is arranged in a substrate of the mirror body (23), the sensor element comprising a plurality of electrical conductor paths (41) integrated in the substrate of the mirror body (23), and the electrical conductor paths (41) form a plurality of intersection points (51), and the electrical conductor paths (41) are electrically conductively connected to one another at the intersection points (51). The invention also relates to a method for measuring the temperature of a mirror (20).

Description

Technical Field

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

[0002] Microlithography projection exposure apparatuses are used to produce integrated circuits with particularly small structures. A mask (=reticle) irradiated with very short-wave deep ultraviolet or extreme ultraviolet radiation (DUV or EUV radiation) is imaged onto the lithographic object in order to transfer the mask structure onto the lithographic object.

[0003] The projection exposure apparatus comprises a plurality of mirrors at which the radiation is reflected. The mirrors have a precisely defined shape and are positioned precisely so that the imaging of the mask onto the lithographic object is of sufficient quality.

[0004] During operation, the projection exposure apparatus is subject to influences which have an influence on the imaging quality. As an example, if thermal expansion leads to changes in the geometry of the mirrors, the wavefront of the radiation reflected at the mirrors changes. For correct operation of the projection exposure apparatus, it is helpful to have information about the temperature of the mirrors. The temperature information can be used, for example, to control a heating unit or a cooling unit so that the temperature of the mirrors is kept at a constant value, or to appropriately adjust the projection exposure apparatus after a temperature change.

[0005] The temperature measurement can be recorded using a temperature sensor arranged near the reflector, or the temperature of the reflector can be inferred from a variable indirectly related to the temperature of the reflector. For example, the temperature of the reflector can be inferred from the temperature of the atmosphere adjacent to the reflector. This indirect measurement method does not have high accuracy. Summary of the invention

[0006] The object of the invention is to propose a reflector arrangement and a method for measuring the temperature of a reflector which avoid these disadvantages. This object is achieved by the features of the independent claims. Advantageous embodiments are given in the dependent claims.

[0007] Therefore, the object is achieved by a reflector device particularly suitable for a microlithography projection exposure device, which comprises a reflector, a sensor unit and a control unit. The reflector comprises a reflector body and a reflecting surface formed on the reflector body. The sensor unit comprises a sensor element and a signal path extending to the control unit so as to transmit a measurement signal representing the temperature of the sensor element to the control unit. The sensor element is formed in a substrate of the reflector body. The sensor element comprises a plurality of electrical conductor tracks integrated into the substrate of the reflector body. The conductor tracks form a plurality of intersections. The conductor tracks are electrically conductively connected to each other at the intersections.

[0008] The invention is based on the concept of integrating a sensor element, the physical state of which changes as a function of the temperature, directly into the substrate of the reflector body and converting a change of state into a measurement signal which can be transmitted to a control unit. The sensor element formed in the substrate of the reflector body enables a direct thermal coupling between the material of the reflector body and the sensor element. In particular, transition losses can be avoided by forming the sensor element as an integral part of the substrate of the reflector body. Changes in the temperature of the reflector body directly affect the sensor element, so that a measurement signal can be obtained which directly represents the temperature of the reflector body in the region of the sensor element.

[0009] In one embodiment, the sensor element comprises an electrical conductor track integrated into a substrate of the reflector body. The electrical printed conductors can be configured such that the resistance varies as a function of the temperature of the reflector body in the region of the conductor track. Suitable materials are known in the form of positive temperature coefficient (PTC) thermistors and in the form of negative temperature coefficient (NTC) thermistors. Preferably, the conductor track consists of a material in which the relationship between temperature and resistance is substantially proportional.

[0010] By applying an electrical signal to the conductor track, the resistance of the conductor track can be measured. The sensor unit can include a signal generator, which is designed to apply the electrical signal to the conductor track. The sensor unit can include a closed circuit, which extends from a first pole of the signal generator via the electrical conductor track to a second pole of the signal generator. A change in the resistance of the conductor track influences the electrical signal, so that a change in the temperature in the region of the electrical conductor track in the region of the mirror body can be inferred from the change in the electrical signal. The relationship between the temperature and the resistance of the conductor track is known in advance or can be determined by calibration.

[0011] The conductor track can extend from the input to the output within the reflector body. Cables or comparable conductors suitable for transmitting electrical signals can be connected to the input and output, and the electrical signals are transmitted via them between the signal generator and the conductor track. The conductor track can include a first section, in which the temperature dependence of the electrical resistance is low, and can include a second section, in which the temperature dependence of the electrical resistance is high. This allows the temperature measurement value of a specific point of the reflector body to be determined in a targeted manner. The second section of the conductor track is placed as a measuring point in the region of the reflector body in which it is desired to measure the temperature, while the first section forms a kind of lead to the second section.

[0012] In one embodiment, the electrical conductor track has a smaller cross section in the second section than in the first section. Furthermore, the first section and the second section can in particular be uniform conductor paths consisting of a uniform conductive material. The electrical conductor track can in this sense comprise a plurality of first sections and second sections. It is also possible that the conductor track consists of a different material in the second section than in the first section, wherein the material in the second section has an increased dependence of the electrical resistance on temperature.

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

[0014] The substrate of the reflector body may include an area adjacent to the electrical conductor track and in which the material of the reflector body is non-conductive. In particular, the electrical conductor track may be electrically insulated relative to the reflecting surface. The electrical conductor track may be electrically insulated relative to a rear side of the reflector body positioned opposite to the reflecting surface. In one embodiment, the electrical conductor track is completely surrounded by the non-conductive material of the reflector body.

[0015] The reflector body may comprise a plurality of electrical conductor tracks, each of which forms a sensor element in the sense of the invention. A signal path may extend from each of the conductor tracks to a control unit. The reflector body may comprise a sensor layer extending parallel to the reflecting surface, the conductor tracks being arranged within the sensor layer. A plurality of conductor tracks makes it possible to obtain temperature information from different regions of the reflector body. Each of the conductor tracks may have one or more of the above-mentioned features.

[0016] The conductor tracks may be electrically insulated from one another within the reflector body. Each of the conductor tracks then makes it possible to obtain temperature information independently of the other conductor tracks. In one embodiment, one or more intersections are provided between the conductor tracks, at which the conductor tracks are electrically conductively connected to one another. The number of intersections may be greater than 10, preferably greater than 50, more preferably greater than 100. Appropriate interconnection of the electrical connections between the conductor tracks and the signal generator makes it possible to conduct electrical signals along different paths through the reflector body and in this way obtain temperature information from different areas of the reflector body.

[0017] Each conductor track may include a switch, which is arranged between the input and the signal generator and establishes an electrical connection between the conductor track and the signal generator in a first switching state and disconnects the electrical connection in a second switching state. In addition, each conductor track may include a corresponding switch arranged between the output and the signal generator. The switches can be controlled so that in each case one switch is closed at the input and one switch is closed at the output, while all other switches are disconnected. This results in an electrical path extending between the input of the first conductor track and the output of the second conductor track, and also extending through exactly one intersection between the first conductor track and the second conductor track. In a variant, there is more than one intersection between the first conductor track and the second conductor track. The sensor unit can be designed so that the switch quickly switches between the switching states. The time period for maintaining the switching state can be, for example, between 1ms and 50ms, preferably between 2ms and 20ms. Appropriate evaluation of different measurement signals makes it possible to obtain temperature information of multiple regions of the reflector body. In order to set the current path more accurately, the conductor track can have additional electrical / electronic components, which have characteristics related to the current flow. For example, such a component may have a reverse direction and a forward direction, or exhibit a frequency dependency. In this way, the local resolution of the temperature information may be improved and / or the evaluation may be facilitated.

[0018] Another possibility of obtaining locally resolved temperature information may be to form a plurality of measuring points in a single conductor track, which measuring points can be controlled separately from each other. By way of example, the measuring points can be designed for electrical signals of different frequencies. In one embodiment, each measuring point is configured as a combination of a temperature-dependent measuring resistor and a band-stop filter configured in parallel therewith. The band-stop filter is at high impedance for a defined frequency and therefore conducts electrical signals of the relevant frequency through the measuring resistor. For other frequencies, the band-stop filter short-circuits the measuring resistor.

[0019] In one embodiment, the electrical conductor track comprises two different metals, which are electrically connected to each other at a connection point. On the basis of the Seebeck effect, the voltage between the two ends of the conductor track changes depending on the temperature at the connection point. The sensor element based on two different metals forms a thermocouple in this way. The thermocouple can be configured so that, apart from the connection point, there is no transition between the different metals within the reflector body. If there are further transitions between the different metals within the reflector body, a careful calibration of the thermocouple is required in order to be able to obtain temperature information of the connection point. The sensor unit can include a voltmeter, which measures the voltage change between the ends of the conductor track.

[0020] In one embodiment, the first section of the conductor track and the second section of the conductor track are connected to two electrodes of a capacitor, the capacitance of which varies as a function of temperature. The capacitor can be configured such that heating of the mirror body causes a change in the electrode spacing. The changed capacitance can be measured and a measurement signal representing the temperature of the mirror body in the region of the capacitor can be derived therefrom. In addition or as an alternative thereto, a dielectric having a temperature-dependent dielectric constant can be arranged between the two electrodes of the capacitor.

[0021] The capacitor may be generated in the form of a local capacitance near the reflective surface. Alternatively, one electrode of the capacitor may be arranged near the reflective surface and the second electrode may be arranged on the rear side of the reflector body. In one embodiment, a continuous electrode surface constituting a common ground of a plurality of measuring electrodes is formed near the reflective surface. The measuring electrodes may be arranged on the rear side of the reflector body or may be accommodated in the reflector body.

[0022] The reflective surface of the reflector is usually formed by a layer system that is highly reflective to EUV radiation and / or DUV radiation. It can be a multilayer coating, in particular a multilayer coating with alternating layers of molybdenum and silicon. With such a coating, about 70% of the incident EUV radiation can be reflected. The term EUV radiation refers to electromagnetic radiation in the extreme ultraviolet spectral range with a wavelength between 5nm and 100nm, in particular with a wavelength between 5nm and 30nm. DUV radiation is in the deep ultraviolet spectral range and has a wavelength between 100nm and 300nm.

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

[0024] If the sensor element comprises a conductor track, it may be a conductor track applied by a coating process. The body or part of the body to which the conductor track is applied may be non-conductive. The conductor track may be manufactured by a conductive material applied along the conductor track. The area between the conductor tracks may be filled with a non-conductive material. The layer arranged between the reflective surface and the body and in which the sensor element is arranged is called the sensor layer. If the sensor element comprises further components, such as a material whose resistance changes in a temperature-dependent manner in the case of resistance measurement, or an electrode of a capacitor in the case of capacitance measurement, or a transition between two different metals in the case of a thermocouple, these components may also be applied by coating. All components of the sensor element may be arranged within the sensor layer. The sensor layer may be covered with a layer consisting of a non-conductive material. Additional layer structures may be implemented thereon. If the layer structure comprises a surface protection layer, the sensor layer may be arranged between the reflective surface and the surface protection layer or between the surface protection layer and the body.

[0025] If the reflector body comprises a main body and a partial body, wherein the reflective surface is applied to the partial body, the sensor layer can be arranged between the reflective surface and the partial body. In other embodiments, the sensor layer is arranged between the main body and the partial body. A sensor element arranged between the reflective surface and the main body of the reflector body has an independent inventive content, even if the sensor element does not comprise a plurality of electrical conductor tracks integrated into a substrate of the reflector body.

[0026] The sensor element may also comprise a grating structure written into the transparent material of the reflector body. The grating structure may be configured such that it affects the incident light signal differently depending on the temperature, so that the temperature can be inferred from the reflected or transmitted part of the light signal. In the event of a temperature change, the transparent material is subjected to a thermal expansion which is transferred to the grating structure. Changes in the grating structure can be measured by a suitable light signal. The sensor unit may comprise a signal generator which sends a light signal into the transparent material of the reflector body and evaluates a portion of the light signal transmitted or reflected at the grating structure in order to determine therefrom a measurement signal representing the temperature of the reflector body in the region of the grating structure. The measurement signal may be conducted as an electrical signal from the signal generator to a control unit of the reflector device. A sensor element comprising a grating structure written into the transparent material of the reflector body has an independent inventive content even if the sensor element does not comprise a plurality of electrical conductor tracks integrated into the substrate of the reflector body.

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

[0028] In addition to the grating structure, an optical channel can be written into the transparent material of the reflector body, along which the light signal is guided to the grating structure. The optical channel can be formed by the material around the channel being processed using a laser, so that the light signal is reflected. As a result of the treatment using the laser, the material of the reflector body acquires a locally increased refractive index. The treated material forms a kind of wall around the channel, so that the optical channel acts like a light guide for the light signal. The light signal can be guided to the interior of the optical channel, so that the light signal propagates within the optical channel up to the grating structure.

[0029] The grating structure then acts like a fiber Bragg grating within an optical channel. The optical channel can be provided with a plurality of grating structures which are spaced apart from one another in the longitudinal direction of the optical channel and which reflect light signals of different wavelengths. Only light of a very limited spectral width near the Bragg wavelength is reflected at each fiber Bragg grating. The other part of the light continues on its path through the optical channel. The heating causes an extension of the corresponding grating structure. Based on the wavelength of the light reflected at the fiber Bragg grating, a measurement signal representing the temperature of the reflector body in the region of the fiber Bragg grating can be generated. The light guide can be provided with at least 3, preferably at least 5, more preferably at least 10 grating structures. The grating structures can be arranged in the light guide equidistantly relative to one another.

[0030] Instead of writing the optical channel into the transparent material of the reflector body, the optical channel can also be formed as a cavity in the reflector body. The cavity can extend up to the region of the reflector body where the grating structure is formed. The cavity can be formed as a bore extending from the edge of the reflector body to the vicinity of the grating structure. It is also possible to arrange the cavity at the junction between two parts of the reflector body and to shape the recess formed in one or both parts by the joining of the parts to form a closed channel.

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

[0032] In order to minimize thermal deformations of the reflector, regardless of the heat generated by the absorbed radiation, the reflector arrangement may be equipped with a cooling system which keeps the temperature of the reflector as constant as possible. The cooling system may comprise a plurality of cooling channels extending through the reflector body along the reflecting surface. The cooling system may comprise a coolant reservoir, from which the cooling channels are supplied with a coolant, in particular water. The fluid whose temperature is measured in order to infer the temperature of the reflector body may be the coolant of the cooling system.

[0033] The temperature of the reflector body in the region of the reflecting surface is of interest in many cases. Therefore, the reflector body can be configured such that the sensor element is arranged in the vicinity of the reflecting surface. The distance between the sensor element and the reflecting surface can be smaller than the distance between the sensor element and the rear side of the reflector body located opposite the reflecting surface, preferably at least 2 times larger, more preferably at least 5 times larger.

[0034] If a cooling channel is formed in the reflector body, the temperature in particular in the region of the reflector body between the cooling channel and the reflecting surface is of interest. The sensor layer is therefore preferably arranged in this region of the reflector body. The sensor element according to the invention can be arranged in the reflector body such that the distance between the reflecting surface and the sensor element is smaller than the distance between the sensor element and the cooling channel.

[0035] A description of an embodiment of the invention is given below, in which the sensor element is formed by the material of the reflector body, and in which the change in the properties of the material is determined and used as a measure of temperature. If the geometry of the reflector body changes, for example, due to temperature changes, this can be detected by means of ultrasound. To this end, ultrasound is directed to the material of the reflector body in order to excite ultrasonic oscillations in the material. In order to obtain information about the temperature of the reflector body, the damping of the ultrasound or the duration until the ultrasound appears again from the reflector body can be determined. In particular, the reflection at the interface of the reflector body can have an effect on the ultrasound, which is temperature-dependent and can therefore be used to generate a measurement signal. In addition to or as an alternative to it, the correlation with temperature can also be derived from the fact that the sound velocity in the material of the reflector body varies according to the elastic modulus, Poisson's ratio and density. If the dependence of these variables on temperature is known, the temperature can be derived from the sound velocity. In all cases, the relationship between the ultrasonic measurement value and the 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 integrated into the mirror body (e.g. optical fibers). For this purpose, laser light is directed onto the material of the mirror body and / or onto the material of components integrated into the mirror body, with the result that an interaction between light waves and acoustic lattice oscillations is established (Brillouin scattering). The frequency detuning of the laser radiation is used as a measurement signal for obtaining information, which interaction can be used for extension and / or temperature measurement. For example, continuous and pulsed laser beams can be input coupled into the material of the mirror body, and the measurement position of the relevant temperature can be inferred from the propagation time of the pulses of the pulsed laser beam. Alternatively, the Raman effect can also be used, which is based on the interaction of light waves with optical phonons instead of acoustic phonons.

[0037] In another variant, eddy currents are induced in the conductive material of the reflector body by applying an alternating magnetic field. For this purpose, a conductive layer can be introduced into the reflector body, which consists of a non-conductive material. In particular, a metal layer in the layer construction of the reflecting surface can be conceived. The eddy currents form an electromagnetic field that can be measured. The intensity of the eddy currents and the associated electromagnetic field generally depends on the resistance and geometry of the reflector body. The selection of a suitable excitation frequency makes it possible to generate a corresponding measurement signal. The temperature dependence of the measurement signal results from the fact that the resistivity of the material of the reflector body changes in a temperature-dependent manner and the distance relative to the measuring coil changes due to the thermal expansion of the reflector body.

[0038] The penetration depth of the eddy currents into the target depends inter alia on the frequency of the alternating magnetic field. The following holds true:

[0039] δ=(2ρ / ω / μ)^0.5

[0040] Wherein δ denotes the standard penetration depth, ρ denotes the resistivity, μ denotes the magnetic permeability and ω denotes the angular frequency of the excitation field. δ corresponds to a penetration depth at which the eddy current intensity still corresponds to 36.8% of the value at the target surface. At a depth of 5δ, the relative eddy current intensity is only 0.7%. The penetration depth can therefore be controlled by the excitation frequency. By means of measurements with different excitation frequencies, the resistance measurement can be assigned to a depth in the mirror body. This makes it possible to vary the depth at which the temperature is measured. In order to prevent magnetic field lines from appearing on the rear side of the target, the thickness of the target should, if possible, be greater than 5δ. Thin conductive measurement areas require high frequencies as magnetic excitation fields, for example frequencies of at least 1 MHz, preferably at least 10 MHz, more preferably at least 100 MHz, more preferably at least 1 THz.

[0041] The measurement can be performed with the aid of an excitation coil and a measuring coil. Both the excitation coil and the measuring coil can be implemented as wound coils. The coils can be flat coils or cylindrical coils, wherein each coil can be implemented with or without a core. The coils can be produced in a coating process and / or a patterning process. The coils can be of single-layer or multi-layer design.

[0042] The excitation coil and / or the measuring coil may be arranged within the reflector body and may form, for example, an integral part of a sensor layer of the reflector body. In an alternative embodiment, the excitation coil and / or the measuring coil are arranged outside the reflector body, for example on the rear side of the reflector, on a separate frame near the rear side of the reflector, on a separate frame near the reflector or at the edge of the reflector. In one embodiment, the excitation coil is arranged as a separate component adjacent to the reflecting surface, while the measuring coil is integrated in the sensor layer of the reflector body. The measuring coil may be produced by coating and patterning.

[0043] The invention further relates to a projection lens of a projection exposure apparatus, wherein a mask is imaged onto a lithographic object via a plurality of mirror arrangements, wherein at least one of the mirror arrangements is configured as a mirror arrangement according to the invention. The projection lens may comprise at least two, preferably at least three, more preferably at least five mirror arrangements according to the invention. The temperature measurement values ​​obtained by the sensor unit according to the invention may be used in a control system of the projection lens in order to control operating parameters of the projection lens. In particular, the operating parameters may be controlled in a closed control loop using the temperature measurement values. The invention further relates to a projection exposure apparatus comprising such a projection lens.

[0044] The invention also relates to a method for measuring the temperature of a reflector of a microlithography projection exposure apparatus. The reflector comprises a reflector body and a reflective surface formed on the reflector body. A sensor element is formed in a substrate of the reflector body. A measurement signal representing the temperature of the sensor element is transmitted to a control system of the microlithography projection exposure apparatus.

[0045] The present disclosure encompasses improvements of the method having features described in the context of the mirror arrangement according to the invention. The present disclosure encompasses improvements of the mirror arrangement having features described in the context of the method according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The invention is described below by way of example based on advantageous embodiments with reference to the accompanying drawings, in which:

[0047] Figure 1 : shows a schematic diagram of a projection exposure apparatus according to the present invention;

[0048] Figure 2 : shows a schematic diagram of a reflector device according to the present invention;

[0049] Figure 3 : Shows the Figure 2 A plan view of a reflector body;

[0050] Figure 4 : Shows the passage through Figure 2 A vertical cross section of the reflector body;

[0051] Figure 5 : Shows the Figure 4 Magnified details of

[0052] Figure 6 : shows an embodiment of a sensor element according to the present invention;

[0053] Figure 7-8 : shows an alternative embodiment of the present invention according to Figure 6 's view;

[0054] Fig. 9 : shows an alternative embodiment of a sensor element according to the present invention;

[0055] Fig.10 : The enlarged image shows the Fig. 9 Fiber Bragg light guides;

[0056] Fig.11 : Shows about Figure 8 variants. DETAILED DESCRIPTION

[0057] Figure 1 A microlithography EUV projection exposure apparatus is schematically illustrated. The projection exposure apparatus comprises an illumination system 10 and a projection lens 22. By means of the illumination system 10 an object field 13 in an object plane 12 is illuminated.

[0058] The illumination system 10 comprises an exposure radiation source 14 which emits electromagnetic radiation in the EUV range, ie in particular with a wavelength between 5 nm and 30 nm. The illumination radiation emerging from the exposure radiation source 14 is firstly focused by a collector 15 into an intermediate focal plane 16 .

[0059] The illumination system 10 comprises a deflection mirror 17, by which the illumination radiation emitted by the exposure radiation source 14 is deflected 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.

[0060] By means of a projection lens 22, the object field 13 is imaged into an image plane 21 using a plurality of mirrors 20. Arranged in the object field 13 is a mask (also called reticle) which is imaged onto a photosensitive layer of a wafer arranged in the image plane 21 .

[0061] The various mirrors of the projection exposure apparatus that reflect the illumination radiation are configured as EUV mirrors. The EUV mirrors are provided with a highly reflective coating. A multilayer coating may be involved, in particular a multilayer coating with alternating layers of molybdenum and silicon. The EUV mirrors reflect approximately 70% of the incident EUV radiation. The remaining approximately 30% is absorbed and leads to heating of the EUV mirrors.

[0062] Figure 2 A mirror arrangement is shown, wherein a mirror body 23 of a mirror 20 is held on a frame structure 29 by means of an actuator 28. The actuator 28 can be used to change the position of the mirror 20 relative to the frame structure 29 for the purpose of aligning and positioning the mirror 20 within the rigid body degree of freedom. A reflective surface 24 is formed on the mirror body 23, at which incident EUV radiation is reflected.

[0063] A cooling channel 27 is formed in the mirror body 23 and extends through the mirror body 23. The cooling channel 27 belongs to a cooling system which comprises a coolant reservoir 33 filled with a cooling liquid and a pump 30. With the aid of the pump 30, the cooling liquid is drawn from the coolant reservoir 33 and guided to the cooling channel 27 via a first connecting line 35 and an input manifold 25. The cooling liquid is guided back to the coolant reservoir 33 via an output manifold 26 adjoining the cooling channel and via a second connecting line 32. The cooling liquid absorbs the heat generated by the 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 hinder the adjustment and alignment of the mirror.

[0064] The cooling channels 27 are aligned along the horizontal extent of the reflector body 23. The cooling channels 27 extend linearly and parallel to each other. The distance between the cooling channels 27 and the reflecting surface 24 is constant over the length of the cooling channels 27 and is of the order of 5 mm. Figure 2 In the schematic diagram of FIG. 1 , only four cooling channels 27 parallel to each other are shown; in reality, the number of cooling channels 27 is higher, such as Figure 4 As shown in the cross-sectional diagram. Figure 3 The figure shows a plan view of the reflective surface 24 of the reflector body 23. Figure 1 In the case of a projection exposure apparatus, each of the reflectors 20 of the projection lens 22 can be configured according to Figure 2 Reflector device.

[0065] The mirror arrangement comprises a control unit 38, which performs various control tasks for the mirror arrangement. In particular, the control unit 38 controls the actuator 28 in order 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 in order to adjust the cooling capacity. One of the input variables processed by the control unit 38 when determining the control command for the actuator 28 is a temperature measurement value regarding the temperature of the mirror body 23, which the control unit 38 obtains from the sensor unit. The temperature measurement value is used as a basis for controlling operating parameters of the mirror arrangement, such as, for example, the cooling capacity of the actuator 28 or of the cooling system or the capacity of a heating unit (not shown). The control can be implemented within a closed control loop.

[0066] Figure 5 An enlarged illustration of the construction of the mirror body 23 in the region between the cooling channel 27 and the reflective surface 24 is shown. The reflective surface 24 is formed by an optical layer system 40 in which alternating layers of molybdenum and silicon are stacked on top of one another. The optical layer system 40 is configured such that approximately 70% of the incident EUV radiation is reflected.

[0067] The sensor layer 45 is formed below the optical layer system 40 and determines the temperature of the mirror body 23 in the region of the sensor layer 45 and thus in the vicinity of the reflective surface 24. Figure 5 In an exemplary embodiment of the invention, conductor tracks 41 are formed in the sensor layer 45, said conductor tracks consisting of a material whose electrical resistance varies with temperature. Suitable materials are known in the form of positive temperature coefficient (PTC) thermistors and in the form of negative temperature coefficient (NTC) thermistors. Preferably, the conductor tracks 41 consist of a material in which the relationship between temperature and electrical resistance is essentially proportional. The sensor layer 45 is produced by additive manufacturing, wherein the sensor layer 45 is shaped such that a non-conductive material is applied between the conductor tracks 41. The top side of the sensor layer 45 is preferably smooth, i.e. without protrusions caused by the conductor tracks 41, in order to provide a good basis for the construction of the optical layer system 40.

[0068] like Figure 6 As shown, the sensor layer 45 comprises a plurality of conductor tracks 41, which extend through the reflector body 23 parallel to each other and parallel to the reflective surface 24. In the exemplary embodiment, the conductor tracks 41 consist of an NTC thermistor material over their entire length within the reflector body 23. The reflector device comprises a signal generator 42, which is designed to transmit an electrical signal to one of the conductor tracks 41 in order to obtain a measurement value of the resistance of the conductor track 41. Since the relationship between the temperature and the resistance of the conductor track 41 is known, the signal generator 42 can transmit a measurement signal in the form of a temperature measurement value to the control unit 38.

[0069] The signal generator 42 is connected via Figure 6 A switching unit 43 schematically shown in FIG. 4 is connected to the conductor tracks 41 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 a conductor track 41 corresponds to the average value of the temperature of the mirror body 23 over the length of the conductor track 41.

[0070] In accordance with Figure 7 In the case of a variant of the present invention, the conductor tracks 41 are configured as structured conductor tracks, the electrical properties of which vary over the length of the conductor tracks 41. Each conductor track 41 comprises a measuring point 44 consisting of an NTC thermistor material. The other sections 39 of the conductor tracks 41 consist of a material having a low electrical resistance and form leads to the measuring points 44. Figure 6 Instead, the temperature information obtained by means of the signal generator 42 can be assigned to a specific location within the sensor layer 45 and thus to a specific area of ​​the reflective surface 24 .

[0071] exist Figure 8 , the sensor layer 45 comprises ten conductor tracks 41 aligned in the horizontal direction and ten conductor tracks 41 aligned in the vertical direction. The conductor tracks 41 are conductively connected to each other at some of the intersections 51, thus generating a plurality of branch points within the sensor layer 45. The switch unit 43 is configured so that one input interface and one output interface are respectively closed, while all other terminals of the conductor tracks 41 are not connected to the signal generator 42. In this way, a plurality of electrical paths can be selected along which the signal output by the signal generator 42 flows through the sensor layer 45. Locally resolved temperature measurements can be obtained by continuously measuring the resistance of a plurality of electrical paths and, if appropriate, forming a suitable difference between the measured values.

[0072] exist Fig.11 In the case of the variant shown, three conductor tracks 41 are connected to each switch of the switching unit 43. If the switching unit 43 is actuated so that one input interface and one output interface are respectively closed, there is exactly one electrical path that the measurement signal can take. Other possible paths for the current are blocked by a diode 55, which allows the current to pass only in one direction. Exactly one measuring point 56 is provided in each of the electrical paths. By actuating only three switches on the input side and three switches on the output side, temperature measurement values ​​can be obtained in this way at nine different positions.

[0073] In accordance with Fig. 9In the case of an alternative embodiment, the reflector body 23 is made of a material that is transparent to visible light. The optical channel 48 is written into the transparent material of the reflector body 23 and extends through the reflector body 23 within the sensor layer 45. The optical channel 48 can be formed by treating the material around the channel 48 using a laser so that the material obtains a locally increased refractive index. The treated material forms a kind of wall around the optical channel 48 so that the optical channel 48 acts like a light guide. The optical signal introduced inside the optical channel 48 propagates in the optical channel 48 as in a light guide.

[0074] Grating structures in the form of fiber Bragg gratings 49 are written into the optical channel 48, which are produced by the same method as for the walls of the optical channel 48. The fiber Bragg gratings 49 are periodic microstructures that are written into the material of the reflector body 23 and reflect light wavelength-selectively. In the optical channel 48, the fiber Bragg gratings 49 are arranged equidistantly relative to each other. Each fiber Bragg grating 49 reflects light of a different wavelength.

[0075] If light with a large bandwidth is introduced into the light guide 46, only light of a narrow limited spectral width is reflected at each of the fiber Bragg gratings 49. The rest of the light continues on its path through the light guide until a different wavelength of light is reflected at the next fiber Bragg grating 49. The heating of the reflector body 23 causes an extension of the fiber Bragg grating 49, as a result of which the wavelength of the light reflected at the fiber Bragg grating 49 changes. Based on the wavelength of the reflected light, a measurement signal can be generated that is representative of the temperature in the region of the fiber Bragg grating 49. Appropriate evaluation of the reflected light signal makes it possible to obtain temperature information for each of the fiber Bragg gratings 49.

[0076] The reflector arrangement comprises a signal generator 47 coupled to an optical channel 48 via a light guide 46. The light signal generated by the signal generator 47 can be 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 transmits it to the control unit 38 via a signal path 50.

Claims

1. A mirror arrangement, 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), wherein the sensor unit (41, 42, 44, 47, 49) comprises a sensor element (41, 49) and a signal path (50) extending to the control unit (38) in order to transmit a measurement signal representing the temperature of the sensor element (41, 49) to the control unit (38), wherein the sensor element (41, 49) is formed in a substrate of the mirror body (23), wherein the sensor element comprises a plurality of electrical conductor tracks (41) integrated into the substrate of the mirror body (23), and wherein the conductor tracks (41) form a plurality of intersections (51), and wherein the conductor tracks (41) are electrically conductively connected to one another at the intersections (51).

2. The reflector device according to claim 1, wherein: The conductor track (41) comprises a first section (39) in which the temperature dependence of the electrical resistance is low, and a second section (44) in which the temperature dependence of the electrical resistance is high.

3. The reflector device according to claim 1 or 2, wherein: The substrate of the mirror body (23) comprises a region adjoining the electrical conductor track (41) and in which the material of the mirror body (23) is electrically non-conductive.

4. A 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. The reflector device according to claim 4, wherein: The sensor unit comprises a signal generator (47) which sends a light signal into the transparent material of the mirror body (23) and evaluates the part of the light signal which is transmitted or reflected at the grating structure (49) in order to determine therefrom a measurement signal which represents the temperature of the mirror body (23) in the region of the grating structure (49).

6. The reflector 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. The reflector device according to any one of claims 1 to 6, wherein: The mirror body (23) comprises a sensor layer (45) which extends at least in regions parallel to the reflective surface (24) and in which the sensor elements (41, 49) are arranged.

8. The reflector device according to any one of claims 1 to 7, wherein: The sensor element (41, 49) is arranged between the reflective surface (24) and the main body of the reflector body (23).

9. The reflector device according to any one of claims 1 to 8, wherein: The reflector body (23) comprises a plurality of cooling channels (27), and wherein the sensor element (41, 49) is arranged between the reflective surface (24) and the cooling channels (27).

10. A projection lens for a microlithography projection exposure apparatus (10, 22), wherein a mask (13) is imaged onto a lithographic object (21) via a plurality of mirror arrangements (20), wherein at least one of the mirror arrangements is configured as a mirror arrangement as claimed in any one of claims 1 to 9.

11. A method for measuring the temperature of a reflector (20) of a microlithography projection exposure device, wherein the reflector (20) comprises a reflector body (23) and a reflecting surface (24) formed on the reflector body (23), wherein a sensor element (41, 49) is formed in a substrate of the reflector body (23), wherein the sensor element comprises a plurality of electrical conductor tracks (41) integrated into the substrate of the reflector body (23), wherein the conductor tracks (41) form a plurality of intersections (51), wherein the conductor tracks (41) are electrically conductively connected to each other at the intersections (51), and wherein a measurement signal representing the temperature of the sensor element (41, 49) is transmitted to a control system of the microlithography projection exposure device.

Images