WO2024068286A1

WO2024068286A1 - Mirror device and method for measuring the temperature of a mirror

Info

Publication number: WO2024068286A1
Application number: PCT/EP2023/075241
Authority: WO
Inventors: Johannes Lippert; Andreas Raba; Markus Raab; Stefan Hembacher; Hans Michael STIEPAN
Original assignee: Carl Zeiss Smt Gmbh
Priority date: 2022-09-28
Filing date: 2023-09-14
Publication date: 2024-04-04
Also published as: DE102022210246A1

Abstract

The invention relates to a mirror device, in particular for a microlithographic projection illumination system, having a mirror (20), a sensor apparatus (37, 39, 46, 47) and a control unit (38). The mirror (20) comprises a mirror body (23) and a reflection surface (24) formed on the mirror body (23). The mirror body (23) is provided with cooling channels (27). The sensor apparatus (37, 39, 46, 47) comprises a sensor component (39, 46) thermally coupled to the mirror body (23), and a signal path (48) extending to the control unit (38) for transferring a measurement signal, representing the temperature of the coupling substance, to the control unit (38). The sensor component (39, 46, 48) is arranged in a cavity (27, 40) of the mirror body (23). The sensor component (39, 46) is arranged in a position between the cooling channels (27) and the reflection surface (24). The invention also relates to a method for measuring the temperature of a mirror (20).

Description

MIRROR DEVICE AND METHOD FOR MEASURING THE TEMPERATURE OF A MIRROR

The invention relates to a mirror device, in particular for a microlithographic projection exposure system, and to a method for measuring the temperature of a mirror.

Microlithographic projection exposure systems are used for the production of integrated circuits with particularly small structures. A mask (= reticle) illuminated with very short-wave, deep ultraviolet or extreme ultraviolet radiation (DUV or EUV radiation) is imaged onto a lithography object in order to transfer the mask structure to the lithography object.

The projection exposure system includes several mirrors on which the radiation is reflected. The mirrors have a precisely defined shape and are precisely positioned so that the image of the mask on the lithographic object has sufficient quality.

During operation, the projection exposure system is exposed to influences that affect the quality of the image. If, for example, thermal expansion leads to a change in the geometric shape of a mirror, the wave front of the radiation reflected by the mirror changes. For the projection exposure system to operate properly, it is helpful to have information about the temperature of the mirror. The temperature information can be used, for example, to control a heating device or a cooling device so that the temperature of the mirror is kept at a constant value, or to to adjust the projection exposure system appropriately after a temperature change.

DE 10 2018 207 126 Al and DE 10 2021 200 788 Al describe methods for determining the temperature of a mirror body. It has been found that the methods described there are less suitable if the mirror body is equipped with cooling channels and that it is not easily possible to determine a temperature measurement value that is valid for the area of the reflection surface in a mirror body equipped with cooling channels.

The object of the invention is to present a mirror device and a method for measuring the temperature of a mirror which avoid these disadvantages. The object is achieved with the features of the independent claims. Advantageous embodiments are specified in the subclaims.

The object is achieved by a mirror device which is particularly suitable for a microlithographic projection exposure system and has a mirror, a sensor device and a control unit. The mirror comprises a mirror body and a reflection surface formed on the mirror body. The mirror body comprises cooling channels. The sensor device comprises a sensor component which is thermally coupled to the mirror body and a signal path which extends to the control unit in order to transmit a measurement signal representing the temperature of the mirror body to the control unit. The sensor component is arranged in a cavity of the mirror body. The sensor component is arranged in a position between the cooling channels and the reflection surface.

A sensor component arranged between the cooling channels and the reflection surface results in an improved coupling of the sensor component with the temperature of the reflection surface. A change in the temperature of the reflection surface acts on the sensor component with less delay, so that a measurement signal can be obtained that corresponds well to the temperature of the reflection surface in the area of the sensor component.

The reflecting surface of the mirror can be designed for high reflectivity of EUV radiation and/or DUV radiation. EUV radiation refers to electromagnetic radiation in the extreme ultraviolet spectral range with wavelengths between 5 nm and 100 nm, in particular with wavelengths between 5 nm and 30 nm. DUV radiation lies in the deep ultraviolet spectral range and has a wavelength between 100 nm and 300 nm. The reflection surface can be formed by a highly reflective coating. It can be a multilayer coating, in particular a multilayer coating with alternating layers of molybdenum and silicon. With such a coating, around 70% of the incident EUV radiation can be reflected. The remaining approximately 30% is absorbed and causes the EUV mirrors to heat up.

In order to keep the thermal deformation of the mirror to a minimum despite the absorbed heat, the mirror device can be equipped with a cooling system with which the temperature of the mirror is kept as constant as possible. The cooling channels of the mirror body according to the invention can be a component of the cooling system. The cooling system can comprise a plurality of cooling channels which extend at a distance from the reflection surface within the mirror body. The cooling system can comprise a coolant supply from which the cooling channels are fed with a coolant, in particular water. The cooling channels according to the invention are used to span a surface within the mirror body that is at a distance from the reflection surface. If a sensor component is arranged in a position between the cooling channels and the reflection surface, this is equivalent to the sensor component being arranged between the surface spanned by the cooling channels and the reflection surface. In one embodiment, the surface is spanned by the axes of the cooling channels. Alternatively, the surface can be spanned by those areas of the wall of the cooling channels that are the smallest distance from the reflection surface.

The cooling channels can be different sections of a cooling system through which the coolant is conducted within the mirror body. The cooling channels can be formed by sections of the cooling system that are arranged between an inlet manifold and an outlet manifold. A cooling fluid can then flow through the cooling channels parallel to one another. It is also possible for the cooling channels to be formed by sections of a cooling system in which the cooling fluid is conducted through the mirror body along a path that is, for example, serpentine. In such an embodiment, the cooling fluid can flow one after the other through the different cooling channels that span the surface.

The mirror device can include a frame structure on which the mirror body is suspended. It can be a movable suspension so that the position of the mirror body is adjustable relative to the frame structure. The mirror device may include one or more actuators to change the position of the mirror body relative to the frame structure. The mirror device can include a supply line with which a cooling fluid is supplied from a coolant supply to the cooling channels. The mirror device can include a discharge line through which the cooling fluid is removed from the mirror body. The supply line and/or the output line can be designed to be flexible, so that a movement of the mirror body relative to the frame structure can be absorbed elastically by the supply line/the output line.

If the cooling system has an input distributor and an output distributor, these can be mounted together with the mirror body relative to the frame structure. This means that the input distributor and the output distributor move together with the mirror body relative to the frame structure. In one embodiment, the input distributor and/or the output distributor are arranged inside the mirror body. The supply line to the input distributor and/or the derivative from the output distributor can bridge the transition from the frame structure to the mirror body. The cooling fluid can be water.

The sensor component can include a coupling substance. A component of the sensor component is referred to as a coupling substance, via which the thermal coupling between the mirror body and the sensor component takes place. For example, the housing of a sensor component can form a coupling substance. The signal path from the sensor component to the control unit can be formed by a cable that extends from the sensor component to the control unit. It is also possible to transmit the temperature measurement value from the sensor component to the control unit via a radio connection.

The cavity in which the sensor component is arranged can be a cavity accessible from the outside, so that the sensor component can be inserted into the cavity of the mirror body after completion of the mirror body. For this purpose, it is advantageous if the cross-section of the access extends over the entire length of the access is larger than the sensor component so that the sensor component can be inserted into the cavity through the access. The access to the cavity can open into a rear side of the mirror body opposite the reflection surface. Insertion of the sensor component is made easier if the access extends in a straight line to the cavity. Accesses that are diverted between the opening and the cavity are also possible. Such accesses can open, for example, into a side surface arranged between the reflection surface and the rear side. The sensor component can be inserted into the cavity using an endoscopic tool. Insertion of the sensor component is made easier if the mirror body is made of a material that is transparent to visible light so that the sensor component is visible from the outside.

In other embodiments, the cavity can be closed all around or the cross section of the access can be smaller than the sensor component. The sensor component can be introduced into the cavity during the production of the mirror body. For example, the mirror body can be composed of a first mirror body part and a second mirror body part. The first mirror body part can have a recess into which the sensor component is inserted. In the assembled state of the mirror body, the access to the recess can be covered by the second mirror body part. It is also possible for a cavity formed in the mirror body part, in which the sensor component is arranged, to be closed by additive manufacturing steps during the completion of the mirror body.

The first mirror body part and the second mirror body part can be joined together by heating the parts so that bonds form on a molecular level. This requires high temperatures of, for example, at least 600 °C is required. The risk of damage to the sensor device can be reduced if the mirror body parts are joined at a lower temperature. For example, the mirror body parts can be glued together. Soldering or brazing processes are also often possible without damaging the sensor device because the temperature increase remains local.

In order to determine the temperature of the mirror body in the area of the reflection surface, the mirror body can be designed such that the sensor component arranged in the cavity is arranged near the reflection surface. The distance of the sensor component to the reflection surface can be smaller than the distance of the sensor component to the rear side of the mirror body opposite the reflection surface, preferably at least a factor of 2 larger, more preferably at least a factor of 5 larger. The thickness of the mirror body between the reflection surface and the back can be between 30 mm and 800 mm, for example. The distance between the sensor component and the reflection surface can be, for example, between 2 mm and 30 mm, preferably between 5 mm and 15 mm.

According to the invention, the temperature in an area of the mirror body lying between the cooling channels and the reflection surface is of particular interest. The sensor component can be arranged such that the distance between the reflection surface and the sensor component is smaller than the distance between the sensor component and the cooling channels. In one embodiment, the sensor component is arranged in a cavity which is formed by a branch of the cooling channel facing the reflection surface. The opening in the wall of the cooling channel then provides access to the cavity. The cooling channel corresponds to the channel in which the cooling liquid moves. A cavity in the form of a branching off from the cooling channel The blind hole is not part of the cooling channel in this sense.

In one variant, the cavity is designed as a channel with a stepped cross-section. The transition between a larger cross-section and a smaller cross-section can be formed by a conical surface. The sensor component can be connected by placing a conical outer surface of the sensor component on the conical transition of the channel. In this way, several sensor components can be arranged one behind the other in a channel.

The sensor component can be arranged in the cavity such that the sensor component is thermally coupled to the mirror body. The sensor component can be connected in a suitable manner to the wall of the cavity, in particular to a wall surface pointing in the direction of the reflection surface. The connection between the sensor component and the wall of the cavity can be made, for example, by gluing, soldering or clamping. The cavity and/or the access to the cavity can form a hollow space in the mirror body or be filled with a material, for example cast. For the purpose of deformation decoupling in the direction of the reflection surface, the cavity can be provided with grooves.

The measurement signal sent to the control unit can be an electrical signal. The control unit can evaluate the measurement signal to generate a control signal with which an operating parameter of the mirror device or of the projection exposure system in which the mirror device is used is set. The measurement signal can be transmitted to the control unit via an electrical conductor or via a radio connection. The electrical conductor can be a cable that is led outwards from the cavity of the mirror body. For this purpose, it is advantageous if the cavity is a cavity that is accessible from the outside. The cable can extend along an access through which the sensor component was also introduced into the cavity. In particular, the cable can extend along an access whose cross-section is smaller than the sensor component.

The electrical conductor can also be a conductor track that is formed in the substrate of the mirror body. For example, one or more conductor tracks can be formed in a mirror body that otherwise consists of a non-conductive material. Conductor tracks that are applied in the form of a coating to a surface of the mirror body, in particular on a wall surface of the cavity, are also possible. The conductor tracks can be connected to electrical contacts of the sensor component and provide an electrical connection to a control unit of the mirror device.

If the mirror device includes a cooling system, the electrical conductors can extend along a cooling channel in the form of cables or conductor tracks coated on the channel wall. This will come into consideration in particular if the cavity branches off from the cooling channel. Conductor tracks that extend along a joint between a first mirror body part and a second mirror body part are also possible.

If the mirror device comprises a plurality of temperature sensors, a separate electrical conductor path can be provided for each temperature sensor, via which the measurement signal is transmitted to the control unit. It is also possible that the number of electrical conductor routes is smaller than the number of temperature sensors and that several temperature sensors are controlled with different electrical signals via a single conductor route. The different electrical signals can, for example, have different frequencies.

Before installation in the mirror body, the sensor component can be a finished part that is inserted into the cavity as such. All types of conventional temperature sensors that have dimensions suitable for the cavity can be considered. Instead of a finished part, it is also possible to apply the sensor component directly to the material of the mirror body during manufacture of the mirror body, for example by coating, and to create a signal path to the control unit in a suitable manner.

In one embodiment, one or more light guides are arranged as a sensor component in cavities of the mirror body. The temperature information can result from the fact that the material of the light guide is subject to thermal expansion when the temperature changes. The light guide can be provided with a fiber Bragg grating. A fiber Bragg grating is a periodic microstructure written into the light guide that reflects light in a wavelength-selective manner. If light with a large bandwidth is introduced into the light guide, only light of a very limited spectral width around the Bragg wavelength is reflected on the fiber Bragg grating. The remaining portions of the light continue their path through the light guide. Heating causes the light guide to stretch and thus the grating to stretch. Based on the wavelength of the light reflected on the fiber Bragg grating, a measurement signal can be generated that represents the temperature in the area of the fiber Bragg grating. The temperature-dependent expansion of the fiber Bragg lattice can be overlaid with other temperature-dependent effects. If the refractive index of the light guide is temperature-dependent, the speed of light and thus the wavelength of the light in the fiber material varies. This also has an effect on the reflected light components and can be used to generate temperature information. The mirror device can include a signal generator assigned to the light guide, which is designed to introduce a light signal into the light guide and to generate a temperature measurement value from reflected or transmitted portions of the light, which represents the temperature of the mirror body in the area of the light guide. The signal generator can send the temperature measurement value to the control unit as a measurement signal.

The light guide can be provided with a plurality of fiber Bragg gratings, which are formed in the light guide at a distance from one another. The fiber Bragg gratings can be designed to be reflective for different wavelengths of light. By appropriately evaluating the reflected light signals, temperature information can be obtained for each of the fiber Bragg gratings. The light guide can be provided with at least 3, preferably at least 5, more preferably at least 10 fiber Bragg gratings. The fiber Bragg gratings can be arranged equidistant from one another in the light guide.

For good thermal coupling between the glass fiber and the mirror body, the space between the glass fiber and the wall of the cavity can be filled with a material, in particular with a material with good thermal conductivity. The material can be mechanically soft, so that there is no mechanical coupling between the mirror body and the light guide, so that thermal expansion of the mirror body is not transferred to the light guide. In other In some embodiments, the material is mechanically hard, so that in addition to the thermal coupling, a mechanical coupling is achieved. Thermal expansion of the mirror body can then cause an expansion of the light guide, in particular an expansion in the longitudinal direction of the light guide. Stretching the light guide in the longitudinal direction also affects the reflected light signal and can be used to generate temperature information.

In a further embodiment, the sensor component comprises a thermocouple made of two different metals that are electrically connected to one another at a connection point. A conductor can be led outwards from each connection point. Based on the Seebeck effect, the voltage between the two conductors led outwards changes depending on the temperature at the connection point. The thermocouple can be a component of a sensor component that is introduced into the cavity.

The thermocouple can be designed in such a way that apart from the junction there is no transition between different metals within the mirror body. If there are further transitions between different metals within the mirror body, careful calibration of the thermocouple is necessary so that the temperature reading is not falsified.

A comparative example is also disclosed in which a fluid, in particular a liquid, is arranged in the cavity of the mirror body. The cavity can have the shape of a channel that extends through the mirror body between an inlet end and an outlet end. The temperature of the fluid depends on the amount of heat the fluid as it flows through the channel , which in turn is a direct measure of the temperature of the mirror body .

The sensor device may include a first temperature sensor to measure the temperature of the fluid in the channel. The first temperature sensor may be located at the exit end of the channel. In order to be able to draw conclusions about the temperature of the mirror body from the measured value of the first temperature sensor, it is advantageous to have a reference value for the initial state of the fluid, to which the temperature measured value can be set in relation. The reference value can result, for example, from the fact that the fluid is introduced into the channel with a defined initial temperature and/or a defined volume flow. The difference between the temperature measurement value and the reference value determines how much heat the fluid has absorbed as it flows through the channel. The volume flow can be continuously measured during operation of the mirror device. Ongoing measurement of the volume flow can be dispensed with if the volume flow is initially calibrated once and the corresponding volume flow is maintained during operation of the mirror device. The volume flow can also be determined mathematically, subject to a loss of accuracy.

In one variant, the sensor device comprises a second temperature sensor, which is arranged such that a section of the channel is enclosed between the first temperature sensor and the second temperature sensor. The difference between the measured value of the first temperature sensor and the measured value of the second temperature sensor can be used to determine the amount of heat that the fluid has absorbed in the channel section between the two temperature sensors. In this case too, it is advantageous if information about the volume flow is available, either through ongoing measurement or may be provided by an initial calibration or by a computational determination.

If the first temperature sensor is arranged at the outlet end of the channel and the second temperature sensor at the inlet end of the channel, the measurement is integrated over the entire amount of heat that the fluid has absorbed in the channel section. It is not possible to determine in which area of the duct section the heat was absorbed. In one embodiment, the channel is provided with more than two temperature sensors, for example with at least three, preferably with at least five temperature sensors. The temperature sensors can be distributed between the input end and the output end of the channel. Based on the temperature difference between adjacent temperature sensors, it can be determined in which area of the channel the fluid has absorbed how much heat.

The mirror body can be provided with a plurality of channels in which information about the temperature of the mirror body is obtained in this way. In one embodiment, the channels extend between an input distributor and an output distributor, so that the fluid can be supplied and removed via a single line. It is possible to each provide the channels between the input distributor and the output distributor with one or more temperature sensors in order to obtain temperature measurements from the individual channels. Additionally or alternatively, an average value across all channels arranged between the input distributor and the output distributor can also be determined using a temperature sensor in the input distributor and a temperature sensor in the output distributor. The volume flow of the fluid can also be measured in one of the distributors or in each of the channels. The invention also includes the combination that the temperature in each of the channels, but the volume flow is only measured in one of the distributors.

The invention also relates to a projection lens of a projection exposure system in which a mask is imaged onto a lithography object using a plurality of mirror devices, at least one of the mirror devices being designed as a mirror device according to the invention. The projection lens can comprise at least two, preferably at least three, more preferably at least five mirror devices according to the invention. The temperature measurement value obtained with the sensor device according to the invention can be used in a control system of the projection lens in order to control an operating parameter of the projection lens. In particular, the operating parameter can be regulated in a closed control loop using the temperature measurement value. The invention further relates to a projection exposure system with such a projection lens.

The invention also relates to a method for measuring the temperature of a mirror of a microlithographic projection exposure system. The mirror comprises a mirror body and a reflection surface formed on the mirror body. The mirror body includes cooling channels. A cavity is formed in the mirror body, in which a sensor component that is thermally coupled to the mirror body is arranged. A measurement signal representing the temperature of the coupling substance is transmitted to a control system of the microlithographic projection exposure system. The sensor component is arranged in a position between the cooling channels and the reflection surface.

The disclosure includes further developments of the method with features that are relevant in connection with the mirror device. The disclosure includes further developments of the mirror device with features that are described in connection with the method according to the invention.

The invention is described below by way of example with reference to the accompanying drawings using advantageous embodiments. Show it:

Fig. 1: a schematic representation of a projection exposure system according to the invention;

Fig. 2: a schematic representation of a mirror device according to the invention;

Fig. 3: a horizontal section of a mirror body according to a comparative example;

Fig. 4: a top view of the mirror body from Fig. 3;

Fig. 5: a vertical section of the mirror body from

Fig.2;

6-9: a view corresponding to FIG. 5 in various embodiments of the invention;

Fig. 10: an alternative embodiment of the invention;

Fig. 11: the fiber Bragg light guide from Fig. 10 in an enlarged view;

Fig. 12: an embodiment of a sensor component according to the invention.

A microlithographic EUV projection exposure system is shown schematically in FIG. The projection exposure The lighting system includes a lighting system 10 and a projection lens 22. With the help of the lighting system 10, an object field 13 in an object plane 12 is illuminated.

The lighting system 10 includes an exposure radiation source 14 that emits electromagnetic radiation in the EUV range, i.e. in particular with a wavelength between 5 nm and 30 nm. The illumination radiation emanating from the exposure radiation source 14 is first bundled into an intermediate focus plane 16 using a collector 15 .

The illumination system 10 comprises a deflection mirror 17, with 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.

With the aid of the projection lens 22, the object field 13 is imaged into an image plane 21 via a plurality of mirrors 20. A mask (also called a reticle) is arranged in the object field 13 and is imaged onto a light-sensitive layer of a wafer arranged in the image plane 9.

The various mirrors of the projection exposure system, on which the illumination radiation is reflected, are designed as EUV mirrors. The EUV mirrors are provided with highly reflective coatings. These can be multilayer coatings, in particular multilayer coatings with alternating layers of molybdenum and silicon. The EUV mirrors reflect around 70% of the incident EUV radiation. The remaining approximately 30% is absorbed and causes the EUV mirrors to heat up. In Fig. 2 shows a mirror device in which a mirror body 23 of a mirror 20 is held on a frame structure 29 via actuators 28. The position of the mirror 20 relative to the frame structure 29 can be changed via the actuators 28 in order to align and position the mirror 20 within the rigid body degrees of freedom. A reflection surface 24 is formed on the mirror body 23, on which incident EUV radiation is reflected.

Cooling channels 27 are formed in the interior of the mirror body 23 and extend through the mirror body 23 . The cooling channels 27 span a surface that is at a distance from the reflection surface 24 of 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. With the pump 30, coolant is sucked in from the coolant supply 33 and directed to the cooling channels 27 via a first connecting line 35 and an inlet distributor 25. The cooling liquid is fed back to the coolant supply 33 via an output distributor 26 connected to the cooling channels and a second connecting line 32. The cooling liquid absorbs heat generated by the absorbed EUV radiation and removes it from the mirror body 23. At the transition between the frame structure 29 and the mirror body 23, the connecting lines 32, 35 are designed as flexible hose lines so that the adjustment and alignment of the mirrors are not hindered.

The cooling channels 27 are aligned along the horizontal extent of the mirror body 23. The cooling channels 27 extend in a straight line and parallel to one another. The distance between the cooling channels 27 and the reflection surface 24 is constant over the length of the cooling channels 27 and is on the order of 5 mm. In other embodiments, the distance between the cooling channels 27 and the reflection surface 24 varies and between the cooling channels 27. In the schematic representation of Fig. 2, only four mutually parallel cooling channels 27 are shown; in fact, the number of cooling channels 27 is higher, as shown in the sectional view in FIG. 5 shows. In the projection exposure system from Fig. 1 is each of the mirrors 20 of the projection lens 22 as a mirror device according to FIG. 2 trained. It is also possible to equip only part of the mirrors 20 in this way.

The mirror device includes a control unit 38, which takes on various control tasks for the mirror device. Among other things, 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 that the control unit 38 processes when determining the control commands for the actuators 28 are temperature measurements about the temperature of the mirror body 23, which the control unit 38 receives from a sensor device. Based on the temperature measurements, operating parameters of the mirror device are controlled, such as the actuators 28 or the cooling capacity of the cooling system. The control can take place within a closed control loop.

In Fig. 3 shows an embodiment of a mirror device in which the input distributor 25 and the output distributor 26 lie outside the mirror body 23. The sections of the cooling channels 27 located within the mirror body 23 form cooling sections 36 through which the heat is absorbed by the reflection surface 24. Within the area shown in Fig. 3 cooling channel 27 shown below, three temperature sensors 37 are arranged, one of which is positioned at the input end of the cooling section 36, one at the output end of the cooling section 36 and one in the middle. Each of the temperature sensors 37 measures the temperature of the cooling liquid flowing through the cooling section 36. The measurement signal is conducted outside to a control unit 38 via cables arranged in the cooling channel 27.

As it flows through the cooling section 36, the cooling liquid heats up as heat is absorbed by the mirror body 23. From the temperature difference of the cooling liquid between the inlet end and the middle of the cooling section 36, it can be determined what temperature the mirror body 23 has in the first half of the cooling section 36. The temperature in the second half of the cooling section 36 can be determined from the temperature difference between the center of the cooling section 36 and the output end. An electrical signal path extends from the temperature sensor 37 to the control unit 38, via which the measurement signal is transmitted.

Two temperature sensors 37 are arranged in another cooling channel 27 of the mirror body 23. With the measured values of the two temperature sensors 37, an average value of the temperature in the area of the cooling channel between the two temperature sensors 37 can be determined.

In the variant according to Fig. 4, a temperature sensor 37 is arranged within the input distributor 25 and within the output distributor 26. With these two temperature sensors 37, an average value of the temperature can be determined across all cooling channels 27 arranged between the input distributor 25 and the output distributor 26.

In the embodiment according to the invention according to Fig. 6, a cavity 40 is formed in the mirror body 23, which extends from the rear side 42 of the mirror body 23 to the vicinity of the reflection surface 24. A temperature sensor 39 is attached to a wall of the cavity 40 facing the reflection surface 24. The temperature sensor 39 is glued to the wall. so that the temperature sensor 39 is thermally coupled with the material of the mirror body 23. The cavity 40 has an access with a constant cross-section so that the temperature sensor

39 as a finished sensor component can be inserted into the cavity 40 from the back 42 of the mirror body 23.

A cable 41 is led out of the cavity 40 to transmit the measurement signal to the control unit 38. Furthermore, the cavity 40 forms a freely accessible hollow space.

In Fig. 7, the cavity 40 is a branch to a cooling channel 27. A sensor component in the form of a temperature sensor 39 is arranged in the cavity 40 . The temperature measurement value is transmitted to the control unit 38 via a cable 41 that is routed to the outside along the cooling channel 27 . The cavity

40 is cast with a substance so that the flow of the cooling liquid through the cooling channel 27 is not impaired by the cavity 40.

Fig. 8 shows an embodiment in which the temperature sensor 39 was introduced into the cavity 40 during production. The cable 41 is guided through an access to the cavity 40, the cross section of which is smaller than the sensor component 39, so that subsequent insertion of the temperature sensor 39 into the cavity 40 is not possible.

In the embodiment according to Fig. 9, the mirror body 23 is assembled from a base body 44 and a second partial body 45. The joining plane between the base body 44 and the second partial body 45 is marked with 43. In the second partial body 45, a bore is formed for each cavity 40, which forms the cavity 40 for the temperature sensor 39. In the base body 44, a bore with a smaller diameter is formed for each cavity 40, through which the cable 41 is led to the outside. The temperature sensors 39 are inserted into the bores before joining. After joining the two Components there is no longer any access that is large enough to insert the temperature sensors 39 into the cavities 40 .

In Fig. 10, a light guide 46 is inserted into a cavity 40 in the form of a channel. The space between the light guide 46 and the wall of the cavity 40 is filled with a substance in order to thermally couple the light guide 46 to the mirror body 23. If the temperature in the mirror body 23 changes, the temperature of the light guide 46 also changes. According to Fig. 11, the light guide 46 is provided with a plurality of fiber Bragg gratings 49 which are formed in the light guide 46 at an equidistant distance from one another.

The fiber Bragg gratings 49 are periodic microstructures written into the light guide which reflect light in a wavelength-selective manner. In the light guide 46, each of the fiber Bragg gratings 49 reflects a different wavelength of light. If light with a wide bandwidth is introduced into the light guide 46, only light with a very limited spectral width is reflected at each of the fiber Bragg gratings 49. The remaining portions of the light continue on their way through the light guide until a different wavelength of light is reflected at the next fiber Bragg grating 49. Heating causes the light guide 46 to stretch and thus the fiber Bragg gratings 49 to stretch. Based on the wavelength of the light reflected at the fiber Bragg grating, a measurement signal can be generated which represents the temperature in the region of the fiber Bragg grating 49. By suitable evaluation of the reflected light signals, temperature information can be obtained for each of the fiber Bragg gratings 49.

The mirror device includes a signal generator 47, which generates the light signal and introduces it into the light guide 46. The signal generator 47 determines from the reflected light components a temperature measurement value and transmits this to the control unit 38 via a signal path 48.

Fig. 12 shows a temperature sensor 39 in which the coupling substance is designed as a thermocouple. The thermocouple comprises a first conductor track 50 and a second conductor track 51, which are electrically connected to one another at a connection point 53. The first conductor track 50 consists of a first metal, and the second conductor track 51 consists of a second metal that is different from the first metal. Based on the Seebeck effect, the voltage between the two conductors 50, 51 leading to the outside changes depending on the temperature at the connection point 53. The thermocouple can be a component of a sensor component 39 introduced into the cavity 40.

Claims

Claims Mirror device, in particular for a microlithographic projection exposure system, with a mirror (20), a sensor device (39, 46, 48) and a control unit (38), the mirror (20) having a mirror body (23) and a mirror body (23 ) formed reflection surface (24), the mirror body (23) comprising cooling channels (27), the sensor device (39, 46, 48) having a sensor component (39, 46) thermally coupled to the mirror body (23) and a sensor component (39, 46) which is thermally coupled to the mirror body (23). Control unit (38) extending signal path (48) in order to transmit a measurement signal representing the temperature of the mirror body (23) to the control unit (38), the sensor component (39, 46, 48) being in a cavity (27, 40) of the Mirror body (23) is arranged and wherein the sensor component (39, 46, 48) is arranged in a position between the cooling channels (27) and the reflection surface. Mirror device according to claim 1, wherein the cavity (27, 40) is an externally accessible cavity (27, 40) with an access whose cross section is larger than the sensor component (39, 46). Mirror device according to claim 1 or 2, wherein the distance between the sensor component (39, 46, 48) and the reflection surface (24) is smaller than the distance between the sensor component (39, 46) and the back (42) of the mirror body (23) . Mirror device according to one of claims 1 to 3, wherein the distance between the sensor component (39, 46, 48) and the reflection surface (24) is between 2 mm and 30 mm, preferably between 5 mm and 15 mm.

5. Mirror device according to one of claims 1 to 4, wherein access to the cavity (40) opens into a rear side (42) of the mirror body (23) opposite the reflection surface (24).

6. Mirror device according to one of claims 1 to 5, wherein the sensor component (39, 46, 48) is connected to a wall of the cavity (27, 40).

7. Mirror device according to one of claims 1 to 6, wherein the measurement signal is led out of the mirror body (23) via a cable (41), starting from the cavity (40) of the mirror body (23).

8. Mirror device according to claim 7, wherein the cross section of the access through which the cable (41) is guided is smaller than the sensor component (39, 46, 48).

9. Mirror device according to one of claims 1 to 8, wherein the cavity (40) forms a branch of a cooling channel (27).

10. Mirror device according to one of claims 1 to 6, wherein the measurement signal is transmitted via a conductor track which is formed in the substrate of the mirror body (23).

11. Mirror device according to one of claims 1 to 10, wherein the sensor component is a light guide (46) inserted into the cavity (40) and wherein the light guide (46) is provided with one or more fiber Bragg gratings (49).

12. Mirror device according to claim 11, wherein the light guide (46) is thermally coupled to the material of the mirror body (23) by filling the space between the light guide (46) and the wall of the cavity (40) with a substance. Projection objective for a microlithographic projection exposure system (10, 22), in which a mask (13) is imaged onto a lithography object (21) using a plurality of mirror devices (20), wherein at least one of the mirror devices is designed as a mirror device according to one of claims 1 to 12. Method for measuring the temperature of a mirror (20) of a microlithographic projection exposure system, in which the mirror (20) has a mirror body (23) and a reflection surface (24) formed on the mirror body (23), wherein the mirror body (23) comprises cooling channels (27), wherein a cavity (27, 40) is formed in the mirror body (23), wherein a sensor component (39, 46, 48) thermally coupled to the mirror body (23) is arranged in the cavity (27, 40), wherein a measurement signal representing the temperature of the mirror body (23) is transmitted to a control unit (38) of the microlithographic projection exposure system, and wherein the sensor component (39, 46) is arranged in a position between the cooling channels (27) and the reflection surface (24).