EUV mirror system, method for operating an EUV mirror system, projection lens for a microlithographic projection exposure apparatus

Abstract

The invention relates to an EUV mirror system comprising a vacuum chamber (23), an EUV mirror (17, 28, M1-M6) arranged in the vacuum chamber (23) and a heating device (35) for the EUV mirror (17, 28, M1-M6). The EUV mirror (17, 28, M1-M6) comprises a mirror body (30) and an optical surface (32) formed on the mirror body (30). A separating wall (28) used to delimit a mini environment (29) adjacent to the optical surface (32) of the EUV mirror (17, 28, M1-M6) from a main space (34) of the vacuum chamber is arranged in the vacuum chamber (23). The heating device (35) comprises a radiation source (26) and a mirror element (31) such that heating radiation (36) emitted by the radiation source (26) is reflected off the mirror element (31) and guided to the optical surface (32) of the EUV mirror (17, 28, M1-M6). The mirror element (31) is arranged outside of the mini environment (29). The mirror element (31) is designed as a MEMS mirror module. The heating radiation (36), coming from the MEMS mirror module, is guided through the separating wall (28) to the optical surface (32). The invention also relates to a method for operating an EUV mirror system.

Description

EUV mirror system, method for operating an EUV mirror system, projection lens for a microlithographic projection exposure system

[0001] The present patent application claims priority from the German patent application DE 10 2023 210 716 . 3 filed on 30 October 2023, to which reference is made and whose content is fully incorporated here (“incorporation by reference”).

[0002] The invention relates to an EUV mirror system, a method for operating an EUV mirror system, a projection object for a microlithographic projection exposure system and a computer program product.

[0003] Microlithographic projection exposure systems are used for the production of integrated circuits with particularly small structures. A photomask illuminated with very short-wavelength, extreme ultraviolet radiation (EUV radiation) is imaged onto a lithographic object to transfer the mask structure onto the lithographic object.

[0004] The projection exposure system comprises several EUV mirrors, each with an optical surface from which the EUV radiation is reflected. The EUV mirrors have a precisely defined shape and are positioned precisely to ensure that the image of the mask onto the lithographic object is of sufficient quality.

[0005] During operation, the projection exposure system is subject to influences that affect the image quality. For example, if thermal expansion leads to a change in the geometric shape of a mirror, the wavefront of the radiation reflected by the mirror changes. This can be corrected by applying targeted heat. To counteract undesirable deformations of the EUV mirror or to deliberately cause a desired deformation, it may be advantageous to equip the EUV mirror system with a heating device.

[0006] It may be desirable to distribute the heat supplied by the heating system differently across the surface of the EUV mirror in various operating states of the projection exposure system. For this purpose, the heating system can comprise several heating channels whose heating power can be adjusted independently of each other. Such heating systems are usually mechanically complex and have limited variability in the distribution of heating power.

[0007] The invention is based on the objective of presenting an EUV mirror system, a method for operating an EUV mirror system, and a projection object for a microlithographic projection exposure system, with which these disadvantages are reduced. This objective is achieved by the features of the independent claims. Advantageous embodiments are specified in the dependent claims.

[0008] An EUV mirror system according to the invention comprises a vacuum chamber, an EUV mirror arranged in the vacuum chamber, and a heating device for the EUV mirror, wherein the EUV mirror has a mirror body and an optical surface formed on the mirror body. A partition is arranged in the vacuum chamber, separating a mini-environment adjacent to the optical surface from a main chamber of the vacuum chamber. The heating device comprises a radiation source and a mirror element, such that radiation emitted by the radiation source is reflected by the mirror element and directed onto the optical surface of the EUV mirror. The mirror element is located outside the mini-environment. The mirror element is designed as a MEMS mirror module. The heating radiation from the MEMS mirror module is directed through the partition onto the optical surface.

[0009] By designing the mirror element as a MEMS mirror module, it becomes possible to distribute the heat radiation with high variability across the optical surface of the EUV mirror. However, the problem arises that aggressive conditions prevail in the vicinity of the optical surface of the EUV mirror during operation of the projection exposure system. If the MEMS mirror module were exposed to these aggressive conditions, rapid degradation of the MEMS mirror module would be expected. The invention exploits the fact that heat radiation, unlike EUV radiation, has the property of being able to pass through matter. Therefore, an exposure channel can be formed for the EUV radiation, which propagates within a mini-environment enclosed by a partition. The EUV radiation can thus strike the optical surface of the EUV mirror and be reflected there without passing through matter.In contrast, the heat radiation coming from the MEMS mirror module can be directed through the partition onto the optical surface without the MEMS mirror module being exposed to the aggressive conditions in the mini-environment.

[0010] The MEMS mirror module can comprise a support substrate and a plurality of micromirrors formed on the support substrate. Each micromirror can be connected to the support substrate via a solid-state joint. Each micromirror can be associated with an actuator, such that actuating the actuator changes the orientation of the micromirror relative to the support substrate. The actuator can be designed to rotate the micromirror by a dimension parallel to its reflection. The surface is tilted along an axis aligned with the surface. In one embodiment, the micromirror can be tilted around two mutually perpendicular axes. This makes it possible to direct a beam of light reflected from the micromirror in two degrees of freedom. It is possible to direct the beams of light from several micromirrors onto the same areas or onto different areas on the optical surface of the EUV mirror. In this way, the distribution of the heat radiation across the optical surface of a single EUV mirror can be varied in many ways. It is also possible for a first EUV mirror and a second EUV mirror to be illuminated with heat radiation from a single MEMS mirror module.The MEMS mirror module can be configured so that the proportion of heat radiation between the first EUV mirror and the second EUV mirror is variable, so that in a first operating state more heat radiation hits the first EUV mirror than in a second operating state, and that in the first operating state less heat radiation hits the second EUV mirror than in the second operating state.

[0011] The MEMS mirror module can comprise a large number of micromirrors, for example, at least 100 micromirrors, preferably at least 1000 micromirrors. The micromirrors can form an array of micromirrors. Each micromirror can have a surface coated with a reflective layer for the heat radiation. The micromirrors can be arranged on the substrate such that the surfaces of the micromirrors together form a reflective surface of the MEMS mirror module.

[0012] To allow the heat radiation between the MEMS mirror module and the optical surface of the EUV mirror to pass through the partition, the partition includes an area in which the partition wall is made of a material transparent to heat radiation. For example, the partition wall in this area can be made of glass. The partition wall can be designed such that the transparent area is limited to a portion of the total surface of the partition wall. In particular, the transparent area can be limited to less than 20%, preferably less than 10%, and more preferably less than 5% of the total surface of the partition wall. Design configurations in which the partition wall consists of a larger proportion or entirely of a transparent material are also included.

[0013] The heat radiation reflected as a beam by the MEMS mirror module can have a smallest constriction whose cross-section is smaller, in particular by at least 50%, preferably by at least 70%, and more preferably by at least 90%, than the reflective surface of the MEMS mirror module. If the smallest constriction is located near the point where it passes through the partition, a small transparent area in the partition is sufficient to allow the heat radiation to pass through. The distance between the smallest constriction and the MEMS mirror module can be at least 2 times, preferably at least 5 times, and more preferably at least 10 times greater than the distance between the smallest constriction and the area where the heat radiation passes through the partition.In this sense, the distance corresponds to the distance traveled by the heat radiation between the MEMS mirror module and the smallest constriction, or between the smallest constriction and the passage through the partition.

[0014] The EUV mirror system can be designed in such a way that there is no direct line of sight between the optical surface of the A connection exists between an EUV mirror and a MEMS mirror module. To avoid a direct line of sight between the MEMS mirror module and the optical surface of the EUV mirror, a mirror can be positioned between the MEMS mirror module and the optical surface of the EUV mirror, at which the heat radiation is reflected. The mirror can be designed as a plane mirror, so that the direction of the heat radiation is deflected without changing the beam shape.

[0015] In one embodiment, the EUV mirror system comprises a first EUV mirror and a second EUV mirror, both located within the mini-environment. The EUV mirror system can be designed such that both the first and second EUV mirrors can be variably exposed to heat radiation as described. The EUV mirror system can include a first heating device designed to direct heat radiation onto the first EUV mirror and a second heating device designed to direct heat radiation onto the second EUV mirror. Each of the two heating devices can have the features described in the context of a single heating device.

[0016] It is also possible that the EUV mirror system includes a heating device with a single MEMS mirror module, whereby heating radiation reflected from the single MEMS mirror module is directed to both the first EUV mirror and the second EUV mirror. A first mirror can be arranged between the MEMS mirror module and the first EUV mirror, reflecting heating radiation from the MEMS mirror module and directing it to the first EUV mirror. A second mirror can be arranged between the MEMS mirror module and the second EUV mirror, reflecting heating radiation from the MEMS mirror module and directing it to the second EUV mirror.

[0017] The MEMS mirror module can be located within the vacuum chamber, and thus in a main compartment of the vacuum chamber, which is separated from the mini-environment by the partition. The term "main compartment" does not imply anything about the relative size of the sub-compartments within the vacuum chamber.

[0018] The invention also encompasses the possibility of arranging the MEMS mirror module outside the vacuum chamber. The heat radiation reflected by the MEMS mirror module then passes through the wall of the vacuum chamber and through the partition before reaching the optical surface of the EUV mirror. For this purpose, the wall of the vacuum chamber can include a region that is transparent to the heat radiation. The heat radiation can propagate in a straight line between the MEMS mirror module located outside the vacuum chamber and the optical surface of the EUV mirror. It is also possible for the heat radiation to be deflected once or multiple times between the MEMS mirror module and the optical surface.

[0019] The radiation source can comprise a radiation core to which energy is supplied and in which an energy conversion takes place, such that electromagnetic radiation is emitted from the core component. The wavelength of the electromagnetic radiation is such that it acts as heating radiation. The heating radiation can, for example, be infrared radiation with a wavelength between 800 nm and 1900 nm, preferably with a wavelength between 1050 nm and 1600 nm.

[0020] The radiation source can include one or more optical elements that capture the heat radiation emitted by the radiation core and focus it into a beam. These optical elements can include, for example, mirrors and / or lenses. The EUV mirror system It can be designed so that the beam is directed straight towards the MEMS mirror module. In other configurations, the beam can be fed into an optical fiber and, after exiting the fiber, directed towards the MEMS mirror module. In such a case, the exit end of the optical fiber or an optical element attached directly to the exit end of the optical fiber is considered the light source.

[0021] The light source's emission point can be located within the vacuum chamber, particularly within the main chamber. This also includes designs where the emission point is located outside the vacuum chamber. Regardless of where the heat radiation exits the source, the source may include components located outside the vacuum chamber. For maintenance purposes, it is advantageous to have components located outside the vacuum chamber because they can be replaced without opening the chamber.

[0022] In one embodiment, the heat radiation emitted by the radiation core is guided within the radiation source via exactly one optical fiber. This is a simplification compared to known heating radiators, in which the heat radiation is guided to an exit area of ​​the heating radiator via several optical fibers arranged parallel to each other. It is not excluded within the scope of the invention that several optical fibers are connected in series within the radiation source, each of which carries the entire heat radiation.

[0023] The EUV mirror system can include beam-shaping optics that direct the heat radiation generated in the radiation source onto the MEMS mirror module. Beam-shaping optics refers to an optical component or arrangement of optical components that shapes the heat radiation into a beam directed onto the MEMS mirror module. The beam-shaping optics can be designed to illuminate the MEMS mirror module with uniform brightness. The beam-shaping optics can be part of the radiation source or positioned between the radiation source and the MEMS mirror module.

[0024] During operation of the projection exposure system, a high vacuum can be present in the main chamber of the vacuum chamber, with the pressure, for example, between IO -6 mbar and IO - 9 mbar, preferably between IO -7 and IO -8The EUV mirror system can include a vacuum pump designed to generate a high vacuum in the vacuum chamber.

[0025] The EUV mirror system can include a purge gas port leading to the mini-environment. This purge gas port can be used to supply a hydrogen purge gas to the mini-environment, creating an atmosphere within the mini-environment that differs from that of the main vacuum chamber. The pressure within the mini-environment can be in the fine vacuum range, for example, between 10 -1 mbar and 10 -3 mbar. The hydrogen purge gas can be used to remove contaminants from the mini-environment, and especially from mirror surfaces located there. These contaminants can be, in particular, carbon species that arise from the interaction between EUV radiation and substances present in the vacuum atmosphere.

[0026] The EUV mirror system can include a control unit containing information about the temperature of the EUV mirror. The data is processed to generate a control signal that operates the heating device. Information about the temperature of the EUV mirror can be a measurement obtained from a temperature sensor. Alternatively, the temperature information can be obtained in another way. The temperature information can refer to the temperature of the optical surface of the EUV mirror. The control unit can be designed to generate a control signal that operates the radiation source to adjust its power output. The control unit can be designed to control the MEMS mirror module to adjust the distribution of the heating radiation across the optical surface of the EUV mirror. The control unit can be designed to adjust the overall orientation of the MEMS mirror module relative to the EUV mirror based on suitable input information.

[0027] The invention also relates to a projection lens for a microlithographic projection exposure system with such an EUV mirror system, with which a photomask arranged in a lens plane is projected onto an image plane. The invention further relates to a microlithographic projection exposure system with such a projection lens.

[0028] The invention further relates to a method for operating an EUV mirror system, wherein the EUV mirror system comprises a vacuum chamber, an EUV mirror arranged in the vacuum chamber, and a heating device for the EUV mirror. The EUV mirror comprises a mirror body and an optical surface formed on the mirror body. A partition is arranged in the vacuum chamber, separating a mini-environment adjacent to the optical surface of the EUV mirror from a main chamber of the vacuum chamber. Heat radiation emitted by a heating device is directed onto the optical surface of the EUV mirror via a mirror element. The mirror element is located outside the mini-environment. The mirror element is designed as a MEMS mirror module.

[0029] The disclosure includes further developments of the EUV mirror system with features described in connection with the inventive method.

[0030] The invention is described below by way of example with reference to the accompanying drawings and advantageous embodiments. The drawings show: Fig. 1: a schematic representation of a microlithographic projection exposure system; Fig. 2: a heating device for an EUV mirror; Fig. 3, 4: Intermediate products in the production of MEMS- Mirror module from Fig. 2; Fig. 5: a schematic representation of a first embodiment of a mirror system according to the invention; Fig. 6: a schematic representation of a second embodiment of a mirror system according to the invention.

[0031] Figure 1 schematically depicts a microlithographic EUV projection exposure system. The projection exposure system comprises an exposure beam source 14, an illumination system 10, and a projection object 22, which are operated together in a vacuum chamber 23.

[0032] The exposure source 14 generates electromagnetic radiation in the EUV range, specifically with a wavelength between 5 nm and 30 nm. The exposure radiation emitted by the exposure source 14 is focused by a collector 15 into an intermediate focal plane 16. Exposure radiation passing from the intermediate focal plane 16 is directed by the illumination system 10 into an object plane 12, so that an object field in the object plane 12 is illuminated with uniform radiation intensity.

[0033] The illumination system 10 comprises a deflecting mirror 17, which deflects the illumination radiation onto a first faceted mirror 18. A second faceted mirror 19 is arranged downstream of the first faceted mirror 18. The facets of the first faceted mirror 18 are imaged onto the object plane 12 by the second faceted mirror 19.

[0034] In the object plane 12, a photomask 13 is arranged, which is imaged onto an image plane 21 via a plurality of mirrors M1-M6 of the projection object 22. A structure formed on the photomask 13 is transferred to a radiation-sensitive layer of a wafer 20 arranged in the image plane 21. The photomask 13 is suspended from a first scanning device 24, and the wafer 20 rests on a second scanning device 25, so that the wafer 20 can be exposed in a scanning operation in which the photomask 13 and the wafer 20 are moved synchronously with each other.

[0035] Each of the EUV mirrors 17, 18, 19, M1-M6 in Fig. 1 is provided with a multilayer system that forms an optical surface with high reflectivity for EUV radiation. This is explained in more detail below with reference to Fig. 2. The EUV mirror comprises a mirror body 30 made of an ultra-low thermal expansion mirror substrate material. An example of such a The material is a titanium silicate glass marketed under the name ULE™ by Corning Inc., which exhibits a so-called zero-crossing temperature. At this zero-crossing temperature, which is approximately 30 °C for ULE™, the coefficient of thermal expansion has a zero crossing in its temperature dependence, at which point there is no or only negligible thermal expansion of the mirror substrate material.

[0036] A multilayer coating system with alternating layers of molybdenum and silicon is applied to the mirror body 30, forming an optical surface 32 of the EUV mirror 33. With such a coating, approximately 70% of the incident EUV radiation can be reflected. The remaining approximately 30% is absorbed, leading to heating of the EUV mirror. The optical surface 32 is optimized for the reflection of EUV radiation in the extreme ultraviolet spectral range with wavelengths between 5 nm and 30 nm.

[0037] The interior of vacuum chamber 23 is placed under high vacuum during operation of the projection exposure system using a vacuum pump (not shown) at a pressure of, for example, IO. -8mbar. Inside the vacuum chamber 23, an inner housing is formed that surrounds the EUV beam path and is separated from a main chamber 34 of the vacuum chamber 23 by a partition 28. In Fig. 1, only sections of the partition 28 are indicated; in fact, the inner housing surrounds further sections of the EUV beam path. The inner housing is designed so that the EUV beam path can take its path over the various optical elements 17, 18, 19, M1-M6 without the partition 28 obstructing it. The area arranged in the inner housing and enclosed by the partition 28 is referred to as the mini-environment 29.

[0038] The inner housing 28 is not macroscopically sealed from the main chamber 34 of the vacuum chamber 23. For example, gaps may be formed between the partition 28 and optical elements 17, 18, 19, M1-M6, at which the EUV beam path is reflected, allowing mechanical adjustment of the optical elements. Nevertheless, the inner housing makes it possible to set pressure and concentration ratios in the mini-environment 29 under the high-vacuum conditions prevailing in the vacuum chamber 23 that differ significantly from the conditions in the main chamber 34 of the vacuum chamber 23.

[0039] During operation of the projection exposure system, a hydrogen purge gas is introduced into the mini-environment 29. Through interaction between the EUV radiation and the hydrogen, a plasma is generated, forming, among other things, ionic plasma species (H+) or radical plasma species (H). The plasma has the effect of removing contaminants, which can arise, for example, from outgassing from components of the projection exposure system, from the surfaces of the optical elements arranged in the mini-environment 29.

[0040] The projection exposure system comprises a heating device 35 designed to direct infrared radiation as heating radiation onto the optical surface 32 of an EUV mirror 33, 50 of the projection object 22 in order to supply heat to the EUV mirror 33, 50 with a predetermined spatial distribution. This is illustrated in Fig. 1 using the EUV mirror M1 as an example. The wavelength of the infrared radiation can, for example, be between 1050 nm and 1600 nm, and the heating power can, for example, be between 2 W and 100 W. The supply of heating radiation causes a local thermal expansion, which can be specifically designed so that a wavefront reflected at the EUV mirror 33, 50 is influenced in a desired way.

[0041] The heating device 35 comprises a radiation source 26 and a mirror element in the form of a MEMS mirror module 31. Heating radiation 36 emitted by the radiation source 26 is reflected by the MEMS mirror module 31 and from there strikes the optical surface 32 of the EUV mirror. As shown in Fig. 2, the radiation source 26 comprises an optical fiber 38 and a beam-shaping optic 37. The heating radiation 36 is guided via the optical fiber 38 to the beam-shaping optic 37, where the heating radiation 36 exits the radiation source 26. The exiting beam is shaped such that the reflective surface of the MEMS mirror module 31 is illuminated with uniform brightness.

[0042] The heating device 35 comprises a control unit 39, which controls the components of the heating device 35 depending on various input variables. Figure 2 shows, by way of example, an infrared sensor 40, which acquires a measured value of the temperature of the optical surface 32 and supplies it to the control unit 39. The control unit 39 controls the radiation source 26 to adjust the amount of emitted heating radiation. The control unit 39 also controls the MEMS mirror module 31 to adjust the distribution of heat across the optical surface 32.

[0043] The functionality of the MEMS mirror module 31 is explained using an exemplary method for manufacturing a MEMS mirror module 31. Figures 3 and 4 show intermediate stages in the manufacturing of a MEMS mirror module 31. A substrate body 42, which can be made of silicon, for example, is provided. A coating 41 with high re- A reflectivity for infrared radiation is applied. A photoresist is applied to the coating 41. By appropriately exposing the photoresist, areas are defined in which material is removed by a subsequent processing step. Figure 4 shows a state in which material has been removed between individual protruding structures, so that the protruding structures are separated from each other down to the substrate body 42. After completion of the manufacturing process, each of the protruding structures forms a micromirror 44 of the MEMS mirror module 31. Such a micromirror 44 has a mirror body that is connected to the remaining base of the substrate body 42 via a schematically depicted solid-state hinge 43. During the manufacturing process, the micromirrors 44 are provided with actuators (not shown) by which the orientation of the micromirrors 44 relative to the substrate body 42 can be changed.A change in the orientation of a micromirror 44 is made possible by an elastic deformation of the solid joint 43.

[0044] In Fig. 2, the MEMS mirror module 31 is controlled by the control unit 39. The control unit 39 sends control signals to the MEMS mirror module 31, which then actuates the actuators to align the micromirrors 44 in a desired manner relative to the substrate body 42. In a further function, the control unit 39 uses suitable sensor data to check whether the substrate body 42 has the correct position and orientation within the EUV mirror system and adjusts it if necessary.

[0045] By illuminating the MEMS mirror module 31 with uniform brightness from the radiation source 26, the same amount of heat can be conducted via each of the micromirrors 44 towards the optical surface 32 of the EUV mirror 33. By appropriately aligning the micromirrors 44, the heat distribution across the optical surface 32 can be adjusted very flexibly. There can be areas on the optical surface 32 that do not receive any heat radiation 36 from the MEMS mirror module 31. Heat radiation 36 from two or more micromirrors 44 can be directed to other areas of the optical surface 32. In this way, the heat radiation 36 can be adjusted, for example, so that the heat input from the heat radiation is complementary to the heat supplied by the EUV radiation. Thus, a uniformly distributed amount of heat can be supplied to the optical surface 32 via the heat radiation and the EUV radiation.

[0046] Figure 5 shows an EUV mirror system according to the invention, in which the partition 28, which separates the mini-environment 29 from the main chamber 34 of the vacuum chamber 23, adjoins the optical surface 32 of the EUV mirror 33. A passage 46, made of a material transparent to the heating radiation, is formed in the partition 28. The heating radiation 36 exits the heating device 26 and is directed onto the MEMS mirror module 31. By appropriately adjusting the micromirrors 44 of the MEMS mirror module 31, the distribution of the supplied heat over the optical surface 32 is defined. The overall beam path formed by the beams emanating from the micromirrors 44 has a minimum constriction 45, which, in the embodiment according to Figure 5, coincides with the passage 46. With this form of the heat beam path, it becomes possible to keep the part of the partition wall 28 made of transparent material small.The vast majority of partition 28 consists of a conventional material that is non-transparent to infrared radiation.

[0047] By arranging the MEMS mirror module 31 outside the mini-environment 29, the MEMS mirror module 31 not in contact with the aggressive hydrogen plasma in the mini-environment 29. The degradation of the MEMS mirror module 31 therefore proceeds significantly slower.

[0048] In the alternative embodiment shown in Fig. 6, two mirrors 48, 49 are arranged in the heating radiation path between the MEMS mirror module 31 and the partition 28. The heating radiation 36 is directed via the first mirror 48 onto a first EUV mirror 33 of the EUV mirror system. The heating radiation 36 is directed via the second mirror 49 onto the optical surface of a second EUV mirror 50 of the EUV mirror system. The micromirrors 44 of the MEMS mirror module 31 are aligned such that the desired heat distribution is achieved on each of the EUV mirrors 33, 50.

[0049] This design reduces the equipment requirements because a single MEMS mirror module 31 is sufficient to supply two EUV mirrors 33, 50 with heating radiation 36. Furthermore, by appropriately controlling the micromirrors 44 and the MEMS mirror module 31, it becomes possible to vary the distribution of the heat output between the two EUV mirrors 33, 50. If a micromirror 44 is adjusted so that the outgoing heating radiation no longer strikes the first mirror 48 but the second mirror 49, the corresponding amount of heating power is redirected from the first EUV mirror 33 to the second EUV mirror 50.

Claims

Patent claims 1. EUV mirror system, comprising a vacuum chamber (23), an EUV mirror (17, 28, M1-M6) arranged in the vacuum chamber (23) and a heating device (35) for the EUV mirror (17, 28, M1-M6), wherein the EUV mirror (17, 28, M1-M6) has a mirror body (30) and an optical surface (32) formed on the mirror body (30), wherein a partition wall (28) is arranged in the vacuum chamber (23), with which a mini-environment (29) adjacent to the optical surface (32) of the EUV mirror (17, 28, M1-M6) is delimited from a main space (34) of the vacuum chamber, wherein the heating device (35) comprises a radiation source (26) and a mirror element (31), so that heating radiation (36) emitted by the radiation source (26) is reflected at the mirror element (31) and directed onto the optical surface (32) of the EUV mirror (17, 28, M1-M6), wherein the mirror element (31) is arranged outside the mini-environment (29), wherein the mirror element (31) is designed as a MEMS mirror module, and wherein the heating radiation (36) coming from the MEMS mirror module is guided through the partition wall (28) onto the optical surface (32).

2. EUV mirror system according to claim 1, wherein the MEMS mirror module (31) comprises a carrier substrate (42) and a plurality of micromirrors (44) formed on the carrier substrate (42).

3. EUV mirror system according to claim 2, wherein each micromirror (44) is connected to the carrier substrate (42) via a solid-state joint (43).

4. EUV mirror system according to claim 2 or 3, wherein each micromirror (44) is provided with a coating reflective of the heating radiation (36).

5. EUV mirror system according to one of claims 1 to 4, the partition wall (28) comprises a region (46) in which the partition wall (28) consists of a material transparent to the heating radiation (36).

6. EUV mirror system according to claim 5, wherein the transparent area (46) is less than 20%, preferably less than 10 % , more preferably less than 5 % of the total area of ​​the partition wall (28).

7. EUV mirror system according to one of claims 1 to 6, wherein the MEMS mirror module (31) has a smallest constriction (45), wherein the cross section of the smallest constriction (45) is at least 50% smaller, preferably at least 70% smaller, more preferably at least 90% smaller than the reflection surface of the MEMS mirror module (31).

8. EUV mirror system according to claim 7, wherein the distance between the smallest constriction (45) and the MEMS mirror module (31) is at least a factor of 2, preferably at least a factor of 5, more preferably at least a factor of 10 greater than the distance between the smallest constriction (45) and the region (46) in which the heating radiation (36) passes through the partition wall (28).

9. EUV mirror system according to one of claims 1 to 8, wherein a mirror (48, 49) is arranged between the MEMS mirror module (31) and the optical surface (32) of the EUV mirror (33, 50), at which mirror the heating radiation (36) is reflected.

10. EUV mirror system according to one of claims 1 to 9, comprising a first EUV mirror (33) and a second EUV mirror (50), wherein the heating radiation (36) reflected at an individual MEMS mirror module (31) is directed onto the first EUV mirror 33 and onto the second EUV mirror (50).

11. EUV mirror system according to one of claims 1 to 10, wherein the light exit of the radiation source (26) is arranged within the vacuum chamber (23).

12. EUV mirror system according to one of claims 1 to 11, comprising a purge gas connection for supplying a hydrogen purge gas to the mini-environment (29).

13. Projection objective for a microlithographic projection exposure system with an EUV mirror system according to one of claims 1 to 12, with which a photomask (13) arranged in an object plane (12) is imaged into an image plane (21).

14. Method for operating an EUV mirror system, wherein the EUV mirror system comprises a vacuum chamber (23), an EUV mirror (17, 28, M1-M6) arranged in the vacuum chamber (23) and a heating device (35) for the EUV mirror (17, 28, M1-M6), wherein the EUV mirror (17, 28, M1-M6) has a mirror body (30) and an optical surface (32) formed on the mirror body (30), wherein a partition wall (28) is arranged in the vacuum chamber (23), with which partition wall a mini-environment (29) adjacent to the optical surface (32) of the EUV mirror (17, 28, M1-M6) is delimited from a main space (34) of the vacuum chamber, wherein heating radiation emitted by a heating device (35) is directed via a mirror element (31) onto the optical surface (32) of the TEU Mirror (17, 28, M1-M6), wherein the mirror element (31) is arranged outside the mini-environment (29), wherein the mirror element (31) is designed as a MEMS mirror module, and wherein the heating radiation (36) coming from the MEMS mirror module is guided through the partition wall (28) onto the optical surface (32).

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