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

Abstract

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 partition (28) is arranged in the vacuum chamber (23), separating a mini-environment (29) adjacent to the optical surface (32) of the EUV mirror (17, 28, M1-M6) from a main chamber (34) of the vacuum chamber. 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 by the mirror element (31) and directed onto the optical surface (32) of the EUV mirror (17, 28, M1-M6). The mirror element (31) is arranged outside the mini-environment (29). The mirror element (31) is designed as a MEMS mirror module.

Description

[0001] The invention relates to an EUV mirror system, a method for operating an EUV mirror system, a projection lens for a microlithographic projection exposure system and a computer program product.

[0002] 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 (EUV) radiation is imaged onto a lithographic object to transfer the mask structure to the object.

[0003] The projection exposure system comprises several EUV mirrors, each with an optical surface that reflects the EUV radiation. The EUV mirrors have a precisely defined shape and are precisely positioned to ensure sufficient image quality from the mask onto the lithographic object.

[0004] During operation, the projection exposure system is exposed 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. Targeted heat can counteract unwanted deformation of the EUV mirror or specifically cause a desired deformation. Therefore, it may be advisable to equip the EUV mirror system with a heating device.

[0005] It may be desirable to distribute the heat supplied by the heating device differently across the surface of the EUV mirror in different operating states of the projection exposure system. For this purpose, the heating device can comprise several heating channels whose heating power can be adjusted independently of one another. Such heating devices are usually mechanically complex and have limited variability in the distribution of the heating power.

[0006] The invention is based on the object of presenting an EUV mirror system, a method for operating an EUV mirror system, and a projection lens for a microlithographic projection exposure system that mitigate these disadvantages. This object is achieved by the features of the independent claims. Advantageous embodiments are specified in the subclaims.

[0007] 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. The EUV mirror has a mirror body and an optical surface formed on the mirror body. A partition wall is arranged in the vacuum chamber, separating a mini-environment adjacent to the optical surface from a main space 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 arranged outside the mini-environment. The mirror element is designed as a MEMS mirror module.

[0008] By designing the mirror element as a MEMS mirror module, it is possible to distribute the heating 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, unlike EUV radiation, heating radiation has the property of being able to penetrate through matter. An exposure channel can therefore be created for the EUV radiation, which propagates within a mini-environment enclosed by a partition wall. The EUV radiation can therefore strike the optical surface of the EUV mirror and be reflected there without passing through matter.On the other hand, the heating radiation coming from the MEMS mirror module can be guided through the partition wall onto the optical surface without the MEMS mirror module being exposed to the aggressive conditions in the mini-environment.

[0009] The MEMS mirror module can comprise a carrier substrate and a plurality of micromirrors formed on the carrier substrate. Each micromirror can be connected to the carrier substrate via a solid-state joint. Each micromirror can be assigned an actuator so that actuation of the actuator changes the orientation of the micromirror relative to the carrier substrate. The actuator can be designed such that the micromirror is tilted about an axis aligned parallel to its mirror surface. In one embodiment, the micromirror can be tilted about two mutually perpendicular axes. This makes it possible to align a beam of rays reflected by the micromirror in two degrees of freedom. It is possible to direct the beams of rays from multiple micromirrors onto the same areas or onto different areas on the optical surface of the EUV mirror.In this way, the distribution of the heating radiation across the optical surface of a single EUV mirror can be varied in a wide variety of ways. It is also possible for a first EUV mirror and a second EUV mirror to be exposed to heating radiation from a single MEMS mirror module. The MEMS mirror module can be configured such that the proportion of heating radiation between the first EUV mirror and the second EUV mirror is variable, so that in a first operating state, more heating radiation strikes the first EUV mirror than in a second operating state, and that in the first operating state, less heating radiation strikes the second EUV mirror than in the second operating state.

[0010] 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 span an array of micromirrors. Each micromirror can have a surface provided with a coating that reflects the heating radiation. The micromirrors can be arranged on the carrier substrate such that the surfaces of the micromirrors together span a reflective surface of the MEMS mirror module.

[0011] To allow the heating radiation to pass through the partition between the MEMS mirror module and the optical surface of the EUV mirror, the partition comprises a region in which the partition is made of a material that is transparent to the heating radiation. For example, the partition can be made of glass in this region. The partition can be designed such that the transparent region is limited to a section of the total area of ​​the partition. In particular, the transparent region can be limited to less than 20%, preferably less than 10%, more preferably less than 5% of the total area of ​​the partition. Embodiments in which the partition consists largely or entirely of a transparent material are also encompassed.

[0012] The heating radiation reflected as a beam by the MEMS mirror module can have a smallest constriction whose cross-section is smaller, in particular at least 50% smaller, preferably at least 70% smaller, more preferably at least 90% smaller than the reflection surface of the MEMS mirror module. If the smallest constriction is located near the passage through the partition, a small transparent area in the partition is sufficient to allow the heating radiation to pass through. The distance between the smallest constriction and the MEMS mirror module can be 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 and the area in which the heating radiation passes through the partition.The distance in this sense corresponds to the distance traveled by the heating radiation between the MEMS mirror module and the smallest constriction or between the smallest constriction and the passage through the partition wall.

[0013] The EUV mirror system can be designed so that there is no direct line of sight between the optical surface of the EUV mirror and the 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 arranged between the MEMS mirror module and the optical surface of the EUV mirror, which reflects the heating radiation. The mirror can be designed as a flat mirror, so that the direction of the heating radiation is redirected without changing the beam shape.

[0014] In one embodiment, the EUV mirror system comprises a first EUV mirror and a second EUV mirror, both arranged within the mini-environment. The EUV mirror system can be designed such that both the first EUV mirror and the second EUV mirror can be variably exposed to heating radiation in the manner described. For this purpose, the EUV mirror system can comprise a first heating device configured to direct heating radiation onto the first EUV mirror and a second heating device configured to direct heating 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.

[0015] It is also possible for the EUV mirror system to comprise a heating device with a single MEMS mirror module, wherein heating radiation reflected by 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, at which first mirror heating radiation coming from the MEMS mirror module is reflected and directed to the first EUV mirror. A second mirror can be arranged between the MEMS mirror module and the second EUV mirror, at which second mirror heating radiation coming from the MEMS mirror module is reflected and directed to the second EUV mirror.

[0016] The MEMS mirror module can be arranged within the vacuum chamber, i.e., in a main chamber of the vacuum chamber, which is separated from the mini-environment by the partition wall. The term "main chamber" does not specify the relative size of the sub-chambers within the vacuum chamber.

[0017] The invention also encompasses the possibility of arranging the MEMS mirror module outside the vacuum chamber. The heating radiation reflected by the MEMS mirror module then passes through the wall of the vacuum chamber and through the partition wall before the heating radiation strikes the optical surface of the EUV mirror. For this purpose, the wall of the vacuum chamber can comprise a region that is transparent to the heating radiation. The heating radiation can propagate in a straight line between the MEMS mirror module arranged outside the vacuum chamber and the optical surface of the EUV mirror. It is also possible for the heating radiation to be deflected once or multiple times between the MEMS mirror module and the optical surface.

[0018] The radiation source can comprise a radiation core to which energy is supplied and in which an energy conversion takes place, so that electromagnetic radiation is emitted from the core component. The wavelength of the electromagnetic radiation is such that the electromagnetic radiation 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.

[0019] The radiation source can comprise one or more optical elements with which the heating radiation emitted by the radiation core is captured and directed into a beam. The optical elements can include, for example, mirrors and / or lenses. The EUV mirror system can be designed such that the beam is directed directly toward the MEMS mirror module. In other embodiments, the beam can be fed into a light guide and, after exiting the light guide, directed toward the MEMS mirror module. In such a case, the exit end of the light guide or an optical element attached directly to the exit end of the light guide is considered the light exit of the radiation source.

[0020] The light exit of the radiation source can be arranged within the vacuum chamber, in particular within the main space of the vacuum chamber. Also included are embodiments in which the light exit of the radiation source is arranged outside the vacuum chamber. Regardless of where the heating radiation exits the radiation source, it is possible for the radiation source to comprise components arranged outside the vacuum chamber. For maintenance purposes, it is advantageous if components are arranged outside the vacuum chamber because they can be replaced without having to open the vacuum chamber.

[0021] In one embodiment, the heat radiation emitted by the radiation core is guided within the radiation source via a single optical fiber. This is a simplification compared to known radiant heaters, in which the heat radiation is guided to an exit area of ​​the radiant heater via several parallel optical fibers. Within the scope of the invention, it is not excluded that several optical fibers are connected in series within the radiation source, each of which guides the entire heat radiation.

[0022] The EUV mirror system can include beam-shaping optics, which direct the heating radiation generated in the radiation source to the MEMS mirror module. Beam-shaping optics is an optical component or an arrangement of optical components used to shape the heating radiation into a beam of rays 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 a component of the radiation source or arranged between the radiation source and the MEMS mirror module.

[0023] During operation of the projection exposure system, a high vacuum can be present in the main chamber of the vacuum chamber, with the pressure being, for example, between 10 -6 mbar and 10 -9 mbar, preferably between 10 -7 and 10 -8mbar. The EUV mirror system may include a vacuum pump configured to create a high vacuum in the vacuum chamber.

[0024] The EUV mirror system can include a purge gas connection leading to the mini-environment. The purge gas connection can be used to supply a hydrogen purge gas to the mini-environment, so that the atmosphere in the mini-environment differs from the main space of the vacuum chamber. The pressure in 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, especially from the mirror surfaces located there. These contaminants can be carbon species, in particular, formed by the interaction between the EUV radiation and substances present in the vacuum atmosphere.

[0025] The EUV mirror system can comprise a control unit in which information about the temperature of the EUV mirror is processed to generate a control signal with which the heating device is controlled. The information about the temperature of the EUV mirror can be a measured value obtained using a temperature sensor. It is also possible to obtain the temperature information in another way. The temperature information can relate to the temperature of the optical surface of the EUV mirror. The control unit can be designed to generate a control signal with which the radiation source is controlled in order to adjust the power of the radiation source. The control unit can be designed to control the MEMS mirror module in order 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 alignment of the MEMS mirror module relative to the EUV mirror based on suitable input information.

[0026] 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 an object plane is imaged into an image plane. The invention further relates to a microlithographic projection exposure system with such a projection lens.

[0027] 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 wall is arranged in the vacuum chamber, with which a mini-environment adjacent to the optical surface of the EUV mirror is separated from a main space of the vacuum chamber. Heat radiation emitted by a heating device is guided onto the optical surface of the EUV mirror via a mirror element. The mirror element is arranged outside the mini-environment. The mirror element is designed as a MEMS mirror module.

[0028] The disclosure includes further developments of the EUV mirror system with features described in connection with the method according to the invention. The disclosure includes further developments of the method with features described in connection with the EUV mirror system according to the invention.

[0029] The invention is described below by way of example with reference to advantageous embodiments in the accompanying drawings. They show: Fig. 1: a schematic representation of a microlithographic projection exposure system; Fig. 2: a heating device for an EUV mirror; Fig. 3, Fig. 4: Intermediate products in the production of the 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.

[0030] In Fig. Figure 1 schematically illustrates a microlithographic EUV projection exposure system. The projection exposure system comprises an exposure beam source 14, an illumination system 10, and a projection lens 22, which are operated together in a vacuum chamber 23.

[0031] The exposure beam source 14 generates electromagnetic radiation in the EUV range, i.e., in particular, with a wavelength between 5 nm and 30 nm. The exposure beam emanating from the exposure beam source 14 is focused into an intermediate focal plane 16 by a collector 15. Exposure beam emanating from the intermediate focal plane 16 is guided into an object plane 12 by the illumination system 10, so that an object field in the object plane 12 is illuminated with uniform radiation intensity.

[0032] The illumination system 10 comprises a deflecting mirror 17, with which the exposure radiation is deflected onto a first facet mirror 18. A second facet mirror 19 is arranged downstream of the first facet mirror 18. The second facet mirror 19 images the facets of the first facet mirror 18 onto the object plane 12.

[0033] A photomask 13 is arranged in the object plane 12 and is imaged into an image plane 21 via a plurality of mirrors M1-M6 of the projection lens 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 process in which the photomask 13 and the wafer 20 are moved synchronously with one another.

[0034] Each of the EUV mirrors 17, 18, 19, M1-M6 in Fig. 1 is equipped with a multilayer coating system that forms an optical surface with high reflectivity for EUV radiation. This is demonstrated below using Fig. 2. The EUV mirror comprises a mirror body 30 made of a mirror substrate material with ultra-low thermal expansion ("ultra-low expansion material"). An example of such a material is a titanium silicate glass marketed under the name ULE™ by Corning Inc., which has a so-called zero-crossing temperature. At this zero-crossing temperature, which for ULE™, for example, is approximately 30°C, the thermal expansion coefficient exhibits a zero crossing in its temperature dependence, in the vicinity of which no or only negligible thermal expansion of the mirror substrate material occurs.

[0035] 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 and leads to heating of the EUV mirrors. 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.

[0036] During operation of the projection exposure system, the interior of the vacuum chamber 23 is placed under high vacuum with a vacuum pump (not shown) at a pressure of, for example, 10 -8 mbar. In the interior of the vacuum chamber 23, an inner housing is formed which surrounds the EUV beam path and which is separated from a main chamber 34 of the vacuum chamber 23 by a partition wall 28. In Fig. 1 only shows sections of the partition 28; in fact, the inner housing encloses 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 getting in the way. The area arranged in the inner housing and enclosed by the partition 28 is referred to as the mini-environment 29.

[0037] The inner housing 28 is not macroscopically sealed from the main chamber 34 of the vacuum chamber 23. For example, gaps can 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 allows pressure and concentration ratios to be set in the mini-environment 29 under the high-vacuum conditions prevailing in the vacuum chamber 23, which differ significantly from the conditions in the main chamber 34 of the vacuum chamber 23.

[0038] 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, whereby, among other things, ionic plasma species (H +) or radical plasma species (H) are formed. The plasma has the effect of removing contamination, which can arise, for example, from outgassing from components of the projection exposure system, from the surfaces of the optical elements arranged in mini-environment 29.

[0039] The projection exposure system comprises a heating device 35, which is designed to direct infrared radiation as heating radiation onto the optical surface 32 of an EUV mirror 33, 50 of the projection lens 22 in order to supply heat to the EUV mirror 33, 50 with a predetermined spatial distribution. Fig. This is illustrated in Figure 1 using the example of the EUV mirror M1. The wavelength of the infrared radiation can be, for example, between 1050 nm and 1600 nm, and the heating power can be, for example, between 2 W and 100 W. The supply of heating radiation causes a local thermal expansion, which can be specifically designed to influence a wavefront reflected by the EUV mirror 33, 50 in a desired manner.

[0040] 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 impinges on the optical surface 32 of the EUV mirror. According to Fig. 2, the radiation source 26 comprises a light guide 38 and a beam-shaping optic 37. The heating radiation 36 is guided via the light guide 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 reflection surface of the MEMS mirror module 31 is illuminated with uniform brightness.

[0041] The heating device 35 comprises a control unit 39, which controls the components of the heating device 35 depending on various input variables. Fig. Figure 2 shows an example of an infrared sensor 40, which detects a measured value of the temperature of the optical surface 32 and feeds it to the control unit 39. The control unit 39 controls the radiation source 26 to adjust the amount of heat radiation emitted. Furthermore, the control unit 39 controls the MEMS mirror module 31 to adjust the heat distribution across the optical surface 32.

[0042] The operation of the MEMS mirror module 31 is explained using an exemplary method for manufacturing a MEMS mirror module 31. In the Fig. 3, Fig. Figure 4 shows intermediate stages in the manufacture of a MEMS mirror module 31. A substrate body 42 is provided, which may be made of silicon, for example. A coating 41 with high reflectivity for infrared radiation is applied to a surface of the substrate body 42. A photoresist is applied to the coating 41. By suitable exposure of the photoresist, regions are defined in which material is removed in a subsequent processing step. Fig. 4 shows a state in which material has been removed between individual protruding structures, so that the protruding structures are separated from one another all the way into 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 illustrated flexure joint 43. During the manufacturing process, the micromirrors 44 are provided with actuators (not shown) via 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 flexure joint 43.

[0043] In Fig. 2, the MEMS mirror module 31 is under the control of the control unit 39. The control unit 39 sends control signals to the MEMS mirror module 31, so that the actuators are controlled to align the micromirrors 44 in a desired manner relative to the substrate body 42. In a further function, the control unit 39 checks, based on suitable sensor data, whether the substrate body 42 has the correct position and orientation within the EUV mirror system and adjusts it if necessary.

[0044] By illuminating the MEMS mirror module 31 with uniform brightness by the radiation source 26, the same amount of heat can be directed toward the optical surface 32 of the EUV mirror 33 via each of the micromirrors 44. By appropriately aligning the micromirrors 44, the heat distribution across the optical surface 32 can be adjusted very flexibly. There may be areas on the optical surface 32 that are not impacted by the heating radiation 36 from the MEMS mirror module 31. The heating radiation 36 can be directed to other areas of the optical surface 32 by two or more micromirrors 44. In this way, the heating radiation 36 can be adjusted, for example, such that the heat supplied by the heating 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 heating radiation and the EUV radiation.

[0045] In Fig. 5 shows an EUV mirror system according to the invention, in which the partition 28, by which the mini-environment 29 is separated from the main space 34 of the vacuum chamber 23, adjoins the optical surface 32 of the EUV mirror 33. A passage 46 is formed in the partition 28, which passage consists of a material transparent to the heating radiation. The heating radiation 36 exits the heating device 26 and is guided onto the MEMS mirror module 31. By appropriately adjusting the micromirrors 44 of the MEMS mirror module 31, it is defined how the supplied heat is to be distributed over the optical surface 32. The overall beam path, which is formed by the beam bundles emanating from the micromirrors 44, has a smallest constriction 45, which in the exemplary embodiment according to Fig. 5 coincides with the passage 46. This shape of the heating beam path makes it possible to keep the part of the partition 28 made of transparent material small. The vast majority of the partition 28 consists of a conventional material that is non-transparent to infrared radiation.

[0046] By locating the MEMS mirror module 31 outside the mini-environment 29, the MEMS mirror module 31 does not come into contact with the aggressive hydrogen plasma in the mini-environment 29. The degradation of the MEMS mirror module 31 is therefore significantly slower.

[0047] In the alternative embodiment in Fig.6, two mirrors 48, 49 are arranged in the heating beam path between the MEMS mirror module 31 and the partition wall 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.

[0048] Such a design reduces the equipment complexity because a single MEMS mirror module 31 is sufficient to supply two EUV mirrors 33, 50 with heating radiation 36. By appropriately controlling the micromirrors 44 of the MEMS mirror module 31, it is also 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 hits the first mirror 48, but rather the second mirror 49, the respective amount of heating output is redirected from the first EUV mirror 33 to the second EUV mirror 50.

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) and wherein the mirror element (31) is designed as a MEMS mirror module., [2] The 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 region (46) constitutes 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 a single MEMS mirror module (31) is directed to the first EUV mirror 33 and to 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 EUV mirror (17, 28, M1-M6), wherein the mirror element (31) is arranged outside the mini-environment (29) and wherein the mirror element (31) is designed as a MEMS mirror module.

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