Mirror, in particular for a microlithographic projection exposure system

Abstract

The invention relates to a mirror, in particular for a microlithographic projection exposure system, wherein the mirror has an optical active surface (10a, 20a, 30a, 40a), a substrate (11, 21, 31, 41), a reflection layer system (18, 28, 38, 48) for reflecting electromagnetic radiation incident on the optical active surface, at least one resistance layer (13, 23, 33, 43a, 43b), at least one electrode (12, 22, 32, 42a, 42b) located on the side of said resistance layer facing the reflective layer system, and at least one counter electrode (14, 24, 34, 44a, 44b) located on the side of the resistance layer facing the substrate, wherein the resistance layer can be heated in response to the application of an electrical voltage between the electrode and the counter electrode in order to produce a deformation effect on the optical active surface. The mirror is characterised in that the resistance layer has a local variation of at least one of the following parameters in a lateral plane defined by the resistance layer: the layer thickness of the resistance layer, the specific electrical resistance of the resistance layer, the stoichiometric composition of the resistance layer, and / or in that the resistance layer is structured in a manner deviating from a continuously full-surface design.

Description

[0001] Mirrors especially for microlithographic

[0002] Projection exposure system

[0003] This application claims priority from German patent application DE 10 2024 201 989.5, filed on March 4, 2024. The content of this DE application is incorporated by reference into the present application text.

[0004] BACKGROUND OF THE INVENTION

[0005] Field of the invention

[0006] The invention relates to a mirror, in particular for a microlithographic projection exposure system.

[0007] State of the art

[0008] Microlithography is used to manufacture microstructured components, such as integrated circuits or LCDs. The microlithography process is carried out in a so-called projection exposure system, which has an illumination device and a projection lens. The image of a mask (= reticle) illuminated by the illumination device is projected by the projection lens onto a substrate (e.g., a silicon wafer) coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection lens in order to transfer the mask structure onto the light-sensitive coating of the substrate. In a projection exposure system designed for the EUV range, i.e., at wavelengths of, for example,about 13 nm or about 7 nm, due to the lack of availability of suitable light-transmitting refractive materials, reflective optical elements are used as optical components for the imaging process.

[0009] A problem that arises during the operation of a projection exposure system designed for EUV, for example, is that the mirrors experience heating and associated thermal expansion or deformation, particularly due to the absorption of the radiation emitted by the (EUV) light source, which in turn can impair the imaging properties of the optical system. This is particularly the case when using illumination settings with comparatively small illumination poles (e.g., in dipole or quadrupole illumination settings), in which the mirror heating or deformation varies greatly across the effective optical surface of the mirror.

[0010] Known approaches to overcoming this problem include, for example, the use of a wavefront correction element with electrically conductive tracks distributed over at least one surface, via whose electrical control the interaction of the wavefront correction element with incident electromagnetic radiation can be influenced. Depending on the design (transmissive or reflective), the resulting manipulation of the wavefront of the electromagnetic radiation can be based, in particular, on a change in the refractive index and / or deformation of the wavefront correction element caused by the electrical control of the tracks.

[0011] In other approaches, a sector heater is used to cause a predetermined pattern of deformations or to counteract unwanted deformations.

[0012] One problem that occurs with the known use of an infrared (IR) radiation-based heating device is, among other things, high power loss, since comparatively large heat loads are generated outside the area actually to be heated (especially in the area of ​​adjacent optical components).

[0013] In another known approach, a heating layer integrated into the layer structure of the mirror is used in combination with an adjacent electrode arrangement of laterally adjacent electrodes to generate a possibly locally varying heating pattern in order to generate a predetermined deformation pattern by targeted electrical control of the electrode arrangement. Fig. 5 shows an exemplary structure of a conventional mirror. The mirror 50 comprises a mirror substrate 51, a reflective layer system 58 (e.g., a molybdenum-silicon (Mo-Si) layer stack), and an electrode arrangement comprising a plurality of electrodes 52, which can be electrically controlled via electrical leads 56 or supplied with a selectively adjustable electric current. The mirror 50 has an electrically conductive mediator layer 53 serving as a heating layer. 55 denotes a smoothing and insulating layer (e.g.,made of quartz glass, SiO2), which in particular electrically insulates the electrodes of the electrode arrangement 52 from one another.

[0014] One problem that arises with the above-described use of a heating layer in combination with an adjacent electrode array consisting of laterally adjacent electrodes is, among other things, the requirement for complex control technology for the targeted activation of the lateral structures. Furthermore, a power margin is required to control the electrode array, since a potential difference also exists at unrelated electrodes, thus resulting in power loss. Furthermore, lateral short circuits can occur when electrical current is applied, causing an undefined deflection near the respective electrode.

[0015] For the prior art, reference is made to DE 10 2017 205 405 A1 as an example only. SUMMARY OF THE INVENTION

[0016] It is an object of the present invention to provide a mirror, in particular for a microlithographic projection exposure apparatus, which enables a locally limited adjustment of temperature fields varying over the mirror surface and the generation of a locally adjustable deformation while at least partially avoiding the problems described above.

[0017] This object is achieved by the mirror according to the features of independent patent claim 1.

[0018] A mirror according to the invention, wherein the mirror has an optical effective surface, comprises:

[0019] - a substrate;

[0020] - a reflective layer system for reflecting electromagnetic radiation incident on the optical effective surface;

[0021] - at least one resistive layer;

[0022] - at least one electrode located on the side of this resistance layer facing the reflective layer system; and

[0023] - at least one counter electrode located on the side of the resistance layer facing the substrate;

[0024] - wherein the resistance layer is heatable in response to the application of an electrical voltage between the electrode and the counter electrode to produce a deformation effect on the optical active surface.

[0025] The mirror is characterized in that the resistance layer has a local variation of at least one of the following parameters in a lateral plane defined by the resistance layer: layer thickness of the resistance layer,

[0026] - Specific electrical resistance of the resistance layer,

[0027] - Stoichiometric composition of the resistance layer, and / or that the resistance layer is structured in a manner that deviates from a continuous, full-surface design.

[0028] The present invention is based in particular on the concept of realizing a desired thermally induced deformation in a mirror by applying an electric current flowing in the stacking direction of the layer structure (ie perpendicular to a lateral plane defined by the resistance layer) to a layer referred to here and hereinafter as a "resistance layer" and serving as a "heating layer" via at least one electrode(s) or counterelectrode(s) located above or below this resistance layer in the stacking direction of the layer structure of the mirror.

[0029] Due to this current flow between the electrode and counter electrode through the resistance layer (i.e. "vertically" or perpendicular to a lateral plane defined by the resistance layer), the achieved heat generation is locally limited essentially to the area of ​​the respective electrode or the adjacent area of ​​the resistance layer, so that the current flow and the associated heating of the resistance layer are comparatively easy to control. In particular, existing conductor tracks are only slightly heated parasitically, and moreover, the system is not or only slightly influenced by lateral temperature gradients. This ultimately simplifies control, since corresponding parameters such as lateral temperature gradients do not have to be taken into account during temperature control.As a result, the invention achieves a precise and locally limited adjustment of a desired temperature distribution—and thus, for example, the corresponding correction of thermally induced surface deformations—with a comparatively simple and robust structure. The layer structure present in the mirror according to the invention enables the realization of comparatively high heating outputs (e.g., 1 W / cm). 2 and above) with simultaneously achievable high spatial resolution with regard to the set temperature profile, whereby this resolution can be in the micrometer (pm) range laterally, ie in a plane running perpendicular to the stacking direction of the layer stack.

[0030] In this case, the requirements to be placed on the necessary structuring of an electrode arrangement can be significantly reduced compared to the conventional use of an electrode arrangement comprising laterally adjacent electrodes as described above, since in the mirror according to the invention the spatial resolution with regard to the set temperature profile is determined by the coating process used in the production of the layer structure of the mirror (in particular in the formation of the resistance layer).

[0031] Furthermore, in a manner advantageous from a manufacturing perspective, the individual process steps in the production of the respective components of the mirror according to the invention can be carried out directly one after the other and without temporarily leaving the coating system.

[0032] By suitable local variation of at least one of the above-mentioned parameters layer thickness of the resistance layer, specific electrical resistance of the resistance layer and stoichiometric composition of the resistance layer, additional degrees of freedom in temperature control and the associated adjustment of a thermally induced local deformation in the mirror are provided.

[0033] By structuring the resistance layer in a manner that differs from a continuous, full-surface design - in addition to or as an alternative to the above-mentioned local variation - such targeted structuring can further improve or increase the correction options available for temperature control and the associated adjustment of a thermally induced local deformation in the mirror with regard to the wavefront aberrations occurring during operation of the mirror or the associated optical system.

[0034] According to one embodiment, the electrode and / or the counter electrode is structured in a manner that differs from a continuous, full-surface design.

[0035] According to one embodiment, the mirror has an electrode arrangement comprising a plurality of independently controllable electrodes on the side of the resistance layer facing the reflection layer system and / or on the side of the resistance layer facing the substrate.

[0036] According to one embodiment, the ratio between the electrical conductivity of the electrode and the electrical conductivity of the resistance layer is at least 1000.

[0037] According to one embodiment, the resistance layer has an electrical conductivity of less than 10 -3 Siemens / meter (S / m), especially in the range of 10 -4 Siemens / meter (S / m) up to 10 -7 Siemens / meter (S / m).

[0038] According to one embodiment, the resistance layer comprises a material from the group containing semiconducting oxides, semiconducting nitrides, semiconducting oxynitrides, semiconducting carbides, semiconducting boranes and metallic semiconductors, in particular germanium (Ge) or silicon (Si).

[0039] According to one embodiment, the electrode and the counter electrode comprise a material from the group comprising platinum (Pt), palladium (Pd), silver (Ag), copper (Cu), gold (Au), aluminum (Al), tin (Sn), zinc (Zn), nickel (Ni), tungsten (W), chromium (Cr), ruthenium (Ru), molybdenum (Mo) and alloys thereof.

[0040] According to one embodiment, the mirror has at least two, in particular at least three resistance layers, which are arranged at different distances from the reflection layer system, wherein each of these resistance layers is assigned at least one electrode located on the side of the respective resistance layer facing the reflection layer system and at least one counter electrode located on the side of the respective resistance layer facing the substrate.

[0041] According to one embodiment, at least two of these resistance layers have a partial overlap in a direction perpendicular to their respective lateral plane.

[0042] With such a partial overlap of different resistance layers, a comparatively soft or less steep zone transition can be achieved between the individual zones of different deformation, which are caused by the heating of the resistance layers.

[0043] According to one embodiment, the mirror has at least one additional functional layer, in particular in the form of a smoothing and insulating layer, a diffusion barrier layer, an adhesion-improving layer and / or an expansion-increasing layer.

[0044] According to one embodiment, a measuring device for measuring the electrical resistance of the at least one resistance layer, in particular a Wheatstone bridge, is further provided.

[0045] According to one embodiment, the mirror is designed for an operating wavelength of less than 200 nm. According to another embodiment, the mirror is designed for an operating wavelength of less than 30 nm, in particular less than 15 nm.

[0046] The invention further relates to an optical system of a microlithographic projection exposure apparatus, in particular an illumination device or a projection objective, as well as a microlithographic projection exposure apparatus with at least one mirror according to the invention.

[0047] Further embodiments of the invention can be found in the description and the dependent claims.

[0048] The invention is explained in more detail below with reference to embodiments shown in the attached figures.

[0049] BRIEF DESCRIPTION OF THE DRAWINGS

[0050] They show:

[0051] Figures 1-4 are schematic representations to explain different embodiments of a mirror according to the invention;

[0052] Figure 5 is a schematic representation of a conventional mirror structure; and

[0053] Figure 6 shows a schematic representation of the possible configuration of a microlithographic projection exposure system designed for operation in the EUV. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0054] Fig. 6 shows a schematic representation of an exemplary projection exposure system 600 designed for operation in the EUV, in which the present invention can be implemented.

[0055] According to Fig. 6, an illumination device in a projection exposure system 600 designed for EUV comprises a field facet mirror 603 and a pupil facet mirror 604. The light from a light source unit, which comprises a plasma light source 601 and a collector mirror 602, is directed onto the field facet mirror 603. A first telescopic mirror 605 and a second telescopic mirror 606 are arranged in the light path downstream of the pupil facet mirror 604. A deflection mirror 607 is arranged downstream in the light path, which deflects the radiation incident upon it onto an object field in the object plane of a projection lens comprising six mirrors 651-656. At the location of the object field, a reflective structure-bearing mask 621 is arranged on a mask table 620, which is imaged by means of the projection lens into an image plane in which a substrate 661 coated with a light-sensitive layer (photoresist) is located on a wafer table 660.

[0056] During operation of the projection exposure system 600, at least one arbitrary mirror can be designed to correct occurring wavefront aberrations, wherein possible configurations of this mirror are described below with reference to the schematic representations of Figs. 1-4.

[0057] Fig. 1 shows a schematic representation to explain an embodiment of the mirror according to the invention. The mirror 10 can in particular be an EUV mirror of an optical system, in particular of the projection objective or the illumination device of a microlithographic projection exposure apparatus, for example with the structure described with reference to Fig. 6. The mirror 10 comprises in particular a mirror substrate 11, which is made of any suitable mirror substrate material. A suitable mirror substrate material is, for example, titanium dioxide (TiO 2 )-doped quartz glass, wherein merely by way of example (and without the invention being restricted thereto) the materials sold under the brand names ULE® (from Corning Inc.) or Zerodur® (from Schott AG) can be used.Furthermore, the mirror 10 has, in a manner known per se, a reflective layer system 18 which, in the illustrated embodiment, merely comprises, by way of example, a molybdenum-silicon (Mo-Si) layer stack. Without the invention being limited to specific configurations of the reflective layer system, a suitable structure, by way of example only, can comprise approximately 50 layers or layer packages of a layer system made of molybdenum (Mo) layers with a layer thickness of, for example, 2.4 nm each and silicon (Si) layers with a layer thickness of, for example, 3.3 nm each. In further embodiments, the mirror can also be designed for use under so-called grazing incidence. In this case, the reflective layer system can, for example, in particular have only a single layer made of, for example, ruthenium (Ru), niobium (Nb) or molybdenum (Mo) with an exemplary thickness of 30 nm.

[0058] The exposure of the optical effective surface 10a of the mirror 10 to electromagnetic EUV radiation during operation of the optical system can result in an inhomogeneous volume change of the mirror substrate 11 due to the temperature distribution resulting from the absorption of radiation impinging inhomogeneously on the optical effective surface 10a. To correct such an undesirable volume change or to correct other aberrations occurring during operation of the microlithographic projection exposure system, the mirror 10 is designed in accordance with the invention, as will be explained in more detail below.

[0059] According to Fig. 1, the mirror 10 according to the invention has a structured resistance layer 13, wherein a structured electrode 12 is arranged on the side of this resistance layer 13 facing the reflection layer system 18, which electrode can be electrically controlled via an electrical lead 16. Furthermore, the mirror 10 has a structured counterelectrode 14 on the side of the structured resistance layer 13 facing the substrate 11, which counterelectrode can be electrically controlled via an electrical lead 17.

[0060] During operation of the mirror 10 according to the invention, different electrical potentials can thus be applied to the electrode 12 and the counter electrode 14, whereby the electrical voltage generated thereby between the electrode 12 and the counter electrode 14 causes a "vertical" (i.e., running along the z-direction in the drawn coordinate system) electrical current flow across the resistance layer 13. This electrical current leads, depending on the potentials applied to the electrodes, to a locally induced heating of the resistance layer 13 and a concomitant thermally induced deformation of the optical effective surface 10a.

[0061] The heat generated locally is essentially limited to the area of ​​the respective electrode or the adjacent area of ​​the resistance layer, making the current flow and the associated heating of the resistance layer relatively easy to control. The electrical resistance and thus the heating effect can be determined via a Wheatstone bridge and are not influenced by any surrounding electrodes.

[0062] In Fig. 1, "15" denotes an insulation layer in which the electrode 12, the resistance layer 13, and the counter electrode 14 are arranged. The insulation layer 15 can be made, for example, of quartz glass (SiO2), silicon (Si), or SiOx. Furthermore, additional functional layers not shown in Fig. 1 (such as diffusion barrier layers, adhesion-enhancing layers, expansion-enhancing layers, etc.) can be provided in the layer structure of the mirror 10.As a result, the combined use of electrode 12, resistance layer 13 and counter electrode 14 in the mirror 10 according to the invention enables specifically adjustable power inputs into the mirror according to the invention despite - for example, in comparison to the wavefront correction elements described at the beginning - comparatively coarse structures of the electrode arrangement, wherein at the same time the coupling of the heat power is limited to the mirror itself - in contrast to the conventional use of infrared (IR) heating devices described at the beginning.

[0063] The invention is not limited to a specific geometric configuration of the electrode arrangement or the resistance layer. Merely exemplary configurations of the electrode / counterelectrode arrangement and the supply lines, as well as the resistance layer, which are advantageous in different respects, are described below with reference to Figs. 2 to 4.

[0064] Fig. 2 shows a schematic representation to explain a further embodiment of the mirror according to the invention, wherein, in comparison to Fig. 1, analogous or essentially functionally identical components are designated by reference numerals increased by “10”.

[0065] According to Fig. 2, the mirror 20 has a continuous, full-surface resistance layer 23, wherein on the side of this resistance layer 23 facing the reflection layer system 28 there is arranged a structured electrode 22 which can be electrically controlled via an electrical supply line 26. Furthermore, the mirror 20 according to the invention has, on the side of the resistance layer 23 facing the substrate 21, a counterelectrode 24 which is formed continuously over the full surface of the resistance layer 23 and can be electrically controlled via an electrical supply line 27. Via the electrode 22 and the counterelectrode 24, a "vertical" electrical current flow (i.e. running along the z-direction in the drawn coordinate system) can be generated in the resistance layer 23, analogous to the embodiment of Fig. 1. In a further embodiment, not shown, in contrast to Fig.2 Conversely, the electrode 22 is designed to be full-surface and the counter electrode 27 is designed to be structured.

[0066] Fig. 3a and 3b show schematic representations in plan view (Fig. 3a) and sectional view (Fig. 3b) to explain a further embodiment of the mirror according to the invention, wherein, compared to Fig. 1, analogous or essentially functionally identical components are designated by reference numerals increased by “20”.

[0067] 3a and 3b, the mirror 30 has a continuous, full-surface resistance layer 33, wherein on the side of this resistance layer 33 facing the reflection layer system 38, a plurality of structured electrodes 32 of an electrode arrangement are arranged, each of which can be electrically controlled via electrical leads 36. Furthermore, the mirror 30 according to the invention has, on the side of the resistance layer 33 facing the substrate 31, a counterelectrode 34 which is formed continuously over the full surface of the resistance layer 33 and which can be electrically controlled via an electrical lead 37. Via the electrodes 32 and the counterelectrode 34, a "vertical" electrical current flow (i.e. running along the z-direction in the drawn-in coordinate system) can be generated in a targeted manner in individual zones of the resistance layer 33, analogous to the embodiments described above.

[0068] Fig. 4 shows a schematic representation to explain a further embodiment of the mirror according to the invention, wherein, compared to Fig. 1, analogous or essentially functionally identical components are designated by reference numerals increased by “30”.

[0069] According to Fig. 4, the mirror 40 has two structured resistance layers 43a, 43b, wherein a structured electrode 42a is arranged on the side of the resistance layer 43a facing the reflection layer system 48, which can be controlled via an electrical supply line 46a. On the side of the resistance layer 43b facing the reflection layer system 48, a structured electrode 42b is arranged, which can be electrically controlled via an electrical supply line 46b. Furthermore, the mirror 40 according to the invention has, on the side of the structured resistance layer 43a facing the substrate 41, a counterelectrode 44a extending over its entire surface, which can be electrically controlled via an electrical supply line 47a. On the side of the structured resistance layer 43b facing the substrate 41, a counterelectrode 44b is arranged over its entire surface, which can be electrically controlled via an electrical supply line 47b.Analogous to the embodiments described above, a “vertical” (ie running along the z-direction in the drawn coordinate system) electrical current flow can be generated in the resistance layers 43a, 43b via the electrodes 42a, 42b and the counter electrodes 44a, 44b.

[0070] According to Fig. 4, the resistance layers 43a, 43b have a partial overlap in a direction perpendicular to their respective lateral plane (xy plane) (ie in the z direction in the drawn coordinate system), with the result that a comparatively soft or less steep zone transition is achieved between the individual zones of different deformation, which are caused by the heating of the resistance layers 43a, 43b.

[0071] It should be noted that in the aforementioned mirror substrate materials, the thermal expansion coefficient exhibits a zero crossing in its temperature dependence at the so-called zero-crossing temperature, in the vicinity of which no or only negligible thermal expansion occurs. Thus, in certain scenarios, it may be sufficient to keep the mirror at the aforementioned zero-crossing temperature. For a mirror with finite thermal expansion, the deformation can be controlled by adjusting the local power. It may be advantageous to continuously provide a certain heating power, which can be turned down or switched off as needed, thus eliminating the need for an additional cooler.It may be useful to deliberately choose a higher zero-crossing temperature of the substrate in order to be able to remove heat output when choosing the “operating point” accordingly, thus enabling an opposite or negative adjustment direction.

[0072] Although the invention has been described with reference to specific embodiments, numerous variations and alternative embodiments will become apparent to those skilled in the art, e.g., by combining and / or interchanging features of individual embodiments. Accordingly, it will be understood by those skilled in the art that such variations and alternative embodiments are encompassed by the present invention, and the scope of the invention is limited only by the appended claims and their equivalents.

Claims

Patent claims 1 . Mirror, the mirror having an optical effective surface, with: • a substrate (11, 21, 31, 41); • a reflective layer system (18, 28, 38, 48) for reflecting electromagnetic radiation incident on the optical active surface (10a, 20a, 30a, 40a); • at least one resistance layer (13, 23, 33, 43a, 43b); • at least one electrode (12, 22, 32, 42a, 42b) located on the side of this resistance layer (13, 23, 33, 43a, 43b) facing the reflection layer system (18, 28, 38, 48); and • at least one counter electrode (14, 24, 34, 44a, 44b) located on the side of the resistance layer (13, 23, 33, 43a, 43b) facing the substrate (11, 21, 31, 41); • wherein the resistance layer (13, 23, 33, 43a, 43b) is heatable in response to the application of an electrical voltage between the electrode (12, 22, 32, 42a, 42b) and the counter electrode (14, 24, 34, 44a, 44b) to produce a deformation effect on the optical active surface (10a, 20a, 30a, 40a); characterized in that the resistance layer (13, 23, 33, 43a, 43b) has a local variation of at least one of the following parameters in a lateral plane defined by the resistance layer: - Layer thickness of the resistance layer (13, 23, 33, 43a, 43b), - Specific electrical resistance of the resistance layer (13, 23, 33, 43a, 43b), - Stoichiometric composition of the resistance layer (13, 23, 33, 43a, 43b), and / or that the resistance layer (13, 43a, 43b) is structured in a manner that deviates from a continuous, full-surface design.

2. Mirror according to claim 1, characterized in that an electric current caused by applying an electric voltage between the electrode (12, 22, 32, 42a, 42b) and the counter electrode (14, 24, 34, 44a, 44b) in the resistance layer (13, 23, 33, 43a, 43b) has a direction which is perpendicular to a lateral plane defined by the resistance layer (13, 23, 33, 43a, 43b).

3. Mirror according to claim 1 or 2, characterized in that the electrode (12, 22, 32, 42a, 42b) and / or the counter electrode (14) is structured in a manner deviating from a continuous full-surface design.

4. Mirror according to one of claims 1 to 3, characterized in that it has an electrode arrangement comprising a plurality of independently controllable electrodes (32) on the side of the resistance layer (33) facing the reflection layer system (38) and / or on the side of the resistance layer facing the substrate.

5. Mirror according to one of the preceding claims, characterized in that the ratio between the electrical conductivity of the electrode (12, 22, 32, 42a, 42b) and the electrical conductivity of the resistance layer (13, 23, 33, 43a, 43b) is at least 1000.

6. Mirror according to one of the preceding claims, characterized in that the resistance layer (13, 23, 33, 43a, 43b) has an electrical conductivity of less than 10 -3 Siemens / meter (S / m), especially in the range of 10 -4 Siemens / meter (S / m) up to 10 -7 Siemens / Meter (S / m).

7. Mirror according to one of the preceding claims, characterized in that the resistance layer (13, 23, 33, 43a, 43b) comprises a material from the group containing semiconducting oxides, semiconducting nitrides, semiconducting oxynitrides, semiconducting carbides, semiconducting boranes and metallic semiconductors, in particular germanium (Ge) or silicon (Si).

8. Mirror according to one of the preceding claims, characterized in that the electrode (12, 22, 32, 42a, 42b) and the counter electrode (14, 24, 34, 44a, 44b) comprise a material from the group comprising platinum (Pt), palladium (Pd), silver (Ag), copper (Cu), gold (Au), aluminum (Al), tin (Sn), zinc (Zn), nickel (Ni), tungsten (W), chromium (Cr), ruthenium (Ru), molybdenum (Mo) and alloys thereof.

9. Mirror according to one of the preceding claims, characterized in that it has at least two, in particular at least three resistance layers (43a, 43b) which are arranged at different distances from the reflection layer system (48), wherein each of these resistance layers (43a, 43b) is assigned at least one electrode (42a, 42b) located on the side of the respective resistance layer (43a, 43b) facing the reflection layer system (48) and at least one counter electrode (44a, 44b) located on the side of the respective resistance layer (43a, 43b) facing the substrate (41).

10. Mirror according to claim 9, characterized in that at least two of these resistance layers (43a, 43b) have a partial overlap in a direction perpendicular to their respective lateral plane. 1 1 . Mirror according to one of the preceding claims, characterized in that it has at least one additional functional layer, in particular in the form of a smoothing and insulating layer, a diffusion barrier layer, an adhesion-improving layer and / or an expansion-increasing layer.

12. Mirror according to one of the preceding claims, characterized in that a measuring device for measuring the electrical resistance of the at least one resistance layer (13, 23, 33, 43a, 43b), in particular a Wheatstone bridge, is further provided.

13. Mirror according to one of the preceding claims, characterized in that it is designed for an operating wavelength of less than 200 nm.

14. Mirror according to one of the preceding claims, characterized in that it is designed for an operating wavelength of less than 30 nm, in particular less than 15 nm.

15. Optical system of a microlithographic projection exposure apparatus, in particular illumination device or projection objective, with at least one mirror which is designed according to one of claims 1 to 14.

16. Microlithographic projection exposure apparatus with an illumination device and a projection objective, characterized in that the projection exposure apparatus has a mirror which is designed according to one of claims 1 to 14.

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