Mirror, in particular for microlithographic projection exposure systems

Abstract

The invention relates to a reflector, in particular a reflector for a microlithographic projection exposure system. Mirror having an effective optical surface, a reflective layer system for reflecting electromagnetic radiation of an operating wavelength incident on the effective optical surface, a mirror substrate (105, 205, 305) made of a mirror substrate material and in which a structure (106, 206, 306) differing in refractive index from the surrounding mirror substrate material is arranged, and a structure (105, 205, 305) located on the mirror substrate (105, 205, 305) located on the mirror substrate (105, 205, 305) and a layer stack between the mirror substrate (105, 205, 305) and the reflective layer system, wherein the layer stack has an absorber layer (110, 210, 310), an AR layer (120, 220, 320) and a smooth layer (130, 230, 330) one after the other in a stacking direction extending from the mirror substrate (105, 205, 305) to the reflective layer system.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the priority of German patent application DE 10 2022 205302.8 filed on May 25, 2022. The content of this DE application is also incorporated into the text of the present application by reference. Technical Field

[0003] The present invention relates to a reflecting mirror, in particular to a reflecting mirror for a microlithography projection exposure device, and a manufacturing method thereof. Background Art

[0004] Microlithography is used to produce microstructured components, such as integrated circuits or LCDs. The microlithography process is carried out in a so-called projection exposure apparatus, which comprises 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 photosensitive layer (=photoresist) and arranged in the image plane of the projection lens, in order to transfer the mask structure to the photosensitive coating of the substrate.

[0005] In projection lenses designed for the EUV range, ie at wavelengths of, for example, about 13 nm or about 7 nm, mirrors are used as optical components for the imaging process due to the lack of availability of suitable light-transmitting refractive materials.

[0006] In this context, it is also known to configure one or more mirrors in an EUV system as an adaptive mirror with an actuator layer consisting of a piezoelectric material, wherein an electric field with a locally varying intensity is generated across the piezoelectric layer by voltages applied to electrodes arranged on both sides relative to the piezoelectric layer. In the event of a local deformation of the piezoelectric layer, the reflective layer system of the adaptive mirror also deforms, as a result of which (possibly also time-variable) imaging aberrations are compensated, for example at least partially, by appropriate actuation of the electrodes.

[0007] Figure 8The schematic diagram shows the general construction of an adaptive mirror 10, which comprises a mirror substrate 12 and a reflective layer system 21. The mirror 10 comprises a piezoelectric layer 16, for example made of lead zirconate titanate (Pb(Zr, Ti)O3, PZT). Electrode arrangements 14, 20 are located above and below the piezoelectric layer 16, respectively, by means of which an electric field for generating a local variable deformation can be applied to the mirror 10. The second electrode arrangement 14 facing the substrate 12 is configured as a continuous planar electrode with a constant thickness, while the first electrode arrangement 20 comprises a plurality of electrodes 20a, 20b, 20c, ..., to which a voltage relative to the first electrode arrangement 14 can be applied, respectively, via supply lines 19a, 19b, 19c, ... The electrodes 20a, 20b, 20c, ... are embedded in a smoothing layer 18 made of quartz (SiO2), which also serves to level the electrode arrangement 20. Furthermore, the mirror 10 comprises an adhesion layer 13 , for example composed of titanium Ti, and a buffer layer 15 between the mirror substrate 12 and a bottom electrode 114 facing the mirror substrate 12 .

[0008] During operation of an optical system comprising the mirror 10, application of a voltage to the electrode arrangements 14 and 20 by means of an electric field formed in the region of the piezoelectric layer 16 results in a deflection of the piezoelectric layer 16. In this way, an actuation of the mirror 10 (e.g. for compensation of optical aberrations, e.g. due to thermal deformations in the event of EUV radiation incident on the optically active surface 11) can be achieved. The dielectric layer 17 is connected to the electrodes 20a, 20b, 20c, ... (which are only shown for illustration purposes) Figure 8 The piezoelectric layer 16 is in direct electrical contact with the piezoelectric material 20a, 20b, 20c, ... of the electrode arrangement 20 within the piezoelectric layer 16, wherein the dielectric layer has only a low electrical conductivity (e.g., less than 200 Siemens / meter (S / m)), with the result that the potential difference existing between adjacent electrodes 20a, 20b, 20c, ... substantially drops across the dielectric layer 17 and therefore also drops in the piezoelectric material between the electrodes.

[0009] During the production of the adaptive mirror 10, it is a demanding challenge to ensure that the reflective layer system 21 is applied while complying with the required specifications. One problem that arises here in practice is, in particular, to achieve interferometric measurements of the corresponding surface-treated layer without the measurement being influenced by the metallic structure of the electrode arrangement 20 and the piezoelectric layer 16 during the manufacturing process before the reflective layer system 21 is applied, since such influences would lead to a distortion of the interferometric measurement results and thus to insufficient availability of material removal to be performed in each case during the manufacturing process.

[0010] Figure 7A schematic and very simplified representation is shown for illustrating the above problem. The reflector 700 has a structure 706 hidden in the reflector substrate, here marked as "705" (having a different refractive index than the surrounding reflector substrate material). The reflector substrate 705 is provided with an optically active surface ( Figure 7 The interface of the reflective layer system of the reflector 700 (not shown) is marked "701". During the manufacture of the reflector 700, the interferometric investigations carried out in order to characterize the surface form or pattern (i.e. the variation of the actual surface form from the target form) include exposure to electromagnetic measuring radiation of a suitable measuring wavelength, which is typically in the visible range of 400nm to 750nm, wherein relevant surface information is generated from phase differences by comparison with corresponding reference radiation or waves. However, the presence of said structure 706 having a different refractive index than the surrounding reflector substrate material (as indicated in the area marked "710") results in further reflection of the measuring radiation at the structure 706 itself (i.e. in the area 710 of the beam 711), which in turn causes further interference (i.e. according to Figure 7 , between beams 712 and 713) (because the distance of structure 706 from optically active surface 701 or the optical path difference between beams 712 and 713 is smaller than the coherence length of the electromagnetic measurement radiation). As a result of the destructive influence of this additional interference on the result obtained in the interferometric measurement, the pattern of mirror 700 is determined incorrectly, with the consequence that the manufacture of the mirror determined on the basis of this pattern cannot be carried out with the required accuracy.

[0011] To overcome the above problems, refer again to Figure 8 For the purpose of achieving an absorption effect, the smoothing layer can be produced, for example, from doped quartz glass (ie doped SiO 2 ). However, as a result of this configuration, firstly, the deviation from the ideal material for optimal processability impairs the processability of the smoothing layer and, secondly, a higher layer thickness is required to achieve the desired function.

[0012] As prior art, reference is made merely by way of example to DE 10 2017 213 900 A1, DE 10 2015 208214 A1 and DE 10 2014 204 171 A1. Summary of the invention

[0013] It is an object of the present invention to provide a mirror, in particular for a microlithographic projection exposure apparatus, and a method for its production which make it possible to achieve the highest possible surface quality while complying with the required specifications, for example in the EUV range.

[0014] This object is achieved according to the features of the independent patent claims.

[0015] The reflector of the present invention, wherein the reflector has an optically effective surface, has:

[0016] - a reflective layer system for reflecting electromagnetic radiation of an operating wavelength incident on said optically active surface;

[0017] a mirror substrate which has been made of a mirror substrate material and in which structures having a different refractive index than the surrounding mirror substrate material are arranged; and

[0018] - a layer stack present between the mirror substrate and the reflective layer system;

[0019] - wherein the layer stack comprises, consecutively in a stacking direction extending from the mirror substrate to the reflective layer system, an absorber layer, an AR layer and a smoothing layer.

[0020] The present invention is based in particular on the following concept: in a mirror having structures hidden in its mirror substrate (e.g. electrodes) which have a refractive index different from the rest of the mirror substrate material, by providing a suitable layer stack between the mirror substrate and the reflective layer system it is ensured that: firstly, interference pattern measurements which may usually be required repeatedly during mirror manufacturing can be carried out without the destructive influence of the structures hidden in the mirror substrate as described at the beginning, and secondly, smoothing steps required during mirror manufacturing (e.g. polishing) can be carried out in a very optimized manner, which means that the corresponding optical processability is maintained.

[0021] In the layer stack arranged according to the invention between the reflector substrate and the reflective layer system, the absorber layer achieves the effect that the measuring radiation penetrating into the reflector during the mentioned interference pattern measurement is at least largely absorbed (i.e. practically no reflected measuring radiation which interferes with the pattern measurement emerges from the reflector), while the AR layer between the smoothing layer and the absorber layer achieves the effect that also no significant reflection occurs at the transition to the absorber layer. At the same time, the already mentioned functions of the absorber layer and the AR layer make it possible to configure the smoothing layer even without reference to structures hidden in the substrate and their potentially disruptive influence on the interference pattern measurement, and thus to optimize the smoothing layer with respect to the smoothing (polishing) process to be carried out for the manufacture of the reflector.

[0022] In general, the layer stack according to the invention not only justifies the requirements for smoothness that exist from a manufacturing point of view, but also, during the manufacturing process, by means of structures hidden in the mirror substrate (for example, by means of electrodes of the electrode arrangement and by means of piezoelectric layers, in the adaptive mirror described at the beginning), prevents the influences or distortions described at the beginning from occurring in the measurement results obtained in the interferometric measurement analysis of the individual surface-treated layers.

[0023] In particular, according to the present invention, there is no need for any manipulation of the smoothing layer by appropriate doping in order to ensure that the above-mentioned metallic structure of the electrode arrangement and the piezoelectric layer is "invisible" in the interferometric analysis, since the latter's function is realized by the further layers present in the layer stack of the present invention, namely the AR layer and the absorber layer.

[0024] In one embodiment, the absorber layer has a relative humidity of less than 10 nm for at least one measurement wavelength in the range of 400 nm to 750 nm. -5 The term "transmittance" here and hereinafter should be taken to mean the transmittance through the layer stack twice (ie after reflection of the electromagnetic radiation in question at the absorber layer).

[0025] In one embodiment, the absorber layer has a thickness in the range of 50 nm to 2 μm.

[0026] In one embodiment, the absorber layer includes at least one material from the group consisting of amorphous silicon (a-Si), non-oxidized and non-nitrided a-Si compounds, and metals tantalum (Ta), titanium (Ti), chromium (Cr), nickel (Ni), aluminum (Al), and alloys of these metals.

[0027] In one embodiment, the smoothing layer is made of a material selected from the group consisting of silicon dioxide (SiO2), SiOx compounds, hafnium dioxide (HfO2), titanium dioxide (TiO2), amorphous silicon (a-Si) and crystalline silicon (c-Si).

[0028] In one embodiment, the AR layer has an average refractive index between the average refractive index of the smoothing layer and the average refractive index of the absorber layer.

[0029] In one embodiment, the AR layer has a refractive index that continuously rises or falls along the stacking direction between the average refractive index of the absorber layer and the average refractive index of the smoothing layer.

[0030] In one embodiment, the AR layer has an alternating sequence of layers of relatively low refractive index, particularly silicon dioxide (SiO2), and layers of relatively high refractive index, particularly amorphous silicon (a-Si).

[0031] In one embodiment, the mirror has a piezoelectric layer which is arranged between the mirror substrate and the reflective layer system and which can be subjected to an electric field via an electrode arrangement to generate a locally variable deformation.

[0032] According to one embodiment, the mirror is designed for an operating wavelength of less than 30 nm, in particular less than 15 nm. However, the invention is not limited thereto, and therefore in further applications, the invention can also advantageously be implemented in an optical system with an operating wavelength in the VUV range (e.g. less than 200 nm).

[0033] According to one embodiment, the mirror is a mirror for a microlithography projection exposure apparatus.

[0034] According to another aspect, the present invention also relates to a method for manufacturing a reflector, wherein the method comprises the following steps:

[0035] - providing a mirror substrate made of a mirror substrate material, wherein there is a structure formed in the mirror substrate, the refractive index of the structure being different from the surrounding mirror substrate material;

[0036] - applying a layer stack on top of the mirror substrate, wherein the layer stack has an absorber layer, an AR layer and a smoothing layer successively in the stacking direction; and

[0037] - applying a reflective layer system for reflecting incident electromagnetic radiation having an operating wavelength;

[0038] - wherein during the manufacture of the mirror at least one interferometric pass measurement is performed using electromagnetic measuring radiation.

[0039] The reflector can be used in particular as a reflector for a microlithography projection exposure apparatus. However, the invention is not limited thereto. In other applications, the reflector of the invention can also be employed or utilized, for example, in an apparatus for mask metrology.

[0040] The invention further relates to an optical system, in particular an illumination device or a projection lens of a microlithography projection exposure apparatus, comprising at least one reflector having the above-mentioned features, and also to a microlithography projection exposure apparatus.

[0041] Further configurations of the invention will be apparent from the description and the dependent claims.

[0042] The invention is explained in detail hereinafter with reference to the working examples shown in the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings show:

[0044] Figure 1a Schematic diagram for illustrating the mode of action of the reflector according to the invention or the layer stack provided therein;

[0045] Figure 1b A schematic diagram of a possible configuration of a reflector of the present invention in a first embodiment;

[0046] Figure 2-3b A schematic diagram or chart for explaining the construction and mode of action of the reflector of the present invention in the second embodiment;

[0047] Figure 4-5bA schematic diagram or chart for explaining the construction and mode of action of the reflector of the present invention in the third embodiment;

[0048] Figure 6 Schematic diagram of the construction of a microlithography projection exposure apparatus designed for operation in EUV;

[0049] Figure 7 A schematic diagram for explaining problems occurring in interferometric characterization of the surface of a conventional mirror in the prior art; and

[0050] Figure 8 Schematic diagram for illustrating a possible design of an adaptive mirror according to the prior art. DETAILED DESCRIPTION

[0051] First refer to Figure 1a-5b The schematic diagrams or figures use different embodiments to describe the structure and function mode of the reflector of the present invention.

[0052] These embodiments have in common that, in order to avoid troublesome influences of interferometric measurements for pattern measurement caused by structures present in the mirror substrate having a refractive index different from that of the surrounding mirror substrate material, a layer stack is provided in each case on top of the mirror substrate and that, in addition to a smoothing layer ensuring optical processability, the layer stack has an absorber layer (for the purpose of absorbing the electromagnetic measuring radiation penetrating the smoothing layer) and an AR layer (for the purpose of avoiding reflections of the measuring radiation into the absorber layer at the boundaries).

[0053] As a result, due to the above-mentioned functionalities of the absorber layer and the AR layer, the smoothing layer itself can be configured without reference to the said structures hidden in the substrate and their potentially destructive influence on the interference pattern measurement, and can therefore be optimized with respect to the smoothing (e.g. polishing) process used for mirror manufacturing.

[0054] Figure 1a The above described mode of operation is first presented in a schematic and greatly simplified illustration with reference to a reflector 100 according to the invention having a structure 106 hidden in its reflector substrate 105. Suitable reflector substrate materials are, for example, titanium dioxide (TiO2)-doped quartz glass; usable materials, purely by way of example (and the invention is not limited thereto), are Trade name (from Corning Inc.) or Material sold under the trade name AUTOMATIZ® (from Schott AG).

[0055] The reflector 100 may be an EUV reflector of an optical system, in particular a projection lens of a microlithography projection exposure device or an EUV reflector of an illumination device. More specifically, the reflector 100 may be an adaptive reflector having an actuator layer made of a piezoelectric material, wherein an electric field with a locally varying intensity is generated across the piezoelectric layer by applying a voltage to electrodes arranged on both sides of the piezoelectric layer, as described at the beginning with reference to Figure 8 As explained.

[0056] In this case, the structure 106 hidden in the mirror substrate 105 may in particular be the electrode or the piezoelectric layer.

[0057] As a result of the above-described layer stack of the invention described in detail below with reference to different embodiments (compared to what has already been described by way of introduction) Figure 7 Compared with the conventional situation), the damage hidden in the reflector substrate 105 (for example, in Figure 1a The reflection measured by the interference pattern on the part of the structure 106 (in the area marked as "A" in FIG. 1 ) results in that the measurement rays (e.g., the reflected measurement rays "112" and "122") reflected only at the interface 101 between the reflector substrate 105 and the environment are Figure 1a The incident measurement rays 111 and 121) contribute to the interference pattern measurement.

[0058] Figure 1b A possible configuration of the mirrors in the region marked with "A" in FIG. 1A in the first embodiment is shown in a diagrammatic illustration which is likewise merely schematic. Figure 1b The mirror has an absorber layer 110, an AR layer 120 and a smoothing layer 130 continuously in a stacking direction extending from the mirror substrate 105 to the interface 101 (or a reflective layer system applied thereto, such as a molybdenum-silicon (Mo-Si) layer stack).

[0059] For the measurement wavelength used (which is typically in the visible range between 400 nm and 750 nm, and may be 532 nm or 633 nm by way of example only), the absorber layer 110 has a wavelength of less than 10 -5 The transmittance and suitable thickness of the absorber layer 110 are determined, for example, in the range of 50 nm to 2 μm, depending on the material of the absorber layer 110. Illustrative suitable materials for the absorber layer are amorphous silicon (a-Si), non-oxidized and non-nitrided a-Si compounds, and metals such as tantalum (Ta), titanium (Ti), chromium (Cr), nickel (Ni), aluminum (Al), and alloys of these metals.

[0060] The smoothing layer 130 optimized for the smoothing (polishing) process for mirror manufacturing can be made of pure silicon dioxide (SiO2) in particular. However, the present invention is not limited thereto, and therefore, in other embodiments, other materials can also be used for the smoothing layer, in particular SiOx compounds, hafnium dioxide (HfO2), titanium dioxide (TiO2), amorphous silicon (a-Si) and crystalline silicon (c-Si), depending on the smoothing optical processing operation to be performed.

[0061] In order to achieve the above-mentioned function, ie, to avoid reflection at the boundary of the absorber layer 110 , the AR layer 120 has an average refractive index between the average refractive index of the absorber layer 110 and the average refractive index of the smoothing layer 130 .

[0062] Figure 2 Another embodiment is shown schematically, in which Figure 1b Components that are similar or have substantially the same function are marked with reference numerals that are increased by "100". Figure 2 ,and Figure 1b In contrast, the refractive index of the AR layer 220 continuously rises or falls between the average refractive index of the absorber layer 210 and the average refractive index of the smoothing layer 230 along the stacking direction.

[0063] in this regard, Figure 3a An illustrative refractive index progression within a layer stack is shown, where the refractive index n is reported from the relatively high-refractive-index absorber layer (here composed of amorphous silicon) down to the smoothing layer (here composed of SiO2) depending on the stacking direction. Figure 3b As is evident from the reflection spectra shown in , in this embodiment a particularly broadband AR effect is achieved, which enables greater tolerances with regard to the thickness of the layers deposited for mirror production.

[0064] Figure 4 Another embodiment is shown schematically, wherein Figure 2 Components that are similar or have substantially the same function are labeled with reference numerals that are incremented by "100".

[0065] and Figure 2 compared to, Figure 4 The AR layer 320 in is made of an alternating sequence of layers of relatively low refractive index (in this case made of SiO2) and layers of relatively high refractive index (in this case made of amorphous silicon), of which only two are shown in each case in the simplified figure. Figure 5a A graph of the corresponding refractive index progression is shown, where "d" again denotes the thickness based on the stacking direction from the absorber layer 310 to the smoothing layer 330. Figure 5b The reflection spectrum shown, the effect of the AR layer 320 is to achieve a reduced reflectivity in a wavelength band, which in turn depends on the layer thickness used.

[0066] Figure 6 A possible configuration of a microlithography projection exposure apparatus designed for operation in EUV is shown in schematic form in a meridional section as an example of an optical system in which one or more mirrors of the invention can be provided. However, in other applications, the invention can also be advantageously implemented in a projection exposure apparatus designed for operation in DUV (i.e. at wavelengths of less than 250 nm, in particular less than 200 nm) or in another optical system.

[0067] according to Figure 6 , the projection exposure device 601 comprises an illumination device 602 and a projection lens 610. In addition to the light source or radiation source 603, an embodiment of the illumination device 602 of the projection exposure device 601 also has an illumination optical unit 604 for illuminating an object field 605 in an object plane 606. In an alternative embodiment, the light source 603 can also be provided as a module separate from the rest of the illumination device. In this case, the illumination device does not include the light source 603. What is exposed here is a mask master 607 arranged in the object field 605. The mask master 607 is held by a mask master holder 608. The mask master holder 608 can be displaced via a mask master displacement drive 609, in particular in the scanning direction. As an illustration, Figure 6 A Cartesian xyz coordinate system is shown. The x direction extends perpendicular to the plane of the drawing. The y direction extends horizontally and the z direction extends vertically. The scanning direction is along Figure 6 The z direction extends perpendicular to the object plane 606.

[0068] The projection lens 610 serves to image the object field 605 into an image field 611 in an image plane 612. The structures on the reticle 607 are imaged on a photosensitive layer of a wafer 613 arranged in the region of the image field 611 in the image plane 612. The wafer 613 is held by a wafer holder 614. The wafer holder 614 can be displaced, in particular in the y direction, by a wafer displacement drive 615. Firstly, the displacement of the reticle 607 by the reticle displacement drive 609 and, secondly, the displacement of the wafer 613 by the wafer displacement drive 615 can be synchronized with each other.

[0069] The radiation source 603 is an EUV radiation source. The radiation source 603 in particular emits EUV radiation, which is also referred to as used radiation or illumination radiation hereinafter. In particular, the used radiation has a wavelength in the range between 5 nm and 30 nm. The radiation source 603 may be, for example, a plasma source, a synchrotron-based radiation source or a free electron laser (FEL). The illumination radiation 616 emitted from the radiation source 603 is focused by a light collector 617 and propagates through an intermediate focus in an intermediate focal plane 618 into the illumination optical unit 604. The illumination optical unit 604 comprises a deflection mirror 619 and a first facet mirror 620 (with a schematically indicated facet 621) and a second facet mirror 622 (with a schematically indicated facet 623) arranged in the beam path downstream of the deflection mirror 619.

[0070] The projection lens 610 comprises a plurality of mirrors Mi (i=1, 2, ...), which are numbered consecutively according to their arrangement in the beam path of the projection exposure apparatus 601. Figure 6 In the example shown, the projection lens 610 comprises six mirrors M1 to M6. Alternative solutions with four, eight, ten, twelve or a different number of mirrors Mi are also possible. The penultimate mirror M5 and the last mirror M6 each have a through opening for the illumination radiation 16. The projection lens 610 is a doubly shielded optical unit. The projection lens 610 has an image-side numerical aperture greater than 0.5 and can also be greater than 0.6 and can be, for example, 0.7 or 0.75.

[0071] Although the present invention has been described based on specific embodiments, many variations and alternative embodiments will be apparent to those skilled in the art, such as by combining and / or exchanging the features of the various embodiments. Therefore, it is apparent to those skilled in the art that these variations and alternative embodiments are also included in the present invention, and the scope of the present invention is limited only to the scope of the attached patent claims and their equivalents.

Claims

1. A reflector, wherein the reflector has an optically effective surface, the reflector comprising: a reflective layer system for reflecting electromagnetic radiation of an operating wavelength incident on said optically active surface; a reflector substrate (105, 205, 305) which has been made of a reflector substrate material and in which a structure (106, 206, 306) having a different refractive index than the surrounding reflector substrate material is arranged; and A layer stack between the reflector substrate (105, 205, 305) and the reflective layer system; The layer stack comprises an absorber layer (110, 210, 310), an AR layer (120, 220, 320) and a smoothing layer (130, 230, 330) in succession in a stacking direction extending from the reflector substrate (105, 205, 305) to the reflective layer system.

2. The reflector according to claim 1, characterized in that The absorber layer (110, 210, 310) has a relative humidity of less than 10 nm for at least one measuring wavelength in the range of 400 nm to 750 nm. -5 The transmittance.

3. The reflector according to claim 1 or 2, characterized in that: The absorber layer (110, 210, 310) has a thickness in the range of 50 nm to 2 μm.

4. The reflector according to any one of claims 1 to 3, characterized in that The absorber layer (110, 210, 310) includes at least one material from the group consisting of amorphous silicon (a-Si), non-oxidized and non-nitrided a-Si compounds, and metals tantalum (Ta), titanium (Ti), chromium (Cr), nickel (Ni), aluminum (Al), and alloys of these metals.

5. A reflector according to any one of the preceding claims, characterized in that The smoothing layer (130, 230, 330) is made of silicon dioxide (SiO2), SiO x It is made of a material from the group consisting of compounds, hafnium dioxide (HfO2), titanium dioxide (TiO2), amorphous silicon (a-Si) and crystalline silicon (c-Si).

6. A reflector according to any one of the preceding claims, characterized in that The AR layer (120, 220, 320) has an average refractive index between an average refractive index of the smoothing layer (130, 230, 330) and an average refractive index of the absorber layer (110, 210, 310).

7. A reflector according to any one of the preceding claims, characterized in that The AR layer (220) has a refractive index that continuously rises or falls between an average refractive index of the absorber layer (210) and an average refractive index of the smoothing layer (230) in a stacking direction.

8. A reflector according to any one of the preceding claims, characterized in that The AR layer (320) has an alternating sequence of layers with a relatively low refractive index, in particular silicon dioxide (SiO2), and layers with a relatively high refractive index, in particular amorphous silicon (a-Si).

9. A reflector according to any one of the preceding claims, characterized in that The mirror has a piezoelectric layer which is arranged between a mirror substrate (105, 205, 305) and a reflective layer system and which can be subjected to an electric field via an electrode arrangement to produce a locally variable deformation.

10. The reflector according to claim 9, characterized in that The structure (106, 206, 306) is at least partially formed by electrodes of one of the electrode arrangements.

11. A reflector according to any one of the preceding claims, characterized in that The mirror is designed for an operating wavelength of less than 30 nm, in particular less than 15 nm.

12. A reflector according to any one of the preceding claims, characterized in that The mirror is a mirror for a microlithography projection exposure apparatus.

13. A method of manufacturing a reflector as claimed in any one of the preceding claims, wherein the method comprises the following steps: - providing a reflector substrate (105, 205, 305) made of a reflector substrate material, wherein a structure (106, 206, 306) having a different refractive index than the surrounding reflector substrate material is formed in the reflector substrate (105, 205, 305); - applying a layer stack on top of the mirror substrate (105, 205, 305), wherein the layer stack has an absorber layer (110, 210, 310), an AR layer (120, 220, 320) and a smoothing layer (130, 230, 330) successively in the stacking direction; and - applying a reflective layer system for reflecting incident electromagnetic radiation having an operating wavelength; -in, During the manufacture of the mirror, at least one interferometric pass measurement is performed using electromagnetic measuring radiation.

14. An optical system, in particular an illumination device or a projection lens of a microlithography projection exposure apparatus, characterized in that The optical system comprises a reflector according to any one of claims 1 to 12.

15. A microlithography projection exposure device (200), comprising an illumination device and a projection lens, characterized in that: The projection exposure apparatus comprises an optical system according to claim 14.

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