EP4193222A1

EP4193222A1 - Mirror, in particular for a microlithographic projection exposure apparatus

Info

Publication number: EP4193222A1
Application number: EP20760779.7A
Authority: EP
Inventors: Toralf Gruner; Norman Baer; Koos VAN BERKEL; Laurentius Johannes Adrianus Van Bokhoven; Maike Lorenz; Thomas Monz; Eva Schneider; Hans-Michael STIEPAN; Bob Streefkerk
Original assignee: Carl Zeiss SMT GmbH; ASML Netherlands BV
Current assignee: Carl Zeiss SMT GmbH; ASML Netherlands BV
Priority date: 2020-08-07
Filing date: 2020-08-07
Publication date: 2023-06-14
Also published as: TW202210953A; CN115997170A; CN115997170B; WO2022028709A1; TWI894319B

Abstract

The invention relates to a mirror, in particular for a microlithographic projection exposure apparatus. A mirror according to the invention has an optical effective surface (101, 201, 301), a mirror substrate (110, 210, 310, 410), a reflection layer system (120, 220, 320) for reflecting electromagnetic radiation that is incident on the optical effective surface (101, 201, 301), at least one actuator layer which is configured to transmit an adjustable mechanical force on the reflection layer system (120, 220, 320), thereby producing a locally variable deformation of the optical effective surface (101, 201, 301), and at least one cooling device configured to at least partially dissipate heat generated by said actuator layer.

Description

Mirror, in particular for a microlithoqraphic projection exposure apparatus

BACKGROUND OF THE INVENTION

Field of the invention

The invention relates to a mirror, in particular for a microlithographic projection exposure apparatus.

Prior art

Microlithography is used for producing microstructured components, such as for example integrated circuits or LCDs. The microlithography process is carried out in a so-called projection exposure apparatus having an illumination device and a projection lens. The image of a mask (reticle) illuminated by means of the illumination device is in this case projected by means of the projection lens onto a substrate (for example 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 to the light-sensitive coating of the substrate.

In projection lenses designed for the EUV range, i.e. at wavelengths of e.g. approximately 13 nm or approximately 7 nm, owing to the lack of availability of suitable light-transmissive refractive materials, mirrors are used as optical components for the imaging process.

One problem which arises in practice is that, in particular as a result of the absorption of the radiation emitted by the EUV light source, the EUV mirrors heat up and thus undergo an associated deformation, which in turn can negatively affect the imaging properties of the optical system. This is the case in particular if illumination settings with comparatively small illumination poles are used (e.g. in dipole or quadrupole illumination settings), in which the mirror warming or deformation varies strongly over the optical effective surface of the mirror.

Variations in gravity in dependence on the placement site or the geographic location of the system, for example, are another cause of aberrations occurring during aberration of a projection exposure apparatus.

It is in particular known, for at least partially compensating the above-described problems and also generally for increasing the image position accuracy and image quality (both along the optical axis, or in the light propagation direction, but also in the lateral direction, or perpendicular to the optical axis or light propagation direction), to design one or more mirrors in an EUV system as an adaptive (i.e. actively deformable) mirror. Such an adaptive mirror can in particular comprise an actuator layer made of a piezoelectric material, wherein an electric field of locally varying strength is generated across said piezoelectric layer by applying an electric voltage to electrodes arranged on both sides of the piezoelectric layer. In the case of a local deformation of the piezoelectric layer, the reflection layer stack of the adaptive mirror also deforms, with the result that (possibly also temporally variable) imaging aberrations can be compensated for at least partially by appropriately controlling the voltage applied to the electrodes.

Even though the above-described principle of an adaptive mirror makes efficient aberration correction in conjunction with the deformation or actuation of the mirror possible to some degree, the requirement of greater actuations or deformations brings about the problem that high voltages for the piezoelectric actuation result in parasitic heat occurring in the layer structure of the mirror, which inter alia may incur undesired mirror deformations and also may lead to uncontrolled variations of the so-called “d33 coefficient" that is characteristic of the voltage-induced expansion of the piezoelectric layer and thus also in a change of the actuation effect for the deformation of the mirror. The d33 coefficient is here defined by AD= d33*U, wherein AD denotes the (absolute) thickness change and II denotes the electric voltage.

Further possible consequences of high electric voltages (e.g. more than 20V) for the piezoelectric actuation are damages to the piezoelectric layer and a resulting decrease in service life.

Regarding the prior art, reference is only made by way of example to WO 2018/177649 A1.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a mirror, in particular for a micro- lithographic projection exposure apparatus, which makes deformation or actuation via the displacement distances required for example for aberration correction possible, while at least partially avoiding the abovementioned problems.

This object is achieved by way of the mirror according to the features of independent claim 1 .

A mirror according to the invention, the mirror having an optical effective surface, has:

- a mirror substrate;

- a reflection layer system for reflecting electromagnetic radiation that is incident on the optical effective surface;

- at least one actuator layer which is configured to transmit an adjustable mechanical force on the reflection layer system, thereby producing a locally variable deformation of the optical effective surface; and - at least one cooling device configured to at least partially dissipate heat generated by said actuator layer.

The mirror can be in particular a mirror for a microlithographic projection exposure apparatus. However, the invention is not limited thereto. In other applications, a mirror according to the invention can also be employed or utilized for example in a system for mask metrology.

The invention is based in particular on the concept of providing, in an adaptive mirror having an actuator layer which is configured to transmit an adjustable mechanical force on the reflection layer system and to thereby produce a locally variable deformation of the optical effective surface, a cooling device configured to at least partially dissipate heat generated by said layer in order to achieve a more stable, more safe and more exact operation of the adaptive mirror and, therefore, an improved correction of imaging aberration provided by the adaptive mirror.

The effect of a more exact operation of the adaptive mirror being achieved with the inventive cooling concept is inter alia due to a better-defined functionality of the actuator layer, since the material parameters of the actuator layer being relevant for the mechanical force transmitted on the reflection layer system, in particular the afore-mentioned d33 coefficient of a piezoelectric layer, can be kept essentially constant (despite of the principally existing temperature-dependency of those parameters).

The effect of a more exact operation of the adaptive mirror being achieved with the inventive cooling concept is also due the fact that a combination of heating and cooling (which can be realized e.g. if the mirror comprises a segmented heating arrangement configured to thermally induce a locally variable deformation of the optical effective surface) leads to a significantly faster reaction of the adaptive mirror if compared with a simple heating (without cooling). Furthermore, the inventive cooling concept makes it possible to enhance the heat introduced into the mirror for actuations (e.g. in order to realize larger displacement distances of a piezoelectric layer) while on the same time thermally induced damages are effectively avoided by said cooling, so that a particularly safe operation of the adaptive mirror is always ensured.

According to one embodiment, said at least one actuator layer comprises a piezoelectric or 2^nd order electrostrictive layer to which an electric field can be applied to produce said locally variable deformation of the optical effective surface.

According to one embodiment, said at least one actuator layer is arranged between the mirror substrate and the reflection layer system.

According to one embodiment, said at least one actuator layer is arranged on the side of the mirror substrate that is opposite to said reflection layer system.

According to one embodiment, said cooling device comprises at least one cooling channel that is arranged in the mirror substrate.

According to one embodiment, a distance between said at least one cooling channel and a boundary that bounds the mirror substrate in the direction perpendicular to the optical effective surface is less than 20mm, in particular less than 10mm.

If the mirror comprises an actuator layer in the form of a piezoelectric layer arranged between the mirror substrate and the reflection layer system, it may be particularly advantageous if the at least one cooling channel is arranged in the mirror substrate close to its boundary facing to the reflection layer system, in order to dissipate heat from the piezoelectric layer in a particularly efficient way. If the mirror comprises an actuator layer in the form of a piezoelectric layer or 2^nd order electrostrictive layer arranged on the side of the mirror substrate that is opposite to said reflection layer system, in may be particularly advantageous if the at least one cooling channel is arranged in the mirror substrate close to its boundary facing away from the reflection layer system or facing to the backside of the mirror, in order to efficiently dissipate heat from the piezoelectric layer.

According to one embodiment, the mirror further comprises a controller configured to control operation of said cooling device dependent on the operation of said actuator layer.

According to one embodiment, the mirror further comprises a segmented heating arrangement configured to thermally induce a locally variable deformation of the optical effective surface.

According to one embodiment, the controller is further configured to control operation of said cooling device dependent on the operation of said segmented heating arrangement.

According to one embodiment, the segmented heating arrangement comprises an electrode arrangement configured to be electrically driven to thereby thermally induce said deformation of the optical effective surface.

According to one embodiment, the segmented heating arrangement comprises at least one irradiation source configured to irradiate the mirror substrate with electromagnetic radiation to thereby thermally induce said deformation of the optical effective surface.

According to one embodiment, the mirror is designed for an operating wavelength of less than 250 nm, in particular less than 200 nm, more particularly less than 160nm.

According to one embodiment, the mirror is designed for an operating wavelength of less than 30 nm, in particular less than 15 nm. The invention furthermore relates to an optical system of a microlithographic projection exposure apparatus, in particular an illumination device or a projection lens, with at least one mirror having the above-described features, and also to a microlithographic projection exposure apparatus.

Further configurations of the invention can be gathered from the description and the dependent claims.

The invention is explained in greater detail below on the basis of exemplary embodiments illustrated in the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Figure 1 shows a schematic illustration for elucidating the construction of an adaptive mirror according to one embodiment of the invention, said mirror comprising an actuator layer in form of a piezoelectric layer;

Figure 2 shows a schematic illustration for elucidating the construction of an adaptive mirror according to a further embodiment of the invention, said mirror comprising an actuator layer in form of a piezoelectric or 2^nd order electrostrictive layer;

Figure 3a-3b show schematic illustrations for elucidating the construction of an adaptive mirror according to a further embodiment of the invention, said mirror comprising a segmented heating arrangement having an electrode arrangement; Figure 4 shows a schematic illustration for elucidating the construction of an adaptive mirror according to a further embodiment of the invention, said mirror comprising a segmented heating arrangement having an irradiation source;

Figure 5 shows a schematic illustration of the possible construction of a microlithographic projection exposure apparatus designed for operation in the EUV; and

Figure 6 shows a schematic illustration of the possible construction of a microlithographic projection exposure apparatus designed for operation in the DUV.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following, different embodiments of an adaptive mirror having an actuator layer which is configured to transmit an adjustable mechanical force on the reflection layer system and to thereby produce a locally variable deformation of the optical effective surface are described. These embodiments have in common that a cooling device is provided which is configured to at least partially dissipate heat generated by said actuator layer in order to achieve a stable, safe and exact operation of the adaptive mirror and, therefore, an improved correction of imaging aberration provided by the adaptive mirror.

Fig. 1 shows a schematic illustration for elucidating the construction of a mirror according to the invention in one embodiment of the invention. Without the invention being restricted thereto, the mirror 100 can be an EUV mirror of an optical system, in particular of the projection lens or of the illumination device of a microlithographic projection exposure apparatus.

The mirror 100 having an optical effective surface 101 comprises in particular a mirror substrate 110, which is made from any desired suitable mirror substrate material. A suitable mirror substrate material is e.g. quartz glass doped with titanium dioxide (TiC ), as e.g. the material sold under the trade name ULE® (by Coming Inc.). A further suitable mirror substrate material is e.g. a lithium-alumin- ium-silicon oxide-glass ceramic, as e.g. the material sold under the trade name Zerodur® (by Schott AG). The mirror 100 further comprises a reflection layer stack 120 (for example as a multilayer system made of molybdenum and silicon layers).

Without the invention being restricted to specific configurations of this layer stack, one suitable construction that is merely by way of example can comprise approximately fifty plies or layer packets of a layer system comprising molybdenum (Mo) layers having a layer thickness of in each case 2.4 nm and silicon (Si) layers having a layer thickness of in each case 3.4 nm. In further embodiments, the mirror can also be configured for use with so-called grazing incidence. In this case, the reflection layer system can comprise for example in particular just one individual layer composed of e.g. ruthenium (Ru) having an exemplary thickness of 30 nm.

The impingement of electromagnetic EUV radiation (indicated by an arrow in Fig. 1 ) on the optical effective surface 101 of the mirror 100 during operation of the optical system may lead to an inhomogeneous volume change of the mirror substrate 110 due to the temperature distribution which results from the absorption of the radiation which impinges inhomogeneously on the optical effective surface 101.

The mirror 100 has between the mirror substrate 110 and the reflection layer system 120 a piezoelectric layer 130 which is produced from a piezoelectric material, such as for example lead zirconate titanate (Pb(Zr,Ti)O3).

The piezoelectric layer 130 is arranged between a first electrode 140, which according to Fig. 1 is applied to an adhesive layer 150 (in the example made of TiC ) provided on the mirror substrate 110, and a second structured electrode 160, wherein another adhesive layer 151 and 152 (in the example made of LaNiOs) is disposed between the electrodes 140 and 160 (which in the example are made from platinum (PT)) and the piezoelectric layer 130. The adhesive layer 151 and 152 serves to make available crystalline growth conditions for the piezoelectric layer that are as optimum as possible.

According to Fig. 1 , but without the invention being restricted thereto, a screening layer 170 (which in the example is made from platinum (PT) just like the electrodes 140, 160 and which is optional in principle) is furthermore disposed on the bottom side of the reflection layer stack 120, which faces the structured electrode 160. According to Fig. 1 , a SiO2 layer 165 is disposed between the piezoelectric layer 130 and the screening layer 170.

By applying a locally varying electric voltage, a locally varying deflection of the piezoelectric layer 130 can be produced, which in turn converts into a deformation of the reflection layer stack 120 and thus into a wavefront change for light that is incident on the optical effective surface 101 and which can be used for aberration correction.

The above-mentioned mirror substrate materials exhibit a so-called zero crossing temperature, where the coefficient of thermal expansion has a zero crossing in its temperature dependence, so that no or only a negligible thermal expansion takes place. Consequently, in specific scenarios, it may be desirable to keep the mirror 100 at said zero crossing temperature.

According to Fig. 1 , the mirror 100 comprises a plurality of cooling channels 115 being arranged in the mirror substrate 110 close to its boundary facing to the reflection layer system 120, in order to dissipate heat from the piezoelectric layer 130 in a particularly efficient way. A cooling medium (for example water) flows through the cooling channels 115. In exemplarily embodiments, a distance between each of said cooling channels 115 and the boundary facing to the reflection layer system 120 may be less than 20mm, in particular less than 10mm. Furthermore, a cooling power of the plurality of cooling channels 115 may be at least 0.1 W, particularly more than 0.5 W, particularly more than 1 W.

Fig. 2 shows a schematic illustration for elucidating the construction of a mirror 200 according to the invention in a further embodiment of the invention. The mirror 200 according to Fig. 2 differs from the afore-described mirror 100 of Fig. 1 in particular by the fact that a piezoelectric or 2^nd order electrostrictive layer 230 is arranged on the side of the mirror substrate 210 that is opposite to said reflection layer system 220.

According to the embodiment of Fig. 2, an electric voltage being applied along the surface normal (i.e. perpendicular to the optical effective surface 201 , using electrodes which are not illustrated in Fig. 2) results in a mechanical stress in a direction parallel to the optical effective surface 201 (i.e. perpendicular to the surface normal) making use of a material that exhibits a 2^nd order electrostrictive effect or making use of the dsi -coefficient of a piezoelectric material. This mechanical stress effects a deformation perpendicular to the optical effective surface 201 .

In contrast to this, according to the embodiment of Fig. 1 , an electric voltage being applied along the surface normal (i.e. perpendicular to the optical effective surface 101 ) directly results in a deformation into a direction perpendicular to the optical effective surface 101 (i.e. parallel to the surface normal), making use of the d33 coefficient.

Furthermore, while according to the embodiment of Fig. 2 the piezoelectric or 2^nd order electrostrictive layer 230 is arranged on the side of the mirror substrate 210 that is opposite to the reflection layer system 220 (i.e. the backside of the mirror 200), the embodiment of Fig. 1 has the piezoelectric layer 130 between the substrate and the reflection layer system 120. Additional functional layers (such as e.g. diffusion barrier layers, adhesionenhancing layers, etc.), not depicted in Fig. 2, can be provided in the layer construction of the mirror 200.

Since Fig. 2 just serves for simplified illustration of this embodiment, reference is made to the above description of Fig. 1 concerning the material of said piezoelectric or 2^nd order electrostrictive layer 230 and also concerning the materials and effects of possible further functional layers that may be present in the mirror 200. In particular PZT (= Pb(Zr_xTii-_x)O3) can be used for layer 230. Another material that can be used for layer 230 is PMN (= Pb(Mgi/3Nb2/3)O3)

While the mirror 200 also comprises a plurality of cooling channels 215, these cooling channels 215 are arranged in the mirror substrate 210 close to its boundary facing away from the reflection layer system 220 or facing to the backside of the mirror, in order to dissipate heat from the piezoelectric layer 230 in a particularly efficient way.

Fig. 3a-3b and Fig. 4 show schematic illustrations for elucidating the construction of a mirror according to further embodiments of the invention. These embodiments have in common that a segmented heating arrangement is provided, said segmented heating arrangement being configured to thermally induce a locally variable deformation of the optical effective surface.

The mirror 300 in accordance with Fig. 3a comprises, in order to correct an undesired volume change or else in order to correct other aberrations that occur during operation of the microlithographic projection exposure apparatus on account of the absorption of radiation impinging inhomogeneously on the optical effective surface 301 , an electrode arrangement 380 comprising a plurality of electrodes 381 , which are electrically drivable or able to have a selectively settable electric current applied to them via electrical leads 382. Furthermore, the mirror 300 comprises an electrically conductive layer 385. The mirror 300 may also optionally comprise, similar to Fig. 2, a piezoelectric or 2^nd order electrostrictive layer 330 being arranged on the side of the mirror substrate 310 that is opposite to the reflection layer system 320.

In Fig. 3a, "365" denotes a smoothing and insulation layer, which electrically insulates in particular the electrodes 381 of the electrode arrangement 380 from one another and can be produced from quartz glass (S iC>2), for example.

Again, additional functional layers (such as e.g. diffusion barrier layers, adhesion-enhancing layers, etc.), not depicted in Fig. 3a, can also be provided in the layer construction of the mirror 300.

During operation of the mirror 300, different electrical potentials can be applied to the individual electrodes 381 of the electrode arrangement 380, wherein the electrical voltages generated thereby between the electrodes 381 bring about an electric current flow via the electrically conductive layer 385. The heat induced by said electric current results in a locally varying heating-up of the mirror surface depending on the potentials respectively applied to the individual electrodes 381 .

The embodiment according to Fig. 3a is not restricted to a specific geometric configuration of the electrode arrangement 380. The electrodes 381 can be provided in any suitable distributions (e.g. in a Cartesian grid, in a hexagonal arrangement, etc.). In further embodiments, electrodes 381 can also be positioned only in specific regions. An example for a geometric configuration of the electrode arrangement 380 is exemplarily illustrated in Fig. 3b.

The combined use of electrode arrangement 380 and electrically conductive layer 385 in the case of the mirror 300 - despite comparatively coarse structures of the electrode arrangement - enables continuously varying power inputs into the mirror according to the invention, wherein at the same time the coupling-in of the thermal power - in contrast for instance to the use of infrared (IR) heating devices - is limited to the mirror itself. On account of the material selection, there is a comparatively high electrical resistance in the electrically conductive layer 385, such that the electrical voltage is dropped there, whereas, on account of the comparatively significantly higher electrical conductivity in the leads 382, no voltage or heat is dropped in the leads 382 and in this respect fine structures are not required in order to generate the high electrical resistances.

According to Fig. 3a, the mirror 300 comprises a plurality of cooling channels 315 being arranged in the mirror substrate 310 close to its boundary facing to the reflection layer system 320, in order to dissipate heat from the electrically conductive layer 385 in a particularly efficient way.

Fig. 4 shows a schematic illustration for elucidating the construction of a mirror according to a further embodiment of the invention. The mirror 400 according to Fig. 4 (which is just shown in a very simplified manner) differs from the afore- described mirror 300 in particular by the fact that a segmented heating arrangement comprises a plurality of irradiation sources 481 configured to irradiate the mirror substrate 410 with electromagnetic radiation to thereby thermally induce said deformation of the optical effective surface. The irradiation results in a locally varying heating-up of the mirror surface depending on the operation of the individual irradiation sources 481 , which can be controlled independently from each other. The wavelength of the electromagnetic radiation (which may e.g. be infrared irradiation) is such that the material of the mirror substrate 410 is essentially transparent in the respective wavelength region.

According to Fig. 4, the mirror 400 comprises a plurality of cooling channels 415 being arranged in the mirror substrate 410 close to its boundary facing to the reflection layer system (not shown in Fig. 4), in order to dissipate heat from the mirror in a particularly efficient way.

Furthermore, the design and arrangement of the irradiation sources 481 is preferably such that said irradiation does not (or at least not in a significant extend) interfere with the cooling channels 415. Fig. 5 shows a schematic illustration of one exemplary projection exposure apparatus which is designed for operation in the EUV and in which the present invention can be realized. In accordance with Fig. 5, an illumination device in a projection exposure apparatus 500 designed for EUV comprises a field facet mirror 503 and a pupil facet mirror 504. The light from a light source unit comprising a plasma light source 501 and a collector mirror 502 is directed onto the field facet mirror 503. A first telescope mirror 505 and a second telescope mirror 506 are arranged in the light path downstream of the pupil facet mirror 504. A deflection mirror 507 is arranged downstream in the light path, said deflection mirror directing the radiation impinging on it onto an object field in the object plane of a projection lens comprising six mirrors 551 -556. A reflective structurebearing mask 521 on a mask stage 520 is arranged at the location of the object field, said mask being imaged into an image plane with the aid of the projection lens, in which image plane is situated a substrate 561 coated with a light-sensitive layer (photoresist) on a wafer stage 560.

Fig. 6 shows a schematic illustration of one exemplary projection exposure apparatus which is designed for operation in the DUV and in which the present invention can be realized. The projection exposure apparatus 600 comprises a beam shaping and illumination system 610 and a projection lens 620. In this case, DUV stands for “deep ultraviolet” and denotes a wavelength of the working light of between 30 nm and 250 nm. The beam shaping and illumination system 610 and the projection lens 620 can be arranged in a vacuum housing and/or surrounded by a machine room with corresponding drive devices. The projection exposure apparatus 600 has a DUV light source 601 . By way of example, an ArF excimer laser that emits radiation 602 in the DUV range at 193 nm, for example, can be provided as the DUV light source 601 .

The beam shaping and illumination system 610 illustrated in FIG. 6 guides the DUV radiation 602 onto a mask 605. The mask 605 is embodied as a transmissive optical element and can be arranged outside the beam shaping and illumination system 610 and the projection lens 620. The mask 605 has a structure which is imaged onto a substrate or wafer 630 in a reduced fashion via the projection lens 620. The projection lens 620 has a plurality of lens elements (of which three lens elements 621-623 are schematically and exemplarily shown in Fig. 6) and least one mirror (in Fig. 6 two mirrors 624, 625 are schematically and exemplarily shown) for imaging the mask 605 onto the wafer 630. In this case, individual lens elements 621 -623 and/or mirrors 624, 625 of the projection lens 620 can be arranged symmetrically in relation to an optical axis OA of the projection lens 620. It should be noted that the number of lens elements and mirrors of the DUV lithography apparatus 600 is not restricted to the number illustrated. More or fewer lens elements and/or mirrors can also be provided. Furthermore, the mirrors are generally curved on their front side for beam shaping. An air gap between the last lens element 623 and the wafer 630 can be replaced by a liquid medium 626 which has a refractive index of >1. The liquid medium 626 can be high-purity water, for example. Such a construction is also referred to as immersion lithography and has an increased photolithographic resolution.

Even though the invention has been described on the basis of specific embodiments, numerous variations and alternative embodiments are evident to the person skilled in the art, e.g. through combination and/or exchange of features of individual embodiments. Accordingly, it goes without saying for the person skilled in the art that such variations and alternative embodiments are concomitantly encompassed by the present invention, and the scope of the invention is restricted only within the meaning of the appended patent claims and the equivalents thereof.

Claims

Claims A mirror, wherein the mirror has an optical effective surface, having

• a mirror substrate (110, 210, 310, 410);

• a reflection layer system (120, 220, 320) for reflecting electromagnetic radiation that is incident on the optical effective surface (101 , 201 , 301 );

• at least one actuator layer which is configured to transmit an adjustable mechanical force on the reflection layer system (120, 220, 320), thereby producing a locally variable deformation of the optical effective surface (101 , 201 , 301 ); and

• at least one cooling device configured to at least partially dissipate heat generated by said actuator layer. The mirror as claimed in claim 1 , characterized in that said at least one actuator layer comprises a piezoelectric or 2^nd order electrostrictive layer (130, 230, 330) to which an electric field can be applied to produce said locally variable deformation of the optical effective surface (101 , 201 , 301 ). The mirror as claimed in claim 1 or 2, characterized in that said at least one actuator layer is arranged between the mirror substrate (110) and the reflection layer system (120). The mirror as claimed in claim 1 or 2, characterized in that said at least one actuator layer is arranged on the side of the mirror substrate (210, 310) that is opposite to said reflection layer system (220, 320). The mirror as claimed in one of the preceding claims, characterized in that said cooling device comprises at least one cooling channel (115, 215, 315, 415) that is arranged in the mirror substrate (110, 210, 310, 410). The mirror as claimed in claim 5, characterized in that a distance between said at least one cooling channel (115, 215, 315, 415) and a boundary that bounds the mirror substrate (110, 210, 310, 410) in a direction perpendicular to the optical effective surface is less than 20mm, in particular less than 10mm. The mirror as claimed in one of the preceding claims, characterized in that it further comprises a controller configured to control operation of said cooling device dependent on the operation of said actuator layer. The mirror as claimed in one of the preceding claims, characterized in that it further comprises a segmented heating arrangement configured to thermally induce a locally variable deformation of the optical effective surface (301 ). The mirror as claimed in claim 7 and 8, characterized in that the controller is further configured to control operation of said cooling device dependent on the operation of said segmented heating arrangement. The mirror as claimed in claim 8 or 9, characterized in that the segmented heating arrangement comprises an electrode arrangement (380) configured to be electrically driven to thereby thermally induce said deformation of the optical effective surface (301 ). The mirror as claimed in claim 8 or 9, characterized in that the segmented heating arrangement comprises at least one irradiation source (481 ) configured to irradiate the mirror substrate (410) with electromagnetic radiation to thereby thermally induce said deformation of the optical effective surface. The mirror as claimed in one of the preceding claims, characterized in that the mirror is designed for an operating wavelength of less than 250 nm, in particular less than 200 nm, more particularly less than 160nm. 19

13. The mirror as claimed in 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. 14. The mirror as claimed in one of the preceding claims, characterized in that said mirror is a mirror for a microlithographic projection exposure apparatus.

15. An optical system, in particular an illumination device or projection lens of a microlithographic projection exposure apparatus, characterized in that the optical system has a mirror as claimed in one of the preceding claims.

16. A microlithographic projection exposure apparatus (500, 600) having an illumination device and a projection lens, characterized in that the projection exposure apparatus has an optical system as claimed in claim 15.