CN115997170A - Mirror, in particular for a microlithographic projection exposure apparatus - Google Patents

Mirror, in particular for a microlithographic projection exposure apparatus Download PDF

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Publication number
CN115997170A
CN115997170A CN202080104190.5A CN202080104190A CN115997170A CN 115997170 A CN115997170 A CN 115997170A CN 202080104190 A CN202080104190 A CN 202080104190A CN 115997170 A CN115997170 A CN 115997170A
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mirror
layer
mirror according
optically active
exposure apparatus
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Inventor
T·格鲁纳
N·巴尔
K·范伯克尔
L·J·A·范博克霍文
M·洛伦兹
T·蒙兹
E·施奈德
H-M·斯蒂潘
B·斯特里夫柯克
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Carl Zeiss SMT GmbH
ASML Netherlands BV
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Carl Zeiss SMT GmbH
ASML Netherlands BV
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70216—Mask projection systems
    • G03F7/70258—Projection system adjustments, e.g. adjustments during exposure or alignment during assembly of projection system
    • G03F7/70266—Adaptive optics, e.g. deformable optical elements for wavefront control, e.g. for aberration adjustment or correction
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70216—Mask projection systems
    • G03F7/70316—Details of optical elements, e.g. of Bragg reflectors, extreme ultraviolet [EUV] multilayer or bilayer mirrors or diffractive optical elements
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/708—Construction of apparatus, e.g. environment aspects, hygiene aspects or materials
    • G03F7/70858—Environment aspects, e.g. pressure of beam-path gas, temperature
    • G03F7/70883—Environment aspects, e.g. pressure of beam-path gas, temperature of optical system
    • G03F7/70891—Temperature

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  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Atmospheric Sciences (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Epidemiology (AREA)
  • Public Health (AREA)
  • Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)
  • Optical Elements Other Than Lenses (AREA)

Abstract

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

Description

Mirror, in particular for a microlithographic projection exposure apparatus
Technical Field
The present invention relates to mirrors, in particular for microlithographic projection exposure apparatus.
Background
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 having an illumination device and a projection lens. In this case, an image of the mask (reticle) illuminated by the illumination device is projected by means of a projection lens onto a substrate (for example 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 onto the photosensitive coating of the substrate.
In projection lenses designed for the EUV range (i.e. wavelengths of about 13nm or about 7 nm), mirrors are used as optical components for the imaging process due to the lack of suitable light-transmitting refractive materials available.
One problem that arises in practice is that, in particular due to absorption of the radiation emitted by the EUV light source, the EUV mirror heats up and thus undergoes a related deformation, which in turn can have a negative effect on the imaging properties of the optical system. This is especially the case if an illumination setting with relatively small illumination poles is used (e.g. in dipole or quadrupole illumination settings), wherein the temperature rise or deformation of the mirror varies strongly over the optically active surface of the mirror.
For example, gravity variations depending on the place or geographical position of the system are another cause of aberrations occurring during aberrations of the projection exposure apparatus.
It is particularly known to design one or more mirrors in an EUV system as adaptive (i.e. actively deforming) mirrors in order to at least partially compensate for the above-mentioned problems, and also in general in order to improve image position accuracy and image quality (both along the optical axis, or in the direction of light propagation, and also in the lateral direction, or perpendicular to the optical axis or light propagation direction). Such an adaptive mirror may in particular comprise an actuator layer made of a piezoelectric material, wherein an electric field of locally varying strength is generated across the piezoelectric layer by applying a voltage to electrodes arranged on both sides of the piezoelectric layer. In case the piezoelectric layer is locally deformed, the reflective layer stack of the adaptive mirror is also deformed, as a result of which (possibly also time-varying) imaging aberrations can be at least partially compensated by a suitable control of the voltage applied to the electrodes.
Although the above-described principle of adaptive mirrors allows effective aberration correction to a certain extent in combination with deformation or actuation of the mirrors, the requirement for a larger actuation or deformation presents the problem that the high voltage of the piezo actuation leads to parasitic heat in the layer structure of the mirrors, which may in particular lead to undesired deformation of the mirrors, and also to so-called "d" s 33 Coefficient "uncontrolled change, where d 33 The coefficient is characteristic of the expansion of the piezoelectric layer caused by the voltage, and thus the actuation effect of the mirror deformation is also changed. d, d 33 The coefficient is defined herein as Δd=d 33 * U, where Δd represents the (absolute) thickness variation, U represents the voltage.
Other consequences of high voltages (e.g., over 20V) on piezoelectric actuation can be damage to the piezoelectric layer and result in reduced service life.
With respect to the prior art, reference may be made for example only to WO 2018/177649 A1.
Disclosure of Invention
It is an object of the present invention to provide a mirror, in particular for a microlithographic projection exposure apparatus, which can be deformed or actuated by a displacement distance required for example for aberration correction, while at least partly avoiding the above-mentioned problems.
This object is achieved, for example, by a mirror according to the features of independent claim 1.
According to the invention, a mirror having an optically active surface has:
a mirror substrate;
a reflective layer system to reflect electromagnetic radiation incident on the optically active surface;
at least one actuator layer configured to transmit an adjustable mechanical force on the reflective layer system, thereby producing a locally variable deformation of the optically effective surface; and
at least one cooling device configured to at least partially dissipate heat generated by the actuator layer.
The mirror may in particular be a mirror for a microlithographic projection exposure apparatus. However, the present invention is not limited thereto. In other applications, such as in a system for mask metrology, mirrors according to the present invention may also be employed or utilized.
Embodiments of the invention are based in particular on the following concepts: in an adaptive mirror having an actuator layer configured to transmit an adjustable mechanical force on a reflective layer system and thereby produce a locally variable deformation of an optically effective surface, a cooling device configured to at least partially dissipate heat produced by the layer is provided to enable more stable, safer and more accurate operation of the adaptive mirror and thereby improve correction of imaging aberrations provided by the adaptive mirror.
The effect of the more precise operation of the adaptive mirror achieved with the cooling concept of the invention is due in particular to a better definition of the functionality of the actuator layer, since the material parameters of the actuator layer (in particular the d of the piezoelectric layer described above) are related to the mechanical forces transmitted over the reflective layer system 33 The coefficients) may remain substantially constant (although in principle there is a temperature dependence of these parameters).
The effect of the more accurate operation of the adaptive mirror achieved with the cooling concept of the invention is also due to the fact that: the combination of heating and cooling (which may be achieved, for example, if the mirror comprises a segmented heating arrangement configured to thermally induce locally variable deformation of the optically active surface) may result in a significantly faster response of the adaptive mirror than a simple heating (without cooling).
Furthermore, the cooling concept of the present invention allows to increase the heat introduced into the mirror for actuation (e.g. in order to achieve a larger displacement distance of the piezoelectric layer) while effectively avoiding thermally induced damage by this cooling, thereby always ensuring a particularly safe operation of the adaptive mirror.
According to an embodiment, the at least one actuator layer comprises a piezoelectric or second order electrostrictive layer, wherein an electric field can be applied to the piezoelectric or second order electrostrictive layer to produce the locally variable deformation of the optically active surface.
According to an embodiment, the at least one actuator layer is arranged between the mirror substrate and the reflective layer system.
According to an embodiment, the at least one actuator layer is arranged on the side of the mirror substrate opposite the mirror layer system.
According to an embodiment, the cooling device comprises at least one cooling channel arranged in the mirror substrate.
According to an embodiment, the distance between the at least one cooling channel and the boundary delimiting the mirror substrate in a direction perpendicular to the optically active surface is less than 20mm, in particular less than 10mm.
If the mirror comprises an actuator layer arranged in the form of a piezoelectric layer between the mirror substrate and the reflective layer system, it is particularly advantageous if at least one cooling channel is arranged in the mirror substrate close to its boundary facing the reflective layer system in order to dissipate heat from the piezoelectric layer in a particularly efficient manner. If the mirror comprises an actuator layer in the form of a piezoelectric layer or a second-order electrostrictive layer arranged on the side of the mirror substrate opposite the mirror system, it is particularly advantageous if at least one cooling channel is arranged in the mirror substrate close to its boundary facing away from the mirror system or towards the mirror backside in order to effectively dissipate heat from the piezoelectric layer.
According to an embodiment, the mirror further comprises a controller configured to control the operation of the cooling device in accordance with the operation of the actuator layer.
According to an embodiment, the mirror further comprises a segmented heating arrangement configured to thermally induce locally variable deformation of the optically active surface.
According to an embodiment, the controller is further configured to control the operation of the cooling device according to the operation of the staged heating configuration.
According to an embodiment, the segmented heating arrangement comprises an electrode arrangement configured to be electrically driven to thereby thermally induce the deformation of the optically active surface.
According to an embodiment, the staged heating configuration comprises at least one radiation source configured to irradiate the mirror substrate with electromagnetic radiation to thermally induce the deformation of the optically active surface.
According to an embodiment, the mirror is designed for an operating wavelength of less than 250nm, in particular less than 200nm, more in particular less than 160 nm.
According to an embodiment, the mirror is designed for an operating wavelength of less than 30nm, in particular less than 15 nm.
The invention further relates to an optical system, in particular an illumination device or a projection lens, of a microlithographic projection exposure apparatus comprising at least one mirror having the above-mentioned features, and also to a microlithographic projection exposure apparatus.
Further configurations of the invention can be seen from the detailed description and the dependent claims.
The invention will be explained in more detail below on the basis of exemplary embodiments shown in the drawings.
Drawings
In the figure:
FIG. 1 shows a schematic diagram to illustrate the construction of an adaptive mirror comprising an actuator layer in the form of a piezoelectric layer, according to an embodiment of the invention;
fig. 2 shows a schematic diagram for illustrating the construction of an adaptive mirror according to another embodiment of the invention, which mirror comprises an actuator layer in the form of a piezoelectric or second-order electrostrictive layer;
FIGS. 3a-3b show schematic diagrams illustrating the construction of an adaptive mirror according to another embodiment of the invention, the mirror comprising a segmented heating configuration with an electrode configuration;
FIG. 4 shows a schematic diagram illustrating the construction of an adaptive mirror including a segmented heating configuration with a radiation source in accordance with another embodiment of the present invention;
fig. 5 shows a schematic diagram of a possible configuration of a microlithographic projection exposure apparatus designed for operation in EUV; and
fig. 6 shows a schematic diagram of a possible configuration of a microlithographic projection exposure apparatus designed for operation under DUV.
Detailed Description
In the following, different embodiments of an adaptive mirror having an actuator layer configured to transmit an adjustable mechanical force on a reflective layer system and thereby produce a locally variable deformation of an optically effective surface are described. Common to these embodiments is the provision of a cooling device configured to at least partially dissipate heat generated by the actuator layer to enable stable, safe and accurate operation of the adaptive mirror and thus improve correction of imaging aberrations provided by the adaptive mirror.
Fig. 1 shows a schematic view for explaining the construction of a mirror according to the present invention in an embodiment of the present invention. The mirror 100 may be an EUV mirror of an optical system, in particular of a projection lens or an illumination device of a microlithographic projection exposure apparatus, although the invention is not limited thereto.
The mirror 100 having an optically active surface 101 particularly comprises a mirror substrate 110 made of any desired suitable mirror substrate material. Suitable mirror substrate materials are, for example, doped titanium dioxide (TiO 2 ) For example under the trade name of quartz glass
Figure BDA0004113426930000051
(corning company) materials sold. Another suitable reflector substrate material is, for example, lithium-aluminum-silicon oxide-glass ceramic, for example under the trade name +.>
Figure BDA0004113426930000052
(Schott AG) materials sold. The mirror 100 further comprises a reflective layer stack 120 (e.g., a multi-layer system made of molybdenum and silicon layers).
The invention is not limited to this particular configuration of layer stack, but one suitable configuration may comprise, by way of example only, about fifty layers or groups of layers of a layer system comprising a molybdenum (Mo) layer and a silicon (Si) layer having a layer thickness of 2.4nm, respectively. In a further embodiment, the mirror may also be configured for so-called grazing incidence (grazing incidence). In this case, the reflective layer system may comprise, for example, in particular only one single layer, which is composed of ruthenium (Ru) having an exemplary thickness of, for example, 30 nm.
During operation of the optical system, impingement of electromagnetic EUV radiation (represented by arrows in fig. 1) on the optically active surface 101 of the mirror 100 may result in non-uniform volume changes of the mirror substrate 110 due to the temperature distribution resulting from absorption of radiation impinging unevenly on the optically active surface 101.
The mirror 100 has a piezoelectric layer 130 between the mirror substrate 110 and the reflective layer system 120, wherein the piezoelectric layer 130 is made of a piezoelectric material, for example lead zirconate titanate (Pb (Zr, ti) O) 3 )。
The piezoelectric layer 130 is arranged between a first electrode 140 and a second structured electrode 160, wherein the first electrode 140 is applied according to fig. 1 to an adhesive layer 150 (which in the example is made of TiO) provided on the mirror substrate 110 2 Made of LaNiO in the example) in which further adhesion layers 151 and 152 (made of LaNiO in the example) 3 Made) are disposed between electrodes 140 and 160, which in the example are made of Platinum (PT), and piezoelectric layer 130. The adhesion layers 151 and 152 serve to provide the best possible crystal growth conditions for the piezoelectric layer.
According to fig. 1, but the invention is not limited thereto, a shielding layer 170, which in this example is made of Platinum (PT) as the electrodes 140, 160 and which is in principle selective, is further provided on the bottom side of the reflective layer stack 120 facing the structured electrode 160. According to FIG. 1, siO 2 Layer 165 is disposed between piezoelectric layer 130 and shield layer 170.
By applying a locally varying voltage, a locally varying deflection of the piezoelectric layer 130 can be generated, which in turn is converted into a deformation of the reflective layer stack 120 and thus into a wavefront variation of the light incident on the optically effective surface 101, and can be used for aberration correction.
The above-mentioned mirror substrate materials exhibit a so-called zero-crossing temperature (zero crossing temperature), wherein the coefficient of thermal expansion has zero crossings in its relation to temperature, and therefore no or only negligible thermal expansion occurs. Thus, in certain situations, it may be desirable to maintain the mirror 100 at this zero-crossing temperature.
According to fig. 1, the mirror 100 comprises a plurality of cooling channels 115 which are arranged in the mirror substrate 110 close to its boundary facing the reflective layer system 120 in order to dissipate heat from the piezoelectric layer 130 in a particularly efficient manner. A cooling medium (e.g., water) flows through the cooling channels 115. In an exemplary embodiment, the distance between each of the cooling channels 115 and the boundary facing the reflective layer system 120 may be less than 20mm, in particular less than 10mm. Furthermore, the cooling power of the plurality of cooling channels 115 may be at least 0.1W, particularly greater than 0.5W, and particularly greater than 1W.
Fig. 2 shows a schematic diagram for explaining the construction of a mirror 200 according to the present invention in another embodiment of the present invention. The mirror 200 according to fig. 2 differs from the mirror 100 of fig. 1 described above in particular by the fact that: a piezoelectric or second order electrostrictive layer 230 is arranged on the opposite side of the mirror substrate 210 from the reflective layer system 220.
According to the embodiment of fig. 2, d is used with a material exhibiting a second order electrostrictive effect or with a piezoelectric material 31 Coefficient, voltage applied along the surface normal (i.e., perpendicular to the optically active surface 201, which uses the plot2) generates a mechanical stress in a direction parallel to the optically active surface 201 (i.e. perpendicular to the surface normal). This mechanical stress affects deformations perpendicular to the optically active surface 201.
In contrast, according to the embodiment of FIG. 1, d is utilized 33 The coefficient, the voltage applied along the surface normal (i.e. perpendicular to the optically active surface 101) directly results in a deformation in the direction perpendicular to the optically active surface 101 (i.e. parallel to the surface normal).
Furthermore, according to the embodiment of fig. 2, a piezoelectric or second order electrostrictive layer 230 is arranged on the opposite side of the mirror substrate 210 from the reflective layer system 220 (i.e. the back side of the mirror 200), whereas the embodiment of fig. 1 has a piezoelectric layer 130 between the substrate and the reflective layer system 120.
Additional functional layers (e.g., diffusion barrier layers, adhesion-promoting layers, etc.) not shown in fig. 2 may be provided in the layer structure of the mirror 200.
Since fig. 2 is only used for a simplified illustration of this embodiment, reference is made to the description above in fig. 1 regarding the material of the piezoelectric or second-order electrostrictive layer 230 and regarding the material and effect of other possible functional layers that may be present in the mirror 200. In particular, PZT (=pb (Zr) x Ti 1-x )O 3 ) May be used for layer 230. Another material that can be used for layer 230 is PMN (=pb (Mg) 1/3 Nb 2/3 )O 3 )。
Although 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 reflective layer system 220 or at the boundary facing the mirror backside in order to dissipate heat from the piezoelectric layer 230 in a particularly efficient manner.
Fig. 3a-3b and fig. 4 show schematic diagrams for elucidating the construction of a mirror according to a further embodiment of the invention. Common to these embodiments is the provision of a segmented heating arrangement configured to thermally induce locally variable deformation of the optically active surface.
To correct for unwanted volume changes or to correct for other aberrations occurring during operation of the microlithographic projection exposure apparatus due to absorption of radiation impinging unevenly on the optically effective surface 301, the mirror 300 according to fig. 3a comprises an electrode configuration 380 with a plurality of electrodes 381, which electrodes 381 are electrically drivable or can have selectively settable currents applied thereto via electrical leads 382. In addition, the mirror 300 includes a conductive layer 385. Similar to fig. 2, the mirror 300 may also optionally include a piezoelectric or second order electrostrictive layer 330, which is disposed on a side of the mirror substrate 310 opposite the reflective layer system 320.
In fig. 3a, "365" denotes a smoothing and insulating layer which in particular electrically insulates the electrodes 381 of the electrode arrangement 380 from one another and which can be made of, for example, quartz glass (SiO 2 ) Is prepared.
Also, additional functional layers (e.g., diffusion barrier layers, adhesion-promoting layers, etc.) not shown in fig. 3a may be provided in the layer structure of the mirror 300.
During operation of the mirror 300, different potentials may be applied to the individual electrodes 381 of the electrode configuration 380, wherein the voltage thus generated between the electrodes 381 generates a current through the conductive layer 385. The heat caused by this current causes locally varying heating of the mirror surface, depending on the potentials applied to the respective electrodes 381.
The embodiment according to fig. 3a is not limited to a specific geometry of the electrode configuration 380. The electrodes 381 may be arranged in any suitable distribution (e.g., a cartesian grid, a hexagonal configuration, etc.). In further embodiments, electrode 381 may also be positioned only in specific areas. An example of the geometry of the electrode configuration 380 is schematically shown in fig. 3 b.
In accordance with the present invention, the combined use of the electrode configuration 380 and the conductive layer 385 in the case of the mirror 300 (although the structure of the electrode configuration is relatively coarse) enables a continuous change of the power input into the mirror, wherein at the same time the coupling of thermal power (e.g. compared to the use of Infrared (IR) heating means) is limited to the mirror itself. Due to the material selection, there is a relatively high resistance in conductive layer 385, such that the voltage drops there, while due to the relatively significantly higher conductivity in wire 382, there is no voltage or heat drop in wire 382, and no fine structure is required in this regard to create high resistance.
According to fig. 3a, the mirror 300 comprises a plurality of cooling channels 315 arranged in the mirror substrate 310 close to its boundary facing the reflective layer system 320 in order to dissipate heat from the conductive layer 385 in a particularly efficient manner.
Fig. 4 shows a schematic view for explaining the construction of a mirror according to another embodiment of the present invention. The mirror 400 according to fig. 4, which is shown only in a very simplified manner, differs from the mirror 300 described above in particular by the fact that: the staged heating configuration 480 includes a plurality of radiation sources 481 configured to irradiate the mirror substrate 410 with electromagnetic radiation to thermally induce such deformation of the optically active surface. Depending on the operation of the individual radiation sources 481, which can be controlled independently of each other, the radiation causes locally varying heating of the mirror surface. The wavelength of electromagnetic radiation (which may be, for example, infrared radiation) is such that the material of the mirror substrate 410 is substantially transparent in the corresponding wavelength range.
According to fig. 4, the mirror 400 comprises a plurality of cooling channels 415 arranged in the mirror substrate 410 near its boundary facing the reflective layer system (not shown in fig. 4) in order to dissipate heat from the mirror in a particularly efficient manner.
Furthermore, the design and configuration of the radiation source 481 is preferably such that the radiation does not (or at least does not to a large extent) interfere with the cooling channels 415
Fig. 5 shows a schematic diagram of an exemplary projection exposure apparatus, which is designed for operation in EUV and in which the invention can be implemented. According to fig. 5, the illumination device in a projection exposure apparatus 500 designed for EUV comprises a field facet mirror 503 and a pupil facet mirror 504. Light from a light source unit including a plasma light source 501 and a collector mirror 502 is directed onto a field facet mirror 503. A first telescope mirror (telescope mirror) 505 and a second telescope mirror 506 are arranged in the optical path downstream of the pupil facet mirror 504. A deflection mirror 507 is arranged downstream of the light path, which deflects radiation incident thereon onto an object field in the object plane of a projection lens comprising six mirrors 551-556. A mask 521 with a reflective structure on a mask stage 520 is arranged at the location of the object field, which mask is imaged into an image plane by means of a projection lens, wherein a substrate 561 coated with a photosensitive layer (photoresist) on a wafer stage 560 is provided in the image plane.
FIG. 6 shows a schematic diagram of an exemplary projection exposure apparatus designed for operation in a DUV and in which the invention can be implemented. 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 light" and means that the wavelength of the working light is between 30nm and 250 nm. The beam shaping and illumination system 610 and the projection lens 620 may be arranged in a vacuum enclosure and/or enclosed by a machine room with corresponding driving means. The projection exposure apparatus 600 has a DUV light source 601. For example, an ArF excimer laser emitting radiation 602 in the 193nm DUV range can be provided as the DUV light source 601.
The beam shaping and illumination system 610 shown in fig. 6 directs DUV radiation 602 onto mask 605. The mask 605 is implemented as a transmissive optical element and may be disposed outside of the beam shaping and illumination system 610 and the projection lens 620. Mask 605 has a structure that is imaged onto a substrate or wafer 630 in a demagnified manner via projection lens 620. The projection lens 620 has a plurality of lens elements (three of which 621-623 are shown schematically and exemplarily in fig. 6) and at least one mirror (two mirrors 624, 625 are shown schematically and exemplarily in fig. 6) for imaging the mask 605 onto the wafer 630. In this case, the individual lens elements 621-623 and/or the mirrors 624, 625 of the projection lens 620 may be symmetrically arranged with respect to the optical axis OA of the projection lens 620. It should be noted that the number of lens elements and mirrors of DUV lithographic apparatus 600 is not limited to the number shown in the figures. More or fewer lens elements and/or mirrors may also be provided. Furthermore, the front side of the mirror is typically curved for beam shaping. The air gap between the last lens element 623 and the wafer 630 may be replaced by a liquid medium 626 having a refractive index greater than 1. For example, the liquid medium 626 may be high purity water. This configuration is also known as immersion microlithography and has a higher optical lithography resolution.
Even though the invention has been described based on specific embodiments, many variations and alternative embodiments will be apparent to a person skilled in the art, e.g. by a combination and/or exchange of features of the various embodiments. It is therefore evident that such variations and alternative embodiments are also encompassed by the present invention for a person skilled in the art, and that the scope of the present invention is limited only by the meanings of the appended patent claims and their equivalents.

Claims (16)

1. A mirror, wherein the mirror has an optically effective surface, having:
a mirror substrate (110, 210,310, 410);
a reflective layer system (120, 220, 320) for reflecting electromagnetic radiation incident on the optically active surface (101, 201, 301);
at least one actuator layer configured to transmit an adjustable mechanical force on the reflective layer system (120, 220, 320), thereby producing a locally variable deformation of the optically effective surface (101, 201, 301); and
at least one cooling device configured to at least partially dissipate heat generated by the actuator layer.
2. The mirror according to claim 1, wherein the at least one actuator layer comprises a piezoelectric or second order electrostrictive layer (130, 230, 330), wherein an electric field can be applied to the piezoelectric or second order electrostrictive layer to produce the locally variable deformation of the optically effective surface (101, 201, 301).
3. Mirror according to claim 1 or 2, characterized in that the at least one actuator layer is arranged between the mirror substrate (110) and the reflective layer system (120).
4. Mirror according to claim 1 or 2, characterized in that the at least one actuator layer is arranged on the side of the mirror substrate (210, 310) opposite the reflective layer system (220, 320).
5. Mirror according to one of the preceding claims, characterized in that the cooling means comprise at least one cooling channel (115, 215,315, 415) arranged in the mirror substrate (110, 210,310, 410).
6. Mirror according to claim 5, characterized in that the distance between the at least one cooling channel (115, 215,315, 415) and the boundary delimiting the mirror substrate (110, 210,310, 410) in a direction perpendicular to the optically active surface is less than 20mm, in particular less than 10mm.
7. Mirror according to one of the preceding claims, further comprising a controller configured to control the operation of the cooling means in dependence of the operation of the actuator layer.
8. Mirror according to one of the preceding claims, further comprising a segmented heating arrangement configured to thermally induce a locally variable deformation of the optically active surface (301).
9. The mirror of claim 7 or 8, wherein the controller is further configured to control operation of the cooling device in accordance with operation of the staged heating configuration.
10. The mirror according to claim 8 or 9, wherein the segmented heating arrangement comprises an electrode arrangement (380) configured to be electrically driven to thereby thermally induce the deformation of the optically active surface (301).
11. The mirror according to claim 8 or 9, wherein the staged heating configuration comprises at least one radiation source (481) configured to irradiate the mirror substrate (410) with electromagnetic radiation to thermally induce the deformation of the optically active surface.
12. Mirror according to one of the preceding claims, characterized in that it is designed for an operating wavelength of less than 250nm, in particular less than 200nm, more in particular less than 160 nm.
13. Mirror according to one of the preceding claims, characterized in that it is designed for operating wavelengths of less than 30nm, in particular less than 15 nm.
14. Mirror according to one of the preceding claims, characterized in that it is a mirror for a microlithographic projection exposure apparatus.
15. An optical system, in particular an illumination device or a 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. Microlithographic projection exposure apparatus (500, 600) with an illumination device and a projection lens, characterized in that the projection exposure apparatus has an optical system as claimed in claim 15.
CN202080104190.5A 2020-08-07 2020-08-07 Mirror, in particular for a microlithographic projection exposure apparatus Pending CN115997170A (en)

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