DE102022202450A1 - Method for operating an optical system, and optical system - Google Patents

Abstract

The invention relates to a method for operating an optical system and an optical system, the optical system having at least one mirror (100) with a mirror substrate (110) and a reflection layer system (120), with a fluid channel arrangement having a A plurality of fluid channels (131-135) is arranged, through which a fluid with a variably adjustable fluid temperature can flow independently of one another, electromagnetic radiation being directed onto an optically used partial area (125) of the reflection layer system (120), with at least one first fluid channel ( 133) is located in a first mirror substrate area covered by this sub-area (125) and wherein at least one second fluid channel (132, 134) is located in a second mirror substrate area located outside of this first mirror substrate area and not covered by the optically used sub-area (125), wherein one fluid temp ature is set to a first value (T1) when fluid enters the at least one first fluid channel (133), and wherein a fluid temperature is set to a second value (T2) when fluid enters the at least one second fluid channel (132, 134). is set, which is greater than the first value (T1).

Description

BACKGROUND OF THE INVENTION

field of invention

The invention relates to a method for operating an optical system and an optical system.

State of the art

For optical applications in the EUV range (e.g. wavelengths below 30 nm) or in the X-ray range (e.g. wavelengths below 0.1 nm), mirrors are used as optical components due to the lack of availability of suitable light-transmitting refractive materials. Examples are synchrotron mirrors and mirrors that are used in the illumination device or the projection objective of a microlithographic projection exposure system.

A problem that occurs in practice is that such mirrors, among other things, experience heating as a result of absorption of the incident radiation and an associated thermal expansion or deformation, which in turn can result in impairment of the imaging properties of the associated optical system. Various approaches are known for avoiding surface deformations caused by heat input and the associated optical aberrations, for example active cooling using fluid channels through which a (cooling) fluid can flow in each case.

However, the temperature profiles achieved in the mirror substrate or on the optical active surface can - especially in the case of comparatively strongly localized heat inputs from the impinging electromagnetic radiation - possibly have a pronounced inhomogeneity over the optically used area with the result that the thermally induced temperature profiles resulting from the respective temperature profiles Deformation profiles in the operation of the relevant optical system bring about optical aberrations that cannot be corrected, or can only be corrected with difficulty. This can only be the case with a synchrotron mirror, for example, in which typically during operation of the synchrotron the current heat-affected zone corresponding to the area currently optically used is relatively small relative to the entire mirror surface and also varies locally during operation. As a result, limitations in the performance of the optical system having the respective mirror can result.

The prior art is only given as an example US 10,955,595 B2 referred.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method for driving an optical system and an optical system which enable thermally induced deformation to be avoided effectively while alleviating the above-described problems.

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

• - wobei elektromagnetische Strahlung auf einen optisch genutzten Teilbereich des Reflexionsschichtsystems gelenkt wird, wobei sich wenigstens ein erster Fluidkanal in einem von diesem Teilbereich abgedeckten ersten Spiegelsubstratbereich befindet und wobei sich wenigstens ein zweiter Fluidkanal in einem außerhalb dieses ersten Spiegelsubstratbereichs befindlichen, nicht von dem optischen genutzten Teilbereich abgedeckten zweiten Spiegelsubstratbereich befindet;
• - wobei eine Fluidtemperatur bei Eintritt von Fluid in den wenigstens einen ersten Fluidkanal auf einen ersten Wert (T₁) eingestellt wird; und
• - wobei eine Fluidtemperatur bei Eintritt von Fluid in den wenigstens einen zweiten Fluidkanal auf einen zweiten Wert (T₂) eingestellt wird, welcher größer ist als der erste Wert (T₁) .

According to one aspect of the invention, the invention relates to a method for operating an optical system, the optical system having at least one mirror with a mirror substrate and a reflection layer system, a fluid channel arrangement having a plurality of fluid channels being arranged in the mirror substrate and being independently of one another fluid with variably adjustable fluid temperature can flow through,

• - wherein electromagnetic radiation is directed onto an optically used sub-area of the reflection layer system, wherein at least one first fluid channel is located in a first mirror substrate area covered by this sub-area and wherein at least one second fluid channel is located in a sub-area outside of this first mirror substrate area, not used by the optical sub-area covered second mirror substrate area;
• - wherein a fluid temperature upon entry of fluid into the at least one first fluid channel is set to a first value (T ₁ ); and
• - wherein a fluid temperature when fluid enters the at least one second fluid channel is set to a second value (T ₂ ), which is greater than the first value (T ₁ ).

For the purposes of the present application, the term “reflection layer system” is intended to encompass both an individual layer and a multiple layer system.

The invention is based in particular on the concept of achieving at least partial homogenization of the temperature field that occurs during operation in the optically used area in a mirror with fluid channels present in its mirror substrate, in that for different fluid channels of the fluid channel arrangement the fluid temperatures set at the point of entry into said fluid channels be chosen differently. Here, the fact that the Fluidtempe temperature for a fluid channel, which is located in a mirror substrate area that is not covered by the optically used area, is selected to be higher than the fluid temperature for a fluid channel located in a mirror substrate area that is covered by the optically used area, it can be achieved that the impinging electromagnetic radiation on the ( possibly strongly localized) optically used area caused by the thermally induced deformation, which is caused by the comparatively warmer fluid outside said optically used area, is effectively compensated with the result that an undesirable inhomogeneity of the deformation profile is reduced as a result.

The width (perpendicular to the fluid flow direction) of the fluid channel covered by the optically used subarea is preferably greater than the corresponding width of the optically used subarea.

The invention is also based on the consideration that in principle not every deformation is problematic with regard to optical aberrations caused during operation of the respective optical system, in particular constant offsets (in the sense of a translatory displacement of the optical effective surface) or also constant linear deformation profiles are usually relatively easy to correct in the optical system. In contrast, deformation profiles that are difficult or impossible to optically correct are typically aspherical deformation profiles with pronounced waviness (for example a comparatively high wavefront component corresponding to a Zernike representation for the third-order Zernike polynomial). As a result, according to the invention, it is not necessary to avoid any deformation in the optically used area, but rather, with regard to effective aberration correction, it is sufficient to realize deformation profiles that are as homogeneous as possible (i.e. have small gradients and/or small differences between maximum and minimum deformation amplitude), which in turn Ways of setting different fluid temperatures according to the invention can be achieved.

According to one embodiment, fluid flows through adjacent fluid channels of the fluid channel arrangement in opposite directions. As a result, an undesired temperature gradient in the direction of flow as a result of heating of the fluid while it is flowing through the relevant fluid channel can be reduced.

According to one embodiment, exactly two different values (T ₁ , T ₂ ) are set for the fluid temperatures when fluid enters the fluid ducts of the fluid duct arrangement.

According to one embodiment, the first value (T ₁ ) and the second value (T ₂ ) of the respective fluid temperature are selected in such a way that a thermally induced deformation profile resulting from the heat loads of the electromagnetic radiation and the fluid channel arrangement in the optically used partial area is reduced by a maximum of 50%, in particular a maximum of 30%, further in particular a maximum of 10% in the PV value varies. The PV value (PV= "Peak-to-Valley") designates the difference between the maximum and minimum value within the local distribution of the deformation profile, with the percentage criterion here being related to the largest of these values (ie the maximum value). .

According to one embodiment, a thermally induced deformation profile resulting from the thermal loads of the electromagnetic radiation and the fluid channel arrangement varies by a maximum of 50%, in particular by a maximum of 30%, more particularly by a maximum of 10% in the optically used sub-area in the root mean square (RMS value).

According to one embodiment, the first value (T ₁ ) and the second value (T ₂ ) of the respective fluid temperature are selected such that in a thermally induced deformation profile resulting from the heat loads of the electromagnetic radiation and the fluid channel arrangement, a maximum value of the local deformation gradient in the optical used portion is less than 30%, more particularly less than 10%.

According to one specific embodiment, there is exactly one fluid channel in the first mirror substrate area covered by the optically used subarea.

According to one embodiment, the mirror is designed for a working wavelength of less than 30 nm, in particular less than 15 nm.

According to one embodiment, the optical system is a beamline (i.e. a beam guidance unit or beam pipe) of a synchrotron or a free-electron laser.

According to a further embodiment, the optical system is a projection objective or an illumination device of a microlithographic projection exposure system.

The invention also relates to an optical system with at least one mirror with a mirror substrate and a reflection layer system, wherein a fluid channel arrangement with a plurality of fluid channels through which a fluid with a variably adjustable fluid temperature can flow independently of one another is arranged in the mirror substrate, and a temperature control device , via which the inlet temperatures of the fluid when it enters the respective fluid channels can be adjusted independently of one another, the temperature control device being configured to carry out a method having the features described above.

Further configurations of the invention can be found in the description and in the dependent claims.

The invention is explained in more detail below with reference to exemplary embodiments illustrated in the attached figures.

character list

• 1a-1b schematische Darstellungen zur Erläuterung des möglichen Aufbaus eines Spiegels gemäß einer Ausführungsform der Erfindung;
• 2 eine schematische Darstellung zur Veranschaulichung der möglichen Wirkungsweise des erfindungsgemäßen Verfahrens;
• 3 eine schematische Darstellung zur Erläuterung einer möglichen Anwendung eines erfindungsgemäßen optischen Elements in einem Synchrotron; und
• 4 eine schematische Darstellung des möglichen Aufbaus einer für den Betrieb im EUV ausgelegten mikrolithographischen Projektionsbelichtungsanlage.

Show it:

• 1a-1b schematic representations to explain the possible structure of a mirror according to an embodiment of the invention;
• 2 a schematic representation to illustrate the possible mode of operation of the method according to the invention;
• 3 a schematic representation to explain a possible application of an optical element according to the invention in a synchrotron; and
• 4 a schematic representation of the possible structure of a designed for operation in the EUV microlithographic projection exposure system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

1a-1b show a possible embodiment of a mirror 100 according to the invention in merely schematic representations. Depending on the specific application scenario, the mirror 100 can be a plane mirror or also have any other (eg spherical or cylindrical) geometry.

The mirror 100 has a mirror substrate 110 (which is made of monocrystalline silicon (Si) in the example) and a reflection layer system 120 (in the example a single layer made of gold (Au) and with an exemplary thickness in the range from 20 nm to 50 nm).

In further embodiments, the reflection layer can also be made of another noble metal, for example platinum (Pt), rhodium (Rh), silver (Ag), ruthenium (Ru), palladium (Pd), osmium (Os) or iridium (Ir). Furthermore, the reflection layer can also be made of an organic material, for example carbon (C), boron carbide (B ₄ C) or silicon carbide (SiC).

Depending on the intended use, the mirror 100 can be a mirror designed for operation under grazing incidence or also a mirror designed for operation under normal incidence. In the latter case, the mirror typically has a multiple layer system in the form of, for example, an alternating sequence of individual layers made of, for example, at least two different layer materials as the reflection layer system. Furthermore, in further embodiments, the mirror substrate 110 can also be produced from a different substrate material, for example one that also has silicon, for example silicon dioxide (SiO ₂ ) or ^Zerodur® (from Schott AG). Furthermore, depending on the intended use, a titanium silicate glass marketed by Corning Inc. under the name ^ULE® , for example, can also be used as the substrate material.

The mirror according to the invention can be used, for example, as a deflection mirror or beam-guiding optical component in a synchrotron, as is shown in 3 is shown only schematically for a mirror 300. According to 3 In such a synchrotron, the electromagnetic radiation 350 generated by accelerating or deflecting an electron beam 370 (in the form of a divergent X-ray beam in the example) strikes a mirror 300. The mirror can also be positioned in a so-called beamline, on which the radiation generated in the synchrotron electromagnetic radiation hits. An elliptical “footprint” generated on the mirror 300 in the example is labeled “301” as the optically used area, and the electromagnetic radiation emitted by the mirror 300 after reflection (in the form of a convergent x-ray beam in the example) is labeled “360”.

How out 1a in schematic top view and 1b recognizable in a schematic sectional view, the mirror 100 according to the invention has a fluid channel arrangement of a plurality of fluid channels 131-135, through which a fluid (eg cooling water) with a variably adjustable fluid temperature can flow independently of one another. The temperatures present at the point of entry into the fluid channels 131-135 can be set independently of one another via a temperature control device (not shown). Furthermore, as in 1a indicated by the drawn arrows, adjacent fluid channels can flow through in opposite directions. By implementing this counterflow principle, which is known per se, an undesired temperature gradient in the direction of flow (i.e. in the positive or negative x-direction according to the coordinate system drawn in) can initially occur, which would otherwise result from a typically occurring heating of the fluid during the flow through the relevant fluid channel as a result of the im During operation, the thermal load acting on the mirror 100 would be reduced.

With "125" is in 1a as well as 1b denotes an optically used area (“footprint”). In the scenario shown, this is a comparatively strongly localized area of the mirror surface on which the electromagnetic radiation (e.g. EUV radiation) is currently impinging and, without suitable countermeasures, an undesirable temperature or deformation profile and associated optical aberrations of the mirror 100 having optical system leads.

How now further in 1a is indicated, according to the invention there is no setting of a uniform, constant fluid temperature upon entry into the respective fluid channels. Rather, said fluid temperature is selected differently in that, in particular for the fluid channels 132 and 134, which are located in a mirror substrate area not covered by the optically used area 125, a fluid temperature T ₂ is set that is greater than the fluid temperature T ₁ that is required for the Fluid is adjusted upon entry into the fluid channel 133 located in the mirror substrate area covered by the optically used area 125 .

As also in 1a is indicated, the fluid in question has a fluid temperature T ₁ +ΔT ₁ or T ₂ +ΔT ₂ that is higher than the value at entry after flowing through the respective fluid channel and upon exit from the respective fluid channel, which typically indicates the heating of the fluid in question during Along currents at the optically used area 125 is due.

As a result of the different or variable settings of the temperatures T ₁ , T ₂ , two degrees of freedom are provided for the thermal actuation of the mirror 100, namely the resulting absolute average temperature of the mirror 100 and the temperature difference between the respective fluid temperatures when entering the fluid channels. By suitably selecting said temperature difference, a suitable temperature field can ultimately be generated which, in terms of shape and spatial frequency, is essentially complementary to that temperature field which arises due to the heat load from impinging mirror 100 with electromagnetic radiation (at constant fluid temperature).

As already explained above, the targeted setting of different fluid temperatures T ₁ , T ₂ according to the invention is carried out with the aim of avoiding a deformation profile in optically used region 125 that is unfavorable with regard to optical aberrations. 2 shows a schematic and highly simplified basic sketch to illustrate the effect achieved according to the invention. It should be noted here that typically the aforementioned avoidance of an undesired deformation profile (in particular the avoidance of aspheric deformations or a pronounced “ripple”) is generally only relevant for the optically used region 125 . It should also be noted that a "constant deformation" in the sense of a simple constant offset (ie a purely translatory displacement of the optical effective surface in the optically used area 125 along the z-direction in the coordinate system shown) is usually harmless, since such a constant offset can be corrected relatively easily in the associated optical system.

From the above considerations it follows that the dot-dash line "C" in 2 can be regarded as corresponding to a desired (since locally constant) target deformation profile. Furthermore, it is assumed that the long-dashed curve labeled “A” represents a deformation profile that results without implementing the concept according to the invention or if matching fluid temperatures are selected when entering the respective fluid channels. Using the concept according to the invention, a deformation profile corresponding to the short-dashed curve labeled “B” can now be achieved, which largely comes close to the target deformation profile represented by curve “C”.

Furthermore, a local change in the optically used region 125 that typically takes place during operation of the optical system having the mirror 100 can be taken into account by setting the respective fluid temperatures in a manner that varies over time when entering the fluid channels.

Although in the exemplary embodiment shown the optically used area only covers one of the fluid channels (namely the fluid channel 133) or the associated mirror substrate area, the invention is not restricted to this. In further embodiments, the optically used area or "footprint" can also extend over several Cooling channels extend. In such a scenario, the relevant fluid channels located within the mirror substrate area covered by the optically used area can also be subjected to different fluid temperatures in order to reduce or minimize undesirable temperature or deformation gradients depending on the application scenario.

In quantitative terms, the inventive homogenization of the deformation profile resulting in the optically used area, for example, via the PV value (PV= "Peakto-Valley") according to the difference between the maximum and the minimum value within the local distribution of the deformation profile or via the deformation gradients resulting in the optically used area of the optical effective surface can be described. In this case, a specific grid of points on the optically used area can be taken as a basis, merely by way of example, in which case the local or tangential deformation gradient can then be determined in each case for the relevant points. An improvement in the deformation profile can then be assumed within the meaning of the invention if the maximum deformation gradient occurring over said point grid is reduced (and minimized if possible). Furthermore, the mean square deviation (= RMS value) of the "z-displacement" resulting from deformation due to said point grid in relation to the in 2 drawn-in coordinate system can be determined, an improved deformation profile then being assumed within the meaning of the invention if the said mean square deviation is reduced (and minimized if possible), which in turn ultimately corresponds to a largely constant deformation profile.

kann der jeweilige Ort des Wärmeeintrags identifiziert und die zur Homogenisierung des Temperaturprofils geeignete Differenz ΔT_K,E der Fluidtemperaturen am Fluidkanaleintritt $$\mathrm{\Delta }{\text{T}}_{\text{K}\text{,E}}={\text{T}}_{\text{1}}-{\text{T}}_{\text{2}}$$

erzeugt werden.To set the suitable fluid temperatures, according to the invention, a temperature measurement is carried out at the respective fluid channel outlet (ie the temperatures T ₁ +ΔT ₁ and T ₂ +ΔT ₂ are determined). Preferably, the respective fluid temperature T ₁ or T ₂ at the fluid channel inlet is also measured, so that a complete heat balance can be calculated. Based on the difference ΔT _K,A of the fluid temperatures at the fluid channel outlet $$\mathrm{\Delta }{\text{T}}_{\text{K}\text{,A}}=\left({\text{T}}_{\text{1}}+\mathrm{\Delta }{\text{T}}_{\text{1}}\right)-\left({\text{<figure-callout id="2" label="T" filenames="DE102022202450A1\_0007.png" state="{{state}}">T</figure-callout>}}_{\text{2}}+\mathrm{\Delta }{\text{T}}_{\text{2}}\right)$$

the respective location of the heat input can be identified and the difference ΔT _K,E of the fluid temperatures at the fluid channel inlet suitable for homogenizing the temperature profile $$\mathrm{\Delta }{\text{T}}_{\text{K}\text{,E}}={\text{T}}_{\text{1}}-{\text{<figure-callout id="2" label="T" filenames="DE102022202450A1\_0007.png" state="{{state}}">T</figure-callout>}}_{\text{2}}$$

be generated.

In further embodiments, temperature sensors can also be provided at different positions of the mirror and preferably in the vicinity of the active optical surface, in which case the corresponding temperature measurements can then be used as a basis for setting the appropriate fluid temperatures at the respective fluid channel inlet.

As described above, suitable temperature control of the fluid at the respective fluid channel inlet can achieve homogenization of a temperature or deformation profile that ultimately results in the operation of the associated optical system. In a further application, however, the mirror according to the invention can also be deformed in a targeted manner by suitable adjustment of the fluid temperatures, in order to compensate for wavefront aberrations present elsewhere in the optical system.

Although reference was made to a synchrotron mirror in the embodiments described above, the invention can also be implemented in other optical systems, in particular, for example, in an illumination device or a projection lens of a microlithographic projection exposure system.

4 shows a schematic meridional section of the possible structure of a microlithographic projection exposure system designed for operation in the EUV. According to 4 the projection exposure system 1 has an illumination device 2 and a projection lens 10 . One embodiment of the illumination device 2 of the projection exposure system 1 has, in addition to a light or radiation source 3, illumination optics 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a separate module from the rest of the illumination device. In this case, the lighting device does not include the light source 3 . In this case, a reticle 7 arranged in the object field 5 is exposed. The reticle 7 is held by a reticle holder 8 . The reticle holder 8 can be displaced in particular in a scanning direction via a reticle displacement drive 9 . In 4 a Cartesian xyz coordinate system is drawn in for explanation. The x-direction runs perpendicular to the plane of the drawing. The y-direction is horizontal and the z-direction is vertical. The scan direction is in 4 along the y-direction. The z-direction runs perpendicular to the object plane 6.

The projection lens 10 is used to image the object field 5 in an image field 11 in a Image plane 12. A structure on the reticle 7 is imaged onto a light-sensitive layer of a wafer 13 arranged in the region of the image field 11 in the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be displaced in particular along the y-direction via a wafer displacement drive 15 . The displacement of the reticle 7 via the reticle displacement drive 9 on the one hand and the wafer 13 on the other hand via the wafer displacement drive 15 can be synchronized with one another.

The radiation source 3 is an EUV radiation source. The radiation source 3 emits in particular EUV radiation, which is also referred to below as useful radiation or illumination radiation. In particular, the useful radiation has a wavelength in the range between 5 nm and 30 nm. The radiation source 3 can be, for example, a plasma source, a synchrotron-based radiation source or a free-electron laser (“free-electron laser”, FEL). act. The illumination radiation 16, which emanates from the radiation source 3, is bundled by a collector 17 and propagates through an intermediate focus in an intermediate focal plane 18 into the illumination optics 4. The illumination optics 4 has a deflection mirror 19 and, downstream of this in the beam path, a first facet mirror 20 (with schematically indicated facets 21) and a second facet mirror 22 (with schematically indicated facets 23).

The projection lens 10 has a plurality of mirrors Mi (i=1, 2, . . . ) which are numbered consecutively according to their arrangement in the beam path of the projection exposure system 1. At the in the 4 In the example shown, the projection lens 10 has six mirrors M1 to M6. Alternatives with four, eight, ten, twelve or another number of mirrors Mi are also possible. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16 . The projection objective 10 is a doubly obscured optics. The projection objective 10 has a numerical aperture on the image side which is greater than 0.5 and which can also be greater than 0.6 and which can be 0.7 or 0.75, for example.

During operation of the microlithographic projection exposure system 1, the electromagnetic radiation impinging on the optical effective surface of the mirror is partially absorbed and, as explained above, leads to heating and an associated thermal expansion or deformation, which in turn results in impairment of the imaging properties of the optical system can. The inventive concept can be particularly advantageous for any mirror of the microlithographic projection exposure system 1 of 4 be applied. This can be used to avoid or compensate for thermally induced deformations of the relevant mirror itself (e.g. to compensate for a local distribution of the zero crossing temperature) or also to provide an additional degree of freedom with regard to setting the wavefront properties of the entire optical system, i.e. without or with a(r) corrective effect achieved by the mirror in question.

The invention can also be advantageously implemented in a projection exposure system designed for operation in DUV (i.e. at wavelengths less than 250 nm, in particular less than 200 nm) or also in another optical system.

Although the invention has also been described on the basis of specific embodiments, numerous variations and alternative embodiments will become apparent to the person skilled in the art, e.g. by combining and/or exchanging features of individual embodiments. Accordingly, it will be understood by those skilled in the art that such variations and alternative embodiments are intended to be encompassed by the present invention, and the scope of the invention is limited only in terms of the appended claims and their equivalents.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US10955595B2 [0005]

Claims (15)

Method for operating an optical system, wherein the optical system has at least one mirror (100) with a mirror substrate (110) and a reflection layer system (120), wherein in the mirror substrate (110) a fluid channel arrangement with a plurality of fluid channels (131-135) is arranged through which a fluid with a variably adjustable fluid temperature can flow independently of one another, • wherein electromagnetic radiation is directed onto an optically used partial area (125) of the reflective layer system (120), with at least one first fluid channel (133) being located in one of this partial area (125) covered first mirror substrate area and wherein at least one second fluid channel (132, 134) is located in a second mirror substrate area located outside of this first mirror substrate area and not covered by the optically used partial area (125); • wherein a fluid temperature when fluid enters the at least one first fluid channel (133) is set to a first value (T ₁ ); and • wherein a fluid temperature is set to a second value (T ₂ ), which is greater than the first value (T ₁ ), when fluid enters the at least one second fluid channel (132, 134). procedure after claim 1 , characterized in that at least two fluid channels (132, 134) are located outside of this first mirror substrate area and not covered by the optically used partial area (125) second mirror substrate area on opposite sides of the first fluid channel (133). procedure after claim 1 or 2 , characterized in that fluid flows through adjacent fluid channels of the fluid channel arrangement in the opposite direction. Procedure according to one of Claims 1 until 3 , characterized in that a total of exactly two different values (T ₁ , T ₂ ) are set for the fluid temperatures when fluid enters the fluid channels of the fluid channel arrangement. Method according to one of the preceding claims, characterized in that the first value (T ₁ ) and the second value (T ₂ ) are selected such that a thermally induced deformation profile resulting from the thermal loads of the electromagnetic radiation and the fluid channel arrangement in the optically used partial area (125) varies by a maximum of 50%, in particular a maximum of 30%, further in particular a maximum of 10% in the PV value. Method according to one of the preceding claims, characterized in that a thermally induced deformation profile resulting from the thermal loads of the electromagnetic radiation and the fluid channel arrangement in the optically used sub-area (125) by a maximum of 50%, in particular a maximum of 30%, further in particular a maximum of 10% in the square Mean (RMS value) varies. Method according to one of the preceding claims, characterized in that the first value (T ₁ ) and the second value (T ₂ ) are selected in such a way that a maximum value results in a thermally induced deformation profile resulting from the thermal loads of the electromagnetic radiation and the fluid channel arrangement of the local deformation gradient in the optically used partial area (125) is less than 30%, more particularly less than 10%. Method according to one of the preceding claims, characterized in that there is exactly one fluid channel (133) in the first mirror substrate area covered by the optically used partial area (125). procedure after claim 8 , characterized in that the width running perpendicular to the fluid flow direction of this fluid channel (133) covered by the optically used partial area (125) is greater than the corresponding width of the optically used partial area (125). Method according to one of the preceding claims, characterized in that the mirror (100) is designed for a working wavelength of less than 30 nm, in particular less than 15 nm. Procedure according to one of Claims 1 until 10 , characterized in that the optical system is a beam guidance unit (“beamline”) of a synchrotron or a free-electron laser. Procedure according to one of Claims 1 until 10 , characterized in that the optical system is a projection lens or an illumination device of a microlithographic projection exposure system (1). Optical system, with • at least one mirror (100) with a mirror substrate (110) and a reflection layer system (120), wherein in the mirror substrate (110) a fluid channel arrangement with a plurality of fluid channels (131-135) is arranged, each of which is fluid with a variably adjustable fluid temperature can flow through; and • a temperature control device, via which the inlet temperatures of the fluid when it enters the respective fluid channels (131-135) can be adjusted independently of one another; • wherein the temperature control device is configured to carry out a method according to any one of the preceding claims. Optical system after Claim 13 , characterized in that this is a synchrotron. Optical system after Claim 13 , characterized in that this is a projection objective or an illumination device of a microlithographic projection exposure system (1).

Images