DE102011080052A1 - Mirror, optical system with mirror and method for producing a mirror - Google Patents

Abstract

A mirror has a substrate (112) made of a substrate material having a specific thermal conductivity of less than 10 W / (m · K) and a reflection coating (116) applied to the substrate suitable for vacuum ultraviolet radiation or radiation from the extreme ultraviolet range is reflective. Between the substrate (112) and the reflective coating (116) is disposed a heat distribution intermediate layer (120, 220) consisting of a layer material having a specific thermal conductivity at least 10 times the specific thermal conductivity of the substrate material.

Description

Technical area

The invention relates to a mirror according to the preamble of claim 1, to an optical system with a mirror according to the preamble of claim 15, and to a method of manufacturing a mirror according to the preamble of claim 18. A preferred field of application is microlithography at working wavelengths from the field of vacuum ultraviolet radiation (VUV) radiation or extreme ultraviolet radiation (EUV).

Description of the Prior Art

For the production of semiconductor components and other finely structured components, predominantly microlithographic projection exposure methods are used today. In this case, masks (reticles) or other pattern-generating means are used which carry or form the pattern of a structure to be imaged, e.g. a line pattern of a layer (layer) of a semiconductor device. The pattern is positioned in a projection exposure apparatus between a lighting system and a projection lens in the region of the object surface of the projection lens and illuminated with an illumination radiation provided by the illumination system. The radiation changed by the pattern passes through the projection lens as projection radiation, which images the pattern onto the substrate to be exposed coated with a radiation-sensitive layer.

The pattern is illuminated by means of an illumination system which shapes from the radiation of a primary radiation source an illumination radiation directed onto the pattern, which is characterized by specific illumination parameters and impinges on the pattern within an illumination field of defined shape and size. Within the illumination field there should be a given local intensity distribution, which should normally be as uniform as possible.

As a rule, different illumination modes (so-called illumination settings) are used, which can be characterized by different local intensity distributions of the illumination radiation in a pupil surface of the illumination system, depending on the type of structures to be imaged. In this way, a specific illumination angle distribution or a specific distribution of the incident intensity in the angular space can be specified in the illumination field.

In order to be able to produce ever finer structures, different approaches are pursued. For example, the resolution of a projection lens can be increased by increasing the image-side numerical aperture (NA) of the projection lens. Another approach is to work with shorter wavelengths of electromagnetic radiation.

For applications in the field of microlithography optical systems are now often used that work with vacuum ultraviolet radiation (VUV radiation), in particular at about 193 nm operating wavelength, or with radiation from the extreme ultraviolet (EUV).

Attempting to improve the resolution by increasing the numerical aperture may present problems in that as the numerical aperture increases, the depth of focus (DOF) achievable decreases. This is disadvantageous because, for example, for reasons of achievable flatness of the substrates to be patterned and mechanical tolerances, a depth of field in the order of at least 0.1 microns is desirable.

For this reason, among other things, optical systems have been developed which operate at moderate numerical apertures and which achieve the increase in resolving power essentially by the short wavelength of the extreme ultraviolet (EUV) electromagnetic radiation used, in particular at working wavelengths in the range between 5 nm and 30 nm. In the case of EUV lithography with working wavelengths around 13.5 nm, for example, at image-side numerical apertures of NA = 0.3, theoretically a resolution of the order of 0.03 μm can be achieved at typical depths of field in the order of about 0.15 μm.

Radiation from the extreme ultraviolet range can not be focused or guided by refractive optical elements because the short wavelengths are absorbed by the known optical materials transparent at higher wavelengths. Therefore, mirror systems are used for EUV lithography. An EUV mirror-reflecting mirror typically has a substrate on which is deposited a multilayer multilayer multilayer reflective coating of ultraviolet ray (EUV) radiation, which has many layer pairs of alternating low refractive index layers and high refractive layer material. Layer pairs for EUV mirrors are often built up with the layer material combinations molybdenum / silicon (Mo / Si) or ruthenium / silicon (Ru / Si).

EUV mirrors with multilayer reflective coatings typically achieve maximum reflectivities of around 70%. A proportion of the unreflected radiation intensity of the incident radiation is absorbed in the layer materials to generate heat. The absorption of radiation results in local heating in the irradiated areas. As a result of the heating, deformation of the mirror surface may occur due to thermal expansion of the reflection coating and possibly the regions of the substrate adjacent thereto. These thermally induced deformations can manifest as aberrations when using the EUV mirrors in an imaging system. These are usually not fully compensated or only with great equipment. Depending on the spatial distribution of the irradiation intensity on the mirror surface, very different aberrations can be induced. The thermally induced deformations are usually reversible, so that the mirror surface returns to its original shape after switching off the illumination.

If necessary, a local increase in temperature at a mirror surface can also lead to non-reversible errors in the area of the mirror surface, e.g. to increased layer compaction in the reflective coating. The optical performance of the optical system may therefore suffer over the life of the optical system or as a function of the accumulated radiation dose.

Numerous proposals have already been made for preventing or reducing thermally induced errors in EUV mirror optical systems.

One approach to limiting thermally-induced perturbations in optical systems is to use materials with extremely low thermal expansion coefficients in fabricating the optical elements so that thermal expansion-related perturbations are reduced from the beginning to a tolerable level. It is known, for example, to use glass ceramics as substrate material for mirrors. A suitable for the production of mirror substrates for microlithography systems glass ceramic is sold under the trade name ZERODUR ^® (Schott AG). For these glass-ceramics, thermal expansion coefficients of 0 + 0.10 · 10 ^-6 K ^-1 are specified for the temperature range between 0 ° C and 50 ° C. Another suitable glass-ceramic having substantially the same coefficient of thermal expansion is sold under the trade designation CLEARCERAM ^® (Ohara, Inc.). Even lower coefficients of thermal expansion are achieved with certain titanium silicate glasses, also known as "Ultra Low Expansion Glass". For such a titanium silicate glass, which is marketed by Corning, Inc. under the trade designation ULE ^®, a medium thermal expansion coefficient of 0 + 30 × 10 ^-9 K ^-1 is specified for the temperature range between 5 ° C and 35 ° C ,

In the European patent application EP 0 955 565 A2 For example, EUV mirrors are described for use in a lighting system or projection lens of a microlithography projection exposure apparatus in which the substrate of the EUV mirror is made of a metallic substrate material, such as aluminum, copper, beryllium, silver, gold or an alloy having one or more of these elements. On the front side of the substrate, a thin film of an amorphous material is applied, whose front side facing away from the substrate is smoothed by polishing and thus can serve as a support surface for the reflection coating applied thereto. By using a metallic substrate material with high thermal conductivity is to be achieved that the heat that develops when irradiating the mirror surface in the region of the reflective coating can be dissipated quickly and efficiently to the cooled back of the mirror substrate. Errors due to thermal deformation in the mirror surface should be avoided.

From the patent application US 2002/0074115 A1 (corresponding DE 100 50 125 ) a device for temperature compensation for thermally stressed body made of materials of low specific thermal conductivity is known, wherein a thermally stressed body may be, for example, a mirror support for an optical system. In the apparatus, a heat distribution device having one or more heat distribution bodies is adapted to surfaces of the thermally stressed body such that a gap remains between the thermally stressed body and a heat distribution body for the purpose of thermal coupling of the thermally stressed body and heat distribution body with simultaneous mechanical decoupling a fluid is filled. This is intended to achieve a separation between a mechanical coupling and a thermal coupling with respect to the thermally stressed body. For example, solid solids on copper, aluminum or silver are proposed as the heat distribution body, for example water or mercury or metal alloys which are liquid at room temperature as the coupling fluid.

From the international patent application WO 2010/020337 A1 is a reflective reticle known for EUV lithography, which thermally reduce or avoid induced pattern distortions. The reflective reticle has an optical layer serving as a pattern carrier layer made of a material having an extremely low coefficient of thermal expansion. In one embodiment, Ultra Low Expansion glass (ULE glass) is used. By contrast, the substrate of the reticle consists of a substrate material whose thermal conductivity is significantly greater than the thermal conductivity of the optical layer. In one embodiment, the substrate is made of cordierite, a ceramic material which has a virtually zero thermal expansion coefficient at typical temperatures for use with EUV mirrors, but about twice as high thermal conductivity over other conventional materials having a very low coefficient of thermal expansion W / (m · K) at 25 ° C). Disposed between the substrate and the optical layer is a conductive layer which is in contact with the substrate surface and / or a facing surface of the optical layer and, in one embodiment, is made of aluminum.

To reduce thermally induced errors in lenses or mirrors has also been proposed to compensate for inhomogeneous heating of the optical component due to inhomogeneous radiation by less heavily irradiated areas heated and / or more heated areas are cooled, so that a homogenization of the temperature distribution results (eg EP 0 678 768 B1 ).

TASK AND SOLUTION

It is an object of the invention to provide a mirror, e.g. can be used in an optical system of a microlithography projection exposure apparatus and offers a high stability of the reflection properties under different operating conditions and over the entire lifetime of the projection exposure apparatus. It is another object to provide a mirror that is relatively insensitive to the negative effects of inhomogeneous exposure to radiation.

To solve these objects, the invention provides a mirror with the features of claim 1. Furthermore, an optical system having the features of claim 15 is provided. Furthermore, a method of manufacturing a mirror having the features of claim 18 is provided.

Advantageous developments are specified in the dependent claims. The wording of all claims is incorporated herein by reference.

In a mirror with such a structure, the heat that is generated during the irradiation in the reflection coating is derived for the most part not by the substrate material equipped with relatively low specific heat conductivity, but by the heat transfer intermediate layer which is much better heat-conductive than the substrate. A predominant portion of the heat dissipation therefore does not occur perpendicular to the reflection coating through the substrate in the direction of the rear side, but parallel to the reflection coating through the heat distribution intermediate layer in the lateral direction in a region between the reflection coating and the substrate. The heat flow follows a significant proportion of the lateral temperature gradient within the heat distribution intermediate layer, so that heat from locally heated areas laterally (laterally) in relatively cooler areas redistributed, which may possibly heat slightly due to the supplied heat energy.

The lateral redistribution of heat energy effectively acts in the direction of equalization or homogenization of the thermal load of the mirror surface with locally concentrated irradiation. The heat distribution intermediate layer thus acts as a homogenization layer. It is not necessary that a completely homogeneous (uniform) temperature distribution is actually achieved. Above all, it is important to reduce or reduce lateral temperature gradients or to reduce the temperature inhomogeneity.

Due to the lateral redistribution of heat energy within the heat distribution intermediate layer, it is achieved that an inhomogeneous irradiation intensity distribution at the mirror surface which is frequently desired during operation of the projection exposure apparatus does not lead to the same or a corresponding inhomogeneous temperature distribution in the substrate material and the associated thermally induced deformations of the mirror surface. Rather, due to the lateral redistribution of heat energy, a partial decoupling of the heat input into the substrate material from the local distribution of the heat generation in the reflection coating is achieved. The heat distribution intermediate layer distributes the radiation introduced by radiation in the region between the reflection coating and the mirror substrate and thereby homogenizes or homogenizes both the temperature distribution in the substrate and the temperature distribution in the reflection coating.

The reflection coating is located on the side facing away from the substrate of the heat distribution intermediate layer and thus on the Light entry side of the mirror. The reflection coating, which is preferably constructed of a plurality of individual layers, is preferably designed so that virtually no intensity or only a negligible proportion of the incident radiation reaches the substrate. The incident radiation is therefore reflected by the reflection coating predominantly (eg to more than 40% or more than 60%) and possibly absorbed to a part. The transmittance of the reflection coating at the operating wavelength is typically significantly lower than the reflectance. The reflection coating has a relatively high reflectance for the working wavelength range of the mirror, which is usually more than 40% or more than 60%. Reflective coatings designed for vacuum ultraviolet radiation typically achieve reflectivities greater than 90% or even greater than 95%. For reflective coatings that are reflective of extreme ultraviolet radiation, the achievable maximum reflectivities are typically lower and typically at most 70%.

The mirror has a substrate of a substrate material with poor thermal conductivity. A "poor thermal conductivity" in the context of this application is given in particular if the substrate material has a specific thermal conductivity of less than 10 W / (m · K). For many substrate materials that may be attractive due to low thermal expansion and / or other reasons, the thermal conductivity is still significantly lower. In particular, the specific thermal conductivity of the substrate material may be about 3 W / (m · K) or less.

In order to concentrate a heat redistribution largely on the area of the heat distribution intermediate layer, it may therefore be favorable to use substrate materials with very low thermal conductivity. In some embodiments, the substrate material has a specific thermal conductivity of less than 2W (mK) or less than 1.5W (mK). In particular, the aforementioned titanium-silicate glasses (eg ULE ^® with approximately 1.31 W / (m · K) at 25 ° C) or glass ceramics (such as Zerodur ^® (with about 1:46 W / (m · K) or CLEARCERAM ^® with about 1.51 W / (m · K)) or comparable substrate materials are used.

In general, it is advantageous if the heat conduction ratio WLV between the specific heat conductivity of the layer material and the specific heat conductivity of the substrate material is as large as possible. In some embodiments, WLV> 50 or WLV> 70 or even WLV> 100. This promotes a high homogenizing effect.

A prerequisite for an effective lateral redistribution of thermal energy by the heat distribution intermediate layer is the highest possible specific thermal conductivity of the layer material of the heat distribution intermediate layer, which is also referred to in this application as an intermediate layer material. In general, it is advantageous if the interlayer material has a specific thermal conductivity of more than 50 W / (m · K) or more than 100 W / (m · K) or more than 200 W / (m · K) or more than 500 W / (m · K).

The interlayer material may be, for example, a metal or a metal alloy. Because of their high specific thermal conductivity, for example, aluminum or copper or silver or alloys with one of these materials as the main constituent in question, if necessary, nickel or other metals.

In some embodiments, the interlayer material is a non-metallic material. For example, the use of crystalline semiconductor materials as interlayer material is possible. For example, the heat distribution intermediate layer can consist exclusively or predominantly of crystalline silicon or crystalline germanium.

Crystalline semiconductor materials are here u. a. considered advantageous for the following reasons. In metals, the heat transfer occurs mainly by electrons. In the Wiedemann-Frantzian law, the electrical and thermal conductivity in metals is linked together by the Lorentz number. In crystalline insulators or semiconductors, on the other hand, heat transport is dominated by lattice vibrations (phonons). The more undisturbed the grid can vibrate (so no impurities, impurities, alloys, etc.), the better the heat conduction. Fully or predominantly crystalline structures can thus be advantageous over also possible, partially or completely amorphous structures.

In some embodiments, the interlayer material, i. H. the layer material of the heat distribution intermediate layer, substantially of carbon. Depending on the hybridization conditions, the material properties of this layer material flow smoothly over from those of the graphite to those of the diamond. Preferably, diamond like carbon (DLC) is used as the interlayer material. A carbon layer may have a thermal conductivity of 500 W / (m · K) or more, or even 800 W / (m · K) or more, or even 1000 W / (m · K) or more, so that, in principle, a very efficient heat redistribution is possible.

Again, the structure of the interlayer material at the atomic level is important. Due to their symmetry, certain lattice forms prefer the heat transfer: Thus, due to the purely cubic crystal geometry and the equal length of tetrahedral bonds (sp ³ ), the phonon propagation over very wide ranges is undisturbed, resulting in the good thermal conductivity. The more amorphous the layer, the lower the thermal conductivity. Therefore, the thermal conductivity of DLC is variable and varies depending on the manufacturing method. The diamond-like properties of DLC are determined by the percentage of sp ³ hybridizations that make up the diamond crystal structure. A high proportion of sp3 hybridizations is considered favorable.

A layer consisting essentially of diamond-like carbon (DLC) is also referred to simply as "DLC layer" in this application.

In order to allow a sufficiently strong heat flow within the heat distribution intermediate layer under all operating conditions, the heat distribution intermediate layer should generally have a layer thickness of at least 1 μm. With layer thicknesses clearly below, an effective heat distribution is usually only imperfectly possible. Frequently, layer thicknesses of 10 μm or more are advantageous.

The ability of the heat distribution intermediate layer to effectively redistribute heat energy may also be indicated by the heat conduction product WLP, which for the purposes of this application is defined as the product of the specific thermal conductivity of the interlayer material (in [W / (m.K)]) and the layer thickness of the heat distribution intermediate layer (in [m]). Preferably, the heat conduction product WLP of the heat distribution intermediate layer is at least 1 × 10 ^-3 W / K, in particular, the heat conduction product may be greater than 1 × 10 ^-2 W / K or even greater than 1 × 10 ^-1 W / K.

On the other hand, while it may be desirable to have the largest possible layer thicknesses of the heat distribution intermediate layer in view of maximizing the heat distribution efficiency, it is also to be noted that adverse effects due to thermal expansion of the heat distribution intermediate layer may increase with increasing layer thickness. Therefore, it is usually favorable if the heat distribution intermediate layer has a layer thickness of at most 500 μm, wherein preferably the layer thickness is less than 200 μm. If these upper limits of the layer thickness are significantly exceeded, as a rule there are hardly any advantages with regard to the heat distribution, while possible problems due to thermal expansion can instead increase.

In preferred embodiments, the layer thickness of the heat distribution intermediate layer is between about 20 microns and about 100 microns. This achieves a good compromise between efficient heat distribution and low absolute thermal expansion.

Since reflection coatings in the EUV or VUV range often have total layer thicknesses in the order of up to 1 μm, a layer thickness ratio between the layer thickness of the heat distribution intermediate layer and the total layer thickness of the reflection coating applied directly or with intermediate layer is at EUV levels and VUV Mirrors usually at least 10 or at least 50.

The heat distribution intermediate layer may be in direct contact with the reflection coating applied thereon, whereby a particularly good heat conduction contact is possible. A first (substrate-next) layer of the reflection coating can therefore be or are applied directly to the heat distribution intermediate layer.

If the free surface of the heat distribution intermediate layer should not be directly coated after its production, for example due to a surface roughness exceeding the specification, the surface of the heat distribution intermediate layer may be processed by polishing or another smoothing material processing process before applying a subsequent layer to produce low surface roughness. It is also possible to reduce the surface roughness of the heat distribution intermediate layer by a smoothing coating process by forming a smoothing layer between the heat distribution intermediate layer and the reflection coating.

In other embodiments, prior to the application of the reflective coating, a polishing layer is applied to the heat distribution intermediate layer which consists of a polishing layer material which can be provided with an optically smooth surface by means of polishing. In some embodiments, for this purpose, a layer of amorphous silicon is applied, which can be processed by polishing with established machining processes with high surface quality, in particular with low surface roughness. Subsequently, the reflection coating can be applied.

The heat distribution intermediate layer may be applied directly to a correspondingly processed front surface of the substrate such that the interlayer material is in direct contact with the substrate material. In other embodiments, between the heat distribution intermediate layer and the substrate (at least) another intermediate layer is arranged, the layer properties of which may be designed, for example, such that an improved bond strength between substrate and heat distribution intermediate layer results. Depending on the substrate material, the layer material of the further intermediate layer can also be selected such that an adaptation of the thermal expansion coefficients between heat distribution intermediate layer and substrate results. In some embodiments, the further intermediate layer is an intermediate adhesion layer, wherein, for example, hexamethyldisiloxane (HDMSO), titanium or chromium may be provided as a material for the further intermediate layer.

In some embodiments, a mirror has only a single heat distribution interface between substrate and reflective coating. This can be favorable, inter alia, for reasons of ease of manufacture. However, it is also possible to provide two or more intermediate heat distribution layers, between which further layers of poorer or more thermally conductive layer materials may be located. As a result, if necessary, a profile with varying thermal conductivity can be created perpendicular to the layer extension. Such layer structures may e.g. also be low in order to keep low layer stresses in the heat distribution intermediate layer.

According to another formulation, the invention relates to a mirror comprising a substrate made of a substrate material and a reflective coating applied to the substrate which is reflective of vacuum ultraviolet radiation or extreme ultraviolet radiation, the mirror being characterized by heat distribution intermediate layer disposed between the substrate and the reflection coating, which has a layer thickness and consists of a layer material having a specific thermal conductivity, wherein a heat conduction product of the heat distribution intermediate layer is defined as the product of the specific thermal conductivity of the layer material and the layer thickness of the heat distribution Intermediate layer and wherein the heat conduction product of the heat distribution intermediate layer is at least 1 × 10 ^-3 W / K.

The heat conduction product may even be greater than 1 × 10 ^-2 W / K, in particular greater than 1 × 10 ^-1 W / K.

In particular in connection with substrates which have poor thermal conductivity (with a specific thermal conductivity of less than 10 W / (m.K)), considerable practical advantages can result. Substantial heat redistribution is also possible with higher thermal conductivity substrate materials whose specific thermal conductivity is equal to or greater than 10 W / (m · K).

The invention also relates to an optical system for a microlithography projection exposure apparatus having at least one mirror of the type described in this application. The optical system usually has one or more further optical elements. For systems operating at working wavelengths from the VUV range, the other optical elements may be lenses and / or mirrors. Systems for EUV lithography usually provide one or more additional mirrors and no lenses. The optical system may, for example, be a projection objective of a microlithography projection exposure apparatus. By using at least one mirror according to this disclosure, thermally induced aberrations, e.g. due to deformations of the wavefront, are significantly reduced compared to conventional systems. Alternatively or additionally, at least one mirror of the type described in this application can be used in an illumination system of a microlithography projection exposure apparatus.

The invention also relates to methods for producing a mirror. In this case, a substrate made of a substrate material is used, which has a specific thermal conductivity of less than 10 W / (m · K). A front surface of the substrate is processed to produce a surface having a predetermined surface shape. The term "surface shape" refers to both the macro-shape (eg concave, convex, plane, non-rotationally symmetric (free-form surface), waviness etc. as well as to the microform (eg characterized by values for surface roughness, etc.) Furthermore, a reflection coating The reflective coating is reflective to vacuum ultraviolet radiation or extreme ultraviolet radiation In the finished mirror, the reflective coating is carried by the substrate The method is characterized in that after processing the front surface of the substrate and prior to generation Reflective coating a heat distribution intermediate layer is produced, which consists of a layer material having a specific thermal conductivity, the at least 10th times as great as the specific thermal conductivity of the substrate material.

These and other features will become apparent from the claims but also from the description and drawings, wherein the individual features each alone or more in the form of sub-combinations in an embodiment of the invention and in other fields be realized and advantageous and protectable Can represent versions. Embodiments are illustrated in the drawings and are explained in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

1 shows a schematic sectional view of an embodiment of an EUV radiation-reflective mirror according to the invention;

2 shows a schematic detail of the illuminated area A from 1 ;

3 shows a schematic lateral temperature profile in the region of the illuminated area A. 2 ;

4 to 8th show simplified simulations of the spatial temperature distribution in a substrate cross-section along a cutting axis, which begins in the center of an illuminated area and ends at the edge of the substrate;

9 shows a comparative diagram in which the temperatures at selected points of the mirror are shown as a function of the layer thickness of the heat distribution intermediate layer;

10 shows an embodiment of an EUV microlithography projection exposure apparatus with a projection lens, which includes a mirror according to an embodiment of the invention; and

11 shows a schematic sectional view of an embodiment of a reflective VUV radiation mirror according to the invention.

DETAILED DESCRIPTION PREFERRED

EMBODIMENTS

1 shows a schematic representation of an embodiment of an EUV mirror 100 , The term "EUV level" in this context means that the mirror is designed to have the highest possible degree of reflection in the wavelength range of extreme ultraviolet radiation (EUV radiation). 2 shows a schematic detail of the illuminated area A from 1 ,

The below also simply as a mirror 100 designated EUV levels 100 is designed as a front surface mirror and has a substrate 112 , whose concave curved front surface 114 is formed as an optical surface processed with optical quality. The mirror 100 is intended for installation in an optical system of an EUV microlithography projection exposure apparatus and has on its front surface 114 a reflective coating 116 in the form of a multi-layer arrangement, which has a high reflectance for EUV radiation with a useful wavelength in the range of 5 to 15 nm. The reflection coating can be constructed, for example, with molybdenum / silicon alternating layers. It can have uniform or locally varying layer thicknesses.

In general, an EUV-reflective reflection coating has a multilayer laminate having a plurality of bilayers, each having alternately deposited layers of a higher refractive index (also called a spacer) layer material and a relatively lower real part laminate the refractive index (also called "absorber") have. In the example, relatively thin layers of molybdenum (Mo) are applied as an absorber material alternately with relatively thicker layers with silicon (Si) as a spacer material. A layer pair may also contain at least one further layer, in particular an intermediate barrier layer, which may for example consist of C, B ₄ C, Si _x N _y , SiC or a composition with one of these materials and should prevent interdiffusion at the interface. As a result, permanently sharply defined interfaces can be ensured even under radiation exposure. At the surface of the layer stack remote from the substrate, it is also possible to apply a cap layer to protect the underlying layers. The cover layer may, for example, ruthenium, rhodium, gold, palladium, silicon, titanium or molybdenum as well as optionally their oxides, nitrides or carbides (for example, SiO _2, Si _x N _y, SiC) or contain one of these materials. The free surface of the cover layer forms the beam entry surface. Also possible are non-periodic reflective coatings.

Examples of suitable EUV reflection coatings are, for example, in the patent US 6,011,646 whose disclosure content is incorporated herein by reference.

The EUV radiation 130 falls in operation from the substrate 112 On the opposite side of the reflective coating and is reflected at the coated front surface. The multilayer reflection coating acts as a Bragg reflector.

The mirror 100 is exemplified as a concave mirror with positive refractive power. However, it can also be embodied as a convex mirror with negative refractive power or as a plan mirror without refractive power. The optical surface may be designed as a spherical or aspherical rotationally symmetric surface, but possibly also as a non-rotationally symmetric (rotationally asymmetric) freeform surface. The diameter of the mirror is adapted to the respective application. In a projection objective for a microlithography projection exposure apparatus, the diameter is typically between 100 mm and 500 mm; larger or smaller diameters are also possible.

The substrate 112 consists of a substrate material with an extremely low coefficient of thermal expansion, which is less than 0.1 · 10 ^-6 K ^-1 in the range around room temperature (at 20 ° C), wherein the coefficient of thermal expansion is preferably at least half an order of magnitude lower, eg at maximum 5 · 10 ^-8 K ^-1 . Such materials are sometimes referred to as ultra-low-expansion materials.

In the embodiment, the substrate 112 essentially of a titanium silicate glass ((SiO ₂ -TiO ₂ ) glass) with a high proportion of at least 90% by weight SiO ₂ and a predominantly titanium oxide (TiO ₂ ) remaining portion (eg about 7% by weight) , Suitable glass materials are available for example under the brand ULE ^® glass (Corning, Inc). For the temperature range between 5 ° C and 35 ° C, a mean thermal expansion coefficient of 0 + 30 · 10 ^-9 K ^{-1 is} given. Also, the specific thermal conductivity of the substrate material is very low at about 1.31 W / (m · K) at 25 ° C.

In a non-illustrated embodiment, the substrate material of the substrate is a glass-ceramic containing crystalline phase portions distributed in a glass matrix. By combining the thermal characteristics of the different phases extremely low coefficients of thermal expansion can be achieved, which in some temperature ranges can even be zero or slightly negative.

Between the substrate 112 and the reflection coating 116 The multilayer multilayer coating is a single heat distribution intermediate layer 120 arranged, which consists of a layer material (intermediate layer material) whose specific thermal conductivity is at least one order of magnitude, ie at least by a factor of 10) greater than the specific thermal conductivity of the substrate material.

In the example, the heat distribution intermediate layer without the interposition of another intermediate layer is directly on the front surface 114 of the substrate 112 applied so that a large-area physical contact between the substrate near the first interface 122 the heat distribution intermediate layer and the front surface 114 consists. Furthermore, the substrate-remote second interface 124 the heat distribution intermediate layer directly into contact with the substrate-next single layer of the reflective coating 116 , which is thus applied directly to the heat distribution intermediate layer without the interposition of another layer.

The heat distribution intermediate layer consists essentially of diamond-like carbon (DLC), which is why it can simply be referred to as a "DLC layer". In this material, the carbon atoms are essentially without long-range order. Depending on the sp ² : sp ³ hybridization ratio, the material properties are between those of graphite and those of diamond. Both the thermal expansion and thermal conductivity of DLC layers are highly dependent on the ratio of sp ³ (diamond) to sp ² (graphite) hybridization. Since the thermal expansion coefficient of diamond at about 1.2 · 10 ^-6 1 / K and that of graphite depending on the orientation between about 0.5 and 6 · 10 ^-6 1 / K, the thermal expansion coefficient of the DLC layer is in the first approximation in the order of 1 · 10 ^-6 1 / K.

A special feature of this layer material is the extremely high specific thermal conductivity, which is significantly greater than that of highly conductive metals and in the example may be in the order of up to about 1000 W / (m · K), possibly even higher. The specific thermal conductivity of the heat distribution intermediate layer thus exceeds the specific thermal conductivity of the substrate material (about 1.31 W / (m · K)) and also that of the reflection coating 116 (about 0.1 W / (m · K) to about 2.5 W / (m · K) depending on the basis of the estimate) by several orders of magnitude.

The perpendicular to the surface normal of the substrate front surface 114 (in the z direction) measured layer thickness of the heat distribution intermediate layer is dimensioned so that the heat distribution intermediate layer is able to transport larger amounts of heat in the lateral direction, ie in all directions perpendicular to the layer normal. In the example case of EUV mirrors, layer thicknesses in the range between approximately 20 μm and approximately 100 μm have for this purpose proved to be suitable. The optimum layer thickness depends primarily on the thermal conductivity achievable in the diamond-like intermediate layer, which in turn depends on the layer deposition process.

The heat distribution intermediate layer is accordingly characterized by a heat conduction product WLP in the order of 0.02 to 0.1 W / K.

By the interposition of a very good thermal conductivity heat distribution intermediate layer between the relatively poor thermal conductivity reflective coating 116 and the likewise very poorly thermally conductive substrate material, it is possible, the substrate material to a considerable extent of operationally occurring inhomogeneous temperature distributions in the region of the reflection coating 116 to decouple. It can thereby be achieved that spatially inhomogeneous irradiation, which may well be desired depending on the illumination setting of the optical system, does not or only to a tolerable extent lead to inhomogeneous heating of the substrate and associated thermally induced deformations of the mirror near the mirror surface. This is based on the 2 to 9 explained in more detail. The lifetime of the reflection coating can also be extended if necessary by reducing disadvantageous thermally induced layer changes, such as compaction.

In the example of 1 becomes the mirror 100 operated projection exposure system operated with a dipole illumination setting. The mirror is disposed near a pupil surface of the projection lens. A significant portion of the radiation passing through the optical system is thereby substantially at two diametrical to the optical axis 113 concentrated opposite and lying away from the optical axis areas A and B. There, the illumination intensity is particularly high compared to surrounding areas.

The locally concentrated irradiation of the reflection coating 116 in area A, due to absorption processes within the layer materials of the reflection coating, local heating of the area of the local irradiation occurs in comparison with the adjacent, non or less intensively irradiated areas. If the x-coordinate x = 0 is chosen for the center of the irradiated area A, then the in 3 Such a local temperature increase would, in the absence of a heat distribution intermediate layer, lead to a local heating of the substrate material below the irradiated area, which in turn would result in a more or less pronounced deformation depending on the thermal expansion coefficient of the substrate material would cause. Even if, as in this case, a substrate material with a very low coefficient of thermal expansion is selected, the thermally induced deformations can have a disturbing effect.

By interposing a very good thermal conductivity heat distribution intermediate layer, the substrate material can be largely decoupled from the spatially inhomogeneous heat generation in the region of the reflection coating. In 2 this is schematically indicated by means of heat flow arrows that a large part of the heat generated through the heat distribution intermediate layer is parallel to the layer extension or perpendicular to the z-direction laterally outward (heat flow arrows W1, W2) and only a much smaller proportion (heat flow arrows W3, W4) can still get into the substrate. Accordingly, the substrate material is thermally largely decoupled from the reflective coating.

The thermally homogenizing effect of the heat distribution intermediate layer is primarily dependent on the specific thermal conductivity of the intermediate layer material and its layer thickness. For the quantitative demonstration of the homogenizing effect, simulations were carried out, the results of which were described in the 4 to 8th represented and in 9 are summarized again.

The 4 to 8th show in each case the simplified simulations of the temperature distribution in a substrate cross-section along a cutting axis which begins in the center of an illuminated area (for example the illuminated area A) (x = 0 mm) and ends at the edge of the substrate (x = 50 mm). The ordinate plots the depth coordinate z [mm], which runs in the normal direction of the mirror surface or the layer extent. At z = 0 mm, the interface between the heat distribution intermediate layer is located 120 and the reflective coating 116 , That is, the substrate facing interface of the reflection coating 116 , For the simulations, the reflective coating has a thickness of 1 μm and is homogeneously heat-treated between x = 0 mm and x = 10 mm.

Between the reflection coating and the substrate, heat distribution intermediate layers of different layer thickness (0 μm, 1 μm, 10 μm, 50 μm and 100 μm) were simulated. Due to the low layer thicknesses of the two layers (heat distribution intermediate layer and Reflection coating) compared to the substrate, they are not recognizable as separate elements in the figures. The geometry of the array and the power densities of the incident illumination or heat generation were taken from typical scenarios of thermal mirror loading in an EUV projection lens. Since the negative x-axis shows the same temperature curve, these redundant points were not displayed.

For simulatory reasons, a flat heat sink with a constant temperature T = 300 K was assumed at z = -20 mm. In all simulations, the coldest spot T ₄ was located near the heat sink at the outer edge of the considered area, ie at a location greatest distance to the area of heat input. Directly in the center of the irradiation spot on the free surface is the point x = 0 mm with the highest temperature T ₁ . The temperature T ₂ prevails at the edge of the illuminated area at x = 10 mm, while the temperature T ₃ prevails on the surface at the edge of the illustrated substrate area (x = 50 mm). The lines within the diagrams respectively represent isothermal lines (isotherms), ie lines of the same temperature T relative to the temperature T ₄ at the coldest point.

Already a first qualitative comparison of the figures shows that the heat is distributed spatially with increasing layer thickness of the heat distribution intermediate layer on the mirror and in the substrate and thus both absolute and relative temperatures fall in the illuminated area.

While, for example, without a heat distribution intermediate layer ( 4 ) in the center of the illuminated area temperature increases compared to the coldest point up to about 55 K, the corresponding elevation at 10 micron layer thickness ( 6 ) only about 35 K and at 100 microns layer thickness ( 8th ) is only slightly above 20 K. It can be seen directly from the spatial density of the isothermal lines that the temperature gradients within the substrate become ever smaller as the layer thickness of the heat distribution intermediate layer increases.

9 shows a comparative diagram in which the temperatures T (in [K]) at the selected points with temperatures T ₁ to T ₄ depending on the layer thickness d [μm] of the heat distribution intermediate layer (x-axis) are shown. As mentioned, the point x = 0 mm with the highest temperature T ₁ is located directly in the center of the irradiation spot. At this location, the decrease in temperature is greatest with increasing layer thickness of the heat distribution intermediate layer. At the edge of the illuminated area (point x = 10 mm, temperature T ₂ ), a decrease in the temperature is likewise recognizable, with both the extent of the absolute temperatures and the extent of the decrease being somewhat lower than in the center of the illumination spot. At the edge of the area shown (x = 50 mm, T ₃ ), the temperature rises slightly from 324 K to approximately 326.5 K due to the homogenizing effect of the heat distribution intermediate layer. Especially this slight increase in temperature shows that heat is redistributed by the heat distribution intermediate layer from the particularly strongly heated area to less heated areas, so that a homogenizing effect results. The coldest spot T ₄ in the vicinity of the heat sink constantly maintains its temperature 324 K.

The results shown by way of example can be transmitted qualitatively for other power densities. For example, to account for the influence of increased power density at the location of heat generation, the difference between the warmest and the coldest points is formed and compared for a 100 μm simulation and without a heat distribution intermediate layer. The difference between T ₁ and T ₄ without the heat distribution intermediate layer is about 9.4 K, while in the presence of a 100 μm thick heat distribution intermediate layer, the difference is only 4.0 K and thus only just under 43% of the original temperature.

Now, if the power density increases, these relative temperature strokes scale largely linear. For example, if the power density is increased by a factor of 5, the temperature difference will increase to 47 K in the absence of a heat distribution interlayer, while with the 100 μm DLC layer the difference would also reach the 43% value of 20K.

In contrast to various heating scenarios in which more and more heating power must be introduced to homogenize the temperature distribution and thus the absolute temperatures continue to increase, the relative temperature distribution remains the same for a given thickness of the homogenization when using a homogenization layer or heat distribution intermediate layer. As a result, the increase in absolute temperatures is much less pronounced than in heating scenarios.

Thus, using a heat distribution interlayer, the relative thermal expansion of the substrate material can be significantly reduced as compared to conventional systems without a heat distribution interlayer. Furthermore, the life of the reflection coating can be increased because the local thermal Load of the reflective coating in the example case is almost halved.

In a method of making an EUV mirror with heat distribution intermediate layer, the front surface first becomes 114 of the substrate 112 polished to optical quality, for example, a roughness of less than about 10 nm is generated. After that, it is directly on the polished front surface 114 the heat distribution intermediate layer applied by a suitable coating method. In the exemplary embodiments, the heat distribution intermediate layer is applied by means of plasma-enhanced chemical vapor deposition (PECVD). Good layer qualities can be achieved, for example, with growth rates between approximately 1 μm / h and 2 μm / h.

In the usually desired layer thicknesses of the DLC layer in the range between 10 .mu.m and 100 .mu.m or more usually the free surface of the DLC layer after completion of the coating is not directly suitable for applying the reflection coating, as usually high demands the deformation and the pass of the surface to be coated are to be fulfilled. Therefore, in preferred embodiments, after the deposition of the heat distribution interlayer, a surface suitable as a reflective coating underlay is provided which satisfies the dimensional and dimensional tolerances. For this purpose, immediately the free surface of the DLC layer can be processed by a polishing step to reduce the surface roughness and to produce the mold. Since a polishing of the very hard layer material is expensive, it is provided in some embodiments to apply a polishing layer made of a polishable layer material, for example amorphous silicon, before the deposition of the reflection coating. Its surface is then polished before the first layer of the reflective coating 116 is applied.

For the production of the multilayer coating arrangement serving as reflection coating, all conventional production methods can be used.

Although the heat distribution intermediate layer, as in the example, directly on the optical quality machined front surface 114 can be applied to the substrate, it is provided in other embodiments, to introduce between the substrate surface and the heat distribution intermediate layer still another intermediate layer. It may be, for example, an intermediate adhesion layer that improves the adhesion between the substrate and the heat distribution intermediate layer. The further intermediate layer can also be designed so that it can serve as a stress compensation layer.

Depending on the material combinations, however, it is also possible in many cases that functionalities such as stress compensation or protection of the substrate from EUV radiation can also be realized by the heat distribution intermediate layer. As a result, the production of such an EUV mirror in relatively few steps is possible. In addition, the number of necessary interfaces within the layer structure is kept low, which can be advantageous overall for the lifetime of the entire layer system.

An EUV mirror with heat distribution interlayer offers particular advantages when there is a risk that high local power input and poor thermal conductivity of the substrate could affect the performance of the entire layer assembly or the EUV mirror-equipped optical system.

10 shows optical components of an EUV microlithography projection exposure machine 1000 for exposing one in the region of an image plane 1060 a projection lens 1030 arranged radiation-sensitive substrate having at least one image of one in the region of an object plane 1020 of the projection lens arranged pattern of a reflective pattern generating device or mask.

The plant is using the radiation of a primary radiation source 1014 operated. A lighting system 1010 serves to receive the radiation from the primary radiation source and to form illumination radiation directed at the pattern. The projection lens 1030 serves to image the structure of the pattern onto a photosensitive substrate.

The primary radiation source 1014 may be, inter alia, a laser plasma source or a gas discharge source or a synchrotron-based radiation source. Such radiation sources generate radiation 1020 in the EUV range, in particular with wavelengths between 5 nm and 15 nm. In order for the illumination system and the projection objective to be able to work in this wavelength range, they are constructed with components that are reflective for EUV radiation.

The of the radiation source 1014 outgoing radiation 1020 is done by means of a collector 1015 collected and into the lighting system 1010 directed. The lighting system comprises a mixing unit 1012 , a telescope optics 1016 and a field-forming mirror 1018 , The lighting system shapes the radiation and illuminates it Illuminating field made in the object plane 1020 of the projection lens 1030 or near it. The shape and size of the illumination field determine the shape and size of the effectively used object field in the object plane 1020 ,

In the object plane 1020 When operating the system a reflective reticle or another reflective pattern generating device is arranged. The projection lens 1030 here has six mirrors M1 to M6 and forms the pattern of the pattern generating device in the image plane, in which a substrate to be exposed, for example, a semiconductor wafer is arranged.

The mixing unit 1012 consists essentially of two faceted mirrors 1070 . 1080 , The first facet mirror 1070 is arranged in a plane of the illumination system that is the object plane 1020 is optically conjugated. It is therefore also called a field facet mirror. The second facet mirror 1080 is arranged in a pupil plane of the illumination system, which is optically conjugate to a pupil plane of the projection lens. It is therefore also referred to as a pupil facet mirror.

With the help of the pupil facet mirror 1080 and the downstream in the beam path imaging optical assembly, the telescope optics 1016 and the grazing incidence field-forming mirror 1018 includes the individual specular facets (individual mirrors) of the first facet mirror 1070 mapped into the object field.

The spatial (local) illumination intensity distribution at the field facet mirror 1070 determines the local illumination intensity distribution in the object field. The spatial (local) illumination intensity distribution at the pupil facet mirror 1080 determines the illumination angle intensity distribution in the object field.

EUV projection exposure systems with similar basic structure are for example from WO 2009/100856 A1 or WO 2010/049020 A1 the disclosure of which is incorporated herein by reference.

Individual mirrors of the microlithography projection exposure apparatus, in particular at least one mirror of the illumination system 1010 and / or at least one mirror of the projection lens 1030 , are embodied as thermally self-compensating EUV mirrors according to one embodiment of this disclosure.

Thermally critical components are, in particular, the mirrors of the projection objective 1030 which, due to the heating by the EUV radiation, only change their shape to a small extent, whereby, however, the image of the object in the image plane 1060 can be disturbed sensitively. In order to minimize heat-induced deformations of the mirrors, all mirrors M1 to M6 have a mirror substrate made of a titanium silicate glass with a thermal expansion coefficient of a few 10 ^-9 K ^-1 (ie few parts per billion per Kelvin). In particular, a material may be used for which a mean thermal expansion coefficient of 0 + 30 · 10 ^-9 K ^{-1 is} given for the temperature range between 5 ° C and 35 ° C.

The heating of the mirror of the projection lens 1030 depends on the one hand on their order in the beam path. Thus, the integral power of the incident EUV radiation decreases from mirror to mirror due to absorption in the multilayer coatings. On the other hand, the heating also depends on the diameter of the mirror. If it is a small mirror, then the integral light output hits a smaller area than with a large mirror, so that smaller mirrors are heated more. This is the case, in particular, in the third mirror M3 and the fifth mirror M5 in the beam passing direction.

Furthermore, the heating of the mirrors does not always take place homogeneously over the mirror surface. In particular, the second mirror M2 of the projection objective, which is in the beam passing direction, becomes 1030 , which is arranged in the pupil plane, depending on the so-called lighting setting usually have a non-homogeneous illumination. The illumination setting determines the angle spectrum with which an object to be imaged within the object field of the illumination system 1010 is illuminated. In other words, the illumination setting describes the local intensity distribution of the illumination of the entrance pupil of the projection objective. This may be, for example, a conventional illumination setting (corresponding to an axis-centered circular illumination area in the entrance pupil), an annular, a dipole, a quadrupole or another multipole illumination setting.

In a dipole illumination setting, the illumination of a pupil plane is characterized by two diametrically opposed intensity maxima lying outside the reference axis of the optical system. Thus, the mirror M2 arranged in the pupil plane is heated by absorption in the multilayer reflection coating mainly in two diametrically opposite regions (cf. 1 ). This may result in an astigmatic deformation of the mirror surface, in which the orientation of the Connection line of the particularly warm zones on the orientation of the dipole depends. The heat distribution can therefore essentially have a 2-fold rotational symmetry.

In order to minimize the effects of non-uniform heating on imaging quality, an EUV mirror may be used in accordance with one embodiment of this disclosure. For example, the second mirror M2 may be between the substrate 112 and the multilayer reflective coating 116 a very good heat-conducting heat distribution intermediate layer 120 diamond-like carbon (DLC), which automatically effects lateral heat redistribution.

As a result, temperature gradients in the region of the mirror surface in the direction of a temperature homogenization are automatically reduced or reduced, so that the lateral redistribution of heat energy leads to a reduction of thermally induced aberrations.

If a different or different oriented inhomogeneous heat load of the mirror surface occurs after a change in the illumination setting, the EUV mirror automatically adapts (automatically) to the new intensity distribution and compensates for a considerable part of the inhomogeneity by lateral redistribution of the heat energy.

11 shows a schematic section through an embodiment of a VUV mirror 200 , The term "VUV mirror" in this context means that the mirror is designed to have the highest possible degree of reflection in the wavelength range of the vacuum ultraviolet radiation (VUV radiation).

The VUV mirror 200 is designed as a dielectrically enhanced front surface mirror and has a substrate 212 from a glass material or a glass ceramic. The front surface 214 of the substrate is formed as an optical quality processed optical surface. The mirror 200 is intended for installation in an optical system of a VUV microlithography projection exposure apparatus (eg projection lens) and has on its front surface 214 a reflective coating 216 in the form of a multi-layer array suitable for VUV radiation having a useful wavelength in the range of 193 nm has a high reflectance of more than 95%.

The reflection coating 216 consists essentially of an optically dense aluminum layer 217 with a layer thickness of approx. 150 nm and a dielectric interference layer system applied thereto 219 with three layers of alternately low refractive and high refractive dielectric material, eg fluoride materials and / or oxide materials. Their optical layer thicknesses can be in the range of 20% to 30% of the working wavelength.

Examples of suitable VUV reflection coatings are, for example, in the patent US 6,809,871 B2 whose disclosure content is to this extent made by reference to the content of this description.

Between the substrate 212 and the reflection coating 216 is a single heat distribution intermediate layer 220 arranged, which consists of a layer material (intermediate layer material) whose specific thermal conductivity is at least one order of magnitude, ie at least by a factor of 10) greater than the specific thermal conductivity of the substrate material.

In the example, the heat distribution intermediate layer without the interposition of another intermediate layer is directly on the front surface 214 of the substrate 212 applied so that a large-area physical contact between the substrate near the first interface 222 the heat distribution intermediate layer and the front surface 114 consists. Furthermore, the substrate-remote second interface 224 the heat distribution intermediate layer directly into contact with the substrate-next single layer of the reflective coating 116 that through the aluminum layer here 217 is formed.

The heat distribution intermediate layer has a layer thickness which is at least 10 times as large as the layer thickness of the aluminum layer belonging to the reflection coating 217 and consists essentially of diamond-like carbon (DLC), whose specific thermal conductivity is several times greater than that of aluminum.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• EP 0955565 A2 [0014]
• US 2002/0074115 A1 [0015]
• DE 10050125 [0015]
• WO 2010/020337 A1 [0016]
• EP 0678768 B1 [0017]
• US 6011646 [0061]
• WO 2009/100856 A1 [0102]
• WO 2010/049020 A1 [0102]
• US 6809871 B2 [0114]

Claims (19)

Mirror ( 100 . 200 ) with: a substrate ( 112 . 212 ), which consists of a substrate material having a specific thermal conductivity of less than 10 W / (m · K) and a reflection coating applied to the substrate ( 116 . 216 ), which is reflective for ultraviolet or ultraviolet radiation ultraviolet radiation, characterized by a between the substrate ( 112 . 212 ) and the reflection coating ( 116 . 216 ) heat distribution intermediate layer ( 120 . 220 ) of a layer material having a specific thermal conductivity which is at least 10 times the specific thermal conductivity of the substrate material. A mirror according to claim 1, wherein a heat conduction ratio WLV between the specific heat conductivity of the sheet material and the specific heat conductivity of the substrate material is greater than 50. A mirror according to claim 1 or 2, wherein the layer material of the heat distribution intermediate layer ( 120 . 220 ) has a specific thermal conductivity of more than 50 W / (m · K), wherein the specific thermal conductivity of the layer material is preferably greater than 500 W / (m · K). A mirror according to any one of the preceding claims, wherein the layer material of the heat distribution intermediate layer ( 120 . 220 ) consists essentially of carbon, in particular substantially diamond-like carbon. A mirror according to any one of the preceding claims, wherein the heat distribution intermediate layer ( 120 . 220 ) has a layer thickness of at least 1 micron, wherein the layer thickness is preferably at least 10 microns. A mirror according to any one of the preceding claims, wherein the heat distribution intermediate layer ( 120 ) has a layer thickness of less than 500 microns, in particular less than 200 microns. A mirror according to any one of the preceding claims, wherein the heat distribution intermediate layer ( 120 . 220 ) has a layer thickness between 10 microns and 100 microns. A mirror according to any one of the preceding claims, wherein a heat conduction product of the heat distribution intermediate layer ( 120 . 220 ) is defined as the product of the specific thermal conductivity of the layer material and the layer thickness of the heat distribution intermediate layer, wherein the heat conduction product of the heat distribution intermediate layer is at least 1 × 10 ^-3 W / K, wherein the heat conduction product is in particular greater than 1 × 10 ^-2 W / K is. A mirror according to any one of the preceding claims, wherein between the heat distribution intermediate layer and the reflective coating is disposed a polishing layer consisting of a polishing layer material which can be provided with a smooth optical surface by means of polishing. A mirror according to any one of the preceding claims, wherein a further intermediate layer is disposed between the heat distribution intermediate layer and the substrate. Mirror according to one of the preceding claims, in which the reflection coating ( 116 ) comprises an ultraviolet region (EUV) ultraviolet ray reflective multilayer laminate comprising a plurality of pairs of layers having alternating layers of a high refractive layer material and a low refractive layer material. Mirror ( 100 . 200 ) with: a substrate ( 112 . 212 ), which consists of a substrate material, and a reflection coating applied to the substrate ( 116 . 216 ), which is reflective for ultraviolet or ultraviolet radiation ultraviolet radiation, characterized by a between the substrate ( 112 . 212 ) and the reflection coating ( 116 . 216 ) heat distribution intermediate layer ( 120 . 220 ) which has a layer thickness and consists of a layer material having a specific heat conductivity, wherein a heat conduction product of the heat distribution intermediate layer ( 120 . 220 ) is defined as the product of the specific thermal conductivity of the layer material and the layer thickness of the heat distribution intermediate layer and wherein the heat conduction product of the heat distribution intermediate layer is at least 1 × 10 ^-3 W / K. A mirror according to claim 12, wherein the heat conduction product is greater than 1 x 10 ^-2 W / K, in particular greater than 1 x 10 ^-1 W / K. Mirror according to claim 12 or 13, characterized by the features of the characterizing portion of at least one of claims 2 to 2 to 7 or 9 to 11. Optical system of a microlithography projection exposure apparatus with at least one mirror according to one of claims 1 to 14. An optical system according to claim 15, wherein the optical system comprises a projection objective ( 1030 ) of the microlithography projection exposure apparatus. Optical system according to Claim 16, in which the mirror (M2) is located in the region of a pupil plane of the projection objective ( 1030 ) is arranged. A method of manufacturing a mirror comprising the steps of: providing a substrate made of a substrate material having a specific thermal conductivity of less than 10 W / (m · K); Processing a front surface of the substrate to produce a surface having a predetermined surface shape; and Producing a reflection coating, wherein the reflection coating is reflective for vacuum ultraviolet radiation or extreme ultraviolet radiation, characterized in that after the processing of the front surface of the substrate and before the generation of the reflection coating, a heat distribution intermediate layer consisting of a layer material having a specific thermal conductivity at least 10 times the specific thermal conductivity of the substrate material is produced. The method of claim 18, wherein the heat distribution intermediate layer is applied directly to the front surface of the substrate.

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