DE102012204833A1 - Mirror i.e. facet mirror, for use in lighting system for projection exposure system, has layer partially formed from graphene and arranged as finishing layer on layer arrangement, and substrate made of material e.g. glass and ceramic - Google Patents

Abstract

The mirror has a layer (500) partially formed from graphene. The layer is arranged as a finishing layer on a layer arrangement. A substrate is made of material e.g. glass, quartz glass, glass ceramic and ceramic. An adhesive layer is arranged between the graphene layer and the layer arrangement, where the layer arrangement comprises a layer subsystem. The graphene-containing layer is provided on a copper foil (501) by a chemical vapor deposition (CVD) method. The graphene-containing layer is arranged on a carrier film. An independent claim is also included for a method for manufacturing a mirror.

Description

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The present invention relates to mirrors for projection exposure apparatuses, in particular mirrors for projection exposure apparatuses operated with light in the wavelength range of the extreme ultraviolet spectrum and smaller wavelengths, and to methods for producing such mirrors.

STATE OF THE ART

Microlithography projection exposure equipment is used for the production of microstructured components by means of a photolithographic process. In this case, a structure-carrying mask, the so-called reticle, is illuminated with the aid of a light source unit and an illumination optical system and imaged onto a photosensitive layer with the aid of projection optics. In this case, the light source unit provides radiation which is conducted into the illumination optics. The illumination optics serve to provide a uniform illumination with a predetermined angle-dependent intensity distribution at the location of the structure-supporting mask. For this purpose, various suitable optical elements are provided within the illumination optics. The thus-exposed structure-bearing mask is imaged onto a photosensitive layer with the aid of the projection optics. In this case, the minimum structure width that can be imaged with the aid of such projection optics is determined inter alia by the wavelength of the radiation used. The smaller the wavelength of the radiation, the smaller the structures can be imaged using the projection optics. For this reason, it is advantageous to use radiation in the EUV (extreme ultraviolet) wavelength range with wavelengths of 5 nm to 20 nm. At these wavelengths, mirrors are used as optical elements which must have a high reflectivity.

For example, mirrors for the EUV wavelength range around 13 nm with high reflectivity values are off DE 101 55 711 A1 known. The mirrors described therein consist of a layer arrangement applied to a substrate, which has a sequence of individual layers, a so-called multi-layer layer, wherein the layer arrangement comprises a plurality of layer subsystems, each of which has a periodic sequence of at least two individual layers forming a period different materials, wherein the number of periods and the thickness of the periods of the individual subsystems decrease from the substrate to the surface. Such mirrors have a reflectivity of greater than 30% at an incident angle interval between 0 ° and 20 °.

The angle of incidence is here defined as the angle between the direction of incidence of a light beam and the surface normal of the mirror at the point of impact of the light beam on the mirror. The angle of incidence interval results from the angular interval between the largest and the smallest considered angle of incidence of a mirror.

To achieve a high reflectivity of mirrors for the EUV wavelength range and losses due to stray light must be avoided, which leads to high demands on the surface roughness of such mirrors in the so-called HSFR (high spatial frequency roughness) range, see U. Dinger et al. "Mirror substrates for EUV lithography: progress in metrology and optical fabrication technology" in Proc. SPIE Vol. 4146, 2000 , in particular for the definition of the surface roughness in the HSFR region with spatial wavelengths of roughness of 10 nm to 1 μm and in the MSFR region with spatial wavelengths of roughness of 1 μm to 1 mm. Furthermore, such mirrors must ensure the high reflectivity values and the desired optical imaging quality over several years under continuous irradiation with EUV radiation of high intensity.

In this sense, it is important that mirrors, in particular mirrors for illumination systems, which are used within microlithography projection exposure apparatuses at wavelengths of less than 250 nm, have low surface roughness values in the HSFR range in order to avoid stray light losses.

DISCLOSURE OF THE INVENTION

OBJECT OF THE INVENTION

It is therefore an object of the present invention to provide mirrors for projection exposure apparatuses and corresponding production methods, which are distinguished by the fact that particularly smooth surfaces or boundary surfaces are present or can be provided in mirror layer systems in order to avoid scattering losses and to ensure high reflectivity. In particular, mirrors for lighting systems, such as faceted mirrors with low roughness are to be provided, which also maintain the properties over the longest possible service life. The corresponding manufacturing processes should be as efficient and easy as possible.

TECHNICAL SOLUTION

This object is achieved by mirrors having the features of claims 1 or 3 as well as methods for producing mirrors having the features of claims 7, 11 or 13 as well as an illumination system for a projection exposure apparatus having the features of claim 17. Advantageous embodiments are the subject of the dependent claims ,

In order to provide mirrors with surfaces within mirror layer systems with low roughness, is already in the DE 10 2010 041 502.2 respectively. US 61 / 387,214 It has been proposed to provide graphene layers which can bring about a smoothing, in particular in the high frequency spatial frequency range or in the shortwave spatial wave range. This is also the basis of the present invention. Accordingly, the disclosure of DE 10 2010 041 502.2 and US 61 / 387,214 fully incorporated herein by reference.

According to a first aspect of the present invention, the invention is based on the fact that, due to its properties, graphene is suitable for serving as a finishing layer for a layer arrangement of a mirror and can thereby provide a particularly smooth surface which at the same time satisfies the requirements for an inert finishing layer is insensitive to environmental influences and can reliably protect the underlying layers of a layer arrangement. Accordingly, a mirror is proposed for a projection exposure apparatus comprising a substrate and a layer arrangement, wherein the layer arrangement comprises at least one layer subsystem, which consists of a periodic sequence of at least two periods of individual layers, wherein the periods comprise two individual layers of materials, the different optical Have refractive indices, wherein at least one graphene layer is provided, which serves as a final layer.

According to a further aspect of the present invention, for which protection is sought on its own and in combination with other aspects of the present invention, a mirror is proposed which comprises a substrate and a layer arrangement, wherein the layer arrangement comprises at least one layer subsystem consisting of a periodic sequence of at least two periods of monolayers, the periods comprising two monolayers of materials having different optical refractive indices, and wherein at least one graphene layer is provided. In addition, the substrate comprises a material of glass, quartz glass, ceramic, glass ceramic, silicon carbide, silicon infiltrated silicon carbide or amorphous silicon. As has been shown, graphene layers can also be arranged on such substrate materials, which lead to surface roughnesses being adjustable even for hard-to-polish facet mirrors or mirror facets, which make possible a corresponding use for mirrors for projection exposure apparatuses. In particular, a graphene layer can be provided as an intermediate layer between the substrate and a subsequent layer arrangement for reflection layers, so that smooth multi-layer layers can be formed. Accordingly, in the context of the present invention, the substrate is understood to be the base body of the mirror or of an independent mirror element, such as a mirror facet of a multi-part facet mirror, which does not yet have a coating. Optionally, the body contains a layer of easily polishable material, such as. B. the aforementioned amorphous silicon.

According to a further aspect of the present invention, for which protection is sought independently and independently of the other aspects as well as in combination with these aspects, it is proposed to arrange between a layer of graphene which is arranged underneath a layer arrangement of a mirror for a projection exposure apparatus and the layer arrangement to provide a primer layer to allow a good adhesion of the layer arrangement on the graphene layer and thus to ensure a reliable formation of a corresponding mirror.

The primer layer can be formed, for example, from nickel, which has a similar crystal structure, such as graphene.

For the purposes of this application, a layer of graphene is correspondingly understood to mean a layer which consists of at least one monolayer of carbon atoms, the carbon atoms having an sp ² hybridization.

However, the carbon atoms do not have to have one hundred percent sp ² hybridization, but in the context of the present invention it is already to be said that graphene or a graphene layer, if the planar monocrystalline structure of carbon has an sp ² hybridization of more than 75%. , in particular more than 90% of the carbon atoms. This can be determined, for example, by Raman spectroscopy or EDX experiments (EDX energy dispersive x-ray spectroscopy).

In the context of the present invention, a graphene layer also includes a graphene layer. containing layer, if not the entire layer is formed as a graph, but only parts have a graphene shape. In particular, graphene islands in layer formation may be sufficient to speak of a graphene layer in the present invention.

According to another aspect of the present invention, for which protection is sought independently and independently of the other aspects of the present invention, as well as in combination with these other aspects of the invention, a method is proposed in which a graphene layer by means of a layered base, on the graphene layer is arranged, is applied to a surface of a mirror substrate for a mirror of a projection exposure apparatus. In this case, the mirror substrate is understood to be the mirror in the production state in which the graphene layer is to be applied to a surface of the mirror substrate. It may therefore be a still completely uncoated or provided with a polishable layer mirror substrate from a mirror base according to the previous definition of a substrate or a mirror substrate, which already has partial layers of a layer arrangement. The latter thus differs from the substrate described above by the already applied layers. In the proposed method, the graphene layer-layered body composite is deposited on the mirror substrate so that both the layered body and the graphene layer can be placed in contact with the mirror substrate.

In the variant that the layer base body is arranged on the mirror substrate, the layer base body is connected by a suitable bonding method with the mirror substrate, since the layer base body remains on the mirror. All suitable methods can be used for bonding the layer base body to the mirror substrate, such as, for example, bonding, thermal bonding methods, soldering or other bonding methods. A wringing of the layer base body on the mirror substrate is conceivable.

In the second alternative, in which the graphene layer is applied to the mirror substrate, the layer base body is removed after application by suitable means, for example by stripping, chemical or thermal dissolution or the like.

The graphene layer can be deposited on the layer base by chemical vapor deposition (CVD) and then placed directly on the corresponding mirror substrate.

Furthermore, according to another aspect of the present invention, for which protection is independently sought after independently of the other aspects of the present invention, as well as in combination with these other aspects of the invention, the graphene-containing layer can be deposited directly on the mirror or mirror substrate are deposited by an atomic layer deposition (ALD atomic layer deposition). In this case, individual monolayers are deposited on graphene by a special chemical vapor deposition method, wherein the reaction components for the chemical reaction of the chemical vapor deposition are introduced separately from one another and successively into the reaction chamber. In addition, between the partial reactions, the reaction chamber can still be purged with an inert gas, so that the reactions are limited to the surface. Of course, several layers of graphene can be deposited one behind the other to obtain a suitable graphene layer.

In another method, which in turn is sought after independently and independently and in combination with the other aspects of the present invention, a graphene layer or a graphene-containing layer can be applied to a mirror by means of a so-called balloon membrane pressure technique , Here, an elastically deformable pressure membrane is provided which with a pressure medium, such as. B. a gaseous pressure medium or a liquid pressure medium is pressed against a mirror substrate of the mirror to be produced. Arranged on the pressure membrane is a graphene-containing layer or a graphene layer, which is transferred to the mirror substrate when the pressure membrane is pressed against the mirror substrate. The graphene-containing layer may be arranged on a carrier film in order to form a so-called composite film with the carrier film. The composite foil is in this case pressed onto the mirror substrate such that the graphene layer comes into direct contact with the mirror substrate.

The composite foil can be arranged floatingly on the pressure membrane via a liquid film in order to avoid the transmission of transverse forces and thus the cracking of the graphene layer. The carrier film of the composite film is removed after application of the graphene layer on the mirror substrate by stripping, chemical or thermal dissolution.

With such a method, in particular, a monolithic facet mirror with a Be provided a plurality of mirror facets or facet surfaces with a graphene layer, even if there should be levels between the facet surfaces.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings show in a purely schematic manner in FIG

1 a facet mirror in a projection exposure apparatus with a lighting system;

2 a perspective view of a first embodiment of a mirror according to the invention;

3 a further illustration of a facet mirror according to the invention;

4 in the sub-images 4a and 4b further embodiments of a facet mirror;

5 a still further illustration of an embodiment of a facet mirror;

6 a schematic representation of another mirror according to the invention;

7 a schematic representation of the mirror according to the invention with a protective layer SPL;

8th a schematic representation of another mirror according to the invention;

9 a schematic representation of a mirror according to the invention with a protective layer subsystem SPLS;

10 a schematic representation of another mirror according to the invention;

11 a schematic representation of a mirror according to the invention with a protective layer subsystem SPLS;

12 a representation of a first form of application of a graphene layer;

13 in the sub-images a) to c) different manufacturing steps for forming a facet mirror according to the invention;

14 a further embodiment for the application of a graphene layer on a facet mirror;

15 a perspective view of a monolithic facet mirror for use in the present invention;

16 a further illustration of a method for applying a graphene layer on a mirror, in particular a monolithic facet mirror; and in

17 an overview of the classification of surface defects according to the spatial wavelength or the spatial frequency according to Passe / MSFR / HSFR and VHSFR.

EMBODIMENTS

The 1 shows a facet mirror 301 in a projection exposure machine with a lighting system 302 , The light from a light source 303 , For example, a plasma source is via a collector mirror 304 on the facet mirror 301 directed, from where there is a distracting mirror 305 with a desired uniform illumination on the reticle 306 is directed. That in the reticle 306 included pattern is over the projection lens 307 on a wafer 308 zoomed in to view the structures of the reticle 306 train.

The 2 to 5 show various embodiments, as a corresponding facet mirror can be constructed. In the embodiments of the 2 . 3 such as 4a and 4b is each a basic body 100 given, one or more bearing surfaces 105 in which mirror facets 110 can be stored. As can be seen from the pictures, the mirror facets 110 be curved and formed with different orientation to reflect the light in the desired manner.

In the 5 an alternative embodiment of a facet mirror or a part thereof is shown. The mirror facet 210 is here on a stamp-like carrier element 200 arranged, which in a carrier body 220 is included and together with the mirror facet 210 with respect to the carrier body 220 by means of an actuator system 207 can be moved so as to provide different reflection angles for the incident light. A corresponding facet mirror is provided by a multiplicity of mirror facets 210 on corresponding support elements 200 educated. Alternatively, the present invention can also be used in a multi-mirror arrangement (MMA Micro Mirror Array) or in micro-electro-mechanical systems (MEMS micro electromechanical systems), as used, for example, in US Pat WO 2009/100 856 A1 are described.

In addition, corresponding facet mirrors may also be designed as monolithic mirrors having a multiplicity of mirror facets, such as, for example, those in US Pat 15 shown basic body for a faceted mirror indicates.

All these facet mirrors have in common that they have very small mirror facets with edge lengths in the range of a few to a few tens of microns to a few millimeters, which are difficult polishable. However, in order to avoid losses due to scattered light, these mirror elements must have a smoothly formed mirror surface.

In addition, such mirrors are provided with so-called multi-layer layers which provide a high reflectivity for the light used, for example light with a wavelength in the extreme ultraviolet wavelength spectrum (EUV). Also for the reflectivity, it is necessary that the corresponding interfaces of the so-called multi-layer system are smooth.

The following are based on the 6 to 11 possible layer structures or multi-layer systems described how they can be provided in the mirrors according to the invention.

The 6 shows a schematic representation of a mirror according to the invention 1a for the EUV wavelength range with a substrate S and a layer arrangement. In this case, the layer arrangement comprises a plurality of layer subsystems P ', P''andP''', each consisting of a periodic sequence of at least two periods P ₁ , P ₂ and P ₃ to individual layers, wherein the periods P ₁ , P ₂ and P ₃ comprise two monolayers of different materials for a high refractive index layer H ', H''andH''' and a low refractive index layer L ', L''andL''' and within each layer subsystem P ', P '' and P '''have a constant thickness d ₁ , d ₂ and d ₃ , which differs from a thickness of the periods of an adjacent layer subsystem. In this case, the layer system P '''furthest from the substrate has a number N _{3 of} the periods P ₃ which is greater than the number N _{2 of} the periods P ₂ for the second-most removed layer subsystem P''from the substrate. In addition, the second most distant layer subsystem P "from the substrate has such a sequence of periods P ₂ that the first high refractive layer H"'of the substrate farthest from the substrate P "' immediately adjoins the last high refractive layer H '' of the second-most distant from the substrate layer subsystem P '' follows.

Thus, in 6 the order of the high H '' and low-refractive L '' layers within the periods P ₂ in the second most distant layer subsystem P '' from the substrate versus the order of the high H ', H''' and low breaking L ', L'' Layers within the other periods P ₁ , P _{3 of} the other layer subsystems P ', P''' vice versa, so that the first low-refractive layer L '' of the second-most distant from the substrate layer subsystem P '' optically effective on the last low-refractive Layer L 'of the layer subsystem P' closest to the substrate follows. Thus, the second most distant from the substrate layer subsystem P '' differs from the substrate 1 in the order of layers also of all other layer subsystems 8th to 11 , which are described below.

Directly on the substrate, a smoothing layer R can be provided, which adjusts the substrate surface to the required, low roughness. According to the invention, the smoothing layer R may be formed of or include graphene.

Over the smoothing layer R, an adhesion promoter layer A can be arranged, which serves to reliably adhere the layer arrangement to the smoothing layer R. In the case of a smoothing layer R made of graphene, the adhesion promoter layer A can be formed, for example, from nickel.

At the mirror of 6 For example, according to the invention, the finishing layer M and / or the barrier layers B may be formed from or contain graphene. In particular, the layer arranged directly on the substrate may be formed from graphene in order to smooth the surface of the substrate in the HSFR region, so that the substrates according to the invention can be used.

The 7 shows the mirror according to the invention 1a ' , which as far as possible the mirror according to the invention 1a of the 6 equivalent. The difference between these mirrors is only that the mirror 1a ' there is a protective layer SPL with the thickness d _p and a layer of graphene G between the upper three layer subsystems P ', P "and P"' and the substrate S. Such a protective layer SPL serves to protect the substrate from excessive doses of EUV radiation, since mirror substrates of z. B. Zerodur ^® or ULE ^® at high doses of EUV radiation irreversible compression in the order of a few percent by volume show. The layer of graphene G compensates for the surface roughness of the protective layer SPL, so that stray light losses are avoided. A mirror protection layer SPL made of a metal such. As nickel (Ni) with a thickness of about 50 to 100 nm has enough absorption, so that only very little EUV radiation penetrates to the underlying substrate S. As a result, the substrate is even at high doses of EUV radiation, which in the long-term Operation of a microlithography system occur, sufficiently protected. Thus, it can be prevented that the optical imaging properties of a mirror after only a few months or years are no longer sufficient for operation of the microlithography system due to the irreversible surface change of the substrate.

Likewise, a 2 to 5 μm thick quartz layer as a protective layer SPL has sufficient absorption to sufficiently protect the substrate. Such a quartz layer can be applied to the substrate by means of a CVD method, in particular a PICVD, PACVD or a PECVD method, since these mentioned coating methods lead to very compact layers which are stable even under EUV radiation and no irreversible densifications demonstrate. Likewise, the said metal layers, such as. As nickel, stable under EUV radiation and show no irreversible compression.

The explanation why quartz layers, unlike the substrate material, are stable under high doses of EUV radiation, although the substrate materials are also based on the quartz base material, is probably due to the manufacturing process of the substrate materials which takes place at high temperatures. This is believed to freeze an intermediate thermodynamic state in the substrate material which, under high doses of EUV radiation, becomes a thermodynamic ground state, thereby making the substrate material more compact. Conversely, the quartz layers are applied by the methods mentioned at low temperatures, which presumably from the beginning a thermodynamic ground state of the material is realized, which can not be converted by high doses of EUV radiation in another thermodynamically lower ground state.

In addition to quartz and nickel, cobalt is also considered an SPL layer.

As an alternative to a single protective layer SPL, it is also possible to use a layer subsystem P 'of the mirror 1a out 6 be designed so that it provides sufficient protection for the underlying substrate due to its absorption. For this purpose, the layer subsystem should have correspondingly many layers. In particular, a layer subsystem P 'whose number of periods exceeds the number of periods of the layer subsystems P''andP''' of a layer arrangement for an EUV level is suitable for this purpose.

At the same time, the reflectivity properties, the transmission properties and the voltage properties of all layers must be taken into account simultaneously with every overall optimization of a layer arrangement.

Likewise, special protective layer subsystems SPLS, as described below with reference to 9 and 11 are discussed, suitable for the substrate of the mirror 1a of the 6 sufficiently to protect against EUV radiation. At least one layer of graphene is used to smooth the surface. In addition, layers of graphene in both the SPLS protective layer subsystem of 9 and 11 , as well as in the layer subsystems of 1 to 3a as so-called barrier layers (barrier layers) B, which prevent the interdiffusion of adjacent layers can be used.

A layer of graphene consists of at least one monolayer of graphene. Mono- or bi-layers of graphene can be neglected in terms of their refractive index in the design of the layer design. By contrast, graphene layers from a thickness of about four monolayers on graphene in the layer design must be taken into account. Since there are no values for the refractive index of a few layers of graphene at 13.5 nm, the values of graphite can be used to design layer designs.

Layers of graphene may be deposited or transferred to areas of any size in accordance with the following procedures. In this case, layers of graphene can be formed which have both monolayers and multilayers of graphene. As a result, the unevenness of the layer immediately below the graph can be compensated.

The 8th shows a schematic representation of a mirror according to the invention 1b for the EUV wavelength range comprising a substrate S and a layer arrangement. In this case, the layer arrangement comprises a plurality of layer subsystems P ', P''andP''', each consisting of a periodic sequence of at least two periods P ₁ , P ₂ and P ₃ to individual layers, wherein the periods P ₁ , P ₂ and P ₃ comprise two monolayers of different materials for a high refractive index layer H ', H''andH''' and a low refractive index layer L ', L''andL''' and within each layer subsystem P ', P '' and P '''have a constant thickness d ₁ , d ₂ and d ₃ , which differs from a thickness of the periods of an adjacent layer subsystem. In this case, the layer system P '''furthest from the substrate has a number N _{3 of} the periods P ₃ which is greater than the number N _{2 of} the periods P ₂ for the second-most removed layer subsystem P''from the substrate. In this case, this is the second-largest of the substrate removed layer subsystem P '' unlike the embodiment to 1 a sequence of the periods P ₂ , which corresponds to the sequence of the periods P ₁ and P _{3 of} the other layer subsystems P 'and P''', so that the first high refractive layer H '''of the substrate farthest from the substrate subsystem P''' optically effectively follows the last low-refractive layer L '' of the second-most distant from the substrate layer subsystem P ''.

The 9 shows a mirror according to the invention 1b ' according to the mirror according to the invention 1b of the 8th whose third layer subsystem P 'is designed as a protective layer subsystem SPLS. The protective layer subsystem SPLS comprises several periods of a high-refractive-index layer H _p , a low-refractive-index layer L _p and two barrier layers B. The low-refractive-index layer consists of a metal such as a metal. As nickel or cobalt, and accordingly has a high absorption for EUV radiation.

The total thickness of the layers Lp of the protective layer subsystem SPLS corresponds approximately to the thickness of the protective layer SPL according to the mirror according to the invention 1a ' out 7 , It is understood that between the layer arrangement of the mirror 1b and the substrate, a protective layer SPL according to the embodiment 1a ' of the 7 or as a replacement of the protective layer subsystem SPLS of the mirror 1b ' of the 9 can be used.

The advantage of a protective layer subsystem SPLS over a single protective layer SPL is that the high-refractive layers prevent any crystal growth of the metal layers. Such crystal growth leads to rough surfaces of the metal layers and this in turn to undesirable scattered light losses, as already mentioned above. For the metal nickel, silicon is suitable as a material of a high refractive index layer of a period, while beryllium is suitable as a high refractive index layer for the metal cobalt.

In order to prevent interdiffusion of these layers mentioned, barrier layers B can be used, as discussed below in connection with other high and low refractive layers in the context of this application. In particular, layers of graphene as barrier layers B, on the one hand, prevent interdiffusion and, on the other hand, lead to "atomically smooth" surfaces.

The 10 shows a schematic representation of another mirror according to the invention 1c for the EUV wavelength range comprising a substrate S and a layer arrangement. In this case, the layer arrangement comprises a plurality of layer subsystems P '' and P ''', each consisting of a periodic sequence of at least two periods P ₂ and P ₃ to individual layers, wherein the periods P ₂ and P _3, two individual layers of different materials for a high refractive layer H "and H" and a low refractive layer L "and L"', and within each layer subsystem P "and P"' have a constant thickness d ₂ and d ₃ which deviates from a thickness of the periods of an adjacent layer subsystem. In this case, the most distant from the substrate layer subsystem P '''may have a number N _{3 of} the periods P ₃ , which is greater than the number N _{2 of} the periods P ₂ for the second-most distant from the substrate layer subsystem P''. This embodiment can also be used as a variant of the representation of the mirror 1c in 10 according to mirror 1a show the reverse order of the layers in the second most distant layer subsystem P "from the substrate S, so this embodiment also has the feature that the first high refractive layer H '''of the substrate farthest layer subsystem P''' is optically effective to the last low refractive layer L "of the second most distant layer subsystem P" from the substrate.

In particular, with a small number of layer subsystems of, for example, only two layer subsystems, high reflectivity values are obtained when the period P ₃ for the substrate farthest from the substrate P '''has a thickness of the high refractive layer H'" , which is more than 120%, in particular more than twice the thickness of the high-refraction layer H "of the period P ₂ of the substrate of the second-most distant layer subsystem P".

The 11 shows a schematic representation of another mirror according to the invention 1c ', which is different from the mirror 1c of the 10 in that the layer subsystem P "closest to the substrate is formed as a protective layer subsystem SPLS.

This protective layer subsystem SPLS consists in 11 only from layers B interrupted by barrier layers B. The barrier layers B serve, as already mentioned above 9 discussed breaking the crystal growth of the layers L _p . It is understood that in 11 represented protective layer subsystem SPLS by other protective layers SPL or other protective layer subsystems SPLS, as related to 7 and 9 could be replaced. This in 11 Protective layer subsystem SPLS shown here merely provides a simplified protective layer subsystem SPLS in comparison with the one in FIG 9 shown protective layer subsystem in which was dispensed with the high-refractive layers H _p .

Thus, the protection layer subsystem SPLS is the 11 according to the protective layer SPL of 7 purely limited to the protective function for the substrate (S) by absorption and therefore has little interaction with the optical properties of the other layer subsystems. On the other hand, the protective layer subsystem has the 9 a dual function in that it provides protection of the substrate by its absorption properties and by its reflection properties contributes to the reflection and thus the optical performance of the mirror. The transition from the designation of a layer system from a protective layer subsystem SPLS to a layer subsystem P ', P''orP''' of the layer arrangement is in this case flowing, as described above in connection with FIG 7 already discussed, also a layer subsystem P 'of the mirror 1a with appropriate design contributes to a plurality of periods both the reflectivity effect of the mirror, as well as due to the increased absorption of the plurality of periods a protective effect on the substrate takes over. In contrast to the reflectivity, all layers of a layer arrangement must be taken into account when considering the layer voltages of a layer design.

The layer subsystems of the layer arrangement of the mirrors according to the invention to the 6 to 11 follow each other directly and are not separated by any other layer system. However, a separation of the layer subsystems by a single intermediate layer is conceivable for adapting the layer subsystems to one another or for optimizing the optical properties of the layer arrangement. However, the latter does not apply to the two layer subsystems P '' and P '''of the first embodiment 6 and the corresponding variant too 10 , as this would prevent the desired optical effect by reversing the sequence of layers in P ''.

In the in the 6 to 11 Layers designated H, H _p , H ', H''andH''' are layers of materials which are in the EUV wavelength range as compared to those as L, L _p , L ', L "and L '''designated layers of the same layer subsystem can be referred to as high refractive, so have corresponding refractive indices. Conversely, those in the 6 to 11 layers denoted L, L _p , L ', L''andL''' around layers of materials which are in the EUV wavelength range in comparison with those as H, H _p , H ', H''andH''' designated layers of the same layer subsystem may be referred to as low refractive. Thus, the terms high refractive and low refractive are relative terms relative to the respective partner layer in a period of a layered subsystem. Layer subsystems usually only work when a layer having a high refractive index is combined with a layer having a relatively lower optical refractive index as the main component of a period of the layer subsystem. In general, the material silicon is used for highly refractive layers. In combination with silicon, the materials molybdenum and ruthenium can be chosen as low-refractive layers.

Between the individual layers of a period is located in the 6 to 11 each a barrier layer B, which consists of a material which is selected or compounded from the group of materials: B ₄ C, C, graphene, Si-nitride, Si-carbide, Si-boride, Mo-nitride, Mo Carbide, Mo-boride, Ru-nitride, Ru-carbide and Ru-boride. By means of such a barrier layer, the interdiffusion between the two individual layers of a period is suppressed, whereby the optical contrast is increased during the transition of the two individual layers. When using the materials molybdenum and silicon for the two individual layers of a period, a barrier layer above the silicon layer is sufficient from the substrate to provide a sufficient contrast.

In this case, the second barrier layer above the molybdenum layer can be dispensed with. In this respect, at least one barrier layer should be provided for the separation of the two individual layers of a period, wherein the at least one barrier layer may well be composed of different materials or their compounds mentioned above and may also show a layered structure of different materials or compounds.

Barrier layers comprising the material B ₄ C and a thickness of between 0.35 nm and 0.8 nm, preferably between 0.4 nm and 0.6 nm (their in practice too high reflectivity values of the layer arrangement Ruthenium and silicon show barrier layers of B ₄ C with values between 0.4 nm and 0.6 nm for the thickness of the barrier layer a maximum of reflectivity.

Graphene barrier layers lead to very smooth surfaces and thus reduce stray light losses.

The number N _p , N ₁ , N ₂ and N _{3 of} the periods P _p , P ₁ , P ₂ and P _{3 of} the layer subsystems SPLS, P ', P''andP''' can in the mirrors according to the invention 1a . 1a ' . 1b . 1b ' . 1c and 1c ' each up to 100 periods in the 6 to 11 Individual periods P _p , P ₁ , P ₂ and P _{3 shown} include. Furthermore, can between the in the 6 to 11 layer arrangement shown and the substrate S, an additional intermediate layer or an additional intermediate layer arrangement are provided, which serves for voltage compensation of the layer arrangement with respect to the substrate.

As materials for the additional interlayer and the additional interlayer array for stress compensation, the same materials can be used in the same sequence as for the layer arrangement itself. In the case of the interlayer arrangement, however, the barrier layer between the individual layers can be dispensed with since the intermediate layer or the interlayer arrangement as a rule contributes negligibly to the reflectivity of the mirror and thus the question of an increase in contrast by the barrier layer is irrelevant. Likewise, multi-layer arrangements of alternating chromium and scandium layers or amorphous molybdenum or ruthenium layers as an additional intermediate layer or interlayer arrangement for stress compensation would be conceivable.

The latter can also be chosen in their thickness so z. B. greater than 20 nm, so that an underlying substrate is sufficiently protected from EUV radiation. In this case, the additional intermediate layer or the additional interlayer arrangement would likewise act as a protective layer SPL or as a protective layer subsystem SPLS and protect the substrate from EUV radiation.

The layer arrangements of the mirrors according to the invention 1a . 1a ' . 1b . 1b ' . 1c and 1c ' be in the 6 to 11 completed by a cover layer system C, which at least one layer of a chemically inert material, such as. Graphene, Rh, Pt, Ru, Pd, Au, SiC, Si _x N _y , SiO ₂ , etc. as the final layer M includes. This finishing layer M thus prevents the chemical change of the mirror surface due to environmental influences. In addition, when graphene is used as the finishing layer, a smooth formation of the layer is advantageous. The cover layer system C in the 6 to 11 consists of a high-breaking layer H, a low-refraction layer L and a barrier layer B, in addition to the finishing layer M.

The thickness of one of the periods P _p , P ₁ , P ₂ and P ₃ results from the 6 to 11 as the sum of the thicknesses of the individual layers of the corresponding period, ie, the thickness of the high-refractive-index layer, the thickness of the low-refractive-index layer, and the thickness of two barrier layers. Thus, the layer subsystems SPLS, P ', P''andP''' in the 6 to 11 are distinguished from each other with the same choice of material that their periods P _p , P ₁ , P ₂ and P _{3 have} a different thickness d _p , d ₁ , d ₂ and d ₃ . As different layer subsystems SPLS, P ', P''andP''' with the same choice of material are thus understood in the context of the present invention, layer subsystems whose generated periods P _p , P ₁ , P ₂ and P ₃ in their thicknesses d _p , d ₁ , d ₂ and d ₃ differ by more than 0.1 nm, as below a difference of 0.1 nm can no longer be assumed by another optical effect of the layer subsystems with otherwise equal division of the periods between high and low refractive layer , In addition, identical layer subsystems on different production systems can vary in their production by their amount per se during their production. In the case of a layer subsystem SPLS, P ', P''andP''' having a period of molybdenum and silicon, the second barrier layer within the period P _p , P ₁ , P ₂ and P _{3 may be} omitted as described above , so that the thickness of the periods P _p, P _1, P ₂ and P ₃ from the thickness of the high refractive index layer, the thickness of the low refractive index layer and the thickness results in this case by a barrier layer.

The individual layers can by known methods, such. As CVD (chemical vapor deposition) - or PVD (physical vapor deposition) - method are deposited.

As already mentioned above, the high refractive index layers H, H ', H ", H'", H _{P may} comprise silicon or beryllium, while the low refractive index layers L, L ', L ", L'", L _P molybdenum, ruthenium, nickel, cobalt or SiO ₂ (L _P ) may include. However, other materials are conceivable, in particular materials that are suitable for other wavelength ranges, and the embodiments of the 6 to 11 are merely illustrative of how the present invention may be practiced.

The 12 to 16 show examples of different methods by which graphene can be arranged in or on a mirror for a projection exposure machine.

The 12 shows a perspective view, such as a Graphene layer can be applied to a mirror substrate, the mirror substrate, for example, a mirror facet similar to the mirror facets 110 the embodiments of the 2 to 4 can be made of a copper material. In the embodiment shown the 12 is the graphene layer 500 on a copper foil 501 arranged as a carrier film. The graphene layer may be on the copper foil 501 for example by CVD deposition to be ordered. The copper foil can according to the embodiment of the 12 by gluing, for example with a resin adhesive or by soldering over silver solder pastes on the mirror substrate in the form of the mirror facet 110 be applied. Also, thermal bonding methods such as diffusion bonding or other bonding techniques are conceivable. For example, it is conceivable for the graphene layer to be arranged on the carrier film by way of wringing against the substrate, the wringing being used to utilize adhesion forces of bodies to one another, which occur with a very narrow and defined arrangement of the bodies with precisely formed surfaces.

The 13 shows in the panels a), b) and c) the various stages of production and use of corresponding mirror. In the 13a ) is a mirror facet 110 shown from a copper material on which a graphene layer 500 on a copper carrier foil 501 on the copper substrate 110 is arranged. Around an exact edge area of the graphene layer 500 can define the copper carrier foil 501 with the graphene layer 500 around the surface edge of the copper substrate 110 be arranged angled. Additionally, along the peripheral edge of the copper substrate 110 the carrier film 501 with the graphene layer 500 be cut so that excess carrier film 501 along with the excess graphene layer 500 can be removed. On a correspondingly prepared mirror facet can then according to 13b ) a so-called multilayer layer arrangement 502 with a plurality of sub-layers, as previously described in detail, are arranged to form the finished mirror facet. Several of these mirror facets can be combined to form a facet mirror 505 be collated, the impacting EUV light, as with the arrows in 13c ), reflected in a suitable manner.

The 14 shows a further embodiment of the arrangement of a graphene layer on a mirror substrate 110 , In this variant, in turn, a graphene layer 500 on a layer base in the form of a copper carrier foil 501 provided. However, unlike the embodiment of the 12 and 13 not the copper carrier foil 501 permanently arranged on the mirror substrate, but the graphene layer 500 is brought directly into contact with the mirror substrate and placed on this. The copper carrier foil 501 is then removed, for example, by chemical etching. For this purpose, only the mirror substrate must be sealed with respect to the etchant, as long as the mirror substrate is not inert to the etchant.

In addition to the previously described facet mirrors with a plurality of mirror facets, which are assembled in a suitable manner, monolithic facet mirror arrangements can also be produced from a substrate such as, for example, silicon or quartz glass. An example of this is in 15 shown a corresponding mirror substrate made of silicon with multiple facets 601 and the differently shaped and aligned facet surfaces. For example, such mirror substrates for monolithic facet mirror arrays may be formed in gray-lithographic or multi-faceted binary-lithographic fashion, wherein in a lithography process, the curvature and orientation of mirror facets of the mirror facets are formed either in accordance with a gray-tone image in the lithography process, or in steps in binary increments be generated.

The roughnesses of such mirror facets are in the range of 0.4 to 2 μm rms HSFR and thus have an excessively high roughness for the intended use. To avoid stray light and reflection losses due to the rough substrate surface and unevenly deposited multi-layer layers, a roughness in the range of 0.2 μm RMS HSFR is desired.

This is inventively achieved in that again on the substrate 600 , which may for example be formed of silicon, a graphene layer is applied, which causes a corresponding smoothing. The graphene layer can be effected for example by an atomic layer deposition, in which only a monolayer of carbon is deposited, which is formed in particular in the form of graphene. The atomic layer deposition, also referred to as atomic layer deposition ALD, based on a chemical vapor deposition (CVD), wherein the components required for the chemical reaction are introduced separately and by cleaning steps separately in the reaction chamber, so by the remaining, on residual amounts adhering to the surfaces are deposited on the surface only by atomic monolayers. On such a prepared monolithic substrate 600 with a variety of mirror facets 601 In turn, one of the previously described multi-layer arrangements can be applied.

The 16 shows another way, as with the help of a so-called balloon-membrane-pressure graphs on a mirror and in particular a facet mirror, as in the 15 is shown, can be transmitted. The 16 shows that the mirror substrate 600 the facet mirror with the mirror facets 601 even steps between the mirror facets 601 can have and yet sufficient graphene layer transfer can be accomplished by a so-called balloon membrane pressure technique.

In the case of the balloon membrane pressure technique, the graphene layer to be applied is in particular in the form of a composite film 701 with a copper foil or a polymethyl methacrylate PMMA foil as a carrier foil on a pressure membrane 700 arranged, for example, deformable via air pressure and against the mirror substrate 600 is pressable. Preferably, between the pressure membrane 700 and the composite foil 701 be provided with the graphene layer and the carrier film, a liquid film, so that due to corresponding surface tensions the composite film 701 with the graphene layer on the pressure membrane 700 swims. This can be avoided that lateral forces on the composite film 701 be transferred with the graphene layer and so to a cracking of the graphene layer or the composite film 701 could lead.

As by the dashed line 703 is shown when applying a corresponding air pressure on the Andruckmembran 700 this in the direction of the mirror substrate 600 deformed and the composite film with the graphene layer can be pressed onto the mirror substrate. Because the graphene layer in the composite film 701 opposite the side of the pressure membrane 700 is arranged, is in contact with the mirror substrate 600 the graphene layer on the mirror substrate 600 transfer. In addition to the use of air as a pressure medium to actuate the Andruckmembran 700 Other media are conceivable, especially liquid media.

With the application and use of graphene described above, mirrors with low roughness values, in particular in the HSFR range, can be achieved, so that low scattering losses occur and the reflectivity of the mirrors is also improved.

For the subdivision of surface roughnesses into spatial frequency ranges with the High Spatial Frequency Roughness (HSFR range) with spatial wavelengths of the roughness of 10 nm to 1 μm, the Medium Spatial Frequency Roughness (MSFR range) with spatial wavelengths of the roughness of 1 μm to 1 mm and the Figure Range (surface shape error or Passe also called) with spatial wavelengths of 1 mm to the free optical diameter is on U. Dinger et al. "Mirror substrates for EUV lithography: progress in metrology and optical fabrication technology" in Proc. SPIE Vol. 4146, 2000 , referenced.

Furthermore, for clarity, the spatial frequency ranges Passe, MSFR, HSFR and Very HSFR (VHSFR) are calculated on the basis of the associated spatial wavelengths λ and on the basis of the associated spatial frequencies f = 1 / λ in 17 shown. Compared to the above-mentioned publication by U. Dinger et al. In the meantime, the HSFR range is in the HSFR range with spatial wavelengths of 50 nm to 1 μm or spatial frequencies of 1 μm ^-1 to 0.02 nm ^-1 and the Very HSFR range (VHSFR) with spatial wavelengths of 10 nm to 50 or spatial frequencies of from 0.02 nm ^-1 to 0.1 nm ^-1 divided.

The deviation of a real area from the ideal design area of an optical element in the spatial wavelength range of 1 mm to the diameter of the optical element is referred to as a surface shape error or as a passe error. These deviations are generated in the shape processing of the optical element by molding machines and lead to aberrations of the optical system such as astigmatism, coma, distortion and the like. Such deviations of a real optical element from the ideal surface shape can be measured by an interferometer over the entire surface of the optical element and reduced by shape correction processes such as ion beam machining. The specifications for EUV mirrors are approximately 0.1 nm rms surface shape errors.

The deviation of a real area from the ideal design area of an optical element in the MSFR area leads to a dot image broadening. In English usage Flare is used here. An optical system with optical elements with high roughness values in the MSFR range, given in the unit nm rms MSFR, creates an atrium around the point image of a bright point to be imaged, widening the point image and thus reducing the contrast of the image. Roughnesses in the MSFR area are usually caused by the damage to the surface during the shaping process by, for example, diamond cutting. These roughnesses are measured with microscope interferometers on an area of 0.25 mm x 0.25 mm of the optical element and can be reduced by polishing the surface or by ion beam machining. The specifications for EUV mirrors are approximately 0.1 nm rms MSFR.

On the other hand, the deviation of a real area from the ideal design area of an optical element in the HSFR area results in stray light losses because light is diffracted by the high-frequency HSFR structures. These roughnesses in the HSFR range are determined by means of AFM microscopes on an area of 10 μm × 10 μm with a spatial resolution of 0.3 to 3 μm or on an area of 1 μm × 1 μm with a spatial resolution of 10 to 300 nm of the optical Elements measured and can through so-called Superpoliturverfahren be reduced. The specifications for EUV mirrors are approximately 0.1 nm rms HSFR.

A monolayer of graphene, which extends over at least an area of about 0.5 .mu.m.times.0.5 .mu.m of an optical element, ideally exhibits an unmeasurable surface roughness in the HSFR range in the HSFR range and also in the VHSFR range. Only in the spatial frequency range above VHSFR with spatial wavelengths of less than 1 nm has a monolayer of graphene ever an intrinsic roughness. This spatial frequency range is in 17 indicated by the solid arrow for graphs. Such a monolayer of graphene thus avoids stray light losses because the graphene structure distances are too small to diffract light of the EUV wavelength. In accordance with the present invention, this is particularly useful for mirrors that are difficult to polish, such as facet mirrors, particularly monolithic facet mirrors or single mirror facets of multiple mirror arrays, to produce low roughness surfaces and / or interfaces.

Homogeneous layers of graphene make it possible to reduce the roughness in the HSFR region to rms values below the measurement accuracy and to minimize the scattered light losses at mirrors with such graphene layers. The graphene layers may well have areas along the mirror surface with a different number of graphene layers. Although the transitions in these areas contribute to the roughness in the MSFR region, as in 17 however, MSFR roughnesses on this scale, particularly on a layer deposited on the graphene layer, can be corrected by polishing techniques such as ion beam machining. In this respect, it is through the use of graphene layers for the mirrors according to the invention 1a . 1a ' . 1b . 1b ' . 1c and 1c ' it is possible to reduce the roughness of at least these graphene layers to less than 0.1 nm rms HSFR, in particular less than 0.04 nm rms HSFR. Further, the theoretical roughness of graphene layers of R _q = 0.065 nm rms above HSFR contributes to the growth of other layers growing on the graphene layers due to lack of impurities such that their surface also has lower roughness values in the HSFR region.

Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that the invention is not limited to these embodiments, but rather modifications are possible in such a way that individual features omitted or other combinations of features are made as long as the scope of protection of the appended claims is not abandoned. The disclosure of the present invention includes all combinations of all presented individual features.

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

• DE 10155711 A1 [0003]
• DE 102010041502 [0009, 0009]
• US 61/387214 [0009, 0009]
• WO 2009/100856 A1 [0045]

Cited non-patent literature

• U. Dinger et al. "Mirror substrates for EUV lithography: progress in metrology and optical fabrication technology" in Proc. SPIE Vol. 4146, 2000 [0005]
• U. Dinger et al. "Mirror substrates for EUV lithography: progress in metrology and optical fabrication technology" in Proc. SPIE Vol. 4146, 2000 [0098]

Claims (19)

Mirror ( 1a ; 1a '; 1b ; 1b '; 1c ; 1c ' ) for a projection exposure apparatus comprising a substrate (S) and a layer arrangement, wherein the layer arrangement comprises at least one layer subsystem (P ''') consisting of a periodic sequence of at least two periods (P ₃ ) on individual layers, the periods (P ₃ ) comprise two individual layers of materials which have different optical refractive indices and wherein the mirror comprises at least one layer which is formed at least partially from graphene, characterized in that the layer with graphene as the final layer (M) is arranged on the layer arrangement and / / or the mirror comprises a substrate (S) comprising at least one material selected from the group consisting of glass, quartz glass, glass ceramic, ceramic, SiC, SiSiC and amorphous silicon. Mirror according to claim 1, characterized in that the layer is formed with graphene below the layer arrangement. Mirror according to claim 1 or 2, characterized in that an adhesion promoter layer (A) is arranged between the layer with graphene and the layer arrangement. Mirror ( 1a ; 1a '; 1b ; 1b '; 1c ; 1c ' ) for a projection exposure apparatus comprising a substrate (S) and a layer arrangement, wherein the layer arrangement comprises at least one layer subsystem (P ''') consisting of a periodic sequence of at least two periods (P ₃ ) on individual layers, the periods (P ₃ ) comprise two individual layers of materials which have different optical refractive indices and wherein the mirror comprises at least one layer (G, SPL, B) which is formed at least partially from graphene and is arranged below the layer arrangement, characterized in that between the layer a bonding agent layer (A) is arranged with graphene (R) and the layer arrangement. Mirror according to one of claims 2 to 4, characterized in that the adhesive layer (A) is formed of nickel. Mirror according to one of claims 4 to 5, characterized in that a further layer with graphene as the final layer (M) is arranged on the layer arrangement and / or the substrate (S) comprises at least one material selected from the group consisting of glass , Quartz glass, glass ceramic, ceramic, SiC, SiSiC and amorphous silicon. Mirror according to one of the preceding claims, characterized in that the mirror is a facet mirror. Method for producing a mirror for a projection exposure apparatus, in particular a mirror according to one of the preceding claims, in which first a mirror substrate ( 110 ) is provided with a mirror surface, characterized in that furthermore a layer ( 500 ), which at least partially has graphene, on a layer base body ( 501 ), wherein the layer base body with the layer of graphene with the layer base body or with the layer with graphene is arranged on the mirror substrate. Method according to claim 8, characterized in that the layer basic body ( 501 ) is placed on the mirror substrate by a method selected from the group consisting of wringing, gluing, thermal bonding, bonding and soldering. Method according to claim 8 or 9, characterized in that the graphene-containing layer ( 500 ) on the layer main body ( 501 ) is deposited by a CVD method. Method according to one of claims 8 to 10, characterized in that the mirror substrate ( 110 ) and / or the layer main body ( 501 ) comprise at least one material from the group comprising metals, metal alloys, copper, copper alloys, glass, quartz glass, glass ceramic, ceramic, SiC, SiSiC and amorphous silicon. A method according to claim 8, characterized in that at a between the mirror substrate ( 110 ) and the layer main body ( 501 ) arranged graphene-containing layer ( 500 ) the layer base body is dissolved chemically or thermally or removed by detachment. Method for producing a mirror for a projection exposure apparatus, in particular a mirror according to one of Claims 1 to 7, in which first a mirror substrate ( 600 ) with at least one mirror surface ( 601 ), characterized in that the mirror surface ( 601 ) is coated with carbon in one or more individual atomic layers by atomic layer deposition. A method according to claim 13, characterized in that the carbon is at least partially formed in the form of graphene. Method for producing a mirror for a projection exposure apparatus, in particular A mirror according to any one of claims 1 to 7, wherein first a mirror substrate ( 600 ) with a mirror surface ( 601 ), characterized in that a layer which is formed at least partially from graphene, on an elastically deformable pressure membrane ( 700 ) is provided, wherein the pressure membrane is pressed by means of a pressure medium against the mirror substrate with the mirror surface, so that the graphene-containing layer is disposed on the mirror substrate. A method according to claim 15, characterized in that the pressure membrane has a liquid layer, so that the arranged on the pressure membrane layer is floatingly mounted. A method according to claim 15 or 16, characterized in that the graphene-containing layer is disposed on a carrier foil, which is removed after the application of the graphene-containing layer on the mirror substrate. Method according to one of claims 8 to 17, characterized in that the mirror is a monolithic facet mirror with a plurality of facet surfaces ( 601 ) contained in the mirror substrate ( 600 ), or is a facet mirror or a multi-mirror array having a plurality of individual mirrors. Illumination system for a projection exposure apparatus with a mirror according to one of Claims 1 to 7 and / or produced according to the method according to one of Claims 8 to 18.

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