Optical arrangement with a mirror for reflecting EUV radiation in the spectral range between 6 nm and 10 nm

Abstract

Optical arrangement (100) with - at least one mirror (10) for reflecting EUV radiation (17) in the spectral range between 6 nm and 10 nm, comprising a layer stack (5) having a plurality of layer pairs (4), each containing a first layer and a second layer, wherein the second layer is an oxidation-inhibiting layer (2) comprising a lanthanum oxide, a cerium oxide, a thorium oxide, a uranium oxide, or diamond-like carbon, and wherein the first layer is a further layer (3) comprising lanthanum, cerium, uranium, thorium, a lanthanum nitride, a lanthanum carbide, a cerium nitride, a cerium carbide, a thorium nitride, a thorium carbide, a uranium nitride, or a uranium carbide, - an EUV radiation source (11) suitable for emitting EUV radiation (17) with a wavelength between 6 nm and 10 nm, and - at least one beam-shaping element (12) having the at least one mirror (10), wherein the EUV radiation (17) emitted by the EUV radiation source (11) predominantly impinges on the at least one mirror (10) in an angular range between 0° and 20° relative to the surface of the mirror (10).

Description

[0001] The invention relates to an optical arrangement with a mirror suitable for reflecting extreme ultraviolet radiation (EUV radiation) in the spectral range between 6 nm and 10 nm.

[0002] In this wavelength range, the wavelength around 6.7 nm is of particular importance because radiation of this wavelength could be used in a next generation of EUV lithography (BEUVL, Beyond Extreme Ultraviolet Lithography).

[0003] Plasma-based radiation sources allow the construction of relatively compact and cost-effective systems for applications in the EUV spectral range. Such plasmas are generated either by irradiating a target with intense pulsed laser radiation or in a pulsed high-current gas discharge. The target or operating gas is heated to such an extent that it is excited to emit characteristic, short-wavelength radiation.

[0004] Such radiation sources emit light approximately isotropically. For effective use in an application, an optical element is therefore required to collect and focus the light. Focusing then occurs either directly onto the workpiece to be processed or irradiated, or it is further used in a downstream optical system, for example, to image structures in a microscope or to create structures in a resist. For example, corresponding systems are used in the field of EUV lithography technology development at an operating wavelength of 13.5 nm.

[0005] In addition to radiation, plasma-based radiation sources also emit debris in the form of fast ions or neutral particles from the target or electrode material. This debris leads to mirror degradation or a reduction in reflectance due to removal by fast particles (sputtering) or deposition of slow particles on the surface.

[0006] The document US 2014 / 0 198 306 A1 describes a multilayer mirror for use in lithography.

[0007] The document DE 10 2011 109 941 A1 describes a mirror for X-rays.

[0008] The document DE 10 2012 202 850 A1 relates to a method for optimizing a protective layer system for an optical element, an optical element and an optical system for EUV lithography.

[0009] One problem to be solved is therefore to specify a mirror for reflecting EUV radiation in the spectral range between 6 nm and 10 nm for an optical arrangement comprising at least one such mirror, wherein the at least one mirror and the optical arrangement are characterized by improved stability against degradation under the influence of the ions and / or neutral particles emitted by an EUV radiation source.

[0010] This object is achieved by an optical arrangement according to the independent patent claim. Advantageous embodiments and further developments of the invention are the subject of the dependent claims.

[0011] The mirror described here is intended for reflecting EUV radiation in the spectral range between 6 nm and 10 nm, preferably between 6 nm and 7 nm, in particular at about 6.7 nm.

[0012] The mirror comprises at least one oxidation-inhibiting layer arranged on a substrate, which layer comprises or consists of a lanthanum oxide, a cerium oxide, a thorium oxide, a uranium oxide, or diamond-like carbon (DLC). The oxidation-inhibiting layer does not have to be directly adjacent to the substrate; rather, one or more additional layers can be arranged between the substrate and the oxidation-inhibiting layer. The oxidation-inhibiting layer is, in particular, the outermost layer on the side of the mirror facing away from the substrate—in other words, the cover layer of the mirror.

[0013] It has been found that a mirror coated with an oxidation-inhibiting layer comprising lanthanum oxide, cerium oxide, thorium oxide, uranium oxide, or diamond-like carbon exhibits comparatively high reflectance in the EUV spectral range between 6 nm and 10 nm. At the same time, a mirror coated with an oxidation-inhibiting layer is characterized by very low susceptibility to oxidation and damage from impinging particles (sputtering). The mirror coated with the oxidation-inhibiting layer is thus particularly resistant to oxidation and erosion, particularly under the influence of radiation and the emitted ions and neutral particles of an EUV radiation source. The mirror is therefore characterized by improved long-term stability when operated within the range of influence of an EUV radiation source.

[0014] If the oxidation-inhibiting layer is applied to the substrate as a single layer, the layer preferably has a thickness of at least 50 nm, preferably from 50 nm to 100 nm, in order to achieve a sufficiently high reflectivity.

[0015] In one embodiment of the mirror, at least one further layer is arranged between the substrate and the oxidation-inhibiting layer. The further layer can comprise or consist of lanthanum, cerium, thorium, or uranium. These materials are characterized by particularly high reflection in the spectral range from 6 nm to 10 nm, but are not as stable as the oxides of La, Ce, U, or Th, or diamond-like carbon. Due to the oxidation-inhibiting layer arranged on top, the mirror is also characterized by high resistance to oxidation. In this embodiment, the oxidation-inhibiting layer functions as a protective layer. In this embodiment, the thickness of the oxidation-inhibiting layer is advantageously dimensioned such that, on the one hand, there is sufficient protection and, on the other hand, the highest possible reflection is achieved.The thickness of the oxidation-inhibiting layer above the at least one further layer is preferably between 1 nm and 10 nm, in particular between 1 nm and 5 nm.

[0016] The at least one additional layer preferably has a thickness between 50 nm and 100 nm. This enables high reflection even when the oxidation-inhibiting layer arranged above it is comparatively thin.

[0017] In a further embodiment, the at least one further layer comprises or consists of a lanthanum nitride, a lanthanum carbide, a cerium nitride, a cerium carbide, a thorium nitride, a thorium carbide, a uranium nitride, or a uranium carbide. The aforementioned nitrides and carbides of La, Ce, Th, and U are characterized in particular by high resistance to erosion, i.e., damage caused by material removal. The at least one further layer comprising a lanthanum nitride, a lanthanum carbide, a cerium nitride, a cerium carbide, a thorium nitride, a thorium carbide, a uranium nitride, or a uranium carbide further improves the resistance of the mirror to erosion caused by impinging ions and / or neutral particles.

[0018] The mirror comprises a layer stack comprising several layer pairs. The layer pairs each contain a first layer and a second layer and, in particular, can consist of only the first layer and the second layer.

[0019] The first layer of the layer pairs corresponds to the previously described further layer in terms of materials and advantageous properties, and the second layer of the layer pairs corresponds to the previously described oxidation-inhibiting layer in terms of materials and advantageous properties. In particular, the layer stack has a second layer, i.e., an oxidation-inhibiting layer, as a cover layer.

[0020] According to one embodiment, the first layer of the layer pairs can comprise lanthanum, thorium, or uranium. Preferably, the first layer comprises or consists of a lanthanum nitride, a lanthanum carbide, a cerium nitride, a cerium carbide, a thorium nitride, a thorium carbide, a uranium nitride, or a uranium carbide. The first layer can therefore, in particular, contain one of the materials that, as described above, are suitable for the at least one further layer between the substrate and the oxidation-inhibiting layer and are characterized by particularly good resistance to erosion by impinging ions or neutral particles.

[0021] The second layer of the layer pair contains or consists of a lanthanum oxide, a cerium oxide, a thorium oxide, a uranium oxide, or diamond-like carbon. The second layer of the layer pair can therefore, in particular, contain one of the materials suitable as an oxidation-inhibiting layer. These materials are characterized by particularly high resistance to oxidation. The cover layer of the layer stack is preferably a second layer, so that the mirror is protected from the outside by the oxidation-inhibiting layer.

[0022] The use of a layer stack consisting of alternating first and second layers, each characterized by good oxidation or erosion resistance to impinging ions or neutral particles, has the advantage over a mirror that only has the oxidation-inhibiting layer and possibly another layer in that a large number of interfaces prevent oxidation and / or erosion. The mirror with the layer stack is therefore characterized by particularly good oxidation and erosion resistance. In an advantageous embodiment, the layer stack can contain more layer pairs than contribute to the reflection due to the limited penetration depth of the radiation. In this case, the reflection is not significantly reduced even if one or more layers on the surface of the mirror are damaged by erosion (material removal) and are therefore completely or partially lost.

[0023] In particular, the layer stack can be a periodic layer stack in which the layer pairs each have the same thickness (period thickness). Since the mirror is intended for use under grazing incidence, the period thickness does not need to be adapted to the wavelength. This distinguishes the mirror from EUV mirrors typically used under normal incidence, where the period thickness is approximately half the wavelength. The layer stack also does not necessarily have to be periodic, i.e., the thicknesses of the layer pairs in the layer stack can differ from one another.

[0024] The first layers and the second layers of the layer pairs preferably each have a thickness between 1 nm and 10 nm. The number of layer pairs in the layer stack is preferably between 5 and 20, for example, approximately 10.

[0025] Furthermore, an optical arrangement with at least one mirror as described above is specified. The optical arrangement comprises a radiation source suitable for emitting EUV radiation with a wavelength between 6 nm and 10 nm. The optical arrangement further comprises at least one beam-shaping element having the at least one mirror.

[0026] The EUV radiation source is preferably a plasma radiation source. The EUV radiation source can, in particular, be a discharge-based radiation source having an electrode system for generating a plasma. In such a discharge-based radiation source, a pulsed electric current of a discharge compresses and heats a gas to such an extent that EUV radiation is emitted. Krypton is particularly suitable as a working gas for generating EUV radiation in the wavelength range between 6 and 10 nm. The krypton plasma generated by an electrical discharge in the radiation source can, for example, emit radiation with a power of 50 W or more in the 6-10 nm range into the half-space. Radiation with a power of approximately 15 W can be collected by a beam-shaping element having an aperture angle of, for example, approximately 45° relative to the optical axis.

[0027] The EUV radiation emitted by the radiation source predominantly impinges on the at least one mirror of the beam-shaping element, in particular more than 50% or preferably more than 75%, within an angular range between 0° and 20° relative to the surface of the mirror. In other words, the beam-shaping element is used with grazing incidence. The specified angular range between 0° and 20° refers to the angle relative to the surface of the mirror, which is also referred to as the grazing angle. Unlike the angle of incidence generally used in optics, the grazing angle is not measured relative to the normal, but rather relative to the surface.

[0028] The beam-shaping element is preferably designed to focus the EUV radiation. The EUV radiation is therefore preferably imaged by the beam-shaping element into a focal point or focal plane.

[0029] According to a preferred embodiment, the beam-shaping element is a Wolter optic, in particular a Wolter multi-shell collector. A Wolter optic is based on mirrors that reflect radiation under grazing incidence. Since a single mirror can only capture a small portion of the incident radiation under grazing incidence, a Wolter optic typically contains a plurality of nested mirrors. The beam-shaping element embodied as a Wolter optic can, in particular, comprise a plurality of concentric, rotationally symmetric mirrors. The mirrors are preferably nested concentrically to an optical axis. The mirrors advantageously each reflect EUV radiation under grazing incidence at angles of predominantly less than 20°, measured to the surface of the respective mirror.

[0030] The at least one mirror preferably has a parabolic, elliptical, or hyperbolic shape, at least in some areas. Alternatively, the mirror can also be designed as a freeform surface with any desired surface shape adapted to the respective application. The beam-shaping element can in particular be formed by a combination of several mirrors.

[0031] According to at least one embodiment, the optical arrangement further includes a device for reducing debris from the EUV radiation source. The term "debris" refers to ions or neutral particles emitted by the EUV radiation source. The emission of such ions and neutral particles is generally an undesirable side effect when generating EUV radiation using a plasma source, since the emitted ions or neutral particles can lead to contamination or damage to the optical components of the optical arrangement.

[0032] The optical arrangement described herein advantageously utilizes the previously described mirror, which is comparatively insensitive to damage by debris. Additionally, it is helpful to reduce the impact of debris on the beam-shaping element using the debris reduction device. For this purpose, the debris reduction device preferably comprises a foil trap. A gas, in particular a noble gas such as xenon or argon, can be present at least in certain regions in the foil trap in order to decelerate heavy particles from the plasma, such as krypton, gadolinium, or terbium, through collisions.

[0033] According to a further advantageous embodiment, the optical arrangement contains a spectral filter for suppressing visible light and / or radiation of other wavelengths that lie outside the relevant EUV radiation range. For this purpose, the spectral filter can, in particular, comprise a foil comprising at least one of the materials tin, boron carbide, cerium, or lanthanum.

[0034] The invention will be explained below by means of exemplary embodiments in connection with the Fig. 1 to 7 are explained in more detail.

[0035] They show: Fig. 1 a schematic representation of a mirror for EUV radiation according to an embodiment, Fig. 2 a graphical representation of the reflection of mirrors for EUV radiation according to various embodiments, Fig. 3 a schematic representation of a mirror for EUV radiation according to a further embodiment, Fig. 4 a graphical representation of the reflection of mirrors for EUV radiation according to various embodiments, Fig. 5 a schematic representation of a mirror for EUV radiation according to a further embodiment, Fig. 6 a graphical representation of the reflection of mirrors for EUV radiation according to various embodiments, and Fig. 7 an optical arrangement according to an embodiment, which has several mirrors for EUV radiation.

[0036] Identical or functionally identical components are provided with the same reference numerals in the figures. The components depicted and their relative sizes are not to scale.

[0037] The Fig. The mirror 10 for EUV radiation, shown schematically in cross-section in FIG. 1, comprises a substrate 1 and an oxidation-inhibiting layer 2 arranged on the substrate. The substrate 1 can, in particular, be a base body of a beam-shaping optical element. The surface of the substrate 1 can be flat or curved. The substrate 1 is preferably machined prior to coating with the oxidation-inhibiting layer 2 according to the requirements of the application of the mirror 10 with regard to surface shape and surface roughness.

[0038] The oxidation-inhibiting layer 2 is applied to the surface of the substrate 1 by a coating process. The coating of the substrate 1 can be carried out, in particular, by sputtering, although other coating processes can also be used alternatively.

[0039] The mirror 10 is designed to reflect EUV radiation 17 in the wavelength range from 6 nm to 10 nm under grazing incidence. The grazing angle θ (measured with the surface of the mirror 10) at which the EUV radiation impinges on the mirror 10 is preferably between 0° and 20°.

[0040] The oxidation-inhibiting layer 2 applied to the substrate advantageously comprises a lanthanum oxide (LaO x ), a cerium oxide (CeO x ), a thorium oxide (ThO x ), a uranium oxide (UO x ) or diamond-like carbon. These materials are characterized by high reflection in the wavelength range from 6 nm to 10 nm and, at the same time, high stability against oxidation and erosion by ions or neutral particles emitted by an EUV radiation source. The mirror 10 is therefore characterized by high stability in the environment of an EUV radiation source.

[0041] In Fig. 2 is the calculated reflection R as a function of the grazing angle θ for s-polarized radiation with a wavelength λ= 6.7 nm for various embodiments of the mirror according to Fig. 1. The illustrated embodiments each have a 100 nm thick oxidation-inhibiting layer 2 on a substrate 1, wherein the oxidation-inhibiting layer 2 La 2 O 3 , CEO 2 , UO 2 , ThO 3 or DLC.

[0042] In Fig. Figure 3 shows a further embodiment of the mirror for EUV radiation, in which a further layer 3 is arranged between the substrate 1 and the oxidation-inhibiting layer 2. As in the previous embodiment, the oxidation-inhibiting layer 2 advantageously comprises a lanthanum oxide (LaO x ), a cerium oxide (CeO x ), a thorium oxide (ThO x ), a uranium oxide (UO x) or diamond-like carbon and protects the mirror 10 in particular from oxidation and erosion by impinging particles.

[0043] According to one embodiment, the further layer 3 between the substrate 1 and the oxidation-inhibiting layer 2 contains lanthanum, cerium, thorium, or uranium. With these materials, high reflection in the relevant EUV spectral range from 6 nm to 10 nm can be achieved. In a particularly preferred embodiment, the further layer 3 contains a lanthanum nitride (LaN x ), a lanthanum carbide (LaC x ), a cerium nitride (CeN x ), a cerium carbide (CeC x ), a thorium nitride (ThN x ), a thorium carbide (ThC x ), a uranium nitride (UN x ) or a uranium carbide (UC x ) or consists of one of these materials. The aforementioned nitrides and carbides of La, Ce, Th, and U are characterized by particularly good erosion resistance and high reflectivity.

[0044] The oxidation-inhibiting layer 2 can be made comparatively thin if at least one further layer 3 is arranged between the substrate 1 and the oxidation-inhibiting layer 2. The thickness of the oxidation-inhibiting layer 3 is preferably between 1 nm and 10 nm, particularly preferably between 1 nm and 5 nm, for example approximately 3 nm. The at least one further layer 3 is preferably between 50 nm and 100 nm thick.

[0045] In Fig. 4 is the calculated reflection R as a function of the grazing angle θ for s-polarized radiation with a wavelength λ = 6.7 nm for various embodiments of the mirror according to Fig. 3. The illustrated embodiments each have a 3 nm thick oxidation-inhibiting layer 2 made of diamond-like carbon. The further layer 3 is 100 nm thick and consists of La, LaN, LaC, or La 2 O 3 .

[0046] In Fig. 5 shows a further exemplary embodiment of the mirror 10 for EUV radiation. In this exemplary embodiment, the mirror 10 has a layer stack 5 which has layer pairs 4 each consisting of a further layer 3 and an oxidation-inhibiting layer 2. The advantageous configurations of the further layer 3 and the oxidation-inhibiting layer 2 in the layer pairs correspond to the previously described exemplary embodiments. In the exemplary embodiment shown, the layer stack is a periodic layer stack which, for example, has five periods. The alternating arrangement of the oxidation-inhibiting layers 2 and the further layers 3 in a layer stack 5 results in a particularly oxidation- and erosion-resistant mirror 10. The further layers 3 in the layer stack 5 are preferably thicker than the oxidation-inhibiting layers 2 in order to achieve particularly high reflectivity.Preferably, the further layers 3 are more than 5 nm thick and the oxidation-inhibiting layers 2 are less than 5 nm thick.

[0047] In Fig. 6 is the calculated reflection R as a function of the grazing angle θ for s-polarized radiation with a wavelength λ= 6.7 nm for two embodiments of the mirror according to Fig. 5 and a comparative example not according to the claims are shown. The exemplary embodiments have a periodic layer stack 5 with ten layer pairs 4 made of a lanthanum layer 3 and an oxidation-inhibiting layer 2 made of diamond-like carbon. The period thickness is 10 nm, wherein in a first example the lanthanum layer 3 has a thickness of 8 nm and the diamond-like carbon layer 2 has a thickness of 2 nm. In a second example shown, the lanthanum layer 3 has a thickness of 7 nm and the diamond-like carbon layer 2 has a thickness of 3 nm. For comparison, the reflection of a 100 nm thick single layer of lanthanum is shown.

[0048] The Fig. 7 schematically shows an optical arrangement 100 that makes use of the previously described mirror. In the exemplary embodiment, the optical arrangement 100 is an exposure system that images radiation emitted by an EUV radiation source 11 into a focal point 13. The EUV radiation source 11 can be, for example, a discharge-based plasma source. In the EUV radiation source 11, for example, a krypton plasma is generated that emits, among other things, radiation in the spectral range from 6 nm to 10 nm. The EUV radiation 17 emitted by the EUV radiation source 11 is imaged into the focal point 13 by means of a beam-shaping element 12. In the exemplary embodiment shown, the beam-shaping element 12 is a Wolter optic, in particular a Wolter multi-shell collector. The beam-shaping element 12 has, in particular, a plurality of nested mirrors 10, which are preferably arranged concentrically around a common optical axis 16.

[0049] The plurality of mirrors 10 of the beam-shaping element 12 are each EUV mirrors, which are advantageous as previously described in connection with the embodiments of the Fig. 1 to 6 are formed. In particular, the mirrors 10 each comprise a substrate and a reflective, oxidation- and erosion-resistant coating applied thereto according to these embodiments.

[0050] The EUV radiation 17 is reflected at the plurality of mirrors 10 of the beam-shaping element 12, each with grazing incidence, wherein the grazing angle θ of the radiation incident on the mirrors 10 is predominantly in the range between 0° and 20°, particularly preferably in the range between 0° and 10°. It can be provided that a double reflection occurs at the mirrors 10 with grazing incidence. The mirrors 10 can be curved at least in some areas. In particular, the mirrors can be shaped at least in some areas parabolic, elliptical, hyperbolic, or as a freeform surface.

[0051] The optical arrangement 100 advantageously further comprises a spectral filter 15 to suppress spectral components outside the wavelength range of 6 nm to 10 nm. Suitable spectral filters are, in particular, films made of Sn, B4C, Zr, Ce, or La, or combinations thereof. Furthermore, xenon, which is introduced, for example, as a gas into a vacuum chamber of the optical arrangement, can also be used as a spectral filter to suppress EUV radiation outside the wavelength range of 6 nm to 10 nm relevant here.

[0052] Furthermore, the optical arrangement 100 advantageously includes a device 14 for reducing debris. The device 14 is advantageously arranged between the EUV radiation source 11 and the beam-shaping element 12 in order to reduce the impact of ions or neutral particles from the EUV radiation source on the mirrors 10 of the beam-shaping element 12. The device 14 can, in particular, be a foil trap for decelerating the ions or neutral particles emitted from the EUV radiation source 11. Such a foil trap 14 is known per se in connection with an EUV radiation source and can, in particular, have foils arranged in a lamella-like manner, which capture particles emitted from the EUV radiation source.

[0053] A gas such as xenon or argon can advantageously be supplied to the area of ​​the foil trap, with the gas atoms slowing down the emitted ions or atoms from the EUV radiation source through collisions. For the present application, xenon is particularly used in conjunction with the foil trap. The heavy xenon atoms slow down heavy particles from the plasma, such as krypton, gadolinium, or terbium, particularly effectively. When using lighter elements as the radiation source, the use of a lighter collision partner in the foil trap can be advantageous, in particular the use of argon. Furthermore, it is also conceivable to use magnetic fields to deflect or slow down charged particles from the plasma of the EUV radiation source 11.

[0054] The EUV radiation source 11 can, for example, emit radiation with a radiant power of more than 50 W in the wavelength range from 6 nm to 10 nm into a half-space. The beam-shaping element 12, which is exemplified here as a Wolter multi-shell collector, can collect a radiant power of approximately 15 W, for example, at a technically feasible aperture angle of approximately 45°. However, losses due to the device 14 for reducing debris, a reflectivity of the mirrors 10 of less than 100%, and losses due to the spectral filter 15 must be taken into account. These losses can attenuate the radiation by a factor of approximately 3 to 5. Taking these losses into account, a radiant power of approximately 3 W to 5 W can still be achieved at the focus 13. List of reference symbols 1 substrate 2 oxidation-inhibiting layer 3 more layers 4 shift pairs 5 layer stacks 10 mirrors 11 EUV radiation source 12 Beam shaping element 13 Focus 14 Device for reducing debris 15 spectral filters 16 optical axis 17 EUV radiation 100 optical arrangement

Claims

[1] Optical arrangement (100) with - at least one mirror (10) for reflecting EUV radiation (17) in the spectral range between 6 nm and 10 nm, which comprises a layer stack (5) having a plurality of layer pairs (4), each containing a first layer and a second layer, wherein the second layer is an oxidation-inhibiting layer (2) comprising a lanthanum oxide, a cerium oxide, a thorium oxide, a uranium oxide or diamond-like carbon, and wherein the first layer is a further layer (3) comprising lanthanum, cerium, uranium, thorium, a lanthanum nitride, a lanthanum carbide, a cerium nitride, a cerium carbide, a thorium nitride, a thorium carbide, a uranium nitride or a uranium carbide, - an EUV radiation source (11) suitable for emitting EUV radiation (17) with a wavelength between 6 nm and 10 nm, and - at least one beam-shaping element (12) having the at least one mirror (10), wherein the EUV radiation (17) emitted by the EUV radiation source (11) predominantly impinges on the at least one mirror (10) in an angular range between 0° and 20° relative to the surface of the mirror (10). [2] Optical arrangement according to claim 1, wherein the beam-shaping element (12) is arranged to focus the EUV radiation (17). [3] Optical arrangement according to claim 1 or 2, wherein the beam-shaping element (12) is a Wolter optic. [4] Optical arrangement according to one of the preceding claims, wherein the at least one mirror (10) has at least in some regions a parabolic, elliptical or hyperbolic shape or a free form. [5] Optical arrangement according to one of the preceding claims, wherein the optical arrangement (100) comprises a spectral filter (15) for suppressing radiation outside the wavelength range from 6 nm to 10 nm, and wherein the spectral filter (15) comprises a foil comprising at least one of the materials tin, boron carbide, cerium or lanthanum. [6] An optical arrangement according to any one of the preceding claims, wherein the first layers and the second layers each have a thickness of 1 nm to 10 nm. [7] An optical arrangement according to any one of the preceding claims, wherein the first layers are more than 5 nm thick and the second layers are less than 5 nm thick.

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