Mirror layer and mirror for a lithographic apparatus

Abstract

At least 447 kJmol -1 A mirror layer for a lithographic apparatus is provided, the mirror layer comprising at least one element that forms a chemical bond with silicon with a bond dissociation energy of 0.05 to 0.05. Also provided are methods for manufacturing the mirror layer, mirrors comprising the mirror layer described herein, and lithographic apparatuses comprising the mirror layer or mirror. Further described are the use of molybdenum sulfide silicide, molybdenum oxide silicide, molybdenum selenide silicide, or molybdenum fluoride silicide in the mirror layer or mirror, and the use of the mirror layer or mirror in a lithographic apparatus or method.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Application No. 22201625.5, filed October 14, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a mirror layer for a lithographic apparatus, in particular an EUV lithographic apparatus, and to a mirror for the lithographic apparatus, a method for controlling diffusion of material in a mirror layer or mirror for the lithographic apparatus, a method for manufacturing a mirror layer or mirror for the lithographic apparatus, and the use of such a mirror layer or mirror in a lithographic apparatus or process. [Background technology]

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern from a patterning device (e.g. a mask) onto a layer of radiation-sensitive material (resist) provided on the substrate.

[0004]

[0004] The wavelength of the radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features that can be formed on the substrate. Lithographic apparatus using EUV radiation, which is electromagnetic radiation having a wavelength in the range of 4 to 20 nm, can be used to form smaller features on a substrate compared to conventional lithographic apparatus (which may, for example, use electromagnetic radiation having a wavelength of 193 nm).

[0005] A lithographic apparatus includes a patterning device (e.g. a mask or reticle). Radiation is provided through or reflected by the patterning device to form an image on a substrate. A membrane assembly, also called a pellicle, may be provided to protect the patterning device from airborne particles and other forms of contamination. Contamination on the surface of the patterning device can cause manufacturing defects on the substrate.

[0006]

[0006] Lithographic apparatuses use mirrors to shape radiation within the apparatus and direct it from the radiation source to the patterning device and onto the substrate. The mirrors must be manufactured with great precision and must be able to withstand the environment within the lithographic apparatus, including being illuminated by intense radiation. Mirrors can be constructed from alternating layers of different materials to provide Bragg reflection. Such alternating layers can include, for example, alternating silicon and molybdenum layers. Mirrors can be provided with protective caps to protect underlying layers from the harsh environment within the lithographic apparatus. Existing mirror cap materials can cause the release of substances such as silicon, which may be called hydrogen-induced outgassing, which can lead to contamination within the lithographic apparatus. Contamination is undesirable as it can adversely affect the performance of the lithographic apparatus.

[0007]

[0007] It would therefore be desirable to provide a mirror that can withstand the harsh environments of a lithography apparatus, particularly an EUV lithography apparatus. In particular, it would be desirable to provide a mirror that can withstand higher powers than previously possible. It would also be desirable to provide a mirror that limits or eliminates contamination of the lithography apparatus due to the release of material from the mirror, which may be referred to as hydrogen-induced outgassing.

[0008]

[0008] The present invention has been devised with the aim of addressing at least some of the above-mentioned problems. Summary of the Invention

[0009] According to a first aspect of the present disclosure, at least 447 kJ mol -1 Alternatively, a mirror layer is provided that includes at least one element that forms a chemical bond with silicon with a bond dissociation energy of at least 4.6 eV.

[0010]

[0010] The selection of materials for the mirror is based on criteria such as thermodynamic redox stability, hydride formation, volatility, and heat resistance, among others. The bond dissociation energy of the material forming the mirror layer has also been found to be an important selection criterion. The mirror layer may be one or more layers included in a mirror comprising a stack of different materials. A mirror layer does not necessarily contribute to the reflective properties of the mirror, but may be included to protect one or more layers that contribute to the reflective properties of the mirror. In particular, the presence of bonds stronger than silicon-carbon bonds (which have a bond dissociation energy of approximately 3.6 eV) in the mirror layer implies reduced migration of materials such as silicon and ultimately outgassing from the mirror layer. While not wishing to be bound by scientific theory, it is believed that bonds within the material are less susceptible to bond-breaking events and, as a result, exhibit less and slower diffusion. In other words, the desired bond dissociation energy according to the present disclosure is equal to or greater than the bond dissociation energy of the silicon-carbon bond + 1 eV, i.e., 3.6 eV + 1 eV = 4.6 eV (i.e., 447 kJ mol -1 (Above)Above.

[0011]

[0011] Elements that can form bonds with silicon with such strength include sulfur, oxygen, selenium, and fluorine. Stated another way, the minimum bond dissociation energy may be 4.6 eV.

[0012] For example, Si-S bonds in a mirror layer have a higher bond dissociation energy than Si-N bonds in a similar mirror layer. Oxygen, selenium, and fluorine have higher EUV absorption coefficients than nitrogen or amorphous carbon, while the bond dissociation energies of oxygen, selenium, and fluorine with silicon are greater than the bond dissociation energies of nitrogen and amorphous carbon with silicon, resulting in less outgassing of materials from the mirror layer. It is envisioned that improving bond strength would result in fewer bonds being broken when EUV light interacts with the EUV mirror. Improving bond strength can be particularly useful during plasma exposure, as the energy of hydrogen ions can be less than 10 eV, while EUV light can be approximately 92 eV. Therefore, such improvement is particularly relevant to degradation by hydrogen plasma.

[0013]

[0013] The higher the bond dissociation energy, the fewer bond-breaking events occur when photons and / or low-energy hydrogen ions with energies less than or up to 10 eV are incident on the mirror layer. This results in less migration of materials such as silicon through the material to the outer surface of the mirror or mirror layer, and therefore less outgassing of materials such as silicon. Because sulfur has a lower EUV absorption coefficient and a higher bond dissociation energy than nitrogen and carbon, sulfur-carbon bonds are less likely to break during use. Silicon has a lower EUV absorption coefficient than sulfur, but also a lower bond dissociation energy, making silicon outgassing more likely. Furthermore, sulfur is not a concern as it contributes significantly to the contamination of optical systems in lithography apparatuses.

[0014]

[0014] The mirror layer may include silicon sulfide. The mirror layer may consist of silicon sulfide. The mirror layer may include or consist of one or more of silicon oxide, silicon selenide, or silicon fluoride, or a combination of one or more matrix materials described herein. The mirror layer may include silicon and a metal, a metal silicide, a metal fluoride, a metal boride, a metal carbide, a metal oxide, and / or a metal selenide. The mirror layer may include i) one or more of silicon carbide, germanium carbide, silicon fluoride, germanium fluoride, silicon boride, germanium boride, silicon oxide, and germanium oxide, and ii) a metal. The mirror layer may include i) one or more of a metal, a metal silicide, a metal fluoride, a metal boride, a metal carbide, a metal oxide, and / or a metal selenide; and ii) one or more of silicon carbide, germanium carbide, silicon fluoride, germanium fluoride, silicon boride, germanium boride, silicon oxide, and germanium oxide.

[0015]

[0015] The mirror layer may include one or more of a metal carbide, a metal boride, a metal nitride, a metal fluoride, a metal silicide, or a metal. The metal (which may be any of the compounds or elemental metals mentioned above) may be selected from one or more of molybdenum, zirconium, yttrium, lanthanum, scandium, niobium, iridium, chromium, vanadium, platinum, rhodium, hafnium, and ruthenium. Yttrium oxide, zirconium oxide, hafnium oxide, and carbon nitride show particular potential because they contain bonds with bond dissociation energies greater than 4.6 eV. Furthermore, such materials have ultimate tensile strengths comparable to silicon.

[0016] The sulfur-containing mirror layer is SiS 2-y where 0≦y<2. The inclusion of sulfur in the mirror layer is believed to reduce outgassing by binding strongly to silicon, thereby inhibiting silicon migration and outgassing.

[0017]

[0017] The mirror layer is at least partially Mo a Si b S c may have the formula, where 0 < a ≤ 30, 50 ≤ b ≤ 90, and 0 < c ≤ 50 (in mol%). In multiple embodiments, 10 ≤ a ≤ 30 (in mol%). In multiple embodiments, 60 ≤ b ≤ 70 (in mol%). In multiple embodiments, 20 ≤ c ≤ 30 (in mol%). The thermodynamic stability of the mirror layer may depend on the relative amounts of metal, silicon, and sulfur. The amount of sulfur is controlled to avoid formation of a gas phase at a given temperature and further to avoid unwanted oxidation. The amount of silicon is controlled to provide sufficient strength to the mirror layer while reducing the likelihood of silicon gas evolution.

[0018]

[0018] The mirror layer may include silicon and a metal, preferably molybdenum, and the Si:metal (Mo) ratio (in mol%) may deviate from 2.0. In other words, the Si:metal ratio is lower than the stoichiometric value. That is, the amount of silicon is less than the stoichiometric value. Thus, the mirror layer is relatively metal-rich, which reduces the likelihood of silicon gas evolution. This also allows the layer to be thinner than when the amount of silicon relative to molybdenum is at the stoichiometric value.

[0019]

[0019] Throughout this disclosure, it will be understood that due to manufacturing tolerances and material tolerances, there may be unintentional minor contaminants present. The contaminants may be present in amounts that are not critical to the performance of the layer. In such embodiments, no additional elements are intentionally included.

[0020]

[0020] According to a second aspect of the present disclosure, a mirror is provided that includes a mirror layer according to the first aspect of the present disclosure.

[0021]

[0021] The mirror may be a multilayer mirror. The mirror may include a stack of layers of different materials. The stack may include alternating layers of silicon and molybdenum.

[0022]

[0022] According to a third aspect of the present disclosure, a method for manufacturing a mirror layer or a mirror according to the first or second aspect of the present disclosure is provided, the method including sputtering, optionally co-sputtering.

[0023]

[0023] In sputtering, preferably co-sputtering, the exact composition of the mirror layer or the mirror can be controlled, thereby enabling the manufacture of a mirror layer or a mirror according to the present disclosure.

[0024]

[0024] According to a fourth aspect of the present disclosure, a lithographic apparatus is provided comprising a mirror layer or a mirror according to the first or second aspect of the present disclosure, or a mirror layer or a mirror manufactured by the method according to the third aspect of the present disclosure.

[0025]

[0025] According to a fifth aspect of the present disclosure, the use of molybdenum silicide sulfide, molybdenum silicide oxide, molybdenum silicide selenide, or molybdenum silicide fluoride in a mirror layer or a mirror is provided.

[0026]

[0026] The mirror layer or the mirror may be a mirror layer or a mirror according to any aspect of the present disclosure. In a plurality of embodiments, the mirror layer or the mirror may have the formula of at least partially Mo a Si b S c where 0 < a ≤ 30, 50 ≤ b ≤ 90, and 0 < c ≤ 50 (in mol%).

[0027]

[0027] According to a sixth aspect of the present disclosure, the use of a mirror layer, a mirror, or a lithographic apparatus according to the first, second, fourth, or fifth aspect of the present disclosure in a lithographic apparatus or method is provided.

[0028]

[0028] Features described in connection with one embodiment can be combined with any features described in connection with another embodiment, and it will be understood that all such combinations are explicitly contemplated and disclosed herein. [Brief explanation of the drawings]

[0029]

[0029] Some embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which like reference symbols indicate corresponding parts, and in which:

[0030] [Figure 1] 1 depicts a lithographic apparatus according to one embodiment of the present invention; [Figure 2]

[0031] 1 illustrates a multi-layer mirror according to one aspect of the present disclosure including a mirror layer according to the present disclosure.

[0031]

[0032] The features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout and generally indicate identical, functionally similar, and / or structurally similar elements. DETAILED DESCRIPTION OF THE INVENTION

[0032]

[0033] Figure 1 shows a lithographic system according to the present invention. The lithographic system comprises a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate a beam of extreme ultraviolet (EUV) radiation B. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g. a mask), a projection system PS, and a substrate table WT configured to support a substrate W. The illumination system IL is configured to condition the radiation beam B before it is incident on the patterning device MA. The projection system is configured to project the radiation beam B (patterned by the mask MA) onto the substrate W. The substrate W may include a pre-formed pattern. In such a case, the lithographic apparatus aligns the patterned radiation beam B with the pre-formed pattern on the substrate W. In this embodiment, a pellicle 15 is shown in the path of the radiation to protect the patterning device MA. It will be understood that the pellicle 15 can be positioned at any required position and can be used to protect any of the mirrors in the lithographic apparatus. Any one or more of the mirrors may be a mirror according to the present disclosure.

[0033]

[0034] The source SO, illumination system IL, and projection system PS may all be constructed and arranged so that they can be isolated from the external environment. A gas (e.g., hydrogen) at a pressure below atmospheric pressure may be provided in the source SO. A vacuum may be provided in the illumination system IL and / or projection system PS. A small amount of gas (e.g., hydrogen) at a pressure well below atmospheric pressure may be provided in the illumination system IL and / or projection system PS.

[0034]

[0035] The radiation source SO shown in FIG. 1 is of a type that can be referred to as a laser-produced plasma (LPP) source. A laser, which may be, for example, a CO laser, is arranged to deposit energy via a laser beam into a fuel, such as tin (Sn), provided from a fuel emitter. While tin is referred to in the following description, any suitable fuel can be used. The fuel can be, for example, in liquid form and can be, for example, a metal or alloy. The fuel emitter can include, for example, a nozzle configured to direct tin in the form of droplets along a trajectory toward the plasma formation region. The laser beam is incident on the tin in the plasma formation region. Deposition of the laser energy into the tin generates a plasma in the plasma formation region. Radiation, including EUV radiation, is emitted from the plasma during de-excitation and recombination of the ions of the plasma.

[0035]

[0036] The EUV radiation is collected and focused by a near-normal incidence radiation collector (sometimes referred to as a more general normal incidence radiation collector). The collector may have a multi-layer structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength, such as 13.5 nm). The collector may have an elliptical configuration with two elliptical foci. As described below, the first focus may be at the plasma formation region and the second focus may be an intermediate focus.

[0036]

[0037] The laser may be remote from the radiation source SO. In such a case, the laser beam may be delivered from the laser to the radiation source SO using a beam delivery system (not shown), e.g. comprising suitable directing mirrors, and / or beam expanders and / or other optics. The laser and radiation source SO together may be considered a radiation system.

[0037]

[0038] The radiation reflected from the collector forms a radiation beam B. The radiation beam B is focused to a point to form an image of the plasma formation region, which image acts as a virtual radiation source for the illumination system IL. The point at which the radiation beam B is focused may be referred to as the intermediate focus. The radiation source SO is positioned such that the intermediate focus is located on or near an opening in the source enclosure.

[0038]

[0039] The radiation beam B passes from the radiation source SO into an illumination system IL configured to condition the radiation beam. The illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. Together, the facetted field mirror device 10 and the facetted pupil mirror device 11 provide the radiation beam B with a desired cross-sectional shape and a desired angular distribution. The radiation beam B passes through the illumination system IL and is incident on a patterning device MA held on a support structure MT. The patterning device MA reflects the radiation beam B and forms a pattern in the radiation beam B. The illumination system IL may include other mirrors or devices in addition to, or instead of, the facetted field mirror device 10 and the facetted pupil mirror device 11.

[0039]

[0040] After reflecting from the patterning device MA, the patterned radiation beam B enters a projection system PS. The projection system comprises a number of mirrors 13, 14, which are arranged to project the radiation beam B onto a substrate W held on a substrate table WT. The projection system PS may apply a demagnification factor to the radiation beam to form an image having smaller features than corresponding features on the patterning device MA. For example, a demagnification factor of 4 may be applied. In Figure 1, the projection system PS has two mirrors 13, 14, but the projection system may include any number of mirrors (e.g. six mirrors).

[0040]

[0041] The radiation source SO shown in Figure 1 may include components not shown, for example, a spectral filter may be provided within the radiation source that is substantially transparent to EUV radiation while substantially blocking radiation of other wavelengths, such as infrared radiation.

[0041]

[0042] In one embodiment, the membrane assembly 15 is a pellicle for a patterning device MA for EUV lithography. The membrane assembly 15 can be used for a dynamic gas lock, a pellicle, or other purposes. In one embodiment, the membrane assembly 15 comprises a membrane formed from at least one membrane layer having an emissivity of 0.3 or greater. To ensure maximum EUV transmission and minimal impact on imaging performance, the membrane is preferably supported only at its edges.

[0042]

[0043] If the patterning device MA is left unprotected, contamination may require the patterning device MA to be cleaned or discarded. Cleaning the patterning device MA interrupts valuable production time, and discarding a patterning device MA is expensive. Replacing the patterning device MA also interrupts valuable production time.

[0043]

[0044] 2 is a schematic diagram of a multi-layer mirror 16 according to one embodiment of the present disclosure, including a mirror layer 17 according to the present disclosure. The mirror 16 includes alternating layers of different materials 18a, 18, which form a Bragg reflector. It will be understood that the mirror may include more layers than those shown in the schematic, and that the relative dimensions of the layers may differ from those shown. In the illustrated embodiment, the mirror layer 17 is a cap layer, but it will be understood that the mirror layer may be one or more of alternating layers of different materials 18a, 18 in other embodiments.

[0044]

[0045] The present invention aims to mitigate hydrogen-induced outgassing (HIO) of Si-containing species from metal silicide-based composite (MSC) mirrors under EUV scanner operating conditions. In some embodiments, the present disclosure provides a method for fabricating a Si-ψ mirror, where the silicon is Si-ψ. y We describe a mirror layer or mirror bonded to a secondary element "ψ" called the matrix. An MSC material selection parameter can be the "bond dissociation energy (BDE)" of the Si-ψ bond in the matrix. The BDE of the Si-ψ bond in the matrix governs the cleavage of the Si-ψ bond during scanner operation, which generates free Si species that can diffuse and be released from the mirror layer or mirror via the HIO process. Therefore, a high BDE of Si-ψ weakens the HIO process. We describe BDE as a parameter for selecting a mirror layer or mirror material.

[0045]

[0046] One aspect of the present invention is a new mirror layer or mirror Si-ψ material combination, where ψ is S, O, Se, or F. For example, when ψ=S, Si-S 2-y The Si-S bonds within the matrix material have a higher bond dissociation energy (BDE) than the Si-N bonds within the SiN matrix. As discussed above, a higher BDE results in fewer bond breaking events when a photon is incident on the material, which can result in less Si migrating through the matrix material to the outer surface, resulting in less Si outgassing. Based on the BDE of Si-S and other compositions described herein, mirror layers or mirrors of the present disclosure exhibit lower outgassing compared to other options such as MoSiN, MoSiSi, and MoSiC.

[0046]

[0047] The BDE threshold is defined herein as any value greater than the Si-N, Si-C, and Si-Si bonds.

[0047]

[0048] In relation to the bond dissociation energy (BDE) between element ψ and Si, and the migration of Si atoms and subsequent outgassing, if the Si-ψ BDE is strong enough, Si migration is suppressed and outgassing can occur only temporarily until Si is depleted from the mirror layer or external region of the mirror. Excess Si can migrate through the mirror layer or mirror and be released in the external region in many of the processes described above as Si outgassing (e.g., SiO2 desorption or SiH4 formation). Therefore, material combinations with potentially low levels of outgassing, such as those described herein, exhibit high Si-ψ bond energy, limiting bond dissociation and thus limiting the Si-ψ bond energy of Si atoms. 2-x Migration through the matrix is ​​restricted and outgassing is similarly restricted.

[0048]

[0049] Here, an exemplary specification for the allowable amount of HIO is a maximum of 1.1×10 outgassed Si atoms per 10,000 scanner wafers. 15 at.cm -2 will be featured.

[0049]

[0050] Two very important parameters that determine whether a volatile species poses a risk of degrading the optical performance of the EUV mirror are, first, the species' ability to adhere to the surface of the EUV mirror, and second, whether the species oxidizes on the surface of the mirror.

[0050]

[0051] At a minimum, the BDE value of the Si-C bond is considered to be the highest among the three types of composite pellicles, MoSiC, MoSiSi, and MoSiN, all of which exhibit Si outgassing, which is hypothesized to be related to atomic migration. Thus, a larger BDE value for the atomic bond is preferable to reduce bond breaking events and subsequent atomic migration. The present invention asserts that the BDE must exceed the "SiC + 1 eV" value to achieve any improvement. According to the present invention, silicon outgassing can be reduced by providing a mirror layer or mirror containing a material that forms strong bonds with silicon. Because the strong silicon-sulfur bond has a higher bond dissociation energy than silicon-nitrogen or silicon-silicon bonds, bond dissociation, which causes silicon migration and outgassing, is less likely to occur when this mirror is illuminated by EUV light and / or subjected to a low-ion-energy H scanner plasma with hydrogen ions having energies less than or up to 10 eV. Sulfur is not significantly associated with contamination of optics within lithographic apparatus, so some sulfur outgassing does not pose a significant contamination concern.

[0051]

[0052] The present invention allows for an uncovered mirror due to the reduced tendency of silicon to outgas.

[0052]

[0053] Mirrors according to the present disclosure can be fabricated by sputtering. Sputtering a molybdenum silicide target and a silicon sulfide target results in a mirror layer with metal-rich molybdenum silicide crystals in a silicon sulfide matrix. Similarly, reactive sputtering of molybdenum disilicide in a hydrogen sulfide atmosphere results in mirrors of the present disclosure. Providing sulfur in the matrix provides strong bonding with silicon, and silicon outgassing can only be observed until silicon is depleted in the outer regions of the mirror where outgassing is more likely. It is believed that the strong bonding with sulfur inhibits silicon migration.

[0053]

[0054] Thus, the present disclosure provides a mirror that can operate in a lithography apparatus, particularly an EUV apparatus, by having comparable or better optical performance compared to other mirrors, while having less silicon outgassing, and having acceptable EUV reflectivity and acceptable emissivity.

[0054]

[0055] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0055]

[0056] The above description is intended to be illustrative and not limiting. Thus, it will be apparent to one skilled in the art that modifications such as those described above can be made to the invention without departing from the scope of the claims set out below.

Claims

1. At least 447 kJmol －１ or a mirror layer for a lithographic apparatus, comprising at least one element that forms a chemical bond with silicon with a bond dissociation energy of at least 4.6 eV.

2. 10. The mirror layer of claim 1, wherein the at least one element is selected from sulfur, oxygen, selenium, or fluorine, and optionally the mirror layer comprises silicon sulfide, silicon oxide, silicon selenide, or silicon fluoride.

3. 3. The mirror layer of claim 1 or 2, wherein the mirror layer comprises one or more of a metal carbide, a metal boride, a metal nitride, a metal fluoride, a metal silicide, or a metal, optionally wherein the metal is selected from one or more of molybdenum, zirconium, yttrium, lanthanum, scandium, niobium, iridium, chromium, vanadium, platinum, rhodium, hafnium, and ruthenium.

4. 3. The mirror layer according to claim 1 or 2, wherein the mirror layer comprises silicon and a metal, a metal silicide, a metal fluoride, a metal boride, a metal carbide, a metal oxide, and / or a metal selenide.

5. 3. The mirror layer of claim 1 or 2, wherein the mirror layer comprises: i) one or more of silicon carbide, germanium carbide, silicon fluoride, germanium fluoride, silicon boride, germanium boride, silicon oxide, and germanium oxide; and ii) a metal.

6. 3. The mirror layer of claim 1, wherein the mirror layer comprises: i) one or more of a metal, a metal silicide, a metal fluoride, a metal boride, a metal carbide, a metal oxide, and / or a metal selenide; and ii) one or more of silicon carbide, germanium carbide, silicon fluoride, germanium fluoride, silicon boride, germanium boride, silicon oxide, and germanium oxide.

7. The mirror layer is made of SiS ２－ｙ 7. The mirror layer according to claim 1, having a composition of: wherein 0≦y<2.

8. The mirror layer is at least partially made of Mo ａ Si ｂ S ｃ 8. The mirror layer according to any one of claims 1 to 7, having the formula: where 0<a≦30, 50≦b≦90, and 0<c≦50 (in mol %).

9. 9. The mirror layer of claim 8, wherein 10≦a≦30 (by mol %).

10. 10. The mirror layer according to claim 8 or 9, wherein 60≦b≦70 (by mol %).

11. Mirror layer according to any one of claims 8 to 10, wherein 20≦c≦30 (in mol %).

12. Mirror layer according to any one of the preceding claims, wherein the mirror comprises silicon and molybdenum, the Si:Mo ratio (in mol %) deviating from 2.

0.

13. A mirror comprising a mirror layer according to any one of claims 1 to 12.

14. Mirror according to claim 13, wherein the mirror is a multi-layer mirror, preferably comprising alternating layers of silicon and molybdenum.

15. A method for producing a mirror layer or mirror according to any one of claims 1 to 14, comprising sputtering, optionally co-sputtering.

16. A lithographic apparatus comprising a mirror layer according to any one of claims 1 to 14, or a mirror layer or mirror produced according to claim 15.

17. Use of molybdenum sulfide silicide, molybdenum oxide silicide, molybdenum selenide silicide, or molybdenum fluoride silicide in the mirror layer or mirror.

18. Use of a mirror according to any one of claims 1 to 14 or a lithographic apparatus according to claim 16 in a lithographic apparatus or method.

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