Mirror layer and mirror for lithographic apparatus

Abstract

A mirror layer for a lithographic apparatus is provided that includes at least one element that forms a chemical bond with silicon, the chemical bond having a bond dissociation energy of at least 447 kJ mol-1. Also provided is a method of manufacturing such a mirror layer, a mirror comprising a mirror layer described herein, and a lithographic apparatus comprising such a mirror layer or mirror. The use of molybdenum silicon sulfide, oxide, selenide or fluoride in a mirror layer or mirror, as well as the use of such a mirror layer or mirror in a lithographic apparatus or method, is also described.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to European application No. 22201625.5 filed on October 14, 2022, and the entire contents of this European application are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to a reflector layer for a lithography apparatus, in particular for an EUV lithography apparatus. The present disclosure also relates to a reflector for a lithography apparatus, a method for controlling diffusion of a material in a reflector layer or a reflector for a lithography apparatus, a method for manufacturing a reflector layer or a reflector for a lithography apparatus, and a use of such a reflector layer or a reflector in a lithography apparatus or process. Background Art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern onto a substrate. A lithographic apparatus may be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern from a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) disposed on a substrate.

[0005] The wavelength of radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of a feature that can be formed on the substrate. A lithographic apparatus using EUV radiation, which is electromagnetic radiation having a wavelength in the range of 4 nm to 20 nm, can be used to form smaller features on a substrate compared to a conventional lithographic apparatus (which may, for example, use electromagnetic radiation having a wavelength of 193 nm).

[0006] The lithographic apparatus includes a patterning device (e.g., a mask or reticle). Radiation is provided through or reflected from the patterning device to form an image on a substrate. A diaphragm assembly (also referred to as 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 may cause manufacturing defects on the substrate.

[0007] Lithographic equipment utilizes reflectors to shape radiation within the equipment and direct the radiation within the equipment from the radiation source to the pattern forming device, and then to the substrate. The reflectors need to be manufactured very accurately and also be able to withstand the environment within the lithographic equipment, including exposure to strong radiation. The reflectors can be constructed of alternating layers of different materials to provide Bragg reflection. Such alternating layers can, for example, include alternating silicon and molybdenum layers. The reflectors can be provided with protective covers to protect the bottom layer from the harsh environment within the lithographic equipment. Existing reflector cover materials can release materials, such as silicon, from them, which can be referred to as hydrogen-induced degassing, which can cause contamination within the lithographic equipment. Contamination may adversely affect the performance of the lithographic equipment and is therefore undesirable.

[0008] It is therefore desirable to provide a mirror that can withstand the harsh environment of a lithographic apparatus, in particular an EUV lithographic apparatus. It is particularly desirable to provide a mirror that can withstand higher powers than previously possible. It is also desirable to provide a mirror that limits or eliminates contamination of the lithographic apparatus caused by release of material from the mirror (which may be referred to as hydrogen-induced outgassing).

[0009] The present invention has been designed in an attempt to address at least some of the problems identified above. Summary of the invention

[0010] According to a first aspect of the present disclosure, there is provided a reflector layer comprising at least one element that forms a chemical bond with silicon, the chemical bond having a strength of at least 447 kJ mol -1 Or a bond dissociation energy of at least 4.6 eV.

[0011] The selection of materials for the reflector is based on criteria such as thermodynamic reduction and oxidation stability, hydride formation, volatility tendency, heat resistance, etc. It has been found that the bond dissociation energy of the material forming the reflector layer is also an important selection criterion. The reflector layer can be one or more layers included in the reflector, and the reflector includes a stack of different materials in the layer. The reflector layer does not have to contribute to the reflective properties of the reflector, and can be included as a protection for one or more layers that contribute to the reflective properties of the reflector. In particular, the presence of stronger bonds in the reflector layer than the silicon-carbon bond (which has a bond dissociation energy of about 3.6 eV) means that the movement and eventual outgassing of materials such as silicon from the reflector layer is attenuated. Without wishing to be bound by scientific theory, it is believed that the bonds in the material are less susceptible to release by bond breaking events and therefore exhibit less and slower diffusion. In other words, the bond dissociation energy expected according to the present disclosure is equal to or greater than the bond dissociation energy of the silicon-carbon bond plus 1 eV, that is, 3.6 eV + 1 eV = 4.6 eV, which is equal to 447 kJ mol -1 or larger.

[0012] Elements that can form such a strong bond with silicon include sulfur, oxygen, selenium, and fluorine. In other words, the minimum bond dissociation energy may be 4.6 eV.

[0013] For example, Si-S bonds in a mirror layer have higher bond dissociation energies than Si-N bonds in a similar mirror layer. Although oxygen, selenium, and fluorine have higher EUV absorption coefficients than nitrogen or amorphous carbon, 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, so outgassing of the material from the mirror layer will be less. It is contemplated to increase the bond strength so that when EUV light interacts with the EUV mirror, less bonds are broken. Increased bond strength can be especially helpful during plasma exposure because the H ion energy can be below 10 eV, while EUV light can be around 92 eV. Therefore, such an improvement is particularly relevant for degradation by H2 plasma.

[0014] When photons and / or low energy H ions with energies below 10 eV or at most 10 eV are incident on the mirror layer, the higher bond dissociation energy results in fewer bond breaking events. This has the consequence that there is less migration of materials such as silicon through the material to the outer surface of the mirror or mirror layer, which in turn results in less outgassing of such materials such as silicon. Sulfur has a lower EUV absorption coefficient than nitrogen and carbon, and also has a higher bond dissociation energy, so sulfur-carbon bonds are less likely to break in use. Although silicon has a lower EUV absorption coefficient than sulfur, it has a lower bond dissociation energy and is therefore more likely to cause silicon outgassing. Furthermore, it is not suspected that sulfur contributes significantly to the contamination of optical devices within the lithographic apparatus.

[0015] The reflector layer may include silicon sulfide. The reflector layer may consist of silicon sulfide. The reflector 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 reflector layer may include silicon and metal, metal silicide, metal fluoride, metal boride, metal carbide, metal oxide and / or metal selenide. The reflector 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) metal. The reflector layer may include i) one or more of metal, metal silicide, metal fluoride, metal boride, metal carbide, metal oxide and / or 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.

[0016] The reflector 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 a metal as any of the aforementioned compounds or elemental metals) may be selected from one or more of the following: 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 include bonds with bond dissociation energies greater than 4.6 eV. Such materials also have an ultimate tensile strength similar to that of silicon.

[0017] The sulfur-containing mirror layer may have the composition SiS 2-y , where 0 ≤ y < 2. It is believed that including sulfur in the mirror layer reduces outgassing by strongly bonding the sulfur to silicon, thereby inhibiting silicon migration and outgassing.

[0018] The mirror layer may at least partially have the molecular formula Mo a Si b S c , wherein, in mol %, 0 < a ≤ 30, 50 ≤ b ≤ 90 and 0 < c ≤ 50. In an embodiment, in mol %, 10 ≤ a ≤ 30. In an embodiment, in mol %, 60 ≤ b ≤ 70. In an embodiment, in mol %, 20 ≤ c ≤ 30. 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 the formation of a gas phase at certain temperatures and also to avoid unwanted oxidation. The amount of silicon is controlled to provide sufficient strength to the mirror layer while reducing the possibility of silicon outgassing.

[0019] The mirror layer may comprise silicon and a metal, preferably molybdenum, and the ratio of Si:metal (Mo) (in mol %) may deviate from 2.0. In other words, the Si:metal ratio is below the stoichiometric value, i.e., less than the stoichiometric value of silicon. In this way, the mirror layer is relatively rich in metal, which reduces the possibility of silicon outgassing. This also allows thinner layers than would be the case with a stoichiometric amount of silicon to molybdenum.

[0020] Throughout this disclosure, it should be understood that due to manufacturing and material tolerances, unintentional micro-contaminants may be present. The amount of the contaminants present may be insignificant to the performance of the layer. In such an embodiment, no additional elements are intentionally included.

[0021] According to a second aspect of the present disclosure, a reflector is provided, comprising the reflector layer according to the first aspect of the present disclosure.

[0022] The reflector may be a multilayer reflector. The reflector may include a stack of multiple layers of different materials. The stack may include alternating layers or silicon and molybdenum.

[0023] According to a third aspect of the present disclosure, there is provided a method of manufacturing a mirror layer or a mirror according to the first or second aspect of the present disclosure, wherein the method comprises sputtering, optionally co-sputtering.

[0024] Sputtering, preferably co-sputtering, provides for the exact composition of the mirror layer or the mirror to be controlled, thereby allowing the manufacturing of the mirror layer or the mirror according to the present disclosure.

[0025] According to a fourth aspect of the present disclosure, a lithography device is provided, comprising: a reflector layer or a reflector according to the first aspect or the second aspect; or a reflector layer or a reflector manufactured by the method according to the third aspect of the present invention.

[0026] According to a fifth aspect of the present disclosure, there is provided a method for using molybdenum silicon sulfide, molybdenum silicon oxide, molybdenum silicon selenide or molybdenum silicon fluoride in a reflector layer or a reflector.

[0027] The reflector layer or reflector may be a reflector layer or reflector according to any aspect of the present disclosure. In an embodiment, the reflector layer or reflector may at least partially have a molecular formula Mo a Si b S c , wherein, in mol %, 0 < a ≤ 30, 50 ≤ b ≤ 90 and 0 < c ≤ 50.

[0028] According to a sixth aspect of the present disclosure, there is provided a use of the mirror layer, the mirror or the lithography device according to the first, second, fourth or fifth aspect of the present disclosure in a lithography device or method.

[0029] It should be appreciated that features described for one embodiment may be combined with any features described for another embodiment, and all such combinations are expressly contemplated and disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which corresponding reference numerals indicate corresponding parts, and in which:

[0031] Figure 1 depicts a lithographic apparatus according to an embodiment of the invention; and

[0032] Figure 2 A multilayer mirror according to one aspect of the present disclosure is depicted, comprising a mirror layer according to the present disclosure.

[0033] The features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, wherein like reference numerals identify corresponding elements throughout. In the drawings, like reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. DETAILED DESCRIPTION

[0034] Figure 1 A lithography system according to the present invention is shown. The lithography system comprises a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam B. The lithography apparatus LA comprises an illumination system IL, a support structure MT configured to support a pattern forming 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 pattern forming device MA. The projection system is configured to project the radiation beam B (now patterned by the mask MA) onto the substrate W. The substrate W may comprise a previously formed pattern. In this case, the lithography apparatus aligns the patterned radiation beam B with the pattern previously formed on the substrate W. In such an embodiment, a pellicle 15 is depicted as being in the path of the radiation and protecting the pattern forming device MA. It will be appreciated that the pellicle 15 may be located in any desired position and may be used to protect any one of a plurality of mirrors in the lithography apparatus. Any one or more of the plurality of mirrors may be a mirror according to the present disclosure.

[0035] The radiation source SO, the illumination system IL and the projection system PS may all be constructed and arranged so that they may be isolated from the external environment. A gas (e.g., hydrogen) at a pressure below atmospheric pressure may be provided in the radiation source SO. A vacuum may be provided in the illumination system IL and / or the projection system PS. A small amount of gas (e.g., hydrogen) at a pressure substantially below atmospheric pressure may be provided in the illumination system IL and / or the projection system PS.

[0036] Figure 1 The radiation source SO shown in is of a type that may be referred to as a laser produced plasma (LPP) source. A laser, which may be, for example, a CO2 laser, is arranged to deposit energy via a laser beam into a fuel, such as tin (Sn), provided from a fuel emitter. Although tin is mentioned in the following description, any suitable fuel may be used. The fuel may, for example, be in liquid form and may, for example, be a metal or an alloy. The fuel emitter may include a nozzle configured to direct tin, for example in the form of droplets, along a trajectory towards a plasma formation region. The laser beam is incident on the tin at the plasma formation region. The deposition of laser energy into the tin generates a plasma at the plasma formation region. Radiation, including EUV radiation, is emitted from the plasma during de-excitation and recombination of ions of the plasma.

[0037] EUV radiation is collected and focused by a near normal incidence radiation collector (sometimes more commonly referred to as a normal incidence radiation collector). The collector may have a multilayer 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. The first focus may be at the plasma formation region, and the second focus may be at an intermediate focus, as discussed below.

[0038] The laser may be separate from the radiation source SO. In this case, the laser beam may be transferred from the laser to the radiation source SO by means of a beam delivery system (not shown in the figure) comprising, for example, suitable directional mirrors and / or beam expanders and / or other optical devices. The laser and the radiation source SO may together be considered a radiation system.

[0039] The radiation reflected by the collector forms a radiation beam B. The radiation beam B is focused at a point to form an image of the plasma formation region, which image serves as a virtual radiation source for illuminating the system IL. The point at which the radiation beam B is focused may be referred to as an intermediate focus. The radiation source SO is arranged so that the intermediate focus is located at or near an opening in an enclosure of the radiation source.

[0040] The radiation beam B is transmitted from the radiation source SO to the illumination system IL, which is configured to condition the radiation beam. The illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11. The faceted field mirror device 10 and the faceted pupil mirror device 11 together provide the radiation beam B with a desired cross-sectional shape and a desired angular distribution. The radiation beam B is transmitted from the illumination system IL and is incident on a pattern forming device MA held by a support structure MT. The pattern forming device MA reflects and patterns the radiation beam B. In addition to the faceted field mirror device 10 and the faceted pupil mirror device 11 or instead of the faceted field mirror device 10 and the faceted pupil mirror device 11, the illumination system IL may also include other mirrors or devices.

[0041] After reflection from the patterning device MA, the patterned radiation beam B enters the projection system PS. The projection system comprises a plurality of mirrors 13, 14 configured to project the radiation beam B onto a substrate W held by a substrate table WT. The projection system PS may apply a reduction factor to the radiation beam so as to form an image where features are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 may be applied. Although the projection system PS is Figure 1 There are two mirrors 13, 14, but the projection system may include any number of mirrors (eg, six mirrors).

[0042] Figure 1The radiation source SO shown in FIG. 1 may include elements not shown. For example, a filter may be provided in the radiation source. The filter may substantially transmit EUV radiation but substantially block radiation of other wavelengths, such as infrared radiation.

[0043] In an embodiment, the membrane assembly 15 is a diaphragm of a pattern forming device MA for EUV lithography. The membrane assembly 15 can be used for a dynamic gas lock or for a diaphragm or for another purpose. In an embodiment, the membrane assembly 15 includes a membrane formed by at least one membrane layer having an emissivity of 0.3 or higher. In order to ensure maximum EUV transmission and minimize the impact on imaging performance, it is preferred that the membrane is supported only at the boundaries.

[0044] If the patterning device MA is not protected, contamination may require the patterning device MA to be cleaned or discarded. Cleaning the patterning device MA interrupts valuable manufacturing time, and discarding the patterning device MA is costly. Replacing the patterning device MA also interrupts valuable manufacturing time.

[0045] Figure 2 is a schematic depiction of a multilayer mirror 16 according to one aspect of the present disclosure, the multilayer mirror including a mirror layer 17 according to the present disclosure. The mirror 16 includes alternating layers 18a, 18b of different materials forming a Bragg reflector. It should be appreciated that the mirror may include more layers than shown in the schematic depiction, and that the relative sizes of the layers may be different than shown. In the depicted embodiment, the mirror layer 17 is a cap layer, but it should be appreciated that in other embodiments, the mirror layer may be one or more of the alternating layers 18a, 18b of different materials.

[0046] The present invention aims to attenuate hydrogen induced outgassing (HIO) of Si-containing species from metal silicide based composite (MSC) mirrors under EUV scanner operating conditions. In an embodiment, the present disclosure describes a mirror layer or mirror in which silicon is bonded to a secondary element "ψ", referred to as Si-ψ y Matrix. The MSC material selection parameter may be the "bond dissociation energy (BDE)" of the Si-ψ bonds in the matrix. The BDE of the Si-ψ bonds in the matrix governs the breaking of the Si-ψ bonds during scanner operation, which produces free Si species that can diffuse via the HIO process and leave the mirror layer or mirror. A high Si-ψ BDE thus results in an attenuated HIO process. The BDE as a parameter for selecting a mirror layer or mirror material is described herein.

[0047] An aspect of the present invention is a new reflector layer or reflector Si-ψ material combination, where ψ = S, O, Se or F. For example, in the case where ψ = S, i.e. the matrix material is Si-S 2-yIn the case of Si-S, the Si-S bonds in the matrix have a higher bond dissociation energy (BDE) than Si-N in a SiN matrix; as stated, a high BDE causes fewer bond breaking events when photons are incident on the material, and may cause a smaller amount of Si to migrate through the matrix material to the outer surface, which therefore causes less Si outgassing. Based on the BDE of Si-S and other compositions described herein, the mirror layer or mirror of the present invention exhibits reduced outgassing compared to other options such as MoSiN, MoSiSi and MoSiC.

[0048] The threshold BDE value is defined as being greater than any value for Si-N bonds, Si-C bonds, and Si-Si bonds.

[0049] In relation to the bond dissociation energy (BDE) of the element ψ with Si and the migration and continuous outgassing of Si atoms, if the Si-ψ BDE is strong enough, Si migration is suppressed and outgassing can only occur temporarily until the mirror layer or the outer region of the mirror is depleted of Si. Excess Si can migrate through the mirror layer or the mirror and can be released at the outer region in a number of processes represented as said Si outgassing, such as SiO2 desorption or SiH4 formation. The material combinations described herein with potential low levels of outgassing therefore exhibit high Si-ψ bonding, such that bond dissociation is limited and Si atoms are transported via the Siψ BDE. 2-x The migration of the substrate as well as the outgassing are also restricted.

[0050] Here, at most 1.1·10 per 10,000 scanner chips 15 at.cm -2 A value of 10 outgassed Si atoms is considered an exemplary specification for acceptable HIO amounts.

[0051] Among the key parameters determining whether a volatile substance poses a risk of degrading the optical performance of an EUV mirror are firstly the probability of adhesion of the substance to the surface of the EUV mirror and secondly whether the substance oxidizes on the surface of the mirror.

[0052] As a minimum, the BDE value of the Si-C bond is considered to be the highest BDE value among the three composite film varieties of MoSiC, MoSiSi and MoSiN, which all exhibit outgassing of Si, which is assumed here to be related to atomic migration. As such, the BDE value of the atomic bond is preferably large to reduce bond breaking events and thereby attenuate subsequent atomic migration. The present invention claims that for any improvement, the BDE must exceed the "SiC+1 eV" value. According to the present invention, it is possible to reduce silicon outgassing by providing a mirror layer or mirror comprising a material that forms a strong bond with silicon. Strong silicon-sulfur bonds have higher bond dissociation energies than silicon-nitrogen bonds or silicon-silicon bonds, and therefore, when the mirror is irradiated with EUV light, and / or when the mirror is subjected to a low ion energy H2 scanner plasma with H ions having energies below 10 eV or at most 10 eV, the probability of bond dissociation leading to silicon migration and outgassing is low. Sulfur is not strongly associated with contamination of optics within lithographic apparatus and therefore does not present a significant contamination problem in situations where some sulfur is outgassed.

[0053] The present invention may allow for unsealed, ie uncovered, mirrors due to the reduced tendency of silicon to outgas.

[0054] The reflector according to the present disclosure can be manufactured via sputtering. Sputtering a molybdenum silicide target and a silicon sulfide target will produce a reflector layer having metal-rich molybdenum silicide crystals in a silicon sulfide matrix. Similarly, reactive sputtering of molybdenum disilicide in a hydrogen sulfide atmosphere will produce the reflector of the present disclosure. By providing sulfur in the matrix, the bond with silicon is stronger, and silicon outgassing can only be observed before the outer regions of the reflector are depleted of silicon that is easily outgassed. It is considered that silicon migration is inhibited by the strong bond with sulfur.

[0055] As such, the present disclosure provides mirrors having similar or better optical performance than other mirrors, but with lower amounts of silicon outgassing and acceptable EUV reflectivity, and also with acceptable emissivity, which allows the mirrors to operate within lithographic equipment, particularly EUV devices.

[0056] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0057] The above description is intended to be illustrative rather than limiting. Accordingly, those skilled in the art will appreciate that modifications may be made to the invention described without departing from the scope of the claims set forth hereinafter.

Claims

1. A mirror layer for a lithographic apparatus comprising at least one element that forms a chemical bond with silicon, the chemical bond having a relative molecular mass of at least 447 kJ mol -1 Or a bond dissociation energy of at least 4.6 eV.

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

3. The reflector layer according to claim 1 or claim 2, wherein: The reflector layer comprises one or more of the following: 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 the following: molybdenum, zirconium, yttrium, lanthanum, scandium, niobium, iridium, chromium, vanadium, platinum, rhodium, hafnium and ruthenium.

4. The reflector layer according to claim 1 or 2, wherein: The mirror layer includes silicon and metal, metal silicide, metal fluoride, metal boride, metal carbide, metal oxide and / or metal selenide.

5. The reflector layer according to claim 1 or 2, wherein: The reflector layer includes 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. The reflector layer according to claim 1 or 2, wherein: The reflector layer includes i) one or more of metal, metal silicide, metal fluoride, metal boride, metal carbide, metal oxide and / or 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. A mirror layer according to any preceding claim, wherein: The mirror layer has a composition SiS 2-y , where 0 ≤ y < 2.

8. A mirror layer according to any preceding claim, wherein The mirror layer at least partially has the molecular formula Mo a Si b S c , wherein, in mol %, 0 < a ≤ 30, 50 ≤ b ≤ 90 and 0 < c ≤ 50.

9. The reflector layer according to claim 8, wherein: 10 ≤ a ≤ 30 (in mol %).

10. A reflector layer according to claim 8 or claim 9, wherein: 60 ≤ b ≤ 70 (in mol %).

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

12. A mirror layer according to any preceding claim, wherein The reflector comprises silicon and molybdenum, and the ratio of Si:Mo (in mol %) deviates from 2.

0.

13. A mirror comprising a mirror layer according to any preceding claim.

14. The reflector according to claim 13, wherein: The mirror is a multilayer mirror, preferably comprising an alternating stack of silicon and molybdenum layers.

15. A method of manufacturing a mirror layer or a mirror according to any preceding claim, wherein: The method comprises sputtering, preferably co-sputtering.

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

17. A method of using molybdenum silicon sulfide, molybdenum silicon oxide, molybdenum silicon selenide or molybdenum silicon fluoride in a reflector layer or a reflector.

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.

Images