Reflective member for EUV lithography

Abstract

A reflective member for use in an EUV lithography apparatus, the reflective member comprising a multilayer stack comprising a plurality of pairs of layers arranged in pairs, each pair comprising a first layer and a second layer, the first layer being formed of a material comprising Si, the second layer being formed of a material comprising at least two of Ru, Nb, and Mo, the second layer being configured to have a refractive index of 0.92 or less and an absorption coefficient of 0.015 or less for light having a wavelength of approximately 13.5 nm.

Description

Technical Field

[0001] (Cross - Reference to Related Applications)

[0001] This application claims the benefit of priority of U.S. Application No. 63 / 393,874, filed Jul. 30, 2022, which is hereby incorporated by reference in its entirety.

[0002]

[0002] The present invention relates to a reflective member, a lithographic apparatus including the reflective member, a method of manufacturing a device including use of the reflective member, an EUV mask, a lithographic apparatus including the EUV mask, and a method of manufacturing a device including use of the EUV mask.

Background Art

[0003]

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. The lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that case, a patterning device, alternatively also referred to as a mask or a reticle, can be used to generate the circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of one or several dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is typically effected by imaging onto a layer of radiation - sensitive material (resist) provided on the substrate. Generally, one substrate will contain a network of adjacent target portions that are patterned sequentially.

[0004]

[0004] Lithography is widely recognized as one of the important steps in the manufacture of ICs as well as other devices and / or structures. However, as the dimensions of the features fabricated using lithography become smaller, lithography has become an increasingly important factor for enabling the manufacture of smaller ICs or other devices and / or structures.

[0005]

[0005] The theoretical estimated value of the limit of pattern printing can be given by the Rayleigh criterion of resolution shown in Equation (1).

[0006]

Equation

[0007] Here, λ is the wavelength of the radiation used, NA is the numerical aperture of the projection system used to print the pattern, k1 is a process-dependent adjustment coefficient also called the Rayleigh constant, and CD is the feature size (or critical dimension) of the feature to be printed. From Equation (1), the reduction of the minimum printable size of the feature can be obtained by three methods, namely, by shortening the exposure wavelength λ, by increasing the numerical aperture NA, or by reducing the value of k1.

[0008]

[0006] In order to shorten the exposure wavelength and thus reduce the minimum printable size, it has been proposed to use an extreme ultraviolet (EUV) radiation source. EUV radiation is electromagnetic radiation having a wavelength in the range of 10 to 20 nm, for example, in the range of 13 to 14 nm. Furthermore, it has been proposed that EUV radiation having a wavelength in the range of 5 to 10 nm, less than 10 nm, for example, 6.7 nm or 6.8 nm, etc., can be used. Such radiation is called extreme ultraviolet or soft x-ray. Possible radiation sources include, for example, a laser-produced plasma source, a discharge plasma source, or a radiation source based on synchrotron radiation provided by an electron storage ring.

[0009]

[0007] Focusing EUV radiation into a beam, guiding it onto a mask, and projecting the patterned beam onto a substrate is difficult because refractive optical elements for EUV radiation cannot be fabricated. Therefore, these functions must be performed using reflectors (i.e., mirrors). Generally, multilayer reflectors (also known as distributed Bragg reflectors) are used, which comprise a plurality of layers arranged in pairs (also known as periods). Each pair comprises a layer with a relatively high refractive index and a layer with a relatively low refractive index. At each interface between the layers, a certain proportion of the radiation passing through the multilayer reflector is reflected. The thickness of each pair is configured such that there is constructive interference between the radiation reflected at each interface. The reflectivity of the multilayer reflector used to reflect EUV radiation is typically about 70%. There may be many multilayer reflectors used in sequence between the EUV radiation source and the substrate in a lithographic apparatus. As a result, the amount of radiation reaching the substrate can be a small proportion of the EUV radiation generated.

[0010]

[0008] Multilayer reflectors can be utilized in a mask that comprises an absorber layer on top of the multilayer stack in addition to the multilayer stack. This absorber layer is patterned with the image to be projected onto the substrate. Since the absorber layer has a certain thickness, when radiation enters the mask at an angle of incidence greater than zero, as required for a reflective mask, a 3D effect such as shadowing of the incident radiation on the mask occurs. This results in errors in the lithography process, such as pattern placement errors and linewidth errors.

[0011]

[0009] In a multilayer reflector, the effective reflectivity plane can be defined as the plane at a depth below the surface of the multilayer reflector that represents the average depth of reflection within the multilayer reflector. The 3D effect (shadowing) becomes more significant when the effective reflectivity plane is deeper below the surface of the multilayer reflector.

[0012]

[0010] In current multilayer reflectors, the relatively high refractive index layers typically comprise silicon (Si), and the relatively low refractive index layers typically comprise molybdenum (Mo). Alternative configurations of multilayer reflectors have been proposed, in which the relatively high refractive index layers comprise Si and the relatively low refractive index layers comprise ruthenium (Ru). The Ru-Si multilayer reflector exhibits a shallower effective reflectivity plane than the Mo-Si multilayer reflector, and thus, when used in a mask, the presented 3D effect (shadowing) is smaller than that of the Mo-Si multilayer reflector. However, the reflectivity of the Ru-Si multilayer reflector is lower than that of the Mo-Si multilayer reflector.

[0013]

[0011] It is an object of the present invention to provide a reflective member having characteristics superior (in terms of reflectivity and 3D effect when used in an EUV mask) to currently available reflective members.

Summary of the Invention

[0014]

[0012] In the present disclosure, a reflective member for use in an EUV lithography apparatus is provided, the reflective member comprising a multilayer stack comprising a plurality of pairs of layers, each pair comprising a first layer and a second layer, the first layer being formed of a material comprising Si, and the second layer being formed of a material comprising at least two of Ru, Nb, and Mo, the second layer being configured to have a refractive index of 0.92 or less and an absorption coefficient of 0.015 or less for light having a wavelength of approximately 13.5 nm.

[0015]

[0013] In the present disclosure, a lithography apparatus comprising the reflective member is also provided.

[0016]

[0014] In the present disclosure, a method of manufacturing a device comprising the use of the reflective member is also provided.

[0017]

[0015] In the present disclosure, there is also provided an EUV photomask including a substrate, a multilayer stack including a plurality of layers arranged in pairs, and a capping layer formed of a material including at least two of Ru, Nb, and Mo, the capping layer being configured to have a refractive index of less than 0.92 and an absorption coefficient of less than 0.015 for light having a wavelength of approximately 13.5 nm.

[0018]

[0016] In the present disclosure, there is also provided a lithographic apparatus including an EUV photomask.

[0019]

[0017] In the present disclosure, there is also provided a method of manufacturing a device including the use of an EUV photomask.

Brief Description of the Drawings

[0020]

[0018] Next, embodiments of the present invention will be described by way of example only with reference to the accompanying schematic diagrams in which corresponding reference numerals indicate corresponding parts.

[0021]

Figure 1

[0019] A lithographic apparatus is schematically illustrated.

Figure 2

[0020] A more detailed view of the lithographic apparatus is illustrated.

Figure 3

[0021] An example of an EUV mask is illustrated in cross section.

Figure 4

[0022] The EUV mask is illustrated in cross section showing two reflected beams.

Figure 5

[0023] For Mo-Si multilayer stacks and Ru-Si multilayer stacks, a plot with reflectivity on the vertical axis and the number of multilayer pairs on the horizontal axis is illustrated.

Figure 6

[0024] For several elements and alloys, a plot with absorption coefficient on the vertical axis and refractive index on the horizontal axis is illustrated.

Figure 7

[0025] For several multilayer stack structures, a plot is illustrated with the reflectance on the vertical axis and the number of multilayer pairs on the horizontal axis.

Figure 8

[0026] For several multilayer stack structures, a plot is illustrated with the reflectance on the vertical axis and the wavelength on the horizontal axis.

Figure 9

[0027] For a plurality of multilayer stack structures, a plot is illustrated with the reflectance on the vertical axis and the incident angle on the horizontal axis.

DETAILED DESCRIPTION OF THE INVENTION

[0022]

[0028] FIG. 1 schematically shows a lithographic apparatus 100 including a source collector module SO according to an embodiment of the present invention. The apparatus 100 includes - an illumination system (or illuminator) IL configured to condition a radiation beam B (e.g., EUV radiation), - a support structure (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask or reticle) MA and connected to a first positioner PM configured to accurately position the patterning device, - a substrate table (e.g., a wafer table) WT constructed to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate, - a projection system (e.g., a reflective projection system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W, and comprises.

[0023]

[0029] The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for guiding, shaping, or controlling the radiation.

[0024]

[0030] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions such as whether the patterning device is held in a vacuum environment. The support structure MT can hold the patterning device MA using mechanical, vacuum, electrostatic or other clamping techniques. The support structure MT may be, for example, a frame or a table, which can be fixed or movable as required. The support structure MT can ensure that the patterning device MA is in a desired position relative to, for example, the projection system PS.

[0025]

[0031] The term "patterning device" should be interpreted broadly as referring to any device that can be used to impart a pattern to a cross-section of a radiation beam, such as for creating a pattern in a target portion C of a substrate W. The pattern imparted to the radiation beam B can correspond to a particular functional layer of a device to be created in the target portion C, such as an integrated circuit.

[0026]

[0032] Examples of patterning devices include masks, programmable mirror arrays, and programmable liquid crystal display (LCD) panels. Masks are well known in lithography and include mask types such as binary masks, alternating phase shift masks, attenuated phase shift masks, and various hybrid mask types. An example of a programmable mirror array employs a matrix array of small mirrors that can each be individually tilted so as to reflect an incident radiation beam in a different direction. The tilted mirrors impart a pattern to the radiation beam reflected by the mirror matrix.

[0027]

[0033] Similar to the illumination system IL, the projection system PS can include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, depending on the exposure radiation used or other factors such as the use of a vacuum. Since other gases may absorb too much radiation, it may be desirable to use a vacuum for EUV radiation. Thus, with the help of a vacuum wall and a vacuum pump, a vacuum environment can be provided throughout the beam path.

[0028]

[0034] As shown here, the lithographic apparatus 100 is of the reflective type (e.g., employing a reflective mask).

[0029]

[0035] The lithographic apparatus 100 may be of the type having two (dual-stage) or more substrate tables WT (and / or two or more support structures MT). In such a "multi-stage" lithographic apparatus, additional substrate tables WT (and / or additional support structures MT) can be used in parallel, or preparation steps can be carried out on one or more other substrate tables WT (and / or one or more other support structures MT) while one or more substrate tables WT (and / or one or more support structures MT) are being used for exposure.

[0030]

[0036] Referring to FIG. 1, the illumination system IL receives an extreme ultraviolet radiation beam from the source collector module SO. The method of generating EUV light includes, but is not necessarily limited to, converting a material having at least one element having one or more emission lines in the EUV region, such as xenon, lithium, or tin, into a plasma state. In one such method, often referred to as laser-produced plasma (“LPP”), the required plasma can be generated by irradiating a fuel, such as a droplet, stream, or cluster of a material having the required line-emitting element, with a laser beam. The source collector module SO may be part of an EUV radiation system including a laser (not shown in FIG. 1) for providing a laser beam for exciting the fuel. The resulting plasma emits output radiation, such as EUV radiation, which is collected using a radiation collector disposed in the source collector module. The laser and the source collector module SO may be separate entities, for example when a CO2 laser is used to provide a laser beam for fuel excitation.

[0031]

[0037] In such a case, the laser is not considered to form part of the lithographic apparatus 100, and the radiation beam B is transmitted from the laser to the source collector module SO, for example with the aid of a beam delivery system comprising suitable guiding mirrors and / or a beam expander. In other cases, for example, when the radiation source is a discharge-produced plasma EUV generator, often referred to as a DPP source, the radiation source may be an integral part of the source collector module SO.

[0032]

[0038] The illumination system IL may comprise an adjuster for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radius ranges of the intensity distribution in the pupil plane of the illumination system IL (generally referred to as σ-outer and σ-inner respectively) are adjustable. Additionally, the illumination system IL may comprise various other components such as a facet field device and a pupil mirror device. The illumination system IL can be used to adjust the radiation beam B to have a desired uniformity and intensity distribution in its cross-section.

[0033]

[0039] The radiation beam B is incident on a patterning device (e.g., a mask) MA held on a support structure (e.g., a mask table) MT and is patterned by the patterning device MA. After being reflected from the patterning device (e.g., a mask) MA, the radiation beam B passes through a projection system PS, and the projection system PS focuses the radiation beam B onto a target portion C of a substrate W. With the help of a second positioner PW and a position sensor PS2 (e.g., an interference device, a linear encoder, or a capacitive sensor), the substrate table WT can be accurately moved, for example, to position various target portions C within the path of the radiation beam B. Similarly, a first positioner PM and another position sensor PS1 can be used to accurately position the patterning device (e.g., a mask) MA with respect to the path of the radiation beam B. The patterning device (e.g., a mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0034]

[0040] The controller 500 controls the overall operation of the lithography apparatus 100 and, in particular, performs the operation processes described below. The controller 500 can be embodied as a suitably programmed general-purpose computer comprising a central processing unit, volatile and non-volatile memory means, one or more input devices and output devices such as a keyboard and screen, one or more network connections, and one or more interfaces to various parts of the lithography apparatus 100. It will be understood that a one-to-one relationship between the control computer and the lithography apparatus 100 is not required. In one embodiment of the invention, one computer can control a plurality of lithography apparatuses 100. In one embodiment of the invention, a plurality of networked computers may be used to control one lithography apparatus 100. The controller 500 can also be configured to control one or more associated processing devices and substrate handling devices of the litho cells or clusters of which the lithography apparatus 100 forms part. The controller 500 can also be configured to be subordinate to a monitoring and control system of the litho cell or cluster and / or an overall control system of the manufacturing facility.

[0035]

[0041] FIG. 2 shows in more detail the lithography apparatus 100 including the source collector module SO, the illumination system IL, and the projection system PS. The EUV emission plasma 210 can be formed by a plasma source. The EUV radiation can be generated by a gas or vapor, such as Xe gas, Li vapor, or Sn vapor, where the emission plasma 210 is created to emit radiation in the EUV region of the electromagnetic spectrum. In one embodiment, an excited tin (Sn) plasma is provided to generate the EUV radiation.

[0036]

[0042] The radiation emitted by the emission plasma 210 is transmitted from the radiation source chamber 211 into the collector chamber 212.

[0037]

[0043] The collector chamber 212 may include a radiation collector CO. Radiation traversing the radiation collector CO can be focused onto a virtual light source point IF. The virtual light source point IF is generally referred to as an intermediate focus, and the source collector module SO is arranged such that the virtual light source point IF is located at or near the opening 221 of the enclosure structure 220. The virtual light source point IF is an image of the radiation emitting plasma 210.

[0038]

[0044] Subsequently, the radiation traverses the illumination system IL. The illumination system IL may include a facet field mirror device 22 and a facet pupil mirror device 24 arranged to provide a desired angular distribution of the non-patterned beam 21 in the patterning device MA and a desired uniformity of radiation intensity in the patterning device MA. When the non-patterned beam 21 is reflected by the patterning device MA held by the support structure MT, a patterned beam 26 is formed, and the patterned beam 26 is imaged onto the substrate W held by the substrate table WT by the projection system PS via the reflection elements 28, 30.

[0039]

[0045] Generally, the illumination system IL and the projection system PS may have more elements than shown. Further, there may be more mirrors than shown in the figure. For example, the projection system PS may have 1 to 6 more reflection elements than shown in FIG. 2.

[0040]

[0046] Alternatively, the source collector module SO may be part of an LPP radiation system.

[0041]

[0047] As shown in FIG. 1, in one embodiment, the lithographic apparatus 100 includes an illumination system IL and a projection system PS. The illumination system IL is configured to emit a radiation beam B. The projection system PS is separated from the substrate table WT by an intervening space. The projection system PS is configured to project a pattern imparted to the radiation beam B onto the substrate W. The pattern is for EUV radiation of the radiation beam B.

[0042]

[0048] The space intervening between the projection system PS and the substrate table WT may be at least partially evacuated. The intervening space may be delimited by a solid surface at the location of the projection system PS, and the radiation used is guided from that solid surface towards the substrate table WT.

[0043]

[0049] FIG. 3 illustrates a mask 300 that can be used within an EUV lithographic apparatus to impart a required pattern to a radiation beam. The mask 300 is an example of a reflective member of the present invention.

[0044]

[0050] The mask 300 shown in FIG. 3 includes a substrate 310, a multilayer stack 320, a capping layer 330, and an absorber layer 340. The substrate 310 is a component that provides a starting point for the manufacture of the multilayer stack 320. The reflective members disclosed herein can be used with any composition of the substrate 310 known to those skilled in the art to be suitable. For example, the substrate 310 can be formed of silicon dioxide and titanium oxide (SiO2-TiO2). Generally, the substrate 310 is formed of a material to which one or more materials of the multilayer stack 320 adhere. The surface of the substrate 310 may be polished to form a smooth and flat surface to improve the adhesion of the materials of the multilayer stack 320 to the substrate 310.

[0045]

[0051] The multilayer stack 320 is formed of a plurality of layers 322, 323 arranged in pairs 321. Each pair includes a layer 322 with a relatively high refractive index and a layer 323 with a relatively low refractive index. That is, when passing through the multilayer stack 320 in a direction perpendicular to the upper surface of the multilayer stack, the material changes from that of the layer 322 with a relatively high refractive index to that of the layer 323 with a relatively low refractive index. At each interface between the layers (i.e., the point where EUV radiation moves from the layer 323 with a relatively low refractive index to the layer 322 with a relatively high refractive index or from the layer 322 with a relatively high refractive index to the layer 323 with a relatively low refractive index in the multilayer stack), a certain proportion of the radiation is reflected. The thickness of each layer 322, 323 of the multilayer stack 320 is configured such that when light is reflected at each interface between the different layers 322, 323 of the multilayer stack 320, the reflected beams are in phase. This means that the reflections from each interface interfere with each other constructively to form the reflected beam.

[0046]

[0052] In the current multilayer stack 320, the number of pairs within the multilayer stack 320 can be between 40 and 50. Each of the layers 322, 323 may be separated by an intermediate film (not shown) to prevent intermixing and silicide formation. The intermediate layer can be formed of, for example, boron carbide (B4C). As described above, the thickness of each layer is determined by the condition that the beams reflected at each boundary interface interfere constructively, and that condition depends on the wavelength of the radiation, as would be known to those skilled in the art. As an example, the layer 322 with a relatively high refractive index may have a thickness between 3 nm and 5 nm, and the layer 323 with a relatively low refractive index may have a thickness between 2 nm and 4 nm.

[0047]

[0053] The capping layer 330 can be located on the upper surface of the multilayer stack 320. The capping layer 330 is provided to improve the durability and chemical stability of the multilayer stack 320. The reflective member disclosed herein can be used with any capping layer 330 known to those skilled in the art to be suitable. As an example, the material of the capping layer may be the same as the material of the layer 322 with a relatively high refractive index or the layer 323 with a relatively low refractive index.

[0048]

[0054] The absorber layer 340 can be located on the upper surface of the capping layer 330. The absorber layer 340 can be composed of a single layer of material or multiple layers of material. The absorber layer 340 is configured to absorb incident radiation. Thus, in a mask configured for use in an EUV lithography apparatus, the material of the absorber layer 340 is a material that absorbs EUV radiation. The reflective member disclosed herein can be used with an absorber layer 340 of any composition known to those skilled in the art to be suitable. For example, the material of the absorber 340 may be formed of a material comprising tantalum nitride (TaN) or tantalum boron nitride (Ta-B-N), and the overall thickness of the absorber layer 340 may be between 50 nm and 70 nm. Alternatively, the absorber layer 340 may be formed of a material comprising nickel (Ni), and the overall thickness of the absorber layer 340 may be between 25 nm and 35 nm.

[0049]

[0055] The absorber layer 340 can be patterned to include an image projected onto the photosensitive film of the substrate. That is, the absorber layer 340 may cover some regions on the surface of the capping layer 330, but may not cover other regions. In other words, some regions of the capping layer 330 may be exposed, and other regions may not be exposed. During operation, EUV radiation is reflected by the mask 300 in regions where the absorber layer 340 is absent and absorbed in regions where the absorber layer 340 is present. The absorber layer 340 can initially be formed on the capping layer 330 so as to cover the entire capping layer 330. Then, a pattern can be formed in the absorber layer 340 using techniques such as electron beam lithography and any known etching process.

[0050]

[0056] A mask configured for use in an EUV lithography apparatus, such as the mask 300, may be formed layer by layer by a process such as physical vapor deposition (PVD), electron beam deposition (EBD), or chemical vapor deposition (CVD).

[0051]

[0057] EUV radiation incident on a mask such as mask 300 typically approaches the mask 300 from an angle of incidence greater than zero (the angle between the incident beam and the line perpendicular to the surface at the point of incidence). This is to allow the reflected beam to travel along a different path than the incident beam. In a lithographic apparatus, the angle of incidence of the beam of EUV radiation incident on the mask 300 can be between 1° and 10° from the normal. For example, the angle of incidence may be 6°. As a result of the height of the absorber layer 340 above the capping layer 330 and the angle of incidence being greater than zero, unwanted shadowing of the exposed area of the mask 300 occurs. This shadowing occurs when the incident EUV radiation is prevented from reaching the exposed area on the top surface of the mask 300 by the absorber layer 340, or when the reflected radiation is prevented from exiting the mask 300 by the absorber layer 340. This shadowing can cause significant errors such as pattern placement errors and line width errors. The errors resulting from shadowing become more significant as the angle of incidence on the mask 300 increases and as the thickness of the absorber layer 340 increases. The errors caused by shadowing also become more significant when the effective reflectivity plane (the plane below the surface of the multilayer reflector that represents the average depth of reflection within the multilayer reflector) is deeper. Figure 4 shows two effective reflection planes 431, 432. The depth of the effective reflection plane of the multilayer stack 320 depends on the material of the layer 322 with a relatively high refractive index and the material of the layer 323 with a relatively low refractive index. Specifically, the depth of the effective reflection plane depends on the refractive indices of the layer 322 with a relatively high refractive index and the layer 323 with a relatively low refractive index. The effective reflection plane 432 is deeper than the effective reflection plane 431. When the incident EUV radiation beam 410 is reflected from the shallower effective reflection plane 431, the reflected beam 421 is not obstructed by the absorber layer 340 and can travel away from the mask 300. However, when the incident EUV radiation beam 410 is reflected from the deeper effective reflection plane 432, the reflected beam 422 is obstructed by the absorber layer 340 and the reflected beam cannot travel away from the mask 300.

[0052]

[0058] In a typical multilayer stack 320, the relatively high refractive index layer may be formed of a material comprising silicon (Si), and the relatively low refractive index layer may be formed of a material comprising molybdenum (Mo). More recently, it has been proposed that the relatively low refractive index layer can instead be formed of a material comprising ruthenium (Ru). A Ru-Si multilayer stack can exhibit an effective reflectance plane that is not deeper than the effective reflectance plane of a Mo-Si multilayer stack. For example, in FIG. 4, the effective reflectance plane 431 may be that of the Ru-Si multilayer stack 300, and the effective reflectance plane 432 may be that of the Mo-Si multilayer stack. For the Ru-Si multilayer stack 320, the effective reflectance plane 431 may be approximately 33 nm below the surface of the multilayer stack 320. For the Mo-Si multilayer stack 320, the effective reflectance plane 432 may be approximately 45 nm below the surface of the multilayer stack 320. The shallower effective reflectance plane 431 of the Ru-Si multilayer stack 320 means that the errors caused by shadowing are less significant. However, the overall reflectance of the Ru-Si multilayer stack 320 can be approximately 5% lower than the reflectance of the Mo-Si multilayer stack 320. Reflectance is defined as the portion of energy reflected at an interface (Equation (2)). This reduction in reflectance corresponds to a loss in throughput.

[0053]

Number

[0054]

[0059] Throughout the following description, values of the refractive index (n) and the absorption coefficient (k) are referred to. A method for measuring such values for a given material is not particularly limited. The values of the refractive index (n) and the absorption coefficient (k) can be determined from measured values of reflectance and the angle of incidence. Specifically, the values of the refractive index (n) and the absorption coefficient (k) can be determined by fitting a curve to a plot of measured values of reflectance and the angle of incidence. The measurement of reflectance and the angle can be performed using a substrate coated with the material for which the values of the refractive index (n) and the absorption coefficient (k) are to be determined. The substrate can be a silicon wafer or a mask plate. The thickness of the material coating can be between 30 nm and 50 nm.

[0055]

[0060] Alternatively, the values of the refractive index (n) and the absorption coefficient (k) can be determined from measurements performed using an interferometer. As an example, the values of the refractive index (n) and the absorption coefficient (k) may be measured using an amplitude-division transmission interferometer. This can involve determining the phase shift (φ) and visibility (V) of the interferogram. A method for measuring the refractive index (n) and the absorption coefficient (k) is described in the following publication: CHANG, Chang; ANDERSON, Erik; NAULLEAU, Patrick. Direct index of refraction measurement at extreme ultraviolet wavelength region with a novel interferometer. Optical Letters, 2001, 27(12).

[0056]

[0061] Such a method can be used to measure the refractive index (n) and absorption coefficient (k) defined in the present invention. The apparatus used in this method includes a radiation source, a small-diameter hole for providing spatially coherent radiation, a diffraction grating that effectively generates an order of a virtual light source from the pinhole, a zone plate that images the virtual light source formed in the diffraction grating onto a plane with a mask, a mask having two openings for passing the zero-order and first-order spots, and a high-sensitivity CCD camera. In this method, the test material passes in and out of one of the openings of the mask, and the CCD camera records the resulting interferogram.

[0057]

[0062] When the test material is present in one of the openings, the fringes of the interferogram shift according to the refractive characteristics of the test material. The phase shift (φ) is the difference between two independently reconstructed phase maps of the interferogram. Then, the refractive index (n) can be calculated using Equation (3). Here, λ is the wavelength and t is the thickness of the sample.

[0058]

Equation

[0059]

[0063] The relative light intensity (α) after propagation through the sample is related to the observed visibility (V) of the interferogram by Equation (4).

[0060]

Equation

[0061]

[0064] From the relative light intensity (α), the absorption coefficient (k) can be calculated using Equation (5).

[0062]

Equation

[0063]

[0065] Table 1 shows the refractive index (n) and absorption coefficient (k) of the elements Ru, Mo, niobium (Nb), and several alloys containing these three elements for a wavelength of approximately 13.5 nm.

[0064]

Table 1

[0065]

[0066] The reflectivity of the multilayer stack 320 depends on the absorption coefficient of the materials from which layers 322 and 323 are formed. Ru has a higher absorption coefficient (k = 0.0171) than Mo (k = 0.0064), which explains why the reflectivity of the Mo - Si multilayer stack 320 is greater than that of the Ru - Si multilayer stack 320. The depth (z eff ) of the effective reflectivity plane depends on the difference in refractive index (n) between the relatively high - refractive - index layer 322 and the relatively low - refractive - index layer 323. This is because the greater the difference in refractive index (n) between the relatively high - refractive - index layer 322 and the relatively low - refractive - index layer 323, the wider the reflectivity band (the range of wavelengths with relatively high reflectivity) of the multilayer stack 320. A wider reflectivity band results in a lower group delay (τ). The approximate depth (z eff ) of the effective reflectivity plane is proportional to the group delay (τ), as shown in Equation (6). Therefore, a wider reflectivity band results in a shallower depth of the effective reflectivity plane.

[0066]

Equation

[0067]

[0067] The lower the refractive index (n) of the relatively low - refractive - index layer 323, the greater the difference in refractive index (n) between the relatively high - refractive - index layer 323 and the relatively low - refractive - index layer 322. Ru has a lower refractive index (n = 0.887) than Mo (n = 0.9237), which explains why the effective reflectivity plane 431 of the Ru - Si multilayer stack 320 is not deeper than the effective reflectivity plane 432 of the Mo - Si multilayer stack 320.

[0068]

[0068] FIG. 5 shows how the reflectivity of the Mo—Si multilayer stack 320 and the Ru—Si multilayer stack 320 varies with the number of pairs 321 within the multilayer stack 320. The plots are based on incident radiation having a wavelength of approximately 13.5 nm and an angle of incidence of 6°. For both the Mo—Si and Ru—Si multilayer stacks 320, while the number of pairs 321 within the multilayer stack 320 is relatively small, the reflectivity increases rapidly as the number of pairs 431 within the multilayer stack 320 increases. As the number of pairs 321 within the multilayer stack 320 increases, the rate of change of the reflectivity with respect to the increase in the number of pairs 321 decreases, and the reflectivity tends towards a constant value. For the Ru—Si multilayer stack 320, the value of the reflectivity for a large number of pairs (approximately 0.75) is lower than the value of the reflectivity of the Mo—Si multilayer stack 320 for a large number of pairs (approximately 0.71). The Ru—Si multilayer stack 320 reaches an approximately constant reflectivity value with a smaller number of pairs (approximately 30) than the Mo—Si multilayer stack 320 (approximately 40).

[0069]

[0069] The present disclosure relates to a material capable of providing a multilayer stack 320 that combines the advantageous reflectivity characteristics exhibited by a Mo—Si multilayer stack 320 and the advantageous effective reflectivity plane characteristics exhibited by a Ru—Si multilayer stack 320 when used in a relatively low refractive index layer 323. Specifically, the material is an alloy comprising at least two of Mo, Ru, and niobium (Nb). As shown in Table 1, Nb has a higher refractive index (n = 0.9337) than either Mo or Ru and a lower absorption coefficient (n = 0.9337) than either Mo or Ru. As a result, the Nb—Si multilayer stack can have a better reflectivity than either the Mo—Si and Ru—Si multilayer stacks 320, but a deeper effective reflection plane (z eff) may have. For light having a wavelength of approximately 13.5 nm, this alloy is configured such that the refractive index is 0.92 or less and the absorption coefficient is 0.015 or less. For light having a wavelength of approximately 13.5 nanometers, this alloy may preferably exhibit a refractive index of less than 0.91, more preferably less than 0.9. For light having a wavelength of approximately 13.5 nm, this alloy may suitably have an absorption coefficient (k) of less than 0.014, preferably less than 0.013, more preferably less than 0.012.

[0070]

[0070] In addition to at least two of Ru, Nb, and Mo, the alloy may also include common impurities such as phosphorus, sulfur, and oxygen. The proportion of such impurities in the alloy may be such that they do not significantly affect the refractive index or absorption coefficient of the alloy. The mass percentage of impurities in the alloy may be less than 5%, preferably less than 1%, more preferably less than 0.1%. That is, the alloy consists essentially of at least two of Ru, Nb, and Mo.

[0071]

[0071] The alloy may include Nb. The alloy may contain Nb in an amount that is not considered a trace element. That is, the mass percentage of Nb in the alloy may be greater than 5%. The mass percentage of Nb in the alloy may preferably be greater than 20%, preferably greater than 40%, more preferably greater than 60%. The mass percentage of Nb in the alloy may be less than 70%, preferably less than 50%, more preferably less than 45%.

[0072]

[0072] The alloy may include Ru. The alloy may contain Ru in an amount that is not considered a trace element. That is, the mass percentage of ruthenium in the alloy may be greater than 5%. Preferably, the mass percentage of ruthenium in the alloy may be greater than 30%, more preferably greater than 35%, more preferably greater than 55%. The mass percentage of Ru in the alloy may be less than 85%, preferably less than 75%, more preferably less than 70%.

[0073]

[0073] The alloy may include Mo. The alloy may contain Mo in an amount that is not considered a trace element. The mass percentage of Mo in the alloy may be 0% or more, preferably greater than 10%, and more preferably greater than 5%. The mass percentage of Mo in the material of the second layer may be less than 70%, preferably less than 50%, and more preferably less than 25%.

[0074]

[0074] The characteristics of the refractive index (n) and the absorption coefficient (k) can be approximated by the weighted average of the refractive index and the absorption coefficient of the components of the alloy. As a result, an equation that approximately relates the composition of the alloy to the values of the refractive index (n) and the absorption coefficient (k) can be formed. To facilitate this, the general formula of the alloy is shown below.

[0075]

Equation

[0076] The subscript numbers of these alloys are intended to represent the molar ratios of the respective elements in the alloy. These numbers do not imply that the alloy is formed in a specific lattice structure in which the various components are held in a regular arrangement as integers with fixed ratios. Since the alloy may contain impurities, the general formula of the alloy is

[0077]

Equation

[0078] can be. Here, I represents the impurities in the alloy. I can represent a single impurity or multiple impurities.

[0079]

[0075] The weighted average equations for the refractive index (n) and the absorption coefficient (k) of the alloy are as follows, where n Ru , n Nb , n Mo , k Ru , kNb and n Mo The values of are shown in Table 1.

[0080]

Number

[0081]

[0076] It should be noted that the weighted average method only provides an approximation. In reality, the alloy may exhibit values of refractive index (n) and absorption coefficient (k) that are smaller (i.e., better) than what would be predicted from the weighted average calculation. For example, in the case of the alloy RuNb2, the approximate refractive index (n) and absorption coefficient (k) by the weighted average of these values of the components are 0.903 and 0.131 respectively, while the actual refractive index (n) and absorption coefficient (k) are 0.898 and 0.0109 respectively.

[0082]

[0077] The weighted average formula can be used to obtain an estimated value of the alloy composition conditions necessary to obtain a predetermined refractive index (n max ) or a predetermined absorption coefficient (k max ).

[0083]

Number

[0084]

[0078] A predetermined refractive index (n max ) can be 0.92, preferably 0.91, more preferably less than 0.9. A predetermined absorption coefficient (k max) can be 0.015, preferably less than 0.014, more preferably less than 0.013, and even more preferably less than 0.012. In one example of the alloy, the mass percentage of Ru may be greater than 50%, preferably greater than 55%, more preferably greater than 59%, and may be less than 70%, preferably less than 65%, more preferably less than 61%. The mass percentage of Mo may be greater than 10%, preferably greater than 15%, preferably greater than 19%, and may be less than 30%, preferably less than 25%, more preferably less than 21%. The mass percentage of Nb may be greater than 10% and less than 30%, preferably greater than 15%, more preferably greater than 19%, and may be less than 30%, preferably less than 25%, more preferably less than 21%. For example, the alloy may be Ru6Mo2Nb2.

[0085]

[0079] In another example of the alloy, the mass percentage of Ru may be greater than 30%, preferably greater than 30%, more preferably greater than 39%, and may be less than 50%, preferably less than 45%, more preferably less than 41%. The mass percentage of Mo may be greater than 10%, preferably greater than 15%, more preferably greater than 19%, and may be less than 30%, preferably less than 25%, more preferably less than 21%. The mass percentage of Nb may be greater than 30%, preferably greater than 35%, more preferably greater than 31%, and may be less than 50%, preferably less than 45%, more preferably less than 41%. For example, the alloy may be Ru4Mo2Nb4. These alloys are only provided as examples of alloys that may meet the requirements of the present invention.

[0086]

[0080] The alloy may contain Ru and Nb, but may not contain Mo. That is, the alloy may consist of Ru, Nb, and ordinary impurities. The mass percentage of Ru may be greater than 20%, preferably greater than 30%, more preferably greater than 32%, and may be less than 40%, preferably less than 35%, more preferably less than 34%. The mass percentage of Nb may be greater than 50%, preferably greater than 60%, more preferably greater than 66%, and may be less than 80%, preferably less than 70%, more preferably less than 67%. For example, the alloy may be RuNb2.

[0087]

[0081] The alloy may contain Ru and Mo, but may not contain Nb. That is, the alloy may consist of Ru, Mo, and ordinary impurities. In one example, the mass percentage of Ru may be greater than 20%, preferably greater than 30%, more preferably greater than 32%, and may be less than 50%, preferably less than 40%, more preferably less than 35%. The mass percentage of Mo may be greater than 50%, preferably greater than 60%, more preferably greater than 65%, and may be less than 80%, preferably less than 70%, more preferably less than 68%. For example, the alloy may be RuMo2. In another example, the mass percentage of Ru may be greater than 30%, preferably greater than 40%, more preferably greater than 45%, and may be less than 70%, preferably less than 60%, more preferably less than 55%. The mass percentage of Mo may be greater than 30%, preferably greater than 40%, more preferably greater than 45%, and may be less than 70%, preferably less than 60%, more preferably less than 55%. For example, the alloy may be RuMo.

[0088]

[0082] The values of the refractive index (n) and the absorption coefficient (k) are plotted on the graph shown in FIG. 6, in which the absorption coefficient (k) is taken on the vertical axis and the refractive index (n) is taken on the horizontal axis, and the values are for a wavelength of approximately 13.5 nm. The plot in FIG. 6 also shows the values of the refractive index (n) and the absorption coefficient (k) of the elements Mo, Ru, and Nb. For each of the three example alloys, the values of the refractive index (n) and the absorption coefficient (k) are between those of Mo and Ru. This means that if any of the example alloys were implemented as the relatively low refractive index layer 323 of the multilayer stack 320, the multilayer stack 320 would exhibit a better reflectivity than the Ru—Si multilayer stack 320 and a shallower effective reflectivity plane than the Mo—Si multilayer stack. Also, the values of the refractive index (n) and the absorption coefficient vary depending on the composition of the alloy. Therefore, by adjusting the composition of the alloy comprising Mo, Ru, and Nb used for the relatively low refractive index layer 323 of the multilayer stack 320, the characteristics of the multilayer stack 320 can be optimized according to the situational requirements.

[0089]

[0083] Figure 7 shows a plot with the reflectivity on the vertical axis and the number of multilayer pairs on the horizontal axis. The plot is based on incident radiation having a wavelength of approximately 13.5 nm and an angle of incidence of 6°. Similar to FIG. 5, values for the Mo—Si multilayer stack 320 and the Ru—Si multilayer stack 320 are plotted, but FIG. 7 also includes values for the RuNb2—Si multilayer stack 320 and the Ru4Mo2Nb4—Si320 multilayer stack 320. The performance of the RuNb2—Si multilayer stack 320 is superior to that of the other multilayer stacks 320. Specifically, as the number of pairs 321 increases, the RuNb2—Si multilayer stack 320 tends to have a higher reflectivity than the other multilayer stacks 320, including the Mo—Si multilayer stack 320. Also, for a relatively small number of pairs (15 - 25), the rate of increase in reflectivity of the RuNb2—Si multilayer stack with an increase in the number of pairs 321 is higher than that of the Mo—Si multilayer stack 320. This means that the RuNb2—Si multilayer stack 320 reaches a steady-state reflectivity value with a smaller number of pairs 321 than the Mo—Si multilayer stack 320. As a result, the reflectivity of the 40-pair RuNb2—Si multilayer stack is higher than the reflectivity of the 40-pair Mo—Si multilayer stack. To exhibit the same reflectivity as the 40-pair Mo—Si multilayer stack, the RuNb2 multilayer stack 320 requires fewer pairs (approximately 30 - 34).

[0090]

[0084] Figure 8 illustrates a plot with reflectivity on the vertical axis and wavelength (nm) on the horizontal axis. The plot is based on a multilayer stack 320 having 40 pairs of 431 and radiation having an incident angle of 6°. The wavelength is the wavelength of the radiation incident on the multilayer stack 320. The plot includes a Mo-Si multilayer stack 320, a Ru-Si multilayer stack 320, a RuNb2-Si multilayer stack 320, and a Ru4Mo2Nb4-Si multilayer stack 320. For all of the plots, the reflectivity valve reaches a peak at a wavelength of approximately 13.5 nm. As would be expected from the previous graph, the peak reflectivity of the RuNb2-Si multilayer stack 320 is the highest, and its value is slightly larger than that of the Mo-Si multilayer stack 320. The peak reflectivity of the Ru-Si multilayer stack 320 is the lowest. The Ru-Si multilayer stack 320 has the broadest reflectivity band, and the Mo-Si multilayer stack 320 has the narrowest reflectivity band. Since the reflectivity band of the RuNb2-Si multilayer stack 320 is wider than that of the Mo-Si multilayer stack 320, the depth of the effective reflectivity plane of the RuNb2-Si multilayer stack 320 is smaller than the depth of the effective reflectivity plane of the Mo-Si multilayer stack 320.

[0091]

[0085] Thus, along with exhibiting a higher reflectivity, the RuNb2-Si multilayer stack 320 will exhibit a less significant shadowing (M3D) effect than the Mo-Si multilayer stack 320. Comparing the RuNb2-Si multilayer stack 320 with the Ru-Si multilayer stack, it is clear that the RuNb2-Si multilayer stack 320 exhibits a much higher reflectivity and does so without resulting in a significant increase in the depth of the effective reflectivity plane (compared to, for example, an increase in the depth of the effective reflectivity plane when the reflectivity is increased by using a Mo-Si multilayer stack instead). Similar observations can be made for the Ru4Mo2Nb4-Si multilayer stack 320. This observation will also apply to other alloys having at least two of Mo, Ru, and Nb and having a refractive index of 0.92 or less and an absorption coefficient of 0.015 or less.

[0092]

[0086] FIG. 9 illustrates a plot with the reflectance on the vertical axis and the angle of incidence (degrees) on the horizontal axis. The plot is based on a multilayer stack 320 having 40 pairs and radiation having a wavelength of approximately 13.5 nm. Shown in the plot are the Mo—Si multilayer stack 320, the Ru—Si multilayer stack 320, the RuNb2—Si multilayer stack 320, and the Ru4Mo2Nb4—Si multilayer stack 320. Generally, the change in reflectance as the angle of incidence increases is not significant for angles less than 9 degrees. In fact, the reflectance actually increases slightly from an angle of incidence of 0 degrees to about 7.5 degrees of incidence. When the angle of incidence exceeds 9 degrees, the reflectance decreases rapidly. As expected, the reflectance over the range of angles of incidence is much lower for the Ru—Si multilayer stack 320 than for the Mo—Si multilayer stack 320. The RuNb2—Si multilayer stack 320 has excellent performance and exhibits a higher reflectance over the entire range of angles of incidence.

[0093]

[0087] In view of the above, the reflecting member according to the present invention may preferably comprise 40 or fewer pairs 321 in the multilayer stack 320, more preferably fewer than 35 pairs 321, and even more preferably fewer than 35 pairs 321. The number of pairs 321 in the multilayer stack 320 may preferably be more than 20. Also, the effective reflectance plane of the reflecting member according to the present invention may be below 45 nm, preferably below 40 nm, and even more preferably below 35 nm below the top surface of the multilayer stack 320. The reflectance of the reflecting member (for radiation having a wavelength of 13.5 nm and an angle of incidence of 6°) may preferably be greater than 0.73, more preferably greater than 0.74, and even more preferably greater than 0.75.

[0094] [

[0088] ] Although the above description mainly refers to the mask 300, the present invention is not limited to this embodiment, and the multilayer stack 320 can be implemented in any reflective member. For example, the reflective member may be used in other components located within a lithographic apparatus, such as an EUV scanner mirror.

[0095] [

[0089] ] When a capping layer 330 is present on the upper surface of the multilayer stack 320, the capping layer 320 may be formed of the same material as the relatively low refractive index layer 323 (i.e., the alloy described in detail above). This can be advantageous even if the relatively low refractive index layer 323 itself is not composed of an alloy. That is, the capping layer 330 may be formed of the alloy disclosed in the present application when the relatively low refractive index layer 323 is formed of another material such as molybdenum.

[0096] [

[0090] ] Although the text may specifically refer to the use of a lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Other possible applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like.

[0097]

[0091] Where context permits, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented by instructions stored on a machine-readable medium that can be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM), random access memory (RAM), magnetic storage media, optical storage media, flash memory devices, electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Also, firmware, software, routines, instructions may be described herein as performing certain actions. However, such descriptions are for convenience only, and such actions actually result from computing devices, processors, controllers, or other devices that execute the firmware, software, routines, instructions, etc., and in execution, may interact with actuators or other devices in the physical world.

[0098]

[0092] Although the present invention may be specifically referred to in the context of a lithographic apparatus in the present text, embodiments of the invention may be used in other apparatuses. Embodiments of the invention may form part of any apparatus for measuring or processing an object such as a mask inspection apparatus, a metrology apparatus, or a wafer (or other substrate) or mask (or other patterning device). These apparatuses may generally be referred to as lithographic tools.

[0099]

[0093] Although the use of embodiments of the invention may be specifically referred to in the context of optical lithography above, it will be understood that the invention is not limited to optical lithography where context permits.

[0100]

[0094] While specific embodiments of the present invention have been described above, it will be understood that the present invention may be practiced otherwise than as described. The above description is intended to be illustrative rather than limiting. Thus, it will be apparent to those skilled in the art that changes may be made to the described invention without departing from the scope of the claims and the scope of the following clauses.

[0101] 1. A reflective member for use in an EUV lithography apparatus, the reflective member comprising a multilayer stack comprising a plurality of pairs of layers arranged in pairs, each pair comprising a first layer and a second layer, the first layer being formed of a material comprising Si, the second layer being formed of a material comprising at least two of Ru, Nb, and Mo, the second layer being configured to have a refractive index of 0.92 or less and an absorption coefficient of 0.015 or less for light having a wavelength of approximately 13.5 nm. A reflective member. 2. The reflective member according to clause 1, wherein the material of the second layer is configured to have a refractive index of less than 0.91, preferably less than 0.9, for light having a wavelength of approximately 13.5 nm. 3. The reflective member according to clause 1 or 2, wherein the material of the second layer is configured to have an absorption coefficient of less than 0.014, preferably less than 0.013, more preferably less than 0.012, for light having a wavelength of approximately 13.5 nm. 4. The reflective member according to any one of clauses 1 to 3, wherein the material of the second layer comprises Nb. 5. The reflective member according to any one of clauses 1 to 4, wherein the material of the second layer comprises Ru. 6. The reflective member according to any one of clauses 1 to 5, wherein the material of the second layer comprises Mo. 7. The reflective member according to any one of clauses 1 to 6, wherein the material of the second layer consists of at least two of Ru, Nb, Mo and ordinary impurities. 8. The reflective member according to any one of clauses 1 to 7, wherein the mass percentage of Nb in the material of the second layer is greater than 5%, preferably greater than 20%, preferably greater than 40%, more preferably greater than 60%. 9. The mass percentage of Ru in the material of the second layer is greater than 30%, preferably greater than 35%, and more preferably greater than 55%, for the reflective member according to any one of clauses 1 to 8. 10. The mass percentage of Mo in the material of the second layer is 0% or more, preferably greater than 10%, and more preferably greater than 5%, for the reflective member according to any one of clauses 1 to 9. 11. The mass percentage of Nb in the material of the second layer is less than 70%, preferably less than 50%, and more preferably less than 45%, for the reflective member according to any one of clauses 1 to 10. 12. The mass percentage of Ru in the material of the second layer is less than 85%, preferably less than 75%, and more preferably less than 70%, for the reflective member according to any one of clauses 1 to 11. 13. The mass percentage of Mo in the material of the second layer is less than 70%, preferably less than 50%, and more preferably less than 25%, for the reflective member according to any one of clauses 1 to 12. 14. The material of the second layer is in the form of Ru x Nb y Mo z Imp a and, Imp represents at least one impurity, x + y + z + a = 1, The composition of the material is such that 0.887x + 0.9337y + 0.9237z is less than 0.92, preferably less than 0.91, and more preferably less than 0.9, for the reflective member according to any one of clauses 1 to 13. 15. The material of the second layer is in the form of Ru x Nb y Mo z Imp a and, Imp represents at least one impurity, x + y + z + a = 1, The composition of the material is such that 0.0171x + 0.0052y + 0.0064z is less than 0.015, preferably less than 0.014, more preferably less than 0.013, and even more preferably less than 0.012, for the reflective member according to any one of clauses 1 to 14. 16. The mass percentage of Ru is greater than 20%, preferably greater than 30%, more preferably greater than 32%, and less than 40%, preferably less than 35%, more preferably less than 34%. The mass percentage of Nb is greater than 50%, preferably greater than 60%, more preferably greater than 66%, and less than 80%, preferably less than 70%, more preferably less than 67%. The reflective member according to any one of clauses 1 to 7. 17. The mass percentage of Ru is greater than 50%, preferably greater than 55%, more preferably greater than 59%, and less than 70%, preferably less than 65%, more preferably less than 61%. The mass percentage of Mo is greater than 10%, preferably greater than 15%, more preferably greater than 19%, and less than 30%, preferably less than 25%, more preferably less than 21%. The mass percentage of Nb is greater than 10%, preferably greater than 15%, more preferably greater than 19%, and less than 30%, preferably less than 25%, more preferably less than 21%. The reflective member according to any one of clauses 1 to 7. 18. The mass percentage of Ru is greater than 30%, preferably greater than 35%, more preferably greater than 39%, and less than 50%, preferably less than 45%, more preferably less than 41%. The mass percentage of Mo is greater than 10%, preferably greater than 15%, more preferably greater than 19%, and less than 30%, preferably less than 25%, more preferably less than 21%. The mass percentage of Nb is greater than 30%, preferably greater than 35%, more preferably greater than 39%, and less than 50%, preferably less than 45%, more preferably less than 41%. The reflective member according to any one of clauses 1 to 7. 19. The reflective member has an effective reflectivity plane that is less than 45 nm below the top surface of the multilayer stack, preferably less than 40 nm below the top surface of the multilayer stack, more preferably less than 35 nm below the top surface of the multilayer stack. The reflective member according to any one of clauses 1 to 18. 20. The reflective member is configured for use as an EUV scanner mirror. The reflective member according to any one of clauses 1 to 19. 21. The reflective member is configured for use as an EUV photomask, and the reflective member further comprises a substrate on which a multilayer stack is formed, and a capping layer positioned on the uppermost surface of the multilayer stack, the reflective member according to any one of clauses 1 to 19. 22. The reflective member according to clause 21, wherein the capping layer is formed of the same material as each second layer. 23. The reflective member according to clause 21 or 22, further comprising an absorber layer positioned on the uppermost surface of the capping layer. 24. A lithographic apparatus comprising a reflective member according to any one of clauses 1 to 23. 25. A method of manufacturing a device including the use of a reflective member according to any one of clauses 1 to 23. 26. A substrate, a multilayer stack comprising a plurality of layers arranged in pairs, a capping layer formed of a material comprising at least two of Ru, Nb, and Mo, An EUV photomask comprising a capping layer configured to have a refractive index of less than 0.92 and an absorption coefficient of less than 0.0015 for light having a wavelength of approximately 13.5 nm. 27. The EUV photomask according to clause 26, wherein the material of the capping layer is configured to have a refractive index of less than 0.91, preferably less than 0.9, for light having a wavelength of approximately 13.5 nm. 28. The EUV photomask according to clause 26 or 27, wherein the material of the capping layer is configured to have an absorption coefficient of less than 0.014, preferably less than 0.013, more preferably less than 0.012, for light having a wavelength of approximately 13.5 nm. 29. The EUV photomask according to clauses 26 to 28, wherein the material of the capping layer comprises Nb. 30. The EUV photomask according to any one of clauses 26 to 29, wherein the material of the capping layer comprises Ru. 31. The EUV photomask according to any one of clauses 26 to 30, wherein the material of the capping layer comprises Mo. 32. The EUV photomask according to any one of clauses 26 to 31, wherein the material of the capping layer consists of at least two of Ru, Nb, and Mo and ordinary impurities. 33. The EUV photomask according to any one of clauses 26 to 32, wherein the mass percentage of Nb in the material of the capping layer is greater than 5%, preferably greater than 20%, preferably greater than 40%, and more preferably greater than 60%. 34. The EUV photomask according to any one of clauses 26 to 33, wherein the mass percentage of Ru in the material of the capping layer is greater than 30%, preferably greater than 35%, and more preferably greater than 55%. 35. The EUV photomask according to any one of clauses 26 to 34, wherein the mass percentage of Mo in the material of the capping layer is 0% or more, preferably greater than 5%, and more preferably greater than 10%. 36. The EUV photomask according to any one of clauses 26 to 35, wherein the mass percentage of Nb in the material of the capping layer is less than 70%, preferably less than 50%, and more preferably less than 45%. 37. The EUV photomask according to any one of clauses 26 to 36, wherein the mass percentage of Ru in the material of the capping layer is less than 85%, preferably less than 75%, and more preferably less than 70%. 38. The EUV photomask according to any one of clauses 26 to 37, wherein the mass percentage of Mo in the material of the capping layer is less than 70%, preferably less than 50%, and more preferably less than 25%. 39. The material of the second layer is Ru x Nb y Mo z I a in the form, where I represents at least one impurity, and the composition of the material is such that 0.887x + 0.9337y + 0.9237z is less than 0.92, preferably less than 0.91, and more preferably less than 0.9. The EUV photomask according to any one of clauses 26 to 38. 40. The material of the capping layer is Ru x Nb y Mo z I ain the form, where I represents at least one impurity, and the composition of the material is such that 0.0171x + 0.0052y + 0.0064z is less than 0.015, preferably less than 0.014, more preferably less than 0.013, and even more preferably less than 0.012, the EUV photomask according to any one of clauses 26 to 39. 41. The mass percentage of Ru is greater than 20%, preferably greater than 30%, more preferably greater than 32%, and less than 40%, preferably less than 35%, more preferably less than 34%. The mass percentage of Nb is greater than 50%, preferably greater than 60%, more preferably greater than 66%, and less than 80%, preferably less than 70%, more preferably less than 67%. The EUV photomask according to any one of clauses 26 to 32. 42. The mass percentage of Ru is greater than 50%, preferably greater than 55%, more preferably greater than 59%, and less than 70%, preferably less than 65%, more preferably less than 61%. The mass percentage of Mo is greater than 10%, preferably greater than 15%, more preferably greater than 19%, and less than 30%, preferably less than 25%, more preferably less than 21%. The mass percentage of Nb is greater than 10%, preferably greater than 15%, more preferably greater than 19%, and less than 30%, preferably less than 25%, more preferably less than 21%. The EUV photomask according to any one of clauses 26 to 32. 43. The mass percentage of Ru is greater than 30%, preferably greater than 35%, more preferably greater than 39%, and less than 50%, preferably less than 45%, more preferably less than 41%. The mass percentage of Mo is greater than 10%, preferably greater than 15%, more preferably greater than 19%, and less than 30%, preferably less than 25%, more preferably less than 21%. The mass percentage of Nb is greater than 30%, preferably greater than 35%, more preferably greater than 39%, and less than 50%, preferably less than 45%, more preferably less than 41%. The EUV photomask according to any one of clauses 26 to 32. 44. A lithographic apparatus comprising the EUV photomask according to any one of clauses 26 to 43. A method of manufacturing a device including the use of an EUV photomask according to any one of clauses 26 to 43.

Claims

1. A reflective member for use in an EUV lithography apparatus, the reflective member comprising a multilayer stack comprising a plurality of pairs of layers arranged in pairs, each pair comprising a first layer and a second layer, the first layer being formed of a material comprising Si, the second layer being formed of a material comprising at least two of Ru, Nb, and Mo, the second layer being configured to have a refractive index of 0.92 or less and an absorption coefficient of 0.015 or less for light having a wavelength of approximately 13.5 nm. A reflective member.

2. The reflective member according to claim 1, wherein the material of the second layer is configured to have a refractive index of less than 0.91, preferably less than 0.9, for light having a wavelength of approximately 13.5 nm.

3. The reflective member according to claim 1 or 2, wherein the material of the second layer is configured to have an absorption coefficient of less than 0.014, preferably less than 0.013, more preferably less than 0.012, for light having a wavelength of approximately 13.5 nm.

4. The reflective member according to any one of claims 1 to 3, wherein the material of the second layer comprises Nb, Ru, and / or Mo.

5. The reflective member according to any one of claims 1 to 4, wherein the material of the second layer consists of at least two of Ru, Nb, Mo and the normal impurities.

6. The reflective member according to any one of claims 1 to 5, wherein the mass percentage of Nb in the material of the second layer is greater than 5%, preferably greater than 20%, preferably greater than 40%, more preferably greater than 60%.

7. The reflective member according to any one of claims 1 to 6, wherein the mass percentage of Ru in the material of the second layer is greater than 30%, preferably greater than 35%, more preferably greater than 55%.

8. The reflective member according to any one of claims 1 to 7, wherein the mass percentage of Mo in the material of the second layer is greater than 10%, more preferably greater than 5%.

9. The reflective member according to any one of claims 1 to 8, wherein the mass percentage of Nb in the material of the second layer is less than 70%, preferably less than 50%, more preferably less than 45%.

10. The mass percentage of Ru in the material of the second layer is less than 85%, preferably less than 75%, and more preferably less than 70%, for the reflective member according to any one of claims 1 to 9.

11. The mass percentage of Mo in the material of the second layer is less than 70%, preferably less than 50%, and more preferably less than 25%, for the reflective member according to any one of claims 1 to 10.

12. The material of the second layer is Ru ｘ Nb ｙ Mo ｚ Imp ａ in the form of, Imp represents at least one impurity, x + y + z + a = 1, The composition of the material is such that 0.887x + 0.9337y + 0.9237z is less than 0.92, preferably less than 0.91, and more preferably less than 0.9, for the reflective member according to any one of claims 1 to 11.

13. The material of the second layer is Ru ｘ Nb ｙ Mo ｚ Imp ａ in the form of, Imp represents at least one impurity, x + y + z + a = 1, The composition of the material is such that 0.0171x + 0.0052y + 0.0064z is less than 0.015, preferably less than 0.014, more preferably less than 0.013, and even more preferably less than 0.012, for the reflective member according to any one of claims 1 to 12.

14. The mass percentage of Ru is greater than 20%, preferably greater than 30%, more preferably greater than 32%, and less than 40%, preferably less than 35%, preferably less than 34%. The mass percentage of Nb is greater than 50%, preferably greater than 60%, more preferably greater than 66%, and less than 80%, preferably less than 70%, more preferably less than 67%, for the reflective member according to any one of claims 1 to 5.

15. The mass percentage of Ru is greater than 50%, preferably greater than 55%, more preferably greater than 59%, and less than 70%, preferably less than 65%, more preferably less than 61%. The mass percentage of Mo is greater than 10%, preferably greater than 15%, more preferably greater than 19%, and less than 30%, preferably less than 25%, more preferably less than 21%. The mass percentage of Nb is greater than 10%, preferably greater than 15%, more preferably greater than 19%, and less than 30%, preferably less than 25%, more preferably less than 21%, for the reflective member according to any one of claims 1 to 5.

16. The mass percentage of Ru is greater than 30%, preferably greater than 35%, more preferably greater than 39%, and less than 50%, preferably less than 45%, more preferably less than 41%. The mass percentage of Mo is greater than 10%, preferably greater than 15%, more preferably greater than 19%, and less than 30%, preferably less than 25%, more preferably less than 21%. The mass percentage of Nb is greater than 30%, preferably greater than 35%, more preferably greater than 39%, and less than 50%, preferably less than 45%, more preferably less than 41%. The reflective member according to any one of claims 1 to 5.

17. The reflective member has an effective reflectance plane that is less than 45 nm below, preferably less than 40 nm below, more preferably less than 35 nm below the top surface of the multilayer stack. The reflective member according to any one of claims 1 to 16.

18. The reflective member is configured for use as an EUV scanner mirror. The reflective member according to any one of claims 1 to 17.

19. The reflective member is configured for use as an EUV photomask. The reflective member further includes a substrate on which the multilayer stack is formed and a capping layer positioned on the top surface of the multilayer stack. The reflective member according to any one of claims 1 to 17.

20. A substrate, A multilayer stack comprising a plurality of pairs of layers, A capping layer formed of a material comprising at least two of Ru, Nb, and Mo, An EUV photomask comprising, wherein the capping layer is configured to have a refractive index less than 0.92 and an absorption coefficient less than 0.0015 for light having a wavelength of approximately 13.5 nm.

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