Reflective member for EUV lithography

Abstract

A reflective member for use in an EUV lithographic apparatus, the reflective member comprising a multilayer stack comprising a plurality of layers arranged in a plurality of pairs, where: each pair comprises a first layer and a second layer; the first layer is formed by a material comprising Si; and the second layer is formed of a material including at least two of Ru, Nb, and Mo, and wherein the second layer is configured to have a refractive index of less than or equal to 0.92 and an absorption coefficient of less than or equal to 0.015 for light having a wavelength of about 13.5 nm.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. application No. 63 / 393,874, filed on July 30, 2022, and the entire contents of that U.S. application are incorporated herein by reference. Technical Field

[0003] The present invention relates to a reflective member, a lithography apparatus including the reflective member, a method of manufacturing a device including the use of the reflective member, an EUV mask, a lithography apparatus including the EUV mask, and a method of manufacturing a device including the use of the EUV mask. Background Art

[0004] A lithographic apparatus is a machine that applies a desired pattern to a substrate, usually to a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that case, a pattern forming device (which is alternatively referred to as a mask or reticle) can be used to produce a circuit pattern to be formed on a single layer of the IC. This pattern can be transferred to a target portion (e.g., a portion including a die, a die, or a number of dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is usually performed via imaging onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will include a network of adjacent target portions that are patterned continuously.

[0005] Photolithography is widely considered to be one of the key steps in the manufacture of ICs and other devices and / or structures. However, as the size of features produced using photolithography becomes smaller and smaller, photolithography is becoming a more decisive factor in enabling the manufacture of small ICs or other devices and / or structures.

[0006] The theoretical estimate of the pattern printing limit can be given by the Rayleigh resolution criterion, as shown in equation (1):

[0007] (1)

[0008] where 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 factor (also called the Rayleigh constant), and CD is the feature size (or critical dimension) of the printed features. As can be seen from equation (1), a reduction in the minimum printable size of a feature can be obtained in three ways: by shortening the exposure wavelength λ, by increasing the numerical aperture NA, or by reducing the value of k1.

[0009] 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 with a wavelength in the range of 10 nm to 20 nm (e.g., in the range of 13 nm to 14 nm). It has been further proposed that EUV radiation with a wavelength less than 10 nm (e.g., in the range of 5 nm to 10 nm, such as 6.7 nm or 6.8 nm) may be used. Such radiation is known as extreme ultraviolet radiation or soft x-ray radiation. Possible sources include, for example, laser-produced plasma sources, discharge plasma sources, or sources based on synchrotron radiation provided by electron storage rings.

[0010] It is difficult to collect EUV radiation into a beam, direct it onto a mask, and project the patterned beam onto a substrate because it is impossible to manufacture refractive optical elements for EUV radiation. Therefore, these functions must be performed using reflectors (i.e., mirrors). Multilayer reflectors (also called distributed Bragg reflectors) are typically used, which include a certain number of layers (also called periods) arranged in multiple pairs. Each pair includes a relatively high refractive index layer and a relatively low refractive index layer. At each interface between the layers, a portion of the radiation traveling through the multilayer reflector is reflected. The thickness of each pair is configured so that there is constructive interference between the radiation reflected at each interface. The reflectivity of a multilayer reflector for reflecting EUV radiation is typically about 70%. In a lithographic apparatus, there may be many multilayer reflectors used in series between an EUV source and a substrate. Therefore, the amount of radiation reaching the substrate may be a small percentage of the EUV radiation generated.

[0011] A multilayer reflector may be used in a mask which, in addition to the multilayer stack, also includes an absorber layer on the top surface of the multilayer stack. This absorber layer is patterned with the image to be projected onto the substrate. The absorber layer has a certain thickness, so when radiation is incident on the mask at an angle of incidence greater than zero, as is necessary for a reflective mask, a 3D effect occurs, such as a shadow of the incident radiation onto the mask. This leads to errors in the lithography process, such as pattern placement errors and line width errors.

[0012] In a multilayer reflector, the effective reflection plane can be defined as a plane below the surface of the multilayer reflector at a depth representing the average depth of reflections within the multilayer reflector. As the effective reflection plane is deeper below the surface of the multilayer reflector, the 3D effect (shadow) becomes more pronounced.

[0013] In current multilayer reflectors, the relatively high refractive index layers typically include silicon (Si), and the relatively low refractive index layers typically include molybdenum (Mo). Alternative configurations of multilayer reflectors have been proposed, in which the relatively high refractive index layers include Si, and the relatively low refractive index layers include ruthenium (Ru). Ru-Si multilayer reflectors exhibit a shallower effective reflection plane than Mo-Si multilayer reflectors, so when they are used in masks, the 3D effect (shadow) exhibited is less than that of Mo-Si multilayer reflectors. However, the reflectivity of Ru-Si multilayer reflectors is lower than that of Mo-Si multilayer reflectors.

[0014] It is an object of the present invention to provide a reflective member having properties superior to currently available reflective members in terms of reflectivity and 3D effect when used in EUV masks. Summary of the invention

[0015] Herein, a reflective component for use in an EUV lithography apparatus is provided, the reflective component comprising a multilayer stack comprising a plurality of layers arranged in a plurality of pairs, wherein: each pair comprises a first layer and a second layer; the first layer is formed of a material comprising Si; and the second layer is formed of a material comprising at least two of Ru, Nb, and Mo, and wherein the second layer is configured to have a refractive index less than or equal to 0.92 and an absorption coefficient less than or equal to 0.015 for light having a wavelength of approximately 13.5 nm.

[0016] Herein, a lithographic apparatus comprising a reflective member is also provided.

[0017] Herein, a method of manufacturing a device including the use of a reflective member is also provided.

[0018] In this article, an EUV mask is also provided, including:

[0019] A substrate; a multilayer stack comprising a plurality of layers arranged in a plurality of pairs; and a cap layer formed of a material comprising at least two of Ru, Nb and Mo, and wherein the cap layer is configured to have a refractive index less than 0.92 and an absorption coefficient less than 0.015 for light having a wavelength of approximately 13.5 nm.

[0020] Herein, a lithography apparatus including an EUV mask is also provided.

[0021] Herein, a method of manufacturing a device including using an EUV mask is also provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which corresponding reference characters indicate corresponding parts.

[0023] Figure 1 A lithographic apparatus is schematically depicted.

[0024] Figure 2 Depicting a more detailed view of a lithography apparatus.

[0025] Figure 3 An example of an EUV mask depicted in cross section.

[0026] Figure 4 An EUV mask showing two reflected beams is depicted in cross section.

[0027] Figure 5 Graphs depicting reflectivity on the vertical axis and the number of multilayer pairs on the horizontal axis for a Mo—Si multilayer stack and a Ru—Si multilayer stack.

[0028] Figure 6 Graph depicting the absorption coefficient on the vertical axis and the refractive index on the horizontal axis for several elements and alloys.

[0029] Figure 7 Graph depicting reflectivity on the vertical axis and number of multilayer pairs on the horizontal axis for several multilayer stack configurations.

[0030] Figure 8 Graph depicting reflectivity on the vertical axis and wavelength on the horizontal axis for several multilayer stack configurations.

[0031] Fig. 9 Graph depicting reflectivity on the vertical axis and angle of incidence on the horizontal axis for several multilayer stack configurations. DETAILED DESCRIPTION

[0032] Figure 1 A lithographic apparatus 100 comprising a source collector module SO according to an embodiment of the present invention is schematically depicted. The apparatus 100 comprises:

[0033] an illumination system (or illuminator) IL configured to condition a radiation beam B (e.g., EUV radiation);

[0034] a support structure (e.g., mask table) MT configured to support a patterning device (e.g., mask or reticle) MA and connected to a first positioner PM configured to accurately position the patterning device;

[0035] a substrate table (eg, wafer stage) WT configured to hold a substrate (eg, a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate; and

[0036] A projection system (eg, a reflective projection system) PS is configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (eg, comprising one or more dies).

[0037] The illumination system IL may include various types of optical components for directing, shaping or controlling the radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof.

[0038] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA, 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 may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may be, for example, a frame or a table, which may be fixed or movable as required. The support structure MT may ensure that the patterning device MA is in a desired position, for example relative to the projection system PS.

[0039] The term “patterning device” should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section so as to create a pattern in a target portion C of the substrate W. The pattern imparted to the radiation beam B may correspond to a specific functional layer in a device created in the target portion C, such as an integrated circuit.

[0040] 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, alternating phase shift, and attenuated phase shift, as well as various hybrid mask types. An example of a programmable mirror array uses a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incident radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam that is reflected by the matrix of mirrors.

[0041] Similar to the illumination system IL, the projection system PS may include various types of optical components suitable for the exposure radiation used or for other factors such as the use of a vacuum, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof. It may be necessary to use a vacuum for EUV radiation since other gases may absorb too much radiation. Therefore, a vacuum environment may be provided to the entire beam path by means of vacuum walls and a vacuum pump.

[0042] As depicted therein, the lithographic apparatus 100 is of a reflective type (eg, employing a reflective mask).

[0043] The lithographic apparatus 100 may be of a 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) may be used in parallel, or preparatory steps may be performed on one or more substrate tables WT (and / or one or more support structures MT) while one or more other substrate tables WT (and / or one or more other support structures MT) are being used for exposure.

[0044] refer to Figure 1 , the illumination system IL receives a beam of extreme ultraviolet radiation from a source collector module SO. Methods for generating EUV light include, but are not necessarily limited to, converting a material having at least one element (e.g., xenon, lithium, or tin) into a plasma state using one or more emission lines in the EUV range. In one such method, often referred to as laser produced plasma "LPP", the desired plasma may be generated by irradiating a fuel (such as a droplet, stream, or cluster of material having the desired line emitting element) with a laser beam. The source collector module SO may be a laser ( Figure 1 The laser is used to provide a laser beam for exciting the fuel. The resulting plasma emits output radiation (e.g., EUV radiation) which is collected using a radiation collector disposed in a source collector module. For example, when a CO2 laser is used to provide a laser beam for fuel excitation, the laser and source collector module SO may be separate entities.

[0045] In such cases, the laser is not considered to form part of the lithographic apparatus 100, and the radiation beam B is delivered from the laser to the source collector module SO by means of a beam delivery system comprising, for example, suitable directing mirrors and / or a beam expander. In other cases, such as when the source is a discharge produced plasma EUV generator (often referred to as a DPP source), the source may be an integral part of the source collector module SO.

[0046] The illumination system IL may include an adjuster for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer radial extent and / or the inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illumination system IL may be adjusted. Additionally, the illumination system IL may include various other components, such as a faceted field mirror arrangement and a faceted pupil mirror arrangement. The illumination system IL may be used to adjust the radiation beam B to have a desired uniformity and intensity distribution in its cross-section.

[0047] 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 reflection from the patterning device (e.g. a mask) MA, the radiation beam B passes through a projection system PS which focuses the radiation beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor PS2 (e.g. an interferometric device, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved, for example, in order to position a different target portion C in the path of the radiation beam B. Similarly, a first positioner PM and a further position sensor PS1 can be used to accurately position the patterning device (e.g. a mask) MA relative 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.

[0048] The controller 500 controls the overall operation of the lithographic apparatus 100, and in particular performs the operation process further described below. The controller 500 may be embodied as a suitably programmed general-purpose computer, which includes a central processing unit, a volatile storage component and a non-volatile storage component, one or more input and output devices (such as a keyboard and a screen), one or more network connections, and one or more interfaces to various parts of the lithographic apparatus 100. It should be understood that the pair relationship between the control computer and the lithographic apparatus 100 is not necessary. In an embodiment of the present invention, one computer may control multiple lithographic apparatuses 100. In an embodiment of the present invention, multiple networked computers may be used to control one lithographic apparatus 100. The controller 500 may also be configured to control one or more associated process devices and substrate conveying devices of a lithographic cell or lithographic cluster, and the lithographic apparatus 100 forms part of the lithographic cell or lithographic cluster. The controller 500 may also be configured to be subordinate to the management control system of the lithographic cell or lithographic cluster and / or the overall control system of the factory (fab).

[0049] Figure 2 The lithographic apparatus 100 is shown in more detail and includes a source collector module SO, an illumination system IL, and a projection system PS. The EUV radiation emitting plasma 210 may be formed by a plasma source. The EUV radiation may be generated by a gas or vapor (e.g., Xe gas, Li vapor, or Sn vapor), wherein the radiation emitting plasma 210 is generated to emit radiation in the EUV range of the electromagnetic spectrum. In an embodiment, an excited tin (Sn) plasma is provided to generate EUV radiation.

[0050] Radiation emitted by radiation emitting plasma 210 passes from source chamber 211 into collector chamber 212 .

[0051] The collector chamber 212 may include a radiation collector CO. Radiation traversing the radiation collector CO may be focused in a virtual source point IF. The virtual source point IF is often referred to as an intermediate focus, and the source collector module SO is arranged such that the virtual source point IF is located at or near an opening 221 in the enclosure structure 220. The virtual source point IF is an image of the radiation emitting plasma 210.

[0052] The radiation then traverses an illumination system IL which may include a faceted field mirror arrangement 22 and a faceted pupil mirror arrangement 24 arranged to provide a desired angular distribution of the unpatterned beam 21 at the patterning device MA, and a desired uniformity of radiation intensity at the patterning device MA. After reflection of the unpatterned beam 21 at the patterning device MA held by the support structure MT, a patterned beam 26 is formed and is imaged by the projection system PS via reflective elements 28, 30 onto a substrate W held by a substrate table WT.

[0053] Typically, there may be more elements in the illumination system IL and the projection system PS than those shown. Furthermore, there may be more mirrors than shown in the figures, for example, there may be more than 100 mirrors in the projection system PS. Figure 2 The reflective elements shown in the figure may have 1 to 6 additional reflective elements.

[0054] Alternatively, the source collector module SO may be part of a LPP radiation system.

[0055] like Figure 1 As depicted in , in an embodiment, the lithographic apparatus 100 comprises 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 a substrate W. The pattern is EUV radiation for the radiation beam B.

[0056] The space intervening between the projection system PS and the substrate table WT may be at least partially evacuated.The intervening space may be defined by a solid surface at the location of the projection system PS, from which employed radiation is directed towards the substrate table WT.

[0057] Figure 3 Depicted is a mask 300 that may be used within an EUV lithography apparatus to impart a desired pattern to a radiation beam. Mask 300 is one example of a reflective member of the present invention.

[0058] Figure 3The mask 300 shown in the figure includes a substrate 310, a multilayer stack 320, a cover layer 330 and an absorber layer 340. The substrate 310 is a component that provides a starting point for manufacturing the multilayer stack 320. The reflective member disclosed herein can be used with any composition of the substrate 310 known to those skilled in the art. For example, the substrate 310 can be formed of silicon oxide and titanium oxide (SiO2-TiO2). Generally, the substrate 310 is formed of a material to which the material of the multilayer stack 320 adheres. The surface of the substrate 310 can be polished, i.e., ground to form a smooth and flat surface, thereby improving the adhesion of the material of the multilayer stack 320 to the substrate 310.

[0059] The multilayer stack 320 is formed of a plurality of layers 322, 323 arranged in pairs 321. Each pair includes a relatively high refractive index layer 322 and a relatively low refractive index layer 323. That is, moving through the multilayer stack 320 in a direction perpendicular to the upper surface of the multilayer stack, the material changes from the material of the relatively high refractive index layer 322 to the material of the relatively low refractive index 323. At each interface between layers (i.e., at a point in the multilayer stack where EUV radiation moves from a relatively low refractive index layer 323 to a relatively high refractive index layer 322 or from a relatively high refractive index layer 322 to a relatively low refractive index layer 323), a portion of the radiation is reflected. The thickness of each layer 322, 323 in the multilayer stack 320 is configured so that when light is reflected at each of the plurality of interfaces between different layers 322, 323 in the multilayer stack 320, the reflected beams are in phase. This means that the reflections from each of the plurality of interfaces constructively interfere with each other to form a reflected beam.

[0060] In the current multilayer stack 320, the number of pairs in the multilayer stack 320 can be between 40 and 50. Each layer in the layers 322, 323 can be separated by an intermediate film (not shown) to prevent intermixing and silicide formation. The intermediate layer can be formed, for example, by boron carbide (B4C). As stated above, the thickness of each layer is determined according to the conditions under which the beams reflected at each interface constructively interfere, which depends on the wavelength of the radiation, as will be known to those skilled in the art. As an example, the relatively high refractive index layer 322 can have a thickness between 3 nm and 5 nm, and the relatively low refractive index layer 323 can have a thickness between 2 nm and 4 nm.

[0061] The cover layer 330 may be located on the upper surface of the multilayer stack 320. The cover layer 330 is provided to improve the durability and chemical stability of the multilayer stack 320. The reflective member disclosed herein may be employed with any cover layer 330 known to those skilled in the art. As an example, the material of the cover layer may be the same as the material of the relatively high refractive index layer 322 or the material of the relatively low refractive index layer 323.

[0062] The absorber layer 340 may be located on the upper surface of the cap layer 330. The absorber layer 340 may include a single material layer or multiple material layers. The absorber layer 340 is configured to absorb incident radiation. Therefore, in a mask configured for use in an EUV lithography device, the material of the absorber layer 340 is a material that absorbs EUV radiation. The reflective member disclosed herein may be employed with an absorber layer 340 known to be suitable for any composition to a person skilled in the art. For example, the material of the absorber 340 may be formed of a material including tantalum nitride (TaN) or tantalum boron nitride (Ta-BN), and the total 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 including nickel (Ni), and the total thickness of the absorber layer 340 may be between 25 nm and 35 nm.

[0063] The absorber layer 340 may be patterned so that it includes an image to be projected onto the photosensitive film of the substrate. That is, the absorber layer 340 may cover some areas on the surface of the cap layer 330 but not other areas. In other words, some areas of the cap layer 330 may be exposed but not other areas. In operation, EUV radiation is reflected by the mask 300 at areas where the absorber layer 340 is not present and is absorbed in areas where the absorber layer 340 is present. The absorber layer 340 may initially be formed on the cap layer 330 so that it covers the entirety of the cap layer 330. The pattern may then be formed in the absorber layer 340 using techniques such as electron beam lithography and any known etching process.

[0064] A mask configured for use in an EUV lithography apparatus, such as 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).

[0065] EUV radiation incident on a mask, such as the mask 300, typically approaches the mask 300 from an angle of incidence (the angle between the incident beam and a line perpendicular to the surface at the point of incidence) that is greater than zero. This causes the reflected beam to travel along a different path from the incident beam. In a lithographic apparatus, the angle of incidence of the EUV radiation beam incident on the mask 300 may be between 1° and 10° with respect to the normal. For example, the angle of incidence may be 6°. Due to the height of the absorber layer 340 above the cap layer 330 and the angle of incidence being greater than zero, undesirable shadowing of exposed areas of the mask 300 occurs. Such shadowing occurs when incident EUV radiation is blocked by the absorber layer 340 from reaching exposed areas of the upper surface of the mask 300, or when reflected radiation is prevented by the absorber layer 340 from traveling outward from the mask 300. Such shadowing may cause significant errors, such as pattern placement errors and line width errors. Errors caused by shadows become more significant as the angle of incidence on the mask 300 increases and as the thickness of the absorber layer 340 increases. Errors caused by shadows also become more significant as the effective reflection plane (the plane below the surface of the multilayer reflector that represents the average depth of reflections within the multilayer reflector) becomes deeper. Figure 4 Two effective reflection planes 431, 432 are shown. The depth of the effective reflection planes in the multilayer stack 320 depends on the materials of the relatively high refractive index layer 322 and the relatively low refractive index layer 323. Specifically, the depth of the effective reflection plane depends on the refractive index of the relatively high refractive index layer 322 and the relatively low refractive index layer 323. 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 hindered by the absorber layer 340 and can travel away from the mask 300. However, when the incident beam 410 is reflected at the deeper effective reflection plane 432, the reflected beam 422 is hindered by the absorber layer 340, and the reflected beam cannot travel away from the mask 300.

[0066] In a typical multilayer stack 320, the relatively high refractive index layer may be formed of a material including silicon (Si), and the relatively low refractive index layer may be formed of a material including molybdenum (Mo). In recent years, it has been proposed that the relatively low refractive index layer may be formed of a material including ruthenium (Ru) instead. A Ru-Si multilayer stack may exhibit an effective reflection plane having a smaller depth than an effective reflection plane of a Mo-Si multilayer stack. For example, in Figure 4, the effective reflection plane 431 may be the effective reflection plane of the Ru-Si multilayer stack 300, and the effective reflection plane 432 may be the effective reflection plane of the Mo-Si multilayer stack. For the Ru-Si multilayer stack 320, the effective reflection plane 431 may be approximately 33 nm below the surface of the multilayer stack 320. For the Mo-Si multilayer stack 320, the effective reflection plane 432 may be approximately 45 nm below the surface of the multilayer stack 320. The shallower effective reflection plane 431 of the Ru-Si multilayer stack 320 means that the error caused by shadowing is less significant. However, the total reflectivity of the Ru-Si multilayer stack 320 may be approximately 5% less than the reflectivity of the Mo-Si multilayer stack 320. Reflectivity is defined as the fraction of energy that is reflected at the interface (Equation (2)). This reduction in reflectivity corresponds to a throughput loss.

[0067]

[0068] R = reflectivity; E i = energy of the incident beam; E r = the energy of the reflected beam

[0069] Throughout the following description, reference is made to values ​​of refractive index (n) and absorption coefficient (k). The method of measuring such values ​​for a given material is not particularly limited. The values ​​of refractive index (n) and absorption coefficient (k) can be determined based on measured values ​​of reflectivity and angle of incidence. Specifically, the values ​​of refractive index (n) and absorption coefficient (k) can be determined by curve fitting to the curve of the measured values ​​of reflectivity and angle of incidence. The measurement of reflectivity and angle can be performed using a substrate coated with the material whose values ​​of refractive index (n) and absorption coefficient (k) are to be determined. The substrate can be a silicon wafer or a mask. The thickness of the material coating can be between 30 nm and 50 nm.

[0070] Alternatively, the values ​​of the refractive index (n) and the absorption coefficient (k) may be determined from measurements made using an interferometer. As an example, the values ​​of the refractive index (n) and the absorption coefficient (k) may be measured using amplitude division transmission interferometry. This may involve determining the phase shift ( ) and visibility (V). Methods for measuring the refractive index (n) and absorption coefficient (k) are given in the following publications:

[0071] 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).

[0072] This method can be used to measure the refractive index (n) and absorption coefficient (k) defined herein. The apparatus used in the method may include: a radiation source; a small diameter aperture for providing spatially coherent radiation; a diffraction grating for effectively generating a multi-order virtual source from a pinhole; a zone plate for imaging the virtual source formed at the diffraction grating to a plane where a mask is located; a mask including two openings that allow the passage of zero-order and first-order spots; and a sensitive CCD camera. In the method, a test material is moved into and out of one of the openings in the mask, and the CCD camera records the resulting interference pattern.

[0073] When a test material is present in one of the plurality of openings, the fringes of the interference pattern are shifted according to the refractive properties of the test material. ) is the difference between the two independently reconstructed phase maps of the interferogram. The refractive index (n) can then be calculated using equation (3), where λ is the wavelength and t is the thickness of the sample.

[0074]

[0075] The relative optical intensity (α) after propagation through the sample is related to the observed visibility (V) of the interference pattern by equation (4).

[0076]

[0077] From the relative optical intensity (α), the absorption coefficient (k) can be calculated using equation (5).

[0078]

[0079] Table 1 gives the refractive index (n) and absorption coefficient (k) of the elements Ru, Mo, niobium (Nb), and a number of alloys containing those three elements for a wavelength of about 13.5 nm.

[0080]

[0081] The reflectivity of the multilayer stack 320 depends on the absorption coefficient of the materials forming the layers 322, 323. The absorption coefficient of Ru (k = 0.0171) is higher than that of 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 ) 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 a larger difference in refractive index (n) between the relatively high refractive index layer 322 and the relatively low refractive index layer 323 results in a wider reflectivity band (a wavelength range in which reflectivity is relatively high) of the multilayer stack 320. A wider reflectivity band results in a lower group delay (τ). The approximate depth (z) of the effective reflection plane eff ) 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 reflection plane.

[0082]

[0083] 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. The refractive index of Ru (n=0.887) is lower than the refractive index of Mo (n=0.9237), which explains why the effective reflection plane 431 of the Ru-Si multilayer stack 320 is not as deep as the effective reflection plane 432 of the Mo-Si multilayer stack 320.

[0084] Figure 5 How the reflectivity of a Mo-Si multilayer stack 320 and a Ru-Si multilayer stack 320 varies with the number of pairs 321 in the multilayer stack 320 is shown. The graph is based on incident radiation having a wavelength of about 13.5 nm and an incident angle of 6°. For both the Mo-Si and Ru-Si multilayer stacks 320, although the number of pairs 321 in the multilayer stack 320 is relatively low, the reflectivity increases rapidly as the number of pairs 321 in the multilayer stack 320 increases. As the number of pairs 321 in the multilayer stack 320 increases, the rate of change of the reflectivity relative to the increase in the number of pairs 321 decreases, and the reflectivity tends to a stable value. For the Ru-Si multilayer stack 320, the reflectivity value (about 0.75) in the case of a larger number of pairs is lower than the reflectivity value (about 0.71) of the Mo-Si multilayer stack 320 in the case of a larger number of pairs. The Ru—Si multilayer stack 320 reaches approximately a stable reflectivity value with a smaller number of pairs (approximately 30) than the Mo—Si multilayer stack 320 (approximately 40).

[0085] The present disclosure relates to a material that, when used in the relatively low refractive index layer 323, can provide a multilayer stack 320 that combines the favorable reflective properties exhibited by the Mo-Si multilayer stack 320 with the favorable effective reflection plane properties exhibited by the Ru-Si multilayer stack 320. Specifically, the material is an alloy including at least two of Mo, Ru, and niobium (Nb). As shown in Table 1, Nb has a higher refractive index (n=0.9337) than both Mo and Ru and a lower absorption coefficient (n=0.9337) than both Mo and Ru. Therefore, the Nb-Si multilayer stack can have a reflectivity superior to that of the Mo-Si and Ru-Si multilayer stacks 320, but has a deeper effective reflection plane (z eff ). For light having a wavelength of about 13.5 nm, the alloy is constituted such that the refractive index is less than or equal to 0.92 and the absorption coefficient is less than or equal to 0.015. For light having a wavelength of about 13.5 nanometers, the alloy may preferably exhibit a refractive index of less than 0.91 and further preferably less than 0.9. For light having a wavelength of about 13.5 nm, the alloy may have an absorption coefficient (k) preferably less than 0.014, preferably less than 0.013 and further preferably less than 0.012.

[0086] 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 have a significant effect on 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% and further preferably less than 0.1%. That is, the alloy is substantially composed of at least two of Ru, Nb and Mo.

[0087] The alloy may include Nb. The amount of Nb contained in the alloy may be such that it cannot be 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%, and further preferably greater than 60%. The mass percentage of Nb in the alloy may be less than 70%, preferably less than 50%, and further preferably less than 45%.

[0088] The alloy may include Ru. The amount of Ru contained in the alloy may be such that it cannot be 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%, further preferably greater than 35%, and further preferably greater than 55%. The mass percentage of Ru in the alloy may be less than 85%, preferably less than 75%, and further preferably less than 70%.

[0089] The alloy may include Mo. The amount of Mo contained in the alloy may be such that it cannot be considered as a trace element. The mass percentage of Mo in the alloy may be greater than or equal to 0%, preferably greater than 10% and further 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 further preferably less than 25%.

[0090] The properties of refractive index (n) and absorption coefficient (k) can be approximated by a weighted average of the refractive index and absorption coefficient of the components of the alloy. Therefore, an expression can be formed that approximately relates the composition of the alloy to the values ​​of the refractive index (n) and absorption coefficient (k). To facilitate this, the formula for the alloy is given below:

[0091]

[0092] The subscript numbers in these alloys are intended to indicate the molar ratio of each element in the alloy. The numbers do not indicate that the alloy is formed of a specific lattice structure in which the various components are held in a regular array so that the ratio, i.e., the molar ratio, is a fixed integer. Because the alloy may include impurities, the general formula of the alloy may be:

[0093]

[0094] Wherein I represents the impurities in the alloy. I can represent a single impurity or multiple impurities.

[0095] The weighted average expression of the refractive index (n) and absorption coefficient (k) of the alloy is as follows, where n Ru 、n Nb 、n Mo , k Ru , k Nb and n Mo The values ​​of are given in Table 1.

[0096]

[0097]

[0098] It should be noted that the weighted average method only provides approximate values. In reality, alloys may exhibit values ​​of refractive index (n) and absorption coefficient (k) that are less than (i.e., better than) what would be expected from the weighted average calculation. For example, for the example alloy RuNb2, the approximate refractive index (n) and absorption coefficient (k) from the weighted average of those values ​​for the components are 0.903 and 0.131, respectively, but the actual refractive index (n) and absorption coefficient (k) are 0.898 and 0.0109, respectively.

[0099] The weighted average expression can be used to obtain the value for obtaining a predetermined refractive index (n max ) or a predetermined absorption coefficient (k max ) An estimate of the conditions of the required alloy composition.

[0100]

[0101]

[0102] The predetermined refractive index (n max ) may be 0.92, preferably 0.91 and further preferably less than 0.9. The predetermined absorption coefficient (k max ) may be 0.015, preferably less than 0.014, further preferably less than 0.013, and further preferably less than 0.012. In an exemplary alloy, the mass percentage of Ru may be greater than 50%, preferably greater than 55%, further preferably greater than 59%, less than 70%, preferably less than 65%, and further preferably less than 61%; the mass percentage of Mo may be greater than 10%, preferably greater than 15%, preferably greater than 19%, less than 30%, preferably less than 25%, and further preferably less than 21%; and the mass percentage of Nb may be greater than 10%, preferably greater than 15%, further preferably greater than 19%, less than 30%, preferably less than 25%, and further preferably less than 21%. For example, the alloy may be Ru6Mo2Nb2.

[0103] In another example alloy, the mass percentage of Ru may be greater than 30%, preferably greater than 30%, further preferably greater than 39%, less than 50%, preferably less than 45%, and further preferably less than 41%; the mass percentage of Mo may be greater than 10%, preferably greater than 15%, further preferably greater than 19%, less than 30%, preferably less than 25%, and further preferably less than 21%; and the mass percentage of Nb may be greater than 30%, preferably greater than 35%, further preferably greater than 31%, less than 50%, preferably less than 45%, and further preferably less than 41%. For example, the alloy may be Ru4Mo2Nb4. These alloys are provided only as examples of alloys that may meet the requirements of the present invention.

[0104] The alloy may include Ru and Nb, but not Mo. That is, the alloy may consist of Ru, Nb and common impurities. The mass percentage of Ru may be greater than 20%, preferably greater than 30%, further preferably greater than 32%, less than 40%, preferably less than 35%, and preferably less than 34%; and the mass percentage of Nb may be greater than 50%, preferably greater than 60%, further preferably greater than 66%, less than 80%, preferably less than 70%, and further preferably less than 67%. For example, the alloy may be RuNb2.

[0105] The alloy may include Ru and Mo, but not Nb. That is, the alloy may be composed of Ru, Nb and common impurities. In an example, the mass percentage of Ru may be greater than 20%, preferably greater than 30%, further preferably greater than 32%, less than 50%, preferably less than 40%, and further preferably less than 35%; and the mass percentage of Mo may be greater than 50%, preferably greater than 60%, further preferably greater than 65%, less than 80%, preferably less than 70%, and further 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%, further preferably greater than 45%, less than 70%, preferably less than 60%, and further preferably less than 55%; and the mass percentage of Mo may be greater than 30%, preferably greater than 40%, further preferably greater than 45%, less than 70%, preferably less than 60%, and further preferably less than 55%. For example, the alloy may be RuMo.

[0106] The values ​​of refractive index (n) and absorption coefficient (k) are plotted on Figure 6 , where the absorption coefficient (k) is on the vertical axis and the refractive index (n) is on the horizontal axis, and the values ​​are for a wavelength of about 13.5 nm. Figure 6 The values ​​of the refractive index (n) and the absorption coefficient (k) of the elements Mo, Ru and Nb are also shown on the graph in . 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 is implemented as the relatively low refractive index layer 323 in the multilayer stack 320, the multilayer stack 320 will exhibit a reflectivity superior to that of the Ru-Si multilayer stack 320 and an effective reflection plane shallower than that of the Mo-Si multilayer stack. In addition, the values ​​of the refractive index (n) and the absorption coefficient vary depending on the composition of the alloy. Therefore, by customizing the composition of the alloy including Mo, Ru and Nb used in the relatively low refractive index layer 323, the multilayer stack 320, the properties of the multilayer stack 320 can be optimized for contextual requirements.

[0107] Figure 7 A graph plotting reflectivity on the vertical axis and the number of multilayer pairs on the horizontal axis. The graph is based on incident radiation having a wavelength of approximately 13.5 nm and an angle of incidence of 6°. Figure 5 In FIG. 1 , the values ​​of the Mo-Si multilayer stack 320 and the Ru-Si multilayer stack 320 are plotted, but Figure 7 The values ​​of the RuNb2-Si multilayer stack 320 and the Ru4Mo2Nb4-Si320 multilayer stack 320 are also included. The performance of the RuNb2-Si multilayer stack 320 is superior to the performance 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). In addition, although the number of pairs is relatively low (15 to 25), the rate of increase in the reflectivity of the RuNb2-Si multilayer stack as the number of pairs 321 increases is higher than the rate of increase of the Mo-Si multilayer stack 320. This means that the RuNb2-Si multilayer stack 320 approximately reaches a steady-state value of reflectivity with a smaller number of pairs 321 than the Mo-Si multilayer stack 320. Therefore, the reflectivity of the RuNb2-Si multilayer stack with 40 pairs is higher than the reflectivity of the Mo-Si multilayer stack with 40 pairs. To exhibit the same reflectivity as the Mo—Si multilayer stack having 40 pairs, the RuNb 2 multilayer stack 320 requires fewer pairs (approximately 30 to 34).

[0108] Figure 8 A graph depicting reflectivity on the vertical axis and wavelength in nm on the horizontal axis. The graph is based on a multilayer stack 320 having 40 to 431 and radiation at an incident angle of 6°. Wavelength is the wavelength of incident radiation of the multilayer stack 320. The graph includes Mo-Si multilayer stack 320, Ru-Si multilayer stack 320, RuNb2-Si multilayer stack 320, and Ru4Mo2Nb4-Si multilayer stack 320. For all curves, the reflectivity valve reaches a peak at a wavelength of approximately 13.5 nm. As would be expected from the aforementioned graphs, the peak reflectivity of the RuNb2-Si multilayer stack 320 is the highest, and its value is slightly greater than the peak reflectivity 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 widest reflectivity band, and the Mo-Si multilayer stack 320 has the narrowest reflectivity band. The reflectivity band of the RuNb2-Si multilayer stack 320 is wider than that of the Mo-Si multilayer stack 320, so the depth of the effective reflection plane of the RuNb2-Si multilayer stack 320 will be smaller than the depth of the effective reflection plane of the Mo-Si multilayer stack 320.

[0109] Thus, in addition to 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 to the Ru-Si multilayer stack, it is apparent that the RuNb2-Si multilayer stack 320 exhibits a much higher reflectivity, and that it does so without causing a significant increase in the depth of the effective reflection plane (compared to, for example, if the reflectivity were to be increased by using a Mo-Si multilayer stack instead). Similar observations can be made for the Ru4Mo2Nb4-Si multilayer stack 320. The observations will also apply to other alloys including at least two of Mo, Ru, and Nb and having a refractive index less than or equal to 0.92 and an absorption coefficient less than or equal to 0.015.

[0110] Fig. 9 A graph depicting reflectivity on the vertical axis and angle of incidence in degrees on the horizontal axis. The graph is based on a multilayer stack 320 having 40 pairs and radiation having a wavelength of approximately 13.5 nm. Mo-Si multilayer stacks 320, Ru-Si multilayer stacks 320, RuNb2-Si multilayer stacks 320, and Ru4Mo2Nb4-Si multilayer stacks 320 are shown in the graph. Typically, below 9 degrees, the reflectivity does not change significantly with increasing angle of incidence. In fact, the reflectivity actually increases slightly from an angle of incidence of 0 degrees to an angle of incidence of about 7.5 degrees. When the angle of incidence exceeds 9 degrees, the reflectivity decreases rapidly. As expected, the reflectivity of the Ru-Si multilayer stack 320 across the entire range of angles of incidence is much lower than that of the Mo-Si multilayer stack 320. The RuNb2-Si multilayer stack 320 has excellent performance, exhibiting a higher reflectivity over the entire range of angles of incidence.

[0111] In view of the above, the reflective member according to the present invention may preferably include less than or equal to 40 pairs 321, further preferably less than 35 pairs 321, and further preferably less than 35 pairs 321 in the multilayer stack 320. The number of pairs 321 in the multilayer stack 320 may preferably be greater than 20. In addition, the effective reflection plane of the reflective member according to the present invention may be less than 45 nm below the uppermost surface of the multilayer stack 320, preferably less than 40 nm below the uppermost surface of the multilayer stack 320, and further preferably less than 35 nm below the surface of the multilayer stack. The reflectivity of the reflective member (for radiation with a wavelength of 13.5 nm and an incident angle of 6°) may preferably be greater than 0.73, further preferably greater than 0.74, and further preferably greater than 0.75.

[0112] 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 component. For example, the reflective component can be used in other components located within the lithographic apparatus, such as EUV scanner mirrors.

[0113] When a cap layer 330 is present on the upper surface of the multilayer stack 320, the cap layer 320 can 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 when the relatively low refractive index layer 323 itself is not composed of the alloy. That is, when the relatively low refractive index layer 323 is formed of another material such as molybdenum, the cap layer 330 can be formed of the alloy disclosed in the present application.

[0114] Although specific reference may be made herein to the use of lithographic apparatus in IC manufacturing, it should be understood that the lithographic apparatus described herein may have other applications. Possible other 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, etc.

[0115] Where context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented by instructions stored on a machine-readable medium, which may 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 that can be read by a machine (e.g., a computing device). For example, a machine-readable medium may include a read-only memory (ROM); a random access memory (RAM); a magnetic storage medium; an optical storage medium; a flash memory device; an electrical, optical, acoustic, or other form of propagation signal (e.g., a carrier wave, an infrared signal, a digital signal, etc.); etc. In addition, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are for convenience only, and such actions actually result from a computing device, processor, controller, or other device that executes firmware, software, routines, instructions, etc. and that, when performing such operations, may cause an actuator or other device to interact with the physical world.

[0116] Although specific reference may be made herein to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or another substrate) or a mask (or another patterning device). These apparatuses may generally be referred to as lithographic tools.

[0117] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention is not limited to optical lithography where the context permits.

[0118] Although specific embodiments of the present invention have been described above, it will be appreciated that the present invention may be practiced in other ways than those described. The above description is intended to be illustrative rather than restrictive. Therefore, it will be appreciated by those skilled in the art that modifications may be made to the present invention as described without departing from the scope of the claims and aspects set forth below.

[0119] 1. A reflective member for use in an EUV lithography apparatus, the reflective member comprising a multilayer stack, the multilayer stack comprising a plurality of layers arranged in a plurality of pairs, wherein:

[0120] Each pair includes a first layer and a second layer;

[0121] The first layer is formed of a material including Si; and

[0122] The second layer is formed of a material including at least two of Ru, Nb, and Mo, and wherein the second layer is configured to have a refractive index less than or equal to 0.92 and an absorption coefficient less than or equal to 0.015 with respect to light having a wavelength of approximately 13.5 nm.

[0123] 2. The reflective member according to aspect 1, wherein the material of the second layer is configured to have a refractive index of less than 0.91 and preferably less than 0.9 for light having a wavelength of about 13.5 nm.

[0124] 3. The reflective member according to aspect 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 and further preferably less than 0.012 for light having a wavelength of about 13.5 nm.

[0125] 4. The reflective member according to any one of the preceding aspects, wherein the material of the second layer comprises Nb.

[0126] 5. The reflective member according to any one of the preceding aspects, wherein the material of the second layer includes Ru.

[0127] 6. The reflective member according to any one of the preceding aspects, wherein the material of the second layer comprises Mo.

[0128] 7. The reflective member according to any one of the preceding aspects, wherein the material of the second layer consists of at least two of Ru, Nb, Mo and common impurities.

[0129] 8. The reflective member according to any one of the preceding aspects, 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% and further preferably greater than 60%.

[0130] 9. The reflective member according to any one of the preceding aspects, wherein the mass percentage of Ru in the material of the second layer is greater than 30%, preferably greater than 35% and further preferably greater than 55%.

[0131] 10. The reflective member according to any one of the preceding aspects, wherein the mass percentage of Mo in the material of the second layer is greater than or equal to 0%, preferably greater than 10% and further preferably greater than 5%.

[0132] 11. The reflective member according to any one of the preceding aspects, wherein the mass percentage of Nb in the material of the second layer is less than 70%, preferably less than 50% and further preferably less than 45%.

[0133] 12. The reflective member according to any one of the preceding aspects, wherein the mass percentage of Ru in the material of the second layer is less than 85%, preferably less than 75% and further preferably less than 70%.

[0134] 13. The reflective member according to any one of the preceding aspects, wherein the mass percentage of Mo in the material of the second layer is less than 70%, preferably less than 50% and further preferably less than 25%.

[0135] 14. A reflective member according to any one of the preceding aspects, wherein the material of the second layer has the form Ru x Nb y Mo z Imp a , and where:

[0136] Imp represents at least one impurity;

[0137] x+y+z+a=1; and

[0138] 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 further preferably less than 0.9.

[0139] 15. A reflective member according to any one of the preceding aspects, wherein the material of the second layer has the form Ru x Nb y Mo z Impa , and where:

[0140] Imp represents at least one impurity;

[0141] x+y+z+a=1; and

[0142] The composition of the material is such that 0.0171x+0.0052y+0.0064z is less than 0.015, preferably less than 0.014, further preferably less than 0.013 and further preferably less than 0.012.

[0143] 16. A reflective component according to any one of aspects 1 to 7, wherein the mass percentage of Ru is greater than 20%, preferably greater than 30%, further preferably greater than 32%, less than 40%, preferably less than 35% and preferably less than 34%, and the mass percentage of Nb is greater than 50%, preferably greater than 60% and further preferably greater than 66%, less than 80%, preferably less than 70% and further preferably less than 67%.

[0144] 17. A reflective component according to any one of aspects 1 to 7, wherein: the mass percentage of Ru is greater than 50%, preferably greater than 55%, further preferably greater than 59%, less than 70%, preferably less than 65% and further preferably less than 61%; the mass percentage of Mo is greater than 10%, preferably greater than 15%, further preferably greater than 19%, less than 30%, preferably less than 25% and further preferably less than 21%; and the mass percentage of Nb is greater than 10%, preferably greater than 15%, further preferably greater than 19%, less than 30%, preferably less than 25% and further preferably less than 21%.

[0145] 18. A reflective component according to any one of aspects 1 to 7, wherein: the mass percentage of Ru is greater than 30%, preferably greater than 35%, further preferably greater than 39%, less than 50%, preferably less than 45% and further preferably less than 41%; the mass percentage of Mo is greater than 10%, preferably greater than 15%, further preferably greater than 19%, less than 30%, preferably less than 25% and further preferably less than 21%; and the mass percentage of Nb is greater than 30%, preferably greater than 35%, further preferably greater than 39%, less than 50%, preferably less than 45% and further preferably less than 41%.

[0146] 19. A reflective component according to any one of the preceding aspects, wherein the reflective component has an effective reflection plane, the distance of the effective reflection plane below the uppermost surface of the multilayer stack is less than 45 nm, the distance below the uppermost surface of the multilayer stack is preferably less than 40 nm, and the distance below the uppermost surface of the multilayer stack is further preferably less than 35 nm.

[0147] 20. The reflective member according to any of the preceding aspects, wherein the reflective member is configured for use as an EUV scanner mirror.

[0148] 21. A reflective component according to any one of aspects 1 to 19, wherein the reflective component is configured to be used as an EUV mask, and the reflective component also includes a substrate and a cover layer, the multilayer stack is formed on the substrate, and the cover layer is positioned on the uppermost surface of the multilayer stack.

[0149] 22. The reflective member according to aspect 21, wherein the cover layer is formed of the same material as each second layer.

[0150] 23. The reflective member of aspect 21 or 22, wherein the reflective member further comprises an absorber layer positioned on an uppermost surface of the cover layer.

[0151] 24. A lithographic apparatus comprising a reflective member according to any one of the preceding aspects.

[0152] 25. A method of manufacturing a device, comprising using the reflective member according to any one of aspects 1 to 23.

[0153] 26. An EUV mask, comprising:

[0154] substrate;

[0155] a multilayer stack comprising a plurality of layers arranged in a plurality of pairs; and

[0156] A cap layer is formed of a material including at least two of Ru, Nb, and Mo, and wherein the cap 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.

[0157] 27. The EUV mask of clause 26, wherein the material of the cap layer is configured to have a refractive index of less than 0.91 and preferably less than 0.9 for light having a wavelength of about 13.5 nm.

[0158] 28. The EUV mask according to clause 26 or 27, wherein the material of the cap layer is configured to have an absorption coefficient of less than 0.014, preferably less than 0.013 and further preferably less than 0.012 for light having a wavelength of about 13.5 nm.

[0159] 29. The EUV mask according to clauses 26 to 28, wherein the material of the cap layer comprises Nb.

[0160] 30. The EUV mask according to any one of clauses 26 to 29, wherein the material of the cap layer comprises Ru.

[0161] 31. The EUV mask according to any one of clauses 26 to 30, wherein the material of the cap layer comprises Mo.

[0162] 32. The EUV mask according to any one of clauses 26 to 31, wherein the material of the cap layer consists of at least two of Ru, Nb, Mo and common impurities.

[0163] 33. The EUV mask according to any one of clauses 26 to 32, wherein the mass percentage of Nb in the material of the cap layer is greater than 5%, preferably greater than 20%, preferably greater than 40% and further preferably greater than 60%.

[0164] 34. The EUV mask according to any one of clauses 26 to 33, wherein the mass percentage of Ru in the material of the cap layer is greater than 30%, preferably greater than 35% and further preferably greater than 55%.

[0165] 35. The EUV mask according to any one of clauses 26 to 34, wherein the mass percentage of Mo in the material of the cap layer is greater than or equal to 0%, preferably greater than 5% and further preferably greater than 10%.

[0166] 36. The EUV mask according to any one of clauses 26 to 35, wherein the mass percentage of Nb in the material of the cap layer is less than 70%, preferably less than 50% and further preferably less than 45%.

[0167] 37. The EUV mask according to any one of clauses 26 to 36, wherein the mass percentage of Ru in the material of the cap layer is less than 85%, preferably less than 75% and further preferably less than 70%.

[0168] 38. The EUV mask according to any one of clauses 26 to 37, wherein the mass percentage of Mo in the material of the cap layer is less than 70%, preferably less than 50% and further preferably less than 25%.

[0169] 39. An EUV mask according to any one of clauses 26 to 38, wherein the material of the second layer has the form Ru x Nb y Mo z I a , wherein 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 further preferably less than 0.9.

[0170] 40. The EUV mask according to any one of clauses 26 to 39, wherein the material of the cap layer has the form Ru x Nb y Mo z I a , wherein 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, further preferably less than 0.013 and further preferably less than 0.012.

[0171] 41. An EUV mask according to any one of aspects 26 to 32, wherein the mass percentage of Ru is greater than 20%, preferably greater than 30%, further preferably greater than 32%, less than 40%, preferably less than 35% and preferably less than 34%, and the mass percentage of Nb is greater than 50%, preferably greater than 60% and further preferably greater than 66% and less than 80%, preferably less than 70% and further preferably less than 67%.

[0172] 42. An EUV mask according to any one of aspects 26 to 32, wherein: the mass percentage of Ru is greater than 50%, preferably greater than 55%, further preferably greater than 59%, less than 70%, preferably less than 65% and further preferably less than 61%; the mass percentage of Mo is greater than 10%, preferably greater than 15%, further preferably greater than 19%, less than 30%, preferably less than 25% and further preferably less than 21%; and the mass percentage of Nb is greater than 10%, preferably greater than 15%, further preferably greater than 19%, less than 30%, preferably less than 25% and further preferably less than 21%.

[0173] 43. An EUV mask according to any one of aspects 26 to 32, wherein: the mass percentage of Ru is greater than 30%, preferably greater than 35%, further preferably greater than 39%, less than 50%, preferably less than 45% and further preferably less than 41%; the mass percentage of Mo is greater than 10%, preferably greater than 15%, further preferably greater than 19%, less than 30%, preferably less than 25% and further preferably less than 21%; and the mass percentage of Nb is greater than 30%, preferably greater than 35%, further preferably greater than 39%, less than 50%, preferably less than 45% and further preferably less than 41%.

[0174] 44. A lithographic apparatus comprising an EUV mask according to any one of clauses 26 to 43.

[0175] 45. A method of manufacturing a device comprising using the EUV mask 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, the multilayer stack comprising a plurality of layers arranged in a plurality of pairs, wherein: Each pair includes a first layer and a second layer; The first layer is formed of a material including Si; and The second layer is formed of a material including at least two of Ru, Nb, and Mo, and wherein the second layer is configured to have a refractive index less than or equal to 0.92 and an absorption coefficient less than or equal to 0.015 with respect to light having a wavelength of approximately 13.5 nm.

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 and preferably less than 0.9 for light having a wavelength of about 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 and further preferably less than 0.012 for light having a wavelength of about 13.5 nm.

4. A reflective member according to any one of the preceding claims, wherein: The material of the second layer includes Nb, Ru and / or Mo.

5. A reflective member according to any one of the preceding claims, wherein: The material of the second layer consists of at least two of Ru, Nb, Mo and common impurities.

6. A reflective member according to any one of the preceding claims, 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% and further preferably greater than 60%.

7. A reflective member according to any one of the preceding claims, wherein: The mass percentage of Ru in the material of the second layer is greater than 30%, preferably greater than 35% and further preferably greater than 55%.

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

9. A reflective member according to any one of the preceding claims, wherein: The mass percentage of Nb in the material of the second layer is less than 70%, preferably less than 50% and further preferably less than 45%.

10. A reflective member according to any one of the preceding claims, wherein: The mass percentage of Ru in the material of the second layer is less than 85%, preferably less than 75% and further preferably less than 70%.

11. A reflective member according to any one of the preceding claims, wherein The mass percentage of Mo in the material of the second layer is less than 70%, preferably less than 50% and further preferably less than 25%.

12. A reflective member according to any one of the preceding claims, wherein: The material of the second layer has the form Ru x Nb y Mo z Imp a , and where: Imp represents at least one impurity; x+y+z+a=1; 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 further preferably less than 0.

9.

13. A reflective member according to any one of the preceding claims, wherein: The material of the second layer has the form Ru x Nb y Mo z Imp a , and where: Imp represents at least one impurity; x+y+z+a=1; 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, further preferably less than 0.013 and further preferably less than 0.

012.

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

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

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

17. A reflective member according to any one of the preceding claims, wherein: The reflective member has an effective reflection plane which is less than 45 nm below the uppermost surface of the multilayer stack, preferably less than 40 nm below the uppermost surface of the multilayer stack and further preferably less than 35 nm below the uppermost surface of the multilayer stack.

18. A reflective member according to any one of the preceding claims, wherein: The reflective member is configured for use as an EUV scanner mirror.

19. The reflective member according to any one of claims 1 to 17, wherein: The reflective member is configured for use as an EUV mask and further includes a substrate on which the multilayer stack is formed and a cap layer positioned on an uppermost surface of the multilayer stack.

20. An EUV mask, comprising: substrate; a multilayer stack comprising a plurality of layers arranged in a plurality of pairs; as well as A cap layer is formed of a material including at least two of Ru, Nb, and Mo, and wherein the cap 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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