WO2024179767A1

WO2024179767A1 - Membrane for euv lithography

Info

Publication number: WO2024179767A1
Application number: PCT/EP2024/052516
Authority: WO
Inventors: Zomer Silvester HOUWELING; Mahnaz GHIASI KABIRI; Adrianus Johannes Maria GIESBERS; Lambertus Idris Johannes Catharina BERGERS
Original assignee: ASML Netherlands BV
Current assignee: ASML Netherlands BV
Priority date: 2023-03-02
Filing date: 2024-02-01
Publication date: 2024-09-06
Anticipated expiration: 2025-09-02
Also published as: CN120712518A; TW202439007A

Abstract

A membrane configured to transmit extreme ultraviolet radiation comprising a nanostructure configured to absorb deep ultraviolet radiation, and a method for forming the membrane. The membrane may form part of EUV lithographic apparatus, e.g. as part of a spectral purity filter, a pellicle assembly or a dynamic gas lock assembly.

Description

MEMBRANE FOR EUV LITHOGRAPHY

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 23159614.9 which was filed on 2 March 2023, and which is incorporated herein in its entirety by reference.

FIELD

[0002] The present invention relates to a membrane, a patterning device assembly and a dynamic gas lock assembly for EUV lithography.

BACKGROUND

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

[0004] To project a pattern on a substrate a lithographic apparatus uses electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation having a greater wavelength such as, for example, 193 nm.

[0005] The radiation used by the lithographic apparatus may comprise unwanted wavelengths of radiation such as, for example, deep ultraviolet (DUV) radiation and/or infrared radiation. The unwanted wavelengths of radiation may contribute to lithographic errors.

[0006] It is desirable to reduce the presence of the unwanted wavelengths of radiation whilst maintaining or increasing transmission of the EUV radiation.

SUMMARY

[0007] According to a first aspect of the present disclosure, there is provided a membrane configured to transmit extreme ultraviolet radiation comprising a nanostructure configured to absorb deep ultraviolet radiation.

[0008] Extreme ultraviolet (EUV) radiation may comprise radiation having a wavelength of about 4 nm or more. Extreme ultraviolet radiation may comprise radiation having a wavelength of about 20 nm or less.

[0009] The membrane of the present disclosure has been found to have increased EUV radiation transmissivity compared to known membranes. The membrane may be configured to have an EUV transmissivity of about 90% or more. The membrane may be configured to have an EUV transmissivity of about 95% or more.

[00010] Deep ultraviolet radiation may comprise radiation having a wavelength of about 100 nm or more. Deep ultraviolet radiation may comprise radiation having a wavelength of about 400 nm or less. [00011] The membrane may be configured to have a DUV absorptivity of about 80% or less. The membrane may be configured to have a DUV absorptivity of about 30% or more. The membrane may be configured to have a DUV absorptivity of about 40% or more. The membrane may be configured to have a DUV absorptivity of about 50% or more. The membrane may be configured to have a DUV absorptivity of about 60% or more. The membrane may be configured to have a DUV absorptivity of about 70% or more.

[00012] The nanostructure may comprise constituent elements (e.g. nanoparticles) having a size of about 1 nm or more. The nanostructure may comprise constituent elements having a size of about 100 nm or less. The nanostructure may comprise constituent elements having a size of about 50 nm or less. The nanostructure may comprise constituent elements having a size of about 25 nm or less. The nanostructure may comprise constituent elements having a size of about 10 nm or less. The nanostructure may comprise constituent elements having a size of about 7 nm or less. The nanostructure may comprise constituent elements having a size of about 5 nm or less.

[00013] The nanostructure may utilize one or more nanoscale absorption mechanisms such as, for example, quantum confinement of radiation, plasmon excitations and/or the formation of plasmon polaritons, metal-ligand charge transfer effects, etc. to advantageously achieve equivalent or increased DUV radiation and/or infrared radiation absorption at smaller membrane thicknesses compared to known membranes. In this way, the nanostructure is advantageously able to filter out an equivalent or improved amount DUV radiation and/or infrared radiation whilst the membrane is thin enough to maintain or increase EUV transmission compared to known membranes. For example, the membrane of the present disclosure may be about half, or less than half, the thickness of known membranes, thereby improving EUV radiation transmission, whilst providing an equivalent or increased amount of DUV radiation and/or infrared radiation absorption.

[00014] Known membranes are complex multilayered structures that are synthesized in a multi-step manufacturing process. The membrane of the present disclosure provides equivalent or improved performance using a simpler structure and manufacturing process compared to known membranes.

[00015] The nanostructure may comprise semiconductor nanoparticles.

[00016] Semiconductor nanoparticles have been found to provide advantageous characteristics to the membrane such as increased EUV radiation transmission, increased DUV radiation and/or infrared radiation absorption, increased emissivity for improved temperature regulation, adequate mechanical strength at reduced membrane thicknesses, adequate tension to reduce risk of the membrane sagging or snapping, etc., compared to known membranes.

[00017] The semiconductor nanoparticles may comprise silicon crystals. [00018] Silicon crystal nanoparticles have been found to provide advantageous characteristics to the membrane such as increased EUV radiation transmission, increased DUV radiation and/or infrared radiation absorption, increased emissivity for improved temperature regulation, adequate mechanical strength at reduced membrane thicknesses, adequate tension to reduce risk of the membrane sagging or snapping, etc., compared to known membranes.

[00019] A size of the silicon crystals may be about 7 nm or less. A size of the silicon crystals may be about 5 nm or less.

[00020] The term “size” of the silicon crystals may refer to an average crystal diameter when the crystals are spherical, and may refer to a length of the major axis when the crystals are non-spherical.

[00021] Silicon crystals of about 7 nm or less have been found to provide advantageous characteristics to the membrane such as increased EUV radiation transmission, increased DUV radiation and/or infrared radiation absorption, increased emissivity for improved temperature regulation, adequate mechanical strength at reduced membrane thicknesses, adequate tension to reduce risk of the membrane sagging or snapping, etc., compared to known membranes.

[00022] The semiconductor nanoparticles may comprise quantum dots.

[00023] An average quantum dot size may be smaller than the Bohr exciton (i.e. a quasiparticle corresponding to a bound state of an electron-hole pair) radius.

[00024] The term “size” of the quantum dots may refer to an average particle diameter when the quantum dots are spherical, and may refer to a length of the major axis when the quantum dots are non- spherical.

[00025] The quantum dots advantageously provide enhanced and tunable optical performance as a result of quantum confinement of electromagnetic radiation. The nanostructure of the membrane comprising quantum dots is engineered such that the size of the semiconductor nanoparticles are smaller than the Bohr exciton radius, resulting in quantum confinement of the wave functions of its electrons causing the electronic structure to become size-dependent, and with that, its electronic and optical properties. That is, the quantum dots may be sized such that they reside in the strong quantum confinement regime rather than the intermediate or weak quantum confinement regime.

[00026] The quantum dots are configured to absorb DUV radiation. Discrete electron energy levels present in the quantum dots may be suited to absorption of DUV radiation by selecting a size and/or shape of the quantum dots.

[00027] The quantum dots may have sizes of about 5 nm or more. The quantum dots may have sizes of about 7 nm or less. These sizes have been found to be particularly effective in absorbing DUV radiation.

[00028] The quantum dots may comprise crystals of a rounded morphology, e.g. spherical or at least partially spherical.

[00029] The quantum dots may form a well-defined crystal lattice. [00030] Depending on the materials used to form the quantum dots in the membrane, the quantum dots may be made of a wide variety of materials, each having their own application.

[00031] The quantum dots may comprise silicon quantum dots.

[00032] Silicon quantum dots have been found to be particularly effective in absorbing DUV radiation whilst maintaining or improving an EUV radiation transmissivity of the membrane compared to known membranes.

[00033] The silicon quantum dots may have sizes of about 5 nm or more. The silicon quantum dots may have sizes of about 7 nm or less. These sizes have been found to be particularly effective in absorbing DUV radiation and/or providing improved emissivity.

[00034] The silicon may be doped. Doping the silicon may improve an emissivity of the silicon. Possible dopants include, for example, Phosphorus, Boron, Arsenic, Gallium, Aluminum, Indium, Antimony, Bismuth and Germanium.

[00035] The nanostructure may comprise metallic nanoparticles.

[00036] For metallic nanoparticles, the collective interaction of their electrons with an external electromagnetic field (i.e. incident radiation) can cause localized surface plasmon polaritons, which are collective charge oscillations. The consequences of the plasmon excitation include selective photon absorption, scattering and enhancement of light intensity at a certain resonance wavelength (e.g. enhanced absorption of DUV radiation).

[00037] Metallic nanoparticles have been found to provide advantageous characteristics to the membrane such as increased EUV radiation transmission, increased DUV radiation and/or infrared radiation absorption, increased emissivity for improved temperature regulation, adequate mechanical strength at reduced membrane thicknesses, adequate tension to reduce risk of the membrane sagging or snapping, etc., compared to known membranes.

[00038] The metallic nanoparticles may comprise MoSi2 crystals.

[00039] MoSi2 crystals have been found to provide advantageous characteristics to the membrane such as increased EUV radiation transmission, increased DUV radiation and/or infrared radiation absorption, increased emissivity for improved temperature regulation, adequate mechanical strength at reduced membrane thicknesses, adequate tension to reduce risk of the membrane sagging or snapping, etc., compared to known membranes.

[00040] The metallic nanoparticles may comprise Mo Sh crystals and/or Mo sSi crystals.

[00041] Mo Si s crystals and/or Mo^Si crystals have been found to improve an emissivity of the membrane.

[00042] The metallic nanoparticles may comprise Ga crystals.

[00043] The nanostructure may comprises a matrix of semiconductor nanoparticles and metallic nanoparticles.

[00044] A matrix of semiconductor nanoparticles and metallic nanoparticles has been found to provide advantageous characteristics to the membrane such as increased EUV radiation transmission, increased DUV radiation and/or infrared radiation absorption, increased emissivity for improved temperature regulation, adequate mechanical strength at reduced membrane thicknesses, adequate tension to reduce risk of the membrane sagging or snapping, etc., compared to known membranes.

[00045] The semiconductor nanoparticles may comprise Si crystals. The metallic nanoparticles may comprise MoSi2 crystals. The metallic nanoparticles may comprise Mo Si s crystals. The metallic nanoparticles may comprise Mo (Si crystals.

[00046] A matrix of silicon crystals and molybdenum silicide crystals has been found to provide advantageous characteristics to the membrane such as increased EUV radiation transmission, increased DUV radiation and/or infrared radiation absorption, increased emissivity for improved temperature regulation, adequate mechanical strength at reduced membrane thicknesses, adequate tension to reduce risk of the membrane sagging or snapping, etc., compared to known membranes.

[00047] The membrane may comprise N.

[00048] Introducing N has been found to advantageously improve tension characteristics of the membrane such that the membrane has a lower risk of snapping or sagging compared to known membranes.

[00049] The membrane may comprise less than about 5 atomic% of N.

[00050] The membrane may comprise trace amounts of N (i.e. less than about 5 atomic%). The trace amounts of N may be sandwiched in oxide shells that contain nitrogen. Native oxide shells may grow naturally in the nanostructure. The matrix may be referred to as MoSiSi:N. The MoSiSi:N membrane has been found to have an EUV radiation transmissivity of greater than about 95%. The presence of trace amounts of N in the core of the MoSiSi:N membrane may provide enhanced DUV absorption.

[00051] The membrane may comprise between about 5 atomic% of N and about 20 atomic% of N. [00052] The membrane may comprise non-trace amounts of N (i.e. greater than or equal to about 5 atomic% and less than or equal to about 20 atomic%). The matrix may be referred to as MoSiN. MoSiN may advantageously improve an emissivity of the membrane. This in turn may reduce or remove the need for an emissivity layer (e.g. Ru and/or Mo), thereby improving an EUV radiation transmissivity of the membrane compared to known membranes.

[00053] The membrane may have a thickness of about 8 nm or less.

[00054] The membrane of the present disclosure is much thinner than known membranes, thereby advantageously improving EUV radiation transmission compared to known membranes whilst maintaining or improving other desirable characteristics such as increased DUV radiation and/or infrared radiation absorption, increased emissivity for improved temperature regulation, adequate mechanical strength at reduced membrane thicknesses, adequate tension to reduce risk of the membrane sagging or snapping, etc., compared to known membranes.

[00055] The membrane may comprise a core layer and a capping layer. The nanostructure may be present in the core layer. [00056] The introduction of a capping layer advantageously improves upon mechanical and/or optical characteristics of the membrane and/or protects the core layer of the membrane and/or enables a greater number of functions to be performed by the membrane.

[00057] The core layer may have a thickness of about 5 nm or less.

[00058] Spectroscopy reveals an increase in DUV radiation absorption achieved by the membrane compared to known membranes when the thickness of the core layer reaches very small thicknesses (e.g. 5 nm or less). This may be ascribed to nanoscale absorption mechanisms such as, for example, quantum confinement of radiation, plasmon excitations and/or the formation of plasmon polaritons, metal-ligand charge transfer effects, etc., depending on the constituent elements of the nanostructure.

[00059] The core layer may have a thickness corresponding to the size of a single nanoparticle that forms a constituent element of the nanostructure. That is, the core layer may have a thickness corresponding to a single grain of the nanostructure.

[00060] The capping layer may comprise SiCE and/or ZrCK

[00061] A capping layer comprising SiCE and/or ZrCE advantageously provides protection against contaminants. For example, hydrocarbons and/or metals such as tin may outgas from, for example, the resist on the substrate W. The capping layer protects the core layer from these contaminants.

[00062] The capping layer may comprise Ru and/or Mo.

[00063] A capping layer comprising Ru and/or Mo advantageously improves an emissivity of the membrane. This allows the membrane to absorb more infrared radiation, improving a spectral filter function of the membrane. In general, improving an emissivity of the membrane also improves a temperature regulation of the membrane by allowing absorbed heat to be radiated out from the membrane.

[00064] The addition of one or more capping layers comprising materials such as SiCE and/or ZrCE and/or Ru and/or Mo may decrease an EUV radiation transmissivity of the membrane. However, due to the nanostructure of the core layer, the membrane still achieves equivalent or improved EUV radiation transmissivity compared to known membranes.

[00065] The membrane may comprise a freestanding portion.

[00066] Known membranes rely upon a host material or a substrate for supporting the membrane. The membrane of the present disclosure does not require a host or substrate, thereby advantageously reducing undesired interactions (e.g., EUV radiation absorption) compared to known membranes.

[00067] According to a second aspect of the present disclosure, there is provided a spectral purity filter for EUV lithography comprising the membrane of the first aspect.

[00068] According to a third aspect of the present disclosure, there is provided a patterning device assembly for EUV lithography comprising the membrane of the first aspect.

[00069] The patterning device assembly may comprise a membrane (i.e. a pellicle) according to the first aspect of the present disclosure, a frame for supporting the pellicle and a patterning device attached to the frame. [00070] According to a fourth aspect of the present disclosure, there is provided a dynamic gas lock assembly for EUV lithography comprising the membrane of the first aspect.

[00071] According to a fifth aspect of the present disclosure, there is provided a lithographic system comprising the membrane of the first aspect.

[00072] The lithographic system may comprise a first chamber comprising a projection system. The projection system may be configured to project a patterned radiation beam onto a substrate. The lithographic system may comprise a second chamber comprising a substrate table. The substrate table may be configured to hold the substrate. The lithographic system may comprise a channel extending between the first chamber and the second chamber. The channel may be configured to receive a flow of purging fluid. A perimeter of the channel may be defined by a wall. The wall of the channel may comprise a purging fluid inlet. The channel and the flow of purging fluid may be referred to as a dynamic gas lock assembly.

[00073] According to a sixth aspect of the present disclosure, there is provided a method of forming a membrane configured to transmit extreme ultraviolet radiation comprising forming a nanostructure configured to absorb deep ultraviolet radiation.

[00074] Forming the nanostructure may comprise physical vapor deposition. Physical vapor deposition may comprise sputter deposition.

[00075] Forming the nanostructure may comprise chemical vapor deposition. Chemical vapor deposition may comprise atomic layer deposition.

[00076] Use of deposition processes advantageously avoids the use of more complex and less effective chemical methods involving solvents. The deposition process may be CMOS-compatible.

[00077] Forming the nanostructure may comprise sputter deposition using a sputter target.

[00078] The sputter target may be a MoSiSi sputter target. The sputter target may be a molybdenum silicide sputter target. The sputter target may comprise about 15 atomic% of Mo or more. The sputter target may comprise about 25 atomic% of Mo or less.

[00079] The method may comprise using a first sputter target comprising Si. The method may comprise using a second sputter target comprising MoSi2.

[00080] The method may comprise using a first sputter target comprising a matrix material and a second sputter target comprising an inclusion material. The matrix material may comprise silicon. The matrix material may comprise silicon nitride. The inclusion material may comprise molybdenum silicide. The inclusion material may comprise zirconium silicide. The inclusion material may comprise ruthenium silicide. The inclusion material may comprise tungsten silicide.

[00081] The method may comprise adjusting a power provided to the sputter target to adjust a composition of the membrane.

[00082] The method may comprise providing a power of about 50 W or more to the sputter target. The method may comprise providing a power of about 1000 W or less to the sputter target. The method may comprise providing a power of about 300 W or less to the sputter target. [00083] The method may comprise performing the deposition in the presence of N2. The method may comprise performing the deposition in the presence of a flow of N2 gas.

[00084] Nitriding of the metal silicide or silicon may be effected by sputtering a metal silicide or silicon substrate with a plasma. The sputtering may be reactive sputtering. The plasma may be any suitable plasma. The plasma may comprise nitrogen. The plasma may comprise a mixture of argon and nitrogen gas. The argon gas may be included to provide an inert atmosphere. A ratio of argon to nitrogen may be varied. Having a larger proportion of nitrogen in the gas mixture may result in a greater amount of nitrogen being incorporated into the membrane.

[00085] The sputter target may comprise Mo and Si. The sputter target may comprise a Mo content of about 20 atomic%.

[00086] This Mo content advantageously achieves trace amounts of N in the nanostructure, which has been found to improve DUV absorption.

[00087] The sputter target may comprise Mo and Si. The sputter target may comprise a Mo content of about 22.5 atomic%.

[00088] This Mo content advantageously achieves non-trace amounts of N in the nanostructure, which has been found to improve emissivity and infrared absorption, even at very small thicknesses (e.g. about 5 nm or less). This advantageously reduces or removes the need for an emissivity capping layer (e.g. Ru-Mo), which in turn improves EUV radiation transmissivity and reduces a complexity of the membrane structure.

[00089] It will be appreciated that the features described in respect of any of the aspects may be combined with the features described in respect of any of the other aspects of the present disclosure. All combinations of aspects of the present disclosure may be combined with one another, except where the features of the aspects of the present disclosure are mutually exclusive.

BRIEF DESCRIPTION OF THE DRAWINGS

[00090] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which corresponding reference symbols indicate corresponding parts, and in which:

Fig. 1 schematically depicts a lithographic system comprising a lithographic apparatus, a radiation source and three membranes in accordance with an aspect of the present disclosure.

Fig. 2 schematically depicts a view from the side of a membrane in accordance with the present disclosure.

Fig. 3 shows two scanning transmission electron microscopy images of a membrane formed in accordance with the present disclosure.

Fig. 4 shows the DUV absorption of different membranes having a nanostructure comprising MoSi2 crystals and Si crystals in accordance with the present disclosure. Fig. 5 schematically depicts a view from the side of a first multilayer membrane according to the present disclosure.

Fig. 6 schematically depicts a view from the side of a second multilayer membrane according to the present disclosure.

DETAILED DESCRIPTION

[00091] Fig. 1 shows a lithographic system comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS and a substrate table WT configured to support a substrate W.

[00092] The illumination system IL is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident upon the patterning device MA. Thereto, the illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. The faceted field mirror device 10 and faceted pupil mirror device 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to, or instead of, the faceted field mirror device 10 and faceted pupil mirror device 11.

[00093] After being thus conditioned, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B’ is generated. The projection system PS is configured to project the patterned EUV radiation beam B’ onto the substrate W. For that purpose, the projection system PS may comprise a plurality of mirrors 13,14 which are configured to project the patterned EUV radiation beam B’ onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B’, thus forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is illustrated as having only two mirrors 13, 14 in Figure 1, the projection system PS may include a different number of mirrors (e.g., six or eight mirrors).

[00094] The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus LA aligns the image, formed by the patterned EUV radiation beam B’, with a pattern previously formed on the substrate W.

[00095] A relative vacuum, i.e. a small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL, and/or in the projection system PS.

[00096] The radiation source SO shown in Figure 1 is, for example, of a type which may be referred to as a laser produced plasma (LPP) source. A laser system 1, which may, for example, include a CO2 laser, is arranged to deposit energy via a laser beam 2 into a fuel, such as tin (Sn) which is provided from, e.g., a fuel emitter 3. Although tin is referred to in the following description, any suitable fuel may be used. The fuel may, for example, be in liquid form, and may, for example, be a metal or alloy. The fuel emitter 3 may comprise a nozzle configured to direct tin, e.g. in the form of droplets, along a trajectory towards a plasma formation region 4. The laser beam 2 is incident upon the tin at the plasma formation region 4. The deposition of laser energy into the tin creates a tin plasma 7 at the plasma formation region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during deexcitation and recombination of electrons with ions of the plasma.

[00097] The EUV radiation from the plasma is collected and focused by a collector 5. Collector 5 comprises, for example, a near-normal incidence radiation collector 5 (sometimes referred to more generally as a normal-incidence radiation collector). The collector 5 may have a multilayer mirror structure which is arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may have an ellipsoidal configuration, having two focal points. A first one of the focal points may be at the plasma formation region 4, and a second one of the focal points may be at an intermediate focus 6, as discussed below.

[00098] The laser system 1 may be spatially separated from the radiation source SO. Where this is the case, the laser beam 2 may be passed from the laser system 1 to the radiation source SO with the aid of a beam delivery system (not shown) comprising, for example, suitable directing mirrors and/or a beam expander, and/or other optics. The laser system 1, the radiation source SO and the beam delivery system may together be considered to be a radiation system.

[00099] Radiation that is reflected by the collector 5 forms the EUV radiation beam B. The EUV radiation beam B is focused at intermediate focus 6 to form an image at the intermediate focus 6 of the plasma present at the plasma formation region 4. The image at the intermediate focus 6 acts as a virtual radiation source for the illumination system IL. The radiation source SO is arranged such that the intermediate focus 6 is located at or near to an opening 8 in an enclosing structure 9 of the radiation source SO.

[000100] Although Figure 1 depicts the radiation source SO as a laser produced plasma (LPP) source, any suitable source such as a discharge produced plasma (DPP) source or a free electron laser (FEL) may be used to generate EUV radiation.

[000101] EUV sources, such as those which generate EUV radiation using a plasma, in practice do not only emit desired 'in-band' EUV radiation, but also undesirable (out-of-band) radiation. This out- of- band radiation is most notably in the deep UV (DUV) radiation range (from 100 to 400 nm). Moreover, in the case of some EUV sources, for example laser produced plasma EUV sources, the radiation from the laser, usually at about 10.6 microns, may also form a significant source of undesirable (out-of-band) infrared (IR) radiation.

[000102] In a lithographic apparatus LA, spectral purity is desired for several reasons. One reason is that the substrate W resist is sensitive to out of-band wavelengths of radiation, and thus the image quality of exposure patterns applied to the resist may be deteriorated if the resist is exposed to such out- of-band radiation. Furthermore, out-of-band infrared radiation, for example the 10.6 micron radiation in some laser produced plasma sources, leads to unwanted and unnecessary heating of the patterning device MA, substrate W, and optics 10, 11 , 13, 14 within the lithographic apparatus LA. Such heating may lead to damage of these components, a reduction of their operational lifetime, and/or defects or distortions in patterns projected onto and applied to the resist-coated substrate W.

[000103] In a lithographic apparatus LA (and/or method) it is desirable to reduce the losses in intensity of EUV radiation which is being used to apply a pattern to the resist coated substrate W. One reason for this is that, ideally, as much EUV radiation as possible should be available for applying a pattern to a substrate W, for instance to reduce the exposure time and increase throughput. At the same time, it is desirable to reduce the amount of undesirable radiation (e.g. out-of-band) radiation that is passing through the lithographic apparatus LA and which is incident upon the substrate W.

[000104] A membrane 100, 200, 300 may be provided to reduce the presence of out-of-band radiation (e.g. DUV and/or infrared radiation) whilst maintaining high levels of EUV radiation transmission in the lithographic apparatus LA. The membrane 100, 200, 300 may be referred to in the art as an EUV membrane. The membrane 100, 200, 300 typically comprises a film having a free-standing portion configured to transmit as much EUV radiation as possible to ensure maximum throughput. The membrane 100, 200, 300 may also provide additional functions depending on its location in the lithographic apparatus LA. In the example of Fig. 1, membranes 100, 200, 300 are provided at three locations.

[000105] A first membrane 100 is located in the radiation source SO and forms part of a spectral purity filter. The spectral purity filter may be located in other parts of the lithographic system. The spectral purity filter 100 may be substantially transmissive for EUV radiation but substantially blocking for other wavelengths of radiation such as deep ultraviolet (DUV) radiation and/or infrared radiation. The spectral purity filter may comprise a frame and the membrane 100 may extend across the frame in a free-standing manner.

[000106] A second membrane 200 is located proximate the patterning device MA and forms part of a patterning device assembly which may be referred to as a pellicle. Radiation interacts with the patterning device MA to form an image on a substrate W. Contamination (e.g. particulate contamination) on the surface of the patterning device MA may negatively affect an imaging of the lithographic apparatus LA and cause manufacturing defects on the substrate W. The membrane 200 may be provided to protect the patterning device MA from airborne particles and other forms of contamination. The membrane 200 for protecting the patterning device MA may be referred to as a pellicle or may form part of a pellicle assembly. The pellicle assembly may comprise a frame and the membrane 200 may extend across the frame in a free-standing manner. A pellicle 200 has a set of performance specifications that are achieved by the characteristics of the pellicle’s constituent materials and structure. Relevant performance specifications include that the pellicle 200 does not distort imaging, sufficiently transmits EUV radiation, and does not contaminate critical components in the lithographic apparatus LA. The primary function of the pellicle 200 is to protect the patterning device MA from corpuscular contaminants.

[000107] A third membrane 300 is located between the projection system PS and the substrate W and forms part of a dynamic gas lock assembly. The third membrane 300 may be referred to as a dynamic gas lock membrane. The projection system PS of the lithographic apparatus LA is held in a first chamber 15 and the substrate table WT is held in a second chamber 16. The first chamber 15 and the second chamber 16 are held under vacuum conditions. Contaminants may be generated in the second chamber 16 and diffuse towards the first chamber 15. For example, hydrocarbons and/or metals such as tin may outgas from the resist on the substrate W and travel towards highly sensitive optical components within the projection system PS. Exposing the substrate to EUV radiation may cause an increase in the amount of contaminants generated in the second chamber 16. The contaminants may accumulate on optical components in the projection system PS thereby negatively affecting the performance of the optical components. For example, contaminants may accumulate on a reflective surface of a mirror in the projection system PS and reduce the reflectivity of the mirror. A reduction of the reflectivity of a mirror in the projection system PS may reduce the amount of EUV radiation reaching the substrate W, which may in turn reduce a throughput of the substrate because a longer amount of time is needed for the same EUV dose to be applied to the substrate W. The lithographic system may comprise a dynamic gas lock assembly configured to protect optical components in the first chamber 15 from contaminants generated in the second chamber 16.

[000108] The dynamic gas lock assembly may comprise a channel 17 extending between the first chamber 15 and the second chamber 16. The channel 17 has a perimeter that is defined by a wall 19. The channel 17 may be provided with a flow of purging fluid through a purging fluid inlet (not shown) provided in the wall 19 of the channel 17. The purging fluid may, for example, comprise Hydrogen gas. Other fluids may be used, e.g. Helium, Nitrogen, Argon and/or any mixture thereof. A purging fluid may be selected that has a low diffusion coefficient for contaminants present in the lithographic apparatus (e.g. lower than the diffusion coefficient of Hydrogen gas). The flow of purging fluid that flows through the channel 17 towards the second chamber 16 forms a purging fluid curtain. The purging fluid curtain is configured to reduce the amount of contaminants reaching the second chamber 16 from the first chamber 15, thereby protecting the projection system PS from contamination. The channel 17 and the purging fluid curtain are both configured to allow EUV radiation to pass from the first chamber 15 to the second chamber 16 such that a lithographic exposure may take place. The membrane 300 may stop contaminants from reaching the first chamber 15 via the channel 17 or significantly reduce the amount of contamination reaching the first chamber 15 from the second chamber 16.

[000109] Before the patterned radiation beam B’ leaves the projection system PS and reaches the substrate W to form patterns in the EUV-sensitive resist, the EUV radiation present in the patterned radiation beam B’ may be filtered from the out-of-band radiation present in the patterned radiation beam B’. The out-of-band radiation may comprise DUV radiation (e.g. having a wavelength within the inclusive range of about 100 nm to about 400 nm). The DUV radiation may not contribute to the imaging of the patterning device MA on the substrate W but may provide an unwanted global background contribution, which may result in a loss of contrast at the substrate W. For this reason, a dynamic gas lock membrane 300 may be provided to reduce the presence of DUV radiation and/or infrared radiation before the patterned radiation beam B’ is incident upon the substrate W.

[000110] The dynamic gas lock assembly may be located elsewhere in the lithographic system and/or further dynamic gas lock assemblies may be provided. For example, a dynamic gas lock assembly may be configured to protect the illumination system IL. A dynamic gas lock assembly may be located at the intermediate focus 6. For example, the dynamic gas lock assembly may be located between the radiation source SO and the illumination system IL.

[000111] EUV incident on a membrane 100, 200, 300 will apply heating to the membrane 100, 200, 300. The heating causes the temperature of the membrane 100, 200, 300 to increase. For example, the membrane 100, 200, 300 may reach temperatures of about 800-900 °C. Future EUV sources may have higher power and apply higher heat loads. If the temperature of the membrane 100, 200, 300 rises too much, the performance or lifetime of the membrane 100, 200, 300 may be reduced. The membrane 100, 200, 300 may even fail completely. It is desirable for the membrane 100, 200, 300 to have a combination of high emissivity for thermal regulation (i.e. increasing the rate at which the membrane can radiate heat away) and robust mechanical properties for a low possibility of failing (e.g. snapping). It is also desirable for the membrane to have high EUV transmissivity, and high absorption of out-of- band wavelengths (e.g. DUV radiation and/or infrared radiation).

[000112] Fig. 2 schematically depicts a view from the side of a membrane 400 in accordance with the present disclosure. The membrane 400 of Fig. 2 may be used as any of the three membranes 100, 200, 300 shown in Fig. 1. The membrane 400 is configured to transmit EUV radiation. The membrane 400 comprises a nanostructure configured to absorb DUV radiation. The nanostructure may comprise constituent elements (e.g. nanoparticles and/or nanoscale granules) having a size (e.g. a diameter or length, e.g. major axis length) in the nanoscale, e.g. from about 1 nm to about 100 nm. The nanostructure utilizes one or more nanoscale absorption mechanisms such as, for example, quantum confinement of radiation, plasmon excitations and/or the formation of plasmon polaritons, metal-ligand charge transfer effects, etc., to advantageously achieve equivalent or increased DUV radiation and/or infrared radiation absorption at smaller membrane 400 thicknesses compared to known membranes. In this way, the nanostructure is advantageously able to filter out an equivalent or improved amount of DUV radiation and/or infrared radiation whilst the membrane 400 is thin enough to maintain or increase EUV transmission compared to known membranes.

[000113] The nanostructure may comprise semiconductor nanoparticles such as, for example, silicon crystals. A size of each silicon crystal may be about 7 nm or less, e.g. about 5 nm or less. The silicon crystals may be small enough to form silicon quantum dots. The average quantum dot size may be smaller than the Bohr exciton (i.e. a quasiparticle corresponding to a bound state of an electron-hole pair) radius. The quantum dots advantageously provide enhanced and tunable optical performance as a result of quantum confinement of electromagnetic radiation. The nanostructure of the membrane 400 comprising quantum dots is engineered such that the size of the semiconductor nanoparticles are smaller than the Bohr exciton radius, resulting in quantum confinement of the wave functions of electrons. This causes the electronic structure of the nanoparticles to become size-dependent, and with that, the electronic and optical properties of the nanoparticles. That is, the quantum dots may be sized such that the quantum dots reside in the strong quantum confinement regime rather than the intermediate or weak quantum confinement regimes. The quantum dots are configured to absorb DUV radiation. Discrete electron energy levels present in the quantum dots may be tailored for absorption of DUV radiation by selecting a size and/or shape of the quantum dots.

[000114] The nanostructure of the membrane 400 may comprise metallic nanoparticles such as, for example, MoSi2 crystals or Ga crystals. For metallic nanoparticles, the collective interaction of their electrons with an external electromagnetic field (i.e. incident radiation) can cause localized surface plasmon polaritons, which are collective charge oscillations. The consequences of the plasmon excitation include selective photon absorption, scattering and/or emission at a resonance wavelength.

[000115] The nanostructure of the membrane 400 may comprise a matrix of semiconductor nanoparticles and metallic nanoparticles such as, for example, Si crystals (e.g. Si quantum dots) and the metallic nanoparticles MoSi2 crystals. The relative volume fraction of MoSi2 in the membrane 400 may be about 70% or more of the total volume fraction of both MoSi2and Si. The relative volume fraction of MoSi2 in the membrane 400 may be about 100% or less of the total volume fraction of both MoSi2 and Si. The relative volume fraction of MoSi2 in the membrane 400 may increase as the thickness of the membrane 400 decreases.

[000116] The membrane 400 may further comprise N. For example, the membrane 400 may comprise trace amounts of N. The N may be sandwiched between native oxide shells that also contain trace amounts of N and grow naturally on the external surfaces of the membrane 400. The trace amounts of N in the membrane 400, including the native oxide shells that contain N, may amount to less than about 5 atomic%. A membrane 400 comprising trace amounts of N may be referred to as a MoSiSi:N membrane. The MoSiSi:N membrane 400 has been found to have an EUV radiation transmissivity of greater than about 95%. The presence of trace amounts of N in the MoSiSi:N membrane 400 also contributes to enhanced DUV radiation absorption compared to known membranes. Alternatively, the membrane may comprise non-trace amounts of N. A membrane comprising non-trace amounts of N may be referred to as a MoSiN membrane. Non-trace amounts of N may advantageously improve an emissivity of the MoSiN membrane. This in turn may reduce or remove the need for an emissivity layer (e.g. Ru and/or Mo), thereby improving an EUV radiation transmissivity of the membrane compared to known membranes. [000117] The membrane 400 may have a thickness of about 8 nm or less, e.g. about 5 nm or less. The membrane 400 is much thinner than known membranes, thereby advantageously improving EUV radiation transmission of the membrane 400 compared to known membranes whilst maintaining or improving other desirable characteristics such as increased DUV radiation and/or infrared radiation absorption, increased emissivity for improved temperature regulation, adequate mechanical strength at reduced membrane thicknesses, adequate tension to reduce risk of the membrane sagging or snapping, etc., compared to known membranes.

[000118] The membrane 400 comprises a freestanding portion 410. The freestanding portion 410 is held at its edges by support structure 420. The membrane 400 may be produced for example using a mask to define a region of the support structure 420 to be etched and then etching the defined region. The support structure 420 may comprise a silicon wafer supporting the membrane 400. Etching of the defined region may comprise removing a portion of the silicon wafer to release the freestanding portion 410 of the membrane 400. The support structure 420 may be thought of as a frame for holding the free standing portion 410 of the membrane 400. EUV radiation is transmitted through the free standing portion 410 of the membrane 400 without undergoing any unnecessary interactions with other structures, such as the support structure 420. As such, a high level of EUV transmission is achieved.

[000119] Fig. 3 shows two scanning transmission electron microscopy images of a membrane formed in accordance with the present disclosure. The image on the left of Fig. 3 is taken at a first magnification and includes a distance scale indicating a distance of 50 nm. The image on the right of Fig. 3 is taken at a greater magnification then the first magnification and includes a distance scale indicating a distance of 10 nm. The membrane of Fig. 3 comprises a matrix of silicon quantum dots 430 (i.e. the smaller, black crystals), MoSi2 crystals 440 (i.e. the larger, grey crystals) and trace amounts of N (not visible in Fig. 3). The membrane has a thickness of about 8 nm. The membrane was annealed at a temperature of 700 °C. As can been seen from Fig. 3, the MoSi2 metallic nanoparticles have a rounded morphology, e.g. spherical or at least partially spherical, and form a well-defined crystal lattice. The crystal lattice of silicon quantum dots is not visible in Fig. 3.

[000120] Fig. 4 shows the DUV absorption of different membranes having a nanostructure comprising MoSi2 crystals and Si crystals in accordance with the present disclosure. The membranes have different characteristics and/or different formation processes. A first membrane 450 has a thickness of 8 nm, comprises trace amounts of N in the nanostructure, and was annealed at a temperature of 700°C. A second membrane 451 has a thickness of 12 nm, comprises trace amounts of N in the nanostructure, and was annealed at a temperature of 700°C. A third membrane 452 has a thickness of 12 nm, comprises trace amounts of N in the nanostructure, and was annealed at a temperature of 900°C. A fourth membrane 453 has a thickness of 20 nm, comprises trace amounts of N in the nanostructure, and was annealed at a temperature of 900°C. A fifth membrane 454 has a thickness of 20 nm, does not include N in the nanostructure, and was annealed at a temperature of 900°C. A sixth membrane 455 has a thickness of 30 nm, does not include N in the nanostructure, and was annealed at a temperature of 900°C. A seventh membrane 456 has a thickness of 40 nm, does not include N in the nanostructure, and was annealed at a temperature of 900°C.

[000121] As can be seen from Fig. 4, thin membranes of thickness between about 8 nm and about 20 nm comprising trace amounts of N 450-453 provide superior optical absorption in the DUV region compared to thicker membranes of thicknesses of, for example, between about 20 nm and about 40 nm that do not include N in the nanostructure 454-456. Over the entire DUV region the absorption provided by the membranes 450-456 is greater compared to known membranes that are thicker (e.g. having thicknesses of between about 30 nm and about 50 nm). This enhanced DUV absorption at smaller thicknesses is due to nanoscale absorption mechanisms performed by the nanostructure of the membrane such as, for example, quantum confinement of radiation, plasmon excitations and/or the formation of plasmon polaritons, metal-ligand charge transfer effects, etc.

[000122] Fig. 5 schematically depicts a view from the side of a first multilayer membrane 500 according to the present disclosure. The membrane 500 of Fig. 5 may be used as any of the three membranes 100, 200, 300 shown in Fig. 1. The membrane 500 comprises a core layer 510 and two capping layers 520, 530. At least one of the capping layers 520, 530 may be optional. For example, it may not be necessary to include a capping layer 520, 530 to protect the core layer 510 from a scanner environment of a lithographic apparatus. The nanostructure of the membrane 500 is present in the core layer 510. In the example of Fig. 5, the nanostructure comprises a MoSiSi:N membrane. That is, the core layer 510 comprises silicon crystals, MoSi2 crystals and trace amounts of N. Whilst the MoSiSi:N membrane 510 provides improved DUV absorption at smaller thicknesses compared to known membranes, an emissivity and/or infrared absorption of the membrane 500 may be improved with the use of the first capping layer 520. The first capping layer 520 may additionally shield the core layer 510 from the scanner environment of a lithographic apparatus.

[000123] The first capping layer 520 may comprise one or more elements configured to improve an emissivity and/or infrared absorption of the membrane 500. For example, the first capping layer 520 may comprise Ru and/or Mo. The first capping layer 520 may have a thickness of about 10 nm or less, e.g. about 9 nm, 8 nm, 7 nm, 6 nm, 5 nm or 4 nm or less. The first capping layer 520 may have a thickness of about 3 nm or more. The first capping layer 520 may have a high emissivity in the infrared wavelength range. For example, where the emissivity varies between 0 (minimum) and 0.5 (maximum), the emissivity may be greater than 0.2, optionally greater than 0.3, optionally greater than 0.4. The first capping layer 520 therefore radiates heat away effectively and prevents the membrane 500 from overheating.

[000124] Fig. 6 schematically depicts a view from the side of a second multilayer membrane 600 according to the present disclosure. The membrane 600 of Fig. 6 may be used as any of the three membranes 100, 200, 300 shown in Fig. 1. The membrane 600 comprises a core layer 610 and two capping layers 530 configured to protect the core layer 610 from the scanner environment of a lithographic apparatus. At least one of the capping layers 530 may be optional. The nanostructure of the membrane 600 is present in the core layer 610. In the example of Fig. 6, the nanostructure comprises a MoSiN membrane 610. The core layer 610 comprises silicon crystals. The core layer 610 comprises MoSi2 crystals and/or Mo Si s crystals and/or Mo ^Si crystals. The core layer 610 comprises non-trace amounts of N. The greater presence of N, Mo Sh crystals and/or Mo^Si crystals may improve an emissivity of the membrane 600. Like the membrane 500 of Fig. 5, the MoSiN membrane 600 provides improved DUV absorption at lower thicknesses compared to known membranes. However, the increased amount of N present in the core layer 610 and the presence of emissive Mo Si s crystals and/or Mo sSi crystals improves an emissivity and/or infrared absorption of the core layer 610 compared to the core layer 510 of Fig. 5. As such, the membrane 600 of Fig. 6 does not include the first capping layer 520 of Fig. 5. The total thickness of the membrane 600 of Fig. 6 may therefore be less than the total thickness of the membrane 500 of Fig. 5. The membrane 600 of Fig. 6 may have a greater EUV transmissivity than the membrane 500 of Fig. 5 due to its reduced total thickness. The membrane 600 of Fig. 6 may not include capping layers 530, thereby further reducing its thickness and improving its EUV transmissivity.

[000125] The materials used in various layers of the multilayer membranes 500, 600 may fulfill various functional requirements. For example, the membranes 500 may comprise an emissivity layer 520 to increase heat load resistance. As another example, the membranes 500, 600 may comprise one or two outer capping layers 530 to protect the core layer 510, 610 from the harsh EUV scanner environment and increase the membranes’ 500, 600 operational lifetime. The outer capping layers 530 may comprise SiCE and/or ZrCE. The outer capping layers 530 may form outermost surfaces of the membrane 500, 600. The outer capping layer 530 may have a thickness of about 10 nm or less. For example, the outer capping layer 530 may have a thickness of about 9 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, or 2 nm or less. The outer capping layer 530 may have a thickness of about 1 nm or more.

[000126] In both the examples of Fig. 5 and Fig. 6, the core layers 510, 610 may have a thickness of about 5 nm or less. Spectroscopy performed on the membranes of Figs. 2, 5 and 6 has revealed an increase in DUV radiation absorption compared to known membranes when the thickness of the core layer reaches very small thicknesses (e.g. 5 nm or less). This may be ascribed to nanoscale absorption mechanisms such as, for example, quantum confinement of radiation, plasmon excitations and/or the formation of plasmon polaritons, metal-ligand charge transfer effects, etc., depending on the constituent elements of the nanostructure. The core layers 510, 610 may have a thickness corresponding to the size of a single nanoparticle that forms a constituent element of the nanostructure. That is, the core layers 510, 610 may have a thickness corresponding to a single grain of the nanostructure. For example, if the nanostructure comprised silicon quantum dots having a diameter of 5 nm then the thickness of the core layer 510, 610 may also be 5 nm.

[000127] A method of forming a membrane in accordance with the present disclosure comprises forming a nanostructure configured to absorb deep ultraviolet radiation. Forming the nanostructure may comprise performing physical vapor deposition, such as sputter deposition. Forming the nanostructure may comprise performing chemical vapor deposition, such as atomic layer deposition.

[000128] A composition of the membrane may be at least partially determined by a contents of the sputter target. The sputter deposition may involve the use of a MoSiSi sputter target. The MoSiSi sputter target may comprise 15 atomic% Mo or more. The MoSiSi sputter target may comprise 25 atomic% Mo or less.

[000129] The sputter deposition may involve the use of two or more sputter targets. For example, a first sputter target may comprise Si and a second sputter target may comprise MoSi2. As another example, the first sputter target may comprise a matrix material. The matrix material may comprise silicon or silicon nitride. As a further example, the second sputter target may comprise an inclusion material such as, for example, one or more of molybdenum silicide, zirconium silicide, ruthenium silicide and tungsten silicide.

[000130] The composition of the membrane may be at least partially determined by a power provided to the sputter target during the sputter deposition process. That is, adjusting a power (e.g. a bias or an RF power) provided to the sputter target may adjust a composition of the membrane that is formed as a result of the sputter deposition process. A power of about 50 W or more may be provided to the sputter target. A power of about 1000 W or less may be provided to the sputter target. A power of about 300 W or less may be provided to the sputter target. For example, the sputter deposition may involve using a sputter target comprising an inclusion material such as, for example, one or more of molybdenum silicide, zirconium silicide, ruthenium silicide and tungsten silicide, and providing a power of between about 50 W and about 300 W to the sputter target to form a membrane comprising a volume% of the inclusion material of between about 10 volume% and about 60 volume%, preferably between about 15 volume% and about 50 volume%.

[000131] The method may comprise performing the deposition in the presence of N2. A flow of N2 gas may be provided to incorporate N into the membrane. The nitriding of the metal silicide or silicon is effected by sputtering the metal silicide or silicon substrate with a plasma. The sputtering may be reactive sputtering. The plasma may be any suitable plasma. The plasma preferably comprises nitrogen. Preferably, the plasma comprises a mixture of argon and nitrogen gas. The argon gas is included in order to provide an inert atmosphere. Argon is preferably used as it is cheaper than other noble gases, but other noble gases could be used. The ratio of argon to nitrogen may be varied. Having a larger proportion of nitrogen in the gas mixture will result in a greater amount of nitrogen being incorporated into the metal silicide film. The contents of the sputter target may at least partially determine the presence of N in the membrane. For example, the sputter target may comprise a Mo content of about 20 atomic%, which has been found to produce trace amounts of N (e.g. less than about 5 atomic%) in the nanostructure of the membrane. As another example, the sputter target may comprise a Mo content of about 22.5 atomic%, which has been found to produce non-trace amounts of N (e.g. greater than about 5 atomic% and less than about 20 atomic%) in the nanostructure. [000132] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, 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, liquidcrystal displays (LCDs), thin-film magnetic heads, etc.

[000133] Although specific reference may be made in this text 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 other substrate) or mask (or other patterning device). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non- vacuum) conditions.

[000134] Where the context allows, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as 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 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, acoustical or other forms of propagated signals (e.g. carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. and in doing that may cause actuators or other devices to interact with the physical world.

[000135] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

1. A membrane configured to transmit extreme ultraviolet radiation comprising a nanostructure configured to absorb deep ultraviolet radiation.

2. The membrane of claim 1, wherein the nanostructure comprises semiconductor nanoparticles.

3. The membrane of claim 2, wherein the semiconductor nanoparticles comprise silicon crystals.

4. The membrane of claim 3, wherein a size of the silicon crystals is about 7 nm or less.

5. The membrane of any of claims 2 to 4, wherein the semiconductor nanoparticles comprise quantum dots.

6. The membrane of claim 5, wherein the quantum dots comprise silicon quantum dots.

7. The membrane of any preceding claim, wherein the nanostructure comprises metallic nanoparticles.

8. The membrane of claim 7, wherein the metallic nanoparticles comprise MoSi2 crystals.

9. The membrane of claim 7, wherein the metallic nanoparticles comprise Mo Si s crystals and/or

MosSi crystals.

10. The membrane of claim 7, wherein the metallic nanoparticles comprise Ga crystals.

11. The membrane of any preceding claim, wherein the nanostructure comprises a matrix of semiconductor nanoparticles and metallic nanoparticles.

12. The membrane of claim 11, wherein the semiconductor nanoparticles comprise Si crystals and the metallic nanoparticles comprise at least one of MoSi2 crystals, Mo Si s crystals and Mo sSi crystals.

13. The membrane of any preceding claim, comprising N.

14. The membrane of claim 13, comprising less than about 5 atomic% of N.

15. The membrane of claim 13, comprising between about 5 atomic% of N and about 20 atomic% of N.

16. The membrane of any preceding claim, having a thickness of about 8 nm or less.

17. The membrane of any preceding claim, wherein the membrane comprises a core layer and a capping layer, wherein the nanostructure is present in the core layer.

18. The membrane of claim 17, wherein the core layer has a thickness of about 5 nm or less.

19. The membrane of claim 17 or claim 18, wherein the capping layer comprises SiCT and/or ZrCT.

20. The membrane of any of claims 17 to 19, wherein the capping layer comprises Ru and/or Mo.

21. The membrane of any preceding claim, comprising a freestanding portion.

22. A spectral purity filter for EUV lithography comprising the membrane of any of claims 1 to 21.

23. A patterning device assembly for EUV lithography comprising the membrane of any of claims 1 to 21.

24. A dynamic gas lock assembly for EUV lithography comprising the membrane of any of claims 1 to 21.

25. A lithographic system comprising the membrane of any of claims 1 to 21.

26. A method of forming a membrane configured to transmit extreme ultraviolet radiation comprising forming a nanostructure configured to absorb deep ultraviolet radiation.

27. The method of claim 26, wherein forming the nanostructure comprises physical vapor deposition or chemical vapor deposition.

28. The method of claim 27, wherein forming the nanostructure comprises sputter deposition using a sputter target.

29. The method of claim 28, wherein the sputter target is a molybdenum silicide sputter target comprising between about 15 atomic% and about 25 atomic% of Mo.

30. The method of claim 28, comprising using a first sputter target comprising Si and a second sputter target comprising MoSi2.

31. The method of claim 28, comprising using a first sputter target comprising a matrix material and a second sputter target comprising an inclusion material, wherein the matrix material comprises silicon or silicon nitride, and wherein the inclusion material one or more of molybdenum silicide, zirconium silicide, ruthenium silicide and tungsten silicide

32. The method of any of claims 28 to 31, comprising adjusting a power provided to the sputter target to adjust a composition of the membrane.

33. The method of any of claims 28 to 32, comprising providing a power of between about 50 W and about 1000 W to the sputter target.

34. The method of any of claims 27 to 33, comprising performing the deposition in the presence of N₂.

35. The method of claim 34, wherein the sputter target comprises Mo and Si, and wherein the sputter target comprises a Mo content of about 20 atomic%.

36. The method of claim 34, wherein the sputter target comprises Mo and Si, and wherein the sputter target comprises a Mo content of about 22.5 atomic%.