Pellicle membrane for lithographic apparatus

Abstract

A pellicle membrane for a lithographic apparatus is provided, the membrane comprising uncovered carbon nanotubes. Also provided is a method of regenerating a pellicle membrane, the method comprising decomposing a precursor compound and depositing at least some of the decomposition product onto the pellicle membrane. Also provided is a method of reducing the etch rate of a pellicle membrane, the method comprising providing an electric field in the region of the pellicle membrane to redirect ions from the pellicle membrane, or providing a heating element to desorb radicals from the pellicle membrane, preferably wherein the pellicle membrane is a carbon nanotube pellicle membrane; also provided is an assembly for a lithographic apparatus comprising a bias electrode adjacent a pellicle membrane or comprising a pellicle membrane or a heating device for a pellicle membrane.

Description

[0001] This application is a divisional application of patent application number 2020800598112 in the name of ASML NETHERLANDS B.V. entered into the Chinese national phase on 23 February 2022, having an international filing date of 20 August 2020, international application number PCT / EP2020 / 073323, and title “Protective film septum for a lithographic apparatus”.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to EP application 19193590.7 filed on 26 August 2019, EP application 19203575.6 filed on 16 October 2019, EP application 19205058.1 filed on 24 October 2019, and EP application 20161779.2 filed on 9 March 2020, which are incorporated herein in their entirety by reference. TECHNICAL FIELD

[0004] The present invention relates to a protective film septum for a lithographic apparatus, a method of regenerating a protective film septum, a method of reducing the etch rate of a protective film, and an assembly for a lithographic apparatus. BACKGROUND

[0005] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. The lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). The lithographic apparatus can, for example, project a pattern from a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.

[0006] The wavelength of the radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features which can be formed on that substrate. In comparison with conventional lithography using a wavelength of 193 nm, for example, a lithographic apparatus using EUV radiation (i.e., having a wavelength within a range of 4-20 nm) can be used to form smaller features on a substrate.

[0007] A lithographic apparatus includes a patterning device (e.g., a mask or reticle). Radiation is provided to pass through or reflect from the patterning device to form a pattern on a substrate. A septum assembly (also referred to as a protective film) can be provided to protect the patterning device from airborne particles and other forms of contamination. Contamination on the surface of the patterning device can result in manufacturing defects on the substrate.

[0008] In addition to the patterning device, a pellicle can be provided for protecting the optical components. The pellicle can also be used to provide a passage for the lithographic radiation between areas of the lithographic apparatus that are sealed from each other. The pellicle can also be used as a filter, such as a spectral purity filter, or as part of a dynamic airlock of the lithographic apparatus.

[0009] The mask assembly can include a pellicle protecting the patterning device (e.g. mask) from particle contamination. The pellicle can be supported by a pellicle frame to form a pellicle assembly. The pellicle can be attached to the frame, for example by gluing or otherwise attaching the pellicle border region to the frame. The frame can be permanently or releasably attached to the patterning device.

[0010] Due to the presence of the pellicle in the optical path of the EUV radiation beam, the pellicle needs to have a high EUV transmittance. A high EUV transmittance allows a large proportion of the incident radiation to pass through the pellicle and the amount of EUV radiation absorbed by the pellicle can reduce the operating temperature of the pellicle. Since the transmittance depends at least in part on the thickness of the pellicle, it is desirable to provide a pellicle that is as thin as possible while retaining sufficient strength to withstand the sometimes harsh environment within the lithographic apparatus.

[0011] It is therefore desirable to provide a pellicle that is able to withstand the harsh environment of a lithographic apparatus, in particular an EUV lithographic apparatus.

[0012] Although the present application generally refers to a pellicle in the context of a lithographic apparatus, in particular an EUV lithographic apparatus, the present invention is not limited to a pellicle and a lithographic apparatus and it should be understood that the subject matter of the present invention can be used in any other suitable apparatus or situation.

[0013] For example, the methods of the present invention can equally be applied to spectral purity filters. Some EUV sources, such as EUV sources that use a plasma to generate EUV radiation, emit not only the desired "in-band" EUV radiation, but also undesired (out-of-band) radiation. This out-of-band radiation is most significant in the deep UV (DUV) radiation range (100 nm to 400 nm). Also, in the case of some EUV sources (e.g. laser produced plasma EUV sources), radiation from the laser (typically at 10.6 microns) presents significant out-of-band radiation.

[0014] In a lithographic apparatus, spectral purity is required for several reasons. One reason is that resists are sensitive to out-of-band wavelengths of radiation, so if the resist is exposed to such out-of-band radiation, the image quality of the pattern imposed to the resist can be degraded. Also, out-of-band radiation in some laser-produced plasma sources, such as 10.6 micron radiation, can cause unwanted and undesirable heating of the patterning device, the substrate and the optics within the lithographic apparatus. Such heating can cause damage to these elements, a reduction in their lifetime, and / or defects or distortions in the pattern projected onto and imposed to the resist-coated substrate.

[0015] For example, a typical spectral purity filter can be formed from a silicon base structure (e.g. a silicon grid, or other member provided with holes) coated with a reflective metal, such as molybdenum. In use, a typical spectral purity filter can be subjected to a high thermal load from, for example, incident infrared and EUV radiation. This thermal load can cause the temperature of the spectral purity filter to be higher than 800 °C. Under the high thermal load, the coating can delaminate due to a difference in the linear expansion coefficient between the reflective molybdenum coating and the underlying silicon support structure. Delamination and degradation of the silicon base structure is accelerated by the presence of hydrogen, which is often used as a gas in the environment in which the spectral purity filter is used to inhibit debris (e.g. debris such as particles) from entering or exiting a particular part of the lithographic apparatus. Thus, the spectral purity filter can be used as a pellicle, and vice versa. Therefore, references to a “pellicle” in this application are also references to a “spectral purity filter”. Although mainly references are made to a pellicle in this application, all features can equally be applied to a spectral purity filter.

[0016] Further, it is desirable to increase the lifetime of optical elements within a lithographic apparatus, such as a collector mirror, a pellicle, or a component of a dynamic gas lock. These optical elements are exposed to the harsh environment of the lithographic apparatus when the lithographic apparatus is in use, so these optical elements can be damaged over time. It is desirable to prevent, reduce, or eliminate damage to the optical elements.

[0017] In a lithographic apparatus (and / or method), it is desirable to minimize the loss of intensity of the radiation used to impose a pattern onto a resist-coated substrate. One reason is that, ideally, as much radiation as possible should be available to impose a pattern onto a substrate, for example to reduce the exposure time and increase throughput. At the same time, it is desirable to minimize the amount of undesired radiation (e.g. out-of-band radiation) that passes through the lithographic apparatus and is incident on the substrate.

[0018] Furthermore, it is desirable to ensure that the spectral purity filters and / or pellicle membranes used in lithographic methods or apparatus have a sufficient lifetime and do not rapidly deteriorate over time due to the high thermal or radiation load to which they are exposed and / or due to hydrogen and corresponding active species to which they are exposed, such as radicals including H* and HO* and ions including H+, H2+ and H3+. Therefore, it is desirable to provide an improved (or alternative) spectral purity filter and / or pellicle membrane, or to adapt the lithographic apparatus and / or method such that the environment is less aggressive to the pellicle membrane and / or spectral purity filter.

[0019] The present invention has been devised to try to address at least some of the above mentioned problems. SUMMARY

[0020] According to a first aspect of the present invention, there is provided a pellicle membrane for a lithographic apparatus, the membrane comprising uncoated carbon nanotubes.

[0021] In use, the pellicle membrane is located in the direct optical path of radiation used in the lithographic apparatus, such as EUV radiation. Together with the operation at low ambient pressure, this results in the membrane reaching high temperatures that can exceed 600°C. This can prompt chemical and structural deterioration of the pellicle membrane that can result in loss of imaging performance or even failure of the pellicle. To reduce the operating temperature of the pellicle, one or more emissive layers are typically included that increase the emissivity of the pellicle, thereby reducing the operating temperature of the pellicle at a given power. A continuous pellicle membrane provided with emissive layers has an operating temperature in the range of 400°C to 650°C in EUV lithographic apparatuses where the EUV source power (at the intermediate focus) ranges from 150 W to 300 W, with higher temperatures expected in the case of higher power sources. In addition, a cover layer can be provided that reduces or prevents chemical deterioration of the pellicle membrane. To maintain an acceptable transmissivity and infrared (IR) emissivity of the pellicle, the one or more emissive metal or conductive layers are thin. However, a metal film deposited on an inert substrate is in an energetically unfavorable state. Heating the metal membrane applied on top of an inert (non-metal) substrate can result in thermal instability at temperatures well below the melting point of the metal. Due to the provision of sufficient activation energy, the membrane forms pores by a surface diffusion process and the pores grow with time at a rate that is strongly dependent on temperature. When the pores coalesce, the material on the surface forms irregularly shaped islands. This process is known as dewetting and island formation. By providing an adhesion layer between the metal film and the substrate, dewetting and island formation can be reduced, but the metal film is still in an energetically unfavorable state. A thin layer of metal applied on a pellicle loses its high emissivity properties once it breaks up into multiple islands, thus rendering it useless.

[0022] It has been recognized that a protective film membrane comprising uncoated carbon nanotubes is suitable for use in a lithographic apparatus, particularly an EUV lithographic apparatus, especially where EUV plasma induced carbon etching can be sufficiently suppressed. Previously, carbon nanotubes with a capping layer have only been considered due to the potential for carbon etching and failure of carbon nanotubes (CNTs) in an EUV H2 plasma environment. However, capping carbon nanotubes with a material resistant to hydrogen plasma to provide EUV plasma resistance and using them as a protective film membrane in a lithographic apparatus is not appropriate. In addition, capping carbon nanotubes reduces the transmissivity compared to uncoated nanotubes, which is also undesirable.

[0023] A protective film based on uncoated carbon nanotubes can further comprise a plurality of nanoparticles. Nanoparticles are less prone to dewetting or island formation than a conformal coating or capping layer, so the transmissivity and emissivity of the protective film is not affected during use. Furthermore, nanoparticles are not as energetically disadvantaged as a corresponding metal membrane, so are more stable during use. In addition, EUV scattering and absorption by a sub-monolayer of nanoparticles applied to the nanotubes is naturally lower than the scattering and absorption by a conformal or partially conformal layer of comparable thickness applied to the nanotubes.

[0024] The nanoparticles are preferably associated with the carbon nanotubes. Thus, the nanoparticles are attached to the nanotubes rather than being separate from the nanotubes. It is desirable to avoid contamination of the lithographic apparatus, particularly of optical elements such as mirrors or reticles, so it is desirable that the nanoparticles cannot be easily removed from the protective film membrane.

[0025] The nanoparticles can be deposited on the surface of the carbon nanotubes. The nanoparticles can be deposited within the carbon nanotubes. The nanoparticles can be deposited on the surface of the carbon nanotubes and within the carbon nanotubes.

[0026] The nanoparticles can be attached to the surface of the carbon nanotubes by any suitable technique, and the application is not particularly limited by the technique chosen. Methods for producing carbon nanotube-nanoparticle structures can for example be based on so-called wet-chemical or on physical deposition. In a wet-chemical method, the surface of the nanotubes can be functionalized, after which nanocrystals can be combined to the nanotubes by covalent, non-covalent, or electrostatic interactions. In physical deposition, the nanoparticles can be attached to the nanotubes by physical adsorption.

[0027] Similarly, any suitable technique for providing nanoparticles within the nanotubes can be used, and the application is not particularly limited by the technique used. One technique is a wet impregnation method, in which a solution of a metal salt precursor is introduced into the nanotubes, which are then reduced with hydrogen. A calcination step can also be required.

[0028] It has been found that the carbon etching mechanism in EUV lithography apparatuses is a two-factor process. Specifically, both hydrogen ions (e.g. H+, H3+) and hydrogen radicals H* are required to etch carbon. Without wishing to be bound by scientific theory, it is believed that carbon-carbon bonds in the nanotubes can be broken by high-energy hydrogen ions. The broken bonds can be passivated by adsorbed hydrogen radicals. If passivation does not occur, the bonds can recover. It is believed that the addition of nanoparticles increases the recombination rate of adsorbed hydrogen radicals, thus reducing the chance of passivation of broken carbon-carbon bonds by hydrogen radicals. Thus, the rate of etching of the carbon nanotubes is reduced.

[0029] For example, in embodiments in which the carbon nanotubes are arranged with nanoparticles, adsorbed hydrogen atoms can diffuse along the carbon nanotubes. The hydrogen atoms can either recombine into molecular hydrogen and be released as hydrogen gas, or can passivate broken carbon bonds, ultimately resulting in the release of hydrocarbons. The recombination of hydrogen atoms occurs more quickly on the nanoparticles than on the nanotubes, so the presence of the nanoparticles increases the recombination rate of hydrogen, thus reducing the rate of passivation of broken carbon bonds and reducing the rate of etching of the nanotubes.

[0030] It has been found that the presence of nanoparticles within the nanotubes also serves to increase the rate of recombination of hydrogen atoms into molecular hydrogen. Hydrogen atoms adsorbed on the outer surface of the CNT can pass through the graphene or graphene-like film by hopping / diffusion, thus reaching the nanoparticles arranged on the inner surface of the CNT. Again, without wishing to be bound by scientific theory, it is believed that the presence of the nanoparticles increases the recombination rate of adsorbed hydrogen atoms, despite the nanoparticles being located within the nanotubes. A further advantage of this embodiment is that it is almost impossible to remove the nanoparticles from the nanotubes, so there is very little risk of the nanoparticles being released from the protective film membrane and contaminating other parts of the lithography apparatus.

[0031] The nanotubes comprising the (EUV) protective film membrane can form a gas-permeable web. Protective film membranes are typically very thin, free-standing membranes, so if there is a pressure difference between the two faces of the membrane, the protective film membrane is susceptible to deformation. Even a small pressure difference can cause deformation of the protective film membrane. Other protective film membranes comprise monolithic membranes, which are effectively impermeable to gas. In contrast, one embodiment of the present application provides a gas-permeable protective film membrane. This avoids any pressure difference across the membrane, thus reducing the deformation of the membrane.

[0032] The carbon nanotubes can be single-walled or multi-walled. The protective film membrane can comprise single-walled nanotubes, multi-walled nanotubes, or a combination thereof. Preferably, the protective film membrane comprises single-walled nanotubes.

[0033] The diameter of the nanoparticles can range from about 1 nm to about 100 nm. Preferably, the diameter of the nanoparticles can range from about 5 nm to about 25 nm. The diameter of the nanoparticles is preferably measured by transmission electron microscopy. It will be appreciated that other measurement techniques can be used. The diameter of any nanoparticles deposited within the carbon nanotubes will depend on the inner diameter of the nanotubes. Thus, the diameter of any internal nanoparticles can reach the inner diameter of the nanotube in which they are deposited.

[0034] The diameter of the nanoparticles need not necessarily be the same for each nanoparticle within the total population of nanoparticles. Thus, some nanoparticles can be larger or smaller than others. In embodiments, the average diameter of the nanoparticles is from about 1 nm to about 100 nm, preferably from about 5 nm to about 25 nm.

[0035] Nanoparticles of these sizes are advantageous as they reduce imaging distortion by refraction and extinction of EUV radiation.

[0036] The diameter of the nanoparticles is preferably less than half the critical dimension of the pattern of the corresponding mask blank. Thus, preferably none or substantially none of the nanoparticles have a diameter greater than half the critical dimension of the pattern of the corresponding mask blank. In the event that nanoparticles do transfer from the pellicle membrane to the mask blank, the impact on the patterning will not be detrimental if the nanoparticles are less than about half the critical dimension of the mask blank to which they are transferred. With current technology, this provides a preferred regime for nanoparticles having a diameter less than or equal to about 10 nm. As the critical dimension decreases, the size of the nanoparticles will also need to decrease.

[0037] The average distance between adjacent nanoparticles can be greater than the diameter of the nanoparticles. For example, when the diameter of the nanoparticles is 10 nm (as measured by TEM), the average distance between adjacent nanoparticles is preferably greater than 10 nm.

[0038] The average distance between adjacent nanoparticles can be from about 1 times to about 50 times the diameter of the nanoparticles. The average distance between adjacent nanoparticles can be greater than or equal to about ten times the diameter of the nanoparticles. Slightly lower average distances are also acceptable.

[0039] As the nanoparticles will slightly reduce the transmissivity of the pellicle membrane, it is desirable to balance the increased advantage of hydrogen atom recombination with the disadvantage of lower transmissivity. By distributing the nanoparticles throughout the pellicle membrane, the reduction in transmissivity can be managed while still retaining the protective properties of the nanoparticles. Additionally, distributing the nanoparticles also reduces or prevents the agglomeration of the nanoparticles, where agglomeration of the nanoparticles can lead to an increase in the size of the particles and lower transmissivity.

[0040] The nanoparticles preferably comprise a material having a higher hydrogen recombination coefficient than the nanotubes. The recombination coefficient of the nanoparticles is preferably from about 0.1 to about 1. The recombination efficiency is the percentage of adsorbed atoms that form molecules before leaving the surface. Thus, a number of 1 indicates that all of the adsorbed atoms form molecules before leaving the surface, while a number of 0.1 indicates that about 10% of the adsorbed atoms form molecules before leaving the surface. The recombination rate of carbon nanotubes is about 10"3, which is the same as graphene or amorphous carbon. Since the recombination rate of the nanoparticles is greater than the recombination rate of carbon nanotubes, it is believed that the adsorbed hydrogen atoms recombine more rapidly, thus limiting the possibility that a broken carbon-carbon bond will be passivated.

[0041] The nanoparticles can comprise a metal, a metal oxide, a doped metal, an alloy, or combinations thereof.

[0042] The nanoparticles can comprise Nb, Mo, Ru, Rh, Pt, Pd, W, Cr, Ni, Fe, Co, Ag, Au, Zr, Y, and combinations thereof.

[0043] The nanoparticles can additionally comprise O, N, B, Si, C, H, P, S, Cl, and combinations thereof.

[0044] Thus, the nanoparticles can comprise one or more of the metals described herein doped or mixed with one or more of O, N, B, Si, C, P, S, Cl, and H.

[0045] The nanoparticles can comprise a composite material. In other words, the nanoparticles can be composite nanoparticles. Thus, there can be two or more different materials that form the nanoparticles. Some materials can be used to increase the recombination rate of the adsorbed hydrogen atoms, while other materials can help improve the binding to the CNTs.

[0046] These materials (at least the metallic phase of the nanoparticles) have a much higher recombination rate than carbon, so nanoparticles comprising such materials extend the lifetime of the carbon nanotube-based protective film membrane by reducing the rate at which adsorbed hydrogen atoms passivate carbon-carbon bonds.

[0047] The surface density of the nanoparticles can be greater than about 500 particles per square micron, preferably greater than about 1000 particles per square micron.

[0048] Having too few nanoparticles would mean that at least some portions of the carbon nanotubes are not effectively protected from the effects of hydrogen atom passivation. Thus, while portions of the carbon nanotubes adjacent to the nanoparticles will be protected, portions of the carbon nanotubes that are too far from the nanoparticles will not be protected.

[0049] Additionally or alternatively, the uncovered carbon nanotubes can have been passivated. The passivation can be chemical passivation. The uncovered carbon nanotubes can be altered by chemical adsorption of a chemical substance to the surface of the nanotubes. The surface can be altered by chemical adsorption (as opposed to physical adsorption) or by a reaction of the substance with the surface of the carbon nanotubes via a process such as nitridation, oxidation or halogenation. Hydrogenation is explicitly excluded as hydrogenation would likely increase the etching process, thereby creating an effect opposite to the desired effect. Thus, intentional hydrogenation of the carbon nanotubes is not desired. It will be appreciated that the protective membrane septum can be hydrogenated upon use due to the environment within the EUV lithography apparatus, but this hydrogenation is an unwanted side effect caused by the way the apparatus is operated. Passivation can also be achieved by adding strontium, boron, beryllium or silicon atoms to the surface of the carbon nanotubes.

[0050] As this method requires a chemical modification of the surface of the carbon nanotubes themselves, this method is different from applying a coating to the surface of the carbon nanotubes, and a chemical modification of the surface of the carbon nanotubes themselves means that no interface layer is formed. There is also no delamination effect caused by different coefficients of thermal expansion, as seen in systems comprising coated carbon nanotubes.

[0051] Without wishing to be bound by scientific theory, it is believed that the alteration of the surface of the nanotubes weakens the etching of the plasma by a number of mechanisms. The atoms attached to the surface of the carbon nanotubes protect the carbon atoms of the nanotubes from the impact of the etching ions, where in the case of an EUV-induced hydrogen plasma, the etching ions are primarily hydrogen ions. The surface atoms must be etched first, thus creating an elastic time or delay before the carbon atoms are etched. There can also be other mechanisms that protect the carbon nanotubes. It will be appreciated that the surface atoms can be etched, but the protective membrane septum can be repaired by re-passivating the surface. This can be achieved by the method according to the second aspect of the application.

[0052] Preferred surface modifications are oxidation, nitridation, and halogenation. For halogenation, fluorination and chlorination are preferred due to the strength of the carbon-halogen bond, in particular the carbon-fluorine bond. Thus, there is provided a protective membrane septum for a lithography apparatus, the protective membrane comprising uncovered carbon nanotubes, wherein at least a portion of the surface of the uncovered carbon nanotubes has been chemically passivated. Preferably, the chemical passivation comprises nitridation, oxidation, and / or halogenation. The chemical passivation does not comprise hydrogenation. Optionally or additionally, the surface can be modified by adding strontium, boron, beryllium, and / or silicon atoms.

[0053] In embodiments, the uncoated carbon nanotubes are doped with atoms other than carbon. Preferably, the uncoated carbon nanotubes are doped with one or more of nitrogen, boron, and silicon. Doping of the core carbon nanotube structure requires the incorporation of foreign atoms into the core structure. Defects in the carbon nanotube structure, which can be naturally occurring or can be intentionally created, can be filled with atoms other than carbon, such as nitrogen, boron, or silicon.

[0054] The protective film, including carbon nanotubes that have been modified to additionally include nitrogen, boron, and / or silicon in their core structure, reduces the susceptibility to etching by hydrogen ions and radicals due to the altered chemical bond state that changes reactivity. Additionally, the nanotubes are metallic regardless of the chirality or number of walls. This increases the emissivity of the nanotubes, which in turn reduces the operating temperature of the protective film at a given power, thereby extending the lifetime of the protective film. The nanotubes can also be physically stronger than nanotubes that include defects in the core structure.

[0055] An aerogel layer can be provided on one or both faces of the protective film membrane. Aerogels are materials with very high porosity and very low density. The porosity of the aerogel can exceed 95%, exceed 97%, exceed 99%, or even be as high as 99.9%. The density can be less than 0.01 g / cm3.

[0056] Due to the very high porosity and density, aerogels have a high EUV transmissivity. Due to the high EUV transmissivity of the aerogel, the aerogel does not substantially reduce the transmissivity of the protective film membrane, and the aerogel can provide a protective layer for the carbon nanotubes as the aerogel acts as a barrier between the hydrogen plasma and the carbon nanotube-based protective film membrane. Due to the high porosity of the aerogel, pressure differentials on the protective film membrane are avoided.

[0057] The aerogel can comprise niobium, molybdenum, or zirconium. These materials are resistant to the hydrogen plasma environment within the lithographic apparatus.

[0058] The thickness of the aerogel layer or each aerogel layer can be less than 2 microns, less than 1 micron, or less than 0.5 microns.

[0059] Thus, according to a further aspect of the present application, there is provided an optical element for a lithographic apparatus, the optical element comprising an aerogel.

[0060] The optical element can be a protective film membrane, a mirror, a reticle, or a spectral purity filter. The optical element can be located at an intermediate focus position to prevent or reduce the transfer of contaminants from one part of the lithographic apparatus to another part.

[0061] The optical element can comprise a protective film membrane according to any aspect of the application.

[0062] According to a second aspect of the application, there is provided a method of regenerating and / or conditioning a guard membrane separator, the method comprising decomposing a precursor compound and depositing at least some of the decomposition products onto the guard membrane separator.

[0063] As described, the carbon nanotubes are etched by hydrogen within the lithography apparatus. During etching, carbon atoms are removed from the carbon nanotubes to become hydrocarbons. Over time, the removal of carbon from the nanotubes weakens the guard membrane separator, which can lead to particle formation or failure of the guard membrane separator. By providing and decomposing a precursor compound to produce decomposition products, the decomposition products are able to repair any damage to the guard membrane separator, thereby extending its lifetime.

[0064] The precursor can be a hydrocarbon. When the hydrocarbon is decomposed within the lithography apparatus, the hydrocarbon is decomposed into carbon and hydrogen. In the case where the guard membrane separator comprises carbon nanotubes, the carbon produced by the decomposition is able to repair damage to the nanotubes. Although it is believed that the guard membrane can be etched and release hydrocarbons, the concentration of hydrocarbons is low, so providing additional hydrocarbons enables the rate at which carbon is redeposited on the guard membrane separator to approximately balance the rate at which carbon is etched from the guard membrane. It will be appreciated that if the rate at which carbon is etched from the guard membrane separator is the same as the rate at which carbon is redeposited, then the guard membrane can have a substantially extended lifetime. The rate and amount of hydrocarbons introduced into the lithography apparatus will vary depending on the operating conditions within the lithography apparatus, such as the power level at which the apparatus is operating and the partial pressure of hydrogen present within the apparatus. The rate and amount of hydrocarbons introduced can be adjusted to balance the etching of the carbon nanotube guard membrane. It will be appreciated that this method need not take place within the lithography apparatus, but can be performed externally to the lithography apparatus. Thus, the present method can be performed as a pre-conditioning step before the guard membrane is used in the lithography apparatus, or can be performed after the guard membrane has been used in the lithography apparatus to repair any damage caused to the guard membrane during use.

[0065] The hydrocarbon can be saturated or unsaturated. The hydrocarbon can be a C1-C4 hydrocarbon, or an aromatic (C6 or greater) hydrocarbon or a cyclic (C5 or greater) hydrocarbon, and can also include any of N, O, B, P, and CI. Ethylene or acetylene can be used as the hydrocarbon. As unsaturated hydrocarbons have a greater carbon to hydrogen ratio than saturated hydrocarbons, unsaturated hydrocarbons can be advantageous.

[0066] The hydrocarbon can be decomposed into carbon and hydrogen by EUV radiation. The hydrocarbon can also be decomposed by other means, and the decomposition is not to be considered as taking place by exposure to EUV radiation alone. As shorter chain hydrocarbons are less likely to deposit and stick to surfaces within the lithography apparatus other than the guard membrane and cause a persistent loss of reflectivity of the optical components, shorter chain hydrocarbons can be preferred. Finally, in the case of a terminated injection of the hydrocarbon, this carbon rich layer would be cleaned by the EUV H2 plasma.

[0067] The precursor compound can be provided continuously or intermittently. Continuous provision of the precursor compound can be used where the etch rate of the protective film septum is constant, so that where the rate of etching carbon from the protective film is substantially equal to the rate of carbon deposition onto the protective film septum, continuous addition of the hydrocarbon provides a steady state of the protective film septum. The precursor compound can be provided intermittently, such that additional hydrocarbon material is only present for a predetermined time, so as not to adversely affect the throughput of the lithographic apparatus, which can be temporarily reduced due to the deposition of an opaque carbon layer on some optical elements.

[0068] The amount of precursor compound can be adjusted in accordance with one or more of: the etch rate of the protective film septum, the operating power of the lithographic apparatus in which the protective film septum is deposited, and the working lifetime of the protective film septum. For example, where the etch rate of the protective film is higher (the etch rate of the protective film is higher when the apparatus is operated at higher power), a greater amount of precursor compound can be introduced to compensate for the higher etch rate. Where the apparatus is operated at lower power, the amount of precursor compound introduced can be reduced to avoid unwanted build-up of carbon on the protective film septum or other areas of the apparatus.

[0069] The method can comprise directing the precursor compound towards the protective film septum or at least locally towards a reticle mini-environment (RME) coupled to the scanner environment. Since the precursor compound is intended to be decomposed and to repair the protective film septum, it is preferable that the carbon resulting from the decomposition is deposited on the protective film septum rather than on other areas of the apparatus. Thus, directing the flow of precursor compound towards the protective film septum increases the likelihood of carbon deposition on the protective film septum.

[0070] In embodiments of the second aspect of the application, there is provided a method of conditioning and / or repairing a carbon nanotube protective film septum, the method comprising the step of annealing the carbon nanotube protective film septum in a hydrocarbon-containing atmosphere.

[0071] Annealing in a hydrocarbon-containing atmosphere allows for the repair of any dangling bonds and replacement of hydrogen bonded to carbon defect sites with carbon from the hydrocarbon atmosphere. The annealing can be performed at a temperature of about 700K to 900K. It will be appreciated that other temperatures can be used as required. The annealing in a hydrocarbon atmosphere can be referred to as reactive annealing. It will be appreciated that decomposition of the hydrocarbon precursor occurs during this reactive annealing step. The hydrocarbon-containing gas can be ionised to form a plasma. Ionisation to a plasma increases the reaction rate, which allows for the use of lower temperatures, and increases the reaction selectivity.

[0072] The method of the second aspect of the application can further comprise a vacuum annealing step, optionally wherein the vacuum annealing step is before and / or after the step of annealing in a hydrocarbon-containing atmosphere.

[0073] The method can further comprise a reducing anneal step. The reducing anneal step can be performed before and / or after the reactive anneal step. The reducing anneal can be performed in a reducing gas, such as hydrogen. The reducing anneal step removes loosely bound and amorphous carbon deposits as well as other contaminants, such as residual seed nanoparticles from the carbon nanotube growth process.

[0074] Preferably, the final anneal step is a vacuum or reducing anneal step. This is to avoid transient effects during exposure in the scanner environment, which has a higher reducing nature due to the presence of EUV radiation as well as hydrogen plasma and ions. The protective film membrane according to the method of the second aspect of the application can be a protective film membrane according to any other aspect, in particular the first aspect, of the application.

[0075] In an exemplary method, the following steps are performed:

[0076] 1. vacuum or reducing anneal;

[0077] 2. reactive anneal in a hydrocarbon environment;

[0078] 3. optionally repeating steps 1 and 2; and

[0079] 4. vacuum or reducing anneal.

[0080] This exemplary method is useful for protective film membranes that have not yet been exposed to a scanner environment. For protective film membranes that have already been exposed to a scanner environment, the method can be modified to start with the reactive anneal step instead of starting with the passive or reducing recovery step.

[0081] Even in the case where no reactive anneal step is included during the manufacture of the carbon nanotube protective film membrane, there can be a vacuum and / or reducing anneal step prior to exposing the protective film to a scanner environment. Therefore, there is provided a method of conditioning a protective film membrane, the method comprising the step of vacuum and / or reducing annealing the protective film membrane prior to use in a lithographic apparatus.

[0082] Any of the above anneal steps can be performed at a temperature of about 700 K to about 900 K.

[0083] Heating of the protective film membrane during annealing can be performed by any suitable means. For example, the protective film membrane can be heated by exposure to a hot gas, either in a conductive and / or convective manner. The protective film membrane can be heated by passing an electric current through the protective film membrane. The protective film membrane can be heated by laser heating. Combinations of different heating methods are also contemplated.

[0084] According to a third aspect of the application, there is provided a method of reducing the etch rate of a guard film, the method comprising providing one or more biasing elements in the vicinity of the guard film or a region of the guard film. The bias is relative to the grounded vacuum vessel of the lithographic apparatus in which the guard film is disposed. The bias will redirect the flow of positive ions away from the guard film. Preferably, any or most of the biasing elements have a negative potential relative to the (grounded) scanner vacuum vessel to avoid elevated EUV plasma potential, which can be detrimental to the EUV optics. Thus, although the relative bias of the guard film or other elements can be positive, the absolute potential is preferably all negative to avoid an increase in plasma potential.

[0085] As the plasma comprises positively charged hydrogen atoms, providing a suitable bias / electric field will redirect the flow of etching ions away from the guard film. As the flow of etching ions is reduced, the lifetime of the guard film membrane will be extended. The guard film membrane can be a carbon nanotube guard film membrane, but the method can equally be used for other guard film membrane materials.

[0086] The method can comprise biasing the guard film membrane relative to the reticle (front side) and / or the ReMa blades and / or the UNICOM. The ReMa blades are part of a reticle mask unit (REMA) which is a shutter system comprising four independently moving mask blades. The REMA unit uses (metal) blades to block light from specific areas of the reticle. Among these blades, two Y-blades are oriented in the scan direction, while two X-blades are oriented perpendicular to the scan direction. The UNICOM is an optical filter used to condition the illumination near the reticle to ensure slit uniformity. The filter typically comprises two movable plates that can be moved along the Y-scan axis to condition the illumination. As the guard film membrane is etched by a flow of positive hydrogen ions, the flow of hydrogen ions towards the guard film is reduced / redirected by biasing the guard film membrane relative to the nearest surface(s) (e.g. by applying an absolute negative potential, or by applying a positive bias between the guard film and other electrodes relative to each other). Alternatively or additionally, the method can comprise biasing the surfaces relative to the guard film, rather than biasing the guard film relative to the surfaces; while the guard film is floating (or floating) or grounded, e.g. biasing or biasing the reticle (front side) and / or the ReMa blades and / or the UNICOM to extract ions generated within the EUV cone before they reach the guard film. Although absolute positive potential electrodes can be used in the reticle mini-environment, such potentials can increase the plasma potential and ion energy near sensitive components, so in such embodiments additional measures can be required to protect these components.

[0087] According to a fourth aspect of the application, there is provided an assembly for a lithographic apparatus, the assembly comprising a bias shield membrane diaphragm and / or other surfaces within the RME. The other surface can be a reticle face, a ReMa blade or a UNICOM or Y-shaped nozzle. A Y-shaped nozzle is a nozzle that directs a supply of a supply gas in a scanning direction along the reticle. Alternatively or additionally, the bias shield membrane diaphragm and / or the reticle face are floating, while the ReMa blade or the UNICOM have a negative bias with respect to the grounded vacuum vessel wall.

[0088] Preferably, the absolute potential applied to any electrode in the RME is negative or limited to no more than +50 V to avoid an increase in EUV plasma potential, which can otherwise impact the EUV optics with too high energy ions. The absolute potential applied to a surface in the RME can be less than or equal to about -500 V, preferably less than or equal to about -250 V, more preferably less than or equal to about -50 V. The bias is kept relatively low to avoid sparking. A spark can discharge a capacitor (e.g. a bias shield / reticle mask unit or a bias shield / reticle) by EUV-absorbing ionized gas. A single spark can cause a bias shield diaphragm to fail or at least introduce a defect. Even at relatively low voltages, such a bias is sufficient to repel a large fraction of the ions introduced by each EUV flash adjacent to the bias shield. Additionally, limiting the bias of the bias shield relative to the nearest electrode to 100 V or less limits the electrostatic pressure acting on the bias shield. This avoids unwanted deflection or rupture of the bias shield diaphragm.

[0089] The bias source can be current limited and / or pulsed, the bias pulses preferably being synchronized with the EUV flashes.

[0090] The bias shield diaphragm can have a bias relative to one or more of: a reticle mask unit, a reticle, a UNICOM or any other electrode within the reticle micro-environment (including an auxiliary ground electrode).

[0091] The assembly can comprise a reticle mask unit comprising a first blade and a second blade, wherein an electrical bias is provided between the first blade and the second blade or between the blades and the grounded vacuum vessel. The UNICOM can be biased. The Y-shaped nozzle can be biased. The (floating) bias shield can follow the bias of the blade or Y-shaped nozzle due to extraction of photoelectrons or via capacitive coupling.

[0092] At least one auxiliary ground electrode can be provided. The ground electrode prevents field lines from extending too far, and thus can prevent sparking within the lithographic apparatus, which can damage components within the apparatus (such as the bias shield).

[0093] According to a fifth aspect of the application, there is provided a pellicle apparatus for a lithographic apparatus, wherein the pellicle apparatus comprises a pellicle membrane and a pellicle heating device.

[0094] It will be appreciated that, in normal operation of an EUV lithographic apparatus, the pellicle membrane will be heated by the EUV radiation beam. The present application provides a heating device which provides heating in addition to that provided by the EUV radiation or other radiation intended for lithography.

[0095] As described herein, etching of carbon-based pellicle membranes is a two-factor process which requires both hydrogen ions and hydrogen radicals. The hydrogen ions have sufficient energy to break carbon-carbon bonds within the pellicle membrane, and then the adsorbed hydrogen radicals can passivate the broken carbon-carbon bonds. Previously, pellicles have been designed and engineered to reduce the operating temperature of the pellicle membrane in an attempt to extend the useful lifetime of the pellicle membrane. As part of this, additional emissive layers have been added to the pellicle to increase the emissivity of the pellicle, thereby reducing the operating temperature of the pellicle membrane at a given power. Contrary to this, it has been surprisingly found that heating the pellicle material can extend the operating lifetime of the pellicle, particularly for carbon-based pellicles such as carbon nanotube pellicles. Without wishing to be bound by scientific theory, it is believed that by increasing the temperature of the pellicle membrane, the concentration of adsorbed hydrogen atoms can be significantly reduced. As hydrogen adsorption onto graphene-type structures such as the surface of carbon nanotubes is exothermic (typically for any condensation-like process), heating the pellicle membrane causes the amount of adsorbed hydrogen atoms to decrease (which can be thought of as a kind of evaporation process). It is estimated that, with a constant flow / concentration of H* near the pellicle, the concentration of adsorbed hydrogen atoms at 300K (about room temperature) is many orders of magnitude (about 109) higher than the concentration of adsorbed hydrogen atoms at 1300K. By reducing the concentration of adsorbed hydrogen atoms, the likelihood of broken carbon-carbon bonds being passivated is reduced, and also the etching rate of the pellicle is reduced.

[0096] The heating device can be configured to heat a predetermined portion of the pellicle membrane. As mentioned, etching is caused by hydrogen radicals and hydrogen ions. In the reticle micro-environment of the lithographic apparatus (the reticle micro-environment being the area surrounding the pellicle), the radiation beam for lithography (typically an EUV radiation beam) produces hydrogen ions and radicals. The ions recombine after a single collision with the walls of the apparatus, whereas the radicals do not recombine so readily and are therefore able to travel further than the ions. As the ions are believed to be the main cause of carbon-carbon bond breaking, it is advantageous to reduce the concentration of adsorbed hydrogen atoms in the area of the pellicle membrane where the ions interact with the pellicle membrane. As this is not the entire pellicle membrane, additional heating can be provided to only selected portions of the pellicle membrane.

[0097] The predetermined portion of the protective film membrane can be the portion that is subjected to the strongest flow of hydrogen ions. As described, since etching is considered to be a two-factor process, heating of the protective film in the area that is subjected to the highest ion flow reduces the concentration of adsorbed hydrogen atoms in the heated area, thus reducing the etching rate of the protective film membrane. While it will be appreciated that it is most important to heat the protective film membrane where both hydrogen atoms and hydrogen ions are present, it is of course also possible to heat a larger proportion or even all of the protective film membrane.

[0098] The heating device can comprise one or more lasers. The lasers can operate in the visible or infrared spectrum. In fact, any frequency that heats the protective film membrane can be used. Any number of laser beams can be used. The laser beams can be directed to the area of the protective film membrane to be heated. There can be one or more optical elements that direct the laser light to the protective film membrane. The one or more optical elements can reflect, refract or diffract the incoming laser light onto the protective film membrane. The one or more optical elements can be on the reticle mask unit blade. Preferably, the lasers are in the visible and / or IR region, since light of these wavelengths is already present in the lithographic apparatus, there is no need to consider introducing light with "new" wavelengths into the apparatus. A further advantage of using VIS or IR radiation is that they do not develop the resist, so they can to some extent be tolerated towards the substrate.

[0099] The heating device can comprise one or more resistive heating elements. Resistive heating elements rely on the passage of an electric current through a material. Since the protective film membrane preferably comprises carbon nanotubes, these carbon nanotubes can be used as resistive heating elements. Thus, a current source can be attached to the protective film membrane, and the passage of current through the membrane will warm it up and drive off the adsorbed hydrogen atoms.

[0100] An electrically conductive strip can be provided to distribute the current over at least a portion of the protective film membrane. Carbon nanotubes have a high electrical conductivity along their length, and there is a high electrical resistance between adjacent nanotubes. Thus, to more effectively distribute the current over the entire protective film membrane, an electrically conductive strip can be provided that distributes the current over the entire protective film membrane. In contrast, a single electrical connection to the protective film membrane can result in an uneven distribution of the current. It will be appreciated that the electrically conductive strip can be configured to direct the flow of current in a particular portion of the protective film membrane, which is preferably the portion that is subjected to the strongest flow of hydrogen ions.

[0101] The guard membrane diaphragm preferably comprises carbon nanotubes. Preferably, the guard membrane diaphragm is a guard membrane diaphragm according to any aspect of the application. Carbon nanotubes are able to withstand temperatures in excess of 1000 °C or higher and thus will not be damaged by the temperature increase. Furthermore, the guard membrane diaphragm according to the application can also be configured to increase the recombination rate of the adsorbed hydrogen atoms, thus can be used in combination with additional heating of the guard membrane diaphragm to further reduce the etching rate of the guard membrane diaphragm. In addition, the method and apparatus for reducing the flow of hydrogen ions can also be used in combination with a heated guard membrane and / or a guard membrane comprising nanoparticles.

[0102] According to a sixth aspect of the application, there is provided a method of prolonging the working life of a guard membrane diaphragm, the method comprising selectively heating regions of the guard membrane diaphragm.

[0103] Similar considerations applicable to the fifth aspect of the application can be applicable to the sixth aspect. Heating of regions of the guard membrane diaphragm reduces the concentration of adsorbed hydrogen atoms and thus the etching rate of the guard membrane diaphragm. It will be appreciated that the guard membrane diaphragm will be heated by the (EUV) light used for the lithography itself and the heating described herein is heating in addition to the normal heating.

[0104] The method can comprise heating regions of the guard membrane diaphragm that are subjected to the strongest flow of hydrogen ions during operation. Although the entire guard membrane diaphragm can be heated, it is most important to heat the regions of the guard membrane diaphragm that are subjected to the strongest flow of hydrogen ions as this is the region where the most etching occurs.

[0105] The heating can be effected by directing a laser beam onto the guard membrane diaphragm. The laser beam is preferably in the visible or IR region. A laser beam is advantageous as the power of the laser beam can be easily adjusted and the laser can be directed precisely to the desired region of the guard membrane diaphragm.

[0106] The laser can be directed by one or more optical elements. As it is not possible to trigger the laser directly at the guard membrane diaphragm, optical elements can be provided that direct the laser onto the desired region of the guard membrane diaphragm.

[0107] Alternatively or additionally, the additional heating can be effected by passing an electric current through the guard membrane diaphragm or otherwise providing additional heating. The electric current will cause the guard membrane diaphragm to warm up and reduce the concentration of adsorbed hydrogen atoms. The electric current can be varied to provide different amounts of additional heating. The electric current can also be provided to selected portions of the guard membrane diaphragm to heat in the regions that are subjected to the strongest flow of hydrogen ions.

[0108] The protective film membrane used in this aspect of the application can be a protective film membrane as described in any aspect of the application. Furthermore, the method of the sixth aspect can be combined with the apparatus and method of any other aspect described herein.

[0109] According to a seventh aspect of the application, there is provided a protective film membrane for a lithographic apparatus, the membrane comprising a network of misaligned nanotubes.

[0110] Misaligned nanotubes can also be referred to as randomly aligned nanotubes. The network of random nanotubes has porosity. The porosity reduces EUV absorption, thus increasing EUV transmissivity, which results in higher scanner throughput. The porosity also prevents a gradual increase or build-up of pressure difference between the two sides of the protective film. As a result, the protective film deflects less during exhaust and pumping actions, which reduces the risk of the protective film being damaged or failing. In addition, the mass distribution over the surface in the plane of such misaligned network is very uniform, which helps to avoid imaging artefacts. Furthermore, in case a ballistic ion with sufficient momentum hits the membrane in the random misaligned network, any crack propagation stops after the typical size of the travel hole, which can be about 100 nm, and the membrane remains intact.

[0111] The network can comprise a three-dimensional porous network.

[0112] The nanotubes can be single-walled, double-walled, multi-walled, and / or coaxial. A coaxial nanotube is a composite nanotube in which one nanotube is disposed within another nanotube. The inner or core nanotube can be the same or different from the outer or covering nanotube. Double-walled carbon nanotubes and multi-walled nanotubes have chirality, and single-walled nanotubes can have chirality depending on them. Having chirality can help to reduce the operating temperature of the protective film.

[0113] The protective film membrane can comprise a single type of nanotube or two or more types of nanotubes. Thus, the protective film membrane according to the application can be homogenous, i.e. all nanotubes are made of the same material. The protective film membrane can be heterogeneous, i.e. different types of nanotubes can be used to form the protective film membrane. By forming a protective film membrane of a single type of nanotube, the physical properties of the membrane are uniform. By forming a protective film membrane from two or more types of nanotubes, the protective film membrane can benefit from having specific different properties of each material, such as etch resistance and strength.

[0114] The membrane can comprise carbon, boron nitride, and / or a transition metal chalcogenide. Each of these materials is capable of forming nanotubes that can be made into a membrane. Carbon nanotubes are stable at high temperatures well above the operating temperature of existing protective films. Boron nitride nanotubes are also thermomechanically stable at the temperatures faced by protective films in EUV lithography equipment and are also oxidation resistant up to about 900°. Boron nitride nanotubes are also electrically insulating and can be readily synthesized by known methods such as arc discharge, chemical vapor deposition, and laser ablation.

[0115] The transition metal can be selected from Mo, W, Sb, or Bi. Thus, the transition metal (TM) can be Mo. The TM can be W. The TM can be Sb. The TM can be Bi.

[0116] The chalcogenide can be selected from S, Se, or Te. Thus, the chalcogenide can be S. The chalcogenide can be Se. The chalcogenide can be Te.

[0117] For example, the transition metal chalcogenide can be tungsten disulfide or antimony telluride.

[0118] At least some of the nanotubes can comprise a capping material. The capping material can be selected from metal oxides, silicon oxide, and hexagonal boron nitride. Such a capping material can serve to protect the nanotubes from damage. Damage can occur due to oxidation or reduction. For example, when the nanotubes are carbon nanotubes, they can be susceptible to attack by hydrogen ions and free radicals. The capping material can be resistant to such hydrogen etching, thus extending the lifetime of the protective film. It is important that the thermal expansion coefficients of the core material and the capping material be similar to avoid the introduction of thermal stresses as the temperature rises during operation. The thermal stability, oxidation resistance, and hydrogen-induced gas release of the capping layer are also important considerations when selecting the capping layer. Silicon oxide can be particularly suitable for carbon nanotubes and boron nitride nanotubes. Hexagonal boron nitride can be particularly suitable for carbon nanotubes.

[0119] The metal of the metal oxide can be selected from aluminum, zirconium, yttrium, tungsten, titanium, molybdenum, and hafnium. These metal oxides have been found to have suitable physical and chemical properties for use as capping layers for nanotubes, particularly carbon nanotubes and boron nitride nanotubes.

[0120] Hexagonal boron nitride and aluminum trioxide can be used as a capping material with special purposes. The aluminum trioxide can be in the alpha phase. Although the aluminum trioxide can absorb EUV light due to the presence of oxygen, the aluminum trioxide is resistant to further oxidation (the aluminum trioxide is already in an oxidized state) and also to reduction. The aluminum trioxide can also be applied with good consistency to the material on which it is deposited. The aluminum trioxide can be deposited at a suitable temperature of about 150 °C to 350 °C, in which case the aluminum trioxide is deposited in an amorphous state. Subsequently, the amorphous aluminum trioxide can be annealed at a temperature of about 1115 ° to crystallize into the adamant (alpha) state. The annealing can also reduce the number of defects in the protective film membrane.

[0121] The protective film membrane can comprise a coaxial nanotube. The coaxial nanotube can comprise a carbon nanotube core within a hydrogen-resistant nanotube. By placing one nanotube within another, the nanotubes undergo lower thermal mechanical stress caused by heating. Since the outer nanotube is not connected or only weakly connected to the inner nanotube, a wider variety of materials can be used, even materials with very different coefficients of thermal expansion. Thus, the inner nanotube can be selected for strength, and the outer nanotube can be selected for etch resistance. In this way, the protective film membrane comprising such a coaxial nanotube can show both higher strength and higher chemical stability. Thus, any capping material that is able to form a nanotube and is resistant to the environment in which the EUV lithography apparatus is operated can be used.

[0122] The coaxial nanotube can comprise a boron nitride nanotube, a molybdenum disulfide or tungsten sulfide shell around a carbon nanotube core. The carbon nanotube core is very strong and is able to withstand very high temperatures. The outer nanotube material is resistant to the environment in which the EUV lithography apparatus is operated, in particular to hydrogen etching. Thus, the protective film membrane comprising such a coaxial nanotube is strong and also resistant to hydrogen etching.

[0123] According to an eighth aspect of the application, there is provided a lithography apparatus according to the first, fourth, fifth, seventh or ninth aspect of the application.

[0124] According to a ninth aspect of the application, there is provided a method of conditioning a carbon nanotube protective film membrane, the method comprising selectively removing nanoparticle contaminants and / or amorphous carbon from the protective film membrane by heating the protective film membrane with electromagnetic radiation, wherein the conditioning takes place outside the lithography apparatus.

[0125] Carbon nanotube (CNT) separator membranes can include metal-containing nanoparticles that are used as catalysts during the synthesis of the CNTs. Such nanoparticles or residues of their presence in the CNT separator membranes can cause a loss of transmissivity of EUV and can also introduce a risk of reticle contamination. Typically, gaseous etching species are present during CNT synthesis to reduce the catalyst nanoparticles to their metallic state, thereby enhancing the catalytic activity. The gaseous etching species typically originate from hydrogen or ammonia. The etching species also etch some of the amorphous carbon that is formed. However, once the CNT synthesis is complete, some amorphous carbon can remain, which can cause dangling bonds or missing atoms in the structure. It is desirable to remove any remaining amorphous carbon as well as the catalyst nanoparticles. The catalyst nanoparticles can include iron, iron oxide, cobalt, nickel, chromium, molybdenum, and / or palladium.

[0126] Irradiation of the carbon nanotube type protective film separator membrane with electromagnetic radiation causes the protective film to warm up. Due to the much higher light absorbance of the metal particles compared to the very low light absorbance of the CNT separator membrane, the immediate vicinity of the metal nanoparticle contaminant as well as the metal nanoparticle contaminant itself warms up during irradiation. It has been found that this can remove the metal nanoparticle contaminant from the protective film separator membrane. This conditioning step is performed outside of the lithographic apparatus and prior to use as a protective film to avoid potential contamination of the interior of the lithographic apparatus.

[0127] The CNT protective film separator membrane can be heated in a vacuum or a reducing environment. To avoid oxidation of the carbon nanotubes, the heating can be performed in a vacuum. In embodiments that utilize a reducing environment, the metal-containing nanoparticle contaminant, which can include iron oxide, is reduced to its metallic form. In addition, any remaining amorphous carbon is removed. Furthermore, the crystallinity of the CNTs is increased.

[0128] The reducing environment can be a hydrogen environment. Additionally or alternatively, ammonia gas can be used to create the reducing environment.

[0129] In other embodiments, a gas that reacts with the metal catalyst nanoparticles can be used. For example, carbon monoxide, oxygen, or other suitable gas can react with the metal catalyst under low energy light irradiation to form a volatile compound. The carbon monoxide (which can be formed by the reaction of oxygen with carbon in the separator membrane) can bind with the metal to form a metal carbonyl, which can then be removed by light-induced excitation. In addition, the amorphous carbon can be removed as carbon monoxide in a similar manner to the removal of amorphous carbon as a hydrocarbon in a reducing environment.

[0130] Any wavelength of light that can be absorbed by the metal nanoparticles to warm them up can be used. For example, an infrared or near infrared wavelength such as 810 nm can be used. The wavelength of light used can be from about 700 nm to about 1000 nm. The wavelength of such light can be readily provided and is safe and easy to use.

[0131] The CNT guard film septum can be heated at any suitable time. A suitable time is a time in which more than 50% of the metal-containing nanoparticle contaminants are removed. In embodiments, a suitable time is a time in which more than 60%, more than 70%, more than 80% or more than 90% of the nanoparticle contaminants are removed. The number of metal contaminants can be readily determined by scanning electron microscopy so that the length of time required to remove the desired proportion of metal nanoparticles can be determined in a routine manner.

[0132] The CNT septum can be heated for up to 10 minutes, up to 5 minutes or up to 2 minutes. The CNT septum can be heated for 15 s, 30 s, 45 s, 60 s, 75 s or 90 s.

[0133] The electromagnetic radiation used to heat the guard film septum can be low power. Thus, the power can be less than 20 W / cm 2 , less than 15 W / cm 2 , less than 10 W / cm 2 or less than 5 W / cm 2 . The power can be about 3 W / cm 2 , 2 W / cm 2 , 1 W / cm 2 or 0.5 W / cm 2 . Such low power allows for the removal of nanoparticles and / or amorphous carbon while also avoiding the risk of damage to the guard film septum.

[0134] It will be appreciated that features described in relation to one embodiment can be combined with any of the features described in relation to another embodiment and all such combinations are explicitly contemplated and disclosed herein. BRIEF DESCRIPTION OF DRAWINGS

[0135] Embodiments of the application 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:

[0136] Figure 1 A lithographic apparatus according to an embodiment of the application is depicted;

[0137] Figure 2 A schematic diagram of a prior art guard film septum comprising a bundle of carbon nanotubes including a capping layer is depicted;

[0138] Figure 3a and3b schematic diagram of a protective film membrane according to the present invention;

[0139] Figure 4a and 4b schematic diagram of a protective film membrane according to the present invention;

[0140] Figure 5 schematic diagram of a lithographic apparatus comprising an electrically biased protective film / mask blank;

[0141] Figure 6 schematic diagram of a lithographic apparatus comprising an electrically biased protective film / mask blank mask unit;

[0142] Figure 7a and 7b schematic diagram of a lithographic apparatus comprising an electrically biased mask blank mask unit blade;

[0143] Figure 8 schematic diagram of the main processes involved in etching of a carbon nanotube based protective film membrane;

[0144] Figure 9 depicts the approximate range of a mask blank micro-environment and EUV radiation, hydrogen ions and hydrogen radicals;

[0145] Figure 10 Embodiments of the present invention are described;

[0146] Figure 11a and 11b Embodiments of the present invention are depicted;

[0147] Figure 12a and 12b Embodiments of the method according to the present invention are depicted;

[0148] Figure 13 schematic cross-sectional diagram of a protective film membrane according to the present invention comprising an aerogel layer;

[0149] Figure 14a and 14b depict scanning electron microscope images of the same CNT membrane according to an embodiment of the present invention before (Fig. 9a) Figure 14a ) and after (Fig. 9b) Figure 14b ) conditioning of the CNT membrane;

[0150] Figure 15 depict Raman spectra of a CNT membrane according to an embodiment of the present invention before and after conditioning of the CNT membrane; and

[0151] Figure 16 depict FTIR spectra of a CNT membrane according to an embodiment of the present invention before and after conditioning of the CNT membrane.

[0152] The features and advantages of the present application will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. DETAILED DESCRIPTION

[0153] Figure 1 A lithographic system according to the present application is shown comprising a protective film 15 (also referred to as a pellicle assembly). The lithographic system comprises a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam B. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS, and a substrate table WT configured to support a substrate W. The illumination system IL is configured to condition the radiation beam B before it enters the patterning device MA. The projection system is configured to project the (now patterned by mask MA) radiation beam B onto the substrate W. The substrate W can include previously formed patterns. In this case, the lithographic apparatus aligns the patterned radiation beam B with a pattern previously formed on the substrate W. In this embodiment, the protective film 15 is described as being in the path of the radiation and protecting the patterning device MA. It will be appreciated that the protective film 15 can be located at any desired location and can be used to protect any mirror in the lithographic apparatus.

[0154] The radiation source SO, the illumination system IL, and the projection system PS can all be configured and arranged so that they can be isolated from the external environment. A gas (e.g., hydrogen) at a pressure lower than atmospheric pressure can be provided in the radiation source SO. A vacuum can be provided in the illumination system IL and / or the projection system PS. A small amount of gas (e.g., hydrogen) at a pressure much lower than atmospheric pressure can be provided in the illumination system IL and / or the projection system PS.

[0155] Figure 1 The radiation source SO shown in FIG. 1 is of a type that can be referred to as a laser produced plasma (LPP) source. A laser (which can for example be a CO2laser) is arranged to deposit energy into a fuel (such as tin (Sn) provided from a fuel emitter) by a laser beam. Although tin is described in the following description, any suitable fuel can be used. The fuel can for example be in liquid form and can for example be a metal or an alloy. The fuel emitter can comprise a nozzle configured to direct tin in the form of droplets along a trajectory towards a plasma formation region. The laser beam is incident on the tin at the plasma formation region. The laser energy deposited into the tin generates a plasma at the plasma formation region. Radiation (including EUV radiation) is emitted from the plasma during de-excitation and recombination of ions of the plasma.

[0156] EUV radiation is collected and focused by a near-normal-incidence radiation collector (sometimes more generally referred to as a normal-incidence radiation collector). The collector can have a multilayer structure arranged to reflect EUV radiation (e.g. EUV radiation having a desired wavelength such as 13.5 nm). The collector can have an elliptical configuration with two elliptical focal points. The first focal point can be located at the plasma formation region and the second focal point can be located at an intermediate focus point, as described below.

[0157] The laser can be separate from the radiation source SO. In this case, the laser beam can be passed from the laser to the radiation source SO with the aid of a beam delivery system (not shown), which can include for example suitable directing mirrors and / or a beam expander, and / or other optical components. The laser and the radiation source SO can together be considered to form a radiation system.

[0158] The radiation reflected by the collector forms a radiation beam B. The radiation beam B is focused to a spot to form an image of the plasma formation region which acts as a virtual source of the illumination system IL. The spot at which the radiation beam B is focused can be referred to as the intermediate focus. The radiation source SO is arranged such that the intermediate focus is located at or adjacent to an opening in an enclosing structure of the radiation source.

[0159] The radiation beam B passes from the radiation source SO to the illumination system IL, which is configured to condition the radiation beam. The illumination system IL can include a faceted field mirror device 10 and a faceted pupil mirror device 11. Together, the faceted field mirror device 10 and the faceted pupil mirror device 11 provide a radiation beam B having a desired cross-sectional shape and a desired angular distribution. The radiation beam B passes from the illumination system IL and is incident on the patterning device MA held by the support structure MT. The patterning device MA reflects and patterns the radiation beam B. Instead of, or in addition to, the faceted field mirror device 10 and the faceted pupil mirror device 11, the illumination system IL can include other mirrors or devices.

[0160] After reflection from the patterning device MA, the patterned radiation beam B passes into the projection system PS. The projection system includes a plurality of mirrors 13, 14 which are configured to project the radiation beam B onto the substrate W held by the substrate table WT. The projection system PS can apply a reduction factor to the radiation beam, thereby forming an image having features that are smaller than corresponding features on the patterning device MA. A reduction factor of, for example, 4 can be applied. Although in Figure 1 the projection system PS has two mirrors 13, 14, the projection system can include any number of mirrors (e.g. six mirrors).

[0161] Figure 1The radiation source SO shown in the middle can include components not shown. For example, a spectral filter can be provided in the radiation source. The spectral filter can be substantially transmissive for EUV radiation, but substantially blocking for other wavelengths of radiation, such as infrared radiation.

[0162] In embodiments, the septum assembly 15 is a pellicle for a patterning device MA for EUV lithography. The septum assembly 15 of the present invention can be used for a dynamic airlock or for a pellicle or for other purposes. In embodiments, the septum assembly 15 comprises a pellicle formed of at least one septum layer, the pellicle layer being configured to transmit at least 90% of incident EUV radiation. To ensure maximum EUV transmissivity and to minimize the impact on imaging performance, the pellicle is preferably supported only at the boundaries.

[0163] If the patterning device MA is not protected, then contamination can make the patterning device MA require cleaning or disposal. Cleaning the patterning device MA interrupts valuable manufacturing time, while disposal of the patterning device MA is costly. Replacing the patterning device MA also interrupts valuable manufacturing time.

[0164] Figure 2 is a schematic of a bundle of carbon nanotubes 100, wherein the carbon nanotubes comprise a capping layer 101. The carbon nanotubes have a typical diameter from about 2 nm to about 30 nm, and the capping layer 101 has a thickness h that is typically less than about 10 nm, typically about 1 nm. Despite the capping layer being very thin, the transmissivity of the pellicle septum comprising the conformal coating is reduced relative to a pellicle septum comprising uncapped nanotubes. In addition, as described above, the thin layer can be susceptible to dewetting. In addition, as shown above, capping the nanotubes can make the pellicle EUV scattering intolerant. The bundle of nanotubes can comprise a pellicle septum. The pellicle septum can be attached to a frame that supports the pellicle septum.

[0165] Figure 3a is a schematic of a bundle of carbon nanotubes 102 according to an embodiment of the present invention, wherein the outer surface of the carbon nanotubes is arranged with nanoparticles 103. The diameter of the nanoparticles is denoted Dnp. The diameter of the nanoparticles can be measured by any suitable method. Preferably, the diameter is measured by TEM (Transmission Electron Microscopy). The diameter of the nanoparticles can be in the range from a maximum diameter to a minimum diameter. The size of the particles does not have to be identical, but it is preferred that the nanoparticles are in a relatively narrow size range. The relatively narrow size range can include ± 15 nm, ± 10 nm or ± 5 nm. It will be appreciated that due to manufacturing limitations, some nanoparticles can be outside the tolerance. The term Lnp is used to denote the distance between adjacent or neighbouring nanoparticles. It will be appreciated that this can be nanoparticles on the same nanotube or nanoparticles on different nanotubes.

[0166] Figure 3b It is schematically depicted how carbon nanotubes are etched due to the presence of adsorbed hydrogen atoms and hydrogen ions causing carbon-carbon bond breakage. Hydrogen radicals H* are able to adsorb to the surface of the carbon nanotube and migrate along the nanotube until they reach the nanoparticle. Since the rate of recombination of hydrogen radicals into molecular hydrogen at the nanoparticle is faster than at the carbon nanotube, the rate of molecular hydrogen production at the nanoparticle is greater than at any location on the carbon nanotube, thus removing the adsorbed hydrogen atoms, and thus the accumulation of adsorbed hydrogen atoms, making it less likely that the broken carbon-carbon bond is passivated. Conversely, in regions not protected by the nanoparticle, the adsorbed hydrogen radicals do not recombine so readily, and thus when a hydrogen ion causes a carbon-carbon bond to break, this can lead to passivation of the bond, and ultimately release of a hydrocarbon from the nanotube, causing damage to the nanotube.

[0167] Figure 4a and 4b Embodiments similar to Figure 3a and 3b are depicted, but in which the nanoparticles are disposed within the nanotube. As in Figure 3a and 3b a bundle 105 of carbon nanotubes 107 is described, in which the nanoparticles 106 are within the carbon nanotubes. It will be appreciated that some embodiments can have nanoparticles disposed on the interior and exterior of the nanotubes. Wnpis the diameter of the nanoparticles, Unpis the distance between adjacent or neighbouring nanoparticles. As Figure 3b shown, the adsorbed hydrogen atoms are able to migrate along the nanotube, and at the nanotube, the adsorbed hydrogen atoms recombine into molecular hydrogen, which is then able to desorb from the nanotube. Despite being within the nanotube, the nanoparticles can still increase the recombination of hydrogen atoms, and thus protect the nanotube from etching.

[0168] Figure 5A patterned reticle 108 mounted on a chuck 109 by a clamp 110 with fiducial marks 111 and 112 is depicted. The reticle 108 is covered by a pellicle 131. It will be appreciated that the pellicle can be a pellicle according to the present invention or other types of pellicles. The pellicle 131 can be connected to the reticle by an optional insulating structure 120 to form a floating pellicle. The pellicle 131 is connected to a bias electrode by a connection 121. The reticle frontside quality area 132 is connected to other bias electrodes by connections 121. Reticle mask leaves (REMA leaves) 151 and 152 and a uniformity correction module (UNICOM) 180 define the illumination of the reticle 108 with EUV radiation 200. It will be appreciated that REMA leaves and UNICOM are used in actual EUV lithography apparatuses and are included for other cases. The present invention can be practiced without these features. The bias between the pellicle 131 and the reticle 108 deflects ions that are generated by ionizing gas between the pellicle 131 and the reticle 108 and / or that are transported through a hole in the pellicle 131 from a volume between the pellicle and the REMA leaves 151, 152 and with diffusion away from the pellicle 131 towards the reticle 108. This reduces etching of the pellicle membrane, which can be a carbon nanotube pellicle membrane.

[0169] Figure 6 An arrangement is depicted that provides an electrical bias between the pellicle and the REMA leaves 151, 152. The UNICOM 180 can also be provided with a similar or comparable potential as the REMA leaves. As shown by the arrangement of Figure 5 The pellicle 131 is connected to an electrode by a connection 121. Optionally, the pellicle can be floating, so the connection 121 can be omitted. The potential of the REMA leaves 151, 152 is a negative potential. In use, not only a bias can be introduced between the pellicle and the electrode, but also between the EUV plasma itself (mainly contained within the EUV cone) and the electrode. Typically, the plasma potential is slightly positive (+5...+25 V) with respect to the closest electrode (typically the closest electrode is the grounded vacuum container wall), so by introducing an absolutely negative potential electrode (e.g. a REMA leaf or a UNICOM or a Y-jet), positive ions can be extracted from the plasma and redirected away from the (floating or biased) pellicle.

[0170] Figure 7a and 7b An arrangement is depicted that provides an electrical bias between the REMA leaves 151, 152. As in the Figure 7bAs best seen in FIG. 15, there are larger REMA blades 151 and smaller REMA blades 152. Preferably, the larger REMA blades 151 are less negatively biased relative to the grounded vacuum vessel than the smaller REMA blades 152, so as to reduce the possible capacitive (negative) bias of the floating guard film.

[0171] Figure 8 The primary processes involved in the etching of carbon nanotubes are depicted. Arrow 301 depicts the removal of adsorbed hydrogen atoms through associated desorption of H2. The transfer of adsorbed hydrogen atoms (also known as hydrogen radical hopping) is shown by arrow 302. Arrow 300 depicts the adsorption of hydrogen radicals, and arrow 303 depicts the desorption of hydrogen radicals. Line 304 depicts the breaking of carbon-carbon bonds through hydrogen ions. Of the various processes depicted, hydrogen radical desorption 303 has the largest associated energy barrier, while the other processes have smaller energy barriers. Thus, by heating the guard film, the process with the highest energy barrier (i.e., hydrogen atom desorption) is accelerated the most. Thus, while all processes can be accelerated, the desorption of hydrogen atoms is accelerated to a greater extent than the other processes. In addition, process 304 involving hydrogen ions is related to the energy of the incident hydrogen ions, so is less (or not at all) dependent on the guard film temperature.

[0172] Figure 9 A reticle microenvironment (RME) around reticle 430 is depicted, and the approximate extent of the EUV radiation beam (W_EUV), the extent of the primary hydrogen ion stream (W_ion), and the width of the primary hydrogen radical stream (W_radical) are shown. It will be appreciated that the pyramids describing these regions are for illustration purposes, and to aid in understanding the present invention. Guard film 401 is supported on reticle 400 by optional flexure 402. EUV pyramids 420 create radicals and ions within the RME with different extents. Typically, the distance between reticle mask unit blades 411 and 410 is similar to the width of the EUV radiation beam (W_EUV). Typically, due to the limited thermal conductivity of the porous carbon nanotube membrane, the hottest region of the guard film is only slightly larger than W_EUV. Since hydrogen ions recombine after one collision with the surface, the extent of the ions (W_ion) is similar to W_EUV plus about 2 to 4 times the distance (H_rema) between the reticle mask unit blades and the guard film 401. H_rema is typically about 2 mm to 5 mm. On the other hand, since radicals can survive multiple collisions with the surface, the extent of the radicals (W_radical) is larger and can be similar to the size of the guard film. Thus, the region that is subjected to both the ion stream and the radical stream is not the entire surface of the guard film. Thus, only this overlapping region can be heated to reduce the concentration of adsorbed hydrogen radicals so that etching is slow.

[0173] Figure 10 An embodiment of the invention is depicted in which a laser is used to provide additional heat to the pellicle membrane. As described, laser beams 510 and 520 are provided. It will be appreciated that the invention is not limited to just two laser beams and that fewer or more laser beams may be used as required. In the described embodiment, each laser beam has an associated optical element 510, 521 which directs the laser beam to the pellicle. The approximate width of the additional heating area is shown as W_ext.heat. The heating effect of the laser suppresses the concentration of adsorbed radicals in the areas of strongest ion flux, thereby reducing the etch rate. Selective heating limits the total heat load on the reticle. Any suitable laser power may be chosen, for example it may be desirable to provide a laser beam at 0.1 W / cm 2 Up to 10w / cm 2 The power of the transmitted radiation 512, 522 (directed to the reticle) is estimated to be a percentage of the incident power (e.g., approximately 5% to 50%) and is almost entirely reflected by the reticle in the same manner as the IR radiation from the thermal pellicle, so this is a heat load that the reticle can withstand.

[0174] Figure 11a and 11b An embodiment of the present invention including resistive heating is depicted. A current source 600 is connected to the pellicle 401 via contacts 601, 602 and / or wires integrated into the chuck or fixture. By providing a highly conductive strip 630 on the pellicle frame 610 and supplying current to such strip, a current 640 within the pellicle diaphragm 620 can be made substantially uniform. The conductive strip 630 can be configured to distribute the current to the portion of the pellicle diaphragm that experiences the strongest hydrogen ion flow.

[0175] Figure 12a and 12b A schematic flow diagram is depicted relating to a method for regenerating, conditioning, and / or restoring a protective membrane diaphragm. Figure 12aAfter manufacture, the guard membrane diaphragm undergoes a vacuum or reducing anneal step 701. This removes any loosely bound amorphous carbon and other contaminants, such as residual seed nanoparticles from the carbon nanotube growth process. The guard membrane diaphragm then undergoes a reactive anneal process 702 in a hydrocarbon containing atmosphere. The hydrocarbon can be any hydrocarbon, but it is preferred to use a short chain (C1-4) hydrocarbon, such as methane, ethane, propane or butane. The hydrocarbon can be saturated or unsaturated. As unsaturated hydrocarbons have a higher carbon to hydrogen ratio, it is preferred that the unsaturated hydrocarbon (such as ethene or acetylene). After the reactive anneal step 702, the guard membrane diaphragm can again undergo a vacuum or reducing anneal 701 by path 705. Prior to use in the scanner 704, the guard membrane diaphragm undergoes a vacuum anneal step 703 to avoid transient effects occurring during exposure to the scanner environment. Such transient effects include changes in the transmissivity of EUV of the guard membrane diaphragm after exposure to EUV radiation and hydrogen ions and radicals in the scanner environment within the lithographic apparatus. In another approach, the guard membrane diaphragm can be used in the scanner without undergoing a reactive anneal, as indicated by arrow 706.

[0176] Figure 12b A flow diagram is depicted relating to a method of rejuvenating, conditioning and / or restoring a guard membrane diaphragm that has been exposed to the scanner environment of a lithographic apparatus. As the guard membrane diaphragm has been exposed to a more reducing atmosphere within the lithographic apparatus, it is not necessary to further anneal the guard membrane in a reducing anneal step. Furthermore, the guard membrane diaphragm can have been damaged during use, so it will be necessary to repair any damage, which can be achieved by performing a reactive anneal in a hydrocarbon atmosphere. After the reactive anneal 702, the guard membrane diaphragm can undergo a vacuum or reducing anneal 701. This can be repeated. Once the guard membrane diaphragm has been sufficiently repaired, the guard membrane diaphragm can again be used 704 in the lithographic apparatus.

[0177] Figure 13 A cross-section of a guard membrane diaphragm is depicted comprising a layer of aerogel 801 on each face. It will be appreciated that in some embodiments, the layer of aerogel 801 is provided on only one face. The layer of aerogel 801 is able to protect the underlying layer of guard membrane diaphragm 800 from etching by hydrogen plasma. It will be appreciated that other optical elements of the lithographic apparatus can also be similarly protected by aerogel.

[0178] Figure 14a and 14b are scanning electron microscope images of regions of the same CNT diaphragm. In Figure 14a the CNT diaphragm has not been conditioned according to the method of the ninth aspect of the application. Nanoparticle contaminants can be clearly seen as white spots distributed across the CNT film. Figure 14bThe same CNT separator that has been conditioned is depicted. Specifically, the CNT separator was conditioned by exposure to radiation at 810 nm. It can be seen that the number of nanoparticle contaminants has been greatly reduced.

[0179] Figure 15 Raman spectra of an unconditioned CNT separator and a CNT separator that has been conditioned according to the ninth aspect of the application are depicted. Two peaks are observed. The first peak at about 1350 cm"1 shows a higher line associated with the original (unconditioned) CNT separator than with the conditioned CNT. At this Raman shift, a higher line indicates a greater degree of defects or a greater amount of defects, which indicates either defective CNTs, amorphous carbon, or both. By conditioning the protective film separator of CNTs, the amount of defects, amorphous carbon, or both is reduced. The peak at about 1580 cm"1 shows a higher line associated with the conditioned CNT protective film separator than with the unconditioned CNT protective film separator. The peak at about 1580 cm"1 is associated with the amount of amorphous carbon, which demonstrates that the conditioned CNT protective film separator has a greater amount of crystalline carbon than the unconditioned CNT protective film separator.

[0180] Figure 16 FTIR spectra obtained from the conditioned and unconditioned regions of a CNT protective film separator are depicted. The spectrum obtained from the original (unconditioned) CNT protective film separator shows a lower peak at about 2.5 microns, a similar absorption spectrum at about 4 microns, and a generally higher absorption spectrum at wavelengths above 4 microns. In contrast, the conditioned (illuminated) CNT protective film separator has a higher absorption peak at 2.5 microns and then a generally lower absorption spectrum at wavelengths above 4 microns. The distinct peak at 2.5 microns further indicates that the CNT separator has a higher crystalline quality after conditioning.

[0181] It will be appreciated that various aspects of the application can be provided or combined. For example, embodiments that include an electrical bias can be used in combination with the protective film separators described herein or in combination with other types of protective film separators. Methods of regenerating a protective film can be used in combination with methods of electrical biasing and can further include the use of the protective film separators described herein or other types of protective film separators.

[0182] Although specific reference can be made in this text to the use of the lithographic apparatus in the manufacture of ICs, it should be recognized that the lithographic apparatus described herein can have other applications. For example, it can be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays such as liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The substrates referred to herein can be processed, before or after exposure, in for example, one or more of the steps of a track (a tool that typically applies a resist layer to a substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where applicable, the disclosure herein can be applied to such and other substrate processing tools. Further, the substrates can be processed more than once, for example, to create a multi-layer IC, so the term substrate as used herein can also refer to a substrate that already contains multiple processed layers.

[0183] While specific embodiments of the application have been described above, it will be appreciated that the application can be practiced otherwise than as described. For example, the various layers can be replaced by other layers performing the same function.

[0184] The description above is intended to be illustrative, and not restrictive. For example, while the above describes a number of embodiments of the present application, a person of ordinary skill in the art will be able to think of changes and modifications to the described application without departing from the scope of the claims and the following numbered clauses.

[0185] 1. A pellicle membrane for a lithographic apparatus, the membrane comprising uncoated carbon nanotubes.

[0186] 2. A pellicle membrane for a lithographic apparatus, the membrane further comprising a plurality of nanoparticles, optionally wherein the nanoparticles are composite nanoparticles.

[0187] 3. The pellicle membrane according to clause 2, wherein the nanoparticles are associated with the carbon nanotubes.

[0188] 4. The pellicle membrane according to clause 2 or 3, wherein the nanoparticles are disposed on the surface of the carbon nanotubes, or within the carbon nanotubes, or on the surface of the nanotubes and within the nanotubes.

[0189] 5. The pellicle membrane according to any of the preceding clauses, wherein the nanotubes form a gas permeable mesh.

[0190] 6. The pellicle membrane according to any of the preceding clauses, wherein the carbon nanotubes are selected from single-walled nanotubes, multi-walled nanotubes, and combinations thereof.

[0191] 7. The pellicle membrane according to any of the preceding clauses, wherein the nanoparticles have a diameter of about 1 nm to about 100 nm, preferably about 1 nm to about 25 nm.

[0192] 8. The guard film separator of any of the preceding clauses, wherein the diameter of the nanoparticles is less than half of the critical dimension of the pattern of the corresponding mask.

[0193] 9. The guard film separator of any of the preceding clauses, wherein the average distance between adjacent nanoparticles is greater than the diameter of the nanoparticles.

[0194] 10. The guard film separator of clause 9, wherein the average distance between adjacent nanoparticles is about 1 to about 50 times the diameter of the nanoparticles.

[0195] 11. The guard film separator of clause 9, wherein the average distance between adjacent nanoparticles is greater than or equal to ten times the diameter of the nanoparticles.

[0196] 12. The guard film separator of any of the preceding clauses, wherein the nanoparticles comprise a material having a higher hydrogen recombination coefficient than the nanotubes.

[0197] 13. The guard film separator of clause 12, wherein the recombination coefficient of the nanoparticles is about 0.1 to about 1.

[0198] 14. The guard film separator of any of the preceding clauses, wherein the material comprising the nanoparticles is selected from the group consisting of a metal, a metal oxide, a doped metal, an alloy, or combinations thereof.

[0199] 15. The guard film separator of any of the preceding clauses, wherein the material comprising the nanoparticles is selected from the group consisting of Nb, Mo, Zr, Y, Ru, Rh, Pt, Pd, W, Cr, Ni, Fe, Co, Ag, Au, and combinations thereof.

[0200] 16. The guard film separator of clause 14 or 15, wherein the nanoparticles additionally comprise O, N, B, Si, C, H, S, P, CI, and combinations thereof.

[0201] 17. The guard film separator of any of the preceding clauses, wherein the surface density of the nanoparticles is greater than about 500 particles per square micron, preferably greater than about 1000 particles per square micron.

[0202] 18. The guard film separator of any of the preceding clauses, wherein the uncovered carbon nanotubes have been passivated, preferably chemically passivated.

[0203] 19. The guard film separator of clause 18, wherein the uncovered carbon nanotubes have been passivated by chemical adsorption of a chemical species to the surface of the nanotubes.

[0204] 20. The guard membrane separator according to any of clauses 18 or 19, wherein the uncoated carbon nanotubes have been passivated by nitridation, oxidation or halogenation, or by adding strontium, boron, beryllium and / or silicon to the surface of the carbon nanotubes.

[0205] 21. The guard membrane separator according to any of the preceding clauses, wherein the surface of the uncoated carbon nanotubes has not been intentionally hydrogenated.

[0206] 22. The guard membrane separator according to any of clauses 18 to 21, wherein the uncoated carbon nanotubes have been passivated by fluorination or chlorination.

[0207] 23. A guard membrane separator for a lithographic apparatus, the separator comprising uncoated carbon nanotubes, wherein at least a portion of the surface of the uncoated carbon nanotubes has been chemically passivated, preferably wherein the chemical passivation comprises nitridation, oxidation and / or halogenation.

[0208] 24. The guard membrane separator according to any of the preceding clauses, wherein the uncoated carbon nanotubes are doped with atoms other than carbon, optionally wherein the atoms other than carbon are nitrogen, boron and / or silicon.

[0209] 25. A method of regenerating and / or conditioning a guard membrane separator, the method comprising decomposing a precursor compound and depositing at least some of the decomposition products onto the guard membrane separator.

[0210] 26. The method according to clause 25, wherein the guard membrane separator is according to any of clauses 1 to 24.

[0211] 27. The method according to clause 25 or 26, wherein the precursor is a hydrocarbon, preferably wherein the hydrocarbon is a saturated or unsaturated C1-4 hydrocarbon, or a cyclic hydrocarbon (C5 or greater), or an aromatic hydrocarbon (C6 or greater), optionally the precursor comprises at least one of O, N, B, P, S, Cl.

[0212] 28. The method according to any of clauses 25 to 27, wherein the precursor compound is provided continuously or intermittently.

[0213] 29. The method according to any of clauses 25 to 28, wherein the amount of precursor compound is conditioned according to one or more of: the etch rate of the guard membrane separator, the operating power of the lithographic apparatus in which the guard membrane separator is disposed, and the working life of the guard membrane separator.

[0214] 30. The method according to any of clauses 25 to 29, wherein the method comprises directing the precursor compound towards the guard membrane separator.

[0215] 31. The method according to any one of clauses 25 to 29, wherein the method comprises a method of conditioning and / or repairing a carbon nanotube protective membrane separator, the method of conditioning and / or repairing a carbon nanotube protective membrane separator comprising a step of annealing the carbon nanotube protective membrane separator in a hydrocarbon containing atmosphere.

[0216] 32. The method according to clause 31, wherein annealing is performed at a temperature of about 700 K to about 900 K.

[0217] 33. The method according to any one of clauses 25 to 32, wherein the method comprises a vacuum annealing step, optionally wherein the vacuum annealing step is before and / or after the step of annealing the protective membrane separator in a hydrocarbon containing atmosphere.

[0218] 34. The method according to any one of clauses 25 to 33, wherein the method comprises a reducing annealing step, optionally wherein the reducing annealing step is before and / or after the reactive annealing step, optionally wherein the reducing annealing step is performed in a reducing gas, such as hydrogen.

[0219] 35. The method according to any one of clauses 25 to 34, wherein the final annealing step is a vacuum annealing step or a reducing annealing step.

[0220] 36. The method according to any one of clauses 25 to 35, wherein the protective membrane separator is a protective membrane separator according to any one of clauses 1 to 24.

[0221] 37. A method of regenerating and / or conditioning a protective membrane separator, optionally a separator according to any one of clauses 1 to 24, the method comprising the steps of:

[0222] a) vacuum or reducing annealing;

[0223] b) reactive annealing in a hydrocarbon environment;

[0224] c) optionally repeating steps a) and b); and

[0225] d) a final vacuum or reducing annealing step.

[0226] 38. A method of reducing the etching rate of a protective membrane separator, the method comprising providing at least one biasing element in a region of the protective membrane separator, preferably wherein the protective membrane separator is a carbon nanotube protective membrane separator.

[0227] 39. An assembly for a lithographic apparatus, the assembly comprising a pellicle diaphragm biased relative to a nearest neighbour electrode, the assembly can comprise a reticle front face and / or a shutter system and / or an optical filter and / or a purge gas supply, optionally wherein the pellicle diaphragm and / or the reticle front face are floating, while the shutter system and / or the optical filter are negatively biased relative to a grounded vacuum vessel wall.

[0228] 40. The assembly according to clause 39, wherein the absolute bias between any electrodes is less than or equal to about -500 V, preferably less than or equal to about -250 V, and more preferably less than or equal to about -50 V, optionally wherein all electrodes are negative relative to the grounded vacuum vessel wall.

[0229] 41. The assembly according to clause 39 or 40, wherein the bias is current limited or pulsed, wherein the pulses are optionally synchronised with EUV pulses.

[0230] 42. The assembly according to any of clauses 39 to 41, wherein the pellicle diaphragm has a bias relative to one or more of: a reticle mask unit, a reticle, an optical filter and auxiliary electrodes within a reticle micro-environment.

[0231] 43. The assembly according to any of clauses 39 to 42, wherein the assembly comprises a reticle mask unit, the reticle mask unit comprising a first blade and a second blade, wherein an electrical bias is provided between the blades.

[0232] 44. The assembly according to any of clauses 39 to 43, wherein a grounded electrode is provided.

[0233] 45. A pellicle apparatus for a lithographic apparatus, wherein the pellicle apparatus comprises a pellicle diaphragm and a pellicle heating device.

[0234] 46. The pellicle apparatus according to clause 45, wherein the heating device is configured to heat a predetermined portion of the pellicle diaphragm.

[0235] 47. The pellicle apparatus according to clause 45 or clause 46, wherein the predetermined portion of the pellicle diaphragm is the portion that is subject to the strongest hydrogen ion flux.

[0236] 48. The pellicle apparatus according to any of clauses 45 to 47, wherein the heating device comprises i) one or more lasers and / or ii) one or more resistive heating elements.

[0237] 49. The pellicle apparatus according to clause 48, wherein the one or more lasers operate in the visible or infrared spectrum.

[0238] 50. The guard membrane apparatus of clause 47 or 48 i), wherein the apparatus further comprises at least one optical element configured to direct a laser onto the guard membrane septum.

[0239] 51. The guard membrane apparatus of clause 48 ii), wherein the guard membrane septum is connected to a current source such that the material comprising the guard membrane septum acts as a resistive heater.

[0240] 52. The guard membrane apparatus of clause 48 ii) or 51, wherein an electrically conductive strip is provided to distribute current over at least a portion of the guard membrane septum.

[0241] 53. The guard membrane apparatus of any one of clauses 45 to 52, wherein the guard membrane septum comprises carbon nanotubes, preferably wherein the guard membrane septum comprises a guard membrane septum according to any one of clauses 1 to 17.

[0242] 54. A method of prolonging the working life of a guard membrane septum, the method comprising selectively heating regions of the guard membrane septum.

[0243] 55. The method of clause 54, wherein the method comprises heating regions of the guard membrane that are subjected to the strongest flow of hydrogen ions during operation.

[0244] 56. The method of clause 54 or 55, wherein the heating is achieved by directing a laser beam onto the guard membrane septum.

[0245] 57. The method of clause 54, 55 or 56, wherein the laser beam is directed by one or more optical elements.

[0246] 58. The method of clause 54 or 55, wherein the heating is achieved by passing a current through the guard membrane septum.

[0247] 59. The method of clause 58, wherein the guard membrane septum is a guard membrane septum according to any one of clauses 1 to 24.

[0248] 60. A guard membrane septum for a lithographic apparatus, the septum comprising a network of misaligned nanotubes.

[0249] 61. The guard membrane septum of clause 50, wherein the network comprises a three- dimensional porous network.

[0250] 62. The guard membrane septum of clause 60 or 61, wherein the nanotubes are single-walled, double-walled, multi-walled and / or homocentric.

[0251] 63. The guard membrane of any one of clauses 60-62, wherein the membrane comprises a single type of nanotube, or two or more types of nanotubes.

[0252] 64. The guard membrane of any one of clauses 60-63, wherein the membrane comprises carbon, boron nitride, and / or a transition metal chalcogenide.

[0253] 65. The guard membrane of clause 64, wherein the transition metal is selected from Mo, W, Sb, or Bi.

[0254] 66. The guard membrane of clause 64 or 65, wherein the chalcogenide is selected from S, Se, or Te.

[0255] 67. The guard membrane of any one of clauses 60-66, wherein at least some of the nanotubes comprise a capping material.

[0256] 68. The guard membrane of clause 67, wherein the capping material is selected from a metal oxide, silicon oxide, and hexagonal boron nitride.

[0257] 69. The guard membrane of clause 68, wherein the metal of the metal oxide is selected from aluminum, zirconium, yttrium, tungsten, titanium, molybdenum, and hafnium, preferably alpha aluminum oxide.

[0258] 70. The guard membrane of any one of clauses 60-69, wherein the membrane comprises coaxial nanotubes.

[0259] 71. The guard membrane of clause 70, wherein the coaxial nanotube comprises a carbon nanotube core within a hydrogen etch resistant nanotube.

[0260] 72. The guard membrane of clause 71, wherein the coaxial nanotube comprises a boron nitride nanotube, a molybdenum disulfide, or a tungsten sulfide shell around the carbon nanotube core.

[0261] 73. An optical element for a lithographic apparatus, the optical element comprising an aerogel.

[0262] 74. The optical element of clause 73, wherein the optical element is a guard membrane, a mirror, a reticle, or a spectral purity filter.

[0263] 75. The optical element of clause 73 or 74, wherein the optical element comprises the guard membrane of any one of clauses 1-24, 45-53, or 60-72.

[0264] 76. A lithographic apparatus comprising the guard membrane of any one of clauses 1-24, 45-53, or 60-72.

[0265] 77. A method of conditioning a carbon nanotube protective film separator, the method comprising selectively removing metal-containing nanoparticles and / or amorphous carbon from a protective film separator by heating the protective film separator with electromagnetic radiation, wherein the conditioning is performed outside a lithographic apparatus.

[0266] 78. The method of any of clauses 77, wherein the CNT protective film separator is heated in a vacuum or a reducing environment.

[0267] 79. The method of clause 78, wherein the reducing environment comprises one or both of hydrogen gas and ammonia gas.

[0268] 80. The method of any of clauses 77, wherein the CNT protective film separator is heated in an environment comprising one or more of carbon monoxide and oxygen.

[0269] 81. The method of any of clauses 77-80, wherein the CNT protective film separator is heated for a time sufficient to remove more than 50%, more than 60%, more than 70%, more than 80%, or more than 90% of the metal nanoparticles.

[0270] 82. The method of any of clauses 77-81, wherein the CNT separator is heated for 15 seconds, 30 seconds, 45 seconds, 60 seconds, 75 seconds, 90 seconds, or for up to 2 minutes, up to 5 minutes, or up to 10 minutes.

[0271] 83. The method of any of clauses 77-82, wherein the electromagnetic radiation has a power of about 0.5 W / cm 2 , 1 W / cm 2 , 2 W / cm 2 , 3 W / cm 2 , less than 5 W / cm 2 , less than 10 W / cm 2 , less than 15 W / cm 2 , or less than 20 W / cm 2 .

[0272] 84. The method of any of clauses 77-83, wherein the electromagnetic radiation is infrared or near-infrared radiation, optionally wherein the radiation has a wavelength of about 700 nm to about 1000 nm.

Claims

1. A pellicle device for extending the working life of a pellicle diaphragm, wherein: The pellicle apparatus includes a pellicle membrane and a pellicle heater, and wherein the pellicle membrane includes carbon nanotubes.

2. The pellicle device according to claim 1, wherein: The heating device is configured to heat a predetermined portion of the pellicle membrane to selectively remove nanoparticles and / or amorphous carbon from the pellicle membrane.

3. The pellicle device according to claim 2, wherein: The predetermined portion of the pellicle membrane is a portion that is subjected to the strongest hydrogen ion flow.

4. The protective membrane device according to claim 1 or 2, wherein: The heating device comprises i) one or more lasers and / or ii) one or more resistive heating elements.

5. The pellicle device according to claim 4, wherein: The one or more lasers operate in the visible spectrum or the infrared spectrum.

6. The pellicle device according to claim 3, wherein: The pellicle apparatus further includes at least one optical element configured to direct laser light onto the pellicle membrane.

7. The pellicle device according to claim 4, wherein: The pellicle membrane is connected to a source of electrical current such that the material comprising the pellicle membrane acts as a resistive heater.

8. The pellicle device according to claim 4, wherein: Conductive strips are provided to distribute current across at least a portion of the pellicle diaphragm.

9. A method of extending the operating life of a pellicle membrane comprising carbon nanotubes, the method comprising selectively heating regions of the pellicle membrane.

10. The method according to claim 9, wherein: The method includes heating a region of the pellicle membrane that is subject to the strongest hydrogen ion flux during operation.

11. The method according to claim 9 or 10, wherein: Heating is achieved by directing a laser beam onto the pellicle membrane.

12. The method according to claim 9 or 10, wherein: The laser beam is directed by one or more optical elements.

13. The method according to claim 9 or 10, wherein: Heating is achieved by passing an electric current through the pellicle membrane.

14. A method of conditioning a carbon nanotube pellicle membrane, the method comprising selectively removing metal-containing nanoparticles and / or amorphous carbon from the pellicle membrane by heating the pellicle membrane with electromagnetic radiation, optionally wherein: The adjustments are performed outside the lithographic apparatus.

15. The method according to claim 14, wherein The carbon nanotube protective membrane is heated in a vacuum or reducing environment.

16. The method according to claim 15, wherein The reducing environment includes one or both of hydrogen and ammonia.

17. The method according to claim 14, wherein: The carbon nanotube pellicle membrane is heated in an environment including one or more of carbon oxides and oxygen.

18. The method according to claim 14 or 15, wherein The power of the electromagnetic radiation is less than 20W / cm 2 .

19. The method according to claim 14 or 15, wherein: The electromagnetic radiation is infrared or near infrared radiation, optionally wherein the electromagnetic radiation has a wavelength of about 700 nm to about 1000 nm.

20. A pellicle membrane for a lithographic apparatus, the pellicle membrane comprising a network of unaligned boron nitride and / or transition metal chalcogenide nanotubes.

21. The pellicle membrane of claim 20, wherein: The network comprises a three-dimensional porous network.

22. The pellicle membrane according to claim 20 or 21, wherein: The nanotubes are single-walled, double-walled, multi-walled and / or coaxial.

23. The pellicle membrane of claim 20 or 21, wherein: The pellicle membrane includes a single type of nanotube, or two or more types of nanotubes.

24. The pellicle membrane of claim 20 or 21, wherein: The pellicle membrane comprises carbon.

25. The pellicle membrane of claim 24, wherein: The transition metal is selected from Mo, W, Sb or Bi.

26. The pellicle membrane of claim 24, wherein: The chalcogenide is selected from S, Se or Te.

27. The pellicle membrane of claim 20 or 21, wherein: At least some of the nanotubes include a capping material.

28. The pellicle membrane of claim 27, wherein: The covering material is selected from metal oxides, silicon oxide and hexagonal boron nitride.

29. The pellicle membrane of claim 27, wherein: The thermal expansion coefficients of the nanotube material and the covering material are similar.

30. The pellicle membrane of claim 28, wherein The metal of the metal oxide is selected from the group consisting of aluminum, zirconium, yttrium, tungsten, titanium, molybdenum and hafnium.

31. The pellicle membrane of claim 20 or 21, wherein: The pellicle membrane includes coaxial nanotubes.

32. The pellicle membrane of claim 31 , wherein: The coaxial nanotube includes a core within a hydrogen etch resistant nanotube.

33. The pellicle membrane of claim 32, wherein: The coaxial nanotubes include a boron nitride nanotube, molybdenum disulfide, or tungsten sulfide shell surrounding the core.

34. The pellicle membrane of claim 20 or 21, wherein: The transition metal chalcogenide is tungsten disulfide or antimony telluride.

35. An optical element for a lithographic apparatus, a metrology tool or an inspection tool, the optical element comprising a pellicle membrane according to any one of claims 20 to 34.

36. The optical element according to claim 35, wherein The optical element is a pellicle membrane for particle suppression, a mirror, a reticle, or a spectral purity filter.

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