Pellicle membrane for lithographic apparatus

Abstract

To provide a pellicle which is able to withstand a harsh environment of a lithographic apparatus.SOLUTION: A pellicle membrane for a lithographic apparatus is provided which includes uncapped carbon nanotubes. A method of regenerating a pellicle membrane is also provided which includes decomposing a precursor compound and depositing at least some of the decomposition products on the pellicle membrane. A method of reducing the etch rate of a pellicle membrane is also provided which includes providing an electric field into the region of the pellicle membrane to redirect ions from the pellicle, or heating an element to desorb radicals from the pellicle, where the pellicle membrane is preferably a carbon nanotube pellicle membrane. An assembly for a lithographic apparatus is also provided which includes a biased electrode near or includes the pellicle membrane or heating means for the pellicle membrane.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Patent Application No. 19193590.7 filed on August 26, 2019, European Patent Application No. 19203575.6 filed on October 16, 2019, European Patent Application No. 19205058.1 filed on October 24, 2019, and European Patent Application No. 20161779.2 filed on March 9, 2020, each of which is incorporated by reference in its entirety into this specification.

[0002] The present invention relates to a pellicle membrane for a lithographic apparatus, a method for regenerating a pellicle membrane, a method for reducing the etch rate of a pellicle membrane, and an assembly for a lithographic apparatus. [Background technology]

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

[0004]

[0004] The wavelength of radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features that can be formed on the substrate. Lithographic apparatus using EUV radiation, which is electromagnetic radiation having a wavelength within 4-20 nm, can be used to form smaller features on a substrate than conventional lithographic apparatus, which can use electromagnetic radiation with a wavelength of, for example, 193 nm.

[0005]

[0005] A lithographic apparatus includes a patterning device (e.g. a mask or reticle). Radiation is provided through or reflected from the patterning device to form an image on a substrate. To protect the patterning device from airborne particles and other forms of contamination, a membrane assembly, also called a pellicle, may be provided. Contamination on the surface of the patterning device can cause manufacturing defects on the substrate.

[0006]

[0006] A pellicle may be provided to protect optical components other than the patterning device. A pellicle may be used to provide a passage for lithographic radiation between areas of the lithographic apparatus that are sealed from each other. A pellicle may be used as a filter, such as a spectral purity filter, or as part of a dynamic gas lock in the lithographic apparatus.

[0007]

[0007] The mask assembly may include a pellicle that protects the patterning device (e.g., mask) from particle contamination. The pellicle may be supported by a pellicle frame to form a pellicle assembly. The pellicle may be attached to the frame, for example, by gluing or otherwise attaching a pellicle boundary area to the frame. The frame may be permanently or removably attached to the patterning device.

[0008]

[0008] The presence of a pellicle in the path of the EUV radiation beam requires that the pellicle have a high EUV transmittance. High EUV transmittance allows a greater proportion of the incident radiation to pass through the pellicle, which may reduce the operating temperature of the pellicle by reducing the amount of EUV radiation absorbed by 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 still ensuring that it is strong enough to withstand the sometimes harsh environment within the lithographic apparatus.

[0009] It is therefore desirable to provide a pellicle that can withstand the harsh environment of a lithographic apparatus, particularly an EUV lithographic apparatus.

[0010]

[0010] Although this application refers to pellicles in the context of lithographic apparatus generally, and EUV lithographic apparatus in particular, it will be understood that the present invention is not limited to only pellicles and lithographic apparatus, and the subject matter of the present invention may be used in any other suitable apparatus or situation.

[0011]

[0011] For example, the method of the present invention may be equally applied to spectral purity filters. Some EUV sources, such as those that use 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 particularly in the deep UV (DUV) radiation range (100 to 400 nm). Furthermore, in some EUV sources, for example laser-produced plasma EUV sources, the radiation from the laser, typically at 10.6 microns, exhibits significant out-of-band radiation.

[0012]

[0012] Spectral purity is desired in lithographic apparatus for several reasons. One reason is that resist is sensitive to out-of-band wavelengths of radiation, which can degrade the image quality of the pattern applied to the resist if the resist is exposed to such out-of-band radiation. Furthermore, out-of-band infrared radiation, for example the 10.6 micron radiation in some laser-produced plasma sources, can cause unwanted and unnecessary heating of the patterning device, substrate, and optical components in the lithographic apparatus. Such heating can cause damage, reduced lifetime of these elements, and / or defects or distortions in the pattern projected and applied to the resist-coated substrate.

[0013]

[0013] A typical spectral purity filter may be formed from a silicon base structure (e.g. a silicon grid with apertures, or other member) that is coated with a reflective metal, such as molybdenum. In use, a typical spectral purity filter may be subjected to high heat loads, for example from incident infrared and EUV radiation. This heat load may cause the temperature of the spectral purity filter to exceed 800°C. Under high head loads, the coating may spall due to differences in the linear expansion coefficient between the reflective molybdenum coating and the underlying silicon support structure. The spalling 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 suppress debris (e.g. debris such as particles) from entering or leaving certain parts of the lithographic apparatus. Thus, a spectral purity filter may be used as a pellicle, and vice versa. Thus, any reference in this application to a "pellicle" is also a reference to a "spectral purity filter". Although this application primarily refers to a pellicle, all of its features are equally applicable to a spectral purity filter.

[0014]

[0014] It is also desirable to improve the lifetime of optical elements in a lithographic apparatus, such as components of a collector mirror, a pellicle, or a dynamic gas lock. During use, these optical elements are exposed to the harsh environment of the lithographic apparatus, which can cause damage over time. It is desirable to prevent, reduce, or eliminate damage to the optical elements.

[0015]

[0015] In a lithographic apparatus (and / or method), it is desirable to minimise intensity loss of the radiation being used to apply a pattern to a resist-coated substrate. One reason for this is that ideally as much radiation as possible should be available to apply the pattern to the substrate, for example to reduce exposure times and increase throughput. At the same time, it is desirable to minimise the amount of undesired radiation (e.g. out-of-band radiation) that passes through the lithographic apparatus and is incident on the substrate.

[0016]

[0016] Furthermore, it is important that the spectral purity filters and / or pellicles used in the lithographic method or apparatus have a sufficient lifetime and are able to withstand the high thermal or radiation loads to which they may be exposed, and / or the high levels of hydrogen and corresponding activated species (including radicals including H* and HO*, as well as H + , H 2 + and H 3 + It is desirable to ensure that the spectral purity filter and / or pellicle do not degrade exponentially over time as a result of environmental influences such as ions including . It is therefore desirable to provide improved (or alternative) spectral purity filters and / or pellicles, or to adapt the lithographic apparatus and / or method to make the environment less aggressive to the pellicle and / or spectral purity filter.

[0017]

[0017] The present invention has been devised in an attempt to address at least some of the problems identified above. Summary of the Invention

[0018] According to a first aspect of the present invention, there is provided a pellicle membrane for a lithographic apparatus comprising decapped carbon nanotubes.

[0019]

[0019] In use, the pellicle film is in the direct optical path of radiation, such as EUV radiation used in lithography equipment. This, together with operation at low ambient pressure, results in the film reaching high temperatures that can exceed 600°C. This can promote chemical and structural degradation of the pellicle film that can result in loss of imaging performance or even damage to 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. Continuous film pellicles provided with emissive layers typically have operating temperatures in the range of 400-650°C in EUV lithography equipment where the EUV power source is in the range of 150-300W (at the intermediate focus), with higher temperatures being expected with higher power sources. Also, a capping layer may be provided that retards or prevents chemical degradation of the pellicle film. To maintain acceptable transmittance and infrared (IR) emissivity of the pellicle, the one or more luminescent metal or conductive layers are thin. However, metal films deposited on inert substrates are energetically unfavorable. Heating a thin metal film coated on top of an inert (non-metallic) substrate can result in thermal instability at temperatures well below the melting point of the metal. If sufficient activation energy is provided, the film will form pores through a surface diffusion process, which grow over time at a rate that is strongly temperature dependent. When the pores coalesce, the material on the surface forms irregularly shaped islands. This process is called dewetting and island formation. Although dewetting and island formation can be suppressed by providing an adhesion layer between the metal film and the substrate, the metal film is still energetically unfavorable. A thin metal layer coated on a pellicle loses its emissivity properties once it breaks into islands, making it useless.

[0020] It has now been found that pellicle membranes containing decapped carbon nanotubes are suitable for use in lithography tools, particularly EUV lithography tools, particularly where EUV plasma induced carbon etching can be sufficiently suppressed. 2Due to the possibility of carbon etching and damage of carbon nanotubes (CNTs) in plasma environments, only carbon nanotubes with a capping layer have been considered. However, it is not suitable to cap carbon nanotubes with a material resistant to hydrogen plasma to provide EUV plasma resistance and to use them as a pellicle membrane in a lithography tool. Capping of carbon nanotubes is also undesirable as it reduces the transmittance compared to nanotubes with the cap removed.

[0021]

[0021] The decapped carbon nanotube-based pellicle may further include a plurality of nanoparticles. In contrast to conformal coatings or capping layers, the nanoparticles are not susceptible to dewetting or island formation, so the transmittance and emissivity of the pellicle are not affected during use. Also, the nanoparticles are not as energetically disadvantaged as the corresponding metal thin film, so they are more stable during use. It is also natural that the EUV scattering and absorption by a nanoparticle submonolayer is less than that by a conformal or partially conformal layer of comparable thickness applied to the nanotube.

[0022]

[0022] The nanoparticles are preferably associated with the carbon nanotubes. Thus, the nanoparticles are attached to the nanotubes rather than detached from them. It is desirable to avoid contamination of the lithography apparatus, in particular optical elements such as mirrors and reticles, so it is desirable that the nanoparticles cannot be easily removed from the pellicle membrane.

[0023]

[0023] The nanoparticles may be disposed on the surface of the carbon nanotube. The nanoparticles may be disposed within the carbon nanotube. The nanoparticles may be disposed both on the surface of the nanotube and within the nanotube.

[0024]

[0024] The nanoparticles can be attached to the surface of the carbon nanotubes by any suitable method, but the invention is not particularly limited by the selected method. The method used to generate the carbon nanotube-nanoparticle structure can be, for example, based on so-called wet chemistry or based on physical vapor deposition. In the wet chemistry method, the surface of the nanotube can be functionalized, and then the nanocrystals can be assembled on the nanotube by covalent, non-covalent, or electrostatic interactions. In the physical vapor deposition, the nanoparticles can be attached to the nanotube by physical adsorption.

[0025]

[0025] Similarly, any suitable technique for providing nanoparticles within the nanotubes may be used, and the invention is not particularly limited to the technique used. One technique is incipient wetness impregnation, in which a metal salt precursor solution is introduced into the nanotubes and then reduced with hydrogen. A calcination step may also be required.

[0026]

[0026] The mechanism of carbon etching in EUV lithography tools has been found to be a two-component process. Specifically, hydrogen ions (e.g., H + , H 3 + ) and hydrogen radicals H* are both required to etch carbon. Without wishing to be bound by scientific theory, it is believed that the carbon-carbon bonds in the nanotubes can be broken by energetic hydrogen ions. The broken bonds can be passivated by dissolution or adsorbed hydrogen radicals. If passivation does not occur, the bonds can be restored. It is believed that the addition of nanoparticles increases the recombination rate of the adsorbed hydrogen radicals, thus decreasing the likelihood that the broken carbon-carbon bonds will be passivated by hydrogen radicals. Thus, the rate at which the carbon nanotubes are etched is reduced.

[0027]

[0027] For example, in embodiments where carbon nanotubes are decorated with nanoparticles, adatom hydrogen can diffuse along the carbon nanotube. The atomic hydrogen can recombine into molecular hydrogen and degas as hydrogen gas, or it can passivate broken carbon bonds, ultimately resulting in degassing of hydrocarbons. Because atomic hydrogen recombination occurs more rapidly on nanoparticles than on nanotubes, the presence of nanoparticles increases the hydrogen recombination rate, thereby slowing the rate at which broken carbon bonds are passivated and slowing the rate at which the nanotube is etched.

[0028]

[0028] It has been found that the presence of nanoparticles inside the nanotubes also serves to increase the recombination rate of atomic hydrogen to molecular hydrogen. Atomic hydrogen adsorbed on the outer surface of the CNT can pass through the graphene or graphene-like membrane (of chiral CNTs) by hopping / diffusion and eventually reach the nanoparticles decorating the inner surface of the CNT. Again, without wishing to be bound by scientific theory, it is believed that the presence of nanoparticles increases the recombination rate of adsorbed atomic hydrogen, albeit within the nanotube. A further advantage of this embodiment is that since it is almost impossible to remove the nanoparticles from the nanotubes, there is little risk that the nanoparticles will be released from the pellicle membrane and contaminate other parts of the lithography apparatus.

[0029]

[0029] Nanotube containing (EUV) pellicle membranes may form a gas-permeable mesh. Pellicle membranes are generally very thin free-standing membranes that are prone to deformation when there is a pressure difference between the two sides of the membrane. Even a small pressure difference can cause deformation of the pellicle membrane. Other pellicle membranes include a free-standing film that is substantially gas impermeable. In contrast, one embodiment of the present invention provides a gas-permeable pellicle membrane, which prevents deformation of the membrane by preventing a pressure difference between the two sides of the membrane.

[0030]

[0030] The carbon nanotubes may be single-walled or multi-walled. The pellicle membrane may comprise single-walled nanotubes, multi-walled nanotubes, or a combination thereof. Preferably, the pellicle membrane comprises single-walled nanotubes.

[0031]

[0031] The diameter of the nanoparticles may be from about 1 nm to about 100 nm. Preferably, the diameter of the nanoparticles is from about 5 nm to about 25 nm. The diameter of the nanoparticles is preferably measured by transmission electron microscopy. It will be understood that other measurement techniques may also be used. The diameter of any nanoparticle disposed within a carbon nanotube will depend on the inner diameter of the nanotube. Thus, the diameter of any internal nanoparticle may be equal to or less than the inner diameter of the nanotube in which it is disposed.

[0032]

[0032] The diameter of the nanoparticles does not necessarily have to be the same for each nanoparticle in the nanoparticle population. Thus, some nanoparticles may be larger or smaller than others. In an embodiment, the average diameter of the nanoparticles is about 1 nm to about 100 nm, preferably about 5 nm to about 25 nm.

[0033]

[0033] Such nanoparticle sizes are advantageous because they suppress imaging distortions through refraction and attenuation of EUV radiation.

[0034]

[0034] The diameter of the nanoparticles is preferably less than half the critical dimension of the corresponding reticle pattern. Thus, preferably none or substantially none of the nanoparticles have a diameter larger than half the critical dimension of the corresponding reticle pattern. When the nanoparticles are transferred from the pellicle membrane to the reticle, the effect on the patterning is not adversely affected if the nanoparticles are smaller than about half the critical dimension of the reticle to which they are transferred. Current technology prefers nanoparticles with a diameter of about 10 nm or less. As the critical dimension shrinks, the size of the nanoparticles needs to shrink.

[0035]

[0035] The average distance between adjacent nanoparticles may be greater than the diameter of the nanoparticles, for example, if the diameter of the nanoparticles is 10 nm (as measured by TEM), then the average distance between adjacent nanoparticles is preferably greater than 10 nm.

[0036]

[0036] The average distance between adjacent nanoparticles may be about 1 to about 50 times the diameter of the nanoparticles. The average distance between adjacent nanoparticles may be about 10 times or more the diameter of the nanoparticles. Slightly shorter average distances may be acceptable.

[0037]

[0037] Because nanoparticles will slightly reduce the permeability of the pellicle membrane, it is desirable to balance the advantage of increased atomic hydrogen recombination with the disadvantage of reduced permeability. By spreading the nanoparticles over the pellicle membrane, the reduction in permeability is managed while still maintaining the protective properties of the nanoparticles. Also, spreading the nanoparticles also inhibits or prevents the aggregation of nanoparticles, which can lead to an increase in particle size and reduced permeability.

[0038]

[0038] The nanoparticles preferably comprise a material that has a higher hydrogen recombination coefficient than the nanotubes. The recombination coefficient of nanoparticles is preferably from about 0.1 to about 1. The recombination coefficient is the fraction of adatoms that form molecules before leaving the surface. Thus, a figure of 1 indicates that all of the adatoms form molecules before leaving the surface, whereas a figure of 0.1 indicates that about 10% form molecules before leaving the surface. The recombination rate of carbon nanotubes is about 10 -3 , which is the same as for graphene or amorphous carbon. When the recombination rate of nanoparticles is greater than that of carbon nanotubes, the more rapid binding of adatom hydrogen limits the possibility of passivating broken carbon-carbon bonds.

[0039] The nanoparticles may comprise a metal, a metal oxide, a doped metal, an alloy, or a combination thereof.

[0040]

[0040] The nanoparticles may include Nb, Mo, Ru, Rh, Pt, Pd, W, Cr, Ni, Fe, Co, Ag, Au, Zr, Y, and combinations thereof.

[0041]

[0041] The nanoparticles may additionally contain O, N, B, Si, C, H, P, S, Cl, and combinations thereof.

[0042]

[0042] Thus, the nanoparticles may 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.

[0043]

[0043] The nanoparticles may include composite materials. In other words, the nanoparticles may be composite nanoparticles. Thus, there may be two or more different materials forming the nanoparticles. Some materials may act to increase the recombination rate of adatom hydrogen, while other materials may help improve the bonding with the CNTs.

[0044]

[0044] Because these materials (at least the metallic phase of the nanoparticles) have a much higher recombination rate than carbon, nanoparticles containing such materials serve to extend the lifetime of carbon nanotube pellicle films by reducing the rate at which carbon-carbon bonds are passivated by adatom hydrogen.

[0045] The surface density of the nanoparticles may be greater than about 500 particles per square micron, preferably greater than about 1000 particles per square micron.

[0046]

[0046] Too few nanoparticles would mean that at least a portion of the carbon nanotube would not be substantially protected from atomic hydrogen passivation, so that while the portion of the carbon nanotube close to the nanoparticle would be protected, the portion of the carbon nanotube that is too far away from the nanoparticle would not be protected.

[0047]

[0047] Additionally or alternatively, the decapped carbon nanotubes may be passivated. The passivation may be chemical passivation. The decapped carbon nanotubes may be altered by chemisorption of chemical species to the nanotube surface. The surface alteration may be by chemisorption (as opposed to physisorption) or by reaction of species with the carbon nanotube surface via processes such as nitridation, oxidation, or halogenation. Hydrogenation is explicitly excluded as this would have the opposite effect to that expected, possibly by facilitating the etching process. Thus, intentional hydrogenation of the carbon nanotubes is undesirable. It will be appreciated that the pellicle membrane may be hydrogenated in use by the environment in the EUV lithography apparatus, but this hydrogenation is an undesirable side effect of the manner in which the apparatus operates. Passivation may also be achieved by adding strontium, boron, beryllium, or silicon atoms to the surface of the carbon nanotubes.

[0048]

[0048] This approach differs from applying coatings to the surface of carbon nanotubes because it involves chemical modification of the surface of the carbon nanotubes themselves, i.e. no interfacial layer is formed, and there is no delamination effect due to different thermal expansion coefficients, as seen in systems containing coated carbon nanotubes.

[0049]

[0049] Without wishing to be bound by scientific theory, it is believed that alteration of the nanotube surface mitigates etching by the plasma through several mechanisms. The atoms attached to the surface of the carbon nanotube protect the nanotube carbon atoms from bombardment by the etching ions, which in the case of EUV-induced hydrogen plasma are mainly hydrogen ions. The surface atoms must be etched first, which creates a recovery time or delay before the carbon atoms are etched. There may also be other mechanisms that protect the carbon nanotubes. It will be appreciated that although the surface atoms may be etched, the pellicle membrane may be repaired by repassivating the surface. This may be achieved by the method according to the second aspect of the invention.

[0050]

[0050] Preferred surface modifications are oxidation, nitridation and halogenation. Halogenation is preferred, with fluorination and chlorination due to the strength of the carbon-halogen bond, especially the carbon-fluorine bond. Thus, there is provided a pellicle membrane for a lithographic apparatus, comprising decapped carbon nanotubes, where at least a portion of the surface of the decapped carbon nanotubes is chemically passivated. Preferably, the chemical passivation includes nitridation, oxidation and / or halogenation. The chemical passivation does not include hydrogenation. Alternatively or additionally, the surface may be modified by the addition of strontium, boron, beryllium and / or silicon atoms.

[0051] In an embodiment, the decapped carbon nanotube is doped with atoms other than carbon. Preferably, the decapped carbon nanotube is doped with one or more of nitrogen, boron, and silicon. Doping of the core carbon nanotube structure involves the incorporation of foreign atoms into the core structure. Defects in the carbon nanotube structure, which may be naturally present or may be created intentionally, can be filled with atoms other than carbon, such as nitrogen, boron, or silicon.

[0052]

[0052] Pellicles containing carbon nanotubes modified to include additional nitrogen, boron, and / or silicon in their core structure reduce their susceptibility to etching by hydrogen ions and radicals due to changes in chemical bonding states that alter their reactivity. Nanotubes are also metallic regardless of chirality or number of walls. This increases the emissivity of the nanotubes, which in turn increases the life of the pellicle by lowering the operating temperature of the pellicle for a given power. The nanotubes may also be physically stronger than nanotubes that contain defects in their core structure.

[0053]

[0053] A layer of aerogel may be applied to one or both sides of the pellicle membrane. Aerogel is a material with very high porosity and very low density. The porosity of aerogel may be greater than 95%, greater than 97%, greater than 99%, or even up to 99.9%. The density is 0.01 g / cm 3 It may be less than.

[0054]

[0054] Due to its very high porosity and density, aerogel has a high EUV transmittance. Because aerogel does not significantly reduce the transmittance of the pellicle film due to its high EUV transmittance, it can provide a protective layer for carbon nanotubes and act as a barrier between hydrogen plasma and the carbon nanotube-based pellicle film. Due to the high porosity of aerogel, the pressure difference between both sides of the pellicle film is avoided.

[0055]

[0055] Aerogels may contain niobium, molybdenum, or zirconium, which materials are resistant to the hydrogen plasma environment inside the lithographic apparatus.

[0056]

[0056] The or each aerogel layer may have a thickness of less than 2 microns, less than 1 micron, or less than 0.5 microns.

[0057] Thus, according to a further aspect of the present invention there is provided an optical element for use in a lithographic apparatus comprising an aerogel.

[0058]

[0058] The optical element may be a pellicle membrane, a mirror, a reticle, or a spectral purity filter. The optical element may be located at an intermediate focus position to prevent or inhibit the transfer of contaminants from one part of the lithographic apparatus to another.

[0059]

[0059] The optical element may include a pellicle membrane according to any aspect of the present application.

[0060]

[0060] According to a second aspect of the present invention, there is provided a method for regenerating and / or conditioning a pellicle membrane, the method comprising decomposing a precursor compound and depositing at least a portion of the decomposition products on the pellicle membrane.

[0061]

[0061] As described above, carbon nanotubes are etched by hydrogen in a lithography apparatus. During the etching process, carbon atoms are removed from the carbon nanotubes as hydrocarbons. Over time, the removal of carbon from the nanotubes can weaken the pellicle membrane, resulting in the formation of particles or damage to the pellicle membrane. By providing and decomposing precursor compounds to generate decomposition products, the decomposition products can repair any damage to the pellicle membrane, thereby extending its lifespan.

[0062]

[0062] The precursor may be a hydrocarbon. When the hydrocarbon is decomposed in the lithography apparatus, it is decomposed into carbon and hydrogen. If the pellicle film contains carbon nanotubes, the carbon resulting from the decomposition can repair the damage to the nanotubes. It is understood that the pellicle may be etched and release hydrocarbons, but these are in low concentration, so that the supply of additional hydrocarbons will approximately balance the rate at which carbon is redeposited on the pellicle film with the rate at which carbon is etched from the pellicle. It will be understood that if the rate at which carbon is etched from the pellicle film is the same as the rate at which carbon is redeposited, the pellicle may have a significantly longer life. The rate and amount of hydrocarbons that are introduced into the lithography apparatus will vary depending on the operating conditions in the lithography apparatus, such as the power level at which the apparatus is operating and the partial pressure of hydrogen present in the apparatus. It is possible to adjust the rate and amount of hydrocarbons that are introduced to balance the etching of the carbon nanotube pellicle. It will also be understood that this method does not necessarily take place in the lithography apparatus, but can be performed outside the lithography apparatus. Thus, the method may be performed as a pre-conditioning step before the pellicle is used in a lithographic apparatus, or may be performed after the pellicle has been used in a lithographic apparatus to repair damage caused to the pellicle during use.

[0063]

[0063] The hydrocarbons may be saturated or unsaturated. They may be C1-C4 hydrocarbons or aromatic (C6 or higher) or cyclic (C5 or higher) hydrocarbons and may contain any of N, O, B, P, and Cl. Ethene or ethyne may be used as the hydrocarbon. Unsaturated hydrocarbons may be advantageous because they have a higher carbon to hydrogen ratio than saturated hydrocarbons.

[0064]

[0064] Hydrocarbons can be decomposed into carbon and hydrogen by EUV radiation. Hydrocarbons can also be decomposed by other means and decomposition should not be considered solely due to EUV radiation exposure. Short chain hydrocarbons may be preferred as they are less likely to deposit and adhere to surfaces other than the pellicle in the lithography tool and cause a lasting partial loss of reflectivity of the optical components. Ultimately, once the injection of the hydrocarbons is terminated, such carbon rich layers are decomposed by EUV H. 2 It is cleaned by plasma.

[0065]

[0065] The precursor compound may be supplied continuously or intermittently. A continuous supply of the precursor compound may be used when there is a consistent etch rate of the pellicle film, while a continuous addition of the hydrocarbon provides a steady state for the pellicle film when the rate at which carbon is etched from the pellicle is substantially the same as the rate at which carbon is deposited on the pellicle film. The precursor compound may be supplied intermittently such that additional hydrocarbon material is present only for a certain period of time, so that the throughput of the lithography apparatus is not adversely affected, while the throughput may be temporarily reduced by deposition of the opaque carbon layer on some optical elements.

[0066]

[0066] The amount of precursor compound may be adjusted depending on one or more of the etch rate of the pellicle film, the operating power of the lithography apparatus in which the pellicle film is placed, and the operating life of the pellicle film.For example, when the etch rate of the pellicle is high, which may be the case when the apparatus is operating at high power, a larger amount of precursor compound may be introduced to offset the higher etch rate.When the apparatus is operating at lower power, the amount of precursor compound introduced may be reduced to avoid undesired deposition of carbon on the pellicle film or other areas of the apparatus.

[0067]

[0067] The method may include directing a precursor compound to a pellicle film or at least locally in a reticle mini environment (RME) coupled to a scanner environment. Because the precursor compound is intended to decompose and repair the pellicle film, it is desirable to preferentially deposit carbon generated by decomposition on the pellicle film rather than on other areas of the device. Thus, directing a flow of the precursor compound to the pellicle film increases the likelihood that carbon will be deposited on the pellicle film.

[0068] In an embodiment of the second aspect of the present invention, there is provided a method of conditioning and / or repairing a carbon nanotube pellicle film, the method comprising annealing the carbon nanotube pellicle film in a hydrocarbon-containing atmosphere.

[0069]

[0069] Annealing in a hydrocarbon-containing atmosphere results in repair of dangling bonds and exchange of hydrogen bonded to carbon defect sites with carbon from the hydrocarbon atmosphere. Annealing may be performed at a temperature of about 700-900K. It will be understood that other temperatures may be used as required. Annealing in a hydrocarbon atmosphere may be referred to as reactive annealing. It will be understood that decomposition of the hydrocarbon precursor takes place during this reactive annealing step. The hydrocarbon-containing gas may be ionized to form a plasma. Ionization into a plasma increases the reaction rate, allows the use of lower temperatures, and improves reaction selectivity.

[0070]

[0070] The method of the second aspect of the present invention may further comprise a vacuum annealing step, optionally before and / or after the step of annealing in a hydrocarbon-containing atmosphere.

[0071]

[0071] The method may also include a reductive annealing step. The reductive annealing step may be performed before and / or after the reactive annealing step. The reductive annealing may be performed in a reducing gas, such as hydrogen. The reductive annealing step removes loosely bound amorphous carbon deposits and other contaminants, such as seed nanoparticles remaining from the carbon nanotube growth process.

[0072]

[0072] Preferably, the final annealing step is a vacuum annealing step or a reducing annealing step to avoid transient effects during exposure in the scanner environment, which is highly reducing due to the presence of EUV radiation and hydrogen plasma and ions. The pellicle membrane of the method of the second aspect of the invention may be a pellicle membrane according to any other aspect of the invention, in particular according to the first aspect.

[0073]

[0073] In an exemplary method, the following steps are performed: 1. Vacuum annealing or reduction annealing, 2. Reactive annealing in a hydrocarbon environment; 3. Optionally repeating steps 1 and 2; and 4. Vacuum annealing or reduction annealing. This exemplary method is useful for pellicle films that have not yet been exposed to a scanner environment. For pellicle films that have already been exposed to a scanner environment, the method may be modified to begin with a reactive annealing step rather than a passive or reductive healing step.

[0074]

[0074] Even if a reactive annealing step is not included during the manufacture of a carbon nanotube pellicle film, a vacuum annealing step and / or a reduction annealing step may be present prior to exposing the pellicle in a scanner environment. Thus, a method of conditioning a pellicle film is provided that includes vacuum annealing and / or reduction annealing the pellicle film prior to use in a lithography apparatus.

[0075]

[0075] Any of the foregoing annealing steps may be carried out at a temperature of about 700K to about 900K.

[0076]

[0076] Heating of the pellicle membrane during annealing may be performed by any suitable means. For example, the pellicle membrane may be conductively and / or convectively heated by exposure to hot gas. The pellicle membrane may be heated by passing an electric current through the pellicle membrane. The pellicle membrane may be heated by laser heating. A combination of the various heating methods is also conceivable.

[0077] According to a third aspect of the present invention, there is provided a method of reducing the etch rate of a pellicle, comprising providing one or more bias elements proximate or in a region of the pellicle. The bias is with respect to the grounded vacuum vessel of the lithographic apparatus in which the pellicle is located. The bias redirects the flux of positive ions away from the pellicle. Preferably, any or most of the bias elements have a negative potential with respect to the (grounded) scanner vacuum vessel to avoid raising the EUV plasma potential which may be harmful to EUV optics. Thus, while the relative bias of the pellicle or other elements may be positive, the absolute potentials are preferably all negative to limit the rise in plasma potential.

[0078]

[0078] Because the plasma contains positively charged hydrogen atoms, applying an appropriate bias / electric field will redirect the flux of etching ions away from the pellicle. The reduced flux of etching ions will increase the life of the pellicle membrane. The pellicle membrane may be a carbon nanotube pellicle membrane, but this method may be used with other pellicle membrane materials as well.

[0079]

[0079] The method may include biasing the pellicle membrane with respect to the reticle (front surface) and / or the ReMa blades and / or the UNICOM. The ReMa blades are part of the Reticle Masking Unit (REMA), a shutter system that includes four independently moving masking blades. The REMA unit uses (metallic) blades to block light from specific areas of the reticle. Of these blades, two Y-blades are oriented in the scan direction, while two X-blades are perpendicular to the scan direction. The UNICOM is an optical filter whose function is to adjust the illumination near the reticle to ensure slit uniformity. The filter generally includes two movable plates that can move along the Y-scan axis to adjust the illumination. By biasing the pellicle membrane with respect to the nearest surface or surfaces (e.g., by applying an absolute negative potential or applying a positive bias between the pellicle and another electrode with respect to each other), the flux of hydrogen ions toward the pellicle is reduced / redirected, as is the flux of positive hydrogen ions that etches the pellicle membrane. The method may alternatively or additionally include relative biasing of surfaces other than the pellicle, such as, for example, biasing or relative biasing of the reticle (front) and / or ReMa blades and / or UNICOM, to extract ions generated in the EUV cone before they reach the pellicle, while the pellicle remains floating or grounded. Absolute positive potential electrodes may be used in the reticle mini environment, but such potentials may increase the plasma potential and ion energy near the sensing components, so in such embodiments, additional measures may be required for protection of such components.

[0080] According to a fourth aspect of the present invention, there is provided an assembly for a lithographic apparatus, comprising a biased pellicle membrane and / or other surface in a RME. The other surface may be a reticle front surface, a ReMa blade or a UNICOM or a Y nozzle. The Y nozzle is a nozzle for purge gas supply directed in a scanning direction along the reticle. Alternatively or additionally, the pellicle membrane and / or the reticle front surface are floating, while the ReMa blade and / or the UNICOM are negatively biased with respect to a grounded vacuum vessel wall.

[0081]

[0081] Preferably, the absolute potential applied to any of the electrodes in the RME is limited to be negative or below +50V to avoid raising the EUV plasma potential, otherwise the EUV optics may be affected by too energetic ions. The absolute potential applied to the surfaces in the RME may be about -500V or less, preferably about -250V or less, more preferably about -50V or less. The bias is kept relatively low to avoid sparks. Sparks may discharge a capacitor (e.g., pellicle / reticle masking unit or pellicle / reticle) by gas ionized by EUV absorption. A single spark may damage or at least cause defects in the pellicle membrane. Even at a relatively low voltage, such a bias is sufficient to repel most of the ions brought close to the pellicle by each EUV flash. Also, limiting the bias of the pellicle to the nearest electrode to 100V or less limits the electrostatic voltage acting on the pellicle. This avoids undesired bending or breaking of the pellicle membrane.

[0082]

[0082] The bias source may be current limited and / or pulsed, preferably with the bias pulse synchronized to the EUV flash.

[0083]

[0083] The pellicle membrane may be biased relative to one or more of the reticle masking unit, the reticle, the UNICOM, or any other electrodes in the reticle mini environment, including an auxiliary ground electrode.

[0084]

[0084] The assembly may include a reticle masking unit including a first blade and a second blade, where an electrical bias is provided between the first and second blades or between the blades and the grounded vacuum vessel. The UNICOM may be biased. The Y-nozzle may be biased. The (floating) pellicle may follow the bias of the blades or the Y-nozzle due to extraction of photoelectrons or via capacitive coupling.

[0085]

[0085] At least one auxiliary ground electrode may be provided which prevents the field lines from spreading too far and therefore can prevent sparks in the lithographic apparatus which may damage components in the apparatus such as the pellicle.

[0086] According to a fifth aspect of the present invention there is provided a pellicle arrangement for a lithographic apparatus comprising a pellicle membrane and a pellicle heating means.

[0087] It will be appreciated that in normal operation of an EUV lithography apparatus the pellicle membrane will be heated by the EUV radiation beam. The present invention provides a heating means which is in addition to the heating provided by EUV radiation or other radiation for lithography purposes.

[0088]

[0088] As described herein, etching of carbon-based pellicle films is a two-component process that requires both hydrogen ions and hydrogen radicals. Hydrogen ions break carbon-carbon bonds in the pellicle film with sufficient energy, and the broken carbon-carbon bonds can then be passivated by the adsorbed hydrogen radicals. Previously, pellicles have been designed and engineered to reduce the operating temperature of the pellicle film in an attempt to extend the life of the pellicle film. As part of this, an additional emissive layer was added to the pellicle to increase the emissivity of the pellicle, thereby lowering the operating temperature of the pellicle film at a given power. Surprisingly, it has been found that, contrary to this, heating the pellicle material can extend the operating life of pellicles, particularly carbon-based pellicles such as carbon nanotube pellicles. Without wishing to be bound by scientific theory, it is believed that the concentration of adatom hydrogen can be significantly reduced by increasing the temperature of the pellicle film. Since the adsorption of hydrogen on graphene-like structures such as the surface of carbon nanotubes is exothermic (typical of a condensation-like process), heating of the pellicle film results in a lower amount of adatom hydrogen (which can be treated as an evaporation-like process). The concentration of adatom hydrogen at 300 K (approximately room temperature) is many orders of magnitude (approximately 10) lower than the concentration of adatom hydrogen at 1300 K if the flux / concentration of H* near the pellicle is kept constant. 9 ) is estimated to be large. By reducing the concentration of adatom hydrogen, the likelihood of broken carbon-carbon bonds becoming passivated is reduced, and the etch rate of the pellicle is also reduced.

[0089]

[0089] The heating means may be configured to heat a predetermined portion of the pellicle membrane. As mentioned above, etching is caused by hydrogen radicals and hydrogen ions. In the reticle mini environment of the lithography apparatus, which is the area surrounding the pellicle, the radiation beam used for lithography, typically an EUV radiation beam, generates hydrogen ions and hydrogen radicals. Radicals can propagate further than ions, since they do not recombine as easily, whereas ions recombine after one collision with the wall of the apparatus. Since ions are considered to be the main cause of carbon-carbon bond cleavage, it is advantageous to reduce the concentration of adatom hydrogen in the area of ​​the pellicle membrane where the ions interact with the pellicle membrane. Since this is not the entire pellicle membrane, additional heat can be provided only to selected parts of the pellicle membrane.

[0090]

[0090] A given portion of the pellicle membrane may be the portion exposed to the highest hydrogen ion flux. As mentioned above, since etching is considered to be a two-component process, heating the pellicle in the area exposed to the highest ion flux reduces the concentration of adatom hydrogen in the heated region, which in turn reduces the etch rate of the pellicle membrane. It is understood that it is most important to heat the pellicle membrane when both atomic hydrogen and hydrogen ions are present, but it is of course possible to heat a larger percentage or even the entire pellicle membrane.

[0091]

[0091] The heating means may include one or more lasers. The lasers may operate in the visible or infrared spectrum. In fact any frequency that results in heating of the pellicle film may be used. Any number of laser beams may be used. The laser beams may be directed to the area of ​​the pellicle film to be heated. There may be one or more optical elements that direct the laser light to the pellicle film. The one or more optical elements may reflect, refract or diffract the incident laser light onto the pellicle film. The one or more optical elements may be on the blades of the reticle masking unit. The laser light is preferably in the visible and / or IR range, because light of such wavelengths is already present in the lithographic apparatus, so no light with "new" wavelengths is incident on the apparatus that needs to be considered. Another advantage of using VIS or IR radiation is that it does not grow resist and therefore tolerates some scattering towards the substrate.

[0092]

[0092] The heating means may include one or more resistive heating elements. Resistive heating elements rely on the passage of an electric current through a material. As the pellicle membrane preferably comprises carbon nanotubes, these carbon nanotubes may act as the resistive heating elements. Thus, a current source may be attached to the pellicle membrane, and the electric current passing through the membrane will heat it up and drive off adatom hydrogen.

[0093]

[0093] Conductive strips may be provided to distribute the current to at least a portion of the pellicle membrane. Carbon nanotubes are highly conductive along their length, resulting in high electrical resistance between adjacent nanotubes. Therefore, to distribute the current to the pellicle membrane more efficiently, conductive strips may be provided to distribute the current to the pellicle membrane. In contrast, a single electrical connection to the pellicle membrane may result in non-uniform distribution of the current. It will be understood that the conductive strips may be configured to direct the current to a particular portion of the pellicle membrane, preferably the portion exposed to the highest hydrogen ion flux.

[0094]

[0094] The pellicle film preferably comprises carbon nanotubes. Preferably, the pellicle film is a pellicle film according to any of the aspects of the present invention. Carbon nanotubes can withstand temperatures of 1000°C or higher and are therefore not damaged by elevated temperatures. The pellicle film according to the present invention may also be configured to increase the recombination rate of adatom hydrogen, so that additional heat of the pellicle film can be used in combination to further reduce the etch rate of the pellicle film. The method and apparatus for reducing hydrogen ion flux may also be used in combination with heated pellicles and / or pellicles containing nanoparticles.

[0095] According to a sixth aspect of the present invention there is provided a method of extending the operational life of a pellicle membrane, the method comprising selectively heating an area of ​​the pellicle membrane.

[0096]

[0096] Similar considerations apply to the sixth aspect of the invention as they apply to the fifth aspect. Heating an area of ​​the pellicle membrane reduces the concentration of adatom hydrogen and thus reduces the etch rate of the pellicle membrane. It will be understood that the pellicle membrane will be heated by the (EUV) light used for lithography itself, and that the heating described herein is in addition to the normal heating.

[0097]

[0097] The method may include heating the areas of the pellicle membrane that are exposed to the highest hydrogen ion flux during operation. It is possible to heat the entire pellicle membrane, but it is most important to heat the areas of the pellicle that are exposed to the highest hydrogen ion flux, which is where most etching occurs.

[0098]

[0098] Heating may be effected by directing a laser beam onto the pellicle membrane. The laser beam is preferably in the visible or IR range. A laser beam has the advantage that its power can be easily adjusted and the laser light can be precisely directed onto the desired area of ​​the pellicle membrane.

[0099]

[0099] The laser light may be directed by one or more optical elements. Since it may not be possible to fire the laser directly at the pellicle membrane, optical elements may be provided that direct the laser light onto the desired area of ​​the pellicle membrane.

[0100] [000100] Alternatively or additionally, the additional heat may be provided by passing an electric current through the pellicle membrane or otherwise. The electric current causes the pellicle membrane to heat up, which reduces the concentration of adatom hydrogen. The electric current can be varied to provide different amounts of additional heat. Electric current can also be supplied to selected portions of the pellicle membrane to cause heating in areas exposed to the highest hydrogen ion flux.

[0101] [000101] The pellicle membrane used in this aspect of the invention may be a pellicle membrane described in any of the aspects of the invention. Also, the method of the sixth aspect may be combined with the apparatus and method of any of the other aspects described herein.

[0102] [000102] According to a seventh aspect of the present invention there is provided a pellicle membrane for a lithographic apparatus comprising a network of non-aligned nanotubes.

[0103] [000103] Non-aligned nanotubes are sometimes referred to as randomly aligned nanotubes. A network of random nanotubes has porosity. Porosity enhances EUV transmission by lowering EUV absorption, resulting in high scanner throughput. Porosity also suppresses the increase in pressure difference between the two sides of the pellicle. Thus, the pellicle deflects less during venting and pumping operations, reducing the risk of pellicle damage or breakage. Also, the mass distribution at the in-plane surface of such a non-aligned network is very uniform, which helps to avoid imaging artifacts. Also, when a ballistic particle of sufficient momentum impacts the membrane, in a randomly aligned network, the crack propagation stops after traveling a typical dimension of the pores (e.g., about 100 nm) and the membrane remains intact.

[0104] [000104] The network may comprise a three-dimensional porous network.

[0105] [000105] Nanotubes may be single-walled, double-walled, multi-walled, and / or coaxial. A coaxial nanotube is a composite nanotube where one nanotube is disposed within another. The inner or core nanotube may be the same or different from the outer or capping nanotube. Double-walled carbon nanotubes and multi-walled nanotubes are emissive, and single-walled nanotubes may be emissive depending on their chirality. Being emissive may help reduce the operating temperature of the pellicle.

[0106] [000106] A pellicle membrane may include one type of nanotube or more than one type of nanotube. Thus, a pellicle membrane according to the present invention may be homogenous, i.e., all of the nanotubes are made from the same material. A pellicle membrane may be heterogeneous, i.e., various types of nanotubes may be used to form the pellicle membrane. By forming a pellicle membrane of one type of nanotube, the physical properties of the membrane are uniform. By forming a pellicle membrane of more than one type of nanotube, one may benefit from having several different properties of each material, such as etch resistance and strength.

[0107] [000107] The membrane may include carbon, boron nitride, and / or transition metal chalcogenides. Each of these materials can form nanotubes from which the membrane can be made. Carbon nanotubes are stable to high temperatures, significantly above the operating temperatures of existing pellicles. Boron nitride nanotubes are also thermomechanically stable at the temperatures encountered by pellicles in EUV lithography tools, and are also oxidation resistant up to 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.

[0108] [000108] The transition metal may be selected from Mo, W, Sb, or Bi. Thus, the transition metal (TM) may be Mo. TM may be W. TM may be Sb. TM may be Bi.

[0109] [000109] The chalcogenide may be selected from S, Se, or Te. Thus, the chalcogenide may be S. The chalcogenide may be Se. The chalcogenide may be Te.

[0110] [000110] For example, the transition metal chalcogenide can be tungsten disulfide or antimony telluride.

[0111] [000111] At least some of the nanotubes may include a capping material. The capping material may be selected from metal oxides, silicon oxide, and hexagonal boron nitride. Such a capping material may act to protect the nanotubes from damage. Damage may occur by oxidation or reduction. For example, if the nanotubes are carbon nanotubes, they may be susceptible to attack by hydrogen ions and hydrogen radicals. The capping material may be resistant to such hydrogen etching, thereby extending the life of the pellicle. It is important that the thermal expansion coefficients of the core material and the capping material are similar to avoid thermal stresses introduced as temperatures increase during operation. The thermal stability, oxidation resistance, and hydrogen-induced outgassing of the capping layer are also important considerations when selecting the capping layer. Silicon oxide may be particularly suitable for carbon nanotubes and boron nitride nanotubes. Hexagonal boron nitride may be particularly suitable for carbon nanotubes.

[0112] [000112] The metal of the metal oxide may be selected from aluminum, zirconium, yttrium, tungsten, titanium, molybdenum, and hafnium. These metal oxides have been found to have suitable physical and chemical properties to act as capping layers for nanotubes, particularly carbon nanotubes and boron nitride nanotubes.

[0113] [000113] Hexagonal boron nitride and aluminum trioxide may be specifically used as capping materials. The aluminum oxide may be in the alpha phase. Although aluminum oxide may absorb EUV light in the presence of oxygen, it is resistant to further oxidation (already in its oxidized state) and is resistant to reduction. It also shows good compatibility with the materials to be deposited and can be applied. If deposited in the amorphous state, it may be deposited at a moderate temperature of about 150-350°C. The amorphous aluminum oxide may then be annealed at a temperature of about 1115°C to crystallize to the corundum (alpha) state. Annealing may also reduce the number of defects in the pellicle film.

[0114] [000114] The pellicle membrane may include coaxial nanotubes. The coaxial nanotubes may include a carbon nanotube core within a nanotube that is resistant to hydrogen. By having one nanotube inside the other, it experiences reduced thermomechanical stress caused by heating. Because the outer nanotube is not or only weakly bonded to the inner nanotube, a wide variety of materials can be used, even materials with widely different thermal expansion coefficients. Thus, the inner nanotube may be selected for strength and the outer nanotube may be selected for etch resistance. In this way, a pellicle membrane containing such coaxial nanotubes may exhibit high strength and high chemical stability. Thus, any capping material may be used that can form nanotubes and can withstand the environment of an EUV lithography apparatus during operation.

[0115] [000115] Coaxial nanotubes may include boron nitride nanotubes, molybdenum disulfide or tungsten sulfide shells surrounding a carbon nanotube core. The carbon nanotube core is very robust and can withstand very high temperatures. The outer nanotube material is resistant to the environment of an EUV lithography tool during operation, especially hydrogen etching. Thus, a pellicle membrane containing such coaxial nanotubes is robust while being resistant to hydrogen etching.

[0116] [000116] According to an eighth aspect of the invention, there is provided a lithographic apparatus according to the first, fourth, fifth, seventh or ninth aspect of the invention.

[0117] [000117] According to a ninth aspect of the present invention there is provided a method of conditioning a carbon nanotube pellicle film comprising selectively removing nanoparticle contamination and / or amorphous carbon from the pellicle film by heating the pellicle film with electromagnetic radiation, the conditioning being performed outside of a lithographic apparatus.

[0118] [000118] Carbon nanotube (CNT) films may contain metal-containing nanoparticles employed as catalysts during the synthesis of CNTs. Such nanoparticles or their remnants present in the CNT film may cause EUV transmission loss and may also pose a risk of reticle contamination. Typically, gaseous etching species are present during CNT synthesis to reduce the catalytic nanoparticles to their metallic state to enhance catalytic activity. The gaseous etching species are typically derived from hydrogen or ammonia. The etching species also etches the amorphous carbon that is formed. However, once the CNT synthesis is complete, there may still be amorphous carbon remaining that may result in dangling bonds or missing atoms in the structure. It is desirable to remove the remaining amorphous carbon and catalytic nanoparticles. The catalytic nanoparticles may include iron, iron oxide, cobalt, nickel, chromium, molybdenum, and / or palladium.

[0119] [000119] Irradiating a carbon nanotube pellicle film with electromagnetic radiation causes the pellicle to heat up. Due to the high absorbance of the metal particles compared to the extremely low absorbance of the thin CNT film, the immediate vicinity of the metal nanoparticle contaminants and the metal nanoparticle contaminants themselves heat up during irradiation. This has been shown to remove the metal nanoparticle contaminants from the pellicle film. This conditioning step is performed outside the lithographic apparatus prior to use as a pellicle to avoid potential contamination inside the lithographic apparatus.

[0120] [000120] The CNT pellicle film may be heated in a vacuum or reducing environment. Heating may be performed in a vacuum to avoid oxidation of the carbon nanotubes. In embodiments utilizing a reducing environment, metal-containing nanoparticle contaminants, which may include iron oxide, are reduced to their metallic form. Also, remaining amorphous carbon is removed. Additionally, the crystallinity of the CNTs is increased.

[0121] [000121] The reducing environment may be a hydrogen environment. Additionally or alternatively, ammonia may be used to create the reducing environment.

[0122] [000122] In other embodiments, gases that react with the metal catalyst nanoparticles may be used. For example, carbon oxides, oxygen, or other suitable gases may react with the metal catalyst to form volatile compounds under low energy light irradiation. Carbon oxides, optionally formed by reacting oxygen with carbon in the film, may bond to the metal to form metal carbonyls that can then be removed by light-induced excitation. Also, amorphous carbon may be removed as carbon oxides in a manner similar to the removal of amorphous carbon as a hydrocarbon in a reducing environment.

[0123] [000123] Any wavelength of light that can be absorbed by the metal nanoparticles and heat them may be used. For example, infrared or near infrared wavelengths such as 810 nm may be used. The wavelength of light used may be from about 700 nm to about 1000 nm. Such wavelengths of light are easily provided and are safe and easy to handle.

[0124] [000124] The CNT pellicle membrane may be heated for any suitable time. A suitable time is one in which more than 50% of the metal-containing nanoparticle contaminants are removed. In embodiments, a suitable time is one 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 may be readily measured by scanning electron microscopy, so that the length of time required to remove a desired percentage of the metal nanoparticles can be determined periodically.

[0125] [000125] The CNT film may be heated for up to 10 minutes, up to 5 minutes, or up to 2 minutes. The CNT film may be heated for 15 s, 30 s, 45 s, 60 s, 75 s, or 90 s.

[0126] [000126] The electromagnetic radiation used to heat the pellicle membrane may be low power. Thus, the power may be less than 20 W / cm 2 Less than 15W / cm 2 Less than 10W / cm 2 Less than 5W / cm 2 The power may be less than 3 W / cm 2 , 2W / cm 2 , 1W / cm 2 , or 0.5 W / cm 2 Such low power allows for the removal of nanoparticles and / or amorphous carbon while avoiding the risk of damaging the pellicle membrane.

[0127] [000127] It will be understood that features described with respect to one embodiment may be combined with any features described with respect to another embodiment, and that all such combinations are expressly contemplated and disclosed herein. [Brief description of the drawings]

[0128] [000128] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, in which:

[0129] [Figure 1] [000129] An image of a lithographic apparatus according to an embodiment of the invention is depicted. [Diagram 2] [000130] FIG. 1 shows a schematic of a prior art pellicle membrane comprising bundles of carbon nanotubes with a capping layer. [Figure 3a] [000131] A schematic diagram of a pellicle membrane according to the present invention is shown. [Figure 3b] [000131] A schematic diagram of a pellicle membrane according to the present invention is shown. [Figure 4a] [000132] A schematic diagram of a pellicle membrane according to the present invention is shown. [Figure 4b] [000132] A schematic diagram of a pellicle membrane according to the present invention is shown. [Diagram 5] [000133] A schematic of a lithographic apparatus including an electrically biased pellicle / reticle is shown. [Figure 6] [000134] FIG. 1 depicts a schematic of a lithographic apparatus including an electrically biased pellicle / reticle masking unit. [Figure 7a] [000135] A schematic of a lithographic apparatus including an electrically biased reticle masking unit blade is depicted. [Figure 7b] [000135] A schematic of a lithographic apparatus including an electrically biased reticle masking unit blade. [Figure 8][000136] Schematic of the main processes involved in etching carbon nanotube pellicle membranes. [Figure 9] [000137] Figure 1 shows the reticle mini environment and the approximate range of EUV radiation, hydrogen ions and hydrogen radicals. [Figure 10] [000138] An embodiment of the present invention is shown. [Figure 11a] [000139] An embodiment of the present invention is shown. [Figure 11b] [000139] An embodiment of the present invention is shown. [Figure 12a] [000140] An embodiment of a method according to the present invention is shown. [Figure 12b] [000140] An embodiment of a method according to the present invention is shown. [Figure 13] [000141] FIG. 1 shows a schematic cross-section of a pellicle membrane according to the present invention, including an aerogel layer. [Figure 14a] [000142] FIG. 1 shows a scanning electron microscope image of an unprepared CNT film according to an embodiment of the invention. [Figure 14b] [000142] FIG. 1 shows a scanning electron microscope image of a CNT film after preparation, according to an embodiment of the invention. [Figure 15] [000143] Figure 1 shows Raman spectra of pre-conditioned and pre-conditioned CNT films according to an embodiment of the invention. [Figure 16] [000144] Figure 14 shows FTIR spectra of pre- and post-conditioned CNT films according to an embodiment of the present invention.

[0130] [000145] The features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the drawings, in which like reference numbers identify corresponding elements throughout, and in which like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0131] [000146] Figure 1 shows a lithographic system including a pellicle 15 (also called a membrane assembly) according to the present invention. The lithographic system includes a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate a beam of extreme ultraviolet (EUV) radiation B. The lithographic apparatus LA includes 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 is incident on the patterning device MA. The projection system is configured to project the radiation beam B (already patterned by a mask MA) onto the substrate W. The substrate W may include a previously formed pattern. In that case, the lithographic apparatus aligns the patterned radiation beam B with the pattern previously formed on the substrate W. In this embodiment, a pellicle 15 is shown in the path of the radiation to protect the patterning device MA. It will be appreciated that the pellicle 15 may be in any desired position and may be used to protect any of the mirrors within the lithographic apparatus.

[0132] [000147] The source SO, illumination system IL and projection system PS may all be constructed and arranged such that they can be isolated from the external environment. The source SO may be provided with a gas (e.g. hydrogen) at a pressure below atmospheric pressure. A vacuum may be provided to the illumination system IL and / or projection system PS. The illumination system IL and / or projection system PS may be provided with a small amount of gas (e.g. hydrogen) at a pressure significantly below atmospheric pressure.

[0133] [000148] The radiation source SO shown in Figure 1 is of a type that may be called a laser-produced plasma (LPP) source. For example, a CO 2The laser, which may be a laser, is arranged to impart energy via a laser beam to a fuel, such as tin (Sn), provided from a fuel emitter. Although the following description refers to tin, any suitable fuel may be used. The fuel may be, for example, in the form of a liquid, and may be, for example, a metal or an alloy. The fuel emitter may include a nozzle configured to direct the tin, for example in the form of droplets, along a trajectory towards the plasma formation region. The laser beam is incident on the tin in the plasma formation region. The application of laser energy to the tin generates a plasma in the plasma formation region. Radiation, including EUV radiation, is emitted from the plasma during de-excitation and recombination of the ions of the plasma.

[0134] [000149] The EUV radiation is collected and focused by a near-normal incidence radiation collector (sometimes more commonly referred to as a normal incidence radiation collector). The collector may have a multi-layer structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength, such as 13.5 nm). The collector may have an elliptical configuration with two elliptical foci. The first focus may be at the plasma formation region and the second focus may be at an intermediate focus, as discussed below.

[0135] [000150] The laser may be separate from the radiation source SO. The laser beam may then be passed from the laser to the radiation source SO with the aid of a beam delivery system (not shown), e.g. including suitable directing mirrors and / or beam expanders, and / or other optical components. The laser and radiation source SO together may be considered as a radiation system.

[0136] [000151] The radiation reflected by the collector forms a radiation beam B. The radiation beam B is focused at a point to form an image of the plasma formation region, which acts as a virtual radiation source for the illumination system IL. The point at which the radiation beam B is focused may be referred to as an intermediate focus. The radiation source SO is positioned such that the intermediate focus is located at or near an opening of a source closure structure.

[0137] [000152] A radiation beam B enters an illumination system IL configured to condition the radiation beam from a radiation source SO. The illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. Together the facetted field mirror device 10 and the facetted pupil mirror device 11 provide a radiation beam B having a desired cross-sectional shape and a desired angular distribution. From the illumination system IL, the radiation beam B is incident on a patterning device MA held by a support structure MT. The patterning device MA reflects and patterns the radiation beam B. The illumination system IL may include other mirrors or devices in addition to or instead of the facetted field mirror device 10 and the facetted pupil mirror device 11.

[0138] [000153] Following reflection from the patterning device MA, the patterned radiation beam B enters the projection system PS. The projection system includes a number of mirrors 13, 14 configured to project the radiation beam B onto a substrate W held by a substrate table WT. The projection system PS may apply a demagnification factor to the radiation beam to form an image having smaller features than corresponding features on the patterning device MA. For example, a demagnification factor of four may be applied. In Figure 1 the projection system PS includes two mirrors 13, 14, but the projection system may include any number of mirrors (for example six mirrors).

[0139] [000154] The radiation source SO shown in Figure 1 may include components not shown. For example, the radiation source may be provided with a spectral filter that may substantially transmit EUV radiation but substantially block radiation of other wavelengths, such as infrared radiation.

[0140] [000155] In an embodiment, the membrane assembly 15 is a pellicle for a patterning device MA for EUV lithography. The membrane assembly 15 of the present invention can be used as a dynamic gas lock or a pellicle or for another purpose. In an embodiment, the membrane assembly 15 includes a membrane formed from at least one membrane layer configured to transmit at least 90% of the incident EUV radiation. The membrane is preferably supported only at the edges to ensure maximum EUV transmission and minimal impact on imaging performance.

[0141] [000156] If the patterning device MA is left unprotected, contamination may result in the patterning device MA having to be cleaned or discarded. Cleaning the patterning device MA interrupts valuable production time, and discarding the patterning device MA is expensive. Replacing the patterning device MA also interrupts valuable production time.

[0142] [000157] FIG. 2 is a schematic diagram of a bundle of carbon nanotubes 100, the carbon nanotubes including a capping layer 101. A typical diameter of a carbon nanotube is about 2 to about 30 nm, and the thickness h of the capping layer 101 is generally less than about 10 nm, typically about 1 nm. Even though the capping layer is very thin, the transmittance of a pellicle film including a conformal coating is low compared to a pellicle film including nanotubes with the cap removed. Also, as discussed above, thin layers may be prone to dewetting. Also, as discussed above, capping of nanotubes may cause pellicle EUV scattering to become intolerable. The bundle of nanotubes may include a pellicle film. The pellicle film may be attached to a frame that supports the pellicle film.

[0143] [000158] Figure 3a is a schematic diagram of a bundle of carbon nanotubes 102 according to an embodiment of the invention, in which the outer surface of the carbon nanotubes is decorated with nanoparticles 103. The diameter of the nanoparticles is D npThe diameter of the nanoparticles may be measured by any suitable method. Preferably, the diameter is measured by TEM (Transmission Electron Microscopy). The diameter of the nanoparticles may vary from a maximum diameter to a minimum diameter. The size of the particles is not necessarily the same, but it is preferred that the nanoparticles are within a narrow size range. The narrow size range may include ±15 nm, ±10 nm or ±5 nm. It will be understood that due to manufacturing limitations, some nanoparticles may be outside the tolerance range. The term L is used to indicate the distance between adjacent or nearby nanoparticles. np is used. It will be understood that this could be nanoparticles on the same nanotube or nanoparticles on different nanotubes.

[0144] [000159] Figure 3b shows a schematic of how carbon nanotubes can be eroded by the presence of adatom hydrogen and the breaking of carbon-carbon bonds by hydrogen ions. Hydrogen radicals H* can adsorb to the surface of the carbon nanotube and travel along the nanotube until they reach the nanoparticle. The faster recombination rate of hydrogen radicals to molecular hydrogen at the nanoparticle than at the carbon nanotube, and the greater rate of molecular hydrogen production at the nanoparticle than elsewhere on the carbon nanotube, removes the adatom hydrogen, thus removing the concentration of adatom hydrogen and reducing the chance of passivating the broken carbon-carbon bonds. In contrast, in areas not protected by nanoparticles, the adsorbed hydrogen radicals cannot be easily recombined, and therefore when carbon-carbon bonds are broken by hydrogen ions, bond passivation can occur and ultimately hydrocarbons can be released from the nanotube, resulting in damage to the nanotube.

[0145] [000160] Figures 4a and 4b show an embodiment similar to that of Figures 3a and 3b, but with nanoparticles disposed within the nanotubes. As in Figures 3a and 3b, a bundle 105 of carbon nanotubes 107 is shown with nanoparticles 106 within the carbon nanotubes. It will be appreciated that in some embodiments nanoparticles may be disposed both inside and outside the nanotubes. np is the diameter of the nanoparticle, and U np is the distance between adjacent or nearby nanoparticles. Similar to Fig. 3b, adatom hydrogen can migrate along the nanotube where it is recombined into molecular hydrogen and then desorbed from the nanotube. The nanoparticles, despite being inside the nanotube, protect the nanotube from etching by increasing the recombination of atomic hydrogen.

[0146] [000161] Figure 5 shows a patterned reticle 108 attached to a chuck 109 with fiducial markers 111 and 112 by clamps 110. The reticle 108 is covered with a pellicle 131. It will be understood that the pellicle can be a pellicle according to the present invention or another type of pellicle. The pellicle 131 may be coupled to the reticle via an optional insulating structure 120 to form a floating pellicle. The pellicle 131 is connected to a bias electrode via a connector 121. The reticle front quality area 132 is connected to another bias electrode via a connector 122. Reticle masking blades (REMA blades) 151 and 152 and a uniformity correction module (UNICOM) 180 define the illumination of the reticle 108 by EUV radiation 200. It will be understood that the REMA blades and the UNICOM are used in actual EUV lithography equipment and are included in the additional context. The present invention may be practiced without these features. The bias between the pellicle 131 and the reticle 108 deflects ions created by ionizing the gas between the pellicle 131 and the reticle 108 and / or transmitted by diffusion through the pores in the pellicle 131 from the volume between the pellicle and the REMA blades 151, 152 away from the pellicle 131 toward the reticle 108. This inhibits etching of the pellicle membrane, which may be a carbon nanotube pellicle membrane.

[0147] [000162] Figure 6 shows a configuration in which an electrical bias is applied between the pellicle 131 and the REMA blades 151, 152. The UNICOM 180 may also be given a similar or equivalent potential to the REMA blades. As in the configuration of Figure 5, the pellicle 131 is connected to the electrode via the connector 121. Optionally, the pellicle may be left floating, in which case the connector 121 may be omitted. The potential of the REMA blades 151, 152 is negative. In use, a bias may be introduced not only between the pellicle and the electrode, but also between the EUV plasma itself (which is mostly contained within the EUV cone) and the electrode. Typically, the plasma potential is somewhat positive (+5....+25V) with respect to the largest and closest electrode (which is generally the grounded vacuum vessel wall), so by introducing an absolute negative potential electrode (e.g. a REMA blade or a UNICOM or a Y-nozzle), it is possible to extract positive ions from the plasma and redirect them away from the (floating or biased) pellicle.

[0148] [000163] Figures 7a and 7b show an arrangement in which an electrical bias is provided between REMA blades 151, 152. As seen most clearly in Figure 7b, there is a large REMA blade 151 and a small REMA blade 152. Preferably, the large REMA blade 151 has a less negative bias applied to the grounded vacuum vessel than the small REMA blade 152 to reduce the chance of capacitive (negative) bias of the floating pellicle.

[0149] [000164] Figure 8 shows the main processes involved in etching carbon nanotubes. Arrows 301 indicate H 23 shows the removal of adatom hydrogen by associative desorption of hydrogen. The migration of adatom hydrogen (also known as hydrogen radical hopping) is indicated by arrow 302. The adsorption of hydrogen radicals is indicated by arrow 300 and the desorption of hydrogen radicals is indicated by arrow 303. The cleavage of carbon-carbon bonds by hydrogen ions is indicated by line 304. Of the various processes shown, hydrogen radical desorption 303 has the largest associated energy barrier, while the other processes have lower energy barriers. Thus, by heating the pellicle, the process with the highest energy barrier, i.e. atomic hydrogen desorption, is accelerated the most. Thus, while all processes may be accelerated, atomic hydrogen desorption is accelerated more than the other processes. Also, the process involving hydrogen ions 304 has less (or no) dependence on the pellicle temperature since it is related to the energy of the incoming hydrogen ions.

[0150] [000165] FIG. 9 shows the reticle mini environment (RME) surrounding the reticle 430, showing the approximate range of the EUV radiation beam (W_EUV), the range of the main hydrogen ion flux (W_ion), and the width of the main hydrogen radical flux (W_radical). It will be understood that the cones showing these regions are for illustration purposes and to aid in understanding the invention. The pellicle 401 is supported on the reticle 400 via an optional flexure 402. The EUV cone 420 generates radicals and ions of various impacts in the RME. Typically, the distance between the reticle masking unit blades 411 and 410 is approximately the same as the width of the EUV radiation beam (W_EUV). Typically, the hottest region of the pellicle is only slightly larger (e.g., a few millimeters) than W_EUV due to the limited thermal conductivity of the porous carbon nanotube membrane. Since hydrogen ions recombine after one collision with the surface, the ion range W_ion is approximately equal to W_EUV plus about 2-4 times the distance (H_rema) between the reticle masking unit blade and the pellicle 401. H_rema is typically about 2-5 mm. On the other hand, radicals can survive multiple collisions with the surface, so their range (W_radical) is much larger and may be approximately the size of the pellicle. Thus, the area exposed to both the ion and radical fluxes is not the entire surface of the pellicle. As a result, only this overlapping area may be heated to reduce the concentration of adsorbed hydrogen radicals in order to slow down the etching.

[0151] [000166] Figure 10 illustrates an embodiment of the invention using a laser to provide additional heat to a pellicle membrane. As shown, laser beams 510 and 520 are provided. It will be understood that the invention is not limited to only two laser beams and that fewer or more laser beams may be used as needed. In the illustrated example, each laser beam has an associated optic 510, 521 that directs the laser beam onto the pellicle. The approximate width of the additional heating region is indicated as W_ext.heat. The heating effect of the laser light reduces the etch rate by suppressing the adsorbed radical concentration in areas with the highest ion flux. Selective heating limits the overall heat load on the reticle. Any suitable laser power may be selected, for example, between 0.1 and 10 w / cm of absorbed energy to provide the required additional heat. 2 It may be desirable to provide a thermal load of 100 W. The power of the transmitted radiation 512, 522 (directed at the reticle) is estimated to be a fraction of the incident power (e.g., about 5-50%) and is almost completely reflected at the reticle in the same way as IR radiation from a hot pellicle, which is a thermal load that the reticle can withstand.

[0152] [000167] Figures 11a and 11b show an embodiment of the invention including resistive heating. A current source 600 is connected to the pellicle 401 via contacts 601, 602 and / or wires integrated into the chuck or clamp. The current 640 in the pellicle film 620 can be made substantially uniform by providing highly conductive strips 630 on the pellicle frame 610, with the current flowing through such strips. The conductive strips 630 can be configured to distribute the current to the portions of the pellicle membrane exposed to the highest hydrogen ion flux.

[0153] [000168] Figures 12a and 12b show a schematic flow chart of a method for regenerating, conditioning and / or repairing a pellicle membrane. Referring first to Figure 12a, after fabrication, the pellicle membrane undergoes a vacuum or reduction annealing step 701. This removes loosely bound amorphous carbon and other contaminants such as seed nanoparticles remaining from the carbon nanotube growth process. The pellicle membrane then undergoes a reactive annealing process 702 in a hydrocarbon-containing atmosphere. The hydrocarbon may be any hydrocarbon, but it is preferred to use short chain (C1-4) hydrocarbons such as methane, ethane, propane, or butane. The hydrocarbon may be saturated or unsaturated. Unsaturated hydrocarbons such as ethene and ethyne are preferred due to their high carbon to hydrogen ratio. Following the reactive annealing step 702, the pellicle membrane may again undergo a vacuum or reduction annealing 701 via route 705. Prior to use 704 in the scanner, the pellicle film undergoes a vacuum annealing step 703 to avoid transient effects during exposure in the scanner environment. Such transient effects include changes in the EUV transmittance of the pellicle film after exposure to EUV radiation and hydrogen ions and radicals in the scanner environment within the lithographic apparatus. Alternatively, the pellicle film may be used in the scanner without undergoing reactive annealing, as indicated by arrow 706.

[0154] [000169] Figure 12b shows a schematic flow chart of a method for regenerating, conditioning and / or repairing a pellicle film exposed to the scanner environment of a lithographic apparatus. As the pellicle film will have already been exposed to the highly reducing atmosphere in the lithographic apparatus, there is no need to further anneal the pellicle in a reductive annealing step. Also, the pellicle film may become damaged during use, requiring repair of the damage, which is achieved by reactive annealing in a hydrocarbon atmosphere. After reactive annealing 702, the pellicle film may be subjected to a vacuum or reductive annealing 701. This may be repeated. Once the pellicle film is sufficiently repaired, it may be used again in the lithographic apparatus (704).

[0155] [000170] Figure 13 shows a cross-section of a pellicle membrane including a pellicle membrane layer 800 with an aerogel layer 801 on each side. It will be appreciated that in some embodiments, the aerogel layer 801 is provided on only one side. The aerogel layer 800 may protect the underlying pellicle membrane layer 800 from etching by the hydrogen plasma. It will be appreciated that other optical elements of the lithographic apparatus may be protected by aerogel as well.

[0156] [000171] Figures 14a and 14b are scanning electron microscope images of an area of ​​the same CNT film. In Figure 14a, the CNT film has not yet been conditioned according to the method of the ninth aspect of the present invention. The nanoparticle contaminants are clearly visible as white dots dispersed in the CNT film. Figure 14b shows the same CNT film after it has been conditioned. Specifically, the CNT film has been conditioned by exposure to 810 nm radiation. As can be seen, the number of nanoparticle contaminants has been significantly reduced.

[0157] [000172] Figure 15 shows the Raman spectra of an unprepared CNT film and a CNT film prepared according to the ninth aspect of the invention. Two peaks are observed. -1The first peak at approximately 1580 cm indicates that the lines associated with the pristine (unconditioned) CNT film are higher than those associated with the conditioned CNTs. In this Raman shift, higher lines indicate a greater degree of defects or amount of defects, which indicates the presence of defective CNTs, amorphous carbon, or both. Conditioning the CNT pellicle film reduces the amount of defects, amorphous carbon, or both. -1 The peak at about 1580 cm indicates that the line associated with the prepared CNT pellicle film is higher than the line associated with the unprepared CNT film. -1 The peak at is related to the amount of crystalline carbon, indicating that the prepared CNT pellicle film has a higher amount of crystalline carbon than the unprepared CNT pellicle film.

[0158] [000173] Figure 16 shows FTIR spectra obtained from conditioned and unconditioned areas of the CNT pellicle film. The spectrum obtained from the pristine (unconditioned) CNT pellicle film shows a lower peak at about 2.5 microns, roughly the same absorption at about 4 microns, and generally higher absorption at wavelengths above 4 microns. In contrast, the conditioned (irradiated) CNT pellicle film has a much higher absorption peak at 2.5 microns and generally lower absorption at wavelengths above 4 microns. The distinct peak at 2.5 microns further indicates the higher crystalline quality of the CNT film after conditioning.

[0159] [000174] It will be appreciated that various aspects of the invention may be provided in combination. For example, the embodiments including an electrical bias may be used in combination with the pellicle membranes described herein or in combination with other types of pellicle membranes. The method of regenerating a pellicle may be used in combination with the electrical bias method and may further include using the pellicle membranes described herein or another type of pellicle membrane.

[0160] [000175] Although particular reference is made herein to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc. The substrates described herein may be processed, before or after exposure, for example in a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where appropriate, the disclosure herein may be applied to these and other substrate processing tools. Furthermore, a substrate may be processed multiple times, for example to produce a multi-layer IC, and thus the term substrate as used herein may also refer to a substrate that already includes multiple processed layers.

[0161] [000176] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, various layers may be replaced with other layers which perform the same functions.

[0162] [000177] The above description is illustrative and not restrictive. Thus, it will be apparent to one skilled in the art that modifications of the invention as described may be made without departing from the scope of the claims.

[0163] 1. A pellicle membrane for a lithography apparatus, comprising decapped carbon nanotubes. 2. A pellicle membrane for a lithographic apparatus, the membrane further comprising a plurality of nanoparticles, optionally the nanoparticles being composite nanoparticles. 3. A pellicle membrane as described in clause 2, wherein the nanoparticles are associated with carbon nanotubes. 4. A pellicle membrane according to clause 2 or 3, wherein the nanoparticles are disposed on the surface of the carbon nanotubes, or disposed within the carbon nanotubes, or disposed both on the surface of the carbon nanotubes and within the carbon nanotubes. 5. A pellicle membrane according to any one of clauses 1 to 4, wherein the nanotubes form a gas permeable mesh. 6. A pellicle membrane according to any one of clauses 1 to 5, wherein the carbon nanotubes are selected from single-walled nanotubes, multi-walled nanotubes, and combinations thereof. 7. A pellicle membrane described in any of clauses 1 to 6, wherein the diameter of the nanoparticles is from about 1 nm to about 100 nm, preferably from about 1 nm to about 25 nm. 8. A pellicle membrane according to any one of clauses 1 to 7, wherein the diameter of the nanoparticles is less than half the critical dimension of the corresponding reticle pattern. 9. A pellicle membrane according to any of clauses 1 to 8, wherein the average distance between adjacent nanoparticles is greater than the diameter of the nanoparticles. 10. The pellicle membrane of clause 9, wherein the average distance between adjacent nanoparticles is from about 1 to about 50 times the diameter of the nanoparticles. 11. The pellicle membrane of clause 9, wherein the average distance between adjacent nanoparticles is 10 times or more the diameter of the nanoparticles. 12. A pellicle membrane according to any of clauses 1 to 11, wherein the nanoparticles comprise a material having a higher hydrogen recombination coefficient than the nanotubes. 13. The pellicle membrane of claim 12, wherein the recombination coefficient of nanoparticles is from about 0.1 to about 1. 14. A pellicle membrane according to any of clauses 1 to 13, wherein the material comprising the nanoparticles is selected from the group consisting of metals, metal oxides, doped metals, alloys, or combinations thereof. 15. A pellicle membrane according to any one of clauses 1 to 14, 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. 16. The pellicle membrane of clause 14 or 15, wherein the nanoparticles additionally comprise O, N, B, Si, C, H, S, P, Cl, and combinations thereof. 17. A pellicle membrane according to any of clauses 1 to 16, 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. 18. A pellicle membrane according to any of clauses 1 to 17, wherein the decapped carbon nanotubes are passivated, preferably chemically passivated. 19. A pellicle membrane as described in clause 18, wherein the decapped carbon nanotubes are passivated by chemisorption of a chemical species onto the surface of the nanotubes. 20. A pellicle membrane according to clause 18 or 19, wherein the decapped carbon nanotubes have been passivated by nitridation, oxidation or halogenation, or by the addition of strontium, boron, beryllium and / or silicon to the surface of the nanotubes. 21. A pellicle membrane according to any one of clauses 1 to 20, wherein the surface of the decapped carbon nanotubes is not intentionally hydrogenated. 22. A pellicle membrane according to any of clauses 18 to 21, wherein the decapped carbon nanotubes are passivated by fluorination or chlorination. 23. A pellicle membrane for a lithographic apparatus comprising decapped carbon nanotubes, wherein at least a portion of a surface of the decapped carbon nanotubes is chemically passivated, preferably the chemical passivation comprises nitridation, oxidation, and / or halogenation. 24. A pellicle membrane according to any of clauses 1 to 23, wherein the decapped carbon nanotubes are doped with atoms other than carbon, optionally the atoms other than carbon being nitrogen, boron, and / or silicon. 25. A method for regenerating and / or conditioning a pellicle membrane, the method comprising decomposing a precursor compound and depositing at least a portion of the decomposition products on the pellicle membrane. 26. The method according to clause 25, wherein the pellicle membrane is a membrane according to any one of clauses 1 to 24. 27. The method of clause 25 or 26, wherein the precursor is a hydrocarbon, preferably the hydrocarbon is a saturated or unsaturated C1-4 hydrocarbon, or a cyclic hydrocarbon (C5 or higher), or an aromatic hydrocarbon (C6 or higher), and optionally the precursor contains at least one of O, N, B, P, S, Cl. 28. The method of any of clauses 25 to 27, wherein the precursor compound is supplied continuously or intermittently. 29. The method of any of clauses 25 to 28, wherein the amount of precursor compound is adjusted depending on one or more of the etch rate of the pellicle film, the operating power of a lithographic apparatus in which the pellicle film is disposed, and the operating life of the pellicle film. 30. The method of any of clauses 25 to 29, wherein the method includes directing the precursor compound to a pellicle membrane. 31. The method of any of clauses 25 to 29, including a method of conditioning and / or repairing a carbon nanotube pellicle film, the method including the step of annealing the carbon nanotube pellicle film in a hydrocarbon-containing atmosphere. 32. The method of claim 31, wherein the annealing is performed at a temperature of about 700K to about 900K. 33. A method according to any of clauses 25 to 32, wherein the method comprises a vacuum annealing step, optionally before and / or after the step of annealing the pellicle membrane in a hydrocarbon-containing atmosphere. 34. A method according to any of clauses 25 to 33, wherein the method comprises a reductive annealing step, optionally before and / or after the reactive annealing step, and optionally the reductive annealing is carried out in a reducing gas such as hydrogen. 35. The method of any of clauses 25 to 34, wherein the final annealing step is a vacuum annealing step or a reduction annealing step. 36. A method according to any one of clauses 25 to 35, wherein the pellicle membrane is a pellicle membrane according to any one of clauses 1 to 24. 37. A method for regenerating and / or conditioning a pellicle membrane, optionally a membrane according to any of clauses 1 to 24, comprising the steps of: a) vacuum or reduction annealing; b) reactive annealing in a hydrocarbon environment; c) optionally repeating steps a) and b); and d) a final step of vacuum or reduction annealing. 38. A method of reducing the etch rate of a pellicle membrane, the method comprising providing at least one biasing element in a region of the pellicle membrane, preferably the pellicle membrane being a carbon nanotube pellicle membrane. 39. An assembly for a lithographic apparatus including a pellicle membrane biased relative to the nearest electrode and may include a reticle front surface and / or a shutter system and / or an optical filter and / or a purge gas supply, optionally wherein the pellicle membrane and / or reticle front surface are floating while the shutter system and / or optical filter are negatively biased relative to the grounded vacuum vessel wall. 40. An assembly as described in clause 39, wherein the absolute bias between any electrodes is about -500V or less, preferably about -250V or less, more preferably about -50V or less, and optionally all electrodes are negative with respect to the grounded vacuum vessel wall. 41. An assembly as claimed in clause 39 or 40, wherein the bias is current limited or pulsed, optionally with a pulse synchronized to the EUV pulse. 42. An assembly according to any of clauses 39 to 41, wherein the pellicle membrane is biased relative to one or more of the reticle masking unit, the reticle, the optical filter and the auxiliary electrode within the reticle mini environment. 43. An assembly according to any of clauses 39 to 42, wherein the assembly includes a reticle masking unit including first and second blades, an electrical bias being provided between the blades. 44. An assembly according to any of clauses 39 to 43, provided with a ground electrode. 45. A pellicle arrangement for a lithographic apparatus, the pellicle arrangement comprising a pellicle membrane and a pellicle heating means. 46. ​​A pellicle apparatus as described in clause 45, wherein the heating means is configured to heat a predetermined portion of the pellicle membrane. 47. A pellicle device as described in clause 45 or clause 46, wherein the predetermined portion of the pellicle membrane is the portion exposed to the highest hydrogen ion flux. 48. A pellicle apparatus according to any of clauses 45 to 47, wherein the heating means comprises i) one or more lasers, and / or ii) one or more resistive heating elements. 49. A pellicle apparatus as described in clause 48, wherein the one or more lasers operate in the visible or infrared spectrum. 50. A pellicle apparatus as described in clause 47 or 48i), wherein the apparatus further comprises at least one optical element configured to direct laser light onto the pellicle membrane. 51. A pellicle apparatus as described in clause 48ii), wherein the pellicle membrane is connected to a source of electric current such that the material comprising the pellicle membrane acts as a resistive heater. 52. A pellicle device as described in clause 48ii) or clause 51, provided with conductive strips for distributing electrical current to at least a portion of the pellicle membrane. 53. A pellicle device according to any of clauses 45 to 52, wherein the pellicle membrane comprises carbon nanotubes, preferably the pellicle membrane comprises a pellicle membrane according to any of clauses 1 to 17. 54. A method of extending the operational life of a pellicle membrane, comprising selectively heating an area of ​​the pellicle membrane. 55. The method of claim 54, wherein the method includes heating areas of the pellicle that are exposed to the highest hydrogen ion flux during operation. 56. The method of claim 54 or 55, wherein the heating is performed by directing a laser beam onto the pellicle membrane. 57. The method of clause 54, 55 or 56, wherein the laser beam is directed by one or more optical elements. 58. The method according to clause 54 or clause 55, wherein heating is performed by passing an electric current through the pellicle membrane. 59. The method according to clause 58, wherein the pellicle membrane is a pellicle membrane according to any one of clauses 1 to 24. 60. A pellicle membrane for a lithography apparatus comprising a network of non-aligned nanotubes. 61. The pellicle membrane of clause 50, wherein the network comprises a three-dimensional porous network. 62. A pellicle membrane according to clause 60 or 61, wherein the nanotubes are single-walled, double-walled, multi-walled and / or coaxial. 63. A pellicle membrane according to any of clauses 60 to 62, wherein the membrane comprises one type of nanotube or two or more types of nanotubes. 64. A pellicle membrane according to any of clauses 60 to 63, wherein the membrane comprises carbon, boron nitride, and / or a transition metal chalcogenide. 65. A pellicle membrane according to claim 64, wherein the transition metal is selected from Mo, W, Sb, or Bi. 66. A pellicle membrane according to clause 64 or 65, wherein the chalcogenide is selected from S, Se, or Te. 67. A pellicle membrane according to any of clauses 60 to 66, wherein at least a portion of the nanotubes comprise a capping material. 68. A pellicle membrane as described in clause 67, wherein the capping material is selected from metal oxides, silicon oxide, and hexagonal boron nitride. 69. The pellicle 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. 70. A pellicle membrane according to any of clauses 60 to 69, wherein the membrane comprises coaxial nanotubes. 71. A pellicle membrane as described in clause 70, wherein the coaxial nanotubes comprise a carbon nanotube core within the nanotube that is resistant to hydrogen etching. 72. The pellicle membrane of clause 71, wherein the coaxial nanotubes comprise a boron nitride nanotube, molybdenum disulfide, or tungsten sulfide shell surrounding a carbon nanotube core. 73. An optical element for use in a lithographic apparatus, comprising an aerogel. 74. The optical element according to clause 73, wherein the optical element is a pellicle membrane, a mirror, a reticle, or a spectral purity filter. 75. An optical element according to clause 73 or clause 74, wherein the optical element comprises a pellicle membrane according to any one of clauses 1 to 24, 45 to 53, or 60 to 72. 76. A lithographic apparatus comprising a pellicle membrane according to any one of clauses 1 to 24, 45 to 53, or 60 to 72. 77. A method for conditioning a carbon nanotube pellicle film, the method comprising selectively removing metal-containing nanoparticles and / or amorphous carbon from the pellicle film by heating the pellicle film with electromagnetic radiation, the conditioning being performed outside of the lithographic apparatus. 78. The method of claim 77, wherein the CNT pellicle membrane is heated in a vacuum environment or a reducing environment. 79. The method of claim 78, wherein the reducing environment comprises one or both of hydrogen and ammonia. 80. The method of claim 77, wherein the CNT pellicle film is heated in an environment containing one or more of carbon oxide and oxygen. 81. The method of any of clauses 77 to 80, wherein the CNT pellicle membrane 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. 82. The method of any of clauses 77 to 81, wherein the CNT film is heated for 15 s, 30 s, 45 s, 60 s, 75 s, 90 s, or up to 2 minutes, up to 5 minutes, or up to 10 minutes. 83. The power of electromagnetic radiation is about 0.5 W / cm 2 , 1W / cm 2 , 2W / cm 2 , 3W / cm 2 , 5W / cm 2 Less than 10W / cm 2 Less than 15W / cm 2 Less than or equal to 20W / cm 2 83. The method of any of clauses 77 to 82, wherein the 84. The method of any of clauses 77 to 83, wherein the electromagnetic radiation is infrared radiation or near infrared radiation, optionally the radiation having a wavelength of from about 700 to about 1000 nm.

Claims

1. A pellicle membrane for a lithography apparatus comprising decapped carbon nanotubes.

2. A pellicle membrane for a lithographic apparatus, said membrane further comprising a plurality of nanoparticles, optionally said nanoparticles being composite nanoparticles.

3. The pellicle membrane of claim 2 , wherein the nanoparticles are associated with the carbon nanotubes.

4. The pellicle membrane of claim 2 or 3, wherein the nanoparticles are disposed on a surface of the carbon nanotubes, or disposed within the carbon nanotubes, or disposed on the surface of the carbon nanotubes and within the carbon nanotubes.

5. The pellicle membrane of claim 1 , wherein the nanotubes form a gas permeable mesh.

6. 6. The pellicle membrane of claim 1, wherein the carbon nanotubes are selected from single-walled nanotubes, multi-walled nanotubes, and combinations thereof.

7. 7. A pellicle membrane according to any one of claims 1 to 6, wherein the nanoparticles have a diameter of about 1 nm to about 100 nm, preferably about 1 nm to about 25 nm.

8. The pellicle membrane of claim 1 , wherein the nanoparticles have a diameter less than half the critical dimension of the corresponding reticle pattern.

9. 9. A pellicle membrane as described in any one of claims 1 to 8, wherein the average distance between adjacent nanoparticles is greater than the diameter of the nanoparticles.

10. 10. The pellicle membrane of claim 9, wherein the average distance between adjacent nanoparticles is from about 1 to about 50 times the diameter of the nanoparticles.

11. 10. The pellicle membrane of claim 9, wherein the average distance between adjacent nanoparticles is greater than or equal to 10 times the diameter of the nanoparticles.

12. 12. The pellicle membrane of claim 1, wherein the nanoparticles comprise a material having a higher hydrogen recombination coefficient than the nanotubes.

13. 13. The pellicle membrane of claim 12, wherein the recombination coefficient of the nanoparticles is from about 0.1 to about 1.

14. 14. The pellicle membrane of claim 1, wherein the material comprising the nanoparticles is selected from the group consisting of metals, metal oxides, doped metals, alloys, or combinations thereof.

15. 15. The pellicle membrane of any one of claims 1 to 14, wherein the material containing 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.

16. 16. The pellicle membrane of claim 14 or 15, wherein the nanoparticles additionally comprise O, N, B, Si, C, H, S, P, Cl, and combinations thereof.

17. 17. A pellicle membrane according to any of claims 1 to 16, wherein the surface density of said nanoparticles is greater than about 500 particles per square micron, preferably greater than about 1000 particles per square micron.

18. 18. A pellicle membrane according to any of claims 1 to 17, wherein the decapped carbon nanotubes are passivated, preferably chemically passivated.

19. 20. The pellicle membrane of claim 18, wherein the decapped carbon nanotubes are passivated by chemisorption of chemical species to the surface of the nanotubes.

20. 20. The pellicle membrane of claim 18 or 19, wherein the decapped carbon nanotubes have been passivated by nitridation, oxidation, or halogenation, or by addition of strontium, boron, beryllium, and / or silicon to the surface of the nanotubes.

21. 21. The pellicle membrane of claim 1, wherein the surfaces of the decapped carbon nanotubes are not intentionally hydrogenated.

22. 22. The pellicle membrane of any of claims 18 to 21, wherein the decapped carbon nanotubes are passivated by fluorination or chlorination.

23. A pellicle film for a lithographic apparatus comprising decapped carbon nanotubes, wherein at least a portion of a surface of the decapped carbon nanotubes is chemically passivated, preferably the chemical passivation comprises nitridation, oxidation, and / or halogenation.

24. 24. A pellicle membrane as described in any one of claims 1 to 23, wherein the decapped carbon nanotubes are doped with atoms other than carbon, and optionally the atoms other than carbon are nitrogen, boron, and / or silicon.

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