Ultra-thin, ultra-low density films with thin molybdenum disilicide coating for extreme ultraviolet lithography

Abstract

A nanofiber pellicle for extreme ultraviolet (EUV) lithography with a thin molybdenum disilicide (MoSi2) deposition layer on at least one side of the nanofiber pellicle is disclosed. This surface-modified EUV pellicle improves certain properties of the nanofiber pellicle, for example, extending lifespan, while maintaining high EUV transmittance, balancing often contradicting properties.

Description

ULTRA-THIN, ULTRA-LOW DENSITY FILMS WITH THIN MOLYBDENUM DISILICIDE COATING FOR EXTREME ULTRAVIOLET LITHOGRAPHYCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Patent Application No.63 / 754,953, filed February 6, 2025, which is hereby incorporated by reference in its entirety.TECHNICAL FIELD

[0002] This disclosure generally relates to a surface-modified thin film and thin film device used in advanced semiconductor microchip fabrication and, more particularly, to an ultra-thin, ultra-low density nano structured free-standing pellicle film with a thin molybdenum disilicide (MoSi ) deposition layer and pellicle device for extreme ultraviolet (EUV) photolithography.BACKGROUND

[0003] A pellicle is a protective device that covers a photomask and is used in advanced semiconductor microchip fabrication. A photomask may refer to an opaque plate with holes or transparency that allows light to pass through and form a defined pattern. Such photomasks may be commonly used in photolithography and the production of advanced integrated circuits. As a master template, the photomask is repeatedly used to produce a pattern on substrates, commonly referred to as thin slices of silicon known as wafers in the case of semiconductor chip manufacturing.

[0004] Particle contamination can be a significant problem in semiconductor manufacturing. A photomask may be protected from particles by a pellicle, which has a thin transparent film (pellicle film) stretched over a pellicle frame that is attached over a patternedside of the photomask. The pellicle is positioned dose but far enough away from the mask so that moderate to small-sized particles that land on the pellicle film are too far out of focus to be printed. Recently, the microchip manufacturing industry recognized that the pellicle might also protect the photomask from damage stemming from causes other than particles and contaminants, and mandated pellicle use in high-power, high numerical aperture (high-NA) EUV lithography (EUVL).

[0005] Extreme ultraviolet lithography is an advanced optical lithography technology that uses a range of EUV wavelengths, more specifically, a 13.5 nm wavelength. It enables semiconductor microchip manufacturers to pattern the most sophisticated features at 7 nm resolution and beyond, and puts many more transistors without increasing the size of the required space. EUV photomasks work by reflecting light, which is achieved by using multiple alternating layers of molybdenum and silicon. When an EUV light source turns on, the EUV light hits the pellicle film first, passes through the pellicle film, and then bounces back from underneath the photomask, hits the pellicle film once more before it continues its path to print a microchip. Some of the EUV radiation energy is absorbed by the pellicle film during this process, and heat may be generated, absorbed, and accumulated in the pellicle film as a result. The temperature of the pellicle may heat up to anywhere from 300° Celsius (°C) to 1000° C or above.

[0006] While a pellicle must be highly transparent for EUV light to ensure the passing through of the incident and reflected light and light pattern from the photomask and have a low EUV scattering for printing accuracy and acuity without significant loss of EUV light energy for high production yield, its heat resistance and lifetime are important as well.

[0007] In 2016, a poly silicon-based EUV pellicle was developed after decades of research and effort, with only 78% EUV transmission on a simulated, relatively low-power 175-watt EUV light source. Due to increased transistor density demand and higher EUVradiation energies, stringent requirements pose further technical challenges for EUV pellicle developers in pursuing higher transmittance (transmission), lower transmission variation, higher temperature tolerance, and lower light scattering.

[0008] A carbon nanotube-based thin film was developed to provide a certain level of high-temperature tolerance under EUV irradiation for a certain period of time with little light scattering. Furthermore, the heat generated during photolithography raises the pellicle film's temperature from ambient to around 300°C, up to l,000°C, or higher, which shortens its lifetime and eventually breaks it. Any broken pellicle film or pieces of the broken pellicle film may cause damage, contamination, or adhesion of broken pellicle film to the scanner chamber and the mask (a.k.a. reticle) beneath. When a pellicle film is weakened, the scanner may have to stop and vent the chamber during and between microchip printing processes, which in turn increases the risk of damaging the already weakened pellicle film. Accordingly, in such a situation, the scanner will need to shut down and stop production to clean the broken pellicle film debris, resulting in lengthy downtimes.

[0009] In addition to the lifetime requirement, pellicle films must have very little light scattering. Any scattering may reduce image contrast, affecting image reconstruction and EUV photolithography throughput.

[0010] Also, EUV radiation produces plasma due to photoionization of background hydrogen gas that is often used in EUV power generation and delivery systems. These hydrogen ions, radicals, and electrons from the plasma may affect and reduce the lifetime and performance of various components in an EUV lithography scanner, including pellicles, often referred to as hydrogen plasma etching.

[0011] Applying a coating, often referred to as deposition, on a pellicle film has been attempted. Selecting an effective coating material, coating thickness, and coating technology to produce a pellicle film with a deposition layer can be challenging due to the very small massof an ultra-thin, ultra-low-density pellicle film, its fragility, and analysis methodologies of a small, negligible amount of coating material while pursuing goals of minimizing effects on EUV transmittance.SUMMARY

[0012] According to an aspect of the present disclosure, a specifically structured nanofiber film including a deposition layer is disclosed for EUV exposure. The structured nanofiber film may include a plurality of nanofibers that are intersected randomly to form an interconnected network structure in a planar orientation with a thin layer of molybdenum disilicide (MoSi ). The interconnected network structure in a pristine state may have a nanofiber film thickness selected from a lower limit of 3.0 nm to an upper limit of 100.0 nm prior to MoSi deposition, and a uniform visible light transmittance for EUV exposure. After MoSi deposition, the structured nanofiber film may have a minimum EUV transmittance of 88.0% or above. The word “pristine” used herein refers to an uncoated state of the interconnected network structure.

[0013] According to another aspect of the present disclosure, in some embodiments, a thickness of the interconnected network structure may range between the lower limit of 3.0 nm to an upper limit of 60.0 nm.

[0014] According to another aspect of the present disclosure, in some embodiments, a thickness of the interconnected network structure may range between the lower limit of 3.0 nm to an upper limit of 40.0 nm.

[0015] According to another aspect of the present disclosure, in some embodiments, a thickness of the interconnected network structure may range between the lower limit of 3.0 nm to an upper limit of 20.0 nm.

[0016] According to yet another aspect of the present disclosure, in some embodiments, an average thickness of the interconnected network structure may be 11.0 nm.

[0017] According to a further aspect of the present disclosure, in some embodiments, a minimum EUV transmittance of a structured nanofiber film (including a MoSi deposition layer) measured at 13.5 nm wavelength may rise to 90% or above.

[0018] According to a further aspect of the present disclosure, in some embodiments, a minimum EUV transmittance of a structured nanofiber film measured at 13.5 nm wavelength may rise to 92% or above.

[0019] According to a further aspect of the present disclosure, in some embodiments, a minimum EUV transmittance of a structured nanofiber film measured at 13.5 nm wavelength may rise to 95% or above.

[0020] According to yet another aspect of the present disclosure, in some embodiments, a minimum EUV transmittance of a structured nanofiber film measured at 13.5 nm wavelength may rise to 98% or above.

[0021] According to another aspect of the present disclosure, in some embodiments, a minimum EUV transmittance of a structured nanofiber film measured at 13.5 nm wavelength may be 99% or less.

[0022] According to one aspect of the present disclosure, in some embodiments, a minimum visible light transmittance of an interconnected network structure measured at 550 nm wavelength may be 80% or above.

[0023] According to one aspect of the present disclosure, in some embodiments, a minimum visible light transmittance of an interconnected network structure measured at 550 nm wavelength may be 90% or above.

[0024] According to another aspect of the present disclosure, in some embodiments, a minimum visible light transmittance of an interconnected network structure measured at 550 nm wavelength may be 92% or above.

[0025] According to a further aspect of the present disclosure, in some embodiments, a minimum light transmittance of an interconnected network structure at 550 nm wavelength may be 95% or above.

[0026] According to yet another aspect of the present disclosure, in some embodiments, a minimum light transmittance of an interconnected network structure measured at 550 nm wavelength may be 98% or less.

[0027] According to a further aspect of the present disclosure, the plurality of nanofibers may further include single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs), and a number of walls of SWCNTs is one, a number of walls of DWCNTs is two, and a number of walls of MWCNTs is three or more.

[0028] According to another aspect of the present disclosure, SWCNTs account for a percentage between 20-40% of all nanofibers, DWCNTs account for a percentage of 50% or higher of all nanofibers; the remaining nanofibers are MWCNTs, i.e., the SWCNTs, DWCNTs, and MWCNTs together equal 100%.

[0029] According to another aspect of the present disclosure, an average MoSi deposition thickness of the structured nanofiber film may be 3.0 nm or less.

[0030] According to another aspect of the present disclosure, an average MoSi deposition thickness of the structured nanofiber film may range from a lower limit of 0.15 nm and an upper limit of 3.0 or less, preferably, the upper limit being 2.0 nm or less, 1.5 nm or less, 1.0 nm or less, 0.5 nm or less, or 0.3 nm or less, and the lower limit being 0.5 nm or above, 1.0 nm or above, and 1.5 nm, or above.

[0031] According to one aspect of the present disclosure, a MoSi deposition layer may be deposited on a single side (or a first side) of the interconnected network structure or construed to be divided into two layers deposited on both sides of the interconnected network structure, respectively.

[0032] According to another aspect of the present disclosure, a MoSi deposition layer may cover a first side or a single side of the interconnected network structure facing an incoming EUV radiation energy or facing a photomask (or mask).

[0033] According to one aspect of the present disclosure, a MoSi deposition layer may protect the structured nanotube film from hydrogen plasma etching and extend lifetime (lifespan) of the structured nanofiber film.

[0034] According to one aspect of the present disclosure, a MoSi deposition layer may improve mechanical strength of the structured nanofiber film against hydrogen plasma etching, having, for example, a higher rupture pressure.

[0035] According to another aspect of the present disclosure, in some embodiments, a variant pristine structured nanofiber film may have two visible light transmittance measured at 550 nm wavelength (VisT), a higher VisT at a central region of the pristine interconnected network structure for EUV exposure and a lower VisT at a peripheral region of the pristine interconnected network structure not for EUV exposure, the central region being enclosed by the peripheral region.

[0036] According to another aspect of the present disclosure, in some embodiments, the higher VisT may be at least 2% higher than the lower VisT.

[0037] According to another aspect of the present disclosure, in some embodiments, the lower VisT may be selected from a lower limit of 40% to an upper limit of 96%.

[0038] According to another aspect of the present disclosure, in some embodiments, a pristine nanofiber film has at least two EUV transmittance at 13.5 nm (EUVT), a higher EUVTRate at a central region of the structured nanofiber film for EUV exposure, and a lower EUVT Rate at a peripheral region of the structured nanofiber film, the central region being enclosed by the peripheral region. The high EUVT Rate is disclosed in the corresponding embodiments above. A low EUVT Rate has an EUVT at least 1% lower than a high EUVT Rate.

[0039] According to another aspect of the present disclosure, in some embodiments, an interconnected network structure may have two layers, a first layer and a second layer. The first layer and the second layer are stacked together with no void space in between each layer, and each layer includes a first plurality of nanofibers and a second plurality of nanofibers, respectively, that are intersected randomly to form the first layer of the interconnected network structure in a planar orientation and the second layer of the interconnected network structure in a planar orientation. A peripheral region of the two-layer pristine carbon nanofiber film includes the first layer and the second layer; a central region enclosed by the peripheral region includes only the first layer.BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present disclosure is further described in the detailed description which follows, in reference to the noted plurality of drawings, by way of non-limiting examples of preferred embodiments of the present disclosure, in which like characters represent like elements throughout the several views of the drawings.

[0041] FIG. 1 illustrates a flowchart of producing an exemplary interconnected network structure (prior to MoSi deposition) for extreme ultraviolet (EUV) lithography (i.e., an EUV pellicle) by filtration of carbon nanotubes (CNTs) in accordance with an exemplary embodiment.

[0042] FIG. 2 illustrates a flow chart of producing a structured nanofiber film with a single-sided molybdenum disilicide (MoSi ) deposition and / or double-sided MoSi deposition (i.e., one MoSi deposition on each side of the interconnected network structure) in accordance with an exemplary embodiment.

[0043] FIG. 3 illustrates effect of MoSi deposition thickness on structured nanofiber films’ EUV transmittance in accordance with an exemplary embodiment.

[0044] FIG. 4 illustrates effects of a single-sided 0.5 nm-thick MoSi deposition on a pristine and uniform structured nanofiber film in a room temperature hydrogen plasma etching test in accordance with an exemplary embodiment.

[0045] FIG. 5 illustrates effects of a single-sided 2.0 nm-thick MoSi deposition on a uniform-density structured nanofiber film and a dual-density structured nanofiber film in accordance with an exemplary embodiment.

[0046] FIG. 6 illustrates effects on mechanical strength and visible light transmittance of a single-sided 2.0 nm-thick MoSi deposition on uniform-density nanofiber films before and after high-temperature hydrogen plasma etching treatment in accordance with an exemplary embodiment.

[0047] FIG. 7 illustrates efforts of MoSi deposition thickness on uniform-density nanofiber film’s lifetime in accordance with an exemplary embodiment.

[0048] FIG. 8 illustrates EUV transmittance difference of MoSi deposition and Molybdenum (Mo) deposition on uniform-density structured nanofiber films in accordance with an exemplary embodiment.

[0049] FIG. 9 illustrates high-temperature plasma etching results of MoSi deposition and Mo deposition on uniform-density nanofiber film in accordance with an exemplary embodiment.DETAILED DESCRIPTION

[0050] Through one or more of its various aspects, embodiments and / or specific features, sub -components, or processes of the present disclosure, are intended to bring out one or more of the advantages as specifically described above and noted below.

[0051] All numbers expressing quantities of ingredients, reaction conditions, thicknesses, and so forth used in the specification and claims may optionally be understood as being modified in all instances by the term “about.” Accordingly, the numerical parameters set forth in the following specification and attached claims may be approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding approaches.

[0052] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention may be approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Every numerical range given throughout this specification will include every narrower numerical range that falls within such broader numerical range, as if such narrower numerical ranges were all expressly written herein.

[0053] A pellicle may refer to a thin transparent membrane that protects a photomask during semiconductor microchip production. The pellicle construes a protective device with a border frame, the border frame having a central aperture. Both border and aperture are covered by a continuous thin film on top of at least a portion of the border and the entire central aperture. The center portion of such a thin film over the central aperture is free-standing. The pellicle may act as a dust cover or filter, preventing undesirable particles above a certain size andcontaminants from falling onto the photomask during microchip production. Like all pellicles, EUV pellicles must be sufficiently transparent to allow transmission of light and, more importantly, EUV irradiation and adequate amounts of EUV energy for performing EUV lithography. Ahigherlevel of light transmission is desired for more effective EUV lithographybased microchip production, as EUV radiation is absorbed by most materials, including atmospheric air. Meanwhile, EUV radiation sources, especially high-power EUV sources implemented in EUV lithography (EUVL) and high-NAEUVL, are known to be prohibitively costly and scarce.

[0054] As EUV light travels through a pellicle in a vacuum or an EUV scanner chamber filled with a low hydrogen gas pressure, and hits and bounces back from a reticle beneath, a portion of the EUV radiation energy is absorbed by the pellicle, and another portion of EUV light in a deviated direction that is slightly different from the original EUV traveling passage and the bouncing back passage, called scattering. This EUV scattering may create aberrant light patterns from the masks and lead to printing errors, reduced printing resolution, and / or lower microchip production yields when ultimately reaching silicon wafers. The total amount of scattered light that deviates from its original path within a 4.7 degree angle is measured, and the result is a critical parameter in the current industry specification, i.e., the degree of scattering expressed as a percentage.

[0055] Further, EUV pellicles may require a long lifetime to support continuous manufacturing operations, avoiding frequent pellicle replacement that requires EUV scanner pump-down and venting cycles and causes production interruption.

[0056] Additionally, EUV photons may induce a low-density plasma via photoionization of hydrogen gas in the EUV scanner background. This hydrogen gas is often used in the EUV radiation delivery system. The plasma-emitted ions, radicals, and electrons may affect major lithography scanner components, such as optical mirrors, reticles, andpellicles. Regarding a pellicle, hydrogen plasma may reduce its lifetime and weaken its mechanical strength, leading to premature breakage or rupture.

[0057] One suggested resolution is to apply a thin protective coating on the pellicle film. When EUV irradiation is off or during intervals between EUV irradiations, this protective coating releases absorbed heat acquired during the EUV irradiations. It increases the emissivity of pellicle film, reduces pellicle film temperature, and extends the pellicle film lifetime.

[0058] Any selected coating material, after deposition on a pellicle, must ensure overall high EUV transmittance with minimal transmittance reduction. Excessive reduction in EUV transmittance may be unacceptable due to high transmittance specifications of EUV pellicles. Secondly, any protective deposition layer should not alter the scattering pattern in a way contravening the stringent EUV pellicle’s scattering standard. The coating material must be applied to the surface of the pellicle film, remain attached to the surface, and withstand a high-temperature environment without peeling off during and after EUV irradiation, which can result in contamination of the mask, the scanner chamber, and scanner components. The coating material is preferred to enhance a pellicle’s resistance to hydrogen plasma etching and pellicle’s mechanical strength. However, not all known coating materials may meet the EUV pellicle specifications. Several factors may be considered and studied to balance the required specifications, such as high EUV transmittance, long lifetime, and sustained mechanical strength of the nanofiber film.

[0059] In this respect, carbon nanotube pellicle films with selected MoSi deposition thicknesses and the associated production method are disclosed and suggested as a possible solution for EUV applications.Carbon Nanotubes and Carbon Nanotube Films

[0060] Carbon nanotubes (CNTs) generally have several different types, including, without limitation, single-walled CNTs (SWCNTs), double-walled CNTs (DWCNTs), multi-walled CNTs (MWCNTs), and coaxial nanotubes, wherein SWCNTs have one or single wall, DWCNTs have two walls, and MWCNTs have three or more walls, as the name suggests. The coaxial nanotubes have at least two walls, and a material of a first wall of the at least two walls differs from a material of a second wall of the at least two walls, e.g., a CNT inside and a boron nanotube (BNNT) outside or a graphene sheet wrapping around a BNNT with a common axis. These nanotubes may exist substantially pure in one type or, more often, in combination with other types. An individual nanotube may intersect or tangle around one or more other nanotubes to form nanotube bundles. Together, many nanotubes may form a mesh-like, freestanding, or structured or microstructured thin film.

[0061] Among several possible methods to fabricate free-standing nanofiber films for EUV lithography, a filtration-based approach was used to produce exemplary nanofiber films ranging from small to sufficiently large sizes, and from uniform density to dual -density, and this filtration approach allows for quick manufacturing of nanofiber films not only of CNTs but also other high aspect ratio nanoparticles and nanofibers, such as BNNTs or silver nanowires. Since this approach separates nanoparticle synthesis methods and film manufacturing methods, a variety of nanotube or nanofiber types produced by virtually any method may be used. Different types of nanotubes and nanofibers can be mixed in any desired ratio, such as a mixture of two or more CNTs selected from SWCNTs, DWCNTs, MWCNTs, and coaxial nanotubes. As filtration is a self-leveling process in the sense that non-uniformities of film thickness and / or densities during the filtration process are self-corrected by the variations of local permeability on a surface of a filtration membrane and, therefore, a highly desirable film formation process, it is also a promising candidate for the production of highly uniform films. Alteration of the filtration membrane permeability or filtration speed may cause different amounts of CNTs to be deposited on the filtration membrane, thus producing a different type of film, a desired and non-uniform film with two different visible light or EUVtransmittance, two different areal densities, or two different film thickness in defined portions of a nanofiber film, e.g., a central portion of a nanofiber film having a higher visible light and EUV transmittance, a lower areal density, a thinner film thickness vs. a peripheral portion of the same pellicle film having a lower visible light and EUV transmittance, a higher areal density, a thicker film thickness, all of which are collectively referred to as dual -tone nanofiber film, dual or two density nanofiber film.

[0062] After a successful filtration process, a filtered nanofiber film is produced and harvested, ready for MoSi deposition selected from electron-beam, sputtering, direct current (DC) sputtering, radio frequency (RF) sputtering, or other physical vapor deposition methods.

[0063] FIG. 1 illustrates a flowchart for producing a freestanding filtered nanofiber film for EUV lithography in accordance with an exemplary embodiment.

[0064] As FIG. 1 illustrates, a catalyst is removed from carbon nanotubes (CNTs) that are to be used to form a water-based suspension in operation 101. In an example, prior to dispersion into a suspension, the CNTs may be chemically purified to reduce a concentration of catalyst particles to less than 1% weight (wt.) or preferably less than 0.5% wt. as measured by thermogravimetric analysis. Removal of the catalysts is not limited to any particular process or procedure, such that any suitable process may be used to achieve a desirable result.

[0065] In operation 102, a water-based suspension is prepared from the purified CNTs, such that the purified CNTs are evenly dispersed in water. When preparing one or more CNT suspensions, carbon nanotube material may be selected from a single CNT type or two or more different CNT types, and may be mixed with a selected solvent to uniformly distribute nanotubes in a final solution as a suspension. Mixing can include mechanical mixing (e.g., using a magnetic stir bar and stirring plate), ultrasonic agitation (e.g., using an immersion ultrasonic probe), or other methods. In some examples, the solvent can be a protic or aprotic polar solvent, such as water, isopropyl alcohol (IPA), and aqueous alcohol mixtures, e.g.,selected 60% to 95% IPA, N-Methyl-2-pyrrolidone (NMP), dimethyl sulfide (DMS), and a combination thereof. In another example, a surfactant may also be added to promote the uniform dispersion of carbon nanofibers in the solvent. Examples of surfactants include, but are not limited to, anionic surfactants, e.g., sodium dodecyl sulphate (SDS).

[0066] CNT types refer to one or more of MWCNTs, DWCNTs, SWCNTs, and coaxial nanotubes. A carbon nanofiber film may include one CNT type and may also include a mixture of two or more types of CNTs with a variable ratio between the different types of CNTs.

[0067] Each of these three different types of carbon nanotubes (MWCNT, DWCNT, and SWCNT) has different properties. In one example, single-wall carbon nanotubes can be more conveniently dispersed in water or water with a solvent (i.e., with the majority of nanotubes suspended individually and not adsorbed onto other nanotubes) for subsequent production of a sheet of a plurality of carbon nanotubes that are randomly oriented in a planar orientation to form an interconnected network structure. This ability of individual nanotubes to be uniformly dispersed in water or water with a solvent can, in turn, produce a more planarly uniform nanotube film by removing the water and solvent from the nanofiber suspension. This physical uniformity of nanotube suspension can also improve the uniformity of the properties across the film (e.g., even irradiation transmission across a film).

[0068] As used herein, the term “nanofiber” means a fiber having a diameter less than 1pm. The terms “nanofiber” and “nanotube” are used interchangeably and encompass singlewalled carbon nanotubes, double-walled carbon nanotubes and / or multiwalled carbon nanotubes in which carbon atoms are linked together to form a cylindrical structure.

[0069] In operation 103, the CNT suspension is further purified to remove aggregated or agglomerated CNTs from the initial mixture, yielding a CNT supernatant. In an example, different forms of CNTs, undispersed or aggregated, may be separated from fully dispersed CNTs in the suspension via centrifugation. Centrifugation of surfactant-suspended carbonnanotubes may help reduce suspension turbidity and ensure full dispersion of the carbon nanotubes in the final CNT supernatant solution before the next filtration step. However, the disclosure is not limited to these aspects, and other separation methods or processes may be used.

[0070] In operation 104, the CNT supernatant from operation 103 is filtered through a membrane to form a CNT web, which may be a continuous sheet of nanofiber film of intersecting CNTs with a planar interconnected network structure.

[0071] In an example, one technique for making a CNT film uses water or other fluids to deposit nanotubes in a random pattern on a filter membrane. The evenly dispersed CNT-containing mixture is allowed to pass through or forced through the filter membrane, leaving nanotubes on the filter membrane surface to form a structured nanofiber film with a plurality of nanotubes intersecting randomly and in a planar direction, forming an interconnected network structure. The size and shape of the filtered nanofiber film are determined by the size and shape of the desired filtration area of the filter membrane, while the thickness and density of the membrane are determined by the quantity of nanotube material utilized during the filtration process and the permeability of the filtration membrane to the ingredients of the input CNT material, as the impermeable ingredient is captured on the surface of the filter membrane. If the concentration of nanotubes dispersed in the fluid is known, the mass of nanotubes deposited onto the filter membrane can be determined from the amount of fluid that passes through the filter membrane, and the resulting film’s areal density is determined by the input nanotube mass divided by the total filtration surface area. An areal density correlates linearly with visible light transmittance of a nanofiber film. The selected filter membrane is generally not permeable to any CNTs in accordance with the embodiments of this disclosure.

[0072] In operation 105, the CNT film is then detached from the filtration membrane.

[0073] In operation 106, the detached CNT film is then harvested using a harvester frame and then directly transferred and mounted onto virtually any solid substrate, such as a metal frame, a silicon frame, or a pellicle border with a defined aperture. The detached CNT film may be mounted to the pellicle border and cover the border’s aperture to form a pellicle. The mounted CNT film covering the aperture may be freestanding, with dimensions of the aperture as small as 10 millimeters (mm) by 10 millimeters and as large as 110 mm by 140 mm or more, thus serving as an EUV pellicle. Exemplary embodiment of the present disclosure covers a filtered CNT pellicle film and a CNT pellicle film produced by non-filtration methods with a different constitution from known prior art while exhibiting properties meeting or exceeding certain aspects of EUV lithography specification, including, but not limited to, high EUV transmittance (EUVT), low EUV scattering, and long lifetime.

[0074] In an example, a detached CNT film may include a plurality of CNTs having 85% or above SWCNTs. The remaining CNTs may be a mixture of DWCNTs, MWCNTs (3 or more walls), totaling 100%. In other examples, a detached CNT film may include various ratios of different types of CNTs, such as 50% or more to 95% or less DWCNTs, 5% or more to 50% or less SWCNTs, and 0% or more to 45% or less MWCNTs (3 or more walls), the SWCNTs, DWCNTs, and MWCNTs together accounting for 100%. Yet in another example, a detached CNT film may include 45% or more to 85% or less SWCNTs, 50% or less to 15% or more DWCNTs, and 0.2% or more or 10% or less MWCNTs (3 or more walls), the SWCNTs, DWCNTs, MWCNTs, and catalyst together accounting for 100%.

[0075] In another example, a detached CNT film may have a thickness between a lower limit of 3 nm and an upper limit of 100 nm, preferably 60 nm or less, 40 nm or less, or 20 nm or less.

[0076] The harvested CNT film from operation 106 may be optionally annealed in operation 107. In operation 108, the harvested CNT film may be produced with or without the optional annealing in operation 107. A detailed description of annealing is provided below.Annealing Treatment

[0077] Annealing is a process of applying heat to a material to alter its physical and, in some cases, chemical properties, increasing its ductility and reducing its hardness. Annealing may, for example, include Joule heating, convection heating, and radiant heating.

[0078] In radiant heating, an electromagnetic wave, for example, a light source within a visible spectrum, a laser, may be applied directly onto a nanofiber film surface. The photons of the light may heat a given area of a target material.

[0079] Annealing may be thermal annealing, which may use an electromagnetic wave within a non-visible light spectrum, including but not limited to infrared.

[0080] Electromagnetic waves may be selected from a wavelength or wavelengths between 10 nm and 1 mm. A preferred wavelength range may also be selected from between about 400 nm and about 700 nm or between about 700 nm and about 1 mm. Yet another preferred wavelength range may be between about 5 pm and about 20 pm. This heating method may transfer thermal energy to a target material while the thermal energy dissipates into other microscopic motions within the material. In other words, thermal annealing may distribute its energy and heat a target material to raise the temperature uniformly. The thermal annealing may preferably cover the entire target object regardless of the direction of the incoming energy source.

[0081] In light-based annealing, short pulses or flashes of light may heat a nanofiber film within a short duration, which may range from 0.1 milliseconds to 2 seconds. Light-based annealing may include a single flash or a combination of several flashes. The light-basedannealing may deliver a quantity of high energy to heat up and cool down nanofiber films quickly, which is beneficial for avoiding adsorbing additional substance(s) from environment.

[0082] The annealing treatment in the exemplary embodiments includes, but is not limited to, the above-mentioned heating methods. Without wishing to be bound by scientific theory, it is believed that other heating methods and heating devices may also be applicable.

[0083] The common annealing temperature may be any temperature above ambient temperature. The annealing temperature may be selected between 50°C and above, up to 3,000°C or less, preferably between 400°C and above, up to l,200°C and less. A flash duration in light annealing may be as low as 0.1 milliseconds and up to 2 seconds. Thermal annealing may include a slow temperature ramp-up phase, a target-temperature holding period, and a cooling period. The target-temperature holding period may be selected from 5 seconds or more to 60 minutes or less within a furnace.

[0084] Annealing treatment may occur under atmospheric pressure, in partial vacuum, or preferably in a vacuum or near vacuum environment (i.e., less than 15 pascals). Additionally, annealing treatment may occur in the presence of an inert gas, a non-inert gas, or hydrogen. Exemplary inert gases include, but are not limited to, argon, helium, neon, krypton, xenon, and radon. An exemplary non-inert gas may include a hydrocarbon gas, such as methane, ethane, propane, butane, pentane, hexane, and heptane.

[0085] The term “annealing” may include further aspects and broader interpretations in various technical fields and industries applicable to or related to the current disclosure, and one or more of the present innovative contributions herein arise in the materials science and semiconductor fields.

[0086] Annealing of nanofiber films may remove amorphous carbon adsorbed on nanofiber film’s surfaces and improve pristinity of nanofibers (pristine status) measured by the G-band to D-band intensity ratio, thus benefiting, especially, EUV transmittance.Physical Vapor Deposition

[0087] Physical vapor deposition (PVD) represents a versatile thin-film coating process. Common PVD includes, but is not limited to, electron-beam physical vapor deposition (E-beam), magnetron sputtering, evaporative deposition, and pulsed-laser deposition. Embodiments of the present disclosure were developed and demonstrated by one or more PVD methods.

[0088] E-beam is a physical vapor deposition technique to evaporate a source material using high-energy electrons in the form of an intense beam. The E-beam machine causes thermionic emission of electrons, which, after acceleration, provide sufficient energy for evaporating any material, in this instance, molybdenum disilicide (MoSi ), and deposits MoSi on a first surface of an interconnected network structure to produce a nanofiber film. The nanofiber film may be flipped for a second MoSi deposition on a second surface of the nanofiber film, the second surface being opposite of the first surface. A E-beam machine is typically equipped with a deposition thickness monitor to guide the vapor deposition process.

[0089] Magnetron sputtering is another PVD method that offers dense deposition and defect-free deposition of desired material at high process rates, often in a vacuum chamber. The magnetron generates microwaves, with electrons controlled by an external magnetic field. Appling a negative charge to the magnetron causes the release of targeted MoSi molecules that are then collected at the substrate, i.e., a nanofiber film.

[0090] However, aspects of the present disclosure are not limited to the deposition or coating methods listed above. Implementation of the current invention is not limited to E-beam and magnetron sputtering. Other PVD methods, for example, thermal evaporation, remote plasma sputtering, electrochemical deposition, and electroplating, may be explored. Thecurrent disclosure may additionally contemplate atomic layer deposition and chemical vapor deposition to achieve a thin deposition layer(s) over nanofiber film surfaces.Carbon Nanotube Film with Two Transmittances

[0091] An EUV pellicle may have a uniform visit light transmittance or EUV transmittance across a portion of the pellicle film designated for EUV irradiation or EUV exposure, often referred to as a central region of the pellicle film. A peripheral region of the same pellicle film, which surrounds the central region, may have a lower visible light transmittance or EUV transmittance that correlates to a higher thickness or a higher areal density of the pellicle film’s peripheral region. This type of pellicle film may be referred to as two-tone pellicle films or two-density (or dual density) pellicle films.

[0092] The production method in the embodiment of FIG. 1 and related disclosure may be revised to produce the two-density pellicle films. Particular resorts involve altering the permeability of the peripheral portion of a filtration membrane by reducing a thickness of the corresponding peripheral region of the filtration membrane, applying a post-filtration membrane vacuum pressure at a higher negative pressure to the peripheral region compared to a negative pressure applied to a central region of the filtration membrane, or increasing flow rate of nanofiber suspension to the peripheral region of the filtration membrane.

[0093] Another embodiment of the present disclosure further includes a method for producing a two-tone nanofiber film via a floating-catalyst chemical vapor deposition method (FC-CVD).

[0094] A detailed description of two-tone pellicle and production method based on filtration and FC-CVD is disclosed in PCT application WO 2025 / 075913, which is incorporated herein by reference.

[0095] Advantages of two-tone pellicle films include enhanced plasma etching resistance and mechanical strength.

[0096] The MoSi2 deposition disclosed herewith further improves hydrogen plasma etching resistance, as detailed below.Visible and EUV Light Transmittance

[0097] A carbon nanotube film may be measured for its visible light transmittance at 550 nm wavelength (VisT) before and after the optional annealing step, i.e., Operation 107 of FIG. 1, and after any surface modification, for example, coating or deposition (FIG. 2). The same carbon nanofiber film may be further measured using EUV, for example at 13.5 nm wavelength, for its EUV transmittance (EUVT). Since EUV radiation is absorbed by most substances, its measurement may require a vacuum environment and specialized equipment. EUVT measurement is more sensitive than VisT, especially for ultra-thin, highly porous, and highly transparent nanofiber films. In other words, a little change or no change in VisT for the ultra-thin, highly porous, and highly transparent nanofiber film may reflect a measurable change in EUVT, which may alter an EUV pellicle’s qualification status from eligible to non-eligible using EUVT specifications.

[0098] A coating or deposition may reduce VisT and EUVT to varying degrees. Without EUVT measurement, significant challenges exist to understand VisT and, more importantly, EUVT post-surface deposition. Changes of EUVT and its features are further illustrated in FIGS. 3 and 8, and discussed below.MoSii Coated Pellicle Films

[0099] FIG. 2 illustrates a flow chart of preparing a nanofiber film with MoSi deposition layers and producing a MoSi2-coated EUV pellicle.1

[0100] An interconnected network structure produced according to method of FIG. 1 (e.g., a CNT film), the FC-CVD method disclosed above, and any other methods utilized in producing the interconnected network structure in Operation 210 of FIG. 2 may be subject to Operation 220 of FIG. 2 for application of a first thin MoSi deposition on a first surface (or a first side) of the interconnected network structure. In an example, thickness of the first surface may range between 0.15 nm to 3.0 nm. A second thin MoSi coating (deposition) may be deposited on a second surface (or a second side) of the interconnected network structure, the second surface being opposite of the first surface (Operation 230). In an example, thickness of the second surface may range between 0.15 nm to 1.5 nm. The thickness of the first surface may be same or different from the thickness of the second surface.

[0101] Depending on the selected deposition material and its initial physical properties, such as whether it is in solid or vapor form, a deposition method and equipment may be used, including E-beam, magnetron sputtering, or any other methods and devices disclosed above. The first thin MoSi deposition and the second thin MoSi deposition may be performed in parallel, which deviates from the exact order of FIG. 2.

[0102] A nanofiber film may have a first thin MoSi deposition or have both a first thin MoSi2 deposition and a second thin MoSi deposition. A deposition thickness generally refers to a total deposition thickness of one or two depositions on one side or both sides of a nanofiber film, i.e., a first thin MoSi deposition in the absence of a second thin MoSi deposition or a first thin MoSi deposition plus a second thin MoSi2 deposition.

[0103] A first thin MoSi2 deposition thickness may be the same as a thickness of a second thin MoSi deposition, for example, 0.15 nm, 0.25 nm, 0.5 nm, 1.0 nm, or 1.5 nm thick for each deposition on each surface of an interconnected network structure. Alternatively, the first MoSi deposition thicknesses and the second MoSi deposition thicknesses may be different in a way that a thicker deposition is deposited on the first surface of the interconnectednetwork, which may face an EUV light source in an EUV scanner, while the thinner deposition on the second surface of the interconnect network, the second surface being opposite the first surface, and the second surface facing a mask in the EUV scanner. A corresponding ratio (i.e., the first thin MoSi2 deposition thickness vs. the second thin MoSi deposition thickness) may be in a range of 1 to 5 vs. 1 (e.g., a first thin MoSi deposition having a thickness selected from 0.5-2.5 nm vs. a second thin MoSi deposition having a thickness of 0.5 nm, or 1:1 to 5:1), preferably in a range of 1.5:1 to 4:1. This asymmetric total deposition thickness distribution on opposite surfaces of a nanofiber film may address differential EUV radiation energies arriving at each side of an EUV pellicle for maximal pellicle lifetime extension while keeping a total deposition thickness on both sides of an EUV pellicle at minimum and, at the same time, maintain a sufficiently high or optimal EUVT to meet EUV pellicle transmittance specification.

[0104] FIG. 3 lists five example samples, produced in accordance with FIG. 1 with different MoSi2-deposition thicknesses, and their EUVT measurement results. The results demonstrate the effects of MoSi2-deposition thickness on the EUV transmittance of uncoated (or pristine) nanofiber films. All five of these samples have a uniform areal density and / or light transmittance.

[0105] As illustrated in FIG. 3, samples 3 A to 3E have similar VisT. Samples 3 A and 3B’s VisT, measured at 550 nm wavelength, are slightly lower than VisT of Samples 3C-3E, that is 79% vs. 80%, respectively. Therefore, Samples 3C-3E may be slightly more transparent than Samples 3 A-3B, having a slightly higher EUV transmittance (EUVT). Samples 3B, 3C, 3D, and 3E have total MoSi2-deposition thicknesses of 0.5 nm, 2.0 nm, 4.0 nm, and 5.5 nm, respectively. Samples 3B and 3C underwent single-sided E-beam deposition and magnetron sputtering deposition, respectively. Samples 3D and 3E underwent double-sided and equalthickness deposition on both sides of the samples by the magnetron sputtering method, i.e., 2.0 nm on each side for Sample 3D and 2.75 nm on each side for Sample 3E.

[0106] The 0.5 nm-thick MoSi deposition in Sample B reduces EUVT from 94.92% of Sample 3 A (pristine or uncoated) to 92.36% of Sample 3B. Such an EUVT reduction is not apparent when only a VisT is considered. This data demonstrates that EUVT measurement is essential in EUV pellicle evaluation.

[0107] Considering 92.10%, 84.40%, and 83.90% EUVTs of Samples 3C - 3E, respectively, both the total MoSi deposition thickness of 4.0 nm of Sample 3D and 5.5 nm of Sample 3E reduce EUVT to under 85%. According to aspects, a EUVT below 85% may often be considered as not meeting EUV pellicle specification. A total of 3.0 nm-thick MoSi deposition, preferably a total of 2.0 nm-thick deposition, may raise EUVT to 88% or 92%, respectively, in which cases both 88% or 92% EUVTs may be acceptable or exceed EUV pellicle specification. After surface deposition of a pristine nanofiber film, a greater than 7% reduction in EUV transmittance (i.e., from about 95% to about 88%) may be avoided.

[0108] Furthermore, an EUV uniformity is measured for at least one sample listed in FIG. 3. A stringent EUV uniformity test subtracts any two EUVT measurements from the same EUV pellicle, and all results (or EUV variation) are less than 0.4%. At least one of the samples tested from FIG. 3 had an EUVT variation smaller than 0.4%.

[0109] FIG. 4 demonstrates a MoSi deposition, as thin as 0.5 nm-thick deposition on a single side of a nanofiber film, may at least double the nanofiber film’s lifetime.

[0110] Samples 4A and 4B, produced in accordance with methods of FIGS. 1 and 2, have a uniform 80% light transmittance measured at 550 nm wavelength (VisT) when un coated (pristine). Sample 4B has a 0.5 nm-thick single-sided MoSi deposition layer by E-beam. In a room temperature (RT) hydrogen plasma etching test, Sample 4A survived four (4) rounds of tests and then broke while Sample 4B sustained eleven (11) rounds of the same test.

[0111] In a room-temperature hydrogen plasma etching test, a sample pellicle, is placed in a closed, near-vacuum chamber. An 80-watt radio-frequency energy at 13.56 MHz is appliedfor 20 seconds, with a constant hydrogen gas flow of 15 seem through the chamber at ambient temperature. If a sample survives a 20-second test duration, it passes one (1) round of the test.

[0112] FIG. 5 further illustrates effects of a single-sided 2.0 nm-thick MoSi deposition on a uniform-density nanofiber film and a dual-density nanofiber film with improved room temperature hydrogen plasma etching resistance and enhanced mechanical strength. In FIG. 5, testing results of Samples 5A, 5B and 5C are provided.

[0113] In FIG. 5, Samples 5 A and 5B have uniform VisT at 81% and 80%, respectively, produced in accordance with methods of FIGS. 1 and 2. Sample 5C has a 79% VisT measured at its central region and 40% VisT at its peripheral portion (i.e., a dual density nanofiber film), Sample C being produced in accordance with the embodiment described above.

[0114] Sample 5 A received no MoSi deposition and did not survive after 5 rounds of room temperature hydrogen plasma etching test.

[0115] Samples 5B and 5C received a single-sided 2.0 nm-thick MoSi deposition and have 77% post-deposition VisT for Sample 5B and the central portion of Sample 5C. Based on the above noted application, in the room temperature hydrogen plasma etching test, Sample 5B broke after twenty-four (24) rounds of tests, and Sample 5C broke after twenty-eight (28) rounds of tests.

[0116] Additional rupture pressures of Samples 5A and 5 B, after one round of room temperature hydrogen plasma etching test, were measured and shown in FIG. 5.

[0117] In a rupture test, a steady flow of gas is directed perpendicularly at the center of a nanofiber film. The gas pressure increases gradually until the nanofiber film breaks. A gas pressure at the moment the nanofiber film breaks is recorded as a rupture pressure. A distance between a baseline position (i.e., with no gas flow) and the time of rupture of the nanofiber film center is recorded as a deflection distance at rupture. An inert gas, such as nitrogen, is preferred in the rupture test. Comparing to Sample 5A’s rupture pressure of 45.5 Pascals (Pa),Sample B’s rupture pressure of 200.9 Pa is at least three times higher, suggesting a high mechanical strength contributed by the thin MoSi deposition layer.

[0118] The results from FIGS. 4 and 5 demonstrate that a thicker MoSi deposition (i.e., a 2.0 nm-thick deposition) extends the lifetime of a nanofiber film and increases the nanofiber film’s mechanical strength compared to a 0.5 nm-thick MoSi deposition. However, increasing the deposition thickness further may reduce EUV transmittance, as the results in FIG. 3 illustrates.

[0119] In FIG. 6, exemplary samples were subjected to a high-temperature hydrogen plasma etching (HTHPE) test, which simulates conditions in an EUV scanner chamber. These samples were prepared in accordance with the embodiment of FIGS. 1 and 2 and the corresponding descriptions. Samples of FIG. 6 had a uniform 77.7% VisT. FIG. 6 illustrates testing results of three groups of samples, each group including a pair of an uncoated sample and a single-sided coated (c) sample. More specifically, each sample group in FIG. 6, i.e., 6A-6C, has one uncoated sample (i.e., 6A-u, 6B-u, and 6C-u, respectively) and one coated sample having 2.0 nm single-sided MoSi deposition by E-beam method (i.e., 6A-c, 6B-c, and 6C-c, respectively).

[0120] A HTHPE treatment includes placing a nanofiber film in a closed chamber under near-vacuum conditions, injecting a constant hydrogen gas flow of 7.5 Pa, applying a 125-watt radio frequency energy source, raising a temperature to 450°C, and maintaining the 450°C for thirty (30) minutes. This test delivers predominantly hydrogen radicals to the surface of a test sample (i.e., a nanofiber film).

[0121] Sample 6A-u shows a 9.2% increase in VisT, from 77.7% in the pristine nanofiber film to 86.9% after the HTHPE test, indicating a significant increase in visible light transmittance and a substantial loss of internal material from the pristine nanofiber film due to high-temperature etching. Sample 6A-c, although showing a small 0.9% VisT loss due to athin 2.0 nm MoSi2 deposition, achieved an 82.9% VisT after HTHPE, a smaller 6.1% gain in VisT compared to Sample 6A-u, suggesting a lesser loss of internal substance due to the MoSi deposition. This result further suggests the protective effect of the MoSi deposition layer.

[0122] Rupture pressures of the exemplary pristine nanofiber film Sample 6B-u dropped from 339.8 Pa before HTHPE to 25.1 Pa after HTHPE, as high-temperature hydrogen plasma etching causes damage to target material’s integrity; a rupture pressure of the exemplary nanofiber film, which had a 2.0 nm MoSi deposition layer, dropped from 372.8 Pa before HTHPE to 84.5 Pa after HTHPE. These results suggest that a 2.0 nm MoSi deposition layer on the nanofiber film increases the rupture pressure from 339.8 Pa to 372.8 Pa without HTHPE and from 25.1 Pa to 84.5 Pa upon HTHPE.

[0123] The deflection distances of the pristine Sample 6C-u at rupture were reduced from 0.54 mm before HTHPE to 0.29 mm after HTHPE, a 13% drop, and from 0.47 mm before HTHPE to 0.28 mm after HTHPE for Sample 6C-c (also a 2 nm MoSi deposition), a 3.4% drop. The net rupture pressure gain under HTHPE of 59.4 Pa (84.5 Pa - 25.1 Pa) due to 2.0 nm-thick MoSi deposition layer is almost twice as much as a net rupture pressure gain of 33.0 Pa (372.8 Pa - 339.8 Pa) with a 2.0 nm MoSi deposition layer in the absence of HTHPE, suggesting another effective protection rendered by 2.0 nm-thick MoSi deposition under a near EUV scanner environment, and the same MoSi deposition does not cause significant rupture pressure deflection deterioration.

[0124] FIG. 7 shows lifetime test results of nanofiber films with different MoSi2 deposition thicknesses upon a modified high-temperature hydrogen plasma etching tests.

[0125] Samples 7A-7C of nanofiber films were initially prepared according to the embodiment of FIG. 1 and its description, and their VisT were measured as 78.8%. Sample 7A remains uncoated in a pristine state. Samples 7B and 7C received a 0.5 nm-thick MoSi deposition and a 1.0 nm-thick MoSi deposition on a single side of the nanofiber film,respectively. The modified high-temperature hydrogen plasma etching (m-HTHPE) test was performed at 400°C, a temperature lower than the 450°C of the previously described HTHPE test, until the testing subject breaks.

[0126] Samples 7A, 7B, and 7C broke after 13.78 min, 48.88 min, and 296.5 min in the m-HTHPE tests, respectively. The results show a strong correlation between MoSi deposition thickness and nanofiber film’s lifetime. However, as disclosed herein and shown in FIG. 3, an even thicker total MoSi deposition layer, for example, 4.0 nm or 5.5 nm, may reduce EUVT to below 85%, which falls short of the current EUV pellicle specification.

[0127] Taking the EUV pellicle specification into consideration and combining FIGS.3-7 and their embodiments, this disclosure illustrates the benefits of MoSi deposition or coating on a pristine nanofiber film for much-needed hydrogen plasma etching resistance and lifetime extension, either at ambient temperature or at elevated temperatures up to 1,200 °C. With respect to deposition thickness, a thicker MoSi layer appears to provide better etching protection, but without experimentation, its adverse effects and / or disadvantages may be unknown. A preferred MoSi2 deposition thickness may be 3.0 nm total, distributed equally or asymmetrically on both sides (two opposite surfaces) of a nanofiber film, or on a single side of a nanofiber film, reaching a balance between several important pellicle film properties and meeting EUV pellicle specifications.

[0128] This constitution of the present disclosure provides an ultra-thin pellicle film, which allows for very high EUVT (e.g., 88% and above, 92% and above, or 95% and above) while being high-temperature resistant (e.g., at 450°C and above) and mechanically robust.Comparative Pellicle Film Coatings

[0129] FIG. 8 illustrates that both 1.0 nm-thick molybdenum (Mo) deposition layer (Sample 8B) and a 1.0 nm-thick MoSi deposition layer (Sample 8C) showed different EUVT reduction when compared to the pristine Sample 8A.

[0130] Samples 8A-8C were prepared according the embodiment of FIG. 1. AMoSi deposition layer was applied to Samples 8A and 8B in accordance with FIG. 2, while a Mo deposition layer was applied to Sample 8C, following the deposition procedure in accordance with FIG. 2. All three samples, prior to depositions of Samples 8B and 8C, had a pristine 77.7 VisT. Sample 8B with 1.0 nm thick Mo deposition has a 87.59% EUVT, lower than Sample 8A’s 94.65% EUVT (a 7.06% EUVT reduction) and Sample 8C’s 90.52% EUVT (a 4.13% EUVT reduction).

[0131] FIG. 9 shows lifetime test results from Sample 9A, a pristine nanofiber film with a 77.5% VisT, Sample 9B, a pristine nanofiber film having a 68.2% VisT and a single-side 2.0 nm-thick Mo deposition by e-beam, and Sample 9C, a pristine nanofiber film having a 77.4% VisT and a single-side 2.0 nm-MoSi deposition by E-beam. Sample 9B survived less than 30 seconds in an HTHPE test (described above), while Samples 9A and 9C passed 18 minutes and 30 minutes in the same HTHPE test, respectively. The higher pristine film thickness of Sample 8B due to its lower VisT does not seem to extend its lifetime in the HTHPE test. These results demonstrate that not all coating materials provide the same benefit to or exhibit the same trend in a nanofiber film.

[0132] The illustrations of the embodiments described herein are intended to provide a general understanding of the various embodiments. The illustrations are not intended to serve as a complete description of all of the elements and features of products and methods that form the products or methods described herein. Many other embodiments may be apparent to those of skill in the art upon reviewing the disclosure. Other embodiments may be utilized andderived from the disclosure, such that structural and logical substitutions and changes may be made without departing from the scope of the disclosure. Additionally, the illustrations are merely representational and may not be drawn to scale. Certain proportions within the illustrations may be exaggerated, while other proportions may be minimized. Accordingly, the disclosure and the figures are to be regarded as illustrative rather than restrictive.

[0133] One or more embodiments of the disclosure may be referred to herein, individually and / or collectively, by the term “invention” merely for convenience and without intending to voluntarily limit the scope of this application to any particular invention or inventive concept. Moreover, although specific embodiments have been illustrated and described herein, it should be appreciated that any subsequent arrangement designed to achieve the same or similar purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all subsequent adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the description.

[0134] The Abstract of the Disclosure is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, various features may be grouped together or described in a single embodiment for the purpose of streamlining the disclosure. This disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may be directed to less than all of the features of any of the disclosed embodiments. Thus, the following claims are incorporated into the Detailed Description, with each claim standing on its own as defining separately claimed subject matter.

[0135] The above disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments which fall within the true spirit and scope of the present disclosure. Thus, to the maximum extent allowed by law, the scope of the present disclosure is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.

Claims

AMENDED CLAIMSreceived by the International Bureau on 15 May 2026 (15.05.2026)

1. A nanofiber film for extreme ultraviolet (EUV) photolithography comprising:a plurality of nanofibers that are intersected randomly to form an interconnected network structure in a planar orientation, the interconnected network structure having a thickness ranging from a lower limit of 3.0 nm to an upper limit of 100.0 nm; anda first molybdenum disilicide (MoSi2) deposition layer having a first average deposition thickness ranging from a lower limit of 0.15 nm to an upper limit of 3.0 nm, whereinthe first MoSi2deposition layer is deposited on a first surface of the interconnected network structure, andthe nanofiber film comprises an EUV exposure region, the EUV exposure region having a minimum 88% EUV transmittance measured by a 13.5 nm wavelength.

2. The nanofiber film according to Claim 1, further comprisinga second MoSi2deposition layer with a second average deposition thickness on a second surface of the interconnected network structure, the second surface being opposite of the first surface; andthe first average deposition thickness and the second average deposition thickness have a combined deposition thickness ranging from a lower limit of 0.15 nm to an upper limit of 3.0 nm.

3. The nanofiber film according to Claim 2, wherein a ratio of the first average deposition thickness to the second average deposition thickness ranges from 1:1 to 5:1.

4. The nanofiber film according to Claim 2, wherein a ratio of the first average deposition thickness to the second average deposition thickness ranges from 1.5:1 to 4:1.

5. The nanofiber film according to Claim 2, wherein the combined deposition thickness ranges from a lower limit of 0.15 nm to an upper limit of 2.0 nm.

6. The nanofiber film according to Claim 5, wherein a ratio of the first average deposition thickness to the second average deposition thickness ranges from 1:1 to 5:1.

7. The nanofiber film according to Claim 5, wherein a ratio of the first average deposition thickness to the second average deposition thickness ranges from 1.5:1 to 4:1.

8. The nanofiber film according to Claim 1, wherein the nanofiber film has a uniform EUV transmittance across the EUV exposure region and a difference of any two EUV transmittance measurements within the EUV exposure region from same interconnected network structure is less than 0.4%.

9. The nanofiber film according to Claim 1, wherein the nanofiber film has a peripheral region, the peripheral region having a visible light transmittance at least 1.0 % lower than a visible light transmittance of the EUV exposure region, whereinthe peripheral region encloses the EUV exposure region, and a visible light wavelength is applied to the visible light transmittance of the peripheral region and the EUV exposure region.

10. The nanofiber film according to Claim 1, wherein the nanofiber film has a peripheral region, the peripheral region having an EUV transmittance at least 1.5 % lower than an EUV transmittance of the EUV exposure region, whereinthe peripheral region encloses the EUV exposure region, and a 13.5 nm EUV wavelength is applied to EUV transmittance of the peripheral region and the EUV exposure region.

11. The nanofiber film according to Claim 1, wherein a difference of EUV transmittance between the EUV exposure region of the nanofiber film and an EUV exposure region of the interconnected network structure is 7% or less, wherein the EUV exposure region of the nanofiber film overlaps with the EUV exposure region of the interconnected network structure.

12. The nanofiber film according to Claim 1, wherein a lifetime of the nanofiber film is at least twice as a lifetime of the interconnected network structure in a hydrogen plasma etching test, wherein the hydrogen plasma etching test applies an 80-watt 13.56 MHz radio frequency energy under a constant 15 seem hydrogen gas flow at ambient temperature until the nanofiber film breaks.

13. The nanofiber film according to Claim 1, wherein the plurality of the nanofibers further includes single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWDNTs), and multiwalled carbon nanotubes (MWCNTs), andwherein a number of walls of the SWCNTs is one, a number of walls of the DWCNTs is two, and a number of walls of the MWCNTs is three or more.

14. The nanofiber film according to Claim 13, wherein the SWCNTs account for a percentage between 5-50% of the plurality of the nanofibers, the DWCNTs account for 50% or higher to 95% or less of the plurality of the nanofibers, and the MWCNTs account for 0% or more to 45% or less of the plurality of the nanofibers, and wherein the SWCNTs, the DWCNTs, and the MWCNTs together account for 100% of the plurality of the nanofibers.

15. The nanofiber film according to Claim 13, wherein the SWCNTs account for 85% or higher of the plurality of the nanofibers, and the DWCNTs and the MWCNTs together account for remaining of the plurality of the nanofibers.

16. The nanofiber film according to Claim 13, wherein the SWCNTs account for 40% or higher to 85% or less of the plurality of the nanofibers, the DWCNTs count for 15% or more to 50% or less of the plurality of the nanofibers, and the MWCNTs account for 0.2% or more to 10% or less of the plurality of the nanofiber, and wherein the SWCNTs, the DWCNTs, and MWCNTs together account for 100% of the plurality of the nanofibers.

17. The nanofiber film according to Claim 1 further comprisesa pellicle border defining an aperture, andthe nanofiber film is mounted to the pellicle border and covers the aperture.

18. The nanofiber film according to Claim 1, wherein the interconnected network structure is annealed prior to deposition of the first MoSi2deposition layer.

19. A method of producing the nanofiber film of Claim 1, the method comprising:providing the plurality of the nanofibers;forming the interconnected network structure in the planar orientation; anddepositing the first MoSi2deposition layer on the first surface of the interconnected network structure, wherein the plurality of nanofibers are intersected randomly.

20. A method of performing EUV lithography, comprising transmitting EUV radiation through the nanofiber film of Claim 1.

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