Two-density extreme ultraviolet pellicle with enhanced properties

Abstract

A carbon nanofiber pellicle and pellicle film for extreme ultraviolet (EUV) lithography with different light transmission rates is disclosed. The disclosed pellicle film features improved film mechanical strength, less deflection, and increased etching resistance.

Description

TWO-DENSITY EXTREME ULTRAVIOLET PELLICLE WITH ENHANCED PROPERTIES CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority to U. S. Provisional Application No.63 / 542,010 filed on October 2, 2023, which is hereby incorporated by reference in its entirety. TECHNICAL FIELD

[0002] This disclosure generally relates to a thin film and a thin film device used in advanced semiconductor microchip fabrication and, more particularly, to a patterned two-density ultra-thin, ultra-low density, nanostructured free-standing pellicle film and pellicle with enhanced mechanical and etching-resistance properties, said film and film device configured for extreme ultraviolet (EUV) lithography and high numeric aperture (high-NA) EUV. BACKGROUND

[0003] Extreme ultraviolet (EUV) lithography is an advanced optical lithography technology using a range of EUV wavelengths, more specifically, about 13.5 nm. The EUV lithography enables semiconductor microchip manufacturers to pattern sophisticated features at 14 nm resolution and below and place many more transistors without increasing the size of substrates. For more sophisticated semiconductors, at 7 nm or even 5 nm and below, the high NA EUV lithography has been developed and will be deployed to become a reality in the semiconductor industry.

[0004] In EUV lithography, the EUV radiation energy or high-level EUV radiation energy from high-NA EUV lithography with the presence of the low-pressure background hydrogen gas, which is used for anti-oxidation and carbon-cleaning in EUV lithography, introduces ionization of hydrogen, creating reactive hydrogen plasma, which reacts with plasma-facing surfaces, including {P7218806336706.DOCX} 1the surfaces of mirrors, photomasks, and pellicles. Such reactions change the properties of their targets. In the case of mirrors, regular examination, cleaning, and even replacement may be required.

[0005] Particle contamination is another concern in EUV lithography. Despite the adoption of state-of-the-art cleanroom and air filtration techniques, fall-on particles on the photomasks with known and unknown particle sources are still observed after exposure of photomasks in lithography, according to field reports in the semiconductor industry. Such particle contamination, even a tiny amount, is often a significant problem in semiconductor manufacturing, propagating erroneous patterns to subsequent semiconductor chip production. It becomes a more prominent issue in advanced photolithography of much higher-resolution processes and microcircuits, increasing defect rates and affecting product yields as any unexpected particles may alter the printing patterns of logic circuits on the chips, which have no built-in redundancy.

[0006] To avoid particles, a photomask may be covered and protected by an effective pellicle, a thin transparent film stretched over a frame (also referred to as a pellicle border with a central opening or aperture) that may be attached over the patterned side of the photomask. A photomask may be referred to as a reticle. Both photomask and reticle are used interchangeably nowadays and are used in semiconductor microchip fabrication. A photomask is a master template to project EUV radiations repetitively onto a substrate and produce a pattern on a substrate, usually a thin slice of silicon known as a wafer in the case of semiconductor chip manufacturing.

[0007] A pellicle is placed close to but far enough away from the photomask, so moderate- to-small-sized particles that land on the pellicle will be too far out of focus to print. A pellicle acts as a protective device that covers the photomask, also called a reticle. When an EUV light source turns on, the EUV light first hits the pellicle film and then passes through the pellicle film. The EUV photomask underneath the pellicle reflects the light and bounces the EUV light back from the underneath photomask, hitting the pellicle film once more before it continues its path to print a microchip. Some EUV energy is absorbed during this process, and heat may be generated, absorbed, {P7218806336706.DOCX} 2and accumulated within pellicles due to double EUV light passages. The temperature of the pellicle may heat up to anywhere from 500° Celsius to 1000° Celsius or above. Therefore, the pellicle’s heat resistance is essential.

[0008] While heat resistance is essential, the pellicle must also be highly transparent for EUV transmission to ensure the passing through of the EUV light, the reflected light, and the light pattern from the photomask. Increasing a pellicle film thickness to gain film strength and heat resistance or etching may lower EUV transmission, an approach that may disqualify a thickened film for EUV lithography. This is one of the main reasons EUV pellicles are generally required to be very thin, less than 200 nm, preferably less than 100 nm, or less than 40 nm thick.

[0009] Attempts have been made to target a high light transmittance rate by deploying a high carbon nanotube content in a carbon nanotube sheet (e.g., as high as 99% by mass). They may form pellicles with high visible light and EUV transmission rates. Ultra-thin, ultra-low density CNT pellicle films have been reported with satisfactory lifetime.

[0010] However, as pellicle films become thinner and thinner, better mechanical properties of pellicle films are still in high demand, as slow pump-down speeds of EUV scanners may limit equipment utilization and microchip production time. Also, the space between pellicle films and reticles remains tiny and limited, such that any deformation reduction of a pellicle film is commonly pursued.

[0011] The EUV radiation-induced hydrogen plasma also affects a pellicle, besides reflective mirrors, etc., hitting the pellicle with hydrogen ionization and reactive hydrogen plasma, i.e., hydrogen plasma etching, thus introducing defects within the pellicle film and reducing its lifetime.

[0012] Since the microchip manufacturing industry has already adopted EUV pellicles and showed promising initial results in reducing print defects and improving production yields, desires for EUV pellicles for high energy power EUV lithography or high-NA EUV lithography remain strong, especially the pellicle having enhanced heat resistance, mechanical strength, and hydrogen {P7218806336706.DOCX} 3plasma etching resistance. For an EUV pellicle, its in-scanner mechanical strength, film integrity, particle prevention capability, and lifetime become critical and play a crucial role in EUV lithography. If compromised, damaged, or even disintegrated, it may not only lose its protective functionality but also introduce broken pellicle debris, which may cause additional damage and / or contamination to scanners, scanner modules, and scanner’s internal environment. SUMMARY

[0013] According to an aspect of the present disclosure, a specifically structured nanostructure film is disclosed. The nanostructure film includes a plurality of carbon nanotubes (or carbon nanofibers) that intersect randomly to form a single layer of an interconnected nanofiber network structure with a geometric shape and a target size in a planar orientation for at least a surface of the interconnected nanofiber network structure. Furthermore, the intersected or interconnected nanofiber network structure has the plurality of carbon nanotubes dispersed or distributed continuously throughout the entire intersected network and a pattern of at least two light transmission rates, i.e., one light transmission rate is higher than the other. For example, the at least two light transmission rates may include a high or higher light transmission rate and a low or lower light transmission rate. Exemplary light used in light transmission rate measurements includes but is not limited to, visible light, e.g., 550 nm, and EUV light, e.g., 13.5 nm.

[0014] According to another aspect of the present disclosure, the intersected network structure may have at least two thicknesses selected from a range of a lower limit of 3 nm to an upper limit of 200 nm. A thicker region of the interconnected nanofiber network structure has a lower visible light transmission rate or a lower EUV transmission rate (i.e., a lower EUV transmittance), and a thinner region of the interconnected nanofiber network structure has a higher visible light transmission rate or a higher EUV transmission rate (i.e., a higher EUV transmittance).

[0015] According to yet another aspect of the present disclosure, a thicker region of the interested network structure may have a higher areal density of the plurality of the intersected {P7218806336706.DOCX} 4nanofibers, and a thinner region of the interconnected network structure has a lower areal density of the plurality of the intersected nanofibers.

[0016] According to one aspect of the present disclosure, visible light transmission rates are selected from a range between a lower limit of 40% and an upper limit of 97% as measured at 550 nm wavelength for at least two different transmission rates.

[0017] According to a further aspect of the present disclosure, the interconnected nanofiber network structure may have at least two EUV transmission rates selected or measured from a range of a lower limit of 80% to an upper limit of 99% as measured at 13.5 nm wavelength.

[0018] According to another aspect of the present disclosure, the higher transmission rate of both visible and / or EUV wavelengths is at least 2% or higher than the lower transmission rate, up to 50%.

[0019] According to one aspect of the present disclosure, the interconnected nanofiber network structure has a geometric shape with a target size. A preferred geometric shape is a rectangular shape; a preferred target size is 110 mm by 140 mm of a rectangular shape, which meets the current standards of EUV pellicles. The present disclosure is not limited to the shape and the size of an interconnected nanofiber network structure disclosed herein. It may further include geometry of triangle, square, circle, ellipse, heptagon, and octagon. Sizes of an interconnected nanofiber network structure may be larger than 110 mm by 140 mm, such as 120 mm by 150 mm or larger, 130 mm by 160 mm, 110 mm by 280 mm, 220 mm by 140 mm or larger. Sizes of an interconnected nanofiber network structure may be smaller than 110 mm by 140 mm, for example, 25 mm by 25 mm, 20 mm by 20 mm, or 10 mm by 10 mm.

[0020] A preferred pattern of at least two light transmission rates of an interconnected nanofiber network structure includes a lower light transmission rate at a peripheral region of a rectangular shape of the interconnected nanofiber network structure and a higher light transmission rate at a central region of the rectangular shape of the interconnected nanofiber network structure. {P7218806336706.DOCX} 5

[0021] Furthermore, a preferred pattern of at least two light transmission rates of an interconnected nanofiber network structure may include a lower light transmission rate at one or more sections of a periphery up to an entire periphery of a given geometric shape of an interconnected nanofiber network structure and a higher light transmission rate at a central region of the given geometric shape of the interconnected nanofiber network structure.

[0022] The preferred pattern may further include a transition region between the peripheral region and the central region of the intersected nanofiber network structure. The transition region may have variable light transmission rates. A preferred variation of light transmission rates of the transition region is a light transmission rate gradient from low to high, i.e., the lower light transmission rate where it merges with the peripheral region and the higher light transmission rate where it merges with the central region.

[0023] Another embodiment of the present disclosure further includes a width of the peripheral region selected from any measurement between a lower limit of 0.2 mm and an upper limit of 4.0 mm. The width may be 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, or 3.5 mm wide.

[0024] An embodiment of the present disclosure includes a reduced deflection of an interconnected nanofiber network structure (i.e., a first pellicle film having a central region, a transition region, and a peripheral region) compared to a separate interconnected nanofiber network structure (i.e., a second pellicle film), the separate intersected network having a homogenous light transmission rate corresponding to the light transmission rate of the central region of the first pellicle film.

[0025] Another embodiment of the present disclosure further includes a higher deflection of the preceding interconnected nanofiber network structure (the first pellicle film) compared to yet another interconnected nanofiber network structure (a third pellicle film) having a homogenous light transmission rate corresponding to the light transmission rate of the peripheral region of the first pellicle film. {P7218806336706.DOCX} 6

[0026] Another embodiment of the present disclosure further includes a first interconnected nanofiber network structure having at least two non-identical light transmission rates (i.e., a higher light transmission rate and a lower light transmission rate), preferably with a pattern (at least a central region having the higher light transmission rate and a peripheral region having the lower light transmission rate), has less deflection of the interconnected nanofiber network structure compared to a second interconnected nanofiber network structure having a uniform light transmission rate of the higher light transmission rate of the at least two non-identical light transmission rates, more deflection of the interconnected nanofiber network structure compared to a third interconnected nanofiber network structure having a uniform light transmission rate of the lower light transmission rate of the at least two identical light transmission rates, and an identical EUV transmission rate of a region, i.e., the central region of the first interconnected nanofiber network structure, compared to the EUV transmission rate of the second interconnected nanofiber network structure.

[0027] Another embodiment of the present disclosure includes a plurality of carbon nanofibers having at least 50% of double-walled carbon nanotubes, at least 50% of single-walled carbon nanotubes, or at least 50% of multi-wall carbon nanotubes having three or more walled carbon nanotubes, with the rest filled with carbon nanofibers, including different number-walled carbon nanotubes other than already specified, to account for the final 100% content, respectively.

[0028] Another embodiment of the present disclosure includes a plurality of carbon nanofibers having at least 50% double-wall carbon nanotubes, 20% - 40% single-walled carbon nanotubes, and the rest filled with the multi-wall carbon nanotubes (i.e., three or more walled carbon nanotubes) to account for the final 100% content.

[0029] Another embodiment of the present disclosure includes a plurality of carbon nanofibers having at least 50% up to 75% of double-walled carbon nanotubes, at least 20% up to 40% of single-walled carbon nanotubes, and the rest filled with at least 1% three or more walled carbon nanotubes member (multi-wall CNTs) to account for the final 100% content. {P7218806336706.DOCX} 7

[0030] According to an aspect of the present disclosure, a pellicle is disclosed. The pellicle includes a pellicle border or a pellicle frame having an aperture and at least one interconnected nanofiber network structure (also referred to as a pellicle film) mounted to the pellicle border covering the aperture.

[0031] According to one aspect of the present disclosure, a method of producing a pellicle film or a pellicle device for EUV lithography is disclosed. An exemplary method includes steps of producing a pellicle film with at least two non-identical light transmission rates at two corresponding regions of the pellicle film and, preferably by filtration method, mounting the pellicle film to a pellicle border to form a pellicle or an intermediary border, and optionally transferring the pellicle film from the intermediary border onto a pellicle border to form a pellicle or sometimes referred to as pellicle device.

[0032] According to another aspect of the present disclosure, the method further includes steps of having a plurality of carbon nanofibers intersected randomly to form a single layer of an interconnected nanofiber network structure. The plurality of carbon nanofibers is distributed continuously throughout the single layer of the interconnected nanofiber network structure having a central region and a peripheral region and crossing from one of the central region and the peripheral region to another.

[0033] According to another aspect of the present disclosure, the method further includes steps of producing a central region of the pellicle film as one of the two non-identical light transmission regions and a peripheral region of the pellicle film as another one of the two non- identical regions.

[0034] According to yet another aspect of the present disclosure, the method further includes preparing a light transmission rate of the central region higher than a light transmission rate of the peripheral region. One of these two light transmission rates is at least 5% higher than the other, {P7218806336706.DOCX} 8preferably10%, 15%, 20%, 25%, 30%, 40%, or 50% higher from at least one of selected wavelengths, for an example visible light, exemplarily at 550 nm, and EUV, such as 13.5 nm.

[0035] According to another aspect of the present disclosure, the method of producing the pellicle film or the pellicle device for EUV lithography further includes a third region of the pellicle film, the third region being situated between and merged with the two regions having the non- identical light transmission rates. The description of the merge refers to a random intersection of the plurality of carbon nanofibers and continuous distribution of the plurality of carbon nanofibers within all three regions and crossing from one of the three regions into another region. The third region has various light transmission rates varying from one of the two non-identical light transmission rates to another, preferably in a progressive pattern.

[0036] According to another aspect of the present disclosure, a method of performing EUV lithography is disclosed, which includes at least one of the steps disclosed herewith. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] 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.

[0038] FIG.1 illustrates a filtration method for forming an interconnected nanofiber network structure in accordance with an exemplary embodiment.

[0039] FIG.2 is a schematic drawing of a top view of an interconnected nanofiber network structure with a geographic shape, a size having a length and a width, and three regions within the geographic shape in accordance with an exemplary embodiment.

[0040] FIG. 3 is another schematic drawing of a top view of an interconnected nanofiber network structure with a geographic shape, a size having a length and a width, and three regions {P7218806336706.DOCX} 9within the geographic shape mounted on a pellicle frame in accordance with an exemplary embodiment.

[0041] FIG.4 is a schematic drawing of a side view of the interconnected nanofiber network structure having a plurality of nanofibers dispersed continuously within and throughout the interconnected nanofiber network structure shown in FIG. 2 in accordance with an exemplary embodiment.

[0042] FIG. 5 depicts deflection measurement results from three full-size individual interconnected nanofiber network structures mounted on borders having 110 mm x 140 mm apertures under various testing pressures in accordance with an exemplary embodiment.

[0043] FIG. 6 illustrates deflection and rupture testing results from three individual interconnected nanofiber network structures in accordance with an exemplary embodiment.

[0044] FIG. 7 illustrates rupture testing results from two sets of interconnected nanofiber network structures having one or two light transmission rates for each of the interconnected nanofiber network structures measured at 550 nm with and without hydrogen plasma etching treatment. DETAILED DESCRIPTION

[0045] 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.

[0046] A pellicle may refer to a thin transparent film that protects a photomask during semiconductor microchip production. The pellicle contemplates a protective device with a frame (also referred to as a border and used interchangeably herein) with a central opening, an aperture, or a window. Both border and aperture are covered by a continuous thin and transparent film on the top of at least a portion of the border and a portion of the aperture, preferably the entire circumference of the border and the entire aperture. The center portion of such a thin film extending the aperture is {P7218806336706.DOCX} 10free-standing. The pellicle may act as a dust cover or a filter that prevents particles and contaminants from falling onto an object(s) below the pellicle. In extreme ultraviolet (EUV) lithography, an EUV pellicle refers to a particle filter or a fine particle filter to protect the photomask during microchip production or other objects for non-semiconductor fields. However, the pellicle must be sufficiently transparent to allow light transmission to pass through the pellicle to perform lithography. Higher light transmission is desired for more effective lithography. For most EUV lithography applications, an 80% EUV transmission rate from a pellicle may be acceptable. For high-resolution EUV lithography at 7 nm or below, a high-energy EUV scanner, or a high or hyper numeric aperture EUV lithography, a preferred EUV pellicle may require an EUV transmission rate of 90% or above, 92% or above, or 95% or above and up to 99%.

[0047] Further, pellicles for EUV lithography require a large (e.g., equal to or larger than 110 mm x 140 mm), free-standing, and thin-film material with extreme and unique properties. Besides high transparency to EUV irradiation, any unexpected film rupture during microchip production may interrupt ongoing manufacturing processes, leading to possible debris decontamination of the scanner, changing or cleaning of photomasks, and losing microchip production. A film rupture may be caused by shocks and / or environmental pressure changes during pellicle transportation. It may also happen due to pellicle film’s low mechanical strength, reduced mechanical strength, and / or a low or reduced lifetime of pellicle film as the results of scanner pressure changes (i.e., pump-down or vent) and / or in-scanner hydrogen plasma etching.

[0048] The EUV lithography is performed in a vacuum as EUV is absorbed by most materials, including common gases and atmospheric air. Therefore, direct EUV radiation on pellicle film may heat pellicle film quickly. The absorbed energy cannot be released or removed quickly and dependably by conventional cooling methods, such as convective and conductive cooling. A pellicle film temperature may reach a few hundred degrees in a scanner, such as 400ºC or above, 600ºC, 800ºC, 1000ºC, or even 1,200ºC or above quickly. Such elevated high temperatures may have {P7218806336706.DOCX} 11negative impacts, degrading materials, including carbon nanofibers and carbon nanotubes, and resulting in eventually weakened mechanical strength and lifetime of the interconnected nanofiber network structures.

[0049] EUV lithography also requires a low-pressure hydrogen flow to sweep away particles that could muck up the delicate scanner mirrors and provide anti-oxidation and carbon-cleaning functionality to protect the EUV mirror surface and other surfaces inside scanners. In the presence of high-energy EUV radiations within a scanner, the hydrogen gas undergoes an ionization process and creates intensely hot hydrogen plasma, which releases particles and attacks surfaces in close vicinities, such as reticles, pellicles, and reticles’ and pellicles’ surfaces. This hydrogen plasma etching creates another serious challenge for every EUV pellicle. High-quality EUV pellicle films with better mechanical strength, low film deflection, and high etching resistance may be required to achieve high-temperature resistance, extended pellicle lifetime, and high plasma etching requirements. Given the number of high-level stringent properties required, effective EUV pellicles, especially for high-NA EUV lithography, have been conventionally difficult to produce to meet very strict criteria.

[0050] In this aspect, carbon nanotubes and other equivalent nanofibers have been selected as starting materials to create pellicles for this EUV pellicle application due to their excellent thermal and mechanical properties and their capability to form porous films. Additional pellicle film structural details may become crucial to conquer serious challenges in EUV and high NA EUV lithography. Carbon Nanotubes and Carbon Nanotube Films

[0051] Carbon nanotubes (CNTs) or carbon nanofibers, as often referred to herein, are long tubes with small diameters typically measured in nanometers. They have a high aspect ratio of length vs. diameter in a range generally preferred above about 100:1, which may be above about 1000:1. Another preferred aspect ratio may be at least approximately 10,000:1. CNTs are made up of one or {P7218806336706.DOCX} 12more graphene sheets rolled up into a concentric structure. A graphene sheet is a collection of carbon allotrope arranged in a single layer in a hexagonal lattice structure. Each graphene sheet is regarded as a wall of a CNT. A single-wall (or walled) CNT (SWCNT) is made of a single graphene sheet. A double-wall (or walled) CNT (DWCNT) is made of two graphene sheets. Lastly, a multi-wall (or walled) CNT (MWCNT) has multiple graphene sheets. The multi-wall CNTs herewith refer to carbon nanotubes having three or more walls. Other types of CNTs may include, but are not limited to, coaxial nanotubes, conical carbon nanotubes, closed carbon nanotubes, boron nitride nanotubes, and composite coaxial nanotubes of graphene layer(s) and boron nitride layer(s). Other carbon allotropes may also form sheets with excellent properties for pellicle films. Carbon nanotubes may exist substantially pure in one type or often in combination with different types with respect to the number of CNT walls. The CNTs may also exist individually, separated from others, or form bundles. A bundle may include the same type or different types of CNTs, such as SWCNTs with DWCNTs, SWCNTs with MWCNTs, DWCNTs with MWCNTs, etc. Within a bundle, CNTs may have different lengths and diameters. Each bundle, having two or more CNTs, may be aligned in parallel, at least for a portion of their entire lengths. For simplicity and convenience, CNTs in this application may refer to different types of CNTs, for example, different numbers of walls, and include CNTs existing individually or in bundles.

[0052] As used herein, nanofiber may exemplarily refer to a fiber having a diameter of less than 1µm. Nanofiber and nanotube are used interchangeably and may encompass SWCNTs, DWCNTs, MWCNTs, and other carbon allotropes in which carbon atoms are linked together to form a cylindrical structure.

[0053] An individual CNT or a CNT bundle may be intersected with one or more other CNTs or CNT bundles. Together, many CNTs could form a mesh-like microstructure film. One exemplary embodiment may include a free-standing thin film of an interconnected nanofiber or carbon nanofiber {P7218806336706.DOCX} 13network (micro)structure, of which an area of the thin film has no supporting material or substrate on either side of the free-standing thin film.

[0054] Further, among several possible methods to fabricate free-standing thin films, a filtration-based approach was utilized to produce membrane films from small-size films to sufficiently large films having at least two regions for each film with a uniform film thickness or light transmission rate for each region of the at least two regions. A film’s uniform thickness generally correlates to a film’s even light transmission. This filtration-based method allows for the quick manufacturing of films not only of CNTs but also other high aspect ratio nanoparticles and nanofibers, such as boron nitride nanotubes (BNNT) or silver nanowires (AgNW). Since this approach separates the nanotubes or nanoparticle syntheses and the film manufacturing processes, a variety of nanofiber materials produced by virtually any method may be used individually or combined. Different types of nanotubes (SWCNTs, DWCNTs, MWCNTs, or carbon allotropes) may be mixed in any desired ratio. As filtration can be a self-leveling process in the sense that non- uniformities of film thickness during the filtration process are self-corrected by the dynamic variations of local permeability and, therefore, a highly desirable film formation process, it is also a promising candidate for the production of highly uniform films. The self-leveling process may further ensure that the nanoparticles or nanofibers are evenly distributed under a same filtration condition and evenly deposited in an orderly manner. Carbon Nanotube Synthesis

[0055] Carbon nanofibers may be synthesized by different methods, depending on desired product types. Methods include different precursors, e.g., hydrocarbon gases, heating source, reaction catalysts, reaction time, reaction temperature, and reaction atmosphere. The most common methods include but are not limited to arc discharge, electrolysis, laser ablation, chemical vapor deposition (CVD), flame synthesis, mechano-thermal, etc. The well-known CVD methods have {P7218806336706.DOCX} 14evolved to plasma-enhanced PE-CVD, aerosol CVD (AACVD), water-assisted WA-CVD, oxygen- assisted CVD, catalytic CVD, etc.

[0056] These CNT production methods utilize one or more carbon sources, such as acetylene (C2H2), ethylene (C2H4), or other hydrocarbons, in a closed reaction chamber with at least one catalyst and an elevated reaction temperature ranging from 350 to 1,000°C or above.

[0057] Within a CVD reaction chamber, a catalyst may be in a free-floating form within the reaction chamber during the synthesis (FC-CVD). Under pyrolysis of hydrocarbon gas(es), FC-CVD is applied to produce nanofiber sheets. Alternatively, FC-CVD, under different growth conditions, may produce nanofibers, which can be collected as CNT powers for later dispersion and filtration to produce pellicle films, as described below.

[0058] Other commonly deployed CVD synthesis methods start with a catalyst deposition on a substrate, e.g., a silicon wafer, by electron-beam (E-beam) deposition, sputtering, atomic layer deposition, laser-assisted CVD, and plasma-enhanced CVD. A collection of individual nanofibers are vertically aligned on the substrate to each other, with one end of the nanofibers attached to the substrate, like a forest, frequently referred to as a CNT forest. They may be detached from the substrate and harvested as CNT powders for CNT pellicle film production. Film Formation

[0059] An ultra-thin and ultra-low density CNT pellicle film may be produced in accordance with exemplary embodiments of the current disclosure.

[0060] FIG.1 illustrates a filtration method for forming a pellicle film shown in FIGS.2-4 in accordance with an exemplary embodiment.

[0061] Another embodiment of this disclosure may further include any pellicle films produced, to be produced, processed, or to be processed by all means, including any various carbon nanofiber surface modifications, including but not limited to coating or other means of disposing of {P7218806336706.DOCX} 15one or more metal elements, metal oxides, graphene sheets, or CNT surface modifiers, annealing, or a combination thereof on carbon nanofibers and / or CNT films.

[0062] As illustrated in FIG.1, a free-standing carbon nanotube-based pellicle film may be produced via a filtration-based method. In Operation 101, catalysts are removed from carbon nanotubes (CNTs) that are to be used to form a water-based CNT suspension. In an example, prior to dispersion into a CNT suspension, the CNTs may be chemically purified to reduce a concentration of catalyst particles to less than 1% or preferably less than 0.5% wt. (purified CNTs), which may be measured by, for example, thermogravimetric analysis. Removal of the catalysts is not limited to any particular process or procedure, such that any suitable process may be utilized to achieve desirable results.

[0063] In Operation 102, a water-based suspension is prepared using the purified CNTs, such that the purified CNTs are evenly dispersed in the water-based suspension. When preparing one or more CNT suspensions, carbon nanotube material can be mixed with a selected solvent to distribute nanotubes uniformly 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., 60%, 70%, 80%, 90%, 95% IPA, N-Methyl-2-pyrrolidone (NMP), dimethyl sulfide (DMS), and combinations thereof. In another example, a surfactant can also be included to aid the uniform dispersion of carbon nanofibers in the solvent. Examples of surfactants include but are not limited to, anionic surfactants.

[0064] Carbon nanofiber films are generally formed from one of MWCNTs, DWCNTs, or SWCNTs. A carbon nanofiber film may also include a mixture of different types of CNTs (i.e., SWCNTs, DWCNTs, and MWCNTs based on wall numbers of CNTs) with a variable ratio between the different types of CNTs. Other types of CNTs may also be used to produce CNT films by filtration and other known and contemplated methods. {P7218806336706.DOCX} 16

[0065] Each of these three different types of common carbon nanotubes (e.g., MWCNTs, DWCNTs, and SWCNTs) has different properties. In one example, single-wall carbon nanotubes can be more conveniently dispersed in a solvent (i.e., with the majority of nanotubes suspended individually and less adsorbed onto other nanotubes) for subsequent formation into a sheet of randomly oriented and intersected carbon nanotubes. This ability of individual nanotubes to be uniformly dispersed in a solvent and / or solution can, in turn, produce a more planarly uniform nanotube film formed by removing the solvent from the suspended nanofibers. The dispersion uniformity in a solution ensures a uniform distribution of a collection of the individual nanotubes. This physical uniformity can also improve the uniformity of other properties across the film (e.g., transparency and scattering to irradiation, mechanical strength upon pressure changes, and lifetime / durability test).

[0066] In an example, the water-based CNT suspension in Operation 102 may have at least above 85% purity of SWCNTs. The remaining may be a mixture of DWCNTs, MWCNTs, and / or a catalyst. In other examples, a dispersed CNT suspension with various ratios of different types of CNTs may be prepared, such as about 20% / 75% DWCNTs / SWCNTs, about 50% / 45% DWCNTs / SWCNTs, about 70% / 20% DWCNTs / SWCNTs, with MWCNTs accounted for the remaining. A mixture of 10% or more MWCNT and a blended DWCNT and SWCNT at various DWCNT / SWCNT percentage ratios may be prepared and subjected to the same filtration process of forming nanofiber structures. In another example, anionic surfactants may be utilized as the dispersants in the suspension to enhance the uniform dispersion of different types of CNT mixtures.

[0067] In Operation 103, the CNT suspension is further purified to remove the aggregated or agglutinated CNTs from the initial mixture. In an example, different forms of CNTs, undispersed or aggregated vs. fully dispersed, may be separated from the suspension via centrifugation. Centrifugation of surfactant-suspended carbon nanotubes may aid in decreasing the turbidity of the suspension solution and ensuring a complete dispersion of the carbon nanotubes in the final {P7218806336706.DOCX} 17suspension solution before going into the next filtration step. However, aspects of the disclosure are not limited thereto, such that other separation methods or processes may be utilized. According to exemplary aspects, Operation 103 may be optionally performed or performed as a necessary step in the formation of the pellicle film.

[0068] In Operation 104, any CNT suspension, preferably the CNT supernatant after a separation procedure from Operation 103, is then filtered through a filtration membrane to form a CNT nanostructure film, a continuous sheet of film of intersecting CNTs.

[0069] In an example, one technique for making the CNT film uses water or other fluids to place nanotubes in a randomly-dispersed pattern on a filter, preferably a flat filtration membrane. The evenly dispersed CNT-containing mixture is allowed to pass or is forced to pass through the filter, leaving a nanofiber structural layer on the surface of the filter, where the dispersed CNTs become intersected and interconnected. The size and shape of the resulting films are determined by the size and shape of the desired filtration area of the filter, while the thickness and density of the films are determined by the quantity of nanofiber material applied during the filtration process and the permeability of the filtration membrane to each component of the input material, as the non- permeable component is captured on the surface of the filter. If the concentration of nanofibers dispersed in the flow-through filtration fluid is known, the mass of nanofibers deposited onto the filter can be determined from the amount of such fluid that passes through the filter, and the film’s areal density is determined by the nanofiber mass divided by the total filtration area. A filtration area of the filter may be the same or smaller than the size of the filter, depending on the filter’s underlying supporting structure. The selected filter is generally not permeable to any CNTs.

[0070] The filtration-formed CNT film may be a combination of SWCNTs, DWCNTs, and / or MWCNTs in differing compositions. Carbon nanofibers may become intersect randomly to form an interconnected nanofiber network structure as a thin CNT film. A first surface of the interconnected nanofiber network structure, which is in contact with the filtration membrane, is in a planar {P7218806336706.DOCX} 18orientation. An opposite surface of the interconnected nanofiber network structure may have a planar orientation parallel to the first surface, producing a film with a single CNT areal density or a single light transmission rate.

[0071] The opposite surface of the interconnected nanofiber network structure may have different planar arrangements with reference to the planar orientation of the first surface, as detailed below, featuring different light transmission rates of the interconnected nanofiber network structure.

[0072] In Operation 105, the resulting CNT film is then separated from the filtration membrane, starting from a first edge of the CNT film toward a second edge, non-overlapping with the first edge by different mechanisms and methods, e.g., different hydrophobicity / hydrophilicity between nanofiber film and filtration membrane, a soft water flow aiming at the first edge. When fully detached from the filtration membrane, the nanofiber film is ready for the next operation, Operation 106.

[0073] In Operation 106, the detached CNT film is harvested onto a solid substrate, such as a frame, sometimes referred to as a harvesting frame, a harvester frame, or an intermediary frame, depending on the desired subsequent operations and uses of the CNT film. The detached CNT film may be harvested directly and mounted onto a pellicle border with a defined aperture.

[0074] In Operation 107, the CNT film may be characterized through various measurements, including but not limited to, an optical light transmittance (or transmission rate) and / or transmittance uniformity (or transmission variation) test, EUV transmittance (or transmission rate) and / or transmittance uniformity (or transmission variation) test, mechanical strength, deflection test, permeability test, deflection at constant pressure or during simulated scanner pumping down conditions, hydrogen plasma etching test, lifetime test, particle test, may be performed.

[0075] In Operation 107, a CNT film may be annealed, coated, or tension-adjusted. {P7218806336706.DOCX} 19Carbon Nanotube Film with Two Light Transmission Rates

[0076] A plurality of carbon nanofibers or carbon nanotubes produced by different methods may form a single layer of interconnected nanofiber network structure by intersecting between individual nanofibers and / or nanofiber bundles, as shown schematically in FIGS. 2-4. Methods of producing the interconnected nanofiber network structure include but are not limited to a filtration method. A filtration method-made single-layer interconnected nanofiber network structure may have different or even random light transmission rates measured by one or more selected wavelengths. A filtration method-produced single-layer interconnected nanofiber network structure may have film thickness variation. Thicknesses generally correlate to light transmission rates. Many factors may affect the thickness of a resulting film, including permeabilities of an entire or a portion of a filtration membrane, an applied post-filtration membrane vacuum pressure to a portion or an entire filtration membrane, an applied pre-filtration membrane pressure to a portion or an entire filtration membrane, and a filtration rate at a portion or entire filtration membrane. A combination of one or more of these controlling factors may lead to film production with different film areal densities and / or different light transmission rates (different transmittances), while self-leveling of carbon nanofibers or carbon nanotubes continues to perform even depositions of carbon nanofibers or carbon nanotubes under a same set of controlling factors and allows for smooth transitions of carbon nanofibers or carbon nanotube depositions from a first set of controlling factors to a second set of controlling factors. Such a combination makes one-step film production feasible, and it avoids attaching two non-identical layers to form a film with two different densities or light transmission rates film, which has an interface between the two non-identical layers and further introduction of wrinkles and / or folds. Any wrinkles, folds, microscopic wrinkles, or microscopic folds may affect EUV radiation projection in semiconductor production. A cross-section film microstructure may reveal an even areal density and distribution of carbon nanofibers or carbon nanotubes throughout. {P7218806336706.DOCX} 20

[0077] Another embodiment of the present disclosure includes a method of producing a two- light transmission rate film based on a floating catalyst chemical vapor deposition method (FC- CVD). The method includes injecting into or placing inside a vacuum chamber at least one catalyst, floating the at least one catalyst in the vacuum chamber, providing at least one gas(es) (i.e., a hydrocarbon gas(es)) as a carbon source(s), heating the vacuum chamber to pyrolyze the at least one gas(es) for synthesizing carbon nanofibers or carbon nanotubes on the floating catalyst in the vacuum chamber, depositing or capturing the carbon nanotubes on a piece of filter paper or a filter membrane to form a carbon nanotube film, the carbon nanotubes being interconnected and / or intersected. The method may include a first carbon nanotube deposition to produce a pellicle film having one layer (i.e., a single-layer pellicle film) on the filter membrane. The method may further include one or more subsequent carbon nanotube depositions on an open side of the carbon nanotube film to produce a two or more-layer pellicle film (a multi-layer pellicle film). The open side of the carbon nanotube film is opposite to the filter membrane. After the first carbon nanotube deposition or one of the subsequent carbon nanotube depositions, the single-layer or the multi-layer pellicle film may be transferred to a pellicle frame or a pellicle harvesting frame, the open side being interfacing with the pellicle frame or pellicle harvesting frame. The filter membrane is released or removed. The single- layer or multi-layer pellicle film on the pellicle frame or pellicle harvesting frame may accept one or more carbon nanotube depositions described herein. At least one of the first and subsequent carbon nanotube depositions may additionally include an application of a damper or blocker to restrict depositions of the carbon nanotubes on a portion of the filter membrane or a portion of the carbon nanotube film (single layer or multi-layer) to produce a film with at least one layer having at least two light transmission rates in a preselected pattern, including the pattern(s) shown in FIGS. 2-4. The application of the damper may span an entire or a fraction of a duration of the at least one of the first and subsequent carbon nanotube depositions to produce the preselected pattern. The carbon nanotubes within the carbon nanotube depositions may be captured in an orderly manner on the filter {P7218806336706.DOCX} 21membrane or one of the subsequent carbon nanotube depositions and distributed evenly in a cross- section microstructure.

[0078] One of the two film surfaces in contact with a filtration membrane forms a first planar orientation. The other one of the two surfaces may have a number of surface planar orientations, depending on the number of different film areal densities or different light transmission rates. For example, a film with a central region having a high transmission rate or low areal density, a peripheral region having a low transmission rate or high areal density, and a transition region connecting both the central region and peripheral and having a transmission rate gradient from the low transmission rate, when connecting with the peripheral region, to the high transmission rate, when connecting with the central region, has three surface regions. All three regions have and share one common surface planar orientation which was from during filtration and in contact with the filtration membrane. The second surface of the central region has its planar orientation opposite the common surface planar orientation and is parallel to the second surface of the peripheral region. However, the second surface of the transition region opposite to the common surface planar orientation may not be parallel to the second surface of the peripheral region and may not be parallel to the second surface of the central. The plurality of nanofibers within the interconnected nanofiber network is not separated or cannot be delineated by any of these regions. Instead, the plurality of nanofibers is randomly distributed through all regions of the film, the film having different areal densities or different light transmission rates. These features and associated microscopic structural characteristics contribute to the enhancement of the nanofiber network structure with additional experimental results below.

[0079] An interconnected nanofiber network structure may have any geometric shape, including but not limited to a square, a rectangular, a circle, an ellipse, a heptagon, or an octagon with various lengths, widths, and / or diameters.

[0080] An interconnected nanofiber network structure for EUV lithography may prefer a rectangular shape and a target size of 110 mm by 140 mm to cover an aperture of the rectangular {P7218806336706.DOCX} 22shape. The interconnected nanofiber network structure may extend from 1mm to 40 mm on either dimension to bring itself to a size range of 111mm-150 mm x 141mm-170 mm. Different sizes to cover a rectangular aperture of 10 mm by 10 mm, 20 mm by 20 mm, 120 mm by 150 mm, 220 mm by 140 mm, 110 mm by 280 mm, or other variations are contemplated.

[0081] For EUV lithography, the interconnected nanofiber network structure may be very thin, with a lower limit of 3 nm to an upper limit of 200 nm or a lower limit of 3 nm to an upper limit of 100 nm to ensure sufficient EUV transmittance. An EUV pellicle film requires a film, more specifically a portion of a film where EUV passes through, to have limited thickness variation or light transmission variation.

[0082] However, the ultra-thin film requirement plus an even thickness creates a challenge of producing an interconnected nanofiber network structure with sufficient film mechanical strength to sustain human handling, transportation, or pressure changes during air freight and EUV scanner's pump-down and venting processes as well as radical or ionization attacks. Selecting one or more types of nanofibers with respect to the number of walls of carbon nanotubes and structural layout is one of the practical approaches.

[0083] One of the embodiments of the present disclosure includes variations of a peripheral region of an interconnected nanofiber network structure. When mounted on or attached to a support or a pellicle frame, the interconnected nanofiber network structure may be divided into, firstly, a freestanding portion without the support or a freestanding portion covering an aperture of the pellicle frame and, secondly, a non-freestanding portion, which surrounds the freestanding portion and extends outward from the freestanding portion, on the support or a pellicle frame. A peripheral region of a mounted interconnected nanofiber network structure may refer to an outskirt or perimeter of the freestanding portion of the interconnected nanofiber network structure herein, which may represent one of the exemplary embodiments of this disclosure and its ability to improve functionality of the interconnected nanofiber network illustrated hereafter. The peripheral region of the mounted {P7218806336706.DOCX} 23interconnected nanofiber network structure may further include the non-freestanding and mounted portion of the interconnected nanofiber network structure.

[0084] A peripheral region having a lower light transmission rate for a geometric shape of an interconnected nanofiber network structure may have different portions or sections with different lower light transmission rates, with respect to a higher light transmission rate of a non-peripheral region (i.e., a central region), for each portion of the peripheral region. A peripheral region of an exemplary rectangular shape of an interconnected nanofiber network structure having a lower light transmission rate may include one edge of the rectangular (i.e., one straight portion of the peripheral region) shape, two edges, three edges, or all four edges of the rectangular shape. Feature 210 in FIG. 2 depicts a closed peripheral region having four connected straight portions of the peripheral region. A peripheral region may include two edges of a rectangular shape, i.e., a first edge and a second edge, the first edge being opposite the second edge. In this instance, the peripheral region has two unconnected straight portions.

[0085] Another embodiment of the present disclosure further includes a width of the peripheral region. The width may be the same across all potions or sections of the peripheral region or may be different. For example, four edges of a peripheral region of an exemplary rectangular shape may have one width or two widths, a first one for two long edges opposite to each other and a second one for two short edges opposite to each other. A width may be selected from any measurement between a lower limit of 0.2 mm and an upper limit of 4.0 mm. The width may be 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, or 3.5 mm wide. A width of less than 0.2 mm may not provide benefits rendered by any of the embodiments of the present disclosure. A width of larger than 4.0 mm may effectively reduce the usable area of a film, such as a central region, for EUV irradiation. {P7218806336706.DOCX} 24

[0086] An embodiment of the present disclosure further includes a plurality of nanofibers having at least 50% double-wall carbon nanotubes. The rest is filled with single-walled and / or multi- wall carbon nanotubes to account for 100% of the plurality of nanofibers.

[0087] Another embodiment of the present disclosure includes a plurality of nanofibers having at least 50% up to 75% of double-wall carbon nanotubes. The rest is filled with single-walled and / or multi-wall carbon nanotubes to account for 100% of the plurality of nanofibers.

[0088] Yet another embodiment of the present disclosure includes a plurality of nanofibers having at least 20% single-walled carbon nanotubes. The rest is filled with double-wall and / or multi- wall carbon nanotubes to account for 100% of the plurality of nanofibers.

[0089] An embodiment of the present disclosure includes a plurality of nanofibers having at least 50% up to 75% of double-wall carbon nanotubes, 20%-40% of single-walled carbon nanotubes, and 1% or more multi-wall carbon nanotubes, together accounting for 100% of the plurality of the nanofibers.

[0090] An embodiment of the present disclosure further includes a simple and effective structure design as an alternative to address a pellicle film’s mechanical strength requirement and hydrogen plasma etching resistance.

[0091] An interconnected nanofiber network structure or a pellicle film having a plurality of nanofibers and at least two different thicknesses corresponding to at least two different light transmission rates is schematically illustrated in FIGS. 2-4. Pellicle film 200 in FIG. 2 has a peripheral region (Feature 210), a transition region (Feature 220), and a central region (Feature 230). Pellicle film 200 is further mounted on Pellicle border 305 to produce Pellicle 300 in FIG.3, which also has a peripheral region (Feature 310, corresponding to Feature 210), a transition region (Feature 320, corresponding to Feature 220), and a central region (Feature 330, corresponding to Feature 230). FIG. 4 is a cross-section view of the pellicle film 200. FIG. 4 further illustrates and highlights a random but even distribution pattern of the plurality of intersected and interconnected nanofibers in {P7218806336706.DOCX} 25a single-layer layout having the at least two different thicknesses. A lower light transmission rate is preferably assigned to a peripheral region of the pellicle film (Features 210 and 310 of FIGS.2 and 3, respectively). This peripheral region of the pellicle film may be less utilized or unused during microchip production and may or may not be required to meet all EUV pellicle requirements by the then industrial standard. However, this peripheral region, as a part of an ultrathin film, may suffer additional mechanical stress due to its close vicinity to a frame and / or frame edge’s roughness and additional thermal stress due to the accumulation and release of EUV radiation energy by the frame. It may be etched faster than other regions of the film irradiated by EUV radiations due to reflections and / or deflection of hydrogen plasma ions and radicals from the frame, causing an earlier failure of a pellicle film, including a film rupture. Having a thicker peripheral region or less light transmission rate at the peripheral region may extend lifetime of a pellicle film. A central region of the interconnected nanofiber network structure or a pellicle film may have a higher light transmission rate (Features 230 and 330 of FIGS. 2 and 3, respectively). This central region may meet most, if not all, of the then EUV pellicle requirement. The central region may further have an EUV transmission rate, preferably at least 80% or more, 85% or more, 90% or more, 92% or more, 95% or more, and up to 99%. A variation of EUV transmission rates, i.e., a difference in any two EUV transmission rates within the central region, should be less than 2.0%, preferably less than 1.0% or less than 0.4%. A uniform light transmission rate (i.e., uniformity of a pellicle film) in this disclosure may include at least one of these low percentages of EUV transmission variation features (i.e., less than 2.0%, less than 1.0%, or less than 0.4%). The central region may also have an EUV scattering of less than 0.5% or preferably less than 0.3%.

[0092] A lower light transmission rate for the peripheral region of the pellicle film may be selected from a range of at least 40% to 96% based on 550 nm wavelength measurements. A higher light transmission rate for the central region of the pellicle film may be selected from a range of at least 80% to 99% on 550 nm wavelength measurements. Also, a lower light transmission rate should {P7218806336706.DOCX} 26be less than a higher transmission rate for a pellicle film having at least two light transmission rates. A uniform light transmission rate in this disclosure may further include a feature of 550 nm wavelength transmission rate variation measured at any two locations of a pellicle film having a value of less than 5%, preferably less than 1%.

[0093] Another embodiment of the present disclosure may include a transition region that situates between and merges with the peripheral region and the central region (Features 220 and 320 of FIGS. 2 and 3, respectively). A first edge of the transition region, where it merges with the peripheral region, may have all the characteristics of the peripheral region, including the lower light transmission rate, areal density, and / or film thickness. A second and opposite edge of the transition region, where it merges with the central region, may have all the characteristics of the central region, including the higher light transmission rate, areal density, and / or film thickness. The changes of the transition region with respect to one or more of its characteristics, e.g., light transmission rate, areal density, and / or film thickness, may happen gradually and form a gradient from the first edge to the second edge. An exemplary gradient of light transmission rate is a linear gradient. Another exemplary gradient of light transmission rate includes at least one portion of the transition region having a linear gradient of light transmission rate. Furthermore, another exemplary change of light transmission rate for the transition region is a various rate.

[0094] Another embodiment of the present disclosure includes visible light transmission rates, which are selected from a range between a lower limit of 40% and an upper limit of 97% as measured at 550 nm wavelength for at least two different transmission rates. A film or a portion of a film with a 550 mm wavelength transmission rate of 98% or above may be too thin for handling and / or production and may be very susceptible to an external impact. A film or a portion of a film with a 550 mm wavelength transmission rate of less than 40% may be too rigid and / or brittle and may not provide elasticity to support another region (e.g., a central region) of the film. One or more {P7218806336706.DOCX} 27of the at least two 550 nm wavelength transmission rates may preferably be 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 95%.

[0095] Another embodiment of the present disclosure includes one of at least two EUV transmission rates of an interconnected nanofiber network structure selected or measured from a range of a lower limit of 80% to an upper limit of 99% as measured at 13.5 nm wavelength. A region of an interconnected nanofiber network useful or designed for EUV exposure must meet EUV lithography requirements, e.g., a central region of a pellicle film. An EUV transmission rate of less than 80% may not meet such requirements. One or more of the at least two EUV transmission rates may preferably be 85%, 90%, 92%, 95%, 97%, or 98%.

[0096] Another embodiment of the present disclosure includes ratios of the higher transmission rate over the lower transmission rate of the at least two transmission rates in visible and / or EUV wavelengths. The ratios have a lower limit of 2% and an upper limit of 50% with preferred ratios selected from 5%, 10%, 15%, 20%, 25%, 30%, 40%, or 45%.

[0097] An EUV transmission rate generally correlates to a visible light transmission rate in a non-linear manner. Such a correlation may vary depending on the nature of a subject material.

[0098] Another embodiment of the present disclosure includes a random and continuous dispersion of the plurality of carbon nanofibers or carbon nanotubes throughout a single layer of the interconnected nanofiber network structure or pellicle film within all regions having different or patterned light transmission rates (see schematic illustration in FIG.4).

[0099] However, aspects of the present disclosure are not limited thereto, such that different designs may be performed. Improvement in Deflection

[0100] Within an EUV scanner, the space between an EUV pellicle and a reticle is often very limited. A film deflection test is often used to characterize the mechanical properties of an EUV {P7218806336706.DOCX} 28pellicle film to ensure that the film will function as expected and within the limitation, sustains the air or gas flow under the scanner’s pump-down and venting processes, and will not get close or touch the photomask.

[0101] In a deflection test, atmospheric air or a gas, preferably an inert gas, such as argon or nitrogen, is applied perpendicularly to a film or a pellicle film under a constant gas pressure (Pascal or Pa). For a film of a rectangular shape, a flow of the testing gas is preferably pointed at a central spot of the film. A distance from the highest point of the film deformation under a pre-determined constant gas pressure to the film’s baseline, which is established without any gas pressure, is recorded and referred to as deflection distance. The applied gas pressure may continue to increase until a point the film ruptures. A gas pressure causing a film to rupture is referred to as a film’s rupture pressure. A deflection distance at a point of a film rupture is referred to as deflection distance at rupture distance.

[0102] FIG. 5 depicts the deflection measurement results of three different full-size interconnected nanofiber network structures or pellicle films (i.e., Film 10, Film 20, and Film 30 mounted on borders having apertures of 110 mm x 140 mm), with their individual film deflection measurement results being depicted as three curved lines, solid line (Feature 510), dash-dotted line (Feature 520), and dash-dot-dot line (Feature 530), respectively. Although full-size individual interconnected nanofiber network structures having a size of at least 110 mm x 140 mm are disclosed with respect to FIG. 5, aspects of the present disclosure are not limited thereto, such that differing sizes may be utilized.

[0103] The solid line in FIG.5 (Feature 510) represents a deflection distance vs. gas pressure graph of Film 10 having a single and uniform 80% light transmission rate (LTR) measured by 550 nm wavelength.

[0104] The dash-dotted line in FIG.5 (Feature 520) represents a deflection distance vs. gas pressure graph of Film 20 having at least two LTRs, a uniform 50% LTR for its peripheral region {P7218806336706.DOCX} 29having a width of 2.5 mm and a uniform 80% LTR for its central region, both measured by 550 nm wavelength, and a transition region connecting both 80% and 50% LTR-regions and having LTR gradient from 80% LTR to 50% LTR in accordance with one of the embodiments. The dash-dot-dot line in FIG.5 (Feature 530) represents a deflection distance vs. gas pressure graph of Film 30 having a single and uniform 50% LTR measured by 550 nm wavelength. As illustrated in FIG.5, Film 10 has the highest deflection, Film 30 has the lowest deflection, and Film 20 has moderate deflection in between.

[0105] The embodiment of FIG. 5 illustrates the benefits and advantages of the present disclosure and its embodiments. A pellicle film having at least two light transmission rates (e.g., Film 20) and deflection measurements corresponding to the dash-dotted line 520 offers the same light transmission features, including high EUV transmission rates, through its central region having the higher light transmission rate of the at least two light transmission rates as another pellicle film (e.g., Film 10) having a uniform light transmission rate equal to the higher light transmission rate while, more importantly, the pellicle film having deflection measurements represented by dash-dotted line 520 (Film 20) renders reduced deflection compared to another pellicle film having a single and uniform light transmission rate equal to the higher light transmission rate with its deflection measurement results represented by the solid line 510 (e.g., Film 10). Film 20 offers a stronger film mechanical strength.

[0106] The pellicle film having deflection measurements depicted by dash-dotted line 520 (Film 20) has a higher film deflection compared to yet another pellicle film having a single and a uniform light transmission rate equal to the lower light transmission rate (Film 30) with its deflection measurements represented by the dash-dot-dot line 530.

[0107] Furthermore in a deflection test, a pellicle film will eventually rupture as a gas pressure continues to climb. At the time of rupture, the gas flow pressure is recorded as the pressure {P7218806336706.DOCX} 30at rupture (or rupture pressure), the deflection is recorded as the deflection at rupture, and the flow rate is recorded as the flow rate at rupture.

[0108] FIG. 6 lists other testing results of the above three pellicle films (i.e., Film 10, Film 20, and Film 30), with their deflection measurement results shown as solid line (Feature 510), dash- dotted line (Feature520), and dash-dot-dot line (Feature 530) in FIG.5. The deflection test results of applying a constant 2 Pascal (2 Pa) gas pressure in FIG. 6 is a snapshot of FIG. 5. The Film 20 represented by dash-dotted line (Feature 520) has a lower 2 Pa deflection distance of 1.35 mm and ruptures at a higher gas pressure of 17.8 Pa and an elevated deflection distance at rupture (or rupture distance) of 4.42 mm upon the administration of a gas at a higher flow rate of 8930 ml / min compared to the Film 10, which has a 2 Pa deflection distance of 1.85 mm, pressure at rupture (rupture pressure) of 10.4 Pa, deflection distance at rupture of 4.01 mm under a weaker gas flow of 5160 ml / min. Its 4.42 deflection distance at rupture is even higher than the deflection distance at rupture from Film 30, which is 3.22 mm. This result suggests Film 20 may have the highest elasticity or the least brittleness among all three films tested.

[0109] These results further demonstrate the benefits of the present disclosure and its embodiments in enhancing the mechanical strength of interconnected nanofiber network structures or pellicle films while retaining the same EUV pellicle requirements. Hydrogen Plasma Etch Resistance

[0110] The embodiments of the present disclosure are further tested and demonstrated in an exemplary hydrogen plasma etching experiment.

[0111] The etching experiment is defined and performed as the following: placing a pellicle nanofiber film in a closed chamber, applying, for example, 80 watts of radio frequency energy rated 13.56 MHz for 20 seconds, and flowing a hydrogen gas constantly with a flow rate of 15 sccm through the chamber. The hydrogen plasm etching experiment results are summarized in a table shown in FIG.7. {P7218806336706.DOCX} 31

[0112] In FIG. 7, Samples A, B, C and D (A to D) are the exemplary interconnected and intersected nanofiber network structures produced by the exemplary filtration method described above from one carbon nanotube suspension solution. Samples A to D are all single-layer free- standing films. Each of the Samples A, B, C and D covers a frame aperture of 10 mm by 10 mm. Samples A and B have one even light transmission rate (LTR) of 80% measured at 550 nm wavelength. Samples C and D have two LTRs, 80% in their central regions having a size of 5 mm by 5 mm and 50 % at the periphery (excluding the 5 mm by 5 mm area), measured by 550 nm wavelength. Samples B and D were treated by hydrogen plasma etching described above, while Samples A and C are untreated.

[0113] Samples A to D were subject to a deflection rupture test as described above.

[0114] Sample B’s rupture pressure measured at 181.0 Pa is lower than Sample A’s rupture pressure of 530.2 Pa, mainly due to hydrogen plasma etching, and represents a 65.8% rupture pressure reduction from Sample A’s result. Sample D’s rupture pressure, measured at 354.9 Pa, is lower than Sample C’s rupture pressure of 878.3 Pa and has a 59.59% rupture pressure reduction, although both are hydrogen plasma etched. The difference in percentages of rupture pressure reductions or a less percentage drop in rupture pressure demonstrates the benefits of one of the embodiments of the present disclosure, which is a double-areal density film and / or a double-light transmission film, e.g., Samples C and D, contributes to and endorses stronger mechanical properties of a film compared to a single-areal density and / or a single light transmission film.

[0115] Furthermore, Sample C’s rupture pressure, measured at 878.3 Pa, is higher than Sample A’s rupture pressure of 530.2 Pa (a 65.65 % enhancement), showing again the benefits of double areal density and / or double light transmission rate, represented by Sample C, over a single areal density and / or single light transmission rate, like Sample A.

[0116] The value of Sample D’s rupture pressure doubles the value of Sample B’s rupture pressure, i.e., 354.9 Pa vs.181.0 Pa (a 96.08% enhancement). The embodiment of having two areal {P7218806336706.DOCX} 32densities and / or two light transmission rates, such as Sample D, makes a significant difference in a nanofiber film rupture pressure.

[0117] In summary, an intersected and interconnected nanofiber film or pellicle film demonstrates improved film mechanical strength and enhanced hydrogen plasma etching resistance.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 and derived 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.

[0118] 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.

[0119] 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 {P7218806336706.DOCX} 33Description, 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.

[0120] 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. {P7218806336706.DOCX} 34

Claims

What is claimed is:

1. A nanostructure film for extreme ultraviolet (EUV) lithography, the nanostructure film comprising: a plurality of carbon nanofibers that are intersected randomly and continuously to form a first interconnected nanofiber network structure, the first interconnected nanofiber network structure having a first surface in a planar orientation, a geometric shape, and a target size of the geometric shape, wherein the plurality of carbon nanofibers comprises single-walled carbon nanofibers, double-wall carbon nanofibers, and multi-wall carbon nanofibers; the geometric shape comprises a central region having a first light transmission rate, a peripheral region having a second light transmission rate, the peripheral region being non- overlapping with the first central region, the second light transmission rate being different from the first light transmission rate; and a number of walls of the single-walled carbon nanofibers is one, a number of walls of the double-wall carbon nanofibers is two, and a number of walls of the multi-wall carbon nanofibers is three or more. 2 The nanostructure film of Claim 1, further comprising a transition region between the peripheral region and the central region, wherein the transition region connects the peripheral region to the central region, and wherein the transition region has a variable light transmission rate, the variable light transmission rate starting with the second light transmission rate whereat the transition region connects with the peripheral region and {P7218806336706.DOCX} 35ending with the first light transmission rate whereat the transition region connects with the central region.

3. The nanostructure film of Claim 2, wherein the variable light transmission rate forms an even descending gradient from the second light transmission rate to the first light transmission rate. 4 The nanostructure film of Claim 1, wherein the first light transmission rate is higher than the second light transmission rate. 5 The nanostructure film of Claim 4, wherein a deflection of the first interconnected nanofiber network structure is less than a deflection of a second interconnected nanofiber network structure, wherein the plurality of the carbon nanofibers are intersected randomly and continuously to form a second interconnected nanofiber network, and the second interconnected nanofiber network structure has the geometric shape, the target size, and a light transmission rate equal to the first light transmission rate. 6 The nanostructure film of Claim 4, wherein a deflection of the first interconnected nanofiber network structure is more than a deflection of a third interconnected nanofiber network structure, wherein the plurality of the carbon nanofibers are intersected randomly and continuously to form a third interconnected nanofiber network, and the third interconnected nanofiber network structure has the geometric shape, the target size, and a homogeneous light transmission rate equal to the second light transmission rate. {P7218806336706.DOCX} 367. The nanostructure film of Claim 1, wherein the plurality of the carbon nanofibers includes 50% or more of double-wall carbon nanofibers.

8. The nanostructure film of Claim 7, wherein the plurality of the carbon nanofibers includes 50% to 75% of double-wall carbon nanofibers. 9 The nanostructure film of Claim 7, wherein the plurality of the carbon nanofibers further includes 20% to 40% of single-walled carbon nanofibers. 10 The nanostructure film of Claim 7, wherein the plurality of the carbon nanofibers further includes at least 1% of multi-wall carbon nanofibers. 11 The nanostructure film of Claim 1, wherein the central region has an EUV transmission rate of 80% or more. 12 The nanostructure film of Claim 1, wherein the central region has an EUV transmission rate of 90% or more. 13 The nanostructure film of Claim 1, wherein the central region has an EUV transmission rate of 92% or more. 14 The nanostructure film of Claim 1, wherein the central region has an EUV transmission rate of 95% or more. {P7218806336706.DOCX} 3715. The nanostructure film of Claim 1, wherein the geometric shape is a rectangle, wherein the peripheral region encloses the central region, and wherein the peripheral region has four connected straight portions.

16. The nanostructure film of Claim 15, wherein the second light transmission rate of at least one of the four straight portions is higher than the first light transmission rate of the central region.

17. The nanostructure film of Claim 15, wherein the target size of the geometric shape is 110 mm x 140 mm or larger.

18. The nanostructure film of Claim 5, wherein a rupture pressure of the first interconnected nanofiber network structure is higher than a rupture of the second interconnected nanofiber network structure.

19. A method of performing extreme ultraviolet (EUV) lithography, the method comprising transmitting EUV radiation through a pellicle, the pellicle comprising a pellicle border having an aperture, and at least a layer of a plurality of carbon nanofibers that are intersected randomly and continuously to form an interconnected nanofiber network structure, the interconnected nanofiber network structure being mounted to the pellicle border to cover the aperture, the interconnected nanofiber network structure comprising a surface in a planar orientation, a central region having a first light transmission rate, and a peripheral region, the peripheral region being divided into four connected straight portions to enclose the central region, wherein at least one of the four connected straight portions has a {P7218806336706.DOCX} 38second light transmission rate lower than the first light transmission rate, and wherein the central region has an EUV transmission rate at least of 80%.

20. The method of Claim 19, wherein the first interconnected nanofiber network structure further comprises a transition region between the peripheral region and the central region, the transition region having a light transmission rate gradient transitioning from the second light transmission rate whereat the transition region connects with the at least one of the four connected straight portions of the peripheral region to the first light transmission rate whereat the transition region connects with the central region.

21. The method of Claim 19, wherein the aperture is rectangular in shape and has a target size of 110 mm x 140 mm or larger.

22. The method of Claim 20, wherein the transition region has a portion of the transition region having a linear light transmission rate gradient. {P7218806336706.DOCX} 39

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