Extreme Ultraviolet pellicle with improved extreme ultraviolet transmission and method for manufacturing the same

Abstract

A method for enhancing extreme ultraviolet (EUV) transmission and reducing scattering of a carbon nanostructure pellicle film is disclosed. The method includes annealing the carbon nanostructure pellicle film at least once in a heated state before exposing the pellicle film to an EUV lithography process. The method further provides means for maintaining the annealed nanostructure pellicle film in an inert gas environment or in a vacuum.

Description

Technical Field

[0001] Cross - Reference to Related Patent Applications This application claims priority to U.S. Provisional Patent Application No. 63 / 353,908, filed on June 21, 2022, and U.S. Provisional Patent Application No. 63 / 444,011, filed on February 8, 2023. The entire disclosure of each of these documents, including the specification, drawings, and claims, is hereby incorporated by reference into this specification for all purposes.

[0002] The present disclosure generally relates to modified thin films and thin film devices used in semiconductor microchip manufacturing, and more particularly to film - processed ultra - thin, ultra - low - density, nanostructured free - standing pellicle films, and such films and film devices for extreme ultraviolet (EUV) lithography.

Background Art

[0003] A pellicle is a protective device that covers a photomask and is used in semiconductor microchip manufacturing. A photomask can refer to a plate with holes or transparency that allows light to be inserted into a defined pattern. Such photomasks may be widely used in photolithography and the manufacture of integrated circuits. The photomask is used as a master template to create a pattern on a substrate (usually a thin slice of silicon known as a wafer in the case of semiconductor chip manufacturing).

[0004] Particle contamination can often be a significant problem in semiconductor manufacturing. This problem is more pronounced in many advanced photolithography processes with high resolution, as non - negligible particles can change the printed pattern of logic circuits on a chip where redundancy is not built in, affecting the product yield.

[0005] The photomask is protected from particles by a pellicle, which is a thin transparent film stretched over a frame (also called a pellicle border with a central opening) that is attached to cover the pattern surface of the photomask. The pellicle is located near the mask but far enough away from the mask so that medium to small-sized particles that adhere to the pellicle will not be printed because the focus is too far away. However, according to on-site reports in the semiconductor industry, falling particles are still observed even after the exposure period using an unknown particle source.

[0006] In recent years, the microchip manufacturing industry has noticed that the pellicle may protect the photomask from damage caused by reasons other than particles and contaminants.

[0007] Extreme ultraviolet (EUV) lithography is an advanced optical lithography technology that uses the EUV wavelength range (more specifically, a wavelength of about 13.5 nm). With EUV lithography, semiconductor microchip manufacturers can pattern the most intricate features with a resolution of 7 nm or less and place more transistors without increasing the size of the required space. EUV photomasks function by reflecting light. This light reflection is achieved by using multiple alternating layers of molybdenum and silicon. When the EUV light source is activated, the EUV light first hits the pellicle film, passes through it, then bounces back from under the photomask and hits the pellicle film again, and then the EUV light continues along its path to print the microchip. During this process, some of the energy is absorbed, and as a result, heat can be generated, absorbed, and accumulated. The temperature of the pellicle can get hot, ranging from 500 °C to over 1000 °C.

[0008] Although heat resistance is important, the pellicle must also be highly transparent to EUV in order to ensure that the reflected light and the reflected light pattern from the photomask pass through it. This is one of the main reasons why EUV pellicles are generally very thin, with a thickness of less than 200 nm, preferably less than 100 nm, or less than 40 nm.

[0009] In 2016, polysilicon-based EUV pellicles were developed after decades of research and efforts. However, for a simulated relatively low-power 175-watt EUV source, the EUV transmittance was only 78%. The strong demand for increasing transistor density has presented further technical challenges to EUV pellicle developers with strict requirements for higher transmittance, lower transmittance variation, higher temperature tolerance, and strong mechanical strength.

[0010] Attempts have been made to achieve high light transmittance by increasing the carbon nanotube content in the carbon nanotube sheet (for example, reaching 99% by mass). As a result of such attempts, products have emerged that may also meet the requirements for the mechanical strength and / or durability of pellicle films based on current industry standards. Further improvements include meeting more stringent standards, improving the user experience, reducing production costs, and creating economic benefits. Therefore, such carbon nanotube-based thin films need to have a certain thickness to support their structural integrity. As a result, the EUV transmittance of such carbon nanotube-based thin films may require a compromise when dealing with thicker films. Therefore, aiming for further progress, techniques beyond conventional technologies and knowledge that can address both the transmittance of EUV light and the thickness of the pellicle film have been explored and developed.

[0011] Attempts to manufacture ultra-thin, ultra-low-density carbon nanotube (CNT) pellicle films have reached a milestone and been published in WO2021 / 090699. In this application, ultra-thin films (with a thickness of about 3 nm) of the same size as current industry standards have been achieved. However, such ultra-thin films with a thickness of about 3 nm have practical problems because they are easily damaged during product packaging, transportation, handling, and the operation of humans and robots.

[0012] Therefore, alternative film processing methods are required to create a pellicle suitable for cargo transportation while maintaining the characteristics of ultra-thinness and / or ultra-EUV transparency. SUMMARY OF THE INVENTION

[0013] According to an aspect of the present disclosure, a specifically structured nanostructured film is disclosed. The nanostructured film is a plurality of carbon nanofibers randomly crossed to form a network structure interconnected in a planar orientation, wherein the crossed or interconnected network structure has a thickness ranging from a lower limit of 3 nm to an upper limit of 100 nm, the light transmittance at a wavelength of 550 nm is more than 50% to more than 95%, the EUV transmittance is more than 75% to more than 94%, up to 99%, and the nanostructured film (e.g., nanofiber structure) undergoes an annealing process, preferably thermal annealing. A preferred CNT pellicle has a plurality of carbon nanofibers with at least 50% double-layer carbon nanofibers, at least 50% single-layer carbon nanofibers, or at least 50% carbon nanofibers with three or more layers, and the remainder is filled with carbon nanofibers having different numbers of layers, finally accounting for 100% of the content. The present disclosure further includes CNT pellicle films having any combination of single-layer, double-layer, and multi-layer carbon nanotubes and other types of nanofibers. Such a nanofiber structure exhibits further improved EUV transparency during the intended annealing process, converting a nanofiber film structure with low non-EUV lithography compatibility or EUV transparency into a film or pellicle compatible with EUV lithography, and can meet industrial requirements and standards.

[0014] According to another aspect of the present disclosure, the annealing chamber may have one or more gases flowing during annealing.

[0015] According to another aspect of the present disclosure, in some embodiments, the annealing process improves the EUV transmittance and / or reduces EUV scattering.

[0016] According to a further aspect of the present disclosure, in some embodiments, the annealing process increases the EUV transmittance of the nanofiber structure from less than 95% to more than 95%, or further from less than 90% to more than 90% or more than 95%. The difference in EUV transmittance before or after annealing is greater than 0.3%, greater than 1.0%, greater than 2.0%, greater than 5.0%, or greater than 10.0%.

[0017] According to yet another aspect of the present disclosure, in some embodiments, the annealing process means applying electromagnetic irradiation directly or indirectly to a pellicle film or a pellicle device including a pellicle film on a frame. Exemplary electromagnetic irradiation light sources include, but are not limited to, visible light, laser light, infrared rays, ultraviolet rays, radio waves, X-rays, and electromagnetic waves within the spectrum of physical vapor deposition, such as electron beam evaporation.

[0018] According to yet another aspect of the present disclosure, in some embodiments, the annealing process may include thermal annealing by placing a nanofiber structure in a chamber and heating the chamber at 600 °C for 10 minutes.

[0019] According to one aspect of the present disclosure, in some embodiments, the thermal annealing temperature may be 500 °C or higher, preferably 600 °C, 650 °C, 700 °C, 800 °C, or 1,000 °C or higher.

[0020] According to yet another aspect of the present disclosure, the annealing chamber may be a vacuum chamber, a reduced-pressure chamber, or a chamber through which one gas or two or more gases pass.

[0021] According to one aspect of the present disclosure, the vacuum chamber may be part of an EUV scanner, or may have a direct connection with an EUV scanner to convey a newly annealed pellicle film or pellicle device to the scanner, such as within a lithography machine or lithography system, or within a semiconductor manufacturing production line.

[0022] According to another aspect of the present disclosure, thermal annealing of the pellicle film or pellicle device can be performed remotely from an EUV scanner or an actual semiconductor manufacturing site.

[0023] According to one aspect of the present disclosure, thermal annealing of the pellicle film is performed before EUV irradiation without or with limited air exposure, or without or with limited exposure to other non-inert gases.

[0024] According to yet another aspect of the present disclosure, thermal annealing of the pellicle film or pellicle device can be performed in a non-vacuum chamber or in a chamber under reduced pressure filled with one or more selected inert gases. Exemplary inert gases include, but are not limited to, argon, helium, neon, krypton, xenon, and radon.

[0025] According to another aspect of the present disclosure, the nanostructured film has a surface density of about 0.2 μg / cm 2 ~ about 6.0 μg / cm 2 of.

[0026] According to an aspect of the present disclosure, a pellicle is disclosed. The pellicle includes a pellicle boundary defining an opening and at least one nanostructured film attached to the pellicle boundary to cover the opening, and the above-mentioned pellicle film is annealed or thermally annealed at any time before receiving EUV radiation.

[0027] According to one aspect of the present disclosure, a method for manufacturing a pellicle film or pellicle device for EUV lithography is disclosed. The method includes steps of manufacturing a pellicle film, preferably by a filtration method, attaching the pellicle film to a pellicle boundary or an intermediate boundary, annealing the pellicle at a high temperature, and optionally transferring the pellicle film from the intermediate boundary onto the pellicle boundary.

[0028] According to another aspect of the present disclosure, a method of performing EU lithography is disclosed. The method includes annealing the pellicle at a high temperature and then transmitting EUV radiation through the pellicle.

[0029] The present disclosure will be further described with reference to the plurality of drawings referred to in the following detailed description as non-limiting examples of preferred embodiments of the present disclosure. Like characters represent like components throughout the several views of the drawings.

Brief Description of the Drawings

[0030]

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Modes for Carrying Out the Invention

[0031] Through one or more of its various aspects, embodiments and / or specific features, sub-components, or processes of the present disclosure are intended to clarify one or more of the advantages specifically mentioned above and referred to below.

[0032] A pellicle may refer to a thin transparent film that protects a photomask during semiconductor microchip manufacturing. The pellicle contemplates a protective device having a) a border or frame, and 2) a central hole or opening. Both the border and the opening are covered by a continuous thin film that is at least partially on the border and partially on the opening, preferably covering the entire perimeter of the border and the entire upper part of the opening. The central part of such a thin film that extends the opening is self-supporting. The pellicle can function as a dust cover or filter to prevent particles and contaminants from falling onto the photomask during manufacturing. However, the pellicle must be sufficiently transparent to allow the transmission of light necessary for lithography. A higher light transmittance is required for more effective lithography. For most EUV lithography applications, an EUV transmittance of 90% from the pellicle may be sufficient. For high-resolution EUV lithography below 5 nm, high-energy EUV scanners, or high numerical aperture EUV lithography scanners, it may be desirable for the EUV transmittance to be 90% or more, 92% or more, 94% or more, 96% or more, up to a maximum of 99%.

[0033] Furthermore, pellicles for EUV lithography require large (e.g., larger than 110×140 mm) self-supporting thin film materials with extreme and unique properties. In addition to high transparency to EUV radiation, unexpected EUV transmission variations can cause adverse effects during the manufacturing process, leading to poor printing results, abnormal printing patterns, and reduced production yields. Also, EUV pellicle films may be required to be mechanically robust to withstand temperatures exceeding 400 °C, handling, transportation during the photolithography process, and pumping down and evacuation operations. Mechanically weak pellicle films can 1) bend or sag during pressure changes in the scanner chamber, causing damage to the pellicle film itself such as slits or wrinkles, 2) print incorrect images due to contact with the underlying photomask, and 3) break and contaminate the scanner chamber. Pellicle films are required to have not only gas permeability but also the ability to retain micrometer-sized particles. Considering the number of high-level properties required, effective EUV pellicles have been difficult to manufacture conventionally.

[0034] In this aspect, carbon nanotubes and equivalent nanofibers have been proposed as possible starting materials for creating pellicles for this EUV pellicle application due to their excellent thermal and mechanical properties, as well as their ability to form porous films.

[0035] Carbon Nanotubes and Carbon Nanotube Films Carbon nanotubes (CNTs) or carbon nanofibers, often referred to herein, are long tubes having a small diameter typically measured in nanometers. They have a high length-to-diameter aspect ratio, which generally preferably exceeds about 100:1 and may exceed about 1000:1. Another preferred aspect ratio can be at least about 10,000:1. CNTs are composed of one or more graphene sheets wound concentrically. Each individual graphene sheet is considered a wall of the CNT. Single-walled CNTs (SWCNTs) are made of a single graphene sheet. Double-walled CNTs (DWCNTs) are made of two graphene sheets. Finally, multi-walled CNTs (MWCNTs) have a number of graphene sheets. Other types of CNTs can include, but are not limited to, coaxial nanotubes, conical carbon nanotubes, and closed carbon nanotubes. Other carbon allotropes may also have the potential to form sheets with excellent properties as a pellicle film. In the case of CNTs, they may exist in a substantially pure form of one type or often in combination with other types with respect to the number of CNT walls. CNTs may exist individually, separated from others, or form bundles. Bundles may include the same type of CNT or different types of CNTs, such as SWCNTs including DWCNTs, SWCNTs including MWCNTs, etc. Within a bundle, the length and diameter of the CNTs may vary. Each bundle containing two or more CNTs may be aligned parallel over at least a portion of its total length. For simplicity and convenience, CNTs in this application may mean different types of CNTs, such as those having different numbers of walls, and may include CNTs existing individually or in bundles.

[0036] As used herein, nanofibers may, by way of example, mean fibers having a diameter of less than 1 μm. Nanofibers and nanotubes are used interchangeably and may include SWCNTs, DWCNTs, MWCNTs, and other carbon allotropes in which carbon atoms are bonded to each other to form a cylindrical structure.

[0037] Individual CNTs can intersect one or more other CNTs. Many CNTs can together form a mesh-like microstructured film. An exemplary embodiment may include a self-supporting microstructured thin film, in the region of which there is no supporting material or substrate on both sides of the thin film. Such formation is possible, but not guaranteed in all trials, especially in the manufacture of ultra-thin films with properties such as high transparency for EUV lithography pellicles.

[0038] Furthermore, among several possible methods for manufacturing self-supporting films, a filtration-based approach has been utilized to produce film films from small-sized films to sufficiently large films with a uniform film thickness for EUV lithography. Films of uniform thickness generally correlate with uniform light transmittance. This filtration-based method enables the rapid production of not only CNT films but also films of other high aspect ratio nanoparticles and nanofibers (e.g., boron nitride nanotubes (BNNTs) or silver nanowires (AgNWs)). In this approach, since the synthesis of nanotubes or nanoparticles is separated from the film manufacturing process, different types of nanofibers created by substantially any method may be used. Different types of nanotubes (SWCNT, DWCNT, MWCNT, or carbon allotropes) can be mixed in any desired ratio. Filtration can be a self-leveling process in the sense that the non-uniformity of the film thickness during the filtration process is self-corrected by local permeability variations, and thus can be a highly desirable film formation process and also a promising candidate for the production of very uniform films.

[0039] Annealing treatment Annealing refers to the process of applying heat treatment to a given material to change its physical properties, and in some cases chemical properties, to increase its ductility and reduce its hardness. Annealing starts from a heat source, applies heating energy to the material to raise its temperature from the ambient temperature to a predetermined temperature, holds the desired temperature for a preselected treatment period, and then cools the material.

[0040] The heating performed for annealing may be electrical heating that passes an electric current, voltage, and / or electrical energy through the material by direct contact with the material.

[0041] Alternatively, the heating for annealing may be convective heating. In an exemplary convective heating, a heated gas flows over the surface and / or, in some cases, through channels inside the material to raise the target temperature.

[0042] Another heating performed for annealing may be radiative heating where electromagnetic waves are irradiated towards the target material. Light sources within the visible spectrum, including lasers, can heat the target material by directly irradiating radiation onto the target or the target surface. The photons of light can be reflected, re - radiated, or scattered, and due to topographical differences, features, and / or irregularities in a given area of the material, the heating can become non - uniform. If the environment in which such a process is carried out obstructs the optical path to the target, the annealing results may become non - uniform. This non - uniformity brought about by direct light treatment becomes more prominent in areas that are repeatedly irradiated and areas that avoid irradiation when the entire material surface is not irradiated simultaneously. Furthermore, laser treatment can cause the combustion, removal, or sublimation of surface substances. Such "lifted" substances generated by laser treatment, even in trace amounts, can be in the form of small molecules or elements and may re - absorb or re - deposit on the untreated or, in some cases, treated surface, resulting in the formation of new irregularities or worsening the non - uniformity of an existing film.

[0043] However, the embodiments of the present disclosure are not limited thereto, and different heating operations / methods may be performed, or a combination of heating operations may be performed.

[0044] Annealing may be thermal annealing that uses electromagnetic waves within the non-visible light spectrum including, but not limited to, infrared rays (e.g., near-infrared, mid-infrared, and / or far-infrared). Such electromagnetic wavelengths may have a range selected from between about 10 nm and about 1 mm. A preferred range can 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 can be between about 5 μm and about 20 μm. This heating method transfers energy to the target material, and the thermal energy dissipates into other microscopic motions within the material. That is, thermal annealing disperses its energy power to heat the target material and uniformly raises the temperature. This type of thermal annealing can cover the entire object regardless of the direction of the incident energy source. Ceramic heating by a ceramic heating tube with sufficient internal space to accommodate a full-size pellicle is one of many options for implementing heat heating based on the non-visible light spectrum. The heating element may be made of silicon carbide and molybdenum disilicide. Without wishing to be bound by scientific theory, other heating elements and heating devices are considered applicable.

[0045] In the heating tube, one or more heat sources or heating elements may be arranged in a circular arrangement or a tubular arrangement in a cross-sectional view with respect to the shape of the entire heating device. Electromagnetic waves from such heat sources uniformly distribute radiation within the tubular chamber. With an appropriate electromagnetic wave spectrum and emission source, such annealing ensures uniform radiation reaching the CNT pellicle and guarantees covering the entire pellicle area at any time during the process, so that the EUT transmission variation is minimized or lower compared to annealing in a non-full film field.

[0046] Examples of the annealing process in this exemplary embodiment include, but are not limited to, the heating methods described above.

[0047] A typical annealing temperature can be any temperature above ambient temperature. The temperature can be 50 °C or higher, 100 °C or higher, 300 °C or higher, 500 °C or higher, 600 °C or higher, 650 °C or higher, 700 °C or higher, 800 °C or higher, 900 °C or higher, or 1,000 °C or higher. The temperature can also be 3,000 °C or lower, 2,500 °C or lower, 2,000 °C or lower, 1,800 °C or lower, 1,700 °C or lower, 1,600 °C or lower, 1,500 °C or lower, or 1,400 °C or lower. The heating temperature can be within the range of any two of the aforementioned temperatures.

[0048] In selecting the annealing temperature, other factors may need to be further considered, such as an appropriate temperature range according to the material properties of the pellicle boundary, such as the thermal expansion characteristics of the pellicle boundary. Pellicle boundaries with low thermal expansion characteristics (e.g., quartz) are preferred.

[0049] The annealing temperature can increase at a fixed rate or a variable rate depending on the heating device / method used and the heating capacity of the heating device. A typical and practical rate of temperature increase can be about 20 °C / min. A preferred heating schedule rapidly heats the CNT pellicle to avoid or limit potential CNT oxidation by chemical contaminants adhering to the annealing chamber or mixed in the flow-through gas. In the heating schedule, the physical properties, and in some cases the chemical properties, of the pellicle boundary and the balance with thermal expansion may also be taken into account to avoid cracks in the pellicle boundary.

[0050] Cooling after annealing can potentially allow the temperature rise state to naturally return to ambient conditions. Alternatively, in the post-annealing cooling process, to avoid possible wrinkles and maintain the mechanical strength of the film, a cooling gas, ambient temperature gas, or a gas with a temperature that drops over a certain period can be flowed through to cool the annealing chamber. An inert gas is preferred here.

[0051] The annealing process may be carried out under vacuum (e.g., vacuum annealing), partial vacuum, or atmospheric pressure. Further, the annealing process may be carried out in the presence of an inert gas or a non-inert gas such as a hydrocarbon gas. By alternately switching between the inert gas(es) and the hydrocarbon gas(es) during the annealing process, the characteristics of the pellicle film such as light transmittance can be further enhanced, and the mechanical strength of the pellicle film can be increased.

[0052] Exemplary inert gases include, but are not limited to, argon, helium, neon, krypton, xenon, and radon. Exemplary hydrocarbon gases include, but are not limited to, methane, ethane, propane, butane, pentane, hexane, and heptane.

[0053] The gas can flow through the annealing chamber at a constant or variable flow rate. Two or more gas species as a gas mixture can flow through the annealing chamber at a constant or variable flow rate. Also, two or more gases may flow continuously or intermittently. The gas or gas mixture may be preheated before being injected into the annealing chamber and / or actively heated within the annealing chamber for convective heating. The gas or gas mixture can be intentionally selected and injected during annealing. For example, it has been previously reported that applying a hydrocarbon gas repairs structural defects in the nanofibers and nanoparticle formation on the surface of the pellicle film. Due to the nature of handling ultra-thin, ultra-low density films, a constant gas flow or a gas with the least variation in flow rate may be desirable to avoid film rupture, which is contemplated herein.

[0054] The vacuum chamber may be part of an EUV scanner. The vacuum chamber may be directly connected to the EUV scanner as a component, accessory, or attachment of an EUV manufacturing assembly line. The vacuum chamber can also be made stand-alone, near or remote from the scanner, to perform such annealing processes.

[0055] The annealing process can begin by attaching the nanofiber structure to a frame and then placing it directly into an annealing chamber or container. This chamber is evacuated to a vacuum level of about 10 -4 Torr or less or near-vacuum. Next, the chamber is heated to a predetermined temperature. At this point, the pellicle is placed in the chamber for a selected period. The pellicle may be placed in the chamber before heating is initiated. Regardless of the presence or absence of a cooling gas such as argon, after the chamber returns to room temperature and atmospheric pressure, the process is complete, and to avoid exposure to other gases in the atmosphere that may cause contamination, oxidation, or damage, the pellicle can be stored under ambient conditions, in a vacuum, in an inert gas, or a combination thereof.

[0056] Annealing can be performed under electromagnetic irradiation of a single wavelength, which is typically depicted as a bell-shaped curve (single peak) on a graph. Annealing can further include electromagnetic energy from multiple electromagnetic waves with non-overlapping peaks and / or a combination of multiple electromagnetic waves with overlapping peaks, where each peak represents a specific electromagnetic energy source. Multi-wavelength radiation can deliver sufficient electromagnetic energy to the target, thereby shortening the annealing time for mass production of pellicle products and accelerating the annealing process.

[0057] The electromagnetic energy can be delivered in continuous mode or flash mode (e.g., a flash that can last as short as about 0.1 ms). The electromagnetic energy delivered in flash mode (sometimes referred to as flash light) may anneal or re-anneal the pellicle film before or after undergoing an EUV lithography process. The specific settings for the delivery of electromagnetic energy can depend on, but are not limited to, the density, porosity, thickness, and geometric shape of the microstructure of the target material.

[0058] Each flash light can cover the side surface of the entire lithography pellicle film with little irradiation variation, so a uniform annealing result can be obtained. One or more other flash lights may illuminate the opposite side of the pellicle film. In the case of flash light annealing involving flash light irradiation two or more times, possible irradiation bias or unevenness can be avoided by changing, adjusting, or rotating the position of the target film with respect to the flash light source.

[0059] The term annealing may include further aspects and broader interpretations in various technical fields and industries applicable to or related to the present disclosure. One or more innovative contributions herein occur in the fields of materials science and semiconductors.

[0060] Film Formation and Thermal Annealing According to an exemplary embodiment of the present disclosure, an ultra-thin and ultra-low density CNT pellicle film can be manufactured and subsequently a thermal annealing process can be performed.

[0061] FIG. 1 illustrates a filtering method for forming the pellicle film shown in FIG. 2 and then performing an annealing process according to an exemplary embodiment.

[0062] Another embodiment of the present disclosure may further include any pellicle film to be manufactured, to be fabricated, to be processed, or to be processed by any means before the annealing process. Further, another embodiment of the present disclosure includes any other pellicle film having various CNT surface modifications including, but not limited to, coating or other means of one or more metal elements, metal oxides, CNT surface modifiers, or combinations thereof.

[0063] As illustrated in FIG. 1, a self-standing carbon nanotube-based pellicle film may be created by a filtration-based method. In operation 101, the catalyst is removed from the carbon nanotubes (CNTs) used to form the aqueous suspension. In one example, the CNTs can be chemically purified prior to dispersion in the suspension to reduce the concentration of catalyst particles to less than 1 wt%, or preferably less than 0.5 wt%. The concentration may be measured by thermogravimetric analysis. The removal of the catalyst is not limited to any particular process or procedure, and any suitable process may be used to achieve the desired result.

[0064] In operation 102, an aqueous suspension is prepared using the purified CNTs such that the purified CNTs are uniformly dispersed within the aqueous suspension. When preparing one or more CNT suspensions, the carbon nanotube material can be mixed with a selected solvent to uniformly disperse the nanotubes within the final solution as a suspension. Mixing can include mechanical mixing (e.g., using a magnetic stir bar and stir 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 such as 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 facilitate the uniform dispersion of the carbon nanofibers within the solvent. Examples of surfactants include, but are not limited to, anionic surfactants.

[0065] The carbon nanofiber film is typically formed from one of MWCNT, DWCNT, or SWCNT. The carbon nanofiber film may also include a mixture of different types of CNTs (i.e., SWCNT, DWCNT, and / or MWCNT) with varying ratios between the different types of CNTs. Other types of CNTs can also be used to manufacture CNT films by filtration or other known and considered methods.

[0066] These three different types of common carbon nanotubes (e.g., MWCNT, DWCNT, and SWCNT) each have different properties. In one example, single-walled carbon nanotubes can be more favorably dispersed in a solvent for subsequent formation onto a sheet of randomly oriented carbon nanotubes (i.e., most of the nanotubes are individually suspended, reducing adsorption onto other nanotubes). As a result of being able to uniformly disperse the individual nanotubes in the solvent, a more planar and uniform nanotube film can be produced by removing the solvent from the suspended nanofibers. This physical uniformity can also improve the uniformity of other properties of the entire film (e.g., transparency and scattering to irradiation, mechanical strength upon pressure changes, and lifetime / durability tests).

[0067] In one example, the aqueous CNT suspension in operation 102 may have SWCNT with a purity exceeding at least 85%. The remainder can be a mixture of DWCNT, MWCNT, and / or catalyst. In other examples, dispersed CNT suspensions can be prepared that contain different types of CNTs in various ratios, such as about 20% / 75% DWCNT / SWCNT, about 50% / 45% DWCNT / SWCNT, about 70% / 20% DWCNT / SWCNT, etc., where the remainder is occupied by MWCNT. A mixture of MWCNT at 10% or more and DWCNT and SWCNT blended at various DWCNT / SWCNT percentage ratios can be prepared and subjected to the same filtration process to form the nanofiber structure. In one example, an anionic surfactant can be utilized as a dispersant in the suspension to enhance the uniform dispersion of the different types of CNT mixtures.

[0068] In operation 103, the CNT suspension is then further purified to remove agglomerated or stuck CNTs from the initial mixture. In one example, different forms of CNTs (undispersed or agglomerated vs. well-dispersed) may be separated from the suspension by centrifugation. Centrifugation of surfactant-suspended carbon nanotubes can reduce the turbidity of the suspension solution and help ensure complete dispersion of the carbon nanotubes in the final suspension solution before proceeding to the next filtration step. However, aspects of the present disclosure are not limited thereto, and other separation methods or processes may be used. According to an exemplary aspect, operation 103 may be optionally performed or may be performed as a necessary step in the formation of the pellicle film.

[0069] In operation 104, any CNT suspension, preferably the CNT supernatant after the separation procedure from operation 103, is then filtered through a filtration membrane to form a continuous sheet of a film of intersecting CNTs that is a CNT nanostructure film.

[0070] In one example, one technique for making a CNT film is to use water or another fluid to dispose the nanotubes in a random pattern on a filter (often a flat filtration membrane). Pass or force a homogeneously dispersed CNT-containing mixture through the filter, leaving a nanofiber structure layer on the surface of the filter. The resulting film size and shape are determined by the size and shape of the desired filtration area of the filter, while the film thickness and density 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, since non-permeating components are captured on the surface of the filter. If the concentration of nanofibers dispersed in the cross-flow filtrate is known, the mass of nanofibers deposited on the filter can be determined from the amount of fluid passing through the filter, and the areal density of the film can be determined by dividing the nanofiber mass by the total filtration area. Also, the filtration area of the filter may be the same as or smaller than the size of the filter, depending on the underlying support structure of the filter. The selected filter is typically not permeable to any CNTs.

[0071] The filtered CNT film can be a combination of SWCNT, DWCNT, and / or MWCNT with different compositions. The carbon nanofibers can be randomly crossed to form an interconnected network structure in a planar orientation to form a thin CNT film.

[0072] In operation 105, the obtained CNT film is then separated from the filtration membrane starting from the first edge of the CNT film and moving towards the second edge while slightly overlapping the first edge. When completely separated from the filtration membrane, the nanofiber film is ready for the next operation 106. Operation 106 can be either operation 106A or operation 106B.

[0073] In operation 106A, the separated CNT film is collected on a solid substrate such as a frame sometimes called a recovery frame, a collector frame, or an intermediate frame. The separated CNT film can be collected directly and attached on the pellicle boundary. The pellicle boundary has a defined opening.

[0074] Alternatively, in operation 106B, the CNT film can be retrieved and attached to the pellicle boundary. The CNT film can cover the entire opening to form a pellicle or pellicle device ready for EUV photolithography. The separated CNT film can be attached to any frame (e.g., a metal frame, a silicon frame, a quartz frame, or a pellicle boundary) with an opening as small as about 5 mm × 5 mm. There is a high demand for even larger films of 110 mm × 140 mm or more that function as full-size pellicle films for actual EUV scanners. Characteristic evaluations such as optical light transmittance and / or transmittance uniformity (or variation) tests, EUV transmittance and / or transmittance uniformity (or variation) tests, mechanical strength, deflection tests, permeability tests, deflection at a constant pressure or under simulated scanner pumping-down conditions, life tests, and particle tests can be performed on the CNT film. A full-size pellicle for EUV lithography scanning may require an ultrathin self-supporting film (usually larger than 110 mm × 140 mm) based on current industry standards. The full-size pellicle may sometimes be referred to as a full-field pellicle.

[0075] The pellicle frame referred to in this specification can withstand high-temperature treatment to maintain high-temperature annealing. Further, the pellicle frame can have a low coefficient of thermal expansion to avoid or cause the expansion and contraction of the nanofiber film attached thereto. Exemplary frame materials can be selected from silicon dioxide generally known as quartz, silicon carbide, and the like.

[0076] In operation 107, the CNT film on the frame, the pellicle boundary, or the intermediate transfer frame is subjected to a thermal annealing process. The thermal annealing process is performed by placing the CNT film in a sealed chamber or a vacuum chamber in a predetermined temperature-rising state for a specific processing period. However, aspects of the present disclosure are not limited thereto, as various thermal annealing methods may be performed at different temperatures, different periods (durations), and different heat energy sources, for example, different wavelengths or wavelength ranges of electromagnetic waves.

[0077] In one example, the thermal annealing process may be performed at a target temperature of about 500 °C or higher, about 600 °C or higher, about 700 °C or higher, about 800 °C or higher, about 900 °C or higher, and less than about 3,000 °C, less than about 2,500 °C, less than about 2,000 °C, or less than about 1,500 °C. Although the actual annealing temperature is preferably constant, it may vary within a range of ±1 to 10% of a predetermined target temperature measured near the annealing chamber or the annealing target, i.e., the pellicle film. When the target temperature is 600 °C, the actual temperature may be measured between 540 °C and 660 °C.

[0078] Also, in another example, the thermal annealing process may be performed for 1 second to 60 minutes at a target temperature or temperature range. The preferred processing time is 10 minutes to 30 minutes. However, aspects of the present disclosure are not limited thereto, as annealing by a flash of light may be as short as 0.1 milliseconds.

[0079] In another example, the annealing process may be performed in a chamber where the annealing chamber pressure is atmospheric pressure, vacuum, or in between. The annealing chamber generally supports the distribution of thermal energy, preferably a uniform distribution across the chamber. The thermal energy can be directed towards one or more targets such as one or more CNT films. The thermal energy can also diffuse within the chamber, immerse one or more films, and process the entire set of pellicle films uniformly with little or no variation. Annealing variations such as non-uniform energy accumulated on the film or non-uniform energy received by the film can cause, for example, film wrinkles, thickening of the focal film or thinning of the film, premature film breakage, etc. These events or changes can change the light transmittance of the film, worsen the transmittance variation, weaken the mechanical strength of the film, and shorten the lifespan of the film.

[0080] After annealing, the pellicle film may be ready for EUV lithography. In operation 108, the annealed CNT film or nanofiber film is transferred onto the pellicle frame.

[0081] The annealed film placed on the intermediate frame before annealing may be further analyzed by measurements including, but not limited to, visible light (e.g., wavelength 550 nm) and EUV transmittance measurement, visible light and EUV transmittance variation measurement, coating, mechanical tension measurement and film adjustment, or transfer to the pellicle boundary.

[0082] Improvement of EUV Transmittance and Reduction of EUV Scattering by Annealing The transmittance of a selected material measured at visible wavelengths by a given light source is known not to be the same as the transmittance at extreme ultraviolet (EUV). For example, a CNT film manufactured from operation 101 to operation 106A or operation 106B, excluding operation 107, has a transmittance of about 80% when measured at a wavelength of 550 nm and can result in a transmittance of about 94% at EUV 13.5 nm. This observation, combined with other reports, poses difficulties and uncertainties in predicting and correlating the transmittance of a given material at selected visible and EUV wavelengths. Further experimentation is required to establish a correlation between the transmittances at these wavelengths, which can be very difficult or almost impossible. Further processing or modification of the pellicle film makes the prediction of such a correlation even more difficult.

[0083] Exemplary embodiments of the present disclosure include annealed CNT pellicle films that have an increased EUV transmittance and a decreased scattering rate compared to untreated CNT pellicle films. The annealed CNT pellicle films show little change in physical properties. Further, the EUV transmission variation (i.e., the difference in multiple EUV transmittances measured at various positions of the pellicle film) may remain unchanged or show little change after annealing. These improvements are unexpected and different from well-known prior art.

[0084] Exemplary embodiments of the present disclosure meet or exceed EUV pellicle requirements, including but not limited to EUV transmittance, EUV transmission uniformity, deflection rate, and mechanical strength of the film under pressure changes. On the other hand, the exemplary embodiments also provide a method of treating pellicle films other than CNT pellicle films or most DWCNT pellicle films that may be inferior to industrial standards and enhancing their properties to meet or exceed the minimum EUV pellicle requirements. For example, a film with an EUV transmittance of less than 92% may exceed a transmittance of 92% or even be greater than 95% after applying one or more aspects of the present disclosure.

[0085] This configuration of the exemplary pellicle film provides an ultra-thin pellicle film, which enables a high EUV transmittance (e.g., greater than 70%, 80%, 85%, 90%, or 92%), and at the same time, has extremely high heat resistance (e.g., can withstand temperatures exceeding 500 °C), and has mechanical robustness that can withstand human and robotic operations and disturbances, including but not limited to packaging, shipping, atmospheric pressure fluctuations at low and high altitudes, and pressure changes during pump-down and ventilation of EUV scanners. In one example, the minimum EUV transmittance is a value of 80%, and a preferred EUV transmittance can be 90% or more.

[0086] Table 1 shows the exemplary effect of annealing on the EUV transmittance exhibited by the pellicle film formed according to the exemplary embodiments of the present disclosure. In the following example, CNT pellicle film samples were attached to a quartz frame and annealed at 600 °C for 10 minutes in a tubular heating oven under a vacuum of less than 10 -4 Torr. These were stored at ambient temperature in a sealed environment filled with argon until the time of the EUV transmittance test. [Table 1]

[0087] The above exemplary CNT pellicle film showed a transmittance of approximately 80% measured at a wavelength of 550 nm and an average EUV transmittance of approximately 93.88% using nine measurements per sample before annealing. After annealing the same sample, tests were immediately conducted. The transmittance measured at a wavelength of 550 nm showed no statistical difference and instead remained approximately the same as the original value. The average EUV transmittance of the nine measurements was approximately 96.00%, i.e., an increase of approximately 2.12%. When the same pellicle film was stored under ambient conditions and EUV transmittance measurements were taken 1 week, 1 month, and 3 months after the annealing process, the EUV transmittance based on nine measurements per sample was 95.90%, 95.36%, and 94.64% respectively (see Table 1). This investigation demonstrated that films with an EUV transmittance of less than 94% can increase EUV transmittance and reach an EUV transmittance of 95% or more within 2 - 3 months after the annealing process and maintain a satisfactory EUV transmittance. The increase in EUV transmittance may not suffer significant losses during the test period under normal storage conditions and without special equipment. Three months after the annealing process, a significant portion of the increase in EUV transmittance is maintained at a transmittance above 94.5%. Enhancing EUV transmittance by annealing can convert thicker films that may not initially be qualified for EUV lithography due to published EUV pellicle specifications into EUV pellicles for actual EUV lithography.

[0088] Another major issue in EUV lithography is the presence of flare. Flare is unwanted total integrated light scattering at the wafer level. Flare degrades the critical dimensions and imaging performance of EUV printing. Therefore, it is important to control or reduce the scattering of the pellicle film for effective EUV lithography.

[0089] As shown in Table 1 above, the scattering results are also improved by at least one of the embodiments of the present disclosure. By annealing, the scattering of the pellicle film decreases from 0.0811% to 0.0645% when measured at an angle of 4.7° (degrees). This reduction in scattering was partially lost when measured one month after the treatment. However, such an improvement in scattering does not completely disappear after storage for three months under ambient conditions.

[0090] The results shown in Table 1 indicate a strong potential for applying an annealing treatment in the manufacture of EUV pellicle films with unexpected but effective EUV transmission enhancement.

[0091] Effect of repeated annealing treatment Another embodiment of the present disclosure relates to repeated annealing to increase the EUV transmittance after an initial EUV transmission enhancement by annealing and subsequent reduction of the EUV transmission enhancement. For example, the EUV transmittance of the pellicle film measured one month (or four weeks) after the first annealing treatment was 95.36% (see Table 1). This was stored for an additional week under ambient conditions in air and then annealed again. This annealing was five weeks after the primary annealing, and when its EUV transmittance was measured again, a reading of 95.97% was obtained. Thus, the EUV transmission increased by approximately 0.6%.

[0092] This second annealing performed at the five-week point reversed the gradual loss of the acquired EUV transmission and increased the EUV transmission again. This strategy of applying a secondary annealing treatment after the primary annealing treatment and the associated continuous storage time may recover the lost EUV transmission and further enhance the EUV transmission.

[0093] The data presented herein may further provide a method of applying an annealing treatment to a pellicle film and a method of applying a re-annealed pellicle to an EUV scanner before subjecting the annealed nanofiber pellicle film or CNT pellicle film to EUV exposure.

[0094] However, the embodiments of the present disclosure are not limited to two annealing processes, and more annealing processes may be performed. Exemplary embodiments may include subsequent annealing up to a total of 10 times.

[0095] Effect of Gas Species on EUV Transmission Enhancement In the field of EUV lithography, it has previously been reported that both hydrogen ions and hydrogen radicals cause the cleavage of carbon-carbon bonds within carbon nanotubes, i.e., a carbon etching effect. Annealing in the presence of a hydrocarbon gas can repair these cleaved bonds.

[0096] As demonstrated above, the thermal annealing of the present disclosure increases EUV transmission when the annealing reaction is carried out without any gas or in a vacuum chamber. However, the embodiments of the present disclosure are not limited to processes that rely on a vacuum. They include annealing processes in the presence of one or more selected gases. Table 2 illustrates the experimental results for two exemplary gases. [Table 2]

[0097] The pellicle film was treated at 650°C for 30 minutes in the presence of nitrogen or argon, which are representative gases, according to operations 101 to 106A / B in FIG. 1. The results are shown in Table 2. For nitrogen annealing, the transmittance measured at a wavelength of 550 nm increased significantly from 80.08 ± 0.54% to 81.62 ± 0.778%, while there was no increase for argon treatment (measurement results: 79.94 ± 0.64% before annealing and 80.38 ± 0.24% after annealing).

[0098] Nitrogen is a common chemical element and can be contained in various materials. Nitrogen gas is generally considered to be an inert gas and non-reactive. This non-reactivity also applies even at low temperature settings. However, nitrogen gas becomes more reactive and oxidizing at high temperatures. The reason is that when nitrogen flows disorderly at high temperatures, nitrides are formed, which can react with the surface of the material or modify the surface of the material. By avoiding the formation of nitrides, nitrogen gas can be an excellent candidate gas and can be incorporated into one of the embodiments of the present disclosure.

[0099] Argon is another common chemical substance and inert gas known for its stability over a wide temperature range. According to the information provided in Table 2, in argon annealing, the transmittance of the test film measured at 550 nm does not change.

[0100] The results in Table 2 show that some inert gases can cause changes in the CNT material (or other materials), and as a result, can change the visible light transmittance. Other inert gases such as argon can retain the characteristics of CNTs in terms of light transmittance and can later improve the EUV transmittance. Thermal annealing according to one of the embodiments can utilize one or more carefully selected inert gases for EUV transmittance enhancement in a similar manner to vacuum-based thermal annealing.

[0101] Effect of annealing on films with different densities Embodiments of the present disclosure include thermal annealing of pellicle films having different film areal densities, manufactured according to operations 101-106A / B of FIG. 1. Each film has a uniform areal density with an EUV transmittance equal to the EUV pellicle requirement, an EUV transmittance better than the EUV pellicle requirement, or an EUV transmittance worse than the EUV pellicle requirement. The areal density of the film is defined as a finite amount of material on the rendering surface area. In this case, the areal density of the film manufactured by the filtering process is determined by dividing the nanofiber amount or the mass of the nanotubes by the total filtration area. Pellicle films having different areal densities can be manufactured based on the operations and principles of FIG. 1 described above. Once retrieved on the frame, the transmittance of the free-standing film at 550 nm or EUV can be determined.

[0102] FIG. 3 illustrates the correlation between the areal density and the film transmittance at 550 nm, according to an exemplary embodiment.

[0103] As exemplarily provided in FIG. 3, at an areal density value of 0.62 ug / cm 2 , the average 550 nm transmittance can be 93.833% and the standard deviation can be 0.197%. Further, at an areal density value of 0.77 ug / cm 2 , the average 550 nm transmittance can be 92.060% and the standard deviation can be 0.365%. Also, at an areal density value of 0.94 ug / cm 2 , the average 550 nm transmittance can be 90.967% and the standard deviation can be 0.163%, and at an areal density value of 1.49 ug / cm 2 , the average 550 nm transmittance can be 85.217% and the standard deviation can be 0.366%. Finally, at an areal density value of 3.11 ug / cm 2 , the average 550 nm transmittance can be 72.900% and the standard deviation can be 0.965%.

[0104] The areal density of any CNT film is not limited to the list of FIG. 3. The density of the high areal density film can be 6.0 ug / cm 2 or higher. The low areal density film can have a low density of about 0.2 ug / cm 2 for a transmittance of about 98%.

[0105] Table 3 describes the EUV transmission test results of CNT films having different 550 nm transmittances before and after exemplary thermal annealing. [Table 3]

[0106] When measured at a wavelength of 550 nm, an exemplary film with a transmittance of approximately 93.9% has average EUV transmittances of 98.2% and 98.6% before and after annealing, respectively, from 9 EUV transmittance measurements. Another exemplary film with a transmittance of approximately 80.4% has average EUV transmittances of 93.9% and 96.0% before and after annealing. Yet another exemplary film with a transmittance of approximately 70.0% has EUV transmittances of 90.0% and 93.0% before and after annealing. For these three films, immediately after annealing, the EUV transmittance increases by 0.4%, 2.1%, and 3.0%, respectively. As provided in Table 3, based on the decreasing 550 nm transmittance, it can be observed that the greater the film thickness, the greater the magnitude of the increase in EUV transmittance.

[0107] Another embodiment of the present disclosure includes selecting a film having a transmittance of about 50% or more measured at 550 nm, processing the film by annealing according to one of the embodiments, and performing EUV transmittance measurements targeting an EUV transmittance of about 90% or more.

[0108] Embodiments of the present disclosure further include selecting a film having a thickness of 3 nm to 200 nm or a transmittance of 50% to 95% measured at 550 nm, performing thermal annealing, and targeting the annealed film to achieve an EUV transmittance of 90% to 99%.

[0109] As a result of the above demonstration, annealing provides an effective approach for imparting unexpected new values and previously unknown features to existing nanofiber pellicle films. This approach aims to solve the difficult-to-overcome problems faced by ultra-thin, ultra-low density nanofiber pellicle films. For example, films with a greater thickness or a higher areal density arrive at a given lithography scanner with reduced transportation challenges and / or reduced damage caused by transportation and can undergo an annealing process to raise their EUV transmittance to a desired level for EUV lithography.

[0110] Effect of Annealing Temperature on EUV Transmission Enhancement Annealing is known to require elevated temperatures during the process, i.e., temperatures higher than ambient temperature. As shown above, high-temperature annealing shows a significant enhancement of EUV transmission either in vacuum or at atmospheric pressure in the presence of an inert gas such as argon. However, appropriate annealing conditions are important in order to improve the EUV transmittance of CNT pellicle films, maintain film stability, maximize such enhancement without excessive processing and heating energy consumption, and avoid possible reduction of pellicle lifetime.

[0111] Figure 4 illustrates the effect of different annealing temperatures from the results of Fourier transform infrared spectroscopy (FTIR) investigations according to an exemplary embodiment.

[0112] FTIR spectroscopy measures how much light a target sample, such as a liquid, gas, or solid, absorbs at each wavelength across the infrared spectrum. The sample material absorbs some of the infrared light due to its chemical properties, composition, and structural conformation at the molecular level, while other radiation passes through and can reach the detector for recording. The computer analyzes the recorded raw data, called an interferogram, and organizes and displays in a graph the corresponding light absorption or transmittance at each wavelength. For a given sample material, the interferogram has its typical dataset and a computer-generated graph curve like a fingerprint. When the same material is modified, its light absorption characteristics may change due to changes in its structure, chemical composition, chemical residues, and resulting molecular vibration patterns. These changes create a new dataset or a new curve. Comparing the data collected before and after annealing may reveal changes that have occurred and / or accumulated within the sample material. This change correlates with different measurements from the same sample processed in the same way.

[0113] In addition to investigating EUV transmission measurements (see Tables 1 and 2), the differences observed by FTIR may represent the same modification within the nanofiber pellicle film.

[0114] According to an exemplary embodiment, a carbon nanotube is formed by winding one or more layers of graphene sheets composed of carbon atoms and hydrogen atoms. Each graphene sheet is a layer of carbon atoms bonded to each other in a hexagonal (honeycomb) mesh. In a given CNT type, SWCNT, DWCNT, or MWCNT has unique features in its FTIR spectrum. The CNT pellicle film may have one type or a mixed type of CNT, and its FTIR spectral data is unique and may not be the same as the spectrum collected from a pure CNT type. On the other hand, when the CNT population in the pellicle film is modified and / or when the interaction between carbon atoms and hydrogen atoms in the CNT, such as chemical bonding, changes, the spectrum of the pellicle film can change according to what happens to it chemically or structurally. At the molecular level, aliphatic hydrocarbon residues change, which can be detected by FTIR.

[0115] Figure 4 shows the results of an FTIR investigation of the effect of different annealing temperatures of the pellicle film prepared according to operations 101 to 107. Here, an untreated initial state sample is used as a negative control, and target temperatures of 400 °C, 500 °C, 600 °C, 700 °C, and 800 °C are applied for 10 minutes. The FTIR spectra in Figure 4 illustrate the measurement results between wavenumbers 2950~2850 cm -1 The data outside this wavenumber range of 2950~2850 cm -1 shows no significant differences (data not shown). Wavenumber is the spatial frequency of a wave, measured as the number of cycles per unit distance, and when used in spectroscopy, it is defined as the number of wavelengths per unit distance, usually in centimeters (cm -1 ).

[0116] The graph in Figure 4 shows significant differences in light transmittance due to different annealing temperatures. The percentage of transmittance is judged from the individual curves of the graph, and for annealing treatments at 600 °C, 700 °C, and 800 °C, between wavenumbers 2950~2850 cm -1show insignificant differences. For the treatments at 400 °C and 500 °C, the transmittance drops significantly but is still higher than that of the non-annealed initial state sample (see the dip near wavenumber 2920). As shown in Table 1 above, the same annealing treatment at 600 °C for 10 minutes increases the EUV transmittance. When combined with the FTIR results in Figure 4, the treatments at 700 °C and 800 °C may have the same effect as the treatment at 600 °C, but the annealing at 400 °C and 500 °C may not yield the same results. The FTIR analysis in the provided immediate wavenumber range indicates chemical changes that may involve carbon atoms. Such changes contribute to the EUV transmittance enhancement exemplified in this disclosure.

[0117] FTIR can be a powerful alternative to direct EUV transmittance measurements. To obtain a stable nanofiber pellicle film that enhances the desired EUV transmittance from the initial state pellicle film, an annealing temperature of 600 °C or higher may be required within a possible 10% variation.

[0118] Figure 5 illustrates the transmittance measured at wavenumber 2920 in Figure 4 as a percentage, further exemplifying the effectiveness of various temperatures in the above annealing. As shown in Figure 5, the best results are obtained with the treatment at 600 °C, and then it levels off.

[0119] The same investigation as shown in Table 1 was repeated, and measurements at wavenumber 2920 by FTIR were taken on the 1st, 3rd, 5th, and 30th days after annealing, and the results are summarized in Figure 6. The initial sharp rise or increase in transmittance on the 1st day was partially lost over the course of a month. The results by FTIR are similar to the correlation between the thermal annealing in Table 1 and the EUV transmittance enhancement.

[0120] Another embodiment of the present disclosure involves applying a higher effective annealing temperature with a shorter annealing duration, which provides flexibility in the implementation of the production of the pellicle film. Exemplary films were annealed at 700 °C for 10 minutes according to Operations 101 to 106A / B, but when compared with samples annealed at 600 °C for 30 minutes, the differences measured by FTIR were not significant.

[0121] Annealing Duration for EUV Transmission Enhancement At the selected annealing temperature, the annealing time can be 5 minutes or less. In other annealing processes, it may be carried out at the selected temperature for 30 minutes or more. The annealing time or annealing duration can be divided into multiple annealing periods or irradiation periods with respect to electromagnetic wave irradiation for the purpose of analyzing the annealing process at any time during the annealing process.

[0122] Figure 7 illustrates the effect of annealing duration (or annealing time) on the change in the percentage of light transmittance based on FTIR investigation. CNT pellicle films with a transmittance of 80% at 550 nm were annealed at 650 °C at different time intervals. An annealing schedule of 5 minutes may be sufficient for improving the EUV transmittance. Annealing for 20 minutes or 30 minutes can further improve the transmittance, but the improvement is not as dramatic as compared to the effect of the initial 5-minute annealing. Extending the processing duration further may not result in additional benefits.

[0123] However, aspects of the present disclosure are not limited thereto, such that annealing with flash light may be as short as 0.1 ms.

[0124] Although the above disclosure was provided with respect to CNTs, aspects of the present disclosure are not limited thereto, such that different nanotube films such as boron nitride nanotubes (BNNTs), nanofibers, or nanofibers arranged in the film by different methods other than filtration, or nanofibers arranged in different orientations, can utilize the same principle.

[0125] The above thin film can also be conformally coated in various ways before or after the annealing process. Coating methods include, without limitation, electron beam, chemical vapor deposition or physical vapor deposition, atomic layer deposition, spin coating, dip coating, spray coating, sputtering, DC sputtering, and RF sputtering, among others. The coating material may be selected from any one of the following: silicon, SiO2, SiON, boron, ruthenium, boron, zirconium, niobium, molybdenum, rubidium, yttrium, YN, Y2O3, strontium, rhodium, or combinations thereof. The material may also be any one or more metals, metal oxides or metal nitrides, or combinations thereof. However, aspects of the present disclosure are not limited thereto, and combinations of materials may be used in the coating.

[0126] The examples of the embodiments described herein are intended to provide a general understanding of the various embodiments. The figures are not intended to function as a complete description of all elements and features of the products and methods forming the products or methods described herein. Many other embodiments may be apparent to those skilled in the art upon consideration of the present disclosure. Structural and logical substitutions and changes may be made without departing from the scope of the present disclosure since other embodiments may be utilized and derived from the present disclosure. Further, the examples are merely representative and may not be drawn to scale. Some ratios within the examples may be exaggerated while others may be minimized. Therefore, the present disclosure and the figures should be considered illustrative rather than limiting.

[0127] In this specification, the term "invention" may be referred to individually and / or collectively in one or more embodiments of the present disclosure, without any intention to limit the scope of the present application to any particular invention or inventive concept for convenience only. Also, although specific embodiments have been illustrated and described herein, it will be understood that any subsequent arrangement designed to achieve the same or similar purpose may be used in place of the specific embodiments shown. The present disclosure is intended to cover any and all subsequent adaptations or variations of the various embodiments. From consideration of this description, combinations of the foregoing embodiments and other embodiments not specifically described herein will be apparent to those skilled in the art.

[0128] It is submitted with the understanding that the summary of the present disclosure is not used to interpret or limit the scope or meaning of the claims. Additionally, in the foregoing detailed description, for the purpose of simplifying the present disclosure, various features may be grouped together or described in a single embodiment. The disclosure should not be construed as reflecting an intention that the embodiments recited in the claims require more features than are expressly stated in each claim. Rather, as the following claims reflect, the subject matter of the present invention may be directed to less than all of the features of any of the disclosed embodiments. Accordingly, the following claims are incorporated into the detailed description, and each claim stands on its own as defining the separately claimed subject matter.

[0129] The subject matter disclosed above should be considered illustrative and not restrictive, and the appended claims are intended to cover all such modifications, extensions, and other embodiments that are within the true spirit and scope of the present disclosure. Accordingly, to the fullest extent permitted by law, the scope of the present disclosure should be determined by the broadest permissible interpretation of the following claims and their equivalents, and should not be limited or restricted by the foregoing detailed description.

Claims

1. A plurality of randomly intersecting carbon nanofibers having an interconnected network structure, wherein the interconnected network structure has a planar orientation, is annealed, and has an extreme ultraviolet (EUV) transmittance of 90% or more after annealing, the plurality of carbon nanofibers included, a nanostructured film.

2. The nanostructured film according to claim 1, wherein the EUV transmittance after annealing is 92% or more.

3. The nanostructured film according to claim 1, wherein the EUV transmittance after annealing is 95% or more.

4. The nanostructured film according to claim 1, wherein the EUV transmittance after annealing is at least 0.4% higher than the EUV transmittance before annealing of the interconnected network structure.

5. The annealing applies irradiation with at least one electromagnetic wave to at least one side of the entire interconnected network structure during at least one irradiation period, and the at least one irradiation period is a time point during the annealing, the nanostructured film according to claim 1.

6. The nanostructured film according to claim 5, wherein a group of the at least one electromagnetic wave evenly covers the at least one side of the entire interconnected network structure during the at least one irradiation period.

7. The nanostructured film according to claim 5, wherein the at least one electromagnetic wave is selected from 10 nm to 1 mm.

8. The nanostructured film according to claim 1, wherein the interconnected network structure is annealed at least twice or more.

9. The nanostructured film according to claim 1, wherein the second annealing increases the EUV transmittance of the interconnected network structure by at least 0.6%.

10. The nanostructured film according to claim 1, wherein the interconnected network structure has reduced EUV scattering after annealing.

11. A method for improving EUV transmission of an extreme ultraviolet (EUV) pellicle film, comprising: providing a plurality of intersecting carbon nanofibers having an interconnected network structure; first, irradiating at least one side of the entire interconnected network structure with one or more electromagnetic waves during at least one irradiation period; and improving the ratio of EUV transmittance by at least 0.4%, The method wherein the accumulation of the at least one irradiation time period extends over an irradiation duration time.

12. The method according to claim 11, wherein the one or more electromagnetic waves evenly deliver electromagnetic energy covering the entire at least one side surface of the interconnected network structure during the irradiation time period.

13. The method according to claim 11, wherein the one or more electromagnetic waves raise the temperature to a degree selected from 540 °C to 3000 °C and maintain the temperature during the irradiation duration time.

14. The method according to claim 11, wherein the irradiation duration time is selected between 0.1 milliseconds and 60 minutes.

15. The method according to claim 11, wherein the irradiating is performed within a chamber having a pressure setting ranging from a vacuum pressure to an atmospheric pressure.

16. The method according to claim 15, wherein the chamber receives a gas flow, the gas is an inert gas, and the visible light transmittance of the interconnected network structure after irradiation is not substantially changed.

17. The method according to claim 15, further comprising directly connecting the chamber to an EUV lithography scanner.

18. The method according to claim 11, further comprising storing the interconnected network structure in an inert gas environment or in a vacuum.

19. Repeating the irradiating two or more times; Improving the EUV transmittance of the interconnected network structure; The method according to claim 11, further comprising.

20. The method according to claim 19, wherein the improved EUV transmittance is at least 0.6% higher.

21. The method according to claim 11, further comprising performing the irradiating prior to subjecting the plurality of intersecting carbon nanofibers having the interconnected network structure to an EUV lithography process.

22. The method according to claim 11, further comprising performing the irradiating remotely from an EUV lithography scanner.

23. The method according to claim 11, wherein the one or more electromagnetic waves have a wavelength selected from 10 nm to 1 mm.

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