Carbon nanotube growth, catalyst removal, boron nitride nanotube shell formation method

Abstract

Methods of carbon nanotube growth, catalyst removal, boron nitride nanotube shell formation are disclosed. A method for forming a protective film for extreme ultraviolet lithography is provided. The method includes forming a protective film over a filter film and transferring the protective film from the filter film to a film border. Forming the protective film includes growing carbon nanotubes (CNTs) from in situ formed metal catalyst particles in a first reaction zone of a reactor, each of the CNTs including a metal catalyst particle at a growth tip thereof, growing boron nitride nanotubes (BNNTs) around individual CNTs in a second reaction zone of the reactor downstream of the first reaction zone to form heterostructure nanotubes each including a CNT core and a BNNT shell, and collecting the heterostructure nanotubes on the filter film.

Description

Technical Field

[0001] This disclosure generally relates to methods for simultaneous carbon nanotube growth, catalyst removal, and boron nitride nanotube shell formation for EUV thin films. Background Technology

[0002] In the semiconductor integrated circuit (IC) industry, technological advancements in IC materials and design have resulted in several generations of ICs, each smaller and more complex than the previous one. During IC evolution, functional density (e.g., the number of interconnect devices per unit chip area) typically increases, while geometry (e.g., the smallest component (or line) that can be fabricated using a manufacturing process) decreases. This scaling down process generally provides benefits by increasing production efficiency and reducing associated costs. However, this scaling down also increases the complexity of IC processing and manufacturing. Summary of the Invention

[0003] According to a first aspect of this disclosure, a method for forming a protective film for extreme ultraviolet lithography is provided, comprising: forming a protective film on a filter film, wherein forming the protective film comprises: growing carbon nanotubes (CNTs) from in-situ formed metal catalyst particles in a first reaction region of a reactor, each of the CNTs comprising a metal catalyst particle at its growth tip; growing boron nitride nanotubes (BNNTs) around a single CNT in a second reaction region of the reactor downstream of the first reaction region to form heterostructured nanotubes, each comprising a CNT core and a BNNT shell, wherein the metal catalyst particles are partially or completely removed during the growth of the BNNTs; collecting the heterostructured nanotubes on the filter film; and transferring the protective film from the filter film to a film boundary.

[0004] According to a second aspect of this disclosure, a method for forming a protective film for extreme ultraviolet lithography is provided, comprising: growing carbon nanotube (CNT) aerogels from in-situ formed metal catalyst particles in a first reactor, each of the CNT aerogels including a metal catalyst particle at its growth tip; forming a CNT film on a substrate, the CNT film including CNT aggregates obtained by aggregating the CNT aerogels; attaching the CNT film to a film boundary; and growing boron nitride nanotubes (BNNTs) in a second reactor to surround individual CNT aggregates, thereby forming a protective film comprising a network of heterostructured nanotubes, each of the heterostructured nanotubes including a CNT aggregate core and a BNNT shell, wherein the metal catalyst particles are partially or completely removed during the growth of the BNNTs.

[0005] According to a third aspect of this disclosure, a photolithographic patterning method is provided, comprising: reflecting EUV radiation onto a photoresist layer on a semiconductor substrate using a photomask to form a patterned photoresist layer, the photomask having a protective film on a thin film holder fixed on the photomask; developing the photoresist layer to form the patterned photoresist layer; and using the patterned photoresist layer as a mask to etch the semiconductor substrate to form a circuit layout, wherein the protective film comprises a first heterostructured nanotube layer having heterostructured nanotubes aligned along a first direction, and a second heterostructured nanotube layer having heterostructured nanotubes aligned along a second direction different from the first direction, thereby forming a grid of heterostructured nanotubes, each of the heterostructured nanotubes comprising a carbon nanotube (CNT) core and a boron nitride shell surrounding the CNT core. Attached Figure Description

[0006] The various aspects of this disclosure can be best understood by reading in conjunction with the accompanying drawings through the following detailed description. It should be noted that, according to industry standard practice, the various features are not drawn to scale. In fact, for clarity of discussion, the dimensions of the various features may be arbitrarily increased or decreased.

[0007] Figure 1 This is a schematic diagram of a lithography system according to some embodiments of the present disclosure.

[0008] Figure 2A This is a cross-sectional view of a thin-film photomask structure according to some embodiments of the present disclosure.

[0009] Figure 2B Illustrations are shown according to some embodiments Figure 2A The protective film (pellicle membrane).

[0010] Figure 2C It shows Figure 2B A perspective view of the heterostructured nanotubes in the network of heterostructured nanotubes shown.

[0011] Figure 3 This is a flowchart of a method for manufacturing a protective film assembly according to some embodiments.

[0012] Figures 4A-4E It shows in Figure 3 The protective film components at each stage of the method.

[0013] Figure 5 This is a flowchart of a method for manufacturing a protective film assembly according to an alternative embodiment.

[0014] Figures 6A-6D It shows in Figure 5The protective film components at each stage of the method.

[0015] Figure 7 This is a flowchart of a method for manufacturing a protective film assembly according to an alternative embodiment.

[0016] Figures 8A-8D It shows in Figure 7 The protective film components at each stage of the method.

[0017] Figure 9 A CNT film comprising interlaced CNT bundles is shown according to some embodiments. Detailed Implementation

[0018] The following disclosure provides numerous different embodiments or examples for implementing various features of the provided subject matter. Specific examples of components and arrangements are described below to simplify this disclosure. Of course, these are merely examples and are not intended to be limiting. For example, in the following description, forming a first feature above or on a second feature can include embodiments where the first and second features are formed in direct contact, and can also include embodiments where an additional feature can be formed between the first and second features such that the first and second features do not need to be in direct contact. Furthermore, reference numerals and / or letters may be repeated in various examples. This repetition is for simplicity and clarity and does not in itself indicate a relationship between the various embodiments and / or configurations discussed.

[0019] Furthermore, this document may use spatially relevant terms (e.g., “below,” “under,” “down,” “above,” “up,” etc.) to readily describe the relationship of one element or feature shown in the figure relative to another element(s) or feature(s). These spatially relevant terms are intended to cover different orientations of the device in use or operation other than those shown in the figure. The device may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatially relevant descriptors used herein may be interpreted accordingly.

[0020] In semiconductor manufacturing, various photolithography processes are widely used to define device and circuit patterns. Different photolithography processes are used depending on the size of the feature to be defined. In photolithography, a pattern existing on a photomask or mask is transferred to a photosensitive photoresist coating by irradiating the photomask. Light is modulated by the mask pattern and imaged onto the photoresist-coated wafer. Typically, as the pattern becomes smaller, a shorter wavelength is used. In extreme ultraviolet (EUV) lithography, a wavelength of approximately 13.5 nm is often used to produce feature sizes smaller than 32 nanometers.

[0021] However, EUV systems using reflective rather than conventional refractive optics are highly sensitive to contamination. In one example, particulate contamination introduced onto a reflective EUV mask can lead to significant degradation of the lithographic transfer pattern. Therefore, it is necessary to provide a protective film on top of the EUV mask as a shield to protect it from damaging and / or contaminating particles. Furthermore, to avoid a decrease in reflectivity, it is important to use a thin, high-transmittance material as the protective film.

[0022] Carbon nanotubes (CNTs) are transparent enough to limit imaging effects, yet robust enough to withstand handling and prevent particles from falling onto the photomask, making them a suitable protective film material for EUV lithography. However, during high-exposure periods, such as tens of thousands or more, CNTs are susceptible to the hydrogen plasma environment of the EUV scanner. Carbon nanotubes with a protective shell can provide extremely high transmittance to EUV radiation.

[0023] Embodiments of this disclosure provide a method for fabricating a protective film formed from a network of heterostructured nanotubes. The heterostructured nanotubes have a core-shell structure, comprising a CNT as the core and a boron nitride nanotube (BNNT) as the shell. Boron nitride exhibits higher chemical and thermal stability than carbon, thus helping to prevent damage to the carbon nanotube core from EUV exposure and hydrogen flow. The method of this disclosure allows for the growth of the CNT core and BNNT shell using a chemical vapor deposition (CVD) process while removing metal catalyst particles. As a result, the EUV transmission, reliability, and lifetime of the protective film are improved.

[0024] Figure 1 This is a schematic diagram of a lithography system 100 according to some embodiments of the present disclosure. The lithography system 100 may also be referred to herein as a "scanner," and is operable to perform lithography exposure processes using appropriate radiation sources and exposure modes.

[0025] In some embodiments, the photolithography system 100 includes a high-brightness light source 102, an illuminator 104, a mask stage 106, a photomask 108, a projection optics module 110, and a substrate stage 112. In some embodiments, the photolithography system may include... Figure 1 Additional components not shown. In another embodiment, one or more of the high-brightness light source 102, illuminator 104, mask stage 106, photomask 108, projection optics module 110, and substrate stage 112 may be omitted from the lithography system 100 or integrated into the combined components.

[0026] The high-brightness light source 102 can be configured to emit radiation having wavelengths in the range of about 1 nanometer (nm) to 250 nm. In some embodiments, the high-brightness light source 102 generates EUV light with wavelengths concentrated at about 13.5 nm; therefore, the high-brightness light source 102 may also be referred to as an "EUV light source". However, it should be understood that the high-brightness light source 102 should not be limited to emitting EUV light. For example, the high-brightness light source 102 can be used to perform the emission of any high-intensity photons from an excited target material.

[0027] In embodiments where, for example, lithography system 100 is a UV lithography system, illuminator 104 includes various refractive optical components, such as a single lens or a lens system including multiple lenses (zone plates). In embodiments where, for example, lithography system 100 is an EUV lithography system, illuminator 104 includes various reflective optical components, such as a single mirror or a mirror system including multiple mirrors. Illuminator 104 can guide light from high-brightness light source 102 onto mask stage 106, and more specifically onto photomask 108 fixed on mask stage 106. In an example where high-brightness light source 102 generates light in the EUV wavelength range, illuminator 104 includes reflective optics.

[0028] The mask stage 106 can be configured to hold the photomask 108. In some examples, the mask stage 106 may include an electrostatic chuck for holding the photomask 108. This is because gas molecules absorb EUV light, and the lithography system 100 used for EUV lithography patterning is maintained in a vacuum environment to minimize EUV intensity loss. Throughout this document, the terms "photomask," "mask," and "mask plate" are used interchangeably. In some embodiments, the photomask 108 is a reflective mask.

[0029] In some examples, the pellicle 114 may be positioned over the photomask 108, for example, between the photomask 108 and the substrate stage 112. The pellicle 114 can protect the photomask 108 from particles and can keep the particles away from the focal point, so that the particles do not produce an image (which could cause defects on the wafer during the photolithography process).

[0030] The projection optics module 110 can be configured to image a pattern of the photomask 108 onto a semiconductor wafer 116 fixed on a substrate stage 112. In some embodiments, the projection optics module 110 includes refractive optics (e.g., for a UV lithography system). In some embodiments, the projection optics module 110 includes reflective optics (e.g., for an EUV lithography system). Light directed from the photomask 108 can be collected by the projection optics module 110, such light conveying an image of the pattern defined on the photomask 108. The illuminator 104 and the projection optics module 110 can be collectively referred to as the "optical module" of the lithography system 100.

[0031] In some embodiments, semiconductor wafer 116 may be a bulk semiconductor wafer. For example, semiconductor wafer 116 may include a silicon wafer. Semiconductor wafer 116 may include silicon or another elemental semiconductor material, such as germanium. In some embodiments, semiconductor wafer 116 may include a compound semiconductor. Compound semiconductors may include gallium arsenide, silicon carbide, indium arsenide, indium phosphide, another suitable material, or combinations thereof. In some embodiments, semiconductor wafer 116 includes a silicon-on-insulator (SOI) substrate. The SOI substrate may be fabricated using oxygen implantation separation (SIMOX) processes, wafer bonding processes, other suitable processes, or combinations thereof. In some embodiments, semiconductor wafer 116 includes an undoped substrate. However, in other embodiments, semiconductor wafer 116 includes a doped substrate, such as a p-type substrate or an n-type substrate.

[0032] In some embodiments, the semiconductor wafer 116 includes various doped regions (not shown) according to the design requirements of the semiconductor device structure. Doped regions may include, for example, p-type wells and / or n-type wells. In some embodiments, the doped regions are doped with p-type dopants. For example, the doped regions may be doped with boron or boron fluoride. In other examples, the doped regions are doped with n-type dopants. For example, the doped regions may be doped with phosphors or arsenic. In some examples, some doped regions are p-doped while others are n-doped.

[0033] In some embodiments, an interconnect structure may be formed on the semiconductor wafer 116. The interconnect structure may include multiple interlayer dielectric layers, including dielectric layers. The interconnect structure may also include multiple conductive features formed in the interlayer dielectric layers. Conductive features may include conductive lines, conductive vias, and / or conductive contacts.

[0034] In some embodiments, various device elements are formed in a semiconductor wafer 116. Examples of various device elements may include transistors (e.g., metal-oxide-semiconductor field-effect transistors (MOSFETs), complementary metal-oxide-semiconductor (CMOS) transistors, bipolar junction transistors (BJTs), high-voltage transistors, high-frequency transistors, p-channel and / or n-channel field-effect transistors (PFETs and / or NFETs), diodes, or other suitable elements. Various processes may be used to form the various device elements, including deposition, etching, implantation, photolithography, annealing, and / or other suitable processes.

[0035] Device elements can be interconnected through interconnect structures on the semiconductor wafer 116 to form an integrated circuit device. Integrated circuit devices may include logic devices, memory devices (e.g., static random access memory (SRAM) devices), radio frequency (RF) devices, input / output (I / O) devices, system-on-a-chip (SoC) devices, image sensor devices, other suitable devices, or combinations thereof.

[0036] In some embodiments, the semiconductor wafer 116 may be coated with a resist layer sensitive to EUV light. Various components, including those described above, can be integrated together and used to perform photolithography processes.

[0037] Figure 2A This is a cross-sectional view of a thin-film photomask structure 200 according to some embodiments of the present disclosure. For example... Figure 2A As shown, the photomask 108 may include a mask substrate 202 and a mask pattern 204 located on the mask substrate 202.

[0038] In some examples, the mask substrate 202 includes a transparent substrate, such as relatively defect-free fused silica, borosilicate glass, soda-lime glass, calcium fluoride, a low thermal expansion material, an ultra-low thermal expansion material, or other suitable materials. The mask pattern 204 can be positioned over the mask substrate 202 as described above and can be customized based on the semiconductor substrate (e.g., formed during the photolithography process) Figure 1 The mask pattern 204 is designed to be based on the integrated circuit features on a semiconductor wafer 116. The mask pattern 204 can be formed by depositing a material layer and patterning the material layer to have one or more openings and one or more absorption regions, wherein the radiation beam can travel through the one or more openings without being absorbed, and the one or more absorption regions can completely or partially block the radiation beam.

[0039] The mask pattern 204 may include metals, metal alloys, metal silicides, metal nitrides, metal oxides, metal oxynitrides, or other suitable materials. Examples of materials that can be used to form the mask pattern 204 may include, but are not limited to, Cr and Mo. x Si yTa x Si y Mo, Nb x O y Ti, Ta, Cr x N y Mo x O y Mo x N y Cr x O y Ti x N y Zr x N y Ti x O y Ta x N y Ta x O y Si x O y 、Nb x N y Zr x N y Al x O y N z Ta x B y O z Ta x B y N z Ag x O y Ag x N y ,Ni,Ni x O y Ni x O y N z The x / y / z ratio of the compound is not restricted.

[0040] In some embodiments, photomask 108 is an EUV mask. However, in other embodiments, photomask 108 may be an optical mask.

[0041] like Figure 2A As shown, the protective film 114 can be positioned on the photomask 108 to form a closed internal volume 206 surrounded by the protective film 114 and the photomask 108.

[0042] In some embodiments, the protective film 114 includes a protective film frame 210, which may be positioned over at least one of the mask substrate 202 and the mask pattern 204. The protective film frame 210 may be designed to be of various sizes, shapes, and configurations. In some embodiments, the protective film frame 210 may have a circular, rectangular, or any other suitable shape. In some embodiments, the protective film frame 210 may be formed of Si, SiC, SiN, glass, a material with a low coefficient of thermal expansion (e.g., Al alloys, Ti alloys, Invar, Kovar, etc.), other suitable materials, or combinations thereof. In some embodiments, suitable processes for forming the protective film frame 210 may include machining processes, sintering processes, photochemical etching processes, other suitable processes, or combinations thereof.

[0043] like Figure 2A As further illustrated, the protective film 114 may also include a ventilation structure 212 extending through the protective film frame 210. In some embodiments, the ventilation structure 212 may include one or more holes formed through the protective film frame 210. The holes may be of any shape, including circular holes, rectangular holes, slit holes, other shapes, or any combination thereof. The holes may allow airflow through a portion of the thin-film photomask structure 200. In some embodiments, the holes may include filters to minimize the propagation of external particles through the ventilation structure 212. In some embodiments, the ventilation structure 212 may prevent the protective film from breaking during EUV lithography processes.

[0044] like Figure 2A As further shown, the protective film frame 210 is attached to the photomask 108 by a film frame adhesive 214. In some embodiments, the film frame adhesive 214 may be formed of a crosslinking adhesive, a thermoplastic elastomer adhesive, a polystyrene adhesive, an acrylic adhesive, a silicone-based adhesive, an epoxy adhesive, or a combination thereof.

[0045] In some embodiments, a surface treatment may be performed on the protective membrane frame 210 to enhance the adhesion between the protective membrane frame 210 and the protective membrane frame adhesive 214. In some examples, the surface treatment may include oxygen plasma treatment, other suitable treatments, or combinations thereof. However, in other examples, no surface treatment may be performed on the protective membrane frame 210.

[0046] like Figure 2AAs further shown, the protective film 114 may also include a protective film assembly 230, which includes a protective film 232 and a film boundary 234 located above the protective film frame 210. The protective film 232 extends over the patterned area of ​​the photomask 108 to protect the patterned area from contaminant particles. Particles unintentionally deposited on the patterned area of ​​the photomask 108 may introduce defects and cause degradation of the transferred pattern. Particles may be introduced in any of a variety of ways, such as during cleaning processes and / or during the handling of the photomask 108. By keeping contaminant particles outside the focal plane of the photomask 108, it is possible to transfer from the photomask 108 to the semiconductor wafer 116 (… Figure 1 High-fidelity pattern transfer.

[0047] like Figure 2A As shown, the protective film adhesive 240 can be positioned between the film boundary 234 and the protective film frame 210 to attach the protective film 232 to the protective film frame 210. In some embodiments, the protective film adhesive 240 can be formed of a thermoplastic elastomer type adhesive, a polystyrene type adhesive, an acrylic type adhesive, a silicone-based adhesive, an epoxy type adhesive, other suitable adhesives, or combinations thereof. In some embodiments, the protective film adhesive 240 can be formed of a material different from the material constituting the protective film frame adhesive 214.

[0048] The thin film boundary 234 can be attached to the periphery of the protective thin film 232, and thus mechanically support the protective thin film 232. When the protective film photomask structure 200 is fully assembled, the thin film boundary 234 can then be mechanically supported by the protective film frame 210. That is, the protective film frame 210 can mechanically support the thin film boundary 234 and the protective thin film 232 on the photomask 108.

[0049] In some embodiments, the thin film boundary 234 may be formed of Si. In other examples, the thin film boundary 234 may be formed of boron carbide, graphene, carbon nanotubes, SiC, SiN, SiO2, SiON, Zr, Nb, Mo, Cd, Ru, Ti, Al, Mg, V, Hf, Ge, Mn, Cr, W, Ta, Ir, Zn, Cu, F, Co, Au, Pt, Sn, Ni, Te, Ag, other suitable materials, any allotropes of these materials, or combinations thereof.

[0050] In embodiments of this disclosure, the protective film 232 is formed of one or more heterostructured nanotube layers. Each heterostructured nanotube layer may comprise a random or regular network or grid of heterostructured nanotubes. For example, Figure 2B Some embodiments according to this disclosure are shown. Figure 2AAn exemplary protective film 232. In Figure 2B In the example shown, the protective film 232 comprises a network of heterostructured nanotubes. The structural density of the heterostructured nanotube network is selected to maximize EUV radiation transmission while minimizing particle propagation through the protective film 232. For example, in some embodiments, the network of heterostructured nanotubes constituting the protective film 232 may have a structural density between 0.2 and 1, depending on the desired percentage of radiation to be transmitted through the protective film 232. For example, the protective film 232 has an EUV light transmittance greater than 95%.

[0051] For example, Figure 2C It shows Figure 2B The image shows a perspective view of a heterostructured nanotube 250 forming a network of heterostructured nanotubes. As shown, the heterostructured nanotube 250 includes a CNT core 252 surrounded by a BNNT shell 254. In some embodiments, the CNT core 252 is formed from a single CNT and the BNNT shell 254 surrounds the single CNT. In some embodiments, the CNT core 252 is formed from a bundle of CNTs and the BNNT shell 254 surrounds the bundle of CNTs. A CNT bundle may include, for example, 2 to 20 individual CNTs. In a CNT bundle, individual CNTs may be aligned and connected along their longitudinal direction. CNTs in a bundle may also be connected end-to-end, such that the length of the CNT bundle is greater than the length of a single CNT. CNTs are typically connected by van der Waals forces. In some embodiments, the CNT core 252 is formed from a CNT aggregate and the BNNT shell 254 surrounds the CNT aggregate. A CNT aggregate may include more than 10 individual CNTs arranged side-by-side and connected end-to-end, so that the length and diameter of the CNT aggregate are both greater than the length and diameter of a single CNT, respectively. BNNT shell 254 exhibits excellent mechanical strength while maintaining high transmittance to EUV radiation. As a result, the stability of CNTs is improved.

[0052] CNT core 252 can be formed from single-walled, double-walled, or multi-walled carbon nanotubes. Single-walled CNTs can have many different diameters, for example, from about 0.1 nm to 10 nm. Multi-walled CNTs have multiple graphite layers that are typically concentrically arranged around a common axis. The diameter of multi-walled CNTs can range from about 3 nm to about 100 nm. Single-walled or multi-walled CNTs can have a variety of lengths. For example, single-walled or multi-walled CNTs can have lengths from about 10 nm to about 1 μm, from about 20 nm to about 500 nm, or from about 50 nm to about 100 nm. In some embodiments, single-walled or multi-walled CNTs can have an aspect ratio (i.e., the ratio of the length of the CNT to the diameter of the CNT) from about 100:1 to 1000:1.

[0053] The BNNT shell 254 can be a single-walled or multi-walled boron nitride nanotube comprising 1 to 40 layers of boron nitride. The total thickness of the BNNT shell 254 is controlled such that the BNNT shell 254 does not reduce the transparency of the protective film 232 to EUV radiation while providing reliable protection for the CNT core 252. In some embodiments, the total thickness of the BNNT shell 254 can range from about 1 nm to about 20 nm. If the thickness of the BNNT shell 254 is too small, it may be insufficient to protect the CNT core 252 from UV or EUV radiation or attacks by chemicals such as hydrogen ions, hydrogen radicals, or oxygen in certain situations. If the thickness of the BNNT shell 254 is too large, the transparency of the protective film may decrease in certain situations. In some embodiments, the BNNT shell 254 has a thickness of 5 nm.

[0054] Figure 3 This is a flowchart of a method 300 for manufacturing a protective film assembly 230 using a reactor 410, according to some embodiments of the present disclosure. Figures 4A-4E The protective film assembly 230 at various stages of method 300 is shown. It should be understood that, for additional embodiments of the method, additional steps may be provided before, during, and after method 300, and some steps described below may be replaced or eliminated. It should also be understood that, for additional embodiments of the protective film assembly, additional features may be added to the protective film assembly, and some features described below may be replaced or eliminated.

[0055] refer to Figure 3 and Figure 4A According to some embodiments, method 300 includes operation 302, wherein CNT 404 is formed in a first reaction region 412 of reactor 410. Reactor 410 is configured to form the CNT core 252 and BNNT shell 254 constituting the heterostructured nanotube 25 in a continuous process. Figure 4A This is a schematic diagram of reactor 410, which shows the growth of CNT 404 in a first reaction zone 412 of reactor 410 by a gas phase flow method according to some embodiments.

[0056] In operation 302, CNT404 is synthesized, for example, via a catalytic chemical vapor deposition (CVD) process, where the pyrolysis of the carbon source occurs on in-situ formed metal catalyst particles 402. Figure 4A As shown, reactor 410 includes a first reaction zone 412 and a second reaction zone 414 located downstream of the first reaction zone 412. CNT 404 is synthesized in the first reaction zone 412, while BNNT 406 ( Figure 4BThe CNTs 404 are grown to surround the second reaction region 414. In some embodiments, the first reaction region 412 has a length greater than 5 m. In some embodiments, the reactor 410 includes a quartz tube vertically mounted within a heating element 416 adapted to heat the reactor 410. In some embodiments, the heating element 416 is a dual-zone heating element configured to heat the reactor 410 to maintain a first temperature in the first reaction region 412 and a second temperature in the second reaction region 414 of the reactor 410. In some embodiments, the heating element 416 is configured to maintain a temperature gradient between about 500°C and about 1100°C in the first reaction region 412 of the reactor 410, and a temperature in the second reaction region 414 within the range of about 1000°C and about 1100°C.

[0057] A first gas supply unit 420 is fluidly connected to a first reaction zone 412 of reactor 410 via a first gas inlet 422. The first gas supply unit 420 is configured to supply a carrier gas comprising an inert gas (e.g., argon (Ar)) and / or a reactive gas (e.g., hydrogen (H2)) to reactor 410. The first gas inlet 422 may include a nozzle for injecting the reaction mixture.

[0058] The first source material supply unit 430 is fluidly connected to the first reaction zone 412 of the reactor 410 via the first reactant inlet 432. The first source material supply unit 430 is configured to supply raw materials for growing CNT 404 to the first reaction zone 412. In some embodiments, the first reactant inlet 432 is connected to one side of the first gas inlet 422. Therefore, the injection direction is perpendicular to the carrier gas flow direction.

[0059] The second source material supply unit 440 is fluidly connected to the second reaction zone 414 of the reactor 410 via the second reactant inlet 442. The second source material supply unit 440 is configured to supply a boron nitride source for growing boron nitride nanotubes to the second reaction zone 414 of the reactor 410. A shut-off valve 444 is coupled to the second reactant inlet 442 and is used to automatically shut off the flow of vaporized boron nitride source into the reactor 410.

[0060] The second gas supply unit 450 is fluidly connected to the second source material supply unit 440 via the second gas inlet 452. The second gas supply unit 450 is configured to supply carrier gas to the second source material supply unit 440 for conveying the vaporized boron nitride source into the second reaction zone 414 of the reactor 410.

[0061] In the CVD process, a feedstock containing the raw materials for growing CNTs is supplied from the first source material supply unit 430 to the first reaction zone 412 of the reactor 410 via the first reactant inlet 432. In some embodiments, the feedstock includes a carbon source. Examples of carbon sources may include, but are not limited to: gaseous carbon sources, such as methane, ethane, propane, ethylene, and acetylene; and liquid volatile carbon sources, such as benzene, toluene, xylene, trimethylbenzene, methanol, ethanol, and / or octanol. Alternatively, carbon monoxide gas or carbon dioxide gas may be used as the carbon source.

[0062] The feedstock also includes a catalyst precursor from which metal catalyst particles 402 can be generated for subsequent growth of CNTs 404. Examples of catalyst precursors may include, but are not limited to, transition metals such as tungsten, molybdenum, chromium, iron, nickel, cobalt, rhodium, ruthenium, palladium, osmium, iridium, or platinum, and organometallic complexes such as ferrocene, cobalt dicene, nickel dicene, iron carbonyl, iron acetylacetone, or iron oleate. The feedstock may include 0.5 to 5 wt.%, 1 to 5 wt.%, or 1.5 to 4 wt.% of the catalyst precursor based on the amount of carbon source. If an excessive amount of catalyst precursor is used relative to the amount of carbon source, the catalyst can act as an impurity, making it difficult to obtain high-purity CNTs.

[0063] In some embodiments, the feedstock may further include a co-catalyst. The co-catalyst comprises sulfur atoms that interact with the metal catalyst particles 402, thereby promoting the formation of single-walled CNTs. Examples of co-catalysts may include, but are not limited to, thiophene, benzothiophene, benzenethiophene, and hydrogen sulfide. The feedstock may include a co-catalyst in amounts of 0.5 to 5 wt.%, 1 to 5 wt.%, or 1.5 to 4 wt.%, based on the amount of carbon source. If an excessive amount of co-catalyst is used relative to the amount of carbon source, the co-catalyst may act as an impurity, making it difficult to obtain high-purity CNTs.

[0064] In some embodiments, the raw materials include methane as a carbon source, ferrocene as a catalyst precursor, and thiophene as a co-catalyst.

[0065] The feedstock can be delivered to reactor 410 via a carrier gas to ensure a rapid homogeneous reaction. In some embodiments, the carrier gas may include an inert gas (e.g., argon (Ar) or helium (He)) and / or a reactant gas (e.g., hydrogen (H2)). In some embodiments, the ratio of carbon source to carrier gas, i.e., the volume ratio of carbon source to carrier gas, is 5.0 × 10⁻⁶ at room temperature. -8 Up to 1.0×10 -4 v / v or 1.0×10 -7 Up to 1.0×10 -5 v / v. In some embodiments, the carbon source is introduced into reactor 410 at a flow rate ranging from 4 standard cubic centimeters per minute (sccm) to 120 sccm.

[0066] In some embodiments, the feedstock may be preheated to evaporate reactants in the feedstock before or in conjunction with the introduction of the feedstock into the first reaction zone 412 of reactor 410. In some embodiments, the feedstock is maintained at a temperature below the decomposition temperature of the catalyst precursor before entering the first reaction zone 412 of reactor 410. If the temperature exceeds the decomposition temperature of the catalyst precursor, the catalyst clusters may form prematurely in the process and become deactivated before they can participate in the CNT growth process. In some embodiments, the feedstock is maintained at a temperature between 70°C and 200°C.

[0067] Reactor 410 is heated to generate a temperature gradient in the first reaction zone 412. In some embodiments, a temperature gradient from about 500°C to about 1100°C is generated, with the temperature increasing along the length of the first reaction zone 412. In some embodiments, the length of the first reaction zone 412 is greater than 5 meters. Therefore, once the feedstock is injected into the first reaction zone 412 of reactor 410 via the first gas inlet 422, the catalyst precursor decomposes to form metal catalyst particles 402. In some embodiments, the metal catalyst particles 402 may be formed to have a diameter in the range of about 0.5 nm to about 5 nm. When a carbon source comes into contact with the metal catalyst particles 402 in the first reaction zone 412, the carbon source decomposes on the metal catalyst particles 402 at a high temperature (e.g., about 700°C or higher), and CNTs 404 grow from the metal catalyst particles 402 in such a way that the metal catalyst particles 402 are embedded in the growth tips of the CNTs 404. Therefore, the diameter of the CNTs 404 is determined by the size of the metal catalyst particles 402. Each CNT404 formed may comprise a single CNT or a bundle of CNTs comprising, for example, 2 to 20 individual CNTs.

[0068] refer to Figure 3 and Figure 4B According to some embodiments, method 300 proceeds to operation 304, wherein BNNT 406 is formed around CNT 404 in a second reaction region 414 of reactor 410. Figure 4B The diagram is a schematic of reactor 410 according to some embodiments, showing the growth of BNNT 406 around CNT 404 in the second reaction zone 414 of reactor 410.

[0069] like Figure 4B As shown, BNNT 406 can be formed by first providing a boron nitride source 448 in a second source material supply unit 440. In some embodiments, the boron nitride source 448 may include an aminoborane complex, such as an aminoborane (H2B=NH2), an aminoborane (H3N-BH3), a cycloborane (B3N3H3), or a combination thereof.

[0070] The second source material supply unit 440 can then be heated to the temperature at which the boron nitride source 448 is sublimated. The temperature at which sublimation is performed can vary depending on the type of boron nitride source 448 used. In some embodiments, the sublimation of the boron nitride source 448 is performed at a temperature greater than about 50°C and less than about 100°C. In some embodiments, the sublimation of the boron nitride source 448 is performed in a temperature range of 70°C to 90°C, for example, about 70°C, about 75°C, about 80°C, about 85°C, or about 90°C. In some embodiments, when the boron nitride source 448 is ammonia borane, the sublimation of the ammonia borane is performed at about 80°C.

[0071] Next, the vaporized boron nitride source can be mixed with a carrier gas flowing into the second source material supply unit 440 via the second gas inlet 452. In some embodiments, the carrier gas is an inert gas, such as argon. The carrier gas can flow into the second source material supply unit 440 at a flow rate in the range of about 5 sccm to about 15 sccm.

[0072] As CNT 404 enters the second reaction zone 414 of reactor 410, shut-off valve 444 is opened to allow vaporized boron nitride source 448, carried by carrier gas, to flow into the second reaction zone 414 of reactor 410 via second reactant inlet 442. The second reaction zone 414 is maintained at a sufficiently high temperature to promote the growth of BNNT 406 on CNT 404, but not so high as to adversely affect the physical and chemical properties of CNT 404. The temperature of the second reaction zone 414 is also sufficiently high to remove the metal catalyst particles 402 at the tips of the CNT 404. In some embodiments, the temperature of the second reaction zone is maintained at approximately 1000°C to approximately 1100°C.

[0073] At the second reaction region 414, the vaporized boron nitride source comes into contact with CNT 404 and decomposes at the temperature of the second reaction region to form boron nitride. The boron nitride is conformally deposited on the surface of CNT 404 to present the morphological structure of CNT 404, thereby forming BNNT 406 surrounding CNT 404.

[0074] The growth of BNNT 406 can be performed under an inert atmosphere and / or a reducing atmosphere. The inert atmosphere can be generated using an inert gas (e.g., argon or helium). The reducing atmosphere can be generated using hydrogen. When inert gas and hydrogen are used as a mixture, the amount of inert gas can be from about 90% to about 97% by volume, and the amount of hydrogen can be from about 3% to about 10% by volume. The inert gas can be supplied, for example, at a flow rate from about 100 sccm to about 500 sccm, and the hydrogen can be supplied, for example, at a flow rate from about 5 sccm to about 30 sccm. In some embodiments, an argon and hydrogen mixture containing 3% hydrogen is supplied to reactor 410 via a first gas inlet 422.

[0075] The resulting BNNT 406 may comprise any number of boron nitride layers, for example, from a single layer to about 100 layers. For example, in some embodiments, BNNT 406 may comprise one to about 20 layers of boron nitride.

[0076] Thus, multiple heterostructured nanotubes 250 are formed. Each heterostructured nanotube 250 includes a CNT 404 as a core (i.e., CNT core 252) and a BNNT 406 as a shell (i.e., BNNT shell 254). As described above, the CNT 404 can be a single CNT or a bundle of CNTs comprising 2 to 20 individual CNTs.

[0077] The high temperatures used for growing BNNT 406 (i.e., temperatures from 1000°C to approximately 1100°C) cause evaporation of the metal catalyst nanoparticles 402 at the tips of CNT 404, which in turn leads to the removal of the metal catalyst from the heterostructured nanotubes 250. Therefore, after leaving reactor 410, the heterostructured nanotubes 250 contain less than 0.01 atomic% of the catalyst metal. In some embodiments, the catalyst metal is completely removed, leaving the heterostructured nanotubes 250 free of catalyst metal. Since the catalyst metal has a higher absorption coefficient in EUV wavelengths than carbon and boron nitride, simultaneous removal of the catalyst metal during the growth of BNNT 406 helps to improve the EUV transmittance of the protective film 232.

[0078] refer to Figure 3 and Figure 4C According to some embodiments, method 300 proceeds to operation 306, wherein a protective film 232 is formed on substrate 460. Figure 4C The schematic diagram of reactor 410 according to some embodiments shows heterostructured nanotubes 250 leaving reactor 410, thereby forming a protective film 232 on substrate 460.

[0079] like Figure 4CAs shown, a cooling process can be performed on the heterostructured nanotubes 250. The cooling process can be performed, for example, at a rate of about 10°C to about 100°C per minute, or about 20°C to about 80°C per minute. During the cooling process, an inert gas (e.g., argon) can be supplied to the reactor 410 via the first gas inlet 422 to prevent oxidation of the heterostructured nanotubes 250. In some embodiments, argon can flow into the reactor 410 at a flow rate of about 100 sscm to about 800 sscm. The cooling process can be a natural cooling process, which can be implemented by stopping the operation of the heating element 416 or by removing the heating element 416 from the reactor 410.

[0080] Heterogeneous nanotubes 250 are collected at the bottom of reactor 410 by substrate 460. In some embodiments, substrate 460 may include a filter membrane 462. In some embodiments, filter membrane 462 is a porous membrane with pores having a diameter of 0.1 μm to about 5 μm. In one example, the pore size in filter membrane 462 is about 0.1 μm to about 0.6 μm. In another example, the pore size is about 0.45 μm. In some embodiments, filter membrane 462 is formed of or coated with polyethylene terephthalate (PET). In some embodiments, filter membrane 462 is formed of or coated with other suitable materials such as nylon, cellulose, polymethyl methacrylate (PMMA), polystyrene (PS), polytetrafluoroethylene (PTFE), or polybenzoxazole (PBO). In some embodiments, the filter membrane 462 is formed of cellulose-based filter paper. In some embodiments, the filter membrane 462 is a hydrophilic membrane. In some other embodiments, the filter membrane 462 is a hydrophobic membrane.

[0081] In some embodiments, to prevent the heterostructured nanotubes 250 from penetrating the pores of the filter membrane 462, the substrate 460 may further include a support 464 on which the filter membrane 462 is placed. The support 464 may be formed of any suitable material, such as glass or quartz. In some embodiments, the support 464 is formed of a quartz substrate.

[0082] Vacuum suction can be applied to substrate 460 to promote uniform dispersion of heterostructured nanotubes 250 on filter film 462. Thus, one or more uniformly distributed heterostructured nanotubes are formed on filter film 462 to provide protective film 232. The protective film may include, for example, one, two, three, four, or more heterostructured nanotube layers. Each heterostructured nanotube layer may include a random network of heterostructured nanotubes 250.

[0083] In some embodiments, after the protective film 232 is formed, the support 464 may subsequently be removed from the structure.

[0084] refer to Figure 3 and Figure 4D According to some embodiments, method 300 proceeds to operation 308, in which protective film 232 is transferred from filter film 462 to film boundary 234. Figure 4D This is a schematic diagram of the transfer of the protective film 232 from the filter film 462 to the film boundary 234 according to some embodiments.

[0085] like Figure 4D As shown, the transfer of the protective film 232 is performed by first attaching a film boundary 234 along the peripheral portion of the protective film 232. In some embodiments, the film boundary 234 is made of silicon. To attach the film boundary 234 to the protective film 232, in some embodiments, the film boundary 234 is first brought into physical contact with the protective film 232. Assuming sufficient force is applied, the film boundary 234 is then pressed against the protective film 232 to secure the film boundary 234 to the protective film 232. In some embodiments, the film boundary 234 and the protective film 232 are held together by van der Waals forces. In some embodiments, the film boundary 234 is pre-wetted with a polar solvent (e.g., ethanol) before being attached to the protective film 232. Ethanol helps improve the adhesion between the film boundary 234 and the protective film 232, thereby providing a stable contact between them.

[0086] Subsequently, the filter membrane 462 is removed from the protective membrane 232. In some embodiments, the filter membrane 462 can be removed by peeling or pulling it off the protective membrane 232. Figure 4D As shown, after the filter membrane 462 is removed, the protective membrane 232 is supported by the membrane boundary 234 along the periphery of the protective membrane 232.

[0087] In some embodiments, when ethanol is used to improve the adhesion between the protective film 232 and the film boundary 234, after the filter film 462 is removed, the assembly including the protective film 232 and the film boundary 234 is dried in air or under vacuum for a period of time to allow the ethanol to evaporate.

[0088] refer to Figure 3 and Figure 4E According to some embodiments, method 300 proceeds to operation 310, wherein the protective film 232 is densified. Figure 4E This is a schematic diagram of densifying the protective film 232 according to some embodiments.

[0089] like Figure 4EAs shown, the heterostructured nanotubes 250 in the protective film 232 are densified into large bundles of neatly arranged heterostructured nanotubes held together by van der Waals forces. Densification can be performed by first treating the protective film 232 with an organic solvent. The organic solvent is a volatile solvent, such as ethanol, methanol, propanol, dichloroethane, chloroform, or combinations thereof. In some embodiments, the protective film 232 is treated by exposing it to ethanol vapor. After contact with the organic solvent, the heterostructured nanotubes 250 in the protective film 232 are compressed into heterostructured nanotube bundles. The dense heterostructured nanotube structure increases the density of the protective film 232, which helps minimize particle propagation through the protective film 232. The dense heterostructured nanotube structure also helps improve the contact between the protective film 232 and the film boundary 234. After densification, the protective film 232 is then dried in a vacuum or air.

[0090] The protective film 232 thus formed comprises a network of dense heterostructured nanotubes 250. The individual heterostructured nanotubes 250 are randomly arranged within the protective film 232 such that they are not aligned along a predominant or dominant direction. The protective film 232 can have a thickness ranging from approximately 50 nm to approximately 100 nm. Depending on the porosity of the protective film 232, its thickness can be even greater.

[0091] Figure 5 This is a flowchart of a method 500 for manufacturing a protective film assembly 230 according to some alternative embodiments of the present disclosure. Figures 6A-6D The protective film assembly 230 is shown at various stages of method 500. It should be understood that, for additional embodiments of the method, additional steps may be provided before, during, and after method 500, and some steps described below may be replaced or eliminated. Unless otherwise stated, [the following is consistent with...] Figures 4A-4E The same or similar parts Figures 6A-6D The components are given the same reference numerals, therefore their detailed descriptions are omitted.

[0092] refer to Figure 5 and Figure 6A According to some embodiments, method 500 includes operation 502, wherein a CNT film 602 is formed on substrate 460. Figure 6A The diagram shows a CNT film 602 formed on a substrate 460 according to some embodiments.

[0093] CNT membrane 602 comprises a plurality of CNTs 404 in aggregate form (also referred to as CNT aggregates 616). In some embodiments, CNT membrane 602 is formed using a direct spin-dip process based on floating catalyst CVD in apparatus 600. The floating catalyst CVD process is described above. Figure 2AThe description is provided below, therefore its detailed description is omitted. In some embodiments, reactor 610 includes a vertical quartz tube surrounded by a heating element 416 for heating reactor 610. Gas supply unit 420 is fluidly connected to reactor 610 via gas inlet 422 at the upper end of reactor 610. Material source supply unit 430 is fluidly connected to reactor 610 via reactant inlet 432, which is coupled to one side of gas inlet 422. Located within reactor 610 is a nanotube trap 612, which is configured to promote the formation of CNT aggregates. In some embodiments, nanotube trap 612 is in the form of a metal wire loop or a glass wire loop.

[0094] In use, heating element 416 is heated to provide a temperature gradient from about 500°C to about 1100°C along the length of reactor 610. In some embodiments, the length of reactor 610 is greater than 5 meters. A feedstock comprising a carbon source, catalyst precursor, and co-catalyst precursor carried by a carrier gas is injected into reactor 610 via gas inlet 422. In some embodiments, toluene is used as the carbon source, ferrocene as the catalyst precursor, thiophene as the co-catalyst, and hydrogen as the carrier gas to perform CNT synthesis. When the catalyst precursor contained in the feedstock is placed inside reactor 610, the catalyst precursor is decomposed to form metal catalyst particles 402. CNTs 404 are then grown from the metal catalyst particles 402. Figure 6A In this embodiment, CNT 404 is formed as an aerogel. The aerogel-like CNT 404 is arranged by a nanotube trap 612 and then rotated in a direction perpendicular to the airflow direction while being pulled, for example, by a rotating shaft (not shown). The aerogel-like CNT 404 are twisted together, and as the aerogel-like CNT 404 moves relative to the rotating shaft, CNT fibers 614 begin to grow. Additional aerogel-like CNT 404 can be twisted around the growing fibers to extend the length of the CNT fibers 614. The resulting CNT fibers 614 comprise vertically aligned CNT 404.

[0095] Next, the CNT fiber 614 can be densified by exposing it to a densifying agent. Suitable densifying agents may include propanol and alcohols such as ethanol or isopropanol (IPA). In some embodiments, densification can be performed by spraying propanol onto the CNT fiber 614.

[0096] The CNT fibers 614 can then be sliced ​​into sheets. Each sheet includes a CNT aggregate 616 having CNTs 404 connected side-by-side and end-to-end. In some embodiments, the CNT aggregate 616 may contain more than 10 individual CNTs 404. The CNT fiber sheets can be of any suitable length. In some embodiments, the CNT fiber sheets may independently have a length in the range of 100 μm to 100 mm.

[0097] CNT aggregates 616 are collected by a substrate 460 placed near the outlet of reactor 610. In some embodiments, substrate 460 includes a filter membrane 462 on a support 464. In some embodiments, substrate 460 may be rotated along arrow direction 618. A vacuum suction process may also be applied to substrate 460. Substrate rotation and vacuum suction are performed to promote uniform distribution of CNT aggregates 616 on filter membrane 462. Support 464 is subsequently removed after CNT membrane 602 is formed. CNT membrane 602 thus formed comprises a random network of CNT aggregates 616.

[0098] In some embodiments, such as Figure 9 As shown, a roller 650 can be provided downstream of the reactor 610 so that CNT fibers 614 can be collected and wound around the roller 650. In some embodiments, winding is performed at a rate in the range of about 5 rpm to about 100 rpm.

[0099] Subsequently, a CNT film 602 comprising interlaced CNT aggregates 616 is formed from CNT fibers 614, such that the CNT aggregates 616 in the first CNT layer 602a are aligned in a first direction, and the CNT aggregates 616 in the second CNT layer 602b adjacent to the first CNT layer 602a are aligned in a second direction different from the first direction. The interlaced CNT aggregates 616 thus produce a CNT film 602 with a regular network or mesh structure. The interlacing of the CNT aggregates 616 helps to improve the structural integrity of the CNT film 602. The CNT aggregates 616 in the CNT film 602 are then densified by annealing at a temperature in the range of 1000°C to 2000°C.

[0100] refer to Figure 5 and Figure 6B According to some embodiments, method 500 proceeds to operation 504, in which CNT membrane 602 is transferred from filter membrane 462 to membrane boundary 234. Figure 6B The CNT membrane 602 is shown transferring from the filter membrane 462 to the membrane boundary 234 according to some embodiments.

[0101] like Figure 6BAs shown, the transfer of the CNT film 602 is performed by first attaching the film boundary 234 along the peripheral portion of the CNT film 602. In some embodiments, the film boundary 234 is made of silicon. To attach the film boundary 234 to the CNT film 602, in some embodiments, the film boundary 234 is first brought into physical contact with the CNT film 602. Assuming sufficient force is applied, the film boundary 234 is then pressed against the CNT film 602 to secure the film boundary 234 to the CNT film 602. In some embodiments, the film boundary 234 and the CNT film 602 are held together by van der Waals forces. In some embodiments, the film boundary 234 is pre-wetted with a polar solvent (e.g., ethanol) before being attached to the CNT film 602. Ethanol helps to improve the adhesion between the film boundary 234 and the CNT film 602, thereby providing a stable contact between them.

[0102] Subsequently, the filter membrane 462 is removed from the assembly of the CNT membrane 602 and the membrane boundary 234. In some embodiments, the filter membrane 462 can be removed by peeling or pulling it off the CNT membrane 602. Figure 6B As shown, after the filter membrane is removed, the CNT membrane 602 is supported by the membrane boundary 234 along the peripheral portion of the CNT membrane 602.

[0103] After removing the filter membrane 462, the assembly of the protective membrane 232 and the membrane boundary 234 is placed in the ambient atmosphere for a period of time to allow ethanol to evaporate.

[0104] In some embodiments, when ethanol is used to improve the adhesion between the CNT membrane 602 and the membrane boundary 234, after removing the filter membrane 462, the CNT membrane 602 and the membrane boundary 234 are dried in air or under vacuum for a period of time to allow the ethanol to evaporate.

[0105] refer to Figure 5 and Figure 6C According to some embodiments, method 500 proceeds to operation 506, in which CNT film 602 is densified to form CNT film 620. Figure 6C The densification of CNT film 602 according to some embodiments is shown to form CNT film 620.

[0106] refer to Figure 6CThe CNT aggregates 616 in the CNT film 602 are densified to increase the density of the CNT film 602. Densification can be performed by first treating the CNT film 602 with an organic solvent. The organic solvent is a volatile solvent, such as ethanol, methanol, propanol, dichloroethane, chloroform, or combinations thereof. In some embodiments, the CNT film 602 is treated by exposing the CNT film 602 to ethanol vapor. After immersion in the organic solvent, the CNT aggregates 616 in the CNT film 602 are compacted, thereby providing improved contact with the film boundary 234. The resulting CNT film 620 is then dried under vacuum or in air.

[0107] refer to Figure 5 and Figure 6D According to some embodiments, method 500 proceeds to operation 508, wherein BNNT 406 is formed around CNT aggregate 616. Figure 6D The formation of BNNT 406 around CNT aggregate 616 according to some embodiments is shown.

[0108] like Figure 6D As shown, BNNT 406 is formed via a low-pressure thermal CVD process, in which the vaporized boron nitride source undergoes pyrolysis when steam contacts the CNT aggregate 616 in reactor 630. The pyrolysis causes the boron nitride source to decompose into boron nitride. The boron nitride is then deposited on the CNT aggregate 616 as a shell (i.e., BNNT shell 254).

[0109] Reactor 630 includes a horizontally upright quartz tube surrounded by a heating element 416 for heating reactor 630. A first gas supply unit 420 is fluidly connected to reactor 630 at one end of reactor 630 via a first gas inlet 422. A material source supply unit 440, containing a boron nitride source 448, is fluidly connected to reactor 630 via a reactant inlet 442. The material source supply unit 440 is configured to supply a boron nitride source for the growth of BNNT to reactor 630. A second gas supply unit 450 is fluidly connected to the material source supply unit 440 via a second gas inlet 452. The second gas supply unit 450 is configured to supply a carrier gas to the material source supply unit 440.

[0110] The assembly, including the CNT film 620 and the film boundary 234, is placed inside the reactor 630. The reactor 630 is then heated by the heating element 416, causing the temperature of the reactor 630 to gradually increase to a temperature in the range of approximately 1000°C to 1100°C.

[0111] The source material unit 440 is then heated to the temperature at which the boron nitride source 248 is sublimated. The temperature at which sublimation is performed can vary depending on the type of boron nitride source 448 used. In some embodiments, the sublimation of the boron nitride source 448 is performed at a temperature greater than about 50°C and less than about 100°C. In some embodiments, the sublimation of the boron nitride source 448 is performed at a temperature in the range of 70°C to 90°C, for example, about 70°C, about 75°C, about 80°C, about 85°C, or about 90°C. In some embodiments, when the boron nitride source is ammonia borane, the sublimation of the ammonia borane is performed at about 80°C.

[0112] Next, the vaporized boron nitride source is mixed with a carrier gas flowing into the source material supply unit 440 from the second gas supply unit 450 via the second gas inlet 452. In some embodiments, the carrier gas is an inert gas, such as argon. The carrier gas may flow into the source material supply unit 440 at a flow rate in the range of about 5 sccm to about 15 sccm.

[0113] A vaporized boron nitride source, carried by a carrier gas, is then supplied to reactor 630 via reactant inlet 442. The vaporized boron nitride source contacts CNT aggregates 616 and then decomposes to form boron nitride. Boron nitride is conformally deposited on the surface of CNT aggregates 616 to present the morphological structure of CNT aggregates 616, thereby forming BNNT 406 surrounding CNT aggregates 616.

[0114] The growth of BNNT 406 can be performed under an inert atmosphere and / or a reducing atmosphere. The inert atmosphere can be generated using an inert gas (e.g., argon or helium). The reducing atmosphere can be generated using hydrogen. When the inert gas and hydrogen are used as a mixture, the amount of inert gas can be from about 90% to about 97% by volume, and the amount of hydrogen can be from about 3% to about 10% by volume. The inert gas can be supplied, for example, at a flow rate of from about 100 sccm to about 500 sccm, and the hydrogen can be supplied, for example, at a flow rate of from about 5 sccm to about 30 sccm. In some embodiments, an argon and hydrogen mixture containing 3% hydrogen is supplied to reactor 630 via a first gas inlet 422 at a flow rate of 300 sccm. The growth of BNNT 406 is carried out at about 10 -3 To about 10 -2 Execute under low pressure.

[0115] The resulting BNNT 406 may comprise any number of boron nitride layers, for example, from a single layer to about 100 layers of boron nitride. In some embodiments, BNNT 406 may comprise from a single layer to about 20 layers of boron nitride.

[0116] Thus, multiple heterostructured nanotubes 250 are formed. Each heterostructured nanotube 250 includes a CNT aggregate 616 as a core (i.e., CNT core 252) and a BNNT 406 as a shell (i.e., BNNT shell 254).

[0117] The high temperatures used for growing the BNNT shell 254 (i.e., temperatures from 1000°C to approximately 1100°C) cause evaporation of the metal catalyst particles 402 at the tips of the CNTs 404 contained in the CNT aggregate 616, thus resulting in the removal of the metal catalyst from the heterostructured nanotubes 250. Therefore, after leaving the reactor 410, the heterostructured nanotubes 250 contain less than 0.01 atomic% of the catalyst metal. In some embodiments, the catalyst metal is completely removed, such that the heterostructured nanotubes 250 are free of catalyst metal. Since the catalyst metal has a higher absorption coefficient in the EUV wavelength region than carbon and boron nitride, simultaneous removal of the catalyst metal during the growth of BNNT 406 helps to improve the EUV transmittance of the protective film.

[0118] Thus, a protective film 232 comprising a network of heterostructured nanotubes 250 is formed. The individual heterostructured nanotubes 250 are randomly arranged within the protective film 232 such that they are not aligned along a predominant or dominant direction. The protective film 232 can have a thickness ranging from approximately 50 nm to approximately 100 nm. Depending on the porosity of the protective film 232, its thickness can be even greater.

[0119] Figure 7 This is a flowchart of a method 700 for manufacturing a protective film assembly 230 according to an alternative embodiment of the present disclosure. Figures 8A-8D The protective film assembly 230 is shown at various stages of method 700. It should be understood that, for additional embodiments of the method, additional steps may be provided before, during, and after method 700, and some steps described below may be replaced or eliminated. Unless otherwise stated, the materials and methods of forming the components in these embodiments are the same as those in other embodiments. Figures 6A-6D The similar components indicated by similar reference numerals in the illustrated embodiments are substantially the same. Therefore, in Figures 6A-6D The discussion of the illustrated embodiments can be found regarding Figures 8A-8D Details of the component's formation process and materials are shown.

[0120] Method 700 is similar to Method 500, except that in performing Operation 702, the above-mentioned... Figure 6A The process described above forms a CNT membrane 602 comprising a plurality of CNT aggregates 616 on a filter membrane 462. Figure 8A After that, use the above information about... Figure 6BThe process described above is used to perform operation 704 to transfer CNT membrane 602 from filter membrane 462 to membrane boundary 234. Figure 8B Instead of performing operation 506 of method 500 to densify the CNT film 602, operation 508 of method 500 is first performed in method 700. For example... Figure 8C As shown, in operation 706 of method 700, the assembly of CNT membrane 602 and membrane boundary 234 is placed within reactor 630, wherein BNNT 406 is formed around CNT aggregates 616, thereby utilizing the above-mentioned... Figure 6D The process described above is used to provide a protective film 232. The heterostructured nanotubes 250 in the protective film 232 contain less than 0.01 atomic percent of catalyst metal. In some embodiments, the catalyst metal is completely removed, such that the heterostructured nanotubes 250 are free of catalyst metal. In operation 708 of method 700, the above-described... Figure 6C The process described above is used to densify the protective film 232 ( Figure 8D ).

[0121] Subsequently, the protective film assembly 230 obtained in methods 300, 500, or 700 is attached to the protective film frame 210 using a protective film adhesive 240 to form a protective film 114. Next, the protective film 114 is attached to the photomask 108 using a protective film frame adhesive 214, thereby forming the protective film photomask structure 200 of FIG. 2. The processes for forming the protective film 114 and the protective film photomask structure 200 are described in FIG. 2 above.

[0122] One aspect of this specification relates to a method for forming a protective film for extreme ultraviolet lithography. The method includes forming a protective film on a filter membrane and transferring the protective film from the filter membrane to a membrane boundary. Forming the protective film includes growing carbon nanotubes (CNTs) from in-situ formed metal catalyst particles in a first reaction region of a reactor, each CNT including a metal catalyst particle at its growth tip; growing boron nitride nanotubes (BNNTs) around individual CNTs in a second reaction region of the reactor downstream of the first reaction region, thereby forming heterostructured nanotubes each including a CNT core and a BNNT shell; and collecting the heterostructured nanotubes on the filter membrane. The metal catalyst particles are partially or completely removed during the growth of the BNNTs.

[0123] Another aspect of this specification relates to a method for forming a protective film for extreme ultraviolet lithography. The method includes growing carbon nanotube (CNT) aerogels from in-situ formed metal catalyst particles in a first reactor, each of the CNT aerogels comprising a metal catalyst particle at its growth tip. The method also includes forming a CNT film on a substrate comprising CNT aggregates obtained by aggregating the CNT aerogels; attaching the CNT film to a film boundary; and growing boron nitride nanotubes (BNNTs) in a second reactor to surround individual CNT aggregates, thereby forming a protective film comprising a network of heterostructured nanotubes, each of the heterostructured nanotubes comprising a CNT aggregate core and a BNNT shell. The metal catalyst particles are partially or completely removed during the growth of the BNNTs.

[0124] Another aspect of this specification relates to a photolithographic patterning method. The method includes using a photomask to reflect EUV radiation onto a photoresist layer on a semiconductor substrate to form a patterned photoresist layer, the photomask having a protective film on a thin film holder fixed to the photomask; developing the photoresist layer to form the patterned photoresist layer; and using the patterned photoresist layer as a mask to etch the semiconductor substrate to form a circuit layout. The protective film includes a first heterostructured nanotube layer having heterostructured nanotubes aligned along a first direction, and a second heterostructured nanotube layer having heterostructured nanotubes aligned along a second direction different from the first direction, thereby forming a mesh of heterostructured nanotubes. Each of the heterostructured nanotubes includes a carbon nanotube (CNT) core and a boron nitride shell surrounding the CNT core.

[0125] The foregoing outlines features of several embodiments to enable those skilled in the art to better understand various aspects of this disclosure. Those skilled in the art will understand that they can readily use this disclosure as a basis for designing or modifying other processes and structures to achieve the same purposes and / or obtain the same advantages as the embodiments introduced herein. Those skilled in the art will also recognize that these equivalent constructions do not depart from the spirit and scope of this disclosure, and that various changes, substitutions, and modifications can be made without departing from the spirit and scope of this disclosure.

[0126] Example

[0127] Example 1. A method for forming a protective film for extreme ultraviolet lithography, comprising: forming a protective film over a filter film, wherein forming the protective film comprises: growing carbon nanotubes (CNTs) from in-situ formed metal catalyst particles in a first reaction region of a reactor, each of the CNTs comprising a metal catalyst particle at its growth tip; growing boron nitride nanotubes (BNNTs) around a single CNT in a second reaction region of the reactor downstream of the first reaction region to form heterostructured nanotubes, each comprising a CNT core and a BNNT shell, wherein the metal catalyst particles are partially or completely removed during the growth of the BNNTs; collecting the heterostructured nanotubes on the filter film; and transferring the protective film from the filter film to a film boundary.

[0128] Example 2. The method according to Example 1, wherein the protective film comprises less than 0.01 atomic% of catalyst metal.

[0129] Example 3. The method according to Example 2, wherein the protective film does not contain the catalyst metal.

[0130] Example 4. The method according to Example 1, wherein growing the CNT comprises: supplying a feedstock comprising a carbon source, a catalyst precursor, and a co-catalyst carried by a carrier gas to a first reaction zone of the reactor; heating the first reaction zone of the reactor to maintain a temperature gradient along the length of the first reaction zone; heating the catalyst precursor to decompose the catalyst precursor to form the metal catalyst particles; and heating the carbon source to induce the decomposition of the carbon source catalyzed by the metal catalyst particles to provide carbon atoms and grow the CNT from the metal catalyst particles.

[0131] Example 5. The method according to Example 4, wherein the temperature gradient is 500°C to 1100°C.

[0132] Example 6. The method according to Example 4, wherein the carbon source comprises carbon monoxide, the catalyst precursor comprises ferrocene, and the co-catalyst comprises thiophene.

[0133] Example 7. The method according to Example 4, wherein the carrier gas comprises hydrogen.

[0134] Example 8. The method according to Example 1, wherein growing the BNNT comprises: heating a boron nitride source in a source material supply unit to sublimate the boron nitride source; supplying a vaporized boron nitride source carried by a carrier gas to a second reaction zone of the reactor; and heating the vaporized boron nitride source to cause decomposition of the boron nitride source to provide boron nitride and conformal deposition of the boron nitride on the CNT.

[0135] Example 9. The method according to Example 8, wherein the boron nitride source comprises aminoborane, ammoniborane, cycloborane, or combinations thereof.

[0136] Example 10. The method according to Example 8, wherein the decomposition of the boron nitride source is performed at a temperature in the range of 1000°C to 1100°C.

[0137] Example 11. The method according to Example 1 further includes: densifying the protective film.

[0138] Example 12. A method for forming a protective film for extreme ultraviolet lithography, comprising: growing carbon nanotube (CNT) aerogels from in-situ formed metal catalyst particles in a first reactor, each of the CNT aerogels comprising a metal catalyst particle at its growth tip; forming a CNT film on a substrate, the CNT film comprising CNT aggregates obtained by aggregating the CNT aerogels; attaching the CNT film to a film boundary; and growing boron nitride nanotubes (BNNTs) in a second reactor to surround individual CNT aggregates, thereby forming a protective film comprising a network of heterostructured nanotubes, each of the heterostructured nanotubes comprising a CNT aggregate core and a BNNT shell, wherein the metal catalyst particles are partially or completely removed during the growth of the BNNTs.

[0139] Example 13. The method according to Example 12 further includes: densifying the CNT film prior to growing the BNNT to form a CNT film comprising dense CNT aggregates.

[0140] Example 14. The method according to Example 13, wherein densifying the CNT membrane includes exposing the CNT membrane to ethanol.

[0141] Example 15. The method according to Example 12 further includes: densifying the protective film by exposing the protective film to ethanol.

[0142] Example 16. The method according to Example 12, wherein the protective film comprises less than 0.01 atomic% of catalyst metal.

[0143] Example 17. The method according to Example 12, wherein forming the CNT film comprises: forming CNT fibers by rotating the CNT aerogel to aggregate the CNT aerogel, cutting the CNT fibers into a plurality of fiber sheets, each of the plurality of fiber sheets comprising the CNT aggregate; and collecting the plurality of fiber sheets by the substrate.

[0144] Example 18. A photolithographic patterning method comprising: reflecting EUV radiation onto a photoresist layer on a semiconductor substrate using a photomask to form a patterned photoresist layer, the photomask having a protective film on a thin film holder fixed on the photomask; developing the photoresist layer to form the patterned photoresist layer; and using the patterned photoresist layer as a mask to etch the semiconductor substrate to form a circuit layout, wherein the protective film comprises a first heterostructured nanotube layer having heterostructured nanotubes aligned along a first direction, and a second heterostructured nanotube layer having heterostructured nanotubes aligned along a second direction different from the first direction, thereby forming a grid of heterostructured nanotubes, each of the heterostructured nanotubes comprising a carbon nanotube (CNT) core and a boron nitride shell surrounding the CNT core.

[0145] Example 19. The method according to Example 18, wherein the CNT core comprises more than 10 individual CNTs arranged side-by-side and connected end-to-end.

[0146] Example 20. The method according to Example 18, wherein the boron nitride shell comprises 1 to 40 layers of boron nitride.

Claims

1. A method for forming a protective film for extreme ultraviolet lithography, comprising: A protective film is formed on the filter membrane, wherein forming the protective film includes: Carbon nanotubes (CNTs) are grown from in-situ metal catalyst particles in the first reaction region of the reactor, each of the CNTs comprising a metal catalyst particle at its growth tip. Boron nitride nanotubes (BNNTs) are grown in a second reaction region of the reactor downstream of the first reaction region to surround a single CNT, thereby forming heterostructured nanotubes, each comprising a CNT core and a BNNT shell, wherein the metal catalyst particles are partially or completely removed during the growth of the BNNTs; and The heterostructured nanotubes are collected on the filter membrane; and The protective film is transferred from the filter film to the film boundary. The growth of the BNNT includes: The boron nitride source in the heating source material supply unit is used to sublimate the boron nitride source; A vaporized boron nitride source, carried by a carrier gas, is supplied to the second reaction zone of the reactor; and Heating the vaporized boron nitride source causes it to decompose, providing boron nitride and conformal deposition on the CNT.

2. The method according to claim 1, wherein, The protective film comprises less than 0.01 atomic% of catalyst metal.

3. The method according to claim 2, wherein, The protective film does not contain the catalyst metal.

4. The method according to claim 1, wherein, Growing the CNTs includes: The feedstock, including a carbon source, catalyst precursor, and co-catalyst carried by a carrier gas, is supplied to the first reaction zone of the reactor. The first reaction zone of the reactor is heated to maintain a temperature gradient along the length of the first reaction zone; Heating the catalyst precursor to decompose it, thereby forming the metal catalyst particles; and The carbon source is heated to induce the decomposition of the carbon source catalyzed by the metal catalyst particles to provide carbon atoms and grow the CNTs from the metal catalyst particles.

5. The method according to claim 4, wherein, The temperature gradient is from 500 °C to 1100 °C.

6. The method according to claim 4, wherein, The carbon source includes carbon monoxide, the catalyst precursor includes ferrocene, and the co-catalyst includes thiophene.

7. The method according to claim 4, wherein, The carrier gas includes hydrogen.

8. The method according to claim 1, wherein, The boron nitride source includes aminoborane, ammoniborane, cycloborane, or combinations thereof.

9. The method according to claim 1, wherein, The decomposition of the boron nitride source was performed at a temperature ranging from 1000 °C to 1100 °C.

10. The method according to claim 1, further comprising: The protective film is densified.

11. A method for forming a protective film for extreme ultraviolet lithography, comprising: Carbon nanotube (CNT) aerogels are grown from in-situ formed metal catalyst particles in a first reactor, each of the CNT aerogels comprising a metal catalyst particle at its growth tip. A CNT film is formed on a substrate, the CNT film comprising CNT aggregates obtained by aggregating the CNT aerogel; Attach the CNT film to the film boundary; as well as In a second reactor, boron nitride nanotubes (BNNTs) are grown to surround individual CNT aggregates, thereby forming a protective film comprising a network of heterostructured nanotubes, each comprising a CNT aggregate core and a BNNT shell, wherein the metal catalyst particles are partially or completely removed during the growth of the BNNTs. The growth of the BNNT includes: The boron nitride source in the heating source material supply unit is used to sublimate the boron nitride source; A vaporized boron nitride source, carried by a carrier gas, is supplied to the second reaction zone of the reactor; and Heating the vaporized boron nitride source causes it to decompose, providing boron nitride and conformal deposition on the CNT.

12. The method of claim 11, further comprising: The CNT film is densified prior to the growth of the BNNT to form a CNT film comprising dense CNT aggregates.

13. The method according to claim 12, wherein, Densifying the CNT membrane involves exposing the CNT membrane to ethanol.

14. The method of claim 11, further comprising: The protective film is densified by exposing it to ethanol.

15. The method according to claim 11, wherein, The protective film comprises less than 0.01 atomic% of catalyst metal.

16. The method according to claim 11, wherein, Forming the CNT film includes: CNT fibers are formed by rotating the CNT aerogel to aggregate it. The CNT fibers are cut into multiple fiber sheets, each fiber sheet comprising the CNT aggregates; and The plurality of fiber sheets are collected by the substrate.

17. A photolithographic patterning method, comprising: A photomask is used to reflect EUV radiation onto a photoresist layer on a semiconductor substrate to form a patterned photoresist layer. The photomask has a protective film on a thin film holder fixed on the photomask. The photoresist layer is developed to form the patterned photoresist layer; as well as The semiconductor substrate is etched using the patterned photoresist layer as a mask to form a circuit layout. The protective film comprises a first heterostructured nanotube layer having heterostructured nanotubes aligned along a first direction, and a second heterostructured nanotube layer having heterostructured nanotubes aligned along a second direction different from the first direction, thereby forming a grid of heterostructured nanotubes. Each of the heterostructured nanotubes comprises a carbon nanotube (CNT) core and a boron nitride shell surrounding the CNT core, wherein the boron nitride shell is formed in the following manner: The boron nitride source in the heating source material supply unit is used to sublimate the boron nitride source; A vaporized boron nitride source, carried by a carrier gas, is supplied to the reactor; and Heating the vaporized boron nitride source causes it to decompose, providing boron nitride and conformal deposition on the CNT.

18. The method according to claim 17, wherein, The CNT core comprises more than 10 individual CNTs arranged side-by-side and connected end-to-end.

19. The method of claim 17, wherein, The boron nitride shell comprises 1 to 40 layers of boron nitride.

Images