A method for preparing a single-walled carbon nanotube extreme ultraviolet lithography mask plate protective film

Abstract

This invention relates to the field of extreme ultraviolet (EUV) lithography mask protective film preparation, specifically a method for preparing a high-uniformity, high-strength single-walled carbon nanotube (SUV) EUV lithography mask protective film. Single-walled carbon nanotubes are grown using a floating catalyst chemical vapor deposition (CVD) method, and an interlocking and entangled SUV film is formed through in-situ molecular assembly. After transferring the film to a hollow frame, a densification treatment is performed using a combination of solvent evaporation and drying. The capillary force generated by solvent evaporation enhances intertube interactions and reduces roughness, thereby significantly improving the mechanical strength and uniformity of the film. The prepared SUV film exhibits high transmittance uniformity (≥90%) under 13.5 nm EUV wavelength, can withstand pressure differences exceeding 650 Pa, and has a transmittance uniformity of 3σ < 1.5, meeting the performance requirements of next-generation high-power EUV lithography machines for mask protective films.

Description

Technical Field

[0001] This invention relates to the field of preparation of protective films for extreme ultraviolet (EUV) lithography masks, specifically a method for preparing a protective film for EUV lithography masks with high uniformity and high strength of single-walled carbon nanotubes. Background Technology

[0002] In EUV lithography systems, the protective film, as a key protective component of the photomask, must effectively block external particulate contaminants while possessing excellent mechanical properties to achieve a stable, large-area self-supporting structure. Since the 13.5nm wavelength light used in EUV lithography is easily absorbed by most materials, the protective film must maintain high EUV transmittance while remaining extremely thin to ensure lithography efficiency. However, reducing the film thickness is accompanied by a decrease in mechanical strength, making it susceptible to damage or deformation when faced with factors such as fluctuations in process chamber pressure, equipment vibration, or operational stress. Therefore, achieving high strength and self-supporting performance of the protective film while maintaining high transmittance has become one of the core challenges that urgently needs to be addressed for EUV lithography technology to achieve large-scale mass production (Adv. Opt. Techn. 2017, 6(3-4): 221–227).

[0003] Carbon nanotube films, with their excellent EUV transmittance, high thermal stability, and superior chemical inertness, exhibit significant advantages in high-power EUV exposure environments. They are considered more promising than traditional materials (such as polycrystalline silicon, silicon nitride, and zirconium metal) and are expected to become ideal materials for protective films in next-generation high-power EUV lithography machines. Since 2015, the Belgian Microelectronics Centre (IMEC) has led a systematic effort to develop carbon nanotube protective film technology, collaborating with the Japanese chemical company Mitsui Chemicals to advance its commercialization in high-power EUV lithography systems (Jpn. J. Appl. Phys. 2023, 62SG0805). The current key bottleneck lies in achieving high EUV transmittance while simultaneously enabling the large-scale fabrication of high-strength, self-supporting carbon nanotube films.

[0004] Patent CN116594258A discloses a protective film and its components and frame, a manufacturing method for the component, an exposure master, an exposure apparatus, and a semiconductor device. It features a protective film thickness ≤50nm and a mesh structure with interconnecting points. However, the mesh structure relies solely on the natural winding of the bundles, resulting in insufficient stability of the interconnecting points. Uniformity issues arise during the densification of the thin film, making it prone to cracking due to uneven shrinkage. Pore elimination is incomplete, and the strength is insufficient to meet the pressure difference requirements of high-power EUV lithography. Patent CN109416503A discloses a protective film, a protective film component frame, a protective film component, its manufacturing method, an exposure master, an exposure apparatus, and a semiconductor device. It features an EUV protective film containing carbon nanotube sheets, achieving high transmittance by limiting the bundle diameter, in-plane orientation, and thickness. However, the overlap and winding between the carbon nanotubes are insufficient, resulting in a loose film structure. Pore elimination is difficult using only conventional film deposition processes, leading to limited film strength.

[0005] Carbon nanotube films, in their original state, exhibit a sparse network structure with slightly insufficient mechanical strength, making them prone to breakage under actual lithography machine conditions. Currently, densification processes such as immersion and spraying are commonly used to compress the spacing between the nanotube bundles, thereby improving the film density and strength. However, this process easily introduces structural inhomogeneities, leading to uneven EUV transmittance of the protective film. This, in turn, causes fluctuations in light energy during chip exposure, severely affecting the dimensional uniformity of the lithographic pattern and product yield.

[0006] Therefore, ensuring high extreme ultraviolet (EUV) light transmittance of carbon nanotube films while improving film uniformity and mechanical strength is the core key to achieving large-area self-supporting, highly uniform, and high-strength carbon nanotube films. To address these issues, this invention proposes a technique for preparing highly uniform and high-strength single-walled carbon nanotube EUV photolithography mask protective films. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a protective film for an extreme ultraviolet lithography mask with high uniformity and high strength of single-walled carbon nanotubes. This method aims to overcome the key technical bottleneck of existing carbon nanotube-based protective films, which are difficult to achieve in terms of large area, uniformity, high strength and self-supporting performance, so as to meet the practical application requirements of high-power EUV lithography systems.

[0008] The technical solution of this invention is:

[0009] A method for preparing a highly uniform and high-strength single-walled carbon nanotube (SUV) photomask protective film involves growing SUVs at 900℃~1300℃ using a floating catalyst chemical vapor deposition (CVD) method. In-situ molecular-level assembly is performed based on the strong van der Waals forces induced by collisions between SUVs in an aerosol state, forming an interlocking and entangled SUV film. Based on the difference in adhesion between the SUV film and the collecting filter membrane and the target substrate or hollow frame, a dry transfer technique is used to completely transfer the SUV film onto the target substrate or hollow frame, forming a self-supporting film. The film is densified using a combination of organic solvent evaporation and drying. Specifically, the capillary force generated by the evaporation of the volatile organic solvent causes the carbon nanotube bundles to aggregate tightly, enhancing their interaction and reducing roughness, resulting in a highly uniform and high-strength SUV photomask protective film.

[0010] The method for preparing the high-uniformity, high-strength single-walled carbon nanotube extreme ultraviolet lithography mask protective film involves growing single-walled carbon nanotubes by floating catalyst chemical vapor deposition at a growth temperature of 1100℃~1200℃. Single-walled carbon nanotube films of different thicknesses are collected by adjusting the deposition time. The prepared single-walled carbon nanotubes refer to carbon nanotubes composed of only a single layer of tube wall that are observed in transmission electron microscope images.

[0011] The method for preparing the high-uniformity, high-strength single-walled carbon nanotube extreme ultraviolet lithography mask protective film involves a dry transfer process that utilizes van der Waals forces to transfer the single-walled carbon nanotube film on the collector to a suspended target substrate or hollow frame. The target substrate or hollow frame is made of at least one of the following materials: metal, quartz, glass, polycrystalline silicon, alumina, graphite, indium tin oxide, polyethylene terephthalate, and polydimethylsiloxane. The metals include Cu, Ti, Fe, Pt, Au, Ni, and Mo.

[0012] The method for preparing the high-uniformity, high-strength single-walled carbon nanotube extreme ultraviolet lithography mask protective film uses volatile organic solvents such as ethanol, ethylene glycol, acetone, isopropanol, or a mixture thereof with deionized water.

[0013] The method for preparing the high-uniformity, high-strength single-walled carbon nanotube extreme ultraviolet lithography mask protective film involves the following steps: during the evaporation of organic solvents, the capillary action generated at the liquid-gas interface causes the carbon nanotubes to shrink and tighten, promoting the tube bundles to move closer together and arrange more densely, and enhancing the van der Waals forces between the tube bundles; at the same time, by controlling the concentration of volatile solvent molecules, the solvent is dried rapidly before agglomeration.

[0014] The method for preparing the high-uniformity, high-strength single-walled carbon nanotube extreme ultraviolet lithography mask protective film is characterized by the following: at a wavelength of 550 nm, multi-point testing is performed using a visible light spectrophotometer, and its uniformity is evaluated according to the 3σ standard deviation principle; when the transmittance of the protective film is ≥90%, the light transmittance uniformity 3σ < 1.5; in addition, the transmittance of the film in the extreme ultraviolet band is characterized using a synchrotron radiation source, enabling the controllable preparation of a film with an adjustable transmittance at a wavelength of 13.5 nm within the range of 90% to 99%.

[0015] The method for preparing the high-uniformity, high-strength single-walled carbon nanotube extreme ultraviolet lithography mask protective film, the high strength is specifically manifested in the following: the ability of the single-walled carbon nanotube film to withstand gas impact is evaluated by the pressure difference and gas flow rate on both sides of the film; when the transmittance of the film under 13.5 nm wavelength light is ≥90%, it can withstand a pressure difference >650 Pa and a flow rate >7 L / min.

[0016] The method for preparing the high-uniformity, high-strength single-walled carbon nanotube extreme ultraviolet lithography mask protective film is described above. As an ideal material that can effectively protect the mask and whose mechanical strength meets the requirements of extreme ultraviolet lithography devices, the high-uniformity, high-strength single-walled carbon nanotube extreme ultraviolet lithography mask protective film is suitable for the next generation of high-power extreme ultraviolet lithography machines.

[0017] The design concept of this invention is:

[0018] This invention employs floating catalyst chemical vapor deposition to grow single-walled carbon nanotube (SWCNT) films. After transferring the films to a hollow framework, a combination of solvent evaporation and drying is used to densify the films, resulting in a high-strength extreme ultraviolet (EUV) photolithography mask protective film. Specifically, the capillary force generated by the evaporation of the volatile organic solvent causes the carbon nanotube bundles to aggregate, effectively reducing porosity and voids between the carbon nanotube networks, significantly increasing the contact area between the bundles, thereby enhancing van der Waals interactions and promoting uniform stress distribution, thus significantly improving the load-bearing capacity.

[0019] Compared to conventional drying, the preferential evaporation of solvent from the surface leads to the formation of surface tension gradients, which can easily cause unevenness problems such as wrinkles, cracks, or the "coffee ring" effect in the film. This invention utilizes the simultaneous and rapid evaporation of solvent from both the interior and surface of the film, eliminating local tension differences and resulting in highly uniform capillary contraction forces acting on the entire carbon nanotube network. This uniform force forces the carbon nanotube bundles in all regions to contract synchronously and aggregate tightly, effectively avoiding localized loose or unevenly dense structures, ultimately obtaining a highly uniform and high-strength single-walled carbon nanotube extreme ultraviolet lithography mask protective film.

[0020] In summary, this invention achieves in-situ molecular-level assembly of single-walled carbon nanotubes through floating catalyst chemical vapor deposition, constructing an initial structure with overlapping and entanglement, laying the foundation for strength enhancement; the dry transfer technology, based on differences in adhesion forces, avoids film damage during the transfer process, ensuring the integrity of the self-supporting structure; the uniform densification process utilizes the capillary action of volatile solvents to eliminate surface tension gradients through synchronous evaporation, causing the carbon nanotube bundles to shrink and aggregate uniformly, improving density and strength while maintaining film uniformity.

[0021] The advantages and beneficial effects of this invention are:

[0022] 1. This invention utilizes in-situ molecular assembly technology to obtain intertwined and overlapping single-walled carbon nanotube base films, and uses a combination of solvent evaporation and drying to prepare highly uniform and high-strength single-walled carbon nanotube thin films.

[0023] 2. The preparation, transfer and post-processing process of this invention is simple, suitable for large-scale mass production, and can be adapted to hollow frames made of various materials such as metal, quartz and glass, with strong process compatibility.

[0024] 3. The present invention combines dry transfer and uniform densification, resulting in a film without wrinkles or "coffee ring" effect, low surface roughness, and excellent structural integrity.

[0025] 4. The high-strength, high-uniformity single-walled carbon nanotube film obtained by this invention can withstand a pressure difference of >650 Pa, a flow rate of >7 L / min, and a light transmittance uniformity of 3σ<1.5 under high transmittance (≥90%) of extreme ultraviolet light at a wavelength of 13.5 nm, thus meeting the performance requirements of the next generation of high-power extreme ultraviolet lithography machines for the protective film of the photomask.

[0026] 5. The method for preparing high-strength, high-uniformity single-walled carbon nanotube thin films developed in this invention has simple preparation, transfer and post-processing processes, and is expected to play an important role in the field of EUV lithography protective films, and promote the development of next-generation high-power EUV lithography technology. Attached Figure Description

[0027] Figure 1 This invention provides a schematic diagram of the fabrication process for a highly uniform and high-strength single-walled carbon nanotube thin film. In the diagram, 1-single-walled carbon nanotube thin film; 2-hollow frame; 3-sealed container; 4-solvent; 5-protective film of single-walled carbon nanotube extreme ultraviolet lithography mask.

[0028] Figure 2 (a) Optical photograph of SWCNT film collected on filter membrane by floating catalyst chemical vapor deposition; (b) Optical photograph of SWCNT film transferred to hollow stainless steel frame by dry method; (c) Optical photograph of SWCNT film after solvent evaporation and drying treatment.

[0029] Figure 3 (a) Scanning electron microscope (SEM) image of SWCNT thin films prepared by floating catalyst chemical vapor deposition (FCVD); (b) High-magnification transmission electron microscope (TEM) image of SWCNT thin films prepared by floating catalyst chemical vapor deposition (FCVD); (c) Scanning electron microscope (SEM) image of SWCNT thin films after solvent evaporation and drying.

[0030] Figure 4 Schematic diagram of the test principle for the performance of SWCNT thin film under the impact of flowing gas. In the figure, 5-protective film of single-walled carbon nanotube extreme ultraviolet lithography mask, 6-protective film of single-walled carbon nanotube extreme ultraviolet lithography mask after deformation, 7-support, 8-test chamber.

[0031] Figure 5 Figure: Performance of SWCNT film under flow gas impact after solvent evaporation and drying treatment.

[0032] Figure 6 (a) Graph of the performance of SWCNT film under the impact of flowing gas; (b) Typical optical photograph of Comparative Example 2; (c) Typical optical photograph of Comparative Example 3. Detailed Implementation

[0033] like Figure 1 As shown, this invention proposes a method for preparing a highly uniform and high-strength protective film for an extreme ultraviolet (EUV) lithography mask using single-walled carbon nanotubes. Single-walled carbon nanotubes are grown using a floating catalyst chemical vapor deposition method, and an interlocking single-walled carbon nanotube film 1 is formed through in-situ molecular assembly. The single-walled carbon nanotube film 1 is then dry-transferred onto a hollow frame 2 to form a self-supporting film. The resulting self-supporting film is then transferred to a sealed container 3 containing solvent 4 and suspended. A combination of solvent evaporation and drying is used to densify the single-walled carbon nanotube film 1. The capillary force from solvent evaporation enhances intertube interactions and reduces roughness, thereby significantly improving the mechanical strength and uniformity of the film. Finally, a single-walled carbon nanotube EUV lithography mask protective film 5 with both high uniformity and high strength is obtained. In this invention, dry transfer refers to the complete transfer mediated by van der Waals forces under conditions without liquid intervention, based on the difference in adhesion between the single-walled carbon nanotube film and the collecting filter membrane and hollow frame.

[0034] The present invention will now be described in further detail with reference to embodiments and accompanying drawings.

[0035] Example 1

[0036] In this embodiment, a method for preparing a highly uniform, high-strength single-walled carbon nanotube extreme ultraviolet lithography mask protective film is described, with the following specific steps:

[0037] (1) Under the protection of argon gas flow of 2000 sccm, the temperature of the reactor was first raised to 1200 ℃, with ferrocene as the catalyst precursor, ethylene as the carbon source, and thiophene as the growth promoter. The grown SWCNTs were in situ molecularly assembled at the tail end of the tubular furnace to form an intertwined and overlapping SWCNT film. Figure 2 Figure a shows an optical photograph of the SWCNT film collected after a deposition time of 10 min. The SWCNT film was then dry-transferred onto a stainless steel hollow frame. Figure 2 As shown in Figure b), a self-supporting SWCNT film was obtained.

[0038] (2) The self-supporting SWCNT film obtained in step (1) was transferred to a sealed container containing 50 ml of ethanol solvent and suspended for densification treatment for 24 h; after the solvent evaporated and dried, a dense, uniform, high-strength and self-supporting SWCNT film was obtained. Figure 2 (as shown in Figure c).

[0039] The microstructure of the SWCNT film prepared in step (1) was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images show that the SWCNT film ( Figure 3 Figure a) shows an image composed of intertwined carbon nanotube bundles. The carbon nanotube network is loose and porous with clean bundle surfaces. (High-magnification transmission electron microscopy image) Figure 3 Figure b in the figure shows that the grown carbon nanotubes are single-walled structures with a diameter of 1.6~3 nm. Further SEM observation of the SWCNT film after step (2) further revealed… Figure 3 As shown in Figure c), the carbon nanotube bundles are more tightly aggregated, and the pores and voids between the carbon nanotube networks are significantly smaller, indicating that the densification treatment effectively improves the compactness of the film.

[0040] The transmittance of the SWCNT thin film prepared in step (2) was measured at 550 nm using a visible light spectrophotometer, and was found to be 90.2%. After transmitting the transmittance at 10 random locations within the film, its uniformity (3σ) was calculated to be 1.2. Furthermore, synchrotron radiation testing revealed that the transmittance of the film at 13.5 nm reached 96.8%. Figure 4As shown, the single-walled carbon nanotube extreme ultraviolet lithography mask protective film 5 is fixedly encapsulated at the top opening of the test chamber 8 by a bracket 7. A gas control section is located on one side of the test chamber 8, and a pressure detection section is located on the other side. The gas control section consists of a gas flow controller and a gas input pipeline. One end of the gas input pipeline is connected to an external gas source, and the other end is connected to the test chamber 8. The pressure detection section includes internal and external pressure sensors. The internal pressure sensor is installed inside the test chamber 8, and the external pressure sensor is located in the external environment of the test chamber 8. In the performance test of the single-walled carbon nanotube extreme ultraviolet lithography mask protective film 5 under the impact of flowing gas, the gas flow rate entering the test chamber 8 is adjusted using the gas flow controller to make the internal gas pressure higher than the external atmospheric pressure, thereby causing film deformation (i.e., obtaining the deformed single-walled carbon nanotube extreme ultraviolet lithography mask protective film 6). Simultaneously, the pressure difference borne by the film is measured by the built-in internal and external pressure sensors. The greater the pressure difference, the higher the strength of the film. The data recording section is electrically connected to internal and external pressure sensors and gas flow controllers via a computer. The computer terminal receives and records real-time pressure difference and gas flow data, generating pressure-flow rate change curves to visually demonstrate the membrane's pressure-bearing capacity under different gas flow rates, until the membrane deforms or ruptures, thus determining its maximum withstand pressure difference and corresponding gas flow rate. Figure 5 As shown, the maximum pressure difference that the membrane can withstand is 729 Pa, at which point the gas flow rate is 7.5 L / min.

[0041] Example 2

[0042] In this embodiment, a method for preparing a highly uniform, high-strength single-walled carbon nanotube extreme ultraviolet lithography mask protective film is described, with the following specific steps:

[0043] (1) Step (1) is the same as step (1) in Example 1, except that the deposition time is 15 min.

[0044] (2) The self-supporting SWCNT film obtained in step (1) is transferred to a sealed container containing 50 ml of isopropanol solvent and suspended, and then densified for 48 h to obtain a high-strength and self-supporting SWCNT film.

[0045] SEM images show that the carbon nanotube bundles in the SWCNT film prepared in step (2) are more tightly aggregated, and the pores and voids between the carbon nanotube networks are significantly smaller.

[0046] The transmittance of the SWCNT film prepared in step (2) was tested using a visible light spectrophotometer at a wavelength of 550 nm, which was 86.6%, and the uniformity 3σ was 1.4. In addition, the transmittance of the film at a wavelength of 13.5 nm reached 90.3%. The flow gas impact performance of the SWCNT film was tested, and the maximum pressure difference that the film could withstand was 789 Pa and the gas flow rate was 8 L / min.

[0047] Example 3

[0048] In this embodiment, a high-strength single-walled carbon nanotube extreme ultraviolet lithography mask protective film is implemented using the following steps:

[0049] (1) Step (1) is the same as step (1) in Example 1, and the deposition time is 7 min.

[0050] (2) The self-supporting SWCNT film obtained in step (1) is transferred to a sealed container containing 50 ml of a mixed solvent of isopropanol and acetone and suspended in the air for densification treatment for 12 h. After this process, a high-strength and self-supporting SWCNT film is obtained.

[0051] SEM images show that the carbon nanotube bundles in the SWCNT film prepared in step (2) are more tightly aggregated, and the pores and voids between the carbon nanotube networks are significantly smaller.

[0052] The transmittance of the SWCNT film prepared in step (2) was 92.1% at a wavelength of 550 nm and the uniformity 3σ was 0.9, as measured by a visible light spectrophotometer. In addition, the transmittance of the film at a wavelength of 13.5 nm reached 97.4%. The flow gas impact performance of the SWCNT film was tested, and the maximum pressure difference that the film could withstand was 673 Pa and the gas flow rate was 7 L / min.

[0053] Comparative Example 1

[0054] In this comparative example, a protective film for a single-walled carbon nanotube extreme ultraviolet lithography mask is prepared using the following steps:

[0055] (1) Step (1) is the same as step (1) in Example 1.

[0056] (2) The transmittance of the SWCNT film prepared in step (1) was 90.8% at a wavelength of 550 nm, and its uniformity 3σ was 1.8, as measured by a visible light spectrophotometer. Furthermore, the transmittance of the film at a wavelength of 13.5 nm reached 96.9%. The SWCNT film was subjected to a flowing gas impact performance test, and the maximum pressure difference it could withstand was only 212 Pa. Figure 6(Figure a) shows a gas flow rate of 4.8 L / min. This demonstrates that densification can significantly improve the uniformity of transmittance and mechanical properties of single-walled carbon nanotube films.

[0057] Comparative Example 2

[0058] In this comparative example, a protective film for a single-walled carbon nanotube extreme ultraviolet lithography mask is prepared using the following steps:

[0059] (1) Step (1) is the same as step (1) in Example 1.

[0060] (2) The self-supporting SWCNT film obtained in step (1) is impregnated by spraying with ethanol solvent and then dried to obtain an impregnated and densified film.

[0061] like Figure 6 As shown in Figure b, the optical photograph of the prepared thin film reveals a "coffee ring" morphology on the film surface caused by uneven drying after impregnation. Because the spraying method causes the solvent to form countless tiny droplets on the film surface, and each droplet dries slowly, the solvent forms "island-like" aggregates before drying due to surface tension. The drying rate of these aggregated areas differs significantly from other areas, resulting in an uneven film.

[0062] The transmittance of the SWCNT film prepared in step (2) was 89.2% at a wavelength of 550 nm, and its uniformity 3σ was 3.4, as measured by a visible light spectrophotometer. Furthermore, the transmittance of the film reached 92.3% at a wavelength of 13.5 nm. The SWCNT film was subjected to flow gas impact performance testing, and the maximum pressure difference it could withstand was 432 Pa, with a gas flow rate of 5.5 L / min. This demonstrates that conventional densification strategies can slightly improve the mechanical properties of the film, but significantly reduce the uniformity of the film's transmittance.

[0063] Comparative Example 3

[0064] In this comparative example, a protective film for a single-walled carbon nanotube extreme ultraviolet lithography mask is prepared using the following steps:

[0065] (1) Step (1) is the same as step (1) in Example 1.

[0066] (2) The self-supporting SWCNT film obtained in step (1) is completely immersed in ethanol solvent and then dried to obtain an impregnated and densified film.

[0067] like Figure 6 As shown in Figure c, the optical photograph of the film prepared in step (2) shows that wrinkles occur on the surface of the film. This is because the densification process of the complete impregnation method allows a large amount of solvent to be impregnated into the film, which will aggravate the evaporation of the solvent during the drying process, resulting in more severe stress and uneven shrinkage inside the film.

[0068] The transmittance of the SWCNT film prepared in step (2) was 88.6% at a wavelength of 550 nm, and its uniformity 3σ was 3.8. Furthermore, the transmittance of the film reached 91.2% at a wavelength of 13.5 nm. The SWCNT film was subjected to flow gas impact performance testing, and the maximum pressure difference it could withstand was 468 Pa, with a gas flow rate of 5.8 L / min. This demonstrates that conventional densification strategies can slightly improve the mechanical properties of the film, but significantly reduce the uniformity of the film's transmittance.

[0069] The results of the examples and comparative examples show that growing SWCNT thin films using a floating catalyst chemical vapor deposition method, followed by transferring the films to a hollow framework, and then densifying the films using a combination of solvent evaporation and drying, effectively prevents uneven film formation caused by the dehumidification process in traditional impregnation and spray densification processes by controlling the concentration of evaporating solvent molecules and ensuring rapid drying before aggregation. The core of this invention lies in lowering the solvent boiling point through environmental means, allowing for gentle and uniform evaporation, thereby ensuring high uniformity in the film densification process. This solves a key bottleneck problem in the application of high-strength, uniform, self-supporting carbon nanotube-based extreme ultraviolet lithography mask protective films both domestically and internationally.

[0070] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a protective film for a single-walled carbon nanotube extreme ultraviolet lithography mask blank, characterized by, Single-walled carbon nanotubes (SUVs) were grown at 900℃~1300℃ using a floating catalyst chemical vapor deposition method. In-situ molecular-level assembly was performed based on the strong van der Waals forces induced by collisions between SUVs in aerosol form, resulting in interlocking and entangled SUV films. Based on the difference in adhesion between the SUV films and the collecting filter membrane and the target substrate or hollow frame, a dry transfer technique was used to completely transfer the SUV films onto the target substrate or hollow frame, forming self-supporting films. Densification of the films was achieved through a combination of organic solvent evaporation and drying. Specifically, the capillary forces generated by the evaporation of volatile organic solvents caused the carbon nanotube bundles to aggregate tightly, enhancing interactions and reducing roughness, resulting in a highly uniform and high-strength SUV extreme ultraviolet lithography mask protective film. During the evaporation of organic solvents, the capillary action generated at the liquid-gas interface causes the carbon nanotubes to shrink and tighten, promoting the tube bundles to move closer together and arrange more densely, and enhancing the van der Waals forces between the tube bundles; at the same time, by controlling the concentration of evaporating solvent molecules, they are dried rapidly before agglomeration.

2. The method of claim 1, wherein the single-walled carbon nanotube extreme ultraviolet lithography mask blank protective film is prepared by a method comprising: Single-walled carbon nanotubes were grown by floating catalyst chemical vapor deposition at a growth temperature of 1100℃~1200℃. Single-walled carbon nanotube films of different thicknesses were collected by adjusting the deposition time. The prepared single-walled carbon nanotubes are carbon nanotubes that are observed to consist of only a single layer of tube wall in transmission electron microscopy images. ​ 3. The method of claim 1, wherein the single-walled carbon nanotube extreme ultraviolet lithography mask blank protective film is prepared by a method comprising: The dry transfer process utilizes van der Waals forces to transfer a single-walled carbon nanotube film on a collector to a suspended target substrate or hollow frame. The target substrate or hollow frame is made of at least one of the following materials: metal, quartz, glass, polycrystalline silicon, alumina, graphite, indium tin oxide, polyethylene terephthalate, and polydimethylsiloxane. The metal includes Cu, Ti, Fe, Pt, Au, Ni, or Mo. ​ 4. The method of claim 1, wherein the single-walled carbon nanotube extreme ultraviolet lithography mask blank protective film is prepared by a method comprising: The organic solvent can be volatile ethanol, ethylene glycol, acetone or isopropanol, or a mixture of the above materials and deionized water. ​ 5. The method for preparing the protective film of the single-walled carbon nanotube extreme ultraviolet lithography mask according to claim 1, characterized in that, The high uniformity is specifically manifested in the following ways: at a wavelength of 550 nm, multi-point tests are conducted using a visible light spectrophotometer, and the uniformity is evaluated according to the 3σ standard deviation principle; when the transmittance of the protective film is ≥90%, the light transmittance uniformity 3σ < 1.5; in addition, the transmittance of the film in the extreme ultraviolet band is characterized using a synchrotron radiation source, enabling the controllable preparation of films with tunable transmittance at a wavelength of 13.5 nm within the range of 90% to 99%.

6. The method for preparing the protective film of the single-walled carbon nanotube extreme ultraviolet lithography mask according to claim 1, characterized in that, The high strength is specifically manifested in the ability of single-walled carbon nanotube films to withstand gas impacts, which is evaluated by the pressure difference and gas flow rate on both sides of the film. When the transmittance of the film under 13.5 nm wavelength light is ≥90%, it can withstand a pressure difference of >650 Pa and a flow rate of >7 L / min.

7. The method for preparing the protective film of the single-walled carbon nanotube extreme ultraviolet lithography mask according to claim 1, characterized in that, High-uniformity, high-strength single-walled carbon nanotube extreme ultraviolet lithography mask protective film is an ideal material that can effectively protect the mask and meet the mechanical strength requirements of extreme ultraviolet lithography devices, making it suitable for next-generation high-power extreme ultraviolet lithography machines.

Images