Nanotube film, pellicle film, pellicle, exposure original plate, exposure device, method for producing nanotube film, and method for evaluating nanotube film for exposure

Abstract

A nanotube film according to the present disclosure is a nanotube film including a plurality of nanotubes. The ratio of the total area of spots to the area of the main surface of the nanotube film is 7.00 × 10−4% or less. The spots have a luminance of 80% or less of a reference luminance and has an area of 50 μm2 or more in an observation image of an optical microscope on the main surface of the nanotube film. The size of one pixel of the observation image is 1.0 μm to 2.0 μm × 1.0 μm to 2.0 μm. The reference luminance is represented by formula (1).　Formula (1): Reference luminance = average value of luminance over the entire main surface of the nanotube film + 1 × luminance at the height of standard deviation σ of luminance over the entire main surface of the nanotube film

Description

Nanotube film, pellicle film, pellicle, exposure master, exposure device, nanotube film manufacturing method, and nanotube film evaluation method for exposure

[0001] The present disclosure relates to a nanotube film, a pellicle film, a pellicle, an exposure master, an exposure apparatus, a method for manufacturing a nanotube film, and a method for evaluating a nanotube film for exposure.

[0002] The manufacturing process of semiconductor devices includes a lithography process in which a semiconductor wafer is irradiated with light to form a pattern. In the lithography process, for example, a predetermined pattern formed on a photomask is irradiated with light (also referred to as "exposure light"), and the exposure light transmitted through or reflected by the photomask is imaged on the semiconductor wafer, thereby exposing a resist material on the semiconductor wafer to the predetermined pattern. In recent years, as exposure patterns have become increasingly finer, the use of shorter-wavelength EUV (Extreme Ultra Violet) light as exposure light has become more widespread, replacing DUV (Deep Ultra Violet) light.

[0003] In lithography processes, pellicles are used to prevent foreign matter from adhering to the pattern formed on the photomask. The pellicle is attached to the photomask to surround the pattern formed on the photomask. Typically, the pellicle comprises a support frame and a pellicle film. The support frame is arranged to surround the outside of the pattern area formed on the photomask. The pellicle film is stretched over the support frame.

[0004] Patent Document 1 discloses a pellicle film for exposure (hereinafter also referred to as "pellicle film"). The thickness of the pellicle film is 200 nm or less. The pellicle film includes a carbon nanotube film. The carbon nanotube film has bundles formed from a plurality of carbon nanotubes. The bundles have a diameter of 100 nm or less. In the carbon nanotube film, the bundles are oriented in-plane.

[0005] Patent Document 2 discloses a pellicle film for exposure (hereinafter also referred to as "pellicle film"). The pellicle film includes a carbon nanotube film (hereinafter also referred to as "CNT film"). The CNT film has a transmittance of 80% or more for EUV light at a wavelength of 13.5 nm. The CNT film has a thickness of 1 nm to 50 nm. The 3σ (variation) of the reflectance of the CNT film at a wavelength of 285 nm is 15% or less. σ indicates standard deviation. The 3σ of the reflectance is measured under specific conditions using a reflectance spectroscopic film thickness meter. A 3σ of the reflectance of the CNT film at a wavelength of 285 nm of 15% or less indicates that the CNT film has excellent local uniformity in a region including the measurement point.

[0006] Patent Document 1: International Publication No. 2018 / 008594 Patent Document 2: International Publication No. 2021 / 210432

[0007] Non-Patent Document 1: Marina Y. Timmermans et al., Carbon nanotube EUV pellicle tunability and performance in a scanner-like environment, J. Micro / Nanopattern. Mater. Metrol. Vol. 20(3) (2021) Non-Patent Document 2: BL Henke, EM Gullikson, and JC Davis. X-ray interactions: photoabsorption, scattering, transmission, and reflection at E=50-30000 eV, Z=1-92, Atomic Data and Nuclear Data Tables Vol. 54 (no.2), 181-342 (July 1993)

[0008] In response to the recent demand for higher-definition exposure patterns, there is a demand for nanotube films that can suppress the occurrence of exposure defects in the entire area where exposure light is irradiated to expose the resist material on the semiconductor wafer to the intended pattern formed on the photomask. "Exposure defects" refer to cases where the EUV light reflected by the photomask fails to expose the resist material on the semiconductor wafer to the intended pattern formed on the photomask.

[0009] In a lithography process using EUV light (hereinafter also referred to as the "EUV lithography process"), an optical system is designed so that EUV light emitted from a light source can be focused at a target location. Multiple light sources are used to emit EUV light 1. At the location where the EUV light 1 emitted from each of the multiple light sources is irradiated onto an irradiation target, the EUV light 1 is focused so that the surface S2 of a photomask 2 becomes a focal point FP, as shown in FIG. 1 . As a result, the EUV light 1 reflected by the photomask 2 exposes a resist material on a semiconductor wafer to a predetermined pattern. Hereinafter, the cone-shaped focused EUV light 1 will also be referred to as the "light cone 1." The numerical aperture (hereinafter also referred to as "NA") of the light cone 1 in the photomask is, for example, 0.0825, and the pellicle is positioned so that the distance L1 between the pellicle film 3 and the surface S2 of the photomask 2 is approximately 2.5 mm. In this example, the diameter L2 of the cross section of the light cone 1 on the main surface S3 of the pellicle film 3 (hereinafter also referred to as the "light cone cross section") is about 400 μm when the NA is 0.0825. The area of ​​the light cone cross section is 0.126 mm when the NA is 0.0825. ２ is.

[0010] In order to prevent exposure defects, the variation in the amount of light passing through each of the multiple light cone cross sections on the main surface S3 of the pellicle film 3 (hereinafter also referred to as "light amount variation") is required to be 0.4% or less (Non-Patent Document 1). However, it has not been easy to evaluate the light amount variation.

[0011] The present disclosure has been made in consideration of the above circumstances. A problem to be solved by one embodiment of the present disclosure is to provide a nanotube film, a pellicle film, a pellicle, an exposure master, and an exposure apparatus that can suppress the occurrence of exposure defects in the entire area irradiated with exposure light. A problem to be solved by another embodiment of the present disclosure is to provide a method for manufacturing a nanotube film that can manufacture a nanotube film that can suppress the occurrence of exposure defects in the entire area irradiated with exposure light. A problem to be solved by another embodiment of the present disclosure is to provide a method for evaluating a nanotube film for exposure that can more reliably evaluate the occurrence of exposure defects.

[0012] The above-mentioned means for solving the problems include the following embodiments: <1> A nanotube film including a plurality of nanotubes, wherein the ratio of the total area of ​​spots to the area of ​​the main surface of the nanotube film is 7.00 × 10 －４ % or less, and the spots have a brightness of 80% or less of the reference brightness in an image of the main surface of the nanotube film observed with an optical microscope, and ２ a nanotube film having an area of ​​1.0 μm to 2.0 μm×1.0 μm to 2.0 μm, wherein the size of one pixel of the observed image is 1.0 μm to 2.0 μm×1.0 μm to 2.0 μm, and wherein the reference brightness is expressed by the following formula (1): Formula (1): Reference brightness = average brightness of the entire main surface of the nanotube film + 1 × brightness at a height of standard deviation σ of the brightness of the entire main surface of the nanotube film <2> The nanotube is one selected from the group consisting of carbon nanotubes, boron nitride nanotubes, and transition metal disulfide nanotubes, and the transition metal disulfide nanotube contains a transition metal disulfide, and the transition metal disulfide is MX ２wherein M is at least one selected from Mo, W, Pd, Pt, and Hf, and X is at least one selected from S, Se, and Te. <3> The nanotube film according to <1> or <2>, wherein the number of spots is 200 or less. <4> The nanotube film according to any one of <1> to <3>, wherein the nanotubes have a tube diameter of 0.8 nm to 6.0 nm. <5> The nanotube film according to any one of <1> to <4>, wherein the film thickness is 2 nm to 100 nm. <6> The nanotube film according to any one of <1> to <5>, wherein the length of a main surface of the nanotube film in a first direction is 90 mm or more, and the length of a main surface of the nanotube film in a second direction perpendicular to the first direction is 90 mm or more. <7> A pellicle film made of the nanotube film according to any one of <1> to <6>. <8> A pellicle comprising the pellicle film according to <7> and a support frame supporting the pellicle film. <9> An exposure master comprising: a photomask; and the pellicle according to <8> attached to the photomask. <10> An exposure apparatus comprising: an extreme ultraviolet light source that emits extreme ultraviolet light as exposure light; the exposure master according to <9>; and an optical system that guides the exposure light emitted from the extreme ultraviolet light source to the exposure master, wherein the exposure master is positioned so that the extreme ultraviolet light emitted from the extreme ultraviolet light source passes through the pellicle film and irradiates the photomask. <11> A method for producing a nanotube membrane according to any one of <1> to <6>, comprising: preparing a raw material containing a plurality of nanotubes; mixing the plurality of nanotubes with a solvent to prepare a dispersion; centrifuging the dispersion to prepare a separated liquid; and forming the separated liquid into a sheet-like membrane to produce a nanotube membrane, wherein the centrifugal separation is performed two or more times. <12> The method for producing a nanotube membrane according to <11>, wherein an average relative centrifugal force of the centrifugal separation is 200 x g or more.<13> The method for manufacturing a nanotube film according to <11> or <12>, wherein the nanotube film is used as a pellicle film. <14> A method for evaluating a nanotube film for exposure, comprising: preparing an NT film (a) representing a nanotube film having a reference thickness and a plurality of nanotube films having thicknesses different from that of the NT film (a), deriving ΔEUVT(t) as the difference between EUVT(a) representing the transmittance of extreme ultraviolet light through the NT film (a) and EUVT(t) representing the transmittance of extreme ultraviolet light of each of the plurality of nanotube films from the following formula (i), measuring the luminance of each of the plurality of nanotube films, and deriving an allowable relationship between an allowable speckle area Ap and an allowable speckle luminance by applying the relationship between ΔEUVT(t) and the measured value of the luminance of the nanotube film corresponding to the ΔEUVT(t) to the following formula (ii): (In formula (ii), NA represents the numerical aperture of the photomask when the pellicle, which has the nanotube film attached to a pellicle frame, is attached to the photomask. L1 represents the distance between the nanotube film of the pellicle and the photomask. R represents the range of error that is acceptable for variations in light intensity.) <15> A method for evaluating a nanotube film for exposure according to <14>, comprising: measuring the brightness and area of ​​spots on the nanotube film to be evaluated; and comparing the relationship between the measured brightness and area of ​​the spots on the nanotube film to be evaluated and the acceptable relationship. <16> The method for evaluating a nanotube film for exposure according to <15>, wherein the comparing comprises: comparing a measured value of the area of ​​the speckle on the nanotube film to be evaluated with a maximum value of the area Ap corresponding to a measured value of the brightness of the speckle on the nanotube film to be evaluated in the tolerance relationship; determining that there is an exposure defect if there is a speckle whose measured value of the area of ​​the speckle is greater than the maximum value, and determining that there is no exposure defect if there is no speck whose measured value of the area of ​​the speckle is greater than the maximum value. <17> The method for evaluating a nanotube film for exposure according to any one of <14> to <16>, wherein the thickness of the NT film (a) is thinner than the thickness of each of the plurality of nanotube films, and the method comprises measuring the thickness of the NT film (a) and each of the plurality of nanotube films. <18> The method for evaluating a nanotube film for exposure according to any one of <14> to <16>, wherein the NT film (a) has a thickness smaller than the thickness of each of the plurality of nanotube films, measuring the EUVT(a) and the EUV transmittance of each of the plurality of nanotube films, and correlating ΔEUV(t) of a nanotube film having a comparative thickness with the luminance of the nanotube film having a comparative thickness.<19> Measuring the brightness and speckle area of ​​a nanotube film to be evaluated; and comparing a relationship between the measured brightness of the speckles of the nanotube film to be evaluated and the measured area of ​​the speckles with an acceptable relationship between an acceptable speck area Ap and an acceptable brightness of the speckles, wherein the acceptable relationship is obtained by applying the relationship between ΔEUVT(t) and the measured brightness of the nanotube film corresponding to the ΔEUVT(t) to the following formula (ii), and the ΔEUVT(t) is obtained by deriving ΔEUVT(t), which is the difference between EUVT(a) and EUVT(t), from the following formula (i), and the EUVT(a) represents the transmittance of extreme ultraviolet light through an NT film (a) representing a nanotube film having a reference thickness, The method for evaluating a nanotube film for exposure, wherein the EUVT(t) indicates the transmittance of extreme ultraviolet rays of each of a plurality of nanotube films having a thickness different from that of the NT film (a). (In formula (ii), NA represents the numerical aperture of the photomask when the pellicle, which is formed by attaching the nanotube film to a pellicle frame, is attached to the photomask. L1 represents the distance between the nanotube film of the pellicle and the photomask. R represents the allowable error range for variations in light intensity.)

[0013] According to one embodiment of the present disclosure, there may be provided a nanotube film, a pellicle film, a pellicle, an exposure master, and an exposure apparatus that are capable of suppressing the occurrence of exposure defects in the entire region irradiated with exposure light. According to another embodiment of the present disclosure, there may be provided a nanotube film manufacturing method that is capable of manufacturing a nanotube film that is capable of suppressing the occurrence of exposure defects in the entire region irradiated with exposure light. According to another embodiment of the present disclosure, there is provided a method for evaluating a nanotube film for exposure that is capable of more reliably evaluating the occurrence of exposure defects.

[0014] FIG. 1 is a diagram for explaining the focusing of EUV light onto a photomask. FIG. 2 is a graph showing the relationship between ΔEUVT and the brightness of a pellicle film. FIG. 3 is a graph showing the relationship between the allowable brightness of a speck and the allowable area of ​​a speck. FIG. 4 is a diagram showing a model of an air layer / NT film layer / silicon substrate. FIG. 5 is a graph plotting the relationship between reflectance and film thickness when the reflectance at a wavelength of 285 nm and film thickness were measured using the above-mentioned method for a sample in which an uneven NT film was transferred onto a silicon substrate. FIG. 6 is a photograph showing an example of a speck. FIG. 7 is a photograph showing an example of a speck. FIG. 8 is a graph showing the measurement results of the speck area versus the measurement results of the speck brightness in Examples 1-1 and 2-1. FIG. 9 is a graph showing the measurement results of the speck area versus the measurement results of the speck brightness in Examples 1-2 and 2-2. Fig. 10 is a graph showing the measurement results of the area of ​​spots versus the measurement results of the brightness of the spots in Comparative Example 1-1 and Example 2-3. Fig. 11 is a graph showing the measurement results of the area of ​​spots versus the measurement results of the brightness of the spots in Comparative Example 1-2 and Example 2-1.

[0015] In this disclosure, numerical ranges indicated using "to" mean ranges that include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in numerical ranges described in this disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the Examples. In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In this disclosure, when multiple substances corresponding to each component are present, the amount of each component refers to the total amount of the multiple substances unless otherwise specified. In this specification, the term "process" includes not only independent processes, but also processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. In this disclosure, "extreme ultraviolet radiation" (hereinafter also referred to as "EUV") refers to light with a wavelength of 1 nm or more and 30 nm or less. The wavelength of EUV light is preferably 5 nm to 13.5 nm.

[0016] Hereinafter, a pellicle case, a pellicle container, and a pellicle inspection method according to an embodiment of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0017] Claim 1 (1) Nanotube film The nanotube film (hereinafter also referred to as "NT film") of the present disclosure is a nanotube film containing a plurality of nanotubes (hereinafter also referred to as "NT"). The ratio of the total area of ​​specks to the area of ​​the main surface of the nanotube film (hereinafter also referred to as "speckle ratio") is 7.00 × 10 －４ The speckles have a brightness of 80% or less of the reference brightness in an image of the main surface of the nanotube film observed with an optical microscope, and are 50 μm or less. ２ The size of one pixel of the observed image is 1.0 μm to 2.0 μm×1.0 μm to 2.0 μm. The reference brightness is expressed by the following formula (1): Formula (1): Reference brightness = average value of brightness over the entire main surface of the nanotube film + 1 × brightness at height of standard deviation σ of brightness over the entire main surface of the nanotube film

[0018] The speckle rate is measured in the same manner as described in the Examples.

[0019] The nanotube film of the present disclosure, having the above-described configuration, can suppress the occurrence of exposure defects in the entire region irradiated with exposure light. This effect is presumably due to, but not limited to, the following reasons. A description will be given below with reference to FIG. 1 . Spots of a specific thickness may be present in a very small number in the entire region irradiated with exposure light. The spots may inhibit the transmission of the light cone 1 through the pellicle film 3. The presence of spots that inhibit the transmission of the light cone 1 through the pellicle film 3 may result in a light intensity variation of more than 0.4%. In other words, exposure defects may occur. For example, when observing with an optical microscope, if spots with a dark color that does not transmit light are present, the light intensity variation is likely to exceed 0.4%, even if the area of ​​the spots is relatively small. When observing with an optical microscope, if spots with a color that is relatively lighter than the dark color are present, the light intensity variation is likely to exceed 0.4%, even if the area of ​​the spots is relatively large. In order to reduce the light intensity variation to 0.4% or less, it is necessary for the very few specks that may exist in the entire area irradiated with exposure light to satisfy certain conditions. Whether specks satisfy certain conditions can be determined using a judgment curve. The judgment curve shows the relationship between the brightness of specks that reduce the light intensity variation to 0.4% and the area of ​​the specks. Specifically, in order to suppress the occurrence of exposure defects, when specks observed with an optical microscope have a specific brightness, the area of ​​the specks must be equal to or less than the area at that specific brightness on the judgment curve. Details of the judgment curve will be described later. When the speckle ratio of an NT film is 7.00 x 10 －４ % or less indicates that even the slightest specks that may exist in the entire area irradiated with the exposure light satisfy the above-mentioned certain condition. As a result, it is presumed that the nanotube film of the present disclosure can suppress the occurrence of exposure defects in the entire area irradiated with the exposure light.

[0020] It should be noted that the sensitivity of the measurement of reflectance at a wavelength of 285 nm described in Patent Document 1 may decrease for film thicknesses of 30 nm or more, and therefore the reflection spectroscopic film thickness meter may not be able to detect spots.

[0021] (1.1) Judgment Curve The above-mentioned judgment curve will be described below with reference to Figures 1 to 3 when the pellicle film 1 is a carbon nanotube film (hereinafter also referred to as a "CNT film"). The CNT film contains carbon nanotubes (hereinafter also referred to as "CNT").

[0022] As mentioned above, in order to prevent exposure failure, it is required that the variation in the amount of light passing through each of the multiple light cone cross sections on the main surface S3 of the pellicle film 1 be 0.4% or less (Non-Patent Document 1).

[0023] It is known that the relationship between film thickness t (nm) and EUV transmittance (%) (hereinafter also referred to as "EUVT (%)") is shown in the following formula (I) (Non-Patent Document 2). The calculated values ​​of EUV transmittance with respect to the film thickness t of the CNT film using formula (I) are shown in Table 1.

[0024]

[0025]

[0026] For the pellicle film 1, the difference ΔEUVT between the EUV transmittance EUVTav of the average portion and the EUV transmittance EUVTp of the region containing spots (hereinafter also referred to as the "spot region") is expressed by the following formula (II). Whether or not a region contains spots is determined by observation with an optical microscope. When the film thickness t (nm) is 25 nm, "EUVav" in formula (II) is 91.5%.

[0027]

[0028] The relationship between film thickness and brightness can be obtained from a calibration curve that shows the relationship between film thickness and brightness. The calibration curve is created by creating samples with different film thicknesses and measuring the brightness by microscopic observation.

[0029] When the reduction in the amount of light transmitted through the area of ​​the light cone cross section on the main surface S3 of the pellicle film 3 is 0.4%, the area Ap (μm２ The relationship between ΔEUVT (%) and ΔEUVT (%) is expressed by the following formula (III): "Reduction in light amount" refers to the reduction in the amount of light relative to the total amount of light passing through each of multiple light cone cross sections on the main surface S3 of the pellicle film 1 in a spot-free area.

[0030]

[0031] If the distance L1 from the surface S2 of the photomask 2 to the pellicle film 3 is 2.5 mm and the NA of the light cone 1 on the semiconductor wafer is 0.33 (i.e., the NA on the photomask is 0.0825), and if a spot that satisfies the following formula (IV) exists within the cross section of the light cone, the reduction in light intensity at the cross section of the light cone will be 0.4%. Therefore, formula (III) shows the threshold value at which exposure failure may occur.

[0032]

[0033] 542 [μm of the molecule in formula (III) ２ ] is the cross-sectional area of ​​the light cone when the NA of the light cone 1 is 0.33 (i.e., the area of ​​a diameter of about 200 μm (125,600 μm ２ When the transmittance of the spot is 0% (i.e., when ΔEUVT is 100%), Ap is 542 μm ２ When ΔEUVT is 50%, Ap is 1084 μm ２ Ap and ΔEUV are inversely proportional to each other. Therefore, formula (III) is derived as a relational expression in which 542, which is the area of ​​0.4% corresponding to the reduction in the amount of light, is used as the numerator and ΔEUVT (%) is used as the denominator.

[0034] By substituting the relational expression between ΔEUVT and luminance into the above formula (III) (i.e., the relational expression between Ap and ΔEUVT), the following formula (V) is obtained. Formula (V) is a judgment curve. Formula (V) is a relationship between luminance corresponding to a 0.4% reduction in the amount of light and the area of ​​spots Ap (μm ２ ) is shown. When the judgment curve is a relational expression between Ap and the brightness of spots, the presence or absence of exposure defects can be evaluated more cheaply, quickly, and with higher resolution than when the judgment curve is a relational expression between Ap and ΔEUVT.

[0035]

[0036] In formula (IV), α and β represent numerical values ​​and can be derived by exponential approximation as in formula (IV). For example, α is 465 and β is 0.0196. S represents the brightness of spots corresponding to a 0.4% reduction in light intensity.

[0037] When the distance L1 from the surface S2 of the photomask 2 to the pellicle film 3 is 2.5 mm and the NA of the light cone 1 on the semiconductor wafer is 0.33 (i.e., when the NA on the photomask is 0.0825), if there are spots that satisfy the following formula (VI) within the cross section of the light cone, the reduction in light intensity at the cross section of the light cone will be 0.4%.

[0038]

[0039] It should be noted that, in the above, formulas (III) to (VI) have been described for the case where the distance L1 from the surface S2 of the photomask 2 to the pellicle film 3 is 2.5 mm and the NA of the light cone 1 is 0.33. However, if L1 and the NA change, formulas (V) and (VI) can be derived in the same manner except for replacing formulas (III) and (IV) with the concept of formula (VII) below, thereby deriving the relationship between the area of ​​spots where the light intensity reduction in the cross section of the light cone is 0.4% or more and the brightness to be determined.

[0040]

[0041] In formula (VII), π represents the ratio of the circumference of a circle to its diameter.

[0042] (1.1.1) Judgment method using a judgment curve The NT membrane is illuminated, the entire area of ​​the NT membrane is photographed, and the luminance of each pixel is observed to judge the judgment area. In detail, the luminance obtained by taking an image of the entire area of ​​the NT membrane and the standard deviation σ of the luminance of each pixel is calculated as (average luminance + 1 × σ) × 0.8, and this is defined as the "reference luminance." Pixels with a luminance below this reference luminance are judged to be "speckles." If the area of ​​the speckles is 50 μm ２The area where the value is equal to or greater than this is defined as a speckle area. By comparing each observable speckle area with the judgment curve derived by formula (VI), the presence or absence of poor exposure can be evaluated based on whether the low brightness and the area size of the speckle area are positioned above the judgment curve. Speckles where the low brightness and the area size of the speckle area are positioned above the judgment curve are also called "NG speckles."

[0043] The "entire NT film region" may refer to the entire region irradiated with exposure light to expose the resist material on the semiconductor wafer to the desired pattern formed on the photomask. The entire NT film region can be appropriately adjusted depending on the portion of the free-standing film portion that is not irradiated with exposure light to expose the resist material to the desired pattern formed on the photomask. The "free-standing film portion" refers to the portion of the nanotube film that does not overlap with the support frame when the pellicle is viewed from the thickness direction of the nanotube film. The entire NT film region may be, for example, a region inside a position 7 mm away from the boundary between the free-standing film portion and the support frame toward the free-standing film portion (i.e., inward). The entire NT film region may be a region inside a position 6 mm away from the boundary between the free-standing film portion and the support frame toward the free-standing film portion (inward). The entire NT film region may be a region inside a position 5 mm away from the boundary between the free-standing film portion and the support frame toward the free-standing film portion (inward). If the support frame is a rectangular pellicle frame, the entire area of ​​the NT film may be an area inside a location 6 mm away from the boundary between the free-standing film portion and the long side of the pellicle frame toward the free-standing film portion (inward), and an area inside a location 4 mm away from the boundary between the free-standing film portion and the short side of the pellicle frame toward the free-standing film portion (inward). If this does not correspond to the entire area where exposure light is irradiated to expose the resist material on the semiconductor wafer to the desired pattern formed on the photomask, the presence or absence of evaluation may be changed depending on the location.

[0044] (1.2) Spots The proportion of the spotted area is 7.00 x 10 －４ From the viewpoint of further suppressing the occurrence of exposure defects, the proportion of the spotted area is preferably 0.600×10 －４% or less. The closer the speckled area ratio is to 0%, the more preferable. The speckled area ratio may be 0%.

[0045] The number of the speckled regions is preferably 200 or less. This makes it possible to further suppress the occurrence of exposure defects compared to when the number of speckled regions exceeds 200. From the viewpoint of further suppressing the occurrence of exposure defects, the number of speckled regions is more preferably 20 or less. The closer the number of speckled regions is to 0, the more preferable it is. The number of speckled regions may be 0.

[0046] (1.3) Shape The NT membrane is a sheet-like object. The shape of the NT membrane is not particularly limited and may be appropriately selected depending on the application of the NT membrane. Examples of the shape of the NT membrane include rectangular (e.g., rectangular, square, etc.), circular, and elliptical.

[0047] The length of the main surface of the NT film in the first direction and the length of the main surface of the nanotube film in the second direction perpendicular to the first direction are not particularly limited and are appropriately selected depending on the application of the NT film. It is preferable that the length of the main surface of the nanotube film in the first direction is 90 mm or more, and the length of the main surface of the nanotube film in the second direction perpendicular to the first direction is 90 mm or more. This allows the NT film of the present disclosure to expose a larger area than when each of the lengths in the first and second directions is less than 90 mm. The length in the first direction may be 100 mm or more. The length in the first direction may be 300 mm or less, or may be 200 mm or less. The length in the first direction may be 90 mm to 300 mm. The length in the second direction may be the same as the example length in the first direction. The length in the second direction may be the same as or different from the length in the first direction.

[0048] (1.4) Film Thickness The film thickness of the NT film is not particularly limited and is selected appropriately depending on the application of the NT film, etc. The film thickness of the NT film is preferably 2 nm to 100 nm. This makes it easier for the NT film of the present disclosure to ensure the transmittance of EUV light while preventing damage to the NT film and preventing foreign matter from adhering to the photomask, compared to when the film thickness is outside the range of 2 nm to 100 nm. From the viewpoint of preventing damage to the NT film and preventing foreign matter from adhering to the photomask, the film thickness of the NT film is more preferably 3 nm or more, even more preferably 4 nm or more, and particularly preferably 6 nm or more. From the viewpoint of increasing the transmittance of EUV light, the film thickness of the NT film may be 100 nm or less, or may be 80 nm or less.

[0049] (1.4.1) Film Thickness Measurement Method The thickness of the NT film can be obtained by measuring the reflectance using a spectroscopic film thickness meter. However, the conditions for measuring the reflectance are as follows: <Conditions> Diameter of the measurement point: 20 μm When the film thickness is less than 40 nm: Measurement wavelength: Wavelength 200 nm to 600 nm (wavelength interval: 1.3 nm to 1.5 nm) When the film thickness is 40 nm or more: Measurement wavelength: Wavelength 300 nm to 1000 nm (wavelength interval: 1.3 nm to 1.5 nm)

[0050] The film thickness at each measurement point is calculated using the method described below in "Method for converting to film thickness (optical thickness)." The film thickness at each measurement position is also calculated. The value obtained by calculating the average film thickness at each measurement position is designated as the "NT film thickness." Similarly, the σ of the film thickness at each measurement position is calculated from the standard deviation of the film thickness at each measurement point.

[0051] In measuring the film thickness, the method for detecting reflected light is not particularly limited. A photodiode, a photomultiplier tube, or the like may be used to measure the film thickness. A multichannel detector (e.g., a photodiode array, a CCD (Charge Coupled Device), or the like) may be used to measure the film thickness. By detecting the dispersed reflected light with a photodiode array, it is possible to obtain reflectance at multiple wavelengths. The pixel size of the CCD detector may be adjusted to about 50 μm to 100 μm to measure the distribution of reflected light intensity.

[0052] (1.4.1.1) Method of Conversion to Film Thickness (Optical Thickness) First, an NT film is placed on a silicon substrate, and the diagonal of the placed NT film is taken as the X-axis. When placing the NT film on the silicon substrate, the silicon substrate and the NT film are tightly adhered to each other without any gaps. By sandwiching a solvent (e.g., water, an organic solvent, etc.) between the silicon substrate and the NT film and then drying the solvent, the silicon substrate and the NT film can be tightly adhered to each other without any gaps. For example, the NT film floating on the water surface can be scooped up with the silicon substrate and then dried. Placing the NT film on the silicon substrate with the solvent and drying it can tightly adhere the silicon substrate and the NT film to each other. When a pellicle film is attached to a support frame, the NT film can also be placed on the silicon substrate by preparing a silicon substrate wetted with a solvent or the like and contacting the portion of the NT film corresponding to the free-standing film region (i.e., the region not in contact with the support frame) with the silicon substrate. The size of the silicon substrate is not particularly limited. The silicon substrate is preferably a silicon wafer having a size of 8 inches or more, from the viewpoint of closely adhering the NT film over a wide area.

[0053] As a reflectance measuring device, for example, a microspectrophotometer (for example, OPTM, model A-1, manufactured by Otsuka Electronics Co., Ltd.) may be used. As a lens, for example, a reflective 10x lens may be used. As a device for adjusting the diameter of the measurement point, for example, an aperture with a diameter of 200 μm (diameter of measurement point: 20 μm) may be used. An aluminum substrate may be used as a reference for measuring reflection intensity. The reflectance Rs(λ) is calculated by the following formula:

[0054]

[0055] Here, I ｓ (λ) represents the reflection intensity of the NT film on the silicon substrate at wavelength λ. ｒｅｆ (λ) represents the reflection intensity of the reference. ｒｅｆ (λ) represents the absolute reflectance of the reference. When an aluminum substrate is used as the reference, the optical constants of aluminum are known, so R ｒｅｆ(λ) can be calculated. Note that the gain, exposure time, etc. are the same conditions in measuring the reflection intensity of the reference and the NT film on the silicon substrate. This allows the absolute reflectance of the NT film on the silicon substrate to be obtained.

[0056] For each measurement point, a reflectance spectrum is obtained in the wavelength range of 200 nm to 600 nm, with wavelength intervals ranging from 1 nm to 2 nm. Then, using the optical constants (refractive index: n, extinction coefficient: k) shown in Table 2 as the optical constants of the NT film, and a three-layer model of air layer / NT film layer / silicon substrate, the reflectance spectrum in the wavelength range of 225 nm to 500 nm is analyzed by the least squares method to calculate the film thickness at each measurement point. The film thickness at a "measurement position" is the average film thickness at each of the 121 measurement points included in the "measurement position." The method for calculating the film thickness at each measurement point by analyzing the reflectance spectrum in the wavelength range of 225 nm to 500 nm by the least squares method is described below.

[0057] The film thickness is calculated using the following relational expressions (a) to (c) using a three-layer model of air layer / NT film layer / silicon substrate. Note that Fig. 4 is a schematic diagram showing the air layer / NT film layer / silicon substrate model.

[0058] Reflectance R ｓ is the amplitude reflectance r ｓ is expressed by the following formula (a) using

[0059]

[0060] In the above formula (a), * represents a complex conjugate.

[0061] Amplitude reflectance r from the three layers of air layer / NT film layer / silicon substrate ｓ is expressed by the following formula (b).

[0062]

[0063] In the above formula (b), r ０１ represents the amplitude reflectance from the interface between the air layer and the NT film layer. １２represents the amplitude reflectance from the interface between the NT film layer and the silicon substrate. i represents the imaginary unit. In the above formula (b), δ is the phase difference that occurs when light of wavelength λ makes one round trip within the film, and is expressed by the following formula (c):

[0064]

[0065] In the above formula (c), d represents the film thickness, N represents the complex refractive index (N=n−ik), φ represents the angle of incidence, and i represents the imaginary unit.

[0066] The film thickness can be obtained by calculating using the relationship of the above formulas (a) to (c) by the least squares method with the film thickness d as a variable for the reflectance Rs in the wavelength range of 225 nm to 500 nm.

[0067] Fig. 5 is a graph plotting the relationship between reflectance and film thickness when the reflectance and film thickness at a wavelength of 285 nm were measured using the above-mentioned method for a sample in which a non-uniform NT film was transferred onto a silicon substrate. As shown in Fig. 5, the above-mentioned method allows the difference in film thickness to be accurately determined from the reflectance value.

[0068]

[0069] (1.5) Nanotubes NTs may be single-walled nanotubes (hereinafter also referred to as "single-walled NTs") or multi-walled nanotubes (hereinafter also referred to as "multi-walled NTs").

[0070] In this disclosure, "single-walled nanotubes" refer to single-walled nanotubes, and "multi-walled nanotubes" refer to multi-walled nanotubes.

[0071] A plurality of NTs usually form a bundle. The number of NTs forming a bundle is 3 or more, preferably 4 to 100, and more preferably 5 to 50. The NT membrane may also contain NTs that are not formed into bundles.

[0072] The tube diameter of the NTs (i.e., the width of the NTs) is not particularly limited, but is preferably 0.8 nm to 6.0 nm. This allows the NT membrane of the present disclosure to form stronger bundles and thus a tougher membrane than when the NT tube diameter is outside the range of 0.8 nm to 6.0 nm. From the viewpoint of membrane strength, the tube diameter of the NTs is preferably 0.9 nm or more, more preferably 1.0 nm or more. From the viewpoint of membrane strength, the tube diameter of the NTs is preferably 5.0 nm or less, more preferably 5.5 nm or less.

[0073] The length of the NTs is preferably 10 nm or more. When the length of the NTs is 10 nm or more, the NTs are well entangled with each other, and the mechanical strength of the NT film is excellent. The length of the NTs is preferably 10 cm or less, more preferably 1 cm or less, and even more preferably 100 μm or less. From these viewpoints, the length of the NTs is preferably 10 nm to 10 cm, more preferably 10 nm to 1 cm, and even more preferably 10 nm to 100 μm.

[0074] The outer diameter and length of the tubes of the NTs are the arithmetic mean values ​​measured for 20 or more carbon materials (primary particles) by electron microscope observation, which may be a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0075] The number of NTs contained in the NT pellicle film is not particularly limited. The NT pellicle film preferably contains a number of nanotubes, and the nanotubes are preferably one selected from the group consisting of carbon nanotubes, boron nitride nanotubes, and transition metal disulfide nanotubes. The transition metal disulfide nanotubes contain a transition metal disulfide. The transition metal disulfide is preferably MX ２ M is at least one selected from the group consisting of Mo, W, Pd, Pt, and Hf, and X is at least one selected from the group consisting of S, Se, and Te.

[0076] The nanotubes preferably include carbon nanotubes, and are preferably carbon nanotubes. CNTs have high mechanical strength. When the NTs are CNTs, the mechanical strength of the NT pellicle film is superior to that of NT pellicle films made of SiN, polysilicon, or the like.

[0077] The transition metal disulfide nanotubes may be composed of a transition metal disulfide. The transition metal disulfide may be MoS ２ , MoSe ２ , W.S. ２ or WSe ２ It may be.

[0078] (1.6) Applications Applications of the NT film of the present disclosure are not particularly limited, and examples thereof include a pellicle film, a foreign matter filter in an exposure machine, and a conductive thin film.

[0079] (2) Pellicle Membrane The pellicle membrane of the present disclosure is made of the nanotube membrane of the present disclosure. The pellicle membrane of the present disclosure includes the NT membrane of the present disclosure, and therefore exhibits the same effects as the NT membrane of the present disclosure.

[0080] (3) Pellicle The pellicle of the present disclosure includes the pellicle membrane of the present disclosure and a support frame that supports the pellicle membrane. The pellicle of the present disclosure includes the NT membrane of the present disclosure, and therefore exhibits the same effects as the NT membrane of the present disclosure.

[0081] The support frame is cylindrical. The support frame has an end face (hereinafter referred to as the "pellicle membrane end face") on one side in the thickness direction. The NT membrane may be fixed to the pellicle membrane end face via an adhesive layer. The adhesive constituting the adhesive layer is not particularly limited, and examples thereof include acrylic resin adhesives, epoxy resin adhesives, polyimide resin adhesives, silicone resin adhesives, inorganic adhesives, double-sided adhesive tapes, polyolefin adhesives, and hydrogenated styrene adhesives. The concept of adhesive includes not only adhesives but also pressure-sensitive adhesives. The thickness of the adhesive layer is, for example, 10 μm to 1 mm.

[0082] (3.1) Support Frame The support frame has exposure through-holes, which represent spaces through which light transmitted through the NT film passes to reach the photomask.

[0083] The shape of the support frame in the thickness direction of the support frame is, for example, a rectangle. The rectangle may be a square or an oblong.

[0084] The support frame may have a vent hole formed, for example, in a side surface of the support frame. When the support frame is attached to the photomask, the vent hole communicates the internal space of the pellicle with the external space of the pellicle.

[0085] The rectangular support frame has four sides when viewed in the thickness direction. The length of one longitudinal side is preferably 200 mm or less. The size of the support frame is standardized depending on the type of exposure apparatus. A length of one longitudinal side of the support frame of 200 mm or less satisfies the standardized size for EUV exposure. The length of one lateral side is preferably 5 mm to 180 mm, more preferably 80 mm to 170 mm, and even more preferably 100 mm to 160 mm. The height of the support frame (i.e., the length of the support frame in the thickness direction) is preferably 3.0 mm or less, more preferably 2.4 mm or less, and even more preferably 2.375 mm or less. This allows the support frame to satisfy the standardized size for EUV exposure. The height of the support frame standardized for EUV exposure is, for example, 2.375 mm. The mass of the support frame is not particularly limited, but is preferably 20 g or less, more preferably 15 g or less. This makes the support frame suitable for use in EUV exposure.

[0086] The material of the support frame is not particularly limited, and examples thereof include quartz glass, metal, carbon-based material, resin, silicon, and ceramic-based material. The metal may be a pure metal or an alloy. A pure metal is made of a single metal element. Examples of pure metals include aluminum and titanium. An alloy is made of multiple metal elements, or a metal element and a non-metal element. Examples of alloys include stainless steel, magnesium alloy, steel, carbon steel, and invar. Examples of resins include polyethylene. Examples of ceramic-based materials include silicon nitride (SiN), silicon carbide (SiC), and alumina (Al ２ O ３ ) etc.

[0087] The structure of the support frame may be a single item or an assembly. A single item is obtained by carving out a single raw material plate. An "assembly" is an item in which multiple components are integrated. Methods for integrating multiple components include using a known adhesive or using fastening parts. Fastening parts include bolts, nuts, screws, rivets, or pins. When the support frame is an assembly, the multiple components may be made of different materials.

[0088] (3.2) Adhesive Layer The pellicle may further include an adhesive layer. The adhesive layer enables the pellicle to be adhered to a photomask. The support frame has an end face (hereinafter referred to as the "photomask end face") on the other side in the thickness direction. The adhesive layer is formed on the photomask end face. The adhesive layer is a soft, gel-like solid. The adhesive layer preferably has fluidity and cohesion. "Fluidity" refers to the property of contacting and wetting the adherend, the photomask. "Cohesion" refers to the property of resisting peeling from the photomask. The adhesive layer is made of an adhesive resin. Examples of adhesive resins include, but are not limited to, acrylic adhesives, silicone adhesives, styrene adhesives, urethane adhesives, and olefin adhesives. The thickness of the adhesive layer is not particularly limited and is preferably 10 μm to 500 μm.

[0089] (4) Exposure Master The exposure master of the present disclosure includes a photomask and the pellicle of the present disclosure attached to the photomask. Since the exposure master of the present disclosure includes the pellicle of the present disclosure, it exhibits the same effects as the pellicle of the present disclosure.

[0090] The method for attaching the photomask to the pellicle is not particularly limited, and examples include a method using the adhesive layer described above, a method using a fastening part, and a method utilizing the attractive force of a magnet or the like.

[0091] The photomask has a support substrate, a reflective layer, and an absorber layer. The support substrate, reflective layer, and absorber layer are preferably stacked in this order. In this case, the pellicle is attached to the side of the photomask where the reflective layer and absorber layer are provided. The absorber layer partially absorbs EUV light, thereby forming a desired image on a sensitive substrate (e.g., a semiconductor substrate with a photoresist film). Examples of the reflective layer include a multilayer film of molybdenum (Mo) and silicon (Si). The material of the absorber layer may be a material that has high absorption of EUV light and the like. Examples of materials that have high absorption of EUV light and the like include chromium (Cr) and tantalum nitride.

[0092] (5) Exposure Apparatus The exposure apparatus of the present disclosure includes an extreme ultraviolet light source that emits extreme ultraviolet light as exposure light, an exposure master of the present disclosure, and an optical system that guides the exposure light emitted from the extreme ultraviolet light source to the exposure master. The exposure master is positioned so that the extreme ultraviolet light emitted from the extreme ultraviolet light source passes through the pellicle film and irradiates the photomask. The exposure apparatus of the present disclosure achieves the same effects as the exposure master of the present disclosure. Furthermore, since the exposure apparatus of the present disclosure has the above configuration, it can form fine patterns (e.g., line widths of 32 nm or less) and can perform pattern exposure with reduced resolution defects due to foreign matter.

[0093] As the extreme ultraviolet light source, a known extreme ultraviolet light source can be used. As the optical system, a known optical system can be used.

[0094] (6) Nanotube Film Manufacturing Method The nanotube film manufacturing method of the present disclosure is a method for manufacturing the nanotube film of the present disclosure. This manufacturing method includes preparing a raw material containing a plurality of nanotubes (hereinafter also referred to as "NT raw material") (hereinafter also referred to as "preparation step"), mixing the plurality of nanotubes with a solvent to prepare a dispersion (hereinafter also referred to as "mixing step"), centrifuging the dispersion to prepare a separation liquid (hereinafter also referred to as "centrifugation step"), and forming the separation liquid into a sheet-like membrane to produce a nanotube membrane (hereinafter also referred to as "membrane formation step"). The centrifugation is performed two or more times. The preparation step, mixing step, centrifugation step, and membrane formation step are performed in this order.

[0095] The method for producing a nanotube film according to the present disclosure has the above configuration, and therefore can produce the nanotube film according to the present disclosure.

[0096] (6.1) Preparation Step In the preparation step, NT raw materials are prepared.

[0097] The method for preparing the NT raw material is not particularly limited, and examples include methods of obtaining commercially available products and methods of synthesizing carbon nanotube raw materials (hereinafter also referred to as "CNT raw materials"). Examples of commercially available products include eDIPS manufactured by Meijo Nano Carbon Co., Ltd., ZEONANO manufactured by Zeon Nano Technology Co., Ltd., and TUBALL manufactured by OCSiAl. Methods for synthesizing CNT raw materials include the enhanced direct injection pyrolytic synthesis (hereinafter also referred to as the "eDIPS method"), the super-growth method, and the laser ablation method. Among the above methods, the eDIPS method is preferred as a method for synthesizing CNT raw materials. The DIPS method is a gas-phase flow method. Specifically, in the DIPS method, a hydrocarbon-based solution containing a catalyst (or catalyst precursor) and a reaction accelerator is atomized by spraying and introduced into a high-temperature heating furnace, whereby single-walled NTs are synthesized in a flowing gas phase. The e-DIPS method is a gas-phase flow method that is an improvement over the DIPS method. Specifically, the "e-DIPS method" focuses on the particle formation process in which ferrocene, used as a catalyst, has different particle diameters on the upstream and downstream sides of a reactor. Unlike the DIPS method, which uses only an organic solvent as a carbon source, the e-DIPS method is relatively susceptible to decomposition in the carrier gas. In other words, the e-DIPS method controls the growth point of single-walled NTs by mixing in a second carbon source that is more likely to function as a carbon source. For details, see Non-Patent Document 3 below. Commercially available CNT raw materials synthesized by the eDIPS method include "MEIJO eDIPS" manufactured by Meijo Nanocarbon Co., Ltd. Non-Patent Document 3: Saito et al., J. Nanosci. Nanotechnol., 8 (2008), 6153-6157.

[0098] (6.2) Mixing Step In the mixing step, the plurality of nanotubes and a solvent are mixed to prepare a dispersion liquid.

[0099] The method for mixing the NT raw material and the solvent is not particularly limited, and examples thereof include a method using a magnetic stirrer, a method using cavitation (e.g., ultrasonic dispersion), a method using mechanical shear force (e.g., a ball mill, a roller mill, a vibration mill, a kneader, a homogenizer, etc.), and a method using turbulence (e.g., a jet mill, a Nanomizer, etc.).

[0100] The solvent is not particularly limited, and examples thereof include organic solvents, water, etc. Examples of the organic solvent include isopropyl alcohol, ethanol, toluene, xylene, ethylbenzene, n-methylpyrrolidone, N,N-dimethylformamide, propylene glycol, and methyl isobutyl ketone.

[0101] In addition to the NT raw material and solvent, a dispersant may be mixed. The dispersant can disentangle the thick bundles contained in the NT raw material. Examples of dispersants include flavin derivatives, sodium cholate, sodium deoxycholate, sodium dodecylbenzenesulfonate, polyacrylic acid, sodium polyacrylate, polyfluorene (poly(9,9-dioctylfluorenyl-2,7-diyl)), and sodium dodecyl sulfate.

[0102] The content of the NT raw material is not particularly limited, and from the viewpoint of uniformly dispersing the NT raw material in the dispersion, it is preferably 0.0005% by mass to 1% by mass, and more preferably 0.001% by mass to 0.5% by mass, relative to the total amount of the dispersion.

[0103] (6.3) Centrifugation Step In the centrifugation step, the dispersion is centrifuged to produce a separated liquid. The centrifugation is performed two or more times. The separated liquid is obtained by removing many NT masses (e.g., NT aggregates or NT clumps) from the dispersion.

[0104] Examples of the centrifugal separation method include a swing rotor method and an angle rotor method. In the swing rotor method, centrifugation is performed with the container held horizontally. In the angle rotor method, centrifugation is performed with the container tilted at a certain angle. From the viewpoints of achieving a high aggregate removal effect, increasing the ratio of airflow resistance to membrane thickness, and facilitating increasing the maximum pressure, the angle rotor method is preferred as the centrifugal separation method. In the angle rotor method, in order to enhance the centrifugal effect and facilitate removal of aggregates, the angle at which the container is tilted with respect to the direction of gravity is preferably 1° to 100°, and more preferably 10° to 60°. From the viewpoints of preventing membrane rupture and reducing airflow resistance, the angle rotor method is preferred as the centrifugal separation method.

[0105] The number of times of centrifugation is 2 or more. By performing centrifugation 2 or more times, the speckle rate of the NT membrane is 7.00 × 10 －４ % or less. From the viewpoint of the effect of removing aggregates and the purification effect of obtaining NTs with a narrow particle size distribution, the number of times centrifugation is carried out is preferably 2 or more, more preferably 3 or more. From the viewpoint of productivity, the number of times centrifugation is carried out is preferably 10 or less, more preferably 8 or less. From these viewpoints, the number of times centrifugation is carried out may be 2 to 8.

[0106] The rotation speed of the centrifugation is not particularly limited. From the viewpoint of the effect of removing aggregates, the rotation speed of the centrifugation is preferably 1000 rpm (revolutions per minute) or more, more preferably 2000 rpm or more. From the viewpoint of preparing an NT dispersion liquid with a concentration sufficient for membrane formation, the rotation speed of the centrifugation is preferably 50,000 rpm or less, more preferably 30,000 rpm or less. From these viewpoints, the rotation speed of the centrifugation may be 1000 rpm to 50,000 rpm. The rotation speeds of the centrifugation performed multiple times may be the same or different.

[0107] The average relative centrifugal force of the centrifugation is not particularly limited. The average relative centrifugal force of the centrifugation is preferably 200 xg or more. From the viewpoint of ease of removal of aggregates, the average relative centrifugal force of the centrifugation is preferably 200 xg or more, more preferably 300 xg or more, even more preferably 2000 xg or more, and even more preferably more than 5000 xg. From the viewpoint of facilitating the preparation of a dispersion liquid of sufficient concentration for membrane formation, the average relative centrifugal force of the centrifugation is preferably 500,000 xg or less, more preferably 400,000 xg or less. From these viewpoints, the average relative centrifugal force of the centrifugation may be 200 xg to 500,000 xg, may be 2,000 xg to 50,000 xg, or may be more than 5,000 xg and 540,000 xg or less. When centrifugation is performed multiple times, the average relative centrifugal force of each of the multiple centrifugations may be the same or different.

[0108] The duration of each centrifugation is not particularly limited. From the viewpoint of the purification effect of the dispersion, the duration of each centrifugation is preferably 5 minutes or more, more preferably 10 minutes or more. From the viewpoint of productivity, the duration of each centrifugation is preferably 600 minutes or less, more preferably 420 minutes or less. From these viewpoints, the duration of each centrifugation may be 30 minutes to 600 minutes. The duration of each centrifugation performed multiple times may be the same or different.

[0109] (6.4) Membrane Formation Step In the membrane formation step, the separation liquid is formed into a sheet-like membrane to produce a nanotube membrane, thereby obtaining the NT membrane of the present disclosure.

[0110] An example of a method for forming the separation liquid into a sheet-like film is a method in which the separation liquid is applied to a substrate and the solvent is removed by drying or the like. Examples of the application method include blade coating, slit coating, spin coating, and dip coating. The drying method is not particularly limited and may be any known method. Examples of the drying method include a method in which the solvent is dried by leaving the film to stand at room temperature, and a method in which the solvent is dried by heating. If necessary, the dispersant may be removed by washing the NT film with a solvent that dissolves the dispersant in the dispersion liquid.

[0111] (6.5) Nanotube Film The nanotube film manufactured by the nanotube film manufacturing method of the present disclosure is preferably used as a pellicle film, which can suppress the occurrence of exposure defects in the entire area irradiated with exposure light, even when the exposure light is irradiated for a long period of time.

[0112] (7) Evaluation Method of Nanotube Film for Exposure Light The present inventors have conducted research and found that spots having a specific thickness may be present in very small amounts throughout the entire area irradiated with exposure light. These spots may impede the transmission of the light cone 1 (see FIG. 1) through the pellicle film 3 (see FIG. 1). The presence of spots that impede the transmission of the light cone 1 through the pellicle film 3 may result in a light intensity variation of more than 0.4%. In other words, poor exposure may occur. For example, when observed with an optical microscope, if such spots are present that have a dark color that does not transmit light, the light intensity variation is likely to exceed 0.4%, even if the area of ​​the spots is relatively small. It has also been found that when observed with an optical microscope, even if spots that are relatively lighter than the dark color are present, the light intensity variation may exceed 0.4% if the area of ​​the spots is relatively large.

[0113] The evaluation method disclosed in Patent Document 1 has a wide measurement point and may not be able to detect localized spots. In addition, the evaluation method disclosed in Patent Document 1 does not evaluate the entire area of ​​the pellicle film that is irradiated with exposure light (hereinafter also referred to as the "free-standing film portion"), so there is a risk that it may not be possible to reliably evaluate whether or not exposure defects have occurred.

[0114] (8) Method for Evaluating Nanotube Film for Exposure According to First Embodiment The method for evaluating nanotube film for exposure according to the first embodiment of the present disclosure includes: preparing an NT film (a) representing a nanotube film having a reference thickness, and a plurality of nanotube films (hereinafter also referred to as "NT films (t)") having thicknesses different from that of the NT film (a) (hereinafter also referred to as a "preparation step"); deriving ΔEUVT(t), which is the difference between EUVT(a) representing the transmittance of extreme ultraviolet rays through the NT film (a) and EUVT(t) representing the transmittance of extreme ultraviolet rays through each of the plurality of nanotube films (i.e., NT films (t)), from the following formula (i) (hereinafter also referred to as a "transmittance difference derivation step"); measuring the brightness of each of the plurality of nanotube films (hereinafter also referred to as a "first measurement step"); and applying the relationship between the ΔEUVT(t) and the brightness of the nanotube film corresponding to the ΔEUVT(t) to the following formula (ii) to derive an acceptable relationship between the allowable spot area Ap and the allowable spot brightness (hereinafter also referred to as a "judgment curve") (hereinafter also referred to as a "judgment curve derivation process").

[0115]

[0116] In formula (ii), NA represents the numerical aperture of the photomask when the pellicle, in which the nanotube film is attached to a pellicle frame, is attached to the photomask. L1 represents the distance between the nanotube film of the pellicle and the photomask. R represents the allowable error range for light intensity variation. For example, the allowable error range for light intensity variation is 0.4% or less. When the allowable error range for light intensity variation is 0.4%, R is 0.004. π represents the ratio of the circumference of a circle to its circumference.

[0117] The spots have a brightness of 80% or less of the reference brightness in an image of the main surface of the nanotube film observed with an optical microscope, and are 50 μm ２The size of one pixel of the observed image is 1.0 μm to 2.0 μm×1.0 μm to 2.0 μm. The reference brightness is expressed by the following formula (1): Formula (1): Reference brightness = average value of brightness over the entire main surface of the nanotube film + 1 × brightness of standard deviation σ of brightness over the entire main surface of the nanotube film

[0118] The "reference film thickness" refers to the film thickness of the NT film (a) that exhibits a reference EUVT(a) relative to the EUVT(t) of multiple nanotube films having different film thicknesses when deriving ΔEUVT(t) in the evaluation method of a nanotube film for exposure. By setting the reference film thickness, ΔEUVT(t) can be appropriately derived and the nanotube film for exposure can be evaluated. The "multiple nanotube films" refers to nanotube films that are different from the NT film (a) and each of the evaluation NT films described below. The "relationship between the ΔEUVT(t) and the measured value of the luminance of the nanotube film corresponding to the ΔEUVT(t)" refers to the relationship between the measured value of ΔEUVT(t) (a value corresponding to the film thickness) and the measured value of the luminance of the nanotube film used to derive ΔEUVT(t) (a value corresponding to the film thickness) for each of multiple ΔEUVT(t).

[0119] The evaluation method of the nanotube film for exposure of the first embodiment has the above-mentioned configuration, and therefore can evaluate the nanotube film for exposure using the judgment curve as a criterion for determining whether or not an exposure failure has occurred. As a result, the evaluation method of the first embodiment can more reliably evaluate whether or not an exposure failure has occurred. Furthermore, the evaluation method of the first embodiment can evaluate whether or not an exposure failure has occurred without evaluating the extreme ultraviolet transmittance of the nanotube film to be evaluated.

[0120] The preparation step, the transmittance difference deriving step, the first measurement step, and the judgment curve deriving step will be described in detail below.

[0121] The evaluation method of the first embodiment preferably further includes: measuring the brightness and area of ​​spots on a nanotube film to be evaluated (hereinafter also referred to as an "evaluation NT film") (hereinafter also referred to as a "second measurement step"); and comparing the relationship between the measured brightness and the measured area of ​​the spots on the nanotube film to be evaluated with the tolerance relationship (hereinafter also referred to as a "comparison and judgment step"). This allows the evaluation method of the first embodiment to more reliably evaluate whether or not exposure defects have occurred.

[0122] The comparing (i.e., the comparison and judgment process) preferably includes: comparing the measured value of the speck area with the maximum value of the allowable speck area Ap corresponding to the measured value of the brightness of the nanotube film to be evaluated in the tolerance relationship (hereinafter also referred to as the "comparison process"); and judging that there is an exposure defect if there is a speck whose measured value of the speck area is larger than the maximum value, and judging that there is no exposure defect if there is no speck whose measured value of the speck area is larger than the maximum value (hereinafter also referred to as the "judgment process"). This makes it possible for the evaluation method of the first embodiment to more reliably evaluate whether or not an exposure defect has occurred.

[0123] The second measuring step and the comparison and determination step will be described in detail later.

[0124] The evaluation method for a nanotube film for exposure of the first embodiment includes the evaluation method for a nanotube film for exposure of a first aspect and the evaluation method for a nanotube film for exposure of a second aspect. Each of the evaluation method of the first aspect and the evaluation method of the second aspect is a method for evaluating the occurrence of exposure defects without measuring the extreme ultraviolet transmittance of the evaluation NT film itself. The evaluation method of the first aspect is a method that does not measure ΔEUVT(t) by using formula (i) in the process of obtaining a judgment curve using formula (ii). The evaluation method of the second aspect is a method that measures ΔEUVT(t) in the process of obtaining a judgment curve using formula (ii).

[0125] Hereinafter, a first aspect and a second aspect will be described in this order when the evaluation method of the first embodiment includes a second measurement step and a comparative judgment step, and the comparative judgment step includes a comparison step and a judgment step. Note that in the first embodiment, the evaluation method does not have to include at least one of the second measurement step and the comparative judgment step. In the first embodiment, when the evaluation method includes the comparative judgment step, the comparative judgment step does not have to include at least one of the comparison step and the judgment step.

[0126] (8.1) Evaluation Method of First Aspect In the evaluation method of the first aspect, the film thickness of the NT film (a) is thinner than the film thickness of each of the plurality of NT films (t). The evaluation method of the first aspect includes measuring the film thickness of the NT film (a) and each of the plurality of NT films (t) (hereinafter also referred to as a "film thickness measurement step"), a preparation step, a transmittance difference deriving step, a first measurement step, a judgment curve deriving step, a second measurement step, and a comparison and judgment step. The preparation step, film thickness measurement step, transmittance difference deriving step, first measurement step, judgment curve deriving step, second measurement step, and comparison and judgment step may be performed in this order.

[0127] The judgment curve is obtained by performing the preparation step, the film thickness measurement step, the transmittance difference deriving step, the first measurement step, and the judgment curve deriving step. By performing the second measurement step and the comparison judgment step, the judgment curve can be used to more reliably evaluate whether or not the NT film for evaluation has experienced an exposure failure.

[0128] (8.1.1) Preparation Step In the preparation step, an NT film (a) and a plurality of NT films (t) are prepared. The NT film (a) and a plurality of NT films (t) are used to derive a judgment curve.

[0129] Hereinafter, when there is no need to distinguish between the NT membrane (a), the multiple NT membranes (t), and the evaluation NT membrane, the NT membrane (a), the multiple NT membranes (t), and the evaluation NT membrane will be collectively referred to as "NT membranes."

[0130] The NT film includes a plurality of nanotubes (hereinafter also referred to as "NTs"), the details of which will be described later.

[0131] A plurality of NT films (t) are used to draw a judgment curve. The number of NT films (t) is not particularly limited as long as it is two or more points for drawing a judgment curve. From the viewpoint of more appropriate evaluation, the number of NT films (t) is preferably three or more points, and more preferably four or more points.

[0132] In the first aspect, the film thickness of the NT film (a) is thinner than the film thickness of each of the plurality of NT films (t). This makes it less likely that the calculation and computation of ΔEUVT(t) and brightness will be complicated. From the viewpoint of facilitating more appropriate evaluation, the film thickness of the NT film (a) is preferably 10 nm to 50 nm, more preferably 20 nm to 40 nm. The film thickness of the NT film (a) is preferably thinner than that of the evaluation NT film. When the film thickness of the NT film (a) is thinner than that of the evaluation NT film, the derivation and calculation of ΔEUVT(t) are easier. The method for measuring the film thickness of the NT film (a) is the same as the method for measuring the NT film described below.

[0133] The film thickness of the NT film (t) may be different from the film thickness of the NT film (a), and may be thicker or thinner than the film thickness of the NT film (a). From the viewpoint of facilitating evaluation of a wider range of film thicknesses, the film thickness of the NT film (t) is preferably 10 nm to 350 nm, more preferably 50 nm to 300 nm. The film thickness of the NT film (t) is preferably thicker than the film thickness of the NT film (a). When the film thickness of the NT film (t) is thicker than the film thickness of the NT film (a), the derivation and calculation of ΔEUVT(t) are simpler. The measurement method for the NT film (t) is the same as the measurement method for the NT film described below.

[0134] The method for preparing the NT film (a) and the plurality of NT films (t) is not particularly limited, and may be any known method.

[0135] (8.1.2) Film Thickness Measuring Step In the film thickness measuring step, the film thickness of each of the NT film (a) and the plurality of NT films (t) is measured.

[0136] The method for measuring the film thickness is not particularly limited, and may be a method for measuring the reflectance with a spectroscopic film thickness meter, a method for measuring the film thickness by cross-sectional observation, or a method for measuring the film thickness using an atomic force microscope (AFM) or a stylus probe. The method for measuring the reflectance with a spectroscopic film thickness meter is the same as the method exemplified as the method for measuring the film thickness of an NT film in (1.4.1) above.

[0137] (8.1.3) Transmittance Difference Deriving Step In the transmittance difference deriving step, ΔEUVT(t), which is the difference between EUVT(a) and the EUVT(t) of each of the multiple NT films(t), is derived using the following formula (i). This derives ΔEUVT(t) for each of the multiple NT films(t). ΔEUVT(t) indicates the difference between the extreme ultraviolet transmittance EUVT(a) at a reference film thickness and the extreme ultraviolet transmittance EUVT(t) of the multiple NT films(t). By deriving ΔEUVT(t), the allowable spot area Ap can be derived using formula (ii).

[0138]

[0139] The method for deriving ΔEUVT(t) may be any known method.

[0140] (8.1.4) First Measurement Step In the first measurement step, the luminance of each of the plurality of NT films (t) is measured. The measured luminance values ​​of each of the plurality of NT films (t) are used to derive a reference curve.

[0141] The luminance of the NT film (t) may be measured by the same method as that described in the examples.

[0142] (8.1.5) Criterion Curve Derivation Step In the judgment curve derivation step, the relationship between the ΔEUVT(t) and the luminance of the NT film(t) corresponding to ΔEUVT(t) is applied to the following formula (ii) to derive a judgment curve.

[0143]

[0144] In formula (ii), NA represents the numerical aperture of the photomask when the pellicle, in which the nanotube film is attached to a pellicle frame, is attached to the photomask. L1 represents the distance between the nanotube film of the pellicle and the photomask. R represents the allowable error range for light intensity variation. For example, the allowable error range for light intensity variation is 0.4% or less. When the allowable error range for light intensity variation is 0.4%, R is 0.004. It is known that if the numerical aperture of the photomask on the semiconductor wafer is NA and the reduction ratio of the pattern on the semiconductor wafer relative to the pattern on the photomask is x, the numerical aperture NA on the photomask is equal to the value obtained by dividing the numerical aperture NA on the semiconductor wafer by the reduction ratio x.

[0145] The derivation of formula (ii) will be explained with reference to FIG. 1 for the case where R is 0.004. The numerical aperture NA of the photomask when the pellicle is attached to the photomask 2 is expressed by formula (A1). Note that, since exposure using EUV light 1 is performed in a vacuum, the refractive index n in formula (A1) is 1. If the radius of the light cone 1 on the surface of the pellicle film 3 is r (see FIG. 1), the relationship shown in formula (A2) below holds. Substituting formula (A1) into formula (A2) yields formula (A3). The area A of the light cone 1 on the pellicle film 3 is expressed by formula (A4). Some literature suggests that, in order to prevent exposure defects, the variation in the amount of light passing through each of the multiple light cone cross sections on the main surface S3 of the pellicle film 3 must be 0.4% or less (Non-Patent Document 1). When the required light amount variation is 0.4% or less, the area A of the light cone 1 of 0.4% ０．４ is expressed by formula (A5). The allowable area Ap of spots corresponds to the allowable transmittance and is therefore expressed by formula (A6). Substituting formula (A3) into formula (A6), formula (ii) is derived.

[0146]

[0147] The pellicle will be described in detail later.

[0148] (8.1.5.1) Method of Derivation of the Judgment Curve The judgment curve can be derived by applying the relationship between ΔEUVT(t) and the luminance of the NT film(t) corresponding to ΔEUVT(t) to equation (ii), and may be derived by the following method. A list (e.g., Table 2) of ΔEUVT, area Ap, and luminance is created for each of a reference NT film (i.e., NT film(a)) and multiple NT films (i.e., NT films(t)) having thicknesses different from that of the NT film(a). The area Ap is calculated using equation (ii). Next, the measured luminance values ​​and area Ap of each of the multiple NT films(t) are plotted on a graph with luminance on the horizontal axis and area Ap on the vertical axis to derive an approximate equation. The derived approximate equation is the tolerance relationship between the allowable speckle area Ap and the allowable speckle luminance (i.e., the judgment curve). When R in formula (ii) is 0.004, the approximation formula is the relationship between the brightness corresponding to a 0.4% reduction in the amount of light and the area of ​​spots Ap (μm ２ ) (i.e., the judgment curve).

[0149] There are no limitations on the judgment curve as long as it is an approximation that can be evaluated. The judgment curve may be an exponential approximation relational expression or a polynomial approximation relational expression.

[0150] When the judgment curve is an exponential function approximation relational expression, the judgment curve may be expressed, for example, by the following formula (v): When the judgment curve is the relational expression expressed by the following formula (v) (i.e., the relational expression between Ap and the brightness of spots), the presence or absence of exposure defects can be evaluated more cheaply, quickly, and with higher resolution than when the judgment curve is the relational expression between Ap and ΔEUVT.

[0151]

[0152] In formula (v), α and β represent numerical values. The judgment curve shown in formula (v) can be derived by exponential approximation. For example, α is 465 and β is 0.0196. S represents the brightness of spots. When R in formula (ii) is 0.004, S represents the brightness of spots corresponding to a 0.4% reduction in light intensity.

[0153] When the distance L1 from the surface S2 of the photomask 2 to the pellicle film 3 is 2.5 mm, the NA of the light cone 1 on the semiconductor wafer is 0.33, and R in formula (ii) is 0.004 (i.e., when the NA of the photomask is 0.0825), and when a spot that satisfies the following formula (vi) exists within the cross section of the light cone, the reduction in the light intensity at the cross section of the light cone will be 0.4% or more.

[0154]

[0155] When the judgment curve is a relational expression exponent of a polynomial approximation, the judgment curve may be expressed, for example, by the following formula (vii): When the judgment curve is the relational expression expressed by the following formula (vii) (i.e., the relational expression between Ap and the luminance of spots), the presence or absence of an exposure defect can be evaluated more cheaply, quickly, and with higher resolution than when the judgment curve is the relational expression between Ap and ΔEUVT.

[0156]

[0157] In formula (vii), α, β, γ, and δ represent numerical values. The judgment curve shown in formula (vii) can be derived by polynomial approximation. For example, α is 0.0023, β is -0.0132, γ is 9.017, and δ is 540.58. S represents the brightness of spots. When R in formula (ii) is 0.004, S represents the brightness of spots corresponding to a 0.4% reduction in light intensity.

[0158] When the distance L1 from the surface S2 of the photomask 2 to the pellicle film 3 is 2.5 mm, the NA of the light cone 1 on the semiconductor wafer is 0.33 m, and R in formula (ii) is 0.004 (i.e., when the NA of the photomask is 0.0825), and when spots that satisfy the following formula (viii) exist within the cross section of the light cone, the reduction in the light intensity at the cross section of the light cone will be 0.4% or more.

[0159]

[0160] There are no particular limitations on the method for applying the relationship between ΔEUVT(t) and the luminance of the NT film(t) corresponding to ΔEUVT(t) to the following formula (ii), and the following method may be used. ΔEUVT(t) and the luminance of the NT film(t) corresponding to ΔEUVT(t) are determined from a reference NT film (i.e., NT film(a)) and a plurality of NT films (i.e., NT films(t)) having a film thickness different from that of the NT film(a). Next, an approximate formula (for example, the following formula (ix)) (hereinafter also referred to as the "first approximate formula") between ΔEUVT(t) and the luminance of the NT film(t) corresponding to ΔEUVT(t) is determined. Next, by substituting the first approximate formula into formula (ii), the luminance and the area Ap (μm of the spots) corresponding to a 0.4% reduction in the amount of light can be determined. ２ ) may be obtained (i.e., a judgment curve). Equation (ix): ΔEUVT(t)=A×ln(brightness)+B In equation (ix), A and B represent numerical values, and brightness is the brightness of the NT film(t) corresponding to ΔEUVT(t). For example, A is 26.17 and B is 138.14.

[0161] (8.1.6) Second Measurement Step In the second measurement step, the brightness and area of ​​the spots on the evaluation NT film are measured. The measured values ​​of the brightness of the spots on the evaluation NT film and the measured values ​​of the area of ​​the spot region are used in the comparison and evaluation step.

[0162] The method for measuring the brightness and area of ​​the spots may be as follows.

[0163] The evaluation NT film is illuminated, the entire area of ​​the evaluation NT film is photographed, the brightness of each pixel in the observation image is observed, spots are identified based on the brightness measurement values, and the brightness and area of ​​the identified spots are measured. The size of one pixel in the observation image may be 1.0 μm to 2.0 μm x 1.0 μm to 2.0 μm. Specifically, the brightness obtained by calculating (average brightness + 1 × σ) × 0.8 from the average brightness when the entire area of ​​the evaluation NT film is photographed and the standard deviation σ of the brightness of each pixel is defined as the "reference brightness." A plurality of pixels having a brightness equal to or lower than the reference brightness are identified, and if there are adjacent pixels among the plurality of pixels, the pixels will have a certain area including the adjacent pixels. From the plurality of pixels having a brightness equal to or lower than the reference brightness, a pixel having an area of ​​50 μm ２An area where the brightness is equal to or greater than the reference brightness is identified as a speck. A "speck" is an area surrounded by pixels whose brightness is equal to or less than the reference brightness. The brightness of a speck is obtained by dividing the sum of the brightnesses of the pixels that make up the speck by the number of pixels that make up the speck. For example, the area of ​​a speck can be calculated by multiplying the number of pixels that make up the speck by the area of ​​one pixel.

[0164] "The entire area of ​​the NT film for evaluation" is the same as the entire area of ​​the NT film in (1.1.1) above.

[0165] (8.1.7) Comparison and Judgment Step In the comparison and judgment step, the relationship between the measured values ​​of the brightness of the spots on the evaluation NT film and the measured values ​​of the spot area is compared with the judgment curve. In detail, the comparison and judgment step includes a comparison step and a judgment step. The comparison step and judgment step may be performed in this order.

[0166] (8.1.7.1) Comparison Step In the comparison step, the measured value of the spot area of ​​the evaluation NT film is compared with the maximum value of the allowable spot area Ap corresponding to the measured value of the brightness of the evaluation NT film in the tolerance relationship (i.e., the judgment curve).

[0167] When the judgment curve is expressed by the above formula (vi), the maximum value of the area Ap indicates the area Ap when the measured value of the luminance of the evaluation NT film is substituted into the above formula (v).When the judgment curve is expressed by the above formula (viii), the maximum value of the area Ap indicates the area Ap when the measured value of the luminance of the evaluation NT film is substituted into the above formula (vii).

[0168] (8.1.7.2) Judgment process In the judgment process, if there is a spot whose measured area is greater than the maximum value, it is judged that there is an exposure defect, and if there is no spot whose measured area is greater than the maximum value, it is judged that there is no exposure defect.

[0169] When the judgment curve is expressed by the above formula (vi), the relationship between the maximum allowable speckle area Ap and the allowable speckle luminance is expressed by formula (vi). Therefore, by comparing each observable speckle with the relationship expressed by formula (v), the presence or absence of exposure failure can be easily evaluated quantitatively. It can also be evaluated visually. Specifically, the presence or absence of exposure failure can be evaluated based on whether the measured speckle area of ​​the evaluation NT film is located above the speckle area size expressed by formula (v) in terms of the speckle luminance of the evaluation NT film. As shown in Figure 3, speckles whose speckle area size is located above the judgment curve in terms of the speckle luminance of the evaluation NT film (hereinafter also referred to as "NG speckles") can be evaluated as speckles that cause exposure failure.

[0170] (8.1.8) Nanotubes NT are the same as those exemplified as NT in (1.5) above.

[0171] (8.1.9) Pellicle The pellicle of the present disclosure is similar to the pellicle exemplified in (3) above.

[0172] (8.2) Evaluation Method of Second Aspect In the evaluation method of the second aspect, the film thickness of the NT film (a) is thinner than the film thickness of each of the plurality of nanotube films. The evaluation method of the second aspect includes measuring the EUVT(a) and the EUV transmittance of each of the plurality of nanotube films (hereinafter referred to as a "transmittance measurement step"), matching the ΔEUV(t) of a nanotube film having a comparison thickness with the luminance of the nanotube film having a comparison thickness (hereinafter also referred to as a "correspondence step"), a preparation step, a transmittance difference deriving step, a first measurement step, a judgment curve deriving step, a second measurement step, and a comparison judgment step.

[0173] A "nanotube film having a comparable thickness" refers to one of a plurality of nanotube films.

[0174] (8.2.1) Preparation Step In the preparation step, an NT film (a) and a plurality of NT films (t) are prepared. In the second embodiment, the NT film (a) has a thickness thinner than each of the plurality of nanotube films. The preparation step in the second embodiment is the same as that exemplified as the preparation step in the first embodiment.

[0175] (8.2.2) Transmittance measurement step In the transmittance measurement step, the EUV T(a) and the EUV transmittance of each of the plurality of nanotube films are measured. The measured values ​​of the EUV transmittance are used to derive ΔEUV(t), which is required in the judgment curve derivation step.

[0176] There are no particular limitations on the method for measuring EUV transmittance, but examples include the following. Specifically, an EUV transmittance measurement device using an EUV light source such as a Xe plasma light source, a discharge plasma light source, a laser-produced plasma light source, or a synchrotron light source can be used. Examples include a method of measuring the intensity and current value of EUV transmitted light with and without a nanotube film using a photodiode in a vacuum environment or in a hydrogen gas atmosphere of 100 Pa or less, and measuring the ratio between the two, and a method of irradiating a material photosensitive to EUV light and measuring the film thickness ratio.

[0177] (8.2.3) First measurement step In the first measurement step, the luminance of each of the NT film (a) and the plurality of nanotube films is measured. The measured luminance values ​​are used to derive the relationship between the luminance corresponding to ΔEUVT(t), which is required in the judgment curve deriving step.

[0178] The brightness may be an average value of the brightness of all pixels obtained by photographing the entire area of ​​the NT film using an optical microscope and observing the brightness of each pixel. The size of one pixel in the observed image may be 1.0 μm to 2.0 μm × 1.0 μm to 2.0 μm.

[0179] (8.2.4) Corresponding Step In the corresponding step, the ΔEUV(t) of a nanotube film having a comparative thickness is matched with the luminance of the nanotube film having a comparative thickness. In this way, a judgment curve is obtained by using a relational expression that matches the ΔEUV(t) with the luminance of a nanotube film having a comparative thickness. When R in formula (ii) is 0.004, the luminance corresponding to a 0.4% reduction in the amount of light and the area Ap (μm ２ ) can be obtained.

[0180] (8.2.5) Transmittance difference deriving step In the transmittance difference deriving step, ΔEUVT(t), which is the difference between EUVT(a) and the EUVT(t) of multiple NT films(t), is derived from the above formula (i). The transmittance difference deriving step of the second aspect is the same as the transmittance difference deriving step exemplified in the first aspect.

[0181] (8.2.6) Judgment curve derivation step In the judgment curve derivation step, the relationship between ΔEUVT(t) and the corresponding luminance is applied to the above formula (ii) to derive a judgment curve. The judgment curve derivation step of the second aspect is the same as that exemplified as the judgment curve derivation step of the first aspect.

[0182] (8.2.7) Second measurement step In the second measurement step, the brightness and area of ​​the spots on the evaluation NT film are measured. This provides the measurement values ​​of the brightness and area of ​​the spots on the evaluation NT film. The second measurement step of the second embodiment is the same as the second measurement step exemplified in the first embodiment.

[0183] (8.2.8) Comparison and Evaluation Step In the comparison and evaluation step, the relationship between the measured values ​​of the brightness of the spots on the evaluation NT film and the measured values ​​of the spot area is compared with the evaluation curve. The comparison and evaluation step of the second embodiment is the same as that exemplified as the comparison and evaluation step of the first embodiment.

[0184] (9) Evaluation Method of Nanotube Film for Exposure According to a Second Embodiment The evaluation method of a nanotube film for exposure according to a second embodiment of the present disclosure includes: measuring the brightness and speckle area of ​​a nanotube film to be evaluated (i.e., a second measurement method); and comparing the relationship between the measured brightness of the speckles of the nanotube film to be evaluated and the measured speckle area with an allowable relationship between an allowable speck area Ap and an allowable speck brightness (i.e., a comparison and judgment step). The allowable relationship is obtained by applying the relationship between ΔEUVT(t) and the measured brightness of the nanotube film corresponding to the ΔEUVT(t) to the following formula (ii). The ΔEUVT(t) is obtained by deriving ΔEUVT(t), which is the difference between EUVT(a) and EUVT(t), from the following formula (i). The EUVT(a) represents the transmittance of extreme ultraviolet light through an NT film (a) representing a nanotube film having a reference thickness. The EUVT(t) represents the transmittance of extreme ultraviolet rays through each of a plurality of nanotube films having a film thickness different from that of the NT film (a).

[0185]

[0186] In formula (ii), NA represents the numerical aperture of the photomask when the pellicle, which is made by attaching the nanotube film to a pellicle frame, is attached to the photomask. L1 represents the distance between the nanotube film of the pellicle and the photomask. R represents the allowable error range for variations in light intensity.

[0187] The evaluation method of the second embodiment is similar to the evaluation method of the first embodiment except that it includes the second measurement step and the comparison and determination step, and does not need to include at least one of the preparation step, the transmittance difference deriving step, and the first measurement step. Therefore, the evaluation method of the second embodiment can incorporate the evaluation method of the first embodiment.

[0188] The evaluation method of the nanotube film for exposure of the second embodiment has the above-mentioned configuration, so that the occurrence of the exposure failure can be evaluated more reliably. Moreover, by preparing the tolerance relationship in advance, the occurrence of the exposure failure can be evaluated more reliably by the second measurement method and the comparative judgment process. Furthermore, the evaluation method of the second embodiment can evaluate the occurrence of the exposure failure without evaluating the transmittance of the extreme ultraviolet light of the nanotube film to be evaluated.

[0189] The evaluation method of the second embodiment preferably further includes at least one of a preparation step, a transmittance difference deriving step, and a first measurement step. Each of the preparation step, the transmittance difference deriving step, and the first measurement step is the same as those exemplified in the first embodiment. By further including at least one of the preparation step, the transmittance difference deriving step, and the first measurement step, the evaluation method of the second embodiment can more reliably evaluate whether or not exposure failure has occurred.

[0190] In the evaluation method of the second embodiment, the comparison and judgment step preferably includes a comparison step and a judgment step. The comparison step and the judgment step are the same as those exemplified in the first embodiment. In the evaluation method of the second embodiment, the comparison and judgment step includes the comparison step and the judgment step, so that the evaluation method of the second aspect can more reliably evaluate whether or not an exposure failure has occurred.

[0191] The method for evaluating a nanotube film for exposure of the second embodiment includes the method for evaluating a nanotube film for exposure of the first aspect and the method for evaluating a nanotube film for exposure of the second aspect. Each of the evaluation methods of the first aspect and the second aspect is the same as that exemplified in the first embodiment.

[0192] The present disclosure will be described in more detail below with reference to examples, but the invention of the present disclosure is not limited to these examples.

[0193] [1] Examples 1-1 to 1-2 and Comparative Examples 1-1 to 1-2 [1.1] Example 1-1 [1.1.1] Preparation Step As a plurality of NTs, a plurality of single-walled CNTs (crude CNTs, manufactured by Meijo Nano Carbon Co., Ltd., product name: EC1.5-P) synthesized by an improved direct injection pyrolysis synthesis method (eDIPS method) were prepared.

[0194] [1.1.2] Mixing Step: 400 mL of isopropyl alcohol and 50 mL of ethanol were added to 225 mg of NTs, and 270 mg of polyacrylic acid was further added as an additive to obtain a mixed solution. The mixed solution was stirred using a magnetic stirrer to obtain a suspension. The magnetic stirrer rotation speed was 520 rpm. The temperature of the mixed solution during stirring was 25°C. The stirring time was 15 hours.

[0195] The resulting suspension was subjected to a dispersion treatment using a stirring homogenizer. The rotation speed of the stirring homogenizer was 11,000 rpm. The total stirring time was 30 minutes.

[0196] [1.1.3] Centrifugation Step The obtained dispersion was subjected to a first centrifugation process using a high-speed centrifuge. The rotation speed of the first centrifugation process was 5650 x g. The first centrifugation process was carried out for 100 minutes. The temperature of the dispersion was 10°C. As a result, the dispersion was separated into a first precipitate and a first supernatant. The first precipitate contained many CNT masses (e.g., CNT aggregates and CNT clumps).

[0197] A first supernatant was collected from the dispersion after the first centrifugation treatment. A second centrifugation treatment was performed on the first supernatant using a high-speed centrifuge. The rotation speed of the second centrifugation treatment was 5650 x g. The second centrifugation treatment was performed for 100 minutes. The temperature of the dispersion was 10°C. As a result, the first supernatant was separated into a second precipitate and a second supernatant. The second precipitate contained many CNT masses (e.g., CNT aggregates and CNT clumps). A second supernatant was collected from the first supernatant after the second centrifugation treatment. The second supernatant is a separated liquid.

[0198] [1.1.4] Film formation process The separation solution was spin-coated onto a 12-inch silicon substrate (roughness Ra: 0.15 nm) to produce a CNT film. The spin-coating rotation speed was 600 rpm. The CNT film was floated on water and lifted up using a frame. The size of the free-standing part of the film was 150 mm x 120 mm.

[0199] [1.5] Film Thickness Measurement The film thickness of the CNT film was measured using the method described above. The measurement results are shown in Table 3.

[0200] [1.1.6] Measurement of spots [1.1.6.1] Creation of a calibration curve Using a CNT film having a thickness of 25 nm, a CNT film having a thickness of 60 nm, a CNT film having a thickness of 90 nm, a CNT film having a thickness of 120 nm, and a CNT film having a thickness of 270 nm, and a frame region that blocks transmitted light, brightness measurements of transmitted light intensity were performed under the following settings and observation conditions. The measurement results are shown in Table 3.

[0201]

[0202] [1.1.6.1.1] Setting conditions Brightness is expressed in 256 levels. White is the maximum value 255, and black is the minimum value 0. The brightness when measuring only the illumination light without the CNT film is set to be within the range of 200 to 220. The brightness when the illumination light is blocked is set to be within the range of 0 to 10. The brightness of the transmitted light intensity of the CNT film to be evaluated is set to be within the range of 150 to 200. The brightness when the illumination light is blocked is set to be within the range of 0 to 10.

[0203] The film thickness of the CNT film in Example 1-1 was 25 nm. In Example 1-1, the brightness of a CNT film having a thickness of 25 nm was set to be 156 in the calibration curve. The measured value of the brightness of the frame portion with the illumination light blocked was 5.

[0204] [1.6.1.2] Observation and lighting conditions Microscope: Hirox Co., Ltd. "HRX-01" Lens model: HR2500E (magnification: 80x, 1 pixel: 1.78 μm x 1.78 μm) Transmitted illumination: Illumination model "FASTUS OPPX-10024PP2" (brightness setting: 500) Shutter speed: 1 / 250 Gain: 0 Brightness compensation: None Color: Grayscale

[0205] [1.6.1.3] Measurement of luminance Under the above observation and lighting conditions, images were taken at a resolution of 2000 pixels x 1500 pixels or more. Using the image processing software "ImageJ," the average luminance of a central 1000 pixel x 1000 pixel region of the obtained image was measured.

[0206] [1.6.2] Measurement of the brightness and area of ​​spots The setting conditions, observation conditions, and lighting conditions were the same as those used to create the calibration curve.

[0207] The entire area of ​​the CNT film was 140 mm x 108 mm (longer side direction: inside 1.5 mm from the edge of the frame, shorter side direction: inside 1.0 mm from the edge of the frame). The entire area was photographed, and the brightness of each pixel was observed. From the average brightness when photographing the entire 140 mm x 108 mm area of ​​the CNT film and the standard deviation σ of the brightness of each pixel, the brightness that is (average brightness + 1 x σ) x 0.8 was taken as the standard brightness, and pixels with brightness below this standard brightness were determined to be spots. A spot area of ​​50 μm ２ Spots of this size or larger were defined as spot regions. Examples of spot regions are shown in Figures 6 and 7. The area and average brightness information (brightness) of the spot regions observed over the entire 140 mm x 108 mm area of ​​the CNT film were obtained. The results are shown in Figure 8. The "●" (black circle) in Figure 8 represents the area and average brightness information (brightness) of the spot regions.

[0208] [1.1.6.3] Calculation of the speckle ratio In the above-mentioned observation of brightness (paragraph 0124), the proportion of the speckled area was calculated by the following formula (A): Formula (A): proportion of the speckled area = (area of ​​the speckled area / area of ​​the observed area) x 100

[0209] Using a contamination analysis and foreign body inspection system, the brightness is 120 or less and the area is 38 μm ２ The area and average brightness of each foreign substance area were calculated. From these, areas with a brightness of the film's reference brightness x 0.8 or less and within 50 μm were selected. ２ The area was determined as a spot. The total area of ​​multiple spots was calculated. The percentage of spots (%) was calculated using the following formula (B): Formula (B): Percentage of spots (%) = (total spot area / observed area) x 100

[0210] [1.2] Example 1-2 A CNT film was produced in the same manner as in Example 1-1, except that the spin coating conditions were changed to make the CNT film 30 nm thick. The thickness of the CNT film, the number of spots, and the percentage of spots were measured in the same manner as in Example 1-1. The measurement results and calculation results are shown in Table 4 and FIG. 9.

[0211] [1.3] Comparative Examples 1-1 and 1-2 A CNT film was produced in the same manner as in Example 1-1, except that the rotation speed and time of the first centrifugation process were changed to the conditions shown in Table 4 and the second centrifugation process was not performed. The film thickness of the CNT film, the number of spots, and the percentage of spots were calculated in the same manner as in Example 1-1. The measurement results and calculation results are shown in Table 4, Figure 10 (Comparative Example 1-1), and Figure 11 (Comparative Example 1-2).

[0212] [1.4] Exposure Evaluation Using the measurement results of the speckle measurement (see FIGS. 8 to 11), the exposure evaluation was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 4. An acceptable exposure evaluation result is "A".

[0213] [1.4.1] Evaluation criteria "A": The number of NG spots was 0. "B": The number of NG spots was 1 or more.

[0214] [1.5] Results

[0215] The speckle ratios of Comparative Examples 1-1 and 1-2 were 7.00 × 10 －４ % or less. Therefore, the result of the exposure evaluation was "B." As a result, it was found that the CNT films of Comparative Examples 1-1 and 1-2 are not "nanotube films that can suppress the occurrence of exposure defects in the entire region irradiated with exposure light."

[0216] The speckle ratio in Examples 1-1 and 1-2 was 7.00×10 －４ % or less. Therefore, the result of the exposure evaluation was "A." As a result, it was found that the CNT films of Examples 1-1 and 1-2 are "nanotube films that can suppress the occurrence of exposure defects in the entire region irradiated with exposure light."

[0217] [2] Examples 2-1 to 2-4 [2.1] Example 2-1 [2.1.1] Preparation Step Six CNT films were prepared. One was a 25 nm CNT film, serving as a reference nanotube film. The remaining five were prepared as nanotube films with different thicknesses (i.e., CNT films with thicknesses of 60 nm, 90 nm, 120 nm, and 270 nm, and a frame region (i.e., frame portion) that blocks transmitted light). The "frame portion" refers to the overlapping portion of the CNT film with the pellicle frame when the CNT film is attached to the pellicle frame and viewed in the thickness direction of the CNT film. The EUVT(t) of the frame portion is independent of the CNT film thickness.

[0218] [2.1.2] Film Thickness Measurement Step The film thicknesses of six CNT films were measured using the method described above. The measurement results are shown in Table 5. The CNT film having a film thickness of 25 μm was designated "NT film (a)." Of the six CNT films, the CNT film that was not NT film (a) was designated "NT film (t)."

[0219]

[0220] [2.1.3] Transmittance difference deriving step Using the above method, ΔEUVT(t) was derived from the above formula (i). The calculation results are shown in Table 5.

[0221] [2.1.4] First measurement step Using a CNT film having a thickness of 25 nm, a CNT film having a thickness of 60 nm, a CNT film having a thickness of 90 nm, a CNT film having a thickness of 120 nm, a CNT film having a thickness of 270 nm, and a CNT film in a frame region (i.e., frame portion) that blocks transmitted light, the brightness of the transmitted light intensity was measured under the following setting conditions and observation conditions. The measurement results are shown in Table 5.

[0222] [2.1.4.1] Setting conditions Brightness is expressed in 256 levels. White is the maximum value 255, and black is the minimum value 0. The brightness when measuring only the illumination light without the CNT film is set to be within the range of 200 to 220. The brightness when the illumination light is blocked is set to be within the range of 0 to 10. The brightness of the transmitted light intensity of the CNT film to be evaluated is set to be within the range of 150 to 200. The brightness when the illumination light is blocked is set to be within the range of 0 to 10.

[0223] [2.1.4.2] Observation and lighting conditions Microscope: Hirox Co., Ltd. "HRX-01" Lens model: HR2500E (magnification: 80x, 1 pixel: 1.78 μm x 1.78 μm) Transmitted illumination: Illumination model "FASTUS OPPX-10024PP2" (brightness setting: 500) Shutter speed: 1 / 250 Gain: 0 Brightness compensation: None Color: Grayscale

[0224] [2.1.4.3] Luminance Measurement Under the above observation and lighting conditions, images were taken with a resolution of 2000 pixels x 1500 pixels or more. Using the image processing software "ImageJ," the average luminance of a 1000 pixel x 1000 pixel area in the center of the obtained image was measured. The measurement results are shown in Table 5.

[0225] [2.1.5] Step of deriving judgment curve R in the above formula (ii) was set to 0.004. ΔEUVT was substituted into formula (ii) to calculate the area Ap. The calculation results of the area Ap are shown in Table 5. On a graph with luminance on the horizontal axis and area Ap on the vertical axis, the area Ap and luminance of each of the CNT films having thicknesses of 60 nm, 90 nm, 120 nm, and 270 nm in Table 5 were plotted. An approximation formula for the obtained plot was derived by exponential approximation. The approximation formula was expressed by the following formula (viii). Formula (viii): Ap (μm) = 465 × e ０．０１９６×Ｓ In the formula (viii), S represents the luminance of spots corresponding to a reduction in the amount of light of 0.4%.

[0226] [2.1.6] Preparation of NT Membranes for Evaluation As a plurality of NTs, a plurality of single-walled CNTs (crude CNTs, manufactured by Meijo Nano Carbon Co., Ltd., product name: EC1.5-P) synthesized by the improved direct injection pyrolysis synthesis method (eDIPS method) were prepared.

[0227] To 225 mg of NTs, 400 mL of isopropyl alcohol and 50 mL of ethanol were added, and 270 mg of polyacrylic acid was further added as an additive to obtain a mixture. The mixture was stirred using a magnetic stirrer to obtain a suspension. The magnetic stirrer rotation speed was 520 rpm. The temperature of the mixture during stirring was 25°C. The stirring time was 15 hours.

[0228] The resulting suspension was subjected to a dispersion treatment using a stirring homogenizer. The rotation speed of the stirring homogenizer was 11,000 rpm. The total stirring time was 30 minutes.

[0229] The obtained dispersion was subjected to a first centrifugation treatment using a high-speed centrifuge. The rotation speed of the first centrifugation treatment was 5650 x g. The first centrifugation treatment was carried out for 100 minutes. The temperature of the dispersion was 10°C. As a result, the dispersion was separated into a first precipitate and a first supernatant. The first precipitate contained many CNT masses (e.g., CNT aggregates and CNT clumps).

[0230] A first supernatant was collected from the dispersion after the first centrifugation treatment. A second centrifugation treatment was performed on the first supernatant using a high-speed centrifuge. The rotation speed of the second centrifugation treatment was 5650 x g. The second centrifugation treatment was performed for 100 minutes. The temperature of the dispersion was 10°C. As a result, the first supernatant was separated into a second precipitate and a second supernatant. The second precipitate contained many CNT masses (e.g., CNT aggregates and CNT clumps). A second supernatant was collected from the first supernatant after the second centrifugation treatment. The second supernatant is a separated liquid.

[0231] The separation solution was spin-coated onto a 12-inch silicon substrate (roughness Ra: 0.15 nm) to prepare a CNT film (i.e., an NT film for evaluation). The spin-coating rotation speed was 600 rpm. The CNT film was floated on water and lifted up using a frame. The size of the free-standing part of the film was 150 mm x 120 mm.

[0232] [2.1.7] Second measurement step The setting conditions, observation conditions, and illumination conditions were the same as those of the first measurement step.

[0233] The thickness of the CNT film in Example 2-1 was 25 nm. In Example 2-1, the brightness of the CNT film having a thickness of 25 nm was set to 156. The brightness of the frame portion measured with the illumination light blocked was 5.

[0234] The entire area of ​​the CNT film was 140 mm x 108 mm (longer side direction: inside a point 1.5 mm from the edge of the frame, shorter side direction: inside a point 1.0 mm from the edge of the frame). The entire area was photographed, and the brightness of each pixel was observed. From the average brightness when the entire 140 mm x 108 mm area of ​​the CNT film was photographed and the standard deviation σ of the brightness of each pixel, the brightness that was (average brightness + 1 × σ) × 0.8 was defined as the reference brightness. From multiple pixels having brightness equal to or lower than the reference brightness, a pixel with an area of ​​50 μm ２ Multiple pixels constituting the speckles (hereinafter referred to as "speck-constituting pixels") that satisfy the above criteria were selected. Examples of speckles are shown in Figures 6 and 7. In Figures 6 and 7, the speckles indicate the areas surrounded by white lines. The areas of all speckles observed across the entire 140 mm x 108 mm area of ​​the CNT film and the brightness of the speckles were obtained. "Speckle brightness" refers to the average brightness of the multiple speck-constituting pixels. For example, in Figures 6 and 7, the brightness of the white-lined area matches the "reference brightness," while the brightness of the white-lined area is lower than the "reference brightness." The "speckle brightness" is obtained by dividing the sum of the brightness of all speck-constituting pixels in the white-lined area by the number of multiple speck-constituting pixels. The results are shown in Figure 8. The "● (black circle)" in Figure 8 represents the measured area of ​​multiple speckles observed on the CNT film (i.e., the evaluation NT film) and the measured brightness of the speckles.

[0235] Using a contamination analysis and foreign matter inspection system, the film is checked to see if the brightness is equal to or less than 0.8 times the reference brightness of the film and is within 50 μm. ２ The above-mentioned areas were defined as "spots." The total area of ​​multiple spots was calculated. The percentage of spots (%) was calculated using the following formula (A): Formula (A): Percentage of spots (%) = (Total area of ​​spots / Area of ​​observed area) x 100 In formula (A), the area of ​​the observed area was 15,120 mm ２ (140mm x 108mm.

[0236] [2.1.8] Comparison and Evaluation Step Using the relationship between the measured brightness values ​​and the measured area values ​​of the spots on the CNT film (evaluation NT) and the evaluation curve (see FIG. 8), the exposure evaluation was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 6. An acceptable exposure evaluation result is "A."

[0237] [1.8.1] Evaluation criteria "A": The number of NG spots was 0. "B": The number of NG spots was 1 or more.

[0238] [2.2] Example 2-2 A CNT film (i.e., an NT film for evaluation) was prepared in the same manner as in Example 2-1, except that in "[1.6] Preparation of NT film for evaluation," the spin coating conditions were changed to a CNT film thickness of 30 nm. Exposure evaluation of the CNT film was performed in the same manner as in Example 2-1 (see FIG. 9). The measurement results and calculation results are shown in Table 6 and FIG. 9.

[0239] [2.3] Examples 2-3 and 2-4 In "[1.6] Preparation step of NT membrane for evaluation," a CNT membrane (i.e., an NT membrane for evaluation) was prepared in the same manner as in Example 2-1, except that the rotation speed and time of the first centrifugation process were changed to the conditions shown in Table 6 and the second centrifugation process was not performed. Exposure evaluation of the CNT membrane was performed in the same manner as in Example 2-1 (see FIGS. 10 and 11). The measurement results and calculation results are shown in Table 6, FIG. 10 (Example 2-3), and FIG. 11 (Example 2-4).

[0240] [2.4] Results

[0241] The evaluation method of Examples 2-1 to 2-4 was found to be a "method of evaluating a nanotube film for exposure that can more reliably evaluate whether or not exposure defects occur."

[0242] The disclosures of Japanese Patent Application No. 2024-086565, filed on May 28, 2024, and Japanese Patent Application No. 2024-086570, filed on May 28, 2024, are incorporated herein by reference in their entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A nanotube film containing a plurality of nanotubes, wherein the ratio of the total area of ​​the spots to the area of ​​the main surface of the nanotube film is 7.00 x 10 －４ % or less, and the spots have a brightness of 80% or less of the reference brightness in an image of the main surface of the nanotube film observed with an optical microscope, and ２ a nanotube film having an area of ​​1.0 μm to 2.0 μm×1.0 μm to 2.0 μm, wherein the size of one pixel of the observed image is 1.0 μm to 2.0 μm×1.0 μm to 2.0 μm, and the reference brightness is expressed by the following formula (1): Formula (1): Reference brightness = average value of brightness over the entire main surface of the nanotube film + 1 × brightness at height of standard deviation σ of brightness over the entire main surface of the nanotube film.

2. The nanotube is one selected from the group consisting of a carbon nanotube, a boron nitride nanotube, and a transition metal disulfide nanotube, wherein the transition metal disulfide nanotube contains a transition metal disulfide, and the transition metal disulfide is MX ２ 2. The nanotube film of claim 1, wherein M is at least one selected from Mo, W, Pd, Pt, and Hf; and X is at least one selected from S, Se, and Te.

3. The nanotube film of claim 1, wherein the number of spots is 200 or less.

4. The nanotube film according to claim 1, wherein the nanotubes have a tube diameter of 0.8 nm to 6.0 nm.

5. The nanotube film of claim 1, wherein the film thickness is between 2 nm and 100 nm.

6. The nanotube film according to claim 1, wherein the length of the main surface of the nanotube film in a first direction is 90 mm or more, and the length of the main surface of the nanotube film in a second direction perpendicular to the first direction is 90 mm or more.

7. A pellicle membrane comprising the nanotube membrane according to any one of claims 1 to 6.

8. A pellicle comprising: the pellicle membrane according to claim 7; and a support frame that supports the pellicle membrane.

9. An exposure master comprising: a photomask; and the pellicle according to claim 8 attached to the photomask.

10. An exposure apparatus comprising: an extreme ultraviolet light source that emits extreme ultraviolet light as exposure light; an exposure master according to claim 9; and an optical system that directs the exposure light emitted from the extreme ultraviolet light source to the exposure master, wherein the exposure master is positioned so that the extreme ultraviolet light emitted from the extreme ultraviolet light source passes through the pellicle film and is irradiated onto the photomask.

11. A method for producing a nanotube membrane according to any one of claims 1 to 6, comprising: preparing a raw material containing a plurality of nanotubes; mixing the plurality of nanotubes with a solvent to prepare a dispersion; centrifuging the dispersion to prepare a separated liquid; and forming the separated liquid into a sheet-like membrane to produce a nanotube membrane, wherein the centrifugal separation is performed two or more times.

12. The method for producing a nanotube membrane according to claim 11, wherein the average relative centrifugal force of the centrifugation is 200 x g or more.

13. The method for producing a nanotube film according to claim 11, wherein the nanotube film is used as a pellicle film.

14. A method for evaluating a nanotube film for exposure, comprising: preparing an NT film (a) representing a nanotube film having a reference thickness, and a plurality of nanotube films having thicknesses different from that of the NT film (a); deriving ΔEUVT(t), which is the difference between EUVT(a) representing the transmittance of extreme ultraviolet light through the NT film (a) and EUVT(t) representing the transmittance of extreme ultraviolet light through each of the plurality of nanotube films, from the following formula (i); measuring the brightness of each of the plurality of nanotube films; and deriving an allowable relationship between an allowable speckle area Ap and an allowable speckle brightness by applying the relationship between ΔEUVT(t) and the measured value of the brightness of the nanotube film corresponding to ΔEUVT(t) to the following formula (ii): (In formula (ii), NA represents the numerical aperture of the photomask when the pellicle, which is formed by attaching the nanotube film to a pellicle frame, is attached to the photomask. L1 represents the distance between the nanotube film of the pellicle and the photomask. R represents the allowable error range for variations in light intensity.) 15. A method for evaluating a nanotube film for exposure as described in claim 14, comprising: measuring the brightness and area of ​​spots on a nanotube film to be evaluated; and comparing the relationship between the measured brightness and area of ​​spots on the nanotube film to be evaluated and the tolerance relationship.

16. A method for evaluating a nanotube film for exposure as described in claim 15, wherein the comparing step includes: comparing the measured value of the area of ​​the speck on the nanotube film to be evaluated with the maximum value of the area Ap corresponding to the measured value of the brightness of the speck on the nanotube film to be evaluated in the tolerance relationship; and determining that there is an exposure defect if there is a speck whose measured value of the area is larger than the maximum value, and determining that there is no exposure defect if there is no speck whose measured value of the area is larger than the maximum value.

17. A method for evaluating a nanotube film for exposure according to any one of claims 14 to 16, wherein the film thickness of the NT film (a) is thinner than the film thickness of each of the plurality of nanotube films, and the method includes measuring the film thickness of the NT film (a) and each of the plurality of nanotube films.

18. A method for evaluating a nanotube film for exposure according to any one of claims 14 to 16, comprising: a thickness of the NT film (a) being thinner than the thickness of each of the plurality of nanotube films; measuring the EUVT(a) and the EUV transmittance of each of the plurality of nanotube films; and correlating the ΔEUV(t) of a nanotube film having a comparable thickness with the brightness of the nanotube film having a comparable thickness.

19. A method for evaluating a nanotube film, comprising: measuring the brightness and speckle area of ​​the nanotube film to be evaluated; and comparing the relationship between the measured brightness of the speckles of the nanotube film to be evaluated and the measured speckle area with an acceptable relationship between an acceptable speckle area Ap and an acceptable speckle brightness, wherein the acceptable relationship is obtained by applying the relationship between ΔEUVT(t) and the measured brightness of the nanotube film corresponding to ΔEUVT(t) to the following formula (ii), wherein ΔEUVT(t) is obtained by deriving ΔEUVT(t), which is the difference between EUVT(a) and EUVT(t), from the following formula (i), wherein EUVT(a) represents the transmittance of extreme ultraviolet rays through NT film(a), which represents a nanotube film having a reference thickness, The method for evaluating a nanotube film for exposure, wherein the EUVT(t) indicates the transmittance of extreme ultraviolet rays of each of a plurality of nanotube films having a thickness different from that of the NT film (a). (In formula (ii), NA represents the numerical aperture of a photomask when a pellicle having the nanotube film attached to a pellicle frame is attached to the photomask.) L1 indicates the distance between the nanotube film of the pellicle and the photomask. R indicates the allowable error range for variations in light intensity.

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