Protective film and protective film assembly

Abstract

A pellicle film (10) having a porous structure, the pellicle film (10) containing carbon nanotubes, the coefficient of variation in the diameter of voids measured on the surface of the porous structure being 0.7 or less, and the coefficient of variation in the distance between the most adjacent centers of gravity between the voids being 0.6 or less.

Description

TECHNICAL FIELD

[0001] The present application relates to a pellicle film and a pellicle. BACKGROUND

[0002] In a manufacturing process of a semiconductor device or the like, for example, by applying a photoresist to a substrate such as a semiconductor wafer, irradiating light on the substrate on which the photoresist is applied using a photomask, and removing the photoresist, a target circuit pattern can be formed on the substrate.

[0003] When light is irradiated in a state where a foreign matter is attached to the photomask, the circuit pattern formed on the substrate can be hindered by the attached foreign matter. Therefore, in order to suppress the attachment of the foreign matter to the photomask, a pellicle assembly provided with a pellicle for capturing the foreign matter is sometimes used. The pellicle assembly is disposed above the photomask at a distance at which the pellicle does not come into contact with the photomask.

[0004] In recent years, in order to form a more fine circuit pattern, the use of extreme ultraviolet (EUV) is being studied. EUV refers to light having a wavelength of 1 nm or more and 100 nm or less. As the EUV, for example, specifically, light around 13.5 nm ± 0.3 nm is being used. When EUV is irradiated to the pellicle, although the EUV transmits through the pellicle, a part of the irradiated EUV is absorbed by the pellicle. By converting the light energy of the absorbed EUV into heat energy, the temperature of the pellicle rises. Therefore, the pellicle is required to have transmittance of EUV, heat resistance, and durability, and the like.

[0005] In the pellicle assembly used in the process of forming a circuit pattern using EUV, carbon nanotubes are being studied as one of the materials used in the pellicle provided in the pellicle assembly.

[0006] For example, Patent Literature 1 discloses a pellicle including a carbon nanotube including, at least on a surface layer side, a silicon carbide layer in which at least a part of carbon is substituted with silicon.

[0007] PRIOR ART DOCUMENTS

[0008] PATENT LITERATURE

[0009] Patent Literature 1: International Publication No. 2021-172104 SUMMARY

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] The strength and the EUV transmissivity of the protective film containing carbon nanotubes disclosed in Patent Literature 1 are excellent. However, the protective film disclosed in Patent Literature 1 does not mention the deviation of the void property of the surface of the protective film. If the void property deviates, the strength and the EUV transmissivity of the protective film are easily affected, and the protective film is required to be further improved.

[0012] The present application provides a protective film in which the strength of the protective film is improved and the deviation of the EUV transmissivity is suppressed in a protective film containing carbon nanotubes, and a protective film module using the same.

[0013] Method for solving the problem [1]

[0015] A protective film having a porous structure, wherein,

[0016] The protective film contains carbon nanotubes,

[0017] A variation coefficient of a void diameter of a void measured on a surface of the porous structure is 0.7 or less, and a variation coefficient of a nearest-neighbor center-to-center distance between the voids is 0.6 or less. [2]

[0019] The protective film according to [1], wherein,

[0020] The variation coefficient of the void diameter is 0.4 or more and 0.7 or less. [3]

[0022] The protective film according to [1] or [2], wherein,

[0023] The variation coefficient of the nearest-neighbor center-to-center distance is 0.2 or more and 0.5 or less. [4]

[0025] The protective film according to any one of [1] to [3], wherein,

[0026] The length of the carbon nanotubes is 0.1 pm or more and 1000 pm or less. [5]

[0028] The protective film according to any one of [1] to [4], wherein,

[0029] The cross-sectional diameter of the carbon nanotubes is 0.2 nm or more and 50 nm or less. [6]

[0031] The protective film according to [1] to [5], wherein,

[0032] The average value of the void diameter is 20 nm or more and 60 nm or less. [7]

[0034] The protective film according to any one of [1] to [6], wherein

[0035] The protective film is a porous structure in which the carbon nanotubes are accumulated. [8]

[0037] The protective film according to any one of [1] to [7], which has self-supporting property. [9]

[0039] A protective film assembly comprising:

[0040] The protective film according to any one of [1] to [8], and

[0041] A support body having a frame portion and an opening portion surrounded by the frame portion, and supporting the protective film.

[0042] According to one embodiment of the present application, a protective film containing carbon nanotubes can be provided, in which the strength of the protective film is improved and the variation in EUV transmittance is suppressed, and a protective film assembly using the same can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 A plan view schematically showing one example of the protective film assembly of the present embodiment.

[0044] Figure 2 A cross-sectional view showing a II-II cross section of Figure 1

[0045] Figure 3A A plan view schematically showing a protective film assembly for strength evaluation of the protective film.

[0046] Figure 3B A side view schematically showing a protective film assembly for strength evaluation of the protective film.

[0047] Figure 4 An explanatory view schematically showing the strength evaluation of the protective film.

[0048] SYMBOL EXPLANATION

[0049] 10, 10W... protective film

[0050] 11... first protective film surface

[0051] 12... second protective film surface

[0052] 13... edge portion

[0053] 20W... adhesive layer

[0054] ​30, 30W support body

[0055] 31 frame portion

[0056] 32, 32W opening portion

[0057] 33 support surface

[0058] 100 protective film assembly

[0059] WK protective film assembly for strength evaluation DETAILED DESCRIPTION

[0060] (Protective film)

[0061] The protective film of the present embodiment has a porous structure. The protective film contains carbon nanotubes, and the coefficient of variation of the void diameters of the voids measured on the surface of the porous structure is 0.7 or less, and the coefficient of variation of the distances between the centers of gravity of the nearest-neighbor voids is 0.6 or less.

[0062] It can be considered that the protective film of the present embodiment has voids in a state close to uniform by having the above-described configuration. It can be considered therefore that, for the protective film, the variation in the strength of the protective film is suppressed, and the in-plane variation in the transmitted light transmitted through the protective film is also suppressed. As a result, it can be considered that, according to the protective film of the present embodiment, the strength of the protective film is improved, and the variation in the EUV transmittance is suppressed.

[0063] The manner in which the protective film is adjusted so that the coefficient of variation of the void diameters of the voids measured on the surface of the porous structure is 0.7 or less, and the coefficient of variation of the distances between the centers of gravity of the nearest-neighbor voids is 0.6 or less is not particularly limited. The manner can be exemplified by, for example, a manner in which the amount of carbon nanotubes contained in the protective film (for example, the amount of carbon nanotubes contained in a filmized product of carbon nanotubes as an intermediate product at the time of forming the protective film, or the amount of carbon nanotubes in a carbon nanotube dispersion liquid at the time of forming a filmized product of carbon nanotubes) and the dispersion strength of the carbon nanotubes are adjusted in an example of the preferred production method of the protective film described later.

[0064] The carbon nanotubes contained in the protective film of the present embodiment are not particularly limited, and are preferably at least one selected from the group consisting of multi-walled carbon nanotubes (MWCNTs), few-walled carbon nanotubes (FWCNTs), double-walled carbon nanotubes (DWCNTs), and single-walled carbon nanotubes (SWCNTs).

[0065] The carbon nanotubes can be obtained by publicly known production methods such as an arc discharge method, a laser ablation method, and a chemical vapor deposition.

[0066] The length of the carbon nanotubes is preferably, for example, 0.1 μm or more and 1000 μm or less.

[0067] The length of the carbon nanotubes is more preferably 0.5 μm or more, and further preferably 1 μm or more.

[0068] The length of the carbon nanotubes is more preferably 600 μm or less, and further preferably 400 μm or less.

[0069] The cross-sectional diameter of the carbon nanotubes is preferably 0.2 nm or more and 50 nm or less.

[0070] The cross-sectional diameter of the carbon nanotubes is more preferably 0.5 nm or more, and further preferably 1 nm or more.

[0071] The cross-sectional diameter of the carbon nanotubes is more preferably 30 nm or less, and further preferably 20 nm or less.

[0072] Note that, in the present specification, the cross-sectional diameter is sometimes simply referred to as the diameter.

[0073] The coefficient of variation of the void diameters of the voids measured on the surface of the porous structure of the protective film of the present embodiment is 0.7 or less. From the viewpoint of further improving the strength of the protective film and further easily suppressing the variation in the EUV transmittance, the coefficient of variation of the void diameters is preferably 0.68 or less, and more preferably 0.67 or less.

[0074] The lower limit of the coefficient of variation of the void diameters is not particularly limited, and can be, for example, 0.40 or more, or 0.42 or more.

[0075] In the present specification, the void diameter refers to the diameter of an imaginary circle having the same area as the area of the void (i.e., the equivalent circle diameter). The coefficient of variation of the void diameters (CV1) can be calculated as follows: the average value (D1 [unit: nm]) and the standard deviation (σ1 [unit: nm]) of the void diameters are calculated, and the coefficient of variation of the void diameters is calculated based on the following mathematical expression (Mathematical Expression 1).

[0076] Coefficient of variation of void diameters CV1= σ1 / D1 ···(Mathematical Expression 1)

[0077] The coefficient of variation of the inter-pore distance between the centers of gravity of the nearest neighboring pores in the inter-pores measured on the surface of the porous structure of the protective film of the present embodiment is 0.6 or less. From the viewpoint of further improving the strength of the protective film and easily further suppressing the variation in EUV transmittance, the coefficient of variation of the inter-pore distance between the centers of gravity of the nearest neighboring pores is preferably 0.5 or less, more preferably 0.45 or less, and further preferably 0.43 or less.

[0078] The lower limit of the coefficient of variation of the inter-pore distance between the centers of gravity of the nearest neighboring pores is not particularly limited, and can be, for example, 0.2 or more or 0.25 or more.

[0079] In the present specification, the inter-pore distance between the centers of gravity of the nearest neighboring pores refers to the distance between the center of gravity of one pore and the center of gravity of the pore that is nearest to the one pore. That is, for pores that are adjacent to each other with pores therebetween, it refers to the distance from the center of gravity of one pore to the center of gravity of the other pore. The coefficient of variation of the inter-pore distance between the centers of gravity of the nearest neighboring pores (CV2) can be calculated by calculating the average value (D2 [unit: nm]) and the standard deviation (σ2 [unit: nm]) of the inter-pore distance between the centers of gravity of the nearest neighboring pores and calculating the coefficient of variation of the inter-pore distance between the centers of gravity of the nearest neighboring pores based on the following mathematical expression (Mathematical Expression 2).

[0080] Coefficient of variation of inter-pore distance between centers of gravity of nearest neighboring pores CV2 = σ2 / D2 ··· (Mathematical Expression 2)

[0081] For the protective film of the present embodiment, for example, the coefficient of variation of the pore diameter of the pores in the pores measured on the surface of the porous structure can be 0.4 or more and 0.7 or less, and the coefficient of variation of the inter-pore distance between the centers of gravity of the nearest neighboring pores can be 0.2 or more and 0.6 or less.

[0082] From the viewpoint of further improving the strength of the protective film and easily further suppressing the variation in EUV transmittance, the average value of the pore diameter of the pores measured on the surface of the porous structure of the protective film can be, for example, 20 nm or more and 60 nm or less. The average value of the pore diameter can be 25 nm or more or 30 nm or more. The average value of the pore diameter can be 55 nm or less, 50 nm or less, or the like.

[0083] From the viewpoint of further improving the strength of the protective film and easily further suppressing the variation in EUV transmittance, the average value of the inter-pore distance between the centers of gravity of the nearest neighboring pores measured on the surface of the porous structure of the protective film is preferably, for example, 40 nm or more and 95 nm or less. The average value of the inter-pore distance between the centers of gravity of the nearest neighboring pores can be 50 nm or more, 55 nm or more, or the like. The average value of the inter-pore distance between the centers of gravity of the nearest neighboring pores can be 80 nm or less, 68 nm or less, or 67 nm or less.

[0084] In the measurement of the void characteristics of the surface of the porous structure of the protective film, the average value of the void diameter and the coefficient of variation of the void diameter, and the average value of the distance between the centers of gravity of the nearest neighboring voids and the coefficient of variation of the distance between the centers of gravity of the nearest neighboring voids can be measured by a method having the following enumerated steps (1) to (10). By using the following measurement method, a unique threshold value can be determined, and thus, for example, a reasonable result can be easily obtained regardless of the measurer. Specifically, the measurement method of the above void characteristics is shown in the following example.

[0085] (1) A step of preparing a protective film.

[0086] (2) A step of imaging the surface of the above prepared protective film to obtain image data of the protective film.

[0087] (3) A step of setting, as initial threshold values, 3 or more different threshold values at equal intervals in a range from a first pixel value to a second pixel value larger than the first pixel value with respect to the image data, performing binarization processing based on the initial threshold values, respectively, and obtaining binarization-processed image data based on the initial threshold values.

[0088] (4) A step of obtaining initial measured values of the distribution of the void characteristics of the voids of the surface of the protective film by performing Blob analysis on the binarization-processed image data based on the initial threshold values.

[0089] (5) A step of obtaining initial theoretical values of the distribution of the void characteristics by performing a lognormal distribution probability density function based on the initial measured values.

[0090] (6) A step of obtaining an error between the initial measured values and the initial theoretical values.

[0091] (7) In the case where the error between the initial measured values and the initial theoretical values is not the minimum, a step of again setting a threshold value, performing binarization processing on the image data based on the re-set threshold value, obtaining binarization-processed image data based on the re-set threshold value, performing Blob analysis on the binarization-processed image data based on the re-set threshold value, and thereby obtaining re-measured values of the distribution of the void characteristics of the surface of the protective film.

[0092] (8) A step of obtaining a re-measured error of the distribution of the void characteristics by performing a lognormal distribution probability density function based on the re-measured values.

[0093] (9) When the error between the remeasured actual value and the remeasured theoretical value is not the smallest, repeat the steps of obtaining the remeasured actual value and calculating the error with the remeasured theoretical value until the error between the remeasured actual value and the remeasured theoretical value is minimized.

[0094] (10) A step of obtaining, as a final measured value, a distribution of void characteristics calculated based on a threshold value at which the error between the initial measured value and the initial theoretical value, or the error between the remeasured measured value and the remeasured theoretical value, is minimized.

[0095] The threshold at which the error is minimized is preferably determined using various known optimization algorithms. For example, in steps (4) to (9) above, it is preferred to use various known optimization algorithms to search for the threshold at which the error is minimized. In this case, after determining the initial threshold, a unique threshold is determined using the optimization algorithm.

[0096] In the step of obtaining the binarized image data based on the above-mentioned initial threshold, the initial threshold is not limited to the above-mentioned. A plurality of different thresholds of 5 or more can be set at equal intervals in the range from the first pixel value to the second pixel value greater than the above-mentioned first pixel value, or a plurality of different thresholds of 7 or more can be set. The interval between the first pixel value and the second pixel value is preferably greater than 100. The first pixel value is preferably set in the range of 20 or more and 50 or less. The second pixel value is preferably set in the range of 150 or more and 240 or less. Equal interval means that when n thresholds are set as the plurality of different thresholds of 3 or more, the intervals between adjacent thresholds are equal, so that the interval between the nth threshold and the n-1th threshold, and the interval between the n-1th threshold and the n-2th threshold are equal. For the initial threshold, for example, a plurality of different thresholds of 3 or more and 12 or less can be set at equal intervals in the range of pixel value 20 to pixel value 240 as the initial threshold.

[0097] It should be noted that in the step of obtaining the re-measured actual value, the re-set threshold value is not a plurality of three or more different threshold values, but a single threshold value.

[0098] The above-mentioned void characteristics can be measured, for example, by a device equipped with a program for causing a computer to execute the above-mentioned steps (1) to (10). The program can be recorded on a recording medium.

[0099] The thickness of the protective film is preferably 3 nm or more and 1000 nm or less. The thickness of the protective film is preferably 10 nm or more, more preferably 20 nm or more. The thickness of the protective film is preferably 500 nm or less, more preferably 300 nm or less. If the thickness of the protective film is, for example, 3 nm or more and 1000 nm or less, the strength of the protective film is further improved, and it is easy to further suppress the variation in EUV transmittance. Also, the handleability of the protective film is improved.

[0100] The weight per unit area of the protective film is not particularly limited, and is, for example, preferably 0.1 μg / cm 2 or more and 20 μg / cm 2 or less. The weight per unit area of the protective film is more preferably 0.5 μg / cm 2 or more, further preferably 1 μg / cm 2 or more. The weight per unit area of the protective film is more preferably 15 μg / cm 2 or less, further preferably 10 μg / cm 2 or less. If the weight per unit area of the protective film is, for example, 0.1 μg / cm 2 or more and 20 μg / cm 2 or less, the strength of the protective film is further improved, and it is easy to further suppress the variation in EUV transmittance.

[0101] The protective film of the present embodiment is preferably a porous structure in which carbon nanotubes are stacked. The porous structure in which carbon nanotubes are stacked can be manufactured by one example of the preferred manufacturing method of the protective film described later. If it is a porous structure in which carbon nanotubes are stacked, the strength of the protective film is further improved, and it is easy to further suppress the variation in EUV transmittance.

[0102] From the viewpoint of improving the transparency to exposure light, the protective film of the present embodiment preferably has self-supporting properties. The protective film having self-supporting properties means a film in which the protective film itself is in a self-supporting state, and means a film having self-supporting retention (also referred to as a self-supporting film). That is, the protective film having self-supporting properties is a film that can maintain the shape by the protective film itself even in the absence of a substrate or the like.

[0103] (Method for manufacturing protective film)

[0104] The method for manufacturing the protective film is not particularly limited. One example of the preferred manufacturing method of the protective film, for example, has: a step of dispersing carbon nanotubes (step P1); a step of causing the dispersed carbon nanotubes to settle and stack on a gas-permeable member, and obtaining a film product in which a mat-shaped carbon nanotube is formed on the gas-permeable member (step P2); and a step of removing the gas-permeable member from the film product of the carbon nanotubes to obtain the protective film (step P3).

[0105] First, in process P1, carbon nanotubes are dispersed in a liquid as a dispersion medium, and a carbon nanotube dispersion liquid in which carbon nanotubes are dispersed in a liquid is prepared. The liquid can be a liquid containing water. The carbon nanotube dispersion liquid can contain only carbon nanotubes as a dispersed substance. In addition to carbon nanotubes, the carbon nanotube dispersion liquid can contain various additives such as a dispersant that disperses carbon nanotubes.

[0106] For example, by adjusting the balance between the dispersion intensity when dispersing carbon nanotubes in a liquid in process P1 and the weight per unit area of carbon nanotubes when making a film of carbon nanotubes in process P2, a protective film in which the coefficient of variation of the void diameter is 0.7 or less and the coefficient of variation of the distance between the centers of gravity of the nearest neighbors between voids is 0.6 or less is easily obtained. For example, specifically, when the weight per unit area of the above-described carbon nanotubes is set to an amount of a certain degree or more, it is easy to satisfy the range in which the coefficient of variation of the void diameter is 0.7 or less, and if the weight per unit area of the above-described carbon nanotubes is decreased too much, there is a tendency for the coefficient of variation of the void diameter to be greater than 0.7. Also, for example, when the above-described dispersion intensity is suppressed to a certain degree, it is easy to satisfy the range in which the coefficient of variation of the distance between the centers of gravity of the nearest neighbors between voids is 0.6 or less, and if the above-described dispersion intensity is increased too much, there is a tendency for the coefficient of variation of the distance between the centers of gravity of the nearest neighbors between voids to be greater than 0.6.

[0107] For the weight per unit area of the above-described carbon nanotubes and the above-described dispersion intensity, for example, in terms of the amount of carbon nanotubes contained in the film of carbon nanotubes made in process P2, a range of 0.1 μg / cm 2 20 μg / cm 2 or more and 60 μm / s or less, and in terms of the stirring time of the stirrer, a range of 5 minutes or more and 60 minutes or less.

[0108] Next, in process P2, the dispersed carbon nanotubes are settled and accumulated on a gas-permeable member. For example, by filtering the carbon nanotube dispersion liquid prepared in process P1 with a filter membrane as a gas-permeable member, the carbon nanotubes are settled and accumulated, and a film of carbon nanotubes in the form of a mat is formed on the filter membrane. The filter membrane is preferably used, for example, a membrane filter or the like.

[0109] Next, in process P3, by removing the filter membrane from the film of carbon nanotubes in the form of a mat, a protective film containing carbon nanotubes is obtained. Before or after removing the filter membrane from the film of fibers in the form of a mat, a drying process can be provided as necessary. The obtained protective film is a self-supporting film.

[0110] (Protective film assembly)

[0111] The protective film assembly of the present embodiment is provided with the protective film of the above-described embodiment, and a support that has a frame portion and an opening portion surrounded by the frame portion and supports the protective film.

[0112] Hereinafter, the protective film assembly of the present embodiment will be described with reference to the drawings.

[0113] Note that in the drawings referred to in the description of the present specification, there are portions that are enlarged or reduced for ease of explanation.

[0114] Figure 1 a plan view of the protective film assembly 100 viewed from the side on which the protective film 10 is installed, Figure 2 a cross-sectional view of the protective film assembly 100 shown in Figure 1 The protective film assembly 100 shown in the cross-sectional view is provided with the protective film 10 and a support 30 that supports the protective film 10. The support 30 is provided with a frame portion 31 and an opening portion 32 surrounded by the frame portion 31, and the opening portion 32 penetrates from one side to the other side of the support 30. The frame portion 31 and the opening portion 32 are each formed in a rectangular shape, and the four corners of the outer shape of the frame portion 31 each have a circular arc. The frame portion 31 is provided with a support surface 33 that faces the protective film 10. The protective film 10 is formed in a rectangular shape, and is provided with a first protective film surface 11 that faces the support surface 33 of the support 30 and a second protective film surface 12 that is on the opposite side from the first protective film surface 11. The edge portion 13 of the protective film 10 is fixed by a portion of the support surface 33 of the frame portion 31, and the protective film 10 covers the opening portion 32 of the support 30.

[0115] The protective film 10 can use the protective film of the above-described present embodiment. As the material of the support 30, for example, a resin material (polyethylene or the like), a metal material (aluminum, an aluminum alloy, a magnesium alloy, stainless steel, titanium, or the like), a ceramic material (SiC or the like), and a fiber-reinforced plastic material (carbon fiber-reinforced plastic or the like) can be used.

[0116] Note that in the protective film 10, in order to make clear the positional relationship between the side of the support surface 33 of the support 30 that faces the side opposite thereto, the terms of the first protective film surface 11 and the second protective film surface 12 are used for convenience of expression. Therefore, the first protective film surface 11 and the second protective film surface 12 can be used interchangeably depending on the situation, and the first protective film surface 11 and the second protective film surface 12 can be used without distinction from each other.

[0117] Hereinabove, the protective film assembly of the present embodiment has been described with reference to Figure 1 and Figure 2An example of the protective film assembly of the present embodiment is described, but the protective film assembly of the present embodiment is not limited thereto. The protective film assembly of the present embodiment can adopt various modes as long as the effects of the protective film assembly using the protective film of the present embodiment described above can be obtained. The shape and size of each portion of each member configuring the protective film assembly of the present embodiment can be determined, for example, in accordance with the size of a photomask (not shown) when the protective film assembly of the present embodiment is used.

[0118] For example, Figure 1 and Figure 2 The protective film 10 and the support 30 of the protective film assembly 100 shown in Figs. 1 and 2 are each formed in a rectangular shape. The protective film assembly of the present embodiment is not limited thereto, and can be formed in any desired shape such as a circular shape, an elliptical shape, and a polygonal shape.

[0119] In addition, for example, in the protective film assembly 100 shown in Figs. 1 and 2, the edge portion 13 of the protective film 10 is fixed by a portion of the support surface 33 of the support 30. The protective film assembly 100 is not limited thereto, and the edge portion 13 of the protective film 10 can be fixed by the entire surface of the support surface 33 of the support. Figure 1 Figure 2 In addition, for example, in the protective film assembly 100 shown in Figs. 1 and 2, the edge portion 13 of the protective film 10 is fixed by a portion of the support surface 33 of the support 30. The protective film assembly 100 is not limited thereto, and the edge portion 13 of the protective film 10 can be fixed by the entire surface of the support surface 33 of the support.

[0120] In addition, for example, in the protective film assembly 100 shown in Figs. 1 and 2, the edge portion 13 of the protective film 10 is fixed by a portion of the support surface 33 of the support 30. The protective film assembly 100 is not limited thereto, and the edge portion 13 of the protective film 10 can be fixed by the entire surface of the support surface 33 of the support. Figure 1 Figure 2 In addition, for example, in the protective film assembly 100 shown in Figs. 1 and 2, the edge portion 13 of the protective film 10 is fixed by a portion of the support surface 33 of the support 30. The protective film assembly 100 is not limited thereto, and the edge portion 13 of the protective film 10 can be fixed by the entire surface of the support surface 33 of the support.

[0121] (Method for manufacturing protective film assembly)

[0122] An example of the preferred method for manufacturing the protective film assembly of the present embodiment includes a step of preparing the protective film of the present embodiment, a step of preparing a support having a frame portion and an opening portion surrounded by the frame portion and supporting the protective film, and a step of disposing the protective film so as to cover the opening portion and be supported by the support surface of the frame portion. The method for manufacturing the protective film assembly can include a step of disposing an adhesive layer on at least a portion of the support surface of the frame portion, as needed.

[0123] ​​The procedure for preparing the protective film of the present embodiment is the same as that of the above-described embodiment. The procedure for preparing the support is the same as that of the above-described embodiment, in which a support having a desired shape is prepared using a material constituting the support by a publicly known method. The procedure for disposing the protective film is the same as that of the above-described embodiment, in which the protective film is erected so as to cover the opening portion and be supported by the support surface of the frame portion by a publicly known method. In the case where the adhesive layer is provided on at least a part of the support surface of the frame portion, the protective film can be erected so as to be supported by the support surface of the frame portion with the aid of the adhesive layer. In the case where various adhesives are used in the adhesive layer, the procedure for providing the adhesive layer can be performed by applying the adhesive to the support surface to provide an adhesive layer containing the adhesive. In the case where carbon nanotubes are used in the adhesive layer, the procedure for providing the adhesive layer can be performed, for example, by applying a dispersion liquid of carbon nanotubes to the support surface and drying it to provide an adhesive layer containing carbon nanotubes.

[0124] The protective film assembly of the present embodiment is used, for example, in such a manner that the first protective film surface is opposed to a photomask and is disposed separately from the photomask above the photomask. By using the protective film assembly of the present embodiment, the attachment of foreign matter to the photomask can be suppressed, and the variation in EUV transmissivity can be suppressed. In addition, since the strength of the protective film of the present embodiment is improved, damage during the erection of the protective film assembly and during transportation can be suppressed.

[0125] Note that the present application is not limited to the above-described embodiments, and modifications and the like within the scope of achieving the object of the present application are included in the present application.

[0126] Example

[0127] Hereinafter, the present application will be described in more detail by citing examples, but the present application is not limited to any of the examples.

[0128] [Example 1]

[0129] [Manufacture of Protective Film]

[0130] As carbon nanotubes (hereinafter referred to as CNT), CNT having a diameter of 0.2 nm or more and 50 nm or less and a length of 1 μm or more and 250 μm or less were prepared. The prepared CNT was weighed so that the concentration in a water dispersion of the CNT was 0.02 mass%. In addition, as a dispersant, carboxymethyl cellulose (hereinafter referred to as CMC) was weighed so that the concentration in the water dispersion was 0.2 mass%. The weighed CNT and the weighed CMC were put into water, and a water dispersion of the CNT was prepared by dispersing the CNT in the water using a thin film rotary type high-speed stirrer (Primix Corporation, product name "Filmix") at a peripheral speed of 40 m / s for 10 minutes. Note that the shear speed at the time of dispersing the CNT was about 4.0 x 10 5 s-1 Next, the CNT water dispersion liquid was diluted so that the concentration of the CNT was 1 ppm. Next, the diluted CNT water dispersion liquid was introduced into the filter so that the mass of the CNT contained in the protective film (indicated as CNT film-in mass in Table 1) was 0.88 pg / cm2. 2 Next, the CNT water dispersion liquid introduced into the filter was filtered with the membrane filter, and a mat-shaped CNT film product was formed on the membrane filter. Thereafter, the mat-shaped CNT film product was peeled from the membrane filter, and a protective film containing the CNT was produced. The protective film was a film having self-supportability. From the obtained protective film, the coefficient of variation of the void diameter, the average value of the void diameter, the coefficient of variation of the nearest-neighbor inter-center distance between the voids, and the average value of the nearest-neighbor inter-center distance between the voids were calculated based on the void analysis of the protective film described later.

[0131] < Void analysis of protective film >

[0132] The surface of the protective film obtained in each example was observed with a scanning electron microscope (SEM: Scanning Electron Microscope) (manufactured by Carl Zeiss, CrossBeam 550), and image data of the SEM image was obtained. The photographing conditions were set to an acceleration voltage of 1 kV and a magnification of 10,000 times. The field of view was set to 3 or more fields of view.

[0133] Based on the obtained image data of the SEM image, the void diameter (pore size) was analyzed as the equivalent circle diameter. First, for one field of view of the image data of the SEM image, an initial binarization threshold value was set at 7 points of 40, 60, 80, 100, 120, 140, and 160 at equal intervals of 20 pixel values between a pixel value of 40 and a pixel value of 160, and 7 points of binarization-processed image data were obtained at the respective binarization threshold values. This operation was performed on the image data of 3 or more fields of view. Next, for the obtained binarization-processed image data, the distribution of the initial void diameter was determined based on the initial binarization threshold value. Then, the binarization threshold value that minimized the error between the measured value of the distribution of the void diameter and the theoretical value of the distribution of the void diameter was automatically searched for by fitting using Bayesian optimization in such a manner that the measured value of the distribution of the void diameter was well approximated (fitted) to a lognormal distribution. Then, based on the distribution of the void diameter and the distribution of the nearest-neighbor inter-center distance between the voids measured at the binarization threshold value at which the error between the measured value of the distribution of the void diameter and the theoretical value of the distribution of the void diameter was minimized, the coefficient of variation of the void diameter and the coefficient of variation of the nearest-neighbor inter-center distance between the voids were calculated.

[0134] < Strength evaluation of protective film >

[0135] An acrylic plate having a size of 2 cm x 5 cm and a thickness of 2 mm was prepared as a support. In the vicinity of the center of one end side of the acrylic plate, an opening portion having a size of 1 cm x 1 cm surrounded by a frame was provided in a manner of penetrating the acrylic plate. From the region of the opening portion toward the outer side, a portion from the outer periphery of the opening portion to 5 mm was regarded as a support surface, and double-sided tape was attached to the entire surface of the support surface. The edge portion of the protective film obtained in each example was attached to the tape in a manner of covering the opening portion and fixed, and a protective film assembly for strength evaluation of the protective film was produced (refer to Figure 3A and Figure 3B ).

[0136] Here, the strength evaluation of the protective film is described with reference to Figure 3A , Figure 3B and Figure 4 . Figure 3A A plan view of a protective film assembly WK for strength evaluation of the protective film (hereinafter referred to as a protective film assembly WK for strength evaluation) viewed from above the protective film 10W is schematically shown in FIG. 10. Figure 3B A side view of the protective film assembly WK for strength evaluation viewed from the length direction side surface is schematically shown in FIG. 11. The protective film assembly WK for strength evaluation is the protective film assembly for strength evaluation of the protective film produced as described above. The protective film assembly WK for strength evaluation is provided with an opening portion 32W penetrating the support 30W on the first end portion E1 side of the support 30W. A double-sided tape as an adhesive layer 20W is disposed in the region outside the outer periphery of the opening portion 32W. The protective film 10W is attached in a manner that the edge portion of the protective film 10W contacts the adhesive layer 20W. The protective film 10W is attached to the support 30W in a manner of covering the opening portion 32W via the adhesive layer 20W.

[0137] The evaluation method was performed according to the following procedure. Figure 4 A method of evaluating the strength of the protective film using the protective film assembly WK for strength evaluation is schematically shown, and a state of the protective film assembly WK for strength evaluation viewed from the length direction side surface is shown. As shown in FIG. 12, the protective film assembly WK for strength evaluation is provided with the opening portion 32W penetrating the support 30W on the first end portion E1 side of the support 30W. The double-sided tape as the adhesive layer 20W is disposed in the region outside the outer periphery of the opening portion 32W. The protective film 10W is attached in a manner that the edge portion of the protective film 10W contacts the adhesive layer 20W. The protective film 10W is attached to the support 30W in a manner of covering the opening portion 32W via the adhesive layer 20W. Figure 4As shown, first, the strength evaluation protective film assembly WK was arranged on the horizontal table T. The stopper S was arranged so as to contact the second end portion E2 side of the strength evaluation protective film assembly WK. Next, with the second end portion E2 side of the strength evaluation protective film assembly WK not sliding, the first end portion El side was lifted, and the plate-shaped member B having a thickness of 1 mm was sandwiched between the table T and the strength evaluation protective film assembly WK. Next, the plate-shaped member B was pulled out in the horizontal direction H, and the strength evaluation protective film assembly WK was dropped. After the strength evaluation protective film assembly WK was dropped, it was confirmed by visual observation whether the protective film 10W was broken. In the case where it was not broken, the plate-shaped member B having a thickness of 1 mm was stacked, two pieces of the plate-shaped member B were sandwiched, and the two pieces of the plate-shaped member B were pulled out in the horizontal direction H, and the strength evaluation protective film assembly WK was dropped. This operation was repeated until the protective film 10W was broken, and the maximum height at which the protective film 10W was not broken was evaluated as the strength of the protective film 10W. Note that this maximum height corresponds to the maximum number of pieces of the plate-shaped member B when the plate-shaped member B having a thickness of 1 mm is stacked. In the strength evaluation of the protective film 10W, the above-described procedure was performed three times, and the average of the three was taken.

[0138] <Transmission Evaluation at Wavelength 550 nm>

[0139] For each of the protective film assemblies obtained in the examples, the light transmittance at wavelengths of 200 nm to 800 nm was measured using an ultraviolet-visible near-infrared spectrophotometer (Shimadzu Corporation, product name "UV-VIS-NIR SPECTROPHOTOMETER UV-3600"), and the light transmittance (%) at a wavelength of 550 nm was extracted. In the measurement, a large sample chamber MPC-3100 attached was used, and the measurement was performed without using the built-in integrating sphere. In the measurement of the light transmittance at a wavelength of 550 nm, the center of each of six protective film assemblies produced under the same conditions was measured, and the average value was calculated.

[0140] It is known that there is a correlation between the light transmittance at a wavelength of 13.5 nm and the light transmittance at a wavelength of 550 nm in a protective film containing CNTs (for example, refer to Marina et al., "Adjustability and performance of CNT EUV protective film assemblies in a scanner-like environment", published on March 23, 2021 Figure 4(a) (Marina, Y, et al. “CNT EUV pellicle tunability and performance in a scanner-like environment,”. Proc. SPIE 11609, Extreme Ultraviolet (EUV) Lithography XII, 116090Y, (23 March 2021). Figure 4(a).; doi:10.1117 / 12.2584519)). Therefore, by evaluating the deviation of the light transmittance at the wavelength of 550 nm, the evaluation of the deviation of the light transmittance at the wavelength of 13.5 nm (i.e., the evaluation of the deviation of the EUV transmittance) can be performed. Note that if the light transmittance at the wavelength of 550 nm is 85% or more, it is easy to ensure a high EUV transmittance (e.g., the EUV transmittance is 94% or more), for example.

[0141] [Examples 2 to 7 and Comparative Examples 1 to 4]

[0142] A pellicle was produced in the same manner as in Example 1, except that the dispersion strength and the mass of CNT contained in the pellicle (mass in CNT film) were changed in accordance with Table 1, and the void analysis of the pellicle, the strength evaluation of the pellicle, and the transmittance evaluation at the wavelength of 550 nm were performed.

[0143]

[0144] From the above results, it was found that the evaluation results of the strength of the pellicle and the transmittance evaluation results at the wavelength of 550 nm of the pellicle in which the coefficient of variation of the void diameter was 0.7 or less and the coefficient of variation of the distance between the nearest-neighbor centers of gravity between the voids was 0.6 or less were excellent. Therefore, according to one embodiment of the present application, it is possible to provide a pellicle in which the strength of the pellicle is improved and the deviation of the EUV transmittance is suppressed, and a pellicle assembly using the same.

Claims

1. A protective film having a porous structure, wherein the protective film contains carbon nanotubes, a coefficient of variation of a void diameter of a void measured on a surface of the porous structure is 0.7 or less, and a coefficient of variation of a distance between the most adjacent centers of gravity between the voids is 0.6 or less.

2. The protective film according to claim 1, wherein the coefficient of variation of the void diameter is 0.4 or more and 0.7 or less.

3. The protective film according to claim 1 or 2, wherein the coefficient of variation of the distance between the most adjacent centers of gravity is 0.2 or more and 0.5 or less.

4. The protective film according to claim 1 or 2, wherein the carbon nanotubes have a length of 0.1 pm or more and 1000 pm or less.

5. The protective film according to claim 1 or 2, wherein the carbon nanotubes have a cross-sectional diameter of 0.2 nm or more and 50 nm or less.

6. The protective film according to claim 1 or 2, wherein an average value of the void diameter is 20 nm or more and 60 nm or less.

7. The protective film according to claim 1 or 2, wherein the protective film is a porous structure body in which the carbon nanotubes are packed.

8. The protective film according to claim 1 or 2, which has a self-supporting property.

9. A protective film assembly comprising: the protective film according to claim 1 or 2, and a support body having a frame portion and an opening portion surrounded by the frame portion, and supporting the protective film.

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