Pellicle membrane and pellicle

Abstract

Provided is a pellicle membrane (10) having a porous structure. The pellicle membrane (10) contains carbon nanotubes. The average pore size of pores measured on the surface of the porous structure is 60 nm or less. The average distance between nearest neighbor centroids in the pores is 70 nm or less.

Description

[Technical field]

[0001] The present invention relates to a pellicle membrane and a pellicle. [Background technology]

[0002] In a manufacturing process for semiconductor devices and the like, for example, a desired circuit pattern is formed on a substrate such as a semiconductor wafer by applying a photoresist to the substrate, irradiating the substrate with the photoresist through a photomask with light, and removing the photoresist.

[0003] When light is irradiated onto a photomask with foreign matter adhering thereto, the foreign matter may cause problems with the circuit pattern formed on the substrate. For this reason, a pellicle having a pellicle film for capturing foreign matter may be used to suppress the adhesion of foreign matter onto the photomask. The pellicle is placed above the photomask at a distance such that the pellicle film does not come into contact with the photomask.

[0004] In recent years, the use of extreme ultraviolet (EUV) has been considered in order to form finer circuit patterns. EUV refers to light with a wavelength of 1 nm or more and 100 nm or less. Specifically, light rays of about 13.5 nm ± 0.3 nm are beginning to be used as EUV. When EUV is irradiated onto a pellicle film, the EUV passes through the pellicle film, but a portion of the irradiated EUV is absorbed by the pellicle film. The light energy of the absorbed EUV is converted into thermal energy, causing the temperature of the pellicle film to rise. For this reason, the pellicle film is required to have EUV transmittance, heat resistance, durability, etc.

[0005] Carbon nanotubes are being considered as one of the materials to be used in the pellicle membrane of a pellicle used in a process for forming a circuit pattern using EUV.

[0006] For example, Patent Document 1 discloses a pellicle film containing carbon nanotubes, at least on the surface side of which contains a silicon carbide layer in which at least a portion of carbon has been replaced with silicon. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2021-172104 Summary of the Invention [Problem to be solved by the invention]

[0008] The pellicle film containing carbon nanotubes disclosed in Patent Document 1 is said to have excellent strength and EUV transmittance. However, the pellicle film disclosed in Patent Document 1 does not mention the void characteristics on the surface of the pellicle film. The void characteristics are likely to affect the foreign matter collection ability and EUV transmittance. For example, if the void structure, such as the void diameter and the average nearest center distance of the void, is enlarged too much in order to improve the EUV transmittance, the foreign matter collection ability decreases. For this reason, it has been required for the pellicle film to ensure high EUV transmittance while reducing the void structure.

[0009] The present invention provides a pellicle film containing carbon nanotubes that can ensure EUV transmittance even when the pellicle film has a reduced void structure, and a pellicle using the pellicle film. [Means for solving the problem]

[0010] [1] A pellicle membrane having a porous structure, the pellicle membrane comprises carbon nanotubes; The average pore diameter of the pores measured on the surface of the porous structure is 60 nm or less, and the average distance between nearest neighbor centers of the pores is 70 nm or less. Pellicle membrane.

[0011] [2] In the pellicle membrane according to [1], The average void diameter is 20 nm or more and 60 nm or less. Pellicle membrane.

[0012] [3] In the pellicle membrane according to [1] or [2], The average nearest center distance is 40 nm or more and 70 nm or less. Pellicle membrane.

[0013] [4] [1] to [3], wherein the pellicle membrane is The length of the carbon nanotube is 0.1 μm or more and 1000 μm or less. Pellicle membrane.

[0014] [5] [1] to [4], wherein the pellicle membrane is The cross-sectional diameter of the carbon nanotube is 0.2 nm or more and 50 nm or less. Pellicle membrane.

[0015] [6] [1] to [5], wherein the pellicle membrane is The pellicle membrane is a porous structure formed by depositing the carbon nanotubes. Pellicle membrane.

[0016] [7] [1] to [6], wherein the pellicle membrane is A pellicle membrane that is self-supporting.

[0017] [8] [1] to [7], and a pellicle membrane according to any one of the above. A support having a frame and an opening surrounded by the frame, the support supporting the pellicle membrane; Equipped with Pellicle.

[0018] According to one aspect of the present invention, a pellicle film containing carbon nanotubes can be provided that can ensure EUV transparency even when the pellicle film has a reduced void structure, and a pellicle using the pellicle film can be provided. [Brief description of the drawings]

[0019] [Figure 1] FIG. 2 is a plan view illustrating an example of a pellicle according to the present embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing a cross section taken along line II-II of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] (Pellicle membrane) The pellicle membrane according to the present embodiment has a porous structure, the pellicle membrane includes carbon nanotubes, and the average pore diameter of the pores measured on the surface of the porous structure is 60 nm or less, and the average distance between nearest neighbor centers of gravity of the pores is 70 nm or less.

[0021] The pellicle membrane according to the present embodiment has the above-mentioned configuration, and is therefore considered to have a void structure with many relatively small voids, and therefore has a reduced void structure. According to the pellicle membrane according to the present embodiment, it is considered that EUV transparency can be ensured even when the pellicle membrane has a reduced void structure by having many relatively small voids. Furthermore, according to the pellicle membrane according to the present embodiment, since it has a reduced void structure, the pellicle membrane can improve the foreign matter collection ability while ensuring the EUV transparency. In addition, since the pellicle film according to the present embodiment has a reduced pore structure and is considered to have a pore structure of a certain size, the transmittance of the transmitted light passing through the pellicle film is guaranteed and the foreign matter collection ability is improved. As an example of a pore structure of a certain size, for example, in terms of the average pore diameter, a pore structure having an average pore diameter of 20 nm or more is exemplified. In addition, as an example of a pore structure of a certain size, for example, in terms of the average nearest center distance, a pore structure having an average nearest center distance of 40 nm or more is exemplified.

[0022] There is no particular limitation on the means for adjusting the average pore diameter of the pores measured on the surface of the porous structure to 60 nm or less and the average nearest center distance of the pores to 70 nm or less. For example, in one example of a preferred method for producing a pellicle membrane described below, the means includes a means for adjusting the amount of carbon nanotubes contained in the pellicle membrane (for example, the amount of carbon nanotubes contained in a carbon nanotube film that is an intermediate product when forming a pellicle membrane, or the amount of carbon nanotubes in a carbon nanotube dispersion when forming a carbon nanotube film) and the dispersion strength of the carbon nanotubes.

[0023] The carbon nanotubes contained in the pellicle film of this embodiment are not particularly limited, and are preferably at least one type 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 (SWCNTSs).

[0024] Carbon nanotubes can be obtained by known manufacturing methods such as, for example, arc discharge, laser ablation, and chemical vapor deposition.

[0025] The length of the carbon nanotube is preferably, for example, 0.1 μm or more and 1000 μm or less. The length of the carbon nanotubes is more preferably 0.5 μm or more, and further preferably 1 μm or more. The length of the carbon nanotubes is more preferably 600 μm or less, and even more preferably 400 μm or less.

[0026] The cross-sectional diameter of the carbon nanotube is preferably 0.2 nm or more and 50 nm or less. The cross-sectional diameter of the carbon nanotubes is more preferably 0.5 nm or more, and further preferably 1 nm or more. The cross-sectional diameter of the carbon nanotubes is more preferably 30 nm or less, and even more preferably 20 nm or less. In this specification, the cross-sectional diameter may be simply referred to as the diameter.

[0027] In order to ensure EUV transparency, the average pore diameter of the pores measured on the surface of the porous structure of the pellicle membrane may be, for example, 20 nm or more and 60 nm or less. The average pore diameter may be 25 nm or more, or 30 nm or more. The average pore diameter may be 55 nm or less, or 50 nm or less.

[0028] In this specification, the void diameter means the diameter of a hypothetical circle having the same area as the area of ​​the void (that is, the equivalent circle diameter).

[0029] In order to ensure EUV transparency, the average distance between the nearest neighbor centers of the gaps measured on the surface of the porous structure of the pellicle membrane is preferably, for example, 40 nm or more and 70 nm or less. The average distance between the nearest neighbor centers of the gaps may be 45 nm or more, or 50 nm or more. The average distance between the nearest neighbor centers of the gaps may be 68 nm or less, or 67 nm or less.

[0030] In this specification, the distance between the nearest centers of gravity of voids is the distance between the center of gravity of one void and the center of gravity of the void closest to that void, i.e., the distance from the center of gravity of one void to the center of gravity of the other void between adjacent voids.

[0031] That is, the pellicle membrane of this embodiment may have an average pore diameter of the pores measured on the surface of the porous structure of 20 nm or more and 60 nm or less, and the average distance between nearest neighbor centers of gravity of the pores may be 40 nm or more and 70 nm or less.

[0032] In the void characteristics measured on the surface of the porous structure of the pellicle membrane, the void characteristics of the average void diameter and the average nearest center distance of the voids may be measured by a method having the following steps (1) to (10). By adopting the following measurement method, a unique threshold value is determined, so that, for example, it is easy to obtain a plausible result regardless of the person who measures. The measurement method of the void characteristics is specifically as shown in the examples described later.

[0033] (1) Preparing a pellicle membrane. (2) imaging the surface of the prepared pellicle membrane to obtain image data of the pellicle membrane; (3) setting three or more different thresholds at equal intervals as initial thresholds within a range from a first pixel value to a second pixel value greater than the first pixel value, performing binarization processing based on each of the initial thresholds, and obtaining binarized image data based on the initial thresholds. (4) A step of obtaining an initial measured value by calculating the distribution of void characteristics of voids on the surface of the pellicle membrane by performing blob analysis on the binarized image data based on the initial threshold value. (5) A step of calculating an initial theoretical value of the distribution of void characteristics calculated by a probability density function of a log-normal distribution based on the initial measured value. (6) A step of determining an error between the initial measured value and the initial theoretical value. (7) If the error between the initial actual value and the initial theoretical value is not the smallest, the threshold is reset, a binarization process is performed on the image data based on the reset threshold, binarization process image data based on the reset threshold is obtained, and a re-measurement actual value is obtained by calculating the distribution of void characteristics of voids on the surface of the pellicle membrane by performing blob analysis on the binarization process image data based on the reset threshold. (8) A step of calculating an error between the remeasured theoretical value and the distribution of void characteristics calculated by a probability density function of a log-normal distribution, based on the remeasured actual value. (9) If the error between the actual value of the re-measurement and the theoretical value of the re-measurement is not the smallest, a step of obtaining the actual value of the re-measurement and a step of determining the error between the actual value of the re-measurement and the theoretical value of the re-measurement are repeated until the error between the actual value of the re-measurement and the theoretical value of the re-measurement is smallest. (10) A step of obtaining a distribution of void characteristics as a final actual measurement value, the distribution being calculated based on a threshold value at which the error between the initial actual measurement value and the initial theoretical value, or the error between the re-measured actual measurement value and the re-measured theoretical value, is smallest.

[0034] The threshold value at which the error is minimized is preferably determined by using various known optimization algorithms. For example, in the above steps (4) to (9), the threshold value at which the error is minimized is preferably searched for by using various known optimization algorithms. In this case, after the initial threshold value is determined, a unique threshold value is determined by using the optimization algorithm.

[0035] In the step of acquiring the binarized image data based on the initial threshold value, the initial threshold value is not limited to the above, and may be set to 5 or more different threshold values ​​at equal intervals within a range from a first pixel value to a second pixel value greater than the first pixel value, or may be set to 7 or more different threshold values. The interval between the first pixel value and the second pixel value is preferably 100 or more. The first pixel value is preferably set in a range of 20 to 50. The second pixel value is preferably set in a range of 150 to 240. The equal intervals indicate that the intervals between adjacent threshold values ​​are equal, such as when n threshold values ​​are set as the 3 or more different threshold values, the interval between the nth threshold value and the n-1th threshold value and the interval between the n-1th threshold value and the n-2th threshold value are both equal. Specifically, the initial threshold value may be set to 3 or more and 12 or less different threshold values ​​at equal intervals within a range from a pixel value of 20 to a pixel value of 240. In the step of obtaining the actual value of the remeasurement, the threshold value that is reset is not three or more different threshold values ​​but a single threshold value.

[0036] The void characteristics may be measured, for example, by an apparatus having a program that causes a computer to execute the above steps (1) to (10). The program may be recorded on a recording medium.

[0037] The thickness of the pellicle film is preferably 3 nm or more and 1000 nm or less. The thickness of the pellicle film is preferably 10 nm or more, and more preferably 20 nm or more. The thickness of the pellicle film is preferably 500 nm or less, and more preferably 300 nm or less. If the thickness of the pellicle film is, for example, 3 nm or more and 1000 nm or less, EUV transmittance can be more easily ensured. In addition, the operability of the pellicle film is improved.

[0038] The weight per unit area of ​​the pellicle membrane is not particularly limited, and is, for example, 0.1 μg / cm 2 More than 20μg / cm 2The weight per unit area of ​​the pellicle membrane is preferably 0.5 μg / cm or less. 2 More preferably, it is 1 μg / cm or more. 2 More preferably, the weight per unit area of ​​the pellicle membrane is 15 μg / cm or more. 2 More preferably, it is 10 μg / cm or less. 2 It is more preferable that the weight per unit area of ​​the pellicle membrane is, for example, 0.1 μg / cm 2 More than 20μg / cm 2 If it is below this value, it becomes easier to ensure EUV transparency.

[0039] The pellicle membrane according to the present embodiment is preferably a porous structure in which carbon nanotubes are deposited. The porous structure in which carbon nanotubes are deposited can be manufactured by an example of a preferred method for manufacturing a pellicle membrane, which will be described later. If the porous structure is a porous structure in which carbon nanotubes are deposited, it is easier to ensure EUV transmittance.

[0040] The pellicle film according to the present embodiment is preferably self-supporting from the viewpoint of improving transparency to the exposure light. The fact that the pellicle film is self-supporting means that the pellicle film is in a state in which it is self-supporting, and that the pellicle film is a film that has self-supporting properties (also called a self-supporting film). In other words, a pellicle film that is self-supporting is a film that can maintain its shape by itself even without the presence of a substrate or the like.

[0041] (Method of manufacturing pellicle membrane) The method for producing the pellicle membrane is not particularly limited. An example of a preferred method for producing the pellicle membrane includes, for example, a step (P1) of dispersing carbon nanotubes, a step (P2) of precipitating and depositing the dispersed carbon nanotubes on an air-permeable member to obtain a carbon nanotube film formed in a mat shape on the air-permeable member, and a step (P3) of removing the air-permeable member from the carbon nanotube film to obtain a pellicle membrane.

[0042] First, in step P1, carbon nanotubes are dispersed in a liquid as a dispersion medium to prepare a carbon nanotube dispersion liquid in which carbon nanotubes are dispersed in the liquid. The liquid may be a liquid containing water. The carbon nanotube dispersion liquid may contain only carbon nanotubes as a dispersoid. The carbon nanotube dispersion liquid may contain various additives such as a dispersant that disperses carbon nanotubes in addition to carbon nanotubes.

[0043] For example, by adjusting the balance between the dispersion strength when dispersing carbon nanotubes in a liquid in step P1 and the weight per unit area of ​​carbon nanotubes when preparing a carbon nanotube film in step P2, a pellicle film having an average void diameter of 60 nm or less and an average nearest center distance of the voids of 70 nm or less can be obtained. For example, specifically, when the weight per unit area of ​​the carbon nanotubes is set to a certain amount or more, the average void diameter is likely to satisfy the range of 60 nm or less, and when the weight per unit area of ​​the carbon nanotubes is reduced too much, the average void diameter tends to exceed 60 nm. Also, for example, when the dispersion strength is suppressed to a certain range, the average nearest center distance of the voids is likely to satisfy the range of 70 nm or less, and when the dispersion strength is increased too much, the average nearest center distance of the voids tends to exceed 70 nm.

[0044] The weight per unit area of ​​the carbon nanotubes and the dispersion strength are, for example, 0.1 μg / cm as the amount of carbon nanotubes contained in the carbon nanotube film produced in step P2. 2 More than 20μg / cm 2 In addition, when a stirrer is used as a disperser for dispersing carbon nanotubes, the dispersion strength may be, for example, in the range of 10 m / s or more and 60 m / s or less as the peripheral speed of the stirrer, and the stirring time of the stirrer may be, for example, in the range of 5 minutes or more and 60 minutes or less.

[0045] Next, in step P2, the dispersed carbon nanotubes are precipitated and deposited on the breathable member. For example, the carbon nanotube dispersion liquid prepared in step P1 is filtered through a filtration membrane as a breathable member, whereby the carbon nanotubes are precipitated and deposited, forming a mat-shaped carbon nanotube film on the filtration membrane. For example, a membrane filter or the like is preferably used as the filtration membrane.

[0046] Next, in step P3, the filtration membrane is removed from the mat-shaped carbon nanotube membrane to obtain a pellicle membrane containing carbon nanotubes. Before removing the filtration membrane from the mat-shaped fiber membrane, or after removing the filtration membrane from the mat-shaped fiber membrane, a drying step may be performed as necessary. The obtained pellicle membrane is a free-standing membrane.

[0047] (Pellicle) The pellicle of this embodiment comprises a pellicle membrane of the embodiment described above, and a support having a frame and an opening surrounded by the frame, and supporting the pellicle membrane.

[0048] Hereinafter, the pellicle according to the present embodiment will be described with reference to the drawings. In the present specification, when explanations are given with reference to the drawings, some parts of the drawings are illustrated enlarged or reduced in size in order to facilitate explanation.

[0049] FIG. 1 shows a plan view of the pellicle 100 viewed from the surface on which the pellicle film 10 is installed, and FIG. 2 shows a cross-sectional view of the pellicle 100 shown in FIG. 1. The pellicle 100 includes a pellicle film 10 and a support 30 that supports the pellicle film 10. The support 30 includes a frame 31 and an opening 32 surrounded by the frame 31, and the opening 32 penetrates from one surface of the support 30 to the other surface. The frame 31 and the opening 32 are both formed in a rectangular shape, and all four corners of the outer shape of the frame 31 are rounded. The frame 31 includes a support surface 33 facing the pellicle film 10. The pellicle film 10 is formed in a rectangular shape, and includes a first pellicle film surface 11 facing the support surface 33 of the support 30, and a second pellicle film surface 12 opposite to the first pellicle film surface 11. The pellicle membrane 10 has a peripheral portion 13 fixed to a part of the support surface 33 of the frame portion 31 , and covers the opening 32 of the support 30 .

[0050] The pellicle membrane according to the present embodiment described above is used as the pellicle membrane 10. Examples of materials that can be used for the support 30 include resin materials (polyethylene, etc.), metal materials (aluminum, aluminum alloys, magnesium alloys, stainless steel, titanium, etc.), ceramic materials (SiC, etc.), and fiber-reinforced plastic materials (carbon fiber-reinforced plastics, etc.).

[0051] In addition, in order to clarify the positional relationship between the surface of the pellicle film 10 facing the support surface 33 of the support 30 and the surface on the opposite side thereof, the terms first pellicle film surface 11 and second pellicle film surface 12 are used for convenience. For this reason, in some cases, the first pellicle film surface 11 and the second pellicle film surface 12 can be used interchangeably, and the first pellicle film surface 11 and the second pellicle film surface 12 can be used without distinction.

[0052] Although an example of the pellicle according to the present embodiment has been described above with reference to Fig. 1 and Fig. 2, the pellicle according to the present embodiment is not limited to this. The pellicle according to the present embodiment may adopt various forms as long as the effect of the pellicle using the pellicle membrane according to the present embodiment described above can be obtained. The shape and dimensions of each part of each member constituting the pellicle according to the present embodiment may be determined, for example, according to the dimensions of a photomask (not shown) when the pellicle according to the present embodiment is used.

[0053] For example, the pellicle membrane 10 and the support 30 of the pellicle 100 shown in Figures 1 and 2 are both formed in a rectangular shape. The pellicle according to this embodiment is not limited to this, and may be formed in any desired shape such as a circle, an ellipse, or a polygon.

[0054] 1 and 2, for example, the peripheral portion 13 of the pellicle membrane 10 is fixed to a portion of the support surface 33 of the support 30. The pellicle 100 is not limited to this, and the peripheral portion 13 of the pellicle membrane 10 may be fixed to the entire surface of the support surface 33 of the support.

[0055] 1 and 2, the pellicle membrane 10 and the support 30 may be fixed by providing an adhesive layer (not shown). The adhesive layer is a layer that is provided as necessary. The material constituting the adhesive layer is not particularly limited, and may be, for example, various adhesives such as acrylic resin, epoxy resin, silicone resin, polyimide resin, and fluororesin, as well as carbon nanotubes.

[0056] (Method of manufacturing a pellicle) A preferred example of a method for manufacturing a pellicle according to the present embodiment includes the steps of: preparing a pellicle membrane according to the present embodiment; preparing a support having a frame and an opening surrounded by the frame and supporting the pellicle membrane; and providing a pellicle membrane on the support so as to cover the opening and be supported by the support surface of the frame. The manufacturing method may include the step of providing an adhesive layer on at least a portion of the support surface of the frame, if necessary.

[0057] The step of preparing the pellicle film according to the present embodiment may be performed by preparing the pellicle film according to the above-mentioned embodiment. The step of preparing the support may be performed by preparing a support formed in a desired shape by a known method using the material constituting the support. The step of providing the pellicle film may be performed by covering the opening and installing the pellicle film by a known method so as to be supported by the support surface of the frame. When an adhesive layer is provided on at least a part of the support surface of the frame, the pellicle film is installed so as to be supported by the support surface of the frame via the adhesive layer. When various adhesives are used for the adhesive layer, the step of providing the adhesive layer may be performed by applying an adhesive to the support surface to provide an adhesive layer containing the adhesive. When carbon nanotubes are used for the adhesive layer, the step of providing the adhesive layer may be performed by, for example, applying a dispersion of carbon nanotubes to the support surface and drying the same to provide an adhesive layer containing the carbon nanotubes.

[0058] The pellicle according to this embodiment is used, for example, by being disposed above the photomask and spaced apart from the photomask so that the first pellicle film surface faces the photomask. By using the pellicle according to this embodiment, EUV transparency is ensured. In addition, since the pellicle film according to this embodiment has a reduced void structure, the foreign matter capture property is enhanced, and the effect of suppressing adhesion of foreign matter to the photomask is improved.

[0059] The present invention is not limited to the above-described embodiment, and modifications and improvements within the scope of the present invention that can achieve the object of the present invention are included in the present invention. EXAMPLES

[0060] The present invention will be described in more detail below by way of examples, but the present invention is not limited to these examples in any way.

[0061] [Example 1] <Preparation of pellicle membrane> Carbon nanotubes (hereinafter referred to as CNTs) 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 CNTs were weighed so that the concentration of the CNTs in the aqueous dispersion was 0.02 mass%. In addition, carboxymethyl cellulose (hereinafter referred to as CMC) was weighed as a dispersant so that the concentration in the aqueous dispersion was 0.2 mass%. The weighed CNTs and the weighed CMC were put into water, and the CNTs were dispersed in water using a thin film rotary high-speed mixer (manufactured by Primix Corporation, product name "Filmix") at a peripheral speed of 40 m / s for a dispersion time of 25 minutes to prepare an aqueous dispersion of CNTs. The shear rate when the CNTs were dispersed was approximately 4.0 × 10 5 s -1 Next, the aqueous dispersion of CNT was diluted so that the CNT concentration was 1 ppm. Then, the mass of CNT contained in the pellicle membrane (referred to as the mass in the CNT membrane in Table 1) was 0.71 μg / cm 2 The diluted aqueous dispersion of CNT was put into a filter so that the CNT concentration was 100%. Next, the aqueous dispersion of CNT put into the filter was filtered through a membrane filter to form a mat-like CNT film on the membrane filter. Then, the mat-like CNT film was peeled off from the membrane filter to produce a pellicle film containing CNT. The pellicle film was a self-supporting film. From the obtained pellicle film, the average pore diameter and the average nearest center distance of the pores were calculated according to the pore analysis of the pellicle film described later.

[0062] <Analysis of voids in pellicle membrane> The surface of the pellicle film obtained in each example was observed with a scanning electron microscope (SEM) (Carl Zeiss, CrossBeam550), and image data of the SEM image was obtained. The imaging conditions were an acceleration voltage of 1 kV and a magnification of 10,000 times. The field of view was three or more fields of view.

[0063] From the image data of the obtained SEM image, the pore diameter (pore size) was analyzed as a circle equivalent diameter. First, for one field of view of the image data of the SEM image, the initial binarization threshold was set at 7 points of 40, 60, 80, 100, 120, 140, and 160 at equal intervals of 20 pixel values ​​between pixel value 40 and pixel value 160, and 7 points of binarized processed image data were obtained at each binarization threshold. This operation was performed for image data of 3 or more fields of view. Next, the initial pore diameter distribution based on the initial binarization threshold was measured for the obtained binarized processed image data. Then, a binarization threshold that minimizes the error between the actual pore diameter distribution value and the theoretical pore diameter distribution value was automatically searched for by fitting using Bayesian optimization so that the actual pore diameter distribution value closely approximates (fits) the log-normal distribution. Then, the average void diameter and the average nearest center distance of the voids were calculated from the void diameter distribution and the nearest center distance of the voids measured based on the binarization threshold value when the error between the actual void diameter distribution value and the theoretical void diameter distribution value was minimized.

[0064] <Transmittance evaluation at wavelength 550 nm> For the pellicle obtained in each example, the light transmittance was measured from 200 nm to 800 nm using an ultraviolet-visible near-infrared spectrophotometer (manufactured by Shimadzu Corporation, product name "UV-VIS-NIR SPECTROPHOTOMETER UV-3600"), and the light transmittance (%) at a wavelength of 550 nm was extracted. The measurement was performed using the attached large sample chamber MPC-3100, without using the built-in integrating sphere.

[0065] 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 for pellicle films containing CNTs (see, for example, Figure 4(a) of 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, it is possible to evaluate the light transmittance at a wavelength of 13.5 nm (i.e., evaluate the EUV transmittance) by evaluating the light transmittance at a wavelength of 550 nm. If the light transmittance at a wavelength of 550 nm is 85% or more, for example, it is easy to ensure high EUV transmittance (for example, EUV transmittance of 94% or more). If the light transmittance at a wavelength of 550 nm is 50% or more in the pellicle film according to this embodiment, it can be determined that the EUV transmittance is also excellent and high EUV transmittance is obtained.

[0066] [Examples 2 to 5 and Comparative Examples 1 to 4] A pellicle membrane was prepared in the same manner as in Example 1, except that the dispersion strength and the mass of CNTs contained in the pellicle membrane (mass within the CNT membrane) were changed according to Table 1, and a void analysis of the pellicle membrane and an evaluation of its transmittance at a wavelength of 550 nm were performed.

[0067] [Table 1]

[0068] From the above results, it can be seen that a pellicle film having an average pore diameter of 60 nm or less and an average nearest center distance of the pores of 70 nm or less has an excellent transmittance evaluation result at a wavelength of 550 nm. Therefore, according to one embodiment of the present invention, a pellicle film with guaranteed EUV transmittance despite a reduced pore structure and a pellicle using the pellicle film can be provided. In addition, according to one embodiment of the present invention, since the pore structure is reduced, it is expected that the foreign matter collection effect is also high. Note that the transmittance at a wavelength of 550 nm of each comparative example is superior to that of each example, because each comparative example has a relatively large pore structure. And, it can be expected that the comparative example having a relatively large pore structure has a low foreign matter collection effect. [Explanation of symbols]

[0069] 10...pellicle membrane, 11...first pellicle membrane surface, 12...second pellicle membrane surface, 13...periphery, 30...support, 31...frame, 32...opening, 33...support surface, 100...pellicle.

Claims

1. A pellicle membrane having a porous structure, the pellicle membrane comprises carbon nanotubes; The length of the carbon nanotube is 1 μm or more and 250 μm or less, The weight per unit area of ​​the pellicle membrane is 0.53 μg / cm 2 or more and 0.88 μg / cm 2 or less; The average pore diameter of the pores measured on the surface of the porous structure is 30 nm or more and 49.1 nm or less, and the average distance between nearest neighbor centers of gravity of the pores is 50 nm or more and 66.1 nm or less; The light transmittance at a wavelength of 550 nm is 84.7% or more. Pellicle membrane.

2. The pellicle membrane according to claim 1, The pellicle membrane is a single-layer pellicle membrane having a porous structure, The pellicle membrane is a porous structure formed by depositing the carbon nanotubes. Pellicle membrane.

3. The pellicle membrane according to claim 1 or 2, The cross-sectional diameter of the carbon nanotube is 0.2 nm or more and 50 nm or less. Pellicle membrane.

4. The pellicle membrane according to claim 1 or 2, Have independence, Pellicle membrane.

5. The pellicle membrane according to claim 1 or 2, A support having a frame and an opening surrounded by the frame, the support supporting the pellicle membrane; Equipped with Pellicle.

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