Pellicle film and pellicle

Abstract

A pellicle film (10) having a porous structure, wherein the pellicle film (10) contains carbon nanotubes, the aperture ratio of voids measured on the surface of the porous structure is 30% or less, and the light transmittance at a wavelength of 550 nm is 50% or more.

Description

Pellicle membrane and pellicle

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

[0002] In a manufacturing process of a semiconductor device or the like, for example, a photoresist is applied to a substrate such as a semiconductor wafer, and the substrate with the photoresist applied is irradiated with light using a photomask, and the photoresist is removed, thereby forming a desired circuit pattern on the substrate.

[0003] When a photomask is irradiated with light while foreign matter is attached to it, the attached foreign matter may interfere with the circuit pattern formed on the substrate. For this reason, a pellicle equipped with a pellicle film for capturing foreign matter may be used to prevent foreign matter from adhering to 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 approximately 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 absorbed EUV light energy is converted into thermal energy, causing the temperature of the pellicle film to rise. For this reason, pellicle films are required to have EUV transmittance, heat resistance, durability, etc.

[0005] Carbon nanotubes are being considered as one of the materials to be used for the pellicle film of a pellicle used in a process of 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.

[0007] International Publication No. 2021-172104

[0008] The pellicle membrane containing carbon nanotubes disclosed in Patent Document 1 is said to have excellent strength and EUV transmittance. However, the pellicle membrane disclosed in Patent Document 1 does not mention the void characteristics on the surface of the pellicle membrane. The void characteristics are likely to affect the foreign matter capture ability and EUV transmittance. For example, if the aperture ratio of the voids is increased too much in order to improve EUV transmittance, the foreign matter capture ability will decrease. For this reason, further improvements in pellicle membranes have been required.

[0009] The present invention provides a pellicle film containing carbon nanotubes that has good foreign matter collection properties and can achieve high EUV transmittance, and a pellicle using the pellicle film.

[0010] [1] A pellicle membrane having a porous structure, the pellicle membrane containing carbon nanotubes, having a void opening ratio of 30% or less, measured on the surface of the porous structure, and a light transmittance at a wavelength of 550 nm of 50% or more.

[0011] [2] The pellicle membrane according to [1], wherein the opening ratio is 5% or more and 30% or less.

[0012] [3] The pellicle membrane according to [1] or [2], wherein the length of the carbon nanotubes is 0.1 μm or more and 1000 μm or less.

[0013] [4] The pellicle membrane according to any one of [1] to [3], wherein the cross-sectional diameter of the carbon nanotubes is 0.2 nm or more and 50 nm or less.

[0014] [5] The pellicle membrane according to any one of [1] to [4], wherein the pellicle membrane is a porous structure formed by depositing the carbon nanotubes.

[0015] [6] The pellicle membrane according to any one of [1] to [5], which is self-supporting.

[0016] [7] A pellicle comprising: the pellicle membrane according to any one of [1] to [6]; and a support having a frame and an opening surrounded by the frame, and supporting the pellicle membrane.

[0017] According to one aspect of the present invention, a pellicle film containing carbon nanotubes can be provided that has good foreign matter collection properties and can achieve high EUV transmittance, and a pellicle using the pellicle film can be provided.

[0018] 1 is a plan view schematically illustrating an example of a pellicle according to the present embodiment.

[0019] (Pellicle membrane) The pellicle membrane according to the present embodiment has a porous structure. The pellicle membrane contains carbon nanotubes, and has a pore opening ratio of 30% or less and a light transmittance of 50% or more at a wavelength of 550 nm, measured on the surface of the porous structure.

[0020] The pellicle film according to the present embodiment has a void structure with a low aperture ratio, thereby achieving good foreign matter capture. Furthermore, the pellicle film according to the present embodiment exhibits high light transmittance at a wavelength of 550 nm, ensuring the transmittance of transmitted light passing through the pellicle film. As a result, the pellicle film according to the present embodiment is believed to achieve good foreign matter capture and high EUV transmittance. Furthermore, the pellicle film according to the present embodiment has a high light transmittance at a wavelength of 550 nm and is believed to have a certain degree of void aperture ratio, ensuring the transmittance of transmitted light passing through the pellicle film and improving foreign matter capture. An example of a void structure with a certain degree of aperture ratio is a void structure with an aperture ratio of 5% or more (preferably, 18% or more).

[0021] There are no particular limitations on the means for adjusting the pore opening ratio of a pellicle membrane to 30% or less and the light transmittance at a wavelength of 550 nm to 50% or more, as measured on the surface of the porous structure. Examples of such means include, in an example of a preferred method for producing a pellicle membrane described below, 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 the 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.

[0022] The carbon nanotubes contained in the pellicle film according to this embodiment are not particularly limited, and are preferably at least one type selected from the group consisting of multi-walled carbon nanotubes (MWCNT: Multi-Walled Carbon Nanotubes), few-walled carbon nanotubes (FWCNT: Few-Walled Carbon Nanotubes), double-walled carbon nanotubes (DWCNT: Double-Walled Carbon Nanotubes), and single-walled carbon nanotubes (SWCNTS: Single-Walled Carbon Nanotubes).

[0023] Carbon nanotubes can be obtained by known manufacturing methods such as arc discharge, laser ablation, and chemical vapor deposition.

[0024] The length of the carbon nanotubes is, for example, preferably 0.1 μm or more and 1000 μm or less, more preferably 0.5 μm or more, and even more preferably 1 μm or more, and more preferably 600 μm or less, and even more preferably 400 μm or less.

[0025] 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 nanotube is more preferably 0.5 nm or more, and even more preferably 1 nm or more. The cross-sectional diameter of the carbon nanotube 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.

[0026] The lower limit of the pore opening ratio measured on the surface of the porous structure of the pellicle membrane is not particularly limited. The lower limit of the pore opening ratio may be, for example, 5% or more, 10% or more, or 15% or more. From the viewpoint of more easily achieving both good foreign matter capture properties and high EUV transmittance, the pore opening ratio measured on the surface of the porous structure of the pellicle membrane is preferably 18% or more and 30% or less. From the same viewpoint, the pore opening ratio measured on the surface of the porous structure of the pellicle membrane is more preferably 20% or more, and even more preferably 23% or more. The pore opening ratio measured on the surface of the porous structure of the pellicle membrane is more preferably 29% or less, and even more preferably 28% or less.

[0027] In this specification, the opening ratio of voids means the ratio of the total area of ​​voids to the unit area of ​​the surface of the pellicle membrane. The opening ratio is expressed as a percentage.

[0028] From the viewpoint of more easily achieving both good foreign matter collection properties and high EUV transmittance, 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 58 nm or less, 55 nm or less, or 50 nm or less.

[0029] In this specification, the void diameter means the diameter of an imaginary circle having the same area as the area of ​​the void (i.e., the equivalent circle diameter).

[0030] The pore characteristics of the aperture ratio and average pore diameter measured on the surface of the porous structure of a pellicle membrane may be measured by a method including the following steps (1) to (10). By employing the measurement method described below, a unique threshold value is determined, making it easier to obtain plausible results, for example, regardless of the person performing the measurement. The specific method for measuring the pore characteristics is as shown in the examples described below.

[0031] (1) A step of preparing a pellicle membrane. (2) A step of imaging the surface of the prepared pellicle membrane to obtain image data of the pellicle membrane. (3) A step of setting three or more different thresholds as initial thresholds at equal intervals within a range from a first pixel value to a second pixel value greater than the first pixel value for the image data, performing binarization processing based on each of the initial thresholds, and obtaining binarized image data based on the initial thresholds. (4) A step of performing blob analysis on the binarized image data based on the initial thresholds to obtain initial measured values ​​that calculate the distribution of void characteristics of voids on the surface of the pellicle membrane. (5) A step of calculating initial theoretical values ​​of the distribution of void characteristics calculated using a log-normal probability density function based on the initial measured values. (6) A step of calculating the error between the initial measured values ​​and the initial theoretical values. (7) If the error between the initial measured value and the initial theoretical value is not smallest, the threshold is reset, the image data is binarized based on the reset threshold, binarization processing is performed on the image data based on the reset threshold, and the binarized image data based on the reset threshold is subjected to blob analysis to obtain a remeasurement measured value that calculates the distribution of void characteristics of voids on the surface of the pellicle membrane. (8) Based on the remeasurement measured value, an error is calculated between the remeasurement measured value and a theoretical value of the distribution of void characteristics calculated using a log-normal distribution probability density function. (9) If the error between the remeasurement measured value and the theoretical value is not smallest, the steps of obtaining the remeasurement measured value and calculating the error between the remeasurement measured value and the theoretical value are repeated until the error between the remeasurement measured value and the theoretical value is smallest. (10) A step of obtaining the distribution of void characteristics calculated based on the threshold value when the error between the initial measured value and the initial theoretical value, or the error between the re-measured measured value and the re-measured theoretical value, is smallest as the final measured value.

[0032] The threshold value at which the error is minimized is preferably determined by using various known optimization algorithms. For example, in steps (4) to (9) above, it is preferable to use various known optimization algorithms to search for the threshold value at which the error is minimized. In this case, after the initial threshold value is determined, a unique threshold value is determined by using the optimization algorithm.

[0033] In the step of acquiring the binarized image data based on the initial thresholds, the initial thresholds are not limited to the above. Five or more different thresholds may be set at equal intervals within a range from a first pixel value to a second pixel value greater than the first pixel value, or seven or more different thresholds may be set. 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 the range of 20 to 50. The second pixel value is preferably set in the range of 150 to 240. "Equal intervals" refers to the equal intervals between adjacent thresholds, such as when n thresholds are set as the three or more different thresholds, 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. Specifically, the initial thresholds may be set as a plurality of equal intervals within a range from a pixel value of 20 to a pixel value of 240, with an interval of 3 to 12. 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.

[0034] 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.

[0035] From the viewpoint of more easily realizing high EUV transmittance, the light transmittance at a wavelength of 550 nm is preferably 50% or more, more preferably 60% or more, even more preferably 65% ​​or more, and even more preferably 70% or more. There is no particular upper limit for the light transmittance at a wavelength of 550 nm. From the viewpoint of more easily achieving both good foreign matter capture properties and high EUV transmittance, the light transmittance at a wavelength of 550 nm is preferably 98% or less. The method for measuring the light transmittance at a wavelength of 550 nm is as shown in the Examples below.

[0036] 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, it becomes easier to achieve both good foreign matter collection properties and high EUV transmittance. In addition, the operability of the pellicle film is improved.

[0037] The weight per unit area of ​​the pellicle membrane is not particularly limited, and is, for example, 0.1 μg / cm ２ Above, 20μg / cm ２ The 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 The weight per unit area of ​​the pellicle membrane is more preferably 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 or less. ２ Above, 20μg / cm ２ If the thickness is below this, it becomes easier to achieve both good foreign matter collection properties and high EUV transmittance.

[0038] The pellicle membrane according to this embodiment is preferably a porous structure formed by the deposition of carbon nanotubes. The porous structure formed by the deposition of carbon nanotubes can be manufactured by an example of a preferred method for manufacturing a pellicle membrane, which will be described later. A porous structure formed by the deposition of carbon nanotubes makes it easier to achieve both good foreign matter collection properties and high EUV transmittance.

[0039] The pellicle film according to the present embodiment is preferably self-supporting from the viewpoint of improving transparency to exposure light. The term "self-supporting pellicle film" refers to a film that is in a state where the pellicle film itself is self-supporting, and indicates that the pellicle film is a film that has self-supporting properties (also referred to as a self-supporting film). In other words, a self-supporting pellicle film is a film that can maintain its shape by itself even without the presence of a substrate or the like.

[0040] (Method for manufacturing a pellicle membrane) The method for manufacturing a pellicle membrane is not particularly limited. An example of a preferred method for manufacturing a pellicle membrane includes, for example, a step of dispersing carbon nanotubes (step P1), a step 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 (step P2), and a step of removing the air-permeable member from the carbon nanotube film to obtain a pellicle membrane (step P3).

[0041] First, in step P1, carbon nanotubes are dispersed in a liquid as a dispersion medium to prepare a carbon nanotube dispersion in which carbon nanotubes are dispersed in the liquid. The liquid may be a liquid containing water. The carbon nanotube dispersion may contain only carbon nanotubes as a dispersoid. The carbon nanotube dispersion may contain, in addition to carbon nanotubes, various additives such as dispersants that disperse the carbon nanotubes.

[0042] 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, it becomes easier to obtain a pellicle film with a void opening ratio of 30% or less and a light transmittance of 50% or more at a wavelength of 550 nm. Specifically, by increasing the weight per unit area of ​​the carbon nanotubes to a certain amount or more, it becomes easier to achieve a light transmittance of 50% or more at a wavelength of 550 nm and a light opening ratio of 30% or less. On the other hand, by reducing the weight per unit area of ​​the carbon nanotubes too much, the light transmittance at a wavelength of 550 nm will be in the range of 50% or more, but the light opening ratio will tend to exceed 30%. Furthermore, for example, by limiting the dispersion strength to a certain range, it becomes easier to achieve a light transmittance of 50% or more at a wavelength of 550 nm and a light opening ratio of 30% or less. On the other hand, if the dispersion strength is too low, the light transmittance at a wavelength of 550 nm satisfies the range of 50% or more, but the aperture ratio tends to exceed 30%. Note that, if the weight per unit area of ​​the carbon nanotubes is set to a certain amount or more, a suitable range of average void diameter tends to be easily obtained.

[0043] The weight per unit area of ​​the carbon nanotubes and the dispersion strength are, for example, 0.1 μg / cm 3 as the amount of carbon nanotubes contained in the carbon nanotube film produced in step P2. ２ Above, 20μg / cm ２ Furthermore, 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.

[0044] Next, in step P2, the dispersed carbon nanotubes are precipitated and deposited on an air-permeable member. For example, the carbon nanotube dispersion prepared in step P1 is filtered through a filter membrane as an air-permeable member, causing the carbon nanotubes to precipitate and deposit, forming a mat-like carbon nanotube film on the filter membrane. The filter membrane is preferably, for example, a membrane filter.

[0045] Next, in step P3, the filtration membrane is removed from the mat-shaped carbon nanotube membrane to obtain a pellicle membrane containing carbon nanotubes. A drying step may be performed, if necessary, before or after removing the filtration membrane from the mat-shaped fiber membrane. The obtained pellicle membrane is a free-standing membrane.

[0046] (Pellicle) The pellicle according to this embodiment includes the pellicle membrane according to the embodiment described above, and a support that has a frame and an opening surrounded by the frame and supports the pellicle membrane.

[0047] The pellicle according to the present embodiment will be described below with reference to the drawings. Note that in the drawings in this specification, some parts are illustrated enlarged or reduced in size for ease of explanation.

[0048] FIG. 1 shows a plan view of a pellicle 100 viewed from the surface on which the pellicle membrane 10 is installed, and FIG. 2 shows a cross-sectional view of the pellicle 100 shown in FIG. 1. The pellicle 100 comprises a pellicle membrane 10 and a support 30 that supports the pellicle membrane 10. The support 30 comprises a frame 31 and an opening 32 surrounded by the frame 31, with the opening 32 penetrating from one surface of the support 30 to the other. The frame 31 and the opening 32 are both rectangular, and all four corners of the outer shape of the frame 31 are rounded. The frame 31 comprises a support surface 33 facing the pellicle membrane 10. The pellicle membrane 10 is rectangular, and comprises a first pellicle membrane surface 11 facing the support surface 33 of the support 30 and a second pellicle membrane surface 12 opposite the first pellicle membrane surface 11. The pellicle membrane 10 has a peripheral edge 13 fixed to a part of the support surface 33 of the frame 31 , and covers the opening 32 of the support 30 .

[0049] 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 plastic, etc.).

[0050] 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. Therefore, 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 interchangeably.

[0051] While an example of a pellicle according to the present embodiment has been described above with reference to Figures 1 and 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 effects 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 component constituting the pellicle according to the present embodiment may be determined, for example, according to the dimensions of the photomask (not shown) when the pellicle according to the present embodiment is used.

[0052] 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.

[0053] 1 and 2, for example, the peripheral edge 13 of the pellicle membrane 10 is fixed to a portion of the support surface 33 of the support body 30. The pellicle 100 is not limited to this, and the peripheral edge 13 of the pellicle membrane 10 may be fixed to the entire surface of the support surface 33 of the support body.

[0054] 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 needed. 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.

[0055] (Method for Manufacturing a Pellicle) An example of a preferred 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 the 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 optionally include the step of providing an adhesive layer on at least a portion of the support surface of the frame.

[0056] The step of preparing a pellicle membrane according to this embodiment may involve preparing a pellicle membrane according to the above-described embodiment. The step of preparing a support may involve preparing a support formed into the desired shape using the material constituting the support described above by a known method. The step of providing a pellicle membrane may involve covering the opening and installing the pellicle membrane by a known method so that it is supported by the support surface of the frame. When an adhesive layer is provided on at least a portion of the support surface of the frame, the pellicle membrane is installed so that it is 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 involves applying an adhesive to the support surface to provide an adhesive-containing adhesive layer. When carbon nanotubes are used for the adhesive layer, the step of providing the adhesive layer involves, for example, applying a carbon nanotube dispersion to the support surface and drying it to provide an adhesive layer containing carbon nanotubes.

[0057] The pellicle according to this embodiment is used by being disposed above the photomask at a distance from the photomask so that the first pellicle film surface faces the photomask. By using the pellicle according to this embodiment, good foreign matter collection properties can be obtained and high EUV transmittance can be achieved, resulting in an excellent effect of suppressing foreign matter adhesion to the photomask and excellent EUV transmittance.

[0058] The present invention is not limited to the above-described embodiment, and includes modifications and improvements within the scope of achieving the object of the present invention.

[0059] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0060] [Example 1] <Preparation of pellicle film> Carbon nanotubes (hereinafter referred to as 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 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 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, thereby preparing an aqueous dispersion of CNTs. The shear rate when dispersing the CNTs 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 0.61 μg / cm ２ The diluted CNT aqueous dispersion was placed in a filter so that the CNT concentration was 0.01%. Next, the CNT aqueous dispersion placed in the filter was filtered through a membrane filter to form a mat-like CNT film on the membrane filter. The mat-like CNT film was then peeled off from the membrane filter to produce a pellicle film containing CNT. The pellicle film was a self-supporting film. The average pore diameter and opening ratio were calculated from the obtained pellicle film according to the pore analysis of the pellicle film described below.

[0061] <Analysis of voids in pellicle membrane> The surface of the pellicle membrane obtained in each example was observed with a scanning electron microscope (SEM) (CrossBeam 550, manufactured by Carl Zeiss), 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.

[0062] 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 seven values: 40, 60, 80, 100, 120, 140, and 160, at equal intervals of 20 pixel values ​​between the pixel value 40 and the pixel value 160, and seven binarized processed image data were obtained at each binarization threshold. This operation was performed on image data of three 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, by fitting using Bayesian optimization so that the measured value of the pore diameter distribution closely approximates (fits) a log-normal distribution, a binarization threshold that minimizes the error between the measured value of the pore diameter distribution and the theoretical value of the pore diameter distribution was automatically searched for. The average pore diameter and opening ratio were calculated from the pore diameter distribution and opening ratio distribution measured based on the binarization threshold when the error between the actual pore diameter distribution value and the theoretical pore diameter distribution value was minimized.

[0063] <Evaluation of transmittance at a wavelength of 550 nm> For the pellicles obtained in each example, the light transmittance from wavelengths of 200 nm to 800 nm was measured 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.

[0064] 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, by evaluating the light transmittance at a wavelength of 550 nm, it is possible to evaluate the light transmittance at a wavelength of 13.5 nm (i.e., EUV transmittance). If the light transmittance at a wavelength of 550 nm is 85% or more, it is easy to ensure, for example, a high EUV transmittance (for example, an EUV transmittance of 94% or more). In the pellicle film according to this embodiment, if the light transmittance at a wavelength of 550 nm is 50% or more, it can be determined that the EUV transmittance is also excellent and high EUV transmittance has been obtained.

[0065] [Examples 2 to 4 and Comparative Examples 1 to 3] Pellicle films were prepared in the same manner as in Example 1, except that the dispersion strength and the mass of CNTs contained in the pellicle film (mass within the CNT film) were changed according to Table 1, and void analysis of the pellicle film and evaluation of its transmittance at a wavelength of 550 nm were performed.

[0066]

[0067] From the above results, it can be seen that the pellicle membranes of each Example have a lower pore opening rate and a superior light transmittance at a wavelength of 550 nm compared to the pellicle membranes of each Comparative Example. Because the pellicle membranes of each Example have a pore structure with a low opening rate, it is expected that they will also have a high foreign matter capture effect. Furthermore, because the pellicle membranes of each Example have excellent light transmittance at a wavelength of 550 nm, it is expected that they will have high EUV transmittance. Therefore, according to one embodiment of the present invention, a pellicle membrane that can achieve good foreign matter capture performance and high EUV transmittance, and a pellicle using this pellicle membrane, can be provided. The transmittance at a wavelength of 550 nm of each Comparative Example is superior to that of each Example, but this is due to the high opening rate of each Comparative Example. Furthermore, because the opening rate is relatively high, it can be expected that the foreign matter capture effect will be low.

[0068] 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 weight per unit area of ​​the pellicle membrane is 0.1 μg / cm 2 or more and 20 μg / cm 2 or less; The opening ratio of the pores measured on the surface of the porous structure is 30% or less; The light transmittance at a wavelength of 550 nm is 50% or more. Pellicle membrane.

2. 2. The pellicle membrane according to claim 1, The opening ratio is 5% or more and 30% or less. Pellicle membrane.

3. The pellicle membrane according to claim 1 or 2, The length of the carbon nanotube is 0.1 μm or more and 1000 μm or less. Pellicle membrane.

4. 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.

5. The pellicle membrane according to claim 1 or 2, The pellicle membrane is a porous structure formed by depositing the carbon nanotubes. Pellicle membrane.

6. The pellicle membrane according to claim 1 or 2, A pellicle membrane that is self-supporting.

7. 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.