Method for measuring standard deviation of orientation angle of carbon nanotubes contained in pellicle film

Abstract

To provide a pellicle film excellent in mechanical strength.SOLUTION: A pellicle film 10 having a porous structure. The pellicle film 10 contains carbon nanotubes and the pellicle film 10 comprises a first pellicle film surface 11 and a second pellicle film surface 12 opposite to the first pellicle film surface 11. For an image captured of either the first pellicle film surface 11 or the second pellicle film surface 12 of the pellicle film 10, the standard deviation of the orientation angle of the carbon nanotubes, calculated based on an approximate ellipse of the power spectrum image obtained by performing a two-dimensional Fourier transform, is 8.0° or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pellicle film, a pellicle, and a measurement method for measuring the standard deviation of the orientation angle of carbon nanotubes contained in a pellicle film. [Background technology]

[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 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 film, but some of the irradiated EUV is absorbed by the 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 membrane of pellicles used in the process of forming circuit patterns using EUV.

[0006] For example, Patent Document 1 discloses a pellicle film for exposure that includes a carbon nanotube film containing carbon nanotubes. The carbon nanotube film disclosed in Patent Document 1 has a transmittance of 80% or more for EUV light at a wavelength of 13.5 nm, a thickness of 1 nm or more and 50 nm or less, and a reflectance 3σ of 15% or less. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2023-106455 Summary of the Invention [Problem to be solved by the invention]

[0008] In a pellicle film containing carbon nanotubes disclosed in Patent Document 1, the uniformity of the EUV transmittance is improved by increasing the uniformity of the thickness of the pellicle film. However, the pellicle film disclosed in Patent Document 1 is only considered from a macroscopic perspective in terms of thickness uniformity, and does not consider the variation in structure due to the microscopic overlap of carbon nanotube bundles. In conventional pellicle films, there is concern that large variations in the microscopic structure may cause a decrease in mechanical strength. For this reason, further improvements in pellicle films are required.

[0009] The object of the present invention is to provide a pellicle film containing carbon nanotubes, which has excellent mechanical strength, a pellicle using said pellicle film, and a measurement method for measuring the standard deviation of the orientation angle of carbon nanotubes contained in said pellicle film. [Means for solving the problem]

[0010] [1] A pellicle membrane having a porous structure, the pellicle membrane comprises carbon nanotubes; The pellicle membrane has a first pellicle membrane surface and a second pellicle membrane surface opposite to the first pellicle membrane surface, The standard deviation of the orientation angle of the carbon nanotubes is 8.0° or less, which is calculated based on an approximate ellipse of a power spectrum image obtained by performing a two-dimensional Fourier transform on an image of the first pellicle film surface or the second pellicle film surface of the pellicle film. Pellicle membrane.

[0011] [2] [1] The pellicle membrane according to The standard deviation of the orientation angle of the carbon nanotubes is 0.5° or more and 8.0° or less. Pellicle membrane.

[0012] [3] In the pellicle membrane according to [1] or [2], The image of the first pellicle film surface or the second pellicle film surface is an image captured by a scanning electron microscope. Pellicle membrane.

[0013] [4] [1] The pellicle membrane according to any one of [3] to [4], The length of the carbon nanotubes 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 have independence, Pellicle membrane.

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

[0017] [8] A method for measuring the standard deviation of the orientation angle of carbon nanotubes contained in a pellicle film having a porous structure, comprising: providing a pellicle membrane including carbon nanotubes and having a first pellicle membrane surface and a second pellicle membrane surface opposite the first pellicle membrane surface; A step of imaging the first pellicle film surface or the second pellicle film surface of the prepared pellicle film using a scanning electron microscope to obtain image data on the surface of the pellicle film; performing a two-dimensional Fourier transform on the acquired image data to acquire a power spectrum image; a step of drawing an approximation ellipse from an angular distribution diagram of the average amplitude for the acquired power spectrum image, and calculating an average value of the orientation intensity in the radial direction of the approximation ellipse; a step of calculating the inclination of the approximate ellipse based on an ellipse equation with respect to the calculated average value of the orientation strength, and obtaining an orientation angle; Calculating the standard deviation of the orientation angles; Equipped with Measurement method. [Effects of the Invention]

[0018] According to one aspect of the present invention, there are provided a pellicle film containing carbon nanotubes, which has excellent mechanical strength, a pellicle using the pellicle film, and a measurement method that can measure the standard deviation of the orientation angle of carbon nanotubes contained in a pellicle film having excellent mechanical strength. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating an example of a pellicle membrane according to the present embodiment. [Figure 2] FIG. 1 is a schematic diagram showing an example of an angular distribution diagram of the average amplitude in a pellicle film according to the present embodiment. [Figure 3] FIG. 1 is a plan view schematically illustrating an example of a pellicle according to an embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view showing the IV-IV cross section of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, a description will be given of a pellicle film, a pellicle, and a measurement method for measuring the standard deviation of the orientation angle of carbon nanotubes contained in a pellicle film according to a preferred embodiment of the present invention.

[0021] [Pellicle membrane] The pellicle membrane according to this embodiment has a porous structure. The pellicle membrane contains carbon nanotubes. The pellicle membrane has a first pellicle membrane surface and a second pellicle membrane surface opposite the first pellicle membrane surface. The standard deviation of the orientation angle of the carbon nanotubes in the pellicle membrane is 8.0° or less, as determined based on an approximate ellipse of a power spectrum image obtained by performing a two-dimensional Fourier transform on an image of the first pellicle membrane surface or the second pellicle membrane surface of the pellicle membrane.

[0022] The pellicle membrane according to this embodiment has the above-described configuration and is therefore excellent in mechanical strength. The standard deviation of the orientation angle of the carbon nanotubes in the pellicle membrane according to this embodiment, as determined by the above-described method, is 8.0° or less, which is believed to result in the microscopic orientation angles of the carbon nanotubes being uniform. Therefore, the pellicle membrane according to this embodiment is believed to have a surface structure that is close to uniform, resulting in improved mechanical strength.

[0023] Furthermore, in the pellicle film according to the present embodiment, which will be described later, a measurement method for measuring the standard deviation of the orientation angle of the carbon nanotubes contained in the pellicle film makes it possible to quantify the orientation angle of the microscopic carbon nanotubes. By quantifying the orientation angle of the carbon nanotubes at multiple locations, the variation in the orientation angle of the entire pellicle film can be determined. Therefore, the measurement method for measuring the standard deviation of the orientation angle of the carbon nanotubes contained in the pellicle film according to the present embodiment makes it possible to measure the standard deviation of the orientation angle of the carbon nanotubes contained in a pellicle film that has excellent mechanical strength.

[0024] Referring now to FIG. 1, a cross-sectional view of a pellicle film according to this embodiment is schematically shown. The pellicle film 10 has a porous structure and contains carbon nanotubes. The pellicle film 10 has a first pellicle film surface 11 and a second pellicle film surface 12 opposite the first pellicle film surface 11. In the pellicle film 10, the standard deviation of the orientation angles of the carbon nanotubes contained in the pellicle film 10 is 8.0° or less. The standard deviation of the orientation angles of the carbon nanotubes contained in the pellicle film 10 is determined based on an approximate ellipse of a power spectrum image obtained by performing a two-dimensional Fourier transform on an image of the first pellicle film surface 11 or the second pellicle film surface 12. Specifically, it can be measured using a measurement method for measuring the standard deviation of the orientation angles of the carbon nanotubes contained in the pellicle film according to this embodiment, which will be described later. The image of the first pellicle film surface 11 or the second pellicle film surface 12 is preferably an image captured using a scanning electron microscope (SEM).

[0025] In this specification, the terms "first pellicle membrane surface" and "second pellicle membrane surface" are used for convenience in order to clarify the positional relationship between one surface and the other surface of the pellicle membrane. Therefore, in some cases, the terms "first pellicle membrane surface" and "second pellicle membrane surface" can be used interchangeably, and the terms "first pellicle membrane surface" and "second pellicle membrane surface" can be used interchangeably.

[0026] While an example of the pellicle membrane according to the present embodiment has been described above with reference to Figure 1, the pellicle membrane according to the present embodiment is not limited to this. The pellicle membrane according to the present embodiment can adopt various forms as long as the above-described effects can be obtained.

[0027] 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).

[0028] Carbon nanotubes can be obtained by known manufacturing methods such as arc discharge, laser ablation, and chemical vapor deposition.

[0029] 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 even more 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.

[0030] 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.

[0031] In the pellicle membrane of this embodiment, the standard deviation of the orientation angle of the carbon nanotubes is determined based on the approximate ellipse of the power spectrum image obtained by performing a two-dimensional Fourier transform on an image of the first pellicle membrane surface or the second pellicle membrane surface. The standard deviation of the orientation angle of the carbon nanotubes in the pellicle membrane of this embodiment is 8.0° or less. From the viewpoint of making it easier to improve the mechanical strength of the pellicle membrane, the standard deviation of the orientation angle of the carbon nanotubes is preferably 7.0° or less, more preferably 6.0° or less, even more preferably 5.0° or less, and even more preferably 4.0° or less. The lower limit of the standard deviation of the orientation angle of the carbon nanotubes is not particularly limited. From the viewpoint of more easily improving the mechanical strength of the pellicle film, the lower limit of the standard deviation of the orientation angle of the carbon nanotubes is preferably close to 0°, and may be greater than 0°, 0.5° or more, or 1° or more. The standard deviation of the orientation angle of the carbon nanotubes may be, for example, 0.5° or more and 8.0° or less.

[0032] (Method for measuring the standard deviation of the orientation angle of carbon nanotubes contained in a pellicle film) The measurement method for measuring the standard deviation of the orientation angle of carbon nanotubes contained in a pellicle membrane having a porous structure according to this embodiment includes the following steps (S1) to (S6). By employing the following measurement method as a method for measuring the standard deviation of the orientation angle of carbon nanotubes contained in a pellicle membrane, it is possible to quantify the orientation angle of microscopic carbon nanotubes, and to evaluate the standard deviation of the orientation angle as an index of the uniformity of the pellicle membrane structure. As a result, it can be evaluated that the mechanical strength of the pellicle membrane has been improved.

[0033] Step (S1): A step of preparing a pellicle membrane containing carbon nanotubes and having a first pellicle membrane surface and a second pellicle membrane surface opposite to the first pellicle membrane surface. Step (S2): A step of imaging the first pellicle membrane surface or the second pellicle membrane surface of the prepared pellicle membrane using a scanning electron microscope (hereinafter sometimes referred to as SEM) to obtain image data on the surface of the pellicle membrane. Step (S3): A step of performing a two-dimensional Fourier transform on the acquired image data to acquire a power spectrum image. Step (S4): A step of drawing an approximation ellipse from an angle distribution map of the average amplitude for the acquired power spectrum image, and calculating the average value of the orientation intensity in the radial direction of the approximation ellipse. Step (S5): A step of calculating the inclination of the approximate ellipse based on an ellipse equation for the calculated average value of the orientation strength, and obtaining an orientation angle. Step (S6): A step of calculating the standard deviation of the orientation angles.

[0034] In step (S1), a pellicle membrane having a porous structure according to the present embodiment is first prepared. The pellicle membrane prepared in step (S1) may be pellicle membrane 10 shown in FIG. 1. Specifically, pellicle membrane 10 may be a pellicle membrane obtained by a preferred method for producing a pellicle membrane, which will be described later.

[0035] In step (S2), the pellicle membrane prepared in step (S1) is imaged using an SEM to obtain image data of the surface of the pellicle membrane. The image data of the surface of the pellicle membrane may be image data of either the first pellicle membrane surface or the second pellicle membrane surface. The imaging conditions may be any conditions that allow the orientation angle of the carbon nanotubes to be evaluated, and examples include an acceleration voltage in the range of 0.8 kV or more and 8.0 kV or less, and an imaging magnification of 1,000 times or more and 100,000 times or less.

[0036] In step (S3), a two-dimensional Fourier transform is performed on the image data acquired in step (S2) to obtain a power spectrum image. In step (S3), first, the image data of the SEM image acquired in step (S2) is read into the SEM image using the imread function, and the pixel values ​​of the read SEM image are obtained as a numerical array. As the imread function, for example, the imread function of analysis software (Mathworks, "MATLAB (registered trademark)") can be used. Next, the read SEM image is trimmed to a predetermined square region L. The trimmed square region can have, for example, a size of 700 × 700 pixels. Next, a two-dimensional Fourier transform is performed on the numerical array of the trimmed region using the fft2 function to obtain a power spectrum image. As the fft2 function, for example, the fft2 function of analysis software (Mathworks, "MATLAB") can be used. Through this procedure, a power spectrum image can be obtained by performing a two-dimensional Fourier transform on the image data of the SEM image acquired in step (S2).

[0037] In step (S4), an ellipse is drawn from the angular distribution map of the mean amplitude for the power spectrum image acquired in step (S3). Then, the average value of the orientation intensity in the radial direction of the ellipse is calculated. Here, the radial direction refers to the direction from the center coordinate toward the coordinate position corresponding to the periphery of the ellipse. In step (S4), first, the absolute value of the real part of the power spectrum image acquired in step (S3) is obtained using the abs function. For example, the abs function of analysis software (Mathworks, "MATLAB") can be used as the abs function. Next, the center coordinate of the power spectrum array is calculated based on the absolute value of the real part of the acquired power spectrum image. The distance R and angle θ between each pixel and the center coordinate are calculated and stored in an array. Based on the calculated array of distances R and angles θ, the average value of pixel values ​​within an arbitrary angle range Δθ and a distance of 1 / 2 or less (L / 2) of the region L is calculated. For example, when Δθ is 1°, pixel values ​​within the range between 0° and 1° where the distance R is L / 2 or less (R≦L / 2) are acquired and the average value is calculated. Similarly, pixel values ​​where the distance R is less than or equal to L / 2 (R≦L / 2) are obtained in the range between 1° and 2°, and the average value is calculated. Subsequently, pixel values ​​where the distance R is less than or equal to L / 2 (R≦L / 2) are obtained in the range between n° and n+1°, and the average value is calculated. This average value calculation is then repeated up to the range between 359° and 360°. Δθ is not limited to 1°, and may be smaller or larger than 1°. The average value represents the average value in the specified range, for example, the average value in the specified range between n° and n+1° mentioned above. Using this procedure, an approximation ellipse is drawn, and the average value of the radial orientation intensity in the approximation ellipse can be calculated.

[0038] Referring now to FIG. 2, an example of an angular distribution map of the mean amplitude in the pellicle film according to this embodiment is shown. The angular distribution map of the mean amplitude shown in FIG. 2 is obtained based on the power spectrum image by the above-described procedure. M in FIG. 2 represents the mean value M, which is the mean value of the specified range. An ellipse is drawn from the angular distribution map of the mean amplitude by a collection of data for this mean value M.

[0039] In step (S5), the tilt of the approximate ellipse is calculated based on the equation of an ellipse for the average values ​​of the orientation strength calculated in step (S4), thereby obtaining the orientation angle. In step (S5), first, the set of calculated average values ​​is fitted with the equation of an ellipse. The equation of the ellipse is expressed by the following mathematical formula (Math. 1). The ellipse expressed by the following mathematical formula (Math. 1) is an ellipse centered on the central coordinate, with the major and minor axes tilted relative to the x-axis and y-axis, respectively. In the following mathematical formula (Math. 1), a, b, and c represent coefficients, respectively, and x and y are numerical values ​​in the coordinate format of an ideal ellipse.

[0040]

number

[0041] The average value calculated in step (S4) is designated as M, and the deviation between the approximation ellipse obtained from the data set of the average value M and the ideal ellipse is used as an index to minimize the objective function expressed by the following equation (Equation 2), thereby fitting the data set of average values ​​M to an ideal ellipse. In the following equation (Equation 2), a, b, and c respectively represent coefficients, and X and Y respectively represent values ​​obtained by converting the average value M into a Cartesian coordinate format. X is expressed by the following equation (Equation 3), and Y is expressed by the following equation (Equation 4). In the following equations (Equation 3) and (Equation 4), M is the average value M.

[0042]

number

[0043]

number

[0044]

number

[0045] Next, the above equation (Equation 2) is minimized using the fmincon function to determine the coefficients a, b, and c. From the determined coefficients a, b, and c, the tilt of the ellipse (i.e., the orientation angle γ) can be calculated using the following equation (Equation 5). As the fmincon function, for example, the fmincon function of analysis software (Mathworks, "MATLAB") can be used.

[0046]

number

[0047] 2, M represents the mean value M as described above, and IE represents the ideal ellipse. The orientation angle γ is calculated by determining the coefficients a, b, and c that minimize the error between the data set of the mean value M and the ideal ellipse.

[0048] In step (S6), the standard deviation of the orientation angles obtained in step (S5) is calculated. Specifically, the operations from step (S2) to step (S5) are repeated at multiple locations (e.g., 10 fields of view), and the standard deviation of the orientation angles is measured from the average value of the orientation angles at multiple locations.

[0049] The pellicle membrane according to this embodiment has a standard deviation of the orientation angle of the carbon nanotubes contained in the pellicle membrane measured by the above-mentioned operating method of 8.0° or less.

[0050] (Visible light transmittance) The pellicle membrane of this embodiment preferably has a visible light transmittance of 50% or more, more preferably 60% or more, even more preferably 70% or more, and even more preferably 80% or more. It is known that pellicle films containing CNTs have a correlation between their light transmittance at wavelengths of 13.5 nm and 550 nm (see, for example, Figure 4(a) in 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). In the pellicle membrane of this embodiment, if the visible light transmittance obtained by the measurement method described below is 50% or more, the EUV transmittance can be adjusted to 90% or more, and if the visible light transmittance is 80% or more, the EUV transmittance can be adjusted to 95% or more.

[0051] The visible light transmittance of the pellicle film according to this embodiment is, for example, (1) a 14,300 mm2 area image captured from the first pellicle film side while the second pellicle film side is placed at an imaging position and irradiated with white light having a wavelength of 400 nm or more and 750 nm or less from the second pellicle film side. 2 (1) is calculated by the following formula (6) based on (1) an image of the pellicle membrane in a light-transmitted state at 700,000 pixels or more of the area, (2) an image of the imaging position in a bright state at 700,000 pixels or more of the area, where the imaging position not including the pellicle membrane is imaged under the condition of irradiating the white light, and (3) an image of the imaging position in a dark state at 700,000 pixels or more of the area, where the imaging position not including the pellicle membrane is imaged under the condition of blocking light. Note that the images in (2) and (3) above have the same area and number of pixels as the image in (1) above. T={(Tp-Td) / (Tb-Td)}×100…(Math 6) (In the above formula (Equation 6), T represents the visible light transmittance of the pellicle film, Tp represents a pixel value representing the transmission of the white light in the image of the pellicle film in the light-transmitting state, Tb represents a pixel value representing the transmission of the white light in the image at the imaging position in the bright state, and Td represents a pixel value when the white light is not irradiated in the image at the imaging position in the dark state.)

[0052] Specifically, the visible light transmittance of the pellicle film according to this embodiment can be measured by the following steps (S1T) to (S7T). Step (S1T): A step of preparing a pellicle membrane containing carbon nanotubes and having a first pellicle membrane surface and a second pellicle membrane surface opposite to the first pellicle membrane surface. Step (S2T): A step of placing the prepared pellicle membrane at an imaging position with the second pellicle membrane surface facing the imaging position. Step (S3T): A step of irradiating the placed pellicle membrane with white light having a wavelength of 400 nm or more and 750 nm or less from the second pellicle membrane surface side, thereby transmitting the white light through the pellicle membrane. Step (S4T): While irradiating the white light, an image is taken by an imaging means from the side of the first pellicle film that is not irradiated with the white light, and an area of ​​14,300 mm 2 A step of acquiring an image of the pellicle membrane in a light-transmitted state at 700,000 pixels or more. Step (S5T): Under the condition of irradiating the white light, the imaging position not including the pellicle film is imaged, and an area of ​​14,300 mm 2 A process of acquiring an image of the bright state at an imaging position of 700,000 pixels or more. Step (S6T): Without irradiating the white light, the imaging position not including the pellicle film is imaged in a light-shielded state, and an area of ​​14,300 mm 2 A process of acquiring an image of the imaging position in a dark state at 700,000 pixels or more. Step (S7T): A step of calculating the visible light transmittance of the pellicle film using the formula (6) based on the image of the pellicle film in the translucent state (the image of the pellicle film in the translucent state relating to (1)), the image of the bright state imaging position (the image of the bright state imaging position relating to (2)), and the image of the dark state imaging position (the image of the dark state imaging position relating to (3)).

[0053] In step (S7T), when calculating the visible light transmittance of the pellicle film and the standard deviation of the visible light transmittance, a transmittance map of the pellicle film is created based on the images acquired in steps (S4T), (S5T), and (S6T). Based on the created transmittance map of the pellicle film, the visible light transmittance (i.e., the average value of the visible light transmittance) and the standard deviation of the visible light transmittance are determined. The imaging means used to measure the visible light transmittance is not particularly limited, and examples include digital cameras such as digital single-lens reflex cameras.

[0054] It is generally known that there is a correlation between the thickness of a pellicle film and its light transmittance. In one aspect of the pellicle film according to the present embodiment, when the visible light transmittance is, for example, about 80%, the maximum thickness of the pellicle film is, for example, 70 nm or less. Furthermore, in one aspect of the pellicle film according to the present embodiment, when the visible light transmittance is, for example, about 80%, the average thickness of the pellicle film is, for example, 50 nm or less. For example, in one aspect of the pellicle film according to the present embodiment, when the visible light transmittance is 70.8%, the average thickness of the pellicle film is approximately 47 nm. The thickness of the pellicle film according to the present embodiment can be measured using a scanning probe microscope. In consideration of excellent mechanical strength, the average thickness of the pellicle film is preferably, for example, 30 nm or more, and preferably 35 nm or more.

[0055] The weight per unit area of ​​the pellicle membrane is not particularly limited, and is 0.1 μg / cm 2 More than 20μg / cm 2The weight per unit area of ​​the pellicle membrane is preferably 0.3 μg / cm or less. 2 More preferably, it is 0.4 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 More than 20μg / cm 2 If the thickness is less than this, the pellicle membrane is likely to have excellent mechanical strength, and the pellicle membrane is likely to have high EUV transmittance.

[0056] 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 obtain excellent mechanical strength for the pellicle membrane. Furthermore, it is easier to ensure high EUV transmittance for the pellicle membrane.

[0057] 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" refers to a film that is self-supporting by itself, 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.

[0058] There are no particular limitations on the means for adjusting the pellicle membrane so that the standard deviation of the orientation angle of the carbon nanotubes contained in the pellicle membrane measured by the above-mentioned operating method is 8.0° or less. Examples of such means include means for adjusting the dispersion conditions when dispersing carbon nanotubes and the centrifugation conditions when centrifuging the carbon nanotube dispersion in an example of a preferred pellicle membrane production method described below.

[0059] (Method of manufacturing pellicle membrane) The method for producing a pellicle film according to this embodiment is not particularly limited, and various production methods can be applied as long as the standard deviation of the orientation angle of the carbon nanotubes contained in the pellicle film satisfies the above-mentioned numerical range. Examples of the method for producing a pellicle film according to this embodiment include a filtration method (a method in which a pellicle film is obtained by filtering a carbon nanotube dispersion through a filter and then peeling it off from the filter), a coating method (a method in which a carbon nanotube dispersion is applied to a substrate and then peeled off from the substrate to obtain a pellicle film), and an etching method (a method in which a carbon nanotube film is formed on a wafer and then the wafer is etched to obtain a pellicle film).

[0060] As described above, the method for producing the pellicle membrane according to the present embodiment is not particularly limited. An example of a preferred method for producing the pellicle membrane according to the present embodiment is a production method including the following steps.

[0061] An example of a preferred method for manufacturing a pellicle membrane according to this embodiment comprises the steps of: (P1) dispersing carbon nanotubes to obtain a first dispersion of carbon nanotubes; (P2) dispersing the first dispersion by centrifugation to separate the carbon nanotube aggregates, and then collecting the supernatant to obtain a second dispersion of carbon nanotubes; (P3) precipitating and depositing the second dispersion of carbon nanotubes on an air-permeable member to obtain a mat-like carbon nanotube film on the air-permeable member; and (P4) removing the air-permeable member from the carbon nanotube film to obtain a pellicle membrane.

[0062] First, in step (P1), carbon nanotubes are dispersed in a liquid as a dispersion medium to prepare a first dispersion of carbon nanotubes in which the carbon nanotubes are dispersed in the liquid. The liquid may be a liquid containing water. The first dispersion of carbon nanotubes may contain only carbon nanotubes as a dispersoid. The carbon nanotube dispersion may contain, in addition to carbon nanotubes, various additives such as a dispersant that disperses the carbon nanotubes. Furthermore, in step (P1), the method for preparing the first dispersion is not particularly limited. The first dispersion can be prepared using various dispersion devices. For example, the first dispersion may be prepared using a wet atomization device. When the first dispersion is prepared using a wet atomization device, the conditions for the dispersion treatment using the wet atomization device may be, for example, a pressure of 50 MPa or more and 200 MPa or less, and the number of treatments may be one or more and 10 or less.

[0063] The weight of the carbon nanotubes per unit area is, for example, 0.1 μg / cm 2 as the amount of carbon nanotubes contained in the carbon nanotube film produced in step (P3). 2 More than 20μg / cm 2 The following ranges can be mentioned.

[0064] Next, in step (P2), the first dispersion of carbon nanotubes prepared in step (P1) is centrifuged using a centrifuge to separate the carbon nanotube aggregates. The supernatant liquid after the centrifugation is then collected to obtain a second dispersion of carbon nanotubes. The supernatant liquid contains carbon nanotubes. The conditions for the centrifugation are not particularly limited. From the viewpoint of separating the carbon nanotube aggregates, the conditions for the centrifugation are, for example, a relative centrifugal acceleration of 100 kG or more and a processing time of 1 hour or more.

[0065] Next, in step (P3), the supernatant liquid, which is the second dispersion liquid separated in step (P2), is allowed to settle and deposit on an air-permeable member. For example, the supernatant liquid separated in step (P2) is filtered through a filtration membrane as an air-permeable member, causing the carbon nanotubes to settle and deposit, forming a mat-like carbon nanotube membrane on the filtration membrane. Examples of the filtration membrane include a filtration membrane made of nonwoven fabric, and specifically, it is preferable to use a filtration membrane made of nonwoven fabric such as a membrane filter.

[0066] Next, in step (P4), 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. Also, if necessary, both a drying step and an annealing step may be performed, or only an annealing step may be performed without a drying step. The pellicle membrane obtained through the above steps (P1) to (P4) is a self-supporting membrane.

[0067] [Pellicle] The pellicle of this embodiment comprises a pellicle membrane according to the embodiment described above, and a support having a frame and an opening surrounded by the frame, and supporting the pellicle membrane.

[0068] Hereinafter, the pellicle according to this embodiment will be described with reference to the drawings. It should be noted that in the description of the present specification, when drawings are referred to, some parts of the drawings are shown enlarged or reduced in size to facilitate the description.

[0069] FIG. 3 shows a plan view of pellicle 100 viewed from the surface on which pellicle membrane 10 is installed, and FIG. 4 shows a cross-sectional view of pellicle 100 shown in FIG. 3. Pellicle 100 comprises pellicle membrane 10 and a support 30 that supports pellicle membrane 10. Support 30 comprises a frame 31 and an opening 32 surrounded by frame 31, with opening 32 penetrating from one surface of support 30 to the other. Both frame 31 and opening 32 are formed in a rectangular shape, and all four corners of the outer shape of frame 31 are rounded. Frame 31 comprises a support surface 33 facing pellicle membrane 10. Pellicle membrane 10 is the pellicle membrane 10 shown in FIG. 1. 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 the first pellicle film surface 11. The peripheral edge 13 of the pellicle film 10 is fixed to a part of the support surface 33 of the frame 31, and covers the opening 32 of the support 30.

[0070] 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.).

[0071] While an example of a pellicle according to the present embodiment has been described above with reference to Figures 3 and 4, 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 member 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.

[0072] For example, the pellicle membrane 10 and the support 30 of the pellicle 100 shown in Figures 3 and 4 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.

[0073] 3 and 4, 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. However, 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 30.

[0074] 3 and 4, 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.

[0075] (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 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.

[0076] 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 may involve, for example, applying a carbon nanotube dispersion to the support surface and drying it to provide an adhesive layer containing carbon nanotubes.

[0077] The pellicle according to this embodiment is used, for example, by being placed 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, adhesion of foreign matter to the photomask is suppressed. Furthermore, the pellicle according to this embodiment has excellent mechanical strength because it uses the pellicle film according to this embodiment described above. Therefore, damage to the pellicle during installation and transportation is suppressed. Furthermore, the pellicle film according to this embodiment suppresses variation in EUV transmittance while ensuring high EUV transmittance.

[0078] 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. [Example]

[0079] 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.

[0080] [Example 1] <Fabrication 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 CNTs in the first dispersion before dilution was 0.02 mass%. In addition, a surfactant was weighed as a dispersant so that the concentration of CNTs in the first dispersion before dilution was 0.2 mass%. The weighed CNTs and the weighed surfactant were put into water, and the CNTs were dispersed in water using a wet atomizer. The dispersion conditions were a pressure of 70 MPa and three treatments. The mixture was then diluted to a CNT concentration of 1 ppm to prepare a first CNT dispersion. Next, the first CNT dispersion was collected so that the mass of CNTs (referred to as CNT amount in Table 1) was the value shown in Table 1 as the amount of CNT contained in the pellicle membrane.

[0081] Next, the first CNT dispersion was centrifuged using a centrifuge at a relative centrifugal acceleration of 100 kG for 2 hours to separate the CNT aggregates. After centrifugation, the supernatant was collected. This supernatant was used as the second CNT dispersion. Next, the second CNT dispersion 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. The CNT film was heat-treated at 650°C for 30 minutes to produce a pellicle film containing CNT. The pellicle film was a self-supporting film.

[0082] [Evaluation of pellicle membrane] <Standard deviation of orientation angle> The standard deviation of the orientation angle of the CNTs contained in the obtained pellicle film was calculated according to the above-mentioned steps (S1) to (S6). Specifically, the surface of the pellicle film (first pellicle film surface or second pellicle film surface) was observed with an SEM (Carl Zeiss, CrossBeam550), and SEM image data of the pellicle film surface was obtained. The imaging conditions were an acceleration voltage of 1 kV and a magnification of 10,000 times. The field of view was 10. Furthermore, in the above-mentioned step (S3), when acquiring the power spectrum image, the loaded SEM image was trimmed to a square size of 700 × 700 pixels. Furthermore, in the above-mentioned step (S4), when drawing an approximate ellipse, Δθ for calculating the average value was set to 1°.

[0083] <Burst strength of pellicle membrane> The burst strength of the pellicle membrane was measured using a measuring device equipped with a chamber having a partially open opening, a pressure sensor disposed inside the chamber, and a holder for holding a sample at the opening of the chamber. The pellicle membrane obtained in each example was held in the holder, nitrogen gas was flowed into the chamber, and the gas pressure until the pellicle membrane held in the holder of the chamber burst was measured. The gas pressure at which the pellicle membrane burst was taken as the burst strength.

[0084] <Measurement of visible light transmittance> Regarding the visible light transmittance of the obtained pellicle film, a transmittance map of the pellicle film was created according to the above-mentioned steps (S1T) to (S7T), and based on the created transmittance map of the pellicle film, the average value of the visible light transmittance was calculated using the above-mentioned formula (6). As the imaging means used in the procedure of the above-mentioned steps (S1T) to (S7T), a mirrorless camera (Canon Inc., "EOS R5") was used. Note that the images acquired in the above-mentioned steps (S4T), (S5T), and (S6T) were taken from an area of ​​14,300 mm 2 The image has 700,000 pixels. In Table 1, the average visible light transmittance is denoted as AVE.

[0085] [Examples 2 to 4] A pellicle membrane of each example was produced in the same manner as in Example 1, except that the mass of CNT contained in the pellicle membrane was changed according to Table 1, and the pellicle membrane was evaluated.

[0086] [Comparative Examples 1 and 2] Pellicle membranes of Comparative Examples 1 and 2 were prepared in the same manner as Example 1, except that the mass of CNTs contained in the pellicle membrane was changed according to Table 1 and that centrifugation was not performed, and the pellicle membranes were evaluated. [Table 1]

[0087] From the above results, it can be seen that pellicle membranes in which the standard deviation of the orientation angle of the carbon nanotubes contained in the pellicle membrane is 8.0° or less have superior burst strength compared to pellicle membranes in which the standard deviation exceeds 8.0°. In particular, it can be seen that the pellicle membranes of Examples 1 and 4 have superior burst strength despite having higher light transmittance than the pellicle membranes of Comparative Examples 1 and 2. It can also be seen that the pellicle membranes of Examples 2 and 3 have superior burst strength despite having light transmittance similar to that of the pellicle membranes of Comparative Examples 1 and 2. Therefore, according to the present embodiment, a pellicle membrane with excellent mechanical strength and a pellicle using the pellicle membrane are provided. Furthermore, according to the present embodiment, a measurement method capable of measuring the standard deviation of the orientation angle of the carbon nanotubes contained in a pellicle membrane with excellent mechanical strength is provided. [Explanation of symbols]

[0088] 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, M...average value, IE...ideal ellipse.

Claims

1. A pellicle membrane having a porous structure, the pellicle membrane comprises carbon nanotubes; The pellicle membrane has a first pellicle membrane surface and a second pellicle membrane surface opposite to the first pellicle membrane surface, The standard deviation of the orientation angle of the carbon nanotubes is 8.0° or less, which is calculated based on an approximate ellipse of a power spectrum image obtained by performing a two-dimensional Fourier transform on an image of the first pellicle film surface or the second pellicle film surface of the pellicle film. Pellicle membrane.

2. The pellicle membrane according to claim 1, the standard deviation of the orientation angle of the carbon nanotubes is 0.5° or more and 8.0° or less; Pellicle membrane.

3. The pellicle membrane according to claim 1 or 2, The image of the first pellicle film surface or the second pellicle film surface is an image captured by a scanning electron microscope. Pellicle membrane.

4. 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.

5. 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.

6. The pellicle membrane according to claim 1 or 2, have independence, Pellicle membrane.

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

8. A method for measuring the standard deviation of the orientation angle of carbon nanotubes contained in a pellicle film having a porous structure, comprising: providing a pellicle membrane including carbon nanotubes and having a first pellicle membrane surface and a second pellicle membrane surface opposite the first pellicle membrane surface; A step of imaging the first pellicle film surface or the second pellicle film surface of the prepared pellicle film using a scanning electron microscope to obtain image data on the surface of the pellicle film; performing a two-dimensional Fourier transform on the acquired image data to acquire a power spectrum image; a step of drawing an approximation ellipse from an angular distribution diagram of the average amplitude for the acquired power spectrum image, and calculating an average value of the orientation intensity in the radial direction of the approximation ellipse; a step of calculating the inclination of the approximate ellipse based on an ellipse equation with respect to the calculated average value of the orientation strength, and obtaining an orientation angle; Calculating the standard deviation of the orientation angles; Equipped with Measurement method.

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