Thin film, photomask, membrane, graphene sheet and its manufacturing method

Abstract

This invention provides a technology for a thin film that is not easily damaged when force is applied in the thickness direction and can achieve light transmission with high transmittance. The thin film of the present invention comprises a plurality of layers (120) stacked on each other, and one or more openings (120H) in one or more of the plurality of layers (120) are provided, with a width or diameter in the range of 10 to 500 nm.

Description

Technical Field

[0001] This invention relates to photomask protective film. Prior Technology

[0002] The minimum size of a pattern that can be formed using photolithography depends on the wavelength of the light used for exposure. This minimum size can be reduced by using light with shorter wavelengths for exposure.

[0003] Until now, exposure has used ArF excimer laser light with a wavelength of 193 nm. In recent years, the requirements for photolithography to form finer patterns have increased, and extreme ultraviolet light (EUV light) with a wavelength of 13.5 nm has been increasingly used.

[0004] Photomask protective films are used to prevent dust and other contaminants from adhering to photomasks or reticles. Because EUV light is easily absorbed by various substances, thin films of polycrystalline silicon with low absorption rates of EUV light are being developed for use in extreme ultraviolet lithography (EUVL).

[0005] Furthermore, films made of carbon materials such as graphene and carbon nanotubes exhibit better heat resistance than films made of polycrystalline silicon. Consequently, thin films made of carbon materials such as graphene and carbon nanotubes have attracted attention (see Patent Documents 1 to 3). [Previous Technical Documents] [Patent Literature]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-194838 [Patent Document 2] Japanese Patent Application Publication No. 2018-194840 [Patent Document 3] International Publication No. 2018 / 008594 Summary of the Invention

[0007] The purpose of this invention is to provide a technology for a thin film that is not easily damaged when force is applied in the thickness direction and can achieve high transmittance to allow light to pass through.

[0008] According to a first aspect of the present invention, a thin film is provided, which comprises a plurality of mutually stacked layers, and one or more openings having a width or diameter in the range of 10 to 500 nm are provided on one or more of the plurality of layers.

[0009] According to a second embodiment of the present invention, a thin film is provided, which has a plurality of layers stacked on top of each other, and one or more openings are provided in two or more of the plurality of layers.

[0010] According to other embodiments of the invention, a thin film as described above is provided, wherein the aforementioned plurality of layers are composed of materials selected from the group comprising graphene, carbon nanotubes, polycrystalline silicon and silicon nitride.

[0011] Alternatively, according to other embodiments of the invention, a thin film as described above is provided, wherein the aforementioned plurality of layers are composed of a material containing one or more metallic elements selected from the group consisting of zirconium, niobium, molybdenum, tantalum, hafnium, scandium, titanium, vanadium and chromium.

[0012] According to a third embodiment of the present invention, a thin film is provided having a plurality of mutually stacked layers, wherein the plurality of layers are composed of materials selected from the group comprising graphene and carbon nanotubes, and one or more openings are provided in one or more of the plurality of layers.

[0013] According to another embodiment of the invention, a thin film as described above is provided, wherein the width or diameter of one or more of the aforementioned openings is 500 nm or less.

[0014] According to another aspect of the invention, a thin film as described above is provided, wherein at least one of the aforementioned plurality of layers is provided with a plurality of the aforementioned openings, which are regularly arranged.

[0015] According to another embodiment of the invention, a thin film as described above is provided, wherein at least one of the aforementioned plurality of layers is provided with a plurality of the aforementioned openings, the openings being of the same shape.

[0016] According to another embodiment of the invention, a thin film as described above is provided, wherein the aforementioned one or more openings are provided in two or more of the aforementioned plurality of layers, and the two or more layers in which the aforementioned one or more openings are provided are adjacent to each other, wherein the positions of the aforementioned one or more openings are different.

[0017] According to another aspect of the invention, a thin film as described above is provided, wherein no openings are provided in one or more of the aforementioned plurality of layers.

[0018] According to another aspect of the invention, a thin film is provided, wherein the aforementioned one or more layers without the aforementioned opening are at least one of the outermost layers of the aforementioned thin film.

[0019] According to another aspect of the invention, a thin film as described above is provided, wherein a plurality of graphene sheets are stacked on top of each other.

[0020] According to the fourth embodiment of the present invention, a thin film is provided, which is composed of a plurality of mutually stacked graphene sheets, and has an apparent density that is smaller than its true density.

[0021] According to the fifth aspect of the present invention, a thin film is provided, which is composed of a plurality of mutually stacked graphene sheets, having the same thickness as the aforementioned film, and having higher transmittance than a stack composed of graphene sheets as a continuous film.

[0022] According to another embodiment of the present invention, a thin film as described above is provided, having a thickness of 200 nm or less.

[0023] According to a sixth embodiment of the present invention, a photomask protective film is provided, comprising: a thin film as described in any of the above embodiments; and a frame supporting the aforementioned thin film.

[0024] According to the seventh aspect of the present invention, a membrane is provided having a plurality of mutually stacked graphene sheets, wherein one or more of the plurality of graphene sheets have one or more openings.

[0025] According to another aspect of the present invention, a membrane as described above is provided, wherein the width or diameter of one or more of the aforementioned openings is 500 nm or less.

[0026] According to another embodiment of the invention, a film as described above is provided, wherein two or more of the aforementioned plurality of graphene sheets are provided with the aforementioned one or more openings, and for the two or more graphene sheets provided with the aforementioned one or more openings that are adjacent to each other, the positions of the aforementioned one or more openings are different.

[0027] According to another embodiment of the invention, a film as described above is provided, wherein one or more of the aforementioned graphene sheets are not provided with openings.

[0028] According to another aspect of the present invention, a film as described above is provided, wherein the graphene sheet that does not have the aforementioned opening is at least one of the outermost layers of the aforementioned film.

[0029] According to the eighth embodiment of the present invention, a film is provided which is composed of a plurality of mutually stacked graphene sheets, and the apparent density is smaller than the true density.

[0030] According to the ninth aspect of the present invention, a film is provided which is composed of a plurality of mutually stacked graphene sheets, having the same thickness as the aforementioned film, and having higher transmittance than a stack composed of graphene sheets as a continuous film.

[0031] According to the tenth aspect of the present invention, a graphene sheet is provided having one or more openings.

[0032] According to the 11th aspect of the present invention, a method for manufacturing a graphene sheet is provided, comprising: forming a masking layer on a metal layer covering a portion thereof; and generating graphene in the portion of the metal layer not covered by the masking layer.

[0033] According to the 12th aspect of the present invention, a method for manufacturing a graphene sheet is provided, which includes generating graphene on a metal layer having one or more openings. Simple Explanation of the Diagram

[0034] Figure 1 is a schematic cross-sectional view showing the photomask protective film of one embodiment of the present invention mounted on the photomask. Figure 2 is a schematic cross-sectional view showing an example of a thin film that can be used in the photomask of Figure 1. Figure 3 is a perspective view that schematically shows an example of the structure that can be used to form the thin film layer of Figure 2. Figure 4 is a cross-sectional view that schematically shows one step in an example of a method for manufacturing graphene sheets. Figure 5 is a cross-sectional view that schematically shows the next step after the steps in Figure 4. Figure 6 is a cross-sectional view that schematically shows one step in another example of a method for manufacturing graphene sheets. Figure 7 is a cross-sectional view that schematically shows the next step after the steps in Figure 6. Figure 8 is a schematic cross-sectional view showing other examples of thin films that can be used in the photomask protective film of Figure 1. Figure 9 is a schematic cross-sectional view showing another example of a thin film that can be used in the photomask of Figure 1. Figure 10 is a schematic cross-sectional view showing another example of a thin film that can be used in the photomask of Figure 1. Figure 11 is a plan view schematically showing an example of a construction that can be used for the opening. Figure 12 is a plan view schematically showing other examples of structures that can be used for openings. Figure 13 is a plan view schematically showing another example of a construction that can be used for an opening. Figure 14 is a plan view schematically showing another example of a construction that can be used for the opening. Figure 15 is a plan view schematically showing another example of a construction that can be used for the opening. Implementation

[0035] [The form in which the invention is carried out]

[0036] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments described below are further elaborations on any of the aforementioned embodiments. Furthermore, in the drawings referred to below, elements having the same or similar functions are referred to by the same reference numerals, and repeated descriptions are omitted. Also, the dimensions or shapes in the drawings may differ from the actual objects.

[0037] Figure 1 is a schematic cross-sectional view showing a photomask protective film of one embodiment of the present invention mounted on a photomask. In Figure 1, the photomask 2 with the photomask protective film 1 installed is a reflective photomask for EUV lithography. The photomask protective film 1 can also be installed on other photomasks.

[0038] The photomask 2 system includes: a substrate 21, a multilayer reflective film 22, a capping film 23, and an absorption layer 24.

[0039] The substrate 21 has a flat surface. The substrate 21 is made of a material with a low coefficient of thermal expansion, such as synthetic quartz.

[0040] The multilayer reflective film 22 is mounted on the aforementioned surface of the substrate 21. The multilayer reflective film 22 contains two or more layers with different refractive indices relative to EUV light. The multilayer reflective film 22 is designed to exhibit high reflectivity relative to EUV light and low reflectivity relative to other light through multiple reflection interference.

[0041] Here, the multilayer reflective film 22 has different refractive indices relative to EUV light and contains alternating reflective layers 22a and 22b. Reflective layers 22a and 22b are, for example, one made of silicon and the other of molybdenum. Furthermore, in Figure 1, the multilayer reflective film 22 contains a combination of three reflective layers 22a and 22b, but typically contains more combinations, such as about 40 combinations.

[0042] The cover film 23 is disposed on the multilayer reflective film 22. The cover film 23 serves to protect the multilayer reflective film 22 from the effects of etchants or cleaning agents during the patterning of the absorption layer 24 or the cleaning of the photomask 2. The cover film 23 is, for example, made of ruthenium.

[0043] The absorption layer 24 is disposed on the cover film 23. The absorption layer 24 has an opening with a pattern corresponding to the exposure pattern, which corresponds to the photoresist layer on the semiconductor wafer.

[0044] The absorption layer 24 is a layer made of a material that exhibits a high absorption rate relative to EUV light. The absorption layer 24 is, for example, made of tantalum, indium oxide, tellurium oxide, or tin telluride.

[0045] The photomask protective film 1 is installed on the photomask 2. Here, the photomask protective film 1 is used to prevent dust and other particles from adhering to the reflective surface of the photomask 2. In addition, when the photomask is a transmissive type, the photomask protective film 1 can also be installed on both sides of the photomask.

[0046] The photomask protective film 1 series includes a frame 11 and a thin film 12. The frame 11 is mounted on the photomask 2 by means of an adhesive or fixing mechanism (not shown). The frame 11 functions as a spacer for separating the thin film 12 from the photomask 2. The frame 11 is, for example, made of aluminum.

[0047] The thin film 12 is a film with high transmittance relative to the exposure light, specifically relative to EUV light. The thin film 12 is supported on the frame 11 by sandwiching it in the middle and facing the photomask 2. Specifically, the periphery of the thin film 12 is fixed to the frame 11, for example, by an adhesive.

[0048] The thin film 12 is a self-supporting film. Here, "self-supporting film" means a film that can be operated independently without being supported by other components such as a support body. The thin film 12 contains a plurality of layers stacked on top of each other. Preferably, more than one opening is provided in one or more of these layers, or in two or more layers.

[0049] Figure 2 is a schematic cross-sectional view showing an example of a thin film that can be used in the photomask protective film of Figure 1. Figure 3 is a perspective view showing a schematic example of the structure of the layers that can be used to form the thin film of Figure 2.

[0050] The thin film 12 in Figure 2 consists of a plurality of layers 120 stacked on top of each other. The principal surfaces of these layers 120 are substantially parallel to the principal surfaces of the thin film 12.

[0051] Each of the layers 120 has a plurality of openings 120H, as shown in Figures 2 and 3. These openings 120H, as shown in Figure 3, are identical in shape and size. Specifically, each opening 120H is a circular through-hole. These openings 120H are arranged regularly in two intersecting directions.

[0052] The width or diameter of the opening 120H is preferably less than 500 nm, more preferably less than 300 nm, and even more preferably less than 200 nm. If the width or diameter of the opening 120H is increased, the possibility of dust and other particles penetrating the thin film 12 will increase.

[0053] The width or diameter of the opening 120H is preferably 10 nm or more, more preferably 20 nm or more, and even more preferably 30 nm or more. Layer 120 with a small width or diameter of the opening 120H is difficult to manufacture.

[0054] The layer 120 with openings 120H preferably has a porosity or aperture ratio in the range of 5% to 75%, more preferably in the range of 10% to 50%, and even more preferably in the range of 10% to 25%. If the porosity or aperture ratio is reduced, the permeability of the thin film 12 will decrease. If the porosity or aperture ratio is increased, the strength of each layer 120 will decrease, making it difficult to manufacture the thin film 12.

[0055] As shown in Figure 2, the adjacent elements in layer 120 have different positions for the openings 120H. This configuration reduces the likelihood of dust or other particles penetrating the thin membrane 12.

[0056] Each of the layers 120 is, for example, made of a material selected from the group including graphene, carbon nanotubes, polycrystalline silicon, and silicon nitride. Each of the layers 120 is preferably made of a material selected from the group including graphene and carbon nanotubes.

[0057] Furthermore, here, "graphene sheet" means: a layer composed of a single molecule of graphene, or a stack of several layers formed by individual graphene molecules stacked in the thickness direction. Graphene is a molecule with an interatomic distance of approximately 0.142 nm and a thickness of approximately 0.335 nm. A graphene sheet exhibits a higher absorption rate across the entire wavelength range from ultraviolet to infrared light compared to its absorption rate at EUV light wavelengths. Specifically, a graphene sheet exhibits an absorption rate of approximately 0.2% at EUV light wavelengths and approximately 2.3% in the visible light wavelength range.

[0058] Each of layers 120 may also be composed of a material containing more than one metallic element. For example, each of layers 120 may also be composed of a material containing more than one metallic element selected from the group consisting of zirconium, niobium, molybdenum, tantalum, hafnium, scandium, titanium, vanadium, and chromium. In this case, the metallic element is preferably selected from the group consisting of more than one metallic element selected from the group consisting of zirconium, niobium, molybdenum, tantalum, hafnium, scandium, and titanium, and more preferably from the group consisting of more than one metallic element selected from the group consisting of zirconium, niobium, molybdenum, tantalum, hafnium, scandium, and titanium. The mass absorption coefficients of zirconium, niobium, molybdenum, tantalum, hafnium, scandium, and titanium are smaller than those of carbon.

[0059] Each of layers 120, in addition to containing the aforementioned metallic elements, may further contain at least one of carbon and nitrogen. In this case, the metallic element and at least one of carbon and nitrogen can constitute a two-dimensional inorganic compound. This two-dimensional inorganic compound is, for example, a sheet-like compound with a thickness of several atoms, composed of metal carbides, metal nitrides, or metal carbonitrides. In such a layer composed of sheet-like compounds, the numerous sheets are arranged in a manner where their thickness directions are substantially aligned with the thickness direction of the layer. Therefore, in the case where a plurality of layers 120 are layers composed of sheet-like compounds, each of layers 120 is composed of one or more sheets.

[0060] Here, as an example, each of the 120 layers is a graphene sheet.

[0061] The thickness of the thin film 12 is preferably less than 200 nm, more preferably less than 100 nm, and even more preferably less than 70 nm. If the thin film 12 is thickened, the transmittance relative to the exposure light will decrease, specifically the transmittance relative to EUV light. The thickness of the thin film 12 is preferably more than 10 nm, and more preferably more than 20 nm. If the thin film 12 is thinned, its mechanical strength will decrease, and the possibility of dust and other particles penetrating the thin film 12 will increase.

[0062] The thin film 12 preferably exhibits a transmittance of 90% or more at the wavelength of the exposure light. For example, when the exposure light is EUV light, the thin film 12 preferably exhibits a transmittance of approximately 90% or more at the wavelength of EUV light.

[0063] The thin film 12 is preferably designed to prevent dust particles with a diameter exceeding 30 nm from penetrating. That is, the width or diameter of the openings 120H in the thin film 12 and their arrangement are preferably set in a manner that prevents dust particles with a diameter exceeding 30 nm from penetrating.

[0064] The aforementioned thin film 12 can be manufactured, for example, by the following method. Furthermore, as described above, each of the layers 120 is configured to be a graphene sheet.

[0065] Figure 4 is a schematic cross-sectional view showing one step in an example of a method for manufacturing graphene sheets. Figure 5 is a schematic cross-sectional view showing the next step in Figure 4.

[0066] Figure 4 is a schematic cross-sectional view showing one step in the manufacturing method of an example graphene sheet. Figure 5 is a schematic cross-sectional view showing the other steps in the manufacturing method of Figure 4.

[0067] When manufacturing the thin film 12, for example, the structure shown in FIG4 is prepared first. The structure shown in Figure 4 includes a substrate 31, a metal layer 32, and a masking layer 33.

[0068] The substrate 31 has a smooth surface. The substrate 31 is a non-metallic substrate, such as a silicon substrate, a glass substrate, and a sapphire substrate.

[0069] The metal layer 32 is disposed on the surface of the substrate 31. The metal layer 32 is made of metals such as copper and nickel.

[0070] Alternatively, a base layer may be provided between the substrate 31 and the metal layer 32. The base layer may be composed of, for example, aluminum nitride, aluminum oxide, or silicon oxide. Furthermore, if the metal layer 32 has sufficient thickness, the substrate 31 may be omitted.

[0071] The masking layer 33 partially covers the surface of the metal layer 32. Specifically, the masking layer 33 covers the surface of the metal layer 32 only at the location corresponding to the opening 120H of the layer 120.

[0072] The mask layer 33 is, for example, made of a non-metallic material. This non-metallic material is, for example, an organic polymer or an inorganic insulator. The mask layer 33 made of an organic polymer can be obtained, for example, by forming a photoresist layer on the metal layer 32, providing it for pattern exposure or electron beam drawing using ultraviolet light, and then providing it for development. The mask layer 33 made of an inorganic insulator can be obtained, for example, by sequentially forming an inorganic insulating layer and a photoresist layer on the metal layer 32, sequentially providing the photoresist layer for pattern exposure or electron beam drawing and development using ultraviolet light to form an etching mask, and then etching the inorganic insulating layer.

[0073] Next, graphene is formed on the exposed portion of the metal layer 32 by chemical vapor deposition (CVD), such as thermal CVD or plasma CVD. In this CVD, for example, a mixture of methane and hydrogen is used as the feed gas. In this manner, as shown in FIG. 5, a graphene sheet with an opening at a position corresponding to the masking layer 33 is obtained as layer 120. Furthermore, in this method, for example when the metal layer 32 is made of nickel, graphene sheets may also be formed above and below the metal layer 32.

[0074] Repeat the above procedure to create multiple structures as shown in Figure 5. Then, repeat the transfer step of transferring one graphene sheet onto other graphene sheets.

[0075] For example, firstly, an adhesive made of an organic polymer is formed on a graphene sheet. The organic polymer used is, for example, a silicone compound, an acrylic compound, or an epoxy compound. Next, a mask layer 33 and a metal layer 32 are removed by etching. This transfers the graphene sheet from the metal layer 32 to the adhesive. Alternatively, the mask layer 33 can be removed before forming the adhesive layer. Next, the graphene sheet on the adhesive layer is pressed onto other graphene sheets. The graphene sheets are bonded together by van der Waals force. Then, the adhesive layer is removed from the graphene sheets by etching. In this way, a two-layer structure consisting of two overlapping graphene sheets is obtained. Layer structures consisting of three or more overlapping graphene sheets can be obtained by repeating the same operations described above. Subsequently, the masking layer 33 and the metal layer 32, which are in contact with this two-layer or multi-layer structure, are removed by etching. In this way, a thin film 12 composed of graphene sheets is obtained.

[0076] The thin film 12 can also be manufactured using other methods. Figure 6 is a schematic cross-sectional view showing one step in another example of a method for manufacturing graphene sheets. Figure 7 is a schematic cross-sectional view showing the next step after the step in Figure 6.

[0077] The methods shown in Figures 6 and 7 are the same as those described with reference to Figures 4 and 5, except for the following points. Specifically, in the methods shown in Figures 6 and 7, the metal layer 32 is a patterned layer with an opening corresponding to the opening 120H, and the mask layer 33 is omitted. For example, first, the structure shown in Figure 4 is formed, and the metal layer 32 is etched using the mask layer 33 as an etching mask. Next, the mask layer 33 is removed, for example, by etching. Next, graphene is generated on the metal layer 32 using the method described with reference to Figure 5. Then, transfer processes as described with reference to Figures 4 and 5 are performed to obtain a thin film 12 where each layer 120 is composed of graphene sheets.

[0078] The thin film 12 can also be manufactured using other methods. For example, graphene sheets are fabricated as continuous films, with openings formed by punching or laser beam irradiation. Laser beam irradiation uses extremely short pulse lasers, such as picosecond or nanosecond lasers. Apart from fabricating graphene sheets in this manner, the remaining thin films 12, each layer 120 of which is composed of graphene sheets, are obtained using the same method described above.

[0079] As described above, the thin film 12 has one or more openings 120H in one or more layers 120. Therefore, the apparent density of the thin film 12 is lower than its true density. Thus, the thin film 12 has the same thickness as the film and has higher transmittance compared to a laminate composed of graphene sheets as continuous films.

[0080] Furthermore, except for the absence of an opening 120H, the thin film 12 is composed of the same layers as layer 120, making it thicker than a film with the same mass per unit area. Therefore, the thin film 12 deforms less when a force is applied in the thickness direction.

[0081] Therefore, the thin film 12 is difficult to break when force is applied in the thickness direction, and can allow light to pass through with high transmittance.

[0082] Furthermore, in the thin film 12, the position or size of the opening 120H is determined by design. Therefore, for example, the opening 120H can be arranged regularly, or the size of the opening 120H can be made uniform. Therefore, the above structure is suitable for obtaining a thin film 12 with excellent in-plane uniformity in optical properties or mechanical strength.

[0083] Furthermore, since the thin film 12 has a structure formed by stacked layers 120, its optical properties and mechanical strength change according to the number of stacked layers. Therefore, the above structure can adjust the optical properties and mechanical strength according to the number of stacked layers 120.

[0084] The thin film 12 preferably has an apparent density D1 to true density D2 ratio D1 / D2 in the range of 5 to 75, more preferably in the range of 10 to 50, and even more preferably in the range of 10 to 25. If the ratio D1 / D2 is made smaller, the mechanical strength of each layer 120 will decrease, making it difficult to manufacture the thin film 12. If the ratio D1 / D2 is made larger, although it is difficult to cause damage when force is applied in the thickness direction, it is difficult to allow light to pass through with high transmittance.

[0085] Here, the apparent density D1 of the thin film 12 is obtained by dividing the mass per unit area of ​​the thin film 12 by the thickness of the thin film 12. The thickness of the thin film 12 is obtained, for example, by taking scanning electron microscope images of cross-sections of the thin film 12 at 10 points separated by more than 1 mm, measuring the thickness from these images, and then arithmetically averaging these values. Furthermore, the true density D2 of the thin film 12 is the true density of a substance with a specific composition determined by the analysis of the thin film 12. For example, in the case where the thin film 12 is composed of graphene sheets, its true density is the density of graphite without pores.

[0086] As described above, this thin film 12 has higher transmittance than a stack of graphene sheets of the same thickness that are continuous films. That is, this thin film 12 has a smaller linear absorption coefficient μ in the thickness direction than a stack of graphene sheets of the same thickness that are continuous films.

[0087] Furthermore, the linear absorption coefficient μ is calculated using the following equation. I / I0=e-μx In the above equation, I0 represents the intensity of the incident light, I represents the intensity of the transmitted light, e represents the base of the natural logarithm (Napier's constant), and x represents the path length.

[0088] The thin film 12 with openings 120H in layer 120 has a lower apparent density compared to graphite without pores. Therefore, this thin film 12 has a smaller linear absorption coefficient μ in the thickness direction compared to a laminate composed of graphene sheets as continuous films with the same number of layers as 120. Therefore, this thin film 12 allows light to pass through with high transmittance.

[0089] The thin film 12 series can undergo various deformations. Figure 8 is a schematic cross-sectional view showing another example of a thin film that can be used in the photomask protective film of Figure 1. The thin film 12 shown in Figure 8 is the same as the thin film 12 described with reference to Figures 1 to 3, except that the width or diameter of the opening 120H is smaller.

[0090] If the width or diameter of the opening 120H is reduced, the likelihood of the openings 120H connecting with each other between adjacent layers 120 will decrease. Therefore, the likelihood of through-holes forming in the thin film 12 will decrease. Thus, with this structure, the possibility of dust or other contaminants penetrating the thin film 12 can be further reduced.

[0091] Figure 9 is a schematic cross-sectional view showing another example of the thin film that can be used in the photomask of Figure 1. The thin film 12 shown in Figure 9 is the same as the thin film 12 described with reference to Figures 1 to 3, except that the width or diameter of the opening 120H is larger.

[0092] If the width or diameter of the opening 120H is increased, the likelihood of the openings 120H connecting with adjacent layers 120 will increase. However, the more layers 120 are stacked, the more sufficiently the possibility of dust and other particles penetrating the thin membrane 12 can be reduced.

[0093] Figure 10 is a schematic cross-sectional view showing another example of the thin film that can be used in the photomask of Figure 1. The thin film 12 shown in Figure 10 is the same as the thin film 12 described with reference to Figure 9, except that it does not have an opening 120H and the outermost layer 120' is the same as the outermost layer of the layer 120.

[0094] Dust and other particles cannot penetrate the layer 120', which does not have an opening 120H. Therefore, dust and other particles cannot penetrate the thin film 12 containing this layer 120'.

[0095] The thin film 12 shown in Figure 10 is preferably supported on the frame 11 with layer 120' facing outwards. Since there are no openings in layer 120', dust can be easily removed, for example, by blowing air, when the above configuration is used.

[0096] The thin membrane 12 may also contain a layer 120' between adjacent layers 120. Furthermore, the thin membrane 12 may also contain two or more layers 120'. In any case, dust and the like can be prevented from penetrating the thin membrane 12.

[0097] The above explanation is based on the case where the opening 120H is circular, but the shape of the opening 120H is not limited to being circular.

[0098] Figure 11 is a schematic plan view showing one example of a structure that can be used in an opening. Figure 12 is a schematic plan view showing other examples of a structure that can be used in an opening. Figure 13 is a schematic plan view showing other examples of a structure that can be used in an opening. Figure 14 is a schematic plan view showing other examples of a structure that can be used in an opening. Figure 15 is a schematic plan view showing other examples of a structure that can be used in an opening.

[0099] In the structure shown in Figure 11, the opening 120H is square. In the structure shown in Figure 12, the opening 120H is elliptical. In the structure shown in Figure 13, the opening 120H is triangular. In the structure shown in Figure 14, the opening 120H is hexagonal. In the structure shown in Figure 15, the opening 120H is of an irregular shape. Thus, the opening 120H can have various shapes.

[0100] In each layer 120, the openings 120H can be identical in shape and size, or at least different in shape and size. In each layer 120, when the openings 120H are identical in shape and size, the desired physical properties can be easily achieved. In one or more layers 120 and another one or more layers 120, the openings 120H may be the same in shape and size as each other, or they may be different in shape and size at least one of them.

[0101] In each layer 120, the openings 120H can also be configured irregularly, but it is preferable to configure them regularly. In the latter case, the desired physical properties can be easily achieved.

[0102] In one or more layers 120 and another one or more layers 120, the number of openings 120H can be the same or different. Layer 120 may also have only one opening 120H. For example, layer 120 may have only one opening 120H forming a pattern drawn in one stroke like a spiral.

[0103] Layers 120 and 120' can also be made of materials other than graphene. For example, carbon nanotubes, polycrystalline silicon, and silicon nitride can also be used as materials for layers 120 and 120'.

[0104] For example, layer 120 is a thin film 12 made of silicon, which can be obtained by forming a plurality of silicon layers with openings 120H formed using conventional semiconductor processes and bonding them together.

[0105] Layer 120 is a thin film 12 made of carbon nanotubes, which can be manufactured, for example, by the following method. First, a dispersion of carbon nanotubes is prepared by dispersing carbon nanotubes in a dispersant. This dispersion is coated onto a substrate, and the dispersant is removed from the coating to obtain a sheet made of carbon nanotubes. Next, the sheet is irradiated, for example, with a laser beam to obtain layer 120 having openings 120H. A plurality of layers 120 are formed in this manner, and by stacking them in equal layers, a thin film 120 made of carbon nanotubes is obtained.

[0106] One or more layers 120 may be made of the same or different materials from one or more other layers 120. In the latter case, for example, graphene sheets may be used as one or more layers 120, or layers made of carbon nanotubes may be used as one or more other layers 120. Similarly, the materials of layers 120 and layers 120' may be the same or different.

[0107] When layer 120' is the outermost layer of the thin film 12, layer 120' is a coating layer covering the laminate of layer 120. The coating layer may be provided on only one main surface of the laminate of layer 120, or it may be provided on both main surfaces of the laminate.

[0108] The coating layer may also be composed of the material described above for layer 120, or other materials. The coating layer may be, for example, composed of a metal or a semiconductor. According to one example, the coating layer comprises one or more elements selected from the group consisting of silicon, molybdenum, ruthenium, boron, nitrogen, germanium, and hafnium. According to another example, the coating layer comprises boron, boron carbide, zirconium nitride, molybdenum, ruthenium, silicon carbide, titanium nitride, amorphous carbon, graphene, or a combination of two or more of these.

[0109] Furthermore, the above configuration can also be applied to membranes used for other purposes, regarding the thin film 12. Membranes with the above configuration are difficult to break when force is applied in the thickness direction, and exhibit excellent in-plane uniformity in properties such as light transmittance and adsorption.

[0110] 1: Photomask Protective Film 2: Light Mask 11: Framework 12:Thin film 21:Substrate 22: Multilayer reflective film 22a: Reflective layer 22b: Reflective layer 23: Covering film 24: Absorption Layer 31: Substrate 32: Metal layer 33: Masking layer 120: Floor 120': Layer 120H: Opening

Claims

1. A thin film having a plurality of layers stacked on top of each other, wherein one or more openings having a width or diameter in the range of 10 to 500 nm are provided on one or more of the plurality of layers.

2. A thin film having a plurality of layers stacked on top of each other, wherein two or more of the plurality of layers have one or more openings with a width or diameter in the range of 10 to 500 nm.

3. The thin film of claim 1 or 2, wherein the aforementioned plurality of layers are composed of materials selected from the group consisting of graphene, carbon nanotubes, polycrystalline silicon and silicon nitride.

4. The thin film of claim 1 or 2, wherein the aforementioned plurality of layers are composed of a material containing one or more metallic elements selected from the group consisting of zirconium, niobium, molybdenum, tantalum, hafnium, scandium, titanium, vanadium and chromium.

5. A thin film having a plurality of layers stacked on top of each other, the plurality of layers being composed of a material selected from the group consisting of graphene and carbon nanotubes, wherein one or more openings having a width or diameter in the range of 10 to 500 nm are provided on one or more of the plurality of layers.

6. The thin film of any one of claims 1, 2, and 5, wherein at least one of the aforementioned plurality of layers is provided with a plurality of the aforementioned openings, the openings being arranged in a regular manner.

7. The thin film of any one of claims 1, 2, and 5, wherein at least one of the aforementioned plurality of layers is provided with a plurality of the aforementioned openings, the openings being of the same shape.

8. The thin film of any one of claims 1, 2, and 5, wherein the aforementioned one or more openings are provided in two or more of the aforementioned plurality of layers, and the positions of the aforementioned one or more openings are different for adjacent layers among the aforementioned two or more layers having the aforementioned one or more openings.

9. The thin film of any one of claims 1, 2, and 5, wherein no opening is provided above one of the aforementioned plurality of layers.

10. The thin film of claim 9, wherein the aforementioned layer without the aforementioned opening is at least one of the outermost layers of the aforementioned thin film.

11. The thin film of claim 10, wherein a plurality of graphene sheets are stacked on each other.

12. A thin film composed of a plurality of mutually stacked graphene sheets, having an apparent density lower than its true density, wherein one or more of the plurality of graphene sheets have an opening having a width or diameter in the range of 10 to 500 nm.

13. A thin film comprising a plurality of mutually stacked graphene sheets having the same thickness as the aforementioned stacked film, having higher transmittance than a stacked body composed of graphene sheets as a continuous film, wherein one or more of the aforementioned plurality of graphene sheets are provided with an opening having a width or diameter in the range of 10 to 500 nm.

14. The thickness of the thin film, as described in any of the requests 1, 2, 5, 12, and 13, is less than 200 nm.

15. The thin film as requested in item 10 has a thickness of less than 200 nm.

16. A photomask protective film comprising: a thin film as claimed in any one of claims 1 to 15; and a frame supporting the aforementioned thin film.

17. A membrane having a plurality of mutually stacked graphene sheets, wherein one or more of the plurality of graphene sheets have one or more openings with a width or diameter in the range of 10 to 500 nm.

18. The membrane of claim 17, wherein two or more of the aforementioned plurality of graphene sheets are provided with the aforementioned one or more openings, and the adjacent graphene sheets provided with the aforementioned one or more openings are located at different positions.

19. The membrane of claim 17, wherein one or more of the aforementioned plurality of graphene sheets are not provided with an opening.

20. The membrane of claim 19, wherein the graphene sheet which does not have the aforementioned opening is at least one of the outermost layers of the aforementioned membrane.

21. A graphene sheet having one or more openings with a width or diameter in the range of 10 to 500 nm.

22. A method for manufacturing a graphene sheet, the graphene sheet having one or more openings with a width or diameter in the range of 10 to 500 nm, the method comprising: forming a masking layer on a metal layer covering a portion thereof; and generating graphene in a portion of the metal layer not covered by the masking layer.

23. A method for manufacturing a graphene sheet, the graphene sheet having one or more openings with a width or diameter in the range of 10 to 500 nm, the method comprising generating graphene on a metal layer having one or more openings.

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