How graphene is produced

Abstract

To suppress reduction in the properties of a graphene film.SOLUTION: A manufacturing method for graphene includes the steps for forming a frame-shaped holding film on the top surface of a graphene film formed on a metal film, dissolving the metal film in an etchant after forming the holding film, transferring the graphene film onto a transfer substrate after dissolving the metal film, and removing the holding film after transferring the graphene film onto the transfer substrate. This allows transferring a large graphene film onto the transfer substrate while suppressing reduction in the properties.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing graphene. [Background technology]

[0002] As a method for transferring a graphene film formed on a metal film to a substrate, a method is known in which the metal film is dissolved in an etching solution, the graphene film is floated on the liquid surface, and the graphene film floating on the liquid surface is transferred to the substrate (e.g., Patent Documents 1 to 4). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2019-511451 [Patent Document 2] Special Publication No. 2018-531426 [Patent Document 3] US Patent Application Publication No. 2017 / 0028692 [Patent Document 4] US Patent Application Publication No. 2017 / 0057812 Summary of the Invention [Problem to be solved by the invention]

[0004] To prevent the graphene film from scattering, a resist film is applied to the graphene film, and then the metal film is dissolved in an etching solution. Although the resist film formed on the graphene film is eventually removed, some of the resist film may remain on the graphene film as residue. In this case, contamination of the graphene film may occur, resulting in a deterioration of its properties.

[0005] In one aspect, an object is to suppress deterioration of the properties of a graphene film. [Means for solving the problem]

[0006] In one aspect, the method for producing graphene includes the steps of: forming a frame-shaped support film on an upper surface of a graphene film formed on a metal film; dissolving the metal film in an etching solution after forming the support film; transferring the graphene film onto a transfer substrate after dissolving the metal film; and removing the support film after transferring the graphene film onto the transfer substrate. [Effects of the Invention]

[0008] One aspect is that it is possible to suppress deterioration of the properties of the graphene film. [Brief explanation of the drawings]

[0009] [Figure 1] 1(a) to 1(d) are cross-sectional views (part 1) illustrating a method for producing graphene according to Example 1. FIG. [Figure 2] 2(a) to 2(d) are cross-sectional views (part 2) illustrating the graphene manufacturing method according to the first embodiment. [Figure 3] FIG. 3(a) is a plan view of the substrate with the graphene film before the support film is formed, and FIG. 3(b) is a plan view of the substrate with the graphene film after the support film is formed. [Figure 4] FIG. 4 is a microscope image of the transfer substrate after the step of FIG. 2(a) has been carried out. [Figure 5] FIG. 5 is a microscope image of the transfer substrate after the step of FIG. 2(b) has been carried out. [Figure 6] FIG. 6 is a microscope image of the transfer substrate after the step of FIG. 2(d) has been carried out. [Figure 7] 7(a) to 7(c) are cross-sectional views (part 1) showing a method for producing graphene according to a comparative example. [Figure 8] 8(a) to 8(c) are cross-sectional views (part 2) showing a graphene manufacturing method according to a comparative example. [Figure 9] FIG. 9(a) is a top view of the device whose electrical characteristics were evaluated, and FIG. 9(b) is a cross-sectional view taken along the line AA in FIG. 9(a). [Figure 10]10(a) to 10(d) are cross-sectional views (part 1) illustrating a method for producing graphene according to Example 2. FIG. [Figure 11] 11(a) to 11(d) are cross-sectional views (part 2) illustrating the graphene manufacturing method according to the second embodiment. [Figure 12] 12(a) to 12(d) are plan views showing a graphene manufacturing method according to Example 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Example]

[0011] 1(a) to 2(d) are cross-sectional views showing a graphene manufacturing method according to Example 1. As shown in FIG. 1(a), a substrate 10 with a graphene film 30 is prepared. The substrate 10 with the graphene film 30 has a metal film 20 formed on the substrate 10, and the graphene film 30 is formed on the metal film 20. The substrate 10 is, for example, a silicon substrate with an oxide film. The metal film 20 is, for example, a copper film. Note that the substrate 10 and the metal film 20 are not limited to this. The metal film 20 may be any film formed from a metal that serves as a catalyst for graphene. The metal film 20 may be, for example, an iron film, a nickel film, or a cobalt film. The metal film 20 is deposited on the substrate 10 by, for example, sputtering. The thickness of the metal film 20 is, for example, about 1 nm to 1 mm.

[0012] The graphene film 30 is grown on the metal film 20 by, for example, thermal CVD (Chemical Vapor Deposition). In thermal CVD, for example, methane gas is used as a source gas and hydrogen and argon are used as dilution gases. The graphene film 30 may also be grown by other methods, such as plasma CVD or MBE (Molecular Beam Epitaxy). The graphene film 30 may be a single layer or multiple layers. After the graphene film 30 is grown, the substrate 10 with the graphene film 30 attached thereto may be placed in a nitrogen atmosphere for degassing.

[0013] As shown in FIG. 1(b), a frame-shaped support film 40 is formed on the upper surface of the graphene film 30. FIG. 3(a) is a plan view of the substrate 10 with the graphene film 30 before the support film 40 is formed, and FIG. 3(b) is a plan view of the substrate 10 with the graphene film 30 after the support film 40 has been formed. As shown in FIGS. 3(a) and 3(b), a support film 40 having a rectangular outer shape and a circular opening 42 on the inside is formed on the upper surface of the graphene film 30. The support film 40 is formed in contact with the upper surface of the graphene film 30, and the graphene film 30 is exposed through the opening 42 of the support film 40. The size of the opening 42 is determined appropriately and is, for example, approximately 5 mm to 2 cm.

[0014] The holding film 40 is, for example, a tape having an adhesive. The holding film 40 is attached to the upper surface of the graphene film 30 with the adhesive. The tape is preferably a heat-resistant tape such as a polyimide tape that can withstand the drying process described below. The thickness of the heat-resistant tape is, for example, about 0.03 mm to 0.1 mm.

[0015] As shown in FIG. 1( c), the substrate 10 with the graphene film 30 is immersed in an etching solution 74 contained in a container 70 such as a beaker. The etching solution 74 is a liquid capable of dissolving the metal film 20. For example, an iron chloride (FeCl2) aqueous solution or aqua regia is used as the etching solution 74. However, the etching solution 74 is not limited to this. For example, if the metal film 20 is a copper film, an etching solution 74 containing nitric acid (HNO3) may be used, and if the metal film 20 is an iron film, an etching solution 74 containing hydrochloric acid (HCl) may be used. If the metal film 20 is a nickel film or a cobalt film, an etching solution 74 containing nitric acid or hydrochloric acid may be used.

[0016] By immersing the substrate 10 with the graphene film 30 in the etching solution 74, the metal film 20 dissolves in the etching solution 74, and the substrate 10 and the graphene film 30 are separated. The substrate 10 sinks below the etching solution 74, and the graphene film 30 floats on the surface of the etching solution 74. Because the support film 40 is provided on the upper surface of the graphene film 30, even when the graphene film 30 is separated from the metal film 20 and floats on the surface of the etching solution 74, the graphene film 30 is prevented from scattering.

[0017] 1(d), the graphene film 30 floating on the surface of the etching solution 74 is scooped up with another substrate (not shown), and then washed with dilute hydrochloric acid and pure water, etc., and finally floated on the surface of pure water 76 contained in a container 72. Because the support film 40 is provided on the upper surface of the graphene film 30, scattering of the graphene film 30 is suppressed even when the graphene film 30 is washed.

[0018] As shown in FIG. 2( a), the graphene film 30 floating on the surface of the pure water 76 is scooped up with a transfer substrate 60. After the graphene film 30 is scooped up with the transfer substrate 60, while the graphene film 30 is still wet, the graphene film 30 may be positioned, or wrinkles may be smoothed out if any. The transfer substrate 60 is, for example, a silicon substrate with an oxide film, but an appropriate substrate may be selected depending on the intended use of the graphene film 30. Note that, in order to make the transfer substrate 60 hydrophilic, the transfer substrate 60 may be subjected to oxygen plasma ashing before the graphene film 30 is scooped up.

[0019] As shown in FIG. 2(b), the transfer substrate 60 is placed on a heating device 78 such as a hot plate, and moisture adhering to the transfer substrate 60 and the graphene film 30 is evaporated and dried. When placing the transfer substrate 60 on the heating device 78, the transfer substrate 60 may be leaned at an angle against a quartz jig 88 placed on the heating device 78. This makes it easier for moisture to escape from the transfer substrate 60 and the graphene film 30. Furthermore, if the transfer substrate 60 is placed on the heating device 78 without leaning it at an angle against the quartz jig 88, the graphene film 30 may be damaged by water vapor bubbles.

[0020] As shown in FIG. 2( c), after the graphene film 30 is dried, the support film 40 is removed. By heating and drying the graphene film 30, the portions of the graphene film 30 exposed through the openings 42 of the support film 40 and not attached to the support film 40 are separated from the support film 40 due to thermal contraction. This allows the support film 40 to be removed while minimizing the impact on the portions of the graphene film 30 exposed through the openings 42 of the support film 40. For example, if the support film 40 is a tape having an adhesive, the portions of the graphene film 30 exposed through the openings 42 of the support film 40 will thermally contract, allowing the support film 40 to be peeled off from the graphene film 30 while minimizing the impact on these portions. A portion of the graphene film 30 may remain in the portion from which the support film 40 is removed, but this portion will not be used in the device due to the residue of the support film 40. In other words, the portion of the graphene film 30 from which the support film 40 is removed will be used in the device.

[0021] 2(d), the transfer substrate 60 is placed on the heating device 78 again, and the transfer substrate 60 and the graphene film 30 are heated at a temperature higher than that used for drying the graphene film 30 described with reference to FIG. 2(b). This improves the adhesion between the transfer substrate 60 and the graphene film 30.

[0022] [Transfer experiment] An experiment was carried out to transfer a graphene film 30 to a transfer substrate 60 using the method shown in Figures 1(a) to 2(d). Details of each step are described below.

[0023] 1(a): A silicon substrate with an oxide film was used as the substrate 10, a copper film was used as the metal film 20, and a graphene film 30 was grown by thermal CVD on the metal film 20. Thereafter, the substrate 10 with the graphene film 30 was cut out into a square shape with a side length L1 of 12 mm in plan view (see FIG. 3(a)).

[0024] In the step shown in FIG. 1(b), a polyimide tape having a thickness of approximately 10 mm and having an adhesive was used as the support film 40. The support film 40 was attached to the upper surface of the graphene film 30 with the adhesive. The support film 40 had a square outer shape in plan view, and had a circular opening 42 formed inside. The length L2 of one side of the support film 40 (see FIG. 3(b)) was 12 mm, and the diameter D of the opening 42 (see FIG. 3(b)) was 7 mm.

[0025] 1(c): An aqueous solution of iron chloride was used as the etching solution 74. The metal film 20 was dissolved in the etching solution 74, and the graphene film 30 was separated from the substrate 10 and floated on the surface of the etching solution 74.

[0026] Step of Figure 1(d): The graphene film 30 floating on the surface of the etching solution 74 was scooped up with a silicon substrate with an oxide film, washed in pure water for 10 minutes, diluted hydrochloric acid for 10 minutes, and pure water for 10 minutes in that order, and finally left floating on the surface of pure water 76 in the container 72.

[0027] 2(a): A silicon substrate with an oxide film that had been subjected to oxygen plasma ashing for 5 minutes was used as the transfer substrate 60, and the graphene film 30 floating on the surface of pure water 76 was scooped up with the transfer substrate 60. The graphene film 30 scooped up with the transfer substrate 60 was then positioned and smoothed out.

[0028] 2(b): A hot plate was used as the heating device 78, and the transfer substrate 60 was leaned at an angle against a quartz jig 88 placed on the heating device 78. In this state, the temperature of the heating device 78 (hot plate) was set to 60°C, and heat treatment was performed for 1 hour to dry the graphene film 30.

[0029] Step of FIG. 2( c ): After the transfer substrate 60 was removed from the heating device 78 , the support film 40 was peeled off from the upper surface of the graphene film 30 .

[0030] Step of FIG. 2(d): The transfer substrate 60 was placed on the heating device 78 again, and the temperature of the heating device 78 (hot plate) was set to 150° C., and heat treatment was carried out for 1 hour.

[0031] FIG. 4 is a microscopic image of the transfer substrate 60 after the step of FIG. 2(a) has been performed. FIG. 5 is a microscopic image of the transfer substrate 60 after the step of FIG. 2(b) has been performed. That is, FIG. 4 is a microscopic image of the transfer substrate 60 after the graphene film 30 has been scooped, and FIG. 5 is a microscopic image of the transfer substrate 60 after the graphene film 30 has been heated and dried. In FIGS. 4 and 5, the portion of the graphene film 30 that is exposed at the opening 42 in the holding film 40 is referred to as the graphene film 30a. As can be seen from FIGS. 4 and 5, after the graphene film 30 has been heated and dried (FIG. 5), the graphene film 30a exposed at the opening 42 in the holding film 40 has thermally shrunk compared to before the heat treatment (FIG. 4), and the graphene film 30a is separated from the holding film 40.

[0032] FIG. 6 is a micrograph of the transfer substrate 60 after the step of FIG. 2(d) was performed. That is, FIG. 6 is a micrograph of the transfer substrate 60 after the holding film 40 was peeled off from the graphene film 30 and then heat treatment was performed at 150°C for 1 hour. In FIG. 6, as in FIGS. 4 and 5, the portion of the graphene film 30 that was exposed at the opening 42 of the holding film 40 is designated as the graphene film 30a. As shown in FIG. 6, the graphene film 30a exposed at the opening 42 of the holding film 40 thermally contracts and separates from the holding film 40, confirming that the holding film 40 was peeled off from the graphene film 30 while minimizing the impact on the graphene film 30a. Therefore, it can be confirmed that a large area of ​​the graphene film 30a was transferred to the transfer substrate 60. Note that a portion of the graphene film 30b remains around the graphene film 30a where the holding film 40 was attached.

[0033] [Comparative Example] 7(a) to 8(c) are cross-sectional views showing a graphene manufacturing method according to a comparative example. As shown in FIG. 7(a), a substrate 10 with a graphene film 30 is prepared, and a polymer film 90, which is a PMMA (polymenthyl methacrylate) resist, is applied to the upper surface of the graphene film 30. The polymer film 90 is formed on the entire upper surface of the graphene film 30.

[0034] 7(b), the substrate 10 with the graphene film 30 is immersed in an etching solution 74 contained in a container 70, and the metal film 20 is dissolved in the etching solution 74. As a result, the substrate 10 and the graphene film 30 are separated, the substrate 10 sinks below the etching solution 74, and the graphene film 30 floats on the surface of the etching solution 74. Because the polymer film 90 is provided on the upper surface of the graphene film 30, scattering of the graphene film 30 is suppressed even when the graphene film 30 is separated from the metal film 20.

[0035] 7(c), the graphene film 30 floating on the surface of the etching solution 74 is scooped up with another substrate (not shown), and then the graphene film 30 is washed, and finally the graphene film 30 is left floating on the surface of pure water 76 in the container 72. Because the polymer film 90 is provided on the upper surface of the graphene film 30, scattering of the graphene film 30 is suppressed even when the graphene film 30 is washed.

[0036] As shown in FIG. 8( a ), the graphene film 30 floating on the surface of the pure water 76 is scooped up with the transfer substrate 60 .

[0037] 8(b), the transfer substrate 60 is immersed in a container 92 containing a solution 94 that dissolves the polymer film 90. As a result, the polymer film 90 provided on the upper surface of the graphene film 30 is dissolved and removed.

[0038] 8(c), the transfer substrate 60 is taken out of the container 92. Thereafter, the transfer substrate 60 and the graphene film 30 are heated by a heating device (not shown) to dry the transfer substrate 60 and the graphene film 30 and improve the adhesion between the transfer substrate 60 and the graphene film 30.

[0039] [Electrical characteristics evaluation] Devices were fabricated using graphene films 30 transferred by the method of Example 1 and graphene films 30 transferred by the method of the comparative example, and their electrical characteristics were evaluated. FIG. 9(a) is a top view of the device whose electrical characteristics were evaluated, and FIG. 9(b) is a cross-sectional view taken along the line AA in FIG. 9(a). As shown in FIGS. 9(a) and 9(b), the device whose electrical characteristics were evaluated had a gate electrode 82 provided on the bottom surface of a silicon substrate 80 with an oxide film, and a source electrode 84 and a drain electrode 86 provided on the top surface. The gate electrode 82, the source electrode 84, and the drain electrode 86 had a laminated structure of a titanium layer and a gold layer.

[0040] A graphene film 30 connecting a source electrode 84 and a drain electrode 86 is provided on the upper surface of a silicon substrate 80 with an oxide film. The graphene film 30 typically has a length of 1 to 50 μm, a width of 1 to 50 μm, and a thickness of several to several hundred nm. The graphene film 30 was transferred onto the silicon substrate 80 with an oxide film by the methods of Example 1 and Comparative Example described above, and then patterned into a desired shape using photolithography and etching.

[0041] For the device shown in Figures 9(a) and 9(b), probe needles were placed on the source electrode 84 and drain electrode 86, and a current of 10 mV was passed through the drain electrode 86. A voltage varying in 500 mV steps between -40 V and +40 V was applied to the gate electrode 82. This allowed the mobility and contact resistance to be measured. Table 1 shows the measurement results. [Table 1]

[0042] As shown in Table 1, Example 1 had higher mobility and lower contact resistance than the comparative example. It is believed that the transfer method of the comparative example left residue of the polymer film 90 on the upper surface of the graphene film 30, resulting in lower mobility and higher contact resistance. On the other hand, Example 1 used a frame-shaped support film 40, which made it difficult for residue of the support film 40 to remain on the upper surface of the graphene film 30a, resulting in higher mobility and lower contact resistance.

[0043] According to Example 1, as shown in FIGS. 1(b) and 3(b), a frame-shaped support film 40 is formed on the top surface of the graphene film 30. As shown in FIG. 1(c), after the support film 40 is formed, the metal film 20 is dissolved in an etching solution 74. As shown in FIG. 2(a), after the metal film 20 is dissolved, the graphene film 30 is transferred onto a transfer substrate 60. As shown in FIG. 2(c), after the graphene film 30 is transferred onto the transfer substrate 60, the support film 40 is removed. By forming the support film 40 on the top surface of the graphene film 30, scattering of the graphene film 30 is suppressed, and a large graphene film 30a can be transferred onto the transfer substrate 60 as shown in FIG. 6. Furthermore, because the graphene film 30a is a portion where the support film 40 was not formed, residue of the support film 40 is suppressed. Therefore, deterioration of the properties of the graphene film 30a is suppressed.

[0044] In Example 1, as shown in FIG. 3( b), the holding film 40 has a circular opening 42 whose outline is formed by a rounded line in plan view. For example, if the opening 42 has a rectangular shape in plan view, stress tends to concentrate at the corners of the graphene film 30a exposed through the opening 42, making the graphene film 30a more likely to wrinkle. In contrast, if the outline of the opening 42 is formed by a rounded line, stress tends to be distributed over the entire periphery of the graphene film 30a exposed through the opening 42, making the graphene film 30a less likely to wrinkle. Furthermore, when the graphene film 30 is dried using a heating device 78, for example, the entire periphery of the graphene film 30a tends to separate evenly from the holding film 40 due to thermal contraction. This makes it easier to remove the holding film 40 while minimizing the impact on the graphene film 30a, making it easier to transfer a large graphene film 30a onto the transfer substrate 60. Although the opening 42 has been shown to have a circular shape, it may have any shape, such as an oval, as long as the outline is represented by a rounded line.

[0045] 3(b), in Example 1, the holding film 40 has a rectangular outer shape in plan view and has an opening 42 formed on the inside with a rounded outline. This improves the workability of attaching the holding film 40 to the upper surface of the graphene film 30 and peeling the holding film 40 from the graphene film 30, while suppressing the occurrence of wrinkles in the graphene film 30a and enabling the transfer of a large graphene film 30a.

[0046] In Example 1, as shown in FIG. 2(b), after the graphene film 30 is transferred onto the transfer substrate 60, the graphene film 30 on the transfer substrate 60 is heated and dried. Thereafter, as shown in FIG. 2(c), the holding film 40 is removed. By heating and drying the graphene film 30 transferred onto the transfer substrate 60, the graphene film 30a exposed in the openings 42 thermally shrinks and separates from the holding film 40. Therefore, by subsequently removing the holding film 40 from the graphene film 30, the holding film 40 can be removed while minimizing the impact on the graphene film 30a.

[0047] In Example 1, the holding film 40 is formed on the upper surface of the graphene film 30 by adhering the holding film 40, which is a tape having an adhesive, to the upper surface of the graphene film 30. The holding film 40 is removed from the graphene film 30 by peeling the holding film 40 from the graphene film 30. This makes it possible to easily remove the holding film 40 while minimizing the influence on the graphene film 30a remaining on the transfer substrate 60. [Example]

[0048] 10(a) to 11(d) are cross-sectional views showing the graphene manufacturing method according to Example 2. FIGS. 12(a) to 12(d) are plan views showing the graphene manufacturing method according to Example 2. In FIGS. 12(a) to 12(d), the graphene film 30 and the surrounding portion 50 are hatched for clarity. As shown in FIG. 10(a), a substrate 10 with a graphene film 30 is prepared. This is the same as FIG. 1(a) of Example 1, and therefore a description thereof will be omitted.

[0049] As shown in Figures 10(b) and 12(a), the substrate 10 with the graphene film 30 is immersed in an etching solution 74 contained in a container 70. As a result, the metal film 20 dissolves in the etching solution 74, and the substrate 10 and the graphene film 30 are separated. The substrate 10 sinks below the etching solution 74, and the graphene film 30 floats on the surface of the etching solution 74. At this time, since no support film is formed on the upper surface of the graphene film 30, the graphene film 30 may spread out and break into multiple pieces.

[0050] 10(c) and 12(b), the graphene film 30 is washed with dilute hydrochloric acid and pure water, and finally, the graphene film 30 is brought to a state where it floats on the surface of pure water 76 contained in a container 72. In this washing process, the graphene film 30 also disperses and breaks into more pieces.

[0051] As shown in FIG. 10(d), a transfer substrate 60 having a frame-shaped surrounding portion 50 formed thereon is prepared in advance. For example, the surrounding portion 50 has a rectangular outer shape in a plan view and a rectangular opening 52 on the inside (see also FIG. 12(c)). Pure water 54 may be placed in advance inside the surrounding portion 50 using a dropper or the like. Furthermore, to make the transfer substrate 60 hydrophilic, the transfer substrate 60 may be subjected to an oxygen plasma ashing treatment in advance. The surrounding portion 50 is, for example, a tape having an adhesive. The surrounding portion 50 is attached to the upper surface of the transfer substrate 60 by the adhesive. The tape is preferably a heat-resistant tape such as a polyimide tape that can withstand the drying treatment described below.

[0052] Enclosure 50 may have other shapes in plan view, such as a polygonal shape with pentagons or more sides, or a shape with a rounded outline such as a circle or an ellipse. Opening 52 may have a polygonal shape with pentagons or more sides in plan view, a shape with a rounded outline such as a circle or an ellipse, or other shapes.

[0053] 11(a) and 12(c), the graphene film 30 floating on the surface of the pure water 76 is transferred into the enclosure 50 of the transfer substrate 60. For example, the graphene film 30 floating on the surface of the pure water 76 is picked up with tweezers and transferred into the enclosure 50 of the transfer substrate 60.

[0054] As shown in FIG. 11(b), the transfer substrate 60 is placed on a heating device 78, and the moisture in the enclosure 50 is evaporated to dry the graphene film 30.

[0055] 11(c) and 12(d), after the graphene film 30 is dried, the enclosure 50 is removed from the transfer substrate 60. Because the moisture inside the enclosure 50 has evaporated, even when the enclosure 50 is removed, movement of the graphene film 30 is suppressed.

[0056] 11(d), the transfer substrate 60 is placed on the heating device 78 again and heated at a temperature higher than that used for drying the graphene film 30 described with reference to FIG. 11(b). This improves the adhesion between the transfer substrate 60 and the graphene film 30.

[0057] According to Example 2, as shown in FIG. 10(b), the metal film 20 on which the graphene film 30 is formed is dissolved in an etching solution 74. After dissolving the metal film 20, the graphene film 30 is floated on the surface of pure water (liquid) 76 as shown in FIG. 10(c). As shown in FIG. 11(a), the graphene film 30 floating on the surface of the pure water 76 is transferred into the enclosure 50 of a transfer substrate 60, which has a frame-shaped enclosure 50 formed thereon. As shown in FIG. 11(c), after the graphene film 30 is transferred into the enclosure 50, the enclosure 50 is removed from the transfer substrate 60. This allows the graphene film 30 to be transferred to a desired position on the transfer substrate 60 without forming a polymer film on the top surface of the graphene film 30. Because no polymer film is formed on the top surface of the graphene film 30, no polymer film residue remains on the graphene film 30, and deterioration of the properties of the graphene film 30 is suppressed.

[0058] In Example 2, as shown in Fig. 11(b), after the graphene film 30 is transferred into the enclosure 50 of the transfer substrate 60, the graphene film 30 is heated and dried. Thereafter, as shown in Fig. 11(c), the enclosure 50 is removed from the transfer substrate 60. This makes it possible to prevent the graphene film 30 from moving even after the enclosure 50 is removed.

[0059] 10(d), before the graphene film 30 is transferred into the enclosure 50 of the transfer substrate 60, pure water (liquid) 54 is poured into the enclosure 50. This makes it easier to move the graphene film 30 within the enclosure 50, and the graphene film 30 can be aligned to a desired position. For this reason, the amount of pure water 54 poured into the enclosure 50 is preferably an amount that allows the graphene film 30 to be moved while preventing the graphene film 30 from moving freely.

[0060] In Example 2, the surrounding portion 50 is a tape having an adhesive, and is attached to the transfer substrate 60 by the adhesive. As a result, the surrounding portion 50 can be removed by peeling the surrounding portion 50 from the transfer substrate 60, and therefore the surrounding portion 50 can be removed while minimizing the influence on the graphene film 30 inside the surrounding portion 50.

[0061] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims.

[0062] In addition, the following supplementary notes are provided in relation to the above description. (Appendix 1) A method for producing graphene, comprising: a step of forming a frame-shaped support film on an upper surface of a graphene film formed on a metal film; a step of dissolving the metal film in an etching solution after forming the support film; a step of transferring the graphene film onto a transfer substrate after dissolving the metal film; and a step of removing the support film after transferring the graphene film onto the transfer substrate. (Supplementary Note 2) The graphene production method according to Supplementary Note 1, wherein the support film has an opening whose outline is formed by a rounded line in plan view. (Supplementary Note 3) The graphene production method according to Supplementary Note 2, wherein the support film has a rectangular outer shape in a plan view and has the opening on the inside. (Appendix 4) The method for producing graphene according to any one of Appendices 1 to 3, further comprising the step of transferring the graphene film onto the transfer substrate and then heating and drying the graphene film on the transfer substrate. (Appendix 5) The method for producing graphene according to Appendix 4, wherein the support film is removed after the graphene film is dried. (Appendix 6) The method for producing graphene according to Appendix 4 or 5, wherein, by drying the graphene film, a portion of the graphene film exposed through the opening of the supporting film and on which the supporting film is not formed is separated from the supporting film by thermal contraction. (Appendix 7) The method for producing graphene according to any one of Appendices 4 to 6, wherein the graphene film is dried by leaning it at an angle against a quartz jig placed on a heating device. (Appendix 8) The method for producing graphene according to any one of Appendices 1 to 7, wherein the formation of the retention film is carried out by attaching the retention film, which is a tape having an adhesive, to an upper surface of the graphene film, and the removal of the retention film is carried out by peeling the retention film from the graphene film. (Appendix 9) A method for producing graphene, comprising: a step of dissolving a metal film on which a graphene film has been formed in an etching solution; a step of floating the graphene film on the liquid surface after dissolving the metal film; a step of transferring the graphene film floating on the liquid surface into an enclosure of a transfer substrate having a frame-shaped enclosure formed thereon; and a step of removing the enclosure from the transfer substrate after transferring the graphene film into the enclosure of the transfer substrate. (Appendix 10) The method for producing graphene according to Appendix 9, further comprising the step of heating and drying the graphene film after transferring the graphene film into the enclosure of the transfer substrate, and removing the enclosure after drying the graphene film. (Appendix 11) The graphene production method according to appendix 9 or 10, further comprising the step of injecting a liquid into the enclosure of the transfer substrate before transferring the graphene film into the enclosure of the transfer substrate. (Appendix 12) The graphene production method according to any one of Appendices 9 to 11, wherein the surrounding portion is a tape having an adhesive and is attached to the transfer substrate by the adhesive. [Explanation of symbols]

[0063] 10 Substrate 20 Metal Film 30, 30a, 30b Graphene film 40 Retention membrane 42 Aperture 50 Enclosure 52 Aperture 54 Pure water 60 Transfer substrate 70, 72 container 74 Etching Solution 76 Pure water 78 Heating equipment 80 Silicon substrate with oxide film 82 gate electrode 84 Source electrode 86 Drain electrode 88 Quartz Jig 90 Polymer Film 92 Container 94 Solution

Claims

1. forming a frame-shaped support film on an upper surface of the graphene film formed on the metal film; After forming the support film, dissolving the metal film in an etching solution; dissolving the metal film and then transferring the graphene film onto a transfer substrate; and removing the support film after transferring the graphene film onto the transfer substrate.

2. The graphene production method according to claim 1 , wherein the support film has an opening whose outline is formed by a rounded line in plan view.

3. The graphene production method according to claim 2 , wherein the support film has a rectangular outer shape in a plan view and has the opening on the inside.

4. The method for producing graphene according to claim 1 , further comprising the step of heating and drying the graphene film on the transfer substrate after transferring the graphene film onto the transfer substrate.

5. The method for producing graphene according to claim 4 , wherein the support film is removed after the graphene film is dried.

6. 6. The method for producing graphene according to claim 4, wherein, by drying the graphene film, a portion of the graphene film exposed from the opening of the support film and on which the support film is not formed is separated from the support film by thermal contraction.

7. the formation of the support film is carried out by attaching the support film, which is a tape having an adhesive, to the upper surface of the graphene film; The method for producing graphene according to claim 1 , wherein the support film is removed by peeling the support film from the graphene film.

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