JP2012041219A - Method for producing graphene film and method for uniformizing the number of graphene film layers - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for further uniformizing the number of graphene film layers.SOLUTION: A layer partly covering an SiC substrate 100 among layers constituting the graphene film 104 is heated at a prescribed temperature in a hydrogen gas atmosphere to perform selective etching from its edge. Layers totally covering the SiC substrate 100 can be left among the layers of the graphene film 104 and, accordingly, the number of layers of the graphene film 104 can be uniformized.

Description

  The present invention relates to a method for producing a graphene film and a method for making the number of layers of a graphene film uniform, and in particular, a method for producing a graphene film formed on a substrate with the number of layers made uniform, and a method for forming a graphene film on the substrate. The present invention relates to a method for making the number of graphene films uniform.

  Conventionally, as a method for producing a graphene film composed of a single layer or a plurality of layers, a method of cleaving from graphite with a tape and peeling it off is generally used. However, although this method is simple, there is a problem that it greatly depends on the quality of the graphite as a raw material. In addition, the sample size is limited to about 100 μm or less, and the yield of obtaining a specific number of graphene films is low.

  On the other hand, as a method for obtaining a high-quality and large-area graphene film, an attempt has been made to form it on a metal substrate by a chemical vapor deposition (CVD) method. However, the CVD method has a problem that the cost is increased because it is necessary to use a high-quality metal substrate. In addition, since the metal substrate has conductivity, it has been necessary to transfer the graphene film formed on the metal substrate to another insulating substrate in order to apply it to the manufacture of an electronic device.

  In view of such circumstances, it is considered that a method of treating a silicon carbide (SiC) substrate at a high temperature in a vacuum or a gas atmosphere (hereinafter referred to as “SiC surface decomposition method”) is effective (for example, non-patent Reference 1). This is because when the SiC substrate is heated to preferentially desorb silicon atoms on the surface, the carbon atoms remaining on the surface of the SiC substrate spontaneously form a graphene film having an epitaxial relationship with the SiC substrate. The phenomenon is used.

However, it is known that the graphene film formed by the SiC surface decomposition method has a spatial variation in the number of layers (for example, see Non-Patent Document 2). This variation in the number of layers becomes an obstacle to the development of electronic devices and the search for physical properties. Therefore, various studies and reports have been made so far to prevent the spatial variation in the number of layers of the graphene film.
First, it has been reported that more uniform single-layer graphene can be formed in an argon gas atmosphere or a silane gas atmosphere (see, for example, Non-Patent Documents 3 and 4).
In addition, an inclined SiC substrate whose plane orientation is intentionally shifted from the low-index plane without using a just substrate generally used in the SiC surface decomposition method whose plane index substantially coincides with the low-index crystal orientation (its It has also been reported that when a graphene film is formed after a nanometer-order periodic structure is formed on the surface using an inclination angle of, for example, 4 °, etc., spatial variation in the number of layers can be suppressed (for example, Non-patent document 5).

A. J. van Bommel, J. E. Crombeen, and A. van Tooren, Surf. Sci. 48, 463 (1975). H. Hibino, H. Kageshima, F. Maeda, M. Nagase, Y. Kobayashi, and H. Yamaguchi, Phys. Rev. B 77, 075413 (2008). KV Emtsev, A. Bostwick, K. Horn, J. Jobst, GL Kellogg, L. Ley, JL McChesney, T. Ohta, SA Reshanov, J. Rohrl, E. Rotenberg, AK Schmid, D. Waldmann, HB Weber, and T. Seyller, Nature Mater. 8, 203 (2009). R. M. Tromp and J. B. Hannon, Phys. Rev. Lett. 102, 106104 (2009). S. Takana, K. Morita, and H. Hibino, Phys. Rev. B 81, 041406 (R) (2010). C. Riedl, C. Coletti, T. Iwasaki, A. A. Zakharov, and U. Starke, Phys. Rev. Lett. 103, 246804 (2009). T. Ohta, A. Bostwick, T. Seyller, K. Horn, and E. Rotenberg, Science 313, 951 (2006).

  However, even if any of the above-described methods is adopted, it is difficult to completely eliminate the spatial variation in the number of graphene films. This is because it is very difficult to adjust the conditions for growing the graphene film while keeping the number of graphene films uniform.

  The present invention has been made in view of the above-described problems, and an object thereof is to make the number of graphene films more uniform.

The method for producing a graphene film according to the present invention includes a first step of forming a graphene film composed of a plurality of layers on a substrate, and a second step of etching the graphene film by heating to a predetermined temperature in a hydrogen gas atmosphere. Here, the second step may be performed at a pressure of 1 × 10 ⁵ Pa (1 atm) and a temperature of 700 to 1300 ° C.
The substrate may be a SiC substrate made of SiC, and the first step may form a graphene film made of a plurality of layers on the SiC substrate using a SiC surface decomposition method. At this time, a third step of heating the SiC substrate to a temperature of 900 ° C. or higher in a vacuum may be further provided after the second step.

A method for equalizing the number of graphene films according to the present invention is a method for equalizing the number of graphene films formed of a plurality of layers formed on a substrate, wherein the substrate is part of the graphene film. The covering layer is etched by heating to a predetermined temperature in a hydrogen gas atmosphere.
Here, the etching may be performed at a pressure of 1 × 10 ⁵ Pa (1 atm) and a temperature of 700 to 1300 ° C.

  According to the method for producing a graphene film and the method for making the number of graphene films uniform according to the present invention, the graphene film formed on the substrate is etched by heating to a predetermined temperature in a hydrogen gas atmosphere. . Here, the graphene film has a feature that it is difficult to react with hydrogen gas at a portion where there is a bond between carbon atoms, whereas it is easy to react with hydrogen gas at an edge where there is no bond between the carbon atoms. For this reason, by etching in a hydrogen gas atmosphere, the layer of the graphene film that partially covers the substrate can be selectively etched from the edge, leaving the layer of the graphene film that covers the entire substrate. The number of layers of the graphene film can be made uniform.

  Further, the number of graphene films is made uniform by a process of etching the graphene film, which is different from the process of forming the graphene film. Therefore, it can be applied to a graphene film formed by various methods.

  Further, when a graphene film is manufactured using a SiC substrate, the graphene film formed on the SiC substrate is etched by heating to a predetermined temperature in a hydrogen gas atmosphere, and then the SiC substrate is heated at a temperature of 900 ° C. in a vacuum. By further performing the heating step as described above, hydrogen atoms adsorbed on the surface of the SiC substrate can be desorbed. In this case, the lowermost layer of the graphene film is bonded to silicon atoms contained in the SiC substrate, and does not exhibit graphene properties. This helps to extract desired properties from the formed graphene film.

It is process drawing which shows the process of forming a graphene film on the surface of a SiC substrate using a surface decomposition method in the manufacturing method of the graphene film concerning an embodiment of the invention. It is process drawing which shows the process of equalizing the number of layers of the graphene film formed on the surface of a SiC substrate in the manufacturing method of the graphene film concerning an embodiment of the invention. It is the photograph which image | photographed the graphene formed in the SiC substrate in the manufacturing method of the graphene film which concerns on embodiment of this invention by LEEM. It is the photograph which image | photographed the surface of the sample before a hydrogen treatment in the manufacturing method of the graphene film which concerns on Example 1 of this invention by AFM. It is the photograph which image | photographed the surface of the sample after a hydrogen treatment in the manufacturing method of the graphene film concerning Example 1 of this invention by AFM.

  Next, embodiments of the present invention will be described with reference to the drawings.

[Embodiment]
A method for manufacturing a graphene film according to an embodiment of the present invention will be described.
The embodiment of the present invention includes two steps, a step of forming a graphene film on the surface of a SiC substrate using a SiC surface decomposition method and a step of equalizing the number of layers of the formed graphene film.

First, a process of forming a graphene film on the surface of a SiC substrate using a SiC surface decomposition method will be described with reference to FIG.
In this embodiment, the SiC surface decomposition method will be described. However, the advantage of adopting the SiC surface decomposition method is that a high-quality, large-area SiC substrate that is becoming widely used can be used, and the processing is It is simple, can form a good quality graphene film, and because SiC has a relatively large band gap, the graphene film formed on the SiC substrate can be directly used as an electronic device material without being transferred to another substrate. It is done.

  First, as shown in FIG. 1A, a tilted SiC (0001) substrate 100 is prepared. Here, surface 102 of SiC substrate 100 has a structure having a periodicity of √3 × √3.

Next, the prepared SiC substrate 100 is heated at 1060 ° C. for about 1 minute in an ultrahigh vacuum at a pressure of 1 × 10 ⁻⁶ Pa or less. Then, silicon atoms in the SiC substrate 100 are desorbed, and a region having a periodicity of 6√3 × 6√3 (graphene film 104) is mainly at an atomic level as shown in FIG. It appears in the vicinity of a step (hereinafter referred to as “step”). The single-layer graphene film 104 formed in this way has almost the same structure as normal graphene, but does not exhibit unique properties as graphene because it strongly binds to silicon atoms contained in the SiC substrate 100, and does not exhibit buffer properties. It is called a layer.
The conditions for forming the graphene film 104 by desorbing silicon atoms contained in the SiC substrate 100 are not limited to those described above, and can be formed in various pressures and gas atmospheres. For example, the graphene film 104 can be formed by heating to 1000 ° C. or higher in a vacuum at a pressure of 5 Torr (667 Pa) or lower and heating to 1600 ° C. or higher in an argon gas atmosphere at a pressure of 5 Torr (667 Pa) or higher. Since the formation rate of the graphene film 104 depends on pressure and temperature, the pressure, the heating temperature, and the heating time may be adjusted as appropriate depending on the desired number of layers.

When the SiC substrate 100 is subsequently heated, the desorption of silicon contained in the SiC substrate 100 proceeds, so that the region of the graphene film 104 is expanded. As shown in FIG. 1C, the SiC substrate 100 is a single layer. The entire surface is covered with the graphene film 104.
This is because the SiC substrate 100 is covered with the single-layer graphene film 104 (buffer layer), that is, the silicon atoms of the SiC substrate 100 are bonded to the single-layer graphene film 104 (buffer layer). It is a phenomenon based on
Even in the vicinity of the step, the single-layer graphene film 104 (buffer layer) is elastically deformed like a carpet, so that the entire surface of the SiC substrate 100 can be covered.

Further, when the SiC substrate 100 is continuously heated, the silicon atoms at the interface between the buffer layer and the SiC substrate 100 are desorbed, and as shown in FIG. Go.
Here, in the region composed of two layers of graphene in the graphene film 104, the deep layer indicated by the dotted line in FIG. 1D is combined with the silicon atoms included in the SiC substrate 100 to form a buffer layer. Does not exhibit its properties. On the other hand, the surface-side layer indicated by the solid line in FIG. 1D has a property as graphene because the bond with the silicon atoms contained in the SiC substrate 100 is cut off through the lower buffer layer. It can be demonstrated.

  When the SiC substrate 100 is continuously heated, the desorption of silicon atoms at the interface between the buffer layer and the SiC substrate 100 further proceeds. As a result, as illustrated in FIG. 1E, the graphene film 104 has a structure in which the graphene is stacked in different layers from 2 to 4 layers depending on the region. Even when a large number of graphene layers are stacked in this manner, only the deepest layer indicated by the dotted line in FIG. 1E among the layers of the graphene film 104 is bonded to the silicon atoms contained in the SiC substrate 100 to be buffer layers. It becomes. For this reason, even in the region of the graphene film 104 made of N layers of graphene, the deepest layer is bonded to silicon atoms and does not exhibit graphene properties. 1) The physical properties of the layer as graphene will be shown.

By the way, as described above, when the SiC substrate 100 is continuously heated, the silicon atoms contained in the SiC substrate 100 are desorbed and the graphene film 104 composed of a plurality of layers can be formed. However, there is a spatial variation in the number of graphene films 104 formed in this way. If the second layer of graphene nucleated in various places grows, and then the third layer of graphene is formed after these layers are completely connected, a graphene film with a uniform number of layers can be obtained. . However, in actuality, the third layer of graphene nucleates before the second layer becomes completely continuous, resulting in a spatial variation in the number of layers of the graphene film 104. Such a phenomenon also occurs in a multilayered graphene film in the same manner, so that it is inevitable that spatial variations occur in the number of graphene films.
On the other hand, among the layers of the graphene film 104 formed on the SiC substrate 100, the surface layer always grows via the buffer layer, and is thus completely connected without forming an edge. In addition, the step portion is also characterized by covering the entire surface of SiC substrate 100 by elastically deforming like a carpet.

  For this reason, among the layers of the graphene film 104 formed on the surface of the SiC substrate 100, a layer that exists under the layer that entirely covers the surface side of the SiC substrate 100 and that partially covers the SiC substrate 100 is selectively selected. If it can be removed, a graphene film with a uniform number of layers can be left on the substrate, and a graphene film with a uniform number of layers can be formed. If a graphene film with a uniform number of layers can be formed in this way, it will be useful for application to devices and search for physical properties.

  Hereinafter, the process of selectively removing only the layer partially covering the SiC substrate 100 from the graphene film 104 formed on the surface of the SiC substrate 100 to make the number of layers uniform will be described.

FIG. 2 is a process diagram showing a process of equalizing the number of layers of the graphene film formed on the surface of the SiC substrate in the graphene film manufacturing method according to the embodiment of the present invention.
First, hydrogen treatment is performed in which the SiC substrate 100 on which the graphene film 104 including a plurality of layers is formed is heated at 600 to 900 ° C. in a hydrogen gas atmosphere. As a result, hydrogen atoms break the bond between the buffer layer and the silicon atoms contained in the SiC substrate 100, and the hydrogen atoms react with the silicon atoms at the interface of the SiC substrate 100, resulting in FIG. As shown, a hydrogen adsorption layer 106 that adsorbs hydrogen atoms is formed at the interface with the graphene film 104 in the SiC substrate 100 (see, for example, Non-Patent Document 6).
At this time, since the bond between the deepest layer (buffer layer) of the graphene film 104 and the silicon atoms at the interface of the SiC substrate 100 is cut by hydrogen atoms, the deepest part of the graphene film 104 is formed. Some layers will exhibit graphene properties.
Note that when the SiC substrate 100 in such a state is heated in vacuum, hydrogen atoms contained in the hydrogen adsorption layer 106 are desorbed, and as a result, the layer formed in the deepest portion of the graphene film 104 is SiC. It recombines with silicon atoms contained in the substrate 100 and changes to a buffer layer.

  By the way, graphene is a very stable substance, and can exist thermodynamically stably even at a high temperature of 1000 ° C. or higher in a hydrogen gas atmosphere if there is no defect or dangling bond. However, as shown in FIG. 2F, it is considered that the layer formed in the vicinity of the interface in the graphene film 104 is discontinuous, has an edge, and is in an unstable state.

FIG. 3 is a photograph of graphene formed on the SiC substrate 100 taken by a low energy electron microscope (LEEM).
From the LEEM photograph shown in FIG. 3, it was confirmed that the edges exist at a relatively high density and are distributed on a fine scale of 1 micron or less.

At the edge of such a graphene film 104, since the sp ² bond between carbon atoms is cut, the carbon atoms are high in energy and are in an unstable state. For this reason, when the SiC substrate 100 is heated in a hydrogen gas atmosphere, a chemical reaction represented by the following formula (1) occurs at the edge, the carbon atoms in the graphene are sublimated, and the graphene can be etched from the edge. it can.

(Chemical reaction at the edge)
C + 2H ₂ → CH ₄ (1)

  Therefore, if conditions for heating the SiC substrate 100 in a hydrogen gas atmosphere are selected, a layer that covers the SiC substrate 100 partially in the graphene film 104 is left while leaving a layer that covers the entire surface of the SiC substrate 100 in the graphene film 104. It can be selectively etched from that edge. For this reason, as shown in FIGS. 2G to 2I, a layer partially covering the SiC substrate 100 in the graphene film 104 is selectively removed by etching, and finally the number of layers is uniform. The graphene film 104 can be obtained.

Note that, as one of typical conditions for removing the portion of the graphene film 104 partially covering the SiC substrate 100 by etching from the edge, heating is performed in a hydrogen gas atmosphere of 1 × 10 ⁵ Pa (1 atm). What is necessary is just to set temperature to 700-1300 degreeC. This is because the decomposition of hydrogen gas hardly occurs at a low temperature of 700 ° C. or lower, and etching becomes very slow, and the graphene is etched from other than the edge at a high temperature of 1300 ° C. or higher.

  According to the method for manufacturing a graphene film according to the embodiment of the present invention described above, the layers constituting the graphene film 104 are formed by etching the graphene film 104 formed on the SiC substrate 100 in a hydrogen gas atmosphere. Of these, those partially covering the SiC substrate 100 can be selectively etched from the edges. For this reason, only the layer of the graphene film 104 that entirely covers the SiC substrate 100 can be left, and the number of layers of the graphene film 104 can be made uniform.

  In the above-described embodiment, the SiC surface decomposition method is taken as an example of the method for forming graphene on the surface of SiC substrate 100. However, the method does not depend on the method for forming graphene, and is formed on SiC substrate 100. If a graphene film composed of a plurality of layers can be formed, for example, a method of forming graphene by molecular beam deposition of carbon atoms may be used.

  In the above embodiment, the uniform graphene film 104 is formed of two layers. However, the graphene film is not limited to two layers, and may be formed of other layers such as three or four layers. it can.

  Furthermore, in the above-described embodiment, the hydrogen atom adsorption layer 106 in which hydrogen atoms are adsorbed on the interface of the SiC substrate 100 is formed. By heating the SiC substrate 100 in a vacuum, for example, to 900 ° C. or more, Hydrogen atoms contained in the hydrogen atom adsorption layer 106 may be desorbed. By doing so, the lowermost layer of the graphene film 104 is bonded to the silicon atoms of the SiC substrate 100 to become a buffer layer, and does not exhibit the properties as graphene. Useful.

[Example 1]
Next, Embodiment 1 of the present invention will be described with reference to the drawings. Example 1 of the present invention relates to a method of manufacturing a graphene film having a uniform number of layers.

First, a graphene film was formed on the surface of a tilted SiC substrate by heating the tilted SiC (0001) substrate in an ultrahigh vacuum to desorb surface silicon atoms.
Specifically, after introducing an inclined SiC (0001) substrate into an ultra-high vacuum, it was heated at 1600 ° C. for 5 seconds by passing an electric current through the substrate.
FIG. 4 is a photograph of the graphene film thus formed on the surface of the tilted SiC substrate taken with an atomic force microscope (AFM). In FIG. 4, a relatively dark region is a region made of two layers of graphene, and a relatively bright region is a region made of three layers of graphene. From FIG. 4, it was found that in the graphene film formed on the surface of the inclined SiC substrate in this way, the two-layer region and the three-layer region are mixed at substantially the same ratio. As described above, it can be seen that the two-layer graphene covers the surface, and the third-layer graphene is partially distributed thereunder.

Next, the hydrogen treatment which heats the sample obtained in this way in hydrogen gas atmosphere was performed.
Specifically, hydrogen gas was supplied at a flow rate of 1 × 10 ⁻³ m ³ / min, and the sample was heated at 700 ° C. for 30 minutes in a heating furnace maintained at 1 × 10 ⁵ Pa (1 atm). .
FIG. 5 is a photograph of the surface of the sample after hydrogen treatment taken by AFM. In FIG. 5, a relatively bright region is a region made of two layers of graphene, and a relatively dark region is a region made of three layers of graphene. Here, the contrast is inverted as compared with the photograph taken before hydrogen treatment in FIG. 4, but this is a change depending on the state of the AFM probe and the hydrogenation of the substrate, and is not an essential change. .
When FIG. 5 and FIG. 4 are compared, it was confirmed that the area of the region composed of three layers of graphene is reduced after the hydrogen treatment compared to before the hydrogen treatment. This indicates that the graphene film in the third layer was removed by etching during the hydrogen treatment. Therefore, when hydrogen treatment is performed for a longer time, the region composed of three layers of graphene disappears eventually, and as a result, a graphene film in which two layers of graphene layers are uniformly distributed over the entire substrate is obtained. Seem.

  In addition, if this SiC substrate is heated to 900 ° C. or higher in vacuum and hydrogen is desorbed from the SiC substrate, the graphene layer in the second layer is combined with silicon atoms contained in the SiC substrate to become a buffer layer. A graphene film having a single layer property can be obtained. Here, when the tilted SiC substrate is heated at a temperature of 1000 ° C. or higher, the heating time may be relatively short so that silicon atoms contained in the tilted SiC substrate are desorbed and a new graphene layer is not formed. .

[Example 2]
Next, a second embodiment of the present invention will be described. Example 2 of the present invention relates to a method of manufacturing a transistor using a two-layered uniform graphene film as a channel.

First, a three-layered uniform graphene film is formed on a SiC substrate.
As a specific procedure, first, a just SiC (0001) substrate having a semi-insulating property and no inclination is irradiated with an electron beam in an ultrahigh vacuum at a temperature of about 1350 ° C. for 1 minute. And a graphene film in which a region composed of three layers of graphene and a region composed of four layers of graphene are mixed is formed.
Next, hydrogen treatment is performed in the same procedure as in Example 1, and the fourth layer of graphene is removed by etching, so that a three-layered uniform graphene film can be manufactured.

Next, hydrogen at the interface of the SiC substrate is desorbed, and the lowermost graphene of the graphene film is used as a buffer layer.
As a specific procedure, first, the SiC substrate is heated to 900 ° C. or higher in vacuum to desorb hydrogen at the interface. Then, the deepest layer of the graphene film layers is combined with silicon atoms contained in the SiC substrate to form a buffer layer. As a result, a graphene film having properties as a two-layer graphene can be obtained although it is actually composed of three layers of graphene. At this time, when heating to a temperature of 1000 ° C. or higher, the heating time may be shortened so that a new graphene film is not formed on the SIC substrate.

Subsequently, the graphene film formed on the SiC substrate is processed into a channel shape.
Specifically, first, a photoresist is coated on the substrate, and then the coated photoresist is exposed by photolithography so that the channel shape of the transistor remains.
Subsequently, the exposed region of the graphene film that is not protected by the photoresist is removed by dry etching using oxygen plasma.
Thereafter, when the photoresist is washed away, a graphene film processed into a channel shape appears on the surface of the SiC substrate.

Next, a source electrode and a drain electrode that are in contact with the channel are formed.
As a specific procedure, first, a photoresist is coated on the entire surface of the SiC substrate, and patterning is performed so that only the regions where the source and drain electrodes are formed by photolithography, that is, the regions located at both ends of the channel are exposed. To do.
Subsequently, after a metal (for example, chromium and gold) is vapor-deposited over the entire surface of the SiC substrate, the metal vapor-deposited in a region other than the region serving as the source electrode and the drain electrode is removed by lift-off.
Thereby, a source electrode and a drain electrode can be formed.

Subsequently, a gate electrode is formed on the upper portion near the center of the channel portion to complete the transistor.
As a specific procedure, first, an insulating film (for example, SiO ₂ or the like) is deposited over the entire SiC substrate.
Next, a photoresist is applied onto the deposited insulating film, and patterning is performed by photolithography so that only the region where the gate electrode is formed is exposed.
Subsequently, after a metal (for example, chromium and gold) is deposited on the entire SiC substrate, the deposited metal is removed by lift-off in a region other than the region where the gate electrode is formed.
Thereby, a gate electrode can be formed and the transistor which concerns on Example 2 of this invention is obtained.

  The transistor according to the second embodiment of the present invention described above includes a graphene film having properties as a two-layer graphene as a channel. Here, it is known that the graphene film having the property of two layers has a band gap due to the interaction with the SiC substrate (for example, see Non-Patent Document 7). For this reason, in the transistor according to Example 2 of the present invention using the two-layer graphene film as the channel, the current flowing between the source electrode and the drain electrode can be greatly modulated by the voltage applied to the gate electrode. Transistor characteristics can be obtained.

  The present invention can be used in the manufacturing industry of graphene films.

  DESCRIPTION OF SYMBOLS 100 ... SiC substrate, 102 ... Surface, 104 ... Graphene film | membrane, 106 ... Hydrogen adsorption layer.

Claims (6)

A first step of forming a graphene film comprising a plurality of layers on a substrate;
And a second step of etching the graphene film by heating to a predetermined temperature in a hydrogen gas atmosphere. 2. The method for producing a graphene film according to claim 1, wherein the second step is performed at a pressure of 1 × 10 ⁵ Pa and a temperature of 700 to 1300 ° C. 3. In the manufacturing method of the graphene film according to claim 1 or 2,
The substrate is a SiC substrate made of SiC;
The first step includes forming a graphene film composed of a plurality of layers on the SiC substrate by using a SiC surface decomposition method. The method for producing a graphene film according to claim 3, further comprising a third step of heating the SiC substrate to a temperature of 900 ° C. or higher in vacuum after the second step. A method for uniformizing the number of graphene films formed of a plurality of layers formed on a substrate,
A method for uniformizing the number of layers of the graphene film, wherein a layer partially covering the substrate of the graphene film is etched by heating to a predetermined temperature in a hydrogen gas atmosphere. The method for uniformizing the number of layers of the graphene film according to claim 5, wherein the etching is performed at a pressure of 1 × 10 ⁵ Pa and a temperature of 700 to 1300 ° C. 6.