WO2014057612A1 - Process for producing graphene film, graphene film, and transparent conductive film comprising graphene film - Google Patents

Process for producing graphene film, graphene film, and transparent conductive film comprising graphene film Download PDF

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WO2014057612A1
WO2014057612A1 PCT/JP2013/005432 JP2013005432W WO2014057612A1 WO 2014057612 A1 WO2014057612 A1 WO 2014057612A1 JP 2013005432 W JP2013005432 W JP 2013005432W WO 2014057612 A1 WO2014057612 A1 WO 2014057612A1
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substrate
graphene
film
graphene film
contact
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Japanese (ja)
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健志 藤井
まり子 佐藤
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富士電機株式会社
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
    • H01B1/04—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of carbon-silicon compounds, carbon or silicon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/184—Preparation
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/194—After-treatment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02367—Substrates
    • H01L21/0237—Materials
    • H01L21/02425—Conductive materials, e.g. metallic silicides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02521—Materials
    • H01L21/02524—Group 14 semiconducting materials
    • H01L21/02527—Carbon, e.g. diamond-like carbon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02612—Formation types
    • H01L21/02617—Deposition types
    • H01L21/0262—Reduction or decomposition of gaseous compounds, e.g. CVD
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0224—Electrodes
    • H01L31/022466—Electrodes made of transparent conductive layers, e.g. TCO, ITO layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0236—Special surface textures
    • H01L31/02366—Special surface textures of the substrate or of a layer on the substrate, e.g. textured ITO/glass substrate or superstrate, textured polymer layer on glass substrate
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/1884—Manufacture of transparent electrodes, e.g. TCO, ITO

Definitions

  • the present invention relates to a graphene film manufacturing method and a graphene film. More specifically, the present invention relates to a method for producing a graphene film and a graphene film that can be transferred onto a substrate having an uneven surface.
  • single-layer graphene the mobility of carriers (electrons) is about 15000 cm 2 / V ⁇ s, which is known to be higher by one digit or more than silicon. Focusing on this point, various industrial applications of single-layer graphene have been proposed. Its application destinations are diverse, including applications to transistors exceeding Si, spin injection devices, gas sensors for detecting single molecules, and the like. In particular, the application of graphene to conductive thin films and transparent conductive films has attracted attention and is being actively developed.
  • Non-Patent Document 3 reports that a graphene thin film with good film quality can be uniformly formed on a Cu foil by a CVD method. Specifically, by placing a Cu foil inside the CVD furnace, introducing hydrogen while raising the temperature to 1000 ° C., and supplying a hydrocarbon-based gas such as methane there, the surface of the Cu foil Graphene is deposited on the film.
  • the graphene thus formed As an application of a conductive thin film or a transparent conductive film, it is necessary to peel it off from the Cu surface and form it on a target substrate.
  • PMMA Polymethyl methacrylate
  • the Cu foil is removed by etching.
  • the graphene / PMMA film is attached to the final substrate so that the graphene is in contact with the substrate.
  • PMMA is dissolved in an organic solvent such as acetone, graphene can be formed on the surface of the final substrate.
  • the D peak of Raman spectroscopy which is said to be caused by crystal defects, is not observed, and exhibits very good crystallinity. That is, the conventional transfer method can be said to be an effective method when transferring to a flat substrate.
  • the inventors of the present application also attempted to produce a graphene film on a solar cell by using a conventional transfer method similar to Non-Patent Document 3. As a result, graphene could not be transferred onto the solar cell.
  • the inventor of the present application as a cause that could not be transferred, in the solar cell, in order to improve the light confinement efficiency in the electrode formed on the surface of the substrate or in contact with the substrate, texture that is uneven about 30 nm or more This is because the surface of the solar cell to be transferred (the surface of the semiconductor layer on the light receiving surface side) has a texture structure of about 30 nm.
  • the flatness of the graphene is about 1 nm, and the graphene can contact the convex part of the texture during the transfer, but the graphene does not contact the concave part.
  • the graphene peeled off due to insufficient contact between the graphene and the substrate.
  • the present invention aims to solve the above problems. That is, the present invention provides a method for uniformly transferring a graphene film on a substrate having graphene and unevenness by reducing or eliminating contact failure between the graphene and a surface having unevenness such as a texture. This opens up the possibility of applying graphene films to applications such as batteries.
  • the inventor of the present application notices that when graphene is transferred onto an uneven surface having a texture structure such as a solar cell, the unevenness on the surface may cause a reduction in transfer efficiency. It was. Therefore, the inventors of the present application searched for a method for efficiently adhering graphene to an uneven surface. Then, it was confirmed that the graphene itself has a concavo-convex structure so that the graphene fits the concavo-convex surface of the transfer target during transfer, and the efficiency of adhesion of graphene is improved and the transfer efficiency is improved.
  • the second substrate is preferably PMMA (polymethyl methacrylate) or PDMS (polydimethylsiloxane).
  • a graphene film is provided.
  • the first substrate and the second substrate are names used in the present application to distinguish the transition metal substrate and the temporary support film of the resin from each other or other substrates, respectively.
  • the third substrate is an arbitrary substrate of an arbitrary material as long as the first substrate and the second substrate are different substrates.
  • the third substrate is an object that is a substrate or base made of any material including the materials of the first and second substrates.
  • the graphene film formed on the surface of the third substrate is continuously used as a substrate to be supported thereafter. In that case, the third substrate is determined from the viewpoint of the application to which the graphene film is applied.
  • a layer on the light-receiving surface side of the thin film solar cell can be given.
  • This layer also inherits the irregularities formed on the substrate or the like and has irregularities of about 30 nm or more on the surface.
  • the graphene film is used as a transparent electrode layer of a thin film solar cell.
  • Patent Document 1 describes that in a thin-film solar cell made of an amorphous material, the height difference of peaks and valleys (unevenness) on the surface of the lower electrode layer, which is an electrode in contact with the substrate, is 50 nm to 150 nm.
  • the uppermost layer of the solar cell takes over the unevenness on the surface of the lower electrode layer, and the uppermost layer also has an unevenness of about 30 nm.
  • the graphene film having unevenness can be used as a transparent conductive film of a solar cell.
  • the unevenness of the surface layer of the solar cell has randomness. For this reason, even if the first substrate is simply provided with regular irregularities and transferred, the graphene film may not fit well on the surface layer of the solar cell.
  • the unevenness pattern existing in the surface layer on the light-receiving surface side of the solar cell is taken in advance and the unevenness is provided on the surface of the first substrate using this mold, the unevenness of the graphene film is Fits the irregularities of the surface layer of the solar cell.
  • the upper limit is 10 layers. In that case, it is advantageous that the light transmittance in the film thickness direction of the graphene film provided in the present invention is 70% or more.
  • Graphene refers to a substance in a state in which carbon atoms are bonded to each other by sp 2 bonds and formed into a film or a layer having one or more atomic layers. Therefore, in the present application, the meaning of the term graphene includes not only single-layer graphene but also a sheet of carbon atoms including a plurality of atomic layers. In addition, when calling it a graphene film
  • Concavity and convexity refers to a structure raised from a flat state. Therefore, there are various shapes in the method of raising, and it is not limited. In the present application, it refers to a portion having a height of approximately 30 nm or more.
  • “contacting” and “pasting” do not necessarily include only those that are in close contact with each other. For example, what is placed, supported, or placed on the substrate while taking over the unevenness of the substrate is also included in “contact” and “stick”.
  • the use of a graphene film having irregularities on the irregularities on the surface which is the cause of the decrease in transfer efficiency, improves the adhesion efficiency of the graphene film, and the graphene film having high transfer efficiency This opens up the possibility of applying the graphene film to any application that uses electrical conductivity.
  • FIG. 1 is an explanatory diagram of each step of the process of the graphene film manufacturing method of the present embodiment.
  • the surface of the first substrate 11 that is a transition metal substrate is etched to have a concavo-convex of about 30 nm or more like the surface 11a shown in FIG. Forming a surface.
  • a graphene 10 having a sheet-like crystal structure of one or more carbon atoms is grown by supplying a source material containing carbon to the surface 11a.
  • the graphene 10 can be grown by a CVD method or a PVD method (physical vapor deposition).
  • the CVD method heats a transition metal substrate maintained at various conditions such as an ultrahigh vacuum of 1 ⁇ 10 ⁇ 7 Pa or less, a low pressure of about 10 to 10,000 Pa, and an atmospheric pressure to about 600 to 1200 ° C.
  • a hydrocarbon gas such as methane containing carbon atoms is sprayed onto the transition metal substrate in that state. By this treatment, methane gas is cracked (dissociative adsorption). Carbon atoms derived from the supplied gas receive a catalytic effect on the surface of the transition metal substrate, migrate to a long distance, reach the nucleus of graphene, and graphene grows.
  • the transition metal substrate may be formed of a thin film with the surface being a single crystal surface.
  • graphene can be grown by MBE (molecular beam epitaxy) or PLD (pulse laser deposition) as a method for growing graphene by the PVD method.
  • MBE molecular beam epitaxy
  • PLD pulse laser deposition
  • atomic carbon is generated by heating graphite to 1200 to 2000 ° C. in an ultra-high vacuum, and the atomic carbon converted into a molecular beam is supplied onto the surface of the heated transition metal substrate.
  • the graphene film is formed by the catalytic effect of the transition metal substrate.
  • PLD ablate graphite with an KrF excimer laser in an ultra-high vacuum, so that instantaneously evaporated carbon is supplied in a molecular beam state. When the carbon molecular beam is supplied to the heated transition metal substrate, graphene is formed on the surface of the transition metal substrate.
  • the transition metal for the first substrate described above Fe, Co, Ni, Cu, Mo, Ru, Rh, Pd, W, Re, Ir, Pt, or an alloy thereof can be used.
  • the form of the transition metal substrate can be a foil, a thin film, a bulk, and a single crystal or a polycrystal thereof. The most typical of these transition metal substrates is copper foil.
  • the transition metal substrate serves as a support substrate for graphene and, as described above, serves as a catalyst for cracking (decomposing) the supplied carbon-containing gas and promotes the growth of graphene having a sheet-like crystal structure. Indicates.
  • a second substrate 12 that is a resin support film is formed so as to be in contact with the surface of the graphene 10.
  • the second substrate 12 is formed while maintaining the state of the graphene 10 formed on the surface of the first substrate.
  • the second substrate 12 is made of a material capable of holding the graphene 10.
  • the most typical second substrate 12 is obtained by volatilizing a solvent or polymerizing a precursor from a precursor such as a solvent-soluble resin dissolved in a solvent or a prepolymer before becoming a polymer. It is solidified.
  • the resin support film to be the second substrate 12, for example, can exhibit a certain degree of support function, is not affected by the subsequent removal of the first substrate 11, and is final if necessary.
  • the material is selected from materials satisfying the condition that it can be removed without affecting the graphene 10.
  • the graphene 10 at this stage is sandwiched between the first substrate 11 (transition metal substrate) and the second substrate 12 (resin support substrate) (FIG. 1D).
  • the transition metal substrate which is the first substrate 11 is removed.
  • etching with an acid can be employed. This removal process is selected from a technique that does not alter the graphene 10.
  • the graphene 10 is attached to the second substrate 12 and the surface is exposed.
  • the surface of the graphene 10 on the side in contact with the first substrate 11 faces the third substrate 13, which is another substrate, with respect to the surface 13 a of the third substrate 13. paste. Concavities and convexities called texture are formed on the surface 13 a of the third substrate 13.
  • the third substrate 13 is a substrate different from both the first substrate 11 and the second substrate 12.
  • the second substrate 12 is removed as shown in FIG.
  • any technique that hardly affects the graphene 10 and the third substrate 13 can be employed.
  • the third substrate 13 is an inorganic substance such as a silicon substrate or a glass substrate
  • the second substrate 12 can be removed with an organic solvent that dissolves the material of the resin support substrate.
  • the material and properties of the second substrate 12 (resin support film) are those that can be removed in this step.
  • the graphene film can be manufactured by forming the graphene 10 on the surface of the third substrate 13.
  • a technique of scraping the metal uniformly and randomly is optimal.
  • the method it is desirable to use wet etching with acid or dry etching by reactive ion etching.
  • the height of the etching needs to be larger than the unevenness of the third substrate, which is a transfer target, and a structure called a texture such as a solar cell generally has an unevenness of 30 nm or more. 30 nm or more is desirable.
  • the second substrate 14 (resin support substrate) employed in the present embodiment can be made of any material that can satisfy the above-described conditions.
  • a suitable material for the second substrate 12 is PMMA (polymethyl methacrylate) or PDMS (polydimethylsiloxane).
  • PMMA and PDMS can be easily applied with a solution dissolved in a solvent, and it is also easy to volatilize the solvent to form a temporary support film of resin. Furthermore, it can withstand a process (etching process) for removing the first substrate 11 and can easily remove the second substrate itself. Furthermore, a film as much as required for transferring the graphene 10 can be formed.
  • PMMA and PDMS satisfying these conditions are suitable materials used as the second substrate 12 (resin support substrate) in the present embodiment.
  • the shape of the unevenness of the first substrate is inherited, and has the same unevenness of about 30 nm. Therefore, when transferred onto the uneven third substrate, the graphene film The unevenness of the third substrate and the unevenness of the third substrate enter alternately to fit the shape, and the graphene film can adhere to the third substrate, so that the graphene film can be transferred efficiently.
  • the height index of the unevenness can be calculated from a height difference measured by, for example, a scanning electron microscope, a transmission electron microscope, an atomic force microscope, or the like.
  • the unevenness of the texture structure of a general third substrate using this method is, for example, about 30 nm in the semiconductor layer on the light receiving surface side of the solar cell. Therefore, in the preferable configuration of the graphene film, the unevenness is preferably 30 nm or more.
  • the graphene film provided in the present embodiment preferably has 1 or more and 10 or less atomic layers of graphene.
  • the reason is related to the application of the graphene film.
  • Graphene is known to exhibit high mobility, particularly in single layer graphene.
  • the graphene film is used as a transparent conductive film or the like in applications where light transmission is required, there is an upper limit in the number of layers from the viewpoint of transmittance.
  • the upper limit is 10 layers. It is.
  • Example 1 is a sample of a graphene film manufactured according to the above-described embodiment.
  • the materials, amounts used, ratios, processing contents, processing procedures, directions of elements or members, specific arrangements, and the like shown in the following examples can be appropriately changed without departing from the gist of the present invention. Therefore, the scope of the present invention is not limited to the following specific examples. Further, reference is made to the already described drawings.
  • the first substrate 11 As the first substrate 11, a 10 mm square Cu polished (chemical mechanical polished) Cu foil (100 ⁇ m thick) was employed. The arithmetic average roughness Ra of this substrate is about 1 nm.
  • the first substrate 11 is immersed in a mixed solution of 5 ml of hydrochloric acid, 5 ml of hydrogen peroxide, and 25 ml of water for 10 seconds, washed with running water for 5 minutes, and dried, so that the surface of the first substrate 11 has 30 nm unevenness 11a. Formed.
  • the first substrate 11 was placed in a CVD reactor and evacuated to 1 ⁇ 10 ⁇ 3 Pa. Then, the first substrate 11 was heated to 1000 ° C.
  • the substrate was immersed in a mixed solution of 10 ml of hydrochloric acid, 10 ml of hydrogen peroxide and 50 ml of pure water, and etched until the Cu foil as the first substrate 11 was completely removed. Then, the laminated body of the graphene 10 and the 2nd board
  • the third substrate 13 was pressed against the surface of textured SnO / glass (Asahi-U manufactured by Asahi Glass) and heated at 180 ° C. for 30 minutes. By this heating, the PMMA was softened, and the graphene 10 was brought into close contact with the SnO surface of the third substrate 13 that was a SnO / glass substrate.
  • the PMMA of the second substrate 12 was removed from the surface of the graphene 10 by immersing in acetone for 5 minutes. Further, the sample was washed with ultrapure water for 5 minutes to obtain a graphene film sample in which the graphene 10 was disposed on the third substrate 13 as shown in FIG.
  • Example 1 which is a graphene film manufactured according to the present embodiment was observed. It was found that the graphene was transferred uniformly. However, in the micrograph, the difference in density between the graphene and the ground is small, and it is difficult to illustrate in black and white, so illustration is omitted. Thus, the effect of the present invention was demonstrated.

Abstract

The present invention addresses the problem of reducing or eliminating contact failures between graphene and a surface which has recesses and protrusions, e.g., a texture, and thereby evenly transferring graphene and a graphene film to the substrate having recesses and protrusions. The process comprises a step in which recesses and protrusions are formed in a surface of a first substrate that is a transition metal substrate, a step in which a raw material comprising carbon is supplied to the first substrate to thereby grow graphene having a sheet-shaped crystal structure comprising one or more layers of carbon atoms, a step in which a second substrate that is a resinous temporary supporting film is formed so as to be in contact with the surface of the graphene, a step in which the first substrate is removed, a step in which the laminate of the second substrate with the graphene is adhered to a surface of a third substrate so that the surface of the graphene which was in contact with the first substrate faces the third-substrate surface, and a step in which the second substrate is removed.

Description

グラフェン膜の製造方法およびグラフェン膜ならびにグラフェン膜を用いた透明導電膜Method for producing graphene film, graphene film, and transparent conductive film using graphene film
　本発明は、グラフェン膜の製造方法およびグラフェン膜に関する。さらに詳細には本発明は、表面に凹凸のある基板に転写することの出来るグラフェン膜の製造方法およびグラフェン膜に関する。 The present invention relates to a graphene film manufacturing method and a graphene film. More specifically, the present invention relates to a method for producing a graphene film and a graphene film that can be transferred onto a substrate having an uneven surface.
　従来、ｓｐ２結合で互いに結合して炭素原子のシート状の結晶構造を有するグラフェンにおいて、炭素原子の単層のシートからなるグラフェン（単層グラフェンという）が発見されている。単層グラフェンは、非特許文献１及び非特許文献２に記載のように、半整数ホール効果などの２次元性に由来する特異な量子伝導が報告され、物性物理の分野で注目されている。 Conventionally, in graphene having a sheet-like crystal structure of carbon atoms bonded to each other by sp 2 bonds, graphene composed of a single-layer sheet of carbon atoms (referred to as single-layer graphene) has been discovered. As described in Non-Patent Document 1 and Non-Patent Document 2, single-layer graphene has been reported to have specific quantum conduction derived from two-dimensionality such as the half-integer Hall effect, and has attracted attention in the field of physical properties.
　単層グラフェンでは、キャリア（電子）の移動度が約１５０００ｃｍ２／Ｖ・ｓであり、シリコンに比べ一桁以上高い値を示すことが知られている。この点に注目し単層グラフェンの各種の産業応用が提案されている。その応用先は多岐にわたり、Ｓｉを超えるトランジスタへの応用、スピン注入デバイス、単分子を検出するガスセンサーなどを含んでいる。なかでも、導電性薄膜や透明導電膜へのグラフェンの適用が注目されており活発に開発が行われている。 In single-layer graphene, the mobility of carriers (electrons) is about 15000 cm 2 / V · s, which is known to be higher by one digit or more than silicon. Focusing on this point, various industrial applications of single-layer graphene have been proposed. Its application destinations are diverse, including applications to transistors exceeding Si, spin injection devices, gas sensors for detecting single molecules, and the like. In particular, the application of graphene to conductive thin films and transparent conductive films has attracted attention and is being actively developed.
　グラフェンを、導電性薄膜または透明導電膜として利用する際の重要な特性の一つが、低いシート抵抗である。シート抵抗は、膜厚と導電率とに反比例することから、膜厚を厚くするほどシート抵抗は低い値が得られる。また、導電率は移動度に比例するため、良質な膜のグラフェンを成膜して、炭素原子の配列に不整合等を減らすことにより、移動度を高められれば、様々な応用の可能性が拓ける。 One of the important characteristics when using graphene as a conductive thin film or a transparent conductive film is low sheet resistance. Since the sheet resistance is inversely proportional to the film thickness and the electrical conductivity, the lower the sheet resistance, the higher the film thickness. In addition, since the conductivity is proportional to the mobility, if the mobility can be increased by depositing good quality graphene and reducing mismatches with the carbon atom arrangement, there are various applications. Open up.
　また、グラフェンの典型的な製造方法の一つが、ＣＶＤ法である。例えば非特許文献３では、ＣＶＤ法によってＣｕフォイル上に膜質の良いグラフェン薄膜を均一に成膜できることが報告されている。具体的には、ＣＶＤ炉の内部にＣｕフォイルを配置して、１０００℃まで昇温しながら水素を導入しておき、そこにメタンなどの炭化水素系のガスを供給することにより、Ｃｕフォイル表面にグラフェンが成膜される。 One of the typical methods for producing graphene is the CVD method. For example, Non-Patent Document 3 reports that a graphene thin film with good film quality can be uniformly formed on a Cu foil by a CVD method. Specifically, by placing a Cu foil inside the CVD furnace, introducing hydrogen while raising the temperature to 1000 ° C., and supplying a hydrocarbon-based gas such as methane there, the surface of the Cu foil Graphene is deposited on the film.
　こうして形成されたグラフェンを導電性薄膜や透明導電膜の用途として用いるためには、Ｃｕ表面から剥離して目的の基板に形成する必要がある。その手法の典型的なものでは、形成されたグラフェンの上に、樹脂の仮支持膜としてＰＭＭＡ（Polymethyl methacrylate）を形成する。その後、Ｃｕフォイルをエッチングにより取り除く。次いで、グラフェン／ＰＭＭＡ膜を、最終的な基板に対して、グラフェンがその基板に接する向きに貼り付ける。その後にアセトンなどの有機溶媒にてＰＭＭＡを溶解させれば、グラフェンを当該最終的な基板の面の上に形成することができる。実際、この手法（以下、従来の転写法と呼ぶ）により形成したグラフェンにおいては、結晶の欠陥に起因するといわれるラマン分光法のＤピークが観測されず、非常に良質な結晶性を示す。つまり、従来の転写法は平坦な基板に転写する場合には有効な手法といえる。 In order to use the graphene thus formed as an application of a conductive thin film or a transparent conductive film, it is necessary to peel it off from the Cu surface and form it on a target substrate. In a typical method, PMMA (Polymethyl methacrylate) is formed on the formed graphene as a temporary support film of resin. Thereafter, the Cu foil is removed by etching. Next, the graphene / PMMA film is attached to the final substrate so that the graphene is in contact with the substrate. Then, if PMMA is dissolved in an organic solvent such as acetone, graphene can be formed on the surface of the final substrate. In fact, in graphene formed by this method (hereinafter referred to as a conventional transfer method), the D peak of Raman spectroscopy, which is said to be caused by crystal defects, is not observed, and exhibits very good crystallinity. That is, the conventional transfer method can be said to be an effective method when transferring to a flat substrate.
特開平８－２８８５２９号公報JP-A-8-288529
　そこで、本願の発明者らも、非特許文献３と同様の従来の転写法を用いて、太陽電池上へのグラフェン膜の作製を試みた。その結果、太陽電池上には、グラフェンを転写できなかった。本願の発明者は、転写できなかった原因としては、太陽電池では、基板表面や基板上に接して形成される電極に、光の閉じ込め効率を向上させるために、３０ｎｍ程度以上の凹凸であるテクスチャと呼ばれる構造を用いており、転写対象の太陽電池表面（受光面側半導体層表面）にも３０ｎｍ程度のテクスチャ構造が有るためと考える。従来の転写法ではグラフェンの平坦性が１ｎｍ程度であり、転写の際にテクスチャの凸の部分にはグラフェンは接触できるが、凹の部分にはグラフェンは接触せず、結果としてＰＭＭＡを除去した際に、グラフェンと基板との接触が不十分でグラフェンは剥離してしまったと推測される。 Therefore, the inventors of the present application also attempted to produce a graphene film on a solar cell by using a conventional transfer method similar to Non-Patent Document 3. As a result, graphene could not be transferred onto the solar cell. The inventor of the present application, as a cause that could not be transferred, in the solar cell, in order to improve the light confinement efficiency in the electrode formed on the surface of the substrate or in contact with the substrate, texture that is uneven about 30 nm or more This is because the surface of the solar cell to be transferred (the surface of the semiconductor layer on the light receiving surface side) has a texture structure of about 30 nm. In the conventional transfer method, the flatness of the graphene is about 1 nm, and the graphene can contact the convex part of the texture during the transfer, but the graphene does not contact the concave part. As a result, when the PMMA is removed In addition, it is presumed that the graphene peeled off due to insufficient contact between the graphene and the substrate.
　本発明は、上記課題の解決することを目的とする。すなわち本発明は、グラフェンと、表面にテクスチャなどの凹凸のある表面との接触不良を削減または解消することにより、グラフェンと凹凸を持つ基板上に均一にグラフェン膜を転写することを提供し、太陽電池などの用途へのグラフェン膜の適用の可能性を拓くものである。 The present invention aims to solve the above problems. That is, the present invention provides a method for uniformly transferring a graphene film on a substrate having graphene and unevenness by reducing or eliminating contact failure between the graphene and a surface having unevenness such as a texture. This opens up the possibility of applying graphene films to applications such as batteries.
　本願の発明者は、上述したように、太陽電池などのテクスチャ構造を持つ、凹凸のある表面上に、グラフェンを転写すると、表面の凹凸が転写の能率を低下させる要因になりかねないことに気づいた。そこで、本願の発明者らは、凹凸のある表面に効率良くグラフェンが密着する方法を探索した。そして、グラフェン自体を凹凸構造とすることで、転写の際にグラフェンが転写対象の表面の凹凸にフィットとし、グラフェンの付着の効率が向上し転写能率が向上することを確認した。 As described above, the inventor of the present application notices that when graphene is transferred onto an uneven surface having a texture structure such as a solar cell, the unevenness on the surface may cause a reduction in transfer efficiency. It was. Therefore, the inventors of the present application searched for a method for efficiently adhering graphene to an uneven surface. Then, it was confirmed that the graphene itself has a concavo-convex structure so that the graphene fits the concavo-convex surface of the transfer target during transfer, and the efficiency of adhesion of graphene is improved and the transfer efficiency is improved.
　すなわち、本発明のある態様においては、遷移金属基板である第１基板の表面に凹凸を形成する工程と、前記第１基板に炭素を含む原料物質を供給することにより、１層以上の炭素原子のシート状の結晶構造を有するグラフェンを成長させる工程と、該グラフェンの表面に接して樹脂の仮支持膜である第２基板を形成する工程と、前記第１基板を除去する工程と、前記第２基板と前記グラフェンとの積層体を第３基板の表面に対し前記グラフェンの前記第１基板に接していた側の表面を向けて前記積層体を貼り付ける工程と、前記第２基板を除去する工程と、を含むグラフェン膜の製造方法が提供される。 That is, in one aspect of the present invention, a step of forming irregularities on the surface of the first substrate which is a transition metal substrate, and supplying a source material containing carbon to the first substrate, one or more carbon atoms Growing a graphene having a sheet-like crystal structure, forming a second substrate which is a temporary support film of a resin in contact with the surface of the graphene, removing the first substrate, A step of attaching the laminate with the laminate of the two substrates and the graphene facing the surface of the third substrate facing the first substrate with respect to the surface of the third substrate; and removing the second substrate And a process for producing a graphene film.
　第２基板がＰＭＭＡ（ポリメチルメタクリレート）またはＰＤＭＳ（ポリジメチルシロキサン）であることが好ましい。
　また、本発明のある態様においては、凹凸のある遷移金属基板上にグラフェンを成長することで、基板の凹凸を引き継いだ、１層以上の炭素原子がシート状に形成された結晶構造を有する膜である、グラフェン膜が提供される。 The second substrate is preferably PMMA (polymethyl methacrylate) or PDMS (polydimethylsiloxane).
In one embodiment of the present invention, a film having a crystal structure in which one or more carbon atoms are formed in a sheet shape, which inherits the unevenness of the substrate by growing graphene on the uneven transition metal substrate. A graphene film is provided.
　本発明の各態様において、第１基板および第２基板は、それぞれ、遷移金属基板および樹脂の仮支持膜を互いに、または他の基板から区別するために本出願で用いる呼称である。これに対し、第３基板は、第１基板とも第２基板とも別の基板である限り、任意の材質の任意の基板である。つまり、第３基板は、第１および第２基板の材質も含めて任意の材質により作製された基板または基体とする物体である。通常は、第３基板の面の上に形成されたグラフェン膜を、その後に支持する基板とて使用し続ける。その場合、第３基板はグラフェン膜が適用される用途の観点から決定される。 In each aspect of the present invention, the first substrate and the second substrate are names used in the present application to distinguish the transition metal substrate and the temporary support film of the resin from each other or other substrates, respectively. On the other hand, the third substrate is an arbitrary substrate of an arbitrary material as long as the first substrate and the second substrate are different substrates. In other words, the third substrate is an object that is a substrate or base made of any material including the materials of the first and second substrates. Usually, the graphene film formed on the surface of the third substrate is continuously used as a substrate to be supported thereafter. In that case, the third substrate is determined from the viewpoint of the application to which the graphene film is applied.
　第３基板の例としては、薄膜太陽電池の受光面側の層が挙げられる。
この層も、基板などに形成された凹凸を引き継いで、３０ｎｍ程度、またはそれ以上の凹凸を、表面に有するものである。この場合、グラフェン膜は、薄膜太陽電池の透明電極層として用いられる。
例えば、特許文献１には、アモルファス系材料から成る薄膜太陽電池において、基板に接する電極である、下部電極層表面の山谷（凹凸）の高低差が５０ｎｍ～１５０ｎｍであることが記載されている。この下部電極層表面の凹凸を、太陽電池の最上層が引き継ぎ、最上層にも３０ｎｍ程度の凹凸が出来る。このとき、凹凸を有したグラフェン膜は、太陽電池の透明導電膜として用いることができる。
　ただ、太陽電池の表面層が有する凹凸には、ランダムネスが有る。このため、単に第１基板に、規則的な凹凸を設けて転写しても、太陽電池の表面層に、グラフェン膜が、上手くフィットしない場合がある。この場合には、予め、太陽電池の受光面側の表面層に存在している凹凸の型を取り、この型を用いて、第１基板の表面に凹凸を設ければ、グラフェン膜の凹凸が、太陽電池の表面層の凹凸にフィットする。 As an example of the third substrate, a layer on the light-receiving surface side of the thin film solar cell can be given.
This layer also inherits the irregularities formed on the substrate or the like and has irregularities of about 30 nm or more on the surface. In this case, the graphene film is used as a transparent electrode layer of a thin film solar cell.
For example, Patent Document 1 describes that in a thin-film solar cell made of an amorphous material, the height difference of peaks and valleys (unevenness) on the surface of the lower electrode layer, which is an electrode in contact with the substrate, is 50 nm to 150 nm. The uppermost layer of the solar cell takes over the unevenness on the surface of the lower electrode layer, and the uppermost layer also has an unevenness of about 30 nm. At this time, the graphene film having unevenness can be used as a transparent conductive film of a solar cell.
However, the unevenness of the surface layer of the solar cell has randomness. For this reason, even if the first substrate is simply provided with regular irregularities and transferred, the graphene film may not fit well on the surface layer of the solar cell. In this case, if the unevenness pattern existing in the surface layer on the light-receiving surface side of the solar cell is taken in advance and the unevenness is provided on the surface of the first substrate using this mold, the unevenness of the graphene film is Fits the irregularities of the surface layer of the solar cell.
　グラフェンは原子層１層で約２．３％もの高い光吸収を示すため、本発明で透明導電膜としてグラフェン膜を採用すると、１０層を上限とすると好適である。その場合、本発明において提供されるグラフェン膜の膜厚方向の光透過率が７０％以上であると有利である。 Since graphene exhibits high light absorption of about 2.3% in one atomic layer, when a graphene film is employed as the transparent conductive film in the present invention, it is preferable that the upper limit is 10 layers. In that case, it is advantageous that the light transmittance in the film thickness direction of the graphene film provided in the present invention is 70% or more.
　さて、グラフェンとは、ｓｐ２結合で互いに結合して炭素原子が１原子層以上の膜状または層状に形成されている状態の物質を指す。したがって、本出願において、グラフェンという文言の意味としては、単層グラフェンだけではなく、複数の原子層で成る炭素原子のシートも含む。なお、本出願においてグラフェン膜と呼ぶときは、例えば第３基板などの、何らかの基板または基体に支持された状態のグラフェンを意図している。 Graphene refers to a substance in a state in which carbon atoms are bonded to each other by sp 2 bonds and formed into a film or a layer having one or more atomic layers. Therefore, in the present application, the meaning of the term graphene includes not only single-layer graphene but also a sheet of carbon atoms including a plurality of atomic layers. In addition, when calling it a graphene film | membrane in this application, the graphene of the state supported by some board | substrates or base | substrates, such as a 3rd board | substrate, for example is intended.
　凹凸とは、平坦な状態から隆起した構造を呼ぶ。したがって、隆起の仕方にはさまざまな形状があり、限定されるものでは無い。本出願においては、概ね３０ｎｍ以上の高さとなっている部分を指している。 Concavity and convexity refers to a structure raised from a flat state. Therefore, there are various shapes in the method of raising, and it is not limited. In the present application, it refers to a portion having a height of approximately 30 nm or more.
　なお、本発明において、「接して」や「貼り付ける」とは、必ずしも全面的に密着しているものだけを含むものではない。例えば基板の凹凸を引き継いで基板上に載置または支持または配置されているものも、「接して」や「貼り付ける」に含まれる。 In the present invention, “contacting” and “pasting” do not necessarily include only those that are in close contact with each other. For example, what is placed, supported, or placed on the substrate while taking over the unevenness of the substrate is also included in “contact” and “stick”.
　本発明のいずれかの態様においては、転写能率の低下の原因である表面の凹凸に対し、凹凸を有するグラフェン膜を使用することにより、グラフェン膜の付着効率が向上し、転写能率の高いグラフェン膜が提供され、導電性を利用する任意の用途へのグラフェン膜の適用の可能性が拓ける。 In any aspect of the present invention, the use of a graphene film having irregularities on the irregularities on the surface, which is the cause of the decrease in transfer efficiency, improves the adhesion efficiency of the graphene film, and the graphene film having high transfer efficiency This opens up the possibility of applying the graphene film to any application that uses electrical conductivity.
本発明のある実施形態におけるグラフェン膜の製造方法の工程の各段階の様子を示す説明図である。It is explanatory drawing which shows the mode of each step of the process of the manufacturing method of the graphene film in one embodiment of the present invention.
　以下、本発明に係るグラフェン膜の製造方法およびグラフェン膜を、図面を参照して説明する。当該説明に際し特に言及がない限り、全図にわたり共通する部分または要素には共通する参照符号が付されている。また、図中、各実施形態の要素のそれぞれは、必ずしも互いの縮尺比を保って示してはいない。
＜実施の形態１＞
　本実施形態においては、グラフェン膜の製造方法およびグラフェン膜が提供される。図１は、本実施形態のグラフェン膜の製造方法の工程の各段階の説明図である。 Hereinafter, a graphene film manufacturing method and a graphene film according to the present invention will be described with reference to the drawings. In the description, unless otherwise specified, common parts or elements are denoted by common reference numerals throughout the drawings. In the drawings, the elements of the respective embodiments are not necessarily shown while maintaining the mutual scale ratio.
<Embodiment 1>
In the present embodiment, a method for producing a graphene film and a graphene film are provided. FIG. 1 is an explanatory diagram of each step of the process of the graphene film manufacturing method of the present embodiment.
　図１（ａ）に示すようにまず、遷移金属基板である第１基板１１の表面をエッチングすることにより図１（ｂ）に示す、表面１１ａのように３０ｎｍ程度、またはそれ以上の凹凸を持つ表面を形成する。次いで、図１（ｃ）に示すように、表面１１ａに炭素を含む原料物質を供給することにより、１層以上の炭素原子のシート状の結晶構造を有するグラフェン１０を成長させる。 As shown in FIG. 1A, first, the surface of the first substrate 11 that is a transition metal substrate is etched to have a concavo-convex of about 30 nm or more like the surface 11a shown in FIG. Forming a surface. Next, as shown in FIG. 1C, a graphene 10 having a sheet-like crystal structure of one or more carbon atoms is grown by supplying a source material containing carbon to the surface 11a.
　具体的には、グラフェン１０の成長法としては、ＣＶＤ法またはＰＶＤ法（物理的気相堆積）により成膜することができる。このうちＣＶＤ法では、１×１０－７Ｐａ以下の超高真空中や、１０～１００００Ｐａ程度の低圧や大気圧などの、さまざまな条件下に維持した遷移金属基板を６００～１２００℃程度に加熱する。その状態の遷移金属基板に対して、炭素原子を含むメタンなどの炭化水素ガスを吹き付ける。この処理によりメタンガスはクラッキング（解離吸着）される。供給されたガスに由来する炭素原子は、遷移金属基板の表面の触媒効果を受け、長い距離をマイグレーションすることで、グラフェンの核に到達し、グラフェンが成長してゆく。なお、遷移金属基板は、表面を単結晶の表面とし、薄膜により形成されていてもよい。 Specifically, the graphene 10 can be grown by a CVD method or a PVD method (physical vapor deposition). Among them, the CVD method heats a transition metal substrate maintained at various conditions such as an ultrahigh vacuum of 1 × 10 −7 Pa or less, a low pressure of about 10 to 10,000 Pa, and an atmospheric pressure to about 600 to 1200 ° C. To do. A hydrocarbon gas such as methane containing carbon atoms is sprayed onto the transition metal substrate in that state. By this treatment, methane gas is cracked (dissociative adsorption). Carbon atoms derived from the supplied gas receive a catalytic effect on the surface of the transition metal substrate, migrate to a long distance, reach the nucleus of graphene, and graphene grows. The transition metal substrate may be formed of a thin film with the surface being a single crystal surface.
　一方、ＰＶＤ法によるグラフェンの成長方法としては、ＭＢＥ（分子線エピタキシー法）やＰＬＤ（パルスレーザー堆積）などにより、グラフェンを成長させることが可能である。ＭＢＥでは超高真空中でグラファイトを１２００～２０００℃に加熱することで原子状の炭素を発生させ、分子線となった原子状炭素を、加熱した遷移金属基板表面上に供給する。これにより、遷移金属基板の触媒効果によってグラフェンが成膜される。これに対しＰＬＤでは、超高真空中でグラファイトをＫｒＦのエキシマレーザーにてアブレーションすることで、瞬時に蒸発した炭素が分子線の状態で供給される。この炭素の分子線を加熱された遷移金属基板に供給すると、遷移金属基板の表面にグラフェンが成膜される。 On the other hand, graphene can be grown by MBE (molecular beam epitaxy) or PLD (pulse laser deposition) as a method for growing graphene by the PVD method. In MBE, atomic carbon is generated by heating graphite to 1200 to 2000 ° C. in an ultra-high vacuum, and the atomic carbon converted into a molecular beam is supplied onto the surface of the heated transition metal substrate. Thereby, the graphene film is formed by the catalytic effect of the transition metal substrate. On the other hand, PLD ablate graphite with an KrF excimer laser in an ultra-high vacuum, so that instantaneously evaporated carbon is supplied in a molecular beam state. When the carbon molecular beam is supplied to the heated transition metal substrate, graphene is formed on the surface of the transition metal substrate.
　なお、上述した第１基板のための遷移金属には、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｍｏ、Ｒｕ、Ｒｈ、Ｐｄ、Ｗ、Ｒｅ、Ｉｒ、Ｐｔまたはこれらの合金を採用することが可能である。また、遷移金属基板の形態は、フォイル、薄膜、バルク、およびそれらの単結晶、多結晶などとすることができる。これらのうち最も典型的な遷移金属基板は銅箔である。遷移金属基板は、グラフェンの支持基板となるとともに、上述したとおり、供給された炭素を含有するガスをクラッキング（分解）する触媒となり、炭素原子がシート状の結晶構造のグラフェンの成長を促進する作用を示す。 As the transition metal for the first substrate described above, Fe, Co, Ni, Cu, Mo, Ru, Rh, Pd, W, Re, Ir, Pt, or an alloy thereof can be used. . Moreover, the form of the transition metal substrate can be a foil, a thin film, a bulk, and a single crystal or a polycrystal thereof. The most typical of these transition metal substrates is copper foil. The transition metal substrate serves as a support substrate for graphene and, as described above, serves as a catalyst for cracking (decomposing) the supplied carbon-containing gas and promotes the growth of graphene having a sheet-like crystal structure. Indicates.
　次に図１（ｄ）のように、樹脂支持膜である第２基板１２を、グラフェン１０の表面に接するように形成する。具体的には、第１基板の面の上に形成されているグラフェン１０を、その状態を維持しつつ第２基板１２を形成する。この際、第２基板１２は、グラフェン１０を保持することが可能な材質により作製する。例えばグラフェン１０に接した状態で、液状の材質から固化させることが可能で、その後にグラフェン１０を保持しうる材質が、この第２基板１２に適している。最も典型的な第２基板１２は、溶媒に溶けている状態の溶媒可溶性の樹脂や、高分子となる前のプレポリマーなどの前駆体から、溶媒を揮発させたり、前駆体を重合させることによって固化したものである。この第２基板１２となる樹脂支持膜は、例えば、ある程度の支持機能を発揮することができること、後の第１基板１１の除去の際に影響を受けないこと、さらに、必要に応じて最終的にグラフェン１０に影響を与えずに除去可能であること、という条件を満たす材質から選択される。この段階のグラフェン１０は、第１基板１１（遷移金属基板）と第２基板１２（樹脂支持基板）とに挟まれた状態となっている（図１（ｄ））。 Next, as shown in FIG. 1D, a second substrate 12 that is a resin support film is formed so as to be in contact with the surface of the graphene 10. Specifically, the second substrate 12 is formed while maintaining the state of the graphene 10 formed on the surface of the first substrate. At this time, the second substrate 12 is made of a material capable of holding the graphene 10. For example, a material that can be solidified from a liquid material in contact with the graphene 10 and can hold the graphene 10 after that is suitable for the second substrate 12. The most typical second substrate 12 is obtained by volatilizing a solvent or polymerizing a precursor from a precursor such as a solvent-soluble resin dissolved in a solvent or a prepolymer before becoming a polymer. It is solidified. The resin support film to be the second substrate 12, for example, can exhibit a certain degree of support function, is not affected by the subsequent removal of the first substrate 11, and is final if necessary. In addition, the material is selected from materials satisfying the condition that it can be removed without affecting the graphene 10. The graphene 10 at this stage is sandwiched between the first substrate 11 (transition metal substrate) and the second substrate 12 (resin support substrate) (FIG. 1D).
　次いで図１（ｅ）のように、第１基板１１である遷移金属基板を除去する。遷移金属基板を除去するためには、例えば酸によるエッチングを採用することが可能である。この除去の処理は、グラフェン１０を変質させない手法から選択される。第１基板が完全に除去されると、グラフェン１０が第２基板１２に付着して表面を露出させている状態になる。 Next, as shown in FIG. 1E, the transition metal substrate which is the first substrate 11 is removed. In order to remove the transition metal substrate, for example, etching with an acid can be employed. This removal process is selected from a technique that does not alter the graphene 10. When the first substrate is completely removed, the graphene 10 is attached to the second substrate 12 and the surface is exposed.
　その後、図１（ｆ）のように、グラフェン１０の第１基板１１に接していた側の表面を、他の基板である第３基板１３に向けて、第３基板１３の表面１３ａに対して貼り付ける。第３基板１３の表面１３ａにはテクスチャと呼ばれる凹凸が形成されている。なお、第３基板１３は、第１基板１１とも第２基板１２とも別の基板である。 Thereafter, as shown in FIG. 1 (f), the surface of the graphene 10 on the side in contact with the first substrate 11 faces the third substrate 13, which is another substrate, with respect to the surface 13 a of the third substrate 13. paste. Concavities and convexities called texture are formed on the surface 13 a of the third substrate 13. The third substrate 13 is a substrate different from both the first substrate 11 and the second substrate 12.
　最後に図１（ｇ）のように第２基板１２を除去する。この手法としては、グラフェン１０および第３基板１３に対して影響を及ぼしにくい任意の手法を採用することができる。例えば、第３基板１３がシリコン基板やガラス基板などの無機物であるなら、樹脂支持基板の材質を溶解させる有機溶媒によって第２基板１２を除去することができる。第２基板１２（樹脂支持膜）の材質や性状は、本工程において除去可能なものを採用しておく。 Finally, the second substrate 12 is removed as shown in FIG. As this technique, any technique that hardly affects the graphene 10 and the third substrate 13 can be employed. For example, if the third substrate 13 is an inorganic substance such as a silicon substrate or a glass substrate, the second substrate 12 can be removed with an organic solvent that dissolves the material of the resin support substrate. The material and properties of the second substrate 12 (resin support film) are those that can be removed in this step.
　以上の工程により、グラフェン１０を第３基板１３の面の上に形成してグラフェン膜を製造することができる。次に、より詳細な製造条件について説明する。
　本実施形態においては、第１基板である遷移金属をエッチングするためには、金属を均一かつランダムに削り取る手法が最適である。その方法としては酸などによるウエットエッチングや反応性イオンエッチングなどによるドライエッチングを使用することが望ましい。このときエッチングの高さは転写対象である、第３基板の凹凸よりも大きい必要があり、一般的に太陽電池などのテクスチャと呼ばれる構造では３０nm以上の凹凸があるため、本エッチングによる高さは３０nm以上が望ましい。 Through the above process, the graphene film can be manufactured by forming the graphene 10 on the surface of the third substrate 13. Next, more detailed manufacturing conditions will be described.
In the present embodiment, in order to etch the transition metal that is the first substrate, a technique of scraping the metal uniformly and randomly is optimal. As the method, it is desirable to use wet etching with acid or dry etching by reactive ion etching. At this time, the height of the etching needs to be larger than the unevenness of the third substrate, which is a transfer target, and a structure called a texture such as a solar cell generally has an unevenness of 30 nm or more. 30 nm or more is desirable.
　本実施形態において採用する第２基板１４（樹脂支持基板）は、上述した条件を満たすことが可能な任意の材質のものとすることができる。第２基板１２として好適なものは、ＰＭＭＡ（ポリメチルメタクリレート）またはＰＤＭＳ（ポリジメチルシロキサン）である。ＰＭＭＡやＰＤＭＳは、溶媒に溶解させた状態の溶液により、容易に塗布することが可能であり、また、その溶媒を揮発させて樹脂の仮支持膜を形成することも容易である。さらに、第１基板１１の除去のための処理（エッチング処理）にも耐えられる上、第２基板自体を除去することも容易に実施することができる。そしてさらに、グラフェン１０を転写するために要する程度の膜を形成することができる。これらの条件を満たすＰＭＭＡやＰＤＭＳは、本実施形態において第２基板１２（樹脂支持基板）として採用する材質の好適なものである。 The second substrate 14 (resin support substrate) employed in the present embodiment can be made of any material that can satisfy the above-described conditions. A suitable material for the second substrate 12 is PMMA (polymethyl methacrylate) or PDMS (polydimethylsiloxane). PMMA and PDMS can be easily applied with a solution dissolved in a solvent, and it is also easy to volatilize the solvent to form a temporary support film of resin. Furthermore, it can withstand a process (etching process) for removing the first substrate 11 and can easily remove the second substrate itself. Furthermore, a film as much as required for transferring the graphene 10 can be formed. PMMA and PDMS satisfying these conditions are suitable materials used as the second substrate 12 (resin support substrate) in the present embodiment.
　本実施形態において提供されるグラフェン膜では、第１基板の凹凸の形状を引き継ぎ、同じく３０ｎｍ程度の凹凸を有しており、そのため、凹凸のある第３基板上に転写した際には、グラフェン膜の凹凸と第３基板の凹凸が互い違いに入り込み形状にフィットするとともに、グラフェン膜が第３基板に付着することが出来、効率良くグラフェン膜を転写することが出来る。 In the graphene film provided in the present embodiment, the shape of the unevenness of the first substrate is inherited, and has the same unevenness of about 30 nm. Therefore, when transferred onto the uneven third substrate, the graphene film The unevenness of the third substrate and the unevenness of the third substrate enter alternately to fit the shape, and the graphene film can adhere to the third substrate, so that the graphene film can be transferred efficiently.
　ここで、凹凸の高さ指標は例えば走査電子顕微鏡、透過電子顕微鏡、原子間力顕微鏡などによって測定される高低差から算出できる。この方法を用いた一般的な第３基板のテクスチャ構造の凹凸は、例えば太陽電池の受光面側の半導体層では３０ｎｍ程度である。したがって、グラフェン膜の好ましい構成では、好ましくは、凹凸が３０ｎｍ以上とされる。 Here, the height index of the unevenness can be calculated from a height difference measured by, for example, a scanning electron microscope, a transmission electron microscope, an atomic force microscope, or the like. The unevenness of the texture structure of a general third substrate using this method is, for example, about 30 nm in the semiconductor layer on the light receiving surface side of the solar cell. Therefore, in the preferable configuration of the graphene film, the unevenness is preferably 30 nm or more.
　本実施形態において提供されるグラフェン膜は、グラフェンの原子層数が１層以上１０層以下であると好適である。その理由は、グラフェン膜の適用用途に関係している。グラフェンは、特に単層グラフェンにおいて高い移動度を示すことが知られている。他方、グラフェン膜が、光の透過が要求される用途において透明導電膜などとして利用される場合、透過率の点から層数には上限が存在する。具体的には、グラフェンは原子層１層で約２．３％もの高い光吸収を示すため、本実施形態で例えば、透明導電膜としてグラフェン膜を採用すると、１０層を上限とすることが好適である。その場合、本実施形態において提供されるグラフェン膜の膜厚方向の光透過率が７０％以上とすると有利である。
［実施例］
　次に、本実施形態のグラフェン膜の実施例について説明する。実施例１は上述した実施形態に従って作製したグラフェン膜のサンプルである。以下の実施例に示す材料、使用量、割合、処理内容、処理手順、要素または部材の向きや具体的配置等は本発明の趣旨を逸脱しない限り適宜変更することかできる。したがって、本発明の範囲は以下の具体例に限定されるものではない。また、既に説明した図面を引き続き参照する。 The graphene film provided in the present embodiment preferably has 1 or more and 10 or less atomic layers of graphene. The reason is related to the application of the graphene film. Graphene is known to exhibit high mobility, particularly in single layer graphene. On the other hand, when the graphene film is used as a transparent conductive film or the like in applications where light transmission is required, there is an upper limit in the number of layers from the viewpoint of transmittance. Specifically, since graphene exhibits light absorption as high as about 2.3% in one atomic layer, for example, when a graphene film is used as the transparent conductive film in this embodiment, it is preferable that the upper limit is 10 layers. It is. In that case, it is advantageous that the light transmittance in the film thickness direction of the graphene film provided in the present embodiment is 70% or more.
[Example]
Next, examples of the graphene film of the present embodiment will be described. Example 1 is a sample of a graphene film manufactured according to the above-described embodiment. The materials, amounts used, ratios, processing contents, processing procedures, directions of elements or members, specific arrangements, and the like shown in the following examples can be appropriately changed without departing from the gist of the present invention. Therefore, the scope of the present invention is not limited to the following specific examples. Further, reference is made to the already described drawings.
　まず、第１基板１１としては１０ｍｍ角のＣＭＰ研磨（化学的機械研磨）したＣｕフォイル（膜厚１００μｍ）を採用した。この基板の算術平均粗さＲａは、１ｎｍ程度である。この第１基板１１を、塩酸５ｍｌ、過酸化水素５ｍｌ、水２５ｍｌの混合液に１０秒浸漬した後、５分間の流水洗浄し、乾燥させることで、第１基板１１の表面に３０ｎｍの凹凸１１ａを形成した。この第１基板１１をＣＶＤの反応炉に配置し、１×１０－３Ｐａまで真空引きを行った。そして、水素を５Ｐａ（３．８×１０－２Ｔｏｒｒ）導入した状態で、第１基板１１を５０℃／ｍｉｎの昇温レートで１０００℃まで加熱した。その後、第１基板１１を１０００℃に保持した状態で水素の供給を停止し、原料ガスとしてメタンを約４．０×１０２Ｐａ（約３Ｔｏｒｒ）導入した。第１基板１１の基板温度とガス圧を保持した状態で１０ｍｉｎ成膜を行った。成膜後は１００℃／ｓｅｃの冷却レートにて急冷し、第１基板１１にグラフェン１０を成長させた。 First, as the first substrate 11, a 10 mm square Cu polished (chemical mechanical polished) Cu foil (100 μm thick) was employed. The arithmetic average roughness Ra of this substrate is about 1 nm. The first substrate 11 is immersed in a mixed solution of 5 ml of hydrochloric acid, 5 ml of hydrogen peroxide, and 25 ml of water for 10 seconds, washed with running water for 5 minutes, and dried, so that the surface of the first substrate 11 has 30 nm unevenness 11a. Formed. The first substrate 11 was placed in a CVD reactor and evacuated to 1 × 10 −3 Pa. Then, the first substrate 11 was heated to 1000 ° C. at a temperature rising rate of 50 ° C./min with hydrogen introduced at 5 Pa (3.8 × 10 −2 Torr). Thereafter, the supply of hydrogen was stopped while the first substrate 11 was held at 1000 ° C., and methane was introduced at about 4.0 × 10 2 Pa (about 3 Torr) as a source gas. Film formation was performed for 10 minutes while maintaining the substrate temperature and gas pressure of the first substrate 11. After the film formation, the graphene 10 was grown on the first substrate 11 by rapid cooling at a cooling rate of 100 ° C./sec.
　次に、グラフェン１０の表面に、ジククロベンゼンで１０ｗｔ％に溶解したＰＭＭＡ溶液を２０μｌ滴下し、回転数４０００ｒｐｍ、６０秒の条件で、スピンコートした。その後４０℃、３０分間の条件で乾燥させ、ＰＭＭＡ膜による樹脂支持基板として第２基板１２を形成した。 Next, 20 μl of a PMMA solution dissolved in 10 wt% with dichlorobenzene was dropped on the surface of the graphene 10 and spin-coated under the conditions of a rotation speed of 4000 rpm and 60 seconds. Thereafter, the substrate was dried at 40 ° C. for 30 minutes, and a second substrate 12 was formed as a resin support substrate using a PMMA film.
　次いで、塩酸１０ｍｌ、過酸化水素１０ｍｌ、純水５０ｍｌの混合液に浸漬し、第１基板１１としたＣｕフォイルが完全になくなるまでエッチングした。その後、５分間の流水洗浄し、乾燥させることで３０ｎｍの凹凸が付いたグラフェン１０と第２基板１２の積層体を形成した。 Next, the substrate was immersed in a mixed solution of 10 ml of hydrochloric acid, 10 ml of hydrogen peroxide and 50 ml of pure water, and etched until the Cu foil as the first substrate 11 was completely removed. Then, the laminated body of the graphene 10 and the 2nd board | substrate 12 with 30 nm unevenness | corrugation was formed by carrying out running water washing | cleaning for 5 minutes, and making it dry.
　その後、第３基板１３であるテクスチャ付きＳｎＯ/ｇｌａｓｓ（旭硝子製Ａｓａｈｉ－Ｕ）の表面に押し付け、１８０℃、３０分間の条件で加熱した。この加熱により、ＰＭＭＡが軟化し、グラフェン１０を、ＳｎＯ/ｇｌａｓｓ基板である第３基板１３のＳｎＯ表面に密着させた。 Thereafter, the third substrate 13 was pressed against the surface of textured SnO / glass (Asahi-U manufactured by Asahi Glass) and heated at 180 ° C. for 30 minutes. By this heating, the PMMA was softened, and the graphene 10 was brought into close contact with the SnO surface of the third substrate 13 that was a SnO / glass substrate.
　最後に、アセトンにて５分間浸漬することにより、第２基板１２のＰＭＭＡをグラフェン１０の表面から除去した。さらに超純水にて５分間洗浄して、図４のようにグラフェン１０を第３基板１３に配置した、グラフェン膜のサンプルを得た。 Finally, the PMMA of the second substrate 12 was removed from the surface of the graphene 10 by immersing in acetone for 5 minutes. Further, the sample was washed with ultrapure water for 5 minutes to obtain a graphene film sample in which the graphene 10 was disposed on the third substrate 13 as shown in FIG.
　本実施形態に従って作製したグラフェン膜である実施例１サンプルの走査電子顕微鏡像を観察した。グラフェンが均一に転写されていることが判った。ただ顕微鏡写真では、グラフェンと下地との濃淡差が小さく、白黒２値で図示するのは困難なので、図示は省略する。以上により本発明の効果が実証された。 A scanning electron microscope image of the sample of Example 1 which is a graphene film manufactured according to the present embodiment was observed. It was found that the graphene was transferred uniformly. However, in the micrograph, the difference in density between the graphene and the ground is small, and it is difficult to illustrate in black and white, so illustration is omitted. Thus, the effect of the present invention was demonstrated.
　以上、本発明の実施形態を具体的に説明した。上述の実施形態および実施例は、発明を説明するために記載されたものであり、本出願の発明の範囲は、特許請求の範囲の記載に基づいて定められるべきものである。また、各実施形態の他の組合せを含む本発明の範囲内に存在する変形例もまた、特許請求の範囲に含まれるものである。 The embodiment of the present invention has been specifically described above. The above-described embodiments and examples are described for explaining the invention, and the scope of the invention of the present application should be determined based on the description of the scope of claims. Moreover, the modification which exists in the scope of the present invention including other combinations of each embodiment is also included in a claim.
　　１０　グラフェン
　　１１　第１基板
　　１１ａ　表面
　　１２　第２基板
　　１３　第３基板
　　１３ａ　表面
　 10 graphene 11 first substrate 11a surface 12 second substrate 13 third substrate 13a surface

Claims (8)

  1. 遷移金属基板である第１基板の表面に凹凸を形成する工程と、前記第１基板に炭素を含む原料物質を供給することにより、１層以上の炭素原子のシート状の結晶構造を有するグラフェンを成長させる工程と、該グラフェンの表面に接して、樹脂の仮支持膜である第２基板を形成する工程と、前記第１基板を除去する工程と、前記第２基板と前記グラフェンとの積層体を第３基板の表面に対し前記グラフェンの前記第１基板に接していた側の表面を向けて前記積層体を貼り付ける工程と、前記第２基板を除去する工程と、を含むグラフェン膜の製造方法。 A step of forming irregularities on the surface of the first substrate which is a transition metal substrate, and supplying graphene having a sheet-like crystal structure of one or more carbon atoms by supplying a source material containing carbon to the first substrate A step of growing, a step of forming a second substrate which is a temporary support film of resin in contact with the surface of the graphene, a step of removing the first substrate, and a laminate of the second substrate and the graphene A step of attaching the stacked body with the surface of the graphene being in contact with the first substrate with respect to the surface of the third substrate, and the step of removing the second substrate. Method.
  2. 第１基板の表面に凹凸を形成する工程が、ウエットエッチングまたはドライエッチングによって形成される請求項１に記載のグラフェン膜の製造方法。 The method for producing a graphene film according to claim 1, wherein the step of forming irregularities on the surface of the first substrate is formed by wet etching or dry etching.
  3. 第１基板の表面の凹凸が３０ｎｍ以上である請求項１または請求項２のいずれか１項に記載のグラフェン膜の製造方法。 The method for producing a graphene film according to claim 1, wherein the unevenness of the surface of the first substrate is 30 nm or more.
  4. 前記第２基板がＰＭＭＡまたはＰＤＭＳである請求項１に記載のグラフェン膜の製造方法。 The method for producing a graphene film according to claim 1, wherein the second substrate is PMMA or PDMS.
  5. 　前記第３基板が、薄膜太陽電池の受光面側に位置する層である請求項１に記載のグラフェン膜の製造方法。 The method for producing a graphene film according to claim 1, wherein the third substrate is a layer located on a light receiving surface side of the thin film solar cell.
  6. 遷移金属基板が表面に３０ｎｍ以上の凹凸を有し、その形状を引き継ぐことにより、高さ３０ｎｍ以上の凹凸を有して当該基板の表面に接して配置されているグラフェン膜。 A graphene film in which the transition metal substrate has irregularities of 30 nm or more on the surface, and is provided in contact with the surface of the substrate with irregularities of 30 nm or more in height by taking over the shape.
  7. グラフェンの層数が１層以上１０層以下であることを特徴とする請求項６に記載のグラフェン膜。 The graphene film according to claim 6, wherein the number of graphene layers is 1 or more and 10 or less.
  8. 請求項６または請求項７に記載のグラフェンを少なくとも１層有し、膜厚方向の光透過率が７０％以上であるグラフェン膜を用いた透明導電膜。








    　     A transparent conductive film using a graphene film having at least one layer of the graphene according to claim 6 or 7 and having a light transmittance in a film thickness direction of 70% or more.








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