JP2016023128A - Production apparatus of graphene film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production apparatus of a graphene film, with which graphene with higher crystallinity is formed at low temperature and in a short time by solving such problems, being problems of conventional graphene film forming using plasma, that irradiation damage due to ion bombardment is generated and further a metal adheres to a plasma device due to evaporation of the metal in heating a metal base material to high temperature, suppressing generation of the irradiation damage, and at the same time enhancing stability of plasma.SOLUTION: An apparatus with which graphene with high crystallinity can be formed at low temperature and in a short time is provided by preparing: a plasma generator to generate plasma in a treating vessel; a Joule heating device for Joule heating a metal base material for forming a graphene film mounted in the treating vessel; and a vapor scattering prevention device mounted by covering the metal base material for preventing scatter of the vapor evaporated from the metal base material by Joule heating in the treating vessel.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a graphene film manufacturing apparatus for use in a transparent conductive film or the like.

Conductive planar crystals with SP ² bonded carbon atoms are called “graphene”. The graphene is described in detail in Non-Patent Document 1. Graphene is the basic unit of various forms of crystalline carbon films. Examples of crystalline carbon films using graphene include single-layer graphene using one layer of graphene, nanographene that is a stack of several to ten layers of nanometer-sized graphene, and a graphene stack of several to several tens of layers Are carbon nanowalls (see Non-Patent Document 2) that are oriented at an angle close to perpendicular to the substrate surface.

A crystalline carbon film made of graphene is expected to be used as a transparent conductive film or a transparent electrode because of its high light transmittance and electrical conductivity. Furthermore, the carrier mobility of electrons and holes in graphene may be up to 200,000 cm ² / Vs, which is 100 times higher than that of silicon at room temperature. Development of ultra-high-speed transistors aiming at terahertz (THz) operation utilizing the characteristics of this graphene is also underway.

  As for the production method of graphene transparent conductive film, the exfoliation method from natural graphite, the desorption method of silicon by high-temperature heat treatment of silicon carbide, and the formation method on various metal surfaces have been developed. The transparent conductive carbon film using the crystalline carbon film by the method has been studied for a wide variety of industrial applications. Therefore, a film formation method with a high throughput and a large area is desired.

As an example of a method for forming a graphene transparent conductive film, a method by chemical vapor deposition (CVD) on a copper foil surface has been developed (see Non-Patent Documents 3 and 4). This graphene film formation method using copper foil as a base material is based on a thermal CVD method, and methane gas as a raw material gas is thermally decomposed at about 1000 ° C. to form one layer of graphene on the surface of the copper foil. To do.
However, the graphene production method by thermal CVD basically uses a gaseous raw material such as methane gas. In CVD using a gas as a raw material, it is difficult to produce a graphene and form a pattern on a specific part of the base material. Therefore, after forming the graphene on the base material, a process for forming the pattern is performed. There was a need.

  Recently, in order to solve these problems, a resin carbonization is performed by forming a polymethylmethacrylate (PMMA) film on a copper foil by coating and heating it in a mixed gas atmosphere of hydrogen and argon at 800 ° C to 1000 ° C. A method for forming graphene has been developed by this method (see Non-Patent Document 5).

  Recently, a method and apparatus for producing a graphene transparent conductive film suitable for mass production have been developed (see Patent Document 1). In the method for producing a graphene transparent conductive film of this technology, a carbon source material is brought into contact with the surface of a flexible film-forming target having conductivity. The graphene is generated from the carbon source material on the surface of the film formation target by applying an electric current to the film formation target and heating the film formation target to a temperature higher than the graphene generation temperature. That is, this is a thermal CVD method in which graphene is synthesized on the copper foil surface by heating the copper foil to 900 to 1000 ° C. by current heating and exposing it to a mixed gas of argon and hydrogen containing methane gas as a carbon source. However, this method also requires the use of methane gas, a greenhouse gas, to heat the copper foil substrate to near the melting point, and it is difficult to synthesize multilayer graphene with excellent electrical conductivity under the control of the number of layers. .

  In addition, it solves the problem of the high temperature process and the long process time, which is the problem of graphene film formation by the conventional thermal CVD method and resin carbonization method, and new graphene synthesis that forms graphene at a lower temperature in a shorter time The law was developed. In this method, an organic substance such as PMMA or benzotriazole is thinly applied to a metal substrate such as copper foil, and microwave surface wave plasma is irradiated in a gas containing hydrogen under conditions of 500 ° C. or lower. Thereby, it is possible to synthesize | combine graphene on a metal base material (refer patent document 2).

  In addition, without using a carbon-containing gas such as methane gas, a base material made of metal such as copper, which is a metal that is difficult to dissolve carbon, or a trace amount of carbon components adhering to the processing vessel is directly energized and heated. Then, carbon was deposited on the surface of the base material, and a new method for forming a graphene at a lower temperature in a short time and controlling the number of layers by applying a plasma treatment to this was reported (see Non-Patent Document 6). .

JP2013-14484A International Publication No. 2012/108526

Kumi Yamada, Chemistry and Industry, 61 (2008) pp.1123-1127. Y. Wu, P. Qiao, T. Chong, Z. Shen, Adv. Mater. 14 (2002) pp. 64-67. Alfonso Reina, Xiaoting Jia, John Ho, Daniel Nezich, Hyungbin Son, Vladimir Bulovic, Mildred S. Dresselhaus, Jing Kong, Nanoletters, 9 (2009) pp. 30-35. Xuesong Li, Yanwu Zhu, Weiwei Cai, Mark Borysiak, Boyang Han, David Chen, Richard D. Piner, Luigi Colombo, Rodney S. Ruoff, Nano Letters, 9 (2009) pp. 4359-4363. Zhengzong Sun, Zheng Yan, Jun Yao, Elvira Beitler, Yu Zhu, James M. Tour, NATURE, doi: 10.1038 / nature09579. Ryuichi Kato, Kazuo Tsugawa, Yuki Okigawa, Masatou Ishihara, Takatoshi Yamada, Masataka Hasegawa, http://dx.doi.org/10.1016/j.carbon.2014.05.087

  The technique of forming graphene using the copper foil as a base material and using plasma is considered promising as an industrial production method of a graphene transparent conductive film. These methods can form graphene at a lower temperature than thermal CVD, which requires a temperature close to the melting point of copper of 1085 ° C., and the surface of the copper foil can be formed by evaporation or recrystallization of copper during graphene film formation. It has been found that the problem of shape change can be suppressed.

However, the action of forming graphene in the plasma and the accompanying ions contained in the plasma are accelerated by the electric field generated around the substrate and collide with the graphene, causing radiation damage to the graphene There is. In particular, graphene is a carbon film with a thin atomic layer, and the occurrence of irradiation damage due to ion bombardment is a serious problem.
Furthermore, in the method of heating a metal substrate such as copper foil, metal evaporation occurs due to the high temperature of the substrate, and this adheres to the plasma generator, thereby impairing plasma stability or plasma treatment. There has been a problem that the effect of is impaired. For example, when copper foil is heated as a base material, if the temperature of the copper foil exceeds 850 ° C. in a low-pressure atmosphere, copper evaporation occurs, and this adheres to the plasma device, thereby impairing the stability of the plasma, There has been a problem that the effect is impaired.

  The present invention has been made in view of the above circumstances, and is a problem of conventional graphene film formation using plasma, which is the occurrence of irradiation damage due to ion bombardment, and further raises the temperature of a metal substrate. Solves the problem of metal adhesion to the plasma device due to metal evaporation during heating, suppresses the occurrence of radiation damage, and at the same time improves the stability of the plasma, and makes graphene with higher crystallinity at a low temperature for a short time. An object of the present invention is to provide an apparatus for producing a graphene film that can be formed in the following manner.

  As a result of intensive studies to achieve the above object, the inventors of the present invention have developed a heating apparatus for Joule heating of a metal substrate for forming graphene in a graphene film forming apparatus using plasma. It has been found that this problem can be solved by installing a cover around the metal substrate. That is, by installing a cover (carbon activation member) made of a metal such as stainless steel, copper, iridium, platinum, nickel, aluminum, titanium, or a carbon alloy of these metals around the metal base material, The vapor of the metal base material for synthesis is trapped, and the problem of metal adhering to the plasma source and the inner wall of the CVD chamber due to evaporation of the heated metal base material is solved. The present inventors have found that it is possible to form graphene with higher crystallinity at a low temperature in a short time by suppressing ion bombardment from plasma without being directly expected.

The present invention has been completed based on these findings, and is as follows.
[1] A plasma generating device for generating plasma in a processing vessel, a Joule heating device for Joule heating a metal base for film formation of a graphene installed in the processing vessel, and being heated by Joule heating An apparatus for producing a graphene film, comprising: a vapor scattering prevention device provided so as to cover the metallic substrate in order to prevent the vapor evaporated from the metallic substrate from scattering into the processing container.
[2] The apparatus for producing a graphene film according to [1], wherein the metal substrate for forming the graphene film is a copper substrate.
[3] The apparatus for producing a graphene film according to [1] or [2], wherein the vapor scattering prevention device is provided with an opening for introducing a reactive gas.

  According to the apparatus of the present invention, a greenhouse gas methane gas, which is a problem of graphene film formation by the conventional thermal CVD method or resin carbonization method, is a high-temperature process, and the process time is long, and the number of graphene layers In addition to resolving the problem of difficult control, plasma damage caused by ion bombardment of graphene and plasma caused by evaporation of a metal substrate heated to high temperatures It becomes possible to suppress that the effect of the plasma treatment due to the loss of the stability of the plasma due to the adhesion of the metal to the generator is impaired. Since the high-quality graphene transparent conductive film made of highly crystalline graphene can be synthesized by the apparatus of the present invention, the obtained graphene transparent conductive film is a transparent conductive film for touch panel applications, semiconductors such as transistors and integrated circuits Applications to devices or electronic devices, transparent electrodes and electrochemical electrodes that require a large area, biodevices, and the like are possible.

The figure which shows typically one embodiment of the apparatus of this invention Schematic diagram showing a state in which a metal substrate is covered with (a) a non-processed stainless steel plate, (b) a rectangular window processed stainless steel plate, and (c) a circular processed window stainless steel plate. Schematic showing the cross-sectional structure of commercially available copper foil Schematic showing the processed shape of the base material for graphene film formation used in the examples Raman spectrum diagram when film is formed only by Joule heating (with stainless steel plate) covering copper foil substrate (850 ° C, 20 minutes) The figure which shows the Raman spectroscopic spectrum of the graphene which was formed into a film (950 degreeC, 10 minutes) with "stainless steel plate" which covers the copper foil base material The figure which shows the Raman spectroscopic measurement location of the graphene formed into a film on the center part (16mmx16mm) of a copper foil base material The figure which shows the Raman spectroscopic spectrum of the graphene formed into a film (950 degreeC, 10 minutes) without the "stainless steel plate" which covers a copper foil base material The figure which shows the Raman spectroscopic spectrum of the graphene which formed into a film (800 degreeC, 20 minutes) by Joule heating and plasma CVD combined use with "stainless steel plate" which covers copper foil base material The figure which shows the sheet resistance distribution of the graphene which formed into a film (800 degreeC, 20 minutes) by Joule heating and plasma CVD combined use "with a stainless steel plate" which covers a copper foil base material

  The graphene film manufacturing apparatus includes a plasma generation apparatus that generates plasma in a processing container, a Joule heating apparatus for Joule heating a metal substrate for forming a graphene film installed in the processing container, In order to prevent the vapor | steam which is heated by heating and evaporates from the said metal base material into the processing container, it is provided with the vapor | steam scattering prevention apparatus provided covering this metal base material.

Hereinafter, the present invention will be described with reference to the drawings. In addition, this invention is not limited by this.
FIG. 1 is a diagram schematically showing one embodiment of the apparatus of the present invention, in which 101 is a plasma generation chamber, 102 is an antenna, 103 is a dielectric antenna cover, and 104 is a dielectric antenna cover. Metal support member to be supported, 105 is a metal base material, 106 is an electrode for heating and heating the base material, 107 is a power source for heating and heating, 108 is an exhaust pipe, 109 is a raw material gas introduction pipe for plasma processing, and 110 is a processing vessel ( (Chamber), 111 is a current introduction terminal, 112 is a vapor scattering prevention device, 113 is a voltmeter, 114 is plasma, 114 is an RF power source, 116 is an inner wall of the chamber, and 117 is a fixed support base.

  The graphene film manufacturing apparatus shown in FIG. 1 has a metal processing container (110) having an open upper end, and is airtightly connected to the upper end of the processing container (110) via a metal support member (104). A plasma generation device is provided that includes a dielectric antenna cover (103) for introducing the attached high frequency (RF) and an antenna (102) attached to the inside thereof. A 13.56 MHz RF power source (115) is connected to the antenna (102), a necessary gas is introduced into the processing vessel from a plasma processing gas introduction pipe (109), and power from the RF power source is supplied to the antenna. The plasma (114) for plasma processing is excited by the introduction.

In addition, a metal base material (105) is disposed inside the processing container, and the metal base material (105) is connected to the current heating electrode (106) connected to the power source for current heating (107). Is fixed so that the metal substrate can be Joule-heated.
Furthermore, a vapor scattering prevention device (112) is provided so as to cover the metallic substrate.

  The vapor scattering prevention device (112) according to the present invention is a cover (carbon activation member) for a metal substrate (105), and is made of a heated metal by trapping the vapor of the metal substrate for synthesizing graphene. In addition to solving the problem that metal adheres to the plasma source and the inner wall (116) of the CVD chamber due to evaporation of the base material, the plasma generation source is not expected directly from the base material, and ion bombardment from the plasma is suppressed, It is possible to form graphene with higher crystallinity at a low temperature in a short time.

  As described above, the vapor scattering prevention device (112) according to the present invention may be any device that traps the vapor of the metal base material and prevents the plasma generation source from being directly expected from the base material. Although it does not specifically limit, what uses metal, such as stainless steel, copper, iridium, platinum, nickel, aluminum, titanium, and the carbon alloy of those metals is used.

  Further, in the present invention, the metal base material is energized and heated, so it is necessary to install it so as not to be short-circuited by contact with the vapor scattering prevention device (carbon activation member). In the embodiment shown in FIG. 1, the vapor scattering prevention device is grounded (not shown) so as to have the same potential as the processing container (chamber).

The shape of the vapor scattering prevention device (112) in the present invention is to trap the vapor of the metal base material and to cover the metal base material so that the plasma generation source cannot be directly expected from the base material, There is no particular limitation, and in accordance with the shape of the metal substrate, a reaction gas containing carbon active species generated from the raw material gas for graphene film formation (hereinafter simply referred to as “reaction gas”) above the metal substrate. May be installed through a space into which the material is introduced, and may be flat or three-dimensional.
For example, if the metal base material is a quadrangle, a downwardly U-shaped (= concave downward) shape body is set upward according to the shape of the metal base material, and the metal base material If the shape is circular, the circular shape body is processed so as to be recessed downward in the circular peripheral portion thereof, and is set upward according to the shape of the metal substrate.
In addition, as the area of the metal substrate increases, the area of the vapor scatter prevention device increases accordingly, and the vapor scatter prevention device is placed in an optimal position so that evaporation from the metal substrate can be efficiently trapped. Install.

FIG. 2 is a diagram schematically showing an example of a vapor scattering prevention device (carbon activation member) when a rectangular base material is used as the metal base material, and (a) shows a metal base material (105). The example which has arrange | positioned the stainless steel board which has not been processed around is shown. (B) and (c) show the stainless steel plate processed with a rectangular window or a small hole window as the reaction gas introduction hole (118).
In the examples shown in (a) to (c), the left and right sides of the stainless steel plate are opened so that the reaction gas is introduced onto the metal substrate, but only one of them may be opened.

  In the present invention, by adjusting the position and size of the rectangular window or small hole window opened in the vapor scattering prevention device (stainless steel plate), the flow of carbon active species for graphene film formation onto the metal substrate In addition, it is possible to control transport on the metal base material and to control trapping of copper vapor from the metal base material.

In the present invention, the distance between the vapor scattering prevention device (carbon activation member) (112) and the metal substrate (105) is presumed to depend on the area of the metal substrate, the flow of the reaction gas, etc., and is particularly limited. It is not something.
For example, in the examples described later, a tough pitch copper foil having a length of 50 mm and a width of 20 mm shown in FIG. 4 is used as a base material, and a stainless steel shown in FIG. 2A is used as a vapor scattering prevention device (carbon activation member). When the plate (112) is used, the distance between them is 5 mm to 50 mm, preferably 5 mm to 20 mm.

  The apparatus for producing a graphene film of the present invention activates a carbon source by the energy of charged particles or electrons generated by a plasma generation apparatus, and generates a graphene film on a metal substrate, and as a carbon source, Material gas such as methane supplied into the processing vessel (110) through the plasma processing source gas introduction pipe (109) from the outside, or a carbon component contained in the substrate, or adheres to the processing vessel A trace amount of carbon component is used.

According to the graphene film manufacturing apparatus of the present invention, it is possible to form graphene with high crystal quality in a short time compared to the conventional thermal CVD method, resin carbonization method, and graphene synthesis method using plasma treatment. .
Moreover, after growing graphene with the apparatus of the present invention to form a laminate in which graphene is laminated on a metal substrate, the graphene laminate is peeled from the metal substrate to obtain a graphene transparent conductive film You can also. Furthermore, a transparent conductive film can also be obtained by transferring this onto a transparent film such as polyethylene terephthalate (PET).

As the metal substrate for producing the graphene film using the production apparatus of the present invention, copper, iridium, gold or platinum, or a carbon alloy with any of these metals is preferably used. A foil or an electrolytic copper foil is preferably used.
Moreover, it is desirable that the metal base material when producing the graphene film using the production apparatus of the present invention is smooth, and the average surface roughness Ra is 200 to 0.095 nm.

As conditions for heating the substrate used in the present invention, the substrate temperature is preferably 850 ° C. or lower. When using copper foil as a substrate, it is desirable to perform heating slowly in order to suppress changes in the surface shape due to softening of the substrate. For example, if the temperature is raised at about 30 ° C./min, damage to the substrate can be suppressed. However, the heating rate at which graphene is synthesized is not limited to this.
In order to prevent oxidation of the metal substrate, it is important to heat under reduced pressure or under reduced pressure containing hydrogen or a mixed gas of hydrogen and an inert gas. The pressure is desirably 10 Pa or less. Inert gases include helium, neon, argon, and the like.
The heating method is not particularly limited, but current heating is preferable because it is easy to control the heating temperature.

The plasma treatment using the graphene transparent conductive film manufacturing apparatus of the present invention may be a plasma treatment using hydrogen gas under reduced pressure, such as a high frequency inductively coupled plasma treatment, a capacitively coupled high frequency plasma treatment, or a microwave surface wave plasma treatment. , Microwave plasma treatment, DC plasma treatment, or the like can be used.
These plasma power supplies use high-frequency, microwave, DC power supplies, etc., and discharge a source gas at a constant pressure to generate chemically active ions and radicals (excited atoms / molecules). Is done. The plasma CVD technique is a technique in which active particles generated in plasma promote a chemical reaction on the surface of a substrate to form a thin film at a low temperature. On the other hand, in the thermal CVD technique, gas contacts with a substrate having catalytic activity at a high temperature and decomposes for the first time. In the case of a substrate having no catalytic activity, the pyrolysis temperature of the gas at a higher temperature is required. Become. For this reason, the thermal CVD technique is generally a high-temperature process as compared with the plasma CVD technique.

  In order to form a graphene transparent conductive film without changing the surface shape of the metal substrate and without causing metal evaporation, the substrate is heated to a temperature sufficiently lower than the melting point of the metal. At the same time, it is necessary to perform plasma treatment. For example, in the case of a copper foil substrate, it is necessary to perform the treatment at a temperature sufficiently lower than the melting point of copper (1085 ° C.).

Normal microwave plasma treatment is performed at a pressure of 2 × 10 ³ to 1 × 10 ⁴ Pa. At this pressure, the plasma is difficult to diffuse and the plasma concentrates in a narrow region, so that the temperature of the neutral gas in the plasma becomes 1000 ° C. or higher. Therefore, the temperature of a copper foil base material becomes high temperature locally, and copper evaporation from a copper foil surface becomes large, and cannot be applied to the production of graphene. In addition, there is a limit to uniformly expanding the plasma region, and it is difficult to form highly uniform graphene over a large area.
Therefore, in order to keep the temperature of the copper foil substrate during film formation low and to form a highly uniform graphene transparent conductive film over a large area, the mean free of active species in the plasma can be reduced by plasma treatment at a lower pressure. The process becomes longer, and it becomes possible to easily transport active carbon radicals, hydrogen radicals and the like to the substrate. As the conditions for the plasma treatment, the pressure is 50 Pa or less, preferably 2 to 50 Pa, more preferably 3 to 10 Pa.

In the present invention, high-frequency plasma processing or microwave plasma processing that can stably generate and maintain plasma even at 10 ² Pa or less is preferably used.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited to this Example.

(Raman spectroscopy measurement method)
In the verification examples and examples described below, the Raman scattering spectrum was measured. The measuring device is an XploRA type machine manufactured by HORIBA, Ltd., the excitation laser wavelength is 638 nm, the laser beam spot size is 1 μm in diameter, the spectrometer grating is 600, the laser source output is 9.8 mW, A dimmer was not used. The aperture was 300 μm, the slit was 100 μm, and the objective lens was 100 times. The exposure time was 5 seconds, and 5 measurements were integrated to obtain a spectrum.
Non-patent literature (LMMalard, MAPimenta, G) that the peak positions of the 2D band, G band, D band, and D ′ band depend on the number of layers of the graphene film and the excitation wavelength of the laser when measuring the Raman scattering spectrum. Dresselhaus and MSDresselhaus, Physics Reports 473 (2009) 51-87). For example, in the case of a single-layer graphene film using a laser with an excitation wavelength of 514.5 nm, the peak positions of the 2D band, the G band, the D band, and the D ′ band are 2700 cm ⁻¹ , 1582 cm ⁻¹ , 1350 cm ⁻¹ , and 1620 cm ^−1. It is near. The G band is due to the normal six-membered ring, and the 2D band is due to the overtone of the D band. The D band is a peak due to a defect in a normal six-membered ring. The D 'band is also a peak induced by defects, and is thought to be caused by the edge of graphene consisting of several to tens of layers (G. Cancado, MAPimenta, BRANeves, MSSDantas, A. Jorio, Phys. Rev. Lett. 93 (2004) pp. 247401_1-4.). When both G band and 2D band peaks are observed in the Raman scattering spectrum, the film is identified as graphene (see Non-Patent Document 3). In general, it is known that as the number of graphene layers increases, the 2D band shifts to the higher wavenumber side and the half-value width increases. Furthermore, when the excitation wavelength of the laser becomes shorter, the 2D band shifts to the higher wavenumber side.

(Copper foil pretreatment method)
FIG. 3 is a diagram schematically showing a copper foil coated with a commercially available rust preventive agent. As shown in the figure, a commercially available copper foil is composed of a thinly coated rust preventive film (201) and a base material copper foil (202). In the present invention, a copper foil obtained by removing the rust preventive film (201) applied to the base copper foil (202) with a dilute acid was used as a base material. Examples of the rust preventive film include an organic film such as benzotriazole (BTA), an inorganic film such as a zinc film, and the diluted acid includes sulfuric acid.
The processing procedure is as follows.

A method for removing the rust preventive film from the commercially available copper foil will be described. The copper foil is a 6.3 micron thick tough pitch copper foil (manufactured by JX Nippon Mining & Metals) and is rust-proofed with an organic material typified by BTA.
First, the copper foil was processed into a shape suitable for electric heating (see FIG. 4). The size after processing is 50 mm long × 20 mm wide. A method for removing BTA is also described in JP-A-2002-97587 and the like, but it is known that it can be easily removed by dipping in dilute acid. Moreover, the confirmation of the removal can be confirmed by the presence or absence of detection of nitrogen contained in BTA using X-ray photoelectron spectroscopy. In this example, 5 cc of concentrated sulfuric acid (manufactured by Wako Pure Chemical Industries, Ltd., H ₂ SO ₄ ) was diluted to 100 cc with pure water to prepare 5% diluted sulfuric acid, which was used as a rust inhibitor treatment liquid. In this, the processed copper foil base material was immersed for 60 seconds, and the surface antirust material was removed. After thoroughly washing with pure water, it was completely dried to produce a copper foil base material (202) for film formation.

  In the following examples, using the graphene film manufacturing apparatus shown in FIG. 1, the base material energization heating electrode (106) provided inside the processing vessel (110) is used as a metal base material (105). A tough pitch copper foil was fixed, and energization heating and plasma treatment were performed. A voltmeter (113) is connected to the metal current heating electrode (106), and the electric resistance of the metal base material is determined from the voltage at both ends of the metal base material during current heating and the current supplied by the current heating power source (107). The temperature was calculated from the temperature dependence of the electrical resistance. Furthermore, the temperature of the metal substrate was set to a desired value by controlling the current supplied from the power supply for electric heating (107).

  Further, as the vapor scattering prevention device (112), a tough pitch copper as a base material is formed using a stainless steel plate (length in the longitudinal direction of the base material: 50 mm × width 40 mm × height 25 mm) as shown in FIG. Covered the foil. Since the substrate was heated by energization, care was taken not to contact the stainless steel plate and short circuit. The stainless steel plate was grounded so as to have the same potential as the chamber. The distance between the stainless steel plate and the tough pitch copper foil is 15 mm.

(Comparative experiment: only energization heating, no plasma ignition)
1) A tough pitch copper foil was immersed in 5 wt% H ₂ SO ₄ for 1 minute, washed with ion exchange water, and then dried with nitrogen.
2) Install the copper foil base material with “stainless steel plate” covered with a stainless steel plate, and subject the copper base material to annealing (heating) for 10 minutes at 650 ° C., H ₂ 100 sccm, 1 Pa or less only by energization heating. As a result, the tough pitch copper foil was imparted with a flatness having an average surface roughness (Ra) of 10 nm or less, and the grain size of the copper was increased.
3) Subsequently, only by energization heating (10 to 12 W), the base material in which the copper foil base material is covered with the stainless steel plate is kept at 850 ° C., the hydrogen flow rate is 100 sccm, the methane flow rate is 0.2 sccm, and the pressure is 5 Pa. Went. The film formation time was 20 minutes, the energization heating was stopped, the temperature was returned to room temperature, and measured by Raman spectroscopy. FIG. 5 shows the Raman spectrum after film formation. Graphene is not observed at all signals in the range of 1000cm ^-1 ~3000cm ^-1 was not formed. As a result, it has been found that graphene cannot be grown by decomposing methane on a copper substrate only by current heating at 850 ° C. and diffusing carbon active species in a short time.

Example 1
In the following examples, in order to investigate the difference depending on the presence or absence of the stainless steel plate covering the metal substrate in the graphene synthesis by the combined use of the plasma treatment (13.56 MHz) and the electric heating treatment of the metal substrate, the following components are used. Membrane experiments were conducted with “with stainless steel plate” and “without stainless steel plate”.

1) A tough pitch copper foil was immersed in 5 wt% H ₂ SO ₄ for 1 minute, washed with ion exchange water, and then dried with nitrogen.
2) By performing an annealing (heating) treatment for 10 minutes at 650 ° C., H ₂ 100 sccm, 1 Pa or less only by electric heating, the tough pitch copper foil has a flatness with an average surface roughness (Ra) of 10 nm or less. At the same time, the grain size of copper was increased.
3) Subsequently, the base material is kept at 950 ° C. while conducting heating (10 to 12 W), and plasma treatment (1100 W) is performed at a hydrogen flow rate of 100 sccm, a methane flow rate of 0.2 sccm, and a pressure of 5 Pa. Minutes, plasma and electric heating were stopped, and the temperature was returned to room temperature. The difference in crystal quality of the graphene film with and without the stainless steel plate was measured by Raman spectroscopy. Further, after film formation, it was visually confirmed whether or not there was adhesion of copper to the dielectric window (quartz window or alumina window) (103) due to evaporation of the copper foil.

[With stainless steel plate (carbon activation member)]
After coating the copper foil base material (105) with a stainless steel plate (112) and forming a graphene film with the “stainless steel plate”, the dielectric antenna cover (103) (width 110 mm × height 60 mm) was visually observed. As a result, no copper adhesion due to evaporation of the copper foil was observed. On the other hand, on the inside of the stainless steel plate, copper adhesion was observed on all surfaces including the side surface. Furthermore, no copper adhesion was observed on the outside of the stainless steel plate on the side facing the plasma.

  A Raman scattering spectroscopic measurement was performed on graphene formed by coating a copper foil base material with a stainless steel plate and “with a stainless steel plate”. FIG. 6 shows an example of the Raman scattering spectrum of graphene formed on the central part (16 mm × 16 mm) of the copper foil base material shown in FIG. The measurement was performed on five places of a 16 mm × 16 mm sample as shown in FIG. 7 in a state where the synthesized graphene was laminated on the copper foil base material. 6 and FIG. 7 from the respective Raman spectra of the substrate position, the full width at half maximum (FWHM) of the 2D band, the intensity ratio of the 2D band to the G band (I (2D) / I (G)), the D band and the G band Table 1 summarizes the intensity ratio (I (D) / I (G)). From these results, it can be seen from Non-Patent Document 6 that the graphene on the substrate is almost two-layer graphene.

Bands important for the evaluation of graphene by Raman scattering spectroscopy are a 2D band (2665 cm ⁻¹ ), a G band (1598 cm ⁻¹ ), a D band (1342 cm ⁻¹ ), and a D ′ band (1625 cm ⁻¹ ). When both G band and 2D band peaks are observed in the Raman scattering spectrum, the film is identified as graphene (see Non-Patent Document 3). The D band is a peak due to a defect in a normal six-membered ring. Therefore, it is considered that the crystal quality of graphene is worse as the intensity of the D band is larger.
In FIG. 6, the peaks of both the G band and the 2D band are observed at all five measured points. Therefore, the film formed in the present invention is graphene, and two layers from Table 1 and Non-Patent Document 6 are shown. It is clear that it is graphene. In addition, since almost no D band was observed at all five measured locations, it was found that bilayer graphene with very good crystallinity was synthesized.

[No stainless steel plate]
After the graphene film was formed without coating the stainless steel plate with the stainless steel plate and without the stainless steel plate, the dielectric window (103) and the chamber wall were visually confirmed. ) And discoloration due to copper adhesion on the inner wall of the chamber was confirmed. For this reason, in film formation with a “stainless steel plate” where the copper foil base material is covered with a stainless steel plate, the evaporation from the copper is trapped extremely efficiently inside the stainless steel plate, and the copper of the dielectric window of the plasma generating unit is trapped. The adhesion of copper and the adhesion of copper to the inner wall of the chamber were made almost zero. From the above, the effectiveness of the stainless steel copper vapor trap was clarified.

  The Raman scattering spectroscopic measurement of the graphene formed without forming the copper foil base material with the stainless steel plate and “without the stainless steel plate” was performed. An example of the measured Raman scattering spectrum of graphene is shown in FIG. The full width at half maximum of the 2D band, 2D / G ratio, and D / G ratio are shown in Table 2 by Raman spectrum. Non-Patent Document 6 reveals that two-layer graphene is formed on the entire surface of the substrate. The measurement was performed at the same five locations as shown in FIG. 7 in a state where the synthesized graphene was laminated on the copper foil base material.

  In FIG. 8, the peaks of both the G band and the 2D band are observed at all five measured points, and thus it is clear that the film formed by the present invention is graphene. In addition, D bands were observed at all five measured locations. Therefore, it was found that the graphene synthesized without “stainless steel plate” was clearly inferior in crystal quality as compared with the graphene synthesized with “stainless steel plate”.

(Example 2)
In this example, the following experiment was performed in the same manner as in Example 1 except that the temperature was 800 ° C. and the film formation time was 20 minutes.
1) A tough pitch copper foil was immersed in 5 wt% H ₂ SO ₄ for 1 minute, washed with ion exchange water, and then dried with nitrogen.
2) By performing an annealing (heating) treatment for 10 minutes at 650 ° C., H ₂ 100 sccm, 1 Pa or less only by electric heating, the tough pitch copper foil has a flatness with an average surface roughness (Ra) of 10 nm or less. At the same time, the grain size of copper was increased.
3) Subsequently, the substrate was kept at 800 ° C. while conducting heating (10 to 12 W), and plasma treatment (1100 W) was performed at a hydrogen flow rate of 100 sccm, a methane flow rate of 0.2 sccm, and a pressure of 5 Pa. Minutes, plasma and electric heating were stopped, and the temperature was returned to room temperature. A graphene film containing no defects was obtained when covered with a stainless steel plate. The Raman spectrum is shown in FIG.
Further, after film formation, it was confirmed that there was no copper adhesion on the dielectric window (quartz window or alumina window) (103) or the inner wall (115) of the chamber by visual observation as to whether there was copper adhesion due to evaporation of the copper foil.

When both G band and 2D band peaks are observed in the Raman scattering spectrum, the film is identified as graphene (see Non-Patent Document 3).
In FIG. 9, the peaks of both the G band and the 2D band are observed at all five measured points. Therefore, the film formed in the present invention is graphene, and the half value of the 2D band shown in Table 3 is shown in Table 3. overall width (FWHM) is in the range of 24.6cm ^-1 ~32.4cm ^-1, the ratio of the 2D band and G band, becomes 2.2 to 3.8, non-patent document (LM Malard, MA Pimenta, G. Dresselhaus and MS Dresselhaus, Physics Reports 473 (2009) 51-87 and AC Ferrari, JC Meyer, V. Scardaci, C. Casiraghi, M. Lazzeri et al., Phys. Rev. Lett. 97 (2006) 187401) From these, it is clear that these are single-layer graphene. In addition, since no D band was observed at all five measured positions, it was found that single-layer graphene with very good crystallinity was synthesized. From this, it was not possible to form graphene by transporting active carbon on the copper foil only by the current heating at 850 ° C. described in [0044]. It was clarified that high-quality single-layer graphene can be formed on the entire surface of the substrate by transporting and diffusing active carbon on the copper foil even at a low temperature condition of 800 ° C. by using in combination with plasma CVD.

[Sheet resistance measurement and transmittance measurement]
(Sheet resistance of graphene formed in Example 2)
FIG. 10 shows the sheet resistance measured for each point of the substrate. As for the substrate size, the sheet resistance was measured at five locations on a sample of 11 mm × 11 mm. The average value of the sheet resistance was 696 Ω / □, and the transmittance of the film at 550 nm was 97.7%. This transmittance value was consistent with the value reported in RRNair et al., Science 320 (2008) 1308 for single layer graphene. Therefore, by using a combination of Joule heating and plasma CVD at 800 ° C. and providing a cover of a stainless steel plate around the copper foil base material, copper vapor can be prevented from scattering, and there is no defect. We succeeded in synthesizing graphene.

  The graphene film manufacturing apparatus of the present invention can form graphene with high crystal quality in a short time at a low temperature. Therefore, a transparent conductive film for touch panel use, a semiconductor device or an electronic device such as a transistor or an integrated circuit, a wide area It is a very important technology because it can be used for all devices, equipment, and applied products that use graphene such as transparent electrodes, electrochemical electrodes, and biodevices.

DESCRIPTION OF SYMBOLS 101: Plasma generation chamber 102: Antenna 103: Dielectric antenna cover 104: Metal support member which supports a dielectric antenna cover 105: Metal base material 106: Electrode for base material heating heating 107: Power source for power supply heating 108: Exhaust gas Pipe 109: Gas inlet pipe for plasma processing 110: Processing vessel 111: Current introduction terminal 112: Steam scattering prevention device (stainless steel plate)
113: Voltmeter 114: Plasma 115: RF power source +
116: Chamber inner wall 117: Fixed support stand 118: Reactive gas introduction window 201: Rust preventive agent 202: Copper foil

Claims (3)

  A plasma generating device for generating plasma in the processing vessel, a Joule heating device for Joule heating a metal substrate for forming a graphene film installed in the processing vessel, and the metal made by Joule heating. An apparatus for producing a graphene film, comprising: a vapor scattering prevention device provided so as to cover the metal substrate in order to prevent the vapor evaporating from the substrate from scattering into the processing container.   The graphene film manufacturing apparatus according to claim 1, wherein the metal substrate for forming the graphene film is a copper substrate.   The apparatus for producing a graphene film according to claim 1 or 2, wherein the vapor scattering prevention device is provided with an opening for introducing a reactive gas.

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