Composite substrate, method for producing composite substrate, laminate, and method for producing laminate

Abstract

Provided is a composite substrate for graphene formation, the composite substrate having an increased single-layer proportion when a graphene film is formed on the surface thereof.　The composite substrate for producing a graphene film comprises a substrate, an oxide film, and a metal film in this order, wherein the oxide film contains a magnesium oxide, and the lattice spacing calculated from a 220 diffraction line resulting from the magnesium oxide in an XRD chart obtained by performing in-plane XRD measurement is 0.14870 nm or greater.

Description

Composite substrate, method for manufacturing composite substrate, laminate, and method for manufacturing laminate

[0001] The present invention relates to a composite substrate for graphene formation. The present invention also relates to a laminate. More specifically, the present invention relates to a laminate having a graphene film. The present invention also relates to a method for manufacturing the composite substrate and a method for manufacturing the laminate.

[0002] Graphene is one of the allotropes of carbon. ２ Graphene is a sheet-like substance bound together by bonds, and graphite is made up of stacked graphene sheets. Graphene has a hexagonal lattice structure (hexagonal mesh plane) formed by carbon atoms and their bonds.

[0003] It has been reported that graphene may have carrier mobility that exceeds that of silicon (Si) and gallium arsenide (GaAs), and its application to devices such as biosensors, optical sensors, electromagnetic wave sensors, transistors, metasurfaces, and transparent electrodes is being considered.

[0004] As a method for producing graphene, for example, Patent Document 1 discloses a method in which carbon-containing molecules such as methane are supplied to a surface of a metal film of a composite substrate having a substrate, an oxide film, and a metal film in this order, and a graphene film is formed by chemical vapor deposition.

[0005] International Publication No. 2023 / 176648

[0006] In consideration of device applications of graphene, it is preferable to obtain a single-layer graphene film. The present inventors have studied the method for producing graphene using the composite substrate described in Patent Document 1 and found that there is room for improvement in the single-layer ratio of graphene films (the ratio of single-layer graphene films to the total number of graphene films formed).

[0007] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a composite substrate for graphene formation, which has a high single-layer ratio when a graphene film is formed on the surface thereof. Another object of the present invention is to provide a laminate and a method for manufacturing the laminate.

[0008] As a result of intensive investigations into the above-described problems, the present inventors have found that the monolayer ratio of the graphene film can be increased by adjusting the lattice spacing of the oxide film of a composite substrate for graphene formation, and have arrived at the present invention.

[0009] That is, the present inventors have found that the above-mentioned problems can be solved by the following configurations. [1] A composite substrate for producing a graphene film, having a substrate, an oxide film, and a metal film in this order, wherein the oxide film contains magnesium oxide, and in an XRD chart obtained by in-plane XRD measurement, the lattice spacing calculated from the 220 diffraction line derived from the magnesium oxide is 0.14870 nm or more. [2] The composite substrate according to [1], wherein the ratio of the content of oxygen atoms in the oxide film to the content of magnesium atoms in the oxide film is less than 1.0. [3] The composite substrate according to [1] or [2], wherein the metal film contains copper and has a thickness of 500 nm or more. [4] The composite substrate according to [3], wherein the metal film has a lattice spacing of 0.1280 nm or more calculated from 220 diffraction lines derived from a metal having a face-centered cubic crystal structure in an XRD chart obtained by in-plane XRD measurement. [5] The composite substrate according to any one of [1] to [4], wherein the substrate is amorphous. [6] The composite substrate according to [5], wherein the substrate is a quartz substrate. [7] The thermal expansion coefficient of the substrate is 2.0 × 10 －６ (K －１[8] The composite substrate according to any one of [1] to [7], wherein the oxide film has a thickness of 10 to 2000 nm. [9] The composite substrate according to any one of [1] to [8], wherein, when rocking curve analysis of 111 diffraction lines derived from the metal having a face-centered cubic crystal structure of the metal film is performed, the half-width of the 111 diffraction line is 10° or less.

[10] A method for producing the composite substrate for forming graphene according to any one of [1] to [9], comprising forming the oxide film on one surface of the substrate by physical vapor deposition, and forming the metal film on the surface of the oxide film opposite to the substrate side by physical vapor deposition.

[11] A method for producing the composite substrate according to

[10] , wherein the oxide film is formed by sputtering, and the metal film is formed by sputtering.

[12] The method for manufacturing a composite substrate according to

[10] or

[11] , wherein the formation of the oxide film is performed by alternately repeating the formation of a metal magnesium layer and the oxidation of the metal magnesium layer.

[13] A laminate having a substrate, an oxide film, a metal film, and a graphene film in this order, wherein the graphene film has a single layer ratio of 60.00% or more.

[14] The method for manufacturing a laminate according to

[13] , wherein the oxide film is formed on one surface of the substrate by physical vapor deposition, the metal film is formed on a surface of the oxide film opposite to the substrate side by physical vapor deposition, and the graphene film is formed on a surface of the metal film opposite to the oxide film side by chemical vapor deposition.

[0010] According to the present invention, it is possible to provide a composite substrate for graphene formation, which has a high single-layer rate when a graphene film is formed on the surface thereof. Furthermore, according to the present invention, it is also possible to provide a laminate and a method for manufacturing the laminate.

[0011] It is a schematic cross-sectional view showing an example of the configuration of a composite substrate. It is a schematic cross-sectional view showing an example of the configuration of a laminate. It is a diagram for explaining a region of the laminate where Raman spectroscopy measurement is performed. It is a schematic view showing an example of a method for manufacturing the laminate.

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments. Various modifications and substitutions can be made to the following embodiments without departing from the scope of the present invention.

[0013] The meanings of terms used in the present invention are as follows: A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. "Half width" means full width at half maximum (FWHM).

[0014] In this specification, "XRD" is an abbreviation for X-ray diffraction. In this specification, an "XRD chart" is a chart (diagram) obtained by performing an XRD measurement, where the horizontal axis represents the angle and the vertical axis represents the detected intensity of the X-rays. "In-plane XRD" is a method in which X-rays are incident at a grazing angle onto the surface of a measurement sample to be measured, and an XRD chart is obtained by rotating the X-ray incident direction and the diffracted X-ray detector around the axis normal to the surface of the measurement sample. In-plane XRD makes it easy to obtain diffracted rays from lattice planes approximately perpendicular to the surface of the measurement sample. In-plane XRD is also called φ-2θχ scanning. "Out-of-plane XRD" is a method in which an XRD chart is obtained by rotating the X-ray incident direction and the diffracted X-ray detector around the axis parallel to the surface of the measurement sample. In out-of-plane XRD, diffraction lines from lattice planes that are approximately parallel to the surface of the measurement sample are easily obtained. Out-of-plane XRD is also called θ-2θ scanning. Furthermore, "hkl diffraction lines" refer to diffraction lines originating from the (hkl) plane.

[0015] In this specification, the materials constituting the substrate, oxide film, and metal film can be identified by, for example, cutting the composite substrate or laminate in the thickness direction using a focused ion beam (FIB) device and analyzing the cross section of each exposed film. Examples of methods for analyzing the cross section of each film include transmission electron microscope-energy dispersive X-ray analysis (TEM-EDS) and scanning electron microscope-energy dispersive X-ray analysis (SEM-EDS). These methods provide information on the elements contained in each film and their content. In this specification, unless otherwise specified, the content of elements in each film is determined using these methods.

[0016] <Composite Substrate> Fig. 1 is a cross-sectional view schematically showing a composite substrate for graphene formation according to one embodiment of the present invention. As shown in Fig. 1, the composite substrate 1 according to this embodiment has a substrate 2, an oxide film 3, and a metal film 4 in this order.

[0017] In the composite substrate 1 according to this embodiment, the oxide film 3 contains magnesium oxide. In addition, the composite substrate 1 has a lattice spacing of 0.14870 nm or more calculated from the 220 diffraction line derived from magnesium oxide in an XRD chart obtained by performing in-plane XRD measurement.

[0018] Although the mechanism by which the single-layer ratio of a graphene film formed on the surface of the composite substrate of the present invention is high is not entirely clear, the present inventors speculate as follows. In the composite substrate of the present invention, as described above, the lattice spacing of the oxide film is equal to or greater than a predetermined value. Furthermore, the composite substrate of the present invention has a metal film on the oxide film opposite the substrate side. Here, when a graphene film is formed using the composite substrate, the graphene film is formed on the surface of the metal film opposite the substrate side. That is, the graphene film is formed on the metal film while being influenced by the properties of the metal film. The present inventors conducted extensive research into the single-layer ratio of a graphene film and found that adjusting the lattice spacing of the oxide film to the above range and forming a metal film (particularly a metal film containing copper (Cu)) on the oxide film opposite the substrate side is likely to improve the crystallinity of the metal film. It is believed that high crystallinity of the metal film makes it easier to form a single-layer graphene film on the metal film, resulting in a high single-layer ratio of the graphene film.

[0019] Hereinafter, each component of the composite substrate of the present invention will be described in detail. The requirements for the XRD chart obtained by performing the in-plane XRD measurement will be described in detail in the section on the oxide film. Hereinafter, when a graphene film is formed on the surface, the fact that the monolayer ratio of the graphene film is high will also be simply referred to as "the monolayer ratio of the graphene film is high."

[0020] [Substrate] The substrate of the composite substrate of the present invention is not particularly limited as long as an oxide film and a metal film can be formed on one surface thereof. The substrate is preferably amorphous. The substrate being amorphous means that when out-of-plane XRD measurement of the substrate alone is performed, no clear diffraction peaks derived from the substrate are observed, or even if diffraction peaks are observed, the FWHM of the most intense diffraction peak is 1.0° or more in 2θ.

[0021] The substrate is also preferably a quartz substrate. The substrate is also preferably an amorphous quartz substrate. The term "quartz substrate" means that the material constituting the substrate is quartz. Examples of quartz include synthetic quartz and fused quartz, with synthetic quartz being preferred.

[0022] The thermal expansion coefficient of the substrate is 2.0 × 10, which means that the graphene film formed using the composite substrate will be of higher quality. －６ (K －１ ) or less, and 1.5 × 10 －６ (K －１ ) or less is more preferable, and 1.0 × 10 －６ (K －１ The lower limit of the thermal expansion coefficient of the substrate is, for example, −10.0×10 －６ (K －１ In this specification, the thermal expansion coefficient means the thermal expansion coefficient at 300K.

[0023] The substrate may be a commercially available product, and examples of commercially available substrates include "AQ" and "QJ" manufactured by AGC Electronics Inc.

[0024] The thickness of the substrate is preferably 0.2 mm or more, more preferably 0.5 mm or more, and even more preferably 1 mm or more. The upper limit of the thickness of the substrate is, for example, 10 mm.

[0025] The size of the substrate is adjusted appropriately depending on the application of the composite substrate. For example, the area of ​​the substrate is 1 to 1,000,000 mm ２ and 100 to 10,000 mm ２ is preferred.

[0026] [Oxide Film] The composite substrate of the present invention has an oxide film between the substrate and the metal film. The oxide film contains magnesium oxide. Furthermore, in the composite substrate of the present invention, in an XRD chart obtained by performing in-plane XRD measurement, the lattice spacing calculated from the 220 diffraction line derived from magnesium oxide is 0.14870 nm or more. That is, the lattice spacing calculated from the 220 diffraction line derived from magnesium oxide derived from the oxide film is 0.14870 nm or more. The oxide film will be described in detail below.

[0027] As described above, the oxide film contains magnesium oxide. Magnesium oxide refers to a compound containing magnesium (Mg) and oxygen (O). It is also preferable that the crystal structure of magnesium oxide is a rock salt (NaCl) structure. The magnesium oxide content of the oxide film is such that the total content of magnesium (Mg) atoms and oxygen (O) atoms relative to all atoms constituting the oxide film is preferably 80 atomic % or more, more preferably 90 atomic % or more, and even more preferably 95 atomic % or more. The total content may be 100 atomic % or less relative to all atoms constituting the oxide film. That is, the oxide film may be made of magnesium oxide.

[0028] The oxide film may contain an element other than magnesium and oxygen (hereinafter also referred to as "element X1"), such as one or more elements selected from the group consisting of silver (Ag), yttrium (Y), boron (B), aluminum (Al), silicon (Si), calcium (Ca), and iron (Fe).

[0029] The ratio of the oxygen atom content in the oxide film to the magnesium atom content in the oxide film (oxygen atom content / magnesium atom content) is preferably less than 1.0, more preferably 0.99 or less, in order to increase the monolayer ratio of the graphene film. The lower limit of the ratio is preferably 0.90 or more, more preferably 0.95 or more, and even more preferably 0.97 or more. Adjusting the ratio within the preferred range makes it easier to adjust the lattice spacing calculated from the 220 diffraction line derived from magnesium oxide to the preferred range described below. When calculating the ratio, Rutherford backscattering spectroscopy (RBS) is used to determine the magnesium atom content and oxygen atom content in the oxide film. RBS measurement is performed using a Pelletron 3SDH manufactured by National Electrostatics Corporation. The RBS measurement is performed under the following conditions. Incident ions: 2300 keV He ＋＋ Scattering angle: 160° Incident angle: 0° Sample current: 6 nA Irradiation dose: 80 μC

[0030] As described above, the composite substrate (oxide film) of the present invention has a lattice spacing of 0.14870 nm or more calculated from the 220 diffraction line derived from magnesium oxide in an XRD chart obtained by in-plane XRD measurement. In this specification, in-plane XRD is measured using a D8 DISCOVER manufactured by Bruker under the following conditions. Note that X-rays are incident on the metal film side of the composite substrate of the present invention. X-ray source: Cu-Kα ray Output: 45 kV-120 mA Incident optical system: multilayer mirror, 0.2 mm slit, and Soller slit (0.5°) Receiving optical system: Soller slit (0.5°) Detector: multimode detector EIGER 0D mode Scanning range (2θ): 35 to 80° Step width: 0.05° Step time: 2.0 s / step Incident angle: the angle in the range of 1.6 to 3.0° with respect to the substrate surface at which the intensity of the 220 diffraction line derived from magnesium oxide in the XRD chart is highest

[0031] When the in-plane XRD measurement is performed, an XRD chart is obtained in which the horizontal axis represents the angle (2θ) and the vertical axis represents the detected intensity of X-rays. In the XRD chart, the 220 diffraction line derived from magnesium oxide is observed. The 220 diffraction line derived from magnesium oxide is usually observed at 2θ of approximately 61 to 64°. In the composite substrate of the present invention, the lattice spacing calculated from the 220 diffraction line derived from the magnesium oxide is 0.14870 nm or more. The lattice spacing can be calculated using the following formula (1): (1) d = λ / (2 sin θ) In formula (1), d is the lattice spacing, expressed in nm. In formula (1), λ is the wavelength of the X-rays used in the measurement, expressed in nm. In this specification, λ is 0.15405 nm. In formula (1), θ is half the value of the peak position (2θ) of the 220 diffraction line derived from magnesium oxide, expressed in °. The peak position of the diffraction line is read at the peak top position where the detected intensity is greatest.

[0032] Using the above procedure, the lattice spacing (d in formula (1)) calculated from the 220 diffraction line derived from magnesium oxide is calculated. The lattice spacing is 0.14870 nm or more, and is preferably 0.14880 nm or more, more preferably 0.14890 nm or more, and even more preferably 0.14900 nm or more, in order to increase the monolayer ratio of the graphene film. The lattice spacing is often 0.15340 nm or less, and preferably 0.15000 nm or less. The lattice spacing can be adjusted, for example, by the type and content of the element X1 contained in the oxide film. The lattice spacing can also be adjusted, for example, by the ratio of the content of oxygen atoms in the oxide film to the content of magnesium atoms in the oxide film.

[0033] The thickness of the oxide film is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 50 nm or more. The thickness of the oxide film is preferably 3,000 nm or less, more preferably 2,000 nm or less, even more preferably 1,500 nm or less, particularly preferably 1,200 nm or less, and most preferably 500 nm or less. The thickness of the oxide film is determined by observing the cross section of the composite substrate of the present invention using a scanning electron microscope (SEM) and measuring the thickness of the oxide film at, for example, 50,000x magnification. The measurement points are five, and the arithmetic average value is taken as the thickness of the oxide film. An example of an SEM is the "SU-70" manufactured by Hitachi High-Technologies Corporation.

[0034] The substrate and the oxide film are preferably disposed adjacent to each other. That is, the oxide film is preferably formed directly on one surface of the substrate. The method for forming the oxide film will be described in detail later.

[0035] [Metal Film] The composite substrate of the present invention has a metal film on the side opposite to the substrate side of the oxide film. The metal film is not particularly limited as long as graphene can be produced on its surface, but it preferably contains copper (Cu) or nickel (Ni), and more preferably contains copper. When the metal film contains copper, the content of copper atoms relative to all atoms constituting the metal film is preferably 80 atomic % or more, more preferably 90 atomic % or more, and even more preferably 95 atomic % or more. The content of copper atoms may be 100 atomic % or less relative to all atoms constituting the metal film. That is, the metal film may be made of copper.

[0036] When the metal film contains copper, the metal film may contain an element other than copper (hereinafter also referred to as "element X2"), such as one or more elements selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and iron (Fe).

[0037] It is also preferable that the metal film has a face-centered cubic crystal structure. It is also preferable that the metal film has a lattice spacing of 0.1280 nm or more, calculated from the 220 diffraction line derived from the metal having a face-centered cubic crystal structure, in an XRD chart obtained by performing in-plane XRD measurement. It is also preferable that the copper content in the metal film is within the above-mentioned preferred range and satisfies the above-mentioned lattice spacing requirement. The method for measuring in-plane XRD is the same as the method for measuring the oxide film. The method for calculating the lattice spacing is also the same as the method described above for the oxide film. The lattice spacing is often 0.1300 nm or less.

[0038] Furthermore, when rocking curve analysis of the 111 diffraction line originating from the metal having a face-centered cubic crystal structure of the metal film is performed, the half-width of the 111 diffraction line is preferably 10° or less, more preferably 7.0° or less. The half-width of the 111 diffraction line is often 0.1° or more, preferably 1.0° or more. Note that the (111) plane of the metal having a face-centered cubic crystal structure is likely to match with the hexagonal mesh plane formed by the carbon atoms and the bonds of the carbon atoms of graphene, and a small half-width of the 111 diffraction line (high crystallinity) tends to result in a higher monolayer ratio of the graphene film.

[0039] In this specification, the rocking curve analysis of the 111 diffraction ray is performed by the following procedure. First, the 111 diffraction ray is measured by out-of-plane XRD. In this specification, the out-of-plane XRD is performed using a D8 DISCOVER manufactured by Bruker under the following conditions. The X-ray is incident on the metal film side of the composite substrate of the present invention. X-ray source: Cu-Kα ray Output: 45 kV-120 mA Incident side optical system: multilayer mirror, 0.5 mm slit, and 0.5 mmφ collimator Receiving side optical system: OPEN Detector: multimode detector EIGER 2D mode Scanning range (2θ): 30 to 95° Step width: 0.02° Step time: 0.05 s / step

[0040] The peak positions of the 111 diffraction lines originating from the metal having a face-centered cubic crystal structure are identified using the above procedure. The peak positions are determined in the same manner as for the peak positions of oxide films. From the peak positions of the 111 diffraction lines, a rocking curve is obtained by integrating in the 2θ direction within the range of ±2.0° for 2θ and within the range of 251 to 289° for the tilt angle γ.

[0041] The thickness of the metal film is preferably 100 nm or more, more preferably 500 nm or more, even more preferably 1000 nm or more, particularly preferably 1500 nm or more, and most preferably 1800 nm or more. The thickness of the metal film is preferably 5000 nm or less, more preferably 4000 nm or less. It is also preferable that the copper content in the metal film is within the above-mentioned preferred range and that the metal film has the above-mentioned preferred thickness.

[0042] <Method for manufacturing composite substrate> The method for manufacturing a composite substrate for graphene formation of the present invention is not particularly limited as long as the lattice spacing of the oxide film falls within the above-mentioned predetermined range. For example, an example of a method for manufacturing a composite substrate of the present invention is a method in which an oxide film is formed on one surface of a substrate by physical vapor deposition, and a metal film is formed on the surface of the oxide film opposite the substrate side by physical vapor deposition. Preferred aspects of the substrate, the oxide film, and the metal film to be formed are as described above. Hereinafter, the step of forming an oxide film on one surface of a substrate by physical vapor deposition will also be referred to as the "oxide film formation step." Furthermore, hereinafter, the step of forming a metal film on the surface of the oxide film opposite the substrate side by physical vapor deposition will also be referred to as the "metal film formation step."

[0043] [Oxide Film Forming Step] In the oxide film forming step in the above-described example of the composite substrate manufacturing method, an oxide film is formed by a physical vapor deposition (PVD) method. Methods for performing the oxide film forming step include known PVD methods, such as evaporation, sputtering, pulsed laser deposition (PLD), ion plating, and molecular beam epitaxy (MBE), with sputtering being preferred.

[0044] Targets used in the PVD method include metallic magnesium and magnesium oxide. When the target used in the PVD method is metallic magnesium, it is preferable to introduce oxygen gas into the atmosphere used in the PVD method. Furthermore, by adjusting the amount of oxygen gas introduced, the ratio of the oxygen atom content in the oxide film to the magnesium atom content in the oxide film (oxygen atom content / magnesium atom content) can be adjusted to fall within the above-mentioned preferred range.

[0045] When the oxide film formation step is performed by sputtering, DC sputtering, AC sputtering, magnetron sputtering, pulse sputtering, and digital sputtering are available, with digital sputtering being preferred. Digital sputtering refers to a method in which a thin metal thin film is repeatedly exposed to a reactive gas or the like to obtain a thin film of a desired composition. When the oxide film formation step is performed by digital sputtering, it is preferable to alternately form and oxidize a metal magnesium layer. Adjusting the oxidation conditions for the metal magnesium layer makes it easy to adjust the lattice spacing of the oxide film to fall within the above-mentioned range. Adjusting the oxidation conditions for the metal magnesium layer also makes it easy to adjust the ratio of the oxygen atom content in the oxide film to the magnesium atom content in the oxide film (oxygen atom content / magnesium atom content) to fall within the above-mentioned preferred range.

[0046] A more specific method for implementing the digital sputtering method involves, for example, placing a substrate in a first chamber under an inert gas atmosphere, depositing a metal thin film using a sputtering target made of metal, and then transferring the substrate to a second chamber under a mixed gas atmosphere of inert gas and oxygen gas to oxidize the metal thin film. This metal thin film deposition and oxidation process is repeated to form a metal oxide film of a desired thickness. The ratio of the volumetric supply of oxygen gas to the total volumetric supply of inert gas and oxygen gas is preferably 80% or less, more preferably 70% or less, and even more preferably 60% or less. This ratio is preferably 20% or more, more preferably 30% or more, and even more preferably 40% or more. Adjusting this ratio within the preferred range facilitates adjusting the ratio of the oxygen atom content in the oxide film to the magnesium atom content in the oxide film (oxygen atom content / magnesium atom content) within the preferred range.

[0047] The manufacturing conditions for forming an oxide film by sputtering may be adjusted appropriately depending on the thickness of the oxide film to be formed, etc. The substrate temperature in the heat treatment is, for example, 150 to 600° C., preferably 300 to 500° C. The heat treatment time is, for example, 1 to 300 minutes.

[0048] After forming the oxide film by the above method, it is preferable to perform a post-heat treatment. This is because the post-heat treatment further improves the orientation of the oxide film. The temperature of the post-heat treatment is, for example, 200 to 700°C, and preferably 300 to 500°C. The time of the post-heat treatment is, for example, 1 to 300 minutes.

[0049] [Metal Film Forming Step] In the metal film forming step in the above-described example of the composite substrate manufacturing method, a metal film is formed on the surface of the oxide film opposite the substrate side by a PVD method. Methods for performing the metal film forming step include known PVD methods, such as sputtering, pulsed laser deposition (PLD), ion plating, and molecular beam epitaxy (MBE), with sputtering being preferred.

[0050] The conditions for heat treatment of the oxide film-coated substrate when forming a metal film by sputtering may be adjusted as appropriate depending on the types of substrate, oxide film, and metal film, the thickness of the metal film, etc. The substrate temperature during heat treatment is, for example, 20 to 800° C., preferably 200 to 500° C. The heat treatment time is, for example, 1 to 300 minutes.

[0051] After forming the metal film by the above method, it is preferable to perform a post-heat treatment. This is because the post-heat treatment further improves the orientation of the metal film. The temperature of the post-heat treatment is, for example, 200 to 1000°C, and preferably 500 to 700°C. The time of the post-heat treatment is, for example, 1 to 300 minutes.

[0052] In the example of the method for producing a composite substrate of the present invention, it is also preferable to combine the preferred embodiment of the oxide film forming step and the preferred embodiment of the metal film forming step described above.

[0053] <Uses of Composite Substrate> The composite substrate of the present invention is preferably used for producing a graphene film because it has a high graphene monolayer rate. More specifically, it is preferably used for forming a graphene film on the surface of the composite substrate of the present invention opposite the substrate side of the metal film. Hereinafter, a method for forming a graphene film using the composite substrate of the present invention will be described.

[0054] An example of a method for forming a graphene film using the composite substrate of the present invention is a method of contacting a carbon raw material with the surface of a metal film of the composite substrate. A preferred method for forming a graphene film is chemical vapor deposition (CVD), in which graphene is grown by contacting gaseous carbon-containing molecules with the surface of a metal film under a pressure equal to or lower than atmospheric pressure. That is, a preferred method for forming a graphene film using the composite substrate of the present invention is a method in which a graphene film is formed by chemical vapor deposition (CVD) on the surface of the metal film of the composite substrate opposite to the oxide film side. Furthermore, thermal CVD, which is performed while heating, is preferred as the CVD method.

[0055] Examples of carbon-containing molecules used to form graphene films include hydrocarbons and heteroatom-containing molecules. Hydrocarbons with 10 or fewer carbon atoms are preferred, with 5 or fewer carbon atoms being more preferred. Specific examples of hydrocarbons include methane, ethane, ethylene, acetylene, propane, propylene, butane, butadiene, pentane, pentene, cyclopentadiene, hexane, cyclohexane, benzene, and toluene. These may be used alone or in combination. Examples of heteroatom-containing molecules include heteroatom-containing hydrocarbons with 10 or fewer carbon atoms, with 5 or fewer carbon atoms being more preferred and containing a heteroatom selected from oxygen, nitrogen, and boron. Specific examples of heteroatom-containing molecules include alcohols such as methanol and ethanol, and carbon monoxide. In CVD, the carbon-containing molecules are preferably supplied at a constant pressure into a chamber containing a composite substrate having an epitaxial metal film on its surface. The carbon-containing molecules may be supplied into the chamber together with an inert gas such as helium or argon, and hydrogen gas. The pressure of the carbon-containing molecules in the chamber is, for example, atmospheric pressure or less, and the pressure may be 10 －５ ~10 ５ Pa is preferred, 10 －３ ~10 ５ Pa is more preferred.

[0056] The CVD is preferably thermal CVD performed while heating. The heat treatment temperature in thermal CVD is preferably 300 to 1200°C, more preferably 500 to 1100°C, in terms of a fast graphene film formation rate and a graphene film with few defects. The heat treatment time is preferably 1 to 300 minutes, more preferably 10 to 120 minutes. Examples of heating means for the heat treatment include induction heating, radiant heat, laser, infrared rays, microwaves, plasma, and ultraviolet rays.

[0057] Prior to forming a graphene film by CVD, it is also preferable to hydrogen-anneal the metal film on the composite substrate at a temperature lower than that used for CVD. Hydrogen annealing reduces the surface of the metal film, improving the crystallinity of the surface of the metal film at the high temperatures used for CVD. Specifically, hydrogen annealing at low temperatures suppresses metal aggregation or the formation of pits on the surface of the metal film, facilitating the epitaxial growth of a large-area graphene film. It is also effective to perform hydrogen annealing at a temperature used for CVD after performing hydrogen annealing at low temperatures. The composite substrate is placed in a chamber used for CVD and heated to perform hydrogen annealing. The hydrogen annealing temperature is, for example, 300 to 1100°C. The annealing time is preferably 30 to 300 minutes, as this improves the crystallinity of the metal film and the quality of the graphene film. During hydrogen annealing, it is preferable to supply hydrogen to the chamber together with an inert gas. The hydrogen supply rate is, for example, 10 to 600 sccm. It should be noted that "sccm" represents the flow rate under standard conditions, that is, mL / min at 0° C. and atmospheric pressure.

[0058] By the above-described procedure, a graphene film is formed on the composite substrate. The graphene film is a sheet-like member having a hexagonal lattice structure made of carbon atoms. The number of graphene sheets in the graphene film is preferably three or less, more preferably one or two, and even more preferably one.

[0059] The size of the graphene film in the in-plane direction is adjusted appropriately depending on the application of the laminate or the graphene film, but is, for example, 1 to 1,000,000 mm ２ is.

[0060] The thermal expansion coefficient of graphene is (-8.0±0.7) × 10 －６ (K －１ ), and it is preferable that the thermal expansion coefficient of the graphene film is also in the above range. In the laminate, the difference between the thermal expansion coefficient of the substrate and the thermal expansion coefficient of the graphene film is 2×10 －６ (K －１ ) or less is preferable, and 1 × 10 －６ (K －１ ) The following is more preferred.

[0061] The carrier mobility of the graphene film is 1000 (cm ２ / V·s) or more, and 3000 (cm ２ A graphene film having a carrier mobility in the above range is excellent in various properties such as device characteristics as a sensor and a transistor, and SPP (surface plasmon polariton) radio wave characteristics. The upper limit of the carrier mobility of the graphene film is not particularly limited, but is preferably 200,000 (cm ２ / V·s) or less, and 20000 (cm ２ / V·s) or less.

[0062] <Laminate> The laminate of the present invention has a substrate, an oxide film, a metal film, and a graphene film, in this order. The graphene film in the laminate of the present invention has a single-layer ratio of 60.00% or more. The laminate of the present invention will be described below.

[0063] Fig. 2 is a cross-sectional view schematically showing an example of the laminate of the present invention. As shown in Fig. 2, the laminate 6 of the present invention has a composite substrate 1 having a substrate 2, an oxide film 3, and a metal film 4 in this order, and a graphene film 5 disposed on the surface of the metal film 4 of the composite substrate 1. The composite substrate 1, substrate 2, oxide film 3, and metal film 4 of the laminate 6 have been described above, and preferred embodiments are also as described above. The graphene film will now be described.

[0064] [Graphene Film] The graphene film in the laminate of the present invention has a single layer ratio of 60.00% or more.

[0065] In this specification, the single-layer ratio of a graphene film is calculated by the following method. First, a laminate to be measured is prepared. The prepared laminate is observed with an optical microscope to identify a region where a metal film is at least partially present (metal film region). Next, the metal film region is equally divided into nine parts. For example, if the metal film region is square, the metal film region is divided into thirds along one side and then into thirds along a direction perpendicular to the side. As a specific example, the square-shaped metal film region shown in FIG. 3 (the hatched area in FIG. 3 ) is divided into thirds in the left-right direction and the top-bottom direction of the page, resulting in regions A1 to A9. Raman spectroscopy is performed on regions A1 to A9 other than the regions including the vertices of the square-shaped metal film region. That is, Raman spectroscopy is performed on regions A2, A4, A5, A6, and A8 out of regions A1 to A9 shown in FIG. 3 .

[0066] In this specification, Raman spectroscopy is performed using a microscopic laser Raman device (Horiba, Ltd., LabRAM HR800). The measurement conditions are as follows: excitation light wavelength: 532 nm, excitation light irradiation diameter: 2.5 μm, excitation light output: 400 mW, slit width: 100 μm, and grating: 600 g / mm.

[0067] The Raman spectroscopy measurement is performed at any nine points within a predetermined range in each of the regions (regions A2, A4, A5, A6, and A8). A Raman spectrum is obtained by performing the Raman spectroscopy measurement. The predetermined range can be, for example, a 1.11 mm square range from the center of the 3.33 mm square region A2. The nine-point measurement can be performed within a range that is 33.3% of the maximum length of each of the regions. Even when the metal film region is circular, each region can be set in the same manner as above, and the measurement points can be determined. When a Raman spectrum of a graphene film is obtained, peaks corresponding to the G band, which originates from the in-plane motion of carbon atoms in the graphene film, and the 2D band (also called the G' band), which originates from second-order phonon scattering, are observed. The G band is observed at 1590 cm －１ The 2D band is observed around 2700 cm－１ The D band, which is caused by the disorder and defects in the graphene film, is observed around 1350 cm －１ At the nine measurement points in each of the above regions, the G-band peak intensity I Ｇ , the peak intensity of the 2D band I ２Ｄ The ratio (I ２Ｄ / I Ｇ That is, Raman spectroscopy was performed at a total of 45 points, and the above I ２Ｄ / I Ｇ Calculate the above I ２Ｄ / I Ｇ is 1 or more, the graphene film is determined to be a single layer at that measurement point.

[0068] On the other hand, when a G-band peak is observed in the Raman spectrum obtained by the above-mentioned Raman spectroscopy measurement, it suggests the presence of a compound containing sheet-like carbon atoms at that measurement point. It is also understood that graphene films are not formed on substrates or oxide films, but only on metal films. Therefore, when a G-band peak is observed in the Raman spectrum, it can be said that a metal film and a compound containing sheet-like carbon atoms are present at that measurement point.

[0069] In the laminate of the present invention, the single layer ratio of the graphene film is 60.00% or more. The single layer ratio of the graphene film is determined by observing a peak of the G band and measuring the I ２Ｄ / I Ｇ is 1 or more, divided by the number of measurement points (45 measurement points) at which a G band peak is observed, and multiplied by 100. In the laminate of the present invention, the monolayer ratio of the graphene film is preferably 65.00% or more, more preferably 70.00% or more, and even more preferably 80.00% or more. The monolayer ratio of the graphene film may be 100.00%, and is often 98.00% or less.

[0070] In the laminate of the present invention, when determining the single layer ratio of the graphene film, ２Ｄ / IＧ The arithmetic mean value of the values ​​is preferably 1.10 or more, more preferably 1.20 or more, and even more preferably 1.30 or more. ２Ｄ / I Ｇ The arithmetic mean value of the values ​​is often 7.00 or less, and may be 5.00 or less.

[0071] The preferred properties of the graphene in the laminate of the present invention, other than the number of graphene sheets, are as described above in the section on uses of the composite substrate.

[0072] [Other Layers] The laminate of the present invention may optionally have layers other than the composite substrate (substrate, oxide film, and metal film) and the graphene film. Examples of other layers that the laminate may have include an electrode, an insulating layer, and a protective layer.

[0073] Hereinafter, a method for producing a laminate of the present invention will be described with reference to the drawings. Fig. 4 is a schematic diagram showing an example of a method for producing a laminate 10 of the present invention. The laminate 10 of the present invention shown in Fig. 4 has a graphene film 15 having a shape corresponding to the pattern shape of a resist film 16 described below.

[0074] 4A, a composite substrate 11 is prepared, which has a substrate 12, an oxide film 13, and a metal film 14 in this order. The composite substrate 11 is as already described.

[0075] 4B, a resist film 16 is patterned on the surface of the metal film 14. The resist film 16 can be formed using known techniques such as photolithography and electron beam lithography.

[0076] Next, as shown in FIG. 4( c), the portion of the metal film 14 that is not covered with the resist film 16 is removed together with the oxide film 13 disposed thereunder. The metal film 14 and the oxide film 13 can be removed by contacting them with a treatment liquid such as hydrochloric acid, an aqueous solution of iron chloride, or hydrofluoric acid. The type of treatment liquid is appropriately selected from known liquids depending on the type of oxide film and metal film. Examples of contacting methods include immersing the laminate in the treatment liquid at a temperature of 0 to 100°C for 10 minutes to 1 week. Alternatively, the oxide film and the metal film may each be removed by separate, independent treatments.

[0077] 4(d), the resist film 16 disposed on the surface of the metal film 14 is removed. The resist film 16 can be removed using a known developer such as an organic solvent or an alkaline solution depending on the material constituting the resist film 16.

[0078] 4( e), a graphene film 15 is formed on the surface of the metal film 14, thereby producing a stack 10 having, in this order, the substrate 12, the oxide film 13, the metal film 14, and the graphene film 15. The method for forming the graphene film 15 is as already described.

[0079] <Method for Producing Laminate> One embodiment of the method for producing a laminate of the present invention is a method for forming a graphene film on the surface of a metal film of a composite substrate opposite to the oxide film side by chemical vapor deposition (CVD). The method for producing a laminate of the present invention may also include the method for producing the composite substrate. That is, one embodiment of the method for producing a laminate of the present invention is a method for forming the oxide film on one surface of the substrate by physical vapor deposition, forming the metal film on the surface of the oxide film opposite to the substrate side by physical vapor deposition, and forming the graphene film on the surface of the metal film opposite to the oxide film side by chemical vapor deposition. Specific methods and preferred embodiments of the method for forming an oxide film, the method for forming a metal film, and the method for forming a graphene film in the method for producing a laminate are as described above.

[0080] <Applications of Laminate> The graphene film of the laminate of the present invention has a high single-layer ratio and the properties of the graphene film are fully exhibited, and therefore the laminate is preferably applied to devices such as biosensors, optical sensors, electromagnetic wave sensors, transistors, metasurfaces, and transparent electrodes.

[0081] The present invention will be described in more detail below based on examples. The materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the examples shown below. Note that Examples 1 and 4 described below are comparative examples, and Examples 2 and 3 are working examples. Below, Example 2 will be described first, followed by Examples 3, 1, and 4, in that order.

[0082] Example 2 Composite Substrate The composite substrate of Example 2 was obtained by the following procedure. First, a 50 mm square substrate with a thickness of 0.5 mm and a thermal expansion coefficient of 0.6×10 －６ (K －１ A synthetic quartz substrate (manufactured by AGC Electronics Inc.) was prepared.

[0083] Next, the substrate was fixed to a rotating jig in the chamber of a load-lock sputtering system (RAS-1100BII, manufactured by Shincron), and a thin Mg film was formed using an Mg target as the sputtering target. Subsequently, a mixed gas of oxygen gas and an inert gas was introduced into the radical source to oxidize the thin Mg film. The rotating jig was rotated, and the two processes of thin Mg film formation and oxidation were repeatedly repeated to form a magnesium oxide film with a thickness of approximately 100 nm. Specific sputtering conditions for the magnesium oxide film were as follows:

[0084] (Magnesium oxide film formation conditions) Target: Mg (3N) Sputtering gas: Ar gas (flow rate: 150 sccm) Input power: 6 kW Reactive gas: O ２ (flow rate: 40 sccm) and Ar gas (flow rate: 40 sccm) RF power: 3 kW Film formation pressure: 0.18 Pa Rotation speed: 100 rpm

[0085] After forming a magnesium oxide film by post-oxidation sputtering (digital sputtering), the substrate with the magnesium oxide film was annealed in an air atmosphere at 300° C. for 30 minutes. By the above procedure, an oxide film was formed on the substrate.

[0086] Metallic Cu was sputtered onto the surface of the formed oxide film opposite to the substrate side. Specifically, sputtering was repeated to form a Cu film with a thickness of approximately 1000 nm on the surface of the magnesium oxide film. Specific sputtering conditions for the Cu film were as follows:

[0087] (Cu film formation conditions) Target: Cu Sputtering gas: Ar gas (flow rate: 150 sccm) Input power: 500 W Film formation pressure: 0.97 Pa Film formation temperature: 270° C.

[0088] [Measurement] In-plane XRD measurement was performed on the obtained composite substrate of Example 2 using the procedure described above, and the lattice spacing calculated from the 220 diffraction line derived from magnesium oxide was obtained. The ratio of the oxygen atom content in the oxide film to the magnesium atom content in the oxide film was also calculated using the method described above. Furthermore, the lattice spacing calculated from the 220 diffraction line derived from the metal (Cu) having a face-centered cubic crystal structure of the metal film was obtained using the method described above. Additionally, when rocking curve analysis of the 111 diffraction line derived from the metal (Cu) having a face-centered cubic crystal structure of the metal film was performed using the method described above, the half-width of the 111 diffraction line was obtained.

[0089] [Graphene Film Formation] A graphene film was formed on the surface of the metal film of the composite substrate of Example 2 by CVD to obtain a laminate. Specifically, a horizontal tubular furnace was used, and the composite substrate of Example 2 was placed in the center of a quartz tube attached to the tubular furnace. The composite substrate placed in the quartz tube was heated to 1050°C in an Ar atmosphere and then annealed with hydrogen, and the atmosphere inside the quartz tube was replaced with Ar. Next, methane and hydrogen were flowed into the quartz tube as carbon raw materials while maintaining the temperature to form a graphene film. Next, the atmosphere inside the quartz tube was replaced with Ar, and the substrate with the graphene film formed thereon was slowly cooled. The flow rate of argon gas during the heating and cooling processes was approximately 500 sccm. The flow rates of argon gas and hydrogen gas during hydrogen annealing were 500 sccm and 20 sccm, respectively. The flow rates of methane gas and hydrogen gas during CVD were 0.05 sccm and 20 sccm, respectively.

[0090] The obtained graphene film was subjected to Raman spectroscopy by the method described above, and the values ​​shown in the table below, such as the monolayer ratio, were obtained.

[0091] Example 3 A composite substrate of Example 3 was obtained in the same manner as in Example 2, except that the thickness of the formed metal film was 2000 nm, and the same measurements were performed. In addition, a graphene film was formed in the same manner as in Example 2, and Raman spectroscopy measurement was performed.

[0092] Example 1 The composite substrate of Example 1 was obtained in the same manner as in Example 3, and the same measurements were performed, except that a metal film was formed directly on the substrate without forming an oxide film in the procedure of Example 3. Furthermore, a graphene film was formed in the same manner as in Example 3, and Raman spectroscopy measurement was performed.

[0093] Example 4 In the procedure of Example 3, the reactive gas used in forming the oxide film was changed to O ２ A composite substrate of Example 4 was obtained in the same manner as in Example 3, except that only the gas was added and the flow rate was set to 80 sccm, and the same measurements were performed. In addition, a graphene film was formed in the same manner as in Example 3, and Raman spectroscopy measurement was performed.

[0094] <Results> Table 1 shows the manufacturing conditions and measurement results for each film of the composite substrates of Examples 1 to 4, as well as the measurement results for the laminates formed on the composite substrates. In Table 1, the "220 lattice spacing" column for "oxide film" is the value of the lattice spacing calculated from the 220 diffraction ray of magnesium oxide derived from the oxide film. In Table 1, the "220 lattice spacing" column for "metal film" is the value of the lattice spacing calculated from the 220 diffraction ray derived from the metal having a face-centered cubic crystal structure. In Table 1, the "111 diffraction line half width" column is the value of the half width of the 111 diffraction line obtained by performing rocking curve analysis of the 111 diffraction ray derived from the metal having a face-centered cubic crystal structure of the metal film. In Table 1, "I ２Ｄ / I Ｇ The "average value" column is ２Ｄ / I Ｇ is the arithmetic mean value of

[0095]

[0096] From the results shown in Table 1, it was confirmed that the composite substrates of Examples 2 and 3, in which the 220 lattice spacing derived from magnesium oxide is within a predetermined range, have a higher monolayer rate of graphene film compared to the composite substrates of Examples 1 and 4, which do not have an oxide film or in which the lattice spacing is not within the predetermined range. Furthermore, from a comparison between Examples 2 and 3, it was confirmed that when the copper content in the metal film is within the above-mentioned preferred range and the film thickness of the metal film is 1500 nm or more, the monolayer rate of graphene film is higher. The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2024-098082, filed on June 18, 2024, are hereby incorporated by reference as the disclosure of the present invention.

[0097] REFERENCE SIGNS LIST 1, 11 composite substrate 2, 12 substrate 3, 13 oxide film 4, 14 metal film 5, 15 graphene film 6, 10 laminate 20, 30 element 16, 21, 32 resist film 22 opening 23, 31 electrode 24, 33 insulating film

Claims

1. A composite substrate for producing a graphene film, comprising a substrate, an oxide film, and a metal film in this order, wherein the oxide film contains magnesium oxide, and in an XRD chart obtained by in-plane XRD measurement, the lattice spacing calculated from the 220 diffraction line derived from the magnesium oxide is 0.14870 nm or more.

2. The composite substrate according to claim 1, wherein the ratio of the content of oxygen atoms in said oxide film to the content of magnesium atoms in said oxide film is less than 1.

0.

3. The composite substrate according to claim 1 or 2, wherein the metal film contains copper and has a thickness of 500 nm or more.

4. The composite substrate according to claim 3, wherein the metal film has a lattice spacing of 0.1280 nm or more calculated from 220 diffraction lines derived from a metal having a face-centered cubic crystal structure in an XRD chart obtained by in-plane XRD measurement.

5. The composite substrate according to claim 1 or 2, wherein the substrate is amorphous.

6. The composite substrate according to claim 5, wherein the substrate is a quartz substrate.

7. The thermal expansion coefficient of the substrate is 2.0 x 10 －６ (K －１ 3. The composite substrate according to claim 1, wherein the thickness of the composite substrate is 100 nm or less.

8. The composite substrate according to claim 1 or 2, wherein the oxide film has a thickness of 10 to 2000 nm.

9. A composite substrate according to claim 1 or 2, wherein, when rocking curve analysis of the 111 diffraction ray originating from the metal having a face-centered cubic crystal structure of the metal film is performed, the half-value width of the 111 diffraction ray is 10° or less.

10. A method for producing a composite substrate for forming graphene according to claim 1 or 2, comprising forming the oxide film on one surface of the substrate by physical vapor deposition, and forming the metal film on the surface of the oxide film opposite to the substrate side by physical vapor deposition.

11. The method for producing a composite substrate according to claim 10, wherein the oxide film is formed by sputtering, and the metal film is formed by sputtering.

12. The method for producing a composite substrate according to claim 10, wherein the formation of the oxide film is carried out by alternately repeating the formation of a metallic magnesium layer and the oxidation of the metallic magnesium layer.

13. A laminate having a substrate, an oxide film, a metal film, and a graphene film in this order, wherein the graphene film has a single layer ratio of 60.00% or more.

14. A method for manufacturing a laminate according to claim 13, comprising forming the oxide film on one surface of the substrate by physical vapor deposition; forming the metal film on a surface of the oxide film opposite the substrate by physical vapor deposition; and forming the graphene film on a surface of the metal film opposite the oxide film by chemical vapor deposition.

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