JP7671057B2 - Method for fabricating carbon nanomaterial-containing films - Google Patents

Description

One embodiment of the present invention relates to a method for processing a film containing a carbon nanomaterial. For example, one embodiment of the present invention relates to a method for patterning a graphene-containing film formed on a substrate by wet etching.

Carbon nanomaterials, such as carbon nanotubes, graphene, and fullerenes, are materials composed of ^sp2 carbon atoms, and due to their unique two-dimensional or three-dimensional structure, they exhibit extremely high electron mobility, electrical conductivity, thermal conductivity, and mechanical properties. For this reason, carbon nanomaterials have attracted attention as new materials to replace existing materials in various fields. By processing and patterning a film containing a carbon nanomaterial, it is also possible to fabricate electronic devices that utilize the excellent electrical properties of carbon nanomaterials. For example, Patent Documents 1 and 2 and Non-Patent Documents 1 to 3 disclose a method of patterning a graphene thin film formed on a substrate by etching it.

JP 2014-172792 A JP 2013-225649 A

Bell, D. C., et al., "Precision Cutting and Patterning of Graphene with Helium Ions," Nanotechnology, (UK), 2009, Vol. 20, 455301. Cong, C. X., and five others, "Fabrication of Graphene Nanodisk Arrays Using Nanosphere Lithography," Journal of Physical Chemistry C, (USA), 2009, Vol. 113, pp. 6529-6532 Lemme, M. C., et al., "Etching of Graphene Devices with a Helium Ion Beam," ACS Nano, (USA), 2009, Vol. 9, pp. 2674-2676

One of the embodiments of the present invention aims to provide a novel method for etching a film containing a carbon nanomaterial. For example, one of the embodiments of the present invention aims to provide a method for easily and quickly etching a graphene-containing film formed on a substrate.

One embodiment of the present invention is a method for processing a carbon nanomaterial-containing film. The method includes forming a resist mask and/or a metal mask on a carbon nanomaterial-containing film on a substrate, irradiating the carbon nanomaterial-containing film with light in the presence of an etchant that includes an oxidizing agent, and removing the resist mask and/or the metal mask.

The carbon nanomaterial may be selected from carbon nanotubes, graphene, and fullerenes. The carbon nanomaterial-containing film may be a single layer of graphene or a laminated film of graphene.

The oxidizing agent can be selected from hypochlorous acid and sodium hypochlorite. The concentration of the oxidizing agent in the etchant can be adjusted, for example, within the range of 1% by weight to 25% by weight. The etchant may further contain a surfactant, the concentration of which is selected, for example, from 0.01% by weight to 10% by weight. The surfactant may be an ionic surfactant or a nonionic surfactant.

The light irradiation is performed so as to excite the oxidizing agent. For example, the light irradiation may be performed while the carbon nanomaterial-containing film is immersed in the etchant. The light irradiation may use light having a wavelength selected from the range of 200 nm to 400 nm.

One embodiment of the present invention allows a carbon nanomaterial-containing film to be etched under mild conditions in a short time, forming a patterned carbon nanomaterial-containing film.

1A to 1C are schematic cross-sectional views showing a method for processing a carbon nanomaterial-containing film according to one embodiment of the present invention. 2A and 2B are optical microscope photographs of the graphene-containing film of Example 1. Fig. 2A is a photograph before etching, Fig. 2B and Fig. 2C are photographs after immersing in an etchant and irradiating the film with light for 5 minutes and 20 minutes, respectively, and Fig. 2D is a photograph after immersing in an etchant and leaving the film for 120 minutes without irradiating the film with light. 3(A) and 3(B) are Raman spectra of measurement points 1 to 4 shown in FIG. 2(A) and FIG. 2(B), respectively. 4(A) and 4(B) are Raman spectra of measurement points 1 to 4 shown in FIG. 2(C) and FIG. 2(D), respectively. 5A and 5B are optical microscope photographs of the graphene-containing film of Example 2. Fig. 5A is a photograph before etching, and Fig. 5B is a photograph after 5 minutes of light irradiation in a state where the graphene-containing film was immersed in an etchant. 6(A) and 6(B) are Raman spectra of measurement points 1 to 4 shown in FIG. 5(A) and FIG. 5(B), respectively. FIG. 7A is an optical microscope photograph of the graphene-containing film before etching in Example 3, and FIG. 7B is a mapping diagram of 2D band peak intensity in the Raman spectrum of the dotted square region in FIG. 7A. FIG. 8A is an optical microscope image of the graphene-containing film after etching in Example 3, and FIG. 8B is a mapping diagram of 2D band peak intensity of the Raman spectrum of the dotted square region in FIG. 8A. FIG. 9A is a phase distribution image of the graphene-containing film after etching in Example 3 obtained by an atomic force microscope (AFM), and FIG. 9B is a height analysis result along the line A-A′ in FIG. 9A. 1A to 1C are schematic cross-sectional views showing a method for processing a carbon nanomaterial-containing film according to one embodiment of the present invention. 1A to 1C are schematic cross-sectional views showing a method for processing a carbon nanomaterial-containing film according to one embodiment of the present invention. FIG. 12(A) is an optical microscope photograph of sample A after the formation of a metal mask in Example 4, the left diagram in FIG. 12(B) is an optical microscope photograph of sample A after etching, and the right diagram in FIG. 12(B) is a mapping diagram of 2D band peak intensities in the Raman spectrum of the dotted rectangular region in the left diagram. FIG. 13(A) is an optical microscope photograph of sample A after the formation of a metal mask in Example 4, FIG. 13(B) is an optical microscope photograph of sample A after etching, and the left diagram in FIG. 13(C) is an enlarged view of the dotted rectangular portion in FIG. 13(B), and the right diagram in FIG. 13(C) is a mapping diagram of 2D band peak intensity of the Raman spectrum of the dotted rectangular region in the left diagram.

The following describes the embodiments of the invention disclosed in this application. Even if there are other effects and advantages different from those brought about by the following embodiments, those that are clear from the description in this specification or that can be easily predicted by a person skilled in the art are naturally understood to be brought about by the present invention.

One embodiment of the present invention is a method for processing a film containing a carbon nanomaterial by etching. This processing method will be described below with reference to the schematic cross-sectional views of Figures 1(A) to 1(D).

1. Processing method flow In this processing method, first, as shown in FIG. 1(A), a carbon nanomaterial-containing film 110 is formed on a substrate 100. Then, a photoresist 102 is formed on the carbon nanomaterial-containing film 110, and the photoresist 102 is exposed through a photomask 104 (FIG. 1(B)). The exposed photoresist 102 is developed to obtain a resist mask 106 corresponding to the pattern of the photomask 104 (FIG. 1(C)). After this, the substrate 100 on which the carbon nanomaterial-containing film 110 and the resist mask 106 are formed is immersed in an etchant 108 so that the carbon nanomaterial-containing film 110 comes into contact with the etchant 108 (FIG. 1(C)). In this state, the carbon nanomaterial-containing film 110 exposed from the resist mask 106 is irradiated with light, and the carbon nanomaterial-containing film 110 is partially oxidatively decomposed. Subsequently, the resist mask 106 is removed, so that the carbon nanomaterial-containing film 110 that is covered by the resist mask 106 and has not been oxidatively decomposed remains on the substrate 100, forming a patterned carbon nanomaterial film 112 (FIG. 1(D)). Through the above series of processes, the carbon nanomaterial-containing film 110 having a shape corresponding to the arrangement pattern of the resist mask 106 can be formed on the substrate 100. This series of processes will be described in detail below.

2. Substrate There are no particular limitations on the material contained in the substrate 100, and it may be a semiconductor such as silicon or germanium, a compound semiconductor such as gallium nitride, indium phosphide, or cadmium telluride, a ceramic such as alumina, sapphire, or zirconium oxide, a silicon oxide such as glass or quartz, or a polymer such as polyimide or polycarbonate. The substrate may be flexible. Typical examples include a single crystal silicon substrate, a glass substrate, a sapphire substrate, and a quartz substrate.

3. Carbon Nanomaterial-Containing Film Carbon nanomaterials include carbon nanotubes, graphene, and fullerene.

When carbon nanotubes are used as the carbon nanomaterial, there is no restriction on their structure, and they may be single-walled or multi-walled carbon nanotubes. The ends of the carbon nanotubes may be capped, or one or both ends may be open. Therefore, carbon nanomaterials known as carbon nanohorns may also be used in this processing method. Peapods, which contain fullerenes inside carbon nanotubes, may also be used. There is no restriction on the length of the carbon nanotubes.

When graphene is used as the carbon nanomaterial, the carbon nanomaterial-containing film 110 may be a single layer of graphene, or may be a film containing oligographene, nanographene, graphene oxide, or graphite, in which multiple graphenes are stacked. In addition, a part of the basic skeleton of graphene may be oxidized.

When fullerene is used as the carbon nanomaterial, not only _C60 and _C70 but also _C74 , _C76 , _C78 , etc. may be used. Also, fullerene containing metal ions such as scandium, lanthanum, cerium, etc. may be used, or fullerene in which some of the carbon is modified and has functional groups such as ester groups may be used.

The carbon nanomaterial-containing film 110 can be formed by appropriately selecting a known method. For example, a dispersion liquid containing a carbon nanomaterial is prepared, and the suspension is applied to the substrate 100 by applying a wet film formation method such as a spin coating method, a dip coating method, or a printing method, and then the solvent is evaporated to form the carbon nanomaterial-containing film 110. The solvent of the dispersion liquid may be water, or an organic solvent selected from carbonates, ethers, ketones, alcohols, hydrocarbons, halogen-containing hydrocarbons, esters, carboxylic acids, amines, amides, nitroalkanes, sulfur compounds, etc. may be used. A dispersant such as a surfactant may also be added to the dispersion liquid. However, it is preferable to adjust the dispersion liquid so that no dispersant is used or the concentration of the dispersant is low so as not to affect the electrical properties of the carbon nanomaterial-containing film 110 after patterning.

Alternatively, a catalyst for producing carbon nanotubes or graphene may be fixed on the substrate 100, and carbon nanotubes or graphene may be grown from the surface of the substrate 100. Specifically, a catalyst layer containing metals such as iron, cobalt, nickel, or copper is formed on the substrate 100 using a vacuum deposition method, a metal organic CVD (MOCVD) method, a sputtering method, or the like. If necessary, the catalyst layer may be heat-treated in the presence of a reducing gas such as hydrogen. Alternatively, a dispersion liquid containing fine metal particles may be applied to the substrate 100 to form a catalyst layer. Then, carbon nanotubes or graphene are grown using a thermal CVD method. For example, the substrate 100 is heated at a temperature of 600°C to 1200°C in the presence of a raw material gas such as benzene, acetylene, carbon monoxide, methane, or ethanol. When a plasma CVD method is used instead of the thermal CVD method, heating may be performed at a temperature of 400°C to 600°C. This allows carbon nanotubes or graphene to grow from the catalyst as a base point, forming a carbon nanomaterial-containing film 110 on the substrate 100.

When graphene is used, the carbon nanomaterial-containing film 110 may be formed by reducing graphene oxide on the substrate 100. Specifically, graphite powder is oxidized using an oxidizing agent such as potassium permanganate, potassium dichromate, or hydrogen peroxide, and then the graphene oxide produced by the oxidation is dispersed in a solvent such as water to obtain a dispersion. This dispersion is applied to the substrate 100 to form a film containing graphene oxide. Next, the film containing graphene oxide is irradiated with light from a light source such as a mercury lamp in the atmosphere. Oxygen in the graphene oxide is released by the light irradiation, and the carbon nanomaterial-containing film 110 containing graphene is formed on the substrate 100.

Alternatively, the substrate 100 may be bonded to the carbon nanomaterial-containing film 110 formed on another support substrate, and the carbon nanomaterial-containing film 110 may be transferred from the support substrate to the substrate 100. For example, a support substrate having a thin film containing a metal such as iron, cobalt, nickel, or copper formed on its surface is used, and the CVD method is applied to grow carbon nanotubes or graphene using the metal as a catalyst. The film containing carbon nanotubes or graphene is then coated with a film containing a polymer such as polymethylmethacrylate, poly(ethylene terephthalate), or polyimide. The substrate 100 is then bonded via the polymer film, and the thin film containing the metal is chemically removed using an iron chloride solution or the like, so that the carbon nanomaterial-containing film 110 containing carbon nanotubes or graphene is transferred from the support substrate to the substrate 100.

4. Preparation of Resist Mask The resist mask 106 can also be prepared by applying known methods and materials. Specifically, the photoresist 102 is applied to the substrate 100 on which the carbon nanomaterial-containing film 110 is formed by using a wet film formation method, and the solvent is evaporated. Alternatively, the photoresist 102 may be formed by placing a solid resist film on the substrate 100 on which the carbon nanomaterial-containing film 110 is formed. As will be described later, in this processing method, the carbon nanomaterial-containing film 110 is irradiated with light during etching. Therefore, it is preferable to use a negative photoresist so that the resist mask 106 is not solubilized by light irradiation during etching.

After that, a photomask 104 with a desired pattern of transparent parts 104a and light-shielding parts 104b is placed on the photoresist 102, and the photoresist 102 is exposed through the photomask 104 (FIG. 1(B)). The photoresist 102 is then developed using an etchant such as an alkaline aqueous solution to obtain a patterned photoresist 102, i.e., a resist mask 106 (FIG. 1(C)). Note that FIG. 1(C) shows an example in which a negative photoresist 102 is used, and a resist mask 106 is formed in the area corresponding to the transparent parts 104a. Although not shown, a stepper (reduced projection exposure device) or a direct drawing device may be used as the exposure device. In the former, light from a light source that has passed through the photomask 104 is collected by a projection lens, and the collected light is irradiated onto the photoresist 102. In the latter, the photomask 104 is not used, and laser light is directly irradiated onto the photoresist 102.

In addition, a metal mask containing a metal may be used instead of the resist mask 106 or together with the resist mask 106. For example, as shown in FIG. 10(A), a deposition mask 122 having an opening 122a is placed on the substrate 100 on which the carbon nanomaterial-containing film 110 is formed. The metal is then heated and vaporized under high vacuum. As a result, the metal vapor adheres and solidifies on the carbon nanomaterial-containing film 110 through the opening 122a, and a metal mask 124 reflecting the pattern of the opening 122a is obtained (FIG. 10(B)). The metal used here may be any metal that is resistant to the oxidizing agent contained in the etchant used to etch the carbon nanomaterial-containing film 110 described later, such as gold or platinum.

Alternatively, the metal mask 124 may be formed using the resist mask 106 created by the above-mentioned process, without using the deposition mask 122 having the openings 122a. That is, as shown in FIG. 11(A), a metal film 126 is formed by deposition on the carbon nanomaterial-containing film 110 on which the resist mask 106 is formed. The resist mask 106 is then removed by heating or an organic solvent, and a patterned metal mask 124 containing a metal such as gold can be formed (FIG. 11(B)). In this case, the photoresist 102 may be either negative or positive.

5. Etching of the carbon nanomaterial-containing film After the resist mask 106 is formed, the carbon nanomaterial-containing film 110 is etched. The etching is performed by irradiating the carbon nanomaterial-containing film 110 with light in the presence of an etchant. More specifically, the substrate 100 on which the carbon nanomaterial-containing film 110 and the resist mask 106 are formed is placed in a container 120 containing an etchant 108 containing an oxidizing agent, and the carbon nanomaterial-containing film 110 is immersed in the etchant 108. In this state, the carbon nanomaterial-containing film 110 is irradiated with light (FIG. 1(C)). The light may be irradiated from the upper surface of the substrate 100 (the surface on which the carbon nanomaterial-containing film 110 is formed), but if the irradiated light passes through the substrate 100, it may be irradiated from the lower surface opposite to the upper surface.

The oxidizing agents contained in the etchant include chlorine-based oxoacids such as hypochlorous acid, chlorous acid, and chloric acid, and their salts, ozone, hydrogen peroxide, metal permanganates such as potassium permanganate, metal chromates such as potassium chromate and potassium dichromate, and halogens such as chlorine, iodine, and bromine. Among these, chlorine-based oxoacids or their metal salts are preferred, as they have high oxidizing power, are easy to dispose of, and are rapidly decomposed by light. A typical example of a chlorine-based oxoacid is hypochlorous acid, and examples of its metal salts include sodium hypochlorite, potassium hypochlorite, and calcium hypochlorite.

The solvent constituting the etchant may be any solvent that sufficiently dissolves the oxidizing agent, and water, which is inexpensive and non-toxic, is a typical example. In addition to water, the etchant may contain an organic solvent that is highly hydrophilic and does not swell the resist mask 106. For example, it may contain an alcohol-based solvent such as ethanol or isopropanol, a ketone-based solvent such as acetone or methyl ethyl ketone, or an amide-based solvent such as N,N-dimethylformamide or N,N-dimethylacetamide. The concentration of the oxidizing agent in the etchant depends on the type and thickness of the carbon nanomaterial contained in the carbon nanomaterial-containing film 110, but can be selected from a range of, for example, 1% by weight to 25% by weight or 1% by weight to 20% by weight. By selecting the oxidizing agent concentration within this range, a sufficient etching rate can be obtained and the oxidizing agent remaining after etching can be easily removed.

The etchant 108 may further contain a surfactant. There is no restriction on the type of surfactant, and it may be an ionic surfactant or a nonionic surfactant. Examples of the former include saturated or unsaturated aliphatic carboxylates, alkyl sulfates, polyoxyethylene sulfates, alkylbenzene sulfonates, alkyl phosphates, tetraalkylammonium salts, trialkylamine oxides, and betaines having an ammonium cation and a carboxylate anion. Examples of the latter include polyoxyethylene alkyl ethers, fatty acid sorbitan esters, alkyl polyglucosides, fatty acid diethanolamides, and alkyl monoglyceryl ethers. There is no restriction on the concentration of the surfactant in the etchant 108, and it may be selected from a range of, for example, 0.1% by weight or more and 10% by weight or less. By selecting the concentration of the surfactant from the above concentration range, etching can be accelerated, foaming during etching can be suppressed, and the surfactant can be easily removed by washing after etching.

The light source used for light irradiation may be any light source capable of irradiating light corresponding to the absorption wavelength of the oxidizing agent. By selecting a light source in this way, the oxidizing agent in the etchant is optically excited. For example, when hypochlorous acid or sodium hypochlorite is used as the oxidizing agent, the absorption wavelength of these oxidizing agents is between 200 nm and 400 nm, so a light source that emits light of a wavelength selected from this wavelength range may be used. Preferably, a light source capable of covering the above absorption wavelength range is used. Specifically, examples of light sources include a xenon lamp (xenon short arc lamp), a halogen lamp, a high-pressure mercury lamp, a deuterium lamp, and a UV lamp (Xe/Hg far ultraviolet lamp).

Etching may be performed at room temperature (20°C to 25°C), under cooling (0°C or higher and room temperature or lower), or under heating (room temperature or higher and 100°C or lower). To prevent the temperature of the etchant 108 from increasing due to the light source, a cooling device (not shown) may be connected to the container 120, and etching may be performed while maintaining the temperature of the etchant 108 constant. Although not shown, a stirring mechanism may be provided in the container 120, and etching may be performed while stirring the etchant 108. The etching time may be determined appropriately taking into consideration the type and thickness of the carbon nanomaterial contained in the carbon nanomaterial-containing film 110, and may be selected from the range of, for example, 5 seconds to 30 minutes, 1 minute to 30 minutes, or 5 minutes to 20 minutes.

After etching is completed, the substrate 100 is washed with a solvent such as water, alcohol, or ketone. The remaining resist mask 106 is then removed (FIG. 1(D)). To remove the resist mask 106, the substrate 100 may be treated with a known stripping solution. Examples of the stripping solution include an alkaline solution containing tetraalkylammonium hydroxide or amine, and an organic solvent such as N-methyl-2-pyrrolidone (NMP) or acetone. When using a metal mask 124, the metal mask 124 may be removed using an aqueous solution containing potassium iodide and iodine as an etchant.

By the above process, a carbon nanomaterial-containing film 110 patterned on the substrate 100 can be produced. In this processing method, the carbon nanomaterial-containing film 110 is processed by so-called wet etching using the etchant 108. Therefore, compared to processing methods using dry etching, this method has the advantage of being able to process a large number of substrates at once. In addition, as shown in the examples, a practical etching rate cannot be obtained using an etchant alone, whereas the etching rate of the carbon nanomaterial-containing film 110 is dramatically increased by irradiating light. Furthermore, in this processing method, it is not necessary to perform a preliminary treatment (such as forming a film to promote etching) on the carbon nanomaterial-containing film 110 prior to etching. This means that by applying the embodiments of the present invention, it is possible to provide a practical wet etching technology for functional thin films containing various carbon nanomaterials including not only carbon nanotubes but also graphene and fullerene.

1. Example 1
In this Example 1, the results of treating the carbon nanomaterial-containing film 110 with an etchant containing sodium hypochlorite as an oxidizing agent under light irradiation conditions will be described. In addition, in the following Examples 1 to 4, graphene was used as the carbon nanomaterial.

1-1. Experiment A 1 cm x 1 cm single crystal silicon substrate (manufactured by Sigma-Aldrich, the same below) on which single layer graphene was formed via a silicon oxide thin film was used as a sample. This sample was placed in a glass bottle, and 10 mL of an aqueous solution of 0.05 g/mL sodium hypochlorite (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the glass bottle. At room temperature, the surface of the single crystal silicon substrate on which graphene was formed was irradiated with light using a xenon lamp (manufactured by Hamamatsu Photonics, model number LC5, 100 W, irradiation wavelength range 200 to 2000 nm, the same below).

1-2. Results FIG. 2(A) shows an optical microscope (Shimadzu Access Co., Ltd., Nano Search Microscope SFT-4500, the same below) photograph of the sample before the treatment with the sodium hypochlorite aqueous solution. FIG. 3(A) shows Raman spectroscopy spectra measured at measurement points 1 to 4 in FIG. 2(A). The Raman spectroscopy spectra were obtained using an inVia Raman spectrophotometer manufactured by Renishaw. As shown in FIG. 2(A), the graphene-containing film before the treatment was observed as a nearly uniform film. As shown in FIG. 3(A), the D band (1345 cm ⁻¹ ), G band (1595 cm ⁻¹ ), and 2D band (2685 cm ⁻¹ ) specific to a graphene monolayer film were observed at each measurement point, and no difference was observed in the peak intensities of these bands between measurement points 1 to 4. These results indicate that the graphene-containing film forms a nearly uniform monolayer structure on the single crystal silicon substrate.

On the other hand, an optical microscope photograph (Figure 2(B)) of the sample taken 5 minutes after the start of the etching process under light irradiation confirmed that many defects had formed in the graphene-containing film on the single crystal silicon substrate. As can be seen from the Raman spectroscopy spectra (Figure 3(B)) of measurement points 1 to 4 shown in Figure 2(B), almost no graphene-specific bands were observed in any of the spectra except for measurement point 4.

Furthermore, 20 minutes after the start of the etching process under light irradiation, the graphene-containing film could not be confirmed in the optical microscope photograph (Figure 2(C)). In addition, as a result of measuring the Raman spectroscopy spectrum at measurement points 1 to 4 shown in Figure 2(C), although a band specific to graphene could be faintly detected at measurement point 1, the presence of graphene could not be confirmed at the other measurement points (Figure 4(A)).

In contrast, when the sample was left in an aqueous sodium hypochlorite solution at 40°C for 120 minutes without light irradiation, it was confirmed by optical microscope observation that a graphene-containing film remained on the single crystal silicon substrate, as shown in Figure 2(D). Furthermore, the Raman spectroscopy measurements at measurement points 1 to 4 in Figure 2(D) confirmed that graphene clearly remained at measurement points 3 and 4 (Figure 4(B)).

The above results clearly show that light irradiation is extremely effective in accelerating the etching of carbon nanomaterial-containing films containing graphene. Although the detailed mechanism has not yet been clarified, it is believed that the oxidizing agent excited by light decomposes to generate oxygen radicals. It is believed that the oxygen radicals attack the ^sp2 carbon of the carbon nanomaterial, oxidizing the carbon nanomaterial, which results in increased hydrophilicity and improved solubility in the etchant. In addition to or instead of this mechanism, it is believed that a mechanism in which the oxygen radicals cleave some of the carbon-carbon bonds and the carbon nanomaterial is oxidatively decomposed also contributes.

2. Example 2
In this Example 2, the results of investigating the effect of a surfactant on etching of a graphene-containing film will be described.

2-1. Experiment A 6 wt% aqueous solution of sodium hypochlorite containing an alkylamine oxide surfactant (Kitchen Power Bleach, manufactured by Lion Hygiene Co., Ltd., the same applies below) was used as an etchant. A 1 cm x 1 cm single crystal silicon substrate on which single layer graphene was formed via a silicon oxide thin film was placed in a glass bottle, and an etchant was added to the glass bottle so that the sample was completely immersed in the etchant. Then, using a xenon lamp, the surface of the single crystal silicon substrate on which graphene was formed was irradiated with light at room temperature for 5 minutes.

2-2. Results Optical microscope photographs of the sample before and after the treatment with the etchant are shown in FIG. 5(A) and FIG. 5(B), respectively. Raman spectroscopy spectra measured at measurement points 1 to 4 in FIG. 5(A) and FIG. 5(B), respectively, are shown in FIG. 6(A) and FIG. 6(B). Comparing FIG. 5(A) and FIG. 5(B), it can be seen that the graphene confirmed before the treatment with the etchant is hardly observed after the treatment. In addition, comparing FIG. 6(A) and FIG. 6(B), the peaks of each band derived from graphene are clearly detected at all measurement points before the treatment, but these peaks are not observed at any measurement points after the treatment.

The comparative example for this example is the sample in Example 1 with an etching time of 5 minutes (Figures 2(B) and 3(B)). Comparing Figure 5(B) with Figure 2(B), it can be confirmed that the graphene-containing film is removed more quickly by adding a surfactant. In addition, the results shown in Figure 3(B) show that graphene remains at some measurement points in the absence of a surfactant, but the results shown in Figure 6(B) show that no graphene remains at any measurement points when a surfactant is used. These results show that the etching rate is further improved by adding a surfactant.

3. Example 3
In this example, a result of patterning a graphene-containing film including a single-layer graphene by etching using a resist mask will be described.

3-1. Experiment This example was carried out according to the scheme shown in Fig. 1. Specifically, a 1 cm x 1 cm single crystal silicon substrate on which single-layer graphene was formed via a silicon oxide thin film was used as a sample, and a UV resin (hard type) made by Padico Co., Ltd., containing an acrylic resin, was partially applied onto the graphene-containing film. This UV resin was irradiated with a UV lamp (manufactured by AS ONE Corporation, model number SLUV-8) for about 5 minutes to harden it, forming a resist mask.

Then, the sample with the resist mask formed was placed in a glass bottle, and an etchant was added to the glass bottle so that the sample was completely immersed. The etchant used was a 6 wt% aqueous solution of sodium hypochlorite containing an alkylamine oxide surfactant. After that, a xenon lamp was used to irradiate the surface of the single crystal silicon substrate on which the graphene was formed with light at room temperature for 5 minutes. The sample was then removed from the etchant, washed with water, and the resist mask was physically peeled off.

3-2. Results Fig. 7(A) shows an optical microscope photograph of the sample before the resist mask was prepared, and Fig. 7(B) shows the intensity mapping data of the 2D band detected by the Raman spectroscopy spectrum of the region enclosed by the dotted square in Fig. 7(A). From these figures, it was confirmed that the graphene-containing film on the single crystal silicon substrate had a nearly uniform thickness.

Figure 8 (A) is an optical microscope image of a sample obtained by etching a graphene-containing film on which a resist mask was formed and then peeling off the resist mask. In the figure, the band-shaped region marked with the reference numeral 112 is the region where the resist mask was formed. As can be seen from Figure 8 (A), the graphene-containing film remains as a selectively patterned carbon nanomaterial film 112 in the region where the resist mask was formed, and the graphene-containing film has been removed from other regions. This is also confirmed by the 2D band intensity mapping data (Figure 8 (B)) detected by the Raman spectroscopy spectrum of the region surrounded by the dotted rectangle in Figure 8 (A).

9(A) shows a phase distribution image of the sample obtained using an AFM (Shimadzu Access Co., Ltd., Nano Search Microscope, Model No. SFT-4500), and FIG. 9(B) shows the height analysis results of the sample along the line A-B in FIG. 9(A). As can be seen from FIG. 9(A) and FIG. 9(B), the region where the resist mask was formed (the band region marked with the reference symbol 112 in FIG. 9(A)) is higher than other regions where the resist mask was not formed. Specifically, as shown in FIG. 9(B), measurement point 2 in the region where the resist mask was formed is higher than measurement point 1 in the region where the resist mask was not formed. Similarly, measurement point 4 in the region where the resist mask was formed is higher than measurement point 3 in the region where the resist mask was not formed. The difference in height between measurement points 2 and 4 and measurement points 1 and 3 was 0.5 nm to 0.8 nm. These results also prove that the graphene-containing film is present in the region where the resist mask was formed.

4. Example 4
In this example, an example will be described in which a graphene-containing film including a single-layer graphene is patterned by etching using a metal mask.

4-1. Experiment A 1 cm x 1 cm single crystal silicon substrate on which single-layer graphene was formed via a silicon oxide thin film was used as a sample. A metal mask was formed by evaporating a gold thin film (thickness 100 nm) onto this graphene-containing film via a deposition mask or a resist mask. Two types of metal masks with different patterns (metal masks A and B) were used here. Hereinafter, the samples using metal masks A and B will be referred to as samples A and B, respectively. Optical microscope photographs of samples A and B on which metal masks were formed are shown in Figures 12(A) and 13(A), respectively. From these figures, it can be confirmed that a patterned gold thin film was formed as a metal mask in the area marked with the reference numeral 106.

Next, samples A and B with the metal masks formed were placed in glass bottles, and an etchant was added to the glass bottle so that the samples were completely immersed. The etchant used was a 6 wt% aqueous solution of sodium hypochlorite containing an alkylamine oxide surfactant. After that, a xenon lamp was used to irradiate the surface of the single crystal silicon substrate on which the graphene was formed with light at room temperature for 5 minutes. Next, the samples were removed from the etchant and washed with water, and the metal masks were peeled off with an aqueous solution of potassium iodide and iodine.

The left image in Figure 12(B) is an optical microscope photograph of sample A after the metal mask has been peeled off, and the right image is 2D band intensity mapping data detected by Raman spectroscopy of the region enclosed by the dotted rectangle in the left image. As can be seen from the optical microscope photograph in Figure 12(B), the presence of single-layer graphene can be clearly confirmed in the region where the metal mask was formed. The mapping data also shows that single-layer graphene remains in the above region, whereas single-layer graphene has disappeared in the region exposed from the metal mask.

The same thing was confirmed for sample B. Specifically, as shown in FIG. 13(B) and an enlarged view of a portion of it (enclosed in a dotted rectangle) (left side of FIG. 13(C)), it was confirmed by optical microscope observation that single-layer graphene remained in the area where the metal mask had been formed. Furthermore, the 2D band intensity mapping data (right side of FIG. 13(C)) detected by Raman spectroscopy of the area enclosed in the dotted rectangle in FIG. 13(C) shows that single-layer graphene is present in the above-mentioned area, whereas single-layer graphene is not present in the area exposed from the metal mask.

From the above, it was confirmed that a graphene-containing film formed on a substrate can be wet-etched by applying the processing method according to one embodiment of the present invention. This result indicates that this processing method can contribute as a new means for providing electronic devices that contain carbon nanomaterials as conductive members.

100: substrate, 102: photoresist, 104: photomask, 104a: light-transmitting portion, 104b: light-shielding portion, 106: resist mask, 108: etchant, 110: carbon nanomaterial-containing film, 112: patterned carbon nanomaterial film, 120: container, 122: deposition mask, 124: metal mask, 126: metal film

Claims (12)

forming a resist mask and/or a metal mask on a carbon nanomaterial-containing film on a substrate;
irradiating the carbon nanomaterial-containing film with light in the presence of an etchant containing an oxidizing agent; and removing the resist mask and/or the metal mask,
A method for processing a carbon nanomaterial-containing film, wherein the light used in the light irradiation contains light having a wavelength selected from the range of 200 nm or more and 400 nm or less. forming a resist mask and/or a metal mask on a carbon nanomaterial-containing film on a substrate;
irradiating the carbon nanomaterial-containing film with light in the presence of an etchant containing an oxidizing agent; and removing the resist mask and/or the metal mask,
The method for processing a carbon nanomaterial-containing film, wherein the metal mask comprises gold or platinum. forming a resist mask and/or a metal mask on a carbon nanomaterial-containing film on a substrate;
A method for processing a carbon nanomaterial-containing film, comprising: irradiating the carbon nanomaterial-containing film with light in the presence of an etchant containing an oxidizing agent and a surfactant; and removing the resist mask and/or the metal mask. The method of any one of claims 1 to 3, wherein the carbon nanomaterial is a carbon nanotube, graphene, or fullerene. The method according to any one of claims 1 to 3, wherein the carbon nanomaterial-containing film is a single layer of graphene or a laminated film of graphene. The method according to any one of claims 1 to 3, wherein the oxidizing agent is selected from hypochlorous acid and sodium hypochlorite. The method according to any one of claims 1 to 3, wherein the light irradiation is performed so as to excite the oxidizing agent. The method according to claim 1 , wherein the concentration of the oxidizing agent in the etchant is 1% by weight or more and 25% by weight or less . The method according to any one of claims 1 to 3, wherein the formation of the resist mask is performed using a negative photoresist. The method according to any one of claims 1 to 3, wherein the light irradiation is performed while the carbon nanomaterial-containing film is immersed in the etchant. The method of claim 3, wherein the surfactant is an ionic surfactant. The method according to claim 11, wherein the concentration of the surfactant in the etchant is 0.01% by weight or more and 10% by weight or less.

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