Plasma Etching Apparatus and Method for Manufacturing Graphene Thin Film

Abstract

To provide a plasma etching device for generating a nano-pit of a desired shape in a graphene thin film, and a method for manufacturing a graphene thin film.SOLUTION: An etching device 302 according to the present invention includes: a quartz tube 11 divided into a heating region 51 and a high-frequency region 52, the quartz tube being for flowing an etching gas containing hydrogen gas from the high-frequency region 52 to the heating region 51; and a sample board 12 for arranging a sample on which a hydrogen plasma etching is to be performed in the heating region 51 of the quartz tube 11. The sample board 12 is located near the inner wall of the quartz tube 11.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a plasma etching apparatus for performing hydrogen plasma etching on a graphene thin film and a method for manufacturing a graphene thin film.

Background Art

[0002] Graphene is expected as a material for future electronic devices. FIG. 1 is a diagram for explaining the edge structure of graphene. The edge structure of graphene is a zigzag type (FIG. 1(A)), an armchair type (FIG. 1(B)), or a structure in which these are regularly or randomly mixed. And the characteristics of graphene are affected by this edge structure. In particular, this influence becomes remarkable when the ratio of the edge structure occupying the whole becomes large like a nanoribbon.

[0003] For this reason, a manufacturing method capable of controlling the structure of the edge of graphene becomes important. For example, Non-Patent Document 1 discloses forming a graphene line with a width of 120 nm on a graphene thin film by lithography technology and oxygen plasma etching, and then performing anisotropic etching with hydrogen plasma to narrow the width of the graphene line to 20 nm to manufacture GNR. That is, Non-Patent Document 1 discloses a method of starting from a linear defect created by oxygen plasma and widening the width of the linear defect by anisotropic etching to form a GNR with a desired line width.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

[0005] Regarding hydrogen plasma etching for forming GNR, etching conditions and the like have been published (see, for example, Non-Patent Documents 2 and 3). As described above, hydrogen plasma etching can be an important process for controlling the edge structure of graphene. Here, through the verification of the inventors, it has been found that in addition to the parameters of hydrogen plasma etching disclosed in previous literature, the etching results also change depending on the sample position in the etching chamber.

[0006] Therefore, an object of the present invention is to provide a plasma etching apparatus and a method for manufacturing a graphene thin film that can generate nanopits with a desired shape in the graphene thin film by utilizing this new finding.

[0007] In order to achieve the above object, the plasma etching apparatus according to the present invention is configured to adjust the sample position in the etching chamber according to the nanopits to be formed on the graphene thin film.

[0008] Specifically, the plasma etching apparatus of the present invention is divided into a heating region and a high-frequency region, and a quartz tube for flowing an etching gas containing hydrogen gas from the high-frequency region to the heating region, a sample stage for disposing a sample for performing hydrogen plasma etching in the heating region of the quartz tube, a position adjustment unit for moving the position of the sample stage in the radial direction of the quartz tube in the heating region of the quartz tube, and is provided with. Note that the "etching gas containing hydrogen gas" means both the case of only hydrogen gas (including the case where there are residual gases and impurities) and the case where hydrogen gas is mixed with other gases.

[0009] For example, by setting a sample (graphene thin film) near the tube wall of the quartz tube, hexagonal-shaped nanopits can be generated on the graphene thin film. On the other hand, when the sample (graphene thin film) is set at the center of the quartz tube, a large number of irregularly shaped nanopits with a small diameter can be created on the graphene thin film. Therefore, the present invention can provide a plasma etching apparatus capable of generating nanopits with a desired shape on a graphene thin film.

[0010] In particular, when it is desired to generate hexagonal-shaped nanopits on the graphene thin film, the following apparatus (method) may be used. The plasma etching apparatus according to claim 1 of the present invention is divided into a heating region and a high-frequency region, and a quartz tube for flowing an etching gas containing hydrogen gas from the high-frequency region to the heating region, a sample stage for disposing a sample for performing hydrogen plasma etching in the heating region of the quartz tube, and is a plasma etching apparatus provided with, It is characterized in that the sample stage is near the inner wall of the quartz tube.

[0011] In the plasma etching apparatus according to claim 2 of the present invention, the vicinity of the inner wall of the quartz tube is a position separated from the inner wall of the quartz tube by a distance of 30% or more and 40% or less of the radius of the quartz tube.

[0012] The method for manufacturing a graphene thin film according to claim 3 of the present invention is divided into a heating region and a high-frequency region, and a quartz tube through which an etching gas containing hydrogen gas flows from the high-frequency region to the heating region is used to perform hydrogen plasma etching on the graphene thin film. The manufacturing method is as follows: Placing the graphene thin film in the heating region of the quartz tube and near the inner wall of the quartz tube, and Setting the heating region to 200°C or more and 700°C or less It is characterized by.

[0013] The method for manufacturing a graphene thin film according to claim 4 of the present invention is characterized in that the heating region is set to 500°C or more and 700°C or less.

[0014] In the method for manufacturing a graphene thin film according to claim 3 or 4 of the present invention, the vicinity of the inner wall of the quartz tube is a position separated from the inner wall of the quartz tube by a distance of 30% or more and 40% or less of the radius of the quartz tube.

[0015] In addition, the above inventions can be combined as much as possible.

Effect of the Invention

[0016] The present invention can provide a plasma etching apparatus and a method for manufacturing a graphene thin film capable of generating nanopits having a desired shape on the graphene thin film.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0018] Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, components having the same reference numerals indicate the same components.

[0019] (Embodiment 1) FIG. 2 and FIG. 3 are diagrams for explaining the plasma etching apparatus 301 of the present embodiment. The plasma etching apparatus 301 is divided into a heating region 51 and a high-frequency region 52, a quartz tube 11 for flowing an etching gas containing hydrogen gas from the high-frequency region 52 to the heating region 51, a sample stage 12 for arranging a sample for performing hydrogen plasma etching in the heating region 51 of the quartz tube 11, a position adjustment function unit 13 for moving the position of the sample stage 12 in the radial direction D of the quartz tube 11 in the heating region 51 of the quartz tube 11, is provided.

[0020] The plasma etching apparatus 301 is a hydrogen plasma etching apparatus. With the position adjustment function unit 13, the graphene thin film as the sample can be etched near the center of the quartz tube 11 or near the inner wall. The position adjustment function unit 13 may be a lifting device that moves the sample stage 12 as shown in FIG. 2 in the radial direction D. Also, the position adjustment function unit 13 may be a plurality of sample stages (12a, 12b, 12c, ···) with different widths W as shown in FIG. 3. In this case, the sample stage 12 is accommodated inside the quartz tube 11 at a position where the width W is equal to the length of the chord formed by the inner wall of the quartz tube 11. That is, one of the plurality of sample stages (12a, 12b, 12c, ···) that fits at the desired position in the radial direction D is selected and placed inside the quartz tube 11.

[0021] In the hydrogen plasma etching, the plasma etching apparatus 301 has an additional new etching parameter, namely, the position in the radial direction inside the quartz tube, in addition to the conventional etching parameters (for example, heating temperature, distance from the plasma glow (high-frequency region), hydrogen pressure, plasma excitation power, etc.). In this embodiment, the dependence of the new etching parameter for hydrogen plasma etching is disclosed.

[0022] In this embodiment, the inner diameter of the quartz tube 11 is 30 mm. The sample mounted on the sample stage 12 is highly oriented pyrolytic graphite (HOPG) on which a graphene thin film is laminated. Since the reactivity with hydrogen plasma is the same, the sample is not limited to HOPG, and may be kish graphite or a graphene thin film. The size of the sample is 8 mm × 3 mm × 0.5 mm (W × D × H). Note that the sample is not limited to this size. As the etching temperature, isotropic etching occurs when etching is performed at 450°C or lower conventionally, and circular and small nanopits are generated. When etching is performed at 500°C or higher, anisotropic etching occurs, and relatively large hexagonal nanopits, that is, nanopits that can form a zigzag-shaped edge structure, are known to be generated.

[0023] Figure 4 is an image obtained by observing the surface of HOPG with a scanning tunneling microscope (STM) after performing hydrogen plasma etching while changing the position of the sample stage 12 in the plasma etching apparatus 301. The etching parameters are as follows. Heating temperature: 600 °C Hydrogen pressure: 1.5×10 2 Pa RF power: 25 W Etching time: 5 minutes

[0024] Figure 4(a) is an STM image of the HOPG surface etched with the sample stage 12 placed near the inner wall of the quartz tube 11 (5 mm away from the inner wall), and Figure 4(b) is an STM image of the HOPG surface etched with the sample stage 12 placed near the central axis of the quartz tube 11. STM stands for Scanning Tunneling Microscope. Despite the same etching parameters, the HOPG etched at the central axis of the quartz tube 11 (Figure 4(b)) has small and circular nanopits, while the HOPG etched near the inner wall of the quartz tube 11 (Figure 4(a)) has large and hexagonal nanopits. Thus, the nanopit size becomes approximately three times larger when etching near the inner wall than when etching near the central axis. On the other hand, since the density of nanopits generated in the depth direction from the surface of HOPG is higher when etching near the central axis, it can be said that the etching effect becomes weaker when etching near the inner wall.

[0025] From the above, the following was found. In the plasma etching apparatus 301, when performing hydrogen plasma etching on a graphene thin film, the shape of the nanopits formed on the graphene thin film can be changed by adjusting the position in the radial direction where the graphene thin film is placed in the quartz tube 11 as an etching parameter. Specifically, if a graphene film is disposed near the inner wall of the quartz tube 11 (at a position separated from the inner wall by a distance of 30% to 40% of the radius), large hexagonal nanopits can be formed on the graphene film at a heating temperature of 500 °C or higher. On the other hand, if a graphene film is disposed on the central axis of the quartz tube 11, small circular nanopits can be formed on the graphene film at a heating temperature of 200 °C or higher and 700 °C or lower.

[0026] (Discussion) Such changes in etching can be explained by considering the radial changes in H ions such as H radicals and H + , H 2 + , H 3 + . H ions are attenuated in both free space and the sample surface. On the other hand, H radicals mainly recombine on the sample surface at the etching pressure, and the recombination coefficient of H radicals on the quartz inner wall is sufficiently small (see, for example, Non-Patent Document 2). Therefore, near the inner wall of the quartz tube, the density of H radicals becomes higher than the density of H ions. This means that the generation of defects is carried by H ions, and the anisotropic etching of defects is carried by H radicals. This discussion is not inconsistent with other measurement results showing the parameter dependence of hydrogen plasma etching (see, for example, Non-Patent Documents 2 and 3).

[0027] (Other Embodiments) In Embodiment 1, the plasma etching apparatus 301 capable of adjusting the radial position where the sample is disposed in the quartz tube was described. However, when it is desired to form only hexagonal nanopits on the graphene film as the sample, an apparatus in which the sample stage is fixed near the inner wall of the quartz tube may also be used. FIG. 5 is a diagram for explaining the plasma etching apparatus 302.

[0028] The plasma etching apparatus 302 is divided into a heating region 51 and a high-frequency region 52, a quartz tube 11 that flows an etching gas containing hydrogen gas from the high-frequency region 52 to the heating region 51, a sample stage 12 for disposing a sample on which hydrogen plasma etching is performed in the heating region 51 of the quartz tube 11, It is provided with [a certain component], and is characterized in that the sample stage 12 is near the inner wall of the quartz tube 11.

[0029] The plasma etching apparatus 302 has no position adjustment unit 13 compared to the plasma etching apparatus 301 in FIG. 2, and the sample stage 12 is fixed near the inner wall of the quartz tube 11. Here, the vicinity of the inner wall of the quartz tube 11 is a position separated from the inner wall of the quartz tube 11 by a distance of 30% or more and 40% or less of the radius of the quartz tube 11. Specifically, if the inner diameter of the quartz tube 11 is 30 mm, the sample stage 12 is fixed at a position 4.5 mm to 6 mm from the inner wall.

Explanation of symbols

[0030] 11: Quartz tube 12, 12a, 12b, 12c, ···: Sample stage 13: Position adjustment functional unit 51: Heating region 52: High-frequency region 301, 302: Plasma etching apparatus

Claims

1. A quartz tube (11) divided into a heating region (51) and a high-frequency region (52), and an etching gas containing hydrogen gas flows from the high-frequency region to the heating region; A sample stage (12) for arranging a sample for performing hydrogen plasma etching in the heating region of the quartz tube; A plasma etching apparatus (302) comprising: The sample stage is near the inner wall of the quartz tube, and The vicinity of the inner wall of the quartz tube is a position separated from the inner wall of the quartz tube by a distance of 30% or more and 40% or less of the radius of the quartz tube. A plasma etching apparatus characterized by the above.

2. A manufacturing method for performing hydrogen plasma etching on a graphene thin film by using a quartz tube (11) divided into a heating region (51) and a high-frequency region (52), and an etching gas containing hydrogen gas flows from the high-frequency region to the heating region, comprising: Placing the graphene thin film in the heating region of the quartz tube and near the inner wall of the quartz tube; The vicinity of the inner wall of the quartz tube is a position separated from the inner wall of the quartz tube by a distance of 30% or more and 40% or less of the radius of the quartz tube, and Setting the heating region to 200°C or more and 700°C or less. A manufacturing method characterized by the above.

3. The manufacturing method according to Claim 2, characterized in that the heating region is set to 500°C or more and 700°C or less.

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