JP2017014086A - Method for forming graphene and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To directly form the patterns of graphene on various substrates without giving damage or the like.SOLUTION: Provided is a method for forming graphenes comprising: a plasma feed step in the first step S101 where plasma is fed to the plasma of a carbon-containing compound to the surface of a substrate; and a laser irradiation step in the second step 102 where a laser is irradiated on a graphene formation region in the surface of the substrate fed with the plasma. By these steps, graphene is formed on the graphene formation region of the surface of the substrate. As the carbon-containing compound, CHis preferable. As the plasma, the one generated from a gaseous mixture of CHand Ar is preferable. The surface of the graphene formation region of the substrate is preferably composed of a material absorbing a laser to be irradiated.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a graphene forming method and apparatus for forming a graphene pattern.

  Graphene is a single-layer graphite with two-dimensional high electron mobility characteristics, and both semiconductor and metal characteristics can be obtained by nanostructure processing and stacking differences. Expected to be the most promising candidate. In addition, it is expected to be applied to chemical sensors using chemical reaction characteristics peculiar to carbon materials, MEMS sensors using high strength characteristics, transparent electrodes using low refractive index optical characteristics, etc. New function devices may be realized.

K. S. Novoselov et al., "Electric Field Effect in Atomically Thin Carbon Films", SCIENCE, vol.306, pp.666-669, 2004. X. Li et al., "Large-Area Synthesis of High-Quality and Uniform Graphene Films on Copper Foils", SCIENCE, vol.324, pp.1312-1314, 2009. A. Reina et al., "Large Area, Few-Layer Graphene Films on Arbitrary Substrates by Chemical Vapor Deposition", Nano Letters, vol.9, no.1, pp.30-35, 2009.

  In realizing a device using graphene as described above, it is important to form a graphene pattern having a desired shape. In such pattern formation, a well-known lithography technique is used (see Non-Patent Document 1). In general, a lithography process using a resist mask is used for fine processing in an electronic device. When finely processing graphene by a lithography process, the resist pattern is finally removed by dissolution with an organic solvent.

  Since graphene has only one atomic layer in thickness, surface contamination greatly affects the conductive properties of graphene. Therefore, when graphene is made into a device, complete removal of the resist is an important step for stable operation of the device. However, since graphene is composed of the same carbon as the main component of the resist, it is not easy to selectively remove only the resist. In addition, an excessive cleaning process such as dissolution under ultrasonic irradiation includes a problem of destroying the structure of graphene itself, such as exfoliation of graphene from the substrate and oxidation of a part of the graphene structure. In addition, a process such as ashing for removing the resist cannot be used because it simultaneously damages the graphene.

  On the other hand, there is a method of performing fine processing on a desired thin film using an inorganic material as a mask. In this method, a laminated structure of an organic resist mask and an inorganic mask is used. In this method, the uppermost organic resist mask is patterned by a lithography process, and the lower inorganic mask is patterned by a reactive ion etching method or the like. Next, a graphene pattern having a desired shape is obtained by patterning using an inorganic mask.

  This method using an inorganic mask is useful when the thin film to be processed and the inorganic mask have processing selectivity, and is particularly useful when performing fine and high aspect processing. However, even in this method, when the processing target is graphene, there is a problem that the graphene is removed when the inorganic mask is removed.

In general, in the formation of graphene, graphene is grown on a catalytic metal layer such as Cu or Ni (see Non-Patent Document 2). For this reason, it is not easy to form graphene directly on a layer of another material such as SiO ₂ . In such a case, the formed graphene is transferred onto a desired substrate (see Non-Patent Document 3). However, there is a problem that damage occurs during transfer.

  The present invention has been made to solve the above-described problems, and it is an object of the present invention to directly form graphene patterns on various substrates without causing damage. .

  The graphene formation method according to the present invention includes a plasma supply step of supplying a plasma of a compound containing carbon on a substrate, and a laser irradiation step of irradiating a graphene formation region on the surface of the substrate to which the plasma is supplied with a laser. The graphene is formed in the graphene formation region on the surface of the substrate.

In the graphene forming method, the compound may be CH ₄ .

  The graphene forming apparatus according to the present invention supplies a plasma of a compound containing carbon to a processing chamber, a stage on which a substrate placed in the processing chamber is placed, and a surface of the substrate placed on the stage. Plasma supply means and laser irradiation means for irradiating a graphene formation region on the surface of the substrate to which plasma is supplied with laser.

  In the graphene forming apparatus, the laser irradiation unit includes a laser light source and a stage driving unit that moves the stage in the plane direction of the stage, and the relative position between the irradiation position of the laser emitted from the laser light source by the stage driving unit and the substrate. By displacing the position, the graphene formation region on the surface of the substrate is irradiated with laser.

In the graphene forming apparatus, the plasma supply means supplies CH ₄ plasma.

  As described above, according to the present invention, it is possible to obtain an excellent effect that a graphene pattern can be directly formed on various substrates without causing damage.

FIG. 1 is a flowchart for explaining a graphene forming method according to an embodiment of the present invention. FIG. 2 is a configuration diagram showing the configuration of the graphene forming apparatus according to the embodiment of the present invention. FIG. 3 is a configuration diagram illustrating a configuration example of the plasma supply unit 221. FIG. 4 is a characteristic diagram showing the Raman spectrum measurement result of the graphene pattern formed on the sample substrate 1 of Example 1. FIG. 5 is a characteristic diagram showing a Raman spectrum measurement result in a region other than the graphene pattern of the sample substrate 1 of Example 1. 6 is a characteristic diagram showing the Raman spectrum measurement result of the graphene pattern formed on the sample substrate 3 of Example 2. FIG. FIG. 7 is a characteristic diagram showing a Raman spectrum measurement result in a region other than the graphene pattern of the sample substrate 3 of Example 2.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart for explaining a graphene forming method according to an embodiment of the present invention.

  First, in the first step S101, plasma of a compound containing carbon is supplied onto the substrate (plasma supply step). The substrate may be exposed to the plasma. In the second step 102, the graphene formation region on the surface of the substrate to which plasma is supplied is irradiated with a laser (laser irradiation step). Thus, graphene is formed in the graphene formation region on the surface of the substrate. Note that plasma of a compound containing carbon may be supplied to a graphene formation region in a state where a laser is irradiated to the graphene formation region.

For example, the compound containing carbon may be CH ₄ . The plasma may be generated from a mixed gas of CH ₄ and Ar. Further, He may be used instead of Ar. Here, the plasma supply need not be performed in a reduced-pressure atmosphere, and can be performed in an air atmosphere. In addition, the surface of the graphene formation region of the substrate is preferably made of a material that absorbs a laser to be irradiated. In other words, it is only necessary to irradiate a laser having a wavelength that is absorbed by the material constituting the substrate surface in the graphene formation region.

  Note that the temperature of the substrate (graphene formation region) in a state where plasma is supplied (irradiated) is a temperature range in which deposition or the like does not occur only by supplying plasma, and graphene is first formed in combination with laser irradiation. Good. Similarly, as for the gas concentration (partial pressure) of the compound containing carbon supplied for plasma generation, deposition does not occur only by supplying plasma onto the substrate, and graphene is first formed in combination with laser irradiation. A range is good. The temperature is preferably a temperature at which a compound containing carbon is difficult to adsorb on the substrate. In addition, it is important that the temperature of the substrate in processing is in a range that does not damage the substrate.

  Next, a graphene forming apparatus will be described with reference to FIG. FIG. 2 is a configuration diagram showing the configuration of the graphene forming apparatus according to the embodiment of the present invention. This apparatus includes a processing chamber 201, a stage 202, a heater 203, a stage driving unit 204, a light source 205, a beam shape control unit 206, a total reflection mirror 207, a semi-reflection mirror 208, and a condenser lens 209.

  Further, this apparatus includes an illumination unit 211, an imaging unit 212, a semi-reflective mirror 213, and a total reflection mirror 214. The apparatus also includes a plasma supply unit 221, a purge gas supply unit 222, an exhaust device 223, a power supply unit 224, and a control unit 231.

  The stage 202 mounts the substrate 251 and can be moved in the plane direction (xy direction) of the substrate 251 by the stage driving unit 204. The substrate 251 placed on the stage 202 can be heated by a built-in heater 203.

  The light source 205 is, for example, a KrF excimer laser light source that outputs a pulse laser with a wavelength of 248 nm, and the pulse width of the emitted pulse laser is 50 ns. The beam shape of the pulse laser output from the light source 205 is controlled by the beam shape control unit 206. For the beam shape control unit 206, an XY slit, a photomask using a transparent substrate such as quartz for the original plate, a metal mask, or a diffractive optical element can be used. In addition, drawing may be performed on the irradiation surface by a two-beam interference method or the like. Further, the pulse laser whose beam shape is controlled is reflected by the total reflection mirror 207 and the semi-reflection mirror 208, is condensed by the condenser lens 209, passes through the optical window 210, and reaches a desired location on the substrate 251. Irradiated (projected).

  Further, the irradiated portion of the substrate 251 irradiated with the pulse laser is illuminated with illumination light from the illumination unit 211, and this state is captured by the imaging unit 212 and displayed on the display unit (not shown) so as to be visible to the user. . Illumination light from the illumination unit 211 is reflected by the semi-reflective mirror 213, passes through the semi-reflective mirror 208, and is condensed by the condenser lens 209 to illuminate the irradiated portion. Further, the image of the irradiated portion of the substrate 251 passes through the optical window 210, the condensing lens 209, the semi-reflective mirror 208, and the semi-reflective mirror 213 and is reflected by the total reflective mirror 214 and is captured by the imaging unit 212.

  The imaging unit 212 includes, for example, a CCD (Charge Coupled Device) image sensor (not shown), and photoelectrically converts an image formed on the light receiving surface into an electronic image. An electronic image of the irradiated part obtained by the imaging unit 212 is displayed on the display unit. Using such an observation system, an image of the irradiated portion of the substrate 251 placed on the stage 202 is observed, and the height of the stage 202 is adjusted using the image forming state of the obtained image, and the irradiated pulse laser Adjust the imaging position.

  Further, by moving the stage 202 to a desired position in the xy direction, a desired irradiation position (graphene formation region) of the substrate 251 can be irradiated with a pulse laser. A pulse laser irradiation means is constituted by an optical system such as a stage 202, a light source 205, a beam shape control unit 206, and a reflection mirror.

  The inside of the processing chamber 201 can be sealed. The inside of the processing chamber 201 can be evacuated by an exhaust device 223, and the processing chamber 201 can be set to a desired pressure. In addition, an inert gas such as argon can be supplied into the processing chamber 201 by the purge gas supply unit 222. For example, the atmosphere inside the processing chamber 201 can be exhausted by the exhaust device 223 and purged with an inert gas supplied from the purge gas supply unit 222. Although omitted in FIG. 2, the processing chamber 201 includes a gate valve for loading / unloading the substrate 251.

The plasma supply unit 221 supplies plasma of a mixed gas of a compound containing carbon such as CH ₄ and argon to the surface of the substrate 251 placed on the stage 202. In order to control the amount of plasma of a compound containing carbon such as CH ₄ supplied onto the substrate 251 and to generate stable plasma, a mixed gas diluted with Ar gas is used.

  As illustrated in FIG. 3, the plasma supply unit 221 includes electrodes 225 a and 225 b, and glow discharge generated between the electrode 225 a and the electrode 225 b to which the power supply (AC 8.5 kV) is supplied from the power supply unit 224. Plasma is generated from the introduced gas and supplied from the discharge unit 226. In this case, the generated plasma is in a high temperature state, and the temperature of the plasma discharged from the discharge unit 226 into the processing chamber 201 in an atmospheric atmosphere that is in an atmospheric pressure state rapidly decreases.

  When high temperature plasma touches the surface of the substrate 251, there may be a problem such as damage to the surface. Therefore, the interval between the discharge unit 226 and the surface of the substrate 251 is set to 1 mm or more at which the plasma temperature is sufficiently lowered. For example, it should just be about 40 degreeC. Further, if the distance is too far from the discharge portion 226, the plasma density is lowered. Therefore, in order to supply high-density plasma, the interval between the discharge portion 226 and the surface of the substrate 251 is set to 4 mm or less.

  The above-described operations of the stage driving unit 204, the light source 205, the beam shape control unit 206, and the plasma supply unit 221 are controlled by the control unit 231. The control unit 231 controls the light source 205 and the beam shape control unit 206 based on the set values that have been set, and changes the conditions of the pulse laser that is applied to the irradiation location.

  Further, the control unit 231 controls the operation of the stage driving unit 204 based on the set setting value, moves the stage 202, moves the laser irradiation spot on the substrate 251, and draws a desired pattern shape. . For example, the graphene is detected by detecting the predetermined alignment mark by the observation system described above and driving the stage 202 by the stage driving unit 204 based on the coordinate value of the graphene formation region set with the detected alignment mark as a coordinate reference. Laser irradiation may be performed only on the formation region. These operations are the same as those of a well-known electron beam exposure apparatus.

  By irradiating the graphene formation region on the surface of the substrate 251 to which the plasma is supplied from the plasma supply unit 221 with the above-described apparatus, the laser beam is irradiated by the laser irradiation unit using the stage driving unit 204 or the light source 205, so that only the graphene formation region is irradiated Graphene grows. By controlling laser irradiation and stage movement, a graphene pattern having an arbitrary shape can be obtained at a desired location on the substrate 251. Note that the irradiation position of the laser may be displaced instead of moving the stage.

[Example 1]
Next, examples will be described. First, Example 1 will be described. In Example 1, a graphene pattern was formed on the SiO ₂ layer using the graphene forming apparatus described with reference to FIG. First, a silicon substrate is prepared, and an SiO ₂ layer is formed on the surface of the prepared silicon substrate. Here, to prepare a silicon substrate formed with an SiO ₂ layer having a thickness of 100nm silicon substrate formed with SiO ₂ layer (sample substrate 1) and a thickness of 20 nm (sample substrate 2). The silicon substrate absorbs a laser having a wavelength of 248 nm.

Next, laser irradiation conditions will be described. First, the irradiation region (graphene formation region) was 350 μm × 350 μm. The irradiation amount per unit ^{area, 0.15J / cm 2, 0.25J /} cm 2, and the respective conditions of 0.5 J / cm ^2. Moreover, the frequency | count of irradiation was made into each condition of 100,200,500,1000,3000,5000,10000,20000,30000. The plasma generation conditions were such that a mixed gas with Ar having a CH ₄ concentration of 1% by volume was introduced into the plasma supply unit 221 at 10 L / min, and the applied voltage to the electrodes 225a and 225b was 8.5 kV.

  In addition, the inside of the processing chamber 201 was an air atmosphere. The substrate temperature condition was room temperature (about 25 ° C.). In addition, when the temperature of the substrate surface supplying plasma was measured by thermography, the temperature was distributed in the range of 25 to 45 ° C.

As a result of conducting an experiment of graphene pattern formation on the sample substrate 1 and the sample substrate 2 under the above-described conditions, graphene was formed only in the laser irradiation region under the conditions of an irradiation amount of 0.25 J / cm ² and an irradiation frequency of 3000 to 20000. Been formed. FIG. 4 shows the Raman spectrum measurement result of the graphene pattern formed on the sample substrate 1 under the conditions of an irradiation amount of 0.25 J / cm ² and an irradiation frequency of 10,000. As shown in FIG. 4, G and 2D band peaks indicating that graphene was formed were observed. On the other hand, in a region where graphene is not formed other than the same irradiation region (graphene formation region), as shown in FIG. 5, a Raman spectrum showing a mixture of bonds due to carbon sp ² hybrid orbitals and bonds due to sp ³ hybrid orbitals. Was observed.

Further, the SiO ₂ layer was damaged under the condition of the irradiation dose of 0.5 J / cm ² . Even under the condition of the irradiation amount of 0.25 J / cm ² , the SiO ₂ layer (sample substrate 2) having a thickness of 20 nm was damaged. Note that formation of graphene in the irradiated region was not confirmed in any of the sample substrate 1 and the sample substrate 2 under the condition of the irradiation amount of 0.15 J / cm ² .

[Example 2]
Next, Example 2 will be described. In Example 2, a graphene pattern was formed on a Cu substrate using the graphene forming apparatus described with reference to FIG. First, a thin Cu substrate is prepared and used as a sample substrate 3. The Cu substrate absorbs a laser having a wavelength of 248 nm.

Next, laser irradiation conditions will be described. First, the irradiation region (graphene formation region) was 350 μm × 350 μm. The irradiation amount per unit ^{area, 0.15J / cm 2, 0.25J /} cm 2, 0.5J / cm 2, 1J / cm 2, and the respective conditions of 1.5 J / cm ^2. Moreover, the frequency | count of irradiation was made into each condition of 100,200,500,1000,3000,5000,10000,20000,30000. The plasma generation conditions were such that a mixed gas with Ar having a CH ₄ concentration of 1% by volume was introduced into the plasma supply unit 221 at 10 L / min, and the applied voltage to the electrodes 225a and 225b was 8.5 kV.

  In addition, the inside of the processing chamber 201 was an air atmosphere. The substrate temperature condition was room temperature (about 25 ° C.). In addition, when the temperature of the substrate surface supplying plasma was measured by thermography, the temperature was distributed in the range of 25 to 45 ° C.

Result of the experiment of the graphene pattern formed on the sample substrate 3 in each condition mentioned above, the dose ^{0.25J / cm 2, 0.5J / cm} 2, under conditions of irradiation times 5,000 to 20,000, the laser irradiated region only Graphene was formed. FIG. 6 shows the Raman spectrum measurement result of the graphene pattern formed on the sample substrate 3 under the conditions of the irradiation amount of 0.25 J / cm ² and the irradiation frequency of 50000. As shown in FIG. 6, G and 2D band peaks indicating that graphene was formed were observed. On the other hand, in a region where no graphene is formed other than the same irradiation region (graphene formation region), as shown in FIG. 7, a Raman spectrum showing a mixture of bonds due to carbon sp ² hybrid orbitals and bonds due to sp ³ hybrid orbitals. Was observed.

Further, the Cu substrate was damaged under the condition of the irradiation dose of 1 J / cm ² . Even in the conditions of irradiation doses of 0.25 J / cm ² and 0.5 J / cm ² , the Cu substrate was damaged under the conditions of 30000 irradiation times. Note that formation of graphene in the irradiated region was not confirmed under the condition of an irradiation dose of 0.15 J / cm ² .

  As described above, according to the present invention, since the graphene formation region on the surface of the substrate to which the plasma of the compound containing carbon is supplied is irradiated with the laser, various substrates can be used without causing damage. A graphene pattern can be formed directly on the substrate.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious. For example, the generation of plasma is not limited to that by glow discharge, but may be plasma generated by any method such as plasma generated by high frequency or plasma generated by electron cyclotron resonance.

The compound containing carbon is not limited to CH _4, and may be a carbon compound used in a so-called catalytic metal method. The graphene pattern formation conditions are not limited to the above-described ranges, and may be set as appropriate in accordance with the substrate material to be used, the compound containing carbon, the plasma generation conditions, and the like.

  DESCRIPTION OF SYMBOLS 201 ... Processing chamber, 202 ... Stage, 203 ... Heater, 204 ... Stage drive part, 205 ... Light source, 206 ... Beam shape control part, 207 ... Total reflection mirror, 208 ... Semi-reflection mirror, 209 ... Condensing lens, 210 ... Optical window 211 ... illumination part 212 ... imaging part 213 ... semi-reflective mirror 214 ... total reflection mirror 221 ... plasma supply part 222 ... purge gas supply part 223 ... exhaust device 224 ... power supply part 225a, 225b ... Electrodes, 226 ... Discharge unit, 231 ... Control unit, 251 ... Substrate.

Claims (5)

A plasma supplying step of supplying a plasma of a compound containing carbon on a substrate;
A laser irradiation step of irradiating a graphene formation region on the surface of the substrate to which the plasma is supplied with a laser,
Graphene is formed in the graphene formation region of the surface of the substrate. Graphene formation method characterized by things. The graphene formation method according to claim 1,
The method for forming graphene, wherein the compound is CH ₄ . A processing chamber;
A stage for placing a substrate disposed in the processing chamber;
Plasma supply means for supplying a plasma of a compound containing carbon to the surface of the substrate placed on the stage;
A graphene forming apparatus, comprising: a laser irradiation unit that irradiates a graphene forming region on a surface of the substrate to which the plasma is supplied. In the graphene forming apparatus according to claim 3,
The laser irradiation means includes
A laser light source, and stage driving means for moving the stage in the plane direction of the stage,
A graphene forming apparatus, wherein the graphene forming region on the surface of the substrate is irradiated with laser by displacing a relative position between the irradiation position of the laser emitted from the laser light source by the stage driving unit and the substrate. . In the graphene forming apparatus according to claim 3 or 4,
The graphene forming apparatus, wherein the plasma supply means supplies CH ₄ plasma.

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