JP2011178617A - Method for forming graphene film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a graphene film on a substrate. <P>SOLUTION: The method includes: a metal thin film-forming step of forming the metal thin film on a sapphire substrate having a c-plane; a first heat treatment step in a hydrogen atmosphere; a second heat treatment step in a mixed atmosphere of hydrogen and methane; and a cooling step. Thus, the graphene film having less defects is formed on the sapphire substrate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for forming a graphene film on a substrate.

  Graphene (graphite atomic layer) film is expected as a constituent material of various electronic devices. The graphene film can be formed by peeling from bulk graphite using adhesive tape, heating silicon carbide substrate to desorb silicon atoms on the surface, chemical vapor deposition (Chemical Vapor Deposition) A method of growing a graphene film on a metal surface by a CVD method) is known.

  In Patent Document 1, as a conventional technique for disposing a carbon thin film (graphite layer) on a substrate, graphite is formed by CVD on platinum, nickel, cobalt, palladium or an alloy thereof formed on a substrate surface made of alumina or quartz. Techniques for forming layers are disclosed.

  Patent Document 2 discloses a technique in which a graphene film is formed on a silicon substrate by forming a polycrystalline metal thin film made of nickel as a graphitization catalyst layer on a silicon substrate, and further forming a graphene film by a CVD method. Has been.

  Patent Document 3 discloses a technique for forming a graphene film on a nickel single crystal by a CVD method as a conventional technique for disposing a graphene film on a substrate.

  Non-Patent Document 1 discloses a technique of forming a polycrystalline metal thin film made of nickel on a silicon substrate and further forming graphite by a CVD method as a conventional technique for disposing a graphene film on the substrate.

  Non-Patent Document 2 discloses a technique for forming a graphene film by a CVD method using a polycrystalline copper foil as a substrate as a conventional technique for disposing a graphene film on a substrate.

  Non-Patent Document 3 discloses a technique for epitaxially growing a thin film of copper, silver, aluminum, gold, and nickel on a substrate made of sapphire and magnesium oxide.

Japanese Patent No. 3044683 JP 2009-107921 A JP 2009-143799 A

Alfonso Reina et al., Nano Lett. Vol.9 pp.30 (2009) Xuesong Li et al., Science vol.324 pp.1312 (2009) H. Bialas et al., Vaccum vol.45 pp.79 (1994)

  As a technique for forming a graphene film on a substrate, a technique is known in which a metal catalyst film is formed on a substrate and a graphene film is formed on the metal catalyst film by a CVD method. However, when a polycrystalline metal film is used as a base, it is difficult to form a homogeneous graphene film because a large number of metal crystal particles having different orientations are exposed on the surface. Graphenes having different crystal orientations are formed on crystal grains having different orientations. When graphene having different crystal orientations coexists, a single crystal cannot be formed, and a grain interface (grain boundary) is formed or a defect is generated. Grain boundaries and defects in graphene crystals cause electron scattering, which reduces the mobility of electrons in the graphene film, resulting in a decrease in the conductivity of the graphene film and the operating speed of electronic devices using the graphene film Or drop. In addition, graphene films with different film thicknesses may be formed on crystal grains having different orientations due to the difference in precipitation rate, which also causes a decrease in the uniformity of the film thickness of the graphene film. On the other hand, when a single crystal metal is used as a substrate, the above problem does not occur, but there is a problem that the production cost of the single crystal metal substrate is high and it is difficult to produce a single crystal metal substrate having a large area. .

  A method of forming a graphene film according to the present invention that solves the above problem is a method of forming a graphene film on a substrate, wherein the substrate is a c-plane sapphire substrate, and the method includes nickel or cobalt on the substrate. Forming a metal film comprising: a first heat treatment process for recrystallizing the metal film by heating the substrate in a hydrogen gas atmosphere to form an epitaxial metal film; and methane gas for the substrate. And a second heat treatment step of heating in a mixed atmosphere of hydrogen gas.

  According to the present invention, a method for forming a high-quality graphene film on a substrate is provided.

The figure which shows the process of the formation method of a graphene film Sectional drawing which shows the substrate state in the process of the formation method of a graphene film The figure which shows the Raman spectrum of the graphene film obtained in Embodiment 1 and Embodiment 2

In this specification, a structure in which a plurality of carbon atoms are bonded by an sp ² bond to form a six-membered ring structure and take a sheet-like form is referred to as a graphite atomic layer or graphene. In addition to single-atom-layer graphene consisting of only a six-membered ring structure, partially defective graphene, a film in which several to several tens of layers of graphene are stacked, and many graphenes with different orientations Are collectively referred to as a graphene film.

  As the sapphire substrate used in the present invention, a c-plane oriented sapphire substrate can be used.

  Moreover, the metal thin film used by this invention can use the metal thin film which consists of nickel or cobalt.

  By using a nickel or cobalt metal thin film, an epitaxial film with high crystallinity can be formed on c-plane sapphire. In the face-centered cubic lattice crystal structure of the nickel and cobalt metal thin films, the (111) plane and the c-plane of sapphire are substantially lattice-matched, so that the thin film is epitaxially grown on the sapphire c-plane. Further, since graphene is epitaxially grown on the (111) plane of these epitaxial films, generation of grain boundaries and defects in the graphene film can be suppressed, and a high-quality graphene film can be obtained.

(Embodiment 1)
Hereinafter, the step of forming the graphene film according to the first embodiment of the present invention will be described in detail with reference to FIGS.

  First, the sapphire substrate 101 (FIG. 2A) having the c-plane (0001) was cleaned, and a nickel thin film 102 was formed thereon by electron beam evaporation (FIGS. 1A and 2B). Here, the thickness of the nickel thin film was set to 70 nm. Next, the sapphire substrate was held in a heat treatment apparatus, and the interior of the apparatus was placed in a hydrogen gas atmosphere, and a heat treatment at 1000 ° C. was performed as a first heat treatment step (FIG. 1B). By the above treatment, the nickel thin film on the sapphire substrate was recrystallized to form an epitaxial metal film 103 having a crystal orientation on the (111) plane (FIG. 2C). In addition, when the board | substrate which performed the 1st heat treatment process was taken out from the apparatus and evaluated by X-ray diffraction, the nickel thin film formed the (111) plane and orientated, and formed the epitaxial film with respect to the sapphire c plane. It was confirmed that

  In forming the graphene film, after the first heat treatment step, the inside of the apparatus is replaced with a mixed gas atmosphere of 1% methane gas and 99% hydrogen gas without taking out the substrate, and heated again at 1000 ° C. as the second heat treatment step. Processing was performed (FIG. 1 (c)). After the second heat treatment step, the substrate was cooled to near room temperature (FIG. 1D) and taken out from the apparatus.

Through the above steps, a graphene film 104 was formed on the epitaxial metal film 103, and a graphene film-formed substrate 105 was obtained (FIG. 2D). FIG. 3A shows the result of evaluating the obtained graphene film 104 by Raman spectroscopic analysis. As shown in FIG. 3 (a), in the Raman spectrum in the vicinity of 1590 cm ^-1 and near 2750 cm ^-1, a peak of distinct G band and 2D band due to 6-membered ring structure of carbon was observed. On the other hand, a D band peak due to defects was observed in the vicinity of 1370 cm ⁻¹ , but the peak intensity was smaller than the G band peak intensity, and the ratio of D band peak intensity / G band peak intensity (D / G ratio) was as small as 0.09. This result indicates that the graphene film 104 over the substrate 105 is a good graphene film.

(Embodiment 2)
Next, the process of forming the graphene film according to the second embodiment of the present invention will be described in detail with reference to FIGS.

  First, the sapphire substrate 101 (FIG. 2A) having the c-plane (0001) was cleaned, and a cobalt thin film 102 was formed thereon by electron beam evaporation (FIGS. 1A and 2B). Here, the thickness of the cobalt thin film was 150 nm. Next, the sapphire substrate was held in a heat treatment apparatus, and the interior of the apparatus was placed in a hydrogen gas atmosphere, and a heat treatment at 1000 ° C. was performed as a first heat treatment step (FIG. 1B). By the above process, the cobalt thin film on the sapphire substrate was recrystallized to form an epitaxial metal film 103 (FIG. 2C).

  After the first heat treatment step, the inside of the apparatus was replaced with a mixed gas atmosphere of 1% methane gas and 99% hydrogen gas without taking out the substrate, and heat treatment was performed again at 1000 ° C. as the second heat treatment step (FIG. 1). (C)). After the second heat treatment step, the substrate was cooled to near room temperature (FIG. 1D) and taken out from the apparatus.

Through the above steps, the graphene film notation 104 was formed on the epitaxial metal film 103, and the graphene film-formed substrate 105 was obtained (FIG. 2D). FIG. 3B shows the result of evaluating the obtained graphene film 104 by Raman spectroscopic analysis. As shown in FIG. 3 (b), the Raman spectra near 1590 cm ^-1 and near 2720cm ^-1, a peak of distinct G band and 2D band due to 6-membered ring structure of carbon was observed. In the second embodiment, no D-band peak due to defects near 1370 cm ⁻¹ was observed. From this result, it was shown that the graphene film 104 obtained in Embodiment 2 is a good graphene film with fewer defects than that in Embodiment 1.

  The method for forming a graphene film according to the present invention is useful as a method for forming a graphene film on a substrate. In particular, it can be useful for applications of electronic devices and energy devices such as semiconductor films and electrode materials using graphene films.

101 Sapphire substrate 102 Metal film 103 Epitaxial metal film 104 Graphene film 105 Graphene film forming substrate

Claims (1)

A method of forming a graphene film on a substrate,
Forming a metal film made of nickel or cobalt on the substrate;
A first heat treatment step of recrystallizing the metal film by heating the substrate in a hydrogen gas atmosphere to form an epitaxial metal film;
A second heat treatment step of heating the substrate in a mixed atmosphere of methane gas and hydrogen gas,
The method, wherein the substrate is a c-plane sapphire substrate.

Images