JP2009234833A - Carbon nanowall and process for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon nanowall which bridges adjoining protrusions of a rugged substrate. <P>SOLUTION: By using an apparatus for generating an electron-beam-excited plasma, a chemical species having extremely high energy can be produced from a carbon source. By regulating the spacing between protrusions to 200 nm and forming a film of titanium or another metal on the surface, a carbon nanowall bridging adjoining protrusions was able to be formed (2.B). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a so-called carbon nanowall. The carbon nanowall is a laminated structure of graphene (also referred to as a graphene sheet), and is formed standing on a substrate surface, for example.

The present inventors are examining the development of carbon nanostructures such as fullerenes, carbon nanotubes, and graphene, the development of methods for producing these structures, and the development of these structures in electrical / optical devices.
It has also been reported that carbon nanowalls can be formed using electron beam excited plasma (Non-Patent Document 1). A paper by the present inventors will also be submitted (T. Mori et al., Diamond and Related Materials, Science Direct).
Takateru Mori, 54th Applied Physics Related Conference 28a-ZR-8 (2007)

Even if carbon nanowalls were formed by plasma generated by mere high frequency or microwaves, carbon nanowalls were not formed to connect the convex portions adjacent to each other across the concave portions.
The inventors of the present invention have found that carbon nanowalls can be formed on a concavo-convex substrate so as to connect the convex portions adjacent to each other across the concave portions, thereby completing the present invention.

The invention according to claim 1 is characterized in that an electron beam-excited plasma is used to form carbon nanowalls on a substrate having projections and depressions in a bridge shape of adjacent projections across the depressions of the substrate. It is a manufacturing method of carbon nanowall.
The invention according to claim 2 is characterized in that a metal film is formed on at least the convex portion of the substrate.
The invention according to claim 3 is characterized in that the gap between the convex portions is 250 nm or less in the substrate surface direction.
The invention according to claim 4 is a carbon nanowall erected on a substrate on which irregularities are formed, wherein the carbon nanowalls are formed so as to connect adjacent convex portions and convex portions across the concave portions. It is a nanowall.
According to a fifth aspect of the present invention, there is provided a chemical species including at least carbon, in which an electron beam-excited plasma formed by irradiating an electron beam includes an insulating layer inside and a substrate having irregularities on the surface. A carbon nanowall manufacturing method is characterized in that a mixed gas of gas and hydrogen is introduced to selectively grow carbon nanowalls on convex portions and to form bridges on adjacent convex portions. Here, the substrate having the insulating layer inside includes the case where the insulating layer is included in the layer structure of the convex portion.
The invention according to claim 6 is characterized in that the convex portion is charged with plasma and the electric field is concentrated to grow the carbon nanowall in the electric field direction.
The invention according to claim 7 is a radical generated from a mixed gas of at least carbon-containing chemical species and hydrogen by charging an electron beam onto a substrate having an insulating layer inside and having an uneven surface. Is introduced to the surface of the substrate, and carbon nanowalls are selectively grown on the convex portions, and are formed in a bridge shape on the adjacent convex portions.

Plasma by electron beam excitation plasma has extremely large energy. In addition, since the electron beam is irradiated perpendicularly to the target substrate when forming the electron beam excited plasma, the substrate is charged and an electric field is generated perpendicularly to the substrate.
Since the plasma has extremely large energy, active chemical species with extremely high reactivity are generated from a carbon source as a raw material. As a result, coalescence of the highly reactive active chemical species is efficiently generated at the end portion of the carbon nanowall formed on the convex portion, so that the growth rate of the carbon nanowall in the direction parallel to the substrate surface is increased. Becomes larger. Then, for example, if the carbon nanowall formed so as to be erected on the upper part of the convex part has an end of a surface or a laminated surface in the direction of the adjacent convex part, the end part is adjacent to the adjacent convex part. Growing to the club side. Thus, when the growth end of the carbon nanowall comes close to the end of another carbon nanowall on the adjacent convex portion, coalescence occurs, and the adjacent convex portion and the convex portion are connected across the concave portion. Two continuous carbon nanowalls are formed. Alternatively, when the growth end of the carbon nanowall reaches the adjacent convex portion, the carbon nanowall is formed so as to connect the convex portions adjacent to each other across the concave portion.
In addition, since the substrate is charged and an electric field is generated perpendicular to the substrate, the electric charge is concentrated on the edge portion of the convex portion, which may cause the carbon nanowall to grow intensively on the convex portion. At this time, it is considered that carbon nanowalls are likely to grow in the electric field direction perpendicular to the substrate. At this time, it is preferable that an insulating layer is formed inside the substrate because the amount of charge on the convex portion tends to increase.
It is preferable to form a titanium or other metal film on at least the convex portion of the substrate.
In addition, when the gap between the protrusions exceeds 250 nm, it is difficult to form carbon nanowalls that connect the protrusions adjacent to each other across the recess.
Carbon nanowalls that connect adjacent convex portions across the concave portions are new carbon nanowalls that have not been reported before by the present inventors.

  The present invention relates to a novel carbon nanowall, and the formation method is limited at present. However, it is considered that there are various production methods that can form a carbon nanowall.

FIG. 1 is a cross-sectional view showing the configuration of an electron beam excitation plasma generator 100 used in a specific embodiment of the present invention. The electron beam excited plasma generator 100 is a well-known device, but will be described briefly. In the figure, the hatched portion is an insulating region.
Electrons are generated in the filament 1 placed in the argon gas supplied at 2.1 sccm from the argon inlet 8. In this example, a current of 5 A was passed through the filament 1.
This is pulled by the acceleration electrodes 3 a and 3 b, and high-speed electrons jump out from the pinhole plate 2 made of lithium hexaboride toward the porous electrode 4. The acceleration voltage was 100 V and the current was 2 A. In FIG. 1, an area where an electron beam is generated is shown as an electron beam generation area 10.
A substrate 7 fixed by a susceptor 6 and a holder 5 is placed on the right side across the porous electrode 4. The substrate 7 is heated to 570 ° C. by a heating device inside the susceptor 6. The substrate 7 is not grounded (grounded), and plasma processing is performed in a so-called floating state. The atmosphere of the substrate 7 was 2.67 Pa (20 mTorr), and methane was supplied at 4 sccm and hydrogen was supplied at 36 sccm from the carbon source inlet 9 as a carbon nanowall source gas.
Thus, only the electrons in the argon in the electron beam generation region 10 are transmitted to the active species generation region 20 by the partition 4. In the active species generation region 20, methane and hydrogen are activated by a high-energy electron beam, and active chemical species having carbon cause a chemical reaction on the surface of the substrate 7. By supplying an electron beam for 10 minutes, carbon nanowalls were grown on the substrate 7 for 10 minutes.

As the substrate 7, a silicon thin film, a SiC film as an etching stopper layer, and a SiOCH film as an insulating film were sequentially formed on a silicon substrate, and then unevenness was formed by etching. A substrate in this state and a substrate on which a titanium film was further formed were used.
The thickness of the SiC film was 50 nm, the thickness of the SiOCH film was 200 nm, and the SiC film was exposed during the etching for forming irregularities. Note that the SiOCH film does not necessarily need to be completely removed in the recess. Further, when the titanium film was formed, the thickness was 50 nm, and the titanium film was formed on both the concave and convex portions. The SiOCH film was formed using tetraethyl silicate (Si (OC ₂ H ₅ ) 4).

  Carbon nanowalls were formed as described above. In addition, the formation state of the carbon nanowall changed depending on the formation interval of the unevenness and the presence or absence of the titanium film. This is shown below as a photomicrograph.

FIG. A and FIG. B is a case where a substrate in which the titanium film is not formed and the SiOCH film is the uppermost layer is used.
FIG. A is a photomicrograph showing the absence of bridged carbon nanowalls.
FIG. In A, the region marked with circle 1 has carbon nanowalls (white ridges) formed in the exposed portions of the silicon substrate surface, and has no particular characteristics.
FIG. The region marked with A middle circle 2 is a portion having projections and depressions, and quadrangular columnar projections lined up with a gap of 500 nm. The convex part is a part lighter in color than the concave part. Carbon nanowalls (white ridges) are formed on the protrusions. Carbon nanowalls (white ridges) are not formed in the recesses. Moreover, the carbon nanowall formed so that the adjacent convex part and the convex part may be bridged is not found.

FIG. B is a photomicrograph showing the formation of bridged carbon nanowalls.
FIG. Like B, the board | substrate 7 formed the unevenness | corrugation in stripe form. A convex part is a part which attached | subjected A and a recessed part with B, and a convex part is also lighter in color than a recessed part. This is a case where the gap between adjacent convex portions is 200 nm, and carbon nanowalls formed so as to bridge adjacent convex portions and convex portions are formed.

  FIG. A is a photomicrograph of a state in which a titanium film is formed to form bridged carbon nanowalls. FIG. Compared with B, the density of the formed carbon nanowall is higher. This may be because carbon nanowalls are very easily formed by the catalytic action of titanium in the initial stage of carbon nanowall production. On the other hand, the low density even when carbon nanowalls are formed on the surface of the oxide layer may be because the initial product of carbon nanowalls is easily decomposed or inactivated by oxygen atoms.

  FIG. A Raman spectrum is shown in FIG. Shown in B. D-band, G-band, and D′-band were clearly confirmed and proved to be a carbon nanowall having a graphene structure or a laminate structure thereof.

  FIG. A and FIG. B is a micrograph showing a comparative example, in which no bridging carbon nanowalls are formed. At this time, a titanium film was formed. FIG. A is a cross-sectional view, FIG. B is a plan view. The width of the concave portion exceeds 1 μm, and no carbon nanowall is bridged from the convex portion to the convex portion. In addition, although carbon nanowalls are generated in most of the recesses, no carbon nanowalls are generated on the side wall surface of the protrusions and the recesses in the vicinity thereof.

The bridged carbon nanowall of the present invention is considered to be capable of forming an element such as a field effect transistor by using the adjacent convex part as an electrode and the bridged carbon nanowall part as a channel. Such an example is illustrated. FIG. A is a Ti layer forming region for forming a field effect transistor. For example, the entire surface of the silicon substrate is covered with a SiO ₂ insulating film, and FIG. A Ti layer is formed as in A. FIG. In A, there is an SiO ₂ layer below the Ti layer, and the portion where the Ti layer is not formed exposes the SiO ₂ layer. The source region S and the drain region D face each other at the bridge forming portions Sb and Db having a gap of 200 nm, and a gap of 500 nm is formed between them and the gate region G or other region. When carbon nanowalls are formed in such a state by the electron beam excitation plasma of the present invention, bridged carbon nanowalls CNW-B are formed in bridge formation portions Sb and Db with a gap of 200 nm between source region S and drain region D. It is formed. Since the bridged carbon nanowall CNW-B is close to the gate region G of the titanium film, it can be a field effect transistor capable of adjusting the current flowing by the gate voltage.

Sectional drawing which shows the structure of the electron beam excitation plasma generator 100 used in one specific Example of this invention. 2. A is a photomicrograph showing no bridging carbon nanowalls. B is a photomicrograph of bridged carbon nanowalls. 3. 2. A is a photomicrograph showing a bridged carbon nanowall formed on the titanium film surface. B is 3. The Raman spectrum figure of carbon nanowall obtained by A. Cross-sectional micrograph (4.A) and plane micrograph (4.B) on which carbon nanowalls according to the comparative example were formed FIG. 2 is two process diagrams for forming a field effect transistor using a carbon nanowall as a channel according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100: Electron beam excitation plasma generator 1: Filament 2: Pinhole board which consists of lithium hexaboride 3a, 3b: Electrode for acceleration 4: Porous electrode 5: Holder 6: Susceptor 7: Substrate 8: Argon inlet 9: Carbon Source inlet 10: Electron beam generation region 20: Active species generation region

Claims (7)

Using electron beam excited plasma,
A method for producing a carbon nanowall, comprising: forming a carbon nanowall on a substrate having projections and depressions in a bridging shape between adjacent projections across the depression of the substrate. The method for producing a carbon nanowall according to claim 1, wherein a metal film is formed on at least the convex portion of the substrate. The method for producing a carbon nanowall according to claim 1 or 2, wherein a gap between the protrusions is 250 nm or less in the substrate surface direction. A carbon nanowall standing on a substrate on which irregularities are formed, wherein the carbon nanowall is formed so as to connect adjacent convex portions and convex portions across a concave portion. In an electron beam-excited plasma formed by irradiating an electron beam, a substrate having an insulating layer inside and an uneven surface is disposed, and a mixed gas of at least carbon-containing species gas and hydrogen is used. A method for producing carbon nanowalls, comprising introducing carbon nanowalls selectively on convex portions and forming bridges on adjacent convex portions. 6. The method for producing carbon nanowalls according to claim 5, wherein the convex portions are charged with plasma and the electric field is concentrated to grow the carbon nanowalls in the electric field direction. A substrate having an insulating layer inside and having an uneven surface is charged by irradiating it with an electron beam and introducing a radical generated from a mixed gas of at least carbon and a chemical gas containing hydrogen into the substrate surface. A method for producing carbon nanowalls, wherein carbon nanowalls are selectively grown on convex portions and are formed in a bridge shape on adjacent convex portions.