JP3781732B2 - Carbon nanotube manufacturing method, semiconductor device manufacturing method using carbon nanotube, and carbon nanotube manufacturing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing carbon nanotubes, and more particularly to a method for producing carbon nanotubes having desired electronic characteristics, a method for producing a semiconductor device using carbon nanotubes, and a device for producing carbon nanotubes.
[0002]
[Prior art]
A carbon nanotube is a cylindrical material obtained by rolling a single graphite sheet, and has a very fine and stable structure with a diameter of about 1 nm to several tens of nm. (Non-patent Document 1). Therefore, it attracts attention as a finer nanoelectronic device material that exceeds the limit of microfabrication by photolithography. Recently, it has also been suggested that carbon nanotubes may exhibit ballistic conduction, and expectations are high as transistor materials capable of high-speed operation.
[0003]
[Non-Patent Document 1]
Tanaka Kazuyoshi, “Carbon Nanotube” Chemistry, January 30, 2001, 1st Edition
[0004]
[Non-Patent Document 2]
Philip G. Collins and two others, Science, No.292, p.706-709, (2001)
[0005]
[Problems to be solved by the invention]
In order to fabricate an electronic device such as a transistor using carbon nanotubes, it is required to align the electronic properties of the carbon nanotubes, particularly the band gap thereof, to a predetermined value.
[0006]
However, even for the same carbon nanotube, the band gap that determines its electronic properties varies depending on the geometric structure such as chirality (helicality), diameter, and length, and it shows metallic properties or semiconductor properties. Or show.
[0007]
Various methods for synthesizing carbon nanotubes are currently known, including hydrocarbon catalyzed decomposition methods, but it is extremely difficult to align the geometric structure at the synthesis stage. The band gap is usually disjointed and irregular.
[0008]
Recently, in a method for manufacturing a transistor using carbon nanotubes, carbon nanotubes having semiconducting properties to be used for transistors are selected by a technique called “constructive destruction”. In this method, carbon nanotubes are arranged on a silicon substrate, a voltage is applied to each carbon nanotube, and only carbon nanotubes with metallic properties are selectively burned out to identify carbon nanotubes with semiconducting properties (non-patented). Reference 2).
[0009]
However, for practical use, there is a demand for a production method that can control the band gap of carbon nanotubes to a predetermined value according to the application by a simpler and more efficient method.
[0010]
In view of the above-described conventional problems, an object of the present invention is to provide a method for producing a carbon nanotube having a predetermined band gap by a simpler and more efficient method.
[0011]
Another object of the present invention is to provide a semiconductor device using carbon nanotubes having a predetermined band gap.
[0012]
Furthermore, another object of the present invention is to provide a production apparatus suitable for the production method of carbon nanotubes having the predetermined band gap.
[0013]
[Means for Solving the Problems]
The first carbon nanotube production method of the present invention is characterized by a step of synthesizing a carbon nanotube, and a first laser beam having a wavelength λ1 is irradiated to the carbon nanotube in an oxidizing gas-containing atmosphere. A selective oxidation process for selectively oxidizing and gasifying carbon nanotubes excited by light irradiation; The remaining carbon nanotubes are irradiated with a second laser beam having a wavelength λ2 shorter than the wavelength λ1 in a fluorinated gas-containing atmosphere, and the carbon nanotubes excited by the second laser beam irradiation are selectively fluorinated. A selective fluorination treatment step that reacts with gas to form a fluorinated layer on at least the surface of the carbon nanotube, and an oxidation that gasifies and oxidizes the carbon nanotube in which the fluorinated layer is not formed in an oxidizing gas-containing atmosphere A treatment step, and a defluorination treatment step for removing a fluorine component from the carbon nanotube having a fluoride layer remaining without being gasified; It is to have.
[0014]
According to the characteristics of the first carbon nanotube manufacturing method, carbon nanotubes having a band gap or less corresponding to the wavelength λ1 of the first laser light are selectively excited and oxidatively disappear. Accordingly, it is possible to obtain only carbon nanotubes having a certain band gap or more corresponding to the wavelength λ1 of the first laser beam.
[0015]
The second carbon nanotube production method of the present invention is characterized by the steps of synthesizing the carbon nanotubes, irradiating the carbon nanotubes with a first laser beam having a wavelength λ1 in a fluorinated gas-containing atmosphere, A selective fluorination treatment step of selectively reacting carbon nanotubes excited by laser light irradiation with a fluorinated gas to form a fluorinated layer on at least the surface of the carbon nanotubes; An oxidation treatment step for oxidizing and gasifying carbon nanotubes in which no layer has been formed, and a defluorination treatment step for removing fluorine components from carbon nanotubes having a fluoride layer remaining without being gasified is there.
[0016]
According to the characteristics of the second carbon nanotube production method of the present invention, carbon nanotubes having a band gap or less corresponding to the wavelength λ1 of the first laser beam are selectively excited and fluorinated. The surface of the fluorinated carbon nanotube is transformed into fluorinated carbon (FC) having high etching resistance. In the subsequent oxidation treatment, only the portion that has not been transformed into fluoride is oxidized and extinguished. Furthermore, carbon fluoride returns to carbon again by the defluorination treatment. As a result, a carbon nanotube having a certain band gap or less corresponding to the wavelength λ1 of the first laser beam can be obtained.
[0018]
Alternatively, after the second carbon nanotube production method, the second carbon beam having a second wavelength λ 2 longer than the first wavelength λ 1 is irradiated to the carbon nanotube in an oxidizing gas-containing atmosphere, A selective oxidation treatment step of selectively oxidizing and gasifying the carbon nanotubes excited by the laser light irradiation.
[0019]
As described above, when the first and second carbon nanotube production methods are combined, the band gap corresponding to the first wavelength λ1 and the band corresponding to the second wavelength λ2 can be obtained by two times of laser light irradiation. Carbon nanotubes having a more limited range of band gaps between the gaps can be obtained.
[0020]
In the first and second carbon nanotube production methods, the step of synthesizing the carbon nanotubes includes a step of regularly arranging and forming a porous layer having pores with the substrate surface exposed at the bottom, A step of forming a film made of a metal or a metal compound having a catalytic function for a carbon nanotube growth reaction on a substrate surface exposed at the bottom of the hole, and a step of growing carbon nanotubes at least in the pores by a hydrocarbon catalytic decomposition reaction You may have. Here, the substrate includes not only the substrate itself but also a substrate subjected to processing such as element isolation layer and thin film formation.
[0021]
In this case, by finally removing the porous layer by etching, the carbon nanotubes having a predetermined band gap and extending in the direction perpendicular to the substrate surface can be obtained according to the arrangement of the pores of the porous layer. They can be formed on the substrate at regular intervals.
[0022]
According to the first aspect of the present invention, there is provided a method for manufacturing a semiconductor device using a carbon nanotube manufacturing method according to the present invention, and a first conductive film around the bottom of the carbon nanotube. , A step of forming a sidewall with the first insulating film on the side wall surface not filled with the first conductive film of carbon nanotubes, a second insulating film, A step of sequentially forming a conductive film and a third insulating film; and a step of forming a third conductive film on the upper surface of the third insulating film and the carbon nanotube.
[0023]
According to the characteristics of the semiconductor device manufacturing method using the first carbon nanotube described above, the carbon nanotube is used as a channel portion, the first conductive film and the third conductive film are the source / drain electrodes, and the second conductive film. An FET (Field Effect Transistor) having a gate electrode as a gate electrode can be formed.
[0024]
The characteristics of the method for manufacturing a semiconductor device using the second carbon nanotube of the present invention are the steps of manufacturing the carbon nanotube by the carbon nanotube manufacturing method of the present invention, and the first side wall surface of the carbon nanotube with the first insulating film. A step of covering, a step of filling the periphery of the bottom of the carbon nanotube covered with the first insulating film with the first conductive film, and a second insulating film on the side wall surface not filled with the first conductive film of the carbon nanotube. A step of forming a sidewall, a step of sequentially forming a third insulating film, a second conductive film, and a fourth insulating film around the sidewall portion from below; an upper surface of the fourth insulating film and the carbon nanotube; And a step of sequentially forming a fifth insulating film and a third conductive film.
[0025]
According to the characteristics of the semiconductor device manufacturing method using the second carbon nanotube described above, the carbon nanotube is used as a channel portion, the first conductive film and the third conductive film are the source / drain electrodes, and the second conductive film. As a gate electrode, a BARITT structure FET having a barrier layer made of a first insulating film and a fifth insulating film between the source / drain electrode and the carbon nanotube can be obtained.
[0026]
The carbon nanotube production apparatus of the present invention is characterized by a reaction vessel, a laser light transmission window provided on the wall of the reaction vessel, a carbon nanotube production raw material gas, an inert gas, and at least an oxidizing gas or a fluorinated gas. Introducing means for introducing the gas into the reaction vessel; and exhaust means for exhausting the gas in the reaction vessel; A laser oscillation device that is provided outside the reaction vessel and introduces laser light into the reaction vessel through a laser light transmission window, and introduces a carbon nanotube-forming raw material gas and an inert gas into the reaction vessel. In the same reaction vessel, carbon nanotubes are synthesized and part of the carbon nanotubes are selectively removed by irradiating the carbon nanotubes with laser light using at least either an oxidizing gas or a fluorinated gas. That is.
[0027]
According to the characteristics of the carbon nanotube production apparatus, since carbon nanotubes can be synthesized and laser light can be introduced into the reaction vessel through the laser light transmission window, the first production method of the present invention can be used. A selective oxidation treatment or a selective fluorination treatment in the second production method can be performed. Also, the synthesis of carbon nanotubes and the selective oxidation treatment of the carbon nanotubes by laser light irradiation can be performed alternately and continuously.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0029]
(First embodiment)
The method of manufacturing a carbon nanotube according to the first embodiment combines a laser beam irradiation and an oxidation reaction to gasify and extinguish carbon nanotubes having a band gap of a certain energy or less by selective oxidation, so that a certain energy or more is obtained. The main feature is to produce only carbon nanotubes having a band gap.
[0030]
FIG. 1A and FIG. 1B are conceptual diagrams showing the characteristics of the carbon nanotube manufacturing method according to the first embodiment. Here, for convenience of explanation, a carbon nanotube 10a having a band gap Eg of E1 and a carbon nanotube 10b having a band gap of E2 are typically shown. However, actually, there are a plurality of carbon nanotubes. And
[0031]
First, a plurality of carbon nanotubes (hereinafter simply referred to as “carbon nanotubes”) are synthesized using various methods. There is no particular limitation on the synthesis method, and for example, a hydrocarbon catalyst decomposition method, an arc discharge method, a laser ablation method, a plasma synthesis method, and the like can be used. The band gap Eg of the carbon nanotubes immediately after the synthesis is in a non-uniform state with a discrete value usually in the range of 0 ≦ Eg ≦ about 2.5 [eV].
[0032]
In the first embodiment, as shown in FIG. 1A, a carbon nanotube having an irregular band gap is formed in an oxygen atmosphere, that is, oxygen (O ₂ ) Place in a contained atmosphere and irradiate with a laser beam having a predetermined wavelength λ1.
[0033]
The laser beam having the wavelength λ1 has a photon energy represented by E = hc / λ1 (h: Planck constant, c: speed of light, λ1: wavelength). Therefore, among the carbon nanotubes, the carbon nanotube 10a having a band gap E1 of hc / λ1 or less absorbs the laser light having the wavelength λ1 as shown in FIG. Excited state. The carbon nanotubes in the excited state become active and react with surrounding oxygen, and carbon monoxide (CO) and carbon dioxide (CO ₂ CO) _x It becomes gas. That is, as shown in FIG. 1B, the carbon nanotube 10a having a band gap E1 of hc / λ1 or less is selectively oxidized and disappears.
[0034]
On the other hand, as shown in FIG. 2B, the carbon nanotube 10b having a band gap E2 higher than hc / λ1 does not absorb laser light and does not enter an excited state, and therefore does not react with surrounding oxygen. Therefore, it remains as it is.
[0035]
In this way, by irradiating laser light having a specific wavelength λ1 in an oxygen atmosphere after or during synthesis of carbon nanotubes, only carbon nanotubes having a band gap greater than the energy corresponding to the wavelength can be obtained. It becomes possible.
[0036]
In the above description, the case where the carbon nanotube is a direct transition type has been described as an example. However, even when the carbon nanotube is an indirect transition type, only the energy exceeding a certain amount corresponding to the band gap is absorbed and excited electrons are absorbed. When carbon is relaxed, it is heated by the interaction with the phonon and the carbon nanotubes are activated. Accordingly, only carbon nanotubes having a certain band gap or less can be oxidized and extinguished by irradiation with laser light having a specific wavelength.
[0037]
Note that as an oxygen atmosphere at the time of laser light irradiation, oxygen (O ₂ ) Not only the contained atmosphere but any atmosphere containing so-called oxidation that can oxidize excited carbon nanotubes may be used. In addition, the temperature condition of the substrate and the like at that time is adjusted to 420 ° C. or less, more preferably 350 ° C. to 420 ° C. so that only the carbon nanotubes excited by the absorption of laser light are selectively oxidized. . The temperature condition is adjusted according to the desired oxidation rate. Since the carbon nanotubes irradiated with the laser light are oxidized at an accelerated rate, selective oxidation is possible even under thermal oxidation conditions.
[0038]
Note that laser light irradiation is not necessarily performed in a sealed state or under reduced pressure, and can be performed in a reaction vessel with a simple laser light transmission window or in the air.
[0039]
Further, the wavelength λ1 of the laser beam to be irradiated is selected in accordance with the required value of the band gap of the carbon nanotube within the range of band gap 0 ≦ Eg ≦ about 2.5 [eV] that can be taken by the carbon nanotube. There is no particular limitation. For example, when a carbon nanotube larger than the direct transition type band gap Eg is required, a laser beam having a wavelength λ1 satisfying Eg = h · c / λ1 may be used. For example, a YAG laser and glass laser having a wavelength of 1.06 μm, a ruby laser having a wavelength of 0.69 μm, and a dye laser having a wavelength of 0.4 to 0.7 μm can be used. In addition, various semiconductor lasers manufactured by a structure in which a GaInNAs layer is formed on a GaAs substrate or a structure in which a GaInAsP layer is formed on an InP substrate can be used. With such a semiconductor laser, the irradiation energy can be varied in the range of Eg = 0 to 2.5 eV.
[0040]
As described above, according to the first embodiment, the band gap of the carbon nanotube can be changed to the wavelength λ1 of the laser beam only by adding a simple selective oxidation treatment with laser irradiation to the conventional method for synthesizing the carbon nanotube. It becomes possible to make it more than a certain band gap according to In this way, it is highly possible that carbon nanotubes with a uniform band gap can be obtained with a substantially uniform work function. According to this method, a relatively large amount of carbon nanotubes can be collectively processed, and carbon nanotubes having a desired band gap can be selectively extracted. Moreover, since the selective oxidation treatment using laser irradiation described above can be repeatedly performed during the synthesis of carbon nanotubes, carbon nanotubes having a desired band gap can be produced in a relatively large amount.
[0041]
(Second Embodiment)
The method for producing carbon nanotubes according to the second embodiment is to produce only carbon nanotubes having a band gap of a certain energy or less by combining laser light irradiation, fluorination reaction, and subsequent oxidation reaction. Main features.
[0042]
FIG. 3A to FIG. 3D are conceptual diagrams showing the characteristics of the carbon nanotube manufacturing method according to the second embodiment.
[0043]
First, similarly to the method according to the first embodiment, carbon nanotubes are synthesized using various methods. There is no particular limitation on the synthesis method, and for example, a hydrocarbon catalyst decomposition method, an arc discharge method, a laser ablation method, a plasma synthesis method, and the like can be used. The band gap Eg of the carbon nanotubes immediately after being synthesized in this way is usually in an uneven state, with values varying between 0 ≦ Eg ≦ about 2.5 [eV].
[0044]
In the second embodiment, as shown in FIG. 3A, the carbon nanotubes having an irregular band gap obtained by synthesis are placed in a fluorine atmosphere, that is, a fluorine (F) -containing atmosphere, and the carbon nanotubes have a predetermined shape. Is irradiated with a laser beam having a wavelength λ1.
[0045]
Since the laser beam having the wavelength λ1 has photon energy represented by E = hc / λ1, the carbon nanotube 10a having a band gap E1 of hc / λ1 or less among the carbon nanotubes absorbs the laser beam having the wavelength λ1. Since an interband transition of carriers occurs, an excited state is obtained. The carbon nanotubes in the excited state become active and react with surrounding fluorine. Thus, as shown in FIG. 3B, stable fluorocarbon is formed on the surface of the carbon nanotube. That is, the carbon nanotube 10a having a band gap E1 of hc / λ1 or less is selectively fluorinated. At this time, the temperature is preferably 250 ° C to 350 ° C.
[0046]
On the other hand, the carbon nanotube 10b having a band gap E2 higher than hc / λ1 does not absorb the laser beam and does not enter an excited state, so that it does not react with surrounding fluorine and remains as it is.
[0047]
Next, as shown in FIG. 3C, the carbon nanotubes 10a and 10b are placed in an oxygen atmosphere, and oxidation is performed at a temperature of 350 ° C. to 420 ° C. or higher, for example. The temperature condition can be appropriately set according to a desired oxidation rate. The carbon nanotubes 10b subjected to the fluorination treatment are resistant to the high temperature oxidation conditions. However, the carbon nanotubes 12 not subjected to the fluorination treatment are oxidized, as shown in FIG. ₂ CO such as _x It disappears as gas. As a result, only the fluorinated carbon nanotube 10a remains.
[0048]
Thereafter, as shown in FIG. 3 (d), the remaining fluorinated carbon nanotubes 10a are immersed in a highly reducing solution such as hydrazine to perform a defluorination treatment. Thus, by removing fluorine, the carbon nanotube 10a returns to its original state, and it is possible to obtain only the carbon nanotube 10a having a band gap E1 equal to or less than the band gap of hc / λ1.
[0049]
In the above description, the case where the carbon nanotube is a direct transition type has been described as an example. However, even when the carbon nanotube is an indirect transition type, only a certain amount of energy corresponding to the band gap is absorbed, and the carbon nanotube As a result, only carbon nanotubes with a certain band gap or less are selectively fluorinated by irradiation with laser light of a specific wavelength, and other carbon nanotubes are extinguished by oxidation treatment, and the remaining fluorination treatment By defluorinating the carbon nanotubes formed, only carbon nanotubes having a specific band gap or less can be obtained.
[0050]
Furthermore, the fluorine atmosphere when performing laser beam irradiation may be any fluorine-containing atmosphere that can react with excited carbon nanotubes to form stable carbon fluoride, and includes not only fluorine but also ammonium fluoride and fluorine hydrogen. Various fluorinated gas-containing atmospheres such as acids can be used. In addition, the ambient temperature is adjusted to, for example, 350 ° C. or less, preferably 250 ° C. to 350 ° C. so that only the carbon nanotubes excited by the absorption of laser light cause a fluorination reaction. In this case, the fluorination treatment is preferably performed in a sealable reaction vessel with a laser light transmission window.
[0051]
The wavelength λ1 of the laser beam to be irradiated is selected in accordance with the required value of the band gap of the carbon nanotube within the range of band gap 0 ≦ Eg ≦ about 2.5 [eV] that can be taken by the carbon nanotube. There is no particular limitation.
[0052]
In general, a semiconductor having a band gap of Eg [eV] absorbs laser light having a wavelength λ [μm] that satisfies λ1 ≦ 1.239 / Eg, and excites electrons. Therefore, in order to obtain a carbon nanotube having a band gap of Eg [eV] or less, it is desirable to irradiate a laser beam having a wavelength of λ1 (= 1.239 / Eg). For example, a YAG laser and glass laser having a wavelength of 1.06 μm, a ruby laser having a wavelength of 0.69 μm, and a dye laser having a wavelength of 0.4 to 0.7 μm can be used. It is also possible to use a semiconductor laser.
[0053]
As described above, according to the second embodiment, a simple selective fluorination treatment and oxidation treatment are added to the conventional method for synthesizing carbon nanotubes, and a constant value corresponding to the wavelength λ1 of the used laser beam is obtained. Carbon nanotubes having a band gap or less can be obtained. In this way, it is highly possible that carbon nanotubes with a uniform band gap can be obtained with a substantially uniform work function. According to this method, a relatively large amount of carbon nanotubes can be collectively processed, and carbon nanotubes having a desired band gap can be selectively extracted. In addition, since the selective fluorination treatment using the laser irradiation described above can be repeatedly performed during the synthesis of the carbon nanotube, carbon nanotubes having a desired band gap can be manufactured in a relatively large amount.
[0054]
(Third embodiment)
The carbon nanotube manufacturing method according to the third embodiment is characterized by a manufacturing method that combines the manufacturing method according to the first embodiment and the manufacturing method according to the second embodiment, and has a specific energy range. The main feature is to produce only carbon nanotubes having a band gap.
[0055]
First, in accordance with the method according to the first embodiment, a carbon nanotube having a band gap of a certain energy or more is produced. That is, carbon nanotubes having irregular band gaps are prepared in advance using various synthesis methods such as hydrocarbon catalyst decomposition. Next, as shown in FIG. 4A, a laser beam having a wavelength λ1 is irradiated in an oxygen atmosphere to excite only the carbon nanotube 10A having a band gap E11 less than the energy EL1 (= hc / λ1) of the laser beam. And selectively oxidize and extinguish. Then, carbon nanotubes 10B and 10C having band gaps E21 and E31 larger than EL1 (= hc / λ1) are left.
[0056]
Subsequently, as shown in FIG. 4B, the remaining carbon nanotubes 10B and 10C are placed in a fluorine atmosphere and irradiated with laser light having a wavelength λ2 shorter than λ1. Here, since the carbon nanotube 10A having the band gap E11 of energy EL1 (= hc / λ1) or less has already disappeared, the band gap is larger than EL1 (= hc / λ1) and less than EL2 (= hc / λ2). The carbon nanotube 10B having a certain E21 is excited and selectively fluorinated. The carbon nanotube 10C having a band gap E31 larger than EL2 remains as it is.
[0057]
Subsequently, as shown in FIG. 4C, the remaining carbon nanotubes 10B and 10C are placed in an oxygen atmosphere and heated. By this high temperature oxidation treatment, the carbon nanotube 10C having the band gap E31 that has not been fluorinated is oxidized and extinguished.
[0058]
Finally, when the fluorinated carbon nanotube 10B is immersed in a reducing solution such as hydrazine and defluorinated, the original carbon nanotube 10B can be returned. In this way, by performing laser irradiation twice and oxidation, fluorination treatment, and defluorination treatment, the energy of the first laser irradiation light is higher than the energy EL1 (= hc / λ1), and the second laser irradiation light A carbon nanotube 10B having an energy gap of energy EL2 (= hc / λ2) or less can be obtained.
[0059]
In the example described above, the method according to the first embodiment is performed first, but the method according to the second embodiment is performed first, and the method according to the first embodiment is performed later. May be. That is, first, the carbon nanotube is placed in a fluorine atmosphere, irradiated with a laser having a wavelength λ1, subjected to selective fluorination treatment, then subjected to high-temperature oxidation, and a band gap higher than hc / λ1 that has not been subjected to fluorination treatment. The carbon nanotubes having oxidization are oxidized and extinguished. Thereafter, the fluorinated carbon nanotubes having a band gap of hc / λ1 or less are defluorinated. Further, the carbon nanotubes after defluorination are placed in an oxygen atmosphere, and laser light having a wavelength λ2 longer than the wavelength λ1 is irradiated to selectively oxidize and extinguish the carbon nanotubes having a band gap of hc / λ2 or less. In this way, a carbon nanotube having an energy gap lower than the energy EL1 (= hc / λ1) of the first laser irradiation light and higher than the energy EL2 (= hc / λ2) of the second laser irradiation light can be obtained.
[0060]
The treatment for leaving only the carbon nanotubes having a predetermined band gap from the irregular carbon nanotubes described above may be performed during the carbon nanotube synthesis process, or may be repeated a plurality of times.
[0061]
Thus, according to the carbon nanotube manufacturing method of the third embodiment, it is possible to manufacture carbon nanotubes having a more limited band gap. Accordingly, it is possible to control the band gap of the carbon nanotube more accurately. Therefore, among electronic devices, application to device applications such as light-emitting diodes and semiconductor lasers that require accurate band gap control is also possible.
[0062]
(Fourth embodiment)
The method of manufacturing a carbon nanotube according to the fourth embodiment provides a carbon nanotube with a uniform band gap using the method of any of the first to third embodiments described above, and regularly. Carbon nanotubes extending in a direction perpendicular to the substrate surface are arranged on the substrate at equal intervals using a porous layer having arranged pores.
[0063]
The manufacturing method according to the fourth embodiment will be described below with reference to FIGS. 5 (a) to 8 (b).
[0064]
First, as shown in FIG. 5A, a porous layer 30 having pores 32 arranged at equal intervals such as alumite, zeolite, and mesoporous silica is formed on the surface of an arbitrary substrate 20. If the pores 32 do not reach the surface of the substrate 20, sputtering is performed on the entire surface with Ar or the like, the remaining layer at the bottom of the pores 32 is removed, and the surface of the substrate 20 is exposed at the bottom of the pores 32. It is preferable to make it. The size of the pores 32 is not particularly limited, but the size of the carbon nanotubes to be produced is slightly smaller than the diameter of each pore 32, and is a size capable of forming a single carbon nanotube in each pore 32. It is preferable.
[0065]
Next, carbon nanotubes are synthesized. The synthesis method is not limited, and various methods such as a hydrocarbon catalytic decomposition method, an arc discharge method, or a laser ablation method can be used. Here, for example, a hydrocarbon catalytic decomposition method using a thermal CVD method is used. Will be described. As shown in FIG. 5 (b), a Co thin film 40 having a catalytic function for the carbon nanotube formation reaction is formed on the entire surface of the substrate on which the porous layer 30 is formed by sputtering or CVD to a thickness of several nm. ˜about several tens of nm. FIG. 6A is a cross-sectional view showing a state in which the Co thin film 40 is formed on the bottoms of the pores 32 of the porous layer 30 and the surface of the porous layer 30. Instead of the Co thin film 40, a thin film having a function of a graphitization catalyst, such as Fe, Ni, Co, Rh, Pd, Pt, Rh, Pd, Y, La, or the like can be formed. These catalysts are not limited to single metal thin films, but may be metal compound thin films such as Co silicide.
[0066]
Preferably, after the Co thin film 40 is formed, heat treatment is performed, and the Co thin film 40 is agglomerated as shown in FIG. The agglomeration of the Co thin film 40 promotes the supply of the raw material gas to the bottom of the catalyst during the subsequent carbon nanotube growth reaction, and promotes the hydrocarbon catalytic decomposition necessary for the growth of the carbon nanotubes more efficiently.
[0067]
Next, the carbon nanotubes 10 are grown on the surface of the substrate 20 on which the porous layer 30 is formed. The growth of the carbon nanotube 10 is performed by the following procedure using, for example, a thermal CVD apparatus as shown in FIG. The substrate 20 on which the porous layer 30 and the Co thin film 40 are formed is placed in the reaction chamber 100, and the substrate 20 is heated to 300 to 500 ° C. by the heater 110 provided around the reaction chamber 100. The inside of the reaction chamber 100 is depressurized using an exhaust pump 120 such as a rotary pump. ₂ H diluted with ₂ S + H ₂ The gas is introduced and maintained in this state for about 30 minutes to 5 hours, and pretreatment is performed.
[0068]
Next, the inside of the reaction chamber 100 is further depressurized, and acetylene (C ₂ H ₂ ) Or the like is introduced into the reaction chamber 100. The substrate is heated to 500 ° C. to 1000 ° C., and the hydrocarbon gas is thermally decomposed by the catalytic reaction of the Co thin film 40. As shown in FIG. 6 (c), the carbon nanotubes 10 are formed in such a manner that the Co thin film 40 is pushed up in the direction perpendicular to the substrate surface on the bottom of the pores 32 and the surface of the porous layer 30 where the Co thin film 40 is formed. grow up.
[0069]
Before the height of the carbon nanotube 10 reaches the height of the pore 32, the growth of the carbon nanotube is once stopped, and the method of any one of the first to third embodiments is used. The process of aligning the band gap is performed. For example, when the method according to the first embodiment is used, as shown in FIG. 6D, the substrate on which the carbon nanotubes are formed is placed in an oxygen atmosphere and irradiated with laser light having a predetermined wavelength λ1. Then, carbon nanotubes having a band gap of hc / λ1 or less are eliminated by selective oxidation treatment. Thus, as shown in FIG. 6E, only the carbon nanotubes 10 having a band gap E2 higher than hc / λ1 are left. This selective oxidation treatment may be performed outside the CVD apparatus. However, if the CVD apparatus shown in FIG. 9 described later is used, it can also be performed in the reaction chamber used for the carbon nanotube growth reaction.
[0070]
Carbon nanotubes are grown again by hydrocarbon catalytic decomposition. By alternately repeating the carbon nanotube synthesis step and the step of selectively oxidizing and annihilating carbon nanotubes having a certain band gap or less by laser light irradiation, the band gap as shown in FIG. Only carbon nanotubes larger than λ1 can be grown on the substrate surface and the bottom of the pores. Note that a Co film may be formed again before the carbon nanotube synthesis step. In order to prevent the pores 32 from being blocked by the Co film, agglomeration by heating may be performed.
[0071]
Thereafter, by removing the porous layer 30 by etching, the carbon nanotubes 10 grown on the surface of the porous layer 30 are lifted off together with the porous layer 30, and the carbon nanotubes grown from the surface of the substrate 20 where the bottoms of the pores 32 are exposed. Leave only. Thus, the carbon nanotubes 10 extending in the direction perpendicular to the substrate surface and having a uniform band gap can be arranged at equal intervals corresponding to the arrangement of the pores 32 of the porous layer.
[0072]
The arrangement of the carbon nanotubes 10 can be adjusted by adjusting the size of the pores and the spacing between adjacent pores. The Co thin film 40 formed on the bottoms of the pores 32 of the porous layer 30 tends to aggregate into a smaller number or even a single fine particle due to aggregation. Since a single carbon nanotube easily grows with respect to a single fine particle, a carbon nanotube corresponding to the number of nuclei of Co fine particles existing there grows at the bottom of the pore 32. Therefore, this property can be used to adjust the number of carbon nanotubes that grow in each pore.
[0073]
If the carbon nanotube production apparatus shown in FIG. 9 is used, the above-described production method does not take out the substrate from the reaction chamber, and growth of carbon nanotubes and selective oxidation treatment of predetermined carbon nanotubes by laser light irradiation, or The selective fluorination treatment can be performed continuously.
[0074]
In this manufacturing apparatus, a laser beam transmitting window 140 is provided in a reaction chamber 102 of a CVD apparatus, and a laser beam oscillated from a laser oscillator 130 provided outside is used as a laser beam by using a lens system 132 and a mirror system 134. The light is guided into the reaction chamber 102 through the light transmission window 140. Further, as the gas supply source of the CVD apparatus, in addition to the raw material gas source and the inert gas source used for the synthesis of the carbon nanotube, the selective oxidation treatment described in the first to third embodiments or the selective hooking process is used. Oxygen (O ₂ ) Gas and gas supply sources such as fluorine (F) gas are added. If this carbon nanotube manufacturing apparatus is used, when the carbon nanotube is grown, the inside of the reaction chamber is raised to a predetermined temperature, and an inert gas and a carbon nanotube source gas are introduced into the reaction chamber 102. Then, when performing the process of aligning the band gaps of the carbon nanotubes, the reaction chamber is once evacuated and replaced with an inert gas, and then the reaction chamber is adjusted to a predetermined temperature to be inert with oxygen gas or fluorine gas. Introduce gas. Then, a laser beam having a predetermined wavelength is irradiated onto the substrate in the reaction chamber through the laser beam transmission window.
[0075]
According to the fourth embodiment described above, since the carbon nanotubes extending in the direction perpendicular to the substrate and having a predetermined band gap can be arranged on the substrate at equal intervals, the transistors arranged in an array, etc. This is an extremely effective manufacturing method for manufacturing electronic parts.
[0076]
(Fifth embodiment)
In the fifth embodiment, a specific method for producing single-walled carbon nanotubes with a uniform band gap will be described using any of the methods of the first to third embodiments described above.
[0077]
Hereinafter, a manufacturing method according to the fifth embodiment will be described with reference to FIGS. 10 and 11.
[0078]
First, single-walled carbon nanotubes are synthesized using the CVD apparatus shown in FIG. The reaction chamber 102 and the surrounding heating furnace 112, an exhaust pump 122 such as a rotary pump for exhausting the inside of the reaction chamber 102, and each source gas supply line are the same as the CVD apparatus shown in FIGS. In addition, a quartz tube 132 containing a catalyst 142 for carbon nanotube growth reaction is provided in the upstream region of the reaction chamber 102.
[0079]
As the catalyst 142, for example, Fe supported on alumina. ₂ O _Three Use fine particles. This Fe ₂ O _Three The fine particles are 0.245 g Fe (NO ₃ ) ₃ -It is obtained by dissolving 9-hydrate in methanol, heating to 80 ° C, removing methanol using a rotary evaporator, and further heating to 150 ° C.
[0080]
Ar gas as a carrier gas and methane (CH ₄ ) When the gas is introduced into the reaction chamber 102, it passes through the quartz tube 132 containing the catalyst 142, so that the components of the catalyst 142 are also mixed into the reaction chamber 102 together with the source gas and the carrier gas.
[0081]
For example, the inside of the reaction chamber 102 is heated to about 1000 ° C., the source gas is supplied into the reaction chamber 102 under the conditions of a source gas pressure of 1.25 atm and a source gas flow rate of 6.15 l / h, and the reaction is performed for about 10 minutes. Let As a result, single-walled carbon nanotubes having a diameter of 1 nm to 10 nm and a length of 10 μm or less can be obtained by a hydrocarbon catalytic reaction in a gas phase. The carbon nanotubes thus obtained have various band gaps depending on the diameter and chirality state.
[0082]
Next, a process for aligning the band gaps of the carbon nanotubes 12 with uneven band gaps is performed using the method according to any of the first to third embodiments.
[0083]
For example, when the selective oxidation process according to the first embodiment is used, as shown in FIG. 11, the synthesized carbon nanotubes 12 with uneven band gaps are taken out from the reaction chamber 102, and a substrate 22 made of SiC or the like is taken. Place on top. This substrate is not particularly limited as long as it has a large band gap and does not absorb the wavelength of the laser beam to be irradiated.
[0084]
Next, the substrate 22 on which the carbon nanotubes 12 are placed is transferred into a reaction vessel having a laser light transmission window, for example, as shown in FIG. The inside of the reaction chamber is adjusted to an oxygen-containing atmosphere of, for example, O 2: He = 1: 1, and the carbon nanotubes 12 placed on the substrate 22 are irradiated with laser light having a wavelength λ. The wavelength λ of the laser light is selected according to the band gap of the carbon nanotube to be produced. When it is desired to make the band gap of the carbon nanotube larger than Eg [eV], the wavelength λ [μm] of the laser beam to be irradiated may be selected so as to satisfy λ ≦ 1.239 / Eg. For example, when it is desired to make the band gap Eg of the carbon nanotube larger than 1.5 [eV], a laser beam with λ = 826 [nm] may be irradiated. For example, when a YAG laser having a wavelength of 1.064 μm is used as the laser, the band gap of the carbon nanotube can be made larger than 1.16 [eV]. In this case, for example, repetitive 1kHz, peak power density 300kW / cm ² Laser light irradiation is performed under the condition of a pulse width of 300 nsec.
[0085]
Note that the selective oxidation treatment of the excited carbon nanotubes with laser light irradiation may be repeatedly performed during the growth process of the carbon nanotubes.
[0086]
As described above, according to the fifth embodiment, single-walled carbon nanotubes with a uniform band gap can be produced by a simple method.
[0087]
(Sixth embodiment)
In the sixth embodiment, using the method according to the first to third embodiments and the method according to the fourth embodiment described above, the substrate is equally spaced on the substrate in the direction perpendicular to the substrate surface. A specific method for forming extended carbon nanotubes with a uniform band gap will be described. Here, an example in which an alumite layer is used as the porous layer will be described.
[0088]
First, an alumite having pores is formed on a substrate by the following procedure. The substrate is preferably a conductor or semiconductor suitable for anodization, such as a SiC substrate, and further, a substrate that does not absorb laser light in the subsequent laser irradiation treatment and can withstand the temperature during the growth of carbon nanotubes. desirable.
[0089]
For example, an aluminum layer is formed on a SiC substrate using a vacuum deposition method. Specifically, the cleaned SiC substrate is carried into a vacuum chamber of an electron beam evaporation apparatus, and the inside of the vacuum chamber is depressurized to 1E-4 to 6 Pa to perform evaporation. The thickness t (nm) of the aluminum layer is, for example, 2 nm ≦ t ≦ 50 nm.
[0090]
Next, the aluminum layer is anodized in an acidic aqueous solution and alumite treatment is performed. Specifically, the SiC substrate on which the aluminum layer is formed is immersed in a sulfuric acid aqueous solution having a sulfuric acid concentration of 1 to 50 wt%, more preferably 5 to 30 wt%, and a temperature of 0 to 50 ° C., more preferably 5 to 30 ° C. In this sulfuric acid aqueous solution, the current density J [A / dm ² ] 0 <J ≦ 10 [[A / dm ² More preferably, 1 ≦ J ≦ 2 [A / dm ² ], An electric field is applied under the condition of voltage V [V] of 0 <V ≦ 50V, more preferably 5 ≦ V ≦ 20. The aluminum layer is anodized to form an alumite layer that is a porous layer. Under the above conditions, the alumite layer has a pore diameter of 3 to 100 nm and a pore density of 5000 to 500000 / cm at regular intervals. ² Pores are formed. Thus, the pore diameter and the pore density can be adjusted by the current time, the sulfuric acid aqueous solution temperature, the immersion time, and the like. Note that various acidic aqueous solutions such as oxalic acid, phosphoric acid, chromic acid, organic acid + sulfuric acid, boric acid + formamide, and the like can be used instead of the sulfuric acid aqueous solution.
[0091]
Thereafter, alumina remaining at the bottom of the hole is removed by a method such as Ar sputtering, and the surface of the SiC substrate is surely exposed at the bottom of each hole.
[0092]
Next, carbon nanotubes are grown using a hydrocarbon catalytic decomposition method. First, a reaction catalyst, for example, Co is formed on the surface of the SiC substrate on which the alumite layer is formed using a sputtering method or a CVD method. Co film thickness should just be thinner than the thickness of an alumite layer. Thereafter, the SiC substrate is preferably heated to agglomerate Co.
[0093]
For example, this substrate is carried into the reaction chamber 102 of the carbon nanotube production apparatus shown in FIG. The substrate temperature is set to about 400 ° C. by the heater 112, and the reaction chamber 102 is filled with N ₂ H diluted with ₂ S + H ₂ Flow gas and pre-process for about 2 hours.
[0094]
Next, the pressure in the reaction chamber 102 is reduced, and acetylene (C ₂ H ₂ ) Or the like is introduced into the reaction chamber 102. The substrate temperature is heated to 600 to 1400 ° C., more preferably 800 to 1000 ° C., and the raw material gas is pyrolyzed under a Co catalyst to grow carbon nanotubes on the surface of the alumite layer and the bottom of the pores.
[0095]
The carbon nanotubes grow in a direction perpendicular to the substrate surface under the aggregated Co fine particles. When the height of the carbon nanotubes grown from the bottom of the pores of the alumite layer does not reach the thickness of the alumite layer, the source gas in the chamber is exhausted and the growth of the carbon nanotubes is once stopped.
[0096]
Next, using any one of the methods according to the first to third embodiments, the carbon nanotube band gaps with uneven band gaps are aligned. For example, when the selective oxidation process according to the first embodiment is performed, the source gas in the chamber is evacuated, the pressure in the reaction chamber 102 is reduced, and oxygen (O ₂ ) Gas and helium (He) gas are introduced at a flow rate ratio of about 1: 1, and the inside of the reaction chamber 102 is made an oxygen-containing atmosphere.
[0097]
The carbon nanotube is irradiated with laser light having a wavelength λ through the laser light transmission window 140. When it is desired to obtain a direct transition type carbon nanotube larger than the band gap Eg [eV], the wavelength λ [μm] of the laser beam to be irradiated is selected so as to satisfy λ ≦ 1.239 / Eg. For example, when aligning the band gaps of carbon nanotubes to those larger than E = 1.5 [eV], laser light with λ = 826 [nm] may be irradiated. For example, when a YAG laser having a wavelength of 1.064 μm is used as the laser, the band gap of the carbon nanotube can be made larger than 1.16 [eV]. In this case, repeated 1kHz, peak power density 300kW / cm ² Laser light irradiation is performed under conditions such as a pulse width of 300 nsec. Carbon nanotubes having a predetermined band gap or less excited by this laser light irradiation are oxidized and extinguished.
[0098]
Thereafter, carbon nanotubes are again grown on the substrate by the hydrocarbon catalytic decomposition method using the method described above. By repeating the growth of carbon nanotubes and the annihilation process of carbon nanotubes below a predetermined band gap by laser irradiation in an oxidizing atmosphere, carbon nanotubes with a band gap equal to or longer than a predetermined length are converted into pores in the anodized layer and anodized layers. It can be grown on the SiC substrate exposed at the bottom. Note that the Co film may be formed again before the carbon nanotube growth again.
[0099]
Finally, the substrate is immersed in a phosphoric acid solution, and the alumite layer is removed by etching. Through this step, the carbon nanotubes grown on the surface of the alumite layer are also peeled off together with the alumite layer. On the SiC substrate, only carbon nanotubes having a band gap of a certain level or more grown from the bottom of each pore of the alumite layer remain. Further, these remaining carbon nanotubes are arranged at equal intervals according to the positions of the pores.
[0100]
As described above, according to the sixth embodiment, the carbon nanotubes having a uniform band gap are formed on the substrate in the direction perpendicular to the substrate surface by using the porous structure of the alumite layer. Can be manufactured.
[0101]
(Seventh embodiment)
In the seventh embodiment, carbon nanotubes with a uniform band gap extending in a direction perpendicular to the substrate surface are formed on the substrate using the methods according to the first to third embodiments described above. Another method will be described. Here, a method is used in which catalyst fine particles are dispersedly arranged on a substrate using an immersion method.
[0102]
First, catalyst fine particles to be dispersed on a substrate are prepared. The catalyst fine particles are not limited as long as they have a catalytic function for the carbon nanotube growth reaction, and include Co, Ni, NiCo, Rh, Pd, Pt, RhPd, Y, La, or these metals. Fine particles of a metal compound such as silicide can be used. Here, an example using Co fine particles will be described.
[0103]
N ₂ 10% by weight of didodecyl ammonium bromide in toluene in a glove box sufficiently substituted with ₂ ・ 6H ₂ O is dissolved in 0.005M (mol / l) and stirred. Furthermore, 5 M (mol / l) NaBH was added to this solution. ₄ Add, mix and stir again. Thus, a solution in which Co fine particles having a diameter of about 5 nm are dispersed is prepared. Co fine particles are separated from this solution, and the separated Co fine particles are washed with acetone and toluene, and finally Co fine particles are dispersed in acetone.
[0104]
The substrate is immersed in an acetone solution in which Co fine particles are dispersed, pulled up, and dried at room temperature. Thus, as shown in FIG. 12A, about 5 nm of Co fine particles 44 of about 5 nm on the substrate 24, for example, 50 / μm. ² Disperse at a certain density. The dispersion density of the Co fine particles can be adjusted by the Co content concentration in the solution to be immersed, the pulling rate, and the like.
[0105]
Note that the substrate may be any substrate that does not absorb the irradiation laser during the subsequent laser irradiation and can withstand the temperature during carbon nanotube growth. Therefore, glass substrate, SiC substrate, α-Al ₂ O ₃ A substrate or a zeolite substrate can be used.
[0106]
Next, this substrate 24 is carried into a reaction chamber of a thermal CVD apparatus as shown in FIG. 9, and carbon nanotubes are produced under the same conditions as in the sixth embodiment. That is, N ₂ H diluted with ₂ S + H ₂ After the pretreatment in the gas, the substrate temperature is heated to about 600 to 1000 ° C., hydrocarbon catalytic decomposition is performed, and carbon nanotubes are grown. The carbon nanotubes grow in a direction perpendicular to the substrate surface where Co fine particles exist on the substrate 24.
[0107]
When carbon nanotubes have grown to some extent, the pressure in the reaction chamber is reduced, the reaction gas is exhausted, and the growth of carbon nanotubes is stopped.
[0108]
Subsequently, the source gas in the reaction chamber is exhausted under the same conditions as in the sixth embodiment, and O ₂ Gas and He gas are introduced, and the reaction chamber is filled with an oxygen-containing atmosphere, and then the carbon nanotube is irradiated with laser light having a wavelength λ [μm]. When the desired band gap is Eg [eV], a laser beam that satisfies λ ≦ 1.239 / Eg is selected. Further, a pulse laser such as YAG can be used as necessary. Carbon nanotubes having a predetermined band gap or less excited by this laser light irradiation are oxidized and extinguished.
[0109]
Thereafter, carbon nanotubes are grown again on the substrate using the above-described hydrocarbon catalytic decomposition method. By repeating the growth of carbon nanotubes and the annihilation process by selective oxidation of carbon nanotubes below a predetermined band gap by laser light irradiation in an oxygen atmosphere, carbon nanotubes with a band gap of a predetermined length or more are grown on the substrate. Can be made. In this way, for example, carbon nanotubes 14 having a length of 500 nm or more can be grown perpendicularly to the substrate using Co fine particles dispersed on the substrate 24 as nuclei as shown in FIG. 12B. According to this manufacturing method, the distance between adjacent carbon nanotubes is 300 nm, and the density is 10 / μm. ² Carbon nanotubes of a certain degree can be produced.
[0110]
As described above, according to the manufacturing method according to the seventh embodiment, carbon nanotubes extending in a direction perpendicular to the substrate and having a predetermined band gap can be dispersedly arranged on the substrate. The density and dispersion state of the carbon nanotubes can be easily adjusted by the dispersion conditions of the Co fine particles on the substrate.
[0111]
(Eighth embodiment)
In the eighth embodiment, a method for manufacturing an FET using carbon nanotubes manufactured by the method according to the sixth embodiment will be described.
[0112]
Hereinafter, a description will be given with reference to FIGS. 13 (a) to 14 (n).
[0113]
As shown in FIGS. 13A to 13F, carbon nanotubes having a uniform band gap are formed on the SiC substrate 26 by using the method according to the sixth embodiment. Note that conditions similar to those in the sixth embodiment can be used, and thus description of specific conditions is omitted.
[0114]
First, an Al layer 36a having a thickness of 2 nm to 50 nm is formed by electron beam evaporation (FIG. 13A). Next, the Al layer 36a is immersed in a sulfuric acid aqueous solution, and anodization is performed to form an alumite layer 36 having pores arranged at equal intervals (FIG. 13B). Thereafter, if necessary, the surface is sputtered with Ar or the like to expose the SiC substrate surface at the bottom of the pores of the alumite layer 36.
[0115]
In the above example, an alumite layer is formed on the substrate. However, after forming an element isolation region and a semiconductor element necessary for the substrate, an aluminum layer is formed on the substrate surface on which these elements are formed. It may be formed and anodized to form an alumite layer.
[0116]
Next, a Co film 46 having a catalytic function is formed on the surface (FIG. 13C). Thereafter, the SiC substrate is preferably heated to coagulate the Co film.
[0117]
Further, the carbon nanotubes 16 are grown on the surface of the alumite layer and the bottom of the pores using a hydrocarbon catalytic decomposition method. The carbon nanotubes 16 grow in a direction perpendicular to the substrate surface under the aggregated Co fine particles.
[0118]
When the carbon nanotubes are grown, the channel portion is formed when an FET (Field Effect Transistor) is manufactured by introducing, for example, potassium (K) vapor, which is an n-type doping gas, into the reaction chamber together with the source gas. The region is made n-type conductivity. Note that the carbon nanotubes in the non-doped region exhibit p-type conductivity.
[0119]
When the height of the carbon nanotubes grown from the bottom of the pores of the alumite layer 36 does not reach the thickness of the alumite layer 36, the source gas in the chamber is exhausted and the growth of the carbon nanotubes is once stopped.
[0120]
Next, the inside of the reaction chamber is set to an oxygen-containing atmosphere, and the carbon nanotube is irradiated with laser light having a wavelength λ. Carbon nanotubes having a predetermined band gap or less excited by this laser light irradiation are selectively oxidized and extinguished (FIG. 13D).
[0121]
Thereafter, carbon nanotubes having a band gap greater than or equal to a predetermined energy can be obtained by repeating the oxidation and extinction treatment of the carbon nanotubes less than or equal to the predetermined band gap by laser beam irradiation in an oxygen gas-containing atmosphere as necessary. It grows on the SiC substrate exposed at the pore bottom of the alumite layer and the alumite layer (FIG. 13 (e)).
[0122]
Further, the substrate is immersed in a phosphoric acid solution to remove the anodized layer 36 by etching, and the carbon nanotubes formed on the anodized layer 36 are lifted off together. Thus, only the carbon nanotubes 16 having an n-type conductivity having a band gap of a certain level or more grown from the bottom of each pore of the alumite layer 36 remain on the SiC substrate 26 (FIG. 13 (f)). Further, these remaining carbon nanotubes are arranged at equal intervals according to the positions of the pores.
[0123]
Subsequently, an FET structure having a p-type channel portion in the carbon nanotube 16 is fabricated by adding the steps shown in FIGS. 14G to 14N described below. If necessary, the upper layer of carbon nanotubes is etched to align the height (length) of the carbon nanotubes, limit the region where the FET structure is formed, and remove other portions of the carbon nanotubes by etching. May be. Further, the Co film used as a catalyst may be etched together at this time.
[0124]
A metal thin film for a drain electrode, for example, a Co film 50 (first conductive film) is formed on the surface of the SiC substrate 26 on which the carbon nanotubes are formed by using a sputtering method or the like. The Co film 50 is deposited on the surface of the SiC substrate exposed around the carbon nanotubes and the upper surface of the carbon nanotubes 16 (FIG. 14G).
[0125]
Subsequently, using a plasma CVD method or the like, SiO ₂ A film 60 (first insulating film) is formed, and the periphery of the carbon nanotube is SiO, which is an insulating film. ₂ Filled with the film 60 (FIG. 14H).
[0126]
In addition, CF _Four Etching gas such as RIE (Reactive Ion Etching) is used to make SiO ₂ The film 60 is etched back (FIG. 14I), and the Co film 50 on the carbon nanotubes exposed by the etch back is removed by wet etching or the like. Here, it is preferable to heat the substrate at 300 to 600 ° C. in order to reduce the contact resistance between the Co film 50 remaining around the bottom of the carbon nanotube to be the drain electrode and the carbon nanotube 16.
[0127]
Again, SiO ₂ The film 60 is etched back using the RIE method, and the SiO 2 on the side wall portion of the carbon nanotube 16 is etched. ₂ Only the film 60 is left, and the remaining SiO ₂ The film is removed by etching (FIG. 14 (j)). SiO formed in this way ₂ The sidewall thickness of the film 60 is about 15 nm to 1 μm.
[0128]
Next, using a plasma CVD method or the like, SiO ₂ A film 62 is formed. This SiO ₂ The film 62 is deposited on the Co film 50 to be the drain electrode and on the upper surface of the carbon nanotube. Subsequently, a polysilicon layer 70 (second conductive film) is formed by sputtering or LPCVD (Low Pressure CVD) to cover the substrate surface (FIG. 14 (k)).
[0129]
Subsequently, CF is etched using the polysilicon layer 70 as an etching gas. _Four Etch back by RIE using gas. Under these etching conditions, the polysilicon layer 70 and SiO ₂ There is a difference in etching rate of about two digits between the film 62 and a difference in etching rate of three digits or more between the polysilicon layer 70 and the carbon nanotubes 16. SiO selectively etched and deposited on top of carbon nanotubes ₂ The film 62 (second insulating film) is exposed (FIG. 14L).
[0130]
Next, again using a plasma CVD method or the like, SiO ₂ A film 64 (second insulating film) is formed (FIG. 14M). This SiO ₂ The film 64 functions as an interlayer insulating film that electrically insulates the gate electrode formed of the polysilicon layer 70 from the source electrode formed in the next step.
[0131]
Again, CF _Four SiO2 using gas ₂ The film 64 is etched to expose the upper part of the carbon nanotube 16. Under these etching conditions, the carbon nanotubes 16 and SiO ₂ Since there is a difference of about 50 times or more in etching rate from the film 64, SiO 2 ₂ Film 64 and SiO ₂ A part of the film 62 can be selectively etched. A metal thin film for a source electrode, for example, a Co film 80 (third conductive film) is formed on the exposed upper surface of the carbon nanotube. Thereafter, in order to reduce the contact resistance between the Co film 80 and the carbon nanotubes 16, heat treatment is performed at 300 to 600 ° C. (FIG. 14 (n)).
[0132]
Thus, according to the eighth embodiment, it is possible to obtain the FET structure shown in FIG. 14 (n) using carbon nanotubes having a constant band gap. That is, this FET structure has a source electrode made of a Co film 80, a drain electrode made of a Co film 50, and a gate electrode made of a polysilicon layer 70, and a channel is formed in the carbon nanotube 16 that is a semiconductor layer. Thus, since the channel layer is formed on the carbon nanotubes extending perpendicularly to the substrate surface, and the source / drain is formed above and below, a three-dimensional FET structure can be obtained. In addition, since the occupied area on the substrate surface can be reduced as compared with a normal FET structure in which a source / drain and a channel are formed in the in-plane direction of the substrate, the device pattern density can be increased and densification can be achieved. In addition, since the formation positions of the carbon nanotubes correspond to the positions of the pores of the anodized layer having a regular arrangement, they can be formed on the substrate at equal intervals.
[0133]
Furthermore, since carbon nanotubes have ballistic conductivity, there is a high possibility that a transistor having an extremely high operation speed can be provided.
[0134]
In the above description, the Co film is used as the source electrode and the drain electrode, but the present invention is not limited to this. For example, a Ti film can be used. In this case, the heat treatment temperature for reducing the contact resistance with the carbon nanotube is preferably about 600 to 900 ° C.
[0135]
In the above example, since the non-doped carbon nanotubes are p-type, only the carbon tube having the height of the channel portion is doped with K corresponding to the n-type dopant. Can be changed. When forming p-type carbon nanotubes, a p-type dopant source such as Br or I may be introduced into the reaction chamber together with the source gas during the growth of the carbon nanotubes. In the case of forming an n-type carbon nanotube, for example, an n-type dopant such as K, Cs, or Rb may be introduced. For carbon nanotubes extending in a direction perpendicular to the substrate surface, carbon nanotubes of different conductivity types in the height direction can be produced by changing the type of doping material over time as the carbon nanotubes grow. .
[0136]
In the eighth embodiment, the carbon nanotubes are formed by the method using the porous layer according to the sixth embodiment in order to form the carbon nanotubes on the substrate at equal intervals. When it is not necessary to form the carbon nanotubes at intervals, the carbon nanotubes can be produced by the production method according to the seventh embodiment. That is, a method of growing carbon nanotubes by immersing the substrate in a solution in which catalyst fine particles such as Co are dispersed to disperse and arrange the catalyst fine particles on the surface of the substrate may be used. Once carbon nanotubes with uniform band gaps can be formed, the subsequent steps of forming the FET structure can use the same conditions as the manufacturing steps shown in FIGS. 14 (g) to 14 (n).
[0137]
(Ninth embodiment)
In the ninth embodiment, a method for fabricating a FET having a BarriT (Barrier Injection Transit Transistor) structure using carbon nanotubes by applying the method according to the sixth embodiment will be described.
[0138]
Hereinafter, a description will be given with reference to FIGS. 15 (a) to 16 (j).
[0139]
Using the method according to the sixth embodiment, carbon nanotubes with a uniform band gap are produced on the SiC substrate 28. In addition, about the preparation method of a carbon nanotube, since the conditions similar to 6th Embodiment and 8th Embodiment can be used, description about a specific condition is abbreviate | omitted.
[0140]
First, an alumite layer is formed on a SiC substrate. That is, an Al layer is formed on a substrate such as SiC, and this Al layer is further anodized to form an alumite layer having pores arranged at equal intervals. Thereafter, if necessary, the surface is sputtered with Ar or the like to expose the substrate surface at the pore bottoms of the alumite layer.
[0141]
Next, a Co film having a catalytic function is formed on the surface. Thereafter, the substrate is preferably heated to coagulate the Co film. Furthermore, carbon nanotubes are grown on the surface of the alumite layer and the bottom of the pores using a hydrocarbon catalytic decomposition method. The carbon nanotubes grow in a direction perpendicular to the substrate surface under the aggregated Co fine particles. When the height of the carbon nanotubes grown from the bottom of the pores of the alumite layer does not reach the thickness of the alumite layer, the source gas in the chamber is exhausted and the growth of the carbon nanotubes is once stopped.
[0142]
Subsequently, the reaction chamber is filled with an oxygen-containing atmosphere, and the carbon nanotube is irradiated with laser light having a wavelength λ. Carbon nanotubes having a predetermined band gap or less excited by this laser light irradiation are selectively oxidized and disappear.
[0143]
After that, by further repeating the growth of carbon nanotubes and the annihilation treatment by selective oxidation of carbon nanotubes with a predetermined band gap or less by laser light irradiation in an oxidizing atmosphere, The alumite layer and the SiC substrate exposed at the bottom of the pores of the alumite layer are grown.
[0144]
Further, the substrate is immersed in a phosphoric acid solution to remove the alumite layer by etching, and the carbon nanotubes formed on the alumite layer are lifted off together. In this way, only the carbon nanotubes having an n-type conductivity having a band gap of a certain level or more grown from the bottom of each pore of the alumite layer remain on the SiC substrate. Further, these remaining carbon nanotubes are arranged at equal intervals according to the positions of the pores.
[0145]
Subsequently, by adding the steps shown in FIGS. 15A to 16J described below, a FET having a BARTIT structure using carbon nanotubes as a channel portion is manufactured.
[0146]
If necessary, the carbon nanotubes may be etched so that the heights of the carbon nanotubes are uniformed, the region where the FET structure is formed is limited, and carbon nanotubes in other portions may be removed by etching.
[0147]
The surface of the carbon nanotube 18 and the surface of the substrate 28 are made of SiO by plasma CVD. ₂ A film 66 (first insulating film) is formed. At this time, SiO deposited on the side surface of the carbon nanotube ₂ The thickness of the film is 1-50 nm. Next, a metal for drain electrode, for example, Au and / or Pt (hereinafter referred to as Au / Pt) film 52 (first conductive film) is formed by sputtering or the like. The Au / Pt film is deposited on the upper surface of the carbon nanotube 18 and around the bottom of the carbon nanotube 18 (FIG. 15A).
[0148]
Subsequently, using a plasma CVD method or the like, SiO ₂ A film 67 (second insulating film) is formed, and the periphery of the carbon nanotube is SiO, which is an insulating film. ₂ The film 67 is filled (FIG. 15B).
[0149]
Further, using an etching gas such as CF.sub.4, SiO.sub. ₂ The film 67 is etched. By this process, 15 nm to 1 μm of SiO is formed on the side surface of the carbon nanotube 18. ₂ A sidewall by the film 67 remains. The film thickness of the SiO 2 film between the Au / Pt film 52 around the bottom of the carbon nanotube 18 and the carbon nanotube 18 is 1 to 15 nm (FIG. 15C).
[0150]
Next, SiO for electrically insulating the drain electrode and the gate electrode ₂ A film 68 (third insulating film) is formed by sputtering (FIG. 15D).
[0151]
Subsequently, a polysilicon film 72 (second conductive film) is formed by using LPCVD, and a gap between adjacent carbon nanotubes is filled with the polysilicon layer 72 (FIG. 15E).
[0152]
Polysilicon layer 72 is CF _Four Etch back by RIE using gas. Under this etching condition, the polysilicon layer 72 and SiO ₂ There is a difference in etching rate of about two digits between the film 67 and a difference in etching rate of three digits or more between the polysilicon layer 72 and the carbon nanotube 18. It is selectively etched (FIG. 15 (f)).
[0153]
Next, the surface of the polysilicon layer 72 is oxidized to form SiO. ₂ A film 69 (fourth insulating film) is formed (FIG. 16G). CF again _Four SiO by RIE method using ₂ Layer 69 is partially etched away. Under these etching conditions, the carbon nanotubes 16 and SiO ₂ Film 69 (SiO ₂ (Including the films 66 and 67), there is a difference of about 50 times or more in etching rate. ₂ Only the film 69 is selectively etched, and the upper part of the carbon nanotube 18 is exposed (FIG. 16H).
[0154]
Thin SiO 1-15 nm on the exposed carbon nanotube surface ₂ A film 80 (fifth insulating film) is formed (FIG. 16I). Further, an Au / Pt90 film (third conductive film) for the source electrode is formed thereon using a sputtering method or the like. In this way, the BARIT structure shown in FIG. 16 (j) can be obtained.
[0155]
In this BARITT structure, the carbon nanotube 18 forms a channel portion, and a thin insulating layer capable of tunneling electrons is formed between the carbon nanotube, the source electrode, and the drain electrode. In the structure shown in FIG. 16 (j), SiO, which is a side wall formed on the side wall of the carbon nanotube 18, is used. ₂ 67 is a gate insulating film, and a polysilicon layer 72 having a forbidden band at the same energy level as the electrode is used for the gate.
[0156]
When the gate is not biased, no current flows. However, when the gate is positively biased, the conduction band of the carbon nanotube 18 is pushed down to the valence band side, and the channel level becomes the same as the source electrode / drain electrode. At the same level, the element is turned on by the tunnel current.
[0157]
As described above, according to the ninth embodiment, the channel layer is formed on the carbon nanotube extending perpendicularly to the substrate surface, and the source electrode / drain electrode is formed above and below the insulating film via the insulating film. Since it is formed, it is possible to obtain a three-dimensional FET having a BARITT structure. In addition, since the occupied area on the substrate surface can be made smaller than a normal FET structure in which the source / drain and the channel are formed in the in-plane direction of the substrate, the device pattern density can be increased and the device can be densified. Furthermore, since the formation positions of the carbon nanotubes correspond to the positions of the pores of the alumite layer having a regular arrangement, they can be formed on the substrate at equal intervals.
[0158]
In the ninth embodiment, carbon nanotubes are formed by the method using the porous layer according to the sixth embodiment in order to form carbon nanotubes on the substrate at equal intervals. When it is not necessary to form the carbon nanotubes at intervals, the carbon nanotubes can be produced by the production method according to the seventh embodiment. That is, a method of growing carbon nanotubes by immersing the substrate in a solution in which reaction catalyst fine particles such as Co are dispersed to disperse and arrange the catalyst fine particles on the substrate surface may be used. Once carbon nanotubes with uniform band gaps can be formed, the same conditions can be used in the manufacturing steps shown in FIGS. 15A to 16J for forming the subsequent BARITT structure.
[0159]
As mentioned above, although the manufacturing method of the carbon nanotube of this invention was demonstrated along embodiment, the manufacturing method of the carbon nanotube of this invention is not limited to description of embodiment mentioned above, Various deformation | transformation It is obvious to those skilled in the art that improvements are possible.
[0160]
For example, in the eighth and ninth embodiments, examples in which carbon nanotubes are applied to FETs have been described. However, in addition to FETs, applications to light emitting diodes, semiconductor lasers, and the like are possible. In the eighth and ninth embodiments, the selective oxidation according to the first embodiment is used as a method of aligning the band gaps of the carbon nanotubes, but depending on the required band gap value. The method according to the second or third embodiment may be used.
[0161]
【The invention's effect】
As described above, according to the first and second carbon nanotube production methods of the present invention, only the carbon nanotubes having a certain band gap or more or a certain band gap or less according to the wavelength of the irradiated laser beam are used. It becomes possible to obtain. If this manufacturing method is used, a carbon nanotube with a uniform band gap can be provided regardless of the type of carbon nanotube synthesis method. Therefore, application to an electronic device using carbon nanotubes becomes possible.
[0162]
In addition, according to the characteristics of the semiconductor device manufacturing method using the first or second carbon nanotube described above, a nanoscale FET having a channel portion in the carbon nanotube extending in a direction perpendicular to the substrate surface is provided. it can. Furthermore, since the FET extending in the direction perpendicular to the substrate surface can be formed instead of being formed in the substrate surface direction, an extremely fine and dense nanoscale device can be provided.
[0163]
Furthermore, according to the characteristics of the carbon nanotube production apparatus of the present invention, the carbon nanotube production method of the first or second aspect of the present invention can be implemented more efficiently.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a processing method for aligning the band gap of carbon nanotubes according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a relationship between laser light irradiation and excitation in a direct transition type carbon nanotube.
FIG. 3 is a schematic view showing a processing method for aligning the band gap of carbon nanotubes according to a second embodiment of the present invention.
FIG. 4 is a schematic view showing a processing method for aligning the band gap of carbon nanotubes according to a third embodiment of the present invention.
FIG. 5 is a perspective view of a porous layer used in the carbon nanotube production method according to the fourth embodiment of the present invention, and a cross-sectional view showing a state of a Co thin film formed on the porous layer.
FIG. 6 is a process diagram showing a carbon nanotube production method according to a fourth embodiment of the present invention.
FIG. 7 is a schematic configuration diagram of a thermal CVD apparatus that can be used in a carbon nanotube manufacturing method according to a fourth embodiment of the present invention.
FIG. 8 is a process diagram showing a carbon nanotube manufacturing method according to a fourth embodiment of the present invention.
FIG. 9 is an outline of an apparatus capable of synthesizing carbon nanotubes that can be used in the carbon nanotube manufacturing method according to the fourth embodiment of the present invention and annihilating the carbon nanotubes having a predetermined band gap by laser light irradiation. It is a block diagram.
FIG. 10 is a schematic configuration diagram of a thermal CVD apparatus that can be used in a carbon nanotube manufacturing method according to a fifth embodiment of the present invention.
FIG. 11 is a perspective view showing a state of single-walled carbon nanotubes synthesized by the manufacturing method according to the fifth embodiment of the present invention.
FIG. 12 is a perspective view showing a state in which Co fine particles are dispersed on a substrate in a carbon nanotube production method according to a seventh embodiment of the present invention, and is obtained perpendicularly to the substrate surface obtained by the method. It is a perspective view which shows the state of the carbon nanotube extended.
FIG. 13 is a process diagram showing a carbon nanotube manufacturing method according to an eighth embodiment of the present invention.
FIG. 14 is a process diagram showing a method of manufacturing an FET using carbon nanotubes according to an eighth embodiment of the present invention.
FIG. 15 is a process diagram showing a method for manufacturing a FET having a BARITT structure using carbon nanotubes according to a ninth embodiment of the present invention.
FIG. 16 is a process diagram showing a method for manufacturing a FET having a BARITT structure using carbon nanotubes according to a ninth embodiment of the present invention.
[Explanation of symbols]
10a, 10b, 10c ... carbon nanotubes
10, 12, 14, 16, 18 ... carbon nanotubes
20, 22, 24, 26, 28 ... substrate
30, 36 ... porous layer (alumite layer)
32 ... pores
40, 46 ... Co film
44 ... Co fine particles
50 ... Co film
52, 90 ... Au / Pt film
60, 62, 64, 66, 67, 68, 69, 80 ... SiO2 film
70, 72 ... polysilicon layer

Claims (7)

Synthesizing carbon nanotubes;
Selective oxidation in which the carbon nanotubes are irradiated with a first laser beam having a wavelength λ1 in an oxidizing gas-containing atmosphere, and the carbon nanotubes excited by the first laser beam irradiation are selectively oxidized and gasified. Processing steps ;
In the fluorinated gas-containing atmosphere, the remaining carbon nanotubes are irradiated with a second laser beam having a wavelength λ2 shorter than the wavelength λ1, and the carbon nanotubes excited by the irradiation with the second laser beam are selectively used as the carbon nanotubes. A selective fluorination treatment step of reacting with a fluorinated gas to form a fluorinated layer on at least the surface of the carbon nanotube;
An oxidation treatment step of oxidizing and gasifying the carbon nanotubes in which the fluorinated layer is not formed in an oxidizing gas-containing atmosphere;
And a defluorination treatment step of removing a fluorine component from the carbon nanotube having a fluorinated layer remaining without being gasified . Synthesizing carbon nanotubes;
In a fluorinated gas-containing atmosphere, the carbon nanotube is irradiated with a first laser beam having a wavelength λ1, and the carbon nanotubes excited by the irradiation of the first laser beam are selectively reacted with the fluorinated gas, A selective fluorination treatment step of forming a fluorination layer on at least the surface of the carbon nanotube;
An oxidation treatment step of oxidizing and gasifying the carbon nanotubes in which the fluorinated layer is not formed in an oxidizing gas-containing atmosphere;
And a defluorination treatment step of removing a fluorine component from the carbon nanotube having a fluorinated layer remaining without being gasified. Further, after the defluorination treatment step,
In an oxidizing gas-containing atmosphere, the carbon nanotubes are irradiated with a second laser beam having a second wavelength λ2 longer than the first wavelength λ1, and the carbon nanotubes excited by the second laser beam irradiation are selected. And a selective oxidation treatment step of oxidizing and gasifying the carbon nanotube according to claim 2 . The step of synthesizing the carbon nanotubes includes:
Forming a porous layer having pores regularly arranged and having a substrate surface exposed at the bottom;
Forming a film made of a metal or a metal compound having a catalytic function for a carbon nanotube growth reaction on the substrate exposed at the bottom of the pore;
The method for producing carbon nanotubes according to any one of claims 1 to 3 , further comprising a step of growing carbon nanotubes in at least the pores by a hydrocarbon catalytic decomposition reaction. Using the method for producing carbon nanotubes according to any one of claims 1 to 4 , a step of producing carbon nanotubes extending in a direction perpendicular to the substrate surface;
Filling the periphery of the bottom of the carbon nanotube with a first conductive film;
Forming a side wall with a first insulating film on a side wall surface of the carbon nanotube not filled with the first conductive film;
Forming a second insulating film, a second conductive film, and a third insulating film sequentially around the sidewall from below;
Forming a third conductive film on the third insulating film and an upper surface of the carbon nanotube. A method of manufacturing a semiconductor device using a carbon nanotube. Using the method for producing carbon nanotubes according to any one of claims 1 to 4 , a step of producing carbon nanotubes extending in a direction perpendicular to the substrate surface;
Coating the entire side wall surface of the carbon nanotube with a first insulating film;
Filling the periphery of the bottom of the carbon nanotube covered with the first insulating film with a first conductive film;
Forming a side wall with a second insulating film on a side wall surface of the carbon nanotube not filled with the first conductive film;
Forming a third insulating film, a second conductive film, and a fourth insulating film in order around the sidewall from below;
And a fourth insulating film and a step of sequentially forming a fifth insulating film and a third conductive film on the upper surface of the carbon nanotube. A method of manufacturing a semiconductor device using carbon nanotubes . A reaction vessel;
A laser light transmission window provided on the wall of the reaction vessel;
Introducing means for introducing a carbon nanotube-forming raw material gas, an inert gas, and at least one of an oxidizing gas or a fluorinated gas into the reaction vessel;
An exhaust means for exhausting the gas in the reaction vessel ;
A laser oscillator provided outside the reaction vessel and for introducing laser light into the reaction vessel through the laser light transmission window;
The carbon nanotube production raw material gas and the inert gas are introduced into the reaction vessel to synthesize the carbon nanotube, and at least the oxidizing gas or the fluorinated gas is used to irradiate the carbon nanotube with the laser beam. Thus , the carbon nanotube production apparatus is characterized in that the selective removal of a part of the carbon nanotube is performed in the same reaction vessel .

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