JP2002004087A - Method for manufacturing nanostructure and nanostructure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a more regular nanostructure by lessening the disorder and defect made by anodic oxidation. SOLUTION: In the method for manufacturing the nanostructure which anodically oxidizes a layer to be anodically oxidized essentially consisting of Al to form pores, a barrier film is formed by anodic oxidation on the surface of the layer to be anodically oxidized, and after the forming positions of the pores are positioned by removing at least part of the barrier film, the porous film by the anodic oxidation is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a nanostructure and a nanostructure, and more particularly, to a nanostructure having a pore obtained by the production method of the present invention. In addition to devices, it can be used in a wide range as an optical device, a micro device, a three-dimensional structural material, and the like.

[0002]

2. Description of the Related Art <Nanostructures> Metal and semiconductor thin films,
Fine lines, dots, and the like may exhibit unique electrical, optical, and chemical properties by confining the movement of electrons in a size smaller than a certain characteristic length. From such a viewpoint, several hundreds of
There is a growing interest in materials (nanostructures) having a structure finer than nanometers (nm).

As a method for manufacturing a nanostructure, for example, there is a method using a semiconductor processing technique such as a fine pattern drawing technique such as photolithography, electron beam exposure, or X-ray exposure.

In addition to such a manufacturing method, a new nanostructure is to be realized based on a regular structure formed naturally, that is, a structure formed self-regularly. There is an attempt. Many studies have begun on these techniques because there is a possibility that a finer and special structure can be produced more than the conventional method depending on the fine structure used as a base.

[0005] An example of such a self-regular method is anodic oxidation, which can easily produce a nanostructure having nanosize pores in a controlled manner. For example, anodized alumina produced by anodizing aluminum and its alloys in an acidic bath is known. Hereinafter, the anodic oxide film will be described in detail.

<Anodic Alumina: Porous Film> When an Al plate is anodized in an acidic electrolyte such as sulfuric acid, oxalic acid or phosphoric acid, a porous oxide film (porous type anodic oxide film: hereinafter abbreviated as porous film) is obtained. Is formed (eg, RC Furneaux, WR Rigb
y & A. P. Davidson "NATURE" Vo
l. 337, P147 (1989), etc.). FIG.
It is sectional drawing which shows the nanostructure which has the vertical type pore of the conventional example. FIG. 9A is a plan view, and FIG. 9B is a sectional view taken along line CC ′.

[0009] As shown in FIG. 9, the feature of this porous film is that, as shown in FIG. 9, extremely fine columnar pores (nanoholes) 11 having a diameter 2r of several nm to several hundred nm are formed at intervals of 2R to several tens nm to several hundred nm. (Cell size) to have a specific geometric structure of being arranged in parallel. This columnar pore 1
No. 1 has a high aspect ratio and is excellent in the uniformity of the cross-sectional diameter. At the bottom of the pores 11, an insulating layer called a barrier layer is formed, but in the present invention, in order to clearly distinguish the barrier type anodic oxide film (barrier film), which is an anodic oxide film that does not form pores, The barrier layer at the bottom of the pores 11 is simply called a pore bottom insulating layer.

Further, the structure of the porous film can be controlled to some extent by changing the conditions of anodic oxidation.
For example, it is known that the pore spacing can be controlled to some extent by the anodic oxidation voltage, the depth of the pores by the anodic oxidation time, and the pore width by pore wide processing.

In order to improve the verticality, linearity and independence of the pores of the porous film, a two-stage anodic oxidation method is used, that is, the porous film formed by the anodic oxidation is once removed and then removed again. There has been proposed a method of producing a porous film having pores exhibiting better perpendicularity, linearity and independence by performing anodization (“Japan”).
ese Journal of Applied Ph
isics ”, Vol. 35, Part 2. No. 1
B, pp. L126-L129,15 January
1996). Here, this method uses that the depression on the surface of the Al plate formed when the anodic oxide film formed by the first anodic oxidation is removed serves as the starting point of the formation of pores for the second anodic oxidation.

Furthermore, in order to improve the controllability of the shape, spacing and pattern of the pores of the porous film, a method of forming the starting point of the pore formation using a stamper, that is, a substrate having a plurality of projections on its surface To form a porous film having pores exhibiting better shape, spacing and pattern controllability by forming a pit formed by pressing the aluminum plate against the surface of the Al plate as a starting point of pore formation and then performing anodization. (Japanese Patent Application Laid-Open No. 10-112292, Nakao or "Solid State Physics" 31, 493 (199)).
6)). A technique of forming concentric pores instead of honeycomb is reported by Okubo et al. In Japanese Patent Application Laid-Open No. H11-224422.

In addition, Masuda et al. Have reported an example in which an Al film sandwiched between insulators is anodized in the film surface direction to form pores in a row (“Appl. Phys. Let.”).
t. "63, p3155 (1993)).

Various applications have been attempted, focusing on the specific geometric structure of the anodized alumina. The explanation by Masuda is detailed, but the application examples are listed below. For example, there is an application as a film utilizing the wear resistance and insulation resistance of the anodic oxide film, and an application to a filter by peeling the film. Furthermore, coloring, magnetic recording media, EL light-emitting elements, electrochromic elements, optical elements, solar cells, gas sensors, etc. can be achieved by using a technique of filling the pores with a metal or semiconductor or a technique of replicating the pores. Various applications have been attempted. Furthermore, quantum wires,
It is expected to be applied to various fields such as quantum effect devices such as MIM elements and molecular sensors using pores as chemical reaction fields (Masuda "Solid State Physics" 31,493 (199)
6)).

<Anodized Alumina: About Barrier Type Coating> When an Al plate is anodized in an electrolyte such as ammonium borate, a barrier type anodic oxide coating (hereinafter abbreviated as “barrier coating”) having a film shape different from a porous film. (For example, Kobayashi: “Surface Technology” Vol. 40, No. 1)
2, P10.1989, etc.). The feature of this barrier film is that a dense oxide insulating layer having no pores is formed with a voltage-dependent film thickness as compared with a porous film, and the film thickness is approximately voltage (V) × 1.3 (nm). It is. The structure of this insulating layer is mainly composed of amorphous alumina,
Some crystalline alumina may be formed. In order to prevent the formation of crystalline alumina, it is necessary to use an electrolytic solution such as ammonium dihydrogen phosphate, which does not easily produce crystalline alumina.

[0014]

The alumina pores described above are generally formed on the surface of an Al plate, and the direction of the pores is perpendicular to the surface. However, Al substrates usually have severe irregularities, and are often subjected to a process of flattening the aluminum surface by electrolytic polishing. However, it is difficult to achieve sufficient flattening by electrolytic polishing.
need to be polished. In particular, in the case of an Al film formed instead of an Al plate, it is difficult to ensure a thickness sufficient for electrolytic polishing. In the Al film, generally, a concave portion or a convex portion called a hillock is easily formed at a grain boundary, and a flattening technique has been desired.

As described above, a method of forming pores parallel to the substrate has also been reported. However, since an insulating layer is formed after forming an Al film, Al and the anodized layer are not formed. The interface of the insulating layer was disturbed by grain boundaries and hillocks, which was a factor that disturbed the shape of the pores.

In view of these problems, an object of the present invention is to provide a method for producing a nanostructure which reduces disturbances and defects in pores produced by anodic oxidation. It is another object of the present invention to provide a method for manufacturing a nanostructure incorporating an Al layer flattening technique for reducing an Al portion sacrificed by electrolytic polishing. Another object of the present invention is to provide a method for producing a nanostructure having more regular pores. It is a further object of the present invention to provide a more regular nanostructure with less turbulence and defects in the pores.

[0017]

The above objects can be attained by the following constitution and manufacturing method of the present invention. That is, in a method for producing a nanostructure in which pores are formed by anodizing a layer to be anodized mainly containing aluminum, a barrier film is formed on the surface of the layer to be anodized, and then a layer under the barrier layer is formed. Forming a porous film on the anodized layer or the anodized layer after removing the barrier layer.

Here, after producing the barrier film,
It is also effective to form a porous film after removing at least a part of the barrier film. In this case, a manufacturing method in which the removed portion of the barrier film corresponds to the position where the pores are formed, or a method of forming a pore formation starting point after removing the barrier film, or after removing the barrier film It is preferable to form a porous film after forming an insulating layer on the surface of the anodized layer. In the method using the insulating layer, it is also effective to remove the insulating layer at a portion corresponding to the position where the pores are formed, and then form a porous film.

A method for producing a nanostructure in which an anodized layer is an Al film formed on a substrate, the substrate surface is insulative, and a porous film having pores parallel to the substrate is produced. It is valid. Further, the present invention is a method for producing a nanostructure in which an anodized layer is an Al film formed on a substrate and a porous film having pores perpendicular to the substrate is produced.

Further, the nanostructure having pores produced by these production methods is unique to the production method, and is a structure useful as a device application.

The present invention also relates to a method for producing pores in which pores are formed by anodizing a layer containing Al as a main component, comprising the steps of: preparing a layer containing Al as a main component; A first anodic oxidation step in which anodic oxidation proceeds in a first direction with respect to the layer containing as a main component, and subsequent to the first anodic oxidation step, the Al layer is formed in a direction different from the first direction. And a second anodic oxidation step in which anodic oxidation of the layer mainly comprising is performed.

The step of preparing the layer containing Al as a main component is preferably a step of arranging a film containing Al as a main component on the first main surface of the substrate. In the second anodizing step, while oxidizing the layer containing Al as a main component,
Preferably, it is a step of forming pores. Further, it is preferable that the first direction is a direction substantially perpendicular to the first main surface. Further, it is preferable that the second direction is a direction substantially parallel to the first main surface.

Next, in order to explain the operation of the present invention, the prior art will be described first with reference to FIGS. 6 and 7. FIG. Here, FIG. 6 is a diagram showing a conventional example of horizontal anodized pores, and FIG. 7 is a diagram showing a conventional example of vertical anodized pores. In the figure, 11 is pores (nanoholes), 12 is an anodized layer mainly composed of alumina, 14 is a substrate, 32 is an anodized layer mainly composed of aluminum, 61 is a pore bottom insulating layer, and 62 is an upper layer. Insulating layer, 71
Are projections such as hillocks seen on the surface of the anodized layer;
Reference numeral 2 denotes a concave portion such as a grain boundary or a flaw of the anodized layer.

FIG. 7 shows a vertical porous film which is the most common conventional example. Here, FIG. 7A is a cross-sectional view of an anodized layer before anodization, and FIG. 7B is a cross-sectional view of a porous film after anodization. Although the formed aluminum film also depends on the method of lapping, generally, as the film thickness increases, the unevenness of the film surface tends to increase as shown in FIG.

When this Al film is used as an anode and anodized in an acid solution such as sulfuric acid, oxalic acid, phosphoric acid, etc.
The surface of the film begins to oxidize. At this time, since the oxidation of the Al film and the etching of a specific portion progress, the pores 11 begin to be formed in the anodic oxide layer 12. These pores are formed in a direction substantially perpendicular to the surface, but a branching phenomenon occurs in which the growth of some pores stops halfway or the pores are split. In particular, such a defect is likely to be generated at a portion where the surface has irregularities, and the structure tends to be disordered as shown in FIG.

The same can be seen in the horizontal porous anodic oxide film shown in FIG. Here, FIG. 6A is a diagram in which the vicinity of the center of the anodized layer is cut in parallel to the surface of the anodized layer, that is, a diagram cut in the position of BB ′ in FIG. FIG. 6B is a cross-sectional view taken along a line AA ′ in FIG. As shown in the figure, an anodized layer, which is a thin film of Al, is formed by anodizing from one end in a state sandwiched by insulating layers. That is, first, A
The upper insulating layer 62 is further formed thereon, and anodizing is performed from the end of these laminated films to form horizontal pores.
The pores are easily disturbed as in the case of the vertical type described above, and the pores are likely to be lost or branched in the middle. This disorder tends to increase if the Al film has irregularities. In the figure, there is a pore bottom insulating layer 61 between the anodized layer 32 that has not yet been anodized and the pores, and this interface is also disturbed reflecting the disturbance of the pores.

The present inventors have conducted intensive studies to eliminate this disturbance, and have found that by forming a porous film after forming a barrier film on the surface of the anodized layer, disturbance and defects can be reduced. .

This operation will be described with reference to FIG. 5 for the horizontal porous film. FIG. 5 is a view showing a process for producing a horizontal porous body. Where 31 is the surface irregularities,
13 is a barrier film. First, as shown in FIG. 5B, surface irregularities 31 exist on the aluminum surface, which is the anodized layer 32 after film formation. Next, when anodizing is performed in a solution for forming a barrier film such as ammonium borate,
As shown in FIG. 5C, the barrier film 13 is formed on the surface of the anodized layer 32 by a thickness depending on the anodic oxidation conditions. At this time, the remaining anodized layer 32 and barrier film 1
The interface of No. 3 has a flat structure as compared with the irregularities on the surface of the anodized layer 32 before the anodization. When the remaining anodized layer 32 is anodized in a solution capable of forming a porous film from the cross section, horizontal pores with little disturbance are formed as shown in FIG.

A similar effect can be seen in a vertical porous film. This case will be described with reference to FIG. FIG. 3 is a view showing a process for producing a vertical porous body from which a barrier film has been removed. First, as shown in FIG. 3B, surface irregularities 31 exist on the aluminum surface, which is the anodized layer 32 after film formation. Next, when anodic oxidation is performed in a solution for forming a barrier film such as ammonium borate, the barrier film 13 is formed on the surface of the anodized layer 32 by a thickness depending on the anodic oxidation conditions as shown in FIG. It is formed. At this time, the interface between the remaining anodized layer 32 and the barrier film 13 has a flat structure as compared with the irregularities on the surface of the anodized layer 32 before anodization. Next, when the barrier film 13 on the surface is removed by a technique such as etching, the anodized layer 32 having a flat surface is left as shown in FIG. When the remaining anodized layer 32 is anodized in a porous solution,
As shown in FIG. 3E, vertical pores with little disturbance are formed.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments will be described by dividing into horizontal and vertical pores. <About the manufacturing method of the horizontal pore> As the simplest configuration example, there is a configuration as shown in FIG. FIG. 2 is a cross-sectional view showing a nanostructure having horizontal pores of the present invention,
FIG. 2A is a cross-sectional view in the case where the number of porous films is one, and FIG.
(B) is a cross-sectional view when the number of porous films is two. FIG. 2A shows a substrate 14 functioning as an insulating layer on the substrate 14.
And an anodic oxide layer 12 which is a porous film having pores 11 sandwiched between barrier films 13. FIG.
FIG. 2B shows a structure in which an anodic oxide layer 12 and an upper barrier film 22 are further provided thereon. In the figure, 21 is an intermediate barrier film, and 22 is an upper barrier film.

Here, a process for manufacturing the structure shown in FIG. 2A will be described with reference to FIG. (1) Substrate When producing horizontal pores, the substrate surface is preferably insulative. For this, an insulating substrate may be used, or a substrate in which an insulating layer is formed over a conductive substrate may be used. As the insulating material, a material that does not corrode or dissolve during the anodizing treatment is preferable. In addition, if the insulating layer has irregularities, the insulating layer may be disturbed or defective.

(2) Preparation of anodized layer As the anodized layer, Al is generally used.
Other elements may be included as long as they can be anodized with a film containing l as a main component. This Al film is formed by vacuum evaporation using resistance heating, sputtering, CVD
The law can be used. However, it is not preferable unless the method can form a film having a flat surface to some extent. However, in a method other than the epitaxial growth, it is inevitable that surface irregularities as shown in FIG. The thickness of the anodized layer to be formed is not particularly limited, but is preferably several tens nm to several μm in consideration of the pore diameter. By this step, a layer 32 containing Al as a main component is formed on the first main surface of the substrate 14.

(3) Preparation of barrier film In order to prepare a barrier film by anodic oxidation, it is necessary to perform anodic oxidation in a specific solution. Preferred solutions include ammonium borate solutions and tartaric acid solutions. When crystalline alumina is formed and adversely affects the flatness of the surface or interface, it is also effective to use ammonium dihydrogen phosphate, which is an electrolytic solution in which crystalline alumina is hardly generated.

Anodization can be performed with the apparatus shown in FIG.
That is, the reaction vessel 84 is placed in a constant temperature bath 87 capable of keeping the temperature constant, and the reaction vessel is appropriately filled with the electrolytic solution 83. A sample 81 to be anodized and a cathode 82 as a counter electrode are set there, and a voltage is applied between the sample and the counter electrode by a power supply 85. In the first anodic oxidation step, anodic oxidation proceeds in a direction substantially perpendicular to the first main surface of the base 14. In general, a method of controlling the voltage is used for producing the barrier film. Although the thickness of the barrier film depends on the conditions, it is approximately voltage (V) × 1.3 (nm) as described above.
It is about. Although the structure of the insulating layer is mainly composed of amorphous alumina, crystalline alumina may be partially formed. Since the interface between the barrier film and the anodized layer tends to be flat, there is an effect of reducing disturbance and defects of pores in the porous film.

After forming the barrier film, a porous film may be formed. However, when it is not preferable to use the barrier film from the viewpoint of device production, the barrier film is removed and another insulating layer is replaced with the barrier film. It may be made instead. Even in this case, the surface roughness of the anodized layer is suppressed compared to the initial surface roughness, and the surface is flattened, so that the effects of the present invention can be obtained. For this etching treatment, a mixed solution of chromic acid and phosphoric acid can be used, but other etching using plasma or ions may be used.

(4) Preparation of Porous Film Examples of the electrolytic solution used for anodic oxidation include oxalic acid, phosphoric acid, sulfuric acid, and chromic acid solution. Various conditions such as anodizing voltage and temperature can be appropriately set depending on the nanostructure to be manufactured. Generally, a sulfuric acid bath is used at a low anodization voltage of 30 V or less, a phosphoric acid bath is used at a high voltage of 80 V or more, and an oxalic acid bath is used at an intermediate voltage. Before the anodic oxidation, it is effective to perform a process of cutting out a section to be anodized so as not to disturb the initial process of the anodic oxidation. This includes a method of patterning the anodized layer and the barrier layer by a photolithography method, and a method of cutting from the substrate using a cleavage surface of the substrate. By the second anodic oxidation step, anodic oxidation proceeds in a direction substantially parallel to the first main surface of the substrate. Then, in the second anodic oxidation step, Al
Oxidation of the layer mainly composed of and formation of pores are performed. Further, the depth direction of the pores 11 is formed in a direction substantially parallel to the first main surface of the substrate by the first anodization and the second anodization step.

After the anodic oxidation, the pores can be appropriately widened by immersing the pores in an acid solution such as a phosphoric acid solution. By adjusting the acid concentration, the treatment time, and the temperature, a nanostructure having a desired pore diameter can be obtained. To produce a multi-stage porous layer as shown in FIG. 2 (b), the above processes (2), (3) and (4) may be repeated.

<Regarding the method of manufacturing the vertical pores> The simplest example of the structure is shown in FIG. FIG. 1 is a sectional view showing a nanostructure having vertical pores according to the present invention. FIG. 1A is a cross-sectional view showing a state in which a barrier film is left, in which an anodized layer 12 which is a porous film having pores 11 is provided under the barrier film. Figure 1
(B) is a cross-sectional view of the configuration from which the barrier film has been removed. Here, regarding the process of manufacturing the configuration of FIG.
This will be described with reference to FIGS.

(1) Substrate In the case of forming vertical pores, the substrate surface does not need to be insulating. Conversely, in order for the pores to reach the substrate, a conductive substrate or a substrate having a conductive film formed on the surface is required. As this conductive material, Ti, Nb, W, Z
valve metals such as r and Hf, metals such as Pt and Cu,
These alloys and semiconductors such as Si are exemplified. However, if the conductive layer has irregularities, the conductive layer is likely to be disturbed or defective, so that the conductive layer is preferably flat.

(2) Production of anodized layer The anodized layer is produced in the same manner as in the case of the horizontal pores. However, since the length of the pores can be determined by the film thickness, it is necessary to provide a film thickness corresponding to a desired pore length. Actual Al
In consideration of film formation, the film thickness is suitably several tens nm to several tens μm. It is preferable that the surface unevenness of the anodized layer is small as in the case of the horizontal pores.

(3) Preparation of Barrier Film A barrier film is prepared by anodic oxidation in the same manner as in the case of the horizontal pores. However, there are various methods for the subsequent process. For example, there is the following method.

A) A method of forming a porous film by forming a barrier film and then removing the barrier film. After the barrier film is removed by etching or the like, the porous film is formed by anodic oxidation as shown in FIG. Also in this case, the unevenness on the surface of the anodized layer is suppressed compared to the initial unevenness, and the surface is flattened, so that the effect of the present invention can be obtained. In this case, it is also effective to form a concave portion or the like serving as a starting point of pore formation on the surface of the anodized layer after etching the barrier film. The concave portions are formed by a method using photolithography, an interference exposure method, or a FIB (Foc) method.
used ion beam) method, stamp method and the like.

B) After partially removing the barrier film,
A method for producing a porous film. In order to form the porous film while leaving the barrier film, it is necessary to partially remove the barrier film which is an insulating layer. In this case, as shown in FIG. 4D, it is preferable to periodically form the removed portions 41 corresponding to the positions of the pores to be formed in the porous layer, and to use the removed portions 41 as starting points.

C) A method of forming a porous film after removing the barrier film and forming another insulating layer. In the case where it is not preferable to leave the barrier film from the viewpoint of device production, the barrier film may be removed and another insulating layer may be produced instead of the barrier film. In this case, since there is an insulating layer on the surface, as shown in FIG. 4D, the removed portion 41 corresponding to the position of the pore to be formed in the porous layer is formed on the insulating layer to form the porous layer. Is preferably prepared periodically and used as a starting point.

A mixed solution of chromic acid and phosphoric acid can be used for the above-mentioned etching treatment, but other etching using plasma or ions may be used.

As the insulating layer used in place of the barrier film, any insulating layer may be used.
A material that is hardly corroded by an acid during anodic oxidation is preferable. In the case where the starting point is formed in the insulating layer, it is preferable that a fine patterning process can be performed. Specifically, SiO ₂ , A
oxides such as l ₂ O ₃ and nitrides such as SiN and AlN;
In addition, glass, synthetic resin, resist, and the like can be used.
PVD depends on the insulating layer used,
A vacuum film forming method such as a CVD method or a CVD method, a spin coating method, a metal or semiconductor surface oxidation method, or the like can be applied. Also, the anodized layer can be manufactured by a method such as plasma oxidation or thermal oxidation in which only the surface is oxidized.

When these pores are used for device application, it is preferable to provide an electrical connection inside the pores or to provide an electrode layer as a growth stop layer for the pores. Examples of the film composition include valve metals such as Ti, Nb, W, Zr, and Hf, metals such as Pt and Cu, and alloys thereof and semiconductors such as Si. However, in order to ensure the uniformity of the pores, it is preferable that the interface between the anodized layer and the electrode layer has few irregularities.

For application of the device, it is an important step to put inclusions in the pores. Various methods such as a method of impregnating a liquid material using capillary action and a method of vapor deposition in the axial direction of the pores can be used as a method of putting inclusions into the pores, but the material is contained only inside the pores. The method of electrodeposition is preferred for wearing.

According to the present invention, anodized alumina can be used for quantum wires, MIM elements, molecular sensors, coloring, magnetic recording media,
It can be applied in various forms including EL elements, electrochromic elements, optical elements such as photonic bands, electron-emitting devices, solar cells, gas sensors, abrasion-resistant and insulation-resistant films, and filters. And has the effect of significantly expanding its application range. In particular, by embedding a functional material such as a metal, a magnetic material, or a semiconductor in the pores of the nanostructure of the present invention, it can be applied to new electronic devices, magnetic devices, and optical devices.

[0050]

The present invention will be described below with reference to examples.

Embodiment 1 In this embodiment, an example in which a horizontal porous body is manufactured will be described with reference to FIGS. FIG. 5 is a cross-sectional view illustrating a process for producing a pore array, and FIG. 8 is a view of an apparatus for performing anodization. In the figure, 11 is pores (nanoholes), 12 is an anodized layer mainly composed of alumina, 13 is a barrier film, 14 is a substrate, 31 is an uneven surface of an anodized layer, 32
Is an anodized layer. In FIG. 8, reference numeral 81 denotes a sample;
2 is a cathode of a Pt plate, 83 is an electrolytic solution, 84 is a reaction vessel, 85 is a power supply for applying an anodizing voltage, 86 is an ammeter for measuring anodizing current, 87 is a thermostat, and 88 is a sample holder. Although omitted in the figure, the voltage,
A computer that automatically controls and measures the current is incorporated.

(A) Preparation of anodized layer Anodized layer 32 was first prepared using a Si substrate having a surface oxidized layer of about 500 nm shown in FIG.
That is, the Al film is formed to a thickness of 350 by the sputtering method.
Then, the anodized layer 32 shown in FIG. 5B was formed on the surface of the substrate. The film forming condition is DC sputtering method.
The test was performed at 150 W for 70 minutes. As a result, the anodized layer 3
Surface irregularities 31 were formed on the surface of No. 2 to a height of about 50 nm.

(B) Preparation of barrier film Next, in order to prepare a barrier layer, the Al film was anodized in a solution of ammonium borate. Here, the concentration of the ammonium borate solution is 3 wt%, and 3
Treated at room temperature for minutes. As a result, the surface of the Al film
m was uniformly oxidized to become the barrier film 13, and the underlying Al layer remained Al with a thickness of about 250 nm. Further, the barrier film surface and the interface between the barrier film 13 and the remaining Al layer were flattened as shown in FIG.

(C) Anodizing Next, in order to obtain a surface where anodic oxidation starts, the anodized layer and the barrier layer were dry-etched perpendicular to the film surface by dry etching to expose the end surfaces. Then, phosphoric acid 0.3 kept at 5 ° C. using the anodic oxidation apparatus shown in FIG.
The end face was immersed in an M solution, electrodes were taken from the opposite side, and anodized at 130 V. After the anodization was completed, the substrate was immersed in 5% by weight of phosphoric acid for 60 minutes to perform a hole opening treatment.

<Evaluation> The nanostructure fabricated by the above-described method was subjected to FE-SEM (Field Emission-Sc).
annig Electron Microscope
e: Field emission scanning electron microscope)
As shown in FIG.
It was confirmed that the film was formed with a diameter of about 0 nm and a diameter of about 150 nm.

For comparison, without forming a barrier film,
The same pores were formed in a sample in which a 50 nm-thick SiO ₂ film was formed on the anodized layer by a sputtering method.

Example 2 In this example, a method of forming an insulating layer after removing a barrier film will be described with reference to FIGS.

First, a barrier film is formed in the same manner as in Example 1 (FIG. 5C). Then, when the barrier layer was removed by immersion in a mixed solution of chromic acid and phosphoric acid for 2 hours, the unevenness on the surface of the anodized layer was smaller than the surface unevenness 31 observed after the film formation by one third or less. It was becoming. Then, SiO ₂ was deposited to a thickness of 50 nm on the surface. The film was formed by RF sputtering at 100 W for 5 minutes.

Then, when the end face was processed for anodic oxidation in the same manner as in Example 1, and the anodic oxidation was performed, a horizontal porous film having pores with little disturbance similar to that in Example 1 was formed. Was.

Example 3 In this example, a method of forming a porous film after removing a barrier film will be described with reference to FIG.

(A) Preparation of anodized layer Anodized layer 32 was first prepared using a Si substrate without a surface oxidized layer shown in FIG. That is, Al
A film was formed to a thickness of 500 nm by a sputtering method, and an anodized layer 32 shown in FIG. 3B was formed on the substrate surface. The film formation conditions were DC sputtering, 150 W, 1
This was performed for 00 minutes. As a result, surface irregularities 31 having a height of about 70 nm were formed on the surface of the anodized layer 32.

(B) Preparation and Removal of Barrier Film Next, in order to prepare a barrier film, the Al film was anodized in a solution of ammonium borate. Here, the concentration of the ammonium borate solution was 3 wt%, and the treatment was performed at a voltage of 100 V for 3 minutes at room temperature. As a result, the surface of the Al film
0 nm was uniformly oxidized to become the barrier film 13, and the Al layer thereunder remained at about 370 nm as Al. Further, the barrier film surface and the barrier film 13 and the remaining Al
The interface between the layers was flattened as shown in FIG.

Then, when the barrier layer was removed by immersion in a mixed solution of chromic acid and phosphoric acid for 2 hours, the unevenness on the surface of the anodized layer was 3 times smaller than the surface unevenness 31 observed after the film formation.
It was less than one-half the size.

(C) Anodizing Then, the surface was immersed in a 0.3 M oxalic acid solution kept at 15 ° C. using the anodizing apparatus shown in FIG. 8, an electrode was taken from the substrate side, and anodized at 40 V. went. After the anodization was completed, the substrate was immersed in 5 wt% phosphoric acid for 40 minutes to perform a hole opening treatment.

<Evaluation> When the nanostructure produced by the above method was observed by FE-SEM, pores with little disturbance as shown in FIG.
It was confirmed that the film was formed at a thickness of about 0 nm. For comparison, when a pore was formed by anodic oxidation without forming a barrier film, the pore was disturbed as shown in FIG. 7B.

Example 4 In this example, a barrier film was formed using F
A method for forming a porous film after partial removal by the IB method will be described with reference to FIG.

First, a barrier film is formed in the same manner as in Example 3 (FIG. 4C). However, the barrier film is 50n
m. Then, using the FIB method, honeycomb-shaped dots with a spacing of 100 nm were drawn on the surface of the porous film to form a barrier film-removed portion 41, which was processed into the structure shown in FIG. The Ga ions at this time had an ion beam diameter of 30 nm, an ion current of 20 pA, and an acceleration voltage of 30 kV.
The workpiece was irradiated with the focused ion beam in a dot-like manner at intervals of 100 nm using the focused ion beam described above to partially penetrate the porous film.

The sample manufactured by the above process was anodized by using the anodizing apparatus shown in FIG. In this example, the acid electrolyte was a 0.3 M oxalic acid aqueous solution, the solution was kept at 15 ° C. in a thermostatic water bath, and the anodic oxidation voltage was 40 V. After the anodizing treatment, the sample was immersed in a 5 wt% phosphoric acid solution for 40 minutes to widen the pore diameter.

<Evaluation> As a result of FE-SEM observation of the sample manufactured by the above-described manufacturing method, a regular vertical pore array as shown in FIG. 4E was formed. At this time, the pore interval was about 100 nm, and the pore diameter was about 60 nm.

Example 5 In this example, a method of forming a porous film after forming a starting point on a layer to be anodically oxidized by the FIB method after removing a barrier film will be described.

First, in the same manner as in Example 3, the process up to the removal of the barrier film is performed. Then, using the FIB method, honeycomb-shaped dots with a spacing of 100 nm were drawn on the anodized layer, and the starting points were processed on the anodized layer. At this time, the Ga ions were separated at an interval of 100 n using a focused ion beam having an ion beam diameter of 30 nm, an ion current of 10 pA, and an acceleration voltage of 30 kV.
By irradiating the workpiece with a focused ion beam in the form of dots in such a manner as to repeat m, a concave portion was formed on the anodized layer.

The sample manufactured by the above process was anodized by using the anodizing apparatus shown in FIG. In this example, the brewing electrolyte was a 0.3 M oxalic acid aqueous solution, the solution was kept at 15 ° C. in a thermostatic water bath, and the anodizing voltage was 40 V. After the anodizing treatment, the sample was immersed in a 5 wt% phosphoric acid solution for 40 minutes to widen the pore diameter.

<Evaluation> As a result of FE-SEM observation of the sample produced by the above-mentioned production method, a regular vertical pore array was formed as in Example 4. At this time, the pore interval was about 100 nm, and the pore diameter was about 60 nm.

Example 6 In this example, a method for forming a vertical pore, in which a barrier film is removed, an insulating layer is formed, and a starting point is FIB will be described with reference to FIG. First, a barrier film is formed in the same manner as in Example 4 (FIG. 4C). Then, when the barrier layer was removed by immersion in a mixed solution of chromic acid and phosphoric acid for 2 hours, the unevenness on the surface of the anodized layer was smaller than the surface unevenness 31 observed after the film formation by one third or less. It was becoming. Then, SiO ₂ was deposited to a thickness of 50 nm on the surface.
The film was formed by RF sputtering at 100 W for 5 minutes.

Then, under the same conditions as in the partial removal of the barrier film in Example 4, the surface insulating layer was penetrated in the form of honeycomb dots to the anodized layer by the same FIB method (FIG. 4).
(D)). The sample manufactured by the above process was used in Example 4.
Anodizing treatment was performed in the same manner as described above, and a treatment for expanding the pore diameter was performed.

<Evaluation> As a result of FE-SEM observation of the sample produced by the above-mentioned production method, a regular vertical pore array was formed as in Example 4. At this time, the pore interval was about 100 nm, and the pore diameter was about 60 nm.

[0077]

As described above, the following effects can be obtained by the present invention. (1) According to the present invention, irregularities on the surface or interface of the layer to be anodized are flattened, and as a result, disorder and defects in pores formed by anodization can be reduced. (2) In order to flatten the unevenness on the surface of the anodized layer, a manufacturing method can be provided in which the Al portion to be sacrificed by electrolytic polishing is large, and the flattening that could not be performed by an Al film or the like is reduced to a small number of sacrificed portions. . (3) A novel regular nanostructure produced by applying these techniques can be provided.

These allow anodized alumina to be applied in various forms, and greatly expand the range of application. The nanostructure of the present invention can be used as a functional material by itself, but can also be used as a base material, a template, and the like for further novel nanostructures.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a nanostructure having vertical pores of the present invention.

FIG. 2 is a cross-sectional view illustrating a nanostructure having horizontal pores according to the present invention.

FIG. 3 is a view showing a process for producing a vertical porous body from which a barrier film has been removed.

FIG. 4 is a view showing a process for producing a vertical porous body with a barrier film left.

FIG. 5 is a view showing a process for producing a horizontal porous body.

FIG. 6 is a cross-sectional view showing a conventional nanostructure having horizontal pores.

FIG. 7 is a cross-sectional view showing a conventional nanostructure having vertical pores.

FIG. 8 is a diagram showing an apparatus for performing an anodizing treatment.

FIG. 9 is a cross-sectional view showing a conventional nanostructure having vertical pores.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Porous 12 Anodized layer 13 Barrier film 14 Substrate 21 Intermediate barrier film 22 Upper barrier film 31 Surface unevenness 32 Anodized layer 41 Removal part 61 Pore bottom insulating layer 62 Upper insulating layer 71 Convex part 72 Depressed part 81 Sample 82 Cathode 83 electrolyte 84 reaction vessel 85 power supply 86 ammeter 87 constant temperature bath 88 sample holder 91 aluminum plate

Claims (14)

[Claims] In a method for producing a nanostructure in which pores are formed by anodizing a layer to be anodized mainly containing Al, a barrier film is formed on the surface of the layer to be anodized by anodic oxidation. Forming a porous film by anodic oxidation on the anodized layer below the barrier layer or on the anodized layer after removing the barrier layer. 2. The method for producing a nanostructure according to claim 1, wherein after forming the barrier film, at least a part of the barrier film is removed to form a porous film. 3. The method for producing a nanostructure according to claim 2, wherein the removed portion of the barrier film corresponds to a position where a pore is formed. 4. The method for producing a nanostructure according to claim 2, wherein a pore formation starting point is formed after removing the barrier film. 5. The method for producing a nanostructure according to claim 2, wherein after removing the barrier film, an insulating layer is formed on the surface of the anodized layer, and then a porous film is formed. 6. The method for producing a nanostructure according to claim 5, wherein a porous film is formed after removing a portion of the insulating layer corresponding to the position where the pores are formed. 7. The method according to claim 1, wherein said anodized layer is formed on a substrate.
The method for producing a nanostructure according to claim 1 or 5, wherein the porous film is a 1-layer film, the surface of the substrate is insulative, and a porous film having pores parallel to the substrate is produced. 8. The method according to claim 1, wherein said anodized layer is formed on a substrate.
The method for producing a nanostructure according to any one of claims 1 to 4, wherein a porous film having a pore perpendicular to the substrate is formed. 9. A nanostructure produced by the production method according to claim 1. 10. A method for producing pores in which pores are formed by anodizing a layer containing Al as a main component, comprising the steps of: preparing a layer containing Al as a main component; A first anodic oxidation step in which anodic oxidation proceeds in a first direction with respect to the layer to be formed; and
A second anodic oxidation step in which anodic oxidation of the layer containing Al as a main component proceeds in a direction different from the direction of (a). 11. The method according to claim 10, wherein the step of preparing the layer mainly composed of Al is a step of arranging a film mainly composed of Al on the first main surface of the substrate. A method for producing the described pore. 12. The method according to claim 12, wherein the second anodic oxidation step comprises the step of:
The method for producing pores according to claim 11, wherein the step of forming pores is performed while oxidizing a layer containing as a main component. 13. The method according to claim 11, wherein the first direction is a direction substantially perpendicular to the first main surface. 14. The method according to claim 13, wherein the second direction is a direction substantially parallel to the first main surface.