JP3729449B2 - Structure and device having pores - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention provides a structure having pores, anddeviceAbout. The structure obtained by the present invention can be used in a wide range of functional materials such as electronic devices, memory media, and memory elements, and structural materials. In particular, the structure can be used for a perpendicular magnetic recording medium, a solid magnetic memory, a magnetic sensor, a photonic device, and the like.
[0002]
[Prior art]
The present invention relates to a structure having pores, but can be applied without depending on the pore diameter of the pores.
In recent years, among the structures having pores, nano-sized structures (structures having a size of approximately 1 nm to 200 nm, which are hereinafter referred to as “nanostructures”) have increased interest. The technical background will be described focusing on the structure.
[0003]
Of course, nanostructures are attracting attention because they can be expected to have various effects (for example, higher density of recording media) due to their small size. This is because 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.
[0004]
Examples of a method for manufacturing the nanostructure include a manufacturing method using a semiconductor processing technique including a fine pattern drawing technique such as photolithography, electron beam exposure, and X-ray exposure. In the method of manufacturing a nanostructure by a semiconductor processing technique, problems such as poor yield and high cost of an apparatus have been pointed out, and a method that can be manufactured by a simple method with high reproducibility is desired.
[0005]
As a simple method, there is an attempt to realize a novel nanostructure based on a regular structure formed naturally, that is, a structure formed in a self-organized manner.
Many studies have begun to be carried out because, depending on the microstructure used as the base, there is a possibility that a fine and special structure can be produced that exceeds the conventional method.
[0006]
An example of a peculiar structure formed in a self-organized manner is an anodized alumina coating (for example, RC Furneaux, WR Rigby & AP Davidson “NATURE” Vol. 337, P147 (1989)). Etc.).
[0007]
Hereinafter, the anodized alumina coating will be specifically described with reference to the drawings.
8 and 9 are schematic cross-sectional views when anodized alumina nanoholes are formed on an aluminum plate (or film). When the aluminum plate is anodized in an acidic electrolyte, a porous oxide film is formed. In FIG. 8A, 114 is a nanohole, 115 is an anodic oxide film, and 122 is a barrier layer. The barrier layer is an insulating region made of alumina that is present on the bottom surface of the hole portion of the anodic oxide film 115.
[0008]
FIG. 8B is a cross-sectional view when the Al film on the substrate is anodized halfway. In the figure, 123 is a substrate and 124 is an aluminum film.
As shown in FIG. 8A, this porous oxide film is characterized by extremely fine cylindrical nanoholes (pores) 114 having a diameter (2r) of several nanometers to several hundreds of nanometers, and intervals (2R) of several tens of nanometers to several hundreds of nanometers. It has a specific geometrical structure of being arranged in parallel.
Various applications have been attempted focusing on the specific geometric structure of the anodized alumina nanohole.
[0009]
For example, there are applications as a film utilizing the wear resistance and insulation resistance of an anodized film, and 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 can be achieved by using a technology for filling metal, semiconductor, or magnetic material into nanoholes, or using nanohole replica technology. Various applications such as are being tried. In addition, it is expected to be applied to various fields such as quantum effect devices such as quantum wires and MIM elements, and molecular sensors using nanoholes as chemical reaction fields. As for nanoholes, there is a detailed description in Masuda “Solid Physics” 31, 493 (1996).
[0010]
However, since the conventional supporting member in contact with the anodized alumina nanohole layer is generally limited to the aluminum plate 121 (or the aluminum film 124) as shown in FIGS. 8A and 8B, the nanohole described above is used. There were various limitations in the development of devices using layers.
[0011]
[Problems to be solved by the invention]
  Therefore, the present invention is characterized by a support member for a pore layer that includes alumina, and the pore layer is formed with a novel hole having a depth that reaches the underlying conductive layer.StructureThe purpose is to provide. More specifically, the present invention uses a material other than aluminum for the support member.StructureThe purpose is to provide.
[0012]
[Means for Solving the Problems]
  The structure having pores according to the present invention is a structure having pores, and includes a first layer including alumina, Ti, Zr, Hf, Nb, Ta, Mo,W'sA second layer containing at least one, and a third layer made up of Cu, a noble metal, an alloy containing Cu, an alloy containing a noble metal, or a semiconductor material and having conductivity in this order. And the first and second layersAnd not through the third layerHave pores and within the poresIn contact with any of the first, second and third layersIt has an inclusion.
[0013]
  In addition, a device according to the present invention is a device including the above-described structure having pores, wherein the inclusion is a magnetic material.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment: Configuration of a structure having pores)
A structure having pores according to the present invention will be described with reference to the drawings.
1A and 1B are schematic views showing an example of a structure according to the present invention.
[0015]
  1A is a plan view, and FIG. 1B is a cross-sectional view taken along line XX ′ in FIG. 1A. In the figure, 11 is a substrate, 15 is a first layer comprising alumina, 14 is a pore, 13 is Ti, Zr, Hf, Nb, Ta, Mo,W'sThe second layer 12 containing at least one, 12 is a third layer having conductivity.
[0016]
The feature of the structure according to the present invention is that both the first and second layers have pores and these pores are connected. According to the present invention, it is possible to provide a member using a material other than aluminum as a member (the second layer or the third layer) that supports the first layer including alumina. Here, materials other than aluminum are materials that do not contain aluminum as a main component. The main component means a main component of the above material, and is a component having an atomic weight ratio of 20% or more with respect to the material when analyzed using, for example, ICP.
[0017]
In the present invention, the pore penetrates the first and second layers, and the conductive third layer is exposed at the bottom of the pore. Material can be embedded.
[0018]
The pore diameter of the structure having pores in the present invention is not particularly limited, but is 5 nm to 500 nm, preferably 10 nm to 200 nm. Hereinafter, the expression “nanohole” may be used instead of the expression “structure having pores”. Further, the length of the pore is not particularly limited, but can be appropriately set within a range of several nm to several tens of μm, for example.
[0019]
Hereinafter, the first, second, and third layers will be described in detail.
Here, the first layer is a layer obtained by, for example, anodizing a member containing aluminum as a constituent element. When the member is aluminum itself, the first layer is an alumina layer (or an alumina nanohole layer). Of course, the member only needs to have aluminum as a constituent element as a main component, and may contain other constituent elements. The main component means a main component of the member, and is a component having an atomic weight ratio with respect to the member of 20% or more when analyzed using, for example, ICP. The thickness of the first layer is not particularly limited, but can be appropriately set within a range of several nm to several tens of μm, for example.
[0020]
  The second layer is, for example, Ti, Zr, Hf, Nb, Ta, Mo,W'sIt is a layer obtained by anodizing a material containing at least one in the same manner as the first layer. The material may be a metal, a semiconductor or an alloy. It is also preferable that the material is an oxide, for example, an oxide of tungsten (W), as a result of being anodized. According to the study by the inventors, it has been found that the second layer has a function of increasing the bonding strength between the first layer and the third layer. Although details are unknown, it seems to be caused by the fact that the second layer is anodized in the same manner as the first layer. From this point, the second layer may be expressed as a bonding layer.
[0021]
The thickness of the second layer is not particularly limited, but is 1 nm to 100 nm, preferably 1 nm to 50 nm.
Moreover, it is preferable that the thickness of the second layer is thinner than the thickness of the first layer. More preferably, the thickness of the second layer is less than one half of the thickness of the first layer. Further, the thickness of the second layer may be thinner than the thickness of the first and third layers. Also, the thickness of the second layer is preferably thinner than the pore interval (2R in FIG. 1B).
[0022]
In the present invention, both the first layer and the second layer have pores formed by anodizing treatment. When the first layer and the second layer are respectively formed, the two are mutually connected. It is also preferable to have different pore sizes. For example, as shown in FIGS. 2A and 2B. Further, the thickness of the second layer is preferably thinner than the interval between the pores (R in FIG. 1B).
[0023]
The third layer can be made of Cu, a noble metal, an alloy containing Cu, an alloy containing noble metal, or a semiconductor material. Here, the noble metal is selected from, for example, Ag, Au, Pt, Pd, Ir, Rh, Os, or Ru. The semiconductor material is, for example, graphite, Si, InP, GaAs, GaN, SiGe, or Ge. When a metal is used as the material constituting the third layer, the third layer may be expressed as a conductive metal base layer. The third layer may be a thin film or the substrate itself. That is, in FIG. 1B, a conductive material may be selected for the substrate 11 itself without using the third layer 12. Here, when the inclusion is embedded in the pores by electrodeposition or the like, the conductive metal underlayer preferably contains Cu or Pt.
[0024]
As the substrate 11 in FIG. 1B, for example, a quartz substrate, a glass substrate, a metal substrate, a semiconductor substrate, or the like can be applied. Of course, a flexible film such as plastic, polyethylene terephthalate (PET), or polyimide can also be used as the substrate.
Note that the structure described above can be used as a mask or a mold.
[0025]
(Second embodiment: Method for producing structure having pores)
Hereinafter, a method for manufacturing a structure having pores will be described with reference to FIGS.
FIG. 3 is a schematic view showing an example of a manufacturing process of a structure having pores according to the present invention, and FIG. 4 is a schematic view showing an example of an anodizing apparatus used in the present invention.
[0026]
  FIG. 3A is a cross-sectional view of the film configuration before the anodizing step. First layer 52 containing aluminum, Ti, Zr, Hf, Nb, Ta, Mo,W'sA member 55 having a second layer 51 containing at least one and a third layer 12 having conductivity in this order is prepared (step 1). In FIG. 3A, the member 55 is formed on the substrate 11, but the substrate is not essential and may be provided as necessary.
[0027]
Next, as shown in FIG. 3B, the first layer and the second layer are anodized to form pores (step 2). In the figure, reference numeral 15 denotes an anodic oxide film formed by anodizing the first layer 52 containing aluminum. Reference numeral 53 denotes an oxide film formed when the second layer 51 is anodized. Depending on the anodic oxidation conditions and the material used, the oxide film 53 may or may not remain. In FIG. 3B, the case where it remains is shown. When the oxide film 53 remains, it is desirable to perform a process (step 3) of removing the oxide film 53 by etching or the like. Step 3 may be performed as necessary, and is not an essential step.
[0028]
When the oxide film 53 does not remain or is removed by the etching process, a structure as shown in FIG. 3C is obtained. The etching treatment is wet etching with an acidic solution or wet etching with an alkaline solution.
[0029]
It is also effective to perform an annealing process before or after the etching process. Annealing can be performed, for example, in the range of 100 ° C. or more and 1200 ° C. or less. The moisture remaining in the film can be removed by annealing at 100 ° C. or higher, and the crystallinity of the aluminum oxide film that has been anodized by annealing at a higher temperature can be increased. The annealing treatment can be performed in a vacuum or a reducing atmosphere such as hydrogen and an inert gas. Of course, if the conductive third layer 12 is not destroyed, annealing in air or oxygen is also possible.
[0030]
In addition, after the pore structure is manufactured, the surface can be polished, ground, or CMP (Chemical Mechanical Polishing).
In the present embodiment, the first pores 56 formed in the first layer 52 and the second pores 57 formed in the second layer 51 are connected. The diameters of the first and second pores may be the same or different from each other.
[0031]
  Here, the second layer 51 includes Ti, Zr, Hf, Nb, Ta, Mo,W'sA semiconductor, metal, or alloy containing at least one kind.
  The third layer 12 is made of Cu, a noble metal, an alloy containing Cu, an alloy containing noble metal, or a semiconductor material. As the noble metal or semiconductor material, the same materials as those described in Embodiment 1 can be used.
[0032]
The thickness of the second layer is preferably thinner than the thickness of the third layer. Here, the thickness of the second layer is preferably 1 nm or more and 50 nm or less.
[0033]
For example, although the melting point of Al is 660 ° C., the heat treatment above the above temperature could not be applied to the nanoholes formed on the surface. In that sense, in order to use nanoholes as functional materials in various directions, a technique for forming anodized alumina nanoholes on a high melting point substrate is desired.
[0034]
Furthermore, considering the application of anodized alumina nanoholes as electronic devices and the like, a technique for embedding a material in the nanoholes and forming anodized alumina nanoholes that can be electrically connected to the inclusions from the base is desired. If anodized alumina nanoholes can be produced uniformly and stably on the base of a highly conductive material such as metal, it will be possible to produce inclusions in anodized alumina nanoholes by controlled electrodeposition, further expanding the range of applications. I can expect that.
In the present embodiment, a layer having pores can be formed on a support member other than aluminum.
[0035]
In this embodiment, the anodized alumina nanohole anodizes a film containing Al as a main component, oxidizes over the entire film thickness from the surface of the film to the surface of the third layer, and performs anodization at an appropriate time. It is produced by finishing and then performing an etching process as necessary.
[0036]
For this reason, the bottom of the nanohole penetrates to the surface of the conductive metal underlayer, and the nanohole has a feature that the linearity is good to the bottom. In addition, the present inventors provide an appropriate bonding layer at the interface between the anodized alumina nanohole layer and the conductive metal underlayer at the penetration portion at the bottom of the nanohole, thereby bonding the anodized alumina nanohole layer and the conductive metal underlayer. It has been found that strength and adhesion are increased.
[0037]
As an example in which anodized alumina nanoholes are formed on a support member other than aluminum, JP-A-7-272651 is cited. In this publication, an Al film is formed on a Si substrate, the Al film is converted into an anodized film, a barrier layer at the bottom of the nanohole is removed, and a metal layer (Au, A technique is disclosed in which Pt, Pd, Ni, Ag, Cu) are formed, and Si needle crystals are grown by a VLS (Vapor Liquid Solid) method.
[0038]
In this technique, in order to penetrate the nanohole to the surface of the Si substrate, a step of removing the barrier layer at the bottom of the nanohole is performed after the Al film is anodized. As a method for removing the barrier layer, there are a method using a chromic acid-based etching solution, and a method in which the Si substrate and the counter electrode are connected with an external conductor after the anodic oxidation and left in the solution. FIG. 9A is a cross-sectional view in which anodization is completed while leaving the barrier layer 122, and FIG. 9B is a cross-sectional view in the case where the barrier layer 122 is removed by a method such as dry etching. Reference numeral 114 denotes a nanohole, 115 denotes an anodic oxide film, and 125 denotes a barrier layer removing portion. Reference numeral 123 denotes a substrate.
[0039]
However, as a result of intensive studies by the present inventors, when the barrier layer removal step is performed after the anodization step, the nanohole diameter of the barrier layer removal portion disturbs linearity at that portion, as shown in FIG. It presented problems such as discontinuity or non-uniform shape due to nanoholes. In the present embodiment, nanoholes penetrating the alumina layer can be formed, so it is not necessary to remove the barrier layer. In the present embodiment, since pores are formed by anodizing to a depth corresponding to the film thickness of the first layer (for example, an aluminum film), pores with excellent linearity and diameter uniformity are formed. Can be formed.
[0040]
Hereinafter, the above process will be specifically described.
[0041]
(A) Step 1: Film formation step (FIG. 3A)
On the substrate 11, the third layer 12, the second layer 51, and the first layer 52 having conductivity are formed in this order to prepare a sample. These layers can be formed by any film forming method including resistance heating vapor deposition, EB vapor deposition, sputtering, and CVD.
[0042]
For the substrate 11 and the third layer 12, the materials described in Embodiment 1 can be used. The first layer 52 is a layer containing, for example, aluminum as a constituent element. Of course, the member only needs to have aluminum as a constituent element as a main component, and may contain other constituent elements. The main component means a main component of the member, and is a component having an atomic weight ratio with respect to the member of 20% or more when analyzed using, for example, ICP.
[0043]
  The second layer 51 is, for example, Ti, Zr, Hf, Nb, Ta, Mo,W'sA layer containing at least one. The material may be a metal, a semiconductor or an alloy.
[0044]
The thickness of the second layer 51 is not particularly limited, but may be 1 nm to 100 nm, preferably 1 nm to 50 nm. Moreover, it is preferable that the thickness of the second layer is thinner than the thickness of the third layer. More preferably, the thickness of the second layer is less than one half of the thickness of the third layer. Further, the thickness of the second layer may be thinner than the thickness of the first and third layers.
[0045]
(B) Step 2: Anodizing step
The structure according to the present invention is manufactured by anodizing the sample. FIG. 4 is a schematic view showing an example of an anodizing apparatus used in this step.
[0046]
In FIG. 4, 60 is a constant temperature bath, 61 is a reaction vessel, 62 is a counter electrode such as a Pt plate, 63 is an electrolyte, 64 is a sample, 65 is a power source for applying an anodizing voltage, and 66 is an anodizing current. An ammeter to be measured, 67 is a sample holder. Although not shown, it is also preferable to incorporate a computer that automatically controls and measures voltage and current.
[0047]
The sample 64 and the counter electrode 62 are disposed in an electrolytic solution whose temperature is kept constant by a constant temperature water bath, and an anodic oxidation process is performed by applying a voltage between the sample and the counter electrode from a power source. Reference numeral 67 denotes a sample holder for preventing voltage from being applied to unnecessary portions.
[0048]
Examples of the electrolytic solution used for anodization include oxalic acid, phosphoric acid, sulfuric acid, and chromic acid solution. A particularly preferred solution is a sulfuric acid solution for a low voltage (about 30 V), phosphoric acid for a high voltage (60 V to), and an oxalic acid solution for a voltage between them.
[0049]
Also, when alcohol, such as ethanol or isopropyl alcohol, is mixed with 3% or more of the electrolyte solution, there is a pinhole in the Al layer, and the electrolyte solution touches the conductive metal underlayer, resulting in water electrolysis. Even if bubbles are generated, the alcohol tends to break the bubbles, so that anodization tends to be stabilized.
[0050]
Here, the anodizing treatment will be described in detail.
FIG. 5 shows current profiles during anodization when various underlayers (that is, the third layer 12 in FIG. 3A) are used.
[0051]
Here, the base layer is formed on a substrate such as quartz, and then an Al film 52 is formed. Then, an electrode is taken from the third layer 12, and constant voltage anodization is performed in an electrolyte such as oxalic acid. Then, the surface of Al is first oxidized and the current value decreases rapidly (point 71 in FIG. 5). However, when nanoholes start to be formed, the current gradually increases and becomes constant (point 72 in FIG. 5). ). Here, in order to accurately measure the oxidation current, it is necessary to prevent the base layer from coming into contact with the electrolytic solution.
[0052]
When the anodic oxidation reaches the third layer 12 (point 73 in FIG. 5), although depending on the composition of the underlayer, the oxidation of Al and the diffusion of Al ions into the electrolyte are suppressed. The current value decreases (74 point in FIG. 5). However, if the anodic oxidation is continued as it is, the third layer 12 comes into contact with the aqueous solution, and in some cases, electrolysis of water occurs and the current value increases (point 75 in FIG. 5). When this electrolysis occurs, the nanoholes are gradually destroyed. Therefore, when the anodization is completed when the third layer 12 is reached, particularly when a current drop of 5% or more is observed with respect to the current value of 72 points, the bottom of the nanohole can be penetrated. Here, when an oxide is stably present in the material of the third layer (Cu or the like), the current is sufficiently reduced ((a) in FIG. 5), but in Pt or the like, the current reduction is small ((( b)).
[0053]
In the present embodiment, an electrode is taken from the third layer having conductivity, anodized, and the condition of the anodizing process is controlled while monitoring the current change of the anodizing at the end of the anodizing process. Fine pores reaching the surface of the third layer can be formed.
[0054]
As a bonding layer (that is, the second layer 51 in FIG. 3A) between the Al film and the third layer 12, a semiconductor, metal, or metal containing elements of Ti, Zr, Hf, Nb, Ta, Mo, W, Si When anodization is performed with an alloy or the like interposed therebetween, a current reduction region after the end of anodization of Al as shown in FIG. 5A can be obtained more stably. This seems to be because the anodic oxidation and dissolution of the bonding layer proceed gradually. The thickness of the bonding layer is not particularly limited, but is preferably about 1 nm to 50 nm.
[0055]
When this bonding layer is anodized, the oxide of the bonding layer metal layer may remain at the bottom of the nanohole. Etching is preferably performed to remove this and expose the surface of the underlayer. For this etching, it is preferable to use an acidic solution such as phosphoric acid or sulfuric acid, or an alkaline solution such as KOH or NaOH.
[0056]
Although depending on the composition and thickness of the bonding layer, the etching process causes a linear nanohole from the surface of the anodic oxide film (first layer) 15 to the base layer (third layer) 12 as shown in FIG. 1B. In addition, a structure in which the hole diameter of the bonding layer portion is slightly larger than the nanohole diameter as shown in FIG. 2A or a structure in which the hole diameter of the bonding layer portion is slightly smaller than the nanohole diameter as shown in FIG. 2B can be produced.
[0057]
However, the above current change cannot be detected accurately unless the anodic oxidation of the Al film 52 proceeds uniformly. That is, if there is a defect such as a pinhole in the Al film, the current may increase at the end of anodic oxidation. In order to perform the anodic oxidation uniformly, it is effective to make the anodic oxidation area smaller than that of the container or holder for performing the anodic oxidation. In addition, it is more effective to set the sample horizontally than standing the sample and anodizing. It is also effective to make the counter electrode sufficiently larger than the anodized area. When a metal layer (for example, Pt) that is difficult to oxidize is reached, electrolysis of water in the electrolytic solution starts, and the anodic oxide film may be destroyed due to the generation of bubbles at that time. In such a case, it is preferable to stop the anodic oxidation treatment immediately before the anodic oxidation proceeds to the metal layer.
[0058]
In the anodic oxidation process of the present invention, the first layer 52 is oxidized over the entire thickness. When the anodic oxidation proceeds from the Al surface and reaches the third layer 12 having conductivity, a change is observed in the anodic oxidation current, and this can be detected to determine the end of the anodic oxidation.
[0059]
For example, it can be determined that the application of the anodic oxidation voltage is terminated due to a decrease in the anodic oxidation current. By this method, excessive anodic oxidation can be prevented. However, in order to detect this change in current, the anodic oxidation of Al needs to proceed uniformly.
[0060]
In addition, it is also preferable to perform the uneven | corrugated formation process for forming an unevenness | corrugation in the surface of the said 1st layer (for example, aluminum film) prior to performing anodization. In such a case, since the voltage tends to concentrate on the recess, pores are formed starting from the recess. The formation of unevenness is achieved, for example, by directly pressing a member having unevenness to the aluminum film. Alternatively, it can be achieved by forming an aluminum film on a member having irregularities. For example, as shown in FIG. 6, the second layer (bonding layer) may be patterned in advance to form irregularities, and the first layer (for example, an aluminum film) may be formed thereon. In the figure, reference numeral 52 denotes an aluminum film, and 133 denotes the second layer patterned for forming irregularities. In such a case, the second layer need not be anodized. For the patterning, electron beam exposure, interference exposure, focused ion beam sputtering, or the like can be used. It is also preferable to perform anodization after irradiating the surface of the aluminum film with a particle beam (for example, a charged particle beam, a focused ion beam, or an electron beam) in order to form the starting point of the pore. .
[0061]
(C) Step 3: Etching treatment
As described above, when the second layer is anodized, the oxide film 53 may remain. In such a case, an etching process is performed. By etching the pore structure, a non-penetrating portion made of the oxide film 53 at the bottom of the nanohole can be removed by etching. This treatment includes a step of immersing the structure in an acidic solution (for example, phosphoric acid solution) and a step of immersing in an alkaline solution (KOH solution or the like). In particular, when W is used for the second layer 51, alkaline solution treatment is preferable. In addition, this etching process can simultaneously increase the nanohole diameter. It can be set as the nanostructure which has a desired nanohole diameter by acid concentration, processing time, and temperature. This step 3 can be omitted when the oxide film 53 does not remain. FIG. 3C is a cross-sectional view of the state in which the oxide film 53 has been dissolved by etching and the nanohole diameter has been expanded.
[0062]
The alumina nanohole is mainly composed of Al and oxygen, and has a large number of cylindrical nanoholes as shown in FIG. 1A. The nanoholes (pores) 14 are formed substantially perpendicular to the surface of the conductive third layer. And each nanohole is mutually arrange | positioned in parallel and substantially equal intervals. Each nanohole tends to be arranged in a triangular lattice shape as shown in FIG. 1A. The diameter 2r of the nanohole can be set in the range of 5 nm to 500 nm. For example, the diameter 2r of the nanohole can be set to several nm to several hundred nm, and the interval 2R can be set to several tens nm to several hundred nm. The interval and diameter of the nanoholes can be controlled considerably by the process conditions such as the concentration and temperature of the electrolyte used for anodization, the anodization voltage application method, voltage value, time, and subsequent pore-wide treatment conditions. it can.
[0063]
The thickness of the alumina nanohole layer can be controlled by the thickness of the first layer (a film containing Al as a main component). The thickness is, for example, between 10 nm and 100 μm. Conventionally, the depth of the nanoholes was generally controlled by the anodic oxidation time, but in this embodiment, the depth of the nanoholes can be defined by the thickness of the film mainly composed of Al. A uniform alumina nanohole can be formed.
[0064]
(Third embodiment: inclusion in pores)
In the present embodiment, a case will be described in which a material is filled in the pores of a structure having pores obtained by the first or second embodiment.
[0065]
Specifically, the pores of the structure having pores are filled with metal or semiconductor by electrodeposition. In the present invention, since there is a conductive third layer 12 at the bottom of the pores, the electrodeposition controllability is improved. When Co, Cu, Ni, or the like is used as the filling material, these elements are cations in the electrodeposition solution, and thus a negative voltage needs to be applied to the third layer 12.
[0066]
In the present embodiment, the formation of inclusions by electrophoresis or the like is also referred to as electrodeposition. For example, since DNA is negatively charged in an aqueous solution, it is possible to embed the DNA in the pores by applying a positive voltage to the third layer as described above.
[0067]
Of course, even if it is not electrodeposition, the penetration | infiltration from the upper part of a pore, and film-forming methods, such as CVD method, can also be used. Also in electrodeposition, not only metals but also materials such as semiconductors and oxides can be filled.
[0068]
As a structure in which the material is filled in the pores, as shown in FIG. 7A, the inclusion 41 is embedded evenly to the pore surface, the structure in which the laminated film 42 is embedded as shown in FIG. 7B, or FIG. As shown in FIG. 4, there is a structure in which the material 43 is embedded partway through the pores. Further, although not shown, a structure in which inclusions having a structure extending to the outside of the pores are embedded may be used.
[0069]
When the inclusion is a magnetic material, it can be used as a magnetic medium useful as a perpendicular magnetization film or as a quantum effect device when viewed as a thin magnetic wire. If Co and Cu are deposited in the nanoholes as shown in FIG. 7B, a GMR element that responds to a magnetic field can be produced.
[0070]
If the inclusion is structured so as to be embedded in the middle of the pore as shown in FIG. 7C, it is possible to produce an electron-emitting device and a display using the electron-emitting device.
When the inclusion is a luminescent material or a fluorescent material, it can be used as a wavelength conversion layer as well as a light emitting device. A photonic device can also be produced when a dielectric material different from alumina is embedded in the inclusion. In this way, various devices can be manufactured by embedding various materials in the structure having pores.
[0071]
In the present invention, the inclusion may be not only the inside of the anodized nanohole but also the one extending from the inside to the outside of the hole.
FIG. 7D is a cross-sectional view when the pores of the structure of FIG. 3C described in the second embodiment are filled with inclusions 41 such as metal or semiconductor.
[0072]
When electrodepositing a metal into the pores, a negative voltage is applied to the conductive third layer by immersing a substrate having pores in a solution in which the electrodeposited metal is an ion. That's fine. For this solution, for example, an aqueous solution of cobalt sulfate is used. It is also effective to apply an alternating voltage in order to cause sufficient nucleation during electrodeposition.
[0073]
Thus, by embedding a metal, a semiconductor, an oxide, or the like in a structure having pores, it can be applied to a new electronic device. Devices include quantum wires, MIM elements, electrochemical sensors, coloring, magnetic recording media, EL light emitting elements, electrochromic elements, optical elements, wear resistance, insulation resistance coatings, and filters. Of course, the present invention can also be applied to a hard disk as an external (or internal) recording device connected to a computer.
In addition, after sufficient electrodeposition in the pores, surface polishing can be performed to flatten the surface of the pores.
[0074]
It is also effective to perform an annealing process before or after the etching process. Annealing can be performed up to 1200 ° C., moisture remaining in the film can be removed by annealing at 100 ° C. or higher, and the crystallinity of the aluminum oxide film anodized by annealing at a higher temperature can be improved. Also, annealing after filling the inclusions has the effect of controlling the characteristics and structure of the inclusions and improving the adhesion. The annealing treatment described above can be performed not only in a vacuum or in a reducing atmosphere such as hydrogen and an inert gas, but also in air or oxygen if the conductive metal underlayer is not destroyed.
[0075]
【Example】
Hereinafter, the present invention will be described with reference to examples.
[0076]
  Example 1
  In this example, the results when anodized alumina nanoholes were prepared using various metal layers for bonding layers will be described.
  a) Formation of conductive metal underlayer, metal layer for bonding layer, Al film
  Samples with eight different metal layers for bonding layers were prepared. That is, Ti was first deposited on a quartz substrate by RF sputtering to a thickness of 5 nm, and then Cu was deposited as a conductive metal underlayer to a thickness of 20 nm. And Ti, Zr, Hf, Nb, Ta, Mo as the metal layer for the bonding layer,WAfter forming the film to a thickness of 5 nm, an Al film having a thickness of 500 nm was formed.
[0077]
b) Anodizing
Anodization was performed using the anodizing apparatus shown in FIG.
In this example, 0.3 mol / l oxalic acid aqueous solution was used as the electrolytic solution, and the electrolytic solution was kept at 17 ° C. by a constant temperature water bath. Here, the anodic oxidation voltage was DC 40 V, and the electrodes were taken from the conductive metal underlayer side so that the anodic oxidation proceeded uniformly. During the anodizing process, the anodizing current was monitored in order to detect a current indicating that the anodizing progressed from the Al surface and reached the conductive metal underlayer. The anodic oxidation was completed after a current drop of 50% or more of the constant current value shown in FIG. 5 was observed.
After the anodizing treatment, cleaning with pure water and isopropyl alcohol was performed.
[0078]
c) Etching treatment
After the anodizing treatment, etching treatment was appropriately performed by the main treatment of immersing the sample in a 5 wt% phosphoric acid solution for 20 to 45 minutes.
[0079]
The surface and cross section of the sample taken out were observed with a FE-SEM (Field Emission-Scanning Electron Microscope). As a result, as shown in FIG. 1B, the nanohole penetrates to the conductive metal underlayer, and the metal layer for the bonding layer is oxidized to form a part of the bottom anodized layer and the conductive metal underlayer between the nanoholes. It remained.
As a comparative example, a sample in which an Al film was formed on Si was anodized to produce a comparative sample.
[0080]
And when the sample of this example and the comparative example were polished with diamond slurry about half of the anodized layer with the same polishing apparatus, the sample of this example was not damaged, but in the comparative example partly Breakage of peeling of the anodized layer was observed. It was found that the bonding property between the base electrode layer and the anodized alumina nanohole layer is enhanced by providing the bonding layer in this manner. According to the present embodiment, a structure having high adhesion between the nanohole layer and the bonding layer can be obtained, which is useful when there is a polishing process after the nanohole is produced or when a force such as stress is applied during use. Thus, the bondability between the base electrode and the anodized alumina nanohole layer is enhanced, the nanoholes are excellent in the linearity and the uniformity of the diameter to the bottom, and the inclusions can be uniformly applied to the nanoholes.
[0081]
Example 2
A sample was prepared in the same manner as in Example 1. However, W was used for the metal layer for bonding layers, and the thickness of W was changed from 1 to 100 nm. Etching was carried out using a 0.01 mol / l KOH solution for etching for 1 to 10 minutes.
[0082]
When the prepared sample was observed by FE-SEM observation, nanoholes penetrating to the conductive metal base layer as shown in FIG. 1B were obtained when the bonding layer was 50 nm or less. Nanoholes remained without penetrating. Therefore, the bonding layer is preferably 1 to 50 nm.
[0083]
In addition, in the sample having a bonding layer of 5 nm, the straightness of nanoholes was superior in KOH etching compared to Example 1. This is presumably because the oxide of W is easily dissolved in alkali.
[0084]
Example 3
In this example, anodized alumina nanoholes were prepared in the same manner as in Example 1, and then the inclusions were electrodeposited. However, Ag, Pt, Cu, Cr having a thickness of 20 nm was used as the conductive metal underlayer, Ti was formed to a thickness of 2.5 nm as the bonding layer, and etching was performed with phosphoric acid as in Example 1. .
[0085]
After the etching process, Co electrodeposition was performed to electrodeposit Co pillars (columns) in the nanoholes. The plating bath is 5% CoSO_Four ・ 7H₂ O, 2% H_Three BO_Three The DC voltage was -2 V and the electrodeposition time was 20 seconds.
[0086]
And when the cross section of the sample electrodeposited by FE-SEM was observed, it had the form shown to FIG. 7A. Coil was filled in cylindrical nanoholes having a diameter of about 60 nm, and they were arranged in parallel with each other and at approximately equal intervals at intervals of about 100 nm. Further, the pillar diameter was almost uniform up to the bottom of the nanohole. However, the uniformity of electrodeposition between nanoholes was relatively excellent for Pt and Cu.
[0087]
Example 4
In this embodiment, an example in which a nanohole is filled with a laminated magnetic material as shown in FIG. 7B will be described.
[0088]
In the same manner as in Example 3, after penetrating nanoholes were formed on the Cu underlayer, the sample was immersed in a plating bath made of cobalt sulfate 0.5 mol / l and copper sulfate 0.001 mol / l together with a platinum counter electrode. A voltage of −0.56 V and −0.12 V was alternately applied to the Ag / AgCl reference electrode for 15 seconds and 0.1 seconds, respectively, to grow a Cu / Co laminated film on the bottom of the nanohole. A nanostructure shown in FIG.
[0089]
Here, when a voltage of -0.56 V was applied, only Cu, which is an ion having a low electrodeposition potential, was electrodeposited. When -1.2 V was applied, dense Co was mainly electrodeposited, resulting in a laminated film.
[0090]
An electrode was attached to the upper portion of the sample after surface polishing, and the magnetic field dependence of the resistance between the upper portion of the filler and the conductive metal underlayer was examined. As a result, a negative magnetoresistance was shown. This is considered because the filled laminated film showed the GMR effect.
From the above, it can be seen that the present invention is applicable to a magnetic sensor.
[0091]
Example 5
Anodized alumina nanoholes were produced in the same manner as in Example 3. At this time, a 2.5 nm thickness of W was used for the metal layer for the bonding layer, and a 0.01 mol / l solution of KOH was used for etching. After the Co electrodeposition, annealing was performed in vacuum at 400 ° C. for 1 hour. Then, when surface polishing was performed with diamond slurry, the polishing rate was lower than before the annealing treatment, and the average unevenness of the surface after polishing was reduced. This is considered to be because the anodized alumina layer was hardened by the annealing treatment. Moreover, when the same annealing treatment was performed before the etching treatment, a decrease in the etching rate of the alumina nanohole portion was observed. This is considered to be because the chemical resistance of the alumina nanohole portion was increased by the annealing treatment.
[0092]
This means that the shape of the nanohole bottom can be controlled from FIG. 1B to FIG. 2A and FIG. 2B by performing an appropriate annealing process before and after the etching process.
[0093]
The above-described embodiment has the following characteristics.
1) By providing the bonding layer, the bondability between the base electrode and the anodized alumina nanohole layer is enhanced. For this reason, it is durable also in the process and use which require stress, such as grinding | polishing and annealing, and the use of an anodized alumina nanohole can be expanded greatly.
2) Anodized alumina nanoholes with bottoms penetrating on a base electrode such as Cu or platinum can be stably formed. The nanoholes of the anodized alumina nanoholes are excellent in linearity and uniformity in diameter to the bottom of the nanoholes and have few defects.
3) Since the alumina nanohole layer penetrating the conductive metal underlayer can be obtained uniformly, the inclusion of the inclusions in the nanohole can be applied uniformly, so that the magnetic medium, quantum effect device, optical Devices can be realized.
[0094]
These make it possible to apply anodized alumina nanoholes in various forms, and remarkably widen the application range.
In addition, the nanostructure of the present invention can be used as a functional material per se, but can also be used as a base material of a new nanostructure, a mold, or the like.
[0095]
【The invention's effect】
  As described above, according to the present invention, there is a feature in the support member of the pore layer configured to include alumina, and the pore is formed in the pore layer to a depth reaching the base conductive layer. NewStructureCan be provided.
[Brief description of the drawings]
FIG. 1 is a schematic view of a structure having pores according to the present invention.
FIG. 2 is a schematic view of a structure having pores according to the present invention.
FIG. 3 is a schematic view showing a manufacturing process of a structure having pores according to the invention.
FIG. 4 is a schematic view showing an anodizing apparatus according to the present invention.
FIG. 5 is a diagram showing a current profile during anodization.
FIG. 6 is a schematic view showing a part of a manufacturing process of a structure having pores according to the present invention.
FIG. 7 is a diagram showing an example in which a material is filled in pores of a structure having pores according to the present invention.
FIG. 8 is a schematic view showing alumina nanoholes.
FIG. 9 is a schematic view showing alumina nanoholes.
[Explanation of symbols]
11 Substrate
12 Third layer
13 Second layer
14 pores
15 First layer (anodized film)
41 Inclusions
42 Multilayer film
43 Materials
51 Second layer
52 First layer
53 Oxide film
55 members
56 First pore
57 Second pore
60 temperature chamber
61 reaction vessel
62 Counter electrode
63 Electrolyte
64 samples
65 power supply
66 Ammeter
67 Sample holder
114 nanohole
115 Anodized film
121 Aluminum plate
122 Barrier layer
123 Substrate
124 Aluminum film
125 Barrier layer removal section
133 Second layer

Claims (14)

A structure having pores, the first layer comprising alumina, the second layer containing at least one of Ti, Zr, Hf, Nb, Ta, Mo, W , and Cu, or A noble metal, or an alloy containing Cu, an alloy containing noble metal, or a semiconductor material, and having a third layer having conductivity in this order, and penetrating through the first and second layers ; It has pores that do not penetrate through the third layer, and has inclusions in contact with any of the first, second, and third layers in the pores . A structure having pores characterized by the following.   2. The structure having pores according to claim 1, wherein the first layer is an alumina nanohole layer. The structure having pores according to any one of claims 1 to 2 , wherein the pores of the first layer and the second layer have different pore diameters. The second layer, Ti, a structure having Zr, Hf, Nb, Ta, Mo, pores according to any one of claims 1 to 3 which is an alloy containing at least one W. The second layer, the Ti, Zr, Hf, Nb, Ta, Mo, claims 1 to 3 is a layer having pores with a metal layer containing formed by anodizing at least one W The structure which has the pore of any one of these.   2. The structure having pores according to claim 1, wherein the second layer contains an oxide of W. The structure having pores according to any one of claims 1 to 6 , wherein the thickness of the second layer is 1 nm or more and 50 nm or less. The structure having pores according to any one of claims 1 to 7 , wherein the noble metal is Ag, Au, Pt, Pd, Ir, Rh, Os, or Ru. The structure having pores according to any one of claims 1 to 7 , wherein the semiconductor material is graphite, Si, InP, GaAs, GaN, SiGe, or Ge. The structure having pores according to any one of claims 1 to 9 , wherein a thickness of the second layer is thinner than a thickness of the third layer. The structure having pores according to claim 10, wherein a thickness of the second layer is smaller than a half of a thickness of the third layer. The structure having pores according to any one of claims 1 to 11 , wherein a thickness of the second layer is thinner than a thickness of the first and third layers. A device comprising a structure having a pore according to any one of claims 1 to 12, the device characterized in that said inclusions is a magnetic material. The device according to claim 13 , wherein the inclusion is a laminated magnetic body.

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