JP2010077502A - Aluminum having fine structure and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide aluminum having a fine structure having a controlled shape and high aspect ratio about deepness and a method of manufacturing the same. <P>SOLUTION: The aluminum having the fine structure having a pit which has a rectangular opening shape having 1-10 μ length of the short side and the ratio of (the long side length)/(the short side length) of ≥1.5 and the high aspect ratio of (the depth)/(the sort side ) of ≥1 and is formed by electrolytic etching in an aqueous solution containing chloride ion, is provided and its manufacturing method is provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to aluminum having a highly controlled microstructure and a method for producing the same.

  Improvement of a technique for forming a fine and relatively deep structure in a metal is important for enhancing the functionality of the metal material. As a metal micromachining technique that is widely applied industrially, electric discharge machining is known in which a target metal is dug by electric discharge between counter electrodes. Although this method can form a relatively flexible shape, it is difficult to obtain a structure having a size of several tens of microns or less because it is necessary to maintain a gap for discharge between the electrodes. When a finer structure is formed on the metal, an electroforming process is applied. This is a technique in which a mold having a finely shaped inverted structure to be formed on a metal is prepared in advance, and the metal is plated on the mold surface and then separated from each other. In terms of supply, it is difficult to obtain a deep three-dimensional shape. In addition, the types of metals that can be electroformed are limited, and their use is limited because they are relatively expensive. As a technique for forming a deep structure, a technique called an LIGA process, which is an applied technology of electroforming, has been developed, but there is a problem in versatility because of the higher cost.

  On the other hand, in microfabrication of semiconductors, the anisotropic etching characteristics of semiconductors are used to mask the surface of the semiconductor in advance, so that it has a cross-sectional structure corresponding to the mask opening shape and has a relatively high aspect ratio (etched depth). (/ Opening width) high shape is obtained in micron scale or nano scale. This technique has a process of forming a fine and deep structure by etching a substrate using a two-dimensional shape mask, is a relatively inexpensive technique with high production stability and is excellent. However, the types of metals that can be anisotropically etched are limited, and so far, no technology has been realized for forming an arbitrary fine structure with an aspect ratio higher than a certain level. In metal etching using a mask, the aspect ratio is usually only about 0.5 because the metal dissolves uniformly.

Aluminum is known as a metal that can be anisotropically etched electrochemically, and (100) plane-oriented aluminum that has been electrolytically etched in a high temperature aqueous solution containing chloride ions has a square shape of several microns. Many relatively deep pits having openings are formed. However, in this case, the pit arrangement is random. By forming a masking film on the surface of aluminum and then electrolytically etching the aluminum, the formation positions of the tunnel pits having a square opening shape (pits having a depth of a certain level or more are sometimes referred to as “tunnel pits”). Although a control method has been developed, the cross-sectional shape of the pit is limited to a square, and a high aspect ratio fine structure of aluminum having an arbitrary cross-sectional shape has not been obtained so far. In addition, even when a mask having an arbitrary opening shape is formed on aluminum and electrolytic etching is performed, a plurality of tunnel pits having a square cross section having a size smaller than the mask opening are distributed in the mask opening. Corresponding pit formation has been considered impossible.
Surface Technology, Vol. 59, No. 7, 448 (2008)

  The present invention has been made in order to solve the above-described problems in the prior art, and an object thereof is to provide aluminum having a fine structure with a high aspect ratio with respect to depth and a method of manufacturing the same. To do.

  In order to solve the above-mentioned problems, the present inventors have investigated and studied various methods for forming a target high-aspect-ratio aluminum microstructure whose shape is controlled. As a result, a mask corresponding to the target shape is formed on the surface of the aluminum, and after a small amount of metal is deposited, electrolytic etching is performed under appropriate specific conditions, thereby forming a target microstructure with a high aspect ratio. I have found that I can achieve it.

  That is, the aluminum having a microstructure according to the present invention has a rectangular opening shape with a short side length of 1 to 10 microns and a long side / short side length ratio of 1.5 or more on the surface. The depth / short side length ratio is 1 or more (that is, high aspect ratio) pits are formed by electrolytic etching in an aqueous solution containing chloride ions. Become.

  In the aluminum having such a fine structure, at least two of the pits can be connected to each other through at least a part of the opening shape. For example, at least two of the pits are connected to each other between the short sides or the long sides in the opening shape, or the long side in the opening shape of one pit and the short side in the opening shape of the other pit It can be set as the form etc. which were mutually couple | bonded between. Further, if a large number of pits are connected, a pit having a larger shape can be formed.

  Further, the method for producing aluminum having a microstructure according to the present invention comprises forming a mask on the surface of the aluminum having the microstructure as described above, and depositing a trace amount of metal on the mask, and then chloride. In this method, the aluminum is produced by electrolytic etching in an aqueous solution containing ions.

  In the method for producing aluminum having this fine structure, the trace amount of metal is preferably a metal mainly composed of copper from the viewpoint that homogeneous dissolution of aluminum at the mask opening can be achieved.

  Moreover, in the manufacturing method of the aluminum which has the said fine structure, it is preferable to use the aluminum whose exclusive area rate of (100) plane is 90% or more. This makes it possible to accurately form a desired rectangular opening shape.

  Various conditions can be adopted for electrolytic etching of aluminum in aqueous solution containing chloride ions. As preferable conditions, for example, electrolytic etching is performed at a temperature of 40 ° C. or higher using an aqueous solution containing 6 M or more of hydrochloric acid. Can be mentioned.

  Prior to the formation of the mask, the aluminum surface is preferably treated by one or more methods of mechanical polishing, chemical polishing, and electrolytic polishing in order to reduce the roughness of the aluminum surface.

  Various methods can be used for forming the mask. For example, after a mask pattern is formed in advance, the mask may be transferred to the surface of aluminum, or the mask may be directly formed on the surface of aluminum using an ink jet printer.

  According to the aluminum having a microstructure according to the present invention and the manufacturing method thereof, a fine surface structure having a high aspect ratio depth that cannot be achieved by a conventional method can be easily and reliably formed in a highly controlled shape. Moreover, it can be obtained at a low cost. Therefore, it is possible to greatly expand the uses of aluminum having such a fine surface structure, and in particular, it is possible to develop applications that require high functionality of metal materials using the fine surface structure.

In the following, the present invention will be described in more detail with preferred embodiments.
In the method for producing an aluminum having a microstructure according to the present invention, in order to achieve the above-described object of the present invention, a mask having an opening shape corresponding to the target shape is formed on the surface of the aluminum. It is preferable to use an aluminum material whose crystal orientation is controlled. For example, an aluminum foil used for an anode foil of a high-voltage electrolytic capacitor is an aluminum material suitable for the implementation of the present invention because it is relatively inexpensive and is (100) oriented at a high ratio. In this case, as described above, it is preferable to use aluminum having a (100) plane exclusive area ratio of 90% or more. In addition, single crystal aluminum whose crystal orientation is strictly determined can be used.

  As described above, the pit formed in the present invention (in the case of connecting a plurality of pits, the individual primary pits) has a short side length of 1 to 10 microns and a long side / short side. The length ratio is 1.5 or more. The opening shape of the mask is the same as the cross-sectional shape of the target pit, and when the dissolution of the pit wall surface proceeds, the size is slightly reduced in consideration of the dissolution amount of the wall surface. As the material of the mask, one having an opening shape at a micron level and having resistance to electrolytic etching, specifically, excellent in water resistance, acid resistance, and high breakdown resistance is applied.

  The above-mentioned primary pits having such an opening shape are two-dimensionally connected or partially overlapped on the surface of aluminum (that is, at least two primary pits are connected to each other by at least a part of the opening shape). For example, at least two primary pits are coupled to each other between the short sides or the long sides in the opening shape, or the short side in the opening shape of one pit and the short shape in the opening shape of the other pit. Various composite shaped high aspect ratio microstructures can be formed in aluminum, such as by bonding between sides. For this purpose, a mask corresponding to the cross-sectional shape of a target secondary pit (a pit in which a plurality of primary pits are combined) is formed on the surface of aluminum. As described above, even when a mask having a large opening is simply formed on aluminum and general electrolytic etching is performed, only a plurality of square cross-section pits are formed in the opening of the mask. The corresponding pit cannot be obtained. However, as in the present invention, by depositing a small amount of metal on the surface of the aluminum on which the mask is formed, the aluminum can be evenly dissolved over the entire opening of the mask, and the aspect ratio corresponding to the opening shape of the mask is 1 The above pits can be formed.

  As the metal used for the minute precipitation, one or more kinds selected from those having a redox potential higher than that of aluminum are used. Among these, it is preferable that copper is a main component from the viewpoint of homogeneous aluminum dissolution at the mask opening.

  In order to form pits corresponding to the opening shape of the mask, the mask needs to be in close contact with aluminum. If the roughness of the aluminum surface is high, it becomes difficult to bond the mask and aluminum. Therefore, mechanical polishing, chemical polishing, electrolytic polishing, etc. (at least one of these methods) are performed on the aluminum surface before forming the mask. It is preferable to reduce the surface roughness.

  The mask can be manufactured by, for example, a photolithography process in which a photoresist is applied and development is performed after exposure using the photomask, or an electron beam lithography process. Since these processes are expensive in terms of equipment and materials, it is preferable to prepare a stamp having irregularities corresponding to the target mask pattern formed on the surface, form a mask thin film on the surface, and then transfer it to aluminum. In this case, since the mask on the stamp surface needs to be strongly bonded to aluminum only by physical contact, the stamp material and the mask so that the adhesive force between the stamp and the mask is low and the adhesive force between the mask and the aluminum is high. It is necessary to select a material. The stamp material suitable for this purpose is silicone resin, fluororesin or the like, and the mask material is polychloroprene, polybutadiene, acrylonitrile-butadiene, acrylic adhesive, cellulose triacetate or the like. In addition to the stamping process, the method of forming a mask directly on the aluminum surface using an ink jet printer that uses a mask material as the ink component has a high degree of freedom in pattern formation and is not easily affected by the surface roughness of the aluminum. To preferred.

  Aluminum on which a mask is formed and a trace amount of metal is deposited is electrolytically etched, but an aqueous solution containing chloride ions is used as the electrolytic solution. In order to obtain a shape with a high aspect ratio, the electrolyte temperature is preferably 40 ° C. or higher. In addition, the bottom surface of the pit when using (100) plane-oriented aluminum is usually flat. However, when etching at a relatively high temperature, for example, 80 ° C., the bottom surface of the pit can be roughened into a saw-tooth shape. The power supply may be controlled by current control or voltage control, but is performed by superimposing a direct current or an alternating current wave or a rectangular wave on the direct current. The voltage, current density, and quantity of electricity are determined under optimum conditions in consideration of the target pit opening area ratio and pit depth.

The concept of creating a high aspect ratio pit in the present invention is schematically shown in FIGS.
In FIG. 1, a mask 3 having a predetermined rectangular opening 2 is formed on the surface of aluminum 1 as a metal material, and a trace amount of metal is deposited on the surface of aluminum 1 and the entire surface of mask 3. After that, the surface portion corresponding to 2 portions of the mask opening of the aluminum 1 is electrolytically etched in an aqueous solution containing chloride ions to thereby form the pits 4 (1 having a rectangular (short side: a, long side: b) opening shape. Next pit) is formed, and aluminum 5 having a fine structure is manufactured. The short side a and the long side b satisfy 1 μm ≦ a ≦ 10 μm and 1.5a ≦ b.

  2 and 3 show a case where a plurality of pits are joined. In FIG. 2, a mask having a shape in which two rectangular mask openings 11a are joined by passage openings 12a on the surface of aluminum 1a as a metal material. A mask 3a having an opening 2a is formed, and after a trace amount of metal is deposited on the surface of the aluminum 1a and the entire surface of the mask 3a, it corresponds to the mask opening 2a portion of the aluminum 1a in water containing chloride ions. By subjecting the surface portion to be electrolytically etched to form a pit 4a having a target opening shape (secondary pit: a pit having a shape in which the above-mentioned primary pits are joined through a passage), and having a fine structure 5a is manufactured. The opening shape of the pit 4a is a form in which the long side of the rectangular opening 11a and the short side of the rectangular opening 12a are coupled.

  In FIG. 3, a mask having a shape in which two rectangular mask openings shown in FIG. 1 are directly coupled to each other on the surface of aluminum 1b as a metal material (the boundary portion is indicated by a two-dot chain line). A mask 3b having a plurality of openings 2b (square mask openings in the illustrated example) is formed, and a trace amount of metal is deposited on the surface of the aluminum 1b and the entire surface of the mask 3b, and then in an aqueous solution containing chloride ions. The surface portion corresponding to the mask opening 2b portion of the aluminum 1b is subjected to electrolytic etching, whereby a pit 4b having a target opening shape (a square or a rectangle with one side being b and the other side being 2 × a) (secondary pit: as described above) Pits having a shape in which the primary pits are directly coupled are formed, and the aluminum 5b having a fine structure is manufactured.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by this Example.
Example 1
A stamp of polydimethylsiloxane in which linear protrusions having a length of 50 microns were regularly arranged at intervals of 10 microns was produced, and a toluene solution of polychloroprene was spread on the surface and dried. The polychloroprene thin film formed in the indented portion of the stamp surface was transferred to the aluminum foil by bringing the stamp into contact with the aluminum foil for high-voltage electrolytic capacitor that had been subjected to electrolytic polishing. The opening shape of the mask formed on the aluminum surface was about 1 micron in width and about 50 microns in length. After depositing copper with an average film thickness of 10 nm using a sputtering apparatus, it was electrolytically etched in a 7 M hydrochloric acid aqueous solution at 47 ° C. for 4 seconds at a constant current density of 1200 mAcm ⁻² with respect to the apparent area. When the surface structure of aluminum (surface structure 21 in FIG. 4) and the inversion structure of the aluminum surface by the oxide replica (inversion structure 22 in FIG. 5) were observed with a scanning electron microscope, the obtained pits had a width of about 3.6 microns. The length was about 50 microns and the depth was about 7 microns.

Example 2
By a method similar to that of Example 1, a mask having an opening shape of “TMU” characters in a range of 11 microns in length and 26 microns in width was formed on an aluminum foil, and this was subjected to electrolytic etching. When the obtained structure was observed with a scanning electron microscope, formation of pits having a width of about 2 microns and a depth of about 5 microns corresponding to characters was confirmed (pit 23 in FIG. 6).

Comparative Example 1
When aluminum foil was subjected to electrolytic etching in the same manner as in Example 1 except that a small amount of copper was not deposited, it was confirmed that a plurality of square pits were formed without corresponding to the opening shape of the mask.

  The aluminum having a fine structure according to the present invention can be applied to any application in which high functionality of a metal material is demanded particularly utilizing a fine surface structure.

It is the schematic block diagram which showed typically an example of the pit creation of the high aspect ratio in this invention. It is the schematic block diagram which showed typically the other example of pit creation of the high aspect ratio in this invention. It is the schematic block diagram which showed typically the further another example of pit creation of the high aspect ratio in this invention. It is a figure which shows the result of having observed the surface structure of the aluminum which has the fine structure obtained in Example 1 with the scanning electron microscope. It is a figure which shows the result of having observed the inversion structure by the oxide replica of the surface structure of FIG. 4 with the scanning electron microscope. It is a figure which shows the result of having observed the pit of the aluminum which has the fine structure obtained in Example 2 with the scanning electron microscope.

Explanation of symbols

1, 1a, 1b Aluminum 2, 2a, 2b Mask opening 3, 3a, 3b Mask 4, 4a, 4b Pit 5, 5a, 5b Fine structure aluminum 21 Surface structure 22 Inverted structure 23 Pit

Claims (9)

  The surface has a rectangular opening with a short side length of 1 to 10 microns, a long side / short side length ratio of 1.5 or more, and a depth / short side length ratio of 1 An aluminum having a fine structure, wherein the pits as described above are formed by electrolytic etching in an aqueous solution containing chloride ions.   The aluminum having a microstructure according to claim 1, wherein at least two of the pits are bonded to each other by at least a part of the opening shape.   3. The fine structure according to claim 1, wherein a mask is formed on the surface of aluminum, a trace amount of metal is deposited thereon, and then the aluminum is electrolytically etched in an aqueous solution containing chloride ions. A method for producing aluminum having a structure.   The manufacturing method of the aluminum which has the microstructure of Claim 3 whose said trace amount metal is a metal which has copper as a main component.   The method for producing aluminum having a microstructure according to claim 3 or 4, wherein aluminum having a (100) plane exclusive area ratio of 90% or more is used.   The method for producing aluminum having a microstructure according to any one of claims 3 to 5, wherein electrolytic etching is performed at a temperature of 40 ° C or higher using an aqueous solution containing 6M or more of hydrochloric acid.   The method for producing aluminum having a microstructure according to any one of claims 3 to 6, wherein the surface of aluminum is treated by one or more techniques of mechanical polishing, chemical polishing, and electrolytic polishing prior to forming the mask.   The method for producing aluminum having a microstructure according to any one of claims 3 to 7, wherein a mask pattern is formed in advance and then the mask is transferred to the surface of aluminum.   The method for producing aluminum having a microstructure according to any one of claims 3 to 7, wherein a mask is directly formed on the surface of aluminum using an ink jet printer.

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