JP5851165B2 - Method for forming microstructure and method for producing porous alumina composite - Google Patents

Description

The present invention relates to a manufacturing method of forming method and porous alumina composite microstructure having a high aspect ratio.

  Establishment of a technique for forming a fine and relatively deep structure on a substrate, that is, a fine structure having a high aspect ratio, is important for enhancing the functionality of the material. For example, a structure in which a through hole having a high aspect ratio is formed on a substrate is useful for a separation filter that removes foreign substances from gas or liquid. In addition, it is possible to form a composite structure by filling various substances using the formed high aspect ratio structure as a mold, and by dissolving and removing the mold, various structures corresponding to the negative structure of the mold are predetermined. Can be obtained with

  As a microfabrication technology for substrates widely applied industrially, a resist having etching resistance is applied on the substrate, and a desired pattern is exposed by light exposure or electron beam irradiation, and then the resist is selected. There is a technique of processing a substrate by forming a resist pattern by removing the substrate from the substrate and then etching the substrate by a wet etching method using an etchant having a dissolving power for the substrate. Although this method can form a shape corresponding to the resist, etching progresses isotropically during etching, so that a so-called under-etching phenomenon occurs in the non-opening portion of the resist, resulting in a high aspect ratio. It is not possible to obtain a structure with On the other hand, in dry etching in which etching of a substrate is performed based on active species generated in a gas phase using discharge in an appropriate gas, the aspect ratio of the formed structure is improved compared to wet etching. However, the pattern disappears due to the etching of the resist that proceeds at the same time, and further processing becomes difficult, and as the processing shape becomes deeper, it becomes difficult for the active species to enter the fine parts, and the formation of a high aspect ratio structure It becomes difficult. In addition, dry etching generally has a problem that an expensive apparatus is required and the processing speed is low.

Hideki Masuda and Masahiro Sato, Jpn. J. Appl. Phys. Vol. 35 (1996), L126

  The present invention has been made to solve the above-described problems in the prior art, and an object of the present invention is to provide a method of manufacturing a substrate having a fine structure with a high aspect ratio with respect to depth, the shape of which is controlled. .

  In order to solve the above-mentioned problems, the fine structure forming method (first method) according to the present invention is to form a resist pattern on the surface of anodized porous alumina and then perform wet etching to form the resist pattern. The method comprises forming a fine structure having a cross-sectional shape corresponding to the resist pattern and having an aspect ratio of 1 or more by selectively dissolving and removing a portion that has not been formed.

  In the fine structure forming method according to the present invention, it is preferable that the ratio of the diameter of each resist region of the resist pattern to the pore period of the anodized porous alumina is in the range of 3 to 10,000.

  The pore period of the anodized porous alumina is preferably in the range of 10 to 5000 nm.

  The pore depth of the anodized porous alumina is preferably in the range of 0.5 to 50,000 μm.

  Moreover, it is preferable that the said wet etching process consists of an etching process using phosphoric acid.

  Moreover, it is preferable that the said microstructure consists of the through-hole penetrated from the one surface of the said anodic oxidation porous alumina to the other surface.

  Further, it is preferable that the resist pattern is formed on the surface of the anodized porous alumina by being transferred from a previously patterned mask.

  In order to solve the above problems, the fine structure forming method (second method) according to the present invention forms a resist pattern on the surface of anodized porous alumina, and then performs wet etching to form the resist pattern. By selectively dissolving and removing the unexposed portion, a through hole having a cross-sectional shape corresponding to the resist pattern and an aspect ratio of 1 or more is formed, and the through hole is filled with a material different from porous alumina. And then forming a microstructure by dissolving and removing the anodized porous alumina.

  In such a microstructure forming method according to the present invention, it is preferable to fill the through hole with a material different from porous alumina by electrolytic plating or electroless plating.

  In order to solve the above problems, the fine structure forming method (third method) according to the present invention forms a resist pattern on the surface of anodized porous alumina, and then performs wet etching to form the resist pattern. After producing a negative mold having a single microstructure with an aspect ratio of 1 or more, which is formed by selectively dissolving and removing a portion that has not been formed, an aspect ratio is obtained by a mold process using the negative mold as a mold. This is a method characterized in that a positive mold having another fine structure in which is 1 or more is produced.

  In such a microstructure forming method according to the present invention, the mold process may be repeated.

  The one fine structure is a columnar structure extending from one surface of the anodized porous alumina to the other surface, and the other fine structure penetrates from one surface of the positive type to the other surface. It preferably consists of holes.

  Further, the positive type is preferably made of a polymer material.

In order to solve the above-described problem, a method for producing a porous alumina composite according to the present invention forms a through-hole as a fine structure by the fine-structure formation method (first method), and the through-hole is formed in the through-hole. It consists of a method characterized by filling a material different from porous alumina.

According to the fine structure forming method of the present invention, a fine surface structure having a high aspect ratio depth, which could not be achieved by a conventional method, can be obtained easily, reliably and inexpensively in a highly controlled shape. be able to. Accordingly, it is possible to greatly expand the applications of the substrate having such a fine surface structure, and particularly, a substrate having a fine structure having a high aspect ratio, and further, a metal formed by using them as a template, metal oxide Application to applications requiring high aspect ratio structures such as products and polymers becomes possible. Further, it becomes possible to easily and accurately manufacture a composite made of porous alumina and other materials.

In the formation method of the microstructure concerning one embodiment of the present invention, it is a perspective view showing the state where the resist mask was formed on the porous alumina surface. It is a front view which shows the fine structure obtained by performing an etching process from the state of FIG. It is a front view which shows the structure obtained by removing a mask material from the fine structure of FIG. It is a top view which shows the positional relationship of the pore of a porous alumina, and a fine structure. It is a front view which shows the porous alumina before performing etching. It is a front view which shows the porous alumina after etching. The manufacturing method of the porous alumina composite_body | complex which concerns on one embodiment of this invention is shown, (A)-(E) is a top view which shows the porous alumina in each process. An example of the porous alumina substrate which has the fine structure formed by the method concerning the present invention is shown, (A) is a SEM picture of the substrate surface, and (B) is an enlarged picture which expanded a part of (A). It is the SEM image which imaged an example of the negative type which has the fine structure formed by the method concerning the present invention from the slanting upper part. An example of the porous polymer membrane which has the microstructure formed by the method concerning the present invention is shown, (A) is the SEM image of the membrane surface, and (B) is the SEM image of the membrane section.

  The inventor has conducted various investigations and studies on a method capable of forming a target high aspect ratio structure with a controlled shape. As a result, a resist mask corresponding to the target shape is formed on the surface of the anodized porous alumina whose fine pores are perpendicular to the substrate, and wet etching is performed to form the target high aspect ratio microstructure. I found that I can achieve.

  That is, according to the present invention, the minimum pattern portion (short side such as the diameter and thickness of the pattern shape) is 0.1 to 100 μm, the ratio (aspect ratio) between the minimum pattern portion and the depth (long side) is 1 or more, Alternatively, a substrate having a fine structure in which a structure having a higher aspect ratio (for example, an aspect ratio of 10 to 10,000) is formed by wet etching can be manufactured.

  As a typical example of such a fine structure, pores having a constant diameter are arranged at a desired interval, columnar structures having a fixed size are arranged at a predetermined interval, or a combination of rectangles. However, since the shape to be formed corresponds to the pattern of the mask formed on the surface, it is not limited to these.

  In the method of manufacturing a substrate having this fine structure, anodized porous alumina with uniform pores is used as the substrate, or anodized porous alumina with regularly arranged pores is used. It is preferable to use anodized porous alumina that is orthogonal to the substrate.

  Moreover, in the manufacturing method of the said board | substrate which has a fine structure, it is preferable to use the anodized porous alumina which has a pore with a diameter of the range of 5-100 nm.

  Various methods can be employed for forming a mask on the surface. For example, it can be formed by applying a resist on anodized porous alumina as a substrate, and performing development processing after light or electron beam exposure. An etching resistant mask may be formed directly on the anodized porous alumina surface using an ink jet printer. In addition, a method of forming an etching resistant mask by forming a stamp having a desired pattern in advance and then transferring a resist material having etching resistance onto the surface can be used.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In manufacturing a substrate having a fine structure, anodized porous alumina having a structure in which fine pores are perpendicular to the film surface is used as the substrate. Anodized porous alumina is a porous material that is formed by anodizing aluminum in an acidic electrolyte, and has the feature that pores having a uniform diameter are formed perpendicular to the membrane surface by anodization. Have. The formed pores form independent pores, and the diameter and interval of the pores can be adjusted in the range of 5 to 800 nm and 10 to 1000 nm, respectively, depending on the formation voltage at the time of anodization. In addition, after the anodization, the pore diameter can be increased by immersing a soluble etchant such as phosphoric acid. In addition, since the hole depth is proportional to the formation time, it can be adjusted in the range of 0.1 μm to 5 mm. In addition, a structure in which pores are regularly arranged in a wide range can be obtained by optimizing the conditions during anodization (Non-patent Document 1). In the anodic porous alumina having regular pores, the pore shape and the pore diameter are made uniform along with the regularization of the pore arrangement, and the straightness of the pores is improved.

  In addition, for the purpose of removing the part of the structure with low regularity formed in the initial stage of anodization, after anodizing for a certain period of time and regularizing the pore arrangement, the oxide film is selectively removed once by appropriate etching. By anodizing again under the same conditions, the pores are regularized from the outermost surface to the bottom, and as a result, the pore shape and diameter are uniform, and good straightness is maintained in the film thickness direction. Can be obtained.

  FIG. 1 shows a state in which a resist mask 4 having a desired pattern having etching resistance is formed on the anodized porous alumina 1 surface. The shape of the opening 5 of the mask 4 is the same as the cross-sectional shape of the target microstructure. As the material of the mask 4, a material that maintains an opening shape at a micron level and can withstand etching, specifically, a material that is excellent in water resistance, acid resistance, and adhesion is applied.

  The mask is produced, for example, by applying a photoresist on the porous alumina 1 and performing exposure after using the photomask 4 to develop the resist pattern, or performing lithography using an electron beam. It can be done by a process. It can also be formed by patterning a resist material with an ink jet printer. In addition, it is more preferable to use a process in which a stamp having irregularities corresponding to the target mask pattern formed on the surface is prepared in advance, a thin film to be a resist mask 4 is formed on the surface, and then transferred to the surface of the anodized porous alumina 1. be able to. In this case, since the mask 4 on the stamp surface needs to be strongly bonded to the anodized polar alumina 1 only by physical contact, 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 stamp material and a mask 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. Based on this method, once the stamp has been made, it can be used repeatedly, so that it is possible to form a pattern at low cost, and that the mask material penetrates into the porous alumina substrate. It can be avoided.

  FIG. 2 shows a high aspect ratio corresponding to the mask 4 obtained by etching the porous alumina 1 having the mask 4 formed on the surface and selectively dissolving and removing the oxide layer corresponding to the opening 5 of the mask 4. The structure is shown. In the porous alumina 1 having the mask 4 formed on the surface, the exposed portion is selectively dissolved by immersing the oxide layer in a dissolvable etchant. The etchant used at this time is represented by phosphoric acid. In addition to acids, bases can be used. At the time of etching, the etchant quickly penetrates from the opening 5 of the mask 4 to the bottom of the substrate through the pores 2 of the anodized porous alumina 1 and dissolves only the portion of the anodized porous alumina 1 corresponding to the opening 5. To do. In order to obtain a shape corresponding to the resist opening 5 and having a high aspect ratio, it is preferable to perform etching under conditions that dissolve the opening 5 rapidly while suppressing dissolution of the non-opening. For this purpose, phosphoric acid is used as an etchant, the concentration is preferably 10 wt%, and the bath temperature is preferably 20 to 50 ° C., more preferably 25 to 35 ° C. Further, the etching time is an optimum time in which the alumina in the opening 5 of the mask 4 is sufficiently dissolved and the dissolution of the pore wall does not reach the unopened portion. It is necessary to select according to the pore diameter, pore period, and pore depth. In addition, after the dissolution treatment, the mask material is dissolved and removed as necessary, whereby an alumina oxide structure corresponding to the mask pattern can be obtained (FIG. 3).

  FIG. 4 shows the positional relationship between the pores 2 of the porous alumina 1 and the microstructure formed by the present invention. In the figure, the broken line indicates the mask opening boundary 7 of the mask pattern. In the formation process of the fine structure, the etchant enters only the pores 2 corresponding to the openings 5 of the mask 4 in the porous alumina layer and dissolves the oxide layer. As a result, as schematically shown in FIG. 4, the pattern to be formed is constituted by the pores 2 of the porous alumina 1. At this time, if porous alumina 1 having sufficiently fine holes as compared with the pattern to be formed is used as a substrate, a structure having an approximately sufficiently smooth shape can be obtained.

  5 to 6 schematically show a process in which the base metal aluminum 3 is dissolved and removed after the mask 4 is formed and etching is performed. If necessary, the mask 4 may be applied after the metal base 3 is removed. When etching is performed after the metal base 3 is removed, the porous alumina 1 having through holes corresponding to the pattern can be obtained as shown in FIG. The portion of the porous alumina 1 where the hole called the barrier layer 8 is closed is usually dissolved and removed at the same time as the etching. However, in order to ensure a through hole, the barrier layer 8 is removed prior to the etching. It is preferable. For removal of the barrier layer 8, a method of physically removing the barrier layer 8 by a method such as ion milling, in addition to a method of dissolving and removing with an appropriate acid after coating the surface side with an etching resistant material can be used. Since the porous alumina substrate obtained in this manner has orthogonal pores having a size and a period corresponding to the mask pattern, it can be effectively used as a filter for separation and filtration.

  A substrate having a high aspect ratio microstructure can also be used as a mold for forming a high aspect ratio microstructure of various materials. A typical production example of a high aspect ratio fine structure based on a mold process is shown in FIG. In the example of FIG. 7, a metal conductive layer is formed on one surface of the anodized porous alumina 1 in which through holes having a uniform size are formed at predetermined intervals, and the filling metal 10 is filled into the pores 2 by an electroplating process. An alumina / metal composite structure is formed. In order to prevent the porous alumina pores from being filled with metal, it is desirable to form a metal conductive layer on the resist mask forming side surface. For forming the metal conductive layer, a vacuum deposition method, a sputtering method, or the like can be used. In addition to electroplating, electroless plating can be used for metal filling. In addition to the metal, a metal oxide or the like can be filled by a plating method. Furthermore, the metal oxide can be filled by a technique such as a sol-gel method. In addition to this, it is also possible to fill a polymer in addition to a metal and a metal oxide. The formed composite structure is used as it is, and by selectively dissolving the alumina layer with an appropriate etchant, structures corresponding to the negative type of alumina can be obtained with various materials.

  Thus, by sequentially applying the mold process to an appropriate material in sequence, it becomes possible to obtain a structure corresponding to the positive type of the anodized porous alumina 1 and to obtain a fine high aspect ratio structure with various materials. It becomes possible.

  The porous alumina 1 having a high aspect ratio obtained by the present invention, or the fine structure produced using the porous alumina 1 as a mold can be used as a mold for a nanoimprint process. If it is based on the nanoimprint process, it becomes possible to produce a fine structure with high throughput at low cost.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by this Example.

[Example 1]
The electrolytically polished aluminum plate was anodized for 600 minutes under the conditions of 0.3 M oxalic acid, 16 ° C., and 40 V to obtain a porous film having a pore period of 100 nm, a pore diameter of 40 nm, and a thickness of 60 μm. A chloroprene rubber thin film is formed on the PDMS stamp by immersing a polymethylsiloxane (PDMS) stamp with a diameter of 2 μm and a period of 5 μm and having recesses in a triangular lattice shape into a 0.75 wt% chloroprene rubber toluene solution, and then lifting and drying. Then, it was transferred onto porous alumina and annealed at 300 ° C. for 3 minutes. After removing the Al ingot with iodomethanol, etching was performed in phosphoric acid at 30 ° C. and a concentration of 10 wt% for 1 hour 30 minutes. When the obtained structure was observed with a scanning electron microscope, a through hole corresponding to the mask pattern was confirmed (FIG. 8).

[Example 2]
A 20 nm thick Ni layer was sputtered on the surface on the mask forming side of a porous alumina substrate having through-holes with a diameter of 2 μm and a period of 5 μm produced according to the present invention, and subjected to a conductive treatment. The conducting wire was fixed, and Ni was filled in the pores using an electroplating method. Then, it was immersed in 5 wt% NaOH, and the alumina layer was dissolved and removed to obtain a Ni negative mold (FIG. 9). Thereafter, a photo-curing polymer (SU-8) (manufactured by MicroChem Corp) is spin-coated on the Ni negative mold, and after light exposure and annealing, the Ni negative mold is dissolved and removed to have the same diameter of 2 μm as the starting structure. A porous polymer membrane in which direct through holes with a period of 5 μm were arranged was obtained (FIG. 10).

  The high aspect ratio fine structure material obtained by the present invention can be applied to various uses such as filter membranes where a fine high aspect ratio structure is required.

DESCRIPTION OF SYMBOLS 1 Porous alumina 2 Pore 3 Aluminum 4 Mask 5 Opening 6 Selective dissolution part 7 Mask opening boundary 8 Barrier layer 9 Electrode 10 Filling metal 11 Filling polymer

Claims (14)

  After forming a resist pattern on the surface of the anodized porous alumina, a wet etching process is performed to selectively dissolve and remove portions where the resist pattern is not formed, thereby having a cross-sectional shape corresponding to the resist pattern. A fine structure forming method, wherein a fine structure having an aspect ratio of 1 or more is formed.   2. The method for forming a microstructure according to claim 1, wherein a ratio between a diameter of each resist region of the resist pattern and a pore period of the anodized porous alumina is in a range of 3 to 10,000.   The method for forming a microstructure according to claim 1 or 2, wherein a pore period of the anodized porous alumina is in a range of 10 to 5000 nm.   The method for forming a microstructure according to any one of claims 1 to 3, wherein the pore depth of the anodized porous alumina is in the range of 0.5 to 50,000 µm.   The method for forming a microstructure according to claim 1, wherein the wet etching process is an etching process using phosphoric acid.   The method for forming a microstructure according to any one of claims 1 to 5, wherein the microstructure is a through-hole penetrating from one surface of the anodized porous alumina to another surface.   The method for forming a microstructure according to any one of claims 1 to 6, wherein the resist pattern is formed on a surface of the anodized porous alumina by being transferred from a pre-patterned mask.   After forming a resist pattern on the surface of the anodized porous alumina, a wet etching process is performed to selectively dissolve and remove portions where the resist pattern is not formed, thereby having a cross-sectional shape corresponding to the resist pattern. Forming a through-hole having an aspect ratio of 1 or more, filling the through-hole with a substance different from porous alumina, and then dissolving and removing the anodized porous alumina to form a fine structure Structure formation method.   The method for forming a microstructure according to claim 8, wherein a material different from porous alumina is filled in the through hole by electrolytic plating or electroless plating.   After the resist pattern is formed on the surface of the anodized porous alumina, a wet etching process is performed to selectively dissolve and remove portions where the resist pattern is not formed. After forming a negative mold having a fine structure, a positive mold having another fine structure having an aspect ratio of 1 or more is formed by a mold process using the negative mold as a mold. Method.   The method of forming a microstructure according to claim 10, wherein the mold process is repeated.   The one microstructure is a columnar structure extending from one surface of the anodized porous alumina to another surface, and the other microstructure is formed from a through-hole penetrating from one surface of the positive mold to another surface. The method for forming a microstructure according to claim 10 or 11, comprising:   The method for forming a microstructure according to any one of claims 10 to 12, wherein the positive mold is made of a polymer material.   A method for producing a porous alumina composite, wherein the microstructure formed by the method according to any one of claims 1 to 7 comprises a through hole, and the through hole is filled with a substance different from porous alumina.

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