Mold manufacturing method
The method of selectively dissolving and removing nickel-phosphorus plating film using nitric acid forms high-aspect-ratio molds with sufficient strength and uniformity, addressing adhesion and resolution limitations in existing technologies.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- TORAY INDUSTRIES INC
- Filing Date
- 2022-07-12
- Publication Date
- 2026-06-23
AI Technical Summary
Existing methods struggle to efficiently manufacture molds with high aspect ratio structures due to issues with adhesion, isotropic etching, and limited resolution, particularly in forming fine, high-aspect-ratio structures using anodized porous alumina and nickel-phosphorus plating, which affect the strength and uniformity of the mold.
A method involving selective dissolution and removal of nickel-phosphorus plating film using nitric acid, forming high-aspect-ratio structures by etching until the side surface area of recesses or protrusions is four times the surface area, maintaining structural integrity through discrete coverage with a resist film or enhanced nitric acid resistance.
Enables the production of molds with high aspect ratio structures that maintain sufficient strength and uniformity, suitable for precise applications like optics, semiconductors, and medical filters, by controlling etching processes to form discrete convex or concave shapes.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a method for forming a fine structure having a high aspect ratio and a method for manufacturing a mold having a fine structure formed by the method.
Background Art
[0002] In recent years, in various fields such as optics, semiconductors, and medicine, the importance of technologies for forming fine structures has been increasing. In the optical field, a high-precision fine structure forming technology is required. In the semiconductor field, in addition to a high-precision fine structure forming technology, miniaturization of processing dimensions is required to improve the integration degree of semiconductor integrated circuits. In the medical field, for separating objects of a specific size such as cells from various liquids such as blood, the production of fine filters having various pore diameters from nano-size to micron-size is required. Here, as a technology for forming a fine structure on a resin, a thermal imprint technology has been proposed in which the resin is heated to a temperature above the glass transition temperature to be softened, and a heated mold is pressed onto the surface to transfer the shape of the mold to the resin surface, and this has been applied to the development of these products.
[0003] When performing these moldings by the thermal imprint technology, a mold having a shape in which the concavities and convexities are inverted corresponding to the fine structure of the molded product is required. For example, in the molding of a fine filter, a mold having a pillar shape with a height greater than the thickness of the molded product is required.
[0004] As methods for manufacturing these molds, there are a method of machining by cutting using a material with good machinability as the workpiece, a method of applying an etching process with a mask on various metals, silicon, etc., a method of forming a thick film resist by photolithography and then making a mold by electroforming in an inverted manner, and the like.
[0005] However, in the processing by cutting, due to the rigidity of the workpiece and the processing tool, it is difficult to process a high aspect structure with an aspect ratio of about 2 or more, particularly in a fine structure of 1 digit μm or less.
[0006] Furthermore, in etching processes for various metals, etching proceeds not only in the depth direction but also in the planar direction, resulting in isotropic etching. Therefore, it is difficult to process structures with an aspect ratio of 0.5 or greater.
[0007] Furthermore, while a combination of photoprocessing using resists and electroforming can form high-aspect-ratio structures by using MEMS-compatible thick-film resist materials, the resolution of the resist material makes it difficult to form fine, high-aspect-ratio structures of less than one order of magnitude micrometers. As for methods of deep etching in silicon, while high-aspect-ratio shapes can be formed due to the crystal anisotropy of silicon, it is difficult to form arbitrary shapes, and it cannot be said to be a simple manufacturing method. In addition, there is a technology that performs deep etching using silicon by dry etching, but while it can process only a small area, it cannot be said to be a simple method suitable for processing large molds.
[0008] In addition, there is a method for forming molds with fine, high-aspect-ratio structures that uses anodized porous alumina (for example, Patent Document 1). According to this method, after forming a resist pattern on the surface of the anodized porous alumina, the anodized porous alumina is selectively dissolved and removed by wet etching, thereby enabling the production of imprint molds with high-aspect-ratio structures.
[0009] On the other hand, it is known that immersing a nickel-phosphorus plated film in an aqueous nitric acid solution forms countless densely packed micropores on the film surface (for example, Patent Document 2). However, these micropores are for the purpose of forming a black film due to their density. [Prior art documents] [Patent Documents]
[0010] [Patent Document 1] Japanese Patent Publication No. 2013-57102 [Patent Document 2] Japanese Unexamined Patent Publication No. 57-114655 [Overview of the project] [Problems that the invention aims to solve]
[0011] However, in the case of the high-aspect-ratio structure using anodized porous alumina disclosed in Patent Document 1, the porous structure extends beyond the removal area, and except for limited applications where this porous structure is used as is, it is necessary to use it with the resist remaining on the surface. However, even when the resist is left on, the porous structure remains inside, which can cause problems with the strength of the mold. Furthermore, since the resist is applied to a porous structure in the first place, it can be difficult to form a uniform film on the surface of the anodized porous alumina with liquid resist, and dry film resist tends to have insufficient adhesion to the anodized porous alumina, making it difficult to easily manufacture high-aspect-ratio molds with sufficient strength.
[0012] The method for forming micropores on the surface of nickel-phosphorus plating disclosed in Patent Document 2 is intended for forming a black coating and therefore cannot be used as a mold having a high-aspect-ratio structure of a desired shape.
[0013] Therefore, the present invention provides a method for manufacturing a mold that has a high aspect ratio structure with sufficient strength and can be produced in a simple manner. [Means for solving the problem]
[0014] [1] The present invention, which solves the above problems, is a method for manufacturing a mold having a structure formed by nickel-phosphorus plating, The process includes a step of selectively dissolving and removing the portions of a nickel-phosphorus plating film, whose surface is discretely covered with a coating that does not dissolve in nitrate water, with nitrate water, thereby forming the structure that remains undissolved by the nitrate water. The above dissolution and removal process is carried out until the area of the side surface of each remaining protrusion that is not dissolved and removed is four times or more the area of the protrusion observed from the surface of the nickel-phosphorus plating film.
[0015] [2] Another embodiment of the present invention that solves the above problems is a method for manufacturing a mold having a structure formed of nickel-phosphorus plating, The process involves selectively dissolving and removing the uncovered portions of a nickel-phosphorus plated film, whose surface is covered with a coating that does not dissolve in nitrate water, using nitrate water, thereby forming the structure that remains undissolved by the nitrate water. The above dissolution and removal process is carried out until the area of the side surface of each recess to be dissolved and removed is four times or more the area of the recess observed from the surface of the nickel-phosphorus plating film.
[0016] Furthermore, the method for manufacturing the mold of the present invention may be any of the following methods [3] to [6]. [3] A method for manufacturing the mold described in [1] or [2] above, wherein the step of dissolving and removing with nitrate water is performed by first dissolving and removing with concentrated nitrate water and then dissolving and removing with dilute nitrate water. [4] A method for manufacturing a mold according to any of the above [1] to [3], wherein the phosphorus concentration in the nickel-phosphorus plating film is 8 to 15% by mass. [5] A method for manufacturing any of the molds described in [1] to [4] above, comprising the step of dissolving and removing with nitric acid water, removing the coating to expose the nickel-phosphorus plating film, and cutting the surface of the exposed nickel-phosphorus plating film. [6] A method for manufacturing a mold according to any of the above [1] to [5], comprising the step of pressing a metal member having irregularities formed on the surface of the nickel-phosphorus plating film while heating it, prior to the step of dissolving and removing it with nitric acid water, thereby thermally deforming the portion of the nickel-phosphorus plating film that is in contact with the convex portion of the metal member, and thereby forming the thermally deformed portion into the coating. [Effects of the Invention]
[0017] According to the present invention, a mold having a high aspect ratio structure with sufficient strength can be manufactured by a simple method.
Brief Description of the Drawings
[0018] [Figure 1] It is a flowchart showing an example of an embodiment of a method for manufacturing a mold of the present invention. [Figure 2] It is a side view showing an example of the structure of a mold of the present invention.
Embodiments for Carrying Out the Invention
[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart showing an example of an embodiment of a method for manufacturing a mold of the present invention. First, as shown in FIG. 1(a), a resist film 3 having a desired shape is provided as a coating that is not dissolved by nitric acid water on the surface of the nickel-phosphorus plating film 2 applied to the base material 1. Here, as the base material 1, various metal materials such as stainless steel and aluminum, which have good adhesion to the nickel-phosphorus plating film, or any material such as glass and ceramic can be used. The nickel-phosphorus plating film 2 can be formed by electroless plating or electroplating, but it is preferably a film obtained by thickening a general plating film formed by electroless plating, and may contain general additives used for nickel-phosphorus plating. The thickness of the nickel-phosphorus plating film 2 can be arbitrarily selected according to the height of the desired high aspect ratio shape, but preferably it is about 10 to 200 μm. As the resist film 3, a commercially available liquid resist or a dry film resist (DFR) having nitric acid resistance can be used. These resist films can cover the surface of the nickel-phosphorus plating film intermittently by forming a pattern through exposure and development using a general exposure apparatus. In FIG. 1(a), a state in which the surface of the nickel-phosphorus plating film is covered so that the openings of the resist film 3 are discrete is illustrated. Also, as will be described later, by partially heat-treating the surface of the nickel-phosphorus plating film or the like to increase the nitric acid resistance partially, the plating film of the portion with increased nitric acid resistance can be used as a coating that is not dissolved by nitric acid water instead of the resist film.
[0020] The base material 1 with a nickel-phosphorus plating film 2, on which a resist film 3 has been formed on the surface, is immersed in nitric acid water (not shown) and etched. Here, if concentrated nitric acid with a concentration of 40% by mass or more, preferably 50% by mass or more, is used, narrow and deep pores can be formed in the nickel-phosphorus plating film 2 in the areas not covered by the resist film 3. This is thought to be because a nickel oxide film is formed almost instantaneously on the surface of the nickel-phosphorus plating film 2 under concentrated nitric acid. Since etching proceeds in the depth direction only in the limited areas where etching begins before the nickel oxide film is formed, narrow and deep pores are formed. Note that the nitric acid concentration does not need to be higher than the limit set by the concentration method.
[0021] Here, according to the inventors' research, the phosphorus concentration in the nickel-phosphorus plating film affects the size and density of etching points that begin before the nickel oxide film is formed. In order to allow deep holes to develop at high density and at a controllable rate in the areas not covered by the resist film, a phosphorus concentration of 8 to 15 mass% is preferred. If the phosphorus concentration is 15 mass% or less, the number of etching points increases, and deep holes are more easily formed in the areas not covered by the resist film. If the phosphorus concentration is 8 mass% or more, the etching does not progress too quickly in the areas not covered by the resist film, making it easier to control the etching. A phosphorus concentration of 10 to 13 mass% is even more preferred.
[0022] Here, the etching can be terminated appropriately by observing the appearance and color of the nickel-phosphorus plating film 2, but the etching time is preferably between 30 and 600 seconds. When etching is complete, it is preferable to stop the etching by rinsing with water. Alternatively, it is also acceptable to rinse with water, dry, and then perform additional etching. As shown in Figure 1(b), the shape of the intermediate product after etching with concentrated nitric acid is such that countless narrow, deep pores are formed in the areas not covered by the resist film 3.
[0023] The nickel-phosphorus plating film 2 in this state is then immersed in nitric acid solution (dilute nitric acid) with a concentration of approximately 5% to 20% by mass (not shown). In such dilute nitric acid, a nickel oxide film is unlikely to form on the surface of the nickel-phosphorus plating film 2, so the entire nickel-phosphorus plating film 2 is etched in an isotropic direction. This isotropic etching proceeds not only from the outermost surface of the nickel-phosphorus plating film but also from the areas where countless narrow, deep pores have been formed. As a result, the thin remaining portions of the nickel-phosphorus plating film 2 surrounding the countless narrow, deep pores are dissolved and removed, and as shown in Figure 1(c), high-aspect-ratio recessed shapes with openings that almost coincide with the openings of the resist film 3 are formed on the nickel-phosphorus plating film 2 in the areas not covered by the resist film 3.
[0024] In this way, when the surface of the nickel-phosphorus plating film 2 is covered with the resist film 3 in such a discrete manner, discrete recessed shapes can be formed on the surface of the nickel-phosphorus plating film 2. For each of the recessed shapes, a high-aspect-ratio recessed shape can be formed by etching until the area of the side surface of the recess is four times or more than the area observed from the surface of the nickel-phosphorus plating film 2 (opening area). On the other hand, when the surface of the nickel-phosphorus plating film 2 is discretely covered with the resist film 3, discrete convex shapes can be formed on the surface of the nickel-phosphorus plating film 2. For each of the convex shapes, a high-aspect-ratio convex shape can be formed by etching until the area of the side surface of the convex is four times or more than the area observed from the surface of the nickel-phosphorus plating film 2 (surface area of the top of the protrusion).
[0025] Furthermore, if the convex or concave shapes are unique surface shapes (for example, when viewed from the surface of the nickel-phosphorus plating film, circles or squares of the same size are arranged), etching should be performed using that shape until the area of the side surface of the convex (or concave) is four times or more the area observed from the surface of the nickel-phosphorus plating film. If the shapes are not unique, etching should be performed using the most numerous shape until the area of the side surface of the convex (or concave) is four times or more the area observed from the surface of the nickel-phosphorus plating film. It is not necessary to etch the frames or continuous grooves surrounding the convex or concave until the area of the side surface of the convex (or concave) is four times or more the area observed from the surface of the nickel-phosphorus plating film.
[0026] Furthermore, by peeling off the resist film 3, a mold with a high aspect ratio structure can be easily manufactured, as shown in Figure 1(d). In the mold manufactured in this way, the areas around the recesses are not etched, so the nickel-phosphorus plating film remains intact, maintaining high strength and making it suitable for use as a mold.
[0027] On the other hand, even when the surface of the nickel-phosphorus plating film 2 is discretely covered with the resist film 3, a mold can be easily manufactured in which high-aspect-ratio convex shapes are discretely formed on the surface of the nickel-phosphorus plating film 2 by peeling off the resist film 3 after etching. In the mold manufactured in this way, since the convex parts are not etched, high strength is maintained, making it suitable for use as a mold.
[0028] Furthermore, by machining the nickel-phosphorus plating film 2, it is also possible to manufacture a mold having a high-aspect-ratio structure that combines the machined shape and the etched shape. For example, as shown in Figure 2, if discrete sharp protrusions 21 are created in advance by machining, and then the protrusions are discretely covered with a resist film and etched, it is possible to manufacture a mold having a structure in which the sharp shapes formed by machining are located on the top 21 and the columnar parts 22 have a high aspect ratio.
[0029] Alternatively, instead of applying a resist film, nitric acid resistance can be improved by locally modifying the surface state of the nickel-phosphorus plating film. One method for locally modifying the surface state of the nickel-phosphorus plating film is by localized heating.
[0030] This can be achieved by using a metal component with a low aspect ratio, such as one with an aspect ratio of 1 or less, to press the convex portion of the metal component against the surface of the nickel-phosphorus plating film, or by heating the surface of the nickel-phosphorus plating film by scanning it with a beam such as a laser. For example, at high temperatures of 200°C or higher, the nickel-phosphorus plating film is prone to thermal deformation, and it is thought that the thermally deformed portion will locally crystallize from an amorphous state, increasing its resistance to nitric acid. [Examples]
[0031] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples.
[0032] (Example 1) A nickel-phosphorus plating film with a phosphorus concentration of 12% by mass (plating thickness 30 μm) was formed on a 1 mm thick stainless steel plate (SUS304) by electroless plating. A 5 μm thick DFR was then bonded to the plate, and after exposure and development, the DFR remained only in areas with a diameter of 3 μm (pitch 6 μm). After immersing this plate in concentrated nitric acid water with a concentration of 60% by mass for 5 minutes and then rinsing with water, the areas where the DFR did not remain turned black to the naked eye. When the surface was observed with a scanning electron microscope, it was confirmed that there were countless holes with a diameter of approximately 0.1 to 0.8 μm running in the direction of the plate thickness in the blackened areas.
[0033] Next, the plate was immersed in a 10% by mass dilute nitric acid solution for 1 minute and then rinsed with water. In areas where DFR was not present, the black color was reduced, and when observed from the surface with a scanning electron microscope, it was found that in the discolored areas, the micropores were connected, and the entire nickel-phosphorus plating film was gouged out.
[0034] Next, when the remaining circular DFR was removed, a shape was found in the nickel-phosphorus plating film consisting of roughly cylindrical structures with a diameter of 2.8 μm and a height of 30 μm, arranged at a pitch of 6 μm. The area of the top surface of each cylinder was approximately 6.2 μm. 2 ) relative to the surface area of the side (approximately 264 μm²) 2 ) was approximately 43 times. [Explanation of Symbols]
[0035] 1: Base material 2: Nickel-phosphorus plating film 3: Resist film (a coating that does not dissolve in nitrate water) 21:Top 22: Pillar part
Claims
1. A method for manufacturing a mold having a structure formed by nickel-phosphorus plating, The process includes a step of selectively dissolving and removing the portions of a nickel-phosphorus plating film, whose surface is discretely covered with a coating that does not dissolve in nitrate water, with nitrate water, thereby forming the structure that remains undissolved and removed by the nitrate water. The phosphorus concentration in the nickel-phosphorus plating film is 8 to 15% by mass. The aforementioned dissolution and removal process is carried out until the area of the side surface of each remaining protrusion that is not dissolved and removed is four times or more the area of the protrusion observed from the surface of the nickel-phosphorus plating film. A method for manufacturing molds.
2. A method for manufacturing a mold having a structure formed by nickel-phosphorus plating, The process includes a step of forming the structure that remains undissolved by the nitrate water by selectively dissolving and removing the portions of a nickel-phosphorus plated film whose surface is covered with a coating that does not dissolve in nitrate water, such that portions not covered by the coating remain discretely. The phosphorus concentration in the nickel-phosphorus plating film is 8 to 15% by mass. The dissolution and removal process is carried out until the area of the side surface of each recess to be dissolved and removed is four times or more the area observed from the surface of the nickel-phosphorus plating film. A method for manufacturing molds.
3. A method for manufacturing a mold according to claim 1 or 2, wherein the step of dissolving and removing with nitrate water is performed by first dissolving and removing with concentrated nitrate water and then dissolving and removing with dilute nitrate water.
4. A method for manufacturing a mold according to claim 1 or 2, comprising the steps of dissolving and removing with nitric acid water, removing the coating to expose the nickel-phosphorus plating film, and cutting the surface of the exposed nickel-phosphorus plating film.
5. A method for manufacturing a mold according to claim 1 or 2, comprising the step of pressing a metal member on which irregularities have been formed on the surface of the nickel-phosphorus plating film while heating it, prior to the step of dissolving and removing it with nitric acid water, thereby thermally deforming the portion of the nickel-phosphorus plating film that is in contact with the protruding portion of the metal member, and thereby forming the thermally deformed portion as the coating.