JP3126458B2 - Mold and casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting mold and a casting method using the casting mold, and more particularly to a casting mold capable of forming a fine pattern on a casting surface and a casting method using the casting mold.

[0002]

2. Description of the Related Art Conventionally, a mold used for casting is formed by cutting a material such as wood, wax, metal, etc., and wrapping it in a mold such as sand, clay, metal, etc. (Maintaining the shape) and then removing the prototype. In addition, the mold used only once may not use the original mold. In this case, the mold that is formed by reversing the irregularities that appear in the casting (casting) is formed by cutting the block-shaped member. Had been created. In any case, since the irregularities of the mold corresponding to the irregularities appearing in the casting are formed by machining such as cutting, it is difficult to form fine irregularities of about several μm on the surface of the casting. In the case of manufacturing gold coins, a certain amount of labor and cost can be taken to prevent forgery. Therefore, fine irregularities, which are generally difficult to produce, are formed on the surface of a mold by a mechanical method.

By the way, in the case of metal casting, it is not generally practiced to provide fine asperities on a finished casting except for special cases such as the case of gold coins described above. The first reason is that even if minute irregularities are formed in a metal mold, the metal to be cast and the mold form an alloy and cannot be removed from the mold properly. Since the alloy is formed up to the depth of about μm at the interface between the casting and the mold, if the irregularities are larger than a certain degree, it is possible to separate the alloy even if it becomes an alloy.
This is a major problem when trying to form fine irregularities of about m. Furthermore, it is mentioned that it is difficult for metal to be cast into gaps of fine irregularities of the mold. As a cause, when the casting material enters the gap of the fine irregularities, the surface area increases, it is rapidly cooled by heat conduction, the fluidity is lost at the entrance of the fine irregularities, and the casting material is not cast to the deep part of the irregularities It is thought to be because.

On the other hand, a hologram is formed on the surface of a credit card or the like for the purpose of preventing forgery, and this hologram is formed by providing irregularities of about several μm on a polymer film using semiconductor manufacturing technology. ing. Similar irregularities are also provided on a plastic optical disk. In this case, such irregularities
It is formed under conditions close to hot pressing rather than casting.

[0005]

As described above, since the conventional mold is formed by machining such as cutting, there is a problem that it is not suitable for providing a fine pattern on the surface of a casting. Furthermore, even if a fine pattern is provided on a mold, there is a problem that it is difficult to transfer the fine pattern to a casting due to poor alloy formation and poor melt flow.

An object of the present invention is to provide a mold having a pattern of fine irregularities and a casting method for producing a casting having a pattern of fine irregularities on the surface using the mold.

[0007]

According to the present invention, there is provided a mold comprising a metal,
A metal compound, a mold member made of silicon or a silicon compound, a photoresist is applied to the surface of the mold member, the photoresist is exposed to a predetermined pattern and developed, and then the mold is formed using the photoresist as an etching mask. And a mold pattern created by etching the member.

[0008] The casting method of the present invention utilizes the mold of the present invention to flow a casting material having a lower melting point than a mold member into a fluid state into the mold, and then solidifies the casting material.

[0009]

In the mold of the present invention, a mold pattern is provided on the mold member by a semiconductor manufacturing process, so that fine irregularities can be provided on the surface. In addition, since the casting method of the present invention uses the mold of the present invention, it is possible to cast a casting having a fine uneven pattern.

As described above, when a metal material is cast using a mold having fine irregularities, the mold and the molten metal material form an alloy and it is difficult to separate the mold. Is coated with an intermediate layer made of an oxide or a nitride, thereby making it difficult to form an alloy with a metal to be cast. In this case, the oxide or nitride on the surface of the mold may be formed by oxidizing or nitriding the mold member after forming the mold pattern.

Conventionally, silica sand which has high heat resistance and is inexpensive has been used as a raw material of the mold, but a metal, a metal compound, silicon or a silicon compound is used as a material constituting the mold of the present invention. In the present invention, since a semiconductor manufacturing process is used, among these,
It is preferable to use a silicon substrate having a surface formed with silicon dioxide, quartz, alumina, or the like. In addition, ordinary metals can naturally be used, and germanium, gallium arsenide, lithium niobate and the like can also be used. It is preferable to adjust the heat resistance and the coefficient of thermal expansion by ion-implanting copper or the like into a substrate such as silicon or doping a gas such as arsenic.

Further, in order to make it easier for the molten casting material to flow into the fine irregularities during casting, fine electrodes which are exposed in pairs along the mold pattern are provided on the mold side. A voltage may be applied between the paired electrodes. By doing so, the casting material at the portion in contact with the electrode generates heat by energization, which hinders rapid cooling when the casting material flows into the fine irregularities, and produces fine fine irregularities. The material for casting comes to flow.

[0013]

Next, embodiments of the present invention will be described with reference to the drawings.

First, a method of manufacturing a mold according to this embodiment will be described with reference to FIGS.

The shape of the mold raw material may be a cubic block or a wafer according to the shape and size of the casting to be manufactured (hereinafter, the raw material up to the mold is referred to as substrate 1). Here, it is assumed that the substrate 1 is a flat plate as shown in FIG. In the present invention, the fine irregularities may extend over the entire substrate 1 or may be partially used in combination with conventional machining. In order to cast a casting material at the time of casting, it is necessary to first cut the entirety by about several millimeters. For this purpose, machining may be used or etching may be used. As a result, a recess 2 is formed in the center of the substrate 1 which is a mold member (FIG. 1B).

Next, after sufficiently cleaning the substrate 1 to remove dirt, a photoresist 3 is applied to the entire surface (FIG. 1).
(c)). Subsequently, the photoresist 3 in the portion to be the casting surface
A mask 4 having a pattern corresponding to the concavo-convex pattern to be formed on the casting is overlaid on the surface of the substrate and exposed (FIG. 1 (d)). Then, the substrate 1 is developed by immersing it in a developing solution (not shown), and unnecessary portions of the photoresist 3 are removed. As a result, the photoresist 3 is removed in accordance with the pattern of the mask 4, that is, the concavo-convex pattern to be formed on the casting.

Next, only the portion of the substrate 1 that is not protected by the photoresist 3 is etched to form an uneven pattern on the substrate 1. As shown in FIG. 1 (e), the etching may be of a wet type immersed in an etchant 5 or a dry type using plasma. In the case of etching using plasma, anisotropic etching can be used, so that a photoresist provided on a side surface of the substrate 1 or the like can be omitted. In any case, a mold pattern composed of irregularities having a depth of about μm is formed on the surface of the substrate 1, and the mold 6 is completed (FIG. 1).
(f)).

By the way, using a mold having fine irregularities
When casting a metal material, the mold and the molten metal material
The alloy forms an alloy with the material, making mold release difficult.
Cover the surface of the mold member with an intermediate layer made of oxide or nitride.
Forming an alloy with the metal to be cast
It becomes difficult to be. In this case, the oxides and nitrides on the mold surface
After the formation of the mold pattern, oxidation treatment of the mold member or
It may be formed by performing a nitriding treatment. Sand
Chi, in the case of using a substrate 1 made of a material susceptible to make a metal alloy such as silicon or germanium, the surface or is oxidized to hardly make alloy or nitrided. These oxidation or nitridation steps are well known in the field of semiconductor manufacturing. Since the alloy forms at the time of casting from the surface to a depth of at most several μm,
The target depth of the oxidation or nitriding treatment may be about several μm.
When the substrate 1 is made of a compound that is originally difficult to form an alloy, such as quartz (silicon dioxide) or silicon nitride, the oxidation or nitridation process may be omitted.

As shown in FIG. 2, in order to make it easier for the casting material to flow into fine irregularities during casting,
A pair of electrodes 7 and 8 may be provided along the concave and convex pattern formed on the casting surface. These electrodes 7, 8
Are formed on the side walls on both sides of the concave portion in the concave-convex pattern, respectively, by vapor deposition or the like. By preventing electrodes from being provided at the bottom of the recess, each of the electrodes 7, 8
When they are not cast, they do not conduct with each other.

Next, a casting method using the mold 6 will be described with reference to FIGS. 3 (a) and 3 (b).

The casting material 10 is poured into the casting mold 6 obtained as described above in a flowing state, and casting is performed (FIG. 3).
(a)). As a material for casting, a metal is generally used, but in addition, a metal compound, plastic, or the like can be used. The conditions for the casting material 10 include a lower melting point than the raw material of the mold 6 and a difficulty in forming an alloy with the mold 6. As such a combination, there are silicon dioxide (melting point 1883 ° C.) as a material used for the mold 6 and gold (melting point 1063 ° C.) as a material 10 for casting. Heating and dissolving is generally used as a method for bringing the fluid into a fluid state.
It may be softened. In the case of a thermosetting plastic, it is poured in a fluid state at a low temperature. In addition, in order to pour the material 10 for casting into every corner of fine unevenness, it is desirable to perform casting in a vacuum.

After the casting material 10 is cast, it is slowly cooled to room temperature. As a result, in the case of metal, the casting 9 is solidified. Also, in the case of thermoplastics, it may be cooled if it is heated and melted,
If dissolved and softened with a solvent, the solvent may be diffused. Conversely, in the case of a thermosetting plastic, it is cast at a low temperature and is cured by heating. In any case, if the rate of change in volume of the casting material 10 (the coefficient of thermal expansion in the case of heating and melting) is significantly different from that of the casting mold 6, the casting 9 can be successfully formed.
Can not be formed as in the prior art. Therefore, it is preferable to inject and adsorb ions or gas on the surface of the mold 6 in advance to match the volume expansion coefficients. Although not detailed,
There are countless combinations for each material of mold, casting, and injection and adsorption.

When the completed casting 9 is taken out of the mold 6, there are methods of separating the casting 6 from the casting 6 with a strong force, destroying the casting mold 6, or removing the casting mold 6 by back etching. The casting 9 is taken out by combining these methods (FIG. 3 (b)). The rough portion is peeled off by force or broken by smashing the mold 6, and the fragments of the mold 6 remaining in the fine irregularities are removed with a substance that selectively reacts only with the material constituting the mold 6. Is preferred.

As shown in FIG. 2, when using the mold 6 provided with the electrodes 7 and 8 along the concavo-convex pattern, a voltage is applied between the electrodes 7 and 8 when the conductive material is cast. Metals are generally used as the conductive material. However, certain plastics also become conductive when melted by heating, and thus such plastics can also be used. When casting metal, no current flows between the electrodes 7 and 8 before the metal is cast, and the metal is insulated. When a metal flows into this gap, a current flows through the metal via the electrodes 7 and 8, and when the metal has a large electric resistance, heat is generated. When the electric resistance of the metal is small, heat is generated at the interface between the electrodes 7, 8 and the metal. In any case, the metal is heated and the metal is prevented from being cooled at the entrance of the concavo-convex pattern, and the metal can be cast deep into the fine concavo-convex pattern.

Next, the results of actual execution of this embodiment will be described.

EXAMPLE 1 A silicon wafer (melting point: 1414 ° C.) having a diameter of 3.5 inches (88.9 mm) and a thickness of 5 mm was prepared, and the surface thereof was cut by a diamond bit to a diameter of 3 inches (78.9 mm).
6.2 mm) and a circular recess having a depth of 3 mm were formed. After treating the surface with hydrofluoric acid, the substrate is heated to 1100 ° C., and the surface is oxidized with water vapor under normal pressure.
up to a thickness of m. A photoresist agent AZ1370 (manufactured by Hoechst) was applied to the entire surface by a spinner. A mask composed of lines and spaces of 10 μm pitch is overlapped and exposed to ultraviolet light, and a developing solution MF
-312 (manufactured by Hoechst). Next, etching was performed to an average depth of 10 μm by plasma to complete a mold.

This mold was placed on a horizontal table so that the processing surface faced upward, and 99.9% pure gold was heated to 1070 ° C. and poured into a molten state. 3mm of recess
, And allowed to stand until the gold was sufficiently cooled. When the silicon wafer was hit with a hammer, the silicon wafer was broken because it was brittle, but the cast gold mass remained. Then, the silicon adhered to the fine irregularities on the surface of the gold was replaced with hydrofluoric acid: nitric acid: acetic acid =
It was removed by etching with a 1: 4: 6 mixture. In addition,
It is well known that gold is insoluble in etchants of this composition. After removing the etchant by washing with water, it was dried at 120 ° C. to obtain a casting.

Example 2 A rectangular parallelepiped quartz substrate having a width of 5 cm, a length of 5 cm and a thickness of 5 mm was coated with RD2000N (manufactured by Hitachi Chemical Co., Ltd.) as a photoresist agent using a spinner. The surface of 5 cm × 5 cm was exposed using a square mask having a side of 3 cm, and developed with a dedicated developer. Using a mixed solution of hydrofluoric acid and a 40% aqueous ammonium fluoride solution, the quartz substrate was etched to a depth of 2 mm to form a concave portion. The above-mentioned photoresist agent was applied again, the mask used in Example 1 was overlapped and exposed, then developed, and etched to a depth of 10 μm to form irregularities to obtain a mold. Another mold was made in the same manner.

Next, the two molds are pressed from both sides with a vice so that the working surfaces face each other, and molten silver (melting point: 962 ° C.) is poured from a previously opened gate.
It was left to cool. After cooling, the mold was removed from the vise and the casting was removed by opening the two molds to the left and right. The quartz residue adhering to the surface was etched with a mixed solution of hydrofluoric acid and a 40% ammonium fluoride aqueous solution to obtain a silver casting (a silver coin having fine irregularities on both surfaces).

Example 3 Using alumina (melting point 2015 ° C.) as a mold material, silicon dioxide was deposited on the entire surface of the alumina substrate by CVD.
It was deposited to a thickness of 100 nm by a method, and a photoresist was applied thereon. Then, on this photoresist, 1
A mask having a lattice pattern consisting of squares with sides of 10 μm is superposed and exposed, developed, and then etched,
A checkered pattern was formed on the surface of the silicon dioxide. Next, chromium is vapor-deposited on the entire surface of the silicon dioxide on which the checkered pattern has been formed, and a photoresist is applied again. An electrode made of chromium was formed. The electrodes are provided along each side of the grid pattern, and a voltage can be applied between the electrodes provided on two opposite sides of the grid pattern.

Next, while applying a voltage of 100 V between the facing electrodes, titanium (melting point 1675 ° C.) was melted and poured. Generally, a high melting point metal such as titanium solidifies as soon as it enters between fine irregularities, but in this embodiment, since a voltage is applied between the electrodes, fine irregularities formed of lattice fringes are formed. As soon as the molten titanium enters, an electric current flows through the electrode via the electrode, and the part of the titanium in contact with the irregularities generates heat, and the titanium penetrates deep into the fine irregularities. It was confirmed that.

Example 4 A hard polyvinyl chloride resin (containing a stabilizer) was poured into the mold prepared in Example 2 at 160 ° C. under a pressure of 140 kg / cm ² , and after cooling, was taken out. The mold and the plastic were easily separated from each other due to the difference in the rate of volume change from the mold.

Example 5 A solution prepared by dissolving a polystyrene resin in ethyl acetate was poured into the mold prepared in Example 1, and the ethyl acetate was slowly evaporated at 50 ° C. to obtain a casting.

Example 6 Using the mold prepared in Example 3, while applying a voltage between the electrodes, the hard vinyl chloride of Example 4 was poured at 160 ° C. under atmospheric pressure. Entered. Compared to the metal of Example 3, plastic has higher electric resistance, and it is considered that the plastic itself between the irregularities generates heat.

[0035]

As described above, in the mold of the present invention, fine irregularities can be provided on the surface by providing a mold pattern on the mold member by a semiconductor manufacturing process. In this case, a fine uneven pattern can be provided on the surface of the casting, which is effective in preventing forgery in the case of gold coins or the like.
In addition, when an intermediate layer that does not react with the material for the mold is provided on the surface of the mold member, the formation of an alloy between the mold and the material for the mold is suppressed, and the mold releasability is improved. There is. Further, when fine electrodes exposed in pairs along the mold pattern are provided, a voltage is applied between the electrodes during casting, so that the conductive casting material conducts and generates heat. This has the effect that rapid cooling of the casting material is prevented, and the casting material flows deep into the irregularities.

[Brief description of the drawings]

FIGS. 1A to 1F are diagrams illustrating a method for manufacturing a mold according to one embodiment of the present invention.

FIG. 2 is a schematic sectional view showing the configuration of a mold according to another embodiment of the present invention.

FIGS. 3A and 3B are diagrams illustrating a casting method according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Depression 3 Photoresist 4 Mask 5 Etching liquid 6 Mold 7,8 Electrode 9 Casting 10 Casting material

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Claims (6)

(57) [Claims] 1. A mold member made of a metal, a metal compound, silicon or a silicon compound, and a photoresist applied to a surface of the mold member, the photoresist is exposed to a predetermined pattern and developed, and then the photo resist is developed. A mold pattern formed by etching the mold member using a resist as an etching mask. 2. The mold according to claim 1, wherein the surface of the mold member is covered with an intermediate layer made of a material that does not react with a casting material, and the intermediate layer is a compound of an element constituting the mold member. 3. The mold according to claim 2, wherein the intermediate layer is formed by oxidizing or nitriding the surface of the mold member after forming the mold pattern. 4. The mold according to claim 1, wherein fine electrodes exposed in pairs are provided along the mold pattern. 5. A casting material having a lower melting point than a mold member is poured into the casting mold by using the casting mold according to claim 1, and then the casting material is solidified. Casting method. 6. A molten casting material having conductivity and a melting point lower than that of a mold member is applied to the mold while applying a voltage between a pair of electrodes using the mold according to claim 4. A casting method in which the casting material is poured and then cooled and solidified.