Metal film deposition method

Abstract

To provide a film deposition method of a metallic film, which can stably deposit the film with a prescribed pattern.SOLUTION: In a film deposition method of a metallic film, a mask 30 is arranged on a substrate B through an ultraviolet-curable adhesive K whose adhesiveness decreases with hardening by an ultraviolet ray S irradiated, using a mask made of a material that allows the ultraviolet ray S to pass through as the mask 30, in a process in which the mask 30 having a prescribed pattern of throughholes 35 formed is arranged on the substrate B. After the mask is deposited on the substrate B with the prescribed pattern, the ultraviolet-curable adhesive K is cured by radiating the ultraviolet ray S toward the mask 30, and the mask 30 is peeled with the ultraviolet-curable adhesive K from the substrate B.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a method for forming a metal film.

[0002] Conventionally, metal has been partially deposited on the surface of a substrate to form a metal coating having a predetermined pattern. For example, Patent Document 1 discloses the following film formation method. In this film formation method, a mask having through-holes formed in a predetermined pattern is first placed on the substrate. Next, the liquid pressure of the electrolyte solution is applied to the electrolyte membrane, and the electrolyte membrane presses the mask and the substrate. In this state, a voltage is applied between the anode and the substrate, causing metal ions contained in the electrolyte solution to pass through the electrolyte membrane, forming a metal coating on the substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-108586 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the liquid pressure of the electrolyte solution is increased during the above-described film formation method, liquid derived from the electrolyte solution seeps out from the electrolyte membrane toward the substrate. When the through-holes of the mask are filled with the liquid, the liquid pressure of the liquid in the mask approaches the liquid pressure of the electrolyte solution pressing against the electrolyte membrane. This may cause the electrolyte solution to get between the mask and the substrate, making it impossible to stably form a metal coating with the desired pattern.

[0005] The present invention has been made in view of the above points, and an object of the present invention is to provide a method for forming a metal film that can stably form a metal film having a predetermined pattern. [Means for solving the problem]

[0006] In view of the above-mentioned problems, the present invention provides a method for forming a metal film, the method including: a placement step of placing a mask having through-holes formed in a predetermined pattern on a substrate; a pressing step of bringing an electrolyte membrane into contact with the mask and then pressing the electrolyte membrane toward the substrate via the mask using hydraulic pressure of an electrolyte solution in contact with the electrolyte membrane; and a film-forming step of applying a voltage between the substrate and an anode in contact with the electrolyte solution to cause metal ions contained in the electrolyte solution to pass through the electrolyte membrane and form a metal film derived from the metal ions on the substrate in the predetermined pattern. The method is characterized in that in the placement step, the mask is made of a material that transmits ultraviolet light, and the mask is placed on the substrate via an ultraviolet-curable adhesive that hardens when irradiated with ultraviolet light and loses its adhesiveness; and after the film-forming step, ultraviolet light is irradiated toward the mask to harden the ultraviolet-curable adhesive, and the mask together with the ultraviolet-curable adhesive are peeled off from the substrate. [Effects of the Invention]

[0007] According to the present invention, when the mask is placed on the substrate, the mask is placed on the substrate via an ultraviolet-curable adhesive, so that the metal film can be formed on the substrate with the mask in a state of high adhesion. As a result, the electrolyte is prevented from entering between the mask and the substrate, and a metal film having a desired pattern can be stably formed.

[0008] Furthermore, after the metal film is formed, the mask is irradiated with ultraviolet light, which hardens the ultraviolet-curable adhesive and reduces its adhesiveness to the substrate, allowing the mask and the ultraviolet-curable adhesive to be easily peeled off from the substrate. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a flowchart illustrating an example of a method for forming a metal film according to an embodiment of the present invention. [Figure 2] 2 is a schematic cross-sectional view of a substrate and a mask for explaining the arrangement step shown in FIG. 1. FIG. [Figure 3] 1 is a schematic cross-sectional view showing an example of a film forming apparatus used in a method for forming a metal film according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram for explaining the pressing step shown in FIG. [Figure 5] 2A to 2C are schematic cross-sectional views for explaining the film forming process shown in FIG. [Figure 6] FIG. 10 is a cross-sectional view of the substrate taken out of the film forming apparatus after film formation. [Figure 7] FIG. 2 is a schematic cross-sectional view for explaining the peeling step shown in FIG. [Figure 8] FIG. 2 is a schematic cross-sectional view of the substrate after the peeling step shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] A method for forming a metal film according to an embodiment of the present invention will be described below. 1, the metal coating M is formed on the substrate B by performing the steps from the disposing step S1 to the peeling step S4. Each step will be explained below, along with the film forming apparatus used in the film formation.

[0011] 1. Placement process S1 In the placement step S1, a mask 30 having through-holes 35 formed in a predetermined pattern is placed on a substrate B, and then the substrate B is placed on a base 40 together with the mask 30. Alternatively, the substrate B may be placed on the base 40, and then the mask 30 may be placed on the substrate B. Details will be described below.

[0012] First, in this step, a substrate B is prepared for forming a metal film. The substrate B functions as a cathode in the film formation described below. The material of the substrate B is not particularly limited as long as it functions as a cathode (i.e., a surface having electrical conductivity). The substrate B may be made of a non-magnetic metal material such as aluminum or copper, or may have a surface of resin or the like coated with a metal layer such as copper.

[0013] Next, a mask 30 is prepared. The mask 30 has through-holes 35 formed in a predetermined pattern for forming a membrane. The mask 30 is placed on the surface of the substrate B and is disposed between the electrolyte membrane 13 (described later) and the substrate B, so it is preferable that the mask 30 be flexible.

[0014] The mask 30 is made of a material that transmits ultraviolet light and is preferably made of an insulating material. For example, resins such as polyimide, polyethylene terephthalate, and polyethylene naphthalate can be used, and the material is not particularly limited as long as it is flexible when used as the mask 30 and can transmit ultraviolet light.

[0015] In this placement step S1, the mask 30 is placed on the substrate B via an ultraviolet-curable adhesive K (FIG. 2). Here, the ultraviolet-curable adhesive K is an adhesive that hardens and loses its adhesiveness when irradiated with ultraviolet light S, which will be described later. The ultraviolet-curable adhesive K contains components such as monomers, oligomers, a photopolymerization initiator (curing initiator), and additives. When ultraviolet light is irradiated onto the ultraviolet-curable adhesive, the curing initiator absorbs the ultraviolet light, and the resulting energy is used to start a polymerization reaction. Through polymerization, small molecular weight monomers and oligomers bond together to form a polymer, which then hardens.

[0016] Specifically, the ultraviolet-curable adhesive K may be a known adhesive in which a polyfunctional monomer is blended with an adhesive polymer and a curing initiator is added. In this case, when ultraviolet light is irradiated, a polymerization reaction occurs between the polyfunctional monomer (main chain) and the adhesive polymer, causing the ultraviolet-curable adhesive K to cure. Therefore, when adjusting the degree of curing, the crosslinking rate (degree of crosslinking) is adjusted by adjusting the type and amount of polyfunctional monomer added. Note that the curing initiator reacts with the adhesive polymer, eliminating hydrogen groups from the linear chain of the adhesive polymer and generating radicals, and the adhesive polymer polymerizes to these radicals under ultraviolet light, accelerating the above-mentioned crosslinking.

[0017] The curing initiator is not particularly limited as long as it can crosslink through a polymerization reaction. Examples of the curing initiator include 2-methylbenzophenone, 2-ethylanthraquinone, benzoin isopropyl ether, benzil, 4,4'-dimethylbenzil, and 4,4'-bis(diethylamino)benzophenone.

[0018] Alternatively, a UV-curable adhesive may be made using a polyfunctional acrylic monomer or a polyfunctional epoxy monomer as the main component, which is polymerized by UV-S irradiation. For example, in the case of a trifunctional acrylic monomer (TMPTA), the adhesive strength after UV-S irradiation is generally about half of the adhesive strength before UV-S irradiation. In the case of a hexafunctional acrylic monomer (DPTA), the adhesive strength after UV-S irradiation is about one-tenth of the adhesive strength before UV-S irradiation.

[0019] The film formation apparatus 1 for performing the pressing step S2 and film formation step S3 described below will be described below. As shown in Fig. 3, the film formation apparatus 1 is an apparatus that applies a voltage between the anode 11 and the substrate B using a power supply unit 14 while the electrolyte membrane 13 is in contact with the substrate B, thereby reducing metal ions contained inside the electrolyte membrane 13, thereby forming a metal coating on the surface of the substrate B.

[0020] In this embodiment, for convenience of explanation, the positional relationship of the components of the film formation apparatus 1 is specified on the assumption that the electrolyte membrane 13 is placed below the anode 11, and the mask 30 and substrate B are placed further below that. However, as long as a metal coating can be formed on the surface of the substrate B, the positional relationship is not limited to this, and for example, the film formation apparatus 1 in FIG. 3 may be upside down. For example, when the film formation apparatus 1 in FIG. 3 is upside down, the mask 30 may be fixed to the clamper 17.

[0021] 3, the film formation apparatus 1 includes an anode 11, an electrolyte membrane 13, a power supply unit 14 that applies a voltage between the anode 11 and a substrate B, and a container 15 that contains the anode 11 and an electrolytic solution L containing metal ions. A clamper 17 is attached to the container 15, and the clamper 17 fixes the electrolyte membrane 13 by clamping the electrolyte membrane 13, with the opening 15d covered, between the container 15. In this embodiment, a mask 30 is placed on the substrate B, and the electrolyte membrane 13 is disposed between the mask 30 and the anode 11. The film formation apparatus 1 further includes a base 40 on which the substrate B is placed, and a linear actuator 70.

[0022] The base 40 is formed of, for example, a conductive material (e.g., metal), but in this embodiment, it is made of a non-magnetic material such as aluminum, stainless steel, etc. In this case, the negative electrode of the power supply unit 14 is electrically connected to the base 40, and thus the substrate B is electrically connected to the negative electrode of the power supply unit 14 via the base 40.

[0023] The anode 11 is, for example, a non-porous (e.g., non-porous) anode made of the same metal as the metal coating, and is a block-shaped or flat anode. Examples of materials for the anode 11 include copper. The anode 11 may be dissolved by applying a voltage using a power supply 14, but if the film is formed using only the electrolyte L, the anode 11 does not need to be dissolved. The anode 11 is attached to a container 15 made of, for example, an insulating material. The anode 11 is electrically connected to the positive electrode of the power supply 14.

[0024] The electrolytic solution L is a solution containing the metal of the metal coating to be formed in an ionic state, and examples of such metals include copper, nickel, gold, silver, and iron. The electrolytic solution L is a solution in which these metals are dissolved (ionized) with an acid such as nitric acid, phosphoric acid, succinic acid, sulfuric acid, or pyrophosphoric acid. Examples of the solvent for the solution include water and alcohol. For example, when the metal is copper, the electrolytic solution L can be an aqueous solution containing copper sulfate, copper pyrophosphate, or the like.

[0025] The electrolyte membrane 13 is a flexible membrane that can be impregnated (contain) metal ions inside by contacting it with the electrolytic solution L. The electrolyte membrane 13 is not particularly limited as long as it can reduce metal ions on the surface of the substrate B and deposit metal derived from the metal ions when a voltage is applied from the power supply unit 14. Examples of materials for the electrolyte membrane 13 include resins with ion exchange properties, such as fluororesins such as Nafion (registered trademark) manufactured by DuPont.

[0026] As shown in FIG. 3, the anode 11 and the electrolyte membrane 13 are attached to the container 15, and the container 15, the anode 11, and the electrolyte membrane 13 form a container space 15c that contains the electrolytic solution L. The container 15 has an opening 15d that opens to the side of the substrate B, and the electrolyte membrane 13 is attached to the container 15 so as to cover the opening 15d. As shown in FIG. 3, the container 15 is structured so that the electrolytic solution L contained in the container space 15c comes into direct contact with the anode 11 and the electrolyte membrane 13. The container 15 is made of a material that is insoluble in the electrolytic solution L.

[0027] As shown in FIG. 3 , the linear actuator 70 raises and lowers at least one of the housing 15 and the base 40 so that the electrolyte membrane 13 and the mask 30 can be moved toward and away from each other. In this embodiment, the base 40 is fixed, and the housing 15 is raised and lowered by the linear actuator 70. The linear actuator 70 is provided on the upper part of the housing 15. The linear actuator 70 is, for example, an electric actuator that converts the rotational motion of a motor into linear motion using a ball screw or the like (not shown). The linear actuator 70 raises and lowers the housing 15 relative to the base 40, thereby making it possible to move the electrolyte membrane 13 toward and away from the mask 30, which will be described later. Note that the device for raising and lowering the housing 15 may be a hydraulic or pneumatic cylinder or the like.

[0028] The container 15 is formed with a supply flow path 15a that supplies the electrolytic solution L to the storage space 15c and a discharge flow path 15b that discharges the electrolytic solution L from the storage space 15c. The supply flow path 15a and the discharge flow path 15b are holes that communicate with the storage space 15c and are formed on either side of the storage space 15c. The supply flow path 15a is fluidly connected to a liquid supply pipe 50 (described later), and the discharge flow path 15b is fluidly connected to a liquid discharge pipe 52 (described later).

[0029] The film forming apparatus 1 includes a tank 85 and a pump 80. As shown in Fig. 3, the tank 85 contains an electrolytic solution L. The tank 85 and the container 15 are connected to a liquid supply pipe 50 that supplies the electrolytic solution L to the container 15 and a liquid discharge pipe 52 that discharges the electrolytic solution L from the container 15.

[0030] A pump 80 is provided in the liquid supply pipe 50 to supply the electrolytic solution L from the tank 85 to the housing body 15. A pressure adjustment valve 54 is provided in the liquid discharge pipe 52. This prevents the pressure (liquid pressure) of the electrolytic solution L contained in the housing space 15c from exceeding a predetermined pressure.

[0031] By driving the pump 80, the electrolytic solution L is sucked from the tank 85 into the liquid supply pipe 50, and the electrolytic solution L is then pumped from the supply flow path 15a to the storage space 15c. The electrolytic solution L used in the storage space 15c during film formation is returned to the tank 85 via the discharge flow path 15b. At this time, by continuing to rotate the pump 80, the liquid pressure of the electrolytic solution L in the storage space 15c can be maintained at a predetermined pressure.

[0032] 2. Pressing process S2 In the pressing step S2, the electrolyte membrane 13 is brought into contact with the mask 30, and then the electrolyte membrane 13 is pressed against the substrate B via the mask by the liquid pressure of the electrolytic solution L in contact with the electrolyte membrane 13.

[0033] First, in this step, the linear actuator 70 lowers the container 15 relative to the base 40. As a result, the electrolyte membrane 13 covering the opening 15d of the container 15 that contains the electrolytic solution L comes into contact with the mask 30. When the stroke of the linear actuator 70 reaches a predetermined value, the lowering of the container 15 stops.

[0034] Next, the pump 80 is driven to accommodate the electrolyte L in the accommodation space 15c of the accommodation body 15. The electrolyte L sucked from the tank 85 by the pump 80 is supplied to the accommodation body 15 via the liquid supply pipe 50. Since the liquid discharge pipe 52 is provided with the pressure adjustment valve 54, the liquid pressure of the electrolyte L in the accommodation space 15c is maintained at a predetermined pressure by continuing to rotate the pump 80.

[0035] In this manner, when the liquid pressure of the electrolyte solution L contained in the container 15 is increased while the electrolyte membrane 13 is in contact with the mask 30, the liquid pressure acts on the electrolyte membrane 13. This liquid pressure causes the electrolyte membrane 13 to conform to the shape of the mask 30, and presses the electrolyte membrane 13 against the substrate B via the through-holes 35 with a pressing force F, as shown in FIG.

[0036] Here, if the liquid pressure of the electrolyte solution L is increased, a liquid derived from the electrolyte solution L will seep out through the electrolyte membrane 13 toward the substrate B. However, in this embodiment, the mask 30 is adhered to the substrate B via an uncured (before UV irradiation) ultraviolet-curable adhesive K. Therefore, even if the liquid pressure of the electrolyte solution L contained in the container 15 is increased, the mask 30 can continue to be in close contact with the substrate B. As a result, it is possible to prevent the electrolyte solution L from seeping in between the mask 30 and the substrate B.

[0037] 3. About the film formation process S3 In the film formation step S3, as shown in FIG. 5, a voltage is applied between the anode 11 in contact with the electrolytic solution L and the substrate B, causing the metal ions contained in the electrolytic solution L to pass through the electrolyte membrane 13, and a metal coating M derived from the metal ions is formed on the substrate B in a predetermined pattern.

[0038] In this embodiment, as the liquid pressure of the electrolytic solution L increases, the electrolyte membrane 13 presses the substrate B together with the mask 30, and a voltage is applied between the anode 11 and the substrate B to form a metal coating M. As a result, the metal ions contained in the electrolyte membrane 13 migrate to the surface of the substrate B in contact with the electrolyte membrane 13 and are reduced on this surface. As a result, metal is deposited on the surface of the substrate B, and a metal coating M is formed on the surface of the substrate B according to the pattern of the mask 30.

[0039] In this embodiment, in addition to the pressing force F due to the liquid pressure of the electrolyte solution L, the mask 30 is placed on the substrate B via an uncured ultraviolet-curable adhesive K (i.e., a viscous adhesive), which improves the adhesion of the mask 30 during film formation. As a result, metal ions that have migrated to the substrate side through the electrolyte membrane 13 are prevented from entering between the mask 30 and the substrate B together with the liquid that has seeped out of the electrolyte membrane 13, and a metal coating M having a desired pattern can be stably formed.

[0040] After a predetermined time has elapsed since the voltage application, the power supply unit 14 stops applying the voltage. This makes it possible to determine that the metal coating M on the surface of the substrate B has been formed to a predetermined thickness.

[0041] Next, the pump 80 is stopped, and the pressure applied to the substrate B by the hydraulic pressure is released. Furthermore, the linear actuator 70 raises the housing 15 relative to the base 40, separating the electrolyte membrane 13 from the substrate B. When the stroke of the linear actuator 70 reaches a predetermined value, the raising of the housing 15 stops. The substrate B is removed from the base 40 (see FIG. 6).

[0042] 4. Peeling process S4 In the peeling step S4, after the film forming step S3, ultraviolet rays S are irradiated onto the mask 30 to harden the ultraviolet curable adhesive K, and the mask 30 is peeled off from the base material B together with the ultraviolet curable adhesive K.

[0043] Specifically, as shown in Fig. 7, when ultraviolet rays S are irradiated onto the mask 30, the ultraviolet rays S pass through the mask 30 and reach the ultraviolet-curable adhesive K. As a result, the ultraviolet-curable adhesive K is cured by the ultraviolet rays S, and the adhesive strength between the ultraviolet-curable adhesive K and the substrate B decreases. As a result, as shown in Fig. 8, the mask 30 can be easily peeled off from the substrate B together with the ultraviolet-curable adhesive K. In this way, a series of steps in the film formation method using the film formation apparatus 1 is completed.

[0044] In this manner, in this embodiment, the liquid pressure of the electrolyte solution L is applied to the mask 30 via the electrolyte membrane 13 toward the substrate B, thereby pressing the mask 30 against the substrate B via the viscous ultraviolet-curable adhesive K. This makes it possible to prevent the liquid that seeps out from the electrolyte membrane 13 with the migration of metal ions from entering the through-holes 35 and penetrating between the mask 30 and the substrate B, even if the liquid pressure of the electrolyte solution L is increased and a film is formed in the film-forming process. [Example]

[0045] The invention is illustrated by the following examples.

[0046] [Example] A glass epoxy substrate (ABF substrate manufactured by Ajinomoto Co., Ltd.) made by impregnating a layer of glass fiber cloth with epoxy resin was prepared as a substrate for film formation. Copper foil was formed on the surface of this glass epoxy substrate. Next, a copper film was formed using a film formation device used in the metal film formation method according to the embodiment shown in FIG. 3. A copper sulfate aqueous solution (Cu-BRITE-SED) manufactured by JCU Corporation was used as the electrolyte, and a Cu plate was used as the anode. The film formation conditions were as follows: with a mask attached to the substrate via a UV-curable adhesive, the temperature of the electrolyte was 42°C, the liquid pressure of the electrolyte was 0.6 MPa, and the current density was 7 A / dm 2 , film forming area 25cm 2A 10 μm copper film was formed with a cumulative film formation time of 388 seconds. A UV-transmitting polyimide film was used as the mask, and an adhesive with a polyfunctional acrylic monomer as the main component was used as the uncured UV-curable adhesive. After film formation, the UV-curable adhesive was cured by irradiating the mask with UV light, and then the mask and the UV-curable adhesive were removed from the substrate.

[0047] [Comparative Example] A copper film was formed in the same manner as in Example 1. The difference from Example 1 was that no adhesive was used and a mask made of silicone rubber was used.

[0048] <Checking the film formation status> To confirm whether a metal coating of the desired pattern was formed on the substrate formed as described above, the surface of the substrate was observed using an electron microscope. In the examples, the metal coating showed a sharp outline that matched the outline of the through-holes in the mask (no bleeding). In contrast, in the comparative examples, when a metal coating of the desired pattern was not formed, the metal coating did not match the outline of the through-holes in the mask (bleeding). In the comparative examples, it is believed that because no external force was applied to the mask, exuded liquid from the electrolyte membrane flowed between the mask and the substrate, making it impossible to form a metal coating of the desired pattern.

[0049] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various design modifications can be made without departing from the spirit of the present invention as set forth in the claims. [Explanation of symbols]

[0050] 11: anode, 13: electrolyte membrane, 15: container, 15d: opening, 30: mask, 35: through-hole, B: substrate, K: ultraviolet curing adhesive, L: electrolyte, S: ultraviolet light

Claims

[Claim 1] a placement step of placing a mask having through-holes of a predetermined pattern formed therein on a substrate; a pressing step of contacting the electrolyte membrane with the mask and then pressing the electrolyte membrane against the substrate through the mask by hydraulic pressure of the electrolytic solution in contact with the electrolyte membrane; a film formation step of applying a voltage between an anode in contact with the electrolytic solution and the substrate, thereby causing metal ions contained in the electrolytic solution to pass through the electrolyte membrane, and forming a metal film derived from the metal ions on the substrate in the predetermined pattern, In the placing step, a mask made of a material that transmits ultraviolet light is used as the mask, and the mask is placed on the base material via an ultraviolet-curing adhesive that hardens and loses adhesiveness when irradiated with ultraviolet light; A method for forming a metal film, characterized in that after the film formation process, ultraviolet light is irradiated onto the mask to harden the ultraviolet-curable adhesive, and the mask is peeled off from the substrate together with the ultraviolet-curable adhesive.

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