Patent Application
20240344224
This application claims priority to Japanese Patent Application No. 2023-067220 filed on Apr. 17, 2023, incorporated herein by reference in its entirety.
The present disclosure relates to a film forming apparatus that forms a metal film on the surface of a base material.
Japanese Unexamined Patent Application Publication No. 2020-152987 (JP 2020-152987 A) proposes, as this type of technology, a film forming apparatus that includes a positive electrode, a container that houses the positive electrode and a plating solution in contact with the positive electrode, an electrolyte film that seals the plating solution in the container, and a power source that applies a voltage between the positive electrode and a base material, for example. The positive electrode is insoluble in the plating solution. When forming a metal film, by applying a voltage between the positive electrode and the base material with the base material in contact with the electrolyte film, metal ions contained in the plating solution are caused to pass through the electrolyte film to be precipitated on the surface of the base material. Consequently, a metal film is formed on the surface of the base material.
When an insoluble positive electrode is used as described in JP 2020-152987 A, however, an oxygen gas is generated on the surface of the positive electrode because of the electrolysis of water contained in the plating solution. As the generation of an oxygen gas continues, bubbles of the oxygen gas adhere to the surface of the positive electrode, and the adhered bubbles obstruct the flow of electricity from the positive electrode toward the base material. It is assumed that, as a result, a metal film with a uniform film thickness cannot be stably formed.
The present disclosure has been made in view of such an issue, and therefore has an object to provide a film forming apparatus for a metal film capable of stably forming a metal film with a uniform film thickness.
In view of the above issue, an aspect of the present disclosure provides a film forming apparatus that forms a metal film on a surface of a base material. The film forming apparatus includes: a container that contains a plating solution; an electrolyte film that covers an opening of the container formed at a position facing the base material; a positive electrode disposed above the electrolyte film in the container and being insoluble in the plating solution; and a power source that applies a voltage between the positive electrode and the base material. A plurality of curved surfaces convexly curved toward the electrolyte film is arranged on a facing surface that faces the electrolyte film, of a surface of the positive electrode. A through hole that penetrates the positive electrode is formed between the curved surfaces.
In the film forming apparatus according to the aspect of the present disclosure, a voltage is applied by the power source between the positive electrode and the base material with the electrolyte film in contact with the surface of the base material. Consequently, metal ions contained in the plating solution contained in the container pass through the electrolyte film, and are reduced on the surface of the base material to be precipitated as metal. As a result, a metal film is formed on the surface of the base material.
On the other hand, the positive electrode is insoluble in the plating solution, and therefore a solvent of the plating solution is electrolyzed to generate a gas. The generated gas grows into bubbles while adhering to the surface of the positive electrode. A plurality of curved surfaces convexly curved toward the electrolyte film is arranged on the facing surface that faces the electrolyte film, of the surface of the positive electrode. Thus, bubbles adhering to the curved surfaces move from the top of the curved surfaces toward (a side surface of) the bottom of the curved surfaces because of the buoyancy in the plating solution. The moved bubbles pass through the through hole formed between the curved surfaces. As a result, it is possible to suppress the adhering bubbles obstructing the flow of electricity from the positive electrode toward the base material, and to stably form a metal film with a uniform film thickness.
The convexly curved surfaces formed on the positive electrode are not specifically limited in shape and may be round curved surfaces as long as the bubbles generated during film formation can be moved along the curved surfaces. In a more preferable aspect, the curved surfaces may each be a part of a spherical surface. During film formation, electrolysis tends to concentrate on the top of the curved surfaces of the positive electrode, and bubbles are likely to be generated there. As the bubbles generated on the top surfaces of the curved surfaces grow, the bubbles become more likely to move toward (a side surface of) the bottom of the curved surfaces along the curved surfaces because of the buoyancy in the plating solution. As the slope of the spherical curved surfaces increases as the bubbles move toward the bottom of the curved surfaces, the bubbles that have moved from the top become more likely to move to the through hole.
In a more preferable aspect, top regions of the curved surfaces may each be a surface that has been subjected to a water-repellent treatment. During film formation, electrolysis tends to concentrate on the top of the curved surfaces of the positive electrode, and bubbles are likely to be generated there. In this aspect, however, the top regions of the curved surfaces are each a water-repellent surface. Therefore, it is difficult for fine bubbles to uniformly adhere to the top regions, and the generated bubbles are likely to aggregate and grow there. As a result, the grown bubbles are more likely to move toward (a side surface of) the bottom of the curved surfaces because of the buoyancy in the plating solution from the state of adhering to the top regions (surfaces) of the curved surfaces. As a result, the bubbles that have moved from the top are more likely to move to the through hole.
In a more preferable aspect, the film forming apparatus may further include a vibration device that vibrates the positive electrode. According to this aspect, the bubbles adhering to the positive electrode are more likely to be moved along the surface of the positive electrode by vibrating the positive electrode.
In a more preferable aspect, the vibration device may vibrate the positive electrode along a horizontal direction, and vibrate the positive electrode with an amplitude greater than or equal to a hole width of the through hole along the horizontal direction in which the positive electrode is vibrated.
In this aspect, the positive electrode is vibrated with an amplitude greater than or equal to the hole width of the through hole. Therefore, the position of the through hole can be moved to another different position with respect to the surface of the base material. Consequently, a metal film with a more uniform film thickness can be formed on the surface of the base material.
According to the present disclosure, it is possible to stably form a metal film with a uniform film thickness.
Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein:
First, a metal film forming apparatus 1 according to an embodiment of the present disclosure will be described.
As shown in
The film forming apparatus 1 further includes a mounting table 40 on which the base material B is placed, a container 15 that stores the plating solution L, and a pair of linear actuators 70 that move the container 15 up and down. The linear actuator 70 has a rod 72 that moves linearly with respect to the main body 71, and the container 15 is fixed to the tip of the rod 72. In this embodiment, the positive electrode 11 is arranged above the electrolyte film 13, and the mounting table 40 (i.e., the base material B) is arranged below the electrolyte film 13.
The base material B functions as a cathode. The base material B is a base material in a plate shape. In the present embodiment, the base material B is a base material in a rectangular shape. Among the surfaces of the base material B, the opposing surface facing the electrolyte film 13 is a film-forming surface that functions as a cathode. The material of the base material B is not particularly limited as long as it functions as a cathode (that is, a conductive surface). The base material B may be made of a metal material, such as aluminum and copper, for example. When a wiring pattern is formed from the metal film F, as for the base material B, a base material is used in which an underlying layer such as copper is formed on the surface of an insulating base material such as resin. In this case, after forming the metal film F, the underlying layer other than the portion where the metal film F is formed is removed by etching and the like. As a result, a wiring pattern of the metal film F can be formed on the surface of the insulating base material.
The plating solution L is a solution containing the metal of the metal film to be formed in the state of the ions. Examples of such metals include copper, nickel, gold, and silver. The plating solution L is a solution obtained by dissolving (ionizing) these metals with an acid such as nitric acid, phosphoric acid, succinic acid, sulfuric acid, sulfamic acid, or pyrophosphoric acid. Water is used as the solvent for the solution, but the solvent may be alcohol and the like as long as the metal can be contained in the state of the ions. For example, when the metal is copper, the plating solution L may be an aqueous solution containing copper sulfate, copper pyrophosphate, and the like.
The electrolyte film 13 is a membrane that can impregnate (contain) the metal ions internally together with the plating solution L by bringing the electrolyte film 13 into contact with the plating solution L. The electrolyte film 13 is a flexible membrane. The material of the electrolyte film 13 is not particularly limited as long as the metal ions of the plating solution L can move toward the base material B side when the voltage is applied by the power source 14. Examples of materials for the electrolyte film 13 include resin including an ions exchange function, such as fluorine-based resin such as Nafion (registered trademark) manufactured by DuPont. The film thickness of the electrolyte film 13 is preferably in the range of 5 μm to 200 m. More preferably, the film thickness is in the range of 20 μm to 60 μm.
The container 15 is made of a material that is insoluble with respect to the plating solution L. An accommodation space 15a for containing the plating solution L is formed in the container 15. The positive electrode 11 in a flat plate shape is disposed in the accommodation space 15a of the container 15. An opening section 15d is formed on the base material B side (lower side) of the accommodation space 15a. The electrolyte film 13 is attached to the lower part of the container 15 by sandwiching the periphery of the electrolyte film 13 between the frame 17 and the container 15. As a result, the opening section 15d of the container 15 can be covered with the electrolyte film 13, and the plating solution L contained in the accommodation space 15a of the container 15 can be sealed with the electrolyte film 13.
The linear actuator 70 raises and lowers the container 15 by vertically moving the rod 72 with respect to the main body 71 so that the electrolyte film 13 and the base material B can freely come into contact with each other. In this embodiment, the mounting table 40 is fixed and the container 15 moves up and down, but the container 15 may be fixed and the mounting table 40 can be moved up and down. The linear actuator 70 is an electric actuator, and converts rotary motion of the motor into linear motion using a ball screw and the like (not shown). However, a hydraulic actuator or a pneumatic actuator may be used instead of the electric actuator.
The mounting table 40 may include an electrically conductive material, and may be formed with an accommodation recess for accommodating the base material B. The mounting table 40 and the base material B are electrically connected, and the negative electrode of the power source 14 is connected to the mounting table 40.
The container 15 has a supply port 15b for supplying the plating solution L to the accommodation space 15a. The container 15 has a discharge port 15c for discharging the plating solution L from the accommodation space 15a. The supply port 15b and the discharge port 15c are holes communicating with the accommodation space 15a. The supply port 15b and the discharge port 15c are formed to sandwich the positive electrode 11 in the accommodation space 15a. The supply port 15b is connected to the supply path 51. The discharge port 15c is connected to the discharge path 52.
In this embodiment, the supply port 15b is formed at a position where the plating solution L flows onto the opposing surface 11f of the positive electrode 11, and the discharge port 15c is formed at a position higher than the positive electrode 11. As a result, as will be described later, the bubbles generated on the opposing surface 11f of the positive electrode 11 are caused to flow by the plating solution L and head toward the through hole 11b of the positive electrode 11, which will be described later. The bubbles that have reached the through hole 11b can pass through the through hole 11b due to the buoyancy of the plating solution L, and can flow from the upper surface (back surface) side of the positive electrode 11 to the discharge port 15c.
The film forming apparatus 1 further includes a tank 90, a pump 80, and a pressure regulating valve 54. As shown in
In this embodiment, the plating solution L is sucked into the supply path 51 from the tank 90 by driving the pump 80. The sucked plating solution L is pressure-fed from the supply port 15b to the accommodation space 15a. The plating solution L in the accommodation space 15a is returned to the tank 90 through the discharge port 15c. In this way, the plating solution L contained in the container 15 can be circulated outside the container 15. The hydraulic pressure of the plating solution L in the container 15 is adjusted by a pressure regulating valve 54.
The positive electrode 11 is attached within the accommodation space 15a of the container 15 via the vibration device 60. As shown in
In this embodiment, the positive electrode 11 is a positive electrode that is insoluble in the plating solution L. Therefore, even if the voltage of the power source 14 is applied between the positive electrode 11 and the base material B, the positive electrode 11 will not dissolve. Examples of the material for the positive electrode include titanium, titanium alloy, and platinum. For example, when the material of the positive electrode is titanium or a titanium alloy, its surface may be coated with iridium oxide or platinum. By applying these coatings, the reduction reaction of water is promoted, and metal is easily deposited on the surface of the base material B.
In this embodiment, a plurality of curved surfaces 11a a convexly curved toward the electrolyte film 13 are arranged on the surface of the positive electrode 11 that faces the electrolyte film 13. As shown in
Here, if each curved surface 11a is curved in a convex shape so that oxygen gas bubbles attached to the surface can be moved to the through hole 11b by the buoyancy of the plating solution L, etc., the curved surface 11a can be The shape is not particularly limited. In this embodiment, the curved surface 11a is a part of a spherical surface, specifically, a hemispherical curved surface. For example, the curved surface is a part of the peripheral surface of a cylinder, the opposing surface of the positive electrode is a part of the peripheral surface of the cylinder arranged in one direction, and there is a slit-like through hole between them. may be formed.
Furthermore, as shown in
Specifically, the top region 11c (the metal surface thereof) is subjected to water repellent treatment. The water repellent treatment may be a treatment that imparts water repellency to the metal surface by exposing it to plasma or irradiating it with laser in an environment of a reactive gas derived from a water repellent functional group. For example, examples of the water-repellent functional group include an alkyl group such as a saturated fluoroalkyl group (particularly a trifluoromethyl group), a silyl group such as an alkylsilyl group or a fluorosilyl group, or a phenyl group.
In addition, for example, on the premise that the conductivity of the top region 11c is ensured, a conductive film in which a conductive filler is interposed in a water-repellent resin is applied to the top region 11c. may be formed. For example, a film of a metal oxide (e.g., iridium oxide, ruthenium, etc.) having conductivity and water repellency may be formed on the top region 11c. Furthermore, water repellency may be imparted to the top region 11c by providing the top region 11c with a fine fractal structure having concave portions and convex portions. For example, the contact angle of water on the surface of the top region 11c of the curved surface 11a is preferably 90° or more, more preferably 1000 or more.
Further, a portion other than the top region 11c may also be subjected to a water repellent treatment, and more preferably, the other region 11d of the curved surface 11a is subjected to a hydrophilic treatment. For example, by adding a functional group such as a hydroxyl group (—OH), a carbonyl group (—CO), or a carboxyl group (—COOH) to the other region 11d of the curved surface 11a, the top region 11c may become a hydrophilic surface. Specifically, the curved surface 11a other than the other region 11d is masked, the top region 11c is exposed to plasma derived from the atmosphere or a reactive gas such as a hydrocarbon gas, and the top region 11c may be modified to a hydrophilic surface. In addition, a film made of a hydrophilic material may be formed by CVD or the like while masking the surface of the positive electrode 11 except for the top region 11c. A film consisting of the following may be formed. For example, the contact angle of water in the other region 11d is preferably 40° or less.
Further, the film forming apparatus 1 includes a vibration device 60 that vibrates the positive electrode 11. The vibration device 60 is not particularly limited as long as it vibrates the positive electrode 11, and may be an ultrasonic vibration, for example.
In this embodiment, the vibration device 60 vibrates the positive electrode 11 in the horizontal direction. The vibration device 60 vibrates the positive electrode 11 with an amplitude greater than or equal to the hole width D of the through hole 11b along the horizontal direction in which the positive electrode 11 vibrates. The vibration device 60 includes a main body 61 attached to the container 15 and a movable element 62 attached between the main body 61 and the positive electrode 11. The main body 61 is a power source for generating vibrations, and the movable element 62 slides horizontally with respect to the main body 61 by the power from the main body 61. The movable element 62 vibrates in the horizontal direction with a predetermined amplitude due to the power from the main body 61.
More specifically, due to the vibration of the vibration device 60, the positive electrode 11 is moved by a moving distance A1 from the position shown in the upper diagram of
The method for forming the metal film F of this embodiment will be described below. First, as shown in
Next, the pump 80 is driven. As a result, the pump 80 sucks the plating solution L contained in the tank 90, and the plating solution L is force-fed into the accommodation space 15a of the container 15, so that the plating solution L is filled in the accommodation space 15a. Further, the supplied plating solution L passes through the accommodation space 15a of the container 15 and is returned to the tank 90. In this way, the plating solution L within the container 15 can be circulated. Since the pressure regulating valve 54 is provided downstream of the container 15, the hydraulic pressure of the plating solution L in the accommodation space 15a can be adjusted to a set pressure.
Next, as shown in
Here, since the positive electrode 11 is a positive electrode that is insoluble in the plating solution L, the solvent of the plating solution L is electrolyzed and gas is generated. For example, when the solvent is water, oxygen gas is produced. As shown in
In this embodiment, a plurality of curved surfaces 11a that are convexly curved toward the electrolyte film 13 are arranged on the opposing surface 11f of the positive electrode 11 that faces the electrolyte film 13. Therefore, the bubbles P attached to each curved surface 11a of the positive electrode 11 move from the top of the curved surface 11a toward the bottom (side surface) of the curved surface 11a due to the buoyancy in the plating solution L. The bubbles P that have moved pass through the through holes 11b formed between the curved surfaces 11a. As a result, the attached bubbles P can be suppressed from obstructing the flow of electricity from the positive electrode 11 to the base material B, and a metal film F having a uniform thickness can be stably formed.
In particular, during film formation, electrolysis tends to concentrate on the top of the curved surface 11a of the positive electrode 11, and bubbles P are likely to be generated therein. As the slope of the curved surface 11a increases as it advances toward the bottom of the curved surface 11a, which is a part of the spherical surface, the bubbles P that have moved from the top of the curved surface 11a move to the through hole 11b while absorbing other bubbles P. It becomes easier. In particular, when the curved surface 11a is a hemispherical curved surface, such an effect can be further exhibited.
Further, by applying a water repellent treatment to the top region 11c, the top region 11c becomes a water-repellent surface. This makes it difficult for fine air bubbles to uniformly adhere to the region 11c at the top of the curved surface 11a, and the generated bubbles P tend to aggregate and grow. As a result, the grown bubbles P are easily moved from the state attached to the top region 11c of the curved surface 11a toward the bottom (side surface) of the curved surface 11a due to the buoyancy in the plating solution. As a result, the bubbles P that have moved from the top region 11c become easier to move to the through hole 11b.
Furthermore, since the other region 11d of the curved surface 11a except the top region 11c has hydrophilicity, the plating solution L easily enters between the other region 11d of the curved surface 11a and the bubbles P. Therefore, the bubbles P attached to the top region 11c of the curved surface 11a are easily moved toward (the side surfaces of) the bottom of the curved surface 11a due to the buoyancy in the plating solution.
Furthermore, in this embodiment, since the metal film is formed while vibrating the positive electrode 11, the bubbles P attached to the positive electrode 11 can be easily moved along the surface of the positive electrode 11. In particular, since the positive electrode 11 is vibrated with an amplitude greater than or equal to the hole width D of the through hole 11b, the position of the through hole 11b can be moved to a different position with respect to the surface of the base material B. Thereby, the metal film F having a more uniform thickness can be formed on the base material B.
When the film formation is completed, the plating solution L in the container 15 is discharged, and the linear actuator 70 is driven to raise the container 15 with respect to the mounting table 40. Thereby, the base material B can be separated from the electrolyte film 13. Thereafter, the base material B on which the metal film F has been formed is removed from the mounting table 40, a new base material B is placed on the mounting table 40, and the metal film F is formed in the same manner.
Reference Examples 1 to 3 will be explained below.
A test specimen was prepared in which the surface of a plate-shaped titanium base material was coated with iridium oxide as a water-repellent material. The contact angle of water to the surface of the test piece (surface coated with material) was measured by a droplet method in accordance with JISR3257. The results are shown in
A test specimen was prepared in which the surface of a plate-shaped titanium base material was coated with fluororesin as a water-repellent material. The contact angle of water to the surface of the test piece (surface coated with material) was measured in the same manner as in Reference Example 1. The results are shown in
A plate-shaped titanium test specimen was prepared. The contact angle of water to the surface of the test piece (titanium surface) was measured in the same manner as in Reference Example 1. The results are shown in
As shown in
Next, an expanded metal made of titanium was prepared as a base material of an positive electrode, and the material shown in Reference Examples 1 and 2 was coated on the surface of this base material to produce positive electrodes of Reference Examples 1 and 2. As the positive electrode of Reference Example 3, an expanded metal made of titanium was prepared. The positive electrodes of Reference Examples 1 to 3 were energized in a plating solution, and generation of bubbles was confirmed.
As a result, as shown in
Although the embodiment of the present disclosure has been described in detail above, the present disclosure is not limited to the embodiment, and various design changes can be made without departing from the spirit of the present disclosure described in the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-067220 | Apr 2023 | JP | national |
