Metal film formation method

Abstract

To provide a metal film formation method capable of avoiding poor formation of metal films by suppressing entrainment of air between an electrolyte membrane and a substrate.SOLUTION: The film formation method comprises: in a container 15, with an anode 11 in contact with an electrolyte membrane 13, reducing pressure so that the pressure of plating solution L becomes lower than the pressure of air between the electrolyte membrane 13 and a substrate B; bringing the electrolyte membrane 13 into close contact with the surface of the anode 11; disposing the substrate B below the electrolyte membrane 13; lowering the container 15 toward the substrate B while sucking air between the electrolyte membrane 13 and the substrate B from the substrate B side until the electrolyte membrane 13 contacts the substrate B; raising the anode 11 so that the anode 11 is separated from the electrolyte membrane 13 while increasing the pressure of the plating solution L; pressing the substrate B with the electrolyte membrane 13; and forming a metal film F on the substrate B by applying voltage between the anode 11 and the substrate B.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] As an example of this type of technology, Patent Document 1 proposes a film formation method for forming a metal film on the surface of a substrate by electrolytic plating. In this film formation method, an electrolyte membrane is sealed at the opening of a container that contains an anode and a plating solution, and a voltage is applied between the substrate and the anode while the electrolyte membrane is in contact with the substrate, thereby forming a metal film derived from metal ions in the plating solution on the substrate. When the electrolyte membrane is brought into contact with the substrate, the container is moved toward the substrate, and the electrolyte membrane is sucked from the substrate side. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6056987 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the technology of Patent Document 1, when the electrolyte membrane is sucked, the electrolyte membrane may be locally deformed, making it impossible to bring the electrolyte membrane into uniform contact with the substrate. As a result, air may become trapped between the electrolyte membrane and the substrate. This may prevent the metal from being deposited in this area, resulting in poor film formation of the metal coating.

[0005] The present invention has been made in consideration of these points, and its object is to provide a method for forming a metal film that can avoid poor film formation of the metal film by suppressing the entrapment of air between the electrolyte membrane and the substrate. [Means for solving the problem]

[0006] In view of the above-described problems, the method for forming a metal film according to the present invention is a method for forming a metal film derived from metal ions in the plating solution on a substrate by applying a voltage to the substrate and the anode while bringing the electrolyte membrane into contact with a substrate, in a state in which an anode and a plating solution are contained in a container having an opening that opens downward and the opening is sealed with an electrolyte membrane. This film formation method includes the following steps: a contacting step of reducing the pressure of the plating solution to be lower than the pressure of air between the electrolyte membrane and the substrate in a state in which the anode is in contact with the electrolyte membrane within the container, thereby bringing the electrolyte membrane into close contact with the surface of the anode; a substrate arranging step of arranging the substrate below the electrolyte membrane in a state in which the electrolyte membrane and the substrate are spaced apart; a container lowering step of lowering the container toward the substrate while sucking air between the electrolyte membrane and the substrate from the substrate side until the electrolyte membrane comes into contact with the substrate; a pressing step of raising the anode and increasing the pressure of the plating solution to separate the anode from the electrolyte membrane, thereby pressing the substrate with the electrolyte membrane; and a film formation step of applying a voltage between the anode and the substrate to form the metal coating on the substrate. [Effects of the Invention]

[0007] According to the present invention, since the electrolyte membrane is in close contact with the anode in the contacting step, even if the electrolyte membrane is lowered toward the substrate while air is sucked in during the housing lowering step, deformation of the electrolyte membrane due to air suction can be suppressed. This prevents air from being trapped between the electrolyte membrane and the substrate, and allows the electrolyte membrane to be in uniform contact with the substrate during the pressing step. In this way, a metal coating with a stable shape can be formed during the membrane forming step. [Brief explanation of the drawings]

[0008] [Figure 1] 1A is a schematic diagram of a film forming apparatus for carrying out a method for forming a metal film according to an embodiment of the present invention, and FIG. 1B is a schematic diagram of the film forming apparatus for explaining an adhesion step. [Figure 2] FIG. 1A is a schematic diagram of the film forming apparatus for explaining a container lowering step, and FIG. 1B is a schematic diagram for explaining a film forming step. [Figure 3] FIG. 1 is a flow diagram of a method for forming a metal film according to an embodiment of the present invention. [Figure 4] 1 shows the results of measuring the number of defects in metal films formed by the film forming methods of Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a metal film forming apparatus 1 according to this embodiment will be described with reference to Fig. 1(a). As shown in Fig. 1, in this embodiment, the film forming apparatus 1 includes an anode 11, an electrolyte membrane 13, and a power supply 14 that applies a voltage between the anode 11 and a substrate B. The film forming apparatus 1 further includes a container 15 that contains the anode 11 and a plating solution L, and a mounting table 40 on which the substrate B is placed.

[0010] The film forming apparatus 1 further includes a first linear actuator 70A that raises and lowers the housing body 15, and a pair of second linear actuators 70B, 70B that raise and lower the anode 11 accommodated in the accommodation space 15a of the housing body 15.

[0011] The first linear actuator 70A moves the rod 72A linearly to raise and lower the housing 15 so that the electrolyte membrane 13 and the substrate B can be brought into contact with and separated from each other. The first linear actuator 70A has a rod 72A that moves linearly with respect to the main body 71A, and the housing 15 is fixed to the tip of the rod 72A. Each second linear actuator 70B moves the rod 72B linearly to raise and lower the anode 11 relative to the housing 15 so that the anode 11 can be brought into contact with and separated from the electrolyte membrane 13 in the housing space 15a. Each second linear actuator 70B has a rod 72B that moves linearly with respect to the main body 71B. The rod 72B is inserted into the upper wall of the housing 15, and the anode 11 is fixed to the tip of the rod 72B.

[0012] The anode 11 may be either an insoluble anode that does not dissolve in the plating solution L during film formation, or a soluble anode made of the same metal as the metal coating of the film and that dissolves during film formation. In this embodiment, the anode 11 is flat, and the surface facing the electrolyte membrane 13 is flat. A plurality of through holes may be formed in the thickness direction of the anode 11 as long as the anode 11 can be tightly attached in the adhesion step described below and air is not trapped between the electrolyte membrane 13 and the substrate B. This allows the electrolyte membrane 13 to be more uniformly attached to the substrate B by reducing the pressure of the plating solution L in the adhesion step described below.

[0013] The substrate B functions as a cathode. The substrate B is flat, and the surface Ba (film-forming surface) on which the metal film F is formed is planar. For example, the substrate B may be made of a metal material such as aluminum or copper. The anode 11 is electrically connected to the positive electrode of the power source 14. The negative electrode of the power source 14 is electrically connected to the substrate B via the mounting table 40. The plating solution L is a liquid containing the metal of the metal film to be formed in an ionic state. Examples of such metals include copper, nickel, gold, and silver.

[0014] The electrolyte membrane 13 is a membrane that can be impregnated (contained) with metal ions together with the plating solution L by contacting the electrolyte membrane 13 with the plating solution L. The electrolyte membrane 13 is a flexible membrane. There are no particular limitations on the material of the electrolyte membrane 13, as long as it allows the metal ions of the plating solution L to migrate to the substrate B side when a voltage is applied from the power source 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.

[0015] The container 15 has a storage space 15a formed therein for storing the plating solution L. The anode 11 is disposed in the storage space 15a of the container 15. An opening 15d is formed on the side of the storage space 15a facing the substrate B. The opening 15d of the container 15 is covered with the electrolyte membrane 13, so that when the plating solution L is stored in the storage space 15a, the plating solution L in the storage space 15a is sealed by the electrolyte membrane 13.

[0016] The container 15 has a supply port 15b for supplying the plating solution L to the container space 15a and a discharge port 15c for discharging the plating solution L from the container space 15a. The supply port 15b and the discharge port 15c are formed on either side of the container space 15a. The supply port 15b is fluidly connected to a supply pipe 51. The discharge port 15c is fluidly connected to a discharge pipe 52.

[0017] The film forming apparatus 1 includes a supply tank 58. The supply tank 58 is a tank for supplying the plating solution L to the accommodation space 15a of the accommodation body 15. The supply tank 58 accommodates a predetermined amount of the plating solution L, which has been adjusted to a preset metal ion concentration.

[0018] The film forming apparatus 1 includes a circulation mechanism 50. The circulation mechanism 50 circulates the plating solution L between a supply tank 58 and the accommodation body 15. The circulation mechanism 50 includes a supply pipe 51, a discharge pipe 52, and a circulation pump 59. The supply pipe 51 connects the supply tank 58 and the accommodation body 15, and the circulation pump 59 is provided on the supply pipe 51.

[0019] In this embodiment, by driving the circulation pump 59, the plating solution L is sucked from the supply tank 58 into the supply pipe 51 and then pumped from the supply port 15b to the accommodation space 15a. The plating solution L in the accommodation space 15a is returned to the supply tank 58 through the discharge port 15c.

[0020] The discharge pipe 52 connects the supply tank 58 and the accommodation body 15, and is provided with a stop valve 54. The stop valve 54 is opened by a control device (not shown), for example, immediately before step S2 or immediately after step S5, which will be described later, and the plating solution L is supplied from the supply tank 58 to the accommodation space 15a of the accommodation body 15 by the circulation mechanism 50. On the other hand, the stop valve 54 is closed by the control device, for example, immediately before steps S4 and S6, which will be described later, and the pressure of the plating solution in the accommodation space 15a of the accommodation body 15 is adjusted by the pressure adjustment mechanism 60.

[0021] The pressure adjustment mechanism 60 includes a cylinder 62 that contains the plating solution L and a piston 61 that slides inside the cylinder 62. The cylinder 62 is connected to a supply port 15b that supplies the plating solution L to the accommodation body 15. When the piston 61 is advanced relative to the cylinder 62, the pressure of the plating solution L contained in the accommodation body 15 is increased, and when the piston 61 is moved back relative to the cylinder 62, the pressure of the plating solution L contained in the accommodation body 15 is reduced.

[0022] The positive electrode of the power source 14 is connected to the anode 11, and the negative electrode is connected to the mounting table 40. The mounting table 40 and the substrate B are electrically connected, so that the surface Ba of the substrate B acts as a cathode. The mounting table 40 has a recess 41 formed therein to accommodate the substrate B, and a suction passage 43 having a plurality of suction ports formed therein so as to surround the recess 41. The suction passage 43 is connected to an air pump 45 via a pressure adjusting valve 44.

[0023] The flow of the film formation method shown in Fig. 3 will be described below with reference to Fig. 1(b), Fig. 2(a), and Fig. 2(b). The series of steps shown below are performed by the film formation apparatus 1 using the control device described above, but may also be performed manually by an operator, for example.

[0024] First, in step S1, a bonding step is performed. In this step, as shown in Fig. 1(b), in a state where the anode 11 is in contact with the electrolyte membrane 13 in the container 15, the pressure of the plating solution L is reduced to be lower than the pressure of the air between the electrolyte membrane 13 and the substrate B, and the electrolyte membrane 13 is bonded to the surface (opposing surface) of the anode 11.

[0025] Specifically, while the first linear actuator 70A separates the electrolyte membrane 13 from the mounting table 40, the second linear actuator 70B lowers the anode 11 to a position where the anode 11 contacts the electrolyte membrane 13. In this state, the circulation mechanism 50 supplies plating solution L to the accommodation space 15a of the accommodation body 15, and when the accommodation space 15a is filled with the plating solution L, the stop valve 54 is closed. Furthermore, the piston 61 of the pressure adjustment mechanism 60 is retracted relative to the cylinder 62, and the cylinder 62 sucks the plating solution L from the accommodation space 15a until the pressure of the plating solution L becomes lower than the pressure of the air between the electrolyte membrane 13 and the substrate B. As a result, the electrolyte membrane 13 is brought into close contact (adsorbed) with the surface of the anode 11 due to the pressure difference between the air and the plating solution L present on either side of the electrolyte membrane 13.

[0026] Next, in step S2, a substrate placement step is performed. In this step, as shown in FIG. 1(a), the substrate B is placed below the electrolyte membrane 13 with the electrolyte membrane 13 and the substrate B spaced apart. Specifically, the substrate B is placed in a recess 41 formed in the mounting table 40. When this step is performed using a control device, for example, a transfer device (not shown) that transfers the substrate B is moved between the electrolyte membrane 13 and the mounting table 40.

[0027] Next, in step S3, a housing lowering step is performed. In this step, as shown in FIG. 2(a), the housing 15 is lowered toward the substrate B until the electrolyte membrane 13 contacts the substrate B while sucking air between the electrolyte membrane 13 and the substrate B from the substrate B side. Specifically, from the state shown in FIG. 1(b), the housing 15 is lowered by the first linear actuator 70A until the electrolyte membrane 13 contacts the substrate B, and at the same time, the air pump 45 is driven to suck air between the electrolyte membrane 13 and the substrate B through the suction passage 43. This makes it possible to suppress local deformation of the electrolyte membrane 13 caused by the suction force of the air between the electrolyte membrane 13 and the substrate B, while reducing air entrapment between the electrolyte membrane 13 and the substrate B.

[0028] Here, without the pressure regulating valve 44, the suction pressure of the electrolyte membrane 13 increases as the distance between the electrolyte membrane 13 and the substrate B decreases. In this case, if the state of contact between the electrolyte membrane 13 and the anode 11 changes, a portion of the electrolyte membrane 13 deforms and moves away from the anode 11. Therefore, preferably, in step S3, air is sucked from the substrate B side while adjusting the suction pressure of air against the electrolyte membrane 13 so that the state of contact between the electrolyte membrane 13 and the anode 11 is maintained. Specifically, until the electrolyte membrane 13 moves toward the substrate B, the pressure of the pressure regulating valve 44 is set to a predetermined constant pressure so that the magnitude (absolute value) of the liquid pressure (negative pressure) of the plating solution acting on the electrolyte membrane 13 is greater than the magnitude (absolute value) of the suction pressure (negative pressure) of the air acting on the electrolyte membrane 13. In this way, local deformation of the electrolyte membrane 13 caused by the suction force of air between the electrolyte membrane 13 and the substrate B can be more accurately suppressed.

[0029] Next, in step S4, a pressing step is performed. In this step, as shown in FIG. 2(b), the anode 11 is raised so as to separate the anode 11 from the electrolyte membrane 13, and the pressure of the plating solution L is increased so that the electrolyte membrane 13 presses the substrate B. Specifically, the second linear actuator 70B raises the anode 11 so as to separate the anode 11 from the electrolyte membrane 13, and moves the piston 61 of the pressure adjustment mechanism 60 forward relative to the cylinder 62. This supplies the plating solution L from the accommodation space 15a to the cylinder 62. In this way, the electrolyte membrane 13 can be pressed against the substrate B with uniform pressure while being in uniform contact with the substrate B.

[0030] The plating solution L is supplied in this manner until the electrolyte membrane 13 can press the substrate B with a predetermined pressure (predetermined liquid pressure). Here, if the liquid pressure of the plating solution L is increased after the anode 11 is raised, there is a risk that the electrolyte membrane 13 will be partially deformed as the anode 11 is raised. Therefore, it is more preferable to raise the anode 11 at the same time as increasing the pressure of the plating solution L.

[0031] Next, in step S5, a film formation process is performed. In this process, a voltage is applied between the anode 11 and the substrate B to form a metal film F on the substrate B. Specifically, as shown in FIG. 2(b), when a voltage is applied between the anode 11 and the substrate B, metal ions in the plating solution L contained in the container 15 permeate the electrolyte membrane 13 and receive electrons on the surface of the substrate B, resulting in metal deposition. Since the electrolyte membrane 13 presses the substrate B with uniform pressure with almost no air trapped between the electrolyte membrane 13 and the substrate B, a metal film F of stable quality can be formed on the surface of the substrate B. Note that suction by the air pump 45 may be continued in this process. Alternatively, before proceeding to step S6, the stop valve 54 may be temporarily opened, the plating solution L may be circulated by the circulation mechanism 50, and the plating solution L contained in the container 15 may be replaced with the plating solution L in the supply tank 58. After the plating solution L is replaced, the stop valve 54 is closed.

[0032] Next, in step S6, a depressurization step is performed. In this step, after the membrane formation step, with the electrolyte membrane 13 in contact with the substrate B, the anode 11 is lowered until the anode 11 contacts the electrolyte membrane 13, and then the pressure of the plating solution L is reduced to the pressure of the plating solution L in the adhesion step of step S1. In this step, the anode 11 and the container 15 (electrolyte membrane 13) are in the positional relationship shown in FIG. 2(a). With the electrolyte membrane 13 in contact with the substrate B, the second linear actuator 70B lowers the anode 11 to a position where it contacts the electrolyte membrane 13. Thereafter, the piston 61 of the pressure adjustment mechanism 60 is retracted relative to the cylinder 62, and the plating solution L in the container space 15a is forced into the cylinder 62, reducing the pressure of the plating solution L to the pressure in step S1.

[0033] Next, in step S7, a container raising step is performed. In this step, the container 15 is raised relative to the substrate B while the pressure of the plating solution L is reduced until the electrolyte membrane 13 and the substrate B are separated from each other. In this step, the anode 11 and the container 15 (electrolyte membrane 13) are in the positional relationship shown in FIG. 1(b).

[0034] Specifically, the first linear actuator 70A raises the container 15 until the electrolyte membrane 13 separates from the substrate B. Because the plating solution L contained in the container 15 is reduced in pressure before the container 15 is raised, the electrolyte membrane 13 is not deformed by the weight of the plating solution L. Furthermore, even if the pressure of the plating solution L is reduced, the electrolyte membrane 13 is supported in contact with the anode 11, and therefore the portion of the electrolyte membrane 13 in contact with the substrate B is not deformed due to this reduced pressure.

[0035] As a result, in step S8, a substrate removal process is performed to remove the substrate B from below the electrolyte membrane 13, and then the process returns to step S2, where a new substrate B is placed on the mounting table 40, allowing the metal coating F to be formed continuously on the new substrate B.

[0036] Example 1 Using the film-forming apparatus shown in Figure 1(a), copper films were formed sequentially on multiple substrates (same plates). The anode used was an anode with an iridium oxide surface coating. Furthermore, a 1.0 mol / L copper sulfate aqueous solution was used as the plating solution, and the plating solution temperature was 40°C and the current density was 7 A / dm 2 A copper film was formed under the following film formation conditions: a pressure (applied pressure) of 0.6 MPa for the electrolyte membrane and a processing time of 194 seconds. The number of undeposited defects per unit area of ​​the formed film was counted. The results are shown in Figure 4.

[0037] Comparative Example 1 A copper film was formed in the same manner as in Example 1. The difference from Example 1 is that the pressure adjustment mechanism 60 was not used, and the film was formed in the same manner as the film formation method disclosed in Patent Document 1, a prior art. The number of undeposited defects per unit area of ​​the formed film was confirmed. The results are shown in Figure 4.

[0038] In Example 1, there were almost no defects in the copper film, but many defects were found in the copper film in Comparative Example 1. This is thought to be because, as mentioned above, in Example 1, there was almost no air trapped between the electrolyte membrane and the substrate during membrane formation. [Explanation of symbols]

[0039] 11: Electrolyte membrane, 13: Electrolyte membrane, 15: Container, L: Plating solution

Claims

1. A method for forming a metal film, comprising: a container that contains an anode and a plating solution and has an opening that opens downward, and a voltage is applied to the substrate and the anode while the electrolyte membrane is in contact with a substrate, with the opening sealed with an electrolyte membrane, to form a metal film derived from metal ions in the plating solution on the substrate, the method comprising: a contacting step of reducing the pressure of the plating solution to be lower than the pressure of the air between the electrolyte membrane and the base material in a state in which the anode is in contact with the electrolyte membrane in the container, thereby contacting the electrolyte membrane with the surface of the anode; a substrate placement step of placing the substrate below the electrolyte membrane in a state where the electrolyte membrane and the substrate are spaced apart from each other; a housing lowering step of lowering the housing toward the base material while sucking air between the electrolyte membrane and the base material from the base material side until the electrolyte membrane comes into contact with the base material; a pressing step of raising the anode and increasing the pressure of the plating solution so that the anode is spaced apart from the electrolyte membrane, and pressing the substrate with the electrolyte membrane; a film-forming step of forming the metal coating on the substrate by applying a voltage between the anode and the substrate; A method for forming a metal film, comprising:

2. 2. The method for forming a metal coating according to claim 1, wherein, in the container lowering step, the air is sucked from the substrate side while adjusting the suction pressure of the air against the electrolyte membrane so that the electrolyte membrane is maintained in close contact with the anode.

3. a depressurizing step of lowering the anode until the anode comes into contact with the electrolyte membrane while the electrolyte membrane is in contact with the base material after the membrane forming step, and then reducing the pressure of the plating solution to the pressure of the plating solution in the adhesion step; a container raising step of raising the container relative to the substrate while reducing the pressure of the plating solution until the electrolyte membrane and the substrate are separated from each other; 2. The method for forming a metal coating according to claim 1, further comprising a substrate removing step of removing the substrate from below the electrolyte membrane.

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