Deposition apparatus of metallic film and deposition method thereof

Abstract

To provide a deposition apparatus of a metallic film, which can deposit the metallic film whose film thickness is uniform, and whose surface is smooth.SOLUTION: A deposition apparatus 1 comprises: a power supply 14 for applying a voltage to between an anode 11 and a substrate B; a control device 61 for controlling the voltage of the power supply 14; and an ammeter 65 for measuring the value of a current flowing between the anode 11 and the substrate B when the voltage is applied. The control device 61, while increasing the voltage applied between the anode 11 and the substrate B in the state that a plating solution L is stored in a container 15 and a polymer electrolyte 13 contacts the substrate B, includes: calculating the amount of variation of the current value according to the increase of the voltage, or an evaluation value according to the magnitude of the amount of variation; setting a voltage as a deposition voltage at the timing when the evaluation value is a preset specified value or lower; and adjusting the voltage of the power supply 14 as the deposition voltage when the metallic film F is deposited.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] As an example of this type of technology, Patent Document 1 proposes a film formation apparatus that forms a metal film between an anode and a substrate with the electrolyte membrane in contact with the substrate. This film formation apparatus is equipped with a measuring device that measures the AC impedance between the anode and the substrate. The film formation apparatus determines whether film formation is possible based on the imaginary component at a predetermined frequency of the AC impedance measured by the measuring device, which indicates the contact state between the electrolyte membrane and the substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-055435 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the film formation apparatus disclosed in Patent Document 1, when a constant voltage is applied between the anode and the substrate during film formation, the current flowing between the anode and the substrate may be unstable depending on the magnitude of the voltage applied between the anode and the substrate, which may result in unstable quality of the metal coating. Specifically, when the applied voltage is small, the amount of current flowing between the anode and the substrate is small and may be unstable, which may result in uneven thickness of the formed metal coating. On the other hand, when the applied voltage is large, the amount of current flowing between the anode and the substrate is ensured, but the surface of the metal coating may become rough.

[0005] The present invention has been made in consideration of these points, and its object is to provide a metal film deposition apparatus that can deposit a metal film with a uniform thickness and a smooth surface. [Means for solving the problem]

[0006] In view of the above-described problems, the present invention provides a metal film forming apparatus that includes an anode, a container that contains a plating solution, and an electrolyte membrane that covers an opening of the container opposite the anode and thereby seals the plating solution in the container, and that forms a metal film by electrolytic plating on a substrate in contact with the electrolyte membrane. The film forming apparatus further includes a power supply that applies a voltage between the anode and the substrate, a control device that controls the voltage of the power supply, and an ammeter that measures a current value that flows between the anode and the substrate when the voltage is applied. The control device, while the plating solution is contained in the container and the electrolyte membrane is in contact with the substrate, increases the voltage applied between the anode and the substrate, and calculates an evaluation value based on the amount of change in the current value corresponding to the increase in voltage, or a value corresponding to the magnitude of the change. The control device sets the voltage at the timing when the evaluation value becomes equal to or less than a predetermined value as a film formation voltage, and adjusts the voltage of the power supply to the film formation voltage during formation of the metal film. [Effects of the Invention]

[0007] According to the present invention, a film-forming voltage can be set by a control device before forming a metal coating. At this time, the control device sets the film-forming voltage to the voltage at which the evaluation value described above falls below a predetermined value. Therefore, even if a constant film-forming voltage is applied between the anode and the substrate, a stable current can be passed between the anode and the substrate. Furthermore, the film-forming voltage at which the evaluation value falls below the predetermined value is a relatively low voltage within a voltage range that allows a stable current to be passed between the anode and the substrate, thereby preventing the surface roughness of the metal coating from increasing. By forming a film using such a film-forming voltage, a metal coating with a uniform thickness and a smooth surface can be formed. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1A is a schematic diagram of a film-forming apparatus for carrying out the method for forming a metal film according to this embodiment, and FIG. 1B is a schematic diagram for explaining the setting of a film-forming voltage and the formation of a metal film using the film-forming apparatus of FIG. [Figure 2] FIG. 1 is a flow diagram of a method for forming a metal film according to an embodiment. [Figure 3] Graph (a) shows the change in current density when the applied voltage is increased in the film-forming apparatus (SED) of this embodiment and in plating (normal) using a plating bath, and graph (b) shows the relationship between the applied voltage and the evaluation value. [Figure 4] Graph (a) shows the relationship between current density and the change in film thickness of the metal film in Example 1 and Comparative Example 1, and graph (b) shows the relationship between current density and the arithmetic mean roughness of the metal film in Example 1 and Comparative Example 1. [Figure 5] FIG. 1 is a table showing the results of the appearance, surface roughness, and deposition rate (current density) of the metal film for each deposition voltage. DETAILED DESCRIPTION OF THE INVENTION

[0009] A metal coating forming apparatus 1 according to this embodiment will be described below with reference to Figures 1 to 5. As shown in Figure 1, in this embodiment, the film forming apparatus 1 includes an anode 11, an electrolyte membrane 13, and a power source 14 that applies a voltage between the anode 11 and the substrate B.

[0010] The film formation apparatus 1 further includes a container 15 that contains the anode 11 and the plating solution L, and a mounting table 40 on which the substrate B is placed. The film formation apparatus 1 further includes a linear actuator 70 that raises and lowers the container 15. The linear actuator 70 raises and lowers the container 15 by linearly moving a rod 72 so that the electrolyte membrane 13 and the substrate B can be moved toward and away from each other. The linear actuator 70 has a rod 72 that moves linearly relative to a main body 71, and the container 15 is fixed to the tip of the rod 72. The mounting table 40 has a recess 41 formed therein that holds the substrate B.

[0011] The anode 11 is an insoluble anode that does not dissolve in the plating solution L during film formation. The substrate B functions as a cathode. The substrate B may be made of a metal material such as aluminum or copper, and a metal layer serving as a negative electrode may be formed on the surface Ba of the insulating substrate body on which the film is to be formed. 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 solution containing the metal of the metal film to be formed in ionic form. Examples of such metals include copper, nickel, gold, and silver. The plating solution L is preferably kept at 50°C or below to obtain the characteristics of the solid waveform shown in Figure 3(a) described below.

[0012] The electrolyte membrane 13 is a membrane that can be impregnated (contain) metal ions together with the plating solution L by contacting it with the plating solution L. The electrolyte membrane 13 is a flexible membrane. The material of the electrolyte membrane 13 is not particularly limited 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. The thickness of the electrolyte membrane 13 is preferably sufficiently thinner than the thickness of the ion diffusion layer formed on the surface of the substrate in a typical plating bath, and is preferably 50 μm or less.

[0013] 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 an electrolyte membrane 13, and the electrolyte membrane 13 is detachably fixed to the container 15 by a frame 17. As a result, the opening 15d of the container 15 is sealed by the electrolyte membrane 13 with the plating solution L stored in the storage space 15a.

[0014] 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.

[0015] The film forming apparatus 1 includes a supply tank 58 and a circulation mechanism 50 that circulates the plating solution L between the supply tank 58 and the accommodation body 15 in order to supply the plating solution L to the accommodation space 15a of 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 supply pipe 51 is provided with the circulation pump 59. The discharge pipe 52 connects the supply tank 58 and the accommodation body 15, and the discharge pipe 52 is provided with a pressure adjustment valve 54. The pressure adjustment valve 54 adjusts the pressure (liquid pressure) of the plating solution L in the accommodation space 15a to a predetermined pressure.

[0016] 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.

[0017] The power supply 14 applies a preset film formation voltage between the anode and the substrate during film formation. The positive electrode of the power supply 14 is electrically connected to the anode 11, and the negative electrode of the power supply 14 is connected to the substrate B via the mounting table 40. The film formation apparatus 1 further includes a control device 61 that controls the voltage of the power supply 14. The power supply 14 includes, as hardware, an adjustment mechanism (not shown) such as an inverter that adjusts the applied voltage. The control device 61 can control the voltage (output voltage) of the power supply 14 by sending a control signal to the adjustment mechanism of the power supply 14. The film formation apparatus 1 also includes an ammeter 65 that measures the value of the current flowing between the anode 11 and the substrate B when a voltage is applied between the anode 11 and the substrate B in the state shown in FIG. 1(b) described below. The current value measured by the ammeter 65 is input to the control device 61.

[0018] The control by the control device 61 will be described below with reference to Figures 1(a) and 1(b) and the flowchart in Figure 2. First, in step S1, as shown in Figure 1(a), the electrolyte membrane 13 is attached to the housing 15. Furthermore, the substrate B is placed on the mounting table 40 by placing it in the recess 41 of the mounting table 40.

[0019] Next, in step S2, the electrolyte membrane 13 is brought into contact with the substrate B. Specifically, the control device 61 drives the linear actuator 70 to move the housing 15 fixed to the tip of the rod 72 toward the mounting table 40 until the electrolyte membrane 13 abuts against the substrate B (see, for example, FIG. 1(b)).

[0020] Next, in step S3, the plating solution L is accommodated in the accommodation body 15. Specifically, by driving the circulation pump 59, the plating solution L is sucked from the supply tank 58 into the supply pipe 51 and then 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 supply tank 58 via the discharge port 15c. In this manner, the plating solution L is circulated in the accommodation body 15. Note that in this embodiment, steps S2 and S3 may be performed simultaneously, or step S2 may be performed after step S3.

[0021] When forming a metal film in a plating bath, as shown in the dashed waveform (normal) in FIG. 3(a), increasing the applied voltage proportionally increases the current per unit area flowing between the anode and the substrate. On the other hand, when forming a metal film F using the film-forming apparatus 1 of this embodiment, as shown in the solid waveform (SED) in FIG. 3(a), increasing the applied voltage from 0 V increases the current per unit area (current density) flowing between the anode 11 and the substrate B. Further increasing the applied voltage results in a substantially constant current density within a predetermined range (e.g., 0.50 V to 0.85 V). Further increasing the applied voltage results in a corresponding increase in current density. Thus, in the film-forming apparatus 1 of this embodiment, the metal film is formed on the surface of the substrate B while the electrolyte membrane 13 is in contact with the surface Ba of the substrate B. Therefore, unlike forming a metal film in a plating bath, a waveform within a constant current range can be obtained in which the current density remains substantially constant even when the applied voltage is increased. The waveform shown by the solid line in FIG. 3(a) is an example, and the range of applied voltage in which the current density becomes constant varies depending on the material, thickness, etc. of the electrolyte membrane 13.

[0022] In view of this, in this embodiment, in step S4, the control device 61 measures the current value between the anode 11 and the substrate B while increasing the voltage (applied voltage) applied between the anode 11 and the substrate B by a fixed amount (while sweeping the applied voltage). Specifically, with the plating solution L contained in the container 15 and the electrolyte membrane 13 in contact with the substrate B, the control device 61 controls the power source 14 so as to increase the applied voltage by a fixed increment (for example, 0.05 V) from a state in which the applied voltage is 0 V.

[0023] At this time, the control device 61 records the applied voltage value before and after each increment of the applied voltage and the current value before and after the increment. Specifically, for each increment of the applied voltage, the control device 61 records the voltage value before the increase in the applied voltage as Va and the current value passed per unit area at this time as Ia. Next, the control device 61 increases the applied voltage by a fixed increment ΔV. The control device 61 records the voltage value Vb (Va + ΔV) after the increase in the applied voltage and records the current value passed per unit area at this time as Ib. The "current value passed per unit area" refers to the current density, and is the value obtained by dividing the current value passed between the anode 11 and the substrate B measured by the ammeter 65 by the area of ​​the deposition region where the metal coating F is deposited.

[0024] Next, in step S5, the control device 61 calculates the amount of change in the current value relative to the amount of change in the applied voltage. Specifically, the amount of change in the applied voltage is Vb-Va (=ΔV), and the amount of change in the current value is Ib-Ia. This amount of change in the current value corresponds to what is referred to in the present invention as "the amount of change in the current value corresponding to the increment in voltage." Note that, although the amount of change in the current value is calculated from the amount of current per unit area, the amount of change in the current value measured by the ammeter 65 may also be used if it can be used as an evaluation value, which will be described later.

[0025] Here, the amount (magnitude) of change in current value may be used as an evaluation value for setting the film formation voltage. However, in this embodiment, in step S6, the control device 61 performs a non-dimensional process on the amount of change in current value for each increment of applied voltage. Specifically, the control device 61 divides Ib-Ia, which is the amount of change in current value passed per unit area, by Vb-Va, which is the increment of applied voltage. The calculated value (Ib-Ia) / (Vb-Va) corresponds to the slope t of the solid waveform shown in FIG. 3(a).

[0026] Here, this slope t may be used as the evaluation value, but in this embodiment, this slope t is multiplied by the voltage value Vb after the applied voltage is increased, and then further divided by the current value Ib passed per unit area after the applied voltage is increased. That is, in this embodiment, the evaluation value is a dimensionless value calculated by {(Ib-Ia) / (Vb-Va)}·(Vb / Ib).

[0027] 3(a) (specifically, the limiting current, which will be described later) varies depending on the material and thickness of the electrolyte membrane 13, the arrangement of the anode 11 and the electrolyte membrane 13, the concentration of the plating solution L, and the like. However, by using such an evaluation value, the magnitude of the predetermined value that serves as the threshold in step S7, which will be described later, can be set to a similar magnitude. Note that the "value corresponding to the magnitude of the change in the current value" as used in the present invention is the "slope t" or "non-dimensional value" as used in this embodiment.

[0028] Here, when the applied voltage shown in FIG. 3(b) is between 0.05V and 0.45V, the evaluation value is large, exceeding 0.5, and therefore the gradient of the solid line waveform shown in FIG. 3(a) is large. Therefore, even if a constant applied voltage is set as the film-forming voltage in this range, the current (current density) flowing between the anode 11 and the substrate B is difficult to stabilize. On the other hand, when the applied voltage shown in FIG. 3(b) is between 0.50V and 0.85V, the evaluation value is small, being 0.5 or less, and therefore the gradient of the solid line waveform shown in FIG. 3(a) is small. Therefore, if a constant applied voltage is set as the film-forming voltage in this range, a stable, constant current (limiting current) can be flowed between the anode 11 and the substrate B. For example, in FIG. 3(a), when the current density is about 7 A / dm 2 It can be seen that a stable current flows between the anode 11 and the substrate B. Furthermore, when the applied voltage is 0.90 V or higher, the evaluation value exceeds 0.5, and therefore the current (current density) flowing between the anode 11 and the substrate B is unlikely to be stable. Note that the limiting current is a current that remains approximately constant even when the applied voltage is changed within a certain range, and refers to a current that allows stable deposition of a metal coating.

[0029] 3(b) is in the range of 0.50V to 0.85V, a stable and approximately constant current flows between the anode 11 and the substrate B. However, according to experiments by the inventors, the surface roughness of the metal coating F increases as the applied voltage increases. From this perspective, in order to ensure a smooth surface of the metal coating F, it is desirable that the applied voltage (film formation voltage) to be set during film formation is 0.50V within the range of 0.50V to 0.85V. From this perspective, the following determination is made in step S7.

[0030] Specifically, in step S7, it is determined whether the change in the dimensionless current value (i.e., the evaluation value) is equal to or less than a predetermined value. If the evaluation value exceeds the predetermined value (NO), the process returns to step S4. Specifically, using FIG. 3(b) as an example, the applied voltage is increased by 0.05 V at a time, and since the evaluation value exceeds 0.5 until the applied voltage reaches 0.45 V, steps S4 to S7 are repeated. Note that in this embodiment, the threshold value (predetermined value) of the evaluation value is set to 0.5 as an example. However, although it depends on the configuration conditions of the film forming apparatus 1, it has been found that a film forming voltage near the limiting current can be easily identified if the threshold value is 1.0 or less.

[0031] On the other hand, if the evaluation value is equal to or less than the predetermined value (YES), the process proceeds to step S8, where the applied voltage at this timing is set as the film-forming voltage. Specifically, using FIG. 3(b) as an example, when the applied voltage becomes 0.50V, the evaluation value becomes 0.5, so 0.50V is set as the applied voltage. Next, the process proceeds to step S9, where, during the formation of the metal coating F, the voltage of the power supply is adjusted to the film-forming voltage, and the metal coating F is formed by constant voltage control with the film-forming voltage (0.50V) kept constant.

[0032] In addition, for example, when the anode 11 is replaced, the electrolyte membrane 13 is replaced, and the plating solution L is replenished or replaced, the waveform of the solid line shown in FIG. 3(a) changes (specifically, the film formation voltage when the limiting current is reached changes). Therefore, a series of steps S2 to S8 may be performed to reset the film formation voltage (calibration may be performed).

[0033] As described above, according to this embodiment, the control device 61 sets the film-forming voltage to the voltage at which the evaluation value described above falls below a predetermined value. Therefore, even if a constant film-forming voltage is applied between the anode 11 and the substrate B, a stable current (limiting current) can be passed between the anode 11 and the substrate B. Furthermore, the film-forming voltage at which the evaluation value described above falls below a predetermined value is a relatively low voltage within the range of voltages that allows a stable current to be passed between the anode 11 and the substrate B, thereby preventing the surface roughness of the metal coating F from increasing. By forming the film at such a film-forming voltage, a metal coating F with a uniform thickness and a smooth surface can be formed. [Example]

[0034] Example 1 Using the film-forming device shown in Figure 1(a), a copper film (metal film) was formed in an area of ​​1 cm x 2 cm. An anode with an iridium oxide surface coating was used. Furthermore, a 1.0 mol / L copper sulfate aqueous solution was used as the plating solution, and the film-forming voltage set by the control device was 0.5 V. Using constant voltage control with this film-forming voltage held constant, the copper film was formed under film-forming conditions of a plating solution temperature of 40°C and an electrolyte membrane pressing force (pressure) of 0.6 MPa. At this time, the current density of the current flowing between the anode and the substrate was 7.0 A / dm 2 was constant.

[0035] Comparative Example 1 Copper films were formed in the same manner as in Example 1. The difference from Example 1 is that the current density was 1.0 A / dm 2 , 2.5A / dm2 , 6.0A / dm 2 The metal film was formed by constant current control in which a constant current of 1000 kJ / s was passed through the electrode.

[0036] [Evaluation test and results] The thickness change of the copper films formed in Example 1 and Comparative Example 1 was measured. The thickness change was calculated using the formula: (thickness at the center of the copper film - thickness at the edge of the copper film) / thickness at the center of the copper film x 100 (%). Furthermore, the arithmetic mean roughness of the center of the copper films formed in Example 1 and Comparative Example 1 was measured. These results are shown in Figures 4(a) and (b). When the film formation voltage was set and the copper film was formed under constant voltage control as in Example 1, it was found that the thickness of the copper film was uniform and the surface roughness of the copper film was small compared to the copper film of Comparative Example 1, as shown in Figures 4(a) and (b). This is because in the case of Comparative Example 1, a current density of 1.0 A / dm 2 , 2.5A / dm 2 , 6.0A / dm 2 Even if a metal film is formed using constant current control with a constant current density of 7.0 A / dm, the voltage between the anode and the substrate is not stable, which is thought to have resulted in large variations in film thickness and increased surface roughness. 2 If a metal film is formed using constant current control in which a constant current (limiting current) is passed, the voltage between the anode and the substrate will become even less stable, which will likely result in greater variation in film thickness and greater surface roughness of the metal film.

[0037] [Confirmation test] A wiring pattern made of a copper film was formed in the same manner as in Example 1. The difference from Example 1 is that three substrates were prepared, and a copper film was formed by constant voltage control under conditions of a film formation voltage of 0.5 V, and in addition, a copper film was formed by constant voltage control under conditions of a film formation voltage of 0.3 V and 0.7 V. The results of the appearance of the copper film, the surface roughness (arithmetic mean roughness) of the center and edge of the copper film, and the film formation rate (current density) for each film formation voltage are shown in Figure 5.

[0038] As shown in Figure 5, when the deposition voltage is set to 0.3 V and the copper film is deposited under constant voltage control, the current density is lower and deposition takes longer than in other cases. In addition, the current flowing between the anode and the substrate varies, resulting in a copper film with a larger surface roughness than in other cases.

[0039] On the other hand, when the deposition voltage was set to 0.5 V and 0.7 V and the copper film was deposited under constant voltage control, the current density was almost the same (7.0 A / dm 2 ), it can be said that the film is formed at the limiting current at which a copper film with a stable thickness can be formed. Furthermore, when the film formation voltage is set to 0.5 V and the copper film is formed under constant voltage control, the surface roughness Ra is smaller than when the film formation voltage is set to 0.7 V, and it can be said that the copper film surface is smoother. [Explanation of symbols]

[0040] 1: film forming device, 11: anode, 13: electrolyte membrane, 14: power supply, 15: container, 61: control device, F: metal film, L: plating solution

Claims

1. A film formation apparatus comprising: an anode; a container that contains a plating solution; and an electrolyte membrane that covers an opening of the container formed at a position opposite the anode, thereby sealing the plating solution in the container; and the apparatus forms a metal coating on a substrate in contact with the electrolyte membrane by electrolytic plating, The film forming apparatus includes: a power source that applies a voltage between the anode and the substrate; a control device for controlling the voltage of the power supply; an ammeter that measures a value of a current flowing between the anode and the substrate when the voltage is applied, The control device With the plating solution contained in the container and the electrolyte membrane in contact with the substrate, while increasing the voltage applied between the anode and the substrate, calculate, as an evaluation value, an amount of change in the current value corresponding to the increment in the voltage or a value corresponding to the magnitude of the amount of change; a voltage at a timing when the evaluation value becomes equal to or less than a predetermined value is set as a film formation voltage; The metal film forming apparatus is characterized in that, during the formation of the metal film, the voltage of the power supply is adjusted to the film formation voltage.

2. The metal film forming device according to claim 1, characterized in that the control device calculates the evaluation value by multiplying the value obtained by dividing the change in the current value passed per unit area by the voltage increment for each voltage increment by the voltage value after the voltage increase, and further dividing the value by the current value passed per unit area after the voltage increase.

3. A film forming method for forming a metal film by the film forming apparatus according to claim 1, comprising: A method for forming a metal film, comprising: forming a metal film on the substrate while applying the film-forming voltage, which is a constant voltage, to the anode and the substrate.

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