JP2019183241A - Nickel film depositing method - Google Patents

Abstract

To provide a nickel film depositing method capable of preventing a solid electrolyte membrane from being integrated with a nickel film in contact with the solid electrolyte membrane.SOLUTION: A nickel film depositing method includes at least an electrochemical impedance measuring step S11, a current density identifying step S12, and a nickel film depositing step S13. The electrochemical impedance measuring step deposits the nickel film under the condition that the current conducted between an anode 11 and cathode W becomes a different current density and measures an electrochemical impedance of a portion containing a solid electrolyte membrane 13 and a nickel film F in contact with the solid electrolyte membrane per different current density while changing a voltage applied between the anode 11 and the cathode W from a high frequency to a low frequency. The current density identifying step identifies the current density when a value of a real number component on a low frequency side decreases when creating a Cole-Cole plot diagram including a coordinate system in which an X axis serves as the real number component and a Y axis serves as an imaginary component from the electrochemical impedances measured per different current density by plotting in an order of measurement from the high frequency to the low frequency. The nickel film depositing step deposits the nickel film F on a surface of the cathode W at a current density smaller than the identified current density.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for forming a nickel film using a solid electrolyte membrane.

  As a method for forming this type of metal film, for example, in Patent Document 1, a solid electrolyte membrane impregnated with metal ions so as to be in contact with the cathode is placed between the anode and the cathode, and the anode and cathode A method of forming a metal film by applying a voltage between the electrodes and reducing metal ions on the surface of the cathode is disclosed.

  In the film forming method described in Patent Document 1, the resistance value of the solid electrolyte membrane and the charge transfer resistance value are calculated from the electrochemical impedance for each film forming time. From these resistance values, a film formation time for completing the ion exchange of metal ions of the solid electrolyte membrane and a film formation time for integrating the solid electrolyte membrane and the metal film in contact with the solid electrolyte membrane are specified. Thereby, the metal film can be stably formed without the solid electrolyte film and the metal film in contact with the solid electrolyte film being integrated.

JP 2017-137546 A

  However, for example, a copper film and a nickel film differ in the form of crystal precipitation and also in the composition, temperature, pH, etc. of the electrolytic solution. For this reason, when the nickel film is formed by the method described in Patent Document 1, the solid electrolyte film and the nickel film may be integrated. This is because nickel hydroxide is generated due to the lack of nickel ions due to current concentration in the portion including the solid electrolyte membrane and the nickel film in contact therewith, and the generated nickel hydroxide is dehydrated to become nickel oxide. It depends. As a result, it is considered that the solid electrolyte membrane and the nickel film in contact therewith were physically and chemically adhered.

  The present invention has been made in view of the above points. In the present invention, there is provided a method for forming a nickel film capable of preventing the solid electrolyte film and the nickel film in contact with the film from being integrated during film formation. provide.

  In order to solve the above problems, a nickel film forming method according to the present invention includes a solid electrolyte membrane impregnated with nickel ions so as to be in contact with the cathode between the anode and the cathode, A method for forming a nickel film, in which a current is passed between the cathode and a nickel film derived from the nickel ions on the surface of the cathode, wherein the current is applied between the anode and the cathode. After the film is formed under the condition that the currents have different current densities, the voltage applied between the anode and the cathode is changed from a high frequency to a low frequency, and the solid electrolyte membrane and the nickel in contact therewith are changed. From the step of measuring the electrochemical impedance of the portion including the film for each of the different current densities and the electrochemical impedance measured for each of the different current densities, the X axis is used as a real component. When creating a Cole-Cole plot diagram having a coordinate system with the Y-axis as an imaginary component by plotting in the order measured from the high frequency to the low frequency, the value of the real component on the low frequency side is It includes at least a step of specifying the current density when it is decreased, and a step of forming the nickel film on the surface of the cathode at a current density smaller than the specified current density.

  According to the present invention, after the nickel coating is formed, the electrochemical impedance of the portion including the solid electrolyte membrane and the nickel coating in contact therewith is measured for each different current density. When creating a Cole-Cole plot from the electrochemical impedance measured for each current density, the current density when the value of the real component decreases on the low frequency side is specified. Since the nickel film is formed at a current density smaller than the specified current density, integration of the solid electrolyte film and the nickel film in contact with the film can be prevented during the film formation.

It is typical sectional drawing for demonstrating the film-forming method of the nickel membrane | film | coat concerning this embodiment, Comprising: (a) is typical sectional drawing explaining the state before film-forming of the film-forming apparatus, (b ) Is a schematic cross-sectional view illustrating a state of the film forming apparatus 1 during film formation. It is a flowchart explaining the process of the film-forming method of the nickel membrane | film | coat F of this embodiment. (A) Cole-Cole plot obtained from electrochemical impedance before and after film formation when current density is 50, 100, and 150 mA / cm ² , (b) is a partially enlarged view of (a). is there. It is the microscope image of the surface of the test body concerning the board | substrate after forming a nickel membrane, Comprising: (a)-(c) is the test which formed into a film with the current density of 50, 100, and 150 mA / cm < ² >, respectively. It is an image of the body.

  Embodiments according to the present invention will be described below with reference to FIGS. FIG. 1 is a schematic cross-sectional view for explaining a method for forming a nickel film F according to the present embodiment. FIG. 1A is a schematic diagram for explaining a state of the film forming apparatus 1 before film formation. FIG. 1B is a schematic cross-sectional view illustrating a state of the film forming apparatus 1 during film formation.

1. About Film Forming Apparatus 1 In this embodiment, as shown in FIGS. 1A and 1B, a nickel film is formed on the surface of the substrate W using the film forming apparatus 1 with the substrate W as a cathode. The substrate W serving as the cathode is made of a conductive metal material, and examples thereof include copper, nickel, silver, and gold. In addition, the substrate W may be coated with the above-described metal material on an insulating base material.

  As shown in FIGS. 1A and 1B, a film forming apparatus 1 includes a metal anode 11, a solid electrolyte membrane 13 disposed between the anode 11 and a substrate W (cathode), and an anode 11. And a power supply unit 16 that allows current to flow between the substrate W and the substrate W. In the state where the solid electrolyte membrane 13 is in contact with the surface of the substrate W, a constant voltage is applied between the anode 11 and the substrate W by the power supply unit 16, so that the film is formed between the anode 11 and the substrate W at the time of film formation. Current flows.

  In the present embodiment, the film forming apparatus 1 further includes a housing 15, and the housing 15 includes a positive electrode 11 and a solution L (hereinafter referred to as a nickel solution L) containing nickel ions as a material of a nickel film to be formed. And is housed. More specifically, a space 17 for accommodating the nickel solution L is formed between the anode 11 and the solid electrolyte membrane 13. In this embodiment, the anode 11 and the solid electrolyte membrane 13 are spaced apart from each other. However, if nickel ions can be supplied to the solid electrolyte membrane 13, the solid electrolyte membrane 13 is formed on the surface of the anode 11. It may be in contact.

  The anode 11 may have a block shape or a flat plate shape as long as the anode 11 has a size that covers a region where the substrate W is formed. The material of the anode 11 is the same material as that of the nickel film, and is preferably an anode that is soluble in the nickel solution L. Thereby, the film-forming speed | rate of a nickel membrane | film | coat can be raised. Since the nickel solution L before film formation contains nickel ions, the anode 11 may be an anode that is insoluble in the nickel solution L.

  In addition, when the anode 11 and the solid electrolyte membrane 13 are in contact with each other, an anode made of a porous material that allows the nickel solution L to pass through the anode 11 and supplies nickel ions to the solid electrolyte membrane 13 is used. May be.

  In the present embodiment, after forming nickel films on the surfaces of the plurality of substrates W, the solid electrolyte film 13 is replaced, and the nickel films F are formed on the surfaces of the substrates W. The solid electrolyte membrane 13 can be impregnated (contained) with nickel ions by being brought into contact with the above-described nickel solution L, and nickel derived from nickel ions can be deposited on the surface of the substrate W when a voltage is applied. If it is, it will not specifically limit. The film thickness of the solid electrolyte membrane 13 is 100 to 200 μm. Examples of the material of the solid electrolyte membrane include cations such as fluorine resins such as Nafion (registered trademark) manufactured by DuPont, hydrocarbon resins, polyamic acid resins, and selemions (CMV, CMD, CMF series) manufactured by Asahi Glass. A resin having an exchange function can be mentioned.

  Examples of the nickel solution L include a solution containing nickel chloride, nickel sulfate, nickel pyrophosphate, and the like. Further, the nickel solution L further includes a pH buffer solution (pH buffer solution) that has a buffer capacity within a predetermined pH range and does not form an insoluble salt and a complex with nickel ions during film formation. preferable. Furthermore, in order not to inhibit the movement of nickel ions in the solid electrolyte membrane 13, the cation contained in the pH buffer solution is preferably a metal having a smaller ionization tendency than nickel. Examples of such a pH buffer solution include an acetic acid-nickel acetate buffer solution and a succinic acid-nickel succinate buffer solution.

  Furthermore, the film forming apparatus 1 of the present embodiment may include a pressurizing device (not shown) on the top of the housing 15. The pressurizing device can be a hydraulic or pneumatic cylinder, and is a device that presses the substrate W with the solid electrolyte membrane 13. As a result, as shown in FIG. 1B, the nickel solution L is disposed on the surface of the substrate W via the solid electrolyte membrane 13, and the substrate is pressed uniformly by the solid electrolyte membrane 13 by the fluid pressure. A nickel film F can be formed on W. When the anode 11 and the solid electrolyte membrane 13 are in contact, the substrate W may be pressed with the solid electrolyte membrane 13 via the anode 11.

  The film forming apparatus 1 according to the present embodiment further includes a metal pedestal 12 on which the substrate W is placed, and the metal pedestal 12 is electrically connected to the negative electrode of the power supply unit 16. Thereby, the substrate W can be conducted to the negative electrode of the power supply unit 16. On the other hand, the positive electrode of the power supply unit 16 is electrically connected (conducted) to the anode 11 built in the housing 15. The power supply unit 16 may be either a DC power supply or an AC power supply as long as it can form a film.

  By the way, according to the knowledge of the inventor, as shown in the above-described problem, when the nickel film F is formed, the solid electrolyte film 13 and the nickel film F may be brought into close contact with each other. This occurs when the current density during film formation is high, the nickel ion concentration of the nickel solution is low, the film formation temperature is high, the pressure of the solid electrolyte film during film formation is high, or a combination of these. was there. Therefore, the inventor attaches the impedance analyzer 20 to the film forming apparatus 1 while paying attention to the current density during film formation.

  Specifically, in the film forming apparatus 1 according to the present embodiment, the counter electrode 18 disposed on the anode 11, the working electrode 19 disposed on the substrate W, and the anode 11 and the solid electrolyte membrane 13 are disposed. A reference electrode 14 is attached.

  Specifically, the counter electrode 18 passes through the housing 15, one end of the counter electrode 18 is electrically connected to the anode 11, and the other end is exposed to the outside. The working electrode 19 penetrates the metal base 12, one end of the working electrode 19 is electrically connected to the substrate W, and the other end is exposed to the outside. The reference electrode 14 passes through the housing 15, one end of the reference electrode 14 is in contact with the nickel solution L, and the other end is exposed to the outside. When the solid electrolyte membrane 13 is in contact with the surface of the anode 11, the reference electrode 14 is arranged such that one end of the reference electrode 14 is inserted into the solid electrolyte membrane 13 and the other end is exposed to the outside. May be.

  As will be described later, the other end of the counter electrode 18, the working electrode 19, and the reference electrode 14 are connected to the impedance analyzer 20, so that the solid electrolyte membrane 13 and the nickel coating F in contact with the solid electrolyte membrane 13 are formed after the film formation. The electrochemical impedance of the portion containing can be measured. As a material for the counter electrode 18, the working electrode 19, and the reference electrode 14, any material that does not corrode with respect to the nickel solution L may be used. For example, platinum (Pt) may be used.

2. Regarding Film Formation Method of Nickel Film F FIG. 2 is a flowchart for explaining the steps of the film formation method of the nickel film F of the present embodiment. First, in the electrochemical impedance measurement step S11, the electrochemical impedance is measured after the nickel film F is formed under the condition that the currents flowing between the anode 11 and the substrate W (cathode) have different current densities. The method for forming the nickel film F in this step is the same as that in the later-described film forming step S13 except for the current density, and the details will be described in the film forming step S13.

  Specifically, after forming the nickel film F under the conditions of each current density, the anode 11 (specifically, the counter electrode 18) and the substrate W (specifically, in a state where the solid electrolyte film 13 is in contact with the nickel film F). Specifically, the electrochemical impedance of the portion including the solid electrolyte membrane 13 and the nickel coating F in contact therewith is measured while changing the voltage applied to the working electrode 19) from a high frequency to a low frequency. This electrochemical impedance measurement is performed on each film formed at different current densities. In the present embodiment, the electrochemical impedance is the electrochemical impedance between the reference electrode 14 and the working electrode 19. The method for measuring the electrochemical impedance will be described in detail in the following confirmation test.

  Next, a current density specifying step S12 is performed. In this process, first, from the electrochemical impedance measured at different current densities, a Cole-Cole plot diagram having a coordinate system with the X axis as the real component and the Y axis as the imaginary component is changed from the high frequency to the low frequency. Plot points corresponding to each component in the order of measurement. At this time, the current density when the value of the real component decreases on the low frequency side is specified.

  Specifically, when creating a Cole-Cole plot diagram for the nickel film F formed at each current density by plotting in order of measurement from high frequency to low frequency, the real component on the low frequency side Specify the Cole-Cole plot diagram where the value of decreases. Here, according to experiments by the inventors, it is found that when the film is formed at a current density corresponding to the specified Cole-Cole plot diagram, the nickel film F and the solid electrolyte film 13 are integrated. It has been found that these integrations become more prominent as the density increases. Therefore, when the nickel film F is formed at a current density smaller than the current density when the value of the real component decreases on the low frequency side, the solid electrolyte film 13 and the nickel film F in contact therewith are integrated. Never do.

  Next, a film forming step S13 is performed. In this step, the nickel film F is formed on the surface of the substrate W at a current density smaller than the current density specified in the current density specifying step S12. The other film formation conditions are the same as the film formation conditions in the electrochemical impedance measurement step S11.

  Specifically, first, the solid electrolyte membrane 13 is replaced with a new solid electrolyte membrane 13. Next, as shown in FIG. 1A, a new substrate W is placed on the metal base 12. Next, as shown in FIG. 1B, the replaced solid electrolyte membrane 13 is brought into contact with the substrate W using a pressurizing device (not shown). Thereby, the solid electrolyte membrane 13 impregnated with nickel ions is placed between the anode 11 and the substrate W so as to be in contact with the substrate W.

  Next, a constant voltage is applied by the power supply unit 16 so that the current supplied between the anode 11 and the substrate W is smaller than the specified current density. Thereby, the nickel ions contained in the solid electrolyte membrane 13 are reduced on the surface of the substrate W, and the nickel film F derived from the nickel ions can be formed on the surface of the substrate W.

  Here, in this embodiment, since the film is formed at a current density smaller than the current density specified in the current density specifying step S12, in the film forming step S13, the solid electrolyte membrane 13 is brought into contact with the film during the film formation. The nickel film F is not integrated. For this reason, in the second and subsequent film formations, the solid electrolyte membrane 13 and the nickel coating F in contact therewith are not integrated with each other by simply replacing the substrate W with a new one. A film can be formed.

<Confirmation test>
A method for measuring electrochemical impedance and a method for specifying current density will be described by the following confirmation test. First, the film forming apparatus 1 shown in FIG. 1 was prepared. A nickel plate is used as the anode 11 of the film forming apparatus 1, and an aqueous solution containing 0.95 M nickel chloride (NiCl ₂ ) and 0.05 M nickel acetate (Ni (CH ₃ COO) ₂ ) as the nickel solution L. (PH 4.0 and current density 25-175 mA / cm < ² >) were used. In addition, a substrate W in which gold (Au) was formed by sputtering on the surface of a 2-inch silicon (Si) wafer was used. The film thickness of the Au film was 50 nm. Further, a platinum wire was used as the reference electrode 14.

  Next, as an impedance analyzer 20 for measuring electrochemical impedance, an impedance measuring device (HZ7000 (FRA board, 3A booster extension)) manufactured by Hokuto Denko was prepared. As shown in FIGS. 1A and 1B, the counter electrode 18, the working electrode 19, and the reference electrode 14 of the film forming apparatus 1 were connected to the prepared impedance measuring apparatus.

  First, the substrate W was placed on the metal base 12 and the solid electrolyte membrane 13 was attached to the housing 15. Next, as shown in FIG. 1B, after the solid electrolyte membrane 13 was disposed between the anode 11 and the substrate W so as to be in contact with the substrate W, the electrochemical impedance before film formation was measured. .

  Specific measurement conditions for electrochemical impedance were a potential amplitude of 10 mV, a frequency range of 10 mHz to 100 kHz, logarithmically sweeping 5 digits per digit, and a voltage between the counter electrode 18 and the working electrode 19 being 0.05V. Further, the pressure and temperature of the nickel solution L at the time of measurement were set to about 1.0 MPa and 70 ° C., respectively, which are the same as film forming conditions described later.

Next, a current having a current density of 50 mA / cm ² was passed between the anode 11 and the substrate W (cathode) to form a nickel film. The film formation time was 1 minute, the pressure for pressing the substrate W was about 1.0 MPa, and the temperature was 70 ° C. The pressurization was performed by a hydraulic method in which the pressure of the nickel solution in the space 17 was increased.

  Next, the electrochemical impedance after film formation was measured. The electrochemical impedance measurement conditions were the same as the electrochemical impedance measurement conditions before film formation described above. Next, the substrate W and the solid electrolyte membrane 13 were removed.

In the same manner as in the case of the current density of 50 mA / cm ² described above, the electrochemical impedance before film formation is measured for the new solid electrolyte membrane 13, and then the film formation with a current density of 100 mA / cm ² is performed. Under the condition, after the Ni film was formed, the measurement of electrochemical impedance was measured. Further, in the same manner as in the case of the current density of 50 mA / cm ² described above, the electrochemical impedance before film formation is measured for the new solid electrolyte membrane 13, and then the current density is 150 mA / cm ² . Under the film forming conditions, after the Ni film was formed, the measurement of electrochemical impedance was measured. The film formation rates at a current efficiency of 100% at current densities of 50, 100, and 150 mA / cm ² are 1.0, 2.0, and 3.0 μm / min, respectively.

<Result>
A Cole-Cole plot diagram was created from the electrochemical impedance measured before and after the film formation. The results are shown in FIGS. 3 (a) and 3 (b). FIG. 3A is a Cole-Cole plot obtained from the electrochemical impedance before and after film formation when the current density is 50, 100, and 150 mA / cm ² , and FIG. It is a partially enlarged view of a).

  In the coordinate system of the Cole-Cole plot diagrams shown in FIGS. 3A and 3B, the X axis and the Y axis are the real component Z ′ (Ω) and the imaginary component Z ″ (Ω), respectively. In addition, since the Cole-Cole plot diagram is created by plotting points corresponding to the real component and the imaginary component in the order measured from the high frequency to the low frequency, the frequency decreases from the left side to the right side of the diagram.

As shown in FIG. 3A, at three different current densities (50, 100, and 150 mA / cm ² ), the overall impedance after film formation was smaller than the total impedance before film formation. .

As shown in FIG. 3B, the impedance spectrum after film formation has a substantially semicircular locus in the high-frequency region when the current density is 50 and 100 mA / cm ² among three different current densities. It was observed that the real component Z ′ increased as the frequency became lower. On the other hand, in the case of a current density of 150 mA / cm ² , although a substantially semicircular locus was observed in the high frequency region, it was confirmed that the real component Z ′ was reduced on the low frequency side (FIG. 3B). ) (See the dotted circle). This is presumably because the solid electrolyte membrane 13 and the nickel coating F in contact therewith were strongly adhered (integrated), so that the current flowed easily and the resistance decreased.

Here, the inventors observed the surface of the test body according to the substrate removed after film formation in the case of three different current densities, respectively, with a microscope. The results are shown in FIG. FIG. 4 is a microscopic image of the surface of the test body according to the substrate W after the nickel film is formed, and FIGS. 4A to 4C are 50, 100, and 150 mA / cm ² , respectively. It is an image of the test body formed into a film with the current density.

As can be seen from FIGS. 4A to 4C, the integration of the solid electrolyte membrane 13 and the nickel coating F was confirmed only when the current density was 150 mA / cm ² among the three different current densities. . As described above, the impedance spectrum in the case of a current density of 150 mA / cm ² has an abnormal waveform in which the real component Z ′ decreases on the low frequency side. Therefore, since this abnormal waveform becomes an index of integration of the solid electrolyte membrane 13 and the nickel coating F, the current density indicating the abnormal waveform can be specified. Thereby, the integration of the solid electrolyte membrane 13 and the nickel coating F can be prevented by forming the nickel coating with a current density smaller than the specified current density.

  Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention described in the claims. Design changes can be made.

  11: Anode, 13: Solid electrolyte membrane, F: Nickel coating, W: Substrate (cathode), S11: Electrochemical impedance measuring step, S12: Current density specifying step, S13: Film forming step

Claims (1)

A solid electrolyte membrane impregnated with nickel ions is placed between the anode and the cathode so as to be in contact with the cathode, a current is passed between the anode and the cathode, and the nickel is formed on the surface of the cathode. A nickel film forming method for forming a nickel film derived from ions,
Under the condition that the current passed between the anode and the cathode has different current densities, the voltage applied between the anode and the cathode is changed from a high frequency to a low frequency, Measuring the electrochemical impedance of the portion including the solid electrolyte membrane and the nickel coating in contact therewith for each of the different current densities;
A Cole-Cole plot diagram having a coordinate system with the X axis as a real component and the Y axis as an imaginary component is measured from the high frequency to the low frequency from the electrochemical impedance measured for each different current density. Identifying the current density when the value of the real component is reduced on the low frequency side when creating by plotting
Forming a nickel film on the surface of the cathode at a current density lower than the specified current density.