Nickel Foil for Manufacturing Thin Film Capacitors and Method for Manufacturing the Same

Abstract

To provide a method for manufacturing an electrolytic nickel foil for use in a thin-film capacitor electrode, which has low and uniform roughness and high gloss without the need for a chemical mechanical polishing (CMP) process, and an electrolytic nickel foil.SOLUTION: An electrolytic nickel foil includes at least one flat surface having a surface roughness of Ra 0.05 μm or less, Rz 0.20 μm or less, and Rt 0.50 μm or less, and a gloss of about 200 GU or more as measured by 60° specular reflection angle measurement.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an electrolytic nickel foil, particularly an electrolytic nickel foil having low roughness and high glossiness that can be used to manufacture a thin film capacitor without undergoing a CMP polishing process, a method for manufacturing the same, and a thin film capacitor manufactured therefrom.

Background Art

[0002] Semiconductor devices including integrated circuits are required to be capable of high-frequency and high-speed signal transmission and to operate at low voltages. In order to provide stable power supply and minimize noise generation, a low impedance of the system is primarily required. Therefore, thin film ceramic thin capacitors with high capacitance density are used in the packages of printed circuit boards.

[0003] A thin film ceramic thin capacitor is manufactured through a process of depositing a dielectric on a metal foil such as nickel, shaping it, and then depositing another metal on the dielectric. For a capacitor with such a structure, a high flatness of the metal foil is required to prevent short circuits. However, conventionally used metal foils have a problem in that they are not suitable for direct use because of their low surface flatness.

[0004] The most widely adopted method for reducing the roughness of the metal foil used in the manufacture of thin film capacitors is chemical-mechanical polishing (CMP). However, as disclosed in Korean Patent Publication No. 10-2012-0007064, although CMP polishing is effective in reducing roughness, it has disadvantages such as high process costs and long processing times.

[0005] To improve the efficiency of the process and the stability of the capacitors to be manufactured, various studies are underway to obtain a metal thin film with low surface roughness. For example, Korean Patent Application No. 10-2017-0174849 discloses a method for manufacturing an iron-nickel alloy foil with excellent surface roughness. However, according to this invention, the average surface roughness (Ra) is only reduced to about 0.1 μm, which is still not sufficient for manufacturing thin film ceramic capacitors.

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide an electrolytic nickel foil that is low in roughness, uniform, and high in glossiness, and can be used to manufacture thin film capacitors without undergoing a separate CMP polishing process.

[0007] Another object of the present invention is to provide a thin film capacitor manufactured from the electrolytic nickel foil.

[0008] Yet another object of the present invention is to provide a method for manufacturing the electrolytic nickel foil with low roughness and high glossiness without a separate CMP polishing process.

[0009] The above and other objects of the present invention can all be achieved by the present invention described below.

Means for Solving the Problems

[0010] 1. One aspect of the present invention relates to an electrolytic nickel foil. The electrolytic nickel foil has an arithmetic mean surface roughness Ra of about 0.05 μm or less, a ten-point mean roughness Rz of about 0.20 μm or less, a maximum height of protrusions Rt of about 0.50 μm or less, and is achieved by an electrolytic nickel foil having at least one flat surface with a 60° specular glossiness of about 200 GU or more.

[0011] 2. In the specific example of 1 above, the electrolytic nickel foil may have a surface Ra of about 0.03 μm or less, an Rz of about 0.15 μm or less, an Rt of about 0.30 μm or less, and a 60° specular glossiness of about 400 GU or more.

[0012] 3. In the specific example of 1 or 2 above, the overall thickness of the electrolytic nickel foil may be about 1 to 100 μm.

[0013] 4. Another aspect of the present invention relates to a method for manufacturing the electrolytic nickel foil. The manufacturing method may include a step of electroplating using an electrolytic solution containing about 400 to 600 g / L of a nickel ion precursor, about 10 to 30 g / L of a pH buffer, and about 0.5 to 2.0 g / L of a roughness regulator, and having a pH of about 1 to 5.

[0014] 5. In the specific example of 4 above, the nickel ion precursor may be selected from one or more of the group consisting of nickel sulfate, nickel sulfamate, nickel chloride, and nickel nitrate.

[0015] 6. In the specific example of 4 or 5 above, the pH buffer may be selected from boric acid or sodium citrate.

[0016] 7. In the specific example of 4 to 6 above, the roughness regulator may be selected from two or more of the group consisting of saccharin, carboxyethyl isothiuronium chloride, sodium allyl sulfonate, butynediol propoxylate, butynediol ethoxylate, propargyl alcohol propoxylate, pyridinium propyl sulfobetaine, and sodium salt of propanesulfonic acid.

[0017] 8. In the specific examples 4 to 7 above, the electrolytic plating may be one in which a current of about 10 to 100 A / dm 2 is applied at a plating solution temperature of about 40 to 60°C.

[0018] 9. Another aspect of the present invention relates to a thin film capacitor including an electrolytic nickel foil, a dielectric formed on top of the electrolytic nickel foil, and a conductive metal layer formed on the dielectric.

Advantages of the Invention

[0019] The present invention provides an electrolytic nickel foil, a method for manufacturing the electrolytic nickel foil, and a capacitor including the electrolytic nickel foil, which have a small arithmetic mean roughness Ra, ten-point mean roughness Rz, and maximum height Rt of protrusions on the surface and a high 60° specular glossiness and high smoothness even in an unpolished state, so that even when a dielectric is thinly coated, the risk of protrusions (nodules) formed on the electrolytic nickel foil protruding from the dielectric layer and contacting the conductive metal layer to cause a discharge (short) is low.

[0020] In addition, since the present invention has low roughness and high glossiness, it can provide an electrolytic nickel foil that can be used in the manufacture of thin film capacitors without a separate polishing process such as a CMP process, and a method for manufacturing the electrolytic nickel foil with excellent process efficiency.

Brief Description of the Drawings

[0021]

Figure 1a

Figure 1b

Figure 2a

Figure 2b

Figure 2c

Figure 2d

Figure 2e

Figure 3a

Figure 3b

Figure 3c

Figure 3d

Figure 3e

Figure 4

Embodiments for Carrying Out the Invention

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, in the description of the present invention, when it is determined that a specific description of related known technologies or configurations may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

[0023] The terms described below are terms defined in consideration of the functions in the present invention, and since these can vary depending on the intentions or conventions of users or operators, etc., the definitions must be based on the overall content of this specification for explaining the present invention.

[0024] Ra, Rz, and Rt used in this specification are parameters indicating the roughness of electrolytic nickel foil, respectively, and are measured according to the ISO 25178 standard.

[0025] Ra means arithmetic mean roughness, Rz means ten-point height of irregularities, and Rt means maximum height of profile.

[0026] The glossiness of the electrolytic nickel foil means 60° specular glossiness and is a value measured according to the JIS Z 8741 standard. The unit is GU (Gloss Unit).

[0027] The following examples are merely illustrative of the implementation means of the present invention, and the present invention is not limited by the following examples. The following examples should be modified or changed according to the configuration to which the present invention is applied and the conditions under which the present invention is applied.

[0028] Manufacture of electrolytic nickel foil

[0029] The electrolytic nickel foil may contain a nickel ion precursor, a pH buffer, and a roughness regulator, and may be produced by electrolytic plating using an electrolytic solution with a pH concentration of 1 to 5.

[0030] The electrolytic solution contains a nickel ion precursor at about 400 to 600 g / L with respect to the total volume of the electrolytic solution, and the surface roughness and glossiness of the electrolytic nickel foil are excellent within the above range. The nickel ion precursor can be used without limitation as long as it is a precursor used for nickel ion plating. Preferably, it can be selected from the group consisting of nickel sulfate, nickel sulfamate, nickel chloride, and nickel nitrate, and particularly preferably, nickel sulfate or nickel sulfamate can be used.

[0031] The roughness regulator can contain one or more compounds selected from saccharin, carboxyethyl isothiuronium chloride, sodium allyl sulfonate, butynediol propoxylate, butynediol ethoxylate, propargyl alcohol propoxylate, pyridinium propyl sulfobetaine, and sodium salt of propanesulfonic acid. Preferably, saccharin and sodium allyl sulfonate can be used in combination.

[0032] The roughness regulator can be used at a concentration of about 0.01 g / L to 2 g / L, preferably about 0.85 to 1.8 g / L, in the electrolytic solution. In a specific example, when saccharin and sodium allyl sulfonate are applied, they can be used at a concentration of about 0.05 g / L to 1.0 g / L respectively.

[0033] In a specific example, the concentration ratio of saccharin to sodium allyl sulfonate may be about 1:0.01 to 100, preferably about 1:0.05 to 1:20.

[0034] The electrolytic solution can contain a pH buffer agent to adjust the pH concentration. The pH buffer agent can be used without particular limitation as long as it can control the pH concentration of the electrolytic solution to an appropriate level, and can be contained at about 10 to 30 g / L based on the total volume of the electrolytic solution, and the efficiency of the process is excellent within this range. On the other hand, as the type of the pH buffer agent, any can be used as long as it does not cause unnecessary chemical reactions according to the purpose of the present invention. For example, boric acid or sodium citrate can be used. When these pH buffer agents are applied, the stability of the process is improved, and an electrolytic nickel foil excellent in roughness can be manufactured.

[0035] The pH buffer agent is contained in the electrolytic solution at about 15 to 50 g / L. The pH concentration and process control are easy within this range.

[0036] The pH concentration of the electrolytic solution is in the range of about 1 to 5, preferably about 2 to 4. The surface roughness of the electrolytic nickel foil is excellent within this range.

[0037] Electroplating can be performed by a normal method. For example, it can be performed by putting a substrate or a mandrel into the electrolytic solution, performing electroplating, and then removing the substrate or the mandrel.

[0038] In a specific example, the electroplating can be manufactured by applying a current of about 10 A / dm 2 ~100 A / dm 2 to the electrolytic solution, for example, a current of about 15 A / dm 2 ~80 A / dm 2 An electrolytic nickel foil excellent in surface roughness can be produced by an efficient process within this range.

[0039] In a specific example, the electroplating can be performed at a temperature of about 40°C to 60°C. Preferably, it may be about 55°C or higher and less than 60°C. An electrolytic nickel foil excellent in roughness and physical properties is formed under these conditions.

[0040] The current application time can be appropriately adjusted according to the amount of the electrolytic nickel foil. In a specific example, it can be applied for a time of about 300 to 500 seconds, preferably about 350 to 450 seconds. Within this range, the process of the electrolytic nickel foil is efficient and a thin electrolytic nickel foil excellent in roughness and gloss can be manufactured.

[0041] The manufactured electrolytic nickel foil may have a thickness of about 1 μm to 100 μm, preferably in the range of about 3 μm to 75 μm. Within this range, it is excellent in durability and versatility and is suitable for use in products such as thin-film capacitors.

[0042] At least one surface of the electrolytic nickel foil of the present invention is provided with a flat surface having excellent roughness.

[0043] For the flat surface of the electrolytic nickel foil, the roughness coefficients measured by the White-light Scanning Interferometry (WSI) and Phase-Shift Interferometry (PSI) methods are Ra = about 1.2 μm or less, Rz = about 1.0 μm or less, and Rt = about 1.5 μm or less.

[0044] In one specific example, the surface roughness is arithmetic mean roughness Ra = about 0.5 or less, ten-point mean roughness Rz = about 0.2 μm or less, and maximum protrusion height Rt = about 0.5 μm or less.

[0045] In another specific example, the surface roughness is Ra = about 0.03 μm or less, Rz = about 0.15 μm or less, and Rt = about 0.3 μm or less.

[0046] In still another specific example, the surface roughness is Ra = about 0.01 μm to 0.03 μm, Rz = about 0.05 μm to 0.15 μm, and Rt = about 0.1 μm to 0.2 μm.

[0047] Within the above roughness range, the flat surface has excellent roughness without a separate polishing process, and has the advantage of reducing surface defects. If the roughness coefficient exceeds the above range, it may have an adverse effect on the performance of the dielectric layer in the capacitor, resulting in insulation resistance and leakage current. It is possible to provide an excellent electrolytic nickel foil that is not only flat overall within the range of the surface roughness but also has no particularly protruding portions.

[0048] Also, the 60° specular glossiness of the flat surface may be about 50 GU to 800 GU, for example, about 200 GU to 700 GU. When the optical properties of the flat surface are within the above range, the surface is uniform and excellent in flatness.

[0049] Thin film ceramic thin film capacitor

[0050] As shown in FIG. 4, the thin-film ceramic thin-film capacitor 100 including the electrolytic nickel foil of the present invention has a structure in which a nickel thin-film layer 110, a dielectric layer 120, and a conductive metal layer 130 are sequentially laminated.

[0051] After forming the electrolytic nickel foil, dielectric crystal grains are formed on the surface of the electrolytic nickel foil without going through a separate polishing process to coat the entire electrolytic nickel foil. At this time, as a method for forming the thin-film dielectric, sputtering, laser grinding, chemical vapor deposition, and chemical solution deposition methods can be used, but in order to improve the denseness of the dielectric, the sputtering method is preferable.

[0052] An ordinary technician can easily fabricate a capacitor from the electrolytic nickel foil of the present invention through methods such as the sputtering method. For example, the electrolytic nickel foil is positioned on a vapor deposition plate, and after heating the vapor deposition plate to about 500 to 800 °C, a dielectric can be formed on the upper part of the electrolytic nickel foil by sputtering the dielectric.

[0053] After depositing the dielectric with a certain thickness, the dielectric can be plastically deformed to improve the crystallization and densification of the dielectric layer.

[0054] To deposit the electrode, after freezing an electrolytic nickel foil with a dielectric formed on its upper part, a thin-film capacitor can be completed by depositing the electrode on its surface through a sputtering method. Usually, a gold or copper electrode is used for the electrode, but any material that enables electrical connection can be used without limitation.

[0055] Hereinafter, the configuration and operation of the present invention will be described in more detail through preferred embodiments of the present invention. However, this is merely presented as a preferred exemplification of the present invention and in no way limits the present invention thereby.

[0056] Contents not described herein can be technically analogized sufficiently by those skilled in this technical field, so the description thereof is omitted.

[0057] <Example 1>

[0058] An electrolytic solution with a pH of about 3 containing about 450 g / L of nickel sulfate as a nickel ion precursor, about 25 g / L of boric acid as a pH buffer, about 0.1 g / L of saccharin and about 0.8 g / L of sodium allylsulfonate as roughness regulators was used. At a temperature of about 55 °C of the electrolytic solution, a current was applied at a current density of about 20 A / dm 2 for about 400 seconds to produce a nickel foil with a thickness of about 27 μm.

[0059] The produced electrolytic nickel foil had an arithmetic mean surface roughness Ra of about 0.05 μm, a ten-point mean roughness Rz of about 0.19 μm, a maximum protrusion height Rt of about 0.37 μm without being polished, and a 60° specular glossiness of about 445 GU.

[0060] <Examples 2 to 10>

[0061] Electrolytic nickel foils were produced in the same manner as in Example 1 except that the electrolytic solutions and electrolysis conditions described in Table 1 below were applied.

[0062]

Table 1

[0063] <Comparative Examples 1 to 4>

[0064] Electrolytic nickel foil was produced under the same conditions and by the same method as in Example 1, except that the electrolytic solution and electrolysis conditions described in Table 2 below were applied.

[0065]

Table 2

[0066] <Evaluation of Physical Properties>

[0067] Roughness measurement

[0068] Using a roughness measuring instrument (Nano System, model NV-2700), the roughness distribution over the entire surface of one side of the test piece was measured according to the ISO 25178 standard, and Rz, Rt, and Ra in the vertical and horizontal directions were measured with reference to the center point of the test piece.

[0069] Gloss measurement

[0070] The specular gloss at an incident angle of 60° was measured according to the JIS Z 8741 standard using a gloss meter (IG-410 Ultra High Gloss Meter, Horiba). The unit of gloss measurement is GU (Gloss Unit).

[0071] The roughness and gloss of each of the examples and comparative examples measured by the above method are as tabulated in Table 3 below.

[0072]

Table 3

[0073] As can be seen from Table 3 above, it can be confirmed that in Examples 1 to 10, Ra, Rz, and Rt, which are surface roughness coefficients, are all very low, and the glossiness (Gs 60) is high, as compared with Comparative Examples 1 to 4.

[0074] SEM photograph evaluation

[0075] The flat surfaces of the electrolytic nickel foils of Example 1 and Comparative Example 1 were magnified at a ratio of 1,000 times and SEM photographs were taken. The results are as shown in FIGS. 1a and 1b, respectively. Comparing FIGS. 1a and 1b, it can be confirmed that not only is the height of the surface protrusions of Example 1 lower than that of Comparative Example 1, but also the distribution of the heights is uniform.

[0076] 3D profiling

[0077] 3D profiling was performed on the flat surfaces of the electrolytic nickel foils of Example 1 and Comparative Example 1 by a white light scanning interferometer method, and the profiling results shown in FIGS. 2a to 2e for Example 1 and FIGS. 3a to 3e for Comparative Example 1 were derived.

[0078] Comparing FIG. 2a and FIG. 3a obtained through 3D profiling, it can be confirmed that Example 1 has a surface with regularly and low-height surface protrusions as compared with Comparative Example 1. From the fact that discharge, that is, short, occurs at protrusion portions that are significantly higher than the surroundings, it can be easily understood that Example 1 has a very excellent morphology.

[0079] FIGS. 2c and 3c are graphs showing the surface roughness distribution diagrams of the electrolytic nickel foils of Example 1 and Comparative Example 1, respectively. It is confirmed that the distribution of the protrusion height (Rz) in FIG. 2c is narrow and the maximum value (Rt) of the protrusion height is low, which means that the surface of Example 1 is uniform.

[0080] FIGS. 2d and 3d are graphs showing the lateral roughness distribution diagrams of the electrolytic nickel foils of Example 1 and Comparative Example 1, respectively. It can be seen that FIG. 2d of Example 1 is much flatter and has a higher smoothness than FIG. 3d of Comparative Example 1.

[0081] FIG. 2e and FIG. 3e are graphs showing the longitudinal roughness distribution diagrams of the electrolytic nickel foils of Example 1 and Comparative Example 1, respectively, and it can be seen that FIG. 2e of Example 1 is much flatter and has higher smoothness than FIG. 3e of Comparative Example 1.

[0082] Manufacture of capacitor

[0083] <Example 11>

[0084] The electrolytic nickel foil of Example 1 was placed on a sputtering deposition plate, and a pressure of about 3 torr was maintained under a chamber atmosphere composed of 95% argon and 5% oxygen. After heating the deposition plate to about 650 ° C, barium titanate was sputtered onto the electrolytic nickel foil using a barium titanate (BaTiO3) target having a diameter of about 3 inches with an RF power of about 150 W. Deposition was carried out for about 150 minutes to form a dielectric having a thickness of about 0.7 μm.

[0085] The electrolytic nickel foil coated with barium titanate was plastically deformed at an oxygen partial pressure of about 2×10 -7 atm at a temperature of about 900 ° C for about 2 hours and then frozen. A capacitor was fabricated by depositing a copper electrode of about 0.2 μm on the surface of the electrolytic nickel foil coated with barium titanate through a sputtering method.

[0086] <Comparative Example 5>

[0087] A capacitor was fabricated in the same manner as in Example 11 for the electrolytic nickel foil of Comparative Example 1.

[0088] Capacitor short circuit experiment

[0089] For the completed capacitor samples, a digital LCR meter was used to check for the presence or absence of a short circuit by applying a bias voltage of approximately -10 to 10 V at room temperature (25°C), approximately 1 kHz, and an oscillating voltage of approximately 50 mV. As a result, while no short circuit occurred in the capacitor manufactured with the electrolytic nickel foil of Example 1, a short circuit occurred in the capacitor manufactured with the electrolytic nickel foil of Comparative Example 1. Examples of embodiments of the present invention are listed in the following items [Aspect 1] to [Aspect 8]. [Aspect 1] An electrolytic nickel foil characterized in that at least one flat surface has an arithmetic mean roughness Ra of 0.05 μm or less, a ten-point mean roughness Rz of 0.20 μm or less, a maximum height of protrusions Rt of 0.50 μm or less, and a 60° specular glossiness of 200 GU or more. [Aspect 2] The electrolytic nickel foil according to Aspect 1, wherein the flat surface has Ra of 0.03 μm or less, Rz of 0.15 μm or less, Rt of 0.30 μm or less, and a 60° specular glossiness of 400 GU or more. [Aspect 3] The electrolytic nickel foil according to Aspect 1 or Aspect 2, wherein the thickness of the electrolytic nickel foil is 1 to 100 μm. [Aspect 4] A method for manufacturing an electrolytic nickel foil, comprising the step of electroplating using an electrolytic solution containing 400 to 600 g / L of a nickel ion precursor, 10 to 30 g / L of a pH buffer, and 0.5 to 2.0 g / L of a roughness regulator, and having a pH of 1 to 5. [Aspect 5] The method for manufacturing an electrolytic nickel foil according to Aspect 4, wherein the nickel ion precursor is selected from one or more of the group consisting of nickel sulfate, nickel sulfamate, nickel chloride, and nickel nitrate. [Aspect 6] The method for producing an electrolytic nickel foil according to Aspect 4, wherein the roughness regulator is selected from two or more kinds of saccharin, carboxyethyl isothiuronium chloride, sodium allyl sulfonate, butynediol propoxylate, butynediol ethoxylate, propargyl alcohol propoxylate, pyridinium propyl sulfobetaine, and sodium salt of propanesulfonic acid. [Aspect 7] The electrolytic plating is characterized in that a current with a current density of 10 to 100 A / dm is applied at a plating solution temperature of 40 to 60 °C. 2 The method for producing an electrolytic nickel foil according to Aspect 4. [Aspect 8] A thin film capacitor comprising the electrolytic nickel foil according to Aspect 1 or Aspect 2, a dielectric formed on the upper part of the electrolytic nickel foil, and a conductive metal layer formed on the dielectric.

Claims

1. A method for manufacturing an electrolytic nickel foil for manufacturing a thin film capacitor, wherein Ra is 0.05 μm or less, Rz is 0.20 μm or less, Rt is 0.50 μm or less, and the 60° specular glossiness is 400 GU or more, comprising the step of electrolytic plating using an electrolytic solution containing 400 to 600 g / L of a nickel ion precursor, 10 to 30 g / L of a pH buffer, and a roughness regulator, and having a pH of 1 to 5, wherein the roughness regulator contains 0.1 to 1 g / L of saccharin and 0.6 to 0.8 g / L of sodium allylsulfonate.

2. The method for manufacturing an electrolytic nickel foil for manufacturing a thin film capacitor according to claim 1, wherein in the roughness regulator, the concentration ratio of saccharin to sodium allylsulfonate is 1:0.05 to 1:

20.

3. The method for manufacturing an electrolytic nickel foil for manufacturing a thin film capacitor according to claim 1, wherein the roughness regulator is contained in the range of 0.5 to 2.0 g / L.

4. The method for manufacturing an electrolytic nickel foil for manufacturing a thin film capacitor according to claim 1, wherein the nickel ion precursor is selected from one or more of the group consisting of nickel sulfate, nickel sulfamate, nickel chloride, and nickel nitrate.

5. The electrolytic plating is carried out at a plating solution temperature of 40 to 60°C and a current density of 10 to 100 A / dm ２ while applying a current therebetween. A method for manufacturing an electrolytic nickel foil for manufacturing a thin film capacitor according to claim 1, characterized in that

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