Nickel Foil for Manufacturing Thin Film Capacitors and Its Manufacturing Method

Abstract

The present invention relates to an electrolytic nickel foil, wherein the surface roughness Ra of the flat surface on at least one side of the electrolytic nickel foil is 0.05 μm or less, Rz is 0.2 μm or less, and Rt is 0.5 μm or less, and the glossiness measured by measuring the specular reflection angle of 60° is at least 200 GU.

Description

Technical Field

[0001] The present invention relates to an electrolytic nickel foil, and particularly to a low-roughness and high-gloss electrolytic nickel foil capable of manufacturing a thin-film capacitor without undergoing a chemical mechanical polishing (CMP) process, a method for preparing the electrolytic nickel foil, and a thin-film capacitor manufactured from the electrolytic nickel foil. Background Art

[0002] Semiconductor devices including integrated circuits need to be able to transmit high-frequency and high-speed signals and operate at low voltages. In order to supply power stably and minimize noise generation at the same time, it is first necessary for the system to have a low impedance. Therefore, thin-film ceramic thin-film capacitors with a high static capacitance density are used for printed circuit board packaging.

[0003] A thin-film ceramic thin-film capacitor is manufactured by depositing a dielectric on a metal foil such as nickel, firing it, and then depositing a metal on the dielectric. In the case of a capacitor having such a structure, the metal foil needs to have a high flatness to prevent short circuits, but the conventionally used metal foil has a low surface flatness and is therefore not suitable for direct use.

[0004] Chemical mechanical polishing (CMP) is the most widely adopted method for reducing the roughness of metal foils used to manufacture thin-film capacitors. As described in Korean Patent Application Publication No. 10-2012-0007064, CMP is effective in reducing roughness, but its disadvantages are high processing costs and long processing times.

[0005] To obtain a metal thin film with a low surface roughness to improve processing efficiency and the stability of the manufactured capacitor, various studies have been conducted. For example, Korean Patent Application No. 10-2017-0174849 discloses a method for preparing 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 insufficient for manufacturing a thin-film ceramic thin-film capacitor. Summary of the Invention

[0006] [Technical Problem]

[0007] An object of the present invention is to provide an electrolytic nickel foil that can manufacture a thin-film capacitor without undergoing a separate chemical mechanical polishing (CMP) process because the electrolytic nickel foil has low and uniform roughness and high gloss.

[0008] The present invention also aims to provide a thin-film capacitor manufactured from the electrolytic nickel foil.

[0009] The present invention also aims to provide a method for manufacturing an electrolytic nickel foil, which does not require a separate CMP process due to the low roughness and high gloss of the electrolytic nickel foil.

[0010] All of the above and other objects of the present invention can be achieved by the present invention described below.

[0011] [Technical Solution]

[0012] 1. One aspect of the present invention provides an electrolytic nickel foil. The electrolytic nickel foil is obtained by making at least one surface of the electrolytic nickel foil include a flat surface, and the arithmetic mean surface roughness (Ra) of the flat surface is about 0.05 μm or less, the ten-point mean surface roughness (Rz) is about 0.20 μm or less, the maximum surface protrusion height (Rt) is about 0.50 μm or less, and the 60° specular gloss is about 200 GU or more.

[0013] 2. In the first embodiment, the Ra of the electrolytic nickel foil can be about 0.03 μm or less, the Rz can be about 0.15 μm or less, the Rt can be about 0.30 μm or less, and the 60° specular gloss can be about 400 GU or more.

[0014] 3. In the first or second embodiment, the total thickness of the electrolytic nickel foil can be about 1 μm to 100 μm.

[0015] 4. Another aspect of the present invention provides a method for manufacturing an electrolytic nickel foil. The manufacturing method includes electrolytic electroplating with an electrolyte having a pH of about 1 to 5, and the electrolyte contains about 400 g / L to 600 g / L of a nickel ion precursor, about 10 g / L to 30 g / L of a pH buffer, and about 0.5 g / L to 2.0 g / L of a roughness control agent.

[0016] 5. In the fourth embodiment, the nickel ion precursor can be one or more substances selected from the group consisting of nickel sulfate, nickel sulfamate, nickel chloride, and nickel nitrate.

[0017] 6. In the fourth or fifth embodiment, the pH buffer can be selected from boric acid and sodium citrate.

[0018] 7. In the fourth to sixth embodiments, the roughness control agent can be two or more substances selected from the group consisting of saccharin, carboxyethyl isothiuronium chloride, sodium allylsulfonate, butynediol propoxylate, butynediol ethoxylate, propargyl alcohol propoxylate, pyridinepropylsulfobetaine, and sodium propanesulfonate.

[0019] 8. In the fourth to seventh embodiments, it can be carried out at a plating solution temperature of about 40 °C to 60 °C at about 10 A / dm 2 to 100 A / dm 2Apply a current at a current density for electrolytic electroplating.

[0020] 9. Another aspect of the present invention also provides a thin film capacitor, which includes the above-mentioned electrolytic nickel foil, a dielectric formed on the electrolytic nickel foil, and a conductive metal layer formed on the dielectric.

[0021] [Advantageous Effects]

[0022] The present invention can provide an electrolytic nickel foil, a method for manufacturing the electrolytic nickel foil, and a capacitor including the electrolytic nickel foil. Since the arithmetic mean surface roughness (Ra), ten-point mean surface roughness (Rz), maximum surface protrusion height (Rt) of the electrolytic nickel foil are low, and the 60° specular glossiness is high, even when not polished, the electrolytic nickel foil exhibits high smoothness. Therefore, even when a thin dielectric is applied on the electrolytic nickel foil, the risk of short circuit due to protrusions formed on the electrolytic nickel foil passing through the dielectric layer and thus contacting the conductive metal layer is low.

[0023] The present invention can also provide an electrolytic nickel foil and a method for manufacturing the electrolytic nickel foil with excellent processing efficiency. Since the electrolytic nickel foil has low roughness and high glossiness, a thin film capacitor can be manufactured without separately performing a polishing process such as a CMP process. Description of the Drawings

[0024] Figure 1A A 1,000-fold scanning electron microscope (SEM) image of the electrolytic nickel foil of Example 1 is shown.

[0025] Figure 1B A 1,000-fold SEM image of the electrolytic nickel foil of Comparative Example 1 is shown.

[0026] Figure 2A A 3D profilometry image of one surface of the electrolytic nickel foil of Example 1 obtained by white light scanning interferometry is shown.

[0027] Figure 2B An image obtained by measuring one surface of the electrolytic nickel foil of Example 1 by white light scanning interferometry is shown.

[0028] Figure 2C A graph showing the roughness distribution of one surface of the electrolytic nickel foil of Example 1 is shown.

[0029] Figure 2D A graph showing the lateral roughness distribution of the electrolytic nickel foil of Example 1 is shown.

[0030] Figure 2E A graph showing the longitudinal roughness distribution of the electrolytic nickel foil of Example 1 is shown.

[0031] Figure 3A Shows a 3D profiling image of one surface of the electrolytic nickel foil of Comparative Example 1 obtained by white light scanning interferometry.

[0032] Figure 3B Shows an image obtained by three-dimensionally measuring one surface of the electrolytic nickel foil of Comparative Example 1 by white light scanning interferometry.

[0033] Figure 3C Shows a graph illustrating the roughness distribution of one surface of the electrolytic nickel foil of Comparative Example 1.

[0034] Figure 3D Shows a graph illustrating the lateral roughness distribution of the electrolytic nickel foil of Comparative Example 1.

[0035] Figure 3E Shows a graph illustrating the longitudinal roughness distribution of the electrolytic nickel foil of Comparative Example 1.

[0036] Figure 4 Shows a schematic diagram illustrating the cross-sectional structure of the thin film capacitor. Detailed Description of the Invention

[0037] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, when determining that the detailed description of the related art or configuration will unnecessarily obscure the gist of the present invention during the detailed description of the exemplary embodiments of the present invention, the detailed description thereof will be omitted.

[0038] The terms used in the specification are defined in view of the functions used in the present invention and may be changed according to the intentions or habits of the client, operator, and user. Therefore, the definitions of the terms should be understood based on the overall description of the present invention.

[0039] As used herein, Ra, Rz, and Rt are parameters indicating the roughness of the electrolytic nickel foil and are measured according to the ISO25178 standard.

[0040] Ra refers to the arithmetic mean roughness, Rz refers to the ten-point mean roughness, and Rt refers to the maximum protrusion height.

[0041] The glossiness of the electrolytic nickel foil refers to the 60° specular glossiness and is a value measured according to the JIS Z 8741 standard, and its unit is glossiness unit (GU).

[0042] The following embodiments are only examples of the means for implementing the present invention, and the present invention is not limited to the following embodiments, and the following embodiments need to be modified and changed according to the configurations and conditions to which the present invention is applied.

[0043] Preparation of electrolytic nickel foil

[0044] Electrolytic nickel foil can be prepared by electrolytic electroplating with an electrolyte solution containing a nickel ion precursor, a pH buffer, and a roughness control agent and having a pH value of 1 to 5.

[0045] Relative to the total volume of the electrolyte solution, the content of the nickel ion precursor in the electrolyte solution is about 400 g / L to 600 g / L, and within the above range, the surface roughness and glossiness of the electrolytic nickel foil are excellent. The nickel ion precursor can be used without limitation as long as it is a precursor used in nickel ion plating, and the nickel ion precursor is preferably selected from the group consisting of nickel sulfate, nickel sulfamate, nickel chloride, and nickel nitrate. More preferably, nickel sulfate or nickel sulfamate is used.

[0046] The roughness control agent can include one or more compounds selected from saccharin, carboxyethyl isothiourea chloride, sodium allylsulfonate, butynediol propoxylate, butynediol ethoxylate, propargyl alcohol propoxylate, pyridinepropylsulfobetaine, and sodium propanesulfonate. Preferably, a combination of saccharin and sodium allylsulfonate is used.

[0047] In the electrolyte solution, the roughness control agent can be used at a concentration of about 0.01 g / L to 2 g / L, and preferably, at a concentration of about 0.85 g / L to 1.8 g / L. In one embodiment, when saccharin and sodium allylsulfonate are applied, they can each be used at a concentration of about 0.05 g / L to 1.0 g / L.

[0048] In one embodiment, the concentration ratio of saccharin to sodium allylsulfonate can be about 1:0.01 to 100, and preferably, about 1:0.05 to 1:20.

[0049] The electrolyte solution can contain a pH buffer to adjust the pH value. The pH buffer can be used without limitation as long as it controls the pH value of the electrolyte solution at an appropriate level, and relative to the total volume of the electrolyte solution, the content of the pH buffer can be about 10 g / L to 30 g / L. Within the above range, the processing efficiency is excellent. At the same time, for the purpose of the present invention, any type of pH buffer can be used as long as it does not cause unnecessary chemical reactions. For example, boric acid or sodium citrate can be used. When the pH buffer is applied, the process stability can be improved, and electrolytic nickel foil with excellent roughness can be prepared.

[0050] The content of the pH buffer in the electrolyte solution can be about 15 g / L to 50 g / L. Within the above range, it is easy to control the pH value and the process.

[0051] The pH value range of the electrolyte solution is about 1 to 5, and preferably about 2 to 4. Within the above range, the surface roughness of the electrolytic nickel foil is excellent.

[0052] Electrolytic plating can be carried out by conventional methods, and (for example) by inserting a substrate or mandrel into an electrolytic solution, performing electrolytic plating, and then removing the substrate or mandrel, thereby carrying out electrolytic plating.

[0053] In one embodiment, electrolytic plating can be carried out by applying a current to the electrolytic solution at a current density of about 10 A / dm 2 to 100 A / dm 2 , for example, about 15 A / dm 2 to 80 A / dm 2 . Within the above range, an electrolytic nickel foil with excellent surface roughness can be prepared by effective processing.

[0054] In one embodiment, electrolytic plating can be carried out at about 40 °C to 60 °C. Preferably, electrolytic plating is carried out at above about 55 °C to below 60 °C. Under the above conditions, an electrolytic nickel foil with excellent roughness and physical properties is formed.

[0055] The current application time can be appropriately adjusted according to the amount of the electrolytic nickel foil. In one embodiment, the application can be carried out for about 300 seconds to 500 seconds, and preferably about 350 seconds to 450 seconds. Within the above range, a thin electrolytic nickel foil with high processing efficiency and excellent roughness and gloss can be prepared.

[0056] The thickness of the prepared electrolytic nickel foil can be about 1 μm to 100 μm, and preferably, it is about 3 μm to 75 μm. Within the above range, the electrolytic nickel foil has excellent durability and versatility and is suitable for products such as thin film capacitors.

[0057] On at least one surface of the electrolytic nickel foil of the present invention, there is a flat surface with excellent roughness.

[0058] As measured by white light scanning interferometry (WSI) and phase shift interferometry (PSI), the flat surface of the electrolytic nickel foil can have the following roughness parameters: Ra = about 1.2 μm or less, Rz = about 1.0 μm or less, and Rt = about 1.5 μm or less.

[0059] In one embodiment, the flat surface can have the following surface roughness parameters: arithmetic mean roughness (Ra) = about 0.5 or less, ten-point mean roughness (Rz) = about 0.2 μm or less, and maximum peak height (Rt) = about 0.5 μm or less.

[0060] In another embodiment, the flat surface can have the following surface roughness parameters: Ra is about 0.03 μm or less, Rz is about 0.15 μm or less, and Rt is about 0.3 μm or less.

[0061] In yet another embodiment, the flat surface may have the following surface roughness parameters: Ra is about 0.01 μm to 0.03 μm, Rz is about 0.05 μm to 0.15 μm, and Rt is about 0.1 μm to 0.2 μm.

[0062] Within the above roughness range, the flat surface can have excellent roughness without a separate polishing process, thus reducing surface defects. When the roughness parameters exceed the above range, the performance of the dielectric layer in the capacitor is adversely affected, resulting in insulation resistance and leakage current. Within the above surface roughness range, an excellent electrolytic nickel foil can be provided that is not only overall flat but also has no particularly protruding portions.

[0063] In addition, the 60° specular gloss of the flat surface can be about 50 GU to 800 GU, for example, about 200 GU to 700 GU. When the optical properties of the flat surface satisfy the above range, a uniform surface and excellent flatness are obtained.

[0064] Thin-film ceramic film capacitor

[0065] As Figure 4 shown, 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 stacked in sequence.

[0066] After forming the electrolytic nickel foil, the electrolytic nickel foil is completely coated by forming dielectric particles on the surface of the electrolytic nickel foil without a separate polishing process. In this case, as a method for forming a thin-film dielectric, sputtering, laser ablation, chemical vapor deposition, and chemical solution deposition methods can be used, and for improving the densification of the dielectric, the sputtering method is preferred.

[0067] Those skilled in the art will be able to easily manufacture a capacitor from the electrolytic nickel foil by methods such as sputtering. For example, the electrolytic nickel foil can be placed on a deposition plate, the deposition plate can be heated to about 500 °C to 800 °C, and then a dielectric can be formed on the electrolytic nickel foil by sputtering.

[0068] After depositing the dielectric to a predetermined thickness, the dielectric can be fired to improve the crystallinity and densification of the dielectric layer.

[0069] For the deposition of the electrode, the electrolytic nickel foil on which the dielectric is formed can be cooled, and then an electrode can be deposited on its surface by the sputtering method to complete the thin-film capacitor. As the electrode, a gold electrode or a copper electrode is usually used, and any electrode can be used without limitation as long as the electrode is a material capable of electrical connection.

[0070] Hereinafter, the configuration and operation of the present invention will be described in more detail through exemplary embodiments of the present invention. However, these are only given for illustrative purposes of the present invention, and the scope of the present invention should not be construed as being limited by the exemplary embodiments.

[0071] Contents not described herein will be omitted because those skilled in the art can fully infer them technically.

[0072] Example 1

[0073] An electrolytic solution with a pH of about 3 containing the following substances was used: about 450 g / L of nickel sulfate as a nickel ion precursor, about 25 g / L of boric acid as a pH buffer, and about 0.1 g / L of saccharin and about 0.8 g / L of sodium allylsulfonate as roughness control agents, and at an electrolytic solution temperature of about 55 °C, a current was applied at a current density of about 20 A / dm 2 for about 400 seconds to prepare a nickel foil with a thickness of about 27 μm.

[0074] In the unpolished state, the arithmetic mean roughness (Ra) of the surface of the prepared electrolytic nickel foil was about 0.05 μm, the ten-point mean roughness (Rz) was about 0.19 μm, the maximum protrusion height (Rt) was about 0.37 μm, and the 60° specular gloss was about 445 GU.

[0075] Examples 2 to 10

[0076] Electrolytic nickel foils were prepared in the same manner as in Example 1, except that the electrolytic solutions and electrolytic conditions shown in Table 1 below were applied.

[0077] [Table 1]

[0078]

[0079] Comparative Examples 1 to 4

[0080] Electrolytic nickel foils were prepared in the same manner as in Example 1, except that the electrolytic solutions and electrolytic conditions shown in Table 2 below were applied.

[0081] [Table 2]

[0082]

[0083] Evaluation of material properties

[0084] Roughness measurement

[0085] The surface roughness distribution of the entire sample was measured using a roughness meter (model name: NV-2700, purchased from Nano System) according to the ISO 25178 standard, and Rz, Rt, and Ra in the longitudinal and transverse directions based on the center point of the sample were measured.

[0086] Glossiness measurement

[0087] According to the JIS Z 8741 standard, the 60° specular gloss was measured using a gloss meter (IG-410 ultra-high gloss meter, purchased from Horiba) at an incident angle of 60°. The unit of the measured gloss is gloss unit (GU).

[0088] Table 3 below summarizes the roughness and gloss measured by the above methods according to the examples and comparative examples.

[0089] [Table 3]

[0090]

[0091]

[0092] As shown in Table 3, compared with Comparative Examples 1 to 4, in the case of Examples 1 to 10, it can be confirmed that all surface roughness parameters Ra, Rz, and Rt are very low, and the gloss (Gs 60) is high.

[0093] SEM image evaluation

[0094] The flat surfaces of the electrolytic nickel foils of Example 1 and Comparative Example 1 were photographed at a magnification of 1,000 times to obtain SEM images, and the results are as Figure 1A and Figure 1B shown. When comparing Figure 1A and Figure 1B , it can be confirmed that compared with Comparative Example 1, Example 1 not only exhibits a lower surface protrusion height but also exhibits a uniform height distribution.

[0095] 3D profiling

[0096] The flat surfaces of the electrolytic nickel foils of Example 1 and Comparative Example 1 were 3D profiled by white light scanning interferometry to obtain the Figures 2A to 2E of Example 1 and Figures 3A to 3E the profiling results shown of Comparative Example 1.

[0097] When comparing the Figure 2A and Figure 3AWhen it is possible to confirm that, compared with Comparative Example 1, Example 1 exhibits a surface with regularly shaped surface protrusions of low height. Considering that discharges (i.e., short circuits) occur in protrusions that are significantly higher than the surroundings, it can be easily seen that Example 1 has an excellent morphology.

[0098] Figure 2C And Figure 3C respectively show diagrams illustrating the surface roughness distributions of the electrolytic nickel foils of Example 1 and Comparative Example 1, and Figure 2C shows a narrow protrusion height (Rz) distribution and a low maximum protrusion height (Rt), indicating that the surface of Example 1 is uniform.

[0099] Figure 2D And Figure 3D respectively show diagrams illustrating the lateral roughness distributions of the electrolytic nickel foils of Example 1 and Comparative Example 1, and compared with that of Comparative Example 1, Figure 3D that of Example 1 Figure 2D shows excellent flatness and high smoothness.

[0100] Figure 2E And Figure 3E respectively show diagrams illustrating the longitudinal roughness distributions of the electrolytic nickel foils of Example 1 and Comparative Example 1, and compared with that of Comparative Example 1, Figure 3E that of Example 1 Figure 2E shows excellent flatness and high smoothness.

[0101] Capacitor manufacturing

[0102] Example 11

[0103] The electrolytic nickel foil of Example 1 was placed on the deposition plate in the sputtering chamber, and the chamber atmosphere consisting of 95% argon and 5% oxygen was maintained at an atmospheric pressure of about 3 Torr. The deposition plate was heated to about 650 °C, and barium titanate (BaTiO3) with a diameter of about 3 inches was used as a target, and sputtering was carried out at an RF power of about 150 W to form barium titanate on the electrolytic nickel foil. Deposition was carried out for about 150 minutes to form a dielectric layer with a thickness of about 0.7 μm.

[0104] In a chamber set at about 900 °C, the electrolytic nickel foil coated with barium titanate was fired at an oxygen partial pressure of about 2×10 -7 atm for about 2 hours and then cooled. A copper electrode with a thickness of about 0.2 μm was deposited on the surface of the electrolytic nickel foil coated with barium titanate by sputtering to fabricate a capacitor.

[0105] Comparative Example 5

[0106] In the same manner as in Example 11, a capacitor was fabricated using the electrolytic nickel foil of Comparative Example 1.

[0107] Capacitor short-circuit experiment

[0108] A bias voltage of about -10 V to 10 V was applied at room temperature (25 °C), an oscillation voltage of about 1 kHz, and about 50 mV using a digital LCR meter to confirm whether a short circuit occurred in the finished capacitor sample. The results showed that no short circuit occurred in the capacitor manufactured using the electrolytic nickel foil of Example 1, while a short circuit occurred in the capacitor manufactured using the electrolytic nickel foil of Comparative Example 1.

Claims

1. A method for preparing electrolytic nickel foil for thin film capacitors, Among them, The electrolytic nickel foil includes at least one flat surface, the arithmetic mean roughness Ra of the flat surface is 0.05 μm or less, the ten-point mean roughness Rz is 0.20 μm or less, the maximum protrusion height Rt is 0.50 μm or less, and the 60° specular glossiness is 200 GU or more. The method includes electrolytic electroplating with an electrolyte having a pH of 1 to 5, the electrolyte containing 400 g / L to 600 g / L of a nickel ion precursor, 10 g / L to 30 g / L of a pH buffer, and a roughness control agent. The roughness control agent contains 0.1 g / L to 1 g / L of saccharin and 0.4 g / L to 0.8 g / L of sodium allylsulfonate.

2. The method according to claim 1, wherein the nickel ion precursor is one or more substances selected from the group consisting of nickel sulfate, nickel sulfamate, nickel chloride, and nickel nitrate.

3. The method according to claim 1, wherein said electrolytic electroplating is carried out by applying a current at a current density of 10 A / dm 2 to 100 A / dm 2 at 40°C to 60°C.

4. The method according to claim 1, wherein the concentration of the roughness control agent is 0.5 g / L to 2.0 g / L.

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