KR20160050461A - Electroless plating method of copper film through magnetic-bar stirring - Google Patents

Electroless plating method of copper film through magnetic-bar stirring Download PDF

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KR20160050461A
KR20160050461A KR1020140148605A KR20140148605A KR20160050461A KR 20160050461 A KR20160050461 A KR 20160050461A KR 1020140148605 A KR1020140148605 A KR 1020140148605A KR 20140148605 A KR20140148605 A KR 20140148605A KR 20160050461 A KR20160050461 A KR 20160050461A
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South Korea
Prior art keywords
copper
thin film
electroless plating
copper thin
nickel
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KR1020140148605A
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Korean (ko)
Inventor
나사균
이연승
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한밭대학교 산학협력단
한밭대학교 산학협력단
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Priority to KR1020140148605A priority Critical patent/KR20160050461A/en
Publication of KR20160050461A publication Critical patent/KR20160050461A/en

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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/31—Coating with metals
    • C23C18/38—Coating with copper

Abstract

The present invention relates to a method to form a low-resistance copper wiring while forming it by electroless plating in a plating solution including a nickel catalyst, comprising the following: a step of preparing a copper electroless plating solution including a nickel catalyst; a step of dipping a substrate, on which a copper film is desired to be formed, in the plating solution; and a step of forming a copper film by conducting magnetic-bar stirring in the plating solution. According to the present invention, the nickel included in the plating solution is prevented from being contained in the copper film, and a copper film, which has a low resistance but has an excellent surface roughness characteristic, can be formed.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper thin film electroless plating method,

The present invention relates to a copper thin film electroless plating method, and more particularly, to an electroless plating method capable of forming a low resistance copper thin film through magnetic stirring.

As the circuit line width becomes finer due to miniaturization and high performance of a printed circuit board (PCB), it becomes important to secure sufficient electrical conductivity of the metal wiring. For the metal wiring on the printed circuit board, a screen printing method using a metal paste and electroless plating using a plating solution containing a metal ion are used. In order to form a metal wiring with low resistance, a copper thin film forming technique by electroless plating is widely .

Conventionally, formaldehyde is used as a reducing agent in the formation of a copper thin film by an electroless plating method. However, formaldehyde is a primary level carcinogen and causes serious environmental problems. When the electroless plating is performed, There is a problem that the adhesive force of the copper thin film is weakened and the development of alternative reducing agents such as dental phosphates is actively under development. When a substrate susceptible to damage in a strongly acidic or strong basic solution such as an insulating substrate having an insulating layer formed by anodizing the surface of the metal substrate or a flexible substrate for a printed circuit board is used, a neutral plating solution In this case, it is necessary to include a catalyst in the electroless plating solution for smooth plating, and nickel is generally used as the catalyst.

However, if nickel is added to the electroless plating solution, it is impossible to prevent the nickel from being mixed in the copper thin film, resulting in an increase in the resistance of the copper thin film and an increase in the surface roughness of the copper thin film due to the generation of bubbles . Therefore, there is a demand for an electroless copper plating method which uses nickel as a catalyst while exhibiting low resistance and excellent surface roughness characteristics.

Korean Patent Publication No. 2002-0082797

An object of the present invention is to provide an electroless plating method capable of forming a copper thin film having a low resistance by suppressing the mixing of nickel while using nickel as a catalyst. The purpose.

It is another object of the present invention to provide an electroless plating method capable of forming a copper thin film having excellent surface roughness characteristics while using nickel as a catalyst.

According to an aspect of the present invention, there is provided a method of electroless plating a copper foil, comprising: preparing a copper electroless plating solution containing a nickel catalyst; immersing a substrate on which a copper foil is to be formed in the plating solution; And forming a copper thin film while magnetically stirring the plating liquid.

At this time, the magnetic stirrer may include a magnetic rod in the plating liquid, and rotate the magnetic rod by a magnetic rod driving unit provided outside the plating vessel containing the plating liquid.

The pH of the plating solution may be 5 to 9, and the substrate may be an insulating substrate or a flexible substrate.

The first metal layer may be a silver (Ag) layer and the diffusion preventing layer may be a nickel-boron (Ni-B) layer.

A copper thin film according to another aspect of the present invention is a copper thin film formed by spinning a copper electroless plating solution having a pH of 5 to 9 containing a nickel catalyst with a magnetic rod while magnetically vibrating, The nickel content is low.

A printed circuit board according to another aspect of the present invention is a printed circuit board comprising an insulating substrate, a first metal pattern formed on the insulating substrate, a diffusion preventing layer formed on the first metal pattern, and a copper thin film formed on the diffusion preventing layer , The copper foil is formed by electroless plating while magnetically stirring a copper plating solution containing a nickel catalyst, so that the nickel content is lower than that in the case where the copper foil is not magnetized.

According to the present invention, a copper thin film is formed while electrifying copper thin film electroless plating, thereby forming a copper thin film having low resistance by suppressing the mixing of nickel in the copper thin film while using nickel as a catalyst.

Further, according to the present invention, a copper thin film having excellent surface roughness characteristics can be formed while nickel is used as a catalyst in electroless plating.

1 is a flow chart of a copper thin film electroless plating method according to the present invention.
2 is a conceptual view of magnetic stirring according to the present invention.
3 is a schematic view of a metal wiring forming process according to the present invention.
4 is a result of observing the surface of the copper foil according to the rotation speed of the magnetic rod.
Fig. 5 shows the results of measurement of the sheet resistance and mass change of the substrate according to the rotation speed of the magnetic rod.
6 shows the results of observing the degree of bubble formation in the plating vessel depending on whether or not magnetic stirring was performed.
FIG. 7 shows the results of observing the surface shape of the copper thin film according to the rotation speed of the magnetic rod with a field-emission scanning electron microscope.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the embodiments of the present invention. The following description includes specific embodiments, but the present invention is not limited to or limited by the embodiments described. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a flow chart of a copper thin film electroless plating method according to the present invention. Figure 1 illustrates only the essential steps, and of course, additional steps may be included. 1, the electroless plating method for copper thin film according to the present invention comprises the steps of preparing a copper electroless plating solution containing a nickel catalyst (S10), immersing a substrate to be formed with a copper thin film in the plating solution (S20) and forming a copper thin film (S30) while magnetically stirring the plating liquid.

More specifically, each step is characterized in that the copper electroless plating solution provided by step S10 includes a nickel catalyst. The nickel catalyst is a compound capable of supplying nickel ions to the plating solution. For example, NiSO 4 .6H 2 O (nickel sulfate (II) sulfate hexahydrate) may be used. In addition to the nickel catalyst, the plating solution may contain additives such as CuSO 4 .5H 2 O (copper sulfate pentahydrate) for copper ion supply, other reducing agents, buffering agents, and complexing agents. In the present invention, the electroless plating solution is not limited as long as it contains a nickel catalyst as a plating solution capable of forming a copper thin film.

Step S20 is a step of immersing the substrate on which the copper thin film is to be formed in the prepared plating liquid. Here, the substrate may be an insulating substrate, and the insulating substrate may be a flexible substrate such as a substrate on which an insulating layer is formed through an anodizing process or the like, a synthetic resin substrate, or a polyethylene terephthalate (PET) film. In addition, at least one layer of the metal thin film may be formed on the surface of the substrate, wherein at least one of the metal thin films may be a laminate of a silver (Ag) thin film and a nickel-boron (Ni-B) thin film. At this time, the at least one layer of the metal thin film may be formed in a specific pattern so that the copper thin film can selectively grow in the electroless plating process.

Step S30 is a step of forming a copper thin film while magnetically stirring the plating liquid. Here, the magnetic stirrer means that a magnetic bar is placed in a plating solution and a magnetic field is applied from the outside to stir the plating solution. FIG. 2 is a conceptual view of magnetic stirring. As schematically shown in FIG. 2, an electroless plating solution 220 is contained in a plating vessel 210, and a magnetic bar 230 is placed therein. A magnetic rod driving unit 240 is provided below the plating vessel 210 to generate a magnetic field so that the magnetic bar 230 can move within the plating liquid 220. The movement of the magnetic bar 230 is preferably a rotation and the magnetic bar driving unit 240 may be provided with a magnet which is rotated by a motor at a position opposite to the magnetic bar 230. Since the magnetic rod driving unit 240 is well known as a magnetic stirrer, a detailed description of its constitution will be omitted.

As will be described later, when the plating process is performed while the plating solution is stirred with the magnetic rod during electroless plating of the copper thin film, the amount of the nickel catalyst contained in the copper thin film is reduced in addition to the effect expected by general stirring, Thereby making it possible to form a copper film of low resistance. This effect of magnetic stirring is not clearly understood, but it is presumed that by moving the magnetically strong nickel toward the magnetic rod, it reduces the amount contained in the copper thin film grown on the substrate relatively. In addition, the surface roughness characteristics of the copper thin film can be greatly improved by magnetic stirring. In the plating process, bubbles on the surface of the substrate are removed, and nickel is moved toward the magnetic rod to form bubbles It is presumed that the copper film is uniformly formed by reducing the generation of the copper film.

FIG. 3 schematically shows a process of forming a metal wiring on an insulating substrate according to the present invention, and can be applied to a metal wiring forming process of a printed circuit board. Referring to FIG. 3, first metal paste is screen-printed on an insulating substrate such as polyethylene terephthalate (PET) to form a first metal layer, where the first metal may be silver (Ag). The first metal layer forming step is meaningful in that a simple process such as screen printing can form a considerable thickness of the metal wiring and then the copper thin film is selectively grown by electroless plating. After the first metal layer pattern is formed, a diffusion preventing layer capable of preventing diffusion between the copper thin film and the first metal layer is formed on the first metal layer pattern. In this case, the diffusion preventing layer may be a nickel- have. Then, the copper thin film electroless plating according to the present invention is performed in the same manner as described above with reference to Figs. According to such a metal wiring structure, it is possible to secure a sufficient electrical conductivity by the copper thin film only with the first metal layer.

Hereinafter, the effects of the present invention will be described in more detail with reference to examples.

<Examples>

A polyethylene terephthalate (PET) insulating substrate having a silver (Ag) layer as a first metal layer and a nickel-boron (Ni-B) layer as a diffusion preventing layer was prepared in order to confirm the magnetic stirring effect of the present invention. The silver (Ag) layer was formed on the PET substrate by screen printing at room temperature, and then heat-treated at 130 ° C for 30 minutes after printing. The thickness of the silver (Ag) layer was about 15 mu m. The nickel-boron (Ni-B) layer is composed of NiSO 4 .6H 2 O [nickel sulfate; Nickel (II) sulfate hexahydrate], DMAB (dimethylamine borane), succinic acid, lactic acid and ammonium hydroxide (NH 4 OH) solutions. The thickness of the nickel-boron (Ni-B) layer was about 2 탆.

As a plating solution for copper electroless plating, NiSO 4 .6H 2 O (nickel sulfate; Nickel (II) sulfate hexahydrate], CuSO 4 · 5H 2 O [copper sulfate; Copper (II) sulfate pentahydrate] as a reducing agent, NaH 2 PO 2 .H 2 O [sodium dithiophosphate; Sodium phosphinate monohydrate], complexing agent C 6 H 5 Na 3 O 7 .2H 2 O [sodium citrate; Sodium citrate tribasic dihydrate and NH 4 Cl (ammonium chloride) were used. The pH of the plating solution was adjusted to 7 ~ 8 using ammonium hydroxide (NH 4 OH). After the insulating substrate was immersed in a copper electroless plating solution, the magnetic rod was rotated according to the method of the present invention to form a copper thin film at 70 ° C for 1 hour while magnetic stirring was performed. At this time, the rotation speed of the magnetic rod was adjusted to 1000 rpm.

Before the nickel-boron (Ni-B) electroless plating and copper electroless plating, the substrate was subjected to palladium (Pd) catalyzed treatment. The palladium catalyzed treatment was carried out at pH 6.9, 65 ° C., palladium chloride (PdCl 2 ) (SnCl 2 .2H 2 O) and hydrochloric acid (HCl) for 30 minutes.

4 is a result of observing the surface of the copper foil according to the rotation speed of the magnetic rod. As can be seen in FIG. 4, as the rotational speed of the magnetic rod increases, the copper foil formed becomes closer to pure copper color. From this, it can be seen that the content of impurities is reduced in the copper thin film formed by electroless plating due to magnetic stirring.

5 (a) shows the result of measurement of the sheet resistance change of the substrate according to the rotation speed of the magnetic rod, FIG. 5 (b) shows the change of the mass of the substrate with respect to the rotation speed of the magnetic rod, . First, as the result of forming the copper thin film in the plating solution of pH 7, the mass of the copper thin film formed as the rotation speed of the magnetic rod is increased, but the sheet resistance is greatly decreased, It was confirmed that a copper thin film of resistance was formed. On the other hand, when a copper thin film was formed from a plating solution having a pH of 8, there was no significant difference in sheet resistance due to magnetic stirring as shown in FIG. 5 (a) . In other words, the sheet resistance is generally increased when the thickness of the thin film is decreased. Even though the thickness is decreased, the sheet resistance is kept constant. Therefore, even when the plating solution of pH 8 is used, resistance of the copper film formed decreases as the magnetic rod rotation speed increases .

The composition of the copper thin film formed by X-ray photoelectron spectroscopy (XPS) was analyzed to confirm whether the content of nickel in the copper thin film was reduced by magnetic stirring. The results are shown in Table 1, Respectively.

Figure pat00001

According to the results of the composition analysis in Table 1, the nickel content was greatly reduced from 23.62% to 5.35% at pH 7 due to magnetic stirring, and the nickel content was decreased from 45.72% to 24.6% %. This is because when the electroless plating of the copper thin film is carried out by magnetic excitation with the magnetic rod in the plating solution, the nickel content in the copper thin film formed even when the nickel catalyst is used can be greatly reduced, Which is exactly the same as predicted from the copper film color observation result of FIG. 4 and the sheet resistance measurement result of FIG. 5.

6 shows the results of observing the degree of bubble formation in the plating vessel depending on whether or not magnetic stirring was performed. 6 (a) shows that electroless plating is proceeded without magnetic stirring, and that a large amount of bubbles are generated in the plating solution as a whole, and FIG. 6 (b) shows electroless plating with self- Only stirring phenomenon of the plating solution due to magnetic stirring was observed, and bubbles were hardly observed.

FIG. 7 shows the result of observation of the surface shape of the copper thin film according to the rotation speed of the magnetic rod with an electric field-type scanning electron microscope (FE-SEM; Field Emission Scanning Electron Microscope). In both cases where the pH of the plating solution was 7 and 8, it was confirmed that when the magnetic flux was applied, the unevenness of the surface of the copper thin film was reduced and a more uniform thin film was formed than when the magnetic flux was not applied. The surface roughness characteristics were further improved. This is considered to be because the generation of bubbles is reduced according to the magnetic stirring as shown in Fig.

According to the electroless plating method of copper thin film according to the present invention, a simple method of electroless plating while magnetically stirring is used to form a low resistance copper thin film by reducing the nickel content in the copper thin film formed by using the nickel catalyst And it is possible to form a uniform copper thin film having a small surface unevenness. This is effectively used in the field of forming a low resistance metal wiring on an insulating substrate or a flexible printed circuit board in which an insulating layer is formed by anodizing the surface of a metal substrate which requires a low resistance metal wiring and can not use a strongly acidic or strong basic plating solution . In the embodiment, only the case where the pH is from 7 to 8 has been described. However, the magnetic stirring effect according to the present invention is applicable to all plating solutions containing a nickel catalyst, in particular, plating solutions having a pH in the range of 5 to 9 including a nickel catalyst for smooth electroless plating In effect.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. Accordingly, the scope of protection of the present invention should be determined by the description of the claims and their equivalents.

210: Plating vessel
220: electroless plating solution
230: Magnetic rod
240: magnetic rod driving part

Claims (9)

Preparing a copper electroless plating solution containing a nickel catalyst;
Immersing a substrate on which a copper thin film is to be formed in the plating liquid; And
Forming a copper thin film while magnetically stirring the plating liquid;
Wherein the copper thin film electroless plating method comprises: The method according to claim 1,
Wherein the magnetic stirrer includes a magnetic rod in the plating liquid and rotates the magnetic rod by a magnetic rod driving unit provided outside the plating vessel containing the plating liquid. The method according to claim 1,
Wherein the pH of the plating solution is 5 to 9. The copper electroless plating method of claim 1, The method according to claim 1,
Wherein the substrate is an insulating substrate. The method according to claim 1,
Wherein the substrate is a flexible substrate. The method according to claim 1,
Wherein the first metal layer and the diffusion preventing layer are laminated on the substrate. The method according to claim 6,
Wherein the first metal layer is a silver (Ag) layer and the diffusion barrier layer is a nickel-boron (Ni-B) layer. A copper thin film formed by spinning a copper electroless plating solution having a pH of 5 to 9 and containing a nickel catalyst with a magnetic rod while magnetizing the copper thin film and having a nickel content lower than that in a case where magnetic stirring is not performed . An insulating substrate;
A first metal pattern formed on the insulating substrate;
A diffusion barrier layer formed on the first metal pattern;
A copper thin film formed on the diffusion preventing layer;
A printed circuit board comprising:
Wherein the copper foil is formed by electroless plating while magnetically stirring a copper plating solution containing a nickel catalyst, so that the nickel content is smaller than that in the case where the copper foil is not magnetized.
KR1020140148605A 2014-10-29 2014-10-29 Electroless plating method of copper film through magnetic-bar stirring KR20160050461A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111203371A (en) * 2020-01-16 2020-05-29 浙江大学 Preparation method of surface metal pattern

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111203371A (en) * 2020-01-16 2020-05-29 浙江大学 Preparation method of surface metal pattern

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