Plating solution

Abstract

The purpose of the present invention is to provide a plating solution which is capable of forming an antioxidant plating film. Disclosed is a plating solution which contains metal ions and a smoothing agent that has a charge density of 1.5 mEq / g or more. It is preferable that the charge density of the smoothing agent is 2.0-20.0 mEq / g. It is also preferable that the plating solution contains the smoothing agent at a concentration of 10-300 mg / L, while additionally containing a gloss agent at a concentration of 0.1-5 mg / L and an inhibitor at a concentration of 0.1-2,000 mg / L. It is also preferable that the metal ions in the plating solution include copper ions.

Description

Plating solution

[0001] This invention relates to a plating solution. More specifically, it relates to a plating solution capable of forming an antioxidant plating film.

[0002] In recent years, in order to improve the performance of semiconductors and printed circuit boards, the density and miniaturization of metal wiring have been pursued. As a result, metal wiring has become more susceptible to oxidation, which tends to lead to an increase in electrical resistance. Some measures are needed to suppress this oxidative degradation and the resulting increase in electrical resistance.

[0003] Plating technology is widely used to form metal wiring on semiconductors and printed circuit boards. Therefore, there is a need for the development of plating methods and solutions that can suppress the oxidative degradation of the applied metal wiring. However, there are only a few reported examples of such plating techniques (Patent Document 1).

[0004] International Publication No. 2020 / 013188 Brochure

[0005] There is a need for a novel plating solution that can form a plating film that exhibits resistance to oxidation (hereinafter sometimes referred to as an "anti-oxidation plating film"). The present invention has been made in view of this situation, and aims to provide a plating solution capable of forming an anti-oxidation plating film.

[0006] The inventors of the present invention conducted extensive research to solve the above-mentioned problems and, focusing on the charge density of the smoothing agent, which is an additive in the plating solution, discovered that an antioxidant plating film can be formed by using a plating solution containing a smoothing agent with a charge density of a predetermined amount or more, thus completing the present invention.

[0007] In other words, the present invention provides the following (1) to (9): (1) A plating solution containing metal ions and a smoothing agent with a charge density of 1.5 mEq / g or more. (2) The plating solution of (1) above, wherein the smoothing agent is contained at a concentration of 10 to 300 mg / L. (3) The plating solution of (1) or (2) above, further containing a brightening agent, wherein the brightening agent is contained at a concentration of 0.1 to 5 mg / L. (4) Any of the plating solutions of (1) to (3) above, further containing an inhibitor, wherein the inhibitor is contained at a concentration of 0.1 to 2000 mg / L. (5) The plating solution of (4) above, wherein the mass-average molecular weight of the inhibitor is in the range of 200 to 10000. (6) A plating solution according to any of (1) to (5) above, wherein the nitrogen-containing compound constituting the smoothing agent comprises one or more compounds selected from the group consisting of amines, imidazolines, imidazoles, benzimidazoles, indoles, pyridines, quinolines, isoquinolines, anilines, and aminocarboxylic acids. (7) A plating solution according to any of (1) to (6) above, wherein the charge density of the nitrogen-containing compound constituting the smoothing agent is 2.0 to 20.0 mEq / g. (8) A plating solution according to any of (1) to (7) above, wherein the metal ions include copper ions. (9) A method for forming an antioxidant plating film using a plating solution according to any of (1) to (8) above.

[0008] The present invention provides a plating solution capable of forming an antioxidant plating film. Therefore, the present invention makes it possible to form a metal plating film with excellent antioxidant properties on semiconductors, printed circuit boards, and the like.

[0009] The present invention will be described in detail below based on embodiments, but the present invention is not limited to these embodiments.

[0010] <Plating Solution> The plating solution according to this embodiment is a plating solution containing metal ions and a smoothing agent with a charge density of 1.5 mEq / g or more. In addition, the plating solution may contain other additives such as acids, halide ions, brighteners, and inhibitors.

[0011] <About the composition of the plating solution> [Metal ions] The metal ions that constitute the plating solution of this embodiment are not particularly limited, but examples include ions of copper, tin, titanium, chromium, manganese, iron, nickel, cobalt, zinc, silver, gold, platinum, palladium, indium, molybdenum, tungsten, lead, rhenium, rhodium, ruthenium, osmium, iridium, bismuth, and aluminum. It is also possible to use multiple metal ions in combination to make an alloy plating solution. In the plating solution of this embodiment, it is preferable that the metal ions include copper ions.

[0012] The metal ions in the plating solution according to this embodiment are usually obtained by dissolving a metal salt in a solvent such as water. The plating solution according to this embodiment is preferably obtained by dissolving a copper-containing metal salt in water. The copper-containing metal salt is not particularly limited, but examples include copper sulfate, copper pyrophosphate, and copper acetate. Among these, copper sulfate is preferred. Furthermore, when using copper sulfate, copper sulfate pentahydrate is preferred.

[0013] The concentration of metal ions in the plating solution according to this embodiment is not particularly limited, but can be, for example, about 10 to 80 g / L, and is particularly preferably about 35 to 75 g / L. In the case of copper sulfate pentahydrate, a preferred concentration is, for example, 50 to 300 g / L, and particularly 100 to 280 g / L.

[0014] [Smoothing Agent] The plating solution of this embodiment is characterized by containing a smoothing agent with a charge density of 1.5 mEq / g or more. As a result of research by the inventors, it was unexpectedly found that the charge density of the smoothing agent additive greatly affects the antioxidant properties of the plating film formed by the plating solution.

[0015] In other words, the plating solution according to this embodiment contains a smoothing agent with a charge density of 1.5 mEq / g or more, which makes it possible to form a metal plating film with excellent antioxidant properties.

[0016] The smoothing agent is not particularly limited as long as it has a charge density of 1.5 mEq / g or more, but for example, nitrogen-containing compounds can be used.

[0017] (Charge Density) Here, "charge density" as used herein can be expressed as the amount of charge in an acidic medium per unit mass of a compound such as a nitrogen-containing compound constituting a lubricant. For example, in a compound with molecular weight M having n positively charged nitrogen atoms, the charge density is 1000 × n / M (mEq / g). The same applies when a tertiary amine compound, etc., is ionized in an acidic aqueous solution and comes to have n ammonium nitrogen atoms per molecule. Such charge densities can be measured, for example, by colloidal titration.

[0018] As described above, the charge density of the smoothing agent is 1.5 mEq / g or more. Furthermore, the charge density of the smoothing agent is preferably 2.0 mEq / g or more, more preferably 3.0 mEq / g or more, and particularly preferably 4.0 mEq / g or more. There is no particular upper limit to the charge density, but from the viewpoint of filling properties, it may be, for example, 20.0 mEq / g or less, preferably 15.0 mEq / g or less, more preferably 10.0 mEq / g or less, preferably 8.0 mEq / g or less, and preferably 6.0 mEq / g or less. The charge density of the nitrogen-containing compound may be, for example, in the range of 1.5 to 20.0 mEq / g or 2.0 to 20.0 mEq / g, or in the range of 2.0 to 15.0 mEq / g, and even further in the range of 3.0 to 10.0 mEq / g.

[0019] (Compounds constituting the smoothing agent) As mentioned above, the smoothing agent may be any compound as long as its charge density is 1.5 mEq / g or more, but for example, nitrogen-containing compounds can be used. Specifically, examples include, but are not limited to, one or more compounds selected from the group consisting of amines, dyes, imidazolines, imidazoles, benzimidazoles, indoles, pyridines, quinolines, isoquinolines, anilines, aminocarboxylic acids, etc.

[0020] Examples of the amines include linear, branched, or cyclic aliphatic amines, aliphatic diamines, aliphatic triamines, aliphatic polyamines, aromatic amines, aromatic diamines, aromatic triamines, aromatic polyamines, amine compounds having oxyalkylene chains or alkylene chains with amino groups bonded to their ends, and polyamines having a repeating structure with amine compounds having one or more hydroxyl groups as constituent units. Among these, amine compounds having oxyalkylene chains or alkylene chains with amino groups bonded to their ends, polyamines having a repeating structure with amine compounds having one or more hydroxyl groups as constituent units, or imidazoles are preferred. A plating solution containing such nitrogen-containing compounds as a smoothing agent makes it possible to form a metal plating film with superior antioxidant properties.

[0021] (Concentration of smoothing agent) There are no particular restrictions on the concentration of the smoothing agent, and it can be set arbitrarily depending on the object to be plated and the metal salt used. For example, the concentration of the smoothing agent in the plating solution can be about 1 to 500 mg / L.

[0022] Furthermore, among these, the concentration of the smoothing agent is preferably about 300 mg / L or less, more preferably about 200 mg / L or less, even more preferably 180 mg / L or less, still more preferably 150 mg / L or less, and particularly preferably 100 mg / L or less. The concentration of the smoothing agent may be, for example, about 10 to 300 mg / L, more preferably about 15 to 200 mg / L, and especially about 20 to 180 mg / L. A plating solution with such a preferred concentration of smoothing agent can improve the antioxidant properties of the metal plating film and exhibit excellent smoothing performance.

[0023] Furthermore, as will be shown in the examples described later, an unexpected result was obtained: although superior antioxidant properties were obtained by using a smoothing agent with a charge density of 1.5 mEq / g or higher compared to using a smoothing agent with a lower charge density, a relatively low concentration of the smoothing agent was preferable.

[0024] It is known that smoothing agents, when used to smooth plated films, can adsorb to reactive active sites on the surface, suppressing crystal growth during or within the formation of the metal plating film, thereby reducing the size of the crystals. The tendency for metal plating films with higher concentrations of smoothing agents to have poorer antioxidant properties is thought to be because the amount adsorbed to reactive active sites increases with concentration, resulting in finer metal crystals, an increased interface with the outside environment, and thus making the metal plating film more susceptible to oxidation.

[0025] [Other Additives] In the plating solution according to this embodiment, other additives may be included in addition to the smoothing agent. For example, additives such as brighteners, inhibitors, acids, halide ions, complexing agents, antioxidants, conductive salts, wetting agents, and dyes including phthalocyanine compounds may be included. Some of these additives will be described below, but the additives are not limited to these.

[0026] (Brightener) Brighteners not only impart gloss to the plated film, but can also promote the deposition of metal in recesses and contribute to the flattening of the plated surface.

[0027] There are no particular restrictions on the type of glossing agent; examples include, but are not limited to, those containing various aldehydes, benzothiazoles, sulfonic acids, sulfides, and other sulfur-containing compounds. It is also possible to use multiple types of glossing agents in combination.

[0028] Among these, it is preferable to include a brightener containing a sulfur-containing compound. A plating solution containing a sulfur-containing compound as a brightener can exhibit better planarization performance. Preferred sulfur-containing compounds include, but are not limited to, bis(3-sulfopropyl) disulfide (SPS), bis(2-sulfopropyl) disulfide, 3-mercapto-1-propanesulfonic acid, 3-(benzothiazole-2-ylthio)propane-1-sulfonic acid, 3-[N,N-dimethyl(thiocarbamoyl)thio]-1-propanesulfonic acid, 3-[(aminoiminomethyl)thio]-1-propanesulfonic acid, and salts thereof.

[0029] There are no particular restrictions on the concentration of the glossing agent; for example, it can be around 0.1 to 10 mg / L.

[0030] Among these, the concentration of the brightener is preferably 0.3 mg / L or higher, and more preferably 0.5 mg / L or higher. If the concentration of the brightener is, for example, 0.3 mg / L or higher, good gloss and smoothness can be imparted to the metal plating film. On the other hand, from the viewpoint of the antioxidant properties of the metal plating film, a low concentration of brightener is preferable, and a concentration of 7 mg / L or less, and particularly 5 mg / L or less, is also recommended. The concentration of the brightener is also preferably around 0.1 to 7 mg / L, and particularly preferably around 0.1 to 5 mg / L.

[0031] (Inhibitors) Inhibitors can also contribute to the smoothing performance of the plating solution.

[0032] There are no particular restrictions on the inhibitors used; for example, polymer components, specifically polymers with various structures such as linear, branched, cyclic, and network structures, can be used. It is also possible to use multiple types of inhibitors in combination.

[0033] The plating solution preferably contains a nonionic surfactant as an inhibitor. Including such an inhibitor, particularly a polymer component, can further improve the smoothing performance of the plating solution.

[0034] Examples of nonionic surfactants include, but are not limited to, polyethylene glycol (PEG), polyalkylene glycols such as polypropylene glycol, Pluronic® type surfactants, tetronic type surfactants, polyethylene glycol glyceryl ether, and polyethylene glycol dialkyl ether.

[0035] There is no particular limitation on the molecular weight of the inhibitor, but it is preferably within the range of 100 to 20,000, particularly 200 to 10,000 in terms of the mass average molecular weight. With an inhibitor having such a molecular weight, it becomes easier to form a metal plating film with better antioxidant properties. The molecular weight can be measured, for example, by gel permeation chromatography (GPC) or the like using monodisperse polyethylene oxide, polyethylene glycol, etc. as a standard. In determining the molecular weight, for example, reference may be made to OECD test guidelines such as "OECD TG118".

[0036] There is no particular limitation on the concentration of the inhibitor either, and it can be, for example, 0.1 to 5000 mg / L, particularly about 0.1 to 2000 mg / L.

[0037] From the viewpoint of forming a metal plating film with better antioxidant properties, it is preferable that the inhibitor in the plating solution is at a low concentration and may even be absent. The plating solution of the present embodiment preferably does not contain an inhibitor, or if it contains one, the concentration is, for example, about 1 to 1500 mg / L, particularly about 10 to 1000 mg / L.

[0038] It is known that optional components such as inhibitors and brighteners may adsorb to the reactive sites on the plating surface and may suppress crystal growth in the metal plating film. In the plating solution of the present embodiment as well, if the amount of these additives is large, crystal growth of the metal may be suppressed, and as a result, the crystals may be refined, which may lead to a tendency of decreased antioxidant properties.

[0039] (Acid) The plating solution can also contain an acid. There is no particular limitation on the acid used here, and a desired one among the inorganic acids and / or organic acids described above, such as sulfuric acid and nitric acid, can be used according to the composition of the plating solution and the plating target. For example, when the water-soluble metal salt is copper sulfate, it is preferable that the plating solution contains sulfuric acid as the acid. ​​​​(Halide Ions) In the plating solution, halide ions such as chlorine, bromine, iodine, etc. can be contained. As the halide ions, chloride ions (Cl － -) are particularly preferred. The halide ions can improve the glossiness and leveling performance of the plating solution.

[0042] The concentration of the halide ions is the ionic mass concentration in the plating solution, and can be, for example, 0.01 to 150 mg / L, preferably about 10 to 100 mg / L.

[0043] [Evaluation of Antioxidant Property] Here, the antioxidant property of the metal plating film can be evaluated, for example, by subjecting the sample after plating to an oxidation treatment and measuring the thickness of the copper oxide formed on the surface. There are no particular restrictions on the conditions of the oxidation treatment, and it can be carried out, for example, by heat-treating in the air or an oxygen atmosphere at a temperature of about 100 to 200 °C for about 30 to 120 minutes to cause oxidation. The thickness of the copper oxide layer can be measured, for example, by the successive electrochemical reduction method (SERA method) or X-ray photoelectron spectroscopy (XPS). In particular, the SERA method can also measure the thicknesses of metal oxides with different valences, for example, both Cu ２ O and CuO, and is suitable for the analysis of the oxidation state of the metal plating film. In addition, in the XPS analysis, the thickness of the copper oxide layer may be measured, for example, as a value in terms of SiO ２ .

[0044] In the plating film formed by the plating solution according to this embodiment, for example, the thickness of the metal oxide layer after heat-treating at 150 °C for 1 hour in the air, for example, the total thickness of the CuO layer and Cu ２ O layer is 25 nm or less. If the thickness of the metal oxide layer formed by such an oxidation treatment is 25 nm or less, it can be said that the metal plating film has good antioxidant property. The thickness of the metal oxide layer is more preferably 22 nm or less, and particularly preferably 20 nm or less.

[0045] [Regarding the Preparation of the Plating Solution] The plating solution of this embodiment can be prepared using a conventional method from the above components, and the details can be appropriately determined in consideration of the composition and blending amount of each component, etc.

[0046] ≪Method for Forming an Antioxidant Plating Film≫ As described above, by performing a plating treatment using the plating solution of the above embodiment, a metal plating film with excellent antioxidant properties can be formed. The present invention also includes a method for forming an antioxidant plating film using the plating solution of the above embodiment.

[0047] ≪Plating Process≫ Using the plating solution of the above embodiment, it is possible to form metal wiring that is resistant to oxidation and has excellent conductivity on semiconductors and printed circuit boards used in electronic components, for example. Below, a typical embodiment of the plating process using the plating solution of the above embodiment will be described, but the plating processes to which the plating solution of the above embodiment can be applied are not limited to this embodiment.

[0048] [Plating Target] The plating solution of the above embodiment can be used on any target, such as various substrates and wafers. The plating solution of this embodiment can form a metal plating layer that is resistant to oxidation and has good conductivity, and can also fill voids of various sizes ranging from sub-μm to several hundred μm, making it suitable for plating electronic components. Examples of electronic components include, but are not limited to, printed circuit boards, flexible printed circuit boards, film carriers, semiconductor integrated circuits, resistors, capacitors, filters, inductors, thermistors, crystal oscillators, switches, and lead wires. The plating solution of the above embodiment can also be applied to a part of an electronic component, such as a bump electrode on a wafer, to form a film.

[0049] There are no particular restrictions on the substrates to be plated. For example, printed circuit boards, semiconductor package substrates, silicon wafers, ceramics, glass substrates, etc., can be plated. These substrates may contain a mixture of features such as blind via holes, trenches (grooves) for fine wiring, and through-holes that penetrate the substrate.

[0050] [Plating Operation] The plating process using the plating solution described above can be carried out by a normal plating operation. For example, the substrate to be plated may be pretreated as desired, such as degreasing, cleaning, or acid activation, and then a conductive treatment is performed on the substrate, such as forming a metal seed layer that will serve as a power supply layer. This conductive treatment can be carried out by a normal conductive treatment method, such as electroless plating to coat metal (including carbon), so-called direct plating methods using carbon or palladium, sputtering, vapor deposition, or chemical vapor deposition (CVD).

[0051] The conductive substrate is then plated with the plating solution of the above embodiment. The conditions for this are not particularly limited, and ordinary plating conditions can be followed. For example, a solution temperature of about 20 to 30°C and a cathode current density of 0.05 to 5 A / dm². ２ Plating should be performed to a certain extent. The plating time should be set appropriately according to the purpose of the plating. Furthermore, during plating, the liquid may be stirred by aeration, pump circulation, paddle stirring, etc.

[0052] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to these descriptions.

[0053] <Example 1> [Preparation of copper sulfate plating solution] A copper sulfate plating solution with the following composition was prepared according to the present invention. The charge density of nitrogen-containing compound A, which was used as a smoothing agent, was measured using the measurement method described below and was found to be 4.8 mEq / g. <Composition of copper sulfate plating solution> ・Copper sulfate pentahydrate: 100 g / L ・Sulfuric acid: 200 g / L ・Chloride ions: 60 mg / L (Cl － (Concentration, added as hydrochloric acid) • Smoothing agent (nitrogen-containing compound A): 200 mg / L • Brightening agent (SPS): 6 mg / L • Inhibitor (PEG20000*): 3000 mg / L *Mass-average molecular weight: 20000

[0054] [Measurement of Charge Density] The charge density of the leveling agent was measured by titrating a solution containing the leveling agent to which toluidine blue (TB) was added as an indicator under acidic conditions with acetic acid using 1 / 400N potassium polyvinyl sulfate (PVSK) as a titrant for anionic charge at room temperature. The end point was the point at which potassium polyvinyl sulfate (PVSK) reacted with toluidine blue (TB) and the color changed from blue to purple, and the charge density of the leveling agent was calculated from the product of the obtained titration volume and the charge density of the titrant.

[0055] [Copper Sulfate Plating] A brass plate was placed in the above copper sulfate plating solution, and copper sulfate plating was carried out under the following conditions until the surface plating thickness reached 9 μm. <Copper Sulfate Plating Conditions> - Current density: 2 A / dm ２ - Time: 20 minutes - Bath temperature: 25 °C - Bath volume: 500 mL - Stirring: Aeration 2.0 L / min

[0056] (Evaluation of Antioxidant Property) The substrate after plating was heat-treated at 150 °C in the air for 1 hour, and the thickness of the copper oxide formed on the surface (total thickness of the CuO layer and the Cu ２ O layer) was measured to evaluate the antioxidant property. The thickness of the surface copper oxide was measured by the SERRA method and XPS analysis (in terms of SiO ２ conversion). The measurement by the SERRA method was performed using QC-100 manufactured by ECI TECHNOLOGY, and the measurement by XPS was performed using Nexsa G2 manufactured by Thermo Fisher Scientific. The measurement results are shown in Table 1 described later together with the charge density of the leveling agent.

[0057] <<Comparative Example 1>>The same operations as in Example 1 were carried out except that nitrogen-containing compound B was used as the leveling agent. When the charge density of nitrogen-containing compound B was measured in the same manner as in Example 1, it was 1.2 mEq / g. The measurement results of the surface copper oxide thickness after heat treatment are shown in Table 1 described later together with the charge density of the leveling agent.

[0058] <<Example 2>> The same procedure as in Example 1 was followed, except that the concentration of nitrogen-containing compound A as a smoothing agent was set to 50 mg / L, the concentration of the brightening agent was set to 2 mg / L, and PEG1000 (mass-average molecular weight: 1000) was used as an inhibitor with a concentration of 150 mg / L. The measurement results of the surface copper oxide thickness after heat treatment, along with the charge density of the smoothing agent, are shown in Table 1 below.

[0059] <<Comparative Example 2>> The same procedure as in Example 2 was followed, except that nitrogen-containing compound B was used as the smoothing agent. The measurement results of the surface copper oxide thickness after heat treatment, along with the charge density of the smoothing agent, are shown in Table 1 below.

[0060]

[0061] As described above, in Examples 1 and 2, where nitrogen-containing compound A with a charge density of 1.5 mEq / g or more was used as a smoothing agent, the surface copper oxide thickness after heat treatment was suppressed to about 2 / 3 to 3 / 4 compared to Comparative Examples 1 and 2, where nitrogen-containing compound B with a charge density of less than 1.5 mEq / g was used. According to the present invention, it has been shown that a metal plating film with excellent antioxidant properties can be obtained using a plating solution containing a smoothing agent with a charge density of 1.5 mEq / g or more together with metal ions. Furthermore, as shown in Table 1, it was found that the measurement results for surface copper oxide thickness were almost equivalent between the SERA method and XPS analysis. Therefore, in the following examples and comparative examples, only the measurement results by the SERA method will be shown for surface copper oxide thickness.

[0062] <<Example 3>> The same procedure as in Example 2 was followed, except that nitrogen-containing compound C (charge density: 1.7 mEq / g) was used as a smoothing agent at a concentration of 100 mg / L and no inhibitor was included. The surface copper oxide thickness after heat treatment was 15.2 nm.

[0063] <<Comparative Example 3>> The same procedure as in Example 3 was followed, except that nitrogen-containing compound D (charge density: 0.6 mEq / g) was used as a smoothing agent. The surface copper oxide thickness after heat treatment was 28.8 nm.

[0064] From the above, it has become clear that even in a plating solution without inhibitors, a metal plating film with excellent antioxidant properties can be obtained by using a smoothing agent with a charge density of 1.5 Eq / g or higher.

[0065] <<Examples 4-8>> The same procedure as in Example 2 was followed, except that nitrogen-containing compounds E-I (charge density: 1.9-19.9 mEq / g) shown in Table 1 were used as smoothing agents at a concentration of 100 mg / L, and PEG1540 (mass-average molecular weight: 1540) was used as an inhibitor at a concentration of 100 mg / L. The measurement results of the surface copper oxide thickness after heat treatment are shown in Table 2 below, along with the type of smoothing agent and charge density.

[0066]

[0067] As described above, in Examples 4 to 8, where nitrogen-containing compounds E to J with a charge density of 1.5 mEq / g or higher were used as smoothing agents, metal plating films with excellent antioxidant properties were obtained, with a surface copper oxide thickness of less than 20 nm after heat treatment. In particular, Examples 6 to 8, which used smoothing agents with a charge density of 3.0 mEq / g or higher, and Example 6, which used a smoothing agent with a charge density of 3.3 mEq / g, showed particularly good antioxidant properties of the metal plating films.

[0068] Examples 9-12: The same procedure as in Example 3 was followed, except that the concentration of nitrogen-containing compound C (charge density: 1.7 mEq / g) used as a smoothing agent was varied as shown in Table 3. The measurement results of the surface copper oxide thickness after heat treatment are shown in Table 3 below, along with the smoothing agent concentration and the results for Example 3 and Comparative Example 3.

[0069]

[0070] As described above, when the charge density of the smoothing agent was 1.5 mEq / g or higher, the surface copper oxide thickness after heat treatment was 20 nm or less regardless of the concentration within the range of 10 to 200 mg / L, demonstrating excellent antioxidant properties. Furthermore, a tendency was observed for the surface copper oxide thickness after heat treatment to decrease as the concentration of the smoothing agent decreased.

[0071] Examples 13-17 were carried out in the same manner as in Examples 9-12, except that nitrogen-containing compound A (charge density: 4.8 mEq / g) was used as the smoothing agent. The measurement results of the surface copper oxide thickness after heat treatment are shown in Table 4 below, along with the smoothing agent concentration and the results for Comparative Example 3.

[0072]

[0073] As described above, even when nitrogen-containing compound A was used, the surface copper oxide thickness after heat treatment was 20 nm or less regardless of the concentration, and a tendency was observed for the surface copper oxide thickness after heat treatment to decrease when the concentration of the smoothing agent was low.

[0074] Examples 18-19: The same procedure as in Example 12 was followed, except that the concentration of the brightener was varied as shown in Table 5 below. The results of measuring the surface copper oxide thickness after heat treatment are shown in Table 5 below, along with the brightener concentration and the results from Example 12.

[0075]

[0076] Table 5 shows that the lower the concentration of the brightener, the smaller the surface copper oxide thickness after heat treatment, resulting in the formation of a metal plating film with excellent oxidation resistance. In particular, Example 12, where the brightener concentration was 2 mg / L or less, showed a small surface copper oxide thickness after heat treatment.

[0077] As described above, it has become clear that a metal plating film with excellent antioxidant properties can be obtained using a plating solution containing a smoothing agent with a charge density of 1.5 mEq / g or more together with metal ions, according to the present invention.

Claims

1. A plating solution containing metal ions and a smoothing agent with a charge density of 1.5 mEq / g or higher.

2. The plating solution according to claim 1, comprising the smoothing agent at a concentration of 10 to 300 mg / L.

3. The plating solution according to claim 1, further containing a brightening agent, wherein the brightening agent is contained at a concentration of 0.1 to 5 mg / L.

4. The plating solution according to claim 1, further comprising an inhibitor, wherein the inhibitor is contained in a concentration of 0.1 to 2000 mg / L.

5. The plating solution according to claim 4, wherein the mass-average molecular weight of the inhibitor is in the range of 200 to 10000.

6. The plating solution according to claim 1, wherein the nitrogen-containing compound constituting the smoothing agent comprises one or more compounds selected from the group consisting of amines, imidazolines, imidazoles, benzimidazoles, indoles, pyridines, quinolines, isoquinolines, anilines, and aminocarboxylic acids.

7. The plating solution according to claim 1, wherein the charge density of the nitrogen-containing compound constituting the smoothing agent is 2.0 to 20.0 mEq / g.

8. The plating solution according to any one of claims 1 to 7, wherein the metal ions include copper ions.

9. A method for forming an antioxidant plating film using the plating solution described in any one of claims 1 to 7.

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