阅读说明：本技术 电解镀金液及其制造方法、以及镀金方法及金配合物 (Electrolytic gold plating solution, process for producing the same, gold plating method, and gold complex ) 是由 佐佐木晴子 朝川隆信 于 2020-03-02 设计创作，主要内容包括：提供一种不含氰化物且氧化稳定性优异、并且镀金时的电流效率方面良好的电解镀金液。一种使用金配合物作为金源、并且含有螯合剂、传导盐以及缓冲剂的电解镀金液,其中金配合物具有下述通式(1)所表示的乙内酰脲类化合物配位到1价的金离子而成的结构。[化学式1]<Image he="398" wi="549" file="DDA0002397161140000011.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>式(1)中,R<Sub>1</Sub>～R<Sub>4</Sub>各自独立地表示氢原子或1价的有机基团,R<Sub>1</Sub>与R<Sub>2</Sub>中的两者或者任意一者为氢原子,且R<Sub>3</Sub>与R<Sub>4</Sub>中的两者或者任意一者为氢原子。但是,排除R<Sub>1</Sub>为甲基且R<Sub>2</Sub>～R<Sub>4</Sub>全部为氢原子的情况。(Disclosed is an electrolytic gold plating solution which contains no cyanide, has excellent oxidation stability, and has good current efficiency in gold plating. An electrolytic gold plating solution using a gold complex as a gold source, and containing a chelating agent, a conductive salt and a buffer, wherein the gold complex has a structure in which a hydantoin compound represented by general formula (1) is coordinated to a 1-valent gold ion. [ chemical formula 1] In the formula (1), R 1 ～R 4 Each independently represents a hydrogen atom or a 1-valent organic group, R 1 And R 2 Either or both of them are hydrogen atoms, and R is 3 And R 4 Either or both of them are hydrogen atoms. However, excluding R 1 Is methyl and R 2 ～R 4 All are hydrogen atoms.)

1. An electrolytic gold plating solution which uses a gold complex as a gold source and contains a chelating agent, a conductive salt and a buffer agent,

the gold complex has a structure in which a hydantoin compound represented by the following general formula (1) is coordinated to a 1-valent gold ion,

[ chemical formula 1]

In the formula (1), R₁～R₄Each independently represents a hydrogen atom or a 1-valent organic group, R₁And R₂Either or both of them are hydrogen atoms, and R is₃And R₄Either or both of them are hydrogen atoms, except that R is excluded₁Is methyl and R₂～R₄All are hydrogen atoms.

2. The electrolytic gold-plating solution according to claim 1, wherein the chlorine concentration in the electrolytic gold-plating solution is 1000ppm or less.

3. The electrolytic gold-plating solution according to claim 1 or 2, wherein the gold complex is derived from an alkali metal salt.

4. The electrolytic gold-plating liquid according to claim 1 or 2, wherein the chelating agent contains at least one of a hydantoin compound and a succinimide.

5. An electrolytic gold plating solution which uses a gold complex as a gold source and contains a chelating agent, a conductive salt and a buffer agent,

the gold complex has a structure in which a hydantoin compound represented by the following general formula (2) is coordinated to a gold ion having a valence of 1, and the chlorine concentration in the electrolytic gold plating solution is 1000ppm or less,

[ chemical formula 2]

In the formula (2), R₅～R₈Each independently represents a hydrogen atom or a 1-valent organic group, R₅And R₆Either or both of them are hydrogen atoms, and R is₇And R₈Either or both of them are hydrogen atoms.

6. The electrolytic gold-plating solution according to claim 5, wherein the gold complex is derived from an alkali metal salt.

7. The electrolytic gold-plating liquid according to claim 5 or 6, wherein the chelating agent contains at least one of a hydantoin compound and a succinimide.

8. A method for producing an electrolytic gold-plating solution according to any one of claims 1 to 4, characterized by comprising:

a step of reacting chloroauric acid or a chloroauric acid salt, a hydantoin compound represented by the general formula (1), and an alkali metal hydroxide in an aqueous solution to form the gold complex;

a step of cooling the aqueous solution containing the gold complex to extract a gold complex alkali metal salt; and

a step of using the gold complex alkali metal salt to produce the electrolytic gold plating liquid.

9. A method for producing an electrolytic gold-plating solution according to any one of claims 5 to 7, characterized by comprising:

a step of reacting chloroauric acid or a chloroauric acid salt, a hydantoin compound represented by the general formula (2), and an alkali metal hydroxide in an aqueous solution to form the gold complex;

a step of cooling the aqueous solution containing the gold complex to extract a gold complex alkali metal salt; and

a step of using the gold complex alkali metal salt to produce the electrolytic gold plating liquid.

10. A gold plating method for performing plating treatment using the electrolytic gold plating solution according to any one of claims 1 to 7, characterized in that:

at a pH of 5.0 to 10.0, a liquid temperature of 20 to 80 ℃ and a current density of 0.1A/dm²～4.5A/dm²Electrolytic plating is performed under the conditions of (1).

11. A gold complex characterized by: has a structure in which a hydantoin compound represented by the following general formula (1) is coordinated to a 1-valent gold ion,

[ chemical formula 3]

In the formula (1), R₁～R₄Each independently represents a hydrogen atom or a 1-valent organic group, R₁And R₂Either or both of them are hydrogen atoms, and R is₃And R₄Either or both of them are hydrogen atoms, except that R is excluded₁Is methyl and R₂～R₄All are hydrogen atoms.

Technical Field

The present invention relates to an electrolytic gold plating solution used for gold plating of wafers, substrates, and the like, a method for producing the same, and a gold plating method, and further relates to a gold complex that can be used as a raw material of the electrolytic gold plating solution.

Background

As a plating solution used in electrolytic plating and electroless plating methods, a cyanide-based gold plating solution has been conventionally used in which a gold cyanide complex having excellent oxidation stability in the solution is used as a gold supply source. However, the gold cyanide salts are not preferable from the viewpoint of safety in handling and wastewater treatment because of their high toxicity. Further, when a cyanide gold plating solution is used, the resist pattern of the semiconductor member is peeled and damaged by excess cyanide, and thus there is a problem that it is difficult to form a fine circuit pattern.

In view of such problems, it is desirable to use a plating solution using a gold salt or a gold complex containing no cyanogen, and an example thereof is a gold sulfite salt (Na)₃Au(SO₃)₂) A non-cyanide gold plating solution such as a solution.

However, the gold salts and gold complexes contained in these non-cyanide gold plating solutions have a problem of poor oxidation stability and decomposition during plating operation. For example, in the above-mentioned gold sulfite, sulfite ions in the solution are easily oxidized and decomposed by dissolved oxygen in the plating solution and air introduced by stirring or introduction and discharge of the plating object, and the concentration thereof is reduced, so that the oxidation stability of the gold complex is lowered, and the plating solution may be decomposed. When such decomposition occurs, a gold precipitation phenomenon, i.e., gold precipitation or precipitation of the plating solution, occurs in the plating bath tank or the pipe, and the plating operation is hindered. Therefore, in the case of non-cyanide electrolytic plating, plating treatment is performed by adding an additive such as a stabilizer or a complexing agent to the plating solution to prevent decomposition of the plating solution, but such a measure complicates the cost of the stabilizer and the steps for producing the plating solution, and thus the cost thereof increases.

In addition, plating solutions containing gold salts or gold complexes having low oxidation stability also have problems from the viewpoint of storage thereof. In the case of the gold sulfite, since the gold salt is decomposed during storage and a black precipitate is likely to be generated, it is necessary to store the gold sulfite in a light-shielded state, and the management thereof is not easy.

Therefore, as a gold complex which does not contain cyanide and is excellent in oxidation stability, patent documents 1 and 2 disclose a gold complex using a hydantoin compound as a ligand. The gold complex described in patent document 1 is a complex in which chloroauric acid or a chloroauric acid salt and a hydantoin compound are reacted in an aqueous solution to coordinate the hydantoin compound to a gold ion. The gold complex described in patent document 2 is a complex in which a gold hydroxide salt and a hydantoin compound are heated and reacted in an aqueous solution to coordinate the hydantoin compound to a gold ion.

Disclosure of Invention

[ problems to be solved by the invention ]

These gold complexes have a remarkable oxidation stability as compared with conventional non-cyanide gold salts or gold complexes such as the above-mentioned sulfites. In patent documents 1 and 2, it is recommended to use 5, 5-dimethylhydantoin as the hydantoin compound to be coordinated to the gold ion because the oxidation stability of the complex after the reaction is particularly excellent. However, since 5, 5-dimethylhydantoin does not have a hydrogen atom at the carbon at the 5-position, it does not oxidize itself, so that a reaction of reducing gold from a valence of 3 to a valence of 1 does not occur, and it is stabilized in the form of a gold ion complex having a valence of 3. As a result, when gold is plated using an electrolytic gold plating solution produced from the gold ion complex, it is necessary to match the cathodic current density with the 3-valent gold ion complex, which is disadvantageous in terms of current efficiency.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an electrolytic gold plating solution which does not contain a cyanide compound, is excellent in oxidation stability, and is excellent in current efficiency at the time of gold plating.

[ means for solving problems ]

As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by using, as a gold complex used as a gold source, a compound having a structure in which a specific hydantoin compound is coordinated to a 1-valent gold ion.

That is, the electrolytic gold plating solution according to the present invention comprises the following constitution [1 ].

[1] An electrolytic gold plating solution using a gold complex as a gold source and containing a chelating agent, a conductive salt and a buffer agent,

the gold complex has a structure in which a hydantoin compound represented by general formula (1) is coordinated to a 1-valent gold ion.

[ chemical formula 1]

In the formula (1), R₁～R₄Each independently represents a hydrogen atom or a 1-valent organic group, R₁And R₂Either or both of them are hydrogen atoms, and R is₃And R₄Either or both of them are hydrogen atoms. However, excluding R₁Is methyl and R₂～R₄All are hydrogen atoms.

Preferred embodiments of the electrolytic gold plating solution according to the present invention include the following configurations [2] to [4 ].

[2] The electrolytic gold-plating solution according to the above [1], wherein the chlorine concentration in the electrolytic gold-plating solution is 1000ppm or less.

[3] The electrolytic gold-plating liquid according to the above [1] or [2], wherein the gold complex is derived from an alkali metal salt.

[4] The electrolytic gold plating solution according to any one of 1 to 3 above, wherein the chelating agent contains at least one of a hydantoin compound and a succinimide.

The electrolytic gold plating solution according to the present invention has the following constitution [5 ].

[5] An electrolytic gold plating solution using a gold complex as a gold source and containing a chelating agent, a conductive salt and a buffer agent,

the gold complex has a structure in which a hydantoin compound represented by general formula (2) is coordinated to a 1-valent gold ion, and the concentration of chlorine in the electrolytic gold plating solution is 1000ppm or less.

[ chemical formula 2]

In the formula (2), R₅～R₈Each independently represents a hydrogen atom or a 1-valent organic group, R₅And R₆Either or both of them are hydrogen atoms, and R is₇And R₈Either or both of them are hydrogen atoms.

A preferred embodiment of the electrolytic gold plating solution according to the present invention includes the following constitution [6] or [7 ].

[6] The electrolytic gold-plating solution according to the above [5], wherein the gold complex is derived from an alkali metal salt.

[7] The electrolytic gold-plating liquid according to any one of [5] and [6], wherein the chelating agent contains at least one of a hydantoin compound and a succinimide.

The method for producing an electrolytic gold-plating solution according to the present invention includes the following constitution [8] or [9 ].

[8] A method for producing an electrolytic gold-plating solution according to any 1 of [1] to [4], comprising:

a step of reacting chloroauric acid or a chloroauric acid salt, a hydantoin compound represented by the general formula (1), and an alkali metal hydroxide in an aqueous solution to form the gold complex,

a step of cooling the aqueous solution containing the gold complex to extract the gold complex alkali metal salt, and

a step of using the gold complex alkali metal salt to produce the electrolytic gold plating liquid.

[9] A method for producing an electrolytic gold-plating solution according to any 1 of [5] to [7], comprising:

a step of reacting chloroauric acid or a chloroauric acid salt, a hydantoin compound represented by the general formula (2), and an alkali metal hydroxide in an aqueous solution to form the gold complex,

a step of cooling the aqueous solution containing the gold complex to extract the gold complex alkali metal salt, and

a step of using the gold complex alkali metal salt to produce the electrolytic gold plating liquid.

The gold plating method according to the present invention includes the following constitution [10 ].

[10] A gold plating method using the electrolytic gold plating solution according to any one 1 of [1] to [7] for plating treatment,

at a pH of 5.0-10.0, a liquid temperature of 20-80 ℃ and a current density of 0.1A/dm²～4.5A/dm²Electrolytic plating is performed under the conditions of (1).

The gold complex according to the present invention has the following structure [11 ].

[11] A gold complex characterized by having a structure in which a hydantoin compound represented by the following general formula (1) is coordinated to a 1-valent gold ion.

[ chemical formula 3]

In the formula (1), R₁～R₄Each independently represents a hydrogen atom or a 1-valent organic group, R₁And R₂Either or both of them are hydrogen atoms, and R is₃And R₄Either or both of them are hydrogen atoms. However, excluding R₁Is methyl and R₂～R₄All are hydrogen atoms.

[ Effect of the invention ]

The present invention can provide an electrolytic gold plating solution which contains no cyanide, has excellent oxidation stability, and has good current efficiency in gold plating.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the embodiments described below, and can be arbitrarily modified and implemented without departing from the spirit of the present invention.

< electrolytic gold plating solution >

The electrolytic gold plating solution of the present embodiment will be explained. The electrolytic gold plating solution of the present embodiment uses a gold complex as a gold source, and contains at least a chelating agent, a conductive salt, and a buffer. The gold complex has a structure in which a hydantoin compound represented by the following general formula (1) is coordinated to a gold ion having a valence of 1.

[ chemical formula 4]

In the formula (1), R₁～R₄Each independently represents a hydrogen atom or a 1-valent organic group, R₁And R₂Either or both of them are hydrogen atoms, and R is₃And R₄Either or both of them are hydrogen atoms. However, excluding R₁Is methyl and R₂～R₄All are hydrogen atoms.

The gold complex according to the present embodiment is characterized in that: in the electrolytic gold plating solution, the valence number of gold ions is 1. Since the valence number of gold ions is 1, when gold is plated using an electrolytic gold plating solution, the cathodic current density can be made equal to that of a 1-valent gold ion complex, and the cathodic current density can be 1/3 as compared with the case of 3-valent gold ion complex, which is advantageous in terms of current efficiency as compared with the case of 3-valent gold ion complex. Further, since the anode current density can be 1/3 for the above reasons, the oxidative decomposition of the plating bath in the vicinity of the anode can be reduced, and the life of the plating bath can be prolonged, as compared with the case of 3-valent.

In addition, in the gold complex using a hydantoin compound as a ligand, a specific compound among the hydantoin compounds is used so that the valence number of the gold ion becomes 1. Specifically, a hydantoin compound represented by the following general formula (1) is used as a ligand. The identification of the ligand can be achieved simply by separating and qualitatively analyzing the ligand released by the coordination balance in the solution of the gold complex by a method such as liquid chromatography.

[ chemical formula 5]

In the formula (1), R₁～R₄Each independently represents a hydrogen atom or a 1-valent organic group, R₁And R₂Either or both of them are hydrogen atoms, and R is₃And R₄Either or both of them are hydrogen atoms. However, excluding R₁Is methyl and R₂～R₄All are hydrogen atoms.

These hydantoin compounds undergo a reaction of reducing gold from a valence of 3 to a valence of 1 under alkaline conditions and are stabilized in the form of a gold ion complex having a valence of 1.

In the general formula (1), R is₁～R₄Examples of the 1-valent organic group include: methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, neopentyl, dodecyl, hexadecyl and other alkyl groups containing linear and isomeric, secondary, tertiary and other structural isomers; a hydroxyalkyl group; alkenyl groups containing linear and isomeric forms, such as isomeric forms, secondary and tertiary forms, such as vinyl, allyl and isopropenyl; alkoxy groups such as methoxy and ethoxy; carboxylic acids such as acetoxy and propionyloxy; acyl groups such as acetyl and propionyl; aromatic hydrocarbon groups such as phenyl, methylphenyl, hydroxyphenyl and benzyl; and hydroxyl groups, and the like. In addition, from the viewpoint of water solubility and economy, the organic group preferably has 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms, and still more preferably 1 carbon atom.

Specific examples of the hydantoin compound represented by the general formula (1) include: hydantoin (R)₁～R₄All hydrogen atoms), 3-methylhydantoin (R)₂Is methyl and R₁、R₃And R₄All hydrogen atoms), 5-methylhydantoin (R)₃Is methyl and R₁、R₂And R₄All hydrogen atoms), hydantoin-5-acetic acid (R)₃Is acetic acid and R₁、R₂And R₄All being hydrogen atoms). Of these, hydantoin is preferably used from the viewpoint of being the cheapest and economical as a material.

In the above formula (1), the term "excluding R" means that R is not excluded₁Is methyl and R₂～R₄The meaning of all hydrogen atoms "means: in hydantoin compounds, R is excluded₁Is methyl and R₂～R₄"1-methylhydantoin" in the case of all hydrogen atoms.

On the other hand, in hydantoin compounds other than these compounds, that is, for example, in 5, 5-dimethylhydantoin and 1,5, 5-trimethylhydantoin, since the carbon at the 5-position (see the above general formula (1)) has no hydrogen, oxidation does not occur by itself even under alkaline conditions, and therefore, a reaction of reducing gold from a 3-valent state to a 1-valent state does not occur, and gold is stabilized in the form of a 3-valent gold ion complex. Further, hydantoin acids do not have a hydantoin ring structure, and therefore do not oxidize themselves even under alkaline conditions, and therefore, as described above, gold is stabilized as a 3-valent gold ion complex without a reaction of reducing gold from a 3-valent state to a 1-valent state.

Further, since gold and hydantoin-based compounds form a complex by hydrogen dissociation at the nitrogen at the 1-position or the nitrogen at the 3-position and the nitrogen at the 1-position or the nitrogen at the 3-position binds to gold (see the above general formula (1)), a gold complex cannot be formed in 1, 3-dimethylhydantoin in which both the nitrogen at the 1-position and the nitrogen at the 3-position bind to an alkyl group.

In addition, the other electrolytic gold plating solution of the present embodiment also uses a gold complex as a gold source, and contains a chelating agent, a conductive salt, and a buffer. The gold complex has a structure in which a hydantoin compound represented by the following general formula (2) is coordinated to a 1-valent gold ion, and the chlorine concentration in the electrolytic gold plating solution is 1000ppm or less.

[ chemical formula 6]

In the formula (2), R₅～R₈Each independently represents a hydrogen atom or a 1-valent organic group, R₅And R₆Either or both of them are hydrogen atoms, and R is₇And R₈Either or both of them are hydrogen atoms.

These hydantoin compounds also undergo a reaction of reducing gold from a valence of 3 to a valence of 1 under alkaline conditions, and are stabilized in the form of a gold ion complex having a valence of 1.

In the general formula (2), R is₅～R₈Examples of the 1-valent organic group include: alkyl groups containing linear and isomeric structures such as isomeric forms, secondary and tertiary forms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, neopentyl, dodecyl and hexadecyl groups; a hydroxyalkyl group; alkenyl groups containing linear and isomeric forms, such as isomeric forms, secondary and tertiary forms, such as vinyl, allyl and isopropenyl; alkoxy groups such as methoxy and ethoxy; carboxylic acids such as acetoxy and propionyloxy; acyl groups such as acetyl and propionyl; aromatic hydrocarbon groups such as phenyl, methylphenyl, hydroxyphenyl and benzyl; and hydroxyl groups, and the like. In addition, from the viewpoint of water solubility and economy, the organic group preferably has 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms, and still more preferably 1 carbon atom.

Specific examples of the hydantoin compound represented by the general formula (2) include: hydantoin (R)₅～R₈All hydrogen atoms), 1-methylhydantoin (R)₅Is methyl and R₆～R₈All hydrogen atoms), 3-methylhydantoin (R)₆Is methyl and R₅、R₇And R₈All hydrogen atoms), 5-methylhydantoin (R)₇Is methyl and R₅、R₆And R₈All hydrogen atoms), hydantoin-5-acetic acid (R)₇Is acetic acid and R₅、R₆And R₈All being hydrogen atoms). Of these, hydantoin is preferably used from the viewpoint of being the cheapest and economical as a material.

In the electrolytic gold plating solution according to the present embodiment, the chlorine concentration in the electrolytic gold plating solution is preferably 1000ppm or less. Since the concentration of chlorine in the electrolytic gold plating solution is 1000ppm or less, that is, since the electrolytic gold plating solution contains substantially no chlorine, it can be applied to a plating object that is free from chlorine.

Here, in an electrolytic gold plating solution produced by using a gold complex obtained by reacting chloroauric acid or a chloroauric acid salt with a hydantoin-based compound as in patent document 1, a large amount of chloride ions derived from the chloroauric acid or the chloroauric acid salt are contained in the electrolytic gold plating solution, and therefore, it is difficult to apply the electrolytic gold plating solution to a chlorine-free object.

In the present embodiment, the reason why the chlorine concentration in the electrolytic gold plating solution is set to 1000ppm or less as an index that the electrolytic gold plating solution does not substantially contain chlorine is to avoid chlorine in the electrolytic gold plating solution is because chlorine remains on the surface of the gold film, which reduces the adhesion to the substrate or the bond, causes corrosion of the film, and is present at the grain boundary of the gold film to make it difficult to adjust the hardness, and by considering the above, the chlorine concentration in the electrolytic gold plating solution is preferably 500ppm or less, more preferably 300ppm or less, and still more preferably 200ppm or less, in order to realize application to a plating object avoiding chlorine without problems.

A method for obtaining an electrolytic gold plating solution substantially free of chlorine will be described later.

Next, the chelating agent, the conductive salt, and the buffer agent constituting the electrolytic gold plating solution of the present embodiment will be described.

As the chelating agent, hydantoin, 1-methylhydantoin, 5-dimethylhydantoin and succinimide are suitably used, as well as the chelating agent is added separately from the ligand of the gold complex. Among these, it is more preferable to contain at least one of 5, 5-dimethylhydantoin and succinimide as a chelating agent for oxidation stability and deposition uniformity of the gold complex in the plating solution. By using a chelating agent in the electrolytic gold plating solution, a very stable gold plating solution can be obtained. That is, gold precipitation hardly occurs in the plating treatment. This is because these chelating agents are in equilibrium with the ligands of the gold complex, and do not have such a reducing property as sulfurous acid, but have such a property that oxidative decomposition is difficult to occur.

The state of equilibrium or the mixed concentration of the chelating agent and the ligand of the gold complex can be confirmed by ion chromatography, liquid chromatography, or the like.

When the pH is 5 to 7, the amount of the chelating agent is preferably more than 0-fold mol and not more than 4-fold mol with respect to gold. In the case where the amount of the gold complex used is large and the gold complex is frequently replenished, the chelating agent may not be contained in the initial stage because the ligand of the gold complex is released, and the burnt appearance may appear in the case where the amount exceeds 4 times by mol.

In addition, when the pH is 8 to 10, the amount of the chelating agent is preferably 4 to 10 times by mol with respect to gold. When the amount is less than 4 times by mol, a scorched appearance may be observed, or a gold precipitation phenomenon may be observed since the ligand of the gold complex is preferentially subjected to an oxidative decomposition reaction due to basicity as compared with maintaining the balance of the chelating agent and the ligand of the gold complex. In addition, when the amount exceeds 10 times by mole, no change in appearance or oxidation stability is observed, and the effect of increasing the chelating agent is not expected.

As the conductive salt, it is preferable to use any 1 or 2 or more of hydrochloric acid, sulfuric acid, sulfurous acid, sulfamic acid, nitric acid, phosphoric acid, or salts of these acids. When these are used alone or in combination as a conductive salt, the electrolytic gold plating solution according to the present embodiment has very excellent solution stability.

When the conductive salt is contained in the electrolytic gold plating solution according to the present embodiment, the concentration of the conductive salt is preferably in the range of 0.05mol/L to 1.95 mol/L. When the conductive salt concentration is less than 0.05mol/L, the conductivity decreases, so that the current efficiency decreases, and poor appearance of plating is also likely to occur. In addition, when it exceeds 1.95mol/L, no change is seen in conductivity and appearance, and salting-out becomes easy to occur depending on pH.

As the buffer, any 1 or 2 or more of boric acid, succinic acid, phthalic acid, tartaric acid, citric acid, phosphoric acid, or salts of these acids is preferably used. When these are used alone or in combination as a buffer, the pH of the electrolytic gold plating solution according to the present embodiment does not change greatly, and the gold plating solution can be easily maintained at a neutral pH ranging from weak acidity to weak alkalinity (pH of about 5.0 to 10.0).

When the electrolytic gold plating solution according to the present embodiment contains the buffer, the buffer concentration is preferably set to a concentration range of 0.05mol/L to 1.95 mol/L. When the buffer concentration is less than 0.05mol/L, there is no effect of stabilizing pH. In addition, when it exceeds 1.95mol/L, no change is seen in the stability of pH, and salting-out becomes easy to occur depending on the pH.

The total concentration of the conductive salt and the buffer agent is preferably set to a concentration range of 0.1mol/L to 2.0 mol/L. When the total concentration of the conductive salt and the buffer agent is 0.1mol/L to 2.0mol/L, the gold plating solution according to the present embodiment has the most excellent overall balance in actual operation. That is, the solution stability is excellent, the current efficiency is high, and the pH of the plating solution is not greatly changed.

From the viewpoint of preventing salting out in winter, the total concentration of the conductive salt and the buffer is more preferably in the range of 0.1 to 1.0 mol/L.

The concentration of gold in the electrolytic gold plating solution according to the present embodiment is preferably in the range of 0.5g/L to 15g/L, depending on the ratio to the concentration of the chelating agent. It is considered that when the amount is less than 0.5g/L, gold is not electrodeposited unless a voltage of 3V or more is applied, and when the amount exceeds 15g/L, the metal is taken out of the plating tank depending on the object to be plated, which is economically inconvenient and is likely to be salted out in winter.

The gold concentration is preferably in the range of 4g/L to 8 g/L. Within this concentration range, various objects to be plated can be controlled, and the concentration change due to gold consumption can be easily managed.

In the electrolytic gold plating solution according to the present embodiment, the gold complex is preferably derived from an alkali metal salt. As described later, the specific hydantoin compound used in the present embodiment is stabilized in the form of a 1-valent gold ion complex under alkaline conditions, and the gold complex alkali metal salt extracted subsequently is substantially free of chlorine. By producing an electrolytic gold plating solution using the gold complex alkali metal salt, an electrolytic gold plating solution can be produced that can be applied to a chlorine-free object to be plated.

The alkali metal salt includes, for example, a lithium salt, a sodium salt, a potassium salt, a rubidium salt, and a cesium salt, and among these, a sodium salt or a potassium salt is preferable. This is because they are common to existing gold compounds (i.e., gold potassium cyanide, gold sodium sulfite, or the like) and are salts using economically excellent alkali metals.

< method for producing electrolytic gold plating solution >

The method for producing the electrolytic gold plating solution according to the present embodiment will be described. The method for producing an electrolytic gold plating solution of the present embodiment includes: a step of reacting chloroauric acid or a chloroauric acid salt, a hydantoin compound represented by the general formula (1) or the general formula (2), and an alkali metal hydroxide in an aqueous solution to form a gold complex alkali metal salt and extracting the gold complex alkali metal salt; and a step of producing an electrolytic gold plating solution using the gold complex alkali metal salt.

As described above, the electrolytic gold plating solution according to the present embodiment is characterized by containing substantially no chlorine. Therefore, although a gold complex using a hydantoin compound as a ligand can be formed using a gold hydroxide salt as described in patent document 2 as a raw material, the yield of the gold hydroxide salt is usually not as high as about 60% at most, and therefore the cost of gold used as an electrolytic gold plating solution becomes high, which is uneconomical.

Therefore, in order to obtain an electrolytic gold plating solution that can be applied to a plating object that is free from chlorine while suppressing the cost of gold used, the present embodiment is characterized in that the electrolytic gold plating solution is obtained by the following production method.

First, chloroauric acid or a chloroauric acid salt is prepared as a raw material for obtaining a gold complex, as in the conventional art. Further, a hydantoin compound represented by the above general formula (1) or (2) for coordination to a gold ion, and an alkali metal hydroxide such as lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), rubidium hydroxide (RbOH), and cesium hydroxide (CsOH) are prepared.

Then, chloroauric acid or a chloroauric acid salt, the hydantoin compound, and an alkali metal hydroxide are reacted in an aqueous solution to obtain a gold complex having a structure in which the hydantoin compound represented by the general formula (1) or (2) is coordinated to a 1-valent gold ion.

In the present embodiment, the temperature is preferably 40 to 80 ℃ and the reaction time is preferably 30 to 360 minutes as the reaction conditions of the chloroauric acid or the chloroauric acid salt and the hydantoin compound. The reaction temperature is particularly preferably 60 to 75 ℃ and the reaction time is particularly preferably 180 minutes or more.

Even if only chloroauric acid or a chloroauric acid salt is mixed with a hydantoin compound, the hydantoin compound in the liquid functions as a so-called chelating agent, but gold remains in the state of a gold chloride complex and does not form a complex. Further, although gold can be plated with such a liquid, since gold is still 3-valent, the amount of deposition becomes 1/3, and the mechanism of deposition also becomes different from the case of the gold complex according to the present embodiment.

Here, the raw material of the gold complex according to the present embodiment is chloroauric acid or a chloroauric acid salt, and the chloroauric acid salt is preferably a salt of chloroauric acid and an alkali metal (lithium, sodium, potassium, rubidium, cesium) or an alkaline earth metal (magnesium, calcium, strontium, barium), and particularly preferably sodium chloroauric acid or potassium chloroauric acid.

Then, when the gold complex-containing solution obtained as described above is cooled to room temperature (25 ℃ C.) or lower, crystals of the structurally chlorine-free gold complex alkali metal salt precipitate, and solid-liquid separation is performed to extract the gold complex alkali metal salt from the solution. By such treatment, chlorine remains in the solution, and it is needless to say that the extracted gold complex alkali metal salt contains substantially no chlorine. According to this method of operation, the gold complex alkali metal salt can be obtained from the solution in a very high yield without using a gold hydroxide salt.

Subsequently, when an electrolytic gold plating solution is produced using the gold complex alkali metal salt extracted from the solution as a raw material, an electrolytic gold plating solution substantially free of chlorine can be obtained.

For reference, it is described in paragraph 0017 of patent document 1 and paragraph 0013 of patent document 2 that "a gold complex formation reaction occurs in an aqueous solution, and a solution after the reaction can be directly used as a raw material of a plating solution when the complex is supplied for use in a plating solution or the like", but, for example, when gold complex is formed by using chloroauric acid or a chloroauric acid salt as a raw material of a plating solution, if the solution after the reaction is directly used as a raw material of a plating solution, a large amount of chloride ions are contained in the solution after the reaction, and a state in which a large amount of chloride ions are also contained in an electrolytic gold plating solution is obtained, and thus it is difficult to apply the solution to a plating object avoiding chlorine.

< gold plating method >

The gold plating method according to the present embodiment will be described. The gold plating method of the present embodiment is a plating method using the above electrolytic gold plating solution, wherein the plating is performed at a pH of 5.0 to 10.0, a solution temperature of 20 to 80 ℃, and a current density of 0.1A/dm²～4.5A/dm²Electrolytic plating is performed under the conditions of (1).

The pH value of the gold plating solution depends on the concentrations of the buffer and the conductive salt, and is within the range of pH5.0 to 10.0, and if within this range, no abnormality occurs in the appearance of the deposited gold plating. When the pH is less than 5.0, unevenness in plating appearance occurs, and when it exceeds 10.0, when a photoresist (hereinafter referred to as PR) is coated on the object to be plated, PR tends to be dissolved.

The reason why the temperature of the gold plating solution is set to 20 to 80 ℃ is that if the temperature is less than 20 ℃, the plating process is not suitable for handling because the variation is substantially too large, and if the temperature exceeds 80 ℃, the gloss of the deposited gold plating is affected and the solution life is drastically reduced.

The current density during electrolysis was set to 0.1A/dm²～4.5A/dm²The properties of the deposited gold plating were confirmed to be in a very good state in consideration of the pH, the temperature and the gold concentration of the plating solution. The plating properties in this case include overall properties such as appearance, adhesion, leveling, and hardness.

< gold Complex >

The gold complex according to the present embodiment will be described. The gold complex of the present embodiment has a structure in which a hydantoin compound represented by the following general formula (1) is coordinated to a gold ion having a valence of 1.

[ chemical formula 7]

In the formula (1), R₁～R₄Each independently represents a hydrogen atom or a 1-valent organic group, R₁And R₂Either or both of them are hydrogen atoms, and R is₃And R₄Either or both of them are hydrogen atoms. However, excluding R₁Is methyl and R₂～R₄All are hydrogen atoms.

These hydantoin compounds undergo a reaction of reducing gold from a valence of 3 to a valence of 1 under alkaline conditions, and are stabilized in the form of a gold ion complex having a valence of 1.

In the general formula (1), R is₁～R₄Examples of the 1-valent organic group include: alkyl groups containing linear and isomeric, secondary and tertiary structural isomers such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, neopentyl, dodecyl and hexadecyl groups; a hydroxyalkyl group; alkenyl groups containing linear and isomeric, secondary and tertiary structural isomers such as vinyl, allyl and isopropenyl; alkoxy groups such as methoxy and ethoxy; carboxylic acids such as acetoxy and propionyloxy; acyl groups such as acetyl and propionyl; aromatic hydrocarbon groups such as phenyl, methylphenyl, hydroxyphenyl and benzyl; and hydroxyl groups, and the like. In addition, from the viewpoint of water solubility and economy, the organic group preferably has 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms, and still more preferably 1 carbon atom.

Specific examples of the hydantoin compound represented by the general formula (1) include: hydantoin (R)₁～R₄All hydrogen atoms), 3-methylhydantoin (R)₂Is methyl and R₁、R₃And R₄All hydrogen atoms), 5-methylhydantoin (R)₃Is methyl and R₁、R₂And R₄All hydrogen atoms), hydantoin-5-acetic acid (R)₃Is acetic acid and R₁、R₂And R₄All being hydrogen atoms). Of these, hydantoin is preferably used from the viewpoint of being the cheapest and economical as a material.

In the above formula (1), the term "excluding R" means that R is not excluded₁Is methyl and R₂～R₄The meaning of all hydrogen atoms "means: in hydantoin compounds, R is excluded₁Is methyl and R₂～R₄"1-methylhydantoin" in the case of all hydrogen atoms.

The method for obtaining the gold complex is as described in the above < method for producing electrolytic gold plating solution >. The above-described various effects can be obtained by obtaining an electrolytic gold plating solution using the gold complex as a gold supply source.

Note that the article "Nouman A. Malik, X-Ray CrystalStructure of Sodium Bis (N-methyl hydantoinato) gold (I) tetrahydroate; a Linear planar Complex of Pharmacological Interest by Two solenoid Nitrogen ligands, J.C.S.CHEM.COMM., 1978, and p.711-712 ", discloses a gold Complex having a structure in which 1-methylhydantoin is coordinated to a 1-valent gold ion. However, this paper relates to the study of 1-valent Au complexes for the treatment of rheumatoid arthritis, and does not describe the use of the electrolytic gold plating solution as in the present embodiment.