JP2020143308A - Electrolytic gold plating solution and method of producing the same, and gold plating method and gold complex - Google Patents

Abstract

To provide an electrolytic gold plating solution excellent in oxidation stability without including a cyanide compound, and advantageous in electric current efficiency upon carrying out gold plating.SOLUTION: The electrolytic gold plating solution employs a gold complex as a source of gold and contains a chelating agent, an electroconductive salt and a buffer agent, the gold complex having a structure constituted of a monovalent gold ion and a hydantoin based compound represented by the following general formula (1) coordinated thereto (in the formula (1), R1 to R4 each independently represents a hydrogen atom or a monovalent organic group, with either or both of R1 and R2 being a hydrogen atom, and either or both of R3 and R4 being a hydrogen atom, provided that a case of R1 being a methyl group and all of R2 to R4 being a hydrogen atom is excluded).SELECTED DRAWING: None

Description

The present invention relates to an electrolytic gold plating solution used for gold plating on wafers, substrates and the like, a method for producing the same, a gold plating method, and a gold complex applicable as a raw material for the electrolytic gold plating solution.

As the plating solution used in the electrolytic plating and the electroless plating method, a cyanide gold plating solution using a gold cyanide complex having excellent oxidation stability in the solution as a gold supply source has been conventionally used. However, since cyan-based gold salts are highly toxic, there is a problem that they are not preferable from the viewpoint of work safety and wastewater treatment. Further, when a cyanide gold plating solution is used, there is also a problem that it is difficult to form a fine circuit pattern because the surplus cyanide peels off and damages the resist pattern of the semiconductor component.

From such a problem, it is considered desirable to apply a plating solution to which a gold salt or a gold complex containing no cyanide is applied. As an example, a non-gold salt (Na ₃ Au (SO ₃ ) ₂ ) solution such as a gold sulfite solution is considered to be desirable. There is a cyanide gold plating solution.

However, the gold salt or gold complex contained in these non-cyanide gold plating solutions has a problem of poor oxidative stability and decomposition during the plating operation. For example, in the above-mentioned gold sulfite, the sulfite ion in the solution is easily oxidatively decomposed by the dissolved oxygen in the plating solution and the entrainment of air by stirring or taking in and out the object to be plated, and the concentration thereof decreases. The oxidation stability of the plating solution may decrease and the plating solution may decompose. When such decomposition occurs, gold in the plating solution precipitates and precipitates in the plating solution tank or piping, which hinders the plating operation. Therefore, for non-cyan electrolytic plating, additives such as stabilizers and complexing agents are added to the plating solution to prevent the plating solution from decomposing, and the plating process is performed. As a countermeasure, the cost of the stabilizer and the plating solution manufacturing process become complicated, so that the cost increases.

Further, a plating solution containing a gold salt or a gold complex having low oxidative stability has a problem from the viewpoint of its storage. In the case of the above-mentioned gold sulfite, black precipitate is likely to occur due to decomposition of the gold salt during storage, and storage in a light-shielded state is essential, and its management is not easy.

Therefore, as a gold complex having excellent oxidative stability without containing a cyanide compound, the gold complex described in Patent Document 1 and Patent Document 2 using a hydantin compound as a ligand is disclosed. The gold complex described in Patent Document 1 is a complex in which a chloroauric acid or a chloroauric acid salt is reacted with a hydridein compound in an aqueous solution, and a hydridein compound is coordinated with gold ions. Further, the gold complex described in Patent Document 2 is a complex in which a gold hydroxide salt and a hydantoin-based compound are heated in an aqueous solution and reacted to coordinate gold ions with a hydantoin-based compound.

Japanese Unexamined Patent Publication No. 2005-256072 Japanese Unexamined Patent Publication No. 2003-183258

These gold complexes have remarkably oxidative stability as compared with conventional non-cyanide gold salts such as sulfites or gold complexes. Here, in Patent Document 1 and Patent Document 2, the application of 5,5-dimethylhydantoin is recommended as the hydantoin-based compound coordinated to gold ions because the oxidative stability of the complex after the reaction is particularly excellent. There is. However, since 5,5-dimethylhydantoin does not have a hydrogen atom at the 5-position carbon, it does not oxidize by itself, so that the reaction of reducing gold from trivalent to monovalent does not occur, and it is a trivalent gold ion complex. It stabilizes. As a result, when gold plating is performed using an electrolytic gold plating solution produced using this gold ion complex, it is necessary to match the cathode current density with the trivalent gold ion complex, which is disadvantageous in terms of current efficiency. Met.

The present invention has been made in view of the above-mentioned situation, and provides an electrolytic gold plating solution which is excellent in oxidative stability without containing a cyanide compound and is advantageous in terms of current efficiency during gold plating. With the goal.

As a result of diligent studies to solve the above problems, the present inventors use a gold complex used as a gold source having a structure in which a specific hydantoin compound is coordinated with a monovalent gold ion. By doing so, we found that the above problems could be solved.

That is, the electrolytic gold plating solution according to the present invention has the following configuration [1].
[1] An electrolytic gold plating solution containing a chelating agent, a conductive salt, and a buffer using a gold complex as a gold source.
The gold complex is an electrolytic gold plating solution having a structure in which a hydantoin compound represented by the following general formula (1) is coordinated with a monovalent gold ion.

In formula (1), R _{1 to} R ₄ independently represent a hydrogen atom or a monovalent organic group, and either or both of R _{1 and} R ₂ are hydrogen atoms, and R ₃ or R. Both or one of ₄ is a hydrogen atom. However, this excludes the case where R ₁ is a methyl group and all of R _{2 to} R ₄ are hydrogen atoms.

A preferred embodiment of the electrolytic gold plating solution according to the present invention has 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 1000 ppm or less.
[3] The electrolytic gold plating solution according to the above [1] or [2], wherein the gold complex is derived from an alkali 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 an imide succinimide.

The electrolytic gold plating solution according to the present invention has the following configuration [5].
[5] An electrolytic gold plating solution containing a chelating agent, a conductive salt, and a buffer using a gold complex as a gold source.
The gold complex has a structure in which a hydantoin compound represented by the following general formula (2) is coordinated with monovalent gold ions, and the chlorine concentration in the electrolytic gold plating solution is 1000 ppm or less. An electrolytic gold plating solution characterized by.

In formula (2), R _{5 to} R ₈ independently represent a hydrogen atom or a monovalent organic group, and either or both of R _{5 and} R ₆ are hydrogen atoms, and R ₇ or R. Both or one of ₈ is a hydrogen atom.

A preferred embodiment of the electrolytic gold plating solution according to the present invention has the following configuration [6] or [7].
[6] The electrolytic gold plating solution according to [5] above, wherein the gold complex is derived from an alkali salt.
[7] The electrolytic gold plating solution according to the above [5] or [6], wherein the chelating agent contains at least one of a hydantoin compound and an succinimide.

The method for producing the electrolytic gold plating solution according to the present invention comprises the following configuration [8] or [9].
[8] The method for producing an electrolytic gold plating solution according to any one of the above [1] to [4].
A step of reacting a chloroauric acid or a chloroauric acid salt, a hydridein compound represented by the general formula (1), and an alkali hydroxide in an aqueous solution to form the gold complex.
The step of cooling the aqueous solution containing the gold complex to extract the gold complex alkali salt, and
A method for producing an electrolytic gold plating solution, which comprises a step of producing the electrolytic gold plating solution using the gold complex alkaline salt.
[9] The method for producing an electrolytic gold plating solution according to any one of the above [5] to [7].
A step of reacting a chloroauric acid or a chloroauric acid salt, a hydridein compound represented by the general formula (2), and an alkali hydroxide in an aqueous solution to form the gold complex.
The step of cooling the aqueous solution containing the gold complex to extract the gold complex alkali salt, and
A method for producing an electrolytic gold plating solution, which comprises a step of producing the electrolytic gold plating solution using the gold complex alkaline salt.

Further, the gold plating method according to the present invention has the configuration of the following [10].
[10] A method for plating using the electrolytic gold plating solution according to any one of the above [1] to [7].
A gold plating method characterized by electroplating under the conditions of pH: 5.0 to 10.0, liquid temperature: 20 to 80 ° C., and current density: 0.1 to 4.5 A / dm ² .

Further, the gold complex according to the present invention has the following constitution [11].
[11] A gold complex characterized by having a structure in which a hydantoin-based compound represented by the following general formula (1) is coordinated with a monovalent gold ion.

In formula (1), R _{1 to} R ₄ independently represent a hydrogen atom or a monovalent organic group, and either or both of R _{1 and} R ₂ are hydrogen atoms, and R ₃ or R. Both or one of ₄ is a hydrogen atom. However, this excludes the case where R ₁ is a methyl group and all of R _{2 to} R ₄ are hydrogen atoms.

According to the present invention, it is possible to provide an electrolytic gold plating solution which is excellent in oxidation stability without containing a cyanide and is advantageous in terms of current efficiency during gold plating.

Hereinafter, embodiments for carrying out 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 gist of the present invention.

<Electrolytic gold plating solution>
The electrolytic gold plating solution of the present embodiment will be described. 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. This gold complex has a structure in which a hydantoin-based compound represented by the following general formula (1) is coordinated with a monovalent gold ion.

In formula (1), R _{1 to} R ₄ independently represent a hydrogen atom or a monovalent organic group, and either or both of R _{1 and} R ₂ are hydrogen atoms, and R ₃ or R. Both or one of ₄ is a hydrogen atom. However, this excludes the case where R ₁ is a methyl group and all of R _{2 to} R ₄ are hydrogen atoms.

The gold complex according to the present embodiment is characterized in that the valence of gold ions is 1 in the electrolytic gold plating solution. Since the valence of gold ions is 1, the cathode current density can be matched to the monovalent gold ion complex when gold plating is performed using an electrolytic gold plating solution, so that the cathode current density is trivalent. This is because it can be reduced to 1/3 as compared with the case, and is more advantageous in terms of current efficiency than the case where a trivalent gold ion complex is used. Further, as a result, the anode current density can be reduced to 1/3 as compared with the case of trivalent, so that oxidative decomposition of the plating solution in the vicinity of the anode can be reduced and the life of the plating solution can be extended. be able to.

Then, in a gold complex using a hydantoin compound as a ligand, a specific hydantoin compound is used in order to set the valence of the gold ion to 1. Specifically, a hydantoin-based compound represented by the following general formula (1) is used as a ligand. The ligand can be identified by separating and qualitatively analyzing the ligand released by the complex equilibrium in the solution of the gold complex by a method such as a liquid chromatograph.

In formula (1), R _{1 to} R ₄ independently represent a hydrogen atom or a monovalent organic group, and either or both of R _{1 and} R ₂ are hydrogen atoms, and R ₃ or R. Both or one of ₄ is a hydrogen atom. However, this excludes the case where R ₁ is a methyl group and all of R _{2 to} R ₄ are hydrogen atoms.

These hydantoin compounds undergo a reaction of reducing gold from trivalent to monovalent under alkaline conditions and are stabilized by a monovalent gold ion complex.

In the general formula (1), examples of the monovalent organic group represented by R _{1 to} R ₄ include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group and a sec-butyl group. Linear and iso-types such as tert-butyl group, pentyl group, neopentyl group, dodecyl group and hexadecyl group, alkyl groups including structural isomers such as secondary and tertiary, hydroxyalkyl groups, vinyl groups and allyls. Linear and iso-type groups such as groups and isopropenyl groups, alkenyl groups containing structural isomers such as secondary and tertiary, alkoxy groups such as methoxy and ethoxy groups, and carboxylic groups such as acetate and propanoic acid groups. Examples thereof include an acyl group such as an acid, an acetyl group and a propionyl group, an aromatic hydrocarbon group such as a phenyl group, a methylphenyl group, a hydroxyphenyl group and a benzyl group, and a hydroxyl group. Further, the organic group preferably has 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms, and further preferably 1 carbon number from the viewpoint of water solubility and economy.

Specific examples of the hydantoin compound represented by the general formula (1) include hydantoin (when all of R _{1 to} R ₄ are hydrogen atoms) and 3-methyl hydantoin (where R ₂ is a methyl group and R). ₁ , R ₃ and R ₄ are all hydrogen atoms), 5-Methyl hydantoin (when R ₃ is a methyl group and all of R ₁ , R ₂ and R ₄ are hydrogen atoms), 5- Hydantoin acetic acid (when R ₃ is acetic acid and all of R ₁ , R ₂ and R ₄ are hydrogen atoms) can be mentioned. Among these, it is preferable to use hydantoin from the viewpoint of the cheapest and most economical material.

In the above formula (1), "except when R ₁ is a methyl group and all of R _{2 to} R ₄ are hydrogen atoms" means that among hydantoin compounds, R ₁ is a methyl group. and all R ₂ to R ₄ is a case where the hydrogen atom, an effect that excluding "1-methyl hydantoin."

On the other hand, other hydantoin compounds, that is, for example, 5,5-dimethylhydantoin and 1,5,5-trimethylhydantoin, have hydrogen at the 5-position carbon (see the above general formula (1)). Since it does not oxidize itself even under alkaline conditions, the reaction of reducing gold from trivalent to monovalent does not occur, and it is stabilized by a trivalent gold ion complex. Further, since hydantoin acid does not have a hydantoin ring structure, it does not oxidize itself even under alkaline conditions, so that the reaction of reducing gold from trivalent to monovalent does not occur as described above, and trivalent gold does not occur. It is stabilized by an ion complex.

Further, in the gold and the hydantoin compound, the hydrogen on the 1-position or 3-position nitrogen is released, and the 1-position or 3-position nitrogen and gold are bonded to form a complex (see the above general formula (1)). In the case of 1,3-dimethylhydantoin in which an alkyl group is bonded to both the 1-position and 3-position nitrogens, a gold complex cannot be formed in the first place.

Further, 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 buffering agent. This gold complex has a structure in which a hydantoin compound represented by the following general formula (2) is coordinated with monovalent gold ions, and the chlorine concentration in the electrolytic gold plating solution is 1000 ppm or less.

In formula (2), R _{5 to} R ₈ independently represent a hydrogen atom or a monovalent organic group, and either or both of R _{5 and} R ₆ are hydrogen atoms, and R ₇ or R. Both or one of ₈ is a hydrogen atom.

These hydantoin compounds also undergo a reaction of reducing gold from trivalent to monovalent under alkaline conditions and are stabilized by a monovalent gold ion complex.

In the general formula (2), examples of the monovalent organic group represented by R _{5 to} R ₈ include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group and a sec-butyl group. Linear and iso-types such as tert-butyl group, pentyl group, neopentyl group, dodecyl group and hexadecyl group, alkyl groups including structural isomers such as secondary and tertiary, hydroxyalkyl groups, vinyl groups and allyls. Linear and iso-type groups such as groups and isopropenyl groups, alkenyl groups containing structural isomers such as secondary and tertiary, alkoxy groups such as methoxy and ethoxy groups, and carboxylic groups such as acetate and propanoic acid groups. Examples thereof include an acyl group such as an acid, an acetyl group and a propionyl group, an aromatic hydrocarbon group such as a phenyl group, a methylphenyl group, a hydroxyphenyl group and a benzyl group, and a hydroxyl group. Further, the organic group preferably has 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms, and further preferably 1 carbon number from the viewpoint of water solubility and economy.

Specific examples of the hydantin compound represented by the general formula (2) include hydantin (when all of R _{5 to} R ₈ are hydrogen atoms) and 1-methyl hydantoin (where R ₅ is a methyl group and R). If all ₆ to R ₈ is a hydrogen atom), 3-methyl-hydantoin _{(R 6} is a methyl group _and, when all of R 5, _{R 7} and _{R 8} are hydrogen atoms), 5-methyl hydantoin ( When R ₇ is a methyl group and all of R ₅ , R ₆ and R ₈ are hydrogen atoms), 5-Hidantine acetic acid (when R ₃ is acetic acid and all of R ₅ , R ₆ and R ₈ are hydrogen) (If it is an atom). Among these, it is preferable to use hydantoin from the viewpoint of the cheapest and most economical material.

The electrolytic gold plating solution according to this embodiment preferably has a chlorine concentration of 1000 ppm or less in the electrolytic gold plating solution. Since the chlorine concentration in the electrolytic gold plating solution is 1000 ppm or less, that is, chlorine in the electrolytic gold plating solution is substantially not contained, it can be applied to an object to be plated which dislikes chlorine.

Here, in the electrolytic gold plating solution produced by using a gold complex obtained by reacting a gold chloride acid or a gold chloride salt with a hydantoin-based compound as in Patent Document 1, the gold chloride acid or gold chloride is used. Since a large amount of chloride-derived chlorine ions are contained in the electrolytic gold plating solution, it is difficult to apply it to an object to be plated that dislikes chlorine.

In the present embodiment, the chlorine concentration in the electrolytic gold plating solution is set to 1000 ppm or less as an index for substantially not containing chlorine in the electrolytic gold plating solution, but the reason why chlorine in the electrolytic gold plating solution is disliked. As a result, chlorine remains on the surface of the gold film, which reduces the adhesion to the substrate and bonding, and causes corrosion of the film. It exists in the crystal grain boundaries of the gold film and it is difficult to adjust the hardness. In order to exert the application to the object to be plated, which dislikes chlorine, without any problem, the chlorine concentration in the electrolytic gold plating solution is preferably 500 ppm or less, and preferably 300 ppm or less. More preferably, it is 200 ppm or less.

A method for obtaining an electrolytic gold plating solution that does not substantially contain chlorine will be described later.

Subsequently, the chelating agent, the conductive salt, and the buffering agent that constitute the electrolytic gold plating solution of the present embodiment will be described.

As the chelating agent, hydantoin, 1-methylhydantoin, 5-methylhydantoin, 5,5-dimethylhydantoin and succinimide are preferably added separately from the ligand of the gold complex. Among them, it is more preferable to contain at least one of 5,5-dimethylhydantoin and succinimide as a chelating agent for the oxidative stability and precipitation uniformity of the gold complex in the plating solution. By using a chelating agent in the electrolytic gold plating solution, an extremely stable gold plating solution can be obtained. That is, gold precipitation is less likely to occur in the plating process. This is because these chelating agents maintain equilibrium with the ligand of the gold complex, are not reducing substances such as sulfurous acid, and have the property of being less prone to oxidative decomposition.

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

In the case of pH 5 to 7, the amount of the chelating agent is preferably more than 0 times mol and 4 times mol or less with respect to gold. When the amount used is large and the gold complex is frequently replenished, the ligand of the gold complex is liberated. Therefore, it is not necessary to add a chelating agent at the initial stage. It has a burnt appearance.

Further, in the case of pH 8 to 10, it is preferably 4 times or more and 10 times by mole or less with respect to gold. If it is less than 4 times the molar amount, the reaction in which the ligand of the gold complex is oxidatively decomposed by alkalinity is prioritized over the appearance of burning and the chelating agent maintaining equilibrium with the ligand of the gold complex. A sinking phenomenon may be seen. On the other hand, when the molar amount exceeds 10 times, no change is observed in the appearance and the oxidative stability, and the effect of increasing the chelating agent cannot be expected so much.

As the conductive salt, it is preferable to use any one or more of hydrochloric acid, sulfuric acid, sulfurous acid, sulfamic acid, nitric acid, phosphoric acid, and salts thereof. When these substances are used alone or in combination as a conductive salt, the solution stability of the electrolytic gold plating solution according to the present embodiment becomes extremely excellent.

When the above-mentioned conductive salt is contained in the electrolytic gold plating solution according to the present embodiment, the conductive salt concentration is preferably in the concentration range of 0.05 to 1.95 mol / L. If the concentration of the conductive salt is less than 0.05 mol / L, the conductivity is lowered, the current efficiency is lowered, and the appearance of the plating is likely to be poor. On the other hand, if it exceeds 1.95 mol / L, the electrical conductivity and the appearance are not changed, and salting out is likely to occur depending on the pH.

As the buffering agent, it is preferable to use any one or more of boric acid, succinic acid, phthalic acid, tartaric acid, citric acid, phosphoric acid or salts thereof. When these substances are used alone or in combination as a buffer, the pH of the electrolytic gold plating solution according to the present embodiment does not fluctuate significantly, and the pH is weakly acidic to weakly alkaline (pH about 5.0). ~ 10.0) It becomes easy to maintain the plating solution in the vicinity of neutrality.

When the above-mentioned buffering agent is contained in the electrolytic gold plating solution according to the present embodiment, the buffering agent concentration is preferably in the concentration range of 0.05 to 1.95 mol / L. If the buffer concentration is less than 0.05 mol / L, the effect of stabilizing the pH is lost. On the other hand, if it exceeds 1.95 mol / L, the pH stability does not change, and salting out tends to occur depending on the pH.

The total concentration of the conductive salt and the buffer is preferably in the concentration range of 0.1 to 2.0 mol / L. When the total concentration of the conductive salt and the buffer is 0.1 to 2.0 mol / L, the gold plating solution according to the present embodiment has the best total balance in actual operation. That is, the solution stability is excellent, the current efficiency is high, and the pH of the plating solution does not fluctuate significantly.
From the viewpoint of preventing salting out in winter, the total concentration of the conductive salt and the buffer is more preferably in the concentration range of 0.1 to 1.0 mol / L.

The gold concentration in the electrolytic gold plating solution according to the present embodiment is preferably in the concentration range of 0.5 to 15 g / L, although it depends on the ratio with the chelating agent concentration. If it is less than 0.5 g / L, gold electrodeposition does not occur unless a voltage of 3 V or more is applied, and if it exceeds 15 g / L, it is economically inconvenient because it is taken out of the plating tank by the object to be plated. It is possible that there is something that is likely to be salted out in winter.

Further, the gold concentration is preferably in the concentration range of 4 to 8 g / L. In this concentration range, it is possible to control various objects to be plated, and it is easy to control the concentration fluctuation due to the consumption of gold.

In the electrolytic gold plating solution according to the present embodiment, it is preferable that the gold complex is derived from an alkali salt. As will be described later, the specific hydantin compound used in the present embodiment is stabilized with a monovalent gold ion complex under alkaline conditions, and the gold complex alkali salt extracted thereafter is substantially free of chlorine. It becomes a thing. By producing an electrolytic gold plating solution using this gold complex alkaline salt, it is possible to obtain an electrolytic gold plating solution that can be applied to an object to be plated that dislikes chlorine.

Examples of the alkali salt include lithium salt, sodium salt, potassium salt, rubidium salt, and cesium salt, and among them, sodium salt and potassium salt are preferable. This is because these are salts using an economically excellent alkali metal in common with conventional gold compounds such as potassium gold cyanide and sodium gold sulfite.

<Manufacturing method of electrolytic gold plating solution>
A method for producing the electrolytic gold plating solution according to the present embodiment will be described. In the method for producing the electrolytic gold plating solution of the present embodiment, an aqueous solution of gold chloride acid or gold chloride salt, a hydridein compound represented by the general formula (1) or the general formula (2), and an alkali hydroxide is used. It has a step of reacting in the inside to form a gold complex alkali salt and extracting the gold complex alkali salt, and a step of producing an electrolytic gold plating solution using the gold complex alkali salt.

As described above, the electrolytic gold plating solution according to the present embodiment is characterized in that chlorine is substantially not contained. Therefore, it is possible to form a gold complex using a gold hydroxide salt as described in Patent Document 2 as a raw material and using a hydantin compound as a ligand, but usually, the yield of the gold hydroxide salt is high. Since it is not as high as about 60% at most, the cost of gold used as an electrolytic gold plating solution is high, which is not economical.

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

First, as a raw material for obtaining a gold complex, chloroauric acid or chloroauric acid salt is prepared as in the prior art. Further, a hydantin-based compound represented by the above general formula (1) or the above general formula (2) for coordination with gold ions, and further, lithium hydroxide (LiOH), sodium hydroxide (NaOH), and water. Prepare an alkali hydroxide such as potassium oxide (KOH), rubidium hydroxide (RbOH), cesium hydroxide (CsOH), and the like.

Then, by reacting chloroauric acid or chloroauric acid salt, the above-mentioned hydridein compound, and alkali hydroxide in an aqueous solution, monovalent gold ions are converted into the above-mentioned general formula (1) or the above-mentioned general formula ( A gold complex having a structure in which the chloroauric acid compound represented by 2) is coordinated is obtained.

Here, in the present embodiment, the reaction conditions between the chloroauric acid or the chloroauric acid salt and the hydantoin compound are preferably a temperature of 40 to 80 ° C. and a reaction time of 30 to 360 minutes. The reaction temperature is particularly preferably 60 to 75 ° C., and the reaction time is particularly preferably 180 minutes or more.

Even if gold chloride acid or gold chloride salt and a hydridein-based compound are simply mixed, the hydridein compound in the liquid has a function as a so-called chelating agent, but gold remains in the state of a gold chloride complex. No complex formation occurs. Although gold plating can be performed with such a liquid, since gold remains trivalent, the amount of precipitation is reduced to 1/3, and the precipitation mechanism is different from that of the gold complex according to the present embodiment. Become.

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

Subsequently, when the solution containing the gold complex obtained above is cooled to room temperature (25 ° C.) or lower, crystals of the gold complex alkali salt which does not contain chlorine due to its structure are precipitated. Therefore, solid-liquid separation is performed and the solution is separated from the above solution. Extracted as a gold complex alkali salt. By such a treatment, chlorine remains in the solution, and the extracted gold complex alkali salt naturally contains substantially no chlorine. According to this operation method, a gold complex alkali salt can be obtained from the above solution in a very high yield without using a gold hydroxide salt.

After that, if an electrolytic gold plating solution is produced using the gold complex alkaline salt extracted from the solution as a raw material, an electrolytic gold plating solution containing substantially no chlorine can be obtained.

For reference, in paragraph 0017 of Patent Document 1 and paragraph 0013 of Patent Document 2, "a gold complex formation reaction is caused in an aqueous solution, and this complex is used as a plating solution or the like. In this case, the solution after the reaction can be used as it is as a raw material for the plating solution. ”However, for example, when a gold complex is formed from gold chloride acid or gold chloride salt as a raw material, the solution after the reaction. When is used as it is as a raw material for the plating solution, a large amount of chlorine ions are contained in the solution after the reaction, so that the electrolytic gold plating solution also contains a large amount of chlorine ions. It is difficult to apply to the object to be plated, which is disliked.

<Gold plating method>
The gold plating method according to this embodiment will be described. The gold plating method of the present embodiment is a method of plating using the above-mentioned electrolytic gold plating solution, and has pH: 5.0 to 10.0, liquid temperature: 20 to 80 ° C., and current density: 0. Electroplating is performed under the conditions of 1 to 4.5 A / dm ² .

The pH value of the gold plating solution is in the range of pH 5.0 to 10.0 depending on the concentration of the buffer and the conductive salt, and within this range, no abnormality occurs in the appearance of the precipitated gold plating. When the pH is less than 5.0, the appearance of the plating becomes uneven, and when it exceeds 10.0, the PR tends to be dissolved when the photoresist (hereinafter referred to as PR) is coated on the object to be plated. It becomes.

The condition that the temperature of the gold plating solution was set to 20 to 80 ° C. is not suitable for operation because the variation of the plating process is practically too large below 20 ° C., and if it exceeds 80 ° C., it affects the gloss of gold plating This is because the life of the solution is sharply reduced.

The current density during electrolysis was set to 0.1 to 4.5 A / dm ² , because the properties of the precipitated gold plating are very good in consideration of the pH value, liquid temperature, and gold concentration of the above-mentioned plating solution. It was decided after confirming that it would be in a state. The plating properties in this case include comprehensive ones such as appearance, adhesion, leveling, and hardness.

<Gold complex>
The gold complex according to this embodiment will be described. The gold complex of the present embodiment has a structure in which a hydantoin-based compound represented by the following general formula (1) is coordinated with a monovalent gold ion.

In formula (1), R _{1 to} R ₄ independently represent a hydrogen atom or a monovalent organic group, and either or both of R _{1 and} R ₂ are hydrogen atoms, and R ₃ or R. Both or one of ₄ is a hydrogen atom. However, this excludes the case where R ₁ is a methyl group and all of R _{2 to} R ₄ are hydrogen atoms.

These hydantoin compounds undergo a reaction of reducing gold from trivalent to monovalent under alkaline conditions and are stabilized by a monovalent gold ion complex.

In the general formula (1), examples of the monovalent organic group represented by R _{1 to} R ₄ include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group and a sec-butyl group. Linear and iso-types such as tert-butyl group, pentyl group, neopentyl group, dodecyl group and hexadecyl group, alkyl groups including structural isomers such as secondary and tertiary, hydroxyalkyl groups, vinyl groups and allyls. Linear and iso-type groups such as groups and isopropenyl groups, alkenyl groups containing structural isomers such as secondary and tertiary, alkoxy groups such as methoxy and ethoxy groups, and carboxylic groups such as acetate and propanoic acid groups. Examples thereof include an acyl group such as an acid, an acetyl group and a propionyl group, an aromatic hydrocarbon group such as a phenyl group, a methylphenyl group, a hydroxyphenyl group and a benzyl group, and a hydroxyl group. Further, the organic group preferably has 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms, and further preferably 1 carbon number from the viewpoint of water solubility and economy.

Specific examples of the hydantoin compound represented by the general formula (1) include hydantoin (when all of R _{1 to} R ₄ are hydrogen atoms) and 3-methyl hydantoin (where R ₂ is a methyl group and R). ₁ , R ₃ and R ₄ are all hydrogen atoms), 5-Methyl hydantoin (when R ₃ is a methyl group and all of R ₁ , R ₂ and R ₄ are hydrogen atoms), 5- Hydantoin acetic acid (when R ₃ is acetic acid and all of R ₁ , R ₂ and R ₄ are hydrogen atoms) can be mentioned. Among these, it is preferable to use hydantoin from the viewpoint of the cheapest and most economical material.

In the above formula (1), "except when R ₁ is a methyl group and all of R _{2 to} R ₄ are hydrogen atoms" means that among hydantoin compounds, R ₁ is a methyl group. and all R ₂ to R ₄ is a case where the hydrogen atom, an effect that excluding "1-methyl hydantoin."

The method for obtaining this gold complex is as described in <Method for producing electrolytic gold plating solution> above. By using this gold complex as a gold supply source to obtain an electrolytic gold plating solution, the above-mentioned various effects can be obtained.

Incidentally, the prior art documents become paper "Nouman A.Malik," X-Ray Crystal Structure of Sodium Bis (N-methylhydantoinato) gold (I) Tetrahydrate; a Linear Planar Complex of Pharmacological Interest Stabilised by Two Nitrogen Ligands ", J. CS CHEM. COMM., 1978, p.711-712 "discloses a gold complex having a structure in which 1-methylhydrantine is coordinated to a monovalent gold ion. However, this paper relates to the study of a monovalent Au complex for the treatment of rheumatoid arthritis, and there is no description as an application to an electrolytic gold plating solution as in this embodiment.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

<Extraction of gold complex alkali salt>
[Extraction of hydantoin gold complex sodium salt]
An aqueous solution of hydantoin in which 50 g of hydantoin is dissolved in 250 mL of water is adjusted to pH 11.5-12.5 with sodium hydroxide, 25 g of chloroauric acid (HAuCl ₄ ) in gold equivalent is added, and the mixture is added at 65 ° C. for 180 minutes. The reaction was carried out with warm stirring to obtain a hydantoin gold complex.
Subsequently, sodium hydroxide was further added to the obtained aqueous solution having the gold complex to adjust the pH to 9.0, and then the aqueous solution was cooled to room temperature (25 ° C.) or lower to obtain a sodium salt of the hydantin gold complex. Crystals were precipitated. Then, the hydantoin gold complex sodium salt, which is a gold complex alkali salt, was extracted from the aqueous solution by filtration (solid-liquid separation).

[Extraction of hydantoin gold complex potassium salt]
The hydridein gold complex potassium salt was extracted in the same manner as in the operation of [Extraction of hydrantin gold complex sodium salt] except that potassium hydroxide was used instead of sodium hydroxide.

[Extraction of 5-methylhydantoin gold complex sodium salt]
The 5-methylhydantoin gold complex sodium salt was extracted in the same manner as in the operation of [Extraction of hydantoin gold complex sodium salt] except that 63 g of 5-methylhydantoin was used instead of 50 g of hydantoin.

The hydridein gold complex sodium salt, hydrantin gold complex potassium salt and 5-methylhydrantin gold complex sodium salt obtained above may have monovalent gold ions due to the precipitation efficiency in gold plating (details will be described later). confirmed.

<Manufacturing of electrolytic gold plating solution and gold plating treatment>
[Experiment No. 1-12]
Using any of the hydrantin gold complex sodium salt, hydrantin gold complex potassium salt, and 5-methylhydrantin gold complex sodium salt obtained above as the gold complex salt, an electrolytic gold plating solution having each specification as shown in Table 1 is produced. (Experiments Nos. 1 to 12). In addition, Experiment No. In No. 1, no chelating agent was added.

[Experiment No. 13]
An aqueous solution of 5,5-dimethylhydranthin in which 64 g of 5,5-dimethylhydranthin was dissolved in 250 mL of water was adjusted to pH 11.5-12.5 with sodium hydroxide, and 25 g of gold chloride (HAuCl ₄ ) was converted into gold. Was added, and the mixture was heated and stirred at 65 ° C. for 180 minutes to react to obtain a 5,5-dimethylhydantin gold complex.

Sodium hydroxide was further added to the obtained aqueous solution having a gold complex to adjust the pH to 9.0, and then the aqueous solution was cooled to room temperature (25 ° C.) or lower, but the 5,5-dimethylhydantoin gold complex sodium salt was cooled. Could not precipitate the crystals of. Then, the aqueous solution was used as it was as a raw material for the plating solution (5,5-dimethylhydantoin gold solution in Experiment No. 13 in Table 1) to produce an electrolytic gold plating solution having specifications as shown in Table 1 (experiment). No. 13).

[Experiment No. 14]
To an aqueous hydantoin solution in which 50 g of hydantoin was dissolved in 250 mL of water, 25 g of sodium chloroauric acid (NaAuCl ₄ ) in terms of gold was added, and the mixture was heated and stirred at 65 ° C. for 180 minutes to react to obtain a hydantoin gold complex. ..

Sodium hydroxide was further added to the obtained aqueous solution having the gold complex to adjust the pH to 9.0, and then the aqueous solution was cooled to room temperature (25 ° C.) or lower to precipitate crystals of the sodium salt of the hidden gold complex. I couldn't. Then, the aqueous solution was used as it was as a raw material for the plating solution (hydantoin gold solution in Experiment No. 14 in Table 1) to produce an electrolytic gold plating solution having specifications as shown in Table 1 (Experiment No. 14).

Subsequently, Experiment No. 1 in which a gold complex alkali salt was used as a raw material for the electrolytic gold plating solution. Ion chromatographic analysis (manufactured by Thermo SCIENTIFIC, device name: Dionex ICS-2100, separation column: Dionex IonPacTM AS12A (4x200 mm)) was performed on each of the electrolytic gold plating solutions 1 to 12, and the gold concentration was 8 g / L. Then, it was confirmed that when the chlorine concentration in the electrolytic gold plating solution was 550 ppm and the gold concentration was 4 g / L, the chlorine concentration in the electrolytic gold plating solution was 300 ppm (see “Chlorine concentration (ppm)” in Table 1). ).

On the other hand, the aqueous solution in which the gold complex was formed was used as it was as a raw material for the plating solution. Ion chromatographic analysis was performed on each of the electrolytic gold plating solutions 13 and 14 in the same manner as described above. For No. 13, the chlorine concentration was 5800 ppm, and Experiment No. For No. 14, the chlorine concentration was 5700 ppm, which was a very high chlorine concentration (see “Chlorine concentration (ppm)” in the test results in Table 1).

In addition, Experiment No. Using each of the electrolytic gold plating solutions 1 to 14, as a common condition, the plating solution temperature was set to 60 ° C., and a test piece made of brass and subjected to Ni: 5 μm and Au strike plating had a current density of 0.5 A / dm. ^The plating process was performed in step ² . The appearance results of each of the obtained gold-plated films are also shown in Table 1. Here, "○" in the "appearance" of Table 1 indicates that the color tone was bright lemon yellow, and "x" indicates that the color tone was dark brown and burnt, and "-". Indicates that the appearance was not evaluated because the gold ions remained trivalent from the results of the following precipitation efficiencies. In addition, Experiment No. Regarding No. 12, since the amount of the chelating agent added was less than 4 times the molar amount of gold when the pH was 8 to 10, in addition to the burnt appearance, the reaction in which the ligand of the gold complex was oxidatively decomposed by alkalinity. However, a small amount of gold settling occurred, so the column of "appearance" in Table 1 was described as "x, gold settling phenomenon".

Furthermore, Experiment No. The precipitation efficiency in the plating treatment using each of the electrolytic gold plating solutions 1 to 14 was calculated. Table 1 shows the results of precipitation efficiency. From the results in Table 1, Experiment No. The precipitation efficiency (mg / A · min) in 1 to 12 is 95% or more (that is, about 116.3 mg / min) of 122.5 mg / A · min, which is a theoretical value when the gold complex has monovalent gold ions. It showed a value of A · min or more), and it was confirmed that the electrolytic gold plating solution had monovalent gold ions.

On the other hand, Experiment No. The precipitation efficiency (mg / A · min) at 13 and 14 shows a value of about 40.8 mg / A · min, which is a theoretical value when the gold complex has trivalent gold ions, and these electrolytic gold plating It was confirmed that the liquid had trivalent gold ions.

From the above experimental results, Experiment No. It was confirmed that the gold complexes in the electrolytic gold plating solutions 1 to 12 had monovalent gold ions, and it was shown to be advantageous in terms of current efficiency during gold plating. Further, it was confirmed that the electrolytic gold plating solution (Experiments Nos. 1 to 12) produced by using the gold complex alkali salt shown above as a gold source was substantially free of chlorine, and the object to be plated dislikes chlorine. It was shown that it can be applied to.

<Confirmation of oxidative stability of gold complex>
The solution containing 5 g / L of the hydantoin gold complex sodium salt obtained above as gold was adjusted to pH 7.0 and partitioned into 5 bottles. 3.45% hydrogen peroxide solution (H ₂ O ₂ ) was added to each of them so as to have an Au equivalent ratio of 0, 0.5, 1.0, 2.0, 3.0 and 5.0. When stored at room temperature, the appearance did not change even after 95 hours. The pH decreased by 0.4 at the maximum.

Further, a solution containing 5 g / L of gold sodium sulfite (Na ₃ Au (SO ₃ ) ₂ ) as gold was confirmed to have a pH of 9.8 and distributed to 6 bottles. Add 3.45% hydrogen peroxide solution (H ₂ O ₂ ) to each of them so that the Au equivalent ratio is 0, 0.5, 1.1, 1.4, 1.7, 2.0, 5.4. Was added to. When stored at room temperature, a precipitation that seems to be gold was observed from a large amount of hydrogen peroxide added after several hours, and a large amount of precipitation was observed after 68 hours when the amount of hydrogen peroxide added was 1.1 equivalents or more. It was. The pH was significantly reduced when the amount added was 1.1 equivalents or more.

From the above comparative experiments, it was confirmed that the hydantoin gold complex obtained above is superior in oxidative stability of the gold complex to the gold sulfite used as a non-cyanide gold source.

Claims (11)

An electrolytic gold plating solution that uses a gold complex as a gold source and contains a chelating agent, a conductive salt, and a buffer.
The gold complex is an electrolytic gold plating solution having a structure in which a hydantoin compound represented by the following general formula (1) is coordinated with a monovalent gold ion.

(In the formula (1), R _{1 to} R ₄ independently represent a hydrogen atom or a monovalent organic group, and either or both of R _{1 and} R ₂ are hydrogen atoms, and R ₃ or R ₃ or Both or one of R ₄ is a hydrogen atom, except when R ₁ is a methyl group and all of R _{2 to} R ₄ are hydrogen atoms.) The electrolytic gold plating solution according to claim 1, wherein the chlorine concentration in the electrolytic gold plating solution is 1000 ppm or less. The electrolytic gold plating solution according to claim 1 or 2, wherein the gold complex is derived from an alkali salt. The electrolytic gold plating solution according to any one of claims 1 to 3, wherein the chelating agent contains at least one of a hydantoin compound and an imide succinimide. An electrolytic gold plating solution that 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 with monovalent gold ions, and the chlorine concentration in the electrolytic gold plating solution is 1000 ppm or less. An electrolytic gold plating solution characterized by.

(In the formula (2), R _{5 to} R ₈ independently represent a hydrogen atom or a monovalent organic group, and either or both of R _{5 and} R ₆ are hydrogen atoms and R ₇ or R ₇ or one of them. Both or one of R ₈ is a hydrogen atom.) The electrolytic gold plating solution according to claim 5, wherein the gold complex is derived from an alkali salt. The electrolytic gold plating solution according to claim 5 or 6, wherein the chelating agent contains at least one of a hydantoin compound and an imide succinimide. The method for producing an electrolytic gold plating solution according to any one of claims 1 to 4.
A step of reacting a chloroauric acid or a chloroauric acid salt, a hydridein compound represented by the general formula (1), and an alkali hydroxide in an aqueous solution to form the gold complex.
The step of cooling the aqueous solution containing the gold complex to extract the gold complex alkali salt, and
A method for producing an electrolytic gold plating solution, which comprises a step of producing the electrolytic gold plating solution using the gold complex alkaline salt. The method for producing an electrolytic gold plating solution according to any one of claims 5 to 7.
A step of reacting a chloroauric acid or a chloroauric acid salt, a hydridein compound represented by the general formula (2), and an alkali hydroxide in an aqueous solution to form the gold complex.
The step of cooling the aqueous solution containing the gold complex to extract the gold complex alkali salt, and
A method for producing an electrolytic gold plating solution, which comprises a step of producing the electrolytic gold plating solution using the gold complex alkaline salt. A method for plating using the electrolytic gold plating solution according to any one of claims 1 to 7.
A gold plating method characterized by electroplating under the conditions of pH: 5.0 to 10.0, liquid temperature: 20 to 80 ° C., and current density: 0.1 to 4.5 A / dm ² . A gold complex characterized by having a structure in which a hydantoin-based compound represented by the following general formula (1) is coordinated to a monovalent gold ion.

(In the formula (1), R _{1 to} R ₄ independently represent a hydrogen atom or a monovalent organic group, and either or both of R _{1 and} R ₂ are hydrogen atoms, and R ₃ or R ₃ or Both or one of R ₄ is a hydrogen atom, except when R ₁ is a methyl group and all of R _{2 to} R ₄ are hydrogen atoms.)