JP2023168652A - Electrolytic gold plating solution, production method thereof, and plating method using the plating solution - Google Patents

Abstract

To provide an electrolytic gold plating solution having a long lifespan without toxicity, in which plating can be performed with the solution temperature of 35°C or lower and the plating film can uniformly be electrodeposited with excellent plating properties, and a production method of the solution.SOLUTION: An electrolytic gold plating solution includes a non-cyanide soluble gold salt (A) and a complexing agent (B) for complexing gold ions of the gold salt. The complexing agent (B) is a mercaptotetrazole compound expressed by the following general formula (1). The molar ratio (B/A) of the complexing agent (B) to the soluble gold salt (A) is between 10 and 260. The pH of the gold plating solution is less than 3.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electrolytic gold plating solution used for gold plating on wafers, substrates, etc., a method for manufacturing the same, and a plating method using the plating solution. More specifically, the present invention relates to an electrolytic gold plating solution suitable for forming gold-plated bumps, a method for producing the same, and a plating method using the plating solution.

Conventionally, since cyanide has a strong complex-forming power, a gold plating solution in which the gold salt is a cyanide gold salt has been disclosed (for example, Patent Document 1 (Claim 1, Claim 2, Claim 3, Paragraph [0012 ], see paragraph [0025]). Patent Document 1 describes that this gold plating solution contains a cyanide gold salt, a soluble cobalt salt and/or a nickel salt, an organic acid conductive salt, a chelating agent, and a displacement inhibitor for electrolytic hard gold plating solution. It is stated that it contains. Furthermore, Patent Document 1 states that, according to this gold plating solution, since a predetermined organic substitution inhibitor is blended into the gold plating solution, a protective film is formed on the nickel base when no current is applied to the gold plating solution. In addition, this protective film can be easily removed by passing an electric current through the gold plating solution, and the presence of the protective film formed on the nickel base prevents the gold plating solution from coming into contact with it when no current is being applied. However, since no substitution reaction occurs with the nickel base, selective plating is possible, and since no substitution reaction occurs with the nickel base, gold precipitation on the inner wall of the plating tank due to the generation of gold particles is avoided. It is described that it has features such as being able to suppress

As in the invention of Patent Document 1, a plating solution containing gold cyanide salt is highly toxic. For this reason, cyan-free electrolytic gold plating solutions are disclosed (for example, Patent Document 2 (Claim 1, paragraph [0012], paragraph [0037], paragraph [0040], paragraph [0051], paragraph [0054], paragraph See [0061]). Patent Document 2 states that this gold plating solution contains a predetermined monovalent gold complex, an electrolyte, and a crystal modifier selected from metals, and that the pH of the gold plating solution is, for example, 3 to 14, preferably 5 to 8, and the conditions for electrolytic gold plating using this gold plating solution are, for example, a solution temperature of 20 to 80°C, a current density of 0.1 to 6 A/ ^dm2 , and this gold plating solution: It is described that it has extremely excellent stability, remains unchanged for one year after preparation, and that changes in the physical properties of the deposited gold during gold plating operations are unlikely to cause decomposition of the gold plating solution.

International Publication No. 2016/208340 International Publication No. 2016/098789

Generally, when forming gold-plated bumps using a gold plating method, gold plating is performed within a pattern formed using an organic resist on a substrate. However, although the gold plating solution described in Patent Document 2 is non-toxic, if gold plating is performed in an alkaline region where the plating solution exceeds pH 7 within the pH range of 3 to 14, the resist pattern will dissolve. Pattern plating became difficult, and the electrical conductivity of the plating solution became low, resulting in problems in that the plating film was not uniformly electrodeposited. On the other hand, if the plating solution is in the acidic to neutral range with a pH of 3 to 7, and the solution temperature during plating is 40°C or higher within the range of 20°C to 80°C, the resist pattern will change. There is still the problem that it is easily damaged and the plating film is not uniformly electrodeposited.

The object of the present invention is to provide an electrolytic gold plating solution that enables plating at a solution temperature of 35°C or lower, has excellent plating properties such that a plating film is uniformly electrodeposited, has a long service life, and is non-toxic. The purpose is to provide a manufacturing method. Another object of the present invention is to provide a plating method using this plating solution.

The present inventors set the pH of the gold plating solution described in Patent Document 2 to a neutral range in order to facilitate complexation of gold ions, and as a result, the plating film was not uniformly electrodeposited, so the gold plating solution was While increasing the electrical conductivity of the plating solution by setting the pH of the solution to a strongly acidic region of less than 3, selecting a specific complexing agent and adjusting the molar ratio of this complexing agent and the gold salt to a predetermined ratio. Therefore, the present invention was achieved by focusing on the ability to complex gold ions, thereby improving the plating properties of uniformly electrodepositing a plating film, and extending the life of the plating solution.

A first aspect of the present invention is an electrolytic gold plating solution comprising a non-cyanide soluble gold salt (A) and a complexing agent (B) that complexes gold ions of the gold salt, The agent (B) is a mercaptotetrazole compound represented by the following general formula (1), and the molar ratio (B/A) of the complexing agent (B) to the soluble gold salt (A) is 10 or more and 260 or less. The gold plating solution has a pH of less than 3.

However, in formula (1), "*" is a methyl group, ethyl group, propyl group, carboxyl group, acetyl group, phenyl group, hydroxyphenyl group, methoxyphenyl group, alkoxyl group, dimethylaminoethyl group or acetamidophenyl group. be.

A second aspect of the present invention is an invention based on the first aspect, and is an electrolytic gold plating solution that further contains sulfuric acid or an alkylsulfonic acid having 1 or more and 5 or less carbon chains.

A third aspect of the present invention is an invention based on the first or second aspect, and is an electrolytic gold plating solution that does not contain cyan compounds or cyan ions.

A plating method according to a fourth aspect of the present invention is a plating method in which a gold plating film is formed within a resist pattern using the electrolytic gold plating solution according to the first, second, or third aspect.

The manufacturing method according to the fifth aspect of the present invention includes electrolyzing gold metal in the presence of the complexing agent (B) according to the first aspect in sulfuric acid or an alkylsulfonic acid having 1 to 5 carbon chains. After obtaining an electrolytic solution containing a non-cyanide soluble gold salt (A), the electrolytic gold plating solution of the first aspect is produced.

In the electrolytic gold plating solution according to the first aspect of the present invention, a specific mercaptotetrazole compound represented by the above formula (1) is used as a complexing agent, and the molar ratio of the complexing agent (B) and the gold salt (A) is By adjusting the ratio (B/A) to a predetermined ratio of 10 or more and 260 or less, gold ions can be complexed even if the pH is less than 3. In addition, when the pH is less than 3, the electrical resistance of the plating solution is low and the electrical conductivity of the plating solution is high, so that a plating film is uniformly electrodeposited during plating and has excellent plating properties. In addition, since this electrolytic plating solution contains a specific mercaptotetrazole compound, gold plating can be performed at a relatively low temperature (e.g., 35°C or less), and the pH of the plating solution is less than 3. Its acidity has the advantage of reducing damage to the resist pattern during plating. Furthermore, since gold ions are complexed with a specific mercaptotetrazole compound, it exhibits high oxidation stability and has the effect of extending the life of the plating solution after it is manufactured.

In the electrolytic gold plating solution according to the second aspect of the present invention, since the gold plating solution further contains sulfuric acid or an alkylsulfonic acid having a carbon chain of 1 or more and 5 or less, it has the effect of dissolving gold in the aqueous solution by electrolysis.

The electrolytic gold plating solution according to the third aspect of the present invention has low toxicity because the gold plating solution does not contain cyanide compounds or cyanide ions.

In the plating method according to the fourth aspect of the present invention, since a gold plating solution having a pH of less than 3 is used, a uniform gold plating film can be formed within the resist pattern without dissolving the resist pattern during gold plating. I can do it.

In the production method according to the fifth aspect of the present invention, gold metal is electrolyzed in sulfuric acid or an alkylsulfonic acid having 1 to 5 carbon chains in the presence of the complexing agent (B) according to the first aspect. Electrolytic gold plating according to the first aspect is carried out by preparing an aqueous solution of a non-cyanide soluble gold salt (A) with a pH of less than 1, and adjusting the pH of this aqueous solution to less than 3 using a pH adjuster. Manufacture liquid. Therefore, this method has the effect of coordinating only the complexing agent (B) with respect to gold ions.

FIG. 1 is a block diagram of an apparatus for preparing a non-cyanide soluble gold salt of the present invention.

Next, a mode for carrying out the present invention will be described with reference to the drawings.

[Electrolytic gold plating solution]
The electrolytic gold plating solution of this embodiment includes a non-cyanide soluble gold salt (A) and a complexing agent (B) that complexes the gold ions of this gold salt, and the complexing agent (B) is as described above. A mercaptotetrazole compound represented by the general formula (1), in which the molar ratio (B/A) of the complexing agent (B) to the soluble gold salt (A) is 10 to 260, and the pH of the gold plating solution is 3. It is characterized by being less than or equal to

As the complexing agent (B) of the electrolytic gold plating solution, a mercaptotetrazole compound represented by the above-mentioned general formula (1) is used. Such a complexing agent (B) has a high electron density in the tetrazole ring and a strong coordination force of the lone pair of electrons in the mercapto group, so it can accurately complex gold ions and prevent precipitation and precipitation of the gold component. To create a highly stable plating solution that does not cause oxidation. As the mercaptotetrazole compound, 5-mercapto-1-methyltetrazole and I-(2-dimethylaminoethyl)-5-mercaptotetrazole are preferred because of their high solubility in aqueous solutions.

The molar ratio (B/A) of the complexing agent (B) to the soluble gold salt (A) in the electrolytic gold plating solution is 10 or more and 260 or less. If the molar ratio (B/A) is less than 10, there will be a shortage of complexing agent, and the gold ions eluted from the soluble gold salt will not be complexed sufficiently, and the gold component of the plating solution will precipitate or precipitate, resulting in poor stability of the plating solution. Become less sexually active. Moreover, if it exceeds 260, the complexing agent becomes excessive, and the electrodeposition of gold ions is excessively suppressed, resulting in a problem that a dense plating film cannot be obtained. The preferred molar ratio (B/A) is 10 or more and 100 or less.

The concentration of the non-cyanide soluble gold salt (A) in the electrolytic gold plating solution is preferably 0.001 mol/L to 0.1 mol/L. If it is less than 0.001 mol/L, the plating rate tends to be slow, and if it exceeds 0.1 mol/L, the plating bath may become too expensive. Further, the concentration of the complexing agent (B) in the electrolytic gold plating solution is preferably 0.01 mol/L to 3 mol/L. If it is less than 0.01 mol/L, complexation of gold ions tends to be insufficient, and the gold component of the plating solution tends to precipitate. If it exceeds 3 mol/L, it tends to be difficult to dissolve the complexing agent in the aqueous solution.

The pH of the electrolytic gold plating solution is less than 3 in order to increase the electrical conductivity of the plating solution. When this pH becomes 3 or higher, the electrical conductivity of the plating solution decreases, resulting in poor plating properties. The preferred pH is 0-2.

The electrolytic gold plating solution preferably contains sulfuric acid or an alkylsulfonic acid having 1 or more and 5 or less carbon chains. The concentration of sulfuric acid or alkylsulfonic acid having 1 to 5 carbon chains is preferably in the range of 0.01 mol/L to 5 mol/L. If it is less than 0.01 mol/L, the conductivity of the plating solution tends to be low, making it difficult to uniformly electrodeposit a plating film. Moreover, when it exceeds 5 mol/L, the viscosity of the plating solution becomes too high, making it difficult to obtain a dense plating film.

The electrolytic gold plating solution preferably does not contain cyanide compounds or cyanide ions. Low toxicity as it does not contain cyanide compounds or cyanide ions. "Contains no cyanide compounds or cyan ions" means the test method specified in JIS-K0102 (pyridine-pyrazolone spectrophotometry, 4-pyridinecarboxylic acid-pyrazolone spectrophotometry, ion electrode method, or 4-pyridinecarboxylic acid spectrophotometry) - The concentration of cyanide compounds or cyanide ions is 1 ppm or less when an electrolytic gold plating solution is measured by a flow analysis method using pyrazolone coloring.

[Method for producing electrolytic gold plating solution]
The method for producing the electrolytic gold plating solution in this embodiment will be described in detail below.
In the method for producing an electrolytic gold plating solution of this embodiment, it is preferable to utilize electrolysis of gold metal using an ion exchange membrane. In the electrolytic gold plating solution obtained by using this method, the mercaptotetrazole compound is reliably coordinated with gold ions, so that gold plating can be performed reliably.

As shown in FIG. 1, a non-cyanide soluble gold salt is prepared by an electrolytic device 10 in which an anode tank 1 and a cathode tank 2 are connected with a hydrogen ion exchange membrane 3 in between.
First, sulfuric acid or an alkylsulfonic acid having a carbon chain of 1 or more and 5 or less, a complexing agent (B) represented by the above-mentioned general formula (1), and pure water are placed in the anode tank 1. Here, the concentration of sulfuric acid or alkylsulfonic acid having 1 to 5 carbon chains is preferably 0.1 to 5 mol/L. The concentration of the complexing agent (B) is preferably 0.01 to 3 mol/L. Ion-exchanged water or the like can be used as the pure water.

Next, sulfuric acid or an alkylsulfonic acid having a carbon chain of 1 or more and 5 or less and pure water are placed in the cathode tank 2. Here, the concentration of sulfuric acid or alkylsulfonic acid having 1 to 5 carbon chains is preferably 0.01 to 5 mol/L. Next, a soluble plate-shaped or rod-shaped gold metal 4 is used for the anode, and an insoluble Pt/Ti plate 5 made of a titanium (Ti) base plated with platinum (Pt) is used for the cathode. As the gold metal 4, it is preferable to use gold having a purity of 99% or more and processing it into a plate or rod shape.

The electrolytic device 10 having such a configuration electrolyzes the gold metal 4 to elute gold ions and complex them with the complexing agent (B). The obtained electrolytic solution 6 is taken out from the anode tank 1, and this electrolytic solution 6 is subjected to solid-liquid separation using a solid-liquid separator (not shown) to obtain a solution containing a non-cyanide soluble gold salt (A). The electrolysis here can be performed at a liquid temperature of 10°C to 50°C, a current density of 0.01 ASD to 10 ASD, and a gold concentration (concentration of non-cyanide soluble gold salt (A)) of 0.001 mol/L to It is preferable to adjust the amount to 1 mol/L.

Next, the solution containing this non-cyanide soluble gold salt (A) is diluted to produce the electrolytic gold plating solution of this embodiment. Dilution is preferably performed with pure water such as ion-exchanged water or distilled water so that the non-cyanide soluble gold salt (A) is in the range of 0.001 mol/L to 0.1 mol/L. At this time, if the concentration of the complexing agent (B) is decreasing, it is preferable to add the complexing agent (B) additionally in a range of 0.01 mol/L to 3 mol/L. Furthermore, when plating an object that is unstable to strong acids, the pH of the plating solution can be adjusted by neutralization within a range that does not exceed 3, if necessary. Neutralization is preferably carried out using a hydroxide such as sodium hydroxide or a base such as ammonia. In this way, the electrolytic gold plating solution of this embodiment is manufactured.

Next, examples of the present invention will be described in detail together with comparative examples.

First, the six types of complexing agents (types: A to F) used in Examples 1 to 12 and Comparative Examples 1 to 6 and their respective molecular weights are shown in Table 1 below.

<Example 1>
First, a solution containing the following non-cyanide soluble gold salt (A) was prepared, and then this solution was used to prepare an electrolytic gold plating solution.
(Preparation of liquid containing non-cyanide soluble gold salt (A))
A liquid containing a non-cyanide soluble gold salt (A) was prepared with the following composition using a type A complexing agent (B) shown in Table 1 above. The prepared solution was put into an anode tank 1 shown in FIG.
Methanesulfonic acid: 100g/L
5-mercapto-1-methyltetrazole (type A complexing agent (B)): 100 g/L
Remainder: pure water

Next, a solution having the following composition was prepared, and this solution was put into the cathode tank 2 shown in FIG.
Methanesulfonic acid: 100g/L
Remainder: Pure Water In the soluble gold salt preparation apparatus 10 having the above configuration, gold metal 4 was electrolyzed for 50 hours with the liquid temperature set at 25° C. and the anode current density set at 0.1 ASD. The pH of electrolytic solution 6 was less than 1. This electrolytic solution 6 was filtered using three types of filter paper for qualitative analysis to obtain a yellow transparent solution containing a non-cyan soluble gold salt (A) as a filtrate. Here, the gold ion concentration contained in this liquid was measured using an ICP optical emission spectrometer (ICP-OES) and was found to be 10 g/L.

(Preparation of electrolytic gold plating solution)
An electrolytic gold plating solution was prepared according to the following procedure. The above solution containing a non-cyanide soluble gold salt (A) with a pH of less than 1 and a gold ion concentration of 10 g/L is diluted with pure water, and the gold ion concentration is adjusted to 0.5 g/L (0.002538 mol/L). ) was adjusted. Next, 5-mercapto-1-methyltetrazole, which is a type A complexing agent (B), was added to the diluted solution and mixed to prepare an electrolytic gold plating solution. The concentration of the complexing agent (B) in the electrolytic gold plating solution was 10 g/L (0.086103 mol/L), and the pH of the electrolytic gold plating solution was less than 1. The molar ratio (B/A) calculated from the gold ion concentration and the complexing agent concentration was 34.

The contents of Example 1 described above are shown in Table 2 below. Table 2 also shows the contents (molar ratio (B/A) and pH value) of Examples 2 to 12 and Comparative Examples 1 to 6, which will be described below.

<Examples 2 to 12 and Comparative Examples 1 to 6>
As shown in Table 2 above, in Examples 2 to 12 and Comparative Examples 1 to 6, the degree of dilution when diluting the solution containing the non-cyanoid soluble gold salt (A) in Example 1 with pure water was changed. As a result, the gold ion concentration of the non-cyanide soluble gold salt (A) was changed to a value different from that in Example 1. Further, the complexing agent (B) was prepared in the amount shown in Table 2.
Further, as the complexing agent (B) in Examples 2 to 9 and Comparative Examples 1 to 3, and 6, the same complexing agent as in Example 1 was used. Examples 10 to 12 and Comparative Examples 4 and 5 used a different complexing agent from Example 1. In Comparative Examples 4 and 5, a mercaptotriazole compound was used instead of a mercaptotetrazole compound.
Furthermore, in Examples 2 to 12 and Comparative Examples 1 to 6, the amount of complexing agent (B) added when preparing the liquid containing the non-cyanide soluble gold salt (A) was the same as or changed from Example 1. The concentration of the complexing agent in the electrolytic gold plating solution was adjusted.
Furthermore, in Examples 2 to 12 and Comparative Examples 1 to 6, after adding and mixing the complexing agent to the diluted solution in Example 1, a 0.1 mol/L aqueous sodium hydroxide solution was added dropwise to this mixed solution. The pH of the mixed solution was changed as shown in Table 2.

<Comparative test and evaluation>
Eighteen types of electrolytic gold plating solutions of Examples 1 to 12 and Comparative Examples 1 to 6 were prepared and then their stability and plating properties were investigated by the following method. The results are shown in Table 2 above.

(1) Stability of the plating solution The stability of the electrolytic gold plating solution was determined by taking 50 mL of the prepared electrolytic gold plating solution and sealing it in a transparent glass bottle. This bottle was stored for 6 months in a clean oven maintained at a temperature of 40°C. The appearance of the liquid after storage was visually confirmed. During visual inspection, if no precipitate was formed at the bottom of the glass bottle, the stability of the plating solution was judged to be "good", and if precipitate was formed, the stability of the plating solution was judged to be "poor". It was determined that there was.

(2) Regarding plating properties A rod-shaped gold metal with a diameter of 1 mm was used as an anode of an electrolytic plating apparatus. Further, as a cathode, a silicon wafer was used on which a resist pattern having 2000 vias each having a diameter of 100 μm was formed on the wafer surface.
100 mL of the 18 types of electrolytic gold plating solutions obtained in Examples 1 to 12 and Comparative Examples 1 to 6 were each placed in a glass beaker and stirred with a stirrer. The stirred solution was placed in the plating tank of the electrolytic plating apparatus, and the via openings of the resist pattern were plated for 1 hour with the solution temperature set at 30° C. and the cathode current density set at 0.1 ASD.
The silicon wafer was taken out from the plating apparatus, washed and dried, and then the resist pattern was peeled off using an organic solvent. The plating quality is determined to be "good" when the gold plating bumps are formed along the shape of the resist pattern, and the plating quality is determined to be "poor" when the gold plating bumps are not formed according to the resist pattern. It was determined that The results are shown in Table 2 above.

As is clear from Table 2, in Comparative Example 1, a mercaptotetrazole compound was used as the complexing agent (B), the pH of the electrolytic gold plating solution was 1, and the gold plating bumps were formed according to the resist pattern. Although the plating properties were "good," the molar ratio (B/A) of soluble gold salt (A) and complexing agent (B) was too small at 8, so the complexing agent was insufficient and gold ions were not complexed. The stability of the plating solution was "poor" as the plating solution became insufficient and a precipitate formed.

In Comparative Example 2, a mercaptotetrazole compound is used as the complexing agent (B), and the molar ratio (B/A) of the soluble gold salt (A) and the complexing agent (B) is 170, which improves the stability of the plating solution. However, because the pH of the electrolytic gold plating solution was too high (3), hydrogen was generated, the resist pattern peeled off, and the gold plating bumps were not formed according to the resist pattern, resulting in poor plating performance. It was "defective".

In Comparative Example 3, a mercaptotetrazole compound was used as the complexing agent (B), but since the molar ratio (B/A) of the soluble gold salt (A) to the complexing agent (B) was too small at 8, precipitation occurred. occurred, and the stability of the plating solution was "poor." Furthermore, since the pH of the electrolytic gold plating solution was too high as 4, hydrogen was generated, the resist pattern was peeled off, gold plating bumps were not formed in accordance with the resist pattern, and the plating performance was also "poor".

In Comparative Examples 4 and 5, the pH of the electrolytic gold plating solution was 1 and 2, respectively, the gold plating bumps were formed according to the resist pattern, and the plating properties were both "good". In addition, the molar ratio (B/A) of the soluble gold salt (A) and the complexing agent (B) was 97 and 171, respectively, which were appropriate, but since a mercaptotriazole compound was used as the complexing agent, the above-mentioned plating Under these conditions, gold ions were not reliably complexed, precipitation occurred, and the stability of the plating solution was both "poor."

In Comparative Example 6, a mercaptotetrazole compound was used as the complexing agent (B), but since the molar ratio (B/A) of the soluble gold salt (A) to the complexing agent (B) was too high at 305, the complexing agent (B) was too large. Electrodeposition of gold ions by the curing agent was excessively suppressed, the plating film formed within the resist pattern was not dense, and the plating performance was "poor."

In contrast to these comparative examples, in Examples 1 to 12, since the electrolytic gold plating solution had the requirements of the first aspect of the present invention, no plating phenomenon occurred after storage for 6 months, and the resist pattern was correct. Gold-plated bumps were formed on the surface, and the stability and plating properties of the plating solution were all "good."

The electrolytic gold plating solution of the present invention can be suitably used for gold plating on wafers, substrates, etc., particularly for gold plating bumps.

Claims (5)

An electrolytic gold plating solution comprising a non-cyanide soluble gold salt (A) and a complexing agent (B) that complexes gold ions of the gold salt,
The complexing agent (B) is a mercaptotetrazole compound represented by the following general formula (1), and the molar ratio (B/A) of the complexing agent (B) to the soluble gold salt (A) is 10 or more. 260 or less, and the pH of the gold plating solution is less than 3.

However, in formula (1), "*" is a methyl group, ethyl group, propyl group, carboxyl group, acetyl group, phenyl group, hydroxyphenyl group, methoxyphenyl group, alkoxyl group, dimethylaminoethyl group or acetamidophenyl group. be. The electrolytic gold plating solution according to claim 1, further comprising sulfuric acid or an alkylsulfonic acid having 1 or more and 5 or less carbon chains. The electrolytic gold plating solution according to claim 1 or 2, which does not contain cyanide compounds or cyanide ions. A plating method for forming a gold plating film within a resist pattern using the electrolytic gold plating solution according to claim 1, 2 or 3. Gold metal is electrolyzed in sulfuric acid or an alkylsulfonic acid having 1 to 5 carbon chains in the presence of the complexing agent (B) according to claim 1 to form a non-cyanide soluble gold salt (A). A method for producing the electrolytic gold plating solution according to claim 1, after obtaining an electrolytic solution containing the following.

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