TW202319590A - Cyanide-free electrolytic gold plating solution - Google Patents

Abstract

The present invention addresses the problem of providing a cyanide-free electrolytic gold plating solution capable of improving deposition of gold to the bottom of a through hole. The problem is solved by a cyanide-free electrolytic gold plating solution containing a gold sulfite alkali metal salt, a water-soluble amine, a crystal regulator, and a cationic surfactant.

Description

Cyanide-free electrolytic gold plating solution

The invention relates to a cyanide-free electrolytic gold plating solution.

Cyanide-free (intentionally excluding cyanide) electrolytic gold plating solutions are used in the manufacture of wiring materials in semiconductor devices. The electrolytic gold plating solution uses potassium gold cyanide as the gold source, but since cyanide is highly toxic, it will corrode the resist. Therefore, in semiconductor devices, a gold source that does not contain cyanide is generally used, such as gold sulfite alkali salt Or electrolytic gold plating solution such as gold ammonium sulfite.

Patent Document 1 discloses a cyanide-free electrolytic gold plating solution for forming bumps, which contains alkali gold sulfite or ammonium gold sulfite as a gold source, water-soluble amine as a stabilizer, and Sulfites and sulfates, buffers, polyalkylene glycols and/or zwitterionic surfactants. In addition, Patent Document 2 discloses a cyanide-free electrolytic gold plating solution, which further defines the average molecular weight of polyalkylene glycol.

[Prior Art Literature] [Patent Document] [Patent Document 1] Japanese Unexamined Patent Publication No. 2007-92156 [Patent Document 2] Japanese Patent Laid-Open No. 2008-115450

[Problem to be solved by the invention] Cyanide-free electrolytic gold plating solutions are widely used as wiring materials in semiconductor devices using substrates such as Si and GaAs. There are through-holes (wiring lines) that are connected between the conductive layers, and gold-plated coatings are applied from the side walls to the bottom of the through-holes. In recent years, the requirement for a high aspect ratio of the through-hole has become higher and higher, so there is a problem that it is difficult to deposit a gold plating layer at the bottom of the through-hole. In view of the above problems, the object of the present invention is to provide a cyanide-free electrolytic gold plating solution that can improve the precipitation of gold at the bottom of the through hole.

[Technical means to solve the problem] The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and have found that the surfactant in the cyanide-free electrolytic gold plating solution contributes to the easiness of gold precipitation when it is related to the shape of the object to be plated. Specifically, the inventors of the present invention have found that cationic surfactants selectively adsorb to the protrusions of the object to be plated to suppress gold deposition. Based on this discovery, one aspect of the present invention is a cyanide-free electrolytic gold plating solution containing gold sulfite alkali salt, water-soluble amine, crystal regulator and cationic surfactant.

[Efficacy of Invention] Based on the present invention, a cyanide-free electrolytic gold plating solution capable of improving the precipitation of gold at the bottom of the through hole can be provided.

Hereinafter, the present invention will be described in detail, but the description of the constituent elements described below is only an example (representative example) of the embodiment of the present invention, and the present invention is not limited to these contents, and various modifications can be carried out within the scope of the gist. .

The embodiment of the present invention is a cyanide-free electrolytic gold plating solution (hereinafter referred to as electrolytic gold plating solution) containing gold sulfite alkali salt, water-soluble amine, crystal regulator and cationic surfactant. The cationic surfactant contained in the electrolytic gold plating solution, as shown in Figure 1, is selectively adsorbed on the convex portion (the angle formed by the outermost surface and the side wall) of the through hole, inhibits the precipitation of gold on the convex portion, and promotes the gold deposition process. Deposition at the bottom of the via (gold plating film formation). In addition, since the bottom of the through-hole is a place where gold is hardly deposited, as long as the gold-plated film can be formed on the bottom, the gold-plated film can be sufficiently formed on the side wall of the through-hole.

The mechanism by which the cationic surfactant in the electrolytic gold plating solution is selectively adsorbed on the convex part of the object to be plated is not clear, but it may be because the current density of the convex part is the highest when the current is applied, and the positively charged cationic surfactant is activated due to electrostatic interaction. The agent becomes easily adsorbed. The cationic surfactant is not particularly limited, but quaternary ammonium salts and aliphatic amines are preferred. Quaternary ammonium salts include benzethonium chloride, cetylpyridinium chloride cation monohydrate, 1-dodecylpyridinium chloride cation, and the like. Aliphatic amines include dodecylamine sulfate, n-octylamine hydrochloride, dodecylamine hydrochloride, and the like. In addition, one or both of quaternary ammonium salts and aliphatic amines may also be contained.

In this embodiment, the concentration of the cationic surfactant in the electrolytic gold plating solution is not particularly limited, preferably 0.01 mg/L to 10 mg/L, more preferably 0.1 mg/L to 5 mg/L. The higher the concentration of the cationic surfactant, the higher the hardness of the gold plating film tends to be. If it is less than 0.01 mg/L, gold may not be sufficiently separated at the bottom of the through hole. On the other hand, if it is more than 10 mg/L, the crystal state may change.

The gold sulfite alkali salt in the electrolytic gold plating solution is used as a gold source, and its composition is not particularly limited, for example, including gold sodium sulfite, gold potassium sulfite, gold ammonium sulfite, etc. better. In addition, although the concentration of the gold sulfite alkali salt in the electrolytic gold plating solution is not particularly limited, it is usually converted to a gold concentration of 5 g/L to 15 g/L, preferably 7 g/L to 13 g/L.

The water-soluble amine in the electrolytic gold plating solution is used as a stabilizer, and its composition is not particularly limited. For example, it includes triethanolamine, ethylenediaminetetraacetic acid, ethane-1, 2-diamine, etc., especially ethane -1,2-diamine is preferred. The presence of the stabilizer has the effect of stabilizing the gold complex. In addition, the concentration of the water-soluble amine in the electrolytic gold plating solution is not particularly limited, and is generally not less than 5 g/L and not more than 20 g/L, preferably not less than 7 g/L and not more than 15 g/L.

The crystal regulator in the electrolytic gold plating solution includes Tl compound, Pb compound, As compound, etc., and thallium formate, thallium sulfate, and lead acetate are preferred. The presence of the crystallization regulator facilitates the adjustment of the orientation and crystallite size of the obtained gold-plated film. In addition, the concentration of the crystallization regulator in the electrolytic gold plating solution is not particularly limited, and it is usually not less than 5 mg/L and not more than 50 mg/L, preferably not less than 10 mg/L and not more than 30 mg/L.

In this embodiment, the surface tension of the cyanide-free electrolytic gold plating solution is preferably less than 60 mN/m. If the surface tension of the electrolytic gold plating solution is less than 60mN/m, the precipitation of the gold plating layer at the bottom of the through hole is expected to be further improved. In the present disclosure, the surface tension can be measured using the platinum ring method (du Noüy ring method) adopted in JIS-K-2241 (2017).

The preparation method of the electrolytic gold plating solution of this embodiment is not particularly limited. It can be prepared by adding alkali gold sulfite, water-soluble amine, crystal regulator and cationic surfactant to an aqueous solvent containing water and mixing them. In addition, the electrolytic gold plating solution may contain other components, such as conductive salts, pH regulators (buffers), complexing agents, shielding agents, and the like. The addition of conductive salt has the effect of improving the plating leveling ability. The addition of complexing agent can improve the stability of electrolytic gold plating solution. The addition of pH regulators (buffers) has the effect of suppressing local pH fluctuations. The addition of the protective agent has the effect of suppressing the deterioration of the appearance of the film and the change of the hardness.

The component analysis of the cationic surfactant in the electrolytic gold plating solution can be determined by liquid chromatography. In addition, the concentration of the cationic surfactant in the electrolytic gold plating solution can be determined by liquid chromatography.

[Example] Hereinafter, the present invention will be described in more detail by using examples, but the patent scope of the present invention is not limited by the contents described in the examples.

＜Building bath for electrolytic gold plating solution＞ Prepare sodium gold (I) sulfite containing gold concentration 12g/L, sodium sulfite 70g/L as electrolyte, ethane-1,2-diamine 10g/L as stabilizer, thallium formate 20mg/L as crystal regulator. The cyanide-free electrolytic gold plating solution of L (thallium concentration) and various surfactants shown in Table 1.

<Plating conditions: for inserting through holes> Immerse the substrate (substrate: nickel plating layer 2 μm, gold strike plating layer 0.02 μm) with through holes (diameter: 100 μm, depth: 60 μm) into the above electrolytic gold plating solution (liquid temperature 50°C, pH 8.0) for 18 minutes, electrolytic gold plating was performed at a current density of 0.5A/dm ² , then washed with water and dried.

<Electroplating conditions: for hardness measurement> Substrate (substrate: nickel plated layer 2 μm, gold strike layer 0.02 μm) was immersed in the above electrolytic gold plating solution (liquid temperature 52°C, pH 7.8) for 36 minutes at 0.5A/ ^dm2 Electrolytic gold plating is carried out at a certain current density, followed by water washing and drying.

＜Measurement of Surface Tension＞ The surface tension was measured using the platinum ring method (du Noüy ring method) adopted in JIS-K-2241. Put the electrolytic gold plating solution in the petri dish, immerse the platinum ring in the plating solution, lift the platinum ring slowly along the vertical direction to separate, measure the maximum force required to separate the platinum ring, and calculate the surface measurement tension.

＜Evaluation method of film thickness＞ A cross-section was formed on the through-hole of the electrolytic gold-plated substrate using a cross-section polisher, and the gold film thickness was measured from the cross-section using a scanning electron microscope. The film thicknesses of the electrolytic gold plating on the uppermost surface of the substrate and the bottom of the through-hole were measured respectively, and the film thickness ratio (bottom of the through-hole/most surface) was calculated.

＜Particles in solution＞ In the case of unstable electrolytic gold plating solution, gold particles and chemical components will precipitate over time, and the number of particles tends to increase. Therefore, the number of particles in the solution was also analyzed. The analysis method is to filter the electrolytic gold plating solution after bathing with a 0.1 μm membrane filter, and use a particle counter to count the number of particles above 0.5 μm in the solution after standing. Then, the case where the number of particles in the liquid was less than 200/mL was regarded as good, and the case where the number of particles in the liquid was 200/mL or more was regarded as bad.

＜Appearance evaluation of electrolytic gold plating film＞ The surface of the substrate treated with electrolytic gold plating was visually observed to determine whether it was matte or semi-glossy.

＜Hardness measurement of electrolytic gold plating film＞ The Vickers hardness of the electrolytic gold-plated film is measured by heat treatment at 300°C for 30 minutes in the atmosphere, using a microhardness tester (Mitutoyo Corporation, HM-221), and using a Vickers indenter to measure the hardness of the electrolytic hardness before and after heat treatment. The hardness of the gold-plated film was measured five times, and the average value was calculated. In addition, the hardness measurement of the electrolytic gold-plated film is to apply a load to the indenter to form an indentation on the coating, and calculate the hardness from the diagonal of the indentation. Therefore, in the case of a thin film thickness, it may be affected by the base material. . Therefore, in order to avoid the influence from the base material, the film thickness of the electrolytic gold plating film is set to 10 μm or more.

(Example 1 to 6) Use benzethonium chloride (cation surfactant) as surfactant, adjust surfactant concentration to be the electrolytic gold plating solution (embodiment 1) of 0.01mg/L, be the electrolytic gold plating solution (embodiment 1) of 0.1mg/L with the same concentration 2), the same concentration is the electrolytic gold plating solution (embodiment 3) of 1mg/L, the same concentration is the electrolytic gold plating solution (embodiment 4) of 3mg/L, the same concentration is the electrolytic gold plating solution (embodiment 5) of 5mg/L , and the same concentration is the electrolytic gold plating solution (embodiment 6) of 10mg/L. The surface tension of these electrolytic gold plating solutions and the number of particles in the solution were analyzed, and the results are shown in Table 1. As shown in Table 1, the surface tension was less than 60 mN/m, and the number of particles was good.

Using these electrolytic gold plating solutions, electrolytic gold plating was performed under the above-mentioned conditions, an electrolytic gold plating film was formed in the through hole, and then the film thickness (the uppermost surface and the bottom) of the electrolytic gold plating film was measured. As a result, the film thickness ratio (bottom/most surface) was 0.5 or more, and it was confirmed that the electrolytic gold plating film was sufficiently formed on the bottom of the via hole. In addition, electrolytic gold plating was performed on another substrate for hardness measurement under the above conditions to form an electrolytic gold plating film, and then the hardness of the electrolytic gold plating film was measured. As a result, a good result was obtained that the hardness after heating was 50 Hv or more. Furthermore, the appearance of the obtained electrolytic gold-plated film is dull or semi-glossy. A summary of the above results is shown in Table 1.

[Table 1]

(Examples 7 to 12) Use dodecylamine sulfate (cationic surfactant) as surfactant, adjust surfactant concentration to be the electrolytic gold plating solution (embodiment 7) of 0.01mg/L, be the electrolytic gold plating solution of 0.1mg/L with the same concentration (embodiment 8), the same concentration is the electrolytic gold plating solution (embodiment 9) of 1mg/L, the same concentration is the electrolytic gold plating solution (embodiment 10) of 3mg/L, the same concentration is the electrolytic gold plating solution (implementation) of 5mg/L Example 11), and the same concentration is the electrolytic gold plating solution (embodiment 12) of 10mg/L. The surface tension of these electrolytic gold plating solutions and the number of particles in the solution were analyzed, and the results are shown in Table 1. As shown in Table 1, the surface tension was less than 60 mN/m, and the number of particles was good.

Using these electrolytic gold plating solutions, electrolytic gold plating was performed under the above-mentioned conditions, an electrolytic gold plating film was formed in the through hole, and then the film thickness (the uppermost surface and the bottom) of the electrolytic gold plating film was measured. As a result, the film thickness ratio (bottom/most surface) was 0.5 or more, and it was confirmed that the electrolytic gold plating film was sufficiently formed on the bottom of the via hole. In addition, electrolytic gold plating was performed on another substrate for hardness measurement under the above conditions to form an electrolytic gold plating film, and then the hardness of the electrolytic gold plating film was measured. As a result, a good result was obtained that the hardness after heating was 50 Hv or more. Furthermore, the appearance of the electrolytic gold plating film is dull or semi-glossy. A summary of the above results is shown in Table 1.

(Examples 13 to 18) Use cetylpyridinium chloride cation-hydrate (cationic surfactant) as surfactant, adjust surfactant concentration to be the electrolytic gold plating solution (embodiment 13) of 0.01mg/L, the same concentration as 0.1mg/L Electrolytic gold plating solution (embodiment 14), same concentration is the electrolytic gold plating solution (embodiment 15) of 1mg/L, same concentration is the electrolytic gold plating solution (embodiment 16) of 3mg/L, same concentration is the electrolytic gold plating of 5mg/L solution (embodiment 17), and the same concentration is the electrolytic gold plating solution (embodiment 18) of 10mg/L. The surface tension of these electrolytic gold plating solutions and the number of particles in the solution were analyzed, and the results are shown in Table 1. As shown in Table 1, the surface tension was less than 60 mN/m, and the number of particles was good.

Using these electrolytic gold plating solutions, electrolytic gold plating was performed under the above-mentioned conditions, an electrolytic gold plating film was formed in the through hole, and then the film thickness (the uppermost surface and the bottom) of the electrolytic gold plating film was measured. As a result, the film thickness ratio (bottom/most surface) was 0.5 or more, and it was confirmed that the electrolytic gold plating film was sufficiently formed on the bottom of the via hole. In addition, electrolytic gold plating was performed on another substrate for hardness measurement under the above conditions to form an electrolytic gold plating film, and then the hardness of the electrolytic gold plating film was measured. As a result, a good result was obtained that the hardness after heating was 50 Hv or more. Furthermore, the appearance of the electrolytic gold plating film is dull or semi-glossy. A summary of the above results is shown in Table 1.

(Comparative Examples 1 to 6) Use sodium dodecylamine sulfate (anionic surfactant) as surfactant, adjust surfactant concentration to be the electrolytic gold plating solution (comparative example 1) of 0.01mg/L, be the electrolytic gold plating solution of 0.1mg/L with the same concentration (comparative example 2), the same concentration is the electrolytic gold plating solution (comparative example 3) of 1mg/L, the same concentration is the electrolytic gold plating solution (comparative example 4) of 3mg/L, the same concentration is the electrolytic gold plating solution (comparative example 4) of 5mg/L Example 5), and the same concentration is the electrolytic gold plating solution (comparative example 6) of 10mg/L. The surface tension of these electrolytic gold plating solutions and the number of particles in the solution were analyzed, and the results are shown in Table 1. As shown in Table 1, the number of particles was bad.

Using these electrolytic gold plating solutions, electrolytic gold plating was performed under the above-mentioned conditions, an electrolytic gold plating film was formed in the through hole, and then the film thickness (the uppermost surface and the bottom) of the electrolytic gold plating film was measured. As a result, the film thickness ratio (bottom/most surface) was less than 0.5, and it was confirmed that the electrolytic gold plating film was not sufficiently formed on the bottom of the via hole. A summary of the above results is shown in Table 1.

(Comparative Examples 7 to 10) Use sodium dihexyl sulfosuccinate (anionic surfactant) as surfactant, adjust surfactant concentration to be the electrolytic gold plating solution (comparative example 7) of 0.01mg/L, be the electrolytic gold plating solution of 1mg/L with the same concentration ( Comparative example 8), the same concentration is the electrolytic gold plating solution (comparative example 9) of 3mg/L, and the same concentration is the electrolytic gold plating solution (comparative example 10) of 5mg/L. The surface tension of these electrolytic gold plating solutions and the number of particles in the solution were analyzed, and the results are shown in Table 1. As shown in Table 1, the number of particles was bad.

Using these electrolytic gold plating solutions, electrolytic gold plating was performed under the above-mentioned conditions, an electrolytic gold plating film was formed in the through hole, and then the film thickness (the uppermost surface and the bottom) of the electrolytic gold plating film was measured. As a result, the film thickness ratio (bottom/most surface) was less than 0.5, and it was confirmed that the electrolytic gold plating film was not sufficiently formed on the bottom of the via hole. A summary of the above results is shown in Table 1.

(Comparative Examples 11 to 16) Use lauryl dimethylamine acetate betaine (zwitterionic surfactant) as surfactant, adjust surfactant concentration to be the electrolytic gold plating solution (comparative example 11) of 0.01mg/L, the electrolytic gold plating solution (comparative example 11) that same concentration is 0.1mg/L Gold plating solution (comparative example 12), same concentration is the electrolytic gold plating solution (comparative example 13) of 1mg/L, same concentration is the electrolytic gold plating solution (comparative example 14) of 3mg/L, same concentration is the electrolytic gold plating solution of 5mg/L (comparative example 15), and the same concentration is the electrolytic gold plating solution (comparative example 15) of 10mg/L. The surface tension of these electrolytic gold plating solutions and the number of particles in the solution were analyzed, and the results are shown in Table 1. As shown in Table 1, the surface tension is a high value of more than 60 mN/m.

Using these electrolytic gold plating solutions, electrolytic gold plating was performed under the above-mentioned conditions, an electrolytic gold plating film was formed in the through hole, and then the film thickness (the uppermost surface and the bottom) of the electrolytic gold plating film was measured. As a result, the film thickness ratio (bottom/most surface) was less than 0.5, and it was confirmed that the electrolytic gold plating film was not sufficiently formed on the bottom of the via hole. A summary of the above results is shown in Table 1

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[ Fig. 1 ] is a schematic cross-sectional view of a general via hole in a semiconductor device.

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Claims (5)

A cyanide-free electrolytic gold plating solution is characterized in that it contains a gold sulfite alkali salt, a water-soluble amine, a crystal regulator and a cationic surfactant. The cyanide-free electrolytic gold plating solution as claimed in claim 1, wherein the aforementioned cationic surfactant is a quaternary ammonium salt and/or an aliphatic amine. The cyanide-free electrolytic gold plating solution according to claim 1 or 2, wherein the concentration of the cationic surfactant is not less than 0.01 mg/L and not more than 10 mg/L. The cyanide-free electrolytic gold plating solution as claimed in claim 1 or 2, wherein the surface tension is less than 60mN/m. The cyanide-free electrolytic gold plating solution as claimed in item 3, wherein the surface tension is less than 60mN/m.

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