JP2019173162A - Tin or tin alloy plating solution and method of forming bumps using the solution - Google Patents

Abstract

To obtain void-free bumps with high uniformity and small variation in terms of height, even in a pattern which includes bumps of various diameters including large and small diameters, formed after reflow.SOLUTION: A tin or tin alloy plating solution comprises a soluble salt (A) containing at least a stannous salt, an acid or a salt thereof (B) selected from an organic acid and an inorganic acid, a surfactant (C), a benzal acetone (D), and a solvent (E). The plating solution is used to form a pattern having different bump diameters on a substrate. The plating solution contains benzal acetone (D) in an amount of 0.05 g/L-0.2 g/L, and a mass ratio (C/D) of the surfactant (C) to the benzal acetone (D) is 10-200. A mass ratio (E/D) of the solvent (E) to the benzal acetone (D) is 10 or more. The surfactant (C) is preferably a nonionic surfactant in which polyoxyethylene (EO) and polyoxypropylene (PO) are condensed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a tin or tin alloy plating solution for forming a tin or tin alloy plating film by electroplating, and a bump forming method using the solution. More particularly, the present invention relates to a tin or tin alloy plating solution containing benzalacetone, which is suitable for forming solder bumps having different bump diameters on a substrate such as a semiconductor wafer, and a bump forming method using the solution. .

  Patent Document 1 discloses that a via having a structure with a specified aspect ratio or the like is formed on a base material such as a semiconductor chip mounting substrate. Patent Document 1 uses a tin or tin alloy plating bath in which a specific filling organic compound (C) such as benzalacetone and a nonionic surfactant (D) are combined in the via of this structure, A method is disclosed in which vias are filled by electroplating to form protruding electrodes. According to this method, when the bump electrode is formed on the via on the base material by tin or tin alloy electroplating, the coexistence of the component (C) and the component (D) effectively deposits the metal on the upper portion of the via. Suppress and preferentially advance metal deposition from the bottom of the via. As a result, the via can be filled smoothly without the generation of voids.

  Patent Document 2 discloses (a) a divalent tin salt of alkanesulfonic acid, a divalent lead salt of alkanesulfonic acid, a divalent tin salt of alkanesulfonic acid, and a divalent lead salt of alkanesulfonic acid. A bath-soluble metal salt selected from the group consisting of: (b) an alkanesulfonic acid; (c) a brightener such as a mixture of α-naphthaldehyde and benzylideneacetone (benzalacetone); (d) in propylene glycol; An antifoaming agent comprising a mixture of silicone and silica and / or silicate; (e) a first nonionic surfactant comprising an ethoxylated arylphenol; and (f) a second nonionic surfactant comprising an ethoxylated short chain alcohol. An aqueous acidic tin, lead or tin-lead alloy electroplating bath comprising an ionic surfactant is disclosed. And the above-mentioned brightener α-naphthaldehyde is present at a concentration of about 0.02 g / L, about 5 g / L, and benzylideneacetone (benzalacetone) is present at a concentration of about 0.02 g / L to about 5 g / L. Is shown to do. This electroplating bath has the inherent ability to foam little or no during electroplating, even under high speed plating conditions such as those caused by the high current density and / or vigorous circulation of the bath. The bath is said to produce uniform and excellent tin and / or lead deposits.

  Further, Patent Document 3 discloses that metal ions selected from the group consisting of tin ions, lead ions, and mixed ions thereof are about 15.0 g / L to about 350.0 g / L, fluoroborate, fluorosilicic acid. About 100.0 g / L to about 500.0 g / L of a radical selected from the group consisting of salts, sulfamate salts, and mixed salts thereof, and about 10.0.0 g / L of a specific alkylallyl surfactant of an alkoxylated fatty acid. An aqueous acidic tin, lead, or tin-lead alloy electroplating bath having a pH of less than about 3.0 is disclosed, including 0 g / L to about 25.0 g / L. This electroplating bath contains about 0.1 g / L to about 10 carbonyl-containing compounds selected from the group consisting of benzylideneacetone (benzalacetone), 3-butyraldehyde, thiophene aldehyde, tolualdehyde, cinnamaldehyde and anisaldehyde. Further included in an amount of 0.0 g / L. This electroplating bath deposits a sufficiently bright tin-lead alloy plating and provides a simple and efficient electroplating process. Thereby, it is said that a sufficiently bright tin / lead alloy can be manufactured under economical conditions, and a product having a glossy appearance electroplated with a tin / lead alloy is provided.

  In recent years, wiring patterns having different bump diameters and bump pitches are mixed on a base material such as a single wafer substrate. In such a complicated pattern, it is required to form bumps having different bump diameters with a uniform height. According to the plating baths of Patent Documents 1 to 3 above, via filling can be performed smoothly without generating voids, uniform precipitates can be formed without foaming during electroplating, and a product with sufficient gloss can be simplified. In addition, it has excellent features such as being economical to manufacture. However, the plating solutions in these Patent Documents 1 to 3 have different bump diameters on one substrate (hereinafter sometimes referred to as “different diameter”). It is not an issue to achieve the height uniformity (hereinafter also referred to as “bump height uniformity”).

  Specifically, an example of forming bumps with patterns having different bump diameters will be described with reference to FIG. 2. First, as shown in FIG. 2A, first, a titanium layer 2 and a surface of a substrate 1 such as a semiconductor wafer substrate are formed. The copper seed layer 3 is formed sequentially. Next, a resist layer 4 is formed, mask exposure is performed on the resist layer 4, and development is performed to form a resist pattern 5 having vias 4a and 4b having different diameters. Next, copper or nickel is plated on the copper seed layer 3 in the vias 4a and 4b to form the underlayer 6. Next, by supplying power through the copper seed layer 3 using a tin plating solution, electrotin plating is performed inside the vias 4 a and 4 b of the resist pattern 5, and tin plating is deposited in the vias 4 a and 4 b on the base layer 6. Layers (tin plating films) 7a and 7b are respectively formed. Subsequently, as shown in FIG. 2B, the resist layer 4, the copper seed layer 3, and the titanium layer 2 are sequentially removed. Next, the remaining tin plating deposited layers 7a and 7b are melted by a reflow process. Thus, tin bumps 8a and 8b are formed as shown in FIG. In these tin bumps, the height of the bump 8b having a large bump diameter is larger than the height of the bump 8a having a small bump diameter, resulting in a height difference D, and the bump height cannot be made uniform. .

  Even when electroplating is performed using a conventional plating solution containing benzalacetone disclosed in Patent Documents 1 to 3, it is difficult to achieve bump height uniformity.

  In this specification, patterns having different bump diameters, that is, “different diameter patterns” are patterns in which the ratio (Smax / Smin) of the minimum underlayer area Smin to the maximum underlayer area Smax is 1.5 or more. Say. In the conventional plating solution, when Smax / Smin is 1.5 or more, it is difficult to suppress the height variation of the different-diameter bumps. The upper limit value of Smax / Smin is not particularly limited, but is about 30.

Japanese Patent Application Laid-Open No. 2006-74963 Japanese Patent Publication No. 3-17912 U.S. Pat. No. 3,730,853

  The object of the present invention is to make tin or tin that can provide bumps with a uniform bump height with small variations in height of large and small-diameter bumps formed after reflow, even in patterns with different bump diameters. An object of the present invention is to provide an alloy plating solution and a bump forming method using the solution.

  The tin or tin alloy plating solution according to the first aspect of the present invention includes a soluble salt (A) containing at least a stannous salt, an acid selected from an organic acid and an inorganic acid or a salt thereof (B), and a surface activity. A tin or tin alloy plating solution containing an agent (C), benzalacetone (D), and a solvent (E), wherein the plating solution is used to form patterns having different bump diameters on a substrate. The benzalacetone (D) is contained in the plating solution in an amount of 0.05 g / L to 0.2 g / L, and the mass ratio of the surfactant (C) to the benzalacetone (D). (C / D) is 10 to 200, and the mass ratio (E / D) of the solvent (E) to the benzalacetone (D) is 10 or more.

  The tin or tin alloy plating solution according to the second aspect of the present invention is the tin or tin alloy plating solution according to the first aspect, wherein the surfactant (C) is polyoxyethylene (EO) and polyoxypropylene (PO). ) Or a nonionic surfactant obtained by condensing polyoxyethylene (EO) with any one selected from phenol, alkylphenol, styrenated phenol, β-naphthol, bisphenols, and cumylphenol. It is an agent.

  The bump forming method according to the third aspect of the present invention uses the tin or tin plating solution according to the first or second aspect to form a plurality of tin or tin alloy plating deposition layers having different diameters on the substrate. And a step of performing a reflow process to form a plurality of bumps having different bump diameters.

  In the tin or tin alloy plating solution according to the first aspect of the present invention, benzalacetone (D) is contained in the plating solution in an amount of 0.05 g / L to 0.2 g / L. The mass ratio (C / D) of the surfactant (C) to benzalacetone (D) is defined as 10 to 200. The mass ratio (E / D) of the solvent (E) to benzalacetone (D) is defined as 10 or more. As shown in FIG. 1 (a), by supplying power through the copper seed layer 13 using this plating solution, when electrotin plating is performed inside the vias of the resist pattern 15, benzal acetone in the plating solution is removed from the vias. Adsorbs on the bottom and inhibits tin precipitation. Benzal acetone is easily adsorbed to the large-diameter via 14b where the plating solution easily enters, and the effect of suppressing the precipitation of tin is great. On the other hand, the small-diameter via 14a in which the plating solution is difficult to enter has a relatively small amount of benzalacetone adsorbed compared to the large-diameter via 14b, and the effect of suppressing the precipitation of tin is small. Thereby, the film thickness of the plating deposition layer 17b of the large diameter via 14b is formed thinner than the film thickness of the plating deposition layer 17a of the small diameter via 14a. As shown in FIG. 1B, when the resist layer 14 and the seed layers 13 and 12 are sequentially removed, and then the remaining plating deposition layers 17a and 17b are melted by a reflow process, as shown in FIG. Bumps (plating films) 18a and 18b having no bump height variation and no voids are formed. Accordingly, the substrate includes a substrate, a plurality of underlayers having different areas formed on the substrate, and a plurality of solder bumps formed on the plurality of underlayers, and the height of the plurality of solder bumps is uniform. An electronic component with solder bumps having a property of 10% or less can be obtained.

  In the tin or tin alloy plating solution according to the second aspect of the present invention, the surfactant (C) is adsorbed on the surface of the plating film and suppresses the crystal growth of tin to refine the crystal. As a result, the appearance of the plating film is improved, the adhesion between the plating film and the object to be plated is improved, the film thickness is uniformed, etc., and the above effects are more effective in synergy with benzalacetone (D). Demonstrate.

  In the bump forming method according to the third aspect of the present invention, a tin or tin alloy plating deposition layer having a different diameter is formed on the substrate using the tin or tin alloy plating solution according to the first or second aspect. To do. Next, reflow processing is performed. Thereby, even with patterns having different bump diameters, bumps having a uniform height and no voids can be formed.

  According to the invention based on the first to third aspects of the present invention, it is possible to provide an electronic component having different-diameter bumps with bump height uniformity on a base material. By using this electronic component, a highly reliable semiconductor device free from electrical connection failure can be manufactured.

FIG. 1 is a diagram illustrating a process of forming bumps in patterns having different bump diameters in the present embodiment. FIG. 1A is a cross-sectional view in which plating deposition layers having different diameters are formed in the via according to the present invention. FIG. 1 (b) shows a cross-sectional view of a plating deposition layer of different diameters after stripping the resist layer, titanium seed layer and copper seed layer. FIG. 1C shows a cross-sectional view of bumps with different diameters in which the bumps are uniformly formed after the reflow process. FIG. 2 is a diagram showing a process of forming bumps in patterns having different bump diameters in the prior art. FIG. 2A shows a cross-sectional view in which plating deposition layers having different diameters are formed in the via. FIG. 2B shows a cross-sectional view of the plating deposition layer having different diameters after the resist layer, titanium seed layer, and copper seed layer are peeled off. FIG. 2C shows a cross-sectional view of bumps with different diameters in which the bump heights are non-uniformly formed after the reflow process.

  Next, the form for implementing this invention is demonstrated.

  The tin or tin alloy plating solution of the present embodiment comprises a soluble salt (A) containing at least a stannous salt, an acid selected from organic acids and inorganic acids or a salt thereof (B), and a surfactant (C). And a tin or tin alloy plating solution containing benzalacetone (D) and a solvent (E). The characteristic point is that the plating solution is used to form patterns with different bump diameters on the substrate, and benzalacetone (D) is contained in the plating solution in an amount of 0.05 g / L to 0.2 g / L. The mass ratio (C / D) of surfactant (C) to benzalacetone (D) is 10 to 200, and the mass ratio of solvent (E) to benzalacetone (D) (E / D ) Is 10 or more. In addition, the base material of this embodiment includes a semiconductor wafer and a semiconductor chip mounting substrate.

  The tin alloy of this embodiment is an alloy of tin and one or more predetermined metals selected from silver, copper, bismuth, nickel, antimony, indium, and zinc. For example, binary alloys such as tin-silver alloy, tin-copper alloy, tin-bismuth alloy, tin-nickel alloy, tin-antimony alloy, tin-indium alloy, and tin-zinc alloy, tin-copper-bismuth, And ternary alloys such as tin-copper-silver alloys.

[Soluble salt containing at least stannous salt (A)]
The soluble salt (A) of this embodiment is a stannous salt, one or more selected from the group consisting of the stannous salt and silver, copper, bismuth, nickel, antimony, indium, and zinc. It consists of a mixture of metal salts.

  Therefore, the soluble salt (A) in the present embodiment means any soluble salt that generates various metal ions such as Sn2 +, Ag +, Cu +, Cu2 +, Bi3 +, Ni2 +, Sb3 +, In3 +, Zn2 + in the plating solution. Examples of the soluble salt include oxides, halides, inorganic acids or organic acids of these metals, and the like.

  Examples of the metal oxide include stannous oxide, silver oxide, copper oxide, nickel oxide, bismuth oxide, antimony oxide, indium oxide, and zinc oxide. Examples of the metal halide include stannous chloride, bismuth chloride, bismuth bromide, cuprous chloride, cupric chloride, nickel chloride, antimony chloride, indium chloride, and zinc chloride.

  Metal salts of inorganic or organic acids include copper sulfate, stannous sulfate, bismuth sulfate, nickel sulfate, antimony sulfate, bismuth nitrate, silver nitrate, copper nitrate, antimony nitrate, indium nitrate, nickel nitrate, zinc nitrate, copper acetate , Nickel acetate, nickel carbonate, sodium stannate, stannous borofluoride, stannous methanesulfonate, silver methanesulfonate, copper methanesulfonate, bismuth methanesulfonate, nickel methanesulfonate, indium metasulfonate, bismethane Examples thereof include zinc sulfonate, stannous ethanesulfonate, and bismuth 2-hydroxypropanesulfonate.

[Acid selected from organic acids and inorganic acids or salts thereof (B)]
The acid or salt (B) of this embodiment is selected from organic acids and inorganic acids, and salts thereof. Examples of the organic acid include organic sulfonic acids such as alkane sulfonic acid, alkanol sulfonic acid, and aromatic sulfonic acid, and aliphatic carboxylic acids. Inorganic acids include borohydrofluoric acid, silicohydrofluoric acid, and sulfamine. Acid, hydrochloric acid, sulfuric acid, nitric acid, perchloric acid and the like can be mentioned. These salts include alkali metal salts, alkaline earth metal salts, ammonium salts, amine salts, sulfonate salts, and the like. The component (B) is preferably an organic sulfonic acid from the viewpoint of the solubility of the metal salt and the ease of wastewater treatment.

  As said alkanesulfonic acid, what is shown by chemical formula CnH2n + 1SO3H (for example, n = 1-5, preferably 1-3) can be used. Specifically, methanesulfonic acid, ethanesulfonic acid, 1-propanesulfonic acid, 2-propanesulfonic acid, 1-butanesulfonic acid, 2-butanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid, decanesulfone, etc. Examples include acid and dodecanesulfonic acid.

  As said alkanol sulfonic acid, what is shown by Chemical formula CPH2P + 1-CH (OH) -CqH2q-SO3H (for example, p = 0-6, q = 1-5) can be used. Specifically, 2-hydroxyethane-1-sulfonic acid, 2-hydroxypropane-1-sulfonic acid, 2-hydroxybutane-1-sulfonic acid, 2-hydroxypentane-1-sulfonic acid, etc. Hydroxypropane-2-sulfonic acid, 3-hydroxypropane-1-sulfonic acid, 4-hydroxybutane-1-sulfonic acid, 2-hydroxyhexane-1-sulfonic acid, 2-hydroxydecane-1-sulfonic acid, 2- Examples thereof include hydroxydodecane-1-sulfonic acid.

  The aromatic sulfonic acid is basically benzenesulfonic acid, alkylbenzenesulfonic acid, phenolsulfonic acid, naphthalenesulfonic acid, alkylnaphthalenesulfonic acid, or the like. Specifically, 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid, p-phenolsulfonic acid, cresolsulfonic acid, sulfosalicylic acid, nitrobenzenesulfonic acid, sulfobenzoic acid, diphenylamine-4- Examples thereof include sulfonic acid.

  Examples of the aliphatic carboxylic acid include acetic acid, propionic acid, butyric acid, citric acid, tartaric acid, gluconic acid, sulfosuccinic acid, and trifluoroacetic acid.

[Surfactant (C)]
The surfactant (C) of this embodiment has an effect of enhancing the effect of suppressing the precipitation of tin in synergy with benzalacetone (D). Examples of the surfactant (C) include nonionic surfactants obtained by condensation of polyoxyethylene (EO) and polyoxypropylene (PO), or phenols, alkylphenols, styrenated phenols, β-naphthols, bisphenols, and polymers. A nonionic surfactant obtained by condensing polyoxyethylene (EO) with any one selected from milphenol is preferable.

  As the EOPO condensate (condensate obtained by condensing polyoxyethylene (EO) and polyoxypropylene (PO)), specifically, N, N-dipolyalkylene oxide N— represented by the following formula (1): An alkylamine is preferred. This N, N-dipolyalkylene oxide N-alkylamine has one alkyl group (R) having 5 to 20 carbon atoms in the range of ethylene oxide group (EO group) and propylene oxide group. It has two polyalkylene oxide groups (X and Y) each containing (PO group) in a molar ratio (EO group: PO group) independently in the range of 30:70 to 70:30.

  The EO group is hydrophilic and the PO group is hydrophobic. Thereby, the water-solubility of N, N-dipolyalkylene oxide N-alkylamine and the adsorptivity to the surface of tin or a tin alloy are exhibited with good balance. That is, in the plating solution of this embodiment, since the ratio of EO groups and PO groups is in the above range and both the EO groups and PO groups are in a well-balanced state, the nonionic surfactant is tin or a tin alloy. Has a high affinity for and easily adsorbs to the surface of the plating film. A plurality of surfactant molecules are adsorbed on the surface of the plating film to form a layered film and suppress the metal precipitation reaction. For this reason, it is thought that a plating film thickness becomes uniform by this surfactant.

  The N, N-dipolyalkylene oxide N-alkylamine preferably has a mass average molecular weight in the range of 500 to 30,000. If the mass average molecular weight is too small, the effect of suppressing the precipitation of tin or tin alloy may not be sufficient. On the other hand, when the mass average molecular weight is too large, the suppression force becomes too strong, and there is a possibility that a uniform plating film may not be formed. This N, N-dipolyalkylene oxide N-alkylamine may be used alone or in combination of two or more.

  The N, N-dipolyalkylene oxide N-alkylamine content in the plating solution of the present embodiment is preferably in the range of 0.1 g / L to 100 g / L, more preferably 1 g / L to 50 g / L. Range. If the content of N, N-dipolyalkylene oxide N-alkylamine is excessively low or high, a uniform plating film may not be formed.

Examples of the nonionic surfactant obtained by condensing phenol and polyoxyethylene (EO) include polyoxyethylene phenyl ether.
Examples of the nonionic surfactant in which alkylphenol and polyoxyethylene (EO) are condensed include polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether, and polyoxyethylene dodecyl phenyl ether.
Examples of the nonionic surfactant obtained by condensing styrenated phenol and polyoxyethylene (EO) include polyoxyethylene monostyrenated phenyl ether, polyoxyethylene distyrenated phenyl ether, and polyoxyethylene tristyrenation.
Examples of the nonionic surfactant obtained by condensing β-naphthol and polyoxyethylene (EO) include polyoxyethylene β-naphthyl ether.
Nonionic surfactants in which bisphenols and polyoxyethylene (EO) are condensed include polyoxyethylene bisphenol A ether, polyoxyethylene bisphenol E ether, polyoxyethylene bisphenol F ether, polyoxyethylene bisphenol S ether, polyoxy Ethylene bisphenol M ether is mentioned.
Examples of the nonionic surfactant obtained by condensation of cumylphenol and polyoxyethylene (EO) include polyoxyethylene cumylphenyl ether.

  These nonionic surfactants preferably have a mass average molecular weight in the range of 100 or more and 5000 or less. If the mass average molecular weight is too small, the effect of suppressing the precipitation of tin or tin alloy may not be sufficient. On the other hand, when the mass average molecular weight is too large, the suppression force becomes too strong, and there is a possibility that a uniform plating film may not be formed.

  As the surfactant (C) of the present embodiment, other surfactants may be used alone in place of the surfactant. Alternatively, another surfactant may be used in combination with the above surfactant. Examples of other surfactants in this case include ordinary anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants.

  Examples of anionic surfactants include polyoxyethylene (ethylene oxide: containing 12 mol) nonyl ether sulfate polyoxyalkylene alkyl ether sulfate such as sodium sulfate, polyoxyethylene (ethylene oxide: containing 12 mol) dodecyl phenyl ether sodium sulfate, etc. Polyoxyalkylene alkylphenyl ether sulfates, alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate, naphthol sulfonates such as 1-naphthol-4-sulfonic acid sodium, 2-naphthol-3,6-disulfonic acid disodium salt (Poly) alkylnaphthalene sulfonates such as sodium diisopropyl naphthalene sulfonate, sodium dibutyl naphthalene sulfonate, sodium dodecyl sulfate, sodium oleyl sulfate Alkyl sulfates such as beam are exemplified.

  Cationic surfactants include mono-trialkylamine salts, dimethyldialkylammonium salts, trimethylalkylammonium salts, dodecyltrimethylammonium salts, hexadecyltrimethylammonium salts, octadecyltrimethylammonium salts, dodecyldimethylammonium salts, octadecenyl Dimethylethylammonium salt, dodecyldimethylbenzylammonium salt, hexadecyldimethylbenzylammonium salt, octadecyldimethylbenzylammonium salt, trimethylbenzylammonium salt, triethylbenzylammonium salt, hexadecylpyridinium salt, dodecylpyridinium salt, dodecylpicolinium salt, dodecylimidazo Linium salt, oleylimidazolinium salt, octadecylamine acetate , And the like dodecylamine acetate.

  Nonionic surfactants other than the above nonionic surfactants include linear alkyl polyoxyethylene ether, branched alkyl polyoxyethylene ether, alkylphenol polyoxyethylene ether, silicon polyoxyethylene ether, silicon polyoxyethylene ester , Fluorinated polyoxyethylene ether, fluorinated polyoxyethylene ester, sulfated or sulfonated adducts of condensation products of ethylene oxide and / or propylene oxide with alkylamine or diamine.

  Examples of amphoteric surfactants include betaine, carboxybetaine, imidazolinium betaine, sulfobetaine, and aminocarboxylic acid.

[Benzalacetone (D)]
As the benzal acetone (D) of this embodiment, a commercially available one can be used as it is. Moreover, the refined product which removed the impurity contained by refine | purifying what is marketed can be used.
Benzalacetone (D) is adsorbed on the surface of the object to be plated and inhibits the crystal growth of tin by electrodeposition, and thus has an effect of suppressing the deposition of the plating film.
And benzal acetone is easy to adsorb | suck to the large diameter via which a plating solution enters easily, and the inhibitory effect of plating is large. On the other hand, benzalacetone is hardly adsorbed to a small-diameter via in which the plating solution is difficult to enter, and the plating suppression effect is small.
For this reason, compared with the formation of the plating deposition layer with the small diameter via, the formation of the plating deposition layer with the large diameter via is further suppressed. For this reason, the plating film of a large diameter via is formed thinner than the plating film of a small diameter via. When such a plating film is melted by a reflow process, bumps having no variation in height can be obtained.
In addition, it is preferable to increase the amount of benzalacetone according to the size of the difference in the diameters of the different diameter bumps as the difference is larger.

[Solvent (E)]
As a solvent (E) of this embodiment, a C1-C3 alcohol is preferable. An alcohol having 1 to 3 carbon atoms improves the solubility of the surfactant and benzalacetone. Examples of the alcohol include methanol, ethanol, 1-propanol, and 2-propanol (isopropyl alcohol). Alcohol can be used individually by 1 type, but can also be used in combination of 2 or more type.

[Production of tin or tin alloy plating solution]
The tin or tin alloy plating solution of the present embodiment comprises the soluble tin salt (A), an acid selected from organic acids and inorganic acids or salts thereof (B), a surfactant (C), and benzal acetone. It can be prepared by mixing (D), solvent (E), and water (remainder).

  Here, benzalacetone (D) has a concentration of 0.05 g / L to 0.2 g / L in the plating solution, preferably 0.06 g / L to 0.18 g / L, more preferably 0.08 g / L. Add to a concentration of ~ 0.15 g / L. The larger the difference between the via diameters of different sizes, the larger the addition within the above range. If it is less than 0.05 g / L, the effect of the benzalacetone described above is low, and the variation in height of the different-diameter bumps after reflow cannot be reduced. When it exceeds 0.2 g / L, benzal acetone is excessively adsorbed on the bottom of the via and the surface of the plating film is roughened, resulting in a phenomenon generally called scorching / burning, resulting in a black color. This causes poor appearance.

  Further, the surfactant and the ben so that the mass ratio (C / D) of the surfactant (C) to benzalacetone (D) is 10 to 200, preferably 30 to 180, more preferably 50 to 150. Mix with colacetone. When the mass ratio C / D is less than 10 or exceeds 200, the action of suppressing the precipitation of tin due to the synergistic effect of benzalacetone and the surfactant does not work sufficiently, and the precipitation of tin on the large-diameter bump is suppressed. The action to do is weakened. For this reason, the variation in the height of the different-diameter bumps after reflow cannot be reduced.

  The concentration of the surfactant (C) in the plating solution is preferably 5 g / L to 20 g / L. If the amount of the surfactant (C) is excessively small or large, a uniform plating film may not be formed.

  Further, the solvent and benzalacetone are mixed so that the mass ratio (E / D) of the solvent (E) to benzalacetone (D) is 10 or more, preferably 20 or more, more preferably 30 or more. When the mass ratio E / D is less than 10, the required amount of benzal acetone does not dissolve in the solvent, and the plating solution cannot be prepared. The upper limit of the mass ratio E / D is not particularly limited, but is preferably 300 or less. When 300 is exceeded, the solvent more than necessary will be used and there exists a possibility that the cost of a plating solution may rise.

  The concentration of the solvent (E) in the plating solution is preferably 0.5 g / L to 20 g / L. When it is less than 0.5 g / L, benzalacetone (D) is precipitated in the plating solution, and the variation in height of the different-diameter bumps after reflow cannot be reduced. If it exceeds 20 g / L, the cost of the plating solution may increase. 0.5 g / L to 10 g / L is more preferable.

  Moreover, as said predetermined soluble metal salt (A), 1 type can be used independently and 2 or more types of mixtures can also be used. The content of the soluble metal salt (A) in the plating solution is 10 g / L to 200 g / L, preferably 50 g / L to 100 g / L. When the content is outside the proper range, a good plating film cannot be obtained.

  As an inorganic acid, an organic acid, or its salt (B), 1 type can be used individually and 2 or more types of mixtures can also be used. The content in the plating solution is 10 g / L to 300 g / L, preferably 100 g / L to 200 g / L. When the content is outside the proper range, a plating film having a smooth surface and good film thickness uniformity cannot be obtained.

[Bump formation method]
A method for forming bumps using the plating solution of this embodiment will be described. As shown in FIG. 1A, first, a titanium layer 12 and a copper seed layer 13 are sequentially formed on the surface of a base material 11 such as a semiconductor wafer substrate. For example, the titanium layer 12 is formed by a sputtering method to a thickness of about 100 nm, and the copper seed layer 13 is formed by a sputtering method to a thickness of about 500 nm. Thereafter, a resist layer 14 having a predetermined thickness is formed. The resist layer 14 is subjected to mask exposure and developed to form a resist pattern 15 having vias 14a and 14b having different diameters. Subsequently, copper or nickel is plated on the copper seed layer 13 in the vias 14a and 14b to form the underlayer 16. Next, electric tin plating is performed inside the vias 14a and 14b of the resist pattern 15 by supplying power through the copper seed layer 13 using the tin or tin alloy plating solution of the present embodiment described above. Thus, tin or tin alloy plating deposition layers (plating films of tin or tin alloy) 17a and 17b are formed in the vias 14a and 14b on the base layer 16, respectively. Subsequently, as shown in FIG. 1B, the resist layer 14 is peeled off using an organic solvent. Next, the copper seed layer 13 and the titanium layer 12 are sequentially removed by acid. Subsequently, the remaining tin or tin alloy plating deposition layers (tin or tin alloy plating films) 17a and 17b are melted by reflow treatment at 210 to 240 ° C. in a nitrogen atmosphere. As a result, as shown in FIG. 1C, dome-shaped tin or tin alloy bumps 18a and 18b are formed. Note that the tin or tin alloy bump is not limited to a circular cylindrical bump in a top view, but includes a triangular, quadrangular, polygonal prismatic bump in a top view, and an elliptical elliptical bump in a top view. .

  Here, the electroplating is performed in a current density range of 0.1 A / dm 2 or more and 100 A / dm 2 or less, preferably 0.5 A / dm 2 or more and 20 A / dm 2 or less when forming the plating film. If the current density is too low, the productivity deteriorates, and if it is too high, the bump height uniformity deteriorates. The liquid temperature is in the range of 10 ° C to 50 ° C, more preferably in the range of 20 ° C to 40 ° C. Although not shown, in the bump formation method, after forming the base layer, the resist layer 14 is peeled off, another new resist layer is formed, and this resist is formed so as to have the same diameter as the base layer. The layer may be exposed to a mask and developed to form a resist pattern 15 having vias 14a and 14b having different diameters.

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

(Building bath of Sn plating solution)
<Example 1>
First, using benzalacetone (D) and methanol (E), these were mixed so that E / D was 10 by mass ratio, and benzalacetone was dissolved in methanol. Next, methanesulfonic acid (B) as a free acid and a methanol solution of benzalacetone were mixed with an aqueous solution of methanesulfonic acid Sn (A) to obtain a uniform solution. Next, the N, N-dipolyalkylene oxide N-alkylamine of the formula (1) described above was prepared as the surfactant (C). This N, N-dipolyalkylene oxide N-alkylamine has one alkyl group (R) having 12 carbon atoms, and EO group: PO group in a 50:50 molar ratio of EO group and PO group. Two polyalkylene oxide groups (X and Y) containing This surfactant was added so that C / D was 100 by mass ratio. In addition, carbon number of the alkyl group of this surfactant is 12, and a mass average molecular weight is 940. And finally ion-exchange water was added and the Sn plating liquid of the following composition was constructed.
The methanesulfonic acid Sn aqueous solution was prepared by electrolyzing a metal Sn plate in a methanesulfonic acid aqueous solution. Further, the amount of alcohol in the plating solution was measured by gas chromatography, and it was confirmed that the content was almost the same as the blending amount.

(Composition of Sn plating solution)
Methanesulfonic acid Sn (as Sn2 +): 80 g / L
Potassium methanesulfonate (as free acid): 150 g / L
Nonionic surfactant: 12 g / L
Benzalacetone: 0.05 g / L
Methanol: 0.5g / L
Ion-exchange water: balance

  Table 1 shows the types and proportions of components (A) to (E) in the plating solution of Example 1, and Table 4 shows the mass ratio (C / D) and mass ratio (E / D).

<Examples 2 to 11 and Comparative Examples 1 to 5>
The types and proportions of components (A) to (E) in the plating solutions of Examples 2 to 11 and Comparative Examples 1 to 5 were changed as shown in Tables 1 and 3, and the mass ratio (C / D) and mass were changed. The ratio (E / D) was changed as shown in Table 4. Otherwise, the plating solution was erected in the same manner as in Example 1. In Example 6, a SnAgCu plating solution was constructed using methanesulfonic acid Sn, methanesulfonic acid Ag, and methanesulfonic acid Cu as soluble salts.

<Examples 12 to 17>
The types and blending ratios of components (A) to (E) in the plating solutions of Examples 12 to 17 were changed as shown in Table 2, and the mass ratio (C / D) and mass ratio (E / D) are shown. As shown in FIG. Otherwise, the plating solution was erected in the same manner as in Example 1. In Examples 12 to 17, the surfactant (C) shown in Table 2 was used. In Example 13, a SnAg plating solution was constructed using methanesulfonic acid Sn and methanesulfonic acid Ag as soluble salts.
In Tables 1 to 3, “MeOH” means methanol, and “IPA” means isopropyl alcohol.

<Comparison test and evaluation>
As shown in FIGS. 1 (a) to 1 (c), the liquid temperature of 25 ° C. was used on 22 types of silicon wafers using the 22 types of plating baths of Examples 1 to 17 and Comparative Examples 1 to 5. Electroplating was performed under the condition of a current density of 4 A / dm2. Thus, a plating film was formed on the base layer inside the small diameter via and the large diameter via each having a circular top view. Thereafter, the resist layer, the copper seed layer, and the titanium layer were sequentially removed. Subsequently, the remaining plating film was melted by reflow treatment at 240 ° C. in a nitrogen atmosphere. As a result, 2000 small bumps having a diameter of about 20 μm were formed, and 2000 large bumps having a diameter of about 60 μm were formed. (1) The bump height variation (uniformity) after reflow treatment and (2) the appearance of the plating film on the bump surface were evaluated by the following methods. The results are shown in Table 4 above.

(1) Bump height variation (uniformity)
The distance from the surface of the base layer to the top of the dome-shaped bump was taken as the bump height after reflow treatment. The height of each of the 2000 small bumps and 2000 large bumps, a total of 4000, was measured using a laser microscope. The average height, maximum value, and minimum value of 4000 bumps were obtained, and the bump height variation was calculated by the following formula.
Bump height variation (%) = {(maximum value−minimum value) / average value} × 100

(2) Appearance of the plating film on the bump surface Twenty-two kinds of built-in tin and tin alloy plating solutions were separately placed in the hull cell tanks manufactured by Yamamoto Metal Tester Co., Ltd., and a copper hull cell plate was placed as a cathode in the solution. A platinum plate was placed as the anode, and a hull cell test was conducted. The plating conditions were a liquid temperature of 25 ° C., an energization current of 3 A, and a plating treatment time of 5 minutes. During the plating process, the plating solution was stirred with a cathode rocker. The hull cell evaluation was performed according to the following procedure. The appearance of the plating film on the plated hull cell plate was visually confirmed using a current density quick-view plate. A glossy or semi-glossy film was evaluated as “good”. The film with dullness and cloudiness was evaluated as “OK”. The film with scorching / burning was evaluated as “bad”. Evaluation was made based on the above three criteria.

  As is clear from Table 4, in Comparative Example 1, the appearance of the plating film was “OK”. However, since the content ratio in the plating solution of benzal acetone was too small as 0.01 g / L, the bump height variation after reflow treatment was as large as 16.2%, and the bump height uniformity was poor. .

  In Comparative Example 2, the bump height variation after the reflow process was as small as 7.1%, and the bump height was uniform. However, since the content ratio of benzalacetone in the plating solution was an excessive 0.3 / L, the appearance of the plating film was “poor”.

  In Comparative Example 3, the appearance of the plating film was “OK”. However, since the mass ratio (C / D) of the surfactant (C) to the benzalacetone (D) was too small as 5, the bump height variation after reflow treatment was as large as 12.8%. The uniformity was inferior.

  In Comparative Example 4, the appearance of the plating film was “OK”. However, since the mass ratio (C / D) of the surfactant (C) to benzalacetone (D) was too large as 250, the bump height variation after reflow treatment was as large as 21.5%, and the bump height was high. The uniformity was inferior.

  In Comparative Example 5, since the mass ratio (E / D) of the solvent (E) to benzalacetone (D) was too small as 5, benzalacetone was not dissolved in methanol as a solvent. For this reason, neither the height variation of the bump after the reflow treatment nor the evaluation of the appearance of the plating film could be performed.

  On the other hand, as apparent from Table 4, in Examples 1 to 17, the content ratio of benzalacetone (D) in the plating solution, the mass ratio of the surfactant (C) to benzalacetone (D). The mass ratio (E / D) of the solvent (E) to (C / D) and benzalacetone (D) satisfied all the requirements of the first aspect of the present invention. For this reason, the bump height variation after the reflow treatment was as small as 1.8 to 8.6, and the appearance of the plating film was “good” or “good”.

  The tin or tin alloy plating solution of the present invention can be used for circuit boards such as semiconductor wafer boards, printed circuit boards, flexible printed circuit boards, and semiconductor integrated circuits.

DESCRIPTION OF SYMBOLS 11 Base material 12 Titanium layer 13 Copper seed layer 14 Resist layer 14a, 14b Via 15 Resist pattern 16 Underlayer 17a, 17b Tin or tin alloy plating deposition layer (tin or tin alloy plating film)
18a, 18b Tin bump

Claims (3)

A soluble salt (A) containing at least a stannous salt, an acid selected from organic acids and inorganic acids or salts thereof (B), a surfactant (C), benzalacetone (D), a solvent ( E) a tin or tin alloy plating solution,
The plating solution is used to form patterns with different bump diameters on the substrate,
The benzal acetone (D) is included in the plating solution in an amount of 0.05 g / L to 0.2 g / L,
A mass ratio (C / D) of the surfactant (C) to the benzalacetone (D) is 10 to 200;
A tin or tin alloy plating solution, wherein a mass ratio (E / D) of the solvent (E) to the benzalacetone (D) is 10 or more.   The surfactant (C) is a nonionic surfactant in which polyoxyethylene (EO) and polyoxypropylene (PO) are condensed, or phenol, alkylphenol, styrenated phenol, β-naphthol, bisphenols, and cumyl. The tin or tin alloy plating solution according to claim 1, which is a nonionic surfactant obtained by condensing any one selected from phenol and polyoxyethylene (EO).   Using the tin or tin alloy plating solution according to claim 1 or 2, a step of forming a plurality of tin or tin alloy plating deposition layers having different diameters on the substrate, and then performing a reflow treatment, a plurality of bump diameters different from each other. Forming a bump, and a bump forming method.

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