Tin alloy plating solution

Abstract

The tin alloy plating solution of the present invention comprises: (A) a soluble salt containing at least a stannous salt; (B) a soluble salt of a metal less active than tin; (C) an alkanesulfonic acid or a salt thereof containing 9 to 18 carbon atoms in the molecule; (D) a nonionic surfactant containing one or more phenyl groups in the molecule; and (E) a leveling agent.

Description

Technical Field

[0001] The present invention relates to a tin alloy plating solution used for manufacturing bumps as protruding electrodes of tin alloy on a circuit substrate when a semiconductor integrated circuit chip is mounted on the substrate.

[0002] This application claims priority based on Special Application No. 2020-194825 filed in Japan on November 25, 2020, and its contents are incorporated herein. Background Art

[0003] In the past, a method for forming a tin or tin alloy plated deposit layer on a substrate having through holes having various through hole diameters using a tin or tin alloy plating solution for plating the substrate, the tin or tin alloy plating solution comprising (A) a soluble salt containing at least a stannous salt, (B) an acid selected from organic acids and inorganic acids or a salt thereof, (C) a surfactant, (D) a leveling agent, and (E) an additive (for example, refer to Patent Document 1 (Claim 1, paragraphs

[0020] ,

[0043] , and

[0044] )). In the method for forming the tin or tin alloy plated deposit layer, the surfactant is a compound (C1) represented by the following general formula (1) or a compound (C2) represented by the following general formula (2).

[0004] [Chemical formula 1]

[0005]

[0006] In formula (1), R is an alkyl group having 7 to 13 carbon atoms, m is 8 to 11, and n is 1 to 3, and m and n are different.

[0007] [Chemical formula 2]

[0008]

[0009] In formula (2), R is an alkyl group having 9 to 13 carbon atoms, m is 6 to 8, n is 2 to 3, and m and n are different.

[0010] The leveling agent (D) is added to form a uniform and dense coating and to make the coating smooth. In addition, in order to improve the filling property of the through-hole and suppress the generation of voids, a first leveling agent (D-1) and a second leveling agent (D-2) are used. As the first leveling agent (D-1), one or more selected from the group consisting of aliphatic aldehydes, aromatic aldehydes, aliphatic ketones and aromatic ketones can be cited, and as the second leveling agent (D-2), α, β-unsaturated carboxylic acids or their amides or salts thereof can be cited. As the above-mentioned aromatic ketones, benzylidene acetone, 2-chloroacetophenone, 3-chloroacetophenone, 4-chloroacetophenone, 2,4-dichloroacetophenone, 2,4,6-trichloroacetophenone, etc. can be cited.

[0011] In the method for forming a tin or tin alloy plated deposit layer thus constructed, the surfactant (C1, C2) has a specific nonion structure in which n of the polyoxypropylene group and m of the polyoxyethylene group in the general formula (1) and the general formula (2) are respectively within a specified range, thereby suppressing the precipitation of Sn ions during plating, and enabling good plating on the surface of the plated object. In particular, according to the electroplating solution, in the case of a pattern with different bump diameters, even if the bump diameter is large or small, the through-hole filling property of the through-hole on the substrate is excellent, and the height of the formed bump is uniform. It is believed that this is because the polarization resistance becomes larger.

[0012] On the other hand, a method for forming low-melting-point metal bumps on a semiconductor chip or a package by electroplating is disclosed (for example, refer to Patent Document 2 (Claim 1, paragraphs

[0013] and

[0019] ). In the method for forming the low-melting-point metal bumps, a plating bath containing the following components is used, namely, (a) 5 to 300 g / l of at least one alkanesulfonate ion or alkanolsulfonate ion, (b) 0.01 to 10 g / l of Ag ions, and (c) 0.1 to 10 g / l of Sn ions. 2+ and Bi 3+ A silver alloy plating bath containing 0.1 to 40 g / L of one metal ion, (d) 0.01 to 40 g / L of one sulfur-containing compound, and (e) 0.5 to 30 g / L of a nonionic surfactant is used, and current is applied in the form of repeated rectangular pulse waves or multi-stage rectangular waves. In addition, as an acidic component, an alkanesulfonic acid or an alkanolsulfonic acid needs to be used. Preferred examples of the alkanesulfonic acid or the alkanolsulfonic acid include methanesulfonic acid, ethanesulfonic acid, and the like.

[0013] In the method for forming the low-melting-point metal bumps thus constructed, it is possible to form bumps of good shape without using lead. Furthermore, since the bumps obtained by the method for forming the low-melting-point metal bumps do not contain lead, erroneous operation of the semiconductor memory element due to α-ray reversal will not occur, and it is also advantageous from the perspective of environmental pollution. Therefore, the method for forming the low-melting-point metal bumps is extremely advantageous as a method for forming bumps on a semiconductor chip or a package by electroplating.

[0014] Patent Document 1: Japanese Patent No. 6635139 (B)

[0015] Patent Document 2: Japanese Patent Application Publication No. 2000-100850 (A)

[0016] However, in the method for forming a tin or tin alloy plated deposit layer shown in the above-mentioned patent document 1, the aromatic carbonyl compound (benzylideneacetone, cinnamic acid, cinnamaldehyde, benzaldehyde, etc.) added as a leveling agent in order to form a plated film uniformly and densely and make the plated film smooth is reduced due to electrolysis during electroplating, so the analysis management and replenishment operation for maintaining the concentration become complicated, and the decomposition products of the leveling agent accumulate in the plating solution, resulting in the undesirable situation that the plating property deteriorates. In addition, in the method for forming a low-melting-point metal bump shown in the above-mentioned patent document 2, an alkanesulfonic acid or an alkanolsulfonic acid is used as an acidic component. Alkanesulfonic acid or an alkanolsulfonic acid is methanesulfonic acid or ethanesulfonic acid with a small number of carbon atoms and high water solubility. Therefore, although methanesulfonic acid or ethanesulfonic acid has the function of a free acid, it does not have the function of a leveling agent for smoothing the plated film. Summary of the invention

[0017] The object of the present invention is to provide a tin alloy plating solution which does not use aromatic carbonyl compounds (benzylidene acetone, cinnamic acid, cinnamaldehyde, benzaldehyde, etc.) as leveling agents, does not replenish the leveling agent for a long time during electroplating, can form a plated film uniformly and densely, and can make the plated film smooth.

[0018] A tin alloy plating solution as one embodiment of the present invention (hereinafter referred to as "the tin alloy plating solution of the present invention") comprises: (A) a soluble salt or oxide containing at least a stannous salt; (B) a soluble salt or oxide of a metal less active than tin; (C) a leveling agent composed of an alkanesulfonic acid or a salt thereof containing 9 to 18 carbon atoms in the molecule; (D) a nonionic surfactant containing one or more phenyl groups; and (E) a free acid.

[0019] In the above embodiment, the content of the alkanesulfonic acid or its salt may be 0.01 g / L to 1 g / L.

[0020] In the above embodiment, the alkanesulfonic acid or its salt may have 10 to 17 carbon atoms in the molecule.

[0021] In the above aspect, the alkanesulfonic acid may be a secondary alkanesulfonic acid or a salt thereof.

[0022] In the above manner, the metal less active than tin may be silver or copper.

[0023] The tin alloy plating solution of the present invention comprises: (A) a soluble salt or oxide containing at least a stannous salt; (B) a soluble salt or oxide of a metal less active than tin; (C) a leveling agent composed of an alkanesulfonic acid or a salt thereof containing 9 to 18 carbon atoms in the molecule; (D) a nonionic surfactant containing one or more phenyl groups in the molecule; and (E) a free acid, so that aromatic carbonyl compounds (benzylideneacetone, cinnamic acid, cinnamaldehyde, benzaldehyde, etc.) are not used as leveling agents, and the leveling agent is not replenished for a long time during electroplating, and a plated film can be formed uniformly and densely, and the plated film can be made smooth. Here, when an alkanesulfonic acid or a salt thereof (for example, methanesulfonic acid or ethanesulfonic acid) having a carbon number of 8 or less is used as a leveling agent, the alkanesulfonic acid has a high water solubility and will not be adsorbed on the surface of the plated object, so it will not function as a leveling agent and will not have the effect of smoothing the plated film. Furthermore, when an alkanesulfonic acid or a salt thereof having 19 or more carbon atoms is used as a leveling agent, the water solubility of the alkanesulfonic acid or the salt thereof is low, and therefore the alkanesulfonic acid or the salt thereof cannot be dissolved in the plating solution. In contrast, in the present invention, an alkanesulfonic acid or a salt thereof having 9 to 18 carbon atoms is used as a leveling agent, so that an interaction occurs in the plating solution with a phenyl-containing nonionic surfactant to solubilize the alkanesulfonic acid. As a result, a smooth tin alloy plating layer can be obtained by the specific adsorption of the alkanesulfonic acid or a salt thereof having 9 to 18 carbon atoms and the phenyl-containing nonionic surfactant to the tin surface.

[0024] When the content of the alkanesulfonic acid or its salt is 0.01 g / L to 1 g / L, the phenyl-containing nonionic surfactant can easily solubilize the alkanesulfonic acid, and the effect of mutual interaction is easily produced.

[0025] When the number of carbon atoms in the molecule of the alkanesulfonic acid or its salt is 10 to 17, the interaction of the phenyl-containing nonionic surfactant in the liquid to dissolve the alkanesulfonic acid or its salt occurs more rapidly. As a result, a smoother tin alloy plating layer can be obtained by the specific adsorption of the alkanesulfonic acid or its salt having 10 to 17 carbon atoms and the phenyl-containing surfactant to the tin surface.

[0026] When the alkanesulfonic acid is a secondary alkanesulfonic acid or a salt thereof, the solubility in the plating solution is slightly improved compared with a primary alkanesulfonic acid or a salt thereof, and the phenyl-containing nonionic surfactant more rapidly produces an interactive effect to dissolve the alkanesulfonic acid.

[0027] When the metal less active than tin is silver or copper, the solder wettability, mounting strength, bendability, and solder reflowability are excellent, and whisker generation is less likely to occur. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a scanning electron microscope photograph showing the appearance of the bumps of Example 3 of the present invention.

[0029] Figure 2 This is a scanning electron microscope photograph showing the appearance of the bumps of Comparative Example 2. DETAILED DESCRIPTION

[0030] Next, the method for implementing the present invention is described with reference to the accompanying drawings. The tin alloy plating solution of the present invention comprises: (A) a soluble salt or oxide containing at least a stannous salt; (B) a soluble salt or oxide of a metal less active than tin; (C) a leveling agent composed of an alkanesulfonic acid or a salt thereof containing 9 to 18 carbon atoms in the molecule; (D) a nonionic surfactant containing one or more phenyl groups; and (E) a free acid.

[0031] [Tin alloy]

[0032] The tin alloy made from the tin alloy plating solution in this embodiment is an alloy of tin (Sn) and a specified metal selected from silver (Ag), copper (Cu), gold (Au), and bismuth (Bi), for example, binary alloys such as SnAg alloy, SnCu alloy, SnAu alloy, SnBi alloy; and ternary alloys such as SnCuAg alloy.

[0033] [Contains at least a soluble salt or oxide of a stannous salt (A)]

[0034] The soluble salt or oxide (A) containing at least a stannous salt (hereinafter referred to as a soluble salt containing a stannous salt) used in the tin alloy plating solution of the present embodiment is a salt that dissolves in water to generate divalent tin ions. Examples of soluble salts include halides, sulfates, oxides, alkanesulfonates, arylsulfonates and alkanolsulfonates having a carbon number less than 9. Specific examples of alkanesulfonates include methanesulfonates and ethanesulfonates. Specific examples of arylsulfonates include benzenesulfonates, phenolsulfonates, cresolsulfonates and toluenesulfonates. Specific examples of alkanolsulfonates include isethionates.

[0035] The soluble salt (A) containing at least stannous salt (hereinafter referred to as soluble tin salt (A)) can be used alone or in combination of two or more. The content of the soluble tin salt (A) in the tin alloy plating solution of the present embodiment is preferably in the range of 5 g / L or more and 200 g / L or less, and more preferably in the range of 20 g / L or more and 100 g / L or less, when converted into tin amount. When the content of the soluble tin salt (A) is too little, it is usually difficult to cause the precipitation of tin normally within the range of 1 to 20 ASD (amperes per square decimeter) of the current density used for bump electroplating, and good bump forming may not be possible. On the other hand, when the content of the soluble tin salt (A) is too high, in addition to the viscosity of the plating solution becoming high and making it difficult to form bumps, it also contains more tin than necessary, so the cost of the plating bath may be increased.

[0036] [Soluble salt of a metal less active than tin (B)]

[0037] The soluble salt or oxide (B) of a metal less active than tin used in the tin alloy plating solution of the present embodiment (hereinafter referred to as a soluble salt of a metal less active than tin) is a salt dissolved in water. As a metal less active than tin, at least one or two or more metals selected from silver, copper, gold and bismuth can be listed. Examples of these soluble salts (B) of metals less active than tin are the same as those of soluble tin salts (A). Among these metals, it is preferred to contain silver or copper. This is because there are effects such as excellent solder wettability, mounting strength, bendability and reflowability and not easy to generate whiskers. The alloy of tin and silver (SnAg alloy) has a low melting point of 221°C at the eutectic composition (Sn-3.5 mass% Ag), and the alloy of tin and copper (SnCu alloy) has a low melting point of 227°C at the eutectic composition (Sn-1.7 mass% Cu), and both have advantages such as excellent solder wettability, mounting strength, bendability and reflowability, and are not prone to whisker formation. The soluble salt (B) of a metal less active than tin may be used alone or in combination of two or more.

[0038] The content of the soluble salt (B) of a metal less active than tin in the plating solution of the present embodiment is preferably in the range of 0.01 g / L to 10 g / L, and more preferably in the range of 0.1 g / L to 2 g / L, in terms of the amount of metal. When the content of the soluble salt (B) of a metal less active than tin is too little or too much, the composition of the precipitated solder alloy cannot be made into a eutectic composition, and the characteristics as a solder alloy cannot be obtained.

[0039] [Leveling agent (C)]

[0040] The addition of a leveling agent (C) composed of an alkanesulfonic acid or a salt thereof containing 9 to 18 carbon atoms in the molecule is for forming a uniform and dense plating film and making the plating film smooth, further improving through-hole filling properties, and inhibiting the generation of voids. The alkanesulfonic acid containing 9 to 18 carbon atoms in the molecule is represented by the following formula (1) or formula (2), and the alkanesulfonic acid salt containing 9 to 18 carbon atoms in the molecule is represented by the following formula (3) or formula (4).

[0041] R 1 -SO3H(1)

[0042] R 2 -HC(SO3H)-R 3 (2)

[0043] R 1 -SO3Na(3)

[0044] R 2 -HC(SO3Na)-R 3 (4)

[0045] In formula (1) and formula (3), R 1 is an alkyl group, in which R 1 The number of carbon atoms (the total number of carbon atoms in the molecule) is 9 to 18, preferably 10 to 17. In formula (2) and formula (4), R 2 and R 3 It is an alkyl group, and the total number of carbon atoms in the molecule (the total number of carbon atoms in the molecule) is 9 to 18, preferably 10 to 17.

[0046] Here, when an alkanesulfonic acid or a salt thereof having a total carbon number of 8 or less in the molecule, such as methanesulfonic acid or ethanesulfonic acid, is used, the alkanesulfonic acid has a high water solubility and does not adsorb to the surface of the plated object, so it does not function as a leveling agent, and there is a disadvantage that the plated film cannot be smoothed. In addition, when an alkanesulfonic acid or a salt thereof having a total carbon number of 19 or more in the molecule is used, the alkanesulfonic acid has a low water solubility, so there is a disadvantage that the alkanesulfonic acid cannot be dissolved in the plating solution.

[0047] The alkane sulfonic acid is preferably a primary alkane sulfonic acid, a secondary alkane sulfonic acid or a salt thereof, and is further preferably a secondary alkane sulfonic acid or a salt thereof. Here, the reason why the secondary alkane sulfonic acid or a salt thereof is further preferably used as the leveling agent (C) is that, compared with the primary alkane sulfonic acid or a salt thereof, the solubility in the plating solution is slightly improved, and the nonionic surfactant containing phenyl in the plating solution more rapidly produces an interaction that makes the alkane sulfonic acid or a salt thereof solubilized. As the primary alkane sulfonic acid represented by formula (1), 1-nonane sulfonic acid, 1-decane sulfonic acid, 1-dodecane sulfonic acid, 1-tetradecane sulfonic acid, 1-hexadecane sulfonic acid, 1-octadecane sulfonic acid, etc. can be cited. And, as the primary alkane sulfonate represented by formula (3), 1-nonane sodium sulfonate, 1-decane potassium sulfonate, 1-dodecane sodium sulfonate, 1-dodecane potassium sulfonate, 1-tetradecane potassium sulfonate, 1-hexadecane sodium sulfonate, 1-octadecane sodium sulfonate, etc. can be cited.

[0048] On the other hand, as the secondary alkane sulfonic acid represented by formula (2), nonane secondary sulfonic acid, dodecyl secondary sulfonic acid, tetradecyl secondary sulfonic acid, heptadecanyl secondary sulfonic acid, octadecyl secondary sulfonic acid, etc. can be cited. And, as the secondary alkane sulfonate represented by formula (4), sodium nonane secondary sulfonate, calcium dodecyl secondary sulfonate, sodium tetradecyl secondary sulfonate, potassium heptadecanyl secondary sulfonate, sodium octadecyl secondary sulfonate, etc. can be cited. Here, the content of the alkane sulfonic acid or its salt is preferably 0.01 g / L to 1 g / L, and more preferably 0.02 g / L to 0.5 g / L. The reason for limiting the preferred content of the alkane sulfonic acid or its salt to the range of 0.01 g / L to 1 g / L is that if it is less than 0.01 g / L, the effect of its addition is insufficient, and if it exceeds 1 g / L, it may hinder the smoothing of the plated film.

[0049] [Nonionic surfactant containing one or more phenyl groups in the molecule (D)]

[0050] A nonionic surfactant (D) containing one or more phenyl groups in the molecule (hereinafter referred to as a phenyl-containing nonionic surfactant (D)) has the effect of increasing the affinity between the tin alloy plating solution and the object to be plated, and adsorbing on the surface of the plating film when forming the tin alloy plating film to inhibit the crystal growth of the tin alloy in the plating film, making the crystals finer, thereby improving the appearance of the plating film, improving the adhesion to the object to be plated, and making the film thickness uniform.

[0051] Specific examples of the phenyl-containing nonionic surfactant (D) include those obtained by adding and condensing 5 to 50 mol of ethylene oxide (EO) and / or propylene oxide (PO) to phenol, octylphenol, nonylphenol, dodecylphenol, bisphenol A, bisphenol B, bisphenol E, bisphenol F, cumylphenol, polystyrenated phenol, polystyrenated cresol, tribenzylphenol, β-naphthol, etc. These phenyl-containing nonionic surfactants (D) may be used in combination of two or more.

[0052] Furthermore, the added amount of the phenyl-containing nonionic surfactant (D) in the tin alloy plating solution of this embodiment is in the range of more than 0.01 g / L and less than 50 g / L, preferably in the range of more than 0.1 g / L and less than 40 g / L, and more preferably in the range of more than 1 g / L and less than 30 g / L.

[0053] [Free acid (E)]

[0054] As the free acid (E), hydrogen chloride, hydrogen bromide, sulfuric acid, alkanesulfonic acid (carbon number: 1 to 6), arylsulfonic acid or alkanolsulfonic acid can be cited. Specific examples of alkanesulfonic acid include methanesulfonic acid (carbon number: 1) and ethanesulfonic acid (carbon number: 2), but alkanesulfonic acid with carbon number of 7 or more and 18 or less used as the leveling agent (C) of the present embodiment is not used as the free acid (E). Specific examples of arylsulfonic acid include benzenesulfonic acid, phenolsulfonic acid, cresolsulfonic acid or toluenesulfonic acid. Specific examples of alkanolsulfonic acid include isethionic acid. The free acid (E) has the function of improving the conductivity of the tin alloy plating solution. In addition, the free acid (E) can be used alone or in combination of two or more.

[0055] The content of the free acid in the tin alloy plating solution of the present embodiment is preferably in the range of 5 g / L or more and 500 g / L or less, and more preferably in the range of 30 g / L or more and 300 g / L or less.

[0056] [additive]

[0057] The tin alloy plating solution of the present embodiment may further contain additives such as an antioxidant, a complexing agent for tin, and a pH adjuster.

[0058] [Antioxidant]

[0059] The tin alloy plating solution of this embodiment may contain an antioxidant as needed. The antioxidant prevents Sn in the tin alloy plating solution from 2+ The purpose is to prevent oxidation. Examples of antioxidants include ascorbic acid or its salts, pyrogallol, hydroquinone, phloroglucinol, trihydroxybenzene, catechol, methanesulfonic acid or its salts, catecholsulfonic acid or its salts, hydroquinonesulfonic acid or its salts, etc. For example, hydroquinonesulfonic acid or its salts are preferred in an acidic bath, and ascorbic acid or its salts are preferred in a neutral bath. Furthermore, the antioxidants may be used alone or in combination of two or more.

[0060] The amount of antioxidant added to the tin alloy plating solution of this embodiment is generally in the range of 0.01 g / L to 20 g / L, preferably in the range of 0.1 g / L to 10 g / L, and more preferably in the range of 0.1 g / L to 5 g / L.

[0061] [Complexing agent for tin]

[0062] The tin alloy plating solution of this embodiment can be applied to a tin alloy plating bath in any pH range such as acidic, weakly acidic, and neutral. 2+ The ions are stable in strong acid (pH: <1), but tend to produce white precipitates in acidic to neutral conditions (pH: 1 to 7). Therefore, when the tin alloy plating solution of this embodiment is applied to a tin plating bath near neutral conditions, it is preferred to use a stable Sn2+ For the purpose of ionization, a complexing agent for tin is added.

[0063] As tin complexing agent, hydroxycarboxylic acid, polycarboxylic acid, monocarboxylic acid can be used. As a specific example, gluconic acid, citric acid, glucoheptonic acid, gluconolactone, gluceptonic acid lactone, acetic acid, sorbic acid, butyric acid, ascorbic acid, oxalic acid, malonic acid, succinic acid, glycolic acid, malic acid, tartaric acid or their salts etc. are enumerated. Preferably, gluconic acid, citric acid, glucoheptonic acid, gluconolactone, gluceptonic acid lactone or their salts etc. are used. In addition, polyamines or aminocarboxylic acids such as ethylenediamine, 3,6-dithio-1,8-octanediol, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), iminodipropionic acid (IDP), hydroxyethylenediaminetriacetic acid (HEDTA), triethylenetetraaminehexaacetic acid (TTHA), ethylenedioxybis(ethylamine)-N,N,N',N'-tetraacetic acid, mercaptotriazoles, mercaptotetrazoles, glycines, aminotrimethylenephosphonic acid, 1-hydroxyethane-1,1-diphosphonic acid or salts thereof are also effective as complexing agents for tin.

[0064] The tin complexing agent may be used alone or in combination of two or more. The amount of the tin complexing agent added to the tin alloy plating solution of this embodiment is in the range of 0.01 g / L to 20 g / L, preferably in the range of 0.1 g / L to 10 g / L.

[0065] [pH adjuster]

[0066] The tin alloy plating solution of the present embodiment may contain a pH adjusting agent as required. Examples of pH adjusting agents include various acids such as hydrochloric acid and sulfuric acid, various bases such as ammonia water, potassium hydroxide, sodium hydroxide, and sodium bicarbonate. In addition, as pH adjusting agents, monocarboxylic acids such as acetic acid and sorbic acid, dicarboxylic acids such as boric acid, phosphoric acid, oxalic acid, and succinic acid, and hydroxycarboxylic acids such as lactic acid and tartaric acid are also effective. The pH of the tin alloy plating solution is preferably in the range of 0 to 7.

[0067] The tin alloy plating solution of the present embodiment can be prepared by mixing a soluble tin salt (A), a soluble salt of a metal less active than tin (B), a leveling agent (C) composed of an alkanesulfonic acid or a salt thereof containing 9 to 18 carbon atoms in the molecule, a phenyl-containing nonionic surfactant (D), a free acid (E), other components (tin complexing agent, etc.) and water. As water, ion exchange water or distilled water, etc. can be used. Since the tin alloy plating solution contains the above-mentioned components, it is possible not to use aromatic carbonyl compounds (benzylideneacetone, cinnamic acid, cinnamaldehyde, benzaldehyde, etc.) as a leveling agent, and the leveling agent is not replenished for a long time during electroplating, and a plated film can be formed uniformly and densely, and the plated film can be made smooth.

[0068] As a method for forming a plated film using the plating solution of the present embodiment, electroplating is used as described above. The current density when forming the plated film by electroplating is in the range of 0.1 ASD to 100 ASD, preferably in the range of 0.5 ASD to 20 ASD. The liquid temperature is in the range of 10° C. to 50° C., more preferably in the range of 20° C. to 40° C.

[0069] Example

[0070] Next, examples of the present invention will be described in detail together with comparative examples.

[0071] <Example 1>

[0072] In a tin methanesulfonate aqueous solution, methanesulfonic acid as a free acid, 3,6-disulfide-1,8-octanediol as a silver complexing agent, polyoxyethylene phenyl ether as a phenyl-containing nonionic surfactant (a substance obtained by addition condensation of 5 mol of ethylene oxide (EO) in phenol), and sodium 1-nonanesulfonate as a leveling agent composed of alkanesulfonic acid or its salt were mixed and dissolved, and then a silver methanesulfonate solution was added and mixed. Finally, ion exchange water was added to form a bath of a SnAg plating solution (tin alloy plating solution) of the following composition. In addition, a tin methanesulfonate aqueous solution and a silver methanesulfonate aqueous solution were prepared by electrolyzing a metal tin plate and a metal silver plate in a methanesulfonic acid aqueous solution, respectively.

[0073] (Composition of SnAg plating solution (tin alloy plating solution))

[0074] Tin methanesulfonate (as Sn 2+ ): 50g / L

[0075] Silver methanesulfonate (as Ag + ): 0.5g / L

[0076] 3,6-dithio-1,8-octanediol (as silver complexing agent): 1g / L

[0077] Methanesulfonic acid (as free acid): 100g / L

[0078] Polyoxyethylene phenyl ether (phenyl-containing nonionic surfactant): 5g / L

[0079] Sodium 1-nonanesulfonate (as a leveling agent composed of alkanesulfonate): 1g / L

[0080] Ion exchange water: the remainder

[0081] <Examples 2 to 18 and Comparative Examples 1 to 7>

[0082] A bath of SnAg plating solution (tin alloy plating solution) was formed in the same manner as in Example 1 except that the type and content ratio of the phenyl-containing nonionic surfactant and the type and content ratio of the leveling agent composed of an alkanesulfonic acid or its salt were changed as shown in Table 2. In the SnAg plating solutions of Examples 2 to 9, 15, 17 and Comparative Examples 2 to 7, the phenyl-containing nonionic surfactant was obtained by addition-condensation of only ethylene oxide (EO) in the number of moles (EO addition moles) shown in Table 2, but propylene oxide (PO) was not added. In addition, in the SnAg plating solutions of Examples 10 to 14, 16 and 18, the phenyl-containing nonionic surfactant was obtained by addition-condensation of only ethylene oxide (EO) and propylene oxide (PO) in the number of moles (EO addition moles and PO addition moles) shown in Table 2. In Table 2, the phenyl-containing nonionic surfactants shown in the categories A to O and the leveling agents composed of the alkanesulfonic acids or salts thereof shown in the categories A to S are shown in Table 1.

[0083] On the other hand, the "Formula" in the column of the alkanesulfonic acid or its salt in Table 2 is any one of the following formulas (1) to (4).

[0084] R 1 -SO3H(1)

[0085] R 2 -HC(SO3H)-R 3 (2)

[0086] R 1 -SO3Na(3)

[0087] R 2 -HC(SO3Na)-R 3 (4)

[0088] R in formula (1) and formula (3) 1 and R in formula (2) and formula (4) 2 and R 3 The "content ratio" in the column of the alkanesulfonic acid or its salt in Table 2 is the content ratio of the alkanesulfonic acid or its salt when the SnAg plating solution is 100 mass %.

[0089] <Comparative Test 1>

[0090] The SnAg plating solution (tin alloy plating solution) of Examples 1 to 18 and Comparative Examples 1 to 7 was used as an electrolyte, and the electrolyte was adjusted to a liquid temperature of 30°C. A silicon wafer (a resist film with a thickness of 50 μm was formed on the surface while a circular exposed portion with a diameter of 75 μm remained in the center) was immersed in the electrolyte, and electrolytic plating was performed at a current density of 4 ASD to form a bump with a thickness of 40 μm on the circular exposed portion of the silicon wafer. Next, the resist was peeled off from the surface of the silicon wafer with the bump formed thereon with an organic solvent. In addition, the arithmetic mean surface roughness Ra of a 10 μm square near the center of the top of the bump head was calculated using a laser microscope (manufactured by Olympus Corporation: OLS3000). In addition, a Ra of less than 0.5 μm was set as "good", a Ra of 0.5 μm or more and less than 0.7 μm was set as "acceptable", and a Ra of 0.7 μm or more was set as "unacceptable".

[0091] [Table 1]

[0092] Classification Phenyl-containing nonionic surfactants Alkanesulfonic acid or its salt A Polyoxyethylene phenyl ether Sodium 1-nonanesulfonate B Polyoxyethylene cumyl phenyl ether 1-Decanesulfonic acid C Polyoxyethylene polystyrenated phenyl ether Potassium 1-decanesulfonate D Polyoxyethylene bisphenol A ether Sodium 1-dodecyl sulfate E Polyoxyethylene polystyrene cresol ether Potassium 1-dodecylsulfonate F Polyoxyethylene nonylphenyl ether 1-Tetradecylsulfonic acid G Polyoxyethylene bisphenol F ether Potassium 1-Tetradecyl Sulfonate H Polyoxyethylene β-naphthyl ether Sodium 1-hexadecyl sulfate I Polyoxyethylene tribenzyl phenyl ether Sodium 1-octadecylsulfonate J Polyoxyethylene polyoxypropylene polystyrenated phenyl ether Nonane sulfonic acid K Polyoxyethylene polyoxypropylene phenyl ether Dodecyl secondary sulfonic acid L Polyoxyethylene polyoxypropylene polystyrenated cresol ether Tetradecyl sec-sulfonic acid M Polyoxyethylene polyoxypropylene bisphenol A ether Heptadecanyl sulfonic acid N Polyoxyethylene polyoxypropylene dodecylphenyl ether Octadecyl sec-sulfonic acid O Polyoxyethylene polyoxypropylene glycol (phenyl free) Sodium 1-octane sulfonate P 1-Nonadecanesulfonic acid Q Sodium octane sulfonate R Potassium nonadecane sulfonate S Sodium dodecylbenzenesulfonate

[0093] [Table 2]

[0094]

[0095] <Evaluation 1>

[0096] As can be seen from Tables 1 and 2, in Comparative Example 1, the bumps were formed using a SnAg plating solution containing a nonionic surfactant having no phenyl group. Therefore, the surface roughness Ra of the bump tip was as large as 0.94 μm, which was unacceptable.

[0097] In Comparative Example 2, bumps were formed using a SnAg plating solution containing an alkanesulfonate corresponding to Formula (3) but with a total carbon number of 8, which is less than the appropriate range (total carbon number of molecule: 9 to 18). Therefore, the surface roughness Ra of the bump head was as large as 0.79 μm, which was unacceptable.

[0098] In Comparative Example 3, bumps were formed using a SnAg plating solution containing an alkanesulfonic acid salt corresponding to Formula (1) but having a total carbon number of 19, which is greater than the appropriate range (total carbon number of the molecule: 9 to 18). Therefore, the surface roughness Ra of the bump head top was as large as 0.96 μm, which was unacceptable.

[0099] In Comparative Example 4, bumps were formed using a SnAg plating solution containing an alkanesulfonate corresponding to Formula (4) but with a total carbon number of 8, which is less than the appropriate range (total carbon number of molecule: 9 to 18). Therefore, the surface roughness Ra of the bump head was as large as 0.87 μm, which was unacceptable.

[0100] In Comparative Example 5, bumps were formed using a SnAg plating solution containing an alkanesulfonate corresponding to Formula (4) but having a total carbon number of 19, which is greater than the appropriate range (total carbon number of the molecule: 9 to 18). Therefore, the surface roughness Ra of the bump head was as large as 0.81 μm, which was unacceptable.

[0101] In Comparative Example 6, bumps were formed using a SnAg plating solution containing an alkanesulfonate that does not correspond to either of Formula (3) and Formula (4). Therefore, the surface roughness Ra of the bump tip was as large as 0.82 μm, which was unacceptable.

[0102] In Comparative Example 7, the bumps were formed using a SnAg plating solution that did not contain an alkanesulfonic acid or a salt thereof. Therefore, the surface roughness Ra of the bump tip was as large as 1.02 μm, which was unacceptable.

[0103] In contrast, in Examples 1 to 9, 15 and 16, bumps were formed using a SnAg plating solution containing an alkanesulfonic acid or a salt thereof corresponding to Formula (1) or Formula (3) and having a total carbon number in the molecule of 9 to 18 in an appropriate range (total carbon number in the molecule: 9 to 18). Therefore, the surface roughness Ra of the bump head top was as small as 0.12 μm to 0.62 μm, which was good or acceptable.

[0104] In Example 15, the bumps were formed using a SnAg plating solution containing 2 g / L of alkanesulfonate, which was higher than the preferred range (0.01 to 1 g / L). Therefore, the surface roughness Ra of the bump tip was slightly larger at 0.59 μm, which was acceptable.

[0105] In Example 16, the bumps were formed using a SnAg plating solution containing 0.005 g / L of alkanesulfonic acid, which is less than the preferred range (0.01 to 1 g / L). Therefore, the surface roughness Ra of the bump tip was slightly larger at 0.62 μm, which was acceptable.

[0106] On the other hand, in Examples 10 to 14, 17 and 18, bumps were formed using a SnAg plating solution containing an alkanesulfonic acid or a salt thereof corresponding to Formula (2) or Formula (4) and having a total carbon number in the molecule of 9 to 18 in an appropriate range (total carbon number in the molecule: 9 to 18). Therefore, the surface roughness Ra of the bump head top was as small as 0.21 μm to 0.65 μm, which was good or acceptable.

[0107] In Example 17, the bumps were formed using a SnAg plating solution containing 1.5 g / L of alkanesulfonate, which was higher than the preferred range (0.01 to 1 g / L). Therefore, the surface roughness Ra of the bump tip was slightly larger at 0.65 μm, which was acceptable.

[0108] In Example 18, the bumps were formed using a SnAg plating solution containing 0.005 g / L of alkanesulfonate, which is less than the preferred range (0.01 to 1 g / L). Therefore, the surface roughness Ra of the bump tip was slightly larger at 0.51 μm, which was acceptable.

[0109] <Comparative Test 2>

[0110] The appearance of the bumps formed using the plating solutions of Example 3 and Comparative Example 2 was photographed using a scanning electron microscope. The results are shown in FIG. Figure 1 and Figure 2 .

[0111] <Evaluation 2>

[0112] Depend on Figure 2 It can be seen that the surface roughness of the top of the bump formed by the plating solution of Comparative Example 2 is large. Figure 1 It is found that the surface roughness of the top of the bump formed using the plating solution of Example 3 is small.

[0113] Industrial Applicability

[0114] The tin alloy plating solution of the present invention can be used to form a part of electronic components such as bump electrodes of semiconductor wafers or printed circuit boards.

Claims

1. A tin alloy plating solution consisting only of the following substances: (A) a soluble salt comprising at least a stannous salt; (B) soluble salts of metals less reactive than tin; (C) a leveling agent composed of an alkanesulfonic acid or a salt thereof containing 9 to 18 carbon atoms in the molecule; (D) nonionic surfactants containing one or more phenyl groups in the molecule; (E) free acid; and Ion exchange water, The metal (B) which is less active than tin is silver, The leveling agent (C) is one selected from the group consisting of 1-nonane sodium sulfonate, 1-decane sulfonic acid, 1-decane potassium sulfonate, 1-dodecane sodium sulfonate, 1-dodecane potassium sulfonate, 1-tetradecane sulfonic acid, 1-tetradecane potassium sulfonate, 1-hexadecane sodium sulfonate, 1-octadecane sodium sulfonate, nonane secondary sulfonic acid, dodecane secondary sulfonic acid, tetradecane secondary sulfonic acid, heptadecane secondary sulfonic acid and octadecane secondary sulfonic acid, The nonionic surfactant (D) is one selected from polyoxyethylene phenyl ether, polyoxyethylene cumyl phenyl ether, polyoxyethylene polystyrenated phenyl ether, polyoxyethylene bisphenol A ether, polyoxyethylene polystyrene cresol ether, polyoxyethylene nonyl phenyl ether, polyoxyethylene bisphenol F ether, polyoxyethylene β-naphthyl ether, polyoxyethylene tribenzyl phenyl ether, polyoxyethylene polyoxypropylene polystyrenated phenyl ether, polyoxyethylene polyoxypropylene phenyl ether, polyoxyethylene polyoxypropylene polystyrenated cresol ether, polyoxyethylene polyoxypropylene bisphenol A ether and polyoxyethylene polyoxypropylene dodecyl phenyl ether, The content of the soluble tin salt (A) is converted into a tin amount in the range of 5 g / L or more and 200 g / L or less, The content of the soluble salt (B) of the metal less active than tin is in the range of 0.01 g / L or more and 10 g / L or less in terms of the amount of the metal. The content of the leveling agent (C) is in the range of 0.01 g / L to 1 g / L. The content of the nonionic surfactant (D) is in the range of 1 g / L or more and 30 g / L or less, The content of the free acid (E) is in the range of 5 g / L or more and 500 g / L or less.

Images