JP2022063889A - Tin or tin alloy plating solution and formation method of bump using the solution - Google Patents

Abstract

To prevent a void from generating inside a bump in a range of wide current density 2 to 14 ASD.SOLUTION: A tin or tin alloy plating solution includes: a soluble salt (A) at least including a stannous salt; an acid or a salt thereof (B) selected from an organic acid and an inorganic acid; and a surfactant (C). The plating solution includes polypropylene glycol at a proportion of 0.05 to 5 g/L in the plating solution. Mass average molecular weight of the polypropylene glycol is 610 to 740. The surfactant (D) 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 an electrolytic plating method, and a method for forming bumps using the solution. More specifically, the present invention relates to a tin or tin alloy plating solution suitable for forming solder bumps (hereinafter, simply referred to as bumps) for semiconductor wafers and printed circuit boards, and a method for forming bumps using the solution.

Conventionally, there has been a demand for a plating solution that does not generate voids in the bumps when forming the bumps by the electrolytic plating method. As this type of tin or tin alloy plating solution, an electroplating bath for tin or a tin alloy containing an inorganic acid and an organic acid, a water-soluble salt thereof, a surfactant, and a leveling agent is disclosed (for example,). , Patent Document 1 (see paragraph [0012], paragraph [0019], paragraph [0080]).).

The surfactant of Patent Document 1 is at least one nonionic surfactant selected from the group consisting of polyoxyalkylene phenyl ether or a salt thereof, and polyoxyalkylene polycyclic phenyl ether or a salt thereof, and is polyoxyalkylene. The phenyl constituting the phenyl ether and the polycyclic phenyl constituting the polyoxyalkylene polycyclic phenyl ether may be substituted with an alkyl group having 1 to 24 carbon atoms or a hydroxy group, and the leveling agent is an aliphatic aldehyde. , At least one selected from the group consisting of aromatic aldehydes, aliphatic ketones, and aromatic ketones; α, β-unsaturated carboxylic acids or amides thereof, or salts thereof.

Since this Patent Document 1 contains a specific nonionic surfactant and a specific two types of leveling agents, it is excellent in recess filling property and can suppress the generation of voids. It is described that if a plating solution is used, it is possible to provide a good bump that is smooth without recess and does not generate voids after reflow.

On the other hand, a tin or tin alloy dip plating bath with improved removal of cuprous ions for the deposition of tin or tin alloy layers in the manufacture of printed circuit boards, IC substrates, semiconductor devices and the like has been disclosed. (See, for example, Patent Document 2 (claim 1, claim 3, paragraph [0001], paragraph [0008])). This tin or tin alloy aqueous dip plating bath is at least one selected from the group consisting of Sn (II) ions, optionally alloy metal ions, at least one aromatic sulfonic acid or salt thereof, thiourea and derivatives thereof. It comprises one complexing agent and a mixture of at least one first precipitation additive and at least one second precipitation additive.

The at least one first precipitation additive is selected from the group consisting of aliphatic polyhydric alcohol compounds having an average molecular weight in the range of 62 g / mol to 600 g / mol, their ethers, and polymers derived from them. Will be done. Further, the at least one second precipitation additive is selected from the group consisting of a polyalkylene glycol compound having an average molecular weight in the range of 750 to 10,000 g / mol, and the concentration of the at least one second precipitation additive is high. , 1-10% by mass, based on the total amount of at least one first precipitation additive and at least one second precipitation additive. Further, the at least one first precipitation additive is selected from the group consisting of polyethylene glycol and polypropylene glycol.

Patent Document 2 describes that this plating bath can maintain a high deposition rate of tin of 0.05 to 0.1 μm / min while extending the life of the bath. ..

JP-A-2015-193916 Japanese Patent No. 5766301

Recently, with the miniaturization and complexity of semiconductors, devices using bumps have been diversified. As the number of device types increases, bumps are formed by adjusting the current density during plating for each device by the electrolytic plating method for the purpose of forming a plating deposit layer suitable for each device. At this time, in order to achieve the above object, there is a demand for a plating solution that does not generate voids in the bumps in a wide current density range. In this respect, in the plating bath described in Patent Document 1, in Examples 1 to 10, electroplating is performed only with a current density of 2 A / dm ² (hereinafter referred to as ASD), and voids are formed in the bumps. There is a problem that the current density range that can suppress the generation is not wide.

Further, the plating bath described in Patent Document 2 is a dip plating bath, that is, an electroless plating bath, not an electrolytic plating bath. Further, the problems of the plating bath of Patent Document 2 are to extend the bath life and maintain a high tin deposition rate, and do not have a problem of suppressing the generation of voids in the bump.

An object of the present invention is to provide a tin or tin alloy plating solution that suppresses the generation of voids in a bump in a wide range of current densities such as 2ASD to 14ASD, and a method for forming a bump using the solution.

As a result of diligent research to solve the above problems, the present inventor has made polypropylene glycol having a specific mass average molecular weight contained in the plating solution in a specific mass ratio, for example, 2ASD to 14ASD. We have found that the generation of voids in the bump can be suppressed in a wide range of current densities such as, and arrived at the present invention.

The first aspect of the present invention comprises a soluble salt (A) containing at least a tin salt, an acid selected from organic and inorganic acids (B), and a surfactant (C). A tin or tin alloy plating solution, wherein the plating solution contains polypropylene glycol at a ratio of 0.05 g / L to 5 g / L, and the weight average molecular weight of the polypropylene glycol is 610 to 740. It is characterized by that.

The second aspect of the present invention is the invention according to the first aspect, wherein the surfactant (C) is a nonionic surfactant in which polyoxyethylene (EO) and polyoxypropylene (PO) are condensed. Is a tin or tin alloy plating solution.

A third aspect of the present invention is to form a tin or tin alloy plating deposit layer as a plurality of bump precursors on a substrate by using the tin or tin alloy plating solution of the first aspect or the second aspect. It is a bump forming method including a step and then a step of forming a plurality of bumps by performing a reflow process.

The tin or tin alloy plating solution according to the first aspect of the present invention contains 0.05 g / L to 5 g / L of polypropylene glycol having a mass average molecular weight of 610 to 740, and thus has a wide current density range of, for example, 2 ASD to 14 ASD. It is possible to suppress the generation of voids in the bump.
The following are possible reasons for the voids to occur in the bumps.
First, there are two possible mechanisms for voids in solder-plated bumps. The first generation mechanism is a case where the ability of the additive (surfactant) to suppress the precipitation of tin (Sn) is insufficient. In this case, if tin (Sn) is not deposited under appropriately suppressed conditions, a dense plating deposit layer is not formed, and the plating solution is taken into the plating deposit layer, so that voids are formed in the bumps after reflow. Is likely to occur.
The second generation mechanism is when the inhibitory power of the additive (surfactant) is excessive. In this case, hydrogen is generated by electrolysis of water at the same time as the precipitation of Sn, and the generated hydrogen gas is taken into the plating deposit layer, so that voids are likely to be generated in the bump after reflow.
Polypropylene glycol having a mass average molecular weight in the range of 610 to 740 has both hydrophilic and hydrophobic properties, so that it assists in insufficient adsorption of the additive (surfactant) to the cathode surface and is excessive. Since it has the effect of buffering adsorption, it is considered that Sn precipitation is appropriately performed, and as a result, voids are suppressed.

In the tin or tin alloy plating solution according to the second aspect of the present invention, since the surfactant is a nonionic surfactant in which polyoxyethylene (EO) and polyoxypropylene (PO) are condensed, the polypropylene glycol and the above-mentioned polypropylene glycol are used. When used in combination, the generation of voids can be further suppressed.

In the formation of the bumps according to the third aspect of the present invention, the tin or tin alloy plating solution as a plurality of bump precursors is deposited on the substrate by using the tin or tin alloy plating solution according to the first aspect or the second aspect. Layers are formed over a wide range of current densities, eg, 2ASD-14ASD. Next, a reflow process is performed. As a result, the plating deposit layer can be formed with a current density suitable for various devices, and a plurality of bumps with few voids can be formed inside.

It is a top view of the semiconductor wafer which has the resist layer produced in the Example of this invention. It is sectional drawing which shows the situation that the plating deposit layer after plating becomes a bump after reflow. FIG. 2A is a cross-sectional view after plating, FIG. 2B is a cross-sectional view in which a spherical normal bump with a bulging upper part is formed after reflow, and FIG. 2C is a cross-sectional view after reflow. It is sectional drawing of the defect bump which void was formed in the spherical bump which bulged.

Hereinafter, the tin or tin alloy plating solution according to the embodiment of the present invention will be described. This plating solution is used as a material for forming a plating deposit layer of tin or a tin alloy used as a bump for a semiconductor wafer or a printed circuit board.

The tin or tin alloy plating solution of the present embodiment contains a soluble salt (A) containing at least a first tin salt, an acid selected from organic and inorganic acids (B), and a surfactant (C). A tin or tin alloy plating solution containing. The characteristic point is that polypropylene glycol is contained in the plating solution at a ratio of 0.05 g / L to 5 g / L, and the mass average molecular weight of the polypropylene glycol is 610 to 740.

The tin alloy of the present 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 alloys, tin-copper alloys, tin-bismas alloys, tin-nickel alloys, tin-antimon alloys, tin-indium alloys, and tin-zinc alloys, tin-copper-bismus, etc. And ternary alloys such as tin-copper-silver alloys.

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

Therefore, the soluble salt (A) of the present embodiment contains Sn ²⁺ alone in the plating solution, or together with Sn ²⁺ , Ag ⁺ , Cu ⁺ , Cu ²⁺ , Bi ³⁺ , Ni ²⁺ , Contains one or more of any soluble salts that generate various metal ions such as Sb ³⁺ , In ³⁺ , Zn ²⁺ and the like. Examples of the soluble salt include oxides of these metals, halides, and the metal salts of inorganic or organic acids.

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

Metallic salts of inorganic or organic acids include copper sulfate, stannous sulfate, bismuth sulfate, nickel sulfate, antimony sulfate, bismuth nitrate, silver nitrate, copper nitrate, antimonite nitrate, indium nitrate, nickel nitrate, zinc nitrate and copper acetate. , Nickel acetate, nickel carbonate, sodium tinate, 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 acid and inorganic acid or salt thereof (B)]
The acid or salt (B) thereof of the present 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, or aliphatic carboxylic acids, and examples of the inorganic acid include borohydrophobic acid, silicate hydrofluoric acid and sulfamine. Examples include acids, hydrochloric acid, sulfuric acid, nitric acid, perchloric acid and the like. These salts are alkali metal salts, alkaline earth metal salts, ammonium salts, amine salts, sulfonates and the like. As the component (B), an organic sulfonic acid is preferable from the viewpoint of the solubility of the metal salt and the ease of wastewater treatment.

As the alkane sulfonic acid, those represented by the chemical formula C _n H _{2n + 1} SO ₃ H (for example, n = 1 to 5, preferably 1 to 3) can be used. Specifically, methanesulfonic acid, ethanesulfonic acid, 1-propanesulfonic acid, 2-propanesulfonic acid, 1-butanesulfonic acid, 2-butanesulfonic acid, pentansulfonic acid, etc., as well as hexanesulfonic acid and decanesulfonic acid. Acids, dodecane sulfonic acids and the like can be mentioned.

As the alkanolsulfonic acid, those represented by the chemical formula C _p H _{2p + 1} -CH (OH) -C _q H _2q -SO ₃ H (for example, p = 0 to 6, q = 1 to 5) can be used. .. Specifically, in addition to 2-hydroxyethane-1-sulfonic acid, 2-hydroxypropane-1-sulfonic acid, 2-hydroxybutane-1-sulfonic acid, 2-hydroxypentane-1-sulfonic acid, etc., 1- 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- Hydroxidodecane-1-sulfonic acid and the like can be mentioned.

The aromatic sulfonic acid is basically benzenesulfonic acid, alkylbenzenesulfonic acid, phenolsulfonic acid, naphthalenesulfonic acid, alkylnaphthalenesulfonic acid and the like. Specifically, 1-naphthalene sulfonic acid, 2-naphthalene sulfonic acid, toluene sulfonic acid, xylene sulfonic acid, p-phenol sulfonic acid, cresol sulfonic acid, sulfosalicylic acid, nitrobenzene sulfonic acid, sulfobenzoic acid, diphenylamine-4- Examples 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.

The content of the first tin salt in the plating solution of the present embodiment is preferably in the range of 5 g / L or more and 200 g / L or less, more preferably in the range of 20 g / L or more and 100 g / L or less in terms of the amount of tin. It is in.

[Surfactant (C)]
The surfactant (C) used in the plating solution of the present embodiment is preferably a nonionic surfactant in which polyoxyethylene (EO) and polyoxypropylene (PO) are condensed. As this surfactant, a polyoxyethylene polyoxypropylene block polymer (PO-EO-PO) having a polyoxypropylene (PO) terminal and a polyoxyethylene polyoxypropylene block polymer having a polyoxyethylene (EO) terminal. (EO-PO-EO), ethylenediamine EO-PO condensate (ethylenediaminetetrapolyoxyethylenepolyoxypropylene) and the like can be mentioned. Among them, PO-EO-PO is more preferable because it has an excellent interaction with polypropylene glycol. It is more preferable that the EO ratio (molar ratio) in the block polymer is 30% to 50% and the mass average molecular weight of the surfactant is 2000 to 7800 because the surfactant is adsorbed on the cathode surface. Further, it is more preferable that the content of the surfactant in the plating solution is in the range of 0.5 g / L to 10 g / L in order to obtain a uniform plating deposit layer.

[Polypropylene glycol]
The polypropylene glycol in the plating solution of the present embodiment is contained at a ratio of 0.05 g / L to 5 g / L, preferably 0.5 g / L to 4 g / L, and more preferably 1 g / L to 2 g / L. The mass average molecular weight of polypropylene glycol is 610 to 740, preferably 650 to 730, and more preferably 670 to 730. The mass average molecular weights of the above-mentioned surfactant and polypropylene glycol are each determined by size exclusion chromatography (SEC method). If the content of polypropylene glycol is less than 0.05 g / L, the ability to suppress the precipitation of Sn is insufficient, and the plating solution is taken into the plating deposit layer without forming a dense plating deposit layer, so that the bump after reflow Voids are likely to occur inside. If it exceeds 5 g / L, hydrogen is generated at the same time as the precipitation of Sn, and hydrogen gas is taken into the plating deposit layer, so that voids are likely to be generated in the bump after reflow. When the mass average molecular weight of polypropylene glycol is less than 610, the hydrophilicity is too strong and the inhibitory force of the surfactant is weakened by the interaction, and voids are induced in the bump after reflow. On the other hand, when the mass average molecular weight of polypropylene glycol exceeds 740, the hydrophobicity is too strong and the inhibitory force of the surfactant is strengthened by the interaction, and voids are induced in the bump after reflow. When the mass average molecular weight of polypropylene glycol is in the range of 610 to 740, it has both hydrophilic and hydrophobic properties, so that it assists the insufficient adsorption of the surfactant to the cathode surface and excessively adsorbs it. Has the effect of buffering. As a result, Sn is properly deposited, and as a result, voids in the bump after reflow are suppressed.

The plating solution of the present embodiment may further contain an antioxidant, a complexing agent, a pH adjusting agent, and a brightening agent, if necessary.

〔Antioxidant〕
The antioxidant is intended to prevent the oxidation of Sn ²⁺ in the plating solution. Examples of antioxidants include ascorbic acid or a salt thereof, pyrogallol, hydroquinone, fluoroglucinol, trihydroxybenzene, catechol, cresol sulfonic acid or a salt thereof, catechol sulfonic acid or a salt thereof, hydroquinone sulfonic acid or a salt thereof, and the like. Can be mentioned. For example, hydroquinone sulfonic acid or a salt thereof is preferable in an acidic bath, and ascorbic acid or a salt thereof is preferable in a neutral bath.

As the antioxidant, one type may be used alone, or two or more types may be used in combination. The amount of the antioxidant added to the plating solution of the present 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. It is in the range of ~ 5 g / L.

[Complexing agent]
The plating solution of the present embodiment can be applied to a tin or tin alloy plating bath in any pH range such as acidic, weakly acidic, and neutral. Sn ²⁺ ions are stable in strong acidity (pH: <1), but tend to cause white precipitates near acidic to neutral (pH: 1-7). Therefore, when the tin or tin alloy plating solution of the present embodiment is applied to a tin plating bath near neutrality, it is recommended to add a complexing agent for tin for the purpose of stabilizing Sn ²⁺ ions. preferable.

As the complexing agent for tin, oxycarboxylic acid, polycarboxylic acid, and monocarboxylic acid can be used. Specific examples include gluconic acid, citric acid, glucoheptonic acid, gluconolactone, acetic acid, propionic acid, butyric acid, ascorbic acid, oxalic acid, malonic acid, succinic acid, glycolic acid, malic acid, tartrate acid, or salts thereof. And so on. Preferred are gluconic acid, citric acid, glucoheptonic acid, gluconolactone, glucoheptlactone, or salts thereof. In addition, ethylenediamine, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentacetic acid (DTPA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), iminodipropionic acid (IDP), hydroxyethylethylenediaminetriacetic acid (HEDTA), triethylene. Tetramine hexaacetic acid (TTHA), ethylenedioxybis (ethylamine) -N, N, N', N'-tetraacetic acid, mercaptotriazoles, mercaptotetrazole, glycins, nitrilotrimethylphosphonic acid, 1-hydroxyethane-1, 1-Diphosphonic acid, polyamines such as salts thereof, and aminocarboxylic acids are also effective as compositing agents.

As the complexing agent for tin, one kind may be used alone, or two or more kinds may be used in combination. The amount of the complexing agent for tin added in the plating solution of the present embodiment is generally in the range of 0.001 mol to 10 mol with respect to 1 mol of tin in the soluble tin salt compound contained in tin or a tin alloy plating solution. , Preferably in the range of 0.01 mol to 5 mol, more preferably in the range of 0.5 mol to 2 mol.

When the tin alloy plating solution is a SnAg plating solution, a water-soluble sulfide compound or a water-soluble thiol compound can be used as the complexing agent for silver.

[PH regulator]
The plating solution of the present embodiment may contain a pH adjuster, if necessary. Examples of the pH adjuster include various acids such as hydrochloric acid and sulfuric acid, and various bases such as aqueous ammonia, potassium hydroxide, sodium hydroxide and sodium hydrogen carbonate. Further, as the pH adjusting agent, monocarboxylic acids such as acetic acid and propionic acid, dicarboxylic acids such as boric acid, phosphoric acid, oxalic acid and succinic acid, and oxycarboxylic acids such as lactic acid and tartaric acid are also effective.

[Brightening agent]
The plating solution of the present embodiment may contain a brightening agent, if necessary. As the brightening agent, an aromatic carbonyl compound is effective. The aromatic carbonyl compound has the effect of refining the crystal particles of the tin alloy in the tin alloy plated deposit layer. Aromatic carbonyl compounds are carbon atoms of aromatic hydrocarbons with a carbonyl group (-CO-X: where X is a hydrogen atom, a hydroxy group, an alkyl group or a carbon atom having a carbon atom number in the range of 1 to 6). It is a compound to which an alkoxy group (meaning an alkoxy group having a number in the range of 1 to 6) is bonded. Aromatic hydrocarbons include a benzene ring, a naphthalene ring and an anthracene ring. Aromatic hydrocarbons may have substituents. Examples of the substituent include a halogen atom, a hydroxy group, an alkyl group having a carbon atom number in the range of 1 to 6, and an alkoxy group having a carbon atom number in the range of 1 to 6 atoms. The carbonyl group may be directly linked to an aromatic hydrocarbon, or may be bonded via an alkylene group having 1 to 6 carbon atoms. Specific examples of the aromatic carbonyl compound include benzalacetone, cinnamic acid, cinnamaldehyde, and benzaldehyde.

The aromatic carbonyl compound may be used alone or in combination of two or more. The amount of the aromatic carbonyl compound added to the tin alloy plating solution of the present embodiment is generally in the range of 0.01 mg / L to 500 mg / L, preferably in the range of 0.1 mg / L to 100 mg / L, and more preferably in the range of 1 mg / L. It is in the range of L to 50 mg / L.

[Electroplating method]
In the electrolytic plating method of the present embodiment, the above-mentioned tin or tin alloy plating solution is supplied to the plating tank, and the insoluble anode is arranged facing the member to be plated connected to the cathode, for example, a semiconductor wafer. By using the plating solution of the present embodiment, the anode current density at the time of forming the plating deposit layer can be set to a wide range of current densities suitable for various devices. For example, it is preferably in the range of 2 ASD to 14 ASD, and even more preferably in the range of 4 ASD to 12 ASD. If it is less than 2 ASD, the precipitation of Sn may be too slow, and the inhibitory force of the surfactant against the precipitation of Sn may become too strong. If it exceeds 14 ASD, the precipitation of Sn may become too fast, and the inhibitory force of the surfactant against the precipitation of Sn may become too weak. By adding the above-mentioned polypropylene glycol to the plating solution, the above-mentioned suppressing effect is assisted or the suppressing effect is buffered, and the range of the current density in which voids do not occur after reflow is widened. The temperature of the plating solution is preferably in the range of 10 ° C. or higher and 50 ° C. or lower, and more preferably in the range of 20 ° C. or higher and 40 ° C. or lower.

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

(Building bath of SnAg plating solution)
<Example 1>
Methanesulfonic acid as a free acid and thiodiethanol as a compositing agent were mixed and dissolved in an aqueous solution of methanesulfonic acid Sn, and then a solution of methanesulfonic acid Ag was further added and mixed. After becoming a uniform solution by mixing, a nonionic surfactant (polyoxy) having a structural formula (PO-EO-PO) as a surfactant, an EO ratio of 40%, and a mass average molecular weight of 3500. Ethylene polyoxypropylene block polymer), benzalacetone as a brightener, and polypropylene glycol having a mass average molecular weight of 610 were added. Finally, ion-exchanged water was added to form a SnAg plating solution having the following composition. The methanesulfonic acid Sn aqueous solution was prepared by electrolyzing a metal Sn plate, and the methanesulfonic acid Ag aqueous solution was prepared by electrolyzing a metal Ag plate in the methanesulfonic acid aqueous solution.

(Composition of SnAg plating solution)
Methanesulfonic acid Sn (as Sn ²⁺ ): 50 g / L
Methanesulfonic acid Ag (as Ag ⁺ ): 0.2 g / L
Methanesulfonic acid (as free acid): 100 g / L
Thiodiethanol (as a complexing agent): 5 g / L
Surfactant: 5g / L
Benzalacetone (as a brightener): 10 mg / L
Polypropylene glycol: 1g / L
Ion-exchanged water: balance

The mass average molecular weight of polypropylene glycol described in Example 1, the content ratio in the plating solution, the structural formula of the surfactant, the mass average molecular weight, and the EO ratio in the block polymer are shown in Table 1 below.

<Examples 2 to 11, Comparative Examples 1 to 5>
In Examples 2 to 11 and Comparative Examples 1 to 5, polypropylene glycols having a mass average molecular weight shown in Table 1 above were used, and polypropylene glycol was used in the content ratio shown in Table 1 above. As the surfactant, as shown in Table 1 above, polyoxyethylene polyoxypropylene block polymer (PO-EO-PO), polyoxyethylene polyoxypropylene block polymer (EO-PO-EO) or ethylenediamine tetrapolyoxy. Those having a structural formula of ethylene polyoxypropylene (ethylene diamine EO-PO) were used. In addition, a nonionic surfactant having the properties shown in Table 1 above with an EO ratio and a mass average molecular weight was used. The content ratio of the surfactant was 5 g / L in all cases. Other than that, the SnAg plating solutions of Examples 2 to 11 and Comparative Examples 1 to 5 were bathed in the same manner as in Example 1.

(Building bath of Sn plating solution)
<Example 12>
The methanesulfonic acid Sn aqueous solution has methanesulfonic acid as a free acid, thiodiethanol as a compositing agent, and the structural formula (PO-EO-PO) shown in Table 1 above as a surfactant, and has an EO ratio of 40. %, A nonionic surfactant having a mass average molecular weight of 3500, benzalacetone as a brightener, and polypropylene glycol having a mass average molecular weight of 700 were added. Finally, ion-exchanged water was added to form a Sn plating solution having the following composition. The methanesulfonic acid Sn aqueous solution was prepared by electrolyzing a metal Sn plate in the methanesulfonic acid aqueous solution.

(Composition of Sn plating solution)
Methanesulfonic acid Sn (as Sn ²⁺ ): 50 g / L
Methanesulfonic acid (as free acid): 100 g / L
Thiodiethanol (as a complexing agent): 5 g / L
Surfactant: 5g / L
Benzalacetone (as a brightener): 10 mg / L
Polypropylene glycol: 1g / L
Ion-exchanged water: balance

(Building bath of SnCu plating solution)
<Example 13>
Methanesulfonic acid as a free acid and thiodiethanol as a compositing agent were mixed and dissolved in an aqueous solution of methanesulfonic acid Sn, and then a Cu solution of methanesulfonic acid was further added and mixed. After becoming a uniform solution by mixing, a nonionic surfactant having a structural formula (PO-EO-PO) as a surfactant, an EO ratio of 40%, and a mass average molecular weight of 3500, and gloss. As an agent, benzalacetone and polypropylene glycol having a mass average molecular weight of 700 were added. Finally, ion-exchanged water was added to form a SnCu plating solution having the following composition. The methanesulfonic acid Sn aqueous solution was prepared by electrolyzing a metal Sn plate and the methanesulfonic acid Cu aqueous solution by electrolyzing a metal Cu plate in the methanesulfonic acid aqueous solution.

(Composition of SnCu plating solution)
Methanesulfonic acid Sn (as Sn ²⁺ ): 50 g / L
Cu methanesulfonic acid (as Cu ²⁺ ): 0.2 g / L
Methanesulfonic acid (as free acid): 100 g / L
Thiodiethanol (as a complexing agent): 5 g / L
Surfactant: 5g / L
Benzalacetone (as a brightener): 10 mg / L
Polypropylene glycol: 1g / L
Ion-exchanged water: balance

<Comparative test and evaluation>
First, a seed layer for electrical conduction of titanium 0.1 μm and copper 0.3 μm was formed on the surface of a silicon wafer having a diameter of 300 mm by a sputtering method, and a dry film resist (thickness 50 μm) was laminated on the seed layer. .. Next, the dry film resist was partially exposed via an exposure mask, and then developed. Thus, as shown in FIG. 1, the surface of the silicon wafer 1 has a pattern in which 1.6 million vias 2 having an opening having a diameter of 75 μm and an opening area of 1 dm ² are formed at a pitch of 150 μm. A resist layer 3 having a film thickness of 50 μm was formed.

Next, using each of the 18 types of plated solutions of Examples 1 to 13 and Comparative Examples 1 to 5, the anode current densities were set to 4 types of 2ASD, 4ASD, 6ASD, and 8ASD under the following plating conditions. Was set to, and electrolytic plating was performed for each.

(Plating conditions)
Bath amount: 40L
Stirring type: Battle stirring Stirring speed: 10 m / min Bath temperature: 25 ° C
Anode current density: 4 types of 2ASD, 6ASD, 10ASD, 14ASD Anode material: Platinum coated titanium (Pt / Ti) mesh plate

After electroplating the vias of the resist layer, the wafer was taken out from the plating solution, washed and dried. Subsequently, the resist layer was stripped by treating with a resist stripping solution containing tetramethylammonium hydroxide (TMAH) as an alkaline component at 50 ° C. for 30 minutes. Next, the seed layer under the formed bump was etched by treating at 25 ° C. for 5 minutes with an etching solution containing sulfuric acid and hydrogen peroxide solution.
Thus, on one die, with a plating deposit layer having a pattern in which plating deposit layers having a diameter of 75 μm and a film thickness of 45 μm are arranged at a pitch of 150 μm and 1.6 million at equal pitch intervals. A wafer was made.

2 (a) shows the wafer 1 before removing the resist 3 after plating, and FIGS. 2 (b) and 2 (c) show the wafer 1 on which bumps after reflow are formed. In FIG. 2, the same elements as those in FIG. 1 are designated by the same reference numerals. FIG. 2B shows a normal bump 4 without spherical voids after reflow plated so as not to be thicker than the surface of the resist 3, and FIG. 2C shows the upper part after reflow. Although it is a bulging spherical shape, it shows a void mixed bump 4 in which a void 5 is formed in the bump 4.

(Measurement of defect bump)
The wafer 1 from which the resist 3 after plating shown in FIGS. 2 (b) and 2 (c) was removed was reflowed using a reflow device (manufactured by SEMIgear). Reflow was performed in a reducing atmosphere of formic acid and nitrogen in order to remove the surface oxide film of the plating deposit layer, and the melting temperature was set to 250 ° C. Next, using a transmission X-ray device (manufactured by Dage), 275 bumps in total, 5000 bumps, were observed evenly in the plane of the wafer with a diameter of 300 mm after reflow processing, and the voids existing in each bump were observed. The presence was inspected.
For each bump with voids, the void area relative to the bump area was calculated as a percentage. Of the total number of bumps of 5,000, the number of bumps (defect bumps) having voids having a void area of 1% or more was counted. The results are shown in Table 2 for each of the four types of anode current densities.

As is clear from Table 2, since the bumps formed by using the plating solution of Comparative Example 1 do not contain polypropylene glycol, the number of defect bumps is 371 regardless of the four types of anode current densities. There were as many as 3171. In particular, when the plating process was performed with the current density set to 14 ASD, the number of defective bumps was 3171, which was larger than that of the plating process at other current densities.

Regarding the bumps formed using the plating solution of Comparative Example 2, the content of polypropylene glycol in the plating solution was too small, 0.02 g / L, so that the number of defective bumps was smaller than that of Comparative Example 1, but the anode. Regardless of the current density of any of the four types, the number of defect bumps was as large as 64 to 428.

Regarding the bumps formed using the plating solution of Comparative Example 3, the content of polypropylene glycol in the plating solution was too high at 10 g / L, so that the number of defect bumps was smaller than that of Comparative Example 1, but the anode current density. However, the number of defective bumps was as high as 28 to 2028 in any of the four types. In particular, when the plating process was performed with the current density set to 14 ASD, the number of defective bumps was 2028, which was larger than that of the plating process at other current densities.

Regarding the bumps formed by using the plating solution of Comparative Example 4, since the mass average molecular weight of polypropylene glycol was too small as 400, the number of defect bumps was smaller than that of Comparative Example 1, but any of the four types of anode current densities. Even so, the number of defective bumps was as high as 145 to 2547. In particular, when the plating process was performed with the current density set to 2 ASD, the number of defective bumps was 2547, which was larger than that of the plating process at other current densities.

Regarding the bumps formed by using the plating solution of Comparative Example 5, the number of defective bumps was smaller than that of Comparative Example 1 because the mass average molecular weight of polypropylene glycol was 1000, which was too large, but any of the four types of anode current densities. Even so, the number of defective bumps was as high as 892 to 2525. In particular, when the plating process was performed with the current density set to 14 ASD, the number of defective bumps was 2525, which was larger than that of the plating process at other current densities.

On the other hand, in the plating solutions of Examples 1 to 13, the content ratio of polypropylene glycol was 0.05 g / L to 5 g / L, and the mass average molecular weight thereof was 610 to 740. The number of defective bumps in the formed 5000 bumps was 0 to 31 regardless of the four types of anode current densities, which was extremely small.

From the above results, according to the present invention, even if the current density is set to any of 2ASD, 6ASD, 10ASD or 14ASD so as to be suitable for various devices, the bump in the tin-containing bump is obtained at any current density. It was confirmed that the voids inside were reduced.

The plating solution of the present invention can be used to form a part of an electronic component such as a semiconductor wafer or a bump electrode of a printed circuit board.

1 Wafer 2 Via (opening)
3 Resist layer 4 Bump 5 Void

Claims (3)

A tin or tin alloy plating solution containing at least a soluble salt (A) containing a first tin salt, an acid selected from organic and inorganic acids or a salt thereof (B), and a surfactant (C). ,
The plating solution contains polypropylene glycol at a ratio of 0.05 g / L to 5 g / L in the plating solution, and the mass average molecular weight of the polypropylene glycol is 610 to 740. Tin or tin alloy plating. liquid. The tin or tin alloy plating solution according to claim 1, wherein the surfactant (C) is a nonionic surfactant in which polyoxyethylene (EO) and polyoxypropylene (PO) are condensed. Using the tin or tin alloy plating solution according to claim 1 or 2, a step of forming a tin or tin alloy plating deposit layer to be a plurality of bump precursors on a substrate, and then performing a reflow treatment to form a plurality of bumps. A method for forming a bump having a step of forming the bump.

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