WO2021193696A1 - Electroplating solution and electroplating method - Google Patents

Abstract

An electroplating solution comprising (A) a soluble salt containing at least a first tin salt, (B) an acid or a salt thereof, and (C) a surfactant. When electrolysis is carried out at an anodic current density of 0.7 A/dm2, the maximum value of the particle size distribution of air bubbles released from an insoluble anode is 150 μm or more. It is preferred that the surfactant (C) is a nonionic surfactant comprising a polyoxyethylene-polyoxypropylene block polymer (PO-EO-PO) of which the terminal is polyoxypropylene (PO), the proportion of EO in the block polymer (PO-EO-PO) is 35 to 50% by mol, inclusive, and the mass average molecular weight of the nonionic surfactant is 3000 to 5000, inclusive.

Description

Electroplating solution and electroplating method

The present invention relates to an electrolytic plating solution and an electrolytic plating method for forming a tin or tin alloy plating film. More specifically, the present invention relates to an electrolytic plating solution and an electrolytic plating method used for tin or tin alloy plating suitable for forming solder bumps for semiconductor wafers and printed circuit boards.
This application claims priority based on Japanese Patent Application No. 2020-058073 filed in Japan on March 27, 2020 and Japanese Patent Application No. 2021-46364 filed in Japan on March 19, 2021. Is used here.

A device that performs electrolytic plating (hereinafter, may be simply referred to as plating) is generally an anode (hereinafter, may be simply referred to as plating solution) arranged to face each other in a plating tank containing an electrolytic plating solution (hereinafter, may be simply referred to as plating solution). An anode) and a semiconductor wafer or substrate which is a member to be plated connected to the cathode (cathode) are provided, and a voltage is applied to the anode and the member to be plated. By this energization, a plating film is formed on the surface of the member to be plated.

The anode used in this electroplating apparatus can be roughly divided into a soluble anode and an insoluble anode. In tin and tin alloy plating solutions, platinum (Pt) and platinum-coated titanium (Pt) are used as anodes in order to suppress the reaction of the plating solution components (metal components noble than additives and tin) on the anode surface. An insoluble anode made of / Ti) or iridium oxide (IrO ₂ ) or the like is generally used. When an insoluble anode is used, the electrolysis reaction of water, which is represented by the following reaction formula, occurs on the surface of the anode during electrolysis.
2H ₂ O → 4H + + O ₂ ↑ + 4e-
At this time, the oxygen gas (air bubbles) generated on the surface of the anode is desorbed from the surface of the anode and released into the plating solution. Oxygen bubbles released into the plating solution disappear by floating in the plating solution and then reaching the liquid surface to defoam or dissolving in the plating solution as a dissolved gas. However, if the bubbles adhere to the member to be plated connected to the cathode (cathode) before the bubbles disappear, they are likely to prevent the precipitation of plating and cause pit defects, and are incorporated into the plating film. There was a problem that it was easy to cause voids. This problem tends to become apparent when a horizontal type (CUP type, Face down type, or Fountain type) plating device is used, and the anode current density is 0.5 A / dm in particular. ^{It was remarkable when plating was performed with 2} (hereinafter, also referred to as ASD (Ampere per Square Decimeter)) or higher.

Specifically, when the solder bump is formed on the semiconductor wafer in the horizontal plating tank 1, it faces the insoluble anode 3 arranged horizontally in the plating solution 2. Then, the semiconductor wafer (member to be plated) 4 horizontally connected to the cathode is arranged above the anode. During the plating, the semiconductor wafer 4 rotates in a horizontal state. Further, the plating solution 2 is circulated by the suction port 1a, the return port 1b, and the circulation pump 1c provided at the bottom of the plating tank 1, respectively. The bubbles 8 desorbed from the surface of the anode 3 float and adhere to the surface of the semiconductor wafer 4. Therefore, as shown in the enlarged view of FIG. 2, when the bubbles 8 are smaller than the diameter of the via 6 of the resist layer 5 formed by the resist pattern, the bubbles adhering to the bump 7 which is the plating deposit layer in the via. Since the 8 is not detached and the plating is not deposited on the bubble adhesion portion, a pit defect 9a is generated, and the bubble 8 remains in the bump 7 which is a plating deposit layer, and a void 9b is generated inside the bump after reflow. There was a problem that it was easy to do.

Conventionally, in order to solve this problem, a plating method for reducing pit defects by plating in a depressurized plating tank has been disclosed (for example, Patent Document 1 (Claim 1, paragraphs [0001] to []. 0003]).).

Japanese Unexamined Patent Publication No. 2004-43916

Many of the conventional bump electrodes have a diameter of more than 100 μm, and air bubbles adhering to the bumps in the via can be desorbed by device conditions such as stirring. Therefore, the problem that pit defects are generated by air bubbles has been regarded as a problem that can be solved by changing the structure of the plating apparatus and the stirring strength.

However, in recent years, the bump electrode has become finer to a diameter of 100 μm or less, and the depth (depth / diameter) of the via to the diameter of the via in the resist layer has become higher in aspect ratio. ) Has become difficult to desorb depending on the device conditions. Therefore, it is necessary to reduce the occurrence rate of pit defects due to the growth of the plating deposit layer due to the generated bubbles and the voids in the bump after the plating deposit layer has grown. As shown in Patent Document 1, the method of plating in a decompressed plating tank is one method of reducing the occurrence rate of pit defects and voids, but the above problem is still unsolved by this plating method. ..

An object of the present invention is an electrolytic plating solution and an electrolytic plating method for reducing the occurrence rate of pit defects in bumps and voids in bumps, which are caused by the fact that plating does not precipitate due to bubbles generated in the plating solution. Is to provide.

As a result of diligent research to solve the above problems, the present inventor has made oxygen bubbles generated on the surface of the anode (anode) by containing a surfactant having a specific structure in the plating bath. Before being released into the plating solution, it is aggregated on the surface of the anode and enlarged, and the enlarged oxygen bubbles are quickly carried to the liquid surface by buoyancy, so that the oxygen bubbles do not disperse in the plating solution. As a result, it has been found that the adhesion of bubbles having a diameter smaller than the via diameter to the surface of the member to be plated connected to the cathode is reduced, and the occurrence of pit defects and voids is dramatically reduced. Reached.

A first aspect of the present invention is an electrolytic plating solution containing a soluble salt (A) containing at least a stannous salt, an acid or a salt thereof (B), and a surfactant (C), wherein the anode current is present. This electroplating solution is characterized in that the maximum value of the particle size distribution of bubbles released from the insoluble anode when electrolyzed at a density of 0.7 A / dm ^{2 is 150 μm or more.} The maximum value of the particle size distribution may be 200 μm or more. The upper limit is not particularly limited, but may be, for example, 1000 μm or less.

A second aspect of the present invention is the invention according to the first aspect, wherein the surfactant (C) is a polyoxyethylene polyoxypropylene block polymer (PO-) having a polyoxypropylene (PO) terminal. EO-PO) nonionic surfactant, the EO ratio in the block polymer (PO-EO-PO) is in the range of 35% or more and 50% or less in terms of molar ratio, and the nonionic surfactant. An electrolytic plating solution having a mass average molecular weight in the range of 3000 or more and 5000 or less. The EO ratio may be in the range of 35% or more and 45% or less in terms of molar ratio, or may be in the range of 40% or more and 45% or less. The mass average molecular weight may be in the range of 3000 or more and 4500 or less, or may be in the range of 3500 or more and 4500 or less.

A third aspect of the present invention is the invention according to the first aspect, wherein the surfactant (C) is an electrolytic plating solution which is an amphoteric surfactant of alkylsulfobetaine or alkylhydroxysulfobetaine. ..

A fourth aspect of the present invention is the invention according to any one of the first to third aspects, wherein the content of the surfactant (C) is 0.5 g / L or more and 10 g / L. It is an electrolytic plating solution in the range of L or less. The content may be in the range of 1 g / L or more and 5 g / L or less.

A fifth aspect of the present invention is to supply the electroplating solution according to any one of the first to fourth aspects to a plating tank in which an insoluble anode is arranged so as to face a member to be plated connected to a cathode. This is a method of electrolytically plating the member to be plated. It is preferable that the facing surfaces are substantially parallel to each other.

A sixth aspect of the present invention is the invention according to the fifth aspect, which is an electrolytic plating method in which electrolytic plating is performed using a plating tank in which the member to be plated and the insoluble anode are horizontally arranged. The vertical relationship between the member to be plated and the insoluble anode is not limited, but it is preferable that the insoluble anode is located on the lower side and the member to be plated is located on the upper side.

In the electrolytic plating solution of the first aspect of the present invention, as shown in FIG. 1, when the anode current density is ^{electrolyzed at 0.7 A / dm 2} , the particle size distribution of the bubbles 8 released from the insoluble anode 3 is maximized. Since the value is 150 μm or more, it is difficult for bubbles 8 to enter the via 6 of the resist layer 5 formed by the resist pattern. Since the plating deposit layer grows to become bumps 7 in a state where the bubbles 8 do not adhere to the plating deposit layer in the via 6, the occurrence rate of pit defects and voids in the bumps caused by the non-precipitation of plating can be determined. Can be reduced. In FIG. 1, the same elements as those shown in FIG. 2 are designated by the same reference numerals.

In the electrolytic plating solution of the second aspect of the present invention, the surfactant (C) is a nonionic interface of a polyoxyethylene polyoxypropylene block polymer (PO-EO-PO) having a polyoxypropylene (PO) terminal. It is an activator, and the EO ratio in the block polymer (PO-EO-PO) is in the range of 35% or more and 50% or less in terms of molar ratio, and the mass average molecular weight of the nonionic surfactant is 3000 or more and 5000 or less. Is the range of. Since such a surfactant has a property intermediate between hydrophilicity and hydrophobicity, it has a strong adsorptive power to the surface of an insoluble anode and the surface of oxygen bubbles. As a result, as shown in FIG. 1, before the oxygen bubbles 8 generated on the surface of the anode (anode) 3 are released into the plating solution 2, they aggregate on the surface of the anode 3 and become huge, and from the anode 3. It is difficult for the released bubbles to enter the via 6 of the resist layer 5. As a result, the occurrence rate of pit defects and voids can be reduced.

In the electrolytic plating solution of the third aspect of the present invention, since the surfactant (C) is an amphoteric surfactant of alkylsulfobetaine or alkylhydroxysulfobetaine, the adsorption force on the surface of the insoluble anode and the surface of oxygen bubbles. Has the effect of being strong.

In the electrolytic plating solution of the fourth aspect of the present invention, the surfactant (C) is insoluble because the content of the surfactant (C) is in the range of 0.5 g / L or more and 10 g / L or less. A sufficient amount can be adsorbed on the surface of the anode and the surface of oxygen bubbles. As a result, the occurrence rate of pit defects and voids can be further reduced.

In the electroplating method of the fifth aspect of the present invention, since the maximum particle size distribution of the bubbles 8 released from the insoluble anode 3 by the electrolytic plating solution 2 is 150 μm or more, the object to be plated is arranged to face the insoluble anode 3. When the via 6 of the resist layer 5 is formed on the member 4, electrolytic plating is performed without the bubbles 8 being taken into the via. As a result, this plating method can reduce the occurrence rate of pit defects and voids.

In the electroplating method of the sixth aspect of the present invention, since the member 4 to be plated and the insoluble anode 3 are arranged horizontally, the bubbles 8 discharged from the insoluble anode 3 reach the upper member 4 to be plated. However, since the bubbles 8 are enormous, electrolytic plating is performed without the bubbles 8 being taken into the vias 6 of the resist layer 5 formed on the member 4 to be plated. As a result, this plating method can reduce the occurrence rate of pit defects and voids.

It is a schematic view of the electroplating apparatus which shows the situation which electroplating is performed using the electroplating liquid which concerns on this invention, and is the enlarged sectional view of the part of the member to be plated. It is a schematic view of the electrolytic plating apparatus which shows the situation which electroplating is performed using the conventional electroplating liquid, and is the enlarged cross-sectional view of the part of the member to be plated. It is a block diagram of the apparatus which measures the maximum value of the particle size distribution of the bubble emitted from an insoluble anode in an Example. It is a top view of the semiconductor wafer which has the resist layer produced in Example. It is sectional drawing which shows the growth state of the bump (plating deposit layer) in the via (opening) before and after plating. 5 (a) is a cross-sectional view of the member to be plated before plating, and FIG. 2 (b) is a cross-sectional view of the member to be plated in which normal mushroom-shaped bumps are formed. ) Is a cross-sectional view of the member to be plated in which the pit defect is formed. Further, FIG. 2 (e) is a cross-sectional view of the member to be plated in which voids are formed.

The electrolytic plating solution according to the embodiment of the present invention will be described below. This plating solution is used as a material for forming a plating film of tin or a tin alloy used as a solder bump for a semiconductor wafer or a printed circuit board.

The tin or tin alloy plating solution of the present embodiment is an electrolytic plating solution containing a soluble salt (A) containing at least a first tin salt, an acid or a salt thereof (B), and a surfactant (C). The feature is that when the anode current density is ^{electrolyzed at 0.7 A / dm 2} , the maximum particle size distribution of bubbles released from the insoluble anode is 150 μm or more, and may be 200 μm or more. The upper limit is not particularly limited, but may be, for example, 1000 μm or less. Here, the reason why the anode current density is ^{limited to 0.7 ASD (A / dm 2} ) is that pit defects and voids tend to become apparent at 0.7 ASD or more. Further, the maximum particle size distribution of bubbles discharged from the insoluble anode is set to 150 μm or more because the via diameter of the resist layer formed by the resist pattern of the member to be plated is generally in the range of 10 μm or more and less than 100 μm. By setting the maximum particle size distribution of bubbles to 150 μm or more, the probability that bubbles are taken into the plating deposit layer in the via is reduced, and as a result, the occurrence rate of pit defects and voids can be reduced. Is.

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 first tin 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⁺ , It contains one or more arbitrary soluble salts that generate various metal ions such as ^{Sb 3+} , In ³⁺ , and Zn ^2+. Examples of the soluble salt include oxides of these metals, halides, the metal salt of an inorganic acid or an organic acid, and the like.

Examples of metal oxides include stannous oxide, silver oxide, copper oxide, nickel oxide, bismuth oxide, antimony oxide, indium oxide, and zinc oxide. Examples of metal halides 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, antimonyate 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 ethanesulfonic acid, and bismuth 2-hydroxypropanesulfonic 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 20 g / L or more and 100 g / L or less in terms of the amount of tin. Is the range of.

[Acid or salt thereof (B)]
The acid or salt (B) thereof of the present embodiment is one or more acids selected from organic acids, inorganic acids, and salts thereof, or 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. Examples of the inorganic acid include borofluoric acid, silicate hydrofluoric acid, sulfamic acid, 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. Organic sulfonic acids are more preferable from the viewpoint of solubility of metal salts and 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 decanesulfon. Acids, dodecane sulfonic acids and the like can be mentioned.

The alkanolsulfonic acid has a chemical formula of C _p H _{2p + 1} -CH (OH) -C _q H _2q -SO ₃ H (for example, p = 0 to 6, q = 1 to 5, preferably p = 0 to 2). , Q = 1 to 2) 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., as well as 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 acid selected from the organic acid and the inorganic acid or the salt (B) thereof in the plating solution of the present embodiment is not particularly limited, but is, for example, in the range of 10 g / L or more and 500 g / L or less, preferably 50 g. It is preferably in the range of / L or more and 300 g / L or less.

[Surfactant (C)]
Examples of the surfactant (C) used in the plating solution of the present embodiment include a nonionic surfactant and an amphoteric surfactant. These two types of surfactants may be used alone or in combination.
The nonionic surfactant contains polyoxyethylene (EO) and polyoxypropylene (PO), and the terminal is polyoxypropylene (PO). Polyoxyethylene polyoxypropylene block polymer (PO-EO-PO) Can be used. The EO ratio in this block polymer (PO-EO-PO) is in the range of 35% or more and 50% or less in terms of molar ratio, and the mass average molecular weight of this nonionic surfactant is in the range of 3000 or more and 5000 or less. .. When the EO ratio is less than 35% in terms of molar ratio, the hydrophobic tendency of the surfactant becomes strong, and when it exceeds 50%, the hydrophilic tendency of the surfactant becomes strong, and in any case, it is released from the insoluble anode. It becomes difficult to make the maximum value of the particle size distribution of bubbles 150 μm or more. Further, if the mass average molecular weight of the surfactant is less than 3000, the effect of suppressing the precipitation of tin or a tin alloy may not be sufficient, and if it exceeds 5000, the effect of suppressing the precipitation of tin or a tin alloy becomes too strong, and uniform plating is performed. The film may not be formed. The EO ratio is preferably in the range of 35% or more and 45% or less in terms of molar ratio, and more preferably in the range of 40% or more and 45% or less. The mass average molecular weight is preferably in the range of 3000 or more and 4500 or less, and more preferably in the range of 3500 or more and 4500 or less.

The nonionic surfactant of this embodiment is represented by the following formula (1). In formula (1), a, b, and c are the number of repeating units of (PO), (EO), and (PO) in the block polymer, respectively.

Further, as the nonionic surfactant in the present embodiment, ethylenediamine polyoxyethylene obtained by addition polymerization of polyoxyethylene (EO) and polyoxypropylene (PO) to ethylenediamine and having polyoxypropylene (PO) at the end. Polyoxypropylene block polymer can also be used. The EO ratio in this block polymer is in the range of 35% or more and 50% or less in terms of molar ratio, and the mass average molecular weight of this surfactant is in the range of 3000 or more and 5000 or less. When the EO ratio is less than 35%, the hydrophobic tendency of the surfactant becomes strong, and when it exceeds 50%, the hydrophilic tendency of the surfactant becomes strong, and in any case, the particles of bubbles released from the insoluble anode. It becomes difficult to set the maximum diameter distribution value to 150 μm or more. Further, if the mass average molecular weight of the surfactant is less than 3000, the effect of suppressing the precipitation of tin or a tin alloy may not be sufficient, and if it exceeds 5000, the effect of suppressing the precipitation of tin or a tin alloy becomes too strong, and uniform plating is performed. The film may not be formed.

The nonionic surfactant of the present embodiment is also represented by the following formula (2). In formula (2), m and n are the number of repeating units of (PO), (EO) and (PO) in the block polymer, respectively.

The nonionic surfactant represented by the above structure is a block polymer containing polyoxyethylene (EO) and polyoxypropylene (PO), and when polyoxypropylene (PO) is present at the terminal, the surfactant is hydrophobic. It has the effect of strengthening the adsorption force to the insoluble anode and the surface of oxygen bubbles. On the contrary, in this block polymer, when polyoxyethylene (EO) is present at the terminal, there causes a problem that the adsorption force to the insoluble anode and the surface of oxygen bubbles is weakened because the hydrophilicity of the surfactant is strengthened. When the surfactant has these characteristics, when the anode current density is electrolyzed at 0.7 ASD, the maximum value of the particle size distribution of the bubbles released from the insoluble anode is set to 150 μm or more.
The EO ratio can be measured by comparing the intensity ratios of polyoxyethylene (EO) and polyoxypropylene (PO) using NMR (Nuclear Magnetic Resonance). This measuring method is described in detail in "Surfactant Analysis Method" edited by Surfactant Analysis Study Group, Koshobo (published in 1975), and the like.
In addition, the mass average molecular weight can be measured by comparing with a commercially available standard substance using Size Exclusion Chromatography (SEC).

The content of the nonionic surfactant in the plating solution should be in the range of 0.5 g / L or more and 10 g / L or less, and the EO ratio should be in the range of 35% or more and 50% or less in terms of molar ratio. In addition, the mass average molecular weight of the surfactant is in the range of 3000 or more and 5000 or less in order to more accurately set the maximum value of the particle size distribution of bubbles released from the insoluble anode to 150 μm or more. preferable. It is more preferable that the content of the nonionic surfactant in the plating solution is in the range of 1 g / L or more and 5 g / L or less. If the content of this surfactant is less than 0.5 g / L, the maximum value of the particle size distribution of bubbles discharged from the insoluble anode may not be 150 μm or more, and if it exceeds 10 g / L, a uniform plating film is formed. It may not be formed.

The nonionic surfactant of the present embodiment can be used by purifying a commercially available product as EP-461 manufactured by Aoki Oil & Fat Industry Co., Ltd. Further, the surfactant of the present embodiment can be produced by a known technique. For example, it can be synthesized by adjusting the molecular weight of the raw material polyoxyethylene in US Pat. No. 4,726,909 and the reaction amount of the polyoxypropylene to be added.

An amphoteric surfactant can be used as the surfactant (C) of the present embodiment. Specifically, for example, alkyl sulfobetaine or alkyl hydroxysulfobetaine can be used. The alkylsulfobetaine is represented by the following formula (3). For example, lauryl sulfobetaine, stearyl sulfobetaine and the like can be mentioned. The alkylhydroxysulfobetaine is represented by the following formula (4). For example, lauryl hydroxysulfobetaine and the like can be mentioned. In formulas (3) and (4), R represents an alkyl group, respectively. Further, the carbon number of R of alkylsulfobetaine or alkylhydroxysulfobetaine is preferably in the range of 10 or more and 22 or less, respectively. Further, when the content of these amphoteric surfactants in the electrolytic plating solution is in the range of 0.5 g / L or more and 10 g / L or less, the maximum value of the particle size distribution of bubbles released from the insoluble anode is determined. It is preferable to make it more accurately 150 μm or more. It is more preferable that the content of the amphoteric surfactant in the electrolytic plating solution is in the range of 1 g / L or more and 5 g / L or less. The reason why the preferable range of the amphoteric tenside content in the electrolytic plating solution is 0.5 g / L or more and 10 g / L or less is the same as the reason why the content of the nonionic surfactant is set to the preferable range. Is.

Since the surfactant (C) of the present embodiment has the above-mentioned characteristics, when the anode current density is electrolyzed with, for example, 0.7 ASD, the maximum particle size distribution of bubbles released from the insoluble anode is 150 μm or more. To. As a result, even in the via where the bump electrode is miniaturized to a diameter of 100 μm or less, it is difficult for air bubbles to enter the via of the resist layer, and the growth of the plating deposition layer in the via is smoothly performed without being disturbed by the air bubbles. Less likely to cause defects. In addition, it is difficult to generate voids in the plating deposit layer in the via. As a result, the height of the bumps formed when the plating deposit layer is reflowed becomes uniform, and the voids in the bumps are reduced.

By using the above-mentioned surfactant (C), the maximum particle size distribution of bubbles released from the insoluble anode can be set to 150 μm or more when ^{the anode current density is electrolyzed at 0.7 A / dm 2.} ..

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, fluoroglusinol, 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.

One type of antioxidant 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 or more and 20 g / L or less, preferably in the range of 0.1 g / L or more and 10 g / L or less, more preferably 0. It is in the range of 1 g / L or more and 5 g / L or less.

[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 precipitation in the vicinity of acidic to neutral (pH: 1 to 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 necessary 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, glycines, nitrilotrimethylphosphonic acid, 1-hydroxyethane-1, Polyamines and aminocarboxylic acids such as 1-diphosphonic acid or salts thereof are also effective as compositing agents.

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

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, 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.

[Glossing agent]
The plating solution of the present embodiment may contain a brightener, if necessary. As the brightener, an aromatic carbonyl compound is effective. The aromatic carbonyl compound has an action of refining the crystal particles of the tin alloy in the tin alloy plating film. 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 (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. The carbonyl group may be directly linked to an aromatic hydrocarbon, or may be bonded via an alkylene group having 1 or more carbon atoms and 6 or less 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 preferably in the range of 0.01 mg / L or more and 500 mg / L or less. It is more preferably 0.1 mg / L or more and 100 mg / L or less, and even more preferably 1 mg / L or more and 50 mg / L or less.

[Electroplating method]
The electroplating method of the present embodiment is performed using the electroplating apparatus shown in FIG. In the plating tank 1 of this apparatus, an insoluble anode 3 is arranged to face a member to be plated connected to a cathode, for example, a semiconductor wafer 4. The above-mentioned electrolytic plating solution 2 is supplied to the plating tank 1 to perform electrolytic plating. The effect of the present invention is further exhibited in a horizontal plating apparatus in which the insoluble anode 3 is horizontally arranged on the semiconductor wafer 4. In this electrolytic plating apparatus, it is preferable that the facing surfaces of the member 4 to be plated and the insoluble anode 3 are substantially parallel to each other. Further, the vertical relationship between the member to be plated and the insoluble anode is not limited, but as shown in FIG. 1, arranging the insoluble anode on the lower side and the member to be plated on the upper side facilitates replacement of the member to be plated. , Preferable from the viewpoint of mass productivity.
Anode current density at the time of forming the plating film of this embodiment, or equal to 0.1 A / dm ² or more and 5A / dm ² or less. The liquid temperature 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.

(Nonion-based surfactant used in Examples and Comparative Examples)
Polyoxyethylene polyoxypropylene block polymer (PO-EO-PO) or (EO-) containing polyoxyethylene (EO) and polyoxypropylene (PO) used in Examples 1 to 5 and Comparative Examples 1 to 5. Table 1 shows the structural formula of PO-EO), the EO ratio, and the mass average molecular weight of the surfactant.

(Nonion-based surfactant and amphoteric surfactant used in Examples)
Table 2 shows the surfactants used in Examples 6 to 9.

(Sn plating solution construction bath)
<Example 1>
The methanesulfonic acid Sn aqueous solution has methanesulfonic acid as a free acid and the structural formula (PO-EO-PO) shown in Table 1 above as a surfactant, and the EO ratio is 35% in terms of molar ratio, and the mass average. A nonionic surfactant having a molecular weight of 4000 and benzalacetone as a brightener were added. Finally, ion-exchanged water was added to bathe the 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
Surfactant: 5g / L
Benzalacetone (as a brightener): 10 mg / L
Ion-exchanged water: balance

<Examples 2 to 4, Comparative Examples 1 to 5>
In Examples 2 to 4 and Comparative Examples 1 to 5, the structural formula (PO-EO-PO) or (EO-PO-EO), the EO ratio, and the mass average molecular weight are the properties shown in Table 1 above as the surfactant. A nonionic surfactant was used. Other than that, the Sn plating solutions of Examples 2 to 4 and Comparative Examples 1 to 5 were bathed in the same manner as in Example 1.

(SnAg plating solution construction bath)
<Example 5>
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 methanesulfonic acid Ag solution was further added and mixed. After becoming a uniform solution by mixing, it further has the structural formula (PO-EO-PO) shown in Table 1 above as a surfactant, the EO ratio is 50% in molar ratio, and the mass average molecular weight is 5000. A nonionic surfactant and benzalacetone as a brightener were added. Finally, ion-exchanged water was added to bathe the 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
Ion-exchanged water: balance

<Example 6>
As the surfactant, the nonionic surfactant 1 shown in Comparative Example 4 of Table 1 above and the amphoteric surfactant 2 of lauryl hydroxysulfobetaine (12 carbon chains) shown in Table 2 above were used.
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 methanesulfonic acid Ag solution was further added and mixed. After mixing to obtain a uniform solution, the above-mentioned surfactant 1, the above-mentioned surfactant 2, and benzalacetone as a brightening agent were further added. Finally, ion-exchanged water was added to bathe the 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
Nonionic surfactant 1: 5g / L
Amphoteric surfactant 2: 2 g / L
Benzalacetone (as a brightener): 10 mg / L
Ion-exchanged water: balance

<Example 7>
A SnAg plating solution having the same composition as that of Example 6 was used in the bath, except that the amphoteric surfactant 2 of Example 6 was replaced with lauryl sulfobetaine.

<Example 8>
A SnAg plating solution having the same composition as that of Example 6 was used in the bath, except that the amphoteric tenside agent 2 of Example 6 was replaced with stearyl sulfobetaine.

<Example 9>
A SnAg plating solution having the same composition as that of Example 6 was used in the bath, except that the methanesulfonic acid Ag and the nonionic surfactant were removed from Example 6.

<Comparative tests and evaluations>
Using each of the 14 types of plating solutions in Examples 1 to 9 and Comparative Examples 1 to 5, (1) the maximum particle size distribution of bubbles released from the insoluble anode, and (2) the pit after plating. The defect generation rate and (3) void generation rate in the bumps were measured by the following methods.
These results are shown in Table 1 above and Table 3 below.

(1) Measurement of Maximum Particle Size Distribution of Bubbles Released from Insoluble Anode First, an apparatus for measuring the maximum particle size distribution of bubbles will be described with reference to FIG. The plating tank 11 is a tank for performing face-down type (Fountain type) plating, and has a cylindrical shape with an inner diameter of 35 cm and a depth of 50 cm. The height from the bottom surface to the liquid surface was 35 cm. As the insoluble anode (anode) 13, a Pt / Ti disk having a diameter of 300 mm in which a Pt layer having a thickness of 3 μm was formed on a Ti plate having a thickness of 1.5 mm was used and installed so as to be in contact with the bottom surface in the plating tank 11. A pipe 11a serving as a suction port for the circulation pump 11c was installed at a height of 5 cm from the bottom surface of the plating tank 11. On the side wall facing the pipe 11a, a pipe 11b serving as a return port was installed at a position 5 cm in height from the bottom surface. The circulation pump 11c and the pipe 11b serving as the return port were connected by the pipe 11d. A sampling pipe 11e was branched from the pipe 11d, and a transparent measurement cell 11f was installed in the middle of the sampling pipe 11e. In this measuring cell 11f, 11 g of a VisiSize particle size distribution measuring device (manufactured by Oxford Lasers, device model number: SF, analysis software: SOLO) for measuring the size (particle size) of bubbles passing through the measuring cell was installed. .. The inner diameters of the pipes 11a, 11b and 11d were 60 mm, and the inner diameter of the sampling pipe 11e was 40 mm.

After the plating solution 12 was put into the plating tank 11, a silicon wafer 14 having a diameter of 300 mm was fixed in the plating tank 11 as shown in FIG. 3 using a cylindrical jig having an outer diameter of 33 cm (not shown). .. Specifically, the wafer 14 was fixed by immersing the wafer 14 so that the lower surface of the wafer 14 was immersed at a depth of 2 cm from the liquid surface of the plating solution 12. The wafer 14 was connected to the cathode, and the plating solution 12 was stirred by horizontally rotating at a rotation speed of 50 rpm in order to suppress the generation of bubbles due to stirring.

In order to separate the generation of bubbles due to the circulation of the plating solution and the oxygen bubbles generated from the insoluble anode by electroplating, the circulation pump 11c was first operated for 10 minutes without electroplating, and the pipes 11d and 11e After filling the inside with the plating solution 12, the circulation pump 11c was stopped and allowed to stand for 1 hour for degassing. Next, the plating solution was circulated by the circulation pump 11c for 1 hour, and it was confirmed that the number of bubbles having a diameter of 10 μm or less passing through the measurement cell was 100 cells / mL or less. The flow rate in the pipe 11d was set to 5 L / min, and the flow rate in the sampling pipe 11e was controlled to 0.5 L / min to circulate the plating solution 12. Then, the liquid temperature of the plating solution 12 was set to 25 ° C. and the anode current density was set to 0.7 ASD, respectively, and electrolytic plating was performed for 30 minutes.

During the electrolytic plating, as shown in FIG. 3, oxygen bubbles 18 were generated from the insoluble anode 13. The air bubbles 18 were sucked into the suction port pipe 11a, passed through the pipes 11d and 11e, and floated in the plating solution from the return port pipe 11b toward the wafer 14. The size (particle size) of the bubbles 18 passing through the measurement cell 11f was measured by the particle size distribution measuring device 11g described above. The maximum value of the particle size distribution of the measured bubbles is shown in Tables 1 and 3 above. When the particle size distribution has two or more maximum values (so-called two or more peaks), the largest peak is set as the maximum value.

(2) Measurement of pit defect occurrence rate after plating Titanium 0.1 μm and copper 0.3 μm are laminated in this order on the surface of a silicon wafer with a diameter of 300 mm by a sputtering method to form a seed layer for electrical conduction, and the seed layer is formed. A dry film resist (thickness 50 μm) was laminated on top of it. The dry film resist was then partially exposed via an exposure mask and then developed. In this way, as shown in FIG. 4, a resist layer 5 having a pattern in which 1.6 million vias 6 having openings having a diameter of 75 μm are formed at a pitch of 150 μm is formed on the surface of the wafer 4.

Using the plating apparatus shown in FIG. 1, the temperature of the plating solution was set to 25 ° C. and the anode current density was set to 0.7 ASD, and the via 6 of the resist layer 5 was electrolytically plated with a target plating film thickness of 75 μm. Next, the wafer 4 was taken out from the plating tank 1, washed and dried, and then the resist layer 5 was peeled off using an organic solvent. In this way, a bumped wafer having a pattern in which bumps having a diameter of 75 μm are arranged at a pitch of 150 μm and 1.6 million at equal pitch intervals was produced on one die.

FIG. 5 (a) shows the wafer 4 before plating, and FIGS. 5 (b) to 5 (e) show the wafer 4 after plating. In FIG. 5, the same elements as those in FIGS. 1, 2 and 4 are designated by the same reference numerals. In FIGS. 5 (b) to 5 (e), reference numeral 7 is a bump which is a plating deposit layer. The heights of 1.6 million bumps on this wafer were measured using an automatic visual inspection device (Camtek, model number Falcon). From the measured bump height, the pit defect occurrence rate in the bump was calculated by the following formula. As shown in FIGS. 5 (b), bumps plated thicker than the surface of the resist 5 and having a mushroom-shaped cross section are counted as "normal bumps" and as shown in FIGS. 5 (c) and 5 (d). In addition, ungrown bumps (the thickness of the plating film is less than 50 μm, that is, less than about 67% of the target plating film thickness) that does not reach the surface of the resist 5 and whose cross section is not mushroom-shaped have “pit defects”. Counted as defective bumps. Then, the pit defect occurrence rate was calculated by the following formula. The results are shown in Tables 1 and 3 above.
Pit defect occurrence rate (ppm) = (number of defect bumps / total number of bumps) x 10 ⁶

(3) Measurement of void generation rate in bumps After calculating the pit defect generation rate, the void generation rate was measured. The seed layer for electrical conduction of the wafer after plating was removed by etching, and the wafer was reflowed. FIG. 5 (e) shows the void 9b in the bump 7 formed before the reflow. Using a transmission X-ray apparatus (manufactured by Dage), 5000 bumps on the reflowed wafer were observed from above and inspected for the presence of voids. Here, the case where the void area with respect to the bump area (maximum horizontal cross-sectional area of the bump) is 1% or more is counted as a "bump with a void", and the void generation rate is calculated based on the following equation.
Void generation rate (%) = (number of bumps with voids / number of total bumps) x 10 ²
The results are shown in Tables 1 and 3 above.

As is clear from Table 1, in the plating solution of Comparative Example 1, the maximum value of the particle size distribution of bubbles released from the insoluble anode was as small as 51 μm. Therefore, out of the total number of bumps of 1.6 million, the number of bumps having pit defects was 762, and the pit defect occurrence rate was as high as 476 ppm. The number of bumps having voids having a void area of 1% or more was 4, and the void generation rate was 0.1% with respect to the total number of bumps of 5000.

In the plating solution of Comparative Example 2, the maximum value of the particle size distribution of bubbles was as small as 40 μm. Therefore, the number of bumps having pit defects was 857, and the pit defect occurrence rate was as high as 536 ppm. The number of bumps with voids having a void area of 1% or more was 53, and the void occurrence rate was 1.1%.

In the plating solution of Comparative Example 3, the maximum value of the particle size distribution of bubbles was as small as 25 μm. Therefore, the number of bumps having pit defects was 1073, and the pit defect occurrence rate was as high as 671 ppm. The number of bumps with voids having a void area of 1% or more was 126, and the void occurrence rate was 2.5%.

In the plating solution of Comparative Example 4, the maximum value of the particle size distribution of bubbles was as small as 83 μm. Therefore, the number of bumps having pit defects was 135, and the pit defect occurrence rate was as high as 84 ppm. The number of bumps with voids having a void area of 1% or more was 6, and the void occurrence rate was 0.1%.

Further, in the plating solution of Comparative Example 5, although it was a surfactant having a structural formula of PO-EO-PO, the maximum value of the particle size distribution of bubbles was as small as 62 μm. Therefore, the number of bumps having pit defects was 387, and the pit defect occurrence rate was as high as 242 ppm. The number of bumps with voids having a void area of 1% or more was 18, and the void occurrence rate was 0.4%.

On the other hand, as shown in Tables 1 and 3, the plating solutions of Examples 1 to 9 had a large maximum value of the particle size distribution of bubbles of 150 μm or more, and therefore, in the bumps formed from these plating solutions. The pit defect occurrence rate was extremely low at 0 ppm to 15 ppm. The void occurrence rate was 0%.

From the above results, according to the present invention, even if the bump electrode is made finer to a diameter of 100 μm or less and the depth of the resist pattern with respect to the diameter of the via is increased, the plating is deposited due to air bubbles generated in the plating solution. It was confirmed that the occurrence rate of pit defects and voids in the tin-containing bumps was reduced without being hindered.

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. Therefore, it can be used industrially.

1, 11 Plating tank 1a Suction port 11a Piping 1b Return port 11b Piping 1c, 11c Circulation pump 11d Piping 11e Sampling piping 11f Measuring cell 11g Grain size distribution measuring device 2, 12 Plating liquid 3, 13 Insoluble anode 4, 14 Wafer (subject) Plating member)
5 Resist layer 6 Via (opening)
7 bumps (plating deposit layer)
8, 18 Bubbles 9a Pit defect 9b Void

Claims (6)

1. An electrolytic plating solution containing a soluble salt (A) containing at least a stannous salt, an acid or a salt thereof (B), and a surfactant (C).
   An electroplating solution characterized in that the maximum particle size distribution of bubbles discharged from an insoluble anode when electrolyzed at an anode current density of 0.7 A / dm ^{2 is 150 μm or more.}
2. The surfactant (C) is a nonionic surfactant of a polyoxyethylene polyoxypropylene block polymer (PO-EO-PO) having a polyoxypropylene (PO) terminal at the end.
   The EO ratio in the block polymer (PO-EO-PO) is in the range of 35% or more and 50% or less in terms of molar ratio.
   The electrolytic plating solution according to claim 1, wherein the mass average molecular weight of the nonionic surfactant is in the range of 3000 or more and 5000 or less.
3. The electrolytic plating solution according to claim 1, wherein the surfactant (C) is an alkylsulfobetaine or an amphoteric surfactant of alkylhydroxysulfobetaine.
4. The plating solution according to any one of claims 1 to 3, wherein the content of the surfactant (C) is in the range of 0.5 g / L or more and 10 g / L or less.
5. A method of electrolytically plating the member to be plated by supplying the electrolytic plating solution according to any one of claims 1 to 4 to a plating tank in which an insoluble anode is arranged so as to face the member to be plated connected to the cathode.
6. The electrolytic plating method according to claim 5, wherein electroplating is performed using a plating tank in which the member to be plated and the insoluble anode are horizontally arranged.

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