Patent Description:
In the related art, as a method for producing this kind of tin methanesulfonic acid aqueous solution, (<NUM>) a method of subjecting stannous oxide powder and methanesulfonic acid to a neutralization reaction (hereinafter, referred to as a neutralization method), and (<NUM>) a method of electrolytically dissolving a tin metal in methanesulfonic acid (hereinafter, referred to as an electrolytic method) are known. A commercially available tin methanesulfonic acid aqueous solution contains tin having a concentration of <NUM>/L to <NUM>/L and free methanesulfonic acid (hereinafter, also simply referred to as a free acid) having a concentration of <NUM>/L to <NUM>/L.

In general, in a case where an insoluble electrode is used in an electrolytic tin plating bath of a tin methanesulfonic acid aqueous solution, tin ions consumed for plating are fed in the electrolytic plating bath, or a bleed-and-feed operation is performed in which a solution is drained from the electrolytic plating bath and a new tin methanesulfonic acid aqueous solution is added in order to reduce a concentration of free methanesulfonic acid generated by electrolysis.

On the other hand, as a method for preparing an electrolytic tin plating bath, a method is disclosed for chemically dissolving metal tin using a methanesulfonic acid solution having a concentration of <NUM>/L to <NUM>/L as an acidic solution for dissolving the tin by blowing an oxygen-containing gas into a solid-solution flow tank of metal tin particles and an acidic solution, and bringing three-phases of solid, liquid, and gas, which are metal tin particles, an electrolytic tin plating solution, and an oxygen-containing gas, respectively, into contact with one another when preparing an electric tin plating solution for chemically dissolving the metal tin in the acidic solution (Patent Document <NUM>).

Further, documents <CIT>, <CIT>, <CIT> and <CIT> disclose high-concentration tin sulfonate aqueous solutions.

In the method disclosed in Patent Document <NUM>, the methanesulfonic acid solution having a concentration of <NUM>/L to <NUM>/L is used as the acidic solution, and the oxygen-containing gas is blown into the tank to chemically dissolve the metal tin. Therefore, there was a possibility that the metal tin dissolved solution dissolved by this methanesulfonic acid solution has a dissolved oxygen level of <NUM> ppm or more, so that the oxidation of divalent tin ions (Sn<NUM>+) is promoted, the concentration of tetravalent tin ions (Sn<NUM>+) is increased, tin dioxide (SnO<NUM>) is generated, and the solution is turbid. Furthermore, in a case where the above-described bleed-and-feed operation is performed, the amount of a bled solution (hereinafter, referred to as the bled solution amount) increases when a concentration of tin in the tin methanesulfonic acid aqueous solution is low or when a concentration of the free methanesulfonic acid is high, so that there was a problem in that process cost increases. Therefore, the tin methanesulfonic acid aqueous solution having a high concentration of tin and a low concentration of free methanesulfonic acid has been desired for use in an initial make-up of an electrolytic bath or a feed of the electrolytic tin plating solution.

However, in a case where the concentration of tin is increased for the above-described use, in the neutralization method of (<NUM>) described above, there was a problem in that the concentration of tetravalent tin ions (Sn<NUM>+) is increased and tin dioxide (SnO<NUM>) is generated, thereby the solution being turbid. In the electrolytic method of (<NUM>) described above, in order to increase the electrolytic dissolution efficiency of the tin metal, the concentration of free methanesulfonic acid is required to be increased, thereby reducing the solubility of tin methanesulfonic acid, and there was a possibility that tin methanesulfonic acid crystals are precipitated during storage of the solution.

An object of the present invention is to provide a high-concentration tin sulfonate aqueous solution that is transparent, does not deteriorate plating performance, requires a small amount of a feed solution in a case of the feed solution, and has excellent storage stability that crystals are not precipitated even during storage. Another object of the present invention is to provide a method for producing such a high-concentration tin sulfonate aqueous solution.

As a result of diligent studies to improve the neutralization method of (<NUM>) described above, the present inventors have focused on the fact that since the turbidity of the solution is caused by an increase in the concentration of tetravalent tin ions (Sn<NUM>+), in a case where neutralization heat generated when stannous oxide and methanesulfonic acid are reacted is suppressed, the oxidation of divalent tin ions (Sn<NUM>+) is suppressed, and the concentration of tetravalent tin ions (Sn<NUM>+) is lowered, and the solution is not turbid, and the present invention has been achieved.

In a first aspect of the present invention, a high-concentration tin sulfonate aqueous solution is provided in which a divalent tin ion (Sn<NUM>+) concentration is <NUM>/L to <NUM>/L, a tetravalent tin ion (Sn<NUM>+) concentration is <NUM>/L or less, a free methanesulfonic acid concentration is <NUM>/L or less, a concentration of chloride ions is <NUM>/L or less, a Hazen unit color number (APHA) measured in accordance with JIS K0071-<NUM> (<NUM>) is <NUM> or less, and a turbidity measured using an integrating sphere photoelectric photometry method conforming to JIS K <NUM>-<NUM> is <NUM> FTU or less, a total content of the plurality of kinds of metals is <NUM>/L or less in terms of metal, the plurality of kinds of metals including sodium, potassium, lead, iron, nickel, copper, zinc, arsenic, antimony, aluminum, silver, bismuth, magnesium, calcium, titanium, chromium, manganese, cobalt, indium, tungsten, thallium, and cadmium, a content of each of the plurality of kinds of metals is <NUM>/L or less in terms of metal.

In a second aspect of the present invention, a method for producing the high-concentration tin sulfonate aqueous solution according to any one of the first aspect is provided by subjecting stannous oxide powder and methanesulfonic acid to a neutralization reaction, the method including a step of diluting the methanesulfonic acid with pure water to obtain an aqueous methanesulfonic acid solution having a concentration of <NUM>% by mass to <NUM>% by mass, a step of causing the aqueous methanesulfonic acid solution to circulate in a state of being maintained at a temperature of <NUM> or lower, and a step of adding stannous oxide powder whose temperature is adjusted to a temperature of <NUM> or lower to the circulating aqueous methanesulfonic acid solution, and dissolving the stannous oxide powder, wherein the stannous oxide powder contains impurities of a plurality of kinds of metals, a total content of the plurality of kinds of metals is <NUM>/L or less in terms of metal, the plurality of kinds of metals includes sodium, potassium, lead, iron, nickel, copper, zinc, arsenic, antimony, aluminum, silver, bismuth, magnesium, calcium, titanium, chromium, manganese, cobalt, indium, tungsten, thallium, and cadmium, a content of each of the plurality of kinds of metals is <NUM>/L or less in terms of metal, the stannous oxide powder contains chloride ions, and a content of the chloride ions is <NUM>/L or less.

In a third aspect of the present invention according to the second aspect, the method for producing the high-concentration tin sulfonate aqueous solution is provided in which the circulating aqueous methanesulfonic acid solution is bubbled with nitrogen gas and/or degassed with a hollow fiber membrane degassing module is provided.

In the high-concentration tin sulfonate aqueous solution of the first aspect of the present invention, since the divalent tin ions (Sn<NUM>+) have a concentration of <NUM>/L to <NUM>/L, the tetravalent tin ions (Sn<NUM>+) have a concentration of <NUM>/L or less, and the free methanesulfonic acid has a concentration of <NUM>/L or less, the bled solution amount is small in a case where the above-described bleed-and-feed operation is performed after the initial make-up of an electrolytic bath of the electrolytic tin plating solution in this aqueous solution is performed. As a result, in a case of using a feed solution, the amount of the feed solution is small, and the process cost is not increased. In addition, since the concentration of tetravalent tin ions (Sn<NUM>+) is as low as <NUM>/L or less, the solution is not turbid, the Hazen unit color number (APHA) is <NUM> or less, the turbidity is <NUM> FTU or less, and the solution is transparent. In addition, the high-concentration tin sulfonate aqueous solution has excellent storage stability since tin methanesulfonic acid crystals are not precipitated during low-temperature storage. Furthermore, the number of particles generated in the solution due to the generation of tin dioxide (SnO<NUM>) is small, and the quality of semiconductor products is improved.

In the high-concentration tin sulfonate aqueous solution according to the present invention, even when the high-concentration tin sulfonate aqueous solution contains impurities of the plurality of kinds of metals, the total content thereof is as small as <NUM>/L or less in terms of metal, and in the high-concentration tin sulfonate aqueous solution according to the fourth aspect, the content of each of the plurality of kinds of metals is as small as <NUM>/L or less in terms of metal. Therefore, the present invention has the advantage that the plating performance does not deteriorate.

In the high-concentration tin sulfonate aqueous solution according to the present invention, even in a case where sodium or the like that adversely affects the quality of semiconductor products is used as one of the plurality of kinds of metals, since the total content of these metals is as small as <NUM>/L or less in terms of metal, the plating performance does not deteriorate, and this aqueous solution is preferable to improve the quality of semiconductor products in a case of being used for semiconductor applications.

In the high-concentration tin sulfonate aqueous solution according to the present invention, even in a case where the high-concentration tin sulfonate aqueous solution contains chloride ions, since the content thereof is as small as <NUM>/L or less, the plating performance does not deteriorate, and this aqueous solution is preferable to improve the quality of semiconductor products in a case of being used for semiconductor applications.

In the method for producing the high-concentration tin sulfonate aqueous solution according to the second aspect of the present invention, the methanesulfonic acid is diluted with pure water to obtain the aqueous methanesulfonic acid solution having the concentration of <NUM>% by mass to <NUM>% by mass, the stannous oxide powder whose temperature is adjusted to a temperature of <NUM> or lower is then added to this aqueous solution in a state of being circulated at a temperature of <NUM> or lower, and the aqueous methanesulfonic acid solution and the stannous oxide are subjected to a neutralization reaction in the low-temperature state. Therefore, neutralization heat can be suppressed. As a result, the oxidation of divalent tin ions (Sn<NUM>+) is suppressed, the concentration of tetravalent tin ions (Sn<NUM>+) is lowered, and the production of tin dioxide (SnO<NUM>) is suppressed, so that the solution is not turbid.

In the method for producing the high-concentration tin sulfonate aqueous solution according to the third aspect of the present invention, the circulating aqueous methanesulfonic acid solution is bubbled with nitrogen gas and/or degassed with a hollow fiber membrane degassing module, so that the dissolved oxygen amount in the solution can be reduced. As a result, the oxidation of divalent tin ions (Sn<NUM>+) is further suppressed, the concentration of tetravalent tin ions (Sn<NUM>+) is further lowered, and the production of tin dioxide (SnO<NUM>) is further suppressed, so that the solution is not turbid.

In the method for producing the high-concentration tin sulfonate aqueous solution according to the present invention, the stannous oxide contains only a small amount of impurities of the plurality of kinds of metals in terms of metal equivalent of <NUM>/L or less, and in the method for producing the high-concentration tin sulfonate aqueous solution according to the present invention, since each of the plurality of kinds of metals, having only as small a content as <NUM>/L or less, is contained in terms of metal, it is possible to produce the tin sulfonate aqueous solution in which the content of the impurity metals is reduced in the obtained aqueous solution and the plating performance does not deteriorate.

In the method for producing the high-concentration tin sulfonate aqueous solution according to the present invention, even in a case where sodium and the like are used as the plurality of kinds of metals contained in the stannous oxide, which adversely affects the quality of semiconductor products, since the total content of these metals is as small as <NUM>/L or less in terms of metal, it is possible to produce the tin sulfonate aqueous solution that does not deteriorate the plating performance.

In the method for producing the high-concentration tin sulfonate aqueous solution according to the present invention, since the stannous oxide containing only as small as <NUM>/L or less of chloride ions is used, it is possible to produce the tin sulfonate aqueous solution that does not cause the plating performance to deteriorate due to the reduction of the chloride ion concentration of the obtained aqueous solution.

Embodiments for carrying out the present invention will be described.

A high-concentration tin sulfonate aqueous solution of the present embodiment includes divalent tin ions (Sn<NUM>+) having a concentration of <NUM>/L to <NUM>/L, tetravalent tin ions (Sn<NUM>+) having a concentration of <NUM>/L or less, and free methanesulfonic acid having a concentration of <NUM>/L or less.

When the high-concentration tin sulfonate aqueous solution contains impurities of a plurality of kinds of metals, a total content of the plurality of kinds of metals is <NUM>/L or less in terms of metal. A content of each of the plurality of kinds of metals is <NUM>/L or less in terms of metal. When the high-concentration tin sulfonate aqueous solution contains chloride ions, a content of the chloride ions is <NUM>/L or less.

In a case where a concentration of the divalent tin ions (Sn<NUM>+) is less than <NUM>/L, there is a problem in that the bled solution amount increases in a case where the above-described bleed-and-feed operation is performed after an initial make-up of an electrolytic bath is performed on an electrolytic tin plating solution with this aqueous solution. In a case where the concentration is more than <NUM>/L, stannous oxide powder is not dissolved and is precipitated during storage. A preferred range of the concentration of divalent tin ions (Sn<NUM>+) is <NUM>/L to <NUM>/L, and a more preferred range is <NUM>/L to <NUM>/L.

In a case where a concentration of the tetravalent tin ions (Sn<NUM>+) of this aqueous solution is more than <NUM>/L, the aqueous solution is white turbid, and in a case where plating is performed with a plating solution that has been subjected to an initial make-up of an electrolytic bath with such an aqueous solution or a plating solution obtained using such an aqueous solution as a feed solution, plating performance deteriorates. A preferred range of the concentration of the tetravalent tin ions (Sn<NUM>+) is <NUM>/L or less, and a more preferred range is <NUM>/L or less. In addition, in a case where a concentration of the free methanesulfonic acid is more than <NUM>/L, there are problems in that the bled solution amount increases in a case where the above-described bleed-and-feed operation is performed after the initial make-up of an electrolytic bath is performed on an electrolytic tin plating solution with this aqueous solution, and tin methanesulfonic acid is precipitated during storage of this aqueous solution (specifically, during storage at the low temperature of -<NUM> or lower) since solubility of the tin methanesulfonic acid decreases. A preferred range of the concentration of the free methanesulfonic acid is <NUM>/L to <NUM>/L, and a more preferred range is <NUM>/L to <NUM>/L.

In a case where the total content of impurities of the plurality of kinds of metals in this aqueous solution is more than <NUM>/L in terms of metal, and in a case where a content of chloride ions is more than <NUM>/L, the plating performance may deteriorate since metal impurities and chloride ions are involved in a plating reaction. The content of the chloride ions preferably is <NUM>/L or less.

The plurality of kinds of metals constituting the metal impurities includes sodium, potassium, lead, iron, nickel, copper, zinc, arsenic, antimony, aluminum, silver, bismuth, magnesium, calcium, titanium, chromium, manganese, cobalt, indium, tungsten, thallium, and cadmium. In a case where a large amount of such a metal is contained in the plating solution, the plating performance may deteriorate. In the high-concentration tin sulfonate aqueous solution of the present embodiment, the total content of the plurality of kinds of metals as described above is <NUM>/L or less, and preferably <NUM>/L. Since the total content of the plurality of kinds of metals is such a small amount, the plating performance is less likely to deteriorate in a case where the aqueous solution of the present embodiment is used as a solution for an initial make-up of an electrolytic bath of the plating solution and/or as a feed solution. The content of each of the plurality of kinds of metals is <NUM>/L or less, and preferably <NUM>/L, as described above, in terms of metal. Since the content of each of the plurality of kinds of metals is such a small amount, the plating performance is even more less likely to deteriorate in a case where the aqueous solution of the present embodiment is used as a solution for an initial make-up of an electrolytic bath of the plating solution and/or as a feed solution.

In the high-concentration tin sulfonate aqueous solution of the present embodiment, since the concentration of the divalent tin ions (Sn<NUM>+), the concentration of the tetravalent tin ions (Sn<NUM>+), and the concentration of the free methanesulfonic acid are within the above ranges, a Hazen unit color number (APHA) measured in accordance with JIS K0071-<NUM> (<NUM>) is <NUM> or less. The Formazin turbidity obtained by a turbidity measurement with an integrating sphere photoelectric photometry method conforming to JIS K <NUM>-<NUM> is <NUM> FTU or less.

The high-concentration tin sulfonate aqueous solution of the present embodiment includes a step of diluting methanesulfonic acid with pure water to obtain an aqueous methanesulfonic acid solution having a concentration of <NUM>% by mass to <NUM>% by mass, a step of causing the aqueous methanesulfonic acid solution to circulate in a state of being maintained at a temperature of <NUM> or lower, and a step of adding stannous oxide powder whose temperature is adjusted to a temperature of <NUM> or lower to the circulating aqueous methanesulfonic acid solution, and dissolving the stannous oxide powder.

The reason why a concentration of the methanesulfonic acid in the aqueous methanesulfonic acid solution is <NUM>% by mass to <NUM>% by mass is that in a case of exceeding this concentration range, when the tin methanesulfonic acid aqueous solution is finally prepared, the concentration of divalent tin ions (Sn<NUM>+) is not within <NUM>/L to <NUM>/L. The concentration of methanesulfonic acid in the aqueous methanesulfonic acid solution is adjusted by diluting commercially available methanesulfonic acid with pure water. As the pure water, ion-exchanged water, distilled water, or the like can be used. A preferred concentration is <NUM>% by mass to <NUM>% by mass, and a more preferred concentration is <NUM>% by mass to <NUM>% by mass. Next, this aqueous methanesulfonic acid solution is placed into a neutralization tank equipped with a cooling device and caused to circulate by the cooling device in a state of being maintained at a temperature of <NUM> or lower, and preferably <NUM> or lower. As the cooling device, for example, a chiller can be used. Then, the high-concentration tin sulfonate aqueous solution can be obtained such that stannous oxide is added to the aqueous methanesulfonic acid solution being circulated at a temperature of <NUM> or lower and is dissolved. The stannous oxide is powder. Here, a temperature of the stannous oxide powder is adjusted to a temperature of <NUM> or lower. Since the stannous oxide powder is added at <NUM> or lower, neutralization heat generated during neutralization reaction between the aqueous methanesulfonic acid solution and stannous oxide can be suppressed. As a result, the oxidation of divalent tin ions (Sn<NUM>+) is suppressed, the concentration of tetravalent tin ions (Sn<NUM>+) is lowered, and the production of tin dioxide (SnO<NUM>) is suppressed, so that the solution is not turbid.

It is preferable to maintain the temperature of the aqueous methanesulfonic acid solution at <NUM> or lower even during dissolution.

The stannous oxide added to the aqueous methanesulfonic acid solution reduces the content of each of the metal impurities and chloride ions in the aqueous methanesulfonic acid solution, and prevents the plating performance from being deteriorated. Therefore, in a case where impurities of the plurality of kinds of metals or chloride ions are contained, the total content of the plurality of kinds of metals is <NUM>/L or less and more preferably <NUM>/L or less in terms of metal. In addition, the content of each of the plurality of kinds of metals is <NUM>/L or less, and preferably <NUM>/L or less in terms of metal. Furthermore, it is preferable to use stannous oxide having chloride ions of <NUM> ppm or less, and even more preferable to use stannous oxide having chloride ions of <NUM> ppm or less. The stannous oxide having such quality can be obtained by, for example, the method described in <CIT>. In this method, stannous hydroxide is produced by subjecting a stannous salt acidic aqueous solution and a stannous salt alkaline aqueous solution to a neutralization reaction, and performing dehydration to produce stannous oxide. Specifically, the stannous oxide is produced by a neutralization step of neutralizing the stannous salt acidic aqueous solution using aqueous ammonia and ammonium bicarbonate together as the alkaline aqueous solution at a pH of <NUM> to <NUM> and a solution temperature of <NUM> or lower to cause stannous hydroxide precipitation, a step of aging and dehydrating the produced stannous hydroxide precipitation under heating to obtain stannous oxide, and a recovery step of filtering, separating, water washing, and drying the stannous oxide.

A content of metal impurities in the stannous oxide is obtained by measuring each content of sodium, potassium, lead, iron, nickel, copper, zinc, arsenic, antimony, aluminum, silver, bismuth, magnesium, calcium, titanium, chromium, manganese, cobalt, indium, tungsten, thallium, and cadmium contained in the stannous oxide by inductively coupled plasma optical emission spectrometry (ICP-OES).

The content of chloride ions in the stannous oxide is a content obtained such that the stannous oxide is dissolved in an appropriate solvent containing no chloride ions and measured by ion chromatography.

In the method for producing a high-concentration tin sulfonate aqueous solution according to the present embodiment, the circulating aqueous methanesulfonic acid solution is preferably bubbled with nitrogen gas and/or degassed with a hollow fiber membrane degassing module. Therefore, a dissolved oxygen level in the aqueous methanesulfonic acid solution is lowered, the oxidation of divalent tin ions (Sn<NUM>+) is further suppressed, the concentration of tetravalent tin ions (Sn<NUM>+) is further lowered, and "turbidity of the solution is not further increased. The dissolved oxygen level in the aqueous methanesulfonic acid solution is preferably <NUM> ppm or less, and more preferably one ppm or less.

Examples of the present invention will be described in detail with Comparative Examples.

A tin methanesulfonic acid aqueous solution was produced by a neutralization method. First, a neutralization tank equipped with a cooling device (chiller) and connected to a nitrogen bubbling pipe and a hollow fiber membrane degassing module was prepared. On the other hand, a commercially available aqueous methanesulfonic acid solution was diluted with pure water to a concentration of <NUM>% by mass. <NUM> of the aqueous methanesulfonic acid solution whose concentration was adjusted was added into the neutralization tank, and circulated in the neutralization tank in a state of being maintained at a temperature of <NUM> by a chiller. The circulating solution was bubbled with nitrogen gas, and degassed with the hollow fiber membrane degassing module to reduce a dissolved oxygen level to one ppm or less, and a solution temperature was controlled to <NUM> by a chiller. Stannous oxide powder in which a total content of impurities of a plurality of kinds of metals whose temperature was adjusted to <NUM> was <NUM> ppm and a content of chloride ions was <NUM> ppm was gradually added thereto, the solution was uniformly stirred, and the aqueous methanesulfonic acid solution and the stannous oxide powder were subjected to a neutralization reaction. In order to achieve a target concentration of methanesulfonic acid as a free acid in the solution of <NUM>/L and a target concentration of Sn<NUM>+ of <NUM>/L, the stannous oxide powder and pure water were added. Specifically, <NUM> of the stannous oxide powder at <NUM> in total for the neutralization reaction and concentration adjustment was added, and <NUM> of pure water in total for the dilution and concentration adjustment (<NUM>) was added. As a result, a tin methanesulfonic acid aqueous solution was produced.

The temperature of the aqueous methanesulfonic acid solution was maintained at <NUM> by the chiller and circulated in the neutralization tank, the stannous oxide powder whose temperature was adjusted to <NUM> was used, and in order to achieve a target concentration of methanesulfonic acid as a free acid in the solution of <NUM>/L and a target concentration of Sn<NUM>+ of <NUM>/L, the stannous oxide powder and pure water were added. Specifically, <NUM> of the stannous oxide powder at <NUM> in total for the neutralization reaction and concentration adjustment was added, and <NUM> of pure water in total for the dilution and concentration adjustment (<NUM>) was added. Other than this, a tin methanesulfonic acid aqueous solution was produced by the neutralization method in the same manner as in Example <NUM>.

The temperature of the aqueous methanesulfonic acid solution was maintained at -<NUM> by the chiller and circulated in the neutralization tank, the stannous oxide powder whose temperature was adjusted to -<NUM> was used, and in order to achieve a target concentration of methanesulfonic acid as a free acid in the solution of <NUM>/L and a target concentration of Sn<NUM>+ of <NUM>/L, the stannous oxide powder and pure water were added. Specifically, <NUM> of the stannous oxide powder at -<NUM> in total for the neutralization reaction and concentration adjustment was added, and <NUM> of pure water in total for the dilution and concentration adjustment (<NUM>) was added. Other than this, a tin methanesulfonic acid aqueous solution was produced by the neutralization method in the same manner as in Example <NUM>.

A tin methanesulfonic acid aqueous solution was produced by the neutralization method in the same manner as in Example <NUM>, except that the dissolved oxygen level was more than <NUM> ppm and <NUM> ppm or less without degassing. In this case, the added amount of pure water was <NUM> in total for the dilution and concentration adjustment (<NUM>).

A tin methanesulfonic acid aqueous solution was produced by the neutralization method in the same manner as in Example <NUM>, except that the dissolved oxygen level was more than <NUM> ppm and <NUM> ppm or less without bubbling with nitrogen gas.

A tin methanesulfonic acid aqueous solution was produced by the neutralization method in the same manner as in Example <NUM>, except that the dissolved oxygen level was more than <NUM> ppm and <NUM> ppm or less without bubbling with nitrogen gas and without degassing. In this case, the added amount of pure water was <NUM> in total for the dilution and concentration adjustment (<NUM>).

A tin methanesulfonic acid aqueous solution was produced by the neutralization method in the same manner as in Example <NUM>, except that stannous oxide powder in which a total content of impurities of a plurality of kinds of metals was <NUM> ppm and a content of chloride ions was <NUM> ppm was used.

A tin methanesulfonic acid aqueous solution was produced by the neutralization method in the same manner as in Example <NUM>, except that the concentration of the aqueous methanesulfonic acid solution was adjusted to be <NUM>% by mass, a target concentration of methanesulfonic acid as a free acid in the solution was set to <NUM>/L and a target concentration of Sn<NUM>+ was set to <NUM>/L. In this case, the added amount of the stannous oxide at <NUM> was <NUM>, and the added amount of pure water was <NUM> in total for the dilution and concentration adjustment (<NUM>).

A tin methanesulfonic acid aqueous solution was produced by an electrolytic method. First, a metal Sn plate was prepared as an anode electrode and a Pt/Ti electrode was prepared as a cathode electrode in an electrolytic cell, and an anion exchange membrane was installed between the electrodes. <NUM> of a methanesulfonic acid solution having a concentration adjusted to <NUM>% by mass in the same manner as in Example <NUM> was added into an electrolytic cell, and electrolysis treatment was performed in a state where the methanesulfonic acid solution was maintained at a temperature of <NUM>. In order to achieve a target concentration of methanesulfonic acid as a free acid in an electrolyte on the anode side of <NUM>/L and a target concentration of Sn<NUM>+ of <NUM>/L, <NUM> Ah electrolysis was continued, and pure water was added to adjust the concentration. Specifically, the added amount of pure water was <NUM> in total for the dilution and concentration adjustment (<NUM>). As a result, a tin methanesulfonic acid aqueous solution in the electrolytic cell was produced.

In order to achieve a target concentration of methanesulfonic acid as a free acid in an electrolyte on the anode side of <NUM>/L and a target concentration of Sn<NUM>+ of <NUM>/L, <NUM> Ah electrolysis was continued, and pure water was added to adjust the concentration. Otherwise, a tin methanesulfonic acid aqueous solution was produced by the electrolytic method in an electrolytic cell in the same manner as in Comparative Example <NUM>. In this case, the added amount of pure water was <NUM> in total for the dilution and concentration adjustment (<NUM>).

A tin methanesulfonic acid aqueous solution was produced by a neutralization method. The aqueous methanesulfonic acid solution was circulated in the neutralization tank in a state of being maintained at a temperature of <NUM>. Stannous oxide powder maintained at <NUM> was used. In addition, bubbling with nitrogen gas and degassing were not performed, the dissolved oxygen level was set to <NUM> ppm or less, and in order to achieve a target concentration of methanesulfonic acid as a free acid in the solution of <NUM>/L, and a target concentration of Sn<NUM>+ of <NUM>/L, the stannous oxide powder and pure water were added. Specifically, <NUM> of the stannous oxide powder at <NUM> in total for the neutralization reaction and concentration adjustment was added, and <NUM> of pure water in total for the dilution and concentration adjustment (<NUM>) was added. Other than this, a tin methanesulfonic acid aqueous solution was produced in the same manner as in Example <NUM>.

The aqueous methanesulfonic acid solution was circulated in the neutralization tank in a state of being maintained at a temperature of <NUM>. The stannous oxide powder whose temperature was maintained at <NUM> and having a content of chloride ions of <NUM> ppm was used. In addition, bubbling with nitrogen gas and degassing were not performed, the dissolved oxygen level was set to <NUM> ppm or less, and in order to achieve a target concentration of methanesulfonic acid as a free acid in the solution of <NUM>/L, and a target concentration of Sn<NUM>+ of <NUM>/L, the stannous oxide powder and pure water were added. Specifically, <NUM> of the stannous oxide powder at <NUM> in total for the neutralization reaction and concentration adjustment was added, and <NUM> of pure water in total for the dilution and concentration adjustment (<NUM>) was added. Other than this, a tin methanesulfonic acid aqueous solution was produced by the neutralization method in the same manner as in Example <NUM>.

The aqueous methanesulfonic acid solution was circulated in the neutralization tank in a state of being maintained at a temperature of <NUM>. Stannous oxide powder maintained at <NUM> was used. In addition, bubbling with nitrogen gas and degassing were not performed, the dissolved oxygen level was set to <NUM> ppm or less, and in order to achieve a target concentration of methanesulfonic acid as a free acid in the solution of <NUM>/L, and a target concentration of Sn<NUM>+ of <NUM>/L, the stannous oxide powder and pure water were added. Specifically, <NUM> of the stannous oxide powder at <NUM> in total for the neutralization reaction and concentration adjustment was added, and <NUM> of pure water in total for the dilution and concentration adjustment (<NUM>) was added. Other than this, a tin methanesulfonic acid aqueous solution was produced by the neutralization method in the same manner as in Example <NUM>.

The aqueous methanesulfonic acid solution was circulated in the neutralization tank in a state of being maintained at a temperature of <NUM>. The stannous oxide powder adjusted to <NUM> was used. In addition, bubbling with nitrogen gas and degassing were not performed, the dissolved oxygen level was set to <NUM> ppm or less, and in order to achieve a target concentration of methanesulfonic acid as a free acid in the solution of <NUM>/L, and a target concentration of Sn<NUM>+ of <NUM>/L, the stannous oxide powder and pure water were added. Specifically, <NUM> of the stannous oxide powder at <NUM> in total for the neutralization reaction and concentration adjustment was added, and <NUM> of pure water in total for the dilution and concentration adjustment (<NUM>) was added. Other than this, a tin methanesulfonic acid aqueous solution was produced by the neutralization method in the same manner as in Example <NUM>.

The aqueous methanesulfonic acid solution was circulated in the neutralization tank in a state of being maintained at a temperature of <NUM>. The stannous oxide powder adjusted to -<NUM> was used. In addition, bubbling with nitrogen gas and degassing were performed, the dissolved oxygen level was set to <NUM> ppm or less, and in order to achieve a target concentration of methanesulfonic acid as a free acid in the solution of <NUM>/L, and a target concentration of Sn<NUM>+ of <NUM>/L, the stannous oxide powder and pure water were added. Specifically, <NUM> of the stannous oxide powder at <NUM> in total for the neutralization reaction and concentration adjustment was added, and <NUM> of pure water in total for the dilution and concentration adjustment (<NUM>) was added. Other than this, a tin methanesulfonic acid aqueous solution was produced by the neutralization method in the same manner as in Example <NUM>.

The aqueous methanesulfonic acid solution was circulated in the neutralization tank in a state of being maintained at a temperature of <NUM>. The stannous oxide powder adjusted to <NUM> was used. In addition, bubbling with nitrogen gas and degassing were performed, the dissolved oxygen level was set to <NUM> ppm or less, and in order to achieve a target concentration of methanesulfonic acid as a free acid in the solution of <NUM>/L, and a target concentration of Sn<NUM>+ of <NUM>/L, the stannous oxide powder and pure water were added. Specifically, <NUM> of the stannous oxide powder at <NUM> in total for the neutralization reaction and concentration adjustment was added, and <NUM> of pure water in total for the dilution and concentration adjustment (<NUM>) was added. Other than this, a tin methanesulfonic acid aqueous solution was produced by the neutralization method in the same manner as in Example <NUM>.

Each of the production methods (types, production conditions (the presence or absence of bubbling with nitrogen gas, and the presence or absence of hollow fiber membrane degassing), the concentration, temperature, and added amount of the aqueous methanesulfonic acid solution, the concentration of chloride ions, concentration of metal impurities, and added amount of the stannous oxide, and the temperature and added amount of pure water) in Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> described above is shown in Table.

The concentrations (Sn<NUM>+ concentration, Sn<NUM>+ concentration, free acid concentration, chloride ion concentration, and metal impurity concentration) of individual components in the produced tin methanesulfonic acid aqueous solution are shown in Table <NUM> below. A method for measuring or calculating the concentration of each component in the produced tin methanesulfonic acid aqueous solution is as follows.

In order to evaluate each of the production methods (types, production conditions, and the like) of Examples <NUM> to <NUM> (Examples <NUM> and <NUM> not according to the invention) and Comparative Examples <NUM> to <NUM> described above and the produced tin methanesulfonic acid aqueous solution (hereinafter, may be simply referred to as a tin solution), (<NUM>) Hazen unit color number (APHA) measured in accordance with JIS K0071-<NUM> (<NUM>), (<NUM>) Formazin turbidity obtained by turbidity measurement using an integrating sphere photoelectric photometry method, and (<NUM>) Precipitation status of this aqueous solution at low temperature are shown in Table <NUM> described above, and (<NUM>) Ratio of amount of tin solution to be fed when this aqueous solution was fed to the electrolytic tin plating solution is shown in Table <NUM> described above and Table <NUM> described below. These evaluation items were evaluated by the following methods.

The produced tin methanesulfonic acid aqueous solution was separated into a glass cell, and APHA was measured from color measurement using TZ6000 manufactured by NIPPON DENSHOKU INDUSTRIES Co.

The produced tin methanesulfonic acid aqueous solution was separated into a glass cell, and turbidity was measured by a method conforming to JIS K <NUM>-<NUM> using PT-<NUM> manufactured by Mitsubishi Chemical Analytech Co. and a Formazin standard solution.

Tin methanesulfonic acid crystals were precipitated on a bottom of the container when the tin methanesulfonic acid aqueous solution produced in a refrigerator set at -<NUM> was stored in a glass container having a capacity of <NUM> liter for <NUM> hours, and the presence or absence of the crystals was visually confirmed.

The solution amount of the tin methanesulfonic acid aqueous solution used for feeding the electrolytic tin plating solution, that is, a percentage of the tin solution amount to be fed was calculated by the following method.

First, the following pure tin plating solution was subjected to an initial make-up of an electrolytic bath. An insoluble Pt/Ti plate as an anode and a silicon wafer having a surface on which a Cu conductive layer formed by a sputtering method as a cathode were each placed in the plating solution, and electrolyzed to <NUM> Ah/L at a bath temperature of <NUM> and a cathode current density of <NUM> ASD. The plating solution amount decreased due to electrolysis and volatilization of water by electrolysis so that the plating solution was normally caused to circulate in the plating equipment. Therefore, pure water was automatically fed through a solution level sensor during electrolysis to maintain a constant bath volume. A commercially available additive for a pure tin plating solution was used as an additive.

A composition of an Sn plating solution after electrolysis was as follows.

Next, in order to recover the plating solution after electrolysis to an initial concentration, a bleed-and-feed operation was performed using the tin sulfonate aqueous solution of Comparative Example <NUM>. The bleed-and-feed operation is an operation of bleeding a part of the plating solution after electrolysis and feeding the feed solution in order to maintain a constant amount of the solution in the device. The amount of solution required at that time was as follows. The amounts of these solutions are also shown in Table <NUM>.

A more specific description is as follows. <NUM> of the plating solution was bled from <NUM> of the plating solution after electrolytic plating. After the bleeding, <NUM> of the tin solution of Comparative Example <NUM>, <NUM> of the additive, and <NUM> of pure water were added to the <NUM> of the plating solution remaining in the device, and the plating solution amount was recovered to the original amount of <NUM>.

The amount of tin solution to be fed when the tin sulfonate aqueous solution of Comparative Example <NUM> was fed to the electrolytic tin plating solution was a normal feed amount in plating of the related art. In order to evaluate how much the feed amount in other Examples and Comparative Examples decreased as compared with the related art, a percentage (%) of the feed amount in other Examples to the feed amount in Comparative Examples <NUM>: <NUM> was calculated. The results are shown in Table <NUM> described above and Table <NUM> described below. It was determined that a cost reduction effect was obtained in a case where the concentration at which the amount of used tin solution was reduced by <NUM>% or more, that is, in a case where the amount of tin solution to be fed was less than <NUM>%. The bled solution amount and the feed amount (tin solution, additive, and pure water) of Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> are shown in Table <NUM>.

As is clear from Table <NUM> and Table <NUM> described above, in Comparative Example <NUM>, APHA and turbidity were low and transparent, and the precipitation of tin methanesulfonic acid crystals during low-temperature storage was "No precipitation". However, since the Sn<NUM>+ concentration was as low as <NUM>/L, the percentage of the amount of tin solution to be fed was <NUM>%, and there was no effect of reducing the amount of tin solution to be fed.

In Comparative Example <NUM>, APHA and turbidity were low, and the solution was transparent. However, since the free acid concentration was as high as <NUM>/L, the precipitation of tin methanesulfonic acid crystals was observed during low-temperature storage, the bled solution amount was large, and the percentage of the tin sulfonate aqueous solution to be fed was <NUM>%, so that the effect of reducing the amount of tin solution to be fed was not so great.

In Comparative Example <NUM>, the precipitation of tin methanesulfonic acid crystals during low-temperature storage was "No precipitation", but the temperature of methanesulfonic acid was as high as <NUM> during the production of the tin sulfonate aqueous solution, and the temperature of stannous oxide was also as high as <NUM>. Therefore, the Sn<NUM>+ concentration was as high as <NUM>/L, the APHA and turbidity were relatively high, and turbidity was generated. In addition, since the Sn<NUM>+ concentration was as low as <NUM>/L, the percentage of the amount of tin solution to be fed was <NUM>%, and there was no effect of reducing the amount of tin solution to be fed.

In Comparative Example <NUM>, the precipitation of tin methanesulfonic acid crystals during low-temperature storage was "No precipitation", but the temperature of methanesulfonic acid was as high as <NUM> during the production of the tin sulfonate aqueous solution, and the temperature of stannous oxide was also as high as <NUM>. Therefore, the Sn<NUM>+ concentration was as high as <NUM>/L, the APHA and turbidity were high, the solution was white turbid, and the solution was not fed.

In Comparative Example <NUM>, the precipitation of tin methanesulfonic acid crystals during low-temperature storage was "No precipitation", and the percentage of the amount of tin solution to be fed was <NUM>%, which exhibited the effect of reducing the amount of tin solution to be fed. However, during the production of the tin sulfonate aqueous solution, the temperature of stannous oxide was as high as <NUM>. Therefore, the Sn<NUM>+ concentration was as high as <NUM>/L, the APHA and turbidity were relatively high, and turbidity was generated in the solution.

In Comparative Example <NUM>, the precipitation of tin methanesulfonic acid crystals during low-temperature storage was "No precipitation", and the percentage of the amount of tin solution to be fed was <NUM>%, which exhibited the effect of reducing the amount of tin solution to be fed. However, during the production of the tin sulfonate aqueous solution, the temperature of methanesulfonic acid was as high as <NUM>. Therefore, the Sn<NUM>+ concentration was as high as <NUM>/L, the APHA and turbidity were relatively high, and turbidity was generated in the solution.

In Comparative Example <NUM>, the APHA and turbidity were low, the solution was transparent, the percentage of the amount of tin solution to be fed was <NUM>%, and there was the effect of reducing the amount of tin solution to be fed. However, since the free acid concentration of the tin solution was as high as <NUM>/L, the solubility of tin methanesulfonic acid decreased, and the precipitation of tin methanesulfonic acid crystals was observed during low-temperature storage.

In Comparative Example <NUM>, the APHA and turbidity were low, the solution was transparent, the percentage of the amount of tin solution to be fed was <NUM>%, and there was the effect of reducing the amount of tin solution to be fed. However, since the Sn<NUM>+ concentration of the tin solution was as high as <NUM>/L, the precipitation of tin methanesulfonic acid crystals was observed during low-temperature storage.

On the other hand, in Examples <NUM> to <NUM> (Examples <NUM> and <NUM> not according to the invention), the Sn<NUM>+ concentration was <NUM> to <NUM>/L, the Sn<NUM>+ concentration was <NUM>/L or less, and the concentration of the free methanesulfonic acid was <NUM>/L or less. Therefore, as compared with the cases of Comparative Examples <NUM> to <NUM>, the amount of tin solution to be fed could be reduced by <NUM>% or more. In addition, the APHA and turbidity of the tin solution were low, the solution was transparent, and the precipitation of tin methanesulfonic acid crystals was not observed during low-temperature storage.

As shown in Table <NUM>, in Example <NUM> (not according to the invention), the reason why the chloride ion concentration in the tin methanesulfonic acid aqueous solution was <NUM>/L, which was higher than those in Examples <NUM> to <NUM> and <NUM> to <NUM> (Example <NUM> not according to the invention), is that the chloride ion concentration of a raw material in the stannous oxide was <NUM> ppm (Table <NUM>), which was higher than those in Examples <NUM> to <NUM> and <NUM> to <NUM> (Example <NUM> not according to the invention). As shown in Table <NUM>, in Example <NUM> (not according to the invention), the reason why the concentration of metal impurities in the tin methanesulfonic acid aqueous solution was <NUM>/L, which was higher than those in Examples <NUM> to <NUM> (Example <NUM> not according to the invention) and <NUM> to <NUM>, is that the concentration of metal impurities in the stannous oxide of a raw material was <NUM> ppm (Table <NUM>), which was higher than those in Examples <NUM> to <NUM> (Example <NUM> not according to the invention)and <NUM> and <NUM>. Furthermore, as shown in Table <NUM>, in Comparative Example <NUM>, the reason why the chloride ion concentration in the tin methanesulfonic acid aqueous solution was <NUM>/L, which was higher than those in Comparative Examples <NUM> and <NUM> to <NUM>, is that the chloride ion concentration of a raw material in the stannous oxide was <NUM> ppm (Table <NUM>), which was higher than those in Comparative Examples <NUM> and <NUM> to <NUM>.

As shown in Table <NUM>, the reason why each APHA in Examples <NUM>, <NUM>, and <NUM> (Examples <NUM> and <NUM> not according to the invention) was <NUM>, which was higher than those in Examples <NUM> to <NUM>, <NUM>, and <NUM>, is that the hollow fiber membrane degassing was performed as shown in Table <NUM>, but the bubbling with nitrogen gas was not performed. In addition, as shown in Table <NUM>, the reason why the APHA in Example <NUM> was <NUM>, which was higher than those in Examples <NUM> to <NUM>, <NUM>, and <NUM>, is that the bubbling with nitrogen gas was performed as shown in Table <NUM>, but the hollow fiber membrane degassing was not performed. Furthermore, as shown in Table <NUM>, the reason why the APHA was <NUM> and the turbidity was <NUM> in Example <NUM>, which were higher than those in Examples <NUM> to <NUM>, <NUM>, and <NUM>, is that neither the bubbling with nitrogen gas nor the hollow fiber membrane degassing were performed as shown in Table <NUM>.

Claim 1:
A high-concentration tin sulfonate aqueous solution comprising
<NUM>/L to <NUM>/L of a divalent tin ion (Sn<NUM>+);
<NUM>/L or less of a tetravalent tin ion (Sn<NUM>+);
<NUM>/L or less of a free methanesulfonic acid;
<NUM>/L or less of chloride ions; and
impurities of a plurality of kinds of metals, wherein
a Hazen unit color number (APHA) is <NUM> or less,
a turbidity is <NUM> FTU or less,
a total content of the plurality of kinds of metals is <NUM>/L or less in terms of metal,
the plurality of kinds of metals includes sodium, potassium, lead, iron, nickel, copper, zinc, arsenic, antimony, aluminum, silver, bismuth, magnesium, calcium, titanium, chromium, manganese, cobalt, indium, tungsten, thallium, and cadmium,
a content of each of the plurality of kinds of metals is <NUM>/L or less in terms of metal,
the Hazen unit color number (APHA) is measured in accordance with JIS K0071-<NUM> (<NUM>),
and
the turbidity is measured using an integrating sphere photoelectric photometry method conforming to JIS K <NUM>-<NUM>.