JP2012227287A - Coating liquid for boron diffusion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating liquid for boron diffusion capable of diffusing boron at high concentration even using a propylene glycol-based solvent having inferior solubility in a boron compound.SOLUTION: A coating liquid for boron diffusion contains (a) a boron compound, (b) an alcoholic hydroxyl group-containing polymer compound, (c) a propylene glycol derivative, (d) ethylene glycol and (e) water, and is characterized in that the content of the above (a) boron compound is 5 mass% or more and 20 mass% or less in the case of boron oxide (BO).

Description

  The present invention relates to a novel boron diffusion coating solution, and more particularly to a novel boron diffusion coating solution for diffusing boron on the surface of a silicon semiconductor.

  For the manufacture of transistors, diodes, ICs and the like, silicon semiconductor devices having a P-type region in which boron is diffused are used. As a method for diffusing boron in the silicon semiconductor device, a thermal decomposition method, a counter NB method, a dopant host method, a coating method, and the like have been studied. Among them, the coating method is uniform without requiring an expensive apparatus. It is preferably used because it can diffuse and is excellent in mass productivity. In particular, a coating solution containing boron is often applied using a spin coater or the like.

  A conventional coating solution uses an ethylene glycol ether solvent excellent in boron solubility, such as ethylene glycol monomethyl ether, as a solvent. However, the ethylene glycol ether solvent is highly environmentally toxic and has been designated as a PRTR (Pollutant Release and Transfer Register) method type 1 designated chemical substance, and its use has become difficult recently.

  Accordingly, a coating liquid (see claim 1 or claim 2 of Patent Document 1) in which a propylene glycol solvent is used as a solvent for the boron diffusion coating liquid and a nonionic surfactant is further added has been proposed.

  However, since the coating liquid using the propylene glycol ether solvent is inferior in solubility of the boron compound and the boron compound cannot be dissolved at a high concentration, the boron compound instead of the coating liquid using the ethylene glycol ether solvent is used. A coating solution that diffuses boron with high concentration and good reproducibility could not be provided.

Japanese Patent Application Laid-Open No. 09-181009

  The object of the present invention is to allow the present inventors to dissolve a boron compound at a high concentration while using a propylene glycol solvent having poor solubility of the boron compound as a solvent for the boron diffusion coating solution in view of the above-mentioned present situation. It is to provide a coating solution for boron diffusion.

As a result of intensive research, the present inventors have found that (a) boron compounds, (b) alcoholic hydroxyl group-containing polymer compounds, (c) propylene glycol derivatives, (d) ethylene glycol and (e ) When water is included, and the content of the boron compound (a) is boron oxide (B ₂ O ₃ ), it is possible to solve the above-described problems by setting the content to 5% by mass or more and 20% by mass or less. The present invention was completed through repeated headings and further studies.

That is, the present invention relates to the following inventions.
[1] containing (a) a boron compound, (b) an alcoholic hydroxyl group-containing polymer compound, (c) a propylene glycol derivative, (d) ethylene glycol and (e) water, and (a) the content of the boron compound Is boron oxide (B ₂ O ₃ ), it is 5 mass% or more and 20 mass% or less.
[2] (a) The boron compound is at least one selected from the group consisting of boric acid, boron oxide (anhydrous boric acid), ammonium borate, and boron chloride. High concentration boron diffusion coating solution.
[3] The coating solution for boron diffusion according to [1] or [2], wherein the (b) alcoholic hydroxyl group-containing polymer compound is a polyvinyl alcohol resin having a sodium content of less than 10 ppm.
[4] The above [1], wherein (c) the propylene glycol derivative is at least one selected from the group consisting of propylene glycol monomethyl ether, propylene glycol monoethyl ether and propylene glycol mono-n-butyl ether. The coating solution for boron diffusion according to any one of to [3].
[5] The content of (d) ethylene glycol is 15% by mass or more, and (e) the content of water is less than 25% by mass, according to any one of [1] to [4], The coating liquid for boron diffusion as described.
[6] (b) A step of preparing an aqueous solution containing an alcoholic hydroxyl group-containing polymer compound and (e) water, (2) (a) a boron compound, (c) a propylene glycol derivative and ( d) A method for producing a boron diffusion coating solution as described in any one of [1] to [5] above, which comprises a step of mixing ethylene glycol.
[7] The method for producing a coating solution for boron diffusion according to [6], wherein in the step (2), heating is performed to 40 ° C. or higher.

  According to the present invention, there is provided a coating solution for boron diffusion containing a high concentration of a boron-based compound that could not be produced by a conventional method, while using a propylene glycol derivative having little concern about environmental toxicity and poor solubility of the boron compound. It became possible.

  Hereinafter, the boron diffusion coating solution of the present invention will be described in detail.

The boron diffusion coating solution of the present invention contains (a) a boron compound, (b) an alcoholic hydroxyl group-containing polymer compound, (c) a propylene glycol derivative, (d) ethylene glycol, and (e) water, (A) The content of the boron compound is 5% by mass or more and 20% by mass or less when boron oxide (B ₂ O ₃ ) is used.

〔（式中、ｑは０又は１であり、ｑ＝１のとき、Ａは下記一般式（Ｉ’）
−（Ｘ）_ｌ−（Ｙ）_ｍ−（Ｚ）_ｎ− （Ｉ’）
（式中、Ｘ及びＺは、１個の末端エーテル残基をもつ炭素数合計１００以下の含酸素炭化水素基であり、Ｙは、

（式中、Ｒは、炭素数１〜３４の炭化水素基を表す。）若しくは

（式中、Ｒ’は、炭素数２〜１３の炭化水素基を表す。）
であり、ｌ、ｍ及びｎは、０又は１である。）
で表される基であり、ｐは１０〜１０００の整数である。〕
で表される有機ホウ素高分子化合物）等が人体に対する安全性の面で好ましい。前記炭化水素基としては、アルキル基、ビニル基、フェニル基等が挙げられる。前記多価アルコール−ホウ素錯体化合物の市販品としては、例えば、ハイボロンＤＢＰＧ−３（商品名、ボロンインターナショナル社製）等が挙げられる。これらは、単独で又は２種以上を組み合わせて用いることができる。 The (a) boron compound (hereinafter also referred to as the component (a)) is particularly a substance that can be dissolved in a mixed solvent of (c) propylene glycol ether solvent, (d) ethylene glycol, and (e) water. Although not limited, boric acid, boric anhydride, ammonium borate, boron chloride (boron trichloride, etc.), polyhydric alcohol-boron complex compound (for example, the compound according to claim 1 of JP-A-63-37130, That is, the following general formula (I)

[In the formula, q is 0 or 1, and when q = 1, A represents the following general formula (I ′)
-(X) _1- (Y) _m- (Z) _n- (I ')
(Wherein X and Z are oxygen-containing hydrocarbon groups having one terminal ether residue and a total of 100 or less carbon atoms, and Y is

(Wherein R represents a hydrocarbon group having 1 to 34 carbon atoms) or

(In the formula, R ′ represents a hydrocarbon group having 2 to 13 carbon atoms.)
And l, m and n are 0 or 1. )
P is an integer of 10 to 1000. ]
In view of safety to the human body, an organic boron polymer compound represented by Examples of the hydrocarbon group include an alkyl group, a vinyl group, and a phenyl group. Examples of commercially available products of the polyhydric alcohol-boron complex compound include high boron DBPG-3 (trade name, manufactured by Boron International). These can be used alone or in combination of two or more.

The content of (a) boron compound, application method, but is determined by the resistance value required for the semiconductor device, 5-20 wt% when it is contained as boron oxide _(B 2 _{O 3),} preferably 6 to 15 % By mass. (A) When the content of the boron compound is less than 5% by mass, the amount of boron supply decreases, and the expected resistance value of the semiconductor device cannot be obtained. (A) When the content of the boron compound exceeds 20% by mass, the stability of the coating solution may be impaired, or the performance required of the semiconductor device may be impaired due to excessive boron supply, which is not preferable. The resistance value of the semiconductor device required for the boron diffusion coating solution containing a high concentration boron compound as described above is not particularly limited, but is generally 0.50 to 0.75Ω / □.

  The (b) alcoholic hydroxyl group-containing polymer compound (hereinafter also referred to as the component (b)) is not particularly limited. For example, polyvinyl alcohol such as polyvinyl alcohol (hereinafter also referred to as PVA) and modified polyvinyl alcohol. Resin (hereinafter also referred to as PVA resin), vinyl alcohol derivatives such as polyvinyl acetal and polyvinyl butyral, polyethylene oxide polyhydroxymethyl acrylate, polyhydroxyethyl acrylate, polyhydroxypropyl acrylate and the like. Preferably, a PVA-based resin with a reduced sodium content is more preferable, and a PVA-based resin with a sodium content of less than 10 ppm is particularly preferable because contamination of the semiconductor device with sodium can be avoided. These can be used alone or in combination of two or more. “The sodium content of the PVA resin is 10 ppm or less” means that the sodium content of the mass standard in the PVA resin is 0.001 mass% or less. Hereinafter, among the alcoholic hydroxyl group-containing polymer compounds, a PVA resin will be described as an example. Although it does not specifically limit as an average degree of polymerization of the said PVA-type resin, 150-5000 are preferable. When the average degree of polymerization is less than 150, the film forming property of the coating solution is poor, and cracks of the coating film occur during drying, and a uniform coating film cannot be obtained. When the average degree of polymerization exceeds 5000, the viscosity of the coating solution becomes so high that spin coating may not be possible. The saponification degree of the PVA-based resin is not particularly limited, but is preferably 50 mol% or more and less than 99 mol%, and more preferably 60 to 99 mol%. In the present invention, the average polymerization degree (viscosity average polymerization degree) and the saponification degree are both values measured according to JIS K 6726: 1994, and the saponification degree is a value measured by a back titration method.

  (B) The content of the alcoholic hydroxyl group-containing polymer compound is not particularly limited and is determined by the viscosity required for the coating solution, but is usually 0.01 to 10% by mass, preferably 0.5 to 10%. % By mass. (B) When the content of the alcoholic hydroxyl group-containing polymer compound is less than 0.01%, a sufficient resistance cannot be obtained when spin coating is performed, but the target resistance is increased despite the high concentration of the boron compound. Since it may not fall to a value, it is not preferable. (B) When the content of the alcoholic hydroxyl group-containing polymer compound exceeds 10%, the viscosity of the coating solution becomes too high to be spin-coated, or the resin is carbonized during heating and boron. This is not preferable because it affects the diffusion of selenium.

  The production method of the (b) alcoholic hydroxyl group-containing polymer compound of the present invention is not particularly limited, and a known method can be used. Hereinafter, among the methods for producing an alcoholic hydroxyl group-containing polymer compound, a method for producing a PVA resin will be described as an example. Although it does not specifically limit as a manufacturing method of the said PVA-type resin, Industrially, it polymerizes aliphatic vinyl ester by various polymerization methods, such as conventionally well-known bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. And a method of saponifying the obtained polymer by conventionally known alkali saponification and acid saponification. Among the polymerization methods, a method in which an aliphatic vinyl ester is solution-polymerized in a methanol solvent is particularly preferable.

  The acid used for the acid saponification treatment is not particularly limited. For example, hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, phosphorous acid, nitric acid, halogen acid, acetic acid, trifluoroacetic acid, oxalic acid, succinic acid. Examples include acid, adipic acid, tartaric acid, lactic acid, citric acid, methanesulfonic acid, p-toluenesulfonic acid, α- or β-naphthalenesulfonic acid, and 3,4-dimethylbenzenesulfonic acid. An acid saponification catalyst that does not contain sodium is preferable because contamination of the semiconductor device with sodium can be avoided. The alkali saponification catalyst not containing sodium is not particularly limited, and examples thereof include p-toluenesulfonic acid, formic acid, acetic acid, citric acid, lactic acid, succinic acid, hydrochloric acid, and nitric acid. When phosphoric acid is included, formic acid, acetic acid, citric acid, lactic acid, succinic acid, hydrochloric acid and nitric acid have a negative effect on semiconductor devices by creating a level where sulfur or phosphoric acid becomes a recombination center in the silicon crystal. Is preferred. These acid saponification catalysts can be used alone or in combination of two or more.

  The amount of the acid saponification catalyst used depends on the type of compound used, the solvent composition at the time of saponification, and the water content, but when a saponification reaction is carried out in a methanol solvent, an aliphatic vinyl ester polymer is used. On the other hand, it is usually preferably about 0.5 to 500 mm equivalent, more preferably about 1 to 100 mm equivalent.

The alkali used in the alkali saponification treatment is not particularly limited, and examples thereof include sodium hydroxide, sodium alcoholate, tetraalkylammonium hydroxide, cycloamidines (see JP-A-62-225504), phosphazene compounds ( JP-A-2001-81130), guanidine compounds (see JP-A-8-12721), amidine compounds (see JP-A-8-27218) and the like. An alkali saponification catalyst not containing sodium is preferable because contamination of the semiconductor device with sodium can be avoided. The alkali saponification catalyst not containing sodium is not particularly limited. For example, a phosphazene compound, the following general formula (II)
R ¹ R ² R ³ R ⁴ N ⁺ OH ⁻ (II)
(Wherein R ^{1 to} R ⁴ are each independently an alkyl group having 1 to 16 carbon atoms, a benzyl group, or a phenyl group.)
And quaternary ammonium hydroxide, guanidine compound, or amidine compound represented by the formula:

The phosphazene compound is not particularly limited, and examples thereof include 2-tert-butylimino-2-diethylamino-1,3-dimethyl-perhaloid-1,3,2-diazaphosphorine, tert-butylimino-tris (dimethylamino) phosphorane, and tert. -Butylimino-tri (pyrrolidino) phosphorane, 1-ethyl-2,2,4,4,4-pentakis (dimethylamino) -2λ ⁵ , 4λ ⁵ -catenadi (phosphazene), 1-tert-butyl-4,4 4-tris (dimethylamino) -2,2-bis [tris (dimethylamino) phosphalanilideneamino] -2λ ⁵ , 4λ ⁵ -catenadi (phosphazene) and the like.

  In the quaternary ammonium hydroxide represented by the general formula (II), the alkyl group having 1 to 16 carbon atoms may be a branched alkyl group or a linear alkyl group. Moreover, the benzyl group and the phenyl group may be substituted with 1 to 5 substituents. Examples of the substituent include a lower alkyl group having 1 to 6 carbon atoms.

  The quaternary ammonium hydroxide represented by the general formula (II) is not particularly limited. For example, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyl hydroxide Examples thereof include trimethylammonium, tetrabenzylammonium hydroxide, diethyldimethylammonium hydroxide, methyltriethylammonium hydroxide, methyltributylammonium hydroxide, hexadecyltrimethylammonium hydroxide, and phenyltrimethylammonium hydroxide.

  Although it does not specifically limit as a guanidine compound, For example, 1,1,3,3-trimethylguanidine, 1-cyanoethyl-1,3,3-trimethylguanidine, 1-benzyl-1,3,3-trimethylguanidine, 7-methyl-1,5,7-triazabicyclo [4.4.0] decene-5 and the like.

  The amidine compound is not particularly limited. For example, 6-dimethylamino-1,8-diazabicyclo [5.4.0] undecene-7, 6-diethylamino-1,8-diazabicyclo [5.4.0] undecene. -7,6-dipropylamino-1,8-diazabicyclo [5.4.0] undecene-7, 6-dibutylamino-1,8-diazabicyclo [5.4.0] undecene-7, and the like.

  Among these alkali saponification catalysts not containing sodium, phosphazene compounds and quaternary ammonium hydroxide are more preferable, and tetramethylammonium hydroxide, tetrabenzylammonium hydroxide, and benzyltrimethylammonium hydroxide are particularly preferable.

  In the present specification, the saponification catalyst does not contain sodium means that it does not contain a sodium (Na) atom in a constituent molecule like sodium hydroxide (NaOH), and also contains a sodium atom in its composition. It does not contain. That a saponification catalyst does not contain a sodium atom in the composition means that the sodium contained as an impurity etc. in this catalyst is about 500 ppm or less. Such a saponification catalyst preferably has a sodium content of about 100 ppm or less, more preferably about 50 ppm or less, and most preferably contains substantially no sodium. These alkali saponification catalysts can be used alone or in combination of two or more.

  The amount of the alkali saponification catalyst that does not contain sodium depends on the type of compound used, the solvent composition at the time of saponification, and the water content. Usually, it is preferably about 0.5 to 500 mm equivalent, more preferably about 1 to 100 mm equivalent with respect to the ester polymer.

  The fatty acid vinyl ester is not particularly limited, and examples thereof include vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, etc. Among them, vinyl acetate is industrially preferable.

  When the aliphatic vinyl ester is polymerized, the aliphatic vinyl ester may be copolymerized with one or more unsaturated monomers copolymerizable with the aliphatic vinyl ester as long as the effects of the present invention are not impaired. good. Examples of unsaturated monomers copolymerizable with aliphatic vinyl esters include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene, vinylene carbonates, acrylic acid, and methacrylic acid. , Unsaturated acids such as crotonic acid, maleic acid, maleic anhydride, itaconic acid or their salts or mono- or dialkyl esters, nitriles such as acrylonitrile and methacrylonitrile, amides such as diacetone acrylamide, acrylamide and methacrylamide, Alkyl vinyl ethers such as lauryl vinyl ether and stearyl vinyl ether, allyl alcohols such as allyl alcohol, dimethyl allyl alcohol and isopropenyl allyl alcohol, allyl acetate, dimethyl allyl acetate Acetyl group-containing monomer such as isopropenyl allyl acetate, aromatic monomer such as styrene, ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, sodium acrylamide-2-methylpropane sulfonate, etc. Olefin sulfonic acid or its salt, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethyldiallylammonium chloride, dimethylallyl vinyl ketone, N-vinyl pyrrolidone, vinyl chloride, vinylidene chloride, polyoxyethylene (meth) allyl ether, Polyoxyalkylene (meth) allyl ethers such as polyoxypropylene (meth) allyl ether, polyoxyethylene (meth) acrylate, polyoxypropylene (meth) acrylate Such as polyoxyalkylene (meth) acrylate, polyoxyethylene (meth) acrylamide, polyoxyalkylene (meth) acrylamide such as polyoxypropylene (meth) acrylamide, polyoxyethylene (1- (meth) acrylamide-1,1- Dimethylpropyl) ester, polyoxyethylene vinyl ether, polyoxyethylene butyl vinyl ether, polyoxypropylene vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, polyoxypropylene vinylamine, acetoacetic acid, etc. Not limited to this. The proportion of the copolymerization of the aliphatic vinyl ester and the unsaturated monomer copolymerizable with the aliphatic vinyl ester may be arbitrary, and the proportion of the modified monomer in the copolymer resin is usually from 0.1 mol% to 10 mol%. It is common to copolymerize in the range of mol%.

  Furthermore, (i) a modified PVA resin after graft polymerization of the PVA resin and acrylic acid, methacrylic acid or the like to add a functional group to a side chain, or (ii) a method of reacting a PVA resin and diketene, or PVA A post-modified PVA resin such as acetoacetylated PVA obtained by a method of transesterification with acetoacetate is also used.

  Usually, industrially obtained PVA-based resin contains 0.1% by mass or more of sodium acetate as a by-product during the saponification reaction as an impurity. As a method for reducing the sodium content in these PVA resins, (1) saponifying an aliphatic vinyl ester polymer with an acid or alkali saponification catalyst to form a PVA resin, and then an alcohol such as methanol or ethanol Or a method of washing them with a mixed solvent such as alcohol and water, methyl acetate or the like, (2) dissolving a PVA resin in a solvent such as water to make a PVA resin solution, and then passing it through an acid ion exchange resin layer And (3) a method of using a product that does not contain sodium as a saponification catalyst used when saponifying an aliphatic vinyl ester polymer. It is preferable to use a PVA resin in which sodium is reduced by any one of the methods described above.

  The (c) propylene glycol ether solvent (hereinafter also referred to as component (c)) is not particularly limited, and examples thereof include propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-butyl ether and the like. Among them, propylene glycol monomethyl ether is preferable. These can be used alone or in combination of two or more.

  In the present invention, (d) ethylene glycol serves as a solubility improver for boron compounds. As for the content of (d) ethylene glycol (hereinafter also referred to as component (d)), the amount of ethylene glycol is usually 15% by mass or more, preferably 20% by mass or more. When the amount of ethylene glycol is less than 15% by mass, the high concentration boron compound is not completely dissolved, resulting in a non-uniform coating solution.

  Although it does not specifically limit as said (e) water (henceforth (e) component), For example, ultrapure water, ion-exchange water, distilled water etc. are used, and especially ultrapure water is preferable. Among them, it is preferable that there are fewer impurity elements such as alkali metals and heavy metal elements and foreign substances in water. These can be used alone or in combination of two or more. The content of the water (e) is preferably less than 20% by mass with respect to the entire boron diffusion coating solution. When the amount of water exceeds 20% by mass, the storage stability of the coating solution is poor, and when left at room temperature, a high concentration of boron compound may precipitate or the viscosity of the coating solution may change. It is not preferable. It is particularly preferable from the viewpoint of improving the solubility of the high concentration boron compound that the content of (d) ethylene glycol is 15% by mass or more and (e) the content of water is less than 25% by mass.

  Furthermore, the boron diffusion coating solution of the present invention may contain (f) a surfactant in addition to the components (a) to (e). (F) By containing a surfactant, the defoaming property and self-leveling property of the coating solution can be improved.

  The (f) surfactant is not particularly limited. For example, a pluronic surfactant, a polyhydric alcohol surfactant, a polyethylene glycol surfactant, a silicone surfactant, a fluorine surfactant, Preferable examples include so-called nonionic surfactants such as acetylene glycol surfactants. Sodium salt type or sulfonate type ionic surfactants are not preferred because they contain sodium and sulfur. Among the surfactants (f), acetylene glycol surfactants are more preferable.

（式中、Ｒ^２及びＲ^３はそれぞれ炭素数１〜３のアルキル基を示し、Ｒ^１、Ｒ^４はそれぞれ炭素数１〜２０のアルキル基又はアリル基を示し、ｍ及びｎはそれぞれ０〜３０を満たす。）
で示されるアセチレングリコール化合物が好ましい。 As the acetylene glycol surfactant, the following general formula (III)

(In the formula, R ² and R ³ each represent an alkyl group having 1 to 3 carbon atoms, R ¹ and R ⁴ each represent an alkyl group or an allyl group having 1 to 20 carbon atoms, and m and n each represents 0 to 0. 30)
The acetylene glycol compound shown by these is preferable.

  The number of moles of ethylene oxide units added in the acetylene glycol compound represented by the general formula (III) is preferably 0 ≦ m + n ≦ 30 [mol]. When the total number of added moles of ethylene oxide exceeds 30 moles, the solubility in water is increased and the foaming property is further increased, so that the defoaming effect tends to be lowered.

  Examples of the acetylene glycol compound represented by the general formula (III) include 2,5,8,11-tetramethyl-6-dodecin-5,8-diol, 5,8-dimethyl-6-dodecin-5, 8-diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 4,7-dimethyl-5-decyne-4,7-diol, 2,3,6,7-tetra Examples include methyl-4-octyne-3,6-diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, and the like.

Moreover, as an ethoxylated form of the acetylene glycol compound of the general formula (III), for example, an ethoxylated form of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (total number of moles of ethylene oxide added: 6), 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate (total number of moles of ethylene oxide added: 10), 2,4,7,9-tetramethyl-5- Ethoxylated form of decyne-4,7-diol (total number of moles of added ethylene oxide: 4), ethoxylated form of 3,6-dimethyl-4-octyl-3,6-diol (total number of moles of added ethylene oxide: 4) And ethylene oxide derivatives of acetylene glycol such as 2,4,7,9-tetramethyl-5-decyne-4,7- Polyoxy-ol (moles of ethylene oxide added Total: 1.3, the general formula (III) in ^{which R 1} and ^{R 4} are iso- butyl group, ^{R 2} and ^{R 3} are methyl, m + n = 1.3), 2 , 4,7,9-Tetramethyl-5-decyne-4,7-diol ethoxylated compound (total number of moles of ethylene oxide added: 3.5, R ¹ and R ⁴ in the general formula (III) are iso-butyl groups , R ² and R ³ are methyl groups, m + n = 3.5).

  Commercially available products may be used as the surfactant (f), and examples of the commercially available products include Surfinol series and Olphine series manufactured by Nissin Chemical Industry Co., Ltd. These sea surface active agents may be used alone or in admixture of two or more. These (f) surfactants can be used alone or in combination of two or more. About 0.01-5 mass% is sufficient for content of the said (f) surfactant with respect to the whole coating liquid for boron diffusion. If it is less than 0.01% by mass, the effect is not exhibited. Conversely, if it exceeds 5% by mass, the coating solution may be separated due to the solubility of the surfactant in water. Absent.

  Further, the boron diffusion coating solution of the present invention may contain (g) an inorganic filler in addition to the components (a) to (e). (G) By containing an inorganic filler and changing the flow characteristics, it is possible to achieve printing characteristics suitable for spin coating and screen printing.

  The inorganic filler (g) is not particularly limited, and examples thereof include silica (amorphous synthetic silica, colloidal silica), alumina, alumina hydrate, talc, calcium carbonate, silicon nitride, aluminum chloride and the like. . These (g) inorganic fillers can be used alone or in combination of two or more. As content of an inorganic filler, it is 1-35 mass% with respect to the whole coating liquid for boron diffusion, Preferably it is 5-20 mass%. If it is less than 1% by mass, the flow characteristics do not change. Conversely, if it exceeds 35% by mass, the fluidity is greatly impaired and the silicon wafer may not be applied. Examples of the amorphous synthetic silica include wet synthetic silica and gas phase method silica.

  Vapor phase silica is also called a dry method as opposed to a wet method, and is generally made by a flame hydrolysis method. Specifically, a method of making silicon tetrachloride by burning with hydrogen and oxygen is generally known, but silanes such as methyltrichlorosilane and trichlorosilane can be used alone or in silicon tetrachloride instead of silicon tetrachloride. It can be used in a mixed state. Vapor phase silica is commercially available as Aerosil from Nippon Aerosil Co., Ltd. and QS type from Tokuyama Co., Ltd.

  Wet synthetic silica is further classified into precipitated silica, gel silica, and sol silica depending on the production method. Precipitated silica is produced by reacting sodium silicate and sulfuric acid under alkaline conditions, and the silica particles that have grown are agglomerated and settled, and are then commercialized through filtration, water washing, drying, pulverization and classification. Examples of the precipitated silica are commercially available from Tosoh Silica Co., Ltd. as Nipsil (trade name) series and from Tokuyama Co., Ltd. as Toku Seal and Fine Seal (trade name) series. Gel silica is produced by reacting sodium silicate and sulfuric acid under acidic conditions. During aging, the microparticles dissolve and reprecipitate so as to bind the other primary particles, so that the distinct primary particles disappear and form relatively hard aggregated particles having an internal void structure. For example, it is commercially available from Tosoh Silica Co., Ltd. as nip gel (trade name) and from Grace Japan Co., Ltd. as syloid and silo jet (trade name). The sol method silica is also called colloidal silica, and is obtained by heating and aging silica sol obtained through metathesis of sodium silicate acid or the like through an ion exchange resin layer. For example, Snowtex (trade name) from Nissan Chemical Industries, Ltd. Is commercially available.

  In the present invention, if necessary, various additives may be contained as long as the basic physical properties of the coating liquid are not impaired. Examples of the additive include vinyl polymer compounds such as polyvinyl imidazole, polyvinyl pyrrolidone, and polyvinyl caprolactam as viscosity improvers, polyethylene oxide, polypropylene oxide, polyethylene oxide-polypropylene oxide alternating or block copolymers, and the like. Cellulose polymer compounds such as alkylene oxide compounds, polyhydroxymethyl acrylates, polyhydroxyethyl acrylates, polyhydroxypropyl acrylates or the like, polyhydroxyalkyl acrylates or methacrylates such as methacrylates, methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, etc. Various pH adjusters, antiseptics, flame retardants, and wafer diffusion concentration adjustment A compound capable of forming an N-type region, for example, phosphorous compounds such as phosphoric anhydride, phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, melamine phosphate, acid phosphooxyethyl methacrylate and amine salts thereof, Examples include alcohols such as methanol, ethanol, and propanol.

  The boron diffusion coating solution of the present invention is preferably used in the range of 5 to 100 mPa · s at 20 ° C. with a B-type rotational viscometer when applied by spin coating. . In addition, the boron diffusion coating solution of the present invention is preferably used in the range of 500 to 250,000 mPa · s when measured by a B-type rotational viscometer at 20 ° C. when applied by screen printing. It is.

  Hereafter, the manufacturing method of the coating liquid for boron diffusion of this invention is demonstrated in detail.

  The boron diffusion coating solution of the present invention can be produced by a production method including the steps of mixing the components (a) to (e), and will be described below with examples, but is not limited thereto. For example, as one embodiment of the production method, (1) (b) a step of preparing an aqueous solution containing an alcoholic hydroxyl group-containing polymer compound and (e) water, (2) the obtained aqueous solution, (a) boron Examples thereof include a method including a step of mixing a compound, (c) a propylene glycol derivative, and (d) ethylene glycol. In the production method, the components (a), (c) and (d) are mixed prior to the step (1) or simultaneously with the step (1), and the resulting mixture is mixed with the step (1). ) May be mixed.

  Moreover, as another aspect of the said manufacturing method, (1) The process which makes (a) a boron compound and (d) ethylene glycol react previously and forms a complex, (2) The obtained complex and (b) alcohol Examples include, but are not limited to, a method including a step of mixing a functional hydroxyl group-containing polymer compound, (c) a propylene glycol derivative, and (e) water. In another aspect of the production method, the components (b), (c) and (e) are mixed prior to the step (1) or concurrently with the step (1), and the resulting mixture is mixed. The complex obtained in step (1) may be mixed.

  Furthermore, in any of the above production methods, if necessary, one or more selected from the group consisting of (f) a surfactant and (g) an inorganic filler may be mixed. The mixing timing of these components is not particularly limited, and may be performed in step (2), may be performed after step (2), or other steps used in step (2) prior to step (1). When mixing components, they may be mixed together.

  In any of the production methods described above, the mixing is industrially advantageous, and thus heating is preferable, and heating in the step (2) is particularly preferable. Although it does not specifically limit as said heating temperature, Usually 40 degreeC or more is preferable and 50 degreeC or more is more preferable. Moreover, regarding mixing and stirring in the production method of the present invention, commercially available various mixers, stirrers and the like can be used, and no special equipment is required.

  The boron diffusion coating solution of the present invention is used by coating on a silicon wafer. As a coating method on a silicon wafer, a spin coater method and a screen printing method are generally used, but a gravure printing method, a relief printing method, a lithographic printing method, an ink jet printing method, a comma coater method, a die head coater method, a die lip coater. And gravure printing methods can also be used.

  The present invention relates to the coating liquid containing the components (a) to (e) obtained by the above production method or the components (a) to (e) (f) a surfactant and (g) an inorganic filler. A boron diffusion method including a step of applying a coating solution containing one or more kinds to a silicon wafer is also included. Such a coating solution and preferred embodiments thereof are as described above. By including the step of applying such a coating solution, boron can be diffused well into the silicon wafer.

  In the said application | coating method, as a temperature of the coating liquid at the time of apply | coating, about 5-40 degreeC is preferable and about 10-30 degreeC is more preferable.

In the present invention, the coating amount when the coating solution is applied to the silicon wafer varies depending on the type and use of the silicon wafer to which the coating solution is applied. For example, when a semiconductor device is manufactured, the coating amount is about 1 preferably to to 500 g / ^{m 2,} more preferably to about 1 to 300 g / ^{m 2,} more preferably to about 1 to 100 g / ^{m 2,} it is from about 1 to 50 g / ^{m 2} Particularly preferred.

  The method of the present invention further comprises a drying step in which a coating solution applied to a silicon wafer is dried to form a coating film, a degreasing step in which an organic compound in the coating film is decomposed, and a coating film obtained in the degreasing step. It is preferable to include a diffusion step of diffusing. By including such a process, for example, boron can be diffused and penetrated uniformly at a high concentration in a semiconductor device or the like.

  As drying temperature in a drying process, about 60-200 degreeC is preferable and about 100-180 degreeC is more preferable. The drying time may be appropriately set depending on the drying temperature or the like, but is preferably about 1 to 60 minutes, and more preferably about 3 to 30 minutes. It does not specifically limit as a drying method, For example, it can be made to dry by methods, such as ventilation drying and vacuum drying.

  In the degreasing step, it is preferable to remove about 90% or more of the organic compound (organic component) in the coating film. In the degreasing step, the coating film is usually degreased at a temperature of about 250 to 600 ° C., preferably about 300 to 550 ° C., preferably about 1 to 120 minutes, more preferably about 5 to 60 minutes to decompose and remove organic components. It is preferable to do.

In the diffusion step, for example, in the case of manufacturing a semiconductor device, the wafer after the degreasing step is preferably about 700 to 2000 ° C., more preferably about 700, in a state where a single wafer or a plurality of stacked wafers are stacked. It is preferable to hold at ˜1500 ° C. for about 10 minutes to 10 days, preferably about 30 minutes to 7 days. For example, in the manufacture of a semiconductor device, if a desired resistance value is obtained by the degreasing step, the diffusion step may not be performed.
A semiconductor device manufactured by applying the above composition to a silicon wafer by the diffusion method of the present invention is also one aspect of the present invention.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these. In the examples, “%” and “parts” are based on weight unless otherwise specified. Moreover, it shows below about the physical-property measuring method in each Example and a comparative example, a manufacturing method, and a usage method.

Method for Measuring Physical Properties of PVA Resin The polymerization degree, saponification degree, and sodium acetate of the PVA resin used in the present invention were measured according to JIS K 6726: 1994. The degree of saponification is measured by a back titration method. The amount of trace amount of sodium in the PVA resin is reduced by heating after adding an appropriate amount of formic acid to the incinerated product after ashing the PVA resin in a 700 ° C. electric furnace. Furthermore, an aqueous solution in which an appropriate amount of hydrochloric acid was added and dissolved in water was measured by an atomic absorption method.

Preparation Method of Boron Diffusion Coating Solution (A) (a) Boron Compound, (c) Propylene Glycol Derivative, (d) Ethylene Glycol Mixture, (B) (b) Alcoholic Hydroxyl Group-Containing Polymer Compound (e) Water In addition to the above, an aqueous solution dissolved by heating was added, and the mixture was stirred and heated to 60 ° C. and then cooled to room temperature.

Application Method of Boron Diffusion Coating Solution to Silicon Wafer A silicon wafer was a P-type silicon wafer having a diameter of 4 inches, a thickness of 200 μm, and a specific resistance value of 10 to 20 Ω · cm. The boron diffusion coating solution was applied to a silicon wafer using a spin coater (MS-A100, manufactured by Mikasa) at a rotation speed of 3500 rpm and a coating time of 10 seconds. The dripping amount of the coating solution was selected from 1 to 10 ml so as to spread uniformly according to the viscosity of the coating solution.

Drying, degreasing and boron diffusion method after application of boron diffusion coating solution The silicon wafer coated with the boron diffusion coating solution was diffused into the wafer by the following steps (I) to (III).
Process (I): It dried for 5 minutes with the 150 degreeC electric furnace.
Step (II): Next, degreasing was performed in an electric furnace at 500 ° C. for 20 minutes for the purpose of degreasing the organic compound in the coating film.
Step (III): Boron was diffused into the wafer by heat-treating the wafer obtained in the previous step (II) at 1300 ° C. for 60 minutes in a single wafer or in a state where a plurality of wafers were superposed.

Method of measuring electrical resistance of wafer Using resistance measuring instrument (manufactured by Napson Corporation, main body: RT-8A, measuring instrument: RG-7A), one wafer after diffusion is arbitrarily selected, and surface resistivity of the diffusion film Asked.

A production example of the PVA resin is shown below.
[Production Example 1]
After replacing the inside of the reactor equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and pressure gauge with nitrogen, 2800 parts by mass of deoxygenated vinyl acetate monomer and 800 parts by mass of deoxygenated methanol were charged and stirred. When the temperature rise was started and the internal temperature reached 60 ° C., 1 part by weight of initiator (2,2′-azobis (2,4-dimethylvaleronitrile)) was dissolved in 50 parts by weight of separately deoxygenated methanol. Initiator solution was added to initiate the polymerization. After polymerization at 60 ° C. for 5 hours, the polymerization was stopped by cooling. The solid content concentration in the polymerization solution at this time was 55.1% (polymerization yield: 71.8%), and the average polymerization was measured using the obtained polyvinyl acetate resin as PVA having a saponification degree of 100 mol%. The degree was 1710. The obtained polymerization solution was supplied to a demonomer having a multistage number of perforated plates in the tower, and methanol vapor was blown from the bottom of the tower to come into contact with the polymerization solution to remove unreacted vinyl acetate monomer. The solid content concentration of the polyvinyl acetate-methanol solution was 42%. The temperature of this polyvinyl acetate-methanol solution was kept at 40 ° C., and saponification reaction was carried out by adding tert-butylimino-tris (dimethylamino) phosphorane. The form at the end of the saponification reaction is a gel containing the solvent methanol and the by-product methyl acetate, the saponification degree is 88 mol%, the volatile content is 58%, and the by-product sodium is converted to PVA. On the other hand, it was less than 10 ppm (here, ppm indicates a sodium content of 0.001% by mass based on the mass standard in the PVA resin). This gel-like PVA was pulverized to a size of 3 mm square and then dried to lower the volatile content to 4% for the test.

  In the following Examples and Comparative Examples, PVA resins having different average degrees of polymerization were varied by adjusting the ratio of vinyl acetate to methanol as a solvent and the polymerization yield when vinyl acetate was subjected to solution polymerization. The saponification degree of the PVA resin was changed by adjusting the amount of saponification catalyst and the saponification time when performing the saponification reaction.

[Example 1]
To 100 parts by mass of ultrapure water, 30 parts by mass of a PVA resin having an average polymerization degree of 560 saponified with tetramethylammonium hydroxide, a saponification degree of 88 mol% and a sodium content of 6 ppm was added, and then stirred. A PVA aqueous solution was prepared by dispersing / dissolving. This aqueous solution was dropped into a mixture of 446 parts by mass of propylene glycol monomethyl ether, 352 parts by mass of ethylene glycol, and 72 parts by mass of boron oxide, and heated to 60 ° C. with stirring. The coating solution was prepared by cooling to room temperature while continuing stirring after heating. The viscosity of this coating solution at 20 ° C. was 81 mPa · s at 60 rpm with a Brookfield rotational viscometer. The coating solution for diffusion was applied to a silicon wafer by the above method, dried, degreased, and diffused, and the resistance value was measured to find a target value of 0.5Ω / □.

[Example 2]
To 100 parts by mass of ultrapure water, 30 parts by mass of a PVA resin having an average degree of polymerization of 280 saponified using tetramethylammonium hydroxide, a saponification degree of 76 mol% and a sodium content of 1 ppm was added, and then stirred. A PVA aqueous solution was prepared by dispersing / dissolving. This aqueous solution was dropped into a mixture of 635 parts by mass of propylene glycol monomethyl ether, 180 parts by mass of ethylene glycol, and 55 parts by mass of boron oxide, and heated to 60 ° C. with stirring. The coating solution was prepared by cooling to room temperature while continuing stirring after heating. The viscosity of this coating solution at 20 ° C. was 28 mPa · s at 60 rpm with a Brookfield rotational viscometer. This diffusion coating solution was applied to a silicon wafer by the above-described method, dried, degreased and diffused, and the resistance value was measured to find a target value of 0.6Ω / □.

[Example 3]
To 100 parts by mass of ultrapure water, 30 parts by mass of a PVA resin having an average polymerization degree of 560 saponified with tetramethylammonium hydroxide, a saponification degree of 88 mol% and a sodium content of 6 ppm was added, and then stirred. A PVA aqueous solution was prepared by dispersing / dissolving. This aqueous solution was dropped into a mixed solution of 446 parts by mass of propylene glycol monomethyl ether, 310 parts by mass of ethylene glycol, and 160 parts by mass of boron oxide, and heated to 60 ° C. with stirring. The coating solution was prepared by cooling to room temperature while continuing stirring after heating. The viscosity of this coating solution at 20 ° C. was 81 mPa · s at 60 rpm with a Brookfield rotational viscometer. This diffusion coating solution was applied to a silicon wafer by the above-described method, dried, degreased and diffused, and the resistance value was measured. As a result, the desired value was 0.5Ω / □.

[Example 4]
In 180 parts by mass of ultrapure water, 18 parts by mass of a PVA resin having an average degree of polymerization of 2000, a degree of saponification of 60 mol% and a sodium content of less than 10 ppm saponified using tetrabenzylammonium hydroxide is placed in a glass container. Then, the mixture was heated and dissolved with stirring to prepare an aqueous solution. This aqueous solution was dropped into a mixed solution of 472 parts by mass of propylene glycol monomethyl ether, 220 parts by mass of ethylene glycol, and 70 parts by mass of boron oxide, and heated to 60 ° C. with stirring. The coating solution was prepared by cooling to room temperature while continuing stirring after heating. The viscosity of this coating solution at 20 ° C. was 81 mPa · s at 60 rpm with a Brookfield rotational viscometer. This diffusion coating solution was applied to a silicon wafer by the above-described method, dried, degreased and diffused, and the resistance value was measured to find a target value of 0.6Ω / □.

[Example 5]
In 240 parts by mass of ultrapure water, 98 parts by mass of a PVA resin having an average degree of polymerization of 160 saponified with tetrabenzylammonium hydroxide, a saponification degree of 60 mol% and a sodium content of less than 10 ppm is placed in a glass container. Then, the mixture was heated and dissolved with stirring to prepare an aqueous solution. This aqueous solution was dropped into a mixed solution of 406 parts by mass of propylene glycol monomethyl ether, 250 parts by mass of ethylene glycol, and 60 parts by mass of boron oxide, and heated to 60 ° C. with stirring. The coating solution was prepared by cooling to room temperature while continuing stirring after heating. The viscosity of this coating solution at 20 ° C. was 81 mPa · s at 60 rpm with a Brookfield rotational viscometer. This diffusion coating solution was applied to a silicon wafer by the above-described method, dried, degreased and diffused, and the resistance value was measured. As a result, the desired value was 0.5Ω / □.

[Comparative Example 1]
To 100 parts by mass of ultrapure water, 30 parts by mass of a PVA resin having an average polymerization degree of 560 saponified with tetramethylammonium hydroxide, a saponification degree of 88 mol% and a sodium content of 6 ppm was added, and then stirred. A PVA aqueous solution was prepared by dispersing / dissolving. This aqueous solution was dropped into a mixed solution of 798 parts by mass of propylene glycol monomethyl ether and 72 parts by mass of boron oxide, and heated to 60 ° C. with stirring. The coating solution was prepared by cooling to room temperature while continuing stirring after heating. A white precipitate was generated at room temperature, resulting in a non-uniform coating solution that could not be uniformly coated.

[Comparative Example 2]
To 100 parts by mass of ultrapure water, 30 parts by mass of a PVA resin having an average degree of polymerization of 280 saponified using tetramethylammonium hydroxide, a saponification degree of 76 mol% and a sodium content of 1 ppm was added, and then stirred. A PVA aqueous solution was prepared by dispersing / dissolving. This aqueous solution was dropped into a mixture of 705 parts by mass of propylene glycol monomethyl ether, 110 parts by mass of ethylene glycol and 55 parts by mass of boron oxide, and heated to 60 ° C. with stirring. The coating solution was prepared by cooling to room temperature while continuing stirring after heating. A white precipitate was generated at room temperature, resulting in a non-uniform coating solution that could not be uniformly coated.

[Comparative Example 3]
To 100 parts by mass of ultrapure water, 30 parts by mass of a PVA resin having an average polymerization degree of 560 saponified with tetramethylammonium hydroxide, a saponification degree of 88 mol% and a sodium content of 6 ppm was added, and then stirred. A PVA aqueous solution was prepared by dispersing / dissolving. This aqueous solution was added dropwise to a mixture of 446 parts by mass of propylene glycol monomethyl ether, 352 parts by mass of polyethylene glycol 200 and 72 parts by mass of boron oxide, and heated to 60 ° C. with stirring. The coating solution was prepared by cooling to room temperature while continuing stirring after heating. A white precipitate was generated at room temperature, resulting in a non-uniform coating solution that could not be uniformly coated.

[Comparative Example 4]
To 100 parts by mass of ultrapure water, 30 parts by mass of a PVA resin having an average polymerization degree of 560 saponified with tetramethylammonium hydroxide, a saponification degree of 88 mol% and a sodium content of 6 ppm was added, and then stirred. A PVA aqueous solution was prepared by dispersing / dissolving. This aqueous solution was dropped into a mixture of 446 parts by mass of propylene glycol monomethyl ether, 352 parts by mass of mannitol and 72 parts by mass of boron oxide, and heated to 60 ° C. with stirring. Although an attempt was made to produce a coating solution by cooling to room temperature while continuing stirring after heating, boron oxide was not completely dissolved, resulting in a non-uniform coating solution, which could not be applied uniformly.

[Comparative Example 5]
To 280 parts by mass of ultrapure water, 30 parts by mass of a PVA resin having an average degree of polymerization of 560 saponified with tetramethylammonium hydroxide, a saponification degree of 88 mol% and a sodium content of 6 ppm was added, and then stirred. A PVA aqueous solution was prepared by dispersing / dissolving. This aqueous solution was dropped into a mixture of 458 parts by mass of propylene glycol monomethyl ether, 160 parts by mass of ethylene glycol and 72 parts by mass of boron oxide, and heated to 60 ° C. with stirring. The coating solution was prepared by cooling to room temperature while continuing stirring after heating. When left at room temperature for 5 hours, a white precipitate was generated, resulting in a non-uniform coating solution, which could not be uniformly coated.

[Comparative Example 6]
To 100 parts by mass of ultrapure water, 30 parts by mass of a PVA resin having an average polymerization degree of 560 saponified with tetramethylammonium hydroxide, a saponification degree of 88 mol% and a sodium content of 6 ppm was added, and then stirred. A PVA aqueous solution was prepared by dispersing / dissolving. This aqueous solution was dropped into a mixture of 483 parts by mass of propylene glycol monomethyl ether, 352 parts by mass of ethylene glycol and 35 parts by mass of boron oxide, and heated to 60 ° C. with stirring. The coating solution was prepared by cooling to room temperature while continuing stirring after heating. The viscosity of this coating solution at 20 ° C. was 67 mPa · s at 60 rpm. This diffusion coating solution was applied to a silicon wafer by the above method, dried, degreased, and diffused, and the resistance value was measured to be 0.9Ω / □, as described in the intended Examples 1 to 5. The resistance value was higher than 0.5 to 0.6Ω / □.

[Comparative Example 7]
To 100 parts by mass of ultrapure water, 30 parts by mass of a PVA resin having an average polymerization degree of 560 saponified with tetramethylammonium hydroxide, a saponification degree of 88 mol% and a sodium content of 6 ppm was added, and then stirred. A PVA aqueous solution was prepared by dispersing / dissolving. This aqueous solution was dropped into a mixture of 446 parts by mass of propylene glycol monomethyl ether, 352 parts by mass of ethylene glycol and 320 parts by mass of boron oxide, and heated to 60 ° C. with stirring. The coating solution was prepared by cooling to room temperature while continuing stirring after heating. Despite the addition of ethylene glycol, the boron oxide remained undissolved.

  From the above, in the present invention, it was confirmed that a boron diffusion coating solution containing a boron compound at a high concentration can be obtained while using a propylene glycol derivative inferior in solubility of the boron compound (Examples 1 to 3). 5). On the other hand, in Comparative Examples 1 to 7, a boron diffusion coating liquid containing a boron compound at a high concentration cannot be obtained (Comparative Examples 1 to 5 and 7), or even if a boron diffusion coating liquid is obtained, It was confirmed that it was not a practical physical property.

  The boron diffusion coating solution of the present invention contains a high concentration of a boron-based compound that could not be produced by a conventional method while using a propylene glycol derivative that has little concern about environmental toxicity and is poor in solubility of the boron compound. Is possible.

Claims (7)

(A) a boron compound, (b) an alcoholic hydroxyl group-containing polymer compound, (c) a propylene glycol derivative, (d) ethylene glycol, and (e) water, wherein the content of the (a) boron compound is When boron oxide (B ₂ O ₃ ) is used, the coating liquid for boron diffusion is 5% by mass or more and 20% by mass or less.   2. The high-concentration boron diffusion according to claim 1, wherein the boron compound is at least one selected from the group consisting of boric acid, boron oxide (anhydrous boric acid), ammonium borate and boron chloride. Coating liquid.   (B) The coating solution for boron diffusion according to claim 1 or 2, wherein the alcoholic hydroxyl group-containing polymer compound is a polyvinyl alcohol resin having a sodium content of less than 10 ppm.   (C) The propylene glycol derivative is at least one selected from the group consisting of propylene glycol monomethyl ether, propylene glycol monoethyl ether, and propylene glycol mono-n-butyl ether. A coating solution for boron diffusion according to any one of the above.   (D) Content of ethylene glycol is 15 mass% or more, (e) Content of water is less than 25 mass%, Coating for boron diffusion in any one of Claims 1-4 characterized by the above-mentioned liquid.   (1) (b) a step of preparing an aqueous solution containing an alcoholic hydroxyl group-containing polymer compound and (e) water, (2) (a) a boron compound, (c) a propylene glycol derivative and ( d) A method for producing a boron diffusion coating solution according to any one of claims 1 to 5, further comprising a step of mixing ethylene glycol.   (2) The method for producing a boron diffusion coating solution according to claim 6, wherein in the step, heating is performed to 40 ° C or higher.