TW201910265A - Impurity diffusing agent composition and method for forming impurity diffusion layer - Google Patents

Abstract

An object of the present invention is to provide a coating type composition of impurity diffusing agent capable of diffusing boron toward a semiconductor substrate while suppressing external diffusion of a boron compound, and a method for forming an impurity diffusion layer on a surface of a silicon substrate by using the composition of impurity diffusing agent. The solution of the present invention is to use a boron compound having a specific partial structure as the (A) boron compound in a coating type composition of impurity diffusing agent containing the (A) boron compound and a (S) solvent, and the (A) boron compound is used together with a (B) siloxane compound. As the (B) siloxane compound, silsesquioxane is preferred.

Description

Impurity diffusion agent composition and method for forming impurity diffusion layer

The present invention relates to an impurity diffusion agent composition containing a boron compound and a method for forming an impurity diffusion layer using the impurity diffusion agent composition.

When manufacturing various semiconductor elements or solar cells, a semiconductor substrate in which an impurity diffusion component is diffused can be used. As a method of diffusing the impurity diffusion component into a semiconductor substrate such as a silicon substrate, for example, a method of vaporizing the impurity diffusion component and diffusing the impurity diffusion component into the semiconductor substrate is often adopted. Specifically, the semiconductor substrate is arranged in the diffusion furnace at intervals, and the vaporized impurity diffusion component is spread around the semiconductor substrate to diffuse the impurity diffusion component into the semiconductor substrate.

When forming an impurity diffusion layer having a p-type conductivity on a silicon substrate, an impurity diffusion component containing boron is often used. Examples of a method for diffusing an impurity-diffusing component containing boron into a semiconductor substrate include a pyrolysis method, a counter-NB method, a dopant-based method, and a coating method. Among these, a coating method is preferably adopted from the viewpoint that an expensive device is not required, uniform diffusion can be performed, and mass productivity is excellent. In particular, a method of applying a coating liquid containing boron using a spin coater or the like is often employed.

As a coating type diffusing agent composition containing boron, for example, a diffusing agent composition containing a boron compound, a polymer compound containing a hydroxyl group, and a solvent has been proposed, and the boron compound is selected from the group consisting of a boronic ester A group consisting of a dihydrocarbyl boric acid (borinic acid) and a dihydrocarbyl boric acid ester (see Patent Document 1). By using the diffusing agent composition, boron can be favorably diffused into the semiconductor substrate. [Prior Art Literature] [Patent Literature]

[Patent Document 1]: Japanese Patent Laid-Open No. 2016-195203

[Problems to be Solved by the Invention]

However, when the diffusing agent composition described in Patent Document 1 is used, although boron can be well diffused into the semiconductor substrate, on the other hand, due to the influence of external diffusion (out diffusion), the semiconductor Diffusion of boron also occurs in parts of the substrate where boron should not be diffused.

The present invention has been made in view of the problems described above, and an object thereof is to provide a coating-type impurity diffusing agent composition capable of diffusing boron into a semiconductor substrate while suppressing external diffusion of a boron compound, and using the impurity diffusing agent. A method for forming an impurity diffusion layer on the surface of a silicon substrate by a composition. [Means to solve the problem]

The inventors of the present application have found that a boron compound having a specific partial structure is used as the (A) boron compound in a coating-type impurity diffusing agent composition containing (A) a boron compound and (S) a solvent, and The use of (A) a boron compound together with (B) a siloxane compound can solve the above-mentioned problems and complete the present invention. Specifically, the present invention provides the following solutions.

A first aspect of the present invention is an impurity diffusing agent composition characterized by containing (A) a boron compound, (B) a siloxane compound, and (S) a solvent, and (A) the boron compound has a partial structure represented by the following formula , [化 1] (In the above formula, * is the end of the bonding bond to the oxygen atom.)

A second aspect of the present invention is a method for forming an impurity diffusion layer. The formation method includes the following steps: (1) applying the impurity diffusion agent composition according to the first aspect to a main surface of a silicon substrate to form a coating film; A step of diffusing the boron of the (A) boron compound contained in the impurity diffusing agent composition into the silicon substrate. [Effect of the invention]

According to the present invention, it is possible to provide a coating-type impurity diffusing agent composition capable of diffusing boron into a semiconductor substrate while suppressing external diffusion of a boron compound, and using the impurity diffusing agent composition on the surface of a silicon substrate. Method for forming an impurity diffusion layer.

[Best Mode for Carrying Out the Invention] ≪ Impurity Diffuser Composition ≫ The impurity diffuser composition contains (A) a boron compound, (B) a siloxane compound, and (S) a solvent having a specific partial structure. In the following, the essential components or optional components that can be contained in the impurity diffusing agent composition will be described.

<(A) Boron compound> The impurity diffusion agent composition contains (A) a boron compound as an impurity diffusion component. As the (A) boron compound, a compound having a partial structure represented by the following formula can be used. [Chemical 2] (In the above formula, * is the terminal of the bonding bond to the oxygen atom.) The impurity diffusing agent composition may contain two or more (A) boron compounds in combination.

When the above-mentioned (A) boron compound is used in combination with the (B) siloxane compound described later, the following phenomenon occurs: (A) the boron compound diffuses well into the silicon substrate, while using impurities The (A) external diffusion of the boron compound in the coating film formed of the diffusing agent composition is reduced.

Considering this, as one of the reasons, it is presumed that when (A) the diffusion of the boron compound is performed by heating to a high temperature, the main surface of the coating film on the silicon substrate that is not in contact with the silicon substrate is larger than that of silicon The main surface that the substrate contacts is more compact.

Although the reason for this is uncertain, it is speculated that the reason may be the following: due to the intermolecular interaction of the (A) boron compound or the interaction between the (A) boron compound and the (B) siloxane compound, impurity diffusion is used The main surface of the coating film formed of the agent composition that is not in contact with the silicon substrate is highly compacted.

In addition, the (A) boron compound has the above-mentioned partial skeleton that does not contain an organic group, so that the ratio of the organic component is lower than that of other boron compounds having an organic group at both terminal groups, and even if heated, It is also difficult to sublimate. Therefore, if an impurity diffusing agent composition containing the (A) boron compound having the above-mentioned partial structure is used, the (A) boron compound tends to remain in the coating film during heating, and as a result, the (A) boron compound is easily suppressed At the same time, the external diffusion of boron into the semiconductor substrate is good.

In addition, since the (A) boron compound contains a B-B bond, it has a larger specific gravity than other components contained in the impurity diffusing agent composition. In addition, the application of the impurity diffusing agent composition to the semiconductor substrate is generally performed so that the formed coating film is vertically upward, and the semiconductor substrate is vertically downward. Therefore, compared with other components in the coating film, the specific gravity (A) boron compound is more likely to be deposited near the interface between the coating film and the semiconductor substrate when the coating film is formed. As a result, it is considered that a concentration gradient is formed in the coating film. The closer to the semiconductor substrate side, the higher the concentration of the (A) boron compound.形成 If such a concentration gradient is formed, the amount of (A) the boron compound is small on the surface of the coating film that is not in contact with the semiconductor substrate, and therefore, (A) the external diffusion of the boron compound is suppressed. On the other hand, since the amount of the (A) boron compound in the coating film is large near the interface between the coating film and the semiconductor substrate, the diffusion of the (A) boron compound into the semiconductor substrate proceeds well.

For the reasons explained above, it is considered that by using the (A) boron compound and (B) siloxane compound having the above-mentioned partial structure in combination, it is possible to make boron to the semiconductor while suppressing the external diffusion of (A) the boron compound. Good diffusion in the substrate.

As the (A) boron compound, a compound represented by the following formula (a1) or (a2) is preferable in terms of easy availability or synthesis and good diffusibility. [Chemical 3] (In formula (a1), R ¹ and R ² are each independently a hydrogen atom or a monovalent organic group having 1 or more and 6 or less carbon atoms, and in formula (a2), R ³ is 1 or more carbon atoms And a divalent organic group of 6 or less.)

Specific examples of the organic group having 1 to 6 carbon atoms as R ¹ and R ² in formula (a1) include methyl, ethyl, n-propyl, isopropyl, and n-butyl. Chain alkyl groups such as isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, n-pentane-3-yl, sec-pentyl, tert-pentyl, and n-hexyl; Cycloalkyl such as cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl; cycloalkylalkyl such as cyclobutylmethyl, and cyclopentylmethyl; phenyl. R ¹ and R ² may be the same group or different groups, and are preferably the same group.

Specific examples of the divalent hydrocarbon group having 1 to 6 carbon atoms as R ³ in formula (a2) include ethane-1,2-diyl, propane-1,3-diyl, 2-methylpropane-1,3-diyl, 2,3-dimethylbutane-2,3-diyl, cyclobutane-1,2-diyl, and o-phenylene.

Specific preferable examples of the (A) boron compound include the following compounds A1 to A8. Among the following compounds, A1, A2, and A3 are preferred, and A1 is more preferred. [Chemical 4]

The impurity diffusing agent composition may contain (A) a boron compound other than the boron compound as an impurity diffusion component within a range not hindering the subject of the present invention. Specific examples of the other boron compounds include monohydroboric acid, boric acid, boric acid, and the like. The content of the other boron compounds in the impurity diffusing agent composition is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10 relative to the total mass of the (A) boron compound and other boron compounds. Mass% or less, particularly preferably 5 mass% or less, and most preferably 0 mass%.

The content of the (A) boron compound in the impurity diffusing agent composition is not particularly limited as long as it does not hinder the object of the present invention. The content of the (A) boron compound in the impurity diffusing agent composition can be appropriately changed according to a coating method or the like. Typically, the content of the (A) boron compound is preferably 1% by mass or more and 50% by mass or less, more preferably 2% by mass or more and 30% by mass or less with respect to the total mass of the impurity diffusing agent composition. By using the (A) boron compound in an amount within the above range, the (A) boron compound is easily diffused into the silicon substrate.

<(B) Siloxane Compound> As described above, the impurity diffusing agent composition contains a siloxane compound containing a siloxane bond. The siloxane compound is not particularly limited, and various conventionally known siloxane compounds can be used without particular limitation.

Examples of the siloxane skeleton in the (B) siloxane compound include a cyclic siloxane skeleton and a polysiloxane skeleton (for example, linear or branched siloxane (linear) Or branched polysiloxanes), cage-type, ladder-type polysilsesquioxane, etc.). (B) The siloxane compound may be a so-called modified siloxane compound having an unsaturated hydrocarbon group such as a vinyl group or an allyl group, an amine group, an epoxy group, or a hydroxyl group at a side chain or a terminal.

As the (B) siloxane compound, a silsesquioxane is preferred because it is easy to achieve both good diffusion of boron and suppression of external diffusion. The structure of the silsesquioxane is not particularly limited, and may be a cage type or a ladder type.

Preferred specific examples of the (B) siloxane compound include linear siloxane such as polydimethylsiloxane, polyphenylmethylsiloxane, and polydiphenylsiloxane. , Or a ladder-type polysilsesquioxane represented by the following formula. [Chemical 5] (In the above formula, R ^{4 is} each independently a hydrogen atom or a monovalent organic group having 1 or more and 6 or less carbon atoms, and n is the number of repeating units in parentheses.)

In the above formula, as R ⁴ , an organic group having 1 to 6 carbon atoms is preferred. Specific examples of the organic group having 1 to 6 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, N-pentyl, isopentyl, neopentyl, n-pentane-3-yl, sec-pentyl, tert-pentyl, and n-hexyl chain alkyl groups; cyclopropyl, cyclobutyl, cyclopentyl, and Cycloalkyl such as cyclohexyl; cycloalkylmethyl such as cyclobutylmethyl and cyclopentylmethyl; phenyl. Of these groups, methyl and ethyl are preferred, and ethyl is more preferred.

The mass average molecular weight of the (B) siloxane compound in terms of polystyrene is not particularly limited, but is typically preferably 100 or more and 100,000 or less.

The content of the (B) siloxane compound in the impurity diffusing agent composition is not particularly limited as long as it does not hinder the object of the present invention. The content of the (B) siloxane compound in the impurity diffusing agent composition can be appropriately changed according to a coating method or the like. Typically, the content of the (B) siloxane compound is preferably 1% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 40% by mass or less with respect to the total mass of the impurity diffusing agent composition. . By using (B) a siloxane compound in an amount within the above range, it is easy to achieve both good diffusion of boron to the silicon substrate and suppression of external diffusion.

<Other components> The impurity diffusing agent composition may further contain various additives such as a surfactant, a binder resin such as an acrylic resin, and a thixotropy imparting agent such as SiO ₂ fine particles as (A) a boron compound and (B) a siloxane compound. And (C) other components than the polyol.

<(S) Solvent> (I) The impurity diffusing agent composition contains a (S) solvent for the purpose of adjusting coating properties and the like. The (S) solvent is preferably a polar organic solvent.

Specific examples of the organic solvent include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, Ethylene glycol diethyl ether, ethylene glycol dipropyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether Ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monophenyl ether, diethylene glycol Mono- or dialkyl ether diols such as alcohol diethyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether; ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether Acetate, ethylene glycol monopropyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, 2-methoxybutyl acetate , 3-methoxybutyl acetate, 4-methoxybutyl acetate, 2-methyl-3-methoxybutyl acetate, 2-ethoxybutyl acetate, 4-ethoxybutyl acetate , And 4-propoxybutyl acetate, etc. Esters; ketones such as diethyl ketone, methyl isobutyl ketone, ethyl isobutyl ketone, and cyclohexanone; propyl propionate, isopropyl propionate, and 3-methoxypropionate Esters, ethyl 3-methoxypropionate, ethyl 3-ethoxypropionate, ethyl 3-propoxypropionate, propyl 3-methoxypropionate, and 3-methoxypropionic acid Propionates such as isopropyl ester; esters such as butyl acetate, isoamyl acetate, methyl ethyl acetate, methyl lactate, and ethyl lactate; benzyl methyl ether, benzyl ethyl ether, benzene, Aromatics such as toluene, xylene, benzyl alcohol, and 2-phenoxyethanol; methanol, ethanol, propanol, isopropanol, butanol, isobutanol, 2-methoxyethanol, 2-ethoxy Alcohols such as ethanol, 3-methyl-3-methoxybutanol, hexanol, and cyclohexanol; cyclic esters such as γ-butyrolactone; ethylene glycol, propylene glycol, diethylene glycol, and two Polar organic solvents such as diols such as propylene glycol. These can be used alone or in combination of two or more.

The content of the (S) solvent in the impurity diffusing agent composition can be appropriately changed according to the coating and printing method. The content of the (S) solvent in the impurity diffusing agent composition is preferably, for example, 50% by mass or more and 98% by mass or less with respect to the total mass of the impurity diffusing agent composition.

≫Method for producing impurity diffusing agent composition≫ 组成 The impurity diffusing agent composition can be produced by dissolving the necessary or optional components described above in the (S) solvent. It is also possible to filter the impurity diffusing agent composition using a filter having a desired opening diameter to remove impurities insoluble in the (S) solvent.

≫Method of forming impurity diffusion layer≫ ≫The method of forming an impurity diffusion layer in a silicon substrate may be performed using a method including the following steps: 步骤 a step of forming a coating film by coating the aforementioned impurity diffusion agent composition on one main surface of the silicon substrate; And a step of diffusing boron of the boron compound (A) contained in the impurity diffusing agent composition into the silicon substrate.

As the silicon substrate, both an n-type silicon substrate and a p-type silicon substrate can be used. When considering a boron-diffused silicon substrate for a solar cell element having a general structure, an n-type silicon substrate is preferably used.

The method of applying the impurity diffusing agent composition to one main surface of the silicon substrate is not particularly limited. As a specific example of a coating method, a spin coating method, a spray coating method, and various printing methods are mentioned. Examples of the printing method include an inkjet printing method, a roll coating method, a screen printing method, a letterpress printing method, a gravure printing method, and an offset printing method.

After coating, if necessary, the (S) solvent in the coating film is removed to form a layer containing a boron compound. The film thickness of the boron compound-containing layer can be appropriately determined in consideration of (A) the diffusion conditions of the boron compound, (A) the type of the boron compound, and the boron concentration in the silicon substrate after diffusion, and the like. The film thickness of the boron compound-containing layer is typically preferably 10 nm or more and 5000 nm or less, and more preferably 50 nm or more and 3000 nm or less.

Next, the boron (A) boron compound contained in the impurity diffusing agent composition is diffused into the silicon substrate. The diffusion of boron can usually be performed by heating a silicon substrate including a layer containing a boron compound. The temperature of the rhenium heating silicon substrate is not particularly limited, as long as the diffusion of boron is performed well. The temperature for heating the silicon substrate is preferably 900 ° C or higher and 1050 ° C or lower, and more preferably 920 ° C or higher and 1000 ° C or lower.

The time for heating the silicon substrate is not particularly limited as long as the diffusion of boron can be performed well. The time for heating the silicon substrate is preferably 1 minute or more and 120 minutes or less in terms of the time for which the heating temperature is maintained.

The method for heating the silicon substrate to a desired temperature is not particularly limited. Typically, a silicon substrate can be heated using a heating furnace such as an electric furnace. In addition, the silicon substrate may be heated by a method such as laser irradiation. From the viewpoint that it is easy to uniformly heat the silicon substrate, a method using a heating furnace such as an electric furnace is preferred as the heating method.

After the diffusion of boron, the aqueous solution containing hydrofluoric acid can usually be used to remove the layer containing the boron compound. The concentration of the aqueous hydrofluoric acid solution is not particularly limited as long as the layer containing a boron compound can be removed.

By using the aforementioned impurity diffusing agent composition and diffusing boron into the silicon substrate by the method described above, it is possible to form an impurity diffusion layer obtained by well diffusing boron into the silicon substrate while suppressing external diffusion. [Example]

Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited by the following examples.

[Example 1] To a mixed solvent composed of 185 g of ethanol and 555 g of propylene glycol monopropyl ether, 13.0 g of tetrahydroxydiboron was added and dissolved while stirring. Next, 96.0 g of a ladder-type silsesquioxane (PPSQ-E, manufactured by Konishi Chemical Industry Co., Ltd.) in which R ⁴ is ethyl in the following formula was added, and dissolved while stirring to obtain an impurity diffusing agent.组合 物。 Composition. [Chemical 6]

The obtained impurity diffusing agent composition was spin-coated on an n-type silicon wafer, and then dried at 100 ° C and 200 ° C for 1 minute using a hot plate to form a boron compound-containing layer having a film thickness of 310 nm. Next, an organic component of the coating film was oxidized and decomposed in a diffusion furnace at 600 ° C. for 30 minutes in an oxygen atmosphere. Then, the temperature was raised at a rate of 7.5 ° C / min in a nitrogen atmosphere, and diffusion was performed under the conditions of 950 ° C and 30 minutes. Among them, diffusion is performed in a state where an n-type silicon substrate having no layer containing a boron compound is disposed so as to face the layer containing a boron compound on the n-type silicon substrate. The distance between the two n-type silicon substrates was 2.5 mm.测定 The degree of external diffusion can be evaluated by measuring the sheet resistance of an n-type silicon substrate without a layer containing a boron compound.

After the diffusion, two n-type silicon substrates were immersed in a 10% by mass aqueous solution of hydrofluoric acid for 10 minutes, and a layer containing a boron compound on the n-type silicon substrate and an n-type silicon substrate for evaluating external diffusion were immersed. The film formed on the surface was peeled. Next, the sheet resistance value of the n-type silicon substrate after the diffusion of boron from the layer containing the boron compound and the sheet resistance value of the n-type silicon substrate for evaluating external diffusion were measured. The sheet resistance was measured using a 4-terminal method.的 The sheet resistance of the n-type silicon substrate after the diffusion of boron from the layer containing a boron compound was 70 Ω / sq., And the sheet resistance of the n-type silicon substrate for evaluating external diffusion was 680 Ω / sq. The ratio of the two is 9.7 (= 680/70). It can be seen that by using a tetrahydroxydiboride (B) compound containing (A) a boron compound having the aforementioned specific partial structure, and a ladder type halves with (B) a siloxane compound. The impurity diffusing agent composition of the siloxane can suppress the external diffusion and allow the boron to diffuse well into the silicon substrate.

[Example 2] (13.0 g of tetrahydroxydiboron was added to a mixed solvent composed of 185 g of ethanol and 555 g of propylene glycol monopropyl ether, and dissolved while stirring. Next, 96.0 g of Silicone Oligomer (X-24-9590, containing a terminal epoxy group, manufactured by Shin-Etsu Chemical Industry Co., Ltd.) was added, and dissolved while stirring to obtain an impurity diffusing agent composition. Thing.

Using the obtained impurity diffusing agent composition, it carried out similarly to Example 1, and performed the measurement of the diffusion of a boron compound and a sheet resistance value. The sheet resistance of the n-type silicon substrate after the diffusion of boron from the layer containing a boron compound was 34 Ω / sq., And the sheet resistance of the n-type silicon substrate for evaluating external diffusion was 163 Ω / sq. The ratio of the two was 4.8 (= 163/34). It was found that by using a tetrahydroxydiboron compound (A) as a boron compound having the aforementioned specific partial structure and an organosilicon oligomer as (B) a siloxane compound The impurity diffusing agent composition can satisfactorily diffuse boron into the silicon substrate while suppressing external diffusion.

[Comparative Example 1] (1) Change 13.0 g of tetrahydroxydiboron to 20.0 g of boric acid, 740 g of mixed solvent to 860 g of ethanol, and change the amount of PPSQ-E used from 96.0 g to 106.7 g. In the same manner as in Example 1, an impurity diffusing agent composition was obtained. (2) Except that the thickness of the layer containing the boron compound was changed from 310 nm to 300 nm using the obtained impurity diffusing agent composition, the same procedure as in Example 1 was performed to measure the diffusion of the boron compound and the sheet resistance value.薄 The sheet resistance of the n-type silicon substrate after the diffusion of boron from the layer containing a boron compound was 158 Ω / sq., And the sheet resistance of the n-type silicon substrate for evaluating external diffusion was 510 Ω / sq. The ratio of the two is 3.2 (= 510/158). It can be seen that an impurity diffusing agent composition containing boric acid not having the aforementioned specific partial structure and a ladder-type silsesquioxane as a (B) siloxane compound is used. In this case, it is difficult to achieve both suppression of external diffusion and good diffusion of boron.

[Comparative Example 2] To a mixed solvent of 210 g of ethanol and 630 g of propylene glycol monopropyl ether, 61.5 g of bis (neopentyl glycolato) diboron was added, and the mixture was stirred while stirring. Its dissolved. Next, 107.4 g of ladder-type silsesquioxane (PPSQ-E, manufactured by Konishi Chemical Industry Co., Ltd.) was added, and further dissolved while stirring to obtain an impurity diffusing agent composition. Except having used the obtained impurity diffusing agent composition and changing the film thickness of the boron compound-containing layer from 310 nm to 300 nm, the same procedure as in Example 1 was performed to measure the diffusion of the boron compound and measure the sheet resistance value. . The sheet resistance of the n-type silicon substrate after the diffusion of boron from a layer containing a boron compound was 3316 Ω / sq., And the sheet resistance of the n-type silicon substrate for evaluating external diffusion was 12,265 Ω / sq. . The ratio of the two is 3.7 (= 12,265 / 3316). It can be seen that when using bis (neopentylglycol) diboron which does not have the aforementioned specific partial structure, it is a ladder type that is (B) a siloxane compound. In the case of an impurity diffusing agent composition of a silsesquioxane, it is difficult to achieve both suppression of external diffusion and good diffusion of boron. In particular, in Comparative Example 2, the diffusion of boron into the silicon substrate was poor.

[Comparative Example 3] 59.0 g of boric acid was added to 855 g of ethanol, and dissolved while stirring. Next, 78.9 g of an organosilicon oligomer (KR-513, manufactured by Shin-Etsu Chemical Industry Co., Ltd.) was added, and further dissolved while stirring to obtain an impurity diffusing agent composition. Except having used the obtained impurity diffusing agent composition and changing the film thickness of the boron compound-containing layer from 310 nm to 300 nm, the same procedure as in Example 1 was performed to measure the diffusion of the boron compound and measure the sheet resistance value. . The sheet resistance of the n-type silicon substrate after the diffusion of boron from the layer containing a boron compound was 58 Ω / sq., And the sheet resistance of the n-type silicon substrate for evaluating external diffusion was 106 Ω / sq. The ratio of the two is 1.8 (= 106/58). It is understood that when an impurity diffusing agent composition containing boric acid not having the aforementioned specific partial structure and an organosilicon oligomer as a (B) siloxane compound is used. It is difficult to achieve both the suppression of external diffusion and the good diffusion of boron.

[Comparative Example 4] The silicone oligomer (KR-513, manufactured by Shin-Etsu Chemical Industry Co., Ltd.) was changed to a silicone oligomer (X-24-9590, which contains a terminal epoxy group, and Shin-Etsu Chemical Industry (Stock) ), Except that the same procedure as in Comparative Example 3 was performed to obtain an impurity diffusing agent composition. (2) Using the obtained impurity diffusing agent composition, the same procedure as in Comparative Example 3 was performed to measure the diffusion of the boron compound and the sheet resistance value. The sheet resistance of the n-type silicon substrate after the diffusion of boron from the layer containing a boron compound was 58 Ω / sq., And the sheet resistance of the n-type silicon substrate for evaluating external diffusion was 106 Ω / sq. The ratio of the two is 1.8 (= 106/58). It is understood that when an impurity diffusing agent composition containing boric acid not having the aforementioned specific partial structure and an organosilicon oligomer as a (B) siloxane compound is used. It is difficult to achieve both the suppression of external diffusion and the good diffusion of boron.

[Comparative Example 5] (33.6 g of trimethyl borate was added to 850 g of ethanol, and dissolved while stirring. Next, 107.4 g of ladder-type silsesquioxane (PPSQ-E, manufactured by Konishi Chemical Industry Co., Ltd.) was added, and further dissolved while stirring to obtain an impurity diffusing agent composition. Except having used the obtained impurity diffusing agent composition and changing the film thickness of the boron compound-containing layer from 310 nm to 300 nm, the same procedure as in Example 1 was performed to measure the diffusion of the boron compound and measure the sheet resistance value. . The sheet resistance of the n-type silicon substrate after the diffusion of boron from the layer containing a boron compound was 430 Ω / sq., And the sheet resistance of the n-type silicon substrate for evaluating external diffusion was 1197 Ω / sq. The ratio of the two is 2.8 (= 1197/430). It is understood that the use of an impurity diffusing agent containing trimethyl borate that does not have the aforementioned specific partial structure and a ladder-type silsesquioxane as a (B) siloxane compound is used. In the case of a composition, it is difficult to achieve both suppression of external diffusion and good diffusion of boron.

Claims (4)

The impurity diffusing agent composition is characterized by containing (A) a boron compound, (B) a siloxane compound, and (S) a solvent. The (A) boron compound has a partial structure represented by the following formula, [Chem. 1] In the above formula, * is the terminal of the bonding bond to the oxygen atom. The impurity diffusing agent composition according to claim 1, wherein the (A) boron compound is a compound represented by the following formula (a1) or (a2), [Chem 2] In the formula (a1), R ¹ and R ² are each independently a hydrogen atom or a monovalent organic group having 1 or more and 6 or less carbon atoms, and in the formula (a2), the R ³ system has 1 or more carbon atoms and Divalent organic group of 6 or less. The impurity diffusing agent composition according to claim 1 or 2, wherein the (B) siloxane compound is a silsesquioxane. A method for forming an impurity diffusion layer, comprising the following steps: (1) a step of forming a coating film by coating the impurity diffusion agent composition according to any one of claims 1 to 3 on a main surface of a silicon substrate; And a step of diffusing the boron of the boron compound (A) contained in the impurity diffusing agent composition into the silicon substrate.