JP6099437B2 - Diffusion agent composition and method for forming impurity diffusion layer - Google Patents

Description

  The present invention relates to a diffusing agent composition, a method for forming an impurity diffusion layer, and a solar cell.

  Silicon semiconductor devices having a P-type region in which boron is diffused are used for manufacturing transistors, diodes, ICs and the like. Conventionally, as a method for diffusing boron in a silicon substrate, a thermal decomposition method, a counter NB method, a dopant host method, a coating method, and the like have been mainly used. Among these, the coating method has been suitably used because it does not require an expensive apparatus, can be uniformly diffused, and is excellent in mass productivity. In particular, a method of applying a coating solution containing boron with a spin coater or the like was preferred.

  In recent years, in the field of semiconductor manufacturing, in particular in the field of solar cell manufacturing, cost reduction, high throughput, and reduction of environmental load are required. Specifically, for example, when producing a silicon-based solar cell, the amount of diffusion coating solution used should be reduced, and the diffusion carriers and diffusion concentrations may be partially different within the same silicon substrate with fewer steps. It is required to form a region, that is, partially diffuse. In this case, in the conventional spin coating method, the amount of coating liquid used per substrate is large, resulting in high cost and a large amount of waste liquid. Further, since it is necessary to previously form a diffusion protective film or the like on the silicon substrate for partial diffusion, the number of processes increases. Against this background, in recent years, methods have been developed for performing partial diffusion by partially printing a coating solution on a silicon substrate by a selective coating method such as a screen printing method. For example, Patent Document 1 proposes an impurity diffusion coating liquid for screen printing.

JP 2013-8953 A

  As a result of intensive studies, the present inventors have improved the accuracy of the printing pattern of the diffusing material composition formed by the selective coating method described above, and between the impurity diffusion region and the non-diffusion region. In order to improve the diffusion contrast, it has been recognized that there is room for improvement in the conventional diffusing material composition.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a diffusing agent composition capable of improving the accuracy of the printing pattern of the diffusing material composition and improving the diffusion contrast, and the diffusing agent composition. It is in providing the formation method of the used impurity diffusion layer, and a solar cell.

  In order to solve the above problems, an embodiment of the present invention is a diffusing agent composition. This diffusing material composition is a diffusing agent composition used for forming an impurity diffusing agent layer on a semiconductor substrate, and includes a boron compound (A), fine particles (B) containing at least one of silica and alumina, and siloxane. A compound (C) and an organic solvent (D) are contained. Content of microparticles | fine-particles (B) is less than 30 mass% with respect to the whole composition.

  Another embodiment of the present invention is a method for forming an impurity diffusion layer. The impurity diffusion layer forming method includes a pattern forming step of selectively applying the diffusing agent composition of the above-described embodiment to a semiconductor substrate to form an impurity diffusing agent layer having a predetermined pattern, and the diffusing agent composition. A diffusion step of diffusing boron of the boron compound (A) into the semiconductor substrate.

  Yet another embodiment of the present invention is a solar cell. This solar cell includes a semiconductor substrate on which an impurity diffusion layer is formed by the method for forming an impurity diffusion layer of the above-described aspect.

  ADVANTAGE OF THE INVENTION According to this invention, the diffusing agent composition which can aim at the improvement of the precision of the printing pattern of a diffusing material composition, and the improvement of a diffusion contrast, the formation method of the impurity diffusion layer using the said diffusing agent composition, and a solar cell Can be provided.

1A to 1C are process cross-sectional views for explaining a method for manufacturing a solar cell including a method for forming an impurity diffusion layer according to an embodiment. 2A to 2D are process cross-sectional views for explaining a method for manufacturing a solar cell including a method for forming an impurity diffusion layer according to an embodiment.

  Hereinafter, the present invention will be described based on preferred embodiments. The embodiments do not limit the invention but are exemplifications, and all features and combinations described in the embodiments are not necessarily essential to the invention.

  The diffusing agent composition according to the present embodiment is a diffusing agent composition used for forming an impurity diffusing agent layer on a semiconductor substrate, and in particular, an impurity having a predetermined pattern by selective application using a screen printing method. It is a diffusing agent composition suitably used for forming a diffusing agent layer. The diffusing agent composition according to the present embodiment contains a boron compound (A), fine particles (B), a siloxane compound (C), and an organic solvent (D). The diffusing agent composition further contains a polyhydric alcohol (E) as an optional component. Hereinafter, each component of the diffusing agent composition according to the present embodiment will be described in detail.

<Boron compound (A)>
A boron compound (A) is a compound used for manufacture of a solar cell as a dopant. The boron compound (A) is a group III (group 13) element compound, and contains boron which is a P-type impurity diffusion component. The boron compound (A) can form a P-type impurity diffusion layer (impurity diffusion region) in the semiconductor substrate by boron in the boron compound (A). More specifically, the boron compound (A) can form a P-type impurity diffusion layer in the N-type semiconductor substrate by boron in the boron compound (A), and P in the P-type semiconductor substrate. ^{A +} type (high concentration P type) impurity diffusion layer can be formed.

  The concentration of the boron compound (A) is appropriately adjusted according to the thickness of the impurity diffusion layer formed on the semiconductor substrate. For example, the boron compound (A) is preferably contained in an amount of 0.1% by mass or more, more preferably 1.0% by mass or more, based on the total mass of the diffusing agent composition. Moreover, it is preferable that 50 mass% or less of a boron compound (A) is contained with respect to the total mass of a diffusing agent composition, the range of 1-20 mass% is more preferable, and the range of 5-15 mass% is further more preferable. . Moreover, it is preferable that the boron atom in a boron compound (A) is contained in 0.01-10 mass% with respect to the total mass of a diffusing agent composition, and it is contained in 0.1-3 mass%. More preferably.

  Examples of the boron compound (A) include compounds having a structure represented by the following general formula (1).

B (OR ¹ ) ₃ (1)
[In General Formula (1), each R ¹ is independently an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 10 carbon atoms. The three R ¹ may be the same or different. ]

When R ¹ is an alkyl group, a linear or branched alkyl group having 1 to 4 carbon atoms is more preferable. The aryl group is, for example, a phenyl group or a naphthyl group. In addition, the alkyl group and the aryl group may have a substituent.

  Specific examples of the boron compound (A) include trimethyl borate, triethyl borate, tripropyl borate, tributyl borate, tripentyl borate, trihexyl borate, trioctyl borate, triphenyl borate and the like. it can. Among these boron compounds (A), trimethyl borate and triethyl borate are preferable from the viewpoint of suppressing aggregation and precipitation of impurity diffusion components. These boron compounds (A) may be used alone or in combination of two or more.

<Fine particles (B)>
The fine particles (B) contain at least one of silica (SiO ₂ ) and alumina. By containing the fine particles (B) in the diffusing material composition, it is possible to suppress bleeding from occurring in the pattern of the diffusing material composition printed on the substrate, and the accuracy of the printing pattern can be improved. Further, by using silica fine particles and / or alumina fine particles as the fine particles (B), the fine particles (B) can be avoided from causing contamination. As in the case of alumina, any compound containing a metal atom having a valence equal to that of a boron atom can be used as the fine particles (B). The fine particles (B) may be used alone or in combination of two or more.

  Examples of the silica fine particles include silica fine particles obtained by a known method. As a known method, metal silicon is melted and vaporized in a vacuum and introduced into an oxidizing atmosphere to obtain silica fine particles. Metal silicon powder is evaporated and oxidized in a flame containing oxygen to produce silica. A method for obtaining fine particles, a method for vaporizing tetrachlorosilane, jetting into a burner flame and oxidizing it to obtain silica fine particles (Japanese Patent Publication No. 47-46274), an alkali metal silicate such as sodium silicate as a raw material Water glass method, and alkoxysilane method using alkoxysilane such as tetraethoxysilane as a raw material.

  Silica fine particles include, for example, Aerosil series (manufactured by Nippon Aerosil Co., Ltd., “Aerosil” is a registered trademark), Leoro Seal series (manufactured by Tokuyama Co., Ltd., “Leoro Seal” is a registered trademark), WACKER HDK series (manufactured by Asahi Kasei Wacker Co., Ltd.) , “WACKER” is a registered trademark), Cab-O-Sil series (manufactured by Cabot Corporation, “Cab-O-Sil” is a registered trademark), Adelite series (manufactured by ADEKA Corporation, “Adelite” is a registered trademark), Cataloid -S series (catalyst chemical industry Co., Ltd., "Cataloid" is a registered trademark), Quartron series (manufactured by Fuso Chemical Industry, "Quartron" is a registered trademark), and Snowtex series (Nissan Chemical Industry Co., Ltd.) Commercial products such as these can be used.

  Examples of the alumina fine particles include alumina fine particles obtained by a known gas phase method or liquid phase method. As a known gas phase method, metal aluminum is melted and vaporized in a vacuum and introduced into an oxidizing atmosphere to obtain alumina fine particles. Metal aluminum powder is evaporated and oxidized in a flame containing oxygen. Examples thereof include a method for obtaining alumina fine particles, and a method for vaporizing aluminum chloride, ejecting it into a burner flame and oxidizing it to obtain alumina fine particles (Japanese Patent Publication No. 2005-506269). Known liquid phase methods include hydrolysis of alkylaluminum or alkoxyaluminum (Chemical Review No. 48, 1985, ultrafine particles (edited by the Chemical Society of Japan) pages 173 to 175, Academic Society Publishing Center, published in 1985), ammonium Examples include alum pyrolysis, ammonium aluminum carbonate pyrolysis, aluminum salt alkali neutralization, and aluminate hydrolysis.

  The alumina fine particles are, for example, Aeroxide series (Alu-c and Al-65, etc., manufactured by Degussa, “Aeroxide” is a registered trademark), SptrAl series (51, 81, 100, etc., manufactured by Cabot), CAB-O-SPERSE. Series (SpctrAl series water dispersion, manufactured by Cabot Corporation), AKP series (Sumitomo Chemical Co., Ltd., "AKP" is a registered trademark), Tymicron series (manufactured by Daimei Chemical Co., Ltd.), DISPERAL series (manufactured by Sasol, " Commercially available products such as “DISPERAL” is a registered trademark), and DISPAL series (manufactured by Sasol, “DISPAL” is a registered trademark) can be used.

  The alumina fine particles can also be used in the form of a dispersion (for example, alumina sol) dispersed with a known dispersant such as acetic acid, lactic acid, formic acid, nitric acid. As the alumina sol, commercially available products such as Cataloid-A series (manufactured by Catalyst Chemical Industry Co., Ltd.) and alumina sol series (manufactured by Nissan Chemical Industries, Ltd.) can be used.

  Content of microparticles | fine-particles (B) is less than 30 mass% with respect to the whole composition. By making content of microparticles | fine-particles (B) less than 30 mass%, it can suppress that a crack generate | occur | produces in the impurity diffusing agent layer formed on the board | substrate. Moreover, it can suppress that the diffusion contrast between an impurity diffusion area | region and a non-diffusion area | region falls by this. Moreover, content of microparticles | fine-particles (B) is 0.1 mass% or more with respect to the whole composition. The content of the fine particles (B) is preferably 3% by mass or more, more preferably 5% by mass or more, and further preferably 10% by mass or more with respect to the entire composition. By setting the content of the fine particles (B) to 3% by mass or more, the accuracy of the printing pattern can be further improved.

  The average particle diameter of the fine particles (B) is preferably 7 nm to 30 nm. By setting the average particle size of the fine particles (B) to 7 nm or more, aggregation of the fine particles (B) can be suppressed. On the other hand, when the average particle size of the fine particles (B) is 30 nm or less, it is possible to suppress a decrease in viscosity and thixotropy. The fine particles (B) may be either hydrophobic or hydrophilic, but are preferably hydrophobic. Here, “hydrophilic” means having a hydroxyl group (OH group) on the particle surface, and “hydrophobic” means having a methyl group, a trimethylsilyl group, or the like on the particle surface. Since the fine particles (B) are hydrophobic, compatibility with the siloxane compound (C) is increased, and printing accuracy can be improved. The “average particle diameter” is an average diameter of primary particles.

<Siloxane compound (C)>
The siloxane compound (C) forms a network structure in the diffusing material composition printed on the substrate. Therefore, by containing the siloxane compound (C) in the diffusing material composition, boron is scattered from the film of the diffusing agent composition applied on the substrate to the outside, and adheres to the uncoated area of the diffusing agent composition and diffuses. The occurrence of so-called out diffusion can be suppressed. Thereby, the diffusion contrast between the impurity diffusion region and the non-diffusion region can be improved.

Examples of the siloxane compound (C) include a reaction product (C1) obtained by hydrolysis and dehydration condensation of an alkoxysilane represented by the following general formula (2).
R ² _n Si (OR ³ ) _4-n (2)
[In General Formula (2), R ² is a hydrogen atom or an organic group. R ³ is an organic group. n is an integer of 1 or 2. If R ² is a plurality may be a plurality of R ² be the same or different, (OR ³⁾ is the case of multiple multiple (OR ³⁾ s may be the same or different. ]

Examples of the organic group of R ² and R ³ include an alkyl group, an aryl group, an allyl group, and a glycidyl group. In these, an alkyl group and an aryl group are preferable. R ² is more preferably an organic group having 2 or more carbon atoms from the viewpoint of improving diffusion contrast, and more preferably a bulky structure having a ring structure such as an aromatic ring, a heterocyclic ring, or a bridged ring. The organic group for R ³ is, for example, preferably a linear or branched alkyl group having 1 to 5 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms from the viewpoint of reactivity. The aryl group represented by R ² and R ³ is preferably, for example, one having 6 to 20 carbon atoms, and examples thereof include a phenyl group and a naphthyl group.

  In the general formula (2), the alkoxysilane (i) when n is 1 is represented by the following general formula (3), for example.

R ³¹ Si (OR ³² ) _e (OR ³³ ) _f (OR ³⁴ ) _g (3)
[In General Formula (3), R ³¹ represents the same hydrogen atom or organic group as R ² described above. R ³² , R ³³ and R ³⁴ each independently represent the same organic group as the above R ³ . e, f, and g are integers that satisfy 0 ≦ e ≦ 3, 0 ≦ f ≦ 3, 0 ≦ g ≦ 3, and satisfy the condition of e + f + g = 3. ]

  Specific examples of the alkoxysilane (i) include, for example, methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltributoxysilane, methyltripentyloxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriethoxysilane. Propoxysilane, ethyltributoxysilane, ethyltripentyloxysilane, ethyltriphenyloxysilane, propyltrimethoxysilane, propyltriethoxysilane, propyltributoxysilane, propyltripentyloxysilane, propyltriphenyloxysilane, butyltrimethoxy Silane, butyltriethoxysilane, butyltripropoxysilane, butyltributoxysilane, butyltripentyloxysilane, butyltriphenyloxy Silane, methylmonomethoxydiethoxysilane, ethylmonomethoxydiethoxysilane, propylmonomethoxydiethoxysilane, butylmonomethoxydiethoxysilane, methylmonomethoxydipropoxysilane, methylmonomethoxydipentyloxysilane, methylmonomethoxydiphenyloxysilane , Ethyl monomethoxydipropoxysilane, ethyl monomethoxydipentyloxysilane, ethylmonomethoxydiphenyloxysilane, propylmonomethoxydipropoxysilane, propylmonomethoxydipentyloxysilane, propylmonomethoxydiphenyloxysilane, butylmonomethoxydipropoxysilane, Butylmonomethoxydipentyloxysilane, butylmonomethoxydiphenyloxysilane, methylmethoxyethylene Xypropoxysilane, propylmethoxyethoxypropoxysilane, butylmethoxyethoxypropoxysilane, methylmonomethoxymonoethoxymonobutoxysilane, ethylmonomethoxymonoethoxymonobutoxysilane, propylmonomethoxymonoethoxymonobutoxysilane, butylmonomethoxymonoethoxymonobutoxy Examples thereof include silane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltripropoxysilane, and phenyltripentyloxysilane. Note that the alkyl group or alkoxy group having 3 or more carbon atoms in the above specific examples may be linear or branched. The butyl (or butoxy) group is preferably an n-butyl (n-butoxy) group. The same applies to the following specific examples.

  In the general formula (2), the alkoxysilane (ii) when n is 2 is represented by the following general formula (4), for example.

R ⁴¹ R ⁴² Si (OR ⁴³ ) _h (OR ⁴⁴ ) _i (4)
[In General Formula (4), R ⁴¹ and R ⁴² represent the same hydrogen atom or organic group as R ² described above. R ⁴³ and R ⁴⁴ each independently represent the same organic group as R ³ described above. h and i are integers satisfying 0 ≦ h ≦ 2, 0 ≦ i ≦ 2 and satisfying the condition of h + i = 2. ]

  Specific examples of the alkoxysilane (ii) include, for example, methyldimethoxysilane, methylmethoxyethoxysilane, methyldiethoxysilane, methylmethoxypropoxysilane, methylmethoxypentyloxysilane, methylmethoxyphenyloxysilane, ethyldipropoxysilane, and ethylmethoxy. Propoxysilane, ethyldipentyloxysilane, ethyldiphenyloxysilane, propyldimethoxysilane, propylmethoxyethoxysilane, propylethoxypropoxysilane, propyldiethoxysilane, propyldipentyloxysilane, propyldiphenyloxysilane, butyldimethoxysilane, butylmethoxyethoxysilane , Butyldiethoxysilane, butylethoxypropoxysilane, butyldipropoxysilane Butylmethyldipentyloxysilane, butylmethyldiphenyloxysilane, dimethyldimethoxysilane, dimethylmethoxyethoxysilane, dimethyldiethoxysilane, dimethyldipentyloxysilane, dimethyldiphenyloxysilane, dimethylethoxypropoxysilane, dimethyldipropoxysilane, diethyldimethoxysilane, Diethylmethoxypropoxysilane, diethyldiethoxysilane, diethylethoxypropoxysilane, dipropyldimethoxysilane, dipropyldiethoxysilane, dipropyldipentyloxysilane, dipropyldiphenyloxysilane, dibutyldimethoxysilane, dibutyldiethoxysilane, dibutyldipropoxy Silane, dibutylmethoxypentyloxysilane, dibutylmethoxyphene Oxysilane, methylethyldimethoxysilane, methylethyldiethoxysilane, methylethyldipropoxysilane, methylethyldipentyloxysilane, methylethyldiphenyloxysilane, methylpropyldimethoxysilane, methylpropyldiethoxysilane, methylbutyldimethoxysilane, methylbutyldi Ethoxysilane, methylbutyldipropoxysilane, methylethylethoxypropoxysilane, ethylpropyldimethoxysilane, ethylpropylmethoxyethoxysilane, dipropyldimethoxysilane, dipropylmethoxyethoxysilane, propylbutyldimethoxysilane, propylbutyldiethoxysilane, dibutylmethoxy Ethoxysilane, dibutylmethoxypropoxysilane, dibutylethoxypropoxysila , Phenyldimethoxysilane, phenylmethoxyethoxysilane, phenyldiethoxysilane, phenylmethoxypropoxysilane, phenylmethoxypentyloxysilane, phenylmethoxyphenyloxysilane, and the like.

  The siloxane compound (C) preferably contains an alkoxysilane having n of 0 in the general formula (2) as a starting material. In the general formula (2), the alkoxysilane (iii) when n is 0 is represented by, for example, the following general formula (5).

Si (OR ²¹ ) _a (OR ²² ) _b (OR ²³ ) _c (OR ²⁴ ) _d (5)
[In General Formula (5), R ²¹ , R ²² , R ²³ and R ²⁴ each independently represent the same organic group as R ³ described above. a, b, c and d are integers satisfying the condition of 0 ≦ a ≦ 4, 0 ≦ b ≦ 4, 0 ≦ c ≦ 4, 0 ≦ d ≦ 4 and a + b + c + d = 4. ]

  Specific examples of the alkoxysilane (iii) include, for example, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, tetrapentyloxysilane, tetraphenyloxysilane, trimethoxymonoethoxysilane, dimethoxydiethoxysilane, tri Ethoxymonomethoxysilane, trimethoxymonopropoxysilane, monomethoxytributoxysilane, monomethoxytripentyloxysilane, monomethoxytriphenyloxysilane, dimethoxydipropoxysilane, tripropoxymonomethoxysilane, trimethoxymonobutoxysilane, dimethoxydi Butoxysilane, triethoxymonopropoxysilane, diethoxydipropoxysilane, tributoxymonopropoxysilane, dimethoxymono Toximonobutoxysilane, diethoxymonomethoxymonobutoxysilane, diethoxymonopropoxymonobutoxysilane, dipropoxymonomethoxymonoethoxysilane, dipropoxymonomethoxymonobutoxysilane, dipropoxymonoethoxymonobutoxysilane, dibutoxymonomethoxymono Examples thereof include tetraalkoxysilanes such as ethoxysilane, dibutoxymonoethoxymonopropoxysilane, and monomethoxymonoethoxymonopropoxymonobutoxysilane. Among these, tetramethoxysilane and tetraethoxysilane are preferable from the viewpoint of reactivity.

  The reaction product (C1) comprises, for example, one or more selected from the above alkoxysilanes (i) to (ii) and the above alkoxysilane (iii) as an optional component, an acid catalyst, water, It can be prepared by hydrolysis and dehydration condensation in the presence of an organic solvent.

  As described above, water is used for the hydrolysis reaction of alkoxysilane, but in the diffusing agent composition according to the present embodiment, the water content based on the entire composition is 1% by mass or less. Is preferable, it is more preferable that it is 0.5 mass% or less, and it is still more preferable that water is not included substantially. According to this, the storage stability of the diffusing agent composition can be further improved.

  As the acid catalyst, either an organic acid or an inorganic acid can be used. As the inorganic acid, sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid and the like can be used, among which phosphoric acid and nitric acid are preferable. As the organic acid, formic acid, oxalic acid, fumaric acid, maleic acid, glacial acetic acid, acetic anhydride, propionic acid, n-butyric acid and other carboxylic acids, and organic acids having a sulfur-containing acid residue can be used. Examples of organic acids having a sulfur-containing acid residue include organic sulfonic acids, and examples of esterified products thereof include organic sulfates and organic sulfites. Among these, an organic sulfonic acid, for example, a compound represented by the following general formula (6) is particularly preferable.

R ¹³ -X (6)
[In General Formula (6), R ¹³ is a hydrocarbon group which may have a substituent, and X is a sulfonic acid group. ]

In the general formula (6), the hydrocarbon group as R ¹³ is preferably a hydrocarbon group having 1 to 20 carbon atoms. This hydrocarbon group may be saturated or unsaturated, and may be linear, branched or cyclic. When the hydrocarbon group of R ¹³ is cyclic, for example, an aromatic hydrocarbon group such as a phenyl group, a naphthyl group, and an anthryl group is preferable, and a phenyl group is particularly preferable. One or more hydrocarbon groups having 1 to 20 carbon atoms may be bonded to the aromatic ring in the aromatic hydrocarbon group as a substituent. The hydrocarbon group as a substituent on the aromatic ring may be saturated or unsaturated, and may be linear, branched or cyclic. Further, the hydrocarbon group as R ¹³ may have one or a plurality of substituents, such as a halogen atom such as a fluorine atom, a sulfonic acid group, a carboxyl group, a hydroxyl group, An amino group, a cyano group, etc. are mentioned.

  The acid catalyst acts as a catalyst for hydrolyzing alkoxysilane in the presence of water. The amount of the acid catalyst used is 1 to 1000 ppm, particularly 5 to 800 ppm, in the reaction system of the hydrolysis reaction. It is preferable to prepare so that it may become this range. The amount of water added is determined according to the hydrolysis rate to be obtained because the hydrolysis rate of the siloxane polymer changes accordingly.

  Examples of the organic solvent in the reaction system of the hydrolysis reaction include methanol, ethanol, propanol, isopropanol (IPA), monohydric alcohols such as n-butanol, methyl-3-methoxypropionate, and ethyl-3-ethoxypropionate. Alkylcarboxylic acid esters such as ethylene glycol, diethylene glycol, propylene glycol, glycerin, trimethylolpropane, hexanetriol and other polyhydric alcohols, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol mono Butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether , Monoethers of polyhydric alcohols such as diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether or monoacetates thereof, methyl acetate, ethyl acetate, butyl acetate Esters such as, acetone, methyl ethyl ketone, ketones such as methyl isoamyl ketone, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, diethylene glycol dimethyl ether , Diethylene Recall diethyl ether, diethylene polyhydric alcohol ethers all hydroxyl groups of polyhydric alcohols such and alkyl-etherified as methyl ethyl ether, and the like. These organic solvents may be used alone or in combination of two or more.

  By subjecting alkoxysilane to hydrolysis and dehydration condensation reaction in such a reaction system, a reaction product (C1) is obtained. The hydrolysis and dehydration condensation reactions are usually performed for about 1 to 100 hours, but in order to shorten the reaction time, it is preferable to heat in a temperature range not exceeding 80 ° C.

  After completion of the reaction, a reaction solution containing the synthesized reaction product (C1) and the organic solvent used for the reaction is obtained. The reaction product (C1) is separated from the organic solvent by a conventionally known method and can be obtained by the above method in a dry solid state or in a solution state in which the solvent is replaced if necessary.

  Moreover, as a siloxane compound (C), the siloxane polymer (C2) represented by following General formula (7) is mentioned.

In general formula (7), R ⁰¹ is a group containing an ethylenically unsaturated double bond, R ⁰ is an alkylene group having 1 to 9 carbon atoms, and may have a different R ^0. , R ⁰² is an alkyl group, an alkoxy group, an aryl group, or a hydrogen atom, and may have a different R ⁰² , and m: p is in the range of 1:99 to 100: 0, preferably 10 : It is the range of 90-90: 10. m: p can be appropriately set in consideration of Si content, film thickness adjustment, and the like.

In the general formula (7), the group containing an ethylenically unsaturated double bond in R ⁰¹ is preferably one having an ethylenically unsaturated double bond at the terminal, and particularly preferably an acryloyloxy group or a methacryloyloxy group. .

In General Formula (7), examples of the alkylene group having 1 to 9 carbon atoms in R ⁰ include a linear or branched alkylene group. Preferably it is a C1-C7, More preferably, it is a C1-C5 linear alkylene group, Most preferably, they are a methylene group, ethylene group, and n-propylene group.

In the general formula (7), as the alkyl group in R ^02, include alkyl groups having 1 to 10 carbon atoms, e.g., methyl group, ethyl group, propyl group, butyl group, a pentyl group, a hexyl group, a heptyl group, Linear alkyl groups such as octyl group, nonyl group, decyl group; 1-methylethyl group, 1-methylpropyl group, 2-methylpropyl group, 1-methylbutyl group, 2-methylbutyl group, 3-methylbutyl group, 1-ethylbutyl group, 2-ethylbutyl group, 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 4-methylpentyl group and other branched alkyl groups; cyclopentyl group, cyclohexyl group, adamantyl group And cyclic alkyl groups such as norbornyl group, isobornyl group and tricyclodecanyl group. Preferably it is a C1-C5 alkyl group, More preferably, it is a C1-C3 alkyl group, Most preferably, it is a methyl group.

In the general formula (7), examples of the alkoxy group represented by R ⁰² include an alkoxy group having 1 to 5 carbon atoms, and examples thereof include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, and a pentyloxy group. Preferably it is a C1-C3 alkoxy group, More preferably, it is a methoxy group or an ethoxy group.

In the general formula (7), examples of the aryl group represented by R ⁰² include a phenyl group, a biphenyl group, a fluorenyl group, a naphthyl group, an anthryl group, and a phenanthryl group. A phenyl group is preferred. Further, the aryl group of R ⁰² may have a substituent such as an alkyl group.

  The siloxane polymer represented by the general formula (7) is particularly preferably a siloxane polymer (C2-1) represented by the following formula (8), a siloxane polymer (C2-2) represented by the following formula (9), or Examples thereof include a siloxane polymer (C2-3) represented by the following formula (10). In the formula, m and p are the same as described above. Further, s + t = p and u + v = p. The mass average molecular weight (Mw) of a siloxane compound (C) is not specifically limited, Preferably it is 500-30000, More preferably, it is 1000-10000.

  The content of the siloxane compound (C) is preferably in the range of 10% by mass to 50% by mass and more preferably in the range of 15% by mass to 35% by mass with respect to the entire composition. When the content of the siloxane compound (C) is 10% by mass or more, the diffusion selectivity of the diffusing agent composition becomes better, and when the content is 50% by mass or less, it is included in the diffusing agent composition. It is possible to improve the content balance with other components.

<Organic solvent (D)>
The content of the organic solvent (D) is preferably 15 to 70% by mass, more preferably 20 to 50% by mass, based on the entire composition. Moreover, it is preferable that an organic solvent (D) contains the organic solvent (D1) whose boiling point is 190 degreeC or more. Specific examples of the organic solvent (D1) include ethylene glycol, hexylene glycol, propylene glycol diacetate, 1,3-butylene glycol diacetate, diethylene glycol, dipropylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl. Ether, diethylene glycol monobutyl ether, diethylene glycol monophenyl ether, diethylene glycol diethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, ethylene glycol monobutyl ether acetate, ethylene glycol monophenyl ether acetate, diethylene glycol monomethyl ether acetate Diethylene glycol monoethyl ether acetate (EDGAC), diethylene glycol monopropyl ether acetate, diethylene glycol monophenyl ether acetate, dipropylene glycol monomethyl ether acetate, diethylene glycol monobutyl ether acetate, glycerin, benzyl alcohol, 3-methyl-3-methoxybutyl acetate, 3-ethyl-3-methoxybutyl acetate, 2-methoxypentyl acetate, 3-methoxypentyl acetate, 4-methoxypentyl acetate, 2-methyl-3-methoxypentyl acetate, 3-methyl-3-methoxypentyl acetate, 3- Methyl-4-methoxypentyl acetate, 4-methyl-4-methoxypentyl acetate, di Hexyl ether, benzyl acetate, ethyl benzoate, diethyl maleate, .gamma.-butyrolactone, etc. terpineol and the like. These may be used alone or in combination of two or more.

  The diffusing agent composition according to the embodiment may include a solvent other than the organic solvent (D1) described above. However, 70 mass% or more is preferable and, as for content of the organic solvent (D1) with respect to the whole organic solvent (D), 90 mass% or more is more preferable.

  Examples of the solvent other than the organic solvent (D1), that is, the organic solvent (D2) having a boiling point of less than 190 ° C. include ketones such as cyclohexanone, methyl-n-pentyl ketone, methyl isopentyl ketone, and 2-heptanone; ethylene glycol, propylene glycol Polyhydric alcohols such as: propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monomethyl ether (PGME), derivatives of polyhydric alcohols such as dipropylene glycol dimethyl ether, propylene glycol propyl ether; other butyl acetate, ethyl acetoacetate, Examples include esters such as butyl lactate and diethyl oxalate. Among these, propylene glycol monomethyl ether acetate, 2-heptanone and butyl acetate are preferable.

<Polyhydric alcohol (E)>
The polyhydric alcohol (E) is represented by the following general formula (11).

［一般式（１１）中、ｊは０〜３の整数である。ｋは１以上の整数である。Ｒ^４及びＲ^５は、それぞれ独立に、水素原子、水酸基、炭素数１〜５のアルキル基、又は炭素数１〜５のヒドロキシアルキル基である。Ｒ^４及びＲ^５が複数の場合は複数のＲ^４及びＲ^５はそれぞれ同じでも異なってもよい。またｊが２以上である場合、複数のＲ^４及びＲ^５は必ず一つ以上の水酸基又は炭素数１〜５のヒドロキシアルキル基を含む。Ｒ^６及びＲ^７は、それぞれ独立に水素原子又は炭素数１〜３のアルキル基である。］

[In General Formula (11), j is an integer of 0-3. k is an integer of 1 or more. R ⁴ and R ⁵ are each independently a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 5 carbon atoms, or a hydroxyalkyl group having 1 to 5 carbon atoms. R ⁴ and ^{R 5} in the case of a plurality and the plurality of ^{R 4 R 5} may be the same or different. When j is 2 or more, the plurality of R ⁴ and R ⁵ always contain one or more hydroxyl groups or a hydroxyalkyl group having 1 to 5 carbon atoms. R ⁶ and R ⁷ are each independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. ]

  Specific examples of the polyhydric alcohol (E) include ethylene glycol, propylene glycol, 1,3-butanediol, trimethylolpropane, 3-methylpentane-1,3,5-triol, mannitol and the like. These polyhydric alcohols may be used alone or in combination of two or more.

  Boron compound (A), which is a P-type impurity diffusion component, is contained in the diffusing agent composition in the form of boric acid ester, and polyhydric alcohol (E) having a specific structure is contained in the diffusing agent composition, so that diffusion In the agent composition, the polyhydric alcohol (E) and the boron compound (A) efficiently form a complex, thereby suppressing the hydrolysis of the boron compound (A), and the aggregation and precipitation of the boron compound (A). It can be suppressed. Moreover, since the aggregation and precipitation of the boron compound (A) can be suppressed, the occurrence of out diffusion can be suppressed.

  The content ratio of the boron compound (A) and the polyhydric alcohol (E) in the diffusing agent composition is such that the content of the boron compound (A) is 5 times or less the content of the polyhydric alcohol (E). Preferably, it is 2 times mole or less, and the range of 2-1 times mole is further more preferable. Moreover, it is preferable that content of a polyhydric alcohol (E) is more than content of a boron compound (A) from the point that a boron compound (A) can form a complex effectively. The content of the polyhydric alcohol (E) is preferably 60% by mass or less, more preferably 5% by mass or more and 25% by mass or less, and more preferably 10% by mass or more and 20% by mass with respect to the entire composition. More preferably, it is in the range of not more than

  The diffusing agent composition according to the present embodiment may contain a general surfactant, antifoaming agent, and the like as other components. For example, by including a surfactant, it is possible to improve coating properties, planarization properties, and development properties, and to reduce the occurrence of uneven coating of the diffusing agent composition layer formed after coating. Conventionally known surfactants can be used as such surfactants, and silicone surfactants are preferred. Moreover, it is preferable that surfactant is contained in 500-3000 mass ppm with respect to the whole spreading | diffusion agent composition, especially 600-2500 mass ppm. Furthermore, since it is excellent in the peelability of the diffusing agent composition layer after a diffusion process as it is 2000 mass ppm or less, it is more preferable. Surfactants may be used alone or in combination.

  The concentration of metal impurities (other than the metal components contained in the boron compound (A), fine particles (B), and siloxane compound (C) described above) contained in the diffusing agent composition is preferably 500 ppb or less. Thereby, the fall of the efficiency of the photovoltaic effect which arises by containing metal impurities can be suppressed.

<Method for preparing diffusing agent composition>
The diffusing agent composition according to the present embodiment can be prepared by mixing the above-described components by a conventionally known method so as to form a uniform solution in an arbitrary order.

<Method for forming impurity diffusion layer and method for producing solar cell>
Referring to FIGS. 1A to 1C and FIGS. 2A to 2D, a method for forming an impurity diffusion layer in a semiconductor substrate, and the impurity diffusion layer is formed by the method. A method for manufacturing a solar cell including a semiconductor substrate will be described. 1 (A) to 1 (C) and FIGS. 2 (A) to 2 (D) are cross-sectional views for explaining a method for manufacturing a solar cell including a method for forming an impurity diffusion layer according to an embodiment. FIG.

<P-type impurity diffusing agent layer formation: pattern formation step>
As shown in FIG. 1A, for example, an N-type silicon wafer is prepared as the semiconductor substrate 1. The semiconductor substrate 1 is a solar cell substrate having a textured portion 1a on one surface. It should be noted that the texture portion may or may not be provided on the other surface of the semiconductor substrate 1. The texture portion 1a has a structure in which fine irregularities are continuously arranged, and in this structure, irregularities with the same pitch and height are arranged with regularity, and irregularities with various pitches and heights. Are randomly arranged. The pitch of the projections and depressions (the distance in the surface direction to the deepest portion of the recess that is the apex of the projection) is, for example, 1 to 10 μm. The height of the unevenness (height from the deepest part of the concave part to the apex of the convex part) is, for example, 1 to 10 μm. Reflection of light on the surface of the semiconductor substrate 1 can be prevented by the texture portion 1a. The texture structure can be formed using a known wet etching method or the like.

  The diffusing agent composition (P-type diffusion) according to the present embodiment contains boron, which is a P-type impurity diffusion component, on the surface of the semiconductor substrate 1 on the side opposite to the side where the textured portion 1a is provided. Agent composition) is selectively applied to form a P-type impurity diffusing agent layer 2 having a predetermined pattern. The selective application (printing) of the P-type diffusing agent composition to the semiconductor substrate 1 is preferably performed by a screen printing method. The ink jet printing method, screen printing method, spray coating method, roll coat printing method, relief printing method, intaglio printing method, offset printing method and the like can also be used. After the P-type impurity diffusing agent layer 2 having a predetermined pattern is formed, the semiconductor substrate 1 is placed on a hot plate and, for example, a baking process is performed at 150 ° C. for 3 minutes to dry the P-type impurity diffusing agent layer 2.

<Baking of P-type impurity diffusing agent layer>
Next, as shown in FIG. 1B, the semiconductor substrate 1 provided with the P-type impurity diffusing agent layer 2 is put into a heating furnace 200. The heating furnace 200 is, for example, a conventionally known vertical diffusion furnace, and includes a base portion 201, an outer cylinder 202, a mounting table 204, a support member 206, a gas supply path 208, a gas discharge path 210, and a heater 212. With.

  The outer cylinder 202 is assembled to the base portion 201 so that the axial direction is parallel to the vertical direction, and the furnace chamber 203 is formed by the base portion 201 and the outer cylinder 202. The mounting table 204 is circular in a plan view and is arranged at the center of the furnace chamber 203. A plurality of support members 206 are column-like and are erected on the outer edge of the mounting table 204 at intervals in the circumferential direction. A plurality of grooves are provided on the side surface of each support member 206 at intervals in the axial direction. The semiconductor substrate 1 is supported by the support member 206 by engaging the outer edge portion with the groove of the support member 206. The gas supply path 208 is a pipe for supplying atmospheric gas to the furnace chamber 203, and one end is connected to an atmospheric gas tank (not shown) and the other end is connected to the opening 202 a of the outer cylinder 202. The gas discharge path 210 is a pipe line for discharging the gas in the furnace chamber 203, and one end is connected to the opening 202 b of the outer cylinder 202. The heater 212 is provided on the outer periphery of the outer cylinder 202 and heats the inside of the furnace chamber 203.

A plurality of semiconductor substrates 1 are arranged in the furnace chamber 203, and oxygen (O ₂ ) gas, for example, is supplied as an atmospheric gas from the gas supply path 208 into the furnace chamber 203. Then, the semiconductor substrate 1 is heated in an O ₂ gas atmosphere, and the P-type impurity diffusing agent layer 2 is baked to form a silica-based film containing a P-type impurity diffusion component. As the atmospheric gas, in addition to O ₂ gas, nitrogen (N ₂ ) gas, a mixed gas of N ₂ and O ₂ , or the like can be used. The P-type impurity diffusing agent layer 2 is baked by baking. The heating temperature of the P-type impurity diffusing agent layer 2 in firing, that is, the firing temperature is preferably 400 ° C. or higher and 900 ° C. or lower. By setting the firing temperature to 400 ° C. or higher, the P-type impurity diffusing agent layer 2 can be fired more reliably. In addition, by setting the firing temperature to 900 ° C. or less, it is possible to more reliably suppress boron from being externally diffused from the P-type impurity diffusing agent layer 2. The firing time is preferably 10 minutes or more and 60 minutes or less.

  The P-type impurity diffusing agent layer 2 may be fired under humidified conditions. For example, after bubbling through water heated to 90 ° C., the atmosphere gas (about 37.8% RH) that has passed through a tube heated to 120 ° C. is supplied into the furnace chamber 203 to be humidified. Can do.

<Diffusion of P-type impurity diffusion component: diffusion process>
Next, for example, a mixed gas of N ₂ and O ₂ is supplied as an atmospheric gas from the gas supply path 208 into the furnace chamber 203. The mixing ratio of N ₂ and O ₂ in the mixed gas is, for example, 95: 5. Then, the semiconductor substrate 1 is heated at a temperature higher than the firing temperature in a mixed gas atmosphere, and boron of the boron compound (A) contained in the diffusing agent composition is diffused into the semiconductor substrate 1. A P-type impurity diffusion layer 4 (first impurity diffusion layer) is formed (see FIG. 1C). The heating temperature of the semiconductor substrate 1, that is, the thermal diffusion temperature is preferably 950 ° C. or higher and 1100 ° C. or lower. By setting the thermal diffusion temperature to 950 ° C. or higher, the impurity diffusion component can be more reliably thermally diffused. Further, by setting the thermal diffusion temperature to 1100 ° C. or lower, it is more reliable that the impurity diffusion component diffuses into the semiconductor substrate 1 beyond the desired diffusion region and that the semiconductor substrate 1 is damaged by heat. Can be prevented. The diffusion time is preferably 10 minutes or more and 60 minutes or less. Instead of the diffusion furnace, the semiconductor substrate 1 may be heated by conventional laser irradiation.

  After the diffusion step, the P-type impurity diffusing agent layer 2 remaining on the P-type impurity diffusion layer 4 is removed. In the step of removing the P-type impurity diffusing agent layer 2, the semiconductor substrate 1 is immersed in, for example, a 20% hydrofluoric acid aqueous solution for 10 minutes, washed with water, and dried.

<Formation of N-type impurity diffusing agent layer>
Next, as shown in FIG. 2A, after the semiconductor substrate 1 is taken out of the heating furnace 200 and allowed to cool, N is formed on the surface of the semiconductor substrate 1 excluding the region where the P-type impurity diffusion layer 4 is formed. An N-type diffusing agent composition containing a type impurity diffusion component is selectively applied to form an N-type impurity diffusing agent layer 3. A conventionally well-known thing can be used for N type diffusing agent composition. The selective application of the N-type diffusing agent composition to the semiconductor substrate 1 is performed by, for example, an inkjet printing method, a screen printing method, a spray coating method, a roll coat printing method, a relief printing method, an intaglio printing method, an offset printing method, or the like. be able to. After the N-type impurity diffusing agent layer 3 having a predetermined pattern is formed, the semiconductor substrate 1 is placed on a hot plate and, for example, a baking process is performed at 150 ° C. for 3 minutes to dry the N-type impurity diffusing agent layer 3.

<Baking of N-type impurity diffusing agent layer and diffusion of N-type impurity diffusing component>
Next, the semiconductor substrate 1 provided with the N-type impurity diffusing agent layer 3 is put into the heating furnace 200 shown in FIG. A plurality of semiconductor substrates 1 are arranged in the furnace chamber 203, and the N-type impurity diffusing agent layer 3 is fired under the same conditions as the firing conditions of the P-type impurity diffusing agent layer 2. Thereafter, the N-type impurity diffusion component is diffused under the same conditions as the diffusion conditions of the P-type impurity diffusion component to form the N-type impurity diffusion layer 5 (second impurity diffusion layer) on the surface of the semiconductor substrate 1. (See FIG. 2B). Thereafter, the semiconductor substrate 1 taken out from the heating furnace 200 is immersed in a stripping solution such as hydrofluoric acid, and the N-type impurity diffusion agent layer 3 remaining on the N-type impurity diffusion layer 5 is removed. Through the above steps, as shown in FIG. 2B, the semiconductor substrate 1 having the P-type impurity diffusion layer 4 and the N-type impurity diffusion layer 5 formed on the surface can be obtained.

<Formation of solar cells>
Next, as shown in FIG. 2C, the P-type impurity diffusion layer 4 and the N-type impurity diffusion layer of the semiconductor substrate 1 are formed using a well-known chemical vapor deposition method (CVD method) such as a plasma CVD method. A passivation layer 6 made of a silicon nitride film (SiN film) is formed on the surface on which 5 is formed. This passivation layer 6 also functions as an antireflection film. Further, an antireflection film 7 made of a silicon nitride film is formed on the surface of the texture portion 1a.

  Next, as shown in FIG. 2D, the passivation layer 6 is selectively removed by a known photolithography method and etching method, and predetermined regions of the P-type impurity diffusion layer 4 and the N-type impurity diffusion layer 5 are obtained. A contact hole 6a is formed so that is exposed. Then, the contact hole 6a provided on the P-type impurity diffusion layer 4 is filled with metal by, for example, an electrolytic plating method and an electroless plating method, screen printing using a metal paste, or the like, and the P-type impurity diffusion layer 4 And electrode 8 (first electrode) electrically connected to each other. Similarly, an electrode 9 (second electrode) electrically connected to the N-type impurity diffusion layer 5 is formed in the contact hole 6 a provided on the N-type impurity diffusion layer 5. Through the above steps, solar cell 10 according to the present embodiment can be manufactured. Note that the impurity diffusion component diffusion method according to the present embodiment can also be employed when forming a semiconductor substrate used for applications other than solar cells. Note that the order of formation of the P-type impurity diffusion layer 4 and the formation of the N-type impurity diffusion layer 5 is not particularly limited, and the N-type impurity diffusion layer 5 may be formed first, or P in terms of improving manufacturing throughput. The type impurity diffusion layer 4 and the N type impurity diffusion layer 5 may be formed simultaneously. When forming the P-type impurity diffusion layer 4 and the N-type impurity diffusion layer 5 at the same time, after performing the pattern forming process of one impurity diffusing agent layer, before performing the pattern forming process of the other impurity diffusing agent layer, It is preferable to pass through the baking process of one impurity diffusing agent layer. After the firing step, the pattern forming step of the other impurity diffusing agent layer and the diffusion step of both impurity diffusing agent layers can be simultaneously performed to form the P-type impurity diffusing layer 4 and the N-type impurity diffusing layer 5 at the same time. . Moreover, the diffusing agent composition used for the pattern of the impurity diffusing agent layer formed earlier is preferably the P-type diffusing agent composition according to the present embodiment from the viewpoint of the characteristics described later.

  As described above, the diffusing agent composition according to the present embodiment includes the boron compound (A), the fine particles (B) containing at least one of silica and alumina, the siloxane compound (C), and the organic solvent (D). And). And content of microparticles | fine-particles (B) is less than 30 mass% with respect to the whole composition. Thereby, since it can suppress that a bleeding arises in the pattern of the diffusing material composition printed on the board | substrate, the precision of a printing pattern can be improved. Further, since boron out-diffusion from the diffusing agent composition layer applied on the substrate can be suppressed, the diffusion contrast between the impurity diffusion region and the non-diffusion region can be improved. Furthermore, since it can suppress that a crack generate | occur | produces in the impurity diffuser layer formed on the board | substrate, the fall of a diffusion contrast can be suppressed. Moreover, since the viscosity of the diffusing agent composition can be adjusted to a viscosity suitable for screen printing by the fine particles (B), it can be suitably used for selective application of the diffusing agent composition by the screen printing method.

  In addition, in the method for forming an impurity diffusion layer according to the present embodiment, the above-described diffusing agent composition that can suppress the occurrence of printing pattern bleeding and out-diffusion is used, so the impurity diffusion layer is formed with higher accuracy. can do. In addition, since the solar cell according to the present embodiment is formed by using the impurity diffusion layer forming method described above that can form a more accurate impurity diffusion layer, the solar cell has higher performance and higher reliability. It becomes a battery.

  The present invention is not limited to the above-described embodiments, and various modifications such as design changes can be added based on the knowledge of those skilled in the art, and the embodiments to which such modifications are added. Are also included in the scope of the present invention.

  Examples of the present invention will be described below. However, these examples are merely examples for suitably explaining the present invention, and do not limit the present invention.

<Preparation of diffusing agent composition>
Table 1 shows the component compositions and content ratios of the diffusing agent compositions according to Examples 1 to 5, Reference Example 6, and Comparative Examples 1 to 3. The unit of each numerical value in the table is% by mass, and the ratio of each component is the ratio to the total mass of the diffusing agent composition.

The symbols and abbreviations in Table 1 indicate the following compounds.
PPSQ (SR-23): polyphenylsilsesquioxane having a structure represented by the following formula (12) (w is an integer of 1 or more) (product name “SR-23” manufactured by Konishi Chemical)
X-40-9272B: a siloxane compound having a structure in which m = 22, s = 21, and t = 57 in the above formula (9) (manufactured by Shin-Etsu Chemical Co., Ltd., product name “X-40-9272B”)
KR-401N: a siloxane compound having a structure in which m = 8, u = 42, and v = 50 in the above formula (10) (manufactured by Shin-Etsu Chemical Co., Ltd., product name “KR-401N”)
EDGAC: Diethylene glycol monoethyl ether acetate PVA: Polyvinyl alcohol

In each of Examples , Reference Examples and Comparative Examples, trimethyl borate (trimethyl borate) is used as the boron compound (A), silica fine particles (product name “AEROSIL R812” manufactured by Nippon Aerosil Co., Ltd.) are used as the fine particles (B), and an organic solvent. EDGAC was used as (D), and trimethylolpropane (CH ₃ CH ₂ C (CH ₂ OH) ₃ ) was used as the polyhydric alcohol (E). The silica fine particles used were hydrophobic fine particles, and the average particle size was 7 nm. As for the siloxane compound (C), PPSQ (SR-23) is used in Examples 1 , 2 , 5 and Reference Examples 6 and Comparative Examples 1 and 2, X-40-9272B is used in Example 3, and Example 4 is used. Then, KR-410N was used. In Comparative Example 3, a copolymer of isobutyl methacrylate and hydroxyethyl methacrylate having a structure represented by the following formula (13) was used as an acrylic resin instead of the siloxane compound (C). In Comparative Example 4, PVA was used instead of the siloxane compound (C). In addition, since PVA does not melt | dissolve in EDGAC, in the comparative example 4, glycerol and water were used as a solvent.

The diffusing material composition of Example 1 was prepared as follows. That is, first, a dopant liquid composed of trimethylolpropane and trimethylborate was prepared. Next, siloxane resin PPSQ (SR-23) was dissolved in EDGAC to prepare a 50% solution of siloxane resin (hereinafter referred to as resin solution). Thereafter, 28 g of silica fine particles, 56 g of a dopant solution, 84 g of a resin solution, and 42 g of EDGAC were added to a planetary mixer. Then, a paste-like diffusing agent composition was obtained by stirring and mixing. Regarding the diffusing material compositions of other Examples , Reference Examples and Comparative Examples, the diffusing material compositions were prepared in the same procedure as in Example 1 according to the component compositions and contents in Table 1.

<Evaluation of printing pattern accuracy>
The diffusion material compositions of each Example , Reference Example, and each Comparative Example were screen-printed on the surface of a silicon wafer using a screen printer (MT-27444, manufactured by Microtech Co., Ltd.). A screen plate having a line pattern with a width of 500 micrometers (μm) was used for screen printing. The printing speed was 300 mm / s, the substrate temperature was 23 ° C., and the emulsion thickness was 5 micrometers. Thereafter, the silicon wafer was placed on a hot plate and heated at 150 ° C. for 3 minutes to dry the printed pattern. The print pattern of each example , reference example, and each comparative example is observed using an optical microscope, the presence or absence of cracks in the print pattern is checked, and the average value of the line width of the print pattern is measured to determine the print pattern accuracy (print Characteristics). The case where a crack was not confirmed was made favorable (A), and the case where a crack was confirmed was made inappropriate (B). The results are shown in Table 1.

<Evaluation of diffusion contrast>
The diffusing material compositions of each Example , Reference Example, and each Comparative Example were screen-printed on the surface of an N-type silicon wafer using a screen printer (MT-27444, manufactured by Microtech Co., Ltd.). A screen plate having a line pattern with a width of 10 mm was used for screen printing. The printing speed was 300 mm / s, the substrate temperature was 23 ° C., and the emulsion thickness was 5 micrometers. Thereafter, the silicon wafer was placed on a hot plate and heated at 150 ° C. for 3 minutes to dry the printed pattern. Then, the silicon wafer was put into a heating furnace, and the printed pattern was baked by heating at 650 ° C. for 15 minutes in an O ₂ gas atmosphere. Subsequently, the temperature is raised at a predetermined speed, and the silicon wafer is heated at 980 ° C. for 15 minutes in an atmosphere of a mixed gas of N ₂ and O ₂ (N ₂ / O ₂ = 95/5), and boron in the printed pattern is changed to silicon wafer. Thermally diffused inside. After the diffusion treatment, the silicon wafer was immersed in a 20% aqueous hydrofluoric acid solution for 10 minutes, and the BSF (boron silicate glass) generated on the substrate surface was peeled off.

In each silicon wafer printed with the diffusing material composition of each example , reference example and each comparative example, the sheet resistance value of the printed portion and the non-printing portion of the diffusing material composition was measured and the P / N determination was performed. Diffusion contrast (diffusion characteristics) was evaluated. The sheet resistance value was measured by a four-probe method using a sheet resistance measuring device (VR-70, manufactured by Kokusai Electric). P / N determination was performed by measuring the conductivity type of a printing part and a non-printing part using a P / N determination machine (PN / 12α, manufactured by Napson). The results are shown in Table 1.

As shown in Table 1, in Comparative Example 1 that does not include the fine particles (B), an error exceeding 50% with respect to the line width of the screen plate occurred in the print pattern. 5. In Reference Example 6, a printed pattern with an error of 50% or less could be formed. From this, it was confirmed that the printing pattern accuracy is improved when the diffusing material composition contains the fine particles (B). Moreover, in Examples 1-5 which contain 3 mass% or more of microparticles | fine-particles (B), the printing pattern of 15% or less of error was able to be formed. From this, it was confirmed that a more accurate printing pattern can be formed because a diffusing material composition contains 3 mass% or more of microparticles | fine-particles (B).

In Comparative Example 2 containing 30% by mass of fine particles (B), cracks were observed in the printed pattern, whereas in Examples 1 to 5 and Reference Example 6 containing less than 30% by mass of fine particles (B). No cracks were found in the printed pattern. And in the comparative example 2, the conductivity type of a printing part and a non-printing part was P type, and the difference in sheet resistance value was very small. This is considered to be because boron in the print pattern diffused to the outside from the crack portion generated in the print pattern. From this, it was confirmed that by making the content of the fine particles (B) less than 30% by mass, generation of cracks is suppressed and a good diffusion contrast can be obtained.

In Comparative Examples 3 and 4 that do not contain the siloxane compound (C), the conductivity type of the printed part and the non-printed part are both P-type, and the difference in sheet resistance is extremely small, whereas the siloxane compound (C In Examples 1 to 5 and Reference Example 6 including), the conductivity type of the non-printing portion was N-type and the conductivity type of the printing portion was P-type, and the difference in sheet resistance value was large. From this, it was confirmed that the diffusion contrast is improved when the diffusing material composition contains the siloxane compound (C).

  DESCRIPTION OF SYMBOLS 1 Semiconductor substrate, 2 P-type impurity diffuser layer, 3 N-type impurity diffuser layer, 4 P-type impurity diffused layer, 5 N-type impurity diffused layer, 8,9 electrode, 10 solar cell.

Claims (4)

A diffusing agent composition used for forming an impurity diffusing agent layer on a semiconductor substrate,
A boron compound (A);
Fine particles (B) containing at least one of silica and alumina;
A siloxane compound (C);
An organic solvent (D);
A polyhydric alcohol (E) represented by the following general formula (11) ,
Content of the said microparticles | fine-particles (B) is 3 to 30 mass% with respect to the whole composition, The diffusing agent composition characterized by the above-mentioned.

[In General Formula (11), j is an integer of 0-3. k is an integer of 1 or more. R ⁴ and R ⁵ are each independently a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 5 carbon atoms, or a hydroxyalkyl group having 1 to 5 carbon atoms. R ⁴ and ^{R 5} in the case of a plurality and the plurality of ^{R 4 R 5} may be the same or different. When j is 2 or more, the plurality of R ⁴ and R ⁵ always contain one or more hydroxyl groups or a hydroxyalkyl group having 1 to 5 carbon atoms. R ⁶ and R ⁷ are each independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. ] The diffusing agent composition according to claim 1, which is used for forming an impurity diffusing agent layer having a predetermined pattern by selective application of a diffusing material composition using a screen printing method. A pattern forming step of selectively applying the diffusing agent composition according to claim 1 or 2 to a semiconductor substrate to form an impurity diffusing agent layer having a predetermined pattern;
A diffusion step of diffusing boron of the boron compound (A) contained in the diffusing agent composition into the semiconductor substrate;
A method for forming an impurity diffusion layer, comprising: The method for forming an impurity diffusion layer according to claim 3 , wherein in the pattern formation step, a diffusing agent composition is printed on a semiconductor substrate by a screen printing method.

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