JP7647100B2 - Impurity diffusing composition, method for manufacturing semiconductor element and method for manufacturing solar cell using the same - Google Patents

Description

The present invention relates to an impurity diffusion composition, a method for manufacturing a semiconductor element using the same, and a method for manufacturing a solar cell.

Currently, in the manufacture of solar cells, when forming a p-type or n-type impurity diffusion layer in a semiconductor substrate, a method is adopted in which a diffusion source is formed on the substrate and impurities are diffused into the semiconductor substrate by thermal diffusion. For the formation of the diffusion source, CVD and solution coating methods using a liquid impurity diffusion composition are being considered. Among these, the solution coating method is preferably used because it does not require expensive equipment and is suitable for mass production.

When forming a p-type impurity diffusion layer by a solution coating method, a coating solution containing a boron compound and a hydroxyl-containing polymer compound such as polyvinyl alcohol is usually applied to the surface of a semiconductor substrate by spin coating or screen printing, and then thermally diffused. In order to improve the continuous printability during screen printing, a boron-containing diffusion composition has been proposed that does not use water, which is generally used in boron-containing diffusion compositions, but uses a polyhydric alcohol solvent and polyvinyl alcohol with a relatively low saponification degree of 50 to 90 mol% (see, for example, Patent Document 1).

JP 2013-8953 A

However, when using polyvinyl alcohol with a degree of saponification as described in Patent Document 1, there was an issue of insufficient diffusivity.

The present invention has been made based on the above-mentioned circumstances, and aims to provide an impurity diffusion composition that enables uniform diffusion of impurities into a semiconductor substrate and excellent continuous printability during screen printing.

In order to solve the above problems, the impurity-diffusing composition of the present invention has the following configuration. That is, the present invention is an impurity-diffusing composition comprising (A) polyvinyl alcohol, (B) an impurity-diffusing component, and (C) a siloxane, in which the saponification degree of (A) polyvinyl alcohol is 20 mol % or more and less than 50 mol %, (B) the impurity-diffusing component is boric acid, (C) the siloxane comprises at least one partial structure represented by any one of the following general formulas (1) and (2) and at least one partial structure represented by any one of the following general formulas (3) and (4), and the mass ratio (A):(C) of (A) polyvinyl alcohol to (C) siloxane is 30:70 to 75:25 .

(R ¹ and R ² each independently represent any one of a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, an acyloxy group having 1 to 6 carbon atoms, and an alkenyl group having 2 to 10 carbon atoms, and a plurality of R ^1s and R ^2s may be the same or different. R ³ represents an aryl group having 6 to 15 carbon atoms, and a plurality of R ^3s may be the same or different. R ⁴ represents any one of a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, an acyloxy group having 1 to 6 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, and an aryl group having 6 to 15 carbon atoms, and a plurality of R ^4s may be the same or different.)

According to the present invention, it is possible to provide an impurity diffusion composition that enables uniform diffusion of impurities into a semiconductor substrate and excellent continuous printability during screen printing.

1A to 1C are cross-sectional views showing process steps of a manufacturing method for a semiconductor device according to a first embodiment of the present invention. 5A to 5C are cross-sectional views showing process steps of a method for manufacturing a semiconductor device according to a second embodiment of the present invention. 5A to 5C are cross-sectional views showing steps in a method for producing a back junction solar cell using a method for producing a semiconductor element according to a second embodiment of the present invention. 10A to 10C are cross-sectional views showing process steps of a manufacturing method of a semiconductor device according to a third embodiment of the present invention. 10A to 10C are cross-sectional views showing the steps of a method for producing a double-sided power generation solar cell using a method for producing a semiconductor element according to a third embodiment of the present invention. 10A to 10C are cross-sectional views showing process steps of a manufacturing method of a semiconductor device according to a fourth embodiment of the present invention. 10A to 10C are cross-sectional views showing the steps of a method for producing a double-sided power generation solar cell using a method for producing a semiconductor element according to a fourth embodiment of the present invention. 10A to 10C are cross-sectional views showing steps of a method for manufacturing a semiconductor device according to a fifth embodiment of the present invention. 1A to 1C are cross-sectional views showing a process for an example of a barrier property evaluation using an impurity diffusing composition of the present invention.

Hereinafter, preferred embodiments of the impurity diffusion composition according to the present invention and the method for manufacturing a semiconductor device using the composition will be described in detail with reference to the drawings as necessary. Note that the present invention is not limited to these embodiments.

The impurity-diffusing composition according to an embodiment of the present invention comprises (A) polyvinyl alcohol, (B) an impurity-diffusing component, and (C) a siloxane, in which the degree of saponification of the (A) polyvinyl alcohol is 20 mol% or more and less than 90 mol%, and the (C) siloxane comprises at least one of a partial structure represented by any one of the following general formulas (1) and (2) and a partial structure represented by any one of the following general formulas (3) and (4).

R ¹ and R ² each independently represent any one of a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, an acyloxy group having 1 to 6 carbon atoms, and an alkenyl group having 2 to 10 carbon atoms, and a plurality of R ^1s and R ^2s may be the same or different. R ³ represents an aryl group having 6 to 15 carbon atoms, and a plurality of R ^3s may be the same or different. R ⁴ represents any one of a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, an acyloxy group having 1 to 6 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, and an aryl group having 6 to 15 carbon atoms, and a plurality of R ^4s may be the same or different.

In this specification, the "impurity diffusion composition" may be simply referred to as the "composition."

(A) Polyvinyl alcohol The impurity-diffusing composition according to the embodiment of the present invention contains (A) polyvinyl alcohol (hereinafter, sometimes simply referred to as "(A) PVA"). The saponification degree of (A) polyvinyl alcohol is 20 mol% or more and less than 90 mol%. By containing (A) polyvinyl alcohol, a complex is formed with (B) impurity-diffusing component, and a uniform coating can be formed when applied. By making the saponification degree of (A) polyvinyl alcohol 20% or more, the stability of the complex with (B) impurity-diffusing component is increased, and the diffusibility and diffusion uniformity are improved. In addition, by making the saponification degree of (A) polyvinyl alcohol less than 90%, the solubility in an organic solvent is improved. From the viewpoint of improving storage stability, the saponification degree of (A) polyvinyl alcohol is preferably less than 70 mol%, more preferably less than 50 mol%. That is, by setting the degree of saponification of the polyvinyl alcohol (A) to 20 mol % or more and less than 90 mol %, it is possible to provide an impurity diffusing composition which satisfies both solubility in an organic solvent and complex stability, thereby enabling uniform diffusion of impurities into a semiconductor substrate and excellent continuous printability during screen printing.

The average degree of polymerization of (A) polyvinyl alcohol is preferably 150 to 1000 in terms of solubility and complex stability. In the present invention, the average degree of polymerization and the degree of saponification are both values measured in accordance with JIS K 6726 (1994). The degree of saponification is a value measured by the back titration method, one of the methods described in the JIS.

In terms of achieving good thermal diffusion and suppressing organic residues on the substrate after removal of the composition, the content of (A) PVA is preferably 1 to 20 mass% and more preferably 5 to 15 mass% based on 100 mass% of the total composition.

(B) Impurity Diffusion Component The impurity diffusion composition according to the embodiment of the present invention contains (B) an impurity diffusion component. By containing (B) the impurity diffusion component, an impurity diffusion layer can be formed in a semiconductor substrate. As the p-type impurity diffusion component, a compound containing an element of group 13 is preferable, and among them, a boron compound is preferable. As the n-type impurity diffusion component, a compound containing an element of group 15 is preferable, and among them, a phosphorus compound is preferable.

Examples of boron compounds include boric acid, diboron trioxide, methylboronic acid, phenylboronic acid, trimethyl borate, triethyl borate, tripropyl borate, tributyl borate, trioctyl borate, triphenyl borate, etc. Among these, from the viewpoint of doping properties, it is preferable that the impurity diffusing component (B) is boric acid.

Examples of phosphorus compounds include phosphorus pentoxide, phosphoric acid, polyphosphoric acid, methyl phosphate, dimethyl phosphate, trimethyl phosphate, ethyl phosphate, diethyl phosphate, triethyl phosphate, propyl phosphate, dipropyl phosphate, tripropyl phosphate, butyl phosphate, dibutyl phosphate, tributyl phosphate, phenyl phosphate, diphenyl phosphate, and triphenyl phosphate, as well as phosphoric acid esters such as methyl phosphite, dimethyl phosphite, trimethyl phosphite, ethyl phosphite, diethyl phosphite, triethyl phosphite, propyl phosphite, dipropyl phosphite, tripropyl phosphite, butyl phosphite, dibutyl phosphite, tributyl phosphite, phenyl phosphite, diphenyl phosphite, and triphenyl phosphite. Among these, phosphoric acid, phosphorus pentoxide, and polyphosphoric acid are preferred from the viewpoint of doping properties.

The content of the (B) impurity-diffusing component contained in the impurity-diffusing composition can be determined arbitrarily depending on the resistance value required for the semiconductor substrate, but it is preferable that the content be 0.1 to 10 mass % based on 100 mass % of the total composition.

In addition, from the viewpoint of diffusion uniformity, the mass ratio (A):(B) of (A) PVA to (B) impurity diffusing component is preferably 1:1 to 20:1, and more preferably 4:1 to 10:1.

(C) Siloxane The impurity-diffusing composition according to the embodiment of the present invention includes (C) siloxane, and (C) siloxane includes at least one of the partial structures represented by the following general formulas (1) and (2) and the partial structures represented by the above general formulas (3) and (4). The partial structures represented by the general formulas (1) and (2) may be mixed or may be either one. The partial structures represented by the general formulas (3) and (4) may be mixed or may be either one. By including (C) siloxane, the impurity-diffusing composition film can be densified. Also, the diffusibility of the (B) impurity-diffusing component can be improved.

In the impurity-diffusing composition, the mass ratio (A):(C) of (A) polyvinyl alcohol and (C) siloxane is preferably 30:70 to 75:25. By making the mass ratio of (A) PVA 30% or more, diffusibility is likely to be improved, and by making the mass ratio of (A) PVA 75% or less, the adhesive properties specific to PVA are likely to be suppressed, making it easier to suppress sticking during screen printing.

(C) It is preferable that the partial structure represented by either of the general formulas (3) and (4) is contained in the siloxane at 25 mol% or more in terms of Si atoms. This prevents the crosslink density between the polysiloxane skeletons from becoming too high, and cracks are further suppressed even in a thick film. This makes it difficult for cracks to occur during the baking and thermal diffusion processes, thereby improving the stability of impurity diffusion. In addition, after thermal diffusion of the impurities, the impurity diffusion layer can be used as a mask against other impurity diffusing agents. In order to have masking properties, it is better to have a large film thickness after diffusion, and the impurity diffusion composition of the present invention, which is difficult to crack even in a thick film, can be suitably used. In addition, even in a composition to which a thermal decomposition component such as a thickener is added, it is possible to fill the voids generated by thermal decomposition due to the reflow effect of the siloxane, and a dense film with few voids can be formed. Therefore, it is less susceptible to the atmosphere during diffusion, and high masking properties against other impurities can be obtained.

On the other hand, it is preferable that the siloxane contains 95 mol % or less of the partial structure represented by either general formula (3) or (4) in terms of Si atoms. This makes it possible to eliminate peeling residues after diffusion. The residues are thought to be carbides that remain after the organic matter has not been completely decomposed or volatilized, and not only do they hinder doping properties, but they also increase the contact resistance with the electrodes to be formed later, causing a decrease in the efficiency of the solar cell.

From the viewpoint of further improving the crack resistance, masking property, and storage stability and reducing the influence of the diffusion atmosphere, the content of the partial structure represented by either of the general formulas (3) and (4) in the (C) siloxane is more preferably 35 mol% or more, and even more preferably 40 mol% or more. In addition, in order not to generate residues without being influenced by the atmosphere or film thickness, the content of the partial structure represented by either of the general formulas (3) and (4) is preferably 80 mol% or less. When R ¹ , R ² and R ⁴ are alkyl groups, by making the carbon number 6 or less, it is possible to suppress the generation of residues and to fully bring out the reflow effect of the aryl group of R ³ .

The aryl group having 6 to 15 carbon atoms in ^R3 may be either unsubstituted or substituted, and can be selected according to the properties of the composition. Specific examples of the aryl group having 6 to 15 carbon atoms include a phenyl group, a p-tolyl group, a m-tolyl group, an o-tolyl group, a p-hydroxyphenyl group, a p-styryl group, a p-methoxyphenyl group, and a naphthyl group, with the phenyl group, the p-tolyl group, and the m-tolyl group being particularly preferred.

^The alkyl group having ¹ to ⁶ carbon atoms, the alkoxy group having 1 to 7 carbon atoms, the acyloxy group having 1 to 6 carbon atoms, the alkenyl group having 2 to 10 carbon atoms, and the aryl group having 6 to 15 carbon atoms in R 1, R 2, and R 4 may be either unsubstituted or substituted, and can be selected depending on the properties of the composition.

Specific examples of alkyl groups having 1 to 6 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, n-hexyl, trifluoromethyl, 3,3,3-trifluoropropyl, 3-methoxy-n-propyl, glycidyl, 3-glycidoxypropyl, 3-aminopropyl, 3-mercaptopropyl, and 3-isocyanatopropyl groups, but from the standpoint of residues, methyl, ethyl, n-propyl, isopropyl, n-butyl, and t-butyl groups having 4 or fewer carbon atoms are preferred.

Specific examples of alkoxy groups having 1 to 7 carbon atoms include methoxy groups, ethoxy groups, n-propoxy groups, isopropoxy groups, n-butoxy groups, and t-butoxy groups.

Specific examples of alkenyl groups having 2 to 10 carbon atoms include vinyl groups, 1-propenyl groups, 1-butenyl groups, 2-methyl-1-propenyl groups, 1,3-butadienyl groups, 3-methoxy-1-propenyl groups, 3-acryloxypropyl groups, and 3-methacryloxypropyl groups. From the standpoint of residues, however, vinyl groups having 4 or less carbon atoms, 1-propenyl groups, 1-butenyl groups, 2-methyl-1-propenyl groups, 1,3-butadienyl groups, and 3-methoxy-1-propenyl groups are particularly preferred.

Specific examples of acyloxy groups having 1 to 6 carbon atoms include acetoxy groups, propionyloxy groups, acryloyloxy groups, and benzoyloxy groups.

Specific examples of the aryl group having 6 to 15 carbon atoms include the same as those for ^R3 .

In order to form a denser and more crack-resistant film, it is preferable that R ² and R ⁴ represent any one of a hydroxyl group, an alkoxy group having 1 to 6 carbon atoms, and an acyloxy group having 1 to 6 carbon atoms, and R ¹ represents an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 2 to 4 carbon atoms. In other words, it is preferable that all of the constituent units of the polysiloxane are made of trifunctional organosilanes.

It is also preferable that the 20% thermal decomposition temperature of (C) siloxane is 550°C or higher. This allows the reflow effect of (C) siloxane to be obtained after organic components other than (C) siloxane are completely removed by thermal decomposition, resulting in a denser film with less residue. Here, the 20% thermal decomposition temperature is the temperature at which the weight of (C) siloxane decreases by 20% due to thermal decomposition. The thermal decomposition temperature can be measured using a thermogravimetric analyzer (TGA) or the like.

Specific examples of organosilanes that are used as raw materials for the units of general formulas (3) and (4) include phenyltrimethoxysilane, phenyltriethoxysilane, p-hydroxyphenyltrimethoxysilane, p-tolyltrimethoxysilane, p-styryltrimethoxysilane, p-methoxyphenyltrimethoxysilane, diphenyldimethoxysilane, methylphenyldimethoxysilane, 1-naphthyltrimethoxysilane, 2-naphthyltrimethoxysilane, 1-naphthyltriethoxysilane, and 2-naphthyltriethoxysilane. Among these, phenyltrimethoxysilane, p-tolyltrimethoxysilane, and p-methoxyphenyltrimethoxysilane are particularly preferred.

Specific examples of organosilanes that can be used as raw materials for the units of general formulas (1) and (2) include tetrafunctional silanes such as tetramethoxysilane, tetraethoxysilane, and tetraacetoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane, methyltri-n-butoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriisopropoxysilane, ethyltri-n-butoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, n-butyltrimethoxysilane, and n-butyltriethoxysilane. Examples of the organosilanes include trifunctional silanes such as xysilane, glycidyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, trifluoromethyltrimethoxysilane, trifluoromethyltriethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and 3-mercaptopropyltrimethoxysilane, and bifunctional silanes such as dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldiacetoxysilane, and di(n-butyl)dimethoxysilane. These organosilanes may be used alone or in combination of two or more. Among these organosilanes, trifunctional silanes are preferably used in terms of the denseness, crack resistance, residue, and curing speed of the film.

(C) Siloxane can be obtained, for example, by hydrolyzing an organosilane compound and then condensing the hydrolyzate in the presence of a solvent or without a solvent. Various conditions for the hydrolysis reaction, such as acid concentration, reaction temperature, and reaction time, can be set appropriately taking into consideration the reaction scale, size and shape of the reaction vessel, etc., but for example, it is preferable to add an acid catalyst and water to the organosilane compound in a solvent over 1 to 180 minutes, and then react at room temperature to 110°C for 1 to 180 minutes. By carrying out the hydrolysis reaction under such conditions, it is possible to suppress a rapid reaction. The reaction temperature is more preferably 30 to 130°C.

The hydrolysis reaction is preferably carried out in the presence of an acid catalyst. Examples of the acid catalyst include inorganic hydrogen halide acids such as hydrochloric acid, hydrobromic acid, and hydroiodic acid, other inorganic acids such as sulfuric acid, nitric acid, phosphoric acid, hexafluorophosphoric acid, hexafluoroantimonic acid, boric acid, tetrafluoroboric acid, and chromic acid, sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid, and carboxylic acids such as acetic acid, citric acid, formic acid, gluconic acid, lactic acid, oxalic acid, tartaric acid, pyruvic acid, citric acid, succinic acid, fumaric acid, and malic acid. From the viewpoint of doping, the acid catalyst of the present invention preferably contains as few atoms as possible other than silicon, hydrogen, carbon, oxygen, nitrogen, and phosphorus, and it is preferable to use an acid catalyst based on phosphoric acid, formic acid, acetic acid, or carboxylic acid.

The preferred content of the acid catalyst is preferably 0.1 to 5 parts by weight per 100 parts by weight of the total organosilane compounds used in the hydrolysis reaction. By setting the amount of the acid catalyst within the above range, the hydrolysis reaction can be easily controlled so that it proceeds as necessary and sufficiently.

The solvent used in the hydrolysis reaction of the organosilane compound and the condensation reaction of the hydrolyzate is not particularly limited and can be appropriately selected taking into consideration the stability, wettability, volatility, etc. of the resin composition. In addition, two or more types of solvents may be combined, or the reaction may be carried out without a solvent. Specific examples of the solvent include diethylene glycol methyl ethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monomethyl ether acetate, methyl lactate, ethyl lactate, diacetone alcohol, propylene glycol monomethyl ether acetate, 3-methoxy-3-methyl-1-butanol, dipropylene glycol monomethyl ether, dipropylene glycol-n-butyl ether, γ-butyrolactone, diethylene glycol monoethyl ether acetate, butyl diglycol acetate, ethyl acetoacetate, N-methyl-2-pyrrolidone, N,N-dimethylimidazolidinone, dipropylene glycol methyl ether acetate, 1,3-butylene glycol diacetate, diisobutyl ketone, propylene glycol t-butyl ether, propylene glycol n-butyl ether, etc. In addition to these, those described in paragraph 47 of International Publication No. 2015/002132 can be mentioned.

In terms of achieving good thermal diffusion and suppressing organic residues on the substrate after removal of the composition, the content of (C) polysiloxane is preferably 1 to 30 mass% and more preferably 5 to 15 mass% based on 100 mass% of the total composition.

The impurity-diffusing composition according to the embodiment of the present invention preferably further contains a solvent (D). The content of the solvent (D) is preferably 10 to 90 mass %, and more preferably 50 to 80 mass %, based on 100 mass % of the entire composition.

(D) The solvent can be used without any particular restrictions, but from the viewpoint of further improving printability when using a screen printing method, a spin-coat printing method, or the like, a solvent with a boiling point of 100°C or higher is preferable. If the boiling point is 100°C or higher, for example, when the impurity-diffusing composition is printed on a printing plate used in a screen printing method, the impurity-diffusing composition can be prevented from drying and adhering on the printing plate.

The content of the solvent having a boiling point of 100°C or more is preferably 20% by weight or more based on the total amount of the solvent. Examples of solvents having a boiling point of 100°C or more include water (boiling point 100°C), diethylene glycol methyl ethyl ether (boiling point 176°C), ethylene glycol monoethyl ether acetate (boiling point 156.4°C), ethylene glycol monomethyl ether acetate (boiling point 145°C), methyl lactate (boiling point 145°C), ethyl lactate (boiling point 155°C), diacetone alcohol (boiling point 169°C), propylene glycol monomethyl ether acetate (boiling point 145°C), 3-methoxy-3-methyl-1-butanol (boiling point 174°C), dipropylene glycol monomethyl ether (boiling point 188°C), dipropylene glycol-n-butyl ether (boiling point 229°C), γ-butyrolactone (boiling point 204°C), diethylene glycol monoethyl ether Examples of the propylene glycol methyl ether acetate include butyl diglycol acetate (boiling point 217°C), butyl diglycol acetate (boiling point 246°C), ethyl acetoacetate (boiling point 181°C), N-methyl-2-pyrrolidone (boiling point 204°C), N,N-dimethylimidazolidinone (boiling point 226°C), dipropylene glycol methyl ether acetate (boiling point 213°C), 1,3-butylene glycol diacetate (boiling point 232°C), diisobutyl ketone (boiling point 168°C), propylene glycol t-butyl ether (boiling point 151°C), propylene glycol n-butyl ether (boiling point 170°C), acetylacetone (boiling point 140°C), diethylene glycol monobutyl ether (boiling point 171°C), and diethylene glycol monobutyl ether acetate (boiling point 245°C).

In addition, it is preferable that the (D) solvent contains a lactam solvent or a cyclic ester solvent. By containing a lactam solvent or a cyclic ester solvent, it becomes easier to suppress the increase in viscosity of the impurity diffusion composition, and it also becomes easier to efficiently dissolve the (A) PVA. In addition, by containing a lactam solvent or a cyclic ester solvent, the stability of the complex of the (A) PVA and the (B) impurity diffusion component is further improved. As a result, it becomes easier to suppress the phenomenon that the (A) PVA and the (B) impurity diffusion component that have already formed a complex further react to form a three-dimensional complex, and it becomes easier to suppress the thickening of the impurity diffusion composition over time and the generation of gel-like foreign matter due to the thickening. As a result, when the impurity diffusion composition is used for coating, the coating film thickness tends to be uniform, and uniform impurity diffusion is also easily obtained in the subsequent impurity diffusion process.

Examples of lactam solvents include N-methyl-2-pyrrolidone. Examples of cyclic ester solvents include β-propiolactone, β-butyrolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, γ-octalactone, γ-nonalactone, γ-decanolactone, δ-decanolactone, γ-undecalactone, δ-undecalactone, ω-undecalactone, ω-pentadecalactone, etc. These can be used alone or as a mixed solvent of two or more kinds.

The content of the lactam solvent or cyclic ester solvent contained in the impurity-diffusing composition is preferably 20% by mass or more, more preferably 50% by mass or more, of the solvent contained in the impurity-diffusing composition in order to more effectively suppress an increase in viscosity in the impurity-diffusing composition. The upper limit of the content is not particularly limited, but is preferably 90% by mass or less, more preferably 80% by mass or less. Note that when the impurity-diffusing composition contains both a lactam solvent and a cyclic ester solvent, the content represents the total content of both.

In addition, since (A) PVA can also be dissolved as an aqueous solution, (D) solvent may contain water. When (D) solvent contains water, from the viewpoints of storage stability, continuous screen printability, and diffusibility of the solution, the water content in (D) solvent is preferably 0.1 to 10% by mass, and more preferably 0.1 to 5% by mass.

(E) Thixotropic Agent The impurity diffusion composition according to the embodiment of the present invention preferably further contains (E) a thixotropic agent from the viewpoint of screen printability. Here, the thixotropic agent refers to a compound that imparts thixotropy to the impurity diffusion composition. Moreover, imparting thixotropy means increasing the ratio (η ₁ /η ₂ ) of the viscosity at low shear stress (η ₁ ) to the viscosity at high shear stress (η ₂ ). By containing (E) a thixotropic agent, the pattern accuracy of screen printing can be further improved. This is for the following reasons. The impurity diffusion composition containing a thixotropic agent has a low viscosity at high shear stress, so that clogging of the screen is unlikely to occur during screen printing, and a high viscosity at low shear stress, so that bleeding immediately after printing and thickening of the pattern line width are unlikely to occur.

(E) Specific examples of thixotropic agents include cellulose, cellulose derivatives, sodium alginate, xanthan gum polysaccharides, gellan gum polysaccharides, guar gum polysaccharides, carrageenan polysaccharides, locust bean gum polysaccharides, carboxyvinyl polymers, hydrogenated castor oil, hydrogenated castor oil and fatty acid amide wax, special fatty acids, polyethylene oxide, mixtures of polyethylene oxide and amide, fatty acid polycarboxylic acids, phosphate ester surfactants, salts of long-chain polyaminoamide and phosphoric acid, special modified polyamides, bentonite, montmorillonite, magnesian montmorillonite, ferromagnesian montmorillonite, beidellite, aluminous beidellite, saponite, aluminous saponite, laponite, aluminum silicate, magnesium aluminum silicate, organic hectorite, fine particles of silicon oxide (fine silicon oxide particles), colloidal alumina, and calcium carbonate. From the viewpoint of compatibility with other components in the composition and reduction of residue, it is particularly preferable that the thixotropic agent (E) is a fine particle of silicon oxide. The thixotropic agent can be used alone, but it is also possible to combine two or more kinds of thixotropic agents. It is more preferable to use it in combination with a thickener, and a higher effect can be obtained.

The size of the microparticles is preferably a number average particle diameter of 5 nm or more and 500 nm or less. By setting the size in this range, it is possible to obtain moderate intermolecular interactions and impart high thixotropy. The size of the microparticles is preferably a number average particle diameter of 7 nm or more and 100 nm or less, and most preferably 10 nm or more and 30 nm or less.

The size of the microparticles in the present invention is measured by observation with a transmission electron microscope. The major axis of 10 randomly selected particles is measured, and the average is taken as the number average particle size.

There is no limit to the viscosity of the impurity diffusion composition according to the embodiment of the present invention, and it can be changed as appropriate depending on the printing method and film thickness. For example, in the case of a screen printing method, which is one of the preferred printing forms, the viscosity of the diffusion composition is preferably 5,000 mPa·s or more. This is because bleeding of the printed pattern can be suppressed and a good pattern can be obtained. A more preferred viscosity is 10,000 mPa·s or more. There is no particular upper limit, but from the viewpoint of storage stability and handling, a viscosity of 100,000 mPa·s or less is preferable.

Here, when the viscosity is less than 1,000 mPa·s, it is the value measured at 20 rpm using an E-type digital viscometer in accordance with JIS Z 8803 (1991) "Solution viscosity -- Measurement method", and when the viscosity is 1,000 mPa·s or more, it is the value measured at 20 rpm using a B-type digital viscometer in accordance with JIS Z 8803 (1991) "Solution viscosity -- Measurement method".

The thixotropy can be determined from the ratio of viscosities at different rotational speeds obtained by the above-mentioned viscosity measurement method. In the present invention, the thixotropy is defined as the ratio ( _η2 / _η20 ) of the viscosity at a rotational speed of 20 rpm ( _η20 ) to the viscosity at a rotational speed of 2 rpm (η2). In order to form a pattern with good accuracy by screen printing, the thixotropy is preferably 2 or more, and more preferably 3 _or more.

(F) Carboxylic Acid From the viewpoint of adjusting the pH of the composition, the impurity-diffusing composition according to the embodiment of the present invention preferably further contains (F) a carboxylic acid. Examples of the carboxylic acid include formic acid, acetic acid, and oxalic acid. Among them, it is more preferable that the (F) carboxylic acid is formic acid. From the viewpoint of the pH adjusting effect, the content of the (F) carboxylic acid is preferably 0.01 to 0.1 mass % in the entire composition.

(G) Surfactant The impurity-diffusing composition according to the embodiment of the present invention may contain a surfactant. By containing a surfactant, coating unevenness is improved and a more uniform coating film can be obtained. As the surfactant, a fluorine-based surfactant or a silicone-based surfactant is preferably used. When the surfactant is contained, the content of the surfactant in the impurity-diffusing composition is preferably 0.0001 to 1% by weight.

(H) Thickener The impurity diffusion composition according to the embodiment of the present invention may contain a thickener. This allows viscosity adjustment. In addition, the composition can be applied in a more precise pattern by a printing method such as screen printing. In terms of dense film formation and residue reduction, the thickener preferably has a 90% thermal decomposition temperature of 400° C. or less. The thickener is preferably polyethylene glycol, polyethylene oxide, polypropylene glycol, polypropylene oxide, or an acrylic acid ester resin, and among these, polyethylene oxide, polypropylene oxide, or an acrylic acid ester resin is preferable. In terms of storage stability, the thickener is particularly preferably an acrylic acid ester resin. Here, the 90% thermal decomposition temperature is the temperature at which the weight of the thickener is reduced by 90% due to thermal decomposition. The thermal decomposition temperature can be measured using a thermogravimetric analyzer (TGA) or the like.

The content of these thickeners in the impurity diffusion composition is preferably 3% by weight or more and 20% by weight or less. This range makes it easier to obtain a sufficient viscosity adjustment effect and also enables the formation of a denser film.

(pH)
The impurity-diffusing composition according to the embodiment of the present invention preferably has a pH of 4.0 to 6.5. In this range, the complex of (A) PVA and (B) impurity-diffusing component is more stabilized. Furthermore, even if the composition is used for diffusion after being stored for a certain period of time, the uniformity of the impurity diffusion concentration within the substrate surface is well maintained.

Methods for adjusting the pH include, but are not limited to, adding an acid or base to the composition, or adjusting the pH when reducing impurities using an ion exchange resin as described below.

Preferred acids include inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as the above-mentioned (F) carboxylic acid.

As a base, an organic amine is preferred because it does not contain metal elements or halogens.

In particular, from the viewpoint of further improving storage stability, a method that combines the addition of an organic amine with the addition of formic acid, sulfuric acid, nitric acid, acetic acid or oxalic acid, or a method that combines the addition of an organic amine with adjustment using an ion exchange resin is preferred.

Organic amines include aromatic amines and aliphatic amines, but aliphatic amines are preferred because they are highly basic and effective when added in smaller amounts. Tertiary amines are more preferred from the viewpoint of suppressing side reactions with other components of the composition.

Specific examples of aliphatic tertiary amines include, but are not limited to, trimethylamine, triethylamine, triisopropylamine, triisopropanolamine, triethanolamine, pyridine, piperazine, piperidine, pyrrolidine, ethylpiperidine, piperidineethanol, etc. Preferred are aliphatic cyclic tertiary amines such as piperazine, piperidine, pyrrolidine, ethylpiperidine, and piperidineethanol.

The content of the organic amine is preferably 0.01 to 2% by mass of the entire composition. More preferably, it is 0.02 to 0.5% by mass of the entire composition, and even more preferably, it is 0.03 to 0.1% by mass of the entire composition.

The pH in the present invention is a value measured using a pH meter (LAQUA F-71, manufactured by Horiba, Ltd.). The pH is calibrated using the following five types of standard solutions (pH 2, 4, 7, 9, 12) as specified in JIS Z 8802 (2011) "pH measurement method".
pH 2 standard solution (oxalate)
0.05 mol/L potassium tetraoxalate aqueous solution pH 4 standard solution (phthalate)
0.05 mol/L potassium hydrogen phthalate aqueous solution pH 7 standard solution (neutral phosphate: mixture of the following two aqueous solutions)
0.025mol/L Potassium dihydrogen phosphate aqueous solution 0.025mol/L Disodium hydrogen phosphate aqueous solution ○pH 9 standard solution (borate)
0.01 mol/L sodium tetraborate (borax) solution pH 12 standard solution saturated calcium hydroxide solution.

The impurity diffusion composition according to the embodiment of the present invention preferably has an amount of sodium (Na) of 0.05 ppm or less. As a method for reducing Na, methods of purifying each component of the composition by recrystallization, distillation, column fractionation, ion exchange, etc. are used, but a method using an ion exchange resin is preferred.

Ion exchange can be performed by subjecting the entire composition containing components (A) to (C) or at least one of components (A) to (C) to an ion exchange treatment using an ion exchange resin. Because Na may be mixed in during the manufacturing process, it is most preferable to perform ion exchange at the end of the entire composition containing components (A) to (C). Specific methods include, but are not limited to, passing the impurity-diffusing composition through a column packed with cation exchange resin, adding cation exchange resin to a liquid of the impurity-diffusing composition and stirring, and removing the ion exchange resin after ion exchange.

In particular, when a cation exchange resin is used, the pH of the impurity diffusion composition after ion exchange is less than 7, making it possible to reduce impurities and adjust the pH to the desired level at the same time.

As an ion exchange treatment method for adjusting the pH value to 4.0 to 6.5, a method of performing ion exchange treatment using a combination of cation exchange resin and anion exchange resin is preferable. Examples of combination methods include, but are not limited to, a method of appropriately mixing cation exchange resin and anion exchange resin, filling a column with the mixture, and passing the impurity diffusion composition through a column filled with a cation exchange resin and a column filled with an anion exchange resin.

(Solid content concentration)
The solid content of the impurity diffusion composition according to the embodiment of the present invention is not particularly limited, but is preferably in the range of 1% by mass or more and 90% by mass or less. If the solid content is lower than this range, the coating film thickness becomes too thin and it may be difficult to obtain the desired doping property and masking property. If the solid content is higher than this range, the storage stability may decrease.

<Method of Manufacturing Semiconductor Element>
A first embodiment of a method for manufacturing a semiconductor device of the present invention includes a step of applying the impurity diffusion composition of the present invention to a semiconductor substrate to form an impurity diffusion composition film, and a step of diffusing impurities from the impurity diffusion composition film to form an impurity diffusion layer on the semiconductor substrate.

In addition, a second embodiment of the method for manufacturing a semiconductor element of the present invention includes a step of applying an n-type impurity diffusion composition to a semiconductor substrate to form an n-type impurity diffusion composition film, a step of applying the impurity diffusion composition of the present invention, which is a p-type impurity diffusion composition, to form an impurity diffusion composition film, and a step of simultaneously forming an n-type impurity diffusion layer and a p-type impurity diffusion layer by heating the semiconductor substrate.

In addition, a third embodiment of the method for manufacturing a semiconductor element of the present invention includes a step of applying the impurity diffusion composition of the present invention, which is a p-type impurity diffusion composition, to one surface of a semiconductor substrate to form a p-type impurity diffusion composition film, a step of applying an n-type impurity diffusion composition to the other surface of the semiconductor substrate to form an n-type impurity diffusion composition film, and a step of simultaneously forming a p-type impurity diffusion layer and an n-type impurity diffusion layer by heating the semiconductor substrate.

In addition, a fourth embodiment of the method for manufacturing a semiconductor element of the present invention includes a step of partially applying the impurity diffusion composition of the present invention, which is a p-type impurity diffusion composition, to one surface of a semiconductor substrate to form a first p-type impurity diffusion composition film, a step of applying a second p-type impurity diffusion composition to the portion where the first p-type impurity diffusion composition film is not formed to form a low-concentration p-type impurity diffusion composition film, a step of applying an n-type impurity diffusion composition to the other surface of the semiconductor substrate to form an n-type impurity diffusion composition film, and a step of simultaneously forming a high-concentration p-type impurity diffusion layer, a low-concentration p-type impurity diffusion layer, and an n-type impurity diffusion layer by heating the semiconductor substrate.

A fifth embodiment of the method for manufacturing a semiconductor element of the present invention is a method for manufacturing a semiconductor element using a plurality of semiconductor substrates, and includes the following steps (a) to (c). In steps (b) and (c), a pair of semiconductor substrates are arranged such that the surfaces on which the first conductivity type impurity diffusion composition film is formed face each other.
(a) A step of applying the impurity diffusion composition of the present invention to one surface of each semiconductor substrate to form an impurity diffusion composition film of a first conductivity type.
(b) A step of heating the semiconductor substrate on which the first conductivity type impurity diffusion composition film is formed, thereby diffusing the first conductivity type impurity into the semiconductor substrate to form a first conductivity type impurity diffusion layer.
(c) heating the semiconductor substrate in an atmosphere having a gas containing an impurity of a second conductivity type to diffuse the impurity of the second conductivity type into the other surface of the semiconductor substrate, thereby forming an impurity diffusion layer of the second conductivity type.

Below, we will explain the methods of forming impurity diffusion layers that can be applied to the manufacturing methods of these semiconductor elements with reference to the drawings. Note that these are just examples, and the methods that can be applied to the manufacturing method of the semiconductor element of the present invention are not limited to these.

First Embodiment
1 shows an example of a first embodiment of the method for producing a semiconductor device of the present invention. First, as shown in FIG. 1(a), a p-type impurity diffusion composition film 12 is formed on a semiconductor substrate 11.

Examples of the semiconductor substrate include n-type single crystal silicon, polycrystalline silicon, and crystalline silicon substrates mixed with other elements such as germanium and carbon, each having an impurity concentration of 10 ¹⁵ to 10 ¹⁶ atoms/cm ^3. Semiconductors other than p-type crystalline silicon and silicon can also be used. The semiconductor substrate is preferably approximately rectangular with a thickness of 50 to 300 μm and an outer shape of 100 to 250 mm on each side. It is also preferable to etch the surface with a hydrofluoric acid solution, an alkaline solution, or the like. By etching, slice damage and natural oxide films can be removed.

A protective film may be formed on the light receiving surface of the semiconductor substrate. This protective film may be a known protective film such as silicon oxide or silicon nitride, which is formed by a method such as CVD (chemical vapor deposition) or spin-on-glass (SOG).

Methods for applying the impurity diffusion composition include, for example, spin coating, screen printing, inkjet printing, slit coating, spray coating, letterpress printing, and intaglio printing.

After forming a coating film by these methods, it is preferable to dry the impurity diffusion composition film on a hot plate, in an oven, or the like at a temperature in the range of 50 to 200°C for 30 seconds to 30 minutes. From the viewpoint of impurity diffusibility, the film thickness of the impurity diffusion composition film after drying is preferably 100 nm or more, and from the viewpoint of residue after etching, it is preferably 3 μm or less.

Next, as shown in (b) of FIG. 1, impurities are diffused into the semiconductor substrate 11 to form a p-type impurity diffusion layer 13.

The method for diffusing the impurities can be, for example, a known thermal diffusion method. Specifically, for example, methods such as electrical heating, infrared heating, laser heating, and microwave heating can be used.

The time and temperature of thermal diffusion can be appropriately set so as to obtain desired diffusion characteristics such as impurity diffusion concentration, diffusion depth, etc. For example, by performing thermal diffusion at 800° C. or higher and 1200° C. or lower for 1 to 120 minutes, a diffusion layer with a surface impurity concentration of ¹⁰ to ¹⁰ can be formed.

The diffusion atmosphere is not particularly limited, and may be air, or the amount of oxygen in the atmosphere may be appropriately controlled using an inert gas such as nitrogen or argon. From the viewpoint of shortening the diffusion time, it is preferable to set the oxygen concentration in the atmosphere to 3% or less. In addition, sintering may be performed at a temperature in the range of 200°C to 850°C before diffusion, if necessary.

Next, as shown in (c) of FIG. 1, the p-type impurity diffusion composition film 12 formed on the surface of the semiconductor substrate 11 is removed.

As a removal method, for example, a known etching method can be used.

The material used for etching is not particularly limited, but preferably contains at least one of hydrogen fluoride, ammonium, phosphoric acid, sulfuric acid, and nitric acid as an etching component, and water or an organic solvent as other components. By the above process, a p-type impurity diffusion layer can be formed in the semiconductor substrate.

In the above example, a p-type impurity diffusion layer is formed using a p-type impurity diffusion composition film, but this embodiment is not limited to this and can naturally also be applied to a case where an n-type impurity diffusion layer is formed using an n-type impurity diffusion composition film.

Next, a method for manufacturing a solar cell using the method for manufacturing a semiconductor element according to an example of the first embodiment of the present invention will be described with reference to (d) of FIG. 1. The solar cell obtained in this example of the embodiment is a single-sided solar cell.

First, as shown in (d) of Figure 1, a passivation layer 16 is formed on the front surface and a passivation layer 17 is formed on the back surface.

The passivation layers may be made of known materials. These layers may be single or multi-layered. For example, there may be a thermal oxide layer, an aluminum oxide layer, a SiNx layer, and an amorphous silicon layer stacked together.

An aluminum oxide layer is particularly preferred as the passivation layer on the side of passivation layer 17, which also serves as an electrode.

These passivation layers can be formed by deposition methods such as plasma CVD or ALD (atomic layer deposition), or by coating methods.

In one example of this embodiment, passivation layer 16 is formed on a portion of the light receiving surface, and passivation layer 17 is formed on the entire back surface.

Then, as shown in (e) of Figure 1, a contact electrode 18 is formed on the portion of the light-receiving surface where the passivation layer 16 is not present.

Electrodes can be formed by applying an electrode-forming paste and then heat treating it.

This results in a single-sided power generating solar cell 10.

Second Embodiment
2A shows an example of a second embodiment of the method for manufacturing a semiconductor device of the present invention. First, as shown in (a) of FIG. 2A, an n-type impurity diffusion composition film 24 is patterned on a semiconductor substrate 21.

Methods for forming an n-type impurity diffusion composition film include, for example, screen printing, inkjet printing, slit coating, spray coating, letterpress printing, and intaglio printing.

After forming a coating film using these methods, it is preferable to dry the n-type impurity diffusion composition film on a hot plate, in an oven, etc. at a temperature in the range of 50 to 200°C for 30 seconds to 30 minutes.

The thickness of the n-type impurity diffusion composition film after drying is preferably 200 nm or more, taking into account the masking properties against p-type impurities, and is preferably 5 μm or less from the viewpoint of crack resistance.

Next, as shown in (b) of FIG. 2A, a p-type impurity diffusion composition film 22 is formed using the n-type impurity diffusion composition film 24 as a mask.

In this case, as shown in (b) of FIG. 2A, the p-type impurity diffusion composition film may be formed on the entire surface, or may be formed only on the portion where there is no n-type impurity diffusion composition film. Also, the p-type impurity diffusion composition may be applied so that a portion of the p-type impurity diffusion composition overlaps with the n-type impurity diffusion composition film.

Methods for applying the p-type impurity diffusion composition include, for example, spin coating, screen printing, inkjet printing, slit coating, spray coating, letterpress printing, and intaglio printing.

After forming a coating film by these methods, it is preferable to dry the p-type impurity diffusion composition film on a hot plate, in an oven, or the like at a temperature in the range of 50 to 200°C for 30 seconds to 30 minutes. From the viewpoint of the diffusibility of the p-type impurities, the film thickness of the p-type impurity diffusion composition film after drying is preferably 100 nm or more, and from the viewpoint of residue after etching, it is preferably 3 μm or less.

Next, as shown in (c) of FIG. 2A, the n-type impurity diffusion component in the n-type impurity diffusion composition film 24 and the p-type impurity diffusion component in the p-type impurity diffusion composition film 22 are simultaneously diffused into the semiconductor substrate 21 to form an n-type impurity diffusion layer 25 and a p-type impurity diffusion layer 23.

The application method, firing method and diffusion method of the impurity diffusion composition are the same as those described above.

Next, as shown in (d) of FIG. 2A, the n-type impurity diffusion composition film 24 and the p-type impurity diffusion composition film 22 formed on the surface of the semiconductor substrate 21 are removed.

As a removal method, for example, a known etching method can be used.

By using the above process, n-type and p-type impurity diffusion layers can be formed in the semiconductor substrate. By using such a process, the process can be further simplified compared to conventional methods.

Here, an example is shown in which the p-type impurity diffusion composition is applied after the n-type impurity diffusion composition is applied, but it is also possible to apply the n-type impurity diffusion composition after the p-type impurity diffusion composition. That is, it is also possible to apply the p-type impurity diffusion composition instead of applying the n-type impurity diffusion composition in (a) of FIG. 2A, and to apply the n-type impurity diffusion composition instead of applying and diffusing the p-type impurity diffusion composition in (b) of FIG. 2A.

In a second embodiment of the method for manufacturing a semiconductor element of the present invention, it is preferable to apply a p-type impurity diffusion composition after applying the n-type impurity diffusion composition.

Next, a method for manufacturing a solar cell using the method for manufacturing a semiconductor element according to an example of the second embodiment of the present invention will be described with reference to FIG. 2B. The solar cell obtained in this example of the embodiment is a back junction solar cell.

First, as shown in (e) of Fig. 2B, a protective film 26 is formed on the entire back surface of a semiconductor substrate 21 having an n-type impurity diffusion layer 25 and a p-type impurity diffusion layer 23 formed on the back surface. Next, as shown in (f) of Fig. 3, the protective film 26 is patterned by etching or the like to form a protective film opening 26a.

2B(g), an electrode paste is pattern-applied to the area including the opening 26a by stripe application or screen printing, and then fired to form an n-type contact electrode 29 and a p-type contact electrode 28. This results in a back junction solar cell 20.

Third Embodiment
FIG. 3A shows an example of a third embodiment of the method for manufacturing a semiconductor device according to the present invention.

First, as shown in (a) of Fig. 3A, a p-type impurity diffusion composition film 32 is formed on a semiconductor substrate 31 using a p-type impurity diffusion composition of the present invention. Next, as shown in (b) of Fig. 3A, an n-type impurity diffusion composition film 34 is formed on the surface of the semiconductor substrate 31 opposite to the surface on which the p-type impurity diffusion composition film 32 is formed.

Next, as shown in (c) of FIG. 3A, the p-type impurity diffusion composition film 32 and the n-type impurity diffusion composition film 34 are simultaneously diffused into the semiconductor substrate 31 to form a p-type impurity diffusion layer 33 and an n-type impurity diffusion layer 35.

The application method, firing method and diffusion method of the impurity diffusion composition are the same as those described above.

Next, as shown in (d) of FIG. 3A, the p-type impurity diffusion composition film 32 and the n-type impurity diffusion composition film 34 formed on the surface of the semiconductor substrate 31 are removed.

As a removal method, for example, a known etching method can be used.

By using the above process, n-type and p-type impurity diffusion layers can be formed in the semiconductor substrate. By using such a process, the process can be simplified compared to conventional methods.

Here, an example is shown in which a p-type impurity diffusion composition is applied and then an n-type impurity diffusion composition is applied, but it is also possible to apply a p-type impurity diffusion composition after applying an n-type impurity diffusion composition.

Next, a method for manufacturing a solar cell using the method for manufacturing a semiconductor element according to an example of the third embodiment of the present invention will be described with reference to FIG. 3B. The solar cell obtained in this example of the embodiment is a bifacial solar cell.

First, as shown in (e) of Figure 3B, passivation layer 36 and passivation layer 37 are formed on the light-receiving surface and back surface, respectively.

The materials used for the passivation layer, the layer configuration, and the formation method are the same as those in the first embodiment.

In one example of this embodiment, passivation layer 36 and passivation layer 37 are formed on some areas of the light-receiving surface and the back surface.

Then, as shown in (f) of Figure 3B, a p-type contact electrode 38 and an n-type contact electrode 39 are formed on the light-receiving surface and the back surface, respectively, in the areas where the passivation layers 36 and 37 are not present.

Electrodes can be formed by applying an electrode-forming paste and then heat treating it.

This results in a double-sided power generating solar cell 30.

Fourth Embodiment
FIG. 4A shows an example of a fourth embodiment of the method for manufacturing a semiconductor device according to the present invention.

First, as shown in (a) of FIG. 4A, the high concentration p-type impurity diffusion composition of the present invention is partially applied onto a semiconductor substrate 41 to form a high concentration p-type impurity diffusion composition film 42.

Next, as shown in (b) of FIG. 4A, a low concentration p-type impurity diffusion composition is applied to the portion of the semiconductor substrate 41 where the high concentration p-type impurity diffusion composition film 42 is not formed, to form a low concentration p-type impurity diffusion composition film 42'.

Next, as shown in (c) of FIG. 4A, an n-type impurity diffusion composition film 43 is formed on the other side of the semiconductor substrate 41.

4A(d), the high-concentration p-type impurity diffusion composition film 42, the low-concentration p-type impurity diffusion composition film 42', and the n-type impurity diffusion composition film 43 are simultaneously diffused into the semiconductor substrate 41 to form a high-concentration p-type impurity diffusion layer 44, a low-concentration p-type impurity diffusion layer 44', and an n-type impurity diffusion layer 45. The coating method, firing method, and diffusion method for the impurity diffusion composition are the same as those described above.

Next, as shown in (e) of FIG. 4A, the high concentration p-type impurity diffusion composition film 42, the low concentration p-type impurity diffusion composition film 42', and the n-type impurity diffusion composition film 43 formed on the surface of the semiconductor substrate 41 are removed.

As a removal method, for example, a known etching method can be used.

By using the above process, n-type and p-type impurity diffusion layers can be formed in the semiconductor substrate. By using such a process, the process can be simplified compared to conventional methods.

Here, an example is shown in which a p-type impurity diffusion composition is applied and then an n-type impurity diffusion composition is applied, but it is also possible to apply a p-type impurity diffusion composition after applying an n-type impurity diffusion composition.

In addition, although a paste coating method has been exemplified to form low-concentration p-type impurity diffusion layers and n-type impurity diffusion layers, gas diffusion may also be used.

Moreover, a high-concentration p-type impurity diffusion layer refers to a surface p-type impurity concentration of 1×10 ²⁰ or more, and a low-concentration impurity diffusion layer refers to a surface p-type impurity concentration of less than 1×10 ²⁰ .

Next, a method for manufacturing a solar cell using the method for manufacturing a semiconductor element according to an example of the fourth embodiment of the present invention will be described with reference to FIG. 4B. The solar cell obtained in this example of the embodiment is a bifacial solar cell.

First, as shown in (f) of FIG. 4B, a passivation layer 46 is formed on the light receiving surface, and a passivation layer 47 is formed on the back surface. The materials used for the passivation layers, the layer configuration, and the formation method are the same as those in the first embodiment.

In one example of this embodiment, passivation layer 46 and passivation layer 47 are formed on some areas of the light-receiving surface and the back surface.

Then, as shown in (g) of Figure 4B, a p-type contact electrode 48 and an n-type contact electrode 49 are formed on the light-receiving surface and the back surface, respectively, in the areas where the passivation layer 46 and the passivation layer 47 are not present.

Electrodes can be formed by applying an electrode-forming paste and then heat treating it.

This results in a double-sided power generating solar cell 40.

Fifth embodiment
FIG. 5 shows an example of a fifth embodiment of the method for manufacturing a semiconductor device according to the present invention.

(Step (a))
As shown in FIG. 5A, a first conductive type impurity diffusion composition is applied to one surface of a semiconductor substrate 51 to form a first conductive type impurity diffusion composition film 52 .

In the following explanation, the first conductivity type is p-type and the second conductivity type is n-type. In other words, a first conductivity type impurity diffusion composition film is a p-type impurity diffusion composition film. Of course, the first conductivity type and the second conductivity type may be reversed.

5A illustrates an embodiment in which a p-type impurity diffusion composition is applied to the entire surface of one surface of a semiconductor substrate, but the p-type impurity diffusion composition may be applied partially. The method of applying and firing the impurity diffusion composition may be the same as described above.

(Step (b))
As shown in FIG. 5B-1, two semiconductor substrates 51 each having a p-type impurity diffusion composition film 52 formed on one surface are arranged on a diffusion board 110 with the surfaces on which the p-type impurity diffusion composition film 52 is formed facing each other.

The diffusion board has grooves for placing the semiconductor substrate. There are no particular restrictions on the size or pitch of the grooves in the diffusion board. The diffusion board may be inclined relative to the horizontal direction. There are no particular restrictions on the material of the diffusion board as long as it can withstand the diffusion temperature, but quartz is preferred.

Next, as shown in (b)-2 of FIG. 5, the diffusion board 110 on which the semiconductor substrate 51 is placed is heated in a diffusion furnace 100 to diffuse p-type impurities into the semiconductor substrate 51, thereby forming a p-type impurity diffusion layer 53.

At this time, since the pair of semiconductor substrates is arranged as described above, even if p-type impurities diffuse from the p-type impurity diffusion composition film into the air, they are unlikely to reach the surface of the semiconductor substrate opposite to the surface on which the p-type impurity diffusion composition film is formed. This makes it possible to suppress so-called outdiffusion, in which impurities diffuse to locations other than the intended location in the semiconductor substrate. Methods for diffusing the impurity diffusion composition include the same methods as described above.

In addition, prior to step (b), it is preferable to remove at least a portion of the organic components, such as the binder resin, in the p-type impurity diffusion composition film by, for example, heat-treating the semiconductor substrate having a p-type impurity diffusion composition film formed on one surface at a temperature equal to or lower than the heat treatment temperature during diffusion and in an atmosphere containing oxygen. By removing at least a portion of the organic components, such as the binder resin, in the p-type impurity diffusion composition film, the concentration of the impurity components in the p-type impurity diffusion composition film on the semiconductor substrate can be increased, and the diffusibility of the p-type impurity is likely to be improved.

(Step (c))
In the step (c), the semiconductor substrate is heated while a gas containing an n-type impurity is being flowed, thereby forming an n-type impurity diffusion layer 55 .

Examples of gases containing n-type impurities include _POCl3 gas. For example, _POCl3 gas can be obtained by bubbling _N2 gas or nitrogen/oxygen mixed gas into a _POCl3 solution, or by heating the _POCl3 solution. In addition, when the second conductivity type is p-type, examples of gases include _BBr3 and _BCl3 .

The heating temperature is preferably 750°C to 1050°C, and more preferably 800°C to 1000°C.

There are no particular limitations on the gas atmosphere, but a mixed gas atmosphere of nitrogen, oxygen, argon, helium, xenon, neon, krypton, etc. is preferable, a mixed gas of nitrogen and oxygen is more preferable, and a mixed gas of nitrogen and oxygen having an oxygen content of 5 volume % or less is particularly preferable.

In addition, it is preferable to perform step (c) while keeping the same gas atmosphere as step (b), since this can shorten the process time for changing the gas atmosphere. In particular, it is preferable that the ratio of nitrogen to oxygen in the gas atmosphere in step (b) is the same as the ratio of nitrogen to oxygen in the gas atmosphere in step (c). In this case, the preferred ratio is oxygen:nitrogen = 1:99 to 5:95 by volume.

After step (b), a layer of the heat-treated p-type impurity diffusion composition film remains on top of the p-type impurity diffusion layer. It is preferable to use this as a mask against gas containing n-type impurities to carry out step (c). This makes it possible to suppress the intrusion of n-type impurities into the p-type impurity diffusion layer.

Either step (b) or step (c) may be performed first, and step (c) may be performed simultaneously with step (b). When the heat-treated layer of the p-type impurity diffusion composition film is used as a mask, it is preferable to perform step (c) after step (b).

Furthermore, it is more preferable to carry out step (c) continuously after step (b). For example, after step (b), it is preferable to move to step (c) directly without removing the diffusion board from the firing furnace. "Carrying out step (c) continuously after step (b)" means carrying out step (c) immediately after step (b).

It is preferable that the heating temperature when forming the n-type impurity diffusion layer in the step (c) is 50 to 200°C lower than the heating temperature when forming the p-type impurity diffusion layer in the step (b). By setting the heating temperature when forming the n-type impurity diffusion layer in the step (c) to a temperature 50 to 200°C lower than the heating temperature when forming the p-type impurity diffusion layer in the step (b), when the step (c) is performed consecutively after the step (b), the effect of heating on the p-type impurity diffusion layer formed in the step (b) can be minimized, making it easier to control the p-type impurity diffusion.

In step (c), since the heating temperature can be lower when diffusing with a gas containing n-type impurities than when diffusing with a gas containing p-type impurities, it is preferable that the first conductivity type is p-type and the second conductivity type is n-type.

<Method of manufacturing solar cell element>
The method for manufacturing a solar cell of the present invention includes the method for manufacturing a semiconductor element of the present invention. Specifically, the method includes a step of forming an electrode on each impurity diffusion layer of the semiconductor substrate on which the first conductive type impurity diffusion layer and the second conductive type impurity diffusion layer are formed, which are obtained by the above-mentioned steps. Details are described using a single-sided power generation solar cell in FIG. 1, a back junction type solar cell in FIG. 2, and a double-sided power generation solar cell in FIG. 3 and FIG. 4 as examples.

The methods for manufacturing semiconductor elements and solar cells of the present invention are not limited to the above-described embodiments, and various modifications such as design changes may be made based on the knowledge of those skilled in the art. Such modified embodiments are also included within the scope of the present invention.

The impurity diffusion composition of the present invention can also be used in photovoltaic elements such as solar cells, and semiconductor devices in which an impurity diffusion region is patterned on a semiconductor surface, such as transistor arrays, diode arrays, photodiode arrays, and transducers.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Among the compounds used, those using abbreviations are shown below.
GBL: γ-butyrolactone PVA: polyvinyl alcohol MeTMS: methyltrimethoxysilane PhTMS: phenyltrimethoxysilane.

(1) Solution Viscosity and Storage Stability For impurity-diffusing compositions with a viscosity of less than 1,000 mPa·s, the viscosity was measured at a liquid temperature of 25°C and a rotational speed of 20 rpm using a rotational viscometer TVE-25L (E-type digital viscometer) manufactured by Toki Sangyo Co., Ltd. Also, for impurity-diffusing compositions with a viscosity of 1,000 mPa·s or more, the viscosity was measured at a liquid temperature of 25°C and a rotational speed of 20 rpm using a Brookfield RVDV-11+P (B-type digital viscometer). Here, the viscosity immediately after the preparation of the impurity-diffusing composition and the viscosity after storage at 25°C for 30 days after preparation were measured and used as an index of storage stability. Viscosity increase rate of 5% or less was judged as excellent (A), viscosity increase rate of more than 5% and less than 20% was judged as good (B), viscosity increase rate of more than 20% and less than 30% was judged as acceptable (C), and viscosity increase rate of more than 30% was judged as bad (D).

(2) Evaluation of peelability A 6-inch square textured n-type silicon wafer (manufactured by Electronics and Materials Corporation, surface resistance 200 Ω□) was immersed in a 1% hydrofluoric acid solution for 1 minute, washed with water, and then treated on a hot plate at 140° C. for 5 minutes after air blowing.

The impurity diffusion composition to be measured was applied to the silicon wafer using a known coating method so that the pre-baked film thickness was approximately 500 nm. After coating, the silicon wafer was pre-baked at 140°C for 5 minutes.

Each silicon wafer was then placed in an electric furnace and maintained at 900°C for 30 minutes in an atmosphere of nitrogen:oxygen = 99:1 (volume ratio) to thermally diffuse the impurities.

After thermal diffusion, each silicon wafer was immersed in a 5% by weight aqueous solution of hydrofluoric acid at 23°C for 1 minute to remove the diffusing agent and mask. After removal, the silicon wafer was immersed in pure water to wash, and the presence or absence of residue was visually observed on the surface. Those in which surface deposits were visible after 1 minute of immersion and could not be removed by rubbing with a cloth were rated worst (D), those in which surface deposits were visible after 1 minute of immersion but could be removed by rubbing with a cloth were rated bad (C), those in which surface deposits could not be visually confirmed within 1 minute but more than 30 seconds were rated good (B), and those in which surface deposits could not be visually confirmed within 30 seconds were rated excellent (A). From the viewpoint of production takt time, good (B) is acceptable, but excellent (A) is preferable.

(3) Measurement of sheet resistance value The silicon wafer after impurity diffusion used in the peelability evaluation was subjected to p/n judgment using a p/n judger, and the surface resistance was measured using a four-probe surface resistance measuring device RT-70V (manufactured by Napson Co., Ltd.) to obtain the sheet resistance value. The sheet resistance value is an index of impurity diffusibility, and a smaller resistance value means a larger amount of impurity diffusion.

(4) Diffusion uniformity The surface concentration distribution of impurities was measured using a secondary ion mass spectrometer IMS7f (manufactured by Camera Corporation) for the central portion of the silicon wafer after impurity diffusion used in the sheet resistance measurement. From the obtained surface concentration distribution, the surface concentration was read at 10 points at 100 μm intervals, and the ratio of the average to the standard deviation, "standard deviation/average", was calculated. "Standard deviation/average" was judged as excellent (A) when it was 0.3 or less, good (B) when it was greater than 0.3 and less than 0.6, not bad (C) when it was greater than 0.6 and less than 0.9, and bad (D) when it was greater than 0.9. Since the variation in the surface concentration of impurities has a large effect on the power generation efficiency, it is most preferable that it is excellent (A).

(5) Barrier Properties An n-type silicon wafer (manufactured by Ferrotec Silicon Corporation, surface resistivity 410 Ω/□) cut to 3 cm × 3 cm was immersed in a 1% hydrofluoric acid aqueous solution for 1 minute, washed with water, and then treated on a hot plate at 140° C. for 5 minutes after air blowing.

As shown in Fig. 6(a), the p-type impurity diffusion composition of each Example and Comparative Example was applied to the silicon wafer 61 by a known application method so that the pre-baked film thickness was about 500 nm. After application, the silicon wafer was pre-baked at 140°C for 5 minutes to produce a p-type impurity diffusion composition film 62.

Next, as shown in Figure 6 (b), an n-type impurity diffusion composition (OCD T-1, manufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied to another silicon wafer 63 by a known application method so that the pre-baked film thickness was about 500 nm. After application, the silicon wafer was pre-baked at 140°C for 5 minutes to produce an n-type impurity diffusion composition coating film 64.

Next, as shown in Fig. 6(c), the silicon wafer 61 on which the p-type impurity diffusion composition film 62 is formed and the silicon wafer 63 on which the n-type impurity diffusion composition film 64 is formed are placed in an electric furnace with a gap of 5 mm between them, and the impurities are thermally diffused by maintaining the temperature at 900°C for 30 minutes in an atmosphere of nitrogen:oxygen = 99:1 (volume ratio). As a result, as shown in Fig. 6(d), a p-type impurity diffusion layer 65 is formed in the silicon wafer 61, and an n-type impurity diffusion layer 66 is formed in the silicon wafer 63.

After thermal diffusion, each silicon wafer was immersed in a 5 wt % aqueous solution of hydrofluoric acid at 23°C for 1 minute to peel off the hardened diffusing agent (Figure 6 (e)).

Thereafter, the surface concentration distribution of phosphorus element was measured for the silicon wafer 61 using a secondary ion mass spectrometer IMS7f (manufactured by Camera Corporation). A lower surface concentration of phosphorus element means a higher barrier property against phosphorus element diffusing from the opposing n-type impurity diffusion composition. The surface concentration of phosphorus element obtained was judged as excellent (A) when it was 10 ¹⁷ or less, good (B) when it was more than 10 ¹⁷ and 10 ¹⁸ or less, not bad (C) when it was more than 10 ¹⁸ and 10 ¹⁹ or less, and bad (D) when it was more than 10 ¹⁹ .

In the case of an n-type impurity diffusion composition, the measurement is carried out as follows.
An n-type silicon wafer (manufactured by Ferrotec Silicon Corp., surface resistivity 410 Ω/□) cut to 3 cm x 3 cm was immersed in a 1% aqueous hydrofluoric acid solution for 1 minute, washed with water, and then treated on a hot plate at 140°C for 5 minutes after air blowing.

As shown in Figure 6(a), a p-type impurity diffusion composition (manufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied to the silicon wafer 61 by a known application method so that the pre-baked film thickness was about 500 nm. After application, the silicon wafer was pre-baked at 140°C for 5 minutes to produce a p-type impurity diffusion composition film 62.

Next, as shown in Fig. 6(b), the n-type impurity diffusion composition of the present invention was applied to another silicon wafer 63 by a known application method so that the pre-baked film thickness was about 500 nm. After application, the silicon wafer was pre-baked at 140°C for 5 minutes to produce an n-type impurity diffusion composition coating film 64.

Next, as shown in Fig. 6(c), the silicon wafer 61 on which the p-type impurity diffusion composition film 62 is formed and the silicon wafer 63 on which the n-type impurity diffusion composition film 64 is formed are placed in an electric furnace with a gap of 5 mm between them, and the impurities are thermally diffused by maintaining the temperature at 900°C for 30 minutes in an atmosphere of nitrogen:oxygen = 99:1 (volume ratio). As a result, as shown in Fig. 6(d), a p-type impurity diffusion layer 65 is formed in the silicon wafer 61, and an n-type impurity diffusion layer 66 is formed in the silicon wafer 63.

After thermal diffusion, each silicon wafer was immersed in a 5 wt % aqueous solution of hydrofluoric acid at 23°C for 1 minute to peel off the hardened diffusing agent (Figure 6 (e)).

Thereafter, the surface concentration distribution of boron element was measured for the silicon wafer 63 using a secondary ion mass spectrometer IMS7f (manufactured by Camera Corporation). A lower surface concentration of boron element means a higher barrier property against boron element diffusing from the opposing p-type impurity diffusion composition. The obtained surface concentration of boron element was judged as excellent (A) when it was 10 ¹⁷ or less, good (B) when it was more than 10 ¹⁷ and less than 10 ¹⁸ , not bad (C) when it was more than 10 ¹⁸ and less than 10 ¹⁹ , and bad (D) when it was more than 10 ¹⁹ .

(6) Screen Printability The impurity diffusion composition of each of the Examples and Comparative Examples was patterned into stripes by screen printing, and the precision of the stripe width was confirmed.

A semiconductor substrate made of n-type single crystal silicon measuring 156 mm on a side was prepared, and both surfaces were alkaline etched to remove slice damage and natural oxides. During this process, numerous irregularities, typically 40 to 100 μm wide and 3 to 4 μm deep, were formed on both sides of the semiconductor substrate, and this was used as the coating substrate.

A screen printing machine (Microtec Corporation, Model TM-750) was used to form a striped pattern using a screen mask (SUS Corporation, 400 mesh, line diameter 23 μm) with 175 openings, each 200 μm wide and 13.5 cm long, spaced at a pitch of 600 μm.

After screen printing the p-type impurity diffusion composition, the substrate was heated in air at 140°C for 5 minutes and then at 230°C for 30 minutes to form a pattern with a thickness of approximately 1.5 μm, a width of approximately 210 μm, a pitch of 600 μm, and a length of 13.5 cm.

Here, the line width was measured at 10 equally spaced points on any one line, and coating widths with a standard deviation of 12.5 μm or less were judged as excellent (A), those with a standard deviation between 12.5 μm and 15 μm were judged as good (B), those with a standard deviation between 15 μm and 17.5 μm were judged as not bad (C), and those with a standard deviation between 17.5 μm and 20 μm were judged as bad (D).

(7) Continuous Screen Printability The above screen printability evaluation was performed on 1,000 sheets in succession without causing coating defects such as bleeding or smearing, and was judged as excellent (A). The above screen printability evaluation was performed on 100 to 999 sheets in succession with coating defects such as bleeding or smearing, and was judged as good (B). The above screen printability evaluation was performed on 10 to 99 sheets in succession with coating defects such as bleeding or smearing, and was judged as not bad (C). The above screen printability evaluation was performed on 10 sheets in succession with coating defects such as bleeding or smearing, and was judged as bad (D).

(8) Sticking: When no sticking occurred even after 1,000 consecutive screen print evaluations, the test was judged as excellent (A); when sticking occurred within 100 to 999 consecutive screen print evaluations, the test was judged as good (B); when sticking occurred within 10 to 99 consecutive screen print evaluations, the test was judged as not bad (C); and when sticking occurred within 10 consecutive screen print evaluations, the test was judged as bad (D).
In addition, Examples 5, 6, 8 , 9, 11 to 17 , and 19 should be read as Reference Examples 5, 6, 8 , 9, 11 to 17 , and 19, respectively.

Reference Example 1
(1) Synthesis of polysiloxane solution A 1000 mL three-neck flask was charged with 183.25 g of KBM-13 (methyltrimethoxysilane), 266.75 g of KBM-103 (phenyltrimethoxysilane), and 403.36 g of GBL, and an aqueous formic acid solution prepared by dissolving 0.45 g of formic acid in 145.29 g of water was added over 30 minutes while stirring at 40 ° C. After the dropwise addition, the mixture was stirred at 40 ° C. for 1 hour, then heated to 70 ° C. and stirred for 30 minutes. The oil bath was then heated to 115 ° C. One hour after the start of the temperature rise, the internal temperature of the solution reached 100 ° C., and the mixture was heated and stirred for 1 hour (internal temperature: 100 to 110 ° C.). The obtained solution was cooled in an ice bath to obtain polysiloxane solution A (PhTMS (50) / MeTMS (50)). The solids concentration of the polysiloxane solution A was 39.0% by mass, and the weight average molecular weight (Mw) was 2,500.

(2) Preparation of impurity diffusion composition 1 13.42g of the polysiloxane solution A synthesized above, 1.31g of boric acid, 11.63g of polyvinyl alcohol (manufactured by Nippon Vinyl Acetate Poval Co., Ltd.) with a saponification degree of 89 mol% (hereinafter referred to as polyvinyl alcohol (89)), 3.9g of Aerosil VPNKC130 (manufactured by Nippon Aerosil Co., Ltd.) which is fine particle silicon oxide, 24.64g of GBL, 35.1g of terpineol, and 10g of water were mixed and thoroughly stirred to be uniform. Here, the amount of formic acid carried over from the polysiloxane solution A was 0.006% by mass. As shown in Table 2, the evaluation results of the obtained solution were all good.

Reference Example 2
Except for changing the degree of saponification of the polyvinyl alcohol to 70 mol %, an impurity-diffusing composition 2 was obtained in the same manner as in Reference Example 1. The evaluation results of the obtained solution were all good, as shown in Table 2.

Reference Example 3
Except for changing the degree of saponification of the polyvinyl alcohol to 69 mol %, an impurity-diffusing composition 3 was obtained in the same manner as in Reference Example 1. The evaluation results of the obtained solution were all good, as shown in Table 2.

Reference Example 4
Except for changing the degree of saponification of the polyvinyl alcohol to 50 mol %, an impurity-diffusing composition 4 was obtained in the same manner as in Reference Example 1. The evaluation results of the obtained solution were all good, as shown in Table 2.

Example 5
Except for changing the degree of saponification of the polyvinyl alcohol to 49 mol %, the procedure of Reference Example 1 was repeated to obtain an impurity-diffusing composition 5. The evaluation results of the obtained solution were all good, as shown in Table 2.

Example 6
Except for changing the degree of saponification of the polyvinyl alcohol to 20 mol %, an impurity-diffusing composition 6 was obtained in the same manner as in Reference Example 1. The evaluation results of the obtained solution were all good, as shown in Table 2.

Reference Example 7
An impurity-diffusing composition 7 was obtained in the same manner as in Example 5, except that the mass ratio (A):(C) of (A) polyvinyl alcohol and (C) siloxane was set to 20:80. The evaluation results of the obtained solution were all good, as shown in Table 2.

Example 8
An impurity-diffusing composition 8 was obtained in the same manner as in Example 5, except that the mass ratio (A):(C) of (A) polyvinyl alcohol and (C) siloxane was set to 30:70. The evaluation results of the obtained solution were all good, as shown in Table 2.

Example 9
An impurity-diffusing composition 9 was obtained in the same manner as in Example 5, except that the mass ratio (A):(C) of (A) polyvinyl alcohol and (C) siloxane was set to 75:25. The evaluation results of the obtained solution were all good, as shown in Table 2.

Reference Example 10
An impurity-diffusing composition 10 was obtained in the same manner as in Example 5, except that the mass ratio (A):(C) of (A) polyvinyl alcohol and (C) siloxane was set to 80:20. The evaluation results of the obtained solution were all good, as shown in Table 2.

Example 11
Except for changing the solvent from GBL to N-methyl-2-pyrrolidone, the procedure was the same as in Example 5 to obtain an impurity-diffusing composition 11. As shown in Table 2, the evaluation results of the obtained solution were all good.

Example 12
Except for changing the amount of water to 5.0 g, the procedure was the same as in Example 5 to obtain an impurity-diffusing composition 12. As shown in Table 2, the evaluation results of the obtained solution were all good.

Example 13
Except for changing the amount of water to 2.5 g, the procedure was the same as in Example 5 to obtain an impurity-diffusing composition 13. As shown in Table 2, the evaluation results of the obtained solution were all good.

Example 14
0.004 g of formic acid was added to the impurity-diffusing composition 5 so that the amount of formic acid in the composition was 0.01 mass %, thereby preparing an impurity-diffusing composition 14. The evaluation results of the obtained solution were all good, as shown in Table 2.

Example 15
0.094 g of formic acid was added to the impurity-diffusing composition 5 so that the amount of formic acid in the composition was 0.1 mass %, thereby preparing an impurity-diffusing composition 15. The evaluation results of the obtained solution were all good, as shown in Table 2.

Example 16
The impurity-diffusing composition 5 was subjected to treatment (X) with an ion exchange resin to prepare an impurity-diffusing composition 16. The evaluation results of the obtained solution were all good, as shown in Table 2. Here, the treatment (X) with an ion exchange resin refers to the following treatment.
(X) The resulting solution is passed through a column packed with a cation exchange resin (Amberlyst 15JS-HG-DRY, manufactured by Organo Corporation).

Example 17
The impurity-diffusing composition 5 was subjected to a treatment (Y) with an ion exchange resin to prepare an impurity-diffusing composition 17. The evaluation results of the obtained solution were all good, as shown in Table 2. Here, the treatment (Y) with an ion exchange resin refers to the following treatment.
(Y) The resulting solution is passed through a column packed with a mixed cation and anion exchange resin (Amberlyst MSPS2-1-DRY, manufactured by Organo Corporation).

Example 18
0.004 g of formic acid was added to impurity-diffusing composition 13 so that the amount of formic acid in the composition was 0.01 mass %, thereby preparing impurity-diffusing composition 18. The evaluation results of the obtained solution were all good, as shown in Table 2.

Example 19
Except for omitting the fine particle silicon oxide, the procedure was the same as in Example 5 to obtain an impurity-diffusing composition 19. The evaluation results of the obtained solution were as shown in Table 2.

Reference Example 20
Except for using trimethyl borate instead of boric acid, an impurity-diffusing composition 20 was obtained in the same manner as in Example 5. The evaluation results of the obtained solution were as shown in Table 2.

Comparative Example 1
Except for changing the degree of saponification of the polyvinyl alcohol to 90 mol%, an impurity-diffusing composition 21 was obtained in the same manner as in Example 1. As shown in Table 2, the evaluation result of the obtained solution showed that the screen continuous printability was poor.

Comparative Example 2
Except for changing the degree of saponification of the polyvinyl alcohol to 10 mol%, an impurity-diffusing composition 22 was obtained in the same manner as in Example 1. As shown in Table 2, the evaluation result of the obtained solution showed poor diffusion uniformity.

Comparative Example 3
Except for using (MeTMS(100)/PhTMS(0)), the procedure of Example 5 was repeated to obtain an impurity-diffusing composition 23. As shown in Table 2, the evaluation results of the obtained solution showed poor diffusion uniformity.

Comparative Example 4
Except for using (MeTMS(0)/PhTMS(100)), the procedure of Example 5 was repeated to obtain an impurity-diffusing composition 24. As shown in Table 2, the evaluation results of the obtained solution showed poor diffusion uniformity.

10, 20, 30, 40 Solar cell 11, 21, 31, 41, 51, 61, 63 Semiconductor substrate 12, 22, 32, 42, 42', 52, 62 P-type impurity diffusion composition film 13, 23, 33, 44, 44', 53 P-type impurity diffusion layer 24, 34, 43, 64 N-type impurity diffusion composition film 25, 35, 45, 55, 66 N-type impurity diffusion layer 16, 17, 26, 36, 37, 46, 47 Passivation layer 18, 28, 29, 38, 39, 48, 49 Contact electrode 26 Protective film 26a Opening 100 Diffusion furnace 110 Diffusion board

Claims (11)

a polyvinyl alcohol (A), an impurity-diffusing component (B), and a siloxane (C), wherein the degree of saponification of the polyvinyl alcohol (A) is 20 mol % or more and less than 50 mol %, the impurity-diffusing component (B) is boric acid, the siloxane (C) contains at least one partial structure represented by any one of the following general formulas (1) and (2) and at least one partial structure represented by any one of the following general formulas (3) and (4), a mass ratio of the polyvinyl alcohol (A) to the siloxane (C) (A):(C) is 30:70 to 75:25, and the pH is 4.0 to 6.5,
The impurity-diffusing composition further comprises a solvent (D), the water content of which is 0.1 to 5 mass % in the solvent (D) .

(R ¹ and R ² each independently represent any one of a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, an acyloxy group having 1 to 6 carbon atoms, and an alkenyl group having 2 to 10 carbon atoms, and a plurality of R ^1s and R ^2s may be the same or different. R ³ represents an aryl group having 6 to 15 carbon atoms, and a plurality of R ^3s may be the same or different. R ⁴ represents any one of a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, an acyloxy group having 1 to 6 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, and an aryl group having 6 to 15 carbon atoms, and a plurality of R ^4s may be the same or different.) The impurity-diffusing composition according to claim 1, wherein the (D) solvent contains a lactam solvent or a cyclic ester solvent, and the content of the lactam solvent or the cyclic ester solvent in the (D) solvent is 20 mass% or more. 3. The impurity-diffusing composition according to claim 1 , further comprising (E) a thixotropic agent, the (E) thixotropic agent being fine particles of silicon oxide. The impurity-diffusing composition according to any one of claims 1 to 3 , further comprising (F) 0.01 to 0.1 mass % of a carboxylic acid. 5. The impurity-diffusing composition according to claim 4 , wherein the carboxylic acid (F) is formic acid. A method for manufacturing a semiconductor device, comprising the steps of: applying the impurity diffusing composition according to any one of claims 1 to 5 to a semiconductor substrate to form an impurity diffusing composition film; and diffusing impurities from the impurity diffusing composition film to form an impurity diffusion layer on the semiconductor substrate. A method for manufacturing a semiconductor device, comprising the steps of: applying an n-type impurity diffusion composition to a semiconductor substrate to form an n-type impurity diffusion composition film; applying an impurity diffusion composition according to any one of claims 1 to 5 , which is a p-type impurity diffusion composition, to form an impurity diffusion composition film; and heating the semiconductor substrate to simultaneously form an n-type impurity diffusion layer and a p-type impurity diffusion layer. A method for manufacturing a semiconductor device, comprising the steps of: applying the impurity diffusion composition according to any one of claims 1 to 5 , which is a p-type impurity diffusion composition, to one surface of a semiconductor substrate to form a p-type impurity diffusion composition film; applying an n-type impurity diffusion composition to the other surface of the semiconductor substrate to form an n-type impurity diffusion composition film; and heating the semiconductor substrate to simultaneously form a p-type impurity diffusion layer and an n-type impurity diffusion layer. A method for manufacturing a semiconductor device, comprising the steps of: partially coating one surface of a semiconductor substrate with the impurity diffusion composition according to any one of claims 1 to 5 , which is a p-type impurity diffusion composition, to form a first p-type impurity diffusion composition film; coating a second p-type impurity diffusion composition on a portion where the first p-type impurity diffusion composition film is not formed, to form a low-concentration p-type impurity diffusion composition film; coating the other surface of the semiconductor substrate with an n-type impurity diffusion composition to form an n-type impurity diffusion composition film; and heating the semiconductor substrate to simultaneously form a high-concentration p-type impurity diffusion layer, a low-concentration p-type impurity diffusion layer, and an n-type impurity diffusion layer. A method for manufacturing a semiconductor device using a plurality of semiconductor substrates, comprising the steps of (a) to (c) below, in which in steps (b) and (c), a pair of semiconductor substrates are arranged such that their surfaces on which a first conductivity type impurity diffusion composition film is formed face each other.
(a) A step of applying the impurity diffusion composition according to any one of claims 1 to 5 onto one surface of each semiconductor substrate to form an impurity diffusion composition film of a first conductivity type.
(b) A step of heating the semiconductor substrate on which the first conductivity type impurity diffusion composition film is formed, thereby diffusing the first conductivity type impurity into the semiconductor substrate to form a first conductivity type impurity diffusion layer.
(c) heating the semiconductor substrate in an atmosphere having a gas containing an impurity of a second conductivity type to diffuse the impurity of the second conductivity type into the other surface of the semiconductor substrate, thereby forming an impurity diffusion layer of the second conductivity type. A method for manufacturing a solar cell, comprising the method for manufacturing a semiconductor element according to any one of claims 6 to 10 .

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