WO2018012547A1

WO2018012547A1 - Method for producing semiconductor substrate with p-type diffusion layer, semiconductor substrate with p-type diffusion layer, method for producing solar cell element, and solar cell element

Info

Publication number: WO2018012547A1
Application number: PCT/JP2017/025439
Authority: WO
Inventors: 鉄也佐藤; 野尻　剛; 田中　直敬; 岩室　光則; 成宜清水; 真年森下
Original assignee: 日立化成株式会社
Priority date: 2016-07-14
Filing date: 2017-07-12
Publication date: 2018-01-18
Also published as: TW201813116A

Abstract

This method for producing a semiconductor substrate with a p-type diffusion layer comprises: a step wherein a p-type diffusion layer-forming composition, which contains a compound containing boron, is applied onto a semiconductor substrate, thereby forming a p-type diffusion layer-forming composition layer in which the mass of the compound containing boron per unit area is from 0.001 mg/cm² to 0.1 mg/cm²; and a step wherein a p-type diffusion layer is formed on the semiconductor substrate by heating the semiconductor substrate, on which the p-type diffusion layer-forming composition layer has been formed.

Description

Method for manufacturing semiconductor substrate with p-type diffusion layer, semiconductor substrate with p-type diffusion layer, method for manufacturing solar cell element, and solar cell element

The present invention relates to a method for manufacturing a semiconductor substrate with a p-type diffusion layer, a semiconductor substrate with a p-type diffusion layer, a method for manufacturing a solar cell element, and a solar cell element.

An example of a manufacturing process of a solar cell element using an n-type silicon substrate will be described.
First, an n-type silicon substrate having a texture structure formed on the surface is prepared so as to promote the light confinement effect and increase the efficiency. Subsequently, tens of minutes of treatment is performed at 800 ° C. to 1000 ° C. in a mixed gas (BBr ₃ gas) atmosphere of boron tribromide (BBr ₃ ), nitrogen, and oxygen, which is an acceptor element-containing compound, to form n-type silicon. A boron silicate glass (BSG) layer is uniformly formed on the surface of the substrate. Boron diffuses from the BSG layer into the silicon substrate, forming a p-type diffusion layer. In this conventional method, since boron is diffused using a mixed gas, p-type diffusion layers are formed not only on the light receiving surface but also on the side surface and the back surface. Therefore, a side etching process for removing the p-type diffusion layer on the side surface is necessary. Further, the p-type diffusion layer on the back surface needs to be converted into an n ⁺ -type diffusion layer. The p-type diffusion layer on the light-receiving surface is formed by forming a film using silicon nitride or silicon oxide on the p-type diffusion layer on the light-receiving surface. After protection, it was converted into an n ⁺ -type diffusion layer by performing several tens of minutes at 800 ° C. to 900 ° C. in a mixed gas atmosphere of phosphorus trichloride (POCl ₃ ), nitrogen and oxygen.

On the other hand, a technique is also known in which a p-type diffusion layer forming composition comprising a glass powder containing an acceptor element such as boron and a dispersion medium is applied on a semiconductor substrate and thermally diffused to form a p-type diffusion layer. (For example, refer to Patent Document 1).

Japanese Patent No. 544797

However, in the method of forming the p-type diffusion layer using the above-described BBr ₃ gas, the p-type diffusion layer is formed not only on the light receiving surface but also on the side surface and the back surface, and the p-type diffusion layer is selectively formed at a desired position. Is difficult to form. On the other hand, in the method described in Patent Document 1, for example, when a large amount of a boron-containing compound is applied onto a semiconductor substrate, an excessive amount of boron is supplied to the semiconductor substrate. : Boron Rich Layer) is formed thick. Usually, in the case of boron diffusion, BRL is formed on the outermost surface of the semiconductor substrate, and the performance of the solar cell element is lowered. Therefore, the BRL is converted into a glass layer by oxidation treatment, and the BRL is removed by etching. However, when the BRL is thick, it becomes difficult to oxidize all of the BRL, and the BRL remains as a residue on the surface. Degrading device performance.

Embodiments of the present invention provide a method for manufacturing a semiconductor substrate with a p-type diffusion layer in which a p-type diffusion layer can be selectively formed at a desired position on a semiconductor substrate, and generation of residue on the surface is suppressed. It is an object to provide a semiconductor substrate with a p-type diffusion layer manufactured by a manufacturing method, a method for manufacturing a solar cell element, and a solar cell element.

As a result of studies conducted by the inventors in view of the above situation, the boron high concentration layer can be easily removed by setting the mass per unit area of the boron-containing compound provided on the semiconductor substrate within a specific range. It was found that a solar cell element having high performance can be produced.

The present invention includes the following aspects.
<1> A p-type diffusion layer forming composition containing a compound containing boron is applied on a semiconductor substrate so that the mass of the compound containing boron per unit area is 0.001 mg / cm ² to 0.1 mg / forming a p-type diffusion layer forming composition layer of cm ² and heat-treating the semiconductor substrate provided with the p-type diffusion layer forming composition layer to form a p-type diffusion layer on the semiconductor substrate. And a method for manufacturing a semiconductor substrate with a p-type diffusion layer.
<2> The production method according to <1>, wherein the compound containing boron is boron-containing glass particles, and the p-type diffusion layer forming composition further contains a dispersion medium.
<3> The production method according to <2>, wherein the boron-containing glass particles are glass particles containing B ₂ O ₃ .
<4> When the boron-containing glass particles are expressed as oxides, B ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO And at least one selected from the group consisting of: BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ , MoO ₃ , GeO ₂ , Y ₂ O ₃ , CsO ₂ and TiO _2. <3> The production method according to <3>.
<5> The production method according to <3> or <4>, wherein the content of B ₂ O ₃ in the boron-containing glass particles is 0.1% by mass to 60% by mass.
<6> The method according to any one of <2> to <5>, wherein the boron-containing glass particles have an average particle size of 0.5 μm or less.
<7> weight of the compound containing the boron contained in the p-type diffusion layer forming composition layer, per unit ^area, is 0.005mg / cm 2 ~ 0.01mg / cm 2, <1> ~ <6 The manufacturing method of any one of>.
<8> A semiconductor substrate with a p-type diffusion layer manufactured by the manufacturing method according to any one of <1> to <7>.
<9> A method for producing a solar cell element, comprising a step of forming an electrode on the p-type diffusion layer of the semiconductor substrate with a p-type diffusion layer according to <8>.
<10> A solar cell element produced by the method for producing a solar cell element according to <9>.

According to an embodiment of the present invention, a method for manufacturing a semiconductor substrate with a p-type diffusion layer, in which a p-type diffusion layer can be selectively formed at a desired position on a semiconductor substrate and generation of residue on the surface is suppressed, A semiconductor substrate with a p-type diffusion layer manufactured by this manufacturing method, a method for manufacturing a solar cell element, and a solar cell element are provided.

It is sectional drawing which shows notionally an example of the manufacturing process of the solar cell element of this embodiment. It is the top view which looked at the solar cell element from the light-receiving surface. It is a perspective view which expands and shows a part of FIG. 2A.

Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments.
In the following embodiments, the constituent elements (including element steps and the like) are not essential unless explicitly specified, unless otherwise clearly considered essential in principle. The same applies to numerical values and ranges thereof, and the present invention is not limited thereto.
In the present disclosure, the term “process” includes a process independent of another process and the process if the purpose of the process is achieved even when it cannot be clearly distinguished from the other process.
In the present disclosure, numerical ranges indicated using “to” indicate ranges including numerical values described before and after “to” as the minimum value and the maximum value, respectively.
In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerical description. . Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples.
In the present disclosure, each component may contain a plurality of corresponding substances. When multiple types of substances corresponding to each component are present in the composition, the content or content of each component is the total content or content of the multiple types of substances present in the composition unless otherwise specified. Means quantity.
In the present disclosure, a plurality of particles corresponding to each component in the composition may be included. When a plurality of particles corresponding to each component are present in the composition, the particle diameter of each component means a value for a mixture of the plurality of particles present in the composition unless otherwise specified.
In the present disclosure, the “content ratio” represents mass% of each component when the total amount of the p-type diffusion layer forming composition is 100 mass% unless otherwise specified.
In the present disclosure, the term “layer” or “film” refers to a part of the region in addition to a case where the layer or the film is formed over the entire surface of the region when the region where the layer or the film exists is observed as a plan view. The case where it is formed is also included.
In the present disclosure, the term “lamination” indicates that layers are stacked, and two or more layers may be combined, or two or more layers may be detachable.
In the present disclosure, the “glass particle” means a glass (amorphous solid exhibiting a glass transition phenomenon) in the form of particles.
Embodiments of the present invention can be practiced without utilizing some or all of the specific and detailed content described in this disclosure.
In addition, in order to avoid obscuring the concept of the present invention, detailed description or illustration may be omitted for known points.

In the present disclosure, the average particle diameter is obtained as a particle diameter at which the volume accumulation from the small particle diameter side becomes 50% in the particle size distribution measured using the laser diffraction scattering method. The average particle diameter is the median diameter d50 calculated from the particle size distribution.

In the method for manufacturing a semiconductor substrate with a p-type diffusion layer according to this embodiment, a p-type diffusion layer forming composition containing a compound containing boron is applied to the semiconductor substrate, and the compound containing boron per unit area is formed. A step of forming a p-type diffusion layer forming composition layer having a mass of 0.001 mg / cm ² to 0.1 mg / cm ² (hereinafter also referred to as “p-type diffusion layer forming composition layer forming step”), and a step of heat-treating the semiconductor substrate provided with the p-type diffusion layer forming composition layer to form a p-type diffusion layer on the semiconductor substrate (hereinafter also referred to as “p-type diffusion layer formation step”).

The manufacturing method of the semiconductor substrate with a p-type diffusion layer according to this embodiment has the above-described configuration, so that the p-type diffusion layer can be selectively formed at a desired position on the semiconductor substrate, and the surface residue can be formed. Can be suppressed. Although this mechanism is not necessarily clear, it is presumed as follows.
The p-type diffusion layer forming composition can be applied to a desired region on the semiconductor substrate in a desired pattern, and the p-type diffusion layer made of boron contained in the p-type diffusion layer forming composition is placed at a desired position. It can be formed selectively. Further, by setting the mass of the boron-containing compound in the p-type diffusion layer forming composition layer formed on the semiconductor substrate to 0.001 mg / cm ² to 0.1 mg / cm ² , the BRL is formed thick. Therefore, the BRL can be easily removed by etching. Moreover, by making the mass of the compound containing boron in the p-type diffusion layer forming composition in the above range, it is possible to suppress boron from being scattered and diffused to an unnecessary region of the semiconductor substrate.

Hereinafter, a method for manufacturing a semiconductor substrate with a p-type diffusion layer according to an embodiment of the present invention will be described in detail.
First, a p-type diffusion layer forming composition will be described, and then a method for manufacturing a semiconductor substrate with a p-type diffusion layer using the p-type diffusion layer forming composition, a method for manufacturing a solar cell element, and a solar cell element will be described. .

<P-type diffusion layer forming composition>
The p-type diffusion layer forming composition contains a compound containing boron. The p-type diffusion layer forming composition may contain other components as necessary in consideration of impartability and the like.

Here, the p-type diffusion layer forming composition contains a boron-containing compound, and is applied to the semiconductor substrate and then heat-treated to diffuse boron in the boron-containing compound, thereby causing p-type diffusion of the semiconductor substrate. A composition that can form a p-type diffusion layer, which is an impurity diffusion layer, in a region to which the layer-forming composition is applied. By using the p-type diffusion layer forming composition, the p-type diffusion layer can be selectively formed in a desired region of the semiconductor substrate to which the p-type diffusion layer forming composition is applied, and is unnecessary on the back surface, side surface, and the like of the semiconductor substrate. The formation of the p-type diffusion layer can be suppressed.

(Compound containing boron)
Examples of the compound containing boron include inorganic boron compounds such as boron oxide, boron oxoacid, calcium borate, boron nitride, and boric acid; borate ester compounds; glass compounds containing boron (hereinafter referred to as “boron-containing glass compounds”) Boron-doped silicon particles; boron-containing silicon oxide compounds; boron alkoxides; and compounds that can be converted to compounds containing boron oxide at high temperatures (eg, 800 ° C. or higher) that are thermally diffused into the semiconductor substrate (hereinafter referred to as “ Also referred to as “boron oxide precursor”).

Among these, it is preferable to use at least one selected from the group consisting of boron oxide, boric acid, borate ester compounds, boron-containing glass compounds, boron nitride, boron-containing silicon oxide compounds, and boron oxide precursors. From the viewpoint of effective suppression of out diffusion, it is preferably selected from the group consisting of boron nitride, boron-containing glass compounds, and boron-containing silicon oxide compounds, and selected from the group consisting of boron nitride particles or boron-containing glass compounds. It is more preferable that a boron-containing glass compound is used.
In the present disclosure, out-diffusion means that an acceptor element such as boron diffuses in a region other than the region to which the p-type diffusion layer forming composition is applied.
From the viewpoint of suppressing out-diffusion, the boron-containing glass compound and boron nitride are each preferably in the form of particles. By including the boron-containing glass compound particles or boron nitride particles, it tends to be easy to selectively form a p-type diffusion layer in a desired region.

The boron-containing glass compound is preferably boron-containing glass particles, more preferably glass particles containing boron oxide, and still more preferably glass particles containing B ₂ O ₃ and a glass component substance. Two or more types of boron-containing glass particles may be used in combination. When two or more types of boron-containing glass particles are used in combination, for example, when two or more types of boron-containing glass particles having the same component and different average particle sizes are used, two or more types of boron-containing glass particles having the same average particle size and different components are used. When using, the case where two or more types of boron containing glass particles from which an average particle diameter and a kind differ is used is mentioned.

The content of boron oxide in the boron-containing glass compound can be appropriately changed according to the purpose. For example, from the viewpoint of boron diffusivity, the content of boron oxide in the boron-containing glass compound is preferably 0.1% by mass to 60% by mass, and more preferably 0.5% by mass to 50% by mass. More preferably, the content is 1% by mass to 40% by mass. By containing 0.1% by mass or more of boron oxide in the glass compound, the absolute amount of boron to be diffused into the semiconductor substrate tends to be ensured. By setting it to 60% by mass or less, hydrofluoric acid performed after diffusion There is a tendency that the amount of etching residue generated in an etching process using an etching solution such as can be reduced.

When the boron-containing glass particles are glass particles containing B ₂ O ₃ and a glass component substance, the content of B ₂ O _{3 in} the boron-containing glass particles is 0.1% with respect to the total mass of the boron-containing glass particles. The mass is preferably 60% by mass to 60% by mass, more preferably 0.5% by mass to 50% by mass, and still more preferably 1% by mass to 45% by mass. By containing 0.1% by mass or more of B ₂ O ₃ in the boron-containing glass particles, there is a tendency that an absolute amount of boron to be diffused into the semiconductor substrate can be ensured. There is a tendency that the amount of etching residue generated in an etching process using an etching solution such as hydrofluoric acid can be reduced.

The content of the boron-containing glass compound in the p-type diffusion layer forming composition can be appropriately changed according to the purpose. For example, from the viewpoint of boron diffusivity, it is preferably 0.01% by mass to 99% by mass, and preferably 0.1% by mass to 98% by mass with respect to the total mass of the p-type diffusion layer forming composition. More preferably, it is more preferably 0.5% by mass to 50% by mass. By including 0.01% by mass or more of a boron-containing glass compound, the absolute amount of boron to be diffused into the semiconductor substrate can be secured, and by making it 99% by mass or less, the impartability of the p-type diffusion layer forming composition can be increased. There is a tendency to improve.

As the glass component substance contained in the boron-containing glass compound, commonly used components can be used. For example, the glass softening temperature can be set to a desired range, and from the viewpoint of reducing the difference from the thermal expansion coefficient of the semiconductor substrate, the glass component substance when expressed as an oxide is SiO ₂ , K _2. O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ , WO ₃ , MoO ₃ , Y ₂ O ₃ , CsO ₂ , It is preferably at least one selected from the group consisting of TiO ₂ , TeO ₂ , La ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , GeO ₂ , Lu ₂ O ₃ and MnO. From the viewpoint of effectively obtaining the desired effect, the glass component material when expressed as an oxide includes SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO. It is more preferable to use at least one selected from the group consisting of ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ , MoO ₃ , GeO ₂ , Y ₂ O ₃ , CsO ₂ and TiO ₂ , Selected from the group consisting of SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ and MoO _3. More preferably, at least one kind is used.

Specific examples of the boron-containing glass compound include, for example, a B ₂ O ₃ —SiO ₂ -containing glass compound (described in the order of boron oxide-glass component material, the same applies hereinafter), a B ₂ O ₃ —ZnO-containing glass compound, and B _2. Examples thereof include O ₃ —PbO-containing glass compounds and glass compounds using B ₂ O ₃ as both a boron oxide and a glass component substance.
In the above, a glass compound containing one component or two components is mentioned, but a glass compound containing three or more components such as B ₂ O ₃ —SiO ₂ —Al ₂ O ₃ —CaO may be used.
The boron-containing glass compound may be a glass compound containing B ₂ O ₃ and other acceptor element compounds such as Al ₂ O ₃ . For example, a glass compound containing an oxide of two or more kinds of acceptor elements such as an Al ₂ O ₃ —B ₂ O ₃ -containing glass compound may be used.

Boron-containing glass compounds, when expressed as oxides from the viewpoint of the resistance of the impurity diffusion layer to be formed and the suppression of out-diffusion, B ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , K ₂ O , Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ , WO ₃ , MoO ₃ , GeO ₂ , Y ₂ O ₃ , CsO ₂ , TiO ₂ , TeO ₂ , La ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , Lu ₂ O _3, and at least one selected from the group consisting of MnO, preferably B ₂ and _{_{_{_{O 3, Al 2 O 3,}}}} SiO 2, K 2 O, Na 2 O, Li 2 O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V 2 O 5, Sn , And _{_{_{_{ZrO 2, MoO 3, GeO 2}}}} , Y 2 O 3, CsO 2 and it is more preferable to contain at least one, the selected from the group consisting of _{_{_{TiO 2, B 2 O 3,}}} Al 2 O 3 , SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ and MoO _3. It is more preferable to contain at least one selected from the group consisting of B ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, It is particularly preferable to contain at least one selected from the group consisting of ZnO and ZrO ₂ .

The softening temperature of the boron-containing glass particles is preferably 200 ° C. to 1000 ° C. from the viewpoints of diffusibility of components of the p-type diffusion layer forming composition during heat treatment (thermal diffusion), suppression of dripping, etc. More preferably, the shape of the boron-containing glass particles is 300 ° C. to 900 ° C. Examples of the shape of the boron-containing glass particles include a spherical shape, a substantially spherical shape, a flat shape, a block shape, a plate shape, and a scale shape. The boron-containing glass particles are preferably spherical, substantially spherical, flat, or plate-shaped in terms of imparting to a semiconductor substrate and improving diffusion uniformity when a p-type diffusion layer forming composition is used.

The average particle diameter of the boron-containing glass particles is preferably 0.5 μm or less from the viewpoint of easy uniform dispersion of the glass compound in the p-type diffusion layer forming composition and uniformity of boron diffusion. More preferably, it is 4 μm or less, and further preferably 0.35 μm or less. Moreover, although there is no restriction | limiting in the minimum of the average particle diameter of a boron containing glass particle, For example, it is preferable that it is 0.01 micrometer or more, it is more preferable that it is 0.05 micrometer or more, and it is further 0.1 micrometer or more. preferable. The range of the average particle size of the boron-containing glass particles is preferably 0.01 μm to 0.5 μm, more preferably 0.05 μm to 0.4 μm, and preferably 0.1 μm to 0.35 μm. Further preferred.
The average particle diameter is the median diameter d50 calculated from the particle size distribution.

When boron nitride is used as the compound containing boron, the desired form of the boron nitride crystal form can be obtained in any of the hexagonal, cubic, and rhombohedral crystal states. . From the viewpoint of easily controlling the particle size, hexagonal crystals are preferable.

The average particle diameter of the boron nitride particles is preferably 0.01 μm to 50 μm from the viewpoint of uniform dispersion of boron nitride in the p-type diffusion layer forming composition and uniformity of boron diffusion, and preferably 1 μm. More preferably, it is ˜30 μm, and further preferably 2 μm to 20 μm.

The method for preparing boron nitride is not particularly limited, and can be prepared by a usual method. Specifically, a method in which boron particles are heated to 1500 ° C. or higher in a nitrogen stream, a method in which molten anhydrous boric acid and nitrogen or ammonia are reacted in the presence of calcium phosphate, boric acid or an alkali boride, urea, and guanidine , A method of reacting an organic nitrogen compound such as melamine in a high temperature nitrogen-ammonia atmosphere, a method of reacting molten sodium borate and ammonium chloride in an ammonia atmosphere, a method of reacting boron trichloride and ammonia at a high temperature And so on. Any method other than the above may be selected as long as the effects of the present invention can be obtained. Among the above production methods, since a high-purity boron nitride can be obtained, it is preferable to use a method in which boron trichloride and ammonia are reacted at a high temperature.

In addition, the boron-containing compound may be a boron-containing silicon oxide compound. Here, an example of the boron-containing silicon oxide compound will be described. The boron-containing silicon oxide compound means a compound synthesized by reacting a boron-containing compound and a silicon oxide precursor based on a sol-gel reaction, and is distinguished from the above glass compound by a different synthesis method. Therefore, it is expressed as a boron-containing silicon oxide compound.

The boron-containing silicon oxide compound obtained by sol-gel reaction of a silicon oxide precursor and a boron-containing compound has a structure in which the boron-containing compound is dispersed in a network formed by chemical bonding of silicon oxide (siloxane), so that it contains boron. The volatility of the compound is suppressed, and out-diffusion can be suppressed at a high temperature at which a p-type diffusion layer is formed on a semiconductor substrate such as a silicon substrate.

The sol-gel reaction here means that a silicon alkoxide is hydrolyzed to form a silanol group, and the silanol group undergoes a condensation reaction, resulting in a three-dimensionally crosslinked silica gel having a silicon-oxygen bond as a structural unit. It is a reaction that forms a matrix. When a silicon oxide precursor, a boron-containing compound, a solvent used in a sol-gel reaction, water, an acid catalyst or an alkali catalyst are mixed and alcohol and water desorbed from the silicon oxide precursor are removed, silicon oxide is removed. Hydrolysis and condensation reactions of the precursor occur, and a silicon oxide compound containing a boron-containing compound in a siloxane network can be synthesized. Further, since the boron-containing silicon oxide compound can also suppress hygroscopicity, the reaction with the dispersion medium and the reaction with moisture are suppressed, and the chemical stability in the impurity diffusion layer forming composition tends to be improved. is there.

The silicon oxide precursor is not particularly limited as long as it can react with a boron-containing compound to synthesize a boron-containing silicon oxide compound. For example, silicon such as silicon methoxide, silicon ethoxide, silicon propoxide, silicon butoxide, etc. An alkoxide can be mentioned. From the viewpoint of availability, it is preferable to use at least one selected from the group consisting of silicon methoxide and silicon ethoxide as the silicon oxide precursor.

The solvent used for the sol-gel reaction is not particularly limited as long as it can dissolve the polymer of the silicon oxide precursor. Examples of the solvent include alcohol compounds such as ethanol and isopropanol; nitrile compounds such as acetonitrile, glutaronitrile, methoxyacetonitrile, propionitrile, and benzonitrile; and cyclic ether compounds such as dioxane and tetrahydrofuran. These may be used alone or in combination of two or more.
The amount of the solvent used in the sol-gel reaction is preferably 0 to 100 equivalents, more preferably 1 to 10 equivalents, relative to the silicon oxide precursor. When the amount of the solvent is 100 equivalents or less based on the silicon oxide precursor, a sufficient rate of the sol-gel reaction of the silicon oxide precursor tends to be ensured.

An acid catalyst or an alkali catalyst is used as a catalyst for controlling hydrolysis or dehydration condensation polymerization. As the alkali catalyst, alkali metal hydroxide such as sodium hydroxide, ammonia, tetramethylammonium hydroxide and the like are generally used. An inorganic or organic proton acid can be used as the acid catalyst. Examples of the inorganic protonic acid include hydrochloric acid, sulfuric acid, boric acid, nitric acid, perchloric acid, tetrafluoroboric acid, hexafluoroarsenic acid, and hydrobromic acid. Examples of the organic protonic acid include acetic acid, oxalic acid, and methanesulfonic acid. Since the solubility of the sol in the solvent varies depending on the amount of the acid, the amount of the acid catalyst or alkali catalyst may be adjusted so that the sol has a soluble solubility, and is 0.0001 equivalent to the silicon oxide precursor. ˜1 equivalent is preferred.

Examples of the boron-containing compound used in the sol-gel reaction include boron oxide, boric acid, and borate. Boron oxide is a compound represented by B ₂ O ₃ and may be a crystallized product or a glassy material. Boric acid is a compound represented by H ₃ BO ₃ or B (OH) ₃ . A borate is a salt of boric acid, and examples thereof include boric acid nitrate, ammonium salt, chloride salt, and sulfate. These compounds are dissolved in water and exist in the state of H ₃ BO ₃ . In addition to boron oxide, boric acid, and borate, any compound that dissolves in water to form H ₃ BO ₃ is not limited to the type of boron-containing compound. Examples of the compound that dissolves in water to become H ₃ BO ₃ include boric acid esters.
As the boron-containing compound used in the sol-gel reaction, a borate ester is preferable.

As boric acid ester, the compound represented by the following general formula (I) is mentioned, for example. Here, R ⁷ to R ⁹ in the general formula (I) are each independently an organic group having 1 to 10 carbon atoms or a hydrogen atom, and at least one of R ⁷ to R ⁹ has 1 to 10 carbon atoms. Organic group.

The organic group represented by R ⁷ to R ⁹ in the general formula (I) is not particularly limited as long as it has 1 to 10 carbon atoms, and each independently represents, for example, an alkyl group, a functional organic group, a hetero group Examples thereof include an organic group having an atom and an organic group having an unsaturated bond.

The alkyl group represented by R ⁷ to R ⁹ may be linear, branched or cyclic, and is preferably linear or branched. The alkyl group represented by R ⁷ to R ⁹ has 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, and more preferably 1 to 3 carbon atoms. Specific examples of the alkyl group represented by R ⁷ to R ⁹ include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group. Is mentioned.

In the organic group having a functional group represented by R ⁷ to R ⁹ , examples of the functional group include a chloro group, a bromo group, and a fluoro group. The organic group having a functional group represented by R ⁷ to R ⁹ has 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, and preferably 1 to 3 carbon atoms. More preferred. Specific examples of the organic group having a functional group represented by R ⁷ to R ⁹ include a chloroethyl group, a fluoroethyl group, a chloropropyl group, a dichloropropyl group, a fluoropropyl group, a difluoropropyl group, and a chlorophenyl group. And fluorophenyl groups.

In the organic group having a hetero atom represented by R ⁷ to R ⁹ , examples of the hetero atom include a nitrogen atom, an oxygen atom, and a sulfur atom. The organic group having a hetero atom represented by R ⁷ to R ⁹ has 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, and 1 to 3 carbon atoms. Is more preferable. Specific examples of the organic group having a hetero atom represented by R ⁷ to R ⁹ include a dimethylamino group, a diethylamino group, a diphenylamino group, a methyl sulfoxide group, an ethyl sulfoxide group, and a phenyl sulfoxide group. .

The organic group having an unsaturated bond represented by R ⁷ to R ⁹ has 2 to 10 carbon atoms, preferably 2 to 6 carbon atoms, and more preferably 2 to 4 carbon atoms. preferable. Specific examples of the organic group having an unsaturated bond represented by R ⁷ to R ⁹ include an ethylenyl group, an ethynyl group, a propenyl group, a propynyl group, a butenyl group, a butynyl group, and a phenyl group. .

Among these, the organic group represented by R ⁷ to R ⁹ is preferably an alkyl group, and more preferably an alkyl group having 1 to 10 carbon atoms.

As the boric acid ester used for the sol-gel reaction, it is preferable to use at least one selected from the group consisting of trimethyl borate, triethyl borate, tripropyl borate, and tributyl borate.

The content of the boron-containing compound in the boron-containing silicon oxide compound can be appropriately changed according to the purpose. For example, from the viewpoint of boron diffusivity, the content of the boron-containing compound in the boron-containing silicon oxide compound is preferably 0.01% by mass to 95% by mass, and 0.1% by mass to 80% by mass. More preferably, it is more preferably 0.5% by mass to 60% by mass. By including 0.01% by mass or more of the boron-containing compound in the boron-containing silicon oxide compound, there is a tendency that an absolute amount of boron to be diffused into the semiconductor substrate can be ensured. The amount of etching residue generated in the etching process tends to be reduced.

The content rate of the compound containing boron in the p-type diffusion layer forming composition can be appropriately changed according to the purpose. For example, from the viewpoint of diffusibility, the content of the compound containing boron in the p-type diffusion layer forming composition is preferably 0.01% by mass to 99% by mass, and 0.1% by mass or more and 98% by mass. More preferably, it is more preferably 0.5% by mass to 50% by mass, and particularly preferably 1% by mass to 40% by mass.
When the content of the boron-containing compound in the p-type diffusion layer forming composition is 0.01% by mass or more, the p-type diffusion layer can be sufficiently formed, and when it is 99% by mass or less, p The dispersibility of the boron-containing compound in the mold diffusion layer forming composition is improved, and the impartability to the semiconductor substrate tends to be improved.

(Dispersion medium)
The p-type diffusion layer forming composition may further contain a dispersion medium. A dispersion medium is for adjusting a viscosity in a composition, and can mention a solvent and water. The content of the dispersion medium in the p-type diffusion layer forming composition is determined in consideration of the imparting property and the viscosity.

The dispersion medium is not particularly limited. For example, acetone, methyl ethyl ketone, methyl-n-propyl ketone, methyl isopropyl ketone, methyl-n-butyl ketone, methyl isobutyl ketone, methyl-n-pentyl ketone, methyl-n-hexyl ketone, Ketone solvents such as diethyl ketone, dipropyl ketone, diisobutyl ketone, trimethylnonanone, cyclohexanone, cyclopentanone, methylcyclohexanone, 2,4-pentanedione, acetonylacetone; diethyl ether, methyl ethyl ether, methyl-n-propyl Ether, diisopropyl ether, tetrahydrofuran, methyltetrahydrofuran, dioxane, dimethyldioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ether Lenglycol di-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol methyl n-propyl ether, diethylene glycol methyl n-butyl ether, diethylene glycol di-n-propyl Ether, diethylene glycol di-n-butyl ether, diethylene glycol methyl-n-hexyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, triethylene glycol methyl-n-butyl ether, triethylene glycol di-n -Butyl ether, trie Lenglycol methyl-n-hexyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, tetraethylene glycol methyl n-butyl ether, tetraethylene glycol methyl n-hexyl ether, tetraethylene glycol di -N-butyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di-n-propyl ether, propylene glycol di-n-butyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol methyl ethyl ether, di Propylene glycol methyl n-butyl ether , Dipropylene glycol di-n-propyl ether, dipropylene glycol di-n-butyl ether, dipropylene glycol methyl-n-hexyl ether, tripropylene glycol dimethyl ether, tripropylene glycol diethyl ether, tripropylene glycol methyl ethyl ether, tripropylene Glycol methyl-n-butyl ether, tripropylene glycol di-n-butyl ether, tripropylene glycol methyl-n-hexyl ether, tetrapropylene glycol dimethyl ether, tetrapropylene glycol diethyl ether, tetrapropylene glycol methyl ethyl ether, tetrapropylene glycol methyl-n -Butyl ether, tetrapropylene glycol methyl-n-hexyl Ether solvents such as ether and tetrapropylene glycol di-n-butyl ether; methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, n-pentyl acetate, sec-acetate Pentyl, 3-methoxybutyl acetate, methyl pentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, 2- (2-butoxyethoxy) ethyl acetate, benzyl acetate, cyclohexyl acetate, methyl cyclohexyl acetate, nonyl acetate, methyl acetoacetate, Ethyl acetoacetate, diethylene glycol methyl ether acetate, diethylene glycol monoethyl acetate, dipropylene glycol methyl ether acetate, dipropylene glycol ethyl ether acetate, glycol diacetate, methoxy acetate Liethylene glycol, ethyl propionate, n-butyl propionate, isoamyl propionate, diethyl oxalate, di-n-butyl oxalate, methyl lactate, ethyl lactate, n-butyl lactate, n-amyl lactate, ethylene glycol methyl ether pro Pionate, ethylene glycol ethyl ether propionate, ethylene glycol methyl ether acetate, ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, propylene glycol propyl ether acetate, γ-butyrolactone, γ-valerolactone, etc. Ester solvents: acetonitrile, N-methylpyrrolidinone, N-ethylpyrrolidinone, N-propylpyrrolidinone, N-butyl Aprotic polar solvents such as pyrrolidinone, N-hexylpyrrolidinone, N-cyclohexylpyrrolidinone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide; methanol, ethanol, n-propanol, isopropanol, n-butanol, Isobutanol, sec-butanol, t-butanol, n-pentanol, isopentanol, 2-methylbutanol, sec-pentanol, t-pentanol, 3-methoxybutanol, n-hexanol, 2-methylpentanol, sec-hexanol, 2-ethylbutanol, sec-heptanol, n-octanol, 2-ethylhexanol, sec-octanol, n-nonyl alcohol, n-decanol, sec-undecyl alcohol , Trimethylnonyl alcohol, sec-tetradecyl alcohol, sec-heptadecyl alcohol, cyclohexanol, methylcyclohexanol, benzyl alcohol, ethylene glycol, 1,2-propylene glycol, 1,3-butylene glycol, diethylene glycol, dipropylene glycol, Alcohol solvents such as triethylene glycol and tripropylene glycol; phenol solvents such as cresol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether , Diethylene glycol mono-n-hexyl A , Ethoxytriglycol, tetraethylene glycol mono-n-butyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether, and other glycol monoether solvents; And terpene solvents such as alloocimene, limonene, dipentene, pinene, carvone, ocimene, and ferrandrene; water and the like.
A dispersion medium is used individually by 1 type or in combination of 2 or more types.

The content of the dispersion medium in the p-type diffusion layer forming composition is preferably determined in consideration of impartability, viscosity, boron concentration and the like. The viscosity of the p-type diffusion layer forming composition is preferably 10 mPa · s to 1,000,000 mPa · s, preferably 50 mPa · s to 500,000 mPa · s, in consideration of impartability and the like. It is more preferable to contain a dispersion medium. The viscosity is measured at 25 ° C. with a B-type viscometer (spindle No. 4, rotation number 30 times per minute (rpm)).

(Binder)
From the viewpoint of applying the p-type diffusion layer forming composition on the semiconductor substrate and preventing scattering of the boron-containing compound in a dried state, if desired, or adjusting the viscosity of the p-type diffusion layer forming composition, It may further contain a binder.
The binder is not particularly limited. For example, polyvinyl alcohol, polyacrylamide compound, polyvinyl amide compound, polyvinyl pyrrolidone, polyethylene oxide compound, polysulfonic acid, acrylamide alkyl sulfonic acid, cellulose ether compound, cellulose derivative (carboxymethyl cellulose, hydroxyethyl cellulose, ethyl cellulose) Etc.), gelatin, starch and starch derivatives, sodium alginate compounds, xanthan, guar gum and guar gum derivatives, scleroglucan and scleroglucan derivatives, tragacanth and tragacanth derivatives, dextrin and dextrin derivatives, acrylic resin ((meth) acrylic acid resin, (Meth) acrylic acid esters such as dimethylaminoethyl (meth) acrylate resin Butter, and the like), butadiene resins, styrene resins and copolymers thereof, siloxane resins, and metal alkoxides. Among these binders, it is preferable to use a cellulose derivative or an acrylic resin from the viewpoint of easily adjusting the viscosity and thixotropy of the p-type diffusion layer forming composition even in a small amount. These may be used alone or in combination of two or more.

In the present disclosure, “(meth) acrylic resin” means at least one selected from the group consisting of “acrylic resin” and “methacrylic resin”, and “alkyl (meth) acrylate resin” means “alkyl It means at least one selected from the group consisting of “acrylate resin” and “alkyl methacrylate resin”, and “(meth) acrylic ester resin” is from the group consisting of “acrylic ester resin” and “methacrylic ester resin”. It means at least one selected.

The molecular weight of the binder is not particularly limited, and it is desirable to adjust appropriately in view of the desired viscosity of the p-type diffusion layer forming composition.

There is no restriction | limiting in particular in the content rate of the binder in a p-type diffused layer formation composition, It is preferable that it is 15 mass% or less of the whole composition, It is more preferable that it is 12 mass% or less, It is 10 mass% or less. More preferably.

(High viscosity solvent)
The p-type diffusion layer forming composition may further contain a high viscosity solvent. The high-viscosity solvent is not particularly limited, and is isobornylcyclohexanol, isobornylphenol, 1-isopropyl-4-methyl-bicyclo [2.2.2] oct-5-ene-2,3-dicarboxylic acid anhydride And at least one selected from the group consisting of p-mentenylphenol, more preferably at least one selected from the group consisting of isobornylcyclohexanol and isobornylphenol.
These compounds decompose or volatilize at a low temperature (for example, 400 ° C. or less) and have a bulky structure, so that they have high viscosity, and can be used as an alternative to conventionally used binders such as ethyl cellulose.
In particular, when a p-type diffusion layer forming composition is applied to a semiconductor substrate by screen printing or the like, it tends to contain a large amount of a binder such as ethyl cellulose in order to increase the viscosity of the p-type diffusion layer forming composition. . In this case, in the drying process and the heat treatment (firing) process, the binder that cannot be removed becomes a resistor, which may affect the power generation characteristics of the solar cell element. On the other hand, by using a high-viscosity solvent, the amount of the binder tends to be reduced to such an extent that residual does not become a problem.

The content of the high-viscosity solvent in the p-type diffusion layer forming composition can be appropriately changed according to the purpose. For example, from the viewpoint of in-plane uniformity of the coated product by printing, the content of the high-viscosity solvent in the p-type diffusion layer forming composition is preferably 0.01% by mass to 90% by mass, and 1% by mass More preferably, it is ˜80% by mass, and further preferably 1% by mass to 50% by mass.

There is no particular limitation on the ratio of the compound containing boron and the high viscosity solvent. When the p-type diffusion layer forming composition further contains a high-viscosity solvent, the p-type diffusion layer forming composition contains 1% by mass to 50% by mass of the boron-containing compound and 1% by mass to 99% by mass of the high-viscosity solvent. It is preferable to contain 5% by mass to 40% by mass of a compound containing boron and 5% by mass to 95% by mass of a high viscosity solvent.

(Inorganic filler)
The p-type diffusion layer forming composition may further contain an inorganic filler. The inorganic filler is not particularly limited, and examples thereof include silica, clay, and silicon carbide. Among these, it is preferable to use an inorganic filler containing at least silica as a component. By containing the inorganic filler, the p-type diffusion layer forming composition applied to the semiconductor substrate tends to be suppressed from being heated during the drying process. The cause of the thermal sag is that the viscosity of a solvent such as a high viscosity solvent decreases at a temperature of about 100 ° C. to 500 ° C. in the drying step. On the other hand, in the p-type diffusion layer forming composition containing an inorganic filler, a decrease in viscosity is suppressed and thermal sag tends to be suppressed.

The BET specific surface area of the inorganic filler is preferably 50 m ² / g to 500 m ² / g, and more preferably 100 m ² / g to 300 m ² / g. Examples of such an inorganic filler having a high BET specific surface area include fumed silica. The fumed silica may be hydrophilic or hydrophobic.
The inorganic filler having a high BET specific surface area contributes to the suppression of the decrease in the viscosity of the p-type diffusion layer forming composition by the interaction with the solvent whose viscosity has been reduced in the drying process, due to physical or van der Waals forces. The BET specific surface area can be calculated by measuring the amount of nitrogen adsorbed at 77K.

The content of the inorganic filler in the p-type diffusion layer forming composition is preferably 0.01% by mass to 40% by mass, more preferably 0.1% by mass to 20% by mass, and 0.2% More preferably, the content is from 5% by mass to 5% by mass. By setting the content of the inorganic filler in the p-type diffusion layer forming composition to 0.01% by mass or more, an effect of suppressing the occurrence of thermal sag of the imparted product in the drying process tends to be obtained, and 40% by mass. By making the following, the application characteristics of the p-type diffusion layer forming composition tend to be secured.

(Alkoxysilane)
The p-type diffusion layer forming composition may further contain an alkoxysilane. It exists in the tendency for the fall of the viscosity of the p-type diffusion layer forming composition in a drying process to be suppressed because a p-type diffusion layer forming composition contains alkoxysilane.

The alkoxy group constituting the alkoxysilane is preferably a linear or branched alkyloxy group, more preferably a linear or branched alkyloxy group having 1 to 24 carbon atoms. Further, a linear or branched alkyloxy group having 1 to 10 carbon atoms is more preferable, and a linear or branched alkyloxy group having 1 to 4 carbon atoms is particularly preferable.

Specific examples of the alkyloxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, an isopropyloxy group, an isobutyloxy group, a pentyloxy group, a hexyloxy group, an octyloxy group, and a 2-ethylhexyloxy group. , T-octyloxy group, decyloxy group, dodecyloxy group, tetradecyloxy group, 2-hexyldecyloxy group, hexadecyloxy group, octadecyloxy group, cyclohexylmethyloxy group, and octylcyclohexyloxy group. .
As the alkoxysilane, it is preferable to use at least one selected from the group consisting of tetramethoxysilane, tetraethoxysilane, and tetraisopropoxysilane.

When the p-type diffusion layer forming composition contains alkoxysilane, the content of the alkoxysilane in the p-type diffusion layer forming composition can be, for example, 0.01% by mass to 50% by mass. The content is preferably from 05% by mass to 40% by mass, and more preferably from 0.1% by mass to 30% by mass.

(Silane coupling agent)
The p-type diffusion layer forming composition may further contain a silane coupling agent. A silane coupling agent has a silicon atom in one molecule, and has an organic functional group and an alkoxy group. There is no restriction | limiting in particular as a silane coupling agent, For example, the compound represented by the following general formula (II) can be mentioned.

In the general formula (II), n represents an integer of 1 to 3.
X represents an alkoxy group.
Y represents an organic functional group.
R ¹ represents a single bond, an alkylene group having 1 to 10 carbon atoms, or a divalent linking group having 2 to 5 main chain atoms and a nitrogen atom or oxygen atom in the main chain.
R ² represents an alkyl group having 1 to 5 carbon atoms.

In general formula (II), X represents an alkoxy group. Examples of the alkoxy group include a methoxy group and an ethoxy group. When n is 2 or 3, the plurality of X may be different from each other or the same.

In general formula (II), Y represents an organic functional group. Specifically, for example, vinyl group, mercapto group, epoxy group, amino group, styryl group, vinylphenyl group, isocyanurate group, isocyanate group, acrylic group, methacryl group, glycidoxy group, ureido group, sulfide group, carboxyl group , Acryloxy group, methacryloxy group, alkylene glycol group, amino alcohol group, and quaternary ammonium group. Y is preferably a vinyl group, an amino group, an epoxy group, an acryloxy group, or a methacryloxy group, and more preferably an acryloxy group.

In general formula (II), R ¹ is a single bond, an alkylene group having 1 to 10 carbon atoms, or a divalent linking group having 2 to 5 atoms in the main chain and having a nitrogen atom or an oxygen atom in the main chain. To express. The alkylene group represented by R ¹ is preferably an ethylene group or a propylene group. The divalent linking group having a nitrogen atom in the main chain is preferably an amino group or the like. The divalent linking group having an oxygen atom in the main chain is preferably an ether group, an ester group, an alkyl carboxylic acid group or the like.

In general formula (II), R ² represents an alkyl group having 1 to 5 carbon atoms. Of these, a methyl group or an ethyl group is preferable, and a methyl group is more preferable. When n is 1, the plurality of R ² may be different or the same.

Specific examples of the silane coupling agent include those listed in the following groups (a) to (d).
(A) Silane coupling agent having (meth) acryloxy group:
3-acryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyldimethylethoxysilane, 3-methacryloxypropyltriethoxysilane, etc.

(B) Silane coupling agent having epoxy group or glycidoxy group:
3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, etc.

(C) Silane coupling agent having an amino group:
N- (2-aminoethyl) 3-aminopropylmethyldimethoxysilane, N- (aminoethyl) 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, etc.

(D) Silane coupling agent having a mercapto group:
3-mercaptopropyltrimethoxysilane, etc.

In the present disclosure, “(meth) acryloxy group” means at least one selected from the group consisting of “acryloxy group” and “methacryloxy group”.

Components contained in the p-type diffusion layer forming composition, and the content of each component, TG / DTA (Thermo Gravimetric Analyzer / Differential Thermal Analysis, differential thermal-thermogravimetric simultaneous measurement method) thermal analysis, NMR (Nuclear Magnetic Resonance (Nuclear Magnetic Resonance Method), HPLC (High Performance Liquid Chromatography, High Performance Liquid Chromatography Method), GPC (Gel Permeation Chromatography, Gel Permeation Chromatography Method), GC-MS (Gastro Chroma Chromatography) ), IR (Infrared) Pectroscopy, infrared spectroscopy) can be confirmed using MALDI-MS (Matrix Assisted Laser Desorption / Ionization, matrix-assisted laser desorption ionization) and the like.

When the p-type diffusion layer forming composition contains a silane coupling agent, the content of the silane coupling agent in the p-type diffusion layer forming composition is, for example, 0.001% by mass to 5% by mass. Preferably, the content is 0.005% by mass to 3% by mass, and more preferably 0.01% by mass to 1% by mass.

(Lifetime killer element)
In the p-type diffusion layer forming composition, the total amount of lifetime killer elements is preferably 1000 ppm or less, more preferably 500 ppm or less, still more preferably 100 ppm or less, and particularly preferably 50 ppm or less. . When the total amount of lifetime killer elements is 1000 ppm or less, the lifetime of the semiconductor substrate tends to be improved.

Examples of the lifetime killer element include Fe, Cu, Ni, Mn, Cr, W, and Au. The amount of these elements can be analyzed with an ICP (Inductively Coupled Plasma) mass spectrometer, ICP emission spectrometer or atomic absorption spectrometer. The lifetime in the semiconductor substrate can be measured by a microwave photoconductive decay method (μ-PCD method). Since the above elements have a high diffusion rate in the semiconductor substrate, they reach everywhere in the bulk of the semiconductor substrate and function as recombination centers.

(Method for producing p-type diffusion layer forming composition)
The method for producing the p-type diffusion layer forming composition is not particularly limited. For example, it can be obtained by mixing a compound containing boron, a high-viscosity solvent, or the like using a blender, a mixer, a mortar, a rotor, or the like. Moreover, when mixing, you may heat as needed. When heating at the time of mixing, the heating temperature can be, for example, 30 ° C. to 100 ° C.

<Method of manufacturing semiconductor substrate with p-type diffusion layer>
In the method of manufacturing a semiconductor substrate with a p-type diffusion layer according to the present embodiment, a p-type diffusion layer forming composition containing a compound containing boron is applied to the semiconductor substrate, and the mass of the compound containing boron per unit area is added. Forming a p-type diffusion layer forming composition layer having a thickness of 0.001 mg / cm ² to 0.1 mg / cm ² (p-type diffusion layer forming composition layer forming step), and a p-type diffusion layer forming composition layer And a step of forming a p-type diffusion layer on the semiconductor substrate by heat-treating the semiconductor substrate to which p is applied (p-type diffusion layer forming step).
The manufacturing method of the semiconductor substrate with a p-type diffusion layer of the present embodiment may further include other steps as necessary.

(P-type diffusion layer forming composition layer forming step)
In the p-type diffusion layer forming composition layer forming step, the p-type diffusion layer forming composition is applied to at least a part of the region on the semiconductor substrate, and the mass of the compound containing boron per unit area is 0.001 mg / A p-type diffusion layer forming composition layer having a thickness of cm ² to 0.1 mg / cm ² is formed.

mass of the compound containing boron contained in the p-type diffusion layer forming composition layer, per unit ^area, was 0.001mg / cm 2 ~ 0.1mg / cm 2, 0.002mg / cm 2 ~ 0.05mg / it is preferably cm ^{^2,} and more preferably 0.005mg / cm 2 ~ 0.01mg / cm 2. By providing a compound containing 0.001 mg / cm ² or more of boron, diffusion uniformity of boron is improved. Moreover, by making the mass of the compound containing boron 0.1 mg / cm ² or less, it is possible to suppress the formation of a thick BRL and hardly generate a residue. Further, by setting the mass of the compound containing boron to 0.1 mg / cm ² or less, it is possible to prevent boron from scattering to unnecessary regions of the semiconductor substrate.

The mass of the compound containing boron per unit area in the p-type diffusion layer forming composition layer is the amount of the p-type diffusion layer forming composition to be described later, the total area of the p-type diffusion layer forming composition layer, and the p-type diffusion. It can calculate based on the content rate of the compound containing the boron contained in a layer forming composition.

Further, the mass (applied amount) of boron per unit area of the semiconductor substrate in the p-type diffusion layer forming composition layer is preferably 0.05 μg / cm ² or more and less than 10 μg / cm ² , and preferably 0.07 μg / cm ^2. More preferably, it is cm ² to 5 μg / cm ² , and still more preferably 0.3 μg / cm ² to 1 μg / cm ² . When the mass of boron in the p-type diffusion layer forming composition layer is 0.05 μg / cm ² or more, a sufficient amount of boron can be diffused into the semiconductor substrate. In addition, when the mass of boron is less than 10 μg / cm ² , the amount of boron scattered to an unnecessary region can be reduced, and outdiffusion can be suppressed.

The semiconductor substrate is not particularly limited, and a known semiconductor substrate used for solar cell elements can be applied. For example, silicon substrate, gallium phosphide substrate, gallium nitride substrate, diamond substrate, aluminum nitride substrate, indium nitride substrate, gallium arsenide substrate, germanium substrate, zinc selenide substrate, zinc telluride substrate, cadmium telluride substrate, cadmium sulfide Examples include substrates, indium phosphide substrates, silicon carbide, silicon germanium substrates, and copper indium selenium substrates. The semiconductor substrate may be an n-type semiconductor substrate or a p-type semiconductor substrate.

The semiconductor substrate is preferably pretreated before applying (coating) the p-type diffusion layer forming composition. Examples of the pretreatment include the following steps. In the following, an example in which an n-type semiconductor substrate is used will be described, but a p-type semiconductor substrate may be used. The following embodiments are merely examples, and do not limit the present invention.
As pretreatment, an alkaline solution may be applied to the n-type semiconductor substrate to remove the damaged layer, and a texture structure may be obtained by etching. Specifically, for example, a damaged layer on the surface of the n-type semiconductor substrate generated when slicing from an ingot is removed with a 20% by mass aqueous sodium hydroxide solution. Next, etching is performed with a mixed solution of 1% by mass sodium hydroxide and 10% by mass isopropyl alcohol to form a texture structure. By forming the texture structure on the light receiving surface side of the solar cell element, the light confinement effect is promoted, and high efficiency is achieved.

The p-type diffusion layer forming composition is applied (applied) to at least a part of the region on the semiconductor substrate pretreated in this way. In the case of a semiconductor substrate for a back contact type solar cell element, a p-type diffusion layer forming composition is applied on the n-type diffusion layer on the back surface (that is, the surface opposite to the light receiving surface). In the case of a semiconductor substrate for a double-sided light-receiving solar cell element, a p-type diffusion layer forming composition is applied to the back surface.

The method for applying the p-type diffusion layer forming composition is not particularly limited, and examples thereof include a printing method, a spin coating method, a brush coating method, a spray coating method, a doctor blade method, a roll coating method, and an ink jet method. A printing method such as screen printing is preferable from the viewpoints of pattern formability, impartability, and ease of adjusting the mass per unit area of the p-type diffusion layer forming composition.

The mass (applied amount) per unit area of the p-type diffusion layer forming composition to the semiconductor substrate is preferably 0.01 mg / cm ² to 5 mg / cm ² , and preferably 0.1 mg / cm ² to 3 mg / cm ^2. More preferably, it is cm ² , and further more preferably 0.2 mg / cm ² to 1 mg / cm ² . By applying a p-type diffusion layer forming composition of 0.01 mg / cm ² or more, a sufficient amount of boron can be diffused into the semiconductor substrate, and the diffusion uniformity of boron can be improved and the resistance can be lowered. It is in. Moreover, it exists in the tendency which can suppress the out diffusion to the area | region which is not provided by providing p-type diffused layer formation composition of 5 mg / cm < ² > or less.

The application amount of the p-type diffusion layer forming composition can be calculated from the mass change of the semiconductor substrate before and after applying the p-type diffusion layer forming composition. Specifically, from the mass change of the semiconductor substrate before and after applying the p-type diffusion layer forming composition, the mass of the p-type diffusion forming composition (p-type diffusion layer forming composition layer) applied on the semiconductor substrate is calculated. Calculate and measure the total area of the p-type diffusion layer forming composition layer. Based on the mass and total area of these p-type diffusion layer forming composition layers, the mass (applied amount) of the p-type diffusion layer forming composition per unit area can be calculated.
In the present disclosure, the mass of the semiconductor substrate after applying the p-type diffusion layer forming composition represents the mass measured before the drying step described later.

Depending on the composition of the p-type diffusion layer forming composition, there is a drying step for volatilizing the dispersion medium and the like after applying (applying) the p-type diffusion layer forming composition to the semiconductor substrate and before the heat treatment step described later. May be necessary. In this case, drying is performed at a temperature of about 80 ° C. to 300 ° C. for about 1 to 10 minutes when using a hot plate, and about 10 to 30 minutes when using a dryer or the like. This drying condition can be appropriately adjusted depending on the type and amount of the dispersion medium or the like of the p-type diffusion layer forming composition.

(P-type diffusion layer forming step)
In the p-type diffusion layer forming step, the semiconductor substrate provided with the p-type diffusion layer forming composition layer is heat-treated to form a p-type diffusion layer on the semiconductor substrate. By this heat treatment, boron contained in the p-type diffusion layer forming composition layer diffuses into the semiconductor substrate, and a p-type diffusion layer, a p ⁺ -type diffusion layer, and the like are formed. The heat treatment (thermal diffusion treatment) for diffusing boron is preferably performed at 600 ° C. to 1200 ° C., more preferably 800 ° C. to 1050 ° C., and further preferably 850 ° C. to 1000 ° C. The treatment time is preferably 5 to 60 minutes. A known continuous furnace, batch furnace, or the like can be applied to the heat treatment. Hereinafter, a specific example of the p-type diffusion layer forming step when using a silicon substrate will be described.

There is no particular limitation on the gas composition of the atmosphere when performing the heat treatment. An atmosphere in which BRL (when a silicon substrate is used as a semiconductor substrate is referred to as boron silicide) is preferably formed. For example, when the compound containing boron is a glass compound, the glass compound is softened by heat treatment, and the surface of the silicon substrate to which the p-type diffusion layer forming composition is applied is covered with the glass layer. By suppressing the oxidation of the surface of the silicon substrate by reducing the ratio of an oxidizing gas such as oxygen until the heat treatment product of the p-type diffusion layer forming composition such as a glass layer covers the surface of the silicon substrate at the application portion, A boron silicide layer is easily formed. After the heat treatment product of the p-type diffusion layer forming composition coats the surface of the silicon substrate at the application portion, the ratio of the oxidizing gas such as oxygen may be increased.

Specifically, when the compound containing boron is a glass compound, heat treatment is performed in an inert gas atmosphere such as nitrogen alone until the glass compound softens at the softening point and covers the surface of the silicon substrate at the application portion. Is preferred. By adjusting the atmosphere in this way, it becomes easy to form a boron silicide layer having high gettering ability.

When heat treatment is performed in a state where the boron silicide layer is formed, the boron silicide layer getters, for example, impurity metals such as heavy metals (for example, iron and nickel) contained in the silicon substrate and the furnace tube. For this reason, the number of recombination centers in the silicon substrate is reduced, and the lifetime of the silicon substrate tends to be extended.

The gas composition of the atmosphere in the heat treatment after the boron silicide layer is formed is not particularly limited to components other than oxygen. For example, nitrogen, argon, neon, xenon, krypton, helium, carbon dioxide, hydrogen, air, or the like is used. be able to. Among these, from the viewpoint of cost and safety, a gas composition mainly containing oxygen and nitrogen is preferable. When air is used as a gas other than oxygen, the oxygen concentration is adjusted in consideration of the amount of oxygen contained in the air.

The ratio of oxygen can be confirmed with an oxygen concentration meter installed at the exhaust side outlet of the diffusion furnace used for heat treatment. The oxygen concentration meter is not particularly limited, and for example, a zirconia oxygen concentration meter (for example, NZ-3000 manufactured by Horiba, Ltd.) can be used.

Further heat treatment may be performed after the heat treatment or during the heat treatment by changing the oxygen ratio. After the boron silicide layer is formed, the boron silicide layer is oxidized by heat treatment in an atmosphere containing oxygen.
Thereafter, when a hydrofluoric acid etching step for removing a boron silicate glass layer, which will be described later, is performed, the boron silicide layer can be removed at once. In addition, by oxidizing the region (non-applied portion) of the silicon substrate where the p-type diffusion layer forming composition is not applied, a SiO ₂ layer is formed, a mask layer for boron is formed on the silicon substrate, Diffusion to the applying part can be suppressed. The gas composition at this time may contain, for example, 0.1% by volume to 100% by volume of oxygen.

In the present embodiment, the boron silicide layer is usually formed by setting the mass of the compound containing boron per unit area in the p-type diffusion layer forming composition layer to 0.001 mg / cm ² to 0.1 mg / cm ^2. Is not formed thick and tends to be easily oxidized. Therefore, the boron silicide layer tends to be sufficiently removed by the hydrofluoric acid etching process.

A boron silicate glass layer (boron glass layer) is formed as a heat-treated product (baked product) of the p-type diffusion layer forming composition on the surface of the p-type diffusion layer, p ⁺ -type diffusion layer, etc. formed by heat treatment. In many cases, a step of treating the silicon substrate with an etchant may be provided after the heat treatment. Thereby, the produced | generated glass layer is removed by an etching. It is also possible to collectively etch the oxide mask layer on the silicon substrate formed outside the application region of the p-type diffusion layer forming composition with an etching solution.
There is no restriction | limiting in particular as etching liquid, For example, aqueous solution, such as hydrogen fluoride, ammonium fluoride, ammonium hydrogen fluoride, and the aqueous solution of sodium hydroxide are mentioned. As the etching process, a known method such as immersing a silicon substrate in an etching solution can be applied.

Thereafter, the boron silicide layer is preferably oxidized by dry oxidation, wet oxidation using water vapor, or wet oxidation using an oxidizing chemical solution, and then etched. By removing the boron silicide layer, the passivation effect of the passivation layer to be formed next tends to be further extracted.

Dry oxidation using oxygen gas is preferably performed at 400 ° C. to 780 ° C., more preferably 450 ° C. to 750 ° C., and further preferably 500 ° C. to 700 ° C. By performing dry oxidation at 400 ° C. or higher, the boron silicide layer can be effectively oxidized, and thereafter, the boron silicide layer tends to be easily removed by an etching solution. That is, it becomes easy to bring out the passivation effect in the subsequent passivation process. Further, by performing dry oxidation at 780 ° C. or lower, there is a tendency that re-diffusion of impurity metal elements such as Fe gettered into the boron silicide layer into the silicon substrate can be suppressed.

Dry oxidation using oxygen gas is preferably performed in an atmosphere having an oxygen content of 20% by volume to 100% by volume, more preferably in an atmosphere of 50% by volume to 100% by volume, and 80% by volume. More preferably, it is carried out in an atmosphere of up to 100% by volume. By setting the oxygen content to 20% by volume or more, the oxidation rate of the boron silicide layer can be increased.
The oxygen concentration can be confirmed with an oxygen concentration meter installed at the exhaust side outlet of the diffusion furnace used for heat treatment. The oxygen concentration meter is not particularly limited, and for example, a zirconia oxygen concentration meter (for example, NZ-3000 manufactured by Horiba, Ltd.) can be used.

The time for performing dry oxidation is not particularly limited as long as boron silicide is oxidized. For example, it is preferably 1 minute to 1 hour, more preferably 2 minutes to 40 minutes, and even more preferably 5 minutes to 30 minutes. By performing the dry oxidation for 1 minute or longer, the thermal uniformity between the silicon substrates can be sufficiently maintained when processing a plurality of silicon substrates at a time, and variations in performance between the silicon substrates can be sufficiently suppressed. . In addition, by performing dry oxidation in 1 hour or less, the throughput of silicon substrate processing can be improved.

The gas composition other than oxygen gas in the dry oxidation step is not particularly limited, and for example, nitrogen, argon, neon, xenon, krypton, helium, carbon dioxide, hydrogen, air, or the like can be used.

In addition to oxygen gas, at least one chlorine compound selected from the group consisting of hydrochloric acid and dichloroethanol may be added. By using an oxidizing atmosphere containing hydrochloric acid, dichloroethanol, etc., impurity alkali metal atoms (for example, Na), heavy metal atoms (for example, Fe and Ni), etc. contained in the silicon substrate and chlorine atoms combine to volatilize. An impurity substance can be formed and an impurity metal element present in the silicon substrate or the heat treatment apparatus can be captured. That is, the lifetime of the silicon substrate can be extended by suppressing the diffusion of impurities such as alkali metal and heavy metal into the silicon substrate. The ratio of the chlorine compound in the gas composition can be measured using a gas composition analyzer (for example, an automatic gas measuring instrument manufactured by Kyoto Electronics Industry Co., Ltd.).
The content of the chlorine compound is preferably 0.01% by volume to 5% by volume with respect to oxygen, more preferably 0.1% by volume to 4% by volume, and 0.2% by volume to 3% by volume. % Is more preferable.

Dry oxidation may be performed in oxygen plasma. The oxygen plasma is made of, for example, argon gas and oxygen gas, and microwave-excited plasma is allowed to act on the surface of the silicon substrate in an atmosphere having an oxygen flow rate ratio of about 1% by volume under a high pressure of 100 Pa or more. Plasma oxidation treatment may be performed. The treatment temperature is preferably 20 ° C to 500 ° C.

Specific methods for wet oxidation are preferably an oxidation method using oxygen gas and water vapor, an oxidation method using water vapor, or an oxidation method using oxygen gas and hydrogen gas.
Specifically, a method of bubbling deionized water in a bubbler with a carrier gas and oxidizing with water vapor, a method of flowing deionized water vapor as it is and oxidizing, or water vapor generated by reacting oxygen gas and hydrogen gas is generated. It is preferable that the method is used for oxidation. There is no restriction | limiting in particular as carrier gas, For example, nitrogen, argon, neon, xenon, krypton, helium, carbon dioxide, hydrogen, air, and these combinations can be used.

The wet oxidation is preferably performed at 300 ° C. to 780 ° C., more preferably 350 ° C. to 750 ° C., and further preferably 400 ° C. to 700 ° C. By performing wet oxidation at 300 ° C. or higher, the boron silicide layer can be effectively oxidized, and thereafter tends to be easily removed with an etching solution or the like. That is, it becomes easy to bring out the passivation effect in the subsequent passivation process. Further, by performing wet oxidation at 780 ° C. or lower, there is a tendency that impurity metal elements such as Fe gettered to the boron silicide layer can be prevented from re-diffusing into the silicon substrate.

The moisture content of the gas after bubbling is not particularly limited and is preferably 10 ppm (0.001% by mass) to 30% by mass, more preferably 100 ppm (0.01% by mass) to 20% by mass. More preferably, it is 200 ppm (0.02 mass%) to 10 mass%. When the moisture content of the gas is 10 ppm or more, the boron silicide layer tends to be efficiently oxidized, and when it is 30% by mass or less, while achieving a sufficient oxidation rate of the boron silicide layer, The moisture content of the carrier gas tends to be easily controlled.
When the water content is 1% by mass or less, the water content can be controlled by the dew point, and the dew point is preferably -72 ° C to 21 ° C.
The amount of moisture in the carrier gas can be measured by introducing a moisture meter, a dew point meter and a hygrometer in-line. For example, “moisture IQ”, “MIS1” of GE Sensing & Inspection Technologies, Inc. “M Series Probe”, “Aurora”, “Gas concentration monitor IR-300 Series” manufactured by Horiba, Ltd., and the like can be used.

In the case of oxidizing using oxygen gas and hydrogen gas, an external combustion apparatus having a hydrogen gas supply line and an oxygen gas supply line is used, and water vapor generated by burning in the external combustion apparatus is introduced into the heat treatment apparatus. Send in. It is preferable to supply the water vapor together with the dry nitrogen gas, the dry oxygen gas, and the carrier gas to the heat treatment section to control the atmosphere. The gas flow rate is preferably controlled by a mass flow controller. For example, “Digital Mass Flow Controller SEC-Z500X series” or “Digital Mass Flow Controller SEC-N100 series” manufactured by Horiba, Ltd. can be used.

The oxidizing chemical solution in the wet oxidation method using an oxidizing chemical solution is not particularly limited as long as the boron silicide layer can be oxidized. For example, nitric acid, ozone-dissolved water, perchloric acid water, sulfuric acid, hydrogen peroxide solution, mixed solution of hydrochloric acid and hydrogen peroxide solution, mixed solution of sulfuric acid and hydrogen peroxide solution, mixed solution of ammonia and hydrogen peroxide solution, It is preferably at least one oxidizing chemical solution selected from the group consisting of a mixed solution of sulfuric acid and nitric acid, perchloric acid, and boiling water, and is nitric acid, ozone-dissolved water, hydrogen peroxide solution, hydrochloric acid, and hydrogen peroxide solution. More preferably, at least one oxidizing chemical solution selected from the group consisting of a mixed solution of sulfuric acid and a hydrogen peroxide solution, and a mixed solution of ammonia and a hydrogen peroxide solution, nitric acid, hydrochloric acid and peroxidation. It is at least one oxidizing chemical solution selected from the group consisting of a mixed solution of hydrogen water, a mixed solution of sulfuric acid and hydrogen peroxide solution, and a mixed solution of ammonia and hydrogen peroxide solution. There further preferred. By using these oxidizing chemicals, the boron silicide layer tends to be effectively oxidized.

When nitric acid is used as the oxidizing chemical, it is preferable to use a 40% by mass to 98% by mass nitric acid aqueous solution, more preferably a 50% by mass to 80% by mass nitric acid aqueous solution, and 60% by mass to 75% by mass nitric acid. More preferably, an aqueous solution is used. By using a nitric acid aqueous solution having a concentration close to the 68% by mass nitric acid aqueous solution in an azeotropic state, the boiling point becomes high, so that treatment at a high temperature becomes possible. Specifically, since the boiling point of the 68 mass% nitric acid aqueous solution is about 120 ° C., it is possible to immerse at a temperature higher than 100 ° C., which is the boiling point of water, and to promote the oxidation of the boron silicide layer.

When ozone-dissolved water is used as the oxidizing chemical solution, an aqueous solution in which 1% by mass to 80% by mass of ozone is dissolved is preferable, and an aqueous solution in which 10% by mass to 70% by mass of ozone is dissolved is more preferable. An aqueous solution in which 30% by mass to 60% by mass of ozone is dissolved is more preferable. By using an aqueous solution in which 1% by mass to 80% by mass of ozone is dissolved, the boron silicide layer can be effectively oxidized.

When hydrogen peroxide is used as the oxidizing chemical, it is preferably a 1% to 60% by weight aqueous hydrogen peroxide solution, more preferably a 10% to 50% by weight aqueous hydrogen peroxide solution. Further, a 20% to 40% by mass aqueous hydrogen peroxide solution is more preferable. By using a 1% by mass to 60% by mass aqueous hydrogen peroxide solution, the boron silicide layer can be effectively oxidized.

When a mixed solution of hydrochloric acid and hydrogen peroxide solution is used as the oxidizing chemical solution, it is preferably a mixed solution of 1% by mass to 60% by mass hydrochloric acid solution and 1% by mass to 60% by mass hydrogen peroxide solution. . As the oxidizing chemical solution, for example, an SC-2 cleaning solution mixed at 37 mass% HCl aqueous solution: 30 mass% aqueous hydrogen peroxide solution: H ₂ O = 1: 1: 5 (volume ratio) can be used.

When a mixed solution of sulfuric acid and hydrogen peroxide solution is used as the oxidizing chemical solution, it is preferably a mixed solution of 1% by mass to 99% by mass sulfuric acid aqueous solution and 1% by mass to 60% by mass hydrogen peroxide solution. For example, an SPM cleaning solution mixed with 97 mass% sulfuric acid aqueous solution: 30 mass% hydrogen peroxide aqueous solution = 4: 1 (volume ratio) can be used.

When a mixed solution of ammonia and hydrogen peroxide solution is used as the oxidizing chemical solution, it is preferably a mixed solution of 1% to 50% by weight aqueous ammonia solution and 1% to 60% by weight hydrogen peroxide solution. For example, it is possible to use an SC-1 cleaning solution mixed in a 26 mass% aqueous ammonia solution: 30 mass% aqueous hydrogen peroxide solution: H ₂ O = 1: 1: 5 (volume ratio).

When a mixed solution of sulfuric acid and nitric acid is used as the oxidizing chemical solution, it is preferably a mixed solution of 1% by mass to 99% by mass sulfuric acid aqueous solution and 1% by mass to 60% by mass nitric acid aqueous solution, for example, 99% by mass. % Sulfuric acid aqueous solution: 69 mass% nitric acid aqueous solution = 1: 1 (volume ratio) can be used.

When perchloric acid water is used as the oxidizing chemical solution, it is preferably 1% by mass to 80% by mass of perchloric acid water, more preferably 10% by mass to 70% by mass of perchloric acid water. 30% by mass to 60% by mass of perchloric acid water is more preferable. By using 1% by mass to 80% by mass of perchloric acid water, the boron silicide layer can be effectively oxidized.

When sulfuric acid is used as the oxidizing chemical solution, it is preferable to use 1% by mass to 99.5% by mass sulfuric acid aqueous solution, more preferably 30% by mass to 99% by mass sulfuric acid aqueous solution, more preferably 50% by mass to It is more preferable to use a 98.5% by mass aqueous sulfuric acid solution. By using 1% by mass to 99.5% by mass of sulfuric acid aqueous solution, the boron silicide layer can be effectively oxidized (or decomposed).

The oxidation of the boron silicide layer using the oxidizing chemical solution is preferably performed at 25 ° C. to 300 ° C., more preferably 40 ° C. to 200 ° C., and further preferably 80 ° C. to 180 ° C. By performing oxidation at 25 ° C. to 300 ° C., since the diffusion rate of iron is low, it is possible to suppress re-diffusion of impurity metal elements such as iron gettered into the boron silicide layer into the silicon substrate. It is in. That is, the content of the impurity metal element in the silicon substrate can be made as low as possible, and the lifetime of carriers generated in the substrate can be extended.

The treatment time of the step of oxidizing the boron silicide layer is not particularly limited as long as it is a time during which the boron silicide layer is oxidized. For example, the treatment time is preferably 1 minute to 1 hour, more preferably 2 minutes to 40 minutes, and even more preferably 5 minutes to 30 minutes. When the processing time is 1 minute or longer, the thermal uniformity between silicon substrates can be sufficiently maintained when processing a plurality of wafers at a time, and variations in performance between silicon substrates tend to be sufficiently suppressed. Further, by setting the processing time to 1 hour or less, the throughput of the silicon substrate processing tends to be improved.

After oxidizing the boron silicide layer, the boron silicide oxide layer is removed by a known method such as immersing the silicon substrate in an etching solution. Examples of the etchant include aqueous solutions of hydrogen fluoride, ammonium fluoride, ammonium hydrogen fluoride, and the like, and aqueous solutions of sodium hydroxide.

In the above description, a specific example of the p-type diffusion layer forming step in the case of using a silicon substrate has been described. However, the above-described details may be applied when a semiconductor substrate other than the silicon substrate is used.

<Method for manufacturing solar cell element and solar cell element>
In the method for producing a solar cell element, a p-type diffusion layer forming composition containing a compound containing boron is applied on a semiconductor substrate, and the mass of the compound containing boron per unit area is 0.001 mg / cm ² to A step of forming a p-type diffusion layer forming composition of 0.1 mg / cm ² (p-type diffusion layer forming composition layer forming step), and a thermal diffusion treatment on the semiconductor substrate provided with the p-type diffusion layer forming composition And forming a p-type diffusion layer on the semiconductor substrate (p-type diffusion layer formation step), and forming an electrode on the formed p-type diffusion layer (electrode formation step).
For details of the p-type diffusion layer forming composition layer forming step and the p-type diffusion layer forming step, the p-type diffusion layer forming composition layer forming step and the p-type diffusion in the above-described method for manufacturing a semiconductor substrate with a p-type diffusion layer are described. This is the same as the details of the layer forming step.

Specific examples of the solar cell element of the present disclosure will be described with reference to the drawings, but the present invention is not limited thereto. Moreover, the magnitude | size of the member in each figure is notional, The relative relationship of the magnitude | size between members is not limited to this.

Hereinafter, an embodiment of a method for manufacturing a solar cell element will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view conceptually showing an example of a manufacturing process of a solar cell element. In the following, an example in which a silicon substrate is used as the n-type semiconductor substrate will be described. However, in the present invention, the semiconductor substrate is not limited to a silicon substrate.

In FIG. 1 (1), an alkaline solution is applied to the silicon substrate which is the n-type semiconductor substrate 10 to remove the damaged layer, and a texture structure is obtained by etching (the description of the texture structure is omitted in the figure).

In FIG. 1 (2), a p-type diffusion layer forming composition layer 11 is formed by applying a p-type diffusion layer forming composition to the surface that becomes the light receiving surface of the n-type semiconductor substrate 10. *

When the p-type diffusion layer forming composition contains a solvent as a dispersion medium, the p-type diffusion layer forming composition was applied to remove at least part of the solvent contained in the composition before the thermal diffusion treatment. There is a case where a process of heat-treating the subsequent n-type semiconductor substrate 10 is necessary. The heat treatment in this case is performed at a temperature of 80 ° C. to 300 ° C., for example, under conditions of 1 minute to 10 minutes when using a hot plate and 10 minutes to 30 minutes when using a dryer or the like. The heat treatment conditions depend on the type, composition, content, and the like of the solvent contained in the p-type diffusion layer forming composition, and are not particularly limited to the above conditions.

When the p-type diffusion layer forming composition contains a binder as a dispersion medium, the p-type diffusion layer forming composition was applied to remove at least a part of the binder contained in the composition before the thermal diffusion treatment. There is a case where a process of heat-treating the subsequent n-type semiconductor substrate 10 is necessary. For the heat treatment in this case, for example, a condition of treating at a temperature of 300 ° C. to 800 ° C. for 1 minute to 10 minutes is applied. A known continuous furnace, batch furnace or the like can be applied to this heat treatment. The heat treatment conditions depend on the type, composition, content, and the like of the binder contained in the p-type diffusion layer forming composition, and are not particularly limited to the above conditions.

After forming the p-type diffusion layer forming composition layer 11 on the light-receiving surface of the n-type semiconductor substrate 10, the n-type semiconductor substrate 10 is subjected to a thermal diffusion process. By this thermal diffusion treatment, as shown in FIG. 1 (3), the acceptor element is diffused into the n-type semiconductor substrate 10, and a p-type diffusion layer 12 is formed. A known continuous furnace, batch furnace, or the like can be applied to the thermal diffusion treatment. Further, the atmosphere in the furnace at the time of the thermal diffusion treatment can be selected according to desired conditions from an inert gas such as air, oxygen and nitrogen, and a mixed gas thereof.

A glass layer (not shown) such as borate glass is formed on the surface of the p-type diffusion layer 12 formed on the light receiving surface of the n-type semiconductor substrate 10. For this reason, this borate glass is removed by etching. As the etching, any known method such as a method of immersing in an acid such as hydrofluoric acid or a method of immersing in an alkali such as an aqueous sodium hydroxide solution can be applied. In terms of etching ability, an etching treatment with hydrofluoric acid is preferable. Examples of the etching treatment using hydrofluoric acid include a method of immersing the n-type semiconductor substrate 10 in hydrofluoric acid. When the n-type semiconductor substrate 10 is immersed in hydrofluoric acid, the immersion time is not particularly limited. Generally, it can be 0.5 minutes to 30 minutes, preferably 1 minute to 10 minutes.

Further, boron silicide formed on the n-type semiconductor substrate 10 after boron diffusion is removed. When boron silicide is formed on the surface of the n-type semiconductor substrate 10, the surface passivation is hindered, and the power generation performance of the solar cell element is reduced. For this reason, the boron silicide on the surface is oxidized and converted into a boron silicate glass layer, and then etched. The method for removing boron silicide is not particularly limited. For example, hydrofluoric acid may be used for etching with hydrofluoric acid while oxidizing the boron silicide with nitric acid, or boron silicide may be thermally oxidized in a furnace in an oxygen atmosphere and then etched with hydrofluoric acid.

In the method for forming the p-type diffusion layer shown in FIGS. 1 (2) and (3), the p-type diffusion layer 12 is formed at a desired site, and unnecessary p-type diffusion layers are not formed on the back and side surfaces. Therefore, in the conventional method of forming the p-type diffusion layer by the gas phase reaction method, a side etching process for removing the unnecessary p-type diffusion layer formed on the side surface is essential. According to the manufacturing method of the embodiment, the side etching process becomes unnecessary, and the process is simplified. As described above, according to the manufacturing method of the present embodiment, a p-type diffusion layer having a desired shape and a desired shape, in which variation in sheet resistance in the surface is suppressed, is formed in a short time.

In FIG. 1 (4), the n-type diffusion layer forming composition layer 13 is formed by applying the n-type diffusion layer forming composition to the back surface of the n-type semiconductor substrate 10, that is, the surface opposite to the light receiving surface. The method for applying the n-type diffusion layer forming composition can be performed by the same method as the method for applying the p-type diffusion layer forming composition described above to the light receiving surface of the n-type semiconductor substrate 10. As shown in FIG. 1 (5), the thermal diffusion treatment is performed on the n-type semiconductor substrate 10 provided with the n-type diffusion layer forming composition on the back surface in the same manner as the thermal diffusion treatment in the p-type diffusion layer forming composition. By applying, the n ⁺ -type diffusion layer 14 can be formed on the back surface of the n-type semiconductor substrate 10.

As the n-type diffusion layer forming composition, for example, an n-type diffusion layer formation configured in the same manner as the p-type diffusion layer forming composition using glass particles containing a donor element instead of glass particles containing an acceptor element. A composition can be mentioned. Examples of the donor element include Group 15 elements such as P (phosphorus), Sb (antimony), and As (arsenic). Glass particles containing a donor element, when notation component _{_{_{oxides, P 2 O 5, Sb 2}}} O 3, and preferably contains at least one selected from the group consisting of _As 2 _{O 3.}

Also, without using an n-type diffusion layer forming composition, in a mixed gas atmosphere of phosphorus oxychloride (POCl ₃ ), nitrogen and oxygen (hereinafter also abbreviated as “phosphorus oxychloride mixed gas”) at 800 ° C. to 900 ° C. An n-type diffusion layer may be formed by performing several tens of minutes. At this time, in the method using the phosphorus oxychloride mixed gas atmosphere, phosphorus is diffused on the side surface and the back surface of the semiconductor substrate, and the n-type diffusion layer is formed not only on the light receiving surface but also on the side surface and the back surface. Therefore, a mask layer for preventing phosphorus diffusion is formed on the surface of the p-type diffusion layer. The mask layer can be formed by applying a liquid containing a siloxane resin or the like serving as a precursor of SiO ₂ and performing heat treatment (firing).

In FIG. 1 (6), an antireflection film 15 is formed on the p-type diffusion layer 12. The antireflection film 15 is formed by applying a known technique. For example, when the antireflection film 15 is a silicon nitride film, it is formed by a plasma CVD (Chemical Vapor Deposition) method using a mixed gas of SiH ₄ and NH ₃ as a raw material. At this time, hydrogen diffuses into the crystal, and orbitals that do not contribute to the bonding of silicon atoms, that is, dangling bonds and hydrogen are bonded to inactivate defects (hydrogen passivation).

More specifically, the antireflection film 15 has, for example, a flow rate ratio (NH ₃ / SiH ₄ ) of the mixed gas of 0.05 to 1.0 and a reaction chamber pressure of 13.3 Pa (0.1 Torr) to The film is formed under the conditions of 266.6 Pa (2 Torr), a film forming temperature of 300 ° C. to 550 ° C., and a frequency for plasma discharge of 100 kHz or more.

A passivation layer may be formed on the p-type diffusion layer and the n-type diffusion layer. For example, an Al ₂ O ₃ layer may be laminated by an ALD (atomic layer deposition) method, or a SiO ₂ film may be formed by thermal oxidation or the like. In this case, the above-described antireflection film is formed on the passivation layer.

In FIG. 1 (7), a light receiving surface electrode metal paste is printed on the light receiving surface antireflection film 15 by screen printing and dried to form a light receiving surface electrode metal paste layer 16. As a metal paste for light-receiving surface electrodes, for example, a paste containing metal particles and glass particles, and containing a resin binder and other additives as required can be used.

Next, the metal paste layer 18 for the back electrode is formed also on the back surface. The material and forming method of the back electrode metal paste layer 18 are not particularly limited. For example, the back electrode metal paste layer 18 may be formed by applying a metal paste for the back electrode containing a metal such as aluminum, silver, or copper and drying the paste. At this time, a silver paste for forming a silver electrode may be partially provided on the back surface for connection between solar cell elements in the module process.

1 (8), the metal paste layer 16 for the light-receiving surface electrode is fired to complete the solar cell element. When baked in the range of 600 ° C. to 900 ° C. for several seconds to several minutes, the antireflection film 15 that is an insulating film is melted by the glass particles contained in the metal paste for the light receiving surface electrode on the light receiving surface side, and further the n-type semiconductor substrate 10 A part of the surface is also melted, and metal particles (for example, silver particles) in the paste are solidified by forming contact portions with the n-type semiconductor substrate 10. Thereby, the formed light receiving surface electrode 17 and the n-type semiconductor substrate 10 are electrically connected. This is called fire-through. Similarly, on the back surface side, the back electrode metal paste of the back electrode metal paste layer 18 is baked to form the back electrode 19.

An example of the shape of the light-receiving surface electrode 17 will be described with reference to FIGS. 2A and 2B. The light receiving surface electrode 17 includes a bus bar electrode 30 and a finger electrode 32 intersecting with the bus bar electrode 30. FIG. 2A is a plan view of a solar cell element in which the light receiving surface electrode 17 includes a bus bar electrode 30 and a finger electrode 32 intersecting with the bus bar electrode 30 as viewed from the light receiving surface. It is a perspective view which expands and shows a part of 2A.

Such a light-receiving surface electrode 17 can be formed, for example, by means such as screen printing of the above-described metal paste for light-receiving surface electrode, plating of electrode material, deposition of electrode material by electron beam heating in high vacuum, or the like. . The light-receiving surface electrode 17 having the bus bar electrode 30 and the finger electrode 32 is generally used as an electrode on the light-receiving surface side, and is well-known, and known forming means for the bus bar electrode and the finger electrode on the light-receiving surface side are applied. Can do.

In the above description, the solar cell element in which the p-type diffusion layer is formed on the light-receiving surface, the n ⁺ -type diffusion layer is formed on the back surface, and the light-receiving surface electrode and the back electrode are further provided on the respective layers has been described. If a p-type diffusion layer forming composition is used, a back contact type solar cell element can be produced. The back contact type solar cell element has an electrode on the back surface to increase the area of the light receiving surface. That is, in the back contact type solar cell element, it is necessary to form both a p-type diffusion region and an n ⁺ -type diffusion region on the back surface to form a pn junction structure. The p-type diffusion layer forming composition of the present embodiment can form a p-type diffusion site at a specific site, and thus can be suitably applied to the production of a back contact type solar cell element.

Hereinafter, examples of the present invention will be described more specifically, but the present invention is not limited to these examples. Unless otherwise stated, all chemicals used were reagents. “%” Means “% by mass” unless otherwise specified.

[Example 1] (Preparation of p-type diffusion layer forming composition)
A glass lump composed of B ₂ O ₃ , SiO ₂ , Al ₂ O ₃ and CaO (composition molar ratio: 25 mol%, 65 mol%, 5 mol% and 5 mol%, respectively) was pulverized in an agate mortar, and then in a planetary ball mill Further, pulverization was performed to obtain glass particles (compound containing boron) having a spherical particle shape and an average particle diameter of 0.35 μm. 1 g, 2 g and 97 g of the glass particles, ethyl cellulose and terpineol were mixed to form a paste to prepare a p-type diffusion layer forming composition.

The shape of the glass particles was determined by observing using a scanning electron microscope (Hitachi High-Technologies Corporation, “TM-1000 type”). The average particle size of the glass was calculated using a laser scattering diffraction particle size distribution analyzer (Beckman Coulter, “LS 13, 320 type”, measurement wavelength: 632 nm).

Next, a solid pattern (45 × 45 mm ² ) is formed on one surface of an n-type silicon substrate (thickness: 725 μm, specific resistance: 3.1 Ωcm, sheet resistance: 200 Ω / sq.) On which a texture structure is formed by screen printing. The p-type diffusion layer forming composition was applied to form a p-type diffusion layer forming composition layer and dried at 150 ° C. for 1 minute. In screen printing, a screen plate having a mesh size of 460 mesh, a wire diameter of 27 μm, and a transmission volume of 11 cm ³ / m ² was used.

From the mass change of the silicon substrate before and after applying the p-type diffusion layer forming composition, the application amounts of the p-type diffusion layer forming composition and the glass particles were calculated. The application amount of the p-type diffusion layer forming composition was 0.5 mg / cm ² , and the application amount of glass particles (compound containing boron) was 0.005 mg / cm ² .

Next, a silicon substrate having the p-type diffusion layer forming composition layer at 700 ° C. in a diffusion furnace (Koyo Thermo System Co., Ltd., “206A-M100”) flowing N ₂ : 10 L / min. I put the boat I put in. Thereafter, the temperature was increased to 950 ° C. at a temperature increase rate of 15 ° C./min, and heat treatment was performed at 950 ° C. for 30 minutes to diffuse (thermally diffuse) boron into the silicon substrate, thereby forming a p-type diffusion layer. Thereafter, the temperature was lowered to 700 ° C. at 4 ° C./min, and the boat was taken out at 700 ° C.

(Oxidation and etching of boron silicide layer)
The silicon substrate after the thermal diffusion treatment was immersed in a 5% by mass HF aqueous solution for 5 minutes, washed with ultrapure water three times, and then air-dried.

Next, the silicon substrate obtained above was put into a 700 ° C. diffusion furnace in which O ₂ : 10 L / min was flowed, and held for 30 minutes. Next, the semiconductor substrate was taken out, allowed to cool, immersed in a 5% by mass HF aqueous solution for 5 minutes, washed with ultrapure water three times, and then air-dried. The surface was hydrophobic.

(Evaluation of sheet resistance)
The sheet resistance of the application part was measured using a low resistivity meter (Mitsubishi Chemical Corporation, “Loresta MCP-T360”). The sheet resistance of the applying portion is 49Ω / sq. It was found that a p-type diffusion layer was formed.

(Evaluation of out diffusion)
Moreover, as a result of measuring the boron density | concentration diffused to the back surface (surface layer) which has not apply | coated the p-type diffused layer formation composition by SIMS, it is 1 * 10 < ¹⁷ > atoms / cm < ³ >, and there is almost no boron diffused. I understood. The case where the boron concentration in the surface layer was 1 × 10 ¹⁷ atoms / cm ³ or less was not out-diffused and was judged as “good”.

(Evaluation of surface BRL (boron silicide) residue)
A p-type diffusion layer forming composition was applied to both sides of the same silicon substrate as described above, and processed in the same manner to form a p-type diffusion layer. The wafer was put in a polyethylene bag containing an ethanol solution containing 0.05 mol% of iodine, and the lifetime was measured using a μ-PCD method lifetime measuring device WT-2000 (manufactured by Semilab). The lifetime was 150 μsec, and it was found that boron silicide on the surface of the silicon substrate could be removed. When boron silicide remains on the surface of the silicon substrate, the surface passivation of the silicon substrate becomes insufficient, and the lifetime is less than 100 μsec. Therefore, when the lifetime of 100 μsec or more was shown, it was determined that there was no residue on the surface of the silicon substrate and the passivation was “good”.

[Examples 2 to 4 and Comparative Examples 1 and 2]
The treatment was performed in the same manner as in Example 1 except that the content of the boron-containing glass particles and the mesh of the screen plate were changed to the conditions described in Table 1. The evaluation results are summarized in Table 2.

DESCRIPTION OF SYMBOLS 10 ... n-type semiconductor substrate (silicon substrate), 11 ... p-type diffusion layer forming composition layer, 12 ... p-type diffusion layer, 13 ... n-type diffusion layer forming composition layer, 14 ... n ⁺ type diffusion layer, 15 reflection Prevention film, 16 ... Metal paste layer for light receiving surface electrode, 17 ... Light receiving surface electrode, 18 ... Metal paste layer for back electrode, 19 ... Back electrode, 30 ... Busbar electrode, 32 ... Finger electrode

The entire disclosure of Japanese Patent Application No. 2016-139767 filed on July 14, 2016 is incorporated herein by reference. All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually stated to be incorporated by reference, Incorporated herein by reference.

Claims

A p-type diffusion layer forming composition containing a compound containing boron is applied on a semiconductor substrate, and the mass of the compound containing boron per unit area is 0.001 mg / cm 2 to 0.1 mg / cm 2 . Forming a p-type diffusion layer forming composition layer;
Heat-treating the semiconductor substrate provided with the p-type diffusion layer forming composition layer to form a p-type diffusion layer on the semiconductor substrate;
A method for manufacturing a semiconductor substrate with a p-type diffusion layer, comprising:
The production method according to claim 1, wherein the compound containing boron is boron-containing glass particles, and the p-type diffusion layer forming composition further contains a dispersion medium.
The boron-containing glass particles are glass particles containing B 2 O 3, The method according to claim 2.
When the boron-containing glass particles are expressed as oxides, B 2 O 3 and Al 2 O 3 , SiO 2 , K 2 O, Na 2 O, Li 2 O, BaO, SrO, CaO, MgO, BeO, And at least one selected from the group consisting of ZnO, PbO, CdO, V 2 O 5 , SnO, ZrO 2 , MoO 3 , GeO 2 , Y 2 O 3 , CsO 2 and TiO 2. 3. The production method according to 3.
The production method according to claim 3 or 4, wherein the content of B 2 O 3 in the boron-containing glass particles is 0.1 mass% to 60 mass%.
The production method according to any one of claims 2 to 5, wherein an average particle diameter of the boron-containing glass particles is 0.5 µm or less.
Mass compounds containing the boron contained in the p-type diffusion layer forming composition layer, per unit area, is 0.005mg / cm 2 ~ 0.01mg / cm 2, any of claims 1 to 6 The production method according to claim 1.
A semiconductor substrate with a p-type diffusion layer manufactured by the manufacturing method according to any one of claims 1 to 7.
A method for manufacturing a solar cell element, comprising a step of forming an electrode on a p-type diffusion layer of a semiconductor substrate with a p-type diffusion layer according to claim 8.
A solar cell element manufactured by the method for manufacturing a solar cell element according to claim 9.