JP2016046302A - Method for manufacturing semiconductor substrate with diffusion layer, and semiconductor substrate with diffusion layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a method for manufacturing a semiconductor substrate with a diffusion layer, by which a longer lifetime can be realized without increasing the number of processes; and a semiconductor substrate with a diffusion layer.SOLUTION: A method for manufacturing a semiconductor substrate with a diffusion layer comprises the steps of: applying a p-type diffusion layer-forming composition including a compound including an acceptor element to a semiconductor substrate; forming a p-type diffusion layer by performing a thermal diffusion process; and oxidizing the semiconductor substrate.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing a semiconductor substrate having a diffusion layer and a semiconductor substrate having a diffusion layer.

The manufacturing process of the conventional silicon solar cell element is demonstrated.
First, a p-type silicon substrate having a texture structure formed on the light-receiving surface side is prepared so as to promote the light confinement effect, and then in a mixed gas atmosphere of phosphorus oxychloride (POCl ₃ ), nitrogen and oxygen. Several tens of minutes of treatment is performed at 800 ° C. to 900 ° C. to uniformly form an n-type diffusion layer on the surface of the p-type silicon substrate. In this conventional method, since phosphorus is diffused using a mixed gas, n-type diffusion layers are formed not only on the light receiving surface but also on the side surface and the back surface. Therefore, side etching is performed to remove the n-type diffusion layer formed on the side surface. In addition, the n-type diffusion layer formed on the back surface needs to be converted to a p ⁺ -type diffusion layer. Aluminum paste is printed on the back surface and heat-treated (fired) to convert the n-type diffusion layer into the p ⁺ -type diffusion layer. Layering and obtaining ohmic contact are performed together.

  However, the electrical conductivity of the aluminum electrode formed from the aluminum paste is low. Therefore, in order to lower the sheet resistance, the aluminum layer formed on the entire back surface must usually have a thickness of about 10 μm to 20 μm after heat treatment (firing). Furthermore, since the coefficient of thermal expansion differs greatly between silicon and aluminum, a large internal stress is generated in the silicon substrate in the process of heat treatment (firing) and cooling, resulting in damage to crystal grain boundaries, increase in crystal defects, and warpage. Cause.

In order to solve this problem, there is a method of reducing the amount of aluminum paste applied and thinning the back electrode layer. However, if the amount of aluminum paste applied is reduced, the amount of aluminum diffusing from the surface of the p-type silicon substrate to the inside becomes insufficient. As a result, the desired BSF (Back Surface Field) effect (the effect of improving the collection efficiency of the generated carriers due to the presence of the p ⁺ -type diffusion layer) is not sufficient, and there arises a problem that the characteristics of the solar cell deteriorate.

The p-type diffusion layer can also be diffused using BBr ₃ gas. However, in order to form the p-type diffusion layer in a position-selective manner, if the p-type diffusion layer is formed only in the applied portion, the patterning of the diffusion layer is performed. (For example, refer to Patent Document 1).

  In addition, after diffusion of phosphorus and boron to form a diffusion layer, heat treatment is performed at a temperature lower than the diffusion temperature (for example, 600 to 800 ° C.), so that harmful impurities such as heavy metals are gettered to thereby remove carriers in the substrate. A method for extending the life (hereinafter also referred to as lifetime) is known (see, for example, Patent Document 2).

  In addition, it has been reported that a harmful impurity such as heavy metal contained in the substrate is gettered to the boron silicide layer, thereby extending the lifetime. However, the presence of the boron silicide layer hinders the passivation process and causes an increase in resistance in ohmic contact with the electrode, and thus needs to be removed, but is not necessary for hydrofluoric acid. The boron silicide layer can be oxidized and then etched with hydrofluoric acid. However, it is known that the impurities gettered in the boron silicide layer are re-diffused into the substrate in the process of oxidation at a high temperature of 800 ° C. or higher, and the low temperature of 600 ° C. or lower in an oxygen plasma or ultraviolet irradiation ozone atmosphere. There has been proposed a method in which etching is removed after oxidation with (see, for example, Patent Document 3).

  As a method for oxidizing a silicon substrate at a low temperature, a wet oxidation method is known in which oxidation is performed at 100 ° C. to 140 ° C. with an azeotropic nitric acid aqueous solution (see, for example, Patent Document 4).

JP 2013-77804 A JP 2011-166021 A Japanese Patent Laid-Open No. 10-172913 JP 2002-64093 A

  However, in the methods of Patent Document 2 and Patent Document 3, after diffusion, boron silicate glass, which is a diffusion source of boron, is removed by etching with hydrofluoric acid and the like, and then a heat treatment step and a boron silicide removal step are required. The increase in the number leads to an increase in the manufacturing cost of the solar cell. Further, the inventors have found that the gettering effect by the low-temperature heat treatment in Patent Document 2 is not so great in improving the lifetime. Further, it has been found from the results of further examination by the present inventors that the boron silicide oxidation method using plasma or ozone of Patent Document 3 cannot completely suppress the re-diffusion of the impurity element into the substrate.

  An object of the present invention is to provide a method of manufacturing a semiconductor substrate having a diffusion layer that can realize a long lifetime without increasing the number of processes, and a semiconductor substrate having a diffusion layer.

  The present invention is as follows.

<1> A step of applying a p-type diffusion layer forming composition containing a compound containing an acceptor element to a semiconductor substrate, a step of applying a thermal diffusion treatment to form a p-type diffusion layer, and a step of oxidizing the semiconductor substrate A method for manufacturing a semiconductor substrate having a diffusion layer.

<2> The method for producing a semiconductor substrate having a diffusion layer according to <1>, wherein the step of oxidizing the semiconductor substrate is performed by immersing the semiconductor substrate in an oxidizing chemical solution.

<3> A method for producing a semiconductor substrate having the diffusion layer according to <1> or <2>, further including an etching step, and having a diffusion layer.

<4> The oxidizing chemical solution is nitric acid, ozone-dissolved water, hydrogen peroxide solution, a mixed solution of hydrochloric acid and hydrogen peroxide solution, a mixed solution of sulfuric acid and hydrogen peroxide solution, a mixed solution of ammonia and hydrogen peroxide solution, The manufacturing method of the semiconductor substrate which has a diffused layer as described in said <2> or <3> which is at least one oxidizing chemical | medical solution chosen from the mixed solution of sulfuric acid and nitric acid, perchloric acid, and boiling water.

<5> The method for producing a semiconductor substrate having a diffusion layer according to <2> or <3>, wherein the oxidizing chemical solution is an aqueous solution containing 40% by mass to 98% by mass of nitric acid.

<6> A method for producing a semiconductor substrate having a diffusion layer according to any one of <1> to <5>, wherein the step of oxidizing the semiconductor substrate is performed at 60 ° C. to 160 ° C.

<7> A method for producing a semiconductor substrate having a diffusion layer according to any one of <1> to <6>, wherein the acceptor element is boron.

<8> The semiconductor substrate having the diffusion layer according to any one of <1> to <7>, wherein the compound including the acceptor element includes at least one boron compound selected from boric acid, boric acid ester, and B ₂ O _3. Manufacturing method.

<9> The method for producing a semiconductor substrate having a diffusion layer according to any one of <1> to <6>, wherein the compound containing the acceptor element is a glass compound.

<10> At least one glass configuration in which the glass compound is selected from Al ₂ O ₃ , SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, SrO, CaO, MgO, BeO, ZnO, and ZrO _2. The manufacturing method of the semiconductor substrate which has a diffusion layer as described in said <9> containing a component.

<11> A semiconductor substrate having a diffusion layer obtained by the method for producing a semiconductor substrate having a diffusion layer according to any one of <1> to <10>, wherein the iron content is 1 × 10 ¹ to 1 ×. A semiconductor substrate having a diffusion layer of 10 ¹² atoms / cm ³ .

<12> A semiconductor substrate having a diffusion layer obtained by the method for producing a semiconductor substrate having a diffusion layer according to any one of <1> to <10>, wherein the iron content is 1 × 10 ¹ to 1 ×. A semiconductor substrate having a diffusion layer of 10 ¹¹ atoms / cm ³ .

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the manufacturing method of the semiconductor substrate which has a diffused layer which can implement | achieve a long lifetime, and the semiconductor substrate which has a diffused layer, without causing the increase in the number of processes.

It is sectional drawing which shows typically an example of the manufacturing method of the semiconductor substrate (solar cell element) which has a p-type diffused layer. It is sectional drawing which shows typically the other example of the manufacturing method of the semiconductor substrate (solar cell element) which has a p-type diffused layer.

  In this specification, the term “process” is not limited to an independent process, and is included in the term if the intended purpose of the process is achieved even when it cannot be clearly distinguished from other processes. . Moreover, the numerical range shown using "to" shows the range which includes the numerical value described before and behind "to" as a minimum value and a maximum value, respectively. Furthermore, the amount of each component in the composition means the total amount of the plurality of substances present in the composition unless there is a specific notice when there are a plurality of substances corresponding to each component in the composition. In the present specification, “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 addition, in the present specification, the term “layer” includes a configuration of a shape formed in part in addition to a configuration of a shape formed on the entire surface when observed as a plan view.

The method of manufacturing a semiconductor substrate having a diffusion layer according to the present embodiment includes a step of applying a p-type diffusion layer forming composition containing a compound containing an acceptor element to a semiconductor substrate, and applying a thermal diffusion treatment to form the p-type diffusion layer. Forming the semiconductor substrate, and oxidizing the semiconductor substrate.
Therefore, in this embodiment, the p-type diffusion layer forming composition contains a compound containing at least an acceptor element.
In this embodiment, a thermal diffusion process is performed to form a p-type diffusion layer or a p ⁺ -type diffusion layer.

  Here, the p-type diffusion layer forming composition contains a compound containing an acceptor element, and after being applied to the semiconductor substrate, the acceptor element in the compound containing the acceptor element is thermally diffused into the semiconductor substrate to cause impurities in the semiconductor substrate. A material capable of forming a diffusion layer.

(Compound containing acceptor element)
An acceptor element is an element that can form a p-type diffusion layer by diffusing into a semiconductor substrate. As the acceptor element, a Group 13 element can be used, and from the viewpoint of safety and the like, it is preferable to contain at least one of B (boron) and Al (aluminum).
There is no restriction | limiting in particular as a compound containing an acceptor element, Compounds, such as a metal oxide, an ester compound, a nitride, a glass compound, an oxo acid, can be illustrated as the form. As a metal oxide containing an acceptor element, an oxide of a single acceptor element such as B ₂ O ₃ or Al ₂ O ₃ ; a glass component substance is formed in addition to an acceptor element-containing substance such as B ₂ O ₃ or Al ₂ O ₃ Glass compounds containing component (hereinafter also referred to as glass particles) acceptor element); boron, aluminum-doped silicon particles, boron nitride (BN), calcium borate, boric acid and other inorganic boron compounds; boron-containing Examples thereof include silicon oxide compounds; organoaluminum compounds such as aluminum alkoxide and alkylaluminum;

Among these, boric acid, boric acid ester, BN, B ₂ O ₃ , glass particles containing an acceptor element, a boron-containing silicon oxide compound, and B ₂ O ₃ at a high temperature (for example, 800 ° C. or more) thermally diffusing into a semiconductor substrate. It is preferable to use one or more selected from the group consisting of compounds (for example, boric acid) that can be changed into the compounds to be contained. More preferably, glass particles are used.

  The compound containing an acceptor element is preferably BN particles, glass particles containing an acceptor element, or a boron-containing silicon oxide compound, and more preferably glass particles containing a BN particle or an acceptor element. By using glass particles or BN particles containing an acceptor element, out-diffusion (the acceptor element diffuses in addition to the coating part) tends to be suppressed, and is unnecessary except in the region to which the p-type diffusion layer forming composition is applied. Formation of the p-type diffusion layer can be suppressed. That is, a p-type diffusion layer can be formed in a more selective region by including glass particles or BN particles containing an acceptor element.

The glass particles containing an acceptor element can be formed including, for example, an acceptor element-containing substance and a glass component substance. The acceptor element-containing material used for introducing the acceptor element into the glass particles is preferably a compound containing at least one selected from the group consisting of B ₂ O ₃ and Al ₂ O ₃ .

  The content rate of the acceptor element-containing substance in the glass particles containing the acceptor element is not particularly limited. For example, from the viewpoint of acceptor element diffusivity, it is preferably 0.5% by mass or more and 100% by mass or less, and more preferably 2% by mass or more and 80% by mass or less.

Further, from the viewpoint of acceptor element diffusivity, 0.5 mass of one or more selected from the group consisting of B ₂ O ₃ and Al ₂ O ₃ as the acceptor element-containing substance is contained in the p-type diffusion layer forming composition. % To 100% by mass, more preferably 5% to 99% by mass, and particularly preferably 30% to 80% by mass.

When the compound containing the acceptor element is a glass particle, the glass component materials include SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, SrO, BaO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ , WO ₃ , MoO ₃ , Y ₂ O ₃ , CsO ₂ , TiO ₂ , TeO ₂ , La ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , GeO ₂ , Lu ₂ O It is preferable to use at least one selected from the group consisting of ₃ and MnO, SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O _{5, SnO,} the use of _{the ZrO 2, MoO 3, GeO 2} , Y 2 O 3, CsO 2 and at least one selected from the group consisting of TiO ₂ More _preferably, made of _{SiO 2, K 2 O, Na} 2 O, Li 2 O, BaO, SrO, CaO, BaO, MgO, BeO, ZnO, PbO, CdO, V 2 O 5, SnO, ZrO 2 and MoO ₃ It is more preferable to use at least one selected from the group from the viewpoints of setting the softening point within the above prescribed range and reducing the coefficient of thermal expansion of the semiconductor substrate and the difference therebetween.

Specific examples of the glass particles include those containing both the acceptor element-containing substance and the glass component substance. B ₂ O ₃ —SiO ₂ (described in the order of acceptor element-containing substance-glass component substance, the same applies hereinafter) , _B 2 _O 3 -ZnO _system, B ₂ O 3 -PbO _based, B 2 _{O 3} alone system or the like of the acceptor element-containing material as a _B 2 _{O 3} system _including, Al ₂ O 3 acceptor element -SiO ₂ system, etc. Examples of the contained material include glass particles such as a system containing Al ₂ O ₃ .
In the above it has been illustrated glass particles containing one or _{two-component,} B ₂ O ₃ -SiO 2 -CaO, etc., may be glass particles containing more than three components.
_Also, as in the Al _{2 O 3 -B 2} O 3 system or the like, it may be glass particles containing two or more acceptor element-containing material.

The acceptor element-containing glass particles (compound containing acceptor elements in the form of glass particles) include at least one acceptor element-containing substance selected from the group consisting of B ₂ O ₃ and Al ₂ O ₃ , and 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 , Containing at least one glass component material 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. And at least one acceptor element-containing material selected from the group consisting of B ₂ O ₃ and Al ₂ O ₃ , and SiO ₂ , K ₂ O, Na ₂ O, Li _{2 O, BaO, SrO, CaO} , MgO, BeO, selected ZnO, PbO, _CdO, from _{V 2 O 5, SnO, ZrO} 2, MoO 3, GeO 2, Y 2 O 3, the group consisting of CsO ₂ and TiO ₂ It is more preferable to contain at least one kind of glass component substance, and at least one acceptor element-containing substance selected from the group consisting of B ₂ O ₃ and Al ₂ O ₃ , SiO ₂ , K ₂ At least one glass selected from the group consisting of 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 containing a component material, and at least one acceptor element-containing material selected from the group consisting of B ₂ O ₃ and Al ₂ O _{3 SiO 2, K 2 O, Na} 2 O, Li 2 O, BaO, SrO, CaO, MgO, contain BeO, ZnO, and the glass component material at least one selected from the group consisting of ZrO _2, the Is particularly preferred.
Furthermore, the glass particles include Al ₂ O ₃ as the acceptor element-containing material, and at least one selected from the group consisting of SiO ₂ , ZnO, CaO, Na ₂ O, Li ₂ O, and BaO as the glass component material. It is preferable to include. When these component substances coexist than when B ₂ O ₃ which is an acceptor element-containing substance is used alone, the resistance of the formed impurity diffusion layer becomes lower, and the out diffusion can be suppressed. It becomes possible.

When BN is used as a compound containing an acceptor element, the crystal form of BN may be any of hexagonal, cubic, and rhombohedral, but the particle size can be easily controlled. A hexagonal crystal is preferable because it can be formed.
The method for preparing BN is not particularly limited, and can be prepared by a usual method. Specifically, a method in which boron powder is heated to 1500 ° C. or higher in a nitrogen stream, a method in which molten boric acid and nitrogen or ammonia are reacted in the presence of calcium phosphate, boric acid or an alkali boride, urea, guanidine, Examples include 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, etc. However, there is no problem with manufacturing methods other than those described above. Among the above production methods, it is preferable to use a method in which boron trichloride and ammonia are reacted at a high temperature because high-purity BN can be obtained.

  The compound containing an acceptor element may be a boron-containing silicon oxide compound. Here, the boron-containing silicon oxide compound will be described in detail. The boron-containing silicon oxide compound means a compound synthesized by reacting a boron compound with a silicon oxide precursor based on a sol-gel reaction, and boron glass can be distinguished from the glass particles so that the synthesis method is different. It will be described as a contained silicon oxide compound.

  The boron-containing silicon oxide compound obtained by reacting a silicon oxide precursor with a boron compound has a structure in which the boron compound is dispersed in a silicon oxide (siloxane) network, so that the volatility of the boron compound is suppressed, and silicon Outdiffusion tends to be suppressed at a high temperature at which a p-type diffusion layer is formed on a semiconductor substrate such as a substrate.

  The boron-containing silicon oxide compound may be washed with water in advance to remove boron compounds not included in the silicon oxide (siloxane) network. By doing in this way, out diffusion can be suppressed.

  Examples of the method for synthesizing the boron-containing silicon oxide compound include the same method as the method for synthesizing the phosphorus-containing silicon oxide compound described above except that the phosphorus compound is replaced with a boron compound. Examples of the silicon alkoxide, the solvent used for the sol-gel reaction, and the acid and alkali used as a catalyst for controlling hydrolysis and dehydration condensation polymerization are the same as those mentioned in the above-described method for synthesizing the phosphorus-containing silicon oxide compound. It is done.

  In addition, a solution containing a metal nitrate, ammonium salt, chloride salt, sulfate salt or the like is added to the sol solution of the silicon oxide precursor, and then the sol-gel reaction is allowed to proceed to thereby form the boron-containing silicon oxide compound. It may be prepared. Examples of the metal nitrate, ammonium salt, chloride salt, sulfate, and salt solvent that can be used here are the same as those mentioned in the method for synthesizing the phosphorus-containing silicon oxide compound.

Examples of the boron compound used for the sol-gel reaction include boron oxide and boric acid. 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 and B (OH) ₃ . These compounds are dissolved in water and exist in the state of H ₃ BO ₃ . In addition to boron oxide and boric acid, any compound that can be dissolved in water to form H ₃ BO ₃ is not limited to the type of boron compound used as an auxiliary material. Examples of the compound that dissolves in water to become H ₃ BO ₃ include boric acid esters.

As said boric acid ester, the compound represented by the following general formula (I) is mentioned. Here, R < ⁷ > -R < ⁹ > in general formula (I) is respectively independently a C1-C10 organic group or a hydrogen atom.

There is no restriction | limiting in particular as an organic group represented by R < ⁷ > -R < ⁹ > in general formula (I), Each is independently an alkyl group, an organic group which has a functional group, an organic group which has a hetero atom, and an unsaturated bond. The organic group which has.

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 preferably has 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and 1 to 3 carbon atoms. Further preferred. 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. It is done.

In the organic group having a functional group represented by R ^{7 to} R ⁹ , examples of the functional group include chloro, bromo, and fluoro groups. The organic group having a functional group represented by R ^{7 to} R ⁹ preferably has 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and 1 to 3 carbon atoms. More preferably. Specific examples of the organic group having a functional group represented by R ^{7 to} R ⁹ include chloroethyl, fluoroethyl, chloropropyl, dichloropropyl, fluoropropyl, difluoropropyl, chlorophenyl, 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 heteroatom represented by R ^{7 to} R ⁹ preferably has 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and 1 to 3 carbon atoms. More preferably. Specific examples of the organic group having a hetero atom represented by R ^{7 to} R ⁹ include dimethylamino, diethylamino, diphenylamino, methyl sulfoxide, ethyl sulfoxide, and phenyl sulfoxide groups.

The organic group having an unsaturated bond represented by R ^{7 to} R ⁹ preferably has 2 to 10 carbon atoms, more preferably 2 to 10 carbon atoms, and 2 to 4 carbon atoms. More preferably it is. Specific examples of the organic group having an unsaturated bond represented by R ^{7 to} R ⁹ include ethylenyl, ethynyl, propenyl, propynyl, butenyl, butynyl, and phenyl groups.

Among these, the monovalent organic group of 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 in 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 rate of the compound containing the acceptor element in the p-type diffusion layer forming composition is determined in consideration of the coating property, the diffusibility of the compound containing the acceptor element, and the like. In general, the content of the compound containing an acceptor element in the p-type diffusion layer forming composition is preferably 0.1% by mass or more and 95% by mass or less in the p-type diffusion layer forming composition. More preferably, it is more preferably not less than 90% by mass and more preferably not more than 1% by mass and not more than 80% by mass, particularly preferably not less than 2% by mass and not more than 50% by mass. As mentioned above, it is very preferable that it is 20 mass% or less.
When the content of the compound containing the acceptor element in the p-type diffusion layer forming composition is 0.1% by mass or more, the impurity diffusion layer can be sufficiently formed, and when it is 95% by mass or less, p The dispersibility of the compound containing the acceptor element in the composition for forming the diffusion layer is improved, and the coating property to the semiconductor substrate is improved.

(Dispersion medium)
The p-type diffusion layer forming composition may further contain a dispersion medium.
The dispersion medium is a solvent for adjusting the viscosity in the composition.

  Examples of the solvent include acetone, methyl ethyl ketone, methyl-n-propyl ketone, methyl-iso-propyl ketone, methyl-n-butyl ketone, methyl-iso-butyl ketone, methyl-n-pentyl ketone, methyl-n-hexyl ketone, Ketone solvents such as diethyl ketone, dipropyl ketone, di-iso-butyl ketone, trimethylnonanone, cyclohexanone, cyclopentanone, methylcyclohexanone, 2,4-pentanedione, acetonylacetone; diethyl ether, methyl ethyl ether, methyl -N-propyl ether, di-iso-propyl ether, tetrahydrofuran, methyltetrahydrofuran, dioxane, dimethyldioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether Ter, ethylene glycol di-n-propyl ether, ethylene glycol dibutyl 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, G Ethylene glycol methyl-n-hexyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetradiethylene glycol methyl ethyl ether, tetraethylene glycol methyl n-butyl ether, diethylene glycol di-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 dibutyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol methyl ethyl Ether, zip Lopylene 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, tetradipropylene glycol methyl ethyl Ether, tetrapropylene glycol methyl-n-butyl ether Ether solvents such as dipropylene glycol di-n-butyl ether, tetrapropylene glycol methyl-n-hexyl ether, tetrapropylene glycol di-n-butyl ether; methyl acetate, ethyl acetate, n-propyl acetate, i-propyl acetate, acetic acid n-butyl, i-butyl acetate, sec-butyl acetate, n-pentyl acetate, sec-pentyl acetate, 3-methoxybutyl acetate, methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, 2- (2- Butoxyethoxy) ethyl, benzyl acetate, cyclohexyl acetate, methyl cyclohexyl acetate, nonyl acetate, methyl acetoacetate, ethyl acetoacetate, diethylene glycol methyl ether acetate, diethylene glycol monoethyl ether acetate, dipropylene glycol acetate Methyl ether, dipropylene glycol ethyl ether, glycol diacetate, methoxytriglycol acetate, ethyl propionate, n-butyl propionate, i-amyl propionate, diethyl oxalate, di-n-butyl oxalate, lactic acid Methyl, ethyl lactate, n-butyl lactate, n-amyl lactate, ethylene glycol methyl ether propionate, ethylene glycol ethyl ether propionate, ethylene glycol methyl ether acetate, ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate, propylene Ester solvents such as glycol ethyl ether acetate, propylene glycol propyl ether acetate, γ-butyrolactone, γ-valerolactone; N-methylpyrrolidinone, N-ethylpyrrolidinone, N-propylpyrrolidinone, N-butylpyrrolidinone, N-hexylpyrrolidinone, N-cyclohexylpyrrolidinone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, etc. Aprotic polar solvent: methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, sec-butanol, t-butanol, n-pentanol, i-pentanol, 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, phenol, cyclohexanol, methylcyclohexanol, benzyl alcohol, ethylene glycol, Alcohol solvents such as 1,2-propylene glycol, 1,3-butylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol; 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 ether, ethoxytriglycol, tetraethylene glycol mono-n-butyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether Glycol monoether solvents such as α-terpinene, α-terpineol, myrcene, alloocimene, limonene, dipentene, α-pinene, β-pinene, terpineol, carvone, ocimene, and ferrandrene; water and the like It is done. These are used singly or in combination of two or more.

  The content ratio of the dispersion medium in the p-type diffusion layer forming composition is determined in consideration of applicability and viscosity.

(High viscosity solvent)
The p-type diffusion layer forming composition may contain a high viscosity solvent. High viscosity solvents include isobornylcyclohexanol, isobornylphenol, 1-isopropyl-4-methyl-bicyclo [2.2.2] oct-5-ene-2,3-dicarboxylic anhydride, p-mentenyl. It preferably contains at least one selected from phenol and at least one selected from isobornylcyclohexanol and isobornylphenol. These compounds decompose or volatilize at a low temperature (for example, 400 ° C. or lower), and have a high viscosity due to their bulky structure, so that they can be used as an alternative to conventionally used binder resins such as ethyl cellulose. In particular, when a p-type diffusion layer forming composition is applied to a semiconductor substrate by a screen printing method, it is necessary to increase the viscosity. In this case, a large amount of ethyl cellulose is used (for example, 5% by mass in the p-type diffusion layer forming composition). Must be included. In this case, in the drying and firing steps, the resin remains, and this residue becomes a resistor, which may adversely affect the power generation characteristics of the solar cell element. On the other hand, since the amount of the resin binder can be reduced by using the high-viscosity solvent, it can be reduced to such an extent that the residual resin does not become a problem.

  Although there is no restriction | limiting in particular in the ratio of the compound containing an acceptor element, and a high-viscosity solvent, 1 mass% or more of the compound containing an acceptor element in a p-type diffused layer formation composition is 50 mass% or less, and the said high viscosity solvent is 1 mass. The glass powder in the p-type diffusion layer forming composition is preferably contained in an amount of 5% to 40% by mass, and the high-viscosity solvent is contained in an amount of 5% to 95% by mass. preferable.

(3) Binder The p-type diffusion layer forming composition may contain a binder from the viewpoint of preventing scattering of a compound containing an acceptor element in a state of being applied and dried on a substrate, or adjusting the viscosity. .
Examples of the binder include polyvinyl alcohol, polyacrylamides, polyvinyl amides, polyvinyl pyrrolidone, polyethylene oxides, polysulfonic acid, acrylamide alkyl sulfonic acid, cellulose ethers, cellulose derivatives (carboxymethyl cellulose, hydroxyethyl cellulose, ethyl cellulose, etc.), gelatin , Starch and starch derivatives, sodium alginate, xanthan, guar and gua derivatives, scleroglucan and scleroglucan derivatives, tragacanth and tragacanth derivatives, dextrin and dextrin derivatives, (meth) acrylic acid resins, (meth) acrylic acid ester resins (For example, alkyl (meth) acrylate resin, dimethylaminoethyl (meth) acrylate resin, etc.), butadie Resins, styrene resins and copolymers thereof, siloxane resins, can such suitably selected metal alkoxide. 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 even in a small amount.
These are used singly or in combination of two or more.

  The molecular weight of the binder is not particularly limited, and it is desirable to adjust appropriately in view of the desired viscosity as the composition.

  Although there is no restriction | limiting in particular in content of the binder in a p-type diffused layer formation composition, It is preferable that it is less than 10 mass%, it is preferable that it is less than 3 mass%, and it is preferable that it is less than 1 mass%.

(Inorganic filler)
The p-type diffusion layer forming composition may contain an inorganic filler. Examples of the inorganic filler include silica, clay, and silicon carbide. Among these, it is preferable to use a filler containing at least silica as a component. By adding the inorganic filler, it is possible to suppress thermal sagging of the coated material in the step of applying and drying the p-type diffusion layer forming composition to decompose and volatilize the high viscosity solvent. The cause of the thermal sag is that the viscosity of the solvent decreases at a temperature of about 100 ° C. to 500 ° C. where the high viscosity solvent is decomposed and volatilized. When an inorganic filler is included, since a decrease in viscosity can be suppressed, thermal sag can be suppressed.

The BET specific surface area of the inorganic filler is preferably 50 to 500 m ² / g, and more preferably 100 to 300 m ² / g. Among such inorganic fillers having a high BET specific surface area, fumed silica can be exemplified. By using an inorganic filler having a high BET specific surface area, it tends to be easy to suppress a decrease in viscosity due to physical and van der Waals interaction with a solvent whose viscosity has been reduced in the drying step. The BET specific surface area can be calculated by measuring the amount of nitrogen adsorbed at 77K.

  The fumed silica may be either hydrophilic or hydrophobic.

  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 more preferably 0%. .2 mass% to 5 mass%. By setting it as 0.01 mass or more, the effect which suppresses generation | occurrence | production of the thermal dripping in a drying process is acquired, and the application | coating characteristic of a p-type diffused layer formation composition is securable by setting it as 40 mass% or less.

(Alkoxysilane)
The p-type diffusion layer forming composition may further contain an alkoxysilane. By including alkoxysilane, the viscosity of the paste tends to be maintained when the paste is dried. 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, More preferably, it is a linear or branched alkyloxy group having 1 to 10 carbon atoms, and particularly preferably a linear or branched alkyloxy group having 1 to 4 carbon atoms.
Specific examples of the alkoxy group include methyl group, ethyl group, propyl group, butyl group, i-propyl group, i-butyl group, pentyl group, hexyl group, octyl group, 2-ethylhexyl group, t-octyl group, Examples thereof include a decyl group, a dodecyl group, a tetradecyl group, a 2-hexyldecyl group, a hexadecyl group, an octadecyl group, a cyclohexylmethyl group, and an octylcyclohexyl group.
Among these, it is preferable to use tetramethoxysilane, tetraalkoxysilane, or tetraisopropoxysilane.

(Silane coupling agent)
The p-type diffusion layer forming composition may further contain a silane coupling agent. The silane coupling agent has two functional groups different in silicon, organic functional group and alkoxy group in one molecule, and the structure is not particularly limited, but is represented by the following general formula (1) Can be illustrated.
XnR ₂ (3-n) SiR ₁ -Y (1)

In the general formula (1), X represents a methoxy group or an ethoxy group. Y is vinyl group, mercapto group, epoxy group, amino group, styryl group, isocyanurate group, isocyanate group, acrylic group, methacryl group, glycidoxy group, ureido group, sulfide group, carboxyl group, acryloxy group, methacryloxy group, alkyl group , Phenyl group or trifluoroalkyl group, alkylene glycol group, amino alcohol group, quaternary ammonium, and the like. Of these, a vinyl group, an amino group, an epoxy group, an acryloxy group, a methacryloxy group, an alkyl group, and a trifluoroalkyl group are preferable, and an acryloxy group and a trifluoromethyl group are more preferable.
In the general formula (1), R ₁ represents an alkylene group having 0 to 10 carbon atoms or a divalent linking group having 2 to 5 atoms in the main chain and containing a nitrogen atom in the main chain. The alkylene group is preferably an ethylene group or a propylene group. The atomic group containing a nitrogen atom in the linking group is preferably an amino group or the like.
In the general formula (1), R ₂ represents an alkyl group having 1 to 5 carbon atoms, preferably a methyl group or an ethyl group, and more preferably a methyl group. Note that n represents an integer of 1 to 3.

  Specific examples of the silane coupling agent include the following groups (a) to (c). (A) Those having a (meth) acryloxy group: 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyldimethyldiethoxysilane, 3 -Methacryloxypropyltriethoxysilane, etc. (b) having an epoxy group or glycidoxy group: 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 2- (3,4 epoxy) (Cyclohexyl) ethyltrimethoxysilane, and the like (c) those having an amino group: N- (2-aminoethyl) 3-aminopropylmethyldimethoxysilane, N- (aminoethyl) 3-aminopropyltrimethoxysilane, and 3 -A Nopropyltriethoxysilane, etc. (d) Those having a mercapto group: 3-mercaptopropyltrimethoxysilane, etc. (e) Those having an alkyl group: methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, Dimethyldiethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, 1,6-bis (trimethoxysilyl) hexane (F) Those having a phenyl group: phenyltrimethoxysilane, phenyltriethoxysilane, etc. (g) Those having a trifluoroalkyl group: trifluoropropyltrimethoxysilane, etc.

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 an acceptor element and a highly viscous solvent using a blender, a mixer, a mortar, and a rotor. Moreover, when mixing, you may add a heat | fever as needed. When heating at the time of mixing, the temperature can be 30-100 degreeC, for example.
In addition, the component contained in the said p-type diffused layer formation composition and content of each component use thermal analysis, such as TG / DTA, NMR, HPLC, GPC, GC-MS, IR, MALDI-MS etc. Can be confirmed.

  In the p-type diffusion layer forming composition, at least the total amount of lifetime killer elements is preferably 1000 ppm or less, preferably 500 ppm or less, more preferably 100 pm or less, and further preferably 50 ppm or less. By being 1000 ppm or less, the lifetime of the 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 mass spectrometer, an ICP emission spectrometer, or an atomic absorption spectrometer. The lifetime of the carrier can be measured by a microwave photoconductive decay method (μ-PCD method). These elements have a high diffusion rate in the semiconductor substrate, reach everywhere in the bulk of the substrate, and act as recombination centers.

<Manufacturing method of semiconductor substrate having p-type diffusion layer>
The method for producing a semiconductor substrate having a p-type diffusion layer according to the present embodiment is also referred to as a p-type diffusion layer forming composition containing a compound containing an acceptor element and a dispersion medium (hereinafter also referred to as “specific p-type diffusion layer forming composition”). ) Has a step of heat-treating the semiconductor substrate applied to a part of the region (hereinafter also referred to as “heat-treatment step”). The semiconductor substrate to which the specific p-type diffusion layer forming composition is applied may be a purchased product, or the specific p-type diffusion layer forming composition is applied to a partial region on the surface of the semiconductor substrate. You may produce by a process (henceforth a "giving process"). The method for manufacturing a semiconductor substrate having a p-type diffusion layer according to this embodiment may further include other steps as necessary.

(Granting process)
In the applying step, a p-type diffusion layer forming composition containing a compound containing an acceptor element and a dispersion medium is applied to a partial region of the semiconductor substrate.

  A semiconductor substrate in particular is not restrict | limited, The normal thing used for a solar cell element 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 a substrate, a gallium arsenide substrate, an indium phosphide substrate, a gallium nitride substrate, a silicon carbide, a silicon germanium substrate, and a copper indium selenium substrate. The semiconductor substrate is preferably pretreated before applying the p-type diffusion layer forming composition. Examples of the pretreatment include the following steps. In the following description, a p-type semiconductor substrate is used, but an n-type semiconductor substrate may be used.

  An alkaline solution is applied to the p-type semiconductor substrate to remove the damaged layer, and a texture structure is obtained by etching. Specifically, the damaged layer on the surface of the p-type semiconductor substrate generated when slicing from the ingot is removed with a 20% by mass aqueous sodium hydroxide solution. Next, etching is performed with a mixed solution of 1% by mass caustic soda and 10% by mass isopropyl alcohol to form a texture structure. The solar cell element has a texture structure on the light receiving surface side, thereby promoting a light confinement effect and increasing efficiency.

Next, in a mixed gas atmosphere of phosphorus oxychloride (POCl ₃ ), nitrogen and oxygen, several tens of minutes are performed at 800 ° C. to 900 ° C. to uniformly form an n-type diffusion layer on the surface of the semiconductor substrate. At this time, in the method using the phosphorus oxychloride atmosphere, phosphorus is diffused on the side surface and the back surface, 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, side etching for removing the n-type diffusion layer formed on the side surface is performed.

  Then, a specific p-type diffusion layer forming composition is applied to a partial region of the pretreated semiconductor substrate. When a p-type semiconductor substrate is used, a specific 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).

  There is no restriction | limiting in particular in the provision method of a specific p-type diffused layer formation composition, A printing method, a spin coat method, brush coating, a spray coat method, a doctor blade method, a roll coat method, an inkjet method etc. are mentioned.

  The content ratio of the dispersion medium in the p-type diffusion layer forming composition is determined in consideration of applicability and acceptor concentration. The viscosity of the p-type diffusion layer forming composition is preferably 10 mPa · s to 1,000,000 mPa · s, more preferably 50 mPa · s to 500,000 mPa · s in consideration of applicability.

  Depending on the composition of the p-type diffusion layer forming composition, a drying step for volatilizing the solvent may be required after the p-type diffusion layer forming composition is applied to the semiconductor substrate and before the heat treatment step described later. . In this case, drying is performed at a temperature of about 80 ° C. to 300 ° C. for 1 minute to 10 minutes when a hot plate is used, and about 10 minutes to 30 minutes when a dryer or the like is used. This drying condition can be appropriately adjusted according to the solvent composition of the p-type diffusion layer forming composition.

(Diffusion thermal diffusion process)
The diffusion heat treatment for diffusing boron is preferably performed at 600 ° C to 1200 ° C, and preferably 850 ° C to 1000 ° C. By this heat treatment, boron diffuses in the semiconductor substrate, and a p-type diffusion layer, a p ⁺ -type diffusion layer, and the like are formed. A known continuous furnace, batch furnace, or the like can be applied to the heat treatment.

The gas composition of the atmosphere of the diffusion heat treatment is preferably an atmosphere having a proportion of oxygen of 50% by volume or less, more preferably 20% by volume or less, and most preferably 10% by volume or less. By diffusing in an atmosphere where the proportion of oxygen is 50% by volume or less, oxidation of aluminum silicide or boron silicide (hereinafter simply referred to as silicide) can be suppressed. When boron is diffused in a state where silicide is formed, the silicide layer getters impurity elements such as heavy metals (for example, iron, nickel, etc.) in the substrate or from the furnace atmosphere such as a furnace tube. Therefore, the number of recombination centers in the substrate is reduced, and the lifetime of the substrate can be extended.
There are no particular limitations on components other than oxygen, and the composition can be composed of nitrogen, argon, neon, xenon, krypton, helium, carbon dioxide, hydrogen, air, and the like. Among these, from the viewpoint of cost and safety, a gas composition composed of 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 (NZ-3000) manufactured by Horiba, Ltd. can be used.

  After diffusion thermal diffusion, the oxygen ratio may be changed and further heat treatment may be performed. After thermal diffusion, the silicide layer is oxidized by heat treatment in an atmosphere containing oxygen, and the boron silicide layer can be removed at the same time in a hydrofluoric acid etching step for removing the boron silicate glass layer. The gas composition at this time may include, for example, 0.1% by volume to 50% by volume or more of oxygen. Heat treatment at 0.1 volume% to 50 volume% effectively oxidizes the boron silicide layer while easily oxidizing the boron silicide layer, and impurities such as heavy metals gettered to the boron silicide layer. It is easy to suppress re-diffusion of contaminating elements into the semiconductor substrate.

Further, by oxidizing the portion other than the coated portion (non-coated portion) of the p-type diffusion layer forming composition containing boron as an acceptor element to form a SiO ₂ layer, an out-diffusion (p-type diffusion layer forming composition) is formed in the non-coated portion. Boron that has been accepted and diffused to the non-coated portion by volatilization of the acceptor element in the material may be taken into the SiO ₂ layer. This SiO ₂ layer can be removed by a hydrofluoric acid etching process. That is, the out-diffused boron element can be removed. This utilizes the property that SiO ₂ takes up boron.

  The temperature during silicide heat treatment may be the same as or different from the diffusion heat treatment temperature. For example, the gas composition may be changed from the process of lowering the temperature from the diffusion heat treatment temperature.

Since a 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 formed by the heat treatment, the semiconductor substrate is treated with an etching solution after the heat treatment. You may have a process. Thereby, the produced | generated glass layer is removed by an etching. In addition, the oxide mask layer on the Si substrate formed outside the application region of the p-type diffusion layer forming composition is simultaneously etched with the etchant.
Examples of the etching solution include aqueous solutions of hydrogen fluoride, ammonium fluoride, ammonium hydrogen fluoride, and the like, and aqueous solutions of sodium hydroxide. As the etching process, a known method such as immersing a semiconductor substrate in an etching solution can be applied.

(Semiconductor substrate oxidation process)
In the method of manufacturing a semiconductor substrate having a diffusion layer according to this embodiment, the semiconductor substrate is subjected to a thermal diffusion process to form a p-type diffusion layer, and then the semiconductor substrate is oxidized.
In the method of manufacturing a semiconductor substrate having a diffusion layer according to the present embodiment, it is preferable that the semiconductor substrate is oxidized by immersing the semiconductor substrate in an oxidizing chemical solution and oxidizing the boron silicide layer of the semiconductor substrate by a wet process. The boron silicide layer can be oxidized by wet oxidation, and the boron silicide layer oxidized with an etchant such as hydrogen fluoride can be removed thereafter, and the passivation effect of the passivation film to be formed can be maximized. .

  The oxidizing chemical solution is not particularly limited as long as the boron silicide layer can be oxidized. For example, nitric acid, ozone-dissolved water, sulfuric acid, hydrogen peroxide solution, mixed solution of hydrochloric acid and hydrogen peroxide solution, sulfuric acid and hydrogen peroxide solution are available. Preferably, it is at least one oxidizing chemical selected from a mixed solution of ammonia, a mixed solution of ammonia and hydrogen peroxide, a mixed solution of sulfuric acid and nitric acid, perchloric acid, boiling water, nitric acid, ozone-dissolved water, peroxidation More preferably, it is at least one oxidizing chemical solution selected from hydrogen water, hydrochloric acid and hydrogen peroxide mixed solution, sulfuric acid and hydrogen peroxide mixed solution, ammonia and hydrogen peroxide mixed solution, nitric acid, At least one oxidizing chemical solution selected from a mixed solution of hydrochloric acid and hydrogen peroxide solution, a mixed solution of sulfuric acid and hydrogen peroxide solution, and a mixed solution of ammonia and hydrogen peroxide solution. Rukoto is particularly preferred. By using these oxidizing chemicals, the boron silicide layer can 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. It is particularly preferable to use an aqueous solution. By using a nitric acid aqueous solution having a concentration close to that of a 68% 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% nitric acid aqueous solution is about 120 ° C., it is easy to immerse at a temperature higher than 100 ° C. which is the boiling point of water, and the oxidation of the boron silicide layer tends to be promoted.

  When ozone-dissolved water is used as the oxidizing chemical, it is preferably an aqueous solution in which 1% by mass to 80% by mass of ozone is dissolved, more preferably 10% by mass to 70% by mass, and 30% by mass. It is especially preferable that it is -60 mass%. 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 10% to 50% by weight, and more preferably 20% by weight. It is especially preferable that it is -40 mass%. 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, 1% by mass to 60% by mass hydrogen peroxide solution, For example, it is preferable to use an SC-2 cleaning solution mixed at 37 mass% HCl aqueous solution: 30 mass% H ₂ O ₂ aqueous solution: H ₂ O = 1: 1: 5 (volume ratio).

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 solution, 1% by mass to 60% by mass hydrogen peroxide solution, For example, it is preferable to use an SPM cleaning solution mixed in a 97% by mass sulfuric acid aqueous solution: 30% by mass H ₂ O ₂ aqueous solution = 4: 1 (volume ratio).

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

  When using a mixed solution of a mixed solution of sulfuric acid and nitric acid as the oxidizing chemical solution, 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 is preferable. A chemical solution mixed in a 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, and more preferably 30% by mass. It is especially preferable that it is -60 mass%. By using 1 mass% to 80 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, and more preferably 50% by mass. It is particularly preferred to use a ˜98.5% by weight 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).

  As the oxidation of the semiconductor substrate, the oxidation of the boron silicide layer using an oxidizing chemical solution is preferably performed at 25 to 300 ° C, more preferably at 40 to 200 ° C, and at 40 to 180 ° C. Is more preferable, it is particularly preferably performed at 60 ° C to 160 ° C, and most preferably performed at 80 ° C to 160 ° C. By performing the annealing at 25 ° C. to 300 ° C., since the diffusion rate of iron is low, re-diffusion of the impurity metal element gettered in the boron silicide layer into the semiconductor substrate can be suppressed. That is, the content of the impurity metal element in the semiconductor substrate can be made as low as possible, and the lifetime of carriers generated in the substrate can be extended.

It is preferable to remove the boron silicide layer with an etching solution after oxidation. Examples of the etching solution include aqueous solutions of hydrogen fluoride, ammonium fluoride, ammonium hydrogen fluoride, and the like, and aqueous solutions of sodium hydroxide. As the etching process, a known method such as immersing a semiconductor substrate in an etching solution can be applied.
By removing the boron silicide-derived layer, the passivation effect of the passivation film can be maximized.

The content of the iron impurity element in the semiconductor substrate formed with the p-type diffusion layer obtained in the present invention is preferably 1 × 10 ¹ to 1 × 10 ¹² atoms / cm ³ , and preferably 1 × 10 ^{1 to} 5 X10 ¹¹ atoms / cm ³ is more preferable, and 1 × 10 ¹ to 1 × 10 ¹¹ atoms / cm ³ is particularly preferable.

The content of the iron impurity element in the semiconductor substrate can be measured by fluorescent X-ray analysis, secondary ion mass spectrometry, or quasi-steady state photoconductivity measurement (QSSPC). Among these, since the determination of the amount of iron impurities in the QSSPC method has particularly high resolution, it is preferable to use the QSSPC method, and the measurement can be performed using WCT-120 manufactured by Sinton Instruments. A specific analysis method is described in Journal of Applied Physics, Vol. 95, P.I. 1021-1028 (2004) can be referred to.
A semiconductor substrate on which a p-type diffusion layer is formed is prepared, and the substrate surface is passivated by an arbitrary method. Examples of the passivation method include a method of forming a laminated film of a SiO ₂ / SiNx film, a SiNx film, and an Al ₂ O ₃ film, and a method of immersing in an iodine / ethanol solution after hydrofluoric acid treatment.
After measuring the dependency of the lifetime on the excess carrier density by the QSSPC method on the semiconductor substrate on which the p-type diffusion layer with the passivation film is formed, after irradiating light such as halogen light for a certain period of time, the lifetime is increased again by the QSSPC method. Measure carrier density dependence. Since the irradiation time of light depends on the substrate, it is performed until the dependence of the lifetime on the excess carrier density does not change. The amount of Fe impurities in the substrate can be examined from the lifetime before and after the light irradiation. Before light irradiation, iron exists as an Fe-B pair, but the Fe-B pair is separated by light irradiation and dissociates into iron between lattices and boron substituted for crystal lattices. The Fe-B pair and interstitial iron have different lifetimes because the energy levels in the band gap and the electron / hole capture cross sections are different. That is, the iron concentration can be quantitatively measured by comparing the lifetimes before and after the light irradiation.

Specifically, when the lifetimes before and after light irradiation when the excess carrier density is 1 × 10 ¹⁵ cm ⁻³ are τ _dark and τ _light , respectively, the iron concentration [Fe] in the substrate is expressed by the following formula (2). Can be expressed as
[Fe] = C (1 / τ _light −1 / τ _dark ) (2)
Here, C is a constant, and when the semiconductor substrate is a silicon substrate and the measurement temperature is 25 ° C., it is preferable to use a value of −1 × 10 ¹³ to −8 × 10 ¹³ μs · cm ⁻³ (www.sintonsinstruments). .Com), −3.1 × 10 ¹³ μs · cm ⁻³ .

In the semiconductor substrate having the p-type diffusion layer obtained by the manufacturing method of the present embodiment, an electrode can be separately provided on the p ⁺ -type diffusion layer. That is, according to the present embodiment, the formation of the p-type diffusion layer and the formation of the electrode can be performed separately, and the following effects are obtained.

In the conventional manufacturing method, an aluminum paste is printed on the back surface, and this is heat-treated (fired) so that the n-type diffusion layer becomes a p ⁺ -type diffusion layer and an ohmic contact is obtained. However, since the electrical conductivity of the aluminum paste is low, the sheet resistance has to be lowered, and the aluminum layer usually formed on the entire back surface must have a thickness of about 10 μm to 20 μm after heat treatment (firing). Furthermore, since the thermal expansion coefficients of silicon and aluminum differ greatly, a large internal stress is generated in the semiconductor substrate during the heat treatment (firing) and cooling, which causes warpage.

  This internal stress tends to damage the crystal grain boundaries and increase power loss. In addition, warping tends to damage cells in the transportation of solar cell elements and the connection with copper wires called tab wires in the module process. In recent years, due to the improvement of slicing technology, the thickness of the crystalline semiconductor substrate is being reduced, and the cells tend to be easily broken.

However, according to the manufacturing method of the present embodiment, after the n-type diffusion layer is converted into the p ⁺ -type diffusion layer by the specific p-type diffusion layer forming composition, an electrode is separately provided on the p ⁺ -type diffusion layer. That is, the p ⁺ type diffusion layer forming step and the ohmic contact forming step can be separated. Therefore, the material used for the back electrode is not limited to aluminum. For example, Ag (silver), Cu (copper), etc. can be applied, and the back electrode can be formed thinner than the conventional one. Further, it is not necessary to form electrodes on the entire surface, and the electrodes may be partially formed like a comb shape. Therefore, it is possible to reduce internal stress and warpage in the semiconductor substrate that are generated in the course of heat treatment (firing) and cooling.

In the above method for manufacturing a semiconductor substrate having a p-type diffusion layer, a mixed gas of phosphorus oxychloride (POCl ₃ ), nitrogen and oxygen is used to form an n-type diffusion layer on the p-type semiconductor substrate. However, the n-type diffusion layer may be formed using the n-type diffusion layer forming composition. The n-type diffusion layer forming composition contains a Group 15 element such as P (phosphorus) or Sb (antimony) as a donor element.

  Next, a method for manufacturing a semiconductor substrate having a p-type diffusion layer will be described with reference to the drawings. FIG. 1 and FIG. 2 are sectional views showing process drawings schematically showing an example of a method for manufacturing a semiconductor substrate having a p-type diffusion layer. However, this process diagram does not limit the present invention.

  FIG. 1 is a diagram for explaining an example of a manufacturing process of a double-sided light-receiving solar cell element, and will be described using a p-type semiconductor substrate 10.

  First, the p-type semiconductor substrate 10 is preferably washed with an alkaline aqueous solution. By washing with an alkaline aqueous solution, organic substances, particles and the like existing on the surface of the p-type semiconductor substrate 10 can be removed, and the passivation effect is further improved. As a method for cleaning with an alkaline aqueous solution, generally known RCA cleaning and the like can be exemplified. For example, the p-type semiconductor substrate 10 is immersed in a mixed solution of aqueous ammonia and hydrogen peroxide and treated at 60 ° C. to 80 ° C., so that organic substances and particles can be removed and washed. The cleaning time is preferably 10 seconds to 10 minutes, and more preferably 30 seconds to 5 minutes.

  Next, a texture structure (pyramid shape) (not shown in FIG. 1A) is formed on the light receiving surface (front surface) of the p-type semiconductor substrate 10 by alkali etching or the like to suppress reflection of sunlight on the light receiving surface.

Thereafter, as shown in FIG. 1B, the n-type diffusion layer forming composition 11 is applied to a part of the light-receiving surface, and heat-treated as shown in FIG. Form. As the n-type diffusion layer forming composition 11, a liquid containing phosphorus or antimony can be used. For example, a liquid described in JP 2012-084830 A may be used. The heat treatment temperature is preferably 800 ° C to 1000 ° C. There is no particular limitation as an atmosphere of the heat treatment, only nitrogen, only O _2, air composition, etc. are preferably used.

  Next, as shown in FIG. 1D, a PSG (phosphosilicate glass) layer 14 is formed using phosphorus oxychloride or the like, and then, as shown in FIG. 1E, a second n-type diffusion layer 15 is formed. Form. Thereafter, the PSG layer 14 and the heat-treated product (baked product) 12 of the n-type diffusion layer forming composition are removed by immersing in an etching solution such as hydrofluoric acid (FIG. 1 (f)).

  Next, as shown in FIG. 1G, a specific p-type diffusion layer forming composition 16 is applied to the back surface. At this time, the region to which the p-type diffusion layer forming composition is applied may be a part of the back surface or the entire surface of the semiconductor substrate.

Next, as shown in FIG. 1H, heat treatment is performed to form a p ⁺ -type diffusion layer 17. The heat treatment temperature is preferably 800 ° C to 1050 ° C. The atmosphere during boron diffusion is preferably performed in an atmosphere containing 50% by volume or less of oxygen. The diffusion atmosphere is preferably performed in a gas composition that does not inhibit the formation of the boron silicide layer.

Next, as shown in FIG. 1 (i), a heat-treated product (baked product) of the p-type diffusion layer forming composition is immersed in an aqueous solution (etching solution) such as hydrogen fluoride, ammonium fluoride, and ammonium hydrogen fluoride. ) Remove 16 '. Thereby, the p-type semiconductor substrate 10 having the p ⁺ -type diffusion layer 17 is obtained.

Next, in order to oxidize a boron silicide layer (not shown) formed on the surface of the p ⁺ -type diffusion layer 17, it is immersed in an oxidizing liquid such as a 68 mass% nitric acid aqueous solution and heat-treated at 25 ° C. to 300 ° C. Next, an aqueous solution (etching solution) of hydrogen fluoride, ammonium fluoride, and ammonium hydrogen fluoride is used to remove the oxidized boron silicide layer.

Next, as shown in FIG. 1 (j), an antireflection film 18 is formed on the light receiving surface side surface. The antireflection film is formed by applying a known technique. For example, when the antireflection film is a silicon nitride film, it is formed by a plasma CVD method using a mixed gas of SiH ₄ and NH ₃ as a raw material. At this time, hydrogen diffuses into the crystal, and orbits that do not contribute to the bonding of silicon atoms, that is, dangling bonds and hydrogen are combined to inactivate defects (hydrogen passivation).
More specifically, the mixed gas flow ratio NH ₃ / SiH ₄ is 0.05 to 1.0, the pressure in the reaction chamber is 0.1 to 2 Torr, the temperature during film formation is 300 to 550 ° C., and plasma discharge Is formed under the condition of a frequency of 100 kHz or more.

Next, as shown in FIG. 1 (k), a passivation film 19 is formed on the back surface side. The passivation film is formed by applying a known technique. For example, the passivation film may be a SiNx film similarly to the antireflection film, or a SiO ₂ film, a laminated film of a SiO ₂ film and a SiNx film, an Al ₂ O ₃ film, or the like may be used. The SiO ₂ film and SiNx film can be formed by plasma CVD, and the Al ₂ O ₃ film can be formed by atomic layer deposition.

Next, as shown in FIG. 1 (l), the surface electrode metal paste is printed, applied and dried by a screen printing method on the antireflection film on the surface (light receiving surface) to form the light receiving surface electrode 20. The metal paste for a surface electrode contains metal particles and glass particles as essential components, and includes a resin binder and other additives as necessary.
Next, the back electrode 21 is also formed on the p ⁺ -type diffusion layer on the back surface. As described above, in the present invention, the material and forming method of the back electrode are not particularly limited. For example, a back electrode paste containing a metal such as aluminum, silver, or copper may be applied and dried to form the back electrode. At this time, a silver paste for forming a silver electrode may be partially provided on the back surface for connection between cells in the module process.

  Next, as shown in FIG. 1 (m), the electrode is baked to complete a solar battery cell. When baked for several seconds to several minutes in the range of 600 to 900 ° C., the antireflection film, which is an insulating film, is melted by the glass particles contained in the electrode metal paste on the surface side, and the silicon surface is also partially melted in the paste. The metal particles (for example, silver particles) form a contact portion with the silicon substrate 10 and solidify. Thereby, the formed surface electrode and the silicon substrate are electrically connected. This is called fire-through.

The shape of the surface electrode will be described. The surface electrode includes a bus bar electrode and a finger electrode that intersects the bus bar electrode.
Such a surface electrode can be formed by means such as screen printing of the above-described metal paste, plating of the electrode material, or vapor deposition of the electrode material by electron beam heating in a high vacuum. A surface electrode composed of a bus bar electrode and a finger electrode 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 can be applied.

  FIG. 2 is a diagram for explaining an example of a manufacturing method of a back electrode type solar cell element. In FIGS. 2A to 2H, a p type diffusion layer used for a back electrode type solar cell element is shown. A manufacturing process of a semiconductor substrate having the following will be described. In FIG. 2, description will be made using the n-type semiconductor substrate 30.

  In the n-type semiconductor substrate 30 shown in FIG. 2A, a texture structure (pyramid shape) (not shown) is formed on the light receiving surface (surface) by alkali etching or the like. The texture structure suppresses the reflection of sunlight from the light receiving surface.

  After that, as shown in FIG. 2B, a specific p-type diffusion layer forming composition 31 is applied to a part of the back surface, and heat treatment is performed as shown in FIG. To do. The specific p-type diffusion layer forming composition 31 contains glass particles containing a p-type impurity and a dispersion medium. The heat treatment temperature is preferably 800 ° C to 1050 ° C. The heat treatment is performed in an atmosphere having an oxygen concentration of 3% by volume or more. Here, the region other than the application region of the p-type diffusion layer forming composition 31 is oxidized to form an oxide mask layer (not shown).

  Thereafter, the heat-treated product (baked product) 31 'of the p-type diffusion layer forming composition is removed by immersing in an etching solution such as hydrofluoric acid (FIG. 2D). The oxide mask layer is also removed at a time.

Next, as shown in FIG. 2E, a mask layer 33 for preventing diffusion is formed on the surface of the p-type diffusion layer. The mask layer 33 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).

Next, as shown in FIG. 2F, the n-type diffusion layer forming composition 34 is applied to a part of the light receiving surface and the back surface. Next, as shown in FIG. 2G, the n ⁺ -type diffusion layer 35 is formed by heat treatment. The temperature for the heat treatment is preferably 800 ° C to 1050 ° C. There is no particular limitation as an atmosphere of the heat treatment, only nitrogen, only O _2, air composition, etc. are preferably used. As an n type diffused layer formation composition, you may use the thing of Unexamined-Japanese-Patent No. 2012-084830, for example.

  Next, it is immersed in an etching solution such as hydrofluoric acid to remove the heat-treated product (baked product) 34 ′ of the n-type diffusion layer forming composition (FIG. 2 (h)). Thereby, an n-type semiconductor substrate having the p-type diffusion layer 32 is obtained.

<Method for producing solar cell element>
The method for manufacturing a solar cell element includes a step of forming an electrode on a p-type diffusion layer of a semiconductor substrate having a p-type diffusion layer obtained by the above-described manufacturing method. The method for forming the electrode is not particularly limited, and examples thereof include a method in which a metal paste for forming an electrode is applied by a screen printing method or the like and heat-treated (fired). In the semiconductor substrate having the p-type diffusion layer, an antireflection film may be formed on the light receiving surface side before the electrode is formed. An example of a method for manufacturing a solar cell element will be described below.

In the above-described method for manufacturing a semiconductor substrate having a p-type diffusion layer, a p-type semiconductor substrate is used, an n-type diffusion layer is formed on the light receiving surface side, and a p-type diffusion layer is formed on the back surface side. In this case, an antireflection film is formed on the n-type diffusion layer formed on the light receiving surface side. The antireflection film is formed by applying a known technique. For example, when the antireflection film is a silicon nitride film, it is formed by a plasma CVD 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 mixed gas flow ratio NH ₃ / SiH ₄ is 0.05 to 1.0, the reaction chamber pressure is 13.3 Pa to 266.6 Pa (0.1 Torr to 2 Torr), and the temperature during film formation is It is formed under conditions of 300 to 550 ° C. and a frequency for plasma discharge of 100 kHz or more.

  On the antireflection film of the light receiving surface, a metal paste for the light receiving surface electrode is printed by a screen printing method and dried to form the light receiving surface electrode. The metal paste for the light-receiving surface electrode includes metal particles and glass particles as essential components, and includes a resin binder, other additives, and the like as necessary.

Next, a back electrode is also formed on the p ⁺ -type diffusion layer on the back surface. As described above, in the present invention, the material and forming method of the back electrode are not particularly limited. For example, a back electrode paste containing a metal such as aluminum, silver, or copper may be applied and dried to form the back electrode. At this time, a silver paste for forming a silver electrode may be partially provided on the back surface for connection between cells in the module process.

A passivation film may be formed on the p ⁺ type diffusion layer. For example, a method of laminating an Al ₂ O ₃ layer by an ALD (atomic layer deposition) method or a thermally oxidized SiO ₂ film may be formed. At this time, it is preferable that the electrode forming portion is not formed with passivation by masking or the like, or is formed by drilling with a laser or the like after the passivation is formed on the entire surface.

  And an electrode is heat-processed (baking) and a solar cell element is completed. When heat treatment (firing) is performed at a temperature in the range of 600 ° C to 900 ° C for several seconds to several minutes, the antireflection film, which is an insulating film, is melted by the glass particles contained in the electrode metal paste on the light receiving surface side, and the silicon surface is also partially melted. Then, metal particles (for example, silver particles) in the paste form a contact portion with the semiconductor substrate and solidify. Thereby, the formed light-receiving surface electrode and the semiconductor substrate are electrically connected. This is called fire-through.

  The light receiving surface electrode is generally composed of a bus bar electrode and a finger electrode intersecting with the bus bar electrode. Such a light-receiving surface electrode can be formed by means such as screen printing of the above-described metal paste, plating of the electrode material, or vapor deposition of the electrode material by electron beam heating in a high vacuum. The bus bar electrode and the finger electrode can be formed by a known method.

Next, the manufacturing method of a solar cell element is demonstrated, referring drawings.
In FIG. 1, a method for manufacturing a point contact type solar cell element will be described. In the p-type semiconductor substrate 10 having the p ⁺ -type diffusion layer 17 shown in FIG. 1 (i), an antireflection film 18 is formed on the light receiving surface as shown in FIG. 1 (j). Examples of the antireflection film 18 include a silicon nitride film and a titanium oxide film. A surface protective film (not shown) such as silicon oxide may further exist between the antireflection film 18 and the p-type semiconductor substrate 10.

  Next, as shown in FIG. 1K, a back surface passivation layer 19 such as a thermal oxide film or a silicon nitride film is formed on the entire back surface or a partial region. When the back surface passivation layer 19 is formed on the entire back surface of the semiconductor substrate 10, the back surface passivation layer 19 corresponding to the contact portion with the electrode is partially etched, or an electrode containing glass particles having fire-through properties as described later. It is preferable to use a forming paste. In the case of etching, a compound such as ammonium fluoride can be used.

  Thereafter, as shown in FIG. 1 (l), heat treatment is performed to form the light receiving surface electrode 20 and the back surface electrode 21 as shown in FIG. 1 (m). By using a paste containing glass particles having fire-through property as the electrode forming paste, the light receiving surface electrode 20 is formed through the antireflection film 18 as shown in FIG. An ohmic contact with the diffusion layer 13 can be obtained. As described above, a solar cell element having a point contact structure can be obtained.

In FIG. 2, the example of the manufacturing method of a back surface electrode type solar cell element is demonstrated. In the n-type semiconductor substrate 30 having the p-type diffusion layer 32 shown in FIG. 2 (h), a passivation layer 36 is formed on the light receiving surface and the back surface as shown in FIG. 2 (i). Examples of the passivation layer 36 include a silicon nitride film, a titanium oxide film, aluminum oxide, and silicon oxide. The passivation layer 36 on the light-receiving surface side may be improved in the antireflection function, for example, by forming a double-layer film of silicon oxide and silicon nitride. Further, the light-receiving surface side and the back surface side passivation film 36 may be made of different materials, and the back surface passivation film 36 has the surface of the semiconductor substrate having the p-type diffusion layer 32 and the n ⁺ -type diffusion layer 35. The composition of the passivation layer may be changed depending on the surface of the semiconductor substrate.

  Thereafter, as shown in FIG. 2 (j), an electrode forming paste for the p-electrode 37 and the n-electrode 38 is applied, followed by heat treatment to form an electrode. By using a paste containing fire-through glass particles as the electrode forming paste, the p-electrode 37 and the n-electrode 38 are formed through the passivation film 36 as shown in FIG. Can be obtained. A back electrode type solar cell element can be obtained as described above.

<Solar cell element>
The solar cell element is obtained by the above-described manufacturing method. Thereby, in the solar cell element, the p-type diffusion layer is prevented from being formed in an unnecessary region of the semiconductor substrate, and the battery performance is improved.
In the solar cell element, a wiring material such as a tab wire may be disposed on the electrode, and a plurality of solar cell elements may be connected via the wiring material to constitute a solar cell module. Furthermore, the solar cell module may be configured by being sealed with a sealing material.

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

[Example 1]
(Synthesis of glass particles)
B ₂ O _3, the composition molar ratio of _SiO 2, _Al 2 _{O 3} and CaO, respectively 40 mol%, 40 mol%, so that 10 mol% and _{10mol%, B 2 O 3,} SiO 2, Al 2 O 3 and CaSO ₄ (all manufactured by Kojundo Chemical Laboratory Co., Ltd.) was weighed, mixed in an agate mortar, placed in a platinum crucible, held at 1500 ° C. for 2 hours in a glass melting furnace, and then rapidly cooled to a glass lump. Got. This was ground in an agate mortar and then ground in a planetary ball mill to obtain glass particles having a spherical particle shape, an average particle size of 0.35 μm, and a softening temperature of about 800 ° C. 10 g, 6 g, and 84 g of the glass particles, ethyl cellulose, and terpineol were mixed to form a paste to prepare a p-type diffusion layer forming composition (Composition A).

  Next, the composition A was applied to the entire surface of a mirror-shaped n-type silicon substrate (thickness: 725 μm, specific resistance: 3.1 Ωcm, sheet resistance: 200 Ω / sq.) By screen printing at 150 ° C. Dry for 1 minute. Next, the composition A was applied to the entire other surface by screen printing and dried at 150 ° C. for 1 minute.

Next, in a diffusion furnace (206A-M100, manufactured by Koyo Thermo System Co., Ltd.) flowing N ₂ : 10 L / min, a boat with a silicon substrate placed at 650 ° C. was added, and then 15 ° C. / The temperature was raised to 950 ° C. at a heating rate of min and diffusion heat treatment was performed at 950 ° C. for 30 minutes to diffuse boron into the silicon substrate to form a p-type diffusion layer. The temperature was lowered to 650 ° C. at 4 ° C./min, and the boat was taken out at 650 ° C.

  The silicon substrate after diffusion was immersed in a 5 mass% HF aqueous solution for 5 minutes, washed with ultrapure water three times, and then air-dried to obtain a silicon substrate from which the boron silicate glass layer was removed.

(Oxidation of boron silicide layer; oxidation of silicon substrate)
Next, the silicon substrate from which the boron silicate glass layer was removed was immersed in a 68% nitric acid aqueous solution. This was heated to 140 ° C. and treated for 10 minutes. Thereafter, the substrate was taken out, washed with ultrapure water three times, and then air-dried. Subsequently, it was immersed in 5 mass% HF aqueous solution for 5 minutes, washed with ultrapure water three times, and then air-dried.

(Evaluation of sheet resistance)
The sheet resistance of the coated part was measured using a low resistivity meter (Mitsubishi Chemical Corporation, Loresta MCP-T360). The sheet resistance of the coating part is 48Ω / sq. It was found that a p-type diffusion layer was formed.

(Lifetime evaluation)
An SiNx film was formed on both sides with a thickness of 80 nm using an antireflection film forming apparatus (manufactured by Shimadzu Corporation, SLCM-25). Thereafter, it was baked at 800 ° C. for 10 seconds in a tunnel type baking furnace (manufactured by Noritake Co., Ltd.). The lifetime of the silicon substrate was measured. Using a lifetime measuring device WCT-120 (manufactured by Sinton Instruments), measurement was performed by the QSSPC method (pseudo steady state photoconductivity measurement method). The lifetime at an excess carrier density of 5 × 10 ¹⁵ cm ⁻³ was 125 μs. J ₀ representing the saturation current density in the vicinity of the diffusion layer was 98 fA / cm ² . Lifetime higher, J ₀ represents low enough, the good quality of the passivation.

(Evaluation of iron content)
A halogen lamp (100 W) was irradiated for 1 minute from one side of the silicon substrate on which the SiNx film was formed. Thereafter, the lifetime measured by the QSSPC method was measured. From the lifetime when the excess carrier density is 1 × 10 ¹⁵ cm ⁻³ before and after the light irradiation, the iron content is determined using the formula (2) (C = −3.1 × 10 ¹³ μs · cm ⁻³ ). As a result of measurement, it was 2 × 10 ¹¹ atoms / cm ³ .

[Example 2]
The silicon substrate after removing the boron silicate glass layer was immersed in 30% by mass ozone-dissolved water, heated to 95 ° C. and treated for 10 minutes (boron silicide layer oxidation), as in Example 1. It was.
In the same manner as in Example 1, the lifetime after forming the SiNx film was measured by the QSSPC method. Life time is 80μs, _{J 0} was 198fA / cm ^2. The iron content was 6 × 10 ¹¹ atoms / cm ³ .

[Example 3]
The silicon substrate from which the boron silicate glass layer has been removed is immersed in an SC-1 cleaning solution mixed in a 26% by mass ammonia aqueous solution: 30% by mass H ₂ O ₂ aqueous solution: H ₂ O = 1: 1: 5 (volume ratio). This was the same as Example 1 except that this was heated to 85 ° C. and treated for 10 minutes (boron silicide layer oxidation).
In the same manner as in Example 1, the lifetime after forming the SiNx film was measured by the QSSPC method. The lifetime was 105 μs and J ₀ was 121 fA / cm ² . The iron content was 3 × 10 ¹¹ atoms / cm ³ .

[Example 4]
The silicon substrate from which the boron silicate glass layer has been removed is immersed in an SC-2 cleaning solution mixed at 37% by mass HCl aqueous solution: 30% by mass H ₂ O ₂ aqueous solution: H ₂ O = 1: 1: 5 (volume ratio). This was the same as Example 1 except that this was heated to 85 ° C. and treated for 10 minutes (boron silicide layer oxidation).
In the same manner as in Example 1, the lifetime after forming the SiNx film was measured by the QSSPC method. The lifetime was 98 μs, and J ₀ was 125 fA / cm ² . The iron content was 3 × 10 ¹¹ atoms / cm ³ .

[Example 5]
The silicon substrate after removal of the boron silicate glass layer was immersed in an SPM cleaning solution mixed in a 97% by mass sulfuric acid aqueous solution: 30% by mass H ₂ O ₂ aqueous solution: H ₂ O = 1: 1: 5 (volume ratio). The temperature was raised to 85 ° C. and treated for 10 minutes (boron silicide layer oxidation).
In the same manner as in Example 1, the lifetime after forming the SiNx film was measured by the QSSPC method. The lifetime was 96 μs and J ₀ was 95 fA / cm ² . The iron content was 4 × 10 ¹¹ atoms / cm ³ .

[Comparative Example 1]
Example 1 was performed except that the boron silicide layer was not oxidized (oxidation of the silicon substrate).
The lifetime was 47 μs, and J ₀ was 1260 fA / cm ² . Because of the J ₀ high, suggesting that passivation is not performed efficiently by the influence of the boron silicide. The iron content was as high as 5 × 10 ¹² atoms / cm ³ and the lifetime was low. Since the substrate is exposed to a high temperature of about 500 ° C. in the process of forming the antireflection film, the iron gettered in the boron silicide layer is diffused into the silicon substrate during the process, and the iron content in the silicon substrate Seems to have increased.

DESCRIPTION OF SYMBOLS 10 ... p-type semiconductor substrate (silicon substrate), 11 ... n-type diffusion layer forming composition, 12 ... Heat-treated product (baked product) of n-type diffusion layer forming composition, 13 ... First n-type diffusion layer, 14 ... PSG (phosphosilicate glass) layer, 15 ... second n-type diffusion layer, 16 ... p-type diffusion layer forming composition, 16 '... heat-treated product of p-type diffusion layer forming composition (baked product), 17 ... ^{p +} Diffusion layer, 18 ... antireflection film, 19 ... passivation film (back surface passivation layer), 20 ... light receiving surface electrode, 21 ... back electrode, 30 ... n-type semiconductor substrate, 31 ... p-type diffusion layer forming composition, 31 ' ... heat-treated product (baked product) of p-type diffusion layer forming composition, 32 ... p-type diffusion layer, 33 ... mask layer, 34 ... n-type diffusion layer forming composition, 34 '... heat treatment of n-type diffusion layer forming composition things (fired product), 35 ... ^{n +} -type diffusion layer, 36 ... passivation layer (passive Shon film), 37 ... p electrode, 38 ... n electrode.

Claims (12)

  A step of applying a p-type diffusion layer forming composition containing a compound containing an acceptor element to a semiconductor substrate; a step of forming a p-type diffusion layer by applying a thermal diffusion treatment; and a step of oxidizing the semiconductor substrate. A method for manufacturing a semiconductor substrate having a diffusion layer.   The method for manufacturing a semiconductor substrate having a diffusion layer according to claim 1, wherein the step of oxidizing the semiconductor substrate is performed by immersing the semiconductor substrate in an oxidizing chemical solution.   Furthermore, the manufacturing method of the semiconductor substrate which has a diffusion layer of Claim 1 or 2 which has an etching process.   The oxidizing chemical solution is nitric acid, ozone-dissolved water, 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, sulfuric acid and nitric acid 4. The method for producing a semiconductor substrate having a diffusion layer according to claim 2, wherein the mixed solution is at least one oxidizing chemical solution selected from a mixed solution of the above, perchloric acid, and boiling water.   The method for producing a semiconductor substrate having a diffusion layer according to claim 2 or 3, wherein the oxidizing chemical solution is an aqueous solution containing 40 mass% to 98 mass% nitric acid.   The method for manufacturing a semiconductor substrate having a diffusion layer according to claim 1, wherein the step of oxidizing the semiconductor substrate is performed at 60 ° C. to 160 ° C. 6.   The method for producing a semiconductor substrate having a diffusion layer according to claim 1, wherein the acceptor element is boron. It said compound comprising an acceptor element is boric acid, boric acid ester, B ₂ The method of manufacturing a semiconductor substrate having a diffusion layer according to any one of claims 1 to 7 comprising at least one boron compound from the O ₃ is selected.   The method for producing a semiconductor substrate having a diffusion layer according to claim 1, wherein the compound containing the acceptor element is a glass compound. The glass compound includes at least one glass component selected from Al ₂ O ₃ , SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, SrO, CaO, MgO, BeO, ZnO, and ZrO _2. A method for manufacturing a semiconductor substrate having the diffusion layer according to claim 9. It is a semiconductor substrate which has a diffusion layer obtained by the manufacturing method of the semiconductor substrate which has a diffusion layer in any one of Claims 1-10, Comprising: Iron content is 1 * 10 < ¹ > -1 * 10 < ¹² > atoms / cm. A semiconductor substrate having a diffusion layer of ³ . It is a semiconductor substrate which has a diffusion layer obtained by the manufacturing method of the semiconductor substrate which has a diffusion layer in any one of Claims 1-10, Comprising: Iron content is 1 * 10 < ¹ > -1 * 10 < ¹¹ > atoms / cm. A semiconductor substrate having a diffusion layer of ³ .

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