JP2013026579A - Manufacturing method of p-type diffusion layer and manufacturing method of solar cell element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a p-type diffusion layer and a manufacturing method of a solar cell element which are capable of forming a p-type diffusion layer in a specific part and in which characteristic deterioration caused by remaining organic substances is small.SOLUTION: When a p-type diffusion layer is formed using a p-type diffusion layer formation composition containing a glass powder including an acceptor element and a dispersion medium including an organic substance, organic components included in the dispersion medium are sufficiently removed before thermal diffusion treatment.

Description

  The present invention relates to a method for manufacturing a p-type diffusion layer of a solar cell element and a method for manufacturing a solar cell element.

The manufacturing process of the conventional silicon solar cell element is demonstrated.
First, a p-type silicon substrate having a textured structure is prepared so as to promote the light confinement effect and increase the efficiency, and subsequently, 800 ° C. to 900 ° C. in a mixed gas atmosphere of phosphorus oxychloride (POCl ₃ ), nitrogen and oxygen. An n-type diffusion layer is uniformly formed by performing several tens of minutes at a temperature.
In this conventional method, since phosphorus is diffused using a mixed gas, an n-type diffusion layer is formed not only on the surface but also on the side surface and the back surface. For this reason, the side etching process for removing the n type diffused layer of a side surface was required. Further, the n-type diffusion layer on the back surface needs to be converted into a p ⁺ -type diffusion layer. An aluminum paste is applied on the n-type diffusion layer on the back surface, and the p ⁺ -type diffusion is performed from the n-type diffusion layer by the diffusion of aluminum. Was converted into a layer.

  However, an aluminum layer formed from an aluminum paste has a low electrical conductivity, and in order to reduce sheet resistance, an aluminum layer usually formed on the entire back surface must have a thickness of about 10 μm to 20 μm after firing. Furthermore, since the thermal expansion coefficients of silicon and aluminum differ greatly, a large internal stress is generated in the silicon substrate during the firing and cooling processes, causing damage to crystal boundaries, increasing crystal defects, and warping.

In order to solve this problem, there is a method of reducing the coating amount of the paste composition and thinning the back electrode layer. However, if the application amount of the paste composition 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 layer) cannot be achieved, resulting in a problem that the characteristics of the solar cell deteriorate.

  Therefore, for example, a paste composition comprising aluminum powder, an organic vehicle, and an inorganic compound powder having a thermal expansion coefficient smaller than that of aluminum and any one of a melting temperature, a softening temperature, and a decomposition temperature higher than the melting point of aluminum. Has been proposed (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 2003-223813

However, even when the paste composition described in Patent Document 1 is used, there is a case where warpage cannot be sufficiently suppressed.
On the other hand, the present inventors have proposed a method for producing a p-type diffusion layer using a p-type diffusion layer forming composition (diffusion paste) containing the glass powder and the dispersion medium. According to this method, the above-described internal stress and warpage can be reduced.
In the method using the n-type diffusion layer forming composition, although internal stress and warpage can be suppressed, carbide may remain on the semiconductor substrate after thermal diffusion.

  Accordingly, the present invention provides a p-type in which no carbide remains on the semiconductor substrate after thermal diffusion without generating internal stress and warping of the substrate in the manufacturing process of the solar cell element using the semiconductor substrate. It is an object of the present invention to provide a method for producing a p-type diffusion layer and a method for producing a solar cell element using a p-type diffusion layer forming composition capable of forming a diffusion layer.

As a result of intensive studies, the present inventors have found that when an n-type diffusion layer forming composition containing an organic substance is used, the carbide (residue) remaining on the semiconductor substrate after thermal diffusion is melted when the organic substance is thermally diffused. It was found that the residue can be eliminated by removing the organic matter by debinding before heat diffusion. That is, the present invention is as follows.
<1> a step of forming a composition layer by applying a p-type diffusion layer forming composition containing a glass powder containing an acceptor element and a dispersion medium containing an organic substance on a semiconductor substrate;
A first heat treatment step for removing the organic matter from the composition layer;
A second heat treatment step of thermally diffusing the semiconductor substrate after the first heat treatment step;
Is a method of manufacturing a p-type diffusion layer having
<2> The method for producing a p-type diffusion layer according to <1>, wherein the treatment temperature in the first heat treatment step is in a range from 300 ° C. to the softening point of the glass powder.
<3> The method for producing a p-type diffusion layer according to <1> or <2>, wherein a treatment time in the first heat treatment step is 1 minute to 30 minutes.
<4> The p-type according to any one of <1> to <3>, wherein the acceptor element is at least one selected from B (boron), Al (aluminum), and Ga (gallium). It is a manufacturing method of a diffusion layer.
<5> The glass powder is at least one acceptor element-containing material selected from B ₂ O ₃ , Al ₂ O ₃ and Ga ₂ O ₃ , SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O. And at least one glass component material selected from BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ and MoO ₃ , <1> to <4> The method for producing a p-type diffusion layer according to any one of <4>.
<6> Solar cell element having a step of forming an electrode on the p-type diffusion layer of the semiconductor substrate having the p-type diffusion layer obtained by the manufacturing method according to any one of <1> to <5> It is a manufacturing method.

  According to the present invention, in the manufacturing process of a solar cell element using a semiconductor substrate, internal stress in the semiconductor substrate and warpage of the substrate do not occur, and no carbide remains on the semiconductor substrate after thermal diffusion. .

First, a p-type diffusion layer forming composition used in the present invention will be described, and then a p-type diffusion layer using the p-type diffusion layer forming composition and a method for producing a solar cell element will be described.
In this specification, the term “process” is not limited to an independent process, and is included in the term if the intended action of the process is achieved even when it cannot be clearly distinguished from other processes. . In the present specification, a numerical range indicated by using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively. Further, when referring to the amount of each component in the composition in the present specification, when there are a plurality of substances corresponding to each component in the composition, the plurality of the components present in the composition unless otherwise specified. It means the total amount of substance.

[P-type diffusion layer forming composition]
The p-type diffusion layer forming composition of the present invention contains at least the glass powder (hereinafter sometimes simply referred to as “glass powder”) and a dispersion medium, and further added in consideration of applicability and the like. You may contain an agent as needed.
Here, the p-type diffusion layer forming composition refers to a material that contains the glass powder and can form a p-type diffusion layer by thermally diffusing the acceptor element after being applied to a semiconductor substrate. By using the p-type diffusion layer forming composition, the p ⁺ -type diffusion layer forming step and the ohmic contact forming step can be separated, and the choice of electrode material for forming the ohmic contact is widened. spread. For example, if a low resistance material such as silver is used for the electrode, a low resistance can be achieved with a thin film thickness. Further, the electrodes need not be formed on the entire surface, and may be partially formed like a comb shape. As described above, by forming a partial shape such as a thin film or a comb shape, it is possible to reduce the internal stress generated in the semiconductor substrate and to form the p-type diffusion layer while suppressing the occurrence of the warp of the substrate. Become.

Therefore, if the p-type diffusion layer forming composition of the present invention is applied, a conventionally widely used method, that is, printing aluminum paste and firing it to make the n-type diffusion layer into a p ⁺ -type diffusion layer. At the same time, the internal stress in the substrate that occurs in the method of obtaining the ohmic contact is reduced, and the occurrence of warpage of the substrate is suppressed.
Furthermore, since the acceptor component in the glass powder is not easily volatilized even during firing, the formation of a p-type diffusion layer other than the desired region due to the generation of the volatilizing gas is suppressed.

<Glass powder>
The p-type diffusion layer forming composition of the present invention contains at least one of the glass powders.
The acceptor element contained in the glass powder is an element capable of forming a p-type diffusion layer by doping into a semiconductor substrate.
As the acceptor element, a Group 13 element can be used, and examples thereof include B (boron), Al (aluminum), and Ga (gallium).

Examples of the acceptor element-containing material used for introducing the acceptor element into the glass powder include B ₂ O ₃ , Al ₂ O _3, and Ga ₂ O ₃ , and B ₂ O ₃ , Al ₂ O _3, and Ga ₂ O. It is preferable to use at least one selected from ₃ .
The glass powder can control the melting temperature, softening point, glass transition point, chemical durability, and the like by adjusting the component ratio as necessary. Furthermore, it is preferable to contain the glass component substance described below.

Examples of the glass component substance include 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, La 2} O 3, Nb 2 O 5, Ta 2 O 5, Y 2 O 3, TiO 2, GeO 2, TeO 2 , and _Lu 2 _{O 3} and the _like, SiO _{2, K} 2 O , Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ and MoO ₃ are preferable, and a semiconductor substrate and Since no reaction product remains as a residue during hydrofluoric acid treatment, SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, C More preferred is at least one selected from dO, SnO, ZrO ₂ , and MoO ₃ .
The glass component may be a single component or a composite glass containing two or more components.

Specific examples of the glass powder include a system containing both the acceptor element-containing substance and the glass component substance, and a B ₂ O ₃ —SiO ₂ system (acceptor element-containing substance—described in the order of the glass component substance, The same applies hereinafter), B ₂ O ₃ —ZnO system, B ₂ O ₃ —PbO system, B ₂ O ₃ single system and the like containing B ₂ O ₃ as an acceptor element-containing substance; Al ₂ O ₃ —SiO ₂ system, etc. Examples include glass powders such as a system containing Al ₂ O ₃ as an acceptor element-containing substance, and a system containing Ga ₂ O ₃ as an acceptor element-containing substance such as a Ga ₂ O ₃ —SiO ₂ system.

_Further, Al ₂ O 3 _-B 2 _{O 3 system,} Ga ₂ O 3 _-B as 2 _{O 3} system or the like, may be a glass powder containing two or more acceptor element-containing material.
The glass powder is not limited to the one-component glass or the composite glass containing two components as in the above specific examples. For example, a substance having three or more components such as B ₂ O ₃ —SiO ₂ —Na ₂ O is used. The glass powder may be included.

  The content ratio of the glass component substance in the glass powder is preferably set in consideration of the melting temperature, the softening point, the glass transition point, and the chemical durability, and is generally 0.1% by mass to 95% by mass. Or less, more preferably 0.5% by mass or more and 90% by mass or less.

  The softening point of the glass powder is preferably 200 ° C. to 1000 ° C., more preferably 300 ° C. to 900 ° C., from the viewpoints of diffusibility during the diffusion treatment and dripping.

Examples of the shape of the glass powder include a substantially spherical shape, a flat shape, a block shape, a plate shape, a scale shape, and the like. It is desirable that the shape is substantially spherical, flat, or plate-like.
The glass powder preferably has a particle size of 50 μm or less. When glass powder having a particle size of 50 μm or less is used, a smooth coating film is easily obtained. Furthermore, the particle size of the glass powder is more preferably 10 μm or less. The lower limit is not particularly limited, but is preferably 0.01 μm or more.
The particle size of the glass powder represents a volume average particle size and can be measured by a laser scattering diffraction particle size distribution measuring device or the like.

The glass powder is produced by the following procedure.
First, weigh the ingredients and fill the crucible. Examples of the material for the crucible include platinum, platinum-rhodium, iridium, alumina, quartz, carbon, and the like, and are appropriately selected in consideration of the melting temperature, atmosphere, reactivity with the molten material, and the like.
Next, it heats with the temperature according to a glass composition with an electric furnace, and is set as a melt. At this time, it is desirable to stir the melt uniformly.
Subsequently, the obtained melt is poured onto a zirconia substrate, a carbon substrate or the like to vitrify the melt.
Finally, the obtained glass is pulverized to form a powder. A known method such as a jet mill, a bead mill, or a ball mill can be applied to the pulverization.

  The content ratio of the glass powder in the p-type diffusion layer forming composition is determined in consideration of applicability, acceptor element diffusibility, and the like. In general, the content ratio of the glass powder in the p-type diffusion layer forming composition is preferably 0.1% by mass or more and 95% by mass or less, more preferably 1% by mass or more and 90% by mass or less. Preferably, it is 1.5 mass% or more and 85 mass% or less, and it is especially preferable that it is 2 mass% or more and 80 mass% or less.

<Dispersion medium>
The p-type diffusion layer forming composition of the present invention contains at least one dispersion medium containing at least one organic substance.
The dispersion medium is a medium in which the glass powder is dispersed in the composition. Specifically, a binder, a solvent, or the like is employed as the dispersion medium.

  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, gelatin, Starch and starch derivatives, sodium alginate, xanthan, guar and guar 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.), butadiene Resins, styrene resins, copolymers thereof, siloxane resins, and the like can be selected as appropriate. 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.

The solvent is not particularly limited. For example, 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 Ketone solvents such as -n-hexyl ketone, diethyl ketone, dipropyl ketone, di-iso-butyl ketone, trimethylnonanone, cyclohexanone, cyclopentanone, methylcyclohexanone, 2,4-pentanedione, and acetonyl acetone;
Diethyl ether, methyl ethyl ether, methyl-n-propyl ether, di-iso-propyl ether, tetrahydrofuran, methyltetrahydrofuran, dioxane, dimethyl dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, 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, triethylene glycol methyl-n-hexyl ether, tetra Ethylene 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 diether ether, propylene glycol di-n-propyl ether, propylene glycol dibutyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol methyl ethyl ether, dipropylene 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, Ripropylene glycol methyl-n-hexyl ether, tetrapropylene glycol dimethyl ether, tetrapropylene glycol diethyl ether, tetradipropylene glycol methyl ethyl ether, tetrapropylene glycol methyl n-butyl ether, dipropylene glycol di-n-butyl ether, tetrapropylene glycol Ether solvents such as methyl-n-hexyl ether and tetrapropylene glycol di-n-butyl ether;
Methyl acetate, ethyl acetate, n-propyl acetate, i-propyl acetate, n-butyl acetate, i-butyl acetate, sec-butyl acetate, n-pentyl acetate, sec-pentyl acetate, 3-methoxybutyl acetate, methyl pentyl acetate , 2-ethylbutyl acetate, 2-ethylhexyl acetate, 2- (2-butoxyethoxy) ethyl acetate, benzyl acetate, cyclohexyl acetate, methyl cyclohexyl acetate, nonyl acetate, methyl acetoacetate, ethyl acetoacetate, diethylene glycol methyl ether acetate, diethylene glycol acetate Monoethyl ether, dipropylene glycol methyl ether acetate, dipropylene glycol ethyl ether acetate, glycol diacetate, methoxytriglycol acetate, ethyl propionate, n-butyl propionate, i-a propionate , Diethyl oxalate, di-n-butyl oxalate, methyl lactate, ethyl lactate, n-butyl lactate, n-amyl lactate, ethylene glycol methyl ether propionate, ethylene glycol ethyl ether propionate, ethylene glycol methyl ether Ester solvents such as acetate, ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, propylene glycol propyl ether acetate, γ-butyrolactone, γ-valerolactone;
Acetonitrile, N-methylpyrrolidinone, N-ethylpyrrolidinone, N-propylpyrrolidinone, N-butylpyrrolidinone, N-hexylpyrrolidinone, N-cyclohexylpyrrolidinone, N, N-dimethylformamide, N, N-dimethylacetamide, N, N- Aprotic polar solvents such as dimethyl sulfoxide;
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, ethyl Glycol, 1,2-propylene glycol, 1,3-butylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, an alcohol solvent such as 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- glycol monoether solvents such as n-butyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether;
terpene solvents such as α-terpinene, α-terpineol, myrcene, alloocimene, limonene, dipentene, α-pinene, β-pinene, terpineol, carvone, osimene, ferrandolene;
water,
Etc. These are used singly or in combination of two or more.

  The configuration and content ratio of the dispersion medium in the p-type diffusion layer forming composition may be appropriately 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.

<Manufacturing method of p-type diffusion layer and solar cell element>
The method for producing a p-type diffusion layer according to the present invention includes a step of forming a composition layer by applying a p-type diffusion layer forming composition containing a dispersion medium containing the glass powder and an organic substance on a semiconductor substrate, and the composition A first heat treatment step for removing the organic substance from the physical layer and a second heat treatment step for subjecting the semiconductor substrate after the first heat treatment step to thermal diffusion treatment.
In the method for producing the p-type diffusion layer, since the organic substance is sufficiently removed by the first heat treatment step, the glass component contained in the p-type diffusion layer forming composition in the subsequent second heat treatment step. Even if the glass melts, a mixture of the glass component and the organic substance does not occur, and there is no possibility that the carbide derived from the organic substance remains on the substrate. In addition, by using the p-type diffusion layer forming composition, a method widely used in the past, that is, printing an aluminum paste and firing it to make the n-type diffusion layer into a p ⁺ -type diffusion layer simultaneously. The generation of internal stress in the substrate and the warpage of the substrate that are likely to occur in the method of obtaining the ohmic contact is suppressed.
Below, the manufacturing method of the p-type diffused layer and solar cell element of this invention is demonstrated.

First, an alkaline solution is applied to a p-type silicon substrate that is a semiconductor substrate to remove the damaged layer, and a texture structure is obtained by etching.
Specifically, the damaged layer on the semiconductor surface generated when slicing from the ingot is removed with 20% by mass caustic soda. 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. In the solar cell element, by forming a texture structure on the light receiving surface (surface) side, a light confinement effect is promoted, and high efficiency is achieved.

Next, several tens of minutes are performed at 800 ° C. to 900 ° C. in a mixed gas atmosphere of phosphorus oxychloride (POCl ₃ ), nitrogen, and oxygen to uniformly form an n-type diffusion layer. At this time, in the method using the phosphorus oxychloride atmosphere, the diffusion of phosphorus extends to the side surface and the back surface, and the n-type diffusion layer is formed not only on the surface but also on the side surface and the back surface. Therefore, side etching is performed to remove the n-type diffusion layer on the side surface.

Then, the p-type diffusion layer forming composition is applied on the n-type diffusion layer on the back surface of the semiconductor substrate, that is, the surface that is not the light receiving surface. In the present invention, the coating method is not limited, and examples thereof include a printing method, a spin method, a brush coating, a spray method, a doctor blade method, a roll coater method, and an ink jet method.
Is not particularly limited as coating amount of the p-type diffusion layer forming composition, for example, the glass powder content as can be ^{0.01g / m 2 ~100g / m 2} , 0.1g / m 2 ~ it is preferably 10 g / ^{m 2.}

In the manufacturing method of the p-type diffusion layer, in order to volatilize the solvent contained in the composition after application of the p-type diffusion layer forming composition, depending on the composition of the p-type diffusion layer forming composition to be used. The drying process may be performed using a hot plate or a dryer.
The treatment conditions in the drying treatment depend on the solvent composition of the p-type diffusion layer forming composition and are not particularly limited. For example, the drying temperature is preferably about 80 to 300 ° C. The treatment time is preferably about 1 to 10 minutes when a hot plate is used, and about 10 to 30 minutes when a dryer or the like is used.

In the method for producing the p-type diffusion layer, the p-type diffusion layer forming composition is applied to the semiconductor substrate coated with the p-type diffusion layer forming composition before the second heat treatment (thermal diffusion treatment) step described later. A first heat treatment (debinder treatment) step for removing organic components such as an organic binder in the dispersion medium contained in the product is performed. Thereby, it can prevent that the carbide | carbonized_material derived from the said organic substance component remains on a semiconductor substrate after the 2nd heat processing process mentioned later. This is considered as follows.
That is, when an organic binder is used as a dispersion medium in the p-type diffusion layer forming composition, the organic binder is usually baked during the thermal diffusion process for forming the p-type diffusion layer, but almost disappears. A part of the organic component is softened by heat treatment during diffusion and taken into the molten glass to form a mixed organic material. This mixed organic material cannot be removed in any of the heat treatments, and remains on the semiconductor substrate as a carbide. It is thought that the residue of the carbide derived from the organic component causes a bad influence on the characteristics of the solar cell element. On the other hand, by carrying out the first heat treatment step before the second heat treatment (thermal diffusion treatment) step, organic components such as the binder can be reliably removed, and carbide on the semiconductor substrate. The generation of a residue is suppressed. Therefore, even if the p-type diffusion layer forming composition contains an organic binder as a dispersion medium, it is possible to prevent the deterioration of the characteristics of the solar cell element due to the carbide residue.

Examples of the organic component removal method in the first heat treatment step include a method in which heating and baking are performed in an atmosphere containing oxygen gas or in flowing oxygen-containing gas (for example, flowing air).
During the heating and baking, the processing temperature (hereinafter referred to as the heating temperature) is preferably in the range from 300 ° C. to the softening point of the glass powder, and the organic matter can be reliably removed and the heat damage to the wafer substrate is reduced. From the viewpoint of suppression, the temperature is more preferably 300 ° C to 700 ° C, and further preferably 300 ° C to 500 ° C. When the heating temperature is 300 ° C. or higher, the organic component can be sufficiently removed. When the heating temperature is equal to or lower than the softening point of the glass powder, the organic component is taken into the molten glass to form a mixed organic material. There is no fear.

What is necessary is just to set suitably the processing time in the said heating and baking in the range from which the removal effect of the said organic-component is acquired, and it is preferable to set it as 1-30 minutes from a viewpoint of shortening of process time, for example, 1 minute-15 More preferably, the time is 1 minute to 10 minutes. However, the same effect can be obtained in 30 minutes or more.
The treatment conditions in the heating and baking are preferably 300 ° C. to 700 ° C. for 1 minute to 20 minutes, more preferably 400 ° C. to 600 ° C. for 1 minute to 10 minutes, and 450 ° C. to 550 ° C. More preferably, it is 3 minutes to 5 minutes.
In the first heat treatment step, any conventionally known continuous furnace, batch furnace, or the like can be used. Examples thereof include an electric furnace “ACCURON CQ-1200” manufactured by Kokusai Denki.

Subsequently, a second heat treatment step for performing thermal diffusion is performed on the semiconductor substrate coated with the p-type diffusion layer forming composition.
The treatment temperature in the second heat treatment step is, for example, in the range of 600 ° C to 1200 ° C, and preferably in the range of 800 ° C to 950 ° C. By the second heat treatment step, the acceptor element diffuses into the semiconductor substrate, and a p-type diffusion layer is formed.
In the second heat treatment step, a known continuous furnace, batch furnace or the like can be applied. Further, the furnace atmosphere in the second heat treatment step can be appropriately adjusted to air, oxygen, nitrogen or the like. Among these, an oxygen atmosphere is preferable. In this case, the oxygen concentration in the furnace is preferably less than 5% by volume.
The treatment time in the second heat treatment step can be appropriately selected according to the content of the acceptor element contained in the p-type diffusion layer forming composition. For example, it may be 1 minute to 60 minutes, and more preferably 2 minutes to 30 minutes. When the treatment temperature is 600 ° C. or higher, the acceptor element is sufficiently diffused and a sufficient BSF effect is obtained. It can suppress that a board | substrate deteriorates that it is 1200 degrees C or less.
Since a glass layer is formed on the surface of the formed p-type diffusion layer, the glass is removed by etching. As the etching, a known method such as a method of immersing in an acid such as hydrofluoric acid or a method of immersing in an alkali such as caustic soda can be applied.
At this time, if a carbide residue derived from the organic component is present on the semiconductor substrate, the carbide residue does not melt in hydrofluoric acid and remains on the semiconductor substrate. On the other hand, by performing the first heat treatment step described above, the organic component is taken into the glass melted at the time of thermal diffusion to form a mixed organic material, and this mixed organic material may remain on the semiconductor substrate. Disappears.

Further, in the conventional manufacturing method, an aluminum paste is printed on the back surface, and this is baked to change the n-type diffusion layer into a p + type diffusion layer, and at the same time, an ohmic contact is obtained. However, since the electrical conductivity of the aluminum paste is low, the sheet resistance must 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 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 firing and cooling process, causing warping.
This internal stress has a problem that the crystal grain boundary is damaged and the power loss increases. In addition, the warp easily damages the cell in the transportation of the solar cell element in the module process and the connection with a copper wire called a tab wire. In recent years, the thickness of the semiconductor substrate is being reduced due to the improvement of the slicing technique, and the cells tend to be easily broken.

On the other hand, according to the manufacturing method of the present invention, after the n-type diffusion layer is converted into the p ⁺ -type diffusion layer by the p-type diffusion layer forming composition, an electrode is separately formed on the p ⁺ -type diffusion layer. Provide. Therefore, the material used for the back electrode is not limited to aluminum. For example, Ag (silver) or Cu (copper) can be applied, and the thickness of the back electrode can be made thinner than the conventional one. Further, it is not necessary to form the entire surface. Therefore, it is possible to reduce internal stress and warpage in the semiconductor substrate that are generated during the firing and cooling processes.

Then, an antireflection film is formed on the n-type diffusion layer. 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 (0.1 Torr) to 266.6 Pa (2 Torr), It is formed under conditions where the temperature is 300 ° C. to 550 ° C. and the frequency for plasma discharge is 100 kHz or more.

  On the antireflection film on the surface (light receiving surface), the surface electrode metal paste is printed, applied and dried by a screen printing method to form a surface electrode. The metal paste for a surface electrode contains metal particles and glass particles as essential components, and contains an organic binder and other additives 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.

  The electrode is fired to complete the solar cell element. When firing for several seconds to several minutes in the range of 600 ° C. 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 semiconductor surface is also partially melted to form a paste. The metal particles (for example, silver particles) inside form a contact portion with the semiconductor substrate and solidify. Thereby, the formed surface electrode and the semiconductor substrate are electrically connected. This is called fire-through.

The surface electrode includes a bus bar electrode and a finger electrode that intersects the bus bar electrode.
The surface electrode can be formed by means such as screen printing of the above-described metal paste, plating of an electrode material, or vapor deposition of an electrode material by electron beam heating in a high vacuum. As the surface electrode, an 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. The bus bar electrodes and finger electrodes on the light receiving surface side can be formed by known means.

In the above-described method for manufacturing a p-type diffusion layer and a solar cell element, a mixed gas of phosphorus oxychloride (POCl ₃ ), nitrogen and oxygen is used to form an n-type diffusion layer on a p-type silicon substrate that is a semiconductor substrate. However, an n-type layer may be formed using an 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.
In the method using the n-type diffusion layer forming composition for forming the n-type diffusion layer, first, the n-type diffusion layer forming composition is applied to the light receiving surface which is the surface of the p-type semiconductor substrate, and the p-type of the present invention is applied to the back surface. The diffusion layer forming composition is applied and heat-treated at 600 ° C to 1200 ° C. By this heat treatment, the donor element diffuses into the p-type silicon substrate on the front surface to form an n-type diffusion layer, and the acceptor element diffuses on the back surface to form a p ⁺ -type diffusion layer. Except for this step, a solar cell element is produced by the same steps as those described above.

  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 were reagents. “%” Means “% by mass” unless otherwise specified.

[Example 1]
9 g of B ₂ O ₃ —SiO ₂ —RO (R: Mg, Ca, Sr, Ba) glass powder (trade name: TMX-603, manufactured by Toago Material Technology Co., Ltd., softening point: 785 ° C.) 1.4 g of ethyl cellulose and 19.6 g of terpineol were mixed using an automatic mortar kneader to make a paste, thereby preparing a p-type diffusion layer forming composition.
Next, the prepared p-type diffusion layer forming composition is applied to the surface of a p-type silicon substrate having an n-type diffusion layer formed on the surface by screen printing, and dried on a hot plate at 150 ° C. for 5 minutes to obtain a thickness. A layer of about 15 μm was formed.
Subsequently, as the first heat treatment step, the p-type diffusion layer forming composition is heated in an oxygen atmosphere (oxygen concentration 20 vol%, flow rate 0.34 cm / sec) in an electric furnace set at 450 ° C. for 10 minutes. The binder component contained in was sufficiently removed.
Then, as a second heat treatment step, thermal diffusion treatment was performed for 30 minutes in a diffusion electric furnace set at 950 ° C., and then the substrate was immersed in hydrofluoric acid for 5 minutes to remove the glass layer, and washed with running water. . Thereafter, drying was performed.

When the sheet resistance of the surface of the semiconductor substrate on which the p-type diffusion layer is formed is coated with the p-type diffusion layer forming composition, the sheet resistance is 60Ω / □, and B (boron) diffuses to form p-type. A diffusion layer was formed.
The sheet resistance was measured by a four-probe method using a Loresta-EP MCP-T360 type low resistivity meter manufactured by Mitsubishi Chemical Corporation.
Moreover, when the surface of the side which apply | coated the said p-type diffused layer formation composition was observed visually and by SEM and the presence or absence of a residue was examined, the residue of the carbide | carbonized_material was not seen on the said semiconductor substrate. The SEM (scanning electron microscope) used was Philips XL30 manufactured by Philips.

[Example 2]
The p-type diffusion layer was formed in the same manner as in Example 1 except that the heating condition for removing the binder in the first heat treatment step was changed to a temperature of 600 ° C. for 1.5 minutes.
And when the sheet resistance of the surface of the obtained semiconductor substrate on the p-type diffusion layer forming composition application surface side was measured, it was 64Ω / □, and B (boron) was diffused to form a p-type diffusion layer. It was. Further, no carbide residue was found on the semiconductor substrate.

[Comparative Example 1]
The n-type diffusion layer was formed in the same manner as in Example 2 except that the heating temperature in the first heat treatment step was changed to 800 ° C. The heating temperature in the second heat treatment step was 950 ° C. as in Example 1.
After the first heat treatment step at the heating temperature (800 ° C.), the glass contained as the p-type diffusion layer forming composition component was already melted.

The sheet resistance of the surface of the obtained semiconductor substrate on the p-type diffusion layer forming composition application surface side was 66Ω / □, B (boron) diffused, and a p-type diffusion layer was formed.
However, a black carbide residue derived from the binder component that could not be removed was found on the semiconductor substrate. The carbide residue was not removed even by washing with running water.

[Comparative Example 2]
The p-type diffusion layer was formed in the same manner as in Example 1 except that the heating conditions for desorbing the binder in the first heat treatment step were changed to a temperature of 200 ° C. for 10 minutes.
After the treatment (first heat treatment step) under the heating conditions (temperature of 200 ° C. for 10 minutes), the coated surface of the p-type diffusion layer forming composition is brown and the binder is not completely removed. It was.
The sheet resistance of the surface of the obtained semiconductor substrate on the p-type diffusion layer forming composition application surface side was 60Ω / □, B (boron) diffused, and a p-type diffusion layer was formed.
However, a black carbide residue derived from the binder component that could not be removed was found on the semiconductor substrate. The carbide residue was not removed even by washing with running water.

Claims (6)

Providing a p-type diffusion layer forming composition containing a glass powder containing an acceptor element and a dispersion medium containing an organic substance on a semiconductor substrate to form a composition layer;
A first heat treatment step for removing the organic matter from the composition layer;
A second heat treatment step of thermally diffusing the semiconductor substrate after the first heat treatment step;
The manufacturing method of the p-type diffused layer which has this.   The method for producing a p-type diffusion layer according to claim 1, wherein the treatment temperature in the first heat treatment step is in a range from 300 ° C. to the softening point of the glass powder.   The method for producing a p-type diffusion layer according to claim 1 or 2, wherein a treatment time in the first heat treatment step is 1 minute to 30 minutes.   4. The p-type diffusion layer according to claim 1, wherein the acceptor element is at least one selected from B (boron), Al (aluminum), and Ga (gallium). 5. Production method. The glass powder includes at least one acceptor element-containing material selected from B ₂ O ₃ , Al ₂ O ₃ and Ga ₂ O ₃ , SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, And at least one glass component material selected from SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ and MoO _3. The manufacturing method of the p-type diffusion layer of any one of these.   The manufacturing method of the solar cell element which has the process of forming an electrode on the said p-type diffusion layer of the semiconductor substrate which has the p-type diffusion layer obtained by the manufacturing method of any one of Claims 1-5. .