JP2013026578A - Manufacturing method of n-type diffusion layer and manufacturing method of solar cell element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an n-type diffusion layer and a manufacturing method of a solar cell element which are capable of forming an n-type diffusion layer in a specific part and in which characteristic deterioration caused by remaining organic substances is small.SOLUTION: When an n-type diffusion layer 12 is formed using an n-type diffusion layer formation composition 11 containing a glass powder including a donor 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 an n-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 will be described.
First, a p-type silicon substrate having a textured structure formed on the light receiving surface is prepared so as to promote the light confinement effect, and then a donor element-containing compound such as phosphorus oxychloride (POCl ₃ ), nitrogen, oxygen The n-type diffusion layer is uniformly formed by performing several tens of minutes at 800 to 900 ° C. in the mixed gas atmosphere. In this conventional method, since phosphorus is diffused using a mixed gas, n-type diffusion layers are formed not only on the surface but also on the side surface and the back surface. Therefore, a side etching process for removing the side n-type diffusion layer is necessary. 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.

On the other hand, in the semiconductor manufacturing field, by applying a solution containing a phosphate such as phosphorus pentoxide (P ₂ O ₅ ) or ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) as a donor element-containing compound. A method for forming an n-type diffusion layer has been proposed (see, for example, Patent Document 1). In addition, for forming a diffusion layer, a technique is also known in which a paste containing phosphorus as a donor element is applied as a diffusion source on the surface of a semiconductor substrate and thermally diffused to form a diffusion layer (see, for example, Patent Document 2). ). However, in these methods, since the donor element or a compound containing the same is scattered from the solution or paste as the diffusion source, the diffusion of phosphorus is caused by the side surface and the diffusion during the formation of the diffusion layer as in the gas phase reaction method using the mixed gas. An n-type diffusion layer is also formed on the back surface and in addition to the applied portion.

JP 2002-75894 A Japanese Patent No. 4073968

  As described above, in forming a n-type diffusion layer, in the gas phase reaction using phosphorus oxychloride, not only one side (usually the light receiving surface or the surface) that originally requires the n-type diffusion layer but also the other side An n-type diffusion layer is also formed on the surface (non-light-receiving surface or back surface) and side surfaces. In addition, even in a method in which a solution containing a compound containing phosphorus or a paste is applied and thermally diffused, an n-type diffusion layer is formed in addition to the surface as in the gas phase reaction method. Therefore, in order to have a pn junction structure as an element, it is necessary to perform etching on the side surface and convert the n-type diffusion layer to the p-type diffusion layer on the back surface. In general, an aluminum paste which is a Group 13 element is applied to the back surface and fired to convert the n-type diffusion layer into a p-type diffusion layer. Further, in the conventionally known method of applying a paste containing a donor element such as phosphorus as a diffusion source, the compound having the donor element is volatilized and gas is diffused and diffused in a region other than the region where diffusion is required. In particular, it is difficult to form a diffusion layer in a specific region.

On the other hand, the present inventors have proposed a method for producing an n-type diffusion layer using an n-type diffusion layer forming composition (diffusion paste) containing a glass powder containing a donor element and a dispersion medium. According to this method, the diffusion of the donor element to the side surface and the back surface as described above can be suppressed.
In the method using the n-type diffusion layer forming composition, although it is possible to suppress the diffusion of phosphorus to the side surface and the back surface of the substrate, carbides may remain on the semiconductor substrate after thermal diffusion.

  Therefore, the present invention can form an n-type diffusion layer in a specific portion without forming an unnecessary n-type diffusion layer, and there is no carbide remaining on the semiconductor substrate after thermal diffusion. It is an object to provide a method for manufacturing a diffusion layer and a method for manufacturing a solar cell element.

  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 providing an n-type diffusion layer forming composition containing a glass powder containing a donor 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;
It is a manufacturing method of the n type diffused layer which has this.
<2> The method for producing an n-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 an n-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 method for producing an n-type diffusion layer according to any one of <1> to <3>, wherein the donor element is at least one selected from P (phosphorus) and Sb (antimony). is there.
<5> The glass powder is at least one donor element-containing material selected from P ₂ O ₃ , P ₂ O ₅ and Sb 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 , The method for producing an n-type diffusion layer according to any one of <1> to <4>.
<6> A solar cell including a step of forming an electrode on the n-type diffusion layer of the semiconductor substrate having the n-type diffusion layer obtained by the manufacturing method according to any one of <1> to <5>. It is a manufacturing method of an element.

  According to the present invention, it is possible to form an n-type diffusion layer in a specific portion without forming an unnecessary n-type diffusion layer, and there is no remaining carbide on the semiconductor substrate after thermal diffusion. .

It is sectional drawing which shows notionally an example of the manufacturing process of the solar cell element of this invention. (A) is the top view which looked at the solar cell element from the surface, (B) is the perspective view which expands and shows a part of (A).

First, an n-type diffusion layer forming composition used in the present invention will be described, and then an n-type diffusion layer using the n-type diffusion layer forming composition and a method for manufacturing 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. . Further, in the present specification, “to” indicates a range including numerical values described before and after that as a minimum value and a 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.

[N-type diffusion layer forming composition]
The n-type diffusion layer forming composition of the present invention contains a glass powder containing at least a donor element (hereinafter sometimes simply referred to as “glass powder”) and a dispersion medium, and further considers coating properties and the like. Other additives may be contained as necessary.
Here, the n-type diffusion layer forming composition refers to a material that contains the glass powder and can form an n-type diffusion layer by thermally diffusing this donor element after being applied to a semiconductor substrate. By using the composition for forming an n-type diffusion layer containing the glass powder, an n-type diffusion layer is formed at a desired site, and an unnecessary n-type diffusion layer is not formed on the back surface or side surface.

Therefore, if the n-type diffusion layer forming composition of the present invention is applied, the side etching step that is essential in the conventional gas phase reaction method is not required, and the process is simplified. In addition, the step of converting the n-type diffusion layer formed on the back surface into the p ⁺ -type diffusion layer is not necessary. Therefore, the method for forming the p ⁺ -type diffusion layer on the back surface and the material, shape, and thickness of the back electrode are not limited, and the choice of manufacturing method, material, and shape to be applied is widened. Moreover, although mentioned later for details, generation | occurrence | production of the internal stress in the semiconductor substrate resulting from the thickness of a back surface electrode is suppressed, and the curvature of a semiconductor substrate is also suppressed.

  In addition, the glass powder contained in the n type diffused layer formation composition of this invention fuse | melts by baking, and forms a glass layer on an n type diffused layer. However, a glass layer is formed on the n-type diffusion layer even in the conventional gas phase reaction method and the method of applying a phosphate-containing solution or paste, and thus the glass layer produced in the present invention is Similar to the method, it can be removed by etching. Therefore, the n-type diffusion layer forming composition of the present invention does not generate unnecessary products and does not increase the number of steps as compared with the conventional method.

In addition, since the donor component in the glass powder is difficult to volatilize even during firing, it is suppressed that the n-type diffusion layer is formed not only on the surface but also on the back surface and side surfaces due to the generation of the volatilizing gas.
The reason for this is considered that the donor component is bonded to an element in the glass powder or is taken into the glass, so that it is difficult to volatilize.

  Thus, since the n-type diffusion layer forming composition of the present invention can form an n-type diffusion layer having a desired concentration at a desired site, a selective region having a high n-type dopant concentration is formed. It becomes possible to form. On the other hand, it is generally difficult to form a selective region having a high n-type dopant concentration by a gas phase reaction method, which is a general method of an n-type diffusion layer, or a method using a phosphate-containing solution. .

<Glass powder>
The n-type diffusion layer forming composition contains at least one of the glass powders.
The donor element contained in the glass powder is an element that can form an n-type diffusion layer by doping into a semiconductor substrate. As the donor element, a Group 15 element can be used, and examples thereof include P (phosphorus), Sb (antimony), Bi (bismuth), As (arsenic), and the like. From the viewpoints of safety, ease of vitrification, etc., P or Sb is preferred.

Examples of the donor element-containing material used for introducing the donor element into the glass powder include P ₂ O ₃ , P ₂ O ₅ , Sb ₂ O ₃ , Bi ₂ O ₃ and As ₂ O ₃ , and P ₂ O ₃ It is preferable to use at least one selected from P ₂ O ₅ and Sb ₂ O ₃ .

Moreover, the glass powder containing a donor element can control a melting temperature, a softening point, a glass transition point, chemical durability, etc. by adjusting a component ratio as needed. Furthermore, it is preferable to contain the glass component substance described below.
Examples of the glass component material 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 , and 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 . Among them, at least selected from 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. One type is preferable, and a reaction product with the semiconductor substrate does not remain as a residue at the time of hydrofluoric acid treatment. Therefore, SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, At least one selected from PbO, CdO, SnO, ZrO ₂ , and MoO ₃ is more preferable.

Specific examples of the glass powder include a system containing both the donor element-containing substance and the glass component substance, and a P ₂ O ₅ —SiO ₂ system (described in the order of donor element-containing substance-glass component substance, hereinafter the _{same), P 2 O 5 -K 2} O _based, P ₂ O 5 -Na _{2 O-based,} P ₂ O 5 -Li ₂ O _system, P ₂ O 5 _-BaO-based, P ₂ O 5 -SrO system, P ₂ O _{5 -CaO-based,} P ₂ O 5 _-MgO-based, P ₂ O 5 -BeO _based, P ₂ O 5 _-ZnO-based, P ₂ O 5 -PbO _based, P ₂ O 5 -CdO system, _{P 2} O _{5 -SnO-based,} P ₂ O 5 -GeO _{2 system,} P ₂ O 5 -TeO ₂ system such as a donor element-containing material as a system containing _P 2 _{O 5} of the system containing _P 2 _{O 5} of the _{P 2} glass powder system containing Sb ₂ O ₃ as a donor element-containing material elevation instead of O ₅ It is.
Note that a glass powder containing two or more kinds of donor element-containing substances, such as a P ₂ O ₅ —Sb ₂ O ₃ system and a P ₂ O ₅ —As ₂ O ₃ system, may be used.
In the above has been illustrated composite glass containing two _components, P ₂ O ₅ -SiO 2 -CaO, etc., it may be a glass powder containing 3 components or more substances.

  The content ratio of the glass component substance is desirably set in consideration of the melting temperature, softening point, glass transition point, and chemical durability, and is generally 0.1% by mass or more and 95% by mass or less. It is more preferable that it is 0.5 mass% or more and 90 mass% or less.

Specifically, for example, as the glass component substance, SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, SnO, ZrO ₂ , and A glass containing at least one selected from MoO ₃ is preferable because a reaction product with the semiconductor substrate does not remain as a residue during hydrofluoric acid treatment. Moreover, in the case of glass containing vanadium oxide V ₂ O ₅ as a glass component substance (for example, P ₂ O ₅ —V ₂ O ₅ glass), V ₂ O ₅ is used from the viewpoint of lowering the melting temperature and the softening point. The content ratio is preferably 1% by mass or more and 50% by mass or less, and more preferably 3% by mass or more and 40% 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. From the viewpoint of application property to a substrate and uniform diffusibility when an n-type diffusion layer forming composition is used. It is desirable that the shape is substantially spherical, flat or plate-like. The particle size of the glass powder is desirably 100 μm or less. When glass powder having a particle size of 100 μm or less is used, a smooth coating film is easily obtained. Furthermore, the particle size of the glass powder is more desirably 50 μm or less. The lower limit is not particularly limited, but is preferably 0.01 μm or more.
Here, the particle diameter of glass represents a volume average particle diameter, and can be measured by a laser scattering diffraction method particle size distribution measuring apparatus or the like.

The glass powder is produced by the following procedure.
First, raw materials, for example, the donor element-containing material and the glass component material are weighed and filled in a 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 glass is crushed into 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 n-type diffusion layer forming composition is determined in consideration of applicability and donor element diffusibility. In general, the content ratio of the glass powder in the n-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, More preferably, it is 1.5 mass% or more and 85 mass% or less, and 2 mass% or more and 80 mass% or less are especially preferable.

<Dispersion medium>
The n-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 gua derivatives, scleroglucan and scleroglucan derivatives, tragacanth and tragacanth derivatives, dextrin and dextrin derivatives, (meth) acrylic acid resin, (meth) acrylic acid ester resin ( For example, alkyl (meth) acrylate resin, dimethylaminoethyl (meth) acrylate resin, etc.), butadiene Resins, styrene resins, copolymers thereof, Additional be appropriately selected siloxane resin. 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 Acetate, ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, propylene glycol propyl ether acetate, dipropylene glycol methyl ether acetate, dipropylene glycol ethyl ether acetate, γ-butyrolactone, γ-valerolactone, etc. Ester solvents,
Ether acetate solvents such as diethylene glycol methyl ether acetate, diethylene glycol ethyl ether acetate, diethylene glycol-n-butyl ether acetate,
Acetonitrile, 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, 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 methyl ether, ethylene glycol ethyl 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 -Glycol monoether solvents such as 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. Among these, in the case of an n-type diffusion layer forming composition, α-terpineol, diethylene glycol mono-n-butyl ether, and diethylene glycol mono-n-butyl ether are preferable, and α-terpineol, diethylene glycol mono- n-Butyl ether is preferred.
These are used singly or in combination of two or more.

The content ratio of the dispersion medium in the n-type diffusion layer forming composition may be appropriately determined in consideration of applicability and donor concentration.
The viscosity of the n-type diffusion layer forming composition is preferably 10 mPa · s or more and 1000000 mPa · s or less, and more preferably 50 mPa · s or more and 500000 mPa · s or less in consideration of applicability.

<Others>
The n-type diffusion layer forming composition may contain other additives such as a glass remover such as a metal that easily reacts with the glass powder, if necessary.

  The content ratio of the metal is desirably adjusted as appropriate depending on the type of glass and the type of the metal, and is generally preferably 0.01% by mass or more and 10% by mass or less with respect to the glass powder.

<Manufacturing method of n-type diffusion layer and solar cell element>
The method for producing an n-type diffusion layer of the present invention comprises a step of forming a composition layer by applying an n-type diffusion layer forming composition containing a glass powder containing a donor element and a dispersion medium containing an organic substance on a semiconductor substrate; And a first heat treatment step for removing the organic substance from the composition 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 n-type diffusion layer, the organic substance is sufficiently removed by the first heat treatment step. Therefore, the glass component contained in the n-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 n-type diffusion layer forming composition, it is possible to form an n-type diffusion layer at a desired site in the second heat treatment step. Furthermore, a selective region with a high n-type dopant concentration can be formed.
Below, the manufacturing method of the n type diffused layer and solar cell element of this invention is demonstrated, referring FIG. In the drawings, common constituent elements are denoted by the same reference numerals.

First, as shown in FIG. 1A, an alkaline solution is applied to a p-type silicon substrate, which is a semiconductor substrate 10, to remove a 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 (the description of the texture structure is omitted in the figure). 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.

In FIG. 1 (2), the n-type diffusion layer forming composition layer 11 is formed by applying the n-type diffusion layer forming composition to the surface of the semiconductor substrate 10, that is, the surface serving as 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 coated amount of the n-type diffusion layer forming composition, for example, be a 0.01g ^{/ m 2} ~100g ^/ m 2 as a glass powder content, 0.1 g ^/ m 2 to 10 g / M ² is preferable.

In the manufacturing method of the n-type diffusion layer, in order to volatilize the solvent contained in the composition after application of the n-type diffusion layer forming composition, depending on the composition of the n-type diffusion layer forming composition to be used. The drying step may be performed using a hot plate or a dryer.
The treatment conditions in the drying treatment may be appropriately set according to the solvent composition of the n-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 n-type diffusion layer, the n-type diffusion layer is formed on the semiconductor substrate 10 coated with the n-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 composition is performed. Thereby, it can prevent that the carbide | carbonized_material derived from the said organic component remains on the semiconductor substrate 10 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 n-type diffusion layer forming composition, the organic binder is usually baked during the thermal diffusion treatment for forming the n-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 performing 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 on the semiconductor substrate 10 Generation of carbide residue is suppressed. Therefore, even if the n-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 heat damage to the wafer substrate. From the viewpoint of suppressing the temperature, it 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.

In the production method of the present invention, the production method of the p + type diffusion layer (high concentration electric field layer) 14 on the back surface is not limited to the method by conversion from the n type diffusion layer by aluminum to the p ⁺ type diffusion layer, Either method can be adopted. For example, a method of forming the high-concentration electric field layer 14 by applying a composition 13 containing a Group 13 element such as B (boron) onto a semiconductor substrate may be used. Therefore, if this invention is used, the choice of a manufacturing method will spread.
As the composition 13 containing a Group 13 element such as B (boron), for example, a glass powder containing an acceptor element is used instead of a glass powder containing a donor element, and the same as the composition for forming an n-type diffusion layer. A p-type diffusion layer forming composition constituted as described above can be given. The acceptor element may be an element belonging to Group 13, and examples thereof include B (boron), Al (aluminum), and Ga (gallium). The glass powder containing acceptor element preferably comprises at least one selected from _{B 2 O 3, Al 2 O} 3 and _Ga 2 _{O 3.}
The method for applying the p-type diffusion layer forming composition to the back surface of the semiconductor substrate is the same as the method for applying the n-type diffusion layer forming composition on the semiconductor substrate 10 described above.
The high-concentration electric field layer 14 can be formed on the back surface by subjecting the p-type diffusion layer forming composition applied to the back surface to a heat diffusion treatment in the same manner as the heat diffusion treatment in the n-type diffusion layer forming composition described later. it can. The thermal diffusion treatment of the p-type diffusion layer forming composition is preferably performed simultaneously with the thermal diffusion treatment of the n-type diffusion layer forming composition.

Next, in FIG. 1 (3), a second heat treatment step is performed to thermally diffuse the semiconductor substrate 10 on which the n-type diffusion layer forming composition 11 is formed by applying the n-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 donor element diffuses into the semiconductor substrate 10 and the n-type diffusion layer 12 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 donor element contained in the n-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 donor 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.
The heat treatment for forming the n-type diffusion layer 12 can also be performed using a short-time heat treatment (RTP) technique.

When a glass layer (not shown) such as phosphate glass is formed on the surface of the formed n-type diffusion layer 12, this phosphate 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 10, the carbide residue does not melt in hydrofluoric acid and remains on the semiconductor substrate 10. 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.

In the method for forming an n-type diffusion layer of the present invention in which the n-type diffusion layer 12 is formed using the n-type diffusion layer forming composition shown in FIGS. 1 (2) and (3), n is formed only at a desired site. The mold diffusion layer 12 is formed, and an unnecessary n-type diffusion layer is not formed on the back surface or side surface.
Therefore, in the conventional method of forming an n-type diffusion layer by a gas phase reaction method, a side etching process for removing an unnecessary n-type diffusion layer formed on a side surface is essential. According to the manufacturing method of the invention, the side etching process is not required, and the process is simplified.

Further, in the conventional manufacturing method, it is necessary to convert the n-type diffusion layer formed on the back surface into the p-type diffusion layer. As this conversion method, aluminum which is a group 13 element is formed on the back-side n-type diffusion layer. The paste is applied and fired, and aluminum is diffused into the n-type diffusion layer to convert it into the p-type diffusion layer. In this method, the conversion to the p-type diffusion layer is sufficient, and in order to form the p ⁺ -type diffusion layer (the high-concentration electric field layer) 14, an aluminum amount of a certain amount or more is required. It was necessary to form a thick layer. However, since the thermal expansion coefficient of aluminum is significantly different from that of silicon used as a substrate, a large internal stress is generated in the semiconductor substrate during the firing and cooling process, causing the semiconductor substrate to warp. .
This internal stress has a problem that the crystal grain boundary is damaged and the power loss increases. Further, the warpage easily damages the solar cell element 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 slice processing technique, and the solar cell element tends to be easily broken.

  On the other hand, according to the manufacturing method of the present invention, since an unnecessary n-type diffusion layer is not formed on the back surface, there is no need to perform conversion from the n-type diffusion layer to the p-type diffusion layer, and the aluminum layer is thickened. The necessity to do is lost. Thereby, generation | occurrence | production and the curvature of the internal stress in a semiconductor substrate can be suppressed, As a result, it becomes possible to suppress an increase in power loss and damage to a solar cell element.

When the manufacturing method of the present invention is used, the manufacturing method of the p ⁺ -type diffusion layer (high-concentration electric field layer) 14 on the back surface is limited to a method by conversion from an n-type diffusion layer by aluminum to a p ⁺ -type diffusion layer. However, either method can be adopted, and the choice of manufacturing method is expanded.
Furthermore, as will be described later, the material used for the metal paste layer 20 for the back electrode on the back surface is not limited to Group 13 aluminum, and for example, Ag (silver) or Cu (copper) can be applied. The metal paste layer 20 can be made thinner than the conventional one.

In FIG. 1 (4), an antireflection film 16 is formed on the n-type diffusion layer 12. The antireflection film 16 is formed by applying a known technique. For example, when the antireflection film 16 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 to 550 ° C. and the frequency for plasma discharge is 100 kHz or more.

  In FIG. 1 (5), the surface electrode metal paste is printed, applied and dried by a screen printing method on the antireflection film 16 on the surface (light receiving surface) to form the surface electrode metal paste layer 18. The metal paste for a surface electrode contains metal particles and glass particles as essential components, and contains an organic binder, other additives, and the like as necessary.

  Next, a back electrode metal paste layer 20 is also formed on the high concentration electric field layer 14 on the back surface. As described above, in the present invention, the material and forming method of the back electrode metal paste layer 20 are not particularly limited. For example, the back electrode metal paste layer 20 may be formed by applying and drying a back electrode metal paste containing a metal such as aluminum, silver, or copper. At this time, a silver electrode forming silver paste layer may be provided on a part of the back surface for connection between cells in the module process.

  In FIG. 1 (6), the front electrode metal paste layer 18 and the back electrode metal paste layer 20 are fired to complete the solar cell element. When fired for several seconds to several minutes in the range of 600 to 900 ° C., the antireflection film 16 that is an insulating film is melted by the glass particles contained in the electrode metal paste on the surface side, and the surface of the semiconductor substrate 10 is also partially melted. The metal particles (for example, silver particles) in the paste form contact portions with the semiconductor substrate 10 and solidify. Thereby, the formed metal paste layer 18 for surface electrodes and the semiconductor substrate 10 are conducted. This is called fire-through.

  Here, the shape of the surface electrode metal paste layer 18 will be described. The surface electrode metal paste layer 18 includes, for example, a bus bar electrode 30 and finger electrodes 32 intersecting with the bus bar electrode 30. FIG. 2 (A) is a plan view of a solar cell element viewed from the surface, in which the surface electrode metal paste layer 18 is composed of a bus bar electrode 30 and finger electrodes 32 intersecting the bus bar electrode 30. FIG. 2B is an enlarged perspective view showing a part of FIG.

  Such a surface electrode metal paste layer 18 can be formed, for example, by means such as screen printing of the above metal paste, plating of the electrode material, or deposition of the electrode material by electron beam heating in a high vacuum. The metal paste layer 18 for the surface electrode composed of the bus bar electrode 30 and the finger electrode 32 is generally used as an electrode on the light receiving surface side and is well known, and a known means for forming the bus bar electrode and finger electrode on the light receiving surface side is used. Can be applied.

In the above description, a solar cell element in which an n-type diffusion layer is formed on the front surface, a p + -type diffusion layer is formed on the back surface, and a front electrode metal paste layer 18 and a back electrode metal paste layer 20 are further provided on each layer. However, a back contact type solar cell element can be produced by using the n-type diffusion layer forming composition of the present invention.
The back contact type solar cell element has all electrodes provided on the back surface to increase the area of the light receiving surface. That is, in the back contact type solar cell element, it is necessary to form both the n-type diffusion region and the p-type diffusion region on the back surface to form a pn junction structure. The n-type diffusion layer forming composition of the present invention can form an n-type diffusion site only at a specific site, and therefore can be suitably applied to the production of a back contact type solar cell element.

  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]
3 g of P ₂ O ₅ —SiO ₂ —CaO-based glass (P ₂ O ₅ : 50%, SiO ₂ : 43%, CaO: 7%) powder having an average particle diameter of 1 μm and a glass softening point of 700 ° C. and ethyl cellulose 2.1 g and 24.9 g of terpineol were mixed using an automatic mortar kneader to form a paste, thereby preparing an n-type diffusion layer forming composition.
Next, the prepared n-type diffusion layer forming composition was applied to the surface of the semiconductor substrate by screen printing and dried on a hot plate at 150 ° C. for 5 minutes to form a layer having a thickness of about 15 μm.
Subsequently, as the first heat treatment step, the n-type diffusion layer forming composition is heated for 10 minutes in an oxygen atmosphere (oxygen concentration 20 vol%, flow rate 0.34 cm / sec) in an electric furnace set at 450 ° C. The binder component contained in was sufficiently removed.
Then, as a second heat treatment step, a thermal diffusion treatment is performed for 10 minutes in a diffusion electric furnace set at 900 ° C., and then the substrate is immersed in hydrofluoric acid for 5 minutes to remove the glass layer, and washed with running water. went. Thereafter, drying was performed.

When the sheet resistance of the surface of the semiconductor substrate on which the n-type diffusion layer was formed was coated with the n-type diffusion layer forming composition, the sheet resistance was 35Ω / □, and P (phosphorus) diffused and the n-type diffusion layer Was found to be formed. On the other hand, the sheet resistance on the back surface was 1000000 Ω / □ or more, which was not measurable, and the n-type diffusion layer was not 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 n 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 n-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 n-type diffusion layer forming composition application surface side was measured, it was 33Ω / □, and P (phosphorus) was diffused to form an n-type diffusion layer. I understood it. The sheet resistance of the back surface was 1000000 Ω / □ or more, which was not measurable, and the n-type diffusion layer was not formed.
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 900 ° C. as in Example 1.
After the first heat treatment step at the heating temperature (800 ° C.), the glass contained as the n-type diffusion layer forming composition component was already melted.

The sheet resistance of the surface of the obtained semiconductor substrate on the n-type diffusion layer forming composition application surface side was 38Ω / □, P (phosphorus) diffused, and an n-type diffusion layer was formed. The sheet resistance of the back surface was 1000000 Ω / □ or more, which was not measurable, and the n-type diffusion layer was not 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 n-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 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 n-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 n-type diffusion layer forming composition application surface side was 35Ω / □, and P (phosphorus) diffused to form an n-type diffusion layer. The sheet resistance of the back surface was 1000000 Ω / □ or more, which was not measurable, and the n-type diffusion layer was not formed.
However, a black carbide residue derived from the binder component that could not be removed was observed on the semiconductor substrate. The carbide residue was not removed even by washing with running water.

DESCRIPTION OF SYMBOLS 10 Semiconductor substrate 12 N type diffused layer 14 High concentration electric field layer 16 Antireflection film 18 Metal paste layer 20 for surface electrodes Metal paste layer 30 for back electrodes Bus bar electrode 32 Finger electrode

Claims (6)

Applying an n-type diffusion layer forming composition containing a glass powder containing a donor 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 n type diffused layer which has this.   The method for producing an n-type diffusion layer according to claim 1, wherein a treatment temperature in the first heat treatment step is set in a range from 300 ° C to a softening point of the glass powder.   The method for producing an n-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.   The method for producing an n-type diffusion layer according to any one of claims 1 to 3, wherein the donor element is at least one selected from P (phosphorus) and Sb (antimony). The glass powder includes at least one donor element-containing material selected from P ₂ O ₃ , P ₂ O ₅ and Sb 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 n type diffused layer of any one of Claim 4.   The manufacturing method of the solar cell element which has the process of forming an electrode on the said n type diffusion layer of the semiconductor substrate which has the n type diffusion layer obtained with the manufacturing method of any one of Claims 1-5. .