JP2013026344A - Manufacturing method of n-type diffusion layer, manufacturing method of solar cell element, and solar cell element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an n-type diffusion layer capable of forming regions having different donor concentrations at a time in a relatively simple step.SOLUTION: A manufacturing method of an n-type diffusion layer comprises the steps of: forming a silicon oxide film having a patterned average thickness of 0.01 μm or higher and 2 μm or lower on a silicon substrate; forming a glass layer including a donor element on the silicon substrate on which the silicon oxide film was formed; performing thermal diffusion treatment after forming the glass layer; and removing the silicon oxide film and the glass layer after the thermal diffusion treatment.

Description

  The present invention relates to a method for manufacturing an n-type diffusion layer, a method for manufacturing a solar cell element, and a solar cell element. It relates to technology that makes it possible.

The manufacturing process of the conventional silicon solar cell element is demonstrated.
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 In this mixed gas atmosphere, several tens of minutes are performed at 800 ° C. to 900 ° C. to uniformly form the n-type diffusion layer on the substrate. 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. Also, 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, this is fired, and the n-type diffusion is performed by aluminum diffusion. The layer was converted to a p ⁺ type diffusion layer.

On the other hand, selective emitter solar cells have recently attracted attention in order to increase the photoelectric conversion efficiency. Under the light-receiving surface electrodes of a conventional silicon solar cell element described above, the high phosphorus concentration n ⁺⁺ type diffusion layer region than the light-receiving surface is provided, which efficiently collector, n ⁺⁺ type under the light-receiving surface electrode Various methods have been tried to provide a diffusion layer region.

For example, in Patent Document 1, a diffusing agent having a high donor concentration is applied to a portion where an electrode is to be formed to form a high concentration film. Subsequently, a diffusing agent having a lower donor concentration than the previously applied diffusing agent is applied to the entire light-receiving surface by spin coating, a low concentration film is formed on the high concentration film, and heat treatment is performed to diffuse the donor. The high concentration n ⁺⁺ type diffusion layer and the low concentration n ⁺⁺ type diffusion layer are formed.

Further, in Patent Document 2, a paste containing SiO ₂ and / or SiO ₂ precursor is patterned and applied on a semiconductor substrate and baked in an oxygen atmosphere to form a dopant diffusion control mask, followed by doping. Thus, a patterned diffusion layer is formed.

JP 2010-109201 A JP 2007-81300 A

In the method of Patent Document 1 described above, since the high-concentration diffusion material and the low-concentration diffusion material are in contact with each other, the high-concentration n ⁺⁺ type diffusion layer and the low-concentration n ⁺ type diffusion layer can be selectively formed. difficult. Further, if the selective emitter is formed by the method of Patent Document 2, selective doping is possible, but there is a problem that regions having different doping concentrations cannot be formed at a time.

  As described above, the present invention has been made in view of conventional problems, and provides a method for manufacturing a solar cell element capable of forming a plurality of regions having different doping concentrations at a time by a relatively simple process. Is an issue.

Means for solving the problems are as follows.
<1> forming a patterned silicon oxide film having an average thickness of 0.01 μm or more and 2 μm or less on a silicon substrate;
Forming a glass layer containing a donor element on a silicon substrate on which the silicon oxide film is formed in a pattern;
A step of performing a thermal diffusion treatment during or after the formation of the glass layer;
Removing the silicon oxide film and the glass layer after the thermal diffusion treatment;
The 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 glass layer containing the donor element is a glass layer obtained by heating after applying the n-type diffusion layer forming composition.

<3> The composition according to <2>, wherein the n-type diffusion layer forming composition contains a glass powder containing at least one donor element selected from P (phosphorus) and Sb (antimony) and a dispersion medium. A method for manufacturing an n-type diffusion layer.

<4> The method for producing an n-type diffusion layer according to <1>, wherein the glass layer containing the donor element is a glass layer formed using phosphorus oxychloride (POCl ₃ ) as a raw material.

<5> A step of forming an n-type diffusion layer on the silicon substrate by the manufacturing method according to any one of <1> to <4>, and an electrode is formed on the formed n-type diffusion layer. And a method for producing a solar cell element.

<6> A silicon substrate having an n-type diffusion layer produced by the production method according to any one of <1> to <4>,
An electrode provided on the n-type diffusion layer;
A solar cell element having

  According to the present invention, it is possible to form a plurality of regions having different donor concentrations at a time by a relatively simple process.

It is sectional drawing which shows notionally an example of the manufacturing process of the n type diffused layer 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).

  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, “to” indicates a range including the numerical values described before and after the values as a minimum value and a maximum value, respectively.

<Method for producing n-type diffusion layer>
A method for producing the n-type diffusion layer of the present invention will be described.
The method for producing an n-type diffusion layer of the present invention includes (1) a step of forming a patterned silicon oxide film having an average thickness of 0.01 μm or more and 2 μm or less on a silicon substrate, and (2) patterning the silicon oxide film. A step of forming a glass layer containing a donor element on a silicon substrate formed in a shape; (3) a step of performing a thermal diffusion process during or after the formation of the glass layer; and (4) the thermal diffusion process. And at least a step of removing the silicon oxide film and the glass layer.

In the present invention, the donor element is included in order to delay the diffusion of the donor element from the glass layer containing the donor element into the silicon substrate and form a region having a low donor concentration in the silicon substrate, that is, an n ⁺ -type diffusion layer region. A silicon oxide film having a specific thickness is interposed between the glass layer and the silicon substrate.

The manner in which the n ⁺ -type diffusion layer and the n ⁺ -type diffusion layer are formed will be described with reference to FIG.
A selective-emitter Si solar cell having an electrode on the light-receiving surface has an n ⁺⁺ type diffusion layer 5 region having a high donor (phosphorus) concentration under the electrode. In the manufacturing method of the present invention, the silicon oxide film 2 is formed in advance on the light receiving surface of the silicon substrate 10 in a region other than the region where electrodes are to be formed. At this time, the average thickness of the silicon oxide film 2 is set to 0.01 μm or more and 2 μm or less.

Thereafter, a glass layer 3 containing a donor element is formed over the entire light receiving surface using vapor phase diffusion or coating diffusion, and thermal diffusion is performed. In the region where the silicon oxide film 2 is not formed, since the glass layer 3 containing the donor element is in contact with the silicon substrate 10, the n ⁺⁺ type diffusion layer 5 in which the high concentration donor element is diffused is formed. On the other hand, in the region where the silicon oxide film 2 having an average thickness of 0.01 μm or more and 2 μm or less is formed, the donor element from the glass layer 3 existing in the upper layer first diffuses through the silicon oxide film 2 and then delays to form silicon. It diffuses into the substrate 10. Consequently, in a region where the silicon oxide film 2 is formed, a low donor concentration n ⁺ -type diffusion layer 4 is formed than n ⁺⁺ type diffusion layer 5.

Here, if the average thickness of the silicon oxide film 2 is less than 0.01 μm, a sufficient delay effect of the diffusion of the donor element cannot be obtained, and regions having different donor concentrations are hardly formed. On the other hand, if the average thickness is greater than 2 μm, the donor element is not sufficiently diffused into the silicon substrate and the n ⁺ -type diffusion layer 4 is difficult to form.

  As described above, according to the manufacturing method of the present invention, a plurality of regions having different donor concentrations can be formed by a single thermal diffusion treatment, so that thermal damage to the silicon substrate 10 is reduced. Further, since the silicon oxide film 2 on the light receiving surface and the glass layer 3 containing the donor element are removed at a time by the subsequent hydrofluoric acid treatment, the process is simple and the manufacturing cost merit is high.

  Below, the detail of the manufacturing method of the n type diffused layer of this invention is demonstrated, referring FIG. FIG. 1 is a schematic cross-sectional view conceptually showing an example of the manufacturing process of the n-type diffusion layer of the present invention. In the subsequent drawings, common constituent elements are denoted by the same reference numerals.

FIG. 1A shows a p-type semiconductor substrate as the silicon substrate 10. An alkaline solution is applied to the silicon substrate 10 to remove the damaged layer, and a texture structure is obtained by etching.
Specifically, the damaged layer on the silicon 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. 1B, a patterned silicon oxide film 2 is formed on a silicon substrate 10. The silicon oxide film 2 may be any film as long as it is formed on the silicon substrate 10 and finally removed by a chemical solution such as hydrofluoric acid. A solvent dispersion of _two fine particles or a sol-gel solution of an organic silicon compound is selected.

Examples of commercially available solvent dispersions of SiO ₂ fine particles include, for example, IPA-ST (an isopropyl alcohol dispersion containing 30% SiO ₂ fine particles having a diameter of 10 to 20 nm) manufactured by Nissan Chemical Industries, Ltd., and EAC manufactured by Nissan Chemical Industries, Ltd. -ST (ethyl acetate dispersion containing 30% of SiO ₂ fine particles having a diameter of 10 nm to 20 nm).

Examples of commercially available sol-gel solution of the organosilicon compound, Hitachi Chemical Co., Ltd. of the interlayer insulating film coating material HSG-100, and the like organic SiO ₂ based film-forming coating liquid SOG of Tokyo Ohka Kogyo Co., Ltd. Can do.

  A method for forming the silicon oxide film 2 is not particularly limited, and a conventionally known method can be appropriately applied. For example, using the solvent dispersion or sol-gel solution, a silicon oxide film precursor film is formed by a coating method such as a printing method, a spin method, a brush coating method, a spray method, a doctor blade method, a roll coater method, or an ink jet method. And a method of heating this.

  After the application, a drying process for volatilizing the solvent contained in the composition may be necessary. In this case, drying is performed at a temperature of about 80 ° C. to 300 ° C. for 1 minute to 10 minutes when a hot plate is used, and about 10 minutes to 30 minutes when a dryer or the like is used. The drying conditions depend on the solvent composition such as the solvent dispersion or sol-gel solution, and are not particularly limited to the above conditions in the present invention.

  In order to obtain a patterned silicon oxide film, for example, after masking in a pattern with a mask tape, a method of applying the solvent dispersion or sol-gel solution, a method of applying the pattern in an inkjet method, a method of screen printing , Etc.

  The average film thickness of the silicon oxide film is in the range of 0.01 μm to 2 μm, and preferably in the range of 0.1 μm to 0.5 μm. Here, the average film thickness is a value measured by a stylus type step gauge XP-1 manufactured by AMBIOS, and is an average value obtained by measuring five steps at the boundary between the silicon oxide film forming portion and the non-forming portion.

The silicon oxide film is not formed at a position where an electrode is to be formed, but is formed in a region other than that. Thus a high donor concentration n ⁺⁺ type diffusion layer region is formed directly under the electrode, it is the other portion is formed n ⁺ -type diffusion layer region, it is possible to obtain a selective emitter type solar cell element. The position and size of the non-formation region of the silicon oxide film are appropriately adjusted according to the position and size of the desired selective emitter.

In FIG. 1 (3), a glass layer 3 containing a donor element is formed on the patterned silicon oxide film 2. The method for forming the glass layer containing the donor element is not particularly limited, and a conventionally known method or the like can be appropriately employed. Examples thereof include a method of forming with a gas phase diffusion gas such as phosphorus oxychloride (POCl ₃ ) which is a donor element-containing compound, and a method of applying a solution or paste containing a donor element.

The formation method using a gas phase diffusion gas is a method of performing several tens of minutes at 800 ° C. to 900 ° C. in a mixed gas atmosphere of phosphorus oxychloride (POCl ₃ ), nitrogen, and oxygen which are donor element-containing compounds. By this method, phosphosilicate glass (PSG) is formed on the silicon substrate. During thermal diffusion, phosphorus, which is a donor element, diffuses from the PSG into the silicon substrate.

  In the gas phase reaction method using the gas phase diffusion gas, an n-type diffusion layer is formed not only on the surface but also on the side surface and the back surface. Or a side etching process for removing the n-type diffusion layer such as the side surface.

As a method for applying a solution or paste containing a donor element, for example, phosphorus pentoxide (P ₂ O ₅ ) or ammonium dihydrogen phosphate (NH 2) is used as the donor element-containing compound used in the field of semiconductor manufacturing. _And a method of applying a solution containing a phosphate such as ₄ H ₂ PO ₄ ). Moreover, the method of apply | coating the paste which contains phosphorus as a donor element is also mentioned.

  When a phosphate-containing solution or paste is applied, the donor element or its compound scatters from the diffusion source solution or paste during the thermal diffusion treatment, so the gas phase reaction using the above mixed gas Similarly to the method, phosphorus is diffused on the side surface and the back surface when the diffusion layer is formed, and an n-type diffusion layer is formed in addition to the applied portion. Accordingly, a mask or the like is applied to a region where the n-type diffusion layer is not planned to be formed, or a side etching process for removing the n-type diffusion layer such as the side surface is performed.

  Furthermore, the method of apply | coating the n type diffused layer formation composition containing the glass powder containing a donor element and a dispersion medium as shown below, and forming the glass layer containing a donor element is mentioned. When using an n-type diffusion layer forming composition containing glass powder containing a donor element, an n-type diffusion layer is selectively formed in a desired region, unlike the case of applying a phosphate-containing solution or paste. Is possible. 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.

  Liquid application such as a solution containing a donor element, a paste, and an n-type diffusion layer forming composition includes, for example, a printing method, a spin method, a brush coating, a spray method, a doctor blade method, a roll coater method, an ink jet method, and the like. Can be adopted.

The n-type diffusion layer forming composition contains a glass powder containing at least a donor element (hereinafter may be simply referred to as “glass powder”) and a dispersion medium, and in addition, other coating materials are taken into consideration. You may contain an additive as needed.
Here, the n-type diffusion layer forming composition contains a glass powder containing a donor element, and is a material capable of forming an n-type diffusion layer by thermally diffusing this donor element after being applied to a silicon substrate. Say. By using the n-type diffusion layer forming composition containing the donor element in the glass powder, a glass layer containing the donor element is formed at a desired site, and the donor element diffuses into the silicon substrate.

The glass powder containing the donor element according to the present invention will be described in detail.
A donor element is an element that can form an n-type diffusion layer by doping into a silicon 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 glass component materials 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 , Examples include MoO ₃ , MnO, La ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , Y ₂ O ₃ , TiO ₂ , ZrO ₂ , GeO ₂ , TeO _2, and Lu ₂ O _3. SiO ₂ , K _Use at least one selected from 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. preferably, 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 It is more preferable to use at least one selected from oO _3.

Specific examples of the glass powder containing a donor element include a system containing both the donor element-containing material and the glass component material, and a P ₂ O ₅ -SiO ₂ system (in order of donor element-containing material-glass component material). in described, the same applies _{hereinafter), 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-based, 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 -CdO _based, P ₂ O 5 -PbO system , including _P 2 _O 5 _-V 2 _{O 5 system,} P ₂ O 5 _-SnO-based, P ₂ O 5 -GeO _{2 system,} a _P 2 _{O 5} as a donor element-containing material of P ₂ O 5 -TeO ₂ system, etc. Instead of P ₂ O ₅ in a system containing P ₂ O ₅ , a donor element-containing material is used. And glass powder of a system containing Sb ₂ O ₃ .
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 glass powder containing two _{components, P 2 O 5 -SiO 2 -V} 2 O 5, P 2 O 5 -SiO 2 -CaO , etc., may be a glass powder containing more than three components.

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

Specifically, for example, as glass component materials, SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, SnO, ZrO ₂ , and MoO _The glass containing at least one selected from ₃ is preferable because the reaction product with the silicon substrate does not remain as a residue during the 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 the application property to the substrate and the uniform diffusibility when it is an n-type diffusion layer forming composition, It is desirable to have a substantially spherical shape, a flat shape, or a plate shape. 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 an average particle diameter, and can be measured by a laser scattering diffraction particle size distribution measuring apparatus or the like.

The glass powder containing a donor element 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, which 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 containing the donor element in the n-type diffusion layer forming composition is determined in consideration of the coating property and the diffusibility of the donor element. 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.

  The n-type diffusion layer forming composition of the present invention may contain other binder as necessary as a medium (dispersion medium) for dispersing the glass powder.

Other binders include, for example, polyvinyl alcohol, polyacrylamides, polyvinylamides, polyvinylpyrrolidone, polyethylene oxides, polysulfonic acid, acrylamide alkylsulfonic acid, cellulose ethers, cellulose derivatives, carboxymethylcellulose, hydroxyethylcellulose, ethylcellulose, gelatin Starch, 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.), pig Ene resins, styrene resins, copolymers thereof, Additional be appropriately selected siloxane resin.
These are used singly or in combination of two or more.

The weight average molecular weight of the other binder is not particularly limited, and it is desirable to adjust appropriately in view of the desired viscosity as the composition.
The weight average molecular weight is preferably from 5,000 to 500,000, more preferably from 10,000 to 200,000, and most preferably from 20,000 to 100,000, from the viewpoints of solubility in a solvent and handleability of the dissolved product.

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

The content ratio of the solvent in the n-type diffusion layer forming composition is 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, more preferably 50 mPa · S or more and 500000 mPa · S or less in consideration of applicability.
The viscosity can be measured at 25 ° C. and 5 rpm using, for example, an E-type viscometer.

In FIG. 1 (4), thermal diffusion treatment is performed during or after the formation of the glass layer 3. By this thermal diffusion treatment, as shown in the figure, the donor element is diffused at a high concentration at the portion where the glass layer 3 containing the donor element is in contact with the silicon substrate 10, so that a region having a high donor concentration, that is, an n ⁺⁺ type diffusion layer. 5 is formed. On the other hand, at the location where the silicon oxide film 2 exists, the diffusion of the donor element from the glass layer 3 containing the donor element is delayed by the presence of the silicon oxide film 2, and as a result, the donor substrate has a low concentration region, that is, n ^+. A mold diffusion layer 4 is formed.

  The thermal diffusion treatment is preferably performed at 600 ° C to 1200 ° C. A known continuous furnace, batch furnace, or the like can be applied to the thermal diffusion treatment. Further, the furnace atmosphere during the thermal diffusion treatment can be appropriately adjusted to air, oxygen, nitrogen or the like.

  The thermal diffusion treatment time 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.

  Subsequently, as shown in FIG. 1 (5), after the thermal diffusion treatment, the silicon oxide film 2 and the glass layer 3 containing the donor element are removed by etching or the like. 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.

As described above, according to the method for manufacturing an n-type diffusion layer of the present invention, a plurality of regions having different doping concentrations can be formed at a time. The method of the present invention is simpler than the conventional method of patterning a silicon oxide film for each region having a different doping concentration and removing the silicon oxide film by etching.
In addition, when the silicon substrate having a plurality of n-type diffusion layer regions having different doping concentrations obtained by the method of the present invention has a small number of etchings of the silicon oxide film, it is less damaged by etching and is used for a solar cell element Therefore, the efficiency can be improved.

<Method for producing solar cell element>
The manufacturing method of the solar cell element of this invention is demonstrated.
The manufacturing method of the solar cell element of this invention has at least the process of forming an n-type diffused layer on a silicon substrate by said method, and the process of forming an electrode on the formed n-type diffused layer. As described below, the electrode may be formed after the antireflection film 16 (see FIG. 2) is formed on the n-type diffusion layer.

In the case where the surface of the silicon substrate 10 on which the n ⁺ type diffusion layer is formed is used as the light receiving surface, an antireflection film is formed on the surface of the surface of 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 orbits that do not contribute to the bonding of silicon atoms, that is, dangling bonds and hydrogen are combined to inactivate defects (hydrogen passivation).
More specifically, the mixed gas flow rate 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.

Next, the surface electrode metal paste is printed, applied, and dried on the light-receiving surface antireflection film by a screen printing method to form a surface electrode on the region of the n ⁺⁺ type diffusion layer. The metal paste for a surface electrode contains (1) metal particles and (2) glass particles as essential components, and includes (3) a resin binder and (4) other additives as necessary.

Next, a back electrode is formed. Note that a p ⁺ -type diffusion layer is formed in a region where the back electrode is formed in the silicon substrate 10. The method for forming the p ⁺ -type diffusion layer is not particularly limited. For example, p is configured in the same manner as the n-type diffusion layer forming composition using glass powder containing an acceptor element instead of glass powder containing a donor element. The mold diffusion layer forming composition is applied to the back surface of the silicon substrate 10 (the surface opposite to the surface on which the n-type diffusion layer forming composition is applied) and baked to form a p ⁺ -type diffusion layer on the back surface. It may be formed. In addition, an n-type diffusion layer formed on the back surface by a gas phase reaction method using a gas phase diffusion gas or a method using a solution or paste containing a donor element is converted into a p type diffusion layer with aluminum to form a p ⁺ type. A diffusion layer may be formed.

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

And an electrode is baked and a solar cell element is completed. When firing at a temperature of 600 ° C. to 900 ° C. for several seconds to several minutes, the antireflective film as an insulating film is melted by the glass particles contained in the electrode metal paste on the surface side, and the silicon substrate 10 surface is also partially melted. The metal particles (for example, silver particles) in the paste form a contact portion with the silicon substrate 10 and solidify. Thereby, the formed surface electrode and the n ⁺⁺ type ^| mold diffusion layer 5 of a silicon substrate are conduct | electrically_connected. This is called fire-through.

  The shape of the surface electrode will be described. The surface electrode includes 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 in which a surface electrode is composed of a bus bar electrode 30 and a finger electrode 32 intersecting with the bus bar electrode 30 as viewed from the surface. ) Is an enlarged perspective view showing a part of FIG.

  Such a surface electrode can be formed by means such as screen printing of the above-described metal paste, plating of the electrode material, or vapor deposition of the electrode material by electron beam heating in a high vacuum. 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 known forming means for the bus bar electrode and finger electrode on the light receiving surface side can be applied. .

In the above description, the solar cell element in which the n-type diffusion layer is formed on the front surface, the p ⁺ -type diffusion layer is formed on the back surface, and the front surface electrode and the back surface electrode are further provided on the respective layers has been described. If a layer formation composition is used, it is also possible to produce a back contact type solar cell element.

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 at a specific site, and can therefore 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]
(A) Wafer treatment A polyimide tape was applied in the shape of an electrode pattern for a solar cell on a single crystal p-type Si wafer (156 mm × 156 mm, film thickness 170 μm, with surface texture) manufactured by PVG Solutions Inc. On top of that, a coating material (HSG-100) made by Hitachi Chemical Co., Ltd. was formed by spin coating (1000 rpm, 10 seconds) and heated on a hot plate heated to 250 ° C. for 3 minutes. The polyimide tape affixed to the electrode pattern for solar cells was peeled off. When the thickness of the patterned silicon oxide film was measured with a film thickness meter (manufactured by AMBIOS, product name: stylus type step gauge XP-1), the average thickness was 0.3 μm.

  The aforementioned Si wafer was placed in a quartz horizontal tube diffusion furnace having a diameter of 225 mm, and heated at 830 ° C. for 12 minutes while flowing nitrogen gas / oxygen gas / phosphorus oxychloride gas = 12 / 0.6 / 0.1 L / min. .

  When this Si wafer was immersed in 10% hydrofluoric acid for 5 minutes and washed with pure water, the glass layer and silicon oxide film formed on the surface were all dissolved and removed.

  The sheet resistance of the obtained Si wafer was measured by the four-probe method using a Loresta-EP MCP-T360 type low resistivity meter manufactured by Mitsubishi Chemical Corporation. The sheet resistance was measured in the formation region and non-formation region of the silicon oxide film.

(B) Production of Solar Cell A silicon nitride (SiNx) film was laminated on the surface of the above-mentioned Si wafer by using a CVD method to form an antireflection film. Subsequently, in the previous section (a) wafer processing, a DuPont silver paste (trade name: PV159) was patterned and printed by a screen printing method in a region where the silicon oxide film was not formed in the electrode pattern state. The printing conditions (screen plate mesh, printing speed, printing pressure) were appropriately adjusted so as to be 20 μm. This was placed in an oven heated to 150 ° C. for 15 minutes, and the solvent was removed by evaporation.

  Subsequently, an aluminum electrode paste was applied to the entire back surface of the Si wafer so that the film thickness after firing was 30 μm. This was placed in an oven heated to 150 ° C. for 15 minutes, and the solvent was removed by evaporation.

  Subsequently, using a tunnel furnace (manufactured by Noritake Co., Ltd., one-row transport W / B tunnel furnace), a heat treatment (firing) is performed at a firing maximum temperature of 800 ° C. and a holding time of 10 seconds in an air atmosphere to form a desired electrode. The produced solar cell element C-1 was produced.

[Example 2]
(A) Preparation of n-type diffusion layer forming composition P ₂ O ₅ —SiO ₂ —CaO-based glass (P ₂ O ₅ : 50.0%, SiO ₂ : 43%, CaO: 7%) powder 10 g and ethyl cellulose 6.8 g (ethylation degree 50%, weight average molecular weight 50,000) and 2-acetate 2- (2-butoxyethoxy) ethyl 83.2 g were mixed using an automatic mortar kneader to make a paste, and n-type A diffusion layer forming composition was prepared.

(B) Wafer treatment A polyimide tape was applied in the shape of an electrode pattern for solar cells on a single crystal P-type Si wafer (156 mm × 156 mm, film thickness 170 μm, with surface texture) manufactured by PVG Solutions, Inc. On top of that, a coating material (HSG-100) made by Hitachi Chemical Co., Ltd. was formed by spin coating (1000 rpm, 10 seconds) and heated on a hot plate heated to 250 ° C. for 3 minutes. The polyimide tape affixed to the electrode pattern for solar cells was peeled off. When the average thickness of the patterned silicon oxide film was measured in the same manner as in Example 1, it was 0.3 μm.

The n-type diffusion layer forming composition prepared in (a) above was applied to the entire surface on which the silicon oxide film was formed by screen printing, and placed in a dryer heated to 150 ° C. for 15 minutes to evaporate the solvent. I let you.
This was put in a quartz horizontal tube diffusion furnace having a diameter of 225 mm, and heated at 900 ° C. for 10 minutes while flowing nitrogen gas / oxygen gas = 8.0 / 2.0 L / min.
When this Si wafer was immersed in 10% hydrofluoric acid for 5 minutes and washed with pure water, the glass layer and silicon oxide film formed on the surface were all dissolved and removed.
Thereafter, a nitride film and an electrode were formed by the method described in Example 1 to obtain a solar cell element C-2.

[Example 3]
(A) Wafer treatment A polyimide tape was applied in the shape of an electrode pattern for a solar cell on a single crystal P-type Si wafer (156 mm × 156 mm, film thickness 170 μm, with surface texture) manufactured by PVG Solutions Inc. On top of that, IPA-ST (an isopropyl alcohol dispersion containing 30% of SiO ₂ fine particles with a diameter of 10 to 20 nm) was formed by spin coating (1000 rpm, 10 seconds) and heated to 250 ° C. After heating on a hot plate for 3 minutes, the polyimide tape attached to the electrode pattern for solar cells was peeled off. Thereafter, it was placed in a firing furnace heated to 1000 ° C. for 1 hour. When the average thickness of the patterned silicon oxide film was measured in the same manner as in Example 1, it was 0.4 μm.

The n-type diffusion layer forming composition prepared in Example 2 (a) was applied to the entire surface on which the silicon oxide film was formed by screen printing, and placed in a dryer heated to 150 ° C. for 15 minutes for solvent. Transpiration.
This was put in a quartz horizontal tube diffusion furnace having a diameter of 225 mm, and heated at 900 ° C. for 10 minutes while flowing nitrogen gas / oxygen gas = 8.0 / 2.0 L / min.
When this Si wafer was immersed in 10% hydrofluoric acid for 5 minutes and washed with pure water, the glass layer and silicon oxide film formed on the surface were all dissolved and removed.
Thereafter, a nitride film and an electrode were formed by the method described in Example 1 to obtain a solar cell element C-3.

[Comparative Example 1]
In Example 1, it produced similarly except not having formed the silicon oxide film, and obtained solar cell element H-1.

[Comparative Example 2]
In Example 2, it produced similarly except having made the thickness of the silicon oxide film into 2.5 micrometers, and obtained solar cell element H-2.

  Table 1 below shows the measurement results of the sheet resistance values of the silicon oxide film formation region and the non-formation region in the Si wafers of Examples 1 to 3 and Comparative Examples 1 and 2.

As shown in Table 1, in Examples 1-3, the silicon oxide film forming region of the silicon substrate n ⁺ -type diffusion layer is formed, in the non-formation regions have n ⁺⁺ type diffusion layer is formed. On the other hand, in Comparative Example 1 in which no silicon oxide film was formed, the entire surface of the silicon substrate was an n ⁺⁺ layer, and a plurality of regions having different doping concentrations were not formed. Further, in Comparative Example 2 in which the average thickness of the silicon oxide film exceeds 2 μm, the sheet resistance value is high in the region where the silicon oxide film is formed, and the n ⁺ -type diffusion layer is not formed.

<Evaluation of solar cell element>
Evaluation of the produced solar cell element is as follows: WXS-155S-10 manufactured by Wacom Denso Co., Ltd. as pseudo-sunlight, and I-V CURVE TRACER MP-160 (manufactured by EKO INSTRUMENT Co., Ltd.) as a current-voltage (IV) evaluation measuring instrument. ) Was combined with the measuring device. Η (conversion efficiency), FF (fill factor), Voc (open circuit voltage) and Jsc (short circuit current) indicating the power generation performance as a solar cell are JIS-C-8912, JIS-C-8913 and JIS-C-, respectively. It is obtained by performing measurement according to 8914. The obtained measured values are converted into relative values with the measured value of Comparative Example 1 as 100.0, and are shown in Table 2.

Examples 1 to 3, it has a n ⁺ -type diffusion layer and n ⁺⁺ type diffusion layer is formed selective emitter type solar cell element, as compared with Comparative Examples 1 and 2, improved performance of the solar cell element Was.

2 Silicon oxide film 3 Glass layer containing donor element 4 n ⁺ type diffusion layer 5 n ⁺⁺ type diffusion layer 10 Silicon substrate 16 Antireflection film 30 Bus bar electrode 32 Finger electrode

Claims (6)

Forming a patterned silicon oxide film having an average thickness of 0.01 μm or more and 2 μm or less on a silicon substrate;
Forming a glass layer containing a donor element on a silicon substrate on which the silicon oxide film is formed in a pattern;
A step of performing a thermal diffusion treatment during or after the formation of the glass layer;
Removing the silicon oxide film and the glass layer after the thermal diffusion treatment;
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 the glass layer containing the donor element is a glass layer obtained by heating after applying the n-type diffusion layer forming composition.   The n-type diffusion layer according to claim 2, wherein the composition for forming an n-type diffusion layer contains a glass powder containing at least one donor element selected from P (phosphorus) and Sb (antimony) and a dispersion medium. Manufacturing method. The method for producing an n-type diffusion layer according to claim 1, wherein the glass layer containing the donor element is a glass layer formed using phosphorus oxychloride (POCl ₃ ) as a raw material.   A solar process comprising: a step of forming an n-type diffusion layer on a silicon substrate by the manufacturing method according to claim 1; and a step of forming an electrode on the formed n-type diffusion layer. A battery element manufacturing method. A silicon substrate having an n-type diffusion layer manufactured by the manufacturing method according to any one of claims 1 to 4,
An electrode provided on the n-type diffusion layer;
A solar cell element having