JP5842431B2 - Method for producing n-type diffusion layer and method for producing solar cell element - Google Patents

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. More specifically, the present invention relates to a method in which a residue derived from a dispersion medium is small in a specific portion of silicon as a semiconductor substrate. The present invention relates to a technique that makes it possible to form a mold diffusion layer.

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 The n-type diffusion layer is uniformly formed by performing several tens of minutes at 800 ° C. 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 on a silicon substrate surface as a diffusion source 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.

  The present invention has been made in view of the above-described conventional problems, and in a manufacturing process of a solar cell element using a silicon substrate, a specific part is derived from a dispersion medium without forming an unnecessary n-type diffusion layer. It is an object of the present invention to provide a production method for producing an n-type diffusion layer with little residue and a method for producing a solar cell element.

Means for solving the problems are as follows.
<1> Applying an n-type diffusion layer forming composition containing a glass powder containing a donor element and a dispersion medium on a semiconductor substrate; and applying a thermal diffusion treatment to the semiconductor substrate coated with the n-type diffusion layer forming composition. Forming an n-type diffusion layer by applying , etching removing the glass layer formed on the surface of the n-type diffusion layer by thermal diffusion , and etching the glass layer formed on the surface of the n-type diffusion layer And removing the residue derived from the dispersion medium by cleaning the semiconductor substrate on which the n-type diffusion layer has been formed with ultrasonic waves , after removing by the step.
<2> The method for producing an n-type diffusion layer according to <1>, wherein the ultrasonic frequency is in a range of 20 kHz to 100 kHz.
<3> The method for producing an n-type diffusion layer according to <1> or <2>, wherein the cleaning is performed in a range of 1 minute to 60 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). .
<5> The glass powder containing the donor element includes at least one donor element-containing material selected from P ₂ O ₃ , P ₂ O ₅ and Sb ₂ O ₃ , and SiO ₂ , K ₂ O, and Na ₂ O. And at least one glass component material selected from Li ₂ O, 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> Applying an n-type diffusion layer forming composition containing a glass powder containing a donor element and a dispersion medium on a semiconductor substrate; and applying a thermal diffusion treatment to the semiconductor substrate coated with the n-type diffusion layer forming composition. Forming an n-type diffusion layer by applying , etching removing the glass layer formed on the surface of the n-type diffusion layer by thermal diffusion , and etching the glass layer formed on the surface of the n-type diffusion layer And removing the residue derived from the dispersion medium , and forming an electrode on the formed n-type diffusion layer , after removing the semiconductor substrate on which the n-type diffusion layer is formed by ultrasonic waves The manufacturing method of the solar cell element which has.

According to the present invention, by using an n-type diffusion layer forming composition containing a glass powder containing a donor element and a dispersion medium, the donor component is hardly volatilized even during firing, and an unnecessary n-type diffusion layer is formed. The n-type diffusion layer can be formed in a specific portion.
Further, when a donor element containing glass powder and a dispersion medium is used, a part of the dispersion medium may remain as a carbide, but by ultrasonically cleaning the substrate on which the n-type diffusion layer is formed, Residues can be removed.
Therefore, according to the present invention, in the manufacturing process of a solar cell element using a silicon substrate, an n-type diffusion layer with a small amount of residue derived from the dispersion medium is formed in a specific region without forming an n-type diffusion layer in an unnecessary region. It becomes possible to form.

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

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. In addition, other additives may be contained as necessary.
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 an n-type diffusion layer forming composition containing a donor element in 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 composition for forming an n-type diffusion layer of the present invention is applied, the side etching step that is essential in the gas phase reaction method that has been widely employed 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. Although details will be described later, generation of internal stress in the silicon substrate due to the thickness of the back electrode is suppressed, and warpage of the silicon 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 a conventional gas phase reaction method or a method of applying a phosphate-containing solution or paste, and thus the glass layer produced in the present invention is a conventional method. Similarly to the above, 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.

  Further, since the donor component in the glass powder is difficult to volatilize even during firing, the occurrence of an n-type diffusion layer not only on the surface but also on the back surface and side surfaces due to the generation of the volatilizing gas is suppressed. 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. .

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 temperature, a glass transition temperature, 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 _{2 O, Na 2 O, Li} 2 O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V 2 O 5, SnO, be at least one selected from ZrO _2, and MoO ₃ More preferred.

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. Glass powder _Sb 2 _{O 3} system containing _Sb 2 _{O 3} Te and the like.
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.
Although the composite glass containing two components was illustrated above, glass powder containing three or more components such as P ₂ O ₅ —SiO ₂ —V ₂ O ₅ and P ₂ O ₅ —SiO ₂ —CaO may be used.

  The content ratio of the glass component substance in the glass powder is preferably set as appropriate in consideration of the melting temperature, the softening temperature, the glass transition temperature, and the 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 ₃ When the glass contains at least one selected from the above, the content of the glass component substance is preferably in the above range from the viewpoint that the reaction product with the silicon substrate is less likely to remain as a residue during hydrofluoric acid treatment. .
Further, 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 temperature. 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 temperature 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, 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 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, The content is more preferably 1.5% by mass or more and 85% by mass or less, and particularly preferably 2% by mass or more and 80% by mass or less.

Next, the dispersion medium will be described.
The dispersion medium is a medium in which the glass powder is dispersed in the composition. Specifically, a binder or a solvent is employed as the dispersion medium.

  Examples of the binder include polyvinyl alcohol, polyacrylamides, polyvinylamides, polyvinylpyrrolidone, polyethylene oxides, polysulfonic acid, acrylamide alkylsulfonic acid, cellulose ethers, cellulose derivatives, carboxymethyl cellulose, hydroxyethyl cellulose, ethyl cellulose, gelatin, starch And starch derivatives, sodium alginates, xanthan, gua and gua derivatives, scleroglucan and scleroglucan derivatives, tragacanth and tragacanth derivatives, dextrin and dextrin derivatives, (meth) acrylic acid resins, (meth) acrylic acid ester resins (e.g. , Alkyl (meth) acrylate resins, dimethylaminoethyl (meth) acrylate resins, etc.), butadiene resin , Styrene resin, or copolymers thereof, can 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 of the composition.

  Examples of the solvent include acetone, methyl ethyl ketone, methyl-n-propyl ketone, methyl-iso-propyl ketone, methyl-n-butyl ketone, methyl-iso-butyl ketone, methyl-n-pentyl ketone, methyl-n-hexyl ketone, Ketone solvents such as diethyl ketone, dipropyl ketone, di-iso-butyl ketone, trimethylnonanone, cyclohexanone, cyclopentanone, methylcyclohexanone, 2,4-pentanedione, acetonylacetone; diethyl ether, methyl ethyl ether, methyl -N-propyl ether, di-iso-propyl ether, tetrahydrofuran, methyltetrahydrofuran, dioxane, dimethyldioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether Ter, ethylene glycol di-n-propyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol methyl n-propyl ether, diethylene glycol methyl n-butyl ether, diethylene glycol di-n-propyl ether , Diethylene glycol di-n-butyl ether, diethylene glycol methyl-n-hexyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, triethylene glycol methyl n-butyl ether, triethylene glycol di-n- Butyl ether, G Ethylene glycol methyl-n-hexyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetradiethylene glycol methyl ethyl ether, tetraethylene glycol methyl n-butyl ether, diethylene glycol di-n-butyl ether, tetraethylene glycol methyl n-hexyl Ether, tetraethylene glycol di-n-butyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di-n-propyl ether, propylene glycol dibutyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol methyl ethyl Ether, zip Lopylene glycol methyl-n-butyl ether, dipropylene glycol di-n-propyl ether, dipropylene glycol di-n-butyl ether, dipropylene glycol methyl-n-hexyl ether, tripropylene glycol dimethyl ether, tripropylene glycol diethyl ether, tripropylene Glycol methyl ethyl ether, tripropylene glycol methyl-n-butyl ether, tripropylene glycol di-n-butyl ether, tripropylene glycol methyl-n-hexyl ether, tetrapropylene glycol dimethyl ether, tetrapropylene glycol diethyl ether, tetradipropylene glycol methyl ethyl Ether, tetrapropylene glycol methyl-n-butyl ether Ether solvents such as dipropylene glycol di-n-butyl ether, tetrapropylene glycol methyl-n-hexyl ether, tetrapropylene glycol di-n-butyl ether; methyl acetate, ethyl acetate, n-propyl acetate, i-propyl acetate, acetic acid n-butyl, i-butyl acetate, sec-butyl acetate, n-pentyl acetate, sec-pentyl acetate, 3-methoxybutyl acetate, methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, 2- (2- Butoxyethoxy) ethyl, benzyl acetate, cyclohexyl acetate, methyl cyclohexyl acetate, nonyl acetate, methyl acetoacetate, ethyl acetoacetate, diethylene glycol methyl ether acetate, diethylene glycol monoethyl ether acetate, dipropylene glycol acetate Methyl ether, dipropylene glycol ethyl ether, glycol diacetate, methoxytriglycol acetate, ethyl propionate, n-butyl propionate, i-amyl propionate, diethyl oxalate, di-n-butyl oxalate, lactic acid Methyl, ethyl lactate, n-butyl lactate, n-amyl lactate, ethylene glycol methyl ether propionate, ethylene glycol ethyl ether propionate, ethylene glycol methyl ether acetate, ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate, propylene Ester solvents such as glycol ethyl ether acetate, propylene glycol propyl ether acetate, γ-butyrolactone, γ-valerolactone; N-methylpyrrolidinone, N-ethylpyrrolidinone, N-propylpyrrolidinone, N-butylpyrrolidinone, N-hexylpyrrolidinone, N-cyclohexylpyrrolidinone, N, N-dimethylformamide, N, N-dimethylacetamide, N, N- Aprotic polar solvents such as dimethyl sulfoxide; methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, sec-butanol, t-butanol, n-pentanol, i-pentanol, 2- Methylbutanol, sec-pentanol, t-pentanol, 3-methoxybutanol, n-hexanol, 2-methylpentanol, sec-hexanol, 2-ethylbutanol, sec-heptanol, n-octanol, 2-ethylhexanol Nord, sec-octanol, n-nonyl alcohol, n-decanol, sec-undecyl alcohol, trimethylnonyl alcohol, sec-tetradecyl alcohol, sec-heptadecyl alcohol, phenol, cyclohexanol, methylcyclohexanol, benzyl alcohol, ethylene Alcohol solvents such as glycol, 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, polyethylene 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 Glycol monoether solvents such as ether; α-terpinene, α-terpineol, myrcene, alloocimene, limonene, dipentene, α-pinene, β-pinene, terpineol, carvone, ocimene, ferrandrene, and other terpene solvents; Can be mentioned. These are used singly or in combination of two or more. In the n-type diffusion layer forming composition, α-terpineol, diethylene glycol mono-n-butyl ether, and acetic acid diethylene glycol mono-n-butyl ether are preferable, and α-terpineol, diethylene glycol mono-n-butyl ether are preferable from the viewpoint of applicability to the substrate. Are mentioned as preferred solvents.

The content ratio of the dispersion medium 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 to 1,000,000 mPa · s, more preferably 50 mPa · s to 500,000 mPa · s in consideration of applicability.

  Furthermore, the n-type diffusion layer forming composition may contain other additives.

  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.

  Next, the manufacturing method of the n type diffused layer and solar cell element 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 solar cell element of the present invention. In the subsequent drawings, common constituent elements are denoted by the same reference numerals.

In FIG. 1A, an alkaline solution is applied to a silicon substrate which is a p-type semiconductor substrate 10 to remove a 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, 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 p-type semiconductor substrate 10, that is, the surface that becomes 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.
No particular restriction on the coating amount of the n-type diffusion layer forming composition, but for example, it can 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.

Depending on the composition of the n-type diffusion layer forming composition, a drying step for volatilizing the solvent contained in the composition may be necessary after coating. In this case, drying is performed at a temperature of about 80 ° C. to 300 ° C. for about 1 minute to 10 minutes when using a hot plate, and about 10 minutes to 30 minutes when using a dryer or the like. The drying conditions depend on the solvent composition of the n-type diffusion layer forming composition, and are not particularly limited to the above conditions in the present invention.
Moreover, when a resin binder is employ | adopted as a dispersion medium in n type diffused layer formation composition, the removal process for removing a resin binder may be required after drying. In this case, heat treatment is performed using an electric furnace at a temperature of about 300 ° C. to 600 ° C. for about 1 minute to 30 minutes. This heat treatment condition depends on the glass and binder composition of the n-type diffusion layer forming composition, and is not particularly limited to the above condition in the present invention.

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 to a p-type diffusion layer by aluminum. In addition, any conventionally known method can be adopted, and the options for the manufacturing method are expanded. Therefore, for example, a composition containing a Group 13 element such as B (boron) can be applied to form the composition layer 13 and the high-concentration electric field layer 14 can be formed.
As the composition 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 composition is the same as that of the n-type diffusion layer forming composition. A p-type diffusion layer forming composition may be mentioned. 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.}
Furthermore, the method for applying the p-type diffusion layer forming composition to the back surface of the silicon substrate is the same as the method for applying the n-type diffusion layer forming composition described above on the silicon substrate.
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 thermal diffusion treatment similar to the thermal diffusion treatment in the n-type diffusion layer forming composition described later. . 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, the semiconductor substrate 10 on which the n-type diffusion layer forming composition layer 11 is formed is subjected to thermal diffusion treatment at 600 ° C. to 1200 ° C. By this thermal diffusion treatment, as shown in FIG. 1C, the donor element diffuses into the semiconductor substrate, and the n-type diffusion layer 12 is formed. A known continuous furnace, batch furnace, or the like can be applied to the thermal diffusion treatment. Further, the 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.

  Since 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.

  A black residue may be seen on the surface of the n-type diffusion layer formed through the above-described series of steps. This residue is the one in which at least a part of the dispersion medium contained in the n-type diffusion layer forming composition cannot be removed by any of the heat treatments described above, is taken into the softened glass, and remains on the semiconductor substrate as a carbide. It is guessed. Therefore, in order to remove the residue, ultrasonic cleaning is performed on the silicon substrate on which the n-type diffusion layer is formed.

The solvent used for ultrasonic cleaning is not particularly limited, and examples thereof include pure water and ethanol. A semiconductor substrate on which an n-type diffusion layer is formed is immersed in these solvents, and ultrasonic waves are applied.
The frequency of the ultrasonic wave used for cleaning is not particularly limited, but is preferably 20 kHz to 100 kHz, and more preferably 30 kHz to 50 kHz, considering the impact on the inside of the wafer and the magnitude of calibration. Moreover, it may be implemented by combining a plurality of frequencies such as applying 24 kHz and 31 kHz at the same time, and the same effect can be obtained.
The ultrasonic cleaning time is not particularly limited, but is preferably not too long considering the impact on the substrate having the n-type diffusion layer, preferably 1 to 60 minutes, and considering shortening of the process time More preferably, it is 1 minute to 5 minutes.

  Ultrasonic cleaning may be performed during etching of the glass in an etching solution (acid such as hydrofluoric acid, alkali such as caustic soda). In this case, a glass layer such as phosphate glass and carbide can be removed at the same time, and the same effect as when ultrasonic cleaning is performed after etching can be obtained. Furthermore, the number of steps can be simplified.

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 of the present invention shown in FIGS. The n-type 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 an unnecessary n-type diffusion layer formed on the back surface into a p-type diffusion layer. As this conversion method, a group 13 element is added to the n-type diffusion layer on the back surface. A method is adopted in which an aluminum paste is applied and baked to diffuse aluminum into the n-type diffusion layer and convert it into a p-type diffusion layer. In this method, in order to sufficiently convert to the p-type diffusion layer and to form a high concentration electric field layer of p ⁺ layer, an aluminum amount of a certain amount or more is required. Therefore, the aluminum layer is formed thick. There was a need. 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 silicon substrate during the firing and cooling process, causing warpage of the silicon substrate. .
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 silicon substrate has been reduced due to the improvement of the slice processing technique, and the solar cell element tends to be easily broken.

  However, according to the manufacturing method of the present invention, since an unnecessary n-type diffusion layer is not formed on the back surface, it is not necessary to perform conversion from the n-type diffusion layer to the p-type diffusion layer, and the necessity of increasing the thickness of the aluminum layer is eliminated. . As a result, generation of internal stress and warpage in the silicon substrate can be suppressed. As a result, it is possible to suppress an increase in power loss and damage to the solar cell element.

Further, 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 to a p-type diffusion layer with aluminum. Any method can be adopted without any problem, and the choice of manufacturing method is expanded.
For example, using a glass powder containing an acceptor element instead of a glass powder containing a donor element, a p-type diffusion layer forming composition configured in the same manner as the n-type diffusion layer forming composition is formed on the back surface (n The p ⁺ -type diffusion layer (high-concentration electric field layer) 14 is preferably formed on the back surface by applying to the surface opposite to the surface on which the mold diffusion layer forming composition is applied and baking.
As will be described later, the material used for the back surface electrode 20 is not limited to Group 13 aluminum, and for example, Ag (silver) or Cu (copper) can be applied. In addition, it can be formed 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 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.

  In FIG. 1 (5), the surface electrode 18 is formed on the antireflection film 16 on the surface (light-receiving surface) by printing and drying the surface electrode metal paste by screen printing. 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, the back electrode 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 20 are not particularly limited. For example, the back electrode 20 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 solar cell elements in the module process.

  In FIG. 1 (6), 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 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 silicon 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 18 and the silicon substrate 10 are electrically connected. This is called fire-through.

  The shape of the surface electrode 18 will be described. The surface electrode 18 includes a bus bar electrode 30 and finger electrodes 32 intersecting with the bus bar electrode 30. FIG. 2A is a plan view of a solar cell element in which the surface electrode 18 includes a bus bar electrode 30 and a finger electrode 32 intersecting with the bus bar electrode 30 as viewed from the surface. FIG. 2B is an enlarged perspective view illustrating a part of FIG.

  Such a surface electrode 18 can be formed by means such as screen printing of the above-described metal paste, plating of an electrode material, or vapor deposition of an electrode material by electron beam heating in a high vacuum. The surface electrode 18 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 it is possible to apply known forming means for the bus bar electrode and finger electrode on the light receiving surface side. it can.

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 4 is shown as a reference example.

[Example 1]
P ₂ O ₅ —SiO ₂ —CaO glass (P ₂ O ₅ : 50%, SiO ₂ : 43%, CaO: 7%) powder having a substantially spherical particle shape, an average particle diameter of 1 μm, and a softening temperature of 700 ° C. 3 g, 2.1 g of ethyl cellulose, and 24.9 g of terpineol were mixed using an automatic mortar kneader to make a paste, thereby preparing an n-type diffusion layer forming composition.

  The glass particle shape was determined by observing with a TM-1000 scanning electron microscope manufactured by Hitachi High-Technologies Corporation. The average particle size of the glass was calculated using a LS 13 320 type laser scattering diffraction particle size distribution analyzer (measurement wavelength: 632 nm) manufactured by Beckman Coulter, Inc. The softening temperature of the glass was obtained from a differential heat (DTA) curve using a DTG-60H type differential heat / thermogravimetric simultaneous measuring device manufactured by Shimadzu Corporation.

  Next, the prepared paste was applied to the surface of the p-type silicon 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, the binder was desorbed by heating for 1.5 minutes in an electric furnace set to 500 ° C. Then, thermal diffusion treatment was performed for 10 minutes in another electric furnace for diffusion set at 900 ° C., and then the substrate was immersed in hydrofluoric acid for 5 minutes in order to remove the glass layer. Then, it was immersed in pure water, washed with ultrasonic waves of 42 kHz for 3 minutes, and dried.

The sheet resistance on the surface on which the n-type diffusion layer forming composition was applied was 35Ω / □, and P (phosphorus) diffused to form an n-type diffusion layer. The sheet resistance on the back surface was 1000000 Ω / □ or more, which was not measurable, and it was determined that the n-type diffusion layer was not substantially 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.

When the surface on which the n-type diffusion layer forming composition was applied was observed visually and with an SEM and the presence or absence of a residue was examined, no residue was found on the silicon substrate. However, residues were observed on the silicon substrate after immersion in hydrofluoric acid and before ultrasonic cleaning.
In addition, Philips XL30 was used for SEM (scanning electron microscope).

[Example 2]
An n-type diffusion layer was formed in the same manner as in Example 1 except that the ultrasonic cleaning time was 30 minutes.
The sheet resistance of the surface on which the n-type diffusion layer forming composition was applied was 33Ω / □, and P was diffused to form an n-type diffusion layer. The sheet resistance on the back surface was 1000000 Ω / □ or more, which was not measurable, and it was determined that the n-type diffusion layer was not substantially formed.
When the presence or absence of a residue was examined in the same manner as in Example 1, no residue was found on the silicon substrate. However, residues were observed on the silicon substrate after immersion in hydrofluoric acid and before ultrasonic cleaning.

[Example 3]
An n-type diffusion layer was formed in the same manner as in Example 1 except that the ultrasonic wave for ultrasonic cleaning was changed to 20 kHz.
The sheet resistance of the surface on which the n-type diffusion layer forming composition was applied was 35Ω / □, and P was diffused to form an n-type diffusion layer. The sheet resistance on the back surface was 1000000 Ω / □ or more, which was not measurable, and it was determined that the n-type diffusion layer was not substantially formed.
When the presence or absence of a residue was examined in the same manner as in Example 1, no residue was found on the silicon substrate. However, residues were observed on the silicon substrate after immersion in hydrofluoric acid and before ultrasonic cleaning.

[Example 4]
The process up to the thermal diffusion treatment was performed in the same manner as in Example 1, and the glass layer was removed and the ultrasonic cleaning was performed by applying ultrasonic waves of 42 kHz while the thermal diffusion treated substrate was immersed in hydrofluoric acid for 1 minute. It was. Then, it was immersed in pure water and dried.
The sheet resistance of the surface on which the n-type diffusion layer forming composition was applied was 33Ω / □, and P was diffused to form an n-type diffusion layer. The sheet resistance on the back surface was 1000000 Ω / □ or more, which was not measurable, and it was determined that the n-type diffusion layer was not substantially formed.
When the presence or absence of a residue was examined in the same manner as in Example 1, no residue was found on the silicon substrate.

[Example 5]
An n-type diffusion layer was formed in the same manner as in Example 1 except that the ultrasonic cleaning time was set to 70 minutes.
The sheet resistance of the surface on which the n-type diffusion layer forming composition was applied was 37Ω / □, and P was diffused to form an n-type diffusion layer. The sheet resistance on the back surface was 1000000 Ω / □ or more, which was not measurable, and it was determined that the n-type diffusion layer was not substantially formed.
When the presence or absence of a residue was examined in the same manner as in Example 1, no residue was found on the silicon substrate. However, residues were observed on the silicon substrate after immersion in hydrofluoric acid and before ultrasonic cleaning.
In addition, cracks and cracks were observed on some silicon substrates.

[Example 6]
An n-type diffusion layer was formed in the same manner as in Example 1 except that the ultrasonic wave in the ultrasonic cleaning step was changed to 15 kHz.
The sheet resistance of the surface on which the n-type diffusion layer forming composition was applied was 32Ω / □, and P was diffused to form an n-type diffusion layer. The sheet resistance on the back surface was 1000000 Ω / □ or more, which was not measurable, and it was determined that the n-type diffusion layer was not substantially formed.
When the presence or absence of a residue was examined in the same manner as in Example 1, no residue was found on the silicon substrate. However, residues were observed on the silicon substrate after immersion in hydrofluoric acid and before ultrasonic cleaning.
In addition, cracks and cracks were observed on some silicon substrates.

[Comparative Example 1]
An n-type diffusion layer was formed in the same manner as in Example 1 except that ultrasonic cleaning was not performed.
The sheet resistance of the surface on which the n-type diffusion layer forming composition was applied was 35Ω / □, and P was diffused to form an n-type diffusion layer. The sheet resistance on the back surface was 1000000 Ω / □ or more, which was not measurable, and it was determined that the n-type diffusion layer was not substantially formed.
When the presence or absence of a residue was examined in the same manner as in Example 1, a black residue was found on the silicon substrate.

10 p-type semiconductor substrate 12 n-type diffusion layer 14 high-concentration electric field layer 16 antireflection film 18 surface electrode 20 back electrode (electrode layer)
30 Busbar 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 on a semiconductor substrate;
applying a thermal diffusion treatment to the semiconductor substrate coated with the n-type diffusion layer forming composition to form an n-type diffusion layer;
Removing the glass layer formed on the surface of the n-type diffusion layer by thermal diffusion treatment by etching;
removing the glass substrate formed on the surface of the n-type diffusion layer by etching, then cleaning the semiconductor substrate on which the n-type diffusion layer is formed with ultrasonic waves , and removing residues derived from the dispersion medium ;
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 ultrasonic frequency is in a range of 20 kHz to 100 kHz.   The method for producing an n-type diffusion layer according to claim 1 or 2, wherein the cleaning is performed in a range of 1 minute to 60 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 containing the donor element 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. And at least one glass component material selected from O, BaO, 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. Applying an n-type diffusion layer forming composition containing a glass powder containing a donor element and a dispersion medium on a semiconductor substrate;
applying a thermal diffusion treatment to the semiconductor substrate coated with the n-type diffusion layer forming composition to form an n-type diffusion layer;
Removing the glass layer formed on the surface of the n-type diffusion layer by thermal diffusion treatment by etching;
removing the glass substrate formed on the surface of the n-type diffusion layer by etching, then cleaning the semiconductor substrate on which the n-type diffusion layer is formed with ultrasonic waves , and removing residues derived from the dispersion medium ;
Forming an electrode on the formed n-type diffusion layer;
The manufacturing method of the solar cell element which has this.