JP2013026476A - P-type diffusion layer forming composition, manufacturing method of p-type diffusion layer, and manufacturing method of solar cell element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a p-type diffusion layer forming composition, a manufacturing method of a p-type diffusion layer, and a manufacturing method of a solar cell element, capable of forming a p-type diffusion layer while suppressing roughening of a substrate surface, without generating internal stress of a silicon substrate and warpage of a substrate in a manufacturing process of a solar cell element using a semiconductor substrate.SOLUTION: The p-type diffusion layer forming composition contains silicon particles, dispersion media, and glass powders containing acceptor elements. A p-type diffusion layer and a solar cell element having the same can be manufactured by coating the p-type diffusion layer forming composition and treating with thermal diffusion.

Description

  The present invention relates to a p-type diffusion layer forming composition for a solar cell element, a method for producing a p-type diffusion layer, and a method for producing a solar cell element.

The manufacturing process of the conventional silicon solar cell element is demonstrated.
First, a p-type silicon substrate having a textured structure is prepared so as to promote the light confinement effect and achieve high efficiency, and then 800 to 900 ° C. in a mixed gas atmosphere of phosphorus oxychloride (POCl ₃ ), nitrogen and oxygen. The n-type diffusion layer is uniformly formed by performing several tens of minutes. 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, side etching is performed to remove the n-type diffusion layer on the side surface. Further, the back surface of the n-type diffusion layer must be converted into the p ⁺ -type diffusion layer, an aluminum paste is printed on the back, by firing this, the n-type diffusion layer at the same time as the p ⁺ -type diffusion layer , Got ohmic contact.

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

In order to solve this problem, there is a method of reducing the coating amount of the paste composition and thinning the back electrode layer. However, when the application amount of the paste composition is reduced, the amount of aluminum diffusing from the surface of the p-type silicon semiconductor substrate becomes insufficient. As a result, the desired BSF (Back Surface Field) effect (the effect of improving the collection efficiency of the generated carriers due to the presence of the p ⁺ -type layer) cannot be achieved, resulting in a problem that the characteristics of the solar cell deteriorate.

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

Japanese Patent Laid-Open No. 2003-223813

However, even when the paste composition described in Patent Document 1 is used, there is a case where warpage cannot be sufficiently suppressed.
The present invention has been made in view of the above-described conventional problems, and in the manufacturing process of a solar cell element using a semiconductor substrate, while suppressing the roughening of the substrate surface, internal stress in the substrate, It is an object of the present invention to provide a p-type diffusion layer forming composition capable of forming a p-type diffusion layer without causing warpage, a method for producing a p-type diffusion layer, and a method for producing a solar cell element.

Means for solving the problems are as follows.
<1> A p-type diffusion layer forming composition containing glass powder containing an acceptor element, silicon particles, and a dispersion medium.
<2> The p-type diffusion layer forming composition according to <1>, wherein the acceptor element is at least one selected from B (boron), Al (aluminum), and Ga (gallium).
<3> The glass powder containing the acceptor element is at least one acceptor element-containing material selected from B ₂ O ₃ , Al ₂ O _3, and Ga ₂ O ₃ , and SiO ₂ , K ₂ O, and Na ₂ O. And at least one glass component selected from Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ , and MoO _3. The p-type diffusion layer forming composition according to <1> or <2>.

<4> A step of applying the p-type diffusion layer forming composition according to any one of <1> to <3> on a semiconductor substrate;
A step of applying a thermal diffusion treatment;
The manufacturing method of the p-type diffused layer which has this.
<5> A step of applying the p-type diffusion layer forming composition according to any one of <1> to <3> on a semiconductor substrate;
Applying a thermal diffusion treatment to form a p-type diffusion layer;
Forming an electrode on the formed p-type diffusion layer;
The manufacturing method of the solar cell element which has this.

  According to the present invention, in a manufacturing process of a solar cell element using a semiconductor substrate, a p-type diffusion layer is formed without generating internal stress and warping of the substrate while suppressing roughening of the substrate surface. It becomes possible to do.

First, the p-type diffusion layer forming composition of the present invention will be described, and then a p-type diffusion layer using the p-type diffusion layer forming composition and a method for producing a solar cell element will be described.
In this specification, the term “process” is not limited to an independent process, and even if it cannot be clearly distinguished from other processes, the term “process” is used if the intended action of the process is achieved. included. 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. 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 p-type diffusion layer forming composition of the present invention contains at least an acceptor element-containing glass powder (hereinafter sometimes simply referred to as “glass powder”), silicon particles, and a dispersion medium, and further has coating properties and the like. In consideration of the above, other additives may be contained as necessary.
Here, the p-type diffusion layer forming composition includes a glass powder containing an acceptor element, and a material capable of forming a p-type diffusion layer by thermally diffusing the acceptor element after being applied to a silicon substrate. Say. By using the p-type diffusion layer forming composition containing the acceptor element in the glass powder, the p ⁺ -type diffusion layer forming step and the ohmic contact forming step can be separated, and the choice of electrode materials for forming the ohmic contact is expanded. The choice of electrode structure is also widened.
For example, if a low resistance material such as silver is used for the electrode, a low resistance can be achieved with a thin film thickness. Further, the electrodes need not be formed on the entire surface, and may be partially formed like a comb shape. As described above, by forming a partial shape such as a thin film or a comb shape, it is possible to form a p-type diffusion layer while suppressing the occurrence of internal stress in the silicon substrate and warping of the substrate.

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

  Furthermore, since the p-type diffusion layer forming composition of the present invention contains silicon particles, the contact area between the molten glass layer and the semiconductor substrate is reduced. As a result, surface roughening due to the reaction between the molten glass and the surface of the semiconductor substrate can be suppressed, and excellent etching characteristics can be obtained in removing the glass layer. Furthermore, the diffusibility of the acceptor element is excellent.

The glass powder containing the acceptor element according to the present invention will be described in detail.
An acceptor element is an element that can form a p-type diffusion layer by doping into a silicon substrate. As the acceptor element, a Group 13 element can be used, and examples thereof include B (boron), Al (aluminum), and Ga (gallium).

Examples of the acceptor element-containing material used for introducing the acceptor element into the glass powder include B ₂ O ₃ , Al ₂ O ₃ , and Ga ₂ O ₃ , and B ₂ O ₃ , Al ₂ O _3, and Ga ₂ O. It is preferable to use at least one selected from ₃ .

Moreover, the glass powder containing an acceptor 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 , GeO ₂ , TeO _2, and Lu ₂ O _3. SiO ₂ , K ₂ O, It is preferable to use at least one selected from Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ and MoO ₃ .

Specific examples of the glass powder containing an acceptor element include a system containing both the acceptor element-containing substance and the glass component substance, and a B ₂ O ₃ —SiO ₂ system (in order of acceptor element-containing substance—glass component substance). And the same applies hereinafter), B ₂ O ₃ —ZnO system, B ₂ O ₃ —PbO system, B ₂ O ₃ single system, etc., a system containing B ₂ O ₃ as an acceptor element-containing substance, Al ₂ O ₃ —SiO ₂ system including _{for Al} 2 _{O 3} acceptor element-containing substance such as _2-based, Ga ₂ O 3 -SiO ₂ systems include glass powder, such as systems including _Ga 2 _{O 3} as the acceptor element-containing substance in the system or the like.
_Further, Al ₂ O 3 _-B 2 _{O 3 system,} Ga ₂ O 3 _-B as 2 _{O 3} system or the like, may be a glass powder containing two or more acceptor element-containing material.
In the above, a single component glass or a composite glass containing two components is exemplified, but a glass powder containing three or more components such as B ₂ O ₃ —SiO ₂ —Na ₂ O 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.

  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 applicability to a substrate and uniform diffusibility when a p-type diffusion layer forming composition is used. It is desirable to have a substantially spherical shape, flat shape, or plate shape. The particle size of the glass powder is desirably 50 μm or less. When glass powder having a particle size of 50 μm or less is used, a smooth coating film is easily obtained. Further, the particle size of the glass powder is more preferably 10 μm or less. The lower limit is not particularly limited, but is preferably 0.01 μm or more.
Here, the particle diameter of glass represents a volume average particle diameter, and can be measured by a laser scattering diffraction method particle size distribution measuring apparatus or the like.

The glass powder containing an acceptor element is produced by the following procedure.
First, weigh the ingredients and fill the crucible. Examples of the material for the crucible include platinum, platinum-rhodium, iridium, alumina, quartz, carbon, and the like, and are appropriately selected in consideration of the melting temperature, atmosphere, reactivity with the molten material, and the like.
Next, it heats with the temperature according to a glass composition with an electric furnace, and is set as a melt. At this time, it is desirable to stir the melt uniformly.
Subsequently, the obtained melt is poured onto a zirconia substrate, a carbon substrate or the like to vitrify the melt.
Finally, the 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 acceptor element in the p-type diffusion layer forming composition is determined in consideration of applicability, acceptor element diffusibility, and the like. In general, the content ratio of the glass powder in the p-type diffusion layer forming composition is preferably 0.1% by mass or more and 95% by mass or less, more preferably 1% by mass or more and 90% by mass or less, The content is more preferably 1.5% by mass to 85% by mass, and particularly preferably 2% by mass to 80% by mass.

Next, silicon particles will be described.
The p-type diffusion layer forming composition includes silicon particles. The silicon particles are preferably dispersed uniformly in the p-type diffusion layer forming composition.
By including the silicon powder, the diffusion efficiency of the acceptor element in the thermal diffusion treatment can be improved, and the surface roughness of the semiconductor substrate can be suppressed. This can be considered as follows, for example.

  When the p-type diffusion-forming composition contains silicon particles, when the glass powder containing the acceptor element is melted during the thermal diffusion process described later, the molten glass comes into contact with the semiconductor substrate on the semiconductor substrate. Can be prevented from covering the entire surface of the semiconductor substrate. Thereby, it is thought that the production | generation ratio of the acceptor element containing material from molten glass increases, and the diffusion amount of the acceptor element to a silicon substrate increases. Moreover, it can be considered that this improves the etching removability of the glass layer formed on the semiconductor substrate after the thermal diffusion treatment and can suppress the roughening on the surface of the semiconductor substrate.

As will be described later, when the p-type diffusion layer forming composition contains a binder, the binder may burn and decompose during the thermal diffusion treatment. At this time, if the molten glass layer exists in a dense state, the binder may not be sufficiently decomposed even at a high temperature, and may remain as a resin decomposition product residue on the semiconductor substrate. In most cases, this residue can be removed by a subsequent etching process, but it remains in the form of deposits (residue) on the semiconductor substrate. It may become.
However, since the p-type diffusion layer forming composition contains silicon particles, when the glass powder is melted during the thermal diffusion treatment, the silicon particles are in contact with the semiconductor substrate, so that the molten glass layer is in a dense state. It is considered that it is possible to prevent the deposit (residue) from remaining on the semiconductor substrate.

The deposit (residue) on the semiconductor substrate has a size of 1 when an area of 100 μm × 100 μm on the surface of the semiconductor substrate on which the p-type diffusion layer is formed is observed with an optical microscope or a scanning electron microscope. It is recognized as a foreign matter of 0.0 μm or more. Note that the size of the foreign matter being 1.0 μm or more means that the minimum distance between the parallel lines is 1.0 μm or more when sandwiched between a pair of parallel lines so as to contact the outer edge of the projected image of the foreign matter. Means.
Further, the roughening of the surface of the semiconductor substrate means that the surface is observed as a concave shape with a size of 1 μm or more when a 100 μm × 100 μm region of the silicon substrate surface is observed, Evaluation can be performed using an optical microscope or a scanning electron microscope. The size of the concave portion being 1.0 μm or more means that the minimum distance between the parallel lines is 1.0 μm or more when sandwiched between a pair of parallel lines so as to contact the outer edge of the concave portion. means.

The content (purity) of silicon atoms constituting the silicon particles is not particularly limited as long as it is not melted during the thermal diffusion treatment. For example, it is preferably 99% by mass or more, and more preferably 99.999% by mass or more.
The shape of the silicon particles is not particularly limited, and may be any of a substantially spherical shape, a flat shape, a block shape, a plate, and the like. Among these, from the viewpoint of acceptor atom diffusibility and suppression of roughening of the substrate surface, at least one of a substantially spherical shape and a flat shape is preferable, and a substantially spherical shape is more preferable.
Here, that the silicon particles are substantially spherical means that the circularity of the projected image of the silicon particles is 0.85 or more, and preferably 0.90 or more. The circularity of the projected silicon particle image is calculated as a numerical value obtained by dividing the circumference of a circle having the same projected area by the circumference of the silicon particle measured from the projected image, and is an arithmetic operation of 50 silicon particles. Calculated as an average value.

The particle diameter of the silicon particles is not particularly limited. From the viewpoint of acceptor element diffusibility and suppression of roughening of the substrate surface, the volume average particle size is preferably 0.1 μm or more and 50 μm or less, and more preferably 0.5 μm or more and 20 μm or less.
Here, the particle diameter of the silicon particles can be measured using a laser scattering diffraction particle size distribution measuring apparatus or the like as the volume average particle diameter.

  Moreover, the ratio of the particle diameter of the silicon particles and the glass powder is not particularly limited. From the viewpoint of acceptor atom diffusivity and suppression of roughening of the substrate surface, the ratio of the particle diameter of the glass powder particles to the particle diameter of the silicon particles (glass powder particles / silicon particles) is 0.05 to 1000. Preferably, it is 0.1-500.

The content of silicon particles in the p-type diffusion layer forming composition is determined in consideration of coating properties, acceptor element diffusibility, binder combustion / decomposition, and the like. In general, the content of silicon particles in the p-type diffusion layer forming composition is preferably 3% by mass or more and 65% by mass or less, and more preferably 5% by mass or more and 60% by mass or less.
By setting the content of silicon particles to 3% by mass or more, the acceptor element can be efficiently diffused in the semiconductor substrate, and a p-type diffusion layer having excellent characteristics can be formed. In addition, when the content ratio of the silicon particles is 65% by mass or less, the viscosity can be adjusted while the acceptor element is sufficiently diffused, and the impartability to the semiconductor substrate is improved.

  Moreover, the ratio of the content of the silicon particles and the glass powder is not particularly limited. From the viewpoint of acceptor element diffusibility and suppression of roughening of the substrate surface, the ratio of the silicon particle content to the glass powder particle content (silicon particles / glass powder particles) is 0.05 to 500. Preferably, it is 0.1-300.

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, a solvent, or the like is employed as the dispersion medium.

  Examples of the binder include polyvinyl alcohol, polyacrylamides, polyvinyl amides, polyvinyl pyrrolidone, polyethylene oxides, polysulfonic acid, acrylamide alkyl sulfonic acid, cellulose ethers, cellulose derivatives, carboxymethyl cellulose, hydroxyethyl cellulose, ethyl cellulose, gelatin, starch And starch derivatives, sodium alginate, xanthan, guar and guar derivatives, scleroglucan, tragacanth or dextrin derivatives, (meth) acrylic acid resins, (meth) acrylic acid ester resins (eg alkyl (meth) acrylate resins, dimethylamino Ethyl (meth) acrylate resin), butadiene resin, styrene resin and copolymers thereof, siloxane resin, etc. You can choose. 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, for example, acetone, methyl ethyl ketone, methyl-n-propyl ketone, methyl-iso-propyl ketone, methyl-n-butyl ketone, methyl-iso-butyl ketone, methyl-n-pentyl ketone, methyl-n. -Ketone solvents such as hexyl ketone, 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, 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-bu Ether, triethylene 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, dipropylene glycol methyl-n-butyl ether, dipropylene glycol di-n-propyl ether, dipropylene glycol di-n-butyl ether, dipropylene glycol methyl-n-hexyl ether, tripropylene glycol dimethyl ether, tripropylene glycol diethyl ether , Tripropylene glycol methyl ethyl ether, tripropylene glycol methyl n-butyl ether, tripropylene glycol di-n-butyl ether, tripropylene glycol methyl n-hexyl ether, tetrapropylene glycol dimethyl ether, tetrapropylene glycol diethyl ether, tetradipropylene Glycol methyl ethyl ether, tetrapropylene glycol methyl-n Ether solvents such as butyl ether, 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 N-butyl acetate, i-butyl acetate, sec-butyl acetate, n-pentyl acetate, sec-pentyl acetate, 3-methoxybutyl acetate, methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, 2- (acetate) 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, acetic acid Propylene glycol methyl ether, dipropylene glycol ethyl ether acetate, diacetic acid glycol, 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 Esters such as glycol ethyl ether acetate, propylene glycol propyl ether acetate, γ-butyrolactone, γ-valerolactone Agent: acetonitrile, N-methylpyrrolidinone, N-ethylpyrrolidinone, N-propylpyrrolidinone, N-butylpyrrolidinone, N-hexylpyrrolidinone, N-cyclohexylpyrrolidinone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide Aprotic polar solvents such as 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-ethyl Ruhexanol, sec-octanol, n-nonyl alcohol, n-decanol, sec-undecyl alcohol, trimethylnonyl alcohol, sec-tetradecyl alcohol, sec-heptadecyl alcohol, phenol, cyclohexanol, methylcyclohexanol, benzyl alcohol, Alcohol solvents such as ethylene 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 mono Phenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, Ethylene 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 Glycol monoether solvents such as monomethyl ether; terpene solvents such as α-terpinene, α-terpineol, myrcene, alloocimene, limonene, dipentene, α-pinene, β-pinene, terpineol, carvone, osimene, and ferrandolene; water Can be mentioned. These are used singly or in combination of two or more.
In the case of a p-type diffusion layer forming composition, α-terpineol, diethylene glycol mono-n-butyl ether, and 2- (2-butoxyethoxy) ethyl acetate are preferable from the viewpoint of applicability to the substrate.

  The constitution and content ratio of the dispersion medium in the p-type diffusion layer forming composition are determined in consideration of applicability and acceptor concentration.

  Next, the manufacturing method of the p-type diffused layer and solar cell element of this invention is demonstrated.

First, an alkaline solution is applied to a silicon substrate which is a p-type semiconductor substrate 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. In the solar cell element, by forming a texture structure on the light receiving surface (surface) side, a light confinement effect is promoted, and high efficiency is achieved.

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

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

  Depending on the composition of the p-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 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 of the p-type diffusion layer forming composition and are not particularly limited to the above conditions in the present invention.

The semiconductor substrate coated with the p-type diffusion layer forming composition is heat treated at 600 ° C. to 1200 ° C. By this heat treatment, the acceptor element diffuses into the semiconductor substrate, and a p ⁺ -type diffusion layer is formed. A known continuous furnace, batch furnace, or the like can be applied to the heat treatment.
Moreover, the time of heat processing can be suitably selected according to the content rate etc. of the acceptor element contained in a p-type diffused layer formation composition. For example, it may be 1 minute to 60 minutes, and is preferably 2 minutes to 30 minutes.
Since a glass layer is formed on the surface of the p ⁺ type diffusion layer, the glass layer 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.
Since the p-type diffusion layer forming composition contains silicon particles, it is excellent in etching removability of the glass layer.

Further, in the conventional manufacturing method, an aluminum paste is printed on the back surface, and this is baked to change the n-type diffusion layer into a p ⁺ -type diffusion layer, and at the same time, an ohmic contact is obtained. However, the electrical conductivity of the aluminum layer formed from the aluminum paste is low, and in order to reduce the sheet resistance, the aluminum layer usually formed on the entire back surface must have a thickness of about 10 μm to 20 μm after firing. Furthermore, since the thermal expansion coefficients of silicon and aluminum differ greatly, a large internal stress is generated in the silicon substrate during the firing and cooling process, causing warpage.
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, after the n-type diffusion layer is converted into the p ⁺ -type diffusion layer by the p-type diffusion layer forming composition of the present invention, an electrode is separately provided on the p ⁺ -type diffusion layer. . Therefore, the material used for the back electrode is not limited to aluminum. For example, Ag (silver) or Cu (copper) can be applied, and the thickness of the back electrode can be made thinner than the conventional one. Further, it is not necessary to form the entire surface. Therefore, it is possible to reduce internal stress and warpage in the silicon substrate that occur during the firing and cooling processes.

An antireflection film is formed on the n-type diffusion layer formed as described above. 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.

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

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

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

The shape of the surface electrode will be described. The surface electrode includes a bus bar electrode and a finger electrode that intersects the bus bar electrode.
Such a surface electrode can be formed by means such as screen printing of the above-described metal paste, plating of the electrode material, or vapor deposition of the electrode material by electron beam heating in a high vacuum. A surface electrode composed of a bus bar electrode and a finger electrode is generally used as an electrode on the light receiving surface side and is well known, and known forming means for the bus bar electrode and the finger electrode on the light receiving surface side can be applied.

In the above-described method for manufacturing a p-type diffusion layer and a solar cell element, a mixed gas of phosphorus oxychloride (POCl ₃ ), nitrogen and oxygen is used to form an n-type diffusion layer on a silicon substrate which is a p-type semiconductor substrate. Although used, the n-type diffusion layer may be formed using the n-type diffusion layer forming composition. The n-type diffusion layer forming composition contains a Group 15 element such as P (phosphorus) or Sb (antimony) as a donor element.
In the method using the n-type diffusion layer forming composition for forming the n-type diffusion layer, first, the n-type diffusion layer forming composition is applied to the light-receiving surface which is the surface of the p-type semiconductor substrate, and the p-type of the present invention is applied to the back surface. The diffusion layer forming composition is applied and heat-treated at 600 to 1200 ° C. By this heat treatment, the donor element diffuses into the p-type semiconductor substrate on the front surface to form an n-type diffusion layer, and the acceptor element diffuses on the back surface to form a p ⁺ -type diffusion layer. Except for this step, a solar cell element is produced by the same steps as those described above.

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

<Example 1>
B ₂ O ₃ —SiO ₂ —R ₂ O (R: Na, K, Li) glass powder (trade name: TMX-404) having a substantially spherical particle shape, an average particle diameter of 4.9 μm, and a softening temperature of 561 ° C. 20 g of Toago Material Technology Co., Ltd.), 10 g of silicon particles (manufactured by High Purity Chemical Laboratory, volume average particle diameter 10 μm, approximately spherical), 0.5 g of ethyl cellulose, and 2- (2-butoxy acetate) Ethoxy) ethyl 10 g was mixed using an automatic mortar kneader to make a paste to prepare a p-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 a p-type silicon substrate having an n-type layer formed on the surface by screen printing, and dried on a hot plate at 150 ° C. for 5 minutes. Subsequently, thermal diffusion treatment was performed for 30 minutes in an electric furnace set at 1000 ° C., and then the substrate was immersed in hydrofluoric acid for 5 minutes in order to remove the glass layer, and washed with running water.
When the surface was observed with an optical microscope, there was no deposit on the surface, and drying was performed as it was. In addition, the presence or absence of a deposit | attachment observes the p surface of a silicon substrate about 100 micrometers x 100 micrometers arbitrary area | regions using TM-1000 type | mold scanning electron microscope made from Hitachi High-Technologies, Inc., and the magnitude | size is 1 micrometer or more. It was judged as the presence or absence of kimono.

The sheet resistance of the surface on which the p-type diffusion layer forming composition was applied was 98Ω / □, and B (boron) was diffused to form a p-type diffusion layer.

  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 roughening of the surface of the silicon substrate on which the p-type diffusion layer was formed was evaluated, no roughening of the substrate surface was observed. In addition, the roughening of the surface of the silicon substrate was observed with respect to an arbitrary region of 100 μm × 100 μm using a TM-1000 scanning electron microscope manufactured by Hitachi High-Technologies Co., Ltd. evaluated.
Further, no warpage occurred in the silicon substrate.

<Example 2>
A p-type diffusion layer was formed in the same manner as in Example 1 except that the temperature of the thermal diffusion treatment was 1100 ° C.
When the surface of the substrate after hydrofluoric acid treatment and washing with running water was observed with an optical microscope, there was no deposit on the surface.

  The sheet resistance of the surface on which the p-type diffusion layer forming composition was applied was 76Ω / □, and B (boron) was mixed to form a p-type diffusion layer.

When roughening the surface of the silicon substrate on which the p-type diffusion layer was formed was evaluated using a scanning electron microscope, no roughening of the substrate surface was observed.
Further, no warpage occurred in the silicon substrate.

<Example 3>
B ₂ O ₃ —SiO ₂ —RO (R: Mg, Ca, Sr, Ba) glass powder (trade name: TMX-603) having a substantially spherical particle shape, an average particle diameter of 3.2 μm, and a softening temperature of 815 ° C. P-type diffusion layer forming composition was prepared in the same manner as in Example 1 except that Toago Material Technology Co., Ltd. was used, and p-type diffusion layer formation was performed using this composition.
When the surface after hydrofluoric acid treatment and washing with running water was observed with an optical microscope, there was no deposit on the surface.
The sheet resistance of the surface on which the p-type diffusion layer forming composition was applied was 38Ω / □, and B (boron) was diffused to form a p-type diffusion layer.

When roughening the surface of the silicon substrate on which the p-type diffusion layer was formed was evaluated using a scanning electron microscope, no roughening of the substrate surface was observed.
Further, no warpage occurred in the silicon substrate.

<Example 4>
A p-type diffusion layer forming composition was prepared in the same manner as in Example 1 except that the amount of silicon particles was 30 g, and a p-type diffusion layer was formed using this composition.
When the surface after hydrofluoric acid treatment and washing with running water was observed with an optical microscope, there was no deposit on the surface.
The sheet resistance on the surface coated with the p-type diffusion layer forming composition was 84Ω / □, and B (boron) was diffused to form a p-type diffusion layer.

When roughening the surface of the silicon substrate on which the p-type diffusion layer was formed was evaluated using a scanning electron microscope, no roughening of the substrate surface was observed.
Further, no warpage occurred in the silicon substrate.

<Example 5>
A p-type diffusion layer forming composition was prepared in the same manner as in Example 1 except that the amount of silicon particles was 2 g, and a p-type diffusion layer was formed using this composition.
When the surface after hydrofluoric acid treatment and washing with running water was observed with an optical microscope, there was no deposit on the surface.
The sheet resistance of the surface on which the p-type diffusion layer forming composition was applied was 103Ω / □, and B (boron) was diffused to form a p-type diffusion layer.

When roughening the surface of the silicon substrate on which the p-type diffusion layer was formed was evaluated using a scanning electron microscope, no roughening of the substrate surface was observed.
Further, no warpage occurred in the silicon substrate.

<Example 6>
A p-type diffusion layer forming composition was prepared in the same manner as in Example 1 except that the volume average particle diameter of silicon particles was 5.0 μm, and a p-type diffusion layer was formed using this composition.
When the surface after hydrofluoric acid treatment and washing with running water was observed with an optical microscope, there was no deposit on the surface.
The sheet resistance on the surface on which the p-type diffusion layer forming composition was applied was 92Ω / □, and B (boron) was diffused to form a p-type diffusion layer.

<Comparative Example 1>
The composition of the p-type diffusion layer forming composition is B ₂ O ₃ —SiO ₂ —R ₂ O (R: Na, K, Li) having a substantially spherical particle shape, an average particle diameter of 4.9 μm, and a softening temperature of 561 ° C. Example 1 except that 20 g of a glass powder (trade name: TMX-404, manufactured by Toago Material Technology Co., Ltd.), 0.5 g of ethyl cellulose, and 10 g of 2- (2-butoxyethoxy) ethyl acetate were used. In the same manner as described above, a p-type diffusion layer forming composition was prepared, and a p-type diffusion layer was formed using the composition.
When the surface of the cleaned silicon substrate was observed with an optical microscope, there was some deposits on the surface.

  The sheet resistance of the surface on which the p-type diffusion layer forming composition was applied was 93Ω / □, and B (boron) was diffused to form a p-type diffusion layer.

When the roughening of the surface of the silicon substrate on which the p-type diffusion layer was formed was evaluated using a scanning electron microscope, the occurrence of roughening was recognized on the substrate surface.
Further, no warpage occurred in the silicon substrate.

Claims (5)

  A p-type diffusion layer forming composition containing glass powder containing an acceptor element, silicon particles, and a dispersion medium.   The p-type diffusion layer forming composition according to claim 1, wherein the acceptor element is at least one selected from B (boron), Al (aluminum), and Ga (gallium). The glass powder containing the acceptor element is at least one acceptor element-containing substance selected from B ₂ O ₃ , Al ₂ O ₃ and Ga ₂ O ₃ , and 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. Alternatively, the p-type diffusion layer forming composition according to claim 2.   A method for producing a p-type diffusion layer, comprising: applying a p-type diffusion layer forming composition according to any one of claims 1 to 3 on a semiconductor substrate; and applying a thermal diffusion treatment. . Applying a p-type diffusion layer forming composition according to any one of claims 1 to 3 on a semiconductor substrate;
Applying a thermal diffusion treatment to form a p-type diffusion layer;
Forming an electrode on the formed p-type diffusion layer;
The manufacturing method of the solar cell element which has this.