JP6139155B2 - Diffusion agent composition and method for forming impurity diffusion layer - Google Patents

Description

  The present invention relates to a diffusing agent composition and a method for forming an impurity diffusion layer.

  Conventionally, in the manufacture of solar cells, when an N-type impurity diffusion layer is formed in a semiconductor substrate, for example, a diffusing agent containing an N-type impurity diffusing component is changed from a diffusing agent applied to the surface of the semiconductor substrate to an N-type The N-type impurity diffusion layer was formed by diffusing the impurity diffusion component. Specifically, first, a thermal oxide film is formed on the surface of the semiconductor substrate, and then a resist having a predetermined pattern is stacked on the thermal oxide film by photolithography, and the resist is used as a mask with an acid or an alkali. The portion of the thermal oxide film that is not masked is etched, and the resist is removed to form a mask of the thermal oxide film. Then, a diffusing agent containing an N-type impurity diffusing component is applied to form a diffusion composition film in a portion where the mask is open. The portion is diffused at a high temperature to form an N-type impurity diffusion layer.

JP 2001-71489 A JP 2002-75892 A JP 2008-543097 A

  After applying a diffusing agent on the semiconductor substrate, a drying process is performed in a drying furnace. At this time, with the conventional diffusing agent, deposits containing a large amount of phosphorus compounds are likely to accumulate in the furnace or exhaust port of the drying furnace, so it is necessary to stop the drying furnace and frequently remove the deposits. It was. For this reason, the productivity of solar cells has been reduced. Further, when deposits accumulate in the drying furnace, the deposits may fall on the silicon wafer, which may adversely affect the photoelectric conversion efficiency of the solar cell.

  The present invention has been made in view of these problems, and the purpose thereof is to hardly generate a deposit containing a large amount of a phosphorus compound in a furnace when a semiconductor substrate coated with a diffusing agent composition is dried in a drying furnace. It is in the provision of technology that can be made to.

（１）式中、Ｒ^３は炭素数５以上の炭化水素基であり、Ｒ^３が複数ある場合には同一でも異なっていてもよい。ｎは１または２である。 One embodiment of the present invention is a diffusing agent composition. The diffusing agent composition is a diffusing agent composition used for printing an impurity diffusing component on a semiconductor substrate, and contains an impurity diffusing component (A) and a binder resin (B). A) is a phosphate represented by the following general formula (1).

(1) In the formula, R ³ is a hydrocarbon group having 5 or more carbon atoms, and when there are a plurality of R ^{3 s} , they may be the same or different. n is 1 or 2.

  In the diffusing agent composition of the above aspect, the thermal decomposition temperature of the impurity diffusion component (A) may be 200 ° C. or higher. Further, the binder resin (B) may have a weight average molecular weight of 10,000 or more, and the binder resin (B) may be an acrylic resin. Moreover, you may further contain the organic solvent (C) whose boiling point is 100 degreeC or more.

  Another embodiment of the present invention is a method for forming an impurity diffusion layer. A method of forming the impurity diffusion layer includes a pattern forming step of applying a diffusing agent composition according to any one of claims 1 to 5 to a semiconductor substrate to form a pattern, and an impurity of the diffusing agent composition. A diffusion step of diffusing the diffusion component (A) into the semiconductor substrate. In the method of forming an impurity diffusion layer of this aspect, the semiconductor substrate may be used for a solar cell.

  ADVANTAGE OF THE INVENTION According to this invention, when the semiconductor substrate which apply | coated the diffusing agent composition is dried with a drying furnace, the deposit which contains a phosphorus compound in large quantities in a furnace can be made hard to produce.

1A to 1D are process cross-sectional views for explaining a method for manufacturing a solar cell including a method for forming an impurity diffusion layer according to an embodiment. 2A to 2D are process cross-sectional views for explaining a method for manufacturing a solar cell including a method for forming an impurity diffusion layer according to an embodiment. It is a figure which shows the apparatus structure used when analyzing the generated gas at the time of drying.

  The diffusing agent composition according to the embodiment is suitably used for printing impurity diffusion components on a semiconductor substrate. A solar cell is suitable for the use of the semiconductor substrate. The diffusing agent composition contains an impurity diffusing component (A) and a binder resin (B). Hereinafter, the impurity diffusion component (A) and the binder resin (B) will be described in detail.

（１）式中、Ｒ^３は炭素数５以上の炭化水素基であり、Ｒ^３が複数ある場合には同一でも異なっていてもよい。炭素数の上限については例えば２０以下、好ましくは１５以下である。ｎは１または２である。炭化水素基としては、アルキル基、アルケニル基、アリール基、アラルキル基などが挙げられる。 <Impurity diffusion component (A)>
The impurity diffusion component (A) is a phosphate ester represented by the following general formula (1).

(1) In the formula, R ³ is a hydrocarbon group having 5 or more carbon atoms, and when there are a plurality of R ^{3 s} , they may be the same or different. About the upper limit of carbon number, it is 20 or less, for example, Preferably it is 15 or less. n is 1 or 2. Examples of the hydrocarbon group include an alkyl group, an alkenyl group, an aryl group, and an aralkyl group.

  More specifically, the impurity diffusion component (A) is monopentyl phosphate, dipentyl phosphate, monohexyl phosphate, dihexyl phosphate, monohexyl phosphate, dihexyl phosphate, monooctyl phosphate, dioctyl phosphate, phosphoric acid. Examples include monoethylhexyl, diethylhexyl phosphate, tridecyl phosphate, and isotridecyl phosphate. Two or more of these may be used.

  The thermal decomposition temperature of the impurity diffusion component (A) is preferably 200 ° C. or higher. Thereby, when the semiconductor substrate which apply | coated the diffusing agent composition is dried with a drying furnace, the effect of this invention of making it hard to produce the deposit which contains a phosphorus compound in large quantities in a furnace improves more. The upper limit of the thermal decomposition temperature of the impurity diffusion component (A) is not particularly limited and may be, for example, not more than the diffusion temperature in the diffusion step. The thermal decomposition temperature of the impurity diffusion component (A) can be measured using a differential thermothermal gravimetric simultaneous measurement apparatus (TG-DTA). For example, ethylhexyl phosphate (monoester: diester = 1: 1 (molar ratio)) is 229 ° C., and isotridecyl phosphate (monoester: diester = 1: 1 (molar ratio)) is 247 ° C.

  5-70 mass% is preferable and, as for content of the impurity diffusion component (A) with respect to the whole diffusing agent composition, 20-65 mass% is more preferable.

<Binder resin (B)>
The weight average molecular weight of the binder resin (B) is preferably 10,000 or more. Thereby, printability or applicability is improved. More preferably, it is 10000-100,000, More preferably, it is the range of 10000-50000. Moreover, it is preferable that binder resin (B) is an acrylic resin. Thereby, since binder resin decomposes | disassembles and lose | disappears before a spreading | diffusion process, the diffusibility of an impurity diffusion component (A) becomes favorable.

  The acrylic resin is not particularly limited, and includes, for example, a structural unit derived from a (meth) acrylic acid alkyl ester and a structural unit derived from a hydroxy (meth) acrylic acid alkyl ester or a polymerizable compound having a carboxy group. Or an acrylic resin containing a structural unit derived from a polymerizable compound having an ether bond and a structural unit derived from a polymerizable compound having a carboxy group.

  As the (meth) acrylic acid alkyl ester, those having an alkyl group having 1 to 15 carbon atoms are preferable, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate. Butyl (meth) acrylate, sec-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, 2-propylheptyl (meth) acrylate, and the like. As the hydroxy (meth) acrylic acid alkyl ester, those having a hydroxyl group-containing alkyl group having 1 to 5 carbon atoms are preferable, such as 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate. Can be mentioned.

  Examples of the polymerizable compound having an ether bond include 2-methoxyethyl (meth) acrylate, methoxytriethylene glycol (meth) acrylate, 3-methoxybutyl (meth) acrylate, ethyl carbitol (meth) acrylate, phenoxy polyethylene glycol (meta And (meth) acrylic acid derivatives having an ether bond and an ester bond such as acrylate, methoxypolypropylene glycol (meth) acrylate, and tetrahydrofurfuryl (meth) acrylate. These compounds can be used alone or in combination of two or more. In the present specification, (meth) acrylate represents one or both of acrylate and methacrylate.

  Examples of the polymerizable compound having a carboxy group include monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid; 2-methacryloyloxyethyl succinic acid, and 2-methacryloyloxyethyl. Examples include maleic acid, 2-methacryloyloxyethyl phthalic acid, 2-methacryloyloxyethyl hexahydrophthalic acid and other compounds having a carboxy group and an ester bond, and acrylic acid and methacrylic acid are preferred. These compounds can be used alone or in combination of two or more.

  10-80 mass% is preferable and, as for content of binder resin (B) with respect to the whole diffusing agent composition, 20-60 mass% is more preferable.

<Organic solvent (C)>
The diffusing agent composition according to the embodiment may further include an organic solvent (C) having a boiling point of 100 ° C. or higher. When the boiling point is 100 degrees or more, the printability or application property is improved.

  Specific examples of the organic solvent (C) include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, propylene glycol. Monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monopropyl ether, diethylene glycol Cole monobutyl ether, diethylene glycol monophenyl ether, diethylene glycol diethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monopropyl ether acetate, propylene glycol monomethyl ether acetate , Propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, 2-methoxybutyl acetate, 3-methoxybutyl acetate, 4-methoxybutyl acetate, 2-methyl-3-methoxybutyl acetate, 2-ethoxybutyl acetate, 4 -Ethoxy Tyl acetate, 4-propoxybutyl acetate, methyl isobutyl ketone, ethyl isobutyl ketone, cyclohexanone, propyl propionate, isopropyl propionate, methyl-3-methoxypropionate, ethyl-3-methoxypropionate, ethyl-3-ethoxy Propionate, ethyl-3-propoxypropionate, propyl-3-methoxypropionate, isopropyl-3-methoxypropionate, butyl acetate, isoamyl acetate, methyl acetoacetate, methyl lactate, ethyl lactate, benzyl methyl ether Benzyl ethyl ether, benzene, toluene, xylene, butanol, isobutanol, 3-methyl-3-methoxybutanol, hexanol, cyclohexanol, gamma butyrolactone, etc. It is. These may be used alone or in combination of two or more.

  Content of the organic solvent (C) with respect to the whole diffusing agent composition should just be adjusted suitably with the printing method, and 1-70 mass% is preferable.

<SiO ₂ fine particles (D)>
The diffusing agent composition according to the embodiment may further include SiO ₂ fine particles (D). The average particle diameter of the SiO ₂ fine particles (D) is preferably 1 μm or less. Specific examples of the SiO ₂ fine particles (D) include fumed silica. When the diffusing agent composition contains SiO ₂ fine particles (D), it is possible to impart thixotropy or pseudoplasticity to the diffusing agent composition. Thereby, the characteristic of a diffusing agent composition can be made suitable for screen printing.

The content of SiO ₂ fine particles (D) to the entire diffusing agent composition is preferably 3 to 20 wt%, more preferably from 5 to 15% by mass.

  The diffusing agent composition of the present embodiment may further contain a surfactant and an additive as other components. By including the surfactant, it is possible to improve coating properties, planarization properties, and development properties, and to reduce the occurrence of uneven coating of the diffusing agent composition layer formed after coating. As such a surfactant component, a conventionally known component can be used, and a silicone-based surfactant is preferable. Moreover, it is preferable that a surfactant component is contained in 100-10000 mass ppm with respect to the whole diffusing agent composition, Preferably, it is 300-5000 mass ppm, More preferably, it is contained in 500-3000 mass ppm. Furthermore, since it is excellent in the peelability of the diffusing agent composition layer after a diffusion process as it is 2000 mass ppm or less, it is more preferable. Surfactant components may be used alone or in combination.

  Additives are added as necessary to adjust properties such as viscosity of the diffusing agent composition. Examples of the additive include polypropylene glycol.

  According to the diffusing agent composition described above, when a diffusing agent composition is applied to a semiconductor substrate and then subjected to a drying treatment in a drying furnace, the generation of deposits containing a large amount of phosphorus compounds in the furnace is suppressed. can do. In addition, since the deposits in the furnace are reduced, the possibility that phosphorus atoms contained in the deposits fall on the semiconductor substrate can be reduced, so that the photoelectric conversion characteristics of the solar cell manufactured using the semiconductor substrate Can be stabilized.

  Further, the thermal decomposition temperature of the impurity diffusion component (A) is 200 ° C. or higher, the weight average molecular weight of the binder resin (B) is 10,000 or higher, the binder resin (B) is an acrylic resin, and the boiling point is When the semiconductor substrate coated with the diffusing agent composition is dried in a drying furnace by further including one or more arbitrary items of the organic solvent (C) at 100 ° C. or higher. In addition to the effect of the present invention that makes it difficult to produce a deposit containing a large amount of a phosphorus compound, the various effects described above can be further enhanced.

(Method for forming impurity diffusion layer and method for producing solar cell)
With reference to FIG. 1 (A) to FIG. 1 (D) and FIG. 2 (A) to FIG. 2 (D), the above-described diffusing agent composition containing an impurity diffusion component (A) is applied to a semiconductor substrate by coating. A method of forming an impurity diffusion layer, comprising: forming a diffusion composition film or printing to form a pattern; and diffusing the impurity diffusion component (A) in the diffusing agent composition into the semiconductor substrate, and A method for manufacturing a solar cell including a semiconductor substrate on which an impurity diffusion layer is formed will be described. 1A to 1D and FIGS. 2A to 2D are cross-sectional views for explaining a method for manufacturing a solar cell including a method for forming an impurity diffusion layer according to an embodiment. FIG.

  First, as shown in FIG. 1A, a semiconductor substrate 1 such as a P-type silicon substrate is prepared. Then, as shown in FIG. 1B, a texture portion 1a having a fine concavo-convex structure is formed on one main surface of the semiconductor substrate 1 using a known wet etching method. Reflection of light on the surface of the semiconductor substrate 1 is prevented by the texture portion 1a. Subsequently, as shown in FIG. 1C, the diffusing agent composition 2 containing the impurity diffusion component (A) is applied to the main surface of the semiconductor substrate 1 on the textured portion 1a side.

  The diffusing agent composition 2 is applied to the surface of the semiconductor substrate 1 by a roll coat printing method, a screen printing method, or the like (in addition, when a pattern is formed instead of a coating film, the screen printing method is preferable). After forming the impurity diffusing agent layer in this way, the diffusing agent composition 2 applied using a known means such as an oven is dried.

  Next, as shown in FIG. 1D, the semiconductor substrate 1 coated with the diffusing agent composition 2 is placed in an electric furnace and baked. After firing, the impurity diffusion component (A) in the diffusing agent composition 2 is diffused from the surface of the semiconductor substrate 1 into the semiconductor substrate 1 in an electric furnace. The diffusion temperature in the diffusion step is, for example, in the range of 800 to 1000 degrees. Instead of the electric furnace, the semiconductor substrate 1 may be heated by conventional laser irradiation. In this way, the impurity diffusion component (A) is diffused into the semiconductor substrate 1 to form the N-type impurity diffusion layer 3.

  Next, as shown in FIG. 2A, an unnecessary oxide film is removed by a known etching method. Then, as shown in FIG. 2B, a silicon nitride film (SiN film) is formed on the main surface of the semiconductor substrate 1 on the textured portion 1a side using a well-known chemical vapor deposition method (CVD method), for example, a plasma CVD method. A passivation film 4 made of a film is formed. This passivation film 4 also functions as an antireflection film.

  Next, as shown in FIG. 2C, the surface electrode 5 is patterned on the main surface of the semiconductor substrate 1 on the side of the passivation film 4 by, for example, screen printing of silver (Ag) paste. The surface electrode 5 is patterned to increase the efficiency of the solar cell. For example, the back electrode 6 is formed on the other main surface of the semiconductor substrate 1 by screen printing an aluminum (Al) paste.

  Next, as shown in FIG. 2D, the semiconductor substrate 1 on which the back electrode 6 is formed is placed in an electric furnace and baked, and then the aluminum on which the back electrode 6 is formed is transferred into the semiconductor substrate 1. To diffuse. Thereby, the electrical resistance on the back electrode 6 side can be reduced. Through the above steps, solar cell 10 according to the present embodiment can be manufactured.

  The present invention is not limited to the above-described embodiments, and various modifications such as design changes can be added based on the knowledge of those skilled in the art, and the embodiments to which such modifications are added are also possible. It is included in the scope of the present invention. A new embodiment generated by the combination of the above-described embodiment and the following modification has the effects of the combined embodiment and modification.

  The diffusing agent composition according to the above-described embodiment is employed in printing methods such as spin-on method, spray coating method, ink jet printing method, roll coat printing method, screen printing method, letterpress printing method, intaglio printing method, offset printing method and the like. You can also Of these, roll coat printing, screen printing, letterpress printing and intaglio printing are preferred.

  Examples of the present invention will be described below. However, these examples are merely examples for suitably explaining the present invention, and do not limit the present invention.

表１中のアクリル樹脂１、２は、それぞれ下記式（２）、式（３）で表される。

(Diffusion agent composition)
Table 1 shows the components and contents of the diffusing agent compositions of Examples 1 to 8 and Comparative Examples 1 and 2. In addition, about each phosphate ester which concerns on an impurity diffusion component, what mixed the monoester and diester (molar ratio 1: 1) was used.

The acrylic resins 1 and 2 in Table 1 are represented by the following formulas (2) and (3), respectively.

表２に示すように、実施例１〜８の拡散剤組成物を用いた場合には、比較例１，２の拡散剤組成物を用いた場合に比べてガス捕集溶剤中のリン原子濃度が大幅に低減することが確認された。比較例１、２では、拡散剤組成物に含まれるリン化合物が乾燥温度に耐えられずに昇華するが、実施例１〜８の拡散剤組成物に含まれるリン化合物は乾燥温度に耐えて塗布膜中に残存することが示唆された。 (Generated gas analysis)
After applying the diffusing agent composition of each example and each comparative example to a semiconductor substrate, the amount of phosphorus atoms contained in the gas generated during drying was analyzed by the following procedure.
(1) Spread 0.1 g of paste composed of the diffusing agent composition of each example and each comparative example on a silicon wafer with a bar coater.
(2) As shown in the schematic diagram of FIG. 3, the silicon wafer 30 was placed on the hot plate 20, the silicon wafer 30 was heated at 150 ° C. for 3 minutes, and the generated gas was stored in the gas collector 40. The gas is collected in a gas collecting solvent (propylene glycol monomethyl ether) 50.
(3) For each diffusing agent composition, the above (1) and (2) are repeated 10 times, and the phosphorus atom concentration contained in the gas component collected in the gas collection solvent 50 is determined by the ICP-AES (ICP emission) method. It was measured by. The obtained results are shown in Table 2.

As shown in Table 2, when the diffusing agent compositions of Examples 1 to 8 were used, the phosphorus atom concentration in the gas collection solvent was higher than when the diffusing agent compositions of Comparative Examples 1 and 2 were used. Was confirmed to be significantly reduced. In Comparative Examples 1 and 2, the phosphorus compound contained in the diffusing agent composition sublimes without being able to withstand the drying temperature, but the phosphorus compound contained in the diffusing agent composition in Examples 1 to 8 was applied to withstand the drying temperature. It was suggested that it remained in the film.

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate, 1a Texture part, 2 Diffusing agent composition, 3 N-type impurity diffusion layer, 4 Passivation film, 5 Front surface electrode, 6 Back surface electrode, 10 Solar cell, 20 Hot plate, 30 Silicon wafer, 40 Gas collector 50 Gas trapping solvent

Claims (7)

A diffusing agent composition used for printing an impurity diffusing component on a semiconductor substrate,
An impurity diffusion component (A);
A binder resin (B);
Containing
The diffusing agent composition, wherein the impurity diffusion component (A) is a phosphate ester represented by the following general formula (1).

In (1), R ³ is an alkyl or alkenyl group having 5 or more carbon atoms, it may be the same or different when there are a plurality of R ^3. n is 1 or 2.   The diffusing agent composition according to claim 1, wherein the thermal decomposition temperature of the impurity diffusion component (A) is 200 ° C or higher.   The diffusing agent composition according to claim 1 or 2, wherein the binder resin (B) has a weight average molecular weight of 10,000 or more.   The diffusing agent composition according to claim 3, wherein the binder resin (B) is an acrylic resin.   The diffusing agent composition according to any one of claims 1 to 4, further comprising an organic solvent (C) having a boiling point of 100 ° C or higher. A pattern forming step of forming a pattern by applying the diffusing agent composition according to any one of claims 1 to 5 to a semiconductor substrate;
A diffusion step of diffusing the impurity diffusion component (A) of the diffusing agent composition into the semiconductor substrate;
A method for forming an impurity diffusion layer, comprising:   The method for forming an impurity diffusion layer according to claim 6, wherein the semiconductor substrate is used in a solar cell.

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