JPWO2017188177A1 - Etching solution for semiconductor substrate - Google Patents

Abstract

The present invention is an alkaline etching solution for treating the surface of a semiconductor substrate for solar cells, including at least one hydroxystyrene polymer represented by the general formula (1), and an alkaline agent, An etching solution in which the total of monomers and oligomers represented by n of 1 to 8 in the hydroxystyrene polymer is 3.5% or less of the hydroxystyrene polymer. According to the present invention, it is possible to form a texture on a solar cell semiconductor substrate in a shorter time on a relatively low temperature side, and it is excellent in continuous productivity and product storage stability, and a surface with low light reflectance can be stably obtained. The effect is demonstrated. In addition, the pyramid-shaped irregularities with an average of 3 μm or less are stably formed, and the surface shape showing a light reflectance of 10% or less, which was not obtained by the prior art, is not influenced by lot fluctuation of the etching solution raw material. It can be stably applied to the semiconductor substrate.

Description

  The present invention relates to an etching solution for a semiconductor substrate, and more particularly to an etching solution for a semiconductor substrate for a solar cell. Furthermore, this invention relates to the etching power recovery agent, the manufacturing method of the semiconductor substrate for solar cells, and the semiconductor substrate for solar cells.

  In order to increase the power generation efficiency of a solar cell, conventionally, a method has been used in which irregularities are formed on the surface of a semiconductor substrate for solar cells and incident light from the substrate surface is efficiently taken into the substrate. As a method for uniformly forming fine irregularities on the substrate surface, for example, the (100) plane of a single crystal silicon substrate is anisotropically etched using a mixed aqueous solution of sodium hydroxide and isopropyl alcohol, and the (111) plane is A method for forming a pyramid (square pyramid) asperity (texture) is known. However, since this method uses isopropyl alcohol (IPA), there are problems in terms of quality variation due to component variation due to volatilization of IPA, waste liquid treatment, working environment, and safety. In addition, relatively high temperature and long time treatment is required, and improvement in productivity has been demanded. In order to promote the popularization of solar cells, every organization is making efforts to increase the power generation efficiency of solar cells to the limit in order to provide cheaper power than existing thermal power generation and nuclear power generation. In order to obtain a light confinement effect that has a great influence on the power generation efficiency, there is a strong demand for improving the texture quality of the Si wafer surface (reducing the reflectivity). However, a texture technology that can be mass-produced to realize a cell with high power generation efficiency by stably expressing a reflectance of 10% or less (wavelength 600 nm) has not been realized yet.

  In a technique for improving the above, Patent Document 1 discloses that an alkaline etching solution contains a specific aliphatic carboxylic acid and silicon to stabilize the etching rate when etching the substrate surface, and to achieve a desired size. A method of uniformly forming the pyramid-shaped irregularities on the substrate surface is described. Further, there are conventional techniques such as Patent Document 2 and Patent Document 3.

International Publication No. 2007/129555 Special table 2011-515872 JP 2012-114449 A

  However, with the method of Patent Document 1, it is difficult to stably and uniformly form small pyramid-like irregularities with an average of 5 μm or less on the surface, and to stably obtain a light reflectance of 10% or less. In the second half of continuous repeated use, fluctuations such as pyramid size and shape breakage were large due to the consumption of components and the influence of by-products from the etching reaction, and the controllability was poor. At the site of use, a great deal of labor and labor was required to obtain a certain range of pyramid sizes continuously and stably. The uniformity of the texture size not only affects the power generation efficiency, but also has an effect of improving the covering of the passivation film and the protective film that prevents a decrease in the power generation efficiency.

  In addition, the methods of Reference 2 and Reference 3 have also been proposed, but sufficient low reflectance of 10% or less of sunlight has not been obtained, which is not suitable for high-efficiency solar cells with high needs and is a major industrial issue. Was leaving.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, it has been found that by using a hydroxystyrene polymer that satisfies certain conditions, the surface quality and texture structure homogeneity can be greatly improved, the productivity is excellent, and the continuous use (long-run) property can be greatly improved. The present invention has been completed.

  It has also been found that production stability and texture quality can be further improved by using at least one selected from a specific chelating agent and a specific organic compound in the above composition. More specifically, the present invention provides the following.

That is, the gist of the present invention is as follows.
[1] An alkaline etching solution for treating the surface of a semiconductor substrate for solar cells, comprising at least one hydroxystyrene-based polymer represented by the general formula (1), and an alkaline agent,
The total of monomers and oligomers represented by n of 1 to 8 contained in the hydroxystyrene polymer of the general formula (1) is 3.5% or less of the hydroxystyrene polymer.
Etchant;
[2] An etching power recovering agent which is added to the etching liquid after treating the semiconductor substrate for solar cells with the etching liquid according to the above [1], and recovers the etching power of the etching liquid. And at least one hydroxystyrene-based polymer represented by the general formula (1), wherein n is 1 to 8 in the hydroxystyrene-based polymer of the general formula (1) The total is 3.5% or less of the hydroxystyrene-based polymer.
Etching power recovery agent for etchant;
[3] Manufacture of a semiconductor substrate for a solar cell, comprising an etching step of etching the substrate surface of the semiconductor substrate for solar cell with the etching solution according to [1] to form pyramidal irregularities on the substrate surface. Method;
[4] A semiconductor substrate for solar cells, the surface of which is etched with the etching solution according to [1]; and [5] a solar cell comprising the semiconductor substrate for solar cells according to [4]. ;
It is about.

  According to the present invention, it is possible to form a texture on a solar cell semiconductor substrate in a shorter time on a relatively low temperature side, and it is excellent in continuous productivity and product storage stability, and a surface with low light reflectance can be stably obtained. The effect is demonstrated. In addition, the pyramid-shaped irregularities with an average of 3 μm or less are stably formed, and the surface shape showing a light reflectance of 10% or less, which was not obtained by the prior art, is not influenced by lot fluctuation of the etching solution raw material. It can be stably applied to the semiconductor substrate. Furthermore, by increasing the number of batches for continuous production, it is possible to improve production throughput, drastically reduce production cost per sheet, drastically reduce wastewater treatment load and cost, and reduce surface defects, resulting in superior texture quality. Can be formed on a semiconductor substrate for solar cells.

FIG. 1 is a schematic diagram showing an outline of micromask theory. FIG. 2 is a scanning electron micrograph showing the surface structure of the semiconductor substrate after the etching process in Example 6 of the present specification. This figure shows the substrate after the treatment with the etching solution in the first batch. FIG. 3 is a scanning electron micrograph showing the surface structure of the semiconductor substrate after the etching process in Comparative Example 2 of the present specification. In this figure, since “clearance” is confirmed at a position surrounded by a white dotted line, this substrate is not preferable as a semiconductor substrate. FIG. 4 is a scanning electron micrograph showing the surface structure of the semiconductor substrate after the etching process in Comparative Example 5 of the present specification. In this figure, since the “pyramid shape collapse” was confirmed at a position surrounded by a white dotted line, this substrate is not preferable as a semiconductor substrate. FIG. 5 is a photograph showing the surface structure of the semiconductor substrate after the etching process in Comparative Example 2 of the present specification. In this figure, since a comet-like defect was confirmed on the substrate surface, this substrate is not preferable as a semiconductor substrate. FIG. 6 is a diagram showing a photograph of the state in which the etching solution is foamed and criteria for determining foamability. FIG. 7 is a scanning electron micrograph showing the surface structure of the semiconductor substrate after the etching process. The masking agent appears black at the apex of the pyramid, surrounded by a circle. FIG. 8 is a diagram showing the result of EDX analysis of the portion of the substrate of FIG. 7 that appears black at the apex portion of the pyramid and the slope of the pyramid.

  Hereinafter, embodiments of the present invention will be described. In addition, this invention is not limited to the following embodiment.

The etching solution of the present invention is an alkaline aqueous solution for treating the surface of a semiconductor substrate for solar cells, contains at least one alkali component, and satisfies the certain condition and the total amount of oligomers of octamer or less. Is characterized by containing a hydroxystyrene-based polymer whose content is 3.5% or less. It is preferable that at least one selected from the group consisting of a specific lignin sulfonic acid and a salt of lignin sulfonic acid is contained in the etching solution of the present invention. As one preferred embodiment of the etching solution of the present invention, at least one alkali component, polyhydroxystyrene in which the total amount of monomers and oligomers of octamer or less is 3.5% or less, lignin sulfonic acid and / or lignin Examples include a composition containing a sulfonate. Here, in the general formula (1), m, k and p are 0, u is 1, and R ^{1 to} R ³ are H, which is polyhydroxystyrene. As another preferred embodiment of the etching solution of the present invention, a composition comprising at least one alkali component and a hydroxystyrene polymer other than polyhydroxystyrene (hereinafter sometimes referred to as “polyhydroxystyrene derivative”). In this composition, a composition further containing lignin sulfonic acid and / or lignin sulfonate is more preferable.

  More preferably, the etching solution of the present invention further contains a specific chelating agent, silicic acid and / or silicate.

  Features of the present invention are product stability, low foaming at the time of etching even after repeated continuous processing on the pilot line, no overflow of the bathtub, excellent etching solution storage stability, mass production use The long run characteristic fluctuation at the time is small. Furthermore, it is possible to form a stable texture at a lower temperature and in a shorter time than in the prior art, and an improvement in productivity and a reduction in running cost can be expected. In particular, under short-time conditions, consumption of components and generation of by-products due to etching reaction can be suppressed, which is very advantageous for improving long run performance. Such a feature is very convenient for mass production use. This feature is focused on the amount of monomer / oligomer impurities in the polymer used as the main masking agent among a wide variety of possible factors, and the control of this amount contributed to further improvement of the effect. Is based on what has been found by the inventors. When such a feature is small, the texture quality at the time of long run is not stable, the yield is deteriorated, and eventually the processing cost per wafer is increased, which becomes a big obstacle for industrial use.

  The mask agent refers to an agent having an action of adsorbing and protecting the substrate surface during silicon etching. As a pyramid-shaped formation mechanism by silicon etching, Si metal is protected by organic substances adsorbed on the silicon surface, and is protected from etching [dissolution]. The surrounding fast-dissolving surface melts, the slow-dissolving surface remains undissolved, and the pyramid There is an idea that the shape remains undissolved (Fig. 1). Although this masking agent has been discussed without evidence, the inventors have succeeded in making this observation for the first time.

  The etching solution of the present invention is alkaline. Specifically, the pH at 25 ° C. is preferably in the range of 12 to 14, and preferably in the range of 13 to 14. The pH of the etching solution can be set within a desired range by appropriately changing the amount and concentration of an alkali agent described later.

  Examples of the polymer contained in the etching solution in the present invention include the following general formula (1):

[In the formula, m and n are m ≧ 0 and n ≧ 3, respectively, and are arbitrary numbers satisfying the range in which the weight average molecular weight of the polymer represented by the general formula (1) is 1000 to 50,000. K, p and u are 0 ≦ k ≦ 2, 0 ≦ p ≦ 2 and 0 <u ≦ 2, respectively, provided that k, p and u are average values in the polymer; R ^{1 to} R ³ Is H or an alkyl group having 1 to 5 carbon atoms; X is a structural unit of a polymerizable vinyl monomer; Y and Z are the same or different, and

Or a substituent selected from the group consisting of an alkyl group having 1 to 18 carbon atoms or an aryl group having 6 to 18 carbon atoms, wherein M is H, an alkali metal, an alkaline earth metal, or an organic cation (for example, an amine). Y ¹ and Y ⁴ are halogens; Y ²⁻ and Y ³⁻ are counter ions (eg, halogen ions, organic acid anions, inorganic acid anions (eg, nitrate ions), etc.); R ^{4 to} R ⁸ are the same or different, and are a linear or branched alkyl group, an alkyl derivative group, an aromatic group or H, and R ⁶ and R ⁷ are N groups. And R ^{9 to} R ¹⁵ may be the same or different and are a linear or branched alkyl group, an alkyl derivative group, an aromatic group, or H; q, s , T are each 0 or 1; r is 0 1 or 2.). ] The hydroxystyrene type polymer represented by this is mentioned. Such polymers and derivatives thereof may be used alone or in combination of two or more.

  In the general formula (1), m, n, k, p, and u are arbitrary numbers (real numbers) within a certain range. When considering the monomers constituting the polymer, k and p are naturally integers, if considered for each block of the structural unit, m is an integer, and if considered for each molecule, n is an integer. is there. However, the polymer in its essence is a mixture, and it is more appropriate to consider the nature of the polymer as a property of the mixture than to question its individual building blocks. Accordingly, in the present invention, m, n, k, p, and u are displayed as average values in the polymer.

The hydroxystyrene-based polymer includes polyhydroxystyrene and polyhydroxystyrene derivatives. In the general formula (1), m, k, and p are 0, u is 1, and R ^{1 to} R ³ are H in the polyhydroxystyrene. The weight average molecular weight of polyhydroxystyrene is 1000 to 50,000, and n is an arbitrary number of 3 or more. The preferable weight average molecular weight of polyhydroxystyrene is 1000 to 20,000, and more preferably 1000 to 10,000. From the viewpoint of easy availability of polyhydroxystyrene, those having a weight average molecular weight of 1000 or more are preferable, and those having a weight average molecular weight of 50,000 or less are preferable from the viewpoint of uniformity of pyramid size.

  The hydroxystyrene-based polymer represented by the general formula (1) is hydroxystyrene, hydroxy-α-, which has or does not have a substituent represented by Y or Z in the general formula (1). Homopolymers or copolymers of only hydroxystyrene monomers such as methylstyrene or hydroxy-α-ethylstyrene, or these hydroxystyrene monomers and other polymerizable vinyl monomers ( For example, it may be a copolymer with a monomer that provides the structural unit X). The hydroxystyrene monomer of the polymerization unit may be an ortho form, a meta form, a para form or a mixture thereof, but a para form or a meta form is preferred.

  Further, when the hydroxystyrene polymer represented by the general formula (1) is a copolymer, other vinyl monomers, that is, monomers providing the structural unit X include anionic and cationic Examples thereof include known compounds such as ionic monomers such as nonionic monomers, methacrylates, vinyl esters, vinyl ethers, malates, fumarate, and α-olefins.

  Specific examples of these compounds include acrylic acid, methacrylic acid, maleic acid, or their anhydrides and unsaturated carboxylic acid monomers such as monoalkyl esters and carboxyethyl vinyl ether, styrene sulfonic acid, allyl sulfonic acid, etc. Unsaturated sulfonic acid monomers, vinylphosphonic acids, unsaturated phosphate monomers such as vinyl phosphate, α, β-unsaturated carboxylic acid amides such as acrylamide and methacrylamide, methyl acrylate, methyl methacrylate, acrylic Ethyl acid, maleic acid, fumaric acid diesters, α, β-unsaturated carboxylic acid esters, unsaturated carboxylic acid substituted amides such as methylolacrylamide, α, β-unsaturated acrylonitrile, methacrylonitrile, etc. Carboxylic acid nitrile, vinyl acetate, vinyl chloride, chloroacetic acid Nyl etc., divinyl compounds such as divinylbenzene, vinylidene compounds, aromatic vinyl compounds represented by styrene, heterocyclic vinyl compounds represented by vinylpyridine and vinylpyrrolidone, vinyl ketone compounds, monoolefin compounds such as propylene, butadiene Typical examples include conjugated diolefin compounds such as allyl compounds such as allyl alcohol, and glycidyl methacrylate. One or more of these compounds can be suitably used as the vinyl monomer that provides the structural unit X.

  Although it does not specifically limit among these monomers and any can be used, For example, when a polymer is formed, what shows the following structural unit is used suitably.

  As described above, the hydroxystyrene polymer in the present invention may be a homopolymer or a copolymer of only hydroxystyrene monomers, but other polymerizable vinyl monomers, that is, the structural unit X is In the case of providing a copolymer with the vinyl monomer to be provided, the ratio of the vinyl monomer / hydroxystyrene monomer is preferably, for example, from 10/1 to 20/1 in molar ratio. is there.

  If the proportion of the vinyl monomer providing the structural unit X exceeds 20 times the amount (molar ratio) of the hydroxystyrene monomer, the effect of the hydroxystyrene monomer will not be exhibited, which is not preferable. If the proportion of the monomer is less than 10 times, the effect of copolymerization is not exhibited, so there is no need to intentionally copolymerize with the vinyl monomer. Therefore, in the present invention, the number of structural units X of the vinyl monomer is m ≧ 0.

  Examples of the substituent of the hydroxystyrene monomer include the following (i) to (vi).

  Here, M is H, an alkali metal, an alkaline earth metal, or an organic cation (for example, amines), for example, Li, Na, K, Mg, Ca, Sr, Ba, etc. are preferable. Introduction of a sulfone group can be achieved by a conventional sulfonation method using fuming sulfuric acid or sulfuric anhydride as a sulfonating agent.

Here, R ^{4 to} R ⁸ are the same or different, and are a linear or branched alkyl group, an alkyl derivative group, an aromatic group or H, and R ⁶ and R ⁷ each have a ring via an N group. It does not matter if it is formed. Y ²⁻ represents a counter ion such as a halogen ion, an organic acid anion, or an inorganic acid anion. Here, examples of the linear or branched alkyl group include those having 1 to 36 carbon atoms (for example, a methyl group), and examples of the alkyl derivative group include a hydroxyalkyl group, an aminoalkyl group, a phosphoalkyl group, and a mercaptoalkyl. Examples of the aromatic group include a benzyl group substituted with a linear or branched alkyl group having 1 to 16 carbon atoms. Preferably, a linear or branched alkyl group, a hydroxyalkyl group, or an aromatic group substituted with a linear or branched alkyl group having 1 to 5 carbon atoms can be used. The introduction of the tertiary amino group can easily give —CH ₂ —N (R ⁶ ) (R ⁷ ) by Mannich reaction using, for example, dialkylamine and formaldehyde. The introduction of the quaternary ammonium base can be easily carried out by, for example, the Mentokin reaction with an alkyl halide for the tertiary amination product.

Is obtained.

Here, R ⁴ and R ⁵ are the same as described above, and R ^{9 to} R ¹² are the same or different and each represents a linear or branched alkyl group, an alkyl derivative group, an aromatic group, or H. W is S or O, q is 0 or 1, and r is 0, 1 or 2. Here, the linear or branched alkyl group has 1 to 36 carbon atoms, the alkyl derivative group includes a hydroxyalkyl group, an aminoalkyl group, a mercaptoalkyl group, a phosphoalkyl group, etc. And a phenyl group substituted with a linear or branched alkyl group having 1 to 16 carbon atoms. Preferred examples include an aromatic group substituted with a linear or branched alkyl group having 18 carbon atoms, a hydroxyalkyl group, or a linear or branched alkyl group having 1 to 5 carbon atoms.

  What is represented by the formula (iii-1) is reacted with phosphoric acid or a phosphoric ester group-introduced product after methylolation of a hydroxystyrene polymer as disclosed in, for example, JP-A-53-71190. To obtain. For example, as disclosed in JP-A-53-47489, the hydroxystyrene polymer represented by the formula (iii-2) is first halogenated or halomethylated and then trivalent. It is obtained by reacting a phosphorus compound (Arbuzov reaction) and then rearranging it.

Here, R ⁴ and R ⁵ are the same as defined above, and R ¹³ , R ¹⁴ and R ¹⁵ are the same or different and represent a linear or branched alkyl group, an alkyl derivative group, an aromatic group, or H. . S represents 0 or 1. Y ³⁻ represents a counter ion such as a halogen ion, an organic acid anion, or an inorganic acid anion. For example, as shown in Japanese Patent Publication No. 61-34444, a hydroxystyrene-based polymer containing a phosphonium group is reacted with hydrogen halide and formaldehyde to form a halogenomethylation (eg, —CH ₂ Cl). Followed by the action of trivalent phosphites.

Here, Y ¹ and Y ⁴ represent halogen, and R ⁴ , R ⁵ and R ⁶ are the same as described above. t represents 0 or 1;

(vi): Other examples include an alkyl group having 1 to 18 carbon atoms or an aryl group having 6 to 18 carbon atoms.

  In the general formula (1), the number of Y and Z that are substituents of the hydroxystyrene monomer is an average value in the polymer, and 0 ≦ k ≦ 2, 0 ≦ p ≦ 2, Further, the number u of OH is 0 <u ≦ 2.

  The hydroxystyrene-based polymer that can be used as a constituent of the etching solution in the present invention has a weight average molecular weight in the range of 1000 to 50,000, preferably in the range of 1000 to 20,000, more Preferably it is the range of 1000-10,000. From the viewpoint of availability of the polymer, those having a weight average molecular weight of 1000 or more are preferable. From the viewpoint of efficient pyramid formation at low temperature and short time and uniformity of pyramid size, the weight average molecular weight is 5 10,000 or less are preferable.

  For example, JP-A-51-105389, JP-B-62-136, JP-B-57-4791 and the like can be effectively used as a method for synthesizing the hydroxystyrene-based polymer. In this method, p-ethylphenol is synthesized by dehydrogenation using p-ethylphenol as a starting material, and this is obtained by radical polymerization. In the polymer obtained by this technique, synthesis is usually completed in a state where a monomer of a reaction raw material and an oligomer of a polymerization intermediate obtained by polymerizing molecules of dimer to 10-mer are mixed. After that, the product is processed through a purification process. However, in products that are generally available industrially, the above-mentioned monomers and oligomers remain in a certain amount, and the amount actually varies. If the degree of purification is increased by an alkali extraction method (Japanese Patent Publication No. 53-7629) or a flash distillation method (WO99-40132) or a low value is not strictly selected, it cannot be used for texture formation of the present application. Some have removed monomers and oligomers as much as possible, but the price is more than 10 times unrealistic and available high-purity products have reduced oligomers and metal impurities, but new solvent components are introduced in the manufacturing process. This is a major obstacle to the formation of the pyramid texture for the purpose of the present application, and as a result, the reflectance is greatly deteriorated.

  Therefore, it is extremely important for the purpose of the present application that the price is industrially usable, and it is in accordance with the purpose of the present invention to reduce monomer and oligomer impurities to the extent that texture formation is possible and acceptable. There is no need to reduce these to unnecessary purity at cost.

  Further, the total of the monomer of the reaction raw material and the oligomer of the reaction intermediate, particularly the oligomer of octamer or less contained in the hydroxystyrene polymer of the general formula (1) is 3.5% or less of the hydroxystyrene polymer. This is very important.

  The quality of the commercially available general-purpose hydroxystyrene polymer is not stable, and if it is used without selection, the characteristics of the etching solution greatly fluctuate, so that it cannot be used for products requiring precise surface processing such as solar cells. Residue of these monomers + oligomers, hereinafter abbreviated as oligomer amount, is sensitively involved in etching characteristics and pyramid formation. The total amount of these is preferably 3.5% or less, more preferably 2.5% or less, and most preferably 2% or less. If it exceeds 3.5%, the stability of the etching solution deteriorates. First, the etching amount significantly increases, and the texture surface unevenness, defects, uniformity, etc. deteriorate. Especially, the texture is stable under low temperature and short time conditions. Quality cannot be obtained. For example, it is difficult to use because the basic etching characteristics change over time, such as the amount of change exceeds 50% after 1 month storage at 40 ° C. compared to immediately after compounding. When the etching amount is increased, the thickness of the wafer usually used at about 100 to 170 μm is decreased, and the mechanical strength is insufficient such as easy cracking, resulting in a problem that the product yield is lowered. Further, a portion where a pyramid is not formed at the base of the pyramid, a gap occurs, which causes a reduction in reflectance and a poor appearance, which deteriorates texture quality and has a great influence. This phenomenon appears remarkably under low temperature and short time conditions. The lower the amount of the remaining oligomer, the better, but there is a natural limit for industrial use. A type of hydroxystyrene polymer that has been reduced to around 0.1% has been produced, but the price is about 10 times that of general-purpose products and is expensive. Used in the solar cell industry where mass consumption and cost are important. Can not. This high-purity polymer is manufactured by a method different from that of general-purpose styrene polymers. The polymerization initiator is bonded to the end of the polymer to change its properties, and oligomers and metal impurities are extremely low. On the other hand, although the concentration is suppressed, the solvent component remains on the order of several hundred to 1000 ppm, and these become a large disturbing component for texture formation. This strongly affects the pyramid formation, greatly deteriorates the texture quality, and has poorer texture characteristics than general-purpose products. Refining the solvent is expensive and not a good idea.

  From this viewpoint, in this specification, the concentration of the solvent component in the hydroxystyrene polymer is preferably 100 ppm or less, more preferably 50 ppm or less, and even more preferably 10 ppm or less. Solvent components include toluene, THF, ethylene glycol, phenol, paracresol and the like. The concentration of the solvent component of the hydroxystyrene polymer can be measured by a known measurement method, or can be known from the product catalog of the supplier of the hydroxystyrene polymer.

  In this specification, in the hydroxystyrene polymer represented by the general formula (1), the method for measuring the total amount (% by weight) of the monomer and oligomer represented by n of 1 to 8 is described in the examples described later. As described.

  In the present specification, the weight average molecular weight of the hydroxystyrene-based polymer is a value obtained by the same method as the molecular weight / molecular weight distribution measurement method using GPC of lignin sulfonic acid and its salt described later.

  The presence of polar groups such as amino groups, phosphoric acid groups, and sulfone groups (not including hydroxyl groups and aromatic rings) in hydroxystyrene polymers is indicative of the solubility of the polymer in alkaline aqueous solution and the disappearance during etching. It is preferable in terms of foamability. The preferred polar group density range is between 0.01 and 5 on average per 500 units of molecular weight of the polymer. When the polar group density is less than 0.01, the solubility in an aqueous solution and the defoaming property tend to be reduced, and when it exceeds 5, the uniformity of the pyramid shape in the semiconductor substrate for solar cells tends to be impaired.

  Factors such as the molecular weight, constitutional unit, polar group type and density, main chain type and the like of the polymer and derivatives thereof are important factors that play an essential role for the etching solution of the present invention.

  The concentration of the polyhydroxystyrene component in the etching solution of the present invention, that is, the “at least one hydroxystyrene polymer represented by the general formula (1)” is preferably in the range of, for example, 1 to 50,000 ppm. The range of ˜30,000 ppm is more preferred, and the range of 50 to 10,000 ppm is even more preferred. The concentration is preferably 1 ppm or more from the viewpoint of effectively removing bubbles generated during the etching process and efficiently forming irregularities, particularly a pyramid shape, on the substrate surface. From the viewpoint of the appearance quality, 50,000 ppm or less is preferable.

  Lignin sulfonic acid or lignin sulfonate, these are compounds obtained by treating pulp waste liquor by-produced during pulp production by various methods, and the main component is lignin sulfonate or lignin sulfonic acid. The chemical structure of lignin is a compound having a phenylpropane group as a basic skeleton and a three-dimensional network structure.

  Lignin sulfonic acid and lignin sulfonate are given various names depending on the isolation method. For example, when lignin is obtained as a residue, lignin sulfate, lignin hydrochloride, copper ammonium lignin, periodate lignin and the like can be mentioned. 1) Inorganic reagent: lignin sulfonic acid, alkali lignin, thiolignin, chlorlignin, 2) Acidic organic reagent: alcohol lignin, dioxane lignin, phenol lignin, thioglycolic acid Lignin, acetic acid lignin, hydrotropic lignin, 3) By hydrochloric acid organic reagent: Brauns natural lignin, acetone lignin, Nord lignin, Bjorkman lignin and the like. In the present invention, lignin sulfonic acid or a salt thereof obtained by sulfonation using the above-mentioned isolated lignin or a derivative thereof may be used. In addition, lignin sulfonic acid and lignin sulfonate that have undergone chemical modification such as oxidation treatment to increase carboxyl groups can also be used in the present invention. The lignin sulfonic acid and lignin sulfonate that can be used in the present invention may contain impurities during pulp production, but the smaller the amount, the better. When there are many impurities, shape collapse will occur in a part of the pyramid, and the uniformity of the pyramid shape tends to be impaired.

  A large number of lignin sulfonic acids and lignin sulfonates are manufactured and sold by pulp manufacturers. The molecular weight ranges from 1.8 to 1,000,000 and is rich in variety such as various sulfonation degrees, various salts, chemically modified products, and those adjusted with heavy metal ions. The present inventors have found that not all of these various lignin sulfonic acids and salts thereof are suitable for the purpose of the present invention, and that the effect varies depending on the thing, or a specific lignin sulfonic acid or a salt thereof. When used, the present inventors have found that anisotropic etching of a silicon semiconductor substrate proceeds well, a concavo-convex structure (pyramid shape) is formed well, and the achievement of the object of the present invention is greatly improved.

That is, the lignin sulfonic acid or a salt thereof that can be suitably used in the present invention satisfies all the following conditions 1) to 3).
1) A low molecular component having a molecular weight of less than 1000 and a high molecular component having a molecular weight of 100,000 or more are very little or completely removed. Specifically, the peak of the molecular weight distribution is between 1000 and 100,000, preferably between 2000 and 60,000, and at least 50% by mass or more of components are present in this molecular weight region.
2) Sulfone group density (ie, degree of sulfonation) having an average of 0.6 or more and less than 3 per 500 molecular weight units.
3) Those having 0 to 3 carboxyl groups per 500 molecular weight units.

In addition, the measurement of molecular weight and molecular weight distribution in said 1) is implemented by the GPC (gel permeation chromatography) method shown below.
(A) Sample preparation Add the same mass of water to the sample to prepare a sample for GPC.
(B) Column A guard column TSX (manufactured by Tosoh Corporation), one HXL (6.5 mmφ × 4 cm), one TSK3000HXL (7.8 mmφ × 30 cm), and one TSK2500HXL (7.8 mmφ × 30 cm) are used. Connect guard column-3000HXL-2500HXL in order from the inlet side.
(C) Standard material Polystyrene (manufactured by Tosoh Corporation) is used.
(D) Eluent Use water.
(E) Column temperature It shall be room temperature (25 degreeC).
(F) Detector
Use UV (ultraviolet spectrophotometer). The wavelength is quantified by the ultraviolet maximum peak of phenol.
(G) Division method for molecular weight calculation Time division (2 seconds).

  The type of lignin sulfonate that can be used in the present invention is not particularly limited, and the above lignin sulfonic acid Na salt, K salt, Ca salt, ammonium salt, Cr salt, Fe salt, Al salt, Mn salt, Mg Any salt or the like can be used in the present invention.

  Moreover, what chelates heavy metal ions, such as Fe, Cr, Mn, Mg, Zn, Al, in said lignin sulfonic acid or its salt can also be used for this invention.

  Preferably, as long as the conditions 1) to 3) are satisfied, lignin sulfonic acid or a salt thereof to which another organic compound such as naphthalene or phenol or an organic polymer is further added can also be used in the present invention.

  The concentration of “at least one selected from the group consisting of lignin sulfonic acid and its salt” in the etching solution of the present invention is preferably in the range of 0.001 to 10,000 ppm, for example. From the viewpoint of effectively removing bubbles generated during the etching process, and further efficiently forming irregularities on the substrate surface, particularly pyramid shape, the concentration is preferably 0.001 ppm or more, more preferably 0.1 ppm or more, 2 ppm or more is more preferable, and 20 ppm or more is more preferable. On the other hand, 10,000 ppm or less is preferable, 1,000 ppm or less is more preferable, and 500 ppm or less is more preferable, from the viewpoint of making the unevenness formed, particularly a pyramid shape, and an etching rate. A lignin sulfonic acid and its salt may be used individually by 1 type, and may use 2 or more types together.

  It is preferable that at least one component selected from the group consisting of the following chelating agent, silicic acid and silicate is further contained in the alkaline etching solution, so that the initial rise and texture quality can be further improved.

  The chelating agent that can be suitably used in the present invention is an organic chelating compound. Examples of the organic chelate compound include a chelate compound containing a carboxyl group and / or a carboxylate group in the molecule and / or a salt thereof, a chelate compound containing a phosphonic acid (salt) group or a phosphoric acid (salt) group in the molecule, and And / or a salt thereof and other chelate compounds. Below, the specific example of the chelating agent which can be used conveniently in this invention is described.

  Examples of the chelate compound and / or salt thereof containing a carboxyl group and / or a carboxylate group in the molecule include a hydroxycarboxylic acid having a hydroxyl group and / or a salt thereof and a carboxylic acid having no hydroxyl group and / or a salt thereof. Examples of the hydroxycarboxylic acid and / or its salt include citric acid (salt), lactic acid (salt), gallic acid (salt) and the like. Examples of carboxylic acids having no hydroxyl group and / or salts thereof include ethylenediaminetetraacetic acid (salt), diethylenetriaminepentaacetic acid (salt), hydroxyethyl-iminodiacetic acid (salt), 1,2-diaminocyclohexanetetraacetic acid (salt), Ethylenetetramine hexaacetic acid (salt), nitrilotriacetic acid (salt), β-alanine diacetate (salt), aspartate diacetate (salt), methylglycine diacetate (salt), iminodisuccinic acid (salt), serine diacetate (salt) , Aspartic acid (salt) and glutamic acid (salt), pyromellitic acid (salt), benzopolycarboxylic acid (salt), cyclopentanetetracarboxylic acid (salt), etc., carboxymethyloxysuccinate, oxydisuccinate, Maleic acid derivatives, oxalic acid (salt), malonic acid (salt), succinic acid (salt), Tal acid (salt), and adipic acid (salt).

  Examples of the chelating agent containing a phosphonic acid (salt) group or phosphoric acid (salt) group in the molecule and / or a salt thereof include methyldiphosphonic acid (salt), aminotri (methylenephosphonic acid) (salt), 1-hydroxy Ethylidene-1,1-diphosphonic acid (salt), nitrilotrismethylenephosphonic acid (salt), ethylenediaminetetra (methylenephosphonic acid) (salt), hexamethylenediaminetetra (methylenephosphonic acid) (salt), propylenediaminetetra (methylene) Phosphonic acid) (salt), diethylenetriaminepenta (methylenephosphonic acid) (salt), triethylenetetramine hexa (methylenephosphonic acid) (salt), triaminotriethylamine hexa (methylenephosphonic acid) (salt), trans-1,2- Cyclohexanediaminetetra (methylenephosphonic acid) (salt), Recall ether diamine tetra (methylene phosphonic acid) (salt) and tetraethylenepentamine hepta (methylene phosphonic acid) (salt), metaphosphoric acid (salt), pyrophosphoric acid (salt), tripolyphosphoric acid (salt) and hexametaphosphoric acid (salt) Etc.

  Other chelating agents include N, N′-bis (salicylidene) -1,2-ethanediamine, N, N′-bis (salicylidene) -1,2-propanediamine, N, N′-bis (salicylidene) -1,3-propanediamine, N, N′-bis (salicylidene) -1,4-butanediamine and the like.

  When the chelate compound forms a salt, examples of the salt include those described above. In the present specification, one type of chelate compound may be used alone, or two or more types may be used in combination.

  For example, the following group (nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylene chloride) may be used as an example of a preferable chelating agent that can be used in the alkaline etching solution for treating the surface of the semiconductor substrate for solar cells of the present invention. Ethylenetetraamine hexaacetic acid, methyldiphosphonic acid, aminotri (methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, nitrilotrismethylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), hexamethylenediaminetetra ( Methylenephosphonic acid), propylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid), triethylenetetraminehexa (methylenephosphonic acid) and triaminotriethylamine hex It includes at least one or more (methylene phosphonic acid) and organic chelate compound selected from a salt thereof) is.

  Although the density | concentration of the chelating agent in the etching liquid of this invention is not specifically limited, It is preferable that it is 0.1-50,000 ppm. If the said density | concentration is 0.1 ppm or more, it is preferable for the reason of disorder of Tex shape, and if the said density | concentration is 50,000 ppm or less, it is preferable for the reason of ensuring the etching amount. A more preferable range of the concentration is 1 to 10,000 ppm, and more preferably 2 to 5,000 ppm. This range is also effective in terms of storage stability of the product.

  By using such a specific chelating agent, metal ions in the etching solution can be sequestered, and as a result, a semiconductor having a high-performance concavo-convex shape in which a decrease in light absorption efficiency and a decrease in power generation efficiency are prevented. A substrate can be created.

  The type of silicic acid and / or silicate that can be contained in the etching solution of the present invention is not particularly limited, but is preferably at least one selected from the group consisting of metal silicon, silica, silicic acid, and silicate. .

The silicate is preferably an alkali metal silicate, for example, sodium silicate such as sodium orthosilicate (Na ₄ SiO ₄ .nH ₂ O) and sodium metasilicate (Na ₂ SiO ₃ .nH ₂ O), Examples thereof include potassium silicates such as K ₄ SiO ₄ .nH ₂ O and K ₂ SiO ₃ .nH ₂ O, and lithium silicates such as Li ₄ SiO ₄ .nH ₂ O and Li ₂ SiO ₃ .nH ₂ O. These silicates can be used by adding the compound itself to the etching solution, or by directly dissolving silicon materials such as silicon wafers, silicon ingots, silicon cutting powders or silicon dioxide in an alkaline agent. The silicate compound obtained as above may be used as a silicate. In the present invention, JIS No. 1 silicate is preferable from the viewpoint of availability.

  The content of silicic acid and / or silicate in the etching solution of the present invention (the content of silicic acid when containing only silicic acid, the content of silicate when containing only silicate, silicic acid and When silicate is included, the total amount thereof) is not particularly limited, but is preferably 0.01 to 10% by mass, more preferably 0.1 to 5% by mass, and still more preferably 0.2 to 3% by mass. When the silicon material or silicon dioxide is dissolved and supplied, the above concentration range is preferable in terms of Si atoms.

  The content of the above-mentioned silicic acid and / or silicate affects the stabilization of the etching rate. The content of silicic acid and / or silicate that stabilizes the etching rate varies depending on conditions such as the concentration of an alkaline agent described later and the temperature of the etching solution during etching. For this reason, what is necessary is just to determine the content of the optimal silicic acid and / or silicate according to the density | concentration etc. of an alkaline agent.

  The alkali agent is a component necessary for forming pyramidal irregularities on the substrate surface when the substrate surface is etched with an etching solution.

  The kind of alkali agent contained in the etching solution of the present invention is not particularly limited, and any of organic alkali and inorganic alkyl can be used. As the organic alkali, for example, a quaternary ammonium salt such as tetramethylammonium hydroxide, an alkanolamine and the like are preferable. As the inorganic alkali, hydroxides of alkali metals and alkaline earth metals such as sodium hydroxide, potassium hydroxide and calcium hydroxide are preferable, and sodium hydroxide or potassium hydroxide is particularly preferable. These alkali agents may be used alone or in combination of two or more.

  Although the density | concentration of the alkali in etching liquid is not specifically limited, 0.5-50 mass% is preferable, 1-30 mass% is more preferable, It is more preferable that it is 2-20 mass%. In particular, when the alkali concentration is 0.5% by mass or more, the durability of the etching solution is remarkably increased, and even when the etching solution is repeatedly used, unevenness of a desired size can be uniformly formed on the substrate surface. it can. If it exceeds 50% by mass, the viscosity of the solution in which the hydroxystyrene-based polymer is dissolved becomes high, and handling becomes difficult, which is not preferable.

  The etching solution of the present invention may contain other components as long as the effects of the present invention are not impaired. For example, by including an amino acid, a high molecular polymer, glycol ethers or the like as an auxiliary agent, it is possible to enhance the effect (acquiring incident light into the substrate efficiently) by including a hydroxystyrene-based polymer. The solvent of the etching solution of the present invention is preferably water. Furthermore, the etching solution may contain components such as an antioxidant (for example, sodium ascorbate) and sodium sulfite.

  The method for preparing the etching solution of the present invention is not particularly limited, and a conventionally known method can be employed. The composition of the etching solution of the present invention is preferably in the above-mentioned composition range when used, but the composition at the time of shipment can also be made into a conch in order to reduce transportation costs. 10 times or more concocted shipment is preferable.

  Further, in the case of the etching solution of the present invention, by adding an alkaline aqueous solution in which a hydroxystyrene-based polymer is dissolved to an etching solution gradually deteriorated by etching a semiconductor substrate for solar cells, pyramidal unevenness forming ability The effect of recovering is high. For example, a high-quality uneven structure can be stably obtained by adding about 5 to 50% by volume of the initial blending amount at regular intervals of etching. Therefore, the alkaline aqueous solution of the hydroxystyrene polymer in the present invention can be used as an etching power recovery agent.

  The composition of the etching power recovery agent of the present invention includes a hydroxystyrene-based polymer represented by the above general formula (1) and the alkaline agent, and further includes lignin sulfonic acid, the lignin sulfonic acid. It is more preferable to include at least one selected from the group consisting of a salt of the above, a chelating agent, the silicic acid, and a salt of the silicic acid.

  Etching power can be recovered by adding an alkaline agent to an etching solution that has deteriorated by repeatedly treating a semiconductor substrate for solar cells. Furthermore, in order to improve the uniformity of the pyramid shape and the uniformity of the entire surface, the deteriorated etching solution can be obtained by adding the hydroxystyrene-based polymer represented by the general formula (1) together with an alkali agent. The number of etching batches can be increased without replacement. Since the initial bath etching solution can be used continuously, there is an effect of increasing industrial value.

  The manufacturing method of the semiconductor substrate for solar cells of this invention includes the etching process of etching the board | substrate surface of the semiconductor substrate for solar cells and forming an unevenness | corrugation in the substrate surface with the etching liquid of this invention.

  The semiconductor substrate for solar cells is preferably a single crystal silicon substrate (regardless of p-type or n-type), but a single crystal semiconductor substrate using a semiconductor compound such as copper / indium or gallium arsenide can also be used.

  In the etching step, the method of bringing the etching solution of the present invention into contact with the substrate surface is not particularly limited, but a method of immersing the semiconductor substrate for solar cells in the etching solution is preferable. Hereinafter, the production method of the present invention will be described by taking the dipping method as an example.

  The etching step in the dipping method is, for example, a step of putting the etching solution of the present invention in a predetermined container and dipping the semiconductor substrate for solar cells therein.

  In the etching step, the temperature of the etching solution in the container is not particularly limited and can be appropriately set. However, in consideration of production and quality, it is preferably 50 ° C. or higher, more preferably 60 ° C. or higher, and still more preferably. 70 ° C. or higher, more preferably 75 ° C. or higher, further preferably 80 ° C. or higher. From the same viewpoint, it is preferably 98 ° C. or lower, more preferably 95 ° C. or lower, and further preferably 90 ° C. or lower.

  Further, the immersion time of the solar cell semiconductor substrate in the etching solution in the etching step is not particularly limited and can be appropriately set. However, in consideration of production and quality, it is preferably 1 minute or more, more preferably 2 Min. Or more, more preferably 3 min. Or more, further preferably 5 min. Or more, further preferably 10 min. Or more, and from the same viewpoint, preferably 40 min. Or less, more preferably 30 min. It is.

  According to the manufacturing method of the present invention, since the etching solution of the present invention is used, pyramidal irregularities of a desired size are uniformly formed on the substrate surface of a larger number of semiconductor substrates for solar cells than before. Can be formed. Furthermore, what has a composition of the etching agent of this invention can be added in an etching tank as an etching power recovery agent which recovers etching power. By using an etching power recovery agent in this way, the number of continuous use of the etching process can be increased, which is preferable.

  According to such a production method of the present invention, the average size of the pyramid shape formed on the surface of the semiconductor substrate for solar cells after etching can be set to 0.1 to 3 μm.

  According to such a manufacturing method of the present invention, the light reflectance of the semiconductor substrate for solar cells after etching can be greatly reduced. Specifically, the light reflectance at a wavelength of 600 nm of the semiconductor substrate for solar cell after etching can be set to 10% or less. The method for measuring the light reflectance is as described later.

  The semiconductor substrate for solar cells manufactured by the manufacturing method of the present invention is a semiconductor substrate for solar cells manufactured using the etching solution of the present invention, and the substrate surface preferably has a maximum side length of the bottom of 1 to 1. The upper limit is 3 μm, more preferably the upper limit is 2.5 μm, still more preferably the upper limit is 2 μm, and uniform pyramid-like irregularities are formed. Furthermore, according to the present invention, a semiconductor substrate for solar cells with high productivity and low reflectance can be obtained. By using the etching solution of the present invention, it is possible to uniformly form the unevenness of a desired size on the substrate surface at a lower temperature and in a shorter time than using a conventional etching solution. The pyramidal irregularities are convex portions formed by arranging pyramidal (quadrangular pyramidal) convex portions on the surface of the semiconductor substrate for solar cells.

  As the size of the pyramid shape formed on the substrate surface, the average size is preferably 0.1 to 3 μm, more preferably 0.5 to 2.5 μm, and 1.0 to 2.5 μm. More preferably. The average size is preferably 0.1 μm or more from the viewpoint of light reflectivity reduction and impurity diffusion distribution characteristics such as P and B in the battery fabrication process, and from the viewpoint of productivity, the average size is 3 μm or less. It is preferable that Such a pyramid shape having an average size can be achieved by the manufacturing method of the present invention using the etching solution of the present invention.

  One feature of the semiconductor substrate for solar cells of the present invention is that the light reflectance is very small, for example, preferably 10% or less, more preferably 9.5% or less, and even more preferably 9.0% or less. Light reflectance at a wavelength of 600 nm. The method for measuring the light reflectance is as described later.

  As described above, pyramid-shaped irregularities of a desired size are formed without gaps on the surface of the semiconductor substrate for a solar cell formed by etching using the etching solution of the present invention. Therefore, the semiconductor substrate surface for solar cells formed by etching using a conventionally known etching solution and the semiconductor substrate surface for solar cells formed by etching using the etching solution of the present invention have pyramidal unevenness. A distinction can be made based on the size variation, the size of the interval between the pyramidal projections, and the like.

  Furthermore, a solar cell can be produced by a known method using the solar cell semiconductor substrate of the present invention. Solar cells comprising such a semiconductor substrate for solar cells are also encompassed by the present invention.

  The present invention will be described more specifically with reference to the following examples. However, these examples are exemplarily shown.

Examples 1 to 23 and Comparative Examples 1 to 10
An n-type single crystal silicon substrate (a square with a side of 125 mm and a thickness of 160 μm) having a crystal orientation (100) plane on the etching solution prepared according to the composition shown in Table 1A, the conditions shown in Table 1A, And immersed at 50 to 90 ° C. for 1 to 40 minutes. Table 1B shows the results obtained by observing the substrate surface after the etching treatment with the naked eye, a laser microscope, and a scanning electron microscope. The chelating agent used (additive 2) was DTPA (diethylenetriaminepentaacetic acid). A specific etching process is as described in [Etching process] below. The pH at 25 ° C. of the etching solutions in these examples and comparative examples was in the range of 12-14.
The etching solution contained sodium sulfite (Example 2, Example 20 and Comparative Example 5) or sodium ascorbate (Example 10) as additive 3 at a predetermined concentration.

  Table 1B describes an example in which the substrate was evaluated after the first batch of etching treatment. The long run properties of Examples 3 and 6 and Comparative Examples 2 and 6 in which the long run properties were compared were evaluated on the final batch of wafers, respectively. In addition, "-" in each table | surface shows that the density | concentration of an applicable component is 0 ppm, or the measurement or evaluation of the applicable evaluation item was not performed.

[Etching process]
As an etching container, an approximately 3L cylindrical tank made of SUS304 was used, and 3L of an etching solution was put into the tank, and the temperature was raised from below using a SUS casting heater to maintain the temperature range at a set temperature ± 1 ° C. The number of substrates loaded was one. After removing from the etching solution, the substrate was immediately rinsed with running water and dried with warm air. The substrate after drying was evaluated according to the following criteria.

Long run:
On the other hand, the long run property is confirmed by using an approximately 24L box-shaped tank made of SUS304, putting 16L of etching solution into the tank, raising the temperature with an IH heater from the bottom, and setting the temperature range to 90 ° C ± 1 ° C of the set temperature. And was processed without liquid circulation stirring. The number of substrates loaded was 48. This was processed multiple times as one batch. A jig was designed so as not to obstruct liquid convection, and substrates were inserted at intervals of 4 mm. After the processing time reached 15 minutes, the substrate was taken out of the etching solution together with the cassette, and then rinsed with running water was immediately performed and dried with warm air. The substrate after drying was evaluated according to the following criteria. Since there are a plurality of substrates, the evaluation of the long run property is shown as an average value of all the substrates. The long run properties of the etching solutions of some examples and comparative examples were evaluated. The plate was set, and the alkali was exhausted at that time, so the exhausted KOH was determined by an automatic titrator and the equivalent amount of KOH or NaOH was replenished every batch. In addition, for the replenishment of the etching solution, a 30-fold concentrated product was prepared and replenished at 130 mL / batch. The evaluation results are shown in Table 1B. A specific etching process is as described in [Etching process] below.

The long run property was evaluated by the number of batches until a substrate having a reflectance of 600 nm exceeding 10% appeared.
A: 300 batches or more B: 100 to 299 batches C: 30 to 99 batches D: less than 30 batches

Foaming property: The foaming property was evaluated as the amount of foaming after 100 mL of the prepared etching solution was dispensed into a plastic container and vibrated up and down manually for 10 seconds. Evaluation was performed visually.
A: Foaming small B: Foaming during C: Foaming large FIG. 6 shows specific photographs and criteria.

Clearance: Clearance is a phenomenon in which minute gaps (flat portions) in which no pyramids are formed between the pyramids remain, resulting in deterioration of reflectance and poor visual appearance.
Evaluation is carried out with a scanning atomic microscope (SEM). Three fields of view of the target substrate are observed at a magnification of 5000, and the number is evaluated.
A: No clearance B: 5 clearances / surface or less C: 5 clearances / surface or more

Pyramid shape collapse: Pyramid shape failure is the degree of pyramid chipping or slope failure, and is determined by observing it with a scanning electron microscope at a magnification of 5000 times.
A: No collapse B: Slight collapse C: Many collapses

Comet-like defect: A comet-like defect is a vertically elongated, drop-like scratch observed on the surface of a substrate after etching.
A: The comet-like defect defined above does not exist on the substrate surface.
B: Comet-like defects defined above are present in a range of less than 3 area% of the substrate surface.
C: Comet-like defects defined above are present in the range of 3 area% or more and less than 5 area% on the substrate row surface.
D: The comet-like defects defined above are present in the range of 5% by area or more on the substrate surface.

Storage stability: With respect to the etching solutions prepared in the examples, the storage stability of the following etching solutions was evaluated. After preparing the etchants, they were stored at 40 ° C. for 1 month. Then, etching processing was performed by the method shown in each corresponding example using each etching solution after storage, and the amount of etching and the substrate surface after processing were evaluated 5000 times using a scanning electron microscope. And the evaluation of the substrate surface using the etching solution before storage and the evaluation of the substrate surface using the etching solution after storage were compared, and the storage stability was evaluated according to the following criteria.

A: The change rate of the etching amount is less than 50% as compared with immediately after the preparation, and even when the etching solution after storage is used, the collapse of the pyramid shape on the substrate surface is not recognized.
B: The change rate of the etching amount is 50 to 100%, and the texture shape collapse is not recognized.
C: The change rate of the etching amount is 50 to 100%, and the texture shape collapse is recognized.
D: The rate of change in the etching amount is 100% or more, and the deformation of the texture is observed.

Pyramid size: The substrate surface was observed with a laser microscope, and the pyramid size was measured for ten pyramid shapes from the largest. This was performed for 3 fields of view and averaged to obtain an average pyramid size. Some of the substrates were also observed with a scanning electron microscope.

  The above laser microscope uses Keyence Corporation's Laser Microscope VK-X100, was photographed at 100x objective lens (20x eyepiece), 2000x magnification, printed on paper, and the bottom size of the pyramid Measurement was made and the base size was defined as a pyramid size. The scanning electron microscope was observed with an acceleration voltage of 1 to 10 kV using ULTRA55 manufactured by CARL ZEISS or SU3500 manufactured by HITACHI.

  In addition, the scanning electron micrograph which shows the surface structure of the board | substrate after being etched in Example 6 is shown in FIG. Further, scanning electron micrographs showing the surface structure of the substrate after being etched in the comparative example are shown in FIG. 3 (Comparative Example 2), FIG. 4 (Comparative Example 5) and FIG. 5 (Comparative Example 2).

Reflectance of the substrate after etching The reflectance is measured using a spectrophotometer (with an integrating sphere) manufactured by HITACHI UH4150, measuring the light reflectance (2 fields of view) at a wavelength of 300 to 1200 nm, and reflecting the light at a wavelength of 600 nm. Comparison was made using the average value of the rates.

Etching amount The etching amount was determined by measuring the substrate mass difference before and after the etching reaction using a CP224S precision balance manufactured by SARTORIUS.

  The details of the hydroxystyrene polymer used above are shown in Tables 2 and 3.

  In the table, “general-purpose” means a grade of monomer + oligomer of 0.1% or more, which is mainly used for general industrial use (surface treatment agent, polymer flocculant, etc.). The term “monomer + oligomer” used in semiconductor photoresists and the like is less than 0.1%, and “monomer + oligomer” is a polymer having n of 1 to 8 in the general formula (1). Refers to the total amount.

In this specification, in the hydroxystyrene polymer represented by the general formula (1), the method for measuring the total amount of monomers and oligomers represented by n is 1 to 8 is GPC (gel permeation chromatography) shown below. ).
(A) Sample preparation Water was added so that the sample concentration was 1.0 wt% to prepare a sample for GPC.
(B) Column One guard column (6.0 mmφ × 4 cm, manufactured by Tosoh Corporation) and three TSKgel G4000Hxl (7.8 mmφ × 30 cm) were used. The guard column was connected in the order of G-4000Hxl from the inlet side.
(C) Standard material Polystyrene (manufactured by Tosoh Corporation) was used.
(D) The eluent tetrahydrofuran (THF) was used.
(E) Column temperature was 25 ° C.
(F) Detector
An RI (differential refractive index) detector was used.

  The details of the lignin sulfonic acid (salt) (additive 1) used above are shown in Table 4.

  The total of monomers and oligomers in which n is represented by 1 to 8 in the hydroxystyrene polymer of the general formula (1) is 3.5% or less of the hydroxystyrene polymer (Examples 1 to 23) Was used, it was possible to produce a substrate having a low reflectance and a pyramid size within a predetermined range even at a low temperature of 60 ° C. or less or for a short time of 3 minutes or less. Furthermore, the manufactured substrate was an excellent substrate with few surface defects. Furthermore, the etching liquids of Examples 1 to 23 had low foaming properties, long long run properties, and excellent storage stability.

  On the other hand, in the examples (Comparative Examples 1 to 5 and 8 to 10) in which the total of the above monomers and oligomers exceeds 3.5%, it was found that the manufactured substrate had a high reflectance and further had many surface defects. The etching solutions of these comparative examples had large foaming properties, short long run properties, and poor storage stability. Furthermore, even when the total is 3.5% or less, in the examples where the concentration of the solvent component exceeds the predetermined value (Comparative Examples 6 to 7), the reflectance of the manufactured substrate is high, and furthermore, there are many surface defects. I understood. Although the etching solutions of these comparative examples had low foaming properties, they had short long run properties and poor storage stability.

  The etched silicon substrate was observed with a high resolution SEM (10,000 times). The results are shown in FIG. The mask agent is black at the top of the pyramid. As a result of EDX analysis, the black part was carbon, and the carbon was not detected at the EDX level on the pyramid slope (Fig. 8). It can be seen from FIG. 7 (1000 times) that a plurality of masks that appear black are detected.

  The etching solution of the present invention can be used as an etching solution when etching the surface of a semiconductor substrate for solar cells.

Claims (16)

An alkaline etching solution for treating the surface of a semiconductor substrate for solar cells,
The following general formula (1):
[In the formula, m and n are m ≧ 0 and n ≧ 3, respectively, and are arbitrary numbers satisfying the range in which the weight average molecular weight of the polymer represented by the general formula (1) is 1000 to 50,000. K, p and u are 0 ≦ k ≦ 2, 0 ≦ p ≦ 2 and 0 <u ≦ 2, respectively, provided that k, p and u are average values in the polymer; R ^{1 to} R ³ Is H or an alkyl group having 1 to 5 carbon atoms; X is a structural unit of a polymerizable vinyl monomer; Y and Z are the same or different, and
Or a substituent selected from the group consisting of an alkyl group having 1 to 18 carbon atoms or an aryl group having 6 to 18 carbon atoms (wherein M is H, an alkali metal, an alkaline earth metal, or an organic cation; Y ¹ and Y ⁴ are halogen; Y ²⁻ and Y ³⁻ are counter ions; W is S or O; R ^{4 to} R ⁸ are the same or different and are linear or branched An alkyl group, an alkyl derivative group, an aromatic group or H, and R ⁶ and R ⁷ may form a ring via an N group; R ^{9 to} R ¹⁵ are the same or different; And a linear or branched alkyl group, an alkyl derivative group, an aromatic group, or H; q, s, and t are each 0 or 1, and r is 0, 1, or 2.) ]
And at least one hydroxystyrene-based polymer represented by:
The total of monomers and oligomers represented by n of 1 to 8 contained in the hydroxystyrene polymer of the general formula (1) is 3.5% or less of the hydroxystyrene polymer.
Etching solution.   The etching liquid of Claim 1 whose density | concentration of the solvent component in the said hydroxy styrene-type polymer is 100 ppm or less.   The etching liquid according to claim 1 or 2, further comprising at least one component selected from the group consisting of lignin sulfonic acid and lignin sulfonate.   The etching solution according to any one of claims 1 to 3, further comprising at least one component selected from the group consisting of a chelating agent, silicic acid and silicate.   The etching liquid of any one of Claims 1-4 in which the surface shape of the semiconductor substrate for solar cells after the etching which uses this etching liquid has pyramidal unevenness | corrugation. An etching power recovering agent that recovers the etching power of the etching solution by adding to the etching liquid after treating the semiconductor substrate for solar cells with the etching liquid according to any one of claims 1 to 5, Contains an alkaline agent and has the following general formula (1):
[In the formula, m and n are m ≧ 0 and n ≧ 3, respectively, and are arbitrary numbers satisfying the range in which the weight average molecular weight of the polymer represented by the general formula (1) is 1000 to 50,000. K, p and u are 0 ≦ k ≦ 2, 0 ≦ p ≦ 2 and 0 <u ≦ 2, respectively, provided that k, p and u are average values in the polymer; R ^{1 to} R ³ Is H or an alkyl group having 1 to 5 carbon atoms; X is a structural unit of a polymerizable vinyl monomer; Y and Z are the same or different, and
Or a substituent selected from the group consisting of an alkyl group having 1 to 18 carbon atoms or an aryl group having 6 to 18 carbon atoms (wherein M is H, an alkali metal, an alkaline earth metal, or an organic cation; Y ¹ and Y ⁴ are halogen; Y ²⁻ and Y ³⁻ are counter ions; W is S or O; R ^{4 to} R ⁸ are the same or different and are linear or branched An alkyl group, an alkyl derivative group, an aromatic group or H, and R ⁶ and R ⁷ may form a ring via an N group; R ^{9 to} R ¹⁵ are the same or different; And a linear or branched alkyl group, an alkyl derivative group, an aromatic group, or H; q, s, and t are each 0 or 1, and r is 0, 1, or 2.) ]
And the total of monomers and oligomers represented by n in the hydroxystyrene polymer of the general formula (1) is represented by the hydroxystyrene-based polymer. 3.5% or less of the coalescence,
Etching power recovery agent for etchant.   The etching power recovery agent according to claim 6, wherein the concentration of the solvent component in the hydroxystyrene-based polymer is 100 ppm or less.   The semiconductor for solar cells including the etching process of etching the board | substrate surface of the semiconductor substrate for solar cells with the etching liquid of any one of Claims 1-5, and forming a pyramid-shaped unevenness | corrugation in the said substrate surface. A method for manufacturing a substrate.   The manufacturing method of Claim 8 whose average size of the said pyramid shape is 0.1-3 micrometers.   The manufacturing method of Claim 8 or 9 whose light reflectance in wavelength 600nm of the semiconductor substrate for solar cells after an etching is 10% or less.   The semiconductor substrate for solar cells formed by the etching process of the surface with the etching liquid of any one of Claims 1-5.   The semiconductor substrate for solar cells according to claim 11, wherein irregularities are formed on the substrate surface.   The semiconductor substrate for solar cells according to claim 12, wherein the formed uneven projection has a pyramid shape.   The semiconductor substrate for solar cells of Claim 13 whose average size of the said pyramid shape is 0.1-3 micrometers.   The semiconductor substrate for solar cells of any one of Claims 11-14 whose light reflectance in wavelength 600nm is 10% or less.   The solar cell provided with the semiconductor substrate for solar cells of any one of Claims 11-15.