JP2016092228A - Etchant, method for manufacturing semiconductor substrate, semiconductor substrate and solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an etchant which prevents metal ion contamination to reduce the number of liquid exchange times of an etchant and also capable of forming a suitable uneven structure (surface quality, shininess, uniformity, shape) less in collapse or the like when an uneven structure having a projecting portion of a pyramid shape is formed on a semiconductor substrate, and is also preferable in an etching amount and the storage stability of an etchant.SOLUTION: An etchant is an alkaline etchant for forming an uneven structure having a projecting portion of a pyramid shape on the surface of a semiconductor substrate, and contains an alkaline agent and an aminocarboxylic acid chelate compound.SELECTED DRAWING: None

Description

  The present invention relates to an etching solution, a method for manufacturing a semiconductor substrate, a semiconductor substrate, and a solar cell.

  In recent years, various techniques for forming irregularities on the surface of a semiconductor substrate by etching treatment have been proposed. For example, in order to increase the power generation efficiency of a solar cell, a method is used in which irregularities are formed on the surface of a solar cell semiconductor substrate 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) surface of a single crystal silicon substrate is anisotropically etched using a mixed aqueous solution of sodium hydroxide and isopropyl alcohol (IPA), and (111 There is known a method of forming a pyramid shape (quadrangular pyramid) asperity composed of a) surface.

  However, this method has problems in terms of quality fluctuation due to volatilization of IPA, waste liquid treatment, work environment, safety, and the like. In addition, since treatment at high temperature and long time is required, improvement in productivity was also demanded.

  As a method for manufacturing a semiconductor substrate that does not use IPA for anisotropic etching, Patent Document 1 selects from a group consisting of carboxylic acids having at least one carboxyl group in one molecule and having 1 to 12 carbon atoms and salts thereof. Disclosed is a method for manufacturing a semiconductor substrate, characterized in that an uneven structure is formed on a surface of the semiconductor substrate by etching the semiconductor substrate using an alkaline etchant containing at least one selected from the group consisting of silicon and silicon. Yes.

  However, if the etching solution described in Patent Document 1 continues to be etched without liquid replacement, the solution immediately deteriorates and a desired uneven structure cannot be obtained. If there is an abnormality in the concavo-convex structure, the light absorption efficiency of the semiconductor substrate is lowered, which causes a decrease in power generation efficiency in the solar cell. Therefore, until now, in order to obtain a desired concavo-convex structure, the etching solution has to be frequently replaced, which has disadvantages in terms of workability and cost.

International Publication No. 2007/129555

  In view of the above drawbacks, the present inventors have focused on the metal ion contamination of the etching solution from the viewpoint of reducing the number of times of exchanging the etching solution.

  An object of the present invention is to form a concavo-convex structure having a pyramid-shaped convex portion on a semiconductor substrate. It is to provide an etching solution suitable for the etching amount and the storage stability of the etching solution.

The present invention solves the above problems,
[1] An alkaline etchant for forming a pyramidal concavo-convex structure on the surface of a semiconductor substrate, comprising an alkaline agent and an aminocarboxylic acid chelate compound,
[2] A method for producing a semiconductor substrate, comprising an etching step in which a convex-concave structure having a pyramid shape is formed on the surface of the semiconductor substrate using the etching solution according to [1],
[3] A semiconductor substrate manufactured by the manufacturing method according to [2] above,
[4] A solar cell comprising the semiconductor substrate according to [3].

  According to the present invention, when forming a concavo-convex structure with convex portions on a semiconductor substrate, a suitable concavo-convex structure that prevents metal ion contamination, reduces the number of times the etchant is exchanged, and is less likely to collapse. An etching solution that can be formed and that is suitable for the etching amount and the storage stability of the etching solution can also be provided.

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

  Generally, the etching tank is made of SUS, and an alkaline solution at 80 ° C. or higher is often used. For this reason, the etching solution is contaminated with metal ions from SUS. In addition, the etching solution may be subjected to metal ion contamination from the piping material. It has been found that due to this metal ion contamination, if metal ions such as iron, copper, and nickel are present in the etching solution, etching abnormalities are caused, and as a result, the formation of uneven structures such as pyramid shape abnormalities and excessive dissolution is adversely affected. .

  Therefore, the present inventors have examined the use of a chelate compound in an alkaline etching solution in order to prevent metal ion contamination of the etching solution. As a result of intensive studies, it was found that an excellent concavo-convex structure can be formed while using an aminocarboxylic acid chelate compound in an alkaline etching solution while preventing metal ion contamination of the etching solution.

  That is, the etching solution of the present invention contains an alkali agent and an aminocarboxylic acid chelate compound. Optionally, the etching solution of the present invention may contain a sulfonic acid compound, silicic acid, lignin sulfonic acid and the like.

  The etching solution of the present invention contains 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 the etching solution of the present invention.

  The kind of alkaline agent is not particularly limited. Either an organic alkali agent or an inorganic alkali agent can be used. As the organic alkali agent, for example, a quaternary ammonium salt such as tetramethylammonium hydroxide, an alkanolamine and the like are preferable. As the inorganic alkali agent, alkali metal or alkaline earth metal hydroxides 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.

  The grade of the alkali agent is not particularly limited, but semiconductor grade, electronic material grade, general industrial grade, and the like can be used. The general industrial grade is inexpensive, but the metal ion concentration in the alkaline agent is usually higher than other grades. Even such a thing can be used because metal ion contamination is reduced by the aminocarboxylic acid chelate compound.

  The concentration of the alkaline agent in the etching solution of the present invention is not particularly limited. From the viewpoint of durability, the concentration of the alkaline agent in the etching solution of the present invention is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and further preferably 1% by mass or more. From the viewpoint of stabilizing the etching amount, the concentration of the alkaline agent in the etching solution of the present invention is preferably 25% by mass or less, more preferably 15% by mass or less, and further preferably 10% by mass or less. That is, the concentration of the alkaline agent in the etching solution of the present invention is preferably 0.1 to 25% by mass, more preferably 0.5 to 15% by mass, and further preferably 1 to 10% by mass.

  The etching solution of the present invention contains an aminocarboxylic acid chelate compound. A chelate compound is a compound that forms a stable complex with metal ions in the liquid and reduces the influence of the metal ions in the liquid.

  As the aminocarboxylic acid-based chelate compound, an aminocarboxylic acid having 13 to 24 carbon atoms having at least one carboxyl group in one molecule or a salt thereof is preferable from the viewpoint of forming a suitable pyramid shape. Examples of such aminocarboxylic acids include diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, cyclohexanediaminetetraacetic acid, diaminohexanetetraacetic acid, glycol etherdiaminetetraacetic acid, and salts thereof. Among these, diethylenetriaminepentaacetic acid or a salt thereof is preferable.

  Although the density | concentration of the aminocarboxylic acid type chelate compound in the etching liquid of this invention is not specifically limited, It is preferable that it is 0.1-50000 ppm. If it is 0.1 ppm or more, disorder of the pyramid shape can be suppressed, and if it is 50000 ppm or less, the etching amount can be secured and an uneven shape can be formed. A concentration of 1 to 10000 ppm is more preferable in terms of storage stability. A more preferable range of the concentration is 2 to 5000 ppm, and the etching stability is improved.

  Said aminocarboxylic acid type chelate compound may be used independently and may use 2 or more types together. The kind in that case does not ask | require. Moreover, you may use together an aminocarboxylic acid type chelate compound and chelate compounds other than an aminocarboxylic acid type. Among these, a combination with diethylenetriaminepentaacetic acid is preferable.

  As chelate compounds other than aminocarboxylic acid-based compounds, at least one of a chelate compound containing at least one of a carboxyl group and a carboxylate group in the molecule, a phosphonic acid group, and a phosphate group is included. Examples thereof include chelate compounds contained in the molecule.

  Examples of chelate compounds containing at least one of a carboxyl group and a carboxylate group in the molecule include citric acid, lactic acid, gallic acid, gluconic acid, cyclopentanetetracarboxylic acid, carboxymethyloxysuccinate, and oxydisuccinate. , Maleic acid derivatives, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid and their salts.

  Examples of chelate compounds containing at least one of a phosphonic acid group and a phosphoric acid group in the molecule include methyldiphosphonic acid, aminotri (methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, and nitrilotris. Methylenephosphonic acid, ethylenediaminetetra (methylenephosphonic acid), hexamethylenediaminetetra (methylenephosphonic acid), propylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid), triethylenetetraminehexa (methylenephosphonic acid), tri Aminotriethylamine hexa (methylenephosphonic acid), trans-1,2-cyclohexanediaminetetra (methylenephosphonic acid), glycol etherdiaminetetra (methylenephosphonic acid), tetra Chi Ren pentamine hepta (methylene phosphonic acid), metaphosphoric acid, pyrophosphoric acid, tripolyphosphate and hexametaphosphate and salts thereof.

  As long as the effects of the present invention are not impaired, the etching solution of the present invention may further contain a sulfonic acid compound represented by the following general formula (I) from the viewpoint of improving the pyramid shape.

(In the formula, n is an integer of 0 to 5, and each R is independently an alkyl group having 1 to 12 carbon atoms.)

  n is preferably 1 or more and 5 or less. When n is 1 or more, it is preferable because the etching process of the substrate surface can be promoted. From the viewpoint of preventing the etching process from being inhibited, n is preferably 5 or less. A more preferable range of n is 1 or more and 3 or less.

  The alkyl group having 1 to 12 carbon atoms may be linear or branched. Among the alkyl groups, an alkyl group having 1 to 5 carbon atoms is preferable, and a methyl group is particularly preferable among them. In particular, when the number of carbon atoms is within the above preferred range, the number of carbon atoms of the hydrocarbon group of the compound represented by the general formula (I) is reduced. As a result, the BOD (biochemical oxygen demand) and COD (chemical oxygen demand) of the etching solution of the present invention can be reduced.

  Among the sulfonic acid compounds represented by the general formula (I), benzenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid and cumenesulfonic acid are preferable from the viewpoint of improving the pyramid shape, and a pyramid shape having a desired size is preferable. Toluenesulfonic acid is more preferable from the viewpoint of uniformly forming the unevenness on the substrate surface and reducing the odor. Among toluenesulfonic acids, paratoluenesulfonic acid (PTS) is preferable from the viewpoint of availability.

  A sulfonic acid compound may be used independently or may use 2 or more types together.

  The concentration of the sulfonic acid compound in the etching solution of the present invention is not particularly limited. The concentration of the sulfonic acid compound in the etching solution of the present invention is preferably 0.1% by mass or more, more preferably 3% by mass or more from the viewpoint of forming pyramidal irregularities of a desired size on the substrate surface without unevenness. 7 mass% or more is more preferable. The concentration of the sulfonic acid compound in the etching solution of the present invention is preferably 40% by mass or less, more preferably 25% by mass or less, and further preferably 16% by mass or less from the viewpoint of cost. That is, the concentration of the sulfonic acid compound in the etching solution of the present invention is preferably 0.1 to 40% by mass, more preferably 3 to 25% by mass, and further preferably 7 to 16% by mass.

  In the range where the effects of the present invention are not impaired, the etching solution of the present invention is further improved from the viewpoint of improving the uniformity of the pyramid shape of the entire surface by improving the pyramid shape, and at least one of silicic acid and silicate (hereinafter referred to as the following). "Silica etc.") may be included.

  The type of silicic acid 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 of the present invention, or by directly dissolving silicon materials such as silicon wafers, silicon ingots, silicon cutting powders or silicon dioxide in an alkali agent. A silicate compound obtained as a reaction product may be used as a silicate.

  Content of silicic acid or the like in the etching solution of the present invention (if silicic acid alone is included, silicic acid content, if only silicate content is included, silicate content, including silicic acid and silicate) In this case, the total amount of these 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.

  Content of said silicic acid etc. influences stabilization of an etching rate. The content of silicic acid or the like that can stabilize the etching rate varies depending on conditions such as the concentration of an alkali agent described later and the temperature of the etchant during etching. For this reason, what is necessary is just to determine optimal content, such as a silicic acid, according to the density | concentration etc. of an alkaline agent.

  In the range that does not impair the effects of the present invention, the etching solution of the present invention has at least one of lignin sulfonic acid and lignin sulfonate (hereinafter referred to as “lignin sulfonic acid etc.”) from the viewpoint of improving the uniformity of the entire surface. May be included).

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

  Lignin sulfonic acid and the like 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. It may be lignin sulfonic acid or a salt thereof obtained by sulfonation using the above isolated lignin or a derivative thereof as a raw material. In addition, lignin sulfonic acid or the like that has undergone chemical modification such as oxidation treatment to increase the carboxyl group can also be used. The lignin sulfonic acid and lignin sulfonate that can be used may contain impurities during pulp production, but the smaller the amount, the better. When there are many impurities, the uniformity of a pyramid shape will be impaired.

  The weight average molecular weight of lignin sulfonic acid or the like is preferably such that 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 small or completely removed. Specifically, a peak having a molecular weight distribution between 1000 and 100,000, preferably between 2000 and 60,000, and having at least 50% by mass of components in this molecular weight region is used. preferable.

  As the lignin sulfonic acid or the like, it is preferable to use one having a sulfone group density (that is, a sulfonation degree) of an average of 0.6 or more and less than 3 per 500 molecular weights.

  It is preferable to use lignin sulfonic acid having 0 to 3 carboxyl groups per 500 molecular weight units.

Measurement of molecular weight and molecular weight distribution of lignin sulfonic acid and the like is carried out by the GPC (gel permeation chromatography) method shown below.
(A) Sample preparation Add the same weight 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 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 salt, etc. may be used. it can.

  In lignin sulfonic acid or the like, those obtained by chelating heavy metal ions such as Fe, V, Cr, Mn, Mg, Zn, and Al can also be used.

  Furthermore, other organic compounds such as naphthalene and phenol, or lignin sulfonic acid to which an organic polymer is added can also be used.

  The concentration of lignin sulfonic acid or the like in the etching solution of the present invention is not particularly limited, but for example, a range of 0.001 to 10,000 ppm can be used, 0.001 to 1000 ppm is preferable, and 0.001 to 500 ppm is more preferable. From the viewpoint of effectively removing bubbles generated during the etching process and further efficiently forming irregularities on the substrate surface, in particular, pyramid shape, the concentration is preferably 0.001 ppm or more, irregularities to be formed, In particular, 10,000 ppm or less is preferable from the viewpoint of arranging the pyramid shape and from the viewpoint of etching rate.

  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, when a sulfonic acid compound is included, the effects (incident light is efficiently taken into the substrate) due to the inclusion of the sulfonic acid compound are further increased by including amino acids, polymer polymers, glycol ethers, and the like as auxiliary agents. Can do. The solvent of the etching solution of the present invention is preferably water.

  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 in the composition at the time of use, but the composition at the time of shipment can be condensed because it also means a reduction in transportation cost. 2-5 times conch shipping is preferable.

  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 of the present invention can be set to a desired range by appropriately changing the amount and concentration of the alkali agent described later.

  The etching solution of the present invention is used for forming a concavo-convex structure having convex portions on a semiconductor substrate. The etching solution of the present invention is suitably used for an average pyramid size of 0.5 to 20 μm of the maximum side length of the bottom surface of the convex portion on the semiconductor surface. The etching solution of the present invention is used, for example, for surface treatment for forming a concavo-convex structure having convex portions on a semiconductor substrate for solar cells. The etching solution of the present invention is prevented from being contaminated with metal ions, and is preferably used in the etching apparatus used in the examples described later, by the method described later in “Number of times it can be used without liquid replacement”. Can be used 30 times or more. Conventionally, since it has been necessary to change the number of times in about 10 times, the number of times of changing the etching solution can be reduced.

  The method for producing a semiconductor substrate of the present invention includes an etching step in which a convex-concave structure having a pyramid shape is formed on the surface of the semiconductor substrate using the etching solution of the present invention.

  As the semiconductor substrate, a single crystal silicon substrate or a single crystal semiconductor substrate using a semiconductor compound such as germanium or gallium arsenide can 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 the method of immersing the semiconductor substrate in the etching solution of the present invention is preferable. For example, the etching solution of the present invention is placed in a predetermined container and the semiconductor substrate is immersed therein.

  The temperature of the etching solution of the present invention in the container in the etching step is not particularly limited. The etching processing temperature can be set as appropriate. From the viewpoint of productivity and quality, it is preferably in the range of 70 to 98 ° C, more preferably 80 to 95 ° C, and still more preferably 85 to 90 ° C.

  The immersion time of the semiconductor substrate in the etching solution of the present invention in the etching step is not particularly limited. The immersion time can be set as appropriate. From the viewpoint of productivity and quality, it is preferably 5 to 40 minutes, more preferably 10 to 30 minutes, and further preferably 15 to 20 minutes.

  0.5-20 micrometers is preferable, as for the average pyramid size of the maximum side length of the convex part bottom face of the semiconductor substrate surface manufactured with the said manufacturing method, 1-15 micrometers is more preferable, and 1-10 micrometers is more preferable. From the viewpoint of reducing the light reflectance, the average pyramid size of the maximum side length of the bottom surface of the convex portion is preferably 1 μm or more, and preferably 10 μm or less from the viewpoint of productivity.

  Examples of the use of the semiconductor substrate include a solar cell semiconductor substrate. According to this invention, the solar cell provided with this semiconductor substrate for solar cells can be provided.

  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 5
A single crystal silicon substrate (one side 156 mm square, thickness 150 μm) having a crystal orientation (100) plane on the surface was immersed in an etching solution prepared according to the composition shown in Table 1 at 80 to 90 ° C. for 15 to 30 minutes. . The pH of the etching solution at 25 ° C. was in the range of 12-14.

As the alkaline agent, KOH was used. KOH was of a general industrial grade (48% caustic potash (for business use) / Asahi Glass Co., Ltd.). As the sulfonic acid compound, p-toluenesulfonic acid (PTS) was used. As the silicate, JIS No. 1 silicate was used. The lignin sulfonic acid had a weight average molecular weight of 20000 according to the GPC method, a sulfone group density per molecular weight of 500 units, and a number of carboxyl groups per molecular weight of 500 units of 0.5 or less. The remaining component was water.
The specific operation of the etching process is as described below.

  The etching vessel uses a SUS304 tank of about 35 L box shape, and 30 L of etching solution is placed in this tank, heated from the bottom with a SUS casting heater, gently nitrogen bubbling, and liquid circulation stirring (30 L / min) The liquid was stirred and the temperature range was maintained at the set temperature ± 1 ° C. The number of substrates loaded was two. A jig was designed so as not to hinder liquid circulation, and substrates were inserted at intervals of 4 mm. After removing from the etching solution, rinsing with running water was performed immediately and dried with warm air. The substrate after drying was evaluated according to the following criteria.

Surface quality: The uniformity of the entire surface of the substrate (the presence or absence of unevenness and streaks) was visually determined. The results are shown in Table 1.
A: The entire surface is homogeneous with no color unevenness or fine streaks B: Color unevenness or fine streaks exist in a very small part C: Color unevenness or fine streaks exist

Tekali: Pyramid structure irregularities are not formed, the (100) mirror surface remains as it is, a phenomenon that reflects the light and becomes a surface texture that can be seen visually, and the degree is classified and judged as follows . The results are shown in Table 1.
A: No shine B: There is shine in a small part. The area is less than 5%. C: Partially shiny. Especially present at the bottom of the substrate

Pyramid size:
The surface of the substrate was observed with a laser microscope, and the maximum side length of the bottom surface of the convex portion, that is, the pyramid size was measured for 10 pyramid shapes from the largest. This was performed for 3 fields of view and averaged to obtain an average pyramid size. The results are shown in Table 1.

Pyramid size uniformity (variation):
The determination was made based on the existence ratio of a small pyramid size of 50% or less of the average pyramid size of the laser microscope. The results are shown in Table 1.
A: Less than 50% of the average pyramid size is less than 20% B: 20-40% of the above is present C: 40% or more of the above is present

Pyramid shape:
The surface of the substrate was observed with a laser microscope, and a determination was made based on the existence ratio of the pyramid shape having irregularities such as chipping at the apex and roughening of the slope. The results are shown in Table 1.
A: Less than 20% of abnormal shapes B: 20-50% of the same as above C: 50% or more of the same as above

  The above-mentioned laser microscope is manufactured by Keyence Co., Ltd., Laser microscope VK-X100, photographed at a magnification of 2000 times (objective lens 100 times, eyepiece 20 times), printed on paper, and then measured on the base size of the pyramid did.

Etching amount:
The amount of change in the substrate weight before and after etching was weighed to the fourth decimal place with a precision balance (CP224S manufactured by Sartorius), and classified and determined as follows. The results are shown in Table 1.
A: 0.500 g or more and less than 1.000 g B: 1.000 g or more and less than 1.600 g C: less than 0.5 g or 1.600 g or more

Storage stability:
An etching solution was prepared and stored at 40 ° C. for one month, and then an etching process was performed to evaluate the substrate surface. The evaluation of the storage stability of the etching solution was evaluated according to the following criteria by comparing the evaluation of the substrate surface using the etching solution before storage with the evaluation of the substrate surface using the etching solution after storage. The results are shown in Table 1.
A: Almost no deterioration of pyramid shape and surface appearance (surface quality) is observed.
B: Pyramid size uniformity is slightly degraded.
C: A small amount of shine is observed on the substrate surface, and an increase of 20% or more in the etching amount is recognized.

  From the comparison of Examples 1-2 and Comparative Examples 1-2, when the aminocarboxylic acid-based chelate compound is included as the chelating agent, the uniformity of the surface quality, the shine, and the pyramid size are compared with the case where only the other chelating agent is included. It can be seen that the pyramid shape, the etching amount, and the storage stability are excellent.

  From the comparison of Examples 3, 5, 10, and 15, it can be seen that when the amount of the aminocarboxylic acid chelate compound is large, the storage stability is excellent, and when the amount is small, the uniformity of the pyramid size is excellent.

  From the comparison of Examples 10, 20, 21, 22, and 23, it can be seen that, among aminocarboxylic acid-based chelate compounds, diethylenetriaminepentaacetic acid is particularly excellent in pyramid size uniformity, pyramid shape, etching amount, and storage stability. .

  From the comparison between Examples 1 and 5, it can be seen that when the sulfonic acid compound is included, the surface quality, the shine, the uniformity of the pyramid size, and the pyramid shape are excellent as compared with the case where the sulfonic acid compound is not included. Further, from the comparison with Example 5 and Comparative Example 3, even when the sulfonic acid compound was included, the surface quality and the shine were higher when the compound containing the aminocarboxylic acid chelate compound was compared with the case containing only the other chelating agent. It can be seen that the pyramid size uniformity, pyramid shape, etching amount, and storage stability are excellent.

  From the comparison with Example 18 and Comparative Example 4, even when lignin sulfonic acid and the like were included, those containing an aminocarboxylic acid-based chelate compound had surface properties, shine, It can be seen that the pyramid size uniformity, pyramid shape, etching amount, and storage stability are excellent.

  From the comparison of Examples 8 and 11, it can be seen that when silicic acid or the like is included, it can be used without impairing surface quality, shine, pyramid size uniformity, pyramid shape, etching amount, and storage stability.

Number of times it can be used without liquid exchange:
The etching vessel uses a SUS304 tank of about 35 L box shape, and 30 L of etching solution is placed in this tank, heated from the bottom with a SUS casting heater, gently nitrogen bubbling, and liquid circulation stirring (30 L / min) The liquid was stirred and the temperature range was maintained at the set temperature ± 1 ° C. The number of substrates loaded per time was 30 and the treatment was performed a plurality of times. A jig was designed so as not to hinder liquid circulation, and substrates were inserted at intervals of 4 mm. After removing from the etching solution, rinsing with running water was performed immediately and dried with warm air. Further, during the liquid management during this time, the amount of KOH before and after etching was measured by titration with 0.5N HCl each time, and the difference was regarded as the amount of consumption, and the amount of consumption of KOH was added. This operation was repeated using a new substrate. The number of times until the surface quality, shine, and pyramid shape significantly decreased was defined as the number of times that the liquid could be used without liquid exchange.

Reflectivity of the substrate after etching:
The reflectance is measured by using a spectrophotometer (with an integrating sphere) manufactured by Shimadzu Corporation, which is a spectrophotometer (with an integrating sphere), measuring the light reflectance (2 fields of view) at a wavelength of 300 to 1200 nm, and the average value of the light reflectance at a wavelength of 600 nm. It calculated using.

  In Example 8, even if it was used 30 times without changing the liquid, no deterioration was observed in the surface quality, the shine, and the pyramid shape.

  In Comparative Example 5 containing no chelating agent, the surface quality, shine, and pyramid shape significantly decreased when the number of times exceeded 10.

  The comparative example 4 which contains only a phosphonic acid type chelate compound as a chelating agent was able to be used 15 times. Although the comparative example 4 reduced the frequency | count of replacement | exchange compared with the thing which does not contain a chelating agent, it did not reach the etching liquid containing an aminocarboxylic acid type chelate compound.

  From the above, the etching solution of the present invention containing an aminocarboxylic acid-based chelate compound has a smaller number of liquid exchanges than an etching solution containing no chelating agent, and has a surface area that is smaller than that of etching solutions containing only other chelating agents. It can be seen that it is excellent in quality, shine, pyramid size uniformity, pyramid shape, etching amount, and storage stability. Among the examples, Examples 8 and 11 are comprehensively superior to other examples and can be suitably used. The reflectance of the semiconductor substrate of Example 8 was 11.0%.

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

Claims (15)

  An etching solution that is an alkaline etching solution for forming a pyramidal uneven structure on the surface of a semiconductor substrate, and includes an alkali agent and an aminocarboxylic acid chelate compound.   The aminocarboxylic acid-based chelate compound is at least one selected from the group consisting of aminocarboxylic acids having 13 to 24 carbon atoms having at least one carboxyl group in one molecule and salts thereof. The etching liquid as described.   The etching solution according to claim 1, wherein the alkaline agent is at least one of sodium hydroxide and potassium hydroxide.   Content of the said alkali agent is an etching liquid in any one of Claims 1-3 which is 0.1-25 mass% in the said etching liquid.   The aminocarboxylic acid chelate compound is at least one selected from the group consisting of diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, cyclohexanediaminetetraacetic acid, diaminohexanetetraacetic acid, glycol etherdiaminetetraacetic acid, and salts thereof. The etching liquid in any one of Claims 1-4 which exists. Furthermore, the general formula (I):

(In the formula, n is an integer of 0 to 5, and each R independently represents an alkyl group having 1 to 12 carbon atoms.)
The etching liquid in any one of Claims 1-5 containing at least 1 type selected from the group which consists of the sulfonic acid compound represented by these, and its salt.   The etching solution according to claim 6, wherein the sulfonic acid compound is at least one selected from the group consisting of benzenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid, and cumenesulfonic acid.   Furthermore, the etching liquid in any one of Claims 1-7 containing at least any one among a silicic acid and a silicate.   Furthermore, the etching liquid in any one of Claims 1-8 containing at least any one among lignin sulfonic acid and lignin sulfonate.   The etching liquid according to any one of claims 1 to 9, wherein the average of the maximum side length of the bottom surface of the convex portion is 0.5 to 20 µm.   The etching liquid according to claim 1, wherein the semiconductor substrate is a solar cell semiconductor substrate.   The manufacturing method of a semiconductor substrate including the etching process in which a convex part forms a pyramid-shaped uneven structure on the surface of a semiconductor substrate using the etching liquid in any one of Claims 1-11.   A semiconductor substrate manufactured by the manufacturing method according to claim 12.   The semiconductor substrate according to claim 13, wherein the semiconductor substrate is a solar cell semiconductor substrate.   A solar cell comprising the semiconductor substrate according to claim 14.