WO2015041214A1 - Etching liquid for semiconductor substrate - Google Patents

Etching liquid for semiconductor substrate Download PDF

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Publication number
WO2015041214A1
WO2015041214A1 PCT/JP2014/074442 JP2014074442W WO2015041214A1 WO 2015041214 A1 WO2015041214 A1 WO 2015041214A1 JP 2014074442 W JP2014074442 W JP 2014074442W WO 2015041214 A1 WO2015041214 A1 WO 2015041214A1
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WIPO (PCT)
Prior art keywords
etching
semiconductor substrate
sulfonic acid
etching solution
present
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PCT/JP2014/074442
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French (fr)
Japanese (ja)
Inventor
山本　裕三
斎田　利典
伸 大八木
義輝 鎌田
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攝津製油株式会社
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Application filed by 攝津製油株式会社 filed Critical 攝津製油株式会社
Priority to JP2015537925A priority Critical patent/JP6373271B2/en
Priority to CN201480050156.9A priority patent/CN105518834B/en
Publication of WO2015041214A1 publication Critical patent/WO2015041214A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0236—Special surface textures
    • H01L31/02363—Special surface textures of the semiconductor body itself, e.g. textured active layers
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K13/00—Etching, surface-brightening or pickling compositions
    • C09K13/04—Etching, surface-brightening or pickling compositions containing an inorganic acid
    • C09K13/06—Etching, surface-brightening or pickling compositions containing an inorganic acid with organic material
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy

Definitions

  • the present invention relates to an etching solution for a semiconductor substrate, particularly 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.
  • 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.
  • the present invention has been made in order to solve the above-mentioned problems, and its purpose is not to cause the above-mentioned environmental problems and quality fluctuations.
  • An object of the present invention is to provide an etching solution with excellent pyramid size control. It is another object of the present invention to provide a technique for uniformly forming irregularities of a desired size on a substrate surface even when a large number of solar cell semiconductor substrates are continuously etched.
  • the inventors of the present invention have made extensive studies to solve the above problems. As a result, it has been found that the use of lignin sulfonic acid and / or a salt thereof satisfying certain conditions can greatly improve the surface quality and texture structure homogeneity, is excellent in productivity, and can be greatly improved in continuous use.
  • the present invention has been completed.
  • the gist of the present invention is as follows.
  • An alkaline etching solution for treating the surface of a semiconductor substrate for solar cells which contains at least one selected from the group consisting of lignin sulfonic acid and salts thereof.
  • 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.
  • n is an integer of 0 to 5, and each R is independently a hydrogen atom or an alkyl group having 1 to 12 carbon atoms
  • Etching power recovery agent for an etchant comprising at least one selected from the group consisting of lignin sulfonic acid and a salt of lignin sulfonic acid
  • a method for producing a solar cell semiconductor substrate comprising an etching step of etching the substrate surface of the solar cell semiconductor substrate with the etching solution according to [1] to form irregularities on the substrate surface;
  • a semiconductor substrate for a solar cell the surface of which is etched with the etching solution according to [1].
  • the present invention it is possible to form a texture in a shorter time on a relatively low temperature side, and the effect of excellent productivity is exhibited.
  • the surface defects are reduced, a texture having excellent surface quality can be formed.
  • 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 alkaline component, and contains lignin sulfonic acid and / or a salt thereof that satisfy certain conditions. It is characterized by that. Further, at least one selected from a specific sulfonic acid compound and a salt thereof, and silicic acid and / or silicate may be included.
  • 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.
  • Lignin sulfonic acid and its salts Lignin sulfonic acid or lignin sulfonate, which is a compound 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 with a phenylpropane group as the 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.
  • Inorganic reagent lignin sulfonic acid, alkali lignin, thiolignin, chlorlignin, 2) Acidic organic reagent: alcohol lignin, dioxane lignin, phenol lignin, thioglycolic acid Lignin, acetate lignin, hydrotropic lignin, 3) by hydrochloric acid organic reagent: Brauns natural lignin, acetone lignin, Nord lignin, Bjorkman lignin and the like. Lignin sulfonic acid or a salt thereof obtained by sulfonation using the above isolated lignin or a derivative thereof may be used.
  • lignin sulfonic acid and lignin sulfonate that have been chemically modified, such as increasing the carboxyl group by oxidation treatment, can also be used.
  • 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 or the uniformity of the pyramid shape is impaired.
  • Lignin sulfonic acid and lignin sulfonate are manufactured and sold by a large number of 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 prepared 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.
  • 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.
  • 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).
  • 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 molecular weight distribution has a peak between 1000 and 100,000, preferably between 2000 and 60,000, and at least 50% by mass or more of the component is present in this molecular weight region.
  • Sulfone group density ie, degree of sulfonation
  • Those having 0 to 3 carboxyl groups per 500 molecular weight units Those having 0 to 3 carboxyl groups per 500 molecular weight units.
  • 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 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 mm ⁇ ⁇ 4 cm), one TSK3000HXL (7.8 mm ⁇ ⁇ 30 cm), and one TSK2500HXL (7.8 mm ⁇ ⁇ 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.
  • 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.
  • lignin sulfonic acid or a salt thereof obtained by chelating heavy metal ions such as Fe, Cr, Mn, Mg, Zn, and Al can be used in the present invention.
  • lignin sulfonic acid or a salt thereof further added with another organic compound or organic polymer such as naphthalene or phenol 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, for example, 0.001 ppm or more and 10,000 ppm or less. 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, it is preferably 10,000 ppm or less, more preferably 1000 ppm or less, and even more preferably 500 ppm or less from the viewpoint of making the unevenness formed, particularly the pyramid shape, and the etching rate.
  • the lignin sulfonic acid or lignin sulfonate contained in the etching solution of the present invention is obtained by sulfonating a pulp waste solution as a raw material. Moreover, by including it in an alkaline etching solution together with the following sulfonic acid compound represented by the following general formula (I) and / or silicic acid and / or silicate, initial rise and texture quality can be further improved. .
  • the sulfonic acid compound represented by the following general formula (I) has less unpleasant odor compared to aliphatic carboxylic acids such as caprylic acid and heptanoic acid. Work environment can be improved.
  • n is an integer of 0 to 5, and each R is independently a hydrogen atom or an alkyl group having 1 to 12 carbon atoms.
  • N is preferably 1 or more and 5 or less.
  • n is 1 or more, it is preferable because the etching process of the substrate surface can be promoted, and when n is 5 or more, it is not preferable because the etching process is hindered.
  • 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.
  • an alkyl group having 1 to 5 carbon atoms is preferable, and a methyl group is particularly preferable.
  • 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 can be reduced.
  • the substitution position of R on the benzene ring is preferably the para-position or ortho-position of the sulfo group, and particularly preferably the para-position of the sulfo group.
  • sulfonic acid compounds represented by the general formula (I) benzenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid and cumenesulfonic acid are more preferable, and such a sulfonic acid compound may be used alone. Or two or more types may be used in combination.
  • toluenesulfonic acid pyramidal irregularities having a desired size can be formed uniformly on the substrate surface.
  • toluenesulfonic acid is less odorous than aliphatic carboxylic acids such as caprylic acid. Therefore, if toluenesulfonic acid is used, the working environment such as etching can be improved.
  • the preferred toluenesulfonic acid is para-toluenesulfonic acid (PTS).
  • the concentration of the sulfonic acid compound in the etching solution of the present invention is not particularly limited, but is preferably 0.005 to 2.0 mol / L. If the said density
  • silicic acid and / or silicate The kind of silicic acid and / or silicate 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, etc. or silicon dioxide in an alkali as a reaction product. The obtained silicate compound 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 wt%, more preferably 0.1 to 5 wt%, and still more preferably 0.2 to 3 wt%. It is.
  • 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 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 alkali concentration 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
  • Alkali is a component necessary for forming pyramidal irregularities on the substrate surface when the substrate surface is etched with an etching solution.
  • the type of alkali contained in the etching solution of the present invention is not particularly limited, and both organic alkali and inorganic alkyl can be used.
  • organic alkali for example, a quaternary ammonium salt such as tetramethylammonium hydroxide, an alkanolamine and the like are preferable.
  • 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 alkalis may be used alone or in combination of two or more.
  • the concentration of alkali in the etching solution is not particularly limited, but is preferably 0.1% by mass or more and 50% by mass or less. From the viewpoint of exerting an etching effect, 0.1% by mass or more is preferable, 0.5% by mass or more is more preferable, 1% by mass or more is more preferable, 2% by mass or more is more preferable, and 3% by mass or more is more preferable. . On the other hand, from the viewpoint of cost effectiveness, 50% by mass or less is preferable, 30% by mass or less is more preferable, and 25% by mass or less is more preferable. In particular, when the alkali concentration is 3% by mass or more, the durability of the etching solution is remarkably increased, and even when the etching solution is repeatedly used, irregularities of a desired size can be uniformly formed on the substrate surface.
  • the etching solution of the present invention may contain other components as long as the effects of the present invention are not impaired.
  • a chelating agent, an amino acid, a polymer, glycol ethers, etc. as an auxiliary agent, the effect (incident incident light is efficiently taken into the substrate) by including the sulfonic acid compound can be enhanced.
  • the solvent of the etching solution of the present invention is preferably water.
  • the method for adjusting 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. 2-5 times conch shipping is preferable.
  • the etching solution of the present invention has a high effect of recovering the etching power of the deteriorated etching solution when a new etching solution is added to the etching solution gradually deteriorated by etching the semiconductor substrate for solar cells.
  • the above high etching power recovery effect can be obtained by replacing or adding 10% or more of the etching solution with a new etching solution. Therefore, the etching solution of the present invention can be used as an etching power recovery agent.
  • the sulfonic acid compound containing the alkaline agent and represented by the general formula (I) a salt of the sulfonic acid compound, the lignin sulfonic acid, and the lignin sulfonic acid It contains at least one selected from the group consisting of these salts.
  • Etching power can be recovered by adding an alkaline agent to an etching solution that has deteriorated due to repeated processing of 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 sulfonic acid compound represented by the general formula (I), the salt of the sulfonic acid compound, the lignin sulfonic acid and the lignin By adding the above sulfonic acid compound alone or in combination with an alkali agent from a sulfonic acid salt, the number of etching treatment batches can be increased without replacing the deteriorated etching solution. As a result, the initial building bath etching solution can be used continuously, so that the industrial value is enhanced.
  • the sulfonic acid compound represented by the general formula (I) the salt of the sulfonic acid compound, the lignin sulfonic acid and the lignin
  • the manufacturing method of the semiconductor substrate for solar cells of this invention is equipped with the etching process of etching the board
  • a single crystal silicon substrate is preferable, but a single crystal semiconductor substrate using a semiconductor compound such as copper / indium or gallium arsenide can also be used.
  • 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.
  • the production method of the present invention will be described with reference to the method of immersion.
  • 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 immersing the solar cell semiconductor substrate therein.
  • the temperature of the etching solution in the container is not particularly limited and can be set as appropriate, but it is preferably in the range of 70 to 98 ° C. in consideration of production and quality.
  • 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, considering production and quality, it is preferably 10 to 40 minutes.
  • the etching solution 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 ionization 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.
  • 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 has a maximum side length of 1 to 30 ⁇ m at the bottom,
  • the upper limit is preferably 25 ⁇ m, more preferably the upper limit is 20 ⁇ m, and pyramid-shaped uniform irregularities are formed.
  • a semiconductor substrate for solar cells with high productivity and low reflectance can be obtained.
  • the pyramidal irregularities are convex portions formed by arranging pyramidal (quadrangular pyramidal) convex portions on the surface of the semiconductor substrate for solar cells.
  • the size of the pyramid shape formed on the substrate surface is preferably 1 to 30 ⁇ m, more preferably 2 to 20 ⁇ m, and even more preferably 2 to 15 ⁇ m. From the viewpoint of reducing light reflectance, the average size is preferably 1 ⁇ m or more, and from the viewpoint of productivity, the average size is preferably 30 ⁇ m or less.
  • pyramidal 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.
  • Examples 1-22 and Comparative Examples 1-2 A single crystal silicon substrate (one side 156 mm square, thickness 150 ⁇ m) having a crystal orientation (100) plane was immersed in an etching aqueous solution prepared according to the formulation shown in Table 1 at 80 to 90 ° C. for 10 to 30 minutes. .
  • Table 1 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. A specific etching process is as described in [Etching process] below.
  • Examples 23 to 27 and Comparative Examples 3 to 4 Concerning the stamina of the etching solution (continuous use), a large number of substrates (31 sheets / cassette) are set in a substrate support cassette for an etching solution amount of 30 L, and this is processed multiple times as a batch, and the quality of the pyramid Evaluation was made based on the number of batches in which a reference value was set and maintained. At that time, the consumption of alkali was intense, so the consumed KOH was determined by an automatic titrator, and 0.5 to 1.5 times equivalent KOH was replenished every batch.
  • a specific etching process is as described in [Etching process] below.
  • Example 27 of continuous usability p-toluenesulfonic acid (PTS) and lignin sulfonic acid were added in the 18th batch, and the continuous test was continued.
  • the additional amount of PTS was an amount that increased the concentration of PTS in the etching solution by 3% by weight
  • the additional amount of lignin sulfonic acid was an amount that increased the concentration of lignin sulfonic acid in the etching solution by 100 ppm.
  • the conditions and results are shown in Table 2. The number of times of continuous use was evaluated by the number of times when the substrate was evaluated to be ⁇ .
  • Bubble streaks Vertical traces due to bubble traces and liquid flow may be seen starting from the part where the wafer and jig claw contact on the jig (cassette) holding the wafer in the etching tank. The degree was determined by visual observation as follows. A: Strong vertical stripes are not seen. B: Although some vertical stripes are observed, it is an allowable range (a range that is not noticeable when a solar cell panel is used). C: Longitudinal streaks are somewhat strong. F: Strong vertical stripes are observed.
  • Tekali A phenomenon in which unevenness of the pyramid structure is not formed, the (100) mirror surface remains as it is, and it becomes a surface property that reflects light and looks like a mirror. The degree is classified and judged as follows.
  • C Some shine is present.
  • F Tekari is recognized on the entire surface.
  • Pyramid size The surface of the substrate is observed with a laser microscope, and the pyramid size is 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. Some of the substrates were also observed with a scanning electron microscope.
  • the above laser microscope uses Keyence Corporation's Laser Microscope VK-X100, 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 JSM-5310 manufactured by JEOL Ltd., and the acceleration voltage was observed at 15 kV.
  • Pyramid size uniformity 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. 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.
  • Examples 1 to 22 using a specific lignin sulfonic acid showed excellent etching characteristics despite a relatively low temperature (85 ° C.) and a short time (15 minutes), and uniform surface quality (no uneven appearance) It can be seen that the uniformity of the pyramid size is also excellent. Moreover, there is no occurrence of a shining surface (location where pyramids are not formed), which is good. The light reflectance is also kept low. It can be seen that Comparative Examples 1 and 2 are significantly inferior to the Examples in terms of surface quality (appearance unevenness and bubble streaks).
  • Example 27 As shown in Examples 23 to 27, it can be seen that good continuous use characteristics are exhibited. In Example 27, it turns out that the frequency
  • 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.

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Abstract

The present invention relates to an alkaline etching liquid for processing the surface of a semiconductor substrate for a solar battery, the etching liquid including at least one item selected from the group comprising lignin sulphonic acid and salts thereof. Use of the etching liquid of the present invention exhibits the effects of excellent productivity and of being able to form a texture in a short amount of time at relatively low temperatures. Further, the etching liquid produces the effects of the refinement and excellent surface elimination of the bubbles that are generated in large amounts during multi-sheet processing, and yield is increased because floating of a substrate during etching can be eliminated. In addition, textures having excellent surface quality can be formed because surface defects are reduced.

Description

半導体基板用エッチング液Etching solution for semiconductor substrate
　本発明は、半導体基板用エッチング液、特に太陽電池用半導体基板用エッチング液に関する。さらに本発明は、エッチング力回復剤、太陽電池用半導体基板の製造方法、及び太陽電池用半導体基板に関する。 The present invention relates to an etching solution for a semiconductor substrate, particularly 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.
　太陽電池の発電効率を高めるために、従来から太陽電池用半導体基板の表面に凹凸を形成させ、基板表面からの入射光を効率良く基板内部に取り込む方法が用いられている。基板表面に微細な凹凸を均一に形成する方法として、例えば、単結晶シリコン基板の（１００）面を、水酸化ナトリウム及びイソプロピルアルコールの混合水溶液を用いて異方エッチング処理し、（１１１）面で構成されるピラミッド状（四角錐状）の凹凸を形成させる方法が知られている。しかしながら、この方法は、イソプロピルアルコール（ＩＰＡ）を使用するため、ＩＰＡの揮発による成分変動による品質の変動や廃液処理や作業環境、安全性の点で問題がある。また比較的高温・長時間の処理が必要で生産性の点でも改善が求められていた。 In order to increase the power generation efficiency of solar cells, 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 There is known a method of forming a pyramid-shaped (quadrangular pyramid) asperity. 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.
　上記を改善する技術では、特許文献１には、アルカリ性のエッチング液に特定の脂肪族カルボン酸とシリコンとを含有させることで、基板表面をエッチングする際のエッチングレートを安定させて、所望の大きさのピラミッド状の凹凸を基板表面に均一に形成させる方法が記載されている。 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.
国際公開第２００７／１２９５５５号International Publication No. 2007/129555
　しかしながら、特許文献１の手法では、所望の大きさの凹凸が基板表面に形成されるものの、初期のエッチングの立ち上がりの悪さ（初期数バッチは均質な面が得られにくい）や、エッチング時に発生するガスの痕跡がでやすいなど表面欠陥を生じやすい課題があった。また連続繰り返し使用時の後半では成分の消耗やエッチング反応による副生成物の影響でピラミッドサイズの変動が大きくコントロール性に劣るものであった。使用現場では一定範囲のピラミッドサイズを連続的かつ安定的に得るために大変な労力・手間を必要としていた。テクスチャーサイズの均一性は発電効率の影響を与えるばかりでなく、発電効率低下を防ぐパッシベーション用・保護膜の被覆を良くする効果もある。 However, in the method of Patent Document 1, although unevenness of a desired size is formed on the substrate surface, the initial etching start-up is poor (it is difficult to obtain a uniform surface in the initial few batches) or occurs during etching. There was a problem that surface defects were likely to occur, such as gas traces. In the latter half of the continuous repeated use, the pyramid size fluctuated greatly 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 the effect of improving the covering of the passivation film and the protective film that prevents a decrease in power generation efficiency.
　不均一な凹凸が基板表面に形成された太陽電池用半導体基板になることを防ぐためには、所望の大きさの凹凸が基板表面に均一に形成されているか否かを頻繁に確認して、不均一な凹凸が基板表面に形成され始めたときに、エッチング液を交換しなければならない。 In order to prevent a semiconductor substrate for a solar cell having uneven irregularities formed on the substrate surface, it is often necessary to check whether irregularities of a desired size are uniformly formed on the substrate surface. When uniform irregularities begin to form on the substrate surface, the etchant must be replaced.
　本発明は、上記の課題を解決するためになされたものであり、その目的は、上記のような環境問題・品質変動を生じさせない、比較的低温側でより短時間で、かつ立ち上がり性にすぐれ、ピラミッドサイズコントロール性に優れたエッチング液を提供することにある。さらには多枚数の太陽電池用半導体基板を連続してエッチング処理しても、所望の大きさの凹凸を基板表面に均一に形成させるための技術を提供することにある。 The present invention has been made in order to solve the above-mentioned problems, and its purpose is not to cause the above-mentioned environmental problems and quality fluctuations. An object of the present invention is to provide an etching solution with excellent pyramid size control. It is another object of the present invention to provide a technique for uniformly forming irregularities of a desired size on a substrate surface even when a large number of solar cell semiconductor substrates are continuously etched.
　本発明者らは、上記課題を解決するために鋭意研究を重ねた。その結果、ある一定の条件を満たすリグニンスルホン酸及び／又はその塩を用いることで、表面品質、テクスチャー構造の均質性を大きく改善でき、生産性にも優れ、連続使用性も大きく改善できることを見出し本発明の完成に至った。 The inventors of the present invention have made extensive studies to solve the above problems. As a result, it has been found that the use of lignin sulfonic acid and / or a salt thereof satisfying certain conditions can greatly improve the surface quality and texture structure homogeneity, is excellent in productivity, and can be greatly improved in continuous use. The present invention has been completed.
　また上記組成に特定のスルホン酸化合物及びその塩から選択される少なくとも一種と、ケイ酸及び／又はケイ酸塩とを併用することで生産安定性とテクスチャー品質とをいっそう改善できることを見出したものである。より具体的には本発明は以下のものを提供する。 In addition, it has been found that production stability and texture quality can be further improved by using at least one selected from a specific sulfonic acid compound and a salt thereof in the above composition and silicic acid and / or silicate. is there. More specifically, the present invention provides the following.
　即ち、本発明の要旨は、
〔１〕太陽電池用半導体基板の表面を処理するためのアルカリ性のエッチング液であって、リグニンスルホン酸及びその塩からなる群より選択される少なくとも一種を含むエッチング液；
〔２〕前記〔１〕に記載のエッチング液で太陽電池用半導体基板を処理した後に前記エッチング液に添加して、該エッチング液のエッチング力を回復させるエッチング力回復剤であって、アルカリ剤を含み、かつ
　一般式（Ｉ） 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, which contains at least one selected from the group consisting of lignin sulfonic acid and salts thereof;
[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. Including general formula (I)
Figure JPOXMLDOC01-appb-C000003
Figure JPOXMLDOC01-appb-C000003
（式中のｎは０～５の整数であり、Ｒはそれぞれ独立して水素原子又は炭素数１～１２のアルキル基である。）で表されるスルホン酸化合物、前記スルホン酸化合物の塩、リグニンスルホン酸及び前記リグニンスルホン酸の塩からなる群より選択される少なくとも一種を含む、エッチング液のエッチング力回復剤；
〔３〕前記〔１〕に記載のエッチング液で太陽電池用半導体基板の基板表面をエッチングして、前記基板表面に凹凸を形成させるエッチング工程を含む、太陽電池用半導体基板の製造方法；並びに
〔４〕前記〔１〕に記載のエッチング液でその表面がエッチング処理されてなる、太陽電池用半導体基板；に関するものである。 (Wherein n is an integer of 0 to 5, and each R is independently a hydrogen atom or an alkyl group having 1 to 12 carbon atoms), a salt of the sulfonic acid compound, Etching power recovery agent for an etchant, comprising at least one selected from the group consisting of lignin sulfonic acid and a salt of lignin sulfonic acid;
[3] A method for producing a solar cell semiconductor substrate, comprising an etching step of etching the substrate surface of the solar cell semiconductor substrate with the etching solution according to [1] to form irregularities on the substrate surface; [4] A semiconductor substrate for a solar cell, the surface of which is etched with the etching solution according to [1].
　本発明によれば、比較的低温側でより短時間でテクスチャー形成が可能で生産性に優れるという効果が発揮される。また多数枚処理時に多量に発生する泡の微細化や泡の表面脱離性に優れた効果をもたらし、エッチング中の基板の浮きをなくせるので歩留りが向上する。さらに表面欠陥が減ることから表面品質にすぐれたテクスチャーを形成することができる。 According to the present invention, it is possible to form a texture in a shorter time on a relatively low temperature side, and the effect of excellent productivity is exhibited. In addition, it is possible to produce a large amount of bubbles generated during the processing of a large number of sheets and to have an excellent effect on the surface detachability of the bubbles and to eliminate the floating of the substrate during etching, thereby improving the yield. Further, since the surface defects are reduced, a texture having excellent surface quality can be formed.
　以下、本発明の実施形態について説明する。なお、本発明は以下の実施形態に限定されない。 Hereinafter, embodiments of the present invention will be described. In addition, this invention is not limited to the following embodiment.
＜エッチング液＞
　本発明のエッチング液は、太陽電池用半導体基板の表面を処理するためのアルカリ性の水溶液であり、少なくとも１種のアルカリ成分を含み、ある一定の条件を満たすリグニンスルホン酸及び／又はその塩を含むことを特長とする。また特定のスルホン酸化合物及びその塩から選択される少なくとも一種と、ケイ酸及び／又はケイ酸塩とを含ませてもよい。 <Etching solution>
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 alkaline component, and contains lignin sulfonic acid and / or a salt thereof that satisfy certain conditions. It is characterized by that. Further, at least one selected from a specific sulfonic acid compound and a salt thereof, and silicic acid and / or silicate may be included.
　本発明のエッチング液はアルカリ性である。具体的には、２５℃でのｐＨが１２～１４の範囲であることが好ましく、１３～１４の範囲であることが好ましい。後述のアルカリ剤の量や濃度を適宜変更することによって、エッチング液のｐＨを所望の範囲に設定することができる。 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.
[リグニンスルホン酸及びその塩]
　リグニンスルホン酸またはリグニンスルホン酸塩、これはパルプ製造時に副生するパルプ廃液を種々の方法で処理した化合物で、主成分はリグニンスルホン酸塩またはリグニンスルホン酸である。リグニンの化学構造はフェニルプロパン基を基本骨格とし、これが3次元網目構造組織をとった化合物である。 [Lignin sulfonic acid and its salts]
Lignin sulfonic acid or lignin sulfonate, which is a compound 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 with a phenylpropane group as the basic skeleton, and a three-dimensional network structure.
　リグニンスルホン酸やリグニンスルホン酸塩は単離方法によって種々の名称がつけられている。例えばリグニンを残渣として得たものだと、硫酸リグニン、塩酸リグニン、酸化銅アンモニウムリグニン、過ヨウ素酸リグニン等が挙げられる。リグニンを溶解して得たものだと、１）無機試薬によるもの：リグニンスルホン酸、アルカリリグニン、チオリグニン、クロルリグニン、２）酸性有機試薬によるもの：アルコールリグニン、ジオキサンリグニン、フェノールリグニン、チオグリコール酸リグニン、酢酸リグニン、ヒドロトロピックリグニン、３）塩酸性有機試薬によるもの：Brauns天然リグニン、アセトンリグニン、Nordリグニン、Bjorkmanリグニンなどが挙げられる。以上の単離リグニンあるいはその誘導体を原料にしてスルホン化を行ったリグニンスルホン酸またはその塩でもかまわない。この他に酸化処理をしてカルボキシル基を増やすなどの化学変性を行ったリグニンスルホン酸やリグニンスルホン酸塩も用いることができる。本発明に使用できるリグニンスルホン酸およびリグニンスルホン酸塩にはパルプ製造時の不純物を含有していてもかまわないが、その量は少なければ少ないほど好ましい。不純物が多いとピラミッドの一部に形状崩れが発生したり、ピラミッド形状の均一性が損なわれる。 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, acetate lignin, hydrotropic lignin, 3) by hydrochloric acid organic reagent: Brauns natural lignin, acetone lignin, Nord lignin, Bjorkman lignin and the like. Lignin sulfonic acid or a salt thereof obtained by sulfonation using the above isolated lignin or a derivative thereof may be used. In addition, lignin sulfonic acid and lignin sulfonate that have been chemically modified, such as increasing the carboxyl group by oxidation treatment, can also be used. 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 or the uniformity of the pyramid shape is impaired.
　リグニンスルホン酸及びリグニンスルホン酸塩はパルプメーカー各社から非常に数多くの商品が製造販売されている。分子量も１８０～１００万にわたり、各種のスルホン化度、各種の塩、化学変性したもの、重金属イオンで調整したものなどバラエティに富んでいる。本発明者らは、これら各種リグニンスルホン酸及びその塩の全てが本発明の目的に適したものではなく、その効果はものによってはバラツキがあることや、ある特定のリグニンスルホン酸又はその塩を用いた時に、シリコン半導体基板の異方性エッチングが良好に進行し凹凸構造（ピラミッド形状）が良好に形成され本発明の目的の達成度が大きく向上することを見出した。 Lignin sulfonic acid and lignin sulfonate are manufactured and sold by a large number of 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 prepared 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.
　即ち、本発明に好適に使用できるリグニンスルホン酸又はその塩としては、以下の１）～３）の条件の全てを満たすものである。
　　１）分子量１０００未満の低分子成分及び分子量１０万以上の高分子成分が非常に少ないか、又は完全に除去されたもの。具体的には、分子量分布のピークが１０００～１０万の間にあり、好ましくは２０００～６万の間にあり、かつ少なくとも５０質量％以上の成分がこの分子量領域に存在するもの。
　　２）スルホン基密度（即ち、スルホン化度）が分子量５００単位当たり平均０．６以上３未満のもの。
　　３）分子量５００単位当たりのカルボキシル基が０～３個のもの。 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 molecular weight distribution has a peak between 1000 and 100,000, preferably between 2000 and 60,000, and at least 50% by mass or more of the component is 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.
　なお、上記１）での分子量・分子量分布の測定は、以下に示すGPC（ゲル浸透クロマトグラフィー）法により実施する。
（ａ）サンプル調製
　試料に同重量の水を加えて、GPC用のサンプルとする。
（ｂ）カラム
　ガードカラムTSX（東ソー（株）製）HXL（6.5mmφ×4cm）１本と、TSK3000HXL（7.8mmφ×30cm）１本と、TSK2500HXL（7.8mmφ×30cm）１本の構成とする。注入口側よりガードカラム－3000HXL－2500HXLの順に接続する。
（ｃ）標準物質
　ポリスチレン（東ソー（株）製）を用いる。
（ｄ）溶出液
　水を使用する。
（ｅ）カラム温度
　室温（２５℃）とする。
（ｆ）検出器
　UV（紫外分光光度計）を用いる。波長はフェノールの紫外極大ピークにより定量する。
（ｇ）分子量計算のための分割法
　時間分割（２秒）とする。 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 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) A detector UV (ultraviolet spectrophotometer) is used. The wavelength is quantified by the ultraviolet maximum peak of phenol.
(G) Division method for molecular weight calculation Time division (2 seconds).
　本発明に用いることができるリグニンスルホン酸塩の種類は特に制約がなく、上記のリグニンスルホン酸のNa塩、K塩、Ca塩、アンモニウム塩、Cr塩、Fe塩、Al塩、Mn塩、Mg塩などいずれでも本発明に使用できる。 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.
　また、上記のリグニンスルホン酸又はその塩において、Fe、Ｃｒ、Mn、Mg、Zn、Alなどの重金属イオンをキレートさせたものも本発明に使用できる。 In addition, lignin sulfonic acid or a salt thereof obtained by chelating heavy metal ions such as Fe, Cr, Mn, Mg, Zn, and Al can be used in the present invention.
　好ましくは上記１）～３）の条件を満たす限り、さらにナフタレンやフェノール等の他の有機化合物又は有機高分子を付加したリグニンスルホン酸又はその塩も本発明に使用することができる。 Preferably, as long as the above conditions 1) to 3) are satisfied, lignin sulfonic acid or a salt thereof further added with another organic compound or organic polymer such as naphthalene or phenol can also be used in the present invention.
　本発明のエッチング液中の「リグニンスルホン酸及びその塩からなる群より選択される少なくとも一種」の濃度は、例えば０．００１ｐｐｍ以上、１００００ｐｐｍ以下の範囲が好ましく使用できる。エッチング処理中に発生する気泡を効果的に除去し、さらに基板表面に凹凸、特にピラミッド形状を効率的に形成させる観点から、該濃度は０．００１ｐｐｍ以上が好ましく、０．１ｐｐｍ以上がより好ましく、２ｐｐｍ以上がより好ましく、２０ｐｐｍ以上がより好ましい。一方、形成される凹凸、特にピラミッド形状を整ったものにさせる観点からおよびエッチング速度の観点から、１００００ｐｐｍ以下が好ましく、１０００ｐｐｍ以下がより好ましく、５００ｐｐｍ以下がより好ましい。 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, for example, 0.001 ppm or more and 10,000 ppm or less. 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, it is preferably 10,000 ppm or less, more preferably 1000 ppm or less, and even more preferably 500 ppm or less from the viewpoint of making the unevenness formed, particularly the pyramid shape, and the etching rate.
[スルホン酸化合物]
　本発明のエッチング液に含まれるリグニンスルホン酸またはリグニンスルホン酸塩はパルプ廃液を原料としてこれをスルホン化して得られるものである。
　また、下記一般式（Ｉ）で表される下記のスルホン酸化合物、及び／又はケイ酸及び／又はケイ酸塩と共にアルカリ性のエッチング液に含まれることで、より初期立ち上がり性やテクスチャー品質を向上できる。また、下記一般式（Ｉ）で表されるスルホン酸化合物は、カプリル酸やヘプタン酸等の脂肪族カルボン酸と比較して嫌な臭気が少なく、トルエンスルホン酸を使用すれば、エッチング処理等の作業環境を改善できる。 [Sulfonic acid compound]
The lignin sulfonic acid or lignin sulfonate contained in the etching solution of the present invention is obtained by sulfonating a pulp waste solution as a raw material.
Moreover, by including it in an alkaline etching solution together with the following sulfonic acid compound represented by the following general formula (I) and / or silicic acid and / or silicate, initial rise and texture quality can be further improved. . In addition, the sulfonic acid compound represented by the following general formula (I) has less unpleasant odor compared to aliphatic carboxylic acids such as caprylic acid and heptanoic acid. Work environment can be improved.
一般式（Ｉ）： Formula (I):
Figure JPOXMLDOC01-appb-C000004
Figure JPOXMLDOC01-appb-C000004
（式中のｎは０～５の整数であり、Ｒはそれぞれ独立して水素原子又は炭素数１～１２のアルキル基である。） (In the formula, n is an integer of 0 to 5, and each R is independently a hydrogen atom or an alkyl group having 1 to 12 carbon atoms.)
　ｎは１以上５以下であることが好ましい。ｎが１以上であると基板表面のエッチング処理を促進できるという理由で好ましく、ｎが５以上であればエッチング処理が阻害されるという理由で好ましくない。より好ましいｎの範囲は１以上３以下である。 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, and when n is 5 or more, it is not preferable because the etching process is hindered. A more preferable range of n is 1 or more and 3 or less.
　炭素数１～１２のアルキル基は直鎖状であっても分岐状であってもよい。上記アルキル基の中でも、炭素数が１～５のアルキル基が好ましく、その中でも特にメチル基が好ましい。特に炭素数が上記好ましい範囲内にあれば、上記一般式（Ｉ）で表される化合物の炭化水素基の炭素数が少なくなる。その結果、エッチング液のＢＯＤ（生物化学的酸素要求量）、ＣＯＤ（化学的酸素要求量）を小さくできる。 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. 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 can be reduced.
　ｎが１の場合、ベンゼン環上のＲの置換位置は、スルホ基のパラ位、オルト位であることが好ましく、特に好ましくはスルホ基のパラ位である。 When n is 1, the substitution position of R on the benzene ring is preferably the para-position or ortho-position of the sulfo group, and particularly preferably the para-position of the sulfo group.
　上記一般式（Ｉ）で表されるスルホン酸化合物の中でも、ベンゼンスルホン酸、トルエンスルホン酸、キシレンスルホン酸及びキュメンスルホン酸がより好ましく、このようなスルホン酸化合物を一種類で使用しても良く、あるいは二種類以上を併用しても良い。特に、トルエンスルホン酸を使用すれば、所望の大きさのピラミッド状の凹凸を基板表面にムラ無く形成させることができる。また、トルエンスルホン酸は、カプリル酸等の脂肪族カルボン酸と比較して臭いにくい。したがって、トルエンスルホン酸を使用すれば、エッチング処理等の作業環境を改善できる。本明細書において、好ましいトルエンスルホン酸はパラトルエンスルホン酸(ＰＴＳ)である。 Among the sulfonic acid compounds represented by the general formula (I), benzenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid and cumenesulfonic acid are more preferable, and such a sulfonic acid compound may be used alone. Or two or more types may be used in combination. In particular, when toluenesulfonic acid is used, pyramidal irregularities having a desired size can be formed uniformly on the substrate surface. In addition, toluenesulfonic acid is less odorous than aliphatic carboxylic acids such as caprylic acid. Therefore, if toluenesulfonic acid is used, the working environment such as etching can be improved. In this specification, the preferred toluenesulfonic acid is para-toluenesulfonic acid (PTS).
　本発明のエッチング液中のスルホン酸化合物の濃度は特に限定されないが、０．００５～２．０ｍｏｌ／Ｌであることが好ましい。上記濃度が０．００５ｍｏｌ／Ｌ以上であればエッチングの均一性という理由で好ましく、上記濃度が２．０ｍｏｌ／Ｌ以下であればハンドリングという理由で好ましい。より好ましい上記濃度の範囲は０．１５～１．０ｍｏｌ／Ｌである。 The concentration of the sulfonic acid compound in the etching solution of the present invention is not particularly limited, but is preferably 0.005 to 2.0 mol / L. If the said density | concentration is 0.005 mol / L or more, it is preferable for the reason of the uniformity of etching, and if the said density | concentration is 2.0 mol / L or less, it is preferable for the reason of handling. A more preferable range of the concentration is 0.15 to 1.0 mol / L.
［ケイ酸及び／又はケイ酸塩］
　本発明のエッチング液に含まれるケイ酸及び／又はケイ酸塩の種類は特に限定されないが、金属シリコン、シリカ、ケイ酸及びケイ酸塩からなる群から選択される少なくとも一種であることが好ましい。 [Silicic acid and / or silicate]
The kind of silicic acid and / or silicate 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.
　ケイ酸塩としては、アルカリ金属のケイ酸塩が好ましく、例えば、オルソ珪酸ナトリウム（Ｎａ4ＳｉＯ4・ｎＨ2Ｏ）及びメタ珪酸ナトリウム（Ｎａ2ＳｉＯ3・ｎＨ2Ｏ）等のケイ酸ナトリウム、Ｋ4ＳｉＯ4・ｎＨ2Ｏ及びＫ2ＳｉＯ3・ｎＨ2Ｏ等のケイ酸カリウム、Ｌｉ4ＳｉＯ4・ｎＨ2Ｏ及びＬｉ2ＳｉＯ3・ｎＨ2Ｏ等のケイ酸リチウムなどが挙げられる。これらケイ酸塩は、化合物そのものをエッチング液に添加して用いることも可能であるし、シリコンウェハ、シリコンインゴット、シリコン切削粉等のケイ素材料または二酸化ケイ素を直接、アルカリに溶解させて反応物として得られるケイ酸塩化合物をケイ酸塩として用いても構わない。本発明においては、入手容易性の観点から、ＪＩＳ１号ケイ酸塩が好ましい。 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, etc. or silicon dioxide in an alkali as a reaction product. The obtained silicate compound may be used as a silicate. In the present invention, JIS No. 1 silicate is preferable from the viewpoint of availability.
　本発明のエッチング液中のケイ酸及び／又はケイ酸塩の含有量（ケイ酸のみ含む場合にはケイ酸の含有量、ケイ酸塩のみ含む場合にはケイ酸塩の含有量、ケイ酸及びケイ酸塩を含む場合にはこれらの合計量）は特に限定されないが、０．０１～１０ｗｔ％であることが好ましく、より好ましくは０．１～５ｗｔ％、さらに好ましくは０．２～３ｗｔ％である。上記のケイ素材料または二酸化ケイ素を溶解させて供給する場合は、Ｓｉ原子換算で上記の濃度範囲が好ましい。 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 wt%, more preferably 0.1 to 5 wt%, and still more preferably 0.2 to 3 wt%. It is. When the silicon material or silicon dioxide is dissolved and supplied, the above concentration range is preferable in terms of Si atoms.
　上記のケイ酸及び／又はケイ酸塩の含有量は、エッチングレートの安定化に影響を与える。エッチングレートを安定させるケイ酸及び／又はケイ酸塩の含有量は、後述するアルカリの濃度や、エッチングの際のエッチング液の温度等の条件によって変化する。このため、最適なケイ酸及び／又はケイ酸塩の含有量は、アルカリの濃度等に応じて決定すればよい。 The content of the above 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 alkali concentration 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 of an alkali, etc.
［アルカリ］
　アルカリは、エッチング液で基板表面をエッチングする際に、ピラミッド状の凹凸を基板表面に形成させるために必要な成分である。 [alkali]
Alkali is a component necessary for forming pyramidal irregularities on the substrate surface when the substrate surface is etched with an etching solution.
　本発明のエッチング液に含まれるアルカリの種類は特に限定されず、有機アルカリ及び無機アルキルのいずれも使用することができる。有機アルカリとしては、例えば、テトラメチルアンモニウムヒドロキシド等の第４級アンモニウム塩、アルカノールアミン等が好ましい。無機アルカリとしては、水酸化ナトリウム、水酸化カリウム、水酸化カルシウム等のアルカリ金属やアルカリ土類金属の水酸化物が好ましく、水酸化ナトリウム又は水酸化カリウムが特に好ましい。これらアルカリは単独で用いてもよく、２種以上混合して使用してもよい。 The type of alkali contained in the etching solution of the present invention is not particularly limited, and both 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 alkalis may be used alone or in combination of two or more.
　エッチング液中のアルカリの濃度は特に限定されないが、０．１質量％以上、５０質量％以下が好ましい。エッチング効果を発揮させる観点から、０．１質量％以上が好ましく、０．５質量％以上がより好ましく、１質量％以上がより好ましく、２質量％以上がより好ましく、３質量％以上がより好ましい。一方、費用対効果の観点から、５０質量％以下が好ましく、３０質量％以下がより好ましく、２５質量％以下がより好ましい。特にアルカリの濃度が３質量％以上であれば、エッチング液の耐久性が顕著に高まり、エッチング液を繰り返し使用しても、所望の大きさの凹凸を基板表面に均一に形成させることができる。 The concentration of alkali in the etching solution is not particularly limited, but is preferably 0.1% by mass or more and 50% by mass or less. From the viewpoint of exerting an etching effect, 0.1% by mass or more is preferable, 0.5% by mass or more is more preferable, 1% by mass or more is more preferable, 2% by mass or more is more preferable, and 3% by mass or more is more preferable. . On the other hand, from the viewpoint of cost effectiveness, 50% by mass or less is preferable, 30% by mass or less is more preferable, and 25% by mass or less is more preferable. In particular, when the alkali concentration is 3% by mass or more, the durability of the etching solution is remarkably increased, and even when the etching solution is repeatedly used, irregularities of a desired size can be uniformly formed on the substrate surface.
［その他の成分］
　本発明のエッチング液には、本発明の効果を害さない範囲で、その他の成分が含まれていてもよい。例えば、助剤としてキレート剤、アミノ酸、高分子ポリマー、グリコールエーテル類等を含むことで、スルホン酸化合物を含むことによる効果（入射光を効率よく基板内に取り込む）を高めることができる。また、本発明のエッチング液の溶媒は水が好ましい。 [Other ingredients]
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 a chelating agent, an amino acid, a polymer, glycol ethers, etc. as an auxiliary agent, the effect (incident incident light is efficiently taken into the substrate) by including the sulfonic acid compound can be enhanced. The solvent of the etching solution of the present invention is preferably water.
［エッチング液の調製方法］
　本発明のエッチング液の調整方法は特に限定されず、従来公知の方法を採用することができる。本発明のエッチング液組成は使用時の組成は上記の組成範囲が好ましいが、出荷時の組成は輸送コスト削減の意味もあってコンク化することが可能である。２～５倍のコンク化出荷が好ましい。 [Method of preparing etching solution]
The method for adjusting 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. 2-5 times conch shipping is preferable.
＜エッチング力回復剤＞
　また、本発明のエッチング液であれば、太陽電池用半導体基板をエッチング処理することで次第に劣化したエッチング液に新しいエッチング液を加えたときの、劣化したエッチング液のエッチング力を回復させる効果が高い。例えば、エッチング液の１０％以上を新しいエッチング液と入れ替えるまたは追加することで、上記の高いエッチング力回復効果を得ることができる。従って、本発明のエッチング液は、エッチング力回復剤として使用することができる。 <Etching power recovery agent>
Moreover, the etching solution of the present invention has a high effect of recovering the etching power of the deteriorated etching solution when a new etching solution is added to the etching solution gradually deteriorated by etching the semiconductor substrate for solar cells. . For example, the above high etching power recovery effect can be obtained by replacing or adding 10% or more of the etching solution with a new etching solution. Therefore, the etching solution of the present invention can be used as an etching power recovery agent.
　本発明のエッチング力回復剤の組成としては、上記のアルカリ剤を含み、かつ一般式（Ｉ）で表されるスルホン酸化合物、該スルホン酸化合物の塩、上記のリグニンスルホン酸及び該リグニンスルホン酸の塩からなる群より選択される少なくとも一種を含むものである。 As the composition of the etching power recovery agent of the present invention, the sulfonic acid compound containing the alkaline agent and represented by the general formula (I), a salt of the sulfonic acid compound, the lignin sulfonic acid, and the lignin sulfonic acid It contains at least one selected from the group consisting of these salts.
　太陽電池用半導体基板を繰り返し処理して劣化したエッチング液に、アルカリ剤を添加することでエッチング力を回復することができる。さらには、ピラミッド形状の均一性、面全体の均一性を改善するために、上記の一般式（Ｉ）で表されるスルホン酸化合物、該スルホン酸化合物の塩、上記のリグニンスルホン酸及び該リグニンスルホン酸の塩からあるいは上記のスルホン酸化合物を単独または複合で、アルカリ剤と共に添加することにより、劣化したエッチング液を交換しなくても、エッチング処理バッチ数を増やすことができる。このことにより初期建浴エッチング液を連続使用できるので工業的価値を高める効果がある。 Etching power can be recovered by adding an alkaline agent to an etching solution that has deteriorated due to repeated processing of 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 sulfonic acid compound represented by the general formula (I), the salt of the sulfonic acid compound, the lignin sulfonic acid and the lignin By adding the above sulfonic acid compound alone or in combination with an alkali agent from a sulfonic acid salt, the number of etching treatment batches can be increased without replacing the deteriorated etching solution. As a result, the initial building bath etching solution can be used continuously, so that the industrial value is enhanced.
＜太陽電池用半導体基板の製造方法＞
　本発明の太陽電池用半導体基板の製造方法は、本発明のエッチング液で、太陽電池用半導体基板の基板表面をエッチングして、基板表面に凹凸を形成させるエッチング工程を備える。 <Method for producing semiconductor substrate for solar cell>
The manufacturing method of the semiconductor substrate for solar cells of this invention is equipped with 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.
　太陽電池用半導体基板としては、単結晶シリコン基板が好ましいが、銅・インジウムやガリウム砒素等の半導体化合物を用いた単結晶の半導体基板も使用可能である。 As the semiconductor substrate for solar cells, a single crystal silicon substrate is preferable, but a single crystal semiconductor substrate using a semiconductor compound such as copper / indium or gallium arsenide can also be used.
　エッチング工程において、本発明のエッチング液を基板表面に接触させる方法は特に限定されないが、エッチング液に太陽電池用半導体基板を浸漬させる方法が好ましい。以下、浸漬させる方法を例に本発明の製造方法を説明する。 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 with reference to the method of immersion.
　浸漬させる方法でのエッチング工程とは、例えば、所定の容器に本発明のエッチング液を入れ、そこに太陽電池用半導体基板を浸漬する工程である。 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 immersing the solar cell semiconductor substrate therein.
　エッチング工程における、上記容器内のエッチング液の温度は特に限定されず適宜設定することが可能であるが、生産と品質を考慮すると７０～９８℃の範囲にあることが好ましい。 In the etching step, the temperature of the etching solution in the container is not particularly limited and can be set as appropriate, but it is preferably in the range of 70 to 98 ° C. in consideration of production and quality.
　また、エッチング工程における、太陽電池用半導体基板のエッチング液への浸漬時間も特に限定されず適宜設定することが可能であるが、生産と品質を考慮すると１０～４０分であることが好ましい。 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, considering production and quality, it is preferably 10 to 40 minutes.
　本発明の製造方法によれば、本発明のエッチング液を使用するため、連続して従来よりも多くの数の太陽電離用半導体基板の基板表面に所望の大きさのピラミッド状の凹凸を均一に形成させることができる。さらには、本発明のエッチング剤の組成を有するものを、エッチング力を回復させるエッチング力回復剤としてエッチング槽内に添加することができる。このようにエッチング力回復剤を使用することによって、エッチング処理の連続使用回数を増やすこともできるので、好ましい。 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 ionization 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.
＜太陽電池用半導体基板＞
　本発明の製造方法で製造される太陽電池用半導体基板は、本発明のエッチング液を用いて製造した太陽電池用半導体基板であり、その基板表面には、底面の最大辺長が１～３０μｍ、好ましくはその上限値が２５μｍ、さらに好ましくは上限が２０μｍであり、ピラミッド状の均一な凹凸が形成されている。さらに、本発明によれば、高い生産性で低反射率の太陽電池用半導体基板を得ることができる。本発明のエッチング液を用いれば、従来のエッチング液を使用するよりも、所望の大きさの上記凹凸を均一に基板表面に形成させることができる。なお、ピラミッド状の凹凸とは、ピラミッド状（四角錐状）の凸部が太陽電池用半導体基板表面に並ぶことで形成される凸部である。 <Semiconductor substrate for solar cell>
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 has a maximum side length of 1 to 30 μm at the bottom, The upper limit is preferably 25 μm, more preferably the upper limit is 20 μm, and pyramid-shaped uniform 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 having a desired size on the substrate surface, compared to the case of 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.
　基板表面に形成されるピラミッド形状の大きさとしては、その平均サイズが１～３０μｍであることが好ましく、２～２０μｍであることがより好ましく、２～１５μｍであることがさらに好ましい。光反射率低減の観点から、該平均サイズが１μｍ以上であることが好ましく、生産性の観点から、該平均サイズが３０μｍ以下であることが好ましい。 The size of the pyramid shape formed on the substrate surface is preferably 1 to 30 μm, more preferably 2 to 20 μm, and even more preferably 2 to 15 μm. From the viewpoint of reducing light reflectance, the average size is preferably 1 μm or more, and from the viewpoint of productivity, the average size is preferably 30 μm or less.
　上記の通り、本発明のエッチング液を用いてエッチング処理してなる太陽電池用半導体基板表面には、所望の大きさのピラミッド状の凹凸が隙間なく形成されている。したがって、従来公知のエッチング液を用いてエッチング処理してなる太陽電池用半導体基板表面と、本発明のエッチング液を用いてエッチング処理してなる太陽電池用半導体基板表面とは、ピラミッド状の凹凸の大きさのバラつきや、ピラミッド状の凸部間の間隔の大きさ等に基づいて区別することができる。 As described above, pyramidal 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.
　以下に実施例を挙げて本発明をさらに具体的に説明するが、これらの実施例は例示的に示されるものである。 Hereinafter, the present invention will be described more specifically with reference to examples. However, these examples are shown by way of example.
実施例１～２２及び比較例１～２
　表１に示す配合組成に従って調合したエッチング水溶液に、結晶方位（１００）面を表面に有する単結晶シリコン基板（１辺１５６ｍｍ正方形、厚さ１５０μｍ）を８０～９０℃で１０～３０分間浸漬させた。エッチング処理後の基板表面を目視、レーザー顕微鏡、走査型電子顕微鏡で観察した結果を表１に示す。なお、具体的なエッチング処理の操作は、以下の[エッチング処理]に記載の通りである。 Examples 1-22 and Comparative Examples 1-2
A single crystal silicon substrate (one side 156 mm square, thickness 150 μm) having a crystal orientation (100) plane was immersed in an etching aqueous solution prepared according to the formulation shown in Table 1 at 80 to 90 ° C. for 10 to 30 minutes. . Table 1 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. A specific etching process is as described in [Etching process] below.
実施例２３～２７及び比較例３～４
　エッチング液のスタミナ性（連続使用性）に関しては、エッチング液量３０Ｌに対し基板支持用のカセットに多数枚（３１枚／カセット）をセットしこれを１バッチとして複数回処理を行いピラミッドの質の基準値を設けこれを維持できるバッチ回数で評価した。その際アルカリの消耗が激しいので、消耗したＫＯＨを自動滴定装置により求め、その０．５～１．５倍当量のＫＯＨを毎バッチ補給した。なお、具体的なエッチング処理の操作は、以下の[エッチング処理]に記載の通りである。 Examples 23 to 27 and Comparative Examples 3 to 4
Concerning the stamina of the etching solution (continuous use), a large number of substrates (31 sheets / cassette) are set in a substrate support cassette for an etching solution amount of 30 L, and this is processed multiple times as a batch, and the quality of the pyramid Evaluation was made based on the number of batches in which a reference value was set and maintained. At that time, the consumption of alkali was intense, so the consumed KOH was determined by an automatic titrator, and 0.5 to 1.5 times equivalent KOH was replenished every batch. A specific etching process is as described in [Etching process] below.
　連続使用性の実施例２７では、１８バッチ目でパラトルエンスルホン酸(ＰＴＳ)とリグニンスルホン酸を追加して連続試験を継続した。ＰＴＳの追加量は、エッチング液のＰＴＳの濃度が３重量％上昇する量とし、リグニンスルホン酸の追加量は、エッチング液のリグニンスルホン酸の濃度が１００ｐｐｍ上昇する量とした。
　条件と結果を表２に示す。連続使用回数は基板のテカリ評価が△になった時点の回数で評価した。 In Example 27 of continuous usability, p-toluenesulfonic acid (PTS) and lignin sulfonic acid were added in the 18th batch, and the continuous test was continued. The additional amount of PTS was an amount that increased the concentration of PTS in the etching solution by 3% by weight, and the additional amount of lignin sulfonic acid was an amount that increased the concentration of lignin sulfonic acid in the etching solution by 100 ppm.
The conditions and results are shown in Table 2. The number of times of continuous use was evaluated by the number of times when the substrate was evaluated to be △.
[エッチング処理]
　エッチング容器にはＳＵＳ３０４製の約３５Ｌ箱型形状の槽を用い、これに３０Ｌのエッチング液を入れ、下部からＳＵＳ製投げ込みヒーターで昇温し、ゆるやかな窒素バブリングおよび液循環撹拌（３０Ｌ／分）により液撹拌を行い、温度範囲を設定温度±１℃に維持した。基板投入枚数は２～３１枚とした。液循環の妨げとならないよう治具を設計し４ｍｍ間隔で基板を挿入した。エッチング液から取り出したのちは速やかに流水によるリンス洗浄を実施し、温風で乾燥した。乾燥後の基板について、次のような基準で評価した。 [Etching process]
About 35L box-shaped tank made of SUS304 is used for the etching container, and 30L of etching liquid is put into this, and the temperature is raised by a SUS casting heater from the bottom, and gentle nitrogen bubbling and liquid circulation stirring (30L / min) The liquid was stirred and the temperature range was maintained at the set temperature ± 1 ° C. The number of substrates loaded was 2 to 31. 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.
面質：目視にて、ウエハー全面の均一性（ムラ、筋の有無）を判定した。
　Ａ：色ムラや微細な筋がなく全面均質な表面である。
　Ｂ：ごく一部に色ムラや微細な筋が存在する。
　Ｃ：色ムラか微細な筋状部が存在する。
　Ｆ：色ムラや筋ムラが全面に存在する。 Surface quality: The uniformity of the entire wafer surface (the presence or absence of unevenness and streaks) was visually determined.
A: The entire surface is uniform without color unevenness or fine streaks.
B: Color unevenness and fine stripes exist in a very small part.
C: Color unevenness or fine streaks are present.
F: Color unevenness and streak unevenness exist on the entire surface.
気泡筋：エッチング槽内でウエハーを保持する治具（カセット）上でウエハーと治具爪部が接触する部位を起点として、気泡痕跡・液流動起因の縦筋が見られることがある。その程度を目視観察にて下記のとおり判定した。
　Ａ：強い縦筋は見られない。
　Ｂ：若干縦筋が見られるが許容範囲（太陽電池パネルにした際目立たない範囲）である。
　Ｃ：やや強く縦筋が認められる。
　Ｆ：強く縦筋が認められる。 Bubble streaks: Vertical traces due to bubble traces and liquid flow may be seen starting from the part where the wafer and jig claw contact on the jig (cassette) holding the wafer in the etching tank. The degree was determined by visual observation as follows.
A: Strong vertical stripes are not seen.
B: Although some vertical stripes are observed, it is an allowable range (a range that is not noticeable when a solar cell panel is used).
C: Longitudinal streaks are somewhat strong.
F: Strong vertical stripes are observed.
テカリ：ピラミッド構造の凹凸が形成されず、（１００）鏡面がそのまま残存し、光を反射してテカってみえる表面性状になる現象で、その程度を下記にように分類して判定した。
　Ａ：テカリなし。レーザー顕微鏡で観察しても、ピラミッド構造の凹凸で埋め尽くされていることが確認できる。
　Ｂ：テカリなし。目視レベルではテカリは確認できないが、レーザー顕微鏡で観察すると、ピラミッド構造の凹凸が形成されていない領域が確認できる。
　Ｃ：部分的にテカリあり。
　Ｆ：全面にテカリが認められる。 Tekali: A phenomenon in which unevenness of the pyramid structure is not formed, the (100) mirror surface remains as it is, and it becomes a surface property that reflects light and looks like a mirror. The degree is classified and judged as follows.
A: No shine. Even if it observes with a laser microscope, it can confirm that it is filled with the unevenness | corrugation of a pyramid structure.
B: No shine. Although the shine cannot be confirmed at the visual level, when observed with a laser microscope, a region where the irregularities of the pyramid structure are not formed can be confirmed.
C: Some shine is present.
F: Tekari is recognized on the entire surface.
ピラミッドサイズ：基板表面をレーザー顕微鏡で観察し、大きいものから１０個のピラミッド形状についてピラミッドサイズを測定する。これを３視野につき実施し平均化を行い、平均ピラミッドサイズとした。結果を表１に示した。また一部の基板については走査型電子顕微鏡も併用して観察した。 Pyramid size: The surface of the substrate is observed with a laser microscope, and the pyramid size is 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. Some of the substrates were also observed with a scanning electron microscope.
　上記、レーザー顕微鏡は(株)キーエンス社製・レーザーマイクロスコープＶＫ-Ｘ100を用い、対物レンズ１００倍、（接眼レンズ２０倍）、倍率２０００倍で撮影し、紙に印刷後、ピラミッドの底辺サイズを測定し、この底辺サイズをピラミッドサイズとした。走査電子顕微鏡は日本電子（株）製ＪＳＭ－５３１０で加速電圧は１５ｋＶにて観察した。 The above laser microscope uses Keyence Corporation's Laser Microscope VK-X100, 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 JSM-5310 manufactured by JEOL Ltd., and the acceleration voltage was observed at 15 kV.
ピラミッドサイズの均一度（バラツキ）：
　レーザー顕微鏡の上記平均ピラミッドサイズの５０％以下の小さなピラミッドサイズの存在割合で判定した。
　Ａ：平均ピラミッドサイズの５０％未満のものが２０％未満しか存在しない。
　Ｂ：同上のものが２０～４０％存在する。
　Ｃ：同上のものが４０％以上存在する。 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.
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.
Figure JPOXMLDOC01-appb-T000005
Figure JPOXMLDOC01-appb-T000005
Figure JPOXMLDOC01-appb-T000006
Figure JPOXMLDOC01-appb-T000006
　なお、上記で使用したリグニンスルホン酸（塩）のタイプの性質を、表３に示す。 The properties of the type of lignin sulfonic acid (salt) used above are shown in Table 3.
Figure JPOXMLDOC01-appb-T000007
Figure JPOXMLDOC01-appb-T000007
　特定のリグニンスルホン酸を使用した実施例１～２２は比較的低温側（８５℃）、短時間（１５分）にもかかわらず優れたエッチング特性を示し、面質の均一性（外観ムラなし）、ピラミッドサイズの均一性にも優れていることがわかる。またテカリ面（ピラミッド未形成箇所）の発生もなく良好である。光反射率も低い状態を維持している。比較例の１～２はそれぞれ面質（外観ムラ・気泡筋）の点で実施例に大きく劣ることがわかる。 Examples 1 to 22 using a specific lignin sulfonic acid showed excellent etching characteristics despite a relatively low temperature (85 ° C.) and a short time (15 minutes), and uniform surface quality (no uneven appearance) It can be seen that the uniformity of the pyramid size is also excellent. Moreover, there is no occurrence of a shining surface (location where pyramids are not formed), which is good. The light reflectance is also kept low. It can be seen that Comparative Examples 1 and 2 are significantly inferior to the Examples in terms of surface quality (appearance unevenness and bubble streaks).
　実施例２３～２７に示すように、良好な連続使用特性を示すことがわかる。実施例２７では途中で添加剤を補給することにより連続使用回数が増加することがわかる。 As shown in Examples 23 to 27, it can be seen that good continuous use characteristics are exhibited. In Example 27, it turns out that the frequency | count of continuous use increases by replenishing an additive on the way.
　本発明のエッチング液は、太陽電池用半導体基板の表面をエッチング処理する際のエッチング液として使用することができる。 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 (12)

  1. 　太陽電池用半導体基板の表面を処理するためのアルカリ性のエッチング液であって、リグニンスルホン酸及びその塩からなる群より選択される少なくとも一種を含むエッチング液。 An alkaline etchant for treating the surface of a semiconductor substrate for a solar cell, which contains at least one selected from the group consisting of lignin sulfonic acid and salts thereof.
  2. 　一般式（Ｉ）
    Figure JPOXMLDOC01-appb-C000001
     （式中のｎは０～５の整数であり、Ｒはそれぞれ独立して水素原子又は炭素数１～１２のアルキル基である。）で表されるスルホン酸化合物及びその塩からなる群より選択される少なくとも一種をさらに含む、請求項１に記載のエッチング液。     Formula (I)
    Figure JPOXMLDOC01-appb-C000001
     (Wherein n is an integer of 0 to 5, and R is each independently a hydrogen atom or an alkyl group having 1 to 12 carbon atoms) and selected from the group consisting of salts thereof The etching liquid according to claim 1, further comprising at least one of the following.
  3. 　前記スルホン酸化合物が、ベンゼンスルホン酸、トルエンスルホン酸、キシレンスルホン酸及びキュメンスルホン酸からなる群より選択される少なくとも一種である、請求項２に記載のエッチング液。 The etching solution according to claim 2, wherein the sulfonic acid compound is at least one selected from the group consisting of benzenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid and cumenesulfonic acid.
  4. 　ケイ酸及び／又はケイ酸塩をさらに含む、請求項１～３のいずれか１項に記載のエッチング液 The etching solution according to any one of claims 1 to 3, further comprising silicic acid and / or silicate.
  5. 　請求項１～４のいずれか１項に記載のエッチング液で太陽電池用半導体基板を処理した後に前記エッチング液に添加して、該エッチング液のエッチング力を回復させるエッチング力回復剤であって、アルカリ剤を含み、かつ
    　一般式（Ｉ）
    Figure JPOXMLDOC01-appb-C000002
     （式中のｎは０～５の整数であり、Ｒはそれぞれ独立して水素原子又は炭素数１～１２のアルキル基である。）で表されるスルホン酸化合物、前記スルホン酸化合物の塩、リグニンスルホン酸及び前記リグニンスルホン酸の塩からなる群より選択される少なくとも一種を含む、エッチング液のエッチング力回復剤。     An etching power recovering agent that is added to the etching liquid after treating the semiconductor substrate for solar cells with the etching liquid according to any one of claims 1 to 4 to recover the etching power of the etching liquid, Containing an alkaline agent and having the general formula (I)
    Figure JPOXMLDOC01-appb-C000002
     (Wherein n is an integer of 0 to 5, and each R is independently a hydrogen atom or an alkyl group having 1 to 12 carbon atoms), a salt of the sulfonic acid compound, An etching power recovery agent for an etchant, comprising at least one selected from the group consisting of lignin sulfonic acid and a salt of lignin sulfonic acid.
  6. 　請求項１～４のいずれか１項に記載のエッチング液で太陽電池用半導体基板の基板表面をエッチングして、前記基板表面に凹凸を形成させるエッチング工程を含む、太陽電池用半導体基板の製造方法。 A method for producing a semiconductor substrate for a solar cell, comprising an etching step of etching the substrate surface of the semiconductor substrate for solar cells with the etching solution according to any one of claims 1 to 4 to form irregularities on the substrate surface. .
  7. 　前記基板表面に形成される凹凸の凸部がピラミッド形状である、請求項６に記載の製造方法。 The manufacturing method according to claim 6, wherein the uneven protrusions formed on the surface of the substrate have a pyramid shape.
  8. 　前記ピラミッド形状の平均サイズが１～２０μｍである、請求項７に記載の製造方法。 The manufacturing method according to claim 7, wherein an average size of the pyramid shape is 1 to 20 μm.
  9. 　請求項１～４のいずれか１項に記載のエッチング液でその表面がエッチング処理されてなる、太陽電池用半導体基板。 A semiconductor substrate for solar cells, the surface of which is etched with the etching solution according to any one of claims 1 to 4.
  10. 　基板表面に凹凸が形成された、請求項９に記載の太陽電池用半導体基板。 The solar cell semiconductor substrate according to claim 9, wherein irregularities are formed on the substrate surface.
  11. 　形成された凹凸の凸部がピラミッド形状である、請求項１０に記載の太陽電池用半導体基板。 The semiconductor substrate for a solar cell according to claim 10, wherein the formed uneven convex portion has a pyramid shape.
  12. 　前記ピラミッド形状の平均サイズが１～２０μｍである、請求項１１に記載の太陽電池用半導体基板。 The semiconductor substrate for a solar cell according to claim 11, wherein the average size of the pyramid shape is 1 to 20 µm.
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