TW201348406A - Textured germanium wafer composition and method - Google Patents

Abstract

Texturing composition for texturing silicon wafers have one or more surfactants. Methods of texturing silicon wafers having the step of wetting said wafer with a texturing composition having one or more surfactants.

Description

Textured germanium wafer composition and method Cross-reference to related applications

Provisional U.S. Patent Application No. 61/530,760 (Attorney No. 07482Z2) filed on September 2, 2011, and U.S. Patent No. 13/296836 (Attorney No. 07482Z2P) filed on November 15, 2011 And the benefit of U.S. Application Serial No. 61/416,998, filed on Nov. 24, 2010, the entire disclosure of which is hereby incorporated by reference.

The present invention is directed to a method of texturing a textured composition of a tantalum wafer and a textured tantalum wafer having one or more surfactants.

The present invention relates to the texturing of photovoltaic wafer surfaces. In order to improve the conversion efficiency of light energy to electric power, it is desirable to have a very low reflective surface. Regarding single crystal germanium, for example, in a process called texturing, this can be achieved by anisotropic etching of a (100) germanium wafer to form a pyramidal structure on the surface. hope It is expected that the surface of the wafer has a uniform and dense distribution of cones to achieve low reflectivity. The height of the cone is less than 10 μm and the size is uniform. A smaller and uniform pyramid structure ensures good coverage of the passivation layer, which is then deposited on top of the textured surface to prevent loss of efficiency. The smaller and uniform cone structure also ensures that the metal contact lines printed on the surface of the crucible are narrower, allowing more light to pass through to the crucible surface for photoelectric conversion.

With regard to polycrystalline germanium, the surface is often etched using an alkaline or acidic solution to form pits or pores on the surface. These pits often have a diameter and depth of less than 15 μm. It is desirable to have a uniform pore distribution on the surface of the wafer to achieve low reflectivity. The roughness of the surface reduces the reflectance of the wafer and increases the path length of light traveling within the material, and thus enhances the efficiency of light conversion to electricity.

The prior art reference materials include: WO 2009120631 A2, CN 101634026 A, CN 101634027 A, DE 102007058829 A1, WO 2009119995 A2, US 4137123 A, CN 101217173 A, CN 1983644 A, CN 1983645 A, JP 2009123811 A, EP 944114 A2. EP 1890338 A1, Basu, PK et al., Solar Energy Materials & Solar Cells (2010), 94(6), 1049-1054, Basu PK et al., Renewable Energy (2009), 34(12), 2571-2576, WO 2009071333, Gangopadhyay U. et al., Solar Energy Materials & Solar Cells (2006), 90 (18-19), 3094-3101; WO 2008022671; US 5959123; US 6,340,640 B1, US 2003/0119332 A1, US2111/0059570 A1 US 2006/0068597 A1, US 7192885 B2, F. Duerinchx, L. Frisson, PP Michies and others announced at the 17th European Photovoltaic Solar Energy Symposium in Munich, Germany from October 22nd to 26th, 2001. "Towards highly efficient industrial cells and modules from polycrystalline wafers", EP 2 006 892 A1, US 2007/0151944 A1, US 7759258 B2, WO 2009/119995, WO 2010/107863 A1, US 2010/0239818 A1, WO 2011/032880 A1, M. Lipinski et al., "Reduction of surface reflectivity by using double porous silicon layers", Materials Science and Engineering, B101 (2003) 297-299, DH Macdonald et al., "Texturing industrial multicrystalline silicon solar cells", Solar Energy , 76 (2004), 277-283.

There is still a need in the art to provide a textured composition and texturing method for tantalum wafers that reduce the amount of reflectivity and desired loss when processing tantalum wafers, and which are independent of the source of germanium. Because single-crystal and polycrystalline wafer suppliers vary widely and wafers supplied by different vendors vary, for example, different structural defect densities, grain quality, and saw blade damage in the wafer, so We want to have a texturing process associated with the source of the wafer and provide consistent results including low reflectivity and the desired amount of helium loss from wafers from different vendors.

The compositions of the present invention can be used in the texturing methods of the present invention to treat wafers or substrates (these words, wafers and substrates are interchangeably used herein). Silicon wafers processed in accordance with these inventions can be used to fabricate photovoltaic cells. Wafers that are subjected to the compositions and/or methods of the present invention exhibit improved texturization uniformity and reduced reflectivity compared to wafers that have not been treated. Can be issued Other methods and/or other benefits achieved by the composition may include one or more of the following: (1) creating uniform and small oval pits on the wafer surface with desired helium loss; 2) the reduced reflectivity of the textured surface; and (3) consistent texturing results from germanium wafers from different vendors.

What we want is as low-reflective as possible. Our invention provides array compositions and methods to improve the texturing of the wafer surface. Our invention involves treating the wafer surface with a composition comprising one or more surfactants in an acidic texturing solution. The composition modifies the wafer surface by creating a smaller and uniform elliptical pit on the surface of the wafer with the desired enthalpy loss, resulting in improved uniformity of the textured surface with lower surface reflectance. .

The present invention is a texturized composition for texturing germanium wafers comprising, consisting essentially of, or consisting of one or more acids, one or more anionic surfactants (for example anionic sulfur-containing surfaces) The active agent) and water (usually the remainder are water), and methods of texturing the wafer using those compositions.

The anionic sulfur-containing surfactant useful in the texturing composition may be one or more selected from the group consisting of linear alkyl benzene sulfonates (LAS), secondary alkyl benzene sulfonates, lignosulfonates. Class, N-mercapto-N-alkyl taurate, fatty alcohol sulfate (FAS), petroleum sulfonate, secondary alkane sulfonate (SAS), paraffin sulfonate, fat Alcohol ether sulfates (FAES), α-olefin sulfonates, thiosuccinates, alkylnaphthalene sulfonates, isethionates, sulfates, sulfation a group consisting of linear primary alcohols, sulfated polyoxyethylated linear alcohols, sulfated triglyceride oils, and mixtures thereof, and/or selected from the group consisting of secondary alkane sulfate sodium salts, diphenyl ethers A group consisting of disulfonic acids and ether sulfates or mixtures thereof. The texture combination The material may additionally comprise hydrofluoric acid plus any or a mixture of any of the anionic surface agents described herein, with or without nitric acid and/or any other acid.

In another aspect of the invention, one or more sulfur-containing surfactants used in any texturing composition can have the following structure: Wherein R ¹ and R ^{2 are} independently a linear or cyclic alkyl group or a phenyl group or a combination thereof, usually having 1 to 20 carbon atoms, and X is hydrogen or any includes Na, K, tetramethylammonium, tetraethyl A cation of a quaternary ammonium, triethanolamine or ammonium. Further, in another aspect of the invention, the components and compositions described herein are included, and the texturizing composition may comprise one or more selected from the group consisting of phosphoric acid, sulfuric acid or water-soluble carboxylic acids, for example. A group of acids consisting of acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, tartaric acid, succinic acid, adipic acid, propylene tricarboxylic acid and glycerol tricarboxylic acid isomers.

In another aspect of the invention, the texturing composition comprises any of the components described herein, either alone or in combination with other components, in the following amounts: (1) from about 37 to about 42 weight percent HF, From about 3.5 to about 7% by weight of HNO3, from about 0.005 to about 0.25% by weight of surfactant, and the balance being water; (2) from about 24 to about 30% by weight of HF, from about 14 to about 19% by weight of HNO3 From about 0.005 to about 0.25% by weight of the surfactant, and the balance being water; and (3) from about 9 to about 13% by weight of HF, from about 31 to about 39% by weight of HNO3, from about 0.005 to about 0.25% by weight Surfactant, and the remainder is water.

The invention further provides a method of texturing a germanium wafer comprising, consisting essentially of, or consisting of one or more steps comprising the steps of: containing one or more acids, one or more anionic sulfur-containing A textured composition of surfactant and water wets the wafer. The texturizing composition useful in the method is any of the texturing composition components and any other components used in any combination and amount as described above or herein. The method steps can additionally include first and second texturing steps utilizing the first and second texturing compositions, wherein the second texturing composition can comprise one or more bases in a solvent, There may or may not be other rinsing and/or drying steps before and/or after the texturing step. This method may additionally comprise pretreatment and/or purification of the surfactant steps.

1 depicts a flow diagram of a surface texturing process on a tantalum substrate in accordance with an embodiment of the present invention; and FIG. 2A depicts a top view image of a portion of the polycrystalline substrate prior to processing by the process of the present invention. The top view images were photographed on a surface of a polycrystalline substrate at 2000 times (top photo) and 100000 times (bottom photo) using a Hitachi S-4700 FE (field emission) scanning electron microscope (SEM); 2B depicts a top view image of a portion of a polycrystalline substrate after rinsing and drying in a process of the present invention, using a first texturing step of texturing composition Example F (Ex F); The same SEM and magnification as described in Figure 2A; and Figure 2C depicts a top view image of the polycrystalline substrate shown in Figure 2B after further processing of the substrate using the following procedure: a second texturing step with a 0.5% aqueous KOH solution at ambient temperature for 1 minute, washed with deionized water And drying; the images were taken using the same SEM and magnification as described in Figure 2A.

It is to be understood that the following drawings are merely illustrative of exemplary embodiments of the invention and are not to

Crystalline germanium wafers (also referred to herein as substrates) are used to make solar cells that convert light into electricity, also known as photovoltaic cells, photovoltaic cells, or photovoltaic cells. To this end, we want to create textures on the surface of crystalline germanium wafers used in photovoltaic applications. This texture will reduce the reflectivity of the surface and allow more light energy to be converted into electricity to increase the efficiency of the wafer.

When processing a wafer using the compositions and methods of the present invention, the first of a number of steps may involve any cleaning step to remove any contamination of the diced wafer (cut from the ingot), which may be followed by one or more Multi-texturing steps. The texturing process may include a multi-step process, that is, a texturing process that includes one or two or more steps. In a multi-step or two-step texturing process, the texturing process includes contacting the wafer with a solution comprising one or more acids in the first texturing composition or solution, followed by a second texturing step, The second texturing step comprises a second texturing composition or solution comprising one or more bases in the alkaline solution. Any process may be one or two (or More) Additional rinsing steps are included before or after the texturing step. A typical rinse composition is pure water, such as deionized water. It may be a drying step before or after any or each texturing step and/or rinsing step. This drying step can be performed by directing dry air, hot air or nitrogen to the wafer. The one or more textured compositions are typically aqueous solutions.

The first texturing solution is an acidic solution comprising, consisting essentially of, or consisting of one or more acids, one or more surfactants, and a solvent. The acid in the first texturing solution may comprise hydrofluoric acid (HF) and/or nitric acid (HNO3) and may also optionally contain one or more other acids sometimes referred to as conditioning agents. Such regulators include phosphoric acid, sulfuric acid or water soluble carboxylic acids such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, tartaric acid, succinic acid, adipic acid, glycerol tricarboxylic acid and glycerol tricarboxylic acid. The isomer is used to adjust the etch rate of the texturing solution. If one or more conditioning agents are present, typically the texturing solution will comprise from about 0 to 40% by weight of the conditioning agent; in some cases, some conditioning agent may be used in place of the particular embodiment. The first texturing solution may comprise hydrofluoric acid, nitric acid, a surfactant, and a solvent. Typically the acidic texturing solution can have a concentration of from about 5 weight percent (% by weight) to about 70 weight percent of one or more acid or acid mixtures (excluding such conditioning agents) in a solvent. The solvent can be deionized water (DI) or pure water. The first texturing solution can comprise one or more anionic surfactants.

Some examples of a first texturing solution (which is an acidic texturing solution of the invention) useful in the method of the invention comprise, consisting essentially of, or consisting of: (1) from about 37 to about 42 weight percent HF, about 3.5 to about 7% by weight of HNO3, from about 0.005 to about 0.25% by weight of surfactant, and the balance being water (eg, deionized water), for example, about 50.75 in one embodiment. Up to about 59.495 wt% water; or (2) about 24 to about 30 wt% HF, about 14 to about 19 wt% HNO3, about 0.005 to about 0.25 wt% surfactant, and the remainder is water (eg Deionized water), for example, from about 50.75 to about 61.995 wt% water in one particular embodiment; or (3) from about 9 to about 13 wt% HF, from about 31 to about 39 wt% HNO3, about 0.005 Up to about 0.25 wt% of surfactant, and the balance being water (e.g., deionized water), for example, from about 47.75 to about 59.995 wt% water in one embodiment; or (4) in deionized water. From about 75 to about 85% by weight of a 49% by weight HF solution, from about 5 to about 10% by weight of a 70% by weight HNO3 solution in deionized water, and from about 0.005 to about 0.25 % by weight of surfactant and the remainder of the deionization Water; or (5) from about 50 to about 60% by weight of a 49% by weight HF solution in deionized water, from about 20 to about 26% by weight of a 70% by weight HNO3 solution in deionized water, from about 0.005 to about 0.25 weight. % of surfactant and the remainder of deionized water; or (6) from about 20 to about 25 weight percent of a 49% by weight HF solution in deionized water in deionized water Deionized water balance of about 45 to about 55 wt% of 70 wt% HNO3 solution, and about 0.005 to about 0.25% by weight of a surface active agent.

In a specific embodiment, the first texturing solution (which is an acidic texturing solution of the invention) useful in the method of the invention comprises, consists essentially of, or consists of: from about 25 to about 27 weight percent HF, From about 15 to about 17 weight percent HNO3, from about 0.05 to about 0.25 weight percent surfactant, and the balance is water (eg, deionized water), for example, from about 55.75 to about 59.995 weight in one embodiment. % water; or about 53 to about 55% by weight of a 49% by weight HF solution in deionized water, from about 22 to about 24 in deionized water % by weight of a 70% by weight HNO3 solution and from about 0.05 to about 0.25% by weight of surfactant and the remainder of deionized water.

The acid texturing composition can comprise one or more anionic surfactants, including sulfur-containing anionic surfactants. Examples of the anionic surfactant and the sulfur-containing anionic surfactant which can be used in the texturing composition of the present invention include linear alkylbenzene sulfonates (LAS), linear fatty acids and/or salts thereof, Coconut oil fatty acid derivatives, tall oil acid derivatives, sarcosides, acetylated polypeptides, secondary alkyl benzene sulfonates, lignosulfonates, N-mercapto- n-Alkyl taurate, fatty alcohol sulfate (FAS), petrochemical sulfonate, secondary alkane sulfonate (SAS), paraffin sulfonate, fatty alcohol ether sulfate (FAES) ), α-olefin sulfonates, thiosuccinates, alkylnaphthalene sulfonates, isethionates, sulfates, sulfated linear primary alcohols, sulfated polyoxyethylenes Linear alcohols, sulfated triglyceride oils, phosphates and polyphosphates, and perfluorinated anionic surfactants or any of the surfactants disclosed herein and other known surfactants mixture. The textured compositions may comprise alpha-olefin sulfonates having the following structure: Wherein R is an alkyl group, for example, a linear alkyl group having 10 to 18 carbons.

The surfactant used in the texturing composition of the present invention may be one or more sulfur-containing anionic surfactants having a sulfate or sulfonate and may be a secondary alkanesulfonate surfactant or an alkyl sulfate. Ester or a mixture thereof. These surfactants can be used in the form of the free acid and the salt. The surfactant having a sulfonate group may have the following structure: Wherein R ¹ and R ^{2 are} independently a linear or cyclic alkyl group or a phenyl group or a combination thereof, which typically comprises from 1 to 20 carbons and X is hydrogen or any cation, including Na, K, tetramethylammonium, tetra Ethyl ammonium, triethanolamine or ammonium. In some embodiments the sulfo surfactants comprise a linear alkyl group.

A specific example of such a surfactant is the Hostapur® SAS surfactant commercially available from Clariant, which comprises a molecule having the following structure: m+n=10 to 14; the sulfonate group is distributed over the carbon chain such that the carbon chain is predominantly a substituted secondary carbon atom.

Further, the surfactant used in the texturing composition of the present invention may be a fatty alcohol sulfate which is derived from the sulfonation of a fatty alcohol having a carbon chain length of from 8 to 22 atoms. An example of a surfactant that can be used in the texturing compositions of the present invention is having the molecular formula C ₁₂ H ₂₅ O. (C ₂ H ₄ O) ₂ . SO ₃ . Na lauryl sulfate sodium salt. For such surfactants that are commercially produced, the carbon chain length can vary from 10 carbon atoms to 18 carbon atoms. The surfactant may also contain a distribution of a plurality of different carbon chain length surfactants.

Another example is sodium laureth sulfate having the following structure: Wherein "n" is the number of ethoxylate groups in the surfactant chain and can vary from 1 to 5. The carbon chain length can vary from 10 carbon atoms to 18 carbon atoms for such commercially produced surfactants. The surfactant may also contain a distribution of a plurality of different carbon chain length surfactants.

Commercially available surfactants which can be used in the texturized compositions of the present invention include: Hostapur® SAS is a secondary alkanesulfate-sodium salt manufactured by Clariant, Inc.; Calfax® DBA70 is manufactured by Pilot Chemical Company. C12 (branched) diphenyl ether disulfonic acid; AEROSOL® NPES-3030 P is an ether sulfate manufactured by CYTEC CANADA Co., Ltd. Preferred acidic texturing compositions of the present invention may comprise, consist essentially of, and consist of one or more acids, water and at least one selected from the group consisting of Hostapur® SAS, Calfax® DBA70 and AEROSOL® NPES-3030 P or mixtures thereof or A surfactant consisting of a mixture of other surfactants. Preferred surfactants are selected from the group consisting of secondary alkane sulfates, diphenyl ether disulfonic acids, and ether sulfates.

Any surfactant or mixture of surfactants can be used in any amount or at a concentration of from about 0.001% to about 5% by weight, or from about 0.005 to about 4% by weight, or from about 0.005% to 0.25% by weight. %. It should be noted that unless otherwise specified, the weight percentage (% by weight) is like the text. All weight % is based on the total weight of the texturing solution. Useful surfactants can be purified using appropriate techniques to remove metallic impurities. Purification of the surfactant can be one of the first steps performed in preparing the texturized compositions of the present invention. A useful purification technique is to perform ion exchange of the surfactant.

The second texturing composition can be an alkaline etching composition. Examples of the alkaline etching composition include those which are contained in a solvent, have a substantially composition, and are composed of one or more bases, for example, one or more hydroxides. The one or more bases may be selected from the group consisting of potassium hydroxide (KOH), sodium hydroxide (NaOH), aqueous ammonia (NH ₄ OH), tetramethylammonium hydroxide (TMAH; or (CH ₃ ) ₄ NOH) or others. Similar to the alkaline component in solution, typically in the group of water, deionized water (DIW) or pure water. The alkaline solution may have from about 0.1% to about 15% by weight, or from about 0.5% to about 10% by weight, or from about 0.5% to about 5% by weight of one or more bases in deionized (DI) Concentration in water or other solvents.

In the texturing process comprising the first and second texturing steps, the first and second texturing steps respectively use the first and second texturing compositions, and it is believed (although not wishing to be bound by theory) In the first texturing composition, for example, in the HF/HNO3 etching composition, the cerium is oxidized by HNO ₃ followed by SiO 2 to dissolve the formed SiO 2 . An acid texturing process utilizing a composition comprising HF and HNO3 is an exothermic reaction that simultaneously produces a nanolayer on the surface of the crucible. This nanolayer is detrimental to solar cell fabrication due to its high resistivity, high light absorption, and hole-electron recombination in this layer. In some embodiments of the method of the invention, the second texturing composition is subsequently used in the second texturing step to remove the nanolayer in the diluted alkaline solution. Thus, for some embodiments using a texturing process having the two texturing steps, the crystalline germanium surface texturing involves both an acid etch (the first texturing step) and a basic nanopore removal step (the Second texturing step). The acid etching process results in the resulting surface morphology and total enthalpy loss, which are important factors in determining the texturing quality. Because this acidic etching process is isotropic, germanium etching may occur at defects and/or grain boundaries and is independent of crystal orientation. When the amount of enthalpy loss is too low, i.e., less than about 2 μm, the surface of the crucible is covered by microcracks of the damaged layer. This is detrimental to solar cell manufacturing. When the amount of enthalpy loss is too high, that is, more than about 8 μm, the texture disappears, and dislocations and grain boundaries appear. This results in higher surface resistivity and can weaken the mechanical mechanics of the wafer. The acid texturing compositions of the present invention utilize the methods of the present invention to provide an acceptable amount of ruthenium loss, that is, from about 2 to about 8 microns or from about 3 to about 6 microns or from about 4 to about 5 microns.

The first or second (acidic or basic) texturing composition may also include one or more additives to facilitate cleaning and/or texturing (etching) of the wafer surface. Cleaning the additive may help remove debris that remains on the surface. The first or second or other texturizing composition of the present invention may optionally contain one or more other components (additives) including inorganic or organic acids and salts thereof, bases and salts thereof, chelating agents, antifoaming agents , wetting agents and / or etchants or mixtures thereof. In some embodiments, the texturized compositions of the present invention are free or substantially free (wherever they are applied "substantially free" means less than 0.001% by weight, unless otherwise indicated herein) All: Acids and salts thereof, bases and salts thereof, chelating agents, dispersing agents, antifoaming agents, wetting agents and/or etchants as described herein.

The first or second texturing composition, usually the first, may be another It contains inorganic acids, including hydrochloric acid, sulfuric acid, phosphoric acid, sulfamic acid, and the like. Mixtures of these acids and/or their salts can also be used. The texturized composition of the present invention may additionally comprise an organic acid and/or a salt thereof. The organic acids may be selected from a wide range of acids including, but not limited to, acetic acid, oxalic acid, citric acid, maleadiene, malic acid, malonic acid, glucuronic acid, glutaric acid, ascorbic acid, formic acid, ethylenediamine. A variety of different derivatives of tetraacetic acid, diethylenetriaminepentaacetic acid, glycine, aniline, cystine, sulfonic acid, sulfonic acid, and the like, or mixtures thereof. These acid salts can also be used. Mixtures of these acids/salts can also be used. The texturizing compositions of the present invention may contain salts of acids and/or those acids in any amount or in an amount of from 0 to 20% by weight or from 0 to 5% by weight or from 0 to 1% by weight.

The first or second texturing composition, typically second, may additionally comprise one or more bases. The base can be selected from a range of chemicals including, but not limited to, ammonium hydroxide, potassium hydroxide, quaternary ammonium hydroxide, amines, guanidiene carbonate, and organic bases. These bases can be used alone or in combination with other bases. Examples of suitable organic bases include, but are not limited to, hydroxylamines, organic amines (eg, primary, secondary or tertiary aliphatic amines, alicyclic amines, aromatic amines, and heterocyclic amines, Ammonia water and quaternary ammonium hydroxides. Specific examples of such hydroxylamines include: hydroxylamine (NH ₂ OH), N-methylhydroxylamine, N,N-dimethylhydroxylamine, and N,N-diethyl Hydroxylamines. Specific examples of the primary aliphatic amines include: monoethanolamine, ethylenediamine, and isopropanolamine. Specific examples of the secondary aliphatic amines include: diethanolamine, N-methylaminoethanol, and Propylamine and 2-ethylaminoethanol and 2-(2-aminoethylamino)ethanol. Specific examples of the tertiary aliphatic amines include: triethanolamine, dimethylaminoethanol, and ethyl Diethanolamine. Specific examples of the alicyclic amines include: cyclohexylamine and dicyclohexylamine. Specific examples of the aromatic amines include: benzylamine, benzhydrylamine, and N-methylbenzylamine. Specific examples of the heterocyclic amine include: pyrrole, pyrrolidine, pyrrolidone, pyridine, morpholine, pyrazine, hexahydropyridine, N-hydroxyethyl hexahydropyridine, Oxazole and thiazole. Specific examples of quaternary ammonium salts include: tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide, tetrapropylammonium hydroxide, trimethylethylammonium hydroxide, and hydroxide ( 2-hydroxyethyl)trimethylammonium, (2-hydroxyethyl)triethylammonium hydroxide, (2-hydroxyethyl)tripropylammonium hydroxide and (1-hydroxypropyl)trimethyl hydroxide The ammonium-based composition of the present invention may contain a salt of a base and/or a base in any amount or in an amount of from 0 to 20% by weight or from 0 to 5% by weight or from 0 to 1% by weight. The first and/or second texturing composition may additionally comprise one or more chelating agents. The chelating agents may be selected from, but not limited to, ethylenediaminetetraacetic acid (EDTA), N-hydroxyethylethylenediamine. Triacetic acid (NHEDTA), nitrilotriacetic acid (NTA), diethylenetriamine pentaacetic acid (DPTA), ethanol diglycolate, citric acid, glucuronic acid, oxalic acid, phosphoric acid, tartaric acid, methyl di Phosphonic acid, amino sulfonium methylene phosphonic acid, ethylene-bisphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, 1-hydroxypropylene-1,1-diphosphonic acid, Ethyl bis-methylene phosphonic acid, dodecylamino di-methylene Phosphonic acid, nitrogen sulfonium methylene phosphonic acid, ethylenediamine bismethylene phosphonic acid, ethylenediamine fluorene methylene phosphonic acid, hexamethylene diamine phthalmethylene phosphonic acid, diethylene triamine penta Phosphonic acid and 1,2-propylenediamine tetramethylene phosphonic acid or ammonium salts, organic amine salts, malonic acid, succinic acid, dimercaptosuccinic acid, glutaric acid, maleic acid , phthalic acid, fumaric acid, polycarboxylic acids such as tricarbaryl acid, propane-1,1,2,3-tetracarboxylic acid, butane-1,2,3,4- Tetracarboxylic acid, pyromellitic acid, hydroxycarboxylic acid such as glycolic acid, ß-hydroxypropionic acid, citric acid, malic acid, tartaric acid, pyruvic acid, diglycolic acid, salicylic acid, gallic acid Acids, polyphenols such as catechol, pyrogallic acid, phosphoric acids such as pyrophosphoric acid, polyphosphoric acid, heterocyclic compounds such as 8-hydroxyquinoline and diketones such as α-dipyridylacetamidacetone . The texturizing composition of the present invention may contain a chelating agent in any amount or in a concentration of from 0% by weight to 10% by weight or from 0.0001% to 10% by weight.

The first and/or second texturing composition may additionally comprise one or more antifoaming agents. The antifoaming agents may be selected from, but not limited to, polyoxyalkylenes, organophosphates, polyethylene glycol and polypropylene glycol copolymers based on ethylene oxide/propylene oxide (EO/PO). A defoamer, an alcohol, a white oil or a vegetable oil, and the paraffin is a long-chain fatty alcohol, a fatty acid soap or an ester. The texturized compositions may contain an antifoaming agent in any amount or in an amount of from 0.0001% to 5% by weight or from 0.001% to 5% by weight. Some compositions, such as some polyoxyalkylene surfactants, can simultaneously exert the utility of antifoaming agents and surfactants. The first texturing composition may contain an oxidizing agent having a concentration of from 0 to 99% by weight or from 0 to 50% by weight, such as nitric acid, peroxides, nitrates, nitrites, hypochlorites, Chlorates, persulfates, permanganates, peroxysulfuric acid and sulfuric acid.

The total weight percentage of the additive in the texturing composition of the present invention should be less than 10% by weight or less than 5% by weight or should be from 0 to 10% by weight or from 0 to 5% by weight.

The texturing composition of the present invention and the method of the present invention can be used to texture a wafer, which can be a monocrystalline substrate (eg, Si<100> or Si<111>), a microcrystalline germanium substrate, Strained ruthenium substrate, amorphous ruthenium substrate, doped or undoped polysilicon, polycrystalline substrate, glass, sapphire or any type The ruthenium containing substrate. The methods and compositions of the present invention are typically used on polycrystalline tantalum substrates. A first texturing step (in an embodiment of the invention having first and second texturing steps) that may be prior to the second texturing step is a texturing step involving the use of the composition of the invention, the composition comprising The basic composition is, and consists of a mixture of at least one acid or more than one acid, a surfactant or a mixture of more than one surfactant, and a solvent or solvent mixture. In some embodiments, the first texturing step is followed by a second texturing step comprising an alkaline second texturing step.

The wafer is wetted by the first and/or second and/or other textured compositions of the present invention. The wafers can be wetted by flooding, spraying, dipping or other suitable means. In some cases, the first and/or second texturing composition must be agitated to ensure that the composition remains in intimate contact with the surface of the substrate during the texturing process.

Typically, the process has a multi-step texturing process with multiple (eg, two) texturing steps; however, the present invention contemplates that certain texturing compositions and processes involve only the first texturing step. The texturing process can include one or more rinsing steps, one or more washing steps, and/or other steps in addition to the one or more texturing steps. The wafer can be wetted with the first texturing composition of the present invention after any cleaning step. Additionally, the wafer can be wetted with the second texturing composition immediately after the first texturing step or after any other texturing step. From the standpoint of improving the surface reflectivity of the polycrystalline wafer, it is currently most efficient to use the first and second texturing compositions as such texturing steps.

The wafers may be prior to the one or more texturing steps After the separate rinsing step is rinsed. The wetting can be carried out at room temperature or below ambient temperature for any step, for example 0 ° C to 40 ° C or 5 to 25 ° C. The wafer may be wetted by the texturing composition for a period of time that may vary depending on the method by which the first and/or second texturing composition is applied to the wafer. Typically, a single wafer that is processed through the texturing process on a conveyor belt has a much shorter processing time than a batch scale impregnation texturing process. These steps may each be in the range of 1 second to 1 hour. A preferred texturing step time can be between 20 seconds and 30 minutes. The time for each texturing step can be shortened by increasing the temperature of the texturing bath.

The second texturizing composition may or may not intentionally comprise a surfactant, that is, it may be substantially free of surfactants. Substantially free of surfactant means less than 0.001% by weight of surfactant. The second texturizing composition may be formulated to be free of surfactants; however, when the residual surfactant-derived wafer from the first texturing step of the present invention is based on the second texturing composition Some surfactant may be introduced into the texturing bath during wetting.

Some methods of the present invention comprise, consist of, and consist of the steps of: wetting the wafer with the first texturing composition; wetting the wafer with the second texturing composition; rinsing and drying with DIW The wafer. Other methods of the present invention comprise, consisting of, and consisting of: wetting the wafer at about 7 to 15 ° C for about 1 to about 5 minutes using the first texturing composition; rinsing with DIW; and utilizing The second texturing composition wets the wafer at ambient temperature for about 5 seconds to about 5 minutes; the wafer is rinsed and dried using DIW.

1 depicts a flow diagram of one embodiment of a surface texturing process sequence 100 suitable for use on a tantalum substrate. Although the process sequence 100 illustrates a solar cell process, the process sequence 100 may be beneficial to form a textured surface suitable for use in other structures and applications. In one embodiment, the process sequence 100 discussed below is performed in an automated production line having mechanical means adapted to transfer the respective processed substrates to a series of processing baths, the processing baths being adapted to perform the following All processing steps discussed. Although not shown in FIG. 1, alternative embodiments of the process sequence 100 can include other steps, for example, drying steps and/or other rinsing steps between the respective processing steps discussed below. These other rinsing steps can prevent excessive exposure to the processing chemicals during each step and reduce the chance of cross-contamination between adjacent processing baths, for example due to chemical retentate. In the particular embodiment illustrated in FIG. 1, the texturing process includes a first texturing step 104A and a second texturing step 104E, however, although not shown, the salt knows that more than two use the same or selective texturing The texturing step of the composition can be used to texture the substrate. The steps of the invention described below may include means for agitating the composition used in each step.

The process sequence 100 begins at step 102 by providing a substrate. The substrate can have a thickness of between about 100 μm and about 400 μm. In a specific embodiment, the substrate may be a single crystal substrate (for example, Si<100> or Si<111>), a microcrystalline substrate, a polycrystalline germanium substrate, a strained germanium substrate, and an amorphous material. A ruthenium substrate, a doped or undoped polycrystalline ruthenium substrate, glass, sapphire or any type of ruthenium-containing substrate. In a specific embodiment where the substrate is required to be an n-type crystalline germanium substrate, donor atoms are incorporated into the junction during formation of the substrate. Within the crystalline tantalum substrate. Suitable examples of donor atoms include, but are not limited to, phosphorus (P), arsenic (As), antimony (Sb). Alternatively, in a specific embodiment in which a p-type crystalline ruthenium substrate is required, an acceptor-type atom may be incorporated into the crystalline ruthenium substrate during the formation of the substrate. Figure 2A shows a top view image of a portion of the polycrystalline substrate prior to the texturing process. The surface reflectance of the untextured substrate was 36.5%.

At step 103, the substrate is optionally pre-cleaned prior to performing the texturing process (eg, steps 104A-F). In an alternative embodiment (not shown), the pre-cleaning process is a multi-step process for removing unwanted contamination, surface fouling, and/or other materials that may affect subsequent processing steps. In a specific embodiment, in step 103, the pre-cleaning process may wet the substrate by an acid solution and/or a solvent to remove surface particles, native oxide or other contaminants of the substrate. And proceed. The pre-cleaning solution can be an aqueous hydrofluoric acid (HF) solution having a mixture of hydrogen hydride and deionized water in a ratio of between 0.1:100 and about 4:100. In a specific embodiment, the pre-cleaning solution can be a hydrofluoric acid (HF) aqueous solution having a concentration between about 0.1 weight percent and about 4 weight percent, such as between about 1 weight percent and about 2 weight percent. HF between, and the remainder is deionized water. The cleaning solution can comprise ozonated deionized water having between about 1 ppm and 30 ppm of ozone disposed in deionized water. The pre-cleaning process can be carried out on the substrate for between about 5 seconds and about 600 seconds, such as from about 30 seconds to about 240 seconds, for example about 120 seconds. The pre-cleaning solution can also be a standard cleaning solution SC1, a standard cleaning solution SC2 or other suitable and cost effective cleaning solution that can be used to clean the cerium-containing substrate. (SC1 consists of NH ₄ OH (28% by weight), H ₂ O ₂ (30% by weight) and deionized water, typically 1:1:5, often used at 70 ° C; however, it can contain higher a ratio of water. SC2 consists of HCl (73% by weight), H ₂ O ₂ (30% by weight), deionized water, initially produced at a ratio of 1:1:5, often used at 70 ° C; however, A higher proportion of water may be included.) In one example, the pre-cleaning process comprises immersing the substrate in an aqueous solution comprising 2% by volume hydrofluoric acid (HF) at a temperature of between about 1 and 3 minutes at room temperature. Between the time. In step 104A, in a first step of the texturing process, the substrate is wetted by a texturizing composition of the invention comprising a surfactant. The substrate can be wetted by flooding, spraying, dipping or other suitable means. This wetting can be carried out in a bath, along a line of equipment or in a beaker. Examples of suitable first texturing compositions have been described above and include the following embodiment revealers. The wetting can be accomplished below ambient temperature or at room temperature, for example 0 ° C to 25 ° C or 6 to 8 ° C. The time of wetting varies with a number of different methods and can be varied for a single wafer relative to the batch scale impregnation method in the case of a textured bath. The treatment time can range from 1 second to 1 hour. The preferred processing time for the first texturing step can be between 20 seconds and 30 minutes, 30 seconds to 15 minutes, or 1 minute to 5 minutes.

After the surface of the wafer passes through the texturing step, it is usually etched by the first texturing composition, that is, the saw blade is stained and the surface of the wafer is removed by the elliptical pit and the naphthalene The rice is covered with fine holes. Following the first texturing step 104A shown in FIG. 1 is a preferred rinsing step 104B. The rinsing step often comprises wetting the substrate with water or deionized water and may comprise immersing the substrate in a water or deionized water bath for 10 minutes or less or 5 minutes or less.

After the rinsing step 104B, any drying step can be performed 104C removes water, some, most or substantially all of the texturized composition and any other residual chemicals from the surface of the substrate. The drying process can include drying the substrate for 1 to 60 minutes with a stream of nitrogen, a stream of clean dry air, or hot air or nitrogen. Figure 2B shows a top view of the surface of the polycrystalline substrate after step 104C. The surface was covered with uniform pits and nanopores and the surface resistivity was 16.7%.

After step 104D, in the particular embodiment illustrated in Figure 1, the substrate is wetted by the second texturing composition after steps 104A-C to remove the nanopores from the surface. The second texturing (etching) solution can be any composition that is effective in texturing the surface of the substrate, including any known texturing solution. In a specific embodiment, the texturing composition is an alkaline solution in which one or more other additives may be present and is maintained at a temperature between about 0 ° C and about 95 ° C or at a temperature of 10 ° C to 50 ° C or ambient temperature. under. In another embodiment, the alkaline solution used to texture the tantalum substrate can be an aqueous solution comprising one or more of the following: potassium hydroxide (KOH), sodium hydroxide (NaOH), aqueous ammonia (NH) ₄ OH), tetramethylammonium hydroxide (TMAH or (CH ₃ ) ₄ NOH) or other similar base. The alkaline solution can have between about 0.1% to about 15% by weight KOH (or other base or base mixture) in deionized (DI) water, or about 0.25 in deionized water (DI). From 5% by weight to about 10% by weight of KOH (or other base or base mixture), or from about 0.5% to about 5% by weight of KOH (or other base or base mixture) in deionized water (DI).

After the second texturing step 104D is completed, a rinsing step 104E may be performed, for example, a water rinsing step as described above and/or any drying step 104F may be performed to remove some, most, or real All textured compositions and any other residual chemicals. The drying process can include drying the substrate with a stream of nitrogen or a clean stream of dry air or hot air or nitrogen for from 1 to 60 minutes. Figure 2C shows a top view of the surface of the polycrystalline substrate after step 104F. The surface was covered with uniform pits without nanopores and the surface resistivity was 22.9%.

After the texturing process is performed on the surface of the substrate, the substrate resistivity is generally reduced to 30% or less, or 26% or less, or 23% or less by a method of measuring the resistivity described below. .

The following examples illustrate the texturized compositions and methods of the present invention.

Example

Clamp the wafer horizontally into the beaker using the holder. Flushing was performed by overflow flushing using a flow rate of deionized water of approximately 100 milliliters per minute (ml/min) unless otherwise indicated. If the temperature of one step is not specified, the temperature is room temperature. If only part of the composition is indicated herein, the remainder is deionized water. Calculating the total amount of helium loss in the first texturing step by measuring the weight change of the wafer just before and after the texturing step and multiplying the total thickness of the untextured wafer by the weight percentage change Measure the loss of helium. Wafer reflectance measurements were performed on a Perkin-Elmer Lambda 900 UV/VIS/NIR spectrometer. The instrument is equipped with an integrating sphere to obtain the amount of reflected radiation.

Example 1

In this embodiment, single crystal and polycrystalline wafers (in the table below) The identified) is processed by a two-step texturing process (which contains additional rinsing and drying steps; but no saw blade damage or other pre-treatment steps, such as no pre-cleaning steps). The first texturing composition is identified by placing each wafer level into the following table (Tables 1, 1A, 2, 2A, 3, 3A, 4, 4A, 5, 6, and 6A) at 7 to 10 °C. The first texturized composition is wetted for about 1 to 3 minutes and then rinsed with deionized water (DIW) and nitrogen dried, followed by placing the treated wafers vertically at 0.5 weights with ambient temperature A second or 5 wt% aqueous KOH solution (to remove the nanopores) was wetted for a second texturing step of 10 seconds to 1 minute and then rinsed with DIW and dried with nitrogen. The amount of helium loss on both sides is obtained from the change in weight. The reflectance was measured on each wafer on the wafer side facing the bottom of the beaker using a Perkin-Elmer Lambda 900 spectrometer equipped with an integrating sphere. The average weight reflectance ("WAR") was calculated by integrating the amount of reflectance loss under an AM 1.5 standard solar illumination of 400 to 1100 nm.

In the step, the nanopores were removed by wetting each wafer with a 0.5% by weight aqueous KOH solution at ambient temperature for 1 minute. )

The texturized compositions used in the comparative examples and examples shown in Table 1 are in Table 1A below:

The texturized compositions used in the comparative examples and examples shown in Table 2 are in Table 2A below:

The texturized compositions used in the comparative examples and examples shown in Table 3 are in Table 3A below:

The texturized compositions used in the comparative examples and examples shown in Table 4 are in Table 4A below:

Example 2

The texturing composition Example F (Ex F) defined in Table 2A was used for the same two texturing step procedures (with rinsing and drying steps) as used in Example 1 and using different wafer records from different wafer sources. In Table 2. The results are shown in Table 5.

Example 3

Other texturing compositions were tested in the same procedure as described in Example 1. The results are shown in Table 6 (note that the previous three examples were repeated in Table 6). The composition data of Comparative Example I and Example A can be seen in Table 1A and Comparative Example II and Example F can be seen in Table 2A.

The texturing compositions of Examples O, P and Q in Table 6 are in Table 6A below:

Although the present invention has been described with reference to the specified process steps and compositions that can be used in those process steps, including those used in the above embodiments, it will be apparent that other embodiments are possible and are within the scope of the present invention.

Claims (18)

A texturizing composition for texturing a tantalum wafer, wherein the composition comprises one or more acids, one or more anionic sulfur-containing surfactants, and water. The texturing composition of claim 1, wherein the one or more anionic sulfur-containing surfactants are selected from the group consisting of linear alkylbenzene sulfonates (LAS), secondary alkyl benzene sulfonates, Lignosulfonates, N-mercapto-N-alkyl taurate, fatty alcohol sulfates (FAS), petroleum sulfonates, secondary alkane sulfonates (SAS), paraffin sulfonate Acid esters, fatty alcohol ether sulfates (FAES), α-olefin sulfonates, thiosuccinates, alkylnaphthalene sulfonates, isethionates, sulfuric acid A group consisting of esters, sulfated linear primary alcohols, sulfated polyoxyethylated linear alcohols, sulfated triglyceride oils, and mixtures thereof. The texturing composition of claim 1, wherein the one or more anionic sulfur-containing surfactants are selected from the group consisting of sodium dialkyl sulfates, diphenyl ether disulfonic acids, and ether sulfates. Group. The textured composition of claim 1, wherein the texturizing composition comprises hydrofluoric acid. The textured composition of claim 1, wherein the texturizing composition comprises nitric acid and hydrofluoric acid. The textured composition of claim 1, wherein the one or more sulfur-containing surfactants have the following structure: Wherein R ¹ and R ^{2 are} independently a linear or cyclic alkyl group or a phenyl group or a combination thereof, usually having 1 to 20 carbon atoms, and X is hydrogen or any includes Na, K, tetramethylammonium, tetraethyl A cation of a quaternary ammonium, triethanolamine or ammonium. The texturing composition of claim 1, wherein the one or more acids comprise one or more selected from the group consisting of phosphoric acid, sulfuric acid or a water-soluble carboxylic acid, for example, acetic acid, propionic acid, butyric acid, valeric acid, A group consisting of isomers of hexanoic acid, tartaric acid, succinic acid, adipic acid, glycerol tricarboxylic acid, and glycerol tricarboxylic acid. The texturized composition of claim 1, which is selected from the group consisting of: (1) about 37 to about 42% by weight of HF, about 3.5 to about 7% by weight of HNO3, about 0.005 to About 0.25% by weight of surfactant, and the balance being water; (2) about 24 to about 30% by weight of HF, about 14 to about 19% by weight of HNO3, and about 0.005 to about 0.25 % by weight of surfactant, Further, the remainder is water; and (3) from about 9 to about 13% by weight of HF, from about 31 to about 39% by weight of HNO3, from about 0.005 to about 0.25% by weight of surfactant, and the balance being water. The texturing composition of claim 8 wherein the one or more sulfur-containing surfactants are selected from the group consisting of linear alkyl benzene sulfonates (LAS), secondary alkanes. Benzobenzenesulfonate, lignosulfonate, N-fluorenyl-N-alkyl taurate, fatty alcohol sulfate (FAS), petroleum sulfonate, secondary alkane sulfonate (SAS), paraffin sulfonates, fatty alcohol ether sulfates (FAES), α-olefin sulfonates, thiosuccinates, alkyl naphthalene sulfonates, isethionates A group consisting of sulfates, sulfated linear primary alcohols, sulfated polyoxyethylated linear alcohols, sulfated triglyceride oils, and mixtures thereof. The texturing composition of claim 8 wherein the one or more sulfur-containing surfactants are selected from the group consisting of sodium alkane sulfates, diphenyl ether disulfonic acids, and ether sulfates. group. A method of texturing a germanium wafer comprising the steps of wetting a wafer with a texturized composition comprising one or more acids, one or more anionic sulfur-containing surfactants, and water. The method of claim 11, wherein the sulfur-containing surfactant is selected from the group consisting of linear alkylbenzene sulfonates (LAS), secondary alkyl benzene sulfonates, lignosulfonates, N- Mercapto-N-alkyl taurate, fatty alcohol sulfate (FAS), petroleum sulfonate, secondary alkane sulfonate (SAS), paraffin sulfonate, fatty alcohol ether sulfate Classes (FAES), α-olefin sulfonates, thiosuccinates, alkylnaphthalene sulfonates, isethionates, sulfates, sulfated linear primary alcohols, sulfation A group consisting of polyoxyethylated linear alcohols, sulfated triglyceride oils, and mixtures thereof. The method of claim 11, wherein the one or more sulfur-containing surfactants are selected from the group consisting of sodium dialkyl sulfates, diphenyl ether disulfonic acids, and ether sulfates, and The one or more acids comprise hydrofluoric acid. The method of claim 11, further comprising the step of: wetting the wafer with a second texturing composition (referred to as a second wetting step), the step of which is followed by the application of the texturing composition After the wet step (referred to as the first wetting step). The method of claim 14, wherein the second texturing composition comprises one or more bases in a solvent. The method of claim 14, further comprising the steps of: rinsing the wafer after the first wetting step and before the second wetting step, and further rinsing and drying after the second wetting step The wafer. The method of claim 10, wherein the texturizing composition is selected from the group consisting of: (1) from about 37 to about 42% by weight HF, from about 3.5 to about 7% by weight HNO3, about 0.005 to about 0.25% by weight of surfactant, and the balance being water; (2) from about 24 to about 30% by weight of HF, from about 14 to about 19% by weight of HNO3, from about 0.005 to about 0.25% by weight of surface active And the remainder is water; and (3) from about 9 to about 13% by weight HF, from about 31 to about 39% by weight HNO3, from about 0.005 to about 0.25% by weight surfactant, and the balance being water. The method of claim 17, wherein the texturizing composition used in the second texturing step is an aqueous hydroxide solution.