Manufacturing process of a polishing compound

Abstract

A method for producing a polishing composition comprising diluting an undiluted liquid containing abrasive grains, wherein the dilution is carried out using a diluent consisting of only one or more types of water selected from the group consisting of ion-exchange water, pure water, ultrapure water, or distilled water, and wherein the dilution of the undiluted liquid is carried out such that, where R1 is defined as an average secondary particle diameter of the abrasive grains in the undiluted liquid and R2 is defined as an average secondary particle diameter of the abrasive grains in the polishing composition, the ratio R2 / R1 is 1.2 or less, wherein R1 and R2 are determined by a dynamic light scattering method, wherein the polishing composition contains 0.002 wt% or more and 0.5 wt% or less of a water-soluble polymer.where the weight-averaged molecular weight of the water-soluble polymer is 1,000 or more and less than 2,000,000.

Description

Technical field

[0001] The present invention relates to a polishing composition, a method for producing the same, an undiluted liquid for producing a polishing composition, a method for producing a silicon substrate using the polishing composition, and a silicon substrate produced using the polishing composition. State of the art

[0002] A polishing composition containing abrasive grains is used, for example, to polish a silicon substrate (see patent document 1). To stabilize the quality of a polished product obtained by polishing an object, it is important to reduce the aggregates in a polishing composition. In this context, patent document 2 discloses a method for increasing the dispersibility of abrasive grains. However, there is still room for improvement to enhance the quality of a polished product. State of the art documents

[0003] Patent document 1: Japanese patent disclosure no. 2005-518668 Patent document 2: Japanese patent disclosure no. 2001-15461 Summary of the invention: Problems that the invention is intended to solve

[0004] The present invention was made by focusing attention on the generation of aggregates upon dilution of an undiluted liquid containing abrasive grains. It is an object of the present invention to provide a polishing composition suitable for producing a high-quality polished product, a method for producing the same, and an undiluted liquid. It is a further object of the present invention to provide a manufacturing process for a silicon substrate by which a high-quality silicon substrate can be easily produced, as well as to provide a high-quality silicon substrate. Means to solve these problems

[0005] To achieve the items described above and according to one aspect of the present invention, a polishing composition is provided which is obtained by diluting an undiluted liquid containing abrasive grains, wherein, if R1 is defined as an average secondary particle diameter of the abrasive grains in the undiluted liquid and R2 is defined as an average secondary particle diameter of the abrasive grains in the polishing composition, the ratio R2 / R1 is 1.2 or less.

[0006] The undiluted liquid is preferably diluted with a dilution ratio of 2 times or more and 100 times or less.

[0007] The polishing composition is further preferably obtained by filtering a diluted liquid, which is obtained by diluting the undiluted liquid.

[0008] A filter used in filtering the diluted liquid has an opening or hole of preferably 0.05 μm or more and 50 μm or less.

[0009] A filtration rate when filtering the diluted liquid is preferably 0.005 ml / (min × mm). 2 ) or more and 10 ml / (min × mm 2 ) or less at a suction pressure of 50 kPa.

[0010] The polishing composition is preferably used for polishing a silicon substrate material.

[0011] According to a further aspect of the present invention, a method for producing a polishing composition is provided, comprising diluting an undiluted liquid containing abrasive grains, wherein the dilution of the undiluted liquid is carried out such that, if R1 is defined as the average secondary particle diameter of the abrasive grains in the undiluted liquid, and R2 is defined as an average secondary particle diameter of the abrasive grains in the polishing composition, the ratio R2 / R1 is 1.2 or less.

[0012] According to yet another aspect of the present invention, a method for producing a silicon substrate is provided, comprising polishing a silicon substrate material with the polishing composition.

[0013] According to yet another aspect of the present invention, a silicon substrate is provided, obtained by polishing a silicon substrate material with the polishing composition.

[0014] According to yet another aspect of the present invention, an undiluted liquid is provided which is to be diluted 2 times or more and 10 times or less with water when used to prepare a polishing composition, wherein the undiluted liquid contains abrasive grains, and where R1 is defined as an average secondary particle diameter of the abrasive grains in the undiluted liquid and R2 is defined as an average secondary particle diameter of the abrasive grains in the polishing composition, the ratio R2 / R1 is 1.2 or less. Effects of the invention

[0015] The present invention succeeds in simply providing a polished, high-quality product, such as a silicon substrate. Methods for carrying out the invention

[0016] An embodiment of the present invention is described below.

[0017] A polishing composition according to the present invention is produced by a dilution step, in which an undiluted liquid is diluted to obtain a diluted liquid, and by a filtration step, in which the diluted liquid is filtered. The undiluted liquid contains abrasive grains and water.

[0018] If R1 is defined as the average secondary particle diameter of the abrasive grains in the undiluted liquid and R2 is defined as the average secondary particle diameter of the abrasive grains in the polishing compound, the ratio R2 / R1 is 1.2 or less. The polishing compound of the present embodiment is used for polishing a silicon substrate material.

[0019] Abrasive grains are used to mechanically polish a surface. Specific examples of abrasive grains include particles made from a metal oxide, such as silicon dioxide, zirconium dioxide, and titanium dioxide; silicon carbide particles; calcium carbonate particles; and diamond particles. Only one type of abrasive grain can be used alone, or a combination of two or more types.

[0020] The abrasive grains are preferably silicon dioxide particles. Examples of silicon dioxide particles include colloidal silicon dioxide and highly dispersed silicon dioxide. Of these, colloidal silicon dioxide is preferred. When colloidal or highly dispersed silicon dioxide is used, and especially when colloidal silicon dioxide is used, scratches formed on the surface of a silicon substrate during polishing with the polishing compound are reduced.

[0021] The average primary particle diameter of the abrasive grains is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 20 nm or more. Increasing the average primary particle diameter of the abrasive grains improves the polishing rate of a silicon substrate.

[0022] The average primary particle diameter of the abrasive grains is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 40 nm or less. Reducing the average primary particle diameter of the abrasive grains improves the dispersion stability of the polishing composition.

[0023] The average primary particle diameter of the abrasive grains is calculated, for example, from the specific surface area of ​​the abrasive grains, which is determined using the BET method. The specific surface area of ​​the abrasive grains can be determined, for example, using "Flow Sorb II 2300" manufactured by Micromeritics Instrument Corporation.

[0024] The proportion of abrasive particles in the polishing compound is preferably 0.01% by mass or more. Increasing the proportion of abrasive particles improves surface processing properties, such as the polishing rate of the surface to be polished.

[0025] The proportion of abrasive particles in the polishing composition is preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less. Reducing the proportion of abrasive particles improves the dispersion stability of the polishing composition and reduces the residue of abrasive particles on the polished surface.

[0026] Water in the undiluted liquid serves as a dispersion medium or solvent for other components in the undiluted liquid. For example, water with a total transition metal ion concentration of 100 ppb or less is preferably used to minimize the inhibition of the other components' reactions. The purity of the water can be increased by processes such as removing impurity ions using an ion exchange resin, removing foreign matter using a filter, and distillation. In particular, ion exchange water, pure water, ultrapure water, or distilled water is preferably used.

[0027] The pH value of the polishing composition is preferably within the range of 8 to 12 and more preferably within the range of 9 to 11. If the pH value of the polishing composition is in the range of 8 to 12, a preferred polishing rate is easily achieved in practice.

[0028] The undiluted liquid may also contain a water-soluble polymer or a basic compound, if required.

[0029] The water-soluble polymer serves to increase the wettability of a surface to be polished. A water-soluble polymer with at least one functional group in the molecule, which is selected from a cation group, an anion group, and a nonionic group, can be used. A suitable water-soluble polymer can contain a hydroxyl group, a carboxyl group, an acyloxy group, a sulfo group, a quaternary nitrogen structure, a heterocyclic structure, a vinyl structure, or a polyoxyalkylene structure.

[0030] Specific examples of a water-soluble polymer include a cellulose derivative; an imine derivative, such as poly(N-acylalkyleneimine); polyvinyl alcohol; polyvinylpyrrolidone; a copolymer containing polyvinylpyrrolidone in part of the structure; polyvinylcaprolactam; a copolymer containing polyvinylcaprolactam in part of the structure; polyoxyethylene; a polymer with a polyoxyalkylene structure; a polymer with a multiple structure, such as a diblock type, triblock type, random type, and alternating type thereof; and a polyether-modified silicone.

[0031] The water-soluble polymer can be used alone or in a combination of two or more types.

[0032] A water-soluble polymer to be used is preferably a cellulose derivative, polyvinylpyrrolidone, or a polymer with a polyoxyalkylene structure, as these are well-suited to imparting hydrophilic properties. Specific examples of cellulose derivatives include hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, methylcellulose, ethylcellulose, ethylhydroxyethylcellulose, and carboxymethylcellulose. Among the cellulose derivatives, hydroxyethylcellulose is preferred because it has a high ability to impart wettability to a polished surface and facilitate its cleaning.

[0033] The weight-average molecular weight of the water-soluble polymer is preferably 300 or more, more preferably 1,000 or more, even more preferably 10,000 or more, still more preferably 100,000 or more, and particularly preferably 200,000 or more with respect to the polyethylene oxide. Increasing the weight-average molecular weight of the water-soluble polymer enhances the hydrophilic properties of a surface to be polished.

[0034] The weight-average molecular weight of the water-soluble polymer is preferably less than 2,000,000, more preferably less than 1,500,000, even more preferably less than 1,000,000, and most preferably less than 500,000. Reducing the weight-average molecular weight of the water-soluble polymer further improves the stability of the polishing composition.

[0035] The proportion of the water-soluble polymer in the polishing composition is preferably 0.002 wt% or more, more preferably 0.004 wt% or more, and even more preferably 0.006 wt% or more. Increasing the proportion of the water-soluble polymer in the polishing composition further enhances the wettability of the surface to be polished.

[0036] The proportion of the water-soluble polymer in the polishing composition is preferably 0.5 wt% or less, more preferably 0.2 wt% or less, and even more preferably 0.1 wt% or less. Reducing the proportion of the water-soluble polymer in the polishing composition slightly improves its dispersion stability.

[0037] The basic compound serves to chemically polish a surface to be polished and to improve the dispersion stabilization of the polishing composition.

[0038] Specific examples of a basic compound that can be used include a hydroxide or salt of an alkali metal, a quaternary ammonium hydroxide or its salt, ammonia, and an amine. Specific examples of an alkali metal include potassium and sodium. Specific examples of a salt include a carbonate, bicarbonate, sulfate, and acetate. Specific examples of a quaternary ammonium compound include tetramethylammonium, tetraethylammonium, and tetrabutylammonium. Specific examples of a hydroxide or salt of an alkali metal include potassium hydroxide, potassium carbonate, potassium bicarbonate, potassium sulfate, potassium acetate, and potassium chloride. Specific examples of a quaternary ammonium hydroxide or its salt include tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide.Specific examples of amines include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, monoethanolamine, N-(β-aminoethyl)ethanolamine, hexamethylenediamine, diethylenetriamine, triethylenetetraamine, anhydrous piperazine, piperazine hexahydrate, 1-(2-aminoethyl)piperazine, N-methylpiperazine, and guanidine. These basic compounds can be used as a single compound or in combination with two or more other compounds.

[0039] A basic compound to be used is preferably at least one selected from ammonia, an ammonium salt, an alkali metal hydroxide, an alkali metal salt, and a quaternary ammonium hydroxide. Among these, a basic compound to be used is preferably at least one selected from ammonia, potassium hydroxide, sodium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, ammonium hydrogen carbonate, ammonium carbonate, potassium hydrogen carbonate, potassium carbonate, sodium hydrogen carbonate, and sodium carbonate; more preferably at least one selected from ammonia, potassium hydroxide, sodium hydroxide, tetramethylammonium hydroxide, and tetraethylammonium hydroxide; even more preferably at least one selected from ammonia and tetramethylammonium hydroxide; and particularly preferably ammonia.

[0040] The proportion of the basic compound in the polishing composition is preferably 0.001 wt% or more, more preferably 0.002 wt% or more, and even more preferably 0.003 wt% or more. Increasing the proportion of the basic compound in the polishing composition enhances its ability to chemically polish a surface and improves the dispersion stability of the polishing composition.

[0041] The proportion of the basic compound in the polishing composition is preferably 1.0 wt% or less, more preferably 0.5 wt% or less, and even more preferably 0.2 wt% or less. Reducing the proportion of the basic polishing composition improves the smoothness of the polished surface.

[0042] The undiluted liquid may also contain, for example, a surfactant, an organic acid, an organic acidic salt, an inorganic acid, an inorganic acidic salt, or a chelating agent.

[0043] The surfactant serves to suppress the roughness of a polished surface. This simply reduces the degree of haze on the polished surface. Particularly when the polishing compound contains a basic compound, roughness can easily be caused on a polished surface due to the chemical etching of the basic compound; therefore, the use of a surfactant in combination with a basic compound is effective in suppressing roughness.

[0044] The weight-average molecular weight of the surfactant used can be less than 300. The surfactant can be either ionic or non-ionic, and a non-ionic surfactant is preferred. Since a non-ionic surfactant has low foaming properties, handling the polishing compound during preparation and use is simplified. Furthermore, adjusting the pH of the polishing compound is easier when using a non-ionic surfactant than when using an ionic surfactant.

[0045] Specific examples of a nonionic surfactant include oxyalkylene polymers, such as polyethylene glycol and polypropylene glycol; and polyoxyalkylene adducts, such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkylamines, polyoxyethylene fatty acid esters, polyoxyethylene glycol fatty acid esters, and polyoxyethylene sorbitan fatty acid esters. More specific examples include polyoxyethylene polyoxypropylene copolymer, polyoxyethylene glycol, polyoxyethylene propyl ether, polyoxyethylene butyl ether, polyoxyethylene penthyl ether, polyoxyethylene hexyl ether, polyoxyethylene octyl ether, polyoxyethylene 2-ethylhexyl ether, polyoxyethylene nonyl ether, polyoxyethylene dekyl ether, polyoxyethylene isodekyl ether, polyoxyethylene tridekyl ether, polyoxyethylene lauryl ether, polyoxyethylene centetyl ether, polyoxyethylene stearyl ether, polyoxyethylene isostearyl ether, polyoxyethylene oleyl ether, polyoxyethylene phenyl ether, polyoxyethylene octyl phenyl ether, and polyoxyethylene nonyl phenyl ether.Polyoxyethylene dodecyl phenyl ether, polyoxyethylene stearyl phenyl ether, polyoxyethylene lauryl amine, polyoxyethylene stearylamine, polyoxyethylene oleyl amine, polyoxyethylene stearylamide, polyoxyethylene oleyl amide, polyoxyethylene monolaurate ester, polyoxyethylene monostearate ester, polyxyethylene bisstearate ester, polyoxyethylene monoleate ester, polyoxyethylene dioleate ester, Polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitol tetraoleate, polyoxyethylene castor oil and polyoxyethylene hydrogenated castor oil.

[0046] The surfactant can consist of one type or a combination of two or more types.

[0047] The organic acid and its salt, and the inorganic acid and its salt, serve to improve the hydrophilic properties of a polished surface.

[0048] Specific examples of organic acids that can be used include fatty acids, such as formic acid, acetic acid, and propionic acid; aromatic carboxylic acids, such as benzoic acid and phthalic acid; citric acid; oxalic acid; tartaric acid; malic acid; maleic acid; fumaric acid; succinic acid; organic sulfonic acids; and organic phosphonic acids. Specific examples of organic acid salts that can be used include alkali metal salts, such as sodium and potassium salts of organic acids or their ammonium salts.

[0049] Specific examples of inorganic acids that can be used include sulfuric acid, nitric acid, hydrochloric acid, and carboxylic acid. Specific examples of inorganic acid salts that can be used include alkali metal salts, such as sodium and potassium salts of inorganic acids, or ammonium salts thereof.

[0050] Among the organic acid salts and the inorganic acid salts, an ammonium salt is preferred from the point of view of suppressing the metallic contamination of a polished product.

[0051] Organic acids and their salts, and inorganic acids and their salts, can be used alone or in a combination of two or more types.

[0052] The chelating agent serves to suppress metallic impurities in a polished product. Specific examples of chelating agents that can be used include aminocarboxylic acid chelators and organic phosphonic acid chelators. Specific examples of aminocarboxylic acid chelating agents include ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetate, nitrilotriacetic acid, sodium nitrilotriacetate, ammonium nitrilotriacetate, hydroxyethylethylenediaminetriacetic acid, sodium hydroxyethylethylenediaminetriacetate, diethylenetriaminepentaacetic acid, sodium diethylenetriaminepentaacetate, triethylenetetraaminehexaacetic acid, and sodium triethylenetetraminehexaacetate.Specific examples of organic phosphonic acid chelating agents include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetrakis(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, and α-methylphosphonosuccinic acid.

[0053] A well-known mixing device, such as a paddle stirrer, an ultrasonic disperser, or a homogenizer, can be used to mix the raw materials for the undiluted liquid. All raw materials can be mixed simultaneously or in any order.

[0054] The average secondary particle diameter R1 of the abrasive grains in the undiluted liquid is preferably 300 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less. Reducing the average secondary particle diameter R1 allows for a simple increase in the polishing precision of a surface to be polished. The value of the average secondary particle diameter R1 can be determined by a dynamic light scattering method.

[0055] The water used to dilute the undiluted liquid in the dilution step can be one that was previously described as being present in the undiluted liquid. The undiluted liquid is preferably diluted by a process in which water is gradually added to the undiluted liquid while the undiluted liquid is stirred in the mixing device described above. Alternatively, stirring using the mixing device described above can be carried out after the water has been added to the undiluted liquid.

[0056] The dilution ratio D in the dilution step is preferably 2 times or more, more preferably 5 times or more, and even more preferably 10 times or more, with respect to volume. Increasing the dilution ratio D reduces the transport costs of the undiluted liquid and the space required for storing it.

[0057] The dilution ratio D in the dilution step is preferably 100 times or less, more preferably 50 times or less, and even more preferably 30 times or less, with respect to volume. By reducing the dilution ratio D, the stability of the diluted liquid obtained by diluting the undiluted liquid and the stability of the polishing composition obtained by filtering the diluted liquid can be easily ensured.

[0058] The diluted liquid obtained by diluting the undiluted liquid in the dilution step is subsequently subjected to a filtration step. This filtration step is performed to remove aggregates of abrasive particles contained in the diluted liquid. Filtration in this step can be natural filtration, carried out under normal pressure, suction filtration, pressure filtration, or centrifugal filtration.

[0059] The filter used in the filtration step is preferably selected based on its aperture. The filter aperture is preferably 0.05 μm or larger, more preferably 0.1 μm or larger. Increasing the filter aperture makes it easy to achieve a practical filtration rate.

[0060] The filter aperture is preferably 50 μm or less, more preferably 5 μm or less, and even more preferably 0.3 μm or less. Reducing the filter aperture makes it easier to obtain a polishing composition suitable for producing a high-quality silicon substrate.

[0061] The filter opening is specified as a nominal opening by a filter manufacturer.

[0062] The filtration rate in the filtration step is preferably 0.005 ml / (min × mm). 2 ) or more, preferably 0.010 ml / (min × mm) 2 ) or more, and preferably 0.015 ml / (min × mm) 2 ) or more, at a suction pressure of 50 kPa. If the filtration rate in the filtration step increases, the effectiveness of the filtration step is improved.

[0063] The filtration rate in the filtration step is preferably 10 ml / (min × mm). 2) or less, preferably 8 ml / (min × mm) 2 ) or less, and preferably 5 ml / (min × mm) 2 ) or less, at a suction pressure of 50 kPa. If the filtration rate in the filter step decreases, the effectiveness of removing foreign matter is increased, and as a result, a polishing composition suitable for producing a high-quality silicon substrate can be obtained more easily.

[0064] The filtration capacity of the filter, which is the amount of undiluted liquid that passes through the filter before the filter becomes clogged after the supply of undiluted liquid to the filter has begun, is preferably 0.1 ml / mm². 2 or more, preferably 0.2 ml / mm 2 or more, and preferably 0.3 ml / mm 2 or more. If the filtration capacity of the filter decreases, the running costs of the filtration step can be reduced.

[0065] The filtration capacity of the filter is preferably also 10 ml / mm². 2 or less, preferably 8 ml / mm² 2 or less, and preferably 5 ml / mm 2 or less. If the filter's filtration capacity decreases, the effectiveness of removing foreign matter increases, and as a result, the efficiency of the filtration step is improved.

[0066] Filter clogging, as used here, refers to a condition in which the dilute liquid cannot be substantially filtered due to a large amount of foreign matter and aggregates trapped in the filter, and in particular, a condition in which the filtration rate at a suction pressure of 50 kPa is 0.005 ml / (min × mm 2 ) or less.

[0067] The filter material is not particularly limited, as long as it is suitable for removing particles from a water-based solvent. Specific examples of filter materials include cellulose, nylon, polysulfone, polyethersulfone, polypropylene, polytetrafluoroethylene (PTFE), and polycarbonate. With regard to filtration precision, nylon, polypropylene, or polyethersulfone are preferred. Furthermore, when filter life is also taken into consideration, polypropylene is preferred.

[0068] The filter can be a membrane filter or a depth filter. The filter's shape is not particularly restricted. For example, it can be a flat membrane, a pleated type, or a hollow fiber type.

[0069] The polishing composition consists of a filtrate obtained in the filtration step, i.e., the filtered diluted liquid.

[0070] The ratio R2 / R1 of the average secondary particle diameter R2 of the abrasive grains in the polishing composition to the average secondary particle diameter R1 of the abrasive grains in the undiluted liquid is 1.2 or less, preferably 1.15 or less, and more preferably 1.1 or less. By reducing the R2 / R1 ratio, a polishing composition suitable for producing a high-quality silicon substrate can be easily obtained.

[0071] The ratio R2 / R1 is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.7 or more. Increasing the ratio R2 / R1 makes it easy to obtain a polishing composition with a practical polishing rate.

[0072] The value of the average secondary particle diameter R2 of the abrasive grains in the polishing composition can be measured by a dynamic light scattering method, like the average secondary particle diameter R1 in the undiluted liquid.

[0073] The following describes a method for producing a silicon substrate using a polishing composition with regard to the effect of the polishing composition.

[0074] The polishing compound can be used for a polishing step, such as lapping and polishing, using a silicon substrate material cut from a silicon ingot as the object to be polished. Specifically, a polishing pad is pressed against a surface of the silicon substrate material to be polished, while the polishing compound is applied to the surface, and the silicon substrate material and the polishing pad are rotated.

[0075] The amount of aggregates contained in the undiluted liquid tends to increase during the dilution step. If the polishing composition contains a larger amount of aggregates, these aggregates can have a negative effect on the silicon substrate material or the silicon substrate itself. In this context, according to the polishing composition of the present invention, the ratio R2 / R1 of the average secondary particle diameter R2 of the abrasive grains in the polishing composition to the average secondary particle diameter R1 of the abrasive grains in the undiluted liquid is 1.2 or less. That is, the aggregation of the abrasive grains generated by the dilution step is suppressed. Therefore, the silicon substrate material and the silicon substrate are less affected by the aggregates in the polishing composition.

[0076] A silicon substrate, which is a polished product, is obtained by rinsing the silicon substrate after the polishing step and subsequently drying the silicon substrate.

[0077] The polishing composition of the present embodiment exhibits particularly high utility when it contains the abrasive grains, the water-soluble polymer, and water, and is used for the final polishing of the silicon substrate material. In such a polishing composition, bridged aggregates can form among the abrasive grains due to the water-soluble polymer. These bridged aggregates can be generated during the dilution step, in which the undiluted liquid is diluted with water. In many cases, the bridged aggregates generated during the dilution step remain behind without being redispersed in the polishing composition. If these bridged aggregates remain on the silicon substrate after final polishing, surface defects known as light spots (LPDs) can occur.In this context, the aggregates can be prevented from remaining on the silicon substrate after final polishing, since the aggregation of the abrasive grains is suppressed in the polishing composition of the present embodiment.

[0078] When the polishing composition is used for the final polishing of the silicon substrate material, the number of coarse particles contained in the polishing composition, with a size of 0.7 μm or larger, is preferably as small as possible. In particular, the number of coarse particles with a size of 0.7 μm or larger contained in the polishing composition is preferably 4000 or less per 1 ml, preferably 2000 or less per 1 ml, and even more preferably 1500 or less per 1 ml. The number of coarse particles in the polishing composition can be reduced by diluting the undiluted liquid and then filtering the diluted liquid.

[0079] The present embodiment, which has been described in detail above, exhibits the following effects. (1) In the case of the polishing composition of the present embodiment, the ratio R2 / R1 of the average secondary particle diameter R2 of the abrasive grains in the polishing composition to the average secondary particle diameter R1 of the abrasive grains in the undiluted liquid is 1.2 or less. That is, the aggregation of the abrasive grains generated during the dilution step is suppressed. Therefore, a polished product produced using the polishing composition is less affected by aggregates in the polishing composition. Consequently, a high-quality polished product can be easily obtained. (2) If the polishing composition is obtained by diluting the undiluted liquid by a factor of 2 or more and 100 or less, the transport costs of the undiluted liquid can be reduced, and the space required to store the undiluted liquid can be reduced. Furthermore, the stability of the undiluted liquid and the polishing composition can be easily ensured. (3) If the polishing composition is obtained by diluting the undiluted liquid and then filtering the diluted liquid, the R2 / R1 ratio is simply adjusted to 1.2 or less. (4) If the filter used in the filtration step has an opening of 0.05 μm or more and 50 μm or less, the practical filtration rate can be easily obtained, and a polishing composition suitable for producing a polished product of high quality can be easily obtained. (5) If the filtration rate in the filtration step is 0.005 ml / (min × mm) 2 ) or more and 10 ml / (min × mm 2 ) or less at a suction pressure of 50 kPa, the effectiveness of the filtration step is improved and a polishing composition suitable for producing a high-quality polished product can be obtained more easily. (6) When the polishing composition of the present invention is used to polish a silicon substrate material, a high-quality silicon substrate can be easily obtained. (7) Since the undiluted liquid is diluted so that the ratio R2 / R1 of the average secondary particle diameter R2 of the abrasive grains in the polishing composition to the average secondary particle diameter R1 of the abrasive grains in the undiluted liquid is 1.2 or less according to the method of producing a polishing composition of the present embodiment, a polishing composition suitable for producing a polished product of high quality can be obtained. (8) According to the method for producing a silicon substrate, which includes polishing a silicon substrate material with the polishing composition of the present embodiment, a silicon substrate of high quality can be easily obtained. (9) The silicon substrate obtained by polishing a silicon substrate material with the polishing composition has fewer LPDs caused by coarse particles, such as foreign matter and aggregates, in the polishing composition and is of high quality. (10) The polishing composition of the present embodiment is suitable for producing a high-quality polished product, as described in point (1). Therefore, the undiluted liquid used to prepare the polishing composition is also suitable for producing a high-quality polished product.

[0080] The embodiments can be modified as follows. – The polishing composition may also contain a known additive, such as a preservative and an antifungal agent, if required. Specific examples of preservatives and antifungal agents include isothiazolin compounds, paraoxybenzoates, and phenoxyethanol. – The process for producing a polishing composition may further include adding to the diluted liquid obtained by diluting the undiluted liquid a starting material which is less prone to containing foreign matter, or a starting material which is less prone to aggregating. – The filtration step, in which the diluted liquid is filtered, can be omitted. The filtration step can be carried out in a single stage or divided into multiple stages. If the filtration step is divided into multiple stages, the filters used in the stages can be the same. Alternatively, filters with different apertures or materials can be used in the stages. If filters with different apertures are used in the stages, the aperture of the filter used in the last stage is preferably finer than that of the filter used in the preceding stage. – The filtration step can be carried out by batch filtration or by circulation filtration. – The process for producing a polishing composition may further include the step of filtering the undiluted liquid or the step of filtering the starting materials for the polishing composition prior to producing the undiluted liquid. – The abrasive grains can have a spherical or non-spherical shape, such as a peanut shell shape with a narrowed middle area, a spiky shape with a surface with protrusions, or the shape of a rugby ball. The polishing pad used when polishing with the polishing compound is not particularly restricted. The polishing pad can be made of fleece or suede. The polishing pad may or may not contain abrasive particles. – The polishing composition can be a single-component type or a multi-component type, containing one or more components. The polishing compound can be used to produce polished products other than silicon substrates, such as silicon dioxide, plastic, glass, and quartz substrates. Since the polishing compound contains few aggregates, a high-quality polished product can easily be obtained even in such cases. The starting materials for the polishing compound can be modified as needed, depending on the desired polished product. For example, the starting materials can contain resin particles as abrasive grains.

[0081] The following is a technical idea that can be derived from the embodiments and modifications described above.

[0082] A process for producing a polishing composition includes: Diluting an undiluted liquid containing abrasive grains to obtain a diluted liquid; and Filter the diluted liquid, where, if R1 is defined as an average secondary particle diameter of the abrasive grains in the undiluted liquid and R2 is defined as an average secondary particle diameter of the abrasive grains in the polishing composition, the ratio R2 / R1 is reduced by filtering the diluted liquid. Examples:

[0083] The present invention will now be described in more detail with reference to examples and comparative examples.

[0084] Colloidal silicon dioxide, a water-soluble polymer, a basic compound, and an organic acidic salt were mixed with ion-exchange water to prepare the undiluted liquids of Examples 1 to 4 and Comparative Example 1. The components of each undiluted liquid are shown in Table 1.

[0085] The average particle diameter of the colloidal silicon dioxide used was measured by a dynamic light scattering method using UPA-UT151, manufactured by Nikkiso Co., Ltd. The measured average particle diameter values ​​are given in the “Particle Diameter” column of the “Colloidal Silicon Dioxide” column in Table 1.

[0086] “HEC” in the “water-soluble polymer” column of Table 1 represents hydroxyethylcellulose. “PVP” represents polyvinylpyrrolidone. “A1” represents a polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) triblock copolymer. “B1” in the “organic acid salt” column of Table 1 represents triammonium citrate.

[0087] The average secondary particle diameter R1 of the silicon dioxide particles in each undiluted liquid was measured by a dynamic light scattering method using FPAR-100, manufactured by Otsuka Electronics Co., Ltd. The results are shown in the column “R1” in Table 2.

[0088] Each of the undiluted liquids was diluted 20 times by volume with pure water while being stirred using a homogenizer to obtain a diluted liquid. The diluted liquids were then filtered to prepare polishing compositions of Examples 1 to 4 and Comparative Example 1. The diluted liquid was filtered under the conditions described in Table 3, using a filter with an orifice of the size described in the "Orifice" column of Table 2. Filtration rates were obtained with values ​​described in the "Filtration Rate" column of Table 2. The polishing compositions of Example 4 and Comparative Example 1 were prepared without filtering the diluted liquid.

[0089] The average secondary particle diameter R2 of the silicon dioxide particles in each of the polishing compounds was measured by a dynamic light scattering method using FPAR-100, manufactured by Otsuka Electronics Co., Ltd. The results are shown in the column “R2” in Table 2. The ratio of the average secondary particle diameter R2 to the average secondary particle diameter R1 is shown in the column “R2 / R1” of Table 2.

[0090] The number of coarse particles present in each polishing compound, measuring 0.7 μm or larger, was measured using AccuSizerFX, manufactured by Particle Sizing Systems. The results are shown in the “LPC (Large Particle Count)” column of Table 2.

[0091] The surface of the silicon substrate material was polished with each of the polishing compositions under the conditions described in Table 4. The silicon substrate materials used had a diameter of 300 mm, p-conductivity, and a crystal orientation of <100> and exhibited a resistance of 0.1 Ω·x cm or more and less than 100 Ω·x cm. The silicon substrate materials were pre-polished with a polishing slurry (trade name: GLANZOX 1103) manufactured by Fujimi Incorporated. The number of particles present on the surface of each polished silicon substrate, with a size of 37 nm or greater, was measured using a Wafer Inspection Surfscan SP2 manufactured by KLA-Tencor Corporation. The results are shown in the “Particles” column of Table 2.

[0092] The polishing compound of Example 1 was subjected to suction filtration with a filtration pressure differential of 5 kPa using each of the disk filters with materials and structures described in the "Filter Material" and "Filter Structure" columns of Table 5, and having a diameter of 47 mm and an orifice of 0.45 μm. If the amount of polishing compound passed through each filter before clogging, after suction filtration had begun, was more than 2 L, the filter life was rated A. If the amount was 2 L or less, the filter life was rated B. The results are shown in the "Filter Life" column of Table 5.The number of coarse particles contained in the filtrate obtained as a result of suction filtration using each filter, and measuring 0.7 μm or larger, was measured using the AccuSizerFX, manufactured by Particle Sizing Systems. If the number of coarse particles was less than 200 particles per ml, the filter precision was rated as A. If the number was 200 particles / ml or more, the filtration precision was rated as B. The results are presented in the "Filtration Precision" column of Table 5. Table 1 Colloidal silicon dioxide Water-soluble polymer Basic compound Organic acid salt Particle diameter [nm] Content [mass %] Art Weight-averaged molecular weight Content [mass %] Art Content [mass %] Art Salary [Mass %] Example 1 65 9 HEC 250000 0,3 ammonia 0,2 B1 0.2 PvP 45000 0,17 A1 9000 0,01 Example 2 65 9 HEC 250000 0,3 ammonia 0,2 B1 0.1 PvP 45000 0,04 A1 9000 0,05 Example 3 65 9 HEC 250000 0,3 ammonia 0,2 - A1 9000 0,05 Example 4 65 9 HEC 250000 0,3 ammonia 0,2 - A1 9000 0,05 Comparison example 1 65 9 HEC 250000 0,3 ammonia 0,2 - Table 2 R1 [nm] Dilution ratio D Filtration step R2 [nm] R2 / R1 LPC [# / mL] Particles Opening [μm] Filtrationsrate [mL / (min × mm 2 )] Example 1 81 20 times 1,0 0,38 89 1,10 419 52 Example 2 85 20 times 1,0 0,32 96 1,13 1412 65 Example 3 90 20 times 1,0 0,18 106 1,17 1446 79 Example 4 90 20 times - - 108 1,20 2830 130 Comparison example 1 97 20 times - - 122 1,26 8640 288 Table 3 Filtration process: Suction filtration Suction pressure: 50 kPa Filtration time: 5 min Filter type: Cellulose mixed ester membrane filters manufactured by Toyo Roshi Kaisha, Ltd. Filter diameter: 47 mm Table 4 Polishing device: Wafer polishing machine (PNX-332B, manufactured by Okamoto Machine Tool Works, Ltd.) Polishing load: 15 kPa Rotational speed of the plate: 30 rpm Rotational speed of the head: 30 rpm Polishing time: 4 min Temperature of the polishing compound: 20°C Feed rate of the polishing compound: 0.5 l / min (continuous supply without circulation) Table 5 Filter material Filter structure Filter lifespan Filtration precision Nylon 66 A layer, porous B A Polypropylen Multilayer, nonwoven A A Polyethersulfon A layer, porous B A Cellulose mixed ester A layer, porous B B Cellulose acetate A layer, porous B B

[0093] As shown in Table 2, the polishing compositions of Examples 1 to 4 had LPC measurements that were lower than those of the polishing composition of Comparison Example 1. Furthermore, the particle measurements obtained when using the polishing compositions of Examples 1 to 4 were lower than those obtained when using the polishing composition of Comparison Example 1. These results indicate that the polishing composition in which the R2 / R1 ratio is 1.2 or less is suitable for producing a high-quality polished product in which the coarse particles in the polishing composition are less likely to remain.

Claims

[1] Polishing composition obtained by diluting an undiluted liquid containing abrasive grains, wherein, where R1 is defined as an average secondary particle diameter of the abrasive grains in the undiluted liquid and R2 is defined as an average secondary particle diameter of the abrasive grains in the polishing composition, the ratio R2 / R1 is 1.2 or less. [2] Polishing composition according to claim 1, wherein the undiluted liquid is diluted by a dilution ratio of two times or more and one hundred times or less. [3] Polishing composition according to claim 1 or 2, wherein the polishing composition is further obtained by filtering a diluted liquid obtained by diluting the undiluted liquid. [4] Polishing composition according to claim 3, wherein a filter used in filtering the diluted liquid has an opening of 0.05 μm or more and 50 μm or less. [5] Polishing composition according to claim 3 or 4, wherein the filtration rate of the filters of the diluted liquid is 0.005 ml / (min × mm). 2 ) or more and 10 ml / (min × mm 2 ) or less, at a suction pressure of 50 kPa. [6] Polishing composition according to any one of claims 1 to 5, wherein the polishing composition is usable for polishing a silicon substrate material. [7] A method for producing a polishing composition comprising diluting an undiluted liquid containing abrasive grains, wherein the dilution of the undiluted liquid is carried out such that, where R1 is defined as an average secondary particle diameter of the abrasive grains in the undiluted liquid and R2 is defined as an average secondary particle diameter of the abrasive grains in the polishing composition, the ratio R2 / R1 is 1.2 or less. [8] Method for producing a silicon substrate, comprising polishing a silicon substrate material with the polishing composition according to any one of claims 1 to 5. [9] Silicon substrate obtained by polishing a silicon substrate material with the polishing composition according to any one of claims 1 to 5. [10] Undiluted liquid which is to be diluted two or more times and one hundred times less with water when used to prepare a polishing composition, wherein the undiluted liquid contains abrasive grains, and if R1 is defined as an average secondary particle diameter of the abrasive grains in the undiluted liquid and R2 is defined as an average secondary particle diameter of the abrasive grains in the polishing composition, then the ratio R2 / R1 is 1.2 or less.