JP6069308B2 - Method for producing polishing composition - Google Patents

Description

  The present invention relates to a method for producing a polishing composition that suppresses aggregation during the preparation of the polishing composition.

  A polishing composition used for polishing a silicon substrate or a semiconductor wafer having a film such as a metal film and an oxide film on its surface contains silica particles as abrasive grains and a basic compound as an etching agent. It has been known.

  In addition, a technique for preventing excessive etching by blending a water-soluble polymer into a polishing composition is also known. For example, in Patent Document 1, an etching solution is prepared by adding hydroxyethyl cellulose as a water-soluble polymer to an aqueous solution containing a basic compound, and then silica diluted with pure water is added to the etching solution. It is disclosed that a polishing composition is prepared.

  However, the method for producing a polishing composition disclosed in Patent Document 1 has a problem that aggregation (gelation) occurs during the preparation of the polishing composition. The occurrence of this aggregation is considered to be caused by a decrease in the stability of components in the polishing composition. Suppressing the aggregation of the polishing composition is extremely important from the viewpoint of improving the stability of the polishing composition.

JP 2007-300070 A

  The objective of this invention is providing the manufacturing method of polishing composition which can suppress aggregation at the time of preparation of polishing composition.

In order to achieve the above object, the method for producing a polishing composition of the present invention comprises a step of preparing a mixture by mixing silica particles as abrasive grains, a basic compound, and water, And a step of adding a basic aqueous solution containing a functional polymer.

  The polishing composition is preferably used for polishing a silicon substrate.

  The polishing composition is preferably used for final polishing of a silicon substrate.

  According to the present invention, aggregation of the polishing composition can be suppressed during the preparation of the polishing composition.

  Hereinafter, embodiments embodying the present invention will be described.

  The method for producing a polishing composition of the present embodiment includes a step of preparing a mixture by mixing silica particles as abrasive grains, a basic compound, and water, and adding an aqueous solution containing a water-soluble polymer to the mixture. Process. The polishing composition thus obtained is preferably used for polishing the surface of a silicon substrate. The silicon substrate polishing step includes, for example, a preliminary polishing step (primary polishing and secondary polishing) for flattening the surface of a disk-shaped silicon substrate sliced from a silicon single crystal ingot, and a surface of the silicon substrate after the preliminary polishing step And a final polishing step of removing the fine irregularities present in the surface to make a mirror surface. The polishing composition is particularly preferably used in the final polishing step. A silicon substrate whose surface has been polished with a polishing composition can be suitably used for the production of a semiconductor substrate.

  The silica particles function to mechanically polish the surface to be polished. Examples of silica particles include colloidal silica, fumed silica, and sol-gel silica. Among the silica particles, colloidal silica is preferable. When colloidal silica or fumed silica is used, particularly when colloidal silica is used, scratches generated on the polished surface of the silicon substrate are reduced. These silica particles may be used individually by 1 type, and may be used in combination of 2 or more type.

  The average primary particle diameter of the silica particles is preferably 5 nm or more, more preferably 10 nm or more, and further preferably 20 nm or more. As the average primary particle diameter of the silica particles increases, the polishing rate of the silicon substrate improves.

  The average primary particle diameter of the silica particles is preferably 100 nm or less, more preferably 70 nm or less, and still more preferably 50 nm or less. As the average primary particle diameter of the silica particles decreases, the dispersion stability of the polishing composition improves.

  The value of the average primary particle diameter of the silica particles is calculated from the specific surface area measured by the BET method, for example. The specific surface area of the silica particles can be measured using, for example, “Flow SorbII 2300” manufactured by Micromeritex.

  It is preferable that the average secondary particle diameter of a silica particle is 10 nm or more, More preferably, it is 20 nm or more, More preferably, it is 30 nm or more. As the average secondary particle diameter of the silica particles increases, a higher polishing rate is obtained when polishing. The average secondary particle diameter of the silica particles is preferably 200 nm or less, more preferably 150 nm or less, and still more preferably 100 nm or less. As the average secondary particle diameter of the silica particles decreases, the dispersion stability of the polishing composition improves. The average secondary particle diameter of the silica particles can be measured, for example, by a dynamic light scattering method using FPAR-1000 manufactured by Otsuka Electronics Co., Ltd.

  The average value of the major axis / minor axis ratio of the silica particles is preferably 1.0 or more, more preferably 1.05 or more, and still more preferably 1.1 or more. As the average value of the major axis / minor axis ratio increases, a higher polishing rate is obtained. The average value of the major axis / minor axis ratio of the silica particles is preferably 3.0 or less, more preferably 2.0 or less, and still more preferably 1.5 or less. As the average value of the major axis / minor axis ratio decreases, scratches generated on the polished surface decrease.

  The major axis / minor axis ratio is a value relating to the shape of the silica particles, and can be determined using, for example, an electron microscope image of the silica particles. Specifically, in a scanning electron microscope image of a predetermined number (for example, 200) of silica particles, a minimum circumscribed rectangle is drawn for each particle. Next, for each minimum circumscribed rectangle, by calculating a value obtained by dividing the length of the long side (major axis value) by the length of the short side (minor axis value), and calculating the average value thereof The average value of the major axis / minor axis ratio can be determined.

  The true specific gravity of the silica particles is preferably 1.5 or more, more preferably 1.6 or more, and still more preferably 1.7 or more. As the true specific gravity of the silica particles increases, a higher polishing rate is obtained. The true specific gravity of the silica particles is preferably 2.2 or less. The true specific gravity is calculated from the mass of the dried silica particles and the total mass after the silica particles are immersed in ethanol with a known volume.

  The content of the silica particles in the mixture obtained by mixing the silica particles, the basic compound, and water is preferably 1% by mass or more, more preferably 3% by mass or more, and further preferably 5% by mass or more. As the content of silica particles in the mixture increases, it becomes easier to increase the content of silica particles in the polishing composition.

  The content of silica particles in the mixture is preferably 50% by mass or less, more preferably 40% by mass or less, and still more preferably 30% by mass or less. As the content of silica particles in the mixture decreases, aggregation during the preparation of the polishing composition is suppressed.

  The content of silica particles in the finally obtained polishing composition is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and further preferably 0.3% by mass or more. is there. As the content of silica particles increases, surface processing performance such as polishing rate for the surface to be polished improves.

  The content of silica particles in the polishing composition is preferably 10% by mass or less, more preferably 8% by mass or less, and still more preferably 6% by mass or less. As the content of silica particles decreases, the dispersion stability of the polishing composition improves, and the silica particles remaining on the polished surface decrease.

  The basic compound functions to chemically polish the surface to be polished, and improves the polishing rate. The basic compound serves to improve the dispersion stability of the polishing composition.

  Specific examples of the basic compound include alkali metal hydroxides or salts, quaternary ammonium hydroxide or salts thereof, ammonia, amines, and the like. Specific examples of the alkali metal include potassium and sodium. Specific examples of the salt include carbonate, hydrogen carbonate, sulfate, acetate, and the like. Specific examples of the quaternary ammonium include tetramethylammonium, tetraethylammonium, tetrabutylammonium and the like. Specific examples of the alkali metal hydroxide or salt include potassium hydroxide, potassium carbonate, potassium hydrogen carbonate, potassium sulfate, potassium acetate, potassium chloride and the like. Specific examples of the quaternary ammonium hydroxide or a salt thereof 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, triethylenetetramine, anhydrous piperazine , Piperazine hexahydrate, 1- (2-aminoethyl) piperazine, N-methylpiperazine, guanidine and the like. These basic compounds may be used individually by 1 type, and may be used in combination of 2 or more type.

  Preferably, the basic compound is at least one selected from ammonia, ammonium salt, alkali metal hydroxide, alkali metal salt, and quaternary ammonium hydroxide. More preferably, the basic compound is ammonia, potassium hydroxide, sodium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, ammonium bicarbonate, ammonium carbonate, potassium bicarbonate, potassium carbonate, sodium bicarbonate, and carbonate. It is at least one selected from sodium. More preferably, the basic compound is at least one selected from ammonia, potassium hydroxide, sodium hydroxide, tetramethylammonium hydroxide, and tetraethylammonium hydroxide, more preferably at least ammonia and tetramethylammonium hydroxide. On the other hand, most preferably ammonia.

  The content of the basic compound in the mixture obtained by mixing the silica particles, the basic compound, and water is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and further preferably 0.1% by mass. That's it. As the content of the basic compound in the mixture increases, aggregation during the preparation of the polishing composition is suppressed.

  The content of the basic compound in the mixture is preferably 10% by mass or less, more preferably 5% by mass or less, and still more preferably 3% by mass or less. As the content of the basic compound in the mixture decreases, it becomes easier to reduce the content of the basic compound in the polishing composition.

  The content of the basic compound in the polishing composition finally obtained is preferably 0.001% by mass or more, more preferably 0.002% by mass or more, and further preferably 0.003% by mass or more. It is. As the content of the basic compound in the polishing composition increases, the chemical polishing action on the surface to be polished increases, and the dispersion stability of the polishing composition improves.

  The content of the basic compound in the polishing composition is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, and still more preferably 0.2% by mass or less. As the content of the basic compound in the polishing composition decreases, the smoothness of the polished surface improves.

  Water serves as a dispersion medium for silica particles and a solvent for other components. It is preferable that water does not inhibit the function of other components. Examples of such water include water having a total content of transition metal ions of 100 ppb or less. The purity of water can be increased, for example, by removing impurity ions using an ion exchange resin, removing foreign matter using a filter, or distillation. Specifically, for example, ion exchange water, pure water, ultrapure water, distilled water or the like is preferably used.

  The pH of the mixture obtained by mixing the silica particles, the basic compound, and water is preferably 8 or more, more preferably 9 or more. As pH increases, aggregation is suppressed when an aqueous solution containing a water-soluble polymer is added to the mixture. Thereby, the dispersion stability of the polishing composition finally obtained improves.

  The pH of the mixture is preferably 12 or less, more preferably 10.5 or less. As the pH decreases, silica dissolution is suppressed. The pH of the mixture can be adjusted by the blending amount of the basic compound.

  The water-soluble polymer serves to increase the wettability of the surface to be polished. As the water-soluble polymer, those having at least one functional group selected from a cationic group, an anionic group and a nonionic group in the molecule can be used. Specific examples of such a functional group include a hydroxyl group, a carboxyl group, an acyloxy group, a sulfo group, a quaternary nitrogen structure, a heterocyclic structure, a vinyl structure, and a polyoxyalkylene structure.

  Specific examples of the water-soluble polymer include cellulose derivatives, imine derivatives such as poly (N-acylalkyleneimine), polyvinyl alcohol, polyvinyl pyrrolidone, copolymers containing polyvinyl pyrrolidone as part of the structure, polyvinyl caprolactam, polyvinyl caprolactam. , A polyoxyethylene, a polymer having a polyoxyalkylene structure, and a copolymer having a plurality of types of structures such as diblock type, triblock type, random type, and alternating type And polyether-modified silicone. A water-soluble polymer may be used individually by 1 type, and may be used in combination of 2 or more type.

  Among water-soluble polymers, a cellulose derivative, polyvinyl pyrrolidone, or a polymer having a polyoxyalkylene structure is preferable from the viewpoint of imparting good hydrophilicity to the polished substrate surface. Specific examples of the cellulose derivative include hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, carboxymethyl cellulose and the like. Among cellulose derivatives, hydroxyethyl cellulose is preferable because it has a high ability to impart wettability to a polished surface and has good cleaning and removing properties.

  The weight average molecular weight of the water-soluble polymer is preferably 1,000 or more in terms of polyethylene oxide, more preferably 10,000 or more, still more preferably 100,000 or more, and still more preferably 200,000 or more. . As the weight average molecular weight of the water-soluble polymer increases, the hydrophilicity of the polished surface increases.

  The weight average molecular weight of the water-soluble polymer is preferably 2,000,000 or less, more preferably 1,500,000 or less, still more preferably 1,000,000 or less, and most preferably 500,000 or less. is there. As the weight average molecular weight of the water-soluble polymer decreases, the dispersion stability of the polishing composition improves.

  The content of the water-soluble polymer in the aqueous solution is preferably 0.02% by mass or more, more preferably 0.05% by mass or more, and still more preferably 0.1% by mass or more. As the content of the water-soluble polymer in the aqueous solution increases, it becomes easier to increase the content of the water-soluble polymer in the polishing composition.

  The content of the water-soluble polymer in the aqueous solution is preferably 10% by mass or less, more preferably 5% by mass or less, and still more preferably 3% by mass or less. As the content of the water-soluble polymer in the aqueous solution decreases, aggregation during the preparation of the polishing composition is suppressed.

  The content of the water-soluble polymer in the polishing composition finally obtained is preferably 0.002% by mass or more, more preferably 0.004% by mass or more, and further preferably 0.006% by mass. That's it. As the content of the water-soluble polymer in the polishing composition increases, the wettability of the polished surface increases.

  The content of the water-soluble polymer in the polishing composition is preferably 0.5% by mass or less, more preferably 0.2% by mass or less, and still more preferably 0.1% by mass or less. As the content of the water-soluble polymer in the polishing composition decreases, the dispersion stability of the polishing composition improves.

  The aqueous solution is preferably adjusted to a range from approximately neutral to basic, more preferably basic (for example, pH 8 to 12). The pH of the aqueous solution is preferably 8 or more, more preferably 9 or more. As the pH of the aqueous solution increases, aggregation of the silica particles when the aqueous solution is added to a mixture containing silica particles, a basic compound, and water is suppressed. Thereby, the dispersion stability of the polishing composition finally obtained improves.

  The pH of the aqueous solution is preferably 12 or less, more preferably 10.5 or less. As the pH of the aqueous solution decreases, silica dissolution is suppressed.

  The addition rate of the aqueous solution to the mixture is preferably 0.1 mL / min or more, more preferably 1 mL / min or more, and further preferably 5 mL / min or more with respect to 1 L of the mixture. As the addition rate increases, the production efficiency of the polishing composition improves.

  The addition rate of the aqueous solution to the mixture is preferably 500 mL / min or less, more preferably 100 mL / min or less, and further preferably 50 mL / min or less with respect to 1 L of the mixture. As the addition rate decreases, silica agglomeration is suppressed.

  The aqueous solution is preferably filtered before being added to the mixture. By filtration, foreign matters or aggregates contained in the aqueous solution are reduced. Filtration may be natural filtration performed under normal pressure, suction filtration, pressure filtration, or centrifugal filtration.

  The filter used for the filtration is preferably selected based on the mesh opening. The aperture of the filter is preferably 0.05 μm or more, more preferably 0.1 μm or more, and further preferably 0.2 μm or more. As the aperture of the filter increases, the production efficiency of the polishing composition improves.

  The aperture of the filter is preferably 100 μm or less, more preferably 70 μm or less, and even more preferably 50 μm or less. As the aperture of the filter is reduced, the removal efficiency of foreign matters or aggregates contained in the aqueous solution is improved. Thereby, the dispersion stability of the polishing composition is further improved.

  The final polishing composition has a pH of preferably 8 or higher, more preferably 8.5 or higher, and still more preferably 9 or higher. As the pH increases, the chemical polishing action of the polishing composition on the surface to be polished increases, and the dispersion stability of the polishing composition improves. The pH of the polishing composition is preferably 12.5 or less, more preferably 12 or less, and still more preferably 11.5 or less. As the pH decreases, the smoothness of the polished surface improves.

  The polishing composition may contain, for example, a surfactant, an organic acid, an organic acid salt, an inorganic acid, an inorganic acid salt, a chelating agent and the like within a range not impairing the effects of the present invention.

  The surfactant functions to suppress roughness of the polished surface. Thereby, it becomes easy to reduce the haze level of the polished surface. In particular, when the polishing composition contains a basic compound, the polished surface is easily roughened by chemical etching with the basic compound. For this reason, the combined use of a basic compound and a surfactant is effective.

  Specific examples of the surfactant include an ionic or nonionic surfactant having a weight average molecular weight of less than 1000. Among the surfactants, nonionic surfactants are preferable. Since the nonionic surfactant has low foaming property, it is easy to handle at the time of preparation and use of the polishing composition. Moreover, when a nonionic surfactant is used, pH adjustment of polishing composition becomes easy. Specific examples of the nonionic surfactant include oxyalkylene polymers such as polyethylene glycol and polypropylene glycol, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkylamine, polyoxyethylene fatty acid ester, polyoxyethylene Examples include polyoxyalkylene adducts such as ethylene glyceryl ether fatty acid esters and polyoxyethylene sorbitan fatty acid esters.

  More specifically, polyoxyethylene polyoxypropylene copolymer, polyoxyethylene glycol, polyoxyethylene propyl ether, polyoxyethylene butyl ether, polyoxyethylene pentyl ether, polyoxyethylene hexyl ether, polyoxyethylene octyl ether, Polyoxyethylene-2-ethylhexyl ether, polyoxyethylene nonyl ether, polyoxyethylene decyl ether, polyoxyethylene isodecyl ether, polyoxyethylene tridecyl ether, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene Stearyl ether, polyoxyethylene isostearyl ether, polyoxyethylene oleyl ether, polyoxyethylene Phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene styrenated phenyl ether, polyoxyethylene laurylamine, polyoxyethylene stearylamine, polyoxyethylene oleylamine, poly Oxyethylene stearylamide, polyoxyethylene oleylamide, polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene distearate, polyoxyethylene monooleate, polyoxyethylene dioleate, monolaurin Acid polyoxyethylene sorbitan, monopalmitic acid polyoxyethylene sorbita , Monostearate polyoxyethylene sorbitan monooleate polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitan, polyoxyethylene sorbit tetraoleate, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, and the like. As the surfactant, one kind may be used alone, or two or more kinds may be used in combination.

  The organic acid and its salt, and the inorganic acid and its salt serve to improve the hydrophilicity of the polished surface.

  Specific examples of organic acids 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 acid, organic phosphonic acid, etc. are mentioned. Specific examples of the organic acid salt include alkali metal salts such as sodium salt and potassium salt of these organic acids, and ammonium salt.

  Specific examples of the inorganic acid include sulfuric acid, nitric acid, hydrochloric acid, carbonic acid and the like. Specific examples of the inorganic acid salt include alkali metal salts such as sodium salt and potassium salt of these inorganic acids, and ammonium salt.

  Among organic acid salts and inorganic acid salts, ammonium salts are preferable from the viewpoint of suppressing metal contamination of the abrasive product.

  An organic acid and its salt, and an inorganic acid and its salt may be used individually by 1 type, and may be used in combination of 2 or more type.

  The chelating agent functions to suppress metal contamination of the abrasive product by capturing metal impurities and forming a complex. Specific examples of the chelating agent include aminocarboxylic acid chelating agents and organic phosphonic acid chelating agents. Specific examples of the aminocarboxylic acid chelating agent include ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetate, nitrilotriacetic acid, sodium nitrilotriacetate, ammonium nitrilotriacetate, hydroxyethylethylenediaminetriacetic acid, sodium hydroxyethylethylenediaminetriacetate, diethylenetriamine Examples include acetic acid, sodium diethylenetriaminepentaacetate, triethylenetetraminehexaacetic acid, and sodium triethylenetetraminehexaacetate. Specific examples of the organic phosphonic acid chelating agent include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetrakis (methylenephosphonic acid), diethylenetriaminepenta (methylene Phosphonic acid), triethylenetetraamine hexa (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, α-methylphosphonosucci Etc. The. These chelating agents may be used individually by 1 type, and may be used in combination of 2 or more type. Preferably, the chelating agent is an organic phosphonic acid chelating agent, more preferably ethylenediaminetetrakis (methylenephosphonic acid).

  As described above, the method for producing the polishing composition of the present embodiment comprises a step of preparing a mixture by mixing silica particles, a basic compound, and water, and an aqueous solution containing a water-soluble polymer in the mixture. The process of adding. When the stability of the silica particles in the mixture is low (for example, the mixture is almost neutral), when the aqueous solution is added to the mixture, the aggregation of the silica particles is caused by the action of the water-soluble polymer in the aqueous solution. Occur. In particular, high-purity silica particles with few impurities are used in a polishing composition used for final polishing of a silicon substrate. The pH of a solution in which such high-purity silica particles are dispersed in ultrapure water is almost neutral. In this case, before adding the water-soluble polymer to the silica particle dispersion, the pH of the silica particle dispersion is adjusted to basic so as to increase the stability of the silica particles. Aggregation can be suppressed.

  Next, the manufacturing method of the silicon substrate using the said polishing composition is demonstrated.

  When polishing the surface of a silicon substrate using the polishing composition, the polishing composition is supplied to the surface of the silicon substrate and the polishing pad is pressed against the surface to rotate the silicon substrate and the polishing pad. At this time, physical action by friction between the polishing pad and the silicon substrate surface, physical action by friction between silica particles in the polishing composition and the silicon substrate, and basic compound in the polishing composition The surface of the silicon substrate is polished by the chemical action caused by.

  According to the embodiment described in detail above, the following effects are exhibited.

  (1) In the method for producing a polishing composition, an aqueous solution containing a water-soluble polymer is added after preparing a mixture of silica particles, a basic compound, and water. Thereby, aggregation of the silica particle at the time of preparation of polishing composition can be suppressed, and the dispersion stability of polishing composition can be improved.

  (2) The aqueous solution is preferably basic. In this case, aggregation during the preparation of the polishing composition can be further suppressed.

  (3) It is preferable that polishing composition is used for the use which grind | polishes a silicon substrate. In this case, it becomes easy to obtain a high-quality silicon substrate.

  (4) The polishing composition is preferably used for the purpose of final polishing of the silicon substrate. In this case, even when high-purity silica particles with few metal impurities are used as the abrasive grains, aggregation during the preparation of the polishing composition can be suppressed.

  In addition, the said embodiment may be changed as follows.

  In the method for producing a polishing composition, any one of a mixture of silica particles, a basic compound, and water or an aqueous solution containing a water-soluble polymer may be prepared first.

  -Polishing composition may contain well-known additives, such as antiseptic | preservative and a fungicide, as needed. Specific examples of the antiseptic and antifungal agent include, for example, isothiazoline compounds, paraoxybenzoates, phenoxyethanol and the like.

  -Polishing composition may be in the state concentrated at the time of manufacture and sale. That is, the polishing composition may be manufactured and sold in the form of a stock solution of the polishing composition.

  -Polishing composition may be prepared by diluting the undiluted | stock solution of polishing composition with water. In this case, the dilution rate is preferably 2 times or more, more preferably 5 times or more, and further preferably 10 times or more. As the dilution ratio increases, the transportation cost of the stock solution of the polishing composition becomes lower, and the storage location can be saved. The dilution ratio is preferably 100 times or less, more preferably 50 times or less, and further preferably 40 times or less. As the dilution factor decreases, the stability of the stock solution of the polishing composition improves.

  -Each component contained in the polishing composition may be filtered with a filter immediately before the production of the polishing composition. Moreover, polishing composition may be filtered with a filter immediately before use. By performing the filtration treatment, coarse foreign matters in the polishing composition are removed, and the quality is improved.

  The material and structure of the filter used for the filtration process are not particularly limited. Examples of the filter material include cellulose, nylon, polysulfone, polyethersulfone, polypropylene, polytetrafluoroethylene (PTFE), polycarbonate, and glass. Examples of the filter structure include a depth filter, a pleated filter, and a membrane filter.

  -The kind of polishing pad used with the grinding | polishing method using polishing composition is not specifically limited. For example, any of non-woven fabric type, suede type, those containing abrasive grains, and those not containing abrasive grains may be used.

  -When polishing a substrate using the polishing composition, the polishing composition once used for polishing may be collected and used again for polishing the substrate. As a method of reusing the polishing composition, for example, there is a method in which the used polishing composition discharged from the polishing apparatus is once collected in the tank and then recycled from the tank to the polishing apparatus. Can be mentioned. By reusing the polishing composition, the amount of the polishing composition discharged as a waste liquid can be reduced, and the amount of the polishing composition used can be reduced. This is useful in that the environmental load can be reduced and the cost for polishing the substrate can be suppressed.

  When the polishing composition is reused, each component such as a water-soluble polymer in the polishing composition is consumed and lost by polishing. For this reason, it is preferable to supplement the polishing composition with a reduced amount of each component such as a water-soluble polymer. The components to be replenished may be added individually to the polishing composition, or may be added to the polishing composition in a state where two or more components are mixed. The method for preparing the water-soluble polymer follows the method for producing the polishing composition of the above embodiment.

  -Polishing composition may be applied to polishing objects other than a silicon substrate. Specific examples of the polishing object other than the silicon substrate include metals such as stainless steel, silicon oxide substrates, plastic substrates, glass substrates, and quartz substrates. In addition, the component contained in polishing composition may be suitably changed according to a grinding | polishing target object.

  -The shape of the abrasive grains may be spherical or non-spherical. Specific examples of the non-spherical shape include a so-called bowl-shaped shape having an ellipsoid shape having a constriction at the center, a spherical shape having a plurality of protrusions on the surface, and a rugby ball shape.

  Next, the embodiment will be described more specifically with reference to examples and comparative examples.

( Reference Example 1)
70 g of 29% aqueous ammonia as a basic compound was added to 5000 g of pH 7.0 colloidal silica dispersion (concentration: 20% by mass) to prepare a colloidal silica dispersion of pH 10.3. Next, 2000 g of a 2% by weight aqueous solution of hydroxyethyl cellulose having a pH of 7.0 (weight average molecular weight 250,000) as a cellulose derivative was added to the colloidal silica dispersion. Finally, 3000 g of ultrapure water was added to prepare the polishing composition of Reference Example 1.

The polishing composition thus obtained was visually evaluated for the presence or absence of gelation. As a result, it was found that the polishing composition of Reference Example 1 was a uniform solution without gelation.

  Moreover, the presence or absence of gelation was also evaluated by the content of particles having a predetermined particle diameter or more in the polishing composition. Specifically, the number of particles having a size of 0.1 μm or more (hereinafter referred to as LPC) contained in the polishing composition was measured using “Accuriser FX” manufactured by PSS (Particle Sizing Systems). . As a result, the LPC was 53000 / mL.

(Example 2)
60 g of 29% ammonia water was added to 5000 g of pH 7.0 colloidal silica dispersion (concentration 20 mass%) to prepare a colloidal silica dispersion of pH 10.2. Next, 10 g of 29% ammonia water was added to 2000 g of a 2% by mass aqueous solution of hydroxyethyl cellulose (weight average molecular weight 250,000) at pH 7.0 to prepare a pH 10.0 aqueous solution of hydroxyethyl cellulose. Next, 2010 g of the hydroxyethyl cellulose aqueous solution was added to 5060 g of the colloidal silica dispersion. Finally, 3000 g of ultrapure water was added to prepare the polishing composition of Example 2.

  The polishing composition thus obtained was visually evaluated for the presence or absence of gelation. As a result, the polishing composition of Example 2 was a uniform solution without gelation. Further, LPC was measured in the same manner as in Example 1. As a result, the LPC was 44000 / mL, which was a better result than that of Example 1.

(Comparative Example 1)
70 g of 29% ammonia water was added to 2000 g of a 2 mass% aqueous solution of hydroxyethyl cellulose (weight average molecular weight 250,000) to prepare a hydroxyethyl cellulose aqueous solution having a pH of 10.6. Next, 2070 g of the hydroxyethyl cellulose aqueous solution was added to 5000 g of colloidal silica dispersion (concentration: 20% by mass) having a pH of 7.0. Finally, 3000 g of ultrapure water was added to prepare the polishing composition of Comparative Example 1.

  The polishing composition thus obtained was visually evaluated for the presence or absence of gelation. As a result, mild gelation was observed when the hydroxyethyl cellulose aqueous solution and the colloidal silica dispersion were mixed.

(Comparative Example 2)
To 5000 g of colloidal silica dispersion having a pH of 7.0 (concentration of 20% by mass), 2000 g of a 2% by mass aqueous solution of hydroxyethyl cellulose having a pH of 7.0 (weight average molecular weight of 250,000) was added. Next, 70 g of 29% ammonia water was added, and finally 3000 g of ultrapure water was added to prepare a polishing composition of Comparative Example 2.

  The polishing composition thus obtained was visually evaluated for the presence or absence of gelation. As a result, remarkable gelation was observed when the colloidal silica dispersion and the hydroxyethyl cellulose aqueous solution were mixed.

  From these results, it is understood that aggregation of the polishing composition can be suppressed by a procedure of mixing silica particles, a basic compound, and water, and then adding an aqueous solution containing a water-soluble polymer.

Claims (3)

A step of preparing a mixture by mixing silica particles as abrasive grains, a basic compound, and water;
A method for producing a polishing composition comprising the step of adding a basic aqueous solution containing a water-soluble polymer to the mixture. The polishing composition, method for producing a polishing composition according to claim 1, characterized in that used for polishing a silicon substrate. The method for producing a polishing composition according to claim 1 or 2 , wherein the polishing composition is used for final polishing of a silicon substrate.